JP2012148644A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire that can achieve weight reduction without degrading durability and productivity.SOLUTION: The pneumatic tire includes: a bead; a sidewall; a tread; a carcass reinforcing them; and a belt having at least two layers of cross belt layers on the outside of a crown part of the carcass in the tire radial direction. At least one layer of reinforcing member of the cross belt layer is steel cords 10 comprised of a core formed by disposing two core filaments 11 in parallel without being twisted and six sheath filaments 12 twisted around the core. If a core filament diameter is dc and sheath filament diameter is ds, an average sheath filament interval D expressed by the following formula is 25 to 80 μm and an interval between adjacent ones of steel cords 10 is 0.50-1.40 mm: D=[L-6 ds{1+(L/p)}]/6, where L=(π+2)dc+πds.

Description

  The present invention relates to a pneumatic tire (hereinafter, also simply referred to as “tire”), and more particularly, to a pneumatic tire that achieves weight reduction without reducing durability and productivity.

  In recent years, the importance of environmental performance has increased, and there is an increasing need for weight reduction in rubber articles and tires using steel cords as reinforcing members. To reduce the weight of the tire, it is effective to reduce the thickness of the belt made of steel cord. To that end, it is necessary to make the cross section of the steel cord flat and to reduce the diameter (minor axis) of the steel cord. It is effective.

  Normally, when a steel cord having a (1 × N) structure is flattened using a jig such as a press roller, initial elongation occurs when a tensile force is applied to the steel cord, so that the effect as a reinforcing member is reduced. . Thus, for example, Patent Documents 1 to 4 have been proposed as a cord structure having a flat shape without impairing the tensile rigidity of the steel cord. The steel cord described in Patent Document 1 has a 2 + 6 structure, and a technique for infiltrating rubber between filaments by providing a gap between sheath filaments has been proposed. Moreover, the steel cord described in Patent Document 2 attempts to solve the above problem by defining the core filament diameter and the sheath filament diameter. Furthermore, the steel cord described in Patent Document 3 discloses a technique for improving the permeability of rubber into the steel cord by defining the ratio between the core filament diameter and the sheath filament diameter. Furthermore, Patent Document 4 discloses a technique for ensuring rubber permeability by adopting a single twist structure or a layer twist structure of 6 to 10 steel filaments.

Japanese Patent Laid-Open No. 9-158066 JP 2005-120491 A JP 2007-63724 A JP 2007-90937 A

  However, although Patent Documents 1 to 4 have been studied from the viewpoint of rubber permeability, that is, durability, it cannot be said that the productivity of the steel cord has been sufficiently examined, and more than necessary between the sheath filaments. When the gap is open, the sheath filaments are not evenly distributed around the core filaments, resulting in a problem of poor productivity. That is, when the entire steel cord is bent, the tension on each filament is likely to be non-uniform, causing a phenomenon in which some filaments are stretched out. In addition, since the tension is not evenly distributed to the filament when the steel cord is pulled, there is a problem that the strength is reduced.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pneumatic tire that achieves weight reduction without reducing durability and productivity.

  As a result of intensive studies to solve the above problems, the present inventor has solved the above problems by optimizing the interval between the sheath filaments constituting the (2 + 6) structure steel cord and the cord interval. As a result, the present invention has been completed.

That is, the pneumatic tire of the present invention has a pair of bead portions, a pair of sidewall portions that are continuous to the outside in the tire radial direction of both bead portions, and a tread portion that is continuous between both sidewall portions. A carcass made of at least one carcass ply that extends in a toroidal shape between the bead portions and reinforces these portions, and at least two crossing belt layers arranged on the outer side in the tire radial direction of the crown portion of the carcass. In a pneumatic tire provided with a belt,
The reinforcing material of at least one layer of the crossing belt layer is a steel cord comprising a core in which two core filaments are arranged in parallel without being twisted, and six sheath filaments twisted around the core. When the diameter of the sheath filament is ds (mm) and the sheath filament twist pitch is p (mm), the following formula (I),
D = [L−6ds {1+ (L / p) ² } ^1/2 ] / 6 (I)
(Wherein L = (π + 2) dc + πds), the average sheath filament spacing D is 25-80 μm, and
The interval between the steel cords adjacent to each other is 0.50 mm to 1.40 mm.

In the present invention, the dc and the ds are represented by the following formulas (II) to (IV),
dc <ds (II)
0.20 ≦ dc ≦ 0.32 (III)
0.27 ≦ ds ≦ 0.43 (IV)
The belt layer preferably has a thickness of 1.30 mm to 1.65 mm, and the sheath filament preferably has a twist pitch p of 5 to 18 mm. Further, the tensile modulus of elasticity of the rubber-coated steel cord cut out from the tire is preferably 190 GPa or more, and the short diameter of the steel cord is preferably 0.85 mm to 1.05 mm.

  ADVANTAGE OF THE INVENTION According to this invention, the pneumatic tire which implement | achieved weight reduction can be provided, without reducing durability and productivity.

It is a half sectional view showing a preferred embodiment of the pneumatic tire of the present invention. It is sectional drawing of the steel cord which concerns on the pneumatic tire of this invention. It is sectional drawing of the steel cord in case D is less than 25 micrometers. It is sectional drawing of the steel cord in case D is larger than 80 micrometers.

Hereinafter, preferred embodiments of the present invention will be described in detail.
FIG. 1 is a half sectional view showing a preferred embodiment of the pneumatic tire of the present invention. The tire shown in FIG. 1 has a pair of bead portions 1, a pair of sidewall portions 2 that are continuous to the outside in the tire radial direction of both bead portions, and a tread portion 3 that is continuous to both sidewall portions 2. A carcass 4 composed of at least one carcass ply (one in the illustrated example) that extends in a toroidal shape between the bead parts 1 and reinforces each of the parts 1, 2, and 3, and a tire radius of a crown part of the carcass 4 And a belt 5 having at least two layers (four in the illustrated example) of intersecting belt layers arranged on the outer side in the direction.

  The carcass 4 in the illustrated example is composed of a single folded carcass ply. The folded carcass ply includes a main body portion extending in a toroidal shape between a pair of bead cores 6 embedded in the bead portion 1, and each bead core 6. Although it is composed of a folded portion wound around radially outward from the inside in the tire width direction to the outside, the number of plies and the structure of the carcass 4 are not limited to this.

In the present invention, at least one reinforcing material of the crossing belt layer is a steel cord comprising a core in which two core filaments are arranged in parallel without being twisted, and six sheath filaments twisted around the core. When the core filament diameter is dc and the sheath filament diameter is ds, the following formula (I):
D = [L−6ds {1+ (L / p) ² } ^1/2 ] / 6 (I)
An average sheath filament interval D represented by (here, L = (π + 2) dc + πds) is 25 μm to 80 μm. By using a flat steel cord having such a structure as a belt reinforcing material, the weight of the tire can be reduced without deteriorating durability and productivity.

  Hereinafter, the structure of the steel cord according to the present invention will be described in detail. FIG. 2 is an explanatory diagram of the structure of a steel cord according to the pneumatic tire of the present invention. As shown in the figure, a steel cord 10 according to the present invention includes a core in which two core filaments 11 are arranged in parallel without being twisted, and six sheath filaments 12 twisted around the core. By using such a flat steel cord 10, the thickness of the belt layer can be reduced, and the weight of the tire can be reduced. The reason why the number of the core filaments 11 is two is that when the number of the core filaments 11 is three or more, it is difficult to arrange them in parallel without being twisted. Moreover, the rubber permeability to the center part of the steel cord 10 required for ensuring durability can be efficiently ensured by using six sheath filaments 12. When the number of sheath filaments is 5 or less, the rubber permeability is good, but the dispersibility of the sheath filament is deteriorated and the strength is insufficient. On the other hand, when the number of sheath filaments is seven or more, it becomes impossible to secure a sufficient gap for rubber penetration, and durability is lowered.

Here, when the cross section of the steel cord 10 is viewed, the untwisted core filament 11 has a substantially circular shape, but the sheath filament 12 changes in cross section according to the twist pitch. That is, the cross section of the sheath filament 12 approaches a circular shape when the twist pitch is increased, and the cross section of the sheath filament 12 has a feature that the degree of ellipse (flatness) increases when the twist pitch decreases. Therefore, in the present invention, when the diameter of the core filament 11 is dc (mm), the diameter of the sheath filament 12 is ds (mm), and the sheath filament twist pitch is p (mm), the following formula (I),
D = [L−6ds {1+ (L / p) ² } ^1/2 ] / 6 (I)
It is important that the average sheath filament interval D represented by (here, L = (π + 2) dc + πds) is 25 to 80 μm. By combining the diameter dc of the core filament 11, the diameter ds of the sheath filament 12 and the twist pitch p so as to satisfy the above formula (I), it is possible to sufficiently ensure the penetration of rubber into the gap of the sheath filament 12, Since the dispersibility is good, it is possible to suppress filament tension and strength reduction during bending deformation of the steel cord without leaving an extra gap.

  When D is smaller than 25 μm, for example, as shown in FIG. 3, the rubber cannot sufficiently penetrate into the gap between the sheath filaments 12, and when the belt is cut, moisture penetrates and propagates, so-called cut separation occurs. Will occur. On the other hand, when D is larger than 80 μm, for example, the sheath filament 12 is not evenly distributed around the core filament 11 as shown in FIG. Cannot penetrate. In addition, there is a concern that the filament may be stretched or the strength may be reduced. Preferably, the thickness is 30 to 70 μm, more preferably 50 to 60 μm. By setting the value of D within this range, the rubber permeability and the dispersibility of the sheath filament 12 are optimally balanced.

  In the present invention, the distance between adjacent steel cords in the crossing belt is 0.50 mm to 1.40 mm. If the distance between the steel cords is less than 0.50 mm, peeling of the belt layer due to the progress of cracks generated from the ends of the steel cords, so-called belt edge separation (BES), is significantly deteriorated. On the other hand, if the steel cord interval is larger than 1.40 mm, the number of steel cords to be driven is too small, so that sufficient strength as a tire cannot be obtained. Preferably they are 0.70 mm or more and 1.20 mm or less.

In the present invention, the diameter dc of the core filament 11 and the diameter ds of the sheath filament 12 are the following formulas (II) to (IV),
dc <ds (II)
0.20 ≦ dc ≦ 0.32 (III)
0.27 ≦ ds ≦ 0.43 (IV)
It is preferable to satisfy the relationship represented by these. That is, the diameter dc of the core filament 11 and the diameter ds of the sheath filament 12 are different combinations. In particular, the diameter dc of the core filament 11 should be smaller than the diameter ds of the sheath filament 12. Thereby, the short diameter of the flat-shaped steel cord obtained can be made smaller with respect to the case where filaments having the same diameter are combined. Further, by satisfying the above (III) and (IV), the steel cord can obtain higher strength. Preferably 0.23 ≦ dc ≦ 0.27 and 0.30 ≦ ds ≦ 0.35, more preferably 0.24 ≦ dc ≦ 0.26 and 0.32 ≦ ds ≦ 0.34. By setting the core filament diameter dc and the sheath filament diameter ds in this range, weight reduction of the tire can be realized in a balanced manner while maintaining rubber permeability and steel cord strength.

  Furthermore, in the present invention, the thickness of the belt layer is preferably 1.30 mm to 1.65 mm. If the thickness of the belt layer is less than 1.30 mm, sufficient durability may not be obtained, which is not preferable. On the other hand, if the thickness of the belt layer exceeds 1.65 mm, the tire weight reduction effect may not be obtained, which is not preferable. From the viewpoint of reducing the weight of the tire, it is preferably 1.40 mm or more and 1.55 mm or less.

  Furthermore, in this invention, it is preferable that the twist pitch p of the sheath filament 12 is 5-18 mm. When the twist pitch of the sheath filament 12 is less than 5 mm, a sufficient gap between the sheath filaments 12 cannot be ensured. On the other hand, if the twist pitch p of the sheath filament 12 is 5 to 18 mm, the productivity can be improved satisfactorily. In order to obtain the above effect satisfactorily, the thickness is preferably 10 to 16 mm.

  In the present invention, after the tire vulcanization molding, the rubber-coated steel cord cut out from the tire preferably has a tensile elastic modulus of 190 GPa or more. When the tensile modulus of elasticity of the rubber-coated steel cord cut out from the tire is 190 GPa or more, the belt's tagging effect can be sufficiently exhibited, and the tire shape retention and steering stability can be ensured satisfactorily. If it is less than 190 GPa, the steel cord may be initially stretched at the time of internal pressure, which may result in deterioration of the tire shape.

  Furthermore, in the present invention, the short diameter of the steel cord is preferably 0.85 mm to 1.05 mm. By making the short diameter of the steel cord 1.05 mm or less, the belt can be effectively thinned. When the minor axis is 1.00 mm or less, the effect of weight reduction is increased, which is more preferable. However, if the minor axis is less than 0.85 mm, the amount of steel is greatly reduced, and thus the strength required for the belt may not be ensured.

  The pneumatic tire of the present invention has a belt having at least two crossing belt layers, and at least one reinforcing material of the crossing belt layers is arranged in parallel without twisting the two core filaments. Steel cords comprising six sheath filaments twisted around the core, the average sheath filament diameter D satisfies the above relationship, and the distance between adjacent steel cords is 0. It may be 50 mm to 1.40 mm, and the total number and structure of the belt layers are not particularly limited.

  There is no restriction | limiting in particular as a raw material of the steel filament used for this invention, What is used conventionally can be used, However, It is a high carbon steel whose carbon component is 0.80 mass% or more. Is preferred. The effect of the present invention can be obtained satisfactorily by making the filament material a high carbon steel having a high hardness carbon component of 0.80% by mass or more. On the other hand, if the carbon component exceeds 1.5% by mass, the ductility is lowered and the fatigue resistance is inferior.

  The steel cord of the present invention is preferably plated on the cord surface. The composition of the cord surface plating is not particularly limited, but is preferably brass plating composed of copper and zinc, and more preferably the copper content is 60% by mass or more. Thereby, the adhesiveness of a steel filament and rubber can be improved.

  The material of the coating rubber used in the present invention is not particularly limited, and a known rubber can be used, but those having a Mooney viscosity of 50 or more and 110 or less are preferable. If the Mooney viscosity is less than 50, the tire performance is degraded, and if it is greater than 110, a portion where the rubber does not sufficiently permeate locally occurs between the sheath filaments. Here, the Mooney viscosity is a value obtained by measurement according to JIS-K6300.

  As described above, the pneumatic tire of the present invention is particularly suitable as a light truck tire and truck / bus tire because it is lightweight and excellent in durability. In the pneumatic tire of the present invention, as the gas filled in the tire, normal or air having a changed oxygen partial pressure, or an inert gas such as nitrogen can be used.

Hereinafter, the present invention will be described in more detail with reference to examples.
<Examples 1-9, Conventional Examples and Comparative Examples 1-8>
A tire of the type shown in FIG. 2 was produced with a tire size of 11R22.5 / 14PR. The belt is composed of four belt layers, and the second belt layer and the third belt layer (the second layer and the third layer from the inner side in the tire radial direction respectively) form a main crossing layer, and are shown in Tables 1 to 3 The steel cord was applied as a reinforcing member for the entire belt layer, and the steel cord was arranged so that the major axis direction was along the belt width direction. The angles of the belt layers of the first belt layer to the fourth belt layer were + 52 °, + 16 °, −16 °, and −16 °, respectively, with respect to the circumferential direction. The obtained test tire was evaluated for rubber permeability, durability, diameter growth and belt weight according to the following procedure. The productivity of steel cord was also evaluated. The tensile modulus of rubber-coated steel cord cut out from the tire was calculated according to the following procedure.

<Cord tensile modulus>
After each steel cord of Examples 1 to 9, Conventional Example and Comparative Examples 1 to 8 was dissected from the tire and taken out, excess rubber attached to the surface of the steel cord at the grip portion was removed, and a tensile test was performed by a cord tensile tester. Carried out. At that time, the tensile strain was measured by a video extensometer. The distance between the gauge points in the measurement is 100 mm, and the tensile test speed is 10 mm / min. In the obtained stress-strain curve, a slope between two points of a stress at a tensile strain of 0.1% and a stress of 0.5% was calculated to calculate a cord tensile elastic modulus. The cord tension modulus obtained was better than that of the conventional example, and the inferior one was marked as x. The results are shown in Tables 1-3. In addition, the cross-sectional area of the steel cord in the calculation of stress was calculated by π × (dc ² × 2 + ds ² × 6) / 4.

<Rubber permeability>
The steel cords of Examples 1 to 9, Conventional Example and Comparative Examples 1 to 8 were dissected from the tire and taken out, and then immersed in a NaOH-10% aqueous solution and allowed to stand for 24 hours. Was measured. If rubber penetrates into the steel cord, the rubber will not peel off. The case where the rubber peeling length was equal to or less than that of the steel cord of the conventional example was rated as “◯”, and the case where it was inferior as “X”. The results are shown in Tables 1-3.

<Durability>
After the obtained tire was incorporated into an 8.25 inch rim, the internal pressure was filled to 700 kPa, the load was applied to 26.7 kN, a side force of 13.4 kN was intermittently applied, and the peripheral speed of the drum was set to 60 km / The endurance drum test was conducted under the conditions of h. The crack at the belt end was measured 24 hours after running. The case where the crack length was equal to or less than that of the conventional example was evaluated as ◯, and the case where the crack length was inferior was evaluated as ×. The results are shown in Tables 1-3.

<Diameter growth>
After assembling each test tire on an 8.25 inch rim, the diameter growth amount when the internal pressure was filled from 50 kPa to 700 kPa was measured at the center of the belt. The diameter growth amount was suppressed as compared with the belt of the conventional example. The results are shown in Tables 1-3.

<Belt weight>
Each test tire is dissected and the main crossing layer at the center in the width direction has a size of 100 mm in the width direction × 500 mm in the circumferential direction, and the belt layer (the first belt layer and the second belt layer in the thickness direction). Cut out along the rubber at the center of the thickness of the belt layer between the belt layers and between the third belt layer and the fourth belt layer), the weight was measured. The belts that were substantially lighter than the conventional belts were marked with ◯, and the others were marked with ×. The results are shown in Tables 1-3.

<Code productivity>
Each steel cord of Examples 1 to 9, Conventional Example and Comparative Examples 1 to 8 was subjected to bending deformation, and it was visually evaluated whether or not the filament was stretched. Further, the steel cord was cut with pliers, and it was visually evaluated whether the filament breakage (so-called flare property) had deteriorated. In those evaluations, those that were not deteriorated from the conventional examples were marked with ◯, and others that were marked with x. The results are shown in Tables 1-3.

※タイヤから切出したゴム被覆されたスチールコードの引張弾性率

* Tensile modulus of rubber coated steel cord cut out from tire

※タイヤから切出したゴム被覆されたスチールコードの引張弾性率

* Tensile modulus of rubber coated steel cord cut out from tire

※タイヤから切出したゴム被覆されたスチールコードの引張弾性率

* Tensile modulus of rubber coated steel cord cut out from tire

  From the above Tables 1 to 3, it was confirmed that the pneumatic tire of the present invention can realize weight reduction without reducing durability and productivity.

DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall part 3 Tread part 4 Carcass 5 Belt 6 Bead core 10 Steel cord 11 Core filament 12 Sheath filament

Claims (6)

It has a pair of bead portions, a pair of sidewall portions that are continuous to the outside in the tire radial direction of both bead portions, and a tread portion that is continuous between both sidewall portions, and extends in a toroidal shape between the pair of bead portions. A pneumatic tire comprising: a carcass made of at least one carcass ply that reinforces each of these parts; and a belt having at least two crossing belt layers arranged on the outer side in the tire radial direction of the crown part of the carcass. ,
The reinforcing material of at least one layer of the crossing belt layer is a steel cord comprising a core in which two core filaments are arranged in parallel without being twisted, and six sheath filaments twisted around the core. When the diameter of the sheath filament is ds (mm) and the sheath filament twist pitch is p (mm), the following formula (I),
D = [L−6ds {1+ (L / p) ² } ^1/2 ] / 6 (I)
(Wherein L = (π + 2) dc + πds), the average sheath filament spacing D is 25-80 μm, and
A pneumatic tire characterized in that an interval between adjacent steel cords is 0.50 mm to 1.40 mm. The dc and the ds are represented by formulas (II) to (IV) below
dc <ds (II)
0.20 ≦ dc ≦ 0.32 (III)
0.27 ≦ ds ≦ 0.43 (IV)
The pneumatic tire according to claim 1, satisfying a relationship represented by:   The pneumatic tire according to claim 1 or 2, wherein the belt layer has a thickness of 1.30 mm to 1.65 mm.   The pneumatic tire according to any one of claims 1 to 3, wherein a twist pitch p of the sheath filament is 5 to 18 mm.   The pneumatic tire according to any one of claims 1 to 4, wherein the rubber-coated steel cord cut out from the tire has a tensile elastic modulus of 190 GPa or more.   The pneumatic tire according to any one of claims 1 to 5, wherein a short diameter of the steel cord is 0.85 mm to 1.05 mm.

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