JP2007118850A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire equipped with a good maneuvering stability, durability, and cost performance required of a high performance radial tire designed for application to a high performance passenger car. <P>SOLUTION: The pneumatic radial tire includes a carcass 1 as a skeleton which stretches toroidally between a pair of bead parts 11 and is structured so that at least one belt layer 2 formed by lining with rubber the steel cords consisting of a plurality of steel element wires is laid on the outside in radial direction of the crown part of the carcass. The bending rigidity Ec of the steel cords in the condition embedded in the belt layer ranges between 49 and 196 Pa, being 1.0-1.27 times as large as the cord bending rigidity Er in the condition of cords solely not embedded in the belt layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pneumatic radial tire (hereinafter, also simply referred to as “tire”), and more particularly, to a pneumatic radial tire excellent in steering stability used for a high-performance passenger car or the like.

  Generally, a pneumatic radial tire has a carcass extending in a toroidal shape between a pair of bead portions, and a belt layer made of rubberized steel cord is disposed as a reinforcing layer on the outer side in the tire radial direction. The For such a belt layer, the important characteristics required to ensure steering stability as a high-performance radial tire are high tensile rigidity in the circumferential direction, high in-plane bending rigidity, and out-of-plane bending. The rigidity is low.

  In other words, the belt member bears the tension due to the internal pressure and exhibits the effect, but it needs to have a large rigidity in the circumferential direction. For this reason, it is desirable that the belt layer first has high circumferential tensile rigidity. In addition, since the belt member is subjected to in-plane bending deformation during cornering, a tire having a smaller in-plane bending deformation of the belt can generate a large cornering force and exhibit good steering stability. For this reason, it is desirable that the belt layer has a high in-plane bending rigidity.

  Further, in the vicinity of the cornering limit point, the belt layer is subjected to a large in-plane bending deformation. Due to this deformation, the belt layer is subjected to a large compressive deformation inside the bending deformation, and buckling occurs. However, by reducing the out-of-plane bending rigidity of the belt layer, the out-of-plane deformation pressure accompanying compression is reduced, and buckling deformation can be suppressed by the tire internal pressure. Thereby, the drop of the ground pressure is suppressed, and the ground pressure becomes uniform. For this reason, the belt layer desirably has low out-of-plane bending rigidity.

In order to reduce the out-of-plane bending rigidity of the belt layer and improve the handling stability, a technique is known in which a steel cord having a small wire diameter and a low bending rigidity is applied to the belt. Patent Document 2 describes a technique for improving maneuverability and stability during cornering by using a specific steel cord with a thin wire diameter (wire diameter 0.06 to 0.10 mm). A tire having a steel cord defined by bending resistance and tensile elongation is disclosed. Patent Document 3 discloses a tire that is a steel cord made of a predetermined steel filament and that has a predetermined range of values defined by belt bending stiffness, cord strength, and gap amount of the belt cord. Documents 4 to 6 disclose a steel cord for reinforcing tires having a predetermined twist structure and having a predetermined range of values defined by cord strength, elongation at cord breakage, and cord bending rigidity.
JP 59-38102 A (Claims etc.) JP-A-60-185602 (Claims) JP-A 64-855381 (Claims etc.) JP-A 64-85382 (Claims etc.) JP-A 64-85383 (Claims etc.) JP-A 64-85384 (Claims etc.)

  However, as disclosed in the above-mentioned patent document, in the technology for improving the handling stability by applying a double twisted steel cord using a thin strand to the belt layer, the strand diameter is extremely fine, and Due to the double twist, the productivity is low and the cost is high, and the rubber penetration is inferior to the single twist cord generally used as a belt cord. . In particular, the techniques described in Patent Documents 4 to 6 aim to improve rubber penetrability by improving the strand structure, but it has been difficult to obtain rubber penetrability as good as a single twist cord. Therefore, it is limited to special applications such as racing tires, and it has been difficult to apply to more general high-performance radial tires intended for high-performance passenger cars.

  Further, it was found that the bending rigidity increased in the state where the steel cord was applied to the tire as a belt reinforcing cord as compared with the state of the cord alone. That is, it has been found that the effect of reducing the bending rigidity by using a thin wire is not sufficiently exhibited in the tire, and there is room for improvement.

  Accordingly, an object of the present invention is to eliminate the above-mentioned problems of the prior art and to provide a pneumatic system that has excellent handling stability, durability, and cost required for a high-performance radial tire intended for application to a high-performance passenger car. It is to provide a radial tire.

  In order to solve the above-mentioned problems, the present inventor increases bending rigidity as compared with a single cord state when a double-stranded steel cord using a conventional thin wire is applied to a tire as a belt reinforcing cord. Analysis of the phenomenon revealed the following.

  That is, when bending deformation is applied to the steel cord, relative movement occurs between the steel strands, but an interaction that prevents this relative movement occurs between the strands in contact with each other. When manufacturing pneumatic radial tires with belt layers reinforced with steel cords, especially during expansion during vulcanization, tension is applied to the steel cord, so there is pretension in the steel cord within the finished tire. It will be in the state. When tension is applied to the steel cord composed of a plurality of strands, the distance between the strands is reduced, and the pressure between the contacting strands is increased. For this reason, in the state embedded in the tire, the interaction between the strands generated when the cord is bent increases, and the bending rigidity increases as compared with the state of the cord alone (tension zero). In particular, in a double twisted steel cord using a conventional thin wire, when a bend is applied, an interaction between strands as well as an interaction between strands occurs, so that an increase in bending rigidity increases.

  From the above viewpoint, as a result of further intensive studies, the present inventors have found that a tire having desired steering stability, durability, and cost can be realized by adopting the following configuration, and completed the present invention. .

That is, the pneumatic radial tire of the present invention has a carcass extending in a toroidal shape between a pair of bead portions as a skeleton, and a steel cord composed of a plurality of steel strands on the outer side in the radial direction of the crown portion of the carcass. In a pneumatic radial tire in which at least one belt layer formed by pulling is disposed,
The bending rigidity (Ec) of the steel cord embedded in the belt layer is 49 Pa or more and 196 Pa or less, and the cord bending rigidity (Er) in the state of the cord alone not embedded in the belt layer ) 1.0 to 1.27 times.

  In the present invention, the strand diameter of the steel strand is preferably 0.08 to 0.21 mm, and the number of the steel strands is preferably 6 to 12. Further, in the present invention, the steel cord is formed by twisting the plurality of steel strands in the same direction and at the same pitch, and embedded in the belt layer in a state where rubber penetrates between the steel strands. In this case, in particular, the steel cord does not have a core structure in which one or more steel strands are surrounded by other steel strands. Furthermore, it is preferable that the steel cord is composed of a core strand made of one or two steel strands and a one-layer sheath made of another steel strand twisted around the core strand, In this case, in particular, the core strand is composed of two steel strands arranged in parallel without twisting.

According to the present invention, the above-described configuration realizes a pneumatic radial tire that has excellent handling stability, durability, and cost performance, which are necessary as a high-performance radial tire intended for application to a high-performance passenger car. It became possible.

Hereinafter, preferred embodiments of the present invention will be described in detail.
In FIG. 1, the schematic sectional drawing of an example of the pneumatic radial tire of this invention is shown. As shown in the figure, the tire of the present invention has a carcass 1 extending in a toroidal shape between a pair of bead portions 11 as a skeleton, and a steel cord composed of a plurality of steel strands on the outer side in the radial direction of the crown portion. At least one crossed belt layer 2 (2a, 2b) in the illustrated example is disposed.

In the present invention, the flexural rigidity of the steel cord in a state of being buried in the belt layer 2 (Ec), by the following 49Pa (5.0kgf / mm ²⁾ or more and 196Pa (20.0kgf / mm ²⁾ In addition to ensuring sufficient steering stability as a high-performance radial tire, the bending rigidity (Ec) of the steel cord embedded in the belt layer 2 can be obtained in a state where the cord alone is not embedded in the belt layer 2. By specifying 1.0 to 1.27 times the cord bending rigidity (Er), the flexibility of the cord alone can be effectively used in the tire.

  Here, the bending rigidity of the steel cord can be measured using a commercially available Taber stiffness tester (for example, Toyo Seiki Seisakusho Digital Taber stiffness tester). Specifically, for example, when the cord is cut to a predetermined length and then bent 15 degrees from the fulcrum, the cord is flat when the cord has a flat outer shape. . In addition, regarding the bending rigidity of the steel cord taken out from the belt layer 2 of the tire with rubber, after the cord was taken out with rubber, the covering rubber on the cord surface was shaved to a thickness of about 0.1 to 0.5 mm Measure with. On the other hand, regarding the bending rigidity of the steel cord when it is not embedded in the belt layer, is it measured in a state where the rubber on the surface of the steel cord taken out from the tire belt layer with rubber is completely removed with an organic solvent or the like? Alternatively, it may be measured with a raw cord before being embedded in a tire.

  In the present invention, as long as the bending rigidity of the steel cord satisfies the above conditions, the desired effect such as improvement of steering stability can be obtained, and the cord structure of the steel cord is particularly limited. Although it is not a thing, as a steel strand which comprises a steel cord, for example, a strand having a wire diameter of 0.08 to 0.21 mm, preferably 0.10 to 0.20 mm is used.

  By making the strand diameter of the steel strand 0.21 mm or less, preferably 0.20 mm or less, it is easy to make the bending rigidity (Ec) of the steel cord embedded in the belt layer 2 196 Pa or less. become. On the other hand, if the strand diameter is less than 0.08 mm, the cord strength is low with a suitable number of strands to be described later. Therefore, in order to secure the circumferential rigidity as the belt layer 2, the cord driving is greatly increased and densely It is necessary to arrange the cord, and separation between the rubber and the cord is likely to occur. Or circumferential rigidity may be insufficient, and high-speed durability may be impaired.

  Further, the number of steel strands constituting the steel cord is 6 to 12, preferably 7 to 10. The upper limit of the number of strands is set to 12, preferably 10, because the interaction between the strands when the cord is bent tends to increase as the number of strands increases. On the other hand, if the number of strands is less than 6, the cord strength is low at the above-mentioned preferred strand diameter. Therefore, in order to secure the circumferential rigidity as the belt layer 2, the driving of the cord is greatly increased to increase the density. It is necessary to arrange the cord, and separation between the rubber and the cord is likely to occur. Or circumferential rigidity may be insufficient, and high-speed durability may be impaired.

  In the present invention, a steel cord having a 1 × n structure in which all steel strands are twisted in the same direction and at the same pitch is used by being embedded in the belt layer 2 in a state where rubber penetrates between the strands. Is preferred. By embedding the steel cord with the rubber infiltrated between the strands, the rubber intervenes between the strands, so the interaction between the strands when bent is greater than when the strands are in direct contact with each other. Get smaller. In this 1 × n single twist structure, it is easy to make a structure that allows rubber to penetrate into the inside of the cord. For example, an open structure in which an oversized element wire is twisted loosely or a small wave habit is applied. The rubber permeability can be imparted by applying a structure in which twisted strands are twisted.

  When such a 1 × n structure steel cord is applied, it is more preferable that the cord structure does not have a core structure in which one or more steel strands are surrounded by other steel strands. In the case of a cord structure that does not have a core structure, the number of adjacent strands is smaller than in the case where there is a core structure, so that the interaction between the strands when bent is reduced. Moreover, the rubber penetration into the inside of the cord can be made more complete without the core structure.

  Further, when an n + m structure steel cord in which a sheath wire is twisted around the core strand is applied, the number (n) of the strands of the core strand is one or two and the sheath is one layer. When the number of strands (n) of the core strand is 3 or more, a closed space in which rubber is not penetrated by the core strand is likely to occur at the center of the cord, and when the sheath has two or more layers, It becomes difficult to penetrate the rubber into the inner sheath. In this case, more preferably, the number of sheath wires (m) is 5 to 8, and a gap is provided between the sheath wires.

  When such an n + m steel cord is applied, the core strand is more preferably configured by two strands arranged in parallel without twisting. In this case, since the core strands are not twisted together, the interaction between the core strands when bent is reduced.

  In addition, the suitable twist pitch of the steel cord in this invention is about 5-18 mm. If the twist pitch is less than 5 mm, disconnection may occur at the time of twisting, and the productivity deteriorates and costs increase. On the other hand, when the twist pitch exceeds 18 mm, the twist angle becomes small and the twist property may be deteriorated. There is also a difficulty that rubber penetrating becomes difficult.

  In the present invention, it is preferable that the outer shape of the steel cord is flattened and the major axis direction of the flat cross section is arranged along the width direction of the belt layer. As a result, anisotropy occurs in the bending rigidity, so that a belt layer having a large in-plane bending rigidity and a small out-of-plane bending rigidity can be formed as compared with the case where a non-flat steel cord is arranged.

  In addition, as a steel strand used for a steel cord, the tensile strength is usually 3200 to 4000 MPa, and particularly a brass-plated steel wire having about 3300 to 4000 MPa can be suitably used. And within the range of the number of suitable strands, it becomes easy to ensure the circumferential rigidity as the belt layer with an appropriate driving density.

  In the present invention, a steel cord satisfying the above conditions can be obtained by appropriately adjusting the conditions related to the steel strand and the cord structure, and by applying such a steel cord to the belt layer 2, the steering stability can be improved. A pneumatic radial tire excellent in durability and durability can be realized, and the structure and specific materials of other members constituting the tire are not particularly limited. For example, as shown in the drawing, a bead core 3 is embedded in each of the pair of bead portions 11 of the tire of the present invention, and the carcass 1 is folded around the bead core 3 from the inside of the tire to the outside and locked. A tread portion 12 is disposed on the outer periphery of the crown portion of the belt layer 2, and a sidewall portion 13 is disposed on the side portion of the carcass 1. Further, the outer circumferences of the crown portions of the crossing belt layers 2a and 2b have at least a width in the width direction covering the belt layer 2 and are arranged substantially parallel to the tire circumferential direction in order to increase circumferential rigidity. Two layers of cap layers 4 made of rubberized reinforcing cords and rubberized reinforcing cords each having a length in the width direction covering one end in the width direction of the belt layer and arranged substantially parallel to the tire circumferential direction A pair of layer layers 5 can be arranged.

Hereinafter, the present invention will be described in more detail with reference to examples.
As shown in FIG. 1, a pneumatic radial comprising two crossing belt layers 2 a and 2 b made of rubberized steel cord, two cap layers 4 and a pair of layer layers 5 in the radial direction of the crown portion of the carcass. A tire was produced. Steel cords satisfying the conditions shown in Table 1 below were used. The tire size was 225 / 45R17, and the angles of the intersecting belt layers 2a and 2b were ± 60 ° with respect to the tire width direction. A nylon cord was applied to the cap layer 4 and the layer layer 5. Each of the obtained test tires was evaluated according to the following. The results are also shown in Table 1 below.

(Measurement of bending rigidity Ec, Er)
Using a digital taber stiffness tester manufactured by Toyo Seiki Seisakusho Co., Ltd., the cord was cut into a predetermined length and then measured with the cord bent 15 degrees from the fulcrum. In the case of a cord with a flat outer shape, it was set as the rigidity against bending in the minor axis direction. With respect to the bending rigidity (Ec) in the state where it was embedded in the belt layer, the surface of the cord with rubber cut out from the test tire was measured with the rubber cut to a thickness of 0.1 to 0.5 mm. Further, the cord bending rigidity (Er) in the state of the cord alone not embedded in the belt layer was measured in a state where the rubber on the surface of the cord with rubber cut out from the test tire was dissolved and removed with an organic solvent.

(Rubber permeability evaluation)
The rubber permeability of each steel cord was evaluated by immersing the cord in a NaOH-10% aqueous solution and observing the degree of NaOH erosion after 24 hours. In the case of ordinary rubber pene cords, the amount of erosion was 0 (conventional example 1), and this was shown as an index with this being 100. The larger the index, the better the results.

(Steering stability evaluation)
Each test tire was mounted on four wheels of a passenger car at an air pressure of 20.6 kPa (2.1 kgf / cm ² ), and a test driver ran the test course in this test vehicle. The feeling results regarding the handling stability and ride comfort of each test tire by the test driver were rated according to the following evaluation criteria in comparison with the control tire (conventional example 1).
+3: Good +2: Somewhat good +1: Somewhat good ± 0: No change -1: Somewhat bad -2: Somewhat bad -1: Bad

(High-speed durability evaluation)
In the high-speed durability test, each test tire was assembled on a rim having a rim size of 7.5 J × 17 at an air pressure of 300 kPa, and the step speed method was performed according to the test method of JATMA standard. The results are shown as an index with the speed at the time of failure of the test tire of Conventional Example 1 being 100. The higher the number, the better the result.

(Corrosion durability evaluation)
Each test tire was mounted on a standard rim defined in the JATMA standard, filled with an internal pressure corresponding to the maximum load capacity in JATMA YEAR BOOK, and mounted on a passenger car. After traveling 50000 km on the paved road, the tire was dissected to investigate the corrosion length of the cord from the cut flaw. The results were expressed as an index, with Comparative Example 1 taken as 100. The smaller the value, the smaller the corrosion length and the better.

＊１）偏平率Ｄ１／Ｄ２：Ｄ１は偏平断面の短径、Ｄ２は長径を示す。

* 1) Flatness ratio D1 / D2: D1 is the minor axis of the flat section, and D2 is the major axis.

  As shown in Table 1 above, the bending stiffness (Ec) when embedded in the belt layer is 49 Pa or more and 196 Pa or less, and the cord bending rigidity when the cord is not embedded in the belt layer alone. In the tire of the example using the steel cord that is 1.0 to 1.27 times (Er), excellent steering stability and durability can be obtained as compared with the tire of the comparative example that does not satisfy this condition. It was confirmed.

1 is a schematic cross-sectional view of a pneumatic radial tire according to an embodiment of the present invention. 1 is a schematic sectional view of a steel cord used in Example 1. FIG. 3 is a schematic cross-sectional view of a steel cord used in Example 2. FIG. 6 is a schematic cross-sectional view of a steel cord used in Example 3. FIG. 6 is a schematic cross-sectional view of a steel cord used in Example 4. FIG. It is a schematic sectional drawing of the steel cord used for the prior art example 1. FIG. It is a schematic sectional drawing of the steel cord used for the prior art example 2. 3 is a schematic cross-sectional view of a steel cord used in Comparative Example 1. FIG. 6 is a schematic cross-sectional view of a steel cord used in Comparative Example 2. FIG. 6 is a schematic cross-sectional view of a steel cord used in Example 5. FIG.

Explanation of symbols

1 Carcass 2 (2a, 2b) Crossing belt layer 3 Bead core 4 Cap layer 5 Layer layer 11 Bead portion 12 Tread portion 13 Side wall portion

Claims (7)

A carcass extending in a toroidal shape between a pair of bead portions is used as a skeleton, and at least one belt layer formed by rubberizing a steel cord composed of a plurality of steel strands on the outer side in the radial direction of the crown portion of the carcass. In the arranged pneumatic radial tire,
The bending rigidity (Ec) of the steel cord embedded in the belt layer is 49 Pa or more and 196 Pa or less, and the cord bending rigidity (Er) in the state of the cord alone not embedded in the belt layer Pneumatic radial tire characterized by being 1.0 to 1.27 times greater).   The pneumatic radial tire according to claim 1, wherein a strand diameter of the steel strand is 0.08 to 0.21 mm.   The pneumatic radial tire according to claim 1 or 2, wherein the number of the steel strands is 6 to 12.   The steel cord is formed by twisting the plurality of steel strands in the same direction and at the same pitch, and embedded in the belt layer in a state where rubber penetrates between the steel strands. The pneumatic radial tire according to any one of 3.   The pneumatic radial tire according to claim 4, wherein the steel cord does not have a core structure in which one or more steel strands are surrounded by other steel strands.   The air according to claim 3, wherein the steel cord includes a core strand made of one or two of the steel strands and a one-layer sheath made of another steel strand twisted around the core strand. Entering radial tire.   The pneumatic radial tire according to claim 6, wherein the core strand includes two steel strands arranged in parallel without twisting.

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