JP2007303043A - Steel cord for reinforcing rubber, and method for producing pneumatic radial tire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel cord for reinforcing rubber, providing improved rubber penetrability into the inside of the cord without reducing tensile modulus, and having improved durability; and to provide a method for producing a pneumatic radial tire using the steel cord. <P>SOLUTION: The steel cord has a three-layer structure obtained by simultaneously twisting a first layer A including at least one wire 11, a second layer B positioned on the outer periphery side of the first layer A and including a plurality of wires 12, and a third layer positioned on the outer periphery side of the second layer B and including a plurality of wires 13. An unvulcanized rubber formulation R is inserted between the first layer A and the second layer B, and at least the wires 13 of the third layer C are formed. The formed rate of the wire 13 positioned at the top of the third layer C is 90-105%, and the formed rate of the wire 13 not positioned at the top of the third layer C is 95-110% based on the cord diameter D<SB>1</SB>at the top of a cord outline formed when the whole wires 11-13 are arranged in the close-packed state and the cord diameter D<SB>2</SB>not at the top. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a steel cord having a three-layer structure formed by a single twist and a method for manufacturing a pneumatic radial tire using the steel cord, and more particularly, to improve rubber penetration into the cord without reducing tensile rigidity. The present invention relates to a steel cord for reinforcing rubber capable of improving durability and a method for producing a pneumatic radial tire using the same.

  For example, as a steel cord constituting a carcass layer of a heavy duty pneumatic radial tire, a first layer including at least one strand, and a first layer including a plurality of strands positioned on the outer peripheral side of the first layer. A steel cord having a three-layer structure formed by simultaneously twisting two layers and a third layer including a plurality of strands located on the outer peripheral side of the second layer is used (for example, cited references 1 to 3). 3).

However, since a steel cord having a three-layer structure usually has a small gap between the strands of the third layer, there is a drawback that the rubber penetration into the cord is poor when vulcanized after rubber coating. And if the rubber penetration rate into the cord is low, the inner layer strands are not sufficiently restrained by the coat rubber or outer layer strands, so the inner layer strands do not work sufficiently as a tensile material, and the durability of the cord Will be reduced. On the other hand, if the wire is excessively brazed for the purpose of improving rubber permeability, the tensile rigidity of the cord decreases. In this case, in the pneumatic radial tire, the steering stability is lowered.
Japanese Patent Laid-Open No. 11-124781 Japanese Patent Laid-Open No. 2004-9879 JP 2004-42791 A

  The object of the present invention is to improve the rubber penetration into the inside of the cord without lowering the tensile rigidity and to improve the durability, and to manufacture a pneumatic radial tire using the same. It is to provide a method.

  In order to achieve the above object, a steel cord for rubber reinforcement according to the present invention includes a first layer including at least one strand, and a second layer including a plurality of strands positioned on the outer peripheral side of the first layer. In a steel cord having a three-layer structure in which a layer and a third layer including a plurality of strands located on the outer peripheral side of the second layer are simultaneously twisted, the first layer and the second layer The cord diameter at the apex of the cord contour formed when the unvulcanized rubber compound is inserted in between and at least the third layer strands are molded and all the strands are arranged in a close-packed state. In addition, with respect to the cord diameter at the non-vertex, the die forming rate of the wire located at the vertex of the third layer is set to 90 to 105%, and the die of the wire located at the non-vertex of the third layer is typed The rate is 95 to 110%.

  The pneumatic radial tire manufacturing method of the present invention is characterized in that a green tire using the rubber reinforcing steel cord as a carcass layer is formed and the green tire is vulcanized.

  In the present invention, an unvulcanized rubber compound is inserted between the first layer and the second layer in a steel cord having a three-layer structure formed by one-time twisting, and at least a third-layer wire is molded. , Optimize the mold rate. That is, it is located at the apex among the strands constituting the third layer with respect to the code diameter at the apex of the code outline formed when all the strands are arranged in the close-packed state and the code diameter at the non-vertex The forming rate of the wire to be set is 90 to 105%, and the forming rate of the wire located at the non-vertex among the wires constituting the third layer is set to 95 to 110%. In this way, the unvulcanized rubber compound is inserted between the first layer and the second layer, and the third layer strand is formed at the initial stage of vulcanization by appropriately shaping the third layer strand. Since the gap between them becomes large, the rubber permeability between the second layer and the third layer is improved. On the other hand, after vulcanization, the unvulcanized rubber compound between the first layer and the second layer flows to the outside in the cord radial direction due to the cord tension during vulcanization, and the strands of the third layer are cords Since it converges radially inward, it becomes possible to exhibit good tensile rigidity. Thereby, the rubber permeability to the inside of the cord can be improved without reducing the tensile rigidity, and the durability of the steel cord can be improved. Furthermore, the durability of the pneumatic radial tire obtained by using such a steel cord for the carcass layer can be improved.

  In the steel cord for reinforcing rubber, the maximum insertion amount of the unvulcanized rubber compound is formed inside the polygon that circumscribes the second layer strand when all the strands are arranged in a close-packed state. It is preferable to make the amount of voids or less. Thereby, sufficient tensile rigidity can be ensured after vulcanization.

  The rubber reinforcing steel cord has, for example, a so-called 1 + 18 structure in which the number of strands in the first layer is 1, the number of strands in the second layer is 6, and the number of strands in the third layer is 12. Or a 1 × 19 structure, or a so-called 3/24 structure in which the number of strands in the first layer is 3, the number of strands in the second layer is 9, and the number of strands in the third layer is 15. A 1 × 27 structure can be employed. Since such a steel cord generally has poor rubber permeability, a remarkable effect can be obtained by adopting the above configuration.

The method for manufacturing a pneumatic radial tire is particularly effective when the rate of increase in the circumferential length from the initial molding of the carcass layer to after vulcanization is 70% or more at the center position in the tire width direction. The greater the increase in the circumferential length from the initial molding of the carcass layer to after vulcanization, the greater the tension applied to the steel cord of the carcass layer during the tire manufacturing process, and the easier it is to close the gap between the strands of the third layer. By adopting the above configuration, a remarkable effect can be obtained. The circumferential length increase rate from the initial molding of the carcass layer to after vulcanization is defined as L _{1 being} the circumferential length of the carcass layer in the primary green tire molded into a cylindrical shape, and the carcass layer in the tire after vulcanization. When the circumference is L ₂ , it is (L ₂ −L ₁ ) / L ₁ × 100%.

  The steel cord for reinforcing rubber of the present invention is preferably applied to the carcass layer of a pneumatic radial tire, but can also be applied to tire constituent members other than the carcass layer, conveyor belts, and the like.

Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows a steel cord for rubber reinforcement (1 + 18 structure) according to an embodiment of the present invention. In FIG. 1, a steel cord 10 includes a first layer A including one strand 11, a second layer B including six strands 12 positioned on the outer peripheral side of the first layer A, It has a three-layer structure in which the third layer C including twelve strands 13 is simultaneously twisted and positioned on the outer peripheral side of the second layer B. That is, the first layer A, the second layer B, and the third layer C are twisted together in the same twisting process.

  An unvulcanized rubber compound R is inserted between the first layer A and the second layer B. The maximum insertion amount of the unvulcanized rubber compound R is a gap formed inside the polygon circumscribing the strands 12 of the second layer B when all the strands 11 to 13 are arranged in a close-packed state. It should be less than the amount. Further, at least the strands 13 of the third layer C are spirally typed. The forming rate of the strand 13 is set based on the position of the strand 13 and the cord diameter at that position.

  FIG. 2 is a view for explaining the maximum insertion amount of unvulcanized rubber compound and the cord diameter in the rubber reinforcing steel cord of FIG. FIG. 2 illustrates a virtual cross-sectional shape in which all the strands 11 to 13 of the steel cord 10 are arranged in a close-packed state. In FIG. 2, an unvulcanized rubber compound corresponding to the void amount formed inside the polygon circumscribing the strands 12 of the second layer B when all the strands 11 to 13 are arranged in a close-packed state. R is inserted. That is, FIG. 2 shows a state in which the unvulcanized rubber compound R is filled up to the maximum insertion amount. Here, if the insertion amount of the unvulcanized rubber compound R inserted between the first layer A and the second layer B exceeds the specified amount, the amount of rubber inside the cord becomes excessive. The elastic modulus decreases.

In FIG. 2, the third layer C corresponds to the cord diameter D ₁ at the apex of the cord contour formed when all the strands 11 to 13 are arranged in the close-packed state and the cord diameter D ₂ at the non-vertex. The typing rate of the wire 13 located at the top of the third layer C is 90 to 105%, and the typing rate of the wire 13 located at the non-vertex of the third layer C is 95 to 110%. These molding rates are H ₁ / D ₁ × 100 when the wave height of the wire 13 located at the apex is H ₁ and the wave height of the wire 13 located at the non-vertex is H ₂ (see FIG. 11). % And H ₂ / D ₂ × 100%.

  Thus, by setting the molding rate of the strands 13 constituting the third layer C to be larger than usual, a sufficient gap is secured between the strands 13 and 13 of the third layer C, and rubber permeability is improved. Can be improved. Here, if the forming rate of the wire 13 of the third layer C is below the lower limit value, the shape stability of the cord becomes insufficient, so the effect of improving the cord durability is reduced. The cord tensile modulus after vulcanization decreases.

  FIG. 3 shows a state in which the rubber reinforcing steel cord of FIG. 1 is covered with rubber and vulcanized. In FIG. 3, the coat rubber existing outside the cord is omitted. As shown in FIG. 3, when the steel cord 10 is covered with rubber and then vulcanized, the unvulcanized rubber compound penetrated from the outside of the cord into the inside of the cord and the unvulcanized rubber compound previously inserted into the cord The product R is vulcanized to form a vulcanized rubber layer R ′. The vulcanized rubber layer R ′ is integrally connected to a coating rubber (not shown) existing outside the cord, and the element 11 of the first layer A, the element 12 of the second layer B, and the element of the third layer C are connected. The strands 13 are joined together. As a result, the restraining force of the inner layer strands 11 and 12 by the coat rubber and the outer layer strand 13 becomes high, and the inner layer strands 11 and 12 sufficiently work as a tensile material.

  Thus, in the steel cord 10 having a three-layer structure by one-time twisting, the unvulcanized rubber compound R is inserted between the first layer A and the second layer B, and at least the strand of the third layer C By applying a mold to 13 and optimizing the mold ratio, the rubber penetration into the cord can be improved and the cord durability can be improved without lowering the tensile rigidity.

  Here, for comparison, a conventional steel cord for rubber reinforcement will be described. FIG. 4 shows a conventional rubber reinforcing steel cord (1 + 18 structure), and FIG. 5 shows a state where the rubber reinforcing steel cord of FIG. 4 is covered with rubber and vulcanized. In FIG. 5, the coat rubber existing outside the cord is omitted. As shown in FIG. 4, the conventional steel cord 20 has no unvulcanized rubber compound inserted therein. When such a steel cord 20 is covered with rubber and then vulcanized, the vulcanized rubber layer R 'formed inside the cord is insufficient as shown in FIG. If the rubber penetration rate into the cord is low, the binding force of the inner layer wires 11 and 12 by the coat rubber and the outer layer wire 13 becomes insufficient, so that the inner layer wires 11 and 12 work sufficiently as a tensile material. Accordingly, the durability of the cord is reduced.

  FIG. 6 shows a steel cord for rubber reinforcement (3/24 structure) according to another embodiment of the present invention. In FIG. 6, the steel cord 30 includes a first layer A including three strands 11, a second layer B including nine strands 12 positioned on the outer peripheral side of the first layer A, It has a three-layer structure in which the third layer C including 15 strands 13 located at the outer peripheral side of the second layer B is twisted simultaneously. That is, the first layer A, the second layer B, and the third layer C are twisted together in the same twisting process.

  An unvulcanized rubber compound R is inserted between the first layer A and the second layer B. The maximum insertion amount of the unvulcanized rubber compound R is a gap formed inside the polygon circumscribing the strands 12 of the second layer B when all the strands 11 to 13 are arranged in a close-packed state. It should be less than the amount. Further, at least the strands 13 of the third layer C are spirally typed. The forming rate of the strand 13 is set based on the position of the strand 13 and the cord diameter at that position.

  FIG. 7 is a view for explaining the maximum insertion amount and cord diameter of the unvulcanized rubber compound in the steel cord for rubber reinforcement shown in FIG. FIG. 7 illustrates a virtual cross-sectional shape in which all the strands 11 to 13 of the steel cord 30 are arranged in a close-packed state. In FIG. 7, an unvulcanized rubber compound corresponding to the void amount formed inside the polygon circumscribing the strands 12 of the second layer B when all the strands 11 to 13 are arranged in the close-packed state. R is inserted. That is, FIG. 7 shows a state in which the unvulcanized rubber compound R is filled up to the maximum insertion amount. Here, if the insertion amount of the unvulcanized rubber compound R inserted between the first layer A and the second layer B exceeds the specified amount, the amount of rubber inside the cord becomes excessive. The elastic modulus decreases.

In FIG. 7, the third layer C corresponds to the cord diameter D ₁ at the apex and the non-vertex cord diameter D _{2 of the} cord outline formed when all the strands 11 to 13 are arranged in the close-packed state. The typing rate of the wire 13 located at the top of the third layer C is 90 to 105%, and the typing rate of the wire 13 located at the non-vertex of the third layer C is 95 to 110%. These molding rates are calculated in the same manner as described above.

  Thus, by setting the molding rate of the strands 13 constituting the third layer C to be larger than usual, a sufficient gap is secured between the strands 13 and 13 of the third layer C, and rubber permeability is improved. Can be improved. Here, if the forming rate of the wire 13 of the third layer C is below the lower limit value, the shape stability of the cord becomes insufficient, so the effect of improving the cord durability is reduced. The cord tensile modulus after vulcanization decreases.

  FIG. 8 shows a state where the rubber reinforcing steel cord of FIG. 6 is covered with rubber and vulcanized. In FIG. 8, the coat rubber existing outside the cord is omitted. As shown in FIG. 8, when the steel cord 30 is covered with rubber and then vulcanized, the unvulcanized rubber compound penetrated from the outside of the cord into the inside of the cord and the unvulcanized rubber compound previously inserted inside the cord The product R is vulcanized to form a vulcanized rubber layer R ′. The vulcanized rubber layer R ′ is integrally connected to a coating rubber (not shown) existing outside the cord, and the element 11 of the first layer A, the element 12 of the second layer B, and the element of the third layer C are connected. The strands 13 are joined together. As a result, the restraining force of the inner layer strands 11 and 12 by the coat rubber and the outer layer strand 13 becomes high, and the inner layer strands 11 and 12 sufficiently work as a tensile material.

  Thus, in the steel cord 30 having a three-layer structure formed by a single twist, the unvulcanized rubber compound R is inserted between the first layer A and the second layer B, and at least the strand of the third layer C By applying a mold to 13 and optimizing the mold ratio, the rubber penetration into the cord can be improved and the cord durability can be improved without lowering the tensile rigidity.

  Here, for comparison, a conventional steel cord for rubber reinforcement will be described. FIG. 9 shows a conventional rubber reinforcing steel cord (3/24 structure), and FIG. 10 shows a state in which the rubber reinforcing steel cord of FIG. 9 is covered with rubber and vulcanized. In FIG. 10, the coat rubber existing outside the cord is omitted. As shown in FIG. 9, the conventional steel cord 40 has no unvulcanized rubber compound inserted therein. When such a steel cord 40 is covered with rubber and then vulcanized, the vulcanized rubber layer R 'formed inside the cord is insufficient as shown in FIG. If the rubber penetration rate into the cord is low, the binding force of the inner layer wires 11 and 12 by the coat rubber and the outer layer wire 13 becomes insufficient, so that the inner layer wires 11 and 12 work sufficiently as a tensile material. Accordingly, the durability of the cord is reduced.

  The steel cord 10 of the present invention shown in FIG. 1 has a 1 + 18 structure, and the steel cord 30 of the present invention shown in FIG. 6 has a 3/24 structure. A 1 × 27 structure or the like can be employed. The 1 + 18 structure and the 3/24 structure are obtained by making the wire 11 thicker than the wires 12 and 13, while the 1 × 19 structure and the 1 × 27 structure have the same thickness of the wires 11, 12, and 13. It is a thing.

  FIG. 12 shows an example of a pneumatic radial tire obtained using the steel cord for rubber reinforcement of the present invention, where 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. A carcass layer 4 having a plurality of reinforcing cords oriented in the tire radial direction is mounted between the pair of left and right bead portions 3, 3, and the end of the carcass layer 4 is located around the bead core 5 from the inside of the tire to the outside. It is folded back. The steel cord 10 (or 30) described above is used for the carcass layer 4. A plurality of belt layers 6 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 6 are disposed such that the reinforcing cords are inclined with respect to the tire circumferential direction, and the reinforcing cords cross each other between the layers.

  When manufacturing a pneumatic radial tire as described above, a green tire using the steel cord 10 for the carcass layer 4 is formed, and the green tire is vulcanized. More specifically, a cylindrical primary green tire formed by mounting a carcass layer 4 including a plurality of steel cords 10 between a pair of annular bead cores 5 and 5 is formed, while a belt layer 6 is Forming a tread ring including the above, expanding the axial central portion of the primary green tire while reducing the distance between the pair of bead cores 5 and 5, and bonding the tread ring to the outer peripheral side of the primary green tire; A secondary green tire is formed. Thereafter, the secondary green tire is vulcanized in a mold.

  In the manufacturing process of the pneumatic radial tire, a tension is applied to the steel cord 10 constituting the carcass layer 4. In particular, when there is a deformation such that the rate of increase in the circumferential length from the initial molding of the carcass layer 4 to after the vulcanization is 70% or more at the center position in the tire width direction (tire equator position), The influence is increased, and the gap between the strands 13 and 13 of the third layer C of the steel cord 10 is easily closed. However, a predetermined amount of unvulcanized rubber compound R is inserted between the first layer A and the second layer B of the steel cord 10 as described above, and the wire 13 of the third layer C is moderate. Since the molding is applied, even if the rate of increase in the circumferential length from the initial molding of the carcass layer 4 to after vulcanization is 70% or more at the center position in the tire width direction, the rubber penetration into the cord is ensured. It is possible to improve and improve the durability of the cord, and consequently the durability of the pneumatic radial tire.

  When manufacturing a pneumatic radial tire having a tire size of 295 / 80R22.5, it is not added in advance between the first layer and the second layer of the steel cord (1 × 0.22 + 18 × 0.20) constituting the carcass layer. Insert the vulcanized rubber compound, and make the cross-sectional area of the unvulcanized rubber compound (hereinafter referred to as “rubber-coated cross-sectional area”) differently as shown in Table 1, and mold the third layer wire. As shown in Table 1, the forming rates of the strands positioned at the vertex and non-vertex of the third layer were varied (Examples 1 and 2 and Comparative Examples 1 to 4). For comparison, a pneumatic radial tire of the same tire size was manufactured using a steel cord (1 × 0.22 + 18 × 0.20) into which the unvulcanized rubber compound was not inserted for the carcass layer (conventional example 1). .

  In the manufacturing process of the pneumatic radial tire, the cord driving density of the carcass layer at the time of forming the primary green tire is 27/50 mm, and the cord driving density of the carcass layer after vulcanization is 15 at the center position in the tire width direction. / 50 mm. That is, the circumferential length increase rate from the initial molding of the carcass layer to after vulcanization is about 80% at the center position in the tire width direction.

The cross-sectional area of the rubber coating was obtained from the specific gravity of the unvulcanized rubber compound and the consumption per 1000 m of cords after producing a steel cord of 1000 m or more. In the steel cord, when all the strands are arranged in a close-packed state, the void amount formed inside the polygon circumscribing the strands of the second layer, that is, the maximum value of the rubber-coated cross-sectional area is 0. 018 mm ² .

The molding rate of each strand located at the top and non-vertex of the third layer was determined by the following procedure. First, the cord was cut to a length of 10 cm, the rubber outside the cord was removed with a cutter knife, and then the cord was immersed in acetone and heated. The heating time is not particularly limited, but heating may be performed until the cord can be easily distributed. Next, the strand position (vertex or non-vertex) was confirmed, and the strand of the third layer was separated without plastic deformation of the strand. Next, the wave heights H ₁ and H ₂ (mm) of the strands positioned at the vertex and non-vertex of the third layer were measured using a projector. On the other hand, the cord diameters D ₁ and D ₂ at the vertices and non-vertices of the cord contour formed when all the strands are arranged in the closest state were obtained. Then, calculate the typed rate of the strand to be located at the apex of _{H 1 / D 1 × 100%} , the typed rate of the strand located in the non-vertex was calculated from _{H 2 / D 2 × 100%} . A similar test was carried out on 10 cords, and the average value of the molding rates (%) of the strands located at the vertex and non-vertex of the third layer was determined.

  The evaluation tires obtained as described above were evaluated for rubber penetration rate, initial vulcanization modulus after vulcanization, and cord durability by the following measurement methods. The results are also shown in Table 1.

Rubber penetration rate:
A carcass cord was collected from the evaluation tire over the entire length, and the rubber around the cord was removed with a cutter knife. After the strands of the third layer were manually removed one by one, the rubber coverage (%) of the second layer was evaluated using a microscope. That is, the rubber coverage is 100% when the second layer is completely covered with rubber, and the rubber coverage is 0% when the second layer is completely exposed. A similar test was performed on 10 cords, and the average value was obtained.

Initial tensile modulus after vulcanization:
A carcass cord was collected from the evaluation tire over the entire length, and a tensile test was performed on the carcass cord to obtain an initial tensile elastic modulus between loads of 10 to 250N. A similar test was performed on 10 cords, and the average value was obtained. The evaluation results are shown as an index with Conventional Example 1 as 100. A larger index value means a higher initial tensile elasticity after vulcanization.

Cord durability:
A carcass cord was collected from the evaluation tire over the entire length, and a test piece was prepared by embedding the carcass cord in the center of a rubber block having a width of 10 mm, a thickness of 5 mm, and a length of 500 mm under vulcanization conditions at 145 ° C. for 25 minutes. This test piece was mounted on a three-roller testing machine, and a fatigue test was performed under the conditions of a roller diameter of 35 mm and a cord tension of 200N. That is, the roller was reciprocated in the longitudinal direction of the cord while straining the test piece with three rollers, and the number of reciprocations until the cord was broken was measured. A similar fatigue test was performed on 25 cords, and the median number of reciprocations until breakage was determined. The evaluation results are shown as an index with Conventional Example 1 as 100. A larger index value means better cord durability.

  As can be seen from Table 1, each of Examples 1 and 2 improves the rubber penetration into the cord without reducing the tensile rigidity in comparison with the conventional example 1, and improves the cord durability. did it. On the other hand, in Comparative Examples 1 and 3, the effect of improving the cord durability could not be obtained because the forming rate of the wires located at the vertex or non-apex of the third layer was too low and the cord shape became unstable. In Comparative Examples 2 and 4, the initial tensile elastic modulus of the steel cord was lower than that of Conventional Example 1 because the forming rate of the wire located at the top or non-top of the third layer was too high. When the initial tensile elastic modulus is lowered, the steering stability is lowered.

It is sectional drawing which shows the steel cord for rubber reinforcement (1 + 18 structure) which consists of embodiment of this invention. FIG. 2 is a cross-sectional view for explaining a maximum insertion amount of an unvulcanized rubber compound and a cord diameter in the rubber reinforcing steel cord of FIG. 1. FIG. 2 is a cross-sectional view showing a state in which the rubber reinforcing steel cord of FIG. 1 is covered with rubber and vulcanized. It is sectional drawing which shows the conventional steel cord for rubber reinforcement (1 + 18 structure). It is sectional drawing which shows the state which carried out rubber | gum covering and vulcanized the steel cord for rubber reinforcement of FIG. It is sectional drawing which shows the steel cord for rubber reinforcement (3/24 structure) which consists of other embodiment of this invention. It is sectional drawing for demonstrating the maximum insertion amount and cord diameter of the unvulcanized rubber compound in the steel cord for rubber reinforcement of FIG. It is sectional drawing which shows the state which carried out rubber | gum covering and vulcanized the rubber cord for rubber reinforcement of FIG. It is sectional drawing which shows the conventional steel cord for rubber reinforcement (3/24 structure). FIG. 10 is a cross-sectional view showing a state where the rubber reinforcing steel cord of FIG. 9 is covered with rubber and vulcanized. It is a projection figure which shows the strand to which the typing was given. It is a meridian half sectional view showing an example of a pneumatic radial tire obtained using the steel cord for rubber reinforcement of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Belt layer 10,30 Steel cord 11, 12, 13 Wire A 1st layer B 2nd layer C 3rd layer R Unvulcanized rubber compound

Claims (6)

  A first layer including at least one element wire; a second layer including a plurality of element wires positioned on the outer peripheral side of the first layer; and a plurality of lines positioned on the outer peripheral side of the second layer. In a steel cord having a three-layer structure formed by simultaneously twisting a third layer containing strands, an unvulcanized rubber compound is inserted between the first layer and the second layer, and at least the third layer For the cord diameter at the vertex and the cord diameter at the non-vertex of the cord contour formed when all the strands are placed in a close-packed state, the layer strands are typed, A rubber reinforcing steel, characterized in that the forming rate of the wire located at the apex is 90 to 105% and the forming rate of the wire located at the non-vertex of the third layer is 95 to 110%. code.   The maximum insertion amount of the unvulcanized rubber compound is set to be equal to or less than the void amount formed inside the polygon circumscribing the strands of the second layer when all the strands are arranged in a close-packed state. The steel cord for rubber reinforcement according to claim 1.   The number of strands of the first layer is 1, the number of strands of the second layer is 6, and the number of strands of the third layer is 12. The steel cord for rubber reinforcement according to 2.   The number of strands of the first layer is 3, the number of strands of the second layer is 9, and the number of strands of the third layer is 15. The steel cord for rubber reinforcement according to 2.   A method for producing a pneumatic radial tire, comprising forming a green tire using the rubber-reinforced steel cord according to any one of claims 1 to 4 as a carcass layer and vulcanizing the green tire.   6. The method for manufacturing a pneumatic radial tire according to claim 5, wherein a rate of increase in the circumferential length from the initial molding of the carcass layer to after vulcanization is set to 70% or more at the center position in the tire width direction.

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