JP2007303044A - 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, having improved rubber penetrability into the inside of the cord without reducing tensile modulus; and to provide a pneumatic radial tire using the steel cord. <P>SOLUTION: The steel cord 10 has a three-layer structure obtained by successively twisting a first layer A composed of three wires 11, a second layer B positioned on the outer periphery side thereof and including nine wires 12, and a third layer C positioned on the outer periphery side of the second layer B and including fifteen wires 13. An unvulcanized rubber blended material R is inserted between the first layer A and the second layer B, and the cross section area S of the unvulcanized rubber blended material R is regulated so as to satisfy the relation of S<SB>min</SB>≤S≤S<SB>max</SB>[wherein, S<SB>min</SB>and S<SB>max</SB>indicate a minimum value and a maximum value, respectively, and are represented by formulas (1) and (2): formula (1): S<SB>min</SB>=[d<SB>1</SB>×(2√3+3)/3]<SP>2</SP>×π/4-n<SB>1</SB>×d<SB>1</SB><SP>2</SP>×π/4; and formula (2): S<SB>max</SB>=n<SB>2</SB>×[d<SB>1</SB>×(2√3+3)/3+d<SB>2</SB>]<SP>2</SP>/8×sin(2π/n<SB>2</SB>)-n<SB>1</SB>×d<SB>1</SB><SP>2</SP>×π/4-n<SB>2</SB>×d<SB>2</SB><SP>2</SP>×π/4×(180-360/n<SB>2</SB>)/360 (wherein, d<SB>1</SB>is a diameter of a wire in the first layer; d<SB>2</SB>is a diameter of a wire in the second layer; n<SB>1</SB>is the number of wires in the first layer; and n<SB>2</SB>is the number of wires in the second layer)]. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a steel cord having a three-layer structure formed by twisting three times and a method for producing a pneumatic radial tire using the steel cord, and more particularly, to improve rubber permeability 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 a plurality of strands and a second 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 sequentially twisting a layer and a third layer including a plurality of strands located on the outer peripheral side of the second layer is used (for example, cited documents 1 to 3). reference).

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.
JP-A-5-59677 JP-A-5-11605 Japanese Patent Laid-Open No. 11-124781

  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 composed of three strands and a second layer including a plurality of strands positioned on the outer peripheral side of the first layer. And a steel cord having a three-layer structure in which a third layer including a plurality of strands located on the outer peripheral side of the second layer is sequentially twisted, between the first layer and the second layer The unvulcanized rubber compound is inserted into the unvulcanized rubber compound, and the cross-sectional area S of the unvulcanized rubber compound is determined with respect to the minimum value S _min and the maximum value S _max represented by the following equations (1) and (2) It is characterized by having a relationship of _min ≦ S ≦ S _max .
S _min = [d ₁ × (2√3 + 3) / 3] ² × π / 4−n ₁ × d ₁ ² × π / 4 (1)
_{S max = n 2 × [d} 1 × (2√3 + 3) / 3 + d 2] 2/8 × sin (2π / n 2) -n 1 × d 1 2 × π / 4
−n ₂ × d ₂ ² × π / 4 × (180−360 / n ₂ ) / 360 (2)
Where d _{1 is} the wire diameter of the first layer
d ₂ : Element diameter of the second layer
n ₁ : Number of strands in the first layer
n ₂ : Number of strands in the second layer

  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, in a steel cord having a three-layer structure by twisting three times, an unvulcanized rubber compound is inserted between the first layer and the second layer, and the cross-sectional area S of the unvulcanized rubber compound is calculated. Optimize. That is, the cross-sectional area S of the unvulcanized rubber compound is not less than the minimum value S _min corresponding to the void area in the circumscribed circle of the first layer, and a line connecting adjacent strand center points of the second layer. The maximum value S _max corresponding to the void area in the drawn polygon is set. By inserting an unvulcanized rubber compound satisfying such a cross-sectional area S between the first layer and the second layer, the gap between the strands of the third layer becomes large at the initial stage of vulcanization. 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 at the time of vulcanization, and the strands of the third layer are cords Since it converges inward in the radial direction, it becomes possible to exhibit good tensile rigidity. Thereby, the rubber permeability into 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 number of strands in the first layer is three. For example, it is preferable to configure a so-called 3 + 9 + 15 steel cord 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. . 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 upper limit of the circumference increase rate is 300%.

  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 reinforcing rubber comprising an embodiment of the present invention. In FIG. 1, the steel cord 10 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 formed by sequentially twisting a third layer C including 15 strands 13 located 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 sequentially twisted in an independent twisting process.

An unvulcanized rubber compound R is inserted between the first layer A and the second layer B. The cross-sectional area S of this unvulcanized rubber compound has a relationship of S _min ≦ S ≦ S _max with respect to the minimum value S _min and the maximum value S _max represented by the following formulas (1) and (2). Yes.
S _min = [d ₁ × (2√3 + 3) / 3] ² × π / 4−n ₁ × d ₁ ² × π / 4 (1)
_{S max = n 2 × [d} 1 × (2√3 + 3) / 3 + d 2] 2/8 × sin (2π / n 2) -n 1 × d 1 2 × π / 4
−n ₂ × d ₂ ² × π / 4 × (180−360 / n ₂ ) / 360 (2)
Where d _{1 is} the wire diameter of the first layer
d ₂ : Element diameter of the second layer
n ₁ : Number of strands in the first layer
n ₂ : Number of strands in the second layer

FIG. 2 is a view for explaining the minimum value S _min and the maximum value S _max of the cross-sectional area of the unvulcanized rubber compound in the rubber-reinforced steel cord of FIG. As shown in FIG. 2, the minimum value S _min corresponds to the void area in the circumscribed circle O of the first layer A, and the maximum value S _max is drawn by a line connecting adjacent wire center points of the second layer B. It corresponds to the void area in the polygon P. The cross-sectional area S of the unvulcanized rubber compound R is set in a range in which the minimum value S _min is the lower limit value and the maximum value S _max is the upper limit value. Here, the inserted cross-sectional area S of the unvulcanized rubber compound R is below the minimum value S _min is the code inside the rubber is too small, and therefore encoding durability between the first layer A and second layer B On the contrary, when the maximum value _Smax is exceeded, the rubber inside the cord becomes excessive, and the cord tensile modulus after vulcanization is lowered.

  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 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 10 having a three-layer structure by twisting three times, the unvulcanized rubber compound R is inserted between the first layer A and the second layer B, and the unvulcanized rubber compound R By optimizing the cross-sectional area S, it is possible to improve the rubber penetration into the cord without lowering the tensile rigidity and improve the cord durability.

  Here, for comparison, a conventional steel cord for rubber reinforcement will be described. FIG. 4 shows a conventional steel cord for reinforcing rubber, and FIG. 5 shows a state in which the steel cord for reinforcing rubber 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.

  Although the steel cord 10 of the present invention shown in FIG. 1 has a 3 + 9 + 15 structure, a 3 + 9 + 14 structure, a 3 + 8 + 15 structure, a 3 + 8 + 14 structure, a 3 + 8 + 13 structure, or the like can be adopted.

  FIG. 6 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 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 vulcanization is 70% or more at the center position in the tire width direction (tire equator position), the tension applied to the steel cord 10 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, since the predetermined amount of the unvulcanized rubber compound R is inserted between the first layer A and the second layer B of the steel cord 10 as described above, after the vulcanization from the initial molding of the carcass layer 4 Even if the perimeter increase rate is 70% or more at the center position in the tire width direction, the rubber penetration into the cord is improved, the cord durability is improved, and the pneumatic radial tire is extended. It is possible to improve the durability.

  When manufacturing a pneumatic radial tire having a tire size of 295 / 80R22.5, an unvulcanized rubber compound is previously provided between the first layer and the second layer of the steel cord (3 + 9 + 15 × 0.17) constituting the carcass layer. The cross-sectional area of the unvulcanized rubber compound (hereinafter referred to as “rubber-coated cross-sectional area”) was varied as shown in Table 1 (Examples 1-2 and Comparative Examples 1-2). For comparison, a pneumatic radial tire of the same tire size was manufactured using a steel cord (3 + 9 + 15 × 0.17) 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 31/50 mm, and the cord driving density of the carcass layer after vulcanization is 17 at the center position in the tire width direction. / 50 mm. That is, the rate of increase in the circumferential length from the initial molding of the carcass layer to after vulcanization is about 82% 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, the minimum value S _min of the rubber-coated cross-sectional area is 0.037 mm ² and the maximum value S _max is 0.060 mm ² .

  With respect to the evaluation tire obtained as described above, the rubber penetration rate, the wire breakage rate, the initial tensile elastic modulus index after vulcanization, and the cord durability were evaluated by the following measurement methods. Showed.

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.

Wire breakage rate:
A sample for adhesion test according to JIS G3510 with a cord embedding length of 25 mm was taken from the shoulder portion of the evaluation tire. Then, a pull-out test was performed on 100 cords using the adhesion test sample, the number of cords in which the third layer was broken was counted, and the occurrence rate (%) of the broken wires 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 of 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 is apparent from Table 1, in Examples 1 and 2, better results were obtained than in Conventional Example 1 for any of the evaluation items. On the other hand, in Comparative Example 1, since the rubber-coated cross-sectional area was small, the improvement effect was insufficient, and the wire breakage rate was particularly high. In Comparative Example 2, since the rubber-coated cross-sectional area was high, the initial tensile elastic modulus of the steel cord was lower than that of Conventional Example 1. When the initial tensile elastic modulus is lowered, the steering stability is deteriorated.

It is sectional drawing which shows the steel cord for rubber reinforcement which consists of embodiment of this invention. It is sectional drawing for _{demonstrating} the minimum value _Smin and the maximum value _Smax of the cross-sectional area of the unvulcanized rubber compound in the steel cord for rubber reinforcement of FIG. 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. 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 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 Steel cord 11, 12, 13 Strand A A 1st layer B 2nd layer C 3rd layer R Unvulcanized rubber compound

Claims (4)

A first layer composed of three strands, a second layer including a plurality of strands positioned on the outer periphery of the first layer, and a plurality of strands positioned on the outer periphery of the second layer In a steel cord having a three-layer structure in which a third layer including a wire is sequentially twisted, an unvulcanized rubber compound is inserted between the first layer and the second layer, and the unvulcanized rubber compound Rubber reinforcement characterized in that the cross-sectional area S of the object has a relationship of S _min ≦ S ≦ S _max with respect to the minimum value S _min and the maximum value S _max represented by the following formulas (1) and (2) Steel cord.
S _min = [d ₁ × (2√3 + 3) / 3] ² × π / 4−n ₁ × d ₁ ² × π / 4 (1)
_{S max = n 2 × [d} 1 × (2√3 + 3) / 3 + d 2] 2/8 × sin (2π / n 2) -n 1 × d 1 2 × π / 4
−n ₂ × d ₂ ² × π / 4 × (180−360 / n ₂ ) / 360 (2)
Where d _{1 is} the wire diameter of the first layer
d ₂ : Element diameter of the second layer
n ₁ : Number of strands in the first layer
n ₂ : Number of strands in the second layer   The steel cord for rubber reinforcement according to claim 1, wherein the number of strands of the second layer is nine and the number of strands of the third layer is fifteen.   A method for producing a pneumatic radial tire, comprising forming a green tire using the rubber reinforcing steel cord according to claim 1 or 2 as a carcass layer and vulcanizing the green tire.   The method for producing a pneumatic radial tire according to claim 3, wherein the 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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