JP2008050709A - Steel cord, rubber-steel cord composite, and tire for high speed and heavy load - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber-steel cord composite suitable as a reinforcing material for a tire for high speed and heavy load, especially usable as the tire for an airplane, and to provide a pneumatic radial tire for the high speed and heavy load, having improved durability by applying the composite as a rubber-reinforcing material. <P>SOLUTION: The steel cord has a multi-twisted structure obtained by twisting N (N=2 to 8) strands 2 each obtained by twisting a plurality of wires 1, satisfies the formula: ε<SB>C</SB>≥0.005 [wherein, ε<SB>C</SB>is defined by the formula: ε<SB>C</SB>=√(-b/2+√(b<SP>2</SP>/4-c))-1 (wherein b is -1+π<SP>2</SP>(-4R<SP>2</SP>+d<SP>2</SP>)/P<SP>2</SP>; c is π<SP>2</SP>d<SP>2</SP>k(4π<SP>2</SP>R<SP>2</SP>+P<SP>2</SP>)/P<SP>4</SP>; R is (D-d)/2; and k is tan<SP>2</SP>(π/2-π/N))] when d (mm) is the diameter of the strand, D (mm) is the circumcircle diameter of the cord, and P (mm) is the twisting pitch of the cord, and has an elongation at break of ≥2.5%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a steel cord, a rubber-steel cord composite, and a tire for high-speed heavy loads (hereinafter, also simply referred to as “cord”, “composite”, and “tire”, respectively). The present invention relates to a steel cord suitably applied to reinforcement of rubber products, a rubber-steel cord composite using the same, and a tire for high-speed heavy loads.

  Due to recent developments in transportation, tires are required to have higher speed and higher load durability. In particular, for aircraft, in order to take off and landing at high speed and high load, it is required to further improve heat generation durability, cut durability, etc. for tires, but due to the increase in tire size, the conventional structure, These performance improvements are approaching their limits.

  Since high-speed heavy-duty tires for aircraft run on the runway with high-speed and high-load, the tire structure is composed of a carcass that extends in a toroidal shape between a pair of bead portions, and consists of a plurality of cords or filaments on the outer periphery. In general, a reinforcing belt layer is provided, and at least one crown protective layer is further provided on the outer periphery of the reinforcing belt layer. As a reinforcing material for such a crown protective layer, conventionally, organic fibers such as nylon and aramid, and a layered twisted steel cord that has been wave-shaped have been used.

As a technique related to improving the durability of a high-speed heavy load tire, for example, Patent Document 1 discloses a skeletal structure including a carcass in which both ends of a tread pass through a sidewall portion and bend at a bead core of the bead portion, and its radial direction. In high-speed heavy-duty tires located on the outside and provided with a protective layer that protects the skeletal structure from damage to the tread portion, the protective cord of the protective layer is made of a plurality of steels with a filament diameter of 0.15 to 0.35 mm or less A twisted filament having a twist pitch of 3 to 7.5 mm and a diameter of 0.4 to 1.2 mm, and a wave height of 1.3 to 10 mm and a wavelength of 2.0 to 5. Using an embossed cord in which a 0-fold wavy bent portion is continuously formed, and an angle formed by a virtual straight line with the wavy bent portion of the protective cord being straightened by extension with respect to the tire equator is less than 0 ° And With 15 ° or less, the damage of the protective layer itself that occurs when the local deformation such as when foreign substances depression to prevent, discloses techniques to improve the durability improvement of the tire.
JP-A-6-32109 (Claims etc.)

  However, with the recent increase in speed and load due to the increase in size of aircraft, demands for heat generation durability and cut resistance have become more severe. In this case, the reinforcing material of the organic fiber is inferior to the steel cord in terms of adhesion to rubber, and the layer-twisted steel cord has a concern that moisture enters and propagates when cut. Further, simply arranging a steel cord as a reinforcing material is not feasible in terms of expansion during tire manufacture or strain concentration during high-speed rolling. Therefore, it is necessary to apply a steel cord completely penetrated with rubber as a reinforcing material for the protective layer while ensuring initial elongation and elasticity after vulcanization.

  Accordingly, an object of the present invention is to solve the above problems and improve the steel cord structure to obtain a rubber-steel cord composite suitable as a reinforcing material for high-speed heavy-duty tires used particularly as aircraft tires. In addition, it is an object of the present invention to provide a pneumatic radial tire for high-speed heavy load with improved durability by applying this as a rubber reinforcing material.

  As a result of earnest examination, the present inventor can obtain a reinforcing material that can secure high adhesiveness even during heat generation and can exhibit high cutability by using a steel cord having a predetermined double twist open structure. The present invention has been completed by finding that the conventional problems can be solved.

That is, the steel cord of the present invention has a double twisted structure in which N strands (N = 2 to 8) are twisted together by twisting a plurality of strands, and the diameter of the strand is d (mm), When the circumscribed circle diameter of the cord is D (mm) and the twisting pitch of the cord is P (mm), the following formula:
ε _c = √ (−b / 2 + √ (b ² / 4−c)) − 1
(Wherein b is −1 + π ² (−4R ² + d ² ) / P ² , c is π ² d ² k (4π ² R ² + P ² ) / P ⁴ , R is (D−d) / 2, k Ε _c defined by tan ² (π / 2−π / N)) satisfies ε _c ≧ 0.005, and the elongation to break is 2.5% or more. It is what. The steel cord of the present invention preferably satisfies ε _c ≧ 0.015.

  The rubber-steel cord composite of the present invention is characterized in that the steel cord of the present invention is embedded in rubber. In the composite of the present invention, it is preferable that at least one gap exists between the N strands.

  Furthermore, the tire for high-speed heavy loads of the present invention is characterized by comprising a protective layer using the rubber-steel cord composite of the present invention as a reinforcing material, and preferably the protective layer is a tire. The crown is formed by winding the reinforcing material at least once.

More specifically, the tire of the present invention has at least one carcass extending in a toroidal shape across at least a pair of bead cores as a skeleton, and a plurality of cords or filaments on the outer periphery of the carcass as reinforcing elements. In a high speed heavy load tire having a belt layer
At least one crown protective layer formed of a strip formed by orienting the rubber-steel cord composite of the present invention as a whole along the tire circumferential direction is provided on the outer periphery of the belt layer. It is.

  According to the present invention, the above-described configuration ensures high adhesiveness even during heat generation and can exhibit high cutability. Particularly, the steel cord is useful as a reinforcing material for high-speed heavy-duty tires used as aircraft tires. In addition, a rubber-steel cord composite can be obtained, and by applying this as a reinforcing material, a high-speed heavy-duty pneumatic radial tire with improved durability can be realized.

Hereinafter, preferred embodiments of the present invention will be described in detail.
In FIG. 1, sectional drawing of an example of the steel cord of this invention is shown. As shown in the figure, the steel cord of the present invention has a multi-twist structure in which N strands 2 (N = 2 to 8) obtained by twisting a plurality of strands 1 are twisted in the illustrated example. When the diameter of the strand is d (mm), the circumscribed circle diameter of the cord is D (mm), and the twisting pitch of the cord is P (mm),
ε _c = √ (−b / 2 + √ (b ² / 4−c)) − 1
(Wherein b is −1 + π ² (−4R ² + d ² ) / P ² , c is π ² d ² k (4π ² R ² + P ² ) / P ⁴ , R is (D−d) / 2, k Ε _c defined by tan ² (π / 2−π / N) satisfies ε _c ≧ 0.005, and the elongation to break is 2.5% or more.

Since ε _c defined by the above formula satisfies ε _c ≧ 0.005, preferably ε _c ≧ 0.015, as shown in the figure, between the N strands 2 in the steel cord. In at least one place, in the illustrated example, a gap of a certain level or more is formed between all the strands 2, and even when this is embedded in a matrix such as rubber, a gap exists between the strands 2, When the matrix is in a soft state, up to a certain strain can be easily extended with respect to the tensile strain on the cord. As a result, initial stretchability corresponding to expansion at the time of tire manufacture is secured, and as a result, the molding process of the product becomes easy, and the grace period at the time of vulcanization expansion at the time of tire manufacture increases, so that the manufacture is easy. The advantage is obtained.

  On the other hand, if the fluidity of the matrix becomes small like rubber after vulcanization, even if there is a gap between the strands 2 as described above, the steel cord cannot be deformed like a coil spring to make this gap small, The rigidity of steel will be exhibited as if there is no gap. For this reason, the tensile rigidity of the steel cord of the present invention when it becomes a product is hardly affected by the magnitude of strain applied to the steel cord in the processing step, and always has high rigidity. Further, in the product, a state in which a gap remains between the strands is preferable in terms of fatigue. However, in the cord of the present invention as described above, even when the strands 2 are in close contact with each other, Compared to the above, the tensile rigidity is not greatly reduced.

  In addition, since the cord of the present invention has an open structure with a gap between the strands 2, it has excellent rubber penetrability and can effectively prevent moisture from being propagated at the time of damage. Furthermore, the elongation to break is set to 2.5% or more, preferably 4 to 6%, and the elongation after vulcanization is secured. The effect which cancels is also acquired.

  Therefore, according to the present invention, when applied to a tire, it is excellent in heat generation durability and cut durability and does not induce a failure due to the propagation of moisture. It is possible to realize a steel cord having both elongation after vulcanization and a rubber-steel cord composite formed by embedding the steel cord in rubber.

  In addition, the tire of the present invention only needs to have a protective layer using the rubber-steel cord composite of the present invention as a reinforcing material, thereby exhibiting a desired high rigidity in the protective layer, and high speed. It is possible to realize a high-speed heavy-duty tire having durability capable of withstanding heavy loads. In particular, the present invention is useful when applied to aircraft tires that run on a runway with high speed and high load. The tire according to the present invention preferably includes a protective layer formed by winding a reinforcing material made of the rubber-steel cord composite around the tire crown at least once.

  FIG. 2 shows a cross-sectional view of an example of the tire for high speed heavy load of the present invention using the rubber-steel cord composite of the present invention as a reinforcing material. The illustrated tire 10 has at least one layer of a carcass 12 extending in a toroidal shape across at least a pair of bead cores 11 as a skeleton, and at least one belt layer having a plurality of cords or filaments as reinforcing elements on the outer periphery thereof. 13 and at least one crown protective layer 14 formed of a strip formed by orienting the rubber-steel cord composite as a whole along the tire circumferential direction. .

  The tire of the present invention may be any tire as long as the rubber-steel cord composite of the present invention is applied as a reinforcing material for the protective layer, particularly the crown protective layer 14 as shown in the figure. The desired effect of the invention can be obtained, and in addition to the specific cord diameter and twist pitch, the number of reinforcements driven in the reinforcing layer, the specific tire structure and material, etc. It can be set and is not particularly limited. For example, as shown in the drawing, the tire of the present invention includes a pair of bead portions 21, a pair of sidewall portions 22 connected to the bead portions 21, and a tread portion 23 connected in a toroidal shape between the sidewall portions 22. A tread pattern is appropriately formed on the surface of the tread portion 22. An inner liner (not shown) is formed in the innermost layer.

Hereinafter, the present invention will be described in more detail with reference to examples.
(Examples and Comparative Examples)
Under the conditions shown in Table 1 below, rubber-steel cord composites of each comparative example and example were produced. The values of the strand diameter d, the circumscribed circle diameter D of the cord, the twisting pitch P of the cord, ε _c, and the breaking elongation of each composite obtained are shown in Table 1 below.

  Next, in the tire structure shown in FIG. 2, the produced composite was applied as a reinforcing material for the crown protective layer to produce a radial tire for an aircraft having a tire size of 1400 × 530R23. The number of reinforcements and the number of crown protective layers are shown in Table 1 below.

(Adhesive strength evaluation)
The adhesive strength was measured by taking out a reinforcing material sample from each test tire and then peeling it while causing one cord, and measuring the strength value at that time. The measurement was performed three times, and the average value was displayed as an index with Comparative Example 1 being 100. The larger the value, the better the adhesion and the better.

(Corrosion resistance evaluation)
Corrosion resistance was evaluated by visual inspection after taking out a reinforcing material sample from each test tire and leaving it at a humidity of 90% or more and a temperature of 70 ° C. for 1 week. The results are shown as an index with Comparative Example 1 as 100. The larger the value, the better the corrosion resistance.

(High-speed durability test)
The high-speed durability test was performed by assembling each test tire on a rim having a rim size of 1400 × 530R23 and accelerating to a speed of 380 km / h in about 1 minute under normal internal pressure and load conditions. Finished 50 times.
These results are also shown in Table 1 below.

  As shown in the results of Table 1 above, in the tire of each example using a steel cord having a predetermined double twist open structure as a reinforcing material, Comparative Example 1 using an organic fiber reinforcing material and a wavy mold were made. Compared to Comparative Example 2 using a steel cord, it was confirmed that good performance was obtained in a well-balanced manner in terms of adhesive strength, corrosion resistance, and high-speed durability.

It is a schematic sectional drawing which shows the steel cord which concerns on one embodiment of this invention. 1 is a cross-sectional view in the width direction showing a tire for high-speed heavy load according to an embodiment of the present invention. It is a schematic sectional drawing which shows the steel cord which concerns on other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Strand 2 Strand 10 High speed heavy load tire 11 Bead core 12 Carcass 13 Belt layer 21 Bead part 22 Side wall part 23 Tread part

Claims (7)

A strand in which a plurality of strands are twisted together has a twisted structure in which N strands (N = 2 to 8) are twisted, the diameter of the strand is d (mm), and the circumscribed circle diameter of the cord is D (mm) ), When the twisting pitch of the cord is P (mm),
ε _c = √ (−b / 2 + √ (b ² / 4−c)) − 1
(Wherein b is −1 + π ² (−4R ² + d ² ) / P ² , c is π ² d ² k (4π ² R ² + P ² ) / P ⁴ , R is (D−d) / 2, k Ε _c defined by tan ² (π / 2−π / N)) satisfies ε _c ≧ 0.005, and the elongation to break is 2.5% or more. Steel cord. The steel cord according to claim 1, wherein ε _c ≧ 0.015 is satisfied.   A rubber-steel cord composite, wherein the steel cord according to claim 1 or 2 is embedded in rubber.   The rubber-steel cord composite according to claim 3, wherein there is at least one gap between the N strands.   A tire for high-speed heavy loads, comprising a protective layer using the rubber-steel cord composite according to claim 3 as a reinforcing material.   The tire for high-speed heavy loads according to claim 5, wherein the protective layer is formed by winding the reinforcing material around the tire crown at least once. In a high-speed heavy-duty tire having at least one layer of a carcass extending in a toroid shape between at least a pair of bead cores and a belt layer having a plurality of cords or filaments as reinforcing elements on the outer periphery of the carcass,
5. A belt protective layer comprising at least one crown protective layer formed on the outer periphery of the belt layer from a strip formed by orienting the rubber-steel cord composite according to claim 3 as a whole along a tire circumferential direction. High-speed heavy load tires.

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