JPH09256282A - Steel cord for reinforcing rubber product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure of a steel cord capable of securing a fixed interval and readily and surely permeating rubber into the interior of the steel cord even when the steel cord having formed the fixed gap between side wires is sandwiched by rubber sheets, pressurized and vulcanized without previously subjecting the wires to reforming processing in the approximately elliptical steel cord having a great number of the side wires and a center wire having the same thickness. SOLUTION: This steel cord of an open twisting of 1+6 structure is obtained by arranging six side wires 3,4,... around one straight center wire 2 and twisting. The steel cord is compressed and processed to give a flat open structure in which the crosssectional shape of the cord is faced approximately in the same direction in the longer direction of the cord. A center wire 2 is partially forced into between two adjoining side wires during the pressure processing to give the objective steel cord for reinforcing a rubber product in which the maximum amount Hmax of the center wire forced into the side wires at one twisting pitch of the cord is >=30% the diameter of the center wire (d) and <=50% (d).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber product reinforcing steel cord used as a rubber product reinforcing material for automobile tires, conveyor belts and the like. In addition, the fatigue strength of the steel cord against repeated bending loads can be improved, and thus the durability of the rubber product reinforced by the steel cord can be remarkably improved.

[0002]

2. Description of the Related Art Steel cords for reinforcing rubber products have a size of 5 to 5.
A so-called closed twisted cord, in which seven strands are tightly twisted and adhered to each other, and a so-called open twisted cord, in which strands are loosely twisted together, and a strand group that is hardly twisted, and another strand group They are roughly divided into those that are tightly twisted. FIG. 2 shows an example of a closed twist cord. This steel cord 21 has a core wire 21a
The six side wires 21b are twisted around each other in close contact with each other. This steel cord is core wire 21a
When a steel cord 21 is sandwiched between two rubber sheets and compressed to form a composite sheet because a hollow portion D exists around the periphery of the wire and the side wires 21b are in close contact with each other. The rubber material does not penetrate into the cavity D, and the steel cord is simply wrapped with the rubber sheet to form a composite body, and the rubber material completely enters the cavity D of the steel cord, and the rubber sheet and the steel cord are integrated. Was done,
So to speak, it is not a complete complex. In the case where this product is incorporated into an automobile tire, the adhesion between the rubber material and the steel cord is insufficient, which may cause the rubber material to peel off from the steel cord when the automobile is running, causing a so-called separation phenomenon. Is large, and when water in the rubber material or water that has penetrated from the cuts in the tire reaches the hollow portion D of the steel cord 21, this water propagates through the hollow portion D and immediately propagates in the longitudinal direction of the steel cord 21, It will corrode the steel cord, resulting in a significant reduction in its mechanical strength. In order to solve this problem, various steel cord structures have been proposed in which the rubber material is allowed to easily penetrate into the cavity. For example, as shown in FIG. 3, the core wire 32 is made thicker, and a gap C is formed between the side wires 33 that are closely attached and twisted around the core wire, as shown in FIG. So that the core wire 42
To which a small spiral-like stiffening has been previously applied and side wires 43 have been closely adhered and twisted (for example, Japanese Patent Laid-Open No. 6-191218), or as shown in FIG. An example is one in which the side strands 53 are closely attached to and twisted with a wavy curling having a small amplitude (for example, JP-A-6-191217). Further, a so-called open-twisted steel cord (for example, Japanese Patent Laid-Open No. 57-43866) in which strands are over-shaped and loosely twisted with a gap between each strand (for example, Japanese Patent Laid-Open No. 57-43866), or the above-described one as shown in FIG. A so-called flat open-twisted steel cord in which an open-twisted steel cord is flattened by a roller to make an elliptical cross-section (Japanese Patent Application Laid-Open No. Hei 2-
No. 133687) is one such example. In the structure of the conventional steel cord 31 shown in FIG. 3, the rubber material is sufficiently infiltrated into the gap between the core wire 32 and the side wire 33, and as a result, the cavity is not formed, so that moisture inside the steel cord is not formed. However, since the diameter of the core wire 32 is large, the diameter of the steel cord 31 is large, which increases the thickness of the rubber sheet. When this is used in an automobile, the diameter of the steel cord 31 becomes large,
The flexibility of the steel cord against the circumferential bending of the tire is poor, and the riding comfort is impaired. Further, in this product, the core wire 32 is always in contact with the side wire 33, which causes fretting wear, which results in a high fatigue value of the steel cord and low durability. Further, the steel cord 41 shown in FIG.
, The side wire 43 is not always in contact with the core wire 42, so the fatigue value is improved, but since the cross-sectional shape is a substantially circular shape, in which direction the rigidity against bending of the steel cord is The same is true for tires, and ensuring the tire's desired cornering performance (selecting the diameter of the steel cord to ensure the desired tire's lateral rigidity) prevents the tire from bending in the circumferential direction. Rigidity is too high, resulting in poor riding comfort. Also, the above steel cord 4
1 is a closed twisted steel cord 21 as shown in FIG.
The cord diameter becomes thicker than that of the sheet, and the sheet after the calender (rubber coating process) becomes thicker. In addition, since the cord diameter is large, it is not possible to embed the required number of steel cords in the sheet, and the strength of the sheet is increased. Low. Therefore, when this is used for a tire, it is necessary to increase the number of stacked sheets, and as a result, the weight of the tire increases. In addition, the steel cord 51 shown in FIG. 5 in which the core wire 52 has a wavy habit is a substantially track type space (a so-called playground track) space drawn by the movement trajectory of the core wire 52 (indicated by a dotted line in the figure). Since the side wire 53 does not easily enter the enclosed space), the degree of freedom of the core wire 52 is large to some extent. Therefore, the core wire 52 is likely to move between the upper and lower rubber sheets by the external force due to the process of sandwiching and pressing the steel cord to vulcanize and integrate it, and the stability of the steel cord decreases. Therefore, handling workability at the time of manufacturing a steel cord or a rubber sheet is deteriorated. Furthermore, since the steel cords 41 and 51 are subjected to the spiral or corrugated curling process on the core wire, the manufacturing cost increases accordingly. Also, the steel cords 41 and 51 are
Corresponding to the spiral or wavy pitch,
It is necessary to set the twist pitch of the side wire (otherwise, the twisted shape will be lost), and therefore the adjustment work of the twisting machine is not easy and there is a problem in handling workability. FIG.
In the flat open-shaped steel cord 61 shown in Fig. 4, in order for the rubber material to adhere to the entire circumference of each wire 62 and to fully penetrate into the steel cord, the rubber material penetrates the gap between the wires. Sufficient spacing, ie 0.02
It is necessary to make it mm or more. However, if a sufficient gap is provided between each strand in this way, the twisted structure tends to become unstable during the manufacturing of the steel cord, and the strands may be offset or twisted unevenly in the longitudinal direction of the steel cord. There is a problem that becomes. This product has a relatively large degree of freedom for each strand, so when a steel cord is embedded in a rubber sheet and vulcanized and pressed, the gap created by the external force is reduced, or the gap in the gap occurs due to the movement of the strand. ,
The rubber material does not easily get inside the cord. If this happens, buckling is likely to occur due to repeated bending stress, and the life of the steel cord and eventually the rubber product will be shortened. Further, since the flat open steel cord 61 has a large elongation under a low load, it is difficult to handle in the rubber sheet manufacturing process.

[0003]

SUMMARY OF THE INVENTION According to the present invention, a substantially elliptical steel cord having a core wire having a thickness equal to that of a large number of side wires can be formed without pre-curling the core wire. Even when the steel cord with a required gap between the strands is sandwiched with a rubber sheet and pressed to vulcanize, a certain gap is secured and the structure is devised so that the rubber can easily and surely penetrate into the steel cord. The task is to do.

[0004]

Means taken to solve the above problems are constituted by the following elements (a) to (d). (A) A steel cord having a 1 + 6 structure in which six side wires are arranged around one core wire and twisted together,
(B) A flat open structure in which the cross-sectional shape of the cord is approximately the same in the longitudinal direction of the cord by compression processing of an open structure in which side strands are twisted around a straight core wire. ) A core wire is partially interrupted between two adjacent side wires during the pressure processing, and (d) the maximum amount of interruption of the core wire in one twist pitch of the cord is set to the core wire. 30% or more and 50% or less of the wire diameter.

[0005]

[Operation] The operation will be described with reference to FIG. The straight core wire 2 is among the six twisted side wires 3, and since the steel cord 1 is crushed into a substantially elliptical shape by the compression process, the core wire 2 is divided into upper and lower side wires. It is strongly pressed between and is cut between adjacent side strands to be combined with the side strands. The interrupt has a small portion and a large (maximum interrupt) portion in one twist pitch of the cord (see the interrupt state in FIG. 1), and the number of interrupts is a state where the increase / decrease is periodically repeated at one twist pitch interval of the cord. Then, in the interruption amount H (see FIG. 1) interrupted between the adjacent side wires 3 and 4, the outer circumference of the core wire 2 is the side wire 3,
4 is the amount of protrusion from the common tangent line L (distance between the illustrated common tangent line L and the tangent line L ₁ of the core wire 2). This interruption amount H fluctuates periodically between the maximum and minimum along the steel cord, but the magnitude of this maximum value is mainly determined by the steel cord 1.
Is adjusted by the magnitude of its compressive force when crushed into a substantially elliptical shape by compression processing, the twist pitch of steel cords, and the dimensional ratio of side strands. When the steel cord is twisted, the straight core wire becomes the core, so that the twisted structure is stable, and it is possible to prevent the side wires from deviating and the side wires from becoming uneven in twist. Also, in the state of being formed into a crushed elliptical shape, the core wire is firmly combined with the side wire, so the degree of freedom of the side wire is reduced, and therefore the steel cord is sandwiched between the upper and lower rubber sheets. Even when pressure is applied and vulcanization is performed, the gap between the side strands does not easily fluctuate, and a predetermined gap is maintained. Therefore, the rubber easily enters the inside of the steel cord through this gap, and the rubber is sufficiently filled in the steel cord. When the maximum interrupt amount is small, the above-mentioned effects and effects are reduced. Conversely, when the maximum interrupt amount is large, the above-mentioned effects and effects are large. And damage, resulting in reduced fatigue strength of the steel cord. When the maximum interrupt amount Hmax is less than 0.3d with respect to the core wire diameter d, the above-mentioned action of the core wire is small, and therefore the degree of freedom of the side wire is increased, which is practical. Little effect is expected. Conversely, the maximum interrupt amount Hma
When x exceeds 0.5d with respect to the core wire diameter d, the fatigue strength due to the above-mentioned indentation and damage becomes remarkable, which is not desirable in practice. Of course, it is practically possible to make the maximum interruption amount Hmax larger than 0.5d by subjecting the wire to a special surface treatment for preventing the above-mentioned indentation and damage, but the maximum interruption amount Hmax is Even if it is larger than 0.5d, the above-mentioned action and effect do not increase so much. The smaller the number of side strands, the more gradual the bending of the core strand, and the smaller the above-mentioned action and effect. Conversely, if the number of side strands is large, the core strands are sharply bent, so that indentations and damages generated on the strand surface during press working increase, and as a result, the fatigue strength of the steel cord decreases. Therefore, even if the number of side strands is 5 or 7, the action and effect of the present invention are not generated at all, but a steel cord having 6 side strands is the most practical.

[0006]

[Embodiment] The twist pitch of the steel cord is 6 to 20 m.
m. If the thickness is 6 mm or less, wire breakage is likely to occur due to extreme working, and the number of twists per unit length of the steel cord increases, resulting in reduced productivity. In addition, since the peculiar pitch of the core wire is smaller than the twisting pitch of the side wire, if it is less than 6 mm, it is physically difficult to cause the core wire to largely break between the adjacent side wires. On the other hand, when the twist pitch of the steel cord is 20 mm or more, the flexibility of the steel cord becomes small and flare easily occurs, which is not practical. The core wire diameter is 0.2 mm ~
0.4 mm. If the wire is too thin, the strength of the wire will be insufficient, and if it is too thick, the flexibility of the steel cord will be insufficient and the fatigue value will be low. This is more remarkable in the steel cord of the present invention having an elliptical cross-sectional shape, which is 0.4 m.
If it exceeds m, it is not practical.

[0007]

[Embodiment] Next, an embodiment will be described with reference to FIG. This steel cord 1 has six side strands formed around a straight core strand 2 having a strand diameter of 0.35 mm, with a twist pitch of 16 mm and an average cord diameter of 1.07.
It is twisted into a substantially circular shape of mm and is formed into a substantially elliptical shape with a major axis of 1.36 mm and a minor axis of 0.99 mm by a rolling roller. By the pressure processing by this rolling roller, the core wire is plastically deformed and cut between the adjacent side wires. This steel cord is embedded in a resin, and enlarged photographs of each cross section obtained by cutting the steel cord at intervals of 2 mm in the longitudinal direction of the steel cord are eight photographs shown in FIG.
The maximum interrupt amount in this embodiment can be measured by measuring the interrupt amount in the photograph having the maximum interrupt amount (maximum in one twist pitch of the cord). The third photo shows the highest interrupt amount. In order to confirm the characteristics of the steel cord of the present invention, several kinds of the steel cord of the present invention (0.32d
0.43d, 0.48d) and several conventional steel cords and two comparative examples (maximum interrupt amount is 0.17d, 0.58
A comparison test with d) was performed to quantitatively evaluate the rubber penetration rate, rigidity ratio, fatigue resistance, and handling workability. The evaluation results are as shown in Table 1 below.

[Table 1] The test conditions and evaluation method of this test are as follows. The rubber infiltration rate is such that each cord is embedded in rubber with a tensile load of 5 kg applied, and after vulcanization, the cord is taken out of the rubber and the cord is disassembled to observe a certain length of the strand. The ratio of the length with a mark in contact with rubber to the length observed was expressed as a percentage. The rubber penetration rate is usually required to be 70% or more. Fatigue resistance is tested by a 3-point pulley bending fatigue tester using a composite sheet in which multiple steel cords are embedded in a rubber sheet. It is a count of the number of repetitions up to. Experiment No. The fatigue resistance evaluation value of the conventional closed-twist structure of No. 6 is indexed to 100. The higher the value, the higher the fatigue resistance. As shown in FIG. 7, the rigidity ratio is determined by the three-point bending tester using the span (SP = 2) of the test piece 71.
0 mm) is a value obtained by measuring the load G when the steel cord is pressed down by 5 mm, and is a ratio (G / G) of the load G for the minor axis direction of the steel cord and the load G ₁ for the major axis direction of the steel cord. ₁ ) is a percentage display. The smaller this ratio, the higher the flexibility in the circumferential direction of the tire when it is applied to the tire (low rigidity) and the high rigidity in the lateral direction (low lateral flexibility). As shown in FIG. 8, five test cords 82 were horizontally arranged in a row and embedded in a rubber sheet 83 having a 100% modulus of 35 Kg / cm ² to prepare a test piece 81, and a rigidity test was performed on the test piece 81. The rubber sheet 8
The dimensions of 3 are thickness T = 4 mm, width W = 15 mm, and length L.
= 100 mm. The bending rigidity in the minor axis direction is the bending rigidity of the test cord 82 embedded laterally as shown in FIG. 8A, and the bending rigidity in the major axis direction is as shown in FIG. 8B. In addition, the bending rigidity is obtained by vertically embedding the test cord 82. The handling workability is an evaluation of the complexity of the work at the time of manufacturing the steel cord and forming the composite sheet and the handling workability of the steel cord,
In addition, in consideration of the difficulty of processing during manufacturing, the test No. Compared with the steel cord of No. 6, a very inferior one was evaluated as ×, a little inferior one was evaluated as Δ, and a product having no difference was evaluated as ∘. The evaluation of each steel cord is described below based on the results of Table 1. The conventional steel cord having the cross-sectional shape shown in FIG. 2 (Experiment No. 6) is an example of the present invention (Experiment N).
o. 1 to Experiment No. 1 As compared with 3), the rubber penetration rate is extremely inferior, which causes problems such as poor fatigue resistance, lack of flexibility, and thickening of the sheet. A conventional steel cord (experiment No. 7) having a cross-sectional shape shown in FIG. 4 in which a core wire has a substantially spiral habit has a rubber penetration rate of 80, and the rubber penetration rate of the embodiment of the present invention is 100. It is considerably lower than. The rigidity ratio is 99, which is considerably higher than the rigidity ratios 93 to 95 of the embodiment of the present invention. Further, the diameter of the cord on the shorter diameter side is considerably larger than that of the steel cord of the embodiment of the present application. Therefore, when such a cord is used, the seat thickness cannot be reduced, resulting in poor riding comfort. Furthermore, since it is necessary to subject the core wire to a spiral-shaped staking process, the manufacturing cost and the equipment cost are increased, and the handling workability is somewhat poor. The steel cord (experiment No. 8) having the cross-sectional shape shown in Fig. 5 and having the wavy ridge on the core wire has a maximum maximum interrupt amount of 0.15d, which is small, and the rubber penetration rate is 60%, which is low. . This is poor in handling workability at the time of steel cord production and rubber sheet production, and it is particularly difficult to properly control the tension applied to the steel cord. Structurally the same as the embodiment of the present invention, but a comparative example in which the maximum interrupt amount was 0.17d, that is, Experiment No. Four
Has poor stability of steel cord, rubber penetration rate is 65%
And the workability is poor. Maximum interrupt amount 0.58d
The same comparative example, that is, Experiment No. The steel cord of No. 5 is an example of the present invention (Experiments No. 1 to No. 3).
Fatigue resistance is significantly lower than This is because the maximum interruption amount of the cord is too large and the indentation and damage of the wire due to excessive compression processing are remarkable. Compared with the above-mentioned conventional example and comparative example, in the examples of the present invention (Experiments No. 1 to No. 3), the rubber penetration rate was extremely high at 100%, and the fatigue resistance was 105.
˜108, and the rigidity ratio is small, 93 to 95. For this reason, when it is applied to a tire, the tire has a high flexibility in the circumferential direction and therefore a good riding comfort, and a high rigidity in the lateral direction and therefore a good cornering characteristic. Further, handling workability is better than that of the conventional one.

[0008]

[Effect] The steel cord of the present invention has no cavity inside the cord over substantially the entire area in the longitudinal direction of the cord, and has a stable and high rubber penetration property. In addition, since the thickness of the sheet when embedded in rubber can be reduced, the weight of the tire can be reduced, and the fuel efficiency of the vehicle can be improved. Also,
Since the rigidity of the tire in the circumferential direction (rotational direction) can be lowered, the riding comfort can be improved, and the rigidity in the lateral direction of the tire can be increased, so that the cornering performance can be improved. Further, since the steel cord of the present invention is remarkably excellent in the twist stability in the longitudinal direction, the rubber penetration as described above is extremely good, and the workability of handling the steel cord is also very good. Furthermore, since the steel cords are twisted together using the straight strands as the core strands, it can be manufactured with either conventional buncher type or tubular type stranding machines without causing twisting defects (core strands). In the conventional products shown in FIGS. 4 and 5 which are pre-cursed with the above, it is a manufacturing problem that twisting failure occurs.
Since there is no need to adjust the pitch to match the twist pitch of the side wire to the peculiar pitch of the core wire, the pitch adjustment of the side wire is simpler and easier to handle. There is no need to add a sticker. Therefore,
The manufacturing cost can be remarkably reduced as compared with the conventional example shown in FIGS.

[Brief description of drawings]

FIG. 1 is a sectional view of a steel cord according to the present invention.

FIG. 2 is a cross-sectional view of a conventional steel cord in which six side wires are closely attached to each other and twisted around a core wire.

FIG. 3 is a cross-sectional view of a conventional steel cord in which a gap is formed between side strands that are tightly twisted around a core strand having a large diameter.

FIG. 4 is a cross-sectional view of a conventional steel cord in which a core wire is preliminarily provided with a spiral eccentricity having a small radius, and a side wire is closely adhered to the core wire and twisted.

FIG. 5 is a cross-sectional view of a conventional steel cord in which a core wire is preliminarily provided with a wavy curling with a small amplitude, and a side wire is closely attached to the core wire and twisted.

FIG. 6 is a sectional view of a conventional flat open twisted steel cord.

FIG. 7 is a schematic view of a rigidity tester.

FIG. 8A is a perspective view of a test piece in which a steel cord is embedded in the minor axis direction, and FIG. 8B is a perspective view of a test piece in which a steel cord is embedded in the major axis direction.

FIG. 9 is an enlarged photograph of a cross section of a steel cord (1 + 6 structure) according to an example of the present invention in steps of 2 mm in one twist pitch.

[Explanation of symbols]

 1, 21, 31, 41, 51 ... Steel cord 2, 21a, 32, 42, 52 ... Core wire 3, 4, 21b, 33, 43, 53 ... Side wire 61 ... Flat open steel cord 62 ... strands 71, 81 ... test piece 82 ... test cord 83 ... rubber sheet C ... gap D ... cavity H ... interrupt amount d ... Wire diameter

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[Procedure amendment]

[Submission date] June 18, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

[0007]

[Embodiment] Next, an embodiment will be described with reference to FIG. This steel cord 1 has six side strands formed around a straight core strand 2 having a strand diameter of 0.35 mm, with a twist pitch of 16 mm and an average cord diameter of 1.07.
It is twisted into a substantially circular shape of mm and is formed into a substantially elliptical shape with a major axis of 1.36 mm and a minor axis of 0.99 mm by a rolling roller. By the pressure processing by this rolling roller, the core wire is plastically deformed and cut between the adjacent side wires. FIG. 9 shows copy diagrams (1 to 8) of enlarged photographs in which the steel cords are embedded in a resin and each cross section obtained by cutting the steel cords at intervals of 2 mm in the longitudinal direction of the steel cords. The maximum interrupt amount in this embodiment can be measured by measuring the interrupt amount in FIG. 9 in which the interrupt amount is maximum (maximum in one twist pitch of the cord). The third copy has the largest interrupt amount. In order to confirm the characteristics of the steel cord of the present invention, several kinds of the steel cord of the present invention (0.32d
0.43d, 0.48d) and several conventional steel cords and two comparative examples (maximum interrupt amount is 0.17d, 0.58
A comparison test with d) was performed to quantitatively evaluate the rubber penetration rate, rigidity ratio, fatigue resistance, and handling workability. The evaluation results are as shown in Table 1 below.

[Table 1] The test conditions and evaluation method of this test are as follows. The rubber infiltration rate is such that each cord is embedded in rubber with a tensile load of 5 kg applied, and after vulcanization, the cord is taken out of the rubber and the cord is disassembled to observe a certain length of the strand. The ratio of the length with a mark in contact with rubber to the length observed was expressed as a percentage.
The rubber penetration rate is usually required to be 70% or more. Fatigue resistance is
Fatigue test is performed by a 3-point pulley bending fatigue tester using a composite sheet in which multiple steel cords are embedded in a rubber sheet, and the embedded steel cords are fractured through fretting wear, buckling, etc. The number of repetitions is counted. Experiment No. The fatigue resistance evaluation value of the conventional closed-twist structure of No. 6 is indexed to 100. The higher the value, the higher the fatigue resistance. Further, as shown in FIG. 7, the rigidity ratio is a value obtained by measuring the load G when the test piece 71 is pressed down by 5 mm in the span (SP = 20 mm) of the test piece 71 by the three-point bending tester. The ratio (G / G ₁ ) of the load G for the above and the load G ₁ for the major axis direction is expressed in percentage. The smaller this ratio, the higher the flexibility in the circumferential direction of the tire when it is applied to the tire (low rigidity), and the higher the lateral rigidity (low lateral flexibility).
Means that. As shown in FIG. 8, the five test codes 82 are arranged in a row, and the 100% modulus is 35 kg / c.
A test piece 81 was prepared by embedding it in a rubber sheet 83 made of m ² , and a rigidity test was performed on this. The dimensions of the rubber sheet 83 are thickness T = 4 mm and width W = 15 m.
m, length L = 100 mm. The bending stiffness in the minor axis direction is the bending stiffness of the test code 82 embedded horizontally as shown in FIG. 8A, and the bending stiffness in the major axis direction is as shown in FIG. 8B. And test code 8
The bending stiffness of what was embedded vertically. The handling workability is an evaluation of the complexity of the work during the production of the steel cord and the forming of the composite sheet and the handling workability of the steel cord. Compared to the steel cord of No. 6, the one that was very inferior was evaluated as ×, the one that was slightly inferior was evaluated as Δ, and the one with no difference was evaluated as ∘. The evaluation of each steel cord is described below based on the results of Table 1. The conventional steel cord having the cross-sectional shape shown in Fig. 2 (Experiment No. 6) is extremely inferior in rubber infiltration rate as compared with the examples (Experiment No. 1 to Experiment No. 3) of the present invention, and therefore has fatigue resistance. There are problems such as poor quality, lack of flexibility, and thicker sheet. A conventional steel cord (experiment No. 7) having a cross-sectional shape shown in FIG. 4 in which a core wire has a substantially spiral habit has a rubber penetration rate of 80, and the rubber penetration rate of the embodiment of the present invention is 100. It is considerably lower than. The rigidity ratio is 99, which is considerably higher than the rigidity ratios 93 to 95 of the embodiment of the present invention. Also,
The cord diameter on the minor axis side is considerably larger than that of the steel cord of the embodiment of the present application. Therefore, when such a cord is used, the seat thickness cannot be reduced, resulting in poor riding comfort. Furthermore, since it is necessary to subject the core wire to a spiral-shaped staking process, the manufacturing cost and the equipment cost are increased, and the handling workability is somewhat poor. The steel cord (experiment No. 8) having the cross-sectional shape shown in Fig. 5 and having the wavy ridge on the core wire has a maximum maximum interrupt amount of 0.15d, which is small, and the rubber penetration rate is 60%, which is low. . This is poor in handling workability at the time of steel cord production and rubber sheet production, and it is particularly difficult to properly control the tension applied to the steel cord. Structurally the same as the embodiment of the present invention, but a comparative example in which the maximum interrupt amount was 0.17d, that is, Experiment No. In No. 4, the stability of the steel cord is poor, the rubber penetration rate is only 65%, and the handling workability is poor. A similar comparative example in which the maximum interrupt amount was 0.58d, that is, Experiment No. 5
The steel cord of No. 1 is an example of the present invention (Experiment No. 1 to No. 1).
No. Fatigue resistance is significantly lower than that of 3). This is because the maximum interruption amount of the cord is too large and the indentation and damage of the wire due to excessive compression processing are remarkable. Compared with the above-mentioned conventional example and comparative example, the examples of the present invention (Experiment No. 1 to
No. 3) has a very high rubber penetration rate of 100%, a high fatigue resistance of 105-108, and a rigidity ratio of 93-.
It is as small as 95. For this reason, when it is applied to a tire, the tire has a high flexibility in the circumferential direction and therefore a good riding comfort, and a high rigidity in the lateral direction and therefore a good cornering characteristic. Further, handling workability is better than that of the conventional one.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of drawings]

FIG. 1 is a sectional view of a steel cord according to the present invention.

FIG. 2 is a cross-sectional view of a conventional steel cord in which six side wires are closely attached to each other and twisted around a core wire.

FIG. 3 is a cross-sectional view of a conventional steel cord in which a gap is formed between side strands that are tightly twisted around a core strand having a large diameter.

FIG. 4 is a cross-sectional view of a conventional steel cord in which a core wire is preliminarily provided with a spiral eccentricity having a small radius, and a side wire is closely adhered to the core wire and twisted.

FIG. 5 is a cross-sectional view of a conventional steel cord in which a core wire is preliminarily provided with a wavy curling with a small amplitude, and a side wire is closely attached to the core wire and twisted.

FIG. 6 is a sectional view of a conventional flat open twisted steel cord.

FIG. 7 is a schematic view of a rigidity tester.

FIG. 8A is a perspective view of a test piece in which a steel cord is embedded in the minor axis direction, and FIG. 8B is a perspective view of a test piece in which a steel cord is embedded in the major axis direction.

FIG. 9 is a copy of an enlarged photograph of a cross section of a steel cord (1 + 6 structure) of one example of the present invention in steps of 2 mm at one twist pitch.

[Procedure 3]

[Document name to be amended] Drawing

[Correction target item name] Figure 9

[Correction method] Change

[Correction contents]

[Figure 9]

Claims (1)

[Claims] 1. A steel cord for reinforcing a rubber product, which has a substantially elliptical shape and has a core wire having the same thickness as a large number of side wires, in which six side wires are arranged around one core wire. And twisted to form a steel cord with a 1 + 6 structure, and an open structure in which side strands are twisted around a straight core strand is compressed and the cross-sectional shape of the cord is approximately the same in the longitudinal direction of the cord. It has a flat open structure, and the core wire is partially interrupted between two adjacent side wires at the time of the pressure processing, and the maximum amount of interruption of the core wire at the cord 1 twist pitch is set to the core wire. Steel cord for reinforcing the above rubber products, which has a diameter of 30% to 50%.