JP6980965B2 - Steel cord, tire - Google Patents

Description

The present invention relates to a steel cord and a tire.

According to Patent Document 1 and the like, a steel cord used for a tire as a reinforcing material is known. In Patent Document 1, the load load of the steel cord is intended to prevent deformation of the tire at high speed rotation while absorbing the impact by denting to some extent when stepping on unevenness such as stones on the road. It has been proposed to have a predetermined relationship between and elongation.

Japanese Unexamined Patent Publication No. 2002-275772

By the way, in recent years, steel cords are required to have improved impact resistance from the viewpoint of increasing durability against impacts such as when a tire steps on a protrusion on a road surface.

However, the tire reinforcing steel cord disclosed in Patent Document 1 does not absorb the impact and deteriorate the ride quality of the vehicle by setting the load load and the elongation in a predetermined relationship, and at high speed rotation. It is intended to suppress the deformation of the tire. Therefore, it has not been sufficiently studied from the viewpoint of impact resistance.

Therefore, an object of the present disclosure is to provide a steel cord having excellent impact resistance.

According to one aspect of the present disclosure, it has a 1 × n structure in which n (n = 3, or 4) strands are twisted together.
In a cross section perpendicular to the longitudinal direction
When the area of the outermost circumscribed circle is S1 and the area of the strands is S2, a steel cord having a porosity V represented by the following formula (A) of 37% or more and 60% or less is provided.
V (%) = (S1-nS2) / S1 × 100 ... (A)
Further, according to another aspect of the present disclosure, it has a 1 × n structure in which n (n = 5) strands are twisted together.
In a cross section perpendicular to the longitudinal direction
When the area of the outermost circumscribed circle is S1 and the area of the strands is S2, a steel cord having a porosity V represented by the following formula (A) of 33% or more and 55% or less is provided.
V (%) = (S1-nS2) / S1 × 100 ... (A)

According to the present disclosure, it is possible to provide a steel cord having excellent impact resistance.

It is explanatory drawing of the steel cord of the 1 × 4 structure which concerns on one aspect of this disclosure. It is sectional drawing in the plane perpendicular to the longitudinal direction of the steel cord of FIG. It is sectional drawing in the plane perpendicular to the longitudinal direction of the steel cord of the 1 × 3 structure which concerns on one aspect of this disclosure. FIG. 3 is a cross-sectional view of a steel cord having a 1 × 5 structure according to another aspect of the present disclosure in a plane perpendicular to the longitudinal direction. It is explanatory drawing of the Charpy impact test. It is explanatory drawing of the wire which formed the bent part and the non-bent part repeatedly. It is explanatory drawing of the manufacturing method of the wire which the bent part and the non-bent part are repeatedly formed. It is sectional drawing of the tire which concerns on one aspect of this disclosure. It is a figure which showed the belt layer schematically. It is a figure which showed the relationship between the porosity and the shock absorption index of Experimental Examples 1 to 11. It is a figure which showed the relationship between the central area area of Experimental Example 1 to Experimental Example 11 and the shock absorption index. It is a figure which showed the relationship between the porosity and the shock absorption index of Experimental Example 12 to Experimental Example 16. It is a figure which showed the relationship between the central area area of Experimental Example 12 to Experimental Example 16 and the shock absorption index. It is a figure which showed the relationship between the porosity and the shock absorption index of Experimental Example 17 to Experimental Example 26. It is a figure which showed the relationship between the central area area of Experimental Example 17 to Experimental Example 26, and the shock absorption index.

The embodiment for carrying out will be described below.

[Explanation of Embodiments of the present disclosure]
First, embodiments of the present disclosure will be listed and described. In the following description, the same or corresponding elements are designated by the same reference numerals, and the same description is not repeated for them.

(1) The steel cord according to one aspect of the present disclosure has a 1 × n structure in which n (n = 3, or 4) strands are twisted together.
In a cross section perpendicular to the longitudinal direction
When the area of the outermost circle is S1 and the area of the strands is S2, the porosity V represented by the following formula (A) is 37% or more and 60% or less.
V (%) = (S1-nS2) / S1 × 100 ... (A)
According to the study by the inventors of the present invention, by setting the void ratio V to 37% or more, a plurality of strands contained in the steel cord having a 1 × 3 structure or a 1 × 4 structure can be added integrally. It is presumed that it can withstand the impact and absorb the impact applied by the voids in the steel cord.

However, when the porosity V exceeds 60%, the distance between a plurality of strands included in the steel cord having a 1 × 3 structure or a 1 × 4 structure becomes large, so that the integrity between the strands becomes weak. It is presumed that the plurality of strands contained in the steel cord are likely to be individually cut by the impact.

Therefore, according to the steel cord according to one aspect of the present disclosure, by setting the porosity V to 37% or more and 60% or less, it becomes possible to obtain a steel cord having excellent impact resistance.

(2) Further, the steel cord according to another aspect of the present disclosure has a 1 × n structure in which n (n = 5) strands are twisted together.
In a cross section perpendicular to the longitudinal direction
When the area of the outermost circle is S1 and the area of the strands is S2, the porosity V represented by the following formula (A) is 33% or more and 55% or less.
V (%) = (S1-nS2) / S1 × 100 ... (A)
According to the studies by the inventors of the present invention, by setting the porosity V to 33% or more, a plurality of strands contained in the steel cord having a 1 × 5 structure can withstand the impact applied integrally and It is presumed that the voids in the steel cord can absorb the applied impact.
However, when the porosity V exceeds 55%, the distance between the plurality of strands included in the steel cord having a 1 × 5 structure becomes large, so that the integrity between the strands becomes weak and the plurality of strands included in the steel cord. It is presumed that the strands of the wire are easily cut individually by the impact.
Therefore, according to the steel cord according to another aspect of the present disclosure, by setting the porosity V to 33% or more and 55% or less, it becomes possible to obtain a steel cord having excellent impact resistance.
(3) It has a 1 × 3 structure in which the three strands are twisted together.
In a cross section perpendicular to the longitudinal direction
The area of the region surrounded by the straight line connecting the centers of the adjacent strands along the circumferential direction of the outermost circle ^{may be 0.07 mm 2} or more and 0.13 mm ² or less.

(4) It has a 1 × 3 structure in which the three strands are twisted together.
When the Charpy impact value of a 1 × 3 structure steel cord having a porosity V of 35.8% is used as a reference value, the impact absorption index indicating the ratio of the Charpy impact value to the reference value is larger than 100%. It may be 110% or less.

(5) It has a 1 × 4 structure in which the four strands are twisted together.
In a cross section in a plane perpendicular to the longitudinal direction
The area of the region surrounded by the straight line connecting the centers of the adjacent strands along the circumferential direction of the outermost circle ^{may be 0.16 mm 2} or more and 0.32 mm ² or less.

(6) It has a 1 × 4 structure in which the four strands are twisted together.
When the Charpy impact value of a 1 × 4 structure steel cord having a void ratio V of 36.4% is used as a reference value, the impact absorption index indicating the ratio of the Charpy impact value to the reference value is larger than 100%. It may be 140% or less.

(7) It has a 1 × 5 structure in which the five strands are twisted together.
In a cross section perpendicular to the longitudinal direction
The area of a region surrounded by a straight line connecting the centers of the wires adjacent to each other along the circumferential direction of the circumscribed circle may be 0.24 mm ² or more 0.45 mm ² or less.

(8) It has a 1 × 5 structure in which the five strands are twisted together.
When the Charpy impact value of a 1 × 5 structure steel cord having a void ratio V of 32.0% is used as a reference value, the impact absorption index indicating the ratio of the Charpy impact value to the reference value is larger than 100%. It may be 115% or less.

(9) At least one of the n strands may have a bent portion and a non-bent portion repeatedly along the longitudinal direction.

(10) All the n wires may have a bent portion and a non-bent portion repeatedly along the longitudinal direction.

(11) When the height from the plane to the bent portion on the side far from the plane when the strand is placed on a plane is defined as the bending height.
The bending height may be 0.10 mm or more and 0.30 mm or less.

(12) The repeating pitch between the bent portion and the non-bent portion may be 5.0 mm or more and 30.0 mm or less.

(13) The initial elongation when 49N is added may be 0.06% or more and 0.35% or less.

(14) The diameter of the wire may be 0.22 mm or more and 0.42 mm or less.

(15) A tire containing the steel cord according to any one of (1) to (14) can also be used.

[Details of Embodiments of the present disclosure]
Specific examples of the steel cord and the tire according to one embodiment of the present disclosure (hereinafter referred to as “the present embodiment”) will be described below with reference to the drawings. It should be noted that the present invention is not limited to these examples, and is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

[Steel cord]
Hereinafter, the steel cord according to the present embodiment will be described with reference to FIGS. 1 to 7.

The steel cord according to the present embodiment has a 1 × n structure in which n strands, also called filaments, are spirally twisted together.

Here, FIG. 1 shows an example of the configuration of the steel cord 10 of the present embodiment. The steel cord 10 shown in FIG. 1 has a structure in which four strands 11 are twisted together.

The 1 × n structure means a structure in which n strands are twisted so as to form a single layer (one layer). A single layer is a single layer (one layer) along the circumferential direction of one circle in a cross section perpendicular to the longitudinal direction of the steel cord as shown in FIGS. 2, 3 and 4, which will be described later. It means a structure arranged so as to be.

The steel cord 10 shown in FIG. 1 has a 1 × 4 structure in which four strands 11 are twisted so as to form a single layer. FIG. 2 shows a cross-sectional view of the steel cord 10 shown in FIG. 1 in a plane perpendicular to the longitudinal direction. The longitudinal direction of the steel cord 10 is the Y-axis direction in the drawing. Further, the plane perpendicular to the longitudinal direction is a plane parallel to the XZ plane in the drawing.

As shown in FIG. 2, four strands 11 are twisted together, and a central void 12 surrounded by the four strands 11 is formed in the central portion.

FIG. 2 shows an example in which adjacent strands 11 are in contact with each other in a cross section perpendicular to the longitudinal direction. It is possible that all the adjacent strands 11 do not come into contact with each other and a gap is formed between the strands 11.

FIG. 3 shows a configuration example of a cross-sectional view of a steel cord 30 having a 1 × 3 structure in a plane perpendicular to the longitudinal direction. Further, FIG. 4 shows a configuration example of a cross-sectional view of the steel cord 40 having a 1 × 5 structure in a plane perpendicular to the longitudinal direction.

In the steel cord 30 having a 1 × 3 structure shown in FIG. 3, three strands 11 are twisted together so as to form a single layer, and a central void 12 surrounded by the three strands 11 in the center. Is formed. In the steel cord 40 having a 1 × 5 structure shown in FIG. 4, five strands 11 are twisted together so as to form a single layer, and a central void 12 surrounded by the five strands 11 in the center. Is formed.

In FIGS. 3 and 4, a gap 13 between the strands is formed between the adjacent strands 11, but a part or all of the adjacent strands 11 is, for example, like the steel cord 10 shown in FIG. You may be in contact.

When the steel cord of the present embodiment has a 1 × 3 structure or a 1 × 4 structure, the area of the outermost circumscribed circle is S1 and the area of the strands per wire is S2 in the cross section perpendicular to the longitudinal direction. , The void ratio V represented by the following formula (A) is 37% or more and 60% or less.
Further, when the steel cord of the present embodiment has a 1 × 5 structure, the area of the outermost circumscribed circle is S1 and the area of the strands per wire is S2 in the cross section perpendicular to the longitudinal direction. The void ratio V represented by the formula (A) is 33% or more and 55% or less.

A (%) = (S1-nS2) / S1 × 100 ... (A)
Here, the outermost circle in the cross section perpendicular to the longitudinal direction of the steel cord is the outermost circle inscribed by the outer peripheral edges of the four strands 11 in the case of the cross section of the steel cord 10 having the 1 × 4 structure shown in FIG. It means the circumscribed circle 14. Further, in the case of the cross section of the steel cord 30 shown in FIG. 3, it means the outermost circumscribed circle 14 inscribed by the outer peripheral edges of the three strands 11. In the case of the cross section of the steel cord 40 shown in FIG. 4, it means the outermost circumscribed circle 14 inscribed by the outer peripheral edges of the five strands 11. In either case, the circumscribed circle 14 is a perfect circle.

Since the outermost circle 14 corresponds to the outer shape of the steel cord, the diameter of the outermost circle 14 may be referred to as the cord diameter in the present specification.

The porosity V indicates the ratio of the area of the region surrounded by the outermost circle 14 that is not occupied by the strand 11 in the cross section perpendicular to the longitudinal direction of the steel cord. It can be calculated by the formula (A). In the same steel cord, the porosity in the cross section perpendicular to the longitudinal direction of the steel cord is constant regardless of the position of the cross section to be measured, so the cross section at an arbitrary position in the longitudinal direction of the steel cord is used. Can be measured and calculated.

The porosity V in the cross section perpendicular to the longitudinal direction of the steel cord can be adjusted, for example, by the presence or absence of the gap 13 between the strands 11 between the adjacent strands 11 as described above, its size, the size of the central void 12, and the like. ..

Charpy impact test is one of the methods for evaluating the impact resistance of steel cords. In the Charpy impact test, for example, as shown in FIG. 5, a hammer 52 having a mass m is rotated from an initial position A about a rotation shaft 53, and a sample 51 set in advance on the movement path of the hammer 52 is subjected to the rotation. It can be done by swinging it down. After breaking the sample 51, the hammer 52 further advances in the rotational direction and reaches the maximum height position B.

Here, the height of the initial position A based on the position of the sample 51 is defined as h1, and the height of the maximum height position B based on the position of the sample 51 is defined as h2. In this case, mg (h1-h2), which is the difference between the potential energy at the initial position A and the potential energy at the highest height position B, is the absorbed energy when the sample is destroyed. The absorbed energy is the Charpy impact value, and the larger the value, the better the impact resistance of the steel cord.

Since the Charpy impact test can evaluate the energy required to destroy a sample, it has been widely used to evaluate the impact resistance of various wire rods such as piano wire. Conventionally, it is considered that the Charpy impact value is mainly affected by the elongation rate of the wire material and the breaking load, and the influence of the structure of the wire is not known.

However, according to the study by the inventors of the present invention, in a steel cord having a 1 × 3 structure or a 1 × 4 structure, the porosity V is 37% or more and 60% or less by setting the porosity V to 37% or more. It was confirmed that the charpy impact value was higher than that in the case of less than%. Further, it can be confirmed that the Charpy impact value is higher than the case where the porosity V is less than 33% by setting the porosity V to 33% or more and 55% or less in the steel cord having a 1 × 5 structure. rice field. That is, it was found that the structure of the wire rod as a sample has an influence on the impact resistance evaluated by the Charpy impact test.

This is because the porosity V of the steel cord is set to the above-mentioned predetermined value or more according to the structure to counter the impact that a plurality of strands contained in the steel cord are integrally applied, and the voids in the steel cord. However, it is presumed that it is because it absorbs the applied impact.

However, in a steel cord having a 1 × 3 structure or a 1 × 4 structure, if the porosity V of the steel cord exceeds 60%, the distance between a plurality of strands included in the steel cord becomes large, so that the strands are It is thought that the unity between them will be weakened. Therefore, it is presumed that the impact resistance is lowered because the plurality of strands included in the steel cord are easily cut individually by the impact.
Further, in the steel cord having a 1 × 5 structure, it is presumed that the impact resistance is lowered for the same reason when the porosity V of the steel cord exceeds 55%.

As described above, the steel cord of the present embodiment can improve the impact resistance by setting the porosity V within a predetermined range. Therefore, it is preferable to adjust the arrangement of a plurality of strands so that the porosity V is within the above range in the cross section perpendicular to the longitudinal direction of the steel cord.

Further, the steel cord of the present embodiment has a central void 12 which is a void surrounded by a wire in the central portion as shown in FIGS. 2 to 4 in a cross section perpendicular to the longitudinal direction of the steel cord. Is preferable. This is because the impact can be absorbed by the central void 12, and the impact resistance can be particularly enhanced. Therefore, it is preferable that the steel cord of the present embodiment has three or more strands. However, if the number of strands exceeds 5, the diameter of the strands, that is, the diameter of the strands needs to be reduced, which is not preferable because the manufacturing cost increases. Therefore, it is preferable that the steel cord of the present embodiment includes 3 or more and 5 or less strands.

In order to improve impact resistance, it is conceivable that the steel cord has a structure of two or more layers of twisted layers instead of a single layer, but it becomes necessary to reduce the wire diameter of each layer and the twisting process is required. There is a risk of complicating the manufacturing process, such as having two or more processes. Therefore, the steel cord of the present embodiment preferably has a single-layer structure having a 1 × n structure. The multi-layer is a cross section perpendicular to the longitudinal direction of the steel cord, and the strands are arranged along the circumferential direction of one circle to form one layer, and the layers are concentric. Means a structure having multiple layers.

When the number n of the strands contained in the steel cord of the present embodiment is 3, the cross section perpendicular to the longitudinal direction is surrounded by a straight line connecting the centers of the adjacent strands along the circumferential direction of the circumscribed circle. The area of the removed region ^{is preferably 0.07 mm 2} or more and 0.13 mm ² or less.

When the number of strands n is 3, the region surrounded by a straight line connecting the centers of adjacent strands along the circumferential direction of the outermost circle in the cross section perpendicular to the longitudinal direction (hereinafter, "center"). (Also referred to as “region”) will be described with reference to FIG. FIG. 3 shows a cross-sectional view of a steel cord 30 having three strands 11 as described above in a plane perpendicular to the longitudinal direction. When the number n of the strands of the steel cord is 3, if the centers of the strands 11 adjacent to each other along the circumferential direction of the outermost circle 14 are connected by a straight line, the line segment O _31- O ₃₂ and the line segment O are connected. A central region 15 of a triangle surrounded by _32- O ₃₃ and a line segment O _33- O _{31 is formed.}

When the number of strands n is 3 and the area of the central region 15 is 0.07 mm ² or more as described above, it is preferable because a steel cord having excellent impact resistance can be obtained.

When the number n of the strands n is 3 and the area of the central region 15 is 0.07 mm ² or more, it is considered that the central region 15 includes a central void 12 having a size sufficient to absorb an impact. Therefore, when an impact is applied to the steel cord 30, it is presumed that the central region 15 can sufficiently absorb the impact and enhance the impact resistance.

However, when the number n of the strands is 3, if the area of the central region 15 ^{exceeds 0.13 mm 2} , the distance between the strands also increases, so that the integrity between the strands is considered to be weakened. Therefore, the plurality of strands 11 included in the steel cord 30 are likely to be individually cut by the impact, and the impact resistance may be lowered. Therefore, when the number n of the strands is 3, the area of the central region 15 ^{is preferably 0.13 mm 2} or less.

Further, when the number n of the strands contained in the steel cord of the present embodiment is 4, a straight line connecting the centers of the strands adjacent to each other along the circumferential direction of the outermost circle in the cross section perpendicular to the longitudinal direction. The area of the area surrounded by ^{is preferably 0.16 mm 2} or more and 0.32 mm ² or less.

The central region when the number of strands n is four will be described with reference to FIG. FIG. 2 shows a cross-sectional view of a steel cord 10 having four strands 11 as described above in a plane perpendicular to the longitudinal direction. When the number n of the strands of the steel cord is 4, if the centers of the strands 11 adjacent to each other along the circumferential direction of the outermost circle 14 are connected by a straight line, the line segments O _11- O ₁₂ and the line segment O are connected. A central region 15 of a quadrangle surrounded by _12- O ₁₃ , line segment O _13- O _{14, and} line segment O _14- O _{11 is formed.}

When the number of strands n is four and the area of the central region 15 is 0.16 mm ² or more as described above, it is preferable because a steel cord having excellent impact resistance can be obtained.

When the number n of the strands n is 4 and the area of the central region is 0.16 mm ² or more, it is considered that the central region 15 includes the central void 12 having a size sufficient to absorb the impact. Therefore, when an impact is applied to the steel cord 10, it is presumed that the central region 15 can sufficiently absorb the impact and enhance the impact resistance.

However, when the number n of the strands is 4, if the area of the central region 15 ^{exceeds 0.32 mm 2} , the distance between the strands also increases, so that the integrity between the strands is considered to be weakened. For this reason, a plurality of strands included in the steel cord are likely to be individually cut by an impact, which may reduce the impact resistance. Therefore, when the number of strands n is 4, the area of the central region 15 ^{is preferably 0.32 mm 2} or less.

Further, when the number n of the strands contained in the steel cord of the present embodiment is 5, a straight line connecting the centers of the strands adjacent to each other along the circumferential direction of the outermost circle in the cross section perpendicular to the longitudinal direction. area of a region surrounded by it is preferably 0.24 mm ² or more 0.45 mm ² or less.

The central region when the number of strands n is 5 will be described with reference to FIG. FIG. 4 shows a cross-sectional view of a steel cord 40 having five strands as described above in a plane perpendicular to the longitudinal direction. When the number n of the strands of the steel cord is 5, if the centers of the strands 11 adjacent to each other along the circumferential direction of the outermost circle 14 are connected by a straight line, the line segment O _41- O ₄₂ and the line segment O are connected. A pentagonal central region 15 surrounded by _42- O ₄₃ , line segment O _43- O _44, line segment O _44- O _{45, and} line segment O _45- O _{41 is formed.}

When the number of strands n is 5, and the area of the central region 15 is 0.24 mm ² or more as described above, it is preferable because a steel cord having excellent impact resistance can be obtained.

When the number n of the strands n is 5 and the area of the central region is 0.24 mm ² or more, it is considered that the central region 15 includes the central void 12 having a size sufficient to absorb the impact. Therefore, when an impact is applied to the steel cord 40, it is presumed that the impact can be sufficiently absorbed by the central region and the impact resistance can be improved.

However, when the number n of the strands is 5, if the area of the central region 15 ^{exceeds 0.45 mm 2} , the distance between the strands also increases, so that the integrity between the strands is considered to be weakened. For this reason, a plurality of strands included in the steel cord are likely to be individually cut by an impact, which may reduce the impact resistance. Therefore, when the number n of the strands is 5, the area of the central region ^{is preferably 0.45 mm 2} or less.

In the steel cord of the present embodiment, at least one of the n strands contained therein may have a bent portion and a non-bent portion repeatedly along the longitudinal direction. Further, in the steel cord of the present embodiment, all the n strands contained therein may have a bent portion and a non-bent portion repeatedly along the longitudinal direction.

FIG. 6 schematically shows a wire 61 having a bent portion and a non-bent portion repeatedly along the longitudinal direction. The strand 61 shown in FIG. 6 has bent portions 62 and non-bent portions 63 alternately and repeatedly along the longitudinal direction.

Note that FIG. 6 shows an example in which the bent portion 62 is bent at an angle close to 90 degrees, but the present invention is not limited to this, and the bent portion 62 is bent at an angle of less than 90 degrees or larger than 90 degrees, for example. Is also good. Further, the strands in the bent portion 62 do not have to have a clear bending point, and may have a shape curved in an arc shape, for example.

Of the n strands contained in the steel cord of the present embodiment, one or a plurality of strands have a shape having a bent portion and a non-bent portion repeatedly along the longitudinal direction. The porosity V can be adjusted. Therefore, the degree of impact resistance of the obtained steel cord can be selected.

However, since the steel cord contains a wire having a shape in which a bent portion and a non-bent portion are repeatedly formed along the longitudinal direction, not only the porosity V but also the characteristics such as initial elongation are affected. Therefore, depending on the porosity V required for the steel cord and the characteristics such as initial elongation, the number of strands contained in the steel cord having the bent portion and the non-bent portion repeatedly along the longitudinal direction may be increased. , It is preferable to select the shape.

In a wire having a bent portion and a non-bent portion repeatedly along the longitudinal direction, the repeating pitch between the bent portion and the non-bent portion is preferably 5.0 mm or more and 30.0 mm or less. More preferably, it is 0.0 mm or more and 20.0 mm or less.

The repeating pitch between the bent portion and the non-bent portion means the distance between the bent portions having the same shape, and is the longitudinal length of the steel cord from the reference bent portion to the adjacent bent portion. means. Therefore, in the example shown in FIG. 6, the repeating pitch P between the bent portion and the non-bent portion means, for example, the distance from the bent portion 62A to the bent portion 62C adjacent to the bent portion 62A.

By setting the repeating pitch between the bent part and the non-bent part to 5.0 mm or more, it is easy to form the bent part and the non-bent part in the wire, and the porosity V of the steel cord can be accurately determined as required. It is preferable because it is easy to control. However, if the repeating pitch between the bent portion and the non-bent portion is made longer than 30.0 mm, the device for forming the bent portion and the non-bent portion becomes large, and the manufacturing cost may increase. ..

Further, the height from the plane S to the bent portion 62B on the side far from the plane S when the wire is placed on the plane S is defined as the bending height h.

The bending height h is preferably 0.10 mm or more and 0.30 mm or less, and more preferably 0.12 mm or more and 0.28 mm or less.

This is because the porosity V can be particularly increased when the steel cord is used by setting the bending height h to 0.10 mm or more. However, if the bending height h is longer than 0.30 mm, there is a risk of damaging other strands when the strands are twisted together. Therefore, the bending height h is preferably 0.30 mm or less.

As for the strands having the bent portion and the non-bent portion repeatedly along the longitudinal direction, for example, as shown in FIG. 7, a plurality of preforms 71 are arranged, and the strands 72 are placed between the plurality of preforms 71. It can be formed by passing it through. By changing the arrangement, size, and shape of the preform 71, the shape of the bent portion, the length of the non-bent portion, and the like can be selected. The preform 71 can have, for example, a pin type (cylindrical type) or a gear type.

The diameter of the wire contained in the steel cord of the present embodiment, that is, the wire diameter is preferably 0.22 mm or more and 0.42 mm or less, and more preferably 0.25 mm or more and 0.38 mm or less.

By setting the wire diameter to 0.22 mm or more, the breaking load can be sufficiently increased for the steel cord containing the wire.

However, if the wire diameter is made excessively large, the weight of the steel cord containing the wire and the tire using the steel cord will increase, which is not preferable. Therefore, the wire diameter is preferably 0.42 mm or less.

The steel cord of the present embodiment preferably has an initial elongation of 0.06% or more and 0.35% or less, and more preferably 0.07% or more and 0.30% or less when 49N is added.

The initial elongation means the elongation when a load is applied to the steel cord along the longitudinal direction after the steel cord is manufactured by twisting the strands. The initial elongation is the elongation that occurs in the process of reaching a close contact state by applying a load to a plurality of spirally twisted strands. The above-mentioned initial elongation means the ratio of elongation per 500 mm of the steel cord when 49N is applied to the steel cord of the present embodiment.

The steel cord of the present embodiment can be used by embedding it in a tire, for example, as described later. By setting the initial elongation of the steel cord of the present embodiment to 0.06% or more, it is possible to improve the absorption performance of road surface irregularities, that is, the impact absorption performance of the tire in which the steel cord is embedded, and improve the riding comfort. be able to. However, if the initial elongation of the steel cord exceeds 0.35%, the handling workability in the stranded wire process or the like may deteriorate, so it is preferably 0.35% or less.

The Charpy impact value measured by the above-mentioned Charpy impact test is affected by the ambient temperature and humidity. Therefore, the result of the Charpy impact test is displayed as a relative ratio to the Charpy impact value of the reference material.

Specifically, when conducting a Charpy impact test, a reference material to be used as a reference is determined, and the Charpy impact test is performed on the reference material and the evaluation material in the same environment. Then, the Charpy impact value of the reference product is set as a reference value (100%), and the Charpy impact value of the evaluation product is indicated by the impact absorption index which is a ratio to the reference value. When the impact absorption index is 100%, it means that the Charpy impact value is the same for the reference product and the evaluation product.

In the steel cord of the present embodiment, the steel cord having excellent impact resistance can be obtained by selecting the porosity V. Therefore, when confirming the effect of the porosity V, it is preferable that the wire diameter of the wire contained in the steel cord is the same as that of the reference product for calculating the impact absorption index and the evaluation product. ..

When the number n of the strands contained in the steel cord of the present embodiment is 3, the impact absorption index is based on the Charpy impact value of the steel cord having a 1 × 3 structure having a porosity V of 35.8%. Can be used as. When the number n of the strands contained in the steel cord of the present embodiment is 3, the impact absorption index, which is the ratio of the reference value to the Charpy impact value as a percentage, is larger than 100% and 110% or less. It is preferable to have. By setting the impact absorption index to be greater than 100% and 110% or less, a steel cord having excellent impact resistance can be obtained.

For a steel cord having a 1 × 3 structure with a porosity V of 35.8% used as a reference material for the impact absorption index, for example, three strands in which a bent portion and a non-bent portion are not formed in advance are twisted together. Can be produced. The porosity V of the steel cord is relatively small in the steel cord having a 1 × 3 structure.

Then, according to the study by the inventors of the present invention, the impact resistance of the steel cord can be improved by increasing the porosity V. Therefore, the impact absorption index based on the steel cord having a 1 × 3 structure having a porosity V of 35.8% is preferably larger than 100%.

However, if the impact absorption index is to be made larger than 110%, it may be necessary to increase not only the porosity V but also the wire diameter. Increasing the wire diameter increases the weight of the steel cord and the tire using the steel cord, which is not preferable. Therefore, the impact absorption index is preferably 110% or less.

When the number n of the strands contained in the steel cord of the present embodiment is 4, the impact absorption index is based on the Charpy impact value of the 1 × 4 structure steel cord having a void ratio V of 36.4%. Can be used as. When the number n of the strands contained in the steel cord of the present embodiment is 4, the impact absorption index, which is the ratio of the reference value to the Charpy impact value as a percentage, is larger than 100% and 140% or less. Is preferable. By setting the impact absorption index to be greater than 100% and 140% or less, a steel cord having excellent impact resistance can be obtained.

For a steel cord having a 1 × 4 structure with a porosity V of 36.4%, which was used as a reference for the impact absorption index, for example, four strands in which a bent portion and a non-bent portion are not formed in advance are twisted together. Can be made. The porosity V of the steel cord is relatively small in the steel cord having a 1 × 4 structure.

Then, according to the study by the inventors of the present invention, the impact resistance of the steel cord can be improved by increasing the porosity V. Therefore, the impact absorption index based on the steel cord having a 1 × 4 structure having a porosity V of 36.4% is preferably larger than 100%.

However, if the impact absorption index is to be made larger than 140%, it may be necessary to increase not only the porosity V but also the wire diameter. Increasing the wire diameter increases the weight of the steel cord and the tire using the steel cord, which is not preferable. Therefore, the impact absorption index is preferably 140% or less.

When the number n of the strands contained in the steel cord of the present embodiment is 5, the impact absorption index is based on the Charpy impact value of the steel cord having a 1 × 5 structure in which the void ratio V is 32.0%. Can be used as. When the number n of the strands contained in the steel cord of the present embodiment is 5, the impact absorption index, which is a percentage of the Charpy impact value of the reference value, is greater than 100% and 115% or less. Is preferable. By setting the impact absorption index to 115% or less, which is larger than 100%, a steel cord having excellent impact resistance can be obtained.

For a steel cord having a 1 × 5 structure with a porosity V of 32.0% used as a reference for the impact absorption index, for example, five strands in which a bent portion and a non-bent portion are not formed in advance are twisted together. Can be made. The porosity V of the steel cord is relatively small in the steel cord having a 1 × 5 structure.

Then, according to the study by the inventors of the present invention, the impact resistance of the steel cord can be improved by increasing the porosity V. Therefore, the impact absorption index based on the steel cord having a 1 × 5 structure having a porosity V of 32.0% is preferably larger than 100%.

However, if the impact absorption index is to be made larger than 115%, it may be necessary to increase not only the porosity V but also the wire diameter. Increasing the wire diameter increases the weight of the steel cord and the tire using the steel cord, which is not preferable. Therefore, the impact absorption index is preferably 115% or less.

〔tire〕
Next, the tire in this embodiment will be described with reference to FIGS. 8 and 9.

The tire of the present embodiment may include the steel cord described above.

FIG. 8 shows a cross-sectional view of the tire 81 according to the present embodiment on a plane perpendicular to the circumferential direction. Although only the portion on the left side of the CL (center line) is shown in FIG. 8, the same structure is continuously provided on the right side of the CL with the CL as the axis of symmetry.

As shown in FIG. 8, the tire 81 includes a tread portion 82, a sidewall portion 83, and a bead portion 84.

The tread portion 82 is a portion in contact with the road surface. The bead portion 84 is provided on the inner diameter side of the tire 81 with respect to the tread portion 82. The bead portion 84 is a portion in contact with the rim of the wheel of the vehicle. The sidewall portion 83 connects the tread portion 82 and the bead portion 84. When the tread portion 82 receives an impact from the road surface, the sidewall portion 83 elastically deforms and absorbs the impact.

The tire 81 includes an inner liner 85, a carcass 86, a belt layer 87, and a bead wire-88.

The inner liner 85 is made of rubber and seals the space between the tire 81 and the wheel.

The carcass 86 forms the skeleton of the tire 81. The carcass 86 is composed of organic fibers such as polyester, nylon and rayon, steel cords, and rubber.

The bead wire-88 is provided on the bead portion 84. The bead wire-88 receives the pulling force acting on the carcass.

The belt layer 87 tightens the carcass 86 to increase the rigidity of the tread portion 82. In the example shown in FIG. 8, the tire 81 has two belt layers 87.

FIG. 9 is a diagram schematically showing the two-layer belt layer 87. FIG. 9 shows a cross-sectional view of the belt layer 87 in the longitudinal direction, that is, in a plane perpendicular to the circumferential direction of the tire 81.

As shown in FIG. 9, the two belt layers 87 are overlapped with each other in the radial direction of the tire 81. Each belt layer 87 has a plurality of steel cords 91 and rubber 92. A plurality of steel cords 91 are arranged in a row. Further, the rubber 92 covers the steel cord 91, and the entire circumference of each steel cord is covered with the rubber 92. The steel cord 91 is embedded in the rubber 92.

According to the tire of the present embodiment, the steel cord 91 includes the steel cord having excellent impact resistance as described above. Therefore, the tire of the present embodiment can also be a tire having excellent impact resistance.

Although the embodiments have been described in detail above, the embodiments are not limited to the specific embodiments, and various modifications and changes can be made within the scope of the claims.

Specific examples will be given below, but the present invention is not limited to these examples.
(Evaluation method)
First, the evaluation method of the steel cord produced in the following experimental example will be described.
(1) Wire diameter The wire diameter was measured using a micrometer.
(2) A steel cord for evaluating the cord diameter was embedded in a transparent resin, and a sample was cut out so that the surface (cross section) perpendicular to the longitudinal direction of the steel cord was exposed.

Then, using a projector, the diameters of the outermost circles of the plurality of strands included in the cross section were measured and used as the cord diameter.
(3) Air gap ratio From the wire diameter and cord diameter measured in (1) and (2), the area S1 of the outermost circumscribed circle and the area S2 of the wire per wire are calculated, and the following formula (A) is used. Was used to calculate the void ratio V.

V (%) = (S1-nS2) / S1 × 100 ... (A)
(4) Center area area From the observation results of the cross section perpendicular to the longitudinal direction of the steel cord measured when calculating the cord diameter of (2), between the centers of adjacent strands along the circumferential direction of the outermost circle. The area of the central region, which is the region connecting the above with a straight line, was calculated.
(5) Initial elongation Using an autograph (model: AGS-J 1kN manufactured by Shimadzu Corporation), the ratio of elongation per 500 mm of steel cord when 49N was applied was measured and calculated, and used as the initial elongation.
(6) Breaking load Using an autograph (model: AGS-H 10kN manufactured by Shimadzu Corporation), a load is applied along the longitudinal direction of the steel cord, and the load applied to the steel cord at the time of breaking is broken. It was a load.
(7) Impact Absorption Index Using the Charpy impact test device shown in FIG. 5, the Charpy impact value was measured by the Charpy impact test, and the impact absorption index was calculated from the measured Charpy impact value.

Specifically, a Charpy impact test was conducted on the reference material and the sample to be evaluated under the same environment. Then, the Charpy impact value of the reference material was set as a reference value (100%), and the Charpy impact value of the sample to be evaluated was converted into an impact absorption index which is a ratio to the reference value.

In Experimental Examples 2 to 11, the steel cord produced in Experimental Example 1 was used as a reference material (reference code).

In Experimental Examples 13 to 16, the steel cord produced in Experimental Example 12 was used as a reference material (reference code).

In Experimental Examples 18 to 26, the steel cord produced in Experimental Example 17 was used as a reference material (reference code).
(Experimental example)
Steel cords of each of the following experimental examples were prepared and evaluated as described above. All of the steel cords were manufactured by twisting the strands so that the twist pitch was 17.0 mm using a buncher-twisting machine.

Experimental Examples 3 to 10, Experimental Examples 13 to 15, and Experimental Examples 18 to 25 are Examples, and Experimental Examples 1, 2, 11, 12, 16, 17, and 26 are comparative examples.
(Experimental Examples 1 to 11)
As Experimental Examples 1 to 11, steel cords containing four strands and having different porosities were prepared and evaluated.
[Experimental Example 1]
A steel cord having a twisted structure of 1 × 4 was produced by using four strands having a strand diameter of 0.370 mm. For all four strands, the strands in which the bent portion and the non-bent portion were not formed were used.

The evaluation results are shown in Table 1.
[Experimental Example 2]
A steel cord having a twisted structure of 1 × 4 was produced by using four strands having a strand diameter of 0.370 mm. At this time, for one of the four strands, the bent portion and the non-bent portion are provided so that the bending height h is 0.25 mm and the repeating pitch P between the bent portion and the non-bent portion is 10 mm. The formed strand was used. For the remaining three strands, the strands that did not form a bent portion and a non-bent portion were used. The evaluation results are shown in Table 1.
[Experimental Example 3]
A steel cord having a twisted structure of 1 × 4 was produced by using four strands having a strand diameter of 0.370 mm. At this time, for one of the four strands, the bent portion and the non-bent portion are provided so that the bending height h is 0.30 mm and the repeating pitch P between the bent portion and the non-bent portion is 10 mm. The formed strand was used. For the remaining three strands, the strands that did not form a bent portion and a non-bent portion were used. The evaluation results are shown in Table 1.

[Experimental Example 4]
A steel cord having a twisted structure of 1 × 4 was produced by using four strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.25 mm and the repeating pitch P between the bent portion and the non-bent portion was 10 mm for all four strands. A strand was used. The evaluation results are shown in Table 1.
[Experimental Example 5]
A steel cord having a twisted structure of 1 × 4 was produced by using four strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.27 mm and the repeating pitch P between the bent portion and the non-bent portion was 14 mm for all four strands. A strand was used. The evaluation results are shown in Table 1.

[Experimental Example 6]
A steel cord having a twisted structure of 1 × 4 was produced by using four strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.25 mm and the repeating pitch P between the bent portion and the non-bent portion was 14 mm for all four strands. A strand was used. The evaluation results are shown in Table 1.
[Experimental Example 7]
A steel cord having a twisted structure of 1 × 4 was produced by using four strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.28 mm and the repeating pitch P between the bent portion and the non-bent portion was 14 mm for all four strands. A strand was used. The evaluation results are shown in Table 1.

[Experimental Example 8]
A steel cord having a twisted structure of 1 × 4 was produced by using four strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.30 mm and the repeating pitch P between the bent portion and the non-bent portion was 12 mm for all four strands. A strand was used. The evaluation results are shown in Table 1.
[Experimental Example 9]
A steel cord having a twisted structure of 1 × 4 was produced by using four strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.25 mm and the repeating pitch P between the bent portion and the non-bent portion was 8 mm for all four strands. A strand was used. The evaluation results are shown in Table 1.

[Experimental Example 10]
A steel cord having a twisted structure of 1 × 4 was produced by using four strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.30 mm and the repeating pitch P between the bent portion and the non-bent portion was 14 mm for all four strands. A strand was used. The evaluation results are shown in Table 1.
[Experimental Example 11]
A steel cord having a twisted structure of 1 × 4 was produced by using four strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.30 mm and the repeating pitch P between the bent portion and the non-bent portion was 8 mm for all four strands. A strand was used. The evaluation results are shown in Table 1.

The relationship between the porosity of Experimental Examples 1 to 11 and the impact absorption index shown in Table 1 is shown in FIG. 10, and the relationship between the central region area and the impact absorption index is shown in FIG. 11, respectively.

According to the results shown in FIG. 10, the values of the impact absorption index with respect to the porosity in each experimental example are distributed on the approximate curve, and the porosity peaks at 49.6%. It could be confirmed.

In this way, a correlation was found between the porosity and the impact absorption index, and it was confirmed that the impact resistance can be enhanced by selecting the porosity. Further, when the porosity was 37% or more and 60% or less, the impact absorption index became higher than 100%, and it was confirmed that the impact resistance was excellent.

Further, according to the results shown in FIG. 11, it was confirmed that the impact absorption index with respect to the central region area in each experimental example was also distributed on the approximate curve and the central region area ^{peaked at about 0.220 mm 2.} ..

As described above, since there is a correlation between the central region area and the impact absorption index, it was confirmed that the impact resistance can be improved by selecting the central region area. Furthermore, from the evaluation results of the steel cords of Experimental Examples 1 to 11 in which the number of strands contained is 4, the impact absorption index is set by ^{setting the central region area to 0.16 mm 2} or more and 0.32 mm ^{2 or less.} Was higher than 100%, and it was confirmed that the impact resistance was excellent.
(Experimental Example 12 to Experimental Example 16)
Next, as Experimental Examples 12 to 16, steel cords containing 3 strands and different porosities were prepared and evaluated in the same manner as in Experimental Examples 1 to 11. rice field.
[Experimental Example 12]
A steel cord having a twisted structure of 1 × 3 was produced by using three strands having a strand diameter of 0.370 mm. For all three strands, strands that did not form a bent portion and a non-bent portion were used.

The evaluation results are shown in Table 1.
[Experimental Example 13]
A steel cord having a twisted structure of 1 × 3 was produced by using three strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.30 mm and the repeating pitch P between the bent portion and the non-bent portion was 14 mm for all three strands. A strand was used. The evaluation results are shown in Table 1.
[Experimental Example 14]
A steel cord having a twisted structure of 1 × 3 was produced by using three strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.25 mm and the repeating pitch P between the bent portion and the non-bent portion was 14 mm for all three strands. A strand was used. The evaluation results are shown in Table 1.

[Experimental Example 15]
A steel cord having a twisted structure of 1 × 3 was produced by using three strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.25 mm and the repeating pitch P between the bent portion and the non-bent portion was 10 mm for all three strands. A strand was used. The evaluation results are shown in Table 1.
[Experimental Example 16]
A steel cord having a twisted structure of 1 × 3 was produced by using three strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.30 mm and the repeating pitch P between the bent portion and the non-bent portion was 10 mm for all three strands. A strand was used. The evaluation results are shown in Table 1.

The relationship between the porosity of Experimental Examples 12 to 16 and the impact absorption index shown in Table 1 is shown in FIG. 12, and the relationship between the central region area of Experimental Examples 12 to 16 and the impact absorption index is shown in FIG. Shown in.

According to the results shown in FIG. 12, the values of the impact absorption index with respect to the porosity in each experimental example are distributed on the approximate curve, and the impact absorption index peaks when the porosity is about 52.5%. Was confirmed.

In this way, a correlation was found between the porosity and the impact absorption index, and it was confirmed that the impact resistance can be enhanced by selecting the porosity. Further, when the porosity was 37% or more and 60% or less, the impact absorption index became higher than 100%, and it was confirmed that the impact resistance was excellent.

Further, according to the results shown in FIG. 13, it was confirmed that the impact absorption index with respect to the central region area in each experimental example was also distributed on the approximate curve and the central region area ^{peaked at about 0.10 mm 2.} ..

As described above, since there is a correlation between the central region area and the impact absorption index, it was confirmed that the impact resistance can be improved by selecting the central region area. Furthermore, from the evaluation results of the steel cords of Experimental Examples 12 to 16 in which the number of strands contained is 3, the impact absorption index is set ^{to 0.07 mm 2} or more and 0.13 mm ^{2 or less in the central region area.} Was higher than 100%, and it was confirmed that the impact resistance was excellent.
(Experimental Examples 17 to 26)
Next, as Experimental Examples 17 to 26, steel cords containing 5 strands and different porosities were prepared and evaluated in the same manner as in Experimental Examples 1 to 11. rice field.
[Experimental Example 17]
A steel cord having a twisted structure of 1 × 5 was produced by using five strands having a strand diameter of 0.370 mm. As the wire, a wire having no bent portion and a non-bent portion was used.

The evaluation results are shown in Table 1.
[Experimental Example 18]
A steel cord having a twisted structure of 1 × 5 was produced by using five strands having a strand diameter of 0.370 mm. At this time, for three of the five strands, the bent portion and the non-bent portion are provided so that the bending height h is 0.30 mm and the repeating pitch P between the bent portion and the non-bent portion is 14 mm. The formed strand was used. For the remaining two strands, the strands that did not form a bent portion and a non-bent portion were used. The evaluation results are shown in Table 1.
[Experimental Example 19]
A steel cord having a twisted structure of 1 × 5 was produced by using five strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.28 mm and the repeating pitch P between the bent portion and the non-bent portion was 14 mm for all five strands. A strand was used. The evaluation results are shown in Table 1.

[Experimental Example 20]
A steel cord having a twisted structure of 1 × 5 was produced by using five strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.30 mm and the repeating pitch P between the bent portion and the non-bent portion was 14 mm for all five strands. A strand was used. The evaluation results are shown in Table 1.
[Experimental Example 21]
A steel cord having a twisted structure of 1 × 5 was produced by using five strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.25 mm and the repeating pitch P between the bent portion and the non-bent portion was 12 mm for all five strands. A strand was used. The evaluation results are shown in Table 1.

[Experimental Example 22]
A steel cord having a twisted structure of 1 × 5 was produced by using five strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.25 mm and the repeating pitch P between the bent portion and the non-bent portion was 14 mm for all five strands. A strand was used. The evaluation results are shown in Table 1.
[Experimental Example 23]
A steel cord having a twisted structure of 1 × 5 was produced by using five strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.30 mm and the repeating pitch P between the bent portion and the non-bent portion was 12 mm for all five strands. A strand was used. The evaluation results are shown in Table 1.

[Experimental Example 24]
A steel cord having a twisted structure of 1 × 5 was produced by using five strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.25 mm and the repeating pitch P between the bent portion and the non-bent portion was 10 mm for all five strands. A strand was used. The evaluation results are shown in Table 1.
[Experimental Example 25]
A steel cord having a twisted structure of 1 × 5 was produced by using five strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.24 mm and the repeating pitch P between the bent portion and the non-bent portion was 8 mm for all five strands. A strand was used. The evaluation results are shown in Table 1.
[Experimental Example 26]
A steel cord having a twisted structure of 1 × 5 was produced by using five strands having a strand diameter of 0.370 mm. At this time, the bent portion and the non-bent portion were formed so that the bending height h was 0.30 mm and the repeating pitch P between the bent portion and the non-bent portion was 8 mm for all five strands. A strand was used. The evaluation results are shown in Table 1.

The relationship between the porosity of Experimental Examples 17 to 26 and the impact absorption index shown in Table 1 is shown in FIG. 14, and the relationship between the central region area and the impact absorption index is shown in FIG. 15, respectively.

According to the results shown in FIG. 14, the values of the impact absorption index with respect to the porosity in each experimental example are distributed on the approximate curve, and the impact absorption index peaks when the porosity is about 42.0%. Was confirmed.

In this way, a correlation was found between the porosity and the impact absorption index, and it was confirmed that the impact resistance can be enhanced by selecting the porosity. Further, by setting the porosity to 33% or more and 55% or less, the impact absorption index became higher than 100%, and it was confirmed that the impact resistance was excellent.

Further, according to the results shown in FIG. 15, it was confirmed that the impact absorption index with respect to the central region area in each experimental example was also distributed on the approximate curve and the central region area ^{peaked at about 0.35 mm 2.} ..

As described above, since there is a correlation between the central region area and the impact absorption index, it was confirmed that the impact resistance can be improved by selecting the central region area. Furthermore, the evaluation results of the steel cord of the number of wires to be contained in a five Experiment 17 Experiment 26, the central region area With 0.24 mm ² or more 0.45 mm ² or less, the impact absorption index Was higher than 100%, and it was confirmed that the impact resistance was excellent.

In addition, through Experimental Examples 1 to 26, it was confirmed that there is no correlation between the initial elongation and the breaking load, which was conventionally thought to have a large effect on impact resistance, and the impact absorption index. ..

10, 30, 40, 91 Steel cord 11, 61, 72 Wire 12 Central gap 13 Wire gap 14 Outermost circle 15 Central area 51 Sample 52 Hammer 53 Rotation axis A Initial position B Maximum height position 62, 62A , 62B, 62C Bent part 63 Non-bent part P Repeated pitch between bent part and non-bent part h Difference in height of adjacent bent part 71 Preform 81 Tire 82 Tread part 83 Sidewall part 84 Bead part 85 Inner Liner 86 Carcus 87 Belt layer 88 Bead wire-
92 rubber

Claims (10)

It has a 1 × n structure in which n (n = 3) strands are twisted together.
In a cross section perpendicular to the longitudinal direction
When the area of the outermost circle is S1 and the area of the strand is S2, the porosity V represented by the following formula (A) is 37% or more and 60% or less.
V (%) = (S1-nS2) / S1 × 100 ... (A)
Wherein Ri der area of a region surrounded by a straight line connecting the centers of the wires adjacent to each other along the circumferential direction 0.07 mm ² or more 0.13 mm ² or less of the circumscribed circle,
steel cord n at least one of said strands of said strands of this is, that have repeated a bent portion along the longitudinal direction, and a non-bending portion. It has a 1 × n structure in which n (n = 4) strands are twisted together.
In a cross section perpendicular to the longitudinal direction
When the area of the outermost circle is S1 and the area of the strand is S2, the porosity V represented by the following formula (A) is 37% or more and 60% or less.
V (%) = (S1-nS2) / S1 × 100 ... (A)
The area of a region surrounded by a straight line connecting the centers of the wires adjacent to each other along the circumferential direction of the circumscribed circle 0.16 mm ² or more 0.32 mm ² Ri der less,
A steel cord in which at least one of the n strands has a bent portion and a non-bent portion repeatedly along the longitudinal direction. It has a 1 × 3 structure in which the three strands are twisted together.
When the Charpy impact value of a 1 × 3 structure steel cord having a porosity V of 35.8% is used as a reference value, the impact absorption index indicating the ratio of the Charpy impact value to the reference value is larger than 100%. The steel cord according to claim 1, which is 110% or less. It has a 1 × 4 structure in which the four strands are twisted together.
When the Charpy impact value of a 1 × 4 structure steel cord having a void ratio V of 36.4% is used as a reference value, the impact absorption index indicating the ratio of the Charpy impact value to the reference value is larger than 100%. The steel cord according to claim 2, which is 140% or less. The steel cord according to any one of claims 1 to 4 , wherein all the n wires repeatedly have a bent portion and a non-bent portion along the longitudinal direction. When the height from the plane to the bent portion on the side far from the plane when the strand is placed on a plane is defined as the bending height.
The steel cord according to any one of claims 1 to 5, wherein the bending height is 0.10 mm or more and 0.30 mm or less. Wherein a bent portion, the steel cord according to any one of claims 1 to 6 repeating pitch is 5.0mm or more 30.0mm or less between the non-bending portion. The steel cord according to any one of claims 1 to 7 , wherein the initial elongation when 49N is added is 0.06% or more and 0.35% or less. The steel cord according to any one of claims 1 to 8 , wherein the wire has a diameter of 0.22 mm or more and 0.42 mm or less. A tire comprising the steel cord according to any one of claims 1 to 9.

Images