Steel cord and tire

文档序号：976157 发布日期：2020-11-03 浏览：8次中文

阅读说明：本技术 钢帘线和轮胎 (Steel cord and tire ) 是由松冈映史齐藤和彦山下健一高村伸荣铃木益任藤泽浩二于 2019-01-22 设计创作，主要内容包括：该钢帘线具有1×4结构,其中,四条丝线被彼此捻合,其中,所述四条丝线中的至少一条丝线是包括沿着长度方向重复的弯曲部分和非弯曲部分的波浪线；垂直于所述长度方向的横截面具有扁平形状；并且如果在垂直于所述长度方向的多个横截面上绘制外接所述四条丝线的椭圆,则所述椭圆的短轴的斜率在中值的±30度内。(The steel cord has a 1 x 4 structure in which four filaments are twisted with each other, wherein at least one of the four filaments is a wavy line including a curved portion and a non-curved portion repeated in a length direction; a cross section perpendicular to the length direction has a flat shape; and if an ellipse circumscribing the four wires is drawn on a plurality of cross sections perpendicular to the length direction, the slope of the minor axis of the ellipse is within ± 30 degrees of the median.)

1. A steel cord having a 1 x 4 structure in which four plain wires are twisted together,

wherein at least one of the four plain lines is a wave-shaped plain line repeatedly having a curved portion and a non-curved portion in a length direction,

wherein the steel cord has a flat shape in a cross section perpendicular to the length direction, and

wherein, in a plurality of cross sections perpendicular to the length direction, in a case where an ellipse circumscribing the four plain lines is drawn, a slope of a short axis of the ellipse is within ± 30 degrees with respect to a median.

2. A steel cord according to claim 1, wherein when said wave shaped elementary line is placed on a plane, the height from said plane to said bent portion located at the far side of said plane is defined as the bending height, and

wherein the bending height is greater than or equal to 240% and less than or equal to 280% of the diameter of the plain wire of the wave-shaped plain wire.

3. A steel cord according to claim 1 or claim 2, wherein in a plurality of cross sections perpendicular to said length direction, in the case of drawing an ellipse circumscribing said four plain lines, an average of short axis length/long axis length as a ratio of a short axis length to a long axis length of said ellipse is greater than or equal to 0.76 and less than or equal to 0.82.

4. A steel cord according to any one of claims 1 to 3, wherein the plain wire diameter of said plain wire is greater than or equal to 0.25mm and less than or equal to 0.45 mm.

5. A steel cord according to any one of claim 1 to claim 4,

wherein, in a case where an ellipse circumscribing the four element lines is drawn in a cross section perpendicular to the length direction, a short axis direction of the ellipse is defined as a thickness direction,

wherein a maximum length in the thickness direction in a cross section perpendicular to the length direction is defined as a thickness, and

wherein the coefficient of variation of the thickness is less than or equal to 0.05.

6. A tire comprising a steel cord according to any one of claims 1 to 5.

7. Tyre according to claim 6, wherein the steel cords have a rubber penetration degree greater than or equal to 70%.

Technical Field

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

This application is based on and claims priority from japanese patent application 2018-052816, filed 3/20/2018, the entire contents of which are incorporated herein by reference.

Background

For example, patent document 1 proposes a pneumatic tire using a belt cord including a twisted line obtained by twisting four filaments together. The belt cord has an elliptical cross section. In the cross-section, a ratio of a length of a minor axis to a length of a major axis of the elliptical cross-section is within a predetermined range. The individual filaments are arranged in a predetermined arrangement.

[ Prior art documents ]

[ patent document ]

[ patent document 1] Japanese laid-open patent publication No. 2017-190032

Disclosure of Invention

According to one aspect of the present disclosure, the steel cord has a 1 x 4 structure in which four plain wires are twisted together,

wherein at least one of the four plain lines is a wave-shaped plain line repeatedly having a curved portion and a non-curved portion in a length direction,

wherein the steel cord has a flat shape in a cross section perpendicular to the length direction, and

wherein, in a plurality of cross sections perpendicular to the length direction, in the case of drawing an ellipse circumscribing four prime lines, the slope of the minor axis of the ellipse is within ± 30 degrees with respect to the median.

Drawings

Fig. 1 is an explanatory view of a steel cord having a 1 × 4 structure according to one aspect of the present disclosure;

fig. 2 is a sectional view in a plane perpendicular to the length direction of the steel cord of fig. 1;

FIG. 3 is an explanatory view of a wavy element line;

FIG. 4 is an explanatory view of a method of manufacturing a wavy element wire;

fig. 5 is an explanatory diagram of a relationship between a slope of a minor axis of an ellipse circumscribing a prime line in a cross section perpendicular to a length direction of a conventional flat steel cord and a thickness variation of the steel cord;

fig. 6 is an explanatory diagram of the maximum value and the minimum value of the thickness of the steel cord according to an aspect of the present disclosure;

FIG. 7 is an illustration of a flattening apparatus;

FIG. 8 is a cross-sectional view of a tire according to one aspect of the present disclosure; and

fig. 9 is a view schematically showing a belt layer.

Detailed Description

[ problem to be solved by the present disclosure ]

In the invention disclosed in patent document 1, by manufacturing a belt cord having an elliptical cross section and by setting the ratio between the length of the major axis and the length of the minor axis of the cross section within a predetermined range, the volume of the top rubber in the belt of the tire is reduced, and the rolling resistance is reduced.

However, in recent years, further enhancement of the performance of tires has been demanded. Therefore, for example, it is necessary to further reduce the weight of the tire to further reduce the rolling resistance and the like. Meanwhile, there is a need to reduce the frequency of tire replacement and enable a tire excellent in durability to be used for a long time. It is also desirable that the steel cord for a tire is a steel cord capable of forming a tire excellent in durability and light in weight.

Accordingly, the present disclosure has an object to provide a steel cord capable of forming a tire that is light in weight and excellent in durability.

[ Effect of the present disclosure ]

According to the present disclosure, a steel cord capable of forming a tire that is light in weight and excellent in durability can be provided.

[ description of embodiments of the present disclosure ]

First, aspects of the present disclosure will be described by lists. In the following description, the same reference numerals are used to designate the same or corresponding elements, and thus, the description of those elements will not be repeated.

(1) According to an aspect of the present disclosure, the steel cord has a 1 × 4 structure, wherein four plain wires are twisted together, wherein at least one of the four plain wires is a wave-shaped plain wire repeatedly having a curved portion and a non-curved portion along a length direction, wherein the steel cord has a flat shape in a cross section perpendicular to the length direction, and wherein, in a plurality of cross sections perpendicular to the length direction, in a case where an ellipse circumscribing the four plain wires is drawn, a slope of a short axis of the ellipse is within ± 30 degrees with respect to a median value.

The steel cords may for example be arranged in the belt of the tyre. The belt layer includes steel cords and rubber, and the steel cords are embedded in the rubber. The thickness of the belt layer may be selected to enable embedding the steel cords within the rubber. Therefore, by making the cross-sectional shape perpendicular to the longitudinal direction of the steel cord into a flat shape and suppressing the thickness of the steel cord, the thickness of the rubber necessary for embedding the steel cord can be suppressed, and the thickness of the belt layer can also be suppressed.

Further, according to the consideration of the inventors of the present invention, by making the slopes of the short axes of the ellipses, which are four prime lines outside in a plurality of cross sections perpendicular to the length direction, within ± 30 degrees with respect to the median value (these have not been conventionally considered), the variations of the thickness and the maximum thickness can be suppressed.

In this way, the steel cord according to one aspect of the present disclosure is thin, and the variation in thickness and maximum thickness is small. Therefore, the thickness of the belt layer manufactured by using the steel cord can be suppressed, and the weight of the belt layer can be reduced. As a result, the weight of the tire including the belt layer can also be reduced.

Further, by using a wave-shaped plain wire having a curved portion and a non-curved portion repeatedly in the length direction as at least one of the four plain wires included in the steel cord, the degree of penetration of rubber into the interior of the steel cord can be increased when the tire is formed using the steel cord. In this way, by increasing the degree of penetration of rubber into the interior of the steel cord when forming the tire, the area of contact of the element wires included in the steel cord with the rubber can be increased, and the adhesion between the element wires and the rubber can be increased. Therefore, as described above, in the case where the tire is mounted on and used on an automobile or the like, although moisture may permeate through the rubber and enter the tire, by increasing the area of the element wire in contact with the rubber, the contact and reaction of the surface of the element wire with moisture can be reduced. Therefore, high adhesion between the rubber and the element wire can be maintained, and the durability of the tire can be increased.

(2) When the wave-shaped element wire is placed on a plane, a height from the plane to a bent portion located at a far side from the plane is defined as a bent height, and the bent height is greater than or equal to 240% and less than or equal to 280% of a diameter of an element wire of the wave-shaped element wire.

(3) In a plurality of cross sections perpendicular to the length direction, in the case of drawing an ellipse circumscribing four plain lines, an average value of the short axis length/the long axis length as a ratio of the short axis length to the long axis length of the ellipse is greater than or equal to 0.76 and less than or equal to 0.82.

(4) The diameter of the plain wire may be greater than or equal to 0.25mm and less than or equal to 0.45 mm.

(5) In the case where an ellipse circumscribing four plain lines is drawn in one cross section perpendicular to the length direction, the short axis direction of the ellipse is defined as the thickness direction, the maximum length in the thickness direction in the cross section perpendicular to the length direction is defined as the thickness, and the coefficient of variation of the thickness is less than or equal to 0.05.

(6) The tire may include the steel cord according to any one of (1) to (5).

(7) The steel cords of the tire may have a rubber penetration degree of greater than or equal to 70%.

[ details of embodiments of the present disclosure ]

Specific examples of a steel cord and a tire according to one embodiment of the present disclosure (hereinafter referred to as "the present embodiment") are described below with reference to the drawings. It should be noted that the present invention is not limited to these examples, but is set forth in the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

< Steel cord >

Next, a steel cord according to the present embodiment will be described with reference to fig. 1 to 7.

The steel cord according to the present embodiment has a 1 × 4 structure in which four plain wires (also referred to as filaments) are helically twisted together in the length direction.

Here, fig. 1 shows a perspective view of an exemplary configuration of a steel cord 10 according to the present embodiment. Further, in fig. 2 is shown a cross-sectional view of the steel cord 10 shown in fig. 1 in a plane perpendicular to the length direction. It should be noted that the lengthwise direction of the steel cord 10 is the Y-axis direction shown in the drawing. The plane perpendicular to the length direction is a plane parallel to the XZ plane in the drawing.

The steel cord 10 shown in fig. 1 and 2 has a 1 × 4 structure in which four plain wires 11 are twisted together. The 1 × 4 structure refers to a structure in which four plain wires are twisted together to form a single layer (one layer). A monolayer refers to the structure: as shown in fig. 2, in a cross section perpendicular to the lengthwise direction of the steel cord 10, the element wires 11 are arranged in a single layer (one layer) in the circumferential direction of one circle.

The inventors of the present invention have prepared five types of steel cords (each having a structure of 1 × N) by changing the number of the element wires from two to six and selecting the element wire diameter to have the same breaking strength, and have evaluated and studied the cord diameter and quality of these steel cords. It should be noted that N in the 1 × N structure in this case corresponds to the number of element wires included in each steel cord. In each case, the N elemental lines are arranged such that: the element wires form a single layer in a circumferential direction of one circle in a cross section perpendicular to the length direction to have a twisted structure.

As a result, it has been confirmed that the cord diameter of the steel cord can be particularly reduced and the mass can be reduced by manufacturing the steel cord having the 1 × 4 structure (in which the number of element wires included is four) compared to the steel cord of other 1 × N structure. Therefore, the steel cord according to the present embodiment preferably has a 1 × 4 structure because the weight of the tire using the steel cord can be particularly reduced.

The diameter of the plain wire (i.e., the plain wire diameter) included in the steel cord according to the present embodiment is not particularly limited. However, the diameter of the plain wire is preferably greater than or equal to 0.25mm and less than or equal to 0.45mm, and more preferably greater than or equal to 0.35mm and less than or equal to 0.42 mm.

By making the plain wire diameter 0.25mm or more, the breaking load of the steel cord including the plain wire can be sufficiently increased.

In addition, by making the plain wire diameter 0.45mm or less, the quality of the steel cord can be suppressed. Therefore, this is preferable because the weight of the tire using the steel cord can be particularly reduced.

It should be noted that it is preferable that the plain wire diameter (to be described later) of the wavy plain wire also satisfies the above-mentioned preferable range of the plain wire diameter.

Preferably, in the steel cord according to the present embodiment, at least one of the four plain wires is a wave-shaped plain wire repeatedly having a bent portion and a non-bent portion in a length direction.

The cross section perpendicular to the length direction of the steel cord according to the present embodiment is a flat shape as described later. However, in the case where the cross section perpendicular to the longitudinal direction is a flat shape, the gap between the element wires may not be sufficiently ensured, and the degree of penetration of rubber into the inside of the steel cord may be reduced. Therefore, in the steel cord according to the present embodiment, at least one of the four plain wires included in the steel cord is a wave-shaped plain wire having a bent portion and a non-bent portion repeatedly in the length direction. This makes it possible to form a sufficient gap between the element wires and to increase the degree of penetration of rubber into the interior of the steel cord when forming a tire using the steel cord of the present embodiment. In this way, by increasing the degree of penetration of rubber into the interior of the steel cord when forming the tire, the area of contact of the element wires included in the steel cord with the rubber can be increased, and the adhesion between the element wires and the rubber can be increased.

As described above, although moisture may penetrate into the rubber and enter the tire in the case where the tire is mounted on and used on an automobile or the like, the contact and reaction of the surface of the element wire with moisture can be reduced by increasing the area of the element wire in contact with the rubber. Therefore, high adhesion between the rubber and the element wire inside the tire can be maintained, and the durability of the tire can be increased.

It should be noted that the upper limit of the number of the wavy element wires included in the steel cord according to the present embodiment is not particularly limited. For example, all the element wires included in the steel cord may be wavy element wires. However, when the number of wavy element wires is large, for example, the steel cord may be easily untwisted at the end portion in the length direction or the like of the steel cord, and it may be difficult to maintain the profile. Therefore, the number of the wavy element wires included in the steel cord according to the present embodiment is preferably less than or equal to three, and more preferably less than or equal to two.

Here, the wave-shaped element line will be described.

Fig. 3 shows an example of the configuration of the wavy element wire 30. The wave-shaped element wire 30 alternately and repeatedly has a bent portion 31 and a non-bent portion 32 in a length direction.

It should be noted that although fig. 3 shows an example in which the bent portion 31 is bent at an angle close to 90 degrees, the bent portion 31 is not limited to this configuration, but may be bent at an angle smaller than 90 degrees or an angle larger than 90 degrees, for example.

The specific wave shape of the wave-shaped element wire is not particularly limited. However, it is preferable that the bent height h of the wave-shaped element wire is greater than or equal to 240% and less than or equal to 280% of the diameter of the element wire of the wave-shaped element wire.

It should be noted that, as shown in fig. 3, when the wave-shaped element line 30 is placed on the plane S, the height from the plane S to the bent portion 31B (which is the far side from the plane S) is referred to as a bent height h. It should be noted that, in evaluating the bent height h, the wave-shaped element line 30 is arranged in such a manner as shown in fig. 3 that a plane passing through the bent portion 31 and the non-bent portion 32 of the wave-shaped element line 30 is perpendicular to the plane S.

Then, by making the bending height h equal to or more than 240% of the plain wire diameter of the wave-shaped plain wire, the wave-shaped plain wire has a sufficient bending height with respect to the plain wire diameter. That is, a sufficient gap can be formed between the wavy element wire and the other element wires. Therefore, this is preferable because the degree of penetration of the rubber can be increased.

Further, it is preferable that the bending height h is made less than or equal to 280% of the diameter of the element wire of the wave-shaped element wire, because the occurrence of untwisting of the steel cord at the end portion in the longitudinal direction of the steel cord or the like, deformation of the outer shape, and the like can be more reliably prevented.

Preferably, the bent height h of the wavy element wire is greater than or equal to 260% and less than or equal to 280% of the diameter of the element wire.

In the wavy element line, the pitch of the repeating curved portion and the non-curved portion is not particularly limited, but is preferably greater than or equal to 5.0mm and less than or equal to 30.0mm, and for example, more preferably greater than or equal to 5.0mm and less than or equal to 20.0 mm.

The pitch of the repeated bent portions and the non-bent portions refers to a distance between the bent portions having the same shape, and refers to a length of the steel cord in the length direction from the bent portion as a reference to the bent portion away from both the bent portions. Therefore, in the example shown in fig. 3, the pitch P of the repeated bent portions and the non-bent portions refers to, for example, the distance from the bent portion 31A to two bent portions 31C adjacent thereto.

It is preferable that the interval between the repeated bent portions and the non-bent portions is greater than or equal to 5.0mm because it makes it easy to form and precisely control the bent portions and the non-bent portions on the element wire. In addition, it is preferable that the pitch of the repeated bent portions and the non-bent portions is less than or equal to 30.0mm, because it is possible to manufacture the bent portions and the non-bent portions with a relatively simple apparatus and suppress the manufacturing cost.

For example, as shown in fig. 4, a wave-shaped element line may be formed by arranging a plurality of preforms 41 and passing an element line 42 as a wave-shaped element line through the plurality of preforms 41 in a direction indicated by a block arrow in the drawing. The shape of the curved portion, the length of the non-curved portion, and the like can be selected by changing the arrangement, size, and shape of the preform 41. For example, the preform 41 may be pin-shaped (cylindrical) or gear-shaped.

It is preferable that the steel cord according to the present embodiment has a flat shape in a cross section perpendicular to the length direction. Further, in the steel cord of the present embodiment, it is preferable that, in the case of drawing an ellipse circumscribing four plain lines, the slope of the minor axis of the ellipse is within ± 30 degrees from the median in a plurality of cross sections perpendicular to the length direction.

The shape of a cross section perpendicular to the length direction of the steel cord according to the present embodiment will be described with reference to fig. 2.

As shown in fig. 2, the steel cord 10 according to the present embodiment may have a flat shape in which the thickness is smaller than the width in a cross section perpendicular to the length direction. It should be noted that, in fig. 2, the X-axis direction is the width direction, and the Z-axis direction is the thickness direction.

Specifically, the steel cord 10 according to the present embodiment has a shape in which four plain wires 11 are twisted together, and in a cross section perpendicular to the length direction thereof, the steel cord 10 has a flat shapeThe shape in which a circle circumscribing the four element lines 11 is an ellipse C. It should be noted that the length L of the minor axis AS of the ellipse C_ASLength L of greater than major axis AL_ALShort.

The steel cords may for example be arranged in the belt of the tyre. As will be described below with respect to a tire, the belt layer includes steel cords and rubber, and the steel cords are embedded within the rubber. The thickness of the belt layer may be selected to enable embedding of the steel cords within the rubber. Therefore, by making the cross-sectional shape perpendicular to the longitudinal direction of the steel cord a flat shape and suppressing the thickness of the steel cord, the thickness of the rubber necessary for embedding the steel cord can be suppressed, and the thickness of the belt layer can also be suppressed. Therefore, by making the steel cord have a cross-sectional shape of a flat shape, in the case where the steel cord is used for the belt layer, the amount of rubber contained in the belt layer can be suppressed, and the weight of the belt layer can be reduced. Further, the weight of the tire including the belt layer can be reduced.

However, according to the consideration of the inventors of the present invention, in the conventional steel cord having a flat shape in a cross section perpendicular to the longitudinal direction (may be simply referred to as "conventional flat steel cord"), the thickness variation is very large. For this reason, in the case of manufacturing a tire using a conventional flat steel cord, it is necessary to set the thickness of the belt layer according to the portion where the thickness of the steel cord is the largest, and it is impossible to make the belt layer sufficiently thin. Therefore, in the case of manufacturing a tire using a conventional flat steel cord, the weight of the belt or the tire including the belt cannot be sufficiently reduced.

The inventors of the present invention have made further consideration of the cause. As a result, it was confirmed that, in a plurality of cross sections perpendicular to the length direction of the conventional flat steel cord, in the case of drawing an ellipse circumscribing a circle (which is an ellipse circumscribing the prime line), the slope of the minor axis of the ellipse significantly varies depending on the position in the length direction. Specifically, in the case where the slope of the minor axis of the ellipse is measured at a plurality of positions in the longitudinal direction of the steel cord, it can be confirmed that the slope of the minor axis is, for example, distributed within a range of about ± 90 degrees of the median. That is, in the conventional flat steel cord, it can be confirmed that the slope of the minor axis of the ellipse circumscribing the element line varies by about 180 degrees at the maximum in the cross section perpendicular to the length direction. Therefore, it has been found that the thickness of the steel cord varies due to a large variation in the slope of the minor axis of the ellipse circumscribing the base line in the cross section perpendicular to the length direction.

A relationship between a slope of a short axis of an ellipse circumscribing a prime line in a cross section perpendicular to a length direction and a thickness variation of a steel cord in a conventional flat steel cord will be described with reference to fig. 5.

Fig. 5 is a view obtained by superimposing an ellipse C51 and an ellipse C52 (the slopes of their minor axes are different) that circumscribe the element lines in a cross section perpendicular to the length direction of the conventional flat steel cord 50. Ellipse C51 represents the ellipse as follows: in a cross section perpendicular to the length direction, the prime line is circumscribed at a position where the slope of the minor axis AS51 is the reference slope (i.e., the median) of the minor axis. Therefore, the slope of the minor axis AS51 of the ellipse C51 is set to 0 degrees.

Further, the ellipse C52 represents the ellipse: in a cross section perpendicular to the length direction, the element line is circumscribed at a position where the minor axis AS52 is inclined by 90 degrees from the reference slope of the minor axis (i.e., the angle d5 formed between the minor axis AS51 and the minor axis AS52 is 90 degrees).

Therefore, fig. 5 is a view obtained by overlapping ellipses circumscribing the element wires on a cross section perpendicular to the longitudinal direction at two selected positions in the longitudinal direction of the conventional flattened steel wire rope 50. In fig. 5, the vertical direction corresponds to the thickness direction of the steel cord. It should be noted that in fig. 5, illustration of the element lines included in the steel cord is omitted.

AS shown in fig. 5, in the conventional flat steel cord 50, the thickness T51 of the steel cord is equal to the length of the minor axis AS51 of the ellipse C51 at a position where the slope of the minor axis of the ellipse circumscribing the prime line is a median of 0 degrees in a cross section perpendicular to the length direction.

However, at a position where the minor axis of the ellipse that circumscribes the prime line in the cross section perpendicular to the length direction of the ellipse C52 is inclined with respect to the median (0 degrees), the major axis of the ellipse C52 is located in the thickness direction of the steel cord. Therefore, the thickness T52 of the conventional flat steel cord 50 at this position is the same as the length of the major axis of the ellipse C52.

Therefore, in the conventional flat steel cord 50, the slope of the minor axis of the ellipse circumscribing the prime line in the cross section perpendicular to the length direction is distributed within a range of about ± 90 degrees of the median, and the variation is very large. Therefore, in the conventional flat steel cord 50, the thickness varies greatly depending on the position in the length direction, for example, from the thickness T51 corresponding to the length of the minor axis AS51 of the ellipse C51 to the thickness T52 corresponding to the length of the major axis of the ellipse C52 in fig. 5.

In contrast, in the steel cord according to the present embodiment, in a plurality of cross sections perpendicular to the length direction, in the case of drawing an ellipse (which is an ellipse circumscribing a circle) circumscribing four plain lines, the slope of the minor axis of the ellipse is within ± 30 degrees of the median. Here, the maximum and minimum values of the thickness of the steel cord according to the present embodiment are described with reference to fig. 6.

Fig. 6 is a view obtained by superimposing an ellipse C61 and an ellipse C62 (whose minor axes are different in slope) circumscribing four plain lines in a cross section perpendicular to the length direction of the steel cord 60 according to the present embodiment. The ellipse C61 represents an ellipse circumscribing a prime line in a cross section perpendicular to the length direction at a position where the slope of the minor axis AS61 is the reference slope (i.e., median) of the minor axis. Therefore, the slope of the minor axis AS61 of the ellipse C61 is set to 0 degrees.

The ellipse C62 represents an ellipse circumscribing four plain lines in a cross section perpendicular to the length direction at a position where the minor axis AS62 is inclined from the reference slope of the minor axis by 30 degrees (i.e., the angle d6 formed between the minor axis AS61 and the minor axis AS62 of the ellipse C61 is 30 degrees at maximum).

Therefore, fig. 6 is a view obtained by superimposing ellipses selected at two positions in the length direction of the steel cord 60 according to the present embodiment circumscribing four plain lines in a cross section perpendicular to the length direction. In fig. 6, the vertical direction corresponds to the thickness direction of the steel cord. It should be noted that in fig. 6, illustration of the element lines included in the steel cord is omitted.

In the steel cord 60 according to the present embodiment shown in fig. 6, the thickness T61 of the steel cord is the same AS the minor axis AS61 at the position of the ellipse C61, and thus is a minimum value. Further, in the case where the minor axis of the ellipse circumscribing the four plain lines of the ellipse C62 is inclined by 30 degrees at the maximum, the thickness of the steel cord 60 takes the maximum value. Even in this case, the thickness T62 of the steel cord is shorter than the length of the major axis of the ellipse C62. Therefore, there is no significant change in thickness, and the maximum thickness is also suppressed, as compared with the case of the conventional flat steel cord 50 shown in fig. 5.

Therefore, in the steel cord according to the present embodiment, the slopes of the minor axes of the ellipses next to four plain lines in a plurality of cross sections perpendicular to the length direction are within ± 30 degrees of the median, so that the slope variation of the minor axes of the ellipses is suppressed. Therefore, in the steel cord according to the present embodiment, variations in thickness and maximum thickness can be sufficiently suppressed.

Therefore, in the case where the steel cord according to the present embodiment is used as a member of a tire to form a belt layer in accordance with the maximum value of the thickness of the steel cord according to the present embodiment, the thickness of the belt layer can be suppressed and the belt layer can be made thin and lightweight as compared with the case of using a conventional flat steel cord. As a result, the weight of the tire including the belt layer can also be reduced.

It should be noted that the slopes of the minor axes of the ellipses of the four outer steel filaments in a plurality of cross sections perpendicular to the length direction of the steel cord are within ± 30 degrees of the median, which means that the distribution of the slopes of the minor axes with respect to the median is in the range of-30 degrees or more to +30 degrees or less, and in total is within 60 degrees. Hereinafter, as described above, in the case where the maximum variation range of the median orientation of the slope with respect to the short axis positive or negative is within ± 30 degrees of the median, 30 degrees may be referred to as "the maximum variation range of the median with respect to the short axis".

In the steel cord according to the present embodiment, in a plurality of cross sections perpendicular to the length direction, in the case of drawing an ellipse circumscribing four plain lines, the slope of the minor axis of the ellipse is preferably within ± 20 degrees from the median value, more preferably within ± 15 degrees from the median value. That is, the maximum variation range of the median of the slopes with respect to the short axis is more preferably less than or equal to 20 degrees, and still more preferably less than or equal to 15 degrees. This is because, in the case where an ellipse circumscribing four plain lines is drawn in a plurality of cross sections perpendicular to the longitudinal direction, by making the slope of the minor axis of the ellipse within ± 20 degrees from the median value, further within ± 15 degrees from the median value, it is possible to suppress particularly the variation in the thickness and the maximum thickness of the steel cord. As a result, the weight of the belt and the tire including the belt can also be particularly reduced.

In the case of drawing an ellipse circumscribing four plain lines in a plurality of cross sections perpendicular to the lengthwise direction of the steel cord according to the present embodiment, a method of measuring the maximum variation range of the median value of the slopes from the short axis is not particularly limited.

For example, a steel cord is embedded in a transparent resin, and a sample is cut at a plurality of desired positions in the length direction of the steel cord so that a plane (cross section) perpendicular to the length direction of the steel cord is exposed. Subsequently, using a projector, determination can be made by drawing an ellipse circumscribing four prime lines included in the respective cross sections and by measuring the slope of the short axis.

Further, for example, Computed Tomography (CT) is used to measure cross-sectional images perpendicular to the length direction of the steel cord at a plurality of positions. Then, the determination can be made by drawing an ellipse circumscribing four prime lines included in each cross-sectional image and by measuring the slope of the short axis.

In the measurement by either method, it is preferable, for example, to plot an ellipse circumscribing the prime line in the cross section at ten or more measurement points with respect to a range of 5cm or more to 25cm or less in the length direction of the steel cord, to measure the slope of the minor axis of the ellipse and evaluate the change in the slope of the minor axis. It should be noted that the upper limit of the measurement point is not particularly limited, but is preferably 250 points or less, for example, from the viewpoint of productivity. Further, it is preferable that the measuring points are arranged at equal intervals in the length direction of the steel cord.

As described above, in the steel cord according to the present embodiment, in the case where an ellipse circumscribing four plain lines is drawn in a plurality of cross sections perpendicular to the length direction, the change in the slope of the short axis of the ellipse is suppressed. Therefore, in the steel cord according to the present embodiment, the thickness variation thereof can be suppressed.

The thickness variation of the steel cord can be represented by, for example, a variation coefficient, which is a value obtained by dividing the standard deviation by the average value. That is, the thickness variation of the steel cord may be expressed by a variation coefficient, which is a value obtained by measuring the thickness of the steel cord at a plurality of measurement points arranged in the length direction of the steel cord, and by dividing the standard deviation of the thicknesses at the plurality of measurement points by the average value of the thicknesses at the plurality of measurement points. For example, the coefficient of variation of the thickness is preferably less than or equal to 0.05, and more preferably less than or equal to 0.04.

The lower limit of the coefficient of variation in thickness is not particularly limited, but may be, for example, equal to or greater than 0.

In the case where the coefficient of variation in the thickness of the steel cord is less than or equal to 0.05, this means that the variation in the thickness of the steel cord can be suppressed particularly. Therefore, in the case where such a steel cord is used as a member of a tire to form a belt layer according to the maximum value of the thickness of the steel cord, the belt layer can be made particularly thin and lightweight. As a result, the weight of the tire including the belt layer can also be particularly reduced.

The coefficient of variation in the thickness of the steel cord in the present embodiment can be measured and calculated by the following procedure, for example.

First, the thickness is measured at 5 points or more and 15 points or less with respect to the range of 5cm or more to 25cm or less in the length direction of the steel cord according to the present embodiment, and the average value and the standard deviation of the measured values are calculated. Then, the coefficient of variation can be calculated by dividing the standard deviation by the average.

It should be noted that it is preferable that the measuring points are arranged at equal intervals in the length direction of the steel cord.

To measure the thickness of the steel cord, the measurement may be performed by embedding the steel cord in a transparent resin and cutting a cross section in a length direction of the steel cord, similar to the slope of the short axis. Further, the CT may be used to measure cross-sectional images perpendicular to the length direction of the steel cord at a plurality of positions to measure the thickness from the cross-sectional images.

It should be noted that, for measurement, the direction of the short axis direction of the ellipse followed by four plain lines in one desired cross section perpendicular to the length direction of the steel cord is first set as the thickness direction. Then, in other cross sections perpendicular to the length direction of the steel cord, the thickness of the steel cord at each position may be measured by measuring the maximum length in the set thickness direction.

With the steel cord according to the present embodiment, in a plurality of cross sections perpendicular to the length direction, in the case of drawing an ellipse circumscribing four plain lines, the minor axis length L of the ellipse_ASLength L of the major axis_ALThe average value of the ratio of (c) is not particularly limited (see fig. 2), and may be set as needed. It should be noted that the major axis length L_ALIs the length of the major axis AL of the ellipse C (which is the circumscribed circle of the ellipse circumscribing the four element lines 11), and the length L of the minor axis_ASRefers to the length of the minor axis AS of the ellipse C. It should be noted that, in the steel cord according to the present embodiment, the minor axis length/major axis length (L)_AS/L_AL) Is preferably greater than or equal to 0.76 and less than or equal to 0.82, and more preferably greater than or equal to 0.78 and less than or equal to 0.80.

This is because, in a plurality of cross sections perpendicular to the longitudinal direction, in the case of drawing an ellipse circumscribing four plain lines, for example, untwisting can be more reliably suppressed at the end portion or the like of the steel cord according to the present embodiment by making the average value of the minor axis length/major axis length of the ellipse greater than or equal to 0.76.

Further, in a plurality of cross sections perpendicular to the longitudinal direction, in the case of drawing an ellipse circumscribing four plain lines, by making the average value of the minor axis length/major axis length of the ellipse less than or equal to 0.82, the thickness of the steel cord can be suppressed particularly, and also the thickness of the belt layer using the steel cord can be suppressed sufficiently. Therefore, the weight of the tire including the belt layer can be particularly reduced, which is preferable.

In the case of drawing an ellipse circumscribing four plain lines in a plurality of cross sections perpendicular to the length direction, the average value of the minor axis length/major axis length of the steel cord according to the present embodiment (which is the minor axis length L of the ellipse) is measured and calculated_ASLength L of the major axis_ALThe ratio of (b) is not particularly limited.

For example, a steel cord is embedded in a transparent resin, and a sample is cut at a plurality of desired positions in the length direction of the steel cord so that a plane (cross section) perpendicular to the length direction of the steel cord is exposed. Then, using a projector, by drawing an ellipse circumscribing four prime lines included in each cross section and by measuring the lengths of the short axis and the long axis, the short axis length/long axis length at each cross section can be calculated.

Further, for example, CT is used to measure cross-sectional images perpendicular to the length direction of the steel cord at a plurality of positions. Then, by drawing an ellipse circumscribing four prime lines included in the cross-sectional image and by measuring the lengths of the short axis and the long axis, the short axis length/long axis length at each cross-section can be calculated.

In the measurement by either method, in the case of measuring the short axis length/long axis length in a plurality of cross sections, it is preferable, for example, to draw an ellipse circumscribing a prime line in the cross section at ten or more measurement points with respect to a range of 5cm or more to 25cm or less in the length direction of the steel cord, to measure and calculate the short axis length/long axis length of the ellipse.

It should be noted that the upper limit of the measurement point is not particularly limited, but is preferably 250 points or less, for example, from the viewpoint of productivity. Further, it is preferable that the measuring points are arranged at equal intervals in the length direction of the steel cord.

Then, the average of the minor axis length/major axis length of the ellipse in each cross section can be calculated.

According to the steel cord of the present embodiment described above, a tire having light weight and excellent durability can be formed by using the steel cord as a member of the tire.

[ method for producing Steel cord ]

Although the manufacturing method of the steel cord according to the present embodiment is not particularly limited, the manufacturing method of the steel cord according to the present embodiment may include, for example, the steps of:

twisting the four plain threads; and

and a flattening step of flattening the steel cord obtained by the twisting step in the thickness direction.

Since the twisting step can be performed by twisting the plain threads together with a twisting machine according to a conventional method, a detailed description thereof will not be given here. It should be noted that at least one of the four plain threads supplied to the twisting step is preferably a wavy plain thread.

In the flattening step, for example, a flattening device 70 shown in fig. 7 may be used to flatten the steel cord in its thickness direction.

The flattening device 70 may include a base 71 and a first flattening roller part 73 disposed on the base 71. The first smoothing roller part 73 may be constituted by a single roller, but as shown in fig. 7, may include a plurality of first smoothing rollers 73A to 73D. It should be noted that in the case where a plurality of first smoothing rolls are arranged, the number of rolls is not particularly limited. The rotation axes 731A to 731D of the first leveling rollers 73A to 73D included in the first leveling roller section 73 extend perpendicularly to the base section 71 (i.e., in the Z-axis direction shown in the earlier drawings).

Further, the flattening device 70 may include a base 72 and a second flattening roller portion 74 disposed on the base 72. The second smoothing roller part 74 may be composed of a single roller, but as shown in fig. 7, may include a plurality of second smoothing rollers 74A to 74C. It should be noted that in the case where a plurality of second smoothing rolls are arranged, the number of rolls is not particularly limited. The rotation axes 741A to 741C of the plurality of second smoothing rollers 74A to 74C included in the second smoothing roller portion 74 may be configured to extend perpendicularly to the base 72 (i.e., in the Z-axis direction shown in the drawing).

Then, between the first flattening roller section 73 and the second flattening roller section 74, a steel cord 75 made by twisting together four plain wires prepared in the twisting step is supplied, for example, in the X-axis direction in the drawing. Flattening can be performed by pressing the supplied steel cord 75 in the Y-axis direction shown in the drawing by the first flattening roller section 73 and the second flattening roller section 74. Specifically, the first smoothing roller part 73 may press the steel cord 75 in the block arrow 732, and the second smoothing roller part 74 may press the steel cord 75 in the block arrow 742, so that the steel cord 75 may be pressed.

According to the consideration of the inventors of the present invention, since the steel cord is obtained by spirally twisting a plurality of element wires in the longitudinal direction, the steel cord is easily rotated in the circumferential direction thereof with the central axis as the rotation axis when pressed in the thickness direction. It should be noted that the central axis herein refers to an axis passing through the center of a plane perpendicular to the lengthwise direction of the steel cord and parallel to the lengthwise direction before leveling.

In the conventional flat steel cord manufacturing method in which such rotation of the steel cord is never considered, the steel cord will be significantly rotated in the circumferential direction with the central axis as the rotation axis when the flattening process is performed. Therefore, as described above, the slope of the minor axis of the ellipse circumscribing the prime line in the cross section perpendicular to the length direction significantly varies depending on the length direction position.

Therefore, in manufacturing the steel cord according to the present embodiment, in the flattening step, when the steel cord is flattened by the flattening device, it is preferable to suppress the degree of rotation of the steel cord around the central axis as the rotation axis. The rotation of the steel cord around the central axis in the flattening step is preferably within ± 30 degrees from the median value, more preferably within ± 20 degrees from the median value, further preferably within ± 15 degrees from the median value.

The method of suppressing such rotation is not particularly limited, and may be selected as needed.

For example, on the surfaces of the first flattening roller section 73 and the second flattening roller section 74 of the flattening device 70 to be in contact with the steel cord 75, grooves corresponding to the outer shape of the steel cord 75 may be formed so that the steel cord 75 is configured not to rotate. For example, by forming grooves having different shapes on the surface of the first flattening roller section 73 to be in contact with the steel cord 75 and on the surface of the second flattening roller section 74 to be in contact with the steel cord 75, it is possible to suppress the rotation of the steel cord in particular.

< tire >

Next, a tire according to the present embodiment will be described with reference to fig. 8 and 9.

As described above, the tire according to the present embodiment may include a steel cord.

Fig. 8 shows a cross-sectional view taken along a plane perpendicular to the circumferential direction of the tire 81 according to the present embodiment. In fig. 8, only the left part of CL (center line) is shown. However, also on the right side of CL, a similar structure is included successively, where CL is the symmetry axis.

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 that contacts the road surface. Bead portion 84 is disposed toward the interior of tire 81 relative to tread portion 82. The bead portion 84 is a portion that contacts the rim of the wheel. Sidewall portions 83 connect tread portion 82 and bead portion 84. When the tread portion 82 receives an impact through a road surface, the sidewall portion 83 is elastically deformed to absorb the impact.

Tire 81 includes an innerliner 85; a carcass 86; a belt layer 87; and a bead wire 88.

The inner liner 85 is formed of rubber, and seals a gap between the tire 81 and the wheel.

Carcass 86 forms the carcass of tire 81. The carcass 86 is formed of organic fibers (such as polyester, nylon, or rayon) and rubber.

A bead wire 88 is disposed in the bead portion 84. The bead wire 88 receives the tension acting on the carcass.

The belt 87 tightens the carcass 86 to increase the stiffness of the tread 82. In the example shown in fig. 8, the tire 81 includes two belt layers 87.

Fig. 9 is a diagram schematically showing two belt layers 87. Fig. 9 is a sectional view of the belt 87 in the longitudinal direction (for example, in a plane perpendicular to the circumferential direction of the tire 81).

As shown in fig. 9, two belt layers 87 are superposed in the radial direction of the tire 81. Each belt 87 comprises a plurality of steel cords 91 and rubber 92. A plurality of steel cords 91 are arranged side by side in parallel. The described steel cord may be used as the steel cord 91.

It should be noted that the steel cord as described above has a flat shape in a cross section perpendicular to the longitudinal direction, and it is preferable that the thickness direction of the steel cord is arranged to match the thickness direction of the belt layer. When an ellipse circumscribing four plain lines is drawn in a cross section perpendicular to the longitudinal direction of the steel cord, the thickness direction of the steel cord may be, for example, the short axis direction.

The rubber 92 also covers the steel cords 91, and the outer periphery of each steel cord 91 is completely surrounded by the rubber 92. The steel cord 91 is embedded in the rubber 92.

The steel cord as described above has a flat shape in a cross section perpendicular to the length direction, and variations in thickness and maximum thickness are suppressed. Therefore, even when the first rubber thickness t1 (which is the thickness of the rubber 92 disposed on the lower portion of the steel cord 91 in the belt 87) and the second rubber thickness t2 (which is the thickness of the rubber 92 disposed on the upper portion of the steel cord 91) are thinned, the exposure of the steel cord 91 can be suppressed. Therefore, the overall thickness of the belt 87 can be reduced.

Therefore, according to the tire of the present embodiment, the overall thickness of the belt 87 including the above-described steel cord 91 can be suppressed, and the weight of the belt 87 can be reduced. Therefore, the weight of the tire of the present embodiment including the belt layer can also be reduced.

Further, as described above, in the above-described steel cord, the degree of penetration of rubber into the steel cord is high when the tire is formed using the steel cord. Therefore, the area of the rubber in contact with the element wires included in the steel cord increases, and the adhesiveness between the element wires and the rubber increases. Then, in the case where the tire is mounted on and used on an automobile or the like, moisture may penetrate the rubber and enter the tire. As described above, in the tire according to the present embodiment, since the area of the element wire in contact with the rubber is large, the contact and reaction of the element wire surface with moisture can be reduced. Therefore, high adhesion between the rubber and the element wire inside the tire can be maintained, and a tire excellent in durability can be manufactured.

For the steel cord included in the tire of the present embodiment, the degree of penetration of the rubber is preferably high, for example, preferably 70% or more, more preferably 80% or more. It should be noted that since the degree of rubber penetration is preferably high, the upper limit value is not particularly limited, and may be, for example, less than or equal to 100%. The method of evaluating the degree of rubber penetration will be described later with respect to the experimental examples.

In the case where the degree of rubber penetration of the steel cord included in the tire according to the present embodiment is 70% or more, this is preferable because the rubber sufficiently penetrates into the inside of the steel cord and particularly increases the durability of the tire.

The degree of rubber penetration of the steel cord included in the tire according to the present embodiment may be selected depending on the number of wave-shaped element lines, the bending height h, and the like.

According to the tire of the present embodiment described above, the tire can be light in weight and excellent in durability. Further, since the weight reduction is excellent, the rolling resistance, which is the force generated when the tire rotates while being pressed against the drum, can be suppressed. It is also possible to increase the cornering power, which represents the increasing slope of the cornering force with respect to the sideslip angle of the tire. That is, the running stability of the automobile with the tire mounted thereon can be improved.

Although the embodiments have been described in detail above, they are not limited to the specific embodiments. Various modifications and changes may be made within the scope set forth in the claims.

Examples of the invention

Specific examples will be explained below. However, the present invention is not limited to these examples.

(evaluation method)

First, a method of evaluating the steel cord prepared in the following experimental example will be described.

(1) Evaluation of Steel cord

(1-1) coefficient of variation in thickness

For the steel cord prepared for each experimental example, the thickness of the steel cord was measured at five points in the length direction, and the average value thereof was defined as the thickness of the steel cord.

Specifically, first, for a range of 15cm in the length direction of the steel cord prepared for each experimental example, the thickness was measured at five measurement points arranged at equal intervals in the length direction.

To measure the thickness, a cross-sectional image was taken at the above measurement point using CT (model: inspeXio SMX-225CT manufactured by Shimadzu corporation). Then, the short axis direction of the ellipse circumscribing four plain lines in a selected cross section is set as the thickness direction. Subsequently, the maximum length of the steel cord in the set thickness direction at each cross section was measured. Thereby, the thickness of the steel cord in each cross section was measured.

The thickness at the five measurement points was then used to calculate the coefficient of variation of the thickness. The coefficient of variation is a value obtained by dividing the standard deviation calculated using the measurement values of the thicknesses at the five measurement points by the average value.

(1-2) maximum variation range from the median of the slopes of the minor axes of the ellipses externally following four plain lines in a plurality of cross sections perpendicular to the length direction to the average of the minor axis length/major axis length

First, for the steel cord prepared for each experimental example, the cross-sectional shape in the cross section perpendicular to the length direction was measured using CT. Specifically, the cross-sectional image was taken at measurement points every 0.5mm interval over a range of 110mm in the lengthwise direction of the steel cord.

Then, for each of the obtained cross sections, an ellipse circumscribing four prime lines is drawn, and the slope of the minor axis of the ellipse is calculated. Then, the maximum variation range is calculated from the median of the slopes of the short axes.

Further, when the maximum variation range is calculated from the median of the slopes of the short axes, the cross-sectional images measured by using the CT are used to calculate the short axis length/long axis length of the ellipse followed by four plain lines in each cross-section. Specifically, the minor axis length and the major axis length of an ellipse circumscribing four pixel lines drawn in each cross-sectional image measured by using CT are calculated. Then, an average of the short axis length/long axis length calculated for each cross-sectional image is calculated.

(2) Evaluation of tires

(2-1) degree of rubber penetration

The steel cord was taken out of the tire prepared for each experimental example using a cutter.

Then, for each of the taken-out steel cords, one wavy element wire was removed. The percentage of the length of the portion covered with rubber was calculated as the degree of rubber penetration over an observation length of 100mm along the center line in the width direction of the area exposed by removing the single wave-shaped element line. It should be noted that, for experimental example 17, the degree of penetration of rubber was similarly evaluated, except that a single element line selected as needed was removed.

The higher the value of the degree of rubber penetration, the better the penetration of the rubber.

(2-2) Rolling resistance

For the tires prepared for each experimental example, the rolling resistance was measured using a rolling resistance tester according to the ISO28580 standard under the following measurement conditions.

The rim used: 5.5J

Internal pressure: 525kPa

Loading: 15.74kN

Speed: 80km/h

Then, in the case where the rolling resistance of the tire according to experimental example 14 was 100, the rolling resistance of each tire prepared for the other experimental examples was represented by the index. The smaller the index, the better the rolling resistance.

(2-3) durability of tire

The tire prepared for each experimental example was incorporated into a standard rim (size: 5.5J), the tire was inflated and the internal pressure was set to 525 kPa. The tire was attached to a drum type running tester and a total load of 15.74kN was applied to the tire. The tire was run at 80km/h on a drum with a radius of 1.7 m. The distance traveled until tire damage was found was measured. It should be noted that the test is terminated if there is no damage while running 30000 km. The above test results are expressed with an index of 100 for a 30000km ride. The larger the index, the better the durability of the tire.

(2-4) turning power

In order to make the belt surface of the flatband machine to which the sandpaper was attached as a road surface, each pneumatic tire was pressed at a speed of 60km/h, a camber angle of 0 degree, and a load of 5kN, and a slope when a slip angle was changed from 0 degree to 1 degree was measured as a cornering power. It should be noted that the camber angle refers to an angle formed between a vertical plane to the belt surface of the flat belt machine and the radial direction of the tire, and may be referred to as CA (camber angle). Further, the slip angle refers to an angle formed between the traveling direction and the direction in which the tire is directed, and may be referred to as SA (slip angle).

In the case where the cornering power performance of the tire according to experimental example 14 was 100, the cornering power performance of the tires prepared in the other experimental examples was represented by the index. It should be noted that the larger the index, the better the cornering power performance.

(2-5) Belt quality

The quality of the individual belt layers prepared in the manufacture of the tires for each experimental example was measured. In the case where the quality of the belt layer prepared when the tire was manufactured in experimental example 14 was 100, the quality of the belt layer prepared when the tire was manufactured in the other experimental examples was represented by the index. Therefore, as the index decreases, the weight of the belt decreases. It should be noted that the tires in the respective experimental examples including the belt evaluated for the respective experimental examples also showed similar trends.

The manufacturing conditions of the steel cord and the tire of each experimental example will be described below. Experimental examples 1 to 13 are examples, and experimental examples 14 to 17 are comparative examples.

[ Experimental example 1]

First, a steel cord was manufactured by the following procedure.

Four plain wires having a plain wire diameter of 0.415mm were twisted together to form a steel cord having a 1 × 4 structure as a twisted construction (twisting step). It should be noted that a wave-shaped plain wire on which a bent portion and a non-bent portion are formed is used as one of the four plain wires so that the ratio of the bent height h to the diameter of the plain wire is 260% and the pitch P of the repeated bent portion and the non-bent portion is 12 mm.

Since the 1 × 4 structure has been described with reference to fig. 1 and 2 and the bending height h and the repeated pitch P have been described with reference to fig. 3, the description thereof is omitted here.

The steel cord obtained by twisting four plain wires together is supplied to a flattening device 70 shown in fig. 7, and a flattening process is performed to make a cross section perpendicular to the length direction of the steel cord into a flat shape (flattening step). In performing the flattening process, grooves corresponding to the outer shape of the steel cord are formed on the surfaces of the first flattening roller section 73 and the second flattening roller section 74 of the flattening device 70 to be in contact with the steel cord so that the steel cord is configured not to rotate. Specifically, grooves having different shapes are formed on the surface of the first flattening roller section 73 to be in contact with the steel cord and the surface of the second flattening roller section 74 to be in contact with the steel cord. Then, the flattening process is performed while checking the position of the steel cord so that the rotation angle of the steel cord is within ± 20 degrees.

As described above, the steel cord of this experimental example was prepared, and the above-described evaluation was performed on the steel cord.

Next, a tire is prepared by using the prepared steel cord.

First, a rubber composition containing a rubber component and an additive is prepared. The rubber composition contains 100 parts by mass of natural rubber as a rubber component. The rubber composition contained 60 parts by mass of carbon black, 6 parts by mass of sulfur, 1 part by mass of zinc oxide as a vulcanization accelerator, 10 parts by mass of zinc oxide, and 1 part by mass of cobalt stearate as an organic acid cobalt, with respect to 100 parts by mass of the rubber component as an additive.

The steel cord and the rubber composition described above were used to manufacture a pneumatic tire having the structure shown in fig. 8 and 9 and having a size of 225/40R 18.

It should be noted that, in the preparation of the tire, at a temperature of 160 ℃ at 25kgf/cm²Under a pressure of 58 and under an ECU × time.

The ECU (equivalent curing unit) described above can be calculated by the following formula (1).

ECU＝exp((-E/R)×(1/T-1/T0))…(1)

Here, in formula (1), E is activation energy, R is a general gas constant, T0 is a reference temperature, and T is a vulcanization temperature, and E ═ 20kcal/mol, R ═ 1.987 × 0.001kcal/mol · deg, and T0 ═ 141.7 ℃.

Further, the time of ECU × time refers to the vulcanization time in units of minutes.

The obtained tires were evaluated as described above. The evaluation results of the steel cord and the tire are shown in table 1.

[ Experimental examples 2 and 3]

A steel cord was prepared and evaluated similarly to experimental example 1, except that, when the flattening treatment of the steel cord was performed, it was performed in such a manner that the rotation angle of the steel cord was within ± 15 degrees of the median value in experimental example 2 and within ± 30 degrees of the median value in experimental example 2.