Monofilament, steel cord, tire

Abstract

A monofilament having a coating film, wherein the coating film contains copper, zinc, and cobalt, and when the total content ratio of copper, zinc, and cobalt in the coating film is set to 100% by mass, the content ratio of cobalt in the coating film is 0.5% by mass or more and 8% by mass or less. In a cross-section of the monofilament in the long dimension direction including the central axis of the monofilament, when three 1-μm square observation regions including the outer surface of the coating film are set along the central axis such that the distance between the observation regions is 10 mm, the average value of the area ratio occupied by cobalt in the observation regions is 1% or more and 50% or less.

Description

Technical Field

[0001] The present disclosure relates to filaments, steel cord, and tires.

[0002] This application claims priority based on Japanese Application No. 2020-068581 filed on April 6, 2020, and incorporates the entire disclosure of the Japanese application. Background Art

[0003] For example, Patent Document 1 proposes a steel cord for rubber reinforcement, which is characterized by being composed of at least one brass-plated steel wire and containing 0.001 to 0.1 ppm of cobalt on the outermost surface within a depth of 4 nm of the brass-plated steel wire.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2016-087687 Summary of the Invention

[0007] The filament of the present disclosure is a filament having a coating film, wherein the coating film contains copper, zinc, and cobalt, and when the total content ratio of copper, zinc, and cobalt in the coating film is set to 100% by mass, the content ratio of cobalt in the coating film is 0.5% by mass or more and 8% by mass or less. In a cross-section of the filament in the longitudinal dimension direction including the central axis of the filament, when three observation regions of 1 μm square including the outer surface of the coating film are set along the central axis such that the distance between the observation regions is 10 mm, the average value of the area ratio occupied by cobalt in the observation regions is 1% or more and 50% or less. Brief Description of the Drawings

[0008] Figure 1 It is an explanatory view of a filament according to one aspect of the present disclosure.

[0009] Figure 2 It is Figure 1 an enlarged view of region A of

[0010] Figure 3A an explanatory view of an observation region.

[0011] Figure 3B It is an explanatory view of a method for obtaining the thickness of a region where zinc oxide is distributed.

[0012] Figure 3C It is an explanatory view of a method for obtaining the ratio of the copper content in the outer surface region to the copper content in the central side region in the coating film.

[0013] Figure 4It is an explanatory diagram of a monofilament base material.

[0014] Figure 5 It is an explanatory diagram of a plating apparatus conventionally used when forming a Co layer on a monofilament base material.

[0015] Figure 6 It is an explanatory diagram of a structural example of a plating apparatus that can preferably be used when forming a Co layer on a monofilament base material.

[0016] Figure 7 It is an explanatory diagram of a steel cord according to an aspect of the present disclosure.

[0017] Figure 8 It is a cross-sectional view of a tire according to an aspect of the present disclosure.

[0018] Figure 9 It is an explanatory diagram of a belt layer.

[0019] Figure 10 It is an explanatory diagram of a method for measuring durability. Detailed Description

[0020] [Problems to be Solved by the Present Disclosure]

[0021] In recent years, further improvement in tire performance has been demanded. From the viewpoint of improving the durability of tires, when used for tires, a monofilament having excellent adhesion performance to the rubber of the tire is required.

[0022] Therefore, an object of the present disclosure is to provide a monofilament having excellent adhesion performance to rubber.

[0023] [Effects of the Present Disclosure]

[0024] According to the present disclosure, a monofilament having excellent adhesion performance to rubber can be provided.

[0025] [Description of Embodiments of the Present Disclosure]

[0026] First, embodiments of the present disclosure will be listed and described. In the following description, the same reference numerals are assigned to the same or corresponding elements, and the same description thereof will not be repeated.

[0027] (1) A monofilament according to one embodiment of the present disclosure may be a monofilament having a coating film. The coating film contains copper, zinc, and cobalt. When the total content ratio of copper, zinc, and cobalt in the coating film is set to 100% by mass, the content ratio of cobalt in the coating film is 0.5% by mass or more and 8% by mass or less. In a cross-section of the monofilament in the long dimension direction including the central axis of the monofilament, when three 1-μm square observation regions including the outer surface of the coating film are set along the central axis such that the distance between the observation regions is 10 mm, the average value of the area ratio of cobalt in the observation regions is 1% or more and 50% or less.

[0028] Hereinafter, copper may be referred to as Cu, zinc may be referred to as Zn, and cobalt may be referred to as Co.

[0029] When a tire is made by rubber-coating a monofilament having a coating film, Cu contained in the coating film reacts with S (sulfur) contained in the rubber side, and a bonding layer containing Cu2S is formed on the rubber side rather than the interface between the monofilament and the rubber. This bonding layer has the effect of improving the initial bonding performance between the monofilament and the rubber. Therefore, Cu contained in the coating film has the effect of improving the initial bonding performance with the rubber.

[0030] It should be noted that the initial bonding performance refers to the bonding performance between the monofilament and the rubber immediately after vulcanization during tire manufacturing.

[0031] It can be considered that Zn contained in the coating film controls the reaction for forming the above-mentioned bonding layer.

[0032] A tire is mounted on a vehicle or the like and is used while rotating at high speed in a grounded state, so the time it is placed in a high-temperature and high-humidity environment becomes longer. When the tire is placed in a high-temperature and high-humidity environment, sometimes moisture and oxygen permeate through the rubber of the tire and reach near the interface between the monofilament and the rubber, and the bonding performance between the monofilament and the rubber deteriorates.

[0033] Therefore, as the bonding performance of the monofilament, in addition to the initial bonding performance, it is also required that the bonding performance between the monofilament and the rubber in the tire after being placed in a high-temperature and high-humidity environment, that is, the moisture and heat resistance bonding performance, is also excellent.

[0034] It can be considered that when the tire is placed in a high-temperature and high-humidity environment, due to the intrusion of moisture and the like as described above, the composition of the aforementioned bonding layer is affected, and the bonding performance between the monofilament and the rubber deteriorates. However, in the monofilament according to one embodiment of the present disclosure, it can be considered that the change in the composition of the bonding layer is suppressed by containing Co in the coating film, and the moisture and heat resistance bonding performance can also be improved.

[0035] The content ratio of Co in Cu, Zn, and Co in the coating film (hereinafter, also referred to as "the content ratio of Co in the coating film") is preferably 0.5% by mass or more and 8% by mass or less. By making the content ratio of Co in the coating film 0.5% by mass or more, the coating film contains a sufficient amount of Co, and thus the effect of improving the above-mentioned moisture and heat resistance adhesion performance can be fully exerted. In addition, by making the content ratio of Co in the coating film 8% by mass or less, the content ratios of Cu and Zn in the coating film can be sufficiently increased, and the initial adhesion ability can also be improved.

[0036] Thus, by the coating film of a single filament of one aspect of the present disclosure containing Cu, Zn, and Co, when using this single filament to manufacture a tire, the adhesion performance between the single filament in the tire and rubber can be improved. It should be noted that the adhesion performance specifically refers to the initial adhesion performance and the moisture and heat resistance adhesion performance.

[0037] However, in recent years, further improvement of tire performance has been required, and for single filaments, further improvement of the adhesion performance with rubber has been required.

[0038] According to the research of the inventors of the present invention, when the coating film of a single filament contains Cu, Zn, and Co, Cu and Zn are alloyed in the coating film. In contrast, Co is mainly isolated in the form of a simple substance and distributed in an island shape near the outer surface of the coating film. And it is found that by controlling the distribution of this Co, a single filament with excellent adhesion performance with rubber can be formed.

[0039] As described above, it can be considered that Co has the function of improving the moisture and heat resistance adhesion performance. However, Co exists in the form of a simple substance with almost no reaction with Cu and Zn in the coating film as described above. And in the coating film, Co is mainly distributed on the outer surface side of the coating film. Therefore, when the content ratio of Co in the coating film is in the aforementioned range, by making the average value of the area ratio occupied by Co in the observation area 50% or less, the area of the alloy of Cu and Zn exposed on the outer surface of the coating film can be sufficiently ensured, and the formation of the adhesion layer can be promoted. Therefore, a single filament with particularly excellent initial adhesion performance with rubber can be manufactured.

[0040] Co has the function of improving the moisture and heat resistance adhesion performance as described above. Therefore, when the content ratio of Co in the coating film is in the aforementioned range, by making the average value of the area ratio occupied by Co in the observation area 1% or more, the ratio of Co existing near the rubber can be sufficiently increased. Therefore, a single filament with particularly excellent moisture and heat resistance adhesion performance with rubber can be manufactured.

[0041] As described above, by making the average value of the area ratio occupied by Co in the observation area in the above range, a single filament with excellent adhesion performance with rubber, that is, excellent initial adhesion performance and moisture and heat resistance adhesion performance, can be formed.

[0042] (2) Alternatively, when 10 observation regions are set along the central axis such that the distance between the observation regions is 10 mm, the average value of the area ratio of cobalt in the observation regions is 5% or more and 50% or less.

[0043] By increasing the number of set observation regions, even if the observation regions with specific values are included in the area ratio of Co in the observation regions, the influence of the observation regions with specific values can be suppressed.

[0044] Moreover, when 10 observation regions are set, by making the average value of the area ratio of Co in the observation regions 50% or less, the area of the alloy of Cu and Zn exposed on the outer surface of the coating film can be sufficiently ensured as a whole monofilament. Therefore, the formation of the adhesive layer can be promoted, and a monofilament with particularly excellent initial adhesion performance to rubber can be produced.

[0045] In addition, when 10 observation regions are set, by making the average value of the area ratio of Co in the observation regions 5% or more, the proportion of Co existing near the rubber can be sufficiently increased. Therefore, a monofilament with particularly excellent adhesion performance to rubber under humid and hot conditions can be produced.

[0046] (3) Alternatively, in the cross section, when 3 straight first observation lines along the thickness direction of the coating film are set such that the distance between the first observation lines is 10 mm, and the thickness of the region where zinc oxide is distributed is measured along the first observation lines, the average value of the thickness of the region where zinc oxide is distributed on the first observation lines is 0.004 μm or more and 0.007 μm or less.

[0047] It is considered that zinc, especially zinc oxide, controls the reaction for forming the adhesive layer. Therefore, by making the average thickness of the region where zinc oxide is distributed 0.004 μm or more, the formation of the adhesive layer can be promoted, and the initial adhesion performance to rubber can be improved. However, if the average thickness of the region where zinc oxide is distributed becomes too thick, it may sometimes hinder the formation of the adhesive layer. However, when the average thickness of the region where zinc oxide is distributed is 0.007 μm or less, the formation of the adhesive layer is not hindered, and the initial adhesion performance to rubber can be sufficiently improved.

[0048] (4) Alternatively, in the cross-section, when three linear second observation lines along the thickness direction of the coating are set such that the distance between the second observation lines is 10 mm, and the copper content is measured along the second observation lines, if the thickness of the coating on the second observation line is set as T, the copper content in the outer surface region, which is the region between the outer surface of the coating and the point at a distance of 1 / 3T from the outer surface of the coating, on the second observation line is set as Cu1, and the copper content in the central side region, which is the region between the inner surface of the coating and the point at a distance of 1 / 3T from the inner surface of the coating, on the second observation line is set as Cu2, then the ratio Cu of the copper content in the outer surface region to the copper content in the central side region calculated by the following formula (A) ratio has an average value of 90% or more and 97% or less.

[0049] Cu ratio = Cu1÷Cu2×100%...(A)

[0050] When the ratio Cu of the copper content in the outer surface region to the copper content in the central side region ratio has an average value of 90% or more, it means that a lot of copper is distributed on the outer surface side. As described above, copper reacts with sulfur to form an adhesive layer containing Cu2S. Therefore, by having a lot of copper distributed on the surface side of the monofilament, the formation of the adhesive layer can be promoted, and in particular, the initial adhesion performance with rubber can be improved.

[0051] On the other hand, by making the average value of the ratio Cu of the copper content in the outer surface region to the copper content in the central side region ratio 97% or less, the proportion of cobalt distributed near the rubber, which is the outer surface of the coating, can be sufficiently increased. Therefore, the effect of improving the adhesion performance under humid and hot conditions generated by cobalt can also be fully exerted, and a monofilament with particularly excellent initial adhesion performance and adhesion performance under humid and hot conditions can be formed.

[0052] (5) Alternatively, the degree of processing is 3.4 or more and 3.8 or less.

[0053] The degree of processing is an index indicating the degree of wire drawing of the monofilament base material. By making the degree of processing 3.4 or more, the cobalt contained in the coating of the monofilament can be sufficiently dispersed within the coating. Therefore, a monofilament with particularly excellent adhesion characteristics under humid and hot conditions can be formed.

[0054] However, if the processing is excessive, sometimes the coating will become thinner and the cobalt on the outer surface side will peel off. Therefore, the degree of processing is preferably 3.8 or less. By making the degree of processing 3.8 or less, a monofilament with particularly excellent adhesion characteristics under humid and hot conditions with rubber can be formed.

[0055] (6) The steel cord of the present disclosure may include at least one single wire as described in any one of (1) to (5).

[0056] The steel cord of one embodiment of the present disclosure includes the aforementioned single wire. Therefore, when used for a tire, a steel cord with excellent adhesion performance to the rubber of the tire can be produced.

[0057] (7) The tire of the present disclosure may include the steel cord as described in (6).

[0058] The tire of one embodiment of the present disclosure includes the aforementioned steel cord. Therefore, a tire with high adhesion performance between the steel cord and the rubber and excellent durability can be produced.

[0059] [Details of the Embodiment of the Present Disclosure]

[0060] Hereinafter, specific examples of the single wire, steel cord, and tire of one embodiment of the present disclosure (hereinafter referred to as "the present embodiment") will be described with reference to the drawings. It should be noted that the present invention is not limited to these examples, but is shown by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0061] [Single Wire]

[0062] Hereinafter, based on Figures 1 to 3C the single wire of the present embodiment will be described. Figure 1 is a perspective view of the single wire of the present embodiment, Figure 2 is Figure 1 a view showing an enlarged view of region A. Figure 3A is a view schematically showing the observation region. Figure 3B is an explanatory view of the method for obtaining the thickness of the region where zinc oxide is distributed. Figure 3C is an explanatory view of the method for obtaining the ratio of the copper content in the outer surface region in the coating film to the copper content in the central side region.

[0063] The single wire of the present embodiment is a single wire having a coating film, and the coating film may contain copper, zinc, and cobalt.

[0064] Moreover, when the total content ratio of copper, zinc, and cobalt in the coating film is set to 100% by mass, the content ratio of cobalt in the coating film may be 0.5% by mass or more and 8% by mass or less. In addition, in a cross section passing through the central axis of the single wire and parallel to the central axis, when a plurality of 1-μm square observation regions including the outer surface of the coating film are set in the coating film, the average value of the area ratio occupied by cobalt in the observation region may be 1% or more and 50% or less.

[0065] It should be noted that the above cross section of the single wire in which the observation region is set may also be referred to as a cross section in the long dimension direction of the single wire including the central axis of the single wire.

[0066] As shown Figure 1 in FIG. 1, the monofilament 10 of the present embodiment may have a wire 11 and a coating film 12 covering the surface of the wire 11. Hereinafter, the wire 11 and the coating film 12 of the monofilament 10 of the present embodiment will be described.

[0067] (1) Wire

[0068] The wire 11 can be, for example, a steel wire, and more preferably a high-carbon steel wire.

[0069] (2) Coating film

[0070] (Regarding composition)

[0071] The coating film 12 may contain Cu (copper), Zn (zinc), and Co (cobalt).

[0072] When a tire is made by rubber-coating the monofilament 10 having the coating film 12, Cu contained in the coating film 12 reacts with S (sulfur) contained in the rubber side, and a bonding layer containing Cu2S is formed on the rubber side rather than the interface between the monofilament and the rubber. This bonding layer has the effect of improving the initial bonding performance between the monofilament and the rubber. Therefore, Cu contained in the coating film 12 has the effect of improving the initial bonding performance with the rubber.

[0073] It should be noted that the initial bonding performance refers to the bonding performance between the monofilament and the rubber immediately after vulcanization when manufacturing a tire.

[0074] It is considered that Zn contained in the coating film 12 controls the reaction for forming the above-mentioned bonding layer.

[0075] A tire is mounted on a vehicle or the like and is used while rotating at high speed in a grounded state, so the time it is placed in a high-temperature and high-humidity environment becomes longer. When the tire is placed in a high-temperature and high-humidity environment, sometimes moisture and oxygen permeate through the rubber of the tire and reach near the interface between the monofilament and the rubber, and the bonding performance between the monofilament and the rubber deteriorates.

[0076] Therefore, as the bonding performance of the monofilament, in addition to the initial bonding performance, it is also required that the bonding performance between the monofilament and the rubber in the tire after being placed in a high-temperature and high-humidity environment, that is, the moisture and heat resistance bonding performance, is also excellent.

[0077] It is considered that when the tire is placed in a high-temperature and high-humidity environment, due to the intrusion of moisture and the like as described above, the composition of the above-mentioned bonding layer is affected, and the bonding performance between the monofilament and the rubber deteriorates. However, in the monofilament 10 of the present embodiment, it is considered that the change in the composition of the bonding layer is suppressed by the coating film 12 containing Co, and the moisture and heat resistance bonding performance can be improved.

[0078] The content ratio of Co in Cu, Zn, and Co in the coating film 12 is preferably 0.5 mass% or more and 8 mass% or less, more preferably 0.7 mass% or more and 7.95 mass% or less, and still more preferably 2.00 mass% or more and 7.93 mass% or less. The content ratio of Co in the above coating film is the content ratio of Co when the total content ratio of Cu, Zn, and Co in the coating film is set to 100 mass%. By making the content ratio of Co in the coating film 0.5 mass% or more, the coating film contains a sufficient amount of Co, so that the above-described effect of improving the adhesion performance under humid heat can be fully exerted. In addition, by making the content ratio of Co in the coating film 8 mass% or less, the content ratios of Cu and Zn in the coating film can be sufficiently increased, and the initial adhesion ability can also be improved.

[0079] The content ratio of the above Co in the coating film 12 can be calculated by analyzing a dissolution solution obtained by dissolving the coating film of the monofilament using an atomic absorption analyzer or the like.

[0080] Thus, for the monofilament 10 of the present embodiment, by the coating film 12 containing Cu, Zn, and Co, when a tire is manufactured using the monofilament, the adhesion performance between the monofilament and rubber in the tire can be improved. It should be noted that the adhesion performance refers to the initial adhesion performance and the adhesion performance under humid heat.

[0081] (Regarding the average value of the area ratio occupied by Co in the observation region of the coating film)

[0082] However, in recent years, further improvement of tire performance has been required, and for monofilaments, further improvement of the adhesion performance with rubber has been required.

[0083] According to the research of the inventors of the present invention, when the coating film 12 of the monofilament 10 contains Cu, Zn, and Co, Cu and Zn are alloyed in the coating film 12. In contrast, Co is mainly isolated in the form of a simple substance and distributed in an island shape near the outer surface of the coating film 12. And it has been found that by controlling the distribution of Co, a monofilament with excellent adhesion performance with rubber can be formed.

[0084] Regarding the monofilament of the present embodiment, preferably, when a plurality of observation regions are set in a cross section passing through the central axis of the monofilament and parallel to the central axis, the average value of the area ratio occupied by Co in the observation region is within a specified range.

[0085] Use Figure 2 An explanation will be given for the observation region. It should be noted that Figure 2 is a diagram schematically shown and does not reflect the dimensions of each part. Figure 2 is to Figure 1A diagram showing an enlarged view of region A in []. Region A is a plane that passes through the central axis CA1 of the monofilament 10 and is parallel to the central axis CA1. That is, region A is a cross-section of the monofilament 10 in the long dimension direction that contains the central axis CA1 of the monofilament 10. In Figure 1 the X-axis, Y-axis, and Z-axis are shown, and the long dimension direction of the monofilament 10 refers to Figure 1 the direction of the X-axis in []. Region A corresponds to the XZ plane that contains the central axis CA1.

[0086] As Figure 2 shown, the observation region 21 can be set in the coating 12 part and can be set in such a way that the coating 12 is included in the observation region 21. The observation region 21 is preferably set in such a way that it includes the outer surface 12A of the coating 12. The outer surface 12A mentioned here refers to the surface of the coating 12 that is opposite to the surface facing the wire 11, and can also be referred to as the surface exposed to the outside of the monofilament 10 and the coating 12.

[0087] Multiple observation regions 21 can be set. In Figure 2 an example where three observation regions 21A, 21B, and 21C are set is shown, but it is not limited to this method. For example, it is preferably set to three or more and ten or less.

[0088] The observation regions are preferably arranged at equal intervals along the central axis CA1 of the monofilament 10. In Figure 2 this case, it is preferable that the distance L211 between the observation region 21A and the observation region 21B is equal to the distance L212 between the observation region 21B and the observation region 21C. The distance between the above-mentioned observation regions is not particularly limited. For example, the distance L211 and the distance L212 are preferably set to 10 mm. That is, the observation regions are preferably set along the central axis CA1 of the monofilament 10 in such a way that the distance between the observation regions is 10 mm.

[0089] A schematic diagram showing the case where the observation region 21 is observed is shown in Figure 3A . Figure 3A One observation region 21 is shown. The observation region 21 can be formed into a region of 1 μm square, that is, a square region with a side length of 1 μm. Therefore, Figure 3A the side lengths L31 and L32 of the observation region 21 shown in [] are 1 μm.

[0090] And, as Figure 3A shown, the observation region 21 can include the outer surface 12A of the coating 12. As Figure 3A shown, it is preferable to form the observation region 21 in such a way that the outer surface 12A of the coating 12 constitutes one side of the observation region 21. However, since the outer surface 12A of the coating 12 usually has fine irregularities, the observation region 21 can be set in such a way that it includes a part of the outer surface 12A of the coating 12.

[0091] As Figure 3A shown, the coating film 12 may have a region of Co121 and a region of an alloy 122 formed by alloying Cu and Zn. However, it does not mean that Co in the coating film 12 is completely separated from Cu and Zn, and Co in the coating film 12 may also be dissolved in the region of the alloy 122 in a very small amount, etc.

[0092] Moreover, according to the research of the inventors of the present invention, when three observation regions 21 are set, the average value of the area ratio occupied by Co121 in the observation region 21 is preferably 1% or more and 50% or less, more preferably 5% or more and 50% or less, further preferably 9% or more and 50% or less, particularly preferably 20% or more and 50% or less, and most preferably 30% or more and 45% or less.

[0093] It can be considered that Co has the function of improving the adhesion performance under humid heat as described above. However, it can be considered that Co exists in the form of a simple substance with almost no reaction with Cu and Zn in the coating film 12 as described above. And, as Figure 3A shown, in the coating film 12, Co121 is mainly distributed on the outer surface 12A side of the coating film 12. Therefore, when the content ratio of Co in the coating film is in the aforementioned range, by making the average value of the area ratio occupied by Co121 in the observation region 21 be 50% or less, the area of the alloy 122 exposed on the outer surface 12A of the coating film 12 can be sufficiently ensured, and the formation of the adhesive layer can be promoted. Therefore, a monofilament with excellent initial adhesion performance to rubber can be produced.

[0094] Co has the function of improving the adhesion performance under humid heat. Therefore, when the content ratio of Co in the coating film is in the aforementioned range, by making the average value of the area ratio occupied by Co121 in the observation region 21 be 1% or more, the proportion of Co existing near the rubber can be sufficiently increased. Therefore, a monofilament with excellent adhesion performance under humid heat to rubber can be produced.

[0095] As described above, by making the area ratio of Co in the observation region 21 be in the above range, a monofilament with excellent adhesive force to rubber, that is, excellent initial adhesion performance and adhesion performance under humid heat, can be formed.

[0096] In addition, when ten observation regions 21 are set and evaluated using the ten observation regions, the average value of the area ratio occupied by Co121 in the ten observation regions 21 is preferably 5% or more and 50% or less, more preferably 9% or more and 50% or less, further preferably 20% or more and 50% or less, particularly preferably 30% or more and 45% or less.

[0097] By increasing the number of set observation regions 21, even if an observation region with an abnormal value is included, the influence of the observation region with the abnormal value can be suppressed with respect to the area ratio of Co in the observation regions.

[0098] Moreover, when 10 observation regions 21 are set, by making the average value of the area ratio of Co in the observation regions 21 50% or less, as for the entire monofilament, the area of the alloy 122 of Cu and Zn exposed on the outer surface 12A of the coating film 12 can be sufficiently ensured. Therefore, the formation of the adhesive layer can be promoted, and a monofilament with particularly excellent initial adhesion performance to rubber can be produced.

[0099] In addition, when 10 observation regions 21 are set, by making the average value of the area ratio of Co121 in the observation regions 21 5% or more, the proportion of Co present near the rubber can be sufficiently increased. Therefore, a monofilament with particularly excellent moisture and heat resistant adhesion performance to rubber can be produced.

[0100] In the case of setting 10 observation regions 21, similarly to the case of 3 regions, in a cross-section in the longitudinal dimension direction of the monofilament 10 including the central axis CA1 of the monofilament 10, a 1 μm square observation region including the outer surface 12A of the coating film 12 can be set in the coating film 12. At this time, the 10 observation regions 21 can be set along the central axis CA1 such that the distance between the observation regions is 10 mm.

[0101] It should be noted that the method for obtaining the area ratio of Co in the observation region 21 is not particularly limited. For example, first, element mapping within the observation region can be performed using STEM / EDX (Scanning Transmission Electron Microscope / Energy dispersive X-ray spectrometry). Then, based on the obtained results of the element mapping, the area of Co121 can be calculated, and the area ratio of Co in the observation region 21 can be calculated. The area ratio of Co referred to here means the area ratio of the region where Co exists without reacting with other metals.

[0102] (Regarding the thickness of the region where zinc oxide is distributed)

[0103] In a cross-section of the monofilament 10 in the longitudinal dimension direction of the monofilament 10 including the central axis CA1 of the monofilament 10, three straight first observation lines in the thickness direction of the coating film 12 are set such that the distance between the first observation lines is 10 mm. And when measuring the thickness of the region where zinc oxide is distributed along the first observation line, the average value of the thickness of the region where zinc oxide is distributed on the first observation line is preferably 0.004 μm or more and 0.007 μm or less, more preferably 0.005 μm or more and 0.006 μm or less.

[0104] Use Figure 2 To explain the first observation line.

[0105] As Figure 2 shown, the first observation line 22 can be set in the coating film 12 part and can be set along the Z axis which is the thickness direction of the coating film 12, that is, perpendicular to the central axis CA1 and along the Z axis in the figure. The first observation line 22 can be drawn between the outer surface 12A and the inner surface 12B of the coating film 12. It should be noted that the inner surface 12B of the coating film 12 is the surface of the coating film 12 facing the wire 11.

[0106] The first observation lines 22 are preferably arranged at equal intervals along the central axis CA1 of the monofilament 10. In Figure 2 this case, it is preferred that the distance L221 between the first observation line 22A and the first observation line 22B and the distance L222 between the first observation line 22B and the first observation line 22C are equal. The distance L221 and the distance L222 are preferably set to 10 mm. That is, the first observation line 22 is preferably set along the central axis CA1 of the monofilament 10 such that the distance between the first observation lines is 10 mm.

[0107] The method for measuring the thickness of the region where zinc oxide is distributed on the first observation line 22 is not particularly limited. For example, line analysis of zinc and oxygen can be performed along the first observation line using STEM / EDX or the like.

[0108] A diagram schematically showing the line analysis data obtained in this case is shown in Figure 3B .

[0109] Figure 3B The horizontal axis of Figure 3B represents the measurement position, and the vertical axis represents the intensity. As Figure 3B shown, when line analysis is performed from the outer surface 12A to the inner surface 12B of the coating film 12, peaks appear for each element in the region where zinc (Zn) and oxygen (O) are distributed.

[0110] Therefore, the length of the region where the peak of zinc overlaps with the peak of oxygen can be set as the thickness T1 of the region where zinc oxide is distributed on the first observation straight line. Also, the average value of the thicknesses of the regions where zinc oxide is distributed on the three first observation straight lines can be set as the average thickness of the region where zinc oxide is distributed in the monofilament.

[0111] As described above, it is considered that zinc, particularly zinc oxide, controls the reaction for forming the adhesive layer. Therefore, by making the average thickness of the region where zinc oxide is distributed 0.004 μm or more, the formation of the adhesive layer can be promoted and the initial adhesive property with rubber can be improved. However, if the average thickness of the region where zinc oxide is distributed becomes too thick, it may sometimes hinder the formation of the adhesive layer. However, when the average thickness of the region where zinc oxide is distributed is 0.007 μm or less, the formation of the adhesive layer is not hindered and the initial adhesive property with rubber can be sufficiently improved.

[0112] (Regarding the ratio of the copper content in the outer surface region to the copper content in the central side region)

[0113] Here, in a cross-section in the longitudinal direction of the monofilament 10 including the central axis CA1 of the monofilament 10, three straight second observation lines along the thickness direction of the coating film 12 are set such that the distance between the second observation lines is 10 mm.

[0114] And, when the copper content is measured along the second observation line, the copper content Cu1 in the outer surface region on the outer surface 12A side of the coating film 12 on the second observation line is set. In addition, the copper content Cu2 in the central side region on the central axis CA1 side of the coating film 12 on the second observation line is set.

[0115] At this time, the ratio Cu of the copper content Cu1 in the outer surface region to the copper content Cu2 in the central side region, calculated by the following formula (A) ratio is preferably 90% or more and 97% or less, more preferably 92% or more and 96% or less.

[0116] Cu ratio = Cu1 ÷ Cu2 × 100%... (A)

[0117] It should be noted that when the thickness of the coating film on the second observation line is set as T, the outer surface region is the region between the outer surface 12A of the coating film 12 and the point at a distance of 1 / 3T from the outer surface 12A on the second observation line. In addition, the central side region is the region between the inner surface 12B of the coating film 12 and the point at a distance of 1 / 3T from the inner surface 12B on the second observation line.

[0118] The ratio Cu of the content of copper in the outer surface region to the content of copper in the central side region ratio When the average value is 90% or more, it means that a lot of copper is distributed on the outer surface side. As described above, copper reacts with sulfur to form an adhesive layer containing Cu2S. Therefore, by having a lot of copper distributed on the surface side of the monofilament, the formation of the adhesive layer can be promoted, and in particular, the initial adhesive property with rubber can be improved.

[0119] On the other hand, by making the ratio Cu of the content of copper in the outer surface region to the content of copper in the central side region ratio The average value is 97% or less, and the ratio of cobalt distributed on the outer surface of the coating film, that is, near the rubber, can be sufficiently increased. Therefore, the effect of improving the adhesion property under humid heat generated by cobalt can also be sufficiently exerted, and a monofilament having particularly excellent initial adhesion property and adhesion property under humid heat can be formed.

[0120] Use Figure 2 To explain the second observation line.

[0121] As Figure 2 shown, the second observation line 23 can be set in the coating film 12 portion, and can be set along the Z axis which is the thickness direction of the coating film 12, that is, perpendicular to the central axis CA1 along the Z axis in the figure. The second observation line 23 can be drawn between the outer surface 12A and the inner surface 12B of the coating film 12.

[0122] The second observation line 23 is preferably provided at equal intervals along the central axis CA1 of the monofilament 10. In Figure 2 this case, it is preferable that the distance L231 between the second observation line 23A and the second observation line 23B is equal to the distance L232 between the second observation line 23B and the second observation line 23C. The distance L231 and the distance L232 are preferably set to 10 mm. That is, the second observation line 23 is preferably set along the central axis CA1 of the monofilament 10 such that the distance between the second observation lines is 10 mm.

[0123] To explain the method of obtaining Cu1 and Cu2.

[0124] The method for measuring the copper content along the second observation line 23 is not particularly limited. For example, line analysis of copper can be performed along the second observation line using STEM / EDX or the like.

[0125] The diagram schematically showing the data of the line analysis obtained in this case is shown in Figure 3C .

[0126] Figure 3C The horizontal axis of represents the measurement position, and the vertical axis represents the intensity. As Figure 3CAs shown, when line analysis is performed from the outer surface 12A to the inner surface 12B of the coating film 12, a peak appears in the region where copper (Cu) is distributed.

[0127] Here, in the coating film thickness T on the second observation line, the region with a length of 1 / 3T of the coating film 12 on the outer surface 12A side is the outer surface region 33. And, for example, the peak area of the EDX of copper measured in the outer surface region 33 can be set as Cu1.

[0128] In addition, in the coating film thickness T on the second observation line, for example, the region with a length of 1 / 3T of the coating film on the central axis CA1 side, that is, the inner surface 12B side of the coating film, is the central side region 34. And, for example, the EDX peak area of copper measured in the central side region 34 can be set as Cu2.

[0129] The calculated Cu1 and Cu2 can be used to calculate Cu on each second observation line by the aforementioned formula (A). ratio And, the Cu ratio on the three second observation lines can be averaged to obtain the average value of the ratio Cu ratio of the content of copper in the outer surface region of the monofilament to the content of copper in the central side region.

[0130] (Regarding the degree of processing)

[0131] For the monofilament of the embodiment, the degree of processing η is preferably 3.4 or more and 3.8 or less. When the cross-sectional area of the surface of the monofilament base material perpendicular to the long dimension direction is set as S0 and the cross-sectional area of the monofilament of this embodiment after wire drawing is set as S1, it is defined by η = ln(S0 / S1).

[0132] That is, the degree of processing is an index indicating the degree of wire drawing of the monofilament base material. By making the degree of processing 3.4 or more, the cobalt in the coating film of the monofilament can be sufficiently dispersed in the coating film. Therefore, a monofilament with particularly excellent moisture and heat resistant adhesion characteristics can be formed.

[0133] However, if the processing is excessive, sometimes the coating film will become thinner and the cobalt on the outer surface side will peel off. Therefore, the degree of processing η is preferably 3.8 or less. By making the degree of processing η 3.8 or less, a monofilament with particularly excellent moisture and heat resistant adhesion characteristics to rubber can be formed.

[0134] It should be noted that the higher the degree of processing of the monofilament, the higher the tensile strength. On the other hand, the carbon in the monofilament comes from the materials constituting the monofilament, such as wire rods, and thus does not change.

[0135] Therefore, a calibration curve can also be prepared in advance regarding the relationship between the carbon content and the tensile strength of the monofilament and the degree of processing, and the degree of processing can be calculated by measuring the carbon content and the tensile strength of the monofilament.

[0136] [Method for manufacturing monofilament]

[0137] The method for manufacturing the monofilament of the present embodiment will be described. According to the method for manufacturing the monofilament of the present embodiment, the aforementioned monofilament can be manufactured. Therefore, part of the matters that have been described will be omitted.

[0138] The method for manufacturing the monofilament of the present embodiment may include the following steps.

[0139] Monofilament base material production step: A Cu layer, a Zn layer, and a Co layer are formed on the surface of the wire rod to form a monofilament base material.

[0140] Heat treatment step: The monofilament base material is heat-treated.

[0141] Drawing step: The monofilament base material after the heat treatment step is drawn.

[0142] Moreover, in the monofilament base material production step, when forming the Co layer, the distance between the electrode for supplying Co and the wire rod can be kept constant.

[0143] Hereinafter, each step will be described.

[0144] (1) Monofilament base material production step

[0145] In the monofilament base material production step, a monofilament base material can be produced.

[0146] In Figure 4 a cross-sectional view at a cross-section parallel to the central axis CA2 of the monofilament base material 40 and passing through the central axis is schematically shown. Figure 4 A cross-section including the central axis CA2 of the monofilament base material 40, corresponding to the long dimension direction of the monofilament base material 40. In Figure 4 the X-axis, Y-axis, and Z-axis are shown, and the long dimension direction of the monofilament base material 40 refers to Figure 4 the direction of the X-axis in Figure 4 which corresponds to the XZ plane including the central axis CA2. As Figure 4 shown, the monofilament base material 40 may have a Cu layer 42, a Co layer 43, and a Zn layer 44 on the surface of the wire rod 41. It should be noted that the wire rod 41 is the wire rod before drawing, and in the case of distinguishing it from the wire rod of the monofilament, it may also be referred to as the wire rod for the base material.

[0147] Therefore, in the process of manufacturing the monofilament base material, a Cu layer 42, a Co layer 43, and a Zn layer 44 can be formed on the surface of the wire 41. The Cu layer, Co layer, and Zn layer are preferably formed by plating.

[0148] The order of forming each layer is not particularly limited. For example, it is preferred to form the Cu layer 42 on the wire 41 first, and then form the Co layer 43 and the Zn layer 44. The order of forming the Co layer 43 and the Zn layer 44 is also not particularly limited. For example, it is preferred to form the Zn layer 44 after forming the Co layer 43.

[0149] The monofilament can be manufactured by drawing the monofilament base material. However, sometimes a part of the layer disposed on the outermost surface of the monofilament base material comes into contact with a die or the like during the drawing process and is shaved off. And generally, the preferred thickness of the Co layer 43 is thinner than the preferred thicknesses of the Cu layer 42 and the Zn layer 44. Therefore, in order to suppress a large change in the Co content ratio in the coating film of the monofilament obtained after the drawing process from the target composition, it is preferred to form the Co layer 43 before the Zn layer 44 as described above, and suppress the Co layer 43 from being shaved off during the drawing process.

[0150] The thickness of each layer is not particularly limited, and the ratio of each component in the coating film 12 of the monofilament 10 obtained after the drawing process changes according to the thickness of each layer. Therefore, it is preferred to select the thickness of each layer according to the composition of the desired coating film 12 in the monofilament after the drawing process.

[0151] For example, the average value of the thickness T42 of the Cu layer 42 is preferably 0.777 μm or more and 1.290 μm or less, more preferably 0.800 μm or more and 1.254 μm or less. The average value of the thickness T43 of the Co layer 43 is preferably 0.0121 μm or more and 0.138 μm or less, more preferably 0.0352 μm or more and 0.0900 μm or less. The average value of the thickness T44 of the Zn layer 44 is preferably 0.246 μm or more and 0.627 μm or less, more preferably 0.250 μm or more and 0.614 μm or less, and further preferably 0.306 μm or more and 0.557 μm or less.

[0152] The average value of the thickness of each layer of the Cu layer, Co layer, and Zn layer can be calculated by measuring at multiple measurement points and taking the average. The number of measurement points is not particularly limited. For example, it is preferably 3 or more and 10 or less. It should be noted that the above-mentioned multiple measurement points are preferably set in such a way that the distances in the central axis direction of the monofilament base material 40 between the measurement points are equal. The distance between the measurement points is not particularly limited. For example, it can be set to 10 mm.

[0153] It should be noted that the size of the wire and the thickness of each layer are preferably selected such that the degree of processing in the subsequent wire drawing process is 3.4 or more and 3.8 or less. Since the degree of processing has been described, the description is omitted here.

[0154] Moreover, according to the research of the inventors of the present invention, by forming the Co layer 43 with a uniform thickness when forming the Co layer 43, for the single wire obtained after the heat treatment process and the wire drawing process, the average value of the area ratio of the aforementioned Co in the observation region can be within a specified range.

[0155] As described above, it is preferable that the thickness of the Co layer 43 is uniform. When the thickness is measured at a plurality of measurement points, the non-uniformity ratio is preferably 2.6 or less, and more preferably 2.5 or less. The above non-uniformity ratio is a value obtained by dividing the difference between the maximum value and the minimum value of the thickness of the Co layer 43 measured at a plurality of measurement points by the average value of the thickness of the Co layer 43, and can be calculated by the following formula (1).

[0156] (Non-uniformity ratio) = (Maximum value of thickness - Minimum value of thickness) ÷ Average value of thickness... (1)

[0157] When the thickness of the Co layer 43 is measured at a plurality of measurement points, the smaller the above non-uniformity ratio, the more the degree of thickness non-uniformity of the Co layer is suppressed, and it can be said that the thickness is uniform. Moreover, when the non-uniformity ratio of the Co layer 43 is within the above range, when wire drawing is performed to form a single wire, it is easy to make the ratio of the area occupied by Co in the specified observation region within the aforementioned range.

[0158] The lower limit value of the non-uniformity ratio of the thickness of the Co layer 43 is not particularly limited, and can be set to 0.6 or more, for example.

[0159] As described above, the Co layer can be formed by plating. Conventionally, for example, as Figure 5 shown in the plating apparatus 50, the plating solution 52 and the Co source 53 are placed in the plating bath 51. It should be noted that as the Co source 53, granular Co metal or Co compound can be used.

[0160] The electrode plate 54 is connected to the Co source 53, and the Co source 53 becomes an electrode for supplying Co. Moreover, in the plating bath 51, the wire 55 is conveyed from the first roll 551 to the second roll 552, and the wire 55 is passed through the plating bath 51, whereby a Co layer is formed on the wire 55 as the single wire base material.

[0161] However, in Figure 5In the plating apparatus 50 shown, depending on the shape of the Co source 53 which is the electrode for supplying Co, the distance between the electrode for supplying Co and the wire 55 varies. Specifically, for example, like the distance L531 between the Co source 531 and the wire 55 and the distance L532 between the Co source 532 and the wire 55, the distance between the Co source 53 and the wire 55 varies. Therefore, it is difficult to uniformly form a Co layer on the surface of the wire 55 which is the single-wire base material.

[0162] Therefore, in the method for manufacturing a single wire in the present embodiment, when forming the Co layer, it is preferable to keep the distance between the electrode for supplying Co and the wire constant. The specific method is not particularly limited. For example, it can be implemented using Figure 6 the plating apparatus 60 shown. In Figure 6 the plating apparatus 60, the same reference numerals are assigned to the same components as those in Figure 5 the plating apparatus 50 and the description thereof is omitted.

[0163] In Figure 6 the plating apparatus 60 shown, a metal mesh 61 is disposed above the wire 55, and the Co source 53 is disposed on the metal mesh 61. The Co source 53 is immersed in the plating solution 52. A power source (not shown) is connected to the metal mesh 61, and the Co source 53 becomes an electrode. In this case, since the Co source 53 is disposed on the bottom surface of the metal mesh 61, regardless of the shape of the Co source 53, the distance L6 between the Co source 53 which is the electrode for supplying Co and the wire 55 can be kept constant. Therefore, a Co layer can be uniformly formed on the surface of the wire 55.

[0164] Here, an example is shown in which a metal mesh 61 containing the Co source 53 and connected to a power source is disposed above the wire 55. However, as long as the distance between the wire 55 and the electrode for supplying Co is kept constant, it is not limited to this method. For example, it can also be configured such that a plate-like body composed of the Co source is used as the electrode for supplying Co, and the distance between the electrode for supplying Co and the wire 55 is kept constant.

[0165] It should be noted that for the Cu layer and the Zn layer, they can also be formed in the same manner as the Co layer described above. However, since the Cu layer and the Zn layer are thicker than the Co layer, compared with the case of the Co layer, the difference in thickness uniformity caused by the film-forming method is small. Therefore, the film-forming conditions for these layers are not limited to the above method.

[0166] (2) Heat treatment process

[0167] In the heat treatment process, the single-wire base material can be heat-treated.

[0168] The temperature of the heat treatment is not particularly limited, and it is preferably set to a temperature equal to or higher than the alloying temperature of Cu and Zn. In particular, the temperature of the heat treatment is preferably 550°C or higher and 650°C or lower, which is higher than the melting point (419.5°C) at which Zn becomes a liquid phase. The time of the heat treatment is also not particularly limited, and for example, it is preferably 3 seconds or longer and 7 seconds or shorter.

[0169] Through the heat treatment, Cu and Zn are alloyed.

[0170] (3) Drawing process

[0171] In the drawing process, the single-wire base material after the heat treatment process can be drawn.

[0172] The drawing process can be carried out in such a way as to obtain a desired single-wire diameter.

[0173] For example, the average value of the area ratio occupied by Co in the observation area of the coating film, the thickness of the area where zinc oxide is distributed, the ratio of the copper content in the outer surface area to the copper content in the center side area, etc. can be adjusted to a desired range by selecting manufacturing conditions. As the above manufacturing conditions, for example, conditions such as the conditions of the heat treatment process, the degree of processing in the drawing process, surface cleaning of the single-wire base material after the single-wire base material manufacturing process or before the drawing process, and selection of the conditions at this time can be cited.

[0174] 〔Steel cord〕

[0175] Hereinafter, based on Figure 7 the steel cord of the present embodiment will be described.

[0176] The steel cord of the present embodiment may have at least one of the aforementioned single wires.

[0177] The steel cord of the present embodiment may also be composed of one of the aforementioned single wires. In addition, it may be configured as a structure in which a plurality of single wires are twisted together. When the steel cord has a plurality of single wires, at least one single wire may be the aforementioned single wire, or all the single wires may be the aforementioned single wires.

[0178] When the steel cord of the present embodiment has a plurality of single wires, for example, as Figure 7 shown, it may be configured as a steel cord 70 in which a plurality of single wires 71 are twisted together.

[0179] In Figure 7 a steel cord 70 having a 1×4 structure in which four single wires 71 are twisted together in a circumferential direction to form a layer is shown, but it is not limited to this method. For example, the number of single wires may be three or less or five or more. In addition, the steel cord may, for example, also have a structure in which the single wires are twisted into two or more layers.

[0180] The single filaments of the steel cord of the present embodiment may also be so-called corrugated single filaments that repeatedly have bent portions and non-bent portions along the long dimension direction.

[0181] The steel cord of the present embodiment includes the above-mentioned single filaments. Therefore, when the steel cord of the present embodiment is used for a tire, a steel cord with excellent adhesion performance to the rubber of the tire can be produced.

[0182] 〔Tire〕

[0183] Next, based on Figure 8 , Figure 9 the tire in the present embodiment will be described.

[0184] The tire of the present embodiment may include the above-mentioned steel cord.

[0185] Figure 8 A cross-sectional view of the tire 80 of the present embodiment at a plane perpendicular to the circumferential direction is shown. Only the portion on the left side of the CL (center line) is shown in Figure 8 , but the same structure is continuously provided on the right side of the CL with the CL as the axis of symmetry.

[0186] As Figure 8 shown, the tire 80 includes a tread portion 81, a sidewall portion 82, and a bead portion 83.

[0187] The tread portion 81 is the portion in contact with the road surface. The bead portion 83 is provided on the inner diameter side of the tire 80 relative to the tread portion 81. The bead portion 83 is the portion in contact with the rim of the vehicle's wheel. The sidewall portion 82 connects the tread portion 81 and the bead portion 83. When the tread portion 81 receives an impact from the road surface, the sidewall portion 82 elastically deforms to absorb the impact.

[0188] The tire 80 includes an inner liner 84, a carcass 85, a belt layer 86, and a bead wire 87.

[0189] The inner liner 84 is made of rubber and seals the space between the tire 80 and the wheel.

[0190] The carcass 85 forms the skeleton of the tire 80. The carcass 85 is composed of organic fibers such as polyester, nylon, rayon, or a steel cord and rubber. The above-mentioned steel cord may also be used as the carcass 85. That is, a steel cord having at least one of the above-mentioned single filaments may also be used as the carcass 85.

[0191] The bead wire 87 is provided at the bead portion 83. The bead wire 87 receives the tensile force acting on the carcass 85.

[0192] The belt layer 86 fastens the carcass 85 to improve the rigidity of the tread portion 81. In the example shown in Figure 8 , the tire 80 has two belt layers 86.

[0193] Figure 9 FIG. is a diagram schematically showing two belt layers 86. Figure 9 FIG. shows a cross-sectional view of the belt layer 86 at a plane perpendicular to the long dimension direction, i.e., the circumferential direction of the tire 80.

[0194] As Figure 9 shown, the two belt layers 86 are overlapped with each other in the radial direction of the tire 80. Each belt layer 86 has a plurality of steel cord 91 and rubber 92. The plurality of steel cords 91 are arranged in a row. In addition, the rubber 92 covers the steel cords 91, and the entire circumference of each steel cord 91 is covered by the rubber 92. The steel cords 91 are embedded in the rubber 92.

[0195] It should be noted that, as the steel cord 91, the aforementioned steel cord can be used. That is, it can be set as a steel cord having at least one of the aforementioned filaments. Therefore, the steel cord 91 used in the tire of the present embodiment can also be composed of one of the aforementioned filaments. In addition, the steel cord 91 of the present embodiment can also have a structure in which a plurality of filaments are twisted together. In this case, one or more of the filaments included in the steel cord 91 can be set as the aforementioned filament, or all the filaments can be composed of the aforementioned filament.

[0196] According to the tire of the present embodiment, the aforementioned steel cord is included as the steel cord 91. Therefore, for the tire of the present embodiment, a tire having high adhesion performance between the steel cord and the rubber and excellent durability can be manufactured.

[0197] As described above, the embodiments have been described in detail, but are not limited to specific embodiments, and various modifications and changes can be made within the scope described in the claims.

[0198] Examples

[0199] Specific examples are listed below for illustration, but the present invention is not limited to these examples.

[0200] (Evaluation method)

[0201] First, the evaluation method of the single-filament base material and the single filament produced in the following experimental examples will be described.

[0202] (1) Evaluation of single-filament base material

[0203] For the single-filament base material produced in the following experimental examples immediately after the coating film was formed on the wire, i.e., immediately after the single-filament base material manufacturing process, the thicknesses of the Cu layer, Co layer, and Zn layer were measured at multiple locations in a cross-section passing through and parallel to the central axis.

[0204] Three measurement points were set along the central axis of the monofilament base material. It should be noted that the measurement points were set in such a way that the distance between the measurement points in the direction of the central axis of the monofilament base material was 10 mm.

[0205] Then, the average value of the measured values of the thickness of each layer at the measurement points was set as the average thickness of the Cu layer, Co layer, and Zn layer of the monofilament base material, respectively.

[0206] When measuring and calculating the thickness of each layer, first, STEM / EDX (scanning transmission electron microscope / energy dispersive X-ray analysis) was used to map each element in the cross-section passing through the central axis of the monofilament base material and parallel to the central axis. Then, the regions of each layer were determined based on the obtained element mapping images, the thickness of each layer at the above-mentioned measurement points was obtained, and the average value was calculated.

[0207] In Tables 1 to 3, the average thickness of the Cu layer, the average thickness of the Zn layer, and the average thickness of the Co layer are denoted as "Cu layer thickness", "Zn layer thickness", and "Co layer thickness", respectively.

[0208] In addition, for the Co layer, the value obtained by dividing the difference between the maximum value and the minimum value among the measured values at the above-mentioned three measurement points by the average thickness of the Co layer, that is, the non-uniformity ratio of the Co layer thickness calculated by the aforementioned formula (1), is shown in Tables 1 to 3 as the "Co layer thickness non-uniformity ratio".

[0209] (2) Evaluation of the monofilament

[0210] (2-1) Average value of the area ratio of Co in the observation region of the coating

[0211] In the cross-section passing through the central axis of the monofilament produced in the following experimental examples and parallel to the central axis, three 1-μm square observation regions 21A to 21C were set in the coating 12. It should be noted that, as Figure 2 , Figure 3A shown, the observation region 21 was set to include the outer surface 12A of the coating 12. In addition, the distances L211 and L212 between the observation regions 21 were set to 10 mm.

[0212] Then, in each observation region, the area ratio of Co was measured and calculated, and the average value of the area ratios of Co in the three (3) observation regions was calculated. It is shown as "Co area ratio (average of 3 places)" in Tables 1 to 3.

[0213] When calculating the average value of the area ratio of Co in each observation region, first, STEM / EDX (scanning transmission electron microscopy / energy dispersive X-ray analysis) was used to map each element in each of the above-mentioned observation regions in a cross-section passing through and parallel to the central axis of the monofilament. Then, based on the obtained element mapping images, the area ratio of Co in the observation region was determined, and the average value of the 3 (three) observation regions was calculated.

[0214] In addition, except that the number of observation regions was set to 10, similarly, the area ratio of Co was measured and calculated in each observation region, and the average value of the area ratio of Co in the 10 observation regions was calculated. It is shown as "Co area ratio (average of 10)" in Tables 1 to 3.

[0215] It should be noted that when the number of observation regions was set to 10, each observation region was set to include the outer surface 12A of the coating film 12, and the distance between each observation region was set to 10 mm. In addition, when calculating the average value of the area ratio of Co in each observation region, first, STEM / EDX was used to map each element in each of the above-mentioned observation regions in a cross-section passing through and parallel to the central axis of the monofilament. Then, based on the obtained element mapping images, the area ratio of Co in the observation region was determined, and the average value of the 10 observation regions was calculated.

[0216] (2-2) Co content ratio in the coating film

[0217] A part of the monofilament on which the coating film was formed and wire drawing was performed was cut out and immersed in a strip solution to dissolve the coating film. Then, the obtained dissolved solution was analyzed using an atomic absorption analyzer (model: Z-2300, manufactured by Hitachi High-Technologies Corporation). Based on the analysis results, the Co content ratio among Cu, Zn, and Co in the coating film was calculated. That is, the Co content ratio in the coating film was calculated when the total of the Cu, Zn, and Co content ratios in the coating film was set to 100 mass%. It is shown as "Co content ratio in the coating film" in Tables 1 to 3.

[0218] (2-3) Degree of processing

[0219] A calibration curve of the relationship between the carbon content, tensile strength, and degree of processing of the monofilament was prepared in advance.

[0220] Then, the carbon content and tensile strength of the monofilaments produced in the following experimental examples were measured, and the degree of processing was calculated using the above calibration curve.

[0221] The carbon content was analyzed using an atomic absorption analyzer (Model: Z-2300, manufactured by Hitachi High-Technologies Corporation).

[0222] The tensile strength was measured using an Autograph (Model: AGS-5kNX, manufactured by Shimadzu Corporation).

[0223] (2-4) The thickness of the region where zinc oxide is distributed

[0224] In a cross-section of the monofilament 10 in the longitudinal dimension direction including the central axis CA1 of the monofilament 10, three straight first observation lines 22 along the thickness direction of the coating film 12 were set such that the distances L221 and L222 between the first observation lines became 10 mm.

[0225] Then, line analysis of zinc and oxygen was performed along the first observation lines using STEM / EDX. At this time, as Figure 3B shown, the length of the region where the peak of zinc overlaps with the peak of oxygen was set as the thickness T1 of the region where zinc oxide is distributed.

[0226] For each of the first observation lines, the thickness of the region where zinc oxide is distributed was measured as described above, and the average value of the thicknesses of the regions where zinc oxide is distributed measured in the three first observation lines was calculated. The results are shown in the column of "ZnO Thickness" in the table.

[0227] (2-5) The ratio of the copper content in the outer surface region to the copper content in the central side region

[0228] In a cross-section of the monofilament 10 in the longitudinal dimension direction including the central axis CA1 of the monofilament 10, three straight second observation lines 23 along the thickness direction of the coating film 12 were set such that the distances L231 and L232 between the second observation lines became 10 mm.

[0229] Then, line analysis of copper was performed along the second observation lines using STEM / EDX.

[0230] It should be noted that, as Figure 3C shown, when line analysis of copper was performed along the second observation line from the outer surface 12A to the inner surface 12B of the coating film 12, peaks appeared in the region where copper (Cu) is distributed.

[0231] At this time, the thickness of the coating film on the second observation line was set as T, and the region between the outer surface 12A of the coating film 12 on the second observation line and the point at a distance of 1 / 3T from the outer surface 12A of the coating film was set as the outer surface region 33. And the peak area of the EDX of copper measured in the outer surface region 33 was set as the copper content Cu1 on the surface layer side.

[0232] In addition, a region between the inner surface 12B of the coating film 12 on the second observation line and a point at a distance of 1 / 3T from the inner surface 12B of the coating film 12 is defined as the center-side region 34. And the peak area of copper in the EDX measured in the center-side region 34 is defined as the center-side copper content Cu2.

[0233] Then, based on the measurement results obtained on each second observation line, the ratio Cu of the copper content in the outer surface region to the copper content in the center-side region is calculated by the following formula (A). ratio . Then, the Cu ratio obtained from the measurement values on the three second observation lines is averaged and set as the average value of the ratio of the copper content in the outer surface region to the copper content in the center-side region of the single wire. In the table, the results are shown in the column of "Cu ratio (surface side / center side)".

[0234] Cu ratio = Cu1÷Cu2×100%... (A)

[0235] (2 - 6) Adhesion performance index

[0236] (Initial adhesion performance)

[0237] The single wires produced in the following experimental examples were embedded in unvulcanized rubber to form a single wire-rubber composite. Then, the single wire-rubber composite was vulcanized at 160 °C for 20 minutes to produce an evaluation specimen.

[0238] According to ASTM - D - 2229 - 93a, the steel cord was pulled out from the produced evaluation specimen, and the pull-out force at the time of pulling out was measured to evaluate the initial adhesion performance. The evaluation was expressed in terms of an index with the value of Experimental Example 16 set as 100. The larger the value, the better the result.

[0239] In Tables 1 to 3, the results are shown as "Initial" of the adhesion performance index.

[0240] (Wet heat resistance adhesion performance)

[0241] Evaluation specimens were produced under the same conditions as in the case of the initial adhesion performance.

[0242] Then, the evaluation specimens were subjected to a wet heat resistance test of being kept in a thermostatic and humidistatic furnace set to an atmospheric atmosphere, a temperature of 80 °C, and a relative humidity of 95% for 300 hours. For the evaluation specimens after the wet heat resistance test, the pull-out force was measured in the same manner as in the case of the initial adhesion performance to evaluate the wet heat resistance adhesion performance. The evaluation was expressed in terms of an index with the value of Experimental Example 16 taken as 100. The larger the value, the better the result.

[0243] In Tables 1 to 3, the results are shown as "humidity and heat resistance", which is an adhesive property index.

[0244] (2 - 7) Durability index

[0245] A single filament produced in each of the following experimental examples was embedded in unvulcanized rubber to form a single - filament / rubber composite. Then, the single - filament / rubber composite was vulcanized at 160 °C for 20 minutes. A test piece in the shape of a rope with a cross - section containing the single filament, having a thickness of 5 mm and a width of 10 mm, was taken out from the vulcanized single - filament / rubber composite using a cutter.

[0246] Then, as shown in Figure 10 , the obtained test piece 100 was hung on a first roller 1011, a second roller 1012, and a third roller 1013 with a roller diameter of 25 mm. When hanging the test piece 100 on the above - mentioned three rollers, as shown in Figure 10 , the positions of the rollers were adjusted such that the test piece 100 between the first roller 1011 and the second roller 1012 was parallel to the test piece 100 between the second roller 1012 and the third roller 1013. In addition, a load of 29.4 N was applied to the test piece 100 hung on the first roller 1011 to the third roller 1013 along the long - dimension direction. Then, as the movement in the first direction, the first roller 1011 to the third roller 1013 were rotated to move the test piece 100 in the Figure 10 direction of arrow 101 in the figure. Next, as the movement in the second direction, the first roller 1011 to the third roller 1013 were rotated in the reverse direction to move the test piece 100 in the direction opposite to arrow 101 in the figure. The operations of the above - mentioned movement in the first direction and the movement in the second direction were set as one group, and this action was repeated. The rotation speed of each roller was set such that 100 groups of the above - mentioned reciprocating movements could be performed within 1 minute. Then, the number of groups of the reciprocating movements of the test piece until the test piece broke was counted.

[0247] The results of Experimental Example 16 were set as 100 and shown as relative values for evaluation.

[0248] (Regarding the conditions of each experimental example)

[0249] Single filaments were produced and evaluated under the following conditions.

[0250] Experimental Examples 1 to 15 were examples, and Experimental Examples 16 to 21 were comparative examples.

[0251] [Experimental Example 1]

[0252] A single filament was manufactured through the following steps.

[0253] (1) Single - filament base material manufacturing process

[0254] On the surface of a steel wire rod 41, a Cu layer 42, a Co layer 43, and a Zn layer 44 were successively formed by plating to fabricate a single-wire base material 40 (see Figure 4 ).

[0255] The Cu layer was formed using cupric pyrophosphate as a plating solution. The Co layer was formed using cobalt sulfate as a plating solution. The Zn layer was formed using zinc sulfate as a plating solution.

[0256] When forming each layer, the current density, the wire speed of the wire rod supplied to the plating bath, and the composition and concentration of the plating solution were adjusted so that each layer would reach the target thickness.

[0257] The Co layer was formed using the plating apparatus 60 shown in Figure 6 . The distance L6 between the Co source 53, which is an electrode for supplying Co, and the wire 55 was kept constant for film formation. Since the configuration of the plating apparatus 60 has already been described, the description thereof is omitted here.

[0258] The evaluation results of the unevenness ratio of the Co layer thickness, which is the value obtained by dividing the difference between the maximum and minimum values of the Co layer thickness by the average thickness of the Co layer, along with the average values of the thicknesses of the Cu layer, Zn layer, and Co layer in the obtained single-wire base material are shown in Table 1.

[0259] (2) Heat treatment process

[0260] The single-wire base material was heat-treated by heating it at 600 °C for 5 seconds in an air atmosphere, causing the metal components to diffuse and forming a coating film.

[0261] (3) Drawing process

[0262] The obtained wire material with the coating film formed thereon was subjected to drawing processing to obtain a single wire with a coating film having a single-wire diameter of 0.55 mm.

[0263] The obtained single-wire base material and single wire were evaluated as described above. The evaluation results are shown in Table 1.

[0264] [Experimental Examples 2 to 15]

[0265] In the single-wire base material manufacturing process, when forming each layer, the current density, the wire speed of the wire rod supplied to the plating bath, and the composition and concentration of the plating solution were adjusted so that each layer would reach the target thickness. Except for this point, single wires were fabricated in the same manner as in Experimental Example 1.

[0266] The obtained single-wire base material and single wire were evaluated as described above. The evaluation results are shown in Tables 1 and 2.

[0267] [Experimental Examples 16, 17]

[0268] In the process of manufacturing the monofilament base material, the Co layer was not formed into a film, and only the Cu layer and the Zn layer were formed into a film. Then, when each layer was formed into a film, the current density, the wire speed of the wire supplied to the plating bath, and the composition and concentration of the plating solution were adjusted so that each layer became the target thickness. Except for the above points, the monofilament was produced in the same manner as in Experimental Example 1.

[0269] The obtained monofilament was evaluated as described above. The evaluation results are shown in Table 3.

[0270] [Experimental Examples 18 to 21]

[0271] In the process of manufacturing the monofilament base material, when each layer was formed into a film, the current density, the wire speed of the wire supplied to the plating bath, and the composition and concentration of the plating solution were adjusted so that each layer became the target thickness. In addition, when the Co layer was formed into a film, the plating apparatus 50 shown in Figure 5 was used. Therefore, when the Co layer was formed into a film, the distance between the Co source 53, which is the electrode for supplying Co, and the wire 55 was uneven depending on the position. Except for the above points, the monofilament was produced in the same manner as in Experimental Example 1.

[0272] The obtained monofilament base material and monofilament were evaluated as described above. The evaluation results are shown in Table 3.

[0273] [Table 1]

[0274]

[0275] [Table 2]

[0276]

[0277] [Table 3]

[0278]

[0279] From the results of Tables 1 to 3, it was confirmed that: in Experimental Examples 1 to 15, monofilaments having a coating film containing Cu, Zn, and Co were obtained, and when three observation regions were set, the average value of the area ratio occupied by Co in the observation regions was 1% or more and 50% or less.

[0280] Moreover, it was confirmed that: compared with the monofilaments of Experimental Examples 16 to 21 that did not satisfy the above necessary conditions, the monofilaments of Experimental Examples 1 to 15 were excellent in initial adhesion performance and moisture and heat resistance adhesion performance. That is, it was confirmed that the adhesion performance to rubber was excellent.

[0281] In addition, it was confirmed that the durability indexes of the monofilaments in Experimental Examples 1 to 15 were also excellent. Therefore, in a tire using a steel cord containing the monofilaments of Experimental Examples 1 to 15, the durability can be improved, the life can be extended, and thus the replacement frequency can be suppressed.

[0282] Description of Reference Numerals

[0283] 10: Monofilament

[0284] 11: Wire

[0285] 12: Coating

[0286] A: Region

[0287] CA1: Central axis

[0288] 12A: Outer surface

[0289] 12B: Inner surface

[0290] X: X-axis (long dimension direction)

[0291] Y: Y-axis

[0292] Z: Z-axis (thickness direction)

[0293] 21, 21A, 21B, 21C: Observation region

[0294] 22, 22A, 22B, 22C: First observation line

[0295] 23, 23A, 23B, 23C: Second observation line

[0296] L211, L212: Distance

[0297] L221, L222: Distance

[0298] L231, L232: Distance

[0299] 121: Co

[0300] 122: Alloy

[0301] L31, L32: Length of one side

[0302] 33: Outer surface region

[0303] 34: Central side region

[0304] T1: ZnO thickness

[0305] T: Thickness of coating

[0306] 40: Monofilament base material

[0307] 41: Wire

[0308] 42: Cu layer

[0309] 43: Co layer

[0310] 44: Zn layer

[0311] T42: Thickness

[0312] T43: Thickness

[0313] T44: Thickness

[0314] CA2: Central axis

[0315] X: X-axis (long dimension direction)

[0316] Y: Y-axis

[0317] Z: Z-axis

[0318] 50: Plating device

[0319] 51: Plating bath

[0320] 52: Plating solution

[0321] 53, 531, 532: Co source

[0322] 54: Electrode plate

[0323] 55: Wire

[0324] 551: First roller

[0325] 552: Second roller

[0326] L531, L532: Distance

[0327] 60: Plating device

[0328] 61: Metal mesh

[0329] L6: Distance

[0330] 70: Steel cord

[0331] 71: Monofilament

[0332] 80: Tire

[0333] 81: Tread

[0334] 82: Sidewall

[0335] 83: Bead

[0336] 84: Inner liner

[0337] 85: Carcass

[0338] 86: Belt layer

[0339] 87: Bead wire

[0340] CL: Center line

[0341] 91: Steel cord

[0342] 92: Rubber

[0343] 100: Test body

[0344] 1011: First roller

[0345] 1012: Second roller

[0346] 1013: Third roller

[0347] 101: Arrow.

Claims

1. A monofilament having a coating film, wherein, the coating film contains copper, zinc and cobalt, when the total content ratio of copper, zinc and cobalt in the coating film is set to 100% by mass, the content ratio of cobalt in the coating film is 0.5% by mass or more and 8% by mass or less, in a cross-section in the longitudinal dimension direction of the monofilament including the central axis of the monofilament, when three 1-μm square observation regions including the outer surface of the coating film are set along the central axis such that the distance between the observation regions is 10 mm, the average value of the area ratio occupied by cobalt in the observation regions is 34.4% or more and 50% or less, in the coating film, cobalt is distributed in an island shape, and copper and zinc exist in an alloy form, in the cross-section, when three straight first observation lines in the thickness direction of the coating film are set such that the distance between the first observation lines is 10 mm, and the thickness of the region where zinc oxide is distributed is measured along the first observation lines, the average value of the thickness of the region where zinc oxide is distributed on the first observation lines is 0.004 μm or more and 0.007 μm or less, in the cross-section, when three straight second observation lines in the thickness direction of the coating film are set such that the distance between the second observation lines is 10 mm, and the copper content is measured along the second observation lines, let the thickness of the coating film on the second observation lines be T, let the copper content in the outer surface region, which is the region between the outer surface of the coating film and the point at a distance of 1 / 3T from the outer surface of the coating film, on the second observation lines be Cu1, let the copper content in the central side region, which is the region between the inner surface of the coating film and the point at a distance of 1 / 3T from the inner surface of the coating film, on the second observation lines be Cu2, The ratio Cu of the content of copper in the outer surface region calculated by the following formula (A) to the content of copper in the center side region ratio has an average value of 90% or more and 97% or less, Cu ratio = Cu1 ÷ Cu2 × 100% (A).

2. The monofilament according to claim 1, wherein, when ten observation regions are set along the central axis such that the distance between the observation regions is 10 mm, the average value of the area ratio occupied by cobalt in the observation regions is 5% or more and 50% or less.

3. The monofilament according to claim 1 or 2, wherein the degree of processing is 3.4 or more and 3.8 or less.

4. A steel cord comprising at least one monofilament according to any one of claims 1 to 3.

5. A tire comprising the steel cord according to claim 4.

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