Copper-plated steel sheet

Abstract

A copper-plated steel sheet 10 comprises a base steel sheet 20 and a copper plating film 30 formed on at least one surface of the base steel sheet 20. The copper plating film 30 continuously covers the base steel sheet 20 at a thickness of 1.0 μm or more when viewed in a cross section parallel to the thickness direction, and has at least 25 protrusions 31 having a height of 1.0 μm or more per 1000 µm.

Description

[Technical Field]

[0001] This invention relates to copper-plated steel sheets. [Background technology]

[0002] Copper-plated steel sheets, which have a copper plating layer applied to a base steel sheet, have good brazing and solderability and are therefore widely used in various products such as double-wound pipes (automobile brake pipes, fuel supply pipes, etc.), welded pipes (grounding rods, etc.), and oil coolers. Copper-plated steel sheets are also used as a base material for sliding components such as cylindrical coiled bushings (sliding bearings) used in transmissions and the like. For example, Patent Document 1 proposes a sliding member (copper-plated steel sheet) comprising a sliding base material such as a steel sheet, a pure copper plating layer formed on the surface of the sliding base material, and a composite copper plating layer formed on the pure copper plating layer, which includes a plurality of lumpy portions containing copper and graphite and has a Vickers hardness of 120 or less. However, this sliding member is costly to form due to the composite copper plating layer, and may not have sufficient ability to maintain sliding properties (maintenance time of the coefficient of friction) when the load is large.

[0003] Furthermore, Patent Document 2 proposes a multilayer bearing comprising a metal substrate, a porous layer formed on its surface, and a resin composition impregnated and coated into the porous layer (for example, claim 1). Patent Document 2 describes a configuration in which a copper-plated steel sheet is used as the metal substrate and a sintered copper layer is used as the porous layer (0045, 0046, 0051). It is said that the anti-seizure effect is improved by providing such a substrate and porous layer. Although this bearing has excellent product performance, the manufacturing cost can be somewhat disadvantageous because copper plating and sintering are separate processes.

[0004] Furthermore, sliding resin coatings formed from lubricating resins and the like are known to have excellent sliding properties. For example, Patent Document 3 proposes a sliding resin coating (coated product) obtained by applying a paint for improving sliding properties, mainly composed of 95-50% by weight of a matrix resin whose film formation temperature is lower than the melting point of polytetrafluoroethylene resin, and 5-50% by weight of polytetrafluoroethylene resin with an average particle size of 2-40 μm, to the surface of a substrate such as a metal plate and baking it. However, such sliding resin coatings have low adhesion to substrates such as metal plates and tend to peel off from the substrate in sliding environments, so their ability to maintain sliding properties may not be sufficient.

[0005] On the other hand, as a technique for reducing surface irregularities of copper plating films, Patent Document 4 describes a method of forming a copper plating film on an insulating substrate on which a metal film for power supply is formed on the surface, while gradually increasing the current density Dk, and increasing the stirring speed V of the plating solution in accordance with the increase in current density Dk. Non-Patent Document 1 also describes a technique for forming a dendritic copper plating film on a Zn-Al substrate. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2018-197387 [Patent Document 2] International Publication No. 2010 / 079719 [Patent Document 3] Patent No. 4339960 [Patent Document 4] Japanese Patent Publication No. 2013-95968 [Non-patent literature]

[0007] [Non-Patent Document 1] H Tanabe and 7 others, “Cu Dendrite Crystal Ball Formation on a Zn-Al Substrate by Electroplating Method”, e-Journal of Surface Science and Nanotechnology, Vol. 20, No. 4, pp. 232-236, 2022 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The present invention aims to provide a copper-plated steel sheet in which the sliding resin coating is less likely to peel off when the sliding resin coating is applied on top of the copper-plated film. [Means for solving the problem]

[0009] As a result of diligent research on copper-plated steel sheets, the inventors discovered that a copper plating film having a specific surface shape exhibits excellent adhesion not only to the base steel sheet but also to a sliding resin film when such a film is applied on the copper plating film, thus completing the present invention.

[0010] In other words, the present invention relates to a copper-plated steel sheet comprising a base steel sheet and a copper plating film formed on at least one surface of the base steel sheet, The aforementioned copper plating film is It has dendritic protrusions, When viewed in cross-section parallel to the thickness direction, the base steel plate is continuously covered with a thickness of 1.0 μm or more, and the height is 1.0 μm or more. The aforementioned This is a copper-plated steel sheet with 25 or more protrusions per 1000 μm. [Effects of the Invention]

[0011] According to the present invention, when a sliding resin coating is applied on a copper-plated film, it is possible to provide a copper-plated steel sheet in which the sliding resin coating is less likely to peel off. [Brief explanation of the drawing]

[0012] [Figure 1] It is a schematic cross-sectional view of a copper-plated steel sheet according to an embodiment of the present invention. [Figure 2] It is a schematic cross-sectional view of a copper-plated steel sheet according to an embodiment of the present invention, further provided with a sliding resin film. [Figure 3] It is a schematic cross-sectional view of a copper-plated steel sheet for explaining a method of counting protrusions with a height of 1.0 μm or more. [Figure 4] It is a schematic diagram for explaining the formation process of the copper plating film. [Figure 5] It is a SEM image of the copper-plated steel sheet of Example 1. [Figure 6] It is a SEM image of the copper-plated steel sheet of Comparative Example 1. [Figure 7] It is a SEM image of the copper-plated steel sheet of Comparative Example 5. [Figure 8] It is a schematic diagram for explaining the pinion disk evaluation.

Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be specifically described. The present invention is not limited to the following embodiments, and it should be understood that within the scope not departing from the gist of the present invention, modifications, improvements, etc. may be appropriately added to the following embodiments based on the ordinary knowledge of those skilled in the art and still fall within the scope of the present invention. In addition, in this specification, the “%” display regarding components means “mass %” unless otherwise specified.

[0014] FIG. 1 is a schematic cross-sectional view of a copper-plated steel sheet according to an embodiment of the present invention. As shown in FIG. 1, the copper-plated steel sheet 10 according to the embodiment of the present invention includes a base steel sheet 20 and a copper plating film 30 formed on one surface of the base steel sheet 20. In FIG. 1, an example in which the copper plating film 30 is formed on one surface of the base steel sheet 20 is shown, but the copper plating film 30 may be formed on both surfaces of the base steel sheet 20.

[0015] The copper-plated steel sheet 10 according to an embodiment of the present invention may further comprise a sliding resin coating. Figure 2 shows a schematic cross-sectional view of the copper-plated steel sheet according to an embodiment of the present invention that further comprises a sliding resin coating. As shown in Figure 2, the sliding resin coating 40 is provided on the copper plating coating 30.

[0016] Herein, in this specification, "steel plate" means a steel material in the form of a plate (including strips). The base steel sheet 20 is not particularly limited, and various types of steel sheets such as hot-rolled steel sheets and cold-rolled steel sheets can be used. Among these, cold-rolled steel sheets are preferably used as the base steel sheet 20. The composition of the base steel sheet 20 is not particularly limited and can be selected appropriately depending on the application.

[0017] The copper plating film 30 is a film that exhibits good adhesion to the base steel sheet 20 and the sliding resin film 40. Therefore, by providing the copper plating film 30, when the sliding resin film 40 is applied on the copper plating film 30, the sliding resin film 40 is less likely to peel off from the copper-plated steel sheet 10. As a result, it becomes possible to maintain sliding properties over a long period of time even in sliding environments with high loads. The copper plating film 30 continuously covers the base steel sheet 20 with a thickness T of 1.0 μm or more when viewed in cross-section parallel to the thickness direction. This thickness T of the copper plating film 30 represents the minimum thickness of the copper plating film 30 covering the base steel sheet 20. Here, in this specification, "the copper plating film 30 continuously covers the base steel sheet 20" means a state in which there are no parts of the base steel sheet 20 that are exposed because the copper plating film 30 has not been formed.

[0018] By continuously coating the base steel sheet 20 with a copper plating film 30 of the thickness T described above, when a sliding resin film 40 is applied on the copper plating film 30, the sliding resin film 40 becomes less likely to peel off even under heavy sliding loads. From the viewpoint of stably ensuring this effect, the thickness T of the copper plating film 30 is preferably 1.3 μm or more. There is no particular upper limit to the thickness T of the copper plating film 30, but considering manufacturing costs, it is generally 10.0 μm or less, preferably 8.0 μm or less. The thickness T of the copper plating film 30 can be measured by observing a cross-section parallel to the thickness direction of the copper-plated steel sheet 10 using a microscope (e.g., SEM).

[0019] When the copper plating film 30 is viewed in cross-section parallel to the thickness direction, it has 25 or more protrusions 31 with a height of 1.0 μm or more per 1000 μm. If the number of protrusions 31 of this height is within this range, it can be said that the copper in the copper plating film 30 has grown sufficiently in a dendrite (tree-like crystal) form. Furthermore, if the copper plating film 30 has such protrusions 31, when the sliding resin film 40 is applied on the copper plating film 30, an anchoring effect is exerted between the copper plating film 30 and the sliding resin film 40, making it difficult for the sliding resin film 40 to peel off even in sliding environments with heavy loads. From the viewpoint of stably ensuring this effect, it is preferable that there be 40 or more protrusions 31 with a height of 1.0 μm or more per 1000 μm. The upper limit of the number of protrusions 31 with a height of 1.0 μm or more is not particularly limited, as a larger number makes it easier to obtain the anchoring effect, but it is generally 200 or less per 1000 μm.

[0020] Here, the method for counting protrusions 31 with a height of 1.0 μm or more will be explained using a schematic cross-sectional view (Figure 3) of the copper-plated steel sheet 10 parallel to the thickness direction. The number of protrusions 31 with a height of 1.0 μm or more is the number of parts that protrude from the base portion of the copper plating film 30 (provided that the height H is 1.0 μm or more). Here, the base portion of the copper plating film 30 refers to the portion that has the average thickness of the copper plating film 30. Therefore, in form a of Figure 3, there is a part that branches into three, but there is only one part that protrudes from the base portion, so it is counted as one protrusion 31. In form b of Figure 3, there is a part that branches into two, and the root of the part is raised. In this case, if the raised part at the root is less than 1.0 μm and the height H of the protrusion 31 is 1.0 μm or more, it is counted as two protrusions 31. On the other hand, if the protrusion at the base is 1.0 μm or more, even if the height H of the two protrusions 31 is 1.0 μm or more, it is counted as one protrusion 31. In morphology c of Figure 3, the two branched parts are connected at the top, but since there are two parts protruding from the base, it is counted as two protrusions 31. In morphology d of Figure 3, both ends appear to be protruding because they are lower than the base, but since they do not protrude from the base, they are not counted as protrusions 31. Furthermore, the height H of the projection 31 refers to the height in the direction perpendicular to the line connecting both ends of the base of the projection 31.

[0021] The amount of copper deposited on the copper plating film 30 is not particularly limited, but is preferably 10 to 150 g / m². 2 Comfortably 13-120 g / m 2 More preferably 15-60 g / m² 2 By controlling the amount of copper deposition within this range, a copper plating film 30 with good adhesion to the base steel sheet 20 and the sliding resin coating 40 can be stably obtained.

[0022] A discoloration-preventing treatment layer may be formed on the copper plating film 30 to suppress discoloration of the copper plating film 30. Providing a discoloration-preventing treatment layer is effective in suppressing discoloration of the copper plating film 30 over time, and is particularly effective in suppressing discoloration for several days after the formation of the copper plating film 30. The anti-discoloration treatment layer is not particularly limited as long as it does not impair the adhesion of the sliding resin film 40 that is formed thereafter. For example, the anti-discoloration treatment layer can be formed by immersing the base steel sheet 20 in an aqueous solution / dispersion of a commercially available anti-discoloration agent and drying it. Examples of commercially available anti-discoloration agents include VERZONE SeeU Guard D manufactured by Yamato Kasei Co., Ltd., a benzotriazole group-containing silane coupling agent manufactured by Shin-Etsu Chemical Co., Ltd., Gospel (C-30, C-70, or C-220) manufactured by Gospel Chemical Co., Ltd., Top Rinse CU-5 manufactured by Okuno Pharmaceutical Co., Ltd., KPC-2003 manufactured by Kinzoku Kako Gijutsu Kenkyusho Co., Ltd., CU-5600 manufactured by Meltex Co., Ltd., and BTZ-M manufactured by Kyodo Yakuhin Co., Ltd. The anti-discoloration treatment layer may be formed entirely on the copper plating film 30, or it may be formed only partially.

[0023] The sliding resin coating 40 is a coating formed from a resin that has sliding properties. Hereinafter, "sliding resin coating 40" as used herein refers to a resin coating in which a dynamic friction coefficient of 0.2 or less is obtained when a flat portion is taken from a plated steel sheet on which the target resin coating is formed and used as a test material, and a friction and wear test is performed using a surface properties measuring instrument (HEIDON-TYPE14) manufactured by Shinto Kagaku Co., Ltd. under the conditions of a load of 1N, a mating material of a 10mmφ SUS ball, a sliding (movement) speed of 150mm / min, and a test material temperature of 20~30℃. The sliding resin coating 40 is not particularly limited and can be any known in the art. For example, a resin coating with added lubricant or a self-lubricating resin coating can be used as the sliding resin coating 40. Among these, the sliding resin coating 40 is preferably a coating in which polytetrafluoroethylene (PTFE) resin is dispersed in a matrix resin. The matrix resin is not particularly limited, but examples include polyester resin, linear polymer polyester resin, acrylic resin, epoxy resin, polyurethane resin, phenoxy resin, phenolic resin, polyvinylidene fluoride resin (PVdF) / acrylic resin, and vinyl chloride resin.

[0024] The thickness of the sliding resin coating 40 is not particularly limited, but is typically 3 to 40 μm. By controlling the thickness of the sliding resin coating 40 within this range, stable sliding properties can be ensured.

[0025] A discoloration prevention treatment layer, as described above, may be formed between the copper plating film 30 and the sliding resin film 40.

[0026] The method for manufacturing the copper-plated steel sheet 10 according to the embodiment of the present invention is not particularly limited as long as it is a method capable of manufacturing the copper-plated steel sheet 10 having the above-described features, and can be carried out in accordance with known methods. An example of a method for manufacturing the copper-plated steel sheet 10 according to the embodiment of the present invention will be described below.

[0027] A method for manufacturing a copper-plated steel sheet 10 according to an embodiment of the present invention includes an electroplating step of forming a copper plating film 30 on at least one surface of a base steel sheet 20 by electroplating. In the electroplating process, it is preferable to perform copper sulfate plating after copper pyrophosphate plating.

[0028] Copper pyrophosphate plating is performed by immersing the base steel sheet 20 in a copper pyrophosphate plating solution. The conditions for copper pyrophosphate plating are not particularly limited and can be set appropriately in accordance with known methods. Typical conditions are as follows: Composition of copper pyrophosphate plating solution: 50 g / L copper pyrophosphate, 250 g / L potassium pyrophosphate, 10 g / L oxalic acid pH of copper pyrophosphate plating solution: 9.2 Temperature of copper pyrophosphate plating solution: 20-60°C Current density: 1~10A / dm 2 Time: 5-100 seconds The copper pyrophosphate plating can be performed once or multiple times under different conditions.

[0029] Copper sulfate plating is preferably performed by immersing the base steel sheet 20 in a copper sulfate plating solution while changing the flow rate of the copper sulfate plating solution. More specifically, it is more preferable to alternately repeat copper sulfate plating at a low flow rate (e.g., a flow rate of 0.30 m / sec or less) and copper sulfate plating at a high flow rate (e.g., a flow rate of 0.50 m / sec or more). Here, Figure 4 shows a schematic diagram illustrating the formation process of the copper plating film 30. When copper sulfate plating is performed at a low flow rate, copper ions tend to be insufficiently supplied to the plated surface, and the deposited copper is easily destroyed by bubbles caused by hydrogen generated during plating. As a result, particulate copper adheres to the surface (State A). On the other hand, when copper sulfate plating is performed at a high flow rate, copper ions are easily supplied to the plated surface. As a result, the plating grows along the surface, and a copper plating film 30 is formed to cover the entire surface to which particulate copper has adhered (State B). Next, when copper sulfate plating is performed again at a low flow rate, particulate copper adheres in the same way as in State A, and the copper grows as dendritic crystals (dendrites) (State C). Next, when copper sulfate plating is performed again at a high flow rate, a copper plating film 30 is formed to cover the entire surface, reinforcing the dendritic copper and increasing the thickness of the copper plating film 30 (State D). In this way, by repeatedly alternating between copper sulfate plating at a low flow rate and copper sulfate plating at a high flow rate, a copper plating film 30 having the protrusions 31 described above can be formed.

[0030] The number of repetitions of copper sulfate plating at low flow rate and copper sulfate plating at high flow rate, as well as the energizing time per cycle, should be appropriately adjusted according to the composition of the copper sulfate plating solution used, the current density, and the amount of plating to be achieved. Typically, the current density is 20-60 A / dm². 2 The energizing time per cycle (the energizing time for both low-flow and high-flow plating) is 1 to 30 seconds, and the number of repetitions is 5 to 50. Copper sulfate plating can be performed using an electroplating apparatus capable of flowing the plating solution (for example, a flow cell).

[0031] Other conditions for copper sulfate plating are not particularly limited and can be set as appropriate in accordance with known methods. Typical conditions are as follows: Composition of copper sulfate plating solution: 220 g / L copper sulfate, 45 g / L sulfuric acid pH of copper sulfate plating solution: 1.0 Temperature of copper sulfate plating solution: 20-50°C

[0032] A method for manufacturing a copper-plated steel sheet 10 according to an embodiment of the present invention may further include a resin film forming step of forming a sliding resin film 40 on a copper plating film 30. The resin film formation process is not particularly limited as long as a sliding resin film 40 can be formed, and can be carried out in accordance with known methods. In a typical resin film formation process, a sliding resin film 40 can be formed by applying a resin composition containing a matrix resin and a polytetrafluoroethylene (PTFE) resin onto the copper plating film 30 and drying it. The method for applying the resin composition is not particularly limited, and known methods such as dipping, bar coating, roll coating, spin coating, and spraying can be used. The resin composition can be applied in one or more steps so that the formed sliding resin film 40 reaches a predetermined thickness. The drying temperature is not particularly limited and can be set appropriately according to the composition of the resin composition.

[0033] When a discoloration prevention treatment layer is provided on the copper plating film 30, or between the copper plating film 30 and the sliding resin film 40, the discoloration prevention treatment process can be performed after the electroplating process, or between the electroplating process and the resin film formation process. The discoloration prevention treatment process involves applying a solution containing a discoloration inhibitor such as benzotriazole onto the copper plating film 30 and allowing it to dry. The method for applying the solution containing the discoloration inhibitor is not particularly limited, and the known methods described above can be used. Furthermore, the drying temperature is not particularly limited and can be set appropriately depending on the type of solution. [Examples]

[0034] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0035] (Examples 1-8) A cold-rolled steel sheet with a thickness of 0.5 mm was prepared as the base material. Electrolytic degreasing, water washing, and pickling were performed sequentially on this cold-rolled steel sheet. For electrolytic degreasing, the cold-rolled steel sheet was immersed in a sodium-based degreasing agent with a sodium concentration of 5% (at 60°C) with the anode, and a current density of 2 A / dm² was applied. 2 The process was performed for 10 seconds. For pickling, the sheet was immersed in a 2% hydrochloric acid solution (at 20°C) for 30 seconds. Next, the cold-rolled steel sheet was immersed in a copper pyrophosphate plating solution at 60°C, with a current density of 5 A / dm². 2 Copper pyrophosphate plating was performed for a time of 13 seconds. Next, the cold-rolled steel sheet plated with copper pyrophosphate was immersed in a copper sulfate plating solution at 35°C, and copper sulfate plating at low flow rate and copper sulfate plating at high flow rate were alternately performed under the current density and flow rate conditions of the copper sulfate plating solution shown in Table 1, for a total of 21 times (11 times at high flow rate and 10 times at low flow rate). In this way, a copper-plated steel sheet with a copper plating film was obtained. The composition and pH of the pyrophosphate plating solution and copper sulfate plating solution used are as follows. Composition of copper pyrophosphate plating solution: 50 g / L copper pyrophosphate, 250 g / L potassium pyrophosphate, 10 g / L oxalic acid pH of copper pyrophosphate plating solution: 9.2 Composition of copper sulfate plating solution: 220 g / L of copper sulfate, 45 g / L of sulfuric acid pH of copper sulfate plating solution: 1.0 In addition, the flow rate in this example refers to the speed of the plating solution flowing in the direction along the cold-rolled steel sheet between the electrodes (cold-rolled steel sheet - anode).

[0036] Next, the copper-plated steel sheet with a copper plating film was immersed in an aqueous solution of benzotriazole (60 °C) with a concentration of 2 g / L for 3 seconds and dried to form an anti-discoloration treatment layer. Next, a resin composition containing 25% of PTFE particles with an average particle size of 10 μm in a polyester resin (matrix resin) was applied to the copper-plated steel sheet with the anti-discoloration treatment layer formed thereon and dried at 200 °C to form a sliding resin film with a thickness of 20 μm. In some copper-plated steel sheets (Example 8), a sliding resin film was formed without forming an anti-discoloration treatment layer. Here, the average particle size means the particle size at 50% of the integrated value in the particle size distribution determined by the laser diffraction / scattering method.

[0037] (Comparative Examples 1 - 6) Instead of performing copper sulfate plating at a low flow rate and copper sulfate plating at a high flow rate alternately for a total of 21 times, only copper sulfate plating at a low flow rate or a high flow rate was performed 21 times. Next, an anti-discoloration treatment layer and a sliding resin film were formed in the same manner as in the above example.

[0038] The following evaluations were performed on the copper-plated steel sheets obtained in the above examples.

[0039] <Copper deposition amount of copper plating film> The copper-plated steel sheet with only the copper plating film formed was immersed in a mixed aqueous solution of ammonia aqueous solution (ammonia concentration 28%) and hydrogen peroxide to dissolve the copper plating film, and the mass difference [g] before and after the dissolution of the copper plating film was measured. The mass difference was divided by the area [m 2 to calculate the copper deposition amount [g / m 2 .

[0040] <Thickness T (minimum thickness) of copper plating film> A copper-plated steel sheet, with only a copper plating film formed on it, was cut so that a cross-section parallel to the thickness direction could be observed, and the cut surface was filled with resin to serve as the observation surface. Next, the resin-filled test piece was polished to a mirror finish by wet polishing. The mirror-finished surface was observed using a SEM (Hitachi High-Tech Corporation SU6600). In the 2,000x SEM image, the minimum thickness [μm] at a length of approximately 1,000 μm in the direction perpendicular to the thickness direction was defined as the thickness T of the copper plating film. For reference, SEM images of the copper-plated steel sheets of Example 1, Comparative Example 1, and Comparative Example 5 are shown in Figures 5 to 7, respectively (note that the magnification of the SEM images differs in each figure). Also, Figure 5 shows, as an example, the position of the measured thickness T of the copper plating film.

[0041] <Number of protrusions with a height of 1.0 μm or more in the copper plating film> SEM observation was performed in the same manner as for the thickness T of the copper plating film. In the SEM image, the number of protrusions [number of protrusions / 1000 μm] in a length of 1000 μm in the direction perpendicular to the thickness direction was counted according to the counting method described above. Figure 5 shows the locations of the counted protrusions (12 in total) as an example. In Figure 5, auxiliary lines for measuring the height of the protrusions are added only to the counted protrusions.

[0042] <Evaluation of the adhesion strength of copper plating films> The surface of a copper-plated steel sheet, which had only a copper plating film formed on it, was rubbed with an index finger, and the presence or absence of the copper plating film being removed was visually evaluated. In this evaluation, samples with no peeling of the copper plating film are classified as "good" (good adhesion), while samples with peeling of the copper plating film are classified as "poor" (poor adhesion).

[0043] <Evaluation of adhesion of sliding resin coatings> A copper-plated steel sheet with a sliding resin coating was punched out into a 6 mm diameter disc shape. The clearance was set to 0.1 mm. Next, the punched copper-plated steel sheet was cut so that a cross-section parallel to the thickness direction could be observed, and the cut surface was filled with resin to serve as the observation surface. Then, the resin-filled test piece was polished to a mirror finish by wet polishing. The length of the peeling of the sliding resin coating from the punched end face was measured on the mirror-polished surface. The evaluation criteria are as follows. Peel length less than 20 μm: Excellent adhesion of sliding resin coating. Peel length of 20 μm or more and less than 100 μm: Good adhesion of the sliding resin coating (pass) Peel length of 100 μm or more: Poor adhesion of the sliding resin coating (failure)

[0044] <Pin-on-disk evaluation> A 6mm diameter disc-shaped test piece was obtained by punching out a copper-plated steel sheet with a sliding resin coating. This test piece was evaluated using a pin-on-disk friction and wear tester (manufactured by Resca Co., Ltd., model FPR-2100). Specifically, as shown in Figure 8, the test piece was attached to the tip of the tester's pin (14mm in diameter), and the disc (material: SKD11) was rotated to slide it, and the time until the copper plating on the test piece was exposed was measured. The load during sliding was 3kgf, and the rotation speed was 32rpm. The evaluation criteria are as follows. Time until copper plating film is exposed: 200 hours or more: Excellent effect in maintaining sliding properties. Time until copper plating film is exposed: 100 hours or more but less than 200 hours: Good maintenance of sliding properties (pass) Time until copper plating film is exposed is less than 100 hours: Poor maintenance of sliding properties (failure)

[0045] The evaluation results are shown in Table 1.

[0046] [Table 1]

[0047] As shown in Table 1, the copper-plated steel sheets of Examples 1 to 8 had copper plating film thickness T and the number of protrusions within an appropriate range (see SEM image in Figure 5), resulting in good performance in each characteristic evaluation. In contrast, the copper-plated steel sheets of Comparative Examples 1-4 had particulate copper adhering to the surface (see SEM image in Figure 6), resulting in insufficient adhesion of the copper plating film and a small thickness T of the copper plating film. These also showed poor results in each characteristic evaluation. Furthermore, the copper-plated steel sheets of Comparative Examples 5 and 6 had a smooth copper plating film that grew along the surface (see SEM image in Figure 7). These sheets showed poor adhesion of the sliding resin film and poor results in the pin-on-disk evaluation.

[0048] As can be seen from the above results, the present invention provides a copper-plated steel sheet in which the sliding resin coating is less likely to peel off when the sliding resin coating is provided on the copper-plated film. For this reason, a copper-plated steel sheet with a sliding resin coating provided on the copper-plated film can maintain its sliding properties over a long period of time even in sliding environments with heavy loads. [Explanation of Symbols]

[0049] 10 Copper-plated steel sheet 20 Untreated steel sheet 30 Copper plating film 31 Protrusions 40. Sliding resin coating

Claims

1. A copper-plated steel sheet comprising a base steel sheet and a copper plating film formed on at least one surface of the base steel sheet, The copper plating film has dendrite-like protrusions, and when viewed in cross-section parallel to the thickness direction, it continuously covers the base steel sheet with a thickness of 1.0 μm or more, and the number of protrusions with a height of 1.0 μm or more is 25 per 1000 μm or more.

2. The copper-plated steel sheet according to claim 1, further comprising a sliding resin film provided on the copper-plated film.

3. The copper-plated steel sheet according to claim 1, further comprising a discoloration prevention treatment layer provided on the copper plating film.

4. The copper-plated steel sheet according to claim 2, further comprising a discoloration prevention treatment layer provided between the copper plating film and the sliding resin film.

5. A copper-plated steel sheet according to any one of claims 1 to 4, used in a sliding member.

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