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

Copper-plated steel sheet

[0001] The present invention relates to a copper-plated steel sheet.

[0002] Copper-plated steel sheets, which have a copper plating layer formed on a base steel sheet, have excellent brazability and solderability and are therefore widely used in various products such as double-wrapped pipes (e.g., automobile brake pipes, fuel supply pipes), welded pipes (e.g., ground rods), and oil coolers. Copper-plated steel sheets are also used as substrates for sliding members such as cylindrical wound bushings (slide bearings) used in transmissions, etc. For example, Patent Document 1 proposes a sliding member (copper-plated steel sheet) comprising a sliding substrate such as a steel sheet, a pure copper plating layer formed on the surface of the sliding substrate, and a composite copper plating layer formed on the pure copper plating layer, which includes a plurality of copper- and graphite-containing lumps and has a Vickers hardness of 120 or less. However, this sliding member is costly to form the composite copper plating layer, and may not be able to maintain its sliding properties (friction coefficient maintenance time) sufficiently under heavy loads.

[0003] Furthermore, Patent Document 2 proposes a multilayer bearing comprising a metal substrate, a porous layer formed on the surface thereof, and a resin composition impregnated and coated on the porous layer (e.g., 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). The provision of such a substrate and porous layer is said to improve the anti-seizure effect. While this bearing has excellent product performance, the copper plating and sintering are performed in separate manufacturing processes, which can be somewhat disadvantageous in terms of manufacturing costs.

[0004] Furthermore, a sliding resin film formed from a lubricating resin or the like is known as a film with excellent sliding properties. For example, Patent Document 3 proposes a sliding resin film (coated object) in which a sliding property improving paint containing, as main components, 95 to 50 wt % of a matrix resin whose film-forming temperature is lower than the melting point of polytetrafluoroethylene resin and 5 to 50 wt % of a polytetrafluoroethylene resin having an average particle size of 2 to 40 μm is applied to the surface of a substrate such as a metal plate and baked. However, such a sliding resin film has poor adhesion to a substrate such as a metal plate and is easily peeled off from the substrate in a sliding environment, so that the ability to maintain sliding properties may be insufficient.

[0005] On the other hand, as a technique for reducing the unevenness of the surface of a copper plating film, Patent Document 4 describes a method in which, when a copper plating film is formed on an insulating base material having a metal film for power supply formed on its surface while gradually increasing the current density Dk, the stirring speed V of the plating solution is increased in accordance with the increase in current density Dk. Also, Non-Patent Document 1 discloses a technique for forming a dendritic copper plating film on a Zn—Al substrate.

[0006] JP 2018-197387 A International Publication No. 2010 / 079719 Japanese Patent No. 4339960 A Japanese Patent Application Laid-Open No. 2013-95968 A

[0007] 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

[0008] An object of the present invention is to provide a copper-plated steel sheet in which, when a slidable resin film is provided on a copper-plated film, the slidable resin film is unlikely to peel off.

[0009] As a result of extensive research into copper-plated steel sheets, the present inventors have discovered that a copper-plated film having a specific surface shape not only has excellent adhesion to a base steel sheet, but also has excellent adhesion to a sliding resin film when the sliding resin film is provided on the copper-plated film, and have thus completed the present invention.

[0010] That is, the present invention provides 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, wherein the copper plating film continuously covers the base steel sheet to a thickness of 1.0 μm or more when viewed in a cross section parallel to the thickness direction, and the copper-plated steel sheet has 25 or more protrusions with a height of 1.0 μm or more per 1000 μm.

[0011] According to the present invention, it is possible to provide a copper-plated steel sheet in which, when a slidable resin film is provided on a copper-plated film, the slidable resin film is not easily peeled off.

[0012] FIG. 1 is a schematic cross-sectional view of a copper-plated steel sheet according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a copper-plated steel sheet according to an embodiment of the present invention, further comprising a slidable resin film. FIG. 3 is a schematic cross-sectional view of a copper-plated steel sheet for explaining a method for counting protrusions having a height of 1.0 μm or more. FIG. 4 is a schematic view for explaining a process for forming a copper plating film. FIG. 5 is an SEM image of the copper-plated steel sheet of Example 1. FIG. 6 is an SEM image of the copper-plated steel sheet of Comparative Example 1. FIG. 7 is an SEM image of the copper-plated steel sheet of Comparative Example 5. FIG. 8 is a schematic view for explaining pin-on-disk evaluation.

[0013] Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments, and it should be understood that modifications and improvements to the following embodiments, as appropriate, based on the ordinary knowledge of those skilled in the art, without departing from the spirit of the present invention, also fall within the scope of the present invention. In this specification, the "%" designation for components means "% by 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 an embodiment of the present invention comprises a base steel sheet 20 and a copper plating film 30 formed on one surface of the base steel sheet 20. Note that Fig. 1 shows an example in which the copper plating film 30 is formed on one surface of the base steel sheet 20, 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 include a slidable resin film. A schematic cross-sectional view of a copper-plated steel sheet according to an embodiment of the present invention further including a slidable resin film is shown in Fig. 2. As shown in Fig. 2, the slidable resin film 40 is provided on the copper plating film 30.

[0016] Here, in this specification, "steel sheet" refers to a steel material in a plate shape (including a strip shape). The base steel sheet 20 is not particularly limited, and various steel sheets such as a hot-rolled steel sheet and a cold-rolled steel sheet can be used. Among them, a cold-rolled steel sheet is preferably used as the base steel sheet 20. The composition of the base steel sheet 20 is also not particularly limited, and may be selected appropriately depending on the application.

[0017] The copper plating film 30 has good adhesion to the base steel sheet 20 and the slidable resin film 40. Therefore, by providing the copper plating film 30, when the slidable resin film 40 is provided on the copper plating film 30, the slidable resin film 40 is less likely to peel off from the copper-plated steel sheet 10. As a result, it is possible to maintain slidability for a long period of time even under a sliding environment with a large load. When viewed in a cross section parallel to the thickness direction, the copper plating film 30 continuously covers the base steel sheet 20 with a thickness T of 1.0 μm or more. The thickness T of the copper plating film 30 refers to 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 that there is no portion of the base steel sheet 20 where the copper plating film 30 is not formed and the copper plating film 30 is not exposed.

[0018] By continuously coating the base steel sheet 20 with the copper plating film 30 having the above-described thickness T, when a slidable resin film 40 is provided on the copper plating film 30, the slidable resin film 40 is less likely to peel off even under a sliding environment with a heavy load. From the viewpoint of stably ensuring this effect, the thickness T of the copper plating film 30 is preferably 1.3 μm or more. Note that the upper limit of the thickness T of the copper plating film 30 is not particularly limited, but is generally 10.0 μm or less, preferably 8.0 μm or less, taking into consideration production costs and the like. The thickness T of the copper plating film 30 can be measured by observing a cross section of the copper-plated steel sheet 10 parallel to the thickness direction using a microscope (e.g., SEM).

[0019] When viewed in a cross section parallel to the thickness direction, the copper plating film 30 has 25 or more protrusions 31 per 1000 μm, each having a height of 1.0 μm or more. When the number of protrusions 31 of such height is within this range, it can be said that the copper in the copper plating film 30 has sufficiently grown in a dendrite (tree-like crystal) shape. Furthermore, if the copper plating film 30 has such protrusions 31, when a slidable resin film 40 is provided on the copper plating film 30, an anchor effect acts between the copper plating film 30 and the slidable resin film 40, making the slidable resin film 40 less likely to peel off even under a sliding environment with a heavy load. From the viewpoint of reliably ensuring this effect, it is preferable that the number of protrusions 31 per 1000 μm be 40 or more. The upper limit of the number of protrusions 31 of 1.0 μm or more in height is not particularly limited, as the anchor effect is more easily obtained as the number increases, but it is generally 200 or less per 1000 μm.

[0020] Here, a method for counting protrusions 31 with a height of 1.0 μm or more will be described using a schematic cross-sectional view ( FIG. 3 ) of a cross section parallel to the thickness direction of the copper-plated steel sheet 10. The number of protrusions 31 with a height of 1.0 μm or more refers to the number of portions protruding from the base portion of the copper plating film 30 (with a height H of 1.0 μm or more). Here, the base portion of the copper plating film 30 refers to the portion of the copper plating film 30 having an average thickness. Therefore, in the configuration a of FIG. 3 , although there are three branched portions, there is only one portion protruding from the base portion, so it is counted as one protrusion 31. In the configuration b of FIG. 3 , there are two branched portions, and the base portions of these portions are raised. In this case, if the protrusion of the base portion 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 two protrusions 31 is 1.0 μm or more, they are counted as one protrusion 31. In form c of Figure 3, the two branched portions are connected at the top, but since there are two portions protruding from the base, they are counted as two protrusions 31. In form d of Figure 3, both ends are lower than the base and so it appears to be protruding, but since it does not protrude from the base, it is not counted as a protrusion 31. Furthermore, the height H of the protrusion 31 means the height in a direction perpendicular to the line connecting both ends of the base of the protrusion 31.

[0021] The copper coating weight of the copper plating film 30 is not particularly limited, but is preferably 10 to 150 g / m 2 , more preferably 13 to 120 g / m 2 , more preferably 15 to 60 g / m 2 By controlling the copper deposition amount within this range, it is possible to stably obtain a copper plating film 30 that has good adhesion to the base steel sheet 20 and the slidable resin film 40.

[0022] A discoloration prevention treatment layer may be formed on the copper plating film 30 to prevent discoloration of the copper plating film 30. Providing the discoloration prevention treatment layer is effective in preventing discoloration of the copper plating film 30 over time, and is particularly effective in preventing discoloration for several days after the formation of the copper plating film 30. The discoloration prevention treatment layer is not particularly limited as long as it does not impair the adhesion of the subsequently formed slidable resin film 40. For example, the discoloration prevention treatment layer can be formed by immersing the base steel sheet 20 in an aqueous solution / dispersion of a commercially available discoloration prevention agent and drying it. Examples of commercially available anti-tarnish agents include VERZONE See-U-Guard D manufactured by Daiwa 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 Chemical Industries Co., Ltd., KPC-2003 manufactured by Metal Chemical Engineering Research Institute Co., Ltd., CU-5600 manufactured by Meltex Inc., and BTZ-M manufactured by Kyodo Yakuhin Co., Ltd. The anti-tarnish treatment layer may be formed entirely or partially on the copper plating film 30.

[0023] The slidable resin film 40 is a film formed from a resin having slidability. Here, the term "slidable resin film 40" as used herein refers to a resin film having a dynamic friction coefficient of 0.2 or less when a friction and wear test is conducted using a surface property tester (HEIDON-TYPE 14) manufactured by Shinto Scientific Co., Ltd., under the following conditions: a load of 1 N, a 10 mm diameter SUS ball as the mating material, a sliding (movement) speed of 150 mm / min, and a temperature of 20 to 30°C. The slidable resin film 40 is not particularly limited, and any known material in the technical field can be used. For example, a resin film containing a lubricant or a self-lubricating resin film can be used as the slidable resin film 40. Among these, a film in which polytetrafluoroethylene (PTFE) resin is dispersed in a matrix resin is preferred as the slidable resin film 40. The matrix resin is not particularly limited, but examples thereof include polyester resin, linear polymer polyester resin, acrylic resin, epoxy resin, polyurethane resin, phenoxy resin, phenol resin, polyvinylidene fluoride resin (PVdF) / acrylic resin, and vinyl chloride resin.

[0024] The thickness of the slidable resin film 40 is not particularly limited, but is preferably 3 to 40 μm. By controlling the thickness of the slidable resin film 40 to fall within this range, stable slidability can be ensured.

[0025] The aforementioned discoloration prevention treatment layer may be formed between the copper plating film 30 and the slidable resin film 40 .

[0026] The method for producing 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 producing the copper-plated steel sheet 10 having the above-described characteristics, and can be carried out in accordance with a known method. An example of the method for producing the copper-plated steel sheet 10 according to the embodiment of the present invention will be described below.

[0027] The method for producing 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 by electroplating on at least one surface of a base steel sheet 20. In the electroplating step, copper pyrophosphate plating is preferably performed followed by copper sulfate plating.

[0028] Copper pyrophosphate plating is performed by immersing the base steel sheet 20 in a copper pyrophosphate plating solution. The conditions for the copper pyrophosphate plating are not particularly limited and can be appropriately set 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 to 60°C Current density: 1 to 10 A / dm 2 Time: 5 to 100 seconds The copper pyrophosphate plating may be carried out 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 varying the flow rate of the copper sulfate plating solution. More specifically, copper sulfate plating at a low flow rate (e.g., 0.30 m / s or less) and copper sulfate plating at a high flow rate (e.g., 0.50 m / s or more) are preferably performed alternately. A schematic diagram illustrating the process of forming the copper plating film 30 is shown in FIG. 4 . Copper sulfate plating performed at a low flow rate tends to result in an insufficient supply of copper ions to the plating surface, and the deposited copper is easily destroyed by hydrogen bubbles generated during plating. As a result, copper particles adhere to the surface (State A). On the other hand, copper sulfate plating performed at a high flow rate tends to provide a sufficient supply of copper ions to the plating surface. As a result, the plating grows along the surface, forming a copper plating film 30 that covers the entire surface to which the copper particles adhere (State B). Next, when copper sulfate plating is performed again at a low flow rate, particulate copper adheres 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 so as to cover the entire surface, thereby reinforcing the dendritic copper and increasing the thickness of the copper plating film 30 (state D). By alternately repeating copper sulfate plating at a low flow rate and copper sulfate plating at a high flow rate in this manner, a copper plating film 30 having the protrusions 31 described above can be formed.

[0030] The number of times copper sulfate plating at a low flow rate and copper sulfate plating at a high flow rate are repeated and the current application time per cycle may be adjusted appropriately depending on the composition of the copper sulfate plating solution used, the current density, the plating amount to be obtained, etc. Typically, when the current density is 20 to 60 A / dm 2 The current application time per cycle (current application time for plating at a low flow rate and plating at a high flow rate) is 1 to 30 seconds, and the number of cycles is 5 to 50. Copper sulfate plating can be performed using an electroplating device (such as a flow cell) that can cause the plating solution to flow.

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

[0032] The manufacturing method of the copper-plated steel sheet 10 according to the embodiment of the present invention may further include a resin film formation step of forming a slidable resin film 40 on the copper plating film 30. The resin film formation step is not particularly limited as long as it can form the slidable resin film 40, and can be performed according to a known method. In a typical resin film formation step, the slidable resin film 40 can be formed by applying a resin composition containing a matrix resin and a polytetrafluoroethylene (PTFE) resin to 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 once or multiple times so that the slidable resin film 40 has a predetermined thickness. The drying temperature is not particularly limited and can be set appropriately depending on 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 slidable resin film 40, a discoloration prevention treatment step can be performed after the electroplating step or between the electroplating step and the resin film formation step. The discoloration prevention treatment step can be performed by applying a solution containing a discoloration prevention agent such as benzotriazole to the copper plating film 30 and drying it. The method for applying the solution containing the discoloration prevention agent is not particularly limited, and the above-mentioned known methods can be used. The drying temperature is not particularly limited and can be set appropriately depending on the type of solution.

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

[0035] (Examples 1 to 8) A cold-rolled steel sheet having a thickness of 0.5 mm was prepared as a base steel sheet. This cold-rolled steel sheet was subjected to electrolytic degreasing, water washing, and pickling in this order. The electrolytic degreasing was carried out by immersing the cold-rolled steel sheet as an anode in a sodium-based degreasing agent (temperature: 60°C) with a sodium concentration of 5%, and applying a current density of 2 A / dm 2 The pickling was carried out by immersing the cold-rolled steel sheet in a 2% hydrochloric acid aqueous solution (temperature: 20°C) for 30 seconds. Next, the cold-rolled steel sheet was immersed in a copper pyrophosphate plating solution at 60°C, and the current density was set to 5 A / dm 2 Copper pyrophosphate plating was performed for 13 seconds. Next, the cold-rolled steel sheet that had been subjected to copper pyrophosphate plating was immersed in a copper sulfate plating solution at 35°C, and copper sulfate plating at a low flow rate and copper sulfate plating at a 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 cycles (11 cycles at a high flow rate and 10 cycles at a low flow rate). In this way, a copper-plated steel sheet having a copper plating film formed thereon was obtained. The compositions and pH of the pyrophosphate plating solution and copper sulfate plating solution used were as follows: Composition of copper pyrophosphate plating solution: copper pyrophosphate 50 g / L, potassium pyrophosphate 250 g / L, oxalic acid 10 g / L pH of copper pyrophosphate plating solution: 9.2 Composition of copper sulfate plating solution: copper sulfate 220 g / L, sulfuric acid 45 g / L pH of copper sulfate plating solution: 1.0 Furthermore, 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 on which the copper plating film was formed was immersed in a 2 g / L aqueous benzotriazole solution (60 ° C) for 3 seconds and dried to form a discoloration prevention treatment layer. Next, a resin composition containing 25% PTFE particles with an average particle size of 10 μm in a polyester resin (matrix resin) was applied to the copper-plated steel sheet on which the discoloration prevention treatment layer was formed, and dried at 200 ° C to form a 20 μm thick sliding resin film. In some copper-plated steel sheets (Example 8), the sliding resin film was formed without forming a discoloration prevention treatment layer. Here, the average particle size means the particle size at 50% of the integrated value in the particle size distribution determined by laser diffraction / scattering method.

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

[0038] The copper-plated steel sheets obtained in the above examples were evaluated as follows.

[0039] <Copper deposition weight of copper plating film> A copper-plated steel sheet on which only a copper plating film was formed was immersed in a mixed aqueous solution of an ammonia solution (ammonia concentration 28%) and hydrogen peroxide to dissolve the copper plating film, and the mass difference [g] before and after dissolution of the copper plating film was measured. The mass difference was calculated as the area [m 2 ] to obtain the copper coating amount [g / m 2 ] was calculated.

[0040] <Thickness T (Minimum Thickness) of Copper Plating Film> A copper-plated steel sheet having only a copper plating film formed thereon was cut so that a cross section parallel to the thickness direction could be observed, and resin was embedded so that the cut surface served as the observation surface. The resin-embedded test specimen was then subjected to a mirror finish by wet polishing. The mirror-finished surface was observed using an SEM (SU6600 model, manufactured by Hitachi High-Technologies Corporation). The minimum thickness [μm] at a length of approximately 1000 μm perpendicular to the thickness direction in a 2000x SEM image was taken as the thickness T of the copper plating film. For reference, SEM images of the copper-plated steel sheets of Example 1, Comparative Examples 1, and 5 are shown in Figures 5 to 7, respectively (note that the magnification of the SEM images differs in each figure). Figure 5 also 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 on 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 [protrusions / 1000 μm] per 1000 μm length in the direction perpendicular to the thickness direction was counted according to the counting method described above. Note that FIG. 5 shows the positions of the counted protrusions (12 in total) as an example. In FIG. 5, auxiliary lines for measuring the height of the protrusions are added only to the counted protrusions.

[0042] <Evaluation of Adhesion of Copper Plating Film> The surface of a copper-plated steel sheet on which only a copper plating film was formed was rubbed with an index finger, and the presence or absence of peeling of the copper plating film was visually evaluated. In this evaluation, a case in which the copper plating film did not peel off was evaluated as good (good adhesion), and a case in which the copper plating film peeled off was evaluated as poor (poor adhesion).

[0043] <Evaluation of Adhesion of Slidable Resin Film> A copper-plated steel sheet on which a slidable resin film had been formed was punched into a disk having a diameter of 6 mm. The clearance was 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 resin filling was carried out so that the cut surface served as the observation surface. Next, the resin-filled measurement test piece was subjected to a mirror finish by wet polishing. The mirror-finished surface was measured for the peel length of the slidable resin film from the punched edge. The evaluation criteria were as follows: Peel length less than 20 μm: excellent adhesion of the slidable resin film Peel length 20 μm or more but less than 100 μm: good adhesion of the slidable resin film (pass) Peel length 100 μm or more: poor adhesion of the slidable resin film (fail)

[0044] <Pin-on-Disk Evaluation> A disc-shaped test piece with a diameter of 6 mm was obtained by punching from the copper-plated steel sheet on which the slidable resin film had been formed. This test piece was evaluated using a pin-on-disk friction and wear tester (Model FPR-2100, manufactured by Rhesca Corporation). Specifically, as shown in FIG. 8 , the test piece was attached to the tip of the pin (diameter 14 mm) of the tester, and the disc (material: SKD11) was rotated to cause sliding, and the time until the copper plating film on the test piece was exposed was measured. The load during sliding was 3 kgf, and the rotation speed was 32 rpm. The evaluation criteria were as follows: Time until the copper plating film was exposed: 200 hours or more: Excellent effect of maintaining slidability Time until the copper plating film was exposed: 100 hours or more but less than 200 hours: Good effect of maintaining slidability (pass) Time until the copper plating film was exposed: Less than 100 hours: Poor effect of maintaining slidability (fail)

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

[0046]

[0047] As shown in Table 1, the copper-plated steel sheets of Examples 1 to 8 had copper plating film thicknesses T and protrusion numbers within appropriate ranges (see the SEM image in FIG. 5), and therefore achieved good results in each characteristic evaluation. In contrast, the copper-plated steel sheets of Comparative Examples 1 to 4 had copper particles attached to the surface (see the SEM image in FIG. 6), and the copper plating film had insufficient adhesion and a small thickness T. These sheets also achieved poor results in each characteristic evaluation. Furthermore, the copper-plated steel sheets of Comparative Examples 5 and 6 had smooth copper plating films grown along the surface (see the SEM image in FIG. 7). These sheets achieved poor results in the adhesion of the slidable resin film and the pin-on-disk evaluation.

[0048] As can be seen from the above results, the present invention can provide a copper-plated steel sheet in which a slidable resin film is formed on a copper-plated film and the slidable resin film is not easily peeled off. Therefore, the copper-plated steel sheet in which a slidable resin film is formed on a copper-plated film can maintain its slidability for a long period of time even in a sliding environment where a large load is applied.

[0049] 10 Copper-plated steel sheet 20 Base steel sheet 30 Copper-plated film 31 Protrusion 40 Sliding resin film

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, wherein the copper plating film continuously covers the base steel sheet to a thickness of 1.0 μm or more when viewed in a cross section parallel to the thickness direction, and the copper plating film has 25 or more protrusions with a height of 1.0 μm or more per 1,000 μm.

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

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