Copper-plated steel sheet

Abstract

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

Description

[0001] This invention relates to a copper-plated steel sheet.[Background Art]

[0002] Copper-plated steel sheets with copper plated layers provided on base steel sheets are widely used in various products such as double-wound pipes (automotive brake pipes, fuel supply pipes, etc.), welded pipes (ground rods, etc.), and oil coolers because of their good brazeability and solderability. The copper-plated steel sheets are also used as base materials for sliding members such as cylindrical wound bushings (slide bearings) used in transmissions and the like.

[0003] For example, Patent Literature 1 proposes a sliding member (copper-plated steel sheet) including a sliding base material such as a steel sheet, a pure copper plated layer formed on the surface of the sliding base material, and a composite copper plated layer formed on the pure copper plated layer and including a plurality of massive portions containing copper and graphite, the composite copper plated layer having a Vickers hardness of 120 or less. However, this sliding member requires high costs to form the composite copper plated layer, and the capability to maintain slidability (maintaining time of friction coefficient) may be insufficient when the applied load is large.

[0004] In addition, Patent Literature 2 proposes a multilayer bearing comprised of a metal base material, a porous layer formed on the surface of the metal base material, and a resin composition penetrated into and coated onto the porous layer (for example, claim 1). Patent Literature 2 discloses an embodiment in which a copper-plated steel sheet is used as the metal base material and a sintered copper layer is used as the porous layer (paragraphs

[0045] ,

[0046] ,

[0005] . It discloses that providing such a base material and porous layer improves the seizure prevention effect. This bearing has excellent product performance, but it may be somewhat disadvantageous for manufacturing cost, because copper plating and sintering are separate steps in terms of manufacturing.

[0006] Further, sliding resin films formed from lubricating resins are known as films with excellent slidability. For example, Patent Literature 3 proposes a sliding resin film (coated product) obtained by applying a slidability improvement coating material to a surface of a base material such as a metal plate and baking it, the slidability improvement coating material primarily containing 95 to 50 wt% of a matrix resin having a film formation temperature lower than the melting point of polytetrafluoroethylene resin, and 5 to 50 wt% of polytetrafluoroethylene resin having an average particle size of 2 to 40 µm. However, such a sliding resin film has low adhesion to the base material such as a metal plate and easily peel off from the base material in a sliding environment, so that its ability to maintain sliding properties may not be sufficient.

[0007] On the other hand, as a technique for reducing irregularities on the surface of the copper plated film, Patent Literature 4 describes a method in which an agitation speed V of the plating solution is increased in accordance with an increase in current density Dk when forming the copper plated film while gradually increasing the current density Dk on an insulating substrate having a metal film for power supply, which is formed on the surface of the insulating substrate. Non-Patent Literature 1 also describes a technique for forming a dendritic copper plated film on a Zn-Al substrate.[Citation List][Patent Literatures]

[0008] [PTL 1] Japanese Patent Application Publication No. 2018-197387 A [PTL 2] WO 2010 / 079719 A1 [PTL 3] Japanese Patent No. 4339960 B [PTL 4] Japanese Patent Application Publication No. 2013-95968 A [Non-Patent Literature]

[0009] [Non-Patent Literature 1] H Tanabe, et.al., "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[Summary of Invention][Technical Problem]

[0010] An object of the present invention is to provide a copper-plated steel sheet in which a sliding resin film is difficult to peel off when the sliding resin film is provided on the copper plated film.[Solution to Problem]

[0011] As a result of intensive studies for copper-plated steel sheets, the present inventors have found that a copper plated film having a specific surface shape has excellent adhesion not only to a base steel sheet but also to a sliding resin film when the sliding resin film is provided on the copper plated film, and thus completed the present invention.

[0012] That is, the present invention relates to a copper-plated steel sheet comprising a base steel sheet and a copper plated film formed on at least one surface of the base steel sheet, wherein the copper plated film continuously covers the base steel sheet with a thickness of 1.0 µm or more in a cross-section parallel to a thickness direction of the copper plated film, and has 25 or more protrusions having a height of 1.0 µm or more per 1000 µm.[Advantageous Effects of Invention]

[0013] According to the present invention, it is possible to provide a copper-plated steel sheet in which a sliding resin film is difficult to peel off when the sliding resin film is applied on the copper plated film.[Brief Description of Drawings]

[0014] [Fig. 1] Figure 1 is a schematic cross-sectional view of a copper-plated steel sheet according to an embodiment of the present invention. [Fig. 2] Figure 2 is a schematic cross-sectional view of a copper-plated steel sheet further including a sliding resin film according to an embodiment of the present invention. [Fig. 3] Figure 3 is a schematic cross-sectional view of a copper-plated steel sheet for explaining a method of counting protrusions having a height of 1.0 µm or more. [Fig. 4] Figure 4 is a schematic view for explaining a formation process of a copper plated film. [Fig. 5] Figure 5 is a SEM image of a copper-plated steel sheet according to Example 1. [Fig. 6] Figure 6 is a SEM image of a copper-plated steel sheet according to Comparative Example 1. [Fig. 7] Figure 6 is a SEM image of a copper-plated steel sheet according to Comparative Example 5. [Fig. 8] Figure 8 is a schematic view for explaining pin-on-disk evaluation. [Description of Embodiments]

[0015] Hereinafter, embodiments of the present invention will be specifically described. It should be understood that the invention is not limited to the following embodiments, and those which have appropriately added changes, improvements and the like to the following embodiments based on knowledge of a person skilled in the art without departing from the spirit of the invention fall within the scope of the invention.

[0016] It should be noted that, as used herein, the expression "%" in relation to any component means "% by mass", unless otherwise specified.

[0017] Figure 1 is a schematic cross-sectional view of a copper-plated steel sheet according to an embodiment of the present invention.

[0018] As shown in Figure 1, a copper-plated steel sheet 10 according to an embodiment of the present invention includes a base steel sheet 20 and a copper plated film 30 formed on one surface of the base steel sheet 20. Although FIG. 1 shows an example in which the copper plated film 30 is formed on one surface of the base steel sheet 20, the copper plated films 30 may be formed on both surfaces of the base steel sheet 20.

[0019] The copper-plated steel sheet 10 according to an embodiment of the present invention can further include a sliding resin film. Here, Figure 2 shows a schematic cross-sectional view of a copper-plated steel sheet according to an embodiment of the present invention, which further includes a sliding resin coating.

[0020] As shown in Figure 2, the sliding resin film 40 is provided on the copper plated film 30.

[0021] Here, the term "steel sheet" as used herein means a plate-shaped (including strip-shaped) steel material.

[0022] The base steel sheet 20 is not particularly limited, and various steel sheets such as hot-rolled steel sheets and cold-rolled steel sheets can be used. Among them, the cold-rolled steel sheet is preferably used as the base steel sheet 20.

[0023] The composition of the base steel sheet 20 is also not particularly limited and may be appropriately selected according to the application.

[0024] The copper plated film 30 is a film having good adhesion to the base steel sheet 20 and the sliding resin film 40. Therefore, by providing the copper plated film 30, the sliding resin film 40 can be made difficult to peel off from the copper-plated steel sheet 10 when the sliding resin film 40 is provided on the copper plated film 30. As a result, slidability can be maintained over a long period of time even in a sliding environment with a large applied load.

[0025] The copper plated film 30 continuously covers the base steel sheet 20 with a thickness T of 1.0 µm or more in a cross-section parallel to a thickness direction of the copper plated film. The thickness T of the copper plated film 30 means the minimum thickness of the copper plated film 30 covering the base steel sheet 20.

[0026] As used herein, the phrase "the copper plated film 30 continuously covers the base steel sheet 20" means a state in which there is no portion where the base steel sheet 20 is exposed without the copper plated film 30 being formed.

[0027] By continuously covering the base steel sheet 20 with the copper plated film 30 having the thickness T as described above, when the sliding resin film 40 is provided on the copper plated film 30, the sliding resin film 40 becomes difficult to peel off even in a sliding environment with a large applied load. From the viewpoint of stably ensuring this effect, the thickness T of the copper plated film 30 is preferably 1.3 µm or more. The upper limit of the thickness T of the copper plated film 30 is not particularly limited, but considering manufacturing cost and the like, it is generally 10.0 µm or less, and preferably 8.0 µm or less.

[0028] The thickness T of the copper plated 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 (for example, SEM).

[0029] The copper plated film 30 has 25 or more protrusions 31 having a height of 1.0 µm or more per 1000 µm in a cross-section parallel to a thickness direction of the copper plated film. If the number of the protrusions 31 having such a height is within the range, it can be said that the copper in the copper plated film 30 has sufficiently grown in a dendrite (dendritic crystal) form. For the copper plated film 30 having such protrusions 31, when the sliding resin film 40 is provided on the copper plated film 30, an anchor effect works between the copper plated film 30 and the sliding resin film 40, and therefore the sliding resin film 40 becomes difficult to peel off even in a sliding environment with a large applied load. From the viewpoint of stably ensuring this effect, the protrusions 31 having a height of 1.0 µm or more are preferably 40 or more per 1000 µm. The upper limit of the number of the protrusions 31 having a height of 1.0 µm or more is not particularly limited because as the number is larger, it is easier to obtain the anchor effect, but it is generally 200 or less per 1000 µm.

[0030] Here, the method of counting the protrusions 31 having a height of 1.0 µm or more will be described with reference to a schematic view (Figure 3) for a cross section parallel to the thickness direction of the copper-plated steel sheet 10. The number of the protrusions 31 having a height of 1.0 µm or more is the number of portions protruding from a base portion of the copper plated film 30 (however, a portion where the height H is 1.0 µm or more). The base portion of the copper plated film 30 refers to the portion of the copper plated film 30 that has an average thickness. Therefore, in form a of Figure 3, it has a portion branched into three parts, but it is counted as one protrusion 31 because there is only one portion protruding from the base portion. Form b of Figure 3 has a portion branched into two parts, and the root portion of the portion is raised. In this case, if the raised part of the root 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 raised part of the root portion is 1.0 µm or more, it is counted as one protrusion 31 even if the height H of the two protrusions 31 is 1.0 µm or more. In form c of Figure 3, the portion branched into two parts is connected at the upper portion, but it is counted as two protrusions 31 because there are two portions protruding from the base portion. In form d of Figure 3, both ends appear to be raised because they are lower than the base portion, but they are not counted as the protrusions 31 because they are not raised from the base portion.

[0031] The height H of the protrusion 31 means the height in the direction orthogonal to the line connecting both ends of the root portion of the protrusion 31.

[0032] The deposited amount of copper of the copper plated film 30 is not particularly limited, but it is preferably 10 to 150 g / m 2< , more preferably 13 to 120 g / m 2< , and still more preferably 15 to 60 g / m 2< . By controlling the deposited amount of copper to such a range, the copper plated film 30 having good adhesion to the base steel sheet 20 and the sliding resin film 40 can be stably obtained.

[0033] An anti-discoloration treatment layer may be formed on the copper plated film 30 to suppress discoloration of the copper plated film 30. Providing the anti-discoloration treatment layer is effective for suppressing discoloration of the copper plated film 30 over time, and is particularly effective for suppressing discoloration for several days after the formation of the copper plated film 30.

[0034] 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 will be 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 the commercially available anti-discoloration agent include VERZONE CU Guard D manufactured by Daiwa Fine Chemicals Co., Ltd., benzotriazole group-containing silane coupling agents manufactured by Shin-Etsu Chemical Co., Ltd., Gospel (C-30, C-70, or C-220) manufactured by Gospel Kako Co., Ltd., Top Rinse CU-5 manufactured by Okuno Chemical Industries Co., Ltd., KPC-2003 manufactured by Metal Chemical Technology Laboratory Co., Ltd., CU-5600 manufactured by Meltex Co., Ltd., and BTZ-M manufactured by KYODO CHEMICAL CO., LTD.

[0035] The anti-discoloration treatment layer may be formed entirely on the copper plated film 30, or may be formed partially.

[0036] The sliding resin film 40 is a film formed from a resin having slidability. Here, the term "sliding resin film 40" as used herein means a resin film having a coefficient of kinetic friction of 0.2 or less when a friction and wear test is performed under conditions of a load of 1 N, a mating material of a 10 mmφ SUS ball, a sliding (moving) speed of 150 mm / min, and a specimen temperature of 20 to 30°C, using a surface property measuring instrument (HEIDON-TYPE14) manufactured by Shinto Kagaku Co., Ltd., with the specimen being a flat portion taken from a plated steel sheet on which the target resin film is formed.

[0037] The sliding resin film 40 is not particularly limited, and materials known in the art can be employed. For example, a resin film to which a lubricant is added, or a resin film having self-lubricating properties can be used as the sliding resin film 40. Among them, the sliding resin film 40 is preferably a film in which a polytetrafluoroethylene (PTFE) resin is dispersed in a matrix resin. The matrix resin is not particularly limited, and examples include polyester resins, linear macromolecular polyester resins, acrylic resins, epoxy resins, polyurethane resins, phenoxy resins, phenolic resins, polyvinylidene fluoride resins (PVdFs) / acrylic resins, and vinyl chloride resins.

[0038] The thickness of the sliding resin film 40 is not particularly limited, but it may be 3 to 40 µm. By controlling the thickness of the sliding resin film 40 to this range, slidability can be stably ensured.

[0039] The anti-discoloration treatment layer as described above may be formed between the copper plated film 30 and the sliding resin film 40.

[0040] The method for producing the copper-plated steel sheet 10 according to an 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 features, and can be carried out according to a known method. Hereinafter, an example of the method for producing the copper-plated steel sheet 10 according to an embodiment of the present invention will be described.

[0041] The method for producing the copper-plated steel sheet 10 according to an embodiment of the present invention includes an electroplating step of forming the copper plated film 30 on at least one surface of the base steel sheet 20 by electroplating.

[0042] In the electroplating step, it is preferable to perform plating in copper sulfate solution (hereinafter "copper sulfate plating") after carrying out plating in copper pyrophosphate solution (hereinafter "copper pyrophosphate plating").

[0043] The copper pyrophosphate plating is performed by immersing the base steel sheet 20 in a copper pyrophosphate plating solution.

[0044] The conditions for the copper pyrophosphate plating are not particularly limited, and they can be appropriately set according to a known method. Typical conditions are as follows: Composition of copper pyrophosphate plating solution: 50 g / L of copper pyrophosphate, 250 g / L of potassium pyrophosphate, 10 g / L of oxalic acid; pH of copper pyrophosphate plating solution: 9.2; Temperature of copper pyrophosphate plating solution: 20 to 60°C; Current density: 1 to 10A / dm 2< ; and Duration time: 5 to 100 seconds.

[0045] In addition, the copper pyrophosphate plating may be performed once, or may be performed multiple times under different conditions.

[0046] The copper sulfate plating is preferably performed by immersing the base steel sheet 20 in a copper sulfate plating solution while changing the flow velocity of the copper sulfate plating solution. More specifically, it is more preferable to alternately and repeatedly perform copper sulfate plating at a low flow velocity (for example, a flow velocity of 0.30 m / sec or less) and copper sulfate plating at a high flow velocity (for example, a flow velocity of 0.50 m / sec or more).

[0047] Here, Figure 4 is a schematic view for explaining a formation process of the copper plated film 30.

[0048] When copper sulfate plating is performed at a low flow velocity, copper ions tend to be insufficiently supplied to the plating surface, and the deposited copper is easily destroyed by bubbles of 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 velocity, copper ions tend to be sufficiently supplied to the plating surface. As a result, the plating grows along the surface, so that the copper plated film 30 is formed so as to cover the entire surface to which the particulate copper has adhered (state B). Then, when copper sulfate plating is performed again at a low flow velocity, particulate copper adheres as in state A, and the copper grows as dendritic crystals (dendrites) (state C). Then, copper sulfate plating is performed again at a high flow velocity to form a copper plated film 30 so as to cover the entire surface, thus reinforcing the dendritic copper and increasing the thickness of the copper plated film 30 (state D). By alternately and repeatedly performing the copper sulfate plating at the low flow velocity and the copper sulfate plating at the high flow velocity in this manner, the copper plated film 30 with the protrusions 31 as described above can be formed.

[0049] The number of repetitions of the copper sulfate plating at the low flow velocity and the copper sulfate plating at the high flow velocity, and the electrical conduction time per repetition may be appropriately adjusted according to the composition of the copper sulfate plating solution used, the current density, the plating deposition amount to be obtained, and the like. Typically, the current density is 20 to 60 A / dm 2< , the electrical conduction time per one plating (the electrical conduction time for each of the plating at the low flow velocity and the plating at the high flow velocity) is 1 to 30 seconds, and the number of repetitions is 5 to 50 times.

[0050] It should be noted that the copper sulfate plating can be performed using an electroplating apparatus (for example, a flow cell or the like) capable of flowing the plating solution.

[0051] The other conditions for the copper sulfate plating are not particularly limited, and they can be appropriately set according to a known method. Typical conditions are as follows: 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; and Temperature of copper sulfate plating solution: 20 to 50°C.

[0052] The method for producing the copper-plated steel sheet 10 according to an embodiment of the present invention can further include a resin film forming step of forming the sliding resin film 40 on the copper plated film 30.

[0053] The resin film forming step is not particularly limited as long as the sliding resin film 40 can be formed, and it can be performed according to a known method. In a typical resin film forming step, the sliding resin film 40 can be formed by applying a resin composition containing a matrix resin and a polytetrafluoroethylene (PTFE) resin on the copper plated film 30 and drying it.

[0054] The method for applying the resin composition is not particularly limited, and for example, known methods such as an immersion method, a bar coating method, a roll coating method, a spin coating method, and a spray method can be used. The application of the resin composition can be performed one or more times so that the sliding resin film 40 to be formed has a predetermined thickness. The drying temperature is not particularly limited and it may be appropriately set according to the composition of the resin composition and the like.

[0055] When the anti-discoloration treatment layer is provided on the copper plated film 30 or between the copper plated film 30 and the sliding resin film 40, an anti-discoloration treatment step can be performed after the electroplating step or between the electroplating step and the resin film forming step.

[0056] In the anti-discoloration treatment step, a solution containing an anti-discoloration agent such as benzotriazole may be applied on the copper plated film 30 and dried.

[0057] The method for applying the solution containing the anti-discoloration agent is not particularly limited, and the above known method can be used. The drying temperature is not particularly limited and it may be appropriately set according to the type of the solution.[Examples]

[0058] The content of the present invention will be described below in detail with reference to Examples, but the present invention is not construed as being limited thereto.(Examples 1 to 8)

[0059] Cold-rolled steel sheets having a thickness of 0.5 mm were prepared as the base steel sheets. Each of the cold-rolled steel sheets was subjected to electrolytic degreasing, washing with water, and washing with acid in this order. The electrolytic degreasing was performed at a current density of 2 A / dm 2< for 10 seconds while immersing the cold-rolled steel sheet as an anode in a Na-based degreasing agent having a Na concentration of 5% (temperature: 60°C). The washing with acid was performed by immersing the steel sheet in an aqueous hydrochloric acid solution having a hydrochloric acid concentration of 2% (temperature: 20°C) for 30 seconds. The copper pyrophosphate plating was then performed at a current density of 5 A / dm 2< for 13 seconds while immersing the cold-rolled steel sheet in a copper pyrophosphate plating solution at 60°C. The cold-rolled steel sheet on which copper pyrophosphate plating had been performed was immersed in a copper sulfate plating solution at 35°C, and the copper sulfate plating processes at a low flow velocity and the copper sulfate plating processes at a high flow velocity were alternately performed 21 times in total under the conditions of the current density and flow velocity of the copper sulfate plating solution shown in Table 1 (11 plating processes at a high flow velocity and 10 plating processes at a low flow velocity). A copper-plated steel sheet having a copper plated film formed thereon was thus obtained. In addition, the composition and pH of each of the pyrophosphate plating solution and the copper sulfate plating solution used are as follows: Composition of copper pyrophosphate plating solution: 50 g / L of copper pyrophosphate, 250 g / L of potassium pyrophosphate, 10 g / L of 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; and pH of copper sulfate plating solution: 1.0.

[0060] In addition, the flow velocity in Examples refers to the velocity of the plating solution flowing in the direction along the cold-rolled steel sheet between the electrodes (the cold-rolled steel sheet and the anode).

[0061] The copper-plated steel sheet on which the copper plated film had been formed was then immersed in an aqueous benzotriazole solution having a concentration of 2 g / L (60°C) for 3 seconds and dried to form an anti-discoloration treatment layer. A sliding resin film having a thickness of 20 µm was then formed by applying, to the copper-plated steel sheet on which the anti-discoloration treatment layer had been formed, a resin composition containing 25% of PTFE particles having an average particle size of 10 µm in a polyester resin (matrix resin), and drying it at 200°C. In some copper-plated steel sheet (Example 8), the sliding resin film was formed without forming the anti-discoloration treatment layer. Here, the average particle size means a particle size at a cumulative value of 50% in a particle size distribution determined by a laser diffraction / scattering method.(Comparative Examples 1 to 6)

[0062] Instead of alternately performing a total of 21 processes of the copper sulfate plating at the low flow velocity and the copper sulfate plating at the high flow velocity, a total 21 processes of only copper sulfate plating at a low flow velocity or a high flow velocity was performed. The anti-discoloration treatment layer and the sliding resin film were then formed by the same method as that of the above Examples.

[0063] The following evaluations were performed on the copper-plated steel sheets obtained in the above Examples.<Deposited Amount of Copper on Copper Plated Film>

[0064] A copper-plated steel sheet on which only the copper plated film had been formed was immersed in a mixed aqueous solution of an aqueous ammonia solution (ammonia concentration: 28%) and hydrogen peroxide to dissolve the copper plated film, a mass difference [g] before and after the dissolution of the copper plated film was measured, and the deposited amount of copper [g / m 2< ] was calculated by dividing the mass difference by the area [m 2< ] of the region where the copper plated film had been formed.<Thickness T (Minimum Thickness) of Copper Plated Film>

[0065] Each copper-plated steel sheet on which only the copper plated film had been formed was cut so that a cross section parallel to the thickness direction could be observed, and a resin was embedded so that the cut surface became an observation surface. The measuring test piece that had undergone the resin embedding was then mirror-finished by wet polishing. The mirror-finished surface was observed using a SEM (model SU6600 manufactured by Hitachi High-Tech Corporation). In a SEM image at magnitudes of 2,000, the minimum thickness [µm] in a length of approximately 1,000 µm in a direction orthogonal to the thickness direction was taken as the thickness T of the copper plated film. Here, for reference, SEM images of the copper-plated steel sheets according to Example 1 and Comparative Examples 1 and 5 are shown in Figures 5 to 7, respectively (it should be noted that the magnification of the SEM images is different in each figure). Further, Figure 5 shows, as an example, the position of the measured thickness T of the copper plated film.<Number of Protrusions Having Height of 1.0 µm or more on Copper Plated Film>

[0066] SEM observations were performed by the same method as that of the thickness T of the copper plated film. In each SEM image, the number of protrusions [number per 1000 µm] in a length of 1000 µm in the direction orthogonal to the thickness direction was counted according to the counting method described above. It should be noted that, as an example, Figure 5 shows the positions of the counted protrusions (12 in total). In Figure 5, auxiliary lines are drawn to measure the heights of the protrusions only for the counted protrusions.<Evaluation of Adhesion of Copper Plated Film>

[0067] The surface of the copper-plated steel sheet having only a copper plated film was rubbed with an index finger to visually evaluate whether or not the copper plated film had come off.

[0068] In this evaluation, cases where the copper plated film did not come off were expressed as good (good adhesion), and cases where the copper plated film came off were expressed as poor (poor adhesion).<Evaluation of Adhesion of Sliding Resin Film>

[0069] Each copper-plated steel sheet having a sliding resin film was punched into a disk shape with a diameter of 6 mm. In this case, the clearance was set at 0.1 mm. The punched copper-plated steel sheet was then cut so that a cross section parallel to the thickness direction could be observed, and a resin was embedded so that the cut surface became the observation surface. The measuring test piece that had undergone the resin embedding was then mirror-finished by wet polishing. The length of peeling of the sliding resin film from the punched end face was measured for the mirror-finished surface. The criteria for this evaluation are as follows: Peeling length of less than 20 µm: Excellent adhesion of the sliding resin film; Peeling length of 20 µm or more and less than 100 µm: Good adhesion of the sliding resin film (pass); and Peeling length of 100 µm or more: Poor adhesion of the sliding resin film (fail). <Pin-On-Disk Evaluation>

[0070] Disk-shaped test pieces having a diameter of 6 mm were obtained from the copper-plated steel sheets having the sliding resin film by means of punching. These test pieces were evaluated using a pin-on-disk friction and wear tester (Reska Co., Ltd., Model FPR-2100). Specifically, as shown in Figure 8, each test piece was affixed to the tip (having a diameter of 14 mm) of the testing machine's pin, and the disk (material: SKD11) was rotated to cause sliding, and the time until the copper plated film on the test piece was exposed was measured. The applied load during sliding was 3 kgf, and the rotational speed was 32 rpm. The criteria for this evaluation are as follows: Time until the copper plated film is exposed is 200 hours or more: Excellent effect of maintaining slidability; Time until the copper plated film is exposed is 100 hours or more and less than 200 hours: Good effect of maintaining slidability (pass); and Time until the copper plated film is exposed is less than 100 hours: Poor effect of maintaining slidability (fail).

[0071] The results of the above evaluations are shown in Table 1. [Table 1]Copper Sulfate PlatingPresence or Absence of Anti-Discoloration TreatmentCopper Plated FilmCharacterizationCurrent Density [A / dm 2< ]Low Flow Velocity [m / s]High Flow Velocity [m / s]Deposited Amount of Copper [g / m 2< ]Thickness T[µm]Number of Protrusions [ / 1000 µm]Adhesion of Copper Plated FilmAdhesion of Sliding Resin Film [µm]Pin-On-Disk Evaluation [hours]Ex. 1400.151.00Present532.955Good0240Ex. 2400.151.00Present282.446Good18200Ex. 3300.201.50Present101.025Good75125Ex. 4300.201.50Present151.345Good32180Ex. 5500.100.80Present503.1117Good57150Ex. 6500.152.00Present222.089Good85110Ex. 7500.100.80Present522.6143Good95100Ex. 8400.151.00Absent302.643Good20200Com. 1400.10--Present110.973Poor28580Com. 2600.15--Present280.8124Poor38540Com. 3600.10--Present380.8186Poor42035Com. 4600.10--Present260.5130Poor44530Com. 540--1.00Present546.08Good46020Com. 620--1.00Present252.73Good46320

[0072] As shown in Table 1, the copper-plated steel sheets according to Examples 1 to 8 had good results for each characterization because the thickness T of the copper plated film and the number of protrusions were in the appropriate ranges (see the SEM image in Figure 5).

[0073] In contrast, the copper-plated steel sheets according to Comparative Examples 1 to 4 had particulate copper adhering to the surface (see the SEM image in Figure 6), and the adhesion of the copper plated film was insufficient, and the thickness T of the copper plated film was also small. The results of these characterizations were also poor.

[0074] Furthermore, the copper-plated steel sheets according to Comparative Examples 5 and 6 had smooth copper plated films that grew along their surfaces (see the SEM image in Figure 7). These had poor results of the adhesion of the sliding resin film and the pin-on-disk evaluation.

[0075] As can be seen from the above results, according to the present invention, it is possible to provide a copper-plated steel sheet in which a sliding resin film is difficult to peel off when the sliding resin film is applied on the copper plated film. Therefore, the copper-plated steel sheet having the sliding resin film provided on the copper plated film can maintain its slidability for a long period of time, even in a sliding environment where the applied load is larger.[Description of Reference Numerals]

[0076] 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 plated film formed on at least one surface of the base steel sheet, wherein the copper plated film continuously covers the base steel sheet with a thickness of 1.0 µm or more in a cross-section parallel to a thickness direction of the copper plated film, and has 25 or more protrusions having a height of 1.0 µm or more per 1000 µm.

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 an anti-discoloration treatment layer provided on the copper plated film.

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

Images