Surface-treated steel sheet

Abstract

To disclose a surface-treated steel plate with excellent weldability and corrosion resistance.SOLUTION: A surface-treated steel plate has a plating steel plate having a zinc-containing plating layer, and a surface treatment layer provided on at least one main face of the plating steel layer. The surface treatment layer has a coating film, and the coating film contains binder resin, an anti-rust agent, and a conductive agent. Arithmetic average waviness Wa of a surface of the coating film is 0.10 μm or more and 3.00 μm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This application discloses a surface-treated steel sheet.

[0002] Surface-treated steel sheets are used as components in automobiles and other vehicles. A surface-treated steel sheet, for example, comprises a plated steel sheet and a surface treatment layer provided on at least one main surface of the plated steel sheet. In conventional technology, a coating is used as the surface treatment layer, and the weldability and corrosion resistance of the surface-treated steel sheet are improved by adjusting the type and content of the components constituting the coating and the thickness of the coating.

[0003] For example, Patent Document 1 discloses a technique for improving the weldability and corrosion resistance of a surface-treated steel sheet having a coating on at least one side of a plated steel sheet, by including predetermined amounts of a binder resin, non-oxide ceramic particles containing V, and doped zinc oxide particles in the coating.

[0004] Furthermore, Patent Document 2 discloses a technique for improving the weldability and corrosion resistance of a painted metal material having an organic film on its surface, by incorporating a predetermined resin having urethane bonds and predetermined conductive particles into the organic film.

[0005] Furthermore, Patent Documents 3 and 4 disclose a technique for improving the weldability and corrosion resistance of a coated metal plate having a coating layer on its surface, by incorporating a predetermined amount of conductive particles of a predetermined particle size into the coating layer.

[0006] Furthermore, Patent Document 5 discloses a technology for improving the weldability and corrosion resistance of a surface-treated steel sheet, which has a base treatment layer on at least one surface of a zinc-plated steel sheet and an organic resin coating thereon, by including a predetermined amount of ferrosilicon having a predetermined particle size in the organic resin coating and keeping the thickness of the organic resin coating within a predetermined range. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2018 / 092244 [Patent Document 2] Japanese Patent Publication No. 2004-042622 [Patent Document 3] Japanese Patent Publication No. 2004-183080 [Patent Document 4] Japanese Patent Publication No. 2004-183082 [Patent Document 5] Japanese Patent Publication No. 2002-172363 [Overview of the project] [Problems that the invention aims to solve]

[0008] In conventional technology, while the types and content of components constituting the surface treatment layer have been considered to improve the weldability and corrosion resistance of surface-treated steel sheets, methods to improve the weldability and corrosion resistance of surface-treated steel sheets through other means have not been sufficiently explored. In this respect, there is room for improvement in improving the weldability and corrosion resistance of surface-treated steel sheets. [Means for solving the problem]

[0009] This application is one means of solving the above problem, A plated steel sheet having a zinc-containing plating layer, A surface treatment layer provided on at least one main surface of the plated steel sheet, A surface-treated steel sheet having, The surface treatment layer has a coating film, The aforementioned coating film comprises a binder resin, a rust inhibitor, and a conductive agent. The arithmetic mean waviness Wa of the surface of the coating film is 0.10 μm or more and 3.00 μm or less. Surface-treated steel sheet Disclose the following.

[0010] In the surface-treated steel sheet of this disclosure, The coating film may contain a polyester resin as the binder resin.

[0011] In the surface-treated steel sheet of the present disclosure, The coating film may contain ferrosilicon as the conductive agent.

[0012] In the surface-treated steel sheet of the present disclosure, The coating film may contain at least one of a phosphorus compound and a vanadium compound as the rust preventive agent.

[0013] In the surface-treated steel sheet of the present disclosure, The coating film may contain silica as the rust preventive agent.

[0014] In the surface-treated steel sheet of the present disclosure, The coating film deposition amount may be 2 g / m 2 or more and 30 g / m 2 or less.

Advantages of the Invention

[0015] In the surface-treated steel sheet of the present disclosure, the coating film has a predetermined undulation on its surface. In the surface-treated steel sheet of the present disclosure, while high corrosion resistance is ensured by the thick portion of the coating film, high conductivity is ensured by the thin portion of the coating film, and the balance between weldability and corrosion resistance of the entire surface-treated steel sheet is good.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described. Note that these descriptions are intended merely as examples of the embodiments of the present invention, and the present invention is not limited to the following embodiments.

[0017] 1. Surface-treated steel sheet The surface-treated steel sheet according to this embodiment comprises a plated steel sheet having a zinc-containing plating layer and a surface treatment layer provided on at least one main surface of the plated steel sheet. The surface treatment layer has a coating film. The coating film contains a binder resin, a rust inhibitor, and a conductive agent. The arithmetic mean waviness Wa of the surface of the coating film is 0.10 μm or more and 3.00 μm or less.

[0018] 1.1 Plated steel sheet A plated steel sheet may, for example, have a base steel sheet and a zinc-containing plating layer provided on at least one main surface of the base steel sheet. In this application, "main surface" refers to the surface corresponding to the front or back side of the sheet. The zinc-containing plating layer may be provided on only one main surface of the base steel sheet, or on both main surfaces. Furthermore, the zinc-containing plating layer may be provided on the entire main surface of the base steel sheet, or on a part of the main surface.

[0019] Various types of steel sheets with different chemical compositions and microstructures can be used as the base material. The base material may be ordinary steel sheet or steel sheet containing additive elements such as chromium, and the chemical composition and microstructure of the base material should be adjusted considering the desired mechanical properties and formability. Furthermore, the thickness of the base material is not particularly limited; for example, it may be 0.2 mm or more, or 6.0 mm or less.

[0020] The zinc-containing plating layer may be a plating layer having a chemical composition known to those skilled in the art. For example, the zinc-containing plating layer may contain additive elements such as Al in addition to Zn, and may also contain Fe if an alloying treatment has been performed. As an example, the zinc-containing plating layer may be a Zn-Al-Mg alloy plating layer containing at least Al and Mg, or a Zn-Al-Mg-Si alloy plating layer further containing Si. The content (concentration) of each of these may be, in mass%, Al: 0.01 to 60%, Mg: 0.001 to 10%, Si: 0 to 2%, with the remainder being Zn and impurities. The zinc-containing plating layer may be an alloyed hot-dip galvanized layer, a hot-dip galvanized layer, or an electro-galvanized layer. The amount of the zinc-containing plating layer adhering to the base steel sheet is not particularly limited and may be a general amount.

[0021] 1.2 Surface treatment layer The surface treatment layer is provided on at least one main surface of the plated steel sheet. The surface treatment layer may be provided on only one main surface of the plated steel sheet, or on both main surfaces. Furthermore, the surface treatment layer may be provided on the entire main surface of the plated steel sheet, or on a part of the main surface. The surface treatment layer can be laminated on the surface of the zinc-containing plating layer of the plated steel sheet.

[0022] The surface treatment layer has a coating film. The surface treatment layer may consist solely of a coating film, or it may have a two-layer structure consisting of a coating film as an outer layer and a chemical conversion treatment layer as an inner layer. In particular, when the surface treatment layer has this two-layer structure, it can exhibit superior corrosion resistance and other properties.

[0023] 1.2.1 Coating film In the surface-treated steel sheet according to this embodiment, the coating film includes a binder resin, a rust inhibitor, and a conductive agent.

[0024] (Binder resin) The binder resin contained in the coating film may be at least one resin selected from, for example, polyester resin, urethane resin, and acrylic resin. In particular, high performance is easily achieved when the coating film contains polyester resin as the binder resin. When polyester resin is used as the binder resin, it may have a glass transition temperature (Tg) of -20 to 70°C and a number average molecular weight of 3,000 to 30,000. When urethane resin is used as the binder resin, it may have a Tg of 0 to 50°C and a number average molecular weight of 5,000 to 25,000. When acrylic resin is used as the binder resin, it may have a Tg of 0 to 50°C and a number average molecular weight of 3,000 to 25,000. The binder resin may be cured with a curing agent. Examples of curing agents include melamine resin, isocyanate resin, or epoxy resin. The binder resin content in the coating film is not particularly limited and may be, for example, 40% by mass or more, 60% by mass or more, 90% by mass or less, 80% by mass or less, or 70% by mass or less.

[0025] (Rust inhibitor) The rust inhibitor contained in the coating may be an inorganic rust inhibitor or an organic rust inhibitor. The rust inhibitor may be in the form of, for example, particulate matter. The rust inhibitor may be water-soluble or non-water-soluble. If the rust inhibitor is water-soluble, for example, when the coating is exposed to a humid environment, the rust inhibitor in the coating may dissolve and leach into the water, exhibiting a rust-preventive function that suppresses corrosion of the plating layer, etc.

[0026] The amount of rust inhibitor in the coating film can be adjusted as appropriate according to the desired rust-preventive effect. For example, the amount of rust inhibitor in the coating film may be 1 vol% or more, 5 vol% or more, or 10 vol% or more, or it may be 40 vol% or less, 30 vol% or less, or 20 vol% or less.

[0027] In the surface-treated steel sheet according to this embodiment, the coating film may contain at least one of a phosphorus compound and a vanadium compound as a rust inhibitor. Examples of phosphorus compounds that can function as rust inhibitors include phosphoric acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, and tetraphosphoric acid; ammonium salts such as triammonium phosphate and diammonium hydrogen phosphate; metal phosphates with Na, Mg, Al, K, Ca, Mn, Ni, Zn, Fe, etc.; phosphonic acids such as aminotri(methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra(methylenephosphonic acid), and diethylenetriaminepenta(methylenephosphonic acid) and their salts; organic phosphoric acids such as phytic acid and their salts. Furthermore, examples of vanadium compounds that can function as rust inhibitors include vanadium pentoxide, HVO3 metavanadate, ammonium metavanadate, vanadium oxytrichloride VOCl3, vanadium trioxide V2O3, vanadium dioxide, vanadium oxysulfate VOSO4, vanadium oxyacetylacetonate VO(OC(=CH2)CH2COCH3)3, vanadium acetylacetonate V(OC(=CH2)CH2COCH3)3, and vanadium trichloride VCl3.

[0028] The rust inhibitor may contain compounds containing guanidino groups, compounds containing biguanidino groups, compounds containing thiocarbonyl groups, etc.

[0029] Rust-inhibiting pigments can also be used as rust inhibitors. Examples of rust-inhibiting pigments include silica and metal phosphate salts (e.g., aluminum tripolyphosphate). In particular, higher performance is likely to be achieved when the coating film contains silica as a rust inhibitor. When using rust-inhibiting pigments as rust inhibitors, there are no particular limitations on their particle size or content.

[0030] (Conductive agent) The conductive agent contained in the coating film has the function of improving the conductivity of the coating film and thereby improving the weldability of the surface-treated steel sheet. In this application, for example, 1.0 × 10 3Materials having a volume resistivity of Ω / cm or less can serve as conductive agents. Examples of conductive agents include metals and metal compounds. Specifically, these may be metals such as magnesium, aluminum, silicon, calcium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, strontium, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, and tin; alloys such as magnesium, aluminum, silicon, phosphorus, calcium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, arsenic, strontium, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, and tellurium; or compounds such as oxides of the above-mentioned metal elements. Among these, magnesium, aluminum, silicon, chromium, iron, nickel, zinc, tin, zinc-aluminum alloys, zinc-aluminum-magnesium alloys, zinc-aluminum-magnesium-silicon alloys, zinc-iron alloys, zinc-chromium alloys, zinc-nickel alloys, iron-nickel alloys, iron-chromium alloys, stainless steel, ferrosilicon, ferromanganese, ferrophosphor, and zinc oxide are readily available. The content of conductive agents in the coating is not particularly limited and should be determined appropriately considering the desired weldability and corrosion resistance.

[0031] When the conductive agent is doped oxide particles, a Si alloy containing 50% by mass or more of Si, a Si compound containing 50 vol% or more of Si, or a composite thereof, it is easy to improve conductivity (weldability) as well as the adhesion of the electrodeposited coating film to the coating film. In this case, the content of the conductive agent in the coating film may be 5 vol% to 30 vol%.

[0032] When the conductive agent is doped oxide particles, a specific example of such doped oxide particles is doped zinc oxide particles. Examples of doped zinc oxide particles include those obtained by doping zinc oxide particles with at least one doping element selected from the group consisting of Group 13 elements of the periodic table such as B, Al, Ga, and In, and Group 15 elements of the periodic table such as P and As, thereby improving conductivity. When the doping element is Al or Ga, it is easier to further improve conductivity. The content of the doped element may be, for example, 0.05 atom% or more, or 0.1 atom% or more, and may be 5 atom% or less, relative to undoped zinc oxide particles.

[0033] When the conductive agent is a Si alloy or Si compound, a specific example of such Si alloy or Si compound is ferrosilicon, and more specifically, ferrosilicon containing 70% by mass or more of Si. When the coating film contains ferrosilicon as the conductive agent, both conductivity and corrosion resistance tend to improve. In particular, when the coating film contains ferrosilicon containing 70% by mass or more of Si as the conductive agent, it exhibits excellent corrosion resistance and moldability.

[0034] The conductive agent may be, for example, in the form of particles. When the conductive agent is in the form of particles, its average particle diameter is not particularly limited, and an appropriate size may be selected in consideration of the thickness of the coating film and the like. If the particle diameter of the conductive agent is too small relative to the coating film, the conductivity is likely to decrease. On the other hand, if the particle diameter of the conductive agent is too large relative to the thickness of the coating film, the conductive agent is likely to fall off from the coating film. In this regard, the particle diameter of the conductive agent may be 1 / 10 or more or 1 / 5 or more of the thickness of the coating film, and may also be 2 times or less. The average particle diameter of the conductive agent may be, for example, 0.1 μm or more, 0.3 μm or more, 0.5 μm or more, or 1.0 μm or more, and may also be 20 μm or less, 10 μm or less, 8.0 μm or less, 6.0 μm or less, 5.0 μm or less, 4.0 μm or less, or 2.5 μm or less. Note that the "average particle diameter" refers to the average primary particle diameter when the particles present in the coating film exist as primary particles, and the average secondary particle diameter when they exist in an aggregated state. The average particle diameter is measured as follows. That is, the surface-treated steel sheet on which the coating film is formed is cut, its cross-section is exposed and then polished, and the polished cross-section thus obtained is observed with a scanning electron microscope to obtain an observation image. Several particles present in the field of view of the observation image are arbitrarily selected, the equivalent circle diameter of each particle is determined, and the average value thereof is taken as the average particle diameter. Whether the particles in the observation image are the conductive agent can be easily determined by performing elemental analysis or the like.

[0035] (Adhesion amount of the coating film) In the surface-treated steel sheet according to the present embodiment, the adhesion amount of the coating film is not particularly limited as long as it can have the undulations described later. For example, the adhesion amount of the coating film may be 2 g / m 2 or more and 30 g / m 2 or less. If the adhesion amount of the coating film is too small, the corrosion resistance of the surface-treated steel sheet is likely to decrease. If the adhesion amount of the coating film is too large, the weldability of the surface-treated steel sheet is likely to decrease. In the surface-treated steel sheet according to the present embodiment, the adhesion amount of the coating film may be 3 g / m 2 or more or 4 mg / m 2 or more, and may also be 25 g / m 2 or less, 20 g / m 2 or less, or 15 g / m 2The following methods may also be used. Furthermore, the amount of coating on surface-treated steel sheets can be measured by gravimetric methods or cross-sectional observation. For gravimetric measurement, the initial weight of a steel sheet cut to a predetermined size is measured. Then, the coating is removed using a solvent or specialized chemical capable of dissolving the binder resin, or by blast treatment using resin beads or alumina beads. The weight of the steel sheet after removing the coating is then measured, and the difference between these two weights is calculated to determine the amount of coating.

[0036] (Surface waviness of the coating) In the surface-treated steel sheet according to this embodiment, the coating film has a predetermined waviness (irregularity) on its surface. In other words, in the surface-treated steel sheet according to this embodiment, there is unevenness in the amount of coating film attached, and thick and thin portions of the coating film may alternate repeatedly. Specifically, in the surface-treated steel sheet according to this embodiment, it is important that the arithmetic mean waviness Wa of the coating film surface is 0.10 μm or more and 3.00 μm or less. Wa may be 0.15 μm or more or 0.20 μm or more, or 2.80 μm or less or 2.50 μm or less. In the surface-treated steel sheet according to this embodiment, high corrosion resistance can be ensured by the thicker portions of the coating film (around the peaks of the waviness), and high weldability can be ensured by the thinner portions (around the bottoms of the waviness). Furthermore, in the surface-treated steel sheet according to this embodiment, since high corrosion resistance and conductivity can be ensured by the waviness of the coating film as described above, there is no need to add excessive conductive agents or rust inhibitors to the coating film, and the amount of binder resin can be relatively increased, as a result, the workability of the coating film is easily improved. The arithmetic mean waviness Wa of the surface of the coating film on the surface-treated steel sheet can be measured by a roughness meter. Specifically, the cutoff wavelength λ is measured in the roughness measurement. c 0.8mm, λ f The surface waviness of the coating film is measured by setting the roughness to 8 mm.

[0037] The average length WSm of the undulation curve elements on the surface of the coating film may be, for example, 0.4 mm or more or 0.6 mm or more, and 2.0 mm or less or 1.5 mm or less. When the spacing of the undulations is within this range, it is easier to further improve the weldability and corrosion resistance of the surface-treated steel sheet.

[0038] 1.2.2 Chemical treatment layer In the surface-treated steel sheet according to this embodiment, the surface treatment layer may have a chemical conversion treatment layer in addition to the coating film described above. That is, the surface treatment layer may have a two-layer structure consisting of a coating film as an outer layer and a chemical conversion treatment layer as an inner layer.

[0039] By providing a chemical conversion treatment layer as an inner layer on the surface of a plated steel sheet, and further providing the above-mentioned coating film on the surface of the chemical conversion treatment layer, the adhesion of the coating film to the steel sheet is improved, and the corrosion resistance of the surface-treated steel sheet is further improved. The chemical conversion treatment layer may be a layer that substantially does not contain chromium (chromate-free layer). Examples of chromate-free treatment solutions used in the chemical conversion treatment include silica-based treatment solutions mainly composed of silicon compounds such as liquid-phase silica, gas-phase silica, and silicates, zircon-based treatment solutions mainly composed of zircon compounds, and mixtures thereof. The chemical conversion treatment layer may contain a binder resin. For example, the chemical conversion treatment layer may contain at least one of the binder resins exemplified as capable of constituting the above-mentioned coating film, and may also contain a polyester resin. The content of binder resin and the content of components other than binder resin (such as the silicon compounds mentioned above) in the chemical conversion treatment layer are not particularly limited. For example, the binder resin content in the chemical conversion treatment layer may be 0% by mass or more and 80% by mass or less, and the content of components other than the binder resin may be 20% by mass or more and 100% by mass or less. The chemical conversion treatment layer as the inner layer may be an inorganic film containing inorganic components as a binder.

[0040] In the surface-treated steel sheet according to this embodiment, the amount of the chemical conversion treatment layer is not particularly limited. For example, the amount of the chemical conversion treatment layer may be 50 mg / m². 2 More than 2000mg / m 2The corrosion resistance and weldability of surface-treated steel sheets can be further improved under the following conditions. The amount of chemical conversion treatment layer adhering to the surface-treated steel sheet can be measured by X-ray fluorescence and cross-sectional analysis. Specifically, calibration plates are prepared for each chemical conversion treatment. The chemical conversion-treated sheet and the calibration plate are measured using X-ray fluorescence, and the amount of adhesion on the prepared chemical conversion-treated sheet is calculated from the X-ray intensity of the contained elements and the X-ray intensity of the calibration plate.

[0041] 1.2.3 Others The coating film and chemical treatment layer may contain components other than those described above. Examples of these other components include various additives. These include pigments other than the rust-preventive pigments mentioned above (such as bright pigments for improving aesthetics), carbon black, iron oxide, diazo yellow, lubricants, defoamers, and thickeners. The content of these other components in the surface treatment layer is not particularly limited.

[0042] 1.3 Supplement As described above, the surface-treated steel sheet according to this embodiment has a good balance between weldability and corrosion resistance due to the formation of predetermined undulations on the surface of the coating. In the surface-treated steel sheet according to this embodiment, there are irregularities on the surface of the coating due to the undulations, and the electrical resistance of the film itself becomes lower in the recesses of the coating (i.e., thin film areas), and as a result, when electrodeposited, a relatively thick electrodeposited coating is easily formed in these recesses. In other words, the surface-treated steel sheet according to this embodiment has a uniform appearance after electrodepositing and also exhibits excellent corrosion resistance after electrodepositing.

[0043] 2. Method for manufacturing surface-treated steel sheets The above-mentioned surface-treated steel sheet can be manufactured, for example, by the following method. That is, the method for manufacturing the surface-treated steel sheet is: To obtain a plated steel sheet having a zinc-containing plating layer, and A coating film is formed by applying a paint containing a binder resin, a rust inhibitor, and a conductive agent to at least one main surface of the plated steel sheet. It may include.

[0044] Alternatively, the manufacturing method for surface-treated steel sheets is: To obtain a plated steel sheet having a zinc-containing plating layer, A chemical conversion treatment layer is formed by applying a chemical conversion treatment to at least one main surface of the plated steel sheet, and A coating film is formed by applying a paint containing a binder resin, a rust inhibitor, and a conductive agent to the surface of the chemical conversion treatment layer. It may include.

[0045] 2.1 Fabrication of plated steel sheets A plated steel sheet having a zinc-containing plating layer can be obtained, for example, by obtaining a slab by continuous casting, hot-rolling the slab to obtain a hot-rolled sheet, winding the hot-rolled sheet, cold-rolling the hot-rolled sheet to obtain a cold-rolled sheet, annealing the cold-rolled sheet, applying a plating treatment to the sheet after annealing, and optionally performing a skin pass. The continuous casting conditions, hot-rolling conditions, winding conditions, cold-rolling conditions, annealing conditions, and plating conditions may be conventionally known general conditions.

[0046] 2.2 Chemical treatment In the manufacturing method of this disclosure, a chemical conversion treatment layer may be formed as an inner layer by applying a chemical conversion treatment to at least one main surface of the plated steel sheet obtained as described above. The chemical conversion treatment can be carried out by applying the various treatment solutions described above to the surface of the steel sheet and drying it.

[0047] 2.3 Formation of the coating film In the manufacturing method of the present disclosure, a coating film as an outer layer can be formed by applying a paint containing a binder resin, a rust inhibitor, and a conductive agent to the surface of the plated steel sheet obtained as described above, or to the surface of the chemical conversion treatment layer formed as described above, and then drying it. In the manufacturing method of the present disclosure, it is necessary to devise a method of applying the paint in order to form a predetermined waviness on the surface of the coating film. In the inventor's knowledge, a coating film that satisfies the above arithmetic mean waviness Wa is formed when the following conditions (1) to (3) are met. (1) The paint used to form the coating film shall have a cup viscosity of 30 seconds or more and 150 seconds or less at the time of application, and a surface tension of 15 mN / m or more and 55 mN / m or less. (2) Applying paint using a roll coater. (3) When applying paint with a roll coater, the rotation direction of the applicator roll and the direction in which the plated steel sheet to be painted is passed through should be the same.

[0048] When the cup viscosity and surface tension of the above-mentioned paint are within a predetermined range, the undulations (irregularities) formed on the surface of the coating immediately after application are more easily maintained. In addition, in this technical field, when applying paint with a roll coater, it is common to form a uniform coating by setting the rotation direction of the applicator roll and the passage direction of the plated steel sheet to be painted to opposite directions. In contrast, in the manufacturing method of the present disclosure, when applying paint with a roll coater, the rotation direction of the applicator roll and the passage direction of the plated steel sheet to be painted are set to the same direction, resulting in uneven thickness of the coating in the passage direction (specifically, thin and thick parts of the coating alternate in the passage direction), causing undulations on the surface of the coating in the passage direction. Here, the size and spacing of the undulations of the coating formed on the surface of the steel sheet can be controlled by adjusting the rotation speed of the applicator roll, the passage speed of the plated steel sheet, the amount of paint applied by the applicator roll, etc. For example, when the ratio A / B of the peripheral speed A of the applicator roll to the steel sheet feeding speed B is 0.8 to 3.0, it is easy to form the desired waviness on the surface of the coating. If the ratio A / B is too small, the waviness on the surface of the coating tends to become excessively small, and if the ratio A / B is too large, the waviness on the surface of the coating tends to become excessively large. Thus, according to the manufacturing method of the present disclosure, the surface-treated steel sheet according to the present embodiment can be manufactured simply by controlling the coating conditions of the paint, without requiring any new equipment. [Examples]

[0049] The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples. The present invention allows for the adoption of various conditions without departing from its essence and insofar as it achieves its objective.

[0050] 1. Manufacturing of surface-treated steel sheets 1.1 Preparation of plated steel sheet Three types of zinc-plated steel sheets were prepared, and their surfaces were degreased by immersing them in an aqueous solution of a water-based alkaline degreasing agent (FC-301, manufactured by Nippon Parkerizing Co., Ltd.) (concentration 2.5% by mass, 40°C) for 2 minutes. After that, they were washed with water and dried to obtain plated steel sheets for surface treatment.

[0051] GA: Alloyed hot-dip galvanized steel sheet (thickness 0.8 mm, 10% Fe by mass, plating adhesion 45 g / m²) 2 ) ZL: Electrolytic Zn-10 mass% Ni alloy plated steel sheet (thickness 0.8 mm, plating adhesion 40 g / m²) 2 ) SD: Zn-11 mass%Al-3 mass%Mg-0.2 mass%Si alloy plated steel sheet (sheet thickness 0.8 mm, plating adhesion 180 g / m²) 2 )

[0052] 1.2 Formation of the chemical treatment layer Next, the following chemical conversion treatment solution was prepared and applied to both sides of the plated steel sheet using a two-roll coater. After application, the sheet was dried in a hot air oven at a surface temperature of 70°C and then air-dried to form a chemical conversion treatment layer on the surface of the plated steel sheet. The amount of chemical conversion treatment layer applied was 100 mg / m². 2 Furthermore, for some plated steel sheets, the following coating was formed without forming a chemical conversion treatment layer.

[0053] Chemical conversion treatment solution: A treatment solution for forming a chemical conversion coating with an Nv of 10%, consisting of tannic acid, silane coupling agent, silica fine particles, and polyester resin.

[0054] 1.3 Coating Formation Next, in order to form a coating film having the composition shown in Table 1, each component and solvent, a small amount of viscosity modifier (BYK-405, manufactured by BYK), and a surfactant (BYK-333, manufactured by BYK) were mixed to achieve the same solid content concentration as in Table 1, and a coating composition for coating film formation was prepared. This composition was applied to a plated steel sheet or a chemical conversion treated layer using a roll coater to the amount of adhesion shown in Table 1, and dried in an oven under conditions where the maximum temperature reached was 200°C, thereby obtaining a surface-treated steel sheet with a coating film as the surface treatment layer. A two-roll coater with an applicator roll and a pickup roll was used, with the rotation direction of the applicator roll (AR) being the same direction (N) or opposite direction (R) relative to the sheet, and the pickup roll (PR) being rotated so that the AR and PR were in the same direction. The average amount of coating film adhesion was measured by gravimetric method on a 100 mm × 100 mm surface. The components contained in the coating composition are shown below.

[0055] (Rust-preventive pigment) Silica: Silo Mask 02 (manufactured by Fuji Silicia Co., Ltd.) Compound V: Vanadium pentoxide (manufactured by Kishida Chemical Co., Ltd.) P compound: Calcium phosphate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0056] (Conductive pigment) FeSi: Ferrosilicon particles SUS: Stainless steel particles

[0057] (Binder resin) Polyester resin: Byron 200 (manufactured by Toyobo Co., Ltd.) Acrylic resin: Acrydic A-405 (manufactured by DIC Corporation)

[0058] 2. Performance evaluation test 2.1 Spot weldability Two fabricated surface-treated steel plates were stacked, and a CF-type Cr-Cu electrode with a tip diameter of 5 mm and radius of R40 was used to clamp them together under a pressure of 1.96 kN. After applying a welding current of 1 kA, the resistance values ​​of the surfaces in contact with the upper and lower electrodes were measured at five arbitrary points, and the average of these values ​​was used as the contact resistance value. The superiority of the spot weldability was evaluated using the following evaluation points. In this weldability test, a score of "2" or higher was considered to indicate excellent weldability. The evaluation results are shown in Table 1 below. 4: Resistance value between 0mΩ and 1000mΩ 3: Resistance value greater than 1000mΩ and less than or equal to 2500mΩ 2: Resistance value greater than 2500mΩ and less than or equal to 4000mΩ 1: Resistance value exceeds 4000 mΩ

[0059] 2.2 Scratch-resistant red rust The edges of the fabricated surface-treated steel sheets were sealed with tape, and cuts (in the shape of an "X") reaching the steel sheet beneath the plating were created. Then, a cyclic corrosion test was performed for 30 cycles under the following cycle conditions.

[0060] (Cycle conditions) The experiment was conducted using a cycle consisting of salt spray (SST, 5% NaCl, 35°C atmosphere) for 2 hours, drying (60°C) for 2 hours, and wetting (50°C, 98% RH) for 4 hours.

[0061] The following evaluation points were used to assess the superiority of scratch resistance against red rust. A score of "2" or higher in the following evaluation points was considered to indicate excellent scratch resistance against red rust. The evaluation results are shown in Table 1 below. 5: No red rust formation 4: The maximum width of the red rust from the damaged area is 3 mm or less. 3: The maximum width of the red rust from the damaged area is between 3mm and 5mm. 2: The maximum width of the red rust from the damaged area is between 5mm and 7mm. 1: Red rust from the damaged area exceeds 7mm

[0062] 2.3 Process adhesion After bending the fabricated painted steel sheet, test pieces cut to a width of 5 cm were subjected to a 2T bend in a 20°C atmosphere according to the test method conforming to JIS G3312. A tape peel test (tape used: Nichiban Co., Ltd. tape) was then performed on the processed area to observe the occurrence of paint peeling. A pass was defined as a score of 2 or higher according to the evaluation criteria below. 5: No peeling 4. The peeled coating covers less than 5% of the area where the tape was applied. 3: The peeled coating covers 5% to less than 20% of the area where the tape was applied. 2: The peeled coating covers 20% to less than 50% of the area where the tape was applied. 1: The peeled coating covers 50% to less than 70% of the area where the tape was applied.

[0063] 2.4 Corrosion resistance after electrodeposition coating The prepared surface-treated steel sheet was sprayed with a 0.1% by mass aqueous solution of Surffine 5N-8 (manufactured by Nippon Paint Co., Ltd.) at 40°C for 30 seconds (surface adjustment), followed by spraying with a 6% by mass aqueous solution of SD5350 (manufactured by Nippon Paint Co., Ltd.) at 35°C for 2 minutes (chemical conversion treatment), and then sprayed with tap water for 30 seconds (water rinsing). After that, electrodeposition coating was performed using Powernics 110 (manufactured by Nippon Paint Co., Ltd.), sprayed with tap water for 30 seconds (water rinsing), and then heated at 170°C for 20 minutes to bake. The electrodeposition coating film thickness was set to a dry film thickness of 15 μm on GA. Using the electrodeposited steel sheet thus prepared, the edges were sealed with tape, and cut defects (in the shape of an "X") reaching the steel sheet beneath the plating were introduced. Then, a cyclic corrosion test was performed for 300 cycles under the following cycle conditions.

[0064] (Cycle conditions) The experiment was conducted using a cycle consisting of salt spray (SST, 5% NaCl, 35°C atmosphere) for 2 hours, drying (60°C) for 2 hours, and wetting (50°C, 98% RH) for 4 hours.

[0065] The following evaluation points were used to assess the quality of corrosion resistance after electrodeposition coating. A score of "2" or higher was considered to indicate excellent corrosion resistance after electrodeposition coating. The evaluation results are shown in Table 1 below. 5: No red rust formation 4: The maximum width of the red rust from the damaged area is 3 mm or less. 3: The maximum width of the red rust from the damaged area is between 3mm and 5mm. 2: The maximum width of the red rust from the damaged area is between 5mm and 7mm. 1: Red rust from the damaged area exceeds 7mm

[0066] [Table 1]

[0067] The results shown in Table 1 indicate the following:

[0068] In Comparative Example 1, applying the paint using a bar coater reduced surface waviness of the coating and formed a coating with a nearly uniform thickness. As a result, it was difficult to achieve both high weldability and corrosion resistance in the surface-treated steel sheet. In particular, the thin film portion of the coating was insufficient, and sufficient weldability could not be ensured.

[0069] In Comparative Example 2, by applying the paint using a roll coater and setting the rotation direction of the applicator roll to the opposite direction (R) to the sheet feeding direction, the surface waviness of the coating film was reduced, and a coating film with a nearly uniform thickness was formed. As a result, it was difficult to achieve both high weldability and corrosion resistance in the surface-treated steel sheet. In particular, the thin film portion of the coating film was insufficient, and sufficient weldability could not be ensured.

[0070] In Comparative Example 3, although the paint was applied using a roll coater and the rotation direction of the applicator roll was the same as the direction of sheet feeding (N), the other application conditions were not appropriate, resulting in the formation of large undulations (wavy irregularities) on the surface of the coating film. As a result, it was difficult to achieve both high weldability and corrosion resistance in the surface-treated steel sheet. In particular, there was an excessive thin film portion of the coating, and sufficient corrosion resistance could not be ensured.

[0071] In contrast, in Examples 1 to 16, the paint was applied using a roll coater, the rotation direction of the applicator roll was set to the same direction as the sheet feeding direction (N), and other coating conditions were also adjusted. As a result, the waviness of the surface of the coating film was kept within a predetermined range. Consequently, high weldability was ensured in the thin parts of the coating film, and high corrosion resistance was ensured in the thick parts of the coating film, resulting in an excellent balance between weldability and corrosion resistance for the surface-treated steel sheet as a whole. Furthermore, the workability of the coating film was also good.

[0072] Based on these results, the following surface-treated steel sheets can be said to achieve both high weldability and corrosion resistance.

[0073] A plated steel sheet having a zinc-containing plating layer, A surface treatment layer provided on at least one main surface of the plated steel sheet, A surface-treated steel sheet having, The surface treatment layer has a coating film, The aforementioned coating film comprises a binder resin, a rust inhibitor, and a conductive agent. The arithmetic mean waviness Wa of the surface of the coating film is 0.10 μm or more and 3.00 μm or less. Surface-treated steel sheet.

Claims

1. A plated steel sheet having a zinc-containing plating layer, A surface treatment layer provided on the surface of the zinc-containing plating layer on at least one main surface of the plated steel sheet, A surface-treated steel sheet having, The surface treatment layer has a coating film, The aforementioned coating film comprises a binder resin, a rust inhibitor, and a conductive agent. The arithmetic mean waviness Wa of the surface of the coating film is 0.10 μm or more and 3.00 μm or less. The conductive agent includes ferrosilicon containing 70% by mass or more of Si. Surface-treated steel sheet.

2. The coating film includes a polyester resin as the binder resin. The surface-treated steel sheet according to claim 1.

3. The coating film contains at least one of a phosphorus compound and a vanadium compound as the rust inhibitor. The surface-treated steel sheet according to claim 1 or 2.

4. The aforementioned coating film contains silica as the rust inhibitor. A surface-treated steel sheet according to any one of claims 1 to 3.

5. The amount of the coating film adhering is 2 g / m². ２ 30g / m or more ２ The following is: A surface-treated steel sheet according to any one of claims 1 to 4.

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