TW202208685A - Coated steel plate and method for producing the same sequentially configured with a steel plate, a zinc-based plating layer, a phosphate treatment layer, a chromium-free sealing coating, and an organic-based coating - Google Patents

Abstract

The object of the present invention is to provide a coated steel plate having a chromium-free sealing coating and an organic coating with the appearance of the coated steel plate fully blackened and the corrosion resistance and the adhesion of the processed part fully improved, and a manufacturing method of the coated steel plate. For achieving the above object, the present invention relates to a coated steel plate, which is sequentially configured with: a steel plate; a zinc-based plating layer; a phosphate treatment layer, wherein the total adhesion amount of Ni and Co is more than 20 mg/m2 and less than 100 mg/m2, and adhesion amount of the treatment layer is more than 2.0 g/m2 and less than 7.0 g/m2; a chromium-free sealing coating containing an oxyacid salt of group IV metals and a group I metal or a salt thereof; and an organic-based coating. The lightness index (L*) of the surface of the coated steel plate is less than 55.

Description

Coated steel sheet and method for producing the same

The present invention relates to a coated steel sheet and a method for producing the coated steel sheet.

In order to improve the designability of steel sheets used for exteriors, roofs, and the like of buildings, a black appearance is sometimes required. In the coated steel sheet in which the coating film (film) is formed on the surface of the zinc-based coated steel sheet, several methods of blackening the appearance of the zinc-based coated steel sheet by blackening the coating film have been proposed.

For example, in Patent Document 1, it is described that the zinc-based plating material can be blackened by bringing the surface of the zinc-based plating material into contact with a treatment liquid containing a predetermined amount of nickel. ion or cobalt ion, ammonium ion or compound having two primary amine groups, nitrate ion, and fluoride, and the pH is 2.0-4.8.

In addition, in Patent Document 2, it is described that by subjecting a hot dip galvanized steel sheet or hot dip galvanized alloy steel sheet to zinc phosphate treatment in a zinc phosphate treatment bath containing predetermined amounts of Fe ²⁺ , Mn ^2- and Ni ²⁺ , it is possible to Its lightness index is 20-40. [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open No. 7-62554 [Patent Document 2] Japanese Patent Laid-Open No. 8-218158

[The problem to be solved by the invention] According to Patent Document 1 and Patent Document 2, it is considered that the appearance of the zinc-based coated steel sheet can be blackened by surface-treating the zinc-based coated steel sheet with a predetermined treatment liquid.

However, corrosion resistance such as long-term suppression of the occurrence of white rust is also required for painted steel sheets used for building exteriors, roofs, etc. Corrosivity will not increase sufficiently. Therefore, conventionally, in order to improve the corrosion resistance of a zinc-based plated steel sheet, a chromium sealing film and an organic-based film are formed on the surface of a phosphate-treated layer formed by zinc phosphate treatment or the like. The chrome sealing film has the effect of improving the corrosion resistance of the coated steel sheet and improving the adhesion of the organic film (for example, to sufficiently adhere the organic film even after processing).

On the other hand, due to the restriction strengthening in recent years, chromium-free coating is required for the coated steel sheet.

The present invention has been made in view of the above points, and an object of the present invention is to provide a coated steel sheet having a chrome-free sealing film and an organic film substantially not containing chromium (Cr) with sufficiently blackened appearance and corrosion resistance and processing A coated steel sheet in which the adhesiveness of the part is sufficiently improved, and a method for producing such a coated steel sheet. [Means of Solving Problems]

A coated steel sheet according to an embodiment of the present invention for solving the above-mentioned problems is arranged in this order: a steel sheet; a zinc ^- based plating layer; And 100 mg/m ² or less, the adhesion amount of the treated layer is 2.0 g/m ² or more and 7.0 g/m ² or less; chromium-free sealing film, containing oxo acid salts of Group IV metals and Group I metals or their salt; and organic film. The lightness (L*) of the surface of the coated steel sheet is 55 or less.

Moreover, the manufacturing method of the coated steel sheet according to one embodiment of the present invention for solving the above-mentioned problems includes the steps of preparing a coated steel sheet having a zinc-based coating layer; and contacting the zinc-based coating layer. A step of forming a phosphate-treated layer in which the total adhesion amount of Ni and Co is 20 mg/m ² or more and 100 mg/m ² or less, and the adhesion amount of the treated layer is 2.0 g/m ² or more and 7.0 g/m ² or less; the step of imparting a chemical conversion treatment liquid in contact with the phosphate treatment layer and drying it to form a chromium-free sealing film, the chemical conversion treatment liquid containing oxygen-containing Group IV metals acid salt, Group 1 metal or its salt, and ammonium ion, and the pH is 7.0 or more and 9.0 or less; and the step of forming an organic film in contact with the chromium-free sealing film. [Effect of invention]

According to the present invention, it is possible to provide a coating steel sheet having a chrome-free sealing film substantially not containing chromium (Cr) and an organic-type film with a sufficiently blackened appearance, and a sufficiently improved corrosion resistance and adhesion of the processed portion. A coated steel sheet, and a method for producing such a coated steel sheet.

1. Coated steel plate One embodiment of the present invention relates to a coated steel sheet in which a coating film (film) is formed on the surface of a steel sheet. The coated steel sheet has a steel sheet, a zinc-based plating layer, a phosphate-treated layer, a chrome-free sealing film, and an organic-based coating layered in this order, and the lightness (L*) of the surface of the coated steel sheet is 55 or less.

1-1. Steel plate The steel sheet may be any steel sheet capable of forming a zinc-based plating layer, and may be carbon steel including low carbon steel, medium carbon steel, and high carbon steel, or may be alloy steel including Mn, Cr, Si, Ni, and the like. In addition, the steel sheet may be killed steel including Al static steel or the like, or may be rimmed steel. When good press formability is required, a steel sheet for deep drawing including a low-carbon Ti-added steel, a low-carbon Nb-added steel, and the like is preferable as the steel sheet. In addition, a high-strength steel sheet in which the amounts of P, Si, Mn, and the like are adjusted to specific values can also be used.

1-2. Zinc-based plating layer The zinc-based plating layer is a plating layer mainly composed of zinc. The coating layer constituting the zinc-based coating layer can be selected from Zn coating (pure zinc coating), Zn-Al-based alloy coating, Zn-Mg alloy coating, Zn-Ni coating depending on the application of the surface-treated zinc-based coating steel sheet, etc. Select from alloy plating, Zn-Al-Mg alloy plating, etc.

The zinc-based plating layer may be a plating layer formed by any known method such as electroplating, fusion plating, and vapor deposition. Among these, the zinc-based plating layer is preferably a plating layer formed by a hot-dip plating method, since the zinc-based plating layer having a further increased adhesion amount can be easily produced.

In order to improve the corrosion resistance of the coated steel sheet, the zinc-based plating layer preferably contains Al in an amount of 0.1 mass % or more and 22.0 mass % or less.

In order to improve the durability of the zinc-based coating layer when the coated steel sheet is used as an exterior building material in a relatively severe environment such as a seaside area, the zinc-based coating layer preferably has an adhesion amount of 100 g/m ² or more.

1-3. Phosphate treatment layer The phosphate treatment layer is a layer containing phosphate crystals formed on the surface of the zinc-based plating layer.

The phosphate treatment layer is a film formed by arranging a plurality of phosphate crystals containing a compound having a phosphate anion and forming a poorly water-soluble crystal on the surface of the zinc-based plating layer. Examples of phosphate crystals include magnesium phosphate, manganese phosphate, zinc phosphate, iron phosphate, zinc iron phosphate, zinc calcium phosphate, and the like.

The phosphate treatment layer contains Ni and Co. Both Ni and Co may be substituted and precipitated on the surface of the zinc-based plating layer in the form of fine particles to produce a light scattering effect, thereby imparting a black appearance to the coated steel sheet. From the viewpoint of making the appearance of the coated steel sheet more favorable, the total adhesion amount of Ni and Co in the phosphate-treated layer shall be 20 mg/m ² or more. On the other hand, the total deposition amount of Ni and Co in the phosphated layer was set to 100 mg from the viewpoint of suppressing the corrosion resistance of the coated steel sheet due to the above-mentioned substitutional precipitation inhibiting the precipitation of phosphate crystals. /m ² or less. From this viewpoint, the total adhesion amount of Ni and Co in the phosphate treatment layer is preferably 30 mg/m ² or more and 80 mg/m ² or less, more preferably 40 mg/m ² or more and 70 mg/m m ² or less.

In addition, the phosphate treatment layer may contain metal elements such as Mn, Mg, Ca, and Fe, or aliphatic amines as other components.

From the viewpoint of blackening the appearance of the coated steel sheet more favorably by increasing the adhesion amount of phosphate crystals and increasing the thickness of the precipitation layer formed by Ni and Co deposited at positions where the phosphate crystals are not attached, phosphoric acid The adhesion amount of the salt-treated layer is 2.0 g/m ² or more. On the other hand, the adhesion amount of the phosphate-treated layer was set to 7.0 g/m ² or less. From this viewpoint, the adhesion amount of the phosphate treatment layer is preferably 2.5 g/m ² or more and 7.0 g/m ² or less, and more preferably 3.0 g/m ² or more and 6.0 g/m ² or less.

In this embodiment, the lightness (L*) of the surface of the coated steel sheet can be made 55 or less by appropriately controlling the total adhesion amount of Ni and Co in the phosphated layer and the adhesion amount of the phosphated layer. , is preferably 50 or less, more preferably 40 or more and 50 or less. In addition, the said lightness (L*) is the value measured by the spectroscopic reflection measurement method based on Japanese Industrial Standards (JIS) K 5600-4-5 (1999) using a spectrophotometer. .

In addition, in this embodiment, by appropriately controlling the total adhesion amount of Ni and Co in the phosphate-treated layer and the adhesion amount of the phosphate-treated layer, the 60° gloss value of the surface of the coated steel sheet can be set to 10 or less, preferably 8 or less, more preferably 5 or less. In addition, the said 60 degree gloss value is the value measured based on JIS K 5600-4-5 (1999).

1-4. Chromium-free sealing film The chrome-free sealing film is a film formed on the surface of the phosphate treatment layer and containing an oxo acid salt of a Group 4 metal and a Group 1 metal or a salt thereof.

The chromium-free sealing film is a chemical conversion treatment film formed by using a chemical conversion treatment liquid containing an oxo acid salt of a Group IV metal, a Group 1 metal or a salt thereof, and ammonium ions and having a pH of 7.0 or more and 9.0 or less.

The oxo acid salt of the Group IV metal forms a dense chemical conversion treatment film (chromium-free sealing film), thereby improving the corrosion resistance of the coated steel sheet (flat part corrosion resistance and machined part corrosion resistance).

The Group IV metals include Ti, Zr, and Hf. The oxo acid salt of the Group IV metal is a salt of an inorganic acid containing a Group IV metal atom and an oxygen atom. Examples of the salts include hydrogen salts, ammonium salts, alkali metal salts, alkaline earth metal salts, and the like. Among these, from the viewpoint of further improving the corrosion resistance of the coated steel sheet, the oxo acid salt of the Group IV metal is preferably an ammonium salt of an inorganic acid containing a Group IV metal atom and an oxygen atom, and Preferred is ammonium zirconium carbonate.

From the viewpoint of further improving the corrosion resistance of the coated steel sheet, the adhesion amount of the oxo-acid salt of the Group 4 metal in the chromium-free sealing film is preferably 2 mg/m ² in terms of atoms of the Group 4 metal. or more and 80 mg/m ² or less, more preferably 5 mg/m ² or more and 30 mg/m ² or less.

The first group metal or its salt increases the amount of hydroxyl groups in the chemical conversion treatment liquid, and improves the adhesion between the chromium-free sealing film and the phosphate treatment layer, and the adhesion between the chromium-free sealing film and the organic film. Adhesion. In addition, the Group 1 metal or its salt increases the amount of hydroxyl groups in the chemical conversion treatment liquid, and suppresses the bonding of the Group 4 metal and phosphorus in the chemical conversion treatment, thereby suppressing chemical conversion caused by the bonding of these The gelation of the treatment liquid improves the long-term storage (stability) of the chemical conversion treatment liquid.

In addition, the first group metal or its salt increases the amount of hydroxyl groups in the chemical conversion treatment liquid, so that it is difficult to remove moisture when the chemical conversion treatment liquid is dried, thereby preventing excessive chrome-free sealing film during the production process. Cracking caused by drying.

The first group metal includes Li, Na, K, and the like. Among these, from the viewpoint of further improving the adhesion with the phosphate treatment layer and the organic film, and further suppressing the occurrence of the cracks, the first group metal is preferably Na. The first group metal can be phosphates such as sodium diphosphate, potassium diphosphate, and sodium tripolyphosphate, and can also be disodium 1-hydroxyethylene-1,1-bisphosphonate, and 1-hydroxyethylene The organic phosphonic acid such as pentasodium-1,1-bisphosphonate may be other compounds such as hydroxides of the first group metals. Among these, the first group metal is preferably sodium tripolyphosphate, 1-Hydroxyethylene-1,1-bisphosphonate disodium, or 1-hydroxyethylene-1,1-bisphosphonate pentasodium.

From the viewpoint of further improving the adhesiveness with the phosphate treatment layer and the organic film, and further suppressing the occurrence of the cracks, the amount of the first group metal or its salt in the chromium-free sealing film is relatively high. It is preferable that the amount of the metal atoms of the first group is 0.5 parts by mass or more and 21 parts by mass or less with respect to 100 parts by mass of the metal atoms of the fourth group. Also, similarly, the amount of the Group 1 metal or its salt in the chromium-free sealing film is preferably such that the molar ratio of the Group 1 metal atoms to the Group 4 metal atoms is 0.02 or more and 0.8 or less.

The adhesion amount of the chromium-free sealing film is not particularly limited, but can be set to 3 mg/m ² or more and 1000 mg/m ² or less, and from the viewpoint of improving spot weldability, it is preferably 5 mg/m ² or more and 500 mg/m ² or less.

In order to further improve the corrosion resistance of the coated steel sheet in a salt-like condition such as seawater, the chromium-free sealing film may contain oxides, hydroxides or fluorides of V, Mo, P, Ti or Si.

The chromium-free sealing film does not substantially contain hexavalent chromium. Specifically, four test pieces of 50 mm × 50 mm were cut out from the coated steel sheet, and immersed in 100 mL of boiling pure water for 10 minutes. .1 The concentration analysis method of "diphenyl carbazide colorimetry" quantifies the amount of hexavalent chromium eluted in the pure water, and the amount of the hexavalent chromium in this case is below the detection limit.

In addition, the chemical conversion treatment liquid containing each of the above-mentioned components is usually acidic. When such a chemical conversion treatment liquid is used to form a chromium-free sealing film, the phosphate treatment layer or the zinc-based plating layer may be partially dissolved in the chemical conversion treatment liquid. When these layers are partially dissolved in the chemical conversion treatment liquid, the brightness of the coated steel sheet increases, or unevenness in the appearance of the coated steel sheet occurs, and the components of these layers are mixed into the chrome-free sealing film. Sometimes the desired properties of each layer cannot be fully realized.

Therefore, in this embodiment, in order to suppress the dissolution of the said layer, the chemical conversion treatment liquid whose pH is 7.0 or more and 9.0 or less is used to form a chromium-free sealing film. The adjustment method of pH is not specifically limited, From a viewpoint of suppressing the influence on the characteristic which a chromium-free sealing film has, it is preferable to adjust pH to the said range with ammonium ion. At this time, the ammonium salt derived from the ammonium ion contained in the chemical conversion treatment liquid may remain in the chromium-free sealing film.

1-5. Organic film The organic film is formed on the surface of the chromium-free sealing film, and is a film mainly composed of an organic resin.

The organic resin constituting the organic film may be any organic resin generally used for surface treatment of zinc-coated steel sheets, and for example, may be selected from urethane resins, fluororesins, acrylic resins, and polyester resins. suitable choice. The organic film containing these organic resins can improve the corrosion resistance and workability of the coated steel sheet.

Among them, the organic resin is preferably a urethane resin or a polyester resin, and more preferably a urethane resin, from the viewpoint of further improving corrosion resistance and processability.

The urethane resin usually has a structural unit derived from an isocyanate compound and a structural unit derived from a polyol compound.

Examples of the structural unit derived from the isocyanate compound include a structural unit derived from an aliphatic diisocyanate and a structural unit derived from an alicyclic diisocyanate. Examples of the aliphatic diisocyanate include phenylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, and naphthylene diisocyanate. Examples of the alicyclic diisocyanate include cyclohexane diisocyanate, isophorone diisocyanate, norbornane diisocyanate, xylene diisocyanate, and tetramethyl xylene diisocyanate.

Examples of the polyol compound-derived structural unit include a polyolefin polyol-derived structural unit. Examples of the polyolefin polyol include polyester polyol, polyether polyol, polycarbonate polyol, polyacetal polyol, polyacrylate polyol, and polybutadiene polyol.

The organic film may include one or two or more compounds selected from the group consisting of valve metal oxides, valve metal hydroxides, or valve metal fluorides (hereinafter, also referred to as "valve metal" for short). metal compounds"), etc. The valve metal compound can provide an excellent barrier function to the organic film while reducing the environmental load. The valve metal refers to a metal whose oxide exhibits high insulation resistance. As the valve metal, one or two or more metals selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Mo, and W can be exemplified. As the valve metal compound, a known compound can be used.

In addition, by including the soluble fluoride of the valve metal in the organic film, a self-healing action can be imparted to the organic film. The fluoride of the valve metal, after being eluted into the moisture in the environment, becomes a poorly soluble oxide or hydroxide on the surface of the plated steel sheet exposed from the film defect portion and re-precipitates, thereby filling the film defect portion.

In addition, the organic film may contain a soluble or poorly soluble metal phosphate or a complex phosphate in addition to the soluble fluoride of the valve metal. The soluble phosphate is eluted from the organic film to the film defect portion, and reacts with the metal of the plated steel sheet to become an insoluble phosphate, thereby supplementing the self-healing effect of the soluble fluoride of the valve metal. In addition, the poorly soluble phosphate can be dispersed in the organic film to improve the film strength.

The film thickness of the organic film is preferably 3.0 μm or more. When the film thickness of the organic film is 3.0 μm or more, it is difficult for corrosion factors permeating the organic film to reach the plating layer, and the corrosion resistance of the coated steel sheet can be sufficiently improved. The upper limit of the film thickness of the organic film is not particularly limited, and can be set to 15 μm.

The organic film may be a colored film containing an organic pigment or the like, but from the viewpoint of further improving the visibility of the black appearance formed by the phosphate treatment layer and further improving the designability of the coated steel sheet, it is preferably Transparent film.

1-6. Purpose The coated steel sheet can be used for various purposes. In particular, the appearance of the coated steel sheet is sufficiently blackened, and the corrosion resistance and the adhesion of the processed portion are sufficiently improved, so that it can be preferably used as an exterior building material such as a roof of a building.

The coated steel sheet may be a flat plate or a processed product processed into various shapes.

2. Manufacturing method of coated steel sheet The coated steel sheet can be manufactured by a method comprising the following steps: a step of preparing a plated steel sheet having a zinc-based plating layer; a step of forming the phosphate-treated layer; a step of forming the chrome-free sealing film; and the step of forming the organic film.

2-1. Procedure for preparing plated steel sheet In the step of preparing a plated steel sheet, a plated steel sheet obtained by applying the zinc-based plating using the steel sheet as a base steel sheet is prepared. In this step, the produced plated steel sheet may be prepared, or the base steel sheet may be subjected to zinc-based plating by known methods such as electroplating, hot-dip plating, and vapor deposition. The plated steel sheet.

2-2. Step of forming phosphate treatment layer In the step of forming the phosphate treatment layer, a phosphate treatment solution is applied so as to be in contact with the zinc-based plating layer of the plated steel sheet prepared above, and crystals of phosphate are precipitated in the zinc-based plating layer. coating surface.

The phosphate treatment liquid is a treatment liquid containing Ni or Co and phosphate ions. The phosphate treatment solution can be prepared by dissolving phosphate or phosphoric acid and a metal salt capable of generating Ni or Co ions in an aqueous solvent. Examples of the phosphates include magnesium phosphate, manganese phosphate, zinc phosphate, iron phosphate, zinc iron phosphate, zinc calcium phosphate, and the like.

The concentration of phosphate ions in the phosphate treatment solution is preferably 0.03 mol/ L or more and 0.5 mol/L or less. Regarding the ion concentration of Ni or Co in the phosphate treatment solution, when the deposition amount of the phosphate treatment layer is 2.0 g/m ² or more and 7.0 g/m ² or less, the total deposition amount of Ni and Co is 20 mg /m ² or more and 100 mg/m ² or less may be adjusted.

The phosphate treatment solution may further contain a polyamine-based organic inhibitor, and the polyamine-based organic inhibitor includes aliphatic polyamines including polyethylamine, polyethyleneimine, polyetheramine, and polyamine acrylate. Amines; and aromatic polyamines including polyaniline and the like. The polyamine-based organic inhibitor can precipitate the crystal particles of the phosphate with an appropriate interval, and can make the crystal particles of the phosphate finer.

The number average molecular weight of the polyamine-based organic inhibitor is preferably 200 or more and 30,000 or less, from the viewpoint of appropriately adjusting the amount of phosphate crystals to be precipitated. Moreover, it is preferable that the density|concentration of the polyamine-type organic inhibitor in a phosphate treatment liquid is 0.01 mass % or more and 5 mass % or less from a viewpoint of suitably adjusting the quantity of the precipitated phosphate crystal.

The phosphate treatment solution may further contain nitrate ions. Nitrate ions promote the precipitation of phosphate.

The concentration of nitrate ions in the phosphate treatment liquid is preferably 0.01 mol/L or more and 1.0 mol/L or less from the viewpoint of appropriately adjusting the amount of precipitated phosphate crystals.

The phosphate treatment solution may further contain fluoride. In particular, when a phosphate film is formed on the surface of a plating layer containing Al, Al eluted from the plating layer may inhibit the precipitation of phosphate, but the addition of fluoride to the phosphate treatment solution can suppress this elution Adverse effects of Al. Examples of the fluoride include sodium fluoride, potassium fluoride, sodium hydrogen fluoride and the like. The concentration of the fluoride in the phosphate treatment liquid is preferably 0.001 mol/L or more and 0.5 mol/L or less from the viewpoint of appropriately adjusting the amount of precipitated phosphate crystals.

The method for applying the phosphate treatment solution is not particularly limited, and may be appropriately selected from known methods for applying the phosphate treatment solution to the surface of the plating layer. Examples of the imparting method include a roll coating method, a curtain flow method, a spin coating method, a spray method, a dipping method, and the like. By these methods, the phosphate treatment liquid may be provided so that the adhesion amount of the phosphate treatment layer is 2.0 g/m ² or more and 7.0 g/m ² or less.

The temperature of the phosphate treatment liquid at the time of application is preferably 40°C or higher and 80°C or lower. When a phosphate treatment liquid heated to 40° C. or higher and 80° C. or lower is used, a large amount of fine phosphate crystals can be stably precipitated in a short time.

In order to promote the precipitation of phosphate, the zinc-based plated steel sheet may be surface-conditioned with a known surface conditioner before applying the phosphate treatment solution.

2-3. Steps of forming a chrome-free sealing film In the step of forming a chromium-free sealing film, an oxo acid salt containing a Group 4 metal, a Group 1 metal or a salt thereof, and ammonium are provided in contact with the phosphate treatment layer formed above. The chemical conversion treatment liquid having pH 7.0 or more and 9.0 or less is dried to form a chromium-free sealing film on the surface of the phosphate-treated layer.

The chemical conversion treatment liquid is a chemical conversion treatment liquid containing the oxo acid salt of the Group 4 metal and the Group 1 metal or a salt thereof, and adjusted to pH 7.0 or more and 9.0 or less with ammonium ions.

By adjusting the pH of the chemical conversion treatment liquid to 7.0 or more and 9.0 or less, the dissolution of the phosphate-treated layer or the zinc-based plating layer caused by acid or alkali is suppressed, thereby suppressing the occurrence of unevenness in the appearance of the coated steel sheet. , and prevent the components of these layers from being mixed into the chrome-free sealing film and hindering the function of each layer. From this viewpoint, the pH of the chemical conversion treatment liquid is preferably 7.2 or more and 8.5 or less, and more preferably 7.3 or more and 8.0 or less.

The content of the oxo acid salt of the Group 4 metal and the content of the Group 1 metal or a salt thereof is not particularly limited. For example, the concentration of the Group IV metal atoms in the chemical conversion treatment liquid is preferably 5 g/L or more and 40 g/L or less, more preferably 5 g/L or more and 35 g/L or less. In addition, the concentration of the first group metal atoms in the chemical conversion treatment liquid is preferably 0.2 g/L or more. In addition, the amount of the Group 1 metal or its salt in the chemical conversion treatment liquid is preferably such that the Group 1 metal atom is 0.5 parts by mass or more and 21 parts by mass relative to 100 parts by mass of the Group 4 metal atom The following amounts are also preferably such amounts that the molar ratio of the metal atoms of the first group to the metal atoms of the fourth group is 0.02 or more and 0.8 or less.

In addition, in order to further improve the corrosion resistance of the coated steel sheet under the condition of salt water such as seawater, the chemical conversion treatment liquid may contain oxides, hydroxides or fluorides of V, Mo, P, Ti or Si .

The method for applying the chemical conversion treatment liquid is not particularly limited, and may be appropriately selected from known methods such as a roll coating method, a curtain flow method, a spin coating method, a spray method, and a dipping method.

2-4. Steps of forming organic film In the step of forming an organic film, an organic film treatment liquid containing the organic resin is applied and dried so as to be in contact with the chromium-free sealing film formed above, so that the chromium-free film is An organic-type film is formed on the surface of the sealing film.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples. [Example]

1. Coated steel sheet (steel sheet and zinc-based coating layer) A molten Zn-0.1 mass % Al coating layer (coating adhesion amount of 200 g/m ² ) was formed on the surface of SUS430 with a thickness of 0.8 mm and No. 2D finishing. as the plated steel sheet 1 .

The plated steel sheet 2 was formed by forming a molten Zn-6 mass % Al-3 mass % Mg plated layer (coating amount of 140 g/m ² ) on the surface of SUS430 with a thickness of 0.8 mm and No. 2D finishing.

The plated steel sheet 3 was formed by forming a molten Zn-0.1 mass % Al plating layer (a plating amount of 200 g/m ² ) on the surface of ordinary steel having a plate thickness of 0.6 mm.

The plated steel sheet 4 was formed by forming a molten Zn-6 mass % Al-3 mass % Mg plating layer (coating amount of 140 g/m ² ) on the surface of ordinary steel having a plate thickness of 0.6 mm.

2. Preparation of Coated Steel Sheet 2-1. Formation of Phosphate-treated Layer Phosphate treatment layer. The temperature of the phosphate treatment solution was 70°C. The adhesion amount of the phosphate-treated layer formed at this time was 3.3 g/m ² , and the total adhesion amount of Ni and Co in the phosphate-treated layer was 22 mg/m ² .

2-2. Formation of chrome-free sealing film Prepare ammonium zirconium carbonate which is an oxo acid salt of a Group IV metal and has a Zr concentration of 5 g/L, and a salt of a Group I metal with a Na concentration of 5 g/L. A chemical conversion treatment liquid for forming a chromium-free sealing film containing sodium diphosphate (salt of Group 1 metal) in an amount of 0.5 g/L and ammonia in an amount such that the pH of the aqueous solution is 7.5. The chemical conversion treatment liquid was applied to the surface of the plated steel sheet 1 on which the phosphate treatment layer was formed, and was dried in an oven at 200° C. to form a chromium-free sealing film. The coating amount of the chemical conversion treatment liquid was adjusted so that the adhesion amount of the chromium-free sealing film was 10 mg/m ² .

2-3. Formation of organic film An organic film treatment liquid (Vylonal MD-1100, manufactured by Toyobo Co., Ltd.) containing a polyester resin was prepared. The organic-type film treatment liquid was applied and dried on the surface of the plated steel sheet 1 on which the phosphate-treated layer and the chrome-free sealing film were formed to form an organic-type film with a film thickness of 5.0 μm. The coated steel sheet formed as described above was used as the coated steel sheet 1 .

^2-4 . Production of coated steel sheets ² to 30 Except for the total content of Ni and Co, it was carried out in the same manner as the production of the coated steel sheet 1 to obtain the coated steel sheet 2 and the coated steel sheet 3, respectively.

Except that the content of ammonia in the chemical conversion treatment liquid was changed so that the pH of the chemical conversion treatment liquid was 7.1 and 8.9, it was carried out in the same manner as the painted steel sheet 3 to obtain the painted steel sheet 4 and the painted steel sheet 5, respectively.

In addition to changing the type of the organic resin contained in the organic film treatment liquid to urethane resin (made by DIC, Hydran ADS-110), the same as the coated steel sheet 3 In the same way, the coated steel sheet 6 was obtained.

The type of the oxo-acid salt of the Group IV metal contained in the chemical conversion treatment liquid was changed to ammonium titanium fluoride (the oxo-acid salt of the Group IV metal) with a Ti concentration of 2 g/L, and chemically The coated steel sheet 7 was obtained in the same manner as the coated steel sheet 3 except that the content of ammonia in the chemical conversion treatment liquid was adjusted so that the pH of the conversion treatment liquid was 7.1.

It is the same as the coated steel sheet 3, except that the type of the organic resin contained in the organic film treatment liquid is changed to acrylic resin (manufactured by DIC, Voncoat CG-8400). By doing so, the coated steel sheet 8 was obtained.

Except that the immersion time in the phosphate treatment solution was changed so that the adhesion amounts of the phosphate treatment layer were 2.1 g/m ² and 6.8 g/m ² , it was carried out in the same manner as the coated steel sheet 3 to obtain the coating respectively. Steel sheet 9 and painted steel sheet 10 .

The coated steel sheet 11 was obtained in the same manner as the coated steel sheet 3 except that the coated steel sheet was changed to the coated steel sheet 2 .

In addition to changing the type of the organic resin contained in the organic film treatment liquid to urethane resin (made by DIC, Hydran ADS-110), the same as the coated steel sheet 11 In the same manner, the coated steel sheet 12 was obtained.

The coated steel sheet 13 was obtained in the same manner as the coated steel sheet 3 except that the coated steel sheet was changed to the coated steel sheet 3 .

The type of organic resin contained in the organic film treatment liquid was changed to acrylic resin (manufactured by DIC, Voncoat CG-8400), and the film thickness of the organic film was 2.0 μm The coated steel sheet 14 was obtained in the same manner as the coated steel sheet 13, except that the coating amount of the organic-based coating treatment liquid was changed.

Except that the plated steel sheet was changed to the plated steel sheet 4, and the coating amount of the organic film treatment liquid was changed so that the film thickness of the organic film was 6.0 μm, it was carried out in the same manner as the coated steel sheet 3 to obtain a coating. Install the steel plate 15.

The type of the oxo acid salt of the Group IV metal contained in the chemical conversion treatment liquid was changed to titanium ammonium fluoride having a Ti concentration of 2 g/L, and the chemical conversion treatment liquid was adjusted so that the pH of the chemical conversion treatment liquid was 7.1. The coated steel sheet 16 was obtained in the same manner as the coated steel sheet 15 except for the content of ammonia in the conversion treatment liquid.

In addition to changing the type of the organic resin contained in the organic film treatment liquid to urethane resin (made by DIC, Hydran ADS-110), the same as the coated steel sheet 15 In the same manner, the coated steel sheet 17 was obtained.

The Ni and Co in the phosphate treatment solution were changed so that the total deposition amounts of Ni and Co in the phosphate treatment layer were 11 mg/m ² , 18 mg/m ² , 0 mg/m ² , and 110 mg/m ² . Except for the total content of Co, it was carried out in the same manner as the production of the coated steel sheet 1, and the coated steel sheet 18 to the coated steel sheet 21 were obtained, respectively.

The immersion time in the phosphate treatment solution was changed so that the adhesion amounts of the phosphate treatment layer were 1.7 g/m ² and 7.5 g/m ² , and in either case the Ni and Co in the phosphate treatment layer were changed. Except that the total content of Ni and Co in the phosphate treatment solution was changed so that the total adhesion amount was 62 mg/m ² , the same procedure as that of the coated steel sheet 1 was carried out to obtain a coated steel sheet 22 and a coated steel sheet 23, respectively. .

A painted steel sheet 24 was obtained in the same manner as the painted steel sheet 3 except that the salt of the Group 1 metal was not contained in the chemical conversion treatment liquid.

Except that the content of ammonia in the chemical conversion treatment liquid was changed so that the pH of the chemical conversion treatment liquid was 6.5 and 10.6, it was carried out in the same manner as the painted steel sheet 3 to obtain a painted steel sheet 25 and a painted steel sheet 26, respectively.

A painted steel sheet 27 was obtained in the same manner as the painted steel sheet 3 except that the organic film was not formed.

A painted steel sheet 28 was obtained in the same manner as the painted steel sheet 3 except that the chemical conversion treatment liquid did not contain an oxo-acid salt of a Group IV metal.

A painted steel sheet 29 was obtained in the same manner as the painted steel sheet 3 except that the phosphate treatment layer and the chrome-free sealing were not formed.

The coated steel sheet 30 was obtained in the same manner as the coated steel sheet 13, except that the plated steel sheet was changed to the plated steel sheet 4, and the phosphated layer and the chrome-free seal were not formed.

In Tables 1 and 2, the coating steel sheets of coated steel sheets 1 to 30, the adhesion amount of the phosphate treatment layer, the total adhesion amount of Ni and Co in the phosphate treatment layer, and the composition of the chromium-free seal are shown The type of the Group IV metal of the oxo acid salt of the Group IV metal, the type of the Group I metal forming the salt of the Group I metal, the pH of the chemical conversion treatment solution, and the pH of the organic resin constituting the organic film types and their film thicknesses.

[Table 1] Painted steel sheet No. Substrate steel plate Epithelial structure Type of coating Phosphate film Chrome free seal organic film type adhesion amount adhesion amount Ni+Co adhesion amount type pH Resin type Film thickness (g/m ² ) (g/m ² ) (mg/m ² ) Group IV metals Group 1 metals (μm) 1 SUS430 Zn-0.1Al 200 3.3 twenty two Zr Na 7.5 polyester 5 2 200 3.3 95 Zr Na 7.5 polyester 5 3 200 3.3 62 Zr Na 7.5 polyester 5 4 200 3.3 62 Zr Na 7.1 polyester 5 5 200 3.3 62 Zr Na 8.9 polyester 5 6 200 3.3 62 Zr Na 7.5 Urethane 5 7 200 3.3 62 Ti Na 7.1 polyester 5 8 200 3.3 62 Zr Na 7.5 acrylic 5 9 200 2.1 62 Zr Na 7.5 polyester 5 10 200 6.8 62 Zr Na 7.5 polyester 5 11 Zn-3Mg-6Al 140 3.3 62 Zr Na 7.5 polyester 5 12 140 3.3 62 Zr Na 7.5 Urethane 5 13 ordinary steel Zn-0.1Al 200 3.3 62 Zr Na 7.5 polyester 5 14 200 3.3 62 Zr Na 7.5 acrylic 2 15 Zn-3Mg-6Al 140 3.3 62 Zr Na 7.5 polyester 6 16 140 3.3 62 Ti Na 7.1 polyester 5 17 140 3.3 62 Zr Na 7.5 Urethane 5

[Table 2] Painted steel sheet No. Substrate steel plate Epithelial structure Type of coating Phosphate film Chrome free seal organic film type adhesion amount adhesion amount Ni+Co adhesion amount type pH Resin type Film thickness (g/m ² ) (g/m ² ) (mg/m ² ) Group IV metals Group 1 metals (μm) 18 SUS430 Zn-0.1Al 200 3.3 11 Zr Na 7.5 polyester 5 19 200 3.3 18 Zr Na 7.5 polyester 5 20 200 3.3 0 Zr Na 7.5 polyester 5 twenty one 200 3.3 110 Zr Na 7.5 polyester 5 twenty two 200 1.7 62 Zr Na 7.5 polyester 5 twenty three 200 7.5 62 Zr Na 7.5 polyester 5 twenty four 200 3.3 62 Zr - 7.5 polyester 5 25 200 3.3 62 Zr Na 6.5 polyester 5 26 200 3.3 62 Zr Na 10.6 polyester 5 27 200 3.3 62 Zr Na 7.5 - - 28 200 3.3 62 - Na 7.5 polyester 5 29 200 - polyester 5 30 ordinary steel 200 - polyester 5

3. Evaluation of coated steel sheets 3-1. Corrosion resistance The coated steel sheet 1 to the coated steel sheet 30 were put into a salt water spray tester, and the white rust generation area ratio after 240 hours was obtained, and the coated steel sheet 1 to the coated steel sheet were evaluated from the white rust generated area ratio according to the following criteria. 30 corrosion resistance. ◎: The area rate of white rust generation is 5% or less ○: The area rate of white rust generation is more than 5% and 10% or less △: The area ratio of white rust generation is more than 10% and 40% or less ×: The area rate of white rust is more than 40%

3-2. Brightness Using a colorimeter (manufactured by BYK, Spectro-guide gloss S), under the conditions of light source: D65 and viewing angle: 2°, the organic content of coated steel sheets 1 to 30 was measured. The lightness (L*) of the surface of the coating film (the surface of the coated steel sheet 1, which is a chrome-free sealed surface), and the measured lightness was used to evaluate the corrosion resistance of the coated steel sheet 1 to the coated steel sheet 30 according to the following criteria. . ◎: Lightness (L*) is 50 or less ○: Lightness (L*) is more than 50 and less than 55 △: Lightness (L*) greater than 55 and less than 65 ×: Lightness (L*) greater than 65

3-3. Adhesion of processed parts After immersing the coated steel sheet 1 to the coated steel sheet 30 in boiling water for 2 hours, a 1 mm square checkerboard-shaped incision (100 pieces) was formed on the surface with a cutter blade, and the Erichsen testing machine was used for testing. 5 mm overhang processing is performed on the part where the notch is formed. A peeling test was performed on the protruding processed part using an adhesive tape, and the adhesion of the processed parts of the painted steel sheet 1 to the painted steel sheet 30 was evaluated based on the number of peeled notches relative to 100 notches according to the following criteria. sex. ⊚: No peeling of the film was observed ○: The ratio of peeled cuts is more than 0% and 5% or less △: The ratio of peeled cuts is more than 5% and 30% or less ×: The ratio of peeled cuts is more than 30%

3-4. Evaluation results Table 3 and Table 4 show the evaluation results of the corrosion resistance, lightness, and working part adhesion of the coated steel sheet 1 to the coated steel sheet 30 .

[table 3] Painted steel sheet No. Quality performance Corrosion resistance Lightness (L*) Working part adhesion 1 ◎ ○ ◎ 2 ○ ◎ ◎ 3 ◎ ◎ ◎ 4 ◎ ○ ◎ 5 ◎ ○ ◎ 6 ◎ ◎ ◎ 7 ◎ ○ ◎ 8 ◎ ◎ ◎ 9 ◎ ○ ◎ 10 ◎ ◎ ◎ 11 ◎ ◎ ◎ 12 ◎ ◎ ◎ 13 ◎ ◎ ◎ 14 ◎ ◎ ◎ 15 ◎ ◎ ◎ 16 ◎ ○ ◎ 17 ◎ ◎ ◎

[Table 4] Painted steel sheet No. Quality performance Corrosion resistance Lightness (L*) Working part adhesion 18 ◎ × ◎ 19 ◎ △ ◎ 20 ◎ × ◎ twenty one × ◎ ◎ twenty two ◎ △ ◎ twenty three ◎ ◎ △ twenty four ◎ ◎ △ 25 ◎ △ ◎ 26 ◎ △ ◎ 27 × ◎ - 28 × ◎ ◎ 29 × × × 30 × × ×

As is clear from the results in Tables 3 and 4, the steel sheet; the zinc-based plating layer; the total adhesion amount of Ni and Co is 20 mg/m ² or more and 100 mg/m ² or less, and the treated layer is arranged in this order. A phosphate-treated layer with an adhesion amount of 2.0 g/m ² or more and 7.0 g/m ² or less; a chromium-free sealing film containing an oxo acid salt of a Group IV metal and a Group I metal or a salt thereof; and an organic type In the coated steel sheet 1 to the coated steel sheet 17, the lightness (L*) was 55 or less, and the corrosion resistance and the adhesion to the processed part were high.

In addition, as is clear from the comparison of the coated steel sheet 1 with the coated steel sheet 2 and the coated steel sheet 3, when the total adhesion amount of Ni and Co in the phosphate-treated layer is 30 mg/m ² or more and 80 mg/m When it is ² or less, the lightness of the surface of the coated steel sheet becomes lower, and the corrosion resistance becomes higher. In this regard, it is considered that when the total adhesion amount of Ni and Co in the phosphate-treated layer is 30 mg/m ² or more, Ni and Co are sufficiently precipitated, so that the lightness of the surface of the coated steel sheet becomes lower. When the total deposition amount of Ni and Co in the layer is 80 mg/m ² or less, the precipitation of Ni and Co is less likely to inhibit the precipitation of phosphate crystals, so that the corrosion resistance of the coated steel sheet becomes higher.

In addition, as is clear from the comparison of the coated steel sheet 3 with the coated steel sheet 4 and the coated steel sheet 5, when the pH of the chemical conversion treatment liquid is 7.2 or more and 8.5 or less, the lightness of the surface of the coated steel sheet becomes lower. . In this regard, it is considered that when the pH of the chemical conversion treatment liquid is 7.2 or more and 8.5 or less, the dissolution of the phosphate-treated layer in the chemical conversion treatment liquid is suppressed, and the lightness of the surface of the coated steel sheet can be lowered.

In addition, as is clear from the comparison of the painted steel sheet 3 and the painted steel sheet 7, and the comparison of the painted steel sheet 15 and the painted steel sheet 16, when the chromium-free sealing film contains an oxo-acid salt of Zr as a Group IV metal In the case of the oxo acid salt, the lightness of the surface of the coated steel sheet becomes lower than when the chromium-free sealing film contains the oxo acid salt of Ti as the oxo acid salt of the Group IV metal. In this regard, since the pH of the chromium-free sealing treatment liquid is low, the phosphate film and the Ni substitution layer on the surface are slightly removed, and the lightness of the surface of the coated steel sheet is considered to be lower.

In addition, as is clear from the comparison between the coated steel sheet 3 and the coated steel sheet 9, when the adhesion amount of the phosphate-treated layer is 2.5 g/m ² or more and 7.0 g/m ² or less, the lightness of the surface of the coated steel sheet become lower. In this regard, when the adhesion amount of the phosphate treatment layer is 2.5 g/m ² or more and 7.0 g/m ² or less, the adhesion amount of the phosphate film is small, so that the lightness of the surface of the coated steel sheet is considered to be lower.

On the other hand, as is clear from the comparison of the coated steel sheet 3 and the coated steel sheets 18 to ²⁰ , when the total adhesion amount of Ni and Co in the phosphated layer is less than 20 mg/m The brightness of the surface of the steel plate is higher than 55. In this regard, when the total adhesion amount of Ni and Co in the phosphated layer is less than 20 mg/m ² , since the amount of Ni or Co precipitation is small, it is considered that the surface brightness of the coated steel sheet does not decrease.

In addition, as is clear from the comparison between the coated steel sheet 3 and the coated steel sheet 21, when the total adhesion amount of Ni and Co in the phosphated layer exceeds 100 mg/m ² , the corrosion resistance of the coated steel sheet deteriorates. lower. In this regard, it is considered that when the total adhesion amount of Ni and Co in the phosphate-treated layer exceeds 100 mg/m ² , the precipitation of phosphate crystals is inhibited by the precipitated Ni or Co, and thus the surface of the coated steel sheet is considered Corrosion resistance is not improved.

In addition, as is clear from the comparison of the coated steel sheet 3 and the coated steel sheet 22, when the adhesion amount of the phosphated layer is less than 2.0 g/m ² , the lightness of the surface of the coated steel sheet is higher than 55. In this regard, it is considered that when the adhesion amount of the phosphate treatment layer is less than 2.0 g/m ² , the adhesion amount of the phosphate film is small, so that the lightness of the surface of the coated steel sheet is not lowered.

In addition, as is clear from the comparison of the painted steel sheet 3 and the painted steel sheet 23, when the adhesion amount of the phosphated layer exceeds 7.0 g/m ² , the adhesion of the processed portion of the painted steel sheet decreases. In this regard, when the adhesion amount of the phosphate-treated layer exceeds 7.0 g/m ² , the size of the phosphate crystal becomes large, and it is likely to be peeled off in powder form during processing, so that it is difficult to improve the adhesion of the processed part of the coated steel sheet.

In addition, as is clear from the comparison of the coated steel sheet 3 and the coated steel sheet 24, when the chrome-free sealing film does not contain the Group 1 metal or its salt, the corrosion resistance of the coated steel sheet and the adhesion of the processed part decrease. In this regard, it is considered that when the chromium-free sealing film does not contain the Group 1 metal or its salt, the amount of hydroxyl groups in the chemical conversion treatment liquid is insufficient, so that it is difficult to improve the corrosion resistance of the coated steel sheet, and peeling of the organic film occurs, causing the coating It is difficult to improve the adhesion of the processed part of the steel plate.

In addition, as is clear from the comparison of the coated steel sheet 3 with the coated steel sheet 25 and the coated steel sheet 26, when the pH of the chemical conversion treatment liquid deviates from the range of 7.0 or more and 9.0 or less, the lightness of the surface of the coated steel sheet becomes lower. In this regard, when the pH of the chemical conversion treatment liquid is not 7.0 or more and 9.0 or less, the phosphate treatment layer is dissolved in the chemical conversion treatment liquid, and therefore, it is considered that the lightness of the surface of the coated steel sheet is difficult to decrease.

In addition, as can be seen from the comparison between the coated steel sheet 3 and the coated steel sheet 27, when the coated steel sheet does not have an organic-based film, the corrosion resistance and corrosion resistance of the coated steel sheet decrease.

In addition, as is clear from the comparison between the coated steel sheet 3 and the coated steel sheet 28, when the chrome-free sealing film does not contain an oxo acid salt of a Group IV metal, the corrosion resistance of the coated steel sheet decreases.

In addition, as is clear from the comparison of the painted steel sheet 3 and the painted steel sheet 29, and the comparison of the painted steel sheet 15 and the painted steel sheet 30, when the painted steel sheet does not have the phosphate treatment layer and the chrome-free sealing film, the The corrosion resistance, the lightness, and the adhesion of the processed part of the steel plate were not at the desired level. [Industrial Availability]

The coated steel sheet of the present invention can be suitably used, for example, for various electronic equipment, household appliances, medical equipment, automobile bodies, vehicle-mounted products, building materials, and the like. In particular, since the coated steel sheet of the present invention is low in lightness, it is excellent in designability, and is excellent in corrosion resistance and working part adhesion, so that it can be preferably used as a building material.

Claims (7)

A coated steel sheet, comprising in this order: a steel sheet; a zinc ^- based plating layer ^; 2.0 g/m ² to 7.0 g/m ² The lightness (L*) of the surface is 55 or less. The coated steel sheet according to claim 1, wherein the chromium-free sealing film contains an ammonium salt. The coated steel sheet according to claim 1 or claim 2, wherein the zinc-based plating layer contains Al in an amount of 0.1 mass % or more and 20 mass % or less. The coated steel sheet according to claim 1 or claim 2, wherein the adhesion amount of the zinc-based plating layer is 100 g/m ² or more. The coated steel sheet according to claim 1 or claim 2, wherein the chromium-free sealing film contains sodium tripolyphosphate, disodium 1-hydroxyethylene-1,1-bisphosphonate, and 1 A salt in the group consisting of pentasodium hydroxyethylene-1,1-diphosphonate is used as the first group metal or a salt thereof. The coated steel sheet according to claim 1 or claim 2, which is an exterior building material. A method of manufacturing a coated steel sheet, comprising: a step of preparing a plated steel sheet having a zinc-based plating layer; a step of forming a phosphate-treated layer in contact with the zinc-based plating layer, wherein the phosphate-treated layer is , the total adhesion amount of Ni and Co is 20 mg/m ² or more and 100 mg/m ² or less, and the adhesion amount of the treatment layer is 2.0 g/m ² or more and 7.0 g/m ² or less; and the phosphate treatment layer The step of forming a chromium-free sealing film by imparting and drying a chemical conversion treatment liquid, the chemical conversion treatment liquid containing an oxo acid salt of a Group IV metal, a Group I metal or a salt thereof, and ammonium ions, and pH is 7.0 or more and 9.0 or less; and the step of forming an organic film in contact with the chrome-free sealing film.