Zn-based plated steel sheet

Abstract

A Zn-based plated steel sheet includes: a steel sheet; a Zn-based plated layer which contains Zn and 0.05 to 60 mass% of Al and is placed on at least one surface of the steel sheet; and a chromate-free chemical conversion treatment layer which has a deposition amount of 0.1 to 15 g / m² per surface and is placed on the Zn-based plated layer, in which the chemical conversion treatment layer contains 20 mass% or more of a resin, I to 20 mass% of silica particles having an average particle diameter of 5 to 200 nm, and a pigment containing one or more of Cu, Co, or Fe, b of an appearance of the Zn-based plated steel sheet evaluated in a CIE 1976 (L, a, b’) color space is -30 to -2, a 60-degree mirror surface glossiness Gₛ (60°) specified in JIS Z 8741:1997 is 50 to 200, and the Zn-based plated steel sheet exhibits a metallic appearance.

Description

Zn-based plated steel sheet

[0001] The present invention relates to a zinc-based plated steel sheet. This application claims priority to Japanese Patent Application No. 2020-176149, filed on October 20, 2020, the contents of which are incorporated herein by reference.

[0002] Zn-based plated steel sheets are the most widely used type of plated steel sheet with good corrosion resistance. Zn-based plated steel sheets are used in various manufacturing industries, including automobiles, home appliances, and building materials. Among these, Al-added plating has been increasingly used in recent years due to its high corrosion resistance.

[0003] As an example of a Zn-based plated steel sheet developed for the purpose of improving corrosion resistance, a hot-dip Zn-Al-Mg-Si plated steel sheet is described in Patent Document 1. This plated steel sheet has a matte finish on its exterior, and is therefore characterized by its beautiful appearance.

[0004] Conventionally, in order to impart a higher level of rust prevention to zinc-based plated steel sheets, a chromate treatment using hexavalent chromate or the like has been widely performed after plating, and further, as necessary, an organic resin coating has been performed to impart high-value-added functions such as designability, stain resistance, and lubricity. However, against the backdrop of growing environmental concerns, there is a movement to refrain from using chromate treatment. Therefore, there is a surface-treated plated steel sheet described in Patent Document 2 below, which aims to simply impart a higher level of rust prevention function by only applying a single layer of a resin-based coating without performing a chromate treatment.

[0005] It is possible to further improve corrosion resistance by using the coating described in Patent Document 2. However, a zinc-based plated steel sheet containing Al has a problem in that, when stored for a long period of time, the Al contained in the plated layer oxidizes, causing partial or total blackening of the plated surface.

[0006] Japanese Patent No. 3179446 Japanese Patent Application Laid-Open No. 2006-52462

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a zinc-based plated steel sheet containing Al, which can maintain its metallic appearance by making the blackening less noticeable even when the plated surface is partially or entirely blackened, and which has improved corrosion resistance and weather resistance.

[0008] In order to solve the above problems, the present inventors have conducted extensive research and found that by incorporating a pigment into the chemical conversion coating layer, black discoloration on the surface of the plating layer can be made less noticeable and the metallic appearance of the plating layer surface is not impaired.

[0009] [1] A steel sheet; a Zn-based plating layer containing 0.05 to 60 mass% of Al and Zn, disposed on at least one side of the steel sheet; and a coating weight of 0.1 to 15 g / m per side disposed on the Zn-based plating layer. ２ and a chromate-free chemical conversion coating layer of the above formula, wherein the chemical conversion coating layer contains 20 mass % or more of a resin, 1 to 20 mass % of silica particles having an average particle size of 5 to 200 nm, and a pigment containing one or more of Cu, Co, and Fe, and the appearance is determined to be in accordance with CIE 1976 (L ＊ , a ＊ , b ＊ ) b when evaluated in color space ＊ is -30 or more and -2 or less, and the 60-degree specular gloss G specified in JIS Z 8741:1997 ｓ[2] The zinc-based plated steel sheet according to [1], wherein the pigment is one or more of copper(II) phthalocyanine, cobalt(II) phthalocyanine, copper sulfate, cobalt sulfate, iron sulfate, and iron oxide. [3] The zinc-based plated steel sheet according to [1] or [2], wherein, when a mixing ratio of the silica particles to the pigment in the chemical conversion treatment layer is expressed as an amount [Si] calculated as the silicon equivalent of the silica particles and an amount [Cu] calculated as the copper equivalent of the pigment, an amount [Co] calculated as the cobalt equivalent of the pigment, or an amount [Fe] calculated as the iron equivalent of the pigment, the ratio [Si] / ([Cu] + [Co] + [Fe]) is in the range of 1 to 200. [4] The zinc-based plated steel sheet according to any one of [1] to [3], wherein the zinc-based plating layer has an arithmetic mean roughness Ra of 0.5 to 2.0 μm and an arithmetic mean height Sa of 5 nm to 100 nm. [5] The zinc-based plated steel sheet according to any one of [1] to [4], wherein the chemical conversion treatment layer further contains either an Nb compound or a phosphate compound, or both. [6] The zinc-based plated steel sheet according to any one of [1] to [5], wherein the resin in the chemical conversion treatment layer contains one or more resins selected from the group consisting of polyolefin resin, fluororesin, acrylic resin, urethane resin, polyester resin, epoxy resin, and phenol resin. [7] The Zn-based plated steel sheet according to any one of [1] to [6], wherein the Zn-based plating layer contains, in an average composition, 4 to 22% by mass of Al, 1 to 10% by mass of Mg, and the balance being Zn and impurities. [8] The Zn-based plated steel sheet according to any one of [1] to [7], wherein the Zn-based plating layer further contains, in an average composition, 0.0001 to 2% by mass of Si. [9] The Zn-based plated steel sheet according to any one of [1] to [8], wherein the Zn-based plating layer further contains, in an average composition, 0.0001 to 2% by mass of one or more of Ni, Sb, and Pb in a total amount of 0.0001 to 2% by mass.

[10] The zinc-based plated steel sheet according to any one of [1] to [9], wherein the zinc-based plating layer has a patterned portion and a non-patterned portion arranged to have a predetermined shape, the patterned portion and the non-patterned portion each including one or two of a first region and a second region determined by any of the following determination methods 1 to 5, and the absolute value of the difference between the area ratio of the first region in the patterned portion and the area ratio of the first region in the non-patterned portion is 30% or more. [Determination method 1] Virtual grid lines are drawn on the surface of the zinc-based plating layer at intervals of 0.5 mm, and in each of a plurality of regions partitioned by the virtual grid lines, a circle with a diameter of 0.5 mm centered at the center of gravity of each region is defined as a measurement region A, and L in each measurement region A is determined. ＊ The obtained L ＊ 50 points were selected arbitrarily from the values, and the obtained L ＊ The average of 50 points is the standard L ＊ When the value is set as ＊ The value is standard L ＊ The area where the value is equal to or greater than the reference value is called the first area. ＊ [Determination Method 2] Virtual grid lines are drawn at 0.5 mm intervals on the surface of the Zn-based plating layer, and in each of the multiple regions defined by the virtual grid lines, a circle with a diameter of 0.5 mm centered at the center of gravity of each region is defined as a measurement region A. ＊ The value was measured, and L ＊ The area where the value is 45 or more is the first area, L ＊ The region where the value is less than 45 is designated as the second region. [Determination method 3] Virtual lattice lines are drawn on the surface of the Zn-based plating layer at intervals of 0.5 mm, and the arithmetic mean height Sa2 is measured in each of the multiple regions defined by the virtual lattice lines. The region where the obtained arithmetic mean height Sa2 is 1 μm or more is designated as the first region, and the region where it is less than 1 μm is designated as the second region. [Determination method 4] Virtual lattice lines are drawn on the surface of the Zn-based plating layer at intervals of 1 mm or 10 mm, and an X-ray is incident on each of the multiple regions defined by the virtual lattice lines to measure the diffraction peak intensity I of the (0002) plane of the Zn phase for each of the multiple regions. ０００２and the diffraction peak intensity I of the (10-11) plane of the Zn phase １０－１１ and the intensity ratio (I ０００２ / I １０－１１ ) is defined as the orientation ratio. A region where the orientation ratio is 3.5 or more is defined as a first region, and a region where the orientation ratio is less than 3.5 is defined as a second region. [Determination Method 5] Virtual grid lines are drawn on the surface of the Zn-based plating layer at 1 mm intervals, and then, for each of a plurality of regions defined by the virtual grid lines, a circle S is drawn with its center at the center of gravity G of each region. The diameter R of the circle S is set so that the total length of the surface boundary lines of the Zn-based plating layer included within the circle S is 10 mm. The average value of the maximum diameter Rmax and the minimum diameter Rmin among the diameters R of the circles S of a plurality of regions is defined as a reference diameter Rave, and a region having a circle S with a diameter R less than the reference diameter Rave is defined as a first region, and a region having a circle S with a diameter R equal to or greater than the reference diameter Rave is defined as a second region.

[11] The Zn-based plated steel sheet according to any one of [1] to

[10] , wherein the surface of the Zn-based plating layer contains one or more of Co, Fe, and Ni.

[0010] According to the present invention, it is possible to provide a zinc-based plated steel sheet that, even when the plated surface of an Al-containing zinc-based plated steel sheet is partially or entirely discolored black due to oxidation of Al contained in the plated layer, can make the discoloration less noticeable and maintain its metallic appearance, and has improved corrosion resistance and weather resistance.

[0011] The present inventors have found that by adding a pigment to the chemical conversion coating layer to color it blue, the blackened areas on the surface of the plating layer become less noticeable. However, if the blue color is too dark, the metallic appearance of the plating layer surface becomes difficult to see. They have also found that the visibility of the blackened areas and the metallic appearance change depending on whether incident light is reflected on the surface of the plating layer or the surface of the chemical conversion coating layer. Further investigation has revealed that the visibility of the blackened areas and the metallic appearance change depending on whether incident light is reflected on the surface of the plating layer or the surface of the chemical conversion coating layer. ＊ , a ＊ , b ＊ ) b when evaluated in color space ＊ value and the 60-degree specular gloss G defined in JIS Z 8741:1997 ｓ(60°) to be within a predetermined range, the blackened areas on the surface of the plating layer can be made less noticeable, and the metallic appearance can be visually recognized. ＊ Value and 60 degree specular gloss G ｓ It has also been found that by controlling the angle (60°), even when an arbitrary shape such as a letter is displayed on the surface of the plating layer, the arbitrary shape can be easily seen.

[0012] That is, the Zn-based plated steel sheet according to an embodiment of the present invention comprises a steel sheet, a Zn-based plating layer containing 0.05 to 60 mass % of Al and Zn and disposed on at least one surface of the steel sheet, and a Zn-based plating layer having a coating weight of 0.1 to 15 g / m per surface and disposed on the Zn-based plating layer. ２ and a chromate-free chemical conversion coating layer of the above formula (I), which contains 20 mass % or more of resin, 1 to 20 mass % of silica particles having an average particle size of 5 to 200 nm, and a pigment containing one or more of Cu, Co, and Fe, and the appearance is determined to be in accordance with CIE 1976 (L ＊ , a ＊ , b ＊ ) b when evaluated in color space ＊ is -30 or more and -2 or less, and the 60-degree specular gloss G specified in JIS Z 8741:1997 ｓ The zinc-based plated steel sheet has a Zn-based surface roughness (60°) of 50 to 200 and exhibits a metallic appearance. In the zinc-based plated steel sheet of this embodiment, the pigment is preferably one or more of copper (II) phthalocyanine, cobalt (II) phthalocyanine, copper sulfate, cobalt sulfate, iron sulfate, and iron oxide. In the zinc-based plated steel sheet of this embodiment, when the mixing ratio of silica particles to pigment in the chemical conversion treatment layer is expressed as the Si-equivalent amount [Si] of the silica particles and the Cu-equivalent amount [Cu], Co-equivalent amount [Co], or Fe-equivalent amount [Fe] of the pigment, it is preferable that [Si] / ([Cu] + [Co] + [Fe]) is in the range of 1 to 200. The units of the Si-equivalent amount, Cu-equivalent amount, Co-equivalent amount, and Fe-equivalent amount are "g / m" ２In the Zn-based plated steel sheet of this embodiment, it is preferable that the Zn-based plated layer has an arithmetic mean roughness Ra of 0.5 to 2.0 μm, and the chemical conversion treatment layer has an arithmetic mean height Sa of 5 nm to 100 nm.

[0013] [Zn-based plated steel sheet] The Zn-based plated steel sheet of this embodiment will be described below. There are no particular restrictions on the material of the steel sheet that serves as the base for the Zn-based plated layer. General steel and the like can be used as the material without any particular restrictions, and Al-killed steel and some high-alloy steels can also be applied, and there are no particular restrictions on the shape. The Zn-based plated layer of this embodiment is formed by applying a hot-dip galvanizing method, which will be described later, to the steel sheet.

[0014] [Zn-based Plating Layer] Next, the chemical components of the Zn-based plating layer will be described. The Zn-based plating layer preferably contains 0.05 to 60 mass% Al and Zn, and more preferably 0.05 to 60 mass% Al, with the remainder consisting of Zn and impurities. By containing 0.05 mass% or more Al, the corrosion resistance of the Zn-based plating layer can be improved, and by setting the Al content to 60 mass% or less, the amount of Zn contained in the Zn-based plating layer can be relatively increased, thereby ensuring sacrificial corrosion protection. The Zn-based plating layer may contain 40 mass% or more Zn.

[0015] The Zn-based plating layer of this embodiment may contain, in average composition, 4 to 22 mass% Al, 1 to 10 mass% Mg, and the remainder Zn and impurities. The Zn-based plating layer may also contain, in average composition, 0.0001 to 2 mass% Si.

[0016] The reasons for limiting the components of the Zn-based plating layer, which contains 4 to 22 mass % Al, 1 to 10 mass % Mg, and the balance being Zn and impurities, will be explained below.

[0017] The Al content is in the range of 4 to 22 mass%. Al is preferably added to ensure corrosion resistance. If the Al content in the Zn-based plating layer is 4 mass% or more, the effect of improving corrosion resistance is further enhanced. If the Al content is 22 mass% or less, the effect of improving corrosion resistance and weather resistance can be more easily ensured while maintaining the metallic appearance.

[0018] The Mg content is in the range of 1 to 10 mass%. Mg is preferably added to improve corrosion resistance. If the Mg content in the Zn-based coating layer is 1 mass% or more, the effect of improving corrosion resistance is further enhanced. If the Mg content is 10 mass% or less, the generation of dross in the coating bath is suppressed, and the occurrence of areas where the coating is not formed normally due to the adhesion of dross to the coating can be suppressed, and a decrease in corrosion resistance can be suppressed.

[0019] The Mg content may be 0%. That is, the Zn-based plating layer of the Zn-based plated steel sheet of the present embodiment is not limited to a Zn—Al—Mg-based hot-dip plating layer, and may be a Zn—Al-based hot-dip plating layer.

[0020] The Zn-based plating layer may also contain Si in the range of 0.0001 to 2 mass%. Si may be included because it may improve the adhesion of the Zn-based plating layer. The effect of improving adhesion is achieved by including 0.0001 mass% or more of Si, preferably 0.001% or more, and more preferably 0.01% or more. Therefore, it is preferable to include 0.0001 mass% or more of Si. On the other hand, even if the Si content exceeds 2 mass%, the effect of improving plating adhesion saturates, so the Si content is set to 2 mass% or less. From the viewpoint of plating adhesion, the Si content may be set to 0.001 to 1 mass%, or 0.01 to 0.8 mass%.

[0021] The Zn-based plating layer may contain, in average composition, one or more of Ni, Sb, and Pb in a total amount of 0.0001 to 2 mass%, preferably 0.001 to 2 mass%, which can further improve corrosion resistance.

[0022] The remainder of the chemical composition of the Zn-based plating layer is zinc (Zn) and impurities. The impurities include those that are inevitably contained in zinc and other base metals, and those that are contained when the steel dissolves in the plating bath.

[0023] The average composition of the Zn-based plating layer can be measured by the following method. First, the chemical conversion coating layer is removed using a coating remover that does not corrode the plating (e.g., Neo River SP-751 manufactured by Sansai Kako Co., Ltd.). If a surface coating is present on the chemical conversion coating layer, this surface coating is also removed. Then, the Zn-based plating layer is dissolved in hydrochloric acid containing an inhibitor (e.g., Hibilon manufactured by Sugimura Chemical Industry Co., Ltd.), and the average composition can be determined by subjecting the resulting solution to inductively coupled plasma (ICP) atomic emission spectrometry.

[0024] Furthermore, the surface of the Zn-based plating layer preferably contains one or more of Co, Fe, and Ni. Co, Fe, and Ni are attached to the surface of the Zn-based plating layer by performing a Co treatment, an Fe treatment, or an Ni treatment after the formation of the Zn-based plating layer. The presence of these elements on the surface of the Zn-based plating layer can improve blackening resistance. Co, Fe, or Ni is preferably present on the surface of the Zn-based plating layer in the form of a compound.

[0025] [Chemical Conversion Treatment Layer] Next, the chemical conversion treatment layer will be described. The chemical conversion treatment layer of this embodiment contains 20 mass % or more of a resin, 1 to 20 mass % of silica particles having an average particle size of 5 to 200 nm, and a pigment containing one or more of Cu, Co, and Fe. The chemical conversion treatment layer of this embodiment is a coating obtained by applying an aqueous composition containing a resin, silica particles, and pigment to a Zn-based plating layer formed on a steel sheet and drying the composition.

[0026] [Resin] The resin contained in the chemical conversion treatment layer may be a common resin, such as polyolefin resin, fluororesin, acrylic resin, urethane resin, polyester resin, epoxy resin, phenolic resin, etc. These resins may be water-soluble resins, or may be resins (water-dispersible resins) that are originally water-insoluble but can be finely dispersed in water, such as emulsions or suspensions. In addition to water-soluble resins, resins (water-dispersible resins) that are originally water-insoluble but can be finely dispersed in water, such as emulsions or suspensions, are also referred to as resins. In particular, it is preferable to include one or more resins selected from polyolefin resins, fluororesins, acrylic resins, and phenolic resins, as these resins have excellent weather resistance.

[0027] The polyolefin resin is not particularly limited, and examples thereof include those obtained by radically polymerizing ethylene and an unsaturated carboxylic acid such as methacrylic acid, acrylic acid, maleic acid, fumaric acid, itaconic acid, or crotonic acid under high temperature and high pressure, neutralizing the polymer with ammonia, an amine compound, a metal compound such as KOH, NaOH, or LiOH, or ammonia or an amine compound containing any of the above metal compounds, and dispersing the polymer in water.

[0028] The fluororesin is not particularly limited, and examples thereof include homopolymers and copolymers of fluoroolefins. In the case of copolymers, examples include copolymers of fluoroolefins with fluorine-containing monomers other than fluoroolefins and / or monomers not containing fluorine atoms.

[0029] The acrylic resin is not particularly limited, and examples thereof include those obtained by radical polymerization of unsaturated monomers such as styrene, alkyl (meth)acrylates, (meth)acrylic acid, hydroxyalkyl (meth)acrylates, and alkoxysilane (meth)acrylates in an aqueous solution using a polymerization initiator. The polymerization initiator is not particularly limited, and examples thereof include persulfates such as potassium persulfate and ammonium persulfate, and azo compounds such as azobiscyanovaleric acid and azobisisobutyronitrile.

[0030] The urethane resin is not particularly limited, and examples thereof include those obtained by reacting a polyhydric alcohol such as ethylene glycol, propylene glycol, diethylene glycol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, bisphenol hydroxypropyl ether, glycerin, trimethylolethane, or trimethylolpropane with a diisocyanate compound such as hexamethylene diisocyanate, isophorone diisocyanate, or tolylene diisocyanate, and then chain-extending the resulting mixture with a diamine or the like, followed by dispersing the resulting mixture in water.

[0031] The polyester resin is not particularly limited, and examples thereof include those obtained by dehydration condensation of polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, bisphenol hydroxypropyl ether, glycerin, trimethylolethane, trimethylolpropane, and polybasic acids such as phthalic anhydride, isophthalic acid, terephthalic acid, succinic anhydride, adipic acid, sebacic acid, maleic anhydride, itaconic acid, fumaric acid, and himic anhydride, neutralizing the resulting mixture with ammonia, an amine compound, or the like, and dispersing the resulting mixture in water.

[0032] The epoxy resin is not particularly limited, and examples thereof include those obtained by reacting an epoxy resin such as a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, a resorcinol type epoxy resin, a hydrogenated bisphenol A type epoxy resin, a hydrogenated bisphenol F type epoxy resin, a resorcinol type epoxy resin, or a novolac type epoxy resin with an amine compound such as diethanolamine or N-methylethanolamine, followed by neutralization with an organic acid or an inorganic acid; and those obtained by radically polymerizing a high acid value acrylic resin in the presence of the above-mentioned epoxy resin, followed by neutralization with ammonia, an amine compound, or the like, and dispersing the polymer in water.

[0033] The phenolic resin is not particularly limited, and examples thereof include those obtained by reacting a phenolic resin such as a methylolated phenolic resin obtained by addition reaction of an aromatic compound such as phenol, resorcinol, cresol, bisphenol A, or paraxylylene dimethyl ether with formaldehyde in the presence of a reaction catalyst with an amine compound such as diethanolamine or N-methylethanolamine, and then neutralizing the resulting resin with an organic acid or an inorganic acid.

[0034] The resin is contained in the chemical conversion coating layer at a ratio of 20% by mass or more. By making the resin content 20% by mass or more, the chemical conversion coating layer itself does not become brittle, and the Zn-based plating layer can be stably coated. Note that the chemical conversion coating layer may contain components other than the resin, such as Nb compounds and phosphate compounds, in addition to the resin, silica particles, and pigment, and the resin content may be the remainder of these components.

[0035] [Silica Particles] Silica particles are added to improve the corrosion resistance of the chemical conversion coating layer. The average particle size of the silica particles is preferably in the range of 5 to 200 nm. The silica particles are contained in the chemical conversion coating layer at a ratio of 1 to 20 mass %. By increasing the silica particle content to 1 mass % or more, improved corrosion resistance can be achieved. Furthermore, by increasing the silica particle content to 20 mass % or less, the chemical conversion coating layer itself does not become brittle, and the Zn-based plating layer can be stably coated. Because silica particles with an average particle size of less than 5 nm are difficult to obtain and chemical conversion coating layers containing silica particles with an average particle size of less than 5 nm are practically difficult to produce, the lower limit of the average particle size of the silica particles is set to 5 nm or more. Furthermore, if the average particle size of the silica particles exceeds 200 nm, the chemical conversion coating layer may become cloudy, potentially impairing the metallic appearance of the Zn-based plating layer. From the viewpoint of maintaining both the corrosion resistance and strength of the chemical conversion coating layer, the silica particle content in the chemical conversion coating layer is preferably 3 to 15 mass %.

[0036] Generally, inorganic pigments such as silica particles have small particle sizes, and therefore may exist in the chemical conversion treatment layer in the form of secondary particles larger than the primary particle size. The particle size of these secondary particles (particles formed by agglomeration of inorganic pigments) will be referred to as the "secondary particle size" hereinafter. The silica particles in this embodiment may be a mixture of primary particles and secondary particles, and even if primary particles and secondary particles are mixed, it is sufficient that both have an average particle size in the range of 5 to 200 nm. From the viewpoint of maintaining high permeability of the chemical conversion treatment layer, the average particle size of the silica particles is more preferably 5 to 150 nm.

[0037] The average particle size of silica in the chemical conversion coating layer is measured by the following method. First, a thin film sample of the chemical conversion coating layer is prepared by microtome method so that a cross section perpendicular to the rolling direction of the steel sheet of the present invention can be observed. At least five regions of a 20 μm × t μm area of ​​the obtained thin film sample (a region of 20 μm in the direction parallel to the sheet width direction and a film thickness of t μm in the sheet thickness direction) are observed at a magnification of 100,000 times using a 200 kV field emission transmission electron microscope (FE-TEM). The circle-equivalent diameters of all silica particles in the observed region are calculated using the following equation 1, and these circle-equivalent diameters are used as the particle size of each silica particle. The average particle size is determined by averaging these diameters.

[0038] Equivalent circle diameter=2√(S / π) Equation 1 where S is the area of ​​the silica particle, and π is the ratio of the circumference of the particle to its circumference.

[0039] The silica particle content in the chemical conversion coating layer is measured by the following method. First, a plurality of comparison samples having a chemical conversion coating layer with a known silica particle content are prepared in addition to the target sample. The surfaces of these samples are measured using an X-ray fluorescence analyzer, and a calibration curve is drawn from the relationship between the obtained Si detection intensity and the silica particle content. Next, the target sample is measured using the X-ray fluorescence analyzer under the same conditions as the comparison sample, and the silica particle content is determined from the obtained Si detection intensity using the above calibration curve.

[0040] In the present invention, the average particle size of the silica dispersed in water before being dispersed in the paint is maintained in the chemical conversion coating layer, and therefore this value may be used.

[0041] In order to improve the corrosion resistance of the chemical conversion coating layer, titania particles, alumina particles, zirconia particles, etc. may be contained in addition to silica particles.

[0042] [Pigment] The chemical conversion treatment layer contains a pigment containing one or more of Cu, Co, or Fe. The pigment may contain one or more of Cu, Co, or Fe. The chemical conversion treatment layer may also contain one or more pigments containing one or more of Cu, Co, or Fe. Examples of pigments include copper(II) phthalocyanine, cobalt(II) phthalocyanine, copper sulfate, cobalt sulfate, iron sulfate, or iron oxide. By incorporating a pigment into the chemical conversion treatment layer, the chemical conversion treatment layer is colored blue, making blackened areas on the plating layer surface less noticeable. To achieve this effect, the pigment content in the chemical conversion treatment layer is preferably in the range of 0.1 to 10% by mass. By incorporating a pigment content in the chemical conversion treatment layer of 0.1% by mass or more, blackened areas on the zinc-based plating layer surface can be made less noticeable. Furthermore, by setting the pigment content to 10% by mass or less, the metallic appearance of the Zn-based plating layer is not impaired. From the viewpoint of maintaining the metallic appearance, the pigment content is more preferably 0.1 to 5% by mass, and even more preferably 0.1 to 3% by mass.

[0043] The pigment content in the chemical conversion coating layer is measured by the following method. First, a thin-film sample of the chemical conversion coating layer is prepared by microtoming so that a cross section perpendicular to the rolling direction of the zinc-based plated steel sheet of this embodiment can be observed. At least five regions of the obtained thin-film sample, each measuring 20 μm × t μm (20 μm in the direction parallel to the sheet width direction and t μm thick in the sheet thickness direction), are observed at 100,000 times magnification using a 200 kV field emission transmission electron microscope (FE-TEM), and elemental mapping is performed using an energy dispersive X-ray analyzer (EDS or EDX). From the elemental mapping results, the area ratio of the region containing Cu, Co, or Fe is determined. Using the same method as above, the area ratio of the region containing Cu, Co, or Fe is determined for multiple comparison samples having chemical conversion coatings with known pigment contents, and a calibration curve is prepared in advance based on the relationship with the pigment content. The calibration curve is used to determine the pigment content of the target sample.

[0044] The pigment colors the chemical conversion treatment layer blue, making blackened areas on the surface of the Zn-based plating layer less noticeable, but the inclusion of the pigment in the chemical conversion treatment layer may reduce the corrosion resistance of the chemical conversion treatment layer. Therefore, in order to prevent a reduction in the corrosion resistance of the chemical conversion treatment layer, it is preferable to optimize the mixing ratio of silica particles and pigment in the chemical conversion treatment layer of this embodiment. That is, the mixing ratio (mass ratio) of silica particles to pigment in the chemical conversion treatment layer is adjusted based on the Si equivalent amount [Si] of silica particles (g / m ２ ) and the Cu equivalent amount of the pigment [Cu] (g / m ２ ), Co equivalent amount [Co] (g / m ２ ) or Fe equivalent amount [Fe] (g / m ２), [Si] / [Cu], [Si] / [Co], or [Si] / [Fe] is preferably in the range of 1 to 200. By making [Si] / [Cu], [Si] / [Co], or [Si] / [Fe] 1 or greater, the corrosion resistance of the chemical conversion coating layer can be improved even when the chemical conversion coating layer contains a pigment. Furthermore, by making [Si] / [Cu], [Si] / [Co], or [Si] / [Fe] 200 or less, deterioration of the appearance of the Zn-based plating layer can be prevented. From the viewpoint of preventing deterioration of appearance and maintaining corrosion resistance, [Si] / [Cu], [Si] / [Co], or [Si] / [Fe] is more preferably 10 to 150. Furthermore, from the viewpoint of achieving a more beautiful blue coloration of the chemical conversion coating layer, [Si] / ([Cu] + [Co] + [Fe]) is more preferably in the range of 1 to 200.

[0045] The chemical conversion coating layer may further contain either or both of an Nb compound and a phosphate compound. When an Nb compound or a phosphate compound is contained, the corrosion resistance of the Zn-based plating layer is improved.

[0046] As the Nb compound, a conventionally known niobium-containing compound can be used, for example, niobium oxide, niobic acid and its salts, fluoroniobate, fluorooxoniobate, etc. Among them, it is preferable to use niobium oxide from the viewpoint of improving corrosion resistance.

[0047] Examples of phosphoric acid compounds include phosphoric acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, and tetraphosphoric acid, and salts thereof; phosphonic acids such as aminotri(methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra(methylenephosphonic acid), and diethylenetriaminepenta(methylenephosphonic acid), and salts thereof; and organic phosphoric acids such as phytic acid and salts thereof. The cation species of the salts is not particularly limited, and examples include Cu, Co, Fe, Mn, Sn, V, Mg, Ba, Al, Ca, Sr, Nb, Y, Ni, and Zn. These may be used alone, or two or more may be used in combination.

[0048] The Nb compound and the phosphate compound are preferably contained in a total amount of 0.5 to 30 mass% in the chemical conversion coating layer. If the content of the Nb compound and the phosphate compound is 0.5 mass% or more, the corrosion resistance is improved, and if the content of the Nb compound and the phosphate compound is 30 mass% or less, the chemical conversion coating layer does not become brittle and can be stably coated with the Zn-based plating layer.

[0049] The contents of Nb compounds and phosphate compounds in the chemical conversion coating layer are measured by the following method. First, in addition to the target sample, multiple comparison samples having chemical conversion coating layers with known contents of Nb compounds and phosphate compounds are prepared, and their surfaces are measured using an X-ray fluorescence analyzer. A calibration curve is then drawn from the relationship between the detected intensities of Nb and P and the contents of Nb compounds and phosphate compounds. Next, the target sample is measured using the X-ray fluorescence analyzer under the same conditions as the comparison sample, and the contents of Nb compounds and phosphate compounds are determined using the above calibration curve from the detected intensities of Si.

[0050] Furthermore, the amount of the chemical conversion coating layer on one side of the Zn-based plating layer is 0.1 to 15 g / m ２ The deposition amount is 0.1 g / m ２ If the coating weight is 15 g / m or more, the coating weight of the chemical conversion coating layer becomes sufficient, the blackened portion on the surface of the Zn-based plating layer can be made less noticeable, and the corrosion resistance of the Zn-based plating layer can be improved. ２ If the coating amount is less than this, even if the chemical conversion coating layer contains a pigment, the reflection of light on the surface of the chemical conversion coating layer is reduced, and the metallic appearance of the surface of the Zn-based plating layer can be visually recognized. ２ is.

[0051] The chemical conversion coating layer may further contain at least one crosslinking agent selected from the group consisting of a silane coupling agent, a crosslinkable zirconium compound, and a crosslinkable titanium compound. These may be used alone or in combination of two or more.

[0052] When at least one crosslinking agent selected from the group consisting of the above-mentioned silane coupling agents, crosslinkable zirconium compounds, and crosslinkable titanium compounds is contained, the adhesion between the Zn-based plating layer and the chemical conversion treatment layer is further improved.

[0053] The silane coupling agent is not particularly limited, and examples thereof include vinyltrimethoxysilane, vinyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylethoxysilane, N-[2-(vinylbenzylamino)ethyl]-3-aminopropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, and γ-methacryloxypropyltriethoxysilane, which are commercially available from Shin-Etsu Chemical Co., Ltd., Nippon Unicar Co., Ltd., Chisso Co., Ltd., Toshiba Silicones, etc. Examples of suitable silane coupling agents include silane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, etc. The above silane coupling agents may be used alone or in combination of two or more.

[0054] The crosslinkable zirconium compound is not particularly limited as long as it is a zirconium-containing compound having a plurality of functional groups capable of reacting with carboxyl groups or hydroxyl groups, but is preferably a compound soluble in water or an organic solvent, more preferably a water-soluble zirconium compound, such as ammonium zirconyl carbonate.

[0055] The crosslinkable titanium compound is not particularly limited as long as it is a titanium-containing compound having a plurality of functional groups capable of reacting with carboxyl groups or hydroxyl groups, and examples thereof include dipropoxy bis(triethanolaminato)titanium, dipropoxy bis(diethanolaminato)titanium, propoxy tris(diethanolaminato)titanium, dibutoxy bis(triethanolaminato)titanium, dibutoxy bis(diethanolaminato)titanium, dipropoxy bis(acetylacetonato)titanium, dibutoxy bis(acetylacetonato)titanium, dihydroxy bis(lactato)titanium monoammonium salt, dihydroxy bis(lactato)titanium diammonium salt, propanedioxytitanium bis(ethylacetoacetate), oxotitanium bis(monoammonium oxalate), isopropyl tri(N-amidoethyl aminoethyl)titanate, etc. The crosslinking agents may be used alone or in combination of two or more.

[0056] The content of at least one crosslinking agent selected from the group consisting of the silane coupling agent, crosslinkable zirconium compound, and crosslinkable titanium compound is preferably 0.1 to 50% by mass relative to 100% by mass of the solid content of the resin. If the content of this crosslinking agent is less than 0.1% by mass, the effect of improving adhesion may not be obtained, and if the content of this crosslinking agent is more than 50% by mass, the stability of the aqueous composition may be reduced.

[0057] The chemical conversion coating layer may further contain at least one crosslinking agent selected from the group consisting of amino resins, polyisocyanate compounds, blocked polyisocyanates, epoxy compounds, and carbodiimide compounds. These crosslinking agents may be used alone or in combination of two or more.

[0058] When at least one crosslinking agent selected from the group consisting of the amino resins, polyisocyanate compounds, their blocked products, epoxy compounds, and carbodiimide compounds is contained, the crosslink density increases, the barrier properties of the chemical conversion coating layer improve, and the corrosion resistance is further improved.

[0059] The amino resin is not particularly limited, and examples thereof include melamine resin, benzoguanamine resin, urea resin, glycoluril resin, and the like.

[0060] The polyisocyanate compound is not particularly limited, and examples thereof include hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, tolylene diisocyanate, etc. The blocked product thereof is a blocked product of the above polyisocyanate compound.

[0061] The epoxy compound is not particularly limited as long as it is a compound having a plurality of oxirane rings, and examples thereof include adipic acid diglycidyl ester, phthalic acid diglycidyl ester, terephthalic acid diglycidyl ester, sorbitan polyglycidyl ether, pentaerythritol polyglycidyl ether, glycerin polyglycidyl ether, trimethylpropane polyglycidyl ether, neopentyl glycol polyglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 2,2-bis-(4'-glycidyloxyphenyl)propane, tris(2,3-epoxypropyl)isocyanurate, bisphenol A diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether.

[0062] Examples of the carbodiimide compound include compounds obtained by synthesizing an isocyanate-terminated polycarbodiimide through a condensation reaction involving decarbonation of a diisocyanate compound such as an aromatic diisocyanate, an aliphatic diisocyanate, or an alicyclic diisocyanate, and then adding a hydrophilic segment having a functional group reactive with an isocyanate group.

[0063] The content of at least one crosslinking agent selected from the group consisting of the amino resin, polyisocyanate compound, its block product, epoxy compound, and carbodiimide compound is preferably 0.1 to 50% by mass relative to 100% by mass of the solid content of the resin. If the content of this crosslinking agent is less than 0.1% by mass, the effect of improving corrosion resistance may not be obtained, while if the content of this crosslinking agent is more than 50% by mass, the chemical conversion coating layer may become brittle and the corrosion resistance may decrease.

[0064] The chemical conversion coating layer preferably further contains at least one compound selected from the group consisting of vanadium compounds, tungsten compounds, and molybdenum compounds, which may be used alone or in combination of two or more.

[0065] By including at least one compound selected from the group consisting of vanadium compounds, tungsten compounds and molybdenum compounds, the corrosion resistance of the chemical conversion coating layer is improved.

[0066] The vanadium compound is not particularly limited, and any conventionally known vanadium-containing compound can be used. Examples thereof include vanadate salts such as vanadic acid, ammonium vanadate, and sodium vanadate, and phosphovanadate salts such as phosphovanadic acid and ammonium phosphovanadate.

[0067] The tungsten compound is not particularly limited, and any conventionally known tungsten-containing compound can be used. Examples thereof include tungstates such as tungstic acid, ammonium tungstate, and sodium tungstate, and phosphotungstates such as phosphotungstic acid and ammonium phosphotungstate.

[0068] The molybdenum compound is not particularly limited, and conventionally known molybdenum-containing compounds can be used, such as molybdates. The molybdates are not limited in terms of their skeleton or degree of condensation, and examples thereof include orthomolybdates, paramolybdates, and metamolybdates. All salts, such as single salts and double salts, are also included, and examples of double salts include molybdate phosphate.

[0069] The content of at least one selected from the group consisting of the vanadium compound, tungsten compound, and molybdenum compound is preferably 0.01 to 20 mass% relative to 100 mass% of the solid content of the resin. If the content of at least one selected from the group consisting of the vanadium compound, tungsten compound, and molybdenum compound is less than 0.01 mass%, the effect of improving corrosion resistance may not be obtained, whereas if the content of at least one selected from the group consisting of the vanadium compound, tungsten compound, and molybdenum compound exceeds 20 mass%, the chemical conversion coating layer may become brittle and the corrosion resistance may decrease.

[0070] The chemical conversion coating layer may further contain a polyphenol compound.

[0071] The inclusion of the polyphenol compound improves the corrosion resistance of the chemical conversion coating layer and the adhesion of the post-coating film when used in post-coating applications.

[0072] The polyphenol compound is a compound having two or more phenolic hydroxyl groups bonded to a benzene ring or a condensate thereof. Examples of compounds having two or more phenolic hydroxyl groups bonded to a benzene ring include gallic acid, pyrogallol, and catechol. Condensates of compounds having two or more phenolic hydroxyl groups bonded to a benzene ring are not particularly limited, and examples include polyphenol compounds commonly called tannic acid, which are widely distributed in the plant kingdom. Tannic acid is a general term for aromatic compounds with complex structures containing multiple phenolic hydroxyl groups that are widely distributed in the plant kingdom. The tannic acid may be either hydrolyzable tannic acid or condensed tannic acid. The tannic acid is not particularly limited, and examples include hamameli tannin, persimmon tannin, tea tannin, Chinese gallnut tannin, gall tannin, myrobalan tannin, dividivi tannin, algarovila tannin, valonia tannin, and catechin tannin.

[0073] As the tannic acid, commercially available products such as "Tannic Acid Extract A," "B Tannic Acid," "N Tannic Acid," "Industrial Tannic Acid," "Purified Tannic Acid," "Hi Tannic Acid," "F Tannic Acid," and "Localized Tannic Acid" (all manufactured by Dainippon Pharmaceutical Co., Ltd.), and "Tannic Acid: AL" (manufactured by Fuji Chemical Industry Co., Ltd.) can also be used. The polyphenol compounds can be used alone or in combination of two or more.

[0074] The polyphenol compound is preferably contained in an amount of 0.1 to 50% by mass relative to 100% by mass of the solid content of the resin. If the content of the polyphenol compound is less than 0.1% by mass, the effect of improving corrosion resistance may not be obtained, whereas if the content of the polyphenol compound is more than 50% by mass, the stability of the aqueous composition may be reduced.

[0075] The chemical conversion coating layer may further contain a solid lubricant.

[0076] The inclusion of the solid lubricant improves the lubricity of the chemical conversion coating layer, which is effective in improving processability during press molding, preventing scratches caused by molds or handling, and preventing wear and tear on molded products and coils during transportation.

[0077] The solid lubricant is not particularly limited, and examples thereof include known fluorine-based, hydrocarbon-based, fatty acid amide-based, ester-based, alcohol-based, metal soap-based, and inorganic lubricants. The selection criteria for lubricant additives for improving processability require the addition of a substance that exists on the surface of the chemical conversion coating layer rather than dispersed in the formed chemical conversion coating layer, in order to reduce friction between the surface of the molded product and the die and maximize the lubricating effect. That is, if the lubricant is dispersed in the formed chemical conversion coating layer, the surface friction coefficient is high, the chemical conversion coating layer is easily destroyed, and powdery substances peel off and accumulate, resulting in a phenomenon known as powdering, which causes poor appearance and reduced processability. The substance that exists on the surface of the chemical conversion coating layer is selected from those that are incompatible with resins and have low surface energy.

[0078] Among these, polyolefin waxes are preferred because they reduce the coefficient of dynamic friction on the surface, significantly improve processability, and improve corrosion resistance after processing. Examples of such waxes include hydrocarbon waxes such as paraffin, microcrystalline, and polyethylene. Because the film temperature rises during processing due to the heat generated by deformation and friction of the material, a wax melting point of 70 to 160°C is more preferred. Waxes with a melting point below 70°C may soften and melt during processing, preventing the material from exhibiting its excellent properties as a solid lubricant. Furthermore, waxes with a melting point above 160°C may result in the presence of hard particles on the surface, reducing frictional properties and preventing high moldability.

[0079] The particle size of these waxes is more preferably 0.1 to 5 μm. If the particle size of the wax exceeds 5 μm, the distribution of the solidified wax may become non-uniform, and the wax may fall off from the chemical conversion coating layer. If the particle size of the wax is less than 0.1 μm, the processability may be insufficient.

[0080] The solid lubricant is preferably contained in an amount of 0.1 to 30% by mass relative to 100% by mass of the solid content of the resin. If the content of the solid lubricant is less than 0.1%, the effect of improving processability is small, and if the content of the solid lubricant is more than 30%, corrosion resistance may decrease.

[0081] The chemical conversion coating layer is obtained by applying an aqueous composition containing components such as resin, silica particles, blue organic pigment, Nb compound, and phosphate compound to the surface of the Zn-based plating layer and drying it. A solvent may be used in the aqueous composition to improve film-forming properties and form a more uniform and smooth coating. The solvent is not particularly limited as long as it is one commonly used in paints. Examples of the solvent include alcohol-based, ketone-based, ester-based, and ether-based hydrophilic solvents, which are useful for leveling.

[0082] The coating method for the aqueous composition used to form the chemical conversion coating layer involves applying the aqueous composition to the surface of the Zn-based plating layer to form a film. The coating method is not particularly limited, and commonly used methods such as roll coating, air spraying, airless spraying, and immersion can be used as appropriate. To enhance the curing properties of the chemical conversion coating layer, it is preferable to preheat the substrate or thermally dry the substrate after coating. Thermal drying methods include hot air, induction heating, near-infrared radiation, and far-infrared radiation, and these methods may be used in combination. The substrate is heated to a temperature of 50 to 250°C, preferably 70 to 220°C. Heating temperatures below 50°C result in slow evaporation of water, resulting in insufficient film formation and reduced corrosion resistance. Heating temperatures above 250°C can cause thermal decomposition of the resin, reducing corrosion resistance and worsening the appearance due to yellowing and other factors. When thermal drying is performed after coating, the drying time is preferably 1 second to 5 minutes. Furthermore, if the resin is curable by electron beam or ultraviolet radiation, curing by these methods may be used, or a combination of these methods may be used.

[0083] Furthermore, it is preferable that the arithmetic mean roughness Ra of the Zn-based plating layer is 0.5 to 2.0 μm, and the arithmetic mean height Sa of the chemical conversion treatment layer is 5 nm to 100 nm. By having the arithmetic mean roughness Ra of the Zn-based plating layer be 2.0 μm or less, the metallic appearance of the Zn-based plating layer can be maintained at a high level. If Ra exceeds 2.0 μm, light hitting the surface of the Zn-based plating layer is likely to be diffused, and the metallic appearance is likely to be deteriorated. By having the arithmetic mean height Sa of the chemical conversion treatment layer be 100 nm or less, the transparency of the chemical conversion treatment layer can be maintained. On the other hand, if Sa exceeds 100 nm, light hitting the surface of the chemical conversion treatment layer is likely to be diffused, and the transparency of the chemical conversion treatment layer may be reduced. By having the arithmetic mean roughness Ra of the Zn-based plating layer and the arithmetic mean height Sa of the chemical conversion treatment layer be below their respective upper limits, the metallic appearance of the Zn-based plating layer can be maintained. Furthermore, even if the arithmetic mean roughness Ra of the Zn-based plating layer and the arithmetic mean height Sa of the chemical conversion coating layer are both below their respective lower limits, the effect of maintaining metallic appearance and transparency saturates, so they are set to be equal to or greater than their respective lower limits. The arithmetic mean roughness Ra of the Zn-based plating layer is measured and calculated using a 3D laser microscope (manufactured by Keyence Corporation). A standard lens with 20x magnification is used to measure the height Z at measurement intervals of 50 μm. It is preferable to measure 100 points. With 100 measurement points, the arithmetic mean roughness Ra is calculated from the 100 height Z points obtained using heights Z1 to Z100 according to the following formula 2. Zave is the average of the 100 height Z points. Ra = 1 / 100 × Σ [x = 1 → 100] (|height Zx - Zave|) ... formula 2

[0084] The arithmetic mean height Sa of the chemical conversion coating layer is measured and calculated using the following method. A sample cut to a predetermined size from a zinc-based plated steel sheet is gold-vapor-deposited to a thickness of 50 nm on its surface, and the gold-vapor-deposited sample is embedded in resin and polished so that the cross section of the sample in the sheet thickness direction is exposed. The cross section of the sample is observed using a scanning electron microscope at 5000x magnification, and the line roughness of the gold-vapor-deposited layer when observed from a direction perpendicular to the cross section is calculated. The arithmetic mean height Sa of the chemical conversion coating layer is determined by converting the obtained line roughness into a surface roughness difference. Gold vapor deposition is performed to clarify the boundary between the chemical conversion coating layer and the resin, and the thickness of the gold-vapor-deposited layer is negligible compared to the chemical conversion coating layer. Therefore, the arithmetic mean height Sa of the gold-vapor-deposited layer can be used as the arithmetic mean height Sa of the surface of the chemical conversion coating layer.

[0085] The chemical conversion treatment layer is preferably formed on the surface of the Zn-based plating layer without any other coating, etc. In order to obtain a more beautiful metallic appearance, it is also preferable that no other colored coating, low-permeability coating, etc. is provided on the chemical treatment layer.

[0086] From the viewpoint of reflecting the metallic appearance of the plating layer surface even when a chemical conversion coating layer is present, when the Zn-based plated steel sheet of this embodiment is measured with a multi-angle spectrophotometer, the L obtained when light is incident on a plane perpendicular to the surface of the chemical conversion coating layer from an angle of 60° from the surface of the chemical conversion coating layer toward the surface of the chemical conversion coating layer, and the light reflected by the surface of the chemical conversion coating layer is received at an angle of 135° from the surface of the chemical conversion coating layer is ＊ L ＊ １ On the plane, light is incident on the surface of the chemical conversion treatment layer at an angle of 120° from the surface of the chemical conversion treatment layer toward the surface of the chemical conversion treatment layer, and the light reflected on the surface of the chemical conversion treatment layer is received at an angle of 135° from the surface of the chemical conversion treatment layer. ＊ L ＊ ２ When this is done, L ＊ １ / L ＊ ２ It is preferable that the value satisfies the requirement of CIE1976 (L) or higher. This characteristic has been found to be an inherent property of Zn-based plated steel sheets, which have a metallic luster even when a chemical conversion coating layer is present, and consequently have a metallic appearance. ＊ , a＊ , b ＊ ) b when evaluated in color space ＊ By setting L within the range described below, it is possible to make blackening less noticeable while maintaining a more beautiful metallic appearance. ＊ １ / L ＊ ２ is more preferably 3 or more.

[0087] [Appearance] Next, the appearance of the zinc-based plated steel sheet of this embodiment will be described. The appearance of the zinc-based plated steel sheet of this embodiment, as viewed from the chemical conversion coating layer side, is in accordance with CIE1976 (L ＊ , a ＊ , b ＊ ) b when evaluated in color space ＊ is -30 or more and -2 or less, and the 60-degree specular gloss G specified in JIS Z 8741:1997 ｓ (60°) is 50 to 200, and the product has a metallic appearance. ＊ and 60 degree mirror gloss G ｓ The reason for limiting the angle to (60°) will be explained.

[0088] The more light is reflected on the surface of the Zn-based plating layer, the higher the light brightness becomes, and if it is low, the reflection on the chemical conversion coating layer increases. ＊ Otherwise, the metallic appearance of the Zn-based plating layer becomes unrecognizable. Therefore, in order to obtain excellent blackening resistance while still being able to visually recognize the metallic appearance of the Zn-based plating layer, it is necessary to set the predetermined 60-degree specular gloss G ｓ (60°) and b ＊ It was found that it is good to set it to b ＊ It is presumed that this is because the value fluctuates in the increasing direction.

[0089] CIE 1976 (L ＊ , a ＊ , b ＊ ) b when evaluated in color space ＊ When b is less than −30, the blue color of the surface of the zinc-based plated steel sheet becomes darker, and the metallic appearance of the zinc-based plated layer becomes invisible. ＊ If b exceeds -2, the blue color becomes lighter, the blackened areas on the surface of the Zn-based plating layer become more noticeable, and the appearance deteriorates. ＊is in the range of -30 to -2. ＊ From the viewpoint of maintaining the metallic appearance, the lower limit of b is preferably −22, more preferably −15. ＊ From the viewpoint of preventing blackening, the upper limit of the value is preferably −3.5, more preferably −5.

[0090] The appearance of the Zn-based plated steel sheet of this embodiment, as viewed from the chemical conversion coating layer side, is CIE1976 (L ＊ , a ＊ , b ＊ ) color space when evaluated ＊ is preferably 85 or less. ＊ By keeping the value of L below 85, the metallic appearance can be visually recognized as more beautiful. ＊ From the viewpoint of making blackening less noticeable, the value is more preferably 80 or less, and even more preferably 75 or less.

[0091] Also, 60 degree mirror gloss G ｓ When the (60°) is less than 50, the appearance of the Zn-based plated steel sheet approaches white, and the metallic appearance of the Zn-based plated layer becomes invisible. ｓ When the angle (60°) exceeds 200, reflection from the surface of the chemical conversion treatment layer becomes strong, making it difficult to visually recognize the metallic appearance of the Zn-based plating layer. Here, the appearance in the present invention means the appearance of the Zn-based plated steel sheet when viewed from the Zn-based plating layer side disposed on at least one surface of the steel sheet.

[0092] The surface of the Zn-based plating layer according to this embodiment may have patterned portions and non-patterned portions arranged in a predetermined shape. The patterned portions are preferably arranged in a shape that is one of straight lines, curved lines, dots, figures, numbers, symbols, patterns, or letters, or a combination of two or more of these. The non-patterned portions are areas other than the patterned portions. The shape of the patterned portions is acceptable even if they are partially missing, such as missing dots, as long as they can be recognized as a whole. The non-patterned portions may also have a shape that outlines the boundaries of the patterned portions.

[0093] When the surface of the Zn-based plating layer has one or a combination of two or more of straight lines, curved lines, dots, figures, numbers, symbols, patterns, or letters, these areas can be defined as patterned areas, and other areas can be defined as non-patterned areas. The boundary between the patterned area and the non-patterned area can be seen with the naked eye. The boundary between the patterned area and the non-patterned area can also be seen from a magnified image using an optical microscope or a magnifying glass.

[0094] The patterned portion is preferably formed to a size large enough to be discernible with the naked eye, under a magnifying glass, or under a microscope. The non-patterned portion occupies the majority of the Zn-based plating layer (the surface of the Zn-based plating layer), and the patterned portion may be disposed within the non-patterned portion. The patterned portion is disposed in a predetermined shape within the non-patterned portion. Specifically, the patterned portion is disposed within the non-patterned portion so as to form one or a combination of two or more of the following: straight lines, curved lines, figures, dots, figures, numbers, symbols, patterns, or letters. By adjusting the shape of the patterned portion, one or a combination of two or more of the following can be formed on the surface of the Zn-based plating layer. For example, the surface of the Zn-based plating layer may appear as a character string, a string of numbers, a symbol, a mark, a diagram, a design, or a combination thereof, consisting of the patterned portion. This shape is intentionally or artificially formed by the manufacturing method described below, and is not naturally formed.

[0095] In this way, the patterned portion and the non-patterned portion are regions formed on the surface of the Zn-based plating layer, and the patterned portion and the non-patterned portion each include one or two of the first region and the second region.

[0096] The patterned portion and the non-patterned portion each include one or two of a first region and a second region determined by any of the following determination methods 1 to 5, and the absolute value of the difference between the area ratio of the first region in the patterned portion and the area ratio of the first region in the non-patterned portion is 30% or more. When the absolute value of the difference between the area ratio of the first region in the patterned portion and the area ratio of the first region in the non-patterned portion is 30% or more, the patterned portion and the non-patterned portion can be distinguished. If this difference in area ratio is less than 30%, the difference between the area ratio of the first region in the patterned portion and the area ratio of the first region in the non-patterned portion is small, and the patterned portion and the non-patterned portion appear similar in appearance, making it difficult to distinguish the patterned portion. The greater the difference in area ratio, the better, and it is more preferable that this difference in area ratio be 40% or more, and even more preferably that this difference in area ratio be 60% or more.

[0097] That is, the area ratios of the first region and the second region can be determined for the pattern portion. When the area fraction of the first region exceeds 70%, the pattern portion appears relatively white or near-white compared to when the area fraction of the first region is 70% or less. When the area fraction of the first region is 30% or more and 70% or less, the pattern portion appears relatively matte. Furthermore, when the area fraction of the first region is less than 30%, the pattern portion appears relatively metallic. Thus, the appearance of the pattern portion depends on the area fraction of the first region.

[0098] On the other hand, in the non-patterned portion, the area proportions of the first and second regions can also be calculated. As in the patterned portion, the appearance of the non-patterned portion depends on the area proportion of the first region.

[0099] When the difference between the area proportion of the first region in the patterned portion and the area proportion of the first region in the non-patterned portion is 30% or more in absolute value, the patterned portion and the non-patterned portion can be distinguished from each other. If this difference in area proportion is less than 30%, the difference between the area proportion of the first region in the patterned portion and the area proportion of the first region in the non-patterned portion is small, and the patterned portion and the non-patterned portion have similar appearances, making it difficult to distinguish between the patterned portion and the non-patterned portion. The greater the difference in area proportion, the better, and a difference of 40% or more is more preferable, and a difference of 60% or more is even more preferable.

[0100] [Determination Method 1] In Determination Method 1, virtual grid lines are drawn at 0.5 mm intervals on the surface of the Zn-based plating layer, and in each of the multiple regions partitioned by the virtual grid lines, a circle with a diameter of 0.5 mm centered at the center of gravity of each region is defined as a measurement region A. ＊ The obtained L ＊ 50 points were selected arbitrarily from the values, and the obtained L ＊ The average of 50 points is the standard L ＊ When the value is set as ＊ The value is standard L ＊ The area where the value is equal to or greater than the reference value is called the first area. ＊ The region where the value is less than the value is defined as the second region.

[0101] [Determination Method 2] In Determination Method 2, virtual grid lines are drawn at 0.5 mm intervals on the surface of the Zn-based plating layer, and in each of the multiple regions partitioned by the virtual grid lines, a circle with a diameter of 0.5 mm centered at the center of gravity of each region is defined as a measurement region A. ＊ The value was measured, and L ＊ The area where the value is 45 or more is the first area, L ＊ The region where the value is less than 45 is defined as the second region.

[0102] [Determination Method 3] In Determination Method 3, virtual grid lines are drawn on the surface of the Zn-based plating layer at 0.5 mm intervals, and the arithmetic mean height Sa2 is measured in each of the multiple regions defined by the virtual grid lines. The region where the obtained arithmetic mean height Sa2 is 1 μm or more is designated as the first region, and the region where it is less than 1 μm is designated as the second region. The arithmetic mean height Sa2 is measured using a 3D laser microscope (manufactured by Keyence Corporation). In this embodiment, a 20x standard lens is used to measure the height Z within each of the multiple regions defined by the virtual grid lines at measurement intervals of 50 μm. When measuring on a grid, 100 measurement points are obtained within the region. The arithmetic mean height Sa2 is calculated using the following formula 3 using the obtained 100 height Zs, heights Z1 to Z100. Zave is the average of the 100 height Zs. Sa2 = 1 / 100 × Σ [x = 1 → 100] (|height Zx - Zave|) ... formula 3

[0103] [Determination Method 4] In Determination Method 4, virtual lattice lines are drawn on the surface of the Zn-based plating layer at intervals of 1 mm or 10 mm, and X-rays are incident on each of a plurality of regions defined by the virtual lattice lines, whereby the diffraction peak intensity I of the (0002) plane of the Zn phase is measured for each of the regions by an X-ray diffraction method. ０００２ and the diffraction peak intensity I of the (10-11) plane of the Zn phase １０－１１ and the intensity ratio (I ０００２ / I １０－１１ The region where the orientation ratio is 3.5 or more is defined as the first region, and the region where the orientation ratio is less than 3.5 is defined as the second region.

[0104] [Determination Method 5] In Determination Method 5, virtual grid lines are drawn at 1 mm intervals on the surface of the Zn-based plating layer, and then, for each of a plurality of regions partitioned by the virtual grid lines, a circle S is drawn with its center at the center of gravity G of each region. The diameter R of the circle S is set so that the total length of the surface boundary lines of the Zn-based plating layer included within the circle S is 10 mm. The average value of the maximum diameter Rmax and the minimum diameter Rmin among the diameters R of the circles S of the plurality of regions is defined as the reference diameter Rave, and a region having a circle S with a diameter R less than the reference diameter Rave is defined as a first region, and a region having a circle S with a diameter R equal to or greater than the reference diameter Rave is defined as a second region.

[0105] The patterned portion and the non-patterned portion, in which the first region and the second region are identified by determination method 1 or 2, are formed after the formation of the Zn-based plating layer. The patterned portion and the non-patterned portion are formed by applying an acidic solution to the surface of the Zn-based plating layer at 60 to 200°C. More specifically, an acidic solution is prepared and applied to the surface of the Zn-based plating layer by printing means. As the printing means, general printing methods such as printing methods using various types of plates (gravure printing, flexographic printing, offset printing, silk printing, etc.) and inkjet methods can be applied.

[0106] In the areas where the acidic solution is applied, the very surface of the Zn-based plating layer dissolves, and the surface of the Zn-based plating layer changes from its as-plated state. This changes the appearance of the areas where the acidic solution is applied compared to areas where the acidic solution is not applied. In this way, it is presumed that the difference between the area ratio of the first region in the patterned portion and the area ratio of the first region in the non-patterned portion becomes large, making it possible to distinguish between the patterned portion and the non-patterned portion.

[0107] The area to which the acidic solution is applied may be an area corresponding to the patterned portion or an area corresponding to the non-patterned portion.

[0108] The acid solution is preferably an inorganic acid such as hydrochloric acid, nitric acid, or sulfuric acid. The acid concentration in the acid solution is desirably 0.1 to 10 mass %. The temperature of the steel sheet when the acid solution is applied is preferably 60 to 200°C, and more desirably 50 to 80°C. By adjusting the type and concentration of the acid solution, it becomes possible to adjust the area fractions of the first and second regions on the surface of the Zn-based plating layer at the locations where the acid solution is applied.

[0109] If the surface temperature of the Zn-based plating layer when the acidic solution is applied is less than 60°C, it will take time to form the patterned portion or non-patterned portion, which is not preferred. If the surface temperature of the Zn-based plating layer exceeds 200°C, the acidic solution will quickly volatilize, making it impossible to form the patterned portion or non-patterned portion, which is not preferred.

[0110] After the acid solution is applied, it is necessary to rinse with water within 1 to 10 seconds.

[0111] Next, the formation of the patterned portion and non-patterned portion, in which the first and second regions are identified by Determination Method 3, is performed after the formation of the Zn-based plating layer. The patterned portion and non-patterned portion are formed by pressing a roll with a partially increased surface roughness against the surface of the Zn-based plating layer and transferring the roll surface shape to the Zn-based plating layer. For example, to form a patterned portion on the surface of the Zn-based plating layer, the roughness of the portion of the roll surface corresponding to the patterned portion can be increased relative to other portions, thereby forming a patterned portion including many first regions with high surface roughness. Conversely, a roll with a smaller roughness of the portion corresponding to the patterned portion relative to other portions may be used. The roughness (arithmetic mean height Sa2 (μm)) of the roll surface in the portion where the roughness is to be increased should be in the range of 0.6 to 3.0 μm, preferably 1.2 to 3.0 μm. The roughness in the portion where the roughness is to be decreased should be in the range of 0.05 to 1.0 μm, preferably 0.05 to 0.8 μm. It is advisable to perform the transfer when the surface temperature of the Zn-based plating layer is in the range of 100 to 300°C. The difference in roughness between the areas where the roughness is to be increased and the areas where the roughness is to be decreased should be more than 0.2 μm, preferably 0.3 μm or more, in terms of arithmetic mean height Sa2. If the difference in roughness is small, it becomes difficult to distinguish between patterned and non-patterned areas.

[0112] The patterned and non-patterned portions specified by Determination Method 4 are formed by locally spraying a non-oxidizing gas onto the molten metal of a steel sheet immediately after it has been pulled out of a hot-dip galvanizing bath using a gas nozzle. Nitrogen or argon is preferably used as the non-oxidizing gas. While the optimal temperature range varies depending on the composition, the non-oxidizing gas is preferably sprayed when the temperature of the molten metal is in the range of (final solidification temperature - 5) °C to (final solidification temperature + 5) °C. Furthermore, the temperature of the non-oxidizing gas is set to be lower than the final solidification temperature.

[0113] When the Zn-based plating layer is in the above temperature range, the cooling rate of the molten metal increases at the locations where the non-oxidizing gas is sprayed, resulting in a high orientation rate of the Zn-based plating layer after solidification. On the other hand, the cooling rate of the molten metal decreases at the locations where the non-oxidizing gas is not sprayed, resulting in a low orientation rate of the Zn-based plating layer after solidification. Therefore, by adjusting the spraying range of the non-oxidizing gas, it becomes possible to intentionally or arbitrarily adjust the locations where regions with high orientation rate and regions with low orientation rate appear.

[0114] This allows the shapes of the patterned and non-patterned portions to be adjusted as desired, and also makes it possible to distinguish between the patterned and non-patterned portions. The orientation rate increases as the temperature of the sprayed gas decreases, so the orientation rate can be adjusted by the temperature of the sprayed gas. The gas temperature is preferably lower than the final solidification temperature, and for example, the gas temperature may be adjusted to 25 to 250°C.

[0115] The patterned and non-patterned portions identified by Determination Method 5 are formed by locally spraying a non-oxidizing gas at or above the final solidification temperature of the coating onto the molten metal of a steel sheet immediately after it has been pulled out of a hot-dip coating bath using a gas nozzle. Nitrogen or argon is preferably used as the non-oxidizing gas. While the optimal temperature range varies depending on the composition, the non-oxidizing gas is preferably sprayed when the temperature of the molten metal is in the range of (final solidification temperature - 5) °C to (final solidification temperature + 5) °C. Furthermore, the temperature of the non-oxidizing gas is preferably equal to or higher than the final solidification temperature. For example, in a coating composition of 11% Al and 3% Mg, a non-oxidizing gas whose gas temperature is equal to or higher than the final solidification temperature is preferably sprayed when the temperature of the molten metal is 330 to 340 °C.

[0116] The cooling rate of the molten metal decreases in the vicinity of the area where the non-oxidizing gas is sprayed, which causes the boundaries or grain boundaries that appear on the surface to become coarse. Therefore, by adjusting the amount and range of the non-oxidizing gas sprayed, it becomes possible to arbitrarily adjust the size of the boundaries or grain boundaries that appear on the surface.

[0117] By setting the absolute value of the difference between the area ratio of the first region in the patterned portion and the area ratio of the first region in the non-patterned portion to be 30% or more, it becomes possible to distinguish between the patterned portion and the non-patterned portion. The formed patterned portion and non-patterned portion are not formed by printing or painting, and therefore have high durability. Furthermore, since the patterned portion and non-patterned portion are not formed by printing or painting, there is no effect on the corrosion resistance of the Zn-based plating layer. Therefore, the Zn-based plated steel sheet of this embodiment has excellent corrosion resistance.

[0118] A zinc-based plating layer having a patterned portion can provide a zinc-based plated steel sheet having high durability and favorable plating properties such as corrosion resistance. The patterned portion can be formed in an intentional or artificial shape, and can be arranged to have a shape consisting of one or a combination of two or more of straight lines, curved lines, dots, figures, numbers, symbols, patterns, or letters. This allows various designs, trademarks, and other identifying marks to be displayed on the surface of the zinc-based plating layer without printing or painting, thereby improving the identification of the source of the steel sheet and the design quality. Furthermore, the patterned portion can also provide information necessary for process management, inventory management, and other purposes, as well as optional information desired by consumers, to the hot-dip plated steel sheet. This can also contribute to improving the productivity of zinc-based plated steel sheets.

[0119] Furthermore, according to the Zn-based plated steel sheet of the present embodiment, a pigment-containing chemical conversion treatment layer is formed on the Zn-based plating layer on which the pattern portion is formed, thereby further improving the visibility of the pattern portion.

[0120] The present invention will be specifically described below with reference to examples.

[0121] First, a cold-rolled steel sheet having a thickness of 1 mm was prepared, and this was immersed in a plating bath of each composition. ２ Wiping to achieve a plating adhesion of 80 g / m on one side ２ The plating composition of the obtained Zn-based plated steel sheet is shown in Table 1.

[0122] When a patterned portion was formed on the Zn-based plating layer, the pattern was further formed by the following method: The patterned portion and the non-patterned portion each included one or two of the first and second regions determined by any one of determination methods 1 to 5, and the absolute value of the difference between the area ratio of the first region in the patterned portion and the area ratio of the first region in the non-patterned portion was 40%.

[0123] <Pattern 1> A hydrochloric acid solution was applied to a rubber plate having a square pattern of convex or concave portions with sides of 50 mm, and the rubber plate was pressed against the surface of the Zn-based plating layer to apply the acidic solution to the steel sheet, forming a square pattern portion. The surface temperature of the Zn-based plating layer of the hot-dip galvanized steel sheet when the acidic solution was applied was in the range of 60 to 200°C. The area other than the square pattern portion was designated as a non-pattern portion. Then, based on determination method 2, virtual grid lines were drawn on the surface of the Zn-based plating layer at 0.5 mm intervals, and in each of the multiple regions defined by the virtual grid lines, a circle with a diameter of 0.5 mm centered at the center of gravity of each region was designated as measurement region A, and the L in each measurement region A was determined. ＊ The value was measured, and L ＊ The area where the value is 45 or more is the first area, L ＊ The region where the value was less than 45 was designated as the second region.

[0124] <Pattern 2> A patterned portion was formed by pressing a roll having a square pattern with sides of 50 mm against the surface of the Zn-based plating layer with the surface temperature of the Zn-based plating layer set to 100 to 300°C. The area of ​​the square pattern was designated the patterned portion, and the area other than the square pattern was designated the non-patterned portion. Based on Determination Method 3, virtual grid lines were drawn on the surface of the Zn-based plating layer at intervals of 0.5 mm, and the arithmetic mean height Sa2 was measured in each of the multiple regions defined by the virtual grid lines. The region where the obtained arithmetic mean height Sa2 was 1 μm or more was designated the first region, and the region where the obtained arithmetic mean height Sa2 was less than 1 μm was designated the second region. This Zn-based plated steel sheet was designated Example 71.

[0125] <Pattern 3> When the steel sheet was pulled up from the coating bath, nitrogen gas, a type of non-oxidizing gas, was sprayed onto the molten metal on the steel sheet surface using a gas nozzle when the temperature of the molten metal was in the range of (final solidification temperature - 5) °C to (final solidification temperature + 5) °C. The gas temperature was below the final solidification temperature. The molten metal was then cooled to completely solidify. The area where the nitrogen gas was sprayed was controlled to form a square pattern with sides of 50 mm. The area of ​​the square pattern was designated the patterned area, and the area outside the square pattern was designated the non-patterned area. Based on Determination Method 4, virtual lattice lines were drawn on the surface of the Zn-based coating layer at intervals of 1 mm or 10 mm, and an X-ray diffraction method was used in which X-rays were incident on each of the multiple regions defined by the virtual lattice lines to measure the diffraction peak intensity I of the (0002) plane of the Zn phase for each of the regions. ０００２ and the diffraction peak intensity I of the (10-11) plane of the Zn phase. １０－１１ and the intensity ratio (I ０００２ / I １０－１１ The region where the orientation ratio is 3.5 or more was designated as the first region, and the region where the orientation ratio is less than 3.5 was designated as the second region. This Zn-based plated steel sheet was designated as Example 72.

[0126] <Pattern 4> When the steel sheet was pulled up from the coating bath, the temperature of the molten metal was in the range of (final solidification temperature - 5) °C to (final solidification temperature + 5) °C. Heated nitrogen gas, a type of non-oxidizing gas, was sprayed from a gas nozzle onto the molten metal on the steel sheet surface. The nitrogen gas spraying conditions were as shown in Table 1. The temperature was equal to or higher than the final solidification temperature. The molten metal was then cooled to completely solidify. The nitrogen gas spraying area was controlled to form a square pattern with sides of 50 mm. The square patterned areas were designated as patterned areas, and areas outside the square pattern were designated as non-patterned areas. Based on Determination Method 5, virtual grid lines were drawn on the surface of the Zn-based coating layer at 1 mm intervals. Next, for each of the multiple regions defined by the virtual grid lines, a circle S was drawn with its center at the center of gravity G of each region. The diameter R of the circle S was set so that the total length of the surface boundary lines of the Zn-based coating layer included within the circle S was 10 mm. The average value of the maximum diameter Rmax and the minimum diameter Rmin among the diameters R of the circles S in the plurality of regions was defined as the reference diameter Rave, and the region having the circles S whose diameters R were less than the reference diameter Rave was defined as the first region, and the region having the circles S whose diameters R were equal to or greater than the reference diameter Rave was defined as the second region. These Zn-based plated steel sheets were designated as Examples 73 and 74.

[0127] Next, if necessary, the Zn-based plated steel sheet is immersed in a Co sulfate solution, an Fe sulfate solution, or an Ni sulfate solution to deposit Co, Fe, or Ni at a concentration of 1 mg / m on the surface of the Zn-based plated layer. ２ The composition of the Zn plating layer is shown in Tables 3A and 3B.

[0128] The arithmetic mean roughness Ra of the Zn-based plating layer was measured using a 3D laser microscope (manufactured by Keyence Corporation). In this example, a 20x standard lens was used to measure the height Z within each of multiple regions defined by virtual grid lines at measurement intervals of 50 μm. Measurements were taken on a grid, and 100 measurement points were obtained within each region. The 100 height Z points obtained were designated as heights Z1 to Z100, and the arithmetic mean roughness Ra was calculated using the above-mentioned formula 2. Zave was the average of the 100 height Z points.

[0129] Next, an aqueous composition containing various aqueous resins (urethane resin, polyester resin, polyolefin resin, epoxy resin, acrylic resin, phenolic resin, fluororesin), silica particles, niobium oxide, sodium phosphate, various pigments (copper sulfate, cobalt sulfate, iron sulfate, Cu phthalocyanine (copper (II) phthalocyanine), Co phthalocyanine (cobalt (II) phthalocyanine), iron oxide, carbon black, quinacridone red, bismuth vanadium, titanium oxide), was applied to the surface of the zinc-based plating layer of the produced zinc-based plated steel sheet using a bar coater to a dry deposition amount of 1.5 g / m. ２ The coating was applied so that the coating temperature reached 150°C in a hot air drying oven, and then the coating was water-cooled to form a chromate-free chemical conversion coating layer. The contents of niobium oxide and sodium phosphate were each 5%. Table 2A shows the details of the pigment, and Table 2B shows the details of the silica particles.

[0130] Tables 4A to 5B show the composition of the chemical conversion coating layer. In the "20% or more" column of Tables 4A and 4B, when the resin amount in the chemical conversion coating layer was 20% or more, it was marked "○ (good)", and when it was less than 20%, it was marked "× (bad)". In the "Nb oxide" column of Tables 5A and 5B, when niobium oxide was contained, it was marked "○ (good)", and when it was not contained, it was marked "× (bad)". In the "Na phosphate" column, when sodium phosphate was contained, it was marked "○ (good)", and when it was not contained, it was marked "× (bad)". In addition, for Comparative Examples 5 and 6, the drying temperature was outside the range of 50 to 250°C, or the drying time was outside the range of 1 second to 5 minutes.

[0131] (Arithmetic Mean Height of Chemical Conversion Coating Layer) The arithmetic mean height Sa of the chemical conversion coating layer was obtained by the following method. A sample cut to a predetermined size from a zinc-based plated steel sheet was gold-vapor-deposited to a thickness of 50 nm on its surface. The gold-vapor-deposited sample was embedded in resin and polished so that the cross section of the sample in the sheet thickness direction was exposed. The cross section of the sample was observed at 5000x magnification using a scanning electron microscope, and the roughness of the gold-vapor-deposited layer when observed from a direction perpendicular to the cross section was calculated to determine the arithmetic mean height Sa of the chemical conversion coating layer. The gold vapor deposition was performed to clarify the boundary between the chemical conversion coating layer and the resin. Because the thickness of the gold-vapor-deposited layer is negligible compared to the chemical conversion coating layer, the arithmetic mean height of the gold-vapor-deposited layer was used as the arithmetic mean height Sa of the surface of the chemical conversion coating layer.

[0132] (60° specular gloss Gs (60°)) Using a gloss meter (UGV-6P manufactured by Suga Test Instruments Co., Ltd.), the 60° gloss (%) of the surface of the Zn plating layer was measured according to the method specified in JIS Z 8741. A gloss of 50 to 200% was rated as "A," and a gloss of less than 50% was rated as "B." The results are shown in Tables 5A and 5B.

[0133] (b ＊ The surface of the Zn plating layer was measured using a spectrophotometer (SE6000 manufactured by Nippon Denshoku Industries Co., Ltd.), and ＊ If b is between -15 and -5, it is "AAA"; ＊ If it is -22 or more and -3.5 or less (excluding -15 or more and -5 or less), it is "AA"; ＊ When the value was −30 or more and −2 or less (excluding −22 or more and −3.5 or less), it was rated as “A”, and when it was more than −2 or less than −30, it was rated as “B”. The results are shown in Tables 5A and 5B.

[0134] (L ＊ value) Using a spectrophotometer (SE6000 manufactured by Nippon Denshoku Industries Co., Ltd.), ＊ was measured. ＊ If it is 75 or less, it is "AAA", and L ＊ If it is more than 75 and less than 80, it is classified as "AA" and L ＊ If it is over 80 and 85 or less, it is "A" and L ＊ When the value was more than 85, it was rated as "B." The results are shown in Tables 5A and 5B.

[0135] (Metallic Luster) The metallic luster was evaluated using a multi-angle spectrophotometer (MA T12 manufactured by X-rite). The L obtained when light was incident on a plane perpendicular to the surface of the chemical conversion treatment layer from an angle of 60° from the surface of the chemical conversion treatment layer toward the surface of the chemical conversion treatment layer and the light reflected by the surface of the chemical conversion treatment layer was received at an angle of 135° from the surface of the chemical conversion treatment layer was measured. ＊ L ＊ １ On the plane, light is incident on the surface of the chemical conversion treatment layer at an angle of 120° from the surface of the chemical conversion treatment layer toward the surface of the chemical conversion treatment layer, and the light reflected on the surface of the chemical conversion treatment layer is received at an angle of 135° from the surface of the chemical conversion treatment layer. ＊ L ＊ ２ When this is done, L ＊ １ / L ＊ ２ If the number is 3 or more, it is considered "AA" and if the number is 3 or more, it is considered "AA". ＊ １ / L ＊ ２ If the value is 2 or more but less than 3, it is marked as "A" and if the value is 2 or more but ＊ １ / L ＊ ２ A value of less than 2 was rated as "B." The results are shown in Tables 5A and 5B.

[0136] (Blackening Resistance) A zinc-based plated steel sheet was left standing under a high temperature and humidity of 70°C and 80% RH for 12 days, and the blackening resistance was evaluated from the change in color of the zinc plated layer surface before and after the test, as a color difference ΔE ＊ The color difference was evaluated by L ab. ＊ a ＊ b ＊ The chromaticity index in the color system is a ＊ and b ＊ , the lightness index is L ＊ Then, it is expressed by the following formula 4.

[0137] ΔE ＊ ab = √((Δa ＊ ) ２ + (Δb ＊ ) ２ + (ΔL ＊ ) ２ ) … Equation 4

[0138] However, in the above formula, Δa ＊is the a of the Zn-based plating layer before the test ＊ and a of the Zn-based plating layer after the test ＊ is the difference between ＊ is the b of the Zn-based plating layer before the test ＊ and b of the Zn-based plating layer after the test ＊ is the difference between ＊ is the L of the Zn-based plating layer before the test ＊ and L of the Zn-based plating layer after the test ＊ The evaluation was made using the following scoring system, with a score of 4 or 3 being considered a pass. The results are shown in Tables 6A and 6B.

[0139] 4: ΔE ＊ ab≦5 3:5<ΔE ＊ ab≦10 2:10<ΔE ＊ ab≦15 1:ΔE ＊ >15

[0140] (Corrosion Resistance) A salt spray test (JIS Z 2371:2015) was conducted on the zinc-based plated steel sheet. The occurrence of white rust on the Erichsen processed portion after 120 hours of testing was observed and evaluated using the following scoring system. A score of 3 or higher was considered pass. The results are shown in Tables 6A and 6B.

[0141] 4: White rust occurs less than 5%. 3: White rust occurs between 5% and 10%. 2: White rust occurs between 10% and 30%. 1: White rust occurs 30% or more.

[0142] (Metallic Appearance) The surface of the Zn plating layer of the Zn-based plated steel sheet was shown to five panelists, who judged the metallic appearance of the plating. The evaluation was based on the following rating system, with a rating of 4 or 3 being considered acceptable. The results are shown in Tables 6A and 6B.

[0143] 4: Four or more out of five people could see the metallic appearance of the plating. 3: Three out of five people could see the metallic appearance of the plating. 2: Two out of five people could see the metallic appearance of the plating. 1: One or less out of five people could see the metallic appearance of the plating.

[0144] (Weather Resistance) The surface of the Zn-plated layer of the Zn-based plated steel sheet was tested for 500 hours using a Sunshine Weather Meter tester, and the chemical conversion coating layer was evaluated based on the ratio of the initial film thickness to the film thickness after the test using the following rating system, with a rating of 4 or 3 being considered acceptable. The results are shown in Tables 6A and 6B.

[0145] 4: Remaining rate of chemical conversion coating layer is 90% or more 3: Remaining rate of chemical conversion coating layer is 50 to less than 90% 2: Remaining rate of chemical conversion coating layer is 30 to less than 50% 1: Remaining rate of chemical conversion coating layer is less than 30%

[0146]

[0147]

[0148]

[0149]

[0150]

[0151]

[0152]

[0153]

[0154]

[0155]

[0156]

[0157] As shown in Tables 1 to 6B, the zinc-based plated steel sheets of Examples 1 to 74 all had chemical conversion coating layers that satisfied the ranges of the present invention and exhibited good blackening resistance, corrosion resistance, metallic appearance, and weather resistance. Furthermore, the zinc-based plated steel sheets of Examples 14 to 16, which used phenolic resin, polyolefin resin, fluororesin, or acrylic resin as the resin contained in the chemical conversion coating layer, exhibited particularly excellent weather resistance. Furthermore, Examples 70 to 74, in which a patterned portion was formed in the plating layer, exhibited good blackening resistance, corrosion resistance, metallic appearance, and weather resistance, and also showed significantly improved visibility of the patterned portion.

[0158] On the other hand, as shown in Tables 1 to 6B, in Comparative Example 1, the chemical conversion coating layer did not contain any resin, so the chemical conversion coating layer itself became very brittle, and various evaluation tests could not be carried out. In Comparative Example 2, the chemical conversion coating layer did not contain any silica particles, so corrosion resistance was reduced. In Comparative Example 3, the content of silica particles was as high as 30%, so the chemical conversion coating layer itself became very brittle, and various evaluation tests could not be carried out. In Comparative Example 4, the chemical conversion coating layer did not contain any pigment, so blackening resistance was reduced. In Comparative Example 5, the drying conditions during chemical conversion coating layer formation were outside the preferred range, so the b ＊ In Comparative Example 6, the drying conditions during the formation of the chemical conversion coating layer were outside the preferred range, and therefore the 60-degree specular gloss G ｓ The metallic appearance was insufficient because the angle (60°) was outside the range of 50 to 200. In Comparative Example 7, the diameter of the silica particles was 450 nm, so the metallic appearance was insufficient. In Comparative Examples 8 to 11, no pigment containing Cu, Co, or Fe was included, and the blackening resistance was insufficient.

[0159] According to the present invention, in a zinc-based plated steel sheet containing Al, even when the plated surface is partially or entirely blackened due to oxidation of Al contained in the plated layer, the blackening can be made less noticeable, maintaining the metallic appearance, and the corrosion resistance and weather resistance can be improved. Therefore, the present invention has a high industrial applicability.

Claims

1. A steel sheet, a Zn-based plating layer containing 0.05 to 60% by mass of Al and Zn disposed on at least one side of the steel sheet, and a chromium-free chemical conversion treatment layer disposed on the Zn-based plating layer with an adhesion amount of 0.1 to 15 g / m per side ２ are provided. The chemical conversion treatment layer contains 20% by mass or more of a resin, 1 to 20% by mass of silica particles with an average particle size of 5 to 200 nm, and a pigment containing one or more of Cu, Co, or Fe. When evaluated in the CIE1976 (L ＊ , a ＊ , b ＊ ) color space, b ＊ is -30 or more and -2 or less, and the 60-degree specular gloss G ｓ (60°) is 50 to 200, showing a metallic appearance, a Zn-based plated steel sheet.

2. The Zn-based plated steel sheet according to claim 1, wherein the pigment is any one or more of copper (II) phthalocyanine, cobalt (II) phthalocyanine, copper sulfate, cobalt sulfate, iron sulfate, or iron oxide.

3. The Zn-based plated steel sheet according to claim 1 or 2, wherein when the mixing ratio of the silica particles and the pigment in the chemical conversion treatment layer is represented by the amount of Si in terms of Si of the silica particles [Si] and the amount of Cu in terms of Cu, Co in terms of Co, or Fe in terms of Fe of the pigment, [Si] / ([Cu]+[Co]+[Fe]) is in the range of 1 to 200.

4. The Zn-based plated steel sheet according to any one of claims 1 to 3, wherein the arithmetic mean roughness Ra of the Zn-based plating layer is 0.5 to 2.0 μm, and the arithmetic mean height Sa of the chemical conversion treatment layer is 5 nm to 100 nm.

5. The Zn-based plated steel sheet according to any one of claims 1 to 4, wherein the chemical conversion treatment layer further contains either one or both of an Nb compound and a phosphate compound.

6. The Zn-based plated steel sheet according to any one of claims 1 to 5, wherein the resin in the chemical conversion treatment layer contains any one or more resins of polyolefin resin, fluororesin, acrylic resin, urethane resin, polyester resin, epoxy resin, and phenolic resin.

7. The Zn-based plated steel sheet according to any one of claims 1 to 6, wherein the Zn-based plating layer contains, in an average composition, Al: 4% by mass or more and 22% by mass or less, Mg: 1% by mass or more and 10% by mass or less, and the balance consists of Zn and impurities.

8. The Zn-based plated steel sheet according to any one of claims 1 to 7, wherein the Zn-based plating layer further contains, in an average composition, Si: 0.0001 to 2% by mass.

9. The Zn-based plated steel sheet according to any one of claims 1 to 8, characterized in that the Zn-based plating layer further contains, in an average composition, any one or more of Ni, Sb, and Pb, in a total amount of 0.0001 to 2% by mass.

10. A pattern portion and a non-pattern portion are formed in the Zn-based plating layer so as to have a predetermined shape. The pattern portion and the non-pattern portion each include one or two of a first region and a second region determined by any one of the following determination methods 1 to 5. The absolute value of the difference between the area ratio of the first region in the pattern portion and the area ratio of the first region in the non-pattern portion is 30% or more. The Zn-based plated steel sheet according to any one of claims 1 to 9. [Determination method 1] Virtual grid lines are drawn on the surface of the Zn-based plating layer at intervals of 0.5 mm. In each of the plurality of regions partitioned by the virtual grid lines, a circle with a diameter of 0.5 mm centered on the centroid of each region is defined as a measurement region A, and the L ＊ value is measured. Arbitrarily select 50 points from the obtained L ＊ values. When the 50-point average of the obtained L ＊ values is used as the reference L ＊ value, the region where the L ＊ value is equal to or greater than the reference L ＊ value is defined as the first region, and the region where the value is less than the reference L ＊ value is defined as the second region. [Determination method 2] Virtual grid lines are drawn on the surface of the Zn-based plating layer at intervals of 0.5 mm. In each of the plurality of regions partitioned by the virtual grid lines, a circle with a diameter of 0.5 mm centered on the centroid of each region is defined as a measurement region A, and the L ＊ value is measured. The region where the L ＊ value is 45 or more is defined as the first region, and the region where the L ＊ value is less than 45 is defined as the second region. [Determination method 3] Virtual grid lines are drawn on the surface of the Zn-based plating layer at intervals of 0.5 mm. In each of the plurality of regions partitioned by the virtual grid lines, the arithmetic mean height Sa2 is measured. The region where the obtained arithmetic mean height Sa2 is 1 μm or more is defined as the first region, and the region where it is less than 1 μm is defined as the second region. [Determination method 4] Virtual grid lines are drawn on the surface of the Zn-based plating layer at intervals of 1 mm or 10 mm. By the X-ray diffraction method in which X-rays are incident on each of the plurality of regions partitioned by the virtual grid lines, for each region, the diffraction peak intensity I of the (0002) plane of the Zn phase ０００２ and the diffraction peak intensity I of the (10 - 11) plane of the Zn phase １０－１１ are measured, and the intensity ratio (I ０００２ / I １０－１１ ) is taken as the orientation ratio. A region where the orientation ratio is 3.5 or more is defined as the first region, and a region where the orientation ratio is less than 3.5 is defined as the second region. [Determination method 5] Virtual grid lines are drawn on the surface of the Zn-based plating layer at 1 mm intervals, and then, for each of a plurality of regions partitioned by the virtual grid lines, a circle S centered on the center of gravity point G of each region is drawn. For the circle S, the diameter R is set such that the total length of the surface boundary lines of the Zn-based plating layer contained inside the circle S is 10 mm. The average value of the maximum diameter Rmax and the minimum diameter Rmin of the diameters R of the circles S in the plurality of regions is defined as the reference diameter Rave. A region having a circle S with a diameter R less than the reference diameter Rave is defined as the first region, and a region having a circle S with a diameter R greater than or equal to the reference diameter Rave is defined as the second region.

11. The Zn-based plated steel sheet according to any one of claims 1 to 10, wherein the surface of the Zn-based plating layer has any one or more of Co, Fe, and Ni.