KR102626695B1 - Zn-based plated steel sheet - Google Patents

Abstract

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 chromate-free chemical conversion disposed on the Zn-based plating layer with an adhesion amount of 0.1 to 15 g/m2 per side. A treatment layer is provided, and the chemical treatment layer contains 20% by mass or more of resin, 1 to 20% by mass of silica particles with an average particle diameter of 5 to 200 nm, and one or two or more types of Cu, Co, or Fe. Pigment is contained, b* is -30 or more and -2 or less when the appearance is evaluated in the CIE1976 (L*, a*, b*) color space, and the 60-degree mirror gloss G specified in JIS Z 8741:1997 A Zn-based plated steel sheet with _s (60°) of 50 to 200 and exhibiting a metallic appearance.

Description

Zn-based plated steel sheet

The present invention relates to Zn-based plated steel sheets.

This application claims priority based on Patent Application No. 2020-176149 filed in Japan on October 20, 2020, and uses the content here.

The most commonly used plated steel plate with good corrosion resistance is Zn-based plated steel plate. Zn-based plated steel sheets are used in various manufacturing industries, such as automobiles, home appliances, and building materials. Among them, the use of Al-added plating has been increasing in recent years because it has high corrosion resistance.

As an example of a Zn-based plated steel sheet developed for the purpose of improving corrosion resistance, Patent Document 1 describes a hot-dip Zn-Al-Mg-Si plated steel sheet. This plated steel sheet has the characteristic of being excellent in appearance because its appearance shows a pear-shell pattern.

However, conventionally, in order to further impart a high level of rust prevention function to Zn-based plated steel sheets, chromate treatment using hexavalent chromate or the like is widely performed after plating, and further, as necessary, to improve designability, stain resistance, lubricity, etc. In order to provide high value-added functions, coating with organic resin was being performed. However, against the backdrop of heightened 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 for the purpose of providing a high level of rust prevention function simply by treating one layer of a resin-based film without performing chromate treatment.

By using the film described in Patent Document 2, it becomes possible to further improve corrosion resistance. However, when a Zn-based plated steel sheet containing Al is stored for a long period of time, there is a problem in that the Al contained in the plated layer is oxidized, causing the plated surface to turn black partially or entirely.

Japanese Patent No. 3179446 Publication Japanese Patent Publication No. 2006-52462

The present invention has been made in consideration of the above circumstances, and in a Zn-based plated steel sheet containing Al, even when the plating surface is partially or entirely blackened, it is possible to maintain the metallic appearance by making the blackening inconspicuous, Additionally, the goal is to provide a Zn-based plated steel sheet with improved corrosion resistance and weather resistance.

In order to solve the above problem, the present inventors conducted extensive studies and discovered that by containing a pigment in the chemical conversion layer, surface blackening of the plating layer is made less noticeable and the metallic appearance of the plating layer surface is not damaged. did. The present invention adopts the following configuration.

[1] Steel plate,

a Zn-based plating layer disposed on at least one side of the steel sheet and containing 0.05 to 60% by mass of Al and Zn;

A chromate-free chemical conversion layer disposed on the Zn-based plating layer with an adhesion amount of 0.1 to 15 g/m2 per side is provided,

The chemical conversion layer contains 20% by mass or more of resin, 1 to 20% by mass of silica particles with an average particle diameter of 5 to 200 nm, and a pigment containing one or two or more types of Cu, Co, or Fe, ,

When the appearance is evaluated in the CIE1976 (L*, a*, b*) color space, b* is -30 or more and -2 or less, and the 60-degree mirror gloss G _s (60°) specified in JIS Z 8741:1997 is 50 to 200, and exhibits a metallic appearance. Zn-based plated steel sheet.

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

[3] The mixing ratio of the silica particles and the pigment in the chemical conversion layer is the Si equivalent amount of the silica particles [Si], the Cu equivalent amount of the pigment [Cu], the Co equivalent amount [Co], or When expressed in Fe equivalent amount [Fe], [Si]/([Cu]+[Co]+[Fe]) is in the range of 1 to 200, the Zn-based plated steel sheet described in [1] or [2] .

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

[5] The Zn-based plated steel sheet according to any one of [1] to [4], wherein the chemical conversion layer further contains one or both of a Nb compound and a phosphoric acid compound.

[6] [1] to [5] wherein the resin in the chemical conversion layer contains at least one of polyolefin resin, fluorine resin, acrylic resin, urethane resin, polyester resin, epoxy resin, and phenol resin. The Zn-based plated steel sheet according to any one of the above.

[7] The Zn-based plating layer contains, as an average composition, Al: 4 mass% to 22 mass%, Mg: 1 mass% to 10 mass%, and the balance consists of Zn and impurities, [1] to The Zn-based plated steel sheet according to any one of [6].

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

[9] Among [1] to [8], wherein the Zn-based plating layer further contains, in average composition, 0.0001 to 2% by mass of one or more of Ni, Sb, and Pb in total. The Zn-based plated steel sheet according to any one of the items.

[10] In the Zn-based plating layer, a pattern portion and a non-pattern portion arranged to have a predetermined shape are formed,

The pattern portion and the non-pattern portion each include one or two types of a first region and a second region determined by any of the following determination methods 1 to 5,

Any one of [1] to [9], wherein 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. Zn-based plated steel sheet described in .

[Decision method 1]

Virtual grid lines are drawn at 0.5 mm intervals on the surface of the Zn-based plating layer, and in a plurality of areas divided by the virtual grid lines, a measurement area is within a circle with a diameter of 0.5 mm centered on the center of gravity of each area. Let A be used, and measure the L* value in each measurement area A. When 50 points are randomly selected from the obtained L* values and the average of 50 points of the obtained L* values is set as the standard L* value, the area where the L* value is greater than or equal to the standard L* value is called the first area, the reference L* The area below the value is referred to as the second area.

[Decision Method 2]

Virtual grid lines are drawn at 0.5 mm intervals on the surface of the Zn-based plating layer, and in a plurality of areas divided by the virtual grid lines, a measurement area is within a circle with a diameter of 0.5 mm centered on the center of gravity of each area. Let A be, the L* value in each measurement area A is measured, the area where the L* value is 45 or more is set as the first area, and the area where the L* value is less than 45 is set as the second area.

[Decision Method 3]

Virtual grid lines are drawn at 0.5 mm intervals on the surface of the Zn-based plating layer, and the arithmetic mean height Sa2 is measured in each of the plurality of regions defined by the virtual grid lines. The area where the obtained arithmetic mean height Sa2 is 1 µm or more is referred to as the first area, and the area where the obtained arithmetic mean height Sa2 is less than 1 µm is referred to as the second area.

[Decision Method 4]

By drawing virtual grid lines on the surface of the Zn-based plating layer at intervals of 1 mm or 10 mm, and applying The diffraction peak intensity I ₀₀₀₂ of the (0002) plane of the Zn phase and the diffraction peak intensity I _10-11 of the (10-11) plane of the Zn phase were measured, and their intensity ratio (I ₀₀₀₂ /I _10-11 ) was calculated as the orientation ratio. Do this. The area where the orientation ratio is 3.5 or more is referred to as the first area, and the area where the orientation ratio is less than 3.5 is referred to as the second area.

[Decision 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 the plurality of regions divided by the virtual grid lines, a circle S is drawn centered on the center of gravity point G of each region. The diameter R of the circle S is set so that the total length of the surface boundaries of the Zn-based plating layer contained within the circle S is 10 mm. The average value of the largest diameter Rmax and the smallest diameter Rmin among the diameters R of circles S in a plurality of areas is set as the standard diameter Rave, and the area having circles S whose diameter R is less than the standard diameter Rave is set as the first area, and the diameter R is set as the first area. An area having a circle S larger than or equal to the reference diameter Rave is referred to as the second area.

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

According to the present invention, in a Zn-based plated steel sheet containing Al, even when the plated surface turns black partially or entirely due to oxidation of Al contained in the plating layer, the metal appearance can be maintained by making the blackening inconspicuous, Additionally, it is possible to provide a Zn-based plated steel sheet with improved corrosion resistance and weather resistance.

The present inventors found that by adding a pigment to the chemical conversion layer and coloring the chemical conversion layer blue, the blackened portions generated on the surface of the plating layer become less conspicuous. However, if the blue is too dark, it becomes difficult to visually recognize the metallic appearance on the surface of the plating layer. In addition, it was discovered that the visibility of the blackened portion and the visibility of the metal exterior changed when the incident light was reflected from the surface of the plating layer and when the incident light was reflected from the surface of the chemical conversion layer. Therefore, as a result of further examination, the b* value when evaluated in the CIE1976 (L*, a*, b*) color space and the 60-degree mirror gloss G _s (60°) specified in JIS Z 8741:1997 were determined to be It was discovered that by controlling the range so that the blackened area generated on the surface of the plating layer becomes less noticeable, it also becomes possible to visually recognize the metallic appearance. Additionally, it was discovered that by controlling the b* value and the 60-degree mirror gloss G _s (60°), even when arbitrary shapes such as letters were displayed on the surface of the plating layer, the arbitrary shapes became easier to see.

That is, the Zn-based plated steel sheet of the embodiment of the present invention includes 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 Zn-based plating layer disposed on the Zn-based plating layer. , a chromate-free chemical conversion layer with an adhesion amount of 0.1 to 15 g/m2 per side is provided, and the chemical conversion layer includes 20% by mass or more of resin, 1 to 20% by mass of silica particles with an average particle diameter of 5 to 200 nm, and Cu. , a pigment containing one or more types of Co or Fe is contained, and b* when the appearance is evaluated in the CIE1976 (L*, a*, b*) color space is -30 or more and -2 or less, and , is a Zn-based plated steel sheet with a 60-degree mirror gloss G _s (60°) specified in JIS Z 8741:1997 of 50 to 200 and a metallic appearance.

In addition, in the Zn-based plated steel sheet of this embodiment, the pigment is preferably one or two or more of copper (II) phthalocyanine, cobalt (II) phthalocyanine, copper sulfate, cobalt sulfate, iron sulfate, or iron oxide.

In addition, in the Zn-based plated steel sheet of this embodiment, the mixing ratio of the silica particles and the pigment in the chemical conversion treatment layer is the Si equivalent amount of the silica particles [Si], the Cu equivalent amount of the pigment [Cu], and the Co conversion amount. When expressed in terms of amount [Co] or Fe equivalent amount [Fe], it is preferable that [Si]/([Cu]+[Co]+[Fe]) is in the range of 1 to 200. In addition, each unit of Si conversion amount, Cu conversion amount, Co conversion amount, and Fe conversion amount is set to “g/m2.”

In addition, in the Zn-based plated steel sheet of this embodiment, 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 layer is 5 nm to 100 nm.

[Zn-based plated steel sheet]

Hereinafter, the Zn-based plated steel sheet of this embodiment will be described.

There are no particular restrictions on the material of the steel sheet that becomes the base of the Zn-based plating layer. As a material, general steel, etc. can be used without any particular restrictions, and Al killed steel or some high alloy steels can also be applied, and there are no special restrictions on the shape. The Zn-based plating layer according to this embodiment is formed by applying the hot-dip plating method described later to the steel sheet.

[Zn-based plating layer]

Next, the chemical composition of the Zn-based plating layer will be described.

The Zn-based plating layer preferably contains 0.05 to 60% by mass of Al and Zn, and more preferably contains 0.05 to 60% by mass of Al, with the balance consisting of Zn and impurities. By containing 0.05% by mass or more of Al, the corrosion resistance of the Zn-based plating layer can be improved, and by setting the Al content to 60% by mass or less, the amount of Zn contained in the Zn-based plating layer is relatively increased, thereby improving sacrificial corrosion resistance. It becomes possible to secure The Zn-based plating layer may contain 40% by mass or more of Zn.

In addition, the Zn-based plating layer of the present embodiment may contain, as an average composition, Al: 4 to 22% by mass and Mg: 1 to 10% by mass, and the balance may be composed of Zn and impurities. Additionally, the Zn-based plating layer may contain Si: 0.0001 to 2% by mass as an average composition.

Hereinafter, the reason for limiting the components of the Zn-based plating layer, which contains 4 to 22% by mass of Al and 1 to 10% by mass of Mg, and the remainder consists of Zn and impurities, will be explained.

The Al content is in the range of 4 to 22 mass%. Al may be contained to ensure corrosion resistance. If the Al content in the Zn-based plating layer is 4% by mass or more, the effect of improving corrosion resistance becomes higher. When the Al content is 22% by mass or less, the effects of improving corrosion resistance and weather resistance are easily secured while maintaining the metallic appearance.

The Mg content is in the range of 1 to 10 mass%. Mg may be contained to improve corrosion resistance. If the Mg content in the Zn-based plating layer is 1% by mass or more, the effect of improving corrosion resistance becomes higher. When the Mg content is 10% by mass or less, the generation of dross in the plating bath is suppressed, the occurrence of locations where plating is not formed normally due to dross adhering to the plating can be suppressed, and a decrease in corrosion resistance can be suppressed. You can.

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

Additionally, the Zn-based plating layer may contain Si in the range of 0.0001 to 2% by mass.

Since Si may improve the adhesion of the Zn-based plating layer, Si may be contained. Since the effect of improving adhesion is exhibited by containing Si in an amount of 0.0001% by mass or more, preferably 0.001% or more, more preferably 0.01% or more, it is preferable to contain Si in an amount of 0.0001% by mass or more. On the other hand, even if Si is contained in excess of 2% by mass, the effect of improving plating adhesion is saturated, so the Si content is set to 2% by mass or less. From the viewpoint of plating adhesion, the Si content may be in the range of 0.001 to 1% by mass, or 0.01 to 0.8% by mass.

The Zn-based plating layer may contain, in average composition, a total of 0.0001 to 2% by mass, preferably 0.001 to 2% by mass, of one or two or more types of Ni, Sb, and Pb. By containing these elements, corrosion resistance can also be improved.

The remainder of the chemical components of the Zn-based plating layer are zinc (Zn) and impurities. Impurities include those that are inevitably included in zinc and other metals, and those that are included as a result of the steel dissolving in the plating bath.

Additionally, the average composition of the Zn-based plating layer can be measured by the following method. First, the chemical conversion layer is removed using a film release agent that does not erode the plating (e.g., Neo River SP-751 manufactured by Sansai Kako). If a surface layer coating film exists on the chemical conversion treatment layer, the surface layer coating film is also removed. Thereafter, the Zn-based plating layer can be determined by dissolving the Zn-based plating layer in hydrochloric acid containing an inhibitor (for example, Hibiron manufactured by Sugimura Chemical Co., Ltd.) and subjecting the obtained solution to inductively coupled plasma (ICP) emission spectroscopic analysis.

Additionally, it is preferable that the surface of the Zn-based plating layer has any one or two or more elements among Co, Fe, and Ni. Co, Fe, and Ni are attached to the surface of the Zn-based plating layer by performing Co treatment, Fe treatment, or Ni treatment after formation of the Zn-based plating layer. By having these elements on the surface of the Zn-based plating layer, blackening resistance can be improved. Co, Fe or Ni is preferably present on the surface of the Zn-based plating layer in the form of a compound.

[Formulated treatment layer]

Next, the chemical conversion layer is explained. The chemical conversion layer of this embodiment includes 20% by mass or more of 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 two or more types of Cu, Co, or Fe. It is contained. The chemical conversion layer of this embodiment is a film obtained by applying an aqueous composition containing resin, silica particles, and pigment to a Zn-based plating layer formed on a steel sheet and drying it.

[profit]

The resin contained in the chemical conversion layer may be any general resin, and examples include polyolefin resin, fluorine resin, acrylic resin, urethane resin, polyester resin, epoxy resin, and phenolic resin. These resins may be water-soluble resins, or may be resins that are originally water-insoluble but can be microdispersed in water, such as emulsions or suspensions (water-dispersible resins). In addition to water-soluble resins, resins include resins that are originally water-insoluble but can be microdispersed in water, such as emulsions or suspensions (water-dispersible resins). In particular, it is preferable to contain at least one type of resin among polyolefin resin, fluorine resin, acrylic resin, and phenol resin because it has excellent weather resistance.

The polyolefin resin is not particularly limited, and for example, ethylene and unsaturated carboxylic acids such as methacrylic acid, acrylic acid, maleic acid, fumaric acid, itaconic acid, and crotonic acid are radically polymerized at high temperature and pressure, and then ammonia or amine compounds, Examples include those obtained by neutralizing with a metal compound such as KOH, NaOH, LiOH, or ammonia or an amine compound containing the metal compound, followed by water oxidation.

There is no particular limitation on the fluororesin, and examples include homopolymers or copolymers of fluoroolefins. In the case of a copolymer, a copolymer of a fluoroolefin and a fluorine-containing monomer other than the fluoroolefin and/or a monomer that does not have a fluorine atom can be mentioned.

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

The urethane resin is not particularly limited and includes, for example, ethylene glycol, propylene glycol, diethylene glycol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, bisphenol hydroxypropyl ether, glycerin, trimethylolethane, and trimethyl. and those obtained by reacting polyhydric alcohols such as allpropane with diisocyanate compounds such as hexamethylene diisocyanate, isophorone diisocyanate, and tolylene diisocyanate, further chain extending with diamine, and water oxidation.

The polyester resin is not particularly limited and includes, for example, ethylene glycol, propylene glycol, diethylene glycol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, bisphenol hydroxypropyl ether, glycerin, trimethylolethane, Polyhydric alcohols such as 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 hymic anhydride are dehydrated and condensed to produce ammonia. Those obtained by neutralizing with an amine compound or the like and oxidizing in water can be mentioned.

The epoxy resin is not particularly limited and includes, for example, bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, resorcinol-type epoxy resin, hydrogenated bisphenol-A epoxy resin, hydrogenated bisphenol F-type epoxy resin, and resorcinol-type epoxy resin. It is obtained by reacting an epoxy resin such as a resin or a novolak-type epoxy resin with an amine compound such as diethanolamine or N-methylethanolamine and neutralizing it with an organic or inorganic acid, or by radically polymerizing a high acid value acrylic resin in the presence of the epoxy resin. After that, it is neutralized with ammonia or an amine compound, and then obtained by water oxidation.

The phenol resin is not particularly limited and includes, for example, methylolated phenol resin obtained by addition reaction of aromatics such as phenol, resorcinol, cresol, bisphenol A, and paraxylylene dimethyl ether with formaldehyde in the presence of a reaction catalyst. and those obtained by reacting a phenol resin with amine compounds such as diethanolamine and N-methylethanolamine and neutralizing them with an organic acid or inorganic acid.

The resin is contained in the chemical conversion layer at a rate of 20% by mass or more. By setting the resin content to 20% by mass or more, the Zn-based plating layer can be stably covered without the chemical conversion layer itself becoming brittle. In addition, the chemical conversion layer may contain components other than the resin, such as Nb compounds and phosphoric acid compounds, along with the resin, silica particles, and pigments, and the resin content may be the remainder of these components.

[Silica particles]

Silica particles are blended to improve the corrosion resistance of the chemical conversion layer. As silica particles, those with an average particle diameter in the range of 5 to 200 nm are suitable. Silica particles are contained in the chemical conversion layer at a ratio of 1 to 20% by mass. By setting the content of silica particles to 1% by mass or more, the effect of improving corrosion resistance is obtained. Additionally, by setting the content of silica particles to 20% by mass or less, the chemical conversion layer itself does not become brittle and the Zn-based plating layer can be stably covered. Silica particles with an average particle size of less than 5 nm are difficult to obtain, and a chemical conversion layer containing silica particles with an average particle size of less than 5 nm is actually difficult to manufacture and manufacture, so the lower limit of the average particle size of silica particles is 5 nm. This is the above. Additionally, if the average particle diameter of the silica particles exceeds 200 nm, there is a risk that the chemical conversion treatment layer may become cloudy and the metallic appearance of the Zn-based plating layer may be damaged. The content of silica particles is more preferably 3 to 15% by mass in the chemical conversion layer from the viewpoint of maintaining both the corrosion resistance and strength of the chemical conversion layer.

Generally, inorganic pigments such as silica particles have a small particle size, and therefore may exist in the chemical conversion layer in the form of secondary particles having a particle size larger than the primary particle size. The particle size of these secondary particles (particles in which the inorganic pigment is aggregated) is hereinafter referred to as “secondary particle size.” The silica particles in this embodiment may be a mixture of primary particles and secondary particles, and even if they are a mixture of primary particles and secondary particles, the average particle diameter may be in the range of 5 to 200 nm. The average particle size of the silica particles is more preferably 5 to 150 nm from the viewpoint of maintaining high permeability of the chemical conversion layer.

The average particle size of silica in the chemical conversion layer is measured by the following method. First, a thin film sample of the chemical conversion layer is produced by a microtome method so that a cross section perpendicular to the rolling direction of the steel sheet of the present invention can be observed. In an area of 20 μm ) to observe at least 5 areas at a magnification of 100,000x. Using the following formula 1, the equivalent circle diameter of all the silica particles in the observation area is calculated, this equivalent circle diameter is set as the particle size of each silica particle, and the average particle size is obtained by averaging.

Equivalent circle diameter=2√(S/π)...Equation 1

However, S is the area of the silica particle, and π is the circumference.

The content of silica particles in the chemical conversion layer is measured by the following method. First, separately from the target sample, a plurality of comparative samples having a chemical conversion layer with a known content of silica particles were prepared, their surfaces were measured by a fluorescence Draw a calibration curve based on the relationship between contents. Next, the target sample is measured with a fluorescence

Additionally, in the present invention, the average particle size in the state of water-dispersed silica before being dispersed in the paint is maintained even in the chemical conversion layer, so that value may be used.

Additionally, in order to improve the corrosion resistance of the chemical conversion layer, in addition to silica particles, titania particles, alumina particles, zirconia particles, etc. may be contained.

[Pigment]

The chemical conversion layer contains a pigment containing one or two or more types of Cu, Co, or Fe. The pigment may contain one type of Cu, Co, or Fe, or may contain two or more types. Additionally, the chemical conversion layer may contain one type of pigment containing one or two or more types of Cu, Co, or Fe, or two or more types of pigments. Pigments include copper(II) phthalocyanine, cobalt(II) phthalocyanine, copper sulfate, cobalt sulfate, iron sulfate, or iron oxide. By containing a pigment in the chemical conversion layer, the chemical conversion layer is colored blue, making it difficult to notice the blackened portion exposed on the surface of the plating layer. In order to obtain this effect, it is preferable that the pigment content in the chemical conversion layer is in the range of 0.1 to 10 mass%. By setting the pigment content in the chemical conversion treatment layer to 0.1% by mass or more, the blackened portion on the surface of the Zn-based plating layer can be made inconspicuous. Additionally, by setting the pigment content to 10% by mass or less, the metallic appearance of the Zn-based plating layer is not damaged. From the viewpoint of maintaining the metallic appearance, the pigment content is more preferably 0.1 to 5% by mass, and still more preferably 0.1 to 3% by mass.

The content of the pigment in the chemical conversion layer is measured by the following method. First, a thin film sample of the chemical conversion layer is produced by a microtome method so that a cross section perpendicular to the rolling direction of the Zn-based plated steel sheet of this embodiment can be observed. In an area of 20 μm ), observe at least 5 areas at a magnification of 100,000 times, and perform elemental mapping using an energy dispersive X-ray analyzer (EDS or EDX). From the element mapping results, the area ratio of the region where Cu, Co, or Fe exists is obtained. Here, by the same method as above, the area ratio of the region where Cu, Co, or Fe exists in a plurality of comparative samples having a chemical conversion layer with a known pigment content is determined, and the relationship with the pigment content is obtained. Prepare a calibration curve in advance. Using the calibration curve, the content of the target sample pigment is determined.

The pigment colors the chemical conversion layer blue and makes the blackened portion of the surface of the Zn-based plating layer less noticeable. However, if the pigment is included in the chemical conversion layer, the corrosion resistance of the chemical conversion layer may decrease. Therefore, in order to prevent a decrease in the corrosion resistance of the chemical conversion layer, it is desirable to optimize the mixing ratio of silica particles and pigment in the chemical conversion layer of this embodiment. That is, the mixing ratio (mass ratio) of the silica particles and the pigment in the chemical conversion layer is the Si equivalent amount of the silica particles [Si] (g/m2), the Cu equivalent amount of the pigment [Cu] (g/m2), and the Co equivalent amount. When expressed as [Co] (g/m2) or Fe conversion amount [Fe] (g/m2), [Si]/[Cu], [Si]/[Co] or [Si]/[Fe] is 1 It is preferable that it ranges from 200 to 200. By setting [Si]/[Cu], [Si]/[Co] or [Si]/[Fe] to 1 or more, the corrosion resistance of the converted layer can be improved even when the converted layer contains a pigment. Additionally, by setting [Si]/[Cu], [Si]/[Co], or [Si]/[Fe] to 200 or less, deterioration of the appearance of the Zn-based plating layer can be prevented. [Si]/[Cu], [Si]/[Co] or [Si]/[Fe] is more preferably 10 to 150 from the viewpoint of preventing deterioration of appearance and maintaining corrosion resistance. Additionally, from the viewpoint of making the blue coloring of the chemical conversion layer more beautiful, it is more preferable that [Si]/([Cu]+[Co]+[Fe]) is in the range of 1 to 200.

The chemical conversion layer may further contain either or both an Nb compound and a phosphoric acid compound. When an Nb compound or a phosphoric acid compound is contained, the corrosion resistance of the Zn-based plating layer improves.

As the Nb compound, conventionally known niobium-containing compounds can be used, and examples include niobium oxide, niobic acid and its salts, fluoroniobate salts, and fluoroxoniobate salts. Among them, it is preferable to use niobium oxide from the viewpoint of improving corrosion resistance.

Examples of phosphoric acid compounds include phosphoric acids and salts thereof such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, and tetraphosphoric acid; Phosphonic acids and their salt; Organic phosphoric acids such as phytic acid and their salts can be mentioned. There are no particular restrictions on the cationic species of the salt, and examples include Cu, Co, Fe, Mn, Sn, V, Mg, Ba, Al, Ca, Sr, Nb, Y, Ni, and Zn. These may be used individually, or two or more types may be used together.

The Nb compound and the phosphoric acid compound may be contained in a total ratio of 0.5 to 30% by mass in the chemical conversion layer. If the content of the Nb compound or phosphoric acid compound is 0.5% by mass or more, the effect of improving corrosion resistance is obtained, and if the content of the Nb compound or phosphoric acid compound is 30% by mass or less, the chemical conversion layer does not become weak and the Zn-based plating layer can be stably covered. You can.

The content of the Nb compound or phosphoric acid compound in the chemical conversion layer is measured by the following method. First, separately from the target sample, a plurality of comparative samples having a chemical conversion layer with a known content of Nb compound or phosphoric acid compound are prepared, their surfaces are measured by a fluorescence X-ray device, and the resulting Nb or P is detected. A calibration curve is drawn based on the relationship between strength and the content of Nb compound or phosphoric acid compound. Next, the target sample is measured by a fluorescence

Additionally, the adhesion amount of the chemical conversion layer per side of the Zn-based plating layer is 0.1 to 15 g/m2. If the adhesion amount is 0.1 g/m 2 or more, the adhesion amount of the chemical conversion layer becomes sufficient, the surface blackening portion of the Zn-based plating layer can be made inconspicuous, and the corrosion resistance of the Zn-based plating layer can be further improved. Additionally, if the adhesion amount is 15 g/m 2 or less, even if the chemical conversion layer contains a pigment, reflection of light on the surface of the chemical conversion layer decreases, and the metallic appearance of the surface of the Zn-based plating layer can be visually recognized. A more preferable adhesion amount is 0.2 to 2 g/m2.

The chemical conversion 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 individually, or two or more types may be used together.

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

The silane coupling agent is not particularly limited and includes, for example, vinyltrimethoxysilane, vinyltriethoxysilane, and γ-amino sold by Shinetsu Chemical, Nippon Unica, Chisso, Toshiba Silicone, etc. Propyltrimethoxysilane, γ-aminopropylethoxysilane, N-[2-(vinylbenzylamino)ethyl]-3-aminopropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methoxysilane Kryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxy Silane, 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-mercaptopropyl Trimethoxysilane, etc. can be mentioned. The said silane coupling agent may be used individually, or 2 or more types may be used together.

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 a carboxyl group or a hydroxyl group, but a compound soluble in water or an organic solvent is preferable, and a water-soluble zirconium compound is more preferable. . Examples of such compounds include zirconyl ammonium carbonate.

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 a carboxyl group or a hydroxyl group. 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-amideethyl/aminoethyl)titanate, etc. are mentioned. The said crosslinking agent may be used individually, or 2 or more types may be used together.

The at least one crosslinking agent selected from the group consisting of the silane coupling agent, crosslinkable zirconium compound, and crosslinkable titanium compound is preferably contained in an amount of 0.1 to 50% by mass based on 100% by mass of the solid content of the resin. When the content of this crosslinking agent is less than 0.1% by mass, the effect of improving adhesion may not be obtained, and when the content of this crosslinking agent exceeds 50% by mass, the stability of the aqueous composition may decrease.

The chemical conversion layer may further contain at least one crosslinking agent selected from the group consisting of amino resins, polyisocyanate compounds, blocks thereof, epoxy compounds, and carbodiimide compounds. These crosslinking agents may be used individually, or two or more types may be used together.

When at least one crosslinking agent selected from the group consisting of the amino resin, polyisocyanate compound, block body thereof, epoxy compound, and carbodiimide compound is contained, the crosslinking density increases, the barrier property of the chemical conversion layer is improved, and the corrosion resistance is improved. This is further improved.

The amino resin is not particularly limited, and examples include melamine resin, benzoguanamine resin, urea resin, and glycoluril resin.

The polyisocyanate compound is not particularly limited, and examples include hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, and tolylene diisocyanate. In addition, the blocked product is a blocked product of the polyisocyanate compound.

The epoxy compound is not particularly limited as long as it is a compound having a plurality of oxirane rings, and examples include diglycidyl adipic acid, diglycidyl phthalate, diglycidyl terephthalate, and 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, hydrogenated bisphenol A diglycidyl ether, etc. are mentioned.

As the carbodiimide compound, for example, an isocyanate-terminated polycarbodiimide is synthesized by a condensation reaction involving decarbonization of diisocyanate compounds such as aromatic diisocyanate, aliphatic diisocyanate, and cycloaliphatic diisocyanate. and compounds to which a hydrophilic segment having a functional group reactive with an isocyanate group is added.

At least one crosslinking agent selected from the group consisting of the amino resin, polyisocyanate compound, block body thereof, epoxy compound, and carbodiimide compound is preferably contained in an amount of 0.1 to 50% by mass based on 100% by mass of 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, and if the content of this crosslinking agent exceeds 50% by mass, the chemical conversion treatment layer may become weak and corrosion resistance may decrease.

It is preferable that the chemical conversion layer further contains at least one type selected from the group consisting of vanadium compounds, tungsten compounds, and molybdenum compounds. These may be used individually, or two or more types may be used together.

The corrosion resistance of the chemical conversion layer is improved by containing at least one type selected from the group consisting of the vanadium compound, tungsten compound, and molybdenum compound.

The vanadium compound is not particularly limited, and conventionally known vanadium-containing compounds can be used, for example, vanadic acid, ammonium vanadate, vanadate such as sodium vanadate, phosphorus such as phosphovanadic acid and ammonium phosphovanadate, etc. Vanadate salts, etc. can be mentioned.

The tungsten compound is not particularly limited, and conventionally known tungsten-containing compounds can be used, for example, tungstic acid, ammonium tungstate, tungstate salts such as sodium tungstate, phosphorus such as tungstic acid and ammonium phosphotungstate. Tungstate salts, etc. can be mentioned.

The molybdenum compound is not particularly limited, and conventionally known molybdenum-containing compounds can be used, such as molybdate salts. The molybdate salt is not limited in its skeleton or degree of condensation, and examples include orthomolybdate salt, paramolybdate salt, and metamolybdate salt. In addition, it includes all salts such as single salts and double salts, and examples of double salts include molybdate phosphate.

It is preferable to contain at least 1 type selected from the group consisting of the vanadium compound, tungsten compound, and molybdenum compound in an amount of 0.01 to 20% by mass based on 100% by mass of the solid content of the resin. When 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% by mass, the effect of improving corrosion resistance may not be obtained, and the group consisting of the vanadium compound, tungsten compound, and molybdenum compound If the content of at least one selected from the above exceeds 20% by mass, the chemical conversion layer may become brittle and corrosion resistance may decrease.

The chemical conversion treatment layer may further contain a polyphenol compound.

By containing the polyphenol compound, the corrosion resistance of the chemical conversion treatment layer and the adhesion of the post-coating film when used for post-coating purposes, etc. are improved.

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 the benzene ring include gallic acid, pyrogallol, and catechol. The condensate of a compound having two or more phenolic hydroxyl groups bonded to a benzene ring is not particularly limited, and examples include polyphenol compounds widely distributed in the plant kingdom, commonly called tannic acid. Tannic acid is a general term for aromatic compounds with a complex structure having a large number of phenolic hydroxyl groups widely distributed in the plant kingdom. The tannic acid may be hydrolyzable tannic acid or condensed tannic acid. The tannic acid is not particularly limited and includes, for example, hamamelittannin, persimmon tannin, tea tannin, gallnut tannin, brown tannin, myrobalan tannin, DBDB tannin, algarovilla tannin, Valonia tannin, catechin tannin, etc. You can.

The above-mentioned tannic acid includes commercially available ones, for example, “tannic acid extract A”, “B tannic acid”, “N tannic acid”, “common tannic acid”, “purified tannic acid”, “Hi tannic acid”, “F tannic acid”, and “national tannic acid”. "(all manufactured by Dainippon Seiyaku Co., Ltd.), "tannic acid: AL" (manufactured by Fujigaku Kogyo Co., Ltd.), etc. can also be used. The polyphenol compounds may be used individually, or two or more types may be used in combination.

The polyphenol compound is preferably contained in an amount of 0.1 to 50% by mass based on 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, and if the content of the polyphenol compound exceeds 50% by mass, the stability of the aqueous composition may decrease.

The chemical conversion layer may further contain a solid lubricant.

Containing the solid lubricant improves the lubricity of the chemical conversion layer, and is effective in improving processability during press molding, preventing scratches caused by molds or handling, and preventing wear and tear during transportation of molded products or coils.

The solid lubricant is not particularly limited and includes known lubricants such as fluorine-based, hydrocarbon-based, fatty acid amide-based, ester-based, alcohol-based, metal soap-based and inorganic-based lubricants. As a criterion for selecting a lubricating additive to improve processability, selecting a substance present on the surface of the chemical conversion layer rather than one dispersed in the chemical conversion layer in which the added lubricant is formed reduces the friction between the surface of the molded workpiece and the mold. This is necessary to maximize the lubrication effect. That is, when the lubricant is dispersed in the formed chemical conversion layer, the surface friction coefficient is high, making it easy for the chemical conversion layer to be destroyed, and the powdered material is peeled off and deposited, resulting in poor appearance and reduced processability called a powdering phenomenon. As a substance present on the surface of the chemical conversion layer, one that is not compatible with the resin and has low surface energy is selected.

Among these, the use of polyolefin wax is more preferable because the surface kinetic friction coefficient is lowered, processability is greatly improved, and corrosion resistance after processing is also improved. Examples of this wax include hydrocarbon-based waxes such as paraffin, microcrystalline, or polyethylene. During processing, the film temperature increases due to the deformation heat and friction heat of the material, so the melting point of the wax is more preferably 70 to 160°C. If the melting point of the wax is less than 70°C, it may soften and melt during processing and may not exhibit excellent properties as a solid lubricant. Additionally, if the melting point of the wax exceeds 160°C, hard particles are present on the surface and the friction characteristics are reduced, so high molding processability may not be obtained.

The particle size of these waxes is more preferably 0.1 to 5 μm. If the wax particle size exceeds 5 μm, there is a possibility that the solidified wax may be distributed unevenly or fall off from the chemical treatment layer. Additionally, when the wax particle size is less than 0.1 μm, processability may be insufficient.

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

The chemical conversion layer is obtained by applying and drying an aqueous composition containing components such as resin, silica particles, blue organic pigment, Nb compound, and phosphoric acid compound to the surface of the Zn-based plating layer. A solvent may be used in the aqueous composition to improve film forming properties and form a more uniform and smooth film. The solvent is not particularly limited as long as it is commonly used in paints. For example, from the viewpoint of leveling, alcohol-based, ketone-based, ester-based, ether-based hydrophilic solvents, etc. can be mentioned.

The method of coating the aqueous composition used to form the chemical conversion layer is to apply 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 roll coat, air spray, airless spray, dipping, etc. can be appropriately employed. In order to increase the curability of the chemical conversion layer, it is preferable to heat the object to be coated in advance or to heat dry the object to be coated after coating. As a heat drying method, any method such as hot air, induction heating, near infrared, or far infrared may be used, and may be used in combination. The heating temperature of the object to be coated is 50 to 250°C, preferably 70 to 220°C. If the heating temperature is less than 50°C, the evaporation rate of moisture is slow and sufficient film forming properties are not obtained, so corrosion resistance may deteriorate. On the other hand, if the heating temperature exceeds 250°C, thermal decomposition of the resin occurs, corrosion resistance decreases, and the appearance deteriorates due to yellowing or the like. When heat drying after coating, the drying time is preferably 1 second to 5 minutes. Additionally, if the resin is cured by electron beams or ultraviolet rays, curing may be done by irradiation of these, or combined use with heat drying may be used.

In addition, the arithmetic mean roughness Ra of the Zn-based plating layer is preferably 0.5 to 2.0 μm, and the arithmetic mean height Sa of the chemical conversion layer is preferably 5 nm to 100 nm. When the arithmetic mean roughness Ra of the Zn-based plating layer is 2.0 μm or less, the metallic appearance of the Zn-based plating layer can be maintained high. When Ra exceeds 2.0 μm, light hitting the surface of the Zn-based plating layer is likely to be diffusely reflected, and the appearance of the metal is likely to deteriorate. The permeability of the chemical conversion layer can be maintained by the arithmetic mean height Sa of the chemical conversion layer being 100 nm or less. On the other hand, if Sa exceeds 100 nm, light hitting the surface of the chemical conversion layer tends to be diffusely reflected, and there is a risk that the permeability of the chemical conversion layer may decrease. When the arithmetic mean roughness Ra of the Zn-based plating layer and the arithmetic mean height Sa of the chemical conversion layer are each below the upper limit, the metallic appearance of the Zn-based plating layer can be maintained. In addition, even if the arithmetic mean roughness Ra of the Zn-based plating layer and the arithmetic mean height Sa of the chemical conversion layer are each set below the lower limit, the effect of maintaining the metallic appearance and permeability is saturated, so they are each set above the lower limit. The arithmetic average roughness Ra of the Zn-based plating layer is measured and calculated using a 3D laser microscope (manufactured by Keyence Corporation). Using a 20x standard lens, the height Z is measured at a measurement interval of 50 μm. It is desirable to set the measurement score to 100 points. The measurement points are set as 100 points, and the 100 points of the obtained height Z are used as heights Z1 to height Z100 to calculate the arithmetic mean illuminance Ra from the following equation 2. Zave is the average of height Z of 100 points.

Ra=1/100×Σ[x=1→100](|Height Zx-Zave|) ... Equation 2

The arithmetic mean height Sa of the chemical conversion layer is measured and calculated by the following method. Gold is deposited on the surface of a sample cut to a predetermined size from a Zn-based plated steel sheet to a thickness of 50 nm, the gold-deposited sample is embedded in resin, and the cross section of the sample in the plate thickness direction is exposed. The cross section of the sample is observed at a magnification of 5000 times using a scanning electron microscope, and the line roughness of the gold deposition layer when observed from the direction perpendicular to the cross section is calculated. The arithmetic mean height Sa of the converted layer is obtained by converting the obtained line roughness into surface roughness difference. Gold deposition is performed to clarify the boundary between the chemical conversion layer and the resin, and since the thickness of the gold deposition layer is negligible compared to the chemical conversion layer, the arithmetic average height of the gold deposition layer is calculated as the arithmetic average height of the surface of the chemical conversion layer. It can be replaced by the average height Sa.

The chemical conversion layer is preferably formed on the surface of the Zn-based plating layer without any other coating or the like interposing it. In addition, in order to obtain a more beautiful metallic appearance, it is preferable that no other colored film or low-permeability film is provided on the chemically treated layer.

Even if there is a chemical conversion layer, from the viewpoint of reflecting the metallic appearance of the surface of the plating layer, when the Zn-based plated steel sheet of this embodiment is measured by a multi-angle spectrophotometer, the chemical conversion treatment layer is in the plane orthogonal to the surface of the chemical treatment layer. L* obtained when light is incident on the surface of the converted layer from an angle of 60° from the surface of the layer and the light reflected by the surface of the converted layer is received at an angle of 135° from the surface of the converted layer, L* * ₁ , in the above plane, light is incident toward the surface of the converted layer from an angle of 120° from the surface of the converted layer, and the light reflected by the surface of the converted layer is 135 degrees from the surface of the converted layer. When L* obtained when light is received at an angle of ° is taken as L* ₂ , it is desirable to satisfy L* ₁ /L* ₂ ≥ 2. It was discovered that this characteristic is unique to Zn-based plated steel sheets, which have a metallic luster even if there is a chemical conversion treatment layer and, as a result, have a metallic appearance. After setting it to this range, by setting b* when evaluated in the CIE1976 (L*, a*, b*) color space to the range described later, it is possible to maintain a more beautiful metallic appearance while making blackening less noticeable. . It is more preferable that L* ₁ /L* ₂ is 3 or more.

[Exterior]

Next, the appearance of the Zn-based plated steel sheet of this embodiment will be described. The appearance of the Zn-based plated steel sheet of this embodiment as seen from the chemical conversion layer side is that b* is -30 or more and -2 or less when evaluated in the CIE1976 (L*, a*, b*) color space, and JIS Z 8741: The 60-degree mirror gloss G _s (60°) specified in 1997 is 50 to 200, giving it a metallic appearance. Hereinafter, the reasons for the limitation of b* and 60-degree mirror gloss G _s (60°) will be explained.

The more light is reflected from the surface of the Zn-based plating layer, the higher the luminance, and if it is low, the reflection from the chemical conversion layer increases, so if b* is not a certain level, the metallic appearance of the Zn-based plating layer cannot be recognized. Therefore, it was found that in order to be able to visually recognize the metallic appearance of the Zn-based plating layer and have excellent blackening resistance, the predetermined 60-degree mirror gloss G _s (60°) and b* are sufficient. It is presumed that this is because the b* value changes in the direction of increasing during blackening.

When b* when evaluated in the CIE1976 (L*, a*, b*) color space is less than -30, the blue color of the surface of the Zn-based plated steel sheet becomes darker, and the metallic appearance of the Zn-based plated layer becomes invisible. Additionally, when b* exceeds -2, the blue color becomes lighter, blackened portions on the surface of the Zn-based plating layer become noticeable, and the appearance deteriorates. Therefore, b* should be in the range of -30 to -2. The lower limit of b* is preferably -22, and more preferably -15 from the viewpoint of maintaining the metallic appearance. The upper limit of b* is preferably -3.5, and more preferably -5 from the viewpoint of preventing blackening.

In addition, when the Zn-based plated steel sheet of this embodiment is viewed from the chemical conversion layer side, it is preferable that L* is 85 or less when evaluated in the CIE1976 (L*, a*, b*) color space. When L* is 85 or less, there is an effect that the metal appearance can be recognized more beautifully. From the viewpoint of making blackening less noticeable, L* is more preferably 80 or less, and even more preferably 75 or less.

Additionally, when the 60-degree mirror gloss G _s (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. Additionally, when the 60-degree mirror gloss G _s (60°) exceeds 200, reflection from the surface of the chemical conversion layer becomes stronger, 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 side of the Zn-based plating layer disposed on at least one side of the steel sheet.

Additionally, a pattern portion and a non-pattern portion arranged to have a predetermined shape may be formed on the surface of the Zn-based plating layer according to the present embodiment.

The pattern portion is preferably arranged to have any one of straight lines, curved lines, dots, figures, numbers, symbols, patterns, or letters, or a combination of two or more of these. Additionally, the non-pattern portion is an area other than the pattern portion. Additionally, the shape of the pattern portion is acceptable as long as it can be recognized as a whole even if some parts are missing, such as missing dots. Additionally, the non-pattern portion may have a shape in which a thin line surrounds the boundary of the pattern portion.

When any one of straight lines, curved lines, dots, figures, numbers, symbols, shapes, or letters, or a combination of two or more of them, is disposed on the surface of the Zn-based plating layer, these areas are used as pattern portions. And the other areas can be used as non-pattern parts. The boundary between the pattern portion and the non-pattern portion can be recognized with the naked eye. The boundary between the pattern portion and the non-pattern portion may be grasped from an enlarged image using an optical microscope, a magnifying glass, or the like.

The pattern portion may be formed to a size that allows the presence of the pattern portion to be determined with the naked eye, under a magnifying glass, or under a microscope. Additionally, the non-patterned portion is an area that occupies most 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 pattern portion is arranged in a predetermined shape within the non-pattern portion. Specifically, the pattern portion is arranged to be any one of straight portions, curved portions, figures, dots, figures, numbers, symbols, shapes, or letters, or a combination of two or more of these, within the non-pattern portion. It is done. By adjusting the shape of the pattern portion, any one of straight lines, curved lines, figures, dots, figures, numbers, symbols, patterns, or letters, or a combination of two or more of these, appears on the surface of the Zn-based plating layer. . For example, on the surface of the Zn-based plating layer, a character string consisting of a pattern portion, a string of numbers, a symbol, a mark, a line, a design, or a combination thereof appear. This shape is a shape formed intentionally or artificially by a manufacturing method described later, and is not formed naturally.

In this way, the pattern portion and the non-pattern portion are regions formed on the surface of the Zn-based plating layer, and the pattern portion and the non-pattern portion each include one or both of the first region and the second region.

The pattern portion and the non-pattern portion each include one or two types of a first region and a second region determined by any of the following determination methods 1 to 5, and the area ratio of the first region in the pattern portion is The absolute value of the difference between the area ratios of the first region in the non-pattern portion is 30% or more. When 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 in absolute value, the pattern portion and the non-pattern portion can be distinguished. If the difference in area ratio is less than 30%, 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 small, and the appearance of the pattern portion and the non-pattern portion have a similar appearance. This makes it difficult to identify the pattern portion. The larger the difference in area ratio, the better. It is more preferable that the difference in area ratio is 40% or more, and even more preferably, the difference in area ratio is 60% or more.

That is, in the pattern portion, the area ratio of each of the first area and the second area can be obtained. And, when the area fraction of the first region exceeds 70%, the pattern portion appears relatively white or a color close to 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 like a pear shell pattern. Additionally, when the area fraction of the first region is less than 30%, the pattern portion appears to have a relatively metallic luster. In this way, the appearance of the pattern portion depends on the area fraction of the first region.

On the other hand, even in the non-pattern portion, the area ratio of each of the first area and the second area can be obtained. Like the patterned portion, the appearance of the non-patterned portion depends on the area fraction of the first region.

And, when 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 in absolute value, the pattern portion and the non-pattern portion can be distinguished. If the difference in area ratio is less than 30%, 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 small, and the appearance of the pattern portion and the non-pattern portion have a similar appearance. This makes it difficult to identify the pattern portion. The larger the difference in area ratio, the better. It is more preferably 40% or more, and even more preferably 60% or more.

[Decision 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 a plurality of areas divided by the virtual grid lines, each area is within a circle with a diameter of 0.5 mm centered on the center of gravity of each area. Let be the measurement area A, and the L* value in each measurement area A is measured. When 50 points are randomly selected from the obtained L* values and the average of 50 points of the obtained L* values is set as the standard L* value, the area where the L* value is greater than or equal to the standard L* value is called the first area, the reference L* value. The area below the value is referred to as the second area.

[Decision Method 2]

In decision method 2, virtual grid lines are drawn at 0.5 mm intervals on the surface of the Zn-based plating layer, and in a plurality of areas divided by the virtual grid lines, each area is within a circle with a diameter of 0.5 mm centered on the center of gravity of each area. Let be the measurement area A, and measure the L* value in each measurement area A. The area where the L* value is 45 or more is set as the first area, and the area where the L* value is less than 45 is set as the second area. .

[Decision Method 3]

In determination method 3, virtual grid lines are drawn at intervals of 0.5 mm on the surface of the Zn-based plating layer, and the arithmetic mean height Sa2 is measured in each of the plurality of regions defined by the virtual grid lines. The area where the obtained arithmetic mean height Sa2 is 1 µm or more is referred to as the first area, and the area where the obtained arithmetic mean height Sa2 is less than 1 µm is referred to as the second area. 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 a plurality of regions divided by virtual grid lines at a measurement interval of 50 μm. When measurements are made on a grid, 100 measurement points are obtained within the area. Using the obtained height Z of 100 points as height Z1 to height Z100, the arithmetic mean height Sa2 is calculated by the following equation 3. Zave is the average of height Z of 100 points.

Sa2=1/100×Σ[x=1→100](|Height Zx-Zave|) ... Equation 3

[Decision Method 4]

In determination method 4, virtual grid lines are drawn at 1 mm intervals or 10 mm intervals on the surface of the Zn-based plating layer, and X-rays are incident on a plurality of regions defined by the virtual grid lines, respectively. By the X-ray diffraction method, the above For each region, the diffraction peak intensity I ₀₀₀₂ of the (0002) plane of the Zn phase and the diffraction peak intensity I _10-11 of the (10-11) plane of the Zn phase were measured, and their intensity ratio (I ₀₀₀₂ /I _10-11 ) is taken as the orientation ratio. The area where the orientation ratio is 3.5 or more is set as the first area, and the area where the orientation ratio is less than 3.5 is set as the second area.

[Decision Method 5]

In decision 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 the plurality of regions divided by the virtual grid lines, a circle S is drawn centered on the center of gravity point G of each region. The diameter R of the circle S is set so that the total length of the surface boundary of the Zn-based plating layer contained inside the circle S is 10 mm. The average value of the largest diameter Rmax and the smallest diameter Rmin among the diameters R of circles S in a plurality of areas is set as the standard diameter Rave, and the area having circles S whose diameter R is less than the standard diameter Rave is set as the first area, and the diameter R is set as the first area. An area having a circle S larger than or equal to the reference diameter Rave is referred to as the second area.

The formation of the patterned portion and the non-patterned portion, in which the first region and the second region are specified by determination method 1 or 2, is performed after the formation of the Zn-based plating layer. The patterned portion and the non-patterned portion are formed by depositing an acidic solution on the surface of the Zn-based plating layer at a temperature of 60 to 200°C. More specifically, an acidic solution may be prepared and this may be adhered to the surface of the Zn-based plating layer using a printing means. As the printing means, general printing methods such as printing methods using various plates (gravure printing, flexo printing, offset printing, silk printing, etc.) and inkjet methods can be applied.

At the location where the acidic solution adheres, the very surface of the Zn-based plating layer is dissolved, and the surface of the Zn-based plating layer changes from the plated state. As a result, the appearance of the location where the acidic solution has adhered changes compared to the location where the acidic solution has not adhered. In this way, it is assumed that 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 increases, making it possible to distinguish the pattern portion from the non-pattern portion.

The adhesion range of the acidic solution may be an area corresponding to the patterned part or an area corresponding to the non-patterned part.

As the acidic solution, it is preferable to use an inorganic acid such as hydrochloric acid, nitric acid, or sulfuric acid. Additionally, the acid concentration in the acidic solution is preferably 0.1 to 10 mass%. The temperature of the steel sheet when the acidic solution is attached is 60 to 200°C, preferably 50 to 80°C. By adjusting the type and concentration of the acidic solution, it is possible to adjust the area fraction of the first region and the second region on the surface of the Zn-based plating layer at the location where the acidic solution adheres.

If the surface temperature of the Zn-based plating layer when attaching the acid solution is less than 60°C, it is undesirable because it takes time to form the patterned portion or the non-patterned portion, and if the surface temperature of the Zn-based plating layer exceeds 200°C, the acidic This is undesirable because the solution volatilizes immediately, making it impossible to form a patterned portion or a non-patterned portion.

After the acidic solution adheres, it is necessary to wash with water within 1 to 10 seconds.

Next, the formation of the patterned portion and the non-patterned portion, where the first region and the second region are specified by determination method 3, is performed after the formation of the Zn-based plating layer. The pattern portion and the non-pattern portion are formed by pressing a roll with partially increased surface roughness against the surface of the Zn-based plating layer and transferring the surface shape of the roll to the Zn-based plating layer. For example, in order to form a pattern portion on the surface of the Zn-based plating layer, the roughness of the portion corresponding to the pattern portion on the roll surface is increased relative to other portions to form a pattern portion containing many first regions with high surface roughness. formation is possible. Alternatively, a roll may be used in which the illuminance of the portion corresponding to the pattern portion is reduced relative to other portions. The roughness (arithmetic mean height Sa2 (μm)) of the roll surface is set to be in the range of 0.6 to 3.0 μm at the point where the roughness is increased, and preferably 1.2 to 3.0 μm. The range of illuminance at the location where the illuminance is lowered is 0.05 to 1.0 μm, preferably 0.05 to 0.8 μm. Transfer may be performed when the surface temperature of the Zn-based plating layer is in the range of 100 to 300°C. Additionally, the difference between the illuminance at the location where the illuminance is increased and the illuminance at the location where the illuminance is lowered is set to be greater than 0.2 μm, preferably 0.3 μm or more, in terms of the arithmetic mean height Sa2. As the difference in illuminance decreases, it becomes difficult to distinguish between the patterned portion and the non-patterned portion.

The formation of the patterned portion and the non-patterned portion specified by the determination method 4 is performed by locally spraying a non-oxidizing gas onto the molten metal using a gas nozzle on the steel sheet immediately after being pulled from the hot-dip plating bath. As a non-oxidizing gas, nitrogen or argon may be used. Although the optimal temperature range varies depending on the composition, non-oxidizing gas may be sprayed when the temperature of the molten metal is in the range of (final solidification temperature -5)°C to (final solidification temperature +5)°C. Additionally, the temperature of the non-oxidizing gas is set to be lower than the final solidification temperature.

When the Zn-based plating layer is in the above-mentioned temperature range, the cooling rate of the molten metal increases at the location where the non-oxidizing gas is sprayed, and as a result, the orientation ratio of the Zn-based plating layer after solidification increases. On the other hand, at locations where the non-oxidizing gas is not sprayed, the cooling rate of the molten metal decreases, and as a result, the orientation ratio of the Zn-based plating layer after solidification decreases. Therefore, by adjusting the injection range of the non-oxidizing gas, it is possible to intentionally or arbitrarily adjust the appearance points of the region with a high orientation rate and the region with a low orientation rate.

As a result, the shapes of the pattern portion and the non-pattern portion can be arbitrarily adjusted, and it is also possible to distinguish the pattern portion and the non-pattern portion. The lower the temperature of the injected gas, the higher the orientation rate, so the orientation rate can be adjusted depending on the temperature of the injected 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.

The formation of the patterned portion and the non-patterned portion specified by Determination Method 5 involves locally applying a non-oxidizing gas higher than the final solidification temperature of plating to the molten metal using a gas nozzle on a steel sheet immediately after being pulled from a hot-dip galvanizing bath. This is done by spraying. As a non-oxidizing gas, nitrogen or argon may be used. Although the optimal temperature range varies depending on the composition, non-oxidizing gas may be sprayed when the temperature of the molten metal is in the range of (final solidification temperature -5)°C to (final solidification temperature +5)°C. Additionally, it is desirable that the temperature of the non-oxidizing gas is equal to or higher than the final solidification temperature. For example, in a plating composition of Al: 11% and Mg: 3%, a non-oxidizing gas whose gas temperature is equal to or higher than the final solidification temperature may be sprayed when the temperature of the molten metal is 330 to 340°C.

In the vicinity where the non-oxidizing gas is sprayed, the cooling rate of the molten metal decreases, and as a result, boundaries or grain boundaries appearing on the surface become coarse. Therefore, by adjusting the injection amount and range of the non-oxidizing gas, it is possible to arbitrarily adjust the size of the boundary or grain boundary that appears on the surface.

By setting 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 to 30% or more, the pattern portion and the non-pattern portion can be distinguished. Since the formed pattern portion and non-pattern portion are not formed by printing or painting, durability is high. Additionally, since the pattern portion and the non-pattern portion are not formed by printing or painting, there is no influence on the corrosion resistance of the Zn-based plating layer. Therefore, the Zn-based plated steel sheet of this embodiment has excellent corrosion resistance.

In the Zn-based plating layer in which the pattern portion is formed, it is possible to provide a Zn-based plated steel sheet with high durability of the pattern portion and plating characteristics such as suitable corrosion resistance. Since the pattern portion can be shaped intentionally or artificially, the pattern portion is arranged to have any one of straight lines, curves, dots, figures, numbers, symbols, shapes, or letters, or a combination of two or more of these. can do. As a result, various designs, trademarks, and other identification marks can be displayed on the surface of the Zn-based plating layer without printing or painting, thereby improving the source identification and design of the steel sheet. Additionally, the pattern section can provide information necessary for process management, inventory management, etc., or arbitrary information requested by the consumer, to the hot-dip galvanized steel sheet. This can also contribute to improving the productivity of Zn-based plated steel sheets.

And, according to the Zn-based plated steel sheet of this embodiment, a chemical conversion treatment layer containing a pigment is formed on the Zn-based plating layer on which the pattern portion is formed, so the visibility of the pattern portion can be further improved.

Example

Hereinafter, the present invention will be described in detail through examples.

First, a cold rolled steel sheet with a thickness of 1 mm was prepared, this was immersed in a plating bath of each composition, and the plating adhesion amount was adjusted to 80 g/m2 on one side by N ₂ wiping. Table 1 shows the plating composition of the obtained Zn-based plated steel sheet.

In addition, when forming a pattern portion on the Zn-based plating layer, the pattern was further performed by the following method. The pattern portion and the non-pattern portion each include one or two types of a first region and a second region determined by any of determination methods 1 to 5, and the area ratio of the first region in the pattern portion is: The absolute value of the difference in area ratio of the first region in the non-pattern portion was 40%.

<Pattern 1>

A hydrochloric acid solution was attached to a rubber plate having convex portions or concave portions in a square pattern of 50 mm on each side, and this rubber plate was pressed against the surface of the Zn-based plating layer, thereby causing the acid solution to adhere to the steel plate and forming a square-shaped pattern portion. . The surface temperature of the Zn-based plating layer of the hot-dip galvanized steel sheet when the acidic solution was attached was set to be in the range of 60 to 200°C. Additionally, locations other than the square-shaped pattern portion were designated as non-pattern portions. Then, based on determination method 2, virtual grid lines are drawn at intervals of 0.5 mm on the surface of the Zn-based plating layer, and in a plurality of regions divided by the virtual grid lines, each region has a diameter of 0.5 centered on the center of gravity of each region. The inside of the mm circle is set as measurement area A, the L* value in each measurement area A is measured, the area where the L* value is 45 or more is called the first area, and the area where the L* value is less than 45 is called the first area. It was divided into 2 areas. This Zn-based plated steel sheet was used as Example 70.

<Pattern 2>

With the surface temperature of the Zn-based plating layer set at 100 to 300°C, a roll having a square pattern of 50 mm on each side was pressed against the surface of the Zn-based plating layer to form a pattern portion. The portions of the square pattern were designated as pattern portions, and the portions other than the square pattern were designated as non-pattern portions. Based on determination method 3, virtual grid lines were drawn at intervals of 0.5 mm on the surface of the Zn-based plating layer, and the arithmetic mean height Sa2 was measured in each of the plurality of regions defined by the virtual grid lines. The region where the obtained arithmetic mean height Sa2 was 1 μm or more was designated as the first region, and the region where it was less than 1 μm was designated as the second region. This Zn-based plated steel sheet was used as Example 71.

<Pattern 3>

When a steel sheet is pulled from a plating bath, when the temperature of the molten metal is in the range of (final solidification temperature -5)°C to (final solidification temperature +5)°C, a type of non-oxidizing gas is added to the molten metal on the surface of the steel sheet. Nitrogen gas was sprayed through a gas nozzle. The gas temperature was below the final solidification temperature. Afterwards, it was cooled to completely solidify the molten metal. The spray range of nitrogen gas was controlled to form a square pattern with 50 mm on each side. The portions of the square pattern were designated as pattern portions, and the portions other than the square pattern were designated as non-pattern portions. Based on determination method 4, virtual grid lines are drawn at 1 mm or 10 mm intervals on the surface of the Zn-based plating layer, and X-rays are incident on a plurality of regions defined by the virtual grid lines. , for each of the above regions, the diffraction peak intensity I ₀₀₀₂ of the (0002) plane of the Zn phase and the diffraction peak intensity I _10-11 of the (10-11) plane of the Zn phase were measured, and their intensity ratio (I ₀₀₀₂ /I _{10- 11} ) is taken as the orientation ratio. The region where the orientation ratio was 3.5 or more was designated as the first region, and the region where the orientation ratio was less than 3.5 was designated as the second region. This Zn-based plated steel sheet was used as Example 72.

<Pattern 4>

When a steel sheet is pulled from a plating bath, when the temperature of the molten metal is in the range of (final solidification temperature -5)°C to (final solidification temperature +5)°C, a type of non-oxidizing gas is added to the molten metal on the surface of the steel sheet. Nitrogen gas was injected from a gas nozzle in a heated state. The injection conditions of nitrogen gas are as shown in Table 1. It was above the final solidification temperature. Afterwards, it was cooled to completely solidify the molten metal. The spray range of nitrogen gas was controlled to form a square pattern with 50 mm on each side. The portions of the square pattern were designated as pattern portions, and the portions other than the square pattern were designated as non-pattern portions. Then, based on 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 the plurality of regions demarcated by the virtual grid lines, a circle S centered on the center of gravity point G of each region is drawn. I drew it. The diameter R of the circle S was set so that the total length of the surface boundary of the Zn-based plating layer contained inside the circle S was 10 mm. The average value of the largest diameter Rmax and the smallest diameter Rmin among the diameters R of circles S in a plurality of areas is set as the standard diameter Rave, and the area having circles S whose diameter R is less than the standard diameter Rave is set as the first area, and the diameter R is set as the first area. The area having a circle S larger than the reference diameter Rave was designated as the second area. These Zn-based plated steel sheets were used as Examples 73 and 74.

Next, as necessary, the Zn-based plated steel sheet was immersed in a Co sulfate solution, a Fe sulfate solution, or a Ni sulfate solution to deposit 1 mg/m 2 of Co, Fe, or Ni on the surface of the Zn-based plating layer. The composition of the Zn plating layer is shown in Table 3A and Table 3B.

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, using a 20x standard lens, the height Z within each region was measured at a measurement interval of 50 μm in a plurality of regions divided by virtual grid lines. Measurements were made on a grid, and 100 measurement points were obtained within the area. The obtained height Z of 100 points was set as height Z1 to height Z100, and the arithmetic mean roughness Ra was calculated using the above-mentioned equation 2. Zave was set as the average of height Z of 100 points.

Next, various water-based resins (urethane resin, polyester resin, polyolefin resin, epoxy resin, acrylic resin, phenol 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) The aqueous composition containing was applied with a bar coater at a dry adhesion amount of 1.5 g/m2, dried in a hot air drying furnace at a plate temperature of 150°C, and then cooled with water to form a chromate-free chemical conversion layer. The contents of niobium oxide and sodium phosphate were each 5%. Table 2A shows details of the pigment. Additionally, Table 2B shows details of the silica particles.

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

(arithmetic average height of the chemical treatment layer)

The arithmetic mean height Sa of the chemical conversion layer was obtained by the following method. Gold was deposited on the surface of a sample cut to a predetermined size from a Zn-based plated steel sheet to a thickness of 50 nm, the gold-deposited sample was embedded in resin, and the cross section of the sample in the plate thickness direction was polished to be exposed. The cross section of the sample was observed at a magnification of 5000 times using a scanning electron microscope, and the roughness of the gold deposition layer when observed from the direction perpendicular to the cross section was calculated to determine the arithmetic mean height Sa of the chemical conversion layer. Gold deposition was performed to clarify the boundary between the chemical conversion layer and the resin. Since the thickness of the gold deposition layer is negligible compared to the chemical conversion layer, the arithmetic mean height of the gold deposition layer was replaced by the arithmetic mean height Sa of the surface of the chemical conversion layer.

(60 degree mirror gloss G _s (60°))

The 60° glossiness (%) of the surface of the Zn plating layer was measured using a gloss meter (UGV-6P manufactured by Suga Testimonials) based on the method specified in JIS Z 8741. The case where the gloss was 50 to 200% was designated as “A”, and the case where the gloss was less than 50% was designated as “B”. The results are shown in Table 5A and Table 5B.

(b*value)

Using a spectroscopic colorimeter (SE6000 manufactured by Nippon Denshoku Kogyo Co., Ltd.), the surface of the Zn plating layer was measured, and the case where b* was -15 or more and -5 or less was set as "AAA", and if b* was -22 or more. The case where b* is -3.5 or less (excluding -15 or more and -5 or less) is set as "AA", and the case where b* is -30 or more and -2 or less (excluding -22 and -3.5 or less) is "A". and the case exceeding -2 or less than -30 was set as "B". The results are shown in Table 5A and Table 5B.

(L*value)

L* was measured using a spectroscopic colorimeter (SE6000 manufactured by Nippon Denshoku Kogyo Co., Ltd.). The case where L* is 75 or less is set as “AAA”, the case where L* is between 75 and 80 is set as “AA”, the case where L* is between 80 and 85 is set as “A”, and the case where L* is over 85 was set to “B”. The results are shown in Table 5A and Table 5B.

(metallic luster)

Metallic glossiness was evaluated using a multi-angle spectroscopic colorimeter (MA T12 manufactured by X-rite). In a plane perpendicular to the surface of the converted layer, light is incident toward the surface of the converted layer from an angle of 60° from the surface of the converted layer, and the light reflected from the surface of the converted layer is directed to the surface of the converted layer. Let L* _obtained when light is received at an angle of 135° from When the L* obtained when the light reflected from the surface of is received at an angle of 135° from the surface of the chemical conversion layer, L* ₂ is taken as L*2. L* ₁ /L* ₂ of 3 or more is set to "AA", * ₁ /L* ₂ was set to 2 or more and less than 3 as “A”, and L* ₁ /L* ₂ was set to less than 2 as “B”. The results are shown in Table 5A and Table 5B.

(blackening resistance)

Blackening resistance was evaluated by color difference ΔE*ab from the color change of the surface of the Zn plating layer before and after the test when the Zn-based plated steel sheet was left to stand at a high temperature and high humidity at 70°C and 80% RH for 12 days. The color difference is expressed by the following equation 4, when the chromaticity indices in the L*a*b* color system are a* and b*, and the brightness index is L*.

ΔE*ab=√((Δa*) ² +(Δb*) ² +(ΔL*) ² ) ... Equation 4

However, in the above equation, Δa* is the difference between a* of the Zn-based plating layer before the test and a* of the Zn-based plating layer after the test, and Δb* is the difference between b* of the Zn-based plating layer before the test and b* of the Zn-based plating layer after the test. is the difference, and ΔL* is the difference between L* of the Zn-based plating layer before the test and L* of the Zn-based plating layer after the test. The evaluation was determined by giving the ratings shown below, and a rating of 4 or 3 was considered passing. The results are shown in Tables 6A and 6B.

4: ΔE*ab≤5

3: 5<ΔE*ab≤10

2: 10<ΔE*ab≤15

1: ΔE*>15

(corrosion resistance)

A salt spray test (JIS Z 2371:2015) was performed on the Zn-based plated steel sheet. The occurrence of white rust in the area subjected to Eriksen processing was observed after 120 hours of test time, and judgment was made by giving the rating shown below. A score of 3 or higher was considered passing. The results are shown in Tables 6A and 6B.

4: White rust generation less than 5%

3: Occurrence of white rust: 5% or more but less than 10%

2: Occurrence of white rust 10% or more but less than 30%

1: White rust generation: 30% or more

(metal exterior)

The surface of the Zn plating layer of the Zn-based plated steel sheet was judged based on the appearance of the metal plating when shown to five panelists. The evaluation was determined by giving the ratings shown below, and a rating of 4 or 3 was considered passing. The results are shown in Tables 6A and 6B.

4: More than 4 out of 5 people were able to recognize the metallic appearance of the plating.

3: 3 out of 5 people were able to recognize the metallic appearance of the plating.

2: Two out of five people were able to recognize the metallic appearance of the plating.

1: Less than 1 out of 5 people could recognize the metallic appearance of the plating.

(weather resistance)

After testing the surface of the Zn plating layer of the Zn-based plated steel sheet for 500 hours with a Sunshine Weather Meter tester, the chemical conversion layer was evaluated based on the film thickness ratio between the initial and post-test stages by giving the ratings shown below, with a rating of 4 or 3 being passed. It was done as follows. The results are shown in Tables 6A and 6B.

4: Residual rate of chemical conversion layer is 90% or more

3: Residual rate of chemical conversion layer is less than 50 to 90%

2: Residual rate of chemical conversion layer is less than 30 to 50%

1: Residual rate of chemical conversion layer is less than 30%

[Table 1]

[Table 2A]

[Table 2B]

[Table 3A]

[Table 3B]

[Table 4A]

[Table 4B]

[Table 5A]

[Table 5B]

[Table 6A]

[Table 6B]

As shown in Tables 1 to 6B, the Zn-based plated steel sheets of Examples 1 to 74 all have a chemical conversion treatment layer that satisfies the scope of the present invention, and have good blackening resistance, corrosion resistance, metallic appearance, and weather resistance. did.

In addition, the Zn-based plated steel sheets of Examples 14 to 16 that used phenol resin, polyolefin resin, fluororesin, or acrylic resin as the resin contained in the chemical treatment layer were particularly excellent in weather resistance.

Additionally, for Examples 70 to 74 in which a pattern portion was formed on the plating layer, blackening resistance, corrosion resistance, metallic appearance, and weather resistance were good, and visibility of the pattern portion was significantly improved.

On the other hand, as shown in Tables 1 to 6B, in Comparative Example 1, since the chemical conversion layer did not contain resin, the chemical conversion layer itself became very fragile and various evaluation tests could not be performed.

Since Comparative Example 2 did not contain silica particles, corrosion resistance was reduced.

In Comparative Example 3, the content of silica particles was as high as 30%, so the chemical conversion layer itself became very fragile and various evaluation tests could not be performed.

In Comparative Example 4, the chemical conversion treatment layer did not contain pigment, so the blackening resistance was reduced.

In Comparative Example 5, because the drying conditions at the time of forming the chemical conversion layer were outside the preferred range, b* of the chemical conversion layer was outside the range of -30 to -2, and the metallic appearance was insufficient.

In Comparative Example 6, because the drying conditions at the time of forming the chemical conversion layer were outside the desirable range, the 60-degree mirror gloss G _s (60°) on the surface of the chemical conversion layer was outside the range of 50 to 200, resulting in poor metallic appearance. This was insufficient.

In Comparative Example 7, since the diameter of the silica particles was 450 nm, the metallic appearance was insufficient.

Comparative Examples 8 to 11 did not contain pigments containing Cu, Co, or Fe, and the blackening resistance was insufficient.

According to the present invention, in a Zn-based plated steel sheet containing Al, Al contained in the plating layer is oxidized, so that even when the plating surface is partially or entirely blackened, the blackening can be made inconspicuous and the metallic appearance can be maintained, In addition, since it is possible to provide a Zn-based plated steel sheet with improved corrosion resistance and weather resistance, the present invention has high industrial applicability.

Claims (11)

steel plate,
a Zn-based plating layer disposed on at least one side of the steel sheet and containing 0.05 to 60% by mass of Al and Zn;
A chromate-free chemical conversion layer disposed on the Zn-based plating layer with an adhesion amount of 0.1 to 15 g/m2 per side is provided,
The chemical conversion layer contains 20% by mass or more of resin, 1 to 20% by mass of silica particles with an average particle diameter of 5 to 200 nm, and a pigment containing one or two or more types of Cu, Co, or Fe, ,
When the appearance is evaluated in the CIE1976 (L*, a*, b*) color space, b* is -30 or more and -2 or less, and the 60-degree mirror gloss G _s (60°) specified in JIS Z 8741:1997 is 50 to 200, and exhibits a metallic appearance. Zn-based plated steel sheet. According to paragraph 1,
A Zn-based plated steel sheet wherein the pigment is one or two or more of copper (II) phthalocyanine, cobalt (II) phthalocyanine, copper sulfate, cobalt sulfate, iron sulfate, or iron oxide. According to claim 1 or 2,
The mixing ratio of the silica particles and the pigment in the chemical conversion layer is the Si equivalent amount [Si] of the silica particles, and the Cu equivalent amount [Cu], Co equivalent amount [Co], or Fe equivalent amount of the pigment. A Zn-based plated steel sheet where, when expressed as [Fe], [Si]/([Cu]+[Co]+[Fe]) is in the range of 1 to 200. According to claim 1 or 2,
A Zn-based plated steel sheet in which 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 layer is 5 nm to 100 nm. According to claim 1 or 2,
A Zn-based plated steel sheet wherein the chemical conversion treatment layer further contains one or both of an Nb compound and a phosphoric acid compound, and the Nb compound and the phosphoric acid compound are contained in a total ratio of 0.5 to 30% by mass. According to claim 1 or 2,
A Zn-based plated steel sheet wherein the resin in the chemical conversion layer contains at least one of polyolefin resin, fluorine resin, acrylic resin, urethane resin, polyester resin, epoxy resin, and phenol resin. According to claim 1 or 2,
A Zn-based plated steel sheet in which the Zn-based plating layer contains, as an average composition, Al: 4% by mass to 22% by mass, Mg: 1% by mass to 10% by mass, and the balance consists of Zn and impurities. According to claim 1 or 2,
A Zn-based plated steel sheet in which the Zn-based plating layer further contains Si: 0.0001 to 2% by mass in average composition. According to claim 1 or 2,
A Zn-based plated steel sheet, characterized in that the Zn-based plating layer further contains 0.0001 to 2% by mass of one or more of Ni, Sb, and Pb in total as an average composition. According to claim 1 or 2,
A pattern portion and a non-pattern portion arranged to have a predetermined shape are formed in the Zn-based plating layer,
The pattern portion and the non-pattern portion each include one or two types of a first region and a second region determined by any of the following determination methods 1 to 5,
A Zn-based plated steel sheet, wherein 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.
[Decision method 1]
Virtual grid lines are drawn at intervals of 0.5 mm on the surface of the Zn-based plating layer, and in a plurality of areas divided by the virtual grid lines, a measurement area is within a circle with a diameter of 0.5 mm centered on the center of gravity of each area. Let A be used, and measure the L* value in each measurement area A. When 50 points are randomly selected from the obtained L* values and the average of 50 points of the obtained L* values is set as the standard L* value, the area where the L* value is greater than or equal to the standard L* value is called the first area, the reference L* The area below the value is referred to as the second area.
[Decision Method 2]
Virtual grid lines are drawn at 0.5 mm intervals on the surface of the Zn-based plating layer, and in a plurality of areas divided by the virtual grid lines, a measurement area is within a circle with a diameter of 0.5 mm centered on the center of gravity of each area. Let A be, the L* value in each measurement area A is measured, the area where the L* value is 45 or more is set as the first area, and the area where the L* value is less than 45 is set as the second area.
[Decision Method 3]
Virtual grid lines are drawn at 0.5 mm intervals on the surface of the Zn-based plating layer, and the arithmetic mean height Sa2 is measured in each of the plurality of regions defined by the virtual grid lines. The area where the obtained arithmetic mean height Sa2 is 1 µm or more is referred to as the first area, and the area where the obtained arithmetic mean height Sa2 is less than 1 µm is referred to as the second area.
[Decision Method 4]
By drawing virtual grid lines on the surface of the Zn-based plating layer at intervals of 1 mm or 10 mm, and applying The diffraction peak intensity I ₀₀₀₂ of the (0002) plane of the Zn phase and the diffraction peak intensity I _10-11 of the (10-11) plane of the Zn phase were measured, and their intensity ratio (I ₀₀₀₂ /I _10-11 ) was calculated as the orientation ratio. Do this. The area where the orientation ratio is 3.5 or more is referred to as the first area, and the area where the orientation ratio is less than 3.5 is referred to as the second area.
[Decision 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 the plurality of regions divided by the virtual grid lines, a circle S is drawn centered on the center of gravity point G of each region. The diameter R of the circle S is set so that the total length of the surface boundaries of the Zn-based plating layer contained within the circle S is 10 mm. The average value of the largest diameter Rmax and the smallest diameter Rmin among the diameters R of circles S in a plurality of areas is set as the standard diameter Rave, and the area having circles S whose diameter R is less than the standard diameter Rave is set as the first area, and the diameter R is set as the first area. An area having a circle S larger than or equal to the reference diameter Rave is referred to as the second area. According to claim 1 or 2,
A Zn-based plated steel sheet having any one or two or more of Co, Fe, and Ni on the surface of the Zn-based plating layer.