JP2013060640A - Chemical conversion-treated plated steel sheet and method for production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chemical conversion-treated plated steel sheet which includes a hot-dip Zn-Al-Mg alloy-plated steel sheet as a base material, has a chemical conversion-treated film including organic resins, and is excellent in all of weatherability, water resistance, coating film adhesion, anti-glare property and processability.SOLUTION: The chemical conversion-treated film is formed by coating a phosphate treatment liquid on the surface of the hot-dip Zn-Al-Mg alloy-plated steel sheet to form a phosphate film, and coating a chemical conversion treatment liquid on the phosphate film. The chemical conversion treatment liquid contains: a fluorine-containing resin including 0.05-5 mass% of a hydrophilic functional group selected from the group consisting of carboxyl group, sulfonic acid group and their salts and 7-20 mass% of F atom and having a number-average molecular weight within the range from 1,000 to 2,000,000; any of oxyacid salts, fluorides, hydroxides, organic acid salts, carbonates or peroxide salts of group 4A metals; and resin particles having the average grain size of 0.1-10 μm.

Description

  The present invention relates to a chemically treated plated steel sheet excellent in weather resistance, water resistance, blackening resistance, film adhesion, antiglare property and workability and a method for producing the same.

  The molten Zn—Al—Mg alloy plated steel sheet has excellent corrosion resistance and is used in various applications such as exterior building materials. Since the hot-dip Zn—Al—Mg alloy-plated steel sheet contains easily oxidizable Al and Mg, there is a possibility that the gloss will decrease or the blackening phenomenon may occur over time. In addition, although the hot-dip Zn-Al-Mg alloy-plated steel sheet has excellent corrosion resistance, white rust may occur when used in a highly corrosive environment such as a sea salt particle scattering atmosphere or a high-temperature and high-humidity atmosphere. There is sex.

  In order to suppress the occurrence of such blackening phenomenon and white rust, a chemical conversion treatment film containing an organic resin may be formed on the surface of the plated steel sheet (see, for example, Patent Documents 1 and 2). Patent Documents 1 and 2 describe that a chemical conversion treatment film containing an organic resin such as a urethane resin is formed on the surface of a zinc-based plated steel sheet. Thus, by covering the surface of a plated steel plate with a chemical conversion treatment film containing an organic resin, not only blacking resistance and corrosion resistance but also galling resistance can be improved.

  Moreover, in order to improve the corrosion resistance, coating film adhesion, etc. of the plated steel sheet, a phosphate film may be formed on the surface of the plated steel sheet (see, for example, Patent Documents 3 to 6). Patent Documents 3 to 6 describe forming a phosphate film containing phosphate crystals on the surface of a zinc-based plated steel sheet. Thus, corrosion resistance, coating-film adhesiveness, etc. can be improved by coat | covering the surface of a plated steel plate with a phosphate membrane | film | coat.

  On the other hand, in order to improve the weather resistance of the chemical conversion treatment plated steel sheet, a fluororesin having excellent weather resistance may be used as an organic resin constituting the chemical conversion treatment film. Thus, when using a fluororesin for the purpose of an improvement in a weather resistance, an organic solvent type fluororesin composition is used in many cases. However, such organic solvent-based fluororesin compositions have problems such as fire hazard and harmfulness and air pollution.

  Various water-based fluororesin compositions have also been proposed (see, for example, Patent Document 7). However, all such water-based fluororesin compositions require baking at a high temperature (for example, 180 to 230 ° C., see Patent Document 7). Such high-temperature baking is practically impossible in field painting (usually using a normally dry resin), and is disadvantageous even in factory lines where heat drying is the mainstream.

  Furthermore, in order to solve the problems of the water-based fluororesin composition, a water-based fluororesin composition capable of forming a film even at a low temperature by introducing a curable site (organic functional group) has been proposed (for example, Patent Document 8). reference). However, in a film cured by reacting with an organic functional group, the weather resistance deteriorates preferentially from the cured portion, so that the film becomes porous and water resistance decreases. In addition, when the base treatment with an epoxy resin or a urethane resin is performed for improving the adhesion, the organic resin is preferentially deteriorated in weather resistance, and the film adhesion is rapidly lowered. .

JP 2005-15834 A JP 2005-206764 A Japanese Patent Laid-Open No. 2005-126811 JP 2005-126812 A JP 2005-290551 A JP 2005-290552 A JP-A-57-38845 JP-A-5-202260

  As described above, by forming a chemical conversion film containing an organic resin on the surface of the plated steel sheet, corrosion resistance, blackening resistance, and the like can be improved. However, the conventional chemical conversion treatment plated steel sheet formed with the chemical conversion treatment film containing the organic resin sometimes has insufficient weather resistance when used as an exterior building material. In other words, since many organic resins such as urethane resins are deteriorated by ultraviolet rays, when a conventional chemical conversion-treated plated steel sheet is used as an exterior building material, the chemical conversion film covering the surface of the plated steel sheet is lost over time. There is a risk that. If the chemical conversion treatment film is lost in this manner, discoloration, rust, etc. may occur and the appearance may be impaired, which is not preferable as an exterior building material.

  As a means for improving the weather resistance of the chemical conversion coating containing an organic resin, it is conceivable to use a fluororesin having excellent weather resistance as the organic resin constituting the chemical conversion coating. Then, this inventor performed the preliminary experiment which forms a chemical conversion treatment film on the surface of a plated steel plate using the emulsion of the water-based fluororesin which is easy to handle. As a result, it was possible to improve the ultraviolet resistance by using an emulsion of a water-based fluororesin, but on the other hand, the film forming property, water resistance and film adhesion were lowered. As a result of further studies by the present inventors, these deteriorations in quality are because an emulsifier (for example, perfluorooctanoic acid ammonium salt) used in producing an aqueous fluororesin emulsion remains in the chemical conversion film. (See the reference experiment below).

  As mentioned above, the conventional chemical conversion treatment plating steel plate in which the chemical conversion treatment film containing an organic resin was formed might have insufficient weather resistance. In addition, the use of water-based fluororesin as the organic resin can improve the weather resistance (ultraviolet light resistance) of the chemically treated steel sheet, but on the other hand, the film forming property, water resistance and film adhesion are reduced. Therefore, it was impossible to achieve both weather resistance, water resistance, blackening resistance and film adhesion.

  On the other hand, the hot-dip Zn—Al—Mg alloy-plated steel sheet has a high metallic luster particularly in the initial stage of use, and therefore, when used as an exterior building material, the glare sometimes becomes a problem.

  The present invention has been made in view of such a point, and is a chemical conversion-treated plated steel sheet having a chemical conversion film containing an organic resin as a base, and having a weather resistance, a molten Zn-Al-Mg alloy-plated steel sheet as a base material. It aims at providing the chemical conversion treatment plated steel plate which is excellent in all of water resistance, blackening resistance, film adhesion, anti-glare property, and workability.

  The present inventor has developed a high molecular weight fluorine-containing resin in which a phosphate film is formed on the surface of a hot-dip Zn—Al—Mg alloy-plated steel sheet and a hydrophilic functional group is introduced on the phosphate film. Improves weatherability, water resistance, blackening resistance, film adhesion, and antiglare properties of chemical conversion steel sheets based on hot-dip Zn-Al-Mg alloy-plated steel sheets by forming a chemical conversion film cross-linked with a compound As a result, the present invention was completed.

That is, the 1st of this invention is related with the following chemical conversion treatment plated steel plates.
[1] and the hot-dip Zn-Al-Mg alloy plated steel sheet having a plating layer containing a ternary eutectic structure of Al / _Zn / Zn 2 Mg, formed on the surface of the hot-dip Zn-Al-Mg alloy plated steel sheet, A chemical conversion-treated plated steel sheet, comprising: a phosphate film containing phosphate crystal particles; and a chemical conversion film having a thickness of 0.5 to 10 μm formed on the phosphate film; In the formation surface of the acid salt film, the phosphate crystal particles cover 50% by area or more of the surface of the molten Zn—Al—Mg alloy-plated steel sheet; A fluorine-containing resin containing 0.05 to 5% by mass of a hydrophilic functional group selected from the group consisting of an acid group and a salt thereof and 7 to 20% by mass of an F atom; 0.1-5 mass% 4A group A chemical conversion-treated plated steel sheet, comprising a metal compound and resin particles having an average particle diameter of 0.1 to 10 μm; and an area occupancy ratio of the resin particles on the surface of the chemical conversion coating is 0.1 area% or more.
[2] The chemical conversion plated steel sheet according to [1], wherein the fluorine-containing resin has a carboxyl group / sulfonic acid group ratio in the range of 5 to 60 in terms of a molar ratio of carboxyl group / sulfonic acid group.
[3] The chemical conversion plated steel sheet according to [1] or [2], wherein the resin particles are polyethylene-fluororesin particles in which fluororesin fine particles are bonded to the surface of polyethylene resin particles.
[4] The chemical conversion coating further contains a polyethylene resin; the polyethylene-fluororesin particles protrude from the surface of the chemical conversion coating in a part of the surface of the chemical conversion coating; The chemical conversion treatment plated steel sheet according to [3], which covers all or a part of the remaining part of the surface of the chemical conversion treatment film.
[5] The chemical conversion film further contains a phosphate; the amount of the phosphate with respect to the fluorine-containing resin is in the range of 0.05 to 3% by mass in terms of P, [1] to The chemical conversion treatment plated steel plate as described in any one of [4].
[6] The chemical conversion treatment film further contains a silane coupling agent; the amount of the silane coupling agent with respect to the fluorine-containing resin is in the range of 0.5 to 5% by mass. 5] The chemical conversion plated steel sheet according to any one of [5].
[7] The chemical conversion plated steel sheet according to any one of [1] to [6], wherein the 4A group metal is selected from the group consisting of Ti, Zr, Hf, and combinations thereof.

2nd of this invention is related with the manufacturing method of the following chemical conversion treatment plated steel plates.
[8] A method of preparing a hot-dip Zn-Al-Mg alloy plated steel sheet having a plating layer containing a ternary eutectic structure of Al / _Zn / Zn 2 Mg, the surface of the hot-dip Zn-Al-Mg alloy plated steel sheet A phosphate treatment solution containing 0.03 to 0.5 mol / L phosphate in terms of phosphate ion is applied and dried to form a phosphate film containing phosphate crystal particles And a step of applying a chemical conversion treatment liquid on the phosphate film and drying to form a chemical conversion treatment film having a film thickness of 0.5 to 10 μm; In the range of 0.05 to 5% by mass of a hydrophilic functional group selected from the group consisting of sulfonic acid groups and salts thereof and 7 to 20% by mass of F atoms, the number average molecular weight is in the range of 1,000 to 2,000,000. Certain fluorine-containing resins and Group 4A metal oxygen acids , Fluoride, hydroxide, organic acid salt, carbonate or peroxide salt, and resin particles having an average particle size of 0.1 to 10 μm; The amount of oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide salt is in the range of 0.1 to 5% by mass in terms of metal; based on the solid content in the chemical conversion treatment liquid The amount of the resin particles is in the range of 0.5 to 20% by mass, the method for producing a chemical conversion-treated plated steel sheet.
[9] The chemical conversion treatment plated steel sheet according to [8], wherein the fluorine-containing resin has a carboxyl group / sulfonic acid group molar ratio within a range of 5 to 60 in terms of a carboxyl group / sulfonic acid group molar ratio. Production method.
[10] The method for producing a chemically treated plated steel sheet according to [8] or [9], wherein the resin particles are polyethylene-fluororesin particles in which fluororesin fine particles are bonded to the surface of polyethylene resin particles.
[11] The method for producing a chemical conversion plated steel sheet according to [10], wherein the chemical conversion treatment liquid further contains polyethylene resin particles.
[12] The chemical conversion treatment liquid further contains a phosphate; the amount of the phosphate with respect to the fluorine-containing resin is in the range of 0.05 to 3% by mass in terms of P, [8] to The manufacturing method of the chemical conversion treatment plated steel plate as described in any one of [11].
[13] The chemical conversion treatment liquid further contains a silane coupling agent; the amount of the silane coupling agent with respect to the fluorine-containing resin is in the range of 0.5 to 5% by mass. 12] The manufacturing method of the chemical conversion treatment plated steel plate as described in any one of [12].
[14] The method for producing a chemically treated steel sheet according to any one of [8] to [13], wherein the 4A group metal is selected from the group consisting of Ti, Zr, Hf, and combinations thereof.
[15] The phosphating solution further contains a metal ion selected from the group consisting of Ni, Co, Fe, and Mn at a concentration of 0.01 to 0.5 mol / L. [8] to [14 ] The manufacturing method of the chemical conversion treatment plated steel plate as described in any one of.
[16] The phosphating solution contains a polyamine organic inhibitor having at least one functional group of —NH ₂ or ═NH and having a number average molecular weight of 200 to 30,000 at a concentration of 0.01 to 5 mass%. Furthermore, the manufacturing method of the chemical conversion treatment plated steel plate as described in any one of [8]-[15].
[17] The chemical conversion plating according to [16], wherein the polyamine organic inhibitor is one or more aliphatic amines selected from the group consisting of polyethylamine, polyethyleneimine, polyetheramine, and polyaminoacrylate. A method of manufacturing a steel sheet.

  ADVANTAGE OF THE INVENTION According to this invention, the chemical conversion treatment plated steel plate which is excellent in all of a weather resistance, water resistance, blackening resistance, film | membrane adhesiveness, anti-glare property, and workability can be provided. The chemical conversion-treated plated steel sheet of the present invention is useful as, for example, a plated steel sheet for exterior building materials because it is excellent in weather resistance, corrosion resistance, blackening resistance, antiglare property and workability.

1A to 1D are SEM images of a chemical conversion film containing polyethylene resin particles or polyethylene-fluorine resin particles heated at a predetermined temperature. 2A to 2C are schematic cross-sectional views showing the formation process of the chemical conversion coating. 3A to 3C are SEM images showing the formation process of the chemical conversion film. It is a fluorescence X-ray spectrum of the polyethylene- fluorine resin particle in a chemical conversion treatment film. It is a graph which shows the relationship between the quantity of the 4A group metal in a fluororesin membrane | film | coat, and moisture permeability. It is a graph which shows the relationship between the density | concentration of the emulsifier in the emulsion of fluorine-containing resin, and the water vapor transmission rate of a fluorine resin film.

1. Chemical conversion plated steel sheet The chemical conversion plated steel sheet of the present invention includes a molten Zn-Al-Mg alloy plated steel sheet (chemical conversion treated original sheet), a phosphate coating formed on the surface of the molten Zn-Al-Mg alloy plated steel sheet, And a chemical conversion film formed on the phosphate film. The chemical conversion treatment plated steel sheet of the present invention contains a high molecular weight fluorine-containing resin, a group 4A metal compound and resin particles (lubricant) in which the chemical conversion treatment film has introduced a hydrophilic functional group (such as a carboxyl group or a sulfonic acid group). Is a feature.

  Hereinafter, each component of the chemical conversion treatment plated steel plate of this invention is demonstrated.

[Chemical conversion treatment master]
As the chemical conversion raw plate, a hot-dip Zn—Al—Mg alloy-plated steel plate having excellent corrosion resistance and design properties is used.

The molten Zn—Al—Mg alloy-plated steel sheet has a plating layer containing a ternary eutectic structure of Al / Zn / Zn ₂ Mg. Each phase (Al phase, Zn phase, and Zn ₂ Mg phase) forming the ternary eutectic structure of Al / Zn / Zn ₂ Mg has an irregular size and shape, and is intricate with each other. Yes. From the viewpoint of ensuring the reactivity of the phosphate treatment, the higher the area ratio of the ternary eutectic structure on the plating layer surface, the better. Specifically, the area ratio of the ternary eutectic structure on the plating layer surface is preferably 60 area% or more, and more preferably 80 area% or more. For example, it is possible to increase the area ratio of the ternary eutectic structure by lowering the concentration of Al in the plating bath, and to reduce the area ratio of the ternary eutectic structure by making Al 4 mass% or less. It can be almost 100%.

  As the base steel of the hot-dip Zn—Al—Mg alloy-plated steel sheet, low carbon steel, medium carbon steel, high carbon steel, alloy steel, or the like is used. When workability is required, steel sheets for deep drawing such as low carbon Ti-added steel and low carbon Nb-added steel are preferred as the base steel.

[Phosphate film]
The phosphate film is formed on the surface of the above-described molten Zn—Al—Mg alloy-plated steel sheet (chemical conversion treatment original sheet). The phosphate film contains phosphate crystal particles as a main component, and may contain metal elements such as Ni, Co, Fe, and Mn, aliphatic amines, and the like (described later) as other components. The phosphate coating does not necessarily completely cover the surface of the molten Zn-Al-Mg alloy-plated steel sheet, and the surface of the molten Zn-Al-Mg alloy-plated steel sheet is between the phosphate crystal particles. It may be exposed. As is known in the art, the phosphate coating not only improves the corrosion resistance and the adhesion of the chemical conversion coating formed thereon, but also prevents glare by scattering the light from the phosphate crystal particles. Improves performance.

The adhesion amount of the phosphate film is preferably in the range of 0.3 to 2.8 g / m ² . When the adhesion amount of the phosphate film is less than 0.3 g / m ² , the corrosion resistance, film adhesion, antiglare property and the like may not be sufficiently improved. When the adhesion amount of the phosphate film is more than 2.8 g / m ² , the phosphate film may cohesively break when the chemical conversion treatment plated steel sheet of the present invention is formed. The adhesion amount of the phosphate film can be measured by using a fluorescent X-ray analyzer.

  The phosphate crystal particles contained as the main component preferably cover 50 to 98 area% of the surface of the plating layer on the surface on which the phosphate film is formed. When the coverage of the plating layer surface is less than 50 area%, there is a possibility that the corrosion resistance, film adhesion, antiglare property and the like cannot be sufficiently improved. When the coverage of the plating layer surface is more than 98 area%, phosphate crystals may cohesively break depending on the processed shape, and film peeling may occur. The coverage of the plating layer surface with phosphate crystal particles can be measured by image analysis of a scanning electron microscope (SEM) photograph of the plating layer surface imaged.

  The kind of phosphate constituting the phosphate crystal is not particularly limited as long as it is a compound having a phosphate anion and can form a slightly water-soluble crystal. Examples of phosphate crystals include magnesium phosphate, manganese phosphate, zinc phosphate, iron phosphate, zinc iron phosphate, zinc calcium phosphate, and the like.

  The average particle diameter of the crystal grains of the phosphate is preferably in the range of 0.5 to 5.0 μm. If the average particle size is less than 0.5 μm, the corrosion resistance, film adhesion, antiglare property and the like may not be sufficiently improved. On the other hand, when the average particle size exceeds 5.0 μm, the phosphate coating may cohesively break when the chemical conversion plated steel sheet of the present invention is formed. Further, from the viewpoint of improving the adhesion of the phosphate film (phosphate crystal), it is preferable that the base of the crystal grains of the phosphate bite into the plating layer. It is preferable that the average depth of the crystal grains of the phosphate biting into the plating layer is 0.05 μm or more. For the penetration depth of phosphate crystal particles, remove phosphate crystal particles using diammonium chromate aqueous solution, and then observe the traces of phosphate crystal particles using a scanning laser microscope. Can be measured.

[Chemical conversion coating]
The chemical conversion treatment film is formed on the above-described phosphate film. The chemical conversion treatment film may be formed not only on the phosphate crystal particles but also in the voids between the phosphate crystal particles. In the space between the crystal grains of the phosphate, the chemical conversion film may be in direct contact with the surface of the plating layer. The chemical conversion treatment film improves the weather resistance, blackening resistance, workability (lubricity), and the like of the molten Zn—Al—Mg alloy-plated steel sheet.

  An object of the present invention is to improve all of the weather resistance, water resistance, blackening resistance, film adhesion, antiglare property and workability of a chemically treated plated steel sheet. All of weather resistance, water resistance, film adhesion and lubricity are improved. As described above, in order to improve the weather resistance (ultraviolet light resistance) of the chemical conversion coating, a fluorine-containing resin may be used as the organic resin. Fluorine-containing resins are roughly classified into solvent-based fluorine-containing resins and water-based fluorine-containing resins. When a chemical conversion film is formed using a solvent-based fluorine-containing resin, recovery of the volatilized solvent becomes a problem, but when a water-based fluorine-containing resin is used, such a problem does not occur. Therefore, the present inventor tried to form a chemical conversion treatment film excellent in all of weather resistance, water resistance, blackening resistance, film adhesion, and lubricity by using an aqueous fluorine-containing resin that is easy to handle. .

  As described above, according to the preliminary experiment of the present inventor, when a chemical conversion film is formed using an emulsion of a water-based fluorine-containing resin, the water resistance decreases when an emulsion of a water-based fluorine-containing resin is produced. It was considered that the emulsifier used remained in the chemical conversion film (see the reference experiment described later). Then, this inventor thought that the fall of the water resistance of a chemical conversion treatment film could be suppressed if the emulsion of water-type fluorine-containing resin could be manufactured, using few emulsifiers. And as a result of studying various water-based fluorine-containing resins, the present inventor is able to produce water-based emulsions with little use of emulsifiers. It has been found that a chemical conversion treatment film containing almost no can be easily formed.

  Moreover, this inventor examined not only suppressing the fall of the water resistance of a chemical conversion treatment film but improving water resistance. As a result of studying from various viewpoints, it was found that the water resistance of the chemical conversion coating can be remarkably improved by increasing the molecular weight of the aqueous fluorine-containing resin and crosslinking the aqueous fluorine resin with a group 4A metal compound. It was.

  And this inventor is adding a 4A group metal compound to the chemical conversion treatment liquid based on the high molecular weight fluorine-containing resin which introduce | transduced the hydrophilic functional group, and is weather resistance, water resistance, and blackening resistance. It was also found that a chemical conversion treatment film compatible with film adhesion can be formed.

  Furthermore, this inventor examined improving the workability (lubricity) of a chemical conversion treatment plated steel plate. And as a result of studying various means, the present inventor disperses resin particles having an average particle diameter of 0.1 to 10 μm in the chemical conversion treatment film, thereby improving weather resistance, water resistance, blackening resistance, and film adhesion. In addition to the properties, it has been found that a chemical conversion film excellent in workability (lubricity) can be formed.

  The inventor combined the chemical conversion treatment film with the above-described phosphate film, and thus the chemical conversion treatment of the present invention, which is excellent in all of weather resistance, water resistance, blackening resistance, film adhesion, antiglare property and workability. A plated steel sheet was completed.

  In the chemical conversion coating of the chemical conversion plated steel sheet of the present invention, 1) the weather resistance (ultraviolet resistance) is improved by blending a fluorine-containing resin (preferably a fluorine-containing olefin resin). In addition, 2) the use of a fluorine-containing resin into which a hydrophilic functional group has been introduced reduces the use of an emulsifier during emulsion production, 3) the molecular weight of the fluorine-containing resin is increased, and 4) the fluorine-containing resin is 4A. By cross-linking with a group metal compound, weather resistance (ultraviolet light resistance) and water resistance are improved. 5) Workability (lubricity) is improved by dispersing resin particles having an average particle diameter of 0.1 to 10 μm.

  Hereinafter, each component contained in the chemical conversion treatment film will be described.

1) Water-based fluorine-containing resin The chemical conversion film contains a fluorine-containing resin, more specifically, a fluorine-containing olefin resin as a main component. The amount of the fluorine-containing resin contained as a main component in the chemical conversion film is preferably in the range of 70 to 99% by mass. As described above, by using a fluorine-containing resin as the organic resin constituting the chemical conversion coating, the weather resistance (ultraviolet resistance) of the chemical conversion coating can be improved.

  The fluorine-containing resin is preferably a water-based fluorine-containing resin that is easier to handle than the organic solvent-based fluorine resin. “Aqueous fluorine-containing resin” refers to a fluorine-containing resin having a hydrophilic functional group. Preferred examples of the hydrophilic functional group include a carboxyl group, a sulfonic acid group, and salts thereof. Examples of the salt of the carboxyl group or sulfonic acid group include ammonium salt, amine salt, alkali metal salt and the like.

  Preferred aqueous fluorine-containing resins (preferably fluorine-containing olefin resins) have a hydrophilic functional group of 0.05 to 5% by mass. A fluorine-containing resin having 0.05 to 5% by mass of a hydrophilic functional group can be made into an aqueous emulsion without using an emulsifier. The chemical conversion film containing almost no emulsifier can be a chemical conversion film excellent in water resistance.

  The content of the hydrophilic functional group in the aqueous fluorine-containing resin may be obtained by dividing the total molar mass of the hydrophilic functional group contained in the aqueous fluorine-containing resin by the number average molecular weight of the aqueous fluorine-containing resin. Since the molar mass of the carboxyl group is 45 and the molar mass of the sulfonic acid group is 81, the number of each of the carboxyl group and sulfonic acid group contained in the aqueous fluorine-containing resin is determined, and each is multiplied by the molar mass. The total molar mass of the hydrophilic functional group contained in the aqueous fluorine-containing resin is obtained. The number average molecular weight of the water-based fluorine-containing resin is measured by GPC.

The carboxyl group in the water-based fluorine-containing resin forms a hydrogen bond with the plating layer surface and contributes to improving the adhesion between the chemical conversion film and the plating layer surface. However, since H ⁺ is difficult to dissociate, The cross-linking reaction is unlikely to occur. On the other hand, the sulfonic acid group in the water-based fluorine-containing resin tends to dissociate H ^+, but if it remains unreacted in the film without cross-linking reaction with the group 4A metal compound, the water molecule adsorbing action is strong, so There is a risk that the water resistance will be significantly reduced. Therefore, it is preferable that the water-based fluorine-containing resin includes both a carboxyl group and a sulfonic acid group in order to make use of each feature. In this case, the ratio of the carboxyl group to the sulfonic acid group is preferably in the range of 5 to 60 in terms of the molar ratio of carboxyl group / sulfonic acid group.

  The number average molecular weight of the water-based fluorine-containing resin (preferably fluorine-containing olefin resin) contained in the chemical conversion coating is preferably 1000 or more, more preferably 10,000 or more, and particularly preferably 200,000 or more.

  If the molecular weight of the water-based fluorine-containing resin contained in the chemical conversion coating is too small, the water permeability and water resistance of the chemical conversion coating cannot be sufficiently improved. In such a case, moisture or corrosive gas easily penetrates the chemical conversion coating and reaches the plated steel sheet, so that the chemical conversion steel sheet may easily corrode. In addition, when an aqueous fluorine-containing resin with a low molecular weight is used, radicals generated by the action of light energy or the like are likely to act on the end of the polymer chain, so the aqueous fluorine-containing resin is easily hydrolyzed by a synergistic action such as water. There is a risk of being. In order to prevent these problems, the molecular weight of the aqueous fluorine-containing resin contained in the chemical conversion coating may be increased to some extent, or a crosslinked structure may be formed between the aqueous fluorine-containing resins. By increasing the molecular weight of the water-based fluorine-containing resin, the intermolecular force increases and the cohesive strength of the chemical conversion coating increases, so that the water resistance is improved. Moreover, since the bond between atoms in the main chain of the water-based fluorine-containing resin is stabilized, hydrolysis is less likely to occur.

  On the other hand, the number average molecular weight of the water-based fluorine-containing resin contained in the chemical conversion coating is preferably 2 million or less. When the number average molecular weight exceeds 2 million, there is a possibility that a problem may occur in the stability of the treatment liquid such as gelation.

  The content of F atoms in the aqueous fluorine-containing resin contained in the chemical conversion film is preferably in the range of 7 to 20% by mass. When content of F atom is less than 7 mass%, the weather resistance of a chemical conversion treatment film cannot fully be improved. On the other hand, when the content of F atoms is more than 20% by mass, it is difficult to form a paint and the adhesion and drying properties may be reduced. The content of F atoms in the aqueous fluorine-containing resin can be measured by using a fluorescent X-ray analyzer.

  Examples of the aqueous fluorine-containing resin include a copolymer of a fluoroolefin and a hydrophilic functional group-containing monomer. The hydrophilic functional group-containing monomer is a carboxyl group-containing monomer or a sulfonic acid group-containing monomer.

  Examples of fluoroolefins include tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, vinyl fluoride, vinylidene fluoride, pentafluoropropylene, 2,2,3,3-tetrafluoropropylene, 3, 3,3-trifluoropropylene, bromotrifluoroethylene, 1-chloro-1,2-difluoroethylene, 1,1-dichloro-2,2-difluoroethylene and the like are included. These fluoroolefins may be used alone or in combination of two or more. From the viewpoint of weather resistance (ultraviolet light resistance), among these fluoroolefins, perfluoroolefins such as tetrafluoroethylene and hexafluoropropylene, and vinylidene fluoride are preferable. Fluoroolefins containing chlorine such as chlorotrifluoroethylene are not preferred because corrosion due to chlorine ions may occur.

Examples of the carboxyl group-containing monomer include unsaturated carboxylic acids represented by the following formula (1) and unsaturated carboxylic acids such as esters or acid anhydrides thereof.
(In formula, R < ¹ >, R < ² > and R < ³ > are the same or different, and all are a hydrogen atom, an alkyl group, a carboxyl group, or an ester group. N is in the range of 0-20.)

  Examples of the unsaturated carboxylic acid represented by the above formula (1) include acrylic acid, methacrylic acid, vinyl acetic acid, crotonic acid, cinnamic acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester, fumaric acid , Fumaric acid monoester, 5-hexenoic acid, 5-heptenoic acid, 6-heptenoic acid, 7-octenoic acid, 8-nonenoic acid, 9-decenoic acid, 10-undecylene acid, 11-dodecylene acid, 17-octadecylenic acid Oleic acid and the like.

Another example of the carboxyl group-containing monomer is a carboxyl group-containing vinyl ether monomer represented by the following formula (2).
(Wherein R ⁴ and R ⁵ are the same or different, and each is a saturated or unsaturated linear or cyclic alkyl group. N is 0 or 1. m is 0 or 1.)

  Examples of the carboxyl group-containing vinyl ether monomer represented by the above formula (2) include 3- (2-allyloxyethoxycarbonyl) propionic acid, 3- (2-allyloxybutoxycarbonyl) propionic acid, 3- (2-vinylidene). Roxyethoxycarbonyl) propionic acid, 3- (2-vinyloxybutoxycarbonyl) propionic acid and the like.

  Examples of sulfonic acid group-containing monomers include vinyl sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 2-methacryloyloxyethane sulfonic acid, and 3-methacryloyloxy. Propanesulfonic acid, 4-methacryloyloxybutanesulfonic acid, 3-methacryloyloxy-2-hydroxypropanesulfonic acid, 3-acryloyloxypropanesulfonic acid, allyloxybenzenesulfonic acid, methallyloxybenzenesulfonic acid, isoprenesulfonic acid, Examples include 3-allyloxy-2-hydroxypropanesulfonic acid.

  The copolymer of the fluoroolefin and the hydrophilic functional group-containing monomer may be further copolymerized with another copolymerizable monomer as necessary. Examples of other copolymerizable monomers include carboxylic acid vinyl esters, alkyl vinyl ethers, and non-fluorinated olefins.

  Carboxylic acid vinyl esters can improve compatibility and gloss and increase the glass transition temperature. Examples of vinyl carboxylates include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caproate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl cyclohexylcarboxylate, benzoate Vinyl acid, vinyl para-t-butyl benzoate and the like are included.

  Alkyl vinyl ethers can improve gloss and flexibility. Examples of the alkyl vinyl ethers include methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether and the like.

  Non-fluorinated olefins can improve flexibility. Examples of non-fluorinated olefins include ethylene, propylene, n-butene, isobutene and the like.

  A fluoroolefin copolymer having a hydrophilic functional group can be obtained by copolymerizing the above monomers by a known polymerization method. At this time, by adjusting the amount of the fluoroolefin in the raw material monomer composition so that the fluoroolefin copolymer has 0.05 to 5% by mass of the hydrophilic functional group, the fluoroolefin copolymer can be used with almost no emulsifier. An aqueous emulsion of the polymer can be produced. The chemical conversion film formed using an emulsion of a fluoroolefin copolymer containing almost no emulsifier (1% by mass or less) contains almost no emulsifier.

  Thus, the chemical conversion treatment film which hardly contains an emulsifier can be easily formed by using the fluorine-containing resin having a hydrophilic functional group as the aqueous fluorine-containing resin constituting the chemical conversion treatment film. The chemical conversion film thus formed exhibits excellent water resistance with little deterioration in water resistance due to the residual emulsifier.

2) Group 4A metal compound The chemical conversion film contains a group 4A metal compound. The 4A group metal compound easily reacts with a functional group such as a carboxyl group or a sulfonic acid group in the aqueous fluorine-containing resin, and accelerates the curing or crosslinking reaction of the aqueous fluorine-containing resin. Therefore, the water resistance of the chemical conversion film can be improved even by low-temperature drying.

  When a melamine resin or an isocyanate resin is used for cross-linking of the fluorine-containing resin, there is a problem that the weather resistance is easily deteriorated. For example, in a chemical conversion treatment film cured using a melamine resin, weather resistance deterioration is immediately caused by oxidation and hydrolysis of ester bonds and form ether bonds. In addition, weathering deterioration also proceeds when the crosslinked structure is cut by an acidic substance such as sulfate ion or nitrate ion contained in acid rain. In a chemical conversion film cured using an isocyanate resin, the urethane bond formed at the cross-linked portion is weaker than the F bond, so that the cross-linked structure is preferentially cut, and the weather resistance deteriorates.

  On the other hand, by using a group 4A metal compound for crosslinking of the fluorine-containing resin, such a problem can be avoided and weather resistance can be improved.

  The group 4A metal compound also improves film adhesion, water resistance and blackening resistance. That is, in the region where the surface of the plating layer and the chemical conversion film are in direct contact, the strong Al oxide present on the surface of the plating layer reduces the adhesion of the chemical conversion film, but the chemical conversion film has a 4A group. By including a metal compound, it is possible to suppress a decrease in film adhesion due to the Al oxide. The group 4A metal compound also serves as a supply source of group 4A metal ions that react with Al ions eluted by the etching reaction. The reaction product is concentrated at the interface between the plating layer and the chemical conversion film to improve the initial corrosion resistance and blackening resistance. Examples of Group 4A metals include Ti, Zr, Hf, and the like.

  The content of the group 4A metal compound in the chemical conversion coating is preferably in the range of 0.1 to 5 mass% in terms of metal relative to the fluorine-containing resin. When the content is less than 0.1% by mass in terms of metal, the adverse effect due to the concentration of Al oxide cannot be sufficiently suppressed, and the aqueous fluorine-containing resin fat cannot be sufficiently crosslinked. As a result, the water resistance of the chemical conversion coating cannot be sufficiently improved. On the other hand, when the content is more than 5% by mass in terms of metal, the chemical conversion film becomes porous, and the workability and weather resistance may be reduced.

  The metal conversion amount of the group 4A metal compound in the chemical conversion coating can be measured by using a fluorescent X-ray analyzer.

As described above, Al eluted from the plating layer is present in the chemical conversion film. This Al contributes to improvement of corrosion resistance. It is presumed that the corrosion resistance is improved by the presence of Al due to the following mechanism. That is, 1) Since the chemical conversion treatment solution is weakly alkaline, when the chemical conversion treatment solution is applied, Al oxide and metal Al contained in the plating layer are selectively eluted into the chemical conversion treatment solution (Zn is almost eluted). do not do). 2) In the pH range of the chemical conversion treatment solution, Al dissolves in the chemical conversion treatment solution in the state of Al (OH) ₄ ⁻ . 3) When forming the chemical conversion film by drying the chemical conversion liquid, Al in the chemical conversion liquid is taken into the chemical conversion film by dehydration condensation or the like. 4) As a result, the insulating properties and density of the chemical conversion coating are improved, and the corrosion resistance is improved.

3) Resin particle The chemical conversion film contains resin particles. The resin particles are dispersed in the chemical conversion treatment film, and at least a part thereof is exposed (protruded) on the surface of the chemical conversion treatment film (see FIG. 3C). The resin particles protruding on the surface of the chemical conversion treatment film function like a “roller” during the molding process, thereby improving the lubricity of the chemical conversion treatment film surface. As a result, the workability of the chemical conversion-treated plated steel sheet can be improved.

  The average particle diameter of the resin particles is preferably within the range of 0.1 to 10 μm. When the average particle diameter of the resin particles is less than 0.1 μm, most of the resin particles are buried in the chemical conversion coating, so that the lubricity of the chemical conversion coating surface cannot be improved efficiently. On the other hand, when the average particle diameter of the resin particles exceeds 10 μm, the resin particles may be easily dropped during the molding process. If the resin particles fall off in this way, defects will occur in the chemical conversion film, and the corrosion resistance will be reduced. In the present specification, the average particle diameter of the resin particles means a particle diameter (median diameter) at an integrated value of 50% in a particle diameter distribution measured by a laser diffraction scattering method.

  The content of the resin particles in the chemical conversion coating is adjusted so that the area occupancy of the resin particles on the surface of the chemical conversion coating is 0.1 area% or more. If the area occupancy of the resin particles is less than 0.1 area%, the lubricity of the chemical conversion coating cannot be sufficiently improved. The area occupancy ratio of the resin particles on the surface of the chemical conversion coating can be determined by observing the surface of the chemical conversion coating with a scanning electron microscope (SEM).

  The type of resin particles is not particularly limited, but polyethylene-fluorine resin particles are preferable from the viewpoint of heat resistance and dispersibility.

  Polyethylene resin particles are excellent in dispersibility in the chemical conversion treatment liquid because of low specific gravity (for example, 0.95), but poor in heat resistance because of low melting point (for example, 123 ° C.). When resin particles having low heat resistance are used as described above, the shape of the particles may not be maintained when the chemical conversion solution is heated and dried to form a chemical conversion coating. Specifically, when the chemical conversion treatment liquid is heated and dried at about 140 to 180 ° C., the polyethylene resin particles are melted. When the resin particles are thus melted, the resin particles cannot function as “rollers” and cannot contribute to improvement of lubricity.

  On the other hand, the fluororesin particles have a high melting point (for example, 330 ° C.) and excellent heat resistance, but have a large specific gravity (for example, 2.2) and are inferior in dispersibility in the chemical conversion treatment liquid. Thus, when resin particles with low dispersibility in the chemical conversion treatment liquid are used, it becomes difficult to uniformly disperse the resin particles in the chemical conversion treatment film.

  The polyethylene-fluorine resin particles are obtained by bonding (adsorbing) fluororesin fine particles to the surface of the polyethylene resin particles by bringing the fluororesin fine particles into contact with the polyethylene resin particles softened by heating. By bonding fluororesin fine particles to the surface of the polyethylene resin particles, heat resistance to such an extent that the shape of the particles can be maintained even when heated at about 140 to 180 ° C. and dispersibility in the chemical conversion treatment liquid (specific gravity: For example, 1.1) can be made compatible. Moreover, a weather resistance can also be improved by couple | bonding a fluororesin fine particle with the surface of a polyethylene resin particle.

  FIG. 1 is an SEM image (plan view) of a chemical conversion film containing polyethylene resin particles or polyethylene-fluorine resin particles heated to 50 ° C. or 150 ° C. FIG. 1A is an SEM image of a chemical conversion coating formed by applying a chemical conversion treatment liquid containing polyethylene resin particles to the surface of a plated steel sheet and drying at 50 ° C. FIG. FIG. 1B is an SEM image of a chemical conversion film formed by applying a chemical conversion treatment liquid containing polyethylene resin particles to the surface of a plated steel sheet and drying at 150 ° C. FIG. 1C is an SEM image of a chemical conversion coating formed by applying a chemical conversion treatment liquid containing polyethylene-fluororesin particles to the surface of a plated steel sheet and drying at 50 ° C. FIG. 1D is an SEM image of a chemical conversion coating formed by applying a chemical conversion treatment liquid containing polyethylene-fluororesin particles to the surface of a plated steel sheet and drying at 150 ° C.

  As shown in FIG. 1A, when the chemical conversion treatment liquid containing polyethylene resin particles was dried at 50 ° C., the shape of the polyethylene resin particles was maintained, and the polyethylene resin particles protruded from the surface of the chemical conversion treatment film (in the figure). (See “PE”). On the other hand, as shown in FIG. 1B, when the chemical conversion treatment liquid containing polyethylene resin particles is dried at 150 ° C., the polyethylene resin particles are melted, and the polyethylene resin is uniformly distributed on the surface of the chemical conversion treatment film. (See “PE” in the figure).

  As shown in FIG. 1C, when the chemical conversion treatment liquid containing polyethylene-fluororesin particles is dried at 50 ° C., the shape of the polyethylene-fluororesin particles is maintained, and the polyethylene-fluororesin particles are removed from the surface of the chemical conversion coating. It protruded (see “PE-F” in the figure). In addition, as shown in FIG. 1D, when the chemical conversion treatment liquid containing polyethylene-fluororesin particles is dried at 150 ° C., some polyethylene-fluororesin particles (those with a small amount of fluororesin fine particles attached) are melted. However, the remaining polyethylene-fluororesin (those with a large amount of fluororesin fine particles attached) did not melt (see “PE-F” in the figure).

  Thus, when the drying temperature is low, there is no problem even with polyethylene resin particles, but when the drying temperature is high, it is preferable to use polyethylene-fluororesin particles. From the viewpoint of weather resistance, it is preferable to use polyethylene-fluororesin particles.

  The average particle diameter of the polyethylene resin particles constituting the polyethylene-fluororesin particles is not particularly limited as long as the average particle diameter of the polyethylene-fluororesin particles is within a range of 0.1 to 10 μm. Examples of commercially available polyethylene resin particles that can be used include HYTEC E-9016, HYTEC E-1000 (all are Toho Chemical Co., Ltd.), CJ-172B, CJ-137 (all are Koyo Chemical Co., Ltd.), and Permarin KUE-4. Permarin KUE-5 (both are Sanyo Chemical Industries, Ltd.). On the other hand, the average particle diameter of the fluororesin fine particles constituting the polyethylene-fluororesin particles may be appropriately set according to the average particle diameter of the polyethylene resin particles. For example, the average particle diameter of the fluororesin fine particles is preferably 0.3 μm or less.

  The ratio of the fluororesin in the polyethylene-fluororesin particles is preferably in the range of 5 to 40% by mass. When the ratio of a fluororesin is less than 5 mass%, there exists a possibility that the effect by making a fluororesin adhere cannot fully be exhibited. On the other hand, when the ratio of the fluororesin is more than 40% by mass, the polyethylene-fluororesin particles may be easily removed from the chemical conversion film. The ratio of the fluororesin in the polyethylene-fluororesin particles can be measured by using a fluorescent X-ray analyzer.

4) Polyethylene resin When the chemical conversion film contains polyethylene-fluororesin particles, the chemical conversion film preferably further contains a polyethylene resin. Usually, the polyethylene resin coats all or part of the region of the surface of the chemical conversion coating where the polyethylene-fluororesin particles do not protrude (see FIG. 2C). The polyethylene resin that coats the surface of the chemical conversion coating is a polyethylene resin that bleeds on the surface of the chemical conversion coating in the manufacturing process. A polyethylene resin particle improves the workability of a chemical conversion treatment plated steel plate further by improving the lubricity of the chemical conversion treatment film surface with a polyethylene-fluorine resin particle.

  The content of the polyethylene resin in the chemical conversion coating is preferably in the range of 0.1 to 16% by mass with respect to the chemical conversion coating. When the content of the polyethylene resin is less than 0.1% by mass, the effect of the polyethylene resin cannot be exhibited sufficiently. On the other hand, when the content of the polyethylene resin is more than 16% by mass, the weather resistance may be lowered.

5) Phosphate The chemical conversion treatment film preferably further contains a phosphate. Phosphate reacts with the plating layer surface in the region where the plating layer surface and the chemical conversion treatment film are in direct contact, and improves the adhesion of the chemical conversion treatment coating to the molten Zn-Al-Mg alloy plated steel sheet. .

  The type of phosphate is not particularly limited as long as it is a compound having a phosphate anion and is water-soluble. Examples of phosphates include sodium phosphate, ammonium phosphate, magnesium phosphate, potassium phosphate, manganese phosphate, zinc phosphate, orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid (diphosphoric acid), triphosphoric acid, Tetraphosphate etc. are included. These phosphates may be used alone or in combination of two or more.

  The content of the phosphate in the chemical conversion coating is preferably in the range of 0.05 to 3% by mass in terms of P with respect to the fluorine-containing resin. When the P conversion amount is less than 0.05% by mass, the reaction with the plating layer surface is insufficient, and the adhesion of the chemical conversion film cannot be sufficiently improved. On the other hand, when P conversion amount exceeds 3 mass%, reaction with 4A group metal compound will advance excessively, and the crosslinking effect by 4A group metal compound will be impaired.

  The P equivalent amount of phosphate in the chemical conversion coating can be measured by using a fluorescent X-ray analyzer.

6) Silane coupling agent It is preferable that a chemical conversion treatment film contains a silane coupling agent further. By mix | blending a silane coupling agent, the adhesiveness of a chemical conversion treatment film can be improved more. Silane coupling agents include silanes containing one or more functional groups such as amino, epoxy, mercapto, acryloxy, methacryloxy, alkoxy, vinyl, styryl, isocyanate, and chloropropyl groups. A compound is used.

  The content of the silane coupling agent in the chemical conversion film is preferably in the range of 0.5 to 5 mass% with respect to the fluorine-containing resin. When content of a silane coupling agent is less than 0.5 mass%, the adhesiveness of a chemical conversion treatment film cannot fully be improved. On the other hand, when the content of the silane coupling agent exceeds 5% by mass, the film adhesion is saturated and no further improvement is observed.

  The content of the silane coupling agent in the chemical conversion coating can be measured by using a fluorescent X-ray analyzer.

  The film thickness of the chemical conversion coating is preferably in the range of 0.5 to 10 μm. When the film thickness is less than 0.5 μm, sufficient corrosion resistance and discoloration resistance cannot be imparted. On the other hand, even if the film thickness exceeds 10 μm, it cannot be expected to improve the performance with the increase in film thickness.

2. The manufacturing method of a chemical conversion treatment plated steel plate Although the manufacturing method of the chemical conversion treatment plated steel plate of this invention is not specifically limited, For example, it can manufacture with the following method.

  The manufacturing method of the chemical conversion treatment plated steel plate of the present invention is 1) a first step of preparing a molten Zn—Al—Mg alloy plated steel plate (chemical conversion treatment original plate), and 2) a second step of preparing a phosphate treatment solution. 3) a third step of forming a phosphate film on the surface of the molten Zn—Al—Mg alloy-plated steel sheet, 4) a fourth step of preparing a chemical conversion treatment liquid, and 5) a phosphate film. And a fifth step of forming a chemical conversion film on the substrate.

[Preparation of raw material for chemical conversion treatment]
In a 1st step, the above-mentioned hot-dip Zn-Al-Mg alloy plating steel plate is prepared as a chemical conversion treatment original plate.

As described above, the hot-dip Zn—Al—Mg alloy-plated steel sheet to be the chemical conversion treatment original plate preferably has a plating layer containing a ternary eutectic structure of Al / Zn / Zn ₂ Mg. A hot-dip Zn—Al—Mg alloy-plated steel sheet having a plating layer containing a ternary eutectic structure, for example, Al is 2.5 to 22% by mass, Mg is 0.05 to 20.0% by mass, and the balance is substantially the same. It can be manufactured by a hot dipping method using a Zn alloy plating bath. At this time, in order to improve adhesion between the base steel and the plating layer, Si that can suppress the growth of the Al—Fe alloy layer at the interface between the base steel and the plating layer is in the range of 0.005 to 2.0 mass%. It is preferable to add to the plating bath. Further, Ti, B, Ti—B alloy, Ti-containing compound or B-containing compound may be added to the plating bath in order to suppress the formation and growth of the Zn ₁₁ Mg ₂ phase which adversely affects the appearance and corrosion resistance. The amount of these compounds added is preferably set so that B is in the range of 0.001 to 0.045% by mass such that Ti is in the range of 0.001 to 0.1% by mass. . If an excessive amount of Ti or B is added, it may cause a precipitate to grow on the plating layer.

[Preparation of phosphating solution]
In the second step, a phosphating solution is prepared.

  The phosphating solution can be prepared by dissolving the above-mentioned phosphate in an aqueous solvent or dissolving phosphoric acid and a metal salt in an aqueous solvent. The concentration of phosphate ions in the phosphating solution is preferably in the range of 0.03 to 0.5 mol / L. When the phosphate ion concentration is less than 0.03 mol / L, a sufficient number of phosphate crystals cannot be precipitated in a short time in the third step. On the other hand, when the phosphate ion concentration is more than 0.5 mol / L, the stability of the phosphating solution is lowered, and sludge is likely to be generated.

A metal ion selected from the group consisting of Ni, Co, Fe and Mn may be further added to the phosphating solution. By adding these metal ions, it is possible to generate crystal grains of the phosphate biting into the plating layer in the third step. That is, these metal ions are selectively substituted and deposited in the Zn ₂ Mg phase having the lowest surface potential in the ternary eutectic structure of the molten Zn—Al—Mg alloy-plated steel sheet. A compound of Ni, Co, Fe, or Mn, which is a noble metal, precipitates in the Zn ₂ Mg phase, so that the nearby Zn phase is selectively dissolved. The dissolution of the Zn phase proceeds in the depth direction, and phosphate precipitates in the formed depression. As a result, it is possible to generate phosphate crystal grains that have penetrated into the plating layer.

  The concentration of metal ions in the phosphating solution is preferably in the range of 0.01 to 0.5 mol / L. When the concentration of metal ions is less than 0.01 mol / L, there is a possibility that the crystal grains of the phosphate cannot sufficiently penetrate into the plating layer. On the other hand, when the concentration of metal ions exceeds 0.5 mol / L, the amount of substitutional precipitation of these metals becomes excessive, and the corrosion resistance of the molten Zn—Al—Mg alloy-plated steel sheet may be reduced.

A polyamine organic inhibitor having at least one functional group of —NH ₂ or ═NH may be further added to the phosphating solution. The polyamine organic inhibitor is adsorbed on the surface of the plating layer by the action of —NH ₂ or ═NH, and a non-polar group such as a hydrocarbon group oriented on the external side (treatment liquid side) forms a monomolecular film by intermolecular force. Forming and inhibiting the contact between the etching component (such as the aforementioned metal ions) and the plating layer surface. As a result, phosphate crystal particles can be deposited at an appropriate interval, and the phosphate crystal particles can be refined.

  Examples of the polyamine organic inhibitor include aliphatic polyamines such as polyethylamine, polyethyleneimine, polyetheramine, and polyaminoacrylate, and aromatic polyamines such as polyaniline. Considering the stability in the phosphating solution, an aliphatic polyamine is more preferable than an aromatic polyamine as the polyamine organic inhibitor.

  The number average molecular weight of the polyamine organic inhibitor is preferably in the range of 200 to 30,000. When the number average molecular weight is less than 200, the adsorptive power of the polyamine-based organic inhibitor to the plating layer surface is insufficient, and there is a possibility that the crystal grains of phosphate and the formation of voids between the crystal grains are insufficient. If the crystal grains of phosphate and the formation of voids between crystal grains are insufficient, the phosphate coating may cohesively break when the chemical conversion coating steel sheet of the present invention is formed. . On the other hand, when the number average molecular weight exceeds 30,000, precipitation of phosphate crystals is excessively suppressed, and the coverage of phosphate crystal particles may be less than 50%.

  The concentration of the polyamine organic inhibitor in the phosphating solution is preferably in the range of 0.01 to 5% by mass. When the concentration of the polyamine-based organic inhibitor is less than 0.01% by mass, the crystal grains of phosphate are not sufficiently refined and the voids between the crystal grains are insufficient, and the phosphate coating is coherently broken during processing. There is a fear. On the other hand, when the concentration of the polyamine organic inhibitor is more than 5% by mass, precipitation of phosphate crystals is excessively suppressed, and the coverage of phosphate crystal particles may be less than 50%.

  Nitric acid ions may be further added to the phosphating solution. Nitrate ions promote phosphate precipitation in the third step. The concentration of nitrate ions in the phosphating solution is preferably in the range of 0.01 to 1.0 mol / L. When the concentration of nitrate ions is less than 0.01 mol / L, the effect of adding nitrate ions is hardly observed. On the other hand, when the concentration of nitrate ions exceeds 1.0 mol / L, the surface of the plating layer is inactivated by the oxidizing action of nitric acid, and the precipitation of phosphate may be hindered.

  A fluoride may be further added to the phosphating solution. In the third step, Al eluted from the plating layer may hinder the precipitation of phosphate, but the adverse effect of the eluted Al can be suppressed by adding fluoride to the phosphate treatment solution. Examples of fluoride include sodium fluoride, potassium fluoride, sodium hydrogen fluoride and the like. The concentration of fluoride in the phosphating solution is preferably in the range of 0.001 to 0.5 mol / L. When the fluoride concentration is less than 0.001 mol / L, the effect of adding fluoride is hardly observed. On the other hand, when the fluoride concentration exceeds 0.5 mol / L, the etching of the plating layer becomes strong, and the phosphate crystals may be difficult to precipitate.

[Formation of phosphate film]
In the third step, a phosphate film is formed on the surface of the molten Zn—Al—Mg alloy-plated steel sheet prepared in the first step. To form a phosphate film, the phosphate treatment solution prepared in the second step is applied to the surface of the molten Zn-Al-Mg alloy-plated steel sheet prepared in the first step, and the phosphate is precipitated. Then, it may be washed and dried.

  The method for applying the phosphating solution is not particularly limited, and may be appropriately selected from known methods. Examples of such a coating method include a roll coating method, a curtain flow method, a spin coating method, a spray method, and a dip pulling method.

  The temperature of the phosphating solution when applying the phosphating solution is preferably within the range of 40 to 80 ° C. By using a phosphating solution heated to 40 to 80 ° C, phosphate crystal nuclei are easily formed on the surface of the plating layer. As a result, many fine phosphate crystals are precipitated in a short time. Can be made. On the other hand, when the temperature of the phosphating solution is less than 40 ° C., phosphate crystals cannot be sufficiently precipitated in a short time. Further, when the temperature of the phosphating solution is higher than 80 ° C., the stability of the phosphating solution decreases, and sludge generation and water evaporation increase, making it difficult to manage the concentration in continuous operation.

  For example, when a phosphate treatment liquid heated to 40 to 80 ° C. is applied by a spray method, phosphate crystals are deposited in about 2 to 6 seconds to form a phosphate film. Moreover, when the phosphate processing liquid heated at 40-80 degreeC was apply | coated by the immersion pulling-up method, a phosphate crystal | crystallization will precipitate and a phosphate membrane | film | coat will be formed in about 3-9 seconds. Even if the treatment time is longer than the above time, there is no particular problem because the precipitation of phosphate is saturated.

[Preparation of chemical conversion solution]
In the fourth step, a chemical conversion treatment liquid containing a fluorine-containing resin having a hydrophilic functional group as described above (preferably a fluorine-containing olefin resin), a group 4A metal compound, and resin particles is prepared.

  In the chemical conversion treatment liquid, a group 4A metal compound and resin particles (for example, polyethylene-fluorine resin particles) are added to an aqueous emulsion of the fluorine-containing resin (preferably fluorine-containing olefin resin) having the hydrophilic functional group described above. Can be prepared. As the group 4A metal compound to be added to the chemical conversion treatment liquid, a group 4A metal oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate, peroxide salt, or the like is used. Examples of oxyacid salts include hydrates, ammonium salts, alkali metal salts, alkaline earth metal salts, and the like. You may add a polyethylene resin particle, a phosphate, a silane coupling agent, etc. to a chemical conversion liquid as needed.

  The number average molecular weight of the fluorine-containing resin contained in the aqueous emulsion is preferably 1000 or more, more preferably 10,000 or more, and particularly preferably 200,000 or more. As described above, this is to impart water resistance to the chemical conversion coating. On the other hand, from the viewpoint of the stability of the treatment liquid, the number average molecular weight of the fluorine-containing resin is preferably 2 million or less.

  The fluorine-containing resin preferably has a hydrophilic functional group of 0.05 to 5% by mass from the viewpoint of preparing an aqueous emulsion without using an emulsifier.

  The content of the emulsifier in the aqueous emulsion of the fluorine-containing resin is preferably 1% by mass or less. When the emulsifier exceeds 1% by mass, the emulsifier may remain in the chemical conversion film depending on the drying temperature when the chemical conversion film is formed in the third step. If the emulsifier remains in the chemical conversion coating as described above, the water resistance of the chemical conversion coating is remarkably lowered, which is not preferable. As described above, an aqueous emulsion can be prepared even if the amount of the emulsifier is 1% by mass or less as long as it is a fluorine-containing resin having a hydrophilic functional group.

  The emulsifier that may be contained in the aqueous emulsion of the fluorine-containing resin is preferably a fluorine-based emulsifier such as an ammonium salt of perfluorooctanoic acid or an ammonium salt of perfluorononanoic acid from the viewpoint of weather resistance and water resistance. In addition, a known fluorosurfactant can also be used as an emulsifier.

  The content of the fluorine-containing resin in the chemical conversion treatment liquid is preferably in the range of 10 to 70 parts by mass with respect to 100 parts by mass of water. When the content of the fluorine-containing resin is less than 10 parts by mass, the amount of water evaporation increases in the drying process, and the film formability and denseness of the chemical conversion film may be reduced. On the other hand, when content of fluorine-containing resin is more than 70 mass parts, there exists a possibility that the storage stability of a chemical conversion liquid may fall.

  The content of group 4A metal oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide in the chemical conversion solution is 0. A range of 1 to 5 parts by mass is preferable. When the content of these salts is less than 0.1 part by mass, the crosslinking reaction and the reaction with the plating layer surface are insufficient, and the water resistance and film adhesion of the chemical conversion film cannot be sufficiently improved. On the other hand, when the content of these salts exceeds 5 parts by mass, the cross-linking reaction proceeds and the storage stability of the chemical conversion solution may be reduced.

  The content of the resin particles (for example, polyethylene-fluorine resin particles) in the chemical conversion liquid is in the range of 0.5 to 20 parts by mass with respect to 100 parts by mass of the solid content (fluorine-containing resin, 4A group metal compound, etc.). The inside is preferable. As described above, when the resin particle content is less than 0.5% by mass, the lubricity of the chemical conversion coating cannot be sufficiently improved. On the other hand, when the content of the resin particles is more than 20% by mass, the weather resistance of the chemical conversion film may be deteriorated.

  When polyethylene resin particles are further added to the chemical conversion treatment liquid in addition to the polyethylene-fluorine resin particles, the content of the polyethylene resin particles in the chemical conversion treatment liquid is 0.1 to 16 masses per 100 parts by mass of the solid content. Within the range of parts is preferred. As described above, when the content of the polyethylene resin particles is less than 0.1% by mass, the effect of the polyethylene resin cannot be exhibited sufficiently. On the other hand, when the addition amount exceeds 16% by mass, the weather resistance of the chemical conversion coating may be lowered. Moreover, the average particle diameter of the polyethylene resin particles is preferably within a range of 0.1 to 10 μm. When the average particle diameter is less than 0.1 μm, most of the polyethylene resin particles are buried in the chemical conversion film, and the polyethylene resin cannot be bleed on the surface of the chemical conversion film. On the other hand, when the average particle size is more than 10 μm, the polyethylene resin particles may fall off while the chemical conversion solution is being dried.

  When adding a phosphate to a chemical conversion liquid, the phosphate content in the chemical conversion liquid is preferably in the range of 0.05 to 3 parts by mass in terms of P with respect to 100 parts by mass of the fluorine-containing resin. . When the phosphate content is less than 0.05 parts by mass, the adhesion of the chemical conversion film cannot be sufficiently improved. On the other hand, when the content of the phosphate is more than 3 parts by mass, the reaction with the 4A group metal compound may proceed excessively and the crosslinking effect by the 4A group metal compound may be impaired.

  When adding a silane coupling agent to a chemical conversion liquid, content of the silane coupling agent in a chemical conversion liquid has the preferable range of 0.5-5 mass parts with respect to 100 mass parts of fluorine-containing resin. When content of a silane coupling agent is less than 0.5 mass part, the adhesiveness of a chemical conversion treatment film cannot fully be improved. On the other hand, when the content of the silane coupling agent exceeds 5 parts by mass, the film adhesion is saturated and no further improvement is observed. In addition, the stability of the chemical conversion liquid may be reduced.

  Etching agents, inorganic compounds, inorganic lubricants, color pigments, dyes, and the like may be added to the chemical conversion liquid as necessary as other components. Fluoride etc. are used as an etching agent. An etching agent improves the adhesiveness of a chemical conversion treatment film more by activating the plating layer surface. Inorganic compounds (oxides, phosphates, etc.) such as Mg, Ca, Sr, V, W, Mn, B, Si, and Sn improve the water resistance by densifying the chemical conversion film. Inorganic lubricants such as molybdenum disulfide and talc are brought into the coating from the chemical conversion treatment liquid, and further improve the lubricity of the chemical conversion coating and the workability of the chemical conversion plated steel sheet. Moreover, predetermined | prescribed color tone can be provided to a chemical conversion treatment film by mix | blending an inorganic pigment, an organic pigment, organic dye, etc.

[Formation of chemical conversion coating]
In the fifth step, a chemical conversion treatment film is formed on the surface of the molten Zn—Al—Mg alloy-plated steel sheet on which the phosphate film is formed in the third step. To form the chemical conversion film, the chemical conversion solution prepared in the fourth step is applied to the surface of the molten Zn-Al-Mg alloy-plated steel sheet on which the phosphate film has been formed in the third step, and dried. That's fine.

  The method for applying the chemical conversion liquid is not particularly limited, and may be appropriately selected from known methods. Examples of such a coating method include a roll coating method, a curtain flow method, a spin coating method, a spray method, and a dip pulling method.

  The chemical conversion solution may be dried at room temperature, but considering continuous operation, it is preferable to keep the temperature at 50 ° C. or higher to shorten the drying time. However, when the temperature is kept above 300 ° C., the organic component may be thermally decomposed to deteriorate the performance of the chemical conversion coating. In the production method of the present invention, since the content of the emulsifier contained in the chemical conversion treatment liquid is small, even if the drying temperature is about 50 ° C., the emulsifier is hardly contained, and a chemical conversion treatment film having excellent water resistance can be formed. .

  FIG. 2 is a schematic cross-sectional view showing the formation process of the chemical conversion coating. FIG. 2 shows a state in which a chemical conversion treatment liquid to which polyethylene-fluorine resin particles and polyethylene resin particles are added is applied. Moreover, in FIG. 2, the phosphate membrane | film | coat is abbreviate | omitted.

  First, a chemical conversion treatment liquid is applied to the surface of the molten Zn—Al—Mg alloy-plated steel sheet 110 (more precisely, on the phosphate coating) to form a chemical conversion treatment coating 120 (see FIG. 2A). ). Polyethylene-fluorine resin particles 122 and polyethylene resin particles 124 are dispersed in the coating film 120 of the chemical conversion treatment liquid.

  Next, when the temperature is raised to about 50 ° C., the moisture evaporates and a chemical conversion film 120 ′ is formed (see FIG. 2B). At this time, most of the polyethylene-fluorine resin particles 122 and the polyethylene resin particles 124 protrude from the surface of the chemical conversion coating 120 ′. FIG. 3A is an SEM image (plan view) of the chemical conversion coating after the chemical conversion coating is dried at 50 ° C. FIG. Although it is not possible to distinguish between the polyethylene-fluororesin particles and the polyethylene resin particles, it can be seen that these particles protrude from the surface of the chemical conversion coating (see “PE-F or PE” in the figure).

  When the temperature is further increased to about 150 ° C., the polyethylene resin particles 124 are melted and the polyethylene resin is bleed on the surface (see FIG. 2C). The bleed polyethylene resin 124 ′ covers the whole or part of the surface of the chemical conversion coating 120 ′. On the other hand, the polyethylene-fluorine resin particles 122 are maintained as they are without melting. FIG. 3B is an SEM image (plan view) of the chemical conversion coating after the coating of the chemical conversion solution is dried at 150 ° C. It can be seen that only the polyethylene-fluororesin particles protrude from the surface of the chemical conversion coating (see “PE-F” in the figure). FIG. 3C is an SEM image (cross-sectional view) of polyethylene-fluororesin particles protruding from the surface of the chemical conversion coating. It can be confirmed by fluorescent X-ray analysis that the particles protruding from the surface of the chemical conversion coating are polyethylene-fluororesin particles. FIG. 4 is a fluorescent X-ray spectrum of polyethylene-fluororesin particles protruding from the surface of the chemical conversion coating.

  By the above procedure, the chemically treated plated steel sheet of the present invention, which is based on a molten Zn-Al-Mg alloy plated steel sheet and is excellent in all of weather resistance, water resistance, blackening resistance, film adhesion, antiglare property and workability. Can be manufactured.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail with reference to an Example, this invention is not limited by these Examples.

[Example]
1. Preparation of chemical conversion treatment plated steel plate (1) Preparation of chemical conversion treatment original plate Using SPCC having a plate thickness of 0.8 mm as a base material, a molten Zn-6 mass% Al-3 mass% Mg alloy plated steel sheet (plating adhesion amount 45 g / m ² ) Was made. In this example, this molten Zn—Al—Mg alloy-plated steel sheet was used as a chemical conversion treatment original sheet.

(2) Formation of phosphate film A molten Zn-Al-Mg alloy-plated steel sheet is contacted with a phosphate treatment solution having the composition shown in Table 1 heated to 60 ° C for 5 seconds by a spray treatment method, washed with water, and dried. Thus, a phosphate film was formed. It was 1.5 g / m < ² > when the adhesion amount of the phosphate membrane | film | coat was measured using the fluorescent-X-ray-analysis apparatus. Moreover, it was 95% when the coverage of the phosphate crystal | crystallization on the plated steel plate surface was measured using the scanning electron microscope.

(3) Formation of chemical conversion treatment film Next, a chemical conversion treatment liquid having the composition shown in Table 2 was applied to the surface of the molten Zn-Al-Mg alloy-plated steel sheet on which the phosphate film was formed, and heated at a final plate temperature of 140 ° C. It dried and formed the chemical conversion treatment film with a film thickness of 2.0 micrometers.

  The chemical conversion treatment liquids of the treatment liquids Nos. 1 to 12 shown in Table 2 are aqueous emulsions containing a predetermined amount of a fluorine-containing resin containing a carboxyl group and a sulfonic acid group and an emulsifier (nonvolatile content: 25% by mass; see Table 3). 4A group metal compound, polyethylene-fluorine resin particles (resin particles) and the like. The chemical conversion treatment liquid of treatment liquid No. 13 is a group 4A metal compound, polyethylene-fluorine resin particles (resin particles), etc. added to an aqueous emulsion containing a urethane resin and an emulsifier (non-volatile content 25 mass%; see Table 3). Prepared.

  An aqueous emulsion containing a fluorine-containing resin was obtained by adding a predetermined amount of a fluoroolefin, a carboxyl group-containing monomer, a sulfonic acid group-containing monomer and an emulsifier to an aqueous solvent and copolymerizing them. PR135 (Sumika Bayern Urethane Co., Ltd.) was used as an aqueous emulsion containing a urethane resin. A-1891 (Momentive Performance Materials Japan GK) was used as the silane coupling agent.

  The amounts of Group 4A metal, phosphate and silane coupling agent relative to the organic resin in the chemical conversion coating of each chemical conversion plated steel sheet were measured using a fluorescent X-ray analyzer. The contents of phosphate and silane coupling agent were calculated from the measured values of P and Si. Moreover, the area occupation rate of the polyethylene-fluororesin particle | grains in the surface of the chemical conversion treatment film of each chemical conversion treatment plated steel plate was measured using the scanning electron microscope. Table 4 shows the amounts of group 4A metal, phosphate, and silane coupling agent relative to the organic resin in the chemical conversion film to be formed, and the area occupancy ratio of the polyethylene-fluororesin particles on the surface of the chemical conversion film. Shown in

2. Evaluation of Chemically Treated Plated Steel Sheet (1) Accelerated Weathering Test A test piece was cut out from each chemical conversion coated steel sheet, and an accelerated weathering test (xenon lamp method) was performed in accordance with JIS K5600-7-7: 2008. In this test, the process of spraying water for 18 minutes while irradiating the light of a xenon arc lamp for 120 minutes was defined as 1 cycle (2 hours), and this process was repeated 0 to 2000 cycles (0, 1000, 2000 cycles).

(2) Evaluation of weather resistance About each chemical conversion treatment plated steel plate, the thickness of the chemical conversion treatment film before and after the accelerated weathering test was measured by a cross-sectional spectroscope, and the coating film residual ratio was obtained. For each chemical conversion coated steel sheet, “◎” when the coating film residual ratio is 95% or more, “◯” when 80% or more and less than 95%, “△” when 60% or more and less than 80%, 30% When it was less than 60%, it was evaluated as “▲”, and when it was less than 30%, it was evaluated as “x”.

(3) Evaluation of blackening resistance About each chemical conversion treatment plating steel plate, the lightness difference ((DELTA) L ^* value) of the surface of a chemical conversion treatment film before and behind an accelerated weathering test was measured, and blackening resistance was evaluated. For each chemically treated steel sheet, “◎” if the lightness difference (ΔL ^* value) is 1 or less, “○” if it exceeds 1 and 2 or less, and “Δ” or 5 if it exceeds 2 and 5 or less. In the case of exceeding 10 or less, it was evaluated as “▲”, and in the case of exceeding 10, “×”.

(4) Evaluation of corrosion resistance of flat part About each chemical conversion treatment plated steel sheet, a salt spray test (according to JIS Z2371; 120 hours) is performed using the test piece after the accelerated weathering test, and the white rust occurrence area ratio of the flat part is determined. evaluated. For each chemically treated steel sheet, “◎” when the white rust occurrence area ratio is 5% or less, “◯” when it exceeds 5% and 10% or less, and “△” when it exceeds 10% and 30% or less. In the case of more than 30% and not more than 50%, “▲” was evaluated, and in the case of exceeding 50%, “×” was evaluated.

(5) Evaluation of lubricity A test piece having a width of 30 mm and a length of 300 mm was cut out from each chemically treated plated steel sheet. A mold made of SKD11 was brought into contact with both surfaces of each test piece, and the test piece was pulled out at a speed of 100 mm / min while applying a load of 600 kgf through the mold. The pulling force at this time was measured to evaluate the lubricity. For each chemical conversion coated steel sheet, “◎” when the pulling force is 200 kgf or less, “◯” when it exceeds 200 kgf and 250 kgf or less, “△” when it exceeds 250 kgf and 300 kgf or less, “△”, when it exceeds 300 kgf and 400 kgf or less Was evaluated as “▲”, and when exceeding 400 kgf, “×”.

(6) Evaluation of anti-glare property About each chemical conversion treatment plated steel plate, the 60 degree specular glossiness of the surface of a chemical conversion treatment film was measured, and anti-glare property was evaluated. The 60-degree specular gloss was measured using a gloss meter according to JIS Z8741. About each chemical conversion treatment plating steel plate, when 60 degree specular gloss is less than 100, it is "(double-circle)", when 100 or more and less than 150 are "O", when it is 150 or more and less than 200, it is "△", “×”.

(7) Evaluation of film adhesion [Water resistant adhesion]
A test piece was cut out from each chemical conversion-treated plated steel sheet and subjected to a water resistance adhesion test. Each test piece was immersed in hot water at 90 ° C. for 2 hours and then pulled up from the hot water. A cross cut test (based on JIS K5400) was performed using the test piece after the hot water treatment, and the coating film residual ratio was measured. For each test piece, “◎” when the coating film remaining rate is 100%, “◯” when 80% or more and less than 100%, “△” when 60% or more and less than 80%, 30% or more and 60%. The film adhesion was evaluated as “▲” when less than 30% and “×” when less than 30%.

[Processing adhesion]
A test piece was cut out from each chemical conversion coated steel sheet and subjected to a work adhesion test. Each test piece was stretched with Erichsen 5 mm. Similarly to the water-resistant adhesion test, a cross-cut test (based on JIS K5400) was performed using the processed specimen, and the coating film residual ratio was measured. For each test piece, “◎” when the coating film remaining rate is 100%, “◯” when 80% or more and less than 100%, “△” when 60% or more and less than 80%, 30% or more and 60%. The film adhesion was evaluated as “▲” when less than 30% and “×” when less than 30%.

(8) Evaluation result About each chemical conversion treatment plating steel plate (Examples 1-7, Comparative Examples 1-13), the presence or absence of a phosphate film, the kind of chemical conversion treatment used, a weather resistance test, and a blackening resistance test Table 5 shows the evaluation results of the flat portion corrosion resistance test. Moreover, about each chemical conversion treatment plated steel plate (Examples 1-7, Comparative Examples 1-13), the presence or absence of a phosphate membrane | film | coat, the kind of used processing liquid, and the glare-proof test and evaluation result of film | membrane adhesiveness are shown. Table 6 shows.

  The weather resistance was evaluated by the coating film remaining rate of the chemical conversion coating after the accelerated weather resistance test. In the chemical conversion treatment plated steel sheet of Comparative Example 13 in which the chemical conversion treatment film containing the urethane resin was formed, the chemical conversion treatment film disappeared after 1000 cycles (equivalent to outdoor exposure of 10 years). Further, even in the chemical conversion-treated steel sheet of Comparative Example 11 in which a chemical conversion treatment film containing excessively large polyethylene-fluorine resin particles was formed, the polyethylene-fluororesin particles were dropped from the chemical conversion treatment film, so that the weather resistance was inferior. . On the other hand, 2000 cycles (equivalent to outdoor exposure for 20 years) were repeated in the chemical conversion treatment plated steel plates of Examples 1 to 7 in which a chemical conversion treatment film containing a fluorine-containing resin having a predetermined amount of hydrophilic functional group and a 4A group metal compound was formed. Even after this, the film thickness of the chemical conversion film was hardly changed.

Blackening resistance was evaluated by the difference in brightness (ΔL ^* value) before and after the accelerated weather resistance test. In the chemical conversion treatment plated steel sheet of Comparative Example 13 in which the chemical conversion treatment film containing the urethane resin was formed, the blackening of the plating layer progressed with an increase in the number of cycles, and the lightness was lowered. On the other hand, 2000 cycles (equivalent to outdoor exposure for 20 years) were repeated in the chemical conversion treatment plated steel plates of Examples 1 to 7 in which a chemical conversion treatment film containing a fluorine-containing resin having a predetermined amount of hydrophilic functional group and a 4A group metal compound was formed. Even after that, the brightness did not decrease. In the chemical conversion treatment plated steel sheets of Comparative Examples 1 to 7 in which the phosphate film was not formed, the lightness slightly decreased with an increase in the number of cycles.

  Corrosion resistance was evaluated based on the white rust generation area ratio after the salt spray test. In the chemical conversion-treated plated steel sheet of Comparative Example 13 in which a chemical conversion treatment film containing a urethane resin was formed, although the corrosion resistance was good before the accelerated weather resistance test, the corrosion resistance was significantly lowered as the film disappeared. Moreover, the chemical conversion treatment coating steel plate of the comparative examples 8 and 9 which formed the chemical conversion treatment film containing the fluorine-containing resin which has an excessive amount or a small amount of hydrophilic functional groups, and the chemical conversion treatment film which does not contain a 4A group metal compound were formed. In the chemical conversion treatment plated steel plates of Comparative Examples 10 and 12, the corrosion resistance was inferior before the accelerated weathering test. On the other hand, 2000 cycles (equivalent to outdoor exposure for 20 years) were repeated in the chemical conversion treatment plated steel plates of Examples 1 to 7 in which a chemical conversion treatment film containing a fluorine-containing resin having a predetermined amount of hydrophilic functional group and a 4A group metal compound was formed. Even afterwards, the corrosion resistance was good.

  The lubricity was evaluated by the pulling force required when pulling out a test piece to which a load was applied. Since the chemical conversion treatment plated steel plate of Comparative Example 8 had a small amount of polyethylene-fluorine resin particles in the chemical conversion treatment film, the lubricity was inferior. Similarly, the chemically treated plated steel sheet of Comparative Example 12 that did not contain polyethylene-fluororesin particles also had poor lubricity. Moreover, since the chemical conversion treatment plated steel plate of the comparative example 13 had the average particle diameter of the polyethylene-fluororesin particle | grains small, and it was buried in the chemical conversion treatment film, its lubricity was inferior. On the other hand, in the chemical conversion treatment plated steel plates of Examples 1 to 7 in which a chemical conversion treatment film containing a predetermined amount of polyethylene-fluororesin particles having an average particle diameter within a predetermined range was formed, the lubricity was good.

  The antiglare property was evaluated based on the 60 ° specular gloss. In the chemical conversion treatment plated steel plates of Comparative Examples 1 to 7 in which no phosphate film was formed, the specular gloss was very high. On the other hand, in the chemical conversion treatment plated steel plates of Examples 1 to 7 in which the phosphate film was formed, the specular gloss was stable within a predetermined range before and after the accelerated weather resistance test.

  The film adhesion was evaluated by the coating film residual ratio after the hot water treatment or after processing. In the chemical conversion treatment plated steel sheets of Comparative Examples 1 to 7 in which the phosphate film was not formed, both the water resistance adhesion and the work adhesion were inferior. On the other hand, in the chemical conversion treatment plated steel plate of Examples 1-7 which formed the phosphate membrane, both water-proof adhesion and processing adhesion were good.

  From the above results, it can be seen that the chemically treated plated steel sheet of the present invention is excellent in weather resistance, blackening resistance, corrosion resistance, workability (lubricity), film adhesion and antiglare property.

[Reference experiment]
As a reference experiment, the results of examining the relationship between the amount of Group 4A metal and the amount of emulsifier in the fluororesin film and the moisture permeability are shown.

  A predetermined amount of group 4A was added to an aqueous emulsion of a fluorine-containing resin having a hydrophilic functional group prepared by adding a hydrophilic functional group-containing monomer to 1% by mass and adding an emulsifier to 1% by mass. The chemical conversion treatment solution prepared by adding the metal compound was applied to the surface of the plated steel plate with a bar coater and dried by heating at a final plate temperature of 140 ° C. to form a fluororesin film having a thickness of 30 μm. This fluororesin film was peeled off from the plated steel sheet and cut into a predetermined size to obtain a test piece. About each test piece (free fluororesin film | membrane), the water vapor transmission rate was measured based on JISZ0208 (measurement conditions, temperature 40 ± 0.5 degreeC, relative humidity 90 ± 2%, 24 hours).

  FIG. 5 is a graph showing the relationship between the amount of group 4A metal in the fluororesin coating and the moisture permeability. From this graph, it is understood that the moisture permeability of the fluororesin film can be remarkably lowered by setting the amount of the group 4A metal in the fluororesin film to 0.1 mass% or more.

  Add a hydrophilic functional group-containing monomer to 1% by mass and add a predetermined amount of emulsifier to an aqueous emulsion of a fluorine-containing resin having a hydrophilic functional group. A chemical conversion treatment solution prepared by adding 1% by mass in terms of conversion is applied to the surface of the plated steel plate with a bar coater and dried by heating at a final plate temperature of 140 ° C. to form a fluororesin film having a thickness of 30 μm. did. This fluororesin film was peeled off from the plated steel sheet and cut into a predetermined size to obtain a test piece. About each test piece (free fluororesin film | membrane), the water vapor transmission rate was measured based on JISZ0208 (measurement conditions, temperature 40 ± 0.5 degreeC, relative humidity 90 ± 2%, 24 hours).

  FIG. 6 is a graph showing the relationship between the concentration of the emulsifier in the aqueous emulsion of the fluorine-containing resin and the moisture permeability of the fluorine resin film. From this graph, it is understood that the moisture permeability of the fluororesin film can be remarkably reduced by setting the concentration of the emulsifier in the emulsion to 1% by mass or less.

  From the above results, it can be seen that the fluororesin film having a large amount of the group 4A metal compound and a small amount of the remaining emulsifier has excellent water resistance.

  The chemical conversion-treated plated steel sheet of the present invention is useful as, for example, a plated steel sheet for exterior building materials because it is excellent in weather resistance, water resistance, corrosion resistance, discoloration resistance, film adhesion, antiglare property and workability.

DESCRIPTION OF SYMBOLS 110 Molten Zn-Al-Mg alloy plating steel plate 120 Coating film of chemical conversion liquid 120 'Chemical conversion coating 122 Polyethylene-fluorine resin particle 124 Polyethylene resin particle 124' Bleed polyethylene resin

Claims (17)

A hot-dip Zn—Al—Mg alloy-plated steel sheet having a plating layer containing a ternary eutectic structure of Al / Zn / Zn ₂ Mg;
A phosphate film containing phosphate crystal grains formed on the surface of the molten Zn-Al-Mg alloy-plated steel sheet;
A chemical conversion treatment plated steel sheet having a film thickness of 0.5 to 10 μm formed on the phosphate film,
In the formation surface of the phosphate film, the crystal grains of the phosphate cover 50% by area or more of the surface of the molten Zn-Al-Mg alloy-plated steel sheet,
The chemical conversion film is a fluorine-containing resin containing 0.05 to 5% by mass of a hydrophilic functional group selected from the group consisting of a carboxyl group, a sulfonic acid group and a salt thereof and 7 to 20% by mass of F atoms, Containing 0.1 to 5% by mass of a Group 4A metal compound in terms of metal with respect to the fluorine-containing resin, and resin particles having an average particle size of 0.1 to 10 μm,
The area occupation ratio of the resin particles on the surface of the chemical conversion film is 0.1 area% or more.
Chemical conversion plated steel sheet.   The ratio of the carboxyl group and sulfonic acid group which the said fluorine-containing resin has is a chemical conversion treatment plated steel plate of Claim 1 which exists in the range of 5-60 in the molar ratio of a carboxyl group / sulfonic acid group.   The said resin particle is a chemical conversion treatment plated steel plate of Claim 1 which is the polyethylene- fluorine resin particle by which the fluororesin fine particle is couple | bonded with the surface of the polyethylene resin particle. The chemical conversion film further contains a polyethylene resin,
The polyethylene-fluororesin particles protrude from the surface of the chemical conversion coating on a part of the surface of the chemical conversion coating,
The polyethylene resin covers all or part of the remaining part of the surface of the chemical conversion film,
The chemical conversion treatment plated steel plate of Claim 3. The chemical conversion film further contains a phosphate,
The amount of the phosphate with respect to the fluorine-containing resin is in the range of 0.05 to 3% by mass in terms of P.
The chemical conversion treatment plated steel plate of Claim 1. The chemical conversion film further contains a silane coupling agent,
The amount of the silane coupling agent relative to the fluorine-containing resin is in the range of 0.5 to 5% by mass.
The chemical conversion treatment plated steel plate of Claim 1.   The said 4A group metal is a chemical conversion treatment plated steel plate of Claim 1 chosen from the group which consists of Ti, Zr, Hf, and these combination. Preparing a hot-dip Zn—Al—Mg alloy-plated steel sheet having a plating layer containing a ternary eutectic structure of Al / Zn / Zn ₂ Mg;
A phosphate treatment solution containing 0.03 to 0.5 mol / L phosphate in terms of phosphate ions was applied to the surface of the molten Zn—Al—Mg alloy-plated steel sheet, dried, Forming a phosphate film comprising crystal grains of the acid salt;
Applying a chemical conversion treatment liquid on the phosphate film and drying to form a chemical conversion film having a film thickness of 0.5 to 10 μm,
The said chemical conversion liquid contains 0.05-5 mass% of hydrophilic functional groups chosen from the group which consists of a carboxyl group, a sulfonic acid group, and these salts, and 7-20 mass% of F atoms, and a number average molecular weight. Fluorine-containing resin in the range of 1,000 to 2,000,000, oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide salt of group 4A metal, and an average particle size of 0.1 Containing 10 to 10 μm resin particles,
The amount of the oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide of the group 4A metal in the fluorine-containing resin is within a range of 0.1 to 5% by mass in terms of metal. Yes,
The amount of the resin particles relative to the solid content in the chemical conversion treatment liquid is in the range of 0.5 to 20% by mass.
The manufacturing method of a chemical conversion treatment plated steel plate.   The ratio of the carboxyl group and sulfonic acid group which the said fluorine-containing resin has is a manufacturing method of the chemical conversion treatment plated steel plate of Claim 8 which exists in the range of 5-60 in the molar ratio of a carboxyl group / sulfonic acid group.   The said resin particle is a manufacturing method of the chemical conversion treatment plated steel plate of Claim 8 which is the polyethylene- fluorine resin particle by which the fluororesin fine particle is couple | bonded with the surface of the polyethylene resin particle.   The said chemical conversion treatment liquid is a manufacturing method of the chemical conversion treatment plated steel plate of Claim 10 which contains a polyethylene resin particle further. The chemical conversion treatment liquid further contains a phosphate,
The amount of the phosphate with respect to the fluorine-containing resin is in the range of 0.05 to 3% by mass in terms of P.
The manufacturing method of the chemical conversion treatment plated steel plate of Claim 8. The chemical conversion treatment liquid further contains a silane coupling agent,
The amount of the silane coupling agent relative to the fluorine-containing resin is in the range of 0.5 to 5% by mass.
The manufacturing method of the chemical conversion treatment plated steel plate of Claim 8.   The said 4A group metal is a manufacturing method of the chemical conversion treatment plated steel plate of Claim 8 chosen from the group which consists of Ti, Zr, Hf, and these combination.   The chemical conversion treatment plating according to claim 8, wherein the phosphate treatment liquid further contains a metal ion selected from the group consisting of Ni, Co, Fe and Mn at a concentration of 0.01 to 0.5 mol / L. A method of manufacturing a steel sheet. The phosphating solution further contains a polyamine organic inhibitor having at least one functional group of —NH ₂ or ═NH and having a number average molecular weight of 200 to 30,000 at a concentration of 0.01 to 5 mass%. The manufacturing method of the chemical conversion treatment plated steel plate of Claim 8.   The said polyamine type organic inhibitor is manufacture of the chemical conversion treatment plated steel plate of Claim 16 which is 1 type, or 2 or more types of aliphatic amine chosen from the group which consists of polyethylamine, polyethyleneimine, polyetheramine, and polyaminoacrylate. Method.