TWI531677B - Chemically converted plated steel plate and fabricating method thereof - Google Patents

Description

Chemical conversion treatment plated steel plate and manufacturing method thereof

The present invention relates to a chemical conversion-treated Zn-based steel sheet excellent in weather resistance, water resistance, blackening resistance, film adhesion, and workability, and a method for producing the same.

The plated steel sheet is formed with a chemical conversion treatment film containing an organic resin on the surface thereof in order to prevent seizure during molding (see, for example, Patent Document 1 and Patent Document 2). Patent Document 1 and Patent Document 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. By coating the surface of the plated steel sheet with a chemical conversion treatment film containing an organic resin, the seizure resistance can be improved, and corrosion resistance, discoloration resistance, and the like can be improved.

On the other hand, in order to improve the weather resistance of the chemical conversion-treated steel sheet, a fluororesin having excellent weather resistance is used as the organic resin constituting the chemical conversion treatment film. When a fluororesin is used in order to improve weather resistance, an organic solvent-based fluororesin composition is often used. However, such an organic solvent-based fluororesin composition has problems such as fire risk, harmfulness, and air pollution.

Further, various water-based fluororesin compositions have also been proposed (for example, refer to Patent Document 3). However, such a water-based fluororesin composition requires high-temperature baking (for example, 180 ° C to 230 ° C, see Patent Document 3). Such high-temperature burning is practically impossible to achieve on-site coating (usually using air-dried resin), which is also disadvantageous in a factory line where heating and drying are mainstream.

Moreover, in order to eliminate the problem of the aqueous fluororesin composition, it is also proposed A water-based fluororesin composition in which a curable portion (organic functional group) is introduced and a film can be formed at a low temperature (see, for example, Patent Document 4). However, the film obtained by reacting and hardening the organic functional group causes weathering deterioration to occur preferentially from the hardened portion, so that the film becomes porous and the water resistance is lowered. In addition, when the substrate is treated with an epoxy resin or a urethane resin in order to improve the adhesion, the organic resin is preferentially deteriorated in weather resistance, and the film adhesion is rapidly lowered.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2005-15834

Patent Document 2: Japanese Patent Laid-Open Publication No. 2005-206764

Patent Document 3: Japanese Patent Laid-Open Publication No. SHO 57-38845

Patent Document 4: Japanese Patent Laid-Open No. Hei 5-202260

As described above, by forming a chemical conversion treatment film containing an organic resin on the surface of the plated steel sheet, seizure resistance, corrosion resistance, discoloration resistance, and the like can be improved. However, in the case of forming a chemical conversion treated plated steel sheet containing a chemical conversion treatment film of an organic resin, when it is used as an outer packaging building material, the weather resistance is insufficient. In other words, many organic resins such as urethane resins are deteriorated by ultraviolet rays. Therefore, when the chemical conversion-treated steel sheet is used as the outer packaging building material, the chemical conversion treatment film on the surface of the coated steel sheet may pass over time. Disappearing fears. If the chemical conversion treatment film disappears as described above, there is a concern that discoloration, rust, or the like may occur and the appearance is deteriorated, so that the outer packaging material is unsatisfactory.

The method for improving the weather resistance of such a chemical conversion treated steel plate is considered There is a fluororesin excellent in weather resistance as an organic resin constituting a chemical conversion treatment film. Therefore, the inventors conducted preliminary experiments to form a chemical conversion treatment film on the surface of a plated steel sheet using an emulsion of an aqueous fluororesin which is easy to handle. As a result, the ultraviolet ray resistance can be improved by using the emulsion of the aqueous fluororesin, but on the other hand, the film forming property, the water resistance, and the film adhesion are lowered. As a result of further research by the present inventors, it is estimated that the reason for the decrease in the quality is that an emulsifier (for example, ammonium perfluorooctanoate) used in the production of an emulsion of a water-based fluororesin remains in the chemical conversion treatment film (refer to a reference experiment described later). .

As described above, the prior chemical conversion-treated plated steel sheet containing the chemical conversion treatment film containing the organic resin may have insufficient weather resistance. In addition, by using a water-based fluororesin as the organic resin, the weather resistance (UV resistance) of the chemical conversion-treated steel sheet can be improved, but on the other hand, the film forming property, the water resistance, and the film adhesion are lowered, so that it is impossible to At the same time, it has weather resistance, water resistance, blackening resistance and film adhesion.

An object of the present invention is to provide a chemical conversion-treated Zn-based steel sheet having a chemical conversion treatment film containing an organic resin and excellent in weather resistance, water resistance, blackening resistance, film adhesion, and workability.

The present inventors have found that by using a high molecular weight fluorine-containing resin having a hydrophilic functional group as an organic resin and crosslinking the fluorine-containing resin with a Group 4A metal compound, the weather resistance of the chemical conversion treatment film can be improved. The present invention has been completed by further studies on water resistance, blackening resistance, and film adhesion.

That is, the first invention of the present invention relates to the following chemical conversion treatment of a Zn-based steel sheet.

[1] A chemical conversion-treated Zn-based steel sheet comprising: an Al-containing Zn-based alloy plated steel sheet having a Zn-based alloy plating layer containing 0.05% by mass to 60% by mass of Al; and a chemical conversion treated film, It is formed on the surface of the Al-containing Zn-based alloy plated steel sheet and has a film thickness of 0.5 μm to 10 μm; and the chemical conversion treatment film contains: a group selected from the group consisting of a carboxyl group, a sulfonic acid group, and a salt thereof. a fluorine-containing resin having a hydrophilic functional group of 0.05% by mass to 5% by mass and a F atom of 7% by mass to 20% by mass; and a Group 4A metal compound in an amount of 0.1% by mass to 5% by mass based on the fluorine-containing resin And resin particles having an average particle diameter of 0.1 μm to 10 μm; and an area occupation ratio of the resin particles in the surface of the chemical conversion treatment film is 0.1% by area or more.

[2] The chemical conversion-treated Zn-based steel sheet according to [1], wherein a ratio of a carboxyl group to a sulfonic acid group of the fluorine-containing resin is 5 to 60 in terms of a molar ratio of a carboxyl group to a sulfonic acid group. Within the scope.

[3] The chemical conversion-treated Zn-based 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 the polyethylene resin particles.

[4] The chemical conversion-treated Zn-based steel sheet according to [3], wherein the chemical conversion treatment film further contains a polyethylene resin; and the polyethylene-fluororesin particles are in a part of a surface of the chemical conversion treatment film, a surface protrusion of the chemical conversion treatment film; the polyethylene resin coating all or a part of the remaining portion of the surface of the chemical conversion treatment film Minute.

[5] The chemical conversion-treated Zn-based steel sheet according to any one of [1] to [4] wherein the chemical conversion treatment film further contains a phosphate; and the amount of the phosphate is based on the fluorine-containing resin The P conversion is in the range of 0.05% by mass to 3% by mass.

[6] The chemical conversion-treated Zn-based steel sheet according to any one of [1] to [5] wherein the chemical conversion treatment film further contains a decane coupling agent; and the decane coupling agent is the same as the fluorine-containing resin The amount is in the range of 0.5% by mass to 5% by mass.

[7] The chemical conversion-treated Zn-based steel sheet according to any one of [1] to [6] wherein the Group 4A metal is selected from the group consisting of Ti, Zr, Hf, and a combination thereof.

[8] The chemical conversion-treated Zn-based steel sheet according to any one of [1] to [7], further comprising: a base chemical conversion treatment film formed on the Al-containing Zn-based alloy plated steel sheet, and The chemical conversion treatment film contains an oxide or hydroxide of a valve metal and a fluoride of a valve metal.

A second invention of the present invention relates to a method for producing a Zn-based steel sheet for chemical conversion treatment.

[9] A method for producing a Zn-based steel sheet for chemical conversion treatment, comprising the steps of: preparing an Al-containing Zn-based alloy-plated steel sheet having a Zn-based alloy plating layer containing 0.05% by mass to 60% by mass of Al, and Applying a chemical conversion treatment liquid to the surface of the Al-containing Zn-based alloy plated steel sheet and drying it to form a chemical conversion treatment film having a film thickness of 0.5 μm to 10 μm. The chemical conversion treatment liquid contains 0.05% by mass 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% by mass to 20% by mass of the F atom. a fluorine-containing resin having an average molecular weight of from 1,000 to 2,000,000; an oxoacid salt, a fluoride, a hydroxide, an organic acid salt, a carbonate or a peroxy salt of a Group 4A metal; and an average particle diameter of 0.1 μm to 10 μm of resin particles; the amount of the oxoacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxy salt of the Group 4A metal relative to the fluorine-containing resin, in terms of metal The amount of the resin particles is in the range of 0.5% by mass to 20% by mass based on the solid content in the chemical conversion treatment liquid.

[10] The method for producing a Zn-based steel sheet for chemical conversion treatment according to [9], wherein a ratio of a carboxyl group to a sulfonic acid group of the fluorine-containing resin is 5 in terms of a molar ratio of a carboxyl group/sulfonic acid group. Within the range of ~60.

[11] The method for producing a Zn-based steel sheet for chemical conversion treatment according to [9], wherein the resin particles are polyethylene-fluororesin particles in which fluororesin fine particles are bonded to the surface of the polyethylene resin particles.

[12] The method for producing a chemical conversion-treated Zn-based steel sheet according to [11], wherein the chemical conversion treatment liquid further contains polyethylene resin particles.

[13] The method for producing a chemical conversion-treated Zn-based steel sheet according to any one of [9] to [12] wherein the chemical conversion treatment liquid further contains a phosphate; the phosphate is the same as the fluorine-containing resin The amount is in the range of 0.05% by mass to 3% by mass in terms of P.

[14] The chemical conversion treatment Zn plating system according to any one of [9] to [13] In the method for producing a steel sheet, the chemical conversion treatment liquid further contains a decane coupling agent; and the amount of the decane coupling agent is in a range of 0.5% by mass to 5% by mass based on the fluorine-containing resin.

[15] The method for producing a chemical conversion-treated Zn-based steel sheet according to any one of [9] to [14] wherein the Group 4A metal is selected from the group consisting of Ti, Zr, Hf, and a combination thereof.

[16] The method for producing a chemical conversion-treated Zn-based steel sheet according to any one of [9] to [15] wherein, before the step of forming the chemical conversion treatment film, further comprising: the Zn containing Al The surface of the alloy-plated steel sheet is coated with a substrate chemical conversion treatment liquid and dried to form a substrate chemical conversion treatment film; the substrate chemical conversion treatment liquid contains a valve metal salt and a fluoride ion.

According to the present invention, it is possible to provide a chemical conversion-treated Zn-based steel sheet excellent in weather resistance, water resistance, blackening resistance, film adhesion, and workability. The chemical conversion treatment of the Zn-based steel sheet of the present invention is excellent in weather resistance, water resistance, corrosion resistance, discoloration resistance, and workability, and therefore can be effectively used as, for example, a plated steel sheet for exterior packaging materials.

1. Chemical conversion treatment of Zn-plated steel sheets

The chemical conversion treatment Zn-based steel sheet according to the present invention includes a Zn-based alloy plated steel sheet containing Al (chemical conversion treatment substrate), and a chemical conversion treatment film formed on the surface of the Al-containing Zn-based alloy plated steel sheet. A feature of the chemical conversion treatment of the Zn-based steel sheet of the present invention is that the chemical conversion treatment film A high molecular weight fluorine-containing resin, a Group 4A metal compound, and resin particles (lubricants) into which a hydrophilic functional group (such as a carboxyl group or a sulfonic acid group) is introduced is contained.

Hereinafter, each constituent element of the chemical conversion-treated Zn-based steel sheet of the present invention will be described.

[Chemical conversion treatment of the bottom plate]

The chemical conversion treatment substrate is an Al-containing Zn-based alloy plated steel sheet excellent in corrosion resistance and creativity. Here, the "Al-containing Zn-based alloy plated steel sheet" means a steel sheet having a Zn-based alloy plating layer containing 0.05% by mass to 60% by mass of Al. Examples of the Al-containing Zn-based alloy plated steel sheet include: molten Al-Zn plated steel sheet (melted Zn-0.1% Al plating, molten Zn-55% Al plating, molten Zn-6% Al-3% Mg plating, Molten Zn-11%Al-3%Mg-0.2%Si, molten Zn-5%Al-0.75%Mg), alloyed Zn-plated steel sheet (alloyed alloy after alloying by 0.1% Al-Zn plating) Melt Al-Zn plating).

The base steel of the Al-containing Zn-based alloy plated steel sheet is low carbon steel or medium carbon steel, high carbon steel, alloy steel or the like. When workability is required, a steel sheet for deep drawing such as low carbon plus Ti steel or low carbon plus Nb steel is preferable as the base steel.

[Base chemical conversion treatment film]

There is also a case where a substrate chemical conversion treatment film containing an oxide or hydroxide of a valve metal and a fluoride of a valve metal is formed on the surface of an Al-containing Zn-based alloy plated steel sheet used as a chemical conversion treatment substrate. As described above, when the underlying chemical conversion treatment film is formed on the surface of the Al-containing Zn-based alloy plated steel sheet, the chemical conversion treatment film is formed on the surface of the Al-containing Zn-based alloy plated steel sheet by interposing the base chemical conversion treatment film.

The oxide and hydroxide of the valve metal exhibit high insulation resistance. Therefore, the underlying chemical conversion treatment film containing the oxide or hydroxide of the valve metal acts as a resistive element for the movement of electrons. Therefore, the reduction reaction of the dissolved oxygen contained in the moisture in the environment can be suppressed, and the oxidation reaction of the paired Al-containing Zn-based alloy plated steel sheet can also be suppressed. As a result, elution (corrosion) of the metal component from the Al-containing Zn-based alloy plated steel sheet to be a substrate can be suppressed. Among them, a tetravalent compound of a Group IV A element such as Ti, Zr or Hf is a stable compound and forms an excellent high insulating film.

Further, in the chemical conversion treatment film, film defects are inevitably generated at the time of chemical conversion treatment or molding processing. Since the base material of the film defect portion is exposed, the corrosion suppression effect cannot be expected even if the chemical conversion treatment is performed. On the other hand, since the above-mentioned base chemical conversion treatment film also contains a fluoride of a valve metal, it has a self-repairing effect. That is, after the fluoride of the valve metal is dissolved in the moisture in the environment, the surface of the base steel exposed from the film defect portion becomes a poorly soluble oxide or hydroxide and is reprecipitated. As a result, the film defect portion is filled, and thus the self-healing effect is exerted.

The chemical conversion treatment of the Zn-based alloy plated steel sheet of the present invention can be produced by chemically converting a Zn-based alloy plated steel sheet containing Al, and the corrosion resistance of the Zn-based alloy-plated steel sheet before the chemical conversion treatment is insufficient. Therefore, there is a concern that corrosion may occur during the storage or transportation of the Zn-based alloy plated steel sheet before the chemical conversion treatment or during the forming process. Therefore, by forming a substrate chemical conversion site on the Zn-based alloy plated steel sheet before the chemical conversion treatment in advance The film is treated to reliably prevent corrosion of the Zn-based alloy plated steel sheet before the chemical conversion treatment.

When the Al-containing Zn-based alloy plated steel sheet on which the underlying chemical conversion treatment film is formed is stored, transported, or formed (including fusion), some of the underlying chemical conversion treatment film may be peeled off, defective, or missing. Therefore, the surface of the Al-containing Zn-based alloy plated steel sheet is exposed, but the chemical conversion treatment film containing the fluorine-containing resin and the Group 4A metal compound is in direct contact with the exposed surface.

The substrate chemical conversion treatment film exhibits an effect of improving the adhesion between the Al-containing Zn-based alloy plated steel sheet and the chemical conversion treatment film. Therefore, it is considered that the chemical conversion treatment film formed at the portion where the substrate chemical conversion treatment film is peeled off generally has a reduced film adhesion. However, in the chemical conversion treatment film, Al is eluted from the directly contacted plating layer. By the chemical conversion of the Al which is eluted by the film, the corrosion resistance of the chemical conversion treatment film and the film adhesion are improved. As described above, in the portion where the substrate chemical conversion treatment film is peeled off, the adhesion between the chemical conversion treatment film and the Al-containing Zn-based alloy plated steel sheet is also high, and the corrosion resistance of the chemical conversion treatment film is improved. The mechanism for improving the corrosion resistance and the film adhesion of the chemical conversion treatment film by the presence of Al in the chemical conversion treatment film will be described below.

The substrate chemical conversion treatment film can be formed by drying a coating film of the underlying chemical conversion treatment liquid formed on the surface of the Al-containing Zn-based alloy plated steel sheet to be a substrate. The substrate chemical conversion treatment liquid contains: a valve metal salt, a fluoride ion, and water as a solvent. By drying the coating film of the substrate chemical conversion treatment liquid, the valve metal salt becomes a substrate chemical conversion treatment film An oxide or hydroxide or a fluoride of the valve metal contained.

Examples of valve metals include Ti, Zr, Hf, V, Nb, Ta, Mo, and W. The valve metal salt added to the substrate chemical conversion treatment liquid may be a halide or an oxyacid salt of a valve metal or the like. If the added valve metal salt is a fluoride, it can also function as a fluoride ion source.

Examples of the titanium salt include: K _n TiF ₆ (K: alkali metal or alkaline earth metal, n: 1 or 2), K ₂ [TiO(COO) ₂ ], (NH ₄ ) ₂ TiF ₆ , TiCl ₄ , TiOSO ₄ , Ti(SO ₄ ) ₂ , and Ti(OH) ₄ and the like. On the other hand, the fluoride ion source contained in the base chemical conversion treatment liquid may be a valve metal salt containing a fluorine atom or a soluble fluoride (for example, (NH ₄ )F or the like).

In the base chemical conversion treatment liquid, in order to stabilize the valve metal salt, it is preferred to add an organic acid having a chelate action. The organic acid can chelate the metal ion to stabilize the chemical conversion treatment liquid. Therefore, the amount of the organic acid to be added can be set to 0.02 or more in terms of the molar ratio of the organic acid/metal ion. Examples of the organic acid include tartaric acid, citric acid, citric acid, oxalic acid, malonic acid, lactic acid, acetic acid, and ascorbic acid. Among them, a polyhydric phenol such as tartaric acid or a phenolic acid such as citric acid stabilizes the base chemical conversion treatment liquid, and also exhibits a self-repairing action of the fluoride supplement, and is also effective for improving the adhesion.

Various metal orthophosphates or polyphosphates may be added to the substrate chemical conversion treatment liquid. The reason is that a soluble or poorly soluble metal phosphate or complex phosphate is contained in the formed substrate chemical conversion treatment film.

The soluble metal phosphate or composite phosphate is eluted from the substrate chemical conversion treatment film to the defect portion of the film, and the Al-containing Zn alloy as the substrate The plating component (Zn or Al, etc.) of the plated steel sheet reacts to precipitate insoluble phosphate. This complements the self-healing effect of titanium fluoride. Further, when the soluble phosphate is dissociated, the environment is slightly acidic, which promotes hydrolysis of the titanium fluoride and promotes formation of poorly soluble titanium oxide or hydroxide.

The metal of the soluble phosphate or complex phosphate may be an alkali metal, an alkaline earth metal, Mn or the like. The soluble phosphate or the composite phosphate may be added to the base chemical conversion treatment liquid in the form of various metal phosphates, or may be added to the chemical conversion treatment liquid by combining various metal salts with phosphoric acid, polyphosphoric acid, or phosphate. .

On the other hand, the poorly soluble metal phosphate or complex phosphate is dispersed in the substrate chemical conversion treatment film, which eliminates film defects and improves film strength. The metal of the poorly soluble phosphate or complex phosphate may be Al, Ti, Zr, Hf, Zn or the like. The poorly soluble phosphate or the composite phosphate may be added to the chemical conversion treatment liquid in the form of various metal phosphates, or may be added to the chemical conversion treatment liquid by combining various metal salts with phosphoric acid, polyphosphoric acid or phosphate.

An organic wax such as fluorine, polyethylene or styrene may be added to the base chemical conversion treatment liquid, or an inorganic lubricant such as cerium oxide, molybdenum disulfide or talc may be added. By adding these components, the lubricity of the substrate chemical conversion treatment film can be improved. It is considered that the low melting point organic wax exudes on the surface of the film when the coating film of the substrate chemical conversion treatment liquid is dried, and exhibits lubricity. On the other hand, it is considered that the organic wax having a high melting point or the inorganic lubricant is dispersed in the film, but is distributed on the surface of the film in the outermost layer of the film to exhibit lubricity.

When the elemental chemical conversion treatment film obtained by drying the coating film of the base chemical conversion treatment liquid is subjected to elemental analysis by fluorescent X-ray or Electron Spectroscopy for Chemical Analysis (ESCA), the measurement can be performed. The concentration of O and F contained in the film by the chemical conversion treatment of the substrate. The concentration ratio of these elements is preferably 1/100 or more in terms of F/O (atomic ratio). The reason is that the corrosion of the obtained chemical conversion treated steel sheet can be suppressed. In particular, when the element concentration ratio F/O (atomic ratio) is 1/100 or more, the occurrence of corrosion starting from the film defect portion is greatly reduced. The reason for this is presumed to be that a sufficient amount of titanium fluoride is contained in the substrate chemical conversion treatment film to exert a self-repairing effect.

[Chemical conversion treatment film]

The chemical conversion treatment film is formed on the surface of the above Al-containing Zn-based alloy plated steel sheet (chemical conversion treatment substrate). The surface of the chemical conversion treatment substrate may be subjected to a substrate chemical conversion treatment for forming a film or the like as a substrate, or may not be subjected to a substrate chemical conversion treatment. Further, when the surface chemical conversion treatment is not performed on the surface of the chemical conversion treatment substrate, a chemical conversion treatment film is directly formed on the surface of the chemical conversion treatment substrate. This chemical conversion treatment film improves the weather resistance, blackening resistance, workability (lubricity), and the like of the Al-containing Zn-based alloy plated steel sheet.

An object of the present invention is to improve various characteristics of weather resistance, water resistance, blackening resistance, film adhesion, and workability of a chemical conversion-treated Zn-based steel sheet. As described above, in order to improve the weather resistance (UV resistance) of the chemical conversion treatment film, a fluorine-containing resin may be used as the organic resin. The fluorine-containing resin is roughly classified into a solvent-based fluorine resin and a water-based fluorine resin. Using solvent system When the fluorine-containing resin forms a chemical conversion treatment film, the recovery of the volatile solvent is a problem, but when the water-based fluorine resin is used, such a problem does not occur. Therefore, the inventors of the present invention have attempted to form a chemical conversion-treated Zn-based steel sheet having excellent weather resistance, water resistance, blackening resistance, film adhesion, and workability by using a water-based fluororesin which is easy to handle.

As described above, according to the preliminary experiment of the present inventors, the reason why the water resistance is lowered when the chemical conversion treatment film is formed using the emulsion of the aqueous fluororesin is considered to be that the emulsifier used in the production of the emulsion of the aqueous fluororesin remains in the chemical conversion. The film was processed (refer to the reference experiment described later). Therefore, the inventors of the present invention have found that the emulsion of the aqueous fluorine-containing resin can be produced without using an emulsifier, thereby suppressing the decrease in water resistance of the chemical conversion treatment film. In addition, the present inventors have studied various water-based fluororesins and found that a fluorine-containing resin having a fixed amount of a hydrophilic functional group introduced therein can produce an aqueous emulsion almost without using an emulsifier, and can be easily formed into almost no The chemical conversion of the emulsifier treats the film.

Further, the present inventors have not only studied the suppression of the water resistance reduction of the chemical conversion treatment film, but also studied the improvement of the water resistance. Further, it has been found from various viewpoints that it is found that the water resistance of the chemical conversion treatment film can be remarkably improved by increasing the molecular weight of the aqueous fluorine-containing resin and crosslinking the aqueous fluororesin with the Group 4A metal compound.

Further, the present inventors have found that a 4A group metal compound can be further prepared by a chemical conversion treatment liquid based on a high molecular weight fluorine-containing resin having a hydrophilic functional group introduced therein, thereby forming weather resistance and water resistance. Chemical conversion treatment of skin, blackening resistance and film adhesion.

Further, the inventors of the present invention have studied the workability (lubricity) of the Zn-based steel sheet for chemical conversion treatment. Further, the inventors of the present invention have studied various methods and found that by dispersing resin particles having an average particle diameter of 0.1 μm to 10 μm in the chemical conversion treatment film, weather resistance, water resistance, and black resistance can be formed. A chemical conversion treatment film which is excellent in densification and film adhesion and excellent in workability (lubricity).

In the chemical conversion treatment film of the chemical conversion treatment Zn-based steel sheet according to the present invention, 1) the weather resistance (UV resistance) is improved by blending a fluorine-containing resin (preferably a fluorine-containing olefin resin). 2) by using a fluorine-containing resin into which a hydrophilic functional group is introduced, the use of an emulsifier at the time of emulsion production is minimized; and 3) increasing the molecular weight of the fluorine-containing resin; and 4) by using a Group 4A metal compound The fluorine-containing resin is crosslinked to improve weather resistance (UV resistance) and water resistance. Further, 5) the workability (lubricity) is improved by dispersing resin particles having an average particle diameter of 0.1 μm to 10 μm.

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

1) Water-based fluororesin

The chemical conversion treatment 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 treatment film is preferably in the range of 70% by mass to 99% by mass. As described above, by using a fluorine-containing resin as the organic resin constituting the chemical conversion treatment film, the weather resistance (UV resistance) of the chemical conversion treatment film can be improved.

The fluorine-containing resin is preferably a water-based fluorine resin which is easier to handle than the organic solvent-based fluororesin. The term "water-based fluororesin" means having a hydrophilic functional group. Fluorine resin. Preferred examples of the hydrophilic functional group include a carboxyl group, a sulfonic acid group, and a salt of these. Examples of the salt of a carboxyl group or a sulfonic acid group include an ammonium salt, an amine salt, an alkali metal salt and the like.

A preferred water-based fluororesin (preferably a fluorine-containing olefin resin) has a hydrophilic functional group of 0.05% by mass to 5% by mass. The fluorine-containing resin having a hydrophilic functional group of 0.05% by mass to 5% by mass can be made into an aqueous emulsion even if an emulsifier is hardly used. The chemical conversion treatment film containing almost no emulsifier can be made into a chemical conversion treatment film excellent in water resistance.

The content of the hydrophilic functional group in the aqueous fluorine-containing resin may be determined 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 the carboxyl group and the sulfonic acid group contained in the aqueous fluorine-containing resin is determined and multiplied by the molar mass to determine the water system. The total molar mass of the hydrophilic functional group contained in the fluorine-containing resin. The number average molecular weight of the aqueous fluorine-containing resin was measured by gel permeation chromatography (GPC).

The carboxyl group in the water-based fluororesin forms a hydrogen bond with the surface of the plating layer, and contributes to improving the adhesion between the chemical conversion treatment film and the surface of the plating layer. However, since H ^{+ is} difficult to dissociate, it is difficult to occur with the Group 4A metal compound. Cross-linking reaction. On the other hand, a sulfonic acid group in the aqueous fluorine-containing resin, although H ⁺ to dissociate readily, but if cross-linking reaction with a Group 4A metal compound to remain in the unreacted state in the film, there is adsorption of water molecules due Strong concern that the water resistance of the film is significantly lowered. Therefore, in order to utilize various features efficiently, it is preferable to contain both a carboxyl group and a sulfonic acid group in the water-based fluorine-containing resin. 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 the carboxyl group to the sulfonic acid group.

The number average molecular weight of the aqueous fluorine-containing resin (preferably fluorine-containing olefin resin) contained in the chemical conversion treatment film is preferably 1,000 or more, more preferably 10,000 or more, and particularly preferably 200,000 or more.

When the molecular weight of the water-based fluorine-containing resin contained in the chemical conversion treatment film is too small, the water permeability and water resistance of the chemical conversion treatment film cannot be sufficiently improved. In this case, moisture or a corrosive gas or the like easily penetrates the chemical conversion treatment film to reach the plated steel sheet, which may cause corrosion of the plated steel sheet. In addition, when a water-based fluororesin having a small molecular weight is used, a radical generated by the action of light energy or the like easily acts on the end of the polymer chain, so that the water-based fluororesin is easily hydrolyzed by the synergistic action of water or the like. Worry. In order to prevent these problems, the molecular weight of the aqueous fluorine-containing resin contained in the chemical conversion treatment film 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 aqueous fluorine-containing resin, the intermolecular force is enhanced, and the cohesive force of the chemical conversion treatment film is improved, so that the water resistance is improved. Further, since the bonds between the atoms in the main chain of the aqueous fluororesin are stabilized, hydrolysis is hard to occur.

On the other hand, the number average molecular weight of the water-based fluororesin contained in the chemical conversion treatment film is preferably 2,000,000 or less. When the number average molecular weight exceeds 2,000,000, there is a concern that the stability of the treatment liquid such as gelation may cause problems.

The content of the F atom in the aqueous fluorine-containing resin contained in the chemical conversion treatment film is preferably in the range of 7 mass% to 20 mass%. When the content of the F atom is less than 7% by mass, the resistance of the chemical conversion treatment film cannot be sufficiently improved. Waiting. On the other hand, when the content of the F atom exceeds 20% by mass, there is a concern that coating is difficult to form and adhesion and drying properties are lowered. The content of the F atom in the aqueous fluorine-containing resin can be measured by using a fluorescent X-ray analyzer.

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

Examples of the fluoroolefin include: tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, vinyl fluoride, vinylidene fluoride, pentafluoropropylene, 2,2,3,3-tetrafluoropropene, 3,3 , 3-trifluoropropene, bromotrifluoroethylene, 1-chloro-1,2-difluoroethylene, 1,1-dichloro-2,2-difluoroethylene, and the like. These fluoroolefins may be used singly or in combination of two or more. From the viewpoint of weather resistance (UV resistance), among these fluoroolefins, a perfluoroolefin such as tetrafluoroethylene or hexafluoropropylene or vinylidene fluoride is preferable. Chlorine-containing fluoroolefins such as chlorotrifluoroethylene have a concern that corrosion may occur due to chloride ions, which is not preferable.

Examples of the carboxyl group-containing monomer include unsaturated carboxylic acids represented by the following formula (1), or unsaturated carboxylic acids such as esters or acid anhydrides of these carboxylic acids.

(wherein R ¹ , R ² and R ^{3 are the} same or different and each is a hydrogen atom, an alkyl group, a carboxyl group or an ester group. n is in the range of 0 to 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, and cis. Butenedioic acid monoester, fumaric acid, fumaric acid monoester, 5-hexenoic acid, 5-heptenoic acid, 6-heptenoic acid, 7-octenoic acid, 8-decenoic acid , 9-decenoic acid, 10-undecenoic acid, 11-dodecenoic acid, 17-octadecenoic acid, oleic acid, and the like.

Other examples of the carboxyl group-containing monomer include 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 and 3-(2-allyloxybutoxycarbonyl). Propionic acid, 3-(2-vinyloxyethoxycarbonyl)propionic acid, 3-(2-vinyloxybutoxycarbonyl)propionic acid, and the like.

Examples of the sulfonic acid group-containing monomer include: vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, 2-propenylamine-2-methylpropanesulfonic acid, 2 -Methyl propylene methoxy ethane sulfonic acid, 3-methyl propylene methoxy propylene sulfonic acid, 4-methyl propylene methoxy butyl sulfonic acid, 3-methyl propylene oxy oxy hydroxy sulfonic acid , 3-propenyloxypropanesulfonic acid, allyloxybenzenesulfonic acid, methylallyloxybenzenesulfonic acid, isoprenesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, etc. .

The copolymer of the fluoroolefin and the hydrophilic functional group-containing monomer may be further copolymerized with other monomers copolymerizable as needed. Examples of other monomers copolymerizable include vinyl carboxylates, alkyl vinyl ethers, non-fluorine olefins, and the like.

The vinyl carboxylate can improve the compatibility and gloss, or increase the glass transition temperature. Examples of the vinyl carboxylate include: vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl hexanoate, tetraethylene carbonate, vinyl laurate , vinyl stearate, vinyl cyclohexate, vinyl benzoate, p-tert-butyl benzoate, and the like.

Alkyl vinyl ethers improve gloss and softness. 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 the non-fluorine olefins include ethylene, propylene, n-butene, isobutylene and the like.

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

By using a fluorine-containing resin having a hydrophilic functional group as the aqueous fluorine-containing resin constituting the chemical conversion treatment film, a chemical conversion treatment film containing almost no emulsifier can be easily formed. Chemical conversion site thus formed The skin film hardly exhibits deterioration of water resistance due to the residual of the emulsifier, and exhibits excellent water resistance.

2) Group 4A metal compounds

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

When a melamine resin, an isocyanate resin, or the like is used, crosslinking of the fluorine-containing resin has a problem that weathering deterioration easily occurs. For example, in a chemical conversion treatment film which is cured by using a melamine resin, weathering deterioration is immediately caused by oxidation or hydrolysis of an ester bond or a methyl ether bond. Further, the crosslinked structure is cleaved due to an acidic substance such as sulfate ions or nitrate ions contained in the acid rain, which also causes weather resistance deterioration. In the chemical conversion treatment film which is hardened using an isocyanate resin, the urethane bond formed by the crosslinked portion is weaker than the F bond, and thus the crosslinked structure is preferentially cleaved, resulting in weathering deterioration.

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

In addition, the Group 4A metal compound also improves film adhesion, water resistance and blackening resistance. In other words, the strong Al oxide present on the surface of the Al-containing Zn-based alloy plated steel sheet reduces the adhesion of the chemical conversion treatment film, but the chemical conversion treatment film contains a Group 4A metal compound, thereby suppressing the The adhesion of the film caused by the Al oxide is lowered. Further, the Group 4A metal compound also serves as a supply source of Group 4A metal ions which react with Al ions eluted by an etching reaction. Reaction product in the plating layer The interface with the chemical conversion treatment film is concentrated to improve initial corrosion resistance and blackening resistance. Examples of the Group 4A metal include: Ti or Zr, Hf, and the like.

The content of the Group 4A metal compound in the chemical conversion treatment film is preferably in the range of 0.1% by mass to 5% by mass based on the fluorine-containing resin in terms of metal. When the content is less than 0.1% by mass in terms of metal, the adverse effect due to the concentration of the Al oxide cannot be sufficiently suppressed, and the water-based fluororesin cannot be sufficiently crosslinked, and as a result, the water resistance of the chemical conversion treatment film cannot be sufficiently improved. . On the other hand, when the content is more than 5% by mass in terms of metal, the chemical conversion treatment film becomes porous, and there is a concern that workability and weather resistance are lowered.

The metal equivalent amount of the Group 4A metal compound in the chemical conversion treatment film can be measured by using a fluorescent X-ray analyzer.

As described above, Al which is eluted from the plating layer exists in the chemical conversion treatment film. This Al helps to improve corrosion resistance. The reason why the corrosion resistance is improved by the presence of Al is presumed to be the following mechanism. That is, 1) since the chemical conversion treatment liquid is weakly alkaline, when the chemical conversion treatment liquid is applied, the Al oxide and the metal Al contained in the plating layer are selectively eluted into the chemical conversion treatment liquid (the Zn hardly Dissolution). 2) In the pH range of the chemical conversion treatment liquid, Al is dissolved in the chemical conversion treatment liquid in the state of Al(OH) ₄ ^- . 3) When the chemical conversion treatment liquid is dried to form a chemical conversion treatment film, Al in the chemical conversion treatment liquid is incorporated into the chemical conversion treatment film by dehydration condensation or the like. 4) As a result, the insulation property or the density of the chemical conversion treatment film is improved, and the corrosion resistance is improved.

3) Resin particles

The chemical conversion treatment 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 on the surface of the chemical conversion treatment film function as a "roller" during the molding process, thereby improving the lubricity of the surface of the chemical conversion treatment film. As a result, the workability of the chemical conversion-treated Zn-based steel sheet can be improved.

The average particle diameter of the resin particles is preferably in the range of 0.1 μm 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 treatment film, and thus the lubricity of the surface of the chemical conversion treatment film cannot be efficiently improved. On the other hand, when the average particle diameter of the resin particles exceeds 10 μm, there is a concern that the resin particles are likely to fall off during the molding process. If the resin particles are detached as described above, the chemical conversion treatment film is defective, and the corrosion resistance is lowered. In the present specification, the average particle diameter of the resin particles means a particle diameter (median diameter) when the integrated value in the particle diameter distribution measured by the laser diffraction scattering method is 50%.

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

The type of the resin particles is not particularly limited, and heat resistance and dispersibility are From the viewpoint, polyethylene-fluororesin particles are preferred.

The polyethylene resin particles are excellent in dispersibility in a chemical conversion treatment liquid because the specific gravity is small (for example, 0.95), but the heat resistance is deteriorated because the melting point is low (for example, 123 ° C). When the resin particles having low heat resistance are used as described above, when the chemical conversion treatment liquid is heated and dried to form the chemical conversion treatment film, the shape of the particles may not be maintained. Specifically, when the chemical conversion treatment liquid is heated and dried at about 140 ° C to 180 ° C, the polyethylene resin particles are melted. When the resin particles are melted in this manner, the resin particles cannot function as a "roller", and the improvement in lubricity cannot be promoted.

On the other hand, the fluororesin particles have a high melting point (for example, 330 ° C) and are excellent in heat resistance, but the dispersibility in the chemical conversion treatment liquid is deteriorated due to a large specific gravity (for example, 2.2). When the resin particles having low dispersibility in the chemical conversion treatment liquid are used in this manner, it is difficult to uniformly disperse the resin particles in the chemical conversion treatment film.

The polyethylene-fluororesin particles are obtained by bringing the fluororesin fine particles into contact with the polyethylene resin particles softened by heating, and bonding (adsorbing) the fluororesin fine particles to the surface of the polyethylene resin particles. By incorporating fluororesin fine particles on the surface of the polyethylene resin particles, it is possible to simultaneously have heat resistance and dispersibility in the chemical conversion treatment liquid even when heated at about 140 ° C to 180 ° C to maintain the shape of the particles. (specific gravity: for example, 1.1). Further, by incorporating fluororesin fine particles on the surface of the polyethylene resin particles, weather resistance can be improved.

Figure 1 is a polyethylene resin particle or heated to 50 ° C or 150 ° C The SEM image (top view) of the chemical conversion treatment of the polyethylene-fluororesin particles. Fig. 1A is an SEM image of a chemical conversion treatment film 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. 1B is an SEM image of a chemical conversion treatment 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. 1C is an SEM image of a chemical conversion treatment film 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. 1D is an SEM image of a chemical conversion treatment film 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 the polyethylene resin particles is dried at 50 ° C, the shape of the polyethylene resin particles can be maintained, and the polyethylene resin particles are lifted from the surface of the chemical conversion treatment film (refer to the figure). Medium "PE"). On the other hand, as shown in FIG. 1B, when the chemical conversion treatment liquid containing the 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. (Refer to "PE" in the figure).

As shown in FIG. 1C, when the chemical conversion treatment liquid containing the polyethylene-fluororesin particles is dried at 50 ° C, the shape of the polyethylene-fluororesin particles can be maintained, and the polyethylene-fluororesin particles are chemically converted into a film. Surface protrusion (refer to "PE-F" in the figure). Further, as shown in FIG. 1D, when the chemical conversion treatment liquid containing the polyethylene-fluororesin particles is dried at 150 ° C, a part of the polyethylene-fluororesin particles (attached to the fluororesin microparticles) The polyethylene-fluororesin particles having a small amount are melted (see "PE" in the figure), but the remaining polyethylene-fluororesin (polyethylene-fluororesin having a large amount of fluororesin particles attached) is not melted (refer to the figure). Medium "PE-F").

As described above, when the drying temperature is low, there is no problem even if the polyethylene resin particles are used. However, when the drying temperature is high, polyethylene-fluororesin particles are preferably used. Further, from the viewpoint of weather resistance, it is also preferred 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 in the range of 0.1 μm to 10 μm. Examples of commercially available polyethylene resin particles that can be used include: HYTEC E-9016, HYTEC E-1000 (both Toho Chemical Co., Ltd.), CJ-172B, and CJ-137 (all are Xingyang Chemical Co., Ltd. ), PERMARIN KUE-4, PERMARIN KUE-5 (all are Sanyo Chemical Industry Co., Ltd.). On the other hand, the average particle diameter of the fluororesin fine particles constituting the polyethylene-fluororesin particles may be appropriately set in accordance with 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 proportion of the fluororesin in the polyethylene-fluororesin particles is preferably in the range of 5 mass% to 40 mass%. When the proportion of the fluororesin is less than 5% by mass, the effect due to adhesion of the fluororesin may not be sufficiently exhibited. On the other hand, when the ratio of the fluororesin exceeds 40% by mass, there is a concern that the polyethylene-fluororesin particles are likely to fall off from the chemical conversion treatment 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 treatment film contains polyethylene-fluororesin particles, the chemical conversion treatment film preferably further contains a polyethylene resin. Usually, the polyethylene resin coats all or a part of the region where the polyethylene-fluororesin particles are not protruded on the surface of the chemical conversion treatment film (see FIG. 2C). The polyethylene resin covering the surface of the chemical conversion treatment film is a polyethylene resin which oozes to the surface of the chemical conversion treatment film in the production step. The polyethylene resin particles together with the polyethylene-fluororesin particles improve the lubricity of the surface of the chemical conversion treatment film, thereby further improving the processability of the chemical conversion treatment Zn-based plated steel sheet.

The content of the polyethylene resin in the chemical conversion treatment film is preferably in the range of 0.1% by mass to 16% by mass based on the chemical conversion treatment film. When the content of the polyethylene resin is less than 0.1% by mass, the effect of the polyethylene resin cannot be sufficiently exhibited. On the other hand, when the content of the polyethylene resin exceeds 16% by mass, there is a concern that the weather resistance is lowered.

5) Phosphate

The chemical conversion treatment film preferably further comprises a phosphate. The phosphate reacts with the surface of the plating layer of the Al-containing Zn-based alloy plated steel sheet to improve the adhesion of the chemical conversion treatment film to the Al-containing Zn-based alloy plated steel sheet.

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

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

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

6) decane coupling agent

The chemical conversion treatment film preferably further comprises a decane coupling agent. By blending the decane coupling agent, the adhesion of the chemical conversion coating film can be further improved. The decane coupling agent can be used: in the functional group including an amine group, an epoxy group, a decyl group, an acryloxy group, a methacryloxy group, an alkoxy group, a vinyl group, a styryl group, an isocyanate group, a chloropropyl group or the like. One or more kinds of decane compounds.

The content of the decane coupling agent in the chemical conversion treatment film is preferably in the range of 0.5% by mass to 5% by mass based on the fluorine-containing resin. When the content of the decane coupling agent is less than 0.5% by mass, the adhesion of the chemical conversion treatment film cannot be sufficiently improved. On the other hand, when the content of the decane coupling agent exceeds 5% by mass, the film adhesion is saturated, and the above improvement is not observed.

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

The film thickness of the chemical conversion treatment film is preferably in the range of 0.5 μm to 10 μm. When the film thickness is less than 0.5 μm, corrosion resistance or resistance cannot be sufficiently imparted. Color and so on. On the other hand, even if the film thickness exceeds 10 μm, the performance improvement accompanying the increase in the film thickness cannot be expected.

2. Method for producing chemical conversion treatment of Zn-plated steel sheet

The method for producing the chemical conversion treatment Zn-based steel sheet according to the present invention is not particularly limited, and can be produced, for example, by the following method.

The method for producing a chemical conversion-treated Zn-based steel sheet according to the present invention includes: 1) a first step of preparing a Zn-based alloy plated steel sheet containing Al (chemical conversion treatment substrate), 2) a second step of preparing a chemical conversion treatment liquid, and 3 The third step of forming a chemical conversion treatment film on the surface of the Al-containing Zn-based alloy plated steel sheet. Further, when the chemical conversion treatment film is formed on the surface of the Al-containing Zn-based alloy plated steel sheet by interposing the substrate chemical conversion treatment film, before the third step of forming the chemical conversion treatment film, further including: in the Al-containing Zn system The surface of the alloy plated steel sheet forms a step of chemically transforming the film by the substrate.

[Preparation of chemical conversion processing substrate]

In the first step, the above Al-containing Zn-based alloy plated steel sheet is prepared as a chemical conversion treatment substrate.

[Preparation of chemical conversion treatment liquid]

In the second step, a chemical conversion treatment liquid containing a fluorine-containing resin (preferably a fluorine-containing olefin resin) having a hydrophilic functional group, a Group 4A metal compound, and resin particles is prepared.

The chemical conversion treatment liquid may be added with a Group 4A metal compound and resin particles (for example, polyethylene-fluororesin particles) in an aqueous emulsion of a fluorine-containing resin (preferably a fluorine-containing olefin resin) having the above hydrophilic functional group. System Ready. As the Group 4A metal compound to be added to the chemical conversion treatment liquid, an oxoacid salt or a fluoride, a hydroxide, an organic acid salt, a carbonate, a peroxy salt or the like of a Group 4A metal can be used. Examples of the oxyacid salt include a hydrogenate, an ammonium salt, an alkali metal salt, an alkaline earth metal salt, and the like. Further, if necessary, a polyethylene resin particle, a phosphate, a decane coupling agent or the like may be added to the chemical conversion treatment liquid.

The number average molecular weight of the fluorine-containing resin contained in the aqueous emulsion is preferably 1,000 or more, more preferably 10,000 or more, and particularly preferably 200,000 or more. The reason is that water resistance is imparted to the chemical conversion treatment film as described above. On the other hand, the number average molecular weight of the fluorine-containing resin is preferably 2,000,000 or less from the viewpoint of the stability of the treatment liquid.

The fluorine-containing resin preferably has a hydrophilic functional group of 0.05% by mass to 5% by mass from the viewpoint of preparing an aqueous emulsion using almost no 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 is more than 1% by mass, when the chemical conversion treatment film is formed in the third step, there is a concern that the emulsifier remains in the chemical conversion treatment film due to the drying temperature. If the emulsifier remains in the chemical conversion treatment film as described above, the water resistance of the chemical conversion treatment film is remarkably lowered, which is not preferable. As described above, in the case of the fluorine-containing resin having a hydrophilic functional group, the aqueous emulsion can be prepared even when the amount of the emulsifier is 1% by mass or less.

The emulsifier which can 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 perfluorodecanoic acid, from the viewpoint of weather resistance and water resistance. In addition, known fluorine-based surfactants can also be used as Emulsifier.

The content of the fluorine-containing resin in the chemical conversion treatment liquid is preferably in the range of 10 parts by mass to 70 parts by mass based on 100 parts by mass of the water. When the content of the fluorine-containing resin is less than 10 parts by mass, the amount of evaporation of water during drying increases, and the film forming property and compactness of the chemical conversion coating film may be lowered. On the other hand, when the content of the fluorine-containing resin exceeds 70 parts by mass, the storage stability of the chemical conversion treatment liquid may be lowered.

The content of the oxo acid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxy salt of the Group 4A metal in the chemical conversion treatment liquid is preferably in terms of metal in terms of 100 parts by mass of the fluorine resin. 0.1 parts by mass to 5 parts by mass. When the content of these salts is less than 0.1 part by mass, the crosslinking reaction and the reaction with the surface of the plating layer are insufficient, and the water resistance and the film adhesion of the chemical conversion treatment film cannot be sufficiently improved. On the other hand, when the content of these salts exceeds 5 parts by mass, the crosslinking reaction may be carried out, and the storage stability of the chemical conversion treatment liquid may be lowered.

The content of the resin particles (for example, polyethylene-fluororesin particles) in the chemical conversion treatment liquid is preferably 0.5 parts by mass to 20 parts by mass based on 100 parts by mass of the solid content (such as a fluorine-containing resin or a Group 4A metal compound). Within the scope. As described above, when the content of the resin particles is less than 0.5% by mass, the lubricity of the chemical conversion treatment film cannot be sufficiently improved. On the other hand, when the content of the resin particles exceeds 20% by mass, the weather resistance of the chemical conversion treatment film may be lowered.

In addition to the polyethylene-fluororesin particles, in the case where the polyethylene resin particles are further added to the chemical conversion treatment liquid, in the chemical conversion treatment liquid The content of the polyethylene resin particles is preferably in the range of 0.1 part by mass to 16 parts by mass based on 100 parts by mass of the solid content. 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 sufficiently exhibited. On the other hand, when the amount added exceeds 16% by mass, there is a concern that the weather resistance of the chemical conversion treatment film is lowered. Further, the average particle diameter of the polyethylene resin particles is preferably in the range of 0.1 μm 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 treatment film, and the polyethylene resin cannot be oozing out to the surface of the chemical conversion treatment film. On the other hand, when the average particle diameter exceeds 10 μm, there is a concern that the polyethylene resin particles fall off during the drying of the chemical conversion treatment liquid.

When the phosphate is added to the chemical conversion treatment liquid, the content of the phosphate in the chemical conversion treatment liquid is preferably in the range of 0.05 parts by mass to 3 parts by mass in terms of P based on 100 parts by mass of the fluorine-containing resin. When the content of the phosphate is less than 0.05 parts by mass, the adhesion of the chemical conversion treatment film cannot be sufficiently improved. On the other hand, when the content of the phosphate exceeds 3 parts by mass, the reaction with the Group 4A metal compound proceeds excessively, which may impair the crosslinking effect of the Group 4A metal compound.

When the decane coupling agent is added to the chemical conversion treatment liquid, the content of the decane coupling agent in the chemical conversion treatment liquid is preferably in the range of 0.5 parts by mass to 5 parts by mass based on 100 parts by mass of the fluorine-containing resin. When the content of the decane coupling agent is less than 0.5 part by mass, the adhesion of the chemical conversion treatment film cannot be sufficiently improved. On the other hand, when the content of the decane coupling agent exceeds 5 parts by mass, the film adhesion is saturated, and the above improvement is not observed. In addition, There is also concern that the stability of the chemical conversion treatment liquid is lowered.

In the chemical conversion treatment liquid, an etchant or an inorganic compound, an inorganic lubricant, a coloring pigment, a dye or the like may be added as an additional component as needed. Fluoride or the like can be used as the etchant. The etchant further enhances the adhesion of the chemical conversion treatment film by activating the surface of the plating layer. Inorganic compounds (oxides, phosphates, etc.) such as Mg or Ca, Sr, V, W, Mn, B, Si, Sn, etc., make the chemical conversion treatment film denser and improve water resistance. An inorganic lubricant such as molybdenum disulfide or talc further improves the lubricity of the chemical conversion treatment film and the workability of the chemical conversion treatment of the Zn-based steel sheet. Further, by blending an inorganic pigment, an organic pigment, an organic dye or the like, a specific color tone can be imparted to the chemical conversion treatment film.

[Formation of chemical conversion treatment film]

In the third step, a chemical conversion treatment film is formed on the surface of the Al-containing Zn-based alloy plated steel sheet prepared in the first step. In order to form a chemical conversion treatment film, the chemical conversion treatment liquid prepared in the second step may be applied to the surface of the Al-containing Zn-based alloy plated steel sheet prepared in the first step and dried.

The method of applying the chemical conversion treatment 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, a dipping and pulling method, and the like.

The drying of the chemical conversion treatment liquid can be carried out at room temperature. However, in consideration of continuous operation, it is preferably kept at 50 ° C or higher to shorten the drying time. However, when it is kept above 300 ° C, organic components are thermally decomposed to cause chemical conversion. Concerns about the reduction in performance of the film. 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 chemical conversion treatment excellent in water resistance can be formed without containing an emulsifier. Membrane.

Fig. 2 is a schematic cross-sectional view showing a process of forming a chemical conversion treatment film. Fig. 2 shows a form in which a chemical conversion treatment liquid to which polyethylene-fluororesin particles and polyethylene resin particles are added is applied.

First, a chemical conversion treatment liquid is applied onto the surface of the Al-containing Zn-based alloy plated steel sheet 110 to form a coating film 120 of a chemical conversion treatment liquid (see FIG. 2A). Polyethylene-fluororesin 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, water is evaporated to form a chemical conversion treatment film 120 ′ (see FIG. 2B ). At this time, most of the polyethylene-fluororesin particles 122 and the polyethylene resin particles 124 protrude from the surface of the chemical conversion treatment film 120'. 3A is an SEM image (plan view) of a chemical conversion treatment film obtained by drying a coating film of a chemical conversion treatment liquid at 50 °C. Although the polyethylene-fluororesin particles and the polyethylene resin particles could not be distinguished, it was found that these particles protruded from the surface of the chemical conversion treatment film (see "PE-F or PE" in the drawing).

Next, when the temperature is raised to about 150 ° C, the polyethylene resin particles 124 are melted, and the polyethylene resin oozes to the surface (see FIG. 2C). The exuded polyethylene resin 124' is coated with all or a portion of the surface of the chemical conversion treated film 120'. On the other hand, the polyethylene-fluororesin particles 122 are not melted and remain in the original state. Figure 3B shows the coating film of the chemical conversion treatment liquid at 150 ° C The SEM image (plan view) of the chemical conversion treatment film after drying was performed. It is understood that only the polyethylene-fluororesin particles are protruded from the surface of the chemical conversion treatment film (see "PE-F" in the drawing). Fig. 3C is an SEM image (cross-sectional view) of polyethylene-fluororesin particles protruding from the surface of the chemical conversion treatment film. The particles protruding from the surface of the chemical conversion treatment film were confirmed to be polyethylene-fluororesin particles by fluorescent X-ray analysis. Fig. 4 is a fluorescent X-ray spectrum of polyethylene-fluororesin particles protruding from the surface of the chemical conversion treatment film.

According to the above procedure, the chemical conversion-treated Zn-based steel sheet of the present invention which is excellent in weather resistance, water resistance, blackening resistance, film adhesion, and workability can be produced.

[Formation of substrate chemical conversion treatment film]

In the step of forming the substrate chemical conversion treatment film, the substrate chemical conversion treatment liquid is applied onto the surface of the Al-containing Zn-based alloy plated steel sheet prepared in the first step to form a coating film before the chemical conversion treatment film is formed. The substrate chemical conversion treatment liquid can be applied, for example, by a roll coating method, a spin coating method, a spray method, or the like. The coating amount of the substrate chemical conversion treatment liquid is preferably adjusted so that the valve metal adhesion amount is 1 mg/m ² or more. The reason is that the obtained chemical conversion treated steel sheet is provided with sufficient corrosion resistance. Further, the coating amount of the base chemical conversion treatment liquid is preferably adjusted so that the thickness of the formed base chemical conversion treatment film is 3 nm or more and 1000 nm or less. When the thickness is 3 nm or more, sufficient corrosion resistance is exhibited. When the thickness exceeds 1000 nm, there is a fear that cracks may occur due to stress when the steel sheet is to be formed.

The coating film formed on the surface of the Al-containing Zn-based alloy plated steel sheet is not The substrate is subjected to water washing and dried, whereby a substrate chemical conversion treatment film can be formed. It can also be dried at normal temperature. If continuous operation is considered, it is preferable to keep it at 50 ° C or more to shorten the drying time. However, at a drying temperature exceeding 200 ° C, the organic component contained in the chemical conversion treatment film is thermally decomposed to impair the properties imparted by the organic component.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

Instance [Example] 1. Preparation of Zn-based steel plate by chemical conversion treatment

The following three types of Zn-based alloy-plated steel sheets containing molten Al were produced by using SPCC having a thickness of 0.8 mm as a substrate. In the present example, these three kinds of molten Al-containing Zn-based alloy plated steel sheets were used as the chemical conversion treatment substrate.

[Al-containing Zn-based alloy plated steel sheet A]

. Molten Zn-0.18 mass% Al alloy plated steel plate

. Plating adhesion amount 45 g/m ²

[Al-containing Zn-based alloy plated steel plate B]

. Molten Zn-6 mass% Al-3 mass% Mg alloy plated steel sheet

. Plating adhesion amount 45 g/m ²

[Al-containing Zn-based alloy plated steel plate C]

. Molten Zn-55 mass% Al alloy plated steel plate

. Plating adhesion amount 45 g/m ²

The chemical conversion treatment liquid having the composition shown in Table 1 was applied to the surface of each Al-containing Zn-based alloy plated steel sheet, and dried at a plate temperature of 140 ° C. Drying was carried out to form a chemical conversion treatment film having a film thickness of 2.0 μm.

The chemical conversion treatment liquid of the treatment liquid No. 1 to No. 12 shown in Table 1 is a water-based emulsion containing a specific amount of a fluorine-containing resin having a carboxyl group and a sulfonic acid group, and an emulsifier (nonvolatile content: 25% by mass) Referring to Table 2), a Group 4A metal compound, polyethylene-fluororesin particles (resin particles), or the like is added. The chemical conversion treatment liquid of the treatment liquid No. 13 is a water-based emulsion containing a urethane resin and an emulsifier (25% by mass of a nonvolatile component; see Table 2), and a 4A group metal compound or a polyethylene-fluororesin is added. It is prepared by particles (resin particles) or the like.

The aqueous emulsion containing a fluorine-containing resin can be obtained by subjecting a component to a copolymerization reaction by adding a specific amount of a fluoroolefin, a carboxyl group-containing monomer, a sulfonic acid group-containing monomer, and an emulsifier to an aqueous solvent. An aqueous emulsion containing a urethane resin is PR135 (Sumika Bayer Urethane Co., Ltd.). The decane coupling agent was A-1891 (Momentive Performance Materials Japan).

The amount of the Group 4A metal, phosphate, and decane coupling agent relative to the organic resin in the chemical conversion treatment film of each of the chemical conversion treatment Zn-based steel sheets was measured using a fluorescent X-ray analyzer. The content of the phosphate and decane coupling agent was calculated from the measured values of P and Si. In addition, the area occupation ratio of the polyethylene-fluororesin particles in the surface of the chemical conversion treatment film of each of the chemical conversion treatment-coated Zn-based steel sheets was measured using a scanning electron microscope. For each chemical conversion treatment liquid, the amount of the Group 4A metal, phosphate and decane coupling agent relative to the organic resin in the formed chemical conversion treatment film, and the area of the polyethylene-fluororesin particles in the surface of the chemical conversion treatment film. The occupancy rate is shown in Table 3.

2. Evaluation of chemical conversion treatment of Zn-plated steel sheets (1) Promoting weather resistance test

A test piece was cut out from each of the chemical conversion-treated Zn-based steel sheets, and a weather resistance test (a xenon method) was carried out in accordance with JIS K5600-7-7:2008. This test In the middle, the step of spraying the water for 18 minutes during the irradiation of the xenon arc lamp for 120 minutes is set to one cycle (2 hours), and the step is repeated from 0 cycles to 1000 cycles (0 cycles, 500 cycles). , 1000 cycles).

(2) Evaluation of weather resistance

The thickness of the chemical conversion treatment film before and after the weathering test was measured for each chemical conversion-treated Zn-based steel sheet by cross-sectional microscopy, and the coating film residual ratio was determined. In the chemical conversion treatment of the Zn-based steel sheet, the case where the coating film residual ratio is 95% or more is evaluated as "?", and when the coating film residual ratio is 80% or more and less than 95%, it is evaluated as "○", and the coating is applied. When the film residual ratio is 60% or more and less than 80%, it is evaluated as "△", and when the coating film residual ratio is 30% or more and less than 60%, it is evaluated as "▲", and the residual film rate is less than 30%. The evaluation is "X".

(3) Evaluation of blackening resistance

For each chemical conversion treatment, the Zn-based steel sheet was measured for the difference in luminance (ΔL* value) on the surface of the chemical conversion treatment film before and after the weathering test, and the blackening resistance was evaluated. In each of the chemical conversion treatment-coated Zn-based steel sheets, the case where the luminance difference (ΔL* value) was 1 or less was evaluated as “◎”, and the case where the luminance difference (ΔL* value) exceeded 1 or 2 was evaluated as “○”. In the case where the luminance difference (ΔL* value) exceeds 2 and 5 or less, it is evaluated as “Δ”, and when the luminance difference (ΔL* value) exceeds 5 and 10 or less, it is evaluated as “▲”, and the luminance difference is ( When the ΔL* value exceeds 10, it is evaluated as "X".

(4) Evaluation of corrosion resistance of flat portion

For each chemical conversion treated Zn-based steel sheet, a salt spray test was carried out using a test piece after the accelerated weathering test (according to JIS Z2371; 120 small When), the white rust generation area ratio of the flat portion was evaluated. In the Zn-based steel sheet for chemical conversion treatment, the case where the white rust generation area ratio is 5% or less is evaluated as "◎", and the case where the white rust generation area ratio exceeds 5% and 10% or less is evaluated as "○". When the area ratio of white rust generation is more than 10% and 30% or less, it is evaluated as "△", and when the area ratio of white rust is more than 30% and 50% or less, it is evaluated as "▲", and the area ratio of white rust is more than 50%. The situation is evaluated as "X".

(5) Evaluation of lubricity

A test piece having a width of 30 mm and a length of 300 mm was cut out from each of the chemical conversion-treated Zn-based steel sheets. The SKD11 mold was brought into contact with both sides of each test piece, and the test piece was pulled 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, and the lubricity was evaluated. For the chemical conversion treatment of the Zn-based steel sheet, the case where the pulling force is 200 kgf or less is evaluated as "◎", and the case where the drawing force exceeds 200 kgf and 250 kgf or less is evaluated as "○", and the pulling force is exceeded. The case of 250 kgf and 300 kgf or less was evaluated as "△", and the case where the pulling force exceeded 300 kgf and 400 kgf or less was evaluated as "▲", and the case where the pulling force exceeded 400 kgf was evaluated as "x".

(6) Evaluation results

The types of chemical conversion treatment substrates for the chemical conversion treatment of the Zn-based steel sheets (Examples 1 to 21, Comparative Examples 1 to 18), the types of treatment liquids used, and the weather resistance test and blackening resistance test The evaluation results of the flat portion corrosion resistance test and the lubricity test are shown in Tables 4 and 5.

The weather resistance was evaluated by promoting the residual film coating rate of the chemical conversion treatment film after the weather resistance test. In the chemical conversion-treated Zn-based steel sheets of Comparative Example 6, Comparative Example 12, and Comparative Example 18 in which the chemical conversion treatment film containing the urethane resin was formed, in 500 cycles (corresponding to exposure for 5 years outside the house) The chemical conversion treatment film disappears. Further, in the chemical conversion treatment of the Zn-based steel sheets of Comparative Example 4, Comparative Example 10, and Comparative Example 16 in which the chemical conversion treatment film containing the excessively large polyethylene-fluororesin particles was formed, the polyethylene-fluororesin particles were also self-chemically The conversion treatment peels off the film, and thus the weather resistance is deteriorated. On the other hand, in the chemical conversion treatment of the Zn-based steel sheet of Examples 1 to 21 in which the chemical conversion treatment film containing a specific amount of the fluorine-containing resin having a hydrophilic functional group and the Group 4A metal compound is formed, 1000 cycles are repeated. (Equivalent to exposure to outside the house for 10 years), the film thickness of the chemical conversion treatment film hardly changed.

Blackening resistance was evaluated by promoting the difference in luminance (ΔL* value) before and after the weather resistance test. In the chemical conversion-treated Zn-based steel sheets of Comparative Example 6, Comparative Example 12, and Comparative Example 18 in which the chemical conversion treatment film containing the urethane resin was formed, the blackening of the plating layer progressed as the number of cycles increased. , which causes the brightness to decrease. On the other hand, in the chemical conversion treatment of the Zn-based steel sheet of Examples 1 to 21 in which the chemical conversion treatment film containing a specific amount of the fluorine-containing resin having a hydrophilic functional group and the Group 4A metal compound is formed, 1000 cycles are repeated. After the equivalent of 10 years of exposure outside the house, the brightness has hardly decreased.

The corrosion resistance was evaluated by the area ratio of white rust generated after the salt spray test. In forming a chemical conversion treatment film containing a urethane resin In the chemical conversion-treated Zn-based steel sheets of Comparative Example 6, Comparative Example 12, and Comparative Example 18, although the corrosion resistance before the weather resistance test was promoted was good, the corrosion resistance was remarkably lowered as the film disappeared. Further, in Comparative Example 1, Comparative Example 2, Comparative Example 7, Comparative Example 8, Comparative Example 13, and Comparative Example 14 in which a chemical conversion treatment film containing an excessive amount or a small amount of a fluorine-containing resin having a hydrophilic functional group was formed. Chemical conversion treatment of Comparative Example 3, Comparative Example 5, Comparative Example 9, Comparative Example 11, Comparative Example 15, and Comparative Example 17 in which a Zn-based steel sheet was chemically transformed and a chemical conversion treatment film containing no Group 4A metal compound was formed. In the Zn-based steel sheet, the corrosion resistance deteriorated from the time before the accelerated weather resistance test. On the other hand, in the chemical conversion treatment of the Zn-based steel sheet of Examples 1 to 21 in which the chemical conversion treatment film containing a specific amount of the fluorine-containing resin having a hydrophilic functional group and the Group 4A metal compound is formed, 1000 cycles are repeated. (Equivalent to 10 years of exposure outside the house), corrosion resistance is also good.

The lubricity was evaluated by the pulling force required when the test piece to which the load was applied was drawn. In the chemical conversion treatment of the Zn-based steel sheets of Comparative Example 1, Comparative Example 7, and Comparative Example 13, since the amount of the polyethylene-fluororesin particles in the chemical conversion treatment film was small, the lubricity was deteriorated. Similarly, the chemical conversion-treated Zn-based steel sheets of Comparative Example 5, Comparative Example 11 and Comparative Example 17 which did not contain polyethylene-fluororesin particles also deteriorated in lubricity. Further, in the chemical conversion-treated Zn-based steel sheets of Comparative Example 6, Comparative Example 12, and Comparative Example 18, since the average particle diameter of the polyethylene-fluororesin particles was small and was buried in the chemical conversion treatment film, the lubricity was deteriorated. On the other hand, in the formation of a chemical conversion comprising a specific amount of the average particle diameter of the polyethylene-fluororesin particles within a specific range In the chemical conversion treatment of the chemical conversion treatment of the chemical treatment of Examples 1 to 21, the lubricity was good.

According to the above results, the chemical conversion-treated Zn-based steel sheet of the present invention is excellent in weather resistance, blackening resistance, and workability (lubricity).

[Reference experiment]

The reference experiment is a result of investigating the relationship between the amount of the Group 4A metal compound in the fluororesin film, the amount of the emulsifier, and the moisture permeability.

A specific amount of 4A is added to an aqueous emulsion containing a hydrophilic functional group-containing monomer and a fluorine-containing resin having a hydrophilic functional group prepared by adding an emulsifier to 1% by mass. As the group metal compound, the prepared chemical conversion treatment liquid was applied onto the surface of the plated steel sheet by a bar coater, and dried at a plate temperature of 140 ° C to form a fluororesin film having a film thickness of 30 μm. The fluororesin film was peeled off from the plated steel sheet, and cut to a specific size to prepare a test piece. The moisture permeability (measurement conditions, temperature: 40 ° C ± 0.5 ° C, relative humidity: 90% ± 2%, 24 hours) was measured for each test piece (free fluororesin film) in accordance with JIS Z0208.

Fig. 5 is a graph showing the relationship between the amount of the Group 4A metal and the moisture permeability in the fluororesin film. According to the graph, the moisture permeability of the fluororesin film can be remarkably reduced by setting the amount of the Group 4A metal in the fluororesin film to 0.1% by mass or more.

In an aqueous emulsion containing a hydrophilic functional group-containing fluororesin prepared by adding a hydrophilic functional group-containing monomer to a content of 1% by mass and adding a specific amount of an emulsifier, the final concentration is expressed in terms of metal. Adding a Group 4A metal compound in a 1% by mass manner, chemically converting the preparation The treatment liquid was applied onto the surface of the plated steel sheet by a bar coater, and dried at a plate temperature of 140 ° C to form a fluororesin film having a film thickness of 30 μm. The fluororesin film was peeled off from the plated steel sheet, and cut to a specific size to prepare a test piece. The moisture permeability (measurement conditions, temperature: 40 ° C ± 0.5 ° C, relative humidity: 90% ± 2%, 24 hours) was measured for each test piece (free fluororesin film) in accordance with JIS Z0208.

Fig. 6 is a graph showing the relationship between the concentration of the emulsifier in the aqueous emulsion of the fluorine resin and the moisture permeability of the fluororesin film. According to this graph, the moisture permeability of the fluororesin film can be remarkably lowered by setting the concentration of the emulsifier in the emulsion to 1% by mass or less.

From the above results, it is understood that the fluororesin film having a large amount of the Group 4A metal compound and having a small amount of the emulsifier remaining is excellent in water resistance.

The present application claims priority based on Japanese Patent Application No. 2011-199465, filed on Sep. 13, 2011. The contents described in the specification and drawings of the application are all incorporated in the specification.

[Industrial availability]

The chemical conversion treatment of the Zn-based steel sheet of the present invention is excellent in weather resistance, water resistance, blackening resistance, film adhesion, and workability, and thus is effectively used for various applications such as packaging materials. For example, the chemical conversion treatment Zn-based steel sheet of the present invention can be preferably used for: 1) a plastic house or a steel pipe for agricultural sheds, a steel, a pillar, a beam, and a conveying member; 2) a sound insulating wall, a soundproof wall, and a sound absorbing sound. Wall, snow-proof wall, guard rail, high-column, protective grille, pillar; 3) rail vehicle components, wire-hanging components, electrical equipment components, safety environment components, structural members, solar gantry, etc.

The Al-containing Zn-based alloy plated steel sheet is sufficiently adhered to the coating film under high temperature and high humidity, and is excellent in corrosion resistance. Therefore, the chemical conversion treatment Zn-based steel sheet of the present invention is particularly suitable for use as an outer packaging material used in a high-temperature and high-humidity environment.

110‧‧‧Al-containing Zn-based alloy plated steel plate

120‧‧‧ Coating film of chemical conversion treatment liquid

120'‧‧‧Chemical conversion treatment film

122‧‧‧Polyethylene-fluororesin particles

124‧‧‧ Polyethylene resin particles

124'‧‧‧Exuded polyethylene resin

1A to 1D are SEM images of a chemical conversion treatment film containing polyethylene resin particles or polyethylene-fluororesin particles heated at a specific temperature.

2A to 2C are schematic cross-sectional views showing a process of forming a chemical conversion treatment film.

3A to 3C are SEM images showing a process of forming a chemical conversion treatment film.

Fig. 4 is a fluorescence X-ray spectrum of polyethylene-fluororesin particles in a chemical conversion treated film.

Fig. 5 is a graph showing the relationship between the amount of the Group 4A metal and the moisture permeability in the fluororesin film.

Fig. 6 is a graph showing the relationship between the concentration of the emulsifier in the emulsion of the fluorine resin and the moisture permeability of the fluororesin film.

110‧‧‧Al-containing Zn-based alloy plated steel plate

120‧‧‧ Coating film of chemical conversion treatment liquid

122‧‧‧Polyethylene-fluororesin particles

124‧‧‧ Polyethylene resin particles

Claims (10)

A chemical conversion treatment Zn-based steel plate comprising: a Zn-based alloy plated steel plate containing Al, having a Zn-based alloy plating layer containing 0.05% by mass to 60% by mass of Al; and a chemical conversion treated film formed on The surface of the Al-containing Zn-based alloy plated steel sheet has a thickness of 0.5 μm to 10 μm, and the chemical conversion treatment film contains a fluorine-containing resin containing a group selected from the group consisting of a carboxyl group, a sulfonic acid group, and a salt thereof. a hydrophilic functional group of 0.05% by mass to 5% by mass and a F atom of 7% by mass to 20% by mass; and a Group 4A metal compound which is 0.1% by mass to 5% by mass based on the total amount of the fluorine-containing resin; The resin particles having an average particle diameter of 0.1 μm to 10 μm, wherein the ratio of the carboxyl group to the sulfonic acid group of the fluorine-containing resin is in the range of 5 to 60 in terms of the molar ratio of the carboxyl group/sulfonic acid group, and the above chemical conversion The area ratio of the resin particles in the surface of the treated film is 0.1% by area or more, wherein the resin particles are polyethylene-fluororesin particles in which fluororesin fine particles are bonded to the surface of the polyethylene resin particles, and the above chemical conversion treatment is performed. Membrane table In part, from the surface of the chemical conversion coating film projection, wherein said metal selected from the group consisting of 4A Group Ti, Zr, Hf and a combination of the group consisting of. The Zn-based steel sheet for chemical conversion treatment according to the first aspect of the invention, wherein the chemical conversion treatment film further comprises a polyethylene resin, and the polyethylene resin covers the surface of the chemical conversion treatment film. All or part of the rest. The Zn-based steel sheet for chemical conversion treatment according to the first aspect of the invention, wherein the chemical conversion treatment film further contains a phosphate, and the amount of the phosphate is 0.05% by mass in terms of P with respect to the fluorine-containing resin. Within the range of 3 mass%. The Zn-based steel sheet for chemical conversion treatment according to the first aspect of the invention, wherein the chemical conversion treatment film further contains a decane coupling agent, and the amount of the decane coupling agent is 0.5% by mass to 5 mass based on the fluorine-containing resin. %In the range. The chemical conversion treatment Zn-based steel sheet according to the first aspect of the invention, further comprising: a base chemical conversion treatment film formed between the Al-containing Zn-based alloy plated steel sheet and the chemical conversion treatment film, and An oxide or hydroxide containing a valve metal selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Mo, and W, and selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Mo And the fluoride of the valve metal of the group consisting of W. A method for producing a Zn-based steel sheet for chemical conversion treatment, comprising: a step of preparing an Al-containing Zn-based alloy plated steel sheet having a Zn-based alloy plating layer containing 0.05% by mass to 60% by mass of Al; a step of applying a chemical conversion treatment liquid to the surface of the Al-Zn alloy-plated steel sheet and drying it to form a chemical conversion treatment film having a film thickness of 0.5 μm to 10 μm; The chemical conversion treatment liquid includes a fluorine-containing resin containing 0.05% by mass 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 a F atom of 7 mass% to 20 mass%. And the number average molecular weight is in the range of 1,000 to 2 million; the oxo acid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxy salt of the 4A metal; and the average particle diameter is 0.1 a resin particle of μm to 10 μm, wherein a ratio of a carboxyl group to a sulfonic acid group of the fluorine-containing resin is in a range of 5 to 60 in terms of a molar ratio of a carboxyl group/sulfonic acid group; and the above fluorine-containing resin The amount of the oxoacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxy salt of the Group 4A metal is in the range of 0.1% by mass to 5% by mass in terms of metal; relative to the above chemical conversion The solid content in the treatment liquid, wherein the amount of the resin particles is in the range of 0.5% by mass to 20% by mass, wherein the ratio of the carboxyl group to the sulfonic acid group of the fluorine-containing resin is a molar ratio of the carboxyl group to the sulfonic acid group. In the range of 5 to 60, wherein the above Group 4A metal is selected from Ti, Zr In the group consisting of Hf and a combination of these, the drying temperature of the chemical conversion treatment liquid in the step of forming the chemical conversion treatment film is a temperature at which at least a part of the polyethylene-fluororesin particles are not melted. The method for producing a chemical conversion-treated Zn-based steel sheet according to the sixth aspect of the invention, wherein the chemical conversion treatment liquid further contains polyethylene resin particles. Chemical conversion treatment of Zn plating as described in claim 6 In the method of producing a steel sheet, the chemical conversion treatment liquid further contains a phosphate, and the amount of the phosphate is in a range of 0.05% by mass to 3% by mass in terms of P with respect to the fluorine-containing resin. The method for producing a Zn-based steel sheet for chemical conversion treatment according to claim 6, wherein the chemical conversion treatment liquid further contains a decane coupling agent, and the amount of the decane coupling agent is 0.5% by mass based on the fluorine-containing resin. ~5 mass% range. The method for producing a chemical conversion-treated Zn-based steel sheet according to claim 6, wherein before the step of forming the chemical conversion treatment film, the method further comprises: coating a surface of the Al-containing Zn-based alloy-plated steel sheet The substrate chemically transforms the treatment liquid and is dried to form a substrate chemical conversion treatment film, wherein the substrate chemical conversion treatment liquid contains a valve metal selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Mo, and W Salt and fluoride ions.