JP2012177146A - Molded product of plated steel sheet and method for manufacturing the same, and chemical conversion treatment liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a molded product of a Zn-based alloy plated steel sheet having a chemical conversion coating, capable of forming a chemical conversion coating excellent in weather resistance, water resistance and coating adhesion even when a post coat method is used.SOLUTION: In this method for manufacturing the molded product, the chemical conversion treatment liquid is coated on the surface of the molded product made of an Al-containing Zn-based alloy plated steel sheet and is dried to form the chemical conversion coating having a film thickness of 0.5-10 μm. The chemical conversion treatment liquid contains: an emulsion of a fluorine-containing resin with an average particle size of 50-300 nm; and an oxysalt of a Group 4A metal, fluoride, hydroxide, an organic acid salt, carbonate or a peroxide salt. The fluorine-containing resin contains 0.05-5 mass% of hydrophilic functional groups selected from the group consisting of a carboxyl group, a sulfonic acid group and the salts thereof, and 7-20 mass% of F atoms, and has a number average molecular weight within the range of 1,000-2,000,000.

Description

  The present invention relates to a molded product of a Zn-based alloy-plated steel sheet having a chemical conversion coating formed by a post-coating method, a manufacturing method thereof, and a chemical conversion treatment solution used for manufacturing the molded product.

  Conventionally, in various applications such as exterior building materials, molded products of Zn-based alloy-plated steel sheets (for example, round tubes, square tubes, C channels, H-shaped steels, L-shaped steels, etc.) have been used. Since these Zn-based alloy-plated steel sheets may have insufficient corrosion resistance and discoloration resistance as they are, a chemical conversion treatment film containing an organic resin may be formed on the surface thereof. For example, Patent Documents 1 and 2 describe that a chemical conversion treatment film containing an organic resin such as urethane resin is formed on the surface of a Zn-based alloy plated steel sheet. As described in Patent Documents 1 and 2, when forming a Zn-based alloy-plated steel sheet, a chemical conversion film may be formed before the forming process for the purpose of improving galling resistance (pre-coating method). ). On the other hand, since there is a possibility that defects may occur in the chemical conversion coating when forming or welding, the chemical conversion coating may be formed after the molding or welding (post coating method).

  By the way, in order to improve the weather resistance of a chemical conversion treatment film, the fluorine-containing resin which is excellent in a weather resistance may be used as an organic resin which comprises a chemical conversion treatment film. Fluorine-containing resin compositions are roughly classified into solvent-based fluorine-containing resin compositions and water-based fluorine-containing resin compositions. Conventionally, when a fluorine-containing resin is used for the purpose of improving weather resistance, an organic solvent-based fluorine-containing resin composition has been generally used. However, organic solvent-based fluorine-containing resin compositions have problems such as fire hazard and toxicity and air pollution.

  On the other hand, water-based fluorine-containing resin compositions are easier to handle than organic solvent-based fluorine-containing resin compositions, and various types have been proposed (for example, see Patent Document 3). However, many water-based fluorine-containing resin compositions often require baking at a high temperature (for example, 180 to 230 ° C., see Patent Document 3). For example, when a chemical conversion film is formed by a post-coating method, it may be difficult to perform baking at such a high temperature from the viewpoint of equipment at the site after molding.

  Therefore, an aqueous fluorine-containing resin composition into which a curable site (organic functional group) is introduced so as to be able to form a film even by baking at a low temperature has been proposed (for example, see Patent Document 4). However, since the chemical conversion film cured using an organic functional group is preferentially deteriorated in weather resistance from the cured portion, it becomes porous when used outdoors, resulting in a decrease in water resistance.

JP 2005-15834 A JP 2005-206764 A JP-A-57-38845 JP-A-5-202260

  As described above, corrosion resistance, discoloration resistance, and the like can be improved by forming a chemical conversion film containing an organic resin on the surface of a molded product of a Zn-based alloy plated steel sheet. However, a molded product of a Zn-based alloy-plated steel sheet formed with a chemical conversion treatment film containing an organic resin sometimes has insufficient weather resistance when used outdoors. In other words, since many organic resins such as urethane resins are deteriorated by ultraviolet rays, when a formed processed product of a Zn-based alloy plated steel sheet on which a chemical conversion treatment film is formed is used outdoors, the chemical conversion treatment film that covers the surface is formed. It may be lost over time. If the chemical conversion film is lost in this way, corrosion or discoloration occurs on the surface of the Zn-based alloy-plated steel sheet, which may impair the aesthetic appearance.

  As a means for improving the weather resistance of the chemical conversion coating, it is conceivable to use a fluorine-containing resin having excellent weather resistance. Then, this inventor performed the preliminary experiment which forms a chemical conversion treatment film on the surface of a Zn type alloy plating steel plate using the emulsion of water system fluorine content resin which is easy to handle. As a result, it was possible to improve the ultraviolet resistance by using an emulsion of a water-based fluorine-containing resin, but on the other hand, the film forming property, water resistance and film adhesion were lowered.

  As a result of further studies by the present inventor, these deteriorations in quality are due to the fact that an emulsifier (for example, perfluorooctanoic acid ammonium salt) used in producing an aqueous fluorine-containing resin emulsion remains in the chemical conversion film. It was speculated that there was (see the reference experiment below). Such residual emulsifiers are particularly noticeable when baked at low temperatures. Therefore, when the chemical conversion film is formed by a post-coating method in which baking at a high temperature may be difficult, the above-described deterioration in quality becomes a particular problem.

  As described above, a molded product of a Zn-based alloy plated steel sheet on which a chemical conversion film containing an organic resin other than a fluorine-containing resin is formed may have insufficient weather resistance. In addition, by using water-based fluorine-containing resin as the organic resin, the weather resistance (ultraviolet light resistance) of the chemical conversion coating can be improved, but on the other hand, the film-forming property, water resistance and film adhesion are reduced. There was a case.

  The present invention has been made in view of such points, and even with a post-coating method that may be baked at a low temperature, it is possible to form a chemical conversion film excellent in weather resistance, water resistance and film adhesion. It aims at providing the manufacturing method of the shaping | molding processed article of the Zn type alloy plating steel plate which has a chemical conversion treatment film.

  The present inventor uses a high molecular weight fluorine-containing resin emulsion into which a hydrophilic functional group is introduced, and crosslinks these fluorine-containing resins with a group 4A metal compound, thereby enabling the weather resistance and water resistance of the chemical conversion coating. It was also found that all of the film adhesion can be improved. In addition, the present inventor has also found that the film can be formed even when baked at a low temperature by setting the average particle size of the emulsion in the range of 50 to 300 nm. Based on these findings, the present inventor has further studied and completed the present invention.

That is, this invention relates to the manufacturing method of the molded product of the following plated steel plates.
[1] A step of preparing an Al-containing Zn-based alloy-plated steel sheet containing 0.05 to 60% by mass of Al; a step of forming the Al-containing Zn-based alloy-plated steel sheet; Applying a chemical conversion treatment liquid to the surface of the molded product and drying to form a chemical conversion film having a film thickness of 0.5 to 10 μm, comprising the steps of: The chemical conversion treatment liquid contains an emulsion of a fluorine-containing resin having an average particle size of 50 to 300 nm, and a group 4A metal oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide salt. The fluorine-containing resin contains 0.05 to 5% by mass of a hydrophilic functional group selected from the group consisting of a carboxyl group, a sulfonic acid group and salts thereof, and 7 to 20% by mass of F atoms, and several Average molecular weight is 1 In the chemical conversion solution, the amount of the oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide of the group 4A metal relative to the fluorine-containing resin is The manufacturing method of the shaping | molding processed goods of a plated steel plate which exists in the range of 0.1-5 mass% in metal conversion.
[2] The forming process of the plated steel sheet according to [1], wherein the fluorine-containing resin has a carboxyl group / sulfonic acid group molar ratio within a range of 5 to 60 in terms of a molar ratio of carboxyl group / sulfonic acid group. Product manufacturing method.
[3] The forming treatment of a plated steel sheet according to [1] or [2], wherein the chemical conversion treatment liquid further contains 0.05 to 3% by mass of phosphate in terms of P with respect to the fluorine-containing resin. Product manufacturing method.
[4] The plated steel sheet according to any one of [1] to [3], wherein the chemical conversion treatment liquid further contains 0.5 to 5% by mass of a silane coupling agent with respect to the fluorine-containing resin. Method of manufacturing molded products.
[5] The method for producing a formed product of a plated steel sheet according to any one of [1] to [4], wherein the 4A group metal is selected from the group consisting of Ti, Zr, Hf, and a combination thereof.
[6] Any of [1] to [5], wherein the Al-containing Zn-based alloy-plated steel sheet has a base chemical conversion treatment film containing a valve metal oxide or hydroxide and a valve metal fluoride. The manufacturing method of the molded product of the plated steel plate of one term.

The present invention also relates to the following molded products of plated steel sheets.
[7] A step of preparing an Al-containing Zn-based alloy-plated steel sheet containing 0.05 to 60% by mass of Al; a step of forming the Al-containing Zn-based alloy-plated steel sheet; Forming a chemical conversion treatment liquid on the surface of the molded product and drying to form a chemical conversion film having a film thickness of 0.5 to 10 μm. The chemical conversion treatment liquid comprises a fluorine-containing resin emulsion having an average particle size of 50 to 300 nm, and a group 4A metal oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide salt. The fluorine-containing resin contains 0.05 to 5% by mass of a hydrophilic functional group selected from the group consisting of a carboxyl group, a sulfonic acid group and salts thereof, and 7 to 20% by mass of F atoms; And several The molecular weight is in the range of 1,000 to 2,000,000; in the chemical conversion solution, the group 4A metal oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide of the fluorine-containing resin The amount is in the range of 0.1 to 5% by mass in terms of metal, and is a formed product of a plated steel sheet.
[8] The forming process of the plated steel sheet according to [7], wherein the ratio of the carboxyl group and the sulfonic acid group of the fluorine-containing resin is within a range of 5 to 60 in terms of a molar ratio of carboxyl group / sulfonic acid group. Goods.
[9] The forming treatment of the plated steel sheet according to [7] or [8], wherein the chemical conversion coating film further contains 0.05 to 3% by mass of phosphate in terms of P with respect to the fluorine-containing resin. Goods.
[10] The plated steel sheet according to any one of [7] to [9], wherein the chemical conversion film further contains 0.5 to 5% by mass of a silane coupling agent with respect to the fluorine-containing resin. Molded processed products.
[11] The molded product of the plated steel sheet according to any one of [7] to [10], wherein the 4A group metal is selected from the group consisting of Ti, Zr, Hf, and combinations thereof.
[12] A base chemical conversion film containing a valve metal oxide or hydroxide and a valve metal fluoride is further provided between the Al-containing Zn-based alloy-plated steel sheet and the chemical conversion film. ] Formed product of the plated steel plate as described in any one of [11].

Moreover, this invention relates to the following chemical conversion liquids.
[13] A chemical conversion treatment liquid applied to a molded product of an Al-containing Zn-based alloy-plated steel sheet containing 0.05 to 60% by mass of Al: an emulsion of a fluorine-containing resin having an average particle size of 50 to 300 nm; A group 4A metal oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide salt; the fluorine-containing resin is selected from the group consisting of carboxyl groups, sulfonic acid groups and salts thereof Containing 4 to 5% by weight of the selected hydrophilic functional group and 7 to 20% by weight of F atoms, and having a number average molecular weight in the range of 1,000 to 2,000,000; the 4A group for the fluorine-containing resin The amount of the metal oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide salt is a chemical conversion treatment liquid within a range of 0.1 to 5% by mass in terms of metal.
[14] The chemical conversion treatment liquid according to [13], wherein the fluorine-containing resin has a carboxyl group / sulfonic acid group molar ratio of 5 to 60 in terms of a carboxyl group / sulfonic acid group molar ratio.
[15] The chemical conversion treatment solution according to [13] or [14], further containing 0.05 to 3% by mass of a phosphate in terms of P with respect to the fluorine-containing resin.
[16] The chemical conversion liquid according to any one of [13] to [15], further containing 0.5 to 5% by mass of a silane coupling agent with respect to the fluorine-containing resin.
[17] The chemical conversion solution according to any one of [13] to [16], wherein the group 4A metal is selected from the group consisting of Ti, Zr, Hf, and combinations thereof.

  According to the present invention, a Zn-based alloy-plated steel sheet having a chemical conversion treatment excellent in all of weather resistance, water resistance and film adhesion is produced even in a post-coating system that may be baked at a low temperature. Can do. Since the molded product of the Zn-based alloy-plated steel sheet of the present invention is excellent in weather resistance, corrosion resistance, and discoloration resistance, it is useful, for example, as an exterior building material.

The graph which shows the relationship between the quantity of 4A group metal in a fluorine-containing resin film, and moisture permeability Graph showing the relationship between the emulsifier concentration in the emulsion of fluorine-containing resin and the moisture permeability of the fluorine-containing resin film

  The method for producing a molded product of a plated steel sheet according to the present invention (hereinafter also referred to as “the production method of the present invention”) is a process for producing a molded product of a Zn-based alloy-plated steel sheet having a chemical conversion coating formed by a post coating method. Is the method. “Zn-based alloy-plated steel sheet” is not particularly limited. For example, a round tube, a square tube, a C channel, an H-shaped steel, an L-shaped steel, etc., formed using a Zn-based alloy plated steel sheet. is there.

  The production method of the present invention includes 1) a first step of preparing an Al-containing Zn-based alloy plated steel sheet, 2) a second step of forming an Al-containing Zn-based alloy plated steel sheet, and 3) an Al-containing Zn-based steel. And a third step of forming a chemical conversion film on the surface of the molded product of the alloy-plated steel sheet. In the third step, the production method of the present invention uses, in the third step, a chemical conversion treatment liquid containing an emulsion (average particle size: 50 to 300 nm) of a high molecular weight fluorine-containing resin into which a hydrophilic functional group is introduced and a 4A group metal compound. One feature is to form a chemical conversion coating.

  Hereinafter, each step of the manufacturing method of the present invention will be described.

1. First Step In the first step, an Al-containing Zn-based alloy-plated steel plate is prepared as an original plate. On the surface of the Al-containing Zn-based alloy-plated steel sheet, a base chemical conversion treatment film that improves corrosion resistance and film adhesion may be formed.

[Al-containing Zn-based alloy-plated steel sheet]
The “Al-containing Zn-based alloy-plated steel plate” used as the original plate means a steel plate having a Zn-based alloy plated layer containing 0.05 to 60% by mass of Al. Examples of Al-containing Zn-based alloy-plated steel plates include hot-dip Al-Zn-plated steel plates (hot Zn-0.1% Al plating, hot Zn-55% Al plating, hot Zn-6% Al-3% Mg plating, hot melting Zn-11% Al-3% Mg-0.2% Si, molten Zn-5% Al-0.75% Mg), alloyed Zn-plated steel sheet (alloyed after molten 0.1% Al-Zn plating) Alloyed molten Al—Zn plating) and the like.

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

[Base chemical conversion coating]
As described above, a base chemical conversion treatment film may be formed on the surface of the Al-containing Zn-based alloy plated steel sheet. By forming the base chemical conversion treatment film, the corrosion resistance and film adhesion of the Al-containing Zn-based alloy plated steel sheet can be improved. For example, when the Al-containing Zn-based alloy-plated steel sheet must be transported or stored between the production of the Al-containing Zn-based alloy-plated steel sheet and the forming process, corrosion may occur on the surface of the Al-containing Zn-based alloy plated steel sheet. In such a case, if a base chemical conversion treatment film is previously formed on the surface of the Al-containing Zn-based alloy plated steel sheet, the occurrence of corrosion on the surface of the Al-containing Zn-based alloy plated steel sheet can be reliably prevented.

  From the viewpoint of weather resistance, the base chemical conversion treatment film is preferably an inorganic film rather than an organic film based on a urethane resin or an epoxy resin. This is because an organic film based on a urethane resin, an epoxy resin, or the like is preferentially deteriorated in weather resistance, and the corrosion resistance and film adhesion may be drastically lowered with time. Specifically, the inorganic base chemical conversion treatment film preferably contains a valve metal oxide or hydroxide and a valve metal fluoride (see JP 2002-194558 A). Here, “valve metal” refers to a metal whose oxide exhibits high insulation resistance. As the valve metal element, one or more elements selected from Ti, Zr, Hf, V, Nb, Ta, Mo and W are preferable.

By blending an oxide or hydroxide of valve metal, it is possible to impart an excellent corrosion inhibiting action while reducing the environmental load (chromium free). In order to include an oxide or hydroxide of valve metal in the base chemical conversion treatment film, a valve metal salt may be added to the base chemical conversion treatment solution. By drying the base chemical conversion treatment solution containing the valve metal salt, the valve metal salt becomes an oxide or hydroxide of the valve metal. The valve metal salt is, for example, a halide or oxyacid salt of valve metal. For example, examples of titanium salts 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 , Ti (OH) _{4 and the} like.

Moreover, the outstanding self-repairing effect | action can be provided by mix | blending the fluoride of valve metal. The valve metal fluoride dissolves in the moisture in the atmosphere and then becomes a sparingly soluble oxide or hydroxide on the surface of the base material (Al-containing Zn-based alloy plated steel sheet) exposed at the film defect portion. Re-deposited to fill the film defects. In order to include the soluble fluoride of valve metal in the base chemical conversion treatment film, the soluble fluoride of valve metal may be added to the base chemical conversion treatment solution, or the valve metal salt and soluble fluoride (for example, (NH ₄ ) F). Etc.) may be added in combination.

  The base chemical conversion treatment film may contain a soluble or hardly soluble metal phosphate or composite phosphate. Soluble phosphate elutes from the underlying chemical conversion coating to the film defects and reacts with the plating components (Zn, Al, etc.) of the base material (Al-containing Zn-based alloy-plated steel sheet) to become insoluble phosphate. This complements the self-healing action of valve metal soluble fluoride. In addition, the hardly soluble phosphate is dispersed in the base chemical conversion treatment film to improve the film strength. Examples of the metal contained in the soluble metal phosphate or composite phosphate include alkali metals, alkaline earth metals, and Mn. Examples of the metal contained in the hardly soluble metal phosphate or the composite phosphate include Al, Ti, Zr, Hf, and Zn. In order to include a soluble or poorly soluble metal phosphate or composite phosphate in the base chemical conversion treatment film, various metal phosphates may be added to the base chemical conversion treatment solution, or various metal salts and phosphoric acid, Polyphosphoric acid or phosphate may be added in combination.

  Further, the base chemical conversion treatment film may contain an organic wax such as fluorine, polyethylene, or styrene, or an inorganic lubricant such as silica, molybdenum disulfide, or talc. Organic wax or inorganic lubricant improves the lubricity of the base chemical conversion coating. The low melting point organic wax bleeds on the surface of the film when the base chemical conversion treatment liquid is dried, and exhibits lubricity. On the other hand, the high melting point organic wax and the inorganic lubricant are present in a dispersed state in the base chemical conversion coating film, but express lubricity by being distributed in an island shape on the outermost layer.

  The base chemical conversion treatment film can be formed by a known method. For example, a base chemical conversion treatment solution containing valve metal salt or fluoride ions is applied to the surface of an Al-containing Zn-based alloy-plated steel sheet by a method such as roll coating, spin coating, or spraying, and dried without washing. Just do it.

  When forming the base chemical conversion treatment film, an organic acid having a chelating action may be added to the base chemical conversion treatment solution so that the valve metal salt can be stably present in the base chemical conversion treatment solution. Examples of the organic acid include tannic acid, tartaric acid, citric acid, oxalic acid, malonic acid, lactic acid, and acetic acid. Among these, polyoxyphenols such as tartaric acid and polyhydric phenols such as tannic acid stabilize the base chemical conversion treatment liquid and also have the effect of complementing the self-repairing action of the valve metal fluoride. It is also effective in improving adhesion. The addition amount of the organic acid is preferably 0.02 or more in terms of an organic acid / metal ion molar ratio.

The coating amount of the base chemical conversion treatment liquid is not particularly limited, but is adjusted so that the amount of valve metal deposited is 1 mg / m ² or more and the film thickness of the base chemical conversion treatment film is in the range of 3 to 1000 nm. It is preferred that When the adhesion amount of the valve metal is less than 1 mg / m ² or when the film thickness of the base chemical conversion treatment film is less than 3 nm, the corrosion resistance may not be sufficiently improved. On the other hand, when the film thickness of the base chemical conversion treatment film exceeds 1000 nm, cracks may occur when forming in the second step.

  The base chemical conversion treatment solution may be dried at room temperature, but considering continuous operation, it is preferable to keep the temperature at 50 ° C. or higher to shorten the drying time. However, when the temperature is kept above 200 ° C., the organic component may be thermally decomposed, and the effect of the base chemical conversion treatment film may be reduced.

  When the formed base chemical conversion coating is subjected to elemental analysis using fluorescent X-rays, ESCA, or the like, the O concentration and the F concentration in the base chemical conversion coating can be measured. The element concentration ratio F / O (atomic ratio) calculated from these measured values is preferably 1/100 or more from the viewpoint of corrosion resistance. 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 remarkably suppressed. This is presumably because a sufficient amount of valve metal fluoride is contained in the base chemical conversion treatment film and exhibits a self-healing action.

2. Second Step In the second step, the Al-containing Zn-based alloy plated steel sheet prepared in the first step is formed into a desired shape.

  The method for forming the Al-containing Zn-based alloy-plated steel sheet is not particularly limited, and can be appropriately selected according to the shape of the target product. Examples of the forming process include drawing, bending, roll forming, shearing, welding, and thermal spraying.

  For example, when manufacturing a welded steel pipe, an Al-containing Zn-based alloy plated steel sheet is formed into an open pipe shape by roll forming, and then an end portion in the width direction of the Al-containing Zn-based alloy plated steel sheet is welded. Next, after cutting the bead protrusion protruding from the welded steel pipe, a thermal spray repair layer may be formed on the bead cut weld. Thus, when forming a spraying repair layer, the spraying method and the kind of spraying material are not specifically limited, It is preferable to contain 0.05 atomic% or more of Al in the outermost layer of a spraying repairing layer. As will be described later, when Al is contained on the surface of the base material, the film adhesion of the chemical conversion film formed in the third step is improved. For example, by performing triple spraying of Al, Zn and Al, the Al concentration of the outermost surface layer of the sprayed repair layer can be set to about 100 atomic%. The Al concentration of the outermost surface layer of the thermal spray repair layer can be measured by elemental analysis using an XPS apparatus.

3. Third Step In the third step, a chemical conversion treatment liquid is applied to the surface of the molded product of the Al-containing Zn-based alloy-plated steel sheet produced in the second step and dried to form a chemical conversion treatment film.

[Chemical conversion coating]
The chemical conversion coating is formed on the surface of the molded product of the Al-containing Zn-based alloy-plated steel sheet produced in the second step. As described above, the base chemical conversion treatment film may or may not be formed on the surface of the Al-containing Zn-based alloy plated steel sheet. When the base chemical conversion coating is not formed, the chemical conversion coating is directly formed on the surface of the Al-containing Zn-based alloy plated steel sheet. On the other hand, when the base chemical conversion coating is formed, the chemical conversion coating is formed on the base chemical conversion coating.

  The object of the present invention is to improve all of the weather resistance, water resistance and film adhesion of the chemical conversion coating. As described above, in order to improve the weather resistance (ultraviolet light resistance) of the chemical conversion coating, a fluorine-containing resin may be used as the organic resin. Fluorine-containing resins are roughly classified into solvent-based fluorine-containing resins and water-based fluorine-containing resins. When a chemical conversion film is formed using a solvent-based fluorine-containing resin, recovery of the volatilized solvent becomes a problem, but when a water-based fluorine-containing resin is used, such a problem does not occur. Then, this inventor tried to form the chemical conversion treatment film excellent in all of weather resistance, water resistance, and film | membrane adhesiveness using the water-type fluorine-containing resin with easy handling.

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

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

  Furthermore, the present inventor has also studied the film formation by baking at a low temperature. As described above, when the chemical conversion film is formed by the post-coating method, it is sometimes difficult to bake at a high temperature from the surface of the equipment at the site after the molding process. And this inventor discovered that it can form into a film even if it baked at lower temperature (for example, 55 degreeC) than before by making the average particle diameter of the emulsion of water-type fluorine-containing resin into the range of 50-300 nm.

  As mentioned above, this inventor mix | blends a 4A group metal compound further with the chemical conversion liquid based on the emulsion (average particle diameter of 50-300 nm) of the high molecular weight fluorine-containing resin which introduce | transduced the hydrophilic functional group. Thus, it was found that a chemical conversion film excellent in all of weather resistance, water resistance and film adhesion can be formed even by baking at a low temperature.

  In the production method of the present invention, 1) the weather resistance (ultraviolet resistance) of the chemical conversion coating is improved by blending a fluorine-containing resin (preferably a fluorine-containing olefin resin) with the chemical conversion treatment liquid. In addition, 2) the use of a fluorine-containing resin into which a hydrophilic functional group has been introduced reduces the use of an emulsifier during emulsion production, 3) the molecular weight of the fluorine-containing resin is increased, and 4) the fluorine-containing resin is 4A. Crosslinking with a group metal compound improves the weather resistance (ultraviolet light resistance) and water resistance of the chemical conversion coating. Furthermore, 5) By making the average particle diameter of the emulsion of the fluorine-containing resin in the range of 50 to 300 nm, it is possible to form a film even when baking at a low temperature.

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

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

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

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

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

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

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

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

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

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

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

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

（式中、Ｒ^１、Ｒ^２およびＲ^３は同じかまたは異なり、いずれも水素原子、アルキル基、カルボキシル基またはエステル基である。ｎは０〜２０の範囲内である。） Examples of the carboxyl group-containing monomer include unsaturated carboxylic acids represented by the following formula (1) and unsaturated carboxylic acids such as esters or acid anhydrides thereof.

(In formula, R < ¹ >, R < ² > and R < ³ > are the same or different, and all are a hydrogen atom, an alkyl group, a carboxyl group, or an ester group. N is in the range of 0-20.)

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

（式中、Ｒ^４およびＲ^５は同じかまたは異なり、いずれも飽和または不飽和の直鎖または環状アルキル基である。ｎは０または１である。ｍは０または１である。） Another example of the carboxyl group-containing monomer is a carboxyl group-containing vinyl ether monomer represented by the following formula (2).

(Wherein R ⁴ and R ⁵ are the same or different, and each is a saturated or unsaturated linear or cyclic alkyl group. N is 0 or 1. m is 0 or 1.)

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

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

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

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

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

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

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

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

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

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

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

  The group 4A metal compound also improves film adhesion, water resistance and discoloration resistance. That is, the strong Al oxide present on the surface of the Al-containing Zn-based alloy-plated steel sheet decreases the adhesion of the chemical conversion coating, but this Al oxide can be obtained by including a group 4A metal compound in the chemical conversion coating. It is possible to suppress a decrease in film adhesion due to. The group 4A metal compound also serves as a supply source of group 4A metal ions that react with Al ions eluted by the etching reaction. The reaction product is concentrated at the interface between the plating layer and the chemical conversion film to improve the initial corrosion resistance and discoloration resistance. Examples of Group 4A metals include Ti, Zr, Hf, and the like.

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

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

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

  As described above, a base chemical conversion treatment film may be formed on the surface of the Al-containing Zn-based alloy plated steel sheet. The base chemical conversion treatment film has an effect of improving the film adhesion of the chemical conversion treatment film to the Al-containing Zn-based alloy plated steel sheet. Therefore, when the base chemical conversion treatment film is peeled off, missing, or missing due to transportation or molding (including welding), it is considered that the film adhesion of the chemical conversion treatment film in that region is lowered. However, in the region where there is no underlying chemical conversion treatment film, the chemical conversion treatment film containing the fluorine-containing resin and the 4A group metal compound is in direct contact with the surface of the Al-containing Zn-based alloy-plated steel sheet. The film adhesion of the chemical conversion film is improved. Therefore, also in the location where the foundation | substrate chemical conversion treatment film peeled, the adhesiveness of a chemical conversion treatment film and an Al containing Zn type alloy plating steel plate is high, and the corrosion resistance of a chemical conversion treatment film is also high.

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

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

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

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

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

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

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

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

[Formation method of chemical conversion coating]
In order to form the above-mentioned chemical conversion treatment film, the chemical conversion treatment liquid containing the emulsion of the fluorine-containing resin (preferably fluorine-containing olefin resin) having the above-mentioned hydrophilic functional group and the group 4A metal compound is used in the second step. What is necessary is just to apply | coat to the surface of the shaping | molding processed article of the Al containing Zn type alloy plating steel plate produced by (4), and to dry.

  The chemical conversion treatment liquid can be prepared by adding a group 4A metal compound to an emulsion of a fluorine-containing resin having a hydrophilic functional group (preferably a fluorine-containing olefin resin). You may add a phosphate, a silane coupling agent, etc. to a chemical conversion liquid as needed.

  As described above, the fluorine-containing resin contained in the aqueous emulsion contains 0.05 to 5% by mass of hydrophilic functional groups and 7 to 20% by mass of F atoms, and has a number average molecular weight in the range of 1,000 to 2,000,000. Is within.

  The average particle size of the fluorine-containing resin emulsion is preferably in the range of 50 to 300 nm. By setting the average particle size of the emulsion to 300 nm or less, the surface area of the emulsion is increased and it becomes easy to fuse with each other, and film formation can be performed even if baking is performed at a low temperature (for example, 55 ° C.). On the other hand, if the average particle size of the emulsion is less than 50 nm, the storage stability of the chemical conversion liquid may be reduced. For example, when preparing an emulsion by the emulsion polymerization method, the average particle diameter of the emulsion can be set within the above range by optimizing the shear rate and the stirring time.

  The content of the emulsifier in the fluorine-containing resin emulsion is preferably 1% by mass or less. When the emulsifier exceeds 1% by mass, the emulsifier may remain in the chemical conversion film depending on the baking temperature. If the emulsifier remains in the chemical conversion coating as described above, the water resistance of the chemical conversion coating is remarkably lowered, which is not preferable. As described above, an aqueous emulsion can be prepared even if the amount of the emulsifier is 1% by mass or less as long as it is a fluorine-containing resin having a hydrophilic functional group. The emulsifier that may be contained in the emulsion of the fluorine-containing resin is preferably a fluorine-based emulsifier such as an ammonium salt of perfluorooctanoic acid or an ammonium salt of perfluorononanoic acid from the viewpoint of weather resistance and water resistance. In addition, a known fluorosurfactant can also be used as an emulsifier.

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

  As the group 4A metal compound to be added to the chemical conversion treatment liquid, a group 4A metal oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate, peroxide salt, or the like is used. Examples of oxyacid salts include hydrates, ammonium salts, alkali metal salts, alkaline earth metal salts, and the like.

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

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

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

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

  The method for applying the chemical conversion liquid is not particularly limited, and may be appropriately selected according to the shape of the molded product produced in the second step. Examples of such a coating method include a roll coating method, a curtain flow method, a spin coating method, a spray method, a dip pulling method, a dropping method, and the like. The liquid film thickness of the chemical conversion treatment liquid can be adjusted by a felt throttle or an air wiper.

  The coating amount of the chemical conversion treatment liquid is not particularly limited, but it is preferably adjusted so that the film thickness of the chemical conversion treatment film is in the range of 0.5 to 10 μm. As described above, when the film thickness of the chemical conversion film is less than 0.5 μm, corrosion resistance, discoloration resistance, and the like cannot be sufficiently imparted. On the other hand, even if the film thickness exceeds 10 μm, it cannot be expected to improve the performance with the increase in film thickness.

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

  According to the above procedure, a Zn-based alloy-plated steel sheet molded article having a chemical conversion coating excellent in all of weather resistance, water resistance and coating adhesion is produced even in a post-coating method that may be baked at a low temperature. be able to. Since the molded product of the plated steel sheet produced by the production method of the present invention is excellent in weather resistance, corrosion resistance and discoloration resistance, it is useful as an exterior building material, for example.

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

1. Preparation of chemical conversion welded steel pipe An aqueous emulsion of an organic resin shown in Table 1 (all having a nonvolatile content of 25% by mass) was prepared. Water-based emulsions (emulsion Nos. 1 to 20) containing a fluorine-containing olefin resin and an emulsifier are prepared by adding a predetermined amount of fluoroolefin, carboxyl group-containing monomer, sulfonic acid group-containing monomer and emulsifier to an aqueous solvent. It was prepared by a polymerization reaction. The emulsifier was added to the minimum amount (1.0% by mass) because the water permeability decreased with increasing amount. On the other hand, PR135 (Sumika Bayern Urethane Co., Ltd.) was used for the water-based emulsion (emulsion No. 21) containing a urethane resin and an emulsifier.

  In addition, about the emulsion of No. 13, since the hydrophilic functional group amount in resin was insufficient (less than 0.05 mass%), the stable emulsion was not obtained. Moreover, also about the emulsion of No. 16, since the F atomic weight in resin was excessive (over 20 mass%), the stable emulsion was not obtained.

  The chemical conversion liquid shown in Table 2 was prepared using the aqueous emulsion of the obtained organic resin. The chemical conversion treatment liquids Nos. 1 to 18 shown in Table 2 were prepared by adding a group 4A metal compound or the like to an aqueous emulsion containing a fluororesin-containing resin and an emulsifier. On the other hand, the chemical conversion treatment solution of No. 19 was prepared by adding a group 4A metal compound or the like to an aqueous emulsion containing a urethane resin and an emulsifier. A-1891 (Momentive Performance Materials Japan GK) was used as the silane coupling agent.

A base chemical conversion treatment having the composition shown in Table 3 was applied to the surface of a molten Zn-6% Al-3% Mg alloy-plated steel sheet having a thickness of 1.2 mm and a single-sided plating coating amount of 60 g / m ² , and an ultimate plate temperature of 140 A base chemical conversion treatment film was formed by heating and drying at ℃. Table 4 shows the adhesion amount and composition of the formed base chemical conversion coating. In addition, about the below-mentioned Examples 10-12, the foundation | substrate chemical conversion treatment film was not formed.

  The plated steel sheet on which the base chemical conversion coating was formed was formed into an open pipe shape, and then both ends in the width direction were subjected to high-frequency welding to produce a weld-plated steel pipe having a diameter of 20 mm. Next, after bead-cutting the welded portion, a thermal spray repair layer having a width of 10 mm was formed by triple spraying of Al, Zn, and Al.

  After the prepared welded steel pipe is washed with warm water, the chemical conversion treatment solution shown in Table 2 is applied to the surface of the welded steel pipe by dropping, treated with a sponge, and then dried with a dryer at a final plate temperature of 55 ° C. Then, a chemical conversion treatment film was formed.

  About each chemical conversion treatment welded steel pipe, the quantity of the 4A group metal with respect to the organic resin in a chemical conversion treatment film, a phosphate, and a silane coupling agent was measured using the fluorescent-X-ray-analysis apparatus. The contents of phosphate and silane coupling agent were calculated from the measured values of P and Si. Table 5 shows the film thickness and composition of the chemical conversion coating formed for each chemical conversion welded steel pipe.

2. Evaluation of chemical conversion welded steel pipe and chemical conversion solution (1) Accelerated weather resistance test A test piece was cut out from each chemical conversion welded steel pipe, and accelerated weather resistance test (xenon lamp method) in accordance with JIS K5600-7-7: 2008 ). In this test, the process of spraying water for 18 minutes while irradiating the light of a xenon arc lamp for 120 minutes was defined as 1 cycle (2 hours), and this process was repeated 500 cycles or 1000 cycles.

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

(3) Evaluation of blackening resistance About each chemical conversion treatment welded steel pipe, the lightness difference ((DELTA) L ^* value) of the surface of the chemical conversion treatment film before and behind an accelerated weathering test was measured, and blackening resistance was evaluated. For each chemical conversion welded steel pipe, if the lightness difference (ΔL ^* value) is 1 or less, “◎”, if it exceeds 1 and 2 or less, “◯”, if it exceeds 2 and 5 or less, “Δ”, 5 When it exceeded 10 and was 10 or less, it was evaluated as “「 ”and when it exceeded 10, it was evaluated as“ x ”.

(4) Evaluation of corrosion resistance Each chemical conversion welded steel pipe is subjected to a salt spray test (according to JIS Z2371; 120 hours or 240 hours) using a test piece after accelerated weathering test (1000 cycles), and white rust generation area Rate was evaluated. For each chemical conversion welded steel pipe, when the white rust occurrence area ratio is 5% or less, “◎”, when it exceeds 5% and 10% or less, “◯”, and when it exceeds 10% and 30% or less, “△ ”, When it was over 30% and 50% or less, it was evaluated as“ ▲ ”, and when it was over 50%, it was evaluated as“ x ”.

(5) Evaluation of white rust resistance during storage In order to simulate the white rust resistance during storage in the summer for each chemical conversion welded steel pipe, constant temperature and constant temperature using test pieces after accelerated weathering test (1000 cycles) A wet salt test (atmosphere temperature: 60 ° C., relative humidity: RH 95%, 240 hours) was conducted to evaluate white rust resistance during storage. For each chemical conversion welded steel pipe, when the white rust occurrence area ratio is 5% or less, “◎”, when it exceeds 5% and 10% or less, “◯”, and when it exceeds 10% and 30% or less, “△ ”, When it was over 30% and 50% or less, it was evaluated as“ ▲ ”, and when it was over 50%, it was evaluated as“ x ”.

(6) Evaluation of storage stability of chemical conversion liquid Each chemical conversion liquid in Table 2 was stored at a liquid temperature of 40 ° C. for 30 days. The amount of change in viscosity of each chemical conversion treatment liquid before and after storage (a value obtained by subtracting the viscosity before storage from the viscosity after storage) was measured by Ford Cup No. 4 to evaluate the storage stability. For each chemical conversion treatment solution, when the viscosity change is less than 3 seconds, “◎”, when it is 3 seconds or more and less than 10 seconds, “◯”, when it is 10 seconds or more and less than 30 seconds, “△”, for 30 seconds or more The case was evaluated as “×”.

(7) Evaluation result About each chemical conversion treatment welded steel pipe (Examples 1-12, Comparative Examples 1-10), the kind of processing liquid used, its storage stability, a weather resistance test, a blackening resistance test, and corrosion resistance Table 6 shows the evaluation results of the white rust resistance test during testing and storage.

  As shown in Table 6, the weld-plated steel pipe of Comparative Example 1 having a film thickness of the chemical conversion treatment film of less than 0.5 μm is insufficient in water permeability of the chemical conversion treatment film. The white rust resistance was inferior.

  The weld-plated steel pipe of Comparative Example 2 using a chemical conversion treatment solution containing an emulsion having an average particle size of less than 50 nm had good results regarding weather resistance, blackening resistance, corrosion resistance, and white rust resistance during storage. The storage stability of the chemical conversion solution was inferior. On the other hand, the weld-plated steel pipe of Comparative Example 3 using a chemical conversion treatment liquid containing an emulsion having an average particle diameter of more than 300 nm cannot be sufficiently formed because it is baked at a low temperature (for example, 55 ° C.), and has a weather resistance, The blackening resistance, corrosion resistance, and white rust resistance during storage were poor.

  When the amount of the hydrophilic functional group in the fluorine-containing resin was less than 0.05% by mass, an emulsion of the fluorine-containing resin could not be prepared (Table 1; Emulsion No. 13). On the other hand, the weld-plated steel pipe of Comparative Example 4 using a chemical conversion treatment liquid containing an emulsion having a hydrophilic functional group amount exceeding 5 mass% in the fluorine-containing resin has an excessive amount of hydrophilic functional group in the fluorine-containing resin. The water resistance of the chemical conversion film was lowered, and the blackening resistance, corrosion resistance, and white rust resistance during storage were inferior.

  The weld-plated steel pipe of Comparative Example 5 using a chemical conversion treatment solution containing an emulsion having an F atomic weight of less than 7% by mass in the fluorine-containing resin has insufficient weather resistance of the chemical conversion treatment film, so that weather resistance, blackening resistance, Corrosion resistance and white rust resistance during storage were poor. On the other hand, when the F atomic weight in the fluorine-containing resin was more than 20% by mass, an emulsion of the fluorine-containing resin could not be prepared (Table 1; Emulsion No. 16).

  The weld-plated steel pipe of Comparative Example 6 using a chemical conversion treatment solution containing an emulsion having a fluorine-containing resin number average molecular weight of less than 1000 has insufficient water resistance and water resistance of the chemical conversion treatment film. Denaturation, corrosion resistance, and white rust resistance during storage were poor. On the other hand, the weld-plated steel pipe of Comparative Example 7 using a chemical conversion treatment liquid containing an emulsion having a number average molecular weight of more than 2 million of fluorine-containing resin is weather resistance, blackening resistance, corrosion resistance, and white rust resistance during storage. Although it was a favorable result, the storage stability of the chemical conversion liquid was inferior.

  The weld-plated steel pipe of Comparative Example 8 using a chemical conversion treatment liquid in which the amount of Group 4A metal relative to the fluorine-containing resin is less than 0.1% by mass has insufficient water resistance of the chemical conversion treatment film. Corrosion resistance and white rust resistance during storage were inferior. On the other hand, the weld-plated steel pipe of Comparative Example 9 using a chemical conversion treatment liquid in which the amount of the group 4A metal with respect to the fluorine-containing resin is more than 5% by mass has a porous chemical conversion treatment film. Corrosion resistance was poor.

  In the weld-plated steel pipe of Comparative Example 10 using a chemical conversion treatment liquid containing urethane resin as an organic resin, the chemical conversion treatment film disappears after 500 cycles of accelerated weathering test (equivalent to outdoor exposure for 5 years). Blackening, corrosion resistance, and white rust resistance during storage were poor.

  On the other hand, the weld-plated steel pipes of Examples 1 to 12 manufactured by the manufacturing method of the present invention were excellent in weather resistance, blackening resistance, corrosion resistance, and white rust resistance during storage. Moreover, the storage stability of the chemical conversion treatment solution was also good.

[Reference experiment]
As a reference experiment, the results of examining the relationship between the moisture permeability and the amount of the group 4A metal compound and the amount of the emulsifier in the fluorine-containing resin film are shown.

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

  FIG. 1 is a graph showing the relationship between the amount of Group 4A metal and moisture permeability in a fluorine-containing resin film. From this graph, it is understood that the moisture permeability of the fluorine-containing resin film can be remarkably lowered by setting the amount of the group 4A metal in the fluorine-containing resin film to 0.1% by mass or more.

  Add a hydrophilic functional group-containing monomer to 1% by mass and add a predetermined amount of emulsifier to an aqueous emulsion of a fluorine-containing resin having a hydrophilic functional group. A chemical conversion treatment solution prepared by adding 1% by mass in terms of conversion is applied to the surface of the plated steel plate with a bar coater and dried by heating at a final plate temperature of 140 ° C. to form a fluorine-containing resin film having a thickness of 30 μm. Formed. This fluorine-containing resin film was peeled off from the plated steel sheet, cut into a predetermined size, and used as a test piece. Each test piece (free fluorine-containing resin film) was measured for moisture permeability according to JIS Z0208 (measurement conditions, temperature 40 ± 0.5 ° C., relative humidity 90 ± 2%, 24 hours).

  FIG. 2 is a graph showing the relationship between the concentration of the emulsifier in the aqueous emulsion of the fluorine-containing resin and the moisture permeability of the fluorine-containing resin film. From this graph, it is understood that the moisture permeability of the fluorine-containing resin film can be significantly reduced by setting the concentration of the emulsifier in the emulsion to 1% by mass or less.

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

  Since the molded product of the plated steel sheet produced by the production method of the present invention is excellent in weather resistance, corrosion resistance, and discoloration resistance, it is useful in various applications such as exterior building materials. For example, the molded product of the Zn-based alloy-plated steel sheet of the present invention is 1) steel pipe, shape steel, support, beam, conveying member for vinyl house or agricultural house, 2) sound insulation wall, sound insulation wall, sound absorption wall, snow protection wall. , Guard rails, railings, protective fences, columns, 3) members for railway vehicles, overhead wire members, electrical equipment members, safety environment members, structural members, solar mounts, and the like.

Claims (17)

Preparing an Al-containing Zn-based alloy-plated steel sheet containing 0.05 to 60% by mass of Al;
Forming the Al-containing Zn-based alloy-plated steel sheet;
Applying a chemical conversion treatment liquid to the surface of the molded product of the Al-containing Zn-based alloy-plated steel sheet and drying to form a chemical conversion treatment film having a thickness of 0.5 to 10 μm;
A method for producing a molded product of a plated steel sheet, comprising:
The chemical conversion treatment liquid contains an emulsion of a fluorine-containing resin having an average particle size of 50 to 300 nm, and a group 4A metal oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide salt. ,
The fluorine-containing resin contains 0.05 to 5% by mass of a hydrophilic functional group selected from the group consisting of a carboxyl group, a sulfonic acid group and salts thereof, and 7 to 20% by mass of F atoms, and is a number average. The molecular weight is in the range of 1000 to 2 million,
In the chemical conversion treatment liquid, the amount of the oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide salt of the group 4A metal relative to the fluorine-containing resin is 0.1 to 5 mass in terms of metal. In the range of%,
A method for producing a formed product of a plated steel sheet.   The ratio of the carboxyl group and sulfonic acid group which the said fluorine-containing resin has is in the range of 5-60 in the molar ratio of a carboxyl group / sulfonic acid group, The manufacture of the processed product of the plated steel plate of Claim 1 Method.   The said chemical conversion liquid is a manufacturing method of the processed product of the plated steel plate of Claim 1 which further contains 0.05-3 mass% phosphate in conversion of P with respect to the said fluorine-containing resin.   The said chemical conversion liquid is a manufacturing method of the shaping | molding processed article of the plated steel plate of Claim 1 which further contains 0.5-5 mass% silane coupling agent with respect to the said fluorine-containing resin.   The said 4A group metal is a manufacturing method of the processed product of the plated steel plate of Claim 1 chosen from the group which consists of Ti, Zr, Hf, and these combination.   The Al-containing Zn-based alloy-plated steel sheet has a base chemical conversion treatment film containing a valve metal oxide or hydroxide and a valve metal fluoride. Production method. Preparing an Al-containing Zn-based alloy-plated steel sheet containing 0.05 to 60% by mass of Al;
Forming the Al-containing Zn-based alloy-plated steel sheet;
Applying a chemical conversion treatment liquid to the surface of the molded product of the Al-containing Zn-based alloy-plated steel sheet and drying to form a chemical conversion treatment film having a thickness of 0.5 to 10 μm;
A molded processed product of a plated steel sheet manufactured by a manufacturing method including:
The chemical conversion treatment liquid contains an emulsion of a fluorine-containing resin having an average particle size of 50 to 300 nm, and a group 4A metal oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide salt. ,
The fluorine-containing resin contains 0.05 to 5% by mass of a hydrophilic functional group selected from the group consisting of a carboxyl group, a sulfonic acid group and salts thereof, and 7 to 20% by mass of F atoms, and is a number average. The molecular weight is in the range of 1000 to 2 million,
In the chemical conversion treatment liquid, the amount of the oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide salt of the group 4A metal relative to the fluorine-containing resin is 0.1 to 5 mass in terms of metal. In the range of%,
Formed product of plated steel sheet.   The ratio of the carboxyl group and sulfonic acid group which the said fluorine-containing resin has is a shaping | molding processed article of the plated steel plate of Claim 7 which exists in the range of 5-60 in the molar ratio of a carboxyl group / sulfonic acid group.   The said chemical conversion treatment film is a shaping | molding processed article of the plated steel plate of Claim 7 which further contains 0.05-3 mass% phosphate in conversion of P with respect to the said fluorine-containing resin.   The molded product of a plated steel sheet according to claim 7, wherein the chemical conversion film further contains 0.5 to 5% by mass of a silane coupling agent with respect to the fluorine-containing resin.   The said 4A group metal is a molded product of the plated steel plate of Claim 7 chosen from the group which consists of Ti, Zr, Hf, and these combination.   The base chemical conversion treatment film containing a valve metal oxide or hydroxide and a valve metal fluoride is further provided between the Al-containing Zn-based alloy-plated steel sheet and the chemical conversion treatment film. Formed product of plated steel sheet. A chemical conversion treatment liquid applied to a molded product of an Al-containing Zn-based alloy-plated steel sheet containing 0.05 to 60% by mass of Al,
Containing an emulsion of a fluorine-containing resin having an average particle size of 50 to 300 nm, and a group 4A metal oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide salt,
The fluorine-containing resin contains 0.05 to 5% by mass of a hydrophilic functional group selected from the group consisting of a carboxyl group, a sulfonic acid group and salts thereof, and 7 to 20% by mass of F atoms, and is a number average. The molecular weight is in the range of 1000 to 2 million,
The amount of the oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide of the group 4A metal relative to the fluorine-containing resin is in the range of 0.1 to 5% by mass in terms of metal. ,
Chemical conversion solution.   The chemical conversion liquid according to claim 13, wherein a ratio of a carboxyl group and a sulfonic acid group of the fluorine-containing resin is in a range of 5 to 60 in terms of a molar ratio of carboxyl group / sulfonic acid group.   The chemical conversion liquid of Claim 13 which further contains 0.05-3 mass% phosphate in conversion of P with respect to the said fluorine-containing resin.   The chemical conversion liquid of Claim 13 which further contains 0.5-5 mass% silane coupling agent with respect to the said fluorine-containing resin.   The said 4A group metal is a chemical conversion liquid of Claim 13 chosen from the group which consists of Ti, Zr, Hf, and these combination.

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