JP5631231B2 - Chemical conversion Zn-plated steel sheet and method for producing the same - Google Patents

Description

  The present invention relates to a chemically treated Zn-based plated steel sheet having excellent weather resistance, water resistance, blackening resistance and film adhesion, and a method for producing the same.

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

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

  Various water-based fluororesin compositions have also been proposed (see, for example, Patent Document 3). However, all such water-based fluororesin compositions require baking at a high temperature (for example, 180 to 230 ° C., see Patent Document 3). Such high-temperature baking is practically impossible in field painting (usually using a normally dry resin), and is disadvantageous even in factory lines where heat drying is the mainstream.

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

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

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

  As mentioned above, the conventional chemical conversion treatment plating steel plate in which the chemical conversion treatment film containing an organic resin was formed might have insufficient weather resistance. In addition, the use of water-based fluororesin as the organic resin can improve the weather resistance (ultraviolet light resistance) of the chemically treated steel sheet, but on the other hand, the film forming property, water resistance and film adhesion are reduced. Therefore, weather resistance, water resistance and film adhesion could not be made compatible.

  The present invention has been made in view of the above points, and is a chemical conversion treatment Zn-based plated steel sheet having a chemical conversion treatment film containing an organic resin, all of weather resistance, water resistance, blackening resistance and film adhesion. It aims at providing the chemical conversion treatment Zn-plated steel plate which is excellent.

  The present inventor uses an aqueous fluorine-containing resin composition prepared without using an emulsifier as a raw material for the organic resin, and crosslinks these fluorine-containing resins with an organic crosslinking agent and a group 4A metal compound. Thus, the present inventors have found that the weather resistance, water resistance, blackening resistance and film adhesion of the chemical conversion film can all be improved, and further studies have been made to complete the present invention.

That is, the first of the present invention relates to the following chemical conversion treatment Zn-plated steel sheet.
[1] An Al-containing Zn-based alloy plated steel sheet containing 0.05 to 60% by mass of Al, and a chemical conversion film having a thickness of 0.5 to 10 μm formed on the surface of the Al-containing Zn-based alloy plated steel sheet, A chemical conversion-treated Zn-based plated steel sheet having a fluorine-containing resin containing 7 to 20% by mass of F atoms cross-linked by an organic cross-linking agent and a metal relative to the fluorine-containing resin. A conversion-treated Zn-based plated steel sheet containing 0.1 to 5% by mass of a 4A group metal compound in terms of conversion.
[2] The chemical conversion treated Zn-based plated steel sheet according to [1], wherein the organic crosslinking agent is a melamine compound.
[3] The chemical conversion treatment film further contains a phosphate; the amount of the phosphate with respect to the fluorine-containing resin is in the range of 0.05 to 3% by mass in terms of P, [1] or The chemical conversion treatment Zn-plated steel sheet according to [2].
[4] The chemical conversion film further contains a silane coupling agent; the amount of the silane coupling agent with respect to the fluorine-containing resin is in the range of 0.5 to 5% by mass. 3] The chemical conversion treatment Zn-plated steel sheet according to any one of [3].
[5] The chemical conversion-treated Zn-based 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 combinations thereof.
[6] A base chemical conversion film formed between the Al-containing Zn-based alloy-plated steel sheet and the chemical conversion film; further containing a valve metal oxide or hydroxide and a valve metal fluoride. The chemical conversion treatment Zn-plated steel sheet according to any one of [1] to [5].

2nd of this invention is related with the manufacturing method of the following chemical conversion treatment Zn-plated steel plate.
[7] A step of preparing an Al-containing Zn-based alloy-plated steel sheet containing 0.05 to 60% by mass of Al; a chemical conversion treatment liquid is applied to the surface of the Al-containing Zn-based alloy-plated steel sheet, and the film is dried. Forming a chemical conversion film having a thickness of 0.5 to 10 μm; the chemical conversion solution contains 0.05 to 5% by mass of a reactive functional group and 7 to 20% by mass of F atoms, and has a number average. A fluorine-containing resin having a molecular weight in the range of 1000 to 80,000, an organic crosslinking agent having a functional group capable of reacting with the reactive functional group, a group 4A metal oxyacid salt, fluoride, hydroxide, An organic acid salt, a carbonate or a peroxide salt; the amount of the organic crosslinking agent relative to the fluorine-containing resin is in the range of 0.8 to 9.6% by mass; the fluorine-containing resin Against Group 4A metal oxyacid salts, fluorides, hydroxides The amount of the organic acid salt, carbonate or peroxide is within the range of 0.1 to 5% by mass in terms of metal, and is a method for producing a chemical conversion treated Zn-based plated steel sheet.
[8] The fluorine-containing resin has a carboxyl group and a sulfonic acid group as the reactive functional group, and the ratio of the carboxyl group to the sulfonic acid group of the fluorine-containing resin is a molar ratio of carboxyl group / sulfonic acid group. The manufacturing method of the chemical conversion treatment Zn-plated steel plate as described in [7] which is in the range of 5-60 in ratio.
[9] The method for producing a chemically treated Zn-based plated steel sheet according to [7] or [8], wherein the organic crosslinking agent is a melamine compound.
[10] The chemical conversion treatment liquid further contains a phosphate; the amount of the phosphate with respect to the fluorine-containing resin is in the range of 0.05 to 3% by mass in terms of P, [7] to The manufacturing method of the chemical conversion treatment Zn-plated steel plate as described in any one of [9].
[11] The chemical conversion treatment liquid further contains a silane coupling agent; the amount of the silane coupling agent with respect to the fluorine-containing resin is in the range of 0.5 to 5% by mass. 10] The manufacturing method of the chemical conversion treatment Zn-plated steel plate as described in any one of [10].
[12] The method for producing a chemically treated Zn-based plated steel sheet according to any one of [7] to [11], wherein the 4A group metal is selected from the group consisting of Ti, Zr, Hf, and combinations thereof.
[13] Any of [7] to [12], further comprising the step of copolymerizing a fluoroolefin and a reactive functional group-containing monomer in an aqueous solvent in the absence of an emulsifier to prepare the fluorine-containing resin. The manufacturing method of the chemical conversion treatment Zn-plated steel plate as described in one term.
[14] Before the step of forming the chemical conversion treatment film; further comprising the step of applying a base chemical conversion treatment liquid to the surface of the Al-containing Zn-based alloy plated steel sheet and drying to form a base chemical conversion treatment film; The said base chemical conversion liquid is a manufacturing method of the chemical conversion treatment Zn-plated steel plate as described in any one of [7]-[13] containing a valve metal salt and fluoride ion.

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

1. Chemical conversion treatment Zn-plated steel sheet The chemical conversion treatment Zn-plated steel sheet of the present invention has an Al-containing Zn-based alloy-plated steel sheet (chemical conversion-treated original sheet) and a chemical conversion-treated film formed on the surface of the Al-containing Zn-based alloy-plated steel sheet. . The chemical conversion treatment Zn-based plated steel sheet of the present invention is characterized in that the chemical conversion treatment film contains a fluorine-containing resin and a group 4A metal compound crosslinked with an organic crosslinking agent.

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

[Chemical conversion treatment master]
As the chemical conversion treatment original plate, an Al-containing Zn-based alloy plated steel plate having excellent corrosion resistance and design properties is used. Here, “Al-containing Zn-based alloy plated steel sheet” means a steel sheet 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]
In some cases, an Al-containing Zn-based alloy-plated steel sheet used as a chemical conversion treatment original plate has a base chemical conversion treatment film containing a valve metal oxide or hydroxide and a valve metal fluoride. is there. Thus, when the base chemical conversion film is formed on the surface of the Al-containing Zn-based alloy plated steel sheet, the chemical conversion film is formed on the surface of the Al-containing Zn-based alloy plated steel sheet via the base chemical conversion film. .

  Valve metal oxides and hydroxides exhibit high insulation resistance. For this reason, the foundation | substrate chemical conversion treatment film containing the oxide or hydroxide of valve metal acts as a resistor with respect to the movement of an electron. Therefore, the reduction reaction of dissolved oxygen contained in the moisture in the atmosphere is suppressed, and the oxidation reaction of the paired Al-containing Zn-based alloy plated steel sheet is also suppressed. As a result, elution (corrosion) of metal components from the Al-containing Zn-based alloy-plated steel sheet serving as the substrate is suppressed. Of these, tetravalent compounds of Group IV A elements such as Ti, Zr, and Hf are stable compounds and form an excellent highly insulating film.

  In addition, a film defect is inevitably generated in a chemical conversion treatment film at the time of chemical conversion treatment or molding. Since the base material is exposed at the film defect portion, a corrosion inhibiting action cannot be expected even if chemical conversion treatment is performed. On the other hand, since the above-mentioned base chemical conversion treatment film also contains a fluoride of valve metal, it has a self-repairing action. That is, the fluoride of the valve metal dissolves in moisture in the atmosphere and then re-deposits as a hardly soluble oxide or hydroxide on the surface of the base steel exposed from the film defect portion. As a result, since the film defect portion is filled, a self-repairing action is exhibited.

  The chemical conversion-treated Zn-based alloy plated steel sheet of the present invention is manufactured by subjecting an Al-containing Zn-based alloy-plated steel sheet to chemical conversion treatment, but the Zn-based alloy-plated steel sheet before chemical conversion treatment has insufficient corrosion resistance. Therefore, corrosion may occur during storage or transportation of the Zn-based alloy-plated steel sheet before chemical conversion treatment or during forming. Therefore, by forming a base chemical conversion coating on the Zn-based alloy plated steel sheet before the chemical conversion treatment, it is possible to reliably prevent the occurrence of corrosion in the Zn-based alloy plated steel sheet before the chemical conversion treatment.

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

  The base chemical conversion treatment film has an effect of improving the adhesion between the Al-containing Zn-based alloy plated steel sheet and the chemical conversion treatment film. For this reason, the chemical conversion treatment film formed at the place where the base chemical conversion treatment film is peeled or the like is generally considered to have reduced film adhesion. However, Al is eluted from the plating layer in direct contact with the chemical conversion coating. The corrosion resistance and film adhesion of the chemical conversion film are improved by Al eluted in the chemical conversion film. Thus, 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 increases. The mechanism by which the corrosion resistance of the chemical conversion coating is improved by the presence of Al in the chemical conversion coating will be described later.

  The base chemical conversion treatment film can be formed by drying a coating film of the base chemical conversion treatment liquid formed on the surface of the Al-containing Zn-based alloy-plated steel sheet as the base material. The base chemical conversion treatment solution contains valve metal salt, fluoride ions, and water as a solvent. By drying the coating film of the base chemical conversion treatment solution, the valve metal salt becomes an oxide or hydroxide or a fluoride of valve metal contained in the base chemical conversion coating film.

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

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 are included. On the other hand, the fluoride ion source contained in the base chemical conversion treatment liquid may be a valve metal salt containing fluorine atoms, or may be a separate soluble fluoride (for example, (NH ₄ ) F).

  It is preferable that an organic acid having a chelating action is added to the base chemical conversion treatment solution in order to stabilize the valve metal salt. The organic acid can chelate metal ions to stabilize the base chemical conversion treatment solution. Therefore, the addition amount of the organic acid is set so that the molar ratio of organic acid / metal ion is 0.02 or more. Examples of the organic acid include tartaric acid, tannic acid, citric acid, succinic acid, malonic acid, lactic acid, acetic acid, ascorbic acid and the like. Among them, oxycarboxylic acids such as tartaric acid and polyhydric phenols such as tannic acid stabilize the base chemical conversion solution and also complement the fluoride's self-healing action, improving adhesion. It is valid.

  Various chemical orthophosphates and polyphosphates may be added to the base chemical conversion treatment solution. This is because the base chemical conversion treatment film to be formed contains a soluble or hardly soluble metal phosphate or composite phosphate.

  Soluble metal phosphate or composite phosphate elutes from the base chemical conversion coating to the film defects and reacts with the plating components (Zn, Al, etc.) of the Al-containing Zn-based alloy-plated steel sheet as the substrate. Insoluble phosphate is precipitated. In this way, the self-healing action of titanium fluoride is complemented. Further, since the atmosphere is slightly acidified when the soluble phosphate is dissociated, the hydrolysis of titanium fluoride, and hence the generation of a hardly soluble titanium oxide or hydroxide, is promoted.

  The metal of the soluble metal phosphate or composite phosphate can be an alkali metal, an alkaline earth metal, Mn, and the like. The soluble metal phosphate or composite phosphate may be added to the base chemical conversion treatment liquid in the form of various metal phosphates, or a combination of various metal salts and phosphoric acid, polyphosphoric acid or phosphate. You may add to a chemical conversion liquid.

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

  Organic chemical waxes such as fluorine, polyethylene, and styrene, inorganic lubricants such as silica, molybdenum disulfide, and talc can be added to the base chemical conversion treatment liquid. By adding these, the lubricity of the base chemical conversion coating can be improved. It is considered that the low melting point organic wax bleeds on the film surface and develops lubricity when the coating film of the base chemical conversion treatment liquid is dried. On the other hand, high-melting organic waxes and inorganic lubricants are present in a dispersed state in the film, but it is considered that the outermost surface layer of the film is exposed to the surface of the film in an island-like distribution to exhibit lubricity.

  When the base chemical conversion film obtained by drying the coating film of the base chemical conversion liquid is subjected to elemental analysis using fluorescent X-ray, ESCA, etc., the O concentration and the F concentration contained in the base chemical conversion film are measured. This element concentration ratio F / O (atomic ratio) is preferably 1/100 or more. It is for suppressing the corrosion of the obtained chemical conversion treatment steel plate. In particular, when the element concentration ratio F / O (atomic ratio) is 1/100 or more, the occurrence of corrosion starting from a film defect portion is significantly reduced. This is presumably because a sufficient amount of titanium fluoride is contained in the base chemical conversion treatment film and exhibits a self-repairing action.

[Chemical conversion coating]
The chemical conversion treatment film is formed on the surface of the above-mentioned Al-containing Zn-based alloy plated steel sheet (chemical conversion treatment original plate). The surface of the chemical conversion treatment original plate may be subjected to a base chemical conversion treatment such as forming a coating as a base, but the base chemical conversion treatment may not be performed. In addition, when the surface chemical conversion treatment is not performed on the surface of the chemical conversion treatment original plate, a chemical conversion treatment film is directly formed on the surface of the chemical conversion treatment original plate. This chemical conversion film improves the weather resistance and blackening resistance of the Al-containing Zn-based alloy plated steel sheet.

  The object of the present invention is to improve all of the weather resistance, water resistance, blackening 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 organic solvent-based fluorine-containing resins and water-based fluorine-containing resins. When a chemical conversion film is formed using an organic solvent-based fluorine-containing resin composition, recovery of the volatilized solvent becomes a problem, but when using a water-based fluorine-containing resin composition, 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, blackening resistance, and film | membrane adhesion | attachment using the water-system fluorine-containing resin composition easy to handle.

  As described above, according to the preliminary experiment of the present inventor, when the chemical conversion film is formed using the aqueous fluorine-containing resin composition, the water resistance decreases when the aqueous fluorine-containing resin composition is produced. It was thought that the emulsifier used remained in the chemical conversion film. Then, this inventor thought that the fall of the water resistance of a chemical conversion treatment film could be suppressed if an aqueous fluorine-containing resin composition can be manufactured without using an emulsifier.

  Therefore, as a result of investigations from various viewpoints, the present inventor can produce an aqueous fluorine-containing resin composition without using an emulsifier, as long as it is 1) a low molecular weight aqueous fluorine-containing resin. 2) In the case of forming a chemical conversion film using a low molecular weight fluorine-containing resin, a decrease in water resistance of the chemical conversion film becomes a problem, but when a chemical conversion film is formed using a low molecular weight fluorine-containing resin, In addition, it was found that sufficient water resistance can be imparted to the chemical conversion film by crosslinking between polymer chains of the fluorine-containing resin with an organic crosslinking agent and a group 4A metal compound.

  And this inventor is blending an organic type crosslinking agent and a 4A group metal compound further in the chemical conversion treatment liquid based on a low molecular weight water-based fluorine-containing resin, so that weather resistance, water resistance, blackening resistance and film It was found that a chemical conversion treatment film having excellent adhesion can be formed.

  Conventionally, when a fluorine-containing resin film is formed using an organic cross-linking agent, the cross-linking site by the organic cross-linking agent is preferentially weather-resistant and the film becomes porous, which reduces the water resistance of the film. There was a problem that. In response to this problem, the present inventor has found that the use of a combination of an organic crosslinking agent and a group 4A metal compound can suppress the formation of a porous film. The reason is not clear, but 1) the cross-linking reaction of the fluorine-containing resin further proceeds by combining the organic cross-linking agent and the group 4A metal compound, and the high molecular weight of the fluorine-containing resin increases the organic cross-linking agent. The possibility that the bond at the cross-linking site is more stable, and 2) the bond at the cross-linking site by the group 4A metal compound is stable. There is a possibility that the molecular weight is suppressed.

  In the chemical conversion film of the chemical conversion treatment Zn-plated steel sheet of the present invention, 1) weather resistance (ultraviolet resistance) is improved by blending a fluorine-containing resin (preferably a fluorine-containing olefin resin). In addition, 2) avoiding the use of an emulsifier during emulsion production by using a low molecular weight fluorine-containing resin, and 3) water resistance by crosslinking the fluorine-containing resin with an organic crosslinking agent and a group 4A metal compound. It is improving.

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

1) Fluorine-containing resin The chemical conversion film contains a fluorine-containing resin, more specifically, a fluorine-containing olefin resin as a main component. The content of the cross-linked fluorine-containing resin 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 content of F atoms in the fluorine-containing resin contained in the chemical conversion coating 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 fluorine-containing resin can be measured by using a fluorescent X-ray analyzer.

  In the chemical conversion treatment film of the chemical conversion treatment Zn-plated steel plate of this invention, it forms using the water-system fluororesin composition prepared without using an emulsifier. Here, the “aqueous fluorine-containing resin” means a fluorine-containing resin that can be dispersed in an aqueous solvent. The “aqueous fluororesin composition” means an emulsion or suspension of an aqueous fluorine-containing resin.

  Since it is difficult to prepare a high molecular weight fluorine-containing resin without using an emulsifier, the molecular weight of the fluorine-containing resin contained in an aqueous fluororesin composition prepared without using an emulsifier is usually 1000-8. It is within the range of 10,000. When a chemical conversion treatment film is formed using such a low molecular weight fluorine-containing resin, the chemical conversion treatment film has insufficient water resistance, and moisture or corrosive gas easily penetrates the chemical conversion treatment film into the plated steel sheet. As a result, the plated steel sheet may be corroded. Furthermore, when a chemical conversion film is formed using a low-molecular-weight fluorine-containing resin, radicals generated by the action of light energy and the like are likely to act on the end of the polymer chain. There is also a risk of hydrolysis. In order to prevent these problems, in the chemical conversion treatment film of the chemical conversion treatment Zn-plated steel sheet of the present invention, the polymer chains of the fluorine-containing resin are crosslinked with an organic crosslinking agent and a group 4A metal compound.

  The fluorine-containing resin is crosslinked with an organic crosslinking agent and a group 4A metal compound. The fluorine-containing resin before cross-linking has a reactive functional group, and the fluorine-containing resin is cross-linked by reacting this reactive functional group with an organic cross-linking agent or a group 4A metal compound. The kind of the reactive functional group possessed by the fluorine-containing resin before crosslinking is not particularly limited as long as it can react with the organic crosslinking agent and the group 4A metal compound. Examples of reactive functional groups include carboxyl groups, sulfonic acid groups, amino groups, hydroxyl groups and the like. From the viewpoint of enhancing the hydrophilicity of the fluorine-containing resin, a carboxyl group and a sulfonic acid group are preferable as the reactive functional group.

  The fluorine-containing resin before crosslinking preferably has a reactive functional group of 0.05 to 5% by mass. When the amount of the reactive functional group is less than 0.05% by mass, the organic crosslinking agent and the 4A group metal compound cannot be sufficiently crosslinked, and the water resistance of the chemical conversion coating cannot be sufficiently improved. On the other hand, when the amount of the reactive functional group exceeds 5% by mass, an unreacted reactive functional group capable of generating a radical remains when exposed to ultraviolet rays, and this radical does not bind the fluorine-containing resin. By stabilizing and causing decomposition, the weather resistance and water resistance of the chemical conversion film may be lowered.

  The content of the reactive functional group in the fluorine-containing resin may be obtained by dividing the total molar mass of the reactive functional group contained in the fluorine-containing resin by the number average molecular weight of the fluorine-containing resin. For example, when the fluorine-containing resin has a carboxyl group and a sulfonic acid group, since the molar mass of the carboxyl group is 45 and the molar mass of the sulfonic acid group is 81, the carboxyl group and the sulfonic acid group contained in the fluorine-containing resin. Obtain each number; multiply each by the molar mass to determine the total molar mass of reactive functional groups contained in the fluorine-containing resin. The number average molecular weight of the fluorine-containing resin is measured by GPC.

The fluorine-containing resin before crosslinking preferably has both a carboxyl group and a sulfonic acid group as reactive functional groups. The carboxyl group in the fluorine-containing resin forms a hydrogen bond or the like with the plating layer surface and contributes to improving the adhesion between the chemical conversion film and the plating layer surface. However, since H ⁺ is difficult to dissociate, an organic crosslinking agent and A crosslinking reaction with the 4A group metal compound hardly occurs. On the other hand, if the sulfonic acid group in the fluorine-containing resin is easily dissociated from H ^+, but remains in the film unreacted without cross-linking reaction with the organic cross-linking agent and the group 4A metal compound, the water molecule adsorbing action , The water resistance of the film may be significantly reduced. Therefore, it is preferable that the fluorine-containing resin contains 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.

  Examples of the fluorine-containing resin include a copolymer of a fluoroolefin and a reactive functional group-containing monomer. The reactive 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.

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

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

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

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

  A fluoroolefin copolymer having a reactive functional group can be obtained by copolymerizing the above monomers by a known polymerization method. At this time, even if no emulsifier is used, an aqueous composition can be produced as long as it is a low molecular weight fluoroolefin copolymer.

  As described above, the fluorine-containing resin is crosslinked with an organic crosslinking agent from the viewpoint of improving the water resistance of the chemical conversion coating. The type of the organic crosslinking agent that crosslinks the fluorine-containing resin is not particularly limited as long as it has a functional group capable of reacting with the reactive functional group of the fluorine-containing resin. Examples of the organic crosslinking agent include melamine resin, (blocked) isocyanate compound, phenol resin, oxazoline compound, aziridine compound and the like. These compounds may be used alone or in combination of two or more.

  For example, as a melamine resin, a compound obtained by reacting a methylol melamine derivative obtained by condensing melamine and formaldehyde with a lower alcohol (such as methyl alcohol, ethyl alcohol or isopropyl alcohol) and etherified, or a mixture thereof is used. sell. Examples of the methylol melamine derivative include monomethylol melamine, dimethylol melamine, trimethylol melamine, tetramethylol melamine, pentamethylol melamine, hexamethylol melamine and the like.

  Examples of the isocyanate compound include tolylene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, polymethylene polyphenyl polyisocyanate, tolidine diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, tetramethylxylylene diene. Isocyanates, hydrogenated xylylene diisocyanates, hydrogenated diphenylmethane diisocyanates, dicyclohexylmethane diisocyanates and the like can be used.

  Examples of the oxazoline compound include 2-methyl-2-oxazoline, 2-ethyl-2-oxazoline, 2-isopropyl-2-oxazoline, 2-n-propyl-2-oxazoline, 2-methyl-2- Oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline and the like can be used.

  Examples of the aziridine compounds include 1- (methylene-di-p-phenylene) bis-3,3-aziridinyl urea, 1,1 ′-(hexamethylene) bis-3,3-aziridinyl urea, and ethylene bis. -(2-aziridinylpropionate), 2,4,6-triaziridinyl-1,3,5-triazine and the like may be used.

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

  The group 4A metal compound also improves film adhesion, water resistance and blackening 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 blackening resistance. Examples of Group 4A metals include Ti, Zr, Hf, and the like.

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

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

3) 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.

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

  The manufacturing method of the chemical conversion treatment Zn-plated steel sheet of the present invention includes 1) a first step of preparing an Al-containing Zn-based alloy plated steel sheet (chemical conversion treatment original plate), and 2) a second step of preparing a chemical conversion treatment liquid. And 3) a third step of forming a chemical conversion film on the surface of the Al-containing Zn-based alloy plated steel sheet. In addition, when forming a chemical conversion treatment film on the surface of an Al content Zn system alloy plating steel plate via a foundation chemical conversion treatment film, before the 3rd step of forming a chemical conversion treatment film, an Al content Zn system alloy plating steel plate The method further includes the step of applying a base chemical conversion treatment liquid to the surface of the substrate and drying to form a base chemical conversion treatment film.

[Preparation of raw material for chemical conversion treatment]
In the first step, the aforementioned Al-containing Zn-based alloy plated steel sheet is prepared as a chemical conversion treatment original sheet.

[Preparation of chemical conversion solution]
In the second step, a chemical conversion treatment liquid containing a fluorine-containing resin having a reactive functional group (preferably a fluorine-containing olefin resin), an organic crosslinking agent, and a 4A group metal compound is prepared.

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

  The number average molecular weight of the fluorine-containing resin contained in the aqueous composition of the fluorine-containing resin produced in the absence of an emulsifier is usually in the range of 1000 to 80,000. This is because it is difficult to make the molecular weight of the fluorine-containing resin produced without using an emulsifier 80,000 or more.

  The content of the fluorine-containing resin in the chemical conversion treatment liquid is preferably in the range of 10 to 50 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 50 mass parts, there exists a possibility that the storage stability of a chemical conversion liquid may fall.

  Although the content of the organic crosslinking agent in the chemical conversion treatment liquid varies depending on the type of the organic crosslinking agent, it is generally 0.8 to 9.6 parts by mass with respect to 100 parts by mass of the fluorine-containing resin. Within the range is preferable. When the content of the organic crosslinking agent is less than 0.8 part by mass, the crosslinking reaction is insufficient and the water resistance of the chemical conversion coating cannot be sufficiently improved. On the other hand, when the content of the organic crosslinking agent is more than 9.6 parts by mass, the amount of the organic crosslinking agent that remains unreacted without crosslinking reaction increases, and the water resistance and weather resistance of the coating may be reduced. There is.

  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 stability of the processing liquid 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. Fluorine-based, polyethylene-based, styrene-based organic lubricants, and inorganic lubricants such as molybdenum disulfide and talc are brought into the coating from the chemical conversion solution, and the lubricity of the chemical conversion coating, as well as the chemical conversion-treated Zn-based plated steel sheet Improves workability. Moreover, predetermined | prescribed color tone can be provided to a chemical conversion treatment film by mix | blending an inorganic pigment, an organic pigment, organic dye, etc.

[Formation of chemical conversion coating]
In the 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 the chemical conversion treatment film, the chemical conversion treatment solution 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 and cured.

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

  What is necessary is just to set suitably the drying conditions of a chemical conversion liquid according to the kind of organic type hardening | curing agent to be used. However, when the temperature is kept above 300 ° C., the drying temperature is preferably 300 ° C. or lower because the organic component may be thermally decomposed to deteriorate the performance of the chemical conversion film. In the production method of the present invention, since the chemical conversion treatment liquid does not contain an emulsifier, the emulsifier does not remain even when the drying temperature is about 50 ° C., and a chemical conversion coating excellent in water resistance can be formed.

  By the above procedure, the chemical conversion treatment Zn-plated steel plate of this invention which is excellent in all of weather resistance, water resistance, and film | membrane adhesiveness can be manufactured.

[Formation of base chemical conversion coating]
In the step of forming the base chemical conversion coating, before the chemical conversion coating is formed, the base chemical conversion treatment liquid is applied to the surface of the Al-containing Zn-based alloy plated steel sheet prepared in the first step to form a coating film. The base chemical conversion treatment liquid can be applied by, for example, a roll coating method, a spin coating method, a spray method, or the like. The coating amount of the base chemical conversion treatment liquid is preferably adjusted so that the valve metal adhesion amount is 1 mg / m ² or more. It is for providing sufficient corrosion resistance to the chemical conversion treatment steel plate obtained. Moreover, it is preferable to adjust the application quantity of a foundation | substrate chemical conversion liquid so that the thickness of the foundation | substrate chemical conversion treatment film formed may be 3 nm or more and 1000 nm or less. Sufficient corrosion resistance is exhibited at 3 nm or more, and when it exceeds 1000 nm, cracks may occur due to stress when forming a steel sheet.

  By drying the coating film formed on the surface of the Al-containing Zn-based alloy-plated steel sheet without washing with water, a base chemical conversion treatment film can be formed. Although it can dry at normal temperature, when continuous operation is considered, it is preferable to hold at 50 degreeC or more and to shorten drying time. However, when the drying temperature exceeds 200 ° C., the organic component contained in the chemical conversion coating film is thermally decomposed, and the properties imparted with the organic component may be impaired.

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

[Example 1]
1. Preparation of chemical conversion treated Zn-based plated steel sheet The following two types of molten Al-containing Zn-based alloy plated steel sheets were prepared using SPCC having a thickness of 0.8 mm as a base material. In this example, these two types of molten Al-containing Zn-based alloy-plated steel sheets were used as chemical conversion treatment original sheets.
[Al-containing Zn-based alloy-plated steel sheet A]
・ Fused Zn—0.18 mass% Al alloy-plated steel sheet ・ Plating adhesion 45 g / m ²
[Al-containing Zn-based alloy-plated steel sheet B]
・ Fused Zn-6 mass% Al-3 mass% Mg alloy plated steel sheet ・ Plating adhesion 45 g / m ²

  A 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 heat-dried at a final plate temperature of 110 ° C. to form a chemical conversion treatment film having a thickness of 2.0 μm. In addition, since the chemical conversion liquid of No. 10 and No. 12 shown in Table 1 had gelatinized before application | coating, it could not form a chemical conversion treatment film.

  The chemical conversion treatment liquids No. 1 to 13 shown in Table 1 are organic to a fluorine-containing resin aqueous emulsion (see Table 2) having a predetermined amount of reactive functional groups (carboxyl group and sulfonic acid group). It was prepared by adding a system cross-linking agent or a 4A group metal compound. The chemical conversion liquid of chemical conversion liquid No. 14 was prepared by adding a group 4A metal compound or the like to an aqueous emulsion of urethane resin (nonvolatile content: 25% by mass; see Table 2).

  An aqueous emulsion containing a fluorine-containing resin was obtained by adding a predetermined amount of a fluoroolefin, a carboxyl group-containing monomer, and a sulfonic acid group-containing monomer to an aqueous solvent and copolymerizing them in the absence of an emulsifier. . Regarding the organic crosslinking agent, Becamine M-3 (DIC Corporation) was used as the melamine resin. As the isocyanate compound, DNW-5000 (DIC Corporation) was used. As the oxazoline-based compound, Epocros K-2010E (Nippon Shokubai Co., Ltd.) was used. Chemitite DZ-22E (Nippon Shokubai Co., Ltd.) was used as the aziridine compound. PR135 (Sumika Bayern Urethane Co., Ltd.) was used as an aqueous emulsion containing a urethane resin. A-1891 (Momentive Performance Materials Japan GK) was used as the silane coupling agent.

  The amounts of Group 4A metal, phosphate and silane coupling agent relative to the organic resin in the chemical conversion coating of each chemical conversion treatment Zn-plated steel sheet were measured using a fluorescent X-ray analyzer. The contents of phosphate and silane coupling agent were calculated from the measured values of P and Si. Table 3 shows the amounts of Group 4A metal, phosphate, and silane coupling agent with respect to the organic resin in the chemical conversion film formed for each chemical conversion solution.

2. Evaluation of chemical conversion treatment Zn-plated steel sheet (1) Accelerated weather resistance test A test piece was cut out from each chemical conversion treatment Zn-plated steel sheet, and an accelerated weather resistance test (xenon lamp method) was conducted in accordance with JIS K5600-7-7: 2008. Carried out. In this test, the process of spraying water for 18 minutes while irradiating the light of a xenon arc lamp for 120 minutes was defined as 1 cycle (2 hours), and this process was repeated 0 to 1000 cycles (0, 500, 1000 cycles).

(2) Evaluation of weather resistance About each chemical conversion treatment Zn-plated steel sheet, the thickness of the chemical conversion treatment film before and after the accelerated weathering test was measured with a cross-sectional microscope, and the coating film residual rate was determined. About each chemical conversion treatment Zn-plated steel sheet, when the coating film residual ratio is 95% or more, “◎”, when it is 80% or more and less than 95%, “◯”, when it is 60% or more and less than 80%, “△”, When it was 30% or more and less than 60%, “▲” was evaluated, and when it was less than 30%, “×” was evaluated.

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

(4) Evaluation of corrosion resistance of flat part About each chemical conversion treatment Zn-plated steel sheet, a salt spray test (according to JIS Z2371; 120 hours) is performed using the test piece after the accelerated weathering test, and the white rust generation area of the flat part Rate was evaluated. About each chemical conversion treatment Zn-plated steel sheet, when the white rust generation area ratio is 5% or less, “◎”, when it exceeds 5% and 10% or less, “◯”, and when it exceeds 10% and 30% or less, “ “△” was evaluated as “▲” when 30% was exceeded and 50% or less, and “X” was evaluated when 50% was exceeded.

(5) Evaluation result About each chemical conversion treatment Zn-plated steel sheet (Examples 1-16, Comparative Examples 1-8), the kind of chemical conversion treatment original plate, the kind of used processing liquid, a weather resistance test, and a blackening resistance test Table 4 shows the evaluation results of the flat portion corrosion resistance test.

  The weather resistance was evaluated by the coating film remaining rate of the chemical conversion coating after the accelerated weather resistance test. In the chemical conversion treatment Zn-plated steel sheets of Comparative Example 4 and Comparative Example 8 in which a chemical conversion treatment film was formed using a urethane resin, the chemical conversion treatment film disappeared after 500 cycles (equivalent to outdoor exposure for 5 years). Moreover, in the chemical conversion treatment coated steel sheets of Comparative Example 3 and Comparative Example 7 in which the chemical conversion treatment film containing a fluorine-containing olefin resin having an excessive amount of reactive functional groups was formed, the chemical conversion treatment film decreased as the number of cycles increased. Oops. On the other hand, in the chemical conversion treatment Zn-plated steel sheets of Examples 1 to 16 in which the chemical conversion treatment film was formed using a fluorine-containing resin having a predetermined amount of a reactive functional group, an organic crosslinking agent, and a group 4A metal compound, 1000 cycles ( (Equivalent to outdoor exposure for 10 years) The film thickness of the chemical conversion film hardly changed even after repeated.

Blackening resistance was evaluated by the difference in brightness (ΔL ^* value) before and after the accelerated weather resistance test. In the chemical conversion treatment plated steel sheets of Comparative Example 4 and Comparative Example 8 in which the chemical conversion treatment film was formed using a urethane resin, the blackening of the plating layer progressed with an increase in the number of cycles, and the lightness was lowered. On the other hand, in the chemical conversion treatment plated steel plates of Examples 1 to 16 in which a chemical conversion treatment film containing a fluorine-containing resin having a predetermined amount of a reactive functional group, an organic crosslinking agent, and a group 4A metal compound was formed, 1000 cycles (10 exposure outdoors) (Equivalent to year) The brightness did not decrease even after repeated.

  Corrosion resistance was evaluated based on the white rust generation area ratio after the salt spray test. In the chemical conversion treatment Zn-plated steel sheets of Comparative Example 4 and Comparative Example 8 in which a chemical conversion treatment film was formed using a urethane resin, although the corrosion resistance was good before the accelerated weather resistance test, the corrosion resistance was significantly reduced as the film disappeared. have done. Moreover, the comparison which formed the chemical conversion treatment film containing the chemical conversion treatment Zn-plated steel plate of the comparative examples 1 and 5 which formed the chemical conversion treatment film which does not contain a 4A group metal compound, and the fluorine-containing resin which has an excessive amount of reactive functional groups In the chemical conversion treatment Zn-plated steel sheets of Examples 2 and 6, the corrosion resistance was inferior before the accelerated weathering test. On the other hand, in the chemical conversion treatment Zn-plated steel sheets of Examples 1 to 16 in which a chemical conversion treatment film containing a fluorine-containing resin having a predetermined amount of a reactive functional group, an organic crosslinking agent, and a group 4A metal compound was formed, 1000 cycles (outdoors Corrosion resistance was good even after repeated exposure.

  From the above results, it can be seen that the chemically treated Zn-based plated steel sheet of the present invention is excellent in weather resistance, water resistance, blackening resistance and film adhesion.

[Example 2]
1. Preparation of chemical conversion treatment Zn-plated steel sheet (1) Formation of base chemical conversion treatment film Undercoat formation of the composition shown in Table 5 on each surface of the aforementioned Al-containing Zn-based alloy-plated steel sheet A and Al-containing Zn-based alloy-plated steel sheet B After apply | coating a process liquid, it heated and dried at the ultimate plate temperature of 70-170 degreeC, and formed the base chemical conversion treatment film. Using a fluorescent X-ray analyzer, the composition of the formed base chemical conversion coating was analyzed. The results are shown in Table 6.

(2) Formation of chemical conversion treatment film The above-mentioned chemical conversion treatment liquid No. 7 chemical conversion treatment liquid (see Table 1) is applied to the surface of the formed base chemical conversion treatment film, and heated and dried at an ultimate plate temperature of 110 ° C. A chemical conversion film having a thickness of 2.0 μm was formed.

2. Evaluation of chemical conversion treatment Zn-plated steel sheet The accelerated weathering test was implemented about the produced chemical conversion treatment Zn-plated steel sheet by the method similar to the above-mentioned "evaluation of chemical conversion treatment Zn-plated steel sheet". And the weather resistance of the produced chemical conversion treatment Zn-plated steel plate, blackening resistance, and the corrosion resistance of a flat part and a crosscut part were evaluated. Table 7 shows the evaluation results. The corrosion resistance of the cross cut portion was evaluated by the following procedure.

Evaluation of corrosion resistance of cross-cut portion For each chemically treated Zn-based plated steel sheet, after the accelerated weathering test, an X-shaped cut portion (cross-cut portion) was formed on the surface to obtain a test piece exposing the plating layer . The obtained test piece was subjected to a salt spray test (based on JIS Z2371; 120 hours), and the white rust generation area ratio of the cross cut part was evaluated. About each chemical conversion treatment Zn-plated steel sheet, when the white rust generation area ratio is 5% or less, “◎”, when it exceeds 5% and 10% or less, “◯”, and when it exceeds 10% and 30% or less, “ “△” was evaluated as “▲” when 30% was exceeded and 50% or less, and “X” was evaluated when 50% was exceeded.

  In the chemical conversion treatment Zn-plated steel sheets of Examples 17 to 32 in which a chemical conversion treatment film containing a fluorine-containing resin having a predetermined amount of hydrophilic functional group and a group 4A metal compound is formed on the base chemical conversion treatment film, 1000 cycles ( Even after repeated exposure for 10 years, the film thickness and brightness of the chemical conversion film were hardly reduced.

  Moreover, in any Example, the favorable result was shown in the corrosion resistance test of the flat part. Furthermore, in any of the examples, almost good results were shown in the corrosion resistance test of the crosscut portion. This is considered to be because the self-repairing action of the base chemical conversion coating was exhibited and the crosscut portion (film defect portion) was repaired. Especially about the chemical conversion treatment Zn-plated steel sheets of Examples 17 to 22 and 25 to 30 in which phosphorus (P) is contained in the base chemical conversion treatment film, the corrosion resistance of the crosscut portion is more excellent.

  Since the chemical conversion treatment Zn-plated steel sheet of the present invention is excellent in weather resistance, water resistance, blackening resistance and film adhesion, it is useful in various applications such as exterior building materials. For example, the chemical conversion-treated Zn-based plated steel sheet of the present invention includes: 1) steel pipe, shape steel, support, beam, conveying member for a greenhouse or agricultural house, 2) sound insulation wall, sound insulation wall, sound absorption wall, snow insulation wall, guardrail, It can be suitably used for applications such as railings, protective fences, columns, 3) railway vehicle members, overhead wire members, electrical equipment members, safety environment members, structural members, and solar mounts.

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

Claims (14)

An Al-containing Zn-based alloy-plated steel sheet containing 0.05 to 60% by mass of Al;
A chemical conversion treatment Zn-based plated steel sheet having a film thickness of 0.5 to 10 μm formed on the surface of the Al-containing Zn-based alloy plated steel sheet,
The chemical conversion treatment film includes an aqueous fluorine-containing resin composition containing 7 to 20% by mass of F atoms, containing a fluorine-containing resin having a number average molecular weight in the range of 1000 to 80,000 and not containing an emulsifier; A coating formed by applying a chemical conversion treatment liquid containing an organic crosslinking agent and a group 4A metal compound to the surface of the Al-containing Zn-based alloy-plated steel sheet and drying the coating, and the organic crosslinking agent containing said fluorine-containing resin that is crosslinked, and said 4A-group metal compound of 0.1 to 5 mass% in terms of metal relative to the fluorine-containing resin by,
Chemical conversion treatment Zn-plated steel sheet.   The said organic type crosslinking agent is a chemical conversion treatment Zn type plated steel plate of Claim 1 which is a melamine compound. The chemical conversion film further contains a phosphate,
The amount of the phosphate with respect to the fluorine-containing resin is in the range of 0.05 to 3% by mass in terms of P.
The chemical conversion treatment Zn-plated steel sheet according to claim 1. The chemical conversion film further contains a silane coupling agent,
The amount of the silane coupling agent relative to the fluorine-containing resin is in the range of 0.5 to 5% by mass.
The chemical conversion treatment Zn-plated steel sheet according to claim 1.   The said 4A group metal is a chemical conversion treatment Zn-plated steel plate of Claim 1 chosen from the group which consists of Ti, Zr, Hf, and these combination. Formed between the Al-containing Zn-based alloy-plated steel sheet and the chemical conversion film,
The chemical conversion treatment Zn-plated steel plate of Claim 1 which further has the foundation | substrate chemical conversion treatment film containing the oxide or hydroxide of valve metal, and the fluoride of valve metal. Preparing an Al-containing Zn-based alloy-plated steel sheet containing 0.05 to 60% by mass of Al;
Applying a chemical conversion treatment liquid to the surface of the Al-containing Zn-based alloy-plated steel sheet and drying to form a chemical conversion treatment film having a film thickness of 0.5 to 10 μm.
The chemical conversion treatment solution contains a fluorine-containing resin containing 0.05 to 5% by mass of a reactive functional group and 7 to 20% by mass of F atoms, and having a number average molecular weight in the range of 1000 to 80,000 . And an aqueous fluorine-containing resin composition containing no emulsifier, an organic crosslinking agent having a functional group capable of reacting with the reactive functional group, a group 4A metal oxyacid salt, fluoride, hydroxide, organic acid salt Containing either carbonates or peroxides,
The amount of the organic crosslinking agent relative to the fluorine-containing resin is in the range of 0.8 to 9.6% by mass,
The amount of the oxyacid salt, fluoride, hydroxide, organic acid salt, carbonate or peroxide of the group 4A metal in the fluorine-containing resin is within a range of 0.1 to 5% by mass in terms of metal. is there,
The manufacturing method of a chemical conversion treatment Zn-plated steel plate. The fluorine-containing resin has a carboxyl group and a sulfonic acid group as the reactive functional group,
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, Manufacture of the chemical conversion treatment Zn-plated steel plate of Claim 7 Method.   The said organic type crosslinking agent is a manufacturing method of the chemical conversion treatment Zn-plated steel plate of Claim 7 which is a melamine compound. The chemical conversion treatment liquid further contains a phosphate,
The amount of the phosphate with respect to the fluorine-containing resin is in the range of 0.05 to 3% by mass in terms of P.
The manufacturing method of the chemical conversion treatment Zn-plated steel plate of Claim 7. The chemical conversion treatment liquid further contains a silane coupling agent,
The amount of the silane coupling agent relative to the fluorine-containing resin is in the range of 0.5 to 5% by mass.
The manufacturing method of the chemical conversion treatment Zn-plated steel plate of Claim 7.   The said 4A group metal is a manufacturing method of the chemical conversion treatment Zn-plated steel plate of Claim 7 chosen from the group which consists of Ti, Zr, Hf, and these combination. The chemical conversion treatment Zn system according to claim 7, further comprising a step of copolymerizing a fluoroolefin and a reactive functional group-containing monomer in an aqueous solvent in the absence of an emulsifier to prepare the aqueous fluorine-containing resin composition. Manufacturing method of plated steel sheet. Before the step of forming the chemical conversion film,
Applying a base chemical conversion treatment liquid on the surface of the Al-containing Zn-based alloy-plated steel sheet and drying to further form a base chemical conversion treatment film;
The said base chemical conversion liquid is a manufacturing method of the chemical conversion treatment Zn-plated steel plate of Claim 7 containing a valve metal salt and fluoride ion.