KR102431941B1 - painted galvanized steel sheet - Google Patents

Abstract

One aspect of the present invention is a coated galvanized steel sheet having a resin film containing silica and magnesium hydroxide on the surface of the galvanized steel sheet, wherein the total content of silica and magnesium hydroxide in the resin film is 50 to 75 mass%, The content of the resin component of the resin film is 25 to 50 mass %, the mass ratio of the magnesium hydroxide to the silica is 0.2 to 1.5, and the thickness of the resin film is 0.3 to 3.0 μm, It relates to a coated galvanized steel sheet. .

Description

painted galvanized steel sheet

The present invention relates to a coated galvanized steel sheet having, on the surface of the galvanized steel sheet, a film containing an inorganic compound in a resin (hereinafter sometimes referred to as an “inorganic coating”).

Surface-treated steel sheet has excellent corrosion resistance because plating or painting is applied to the surface of the base material. However, in the end surface of the surface-treated steel sheet to which the steel which is a base material is exposed, red rust generate|occur|produces gradually in an atmospheric environment. Red rust generated on the end face of the surface-treated steel sheet not only deteriorates the appearance, but, for example, when it occurs in the vicinity of a circuit board such as an electric product, it falls off from the steel sheet and short-circuits the circuit, resulting in a problem that impairs the safety of the product. There are concerns.

In order to prevent the occurrence of red rust in the cross section of the coated steel sheet, various studies have been made so far. For example, in a general precoated metal plate, since it has a coating film with a thickness of several tens of μm, the protective action by the rust preventive component eluted from the coating film to the cut end surface is large, and the improvement of the cross-sectional corrosion resistance by optimizing the coating film component is achieved. is becoming On the other hand, in a coated steel sheet having a special chemical conversion treatment film having a smaller coating film thickness than a precoated metal sheet, it is difficult to obtain good cross-sectional corrosion resistance because there are few rust preventive components that can be eluted and the cut end surface cannot be sufficiently covered. Therefore, in applications requiring a high degree of cross-sectional corrosion resistance, parts coated or plated after press forming a cold-rolled steel sheet are often applied.

With respect to zinc plating, it is known that magnesium-based compounds exhibit a rust-preventing effect. In recent years, a technology for a highly corrosion-resistant coating containing nano-sized magnesium particles has been developed.

As such a technique, for example, Patent Document 1 discloses a coating composed of a composition containing nanomagnesium hydroxide particles having an average particle diameter of less than 200 nm.

In addition, as a technique for maintaining the corrosion resistance of a film by repairing and passivating a film defect portion by a self-repairing action, Patent Document 2 discloses a film formed using a rust preventive agent for metal containing a composite colloid composed of magnesium hydroxide and fine silica. is starting

On the other hand, as a technique in which a magnesium-containing film is used for a film of a chromium-free organic coated steel sheet, Patent Document 3 discloses a composite containing oxide particles, phosphoric acid and/or phosphoric acid compound, and a magnesium compound on the surface of a zinc-based plated steel sheet. Disclosed is an organic coated steel sheet having an oxide film and having, on the composite oxide film, an organic film containing a reaction product of an organic resin and an active hydrogen-containing compound, and an antirust additive component.

The coating disclosed in Patent Document 1 has a thickness of 2.5 to 75 µm, and does not assume that it is press-molded. Moreover, the coating disclosed in patent document 1 does not express sufficient rust prevention effect after press molding that thickness is several micrometers or less.

For the coating film disclosed in Patent Document 2, it is necessary to use a metal rust preventive agent containing a composite colloid composed of magnesium hydroxide and particulate silica when forming the coating film, but the composite colloid is unstable because it reacts with the treatment liquid component, and the coating causes gelation. It is prone to problems in the process. Moreover, although it is estimated that the coating film disclosed in patent document 2 is effective in corrosion resistance at the point which elutes on a cross section, since it contains a water-soluble component, water resistance is inadequate, and there is a great possibility of discoloration due to dew condensation or wetness with water during transportation.

In the organic coated steel sheet disclosed in Patent Document 3, since the magnesium compound is added in the form of water-soluble ions or molecules during the formation of the composite oxide film, increasing the amount of the magnesium compound added decreases the stability of the treatment solution. For this reason, there is a limit in improving the corrosion inhibitory effect of the composite oxide film by increasing the magnesium component. In addition, the organic coated steel sheet disclosed in Patent Document 3 has problems of low productivity and high manufacturing cost since it is necessary to further form an organic coating after forming the composite oxide coating.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a coated galvanized steel sheet having excellent cross-sectional corrosion resistance even when the thickness of the film is several μm or less.

Japanese Patent Laid-Open No. 2016-104574 Japanese Patent Laid-Open No. 2002-322569 Japanese Patent Laid-Open No. 2002-053979

One aspect of the present invention is a coated galvanized steel sheet having a resin film containing silica and magnesium hydroxide on the surface of the galvanized steel sheet, wherein the total content of silica and magnesium hydroxide in the resin film is 50 to 75 mass%, and It is a coated galvanized steel sheet in which the content of the resin component of the resin film is 25 to 50 mass %, the mass ratio of the magnesium hydroxide to the silica is 0.2 to 1.5, and the thickness of the resin film is 0.3 to 3.0 µm.

MEANS TO SOLVE THE PROBLEM In order to achieve the said objective, the present inventors examined from various angles. As a result, by appropriately adjusting the total content of silica and magnesium hydroxide in the resin film, the mass ratio of magnesium hydroxide to silica, and the thickness of the resin film, the protective action of the cut end surface of the galvanized steel sheet is enhanced, It was found that the object was well achieved, and the present invention was completed.

A coated galvanized steel sheet according to an embodiment of the present invention has a resin film containing silica and magnesium hydroxide on the surface of the galvanized steel sheet. The total content of silica and magnesium hydroxide in the said resin film is 50-75 mass %. Content of the resin component of the said resin film is 25-50 mass %. The mass ratio of the magnesium hydroxide to the silica is 0.2 to 1.5. The thickness of the resin film is 0.3 to 3.0 μm.

According to the said structure, even when the thickness of a film is several micrometers or less, the coated galvanized steel sheet which shows the outstanding corrosion resistance can be provided.

Hereinafter, although this embodiment is demonstrated more concretely, this invention is not limited to these.

[Total content of silica and magnesium hydroxide: 50 to 75 mass %]

In this embodiment, the total content of silica and magnesium hydroxide in a resin film shall be 50-75 mass %. It is estimated that the silica and magnesium hydroxide in a resin film elute from a resin film in a corrosive environment, and express the effect|action which protects a cut end surface. If the total content of silica and magnesium hydroxide in the resin film is less than 50 mass %, the elution amount is not sufficient, so that the protective action of the cross section is not ensured. Preferably it is 55 mass % or more, More preferably, it is 60 mass % or more. On the other hand, when the total content of silica and magnesium hydroxide in the resin film exceeds 75% by mass, the resin content as a binder is insufficient to form a film with many defective portions, so that corrosion resistance as a flat plate is not ensured. Preferably it is 73 mass % or less, More preferably, it is 70 mass % or less.

In addition, in the following description, the inorganic compound contained in the resin film of this embodiment is silica and magnesium hydroxide, and an inorganic film means the resin film containing silica and magnesium hydroxide.

As for the silica used by this embodiment, colloidal silica excellent in compatibility with the aqueous resin mentioned later is preferable. In addition, when the average particle diameter of silica becomes too large, the density of the coating may decrease or coating defects may occur. Therefore, the average particle diameter D ₅₀ is preferably 500 nm or less, and more preferably 450 nm or less. In addition, the average particle diameter D50 of silica means the average particle _diameter when the integrated value (integrated value) of silica becomes 50 mass %.

The magnesium hydroxide used in this embodiment should just be stable as an aqueous dispersion, and the powder and dispersion method of magnesium hydroxide are not specifically limited. The average particle diameter D ₅₀ in a state in which magnesium hydroxide is dispersed in water, that is, the average particle diameter D ₅₀ of magnesium hydroxide in the aqueous magnesium hydroxide dispersion, is preferably smaller than the resin film thickness, for example, preferably 0.7 μm or less. do. Thereby, corrosion of the cross section by insufficient elution amount resulting from the particle|grain magnesium hydroxide falling off from the resin film can be suppressed. On the other hand, the lower limit of the average particle diameter D ₅₀ in a state in which magnesium hydroxide is dispersed in water is not particularly limited, but if the average particle diameter D ₅₀ is too small, the stability of the dispersion (eg, dispersion) may decrease. Therefore, it is preferable that it is 0.1 micrometer or more. More preferably, it is 0.14 micrometer or more. In addition, the average particle diameter D50 of magnesium hydroxide means the average particle _diameter when the integrated value (integrated value) of magnesium hydroxide becomes 50 mass %.

When combining the magnesium hydroxide aqueous dispersion, a polymer dispersing agent (for example, a water-soluble acrylic resin, a water-soluble styrene acrylic resin, a nonionic surfactant) having a small adverse effect on corrosion resistance when a resin film is used may be used.

[Content of the resin component in the resin film: 25 to 50% by mass]

In this embodiment, content of the resin component in a resin film shall be 25-50 mass %. As mentioned above, when the resin component in a resin film runs short, it will become a film|membrane with many defect parts, and corrosion resistance will deteriorate. From such a viewpoint, content of the resin component in a resin film shall be 25 mass % or more. Preferably it is 30 mass % or more. However, when the content of the resin component in the resin film is too large, in addition to deterioration of corrosion resistance due to a decrease in density in the resin film, the resin film is softened, and there is a fear that the occurrence of film scum increases during press molding. From such a viewpoint, content of the resin component in a resin film shall be 50 mass % or less. Preferably it is 40 mass % or less.

[Mass ratio of magnesium hydroxide to silica: 0.2 to 1.5]

In the present embodiment, the mass ratio of magnesium hydroxide to silica is 0.2 to 1.5. Both magnesium hydroxide and silica are known as rust inhibitors for galvanizing. The present inventors discovered that the outstanding corrosion resistance was obtained by mix|blending magnesium hydroxide and silica in a resin film in a specific mass ratio. When the mass ratio of magnesium hydroxide to silica [Mg(OH) ₂ /SiO ₂ ] is in the range of 0.2 to 1.5, excellent corrosion resistance is exhibited. It is preferable that this mass ratio is 0.3 or more, and it is preferable that it is 1.0 or less.

Although the mechanism by which corrosion resistance improves by adjusting the said mass ratio to an appropriate range is unknown, it is thought probably as follows. That is, it is thought that magnesium ions eluted from magnesium hydroxide stabilized a corrosion product having a high protective action against zinc plating generated by silica, and the barrier effect of the stabilized corrosion product was improved. The protective action against the zinc plating means a barrier property that blocks corrosion factors such as water and oxygen. In addition, it is considered that the component eluted from the resin film in a corrosive environment is also affected by the mass ratio of magnesium hydroxide to silica [Mg(OH) ₂ /SiO ₂ ], and by setting the mass ratio within the range of 0.2 to 1.5, It is estimated that the component eluted from the resin film becomes the composition ratio excellent in the protective action of the cross section.

In addition, by using particulate magnesium hydroxide, it becomes possible to increase the addition ratio of the magnesium component in the resin film without impairing the stability of the treatment liquid, and as a result, a corrosion product with a high protective action against zinc plating is supplied to the cut end surface. it is presumed to be

[Resin film thickness: 0.3 to 3.0 μm]

The resin film thickness also affects the corrosion resistance of both the flat plate portion and the end face portion. In the present embodiment, the resin film thickness is 0.3 µm or more. In a flat plate part, if the resin film thickness is 0.2 micrometer, the corrosion resistance of a practically satisfactory level is acquired. However, in the cross section, it is because corrosion resistance is insufficient when the resin film thickness is less than 0.3 µm. In addition, about the upper limit of the resin film thickness, since it depends on the area (board thickness) of a cut surface, it is not necessary to determine in particular. However, since a large-scale drying facility is required when the resin film thickness exceeds 3.0 µm, the resin film thickness is preferably 3.0 µm or less from the viewpoint of manufacturing cost.

[Type of resin]

It does not specifically limit about the kind of resin used by this embodiment, Both aqueous resin and non-aqueous resin can be used. When using an aqueous dispersion of magnesium hydroxide or colloidal silica, it is preferable to use an aqueous resin. Although it does not specifically limit also about such an aqueous resin, It is preferable that it can mix with the aqueous dispersion of magnesium hydroxide and colloidal silica. In addition, the water-based resin in this embodiment points out the resin used as an aqueous dispersion, or water-soluble resin.

As such water-based resin, polyolefin-based resin, polyurethane-based resin, and polyester-based resin are preferable, and among these, polyolefin-based resin and polyurethane-based resin are more preferable. Hereinafter, a polyolefin-type resin and a polyurethane-type resin are demonstrated concretely, respectively.

[Polyolefin resin]

As the polyolefin-based resin, an ethylene-unsaturated carboxylic acid copolymer is preferable. As an ethylene-unsaturated carboxylic acid copolymer, the thing of Unexamined-Japanese-Patent No. 2005-246953 and Unexamined-Japanese-Patent No. 2006-43913 can be used, for example.

Examples of the unsaturated carboxylic acid include (meth)acrylic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, and itaconic acid. Thus, an ethylene-unsaturated carboxylic acid copolymer can be obtained.

The copolymerization ratio of the unsaturated carboxylic acid with respect to ethylene, when the total amount of the monomer is 100 mass %, is preferably 10 mass % or more, more preferably 15 mass % or more, and preferably 40 mass % or less, 25 It is more preferable that it is mass % or less. When the content of the unsaturated carboxylic acid is less than 10% by mass, the film strength effect is not exhibited because there are few carboxyl groups serving as the starting point of intermolecular association by ion clusters, and the emulsion stability of the coating solution (emulsion composition) described later may be poor. . On the other hand, when an unsaturated carboxylic acid exceeds 40 mass %, the corrosion resistance and water resistance of a resin film may be inferior.

Since the said ethylene-unsaturated carboxylic acid copolymer has a carboxyl group, emulsification (water dispersion) of a coating liquid becomes possible by neutralizing with an organic base or a metal ion.

As the organic base, from the viewpoint of not reducing the corrosion resistance of the resin film too much, an amine having a boiling point under atmospheric pressure of 100°C or less is preferable. Specific examples include tertiary amines such as triethylamine; secondary amines such as diethylamine; Primary amines, such as a propylamine, etc. are mentioned, These can be used 1 type or in mixture of 2 or more types. Among these, a tertiary amine is preferable and triethylamine is the most preferable. Moreover, it is preferable to use a monovalent|monohydric metal ion together with the said amine from a viewpoint of improving solvent resistance and film hardness.

It is preferable that the said amine is 0.2 mol or more with respect to 1 mol of carboxyl groups in the ethylene-unsaturated carboxylic acid copolymer from a viewpoint of ensuring corrosion resistance, on the other hand, it is preferable that it is 0.8 mol or less. And, it is more preferable that it is 0.3 mol or more, and, on the other hand, it is more preferable that it is 0.6 mol or less.

The amount of the monovalent metal ion is preferably 0.02 mol or more, more preferably 0.03 mol or more, based on 1 mol of the carboxyl groups in the ethylene-unsaturated carboxylic acid copolymer from the viewpoint of ensuring the emulsion stability of the coating solution. On the other hand, from the viewpoint of ensuring corrosion resistance, it is preferably 0.4 mol or less, and more preferably 0.3 mol or less, based on 1 mol of the carboxyl groups in the ethylene-unsaturated carboxylic acid copolymer. On the other hand, as for the metal compound for providing a monovalent|monohydric metal ion, NaOH, KOH, LiOH, etc. are preferable, and NaOH has the best performance and is preferable.

The ethylene-unsaturated carboxylic acid copolymer is, if necessary, in the presence of a carboxylic acid polymer to be described later, for example, in a container capable of high temperature (about 150 ° C.) and high pressure (about 5 atmospheres) reaction, high-speed stirring 1 to 6 Over time, it becomes emulsified (emulsified). In the emulsification, an appropriate amount of a compound having a surfactant function, such as tall oil fatty acid, may be added. Moreover, you may add a hydrophilic organic solvent, for example, a C1-C5 lower alcohol etc. to some water.

The mass average molecular weight (Mw) of the ethylene-unsaturated carboxylic acid copolymer is preferably 1,000 or more and 100,000 or less in terms of polystyrene. A more preferable lower limit is 3,000 or more, More preferably, it is 5,000 or more. On the other hand, a more preferable upper limit is 70,000 or less, More preferably, it is 30,000 or less. This Mw can be measured by Gel Permeation Chromatography (GPC) using polystyrene as a standard.

A carboxylic acid polymer can also be used as a resin component. As the carboxylic acid polymer, any of the polymers having an unsaturated carboxylic acid as a structural unit exemplified as those usable in the synthesis of the ethylenically-unsaturated carboxylic acid copolymer can be used. Among these, acrylic acid and maleic acid are preferable, and maleic acid is more preferable. The carboxylic acid polymer may contain a structural unit derived from a monomer other than the unsaturated carboxylic acid, but the amount of the structural unit derived from the other monomer is preferably 10% by mass or less in the polymer, more preferably 5% by mass or less. , more preferably a carboxylic acid polymer composed only of unsaturated carboxylic acids. As preferable carboxylic acid polymers, polyacrylic acid, polymethacrylic acid, an acrylic acid-maleic acid copolymer, polymaleic acid, etc. are mentioned. Among these, polymaleic acid is more preferable from a viewpoint of resin film adhesiveness and corrosion resistance. Although the exact mechanism by which corrosion resistance etc. improves by using polymaleic acid is unknown, since the amount of carboxyl groups is large, it is thought that the adhesiveness of a resin film and a galvanized steel sheet improves, and corrosion resistance also improves with it. However, the present invention is not limited to this estimation.

The mass average molecular weight (Mw) of the carboxylic acid polymer used by this embodiment is polystyrene conversion, Preferably they are 500 or more and 30,000 or less. A more preferable lower limit is 800 or more, More preferably, it is 900 or more, Most preferably, it is 1,000 or more. A more preferable upper limit is 10,000 or less, more preferably 3,000 or less, and most preferably 2,000 or less. This Mw can be measured by GPC using polystyrene as a standard.

The content ratio of the ethylene-unsaturated carboxylic acid copolymer and the carboxylic acid polymer is in a mass ratio of 1,000:1 to 10:1, preferably 200:1 to 20:1. When the content ratio of the carboxylic acid polymer is too low, the effect of combining the olefin-acid copolymer and the carboxylic acid polymer may not be sufficiently exhibited. Conversely, when the content of the carboxylic acid polymer is excessive, the olefin-acid copolymer and the carboxylic acid polymer are phase-separated in the coating solution for forming the first layer, and there is a fear that a uniform resin film may not be formed.

[Polyurethane-based resin]

As the polyurethane-based resin, a carboxyl group-containing polyurethane resin is preferable. As a carboxyl group-containing polyurethane resin, the thing of Unexamined-Japanese-Patent No. 2006-43913 can be used, for example.

The carboxyl group-containing polyurethane resin is preferably obtained by subjecting a urethane prepolymer to a chain extension reaction with a chain extender. A urethane prepolymer is obtained by making a polyisocyanate component and a polyol component react, for example.

As the polyisocyanate component, tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI) and dicyclohexylmethane diisocyanate (hydrogenated MDI) consisting of It is preferable to use at least 1 sort(s) of polyisocyanate selected from the group from a viewpoint of obtaining the resin film excellent in corrosion resistance and stability of reaction control. In addition to the above polyisocyanate, other polyisocyanates can be used within a range that does not reduce corrosion resistance or stability of reaction control. However, it is preferable that the content rate of the said polyisocyanate is 70 mass % or more of all polyisocyanate components from a viewpoint of ensuring the corrosion resistance of a resin film, and stability of reaction control. As a polyisocyanate other than the said polyisocyanate component, For example, tetramethylene diisocyanate, hexamethylene diisocyanate, dodecanemethylene diisocyanate, isophorone diisocyanate Anate, xylene diisocyanate, phenylene diisocyanate, etc. are mentioned, These 1 type, or 2 or more types may be used.

As the polyol component, it is preferable to use three types of polyols: 1,4-cyclohexanedimethanol, polyether polyol, and polyol having a carboxyl group from the viewpoint of obtaining a resin film excellent in corrosion resistance and sliding properties. . And as said polyol component, it is more preferable to use 3 types of diol of 1, 4- cyclohexane dimethanol, polyether diol, and the diol which has a carboxyl group. On the other hand, by using 1, 4- cyclohexane dimethanol as the said polyol component, the antirust effect of the polyurethane resin obtained can be improved.

The polyether polyol is not particularly limited as long as it has at least two or more hydroxyl groups in the molecular chain and the main skeleton is constituted by an alkylene oxide unit. Specific examples include polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol and the like, and it is preferable to use polyoxypropylene glycol or polytetramethylene ether glycol. do. The number of functional groups in the polyether polyol is not particularly limited as long as it is at least 2 or more, and for example, trifunctional, tetrafunctional or more polyfunctional may be sufficient. It is preferable that the average molecular weight of a polyether polyol is about 400-4000 from a viewpoint of obtaining the resin film which has moderate hardness. In addition, an average molecular weight can be calculated|required by measuring OH number (hydroxyl value).

The said polyol component WHEREIN: It is preferable that it is 1, 4- cyclohexane dimethanol:polyether polyol =1:1 - 1:19 by mass ratio from a viewpoint of improving the rust prevention effect of a resin film further. In addition, the polyol which has the said carboxyl group will not be specifically limited, if it has an at least 1 or more carboxyl group and at least 2 or more hydroxyl groups. Specific examples include dimethylolpropionic acid, dimethylolbutanoic acid, dihydroxypropionic acid, and dihydroxysuccinic acid.

In the polyol component, in addition to the three types of polyols, other polyols can be used within a range that does not reduce corrosion resistance. However, it is preferable that the content rate of the said three types of polyols is 70 mass % or more of all polyol components from a viewpoint of ensuring the corrosion resistance of a resin film. Polyols other than the said three types of polyols will not be specifically limited if it has two or more hydroxyl groups. For example, a low molecular weight polyol, a high molecular weight polyol, etc. are mentioned. The low molecular weight polyol is a polyol having an average molecular weight of about 500 or less. As a specific example, ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexyl diols such as saindiol; Triols, such as glycerol, trimethylol propane, and hexane triol, are mentioned. A high molecular weight polyol is a polyol whose average molecular weight exceeds about 500. Specific examples include condensed polyester polyols such as polyethylene adipate (PEA), polybutylene adipate (PBA), and polyhexamethylene adipate (PHMA); lactone-based polyester polyols such as poly-ε-caprolactone (PCL); polycarbonate polyols such as polyhexamethylene carbonate; and acrylic polyols.

Although the said chain extender is not specifically limited, For example, polyamine, a low molecular-weight polyol, an alkanolamine, etc. are mentioned. Examples of the polyamine include aliphatic polyamines such as ethylenediamine, propylenediamine, and hexamethylenediamine; aromatic polyamines such as tolylenediamine, xylylenediamine, and diaminodiphenylmethane; alicyclic polyamines such as diaminocyclohexylmethane, piperazine and isophoronediamine; Hydrazines, such as hydrazine, succinic acid dihydrazide, adipic acid dihydrazide, and phthalic acid dihydrazide, etc. are mentioned. Among these, it is preferable to use ethylenediamine and/or hydrazine as the chain extender component. As an alkanolamine, diethanolamine, monoethanolamine, etc. are mentioned, for example.

A carboxyl group-containing polyurethane resin can be emulsified (emulsified) by a well-known method, For example, there exists the following method. That is, the method of neutralizing the carboxyl group of a carboxyl group-containing urethane prepolymer with a base, emulsifying and dispersing in an aqueous medium, and carrying out a chain extension reaction; It is a method of chain extension reaction by emulsifying and dispersing a carboxyl group-containing polyurethane resin with a high shear force in the presence of an emulsifier.

The acid value of the carboxyl group-containing polyurethane resin is preferably 10 mgKOH/g or more from the viewpoint of ensuring the stability of the coating solution, while it is preferably 60 mgKOH/g or less from the viewpoint of ensuring the corrosion resistance of the resin film. The acid value is measured according to JIS-K0070 (1992).

[Additives in coating solution]

In the present embodiment, the resin film is coated with a coating solution on the surface of the galvanized steel sheet using a known coating method, that is, a roll coater method, a bar coater method, a spray method, a curtain flow coater method, or the like, and dried by heating. By doing so, it can be formed. The coating liquid contains a predetermined amount of silica, magnesium hydroxide, and the resin. It is preferable that the resin solid content in a coating liquid is about 15-25 mass %. In addition, the coating liquid may contain various additives in the range which does not impair the effect of this invention for the purpose of improving film performance. As additives, for example, silane coupling agent, dissolution inhibitor, rust inhibitor, wax, crosslinking agent, diluent, anti-skinning agent, surfactant, emulsifying agent, dispersing agent, leveling agent, defoaming agent, penetrating agent, film forming aid, dye, pigment, thickener, lubricant and the like.

For example, when a silane coupling agent is used as an additive, a resin film densifies and corrosion resistance improves. In addition, the adhesion between the galvanized steel sheet and the resin film is improved to improve corrosion resistance. In addition, there is an effect of improving the bonding force between the resin component and the colloidal silica, and the toughness of the film is improved. Among them, the glycidox-based silane coupling agent has high reactivity and has a large effect of improving corrosion resistance. As the glycidyl group-containing silane coupling agent, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxymethyldimethoxysilane, β-( 3,4-epoxycyclohexyl)ethyl trimethoxysilane and the like.

The amount of the silane coupling agent is preferably 0.1 parts by mass or more, more preferably 3 parts by mass or more, and still more preferably 5 parts by mass or more with respect to 100 parts by mass in total of the inorganic compound and the resin component in the inorganic coating. When the amount is less than 0.1 parts by mass, the adhesion between the galvanized steel sheet and the resin film and the bonding force between the resin component and the colloidal silica are insufficient, and there is a risk that the toughness and corrosion resistance of the film may become insufficient. On the other hand, the amount of the silane coupling agent is preferably 10 parts by mass or less, more preferably 9 parts by mass or less, still more preferably 7 parts by mass or less with respect to 100 parts by mass in total of the inorganic compound and the resin component in the inorganic coating. . Even if it exceeds 10 mass parts, it is because there exists a possibility that the adhesive improvement effect of a metal plate and a resin film may not only be saturated, but the functional group in resin may reduce and paintability may fall. Moreover, it is because there exists a possibility that the silane coupling agent may raise|generate a hydrolysis-condensation reaction, stability of a coating liquid falls, and may cause gelation and precipitation of colloidal silica.

In addition, for example, when metavanadate, which is a dissolution inhibitor, is used as an additive, dissolution or dissolution of the galvanized steel sheet is suppressed by dissolution of metavanadate, and corrosion resistance is improved. Metavanadate, in particular, has an effect of improving corrosion resistance of the alloyed hot-dip galvanized steel sheet. Examples of the metavanadate include sodium metavanadate (NaVO ₃ ), ammonium metavanadate (NH ₄ VO ₃ ), and potassium metavanadate (KVO ₃ ). These 1 type, or 2 or more types can be used.

The amount of metavanadate is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and still more preferably 1.5 parts by mass or more with respect to 100 parts by mass in total of the inorganic compound and the resin component in the inorganic coating. It is because the effect of improving corrosion resistance becomes insufficient when it is less than 0.5 mass part. On the other hand, the amount of metavanadate is preferably 5.5 parts by mass or less, more preferably 5.0 parts by mass or less, and still more preferably 4.5 parts by mass or less with respect to 100 parts by mass in total of the inorganic compound and the resin component in the inorganic coating. . When it exceeds 5.5 mass parts, it is because the tendency for bare corrosion resistance to fall slightly is confirmed, and furthermore, it is because there exists a tendency for film adhesiveness to fall remarkably. In addition, the suitable amount of this metavanadate is an amount of V element conversion.

[Types of galvanized steel sheet]

The type of galvanized steel sheet used in the present embodiment is not particularly limited, and any of an electrogalvanized steel sheet, a hot-dip galvanized steel sheet, and an alloyed hot-dip galvanized steel sheet (hereinafter, these may be referred to as "original sheet") is adopted. can do. In addition, there is no restriction|limiting in particular also about the kind of zinc plating layer, The thing containing an alloying element in a plating layer may be sufficient. On the other hand, the galvanized layer is coated on one side or both sides of the base steel sheet, and accordingly the resin film is also coated on one side or both sides of the galvanized steel sheet.

As described above, the coated galvanized steel sheet according to one aspect of the present invention is a coated galvanized steel sheet having a resin film containing silica and magnesium hydroxide on the surface of the galvanized steel sheet, wherein silica and magnesium hydroxide in the resin film The total content of is 50 to 75 mass %, the content of the resin component of the resin film is 25 to 50 mass %, the mass ratio of the magnesium hydroxide to the silica is 0.2 to 1.5, and the thickness of the resin film is 0.3 It is characterized in that it is ∼3.0 μm.

According to this structure, even when the thickness of the resin film is several micrometers or less, the coated galvanized steel sheet which shows the outstanding corrosion resistance is implement|achieved.

Example

Hereinafter, the present invention will be described in more detail by way of Examples. On the other hand, the present invention is not limited by the following examples, and it is possible to carry out the present invention with modifications within the range suitable for the purpose of the first and the latter, and they are all included in the technical scope of the present invention.

(Combination of magnesium hydroxide dispersion)

Magnesium hydroxide particles (manufactured by Kyowa Chemical Industry Co., Ltd., trade name: Kisuma 5Q-S) were dispersed using water as a dispersing agent and a polymer dispersing agent, followed by an aqueous dispersion (resin solid content: about 30% by mass, average particle size D ₅₀ : 0.69 µm) were combined.

The average particle size D ₅₀ of magnesium hydroxide in the dispersion was diluted with a 0.2 mass % aqueous sodium hexametaphosphate solution, and then measured using a laser diffraction scattering particle size distribution analyzer (manufactured by Microtrac Bell, trade name: Microtrac MT3300EXII). .

(Suzy)

As resin at the time of forming a resin film, the Toho Chemical Co., Ltd.|KK polyethylene resin or the Toho Chemical Industry urethane resin was used.

The said Toho Chemical Co., Ltd. product polyethylene resin and its aqueous dispersion liquid were prepared by the following method.

In an autoclave having an emulsification facility equipped with a stirrer, a thermometer, and a temperature controller, an ethylene-acrylic acid copolymer (manufactured by Dow Chemical Co., Ltd., trade name: Primacor 5990I, acrylic acid-derived structural unit: 20% by mass, mass average molecular weight (Mw): 20,000, melt index: 1300, acid value: 150) 200.0 parts by mass, polymaleic acid aqueous solution (manufactured by Nichiyu Corporation, trade name: Nonpole PMA-50W, Mw: about 1100 (in terms of polystyrene), 50 mass% product) 8.0 parts by mass, tri 35.5 parts by mass of ethylamine (0.63 equivalents with respect to the carboxyl group of the ethylene-acrylic acid copolymer), 6.9 parts by mass of a 48% aqueous NaOH solution (0.15 equivalents with respect to the carboxyl group of the ethylene-acrylic acid copolymer), tall oil fatty acid (manufactured by Harima Chemical Co., Ltd., trade name: Hatol FA3) 3.5 mass parts and 792.6 mass parts of ion-exchange water were added, sealed, high-speed stirring was carried out at 150 degreeC and 5 atmospheres for 3 hours, and it cooled to 30 degreeC.

Next, 10.4 parts by mass of γ-glycidoxypropyl trimethoxysilane (manufactured by Momentive Performance Materials, trade name: TSL8350), polycarbodiimide (manufactured by Nisshin Bosha Corporation, trade name: Carbodilite SV-02, Mw) : 2,700, solid content 40% by mass) 31.2 parts by mass and 72.8 parts by mass of ion-exchanged water were added and stirred for 10 minutes to emulsify the ethylene-acrylic acid copolymer to obtain an aqueous dispersion of polyethylene resin mixed with each component (resin solid content) 20.3 mass %, measured according to JIS K6833 (2014).

The urethane resin made from the said Toho Chemical Co., Ltd. product and its aqueous dispersion liquid were prepared by the following method.

60 g of polytetramethylene ether glycol (manufactured by Hodogaya Chemical Industry Co., Ltd., average molecular weight 1,000), 14 g of 1,4-cyclohexanedimethanol, and die 20 g of methylol propionic acid was added, and 30.0 g of N-methylpyrrolidone was further added thereto. Then, 104 g of tolylene diisocyanate was added thereto, and the temperature was raised from 80 to 85°C and reacted for 5 hours. The NCO content of the obtained prepolymer was 8.9%. Further, 16 g of triethylamine was added for neutralization, a mixed aqueous solution of 16 g of ethylenediamine and 480 g of water was added, emulsified at 50° C. for 4 hours, followed by chain extension reaction to obtain an aqueous dispersion of urethane resin (nonvolatile resin component) 29.1%, acid value 41.4).

(Combination of coating solution)

The aqueous dispersion of magnesium hydroxide, the aqueous dispersion of the polyethylene resin or the aqueous dispersion of the urethane resin, and colloidal silica (manufactured by Nissan Chemical Industry Co., Ltd., trade name: Snowtex-XS) are mixed, and the resin solid content is about 5% by mass. liquid was combined.

(Type of original plate)

Electro-galvanized steel sheet (EG): sheet thickness 0.8mm, zinc basis weight: front ^side 18g/m2 , back ^side 18g/m2

(Pre-treatment of galvanized steel sheet)

Degreasing: Alkaline degreasing (manufactured by Nippon Parkerizing, brand name: Fine Cleaner)

Drying: Hot air drying was performed to evaporate moisture.

(Painting method)

Method: Bar Coater

Resin film thickness: The number of bars was selected so that a predetermined film thickness was obtained. About the sample for which the corrosion resistance of a cross section was evaluated, the resin film of the same thickness was formed on both surfaces of a front surface and a back surface.

(drying method)

Time: 1 minute

Condition: Maximum reached 80℃ of painted plate (confirmed by thermo label)

Within the above range, various conditions were changed as shown in Table 1 below to prepare various coated galvanized steel sheets (Test Nos. 1 to 13), and the corrosion resistance of the flat and cross-sections of the obtained coated galvanized steel sheet , was evaluated by the following method.

(Corrosion resistance of flat plate)

The obtained coated galvanized steel sheet (sample) was subjected to a salt spray test in accordance with JIS Z2371 (2015) for 96 hours, and the white rust generation rate on the sample surface (100 × white rust generated area / total area of the resin coated metal sheet) was calculated. And based on the following reference|standard, (circle) was made into pass, and x was made into rejection, and it evaluated.

<Evaluation standard>

○: White rust occurrence rate 15 area% or less

×: White rust occurrence rate exceeds 15% by area

In addition, the obtained coated galvanized steel sheet (sample) was subjected to a salt spray test in conformity with JIS Z2371 (2015) for 480 hours, and the condition of occurrence of red rust on the sample surface was visually observed. And based on the following reference|standard, (circle) was made into pass, and x was made into rejection, and it evaluated.

<Evaluation standard>

○: No occurrence of red rust was observed.

x: Generation|occurrence|production of red rust is confirmed

(Corrosion resistance of the cross section)

In order to make the shape of the burr of the cut surface even, a rectangular test piece having a width of 50 × a length of 120 mm was cut out from a sample for evaluating the corrosion resistance of the cross section using the same shearing equipment. The number of cut-out specimens was determined in Test No. 12 sheets in any of 1 to 13. Each test piece performed the salt spray test based on JIS Z2371 (2015) as it is for 96 hours, without sealing a cross section. Then, each test piece after the salt spray test was wrapped in paper and left to stand in an air-conditioned room (temperature: about 23°C, humidity: about 30%) as a room temperature leaving test for 3 weeks to advance corrosion of the cross section. After completion of the room temperature standing test, test No. For each of 1 to 13, the corrosion condition of the cross-section was photographed in a state where 12 specimens were overlapped, area) was calculated, and their average value was obtained as the red rust occurrence rate of the cross-section. And based on the following criteria, (double-circle) and (circle) were made into pass, and (triangle|delta) was made into rejection, and it evaluated.

<Evaluation standard>

◎: Red rust occurrence rate 15 area% or less of the cross section

○: Red rust occurrence rate of cross section Exceeding 15 area% and less than 30 area%

△: Red rust occurrence rate of cross section exceeds 30 area%

The results are shown in Table 1 below together with the conditions (type of resin, composition ratio of the resin film, [Mg(OH) ₂ /SiO ₂ ], thickness of the resin film) at the time of manufacturing each coated galvanized steel sheet.

As is evident from this result, in the example (No. 8) in which content of resin is 60 mass %, since there was too much content of resin, the corrosion resistance of the cross section was deteriorated. In the examples (No. 9, 13) in which the content of the resin was less than 25% by mass, the content of the resin was too small, so that the film defects increased, and the corrosion resistance of the cross section and the white rust corrosion resistance of the flat plate were deteriorated. In the examples (test Nos. 10 and 12) in which the mass ratio [Mg(OH) ₂ /SiO ₂ ] was outside the range of 0.2 to 1.5, the corrosion resistance of the cross section was deteriorated. And in the example (test No. 11) in which the resin film thickness was 0.2 micrometer, the corrosion resistance of a cross section and the white rust corrosion resistance of a flat part were inferior.

On the other hand, the coated galvanized steel sheets (Test Nos. 1 to 7) of the present invention in which the total content of silica and magnesium hydroxide, the mass ratio [Mg(OH) ₂ /SiO ₂ ], and the resin film thickness were appropriately adjusted (Test Nos. 1 to 7) were flat and excellent corrosion resistance in both of the cross-sections.

This application is based on Japanese Patent Application Japanese Patent Application No. 2018-64767 filed on March 29, 2018 and Japanese Patent Application No. 2019-29020 filed on February 21, 2019, the contents of which are incorporated herein by reference will become

In order to express this invention, although this invention was suitably and fully demonstrated through embodiment, referring specific examples etc. in the above, it recognizes that it is easy for those skilled in the art to change and/or improve the above-mentioned embodiment. Should be. Therefore, unless the modified form or improved form implemented by a person skilled in the art does not deviate from the scope of the claims described in the claims, it is construed that the modified form or the improved form is encompassed by the scope of the claims.

INDUSTRIAL APPLICABILITY The present invention has a wide range of industrial applicability in the technical fields related to steel sheets, galvanized steel sheets, manufacturing methods thereof, and the like.

Claims (1)

A coated galvanized steel sheet having a resin film containing silica and magnesium hydroxide on the surface of the galvanized steel sheet,
The total content of silica and magnesium hydroxide in the resin film is 50 to 75 mass%, and the content of the resin component of the resin film is 25 to 50 mass%,
The mass ratio of the magnesium hydroxide to the silica is 0.2 to 1.5,
A coated galvanized steel sheet, characterized in that the resin film has a thickness of 0.3 to 3.0 μm.