KR20200128564A - Painted galvanized steel sheet - Google Patents

Abstract

An 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% by mass, It relates to a coated galvanized steel sheet, wherein the content of the resin component of the resin film is 25 to 50% by 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. .

Description

Painted galvanized steel sheet

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

The surface-treated steel sheet is plated or painted on the surface of the base material, thereby exhibiting excellent corrosion resistance. However, in the end face of the surface-treated steel sheet to which the steel as the base material is exposed, red rust gradually occurs in an atmospheric environment. The red rust generated on the cross-section of the surface-treated steel sheet not only deteriorates the appearance, but, if it occurs in the vicinity of a circuit board such as an electric product, for example, it falls out of the steel sheet and short-circuits the circuit, causing a problem that impairs product safety There is concern.

In order to prevent the occurrence of red rust in the cross section of the coated steel sheet, various studies have been conducted so far. For example, since a general pre-coated metal plate has a coating film with a thickness of several tens of μm, it is possible to improve cross-sectional corrosion resistance by optimizing the coating film component by using a large protective effect by the rust-preventing component eluted from the coating film to the cut section. Has become. On the other hand, in a coated steel sheet having a special chemical conversion treatment film having a smaller coating film thickness than the precoated metal sheet, since there are few rust-preventing components that can be eluted and cannot sufficiently cover the cut cross-section, it is difficult to obtain good cross-sectional corrosion resistance. Therefore, in applications where high cross-sectional corrosion resistance is required, parts to which coating or plating is applied after pressing a cold-rolled steel sheet are often applied.

As for zinc plating, it is known that magnesium-based compounds exhibit a rust prevention 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 Literature 1 discloses a coating made of a composition containing nano magnesium hydroxide particles having an average particle diameter of less than 200 nm.

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

On the other hand, as a technique using a magnesium-containing film for a film of a chromium-free organic coated steel sheet, Patent Document 3 is a composite containing oxide particles, phosphoric acid and/or phosphoric acid compounds, and magnesium compounds 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 anti-rust additive component.

The coating disclosed in Patent Document 1 has a thickness of 2.5 to 75 μm, and it is not assumed to be press-molded. In addition, when the thickness of the coating disclosed in Patent Document 1 is several μm or less, a sufficient anti-rust effect after press molding is not exhibited.

The coating disclosed in Patent Document 2 requires the use of a metal rust inhibitor containing a complex colloid composed of magnesium hydroxide and fine silica when forming the coating, but the complex colloid is unstable because it reacts with the components of the treatment liquid, and is coated to gel. It is prone to problems in the process. In addition, the film disclosed in Patent Document 2 is estimated to be effective in corrosion resistance because it elutes on a cross section, but since it contains a water-soluble component, the water resistance is insufficient, and there is a high possibility of discoloration due to condensation or wetness 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 when the composite oxide film is formed, the stability of the treatment solution is lowered when the amount of the magnesium compound is increased. For this reason, there is a limit in improving the corrosion inhibiting effect of the composite oxide film by increasing the amount of the magnesium component. Further, the organic coated steel sheet disclosed in Patent Literature 3 has a problem of low productivity and high manufacturing cost because it is necessary to further form an organic film after forming the composite oxide film.

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 Application Publication 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% by 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% by 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.

The present inventors studied from various angles in order to achieve the above object. 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 face of the galvanized steel sheet is enhanced, and the above It was found that the object was satisfactorily 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 resin film is 50 to 75% by mass. The content of the resin component in the resin film is 25 to 50% by 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 above configuration, even when the thickness of the film is several μm or less, a coated galvanized steel sheet exhibiting excellent 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% by mass]

In this embodiment, the total content of silica and magnesium hydroxide in the resin film is 50 to 75% by mass. It is estimated that silica and magnesium hydroxide in the resin film are eluted from the resin film in a corrosive environment, thereby exhibiting an action of protecting the cut section. If the total content of silica and magnesium hydroxide in the resin film is less than 50% by mass, the elution amount is not sufficient, so that the protective action of the end face is not secured. It is preferably 55% by mass or more, and more preferably 60% by mass or more. On the other hand, if the total content of silica and magnesium hydroxide in the resin film exceeds 75% by mass, the resin component used as the binder is insufficient, resulting in a film with many defective parts, and thus corrosion resistance as a flat plate cannot be secured. It is preferably 73 mass% or less, more preferably 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 the inorganic type film means a resin film containing silica and magnesium hydroxide.

The silica used in this embodiment is preferably colloidal silica having excellent compatibility with an aqueous resin described later. In addition, when the average particle diameter of silica is too large, the density of the film may decrease or film defects may occur, so 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 D ₅₀ of silica means the average particle diameter when the integrated value (integrated value) of silica becomes 50 mass %.

The magnesium hydroxide used in the present embodiment may be stable as an aqueous dispersion, and the powder and dispersion method of magnesium hydroxide are not particularly limited. The average particle diameter D ₅₀ in the state in which magnesium hydroxide is dispersed in water, i.e., 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 0.7 μm or less. Do. Thereby, corrosion of the end surface portion due to insufficient elution amount due to the fact that the particulate magnesium hydroxide has fallen out of the resin film can be suppressed. On the other hand, the lower limit of the average particle diameter D ₅₀ in the state in which magnesium hydroxide is dispersed in water is not particularly limited, but if the average particle diameter D ₅₀ is too small, there is a possibility that the stability of the dispersion (for example, dispersion) may decrease. Therefore, it is preferably 0.1 μm or more. More preferably, it is 0.14 μm or more. In addition, the average particle diameter D _{50 of} magnesium hydroxide means the average particle diameter when the integrated value (integrated value) of magnesium hydroxide becomes 50 mass %.

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

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

In this embodiment, the content of the resin component in the resin film is 25 to 50% by mass. As described above, if the resin component in the resin film is insufficient, the film becomes a film with many defective parts, and corrosion resistance deteriorates. From this point of view, the content of the resin component in the resin film is 25% by mass or more. Preferably it is 30 mass% or more. However, if the content of the resin component in the resin film is too large, in addition to the deterioration of corrosion resistance due to a decrease in the compactness in the resin film, the resin film becomes soft, and there is a concern that the generation of film debris during press molding increases. From this point of view, the content of the resin component in the resin film is 50% by mass or less. Preferably it is 40 mass% or less.

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

In this embodiment, the mass ratio of magnesium hydroxide to silica is set to 0.2 to 1.5. Both magnesium hydroxide and silica are known as rust inhibitors for zinc plating. The present inventors have found that excellent corrosion resistance is obtained by blending magnesium hydroxide and silica in a resin film at 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 it is 0.3 or more, and, as for this mass ratio, it is preferable that it is 1.0 or less.

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

In addition, by using particulate magnesium hydroxide, it is 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, corrosion products having a high protective effect against galvanizing can be supplied to the cut section. It is estimated 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 surface portion. In this embodiment, the resin film thickness is set to 0.3 μm or more. In the flat plate portion, if the resin film thickness is 0.2 μm, corrosion resistance at a level without a problem in practical use is obtained. However, this is because corrosion resistance is insufficient in the case where the resin film thickness is less than 0.3 μm in the end surface portion. On the other hand, the upper limit of the thickness of the resin film does not need to be particularly determined because it depends on the area (board thickness) of the cut surface. However, if the resin film thickness exceeds 3.0 µm, a large-scale drying facility is required, and therefore 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 in this embodiment, Any of an aqueous resin and a nonaqueous resin can be used. When using an aqueous dispersion of magnesium hydroxide or colloidal silica, it is preferable to use an aqueous resin. The water-based resin is not particularly limited, but it is preferable that it can be mixed with an aqueous dispersion of magnesium hydroxide and colloidal silica. On the other hand, the water-based resin in this embodiment refers to a resin or a water-soluble resin that has become an aqueous dispersion.

As such a water-based resin, polyolefin-based resins, polyurethane-based resins, and polyester-based resins are preferable, and among these, polyolefin-based resins and polyurethane-based resins are more preferable. Hereinafter, the polyolefin resin and the polyurethane resin will be described in detail, respectively.

[Polyolefin resin]

As the polyolefin resin, an ethylene-unsaturated carboxylic acid copolymer is preferred. As the ethylene-unsaturated carboxylic acid copolymer, those described in JP 2005-246953A or JP 2006-43913A can be used, for example.

Examples of the unsaturated carboxylic acid include (meth)acrylic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, itaconic acid, and the like, and polymerization of one or more of these and ethylene by a known high-temperature high-pressure polymerization method, etc. Thus, an ethylene-unsaturated carboxylic acid copolymer can be obtained.

The copolymerization ratio of unsaturated carboxylic acid to ethylene is preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 40% by mass or less, when the total amount of the monomer is 100% by mass. It is more preferable that it is mass% or less. If the amount of unsaturated carboxylic acid is less than 10% by mass, since there are few carboxyl groups that become the starting point of intermolecular association due to ionic clusters, the film strength effect is not exhibited, and the emulsion stability of the coating liquid (emulsion composition) described later may be inferior. . On the other hand, when the unsaturated carboxylic acid exceeds 40% by mass, there is a possibility that the corrosion resistance and water resistance of the resin film will be inferior.

Since the ethylene-unsaturated carboxylic acid copolymer has a carboxyl group, it becomes possible to emulsify (water disperse) the coating liquid by neutralizing it with an organic base or metal ion.

As the organic base, an amine having a boiling point of 100°C or less under atmospheric pressure is preferable from the viewpoint of not reducing the corrosion resistance of the resin film too much. As a specific example, tertiary amines, such as triethylamine; Secondary amines such as diethylamine; Primary amines, such as propylamine, etc. are mentioned, These 1 type, or 2 or more types may be mixed and used for them. Among these, tertiary amines are preferable, and triethylamine is most preferable. Further, from the viewpoint of improving solvent resistance and film hardness, it is preferable to use a monovalent metal ion together with the amine.

From the viewpoint of securing corrosion resistance, the amine is preferably 0.2 mol or more, and preferably 0.8 mol or less with respect to 1 mol of the carboxyl group in the ethylene-unsaturated carboxylic acid copolymer. And it is more preferable that it is 0.3 mol or more, on the other hand, it is more preferable that it is 0.6 mol or less.

The amount of monovalent metal ions is preferably 0.02 mol or more, and more preferably 0.03 mol or more with respect to 1 mol of carboxyl groups in the ethylene-unsaturated carboxylic acid copolymer from the viewpoint of securing the emulsion stability of the coating liquid. On the other hand, from the viewpoint of securing corrosion resistance, it is preferably 0.4 mol or less, and more preferably 0.3 mol or less per 1 mol of carboxyl groups in the ethylene-unsaturated carboxylic acid copolymer. On the other hand, as a metal compound for imparting a monovalent metal ion, NaOH, KOH, LiOH, etc. are preferable, and NaOH is the most preferable because of its performance.

The ethylene-unsaturated carboxylic acid copolymer is, if necessary, in the presence of a carboxylic acid polymer described later, for example, in a container capable of reaction at high temperature (about 150°C) and high pressure (about 5 atmospheres), high-speed stirring is performed from 1 to 6 It emulsifies (emulsifies) over time. In emulsification, an appropriate amount of a compound having a surfactant function such as a tall oil fatty acid may be added. Further, a hydrophilic organic solvent such as a lower alcohol having 1 to 5 carbon atoms may be added to some water.

The mass average molecular weight (Mw) of the ethylene-unsaturated carboxylic acid copolymer, in terms of polystyrene, is preferably 1,000 or more and 100,000 or less. A more preferable lower limit is 3,000 or more, and even more preferably 5,000 or more. On the other hand, a more preferable upper limit is 70,000 or less, and still more preferably 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 the resin component. As the carboxylic acid polymer, any polymer having an unsaturated carboxylic acid exemplified as a structural unit that can be used in the synthesis of the ethylene-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 structural units derived from monomers other than unsaturated carboxylic acids, but the amount of structural units derived from other monomers is preferably 10% by mass or less, and more preferably 5% by mass or less in the polymer. And a carboxylic acid polymer composed only of an unsaturated carboxylic acid is more preferable. Preferred carboxylic acid polymers include polyacrylic acid, polymethacrylic acid, acrylic acid-maleic acid copolymer, and polymaleic acid. Among these, polymaleic acid is more preferable from the viewpoints of resin film adhesion and corrosion resistance. Although the exact mechanism by which the corrosion resistance and the like are improved by using polymaleic acid is unknown, it is considered that the adhesion between the resin film and the galvanized steel sheet is improved, and the corrosion resistance is also improved due to the large amount of carboxyl groups. However, the present invention is not limited to this estimation.

The mass average molecular weight (Mw) of the carboxylic acid polymer used in this embodiment is in terms of polystyrene, preferably 500 or more and 30,000 or less. A more preferable lower limit value is 800 or more, more preferably 900 or more, and most preferably 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 1,000:1 to 10:1, preferably 200:1 to 20:1 by mass. 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, if the content ratio of the carboxylic acid polymer is excessive, there is a fear that the olefin-acid copolymer and the carboxylic acid polymer are phase-separated in the first layer-forming coating liquid, and a uniform resin film may not be formed.

[Polyuretein resin]

As the polyurethane resin, a polyurethane resin containing a carboxyl group is preferable. As a carboxyl group-containing polyurethane resin, for example, those described in JP 2006-43913 A can be used.

It is preferable that the carboxyl group-containing polyurethane resin is obtained by subjecting a urethane prepolymer to a chain extension reaction with a chain extender. The urethane prepolymer is obtained, for example, by reacting a polyisocyanate component and a polyol component.

As the polyisocyanate component, consisting of tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and dicyclohexylmethane diisocyanate (hydrogenated MDI) It is preferable from the viewpoint of obtaining a resin film excellent in corrosion resistance and stability of reaction control to use at least one polyisocyanate selected from the group. In addition to the polyisocyanate, other polyisocyanates may be used within a range that does not deteriorate corrosion resistance or stability of reaction control. However, the content rate of the polyisocyanate is preferably 70% by mass or more of the total polyisocyanate component from the viewpoint of securing the corrosion resistance of the resin film and stability of reaction control. As polyisocyanates other than the polyisocyanate component, for example, tetramethylene diisocyanate, hexamethylene diisocyanate, dodecanemethylene diisocyanate, isophorone diisocyanate Anate, xylene diisocyanate, phenylene diisocyanate, and the like, and one or two or more of these may be used.

As the polyol component, it is preferable from the viewpoint of obtaining a resin film excellent in corrosion resistance and sliding properties to use 3 types of polyols, 1,4-cyclohexanedimethanol, polyether polyol, and polyol having a carboxyl group. . Further, as the polyol component, it is more preferable to use three types of diols such as 1,4-cyclohexanedimethanol, polyether diol, and diol having a carboxyl group. On the other hand, by using 1,4-cyclohexanedimethanol as the polyol component, the rust-preventing effect of the polyurethane resin obtained can be enhanced.

The polyether polyol is not particularly limited as long as it has at least two hydroxyl groups in the molecular chain and the main skeleton is composed of an alkylene oxide unit. As a specific example, polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol, etc. are mentioned, It is preferable to use polyoxypropylene glycol or polytetramethylene ether glycol. Do. The number of functional groups of the polyether polyol is not particularly limited as long as it is at least 2 or more, and may be, for example, trifunctional or tetrafunctional or more polyfunctional. The average molecular weight of the polyether polyol is preferably about 400 to 4000 from the viewpoint of obtaining a resin film having an appropriate hardness. In addition, the average molecular weight can be calculated|required by measuring an OH value (hydroxyl value).

In the polyol component, in terms of mass ratio, 1,4-cyclohexanedimethanol:polyether polyol=1:1 to 1:19 is preferable from the viewpoint of further enhancing the rust prevention effect of the resin film. Further, the polyol having a carboxyl group is not particularly limited as long as it has at least one or more carboxyl groups and at least two or more hydroxyl groups. As a specific example, dimethylolpropionic acid, dimethylolbutanoic acid, dihydroxypropionic acid, dihydroxysuccinic acid, etc. are mentioned.

In the polyol component, in addition to the above 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 above three types of polyols is 70% by mass or more of all polyol components from the viewpoint of securing the corrosion resistance of the resin film. Polyols other than the three types of polyols are not particularly limited as long as they have a plurality of 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-hex Diols such as sediol; Triols, such as glycerin, trimethylolpropane, and hexane triol, are mentioned. The high molecular weight polyol is a polyol whose average molecular weight exceeds about 500. As specific examples, 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.

The chain extender is not particularly limited, and examples thereof include polyamines, low molecular weight polyols, and alkanolamines. 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 a chain extender component. As an alkanolamine, diethanolamine, monoethanolamine, etc. are mentioned, for example.

The polyurethane resin containing a carboxyl group can be emulsified (emulsified) by a known method, for example, the following method. That is, a method of neutralizing a carboxyl group of a carboxyl group-containing urethane prepolymer with a base and emulsifying and dispersing in an aqueous medium for chain extension reaction; This is a method of emulsifying and dispersing a carboxyl group-containing polyurethane resin with a high shear force in the presence of an emulsifying agent to perform chain extension reaction.

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

[Additives in coating liquid]

In the present embodiment, the resin film is applied to 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, etc., followed by heating and drying. By making it possible to form. The coating liquid contains a predetermined amount of silica, magnesium hydroxide, and the resin. It is preferable that the resin solid content in the coating liquid is about 15 to 25% by mass. In addition, the coating liquid may contain various additives within a range that does not impair the effects of the present invention for the purpose of improving the coating performance. As additives, for example, silane coupling agents, elution inhibitors, rust inhibitors, waxes, crosslinking agents, diluents, anti-skinning agents, surfactants, emulsifiers, dispersants, leveling agents, antifoaming agents, penetrating agents, film forming aids, dyes, pigments, thickeners, lubricants And the like.

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

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 of the total of the inorganic compound and the resin component in the inorganic coating. If it is less than 0.1 parts by mass, the adhesion between the galvanized steel sheet and the resin film, or the bonding strength between the resin component and the colloidal silica may be insufficient, and the toughness and corrosion resistance of the film may be 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, and still more preferably 7 parts by mass or less with respect to 100 parts by mass of the total of the inorganic compound and the resin component in the inorganic coating. . This is because even if it exceeds 10 parts by mass, not only the effect of improving the adhesion between the metal plate and the resin film is saturated, but also the functional group in the resin decreases, so that the paintability may decrease. In addition, this is because the silane coupling agents cause a hydrolytic condensation reaction, the stability of the coating liquid is lowered, and gelation or precipitation of colloidal silica may be caused.

Further, for example, when metavanadate, which is an elution inhibitor, is used as an additive, dissolution or elution of the galvanized steel sheet is suppressed by elution of the metavanadate, and corrosion resistance is improved. In particular, metavanadate has an effect of improving poor corrosion resistance with respect to an alloyed hot dip galvanized steel sheet. Examples of the metavanadate salt include sodium metavanadate (NaVO ₃ ), ammonium metavanadate (NH ₄ VO ₃ ), potassium metavanadate (KVO ₃ ), and the like. One or two or more of these 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 of the total of the inorganic compound and the resin component in the inorganic coating. If it is less than 0.5 parts by mass, the effect of improving bare corrosion resistance becomes insufficient. 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 of the total of the inorganic compound and the resin component in the inorganic coating. . This is because when it exceeds 5.5 parts by mass, not only the tendency of the bare corrosion resistance to slightly decrease is observed, but also the film adhesion tends to be remarkably decreased. On the other hand, the suitable amount of this metavanadate is an amount in terms of V element.

[Type 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 are sometimes referred to as ``original plates'') are employed. can do. In addition, the type of the galvanized layer is not particularly limited, and the plating layer may contain an alloying element. On the other hand, the galvanized layer is coated on one side or both sides of the base steel sheet, and accordingly, a resin film is also coated on one side or both sides of the galvanized steel sheet.

As described above, a coated galvanized steel sheet according to an 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% by mass, the content of the resin component of the resin film is 25 to 50% by 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 by being ∼3.0 μm.

According to this configuration, even when the thickness of the resin film is several μm or less, a coated galvanized steel sheet exhibiting excellent corrosion resistance is realized.

Example

Hereinafter, the present invention will be described in more detail with reference to examples. On the other hand, the present invention is not limited by the following examples, and it is possible to carry out changes in a range suitable for the purpose of the previous and later periods, 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 Industries, Ltd., brand name: Kisuma 5Q-S) were dispersed using a polymer dispersant while using water as a dispersant, and an aqueous dispersion (resin solid content: about 30% by mass, average particle diameter D ₅₀ : 0.69 μm) was combined.

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

(Suzy)

As a resin for forming the resin film, a polyethylene resin manufactured by Toho Chemical Co., Ltd. or a urethane resin manufactured by Toho Chemical Industries was used.

The polyethylene resin manufactured by Toho Chemical Co., Ltd. and the aqueous dispersion thereof were prepared by the following method.

In an autoclave having an emulsification facility equipped with a stirrer, thermometer, and temperature controller, an ethylene-acrylic acid copolymer (manufactured by Dow Chemical, brand name: Primacor 5990I, constitutional unit derived from acrylic acid: 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, brand name: Nonpol PMA-50W, Mw: about 1100 (polystyrene conversion), 50% by mass product) 8.0 parts by mass, tri Ethylamine 35.5 parts by mass (0.63 equivalent to the carboxyl group of the ethylene-acrylic acid copolymer), 6.9 parts by mass of 48% NaOH aqueous solution (0.15 equivalent to the carboxyl group of the ethylene-acrylic acid copolymer), tall oil fatty acid (manufactured by Harima Chemical Co., Ltd., brand name: Hatol FA3) 3.5 parts by mass and 792.6 parts by mass of ion-exchanged water were added and sealed, followed by high-speed stirring at 150°C and 5 atm for 3 hours, and then cooled to 30°C.

Next, 10.4 parts by mass of γ-glycidoxypropyltrimethoxysilane (manufactured by Momentive Performance Materials, brand name: TSL8350), polycarbodiimide (manufactured by Nisshinbosha, brand 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, thereby obtaining an aqueous dispersion of polyethylene resin mixed with each component (resin solid content 20.3% by mass, measured according to JIS K6833 (2014)).

The urethane resin manufactured by Toho Chemical Co., Ltd. and its aqueous dispersion were prepared by the following method.

In a 0.8 L synthesis apparatus equipped with a stirrer, thermometer, and temperature controller, polytetramethylene ether glycol (manufactured by Hodogaya Chemical Industries, Ltd., average molecular weight 1,000) 60 g, 1,4-cyclohexanedimethanol 14 g, die 20 g of methylolpropionic acid was added, and 30.0 g of N-methylpyrrolidone was further added. Then, 104 g of tolylene diisocyanate was added, 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 neutralization was carried out by adding 16 g of triethylamine, and 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 liquid)

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

(Type of original)

Electro-galvanized steel sheet (EG): sheet thickness 0.8mm, a zinc basis weight: Front 18g / m ^2, the back of 18g / m ²

(Pre-treatment of galvanized steel sheet)

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

Drying: Dry with hot air 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. For the sample for evaluating the corrosion resistance of the end surface, a resin film having the same thickness was formed on both surfaces of the front and rear surfaces.

(Drying method)

Time: 1 minute

Conditions: Maximum temperature reached 80℃ of painting plate (confirmed by thermolabel)

Within the above range, as shown in Table 1 below, conditions were varied to produce various coated galvanized steel sheets (test Nos. 1 to 13), and the corrosion resistance of the flat and end faces of the obtained coated galvanized steel sheet was prepared. , Evaluated by the following method.

(Corrosion resistance of flat plate)

For the obtained coated galvanized steel sheet (sample), a salt spray test in accordance with JIS Z2371 (2015) was conducted for 96 hours, and the rate of white rust occurrence on the surface of the sample (100 × area where white rust occurred/total area of resin coated metal sheet) Was calculated. And based on the following criteria, it evaluated by making ○ as pass and X as rejection.

<Evaluation standard>

○: White rust incidence rate 15 area% or less

×: White rust incidence rate exceeds 15% by area

Further, the obtained coated galvanized steel sheet (sample) was subjected to a salt spray test according to JIS Z2371 (2015) for 480 hours, and the state of red rust occurrence on the surface of the sample was observed visually. And based on the following criteria, it evaluated by making ○ as pass and X as rejection.

<Evaluation standard>

○: The occurrence of red rust is not confirmed

×: occurrence of red rust is confirmed

(Corrosion resistance of cross section)

In order to even out the shape of the burr of the cut surface, a rectangular test piece having a width of 50 x 120 mm in length was cut out from a sample for evaluating the corrosion resistance of the cross-section using the same shearing facility. The number of specimens cut out is the test number. In any of 1 to 13, it is 12 sheets. Each test piece was subjected to a salt spray test in accordance with JIS Z2371 (2015) for 96 hours without sealing the end face. Then, the test pieces after the salt spray test were each packaged in a copy paper, and left in an air-conditioned room (temperature: about 23°C, humidity: about 30%) for 3 weeks to advance corrosion of the cross section. After completion of the room temperature test, test No. For each of 1 to 13, a photo of the corrosion condition of the cross-section was taken with 12 specimens stacked on each side, and the rate of occurrence of red rust in each of the harbor cross-section and the burr cross-section (100 × area of red rust/corresponding cross-section of resin-coated metal plate) Area) was calculated, and their average value was calculated as the red rust incidence rate of the cross section. And based on the following criteria, it evaluated by making ◎ and ○ as pass, and making △ disqualified.

<Evaluation standard>

◎: 15 area% or less of red rust incidence in the cross section

○: Red rust incidence rate of cross section exceeds 15 area% and less than 30 area%

△: More than 30% by area of red rust incidence in the cross section

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

As is clear from this result, in the case where the resin content is 60 mass% (No. 8), since the content of the resin is too large, the corrosion resistance of the end surface portion is deteriorating. In the examples in which the resin content was less than 25% by mass (No. 9, 13), since the resin content was too small, film defects increased, and the corrosion resistance of the end face and the white rust corrosion resistance of the flat plate were deteriorated. In an example in which the mass ratio [Mg(OH) ₂ /SiO ₂ ] was outside the range of 0.2 to 1.5 (Test Nos. 10 and 12), the corrosion resistance of the cross-section portion was deteriorating. And, in the example in which the resin film thickness was 0.2 µm (Test No. 11), the corrosion resistance of the end face and the white rust corrosion resistance of the flat plate were deteriorated.

On the other hand, the coated galvanized steel sheet (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, is a flat plate part. And excellent corrosion resistance in both of the end faces.

This application is based on 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. It becomes.

In order to express the present invention, the present invention has been described appropriately and sufficiently through the embodiments while referring to specific examples in the foregoing, but those skilled in the art recognize that it is possible to easily change and/or improve the above-described embodiments. Should be. Therefore, the modified form or the improved form is interpreted as being included in the scope of the claim unless the modified form or improved form carried out by a person skilled in the art is at a level that deviates from the scope of the claim described in the claims.

The present invention has wide industrial applicability in the technical field related to steel sheets, galvanized steel sheets, and their manufacturing methods.

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 resin component content 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,
Painted galvanized steel sheet, characterized in that the thickness of the resin film is 0.3 to 3.0 μm.