TWI774946B - Painted galvanized steel sheet - Google Patents

Abstract

One aspect of the present invention relates to a coated galvanized steel sheet, which is a coated galvanized steel sheet with a resin film comprising silicon dioxide and magnesium hydroxide on the surface of the galvanized steel sheet, wherein the silicon dioxide in the resin film is and the total content of magnesium hydroxide is 75~90 mass %, and the content of the resin component of the aforementioned resin film is 10~25 mass %, the mass ratio of the aforementioned magnesium hydroxide to the aforementioned silicon dioxide is 0.15~3, the aforementioned resin coating film The thickness is 0.20~1.1μm.

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 (hereinafter sometimes referred to as an "inorganic film") containing an inorganic compound in a resin.

In the roll forming process, the surface of the material is subjected to severe sliding of the rolls. Therefore, when roll forming is performed on the coated galvanized steel sheet having the resin film on the surface layer, a part of the resin film peels off to generate film waste. The film waste is mixed with the cooling liquid for roll forming, adheres to the molded product, and deteriorates the appearance of the molded product. In addition, the film waste mixed with the cooling liquid accumulates on the surface of the drain pad for wiping the cooling liquid before cutting the molded product. The film waste accumulated on the surface of the drain pad may cause abnormal noise due to friction with the molded product when the coolant adhering to the molded product is wiped with the drain pad, or cause the size of the molded product to be defective. As a countermeasure, the roll forming apparatus is equipped with a filter for removing the film waste mixed with the cooling liquid. However, when a coated galvanized steel sheet, which generates a large amount of film waste, is used as a material to be formed, the filter is blocked immediately during roll forming, so the frequency of filter replacement increases and the productivity decreases.

During roll forming, in order to reduce the occurrence of film waste, it is required that the film is not easily damaged, and the amount of peeling at the time of damage is small. A film that satisfies such a requirement is, for example, a hard and thin film mainly composed of an inorganic substance. However, for a coated galvanized steel sheet with a special treatment film with a thickness of several μm or less, if the thickness of the film is to be further reduced, the barrier property for protecting the plated surface due to the corrosion factor is significantly reduced, and the corrosion resistance is significantly deteriorated.

Magnesium-based compounds are known to exhibit rust-preventive effects on zinc plating. In recent years, a technology of highly corrosion-resistant coating containing nano-sized magnesium particles has been developed.

As such a technique, for example, Patent Document 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, by repairing the defects of the film by self-healing, passivation is performed to maintain the corrosion resistance of the film. For example, Patent Document 2 discloses the use of a composite colloid composed of magnesium hydroxide and fine silicon dioxide. A film formed by a rust inhibitor for metals.

In addition, a technique of applying a coating containing magnesium to a coating of a chromium-free organic-coated steel sheet, for example, Patent Document 3 discloses that on the surface of a galvanized steel sheet, a coating containing oxide particles, phosphoric acid, and/or a phosphorus oxide compound and a magnesium compound is present. The composite oxide film has, on the composite oxide film, an organic-coated steel sheet comprising a reaction product of an organic resin and a compound containing active hydrogen, and an organic film containing an antirust additive.

However, the thickness of the coating system disclosed in Patent Document 1 is 2.5 to 75 μm, and it is not assumed that it is roll-formed. In addition, the coating disclosed in Patent Document 1 does not exhibit a sufficient rust preventive effect when the thickness is 1 μm or less.

In the film disclosed in Patent Document 2, it is necessary to use a metal rust inhibitor containing a composite colloid composed of magnesium hydroxide and fine silicon dioxide when forming the film. Problems are prone to occur in the coating step for gelation. In addition, since the film disclosed in Patent Document 2 contains a water-soluble component, water resistance is insufficient, and discoloration is conspicuous due to dew condensation, wetting of water during transportation, or the like.

In the organic-coated steel sheet disclosed in Patent Document 3, the magnesium compound is added in the form of water-soluble ions or molecules during the formation of the composite oxide film. Therefore, when the addition amount of the magnesium compound is increased, the stability of the treatment solution decreases. Therefore, there is a limit to improving the corrosion inhibitory effect by the composite oxide film. In addition, the organic-coated steel sheet disclosed in Patent Document 3 has a problem of low productivity and high production cost because it is necessary to form an organic film after forming a 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 with less film waste generated during roll forming and excellent in corrosion resistance. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2016-104574 [Patent Document 2] Japanese Patent Laid-Open No. 2002-322569 [Patent Document 3] Japanese Patent Laid-Open No. 2002-053979

One aspect of the present invention is a coated galvanized steel sheet, which is a coated galvanized steel sheet with a resin film comprising silicon dioxide and magnesium hydroxide on the surface of the galvanized steel sheet, wherein the silicon dioxide and The total content of magnesium hydroxide is 75-90 mass %, and the content of the resin component of the resin film is 10-25 mass %, the mass ratio of the magnesium hydroxide to the silica is 0.15-3, and the resin film is The thickness is 0.20~1.1μm. [Form of implementing the invention]

In order to achieve the above-mentioned object, the inventors of the present invention have conducted examinations from various angles. As a result, it was found that the above objects can be achieved by appropriately adjusting the total content of silicon dioxide and magnesium hydroxide in the resin film, the mass ratio of magnesium hydroxide to silicon dioxide, and the thickness of the resin film, thereby completing the present invention.

The coated galvanized steel sheet according to one embodiment of the present invention has a resin film containing silicon dioxide and magnesium hydroxide on the surface of the galvanized steel sheet. The total content of silicon dioxide and magnesium hydroxide in the resin film is 75 to 90% by mass. Content of the resin component of the said resin film is 10-25 mass %. The mass ratio of the magnesium hydroxide to the silicon dioxide is 0.15-3. The thickness of the resin film is 0.20 to 1.1 μm.

According to the present invention, it is possible to provide a coated galvanized steel sheet which produces less film waste during the roll forming process and exhibits excellent corrosion resistance.

The present embodiment will be described in more detail below, but the present invention is not limited to these.

[Total content of silica and magnesium hydroxide: 75~90% by mass] In the present embodiment, the total content of silicon dioxide and magnesium hydroxide in the resin film is set to 75 to 90% by mass. The inorganic film is mainly composed of an inorganic compound with a larger specific gravity than an organic compound, so a dense film with a high barrier effect on corrosion factors can be obtained. Thereby, there is an advantage that the thickness of the film for obtaining the same corrosion resistance can be made smaller than that of the organic film, which is advantageous in suppressing the occurrence of film waste during roll forming.

In addition, the inorganic compound contained in the resin film of the present embodiment refers to silica and magnesium hydroxide, and the inorganic film refers to a resin film containing silica and magnesium hydroxide.

When the total content of silica and magnesium hydroxide in the resin film is less than 75% by mass, the corrosion resistance deteriorates due to insufficient inorganic components. In addition, since the hardness of the film is insufficient, peeling of the film tends to occur during roll forming. In addition, since the specific gravity of the film waste is small, it is easy to accumulate on the surface of the drainage pad. Preferably it is 77 mass % or more, More preferably, it is 80 mass % or more. On the other hand, when the total content of silica and magnesium hydroxide in the resin film exceeds 90% by mass, the resin component serving as a binder is insufficient, and the film becomes a film with many defective parts. Therefore, even if the occurrence of film waste is suppressed, the corrosion resistance is deteriorated. Preferably it is 88 mass % or less, More preferably, it is 85 mass % or less.

The silica used in the present embodiment is preferably colloidal silica having excellent compatibility with the water-based resin described later. In addition, when the average particle size of silica is too large, the density of the film may be lowered, and there may be a possibility of film defects. Therefore, the average particle size _D50 is preferably 500 nm or less, more preferably 450 nm or less. In addition, the average particle diameter _D50 of silica means the average particle diameter when the accumulated value (accumulated 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 size D ₅₀ of the magnesium hydroxide dispersed in water, that is, the average particle size D ₅₀ of the magnesium hydroxide in the magnesium hydroxide aqueous dispersion is preferably smaller than the thickness of the resin film, such as 0.7 μm or less. good. Thereby, the deterioration of the roll formability resistance and the generation|occurrence|production of a film|membrane defect can be suppressed by the fall-off of the particulate magnesium hydroxide from a resin film. The lower limit of the average particle diameter _D50 in the state where magnesium hydroxide is dispersed in water is not particularly limited. If the average particle diameter _D50 is too small, the stability of the dispersion (for example, the dispersion liquid) may be reduced, so 0.1 More than μm is preferred. More preferably, it is 0.14 μm or more. In addition, the average particle diameter _D50 of magnesium hydroxide means the average particle diameter when the cumulative value (accumulated value) of magnesium hydroxide becomes 50 mass %.

When preparing a magnesium hydroxide aqueous dispersion, when forming a resin film, a polymer dispersant (for example, water-soluble acrylic resin, water-soluble styrene acrylic resin, non-ionic surfactant) that has little adverse effect on corrosion resistance can be used. ).

[Content of resin component in resin film: 10~25% by mass] In this embodiment, content of the resin component in a resin film is 10-25 mass %. As described above, when the resin component in the resin film is insufficient, a film with many defective parts is formed, and the corrosion resistance is deteriorated. From this viewpoint, the content of the resin component in the resin film is 10% by mass or more. Preferably it is 15 mass % or more. However, when the content of the resin component in the resin film is too large, in addition to the deterioration of corrosion resistance caused by the decrease in the density of the resin film, and the softening of the resin film, the occurrence of film waste during roll forming will increase. From this viewpoint, the content of the resin component in the resin film is 25% by mass or less. Preferably it is 20 mass % or less.

[Mass ratio of magnesium hydroxide to silicon dioxide: 0.15~3] In this embodiment, the mass ratio of magnesium hydroxide to silicon dioxide is 0.15~3. Both magnesium hydroxide and silicon dioxide are known as rust inhibitors for galvanizing. The inventors of the present invention have found that excellent corrosion resistance can be obtained even when the thickness of the film is 1 μm or less by mixing magnesium hydroxide and silicon dioxide in a resin film at a specific mass ratio. When the mass ratio of magnesium hydroxide to silicon dioxide [Mg(OH) ₂ /SiO ₂ ] is in the range of 0.15 to 3, excellent corrosion resistance is exhibited. This mass ratio is more preferably 0.3 or more and 2.0 or less.

By adjusting the above mass ratio to an appropriate range, the mechanism for improving the corrosion resistance is not clear, but the following ones are possible. That is, the magnesium ion eluted from magnesium hydroxide stabilizes the corrosion product which is produced by silicon dioxide and has a high protective effect on galvanizing, and improves the barrier effect due to the stabilized corrosion product. The above-mentioned protective effect on galvanizing refers to the barrier property of blocking corrosion factors such as water or oxygen. In addition, it is presumed that the above-mentioned mechanism continues to exhibit excellent corrosion resistance for a long time as a result of increasing the addition ratio of the magnesium component in the resin film without impairing the stability of the treatment solution by using particulate magnesium hydroxide.

[Resin film thickness: 0.20~1.1μm] In the present embodiment, the thickness of the resin film is 0.20 to 1.1 μm. When the resin film thickness is less than 0.20 μm, the corrosion resistance deteriorates. On the other hand, when the thickness of the resin film exceeds 1.1 μm, not only the generation of film waste during roll forming increases, but also it becomes very difficult to ensure electrical conductivity. The resin film thickness is preferably 0.3 μm or more and 0.8 μm or less, from the viewpoint of having a good balance between corrosion resistance and film waste suppression. More preferably, it is 0.3-0.6 micrometer. In addition, when the thickness of the resin film is in the range of 0.3 to 0.8 μm, the balance of corrosion resistance, roll forming resistance, and electrical conductivity is excellent, and it can also be advantageously applied to electrical products that require grounding properties.

[Type of resin] The kind of resin used in this embodiment is not particularly limited, and either water-based resin and non-aqueous-based resin can be used. When using an aqueous dispersion of magnesium hydroxide or colloidal silica, it is better to use an aqueous resin. This water-based resin is not particularly limited, but can be preferably mixed with an aqueous dispersion of magnesium hydroxide and colloidal silica. In addition, the water-based resin in this embodiment means the resin which becomes an aqueous dispersion, or a water-soluble resin.

The water-based resin is preferably a polyolefin-based resin, a polyurethane-based resin, and a polyester-based resin, and among these, a polyolefin-based resin and a polyurethane-based resin are more preferred. Hereinafter, the polyolefin-based resin and the polyurethane-based resin will be specifically described, respectively.

[Polyolefin resin] As the polyolefin-based resin, an ethylene-unsaturated carboxylic acid copolymer is preferred. As an ethylene-unsaturated carboxylic acid copolymer, the thing described in Unexamined-Japanese-Patent No. 2005-246953 or Unexamined-Japanese-Patent No. 2006-43913 can be used, for example.

Unsaturated carboxylic acids include (meth)acrylic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, itaconic acid, and the like. It is polymerized by a high temperature and high pressure polymerization method or the like to obtain an ethylene-unsaturated carboxylic acid copolymer.

The copolymerization ratio of unsaturated carboxylic acid to ethylene is preferably 10 mass % or more, more preferably 15 mass % or more, and preferably 40 mass % or less, when the total monomer amount is 100 mass %, More preferably, it is 25 mass % or less. When the content of unsaturated carboxylic acid is less than 10% by mass, there are few carboxyl groups that serve as origins of intermolecular association due to ion clusters, so that the film strength effect cannot be exhibited. The coating solution (emulsion composition) will be described later. emulsification stability of the material) is poor. Moreover, when the unsaturated carboxylic acid exceeds 40 mass %, there exists a possibility that the corrosion resistance or water resistance of a resin film may be inferior.

Since the said ethylene-unsaturated carboxylic acid copolymer has a carboxyl group, a coating liquid can be emulsified (aqueous dispersion) by neutralizing with an organic base or a metal ion.

As the organic base, an amine having a boiling point under atmospheric pressure of 100° C. or lower is preferable from the viewpoint of not reducing the corrosion resistance of the resin film too much. Specific examples include tertiary amines such as triethylamine; secondary amines such as diethylamine; and primary amines such as propylamine, etc., and one or more of these may be used in combination. Among these, tertiary amines are preferred, and triethylamine is most preferred. Moreover, from the viewpoint of improving solvent resistance and film hardness, it is preferable to use a monovalent metal ion in combination with the above-mentioned amine.

The above-mentioned amine is preferably 0.2 mol or more and 0.8 mol or less with respect to 1 mol of the carboxyl group in the ethylene-unsaturated carboxylic acid copolymer from the viewpoint of ensuring corrosion resistance. Further, it is more preferably 0.3 mol or more and 0.6 mol or less.

The amount of the monovalent metal ion is preferably 0.02 mol or more, more preferably 0.03 mol relative to 1 mol of the carboxyl group in the ethylene-unsaturated carboxylic acid copolymer, from the viewpoint of ensuring the emulsion stability of the coating solution. above the ear. In addition, from the viewpoint of securing corrosion resistance, it is preferably 0.4 mol or less, more preferably 0.3 mol or less, relative to 1 mol of the carboxyl group in the ethylene-unsaturated carboxylic acid copolymer. Further, the metal compound for imparting a monovalent metal ion is preferably NaOH, KOH, LiOH, or the like, and NaOH has the best performance.

The above-mentioned ethylene-unsaturated carboxylic acid copolymer, if necessary, in the presence of the carboxylic acid polymer described later, for example, in a container that can react at high temperature (about 150 ° C) and high pressure (about 5 atmospheres), perform high-speed stirring for 1 to 6 hours, emulsification was performed. During emulsification, a compound having a surfactant function, such as tall oil fatty acid, may be added in an appropriate amount. In addition, a hydrophilic organic solvent, for example, a lower alcohol having about 1 to 5 carbon atoms, etc. may be partially added to the 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 value is 3,000 or more, and still more preferably 5,000 or more. A more preferable upper limit is 70,000 or less, and still more preferably 30,000 or less. The Mw was measured by Gel Permeation Chromatography (GPC) using polystyrene as a standard.

Carboxylic acid polymers can also be used as resin components. The carboxylic acid polymer can be used as an example of a polymer having an unsaturated carboxylic acid as a constituent unit which can be used for the synthesis of the above-mentioned ethylene-unsaturated carboxylic acid copolymer. 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 in the polymer is preferably 10 mass % or less, more preferably 5 mass % Hereinafter, a carboxylic acid polymer composed of only an unsaturated carboxylic acid is still more preferable. Preferred carboxylic acid polymers include polyacrylic acid, polymethacrylic acid, acrylic acid-maleic acid copolymer, polymaleic acid, and the like. Among these, polymaleic acid is more preferable from the viewpoint of resin film adhesion and corrosion resistance. The exact mechanism for improving corrosion resistance, etc. by using polymaleic acid is unknown, but since the amount of carboxyl groups is large, the adhesion between the resin film and the galvanized steel sheet is improved, and the corrosion resistance is also improved. However, the present invention is not limited to this speculation.

The mass average molecular weight (Mw) of the carboxylic acid polymer used in the present embodiment is preferably 500 or more and 30,000 or less in terms of polystyrene. More preferably, the lower limit value is 800 or more, more preferably 900 or more, and most preferably 1,000 or more. More preferably, the 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 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, in terms of mass ratio. 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 cannot be sufficiently exhibited. Conversely, when the content ratio of the carboxylic acid polymer is too large, the olefin-acid copolymer and the carboxylic acid polymer are phase-separated in the coating liquid for forming the first layer, and there is a possibility that a uniform resin film cannot be formed.

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

The carboxyl group-containing urethane resin is preferably obtained by subjecting a urethane prepolymer to a chain extension reaction with a chain extension agent. The urethane prepolymer is obtained, for example, by reacting a polyisocyanate component and a polyol component.

As the above-mentioned polyisocyanate component, at least one polyisocyanate selected from the group consisting of tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI) and dicyclohexylmethane diisocyanate (hydrogenated MDI) is used, It is preferable from the viewpoint of obtaining a resin film excellent in corrosion resistance and stability of reaction control. In addition to the above-mentioned polyisocyanates, other polyisocyanates can be used within the range that the corrosion resistance and the stability of the reaction control are not lowered. However, the content of the above-mentioned polyisocyanate is preferably 70% by mass or more of the total polyisocyanate component from the viewpoint of ensuring the corrosion resistance of the resin film and the stability of the reaction control. Examples of polyisocyanates other than the above-mentioned polyisocyanate components include tetramethylene diisocyanate, hexamethylene diisocyanate, dodecylmethylene diisocyanate, isophorone diisocyanate, xylene diisocyanate, phenylene Diisocyanates and the like may be used alone or in two or more.

The above-mentioned polyol component is the use of 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, it is preferred. good. Moreover, as said polyol component, it is more preferable to use three types of diols, 1, 4- cyclohexane dimethanol, polyether diol, and a carboxyl group-containing diol. Moreover, by using 1, 4- cyclohexane dimethanol as the said polyol component, the rust-proof effect of the obtained polyurethane resin can be improved.

The polyether polyol described above is not particularly limited when the molecular chain has at least two or more hydroxyl groups and the main skeleton is composed of an alkylene oxide unit. Specific examples include polyoxyethylene glycol, polyoxypropylene glycol, polyoxybutylene glycol, and the like, and polyoxypropylene glycol or polyoxybutylene glycol is preferably used. When the number of functional groups of the polyether polyol is at least 2 or more, it is not particularly limited, and for example, trifunctional, tetrafunctional or more polyfunctional may be used. The average molecular weight of the polyether polyol is preferably about 400 to 4,000 from the viewpoint of obtaining a resin film having moderate hardness. In addition, the average molecular weight can be calculated|required by measuring OH valence (hydroxyl valence).

Among the above-mentioned polyol components, from the viewpoint of further improving the rust preventive effect of the resin film, the mass ratio is preferably 1,4-cyclohexanedimethanol:polyether polyol=1:1~1:19. Moreover, when the polyol which has the said carboxyl group has at least 1 or more carboxyl groups and at least 2 or more hydroxyl groups, it will not specifically limit. Specific examples include dimethylolpropionic acid, dimethylolbutanoic acid, dihydroxypropionic acid, dihydroxysuccinic acid, and the like.

Among the above-mentioned polyol components, in addition to the above-mentioned three types of polyols, other polyols may be used within the range where the corrosion resistance is not lowered. However, from the viewpoint of securing the corrosion resistance of the resin film, the content of the above-mentioned three types of polyols is preferably 70% by mass or more of the total polyol components. The polyol other than the above-mentioned three types of polyols is not particularly limited as long as it has 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 with an average molecular weight of about 500 or less. Specific examples include ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, and the like. Alcohols; triols of glycerol, trimethylolpropane, hexanetriol, etc. High molecular weight polyols are polyols with an average molecular weight of over 500. Specific examples include condensation-based polyesters such as polyethylene adipate (PEA), polybutylene adipate (PBA), and polyhexamethylene adipate (PHMA). Polyols; lactone polyester polyols such as poly-ε-caprolactone (PCL); polycarbonate polyols such as polyhexylene carbonate; and acryl polyols, etc.

The said chain extension agent is not specifically limited, For example, a polyamine, a low molecular weight polyol, an alkanolamine, etc. are mentioned. Examples of polyamines include aliphatic polyamines such as ethylenediamine, propylenediamine, and hexamethylenediamine; aromatic polyamines such as tolylylenediamine, xylylenediamine, and diaminodiphenylmethane; diamines Alicyclic polyamines such as cyclohexylmethane, piperazine, isophorone diamine, etc.; hydrazine such as hydrazine, dihydrazine succinate, dihydrazine adipic acid, dihydrazine phthalate, etc. Among these, ethylenediamine and/or hydrazine are preferably used as chain extender components. As an alkanolamine, diethanolamine, monoethanolamine, etc. are mentioned, for example.

The carboxyl group-containing polyurethane resin can be emulsified by a known method, for example, the following methods are mentioned. That is, the carboxyl group of the carboxyl group-containing urethane prepolymer is neutralized with alkali, emulsified and dispersed in an aqueous medium, and the method of chain extension reaction; the carboxyl group-containing polyurethane resin is emulsified. In the presence of an agent, emulsification and dispersion are carried out with high shear force, and the chain extension reaction is carried out.

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, and preferably 60 mgKOH from the viewpoint of ensuring the corrosion resistance of the resin film /g or less. The measurement of the acid value is based on JIS-K0070 (1992).

[Additives in coating solution] In the present embodiment, the resin film can be coated by a known coating method using a coating liquid, that is, a roll coater method, a bar coater method, a spray method, or a curtain flow coater method. etc., it is applied to the surface of a galvanized steel sheet, and it is formed by heating and drying. The coating liquid contains specific amounts of silica, magnesium hydroxide and the above-mentioned resins. The resin solid content in the coating liquid is preferably about 15 to 25 mass %. In addition, the coating liquid may contain various additives within a range that does not inhibit the effect of the present invention for the purpose of improving the film performance. Examples of the additives include silane coupling agents, elution inhibitors, rust inhibitors, waxes, crosslinking agents, diluents, anti-skinning agents, surfactants, emulsifiers, dispersants, and flattening agents. , defoamer, penetrating agent, film-making auxiliaries, dyes, pigments, tackifiers, lubricants, etc.

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 improved, and the corrosion resistance is improved. In addition, it has the effect of improving the bonding force between the resin component and the colloidal silica, improving the strength and toughness of the film. Among them, glycidoxy-based silane coupling agents have high reactivity and have a great effect of improving corrosion resistance. Glycidyl group-containing silane coupling agents include γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-glycidoxymethyl Dimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, etc.

The silane coupling amount 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, based on 100 parts by mass of the total of the inorganic compound and the resin component in the inorganic film. When it is less than 0.1 part by mass, the adhesion between the galvanized steel sheet and the resin film or the bonding force between the resin component and the colloidal silica is insufficient, and there is a concern that the film has insufficient strength, toughness or corrosion resistance. The silane coupling amount 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, based on 100 parts by mass of the total of the inorganic compound and the resin component in the inorganic film. 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 groups in the resin decrease, and there is a possibility that the paintability will decrease. In addition, the silane coupling agents undergo a hydrolysis condensation reaction with each other, which reduces the stability of the coating solution and causes gelation or precipitation of colloidal silica.

In addition, for example, when metavanadate, which is an elution inhibitor, is used as an additive, the dissolution or elution of the galvanized steel sheet is suppressed by the elution of the metavanadate, and the corrosion resistance is improved. Metavanadate has the effect of improving bare corrosion resistance, especially for alloyed hot-dip galvanized steel sheets. As a metavanadate, sodium metavanadate ( _NaVO3 ), _ammonium metavanadate ( _NH4VO3 ), potassium metavanadate ( _KVO3 ) etc. are mentioned, for example. One or more of these can be used.

The amount of metavanadate is preferably 0.5 part by mass or more, more preferably 0.7 part by mass or more, and still more preferably 1.0 part 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 film. When it is less than 0.5 parts by mass, the effect of improving the bare corrosion resistance becomes insufficient. 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 3.0 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 film. . When the content exceeds 5.5 parts by mass, not only the bare corrosion resistance tends to decrease slightly, but also the film adhesion tends to further decrease significantly. In addition, the preferable amount of this metavanadate is the V element conversion amount.

[Type of galvanized steel sheet] The type of galvanized steel sheet used in this embodiment is not particularly limited, and electro-galvanized steel sheet, hot dip galvanized steel sheet, and hot dip galvanized steel sheet (hereinafter, these may be referred to as "original sheet") can be used. In addition, the type of the zinc-plated layer is not particularly limited, either, and the metal-plated layer may contain an alloying element. In addition, the galvanized layer is coated on one side or both sides of the base steel sheet, and 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 silicon dioxide and magnesium hydroxide on the surface of the galvanized steel sheet, and is characterized by two of the resin films. The total content of silicon oxide and magnesium hydroxide is 75-90 mass %, and the content of the resin component of the resin film is 10-25 mass %, the mass ratio of magnesium hydroxide to the silicon dioxide is 0.15-3, the aforementioned The thickness of the resin film is 0.20~1.1μm.

According to this configuration, although the thickness of the resin film is 1.1 μm or less, a coated galvanized steel sheet with less film waste generated during roll forming and showing excellent corrosion resistance can be realized.

[Example]

The following examples are given to illustrate the present invention in more detail. In addition, the present invention is not limited to the following examples, and can be implemented with modifications within the scope of conforming to the technical features described above and below, and they are also included in the technical scope of the present invention.

(Preparation of Magnesium Hydroxide Dispersion) Magnesium hydroxide particles (manufactured by Kyowa Chemical Industry Co., Ltd., trade name: kisuma5Q-S) were used as a dispersant, and a polymer dispersant was used to disperse them to prepare an aqueous dispersion ( Resin solid content: about 30% by mass, average particle diameter D ₅₀ : 0.69 μm).

The average particle size _D50 of the magnesium hydroxide in the dispersion was diluted with a 0.2 mass % aqueous solution of sodium hexametaphosphate, and then used a laser diffraction scattering particle size distribution measuring device (manufactured by Microtrac-bel Co., Ltd., commodity Name: MicrotracMT3300EXII) to measure.

(resin) As the resin for forming the resin film, polyethylene resin manufactured by Toho Chemical Co., Ltd. or urethane resin manufactured by Toho Chemical Industry Co., Ltd. was used.

The above-mentioned polyethylene resin manufactured by Toho Chemical Co., Ltd. and its aqueous dispersion were prepared by the following method.

An ethylene-acrylic acid copolymer (manufactured by Dow Chemical Co., Ltd., trade name: PRIMACOR 5990I, constituent unit derived from acrylic acid: 20% by mass) was placed in an autoclave equipped with an emulsification facility equipped with a stirrer, a thermometer, and a temperature controller. , mass average molecular weight (Mw): 20,000, melt index: 1300, acid value: 150) 200.0 parts by mass, polymaleic acid aqueous solution (manufactured by NOF Corporation, trade name: NONPOL PMA-50W, Mw: about 1100 (polyphenylene) ethylene conversion), 50 mass % product) 8.0 mass parts, triethylamine 35.5 mass parts (relative to the carboxyl group of the ethylene-acrylic acid copolymer: 0.63 equivalent), 48% NaOH aqueous solution 6.9 mass parts (relative to the ethylene-acrylic acid copolymer) The carboxyl group is 0.15 equivalent), 3.5 parts by mass of tall oil fatty acid (manufactured by Harima Chemical Co., Ltd., trade name: HARTALL FA3), 792.6 parts by mass of ion-exchanged water, then sealed, stirred at high speed at 150° C. and 5 atmospheric pressure for 3 hours, and cooled. up to 30°C.

Next, γ-glycidoxypropyltrimethoxysilane (manufactured by Momentive Performance Materials, trade name: TSL8350) was added 10.4 parts by mass, 31.2 parts by mass of polycarbodiimide (manufactured by Nisshinbo Co., Ltd., trade name: carbodilite SV-02, Mw: 2,700, solid content 40% by mass), 72.8 parts by mass of ion-exchanged water, stirred for 10 minutes, ethylene - The acrylic copolymer was emulsified to obtain an aqueous dispersion of polyethylene resin mixed with each component (resin solid content 20.3% by mass, measured in accordance with JIS K6833 (2014)).

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

60 g of polyoxybutylene glycol (manufactured by Hodogaya Chemical Industry Co., Ltd., average molecular weight 1,000) and 1,4-cyclohexanedimethanol were put into a synthesis apparatus equipped with a stirrer, a thermometer, and a temperature controller with an inner capacity of 0.8 L. 14 g, 20 g of dimethylolpropionic acid, and 30.0 g of N-methylpyrrolidone. Then, 104 g of tolyl diisocyanate was put in, the temperature was raised from 80 to 85° C., and the reaction was carried out for 5 hours. The NCO content of the obtained prepolymer was 8.9%. Then add 16 g of triethylamine for neutralization, add a mixed aqueous solution of 16 g of ethylenediamine and 480 g of water, emulsify at 50 ° C for 4 hours, and make the chain extension reaction to obtain a urethane resin aqueous dispersion (non-volatile resin) Composition 29.1%, acid value 41.4).

(Mixing of coating liquid) The above-mentioned magnesium hydroxide aqueous dispersion, the above-mentioned polyethylene resin aqueous dispersion or the above-mentioned urethane resin aqueous dispersion, and colloidal silica (manufactured by Nissan Chemical Industries, Ltd., trade name: SNOWTEX XS) are mixed, A coating liquid with a resin solid content of about 10% by mass was prepared.

(Type of original sheet) (1) Hot dip galvanized steel sheet (GI): sheet thickness 0.8 mm, zinc unit weight: 60 g/m ² (2) Alloy hot dip galvanized steel sheet (GA): sheet thickness 0.8 mm, zinc unit weight : 45g/m ² (3) Electro-galvanized steel sheet (EG): Plate thickness 0.8mm, zinc unit weight: 20g/m ²

(Pre-treatment of galvanized steel sheet) Degreasing: Alkaline degreasing (manufactured by Parkerizing Corporation, Japan, trade name: Fine Cleaner) Drying: Dry with hot air to evaporate water.

(painting method) Method: Coating bar Resin film thickness: Select the resin solid content of the coating solution and the number of coating rods to adjust the resin film thickness.

(drying method) Time: 1 minute Condition: The maximum temperature of the coated board is 80°C (confirmed with thermal paper)

[Example] The above-mentioned (1) hot-dip galvanized steel sheet, the above-mentioned (2) alloyed hot-dip galvanized steel sheet, and the above-mentioned (3) electro-galvanized steel sheet were used as original sheets. For various coated galvanized steel sheets (Test Nos. 1 to 17 in Table 1 and Test Nos. 18 to 35 in Table 2), the following were used for the roll formability and corrosion resistance of the obtained coated galvanized steel sheets method evaluation.

(Roll Formability Resistance) The test piece cut out from the above-mentioned coated galvanized steel sheet was divided into the film adhesion amount (W ₀ ) before the repeated sliding test described later and the film adhesion amount (W ₁ ) after the same test. ) is calculated according to the following formula (1). X in the formula (1) is measured using a fluorescent X-ray analyzer.

式(1)中，X表示皮膜中之矽元素之單位面積的質量(mg/m² )，Y表示被膜中之二氧化矽(SiO₂ )之組成比率(質量%)。

In formula (1), X represents the mass per unit area (mg/m ² ) of the silicon element in the film, and Y represents the composition ratio (mass %) of silicon dioxide (SiO ₂ ) in the film.

Then, it was calculated as the film waste in which the decrease in the film adhesion amount (W ₀ -W ₁ ) occurred, and according to the following criteria, ⊚ and ○ were evaluated as acceptable, and Δ was evaluated as unacceptable.

<Evaluation criteria> ◎: Film waste 300 mg/m ² or less ○: Film waste more than 300 mg/m ² and 450 mg/m ² or less △: Film waste more than 450 mg/m ²

The method of repeating the sliding test is as follows. First, a test piece cut into a rectangle with a width of 40 mm × a length of 300 mm from a coated galvanized steel sheet was installed vertically in a tensile testing machine, and one surface (non-slip surface) of the test piece was in contact with a flat die (Dies) (material: SKD11). Next, the other surface (sliding surface) of the test piece was brought into contact with a jig (semi-cylindrical die, material: SKD11) having a convex portion with a tip radius of 9.1 mm, and a load of 2940 N (300 kgf) was applied to the jig in the horizontal direction, so that the The jig is moved downward at a speed of 300 mm/min within the range where the sliding surface of the test piece and the flat die are in contact, and the sliding operation is performed. After the sliding operation was completed, the jig (half-cylindrical mold) was separated from the sliding surface of the test piece and returned to the position before the sliding operation. The same sliding operation as above is repeated 9 times. That is, the sliding operation is performed 10 times in total and ends.

(corrosion resistance) The above-mentioned coated galvanized steel sheet (sample) was subjected to a salt spray test in accordance with JIS Z2371 (2015) for 24 hours, and the white rust occurrence rate on the surface of the sample was calculated (100×area of white rust occurrence/resin-coated metal sheet full area). Then, according to the following criteria, ○ was evaluated as acceptable, and Δ was evaluated as unacceptable.

<Evaluation Criteria> ○: White rust occurrence rate of 50 area% or less △: The incidence of white rust exceeds 50 area %

Moreover, about the said coated galvanized steel sheet (sample), the salt spray test based on JIS Z2371 (2015) was implemented, and the occurrence state of red rust was investigated. At this time, the salt spray test time (test time) was changed according to the type of the original plate, and the test was carried out.

(A) The case of hot dip galvanized steel sheet and electro-galvanized steel sheet Test time: 480 hours Evaluation method: Calculate the occurrence rate of red rust on the surface of the sample (100×area where red rust occurs/total area of the resin-coated metal plate).

<Evaluation Criteria> ○: The occurrence rate of red rust is 5 area % or less △: The occurrence rate of red rust exceeds 5 area %

(B) In the case of alloyed hot dip galvanized steel sheet Test time: 120 hours Evaluation method: The occurrence of red rust on the surface of the sample was visually observed, and according to the following criteria, ○ was evaluated as acceptable, and Δ was evaluated as unacceptable.

<Evaluation Criteria> ○: The occurrence of red rust (rust) has not been confirmed △: The occurrence of red rust was confirmed

The results were compared with the conditions for producing each coated galvanized steel sheet (type of original sheet, type of resin, composition ratio of resin film, mass ratio of magnesium hydroxide to silicon dioxide [Mg(OH) ₂ /SiO ₂ ], resin film thickness) are shown in Tables 1 and 2 below together.

From these results, it was found that the resin content was too small in the case where the resin content was 5% by mass (Test No. 7 in Table 1, Test No. 24 in Table 2: the following only indicates Test No.), so the original plate was In any of GI and GA, the film defects are also increased, and the corrosion resistance is deteriorated. In addition, in these examples, the mass ratio [Mg(OH) ₂ /SiO ₂ ] is also outside the range of 0.15 to 3.

Test Nos. 14, 15, 31, and 32 are examples in which the mass ratio [Mg(OH) ₂ /SiO ₂ ] is outside the range of 0.15 to 3, and the original plate is either GI or GA, and the corrosion resistance is also deteriorated. Moreover, in the case where the resin film thickness was less than 0.20 μm (Test Nos. 16, 18, 25, and 33), the original plate was either GI or GA, and the corrosion resistance also deteriorated.

On the other hand, in the coated galvanized steel sheets of the present invention that satisfy any of the specific requirements (Test Nos. 1 to 6, 8 to 13, 17, 19 to 23, 26 to 30, 34, and 35), the original sheets are GI, Any of GA and EG, and the resin is either polyethylene resin or urethane resin, also exhibits excellent corrosion resistance and exhibits excellent roll formability.

This application is based on Japanese Patent Application No. 2018-64766 filed on March 29, 2018 and Japanese Patent Application No. 2019-30545 filed on February 22, 2019, the contents of which are contained in applicant of this application.

In order to explain the present invention, the present invention has been appropriately and sufficiently described above with reference to specific examples and the like through embodiments, but those skilled in the art will understand that the above-described embodiments can be easily changed and/or improved. Therefore, if the modified form or improved form implemented by those skilled in the art does not deviate from the level of the right scope of the claim recorded in the scope of the application, the modified form or the improved form is also included in the right scope of the claim item Inside. [Industrial Availability]

The present invention has wide industrial applicability in the technical fields of steel sheets, galvanized steel sheets, and methods for producing them.

Claims (1)

A coated galvanized steel sheet, which is a coated galvanized steel sheet with a resin film containing silicon dioxide and magnesium hydroxide on the surface of the galvanized steel sheet, characterized in that the silicon dioxide and magnesium hydroxide in the resin film are combined. The total content is 75-90 mass %, and the content of the resin component of the resin film is 10-25 mass %, the mass ratio of the magnesium hydroxide to the silicon dioxide is 0.15-3, and the thickness of the resin film is 0.20-3 0.8 μm, and the average particle size of the magnesium hydroxide is 0.7 μm or less.