WO2019188460A1

WO2019188460A1 - Coated galvanized steel sheet

Info

Publication number: WO2019188460A1
Application number: PCT/JP2019/011032
Authority: WO
Inventors: 山本　哲也; 大輝酒井; 礼士白岩
Original assignee: 株式会社神戸製鋼所
Priority date: 2018-03-29
Filing date: 2019-03-18
Publication date: 2019-10-03

Abstract

One aspect of the present invention relates to a coated galvanized steel sheet which has a resin coating film that contains silica and magnesium hydroxide on the surface of a galvanized steel sheet, and which is configured such that: the total content of the silica and the magnesium hydroxide in the resin coating film is 75-90% by mass; the content of a resin component in the resin coating film is 10-25% by mass; the mass ratio of the magnesium hydroxide to the silica is 0.15-3; and the thickness of the resin coating film is 0.20-1.1 μm.

Description

Painted galvanized steel sheet

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

In roll forming, the surface of the material is severely slid by the roll. For this reason, when a roll forming process is performed on a coated galvanized steel sheet having a resin film on the surface layer, a part of the resin film is peeled off to generate a film residue. The film residue mixes with the coolant liquid for roll forming, adheres to the molded product, and deteriorates the appearance of the molded product. Further, the film residue mixed in the coolant liquid is deposited on the surface of the draining pad for wiping the coolant liquid before cutting the molded product. The film residue deposited on the surface of the draining pad may cause abnormal noise due to friction with the molded product when the coolant liquid adhering to the molded product is wiped by the draining pad, or may cause a defective dimension of the molded product. As these measures, the roll forming apparatus is provided with a filter for removing film residue mixed in the coolant liquid. However, when a coated galvanized steel sheet having a large amount of film residue is used as a material to be molded, the filter is clogged immediately during roll forming, and therefore the frequency of replacement of the filter increases, resulting in a decrease in productivity.

In order to reduce the generation of film residue during roll forming, it is required that the film is difficult to break and that the amount of peeling when broken is small. As a film satisfying such requirements, for example, there is a hard and thin film mainly composed of an inorganic substance. However, for coated galvanized steel sheets with a special chemical conversion coating with a thickness of several μm or less, if the coating thickness is further reduced, the barrier property for protecting the plating surface from corrosion factors is significantly reduced. Corrosion resistance will deteriorate significantly.

For galvanizing, it is known that magnesium-based compounds exhibit an antirust effect. In recent years, techniques for highly corrosion resistant coatings containing nano-sized magnesium particles have 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.

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

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

However, the coating disclosed in Patent Document 1 has a thickness of 2.5 to 75 μm and is not assumed to be roll-formed. Further, the coating disclosed in Patent Document 1 does not exhibit a sufficient antirust effect when the thickness is 1 μm or less.

The coating disclosed in Patent Document 2 requires the use of a metal anticorrosive containing a composite colloid composed of magnesium hydroxide and fine silica during film formation. It is stable and prone to problems in the coating process for gelation. Moreover, since the film disclosed in Patent Document 2 contains a water-soluble component, its water resistance is insufficient, and discoloration due to condensation or water wetting during transportation is conspicuous.

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 forming the composite oxide film, the treatment liquid stability decreases when the addition amount of the magnesium compound is increased. . For this reason, there exists a limit in improving a corrosion inhibitory effect by complex oxide film. In addition, the organic coated steel sheet disclosed in Patent Document 3 has a problem in that productivity is low and manufacturing cost is high 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 that has less film residue during roll forming and has excellent corrosion resistance.

JP 2016-104574 A JP 2002-322569 A JP 2002-053979 A

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 75 to 75%. 90% by mass, the content of the resin component of the resin film is 10 to 25% by mass, the mass ratio of the magnesium hydroxide to the silica is 0.15 to 3, and the thickness of the resin film is 0.00. It is a coated galvanized steel sheet having a thickness of 20 to 1.1 μm.

The present inventors examined from various angles in order to achieve the above object. As a result, it has been found that the above object can be achieved brilliantly 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 present invention has been completed.

The 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 75 to 90% by mass. The resin component content of the resin film is 10 to 25% by mass. The mass ratio of the magnesium hydroxide to the silica is 0.15 to 3. The resin film has a thickness of 0.20 to 1.1 μm.

According to the present invention, it is possible to provide a coated galvanized steel sheet with less film residue generated during roll forming and exhibiting excellent corrosion resistance.

Hereinafter, the present embodiment will be described more specifically, but the present invention is not limited thereto.

[Total content of silica and magnesium hydroxide: 75 to 90% by mass]
In the present embodiment, the total content of silica and magnesium hydroxide in the resin film is 75 to 90% by mass. Since the inorganic coating mainly contains an inorganic compound having a specific gravity larger than that of the organic compound, a dense coating with a high barrier effect against corrosion factors can be obtained. Thereby, there exists an advantage which can make the film thickness for obtaining the same corrosion resistance smaller than an organic type film, and it becomes advantageous to generation | occurrence | production suppression of the film debris at the time of roll forming.

The inorganic compound contained in the resin film of this embodiment is silica and magnesium hydroxide, and the inorganic film means a resin film containing silica and magnesium hydroxide.

If 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 not sufficient, film peeling is likely to occur during roll forming. And since the specific gravity of the film residue is small, it is easy to accumulate on the surface of the draining pad. Preferably it is 77 mass% or more, More preferably, it is 80 mass% or more. On the other hand, if the total content of silica and magnesium hydroxide in the resin film exceeds 90% by mass, the resin component serving as the binder is insufficient and the film has many defective parts, so that generation of film residue is suppressed. However, the corrosion resistance deteriorates. 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 excellent in compatibility with an aqueous resin described later. If the average particle size of the silica is too large, or reduced denseness of the film, there is a possibility that or generating a film defects, it is preferred that the average particle size D ₅₀ is 500nm or less, 450 nm or less It is more preferable that Note that the average particle diameter D ₅₀ of the silica, the integrated value of the silica (integrated value) means the average particle diameter when the 50 mass%.

The magnesium hydroxide used in the present embodiment is not particularly limited as long as it is stable as an aqueous dispersion, and the magnesium hydroxide powder and dispersion method are not particularly limited. The average particle diameter D ₅₀ of the magnesium hydroxide in a state of being dispersed in _water, i.e., the average particle diameter D ₅₀ of magnesium hydroxide in magnesium hydroxide aqueous dispersion is preferably less than that of the resin film thickness, for example, 0. It is preferably 7 μm or less. Thereby, deterioration of roll moldability and generation | occurrence | production of a film | membrane defect by the particulate magnesium hydroxide having fallen from the resin film can be suppressed. On the other hand, the lower limit of the average particle diameter D ₅₀ in a state where magnesium hydroxide is dispersed in water is not particularly limited, but if the average particle diameter D ₅₀ becomes too small, the stability of the dispersion (for example, dispersion) is reduced. Since there exists a possibility that it may fall, it is preferable that it is 0.1 micrometer or more. More preferably, it is 0.14 μm or more. Note that the average particle diameter D ₅₀ of the magnesium hydroxide, means the average particle diameter when the cumulative value of magnesium hydroxide (integrated value) of 50 wt%.

When preparing a magnesium hydroxide aqueous dispersion, using a polymer dispersant (for example, a water-soluble acrylic resin, a water-soluble styrene acrylic resin, a nonionic surfactant) that has a small adverse effect on corrosion resistance when a resin film is formed. Also good.

[Content of resin component in resin film: 10 to 25% by mass]
In the present embodiment, the content of the resin component in the resin film is 10 to 25% by mass. As described above, when the resin component in the resin film is insufficient, the film has many defective portions and the corrosion resistance is deteriorated. From such a 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, if the content of the resin component in the resin film is too large, in addition to the deterioration of corrosion resistance due to the decrease in the density of the resin film, the resin film may become soft and the generation of film residue during roll forming may increase. From such a 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 silica: 0.15 to 3]
In the present embodiment, the mass ratio of magnesium hydroxide to silica is 0.15 to 3. Magnesium hydroxide and silica are both known as rust preventives for zinc plating. The present inventors have found that excellent corrosion resistance can be obtained even when the thickness of the coating is 1 μm or less by blending magnesium hydroxide and silica in the resin coating at a specific mass ratio. When the mass ratio [Mg (OH) ₂ / SiO ₂ ] of magnesium hydroxide to silica is in the range of 0.15 to 3, excellent corrosion resistance is exhibited. The mass ratio is preferably 0.3 or more, and more preferably 2.0 or less.

The mechanism by which the corrosion resistance is improved by adjusting the mass ratio to an appropriate range is unknown, but is probably as follows. That is, it is considered that magnesium ions eluted from magnesium hydroxide stabilized a corrosion product having a high protective action against galvanization produced by silica, and improved the barrier effect by the stabilized corrosion product. The protective action against galvanization means a barrier property that blocks corrosion factors such as water and oxygen. And by using particulate magnesium hydroxide, it became possible to increase the addition ratio of the magnesium component in the resin film without impairing the stability of the treatment liquid. It is presumed to show high corrosion resistance.

[Resin film thickness: 0.20 to 1.1 μm]
In the present embodiment, the resin film thickness 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, if the resin film thickness exceeds 1.1 μm, not only the generation of film residue during roll forming increases, but also it becomes very difficult to ensure conductivity. From the viewpoint of achieving a good balance between corrosion resistance and suppression of film residue, the resin film thickness is preferably 0.3 μm or more, and preferably 0.8 μm or less. More preferably, it is 0.3 to 0.6 μm. When the resin film thickness is in the range of 0.3 to 0.8 μm, the balance of corrosion resistance, roll mold resistance, and conductivity is excellent, and it is advantageous for application to electrical appliances that require grounding properties. .

[Resin type]
The type of resin used in the present embodiment is not particularly limited, and any of a water-based resin and a non-aqueous resin can be used. When using an aqueous dispersion of magnesium hydroxide or colloidal silica, it is preferable to use an aqueous resin. Such an aqueous resin is not particularly limited, but is preferably mixed with an aqueous dispersion of magnesium hydroxide and colloidal silica. The aqueous resin in the present embodiment refers to a resin that is an aqueous dispersion or a water-soluble resin.

Such water-based resins are preferably polyolefin-based resins, polyurethane-based resins, and polyester-based resins, and among these, polyolefin-based resins and polyurethane-based resins are more preferable. Hereinafter, the polyolefin resin and the polyurethane resin will be specifically described.

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

Examples of the unsaturated carboxylic acid include (meth) acrylic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, itaconic acid, and the like. An ethylene-unsaturated carboxylic acid copolymer can be obtained by polymerization using a combination method.

The copolymerization ratio of unsaturated carboxylic acid to ethylene is preferably 10% by mass or more, more preferably 15% by mass or more when unsaturated monomer is 100% by mass. 40% by mass or less, and more preferably 25% by mass or less. When the amount of unsaturated carboxylic acid is less than 10% by mass, the coating strength (emulsion composition), which will be described later, is not stable because the number of carboxyl groups that are the starting point of intermolecular association by ion clusters is small. May be inferior. On the other hand, if the unsaturated carboxylic acid exceeds 40% by mass, the corrosion resistance and water resistance of the resin film may be inferior.

Since the ethylene-unsaturated carboxylic acid copolymer has a carboxyl group, the coating liquid can be emulsified (water dispersion) by neutralization 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 significantly reducing the corrosion resistance of the resin film. Specific examples include tertiary amines such as triethylamine; secondary amines such as diethylamine; primary amines such as propylamine, and the like, and one or more of these can be used in combination. Of these, tertiary amines are preferred, and triethylamine is most preferred. Moreover, it is preferable to use a monovalent metal ion together with the amine from the viewpoint of improving solvent resistance and film hardness.

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

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

The ethylene-unsaturated carboxylic acid copolymer is stirred at high speed in a container capable of reacting at a high temperature (about 150 ° C.) and a high pressure (about 5 atm), for example, in the presence of a carboxylic acid polymer described later, if necessary. For 1 to 6 hours to emulsify (emulsify). In emulsification, an appropriate amount of a compound having a surfactant function such as tall oil fatty acid may be added. Further, a hydrophilic organic solvent such as a lower alcohol having about 1 to 5 carbon atoms may be partially added to water.

The mass average molecular weight (Mw) of the ethylene-unsaturated carboxylic acid copolymer is preferably 1,000 or more and 100,000 or less in terms of polystyrene. A more preferable lower limit is 3,000 or more, and further preferably 5,000 or more. A more preferable upper limit value is 70,000 or less, and further 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 as a constituent unit exemplified as one that can be used for 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 a constituent unit derived from a monomer other than the unsaturated carboxylic acid, but the constituent unit amount derived from the other monomer is 10% by mass or less in the polymer. More preferably, it is 5 mass% or less, and the carboxylic acid polymer comprised only from unsaturated carboxylic acid is further more preferable. Preferred carboxylic acid polymers include polyacrylic acid, polymethacrylic acid, acrylic acid-maleic acid copolymer, polymaleic acid and the like. Of 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 is improved by using polymaleic acid is unknown, the adhesion between the resin film and the galvanized steel sheet is improved due to the large amount of carboxyl groups. It is done. However, the present invention is not limited to this estimation.

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. 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 value 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 in terms of mass ratio. This is because if 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. On the contrary, if the content ratio of the carboxylic acid polymer is excessive, the olefin-acid copolymer and the carboxylic acid polymer are phase-separated in the first layer forming coating solution, and a uniform resin film is formed. It is because there is a risk of disappearing.

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

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

It is possible to use at least one polyisocyanate selected from the group consisting of tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI) and dicyclohexylmethane diisocyanate (hydrogenated MDI) as the polyisocyanate component. From the viewpoint of obtaining a resin film having excellent stability. In addition to the above polyisocyanates, other polyisocyanates can be used as long as the corrosion resistance and reaction control stability are not lowered. However, the content of the 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 reaction control. Examples of the polyisocyanate other than the above polyisocyanate component include tetramethylene diisocyanate, hexamethylene diisocyanate, dodecane methylene diisocyanate, isophorone diisocyanate, xylene diisocyanate, and phenylene diisocyanate. One or more of these are used. May be.

From the viewpoint of obtaining a resin film having excellent corrosion resistance and sliding properties, it is preferable to use three types of polyols, 1,4-cyclohexanedimethanol, polyether polyol, and polyol having a carboxyl group, as the polyol component. As the polyol component, it is more preferable to use three kinds of diols of 1,4-cyclohexanedimethanol, polyether diol, and diol having a carboxyl group. In addition, it is thought that the rust prevention effect of the obtained polyurethane resin can be enhanced by using 1,4-cyclohexanedimethanol as the polyol component.

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 alkylene oxide units. Specific examples include polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol and the like, and it is preferable to use polyoxypropylene glycol or polytetramethylene ether glycol. The number of functional groups of the polyether polyol is not particularly limited as long as it is at least 2 or more, and for example, it may be trifunctional or tetrafunctional or 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. The average molecular weight can be determined by measuring the OH value (hydroxyl value).

In the above polyol component, the mass ratio of 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. The polyol having a carboxyl group is not particularly limited as long as it has at least one carboxyl group and at least two hydroxyl groups. Specific examples include dimethylolpropionic acid, dimethylolbutanoic acid, dihydroxypropionic acid, dihydroxysuccinic acid and the like.

In the above polyol component, in addition to the above three kinds of polyols, other polyols can be used as long as the corrosion resistance is not lowered. However, the content of the three kinds of polyols is preferably 70% by mass or more of the total polyol components from the viewpoint of ensuring the corrosion resistance of the resin film. The polyol other than the above three types of polyol 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 having an average molecular weight of about 500 or less. Specific examples include diols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol; glycerin, trimethylolpropane, hexanetriol, etc. Of the triol. The high molecular weight polyol is a polyol having an average molecular weight exceeding about 500. Specific examples include condensed polyester polyols such as polyethylene adipate (PEA), polybutylene adipate (PBA), and polyhexamethylene adipate (PHMA); lactone polyester polyols such as poly-ε-caprolactone (PCL); polyhexamethylene Polycarbonate polyols such as carbonate; and acrylic polyols.

The chain extender is not particularly limited, and examples thereof include polyamines, low molecular weight polyols, and alkanolamines. As polyamines, aliphatic polyamines such as ethylenediamine, propylenediamine and hexamethylenediamine; aromatic polyamines such as tolylenediamine, xylylenediamine and diaminodiphenylmethane; alicyclic polyamines such as diaminocyclohexylmethane, piperazine and isophoronediamine; hydrazine, And hydrazines such as succinic acid dihydrazide, adipic acid dihydrazide, and phthalic acid dihydrazide. Among these, it is preferable to use ethylenediamine and / or hydrazine as a chain extender component. Examples of the alkanolamine include diethanolamine and monoethanolamine.

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

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 liquid, and on the other hand, 60 mgKOH / g or less from the viewpoint of ensuring the corrosion resistance of the resin film. Is preferred. 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, or a curtain flow coater method, and dried by heating. Thus, it can be formed. The coating liquid contains a predetermined amount of silica, magnesium hydroxide and the above resin. The resin solid content in the coating liquid is preferably about 15 to 25% by mass. And a coating liquid may contain various additives in the range which does not inhibit the effect of this invention for the purpose of improving membrane | film | coat performance. Examples of additives include silane coupling agents, elution inhibitors, rust inhibitors, waxes, crosslinking agents, diluents, antiskinning agents, surfactants, emulsifiers, dispersants, leveling agents, antifoaming agents, and penetrants. , 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 becomes dense and the corrosion resistance is improved. Moreover, the adhesiveness of a galvanized steel plate and a resin film is also improved, and corrosion resistance is improved. And there exists an effect which improves the bond strength of a resin component and colloidal silica, and the toughness of a film | membrane improves. Among them, glycidoxy-based silane coupling agents are highly reactive and have a large effect of improving corrosion resistance. Glycidyl group-containing silane coupling agents include γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxymethyldimethoxysilane, β- (3,4-epoxycyclohexyl) ethyl Examples include trimethoxysilane.

The amount of the silane coupling agent is preferably 0.1 parts by mass or more, more preferably 3 parts by mass or more, with respect to 100 parts by mass in total of the inorganic compound and the resin component in the inorganic film. More preferably, it is 5 parts by mass or more. If the amount is less than 0.1 parts by mass, the adhesion between the galvanized steel sheet and the resin film and the bonding force between the resin component and colloidal silica may be insufficient, and the toughness and corrosion resistance of the film may be insufficient. is there. 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, with respect to 100 parts by mass in total of the inorganic compound and the resin component in the inorganic film. More preferably, it is 7 parts by mass or less. 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 may decrease and the paintability may deteriorate. Moreover, it is because silane coupling agents raise | generate a hydrolysis-condensation reaction, the stability of a coating liquid falls and there exists a possibility of causing gelation and precipitation of colloidal silica.

For example, when metavanadate which is an elution inhibitor is used as an additive, dissolution and elution of a galvanized steel sheet are suppressed by elution of metavanadate, and corrosion resistance is improved. Metavanadate is particularly effective in improving the bare corrosion resistance of the galvannealed steel sheet. Examples of the metavanadate include sodium metavanadate (NaVO ₃ ), ammonium metavanadate (NH ₄ VO ₃ ), and potassium metavanadate (KVO ₃ ). These 1 type (s) or 2 or more types can be used.

The amount of metavanadate is preferably 0.5 parts by mass or more and more preferably 0.7 parts by mass or more with respect to 100 parts by mass in total of the inorganic compound and the resin component in the inorganic coating. Preferably, it is 1.0 part by mass or more. This is because if the amount is less than 0.5 parts by mass, the effect of improving the bare corrosion resistance becomes insufficient. On the other hand, the amount of metavanadate is preferably 5.5 parts by mass or less, and 5.0 parts by mass or less with respect to 100 parts by mass in total of the inorganic compound and the resin component in the inorganic coating. Is more preferable, and it is further more preferable that it is 3.0 mass parts or less. This is because when the amount exceeds 5.5 parts by mass, not only the bare corrosion resistance tends to be slightly lowered but also the film adhesion tends to be remarkably lowered. In addition, the suitable amount of this metavanadate is a V element conversion amount.

[Types of galvanized steel sheets]
The type of galvanized steel sheet used in the present embodiment is not particularly limited, and any of electrogalvanized steel sheet, hot dip galvanized steel sheet, and alloyed hot dip galvanized steel sheet (hereinafter, these may be referred to as “original plates”). Can also be adopted. Moreover, there is no limitation in particular also about the kind of zinc plating layer, An alloying element may be included in a plating layer. The galvanized layer is coated on one side or both sides of the base steel plate, and the resin film is accordingly coated on one side or both sides of the galvanized steel plate.

As described above, the coated galvanized steel sheet according to one aspect of the present invention is a coated galvanized steel sheet having a resin film containing silica and magnesium hydroxide on the surface of the galvanized steel sheet, and the silica in the resin film and The total content of magnesium hydroxide is 75 to 90% by mass, the resin component content of the resin film is 10 to 25% by mass, and the mass ratio of the magnesium hydroxide to the silica is 0.15 to 3 And the thickness of the resin film is 0.20 to 1.1 μm.

According to such a configuration, a coated galvanized steel sheet exhibiting excellent corrosion resistance can be realized with less film residue generated during roll forming while the thickness of the resin film is 1.1 μm or less.

Hereinafter, the present invention will be described more specifically with reference to examples. It should be noted that the present invention is not limited by the following examples, and can be implemented with modifications within a range that can be adapted to the gist described above and below, all of which are 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: Kisuma 5Q-S) are used as a dispersant and dispersed using a polymer dispersant to obtain an aqueous dispersion (resin solid content: about 30 wt%, average particle size _D 50: 0.69 .mu.m) was formulated.

The average particle diameter D ₅₀ of the magnesium hydroxide in the dispersion was diluted with 0.2 wt% aqueous solution of sodium hexametaphosphate, a laser diffraction scattering particle size distribution measuring device (Microtrac Bell Co., Ltd., trade name: Micro Measurement was performed using a track MT3300EXII).

(resin)

Polyethylene resin manufactured by Toho Chemical Co., Ltd. or urethane resin manufactured by Toho Chemical Industry was used as the resin for forming the resin film.

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

In an autoclave having an emulsification facility equipped with a stirrer, a thermometer and a temperature controller, an ethylene-acrylic acid copolymer (manufactured by Dow Chemical Co., Ltd., trade name: Primacol 5990I, structural 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 NOF Corporation, trade name: Nonpole PMA-50W, Mw: about 1100 (polystyrene conversion) ), 50% by mass) 8.0 parts by mass, 35.5 parts by mass of triethylamine (0.63 equivalent to the carboxyl group of the ethylene-acrylic acid copolymer), 6.9 parts by mass of 48% NaOH aqueous solution (ethylene -0.15 equivalent to the carboxyl group of the acrylic acid copolymer), tall oil fatty acid (manufactured by Harima Chemicals, Inc., trade name: Hartle FA3) 3.5 parts by mass and 792.6 parts by mass of ion-exchanged water were added and sealed. The mixture was stirred at 150 ° C. and 5 atm for 3 hours at high speed, and then cooled to 30 ° C.

Next, 10.4 parts by mass of γ-glycidoxypropyltrimethoxysilane (Momentive Performance Materials, trade name: TSL8350), polycarbodiimide (Nisshinbo Co., Ltd., trade name: Carbodilite SV-02, Mw) : 2,700, solid content 40% by mass) 31.2 parts by mass and ion-exchanged water 72.8 parts by mass were added and stirred for 10 minutes to emulsify the ethylene-acrylic acid copolymer and mix with each component. A polyethylene resin aqueous dispersion was obtained (resin solid content 20.3% by mass, measured according to JIS K6833 (2014)).

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

In a 0.8 L internal volume synthesizer equipped with a stirrer, thermometer and temperature controller, polytetramethylene ether glycol (Hodogaya Chemical Co., Ltd., average molecular weight 1,000) 60 g, 1,4-cyclohexanedimethanol 14 g Then, 20 g of dimethylolpropionic acid was charged, and 30.0 g of N-methylpyrrolidone was further added. Then, 104 g of tolylene diisocyanate was charged, the temperature was raised from 80 to 85 ° C., and reacted for 5 hours. The obtained prepolymer had an NCO content of 8.9%. Further, 16 g of triethylamine was added for neutralization, a mixed aqueous solution of 16 g of ethylenediamine and 480 g of water was added, emulsified at 50 ° C. for 4 hours, and chain extension reaction was performed to obtain an aqueous urethane resin dispersion (nonvolatile resin component 29 0.1%, acid value 41.4).

(Preparation 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: Snowtex-XS) are mixed to obtain a resin solid content. About 10% by mass of coating liquid was prepared.

(Type of original plate)
(1) Hot-dip galvanized steel sheet (GI): plate thickness 0.8 mm, zinc basis weight: 60 g / m ²
(2) Alloyed galvanized steel sheet (GA): plate thickness 0.8 mm, zinc basis weight: 45 g / m ² (3) Electrogalvanized steel sheet (EG): plate thickness 0.8 mm, zinc basis weight: 20 g / m ²

(Pretreatment of galvanized steel sheet)
Degreasing: Alkaline degreasing (Nippon Parker Rising Co., Ltd., trade name: Fine Cleaner)
Drying: Hot air drying was performed to evaporate water.

(Painting method)
Method: Bar coater Resin film thickness: Resin film thickness was adjusted by selecting the resin solid content of the coating liquid and the number of bars.

(Drying method)
Time: 1 minute Conditions: Maximum reached temperature of the coated plate 80 ° C (confirmed with thermo label)

[Example]
As shown in Tables 1 and 2 within the above range, using (1) hot dip galvanized steel sheet, (2) galvannealed steel sheet and (3) electrogalvanized steel sheet as the original plate. Various coated galvanized steel sheets (Test Nos. 1 to 17 in Table 1 and Test Nos. 18 to 35 in Table 2) were prepared under various conditions, and roll forming resistance and corrosion resistance of the obtained coated galvanized steel sheets. Was evaluated by the following method.

(Roll formability)
With respect to the test piece cut out from the coated galvanized steel sheet, the coating amount before the repeated sliding test described later (W ₀ ) and the coating amount after performing the test (W ₁ ), It calculated based on following formula (1). X in Formula (1) was measured using a fluorescent X-ray analyzer.

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

Then, the reduction amount (W ₀ -W ₁ ) of the film adhesion amount was calculated as the generated film residue, and ◎ and ○ were evaluated as acceptable and Δ as unacceptable based on the following criteria.

<Evaluation criteria>
◎: film residue 300 mg / m ² or less ○: film residue 300 mg / m ^{2 over} 450 mg / m ² or less Δ: film residue over 450 mg / m ²

The method of the repeated sliding test is as follows.
First, a test piece cut out from a coated galvanized steel sheet into a rectangular shape having a width of 40 mm and a length of 300 mm is vertically mounted on a tensile tester, and a flat plate die (material: SKD11) is brought into contact. Next, a jig (semi-cylindrical die, material: SKD11) having a convex portion with a tip radius of 9.1 mm is brought into contact with the other surface (sliding surface) of the test piece, and 2940 N (300 kgf) of the jig is brought into contact with the jig. The sliding operation is performed by moving the jig downward at a speed of 300 mm / min within a range where the flat plate die is in contact with the sliding surface of the test piece while applying a load in the horizontal direction. After completion of the sliding operation, the jig (semi-cylindrical die) is separated from the sliding surface of the test piece and returned to the position before the sliding operation. Repeat the sliding operation similar to the above 9 times. That is, the process ends after a total of 10 sliding operations.

(Corrosion resistance)
A salt spray test based on JIS Z2371 (2015) was conducted for 24 hours on the coated galvanized steel sheet (sample), and the white rust generation rate on the sample surface (100 × area where white rust was generated / resin coating) The total area of the metal plate) was calculated. And based on the following reference | standard, (circle) was set as the pass and (triangle | delta) was evaluated as a disqualification.

<Evaluation criteria>
○: White rust occurrence rate 50 area% or less △: White rust occurrence rate more than 50 area%

In addition, a salt spray test based on JIS Z2371 (2015) was performed on the coated galvanized steel sheet (sample) to investigate the occurrence of red rust. At this time, the test was carried out by changing the salt spray test time (test time) according to the type of the original plate.

(A) In the case of hot-dip galvanized steel sheet and electrogalvanized steel sheet Test time: 480 hours Evaluation method: Calculate the red rust generation rate (100 × area where red rust occurred / total area of resin-coated metal plate) on the sample surface, and On the basis of the criteria, ◯ was evaluated as acceptable and △ was evaluated as unacceptable.

<Evaluation criteria>
○: Red rust incidence 5 area% or less △: Red rust incidence 5 area% or more

(B) In the case of alloyed hot-dip galvanized steel sheet Test time: 120 hours Evaluation method: The state of red rust occurrence on the sample surface was visually observed, and based on the following criteria, ○ was accepted and Δ was rejected. .

<Evaluation criteria>
○: Red rust is not observed △: Red rust is observed

The results are the conditions when each coated galvanized steel sheet is manufactured (type of original plate, type of resin, composition ratio of resin film, mass ratio of magnesium hydroxide to silica [Mg (OH) ₂ / SiO ₂ ], resin Table 1 and Table 2 below are shown together with (film thickness).

As is clear from these results, the examples in which the resin content is 5% by mass (Test No. 7 in Table 1, Test No. 24 in Table 2: hereinafter, only Test No. is shown) Since the content was too small, the film defect was increased and the corrosion resistance was deteriorated when the original plate was either GI or GA. In these examples, the mass ratio [Mg (OH) ₂ / SiO ₂ ] is also outside the range of 0.15 to 3.

Test No. 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 corrosion resistance deteriorates when the original plate is either GI or GA. It was. Further, in the examples where the resin film thickness is less than 0.20 μm (Test Nos. 16, 18, 25, and 33), the corrosion resistance was deteriorated regardless of whether the original plate was GI or GA.

On the other hand, the coated galvanized steel sheet of the present invention (test Nos. 1 to 6, 8 to 13, 17, 19 to 23, 26 to 30, 34, and 35) satisfying all of the prescribed requirements is the original plate. In any of GI, GA, and EG, and in any of the polyethylene resin and the urethane resin, excellent roll resistance was exhibited while exhibiting excellent corrosion resistance.

This application is based on Japanese Patent Application No. 2018-64766 filed on Mar. 29, 2018 and Japanese Patent Application No. 2019-30545 filed on Feb. 22, 2019. The contents thereof are included in the present application.

In order to express the present invention, the present invention has been described appropriately and sufficiently through the embodiments with reference to specific examples and the like. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that this is possible. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not limited to the scope of the claims. To be construed as inclusive.

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

Claims

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 75 to 90% by mass, and the resin component content of the resin film is 10 to 25% by mass,
The mass ratio of the magnesium hydroxide to the silica is 0.15-3,
A coated galvanized steel sheet, wherein the resin film has a thickness of 0.20 to 1.1 μm.