JP2019171868A - Coated galvanized steel sheet - Google Patents

Abstract

To provide a coated galvanized steel sheet that has an excellent corrosion resistance and has a less abrasion even when the steel sheet has a coating film having thickness to ensure conductivity.SOLUTION: The coated galvanized steel sheet is provided that has a first resin coating film formed on the surface of a galvanized steel sheet and containing silica and magnesium hydroxide, and a second resin coating film formed on the surface of the first resin coating film and containing silica, the coated galvanized steel sheet is configured such that: the total content of silica and magnesium hydroxide in the first resin coating film is 50 to 75 mass%; the content of resin component in the first resin coating film is 25 to 50 mass%; the mass ratio of the magnesium hydroxide to the silica in the first resin coating film is 0.1 to 3; and the thickness of the first resin coating film is 0.2 μm or more; the content of silica in the second resin coating film is 50 to 80 mass%; the thickness of the second resin coating film is 0.2 μm or more; and the total thickness of the first resin coating film and the second resin coating film is 0.4 to 1.5 μm.SELECTED DRAWING: None

Description

  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.

  The special chemical conversion treatment product is a surface treatment product in which a thin film of several μm is applied on the surface of a galvanized steel sheet that has been subjected to a chromate treatment or an alternative base treatment not containing a chromium compound. Although the film has a thickness on the order of microns, it is possible to impart various characteristics to the special chemical conversion treatment product by controlling the film composition. Special chemical treatment products are mainly used for indoor use, which is a mild corrosive environment, and are applied to a wide range of products such as home appliances. However, since it may be exposed to human eyes depending on the part used, it is preferable that the special chemical conversion treatment product has no change in appearance due to the initial corrosion of zinc.

  Special chemical conversion products may also be used in corrosive environments that are considerably more severe than indoors, taking advantage of excellent corrosion resistance. Examples of semi-outdoor applications include internal parts of air conditioner outdoor units, doors for houses, and parts around water. For example, for outdoor units, special chemical treatment products are installed as parts in the housing, but the housing is often provided with gaps or holes, and the deterioration of organic compounds due to changes in outside air temperature or ultraviolet rays is significant. Promoted. In such an environment, since the protective action by the film is shortened, measures to suppress red rust such as increasing the basis weight of plating of the special chemical conversion treatment product are taken.

  In order to cope with a severe corrosive environment, it is an effective means to suppress red rust by increasing the film thickness of the special chemical conversion treatment product. However, since the conductivity, which is one of the characteristics of the special chemical conversion treatment product, deteriorates, it becomes difficult to apply it for household appliances. Further, if the thickness of the film is changed for each application, the productivity is lowered, for example, the line must be stopped to change the manufacturing conditions.

  Specialized chemical treatment products have a beautiful and uniform appearance derived from the plating surface, but when subjected to external forces such as vibration or pressing during coil transportation or parts transportation, the appearance of the relevant part changes and the uniform appearance is impaired. There is a problem that it will be. In particular, appearance changes due to vibration during transportation (hereinafter sometimes referred to as “ablation”) often occur suddenly depending on transportation conditions, and it is difficult to take appropriate measures. For this reason, measures that increase costs, such as strengthening packaging during transportation, are required.

  It is known that a magnesium-based compound has a rust prevention effect against galvanization. In recent years, techniques for highly corrosion resistant coatings containing nano-sized magnesium particles have been disclosed.

  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, 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 rust prevention for metals 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.

Japanese Patent Laid-Open No. 2006-104574 JP 2002-322569 A JP 2002-053979 A

  The coating disclosed in Patent Document 1 has a thickness of 2.5 to 75 μm and is not assumed to be press-molded. Further, the coating disclosed in Patent Document 1 has a thickness of several μm or less only by adding magnesium hydroxide particles, and does not exhibit a sufficient antirust effect after press molding.

  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. In addition, the film disclosed in Patent Document 2 has insufficient water resistance because it contains a water-soluble component, and has a high risk of discoloration due to condensation or water wetting during transportation.

  In the organic coated steel sheet disclosed in Patent Document 3, since the magnesium compound is added in the form of water-soluble ions or molecules when forming the composite oxide film, the treatment liquid stability decreases when the amount of magnesium compound added is increased. . For this reason, there is a limit in improving the corrosion inhibiting effect of the composite oxide film by increasing the magnesium component.

  This invention is made | formed in view of the said situation, Even if it is the film | membrane thickness which can ensure electroconductivity, it aims at providing the coated galvanized steel plate which has the outstanding corrosion resistance and few abrasions.

  One aspect of the present invention is a coated galvanized steel sheet having a first resin film containing silica and magnesium hydroxide on the surface of a galvanized steel sheet, and a second resin film containing silica on the surface of the first resin film. The total content of silica and magnesium hydroxide in the first resin film is 50 to 75% by mass, and the content of the resin component in the first resin film is 25 to 50% by mass, The mass ratio of the magnesium hydroxide to the silica in the first resin film is 0.1 to 3, the thickness of the first resin film is 0.2 μm or more, and the silica in the second resin film The content is 50 to 80% by mass, the thickness of the second resin film is 0.2 μm or more, and the total thickness of the first resin film and the second resin film is 0.4 to 1.5 μm. .

  ADVANTAGE OF THE INVENTION According to this invention, even if it is the film thickness which can ensure electroconductivity, it can provide the coated galvanized steel plate which has the outstanding corrosion resistance and few abrasions.

  In order to achieve the above object, the present inventors have studied from various angles. As a result, the total content of silica and magnesium hydroxide in the first resin film, the mass ratio of magnesium hydroxide to silica, and the thickness of the first resin film are appropriately adjusted, and on the surface of the first resin film. And the second resin film containing a predetermined amount of silica, and by appropriately adjusting the thickness of the second resin film and the total thickness of the first resin film and the second resin film, the above object is excellent. The present invention has been completed.

  The coated plated steel sheet according to an embodiment of the present invention has a first resin film containing silica and magnesium hydroxide on the surface of a galvanized steel sheet. The total content of silica and magnesium hydroxide in the first resin film is 50 to 75% by mass. Content of the resin component of the said 1st resin film is 25-50 mass%. The mass ratio of the magnesium hydroxide to the silica is 0.1-3. The thickness of the first resin film is 0.2 μm or more. Furthermore, it has the 2nd resin film which contains a silica by 50-80 mass% on the surface of the said 1st resin film. The thickness of the second resin film is 0.2 μm or more, and the total thickness of the first resin film and the second resin film is 0.4 to 1.5 μm.

  Hereinafter, although this embodiment is described more specifically, the present invention is not limited to these.

[Total content of silica and magnesium hydroxide in the first resin film: 50 to 75% by mass]
In the present embodiment, the total content of silica and magnesium hydroxide in the first resin film is 50 to 75% by mass. Since the inorganic film is mainly composed of an inorganic compound having a specific gravity larger than that of the organic substance, a dense film having a high barrier effect against corrosion factors can be obtained. Thereby, there exists an advantage which can make the film | membrane thickness for obtaining the same corrosion resistance smaller than an organic type film, and it becomes advantageous to expression of electroconductivity. However, if the total content of silica and magnesium hydroxide in the first resin film exceeds 75% by mass, the resin component serving as the binder is not sufficient, and the film becomes a film with many defective portions, and the performance deteriorates. Preferably it is 70 mass% or less, More preferably, it is 65 mass% or less.

  On the other hand, when the total content of silica and magnesium hydroxide in the first resin film is less than 50%, the content of the resin component increases, the denseness of the first resin film decreases, and the film can ensure conductivity. Corrosion resistance at thickness decreases. Preferably it is 55 mass% or more, More preferably, it is 60 mass% or more.

The silica used in the present embodiment is preferably colloidal silica excellent in compatibility with an aqueous resin described later. Further, the average particle size of the silica is too large, or reduced denseness of the film, there is a risk of or to generate coating defects, and the mean particle diameter D ₅₀ is preferably 500nm or less. More preferably, it is 450 nm or less. 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 to the magnesium hydroxide powder and the dispersion method as long as it is stable as an aqueous dispersion. The average particle diameter D ₅₀ of the magnesium hydroxide in a state of being dispersed in water is preferably less than the thickness of the first resin film, be greater than the thickness of the first resin film, a first resin coating surface Since the second resin film formed on the surface has an effect of covering the exposed magnesium hydroxide particles, the corrosion resistance in a more severe corrosive environment is further improved as compared with the case of a single layer. However, if the particle diameter of magnesium hydroxide is too larger than the thickness of the first resin film, the inorganic compound particles may fall off from the film and a desired effect cannot be expected, and a film defect may occur. For these reasons, the particles of magnesium hydroxide preferably has an appropriate average particle diameter D _50. The average particle diameter D ₅₀ is preferably 0.7 μm or less in a state where magnesium hydroxide is dispersed in water.

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) decreases. Since there exists a possibility, 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 first resin film: 25 to 50% by mass]
In this embodiment, content of the resin component in a 1st resin film shall be 25-50 mass%. As described above, when the resin component in the first resin film is insufficient, the film has many defects and the corrosion resistance is deteriorated. From such a viewpoint, the content of the resin component in the first resin film needs to be 25% by mass or more. Preferably it is 30 mass% or more. However, if the content of the resin component in the first resin film is too large, the first resin film becomes soft in addition to a decrease in corrosion resistance due to a decrease in the density of the first resin film, resulting in an increase in film residue during press processing. Concerns arise. From such a viewpoint, the content of the resin component in the first resin film needs to be 50% by mass or less. Preferably it is 45 mass% or less.

[Mass ratio of magnesium hydroxide to silica in first resin film: 0.1 to 3]
In this embodiment, the mass ratio of magnesium hydroxide to silica in the first resin film is 0.1 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 in the case of a thin film by blending magnesium hydroxide and silica in the first resin film at a specific mass ratio. When the mass ratio [Mg (OH) ₂ / SiO ₂ ] of magnesium hydroxide to silica in the first resin film is in the range of 0.1 to 3, good corrosion resistance is exhibited. This mass ratio is preferably 0.4 or more and 2.5 or less, more preferably 1.0 or more and 2.5 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.

[Thickness of first resin film: 0.2 μm or more]
In the present embodiment, the thickness of the first resin film is 0.2 μm or more. When the thickness of the first resin film is less than 0.2 μm, it is difficult to sufficiently cover the galvanized surface regardless of the first resin film, and the corrosion resistance is deteriorated. Preferably it is 0.3 micrometer or more, More preferably, it is 0.4 micrometer or more. On the other hand, the upper limit of the thickness of the first resin film is inevitably determined by the relationship with the total thickness with the second resin film (1.3 μm or less), but from the viewpoint of ensuring good conductivity, It is preferable that it is 1 micrometer or less.

[Silica content in second resin film: 50 to 80% by mass]
In this embodiment, the content of silica in the second resin film is 50 to 80% by mass. The effect of providing the second resin film having a different composition on the first resin film has the effect of covering the coating defects occurring in the first resin film and enhancing the barrier effect, and has a rust preventive action such as silica. An additive may be used as a supply source. Moreover, it contributes to corrosion resistance improvement also by improving the barrier property by 2nd resin film provision. Although it is known that the abrasion is affected by the hardness of the coating, an appropriate silica content has been found in consideration of the coating composition of the second resin coating. That is, when the content of silica in the second resin film is less than 50, the abrasion resistance is insufficient. Preferably it is 55 mass% or more, More preferably, it is 60 mass% or more. However, when the content of silica in the second resin film is more than 80% by mass, the amount of resin in the second resin film is insufficient, and the effect of covering the coating defects of the first resin film due to a decrease in the binder action. Decreases and the corrosion resistance is insufficient. Preferably it is 75 mass% or less, More preferably, it is 70 mass% or less.

[Thickness of second resin film: 0.2 μm or more]
In the present embodiment, the thickness of the second resin film is 0.2 μm or more. When the thickness of the second resin film is less than 0.2 μm, it is difficult to sufficiently cover the first resin film with any second resin film, and the second resin film is formed by forming the second resin film. The effect is reduced. Preferably it is 0.3 micrometer or more, More preferably, it is 0.4 micrometer or more. On the other hand, the upper limit of the thickness of the second resin film is inevitably determined by the relationship with the total thickness with the first resin film (1.3 μm or less), but from the viewpoint of ensuring good conductivity, It is preferable that it is 1 micrometer or less.

[Total thickness of first resin film and second resin film: 0.4 to 1.5 μm]
In the present embodiment, the total thickness of the first resin film and the second resin film is 0.4 to 1.5 μm. The film thickness affects the corrosion resistance and conductivity which are in a trade-off relationship. When the total thickness of the first resin film and the second resin film is less than 0.4 μm, the corrosion resistance is insufficient for any resin film. Preferably it is 0.6 micrometer or more. On the other hand, if the total thickness of the first resin film and the second resin film becomes too thick, good conductivity cannot be secured, so it is necessary to set the thickness to 1.5 μm or less. In order to make the balance between corrosion resistance and conductivity excellent, the total thickness of the first resin film and the second resin film is more preferably 0.4 to 0.8 μm. In addition, since the first resin film and the second resin film each have a thickness of 0.2 μm or more, excellent corrosion resistance can be obtained, so that the film thickness can be arbitrarily selected while balancing with other film characteristics. You can choose to. In particular, in the present embodiment, since the resin film has a two-layer structure, excellent corrosion resistance is exhibited even with a thinner film thickness.

[Resin type]
The type of resin used in the present embodiment is not particularly limited in either the first resin film or the second resin film, and any of water-based resins and non-aqueous resins 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.

  In this embodiment, by making the resin film formed on the surface of the galvanized steel sheet into a two-layer structure, the corrosion resistance can be further improved compared to a single-layer resin film, and in a more severe corrosion resistance environment, Even demonstrates excellent corrosion resistance. In such a two-layer structure, the resin type of the first resin film and the second resin film may be different or the same type, but considering the wettability between the two layers, it may be the same type. preferable. In addition, when forming a resin film having a two-layer structure, a thixotropic agent may be used to improve the wettability between the two layers. In this embodiment, the first resin film is inorganic-rich. Therefore, the wettability of the second resin film with the aqueous resin is good without using a thixotropic agent. However, a thixotropic agent may be used if necessary.

  Hereinafter, unless otherwise specified, the first resin film and the second resin film may be collectively referred to as “resin film”.

[Polyolefin resin]
As the polyolefin resin, an ethylene-unsaturated carboxylic acid copolymer is preferable. As an ethylene-unsaturated carboxylic acid copolymer, what was described in Unexamined-Japanese-Patent No. 2005-246953 and Unexamined-Japanese-Patent No. 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 legal method or the like.

  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. It is because it is inferior to. 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 (aqueous 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 these can be used alone or in combination. Of these, tertiary amines are preferred, and triethylamine is most preferred. From the viewpoint of improving solvent resistance and film hardness, it is preferable to use a monovalent metal ion in combination with the amine.

  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 0.8 mol or less. preferable. And it is more preferable that it is 0.3 mol or more, and it is more preferable that it is 0.6 mol or less on the other hand.

  The amount of the monovalent metal ion is preferably 0.02 mol or more with respect to 1 mol of the carboxyl group in the ethylene-unsaturated carboxylic acid copolymer from the viewpoint of securing 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 high pressure (about 5 atm), for example, in the presence of a carboxylic acid polymer described later, if necessary. Is emulsified (emulsified) for 1 to 6 hours. 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, for example, 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 to 100,000, more preferably 3,000 to 70,000, and still more preferably 5,000 to 3, in terms of polystyrene. Ten thousand. This Mw can be measured by Gel Permeation Chromatography (GPC) using polystyrene as a standard.

  Carboxylic acid polymers 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 (first resin film) and the galvanized steel sheet is improved due to the large amount of carboxyl groups. It is conceivable to improve. 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 to 30,000, more preferably 800 to 10,000, still more preferably 900 to 3,000, and most preferably 1 in terms of polystyrene. , 2,000 to 2,000. 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 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 is not 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 resin film-forming coating solution, and a uniform resin film is not formed. Because there is a fear.

[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 subjecting a urethane prepolymer to a chain extension reaction with a chain extender. The urethane prepolymer is obtained, for example, by reacting a polyisocyanate component and a polyol component.

  The use of 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 provides corrosion resistance and reaction control. 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 polyisocyanate component include tetramethylene diisocyanate, hexamethylene diisocyanate, dodecane methylene diisocyanate, isophorone diisocyanate, xylene diisocyanate, and phenylene diisocyanate, and one or more of these are used. May be.

  From the viewpoint of obtaining a resin film having excellent corrosion resistance and slidability, it is preferable to use three kinds of polyols, 1,4-cyclohexanedimethanol, polyether polyol, and polyol having a carboxyl group, as the polyol component. . And as said polyol component, it is more preferable to use three types of diols, 1,4-cyclohexanedimethanol, polyether diol, and diol having a carboxyl group. In addition, the rust prevention effect of the polyurethane resin obtained can be heightened by using 1, 4- cyclohexane dimethanol as said 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 polyfunctional with 4 or more functions. 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 said polyol component, it is preferable from a viewpoint of further improving the rust prevention effect of a resin film that mass ratio is 1,4-cyclohexanedimethanol: polyether polyol = 1: 1 to 1:19. 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 types of polyols, other polyols can be used within a range that does not lower the corrosion resistance. However, the content of the three types of polyol is preferably 70% by mass or more of the total polyol component 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, hexamethylenediamine; aromatic polyamines such as tolylenediamine, xylylenediamine, diaminodiphenylmethane; alicyclic polyamines such as diaminocyclohexylmethane, piperazine, 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 is densified and the corrosion resistance is improved. In addition, the adhesion between the galvanized steel sheet and the resin film is also improved to improve the corrosion resistance. 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. As a glycidyl group-containing silane coupling agent, 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 (first resin film) is saturated, but also the functional group in the resin may decrease and the paintability may deteriorate. It is. Moreover, it is because silane coupling agent raise | generates a hydrolytic condensation reaction, 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, the dissolution and elution of the galvanized steel sheet is suppressed by the elution of metavanadate and the 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. In addition, a galvanization layer is coat | covered on the single side | surface or both surfaces of a base steel plate, and according to it, a resin film is also coat | covered on the single side | surface or both surfaces of a galvanization steel plate.

  As described above, 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 and magnesium hydroxide in the first resin film. The total content of is 50 to 75% by mass, the content of the resin component of the first resin film is 25 to 50% by mass, and the mass ratio of the magnesium hydroxide to the silica is 0.1 to 3, The first resin film has a thickness of 0.2 μm or more, and has a second resin film containing 50 to 80% by mass of silica on the surface of the first resin film, and the thickness of the second resin film is A coated galvanized steel sheet having a thickness of 0.2 μm or more and a total thickness of the first resin film and the second resin film of 0.4 to 1.5 μm.

  According to this configuration, a coated galvanized steel sheet having excellent corrosion resistance and excellent abrasion resistance can be realized even with a film thickness that can ensure conductivity.

  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, which are all 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 dispersed with a polymer dispersant using water as a dispersant, and 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. In addition, these resin is manufactured by the following method.

[Production method of polyethylene resin]
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 equivalents relative 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 (trade name, manufactured by Harima Chemicals) HARTALL FA3) 3.5 parts by weight, and sealed with ion exchange water 792.6 parts by mass, from 3 hours high speed stirring at 0.99 ° C. and 5 atm, and 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 72.8 parts by mass of ion-exchanged water were added and stirred for 10 minutes to emulsify the ethylene-acrylic acid copolymer and mix with each component The obtained aqueous dispersion of polyethylene resin was obtained (resin solid content 20.3% by mass, measured according to JIS K6833).

[Production method of urethane resin]
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 synthesizer equipped with a stirrer, thermometer and temperature controller, 60 g of polytetramethylene ether glycol (Hodogaya Chemical Co., Ltd., average molecular weight 1,000), 14 g of 1,4-cyclohexanedimethanol 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)
Electro-galvanized steel sheet (EG): Thickness 0.8mm, Zinc weight per unit area: Front surface 18g / m ² , Back surface 18g / m ²

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

(Painting method)
Method: Bar coater Resin film thickness: The resin solid content of the coating liquid and the count of the bar were adjusted so that a predetermined resin film thickness was obtained.

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

Within the above range, the conditions (type of resin of the first resin film, composition ratio of the first resin film, [Mg (OH) ₂ / SiO ₂ ], resin of the second resin film, as shown in Table 1 below. Various types of coated galvanized steel sheets (test Nos. 1 to 19) were prepared by varying the type, the thickness of the second resin film, the composition ratio of the second resin film, and the thickness of the first resin film and the second resin film. Then, the corrosion resistance, conductivity and abrasion resistance of the obtained coated galvanized steel sheet were evaluated by the following methods.

[Corrosion resistance]
The obtained coated galvanized steel sheet (sample) is subjected to a salt spray test specified in JIS Z2371: 2015 for 240 hours, and the white rust generation rate (area where white rust is generated × paint) on the sample surface after the test. The total area of the galvanized steel sheet × 100) was calculated and evaluated according to the following evaluation criteria.

(Evaluation criteria for white rust)
◎: White rust occurrence rate 5 area% or less ○: White rust occurrence rate more than 5 area%, 10 area% or less △: White rust occurrence rate more than 10 area%, 25 area% or less ×: White rust occurrence rate more than 25 area%

  In addition, a salt spray test specified in JIS Z2371: 2015 was performed for 1200 hours on the obtained coated galvanized steel sheet (sample), and the red rust generation rate (area where red rust was generated x coating) after the test The total area of the galvanized steel sheet × 100) was calculated and evaluated according to the following evaluation criteria.

(Evaluation criteria for red rust)
◎: Red rust occurrence rate 5 area% or less ○: Red rust occurrence rate more than 5 area%, 30 area% or less △: Red rust occurrence rate more than 30 area%, 50 area% or less ×: Red rust occurrence rate more than 50 area%

  In any case, “◎” and “◯” were evaluated as pass (good corrosion resistance), and “Δ” and “×” were evaluated as reject (corrosion resistance deterioration).

[Conductivity]
Using an analog tester “CX-270N” (trade name: manufactured by Custom Co., Ltd.), the electrical resistance was measured by sliding the terminal on the sample surface. The conductivity was evaluated according to the following criteria.

(Evaluation criteria)
When the electrical resistance value indicated by the tester is 1000Ω or less, the electrical conductivity is evaluated as good (displayed as “◯”), and when the electrical resistance value exceeds 1000Ω, the electrical conductivity is displayed as poor (“×”). ).

[Abrasion resistance]
Using an abrasion tester (“BF-50UC”, trade name: manufactured by IDEX Co., Ltd.), an abrasion test was conducted under the following test conditions, and the appearance change of the sample surface was visually observed and evaluated according to the following criteria.

(Test conditions)
Frequency: 35Hz
Vertical amplitude: 0.5mm
Horizontal amplitude: 0.3 mm
Time: 5 minutes, 10 minutes Load: 2.5kg

(Evaluation criteria)
5 points: Almost no change in appearance (sliding marks may be observed depending on viewing angle)
4 points: Only a slight change in appearance is observed in a part of the sample 3 points: A change in appearance is observed in a part of the sample 2 points: A change in appearance is observed in the entire sample 1 point: A significant change in appearance is observed in the entire sample Is recognized

(Comprehensive evaluation)
○: Pass (3 points or more for both 5 minutes and 10 minutes)
Δ: Fail (3 points or more in 5 minutes and 2 points or less in 10 minutes)
X: Fail (both 5 and 10 minutes are 2 points or less)
The results are shown in Table 2 below.

  As is apparent from this result, the coated galvanized steel sheet (test Nos. 3, 4, 6, 8, 9, 11, 16) that satisfies the requirements defined in this embodiment is in a more severe corrosive environment. It can be seen that, while exhibiting excellent corrosion resistance, good electrical conductivity is maintained and good abrasion resistance is exhibited.

  On the other hand, in the coated galvanized steel sheet (test No. 1, 2, 5, 7, 10, 12-15, 17-19) lacking any of the requirements defined in this embodiment, the corrosion resistance, conductivity and resistance At least one of the abrasion properties is deteriorated or deteriorated.

Specifically, Test No. No. 1 lacks the resin component in the first resin film, and the corrosion resistance is deteriorated. Test No. Nos. 2 and 10 are examples in which the mass ratio [Mg (OH) ₂ / SiO ₂ ] of magnesium hydroxide to silica of the first resin film is out of the range of 0.1 to 3, and the corrosion resistance is deteriorated.

  Test No. 5 and 14, the total thickness of the first resin film and the second resin film is insufficient (the thickness of each of the first resin film and the second resin film is also insufficient), and the corrosion resistance and abrasion resistance are deteriorated. . Test No. In No. 7, the total thickness of the first resin film and the second resin film is thick, and the conductivity is lowered.

  Test No. In Nos. 12 and 13, the inorganic component of the first resin film is insufficient, and the corrosion resistance and abrasion resistance are deteriorated. Test No. Since No. 15 is a single layer (only the first resin film), the corrosion resistance in a more severe corrosive environment is deteriorated. Test No. In Nos. 17 to 19, the inorganic component of the second resin film is insufficient, and the abrasion resistance is deteriorated.

Claims (1)

A coated galvanized steel sheet having a first resin film containing silica and magnesium hydroxide on the surface of a galvanized steel sheet, and a second resin film containing silica on the surface of the first resin film,
The total content of silica and magnesium hydroxide in the first resin film is 50 to 75 mass%, the content of the resin component in the first resin film is 25 to 50 mass%, and the first resin The mass ratio of the magnesium hydroxide to silica in the film is 0.1 to 3, the thickness of the first resin film is 0.2 μm or more,
And content of the silica in the said 2nd resin film is 50-80 mass%, and the thickness of the said 2nd resin film is 0.2 micrometer or more,
The coated galvanized steel sheet, wherein the total thickness of the first resin film and the second resin film is 0.4 to 1.5 μm.