KR102445014B1 - painted galvanized steel sheet - Google Patents

Abstract

The present invention provides a coated galvanized steel sheet having a resin film containing silica and magnesium hydroxide on the surface of the galvanized steel sheet, wherein the total content of silica and magnesium hydroxide in the resin film is 50 to 75 mass%, the resin film The content of the resin component is 25 to 50 mass %, the mass ratio of the magnesium hydroxide to the silica is 0.10 to 3, and the thickness of the resin film is 0.3 to 1.5 µm.

Description

painted galvanized steel sheet

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

A thin-film coated galvanized steel sheet having a small surface electrical resistance and good conductivity is applied to a material used for products requiring electromagnetic wave shielding properties. The thin-film coated galvanized steel sheet exhibits conductivity by reducing the thickness of the film applied on the surface to about several micrometers.

On the other hand, the thin-film coated galvanized steel sheet also serves as a structural member, and corrosion resistance to prevent corrosion in long-term use is also required. If the coating film thickness is increased, the corrosion resistance can be increased relatively easily, but the conductivity is lowered. Therefore, the thin film which has the outstanding corrosion resistance is calculated|required.

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

As such a technique, for example, Patent Document 1 proposes a “coating composition containing nano magnesium hydroxide particles having an average particle diameter of less than 200 nm”. However, in this technique, it is assumed that the film thickness is 20 micrometers or more, and electroconductivity is not considered at all. In addition, in addition of only magnesium hydroxide, since a sufficient rust prevention effect is not expressed in the area|region where the film thickness is several micrometers, coexistence of electroconductivity and corrosion resistance is difficult.

Moreover, "corrosion-resistant particle|grain coating composition containing metal oxide, such as magnesium oxide which has an average particle diameter of 100 nm or less, and silica as corrosion-resistant particle|grains" is proposed by patent document 2. This composition is an etching primer use, and the use without a top coat is not considered. Moreover, even when there is a top coat which exhibits high corrosion resistance, the film thickness is too large, and favorable electroconductivity is not acquired.

On the other hand, Patent Document 3 proposes "a surface-treated zinc-based plated steel sheet in which an acidic inorganic coating layer containing a magnesium compound is formed in a lower layer with a two-layer coating, and an alkaline organic-inorganic composite coating layer is applied thereon." In this technique, even if the zinc basis weight is lowered, the magnetic part and cross-sectional corrosion resistance are maintained, and the balance of various other performances including conductivity is achieved.

In Patent Document 3, an inorganic layer containing a magnesium compound is disclosed in the lower layer, but the corrosion inhibitory effect of the magnesium compound is not actively utilized, and is added in the form of ions or molecules rather than particles. There is a limit to improving the corrosion inhibitory effect by increasing the amount of added. Moreover, since it is a two-layer system, the subject arises in the point of the fall of productivity and cost.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a coated galvanized steel sheet having good conductivity while exhibiting excellent corrosion resistance.

Japanese Patent Publication No. 2014-523457 Japanese Patent Publication No. 2009-506175 Japanese Patent No. 5457611

A coated galvanized steel sheet according to an embodiment of the present invention is a coated galvanized steel sheet having a resin film containing silica and magnesium hydroxide on the surface of the galvanized steel sheet, wherein the total content of silica and magnesium hydroxide in the resin film is 50 to 75 mass %, the content of the resin component of the resin film is 25 to 50 mass %, the mass ratio of the magnesium hydroxide to the silica is 0.10 to 3, and the thickness of the resin film is 0.3 to 1.5 µm characterized in that

MEANS TO SOLVE THE PROBLEM In order to achieve the said objective, the present inventors examined from various angles. As a result, by appropriately adjusting the total content of silica and magnesium hydroxide in the resin film, the mass ratio, the thickness of the resin film, and the like, it was found that the above object was splendidly achieved, and the present invention was completed.

According to the present invention, a coated galvanized steel sheet having good conductivity while exhibiting excellent corrosion resistance can be realized by the above configuration.

EMBODIMENT OF THE INVENTION Hereinafter, although embodiment of this invention is described more concretely, this invention is not limited to these.

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

In this embodiment, the total content of silica and magnesium hydroxide in a resin film shall be 50-75 mass %. Since the inorganic film has an inorganic compound having a larger specific gravity than that of an organic material as a main component, a dense film having a high barrier effect against corrosion factors is obtained. Therefore, there is an advantage that the film thickness for obtaining the same corrosion resistance can be made smaller than an organic film, and it becomes advantageous for electroconductivity expression. However, when the total content of silica and magnesium hydroxide in the resin film exceeds 75% by mass, the resin component serving as the binder becomes insufficient, so that a film with many defective portions is formed, 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 resin film is less than 50%, the content of the resin component increases, the density in the resin film decreases, and the corrosion resistance at a film thickness that can ensure conductivity is reduced. is lowered Preferably it is 55 mass % or more.

As for the silica used in this embodiment, colloidal silica excellent in compatibility with the aqueous resin mentioned later is preferable. Moreover, when the average particle diameter of silica becomes large too much, since there exists a possibility that the density|density of a film may fall or a film|membrane defect may generate|occur|produce, it is preferable that the average particle _diameter D50 is 500 nm or less. More preferably, it is 450 nm or less. In addition, as long as magnesium hydroxide is stable as an aqueous dispersion, it will not specifically limit with the magnesium hydroxide powder used and a dispersion method.

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

In this embodiment, content of the resin component of a resin film shall be 25-50 mass %. As mentioned above, when the resin component of a resin film runs short, it will become a film|membrane with many defect parts, and corrosion resistance will deteriorate. From such a viewpoint, it is necessary to make content of the resin component of a resin film into 25 mass % or more. Preferably it is 30 mass % or more. However, when the content of the resin component of the resin film is too large, in addition to the corrosion resistance decrease due to the decrease in density in the resin film, the resin film is softened and there is a risk of an increase in the film residue during press working. From such a viewpoint, it is necessary to make content of the resin component of a resin film into 50 mass % or less. Preferably it is 45 mass % or less.

[Mass ratio of magnesium hydroxide to silica: 0.10 to 3]

In the present embodiment, the mass ratio of magnesium hydroxide to silica is 0.10 to 3. Magnesium hydroxide and silica are both known as rust inhibitors for zinc plating. The present inventors discovered that the corrosion resistance excellent even if it was a thin film was obtained by mix|blending magnesium hydroxide and a silica in a specific mass ratio in a resin film. When the mass ratio [Mg(OH) ₂ /SiO ₂ ] of magnesium hydroxide to silica is in the range of 0.10 to 3, good corrosion resistance is shown. This mass ratio becomes like this. Preferably it is 0.2 or more and 2 or less.

Although the mechanism by which corrosion resistance improves by adjusting the said mass ratio to an appropriate range is unknown, it is thought probably as follows. That is, by using particulate magnesium hydroxide (the average particle diameter D ₅₀ of the magnesium hydroxide particles will be described later), the stability of the treatment solution is improved and it is possible to increase the addition ratio of the magnesium component. It is assumed that a synergistic effect is exerted.

[Resin film thickness: 0.3 to 1.5 μm]

In the present embodiment, the resin film thickness is 0.3 to 1.5 µm. When the resin film thickness is less than 0.3 µm, it becomes difficult to sufficiently cover the galvanized surface with any resin film, and the corrosion resistance deteriorates. Preferably it is 0.5 micrometer or more. On the other hand, when the film thickness exceeds 1.5 µm, good conductivity cannot be obtained. Preferably it is 1.3 micrometers or less.

In the coated galvanized steel sheet of this embodiment satisfying the above requirements, the coated galvanized steel sheet exhibits excellent corrosion resistance and also has good conductivity. Moreover, from a viewpoint of further improving corrosion resistance, it is preferable that the average particle _diameter D50 of magnesium hydroxide shall be 0.7 micrometer or less.

[Average particle size D ₅₀ of magnesium hydroxide: 0.7 μm or less]

In a preferred embodiment, the average particle diameter D ₅₀ of magnesium hydroxide: 0.7 µm or less. In the case of adding inorganic compound particles to the resin film, if the particle diameter is excessively larger than the thickness of the resin film, the inorganic compound particles fall off from the film and the desired effect cannot be expected, and there is a possibility that the film may be defective. For this reason, it is preferable that the particle|grains of magnesium hydroxide have suitable average particle _diameter D50. It is preferable that this average particle _diameter D50 is 0.7 micrometers or less in the state which disperse|distributed magnesium hydroxide in water.

The lower limit of the average particle diameter D ₅₀ in a state in which magnesium hydroxide is dispersed in water is not particularly limited, but if the average particle diameter D ₅₀ is too small, the stability of the dispersion (eg, dispersion) may decrease, It is preferable that it is 0.1 micrometer or more. More preferably, it is 0.14 micrometer or more.

In addition, the said "average particle _diameter D50" means an average particle diameter when the integrated value (integrated value) of magnesium hydroxide becomes 50 mass %.

[Type of resin]

It does not specifically limit about the kind of resin used by this embodiment, Both aqueous resin and non-aqueous resin can be used. When using an aqueous dispersion using magnesium oxide or colloidal silica, it is preferable to use an aqueous resin. Although it does not specifically limit also about such an aqueous resin, What can mix with magnesium hydroxide aqueous dispersion or colloidal silica is preferable.

As such water-based resin, polyolefin-based resin, polyurethane-based resin, and polyester-based resin are preferable, and polyolefin-based resin is particularly preferable. In this embodiment, the water-based resin refers to a resin used as an aqueous dispersion or a water-soluble resin.

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

Examples of the unsaturated carboxylic acid include (meth)acrylic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, itaconic acid, and the like. , a copolymer can be obtained.

When the copolymerization ratio of unsaturated carboxylic acid with respect to ethylene makes monomer whole quantity 100 mass %, it is preferable that unsaturated carboxylic acid is 10-40 mass %. When the amount of the unsaturated carboxylic acid is less than 10% by mass, the film strength effect is not exhibited because there are few carboxyl groups serving as the starting point of intermolecular association by ion clusters, and the emulsion stability of the emulsion composition is poor, which is not preferable. The lower limit of the more preferable copolymerization ratio of unsaturated carboxylic acid is 15 mass %. On the other hand, when an unsaturated carboxylic acid exceeds 40 mass %, the corrosion resistance and water resistance of a 1st layer may be inferior. A more preferable upper limit is 25 mass %.

Since the said ethylene-unsaturated carboxylic acid copolymer has a carboxyl group, emulsification (water dispersion formation) becomes possible by neutralizing with an organic base or a metal ion. In the present embodiment, examples of the organic base include primary, secondary, and tertiary amines (preferably triethylamine).

An amine having a low boiling point (preferably an amine having a boiling point of 100° C. or less under atmospheric pressure; for example, triethylamine) does not significantly reduce the corrosion resistance of the resin film. Moreover, it is preferable to use a monovalent|monohydric metal ion in addition to amines. It is preferable that amines be 0.2-0.8 mol (20-80 mol%) with respect to 1 mol of carboxyl groups in an ethylene- unsaturated carboxylic acid copolymer. It can be seen that the amount of monovalent metal ions affects water vapor permeability, and when the amount of monovalent metal compound used increases, the affinity between the resin and water increases, and the water vapor permeability increases, so that carboxyl in the ethylene-unsaturated carboxylic acid copolymer It is preferable to set it as 0.02-0.2 mol (2-20 mol%) with respect to 1 mol of groups. In addition, since excessive alkali content causes deterioration of corrosion resistance, the total amount of amines and metal ions to be used may be in the range of 0.3 to 1.0 mol with respect to 1 mol of carboxyl groups in the ethylene-unsaturated carboxylic acid copolymer. On the other hand, as for the metal compound for providing a monovalent|monohydric metal ion, NaOH, KOH, LiOH, etc. are preferable, and NaOH has the best performance and is preferable.

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

The mass average molecular weight (Mw) of the ethylene-unsaturated carboxylic acid copolymer is preferably 1,000 to 100,000, more preferably 3,000 to 70,000, still more preferably 5,000 to 30,000 in terms of polystyrene. This Mw can be measured by Gel Permeation Chromatography (GPC) using polystyrene as a standard.

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

Mw of the carboxylic acid polymer used by this embodiment becomes like polystyrene conversion, Preferably it is 500-30,000, More preferably, it is 800-10000, More preferably, it is 900-3,000, Most preferably, it is 1,000-2,000. 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 in a mass ratio of 1,000:1 to 10:1, preferably 200:1 to 20:1. When the content 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. Conversely, when the content of the carboxylic acid polymer is excessive, the olefin-acid copolymer in the coating liquid for forming the first layer and the carboxylic acid polymer are phase-separated, and there exists a possibility that a uniform resin film may not be formed.

You may contain a silane coupling agent in the coating liquid at the time of forming a resin film. When the silane coupling agent is used, the adhesion between the galvanized steel sheet and the resin film is improved, and the corrosion resistance is also improved with it. In addition, there is an effect of improving the bonding strength between the resin component and the colloidal silica, and the toughness of the film is improved. Among them, the glycidox-based silane coupling agent has high reactivity, and the effect of improving corrosion resistance is large. Examples of the glycidyl group-containing silane coupling agent include γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxymethyldimethoxysilane, β-( 3,4-epoxycyclohexyl)ethyl trimethoxysilane, etc. are mentioned.

It is preferable that the amount of a silane coupling agent is 0.1-10 mass parts with respect to a total of 100 mass parts of the inorganic compound in an inorganic film, and a resin component. When the amount is less than 0.1 parts by mass, the adhesion between the galvanized steel sheet and the resin film and the bonding strength between the resin component and the colloidal silica are insufficient, so that the toughness and corrosion resistance of the film may become insufficient. However, even if it exceeds 10 mass parts, not only the adhesive improvement effect of a metal plate and a resin film is saturated, but since the functional group in resin reduces, there exists a possibility that paintability may fall. Moreover, there exists a possibility that the silane coupling agent may raise|generate a hydrolysis-condensation reaction, and the stability of a coating liquid may fall, and there exists a possibility of causing gelation and precipitation of colloidal silica. A more preferable amount of a silane coupling agent is 3-9 mass parts, More preferably, it is 5-7 mass parts.

As for the coating liquid used when forming a resin film, it is preferable to make resin solid content into about 15-25 mass %. To this coating solution, wax, crosslinking agent, diluent, anti-skinning agent, surfactant, emulsifier, dispersant, leveling agent, defoaming agent, penetrating agent, film forming aid, dye, pigment, thickener, lubricant, etc. may contain. In addition, about the coating method of a coating liquid, it does not specifically limit, Well-known methods, such as a roll coater, are applicable.

The type of galvanized steel sheet having the above resin coating is not particularly limited, and an electrogalvanized steel sheet, a hot-dip galvanized steel sheet, an alloyed hot-dip galvanized steel sheet (hereinafter, these may be referred to as "original sheets"). Either can be employed. Moreover, it does not specifically limit also about the kind of zinc plating layer, An alloy element may be included in a plating layer. On the other hand, the galvanized layer is coated on one side or both sides of the base steel sheet, and accordingly the resin film is also coated on one side or both sides of the galvanized steel sheet.

Although this specification has disclosed the technique of various aspects as mentioned above, the main technique among them is put together below.

A coated galvanized steel sheet according to an embodiment of the present invention is a coated galvanized steel sheet having a resin film containing silica and magnesium hydroxide on the surface of the galvanized steel sheet, wherein the total content of silica and magnesium hydroxide in the resin film is 50 to 75 mass %, the content of the resin component of the resin film is 25 to 50 mass %, the mass ratio of the magnesium hydroxide to the silica is 0.10 to 3, and the thickness of the resin film is 0.3 to 1.5 µm characterized in that

With such a configuration, a coated galvanized steel sheet having good conductivity while exhibiting excellent corrosion resistance can be realized.

Moreover, in the said coated galvanized steel sheet, it is preferable that the average particle _diameter D50 of the said magnesium hydroxide when it disperse|distributes in water is 0.7 micrometer or less. Thereby, it is thought that corrosion resistance can be improved further.

Hereinafter, the effects of the present invention will be more specifically shown based on examples. However, the following examples are not of the nature to limit the present invention, and design changes in light of the gist of the first half of the present invention are all of the present invention. included in the technical scope.

Example

(magnesium hydroxide)

Various magnesium hydroxide particles having different average particle diameters in the following (a) to (e) were used.

(a) 「139-13951」 (part number): manufactured by Wako Junyaku Industrial Co., Ltd.

(b) Magnesium hydroxide particles having an average particle diameter of 83 µm: manufactured by Kanto Denka Industries, Ltd.

(c) "MH-30" (brand name): Iwatani Chemical Industry Co., Ltd.

(d) "Kisuma 5Q-S" (trade name): Kyowa Chemical Industry Co., Ltd.

(e) "ECOMAGZ-10" (brand name): Dateho Chemical Industry Co., Ltd.

(silica)

Colloidal silica "Snowtex-XS" (trade name) manufactured by Nissan Chemical Industry Co., Ltd. was used. Hereinafter, "Snotex-XS" may be abbreviated as "ST-XS".

(Suzy)

As resin at the time of forming a resin film, the urethane resin ("HUX541": brand name) made by ADEKA Corporation or the polyethylene resin of the Toho Chemical Co., Ltd. product was used. On the other hand, the polyethylene resin is prepared by the following method.

[Method for Producing Polyethylene Resin]

In an autoclave having an emulsification facility equipped with a stirrer, a thermometer, and a temperature controller, an ethylene-acrylic acid copolymer (“Primacol 5990I” (trade name) manufactured by Dow Chemical Corporation; 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 ("Nonpole PMA-50W" (brand name) manufactured by Nichiyo Corporation; Mw: about 1100 (in terms of polystyrene), 50 mass% product) 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 a 48% aqueous NaOH solution (0.15 equivalents relative to the carboxyl group of the ethylene-acrylic acid copolymer), tall oil fatty acid (manufactured by Harima Chemical Co., Ltd.) 3.5 parts by mass of "Hartol FA3" (trade name)) and 792.6 parts by mass of ion-exchanged water were added, sealed, and stirred at 150°C and 5 atmospheres at high speed for 3 hours, followed by cooling to 30°C.

Next, 10.4 parts by mass of a glycidoxy group-containing silane coupling agent (“TSL8350” (trade name) manufactured by Momentive Performance Materials, γ-glycidoxypropyl trimethoxysilane), a carbodiimide group-containing compound ( Nisshinbo Corporation "Carbodilite SV-02" (brand name), polycarbodiimide, Mw: 2,700, solid content 40 mass %) 31.2 mass parts, 72.8 mass parts of ion-exchange water were added, and it stirred for 10 minutes, and ethylene- The acrylic acid copolymer was emulsified, and the emulsion mixed with each component was obtained (resin solid content 20.3 mass %, measured according to JISK6833).

(Preparation of magnesium hydroxide dispersion)

The above-described magnesium hydroxide particles were dispersed using water as a dispersing agent to obtain dispersions of the following (A) to (E). The dispersing agent used at this time is not specifically designated, but a polymeric dispersing agent (eg, a water-soluble acrylic resin, a water-soluble styrene acrylic resin, a nonionic surfactant) which has a small adverse effect on corrosion resistance when a resin film is formed is preferable.

Dispersion (A)

Using the magnesium hydroxide particles of (a) above, resin solid content: about 30% by mass, average particle diameter D ₅₀ : 0.14 μm

Dispersion (B)

Using the magnesium hydroxide particles of (b) above, resin solid content: about 30% by mass, average particle size D ₅₀ : 0.17 μm

Dispersion (C)

Magnesium hydroxide particles of (c) above are used, resin solid content: about 30% by mass, average particle size D ₅₀ : 0.30 μm

Dispersion (D)

Using the magnesium hydroxide particles of (d) above, resin solid content: about 30% by mass, average particle diameter D ₅₀ : 0.69 μm

Dispersion (E)

Using the magnesium hydroxide particles of (d) above, resin solid content: about 30% by mass, average particle diameter D ₅₀ : 1.1 μm

The average particle diameter D ₅₀ of the magnesium hydroxide in the dispersion liquid was measured using a Microtrac "MT3300EXII apparatus" (trade name) manufactured by Microtrac Bell, after diluting it with a 0.2 mass % aqueous sodium hexametaphosphate solution.

(Preparation of coating solution)

Raw materials used: magnesium hydroxide aqueous dispersion, aqueous resin, colloidal silica (ST-XS)

Resin solids: about 5%

(Type of disc)

(1) Electro-galvanized steel sheet (EG)

Plate thickness: 0.8mm

Zinc basis weight: 18 g/m ²

(2) Hot-dip galvanized steel sheet (GI)

Plate thickness: 0.8mm

Zinc basis weight: 90 g/m ²

(Pre-treatment of galvanized steel sheet)

Degreasing: Alkaline degreasing (Nippon Parker Rising Co., Ltd., "Fine Cleaner" (brand name) series)

Drying: Hot air drying was performed to evaporate moisture.

(Painting method)

Method: Bar Coater

Resin film thickness: The number of bars is selected so that a predetermined resin film thickness is obtained.

(drying method)

Method: hot air dryer

Time: 1 minute

Condition: Maximum reached temperature of painted plate 80℃ (confirmed by thermolabel)

[Example 1]

Within the above range, various conditions were changed as shown in Table 1 below to prepare various coated galvanized steel sheets (Test Nos. 1 to 6), and the corrosion resistance and conductivity of the obtained coated galvanized steel sheets were evaluated by the following method. evaluated as

[Corrosion resistance]

Flat plate part: The salt spray test prescribed|regulated to JIS Z2371 (2015) was implemented for 72 hours. The white rust generation rate after the test was computed, and the following evaluation criteria evaluated.

Ruler: A ruler with a depth until reaching the element steel sheet was applied to the sample with a cutter, and the salt spray test prescribed in JIS Z2371 (2015) was performed for 72 hours. The following evaluation criteria evaluated the condition of discoloration and white rust around the magnetic part after the test.

(Evaluation standard)

1. Flat panel

◎: White rust generation rate 1 area% or less,

○: White rust occurrence rate greater than 1 area%, 5 area% or less,

△: White rust occurrence rate greater than 5 area%, less than 10 area%

×: White rust occurrence rate exceeds 10% by area

2. Confidence

◎: No white rust/discoloration near the magnetic part

(circle): White rust/discoloration is confirmed faintly in the vicinity of a self part.

(triangle|delta): white rust/discoloration is confirmed in the vicinity of a self part

x: White rust/discoloration is confirmed in the whole vicinity of self part

[Conductivity]

Using a tester (manufactured by Custom Co., Ltd., "Analog Tester CX-270N"), the electrical resistance value was measured by sliding the terminal on the sample surface.

(Evaluation standard)

When the electrical resistance value was less than 500 Ω, conductivity was evaluated as good (displayed as "○"), and when the electrical resistance value was 500 Ω or more, conductivity was evaluated as poor (displayed as "x").

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

Test No. in Table 1. In 1 to 6, the influence of the resin film thickness on the characteristics of the coated galvanized steel sheet was studied.

As is clear from these results, in the coated galvanized steel sheet of the present invention, in the example in which the resin film thickness was 0.2 µm (Test No. 1 in Table 1), the corrosion resistance was deteriorated. Moreover, in the example (test No. 6 of Table 1) in which the film thickness became 2 micrometers, electroconductivity is falling.

On the other hand, in the coated galvanized steel sheets of the present invention (Test Nos. 2 to 5 in Table 1) in which the resin film thickness was appropriately adjusted, it was found that excellent corrosion resistance was exhibited and good conductivity was maintained.

[Example 2]

Within the above range, various conditions were changed as shown in Table 2 below to prepare various coated galvanized steel sheets (Test Nos. 7 to 9), and the corrosion resistance and conductivity of the obtained coated galvanized steel sheets were evaluated in Example 1 evaluated in the same way as

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

Test No. in Table 2. In 7-9, the influence which the total content of silica and magnesium hydroxide has on the characteristic of a coated galvanized steel sheet was examined.

As is clear from this result, in the coated galvanized steel sheet of the present invention, when the content of silica and magnesium hydroxide in the resin film increases (Test No. 7), the film defects increase and the corrosion resistance deteriorates. Moreover, even if content of resin increases (test No. 9), the density|density of a film becomes inferior, and corrosion resistance is deteriorated.

On the other hand, in the coated galvanized steel sheet (Test No. 8) of the present invention in which the contents of silica, magnesium hydroxide, and resin in the resin film were appropriately adjusted, it was found that excellent corrosion resistance was exhibited and good conductivity was maintained. .

[Example 3]

Within the above range, various conditions were changed as shown in Table 3 below to prepare various coated galvanized steel sheets (Test Nos. 10 to 21), and the corrosion resistance and conductivity of the obtained coated galvanized steel sheets were evaluated in Example 1 evaluated in the same way as

The results are shown in Table 3 below together with the conditions (the type of the original plate, the composition ratio of the inorganic coating, [Mg(OH) ₂ /SiO ₂ ], the thickness of the resin coating) when each coated galvanized steel sheet was manufactured.

Test No. in Table 3. In 10 to 21, the influence of the mass ratio of magnesium hydroxide to silica [Mg(OH) ₂ /SiO ₂ ] on the properties of the coated galvanized steel sheet was studied.

As is clear from these results, in the coated galvanized steel sheet of the present invention, the mass ratio [Mg(OH) ₂ /SiO ₂ ] was out of the range of 0.10 to 3 (Test Nos. 10, 15 to 17, 21) , the corrosion resistance is deteriorated.

On the other hand, in the coated galvanized steel sheet (Test Nos. 11 to 14 and 18 to 20) of the present invention in which the mass ratio [Mg(OH) ₂ /SiO ₂ ] was appropriately adjusted, excellent corrosion resistance was exhibited and good conductivity was exhibited. it can be seen that there is

[Example 4]

Within the above range, various conditions were changed as shown in Table 4 below to prepare various coated galvanized steel sheets (Test Nos. 22 to 26), and the corrosion resistance and conductivity of the obtained coated galvanized steel sheets were evaluated in Example 1 evaluated in the same way as

The results are shown in Table 4 below together with the conditions (the type of the original plate, the composition ratio of the inorganic coating, [Mg(OH) ₂ /SiO ₂ ], the thickness of the resin coating) when each coated galvanized steel sheet was manufactured.

Test No. in Table 4. In 22-26, the influence of the average particle _diameter D50 of magnesium hydroxide (dispersions (A)-(E) mentioned above) on the characteristic of a coated galvanized steel sheet was examined.

As is clear from this result, in the coated galvanized steel sheet of the present invention, in an example in which the average particle diameter D ₅₀ of magnesium hydroxide exceeded 0.7 μm (Test No. 26), the average particle diameter D ₅₀ of the magnesium hydroxide was 0.7 μm or less. Compared with the example (test Nos. 22-25), a difference is seen in corrosion resistance.

This application is based on Japanese Patent Application Japanese Patent Application No. 2017-71278 for which it applied on March 31, 2017 and Japanese Patent Application No. 2017-249154 for which it applied on December 26, 2017, the content of which is included in this application will become

In order to express this invention, although this invention was suitably and fully demonstrated through embodiment, referring specific examples etc. in the above, it is recognized that it is easy for those skilled in the art to change and/or improve the above-mentioned embodiment. Should be. Therefore, unless the modified form or improved form implemented by a person skilled in the art is at a level that deviates from the scope of the claims described in the claims, it is construed that the modified form or the improved form is encompassed by the scope of the claims. .

INDUSTRIAL APPLICABILITY The present invention has wide industrial applicability in the technical field relating to galvanized steel sheet, particularly painted galvanized steel sheet.

Claims (2)

A coated galvanized steel sheet having a resin film containing silica and magnesium hydroxide on the surface of the galvanized steel sheet,
The total content of silica and magnesium hydroxide in the resin film is 50 to 75 mass%, and the content of the resin component of the resin film is 25 to 50 mass%,
A coated galvanized steel sheet, characterized in that the mass ratio of the magnesium hydroxide to the silica is 0.10 to 3, and the thickness of the resin film is 0.3 to 1.5 μm. delete