CN110462101B

CN110462101B - Coated galvanized steel sheet

Info

Publication number: CN110462101B
Application number: CN201880020432.5A
Authority: CN
Inventors: 山本哲也; 江口彻; 酒井大辉
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2017-03-31
Filing date: 2018-02-26
Publication date: 2022-02-25
Anticipated expiration: 2038-02-26
Also published as: MY191924A; WO2018180092A1; CN110462101A

Abstract

The present invention relates to a coated galvanized steel sheet having a resin coating 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 coating film is 50 to 75 mass%, the content of the resin component of the resin coating film is 25 to 50 mass%, the mass ratio of the magnesium hydroxide to the silica is 0.3 to 6, the thickness of the resin coating film is 0.3 to 1.5 [ mu ] m, and the average particle diameter D of the magnesium hydroxide in water dispersion is₅₀Is 0.6 μm or less.

Description

Coated galvanized steel sheet

Technical Field

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

Background

A coated galvanized steel sheet having an inorganic coating on the surface of the galvanized steel sheet is often used for products manufactured by drawing, such as oil filter housings, because the inorganic coating is hard and can withstand severe sliding with a die. Further, since the inorganic coating can provide a dense coating having a good corrosion factor barrier effect, the inorganic coating can be made thinner than the organic coating, and is also suitable for use in applications requiring good conductivity.

In severe working such as deep drawing, a coating film at a portion where a die slides is cut, and therefore, the corrosion resistance after working (this is referred to as "post-working corrosion resistance") is remarkably reduced. In order to improve the corrosion resistance after machining, it is conceivable to increase the thickness of the coating before machining, but the amount of coating slag generated during machining increases. Further, when the film thickness is increased, the conductivity is lowered, and therefore, it is necessary to manufacture the film separately for each application, and the productivity of the production line is lowered. For this reason, even if a thin film is capable of securing conductivity, an inorganic coating film having excellent corrosion resistance after processing is required.

Magnesium compounds are known to exhibit rust-preventing effects on zinc plating. In recent years, a technique for forming a highly corrosion-resistant coating film containing nano-sized magnesium particles has been studied.

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, this technique mentions a film thickness of 20 μm or more, and does not contemplate the use for press working. In addition, no consideration is given to the compound added together with magnesium hydroxide, and sufficient rust-preventing effect is not exhibited in a region where the film thickness is several μm when only magnesium hydroxide is added.

Patent document 2 proposes "a corrosion-resistant particle coating composition containing a metal oxide such as magnesium oxide having an average particle diameter of 100nm or less and silica as corrosion-resistant particles". The composition is used for etch primer applications and does not allow for the use without a top coating film (top coating film). Even in the case of a topcoat coating film exhibiting high corrosion resistance, the coating film thickness is too large, and therefore press working is not used.

On the other hand, patent document 3 proposes "a surface-treated zinc-plated steel sheet having a double-layer coating film formed by forming an acidic inorganic coating layer containing a magnesium compound as a lower layer and forming a basic organic-inorganic composite coating layer thereon". In this technique, by adopting the above-described structure, corrosion resistance of the flaw portion and the end face can be maintained even if the weight per unit area of zinc is reduced, and balance of other various performances is sought.

Patent document 3 discloses an inorganic layer having a lower layer containing a magnesium compound, but the corrosion-inhibiting effect of the magnesium compound is not positively utilized, and the magnesium compound is added not as particles but in the form of ions or molecules, so that there is a limitation in increasing the amount of magnesium added to improve the corrosion-inhibiting effect. Further, since the double layer system is used, problems occur in terms of reduction in 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 that exhibits excellent corrosion resistance even after processing while maintaining good conductivity.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2014-523457

Patent document 2: japanese patent laid-open publication No. 2009-506175

Patent document 3: japanese patent publication No. 5457611

Disclosure of Invention

A coated galvanized steel sheet according to an embodiment of the present invention is a coated galvanized steel sheet having a resin coating film containing silica and magnesium hydroxide on a surface of the galvanized steel sheet, wherein a total content of silica and magnesium hydroxide in the resin coating film is 50 to 75% by mass, a content of a resin component in the resin coating film is 25 to 50% by mass, a mass ratio of the magnesium hydroxide to the silica is 0.3 to 6, a thickness of the resin coating film is 0.3 to 1.5 [ mu ] m, and an average particle diameter D of the magnesium hydroxide in water dispersion is₅₀Is 0.6 μm or less.

Drawings

Fig. 1 is an explanatory view of a test piece with a slide mark formed thereon.

Detailed Description

The present inventors have studied from various points of view in order to achieve the above object. As a result, they found that: the average particle diameter D of the magnesium hydroxide in water dispersion is appropriately determined by containing silica and magnesium hydroxide in the resin film, and appropriately adjusting the total content and mass ratio of these, the thickness of the resin film, and the like₅₀The above object is achieved in an excellent manner, and the present invention has been completed.

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

The embodiments of the present invention will be specifically described below, but the present invention is not limited to these.

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

In the present embodiment, the total content of silica and magnesium hydroxide in the resin film is 50 to 75% by mass. The inorganic coating is hard and can withstand severe sliding with a die during pressing. Further, since the inorganic compound having a large specific gravity is contained in a larger amount than the organic film, a dense film having a good corrosion factor barrier effect can be obtained. However, if the total content of silica and magnesium hydroxide in the resin film exceeds 75 mass%, the resin component as a binder is insufficient, and the film has a large number of defects and thus has poor corrosion resistance. Preferably 70% by mass or less, and more preferably 65% by mass or less.

On the other hand, if the total content of silica and magnesium hydroxide is less than 50%, the resin component increases, and corrosion resistance is lowered due to a decrease in denseness in the resin film, and there is a concern that the film is softened and film chips during press working increase. Preferably 55% by mass or more.

The silica used in the present embodiment is preferably an aqueous system as described laterColloidal silica having excellent resin compatibility. Further, when the average particle diameter is too large, the denseness of the coating film may be reduced or defects of the coating film may occur, and therefore, the average particle diameter D may be too large₅₀Preferably 500nm or less. More preferably 450nm or less. In addition, when magnesium hydroxide is stable as an aqueous dispersion, the magnesium hydroxide powder to be used and the dispersion method are not particularly limited.

[ resin component content of resin coating film: 25 to 50 mass% ]

In the present embodiment, the content of the resin component in the resin film is 25 to 50 mass%. As described above, if the resin component of the resin film is insufficient, the film has a large number of defects, and the corrosion resistance is deteriorated. From such a viewpoint, the resin component of the resin film needs to be 25 mass% or more. Preferably 30% by mass or more. However, if the resin component of the resin film is too large, the corrosion resistance is lowered due to a decrease in the denseness of the resin film, and the film may soften and the film chips during press working may increase. From such a viewpoint, the resin component of the resin film needs to be 50 mass% or less. Preferably 45% by mass or less.

[ mass ratio of magnesium hydroxide to silica: 0.3 to 6, particularly 0.4 to 6]

In the present embodiment, the mass ratio of magnesium hydroxide to silica is 0.3 to 6, particularly 0.4 to 6. Magnesium hydroxide and silica are known as rust inhibitors for galvanization. The present inventors have found that: by blending magnesium hydroxide and silica in a specific mass ratio in the resin film, excellent corrosion resistance can be obtained even in a thin film. Mass ratio of magnesium hydroxide to silica [ Mg (OH) ]₂/SiO₂]In the range of 0.3 to 6, particularly 0.4 to 6, the corrosion resistance is excellent. The mass ratio is preferably 0.7 or more or 5 or less.

Although the mechanism of improving the corrosion resistance by adjusting the mass ratio to an appropriate range is not clear, the present inventors believe that the mechanism is roughly as follows. Namely, it is estimated that: by using particulate magnesium hydroxide (magnesium hydroxide)In the average particle diameter D of the magnesium hydroxide particles₅₀As described later), the stability of the treatment liquid can be improved, and the addition ratio of the magnesium component can be increased, and as a result, the synergistic effect of magnesium hydroxide and silica is exhibited.

[ thickness of resin coating film: 0.3 to 1.5 μm ]

In the present embodiment, the thickness of the resin film is set to 0.3 to 1.5 μm. When the thickness of the resin film is less than 0.3 μm, it becomes difficult to sufficiently coat the galvanized surface even with any type of resin film, resulting in insufficient corrosion resistance. Preferably 0.5 μm or more. On the other hand, if the film thickness exceeds 1.5 μm, good conductivity cannot be obtained. Preferably 1.3 μm or less.

[ average particle diameter D of magnesium hydroxide in Water Dispersion₅₀: less than 0.6 μm]

In the present embodiment, the average particle diameter D of magnesium hydroxide₅₀Is set to 0.6 μm or less. When particles are added to the resin film, if the particle diameter is too large compared to the film thickness, the particles are likely to fall off from the film. In particular, in deep drawing in which severe sliding is applied to a die, the magnesium hydroxide particles need to have an appropriate average particle diameter, and the average particle diameter D is calculated in the state of an aqueous dispersion₅₀Is 0.6 μm or less. Preferably 0.3 μm or less.

Average particle diameter D of aqueous dispersion of magnesium hydroxide particles₅₀The lower limit of (D) is not particularly limited, but D is₅₀If the particle size is too small, the stability of the dispersion may be lowered, and it is preferably 0.1 μm or more. More preferably 0.14 μm or more.

Here, the "average particle diameter D" is₅₀"means an average particle diameter when a value obtained by integrating magnesium hydroxide (integrated value) is 50 mass%.

The coated galvanized steel sheet of the present embodiment satisfying the above-described requirements is a steel sheet that exhibits excellent post-processing corrosion resistance while maintaining good electrical conductivity, and is extremely useful as a steel sheet for deep drawing applications, for example.

[ kind of resin ]

The type of resin used in the present embodiment is not particularly limited, and any of an aqueous resin and a nonaqueous resin can be used. When an aqueous dispersion (for example, an aqueous dispersion) using magnesium oxide or colloidal silica is used, an aqueous resin is preferably used. The aqueous resin is not particularly limited, and it is preferable that an aqueous magnesium hydroxide dispersion and colloidal silica be mixed.

The aqueous resin is preferably a polyolefin resin, a polyurethane resin, or a polyester resin, and among them, a polyolefin resin is preferred. The aqueous resin in the present embodiment means a resin that becomes an aqueous dispersion or a water-soluble resin.

The polyolefin resin is preferably an ethylene-unsaturated carboxylic acid copolymer. As the ethylene-unsaturated carboxylic acid copolymer, the ethylene-unsaturated carboxylic acid copolymers described in Japanese patent laid-open publication No. 2005-246953 and Japanese patent laid-open publication 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, and a copolymer can be obtained by polymerizing ethylene with 1 or more of these by a known high-temperature high-pressure polymerization method or the like.

The copolymerization ratio of the unsaturated carboxylic acid to ethylene is preferably 10 to 40% by mass, based on 100% by mass of the total amount of the monomers. If the unsaturated carboxylic acid content is less than 10% by mass, the carboxyl group which becomes the origin of intermolecular association formed by ion clusters decreases, and therefore the film strength effect cannot be exerted, and the emulsion composition is not preferable because of poor emulsion stability. The lower limit of the copolymerization ratio of the unsaturated carboxylic acid is more preferably 15% by mass. On the other hand, when the unsaturated carboxylic acid content exceeds 40 mass%, the corrosion resistance and water resistance of the first layer may deteriorate. The more preferable upper limit is 25% by mass.

Since the ethylene-unsaturated carboxylic acid copolymer has a carboxyl group, it can be emulsified (dispersed in water) by neutralization with an organic base or a metal ion. In the present embodiment, examples of the organic base include primary amines, secondary amines, and tertiary amines (preferably triethylamine).

The amine having a low boiling point (preferably an amine having a boiling point of 100 ℃ or lower under atmospheric pressure; for example, triethylamine) does not significantly reduce the corrosion resistance of the resin film. Preferably, a 1-valent metal ion is also used together with the amine. The amount of the amine is preferably 0.2 to 0.8 mol (20 to 80 mol%) based on 1 mol of the carboxyl group in the ethylene-unsaturated carboxylic acid copolymer. It is known that the amount of the metal ion having a valence of 1 affects the water vapor permeability, and that when the amount of the metal compound having a valence of 1 is increased, the affinity of the resin with water is increased, and the water vapor permeability is increased, and therefore, it is preferably 0.02 to 0.2 mol (2 to 20 mol%) relative to 1 mol of the carboxyl group in the ethylene-unsaturated carboxylic acid copolymer. Since an excessive amount of the alkali component causes deterioration of corrosion resistance, the total amount of the amine and the metal ion to be used may be in the range of 0.3 to 1.0 mol based on 1 mol of the carboxyl group in the ethylene-unsaturated carboxylic acid copolymer. The metal compound for imparting a 1-valent metal ion is preferably NaOH, KOH, LiOH, or the like, and NaOH is preferred because of its excellent performance.

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

The mass average molecular weight (Mw) of the ethylene-unsaturated carboxylic acid copolymer is preferably 1,000 to 10 ten thousand, more preferably 3,000 to 7 ten thousand, and still more preferably 5,000 to 3 ten thousand in terms of polystyrene. The Mw can be measured by Gel Permeation Chromatography (GPC) using polystyrene as a standard.

As the resin component, a carboxylic acid polymer may also be used. As the carboxylic acid polymer, any of the polymers having an unsaturated carboxylic acid as a constituent unit, which are exemplified as those usable for the synthesis of the ethylene-unsaturated carboxylic acid copolymer, can be used. Among them, 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 amount of the constituent unit derived from another monomer is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably a carboxylic acid polymer composed only of the unsaturated carboxylic acid. Preferred examples of the carboxylic acid polymer include polyacrylic acid, polymethacrylic acid, acrylic acid-maleic acid copolymers, and polymaleic acid, and among them, polymaleic acid is more preferred from the viewpoint of adhesion of the resin film and corrosion resistance. Although the exact mechanism for improving corrosion resistance and the like by using polymaleic acid is not clear, the present inventors believe that: since the amount of carboxyl groups is large, the adhesion between the resin film and the metal plate is improved, and the corrosion resistance is also improved. However, the present invention is not limited to this estimation.

The Mw of the carboxylic acid polymer used in the present embodiment is preferably 500 to 3 ten thousand, more preferably 800 to 1 ten thousand, further preferably 900 to 3,000, and most preferably 1,000 to 2,000 in terms of polystyrene. The Mw can be measured by GPC using polystyrene standards.

The content ratio of the ethylene-unsaturated carboxylic acid copolymer to the carboxylic acid polymer is 1, 000: 1-10: 1, preferably 200: 1-20: 1. 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 other hand, if the content ratio of the carboxylic acid polymer is excessive, the olefin-acid copolymer and the carboxylic acid polymer may be phase-separated in the coating liquid for forming a resin film, and a uniform resin film may not be formed.

The coating liquid for forming the resin coating film may contain a silane coupling agent. When a 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. In addition, the strength and toughness of the coating film are improved while the bonding force between the resin component and the colloidal silica is improved. Among them, a glycidoxy-based silane coupling agent has high reactivity and a large effect of improving corrosion resistance. Examples of the glycidoxysilane coupling agent include gamma-glycidoxypropylmethyldiethoxysilane, gamma-glycidoxypropyltrimethoxysilane, gamma-glycidoxymethyldimethoxysilane, and beta- (3, 4-epoxycyclohexyl) ethyltrimethoxysilane.

The amount of the silane coupling agent is preferably 0.1 to 10 parts by mass based on 100 parts by mass of the total of the inorganic compound and the resin component in the inorganic coating film. If the amount is less than 0.1 part by mass, insufficient adhesion between the metal plate and the resin coating film or insufficient bonding force between the resin component and the colloidal silica may occur, and the toughness or corrosion resistance of the coating film may become insufficient. On the contrary, if the amount exceeds 10 parts by mass, the effect of improving the adhesion between the galvanized steel sheet and the resin film is saturated, and the functional group in the resin is decreased, which may lower the coatability. Further, a hydrolytic condensation reaction occurs between the silane coupling agents, and the stability of the coating liquid is lowered, which may cause gelation or precipitation of colloidal silica. The amount of the silane coupling agent is more preferably 3 to 9 parts by mass, and still more preferably 5 to 7 parts by mass.

In the coating liquid used for forming the resin film, the solid content of the resin is preferably about 15 to 25 mass%. The coating liquid may contain wax, a crosslinking agent, a diluent, an anti-skinning agent, a surfactant, an emulsifier, a dispersant, a leveling agent, an antifoaming agent, a penetrant, a film-forming aid, a dye, a pigment, a thickener, a lubricant, and the like, as long as the effects of the present invention are not impaired. The coating method of the coating liquid is not particularly limited, and a known method such as roll coating can be used.

The kind of the galvanized steel sheet having the resin coating as described above is not particularly limited, and any of an electrogalvanized steel sheet, a hot-dip galvanized steel sheet, and an alloyed hot-dip galvanized steel sheet (hereinafter, these may be referred to as "base sheet") may be used. The kind of the galvanized layer is not particularly limited, and the galvanized layer may contain an alloy element. The galvanized layer is coated on one side or both sides of the base steel sheet, and the resin coating film is also coated on one side or both sides of the galvanized steel sheet.

The present specification discloses the techniques of various embodiments as described above, and the main techniques thereof are summarized as follows.

According to this configuration, a coated galvanized steel sheet can be realized which exhibits excellent corrosion resistance even after processing while maintaining good conductivity.

Further, the coated galvanized steel sheet of the present invention is very useful as a steel sheet for deep drawing applications.

The operation and effect of the present invention will be specifically shown below by examples, but the following examples do not limit the present invention, and all design changes according to the above and following purposes are included in the technical scope of the present invention.

Examples

(magnesium hydroxide)

Various magnesium hydroxide particles having different average particle diameters from (a) to (e) below were used.

(a) "139-: manufactured by Wako pure chemical industries, Ltd

(b) Magnesium hydroxide particles having an average particle diameter of 83 μm: manufactured by KANTO ELECTROCHEMICAL INDUSTRIAL CO., LTD

(c) "MH-30" (trade name): manufactured by Kokushi chemical industries Ltd

(d) "KISUMA 5Q-S" (trade name): manufactured by Kyowa chemical industries Co Ltd

(e) "ECOMAGZ-10" (trade name): manufactured by DATAIHAO chemical industries, Inc

(silica)

Colloidal silica "SNOWTEX XS" (trade name) manufactured by nippon chemical industries co. Hereinafter, "SNOWTEX XS" may be abbreviated as "ST-XS".

(resin)

As a resin for forming the resin film, a polyurethane resin ("HUX 541": trade name) manufactured by ADEKA or a polyethylene resin produced by tokyo chemical co. The polyethylene resin was produced by the following method.

[ Process for producing polyethylene resin ]

An ethylene-acrylic acid copolymer ("PRIMACO 5990I" (trade name) manufactured by Dow chemical Co., Ltd.; constituent 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, an aqueous polymaleic acid solution ("NONPOL PMA-50W" (trade name) manufactured by Nichikoku corporation (Mw: about 1100 (in terms of polystyrene) 8.0 parts by mass, triethylamine 35.5 parts by mass (0.63 equivalent to the carboxyl group of the ethylene-acrylic acid copolymer), an aqueous 48% NaOH solution 6.9 parts by mass (0.15 equivalent to the carboxyl group of the ethylene-acrylic acid copolymer), tall oil fatty acid ("Hartall FA 3" (trade name) manufactured by Hartalmic chemical Co., Ltd.) 3.5 parts by mass, and water were charged into an autoclave equipped with an emulsifying device having a stirrer, a thermometer, and a temperature controller, And 792.6 parts by mass of ion-exchanged water were sealed, stirred at high speed at 150 ℃ and 5 atm for 3 hours, and then cooled to 30 ℃.

Next, 10.4 parts by mass of a glycidoxy group-containing silane coupling agent ("TSL 8350" (trade name) manufactured by momentv performance materials ltd) and γ -glycidoxypropyltrimethoxysilane, a carbodiimide group-containing compound ("CARBODILITE SV-02" (trade name) manufactured by nippon textile, polycarbodiimide, Mw: 2,700, 40 mass% solids) and 72.8 mass parts ion-exchanged water were added, and the mixture was stirred for 10 minutes to emulsify the ethylene-acrylic acid copolymer, thereby obtaining an emulsion in which the respective components were mixed (20.3 mass% solids, measured in accordance with JIS K6833).

(preparation of magnesium hydroxide Dispersion)

The magnesium hydroxide particles were dispersed using water as a dispersant to prepare the following dispersions (a) to (E). The dispersant used in this case is not particularly specified, but when a resin film is formed, a polymer dispersant (for example, a water-soluble acrylic resin, a water-soluble styrene acrylic resin, or a nonionic surfactant) having a small adverse effect on corrosion resistance is preferably used.

Dispersion (A)

The magnesium hydroxide particles using the above (a), resin solid content: about 30% by mass, average particle diameter D₅₀：0.14μm

Dispersion (B)

The magnesium hydroxide particles using the above (b), resin solid content: about 30% by mass, average particle diameter D₅₀：0.17μm

Dispersion (C)

The magnesium hydroxide particles using the above (c), resin solid content: about 30% by mass, average particle diameter D₅₀：0.30μm

Dispersion (D)

The magnesium hydroxide particles using the above (d), resin solid content: about 30% by mass, average particle diameter D₅₀：0.69μm

Dispersion (E)

The magnesium hydroxide particles using the (e), resin solid content: about 30% by mass, average particle diameter D₅₀：1.1μm

With respect to the average particle diameter D of the magnesium hydroxide particles in the dispersion₅₀The dispersion was diluted with a 0.2 mass% aqueous solution of sodium hexametaphosphate and measured using a Microtrac "MT 3300EXII apparatus" (trade name) manufactured by macbeck bayer corporation.

(preparation of coating liquid)

The raw materials used are as follows: aqueous magnesium hydroxide dispersion [ dispersions (A) to (E) above ], aqueous resin, and colloidal silica (ST-XS)

Resin solid content: about 5 percent

(kind of original plate)

(1) Electrogalvanized steel plate (EG)

Plate thickness: 0.8mm

Weight per unit area of zinc: 18g/m²

(2) Molten zinc-plated steel plate (GI)

Plate thickness: 0.8mm

Weight per unit area of zinc: 90g/m²

(pretreatment of galvanized Steel sheet)

Degreasing: alkali degreasing (Nippon Rice-flour noodles series, "FINE CLEANER" (trade name))

And (3) drying: the mixture was dried with hot air to evaporate water.

(coating method)

The method comprises the following steps: bar coating

Thickness of resin film: the number of the bar was selected so as to obtain a predetermined thickness of the resin film.

(drying method)

The method comprises the following steps: hot air drier

Time: 1 minute

Conditions are as follows: the maximum reached temperature of the coated plate was 80 deg.C (confirmed by thermo-label)

[ example 1]

Various coated galvanized steel sheets (test nos. 1 to 6) were produced with various conditions varied within the above range as shown in table 1 below, and the corrosion resistance and conductivity of the obtained coated galvanized steel sheets were evaluated by the following methods.

[ Corrosion resistance ]

A flat plate portion: a salt spray test was carried out for 72 hours as defined in JIS Z2371 (2015). The white rust occurrence rate (area%) after the test was calculated and evaluated by the following evaluation criteria.

A sliding part: in the method shown in FIG. 1, the test piece 1 was pulled out while applying pressure thereto, and sliding marks were given to the surface of the test piece 1 by the flat die 2 (in FIG. 1, each symbol indicates 1: test piece and 2: flat die). Then, a salt spray test was performed for 48 hours as defined in JIS Z2371 (2015). The degree of white rust and discoloration in the vicinity of the sliding portion where the sliding mark was formed and in the periphery thereof was evaluated by the following evaluation criteria. The conditions for applying the sliding mark are as follows.

Applying pressure: 300kgf/cm²(29.4MPa)

The extraction speed is as follows: 300 mm/min

The flat plate die 1 is made of: SKD11(JIS G4404: 2006 alloy tool steel)

Lubricant: is not used

(evaluation criteria)

1. Flat plate part

O: the white rust occurrence rate is 20 area% or less

And (delta): the white rust occurrence rate is more than 20 area% and less than 30 area%

X: the white rust occurrence rate exceeds 30 area%

2. Sliding part

O: no white rust or discoloration at the sliding part and the vicinity thereof

And (delta): slight white rust or discoloration was observed in the sliding portion and the vicinity thereof

X: white rust or discoloration was observed in the sliding portion and the vicinity thereof

[ conductivity ]

The resistance value was measured by sliding a terminal on the surface of the sample using a tester ("analogue tester CX-270N", manufactured by CUSTOM corporation, japan).

(evaluation criteria)

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

The results were compared with the conditions for producing each coated galvanized steel sheet (type of original plate, composition ratio of inorganic coating, [ Mg (OH))₂/SiO₂]The thickness of the resin film) are shown in table 1 below.

In test nos. 1 to 6 of table 1, the influence of the thickness of the resin coating film on the properties of the coated galvanized steel sheet was examined.

From this result, it is clear that: in the case of the coated galvanized steel sheet, the corrosion resistance after working of the example (test No.1) in which the thickness of the resin film reached 0.2 μm was deteriorated. Further, the case (test No.6) in which the thickness of the resin film coated on the zinciferous coated steel sheet reached 2 μm was inferior in conductivity.

In contrast, it is known that: the coated galvanized steel sheets (test nos. 2 to 5) of the present invention, in which the thickness of the resin film was appropriately adjusted, exhibited excellent corrosion resistance after processing while maintaining good conductivity.

[ example 2]

Various coated galvanized steel sheets (test nos. 7 to 9) were produced within the above range by changing various conditions as shown in table 2 below, and the corrosion resistance and the electrical conductivity of the obtained coated galvanized steel sheets were evaluated by the same methods as in example 1.

The results were compared with the conditions for producing each coated galvanized steel sheet (type of original plate, composition ratio of inorganic coating, [ Mg (OH))₂/SiO₂]The thickness of the resin film) are shown in table 2 below.

In test nos. 7 to 9 of table 2, the influence of the total content of silica and magnesium hydroxide on the properties of the coated galvanized steel sheet was examined.

From this result, it is clear that: in the coated galvanized steel sheet, if the content of silica and magnesium hydroxide in the resin film is increased (test No.7), the corrosion resistance is deteriorated. Further, if the content of the resin in the resin film is increased (test No.9), the density of the film is also deteriorated, and the corrosion resistance is deteriorated.

In contrast, it is known that: the coated galvanized steel sheet of the present invention (test No.8) in which the contents of silica, magnesium hydroxide, and resin in the resin film were appropriately adjusted maintained good conductivity and exhibited excellent post-processing corrosion resistance.

[ example 3]

Various coated galvanized steel sheets (test nos. 10 to 21) were produced within the above range by changing various conditions as shown in table 3 below, and the corrosion resistance and the electrical conductivity of the obtained coated galvanized steel sheets were evaluated by the same methods as in example 1.

The results were compared with the conditions for producing each coated galvanized steel sheet (type of original plate, composition ratio of inorganic coating, [ Mg (OH))₂/SiO₂]The thickness of the resin film) are shown in table 3 below.

In test Nos. 10 to 21 in Table 3, the mass ratio of magnesium hydroxide to silica [ Mg (OH) ]₂/SiO₂]The influence on the characteristics of the coated galvanized steel sheet was investigated.

From this result, it is clear that: in the coated galvanized steel sheet, the mass ratio [ Mg (OH) ]₂/SiO₂]Examples deviating from the range of 0.3 to 6 (test nos. 10, 11, 16, 17, 21) were inferior in corrosion resistance after processing.

In contrast, it is known that: the mass ratio [ Mg (OH) is properly adjusted₂/SiO₂]The coated galvanized steel sheets (test Nos. 12 to 15 and 18 to 20) of the present invention maintained good conductivity and exhibited excellent post-processing corrosion resistance.

[ example 4]

Various coated galvanized steel sheets (test nos. 22 to 26) were produced within the above range by changing various conditions as shown in table 4 below, and the corrosion resistance and the electrical conductivity of the obtained coated galvanized steel sheets were evaluated by the same methods as in example 1.

The results were compared with the conditions for producing each coated galvanized steel sheet (type of original plate, composition ratio of inorganic coating, [ Mg (OH))₂/SiO₂]The thickness of the resin film) are shown in table 4 below.

In test Nos. 22 to 26 in Table 4, the average particle diameter D for magnesium hydroxide₅₀The influence of the above-described dispersions (a) to (E) on the properties of the coated galvanized steel sheet was examined.

From this result, it is clear that: in the coated galvanized steel sheet, the magnesium hydroxide has an average particle diameter D₅₀In the case where the thickness exceeds 0.6. mu.m (test Nos. 25 and 26), the corrosion resistance after the working is deteriorated.

In contrast, it is known that: the average particle diameter D of magnesium hydroxide is properly adjusted₅₀The coated galvanized steel sheets (test nos. 22 to 24) of the present invention exhibited excellent corrosion resistance after processing while maintaining good conductivity.

The application is based on Japanese patent application special application 2017-71277 applied on 31/3/2017 and Japanese patent application special application 2017-249153 applied on 26/12/2017, and the content of the application is included in the application.

The present invention has been described in detail with reference to the above embodiments in order to describe the present invention, but it should be understood that modifications and/or improvements can be easily made to the above embodiments by those skilled in the art. Therefore, the modified embodiments or modified embodiments that can be implemented by those skilled in the art are intended to be included in the scope of the claims as long as they do not depart from the scope of the claims set forth in the claims.

Industrial applicability

The present invention has wide industrial applicability in the field of galvanized steel sheets, particularly in the field of coated galvanized steel sheets.

Claims

1. A coated galvanized steel sheet characterized by 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 50-75 mass%, and the content of the resin component in the resin film is 25-50 mass%,

the mass ratio of the magnesium hydroxide to the silica is 0.33 to 6, the thickness of the resin coating is 0.3 to 1.5 μm,

the average particle diameter D of the magnesium hydroxide in water dispersion₅₀Is 0.6 μm or less.

2. The coated galvanized steel sheet according to claim 1, which is used for deep drawing processing.