JP6665829B2 - Film-coated hot-dip Zn-Al-Mg plated steel sheet and method for producing the same - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a coating-coated hot-dip Zn-Al-Mg-based steel sheet having excellent hydrophilicity, durability and weather resistance, which is used as a building material for water spray cooling, and a method for producing the same.

  2. Description of the Related Art Conventionally, in a facility without an air conditioner, such as a factory, a warehouse, and a barn, the roof surface is heated by daylight, and the inside of the building may become higher than the outside temperature due to radiant heat. Therefore, there has been a demand for an inexpensive and simple cooling method.In recent years, from the viewpoint of energy saving and utilization of natural energy, a water spray cooling system that sprays water on the roof and outer walls of the building and cools the building with the heat of evaporation of water has been studied. Have been.

  For example, Patent Literature 1 uses a watering device that can efficiently and inexpensively cool a building by lowering the water pressure applied to the watering device, and keeping the water pressure approximately constant to slowly flow the water little by little, and using the watering device. A roof cooling system is disclosed.

  However, even if water is sprayed little by little while keeping the water pressure low and constant, the water is repelled depending on the type of roofing material, and the entire surface cannot be cooled uniformly. In order to uniformly wet the entire surface with a thin water film with a small amount of water and efficiently promote evaporative cooling, a material having good wettability (high hydrophilicity) is required as a roof material.

  In Patent Literature 2, a photocatalyst layer that becomes hydrophilic in response to photoexcitation is formed in a predetermined region of a structure wall surface or a roof surface, water is supplied to the photocatalyst layer formation region, and latent heat associated with evaporation causes peripheral heat generation. A method for cooling an urban space characterized by cooling air and structures is disclosed.

  However, since the photocatalyst becomes hydrophilic by being excited by ultraviolet rays, it is not possible to maintain hydrophilicity depending on the weather.

Further, Patent Document 3 discloses a fumed silica having an average particle diameter of 1 to 40 nm in an inorganic-based film and an amorphous film having an average particle diameter of 0.1 to 500 μm and an apparent specific volume of 2 to 12 cm ³ / g. There is disclosed a coating composition which forms irregularities by including high quality inorganic powder and exhibits high hydrophilicity.

  As a water spray cooling building material application, since it is always in contact with sunlight, when an organic resin is used, there is a concern about deterioration due to ultraviolet rays. Therefore, an inorganic-based coating as disclosed in Patent Document 3 is preferable.

  However, since the coating contains 0.1 to 500 μm particles for the purpose of imparting irregularities, when used in applications involving processing, the particles in the coating fall off due to sliding and abrasion, and the coating is peeled off. Under severe conditions, the abrasion resistance is insufficient.

Japanese Patent No. 5232439 Japanese Patent No. 3658320 JP 2013-023683 A

  The present invention has been made in view of the above circumstances, and is a steel sheet used as a building material for watering cooling, showing a stable, high hydrophilicity, weather resistance, corrosion resistance, appearance and abrasion resistance. An object of the present invention is to provide a film-coated hot-dip Zn-Al-Mg-based steel sheet having an excellent hydrophilic film and a method for producing the same.

  The present inventors have intensively studied to solve the above problems. As a result, it is possible to solve the above-mentioned problem by forming an uneven shape on the surface by treating a hot-dip Zn-Al-Mg-based plated steel sheet having a specific plating layer with a specific acid, and further forming a hydrophilic film. Was found.

  The present invention has been made based on the above findings, and the gist is as follows.

[1] At least one surface of a steel sheet contains Al: 5.0% by mass or more and less than 10.0% by mass, Mg: 0.2% by mass or more and less than 5.0% by mass, and the balance is Zn and inevitable. A steel plate having a molten Zn—Al—Mg-based plating layer containing impurities and containing a primary Al phase and a ternary eutectic of Al—Zn—MgZn ₂ was subjected to nitric acid of 0.01 mol / L or more and less than 10 mol / L. An acid contacting step of contacting for at least 2 seconds and less than 60 seconds;
A drying step of drying the hot-dip Zn-Al-Mg-based plated steel sheet after the acid contacting step;
A coating step of applying a treatment liquid for forming a hydrophilic film on the hot-dip Zn-Al-Mg-based plated steel sheet after the drying step, and drying to form a hydrophilic film. A method for producing a hot-dip Zn-Al-Mg-based plated steel sheet.

  [2] The method for producing a coating-coated hot-dip Zn-Al-Mg-based steel sheet according to [1], wherein the primary crystal Al phase has an average major axis of 10 μm or less.

  [3] The method for producing a film-coated hot-dip Zn-Al-Mg-based steel sheet according to [1] or [2], wherein the hydrophilic film is an inorganic film.

[4] At least one surface of the steel sheet contains Al: 5.0% by mass to less than 10.0% by mass, Mg: 0.2% by mass to less than 5.0% by mass, with the balance being Zn and inevitable. It consists impurities, and primary crystal Al phase has a Zn-Al-Mg-based plating layer containing ternary eutectic of Al-Zn-MgZn _2, over the molten Zn-Al-Mg plated layer Further, a film-coated hot-dip Zn-Al-Mg-based steel sheet having a hydrophilic film,
In the cross section of the film-coated hot-dip Zn-Al-Mg-based plated steel sheet, when the maximum thickness of the hot-dip Zn-Al-Mg-based plated layer is h, the hydrophilic film and hot-dip Zn- When the length of the curve formed by the interface of the Al-Mg-based plating layer is L, and the sum of the lengths of the curves formed by the interface between the hydrophilic film and the primary Al phase is L _Al And a film-coated hot-dip Zn-Al-Mg-based steel sheet satisfying the following formulas (1) and (2).
1.5 ≦ L / 2h <5.5 (1)
0.40 ≦ L _Al /L<0.90 (2)
[5] The coating-coated hot-dip Zn-Al-Mg-based steel sheet according to [4], wherein the primary crystal Al phase has an average major axis of 10 µm or less.

  [6] The coating-coated hot-dip Zn-Al-Mg-based steel sheet according to [4] or [5], wherein the hydrophilic film is an inorganic film.

  According to the present invention, a coated Zn—Al—Mg-based coated steel sheet excellent in hydrophilicity, durability (abrasion resistance), corrosion resistance, appearance, and weather resistance, which is suitable as a building material for water spray cooling, can be obtained.

FIG. 1 shows the maximum thickness h of the hot-dip Zn-Al-Mg-based plating layer in the cross section of the coating-coated hot-dip Zn-Al-Mg-based steel sheet, and shows the interface between the hydrophilic coating and the hot-dip Zn-Al-Mg-based plating layer. FIG. 3 is a schematic diagram illustrating a length L of a curve to be formed and a sum L _Al of lengths of curves formed by an interface where a hydrophilic film and primary crystal Al are in contact with each other.

  Hereinafter, the present invention will be described specifically. Note that the present invention is not limited to the following embodiments.

  The method for producing a coating-coated hot-dip Zn-Al-Mg-based coated steel sheet of the present invention is characterized in that a specific hot-dip Zn-Al-Mg-based coated steel sheet is subjected to nitric acid of 0.01 mol / L or more and less than 10 mol / L for 2 seconds to 60 seconds. An acid contacting step of making less than a contact, a drying step of drying the plated steel sheet, and after this drying step, a treatment liquid for forming a hydrophilic film is applied on the plated steel sheet and dried to form a film forming step of forming a hydrophilic film. Have.

The above-mentioned "specific hot-dip Zn-Al-Mg-based plated steel sheet" means that at least one surface of the steel sheet has Al: 5.0% by mass or more and less than 10.0% by mass, and Mg: 0.2% by mass or more and 5.0% by mass. A molten Zn—Al—Mg-based plating layer containing less than 0% by mass and the balance consisting of Zn and unavoidable impurities, wherein the molten Zn—Al—Mg-based plating layer is composed of a primary Al phase, an Al— a hot-dip Zn-Al-Mg plated steel sheet containing ternary eutectic of Zn-MgZn _2.

In the hot-dip Zn-Al-Mg-based plated steel sheet, fine grains of the primary Al phase are dispersed in the ternary eutectic of Al-Zn-MgZn ₂ in granular form. And MgZn ₂ are preferentially dissolved and Al remains to obtain an uneven shape. By further forming an inorganic film thereon, even if the inorganic film is not originally so hydrophilic, its hydrophilicity can be enhanced. Furthermore, since the Al remaining on the surface is harder than Zn and has excellent corrosion resistance, the resulting surface has excellent abrasion resistance and corrosion resistance.

  First, each configuration of the hot-dip Zn-Al-Mg-based plated steel sheet of the present invention will be described.

<Hot-dipped Zn-Al-Mg-based plated steel sheet>
The hot-dip Zn-Al-Mg-based coated steel sheet serving as the base of the coating-coated hot-dip Zn-Al-Mg-based steel sheet manufactured in the present invention will be described. The purpose of adding Mg to the hot-dip Zn-Al-Mg-based plated layer of this hot-dip Zn-Al-Mg-based steel sheet is mainly to form a striped Al-Zn- An object of the present invention is to form a ternary eutectic of MgZn ₂ and to form fine Al irregularities on the surface by a subsequent nitric acid dissolution treatment.

  The reason for limiting the component composition of the hot-dip Zn-Al-Mg-based plating layer (hereinafter, simply referred to as “plating layer”) will be described.

Al: 5.0% by mass or more and less than 10.0% by mass When the Al content in the plating layer is less than 5.0% by mass, not a primary Al phase but a primary Zn phase is formed. Zn is soft and inferior to abrasion resistance as compared with Al, so that abrasion resistance is reduced. On the other hand, when the Al content is 10.0% by mass or more, a large amount of top dross mainly composed of Al is generated in the plating bath, which causes a problem of impairing the plating appearance. For the above reasons, the Al content in the plating layer is set to 5.0% by mass or more and less than 10.0% by mass, preferably 6.0% by mass or more and less than 8.0% by mass.

Mg: 0.2% by mass or more and less than 5.0% by mass In the present invention, one of the aims of containing Mg in the plating composition is to form an Al-Zn-MgZn striped around the primary Al phase formed in an island shape. ₂ to form a ternary eutectic and obtain a shape in which Al is finely dispersed.

The plating layer of a general hot-dip Zn—Al-based plated steel sheet (Al: 4.3% by mass, balance Zn) is composed of a binary eutectic of primary Zn and Zn—Al, and the binary eutectic is the surface of the plating layer. And continuously in the vicinity of the plating layer-substrate interface. On the other hand, in the plating layer of the composition of the present invention, a ternary eutectic of Al—Zn—MgZn ₂ exists in a striped shape around the primary Al phase.

In addition, the above-mentioned shape shows, by elemental analysis by SEM-EDX, a portion of a primary Al phase in which only Al is detected and a portion of a ternary eutectic of Al-Zn-MgZn ₂ in which Zn, Al, and Mg are detected. You can check each.

When the content of Mg in the plating layer is less than 0.2% by mass, the area ratio of the ternary eutectic of Al—Zn—MgZn ₂ is reduced, the unevenness after nitric acid treatment is reduced, and even if a hydrophilic film is formed. Sufficient hydrophilicity cannot be obtained. On the other hand, when Mg in the plating layer is 5.0% by mass or more, the primary Al phase becomes fine, but the hardness of the plating layer increases due to an increase in the ternary eutectic of Al—Zn—MgZn ₂ , and bending is performed. In this case, large cracks are easily generated, and the workability is reduced. Dross adhesion also increases. Therefore, the Mg content in the plating layer is set to 0.2% by mass or more and less than 5.0% by mass.

  The average major diameter of the primary Al phase is preferably 10 μm or less. If the average major diameter of the primary Al phase is 10 μm or less, sufficient unevenness can be formed after the nitric acid treatment, and sufficient hydrophilicity can be obtained by forming a hydrophilic film.

  Here, the particle diameter (average major axis) of the primary Al phase is measured as follows. In the cross section SEM in the thickness direction of the steel sheet, in the field of view: vertical: plating layer thickness, horizontal: twice the plating layer thickness, the maximum length of each primary Al phase was measured as the major axis, and the average value was measured. The average major axis. These measurements may be made after any acid treatment.

As described above, by incorporating an appropriate amount of Mg in the plating layer of the hot-dip Zn-Al-Mg plated steel sheet, the primary crystal Al phase fine particulate is dispersed in ternary Akirachu of Al-Zn-MgZn ₂ Has plating composition.

  Such a hot-dip Zn-Al-Mg-based steel sheet and a film-coated hot-dip Zn-Al-Mg-based steel sheet can be obtained, for example, under the following manufacturing conditions.

  The steel sheet used as the base steel sheet may be appropriately selected from known steel sheets according to the application, and is not particularly limited. For example, it is preferable to use a low carbon aluminum killed steel sheet or an extremely low carbon steel sheet from the viewpoint of plating operation. This steel sheet (base steel sheet) is immersed in a hot-dip Zn-Al-based plating bath to perform hot immersion (hot-dip) plating, then pulled out of the plating bath and cooled, and a hot-dip Zn-Al-based alloy plating layer is formed on the steel sheet surface. Form. This plating layer contains Al: 5.0% by mass or more and less than 10.0% by mass, Mg: 0.2% by mass or more and less than 5.0% by mass, and the balance consists of Zn and unavoidable impurities. Therefore, it is preferable that the bath composition of the hot-dip Zn—Al-based plating bath is also adjusted to be substantially the same as the average composition of the plating layer.

  The cooling rate of the plated steel sheet pulled up from the hot-dip Zn—Al-based plating bath is not particularly limited, but the cooling rate up to 250 ° C. is preferably 1 to 15 ° C./sec, and more preferably 2 to 10 ° C./sec. If the cooling rate of the plated steel sheet pulled up from the plating bath to 250 ° C. is less than 1 ° C./sec, primary crystal Al may not be generated. On the other hand, if the cooling rate exceeds 15 ° C./sec, primary Al grains tend to be large.

  The plating bath temperature is preferably in the range of 390 to 480 ° C. When the plating bath temperature is lower than 390 ° C., the viscosity of the plating bath increases, and the plating surface tends to become uneven. On the other hand, if the plating bath temperature exceeds 480 ° C., dross in the plating bath tends to increase. That is, if the plating bath temperature is 390 ° C. or higher, the viscosity of the plating bath is appropriately maintained, and the plating surface is less likely to be uneven. Hateful.

Acid Contact Step The acid contact step is a step of bringing the hot-dip Zn—Al—Mg-based plated steel sheet into contact with 0.01 mol / L or more and less than 10 mol / L nitric acid for 2 seconds or more and less than 60 seconds.

By bringing the plating layer of the above-mentioned hot-dip Zn-Al-Mg-based plated steel sheet into contact with nitric acid, Zn and MgZn ₂ in the plating surface layer (a region from the surface of the plating layer to 10 μm in the plate thickness direction) are dissolved, Irregularities are formed. Al remaining on the surface is harder than Zn, and the resulting surface has excellent wear resistance.

  Hereinafter, the reasons for limiting the nitric acid treatment method will be described.

  If the nitric acid concentration is less than 0.01 mol / L, the effect of dissolution is small, and a concavo-convex shape cannot be obtained. Preferably it is 0.1 mol / L or more. On the other hand, when the concentration is 10 mol / L or more, the dissolution rate is high, the unevenness becomes too large, and the appearance becomes uneven, so that the concentration of nitric acid is less than 10 mol / L. Preferably it is 1 mol / L or less.

  The contact time with nitric acid is 2 seconds or more and less than 60 seconds. When the treatment time is less than 2 seconds, the treatment time is short and the uneven shape cannot be obtained. On the other hand, if the time is 60 seconds or longer, the processing time is long, the productivity is reduced, and the uneven shape becomes too large, which leads to the deterioration of the appearance.

  The temperature of the acid is not particularly specified, and may be a general range of 5 ° C. or more and less than 70 ° C. Although the acid can be used after heating, the effect of promoting dissolution by heating is small.

  There is no particular limitation on the method of contacting the steel sheet with nitric acid. A roll coating method, a bar coating method, a dipping method, a spray coating method and the like can be used. After the steel sheet is brought into contact with the acid, the acid is washed off with water and dried within the above contact time. This corresponds to the drying step in the present invention.

Film forming step The film forming step is a step of applying a treatment liquid for forming a hydrophilic film to the molten Zn-Al-Mg-based plated steel sheet after the above-mentioned drying step, followed by drying to form a film.

The hydrophilic film, the Zn-Al-Mg-based formed on the plated steel sheet as long as it exhibits hydrophilicity, the contact angle theta ₀ of water at the time of forming a film on the smooth surface is 90 ° It is sufficient if it is less than. Preferably it is less than 70 °, more preferably less than 55 °. A lower contact angle can be obtained by forming a hydrophilic film on the unevenness of the Zn-Al-Mg-based plated steel sheet.

  As a kind of the hydrophilic film formed by the treatment liquid for forming a hydrophilic film, an inorganic film is preferable. Since the organic film is denatured by ultraviolet rays, it is difficult to secure long-term hydrophilicity.

  As the inorganic coating, a titanium compound, a zirconium compound, silica, a silane coupling agent, a vanadate compound, a phosphate compound, a nickel compound, a molybdenum compound, or the like can be used in combination.

  In particular, when a phosphoric acid compound is contained, the affinity between the film and water increases, and the contact angle of water when forming the film on a smooth surface is preferably 50 ° or less, which is preferable. However, when the content of the phosphoric acid compound exceeds 50% by mass in the film, the film is easily dissolved in water and the corrosion resistance is reduced. Therefore, the content of the phosphoric acid compound in the film is preferably less than 50% by mass.

  Examples of the phosphoric acid compound include condensed phosphates such as phosphoric acid, primary phosphate, secondary phosphate, tertiary phosphate, pyrophosphate, pyrophosphate, tripolyphosphate, and tripolyphosphate; Examples include phosphoric acid, phosphite, hypophosphorous acid, hypophosphite, phosphonic acid, phosphonate and the like. Examples of the phosphonate include nitrilotrismethylenephosphonic acid, phosphonobutanetricarboxylic acid, ethylenediaminetetramerylenephosphonic acid, methyldiphosphonic acid, and methylenephosphonic acid.

  An organic resin such as an acrylic resin, a urethane resin, and a phenol resin can be included in the film. However, since it is difficult to secure long-term hydrophilicity because it is denatured by ultraviolet rays, the content is preferably 10% by mass or less in the film, and more preferably not contained.

  Further, if the coating contains particles of 0.1 μm or more, the abrasion resistance is reduced. Therefore, even if the coating contains particles of 0.1 μm or more, the content is preferably 5% by mass or less. More preferably, the coating does not contain particles of 0.1 μm or more.

  The thickness of the hydrophilic film is preferably 0.1 μm or more and less than 3 μm. If it is less than 0.1 μm, water and oxygen tend to permeate and the corrosion resistance is reduced. If it is 3 μm or more, the film covers the irregularities, and the effect of improving the hydrophilicity by the effect of the irregularities is reduced. The thickness of the hydrophilic film is measured by observing the cross section with an SEM. The thickness can be calculated by measuring the film thickness at any five points in any five visual fields (10 μm × 10 μm) and taking the average.

  The method for forming the hydrophilic film is not particularly limited. For example, a method of immersing the galvanized steel sheet in a treatment liquid capable of forming a hydrophilic film, or applying a treatment liquid to the galvanized steel sheet Method. The method of applying the treatment liquid may be selected as appropriate depending on the shape of the zinc-coated steel sheet to be treated, and the like. The water-repellent and oil-repellent treatment liquid is applied by a roll coating method, a bar coating method, a dipping method, a spray coating method, or the like. Can be applied. Furthermore, it is also possible to adjust the amount of application, make the appearance uniform, and make the film thickness uniform by the air knife method or the roll drawing method after the application. The treatment liquid may be prepared by a conventionally known method.

  The drying method after the treatment with the treatment liquid capable of forming the hydrophilic film is not particularly limited, and may be room temperature drying or heat drying. As a means for heating and drying, a dryer, a hot air oven, a high-frequency induction heating oven, an infrared oven, or the like can be used. Although the temperature is not particularly limited, it is preferable that the maximum ultimate sheet temperature (Peak Metal Temperature: PMT) is from room temperature to about 200 ° C.

When the maximum thickness of the hot-dip Zn-Al-Mg-based plating layer is h, the coating-coated hot-dip Zn-Al-Mg-based coated steel sheet thus formed has a hydrophilic coating within a range of 2 h in the width direction of the steel sheet. The length of the curve formed by the interface of the hot-dip Zn-Al-Mg-based plating layer is L, and among these curves, the hydrophilic film and the primary Al phase (that is, the convex portion of the hot-dip Zn-Al-Mg-based plating layer) when the sum of the length of the curve formed by the interface in contact with the L _Al, satisfy the following equations (1) and (2).
1.5 ≦ L / 2h <5.5 (1)
0.40 ≦ L _Al /L<0.90 (2)
L / 2h is an index of the surface unevenness, and the film-coated hot-dip Zn—Al—Mg-based steel sheet shows high hydrophilicity in the range of the expression (1). When L / 2h is less than 1.5, the effect of unevenness is small, and the hydrophilicity is reduced. When L / 2h is 5.5 or more, the unevenness is too large, so that the surface pressure is partially increased and the wear resistance is reduced, and the appearance is reduced due to the absorption of light by the unevenness. Preferably, it is 1.7 or more and less than 3.0. L _Al / L is an index of the amount of Al on the surface. If it is in the range of the expression (2), the film-coated hot-dip Zn-Al-Mg-based plated steel sheet shows high wear resistance and good appearance. When L _Al / L is less than 0.40, a lot of soft Zn is present on the surface, so that the wear resistance becomes insufficient. When L _Al / L is 0.90 or more, dissolution of the surface proceeds, and the unevenness is too large, so that the appearance is deteriorated. Preferably, it is 0.5 or more and less than 0.8.

In addition, as for h, L, and L _Al as shown in FIG. 1, the vertical direction: the thickness of the plating layer, and the horizontal: the cross section of the steel plate in the thickness direction in any five fields of view, which is twice the thickness of the plating layer in the steel sheet width direction. Observing the SEM, the average value of the five visual fields of the maximum film thickness of the plating layer is defined as h, and the average value of the five visual fields of the length of the curve formed by the interface between the hydrophilic film and the molten Zn-Al-Mg-based plating layer is defined as h. L, and the average value of the sum of the lengths of the curves formed by the interface where the hydrophilic film and the binary eutectic of Zn-Al contact each other in five visual fields can be calculated as L _Al .

  Next, the present invention will be specifically described based on examples, but is merely an example for describing the present invention, and does not limit the present invention.

  Each plated steel sheet used as a base steel sheet of a surface-treated plated steel sheet (corresponding to a film-coated hot-dip Zn-Al-Mg-based steel sheet) was subjected to plating composition (average composition), plating treatment conditions (plating bath temperature, bath immersion time, plating). Table 1 together with the subsequent cooling rate up to 250 ° C).

  Here, the particle diameter (average major axis (Y μm in Table 1)) of the primary Al phase was measured by the method described above.

Nitric acid is sprayed on the plated steel sheet for a predetermined time, and then sprayed with water, washed with water, dried with a blower, and further coated with a hydrophilic surface treatment composition (a treatment liquid for forming a hydrophilic film) shown in Table 2 on the plated steel sheet. It was applied to the surface and dried so that the maximum temperature reached 80 ° C. in 5 to 20 seconds to obtain a test material. L / 2h and L _Al / L were measured by the method described above. These test materials were evaluated for hydrophilicity, corrosion resistance, weather resistance, and abrasion resistance by the following test methods. The results are shown in Table 3 together with the nitric acid concentration applied to each test material, the composition of the surface treatment composition, and the coating conditions.

(1) Corrosion resistance A salt water spray test according to JIS-Z-2371-2000 was performed on a test material having an end portion and a back surface tape-sealed, and a test time at which a white rust generation area ratio was 5% was measured. The evaluation criteria are as follows.

： １: 192 hours or more −-: 120 hours or more and less than 192 hours Δ: less than 120 hours The appearance was visually observed and evaluated after the above salt spray test. The evaluation criteria are as follows.
◎: White tint, no unevenness ○: Gray tint, no unevenness ○-: Grayish tint, uneven black △: Gray black tint (2) Abrasion resistance Test conditions: Felt contact surface width 20 mm × 10 mm, load: 3.8 kg / cm ² (0.4 MPa), simple reciprocating 100 times on the coating surface. The residual ratio of the film was determined from the fluorescence FX count of Zn before and after the test and in the sample without the film. The evaluation criteria are as follows.

◎: Residual film ratio of 90% or more ：: Residual film ratio of 75% or more and less than 90% ○-: Residual film ratio of 50% or more and less than 75% △: Residual film ratio of less than 50% (3) Hydrophilicity (apparent contact angle)
Each of the obtained samples was processed into a size of 30 mm × 50 mm, and 3 μL of 2 μL of distilled water was dropped on the surface at room temperature. Each contact angle 30 seconds after the drop was measured with a solid-liquid interface analyzer Drop Master 500 (Kyowa) The average of three drops was calculated as a water contact angle. The quality of the water contact angle was determined according to the following criteria.

◎: less than 10 ° ○: less than 30 ° 10 ° or more ○-: less than 40 ° 30 ° or more △: 40 ° or more (4) Weatherability Based on JIS D0205 (1987), when a sunshine weather test was performed for 1000 hours. The decrease in hydrophilicity was evaluated. The evaluation criteria are as follows.

◎: less than + 2 ° ○: + 2 ° or more and less than + 5 ° ○-: + 5 ° or more and less than + 10 ° △: + 10 ° or more

  From the results in Table 3, it was found that all of the samples of the present invention were excellent in hydrophilicity, abrasion resistance and weather resistance. On the other hand, it was found that the sample of the comparative example in which any of the requirements was insufficient could not obtain a satisfactory result for any of the performances.

  ADVANTAGE OF THE INVENTION According to this invention, the coating-coated molten Zn-Al-Mg-based steel sheet excellent in hydrophilicity, abrasion resistance, and weather resistance used as a water spray cooling building material can be obtained.

Claims (4)

At least one surface of the steel sheet contains Al: 5.0% by mass or more and less than 10.0% by mass, Mg: 0.2% by mass or more and less than 5.0% by mass, and the balance consists of Zn and inevitable impurities. A steel sheet having a primary Zn phase having an average major axis of 10 μm or less and a hot-dip Zn—Al—Mg-based plating layer containing a ternary eutectic of Al—Zn—MgZn ₂ is provided in an amount of 0.01 mol / L to 10 mol / L. An acid contacting step of contacting nitric acid less than L for at least 2 seconds and less than 60 seconds, a drying step of drying the hot-dip Zn-Al-Mg-based plated steel sheet after the acid contacting step, and a hot-dip Zn-Al after the drying step the hydrophilic film-forming treatment liquid is applied onto a -Mg-plated steel sheet and dried, it comprises a phosphoric acid compound of less than 50 wt%, the contact angle theta ₀ of water at the time of forming a film on the smooth surface 90 forming a hydrophilic film is less than ° And carrying out the film forming step, a film-coated hot-dip Zn-Al-Mg method of manufacturing a plated steel sheet for use as a water spray cooling building materials. The method of claim 1 , wherein the hydrophilic film is an inorganic film. At least one surface of the steel sheet contains Al: 5.0% by mass or more and less than 10.0% by mass, Mg: 0.2% by mass or more and less than 5.0% by mass, and the balance consists of Zn and inevitable impurities. a primary crystal Al phase average major axis is 10μm or less, Al-Zn-MgZn have Zn-Al-Mg-based plating layer containing ternary eutectic of _2, the molten Zn-Al-Mg plated A coating used as a water spray cooling building material having a hydrophilic coating further containing less than 50% by mass of a phosphoric acid compound on the layer and having a water contact angle θ ₀ of less than 90 ° when the coating is formed on a smooth surface A coated hot-dip Zn-Al-Mg-based coated steel sheet, wherein in the cross-section of the film-coated hot-dip Zn-Al-Mg-based coated steel sheet, the maximum thickness of the hot-dip Zn-Al-Mg-based plated layer is h , and the steel sheet width direction In the range of 2h, hydrophilic The length of the curve formed by the interface between the film and the hot-dip Zn-Al-Mg-based plating layer is L, and the sum of the lengths of the curves formed by the interface where the hydrophilic film and the primary Al phase are in contact with each other is L. as the L _Al, the following formulas (1) and is characterized by satisfying (2), film-coated hot-dip Zn-Al-Mg plated steel sheet to be used as a water spray cooling building materials.
1.5 ≦ L / 2h <5.5 (1)
0.40 ≦ L _Al /L<0.90 (2) The said hydrophilic coating is an inorganic coating, The coating coating molten Zn-Al-Mg system plating steel plate of Claim 3 characterized by the above-mentioned.