JP2009113389A - Precoated steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a precoated metal sheet having fine coating appearance in which spangle is inconspicuous, having no coating appearance failure caused by a bubble removing failure or the like, excelling in processing adhesion between a coated film and a plated steel sheet, and causing no solvent odor peculiar to a solvent-based coating material. <P>SOLUTION: This precoated steel sheet having a fused Zn-Al-based alloy plated layer on at least one surface of a steel sheet is formed with the coated film A on the steel sheet surface having the fused Zn-Al-based alloy plated layer, wherein the fused Zn-Al-based alloy plated layer contains 1-10 mass% of Al, 0.2-1.0 mass% of Mg, 0.005-0.1 mass% of Ni and the rest consisting of Zn and unavoidable impurities, and the coated film A is formed of a solventless solid or powder coating material. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pre-coated steel sheet excellent in surface appearance, work adhesion and corrosion resistance used in the fields of home appliances / kitchens, building materials, automobiles and the like.

  Conventionally, as a base-coated steel sheet (base material) for a pre-coated steel sheet used in the fields of home appliances / kitchens, building materials, automobiles, etc., a molten Zn—Al alloy-plated steel sheet has been widely used. As this hot-dip Zn—Al-based alloy-plated steel sheet, a hot-dip Zn-plated steel sheet (hereinafter referred to as GI) whose Al content in the plating layer is 0.2% by mass or less is mainly about 5% by mass. Galfan (hereinafter referred to as GF), and a gallium steel sheet (hereinafter referred to as GL) having an Al content of about 55% by mass are used. Among these, GF is in high demand especially in the field of building materials because it is less expensive than GL and has better corrosion resistance than GI, but in the future, as the price of Zn rises, As an alternative to thick galvanized steel sheets, demand is expected to increase in fields such as home appliances.

However, GF generally has the following problems.
Tortoise-shaped spangles are formed in GF, but this spangle has a different shape depending on plating conditions (eg, annealing before plating, bath components), cooling conditions after plating (eg, cooling rate), etc. Even when used with this, the turtle shell-shaped spangles may float on the painted surface and impair the appearance after painting. For this reason, in recent years, there has been an increasing demand for GF having a beautiful plating layer having a metallic luster without spangles even for a coating base.

With regard to this GF, for example, for the purpose of improving blackening resistance and corrosion resistance, Ni and / or Ti is added in an amount of 0.003 to 0.15% by mass in a Zn—Al based alloy plating layer of Al: 2 to 15% by mass. By adding and chromating with a specific chromate treatment solution, concentrated Ni and / or Ti is present on the outermost surface portion of the plating layer, and this Ni and / or Ti concentrated portion is integrated with the chromate layer interface. For the purpose of improving the technology (patent document 1) and blackening resistance, Al: 4.0 to 7.0% by mass of a Zn—Al based alloy plating layer, Pb: 0.01% by mass or less, Sn: 0.00%. 005% by mass or less, Ni: 0.005 to 3.0% by mass, Cu: 0.005 to 3.0% by mass, skin pass treatment after plating, and then chromate treatment (patent 2) etc. have been proposed, but the surface-treated plated steel sheets obtained by these conventional techniques are formed with spangles similar to normal GF, so that they have poor appearance as plated steel sheets or coated steel sheets for the reasons described above. Prone to occur.
JP 2003-183800 A JP-A-4-297562

  In general, when a pre-coated steel sheet is continuously produced, it is generally applied by applying a paint to the surface of the strip-shaped steel sheet using a roll coater or a curtain coater. At this time, since the paint needs to have good fluidity, a paint containing a solvent is usually used. In general, these paints may entrap bubbles during mixing, transfer, or painting. As a result, depending on the viscosity of the paint, the bubbles remain in the paint film without disappearing after the paint film is formed. There may be a so-called bubble missing defect that impairs the appearance.

  As a countermeasure, a method of reducing the viscosity of the paint by increasing the amount of solvent in the paint and accelerating bubble removal is adopted, but depending on the characteristics of the coater, it may become impossible to apply the specified film thickness. Occurs. Therefore, conventionally, a method of adding a surfactant or a viscosity modifier to the paint has been used. However, the viscosity of the paint may not achieve the desired effect depending on the amount of additive added and the compatibility with the paint, and if the viscosity decreases, the wettability with the roll or base metal surface May decrease, leading to deterioration of paint appearance and substrate adhesion.

  In addition, pre-coated steel sheets that use organic solvents for paints, especially pre-coated steel sheets that use organic solvents for paints for the top coating layer, which is the outermost product, have odors peculiar to organic solvents, even though they undergo a drying process after coating. Even if it is at a level that does not pose a problem for health, there is a problem that this odor is disliked and may not be suitable for the use environment.

  Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, and is a pre-coated steel sheet based on a hot-dip Zn-Al alloy-plated steel sheet, and has a beautiful painted appearance with no spangle. Another object of the present invention is to provide a pre-coated steel sheet that does not have poor appearance of the coating film due to defective bubble removal, has excellent work adhesion between the coating film and the plated steel sheet, and does not produce a solvent odor peculiar to solvent-based paints.

  As a result of diligent research on the optimal plating composition and coating film to solve the above-mentioned problems, the present inventors have found that the molten Zn-Al-based alloy plating composition is based on a general Al concentration of GF. By including appropriate amounts of Mg and Ni, a beautiful plating appearance with a metallic luster with no spangles or very fine spangles formed can be obtained. A beautifully painted appearance can be obtained, and the coating film formed on the surface of the plated steel sheet can be coated and baked with a solvent-free lump or powder coating to prevent the appearance of the coating film from being defective due to defective bubble removal. It was found that excellent work adhesion between the coating film and the plated steel sheet was obtained. Moreover, the problem of solvent odor can be solved by using such a solvent-free coating.

The present invention has been made on the basis of such knowledge and has the following gist.
[1] In a precoated steel sheet having a molten Zn—Al-based alloy plating layer on at least one surface of the steel sheet, and a coating film (A) formed on the steel sheet surface having the molten Zn—Al-based alloy plating layer,
The molten Zn—Al-based alloy plating layer contains Al: 1.0 to 10% by mass, Mg: 0.2 to 1.0% by mass, Ni: 0.005 to 0.1% by mass, and the balance Consisting of Zn and inevitable impurities,
The precoated steel sheet, wherein the coating film (A) is a coating film formed of a solvent-free lump or powder coating.

[2] In the precoated steel sheet of [1] above, a chemical conversion treatment layer and a primer layer were formed in this order on the steel sheet surface having the molten Zn—Al alloy plating layer, and a coating film (A) was formed thereon. A precoated steel sheet characterized by that.
[3] In the precoated steel sheet of [1] or [2], the coating resin for forming the coating film (A) is an alkyd resin, a polyester resin, an acrylic resin, an epoxy resin, an epoxy ester resin, a silicon-modified polyester resin, A precoated steel sheet comprising at least one selected from silicon-modified acrylic resin, vinyl chloride resin, and fluororesin, and having a glass transition point of 30 to 200 ° C.

  The pre-coated steel sheet of the present invention has a beautiful coating appearance with a metallic luster in which the base-plated steel sheet has no spangles or very fine spangles formed. There is no appearance defect of the coating film due to defective omission, etc., and excellent work adhesion between the coating film and the plated steel sheet, and it does not produce a solvent odor peculiar to solvent-based paints. Can be manufactured.

The pre-coated steel sheet of the present invention has a molten Zn-Al alloy plating layer on at least one surface of the steel sheet, and a coating film (A) made of a specific paint is applied to the steel sheet surface having the molten Zn-Al alloy plating layer. Have.
A hot-dip Zn—Al-based alloy-plated steel sheet (hereinafter referred to as “the present invention-plated steel sheet”) serving as a base material for the precoated steel sheet of the present invention has Al: 1.0 to 10% by mass on at least one surface of the steel sheet, It has Mg: 0.2-1.0 mass%, Ni: 0.005-0.1 mass%, and has the molten Zn-Al type alloy plating layer which remainder consists of Zn and an unavoidable impurity.
In the plated steel sheet of the present invention, Mg added to the hot-dip Zn-A1 alloy plating layer mainly aims at obtaining a beautiful plated appearance with metallic luster in which spangles are not formed or very fine spangles are formed. Yes.

Hereinafter, the reason for limitation of the component composition of the hot-dip Zn—Al-based alloy plating layer (hereinafter simply referred to as “plating layer”) of the plated steel sheet of the present invention will be described.
The main aim of limiting the plating composition in the present invention is to eliminate the spangle peculiar to the hot-dip Zn-Al alloy plating of the GF composition (zero spangle) or to form a very fine spangle and to have a metallic luster without unplating It is to obtain a glossy coating appearance in which plating spangles do not stand out after forming a coating film.
When the Al content in the plating layer is less than 1.0% by mass, an Fe—Zn alloy layer is formed thick at the plating layer-substrate interface, and the workability deteriorates. On the other hand, if the Al content exceeds 10% by mass, a eutectic structure of Zn and Al cannot be obtained, and the Al-rich layer increases and the sacrificial anticorrosive action decreases, so that the corrosion resistance of the end face portion is inferior. Moreover, when it is going to obtain the plating layer in which Al exceeds 10 mass%, the top dross which has Al as a main component will generate | occur | produce easily in a plating bath, and the problem that a plating external appearance is impaired also arises. For these reasons, the Al content in the plating layer is 1.0 to 10% by mass, preferably 3 to 7% by mass.

  Mg content in a plating layer shall be 0.2-1.0 mass%. If the Mg content in the plating layer is less than 0.2% by mass, spangles are large, a beautiful plating appearance with metallic luster cannot be obtained, and blackening resistance is also reduced. As a result of the study by the present inventors, it is preferable that Ni is concentrated in the plating outermost layer portion in order to obtain excellent blackening resistance by adding Ni. It was found that the concentration requires the coexistence of an appropriate amount of Mg. On the other hand, when the Mg content exceeds 1.0% by mass, the color tone changes from gray white to gray and dross adhesion increases. In addition, cracks are likely to occur in the plating layer, and workability is reduced.

Moreover, Ni content in a plating layer shall be 0.005-0.1 mass%. When the Ni content in the plating layer is less than 0.005% by mass, the effect of improving blackening resistance cannot be obtained. It is presumed that this is because even when Mg coexists, the concentration of Ni on the outermost layer portion of the plating layer is small. On the other hand, when the Ni content exceeds 0.1% by mass, although there is an effect of improving blackening resistance, Al—Mg-based dross containing Ni is generated in the plating bath, and the appearance of plating is impaired due to dross adhesion.
For the reasons described above, in the present invention, the Mg content in the plating layer is 0.2 to 1.0 mass%, and the Ni content is 0.005 to 0.1 mass%.

In the plated steel sheet of the present invention, a misch metal containing Ce and / or La can be contained in the plating layer. Although this misch metal containing Ce and / or La has no effect on zero spangle formation, it increases the fluidity of the plating bath, prevents the occurrence of fine unplated pinholes, and smoothes the plating surface. Works.
If the content of misch metal is less than 0.005 mass% in terms of the total amount of Ce and La, the effect of suppressing pinholes cannot be sufficiently obtained, and the effect of smoothing the surface is lost. On the other hand, if the total amount of Ce and La exceeds 0.05% by mass, it will be present as an undissolved suspended matter in the plating bath, which will adhere to the plated surface and impair the plating appearance. For this reason, the misch metal containing Ce and / or La is preferably 0.005 to 0.05% by mass, and preferably 0.007 to 0.02% by mass in terms of the total amount of Ce and La.

  As described above, an appropriate amount of Mg and Ni is contained in the plating layer having the GF composition, and if necessary, a misch metal containing Ce and / or La is contained, so that there is no spangle or very fine spangle. A hot-dip Zn—Al-based alloy-plated steel sheet that is formed, has a metallic luster, has a beautiful plating appearance free from unplating such as minute pinholes, and has excellent blackening resistance can be obtained.

In the precoated steel sheet of the present invention, the coating film (A) formed on the steel sheet surface having the molten Zn—Al alloy plating layer as described above is a coating film formed of a solvent-free bulk or powder coating material.
This coating film (A) is (i) directly formed on the surface of the molten Zn-Al alloy plating layer, (ii) a chemical conversion treatment layer is formed on the surface of the molten Zn-Al alloy plating layer, and is formed on the upper layer. , (Iii) The chemical conversion treatment layer and the primer layer are sequentially formed on the surface of the molten Zn—Al alloy plating layer, and the upper layer is formed as an overcoat layer. The form is common.

Solvent-free bulk or powder paint (synthetic resin paint) resin includes, for example, alkyd resin, polyester resin, acrylic resin, epoxy resin, epoxy ester resin, silicon-modified polyester resin, silicon-modified acrylic resin, vinyl chloride resin, fluorine One or more kinds of resins can be used.
The method for obtaining a lump or powdery synthetic resin coating may be any of commonly used methods such as a dry method using no organic solvent (melt blending method, dry blending method) or a wet method using an organic solvent. Since the wet method requires a lot of energy to remove the organic solvent to form a lump or powder paint, the dry method is preferred. For example, in the dry method, a resin, a pigment such as a color pigment or extender pigment, and other additives are mixed and melted, and then cooled to form a bulk paint having a predetermined particle size, or finely pulverized with a mixer or the like. After that, it is sieved to make a powder paint.

Moreover, it is good to use the resin of a block shape or a powder coating material (synthetic resin coating material) whose glass transition point is 30-200 degreeC, Preferably it is 50-100 degreeC. If the glass transition point of the resin is less than 30 ° C., the coating film may be crushed during the molding process, and scratches may occur on the coating film surface, although it has relatively good processability. Further, blocking may occur when precoated steel sheets are laminated. On the other hand, when the glass transition point exceeds 200 ° C., damage to the coating film surface is suppressed, but the coating film cannot follow the deformation and elongation of the precoated steel sheet due to forming, and the coating film has minute cracks and peeling. May occur.
In order to form the coating film (A) with a solvent-free lump or powder coating, the lump or powder coating is applied while melting to form a coating. Specifically, a method of applying with a roll coater while heating or melting a lump or powder paint, a method of melting the paint on the steel sheet surface by sprinkling lump or powder paint on a heated steel plate, etc. can do.
Although there is no restriction | limiting in particular in the film thickness of a coating film (A), It is desirable to set it as about 20-100 micrometers.

  For solvent-free bulk or powder paints, known paint additives such as chromic rust preventives such as chromic acid, dichromic acid, ammonium chromate, strontium chromate, phosphate chromate, zinc chromate, calcium chromate, etc. Agents, non-chromium rust preventives such as aluminum phosphate, aluminum phosphomolybdate, and ammonium vanadate, colored pigments such as titanium white, iron oxide, and carbon black, extender pigments such as calcium carbonate, UV absorbers, and anti-scratch agents One or more of a fungicide, an antibacterial agent, an antioxidant, an antistatic agent and the like can be added. Moreover, a leveling agent, a dispersant, a repellency inhibitor, a color separation inhibitor, and the like, which are known additives, can be blended as necessary.

As described above, the molten Zn-Al alloy-plated steel sheet on which the coating film (A) made of a solvent-free bulk or powder coating is formed has a chemical conversion treatment layer formed as a base or a chemical conversion treatment layer. A primer layer may be formed on the upper layer. What is necessary is just to apply what is employ | adopted for the normal precoat steel plate as a chemical conversion treatment layer and a primer layer.
For the formation of the chemical conversion treatment layer, a chromate treatment with a treatment liquid mainly composed of normal chromic acid, dichromic acid or a salt thereof may be applied, or a titanium-based or zirconium-based material containing no chromium. You may apply the chromium free process by a process liquid.
The shape of the precoated steel sheet of the present invention may be either a coil shape or a cut plate (sheet) shape.

The precoated steel sheet of the present invention can be produced, for example, by the following method.
First, the hot-dip Zn—Al-based alloy-plated steel sheet can be obtained, for example, under the following production conditions.
The steel plate to be used as the base steel plate may be appropriately selected from known steel plates depending on the application, and is not particularly limited. For example, using a low carbon aluminum killed steel plate or an extremely low carbon steel plate is a viewpoint of the plating work. To preferred. This steel plate (underlying steel plate) is immersed in a hot-dip Zn-Al alloy plating bath and subjected to hot-dip (hot) plating, and then cooled by pulling up from the same plating bath. Form. This plating layer contains Al: 1.0 to 10% by mass, Mg: 0.2 to 1.0% by mass, Ni: 0.005 to 0.1% by mass, and, if necessary, Ce and / or Alternatively, a misch metal containing La is contained in an amount of 0.005 to 0.05 mass% in total of Ce and La, and the balance is made of Zn and inevitable impurities. Therefore, it is preferable to adjust the bath composition of the molten Zn—Al-based alloy plating bath to be substantially the same as the alloy plating layer composition.
Further, as described above, it is preferable that Ni is concentrated in the outermost layer portion of the molten Zn—Al-based alloy plating layer.

The inventors of the present invention, in particular, as a result of earnestly examining the content of Mg and Ni in the molten Zn-Al alloy plating layer, the cooling rate after plating, and the concentration behavior of the plating component elements on the outermost layer of the plating layer, As described above, coexistence of Mg and Ni is indispensable for improvement of blackening, that is, Ni concentration on the outermost layer portion of the plating layer, but this Ni concentration requires up to 250 ° C. after plating. It has been found that the cooling rate has a great influence.
It is known that metals such as Al, Mg, and Ni in the molten Zn-Al alloy plating layer gradually diffuse toward the outermost surface of the plating layer during solidification and normal temperature after plating. In particular, it has been found that the concentration of Mg and Ni on the outermost surface of the plating layer, which has been noted in the experiments by the present inventors, is greatly influenced by the cooling rate up to 250 ° C. after plating. On the other hand, the cooling rate in the temperature range below 250 ° C. hardly affected the concentration of Mg and Ni.

Specifically, by controlling the cooling rate of the plated steel sheet pulled up from the molten Zn—Al alloy plating bath to 250 ° C. to 1 to 15 ° C./second, preferably 2 to 10 ° C./second, It has been found that Ni concentration on the surface layer can be more effectively promoted. When the cooling rate of the plated steel sheet pulled up from the plating bath to 250 ° C. is less than 1 ° C./second, although Ni is sufficiently concentrated in the outermost layer of the plated layer, an alloy layer grows in the plated layer, and a turtle shell pattern As a result, the appearance deteriorates and the workability deteriorates. On the other hand, if the cooling rate exceeds 15 ° C./second, the Mg content in the plating layer is in the range of 0.2 to 1.0 mass% and the Ni content is in the range of 0.005 to 0.1 mass%. Further, the concentration of Ni in the outermost layer portion of the plating layer is reduced, and the effect on blackening resistance is not exhibited. Therefore, the cooling rate of the plated steel sheet pulled up from the molten Zn—Al-based alloy plating bath to 250 ° C. is preferably 1 to 15 ° C./second, more preferably 2 to 10 ° C./second.
The plating bath temperature is preferably in the range of 390 to 500 ° C. If the plating bath temperature is less than 390 ° C., the viscosity of the plating bath increases and the plating surface tends to be uneven, while if it exceeds 500 ° C., dross in the plating bath tends to increase.

In order to form a coating film (A) with a solvent-free lump or powder paint on the surface of a hot-dip Zn-Al alloy-plated steel sheet, as described above, a chemical conversion treatment is performed as necessary, or primer coating is further performed. After the coating, a lump or powder coating is applied while melting to form a coating film. Specifically, a method of applying with a roll coater while heating and melting the lump or powder paint, a method of melting the paint on the steel plate surface by spraying the lump or powder paint on the heated steel plate, etc. are applied. can do. Usually, a baking treatment is performed on the coating film thus applied.
In general, the surface of the steel sheet is cleaned before the primer coating, and as the method, normal processing such as water washing, hot water washing, pickling and alkali degreasing can be performed alone or in combination. .

  Chromate treatment (treatment liquid “ZM-1300”, manufactured by Nihon Parkerizing Co., Ltd.) is applied as a chemical conversion treatment to the surface of a hot-dip Zn—Al-based alloy-plated steel plate (plate thickness: 0.3 mm) having the plating composition shown in Table 1. An epoxy primer ("JT-25", manufactured by Nippon Fine Coating Co., Ltd.) was applied to the substrate, and a primer layer having a film thickness of 5 μm was formed by baking under the conditions of maximum plate temperature: 200 ° C. and processing time of 30 seconds. Next, the top coating material shown in Table 1 was applied to the upper layer, and a top coating layer was formed by baking at a maximum reached plate temperature of 230 ° C. and a processing time of 60 seconds to obtain a precoated steel sheet. . The performance of the precoated steel sheet thus obtained was evaluated by the following test. The results are shown in Table 1.

(1) Bubble removal property The surface and cross section of the pre-coated steel sheet were observed with an SEM to examine the presence or absence of bubbles in the coating film, and evaluated according to the following criteria.
○: No air bubbles ×: Air bubbles present (2) Appearance The state of the plating spangles floating on the painted surface was visually observed and evaluated according to the following criteria.
○: Plating spangle is not lifted △: Plating spangle is slightly lifted X: Plating spangle is slightly lifted

(3) Work adhesion In accordance with JIS G 3312, the test piece is folded with a goby folding machine, and then the same test piece is sandwiched by one piece (1T-180 ° C.) and tightened with a vise. Next, a cellophane tape was applied to the bent portion, and the degree of peeling of the coating film when the cellophane tape was peeled off was evaluated according to the following criteria.
○: No peeling of coating film Δ: Partial peeling of coating film ×: Excessive peeling of coating film (4) Corrosion resistance 5% salt water, salt water at a temperature of 35 ° C. for 1000 hours in accordance with JIS Z 2371 A spray test was conducted, and the occurrence of swelling after the test was evaluated according to the following criteria.
○: No abnormality at all △: Partially blistered ×: Fluffed all over the area According to Table 1, the pre-coated steel sheet of the example of the present invention is free of bubbles during coating, appearance, work adhesion, and corrosion resistance. It turns out that it is excellent.

Claims (3)

In a pre-coated steel sheet having a molten Zn-Al-based alloy plating layer on at least one surface of the steel sheet, and a coating film (A) formed on the steel sheet surface having the molten Zn-Al-based alloy plating layer,
The molten Zn—Al-based alloy plating layer contains Al: 1.0 to 10% by mass, Mg: 0.2 to 1.0% by mass, Ni: 0.005 to 0.1% by mass, and the balance Consisting of Zn and inevitable impurities,
The precoated steel sheet, wherein the coating film (A) is a coating film formed of a solvent-free lump or powder coating.   The precoat according to claim 1, wherein a chemical conversion treatment layer and a primer layer are formed in this order on a steel plate surface having a molten Zn-Al-based alloy plating layer, and a coating film (A) is formed thereon. steel sheet.   The coating resin forming the coating film (A) is selected from alkyd resins, polyester resins, acrylic resins, epoxy resins, epoxy ester resins, silicon-modified polyester resins, silicon-modified acrylic resins, vinyl chloride resins, and fluororesins. The precoated steel sheet according to claim 1 or 2, comprising at least one kind and having a glass transition point of resin of 30 to 200 ° C.