WO2012001981A1

WO2012001981A1 - Coated steel sheet having excellent corrosion resistance and alkali resistance

Info

Publication number: WO2012001981A1
Application number: PCT/JP2011/003750
Authority: WO
Inventors: 大久保　謙一; 尾和　克美; 上田　耕一郎
Original assignee: 日新製鋼株式会社
Priority date: 2010-06-30
Filing date: 2011-06-30
Publication date: 2012-01-05
Also published as: CN103097576B; CN103097576A

Abstract

Disclosed is a coated steel sheet which can keep corrosion resistance even under strongly alkaline corrosive environments and has excellent corrosion resistance and alkali resistance. The coated steel sheet comprises a steel sheet, a chemical-conversion-treated coating film formed on the surface of the steel sheet, a primer coating film formed on the surface of the chemical-conversion-treated coating film, and a top coating film formed on the surface of the primer coating film. The chemical-conversion-treated coating film comprises a fluoride of titanium or a fluoride of zirconium, an oxide or hydroxide of titanium, and an oxide or hydroxide of zirconium. The primer coating film comprises an organic resin, an anti-corrosive pigment comprising one or two compounds independently selected from the group consisting of magnesium phosphate and zirconium phosphate, and barium sulfate.

Description

Painted steel sheet with excellent corrosion resistance and alkali resistance

The present invention relates to a coated steel sheet having excellent corrosion resistance and alkali resistance.

Recently, a microwave oven that supplies water vapor to the heating chamber has been developed in order to give a fluffy feeling when heating food. In a microwave oven having such a steam function, water vapor is generated by heating the evaporating dish to boil the water in the evaporating dish (see, for example, Patent Documents 1 to 3). As a material for the evaporating dish, ceramics, metal materials such as stainless steel and aluminum, and coated steel plates coated with metal materials are used.

On the other hand, since members in the heating chamber of a microwave oven are exposed to boiling salt water, it is known that coating film peeling and swelling are likely to occur due to corrosion. For the purpose of suppressing such peeling and blistering, the surface of a hot-dip aluminized steel sheet is coated with a fluoroacid coating, a primer coating containing a phosphoric acid-based anticorrosive pigment in a heat-resistant resin, and fluororesin particles in the heat-resistant resin. There has been proposed a coated steel sheet in which top coating films containing the above are sequentially laminated (for example, Patent Document 4).

JP 2003-343844 A Japanese Patent Laying-Open No. 2005-055142 JP 2008-170149 A JP 2005-186287 A

腐食 In a microwave oven having a steam function, corrosion of metal materials in the evaporating dish is a problem. That is, in a microwave oven having a steam function, tap water is replenished and boiled repeatedly, so that a large amount of scale water (calcium, magnesium, etc.) accumulates in the evaporating dish. When water adheres to the scale of the tap water, it exhibits strong alkalinity and becomes a severe corrosive environment. Therefore, corrosion of the evaporating dish using the metal material and the members in the heating chamber becomes a problem.

As one means for improving corrosion resistance, it is conceivable to apply a coated steel plate to the evaporating dish. However, even in an evaporating dish using a coated steel plate, in a strong alkaline corrosive environment, the metal material corrodes under the coating film when used for a long time, and an evaporating dish that can withstand long-term use is provided. I couldn't.

The present invention has been made in view of such a point, and an object of the present invention is to provide a coated steel sheet excellent in corrosion resistance and alkali resistance that can maintain corrosion resistance even in a strong alkaline corrosive environment.

The present inventor has found that the above problem can be solved by forming a chemical conversion treatment film containing a predetermined titanium compound and a zirconium compound and further forming a primer coating film containing a predetermined phosphate and barium sulfate on the chemical conversion film. Further studies were made to complete the present invention.

That is, this invention relates to the following heat-resistant non-adhesive coating steel plates.
[1] It has a steel plate, a chemical conversion coating formed on the surface of the steel plate, a primer coating formed on the surface of the chemical conversion coating, and a top coating formed on the surface of the primer coating. A coated steel sheet, wherein the chemical conversion coating includes a fluoride of titanium or a fluoride of zirconium, an oxide of titanium or a hydroxide of titanium, and an oxide of zirconium or a hydroxide of zirconium; The primer coating film includes an organic resin, pigment A composed of one or two compounds selected from the group consisting of magnesium phosphate and zirconium phosphate, and pigment B composed of barium sulfate; The content of the pigment A and the content of the pigment B are 20 to 100 parts by mass with respect to 100 parts by mass of the organic resin. The total content of the pigment A and the pigment B in the primer coating is 40-160 parts by weight relative to the organic resin 100 parts by weight, the coated steel plate.
[2] The total content of the oxide and hydroxide of titanium and the oxide and hydroxide of zirconium with respect to the total content of fluoride of titanium and fluoride of zirconium in the chemical conversion film The coated steel sheet according to [1], wherein the molar ratio is in the range of 0.2 to 3.
[3] The molar ratio of the total content of the zirconium oxide and the hydroxide to the total content of the titanium oxide and the hydroxide in the chemical conversion film is in the range of 0.4 to 2. The coated steel sheet according to [1] or [2].
[4] The organic resin includes one kind or two or more kinds of resins selected from the group consisting of polyethersulfone resin, polyphenylsulfide resin, polyimide resin, and polyamideimide resin. Coated steel sheet according to any one of the above.

According to the present invention, a coated steel sheet having excellent heat resistance, corrosion resistance, water (humidity) resistance and alkali resistance can be provided. Therefore, according to the present invention, it is possible to provide a coated steel sheet that can be used for a long time even in a strongly alkaline corrosive environment.

FIG. 1A is a photograph of a processed part of a painted steel plate No. 7-1. FIG. 1B is a photograph of the processed part of No. 7-2 coated steel sheet.

The coated steel sheet of the present invention is formed on the surface of the steel sheet (coating raw sheet), the chemical conversion coating formed on the surface of the steel sheet, the primer coating formed on the surface of the chemical conversion coating, and the surface of the primer coating. A top coating film. That is, in the coated steel sheet of the present invention, a chemical conversion treatment film, a primer coating film, and a top coating film are sequentially laminated on the steel sheet surface.

Hereinafter, each component of the coated steel sheet of the present invention will be described.

[Painted original plate]
The kind of steel plate used as a coating original plate is not specifically limited. Examples of coated steel sheets include galvanized steel sheets (electrical Zn plating, hot dip Zn plating), galvannealed steel sheets (alloyed hot dip Zn plating alloyed after hot dip Zn plating), zinc alloy galvanized steel sheets (molten) Zn-Mg plating, hot-dip Zn-Al-Mg plating, hot-dip Zn-Al plating), hot-dip Al-plated steel plate, hot-dip Al-Si-plated steel plate, stainless steel plate and the like. From the viewpoint of improving the corrosion resistance in a high temperature environment, a molten Al—Si plated steel sheet is preferred.

In addition to the corrosion resistance in a high-temperature environment, when the processed part corrosion resistance is also required, the steel sheet used as the coating original sheet is preferably a molten Al—Si plated steel sheet that is further annealed after the plating layer is formed. In a portion subjected to bending processing such as 180-degree bending processing, defects such as cracks and peeling may occur in the plating layer, and the base steel may be exposed. If the base steel is exposed in this way, red rust will occur at the part where the base steel is exposed in a severe corrosive environment such as the inside of a microwave oven or microwave oven having a steam function. May decrease. In this way, when the corrosion resistance of the processed part becomes a problem, a molten Al—Si plated steel sheet that is further annealed after forming the plating layer may be used. By further annealing after forming the molten Al—Si plating layer, the molten Al—Si plating layer can be softened. As a result, the molten Al—Si plating layer does not generate cracks or peels off even when combined with compression and tension, and can be deformed following the processing. Therefore, even if composite processing is performed, defects such as cracks and peeling that expose the underlying steel do not occur, and the processed portion corrosion resistance can be improved.

In order to anneal the molten Al—Si plated layer, the molten Al—Si plated steel sheet on which the plated layer is formed may be held at 350 to 500 ° C. for 30 minutes or longer (see Japanese Patent Application Laid-Open No. 62-50454). At this time, the thickness of the alloy layer formed at the interface between the plating layer and the base steel can be reduced by adjusting the cooling rate from when it is pulled up from the molten Al-Si plating bath to annealing. The workability of the Al—Si plating layer can be further improved. Specifically, a steel plate (steel strip) pulled up from a molten Al—Si plating bath (bath temperature of 640 ° C. or higher) is cooled to 400 ° C. at an average cooling rate of 10 ° C./second or higher, and then at 350 to 500 ° C. for 30 ° C. It is preferable to heat for more than a minute (refer to JP 2000-256816 A).

[Chemical conversion coating]
The chemical conversion treatment film includes 1) a fluoride of titanium or a fluoride of zirconium, 2) an oxide of titanium or a hydroxide of titanium, and 3) an oxide of zirconium or a hydroxide of zirconium. By including these titanium compound and zirconium compound in the chemical conversion film, an excellent barrier action can be imparted while reducing the environmental load.

First, the chemical conversion treatment film 1) contains a fluoride of titanium or a fluoride of zirconium. These fluorides dissolve in water and liberate fluorine ions. The liberated fluorine ions react with the underlying coating original plate at the damaged part of the coating film to form an insoluble metal salt, thereby providing self-repairing properties.

These fluorides are necessary components for imparting self-healing properties. However, in the case of members that have many opportunities for contact with water, the amount of fluoride elution increases, and the chemical conversion treatment film becomes porous. Therefore, the adhesion of the chemical conversion film to the coating original plate may be reduced. In particular, in an alkaline aqueous solution, fluorine ions are easily liberated, and the adhesion of the chemical conversion film to the coating original plate is further reduced. In addition, when the chemical conversion treatment film becomes porous, the water permeability and ion resistance of the film are lowered, so that the water resistance (humidity) and alkali resistance of the coated steel sheet may be lowered. Therefore, the presence of an excessive amount of fluoride is not preferable because it leads to a decrease in the adhesion of the chemical conversion treatment film to the coating original plate and a decrease in water resistance (wet) and alkali resistance.

Further, the chemical conversion treatment film includes 2) titanium oxide or titanium hydroxide, and 3) zirconium oxide or zirconium hydroxide. These oxides and hydroxides are almost insoluble in water and alkaline aqueous solutions, and form a strong barrier film on the surface of the painted base plate, improving the corrosion resistance, water resistance (humidity) and alkali resistance of the coated steel sheet. Can be made.

According to the preliminary experiments by the present inventors, when the corrosion resistance was compared with only the chemical conversion coating formed, the titanium oxide was able to improve the corrosion resistance more than the zirconium oxide. Similarly, the hydroxide of titanium can improve the corrosion resistance more than the hydroxide of zirconium. This is presumably because the titanium oxide (hydroxide) becomes an inorganic polymer during the formation of the chemical conversion film, and forms a stronger barrier film than the zirconium oxide (hydroxide). On the other hand, when the corrosion resistance was compared with the primer coating and the top coating formed on the chemical conversion coating, the zirconium oxide improved the coating adhesion and corrosion resistance more than the titanium oxide. I was able to. Similarly, zirconium hydroxide can improve coating film adhesion and corrosion resistance more than titanium hydroxide. This is presumed to be because zirconium oxide (hydroxide) acts as a cross-linking agent for organic resins, thereby improving coating film adhesion and coating film density.

Therefore, the combination of the oxide or hydroxide of titanium and the oxide or hydroxide of zirconium can improve the barrier property, the adhesion of the coating film and the denseness of the coating film, resulting in corrosion resistance. It is considered that the water resistance (humidity) and alkali resistance can be further improved. However, although these oxides and hydroxides are necessary components for imparting corrosion resistance, they are insoluble and therefore almost cannot be expected for self-healing properties.

The chemical conversion coating of the coated steel sheet of the present invention provides self-healing properties by blending a fluoride of titanium and a fluoride of zirconium, and an oxide or hydroxide of titanium and an oxide or hydroxide of zirconium In addition, the barrier properties, coating film adhesion and coating film denseness were improved. Therefore, the chemical conversion film of the coated steel sheet of the present invention can exhibit excellent corrosion resistance, water (humidity) resistance, and alkali resistance.

The film thickness of the chemical conversion coating is not particularly limited, but is preferably adjusted so that the total metal equivalent adhesion amount of titanium and zirconium is in the range of 3 to 100 mg / m ² . When the total metal conversion adhesion amount is less than 3 mg / m ² , corrosion resistance, water resistance (wet) resistance and alkali resistance cannot be sufficiently provided. On the other hand, when the total metal equivalent adhesion amount is more than 100 mg / m ² , the processability of the coating film may be deteriorated. The total metal equivalent adhesion amount of titanium and zirconium can be measured by ICP analysis or the like.

Molar ratio of fluoride (total content of titanium fluoride and zirconium fluoride) to oxide and hydroxide (total content of titanium oxide and hydroxide and zirconium oxide and hydroxide) Is preferably in the range of 0.2 to 3. When the molar ratio is less than 0.2, the self-repairing property cannot be sufficiently imparted, so that the corrosion resistance of the damaged part may be lowered. On the other hand, when the molar ratio is more than 3, the amount of soluble components increases, so that the water resistance and alkali resistance may be lowered.

The molar ratio of the total of zirconium oxide and hydroxide to the total of titanium oxide and hydroxide is preferably in the range of 0.4 to 2. When the molar ratio is less than 0.4, the crosslinking effect of the coating film by the oxide and hydroxide of zirconium and the effect of improving the coating film adhesion cannot be sufficiently exhibited, so that the corrosion resistance, water resistance (humidity) and Alkali resistance may be reduced. On the other hand, when the molar ratio is more than 2, the barrier effect of the oxide and hydroxide of titanium cannot be sufficiently exhibited, so that the corrosion resistance, water resistance (humidity) and alkali resistance may be lowered.

The chemical conversion treatment film may contain other optional components. For example, the chemical conversion treatment film may contain an organic resin such as polyphenol in order to further improve the adhesion with the primer coating film. Moreover, the chemical conversion treatment film may contain oxides, such as Si, Al, and Mg, and a metal compound for barrier property improvement. Further, the chemical conversion film may contain a soluble phosphate or an oxyacid salt such as Mo or V having an oxidizing property in order to further improve the self-repairing property. Oxidizing nitric acid and the oxyacid salt promote the formation of an inorganic polymer of an oxide of titanium or zirconium and promote the dissociation of fluoride when a chemical conversion treatment solution is applied. Therefore, the ratio of the fluoride, oxide and hydroxide of the chemical conversion film can be controlled by blending these oxidizing compounds.

The chemical conversion treatment film can be formed by a known method. For example, if a chemical conversion treatment solution containing titanium fluoride salt or zirconium fluoride salt is applied to the surface of the coating original plate by a method such as roll coating, spin coating, or spraying, it is dried without washing with water. Good. The drying temperature and drying time are not particularly limited as long as moisture can be evaporated. From the viewpoint of productivity, the drying temperature is preferably in the range of 60 to 150 ° C. as the ultimate plate temperature, and the drying time is preferably in the range of 2 to 10 seconds. Moreover, you may add the organic acid which has a chelate action to a chemical conversion liquid so that a titanium salt and a zirconium salt can exist stably in a chemical conversion liquid. Examples of organic acids include tannic acid, tartaric acid, citric acid, oxalic acid, malonic acid, lactic acid and acetic acid.

[Primer coating]
The primer coating film contains one or two kinds of rust preventive pigments (pigment A) and barium sulfate (pigment B) selected from the group consisting of magnesium phosphate and zirconium phosphate based on an organic resin.

The organic resin used as the base of the primer coating is not particularly limited, but 1 or 2 selected from the group consisting of polyethersulfone resin, polyphenylsulfone resin, polyimide resin, and polyamideimide resin from the viewpoint of imparting heat resistance. The above heat resistant resin is preferable.

As the rust preventive pigment (Pigment A), magnesium phosphate, zirconium phosphate or a combination thereof is used. As will be described later, barium sulfate is blended in the primer coating to suppress elution of the anticorrosive pigment, but elution of magnesium phosphate and zirconium phosphate can be suppressed by barium sulfate. On the other hand, barium sulfate hardly suppresses elution with respect to other rust preventive pigments (calcium-based, silicate-based, zinc phosphate, etc.).

The content of magnesium phosphate and zirconium phosphate (Pigment A) is preferably in the range of 20 to 100 parts by mass with respect to 100 parts by mass of the base organic resin. When content is less than 20 mass parts, corrosion resistance cannot fully be exhibited. On the other hand, when the content is more than 100 parts by mass, the elution amount of the rust preventive pigment increases, and the water resistance and alkali resistance may be lowered.

Barium sulfate (pigment B) suppresses excessive elution of magnesium phosphate and zirconium phosphate (pigment A) in an alkaline atmosphere. This suppression is presumably because the eluted phosphate ions and barium ions react and re-deposit. Thereby, since the elution amount of magnesium phosphate and zirconium phosphate can be reduced and water permeability resistance and ion resistance resistance can be maintained, water resistance and alkali resistance can be imparted.

The content of barium sulfate is preferably in the range of 20 to 100 parts by mass with respect to 100 parts by mass of the base organic resin. When the content is less than 20 parts by mass, elution of magnesium phosphate and zirconium phosphate cannot be sufficiently suppressed. On the other hand, when the content exceeds 100 parts by mass, the primer coating film becomes porous, and the water resistance may be lowered.

The total content of magnesium phosphate and zirconium phosphate (pigment A) and barium sulfate (pigment B) is preferably in the range of 40 to 160 parts by mass with respect to 100 parts by mass of the organic resin. When the total content is less than 40 parts by mass, the corrosion resistance cannot be exhibited sufficiently. On the other hand, when the total content exceeds 160 parts by mass, the primer coating film becomes porous, and the water resistance may be lowered.

The mass ratio of barium sulfate (pigment B) to phosphoric acid anticorrosive pigment (pigment A) is preferably in the range of 0.5 to 1.6. When the mass ratio is less than 0.5, elution of magnesium phosphate and zirconium phosphate cannot be sufficiently suppressed. On the other hand, when the mass ratio is more than 1.6, the elution of magnesium phosphate and zirconium phosphate is suppressed excessively, so that the corrosion resistance may be lowered.

The primer coating may be transparent, but may be colored by adding an arbitrary coloring pigment. Examples of the color pigment include titanium oxide, carbon black, chromium oxide, iron oxide and the like. Further, the primer coating film may be added with scaly inorganic additives, inorganic fibers, etc. to improve the coating film hardness and wear resistance. Examples of the flaky inorganic additive include glass flake, graphite flake, synthetic mica flake, synthetic alumina flake, silica flake and the like. Examples of the inorganic fiber include potassium titanate fiber, wollastonite fiber, silicon carbide fiber, alumina fiber, alumina silicate fiber, silica fiber, rock wool, slag wool, glass fiber, carbon fiber and the like.

The film thickness of the primer coating is not particularly limited, but is preferably in the range of 0.5 to 30 μm. When the film thickness is less than 0.5 μm, the effects of corrosion resistance and coating film adhesion may not be sufficiently obtained. Moreover, when a primer coating film is a colored coating film, in order to conceal a coating original plate, the film thickness of 3 micrometers or more is preferable. On the other hand, when the film thickness is more than 30 μm, the surface of the coating film becomes a cocoon skin shape and the appearance is deteriorated, and a crack is easily generated when baking.

The primer coating can be formed by a known method. For example, a primer paint containing an organic resin, magnesium phosphate or zirconium phosphate (pigment A), barium sulfate (pigment B), etc. may be applied to the surface of the chemical conversion treated steel sheet and baked. The method for applying the primer paint is not particularly limited, and may be appropriately selected from the methods used for the production of precoated steel sheets. Examples of such a coating method include a roll coating method, a flow coating method, a curtain flow method, a spray method, and the like. The drying temperature is preferably in the range of 200 ° C. to 400 ° C. as the ultimate plate temperature, and the drying time is preferably in the range of 20 to 180 seconds. In particular, when one or two or more heat resistant resins selected from the group consisting of polyethersulfone resin, polyphenylsulfone resin, polyimide resin and polyamideimide resin are used as the organic resin, the drying temperature is the ultimate plate temperature. More preferably, the temperature is in the range of 300 ° C. to 400 ° C., and the drying time is more preferably in the range of 30 to 180 seconds. If it is dried within this range, the base resin is sufficiently cured, so that the characteristics are easily exhibited.

[Top coating film]
The top coating is not particularly limited, but a coating containing a fluororesin based on a heat resistant resin is preferable from the viewpoint of heat resistance and easy cleaning (non-adhesiveness).

The heat resistant resin contained in the top coating film may be the same as or different from the heat resistant resin contained in the primer coating film. For example, the heat resistant resin contained in the top coating film is a polyethersulfone resin, a polyphenylsulfone resin, a polyimide resin, a polyamideimide resin, or a combination thereof.

As the fluororesin, a heat-meltable fluororesin having a melting point of 270 ° C. or higher is preferable from the viewpoint of imparting heat resistance and easy cleaning. Examples of such fluororesins include polymers or copolymers such as tetrafluoroethylene, hexafluoroethylene, perfluoroalkyl vinyl ether, and chlorotrifluoroethylene. Among these, a tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer is particularly preferable from the viewpoint of durability of easy washing and heat resistance.

The content of the fluororesin is preferably in the range of 10 to 200 parts by mass with respect to 100 parts by mass of the heat resistant resin. When the content is less than 10 parts by mass, the easy cleaning property cannot be exhibited sufficiently. On the other hand, when the content exceeds 200 parts by mass, the adhesion of the top coating to the primer coating tends to decrease.

The top coating may be transparent, but may be colored by adding an arbitrary coloring pigment. Examples of the color pigment include titanium oxide, carbon black, chromium oxide, iron oxide and the like.

You may mix | blend a dark color type | system | group (black type | system | group) near-infrared reflective pigment with a top coating film as a coloring pigment. For example, when the coated steel sheet of the present invention is applied to a microwave oven interior material, a dark color tone is often preferred from the viewpoint of design as the microwave oven interior material. However, when the top coating film of dark color is formed on the interior of the microwave oven, the infrared radiation radiated when the oven is heated is absorbed by the top coating film. This leads to an increase in power. As described above, when the coated steel sheet of the present invention is applied to a microwave oven interior material or the like, from the viewpoint of improving heating efficiency while maintaining a dark color tone, in the wavelength region of 400 to 750 nm (visible light). It is preferable to blend a dark color (black) heat reflective pigment having an average reflectance of 10% or less and an average reflectance of 20% or more in the wavelength range of 750 to 2500 nm (near infrared) into the top coating film. . Examples of dark (black) near-infrared reflective pigments include calcined pigments containing Fe ₂ O ₃ , Cr ₂ O ₃ , CoO or combinations thereof. The content of the dark (black) near-infrared reflective pigment is preferably in the range of 5 to 35 parts by mass with respect to the organic resin. When the content is less than 5 parts by mass, a dark color tone cannot be imparted. On the other hand, when the content is more than 35 parts by mass, the cohesive force of the coating film is lowered, and the processability may be inferior.

In addition, a scale-like inorganic additive or inorganic fiber may be added to the top coating film to improve the coating film hardness and wear resistance. Examples of the flaky inorganic additive include glass flake, graphite flake, synthetic mica flake, synthetic alumina flake, silica flake and the like. Examples of the inorganic fiber include potassium titanate fiber, wollastonite fiber, silicon carbide fiber, alumina fiber, alumina silicate fiber, silica fiber, rock wool, slag wool, glass fiber, carbon fiber and the like.

The film thickness of the top coating is not particularly limited, but is preferably in the range of 5 to 40 μm. When the film thickness is less than 5 μm, the easy cleaning property cannot be maintained sufficiently. On the other hand, when the film thickness is more than 40 μm, the surface of the coating film becomes a cocoon skin shape and the appearance is deteriorated, and a crack is easily generated when baking. From the viewpoint of workability, the film thickness of the top coating film is preferably in the range of 5 to 20 μm.

The top coating can be formed by a known method. For example, a top paint containing an organic resin, a fluororesin (preferably in the form of particles), a color pigment, or the like may be applied to the surface of the primer-coated steel sheet and baked. The method for applying the top paint is not particularly limited, and may be appropriately selected from methods used for producing precoated steel sheets. Examples of such a coating method include a roll coating method, a flow coating method, a curtain flow method, a spray method, and the like. The drying temperature is preferably in the range of 200 ° C. to 450 ° C. as the ultimate plate temperature, and the drying time is preferably in the range of 20 to 180 seconds. In particular, when a polyethersulfone resin, polyphenylsulfone resin, polyimide resin, polyamideimide resin or a combination thereof is used as the heat resistant resin, the drying temperature is more preferably in the range of 300 ° C. to 400 ° C. at the ultimate plate temperature. Preferably, the drying time is more preferably in the range of 30 to 180 seconds. If it is dried within this range, the base resin is sufficiently cured, so that the characteristics are easily exhibited. When the top coating contains a heat-meltable fluororesin, the drying temperature is more preferably in the range of 350 ° C. to 450 ° C. as the ultimate plate temperature, and the drying time is more preferably in the range of 60 to 180 seconds. When it is dried within this range, a sufficient amount of the fluororesin can be moved to the surface of the top coating film to exhibit excellent easy cleaning (non-adhesiveness).

As described above, in the coated steel sheet of the present invention, by including barium sulfate in the primer coating, the primer coating is prevented from becoming porous due to excessive outflow of the anticorrosive pigment from the primer coating, And ion permeability are improved. Moreover, in the coated steel plate of this invention, the barrier property and the self-repairability of a chemical conversion treatment film are improved by including a predetermined titanium compound and a zirconium compound in a chemical conversion treatment film. The coated steel sheet of the present invention is excellent in water resistance (humidity), alkali resistance, and corrosion resistance, and can maintain corrosion resistance even in a highly alkaline corrosive environment.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

[Example 1]
1. Preparation of coated steel plate As a coating original plate, a molten Al-9Si plated steel plate having a thickness of 0.5 mm and a coated amount on one side of 40 g / m ² was prepared. A predetermined amount of chemical conversion treatment liquid having the composition shown in Table 1 (Example: No. 1-1 to No. 1-7, Comparative Example: No. 1-8 to No. 1-10) is applied to the surface of the original coating plate. It was coated with a bar coater so as to be dried at a final plate temperature of 100 ° C. for 10 seconds, and then subjected to chemical conversion treatment steel plates shown in Table 2 (Example: No. 2-1 to No. 2-11, Comparative Example: No. 2-12 to No. 2-15) were prepared. The molar ratio of fluoride to oxide and hydroxide on the surface of each chemical conversion treated steel sheet was measured by X-ray photoelectron spectroscopy (XPS; ESCA). Specifically, after Ti and Zr peaks were separated into waveforms of X—F, X—O and X—OH (X: Ti, Zr), each component was quantified to identify the ratio. The amount of fluoride measured here corresponds to the total content of fluoride of titanium and fluoride of zirconium contained in the chemical conversion film. Similarly, the measured amounts of oxides and hydroxides correspond to the total content of titanium oxides and hydroxides and zirconium oxides and hydroxides contained in the chemical conversion coating. The molar ratio of titanium and zirconium corresponds to the molar ratio of titanium oxide and hydroxide to zirconium oxide and hydroxide.

The primer coatings shown in Table 3 (Example: No. 3-1 to No. 3-6, Comparative Example: No. 3-7) were formed on the surface of the chemical conversion treated steel plates (No. 2-1 to No. 2-15). To No. 3-14) with a bar coater so as to have a predetermined film thickness, 30 seconds at a final plate temperature of 220 ° C. (No. 3-1 paint) or 60 seconds at a final plate temperature of 320 ° C. (No. 3-14) 3-2 to 14 paints) were baked to prepare primer-coated steel sheets. Next, the top coating (No. 4-1 to No. 4-4) shown in Table 4 was applied to the surface of the primer-coated steel plate with a bar coater so as to have a predetermined film thickness, and the final plate temperature was 380 ° C. for 60 seconds. The coated steel sheets shown in Table 5 (Example: No. 5-1 to No. 5-23, Comparative Example: No. 5-24 to No. 5-40) were produced by baking.

When the primer paint and the top paint were based on polyester, Flexcoat 5000 (Nippon Fine Coatings Co., Ltd.) was used. When polyamideimide is used as a base, Torlon 4000TF (Solvay Advanced Polymers Co., Ltd.) is added to a mixed solvent (N-methyl-2-pyrrolidone, methyl isobutyl ketone, xylene), and dissolved and dispersed using a ball mill. A thing was used. When polyethersulfone was used as a base, PES5003P (Sumitomo Chemical Co., Ltd.) was added to the mixed solvent and dissolved and dispersed using a ball mill. In the case of using polyphenylsulfone as a base, Radel R-5000 (Solvay Advanced Polymers Co., Ltd.) was added to the mixed solvent and dissolved and dispersed using a ball mill.

As a perfluoroalkyl vinyl ether polymer, NEOFRON AP (Daikin Industries, Ltd.) was used. Polyflon M (Daikin Industries, Ltd.) was used as the hexafluoroethylene polymer. As the tetrafluoroethylene polymer, Neophron NP (Daikin Industries, Ltd.) was used.

2. Work adhesion test A test piece (50 mm x 50 mm) was cut out from each coated steel sheet, and a work adhesion test was performed. Each test piece was subjected to 180-degree contact bending (inner R: 1 mm). After a cellophane tape was applied to the bending portion of each test piece, the tape was peeled off perpendicularly to the bending ridgeline, and the residual ratio of the coating film was measured to evaluate the work adhesion. When the residual rate of the coating film is 100%, “◎”, when it is 90% or more and less than 100%, “◯”, when it is 80% or more and less than 90%, “△”, when it is 50% or more and less than 80% Was evaluated as “▲”, and the case of less than 50% was evaluated as “x”.

3. Water resistance test A test piece (50 mm x 50 mm) was cut out from each coated steel sheet and subjected to a water resistance test. After each test piece was immersed in hot water of 95 ° C. or higher for 120 hours, a lattice-like cut was made in the coating so that 100 squares of 1 mm square could be formed. After applying a cellophane tape to the part of each test piece where the cut was made, the tape was peeled off perpendicularly to the surface of the test piece, the remaining rate of the coating was measured, and the water resistance was evaluated. When the residual rate of the coating film is 100%, “◎”, when it is 90% or more and less than 100%, “◯”, when it is 80% or more and less than 90%, “△”, when it is 50% or more and less than 80% Was evaluated as “▲”, and the case of less than 50% was evaluated as “x”.

4). Alkali Resistance Test A test piece (50 mm × 50 mm) was cut out from each coated steel sheet and a water resistance test was performed. Each test piece was immersed in an aqueous NaOH solution (pH 14) of 95 ° C. or higher, and the time for the occurrence of coating swelling was measured to evaluate alkali resistance. The case where the film swelling occurs is “◎” when the time is 120 hours or more, “◯” when the time is 80 hours or more and less than 120 hours, “△” when the time is 24 hours or more and less than 80 hours, 2 hours or more and 24 hours The case of less than “▲” and the case of less than 2 hours were evaluated as “x”.

5. Corrosion resistance test A test piece (150 mm x 70 mm) was cut out from each coated steel sheet and subjected to a corrosion resistance test. The upper and lower ends of each test piece were sealed with polyester tape, and a cross-cut was made in the center, followed by a salt spray test (5% NaCl, 35 ° C., 500 hours). After the test, the maximum bulge piece width of the left and right ends of each test piece and the maximum bulge piece width of the crosscut portion were measured to evaluate the corrosion resistance. “◎” if the maximum blister width is less than 0.5 mm, “◯” if it is 0.5 mm or more and less than 1 mm, “Δ” if it is 1 mm or more and less than 2 mm, and “▲” if it is 2 mm or more and less than 3 mm. The case of 3 mm or more was evaluated as “x”.

6). Analysis result Table 6 is a table | surface which shows the analysis result of each coated steel plate. For each coated steel sheet, the lowest evaluation among the evaluation results of the work adhesion test, the water resistance test, the alkali resistance test, and the corrosion resistance test was defined as the “total evaluation” of the coated steel sheet.

As shown in Table 6, the coated steel sheets of the present invention (coated steel sheets No. 5-1 to No. 5-23) showed good results in all of the processed part adhesion, water resistance, alkali resistance and corrosion resistance. It was.

In contrast, the coated steel sheet of No. 5-35, in which the chemical conversion film does not contain titanium oxide and hydroxide, was inferior in the corrosion resistance of the cross-cut portion. This is considered because the barrier effect by the oxide and hydroxide of titanium could not be exhibited. On the other hand, the coated steel sheet of No. 5-34, in which the chemical conversion coating did not contain zirconium oxide and hydroxide, was inferior in corrosion resistance at the end face. This is considered to be because the effect of improving the coating film cross-linking effect and coating film adhesion by zirconium oxide and hydroxide could not be exhibited. Further, the coated steel sheets of No. 5-37 and No. 5-38, in which the chemical conversion coating film did not contain titanium fluoride and zirconium fluoride, had inferior corrosion resistance at the crosscut portion. This is presumably because the self-healing effect by fluorine ions could not be exhibited.

In addition, the coated steel sheet No. 5-29 with a low zirconium phosphate content in the primer coating film was inferior in corrosion resistance. This is presumably because the corrosion resistance by zirconium phosphate could not be exhibited. On the other hand, the coated steel sheet No. 5-27 having a high zirconium phosphate content was inferior in alkali resistance. This is thought to be because the elution amount of zirconium phosphate was large and the primer coating became porous. In addition, the coated steel sheet No. 5-30 in which zinc phosphate was blended instead of magnesium phosphate and zirconium phosphate had poor alkali resistance. This is probably because elution of zinc phosphate could not be suppressed and the primer coating became porous.

In addition, the coated steel plate No. 5-28, which has a low barium sulfate content in the primer coating, was inferior in alkali resistance. Similarly, the coated steel sheet No. 5-31 in which barium sulfate was not blended in the primer coating film was inferior in alkali resistance. This is presumably because the elution of magnesium phosphate and zirconium phosphate could not be sufficiently suppressed, and the primer coating became porous. On the other hand, the coated steel sheet No. 5-26 with a high barium sulfate content was inferior in water resistance. This is thought to be because the primer coating became porous due to an excess amount of barium sulfate.

In addition, the coated steel plate No. 5-24, which has a small total content of pigment A and pigment B in the primer coating film, was inferior in corrosion resistance. This is presumably because the ratio of the pigment to the organic resin was small, and sufficient corrosion resistance could not be imparted. On the other hand, the coated steel sheets of No. 5-25, No. 5-36 and No. 5-39 having a large total content of pigment A and pigment B in the primer coating film were inferior in water resistance. This is probably because the primer coating became porous due to an excessive amount of pigment.

Further, the coated steel sheet of No. 5-40 in which the chemical conversion film was not formed was inferior in all of the adhesion to the processed part, water resistance, alkali resistance and corrosion resistance. Similarly, the coated steel sheet of No. 5-32 in which the primer coating film was not formed was inferior in all of the processed part adhesion, water resistance, alkali resistance and corrosion resistance. Further, the coated steel sheet No. 5-33 in which the top coating film was not formed was inferior in corrosion resistance.

From the above results, it can be seen that the coated steel sheet of the present invention is excellent in corrosion resistance, water resistance and alkali resistance.

[Example 2]
In Example 2, it shows that the process part corrosion resistance of a coated steel plate can also be improved by annealing the coating layer of a coating original plate.

1. Preparation of coated steel sheets The following two types of molten Al-9Si plated steel sheets were prepared as the coating original sheets. The coating original plate A and the coating original plate B are different only in that an annealing treatment is performed after the plating layer is formed.
[Paint original plate A]
-Molten Al-9Si plated steel sheet (plate thickness 0.5mm, single-sided plating adhesion 40g / m ² )
・ No annealing after forming the plating layer [Paint original B]
-Molten Al-9Si plated steel sheet (plate thickness 0.5mm, single-sided plating adhesion 40g / m ² )
-After the plating layer is formed, there is an annealing treatment (heated at 420 ° C for 30 hours)

Using the coated original plate A and the coated original plate B, coated steel plates (Examples: Nos. 7-1 to 7-2) were produced under the same conditions as the No. 5-3 coated steel plates of Example 1. The coated steel sheet of No. 7-1 using the painted original sheet A is the same as the coated steel sheet of No. 5-3 in Example 1.

Specifically, the chemical conversion solution of No. 1-1 shown in Table 1 is applied to the surface of the coating original plate so that the Ti adhesion amount becomes 1.2 mg / m ² and the Zr adhesion amount becomes 2.3 mg / m ^2. The film was applied with a bar coater and dried at a final plate temperature of 100 ° C. for 10 seconds to form a chemical conversion coating. Next, the primer coating of No. 3-3 shown in Table 3 was applied to the surface of the chemical conversion treated steel plate with a bar coater so as to have a film thickness of 4 μm, and baked at a final plate temperature of 320 ° C. for 60 seconds to form a primer coating film. Formed. Next, the top coating of No. 4-1 shown in Table 4 was applied to the surface of the primer-coated steel sheet with a bar coater so as to have a film thickness of 10 μm, and baked at a final plate temperature of 380 ° C. for 60 seconds. Coated steel plates (Examples: Nos. 7-1 and 7-2) were produced.

2. Processed part corrosion resistance test A test piece was cut out from each coated steel sheet and a processed part corrosion resistance test was performed. After performing 180 degree | times adhesion bending process, the end surface of each test piece was sealed. Each test piece after processing was subjected to a wet test at 70 ° C. for 200 hours in accordance with JIS K2246. After the test, the corrosion resistance of the processed part was evaluated by observing whether red rust was generated on the surface of each test piece.

FIG. 1 is a photograph of a processed part of a coated steel sheet after a wet test. 1A is a photograph of a processed part of No. 7-1 coated steel sheet (painted original sheet A; no annealing treatment), and FIG. 1B is a photograph of No. 7-2 coated steel sheet (painted original sheet B; with annealing treatment). It is a photograph of the processed part.

As shown in FIG. 1A, in the coated steel sheet No. 7-1 using the coating original sheet A in which the plating layer was not annealed, red rust was generated in the processed part. This is presumably because cracks occurred in the plating layer or the like during processing, and the base steel was exposed. On the other hand, as shown in FIG. 1B, red rust did not occur at all in the No. 7-2 coated steel sheet using the coated original sheet B with the plated layer annealed. This is considered to be because the plating layer was annealed and softened to suppress cracks in the plating layer during processing.

From the above results, it can be seen that the coated steel sheet of the present invention can also improve the corrosion resistance of the processed part by using a coated original sheet having a plated layer annealed.

[Example 3]
In Example 3, it is shown that the heat reflection characteristics of the coated steel sheet can be improved by adding a near-infrared reflective pigment to the top coating film.

1. Preparation of coated steel plate As a coating original plate, a molten Al-9Si plated steel plate having a thickness of 0.5 mm and a coated amount on one side of 40 g / m ² was prepared.

No. 5 of Example 1 except that the top paint of No. 8-1 or No. 8-2 shown in Table 8 is used instead of the top paint of No. 4-1 shown in Table 4. A coated steel sheet (Example: Nos. 9-1 to 9-2) was produced under the same conditions as those of the coated steel sheet No. -3. The top paint of No. 4-1 and the top paint of Nos. 8-1 to 8-2 differ in whether or not black pigments are blended. Further, the top paint of No. 8-1 and the top paint of No. 8-2 differ in whether or not the blended black pigment is a near-infrared reflective (heat reflective) black pigment.

Specifically, the chemical conversion solution of No. 1-1 shown in Table 1 is applied to the surface of the coating original plate so that the Ti adhesion amount becomes 1.2 mg / m ² and the Zr adhesion amount becomes 2.3 mg / m ^2. The film was applied with a bar coater and dried at a final plate temperature of 100 ° C. for 10 seconds to form a chemical conversion coating. Next, the primer coating of No. 3-3 shown in Table 3 was applied to the surface of the chemical conversion treated steel plate with a bar coater so as to have a film thickness of 4 μm, and baked at a final plate temperature of 320 ° C. for 60 seconds to form a primer coating film. Formed. Next, the top coating of No. 8-1 or No. 8-2 shown in Table 8 was applied to the surface of the primer coated steel plate with a bar coater to a film thickness of 10 μm, and baked at a final plate temperature of 380 ° C. for 60 seconds. The coated steel sheets shown in Table 9 (Examples: Nos. 9-1 and 9-2) were prepared.

42-706A (Dongguan Material Technology Co., Ltd.) was used as the iron / chromium near-infrared reflective pigment blended in the No. 8-1 top paint. MA-100 (Mitsubishi Carbon Co., Ltd.) was used as the carbon black pigment blended in the No. 8-2 top paint.

2. Heat Reflection Test A heat reflectivity test was performed on each coated steel sheet (No. 9-1 to 9-2). A heating chamber (width 34 cm × depth 36 cm × height 23 cm) was prepared using the coated steel plate of No. 9-1 or No. 9-2 as a wall material, and a glass ceramic plate was installed in the heating chamber. The heating chamber was heated by infrared using a glass ceramic plate, and the temperature of the wall surface of the heating chamber was measured over time. Table 10 shows the measurement results of the ceiling surface temperature of the heating chamber.

As shown in Table 10, in the No. 9-2 coated steel sheet in which a general black pigment (carbon black) was blended in the top coating, the temperature of the ceiling surface exceeded 3 minutes after the start of heating. It exceeded 100 ° C. and increased to 134.2 ° C. after 5 minutes. This is considered because the black pigment absorbed near infrared rays. On the other hand, in the coated steel sheet of No. 9-1 in which a black near-infrared reflective pigment is blended in the top coating, the ceiling surface temperature does not reach 80 ° C. even after 5 minutes, and has excellent heat reflection characteristics. Had. Comparing the rate of temperature rise on the ceiling surface, the rate of temperature rise on the ceiling surface of No. 9-1 coated steel sheet containing a black near-infrared reflective pigment is the same as that of No. 9 containing a general black pigment. -2 was about 50% of the rate of temperature rise on the ceiling surface of the coated steel sheet.

From the above results, it can be seen that the coated steel sheet of the present invention can improve the heat reflection characteristics of the coated steel sheet by adding a near-infrared reflective pigment to the top coating film.

This application claims priority based on Japanese Patent Application No. 2010-149013 filed on June 30, 2010. The contents described in the application specification and the drawings are all incorporated herein.

Since the coated steel sheet of the present invention is excellent in heat resistance, corrosion resistance, water resistance and alkali resistance, it is useful, for example, as a precoated steel sheet for members in a heating chamber of a superheated cooker having a steam supply function.

Claims

A coated steel plate having a steel plate, a chemical conversion coating formed on the surface of the steel plate, a primer coating formed on the surface of the chemical conversion coating, and a top coating formed on the surface of the primer coating. There,
The chemical conversion coating film includes a fluoride of titanium or a fluoride of zirconium, an oxide of titanium or a hydroxide of titanium, and an oxide of zirconium or a hydroxide of zirconium.
The primer coating film includes an organic resin, a pigment A composed of one or two compounds selected from the group consisting of magnesium phosphate and zirconium phosphate, and a pigment B composed of barium sulfate,
The content of the pigment A and the content of the pigment B in the primer coating film are 20 to 100 parts by mass with respect to 100 parts by mass of the organic resin, respectively.
The total content of the pigment A and the pigment B in the primer coating film is 40 to 160 parts by mass with respect to 100 parts by mass of the organic resin.
Painted steel sheet.
In the chemical conversion film, the molar ratio of the total content of the oxide and hydroxide of titanium and the oxide and hydroxide of zirconium to the total content of fluoride of titanium and fluoride of zirconium is The coated steel sheet according to claim 1, which is in the range of 0.2 to 3.
In the chemical conversion film, the molar ratio of the total content of the zirconium oxide and hydroxide to the total content of the titanium oxide and hydroxide is in the range of 0.4 to 2. The coated steel sheet according to claim 1.
The coated steel sheet according to claim 1, wherein the organic resin includes one or more kinds of resins selected from the group consisting of a polyethersulfone resin, a polyphenylsulfide resin, a polyimide resin, and a polyamideimide resin.