Coated and plated steel sheets, and painted and plated steel sheets

Abstract

To provide a coated plated steel plate highly capable of self-repairing scratches on a resin layer, and a painted plated steel plate highly capable of self-repairing scratches on a coating layer.SOLUTION: A coated plated steel plate comprises a steel plate, a plated layer, and a resin layer, in the stated order. The plated layer is a plated layer comprising Zn. The resin layer comprises a film-formative resin, and a polycaprolactone capsule that comprises a capsule composed of a polycaprolactone thermoplastic resin, the capsule internally containing a water-insoluble rust inhibitor. There is also provided a painted plated steel plate comprising a coating layer on the surface of the coated plated steel plate.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a coated galvanized steel sheet, and more particularly to a coated galvanized steel sheet provided with a resin layer having self-healing properties. The present invention also relates to a painted galvanized steel sheet provided with a coating film on the surface of the coated galvanized steel sheet.

Background Art

[0002] Hot-dip galvanized steel sheets have been used for a long time in applications such as building materials, automotive materials, and home appliance materials. In recent years, steel sheets having a ternary plating layer containing Al, Zn, and Mg have been proposed (see Patent Document 1).

[0003] On the other hand, a resin film subjected to a hard coat treatment has been used as a protective layer for protecting the surface of an automobile body or the like. However, once the surface of the resin film is damaged, it is impossible to restore it, and thus a technique for imparting self-healing properties to the resin film has been studied.

[0004] For example, Patent Document 2 discloses that a polymer coating having self-healing properties can be formed by dispersing polycaprolactone (hereinafter also referred to as PCL in the specification) thermoplastic resin particles in a matrix of a polyurethane thermosetting resin.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the inventors have found that the technology described in Patent Document 2 may not have sufficient self-healing capabilities. The object of the present invention is to provide a coated plated steel sheet having a coating layer with excellent self-healing properties. [Means for solving the problem]

[0007] The inventors of the present invention conducted extensive research to solve the above problems and discovered that a coating with excellent self-healing properties can be formed by incorporating a hydrophobic rust inhibitor inside a capsule made of PCL thermoplastic resin. By incorporating the PCL capsule into a resin layer, the inventors completed the present invention. The present invention includes the following:

[0008] [1] A coated plated steel sheet comprising a steel sheet, a plating layer, and a resin layer in this order, The aforementioned plating layer is a plating layer containing Zn, The aforementioned resin layer comprises a film-forming resin and polycaprolactone capsules containing a water-poorly soluble rust inhibitor inside capsules made of polycaprolactone thermoplastic resin, wherein the coated plated steel sheet is provided. [2] The coated plated steel sheet of [1], wherein the plating layer containing Zn is a hot-dip galvanized layer or a ternary plating layer containing Al, Zn, and Mg. [3] The rust inhibitor comprises an azole rust inhibitor, as described in [1] or [2]. [4] The coated plated steel sheet according to [1] or [2], comprising benzotriazole as the rust inhibitor. [5] The coated plated steel sheet according to any one of [1] to [4], wherein the number average molecular weight of the polycaprolactone thermoplastic resin is 5,000 or more and 100,000 or less. [6] The coated plated steel sheet according to any one of [1] to [5], wherein the average particle size of the polycaprolactone capsules is 0.5 μm or more and 10.0 μm or less. [7] The coated plated steel sheet according to any one of [1] to [6], wherein the coating-forming resin comprises a urethane resin. A painted plated steel sheet having a coating film on the surface of a coated plated steel sheet as described in any of [8][1] to [6]. [Effects of the Invention]

[0009] The present invention makes it possible to provide coated plated steel sheets and painted plated steel sheets having a resin layer with high self-healing properties. [Brief explanation of the drawing]

[0010] [Figure 1] This is a photograph of the coating surface after an SST test on a 55% Al-Zn plated steel sheet having a resin layer containing PCL capsule 1 (photograph used as a substitute for the drawing). [Figure 2] This is a photograph of the coating surface after an SST test on a 55% Al-Zn plated steel sheet having a resin layer containing PCL capsules 2 (photograph used as a substitute for the drawing). [Figure 3] This is a photograph of the coated surface of a 55% Al-Zn plated steel sheet having a resin layer containing PCL capsules 3, after undergoing an SST test (photograph used as a substitute for the drawing). [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described in detail below. In this specification, unless otherwise specified, the descriptions of numerical ranges such as "X or more and Y or less" or "X to Y" mean a numerical range that includes the lower and upper limits which are the endpoints. When numerical ranges are described in steps, the upper and lower limits of each numerical range can be combined in any way.

[0012] One embodiment of the present invention is a coated plated steel sheet comprising a steel sheet, a plating layer, and a resin layer in that order, wherein the resin layer contains a film-forming resin and PCL capsules, thereby providing a coated plated steel sheet with a high self-healing function for scratches on the plating layer. Furthermore, by providing a coating film on the coated plated steel sheet, a painted plated steel sheet with a high self-healing function for scratches on the plating layer can be provided.

[0013] <Steel plate> In this embodiment, any known steel plate may be used as appropriate, and is not particularly limited.

[0014] <plating layer> The plating layer in this form is a plating layer containing Zn. Examples of the plating layer containing Zn include a hot-dip galvanized layer, an alloyed hot-dip galvanized layer, an electro-galvanized layer, a binary plating layer containing Al and Zn, a binary plating layer containing Zn and Ni, a ternary plating layer containing Al, Zn, and Mg, and the like. Among these, it is preferable to be selected from a hot-dip galvanized layer, a binary plating layer containing Al and Zn, and a ternary plating layer containing Al, Zn, and Mg, from the viewpoint of the self-repairing performance of the plating layer.

[0015] Hot-dip galvanizing refers to a plating layer composition in which the zinc content is 75% by mass or more, and may be 80% by mass or more. Other components include metals belonging to rare earths, metals belonging to alkaline earths, Si, Ni, Cr, and the like. The binary plating layer containing Al and Zn may be a plating layer containing these components, may consist of only these two components, or may contain other components. Other components include metals belonging to rare earths, metals belonging to alkaline earths, Si, Ni, Cr, and the like may be mentioned. The ternary plating layer containing Al, Zn, and Mg may be a plating layer containing these components, may consist of only these three components, or may contain other components. Other components include metals belonging to rare earths, metals belonging to alkaline earths, Si, Ni, Cr, and the like.

[0016] In the binary plating layer containing Al and Zn, the Al content is usually 5% by mass or more and 75% by mass or less, and from the viewpoint of corrosion resistance, it is preferably 20% by mass or more and 70% by mass or less. In the binary plating layer containing Al and Zn, the Zn content is usually 25% by mass or more and 90% by mass or less, and preferably 30% by mass or more and 80% by mass or less.

[0017] In a ternary plating layer containing Al, Zn, and Mg, the content of Al is usually 1% by mass or more and 75% by mass or less, and from the viewpoint of corrosion resistance, it is preferably 10% by mass or more and 70% by mass or less. In a ternary plating layer containing Al, Zn, and Mg, the content of Mg is usually more than 0% by mass and 6% by mass or less, and from the viewpoint of corrosion resistance, it is preferably 0.5% by mass or more and 5% by mass or less. In a ternary plating layer containing Al, Zn, and Mg, the content of Zn is other than the above components in the plating layer and is not particularly limited, and is usually 20% by mass or more and 99% by mass or less, and preferably 30% by mass or more and 70% by mass or less.

[0018] <Resin layer> The resin layer in this form includes a film-forming resin and PLC capsules containing a water-insoluble rust inhibitor. By including PLC capsules containing a water-insoluble rust inhibitor in the resin layer, a resin layer excellent in self-healing properties can be obtained. The film-forming resin is not particularly limited as long as it is a resin capable of forming a film on the surface of the plated steel sheet. Typically, (meth)acrylic resins, urethane resins, silicone resins, phenolic resins, etc. are used. Among these, it is preferable to use urethane resin from the viewpoint of corrosion resistance. In addition to the film-forming resin and PLC capsules, the resin layer may further contain one or more selected from the group consisting of polysiloxane compounds, silicates, zirconium compounds, and titanium compounds.

[0019] <PCL capsule> The PCL capsules contained in the resin layer contain a rust inhibitor inside capsules made of PCL thermoplastic resin. The PCL capsules are particles in which the PCL thermoplastic resin forms a shell and contains a rust inhibitor inside.

[0020] PCL thermoplastic resin is obtained by ring-opening polymerization of ε-caprolactone. The number-average molecular weight of PCL thermoplastic resin is not particularly limited, but is usually 1,000 or more, preferably 5,000 or more, more preferably 10,000 or more, and also usually 100,000 or less, preferably 80,000 or less, and more preferably 60,000 or less. The number-average molecular weight is measured by GPC (gel permeation column chromatography) and converted to polystyrene equivalent. Having the number-average molecular weight of PCL within the above range results in appropriate strength and high airtightness of the PCL capsule, which is preferable as it prevents leakage of the internal rust inhibitor into the chemical solution.

[0021] The average particle size of PCL capsules is not particularly limited, but is usually 0.1 μm or larger, preferably 0.5 μm or larger, and usually 10 μm or smaller, preferably 8 μm or smaller, and more preferably The particle size is 5 μm or less, and particularly preferably 2 μm or less. The average particle size can be calculated by measuring the particle size of 20 or more arbitrarily selected particles during observation with an electron microscope and taking the average. In the case of non-spherical particles, the longest axis is used as the particle size. Having the average particle size of PCL capsules within the above range is preferable because it increases the probability of PCL microcapsule particles being present around the damaged area in the coating, making it easier for the self-healing power of PCL microcapsules to be exerted.

[0022] The rust inhibitor contained inside the PCL capsule is not particularly limited, and examples include water-insoluble rust inhibitors such as amine-based rust inhibitors, azole-based rust inhibitors, nitrite-based rust inhibitors, and ammonium-based rust inhibitors. Water-insoluble means that the dissolution rate is 2g or less per 100g of water at 25°C.

[0023] As a water-insoluble rust inhibitor, known agents with solubility within the above range can be used, but azole-based rust inhibitors are preferred. Examples of azole-based rust inhibitors include azoles such as imidazole, pyrazole, oxazole, isoxazole, thiazole, isothiazole, serenazole, 1,2,3-triazole, 1,2,4-triazole, 1,2,5-oxadiazole, 1,3,4-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole, 1,3,4-thiadiazole, tetrazole, 1,2,3,4-thiatriazole; derivatives thereof; amine salts thereof; and metal salts thereof. Of these, benzotriazole (BTA) is more preferred.

[0024] The amount of rust inhibitor contained in the PCL capsule is not particularly limited, but is usually 1% by mass or more, preferably 3% by mass or more, more preferably 5% by mass or more, and is also usually 30% by mass or less, preferably 20% by mass or less, and more preferably 15% by mass or less.

[0025] The PCL capsules may contain other substances, as long as they do not inhibit the effects of the present invention. Examples of other substances include surfactants, antioxidants, and defoaming agents.

[0026] PCL capsules can be manufactured by known methods. Specifically, the following methods can be used. Prepare a PCL solution by dissolving PCL and a rust inhibitor in an organic solvent, and an aqueous resin solution by dissolving a resin. Mix the PCL solution and the aqueous resin solution, stir, and then remove the organic solvent to obtain a PLC capsule aqueous dispersion. The PLC capsule aqueous dispersion can be incorporated into a film-forming resin or coating resin to form a film-forming resin composition.

[0027] The organic solvent is not particularly limited as long as it can dissolve PCL, and examples include ketone-based organic solvents, ether-based organic solvents, and hydrocarbon-based organic solvents, with dichloromethane being a typical example. The resin is not particularly limited and examples include urea resin, melamine resin, polyvinyl alcohol (PVA), polyacrylamide, and carboxymethylcellulose, with PVA being typically used. When PVA is used, its weight-average molecular weight (Mw) is not particularly limited, but is usually 10,000 or more, preferably 50,000 or more, and usually 300,000 or less, preferably 150,000 or less. The temperature at which the PCL solution and the resin aqueous solution are stirred is not particularly limited, but it is preferably at room temperature (25°C).

[0028] The PCL capsule content in the resin layer is typically 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and typically 30% by mass or less, preferably 20% by mass or less, and more preferably 10% by mass or less, per 100 parts by mass of the coating resin. .

[0029] <Manufacturing method for coated steel sheets> This form of coated plated steel sheet can be manufactured by forming a plating layer on a steel sheet by performing a plating treatment, and then forming a resin layer on top of the plating layer.

[0030] One method for plating steel sheets is to immerse them in a molten plating bath, remove them, and dry them. Alternatively, plating may be performed by vapor deposition or by electrodeposition.

[0031] Before forming the resin layer on the plating layer, the surface of the plating layer may be degreased or pickled, and after each treatment, it may be rinsed with water, and after rinsing with water, it may be dried. Furthermore, chemical conversion treatment may be performed after degreasing or pickling, or chemical conversion treatment may be performed without degreasing or pickling. The type of chemical conversion treatment is not particularly limited, and one or more types of treatments such as chromate conversion treatment, zinc phosphate conversion treatment, bismuth substitution plating, iron phosphate conversion treatment, zirconium conversion treatment, titanium conversion treatment, and hafnium conversion treatment may be performed.

[0032] The resin layer can be formed by preparing a resin layer-forming composition and treating a plated steel sheet with the composition. The treatment of the plated steel sheet with the composition involves applying the composition to the surface of the plated steel sheet or onto the surface using known treatment methods such as roll coating, spraying, dipping, electrolysis, or air knife. After application, the resin layer can be obtained by curing. The curing method is not particularly limited; known methods can be used, and curing should be performed using a method suitable for the resin being used. The composition for forming the resin layer can be prepared by adding the aqueous film-forming resin and PCL capsules to pure water and dispersing them in the water when using an aqueous film-forming resin. The composition may also contain other components as needed, such as inorganic pigments, crosslinking agents, and surfactants.

[0033] Furthermore, a coating film may be formed on the surface of the coated steel sheet. Examples of known coatings for forming the coating film include oil-based paints, various resin paints, rust-inhibiting paints, antifouling paints, powder coatings, electrodeposition paints, water-based paints, and solvent-based paints. A coating can be formed on a coated steel sheet by treating it with paint. The treatment of a coated steel sheet with paint involves applying the paint to the surface of the sheet using known methods such as rolling, electrodeposition (e.g., cationic electrodeposition, anionic electrodeposition, etc.), spray painting, hot spray painting, airless spray painting, electrostatic (powder) coating, roller coating, curtain flow coating, brush painting, bar coating, and fluid immersion. The treatment of a coated steel sheet with paint may involve one treatment or two or more treatments using the same or different types of paints. The thickness of the coating film is not particularly limited, and is usually within the range of 10 μm to 100 μm, but is not limited to this range.

[0034] After coating and drying, a coating film can be obtained. Examples of the drying method include natural drying, vacuum drying, convective heat drying (e.g., natural convection heat drying, forced convection heat drying), radiation drying (e.g., near-infrared drying, far-infrared drying), ultraviolet curing drying, electron beam curing drying, vapor curing, baking drying, and other drying methods. These drying methods may be carried out individually or in combination of two or more.

Examples

[0035] Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples.

[0036] <Plated steel sheet> As the plated steel sheet, a 55% Al-Zn plated steel sheet was prepared.

[0037] <Preparation of PCL Capsule 1> Using PCL thermoplastic resin (number average molecular weight 45,000) and BTA (manufactured by Merck), PCL capsules were prepared according to the following procedure. 5 g of PCL and 0.5 g of BTA were put into 15 g of dichloromethane, and PCL and BTA were dissolved in dichloromethane. Next, an aqueous solution prepared by adding 1 g of PVA (Mw: 85,000 - 120,000) to 50 g of water and dissolving it was put into the above dichloromethane and stirred at room temperature for 1 hour. Thereafter, it was heated to 50 °C to remove dichloromethane, and an aqueous dispersion of PCL Capsule 1 with a particle size of 1.0 - 5.0 μm containing about 9% by mass of BTA was obtained.

[0038] <Preparation of PCL Capsule 2> Using PCL thermoplastic resin (number average molecular weight 10,000) and BTA, an aqueous dispersion of PCL Capsule 2 with a particle size of 0.8 - 2.0 μm containing 1.6% by mass of BTA was obtained in the same procedure as PCL Capsule 1.

[0039] <Preparation of PCL Capsule 3> Aqueous dispersions of PCL capsule 3 were obtained using the same procedure as for PCL capsule 1, except that BTA was not used.

[0040] <Preparation of resin layer forming composition and preparation of coated plated steel sheet> 55% Al-Zn plated steel sheets (coated plated steel sheets 1-3) were immersed in a water-based resin layer-forming composition prepared by blending 5 parts by mass of PCL capsules 1-3 with 100 parts by mass (solid content) of urethane resin (Hydran HW-350, manufactured by DIC Corporation), and after being removed and dried, coated plated steel sheets 1-3 were obtained.

[0041] The obtained coated steel sheets 1 to 3 were subjected to a 120-hour neutral salt spray test according to the salt spray test method (JIS-Z-2371:2015), and the white rust that formed on the surface of the coated steel sheets was observed under a microscope. The results for coated steel sheets 1 to 3 are shown in Figures 1 to 3.

[0042] <Preparation of painted and plated steel sheets> The above coated and plated steel sheets 1 to 3 were coated with paint (V-Knit #500, manufactured by Dainippon Paint Co., Ltd.) using a bar coating method to achieve a dry film thickness of 20 μm, and then baked at a PMT (maximum temperature achievable by the material) of 220°C. Painted and plated steel sheets 1 to 3 were obtained.

[0043] The obtained coated and plated steel sheets were subjected to a 240-hour neutral salt spray test according to the salt spray test method (JIS-Z-2371:2015), and the width of the rust in the coating film (maximum rust width on one side) from the cross-cut portion of the steel sheet was measured. The results are shown in Table 1. The evaluation criteria are as follows: A: Less than 0.1 mm B: 0.1mm or more and less than 0.3mm C: 0.3mm or more

[0044] [Table 1]

[0045] The results of the examples show that by providing a resin layer containing PCL capsules to a plated steel sheet having a Zn-containing plating, it is possible to provide a painted plated steel sheet with a high self-healing function for scratches on the coating. It will be obvious to those skilled in the art that the same paint-plated steel sheet with a high self-healing function for scratches on the coating will be obtained even if the Zn-containing plating is not limited to plating containing Al and Zn, but also includes a binary plating layer containing Zn and Ni, a ternary plating layer containing Al, Zn, and Mg, etc.

Claims

1. A coated plated steel sheet comprising a steel sheet, a plating layer, and a resin layer in this order, The aforementioned plating layer is a plating layer containing Zn, The resin layer comprises a film-forming resin and polycaprolactone capsules containing a water-poorly soluble rust inhibitor inside capsules made of polycaprolactone thermoplastic resin. The aforementioned coating-forming resin is a coated plated steel sheet containing a urethane resin.

2. The coated plated steel sheet according to claim 1, wherein the plating layer containing Zn is a hot-dip galvanized layer or a ternary plating layer containing Al, Zn, and Mg.

3. The coated plated steel sheet according to claim 1 or 2, wherein the rust inhibitor comprises an azole-based rust inhibitor.

4. The coated plated steel sheet according to claim 1 or 2, wherein the rust inhibitor comprises benzotriazole.

5. The coated plated steel sheet according to any one of claims 1 to 4, wherein the number average molecular weight of the polycaprolactone thermoplastic resin is 5,000 or more and 100,000 or less.

6. The coated plated steel sheet according to any one of claims 1 to 5, wherein the average particle size of the polycaprolactone capsules is 0.5 μm or more and 10.0 μm or less.

7. A coated plated steel sheet having a coating film on the surface of a coated plated steel sheet according to any one of claims 1 to 6.

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