JP2014177002A - Coated steel plate and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated steel plate that can be produced by a two-coat two-bake method, has corrosion resistance, and exhibits a black color of sufficiently low brightness and high glossiness while a rust-preventive pigment is blended in an undercoat film.SOLUTION: A coated steel plate 10 has a steel plate 11, an undercoating film 13 and a topcoating film 14 in this order. The undercoating film 13 comprises a resin 15, a black pigment 16 and a rust-preventive pigment 17. The difference obtained by subtracting D50 of the rust-preventive pigment 17 from the film thickness of the undercoating film 13 is 0.5 μm or more. The content of the rust-preventive pigment 17 is 50 pts.mass or less based on 100 pts.mass of the resin 15 and the refractive index of the rust-preventive pigment 17 is 2.1 or less. The refractive index of the topcoating film 14 is 1.45 or more and the haze of the topcoating film 14 is 7% or less. The coated steel plate 10 has corrosion resistance and exhibits high glossiness and a black color such that it has an L value of 10 or less in Hunter Lab color system and a 60° glossiness of 80% or more.

Description

  The present invention relates to a black coated steel sheet having high gloss and a method for producing the same.

  In the home appliance field or the like, a “luxury” feeling may be imparted to a product by imparting gloss to the product. In particular, the glossy black appearance expressed as piano black is very popular. This “glossy black” is generally preferable from the viewpoint of improving the quality of the product, as the gloss is higher and the apparent black is stronger (for example, the brightness is lower).

  As a method for producing a high-gloss colored coated steel sheet, a method of forming an undercoat coating film containing a resin, an antirust pigment and a coloring pigment on a steel sheet, and a clear coating film thereon is known. For example, carbon black is known as a color pigment (see, for example, Patent Document 1). According to this manufacturing method, a high-gloss colored coated steel sheet can be obtained by a two-coat two-bake manufacturing method in which the coating material is applied twice and the applied coating material is baked. The color of this coated steel sheet is determined by the color of the undercoat film.

JP 2004-358743 A

  On the other hand, various rust preventive pigments such as chromium, molybdate, phosphate, and vanadium are generally known as rust preventive pigments. These all have white or yellow and a relatively high brightness color. In the production method described above, in order to produce a high-gloss black coated steel sheet using a black pigment such as carbon black as a color pigment, an undercoat coating film in which a black pigment and an antirust pigment are dispersed is formed. The lightness of the undercoat film is as high as it contains a rust preventive pigment, and is generally too high for the undercoat film to exhibit the desired color, ie, black. Therefore, even if a transparent topcoat film is formed on the undercoat film, the resulting coated steel sheet may exhibit a black color that feels whitish due to the rust preventive pigment. Such a coated steel sheet that exhibits a whitish color even if it is a color that is recognized as black cannot be applied to a use that imparts a high-class feeling to a product even if it exhibits a high gloss.

  The present invention has been made in view of the above points, and can be produced by 2 coats and 2 bake, has corrosion resistance, and is sufficiently provided even though a rust preventive pigment is blended in the undercoat film. An object of the present invention is to provide a coated steel sheet exhibiting low brightness black and high gloss.

  When forming a transparent top coat film on the surface of an undercoat film containing a black pigment and an anti-rust pigment, the present inventors have a lightness of the entire undercoat film depending on the composition of the undercoat film. The present invention was completed by finding that a high-gloss black coated steel sheet that has a brightness lower than the brightness and does not feel the brightness of the rust-preventing pigment and a high gloss can be obtained.

That is, this invention relates to the following coated steel plates.
[1] A steel plate and a coating film formed on the steel plate, wherein the coating film is an undercoat coating film formed on the steel plate and an overcoat formed on the undercoat coating film. The undercoat coating film contains a resin, a black pigment, and a rust preventive pigment, and the difference obtained by subtracting the median diameter of the rust preventive pigment from the film thickness of the undercoat paint coat is 0.5 μm or more. The refractive index of the rust preventive pigment is 2.1 or less, the refractive index of the top coat film is 1.45 or more, and the haze value of the top coat film is 7% or less, A coated steel sheet having a L value of 10 or less according to Hunter's Lab method and a glossiness of 60 ° of 80% or more.
[2] The coated steel sheet according to [1], wherein the content of the rust preventive pigment is 5 to 50 parts by mass with respect to 100 parts by mass of the resin.
[3] The coated steel sheet according to [1] or [2], wherein the film thickness of the top coat film is 3 μm or more.
[4] The coated steel sheet according to any one of [1] to [3], wherein the arithmetic average roughness Ra of the surface of the steel sheet is 0.5 μm or less.
[5] The coated steel sheet according to any one of [1] to [4], wherein the steel sheet is a plated steel sheet.

Moreover, this invention relates to the manufacturing method of the following coated steel plates.
[6] In the method for producing a coated steel sheet having the undercoating film and the overcoating film in this order on the steel sheet, and having the steel sheet, the undercoating film, and the overcoating film, a resin, A step of forming the undercoat film containing a black pigment and a rust preventive pigment and having an L value of 30 or less in Hunter's Lab method, and a refractive index of 1.45 or more on the undercoat film; And a coated steel sheet having a Hunter L value of 10 or less and a 60 ° gloss value of 80% or more, comprising a step of forming the top coat film having a haze value of 7% or less. How to manufacture.
[7] The method for producing a coated steel sheet according to [6], wherein the film thickness of the top coat film is 3 μm or more.
[8] The method for producing a coated steel sheet according to [6] or [7], wherein the arithmetic average roughness R of the surface of the steel sheet is 0.5 μm or less.
[9] The method for producing a coated steel sheet according to any one of [6] to [8], wherein the steel sheet is a plated steel sheet.

  According to the present invention, a coating film having a lightness lower than the lightness of an undercoat coating film containing both a black pigment and an antirust pigment can be obtained. Therefore, a coated steel sheet that can be manufactured in two coats and two bake, has corrosion resistance, and exhibits sufficiently low blackness and high gloss despite having a rust preventive pigment blended in the undercoat film. can do.

It is a figure which shows typically the structure of the coated steel plate of one Embodiment of this invention. It is a figure which shows typically a mode that the incident light to the coating film of a coated steel plate reflects with the antirust pigment in undercoat. FIG. 3A is a diagram schematically showing a state in which light incident on the surface of the undercoat on the steel plate is reflected by the surface, and FIG. 3B is diffused on the surface of the undercoat with the antirust pigment dispersed therein. FIG. 3C is a diagram schematically showing how the diffusely reflected light on the surface of the undercoat coating film in which the anticorrosive pigment is dispersed is attenuated by the top coat film. .

  The coated steel plate which concerns on one Embodiment of this invention is shown in FIG. As shown in FIG. 1, the coated steel plate 10 includes a steel plate 11 and a coating film 12 formed on the steel plate 11. The coating film 12 includes an undercoat coating film 13 and a topcoat coating film 14.

  The type of the steel plate 11 is not particularly limited, and is appropriately selected from known steel plates according to the application of the coated steel plate 10. The steel plate 11 is preferably a plated steel plate from the viewpoint of providing the coated steel plate 10 having high corrosion resistance at a lower cost. A well-known thing can be used for a plating steel plate, The example includes a zinc plating steel plate, a Zn-Al alloy plating steel plate, a Zn-Al-Mg alloy plating steel plate, and an aluminum plating steel plate. The steel plate 11 may be a steel plate other than a plated steel plate, such as a cold-rolled steel plate or a stainless steel plate (including austenitic, martensitic, ferritic, and ferrite / martensite two-phase systems). The thickness of the steel plate 11 is selected according to the use of the coated steel plate 10 and is, for example, 0.1 to 2 mm.

  The arithmetic average roughness Ra of the surface of the steel plate 11 is preferably 0.5 μm or less from the viewpoint of improving the sharpness of the coating film 12. When Ra is larger than 0.5 μm, the sharpness of the coating film 12 represented by the D / I value may be lowered. Ra of the steel plate 11 can be adjusted by a normal process for adjusting the surface roughness of the steel plate, such as temper rolling (skin pass rolling), cold rolling, and polishing with a hub.

From the viewpoint of improving the coating film adhesion and corrosion resistance of the coated steel sheet 10, a chemical conversion treatment film may be formed on the surface of the steel sheet 11. The type of chemical conversion treatment is not particularly limited. Examples of the chemical conversion treatment include chromate treatment, chromium-free treatment, and phosphate treatment. The adhesion amount of a chemical conversion treatment film is not specifically limited, For example, it determines suitably in the range effective for the improvement of the coating-film adhesiveness in the coated steel plate 10, and suppression of corrosion. For example, in the case of a chromate film, the adhesion amount of the film may be adjusted so that the total Cr conversion adhesion amount is 5 to 100 mg / m ² . In the case of a chromium-free coating, the coating amount of the coating is 10 to 500 mg / m ^{2 in} terms of total Ti and Mo conversion in the case of a Ti-Mo composite coating, or in terms of fluorine or total metal elements in the case of a fluoroacid-based coating. What is necessary is just to each adjust so that the adhesion amount may become in the range of 3-100 mg / m < ² >. Moreover, in the case of a phosphate film, the adhesion amount of the film may be adjusted so that the phosphorus conversion adhesion amount is 0.1 to 5 g / m ² .

  The chemical conversion film can be formed by a known method. For example, the chemical conversion solution may be applied to the surface of the metal plate by a roll coating method, a spin coating method, a spray method, or the like, and dried without being washed with water. 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. at the ultimate temperature of the steel plate 11, and the drying time is preferably in the range of 2 to 10 seconds.

  In the coating film 12, the undercoat coating film 13 is in direct contact with the topcoat coating film 14. The undercoat coating film 13 contains a resin 15, a black pigment 16 and a rust preventive pigment 17.

  As the resin 15, a resin usually used for a resin for an undercoat film of a coated steel plate is used. Examples of the resin 15 include resins having a hydroxy group, such as polyester, epoxy resin, and acrylic resin. The resin 15 may be crosslinked by a crosslinking agent. The cross-linking agent is, for example, a compound having two or more functional groups that can be bonded to a specific site (such as a functional group) of the resin 15. Examples of the cross-linking agent include amino resins such as melamine, urea and benzoguanamine or polyisocyanate compounds. The usage-amount of a crosslinking agent is 5-25 mass parts with respect to 100 mass parts resin 15, for example.

  As the black pigment 16, a black pigment usually used for a black pigment for a coated steel sheet can be used. Examples of the black pigment 16 include metal black or non-metal powders such as carbon black, graphite, iron and chromium, and composite powders of metal oxides. Although the particle size of the black pigment 16 is not particularly limited, for example, the median diameter (D50) is 0.01 to 5 μm. The particle size of the black pigment 16 can be adjusted by, for example, pulverization, classification, or mixing of classified products. The content of the black pigment 16 in the undercoat film 13 may be an amount that satisfies the L value of the coated steel sheet described later. For example, if the black pigment 16 is carbon black, the content is 100 parts by mass. 1 to 20 parts by mass relative to the resin 15.

  As the rust preventive pigment 17, among the rust preventive pigments usually used for rust preventive pigments for coated steel sheets, those satisfying at least the following refractive index and median diameter (D50) requirements can be used.

  The refractive index of the rust preventive pigment 17 is 2.1 or less. When the refractive index of the rust preventive pigment 17 is larger than 2.1, the L value of the coating film 12 is high, and whiteness due to the rust preventive pigment is felt in the appearance of the coating film 12, so Appearance may not be obtained. The refractive index of the rust preventive pigment 17 is preferably 2.0 or less and more preferably 1.6 or less from the viewpoint of suppressing whiteness in the appearance of the coating film 12 by the rust preventive pigment 17. The refractive index of the rust preventive pigment 17 is determined according to the method B in JIS K7142. Examples of the rust preventive pigment 17 include various known rust preventive pigments such as chromium, molybdate, phosphate, and vanadium, and more specifically, zinc phosphate and phosphorous acid. Zinc, magnesium zinc phosphate, magnesium phosphate, magnesium phosphite, silica, calcium ion exchange silica, calcium silicate, zirconium phosphate, aluminum trihydrogen phosphate, zinc oxide, zinc, zinc phosphomolybdate, barium metaborate, Strontium chromate, vanadium oxide, ammonium metavanadate, potassium metavanadate and the like are included.

  The difference obtained by subtracting the median diameter of the rust preventive pigment 17 from the film thickness of the undercoat coating film 13 is 0.5 μm or more. Here, the “median diameter” is a diameter (a particle diameter at which the integrated value is 50%) in which the larger side and the smaller side are equal when the powder is divided into two from a certain particle diameter. Hereinafter, it is also referred to as “D50”. When the above difference is 0.5 μm or more, the diffuse reflected light reflected on the surface of the rust preventive pigment 14 is, as indicated by “A” in FIG. Black). When the above difference is less than 0.5 μm, as shown in “B” in FIG. 2, the rust preventive pigment 17 includes particles having a particle size larger than the film thickness of the undercoat coating film 13. There is. In this case, as shown by “B” in FIG. 2, since the diffuse reflected light on the surface of the anticorrosive pigment 17 protruding from the surface of the undercoat coating 13 is not absorbed by the black pigment, The color tone recovery effect may not be obtained. On the other hand, when the above difference is 0.5 μm or more, the particle size of the rust preventive pigment 17 in the undercoat film 13 is sufficiently small with respect to the film thickness of the undercoat film 13 as shown in FIG. Thus, the rust preventive pigment 17 is dispersed in the undercoat coating film 13.

  Although the film thickness of the undercoat coating film 13 is not specifically limited, From a viewpoint of obtaining the rust prevention effect and coloring effect of the steel plate 11, it is 3-15 micrometers, for example. Further, D50 of the rust preventive pigment 17 is preferably 0.5 to 10 μm from the viewpoint of suppressing the diffuse reflected light in the undercoat coating 13 and from being uniformly dispersed in the undercoat coating 13. Is more preferably less than or equal to the film thickness of the undercoat coating film. D90 refers to the particle size at which the integrated value in the particle size distribution is 90%. The D50 or D90 of the rust preventive pigment 17 is determined from, for example, a particle size distribution measured by a laser diffraction / scattering method. Further, the D50 or D90 may be a catalog value. The D50 or D90 can be appropriately adjusted by, for example, pulverization, classification, or mixing of classified products.

  The content of the rust preventive pigment 17 in the undercoat coating 13 is 50 parts by mass or less with respect to 100 parts by mass of the resin 15. When the content of the rust preventive pigment 17 is more than 50 parts by mass with respect to 100 parts by mass of the resin 15, the gloss, blackness, and vividness of the coating film 12 may be insufficient. The content of the rust preventive pigment 17 with respect to 100 parts by mass of the resin 15 is preferably 5 to 50 parts by mass and more preferably 5 to 25 parts by mass from the viewpoint of obtaining both a black appearance and an antirust effect. preferable.

  The top coating film 14 is a clear coating film. The top coat film 14 is composed of a layer that satisfies at least the following refractive index and haze value conditions.

  The refractive index of the top coat film 14 is 1.45 or more. When the refractive index of the top coat film 14 is less than 1.45, the surface reflection of the top coat film 14 becomes small, so that the specular reflection light is greatly attenuated, and the vividness and gloss may be impaired. The refractive index of the top coat film 14 is, for example, a sample coat film having the same components and thickness as the top coat film 14 is prepared, and the light of the sodium D light source is sample coat film in an atmosphere at 20 ° C. Is obtained by measuring the light reflected on the surface with an Abbe refractometer.

The haze value of the top coat film 14 is 7% or less. When the haze value of the top coat film 14 is larger than 7%, the gloss of the paint film 12 is lowered and the sharpness may be lowered. From the viewpoint of enhancing the gloss of the coating film 12, the haze value of the top coat film 14 is preferably 6% or less, and more preferably 5% or less. The haze value of the top coat film 14 is measured by a method conforming to the provisions of JIS K7136, and is determined by the following formula.
Haze (%) = (Td / Tt) × 100
(Td: diffuse transmittance, Tt: total light transmittance)

  The top coat film 14 can be made of a resin that forms a film having at least the above-described refractive index and haze value among resins that form a clear film for a coated steel sheet. Examples of the resin constituting the top coat film 14 include acrylic resin, polyester resin, fluorine resin, acrylic-styrene resin, styrene resin, silicone resin, epoxy resin, phenol resin, urea resin, melamine resin or benzoguanamine resin, and these These resins are urethane-modified, silicone-modified or epoxy-modified resins, and resin compositions in which two or more of these resins are mixed.

  The film thickness of the top coat film 14 is not particularly limited, but is preferably 3 μm or more, more preferably 5 μm or more, and more preferably 10 μm or more from the viewpoint of enhancing the sharpness of the coating film 12. preferable. In addition, the film thickness of the top coat film 14 is preferably 30 μm or less from the viewpoint of cost reduction and prevention of occurrence of cavities (such as local swelling and dents in the top coat film 14) during baking. More preferably, it is 20 μm or less.

  The coated steel sheet 10 may contain extender pigments in addition to the components described above within a range where the effects of the present invention can be obtained. Examples of extender pigments include barium sulfate, silica and calcium carbonate. Moreover, content of the said other component in the coated steel plate 10 is suitably determined from the range from which the effect of this invention is acquired.

  The coating film 12 of the coated steel sheet 10 exhibits a highly glossy black color. Here, “high gloss” means that the 60 ° glossiness of the coating film 12 is 80% or more, and “black” means that the L value in Hunter Lab method of the coating film 12 is 10 or less. Say there is. From the viewpoint of enhancing the visual effect, the gloss level of the coating film 12 is preferably more than 87%, and the L value of the coating film 12 is preferably 6.5 or less. The reason why the coating film 12 exhibits such high gloss black is considered as follows.

  First, it is assumed that the undercoat coating 13a is formed on the surface of the steel plate 11. The undercoat coating film 13a is made of a resin and a color pigment. As shown in FIG. 3A, the light incident on the undercoat film 13a is reflected on the surface of the undercoat film 13a. When a black pigment is used as the coloring pigment, substantially all incident light is absorbed, so that the undercoat coating film 13a appears black. The L value of the undercoat coating film 13a is sufficiently low. Here, when the transparent top coating film 14 is formed on the surface of the undercoat coating film 13a, the coating film including the undercoat coating film 13a and the top coating film 14 exhibits high gloss and vivid black. The L value of this coating film is also sufficiently low similarly to the L value of the undercoat coating film 13a. A high-gloss black-coated steel sheet is usually produced by forming a transparent top coat film on a black coat film having a sufficiently low L value.

  Next, it is assumed that an undercoat coating film 13 b is formed on the surface of the steel plate 11. The undercoat coating film 13 b is made of a resin, a black pigment 16, and an antirust pigment 17. The rust preventive pigment 17 is a powder generally exhibiting a high brightness color such as white or yellow, and is uniformly dispersed in the undercoat coating film 13b. For this reason, as shown in FIG. 3B, a part of the light incident on the undercoat coating film 13b is diffusely reflected on the surface of the undercoat coating film 13b. At this time, diffuse reflected light 18 is generated, and the L value of the undercoat film 13b is sufficiently higher than that of the undercoat film 13a. For this reason, the undercoat coating film 13b looks like a black coating film (dark gray) in which a whitish feel is felt.

  Furthermore, suppose that the transparent top coat film 14 was formed on the undercoat film 13b, and the coating film was formed. The light incident on this coating film passes through the top coating film 14, reaches the surface of the undercoating film 13 b, and is diffusely reflected. When the diffusely reflected light 18 at this time passes through the top coating film 14 and is emitted to the outside, the coating film still looks whitish.

  However, in the present invention, the refractive index of the rust preventive pigment 17, the difference obtained by subtracting D50 of the rust preventive pigment 17 from the film thickness of the undercoat coat 13b, the content of the rust preventive pigment 17 in the undercoat coat 13b, and the top coat film. The refractive index of 14 and the haze value of the top coat film 14 are specified as described above. When the L value of the coating film 12 composed of the undercoat coating film 13b and the top coating film 14 specified under such conditions is measured, the L value of the coating film 12 is sufficiently lower than the L value of the undercoat coating film 13b. Become. For this reason, from the coating film 12, the whitish feeling felt from the undercoat coating film 13b is not felt, and the coating film 12 exhibits high gloss and vivid black. The reason why the L value of the coating film 12 is lower than the L value of the undercoating film 13b is that the diffuse reflected light 18 on the surface of the undercoating film 13b is absorbed in the top coating film 14 as shown in FIG. 3C. This is thought to be due to attenuation.

The coated steel plate 10 can be manufactured, for example, by the following method.
First, the above-described undercoat film 13 is formed on the steel plate 11. The undercoat coating film 13 is formed, for example, by application of a paint for undercoat coating film and baking (1 coat, 1 bake). The L value in the Lab Lab method of the undercoat film 13 is usually 30 or less. When the L value is greater than 30, the L value of the coating film 12 is not sufficiently low, and a desired black may not be obtained. If the L value of the undercoat coating film 13 is 30 or less, it can be appropriately determined from a range in which a sufficient rust prevention effect of the coated steel sheet 10 can be obtained. The L value of the undercoat coating film 13 is determined by the same method as the L value of the coating film 12.

  Next, the above-described topcoat film 14 is formed on the undercoat film 13. The refractive index of the top coat film 14 is 1.45 or more, and the haze value is 7% or less. The top coat film 14 is also formed, for example, by applying a paint for the top coat film and baking it (one coat and one bake).

  Thus, the coated steel plate 10 is manufactured. The coated steel sheet 10 can be produced by two coats and two bake, as is apparent from the above description. Said manufacturing method may also include further processes, such as a paint preparation process and a steel plate preparation process, in the range in which the effect of this invention is acquired.

  Since the coated steel sheet according to the present invention has a high-grade appearance and corrosion resistance, for example, electrical appliances for cooking, plumbing products such as cooking tables and washstands, and interior or exterior building materials, etc. It is suitably used for products that require both corrosion resistance and aesthetics. Moreover, it can also be suitably used for products that mainly require aesthetics, such as electronic musical instruments such as electronic pianos and household audio equipment.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail with reference to an Example, this invention is not limited by these Examples.

[Manufacture of coated steel sheet 1]
(1. Preparation of plated steel sheet)
An electrogalvanized steel sheet (plate thickness: 0.5 mm, plating adhesion amount: 20 g / m ^{2 on} one side) was prepared, and the arithmetic average roughness Ra of the surface was adjusted to 0.16 μm by temper rolling. The surface of the plated steel sheet with the adjusted surface roughness is washed with hot water, and a chromium-free chemical conversion treatment solution is applied to the surface with a bar coater, and the plated steel sheet is maintained at 100 ° C. for 10 seconds. To form a chemical conversion film on the surface of the plated steel sheet. As the chromium-free chemical conversion treatment liquid, a mixed solution of titanium hydrofluoric acid (H ₂ TiF ₆ ): 0.1 mol / L and zircon hydrofluoric acid (H ₂ ZrF ₆ ): 0.1 mol / L is used. Was applied to the plated steel sheet with a bar coater so that the total metal element equivalent adhesion amount of Ti and Zr was 3.5 mg / m ² . Thus, a plated steel sheet A having a Ra of 0.16 μm and subjected to chemical conversion treatment was obtained.

  Plated steel plates B to D were obtained in the same manner as the plated steel plate A, except that Ra on the surface of the plated steel plate was adjusted to 0.38 μm, 0.59 μm, and 0.90 μm, respectively.

(2. Preparation of paint for undercoat film)
A mixture of 100 parts by mass of a polyester resin (Byron (registered trademark of Toyobo Co., Ltd.) 560, manufactured by Toyobo Co., Ltd.) and 10 parts by mass of melamine resin (Cymel (registered trademark of Cytec Technology Corporation) 303; manufactured by Nihon Cytec Industries Co., Ltd.) The resin solution was prepared by adding to the solvent so that the solid content was 40% by mass. To this resin solution, 0.5% by mass of an acidic catalyst (Catalyst 600, manufactured by Nippon Cytec Industries Co., Ltd.) was added to prepare a clear paint. To this clear paint, 5 parts by mass of carbon black (MA-100, manufactured by Mitsubishi Carbon Co., Ltd.) is added with respect to 100 parts by mass of the resin solid content, and calcium silicate (D50: 3.8 μm, D90: 5. 10 parts by mass of 2 μm and a refractive index of 1.49) were added to prepare an undercoat paint 1.

  The refractive index of the rust preventive pigment was measured by the following method according to the method B in JIS K7142. First, particles of a rust preventive pigment for measuring a refractive index were placed on a slide glass, and Cargill standard refraction liquid was dropped onto the particles of the rust preventive pigment, and the rust preventive pigment particles and the refraction liquid were mixed well. Then, irradiate the light of the sodium lamp from the bottom of the slide glass, observe the outline of the particles of the anticorrosive pigment from the top of the slide glass, and determine the refractive index of the refractive liquid when the outline of the particles becomes invisible Of the refractive index. Further, D50 or D90 of the rust preventive pigment was determined from the particle size distribution measured by the laser diffraction / scattering method.

(3. Manufacture of coated steel sheet 1)
The undercoat paint 1 was applied to the plated steel sheet A and baked on the plated steel sheet A at 215 ° C. for 50 seconds to form an undercoat paint film 1 having a thickness of 6 μm. The 60 ° glossiness of the undercoat film 1 is measured with a gloss meter by the same method as the measurement method for a coated steel sheet to be described later, and the L value in Hunter Lab method of the undercoat film 1 is measured by the spectrophotometer. As a result of calculating by the Hunter color difference formula from the measurement result of the color of 1, the glossiness of the undercoat coating film 1 was 7.8%, and the L value was 17.7.

  Next, an acrylic clear paint (C951, manufactured by Nippon Fine Coating Co., Ltd.) was applied to the surface of the undercoat film, and baked on the undercoat film at 230 ° C. for 50 seconds to form an overcoat film having a thickness of 5 μm. Thus, the coated steel plate 1 was manufactured.

  Further, a sample coating film of the above acrylic clear coating is prepared separately under the same conditions as described above, and the surface of the sample coating film is irradiated with light of a sodium D light source in an atmosphere of 20 ° C. with a refractive index of the sample coating film. The light reflected from the surface of the sample coating film was obtained by measuring with an Abbe refractometer. Moreover, the haze value of the sample coating film was measured by the method based on the prescription | regulation of JISK7136, respectively, and it was set as the refractive index and haze value of top coat film. As a result, the refractive index of the top coat film of the coated steel sheet 1 was 1.5, and the haze value was 1.2%.

[Manufacture of coated steel sheet 0]
Undercoat paint 0 was prepared in the same manner as undercoat paint 1 except that calcium silicate was not added. The gloss of the undercoat coating film 0 was 72.0%, and the L value was 8.8. And the top coat film was formed similarly to the coated steel plate 1, and the coated steel plate 0 was manufactured.

[Manufacture of coated steel plates 2 and 3]
A coated steel plate 2 was produced in the same manner as the coated steel plate 1 except that the film thickness of the top coat film was 15 μm.
Also, undercoat paint 2 was prepared in the same manner as undercoat paint 1 except that the content of the rust-preventing pigment was 20 parts by mass. The gloss of the undercoat film 2 was 3.8%, and the L value was 22.1. And the coated steel plate 3 was manufactured like the coated steel plate 1 except having made the film thickness of the top coat film into 15 micrometers.

[Manufacture of coated steel plate 4]
Undercoat paint 4 is prepared in the same manner as undercoat paint 1 except that magnesium phosphate (D50: 2.2 μm, D90: 3.9 μm, refractive index 1.6) is used as the antirust pigment. The undercoat coating film 4 was formed. The glossiness of the undercoat coating film 4 was 8.9%, and the L value was 15.8. And the coated steel plate 4 was manufactured like the coated steel plate 1 except having made the film thickness of the top coat film into 2 micrometers.

[Manufacture of coated steel plates 5 and 6]
A coated steel plate 5 was produced in the same manner as the coated steel plate 4 except that the film thickness of the top coat film was 5 μm.
Also, undercoat paint 6 was prepared in the same manner as undercoat paint 4 except that the content of the rust preventive pigment was 20 parts by mass. The glossiness of the undercoat film 6 was 4.2%, and the L value was 21.6. And the coated steel plate 6 was manufactured like the coated steel plate 4 except having made the film thickness of the top coat film into 15 micrometers.

[Manufacture of coated steel sheets 7-9]
Coated steel plates 7 to 9 were produced in the same manner as the coated steel plate 6 except that the plated steel plates B to D were used instead of the plated steel plate A, respectively.

[Manufacture of coated steel sheet 10]
Undercoat paint 10 is prepared in the same manner as undercoat paint 6 except that magnesium phosphate (D50: 5.3 μm, D90: 7.0 μm, refractive index 1.6) is used as the antirust pigment. Then, undercoat film 10 was formed in the same manner as undercoat film 6 except that the film thickness was 8 μm. The glossiness of the undercoat coating film 10 was 2.0%, and the L value was 24.4. And the coated steel plate 10 was manufactured similarly to the coated steel plate 6.

[Manufacture of coated steel plate 11]
Except for the content of the rust preventive pigment being 3 parts by mass, undercoat paint 11 was prepared in the same manner as undercoat paint 6, and undercoat 11 was formed in the same manner as undercoat 6. . The glossiness of the undercoat film 11 was 63.4%, and the L value was 11.1. And the coated steel plate 11 was manufactured like the coated steel plate 6.

[Manufacture of coated steel plate 12]
A coated steel sheet 12 was produced in the same manner as the coated steel sheet 6 except that the top coat paint was changed to a polyester-based clear paint (FLC5100, manufactured by Nippon Fine Coating Co., Ltd.). In addition, the refractive index of the top coat film of the coated steel plate 12 was 1.55, and the haze value was 5.7.

[Manufacture of coated steel sheet 13]
Undercoat paint 13 was prepared in the same manner as undercoat paint 6 except that zinc oxide (D50: 0.5 μm, D90: 1.5 μm, refractive index 2.0) was used as the antirust pigment. The undercoat film 13 was formed in the same manner as the undercoat film 6. The glossiness of the undercoat film 13 was 63.1%, and the L value was 28.1. And the coated steel plate 13 was manufactured similarly to the coated steel plate 6.

[Manufacture of coated steel sheet 14]
Same as undercoating paint 6 except that zinc powder (D50: 2 μm, D90: 4.1 μm, refractive index 2.4) was used as the antirust pigment and the content of antirust pigment was 40 parts by mass. Undercoat film 14 was prepared, and undercoat film 14 was formed in the same manner as undercoat film 6. The glossiness of the undercoat coating film 14 was 7.8%, and the L value was 32.1. And the coated steel plate 14 was manufactured like the coated steel plate 6.

[Manufacture of coated steel plate 15]
The coated steel sheet 15 is made in the same manner as the coated steel sheet 6 except that the top coat paint is changed to a fluorine-based clear paint (V Freon (registered trademark of Dainippon Paint Co., Ltd.) # 5000, manufactured by Dainippon Paint Co., Ltd.). Manufactured. In addition, the refractive index of the top coat film of the coated steel plate 15 was 1.45, and the haze value was 7.9.

[Manufacture of coated steel plate 16]
Undercoat film 16 was formed in the same manner as undercoat film 3 except that the thickness of the undercoat film was 3 μm. The glossiness of the undercoat coating film 16 was 2.4%, and the L value was 20.6. And the coated steel plate 16 was manufactured similarly to the coated steel plate 3.

[Manufacture of coated steel sheet 17]
Except for the content of the rust preventive pigment being 55 parts by mass, undercoat paint 17 was prepared in the same manner as undercoat paint 13, and undercoat 17 was formed in the same manner as undercoat 13 . The glossiness of the undercoat coating film 17 was 8.8%, and the L value was 35.1. And the coated steel plate 17 was manufactured similarly to the coated steel plate 13.

[Manufacture of coated steel plate 18]
A coated steel sheet 18 was produced in the same manner as the coated steel sheet 6 except that the top coat paint was changed to a fluorine-based clear paint (Dick Flow (registered trademark of DIC Corporation) EF Clear, manufactured by Nippon Fine Coating Co., Ltd.). . In addition, the refractive index of the top coat film of the coated steel plate 18 was 1.42, and the haze value was 6.8.

[Evaluation]
(1. Glossy)
60 degree glossiness (%) of each coating film of the coated steel plates 0 to 18 was measured with a gloss meter (VG-2000, manufactured by Nippon Denshoku Industries Co., Ltd.). Further, the obtained 60 ° glossiness was determined according to the following criteria.
◎: 60 ° glossiness is over 87% ○: 60 ° glossiness is over 80% and 87% or less ×: 60 ° glossiness is 80% or less

(2. Blackness)
The color of each coating film of the coated steel sheets 0 to 18 was measured with a spectrocolorimeter (CM3700d, manufactured by Konica Minolta Optics Co., Ltd.), and an L value was calculated from the measurement result by a Hunter color difference formula. Moreover, the obtained L value was determined according to the following criteria. Furthermore, three test subjects visually evaluated the blackness of the coating films of the coated steel plates 1 to 17 on the basis of the coated steel plate 0 in which no rust preventive pigment was blended, and determined the following criteria.
(Determination of L value)
◎: L value is 6.5 or less ○: L value is more than 6.5 and 10 or less ×: L value is more than 10 (visual determination)
○: Two or more subjects judged as “no difference in blackness compared to painted steel plate 0” ×: One subject judged as “no difference in blackness compared to painted steel plate 0” Less than

(3. Corrosion resistance)
For each coated steel sheet, an X-shaped cross-cut wound is made with a knife so as to reach the plated layer of the plated steel sheet, and a 35% 5% sodium chloride aqueous solution is applied to the cross-cut portion of the coating film for 240 hours in accordance with JIS Z2371. A salt spray test for spraying was performed. The maximum swollen width of the crosscut portion after the test was measured and judged according to the following criteria. In addition, the said maximum swelling width means (width | variety which the penetration | invasion depth of the blister from a crosscut part is the maximum).
◎: Maximum swell width is 2 mm or less ○: Maximum swell width is greater than 2 mm and less than 4 mm △: Maximum swell width is greater than 4 mm and less than 5 mm ×: Maximum swell width is greater than 5 mm

(4. Vividness)
Rs and R (0.3) of the surface of the coated steel sheets 0 to 18 were measured using an image sharpness gloss meter (DGM-30; Murakami Color Research Laboratory Co., Ltd.). The value (image definition and glossiness) was calculated and judged according to the following criteria. Rs is the strength (%) of 30 ° regular reflected light, and R (0.3) is the strength (%) of reflected light at 30 ± 0.3 ° on both sides of the peak angle of regular reflected light.
(formula)
D / I value = {1-R (0.3) / Rs} × 100
(Criteria)
○: D / I value is 70 or more ×: D / I value is less than 70

  Table 1 shows the physical properties of the coated steel sheets 0 to 18, the undercoat film and the top coat film, and the optical measurement values of the obtained coating films, and Table 2 shows the judgment results of the coated steel sheets 0 to 18, respectively.

  As is clear from Table 1 and Table 2, each of the coated steel sheets 1 to 13 has a refractive index of 2.1 or less and a rust preventive pigment having a D50 smaller than the film thickness of the undercoat film by 0.5 μm or more. Of 100 parts by mass of an undercoat coating film and a top coating film having a refractive index of 1.45 or more and a haze value of 7% or less. Each of these coated steel sheets 1 to 13 has an L value of 10 or less, a 60 ° glossiness of 80% or more, a highly glossy and vivid black appearance, and corrosion resistance. In particular, as apparent from the coated steel sheets 1 to 3, 5 to 7 and 10 to 13, the film thickness of the top coat film is 3 μm or more, or the surface roughness Ra of the steel sheet is 0.5 μm or less. A coated steel sheet having a D / I value of 70 or more and a more beautiful appearance can be obtained. In addition, when the content of the rust preventive pigment is in the range of at least 3 parts by weight and less than 40 parts by weight, a black and high gloss appearance of the coated steel sheet can be obtained, and the corrosion resistance increases as the content of the rust preventive pigment increases. There is a tendency to increase.

  On the other hand, as is apparent from the coated steel sheet 0, corrosion resistance is not obtained even though it has an excellent appearance unless the rust preventive pigment is added to the undercoat coating film. Further, as is clear from the black coated steel sheet 14, if the refractive index of the rust preventive pigment is too high, the L value becomes high, and the color clearly feels whitish. Further, as apparent from the black coated steel sheet 15, when the haze value of the top coat film is too high, the glossiness and the sharpness are lowered. Further, as apparent from the coated steel plate 16, when the D50 of the rust preventive pigment is larger than the film thickness of the undercoat coating film, the L value becomes high and the color clearly feels whitish, and the sharpness is further improved. descend. Furthermore, as is clear from the coated steel sheet 17, if the content of the anticorrosive pigment in the undercoat film is too much, the glossiness is lowered, the L value is increased, and the color clearly feels whitish, and The sharpness decreases. Further, as apparent from the coated steel sheet 18, when the refractive index of the top coat film is too low, the reflection on the surface of the top coat film is reduced, so that the regular reflection light on the surface of the top coat film is greatly attenuated, Gloss, blackness and sharpness decrease.

  According to the present invention, a rust preventive pigment and a black pigment, each of an undercoat containing a pigment having both extreme brightness values, and only a two-layer coating consisting of a transparent topcoat formed thereon, A coated steel sheet having a high gloss and black color having an L value of 10 or less and a 60 ° gloss of 80% or more is obtained. Since this coated steel sheet has excellent corrosion resistance because it contains a rust preventive pigment in the undercoat film, it can be produced using various steel sheets. Furthermore, this coated steel sheet can be produced by a simple method of 2 coats and 2 bake. Therefore, further spread of coated steel sheets that produce a high-class feeling is expected.

DESCRIPTION OF SYMBOLS 10 Painted steel plate 11 Steel plate 12 Coating film 13, 13a, 13b Undercoat coating film 14 Topcoat coating film 15 Resin 16 Black pigment 17 Antirust pigment 18 Diffuse reflected light

Claims (9)

Having a steel plate and a coating film formed on the steel plate,
The coating film has an undercoating film formed on the steel plate, and an overcoating film formed on the undercoating film,
The undercoat coating film contains a resin, a black pigment and an antirust pigment,
The difference obtained by subtracting the median diameter of the anticorrosive pigment from the film thickness of the undercoat coating film is 0.5 μm or more,
The refractive index of the rust preventive pigment is 2.1 or less,
The refractive index of the top coat film is 1.45 or more,
The haze value of the top coat film is 7% or less,
A coated steel sheet having a L value of 10 or less according to Hunter's Lab method and a glossiness of 60 ° of 80% or more.   Content of the said rust preventive pigment is a coated steel plate of Claim 1 which is 5-50 mass parts with respect to 100 mass parts of said resins.   The coated steel sheet according to claim 1 or 2, wherein the film thickness of the top coat film is 3 µm or more.   The arithmetic mean roughness Ra of the surface of the said steel plate is a coated steel plate as described in any one of Claims 1-3 which is 0.5 micrometer or less.   The coated steel sheet according to any one of claims 1 to 4, wherein the steel sheet is a plated steel sheet. In the method for producing a coated steel sheet having the steel sheet, the undercoat film and the top coat film by forming an undercoat film and a top coat film in this order on the steel sheet,
On the steel sheet, a resin, a black pigment, and a rust preventive pigment are formed, and the step of forming the undercoat film having an L value of 30 or less in the Hunter Lab method;
A step of forming the topcoat film having a refractive index of 1.45 or more and a haze value of 7% or less on the undercoat film, and an L value in Hunter's Lab method of 10 or less. And a method for producing a coated steel sheet having a 60 ° gloss of 80% or more.   The method for producing a coated steel sheet according to claim 6, wherein the film thickness of the top coat film is 3 μm or more.   The arithmetic mean roughness R of the surface of the said steel plate is a manufacturing method of the coated steel plate of Claim 6 or 7 which is 0.5 micrometer or less.   The said steel plate is a manufacturing method of the coated steel plate as described in any one of Claims 6-8 which is a plated steel plate.

Images