Black coated steel sheet and its manufacturing method

Abstract

This invention relates to black coated steel sheets and their manufacturing methods. Specifically, a coated steel sheet with a glitter pattern is formed through constant humidity heat treatment, and as the glitter pattern undergoes different degrees of blackening, a black coated steel sheet with a marble-like texture and beautiful patterns is obtained after the blackening process is completed, and the manufacturing method thereof.

Description

Technical Field

[0001] This invention relates to a black coated steel sheet and a method for manufacturing the same. Specifically, this invention relates to a method for obtaining a black coated steel sheet with a marble-like texture by controlling the blackness of the steel sheet by different areas. Background Technology

[0002] In fields such as building roofing materials, exterior materials, home appliances, and automobiles, the demand for steel sheets with a black appearance is constantly increasing from an aesthetic (design) perspective. One method for blackening steel sheet surfaces is to apply a black coating to the surface, forming a black film. However, in these fields, from a corrosion resistance perspective, coated steel sheets with coatings such as galvanized, aluminum-zinc, aluminum-magnesium-zinc, silicon-aluminized, and magnesium-aluminized are most commonly used. Such coated steel sheets have a silvery-white metallic luster. Therefore, to achieve a highly aesthetic black appearance through black coating, the coating film must be thickened to conceal the base color, resulting in excessively high coating costs.

[0003] Therefore, as a method to mask the metallic luster and silvery-white color of the coated steel sheet without forming a black coating, a method for blackening the coating itself has been proposed. For example, a method is disclosed to form a thin black coating layer on the surface of the coating by spraying high-temperature water vapor onto a molten aluminum-zinc coated steel sheet for more than 24 hours. Another example is the method for blackening the surface of an alloy-coated steel sheet by contacting a molten aluminum-magnesium-zinc coated steel sheet with water vapor in a sealed container.

[0004] The present invention aims to provide a black-plated steel sheet that utilizes inexpensive zinc-plated steel sheets with adjustable sequins, and partially blackens the sheet to present a beautiful marble-like texture. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] One embodiment of the present invention aims to provide a black coated steel sheet and a method for manufacturing the same. More specifically, one embodiment of the present invention aims to provide a black coated steel sheet with sequins formed by blackening, and a black coated steel sheet with a marble-like texture achieved by adjusting the blackness of different areas.

[0007] (II) Technical Solution

[0008] According to an embodiment of the present invention, a black coated steel sheet comprises a steel sheet and a zinc coating on a surface of the steel sheet. The outermost layer of the zinc coating comprises a black layer, which comprises three or more portions with different blackness. The first portion of the black layer has a thickness of 1 μm or more, the second portion of the black layer has a thickness of 250 nm or more and less than 1 μm, and the third portion of the black layer has a thickness of 200 nm or less.

[0009] The black layer contains oxides or hydroxides of Zn, Pb, Sb, or Al.

[0010] The zinc coating comprises Al: 0.18–0.22 wt%, Pb: 0.06–0.2 wt%, Sb: 0.06–0.08 wt%, and the residual amount is Zn.

[0011] In the black layer, among the sequined patterns with two or more different shades of black, the brightness L* deviation of each sequined pattern is 5 to 40.

[0012] The average brightness L* of the black layer is below 60.

[0013] The black coated steel sheet further includes an inorganic or organic coating on the zinc coating.

[0014] A method for manufacturing a black coated steel sheet according to an embodiment of the present invention includes: a step of placing a coated steel sheet containing a zinc coating into a sealed container; and a constant humidity heat treatment step of injecting water vapor into the sealed container containing the coated steel sheet to perform heat treatment on the coated steel sheet. The zinc coating of the coated steel sheet includes a bright flake pattern.

[0015] The zinc coating comprises Al: 0.18 to 0.22 wt%, Pb: 0.06 to 0.2 wt%, Sb: 0.06 to 0.08 wt%, and the balance Zn.

[0016] In the constant humidity heat treatment step, the oxygen concentration in the sealed container is below 13% by volume.

[0017] In the constant humidity heat treatment step, the heat treatment time is 1 hour to 10 hours.

[0018] During the constant humidity heat treatment step, the humidity of the sealed container is maintained between 50% and 100% RH.

[0019] In the constant humidity heat treatment step, the heat treatment temperature is 100 to 200°C.

[0020] In the constant humidity heat treatment step, the zinc coating undergoes oxidation with varying degrees of blackening along with the glitter pattern.

[0021] Following the constant humidity heat treatment step, the process further includes the step of forming an inorganic or organic coating on the blackened surface.

[0022] (III) Beneficial Effects

[0023] According to one embodiment of the present invention, a black coated steel sheet with a marble-like pattern can be manufactured using a zinc-coated steel sheet with glitter formed on it. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the steel plate surface before and after blackening according to an embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of the steel plate surface and color difference over time according to an embodiment of the invention.

[0026] Figure 3 This is a cross-sectional schematic diagram of the black portion of a blackened steel sheet manufactured according to Embodiment 2 of the invention.

[0027] Figure 4 This is a schematic diagram of the aluminum element distribution (left) and oxygen element distribution (right) of the black portion of a blackened steel sheet manufactured according to Embodiment 2 of the invention.

[0028] Figure 5 This is a cross-sectional schematic diagram of the yellow portion of a blackened steel sheet manufactured according to Embodiment 2 of the invention.

[0029] Figure 6 This is a schematic diagram of the aluminum (left) and oxygen (right) distribution of the yellow portion of a blackened steel sheet manufactured according to Embodiment 2 of the invention.

[0030] Figure 7 This is a cross-sectional schematic diagram of the silver portion of a blackened steel sheet manufactured according to Embodiment 2 of the invention.

[0031] Figure 8 This is a schematic diagram of the aluminum element distribution (left) and oxygen element distribution (right) of the silver portion of a blackened steel sheet manufactured according to Embodiment 2 of the invention. Detailed Implementation

[0032] In this specification, the terms "first," "second," "third," etc., are used to describe various parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, and / or segment from another part, component, region, layer, and / or segment. Therefore, without departing from the scope of the invention, the first part, component, region, layer, and / or segment described below can also be described as a second part, component, region, layer, and / or segment.

[0033] The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms used herein are intended to include the plural forms as well. The word "comprising" as used in this specification can specifically refer to a particular feature, field, integer, step, action, element, and / or component, but does not exclude the presence or addition of other features, fields, integers, steps, actions, elements, components, and / or groups.

[0034] In this specification, if a part is described as being on top of another part, then other parts may exist directly on top of or in between the other part. When a part is described as being directly on top of another part, there are no other parts in between.

[0035] Additionally, unless otherwise specified, % indicates weight, and 1 ppm is 0.0001 wt%.

[0036] In one embodiment of the present invention, the inclusion of an additional element means that a portion of the remaining iron (Fe) is replaced by an additional element, the amount of which is equivalent to the amount of the additional element added.

[0037] Although not otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in dictionaries should be interpreted as having the same meaning as disclosed in relevant technical literature and herein, and should not be interpreted in an idealized or overly formal sense.

[0038] Embodiments of the present invention will be described in detail below to enable those skilled in the art to implement the invention. However, the invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0039] The following is a detailed description of each step.

[0040] According to an embodiment of the present invention, a black coated steel sheet comprises a steel sheet and a zinc coating on one surface of the steel sheet, wherein the outermost layer of the zinc coating comprises a black layer, and the black layer comprises a sequin pattern with a blackness of 2 or more.

[0041] The bright flake pattern on the molten zinc coated steel sheet exhibits large crystalline structures ranging in size from hundreds of μm to thousands of μm.

[0042] This is because the solidification of molten zinc begins at the interface between the coating and the base iron and grows towards the surface of the coating. The orientation of the (0001) face changes with the crystal units, resulting in differences in the gloss of the molten zinc coating and thus forming a glitter pattern. Furthermore, when the molten zinc coating contains one or more of Pb, Sb, and Al, the size of the glitter can be determined by the amount of each element.

[0043] Therefore, the glitter pattern formed on the surface of zinc-coated steel sheet is a pattern produced by different orientations, each with a different degree of blackening, thus forming a pattern on the black-coated steel sheet.

[0044] The black layer comprises three or more portions with different shades of black. The first portion (black) has a thickness of 1 μm or more, the second portion (yellow) has a thickness of 250 nm or more but less than 1 μm, and the third portion (silver) has a thickness of less than 200 nm. Specifically, the first portion of the black layer has a thickness of 1 μm to 3 μm, the second portion has a thickness of 250 nm to 500 nm, and the third portion has a thickness of 100 nm to 200 nm.

[0045] The thickness of the black layer refers to the deepest point in the thickness direction where the oxides of Al, Pb, or Sb emerge from the surface.

[0046] The zinc coating of the black coated steel sheet may contain Al: 0.18-0.22 wt%, Pb: 0.06-0.2 wt%, Sb: 0.06-0.08 wt%, with the balance being Zn.

[0047] The black layer of the black-plated steel sheet contains oxides or hydroxides of Zn, Pb, Sb, or Al.

[0048] In the black layer of the black-plated steel sheet, among two or more sequin patterns with different blackness, the brightness L* deviation of each sequin pattern is 5 to 40.

[0049] That is, depending on the orientation of the zinc coating that forms the sequins, different blackening results may be obtained even under the same blackening conditions, so black-coated steel sheets can have a beautiful marble-like surface.

[0050] The average lightness L* of the black layer on the black-plated steel sheet is 60 or less. Specifically, the lightness L* is 40 or less. More specifically, the lightness L* is 30 or less.

[0051] In this specification, the lightness L* value refers to the lightness value measured by a colorimeter using a spectrophotometer according to the ASTM E1164 method. A lower lightness L* indicates a higher degree of blackness. More specifically, a lightness L* value of 0 represents black, and a lightness L* value of 100 represents white.

[0052] The black coated steel sheet further includes an inorganic or organic coating on the zinc coating.

[0053] The inorganic coating may contain one or more oxides, oxyacid salts, hydroxides, phosphates, and fluorides of Ti, Zr, Hf, V, Nb, Ta, W, Si, and Al. The organic coating may contain a polyurethane resin obtained by reacting a polyol with a polyisocyanate, wherein the polyol is composed of ether-based and ester-based polyols. The proportion of ether-based polyols in the polyol is 5 to 30% by weight. Further forming an inorganic or organic coating protects the black electroplated layer from external impacts and improves processing performance during product manufacturing. Furthermore, if desired, a translucent color can be imparted to the inorganic or organic coating to further enhance its aesthetic appeal.

[0054] A method for manufacturing a black coated steel sheet according to an embodiment of the present invention includes: a step of placing a coated steel sheet containing a zinc coating into a sealed container; and a constant humidity heat treatment step of injecting water vapor into the sealed container containing the coated steel sheet to perform heat treatment on the coated steel sheet. The zinc coating of the coated steel sheet includes a bright flake pattern.

[0055] The zinc coating comprises Al: 0.18 to 0.22 wt%, Pb: 0.06 to 0.2 wt%, Sb: 0.06 to 0.08 wt%, and the balance Zn.

[0056] In the constant humidity heat treatment step, the oxygen concentration in the sealed container is below 13% by volume. More specifically, the oxygen concentration in the sealed container is between 0 and 13% by volume. If the oxygen concentration in the sealed container is too high during the constant humidity heat treatment step, it may lead to a decrease in the blackening rate.

[0057] In the constant humidity heat treatment step, the heat treatment time is 1 hour to 10 hours.

[0058] During the constant humidity heat treatment step, the humidity of the sealed container is maintained at 50 to 100% RH. Specifically, the humidity of the sealed container is maintained at 65 to 100% RH. More specifically, the humidity of the sealed container is maintained at 85 to 100% RH. More specifically, the humidity of the sealed container is maintained at 90 to 100% RH. If the humidity in the sealed container is insufficient during the constant humidity heat treatment step, sufficient blackening cannot be achieved, and the required average lightness (L* below 60) cannot be reached.

[0059] In the constant humidity heat treatment step, the heat treatment temperature is 100 to 200°C. Specifically, the heat treatment temperature is 120 to 180°C. More specifically, the heat treatment temperature is 140 to 160°C. If the heat treatment temperature in the constant humidity heat treatment step is too low, the reaction may not occur. If it is too high, over-reaction may occur, resulting in coating breakage.

[0060] In the constant humidity heat treatment step, the zinc coating undergoes oxidation to varying degrees of blackening along with the glitter pattern. That is, depending on the orientation of the zinc coating forming the glitter pattern, different blackening results are exhibited under the same blackening conditions, thereby enabling the black-coated steel sheet to achieve a beautiful marble-like surface.

[0061] Following the constant humidity heat treatment step, the process further includes forming an inorganic or organic coating on the blackened surface. The further formation of the coating is the same as described in the aforementioned black-coated steel sheet process.

[0062] The invention will be further described in detail below by way of examples. However, the following examples are merely for illustrating the invention in more detail and are not intended to limit the scope of the invention. This is because the scope of the invention depends on the content described in the claims and what can be reasonably inferred therefrom.

[0063] Example

[0064] A molten zinc-coated steel sheet with a shimmering pattern was prepared. The zinc-coated steel sheet was then placed into a sealed container.

[0065] The coated steel sheet is placed inside a sealed container containing the aforementioned internal gas atmosphere. While the container is sealed, a humidity of 95% RH is maintained, and heat treatment is performed at 150°C. The oxygen concentration inside the sealed container is adjusted to below 13% by volume. The blackening heat treatment time is varied for 1 hour, 2 hours, 5 hours, and 10 hours.

[0066] Through constant humidity heat treatment, the coating of the coated steel sheet is oxidized, and the surface transforms into a blackened film as different shades of black are formed according to the sequin pattern.

[0067] Figure 1 The steel plates were blackened for 1 hour at 95% humidity and 150℃. The image shows the steel plates before and after blackening.

[0068] Figure 2 This diagram illustrates the surface and color difference of steel plates under the same conditions, with only the blackening time changed to 1 hour, 2 hours, 5 hours, and 10 hours. As a result, the average lightness (L*) of the black-coated steel plate according to the embodiment of the present invention is less than 60.

[0069] As a result, when blackening zinc-plated steel sheets with a glittery texture, a beautiful marble pattern can be achieved by controlling the blackening time.

[0070] Table 1

[0071] Blackening Time Average colorimeter (L*) Comparative example Before turning black 85.42 Example 1 Blackening for 1 hour 59.20 Example 2 Blackening for 2 hours 57.52 Example 3 Blackening for 5 hours 42.65 Example 4 Blackening for 10 hours 32.79

[0072] Figures 3 to 8The cross-sections of the black, yellow, and silver portions of the steel sheet manufactured through Example 2, as well as the distribution of aluminum (Al) and oxygen (O) elements, were compiled. From... Figures 3 to 8 It can be confirmed that the black part formed a black layer with a thickness of about 1 μm, the yellow part formed a layer with a thickness of about 300 nm, and the silver part formed a layer with a thickness of less than 200 nm.

[0073] This invention can be implemented in various ways and is not limited to the embodiments described above. Those skilled in the art will understand that the invention can be implemented in other specific ways without altering its technical concept or essential features. Therefore, it should be understood that the above embodiments are exemplary in all respects and are not restrictive.

Claims

1. A black coated steel sheet, comprising a steel sheet and a zinc coating on one surface of the steel sheet, The outermost layer of the zinc coating includes a black layer. The black layer contains three or more portions with different shades of black. The thickness of the first black layer is more than 1 μm. The second part of the black layer has a thickness of more than 250 nm and less than 1 μm. The thickness of the third black layer is less than 200nm, and in, In two or more sequin patterns with different black levels in the black layer, the lightness L* deviation of each sequin pattern is between 5 and 40. The zinc coating comprises Al: 0.18–0.22 wt%, Pb: 0.06–0.2 wt%, Sb: 0.06–0.08 wt%, with the balance being Zn. The black layer contains oxides or hydroxides of Zn, Pb, Sb, or Al. The average brightness L* of the black layer is below 60. The lightness L* value refers to the lightness value of the colorimeter measured using a spectrophotometer according to the ASTM E1164 method.

2. The black coated steel sheet according to claim 1, wherein, The black coated steel sheet further includes an inorganic or organic coating on the zinc coating.

3. A method for manufacturing a black coated steel sheet, comprising: The step of loading zinc-coated steel sheets into a sealed container; and A constant humidity heat treatment step is used to heat-treat the coated steel sheet by injecting water vapor into a sealed container containing the coated steel sheet. in, In the constant humidity heat treatment step, the heat treatment time is 1 hour to 10 hours; In the constant humidity heat treatment step, the humidity of the sealed container is maintained at 50 to 100% RH. In the constant humidity heat treatment step, the heat treatment temperature is 100 to 200°C. The outermost layer of the zinc coating, which undergoes a constant humidity heat treatment process, includes a black layer. The black layer contains three or more portions with different shades of black. The thickness of the first black layer is more than 1 μm. The second part of the black layer has a thickness of more than 250 nm and less than 1 μm. The thickness of the third black layer is less than 200nm, and Among the two or more glitter patterns with different black levels in the black layer, the brightness L* deviation of each glitter pattern is between 5 and 40. The zinc coating comprises Al: 0.18–0.22 wt%, Pb: 0.06–0.2 wt%, Sb: 0.06–0.08 wt%, with the balance being Zn. The black layer contains oxides or hydroxides of Zn, Pb, Sb, or Al. The lightness L* value refers to the lightness value of the colorimeter measured using a spectrophotometer according to the ASTM E1164 method.

4. The method for manufacturing black coated steel sheet according to claim 3, wherein, In the constant humidity heat treatment step, the oxygen concentration in the sealed container is below 13% by volume.

5. The method for manufacturing black coated steel sheet according to claim 3, wherein, In the constant humidity heat treatment step, the zinc coating undergoes oxidation with varying degrees of blackening along with the glitter pattern.

6. The method for manufacturing black coated steel sheet according to claim 3, wherein, After the constant humidity heat treatment step, the process further includes the step of forming an inorganic or organic coating on the blackened surface.

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