STAINLESS STEEL SHEET WITH TRANSPARENT COATING

Abstract

This transparent coated stainless steel sheet (10) includes a stainless steel sheet (20) and a transparent coating film (30) formed on at least one surface (20a) of the stainless steel sheet (20) and having an average film thickness of 0.05 µm or more and 3.00 µm or less.

Description

STAINLESS STEEL SHEET WITH TRANSPARENT COATING Technical field [1] The present invention relates to a stainless steel sheet with a transparent coating that has corrosion resistance. This application claims priority over Japanese Patent Application No. 2019-63335 filed on March 28, 2019, the contents of which are incorporated herein by reference. Background of the invention [2] Due to the demand for maintenance-free operation in the industrial world, stainless steel sheets that have excellent corrosion resistance and appearance are used as exterior building materials, such as exterior wall materials and roofing materials. Ferritic stainless steel, classified as 445J1, is used in stainless steel sheets for outdoor applications. [3] Iron dust can adhere to stainless steel sheets exposed to the elements. Although stainless steel sheets are a type of steel with high corrosion resistance, if iron dust adheres to them, initial rust, such as rust stains caused by the iron dust, can develop, and the appearance may deteriorate. Applying a clear coating to the surface of a stainless steel sheet is a common method for preventing deterioration due to initial rust without affecting its appearance. [4] A method for improving the corrosion resistance of a transparently coated stainless steel sheet is known for adding an atmospheric corrosion-resistant pigment to a transparent coating material (e.g., Patent Document 1). The method using an atmospheric corrosion-resistant pigment is effective for coating materials in general. However, the transparency of the atmospheric corrosion-resistant pigment itself is low. Therefore, when the atmospheric corrosion-resistant pigment is added to the transparent coating material, the resulting transparent coating film has a cloudy or turbid appearance. As a result, the high-design characteristics that are exploited by the surface appearance of the stainless steel sheet are compromised.Furthermore, if iron powder adheres to the transparent film regardless of the presence or absence of atmospheric anti-corrosion pigment, initial rust is generated due to the iron powder, causing the surface of the transparently coated stainless steel sheet to deteriorate. [5] To prevent iron dust from adhering to a coated stainless steel sheet, the sheet is coated to prevent fingerprints and smudges (e.g., see Patent Document 2). However, the coated stainless steel sheet described in Patent Document 2 is easily wetted with water because the contact angle between the surface of a coated film and the water is less than 60°. Therefore, in the coated stainless steel sheet of Patent Document 2, there is a concern that water will remain on the coated film and penetrate it, thus impairing its corrosion resistance. frQCRnn / Lznz / E / YiAi Documents of the previous technique Patent document [6] Patent Document 1: Japanese Patent No. 4027848 Patent Document 2: Unexamined Japanese Patent Application, First Publication No. Hll-10795 Description of the invention Problems to be solved by the invention [7] The present invention has been made to solve this problem, and an object of the present invention is to provide a transparent coated stainless steel sheet having excellent design properties and excellent initial resistance to atmospheric corrosion. Solutions to solve the problems [8] The present invention includes the following aspects. [1] A transparently coated stainless steel sheet, comprising: a stainless steel sheet; and a transparent coating film formed on at least one surface of the stainless steel sheet and having an average film thickness of 0.05 pm or more and 3.00 pm or less. [2] The transparently coated stainless steel sheet in accordance with [1], wherein a surface of the transparent coating film is an irregular surface, an interval between two adjacent protruding portions of the irregular surface is 50 pm or more and 500 pm or less, and a height difference between an adjacent protruding portion and a recessed portion on the irregular surface is 2.00 pm or less. [3] The transparently coated stainless steel sheet in accordance with [1] or [2], wherein a contact angle between a surface of the transparent coating film and pure water, an aqueous halide solution or seawater is 90° or more. [4] The transparent coated stainless steel sheet in accordance with any of [1] to [3], wherein the transparent coating film contains organic particles. Effects of the invention [9] In accordance with the present invention, it is possible to provide a transparent coated stainless steel sheet that has excellent design properties and excellent initial resistance to atmospheric corrosion. frQCRnn / Lznz / E / YiAi Brief description of the drawings

[10] Figure 1 is a cross-sectional view showing a schematic configuration of one modality of a transparent-coated stainless steel sheet of the present invention. Figure 2 is a scanning electron microscope image of a surface of a transparent coating film in the transparent coated stainless steel sheet modality of the present invention. Methods for carrying out the invention

[11] A modality of a transparent-coated stainless steel sheet of the present invention will now be described.

[12] Stainless steel sheet with transparent coating ] Figure 1 is a cross-sectional view showing a schematic configuration of one modality of a transparently coated stainless steel sheet of the present modality. As shown in Figure 1, a transparent coated stainless steel sheet 10 of the present embodiment includes a stainless steel sheet 20 and a transparent coating film 30 formed on a surface 20a of the stainless steel sheet 20.

[13] Stainless steel sheet The types of stainless steel sheet 20 are not particularly limited, and examples include steel sheets made of SUS430, SUS430LX, SUS304, SUS316, SUS317J, SUS445J1, SUS445J2, SUS447J1, and similar materials. Among these, for outdoor use, steel sheets made of SUS445J1, SUS445J2, SUS447J1, and similar materials are preferred, as these are ferritic stainless steel sheets with high chromium and high molybdenum content. These ferritic stainless steel sheets with high Cr and high Mo content (frQCRnn / Lznz / E / YiAi) have often been used for large roofs in recent years because ferritic stainless steel sheets with high Cr and high Mo content have less thermal expansion than SUS304, SUS316 and SUS317J, which are austenitic stainless steel sheets that have excellent corrosion resistance and duplex stainless steel sheets that have excellent corrosion resistance.

[14] In addition, as ferritic stainless steel sheets, a stainless steel sheet that includes, in terms of % by mass, C: 0.001% to 0.03%, Si: 0.01% to 1%, Mn: 0.01% to 1.5%, P: 0.005% to 0.05%, S: 0.0001% to 0.01%, Cr: 11% to 30%, N: 0.001% to 0.03% and Al: 0.005% to 1%, a residue of Fe and impurities being desirable. As required, this stainless steel sheet may contain one or more selected types of Sn: 0.01% to 1%, Nb: 0.03% to 0.5%, Ti: 0.03% to 0.5%, Ni: 0.1% to 0.5%, Cu: 0.1% to 0.5%, Mo: 0.1% to 0.5%, V: 0.01% to 0.5%, Zr: 0.01% to 0.5%, Co: 0.01% to 0.5%, Mg: 0.0001% to 0.005%, B: 0.0003% to 0.005%, Ca: 0.005% or less, La: 0.001% to 0.1%, Y: 0.001% to 0.1%, Hf: 0.001% to 0.1% and REM: 0.001% to 0.1% in terms of % by mass, instead of a part of Fe.

[15] The surface finishes of a 20a surface and a 20b surface of the 20 stainless steel sheet are not particularly restricted and, for example, the surfaces are adjusted to be in the state specified by surface finish symbols such as No. 2B, No. 2D, HL frQCRnn / Lznz / E / YiAi and the like in JIS G 4305: 2015.

[16] The thickness of 20 stainless steel sheet is not particularly limited, but, for example, it is preferably 0.1 mm or more and 10.0 mm or less when used for exterior building materials such as roofing materials.

[17] Film with transparent coating The average film thickness of the transparent coating film 30 is 0.05 µm or more and 3.00 µm or less. The average film thickness is preferably 0.10 µm or more, 0.50 µm or more, or 1.00 µm or more. Furthermore, the average film thickness is very preferably 2.50 µm or less or 1.50 µm or less. In a case where the average film thickness of the transparent coating film 30 is less than 0.05 pm, there is a portion where the transparent coating film 30 does not form due to irregularities on the single surface 20a of the stainless steel sheet 20, and the effect of improving the corrosion resistance of the transparent coating film 30 is not shown. On the other hand, in a case where the average film thickness of the transparent layer 30 is greater than 3.00 pm, the color tone of the transparent coating film 30 turns white (turbidity), causing the appearance of the transparent coated stainless steel sheet to deteriorate.

[18] As shown in Figure 1, on the transparent coating film 30, a surface opposite the surface in contact with the stainless steel sheet 20 is designated surface 30a of the transparent coating film 30. Surface 30a of the transparent coating film 30 is an irregular surface. That is, surface 30a of the transparent coating film 30 is an irregular surface that includes a plurality of protruding portions 31 and recessed portions 32.

[19] The average film thickness of the transparent coating film 30 having the irregular surface is measured by observing a cross-section of the transparent coated stainless steel sheet 10 in one thickness direction with a scanning electron microscope (SEM).In the transparent coating film 30, a distance ti is measured from a deeper point 32a of the recessed portion 32 to the single surface 20a of the stainless steel sheet 20 at three points, and an average value of the values ​​measured at these three points is established as the average film thickness of the transparent coating film 30.

[20] On the irregular surface of the transparent coating film 30a, an interval di between the two adjacent protruding portions 31, i.e., the interval di between vertices (highest points of the protruding portions 31) 31a of the two adjacent protruding portions 31, is preferably 50 pm or more and 500 pm or less. The interval di is preferably 100 pm or more, or 200 pm or more. Furthermore, the interval di is very preferably 450 pm or less, or 400 pm or less. In a case where the interval di between the two adjacent protruding portions 31 is within the range described above, deterioration of the transparent coating film 30 due to salt precipitation, as described below, can be avoided. Furthermore, in a case where the interval di between the two adjacent protruding portions 31 is greater than 500 pm, the color tone of the surface of the transparent coating film 30 is uneven, which detracts from its appearance.

[21] Figure 2 shows a scanning electron microscope image of surface 30a of transparent coating film 30.

[22] The interval di between the two adjacent protruding portions 31 on the surface 30a of the transparent coating film 30 is measured as follows: the surface 30a of the transparent coating film 30 is observed using a microscope (VHX-5000 manufactured by KEYENCE CORPORATION), a two-point distance is measured at three points using software attached to the microscope, and an average value is calculated.

[23] On the irregular surface described above, a height difference hl between adjacent projecting portions 31 and recessed portions 32, i.e., a height difference hl between the vertex 31a of projecting portion 31 and the deepest point 32a of recessed portion 32, is preferably 2.00 pm or less. The height difference hl is very preferably 1.80 pm or less, 1.50 pm or less, 1.20 pm or less, or 1.00 pm or less. The lower limit is not particularly restricted, but may be, for example, 0.01 pm or more or 0.03 pm or more. In cases where the height difference hl between adjacent protruding portions 31 and recessed portions 32 is within the range described above, deterioration of the transparent coating film 30 due to salt precipitation, as described below, can be avoided. Furthermore, if the height difference hl between adjacent protruding portions 31 and recessed portions 32 exceeds 2.00 pm, the color tone of the transparent coating film 30's surface will be uneven, resulting in a deteriorated appearance.

[24] The height difference hl between adjacent protruding portions 31 and recessed portions 32, i.e., the height difference hl between vertex 31a of protruding portion 31 and deepest point 32a of recessed portion 32, is measured by observation with a scanning electron microscope (SEM). On the transparent coating film 30, the height difference hl is determined as follows: a distance t2 from the deepest point 32a of recessed portion 32 to the vertices 31a (highest points of the protruding portions 31) of two adjacent protruding portions 31 is measured at three points, and an average value of the values ​​measured at the three points is established as the height difference hl between adjacent protruding portions 31 and recessed portions 32.

[25] A contact angle between the surface 30a of the transparent coating film 30 and that of pure water, an aqueous halide solution, or seawater is preferably 90° or more. The contact angle is very preferably 95° or more or 100° or more. In a case where the contact angle between the surface 30a of the transparent coating film 30 and one of pure water, an aqueous halide solution or seawater is 90° or more, droplets of pure water, an aqueous halide solution or seawater do not deposit on the surface 30a of the transparent coating film 30, and deterioration of the transparent coating film 30 due to salt precipitation can be avoided, as described below.

[26] The contact angle between the surface 30a of the transparent coating film 30 and pure water, an aqueous halide solution, or seawater is measured using a contact angle meter at 25°C. The contact angle is measured at 10 points on the surface 30a of the transparent coating film 30, and its average value is established as the contact angle of the surface 30a of the transparent coating film 30. In principle, the contact angle changes depending on the surface tension of the solution used for measurement. In the present invention, the contact angle is measured with pure water because the contact angle is more affected by the film thickness and irregular shape than by a change in the surface tension of an aqueous halide solution or seawater.That is, since the measured value of a contact angle with an aqueous halide solution or seawater is almost the same as the measured value of a contact angle with pure water, the measured value of the contact angle with an aqueous halide solution or seawater can be replaced by the measured value of the contact angle with pure water.

[27] Next, with regard to the irregularity described above, the reason for limiting the interval di between the two adjacent protruding portions 31 and the height difference hl between the protruding portion 31 and the recessed portion 32 adjacent to each other will be described.

[28] Generally, a transparent coating film is hydrophobic. Therefore, the surface of a transparent coating film exhibits water repellency and is resistant to aqueous solutions. Furthermore, the water repellency of a transparent coating film improves as the surface irregularity of the coating increases, i.e., as the surface roughness of the coating increases.

[29] In the transparently coated stainless steel sheet 10 of the present embodiment, the greater the height difference hl between the adjacent protruding portion 31 and recessed portion 32 on the surface 30a of the transparent coating film 30, the better the water repellency. Regarding the initial resistance to atmospheric corrosion and water repellency, which are important characteristics of the transparently coated stainless steel sheet 10 of the present embodiment, as water repellency increases, the adhesion of an aqueous solution to the stainless steel sheet 20 decreases, and the deterioration of the transparent coating film 30 is suppressed. Deterioration of the transparent coating film 30 allows the aqueous solution to easily reach the stainless steel sheet 20 and accelerates its corrosion.Therefore, improving the water repellency of the transparent coating film 30 is effective in enhancing its initial resistance to atmospheric corrosion. Furthermore, with respect to rust stains caused by iron powder or similar substances, as water repellency increases, the adhesion of the iron powder can be suppressed through a washing effect. Thus, improved water repellency is effective against initial oxidation caused by rust stains. Moreover, the inventors of this product found that the criticality of water repellency occurs when the contact angle between the surface 30a of the transparent coating film 30 and pure water, an aqueous halide solution, or seawater is 90° or greater.

[30] On the other hand, from the standpoint of improving the corrosion resistance of transparently coated stainless steel sheets, an aqueous solution containing chloride ions, such as seawater and condensate, is considered the most severely corrosive environment. Salts, such as sodium chloride (NaCl), are produced from seawater as a result of evaporation, and these salts penetrate the irregular surface of the transparent film and accelerate its deterioration.

[31] Therefore, in the transparent coated stainless steel sheet 10 of the present embodiment, to prevent deterioration of the transparent coating film frQCRnn / Lznz / E / YiAi 30 due to salt precipitation, the interval di between the two adjacent protruding portions 31 and the height difference hl between the adjacent protruding portions 31 and the recessed portion 32 are specified in the intervals described above.

[32] The resin component of the transparent coating film 30 is not particularly restricted, but resins contained in transparent coating materials widely used for exterior building materials, such as fluorinated, urethane, silicone, silicone polyester, and acrylic resin, may be used. The coating material used to form the transparent coating film 30 may be a water-based material or an organic solvent-based material.

[33] Transparent coating film 30 may contain organic particles. In other words, organic particles may be dispersed in transparent coating film 30. The size, quantity, and type of organic particles are not particularly limited as long as the transparency of the transparent coating film 30 is not greatly affected. Examples of organic particles preferably used in the present modality include waxes and metallic soaps used as lubricants.

[34] Examples of waxes include polyethylene wax, carnauba wax, paraffin wax, polytetrafluoroethylene wax, and the like. Examples of metallic soaps include stearate, oleate, laurate, dodecylbenzenesulfonate, and the like. Organic particles other than the waxes and metallic soaps described above can also be used. In addition, one class of organic particles can be used alone, or two or more classes of the same can be mixed and used.

[35] The amount of organic particles in the transparent coating film 30 is not particularly limited and is appropriately adjusted according to the resin component of the transparent coating film 30 and the like.

[36] In the case where the transparent coating film 30 contains the organic particles described above, the corrosion resistance of the transparent coating film 30 is improved.

[37] Clear Coating Film 30 may contain pigments such as silicon oxide, titanium oxide, or similar substances to impart design properties, in addition to the organic particles. If Clear Coating Film 30 contains an excessive amount of these pigments, the unique appearance of the stainless steel sheets may be compromised. Furthermore, even if Clear Coating Film 30 contains a small amount of pigments, to the point where the appearance is not affected, the appearance may deteriorate due to bleaching, known as chalking, during use. Therefore, the amount of pigment in Clear Coating Film 30 is adjusted to be within a range where chalking does not occur.In the case of large areas, such as roofs and exterior materials used on large structures, chalking occurs, causing a deterioration in appearance and potentially incurring enormous repair costs. Therefore, adjusting the pigment quantity is important. frQCRnn / Lznz / E / YiAi

[38] Method of manufacturing stainless steel sheet with transparent coating The method for manufacturing a transparently coated stainless steel sheet according to the present embodiment includes, for example, a step of adjusting a coating material, a step of coating the coating material described above onto a surface 20a of the matte-finish stainless steel sheet 20 to form a coated film, and a step of drying and curing the coated film to form the transparent coating film 30 on a surface 20a of the stainless steel sheet 20. The coating material includes a solution containing the resin component of the transparent coating film 30 or a liquid resin that is an emulsion. The transparently coated stainless steel sheet according to the present embodiment is manufactured using this method for manufacturing a transparently coated stainless steel sheet.

[39] The coating material described above may contain the organic particles described above. By adjusting the amount of organic particles with respect to a certain amount of solid resin contained in the coating material, the amount of organic particles with respect to the resin can be adjusted to form the transparent coating film 30. In a case where the coating material contains the organic particles described above, it is preferable to sufficiently disperse the organic particles in the coating material by an appropriate stirring method before the single surface 20a of the stainless steel sheet 20 is coated with the coating material.

[40] A method for coating a surface 20a of the stainless steel sheet 20 with coating material is not particularly limited. Examples of the coating method include a method in which a predetermined film thickness can be obtained using a roller coater, a stick coater, a sprayer, a curtain flow coater, a brush, or similar means. With these coating methods, the coating material is applied to a surface 20a of the stainless steel sheet 20 and then dried at room temperature or in an oven, a heating oven, or similar to form the required transparent coating film 30. Baking may be performed if necessary. In the case of precisely controlling the irregular shape of the surface 30a of the transparent coating film 30, it is effective to use a roller coater, a stick coater, or similar means.

[41] For example, when applying the coating material to stainless steel sheet 20 using a bar coater or a roller coater, the spacing between two adjacent protruding portions and the height difference between adjacent protruding and recessed portions can be adjusted by changing the application speed. Increasing the application speed widens the spacing between adjacent protruding portions and increases the height difference between adjacent protruding and recessed portions. Furthermore, the spacing between adjacent protruding portions and the height difference between adjacent protruding and recessed portions can be adjusted by repeatedly applying the coating material.

[42] As shown in Figure 1, the transparently coated stainless steel sheet 10 of the present embodiment exemplifies the case where the transparent coating film 30 is formed only on a surface 20a of the stainless steel sheet 20 facing the outer surface, but the shape of the transparently coated stainless steel sheet 10 of the present embodiment is not limited to this. The transparently coated stainless steel sheet 10 of the embodiment may include the transparent coating film 30 formed on both a surface 20a and the other surface 20b of the stainless steel sheet 20.In a case where the transparent coating film 30 is formed only on one surface 20a of the stainless steel sheet 20, the film cannot be formed on the other surface 20b of the stainless steel sheet 20, or a suitable film other than the transparent coating film, for example, a transparent resin film that does not contain organic particles, or a colored resin film containing a coloring pigment can be formed.

[43] Although a base treatment of the stainless steel sheet frQCRnn / Lznz / E / YiAi is not essential, one is generally adopted for coating a metal sheet because the corrosion resistance and adhesion to the coated film can be improved by the base treatment. In the transparent coated stainless steel sheet 10 of the present embodiment, one surface 20a and the other surface 20b of the stainless steel sheet 20 are subjected to a chromate treatment or a chromium-free base treatment. In this way, the adhesion between the stainless steel sheet 20 and the transparent coating film 30 can be improved in addition to the improvement of the corrosion resistance of the stainless steel sheet 20.

[44] According to the transparent coated stainless steel sheet of the present modality, it is possible to improve the design properties and resistance to initial atmospheric corrosion in the use of exterior building materials such as roofing materials and the like. Examples

[45] To confirm the effect of the present invention in detail, the following experiment was carried out. This example shows an instance of the invention, and the present invention is not limited to the following configuration. frQCRnn / Lznz / E / YiAi

[46] Experimental examples As a stainless steel sheet, a 2B product of SUS304 was used which had a sheet thickness of 1.0 mm. A commercially available acrylic coating material (trade name: ECO clear colorless acrylic cracker, manufactured by SUNDAY PAINT CO., LTD.) was applied to a stainless steel sheet surface. With regard to the application of the acrylic coating material, a stick coater and a roller coater were used to form a coated film so that it has an average film thickness (pm) of the clear coating film, an interval (pm) between two adjacent protruding portions, and a height difference (pm) between an adjacent protruding portion and a recessed portion shown in Table 1. Subsequently, the coated film was baked at 120°C for 60 seconds to prepare a stainless steel sheet having a transparent coating film (transparent coated stainless steel sheet).

[47] In Table 1, numbers A1 to A9 are transparent coated stainless steel sheets from the examples of the present invention, each of which satisfies all the conditions in which an average film thickness of the transparent coating film is 0.05 pm or more and 3.00 pm or less, an interval between two adjacent protruding portions on the irregular surface of the transparent coating film is 50 pm or more and 500 pm or less, and a height difference between an adjacent protruding portion and a recessed portion on the irregular surface of the transparent coating film is 2.00 pm or less, and the contact angle between the surface of the transparent coating film and the pure water is 90° or more.

[48] ​​Furthermore, in Table 1, numbers B1 to B11 and numbers C1 to C9 are transparently coated stainless steel sheets from the comparative examples of the present invention, each of which does not satisfy at least one condition in which an average film thickness of the transparent coating film is 0.05 pm or more and 3.00 pm or less, an interval between two adjacent protruding portions of the irregular surface of the transparent coating film is 50 pm or more and 500 pm or less, a height difference between an adjacent protruding portion and a recessed portion on the irregular surface of the transparent coating film is 2.00 pm or less, or a contact angle between the surface of the transparent coating film and pure water is 90° or more.

[49] When applying the acrylic coating material using a stick coater or a roller coater, the spacing between two adjacent protruding portions and the height difference between adjacent protruding and recessed portions can be adjusted by changing the application speed. Increasing the application speed widens the spacing between adjacent protruding portions and increases the height difference between adjacent protruding and recessed portions. Furthermore, the spacing between adjacent protruding portions and the height difference between adjacent protruding and recessed portions can be adjusted by repeatedly applying the acrylic coating material.

[50] Evaluation With respect to each of the transparent coated stainless steel sheets obtained in No. A1 to No. A9, No. B1 to No. BU, and No. C1 to No. C9, the following were evaluated: average film thickness of a transparent coating film, interval between two adjacent protruding portions, height difference between an adjacent protruding portion and a recessed portion, contact angle (water repellency), and corrosion resistance.

[51] Average film thickness of a transparent coating film The average film thickness of the transparent coating film was measured by observing a cross-section of the transparently coated stainless steel sheet in one thickness direction using a scanning electron microscope (trade name: JSM-6490A, manufactured by JEOL Ltd.). On the transparent coating film, the distance from the deepest point of the recessed portion to a surface of the stainless steel sheet was measured at three points, and an average of the values ​​measured at these three points was established as the average film thickness of the transparent coating film. A case where the average film thickness was less than 0.05 µm was deemed unacceptable due to impaired corrosion resistance. Similarly, a case where the average film thickness exceeded 3.00 µm was also deemed unacceptable because the transparent coating film was noticeably cloudy. A case where the average film thickness ranged from 2.00 to 3.00 µm was considered acceptable after thorough testing, as the transparent coating film was slightly cloudy but presented no problems in practical use. The evaluation results are shown in Table 1.

[52] Interval between two adjacent projecting portions The interval between two adjacent protruding portions of the transparent coating film surface was measured by observing the film surface using a microscope (trade name: VHX-5000, manufactured by KEYENCE CORPORATION). The interval was then measured as follows: the distance between two points was measured at three points using software attached to the microscope, and an average value was calculated. A case where the gap between two adjacent protruding portions was less than 50 µm was deemed unacceptable, as it resulted in NaCl precipitation in an aqueous chloride solution, destruction of the transparent coating film, deterioration of the transparent coating film, and impaired corrosion resistance. Similarly, a case where the gap between two adjacent protruding portions exceeded 500 µm was also deemed unacceptable, as the color tone of the transparent coating film after the heat treatment described below was uneven, and the appearance of the transparently coated stainless steel sheet deteriorated. The evaluation results are shown in Table 1. frQCRnn / Lznz / E / YiAi

[53] Height difference between the projecting portion and the recessed portion adjacent to each other The height difference between adjacent protruding and recessed portions on the surface of the transparent coating film was measured by observing the surface of the transparent coating film using a scanning electron microscope (trade name: JSM-6490A, manufactured by JEOL Ltd.). On the transparent coating film, the height difference was determined as follows: a distance was measured from the deepest point of the recessed portion to the vertices (highest points of the protruding portions) of two adjacent protruding portions at three points, and an average value of the values ​​measured at the three points was established as the height difference between the adjacent protruding portion 31 and recessed portion 32. A case was deemed unacceptable when the height difference between adjacent protruding and recessed portions exceeded 2 pm, as the color tone of the transparent coating film after the heat treatment described below was uneven, and the appearance of the transparently coated stainless steel sheet deteriorated. The evaluation results are shown in Table 1.

[54] Contact angle 1.8 pL of pure water were added dropwise onto the surface of the transparent coating film, and the contact angle between the surface of the transparent coating film and the pure water was measured using a contact angle meter (trade name: DMs-401, manufactured by Kyowa Interface Science Co., Ltd.) at 25°C. The contact angle was measured at 10 points on the surface of the transparent coating film, and an average value was established as the contact angle of the transparent coating film surface. A case where the contact angle was less than 90° was deemed unacceptable, as pure water droplets remained on the surface of the transparent coating film, leading to accelerated deterioration of the film and a reduction in the corrosion resistance of the transparently coated stainless steel sheet. The evaluation results are shown in Table 1.

[55] Corrosion resistance The corrosion resistance of each of the transparent coated stainless steel sheets obtained in numbers A1 to A9, B1 to B11 and C1 to C9 was evaluated. Regarding the corrosion resistance of the transparent-coated stainless steel sheet, a dry-wet corrosion test based on JASOM 609 was performed for 50 cycles, and the appearance of the transparent-coated stainless steel sheet was visually observed after the test. A oxidized portion and a normal (non-corroded) portion were binarized, and the area ratio of the oxidized portion was determined by image processing. An acceptable rating of 0 was given when the area ratio of the oxidized portion to the surface of the transparent-coated stainless steel sheet was less than 5%, and an unacceptable rating of X was given when the area ratio of the oxidized portion was 5% or more. The evaluation results are shown in Table 1.

[56] Table Resistance to atmospheric corrosion begins! XXOOOOOOOOOX £Λ115Π(?1|Χ9 uopsuíuu^QXXXXXXXXXX Br ií Unequal X o O o XXXX o XX Transparency Unacceptable Unacceptable Acceptable Acceptable Acceptable Acceptable Acceptable Acceptable Acceptable Acceptable Acceptable Unacceptable Corrosion resistance XXXXOOOXXOO Contact angle Π 75 less than iQ o Si Osí m £ 103 Height difference between the protruding portion and the recessed portion __________íhm]__________ 2¿3 2 or less moo 5t coi CM; 0.05 1.88 3 1.85 3.85 3.34 Interval between protruding portions [µm] 8Á5 20 to 500 rj; Si 332 Zíí «JO <3 g Average film thickness [µm] OJM O o soo 0.05 seo 0.05 0.06 0.07 0.15 1.11 061 Comparative Example Comparative Example Comparative Example Comparative Example Comparative Example Comparative Example Comparative Example Comparative Example Comparative Example Comparative Example Comparative Example ¿ 1 s k. i <sj CQ se B4 B5 86 ¿a B8 B9 018 B11 frQCRnn / ίζηζ / E / γίΛΐ Table 1 (Continued 1) Initial atmospheric corrosion resistance! or । or । or OOOOOO Exhaustive determination ooooooooo T Gloss Transparency L(gua¡ Acceptable 0 Acceptable 0 Acceptable 0 Acceptable | 0 Acceptable | 0 Acceptable | 0 Acceptable | 0 Acceptable | 0 Acceptable | 0 Corrosion resistance O oo OOOOOO Contact angle ['] 16 06 66 108 102 101 o 102 103 Height difference between protruding portion and recessed portion [pm] 1.13 0.51 0.03 OOZ 1.01 1.89 1.75 tn εει Interval between protruding portions (um] 50 112 Z23 495 258 c > c > tu .£ o» ,£ & S id id | ω Example of the invention Example of the invention Example of the invention Example of the invention Example of the invention Example of the invention No. T- | CV | <t>< < < A4 A5 A6 A7 A8 A9 frQCRnn / Lznz / E / YiAi Talola 1 (Continuation 2) Initial atmospheric corrosion resistance 1 O io OOOO o OO Exhaustive determination x | x XXXXXXX Uneven brightness ï X ! O oo 0 | Unacceptable \ X 0 | Unacceptable \ 0 X 0 | Unacceptable \ XX φ 43 <C £ O Resistencia a _ , ., i Transparencia la corrosión r 0 Inaceptable X Inaceptable 0 | Inaceptable 0 | Inaceptable 0 | Inaceptable Ángulo efe contacto ZIL 801 oot co o SIL 107 s OH Diferencia dé altura entre la porción saliente y la porción rebajada tumi 222 1.58 69 L 0.03 3.05 1.25 soo o o s intervalo entre porciones salientes íum} S u> cp or 350 236 to vos 3 Average film thickness (pml) 323 453 coi LíS 5.22 srs 3 os Comparative example Comparative example Comparative example Comparative example Comparative example Comparative example Comparative example Comparative example Comparative example NO — ! CSI U ! OOO <r o so ό o c7 c8 ofrQCRnn / Lznz / E / YiAi

[57] The transparent-coated stainless steel sheet was visually inspected in each longitudinal and width direction. The transparent-coated stainless steel sheet in which no whitening or uneven luster was confirmed in either direction was determined to be acceptable and to have good transparency. The transparent-coated stainless steel sheet was visually inspected in each longitudinal and width direction. The transparent-coated stainless steel sheet in which whitening and uneven luster were confirmed in at least one direction of either the longitudinal or width direction was determined to be unacceptable and to have poor transparency.

[58] The transparent coated stainless steel sheet was visually observed in each longitudinal direction and in the width direction, and the transparent coated stainless steel sheet in which no uneven brightness was observed in both directions was fixed as O. The transparent coated stainless steel sheet was visually observed in each longitudinal direction and in the width direction, and the transparent coated stainless steel sheet in which uneven brightness was observed in at least one direction of the longitudinal or width direction was fixed as X.

[59] In Table 1, in a case where all of the frQCRnn / Lznz / E / YiAi corrosion resistance, transparency, and uneven brightness were acceptable, a complete determination was O, and in a case where at least one of the corrosion resistance, transparency, or uneven brightness was unacceptable, the overall determination was X.

[60] Based on the results in Table 1, it was found that the transparent coated stainless steel sheets obtained in numbers Al to A9 had excellent corrosion resistance, transparency, and uneven brightness.

[61] On the other hand, it was found that at least one of the corrosion resistance, transparency, or uneven brightness in each of the transparent coated stainless steel sheets obtained in No. B1 to No. B11 and No. C1 to No. C9 deteriorated.

[62] In addition, the transparently coated stainless steel sheets shown in Table 1 were installed at a steel mill adjacent to the coast and left for 3 months to evaluate their initial resistance to atmospheric corrosion. A square steel sheet with a side length of 1 m was used as the transparently coated stainless steel sheet. A case in which initial oxidation did not occur even after leaving it for 3 months was rated as 0 and had good initial resistance to atmospheric corrosion, and a case in which initial oxidation occurred was rated as X. The transparently coated stainless steel sheets numbered A1 to A9 had good initial resistance to atmospheric corrosion. Industrial applicability

[63] Since the transparent coated stainless steel sheet of the present invention has excellent design properties and initial resistance to atmospheric corrosion, the transparent coated stainless steel sheet is suitable for outdoor building materials such as roofing materials. Explanation of the reference signs

[64] 10: Transparent coated stainless steel sheet for automotive exhaust system part (transparent coated stainless steel sheet) 20: stainless steel sheet 30: frQCRnn / Lznz / E / YiAi transparent coating film< / r> < / t> ​

Claims

1. A transparently coated stainless steel sheet, comprising: a stainless steel sheet; and a transparent coating film formed on at least one surface of the stainless steel sheet and having an average film thickness of 0.05 pm or more and 3.00 pm or less.

2. The transparent coated stainless steel sheet according to claim 1, wherein a surface of the transparent coating film is an irregular surface, an interval between two adjacent protruding portions of the irregular surface is 50 pm or more and 500 pm or less, and a height difference between an adjacent protruding portion and a recessed portion on the irregular surface is 2.00 pm or less.

3. The transparent coated stainless steel sheet according to claim 1 or 2, wherein a contact angle between a surface of the transparent coating film and pure water, an aqueous halide solution or seawater is 90° or more.

4. The stainless steel sheet with a transparent coating according to any of claims 1 to 3, wherein the transparent coating film contains organic particles.