Surface treatment composition for ternary hot-dip zinc alloy coated steel sheet, ternary hot-dip zinc alloy coated steel sheet surface-treated with the same, and method for producing the same

Abstract

The present invention provides a surface treatment composition capable of imparting excellent corrosion resistance, blackening resistance, alkali resistance and unique surface color properties to ternary hot-dip zinc alloy plated steel sheet. The present invention provides a surface treatment composition comprising, relative to 100% by weight of the solid content of the composition, 70-90% by weight of a resin mixture containing a high molecular weight polysilicon-modified polyurethane main resin, a low molecular weight polysilicon-modified polyurethane auxiliary resin and an epoxy auxiliary resin; 0.5-10% by weight of a discoloration inhibitor; 0.5-10% by weight of an adhesion promoter; 0.5-10% by weight of a rust and corrosion inhibitor; 0.1-2% by weight of a color pigment; and 0.1-1% by weight of a pigment stabilizer.

Description

[Technical Field]

[0001] The present invention relates to a surface treatment composition for a ternary hot-dip zinc alloy coated steel sheet, a ternary hot-dip zinc alloy coated steel sheet surface-treated with the same, and a method for producing the same. [Background technology]

[0002] Generally, steel sheets with a hot-dip zinc alloy coating containing magnesium (Mg) and aluminum (Al), which is a steel material with superior corrosion resistance to red rust compared to pure galvanized steel sheets, have most of their exposed surface composed of zinc (Zn) or zinc alloy, and when exposed to general living environments, especially humid atmospheres, white rust develops on the surface. Furthermore, because magnesium and aluminum contained in the coating have a higher affinity for oxygen than zinc, blackening is likely to occur when there is a lack of oxygen to bond with zinc.

[0003] Conventionally, metal surfaces are coated with 5 to 100 mg / m as part of anti-rust treatment. 2 In the past, the process involved pre-treating steel sheets with chromate, then forming an organic film. However, due to the heavy metals contained in the pre-treatment agent, such as chromium (Cr), additional pre-treatment equipment and processes were required, and the heavy metal wastewater posed safety concerns for workers. Furthermore, the hexavalent chromium-containing solution generated in the wash water and wastewater must be treated using special processes, which increases manufacturing costs. Chromium ions also leach out from chromate-treated plated steel sheets during use or disposal, posing serious environmental pollution problems.

[0004] To solve these problems while maintaining corrosion resistance, conventional techniques have developed surface treatment agents, such as corrosion-resistant metal coating agents, that do not contain chromium. For example, Patent Documents 1 and 2 disclose techniques for forming coating materials by incorporating aluminum biphosphate or by combining tannic acid with sodium acetate, sodium borate, an aromatic carboxylic acid such as imidazole, and a surfactant. However, these techniques suffer from the problem of poor corrosion resistance. Patent Document 3 discloses a surface treatment agent composed of zirconium carbonate, vanadyl ions, a zirconium compound, etc., which, while offering good corrosion resistance, suffers from the problem of being vulnerable to blackening.

[0005] On the other hand, Patent Document 4 discloses a surface treatment agent composed of titanium-based, zirconium-based, phosphate-based, molybdenum-based compounds, etc., but has the problem that it cannot suppress blackening phenomenon in hot-dip zinc alloy-plated steel sheets that use magnesium (Mg), aluminum (Al), etc. Patent Document 5 discloses a surface treatment agent composed of ammonium molybdate, water-dispersible urethane resin, isopropylamine, ammonium zirconium carbonate, an epoxy-based silane coupling agent, and silica sol, but has the problem that it cannot impart sufficient corrosion resistance.

[0006] Meanwhile, in order to use steel materials as building materials, the surface properties must be beautiful, and it is necessary to impart a unique color to the surface of the material so that customers can distinguish it from existing hot-dip galvanized steel materials and hot-dip zinc alloy plated steel materials when using the steel materials. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 53-28857 [Patent Document 2] Japanese Patent Application Publication No. 51-71233 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-332574 [Patent Document 4] Japanese Patent Application Publication No. 7-096699 [Patent Document 5] Japanese Patent Application Laid-Open No. 2005-146340 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been devised in view of the above-mentioned circumstances, and aims to provide a surface treatment composition that can impart excellent corrosion resistance, blackening resistance, alkali resistance and unique surface color characteristics to ternary hot-dip zinc alloy plated steel sheets used as building materials.

[0009] Another object of the present invention is to provide a surface treatment composition that has excellent pigment dispersion stability, does not cause precipitation or aggregation even when used after long-term storage, and can impart excellent corrosion resistance and discoloration resistance to hot-dip zinc alloy-plated steel sheets, particularly in high-temperature, high-humidity environments.

[0010] Furthermore, the present invention aims to provide a surface treatment composition that is harmless to the human body and does not cause problems due to environmental pollution, since it does not contain any heavy metal components such as chromium, which are environmental pollutants.

[0011] Another object of the present invention is to provide a hot-dip zinc alloy coated steel sheet having excellent corrosion resistance, blackening resistance, alkali resistance and unique surface color characteristics, and a method for manufacturing the same. [Means for solving the problem]

[0012] According to one embodiment of the present invention, there is provided a surface treatment composition comprising, relative to 100% by weight of the solids content of the composition, 70 to 90% by weight of a resin mixture including a high molecular weight polysilicon-modified polyurethane main resin, a low molecular weight polysilicon-modified polyurethane auxiliary resin, and an epoxy auxiliary resin; 0.5 to 10% by weight of an anti-tarnish agent; 0.5 to 10% by weight of an adhesion promoter; 0.5 to 10% by weight of a rust and corrosion inhibitor; 0.1 to 2% by weight of a color pigment; and 0.1 to 1% by weight of a pigment stabilizer.

[0013] According to one embodiment of the present invention, there is provided a surface-treated ternary hot-dip zinc alloy-plated steel sheet, comprising: a steel sheet; a ternary hot-dip zinc alloy plating layer formed on at least one surface of the steel sheet; and a surface treatment film layer formed on the ternary hot-dip zinc alloy plating layer, wherein the surface treatment film layer is formed from the surface treatment composition.

[0014] According to one embodiment of the present invention, there is provided a method for producing a surface-treated ternary hot-dip zinc alloy-plated steel sheet, the method comprising: coating the surface treatment composition on a ternary hot-dip zinc alloy-plated steel sheet having a ternary hot-dip zinc alloy plating layer formed thereon; and drying the surface treatment composition to form a surface treatment film layer. [Effects of the Invention]

[0015] By coating the surface treatment composition according to the present invention on a hot-dip zinc alloy-plated steel sheet to form a surface treatment film layer, it is possible to provide a hot-dip zinc alloy-plated steel sheet having excellent corrosion resistance, blackening resistance, alkali resistance and unique surface color properties.

[0016] Furthermore, the surface treatment composition according to the present invention has excellent pigment dispersion stability, does not cause precipitation or aggregation even when used after long-term storage, and can impart excellent surface gloss to hot-dip zinc alloy-plated steel sheets.

[0017] Furthermore, the surface treatment composition of the present invention does not contain any heavy metal components such as chromium, which are environmental pollutants, and is therefore harmless to the human body and does not cause problems due to environmental pollution. DETAILED DESCRIPTION OF THE INVENTION

[0018] While the present invention will be described in detail below with reference to preferred embodiments thereof, the scope of the present invention is not limited to the following embodiments, and the present invention may be modified in various ways.

[0019] The present invention relates to a surface treatment composition for ternary hot-dip zinc alloy-plated steel sheets, which has excellent solution stability and, when applied to ternary hot-dip zinc alloy-plated steel sheets, has excellent flat plate corrosion resistance, processed area corrosion resistance, blackening resistance, alkali resistance, and excellent surface properties. The present invention also relates to a ternary hot-dip zinc alloy-plated steel sheet surface-treated with the surface treatment composition and a method for producing the same.

[0020] A surface treatment composition according to one embodiment of the present invention can contain, relative to 100% by weight of the solids content of the composition, 70 to 90% by weight of a resin mixture containing a high molecular weight polysilicon-modified polyurethane main resin, a low molecular weight polysilicon-modified polyurethane auxiliary resin, and an epoxy auxiliary resin; 0.5 to 10% by weight of a discoloration inhibitor; 0.5 to 10% by weight of an adhesion promoter; 0.5 to 10% by weight of a rust and corrosion inhibitor; 0.1 to 2% by weight of a color pigment; and 0.1 to 1% by weight of a pigment stabilizer.

[0021] In one embodiment, the high molecular weight polysilicon-modified polyurethane base resin is a component that can impart excellent corrosion resistance, water resistance, and solvent resistance to ternary hot-dip zinc alloy plated steel sheet. The high molecular weight polysilicon-modified polyurethane base resin can be synthesized from, but is not limited to, a silicone polymer and a polycarbonate polyol, and has self-crosslinking properties due to the use of a trimer isocyanate polymer during synthesis.

[0022] The weight-average molecular weight (Mw) of the high-molecular-weight polysilicon-modified polyurethane base resin may be 100,000 to 200,000. If the weight-average molecular weight is less than 100,000, it is difficult to ensure sufficient corrosion resistance. On the other hand, if the weight-average molecular weight exceeds 200,000, the solution stability decreases, the hardness of the film increases, and there is a possibility that problems such as reduced processability may occur.

[0023] The glass transition temperature (Tg) of the high molecular weight polysilicon-modified polyurethane base resin may be -20°C to -10°C. If the glass transition temperature is below -20°C, it is difficult to ensure sufficient corrosion resistance. On the other hand, if the glass transition temperature is above -10°C, the solution stability decreases, the hardness of the film increases, and there is a possibility that problems such as reduced processability may occur.

[0024] In one embodiment, the low molecular weight polysilicon-modified polyurethane auxiliary resin is a component that can impart flexibility to ternary hot-dip zinc alloy-plated steel sheets, thereby improving processability and adhesion. The low molecular weight polysilicon-modified polyurethane auxiliary resin can be synthesized from, but is not limited to, a silicone polymer and a polycarbonate polyol. Unlike high molecular weight polysilicon-modified polyurethane base resins, the low molecular weight polysilicon-modified polyurethane auxiliary resin does not have self-crosslinking properties.

[0025] The weight-average molecular weight of the low-molecular-weight polysilicon-modified polyurethane auxiliary resin may be 30,000 to 70,000. If the weight-average molecular weight is less than 30,000, the density of the coating decreases, making it difficult to ensure sufficient corrosion resistance. On the other hand, if the weight-average molecular weight exceeds 70,000, the effect of imparting flexibility to the coating is insufficient, which may result in problems such as reduced processability and adhesion.

[0026] The glass transition temperature (Tg) of the low molecular weight polysilicon-modified polyurethane auxiliary resin may be -30°C to -20°C. If the glass transition temperature is below -30°C, it is difficult to ensure sufficient corrosion resistance due to a decrease in the density of the coating. On the other hand, if the glass transition temperature is above -20°C, the effect of imparting flexibility to the coating is insufficient, which may result in problems such as reduced processability and adhesion.

[0027] In one embodiment, the epoxy auxiliary resin is a component for forming a dense coating on a ternary hot-dip zinc alloy plated steel sheet and improving the corrosion resistance of the sheet.

[0028] The epoxide equivalent ratio of the epoxy auxiliary resin may be 450 to 550 g / eq. If the epoxide equivalent ratio is less than 450 g / eq, the coating density and plate corrosion resistance may not be sufficiently improved. On the other hand, if the epoxide equivalent ratio exceeds 550 g / eq, the coating may become too hard, which may cause problems such as reduced processability.

[0029] The weight-average molecular weight (Mw) of the epoxy auxiliary resin may be 450 to 4,000. If the weight-average molecular weight (Mw) is less than 450, the coating density and plate corrosion resistance are not sufficiently improved. On the other hand, if the weight-average molecular weight (Mw) exceeds 4,000, the coating becomes too hard, which may cause problems such as reduced processability.

[0030] The resin mixture may be a mixture of high molecular weight polysilicon-modified polyurethane base resin, low molecular weight polysilicon-modified polyurethane auxiliary resin, and epoxy auxiliary resin in a weight ratio of 1:4.5:4.5 to 9:0.5:0.5, preferably 1:0.5:0.5 to 9:0.5:0.5, and more preferably 2:0.5:0.5 to 9:0.5:0.5. For example, a mixture of high molecular weight polysilicon-modified polyurethane base resin, low molecular weight polysilicon-modified polyurethane auxiliary resin, and epoxy auxiliary resin in a weight ratio of 2:0.5:0.5 can be used, and ...1:0.5:0.5 can be used.

[0031] If the content of the high molecular weight polysilicon-modified polyurethane base resin in the resin mixture is too low, the flat corrosion resistance, processed corrosion resistance, and alkali resistance of the steel sheet may be reduced. On the other hand, if the content of the high molecular weight polysilicon-modified polyurethane base resin in the resin mixture is too high, the processed corrosion resistance and blackening resistance of the steel sheet may be reduced.

[0032] In one embodiment, the content of the resin mixture may be 70 to 90 wt % relative to 100 wt % of the solids content of the surface treatment composition. If the content of the resin mixture is less than 70 wt %, it may be difficult to ensure sufficient corrosion resistance and alkali resistance, and if the content of the resin mixture is more than 90 wt %, the content of additives for improving the physical properties of the surface treatment composition may be relatively small, which may result in problems such as reduced corrosion resistance and reduced solution stability.

[0033] In one embodiment, the anti-tarnish agent is a component contained in the ternary hot-dip zinc alloy-plated steel sheet to prevent discoloration in a high-temperature and high-humidity environment. The anti-tarnish agent may be one or more compounds selected from the group consisting of ammonium molybdate and sodium molybdate.

[0034] The content of the discoloration inhibitor may be 0.5 to 10 wt% relative to 100 wt% of the solid content of the surface treatment composition. If the content of the discoloration inhibitor is less than 0.5 wt%, sufficient discoloration resistance cannot be expected, and if the content of the discoloration inhibitor exceeds 10 wt%, although the effect of improving discoloration resistance is slight, there is a possibility that a problem of reduced corrosion resistance may occur.

[0035] In one embodiment, the adhesion promoter is a component that improves adhesion between the steel sheet and resin to prevent peeling of the coating and to prevent moisture from penetrating into the plating layer in a high-humidity environment. The adhesion promoter may be at least one selected from the group consisting of ester phosphate, ammonium phosphate, and ammonium zirconium carbonate (AZC).

[0036] The content of the adhesion promoter may be 0.5 to 10 wt % relative to 100 wt % of the solid content of the surface treatment composition. If the content of the adhesion promoter is less than 0.5 wt %, the effects of improving adhesion and preventing moisture penetration may be insufficient, and if the content of the adhesion promoter is more than 10 wt %, the solution stability of the surface treatment composition may decrease.

[0037] In one embodiment, the rust and corrosion inhibitor is a component contained in order to improve the corrosion resistance of the ternary hot-dip zinc alloy plated steel sheet, and may be one or more selected from the group consisting of phosphate-based rust inhibitors, fluorine-based rust inhibitors, vanadium-based rust inhibitors, cerium salt-based rust inhibitors, and selenium salt-based rust inhibitors.

[0038] The content of the rust and corrosion inhibitor may be 0.5 to 10 wt% relative to 100 wt% of the solid content of the surface treatment composition. If the content of the rust and corrosion inhibitor is less than 0.5 wt%, it may be difficult to ensure blackening resistance and alkali resistance, and if the content of the rust and corrosion inhibitor is more than 10 wt%, it may be difficult to ensure corrosion resistance.

[0039] In one embodiment, the color pigment is a component for imparting color to the ternary hot-dip zinc alloy coated steel sheet to impart attractive surface properties. The color pigment may be one or more inorganic pigments selected from the group consisting of titanium, lead, iron, copper, and chromium; and azo-based organic pigments.

[0040] The content of the color pigment may be 0.1 to 2 wt% relative to 100 wt% of the solid content of the surface treatment composition. If the content of the color pigment is less than 0.1 wt%, it may be difficult to achieve sufficient color expression, and if the content of the color pigment is more than 2 wt%, problems such as reduced solution stability and corrosion resistance may occur.

[0041] In one embodiment, the pigment stabilizer is a component that caps the color pigment to uniformly disperse the color pigment in the coating, thereby improving the gloss of the coating. The pigment stabilizer may be, but is not limited to, a carboxyl-based polymer.

[0042] The content of the pigment stabilizer may be 0.1 to 1 wt% based on 100 wt% of the solids content of the surface treatment composition. If the content of the pigment stabilizer is less than 0.1 wt%, it is difficult to ensure sufficient solution stability, and if the content of the pigment stabilizer is more than 1 wt%, there is a possibility that excessive residual components in the coating may actually reduce the gloss of the coating.

[0043] In one embodiment, the surface treatment composition includes water as a solvent to dilute each component, and the water may be deionized water or distilled water. The solvent is included as the balance other than each component of the present invention, and its content may be 60 to 80 wt %. Furthermore, the surface treatment composition according to one embodiment may further include N-ethyl-2-pyrrolidone (NEP) as a co-solvent to ensure solution stability, and the N-ethyl-2-pyrrolidone may be included in an amount of 20 to 40 wt % of the total solvent.

[0044] A ternary hot-dip zinc alloy plated steel sheet surface-treated with a surface treatment composition containing a water-soluble organic resin and an inorganic compound according to one embodiment of the present invention exhibits excellent corrosion resistance and blackening resistance as well as excellent surface color and gloss. Furthermore, the surface treatment composition according to one embodiment of the present invention does not contain hexavalent chromium, a harmful environmental substance, and contains water-soluble organic resins and inorganic compounds that are harmless to the human body as main components, thereby preventing problems of harm to the human body and environmental pollution.

[0045] According to one embodiment of the present invention, there is provided a ternary hot-dip zinc alloy plated steel sheet that has been surface-treated with the above-mentioned surface treatment composition.

[0046] Specifically, the surface-treated ternary hot-dip zinc alloy plated steel sheet may include a steel sheet, a ternary hot-dip zinc alloy plated layer formed on at least one surface of the steel sheet, and a surface treatment coating layer containing an organic resin and an inorganic compound formed on the ternary hot-dip zinc alloy plated layer.

[0047] The base steel sheet and the ternary hot-dip zinc alloy coating layer may include an Al-enriched layer formed at the interface, and the Al-enriched layer may have an area ratio of 70% to 100%. The ternary hot-dip zinc alloy coating layer may include 0.2 to 15 wt% Al, 0.5 to 3.5 wt% Mg, and the balance being Zn and unavoidable impurities.

[0048] In one embodiment, the ternary hot-dip zinc alloy-coated steel sheet includes an Al-enriched layer formed at the interface between the base iron and the Zn-Al-Mg alloy coating layer, and the area ratio of the Al-enriched layer may be 70% to 100%, more preferably 73% to 100%. Here, the area ratio refers to the ratio of the area of ​​the Al-enriched layer to the area of ​​the base iron when viewed from the surface of the coated steel sheet projected in the thickness direction of the base iron, assuming a flat surface without consideration of three-dimensional bending, etc. When the area ratio of the Al-enriched layer is ensured to be 70% or more, the Al-enriched layer has a morphology in which fine particles are continuously formed, which can significantly improve platability and coating adhesion.

[0049] In a ternary hot-dip zinc alloy coated steel sheet according to one embodiment of the present invention, magnesium plays an extremely important role in improving the corrosion resistance of the ternary hot-dip zinc alloy coated steel sheet. By forming a dense zinc hydroxide corrosion product on the surface of the coating layer in a corrosive environment, magnesium effectively prevents corrosion of the ternary hot-dip zinc alloy coated steel sheet. To ensure the desired corrosion resistance, the coating layer must contain at least 0.5 wt. %, more preferably at least 0.9 wt. % magnesium. However, excessive magnesium content can rapidly increase magnesium oxide dross on the surface of the coating bath, counteracting the oxidation prevention effect of the trace element addition. To prevent this, the coating layer should contain at most 3.5 wt. %, more preferably at most 3.2 wt. % magnesium.

[0050] In a ternary hot-dip zinc alloy coated steel sheet according to one embodiment of the present invention, Al suppresses the formation of Mg oxide dross in the coating bath and reacts with Zn and Mg in the coating bath to form a Zn-Al-Mg intermetallic compound, thereby improving the corrosion resistance of the coated steel sheet. To achieve these effects, the coating layer must contain 0.2 wt. % or more of Al, and more preferably 0.9 wt. % or more. However, excessive Al content may deteriorate the weldability and phosphate treatability of the coated steel. To prevent this, the coating layer should contain 15 wt. % or less of Al, and more preferably 12 wt. % or less of Al.

[0051] The surface treatment film layer containing the organic resin and inorganic compound can be formed from a surface treatment composition containing, relative to 100% by weight of the solids content of the composition, 70-90% by weight of a resin mixture containing a high-molecular-weight polysilicon-modified polyurethane base resin, a low-molecular-weight polysilicon-modified polyurethane auxiliary resin, and an epoxy auxiliary resin; 0.5-10% by weight of a discoloration inhibitor; 0.5-10% by weight of an adhesion promoter; 0.5-10% by weight of a rust and corrosion inhibitor; 0.1-2% by weight of a color pigment; and 0.1-1% by weight of a pigment stabilizer. The surface treatment composition has the same technical features as those described above, so a redundant description will not be provided.

[0052] In one embodiment, the surface treatment film layer is a coating layer formed by drying the surface treatment composition described above, and corresponds to the components remaining after all of the volatile substances contained in the surface treatment film layer containing the organic resin and inorganic compound have evaporated. Therefore, the surface treatment film layer containing the organic resin and inorganic compound does not contain the solvent water or N-ethyl-2-pyrrolidone, nor does it contain any solvents contained in the surface treatment components containing the organic resin and inorganic compound. Therefore, the components contained in the surface treatment film layer containing the organic resin and inorganic compound correspond to the content based on 100 wt% of the total solids content.

[0053] According to one embodiment of the present invention, there is provided a method for producing a surface-treated ternary hot-dip zinc alloy-plated steel sheet, the method comprising the steps of: coating the above-described surface treatment composition on a ternary hot-dip zinc alloy-plated steel sheet having a ternary hot-dip zinc alloy plating layer formed thereon; and drying the surface treatment composition to form a surface treatment film layer.

[0054] In one embodiment, the surface treatment composition may be coated to a thickness of 2.5 to 50 μm. The coated surface treatment composition may then be dried to form a dry coating layer, and the dry coating layer may have a thickness of 1 to 10 μm. If the coating thickness of the surface treatment composition is less than 2.5 μm, the surface treatment composition may be applied too thinly to convex portions of the steel sheet roughness, which may result in reduced corrosion resistance. If the thickness exceeds 50 μm, the coating layer may be formed too thick, which may result in reduced workability and increased solution treatment costs, which may result in economical issues.

[0055] The method for coating the surface treatment composition is not particularly limited as long as it is a commonly used coating method, but it is preferable to use any one of coating methods selected from, for example, roll coating, spraying, deposition, spray squeegeeing, and deposition squeegeeing.

[0056] The process of drying the surface treatment composition coated on the ternary hot-dip zinc alloy-plated steel sheet is preferably carried out at a temperature of 70 to 250°C based on the PMT (Pass-to-Module Temperature) of the base steel sheet. If the drying temperature is less than 70°C based on the PMT (Pass-to-Module Temperature) of the base steel sheet, the curing reaction of the organic resin will not be complete, resulting in an insufficient film structure and potentially poor corrosion and alkali resistance. On the other hand, if the drying temperature exceeds 250°C based on the PMT (Pass-to-Module Temperature) of the base steel sheet, productivity will be reduced due to the generation of water vapor and fumes during the water cooling process, and the evaporated water vapor will condense on the top of the drying equipment, potentially resulting in poor surface quality of the product.

[0057] Meanwhile, the drying process is preferably carried out in a hot air drying oven or an induction heating oven. When the surface treatment composition is dried using a hot air drying oven, the internal temperature of the hot air drying oven is preferably 100 to 300°C. When the surface treatment composition is dried using an induction heating oven, the current applied to the induction heating oven is preferably 1000 to 5000 A, more preferably 1500 to 3500 A. If the internal temperature of the hot air drying oven is below 100°C or the current applied to the induction heating oven is less than 1000 A, the curing reaction of the surface treatment composition may not be complete, resulting in poor corrosion resistance and alkali resistance. Furthermore, if the internal temperature of the hot air drying oven exceeds 300°C or the current applied to the induction heating oven exceeds 5000 A, productivity may decrease due to the generation of water vapor and fumes during the water cooling process, and the surface quality of the product may be reduced due to condensation of evaporated water vapor on the upper part of the drying equipment.

[0058] Furthermore, the surface treatment composition is dried to form a surface treatment film layer, and then the surface treatment film layer is water-cooled to finally provide a surface-treated ternary hot-dip zinc alloy plated steel sheet.

[0059] The method for producing a ternary hot-dip zinc alloy coated steel sheet according to one embodiment of the present invention may be carried out in a continuous process, and the speed of the continuous process is preferably 80 to 120 mpm. If the speed of the continuous process is less than 80 mpm, a problem of reduced productivity may occur, and if it exceeds 120 mpm, the solution may splash during the process of drying the surface treatment composition, causing surface defects. [Example]

[0060] EXAMPLES The present invention will be described in detail below with reference to examples. The following examples are provided to aid in understanding the present invention, but are not intended to limit the present invention.

[0061] Preparation of test specimens The ternary hot-dip zinc alloy coated steel sheet (coating amount on one side: 0.5 to 2.0 g / m2) is composed of a ternary hot-dip zinc alloy coating layer consisting of, by weight, 1.5% Mg, 1.5% Al, and the balance Zn. 2 After cutting the sheet into a size of 7 cm x 15 cm (width x length) and removing any oil, each composition was applied to a hot-dip zinc alloy plated steel sheet using a bar coater. Then, the sheet was cured at a PMT (Peak Metal Temperature (temperature of the substrate surface)) of 180±20°C to prepare test specimens.

[0062] Testing and Evaluation Methods The methods and criteria for evaluating the physical properties of the surface-treated steel sheets in the present examples are as follows.

[0063] <Plate corrosion resistance> After treating the test pieces according to the method specified in ASTM B117, the rate of white rust formation on the steel sheets over time was measured, and the evaluation criteria were as follows:

[0064] ◎: It took more than 144 hours for white rust to appear ○: Time taken for white rust to appear was 96 hours or more but less than 144 hours △: Time taken for white rust to appear was between 55 and 96 hours X: Time taken for white rust to appear is less than 55 hours

[0065] <Corrosion resistance of processed parts> The test piece was pushed up to a height of 6 mm using an Erichsen tester, and the degree of white rust was measured after 24 hours. The evaluation criteria were as follows:

[0066] ◎: White rust occurs on less than 5% of the area after 48 hours ○: White rust area after 48 hours is 5% or more but less than 7% X: White rust occurs on 7% or more of the area after 48 hours

[0067] <Blackening resistance> The test piece was left in a thermo-hygrostat maintained at 50°C and a relative humidity of 95% for 120 hours, and the color change (color difference: ΔE) of the test piece before and after the test was observed. The evaluation criteria were as follows:

[0068] ◎:ΔE≦2 ○:2<ΔE≦3 △:3<ΔE≦4 X:ΔE>4

[0069] <Alkali resistance> The test piece was immersed in an alkaline degreasing solution at 60°C for 2 minutes, then rinsed with water and air-blowed, after which the color difference (ΔE) before and after was measured. The alkaline degreasing solution used was Finecleaner L 4460 A: 20g / 2.4L + L 4460 B 12g / 2.4L (pH=12) from Daehan Parkerizing Co., Ltd. The evaluation criteria were as follows:

[0070] ◎:ΔE≦2 ○:2<ΔE≦3 △:3<ΔE≦4 X:ΔE>4

[0071] <Solution stability> The surface treatment composition was placed in a container and placed in a thermostatic oven at 50°C. After storing for 7 days, the presence or absence of precipitates was visually observed and the change in viscosity was measured. The evaluation criteria were as follows:

[0072] ○: No precipitation, viscosity change less than 1 cP △: No precipitation, viscosity change of 1 cP or more but less than 5 cP X: Precipitation occurs or viscosity change is 5 cP or more

[0073] <Glossiness> The gloss of the test piece was measured at an incident angle of 60° using a gloss meter, and the evaluation criteria were as follows:

[0074] ○: Good, gloss value 80 or more X: Poor, gloss value less than 80

[0075] Components of the surface treatment composition The components of the surface treatment compositions used in the examples are as follows:

[0076] - High molecular weight polysilicon modified polyurethane base resin: polyurethane resin with a weight average molecular weight of 150,000 - Low molecular weight polysilicon modified polyurethane auxiliary resin (auxiliary resin 1): polyurethane resin with a weight average molecular weight of 50,000 - Epoxy auxiliary resin (auxiliary resin 2): Epoxy resin with an equivalent ratio of 500g / eq and a weight average molecular weight of 2,000 - Anti-tarnish agent: ammonium molybdate - Adhesion promoter: Ammonium zirconium carbonate - Rust and corrosion inhibitor: Fluorine-based rust inhibitor - Color pigment: Azo organic pigment - Pigment stabilizer: carboxyl polymer - Solvent: A mixed solvent of water and N-Ethyl-2-pyrrolidone (NEP)

[0077] Example 1: Changes in physical properties depending on the content of resin mixture A surface treatment composition was prepared by mixing the above-mentioned main resin, auxiliary resin 1, and auxiliary resin 2 in a weight ratio of 1:0.5:0.5 to prepare a resin mixture, a discoloration inhibitor, an adhesion promoter, a rust and corrosion inhibitor, a color pigment, and a pigment stabilizer in the amounts shown in Table 1. The surface treatment composition contained a mixed solvent of 49 wt% water and 21 wt% N-ethyl-2-pyrrolidone (70 wt% based on the total weight of the composition).

[0078] The solution stability of the surface treatment composition prepared above was evaluated. Furthermore, after applying the surface treatment composition to the above-mentioned test specimen, the flat plate corrosion resistance, processed part corrosion resistance, blackening resistance, and alkali resistance of the test specimen were evaluated. The evaluation results are shown in Table 1 below.

[0079] [Table 1]

[0080] Referring to Table 1 above, Examples 1 to 3, which contain resin mixtures satisfying the content suggested by the present invention, showed good (◯) or better results in all physical properties. However, Comparative Example 1, which contains an excessively small amount of resin mixture, showed poor results in flat plate corrosion resistance, processed part corrosion resistance, and alkali resistance, and Comparative Example 2, which contains an excessively large amount of resin mixture, showed poor results in flat plate corrosion resistance, processed part corrosion resistance, blackening resistance, and solution stability.

[0081] Example 2: Changes in physical properties depending on the content ratio of main resin and auxiliary resin A surface treatment composition was prepared containing 80% by weight of a resin mixture containing the above-mentioned main resin, auxiliary resin 1, and auxiliary resin 2, 5% by weight of a discoloration inhibitor, 5.5% by weight of an adhesion promoter, 8% by weight of a rust and corrosion inhibitor, 1% by weight of a color pigment, and 0.5% by weight of a pigment stabilizer. The surface treatment composition contained a mixed solvent of 49% by weight of water and 21% by weight of N-ethyl-2-pyrrolidone (70% by weight based on the total weight of the composition).

[0082] In the resin mixture, the main resin, auxiliary resin 1, and auxiliary resin 2 were mixed in the weight ratios shown in Table 2 below.

[0083] After applying the surface treatment composition to the above-mentioned test specimen, the flat plate corrosion resistance, processed part corrosion resistance, blackening resistance, and alkali resistance of the test specimen were evaluated, and the evaluation results are shown in Table 2 below.

[0084] [Table 2]

[0085] Referring to Table 2, Examples 4 to 7, in which the weight ratio of the main resin to the auxiliary resin satisfied the content ratio proposed by the present invention, showed results of good (◯) or better in all physical properties. On the other hand, Comparative Example 3, which contained an excessively small amount of water-soluble main resin, showed poor results in flat plate corrosion resistance, processed part corrosion resistance, and alkali resistance, and Comparative Example 4, which contained excessively small amounts of Auxiliary Resin 1 and Auxiliary Resin 2, showed poor results in processed part corrosion resistance and blackening resistance.

[0086] Example 3: Changes in physical properties depending on the content of anti-tarnish agent A surface treatment composition was prepared by mixing the above-mentioned main resin, auxiliary resin 1, and auxiliary resin 2 in a weight ratio of 1:0.5:0.5 to prepare a resin mixture, a discoloration inhibitor, an adhesion promoter, a rust and corrosion inhibitor, a color pigment, and a pigment stabilizer in the amounts shown in Table 3. The surface treatment composition contained a mixed solvent of 49 wt% water and 21 wt% N-ethyl-2-pyrrolidone (70 wt% based on the total weight of the composition).

[0087] The solution stability of the surface treatment composition prepared above was evaluated. Furthermore, after applying the surface treatment composition to the test specimen described above, the flat plate corrosion resistance, processed part corrosion resistance, blackening resistance, and alkali resistance of the test specimen were evaluated. The evaluation results are shown in Table 3 below.

[0088] [Table 3]

[0089] Referring to Table 3 above, Examples 8 to 10, which contained the anti-tarnish agent in the amounts recommended by the present invention, showed good (◯) or better results in all physical properties. On the other hand, Comparative Example 5, which contained an excessively small amount of anti-tarnish agent, showed poor results in blackening resistance and alkali resistance, and Comparative Example 6, which contained an excessively large amount of anti-tarnish agent, showed poor results in flat plate corrosion resistance, processed part corrosion resistance, and solution stability.

[0090] Example 4: Changes in physical properties depending on the content of adhesion promoter A surface treatment composition was prepared by mixing the above-mentioned main resin, auxiliary resin 1, and auxiliary resin 2 in a weight ratio of 1:0.5:0.5 to prepare a resin mixture, a discoloration inhibitor, an adhesion promoter, a rust and corrosion inhibitor, a color pigment, and a pigment stabilizer in the amounts shown in Table 4. The surface treatment composition contained a mixed solvent of 49 wt% water and 21 wt% N-ethyl-2-pyrrolidone (70 wt% based on the total weight of the composition).

[0091] The solution stability of the surface treatment composition prepared above was evaluated. Furthermore, after applying the surface treatment composition to the above-mentioned test specimen, the flat plate corrosion resistance, processed part corrosion resistance, blackening resistance, and alkali resistance of the test specimen were evaluated. The evaluation results are shown in Table 4 below.

[0092] [Table 4]

[0093] Referring to Table 4 above, Examples 11 to 13, which contain adhesion promoters in amounts satisfying the ranges proposed by the present invention, showed good (◯) or better results in all physical properties. However, Comparative Example 7, which contains an excessively small amount of adhesion promoter, showed poor results in plate corrosion resistance, processed part corrosion resistance, and alkali resistance, and Comparative Example 8, which contains an excessively large amount of adhesion promoter, showed poor results in solution stability.

[0094] Example 5: Changes in physical properties depending on the content of anti-rust and anti-corrosion agents A surface treatment composition was prepared by mixing the above-mentioned main resin, auxiliary resin 1, and auxiliary resin 2 in a weight ratio of 1:0.5:0.5 to prepare a resin mixture, a discoloration inhibitor, an adhesion promoter, a rust and corrosion inhibitor, a color pigment, and a pigment stabilizer in the amounts shown in Table 5. The surface treatment composition contained a mixed solvent of 49 wt% water and 21 wt% N-ethyl-2-pyrrolidone (70 wt% based on the total weight of the composition).

[0095] The solution stability of the surface treatment composition prepared above was evaluated. Furthermore, after applying the surface treatment composition to the test specimen described above, the flat plate corrosion resistance, processed part corrosion resistance, blackening resistance, and alkali resistance of the test specimen were evaluated. The evaluation results are shown in Table 5 below.

[0096] [Table 5]

[0097] Referring to Table 5 above, Examples 14 to 16, which contained the rust and corrosion inhibitors in amounts satisfying the ranges proposed by the present invention, showed good (◯) or better results in all physical properties. However, Comparative Example 9, which contained an excessively small amount of rust and corrosion inhibitor, showed poor results in flat plate corrosion resistance and processed part corrosion resistance, and Comparative Example 10, which contained an excessively large amount of rust and corrosion inhibitor, showed poor results in blackening resistance and alkali resistance.

[0098] Example 6: Changes in physical properties depending on the content of color pigment A surface treatment composition was prepared by mixing the above-mentioned main resin, auxiliary resin 1, and auxiliary resin 2 in a weight ratio of 1:0.5:0.5 to prepare a resin mixture, a discoloration inhibitor, an adhesion promoter, a rust and corrosion inhibitor, a color pigment, and a pigment stabilizer in the amounts shown in Table 6. The surface treatment composition contained a mixed solvent of 49 wt% water and 21 wt% N-ethyl-2-pyrrolidone (70 wt% based on the total weight of the composition).

[0099] The solution stability of the surface treatment composition prepared above was evaluated. Furthermore, after applying the surface treatment composition to the above-mentioned test specimen, the test specimen was evaluated for flat plate corrosion resistance, processed part corrosion resistance, blackening resistance, alkali resistance, and the degree of surface color development. The degree of surface color development was evaluated by visually observing the test specimen treated with the surface treatment composition, and the degree of color development was classified as good (○) or poor (X). The evaluation results are shown in Table 6 below.

[0100] [Table 6]

[0101] Referring to Table 6 above, Examples 17 to 19, which contain color pigments in amounts that meet the ranges proposed by the present invention, showed good (◯) or better results in all physical properties. However, Comparative Example 11, which contains too little color pigment, showed poor results in surface color expression, and Comparative Example 12, which contains too much color pigment, showed poor results in plate corrosion resistance, processed part corrosion resistance, and solution stability.

[0102] Example 7: Changes in physical properties depending on the content of pigment stabilizer A surface treatment composition was prepared by mixing the above-mentioned main resin, auxiliary resin 1, and auxiliary resin 2 in a weight ratio of 1:0.5:0.5 to prepare a resin mixture, a discoloration inhibitor, an adhesion promoter, a rust and corrosion inhibitor, a color pigment, and a pigment stabilizer in the amounts shown in Table 7. The surface treatment composition contained a mixed solvent of 49 wt% water and 21 wt% N-ethyl-2-pyrrolidone (70 wt% based on the total weight of the composition).

[0103] The solution stability of the surface treatment composition prepared above was evaluated. Furthermore, after applying the surface treatment composition to the above-mentioned test specimen, the test specimen was evaluated for flat plate corrosion resistance, processed part corrosion resistance, blackening resistance, alkali resistance, and gloss. The evaluation results are shown in Table 7 below.

[0104] [Table 7]

[0105] Referring to Table 7 above, Examples 20 to 22, which contain pigment stabilizer in an amount that satisfies the range proposed by the present invention, showed good (◯) or better results in all physical properties. However, Comparative Example 13, which contains too little pigment stabilizer, showed poor solution stability, and Comparative Example 14, which contains too much pigment stabilizer, showed poor gloss.

[0106] Example 8: Changes in physical properties depending on the thickness of the coating layer and drying temperature The surface treatment composition according to Example 2 was applied to a test specimen using a bar (BAR) and dried in a hot air drying oven. The flat plate corrosion resistance, processed part corrosion resistance, blackening resistance, and alkali resistance of the test specimen were evaluated while controlling the coating layer thickness and PMT temperature as shown in Table 8 below.

[0107] [Table 8]

[0108] As shown in Table 8 above, Examples 23 to 26, in which coating layers of 1 to 10 μm thick were formed, showed results of good (◯) or better in all physical properties. On the other hand, Comparative Example 15, in which the formed coating was excessively thin, showed fair (△) results in flat plate corrosion resistance, blackening resistance, and alkali resistance, and showed a poor result in processed part corrosion resistance. On the other hand, Comparative Example 16, in which an excessively thick coating was formed, showed a poor result in processed part corrosion resistance, and did not show any improved physical properties compared to Example 26, so from an economical point of view, a coating thickness of more than 10 μm is not required. On the other hand, as shown in Table 8 above, Examples 27 to 29, in which coating layers were formed by drying the coating at 70 to 250°C, showed results of good (◯) or better in all physical properties. On the other hand, Comparative Example 17, in which the drying temperature was excessively low, showed poor results in all physical properties because the coating was not sufficiently dried. On the other hand, Comparative Example 18, in which the drying temperature was excessively high, showed poor blackening resistance due to fume drops on the steel sheet caused by condensation of water vapor generated on the steel sheet during the air cooling process (water cooling). Although the examples of the present invention have been described in detail above, it will be obvious to those skilled in the art that the scope of the present invention is not limited thereto, and various modifications and variations are possible within the scope of the technical concept of the present invention as set forth in the claims.

Claims

1. Based on 100% by weight of the solid content of the composition, 70 to 90% by weight of a resin mixture containing a high molecular weight polysilicon-modified polyurethane base resin having a weight average molecular weight (Mw) of 100,000 to 200,000, a low molecular weight polysilicon-modified polyurethane auxiliary resin having a weight average molecular weight (Mw) of 30,000 to 70,000, and an epoxy auxiliary resin; 0.5 to 10% by weight of a discoloration inhibitor; 0.5 to 10% by weight of an adhesion promoter; 0.5 to 10% by weight of rust and corrosion inhibitor; 0.1 to 2% by weight of a color pigment; and 0.1 to 1% by weight of a pigment stabilizer; The surface treatment composition, wherein the high molecular weight polysilicon-modified polyurethane main resin, the low molecular weight polysilicon-modified polyurethane auxiliary resin, and the epoxy auxiliary resin are mixed in a weight ratio of 1:4.5:4.5 to 9:0.5:0.

5.

2. 2. The surface treatment composition according to claim 1, wherein the high molecular weight polysilicon-modified polyurethane base resin has a glass transition temperature (Tg) of -20°C to -10°C.

3. 2. The surface treatment composition according to claim 1, wherein the low molecular weight polysilicon-modified polyurethane auxiliary resin has a glass transition temperature (Tg) of -30°C to -20°C.

4. 2. The surface treatment composition of claim 1, wherein the epoxy co-resin has an epoxide equivalent ratio of 450 to 550 g / eq and a weight average molecular weight (Mw) of 450 to 4,000.

5. 2. The surface treatment composition according to claim 1, wherein the anti-tarnish agent is at least one selected from the group consisting of ammonium molybdate and sodium molybdate.

6. 2. The surface treatment composition according to claim 1, wherein the adhesion promoter is at least one selected from the group consisting of phosphate esters, ammonium phosphates, and ammonium zirconium carbonates.

7. 2. The surface treatment composition according to claim 1, wherein the rust and corrosion inhibitor is at least one selected from the group consisting of a phosphoric acid-based rust inhibitor, a fluorine-based rust inhibitor, a vanadium-based rust inhibitor, a cerium salt-based rust inhibitor, and a selenium salt-based rust inhibitor.

8. 2. The surface treatment composition according to claim 1, wherein the coloring pigment comprises at least one selected from the group consisting of: at least one inorganic pigment selected from the group consisting of titanium, lead, iron, copper, and chromium; and at least one azo-based organic pigment.

9. The surface treatment composition according to claim 1 , wherein the pigment stabilizer is a carboxyl-based polymer.

10. The surface treatment composition further comprises a solvent; 10. The surface treatment composition according to claim 1, wherein the solids content is 20 to 40% by weight, based on the total weight of the surface treatment composition, the remainder being solvent.

11. 11. The surface treatment composition according to claim 10, wherein the solvent comprises 20 to 40% by weight of N-ethyl-2-pyrrolidone (NEP) based on the total weight of the solvent, and the balance being water.

12. steel plate; a ternary hot-dip zinc alloy plating layer formed on at least one surface of the steel sheet; and a surface treatment coating layer formed on the ternary hot-dip zinc alloy plating layer, A surface-treated ternary hot-dip zinc alloy plated steel sheet, wherein the surface treatment film layer is formed from the surface treatment composition according to any one of claims 1 to 9.

13. the ternary hot-dip zinc alloy plating layer includes an Al-enriched layer formed at the interface, The surface-treated ternary hot-dip zinc alloy-plated steel sheet according to claim 12, wherein an area ratio of the Al-enriched layer is 70% to 100%.

14. The ternary hot-dip zinc alloy plated steel sheet according to claim 12, wherein the ternary hot-dip zinc alloy plated layer contains Al: 0.2 to 15 wt %, Mg: 0.5 to 3.5 wt %, the balance being Zn and inevitable impurities.

15. The surface-treated ternary hot-dip zinc alloy plated steel sheet according to claim 12, wherein the surface treatment film layer has a thickness of 1 μm to 10 μm.

16. A step of coating the surface treatment composition according to any one of claims 1 to 9 on a ternary hot-dip zinc alloy plated steel sheet on which a ternary hot-dip zinc alloy plated layer has been formed; and A method for producing a surface-treated ternary hot-dip zinc alloy plated steel sheet, comprising the step of drying the surface treatment composition to form a surface treatment film layer.

17. The method for producing a surface-treated ternary hot-dip zinc alloy plated steel sheet according to claim 16, wherein the surface treatment composition is coated to a thickness of 2.5 μm to 50 μm.

18. The method for producing a surface-treated ternary hot-dip zinc alloy plated steel sheet according to claim 16, wherein the surface treatment composition is dried by raising the temperature to 70 to 250°C in the step of forming the surface treatment film layer.

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