Composition for surface-treating plated steel sheet, plated steel sheet surface-treated using same, and manufacturing method thereof

Abstract

The present invention relates to a composition for surface treating a steel sheet. More specifically, the present invention relates to: a surface treatment solution composition containing trivalent chromium; a hot-dip galvanized steel sheet surface-treated using same; and a manufacturing method thereof.

Description

Composition for surface treatment of galvanized steel sheet, galvanized steel sheet surface-treated using the same, and method for manufacturing the same

[0001] The present invention relates to a composition for surface treatment of a steel sheet, and more specifically, to a composition for surface treatment of a plated steel sheet containing trivalent chromium, a plated steel sheet surface-treated using the same, and a method for manufacturing the same.

[0002] Hot-dip galvanized steel with a zinc (Zn) plating layer exhibits excellent corrosion resistance due to the protective effect of the base iron through the sacrificial method. However, when exposed to a general corrosive environment, especially a humid atmosphere, such hot-dip galvanized steel easily forms white rust, a zinc oxide, on the surface, which deteriorates the quality characteristics of the material. In addition, when hot-dip galvanized steel is exposed to a high temperature and high humidity environment, there is a problem in that the surface color easily changes to black, i.e., blackening occurs.

[0003] To address these issues, previously, hexavalent chromate treatment was applied to hot-dip galvanized steel sheets to ensure corrosion resistance and blackening resistance. However, with hexavalent chromium now designated as a hazardous environmental substance, regulations on its use are currently being strengthened. Furthermore, when hexavalent chromium was used as a surface treatment agent for hot-dip galvanized steel sheets, defects such as blackening or the development of black spots on the steel sheet surface occurred.

[0004] Recently, to address the environmental hazards of hexavalent chromium, methods have been applied to ensure corrosion resistance and blackening resistance of galvanized steel sheets by coating the steel sheet with a surface treatment solution composition containing trivalent chromium. For example, patent documents 1 and 2 describe a method of securing corrosion resistance and blackening by immersing the steel sheet in a composition containing trivalent chromium and performing a chemical conversion treatment. However, the immersion time is long for application to the continuous process of steel mills, and the chemical conversion treatment method has problems such as reduced fingerprint resistance.

[0005] Meanwhile, Patent Documents 3 and 4 disclose a method for coating a composition containing trivalent chromium onto a galvanized steel sheet by spraying or roll-coater. This method is applicable to continuous steel production lines and is advantageous in ensuring fingerprint resistance. However, hot-dip galvanized steel sheets coated with the compositions disclosed in these documents suffer from rapid discoloration in humid environments.

[0006] (Patent Document 1) Republic of Korea Patent Publication No. 10-2006-0123628

[0007] (Patent Document 2) Republic of Korea Patent Publication No. 10-2009-0024450

[0008] (Patent Document 3) Republic of Korea Patent Publication No. 10-2004-0046347

[0009] (Patent Document 4) Japanese Patent Publication No. 2002-069660

[0010] One aspect of the present invention is to provide a composition for surface treatment of a steel plate, which excludes a hexavalent chromium component and contains as main components trivalent chromium, which is harmless to the human body, and an inorganic compound.

[0011] In addition, a plated steel sheet surface-treated using a composition for surface treatment of a plated steel sheet according to one aspect of the present invention and a method for manufacturing the plated steel sheet are provided.

[0012] In addition, the technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0013] According to one aspect of the present invention, a composition for surface treatment of a plated steel sheet is provided, comprising (a) a trivalent chromium compound combined with an organic acid: 15 to 45 wt%, (b) an antioxidant: 0.10 to 2.00 wt%, (c) a silane compound: 1.00 to 25.00 wt%, (d) a polysiloxane copolymer: 15 to 50 wt%, (e) a cobalt-based rust prevention and corrosion prevention agent: 1.0 to 15.0 wt%, (f) a lubricant: 0.10 to 3.00 wt%, and (g) an antifoaming agent: 0.10 to 2.00 wt%.

[0014] In one embodiment of the present invention, the trivalent chromium compound combined with the organic acid may be at least one selected from the group consisting of chromium(III) acetylacetonate, chromium(III) acetate, chromium(III) 2-ethylhexanoate, chromium acetate hydroxide, and potassium chromium(III) oxalate trihydrate.

[0015] In this way, a composition for surface treatment of a plated steel sheet contains a trivalent chromium compound, and by applying the trivalent chromium compound as a compound combined with an organic acid, surface etching of the plated steel sheet, which may occur during surface treatment using a composition containing an existing trivalent chromium compound, can be prevented.

[0016] In one embodiment of the present invention, the composition for surface treatment of a plated steel sheet may be a solution composition containing 5 to 20 wt% of a solid content and a remainder of a solvent, and the solution composition may have a pH of 4 to 6.

[0017] According to another aspect of the present invention, a surface-treated plated steel sheet is provided, comprising: a base steel sheet; a zinc-based plating layer formed on at least one surface of the base steel sheet; and a surface treatment film layer formed on the plating layer.

[0018] In one embodiment of the present invention, the surface treatment film layer formed on the plating layer can be formed using a composition according to one embodiment of the present invention.

[0019] In one embodiment of the present invention, the surface treatment film layer formed on the plating layer may have a thickness of 0.3 to 1.5 μm.

[0020] According to another aspect of the present invention, a method for manufacturing a surface-treated plated steel sheet is provided, comprising the steps of: preparing a plated steel sheet having a zinc-based plated layer formed on at least one surface of a base steel sheet; coating a surface treatment composition on the zinc-based plated layer; and drying the plated steel sheet coated with the surface treatment composition.

[0021] In one embodiment of the present invention, the step of coating a surface treatment composition on a plating layer can be performed using a solution composition according to one embodiment of the present invention.

[0022] In one embodiment of the present invention, the coating treatment may be performed by any one method selected from the group consisting of bar coating, roll coating, spraying, dipping, spray squeezing, and dipping squeezing.

[0023] In one embodiment of the present invention, the step of drying after coating can be performed at a temperature range of 40 to 200°C based on the final temperature reached (PMT) of the steel sheet.

[0024] According to the present invention, a composition for surface treatment of a plated steel sheet comprising a trivalent chromium compound harmless to the human body and an inorganic compound can be provided.

[0025] In particular, when surface-treating a plated steel sheet using the composition provided in the present invention, the surface uniformity and appearance characteristics of the surface-treated plated steel sheet can be excellently secured in addition to the corrosion resistance and blackening resistance of the surface-treated plated steel sheet when the composition is coated.

[0026] Hereinafter, preferred embodiments of the present invention will be described with reference to various examples. However, the embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0027] The present invention provides a composition for surface treatment of a plated steel sheet containing trivalent chromium as a composition capable of surface treatment of a steel sheet, a plated steel sheet surface-treated using the composition, and a method for manufacturing the steel sheet. The present invention will be described in detail below.

[0028] According to one aspect of the present invention, a composition for surface treatment of a plated steel sheet is provided, comprising (a) a trivalent chromium compound combined with an organic acid: 15 to 45 wt%, (b) an antioxidant: 0.10 to 2.00 wt%, (c) a silane compound: 1.00 to 25.00 wt%, (d) a polysiloxane copolymer: 15 to 50 wt%, (e) a cobalt-based rust prevention and corrosion prevention agent: 1.0 to 15.0 wt%, (f) a lubricant: 0.10 to 3.00 wt%, and (g) an antifoaming agent: 0.10 to 2.00 wt%.

[0029] The composition for surface treatment of steel sheets according to one aspect of the present invention does not contain hexavalent chromium, which is a hazardous environmental substance, and contains trivalent chromium, which is harmless to the human body, as a main component, thereby preventing problems such as harm to the human body and environmental pollution. In addition, when surface treatment of a plated steel sheet is performed using the composition for surface treatment of a plated steel sheet according to one aspect of the present invention, the surface-treated plated steel sheet can have excellent corrosion resistance, and surface uniformity and appearance characteristics can also be secured during coating for surface treatment.

[0030] Below, each component constituting the composition for surface treatment of a plated steel sheet according to one aspect of the present invention is described in detail, and it is to be noted that the content of each component shown below is based on 100% by weight of the total.

[0031] (a) Trivalent chromium compound combined with organic acid: 15 to 45 wt%

[0032] A trivalent chromium compound is included as a main component of a composition for surface treatment of a plated steel sheet, and has a beneficial effect in securing corrosion resistance and blackening resistance when surface treatment of a plated steel sheet is performed using such a composition.

[0033] In one embodiment of the present invention, the trivalent chromium compound is a compound combined with an organic acid, and any trivalent chromium compound combined with an organic acid can be used, so there is no particular limitation on its type. However, among the trivalent chromium compounds combined with an organic acid, the trivalent chromium compound may be a trivalent chromium compound having a pH of 4 or higher after dissolution. As a non-limiting example, the trivalent chromium compound may be at least one selected from the group consisting of chromium(III) acetylacetonate, chromium(III) acetate, chromium(III) 2-ethylhexanoate, chromium acetate hydroxide, and potassium chromium(III) oxalate trihydrate.

[0034] When chromium phosphate, chromium nitrate, etc. are used as the chromium compound of the composition for surface treatment of a galvanized steel sheet, when the composition containing such chromium compound is dissolved in a solvent (e.g., water), the pH of the solution composition becomes strongly acidic. The inventors of the present invention have discovered a problem in that when the solution composition is applied (sprayed) to the surface of a galvanized steel sheet (e.g., a hot-dip galvanized steel sheet), the surface is etched, thereby causing stripe-shaped defects to appear on the surface of the surface-treated galvanized steel sheet, resulting in poor surface appearance. Therefore, the composition according to one embodiment of the present invention has a technical significance in that it includes a trivalent chromium compound combined with an organic acid, rather than a compound that lowers the pH of the solution composition, such as chromium phosphate, chromium nitrate, etc., which have been mainly used in the past as a chromium compound.

[0035] In one embodiment of the present invention, the trivalent chromium compound combined with the organic acid may be included in an amount of 15 to 45 wt% based on 100 wt% of the total composition. If the content of the trivalent chromium compound is less than 15 wt%, the solid insoluble film layer becomes thin when the composition is coated on the surface of the plated steel sheet, and thus blackening is induced and corrosion resistance is also reduced as moisture penetration is not effectively blocked on the surface of the plated steel sheet requiring corrosion resistance. On the other hand, if the content of the tertiary chromium compound exceeds 45 wt%, the content of a corrosion-resistant agent or a binder-like silane compound added to improve corrosion resistance is relatively reduced, making it difficult to secure corrosion resistance and blackening resistance of the surface-treated plated steel sheet.

[0036] (b) Antioxidant: 0.10 to 2.00 wt%

[0037] In one embodiment of the present invention, an antioxidant may be added to prevent color unevenness in the form of spots caused by oxidation of the surface of the plated steel sheet before the solvent (solvent) evaporates and dries when applying an acidic solution composition to the surface of the plated steel sheet.

[0038] In one embodiment of the present invention, the antioxidant may be included in an amount of 0.10 to 2.00 wt% based on 100 wt% of the total composition. If the content of the antioxidant is less than 0.10 wt%, the aforementioned effect cannot be sufficiently achieved, and the surface uniformity of the surface-treated plated steel sheet may be poor. On the other hand, if the content exceeds 2.00 wt%, the stability of the solution composition may be compromised, and the corrosion resistance of the surface-treated plated steel sheet may be poor.

[0039] In one embodiment of the present invention, the antioxidant may be a triazole derivative. As a non-limiting example, the triazole derivative may be at least one selected from the group consisting of 1,3,4-thiadiazolidine-2,5-dithione, 1,2,3-triazoles, 3-amino-1,2,4-triazole, and 4-amino-3-hydrazino-5-mercapto-1,2,4-triazol.

[0040] (c) Silane compound: 1.00 to 25.00 wt%

[0041] In one embodiment of the present invention, a silane compound, i.e., a silane coupling agent, may be added to promote drying of the composition and secure high corrosion resistance of the film layer by crosslinking the inorganic component and the organic component.

[0042] In one embodiment of the present invention, the silane compound may be included in an amount of 1.00 to 25.00 wt% based on 100 wt% of the total composition. If the content of the silane compound is less than 1.00 wt%, there is a concern that the corrosion resistance and foreign matter adhesion properties of the film layer may be deteriorated. On the other hand, if the content exceeds 25.00 wt%, the dryness of the film layer increases, forming a film with excessively high hardness, and when processing a plated steel sheet having such a film layer, there is a problem that the corrosion resistance and blackening resistance of the processed area are deteriorated.

[0043] In one embodiment of the present invention, any compound known as a silane coupling agent may be used as the silane compound, and thus the type thereof is not particularly limited. However, as a non-limiting example, the silane compound may be at least one selected from the group consisting of 2-(3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-glycyloxypropyl trimethoxysilane, 3-glycyloxypropyl methyldiethoxysilane, 3-glycyloxypropyl triethoxysilane, N-2-(aminoethyl)-3-aminopropyl methyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyl trimethoxysilane, N-2-(aminoethyl)-3-aminopropyl triethoxysilane, 3-aminopropyl trimethoxy silane, 3-aminopropyl triethoxy silane, 3-ureido propyltrimethoxy silane, and tetraethylorthosilicate.

[0044] (d) Polysiloxane copolymer: 15 to 50 wt%

[0045] In one embodiment of the present invention, the polysiloxane copolymer forms a dense film through organic-inorganic bonding on the surface of a surface-treated plated steel sheet using a surface treatment composition, and imparts flexibility to the film, thereby improving the corrosion resistance of not only the flat portion but also the processed portion of the surface-treated plated steel sheet. In addition, the polysiloxane copolymer not only improves the blackening resistance of the surface-treated plated steel sheet by preventing the penetration of corrosion factors, but also helps improve the processability through the formation of a flexible film.

[0046] In one embodiment of the present invention, the polysiloxane copolymer may be included in an amount of 15 to 50 wt% based on 100 wt% of the total composition. If the content of the polysiloxane copolymer is less than 15 wt%, the corrosion resistance of the flat portion and the processed portion of the surface-treated plated steel sheet cannot be secured, and the blackening resistance and workability are also inferior. On the other hand, if the content exceeds 50 wt%, there is a concern that the alkali resistance of the film layer may be inferior.

[0047] In one embodiment of the present invention, the polysiloxane copolymer may be a copolymer having a molecular weight of 300 to 1500, comprising at least one compound selected from the groups i) and ii) below and iii) an acid catalyst.

[0048] i) At least one siloxane compound selected from the group consisting of polydimethylsiloxane, polyvinylsiloxane, polyphenylmethylsiloxane, and hexamethylsiloxane;

[0049] ii) at least one silane compound selected from the group consisting of methyltrimethoxysilane, ethyltrimethoxysilane, hexamethyldisilane, triethylethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, gamma-glycidoxytriethylsilane, and gamma-glycidoxytrimethylsilane.

[0050] iii) At least one acid catalyst selected from the group consisting of phosphoric acid and organophosphate, oxalic acid, citric acid, and formic acid;

[0051] (e) Cobalt-based anti-corrosion agent: 1.0 to 15.0 wt%

[0052] In one embodiment of the present invention, the cobalt-based anti-rust agent serves to shield cracks in the plating layer that occur during processing of a plated steel sheet surface-treated with a surface treatment composition. By using a surface treatment composition containing such a cobalt-based anti-rust agent, the corrosion resistance of the processed portion of the plated steel sheet can be improved during surface treatment.

[0053] In one embodiment of the present invention, the cobalt-based anti-rust and corrosion agent may be included in an amount of 1.0 to 15.0 wt% based on 100 wt% of the total composition. If the content of the cobalt-based anti-rust and corrosion agent is less than 1.0 wt%, it is difficult to sufficiently obtain the aforementioned effect, and the corrosion resistance is reduced due to excessive cracking occurring in the plating layer during processing of the surface-treated plated steel sheet. On the other hand, if the content exceeds 15.0 wt%, there is a problem of reduced blackening resistance and alkali resistance of the film layer.

[0054] In one embodiment of the present invention, the cobalt-based anti-corrosion agent may be at least one selected from the group consisting of cobalt (II) nitrate, cobalt (II) sulfate, cobalt (II) acetate, cobalt (II) oxalate, cobalt (III) nitrate, cobalt (III) acetate, cobalt (III) oxalate, cobalt (IV) chloride, cobalt (III) oxide, and cobalt (IV) oxide.

[0055] (f) Lubricant: 0.10 to 3.00 wt%

[0056] In one embodiment of the present invention, the lubricant serves to enhance the lubricity of a solution composition prepared by dissolving a surface treatment composition in a solvent. In particular, in one embodiment of the present invention, the organic silane compound contained in the composition increases viscosity under high temperature and high humidity environments, thereby preventing the problem of the applied composition sticking to the roll when the surface-treated plated steel sheet moves through the roll, thereby generating foreign matter.

[0057] In one embodiment of the present invention, the lubricant may be included in an amount of 0.10 to 3.00 wt% based on 100 wt% of the total composition. If the content of the lubricant is less than 0.10 wt%, it is difficult to sufficiently obtain the aforementioned effects, and the composition may experience severe roll adhesion under high temperature and high humidity conditions, resulting in excessive occurrence of foreign material defects. On the other hand, if the content exceeds 3.00 wt%, the shielding effect of the film layer is insufficient, resulting in a problem of reduced corrosion resistance of the plated steel sheet.

[0058] In one embodiment of the present invention, a polyethylene wax containing a trivalent chromium compound as a main component and dispersed with a nonionic dispersant suitable for an acidic composition may be used as a lubricant.

[0059] (g) Defoaming agent: 0.10~2.00 wt%

[0060] In one embodiment of the present invention, a defoaming agent may be included to prevent a decrease in the applicability of the solution composition due to the generation of bubbles in the solution during the stirring process when preparing the solution composition by dissolving the surface treatment composition in a solvent.

[0061] In one embodiment of the present invention, the antifoaming agent may be included in an amount of 0.10 to 2.00 wt% based on 100 wt% of the total composition. If the content of the antifoaming agent is less than 0.10 wt%, the aforementioned effect cannot be sufficiently secured, and thus, not only may the workability be reduced when coating the solution composition on the surface of the plated steel sheet, but also physical properties such as corrosion resistance may be reduced. On the other hand, if the content exceeds 2.00 wt%, the solution stability of the composition is reduced, and there is a concern that surface defects may occur during painting after the film layer is formed by the solution composition.

[0062] In one embodiment of the present invention, a silicone-based defoaming agent may be used as the defoaming agent.

[0063] Meanwhile, a surface treatment composition according to one embodiment of the present invention may have a solid content of 5 to 20 wt% and may include (h) a solvent as the remaining component. That is, a solution composition can be obtained by dissolving the surface treatment composition in a solid state in a solvent.

[0064] In one embodiment of the present invention, water may be used as a solvent, and the water may be used to dilute the components added to the surface treatment composition according to one embodiment of the present invention. Here, water refers to deionized water or distilled water.

[0065] In one embodiment of the present invention, the solvent is added as the remainder excluding the solid content of the composition, and the content may be comprised at 80 to 95 wt%. If the content of the solvent is less than 80 wt%, the spreadability may not be sufficient when the solution composition is coated on a plated steel sheet. On the other hand, if the content exceeds 95%, there is a concern that the adhesion amount of the film layer obtained after coating and drying the solution composition may not be secured.

[0066] A solution composition obtained by dissolving a surface treatment composition according to one embodiment of the present invention in the aforementioned solvent may have a pH in the range of 4 to 6.

[0067] As described above, a surface treatment composition according to one embodiment of the present invention comprises a trivalent chromium compound as a main component, and uses a compound combined with an organic acid as the trivalent chromium compound, thereby having a higher pH than existing compositions containing trivalent chromium compounds. In this way, by increasing the pH of the solution composition for surface treatment of a plated steel sheet, problems such as surface appearance that occur when surface treating a plated steel sheet using an existing solution composition with a low pH can be fundamentally solved.

[0068] In one embodiment of the present invention, if the pH of the solution composition is less than 4, the surface of the surface-treated plated steel sheet may be etched, resulting in a poor surface appearance, which may result in poor corrosion resistance and blackening resistance of the plated steel sheet. On the other hand, if the pH exceeds 6, the solution stability may be reduced, and the corrosion resistance and blackening resistance of the processed area of ​​the surface-treated plated steel sheet may be poor.

[0069]

[0070] Hereinafter, a plated steel sheet according to another aspect of the present invention will be described in detail.

[0071] A surface-treated plated steel sheet according to one aspect of the present invention may include a base steel sheet; a zinc-based plating layer formed on at least one surface of the steel sheet; and a surface-treated film layer formed on the plating layer.

[0072] In one embodiment of the present invention, the base steel sheet may be any steel sheet that can be obtained as a plated steel sheet through a plating process, and the type thereof is not particularly limited. As a non-limiting example, it may be carbon steel containing a certain amount of carbon (C), manganese (Mn), silicon (Si), phosphorus (P), sulfur (S), etc., and such carbon steel is widely known in the art, and the composition of the alloy elements is not particularly limited.

[0073] In one embodiment of the present invention, a zinc-based plating layer may be included on at least one surface of the base steel sheet. The zinc-based plating layer may be a plating layer containing zinc (Zn) as a main component, for example, containing Zn at 50 wt% or more. In addition, the plating layer may be a zinc-based alloy plating layer containing one or more elements, such as aluminum (Al), magnesium (Mg), and silicon (Si), in addition to zinc (Zn). Such a plating layer may be provided on not only one surface but also both surfaces of the base steel sheet.

[0074] In one embodiment of the present invention, a surface treatment film layer may be included on the zinc-based plating layer. That is, a film layer having a certain thickness may be formed on the zinc-based plating layer. In this way, a plated steel sheet including a surface treatment film layer on the zinc-based plating layer may have excellent physical properties such as corrosion resistance, blackening resistance, alkali resistance, and chemical resistance.

[0075] In one embodiment of the present invention, in order to obtain a plated steel sheet having the above-described properties, a surface treatment film layer provided on a zinc-based plating layer may be formed from a composition for surface treatment of a plated steel sheet according to one embodiment of the present invention. That is, the film layer formed from the composition according to one embodiment of the present invention contains a trivalent chromium compound combined with an organic acid as a main component, and by including an antioxidant, a silane compound, a corrosion-resistant agent, a copolymer, a lubricant, an antifoaming agent, etc. in an appropriate amount, a plated steel sheet having the intended properties can be provided.

[0076] In one embodiment of the present invention, the surface treatment film layer may have a thickness of 0.3 to 1.5 μm. The thickness at this time is based on the thickness after drying. If the thickness of the film layer is less than 0.3 μm, there is a problem of poor corrosion resistance as the solution composition is thinly applied to the rough acid portion existing on the surface of the plating layer of the plated steel sheet. On the other hand, if the thickness of the film layer exceeds 1.5 μm, the film layer is formed too thick, which deteriorates the processability and increases the processing cost of the solution composition, which is economically disadvantageous.

[0077] Hereinafter, a method for manufacturing a plated steel sheet, i.e., a surface-treated plated steel sheet, according to another aspect of the present invention will be described. However, it should be noted that the following manufacturing method is merely one example for manufacturing a surface-treated plated steel sheet.

[0078] In one embodiment of the present invention, a surface-treated plated steel sheet can be manufactured through the steps of preparing a plated steel sheet having a zinc-based plating layer formed on at least one surface of a base steel sheet; coating a surface treatment composition on the zinc-based plating layer of the plated steel sheet; and drying the plated steel sheet after the coating.

[0079] In one embodiment of the present invention, any steel sheet capable of producing a plated steel sheet by plating can be used as the base steel sheet for forming a zinc-based plating layer on at least one surface, and thus, there is no particular limitation on its type. In addition, the content of the base steel sheet mentioned above can be replaced.

[0080] In one embodiment of the present invention, the zinc-based plating layer is a plating layer containing zinc (Zn) as a main component, and the addition of elements other than zinc is not excluded. As one example, the elements other than zinc may be at least one selected from aluminum (Al), magnesium (Al), and silicon (Si), and a plating layer containing a mixture of these elements and zinc may be referred to as a zinc-based alloy plating layer. In addition, the content of the zinc-based plating layer mentioned above may be replaced.

[0081] In one embodiment of the present invention, the step of coating a surface treatment composition on a zinc-based plating layer may use any one coating method selected from the group consisting of bar coating, roll coating, spraying, dipping, spray squeezing, and dipping squeezing.

[0082] In one embodiment of the present invention, the surface treatment composition coated on the zinc-based plating layer may be a surface treatment composition for a plated steel sheet according to one embodiment of the present invention. In this case, the composition may be a solution composition, and the solution composition may be prepared by mixing a solvent into a surface treatment composition having a solid content of 5 to 20 wt%, as an example. Here, the solvent may be water, such as deionized water or distilled water.

[0083] In one embodiment of the present invention, the solution composition coated on the zinc-based plating layer may include a trivalent chromium compound combined with an organic acid as a main component, whereby the solution composition may satisfy a pH range of 4 to 6. In this way, by surface treating the plated steel sheet using a solution composition having a specific pH value within a specific range, surface appearance defects that may occur when surface treating the plated steel sheet using a conventional highly acidic, i.e., low pH, solution composition can be prevented.

[0084] In coating the above-described solution composition, as an example, the coating thickness can be set to a range of 2.5 to 12.5 μm. By coating the solution composition with such a thickness, a film layer having a thickness of 0.3 to 1.5 μm can be obtained by performing a subsequent drying process. Here, the thickness of the film layer refers to the thickness after drying. In one embodiment of the present invention, if the coating thickness of the solution composition is less than 2.5 μm, the composition may be thinly applied to the acid portion of the roughness of the plating layer, which may cause a problem of reduced corrosion resistance. On the other hand, if the thickness exceeds 12.5 μm, the film layer becomes too thick after drying, which may deteriorate physical properties such as weldability and workability.

[0085] In one embodiment of the present invention, the step of drying the plated steel sheet coated with the surface treatment composition can be performed at a temperature range of 40 to 200°C based on the PMT (Peak Metal Temperature), which is the final temperature reached by the base steel sheet. If the temperature during the drying is lower than 40°C based on the PMT, drying may not be completed completely, which may result in deterioration of the physical properties of the surface-treated plated steel sheet, such as corrosion resistance and alkali resistance. On the other hand, if the drying temperature exceeds 200°C based on the PMT, the surface-treated plated steel sheet may not be sufficiently cooled during the cooling process in the air (air cooling process) after drying. In this case, packaging of the plated steel sheet, etc. may occur before the cooling is completed, which may cause condensation, ultimately resulting in deterioration of the blackening resistance.

[0086] Meanwhile, in one embodiment of the present invention, the drying process may be performed in a hot air drying furnace or an induction heating furnace. As one example, when drying a solution composition coated on a plated steel sheet using a hot air drying furnace, the internal temperature of the hot air drying furnace may be 100 to 300°C. As another example, when drying a surface-treated solution composition using an induction heating furnace, the current applied to the induction heating furnace may be 1,000 to 5,000 A.

[0087] If the internal temperature of the hot air drying furnace is less than 100℃ or the current applied to the induction heating furnace is less than 1000A, the surface-treated solution composition may not be completely dried, and thus the physical properties of the surface-treated plated steel sheet, such as alkali resistance and oil penetration resistance, may be deteriorated. In addition, if the internal temperature of the hot air drying furnace exceeds 200℃ or the current applied to the induction heating furnace exceeds 5000A, the surface-treated plated steel sheet may be packaged without being sufficiently cooled during the cooling process in the air (air cooling), and in this case, the blackening resistance due to condensation may be deteriorated.

[0088] In one embodiment of the present invention, a step of cooling the plated steel sheet after the drying process has been completed may be further included. At this time, the cooling may be the air cooling process mentioned above, or may be a water cooling process capable of providing a certain cooling rate as needed.

[0089] In one embodiment of the present invention, when the cooling process is a water cooling process, there is no particular limitation on the cooling speed, and it is to be noted that a person skilled in the art can appropriately set it according to the cooling equipment and the thickness of the desired post-drying film layer.

[0090] In one embodiment of the present invention, the process for manufacturing a surface-treated plated steel sheet may be performed as a continuous process, and as an example, the speed during the continuous process may be 50 to 120 mpm. If the speed during the continuous process is less than 50 mpm, there is a concern that productivity may decrease, whereas if it exceeds 120 mpm, the solution-state composition applied to the surface of the plated steel sheet may scatter during the drying process, causing surface defects.

[0091] Hereinafter, the present invention will be described in more detail through examples. However, the description of these examples is merely intended to illustrate the implementation of the present invention and is not intended to limit the present invention. This is because the scope of the present invention is determined by the matters set forth in the claims and matters reasonably inferred therefrom.

[0092] (Example)

[0093] [Standard composition of surface treatment composition]

[0094] A composition for surface treatment of a plated steel sheet was prepared, comprising 37 wt% of a trivalent chromium compound combined with an organic acid, 1.00 wt% of an antioxidant, 12.00 wt% of a silane coupling agent, 40 wt% of a polysiloxane copolymer, 7 wt% of a cobalt-based anti-rust and anti-corrosion agent, 2.00 wt% of a lubricant, and 1.00 wt% of an anti-foaming agent, based on 100 wt% of the composition. The composition at this time was prepared in a solid state.

[0095] Afterwards, the solid content of the composition manufactured as described above was prepared at 14 wt%, and a solvent (water) was added thereto to make the total 100 wt% to prepare a solution composition, and the pH of the solution composition was adjusted to 5.

[0096] The organic acid-bound trivalent chromium compound of the above composition was chromium(Ⅲ) acetate, the antioxidant was 1,2,3-triazole, the silane coupling agent was tetraethylorthosilicate, the polysiloxane copolymer was polyvinylsiloxane, vinyltrimethoxysilane, and a polysiloxane copolymer having a molecular weight of 650 synthesized using phosphoric acid as an acid catalyst. In addition, cobalt(Ⅱ) nitrate was used as a cobalt-based rust prevention and corrosion prevention agent, polyethylene wax was used as a lubricant, and a silicone-based antifoaming agent was used as an antifoaming agent.

[0097] [Production standards for test specimens]

[0098] A hot-dip galvanized steel sheet having a zinc-based plating layer (pure zinc plating layer: composed of Zn and other unavoidable impurities) on the surface was cut into a size of 7 cm (width) x 15 cm (height) and the oil was removed. Thereafter, the prepared composition was applied by spraying it onto the surface of the cut hot-dip galvanized steel sheet using a spray nozzle, and then cured under conditions of 60±20℃ based on the PMT of the base steel sheet to produce a test specimen.

[0099] [Testing and Evaluation Methods]

[0100] For the test specimens manufactured as described above, the flat plate corrosion resistance, machined area corrosion resistance, blackening resistance, alkali resistance, foreign matter adhesion, solution stability, and surface uniformity were evaluated using the following methods, and each result is shown in the [Table] below.

[0101] <Reputational Corrosion Resistance>

[0102] After processing the specimens according to the method specified in ASTM B117, the rate of white rust formation of the galvanized steel sheet over time was measured. The evaluation criteria were as follows.

[0103] ◎: The time taken for white cheong to occur is more than 144 hours

[0104] ○: The time until white rust occurs is 96 hours or more but less than 144 hours.

[0105] △: The time taken for white rust to occur is 55 hours or more but less than 96 hours.

[0106] ×: Time taken for white rust to occur is less than 55 hours

[0107] <Corrosion resistance of processing part>

[0108] The specimen was pushed up to a height of 6 mm using an Erichsen tester, and the degree of white rust formation was measured after 24 hours. The evaluation criteria were as follows.

[0109] ◎: Less than 5% of the area affected by white rust after 48 hours

[0110] △: After 48 hours, the area of ​​white rust occurrence is 5% or more but less than 7%

[0111] ×: After 48 hours, white rust occurs in 7% or more of the area

[0112] <My Black Metamorphosis>

[0113] The color change (color difference: ΔE) of the specimen before and after the test was observed by leaving the specimen in a constant temperature and humidity chamber maintained at 50℃ and 95% relative humidity for 120 hours. The evaluation criteria were as follows.

[0114] ◎: ΔE ≤ 2

[0115] ○: 2 < ΔE ≤ 3

[0116] △: 3 < ΔE ≤ 4

[0117] ×: ΔE > 4

[0118] <Alkaline resistance>

[0119] The specimens were immersed in an alkaline degreasing solution at 60°C for 2 minutes, then rinsed with water and air-blown. The color difference (ΔE) before and after immersion 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.

[0120] ◎: ΔE ≤ 2

[0121] ○: 2 < ΔE ≤ 3

[0122] △: 3 < ΔE ≤ 4

[0123] ×: ΔE > 4

[0124] <Foreign body contamination>

[0125] After rubbing the specimen against a metal tip with a white gauze attached under a load of 2.5 kg, the change in whiteness of the white gauze before and after the test (whiteness color difference: ΔL) was observed. The evaluation criteria were as follows.

[0126] ◎: ΔE ≤ 1.0

[0127] ○: 1.0 < ΔE ≤ 2.0

[0128] △: 2.0 < ΔL ≤ 2.5

[0129] ×: ΔL > 2.5

[0130] <Solution stability>

[0131] Each surface treatment composition was placed in a container and stored in a constant temperature oven at 50°C for 7 days. After that, the presence of sediment was visually observed and changes in viscosity were measured. The evaluation criteria were as follows.

[0132] ○: No sedimentation, viscosity change less than 1CP

[0133] △: No sedimentation, viscosity change 1~5CP

[0134] ×: Sedimentation or viscosity change exceeding 5CP

[0135] Surface uniformity

[0136] The appearance of stripes and / or stains on the surface of the specimen was visually observed and evaluated. The evaluation criteria were as follows.

[0137] ○(Good): No surface stripes and / or stains observed

[0138] ×(Defective): Surface stripes and / or stains observed

[0139] Experimental Example 1. Changes in physical properties according to the content of trivalent chromium compounds

[0140] The types of each component for preparing a surface treatment composition were based on the standard composition described above, and each composition was prepared by applying the contents of each component as shown in Table 1 below. Thereafter, a solvent (water) was added to the solid content of 14 wt% of each composition to make a total of 100 wt%, thereby preparing a solution composition having a pH of 5.

[0141] After preparing test specimens according to the above using each solution composition, the physical properties were evaluated, and the results are shown in Table 1 below.

[0142] ClassificationComposition (based on 100 wt%)Property evaluationTrivalent chromium compoundAntioxidantSilaneCoupling agentPolysiloxaneAntirustAnticorrosion agentLubricantAntifoaming agentPlate corrosion resistanceProcessing corrosion resistanceBlackening resistanceAlkaline solution stabilitySurface uniformityComparative example 1101.0024.005012.02.001.00××○○○×Invention example 1151.0019.005012.02.001.00○◎○○○○Invention example 2301.0014.004012.02.001.00◎◎◎◎○○Invention example 3451.009.00357.02.001.00◎◎◎◎○○Comparative example 2501.009.00307.02.001.00×××○○○

[0143] As shown in Table 1 above, when a trivalent chromium compound to which an organic acid is combined is used as a trivalent chromium compound, and a composition containing the content of each component as suggested in one embodiment of the present invention is surface-treated (Invention Examples 1 to 3), results of good or better were shown in all physical properties.

[0144] On the other hand, Comparative Example 1, which had an insufficient content of trivalent chromium compounds, showed poor results in plate corrosion resistance, machined area corrosion resistance, blackening resistance, and surface uniformity, and Comparative Example 2, which had an excessive content of trivalent chromium compounds, also showed poor results in plate corrosion resistance, machined area corrosion resistance, and blackening resistance.

[0145] Experimental Example 2. Changes in physical properties according to pH of solution composition

[0146] The type and content of each component for preparing a surface treatment composition were prepared based on the aforementioned standard composition. Subsequently, a solvent (water) was added to the 14 wt% solids content of the composition to make a total of 100 wt%, thereby preparing a solution composition. The pH of the solution composition was then adjusted using nitric acid and sodium hydroxide aqueous solutions. At this time, each solution composition having the pH values ​​shown in Table 2 below was prepared.

[0147] After preparing test specimens according to the above using each solution composition, the physical properties were evaluated, and the results are shown in Table 2 below.

[0148] Distinction Solution Composition pH Physical Properties Evaluation Plate Corrosion Resistance Processing Corrosion Resistance Blackening Solution Stability Surface Uniformity Comparative Example 33×××○× Invention Example 44○◎○○○ Invention Example 55◎◎◎◎○ Invention Example 66◎◎◎◎○ Comparative Example 47○×××○

[0149] As shown in Table 2 above, when a composition having a pH satisfying the pH suggested in one embodiment of the present invention was surface-treated (Invention Examples 4 to 6), results of good or better were shown in all physical properties.

[0150] On the other hand, Comparative Example 3, in which the pH of the solution composition was too low, showed poor results in plate corrosion resistance, machined part corrosion resistance, blackening resistance, and surface uniformity, and Comparative Example 4, in which the pH of the solution composition was too high, also showed poor results in machined part corrosion resistance, solution stability, and surface uniformity.

[0151] Experimental Example 3. Changes in physical properties according to antioxidant content

[0152] The types of each component for preparing a surface treatment composition were based on the standard composition described above, and each composition was prepared by applying the contents of each component as shown in Table 3 below. Thereafter, a solvent (water) was added to the solid content of 14 wt% of each composition to make a total of 100 wt%, thereby preparing a solution composition having a pH of 5.

[0153] After producing test specimens according to the above-mentioned method using each solution composition, the physical properties of corrosion resistance, solution stability, and surface uniformity were evaluated, and the results are shown in Table 3 below.

[0154] ClassificationComposition (based on 100 wt%)Property evaluationTrivalent chromium compoundAntioxidantSilaneCoupling agentPolysiloxaneAntirustAnticorrosion agentLubricantAntifoaming agentPlate corrosion resistanceProcessing corrosion resistanceSolution stabilitySurface uniformityComparative example 529021.00407.02.001.00○◎○×Comparative example 6290.0520.95407.02.001.00○◎○×Invention example 7290.1020.90407.02.001.00○◎○○Invention example 8290.5020.50407.02.001.00◎◎◎◎Invention example 9291.0020.00407.02.001.00◎◎◎◎Invention example 10292.0019.00407.02.001.00◎◎◎◎Comparative example 7292.5018.50407.02.001.00×××○

[0155] As shown in Table 3 above, when a composition having a content of each component, including an antioxidant, satisfying the content suggested in one embodiment of the present invention was surface-treated (Invention Examples 7 to 10), results of good or better were shown in all physical properties.

[0156] On the other hand, Comparative Examples 5 and 6, which had insufficient antioxidant content, showed poor surface uniformity, and Comparative Example 7, which had excessive antioxidant content, showed poor plate corrosion resistance, machined area corrosion resistance, and solution stability.

[0157] Experimental Example 4. Changes in physical properties according to the content of silane compound (silane coupling agent)

[0158] The types of each component for preparing a surface treatment composition were based on the standard composition described above, and each composition was prepared by applying the contents of each component as shown in Table 4 below. Thereafter, a solvent (water) was added to the solid content of 14 wt% of each composition to make a total of 100 wt%, thereby preparing a solution composition having a pH of 5.

[0159] After producing test specimens according to the above-mentioned method using each solution composition, the physical properties of corrosion resistance, blackening resistance, and foreign matter adhesion were evaluated, and the results are shown in Table 4 below.

[0160] ClassificationComposition (based on 100 wt%)Property evaluationTrivalent chromium compoundAntioxidantSilaneCoupling agentPolysiloxaneAntirustAnticorrosion agentLubricantAntifoaming agentPlate corrosion resistanceProcessed area corrosion resistanceBlackening resistanceImpurity resistanceComparative example 8341.000.505011.52.001.00××○×Invention example 11341.001.005011.02.001.00○◎○○Invention example 12341.0010.004012.02.001.00◎◎◎◎Invention example 13341.0020.00357.02.001.00◎◎◎◎Invention example 14341.0025.00307.02.001.00◎◎◎◎Comparative example 9291.0030.00307.02.001.00○××○

[0161] As shown in Table 4 above, when a composition having a content of each component including a silane coupling agent satisfying the content suggested in one embodiment of the present invention was surface-treated (Invention Examples 11 to 14), results of good or better were shown in all physical properties.

[0162] On the other hand, Comparative Example 8, which had an insufficient content of silane coupling agent, showed poor results in plate corrosion resistance, machined part corrosion resistance, and foreign matter adhesion, and Comparative Example 9, which had an excessive content of silane coupling agent, showed poor results in machined part corrosion resistance and blackening resistance.

[0163] Experimental Example 5. Changes in physical properties according to the content of polysiloxane copolymer.

[0164] The types of each component for preparing a surface treatment composition were based on the standard composition described above, and each composition was prepared by applying the contents of each component as shown in Table 5 below. Thereafter, a solvent (water) was added to the solid content of 14 wt% of each composition to make a total of 100 wt%, thereby preparing a solution composition having a pH of 5.

[0165] After producing test specimens according to the above-mentioned method using each solution composition, the physical properties of corrosion resistance, blackening resistance, and alkali resistance were evaluated, and the results are shown in Table 5 below.

[0166] ClassificationComposition (based on 100 wt%)Property evaluationTrivalent chromium compoundAntioxidantSilaneCoupling agentPolysiloxaneAntirustAnticorrosion agentLubricantAntifoaming agentPlate corrosion resistanceProcessing corrosion resistanceBlackening resistanceAlkali resistanceComparative example 10441.0025.001015.03.002.00×××○Invention example 15431.0024.001514.02.001.00○○○○Invention example 16361.0020.003010.02.001.00○○◎○Invention example 17291.0010.00507.02.001.00○◎◎○Comparative example 11241.0010.00557.02.001.00○◎○×

[0167] As shown in Table 5 above, when a composition having a content of each component, including a polysiloxane copolymer, satisfying the content suggested in one embodiment of the present invention was surface-treated (Invention Examples 15 to 17), results of good or better were shown in all physical properties.

[0168] On the other hand, Comparative Example 10, which had an insufficient content of polysiloxane copolymer, showed poor results in plate corrosion resistance, machined area corrosion resistance, and blackening resistance, and Comparative Example 11, which had an excessive content of polysiloxane copolymer, showed poor results in alkali resistance properties.

[0169] Experimental Example 6. Changes in physical properties according to the content of cobalt-based anticorrosion agent.

[0170] The types of each component for preparing a surface treatment composition were based on the standard composition described above, and each composition was prepared by applying the contents of each component as shown in Table 6 below. Thereafter, a solvent (water) was added to the solid content of 14 wt% of each composition to make a total of 100 wt%, thereby preparing a solution composition having a pH of 5.

[0171] After producing test specimens according to the above-mentioned method using each solution composition, the physical properties of corrosion resistance, blackening resistance, and alkali resistance were evaluated, and the results are shown in Table 6 below.

[0172] ClassificationComposition (based on 100 wt%)Property evaluationTrivalent chromium compoundAntioxidantSilaneCoupling agentPolysiloxaneRust preventionCorrosion preventionLubricantFoaming agentPlate corrosion resistanceProcessing corrosion resistanceBlackening resistanceAlkali resistanceComparative example 12341.0021.50400.52.001.00××◎◎Invention example 18341.0021.00401.02.001.00○◎◎◎Invention example 19341.0020.00357.02.001.00○◎◎◎Invention example 20311.0015.003515.02.001.00◎◎○○Comparative example 13311.0014.003516.02.001.00◎◎○×Comparative example 14311.0010.003520.02.001.00◎◎××

[0173] As shown in Table 6 above, when a composition including a cobalt-based anti-corrosion agent and having a content of each component satisfying the content suggested in one embodiment of the present invention was surface treated (Invention Examples 18 to 20), results of good or better were shown in all physical properties.

[0174] On the other hand, Comparative Example 12, which had an insufficient content of cobalt-based anti-rust and corrosion inhibitor, showed poor results in plate corrosion resistance and machined part corrosion resistance. Meanwhile, Comparative Example 13, which had a large content of cobalt-based anti-rust and corrosion inhibitor, showed poor alkali resistance, and Comparative Example 14, which had a significantly excessive content, showed poor results not only in alkali resistance but also in blackening resistance.

[0175] Experimental Example 7. Changes in physical properties according to lubricant content

[0176] The types of each component for preparing a surface treatment composition were based on the standard composition described above, and each composition was prepared by applying the contents of each component as shown in Table 7 below. Thereafter, a solvent (water) was added to the solid content of 14 wt% of each composition to make a total of 100 wt%, thereby preparing a solution composition having a pH of 5.

[0177] After producing test specimens according to the above-mentioned method using each solution composition, the physical properties of corrosion resistance, blackening resistance, and foreign matter adhesion were evaluated, and the results are shown in Table 7 below.

[0178] ClassificationComposition (based on 100 wt%)Property evaluationTrivalent chromium compoundAntioxidantSilaneCoupling agentPolysiloxaneAntirustAnticorrosion agentLubricantAntifoaming agentPlate corrosion resistanceProcessed area corrosion resistanceBlackening resistanceImpurity resistanceComparative example 15291.0022.00407.001.00○○○×Comparative example 16291.0021.95407.00.051.00○◎○×Invention example 21291.0021.90407.00.101.00○◎○○Invention example 22291.0021.00407.01.001.00◎◎◎Invention example 23291.0020.00407.02.001.00◎◎◎Invention example 24291.0019.00407.03.001.00◎◎◎◎Comparative example 17291.0018.50407.03.501.00××○○

[0179] As shown in Table 7 above, when a composition having a content of each component, including an active agent, satisfying the content suggested in one embodiment of the present invention was surface-treated (Invention Examples 21 to 24), results of good or better were shown in all physical properties.

[0180] On the other hand, Comparative Examples 15 and 16, which had insufficient lubricant content, showed poor results in foreign matter adhesion, and Comparative Example 17, which had excessive lubricant content, showed poor results in plate corrosion resistance and machined part corrosion resistance.

[0181] Experimental Example 8. Changes in physical properties according to the content of the antifoaming agent

[0182] The types of each component for preparing a surface treatment composition were based on the standard composition described above, and each composition was prepared by applying the contents of each component as shown in Table 8 below. Thereafter, a solvent (water) was added to each composition so that the solid content of 14 wt% became 100 wt% in total, thereby preparing a solution composition having a pH of 5.

[0183] After producing test specimens according to the above-described method using each solution composition, the physical properties of corrosion resistance, blackening resistance, and solution stability were evaluated, and the results are shown in Table 8 below.

[0184] ClassificationComposition (based on 100 wt%)Property evaluationTrivalent chromium compoundAntioxidantSilaneCoupling agentPolysiloxaneAntirustAnticorrosion agentLubricantAntifoaming agentPlate corrosion resistanceProcessing corrosion resistanceBlackening resistanceSolution stabilityComparative example 18291.0021.00407.02.000×××○Comparative example 19291.0020.95407.02.000.05××○○Invention example 25291.0020.90407.02.000.10○◎○○Invention example 26291.0020.50407.02.000.50◎◎◎◎Invention example 27291.0020.00407.02.001.00◎◎◎◎Invention example 28291.0019.00407.02.002.00◎◎◎◎Comparative example 20291.0018.50407.02.002.50○○○×

[0185] As shown in Table 8 above, when a composition having a content of each component, including a defoaming agent, satisfying the content suggested in one embodiment of the present invention was surface-treated (Invention Examples 25 to 28), results of good or better were shown in all physical properties.

[0186] On the other hand, Comparative Example 18, which did not contain an antifoaming agent, showed poor results in plate corrosion resistance, machined area corrosion resistance, and blackening resistance, and Comparative Example 19, which had an insufficient amount of antifoaming agent, showed poor plate corrosion resistance and machined area corrosion resistance. Meanwhile, Comparative Example 20, which had an excessive amount of antifoaming agent, showed poor results in solution stability.

[0187] Experimental Example 9. Changes in physical properties according to drying temperature and film thickness

[0188] The type and content of each component for preparing a surface treatment composition were prepared based on the aforementioned standard composition. Subsequently, a solvent (water) was added to the 14 wt% solids content of the composition to make a total of 100 wt%, thereby preparing a solution composition.

[0189] A hot-dip galvanized steel sheet was cut into a size of 7 cm (width) x 15 cm (height), and after removing oil, the prepared solution composition was spray-coated and dried in an induction furnace (2000 A) to prepare a surface-treated specimen. At this time, the thickness of the film layer (dry thickness) and the PMT standard drying temperature were controlled differently as shown in Table 9 below, and the properties of each specimen were evaluated, and the results are also shown in Table 9 below.

[0190] ClassificationDrying temperature(℃)Film layer thickness(㎛)Property evaluationplateCorrosion resistanceProcessing areaCorrosion resistanceBlackening resistanceAlkali resistanceComparative example 21600.2××△△Inventive example 29600.3◎◎◎◎Inventive example 30600.8◎◎◎◎Inventive example 31601.2◎◎○◎Inventive example 32601.5◎◎○◎Comparative example 22602.0◎×○◎Comparative example 23300.8××××Inventive example 33400.8○○○△Inventive example 341000.8◎◎◎◎Inventive example 352000.8◎◎○◎Comparative example 242200.8◎◎×◎

[0191] As shown in Table 9 above, inventive examples 29 to 32, in which the film layer was formed to a thickness of 0.3 to 1.5 μm after drying and dried at 60°C based on PMT, results were good or better in all physical properties. In addition, inventive examples 34 and 45, in which the film layer was formed to a thickness of 0.8 μm and dried at 40 to 200°C based on PMT, results were good or better.

[0192] On the other hand, in the case of Comparative Example 21, where the thickness of the film layer after drying was thin at 0.2㎛, the corrosion resistance was poor, and the blackening resistance and alkali resistance were somewhat poor, and in Comparative Example 22, where the film layer was formed excessively thick after drying, the corrosion resistance of the processed part was poor.

[0193] In addition, Comparative Example 23, in which the temperature during drying was less than 40℃ based on PMT, showed poor results in all physical properties because the applied solution composition was not sufficiently dried. Comparative Example 24, in which the temperature during drying exceeded 200℃ based on PMT, showed poor blackening resistance. This is because condensation occurred on the upper part of the drying equipment due to water vapor generated from the specimen during the final cooling (water cooling) process after completing the drying process, and this phenomenon caused fume to fall onto the surface of the specimen.

Claims

1. (a) Trivalent chromium compound combined with organic acid: 15 to 45 wt%, (b) Antioxidant: 0.10 to 2.00 wt%, (c) Silane compound: 1.00 to 25.00 wt%, (d) Polysiloxane copolymer: 15 to 50 wt%, (e) Cobalt-based anti-corrosion agent: 1.0 to 15.0 wt%, (f) Lubricant: 0.10 to 3.00 wt%, and (g) A composition for surface treatment of a plated steel sheet, comprising 0.10 to 2.00 wt% of a foaming agent.

2. In paragraph 1, A composition for surface treatment of a plated steel sheet, wherein the trivalent chromium compound combined with the organic acid is at least one selected from the group consisting of chromium(III) acetylacetonate, chromium(III) acetate, chromium(III) 2-ethylhexanoate, chromium acetate hydroxide, and potassium chromium(III) oxalate trihydrate.

3. In paragraph 1, The above antioxidant is a triazole derivative, A composition for surface treatment of a plated steel sheet, wherein the triazole derivative is at least one selected from the group consisting of 1,3,4-thiadiazolidine-2,5-dithione, 1,2,3-triazoles, 3-amino-1,2,4-triazole, and 4-amino-3-hydrazino-5-mercapto-1,2,4-triazol.

4. In paragraph 1, A composition for surface treatment of a plated steel sheet, wherein the silane compound is at least one selected from the group consisting of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycyloxypropyl trimethoxysilane, 3-glycyloxypropyl methyldiethoxysilane, 3-glycyloxypropyl triethoxysilane, N-2-(aminoethyl)-3-aminopropyl methyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyl trimethoxysilane, N-2-(aminoethyl)-3-aminopropyl triethoxysilane, 3-aminopropyl trimethoxy silane, 3-aminopropyl triethoxy silane, 3-ureido propyltrimethoxy silane, and tetraethylorthosilicate.

5. In paragraph 1, The above polysiloxane copolymer is a composition for surface treatment of a plated steel sheet, which is a copolymer having a molecular weight of 300 to 1500, comprising at least one compound selected from the groups i) and ii) below and iii) an acid catalyst. i) at least one siloxane compound selected from the group consisting of polydimethylsiloxane, polyvinylsiloxane, polyphenylmethylsiloxane, and hexamethylsilonic acid; ii) at least one silane compound selected from the group consisting of methyltrimethoxysilane, ethyltrimethoxysilane, hexamethyldisilane, triethylethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, gamma-glycidoxytriethylsilane, and gamma-glycidoxytrimethylsilane. iii) at least one acid catalyst selected from the group consisting of phosphoric acid and organophosphate, oxalic acid, citric acid, and formic acid; 6. In paragraph 1, A composition for surface treatment of a plated steel sheet, wherein the cobalt-based anti-corrosion agent is at least one selected from the group consisting of cobalt (II) nitrate, cobalt (II) sulfate, cobalt (II) acetate, cobalt (II) oxalate, cobalt (III) nitrate, cobalt (III) acetate, cobalt (III) oxalate, cobalt (IV) chloride, cobalt (III) oxide, and cobalt (IV) oxide.

7. In paragraph 1, The above lubricant is a composition for surface treatment of a plated steel sheet, which is a polyethylene wax dispersed with a nonionic dispersant.

8. In paragraph 1, The above-mentioned antifoaming agent is a composition for surface treatment of plated steel sheets, which is a silicone-based antifoaming agent.

9. In paragraph 1, The above composition is a solution composition containing 5 to 20 wt% of solid content and a residual solvent. The above solution composition is a composition for surface treatment of a plated steel sheet having a pH of 4 to 6.

10. Steel plate; A zinc-based plating layer formed on at least one surface of the above steel plate; and Includes a surface treatment film layer formed on the above plating layer, A surface-treated plated steel sheet, wherein the surface treatment film layer is formed using a composition according to any one of claims 1 to 9.

11. In paragraph 10, A surface-treated plated steel sheet, wherein the surface treatment film layer has a thickness of 0.3 to 1.5 ㎛.

12. A step for preparing a galvanized steel sheet having a zinc-based galvanized layer formed on at least one side of the steel sheet; A step of coating a surface treatment composition on the zinc-based plating layer; and It comprises a step of drying a plated steel sheet coated with the above surface treatment composition, A method for manufacturing a surface-treated plated steel sheet, wherein the surface treatment composition is a composition according to any one of claims 1 to 9.

13. In paragraph 12, A method for manufacturing a surface-treated galvanized steel sheet, wherein the above coating treatment is performed by any one method selected from the group consisting of bar coating, roll coating, spraying, dipping, spray squeezing, and dipping squeezing.

14. In paragraph 12, A method for manufacturing a surface-treated plated steel sheet, wherein the above coating step is to apply a surface treatment composition with a coating thickness of 2.5 to 12.5 μm.

15. In paragraph 12, A method for manufacturing a surface-treated galvanized steel sheet, wherein the above drying step is performed at a temperature range of 40 to 200°C based on the final temperature (PMT) of the steel sheet.

16. In paragraph 12, A method for manufacturing a surface-treated galvanized steel sheet, wherein the above drying step is performed in a hot air dryer or an induction heating furnace.

17. In paragraph 12, A method for manufacturing a surface-treated plated steel sheet, further comprising a step of air-cooling or water-cooling the plated steel sheet after the above drying step.

18. In paragraph 12, The manufacturing method of the above-mentioned galvanized steel plate is a continuous process, A method for manufacturing a surface-treated galvanized steel sheet, wherein the speed of the above continuous process is 50 to 120 mpm.