Solution composition for steel sheet surface treatment, steel sheet surface treated with the same, and method for manufacturing the same

Abstract

The present invention relates to a solution composition capable of improving the pitting corrosion resistance and blackening resistance of a steel sheet, a steel sheet surface-treated using the same, and a method for producing the steel sheet.

Description

[Technical Field]

[0001] The present invention relates to a solution composition capable of improving the pitting corrosion resistance and blackening resistance of a steel sheet, a steel sheet surface-treated using the same, and a method for producing the steel sheet. [Background technology]

[0002] Highly corrosion-resistant hot-dip plated steel materials, which have a coating layer containing zinc (Zn), magnesium (Mg), and aluminum (Al), are known to have excellent red rust corrosion resistance.

[0003] However, since the exposed surface of such highly corrosion-resistant hot-dip plated steel materials is mostly composed of zinc or zinc alloys, they are prone to develop spot-like corrosion defects on the surface when exposed to general environments, particularly humid atmospheres, resulting in poor appearance. Furthermore, in recent years, foreign matter defects have also been observed in which the coating layer of the hot-dip plated steel material adheres to rolls when passing through them in processing plants.

[0004] To address these issues, conventionally, hexavalent chromium or chromate treatment has been applied to plated steel sheets to ensure corrosion resistance and blackening resistance. However, hexavalent chromium has been designated as a hazardous environmental substance, and regulations on its use are currently being tightened. Furthermore, when hexavalent chromium is used as a surface treatment agent for plated steel sheets, defects such as the steel sheet surface turning black or black spots appearing can occur.

[0005] Therefore, currently, a method has been developed in which a surface treatment solution composition containing trivalent chromium is coated on a plated steel sheet to ensure corrosion resistance and blackening resistance of the plated steel sheet.

[0006] For example, Patent Document 1 applies a chemical conversion treatment method in which a steel sheet is immersed in a composition containing trivalent chromium. This method requires a long immersion time to be applicable to the continuous processes of steel companies, and the chemical conversion treatment method has problems such as impairing the fingerprint resistance of the steel sheet.

[0007] On the other hand, Patent Documents 2 and 3 disclose that coating a composition containing trivalent chromium onto plated steel sheets using a spray or roll coater method can be applied to continuous production lines at steel companies and fingerprint resistance can be ensured. However, these compositions contain porous silica components, which make them unsuitable for Mg- and Al-based alloys, which tend to discolor rapidly in humid environments. Furthermore, porous silica has a strong hygroscopic property, which can cause rapid discoloration in Zn-Mg-Al-based alloy steel sheets. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Korean Patent Publication No. 10-2009-0024450 [Patent Document 2] Korean Patent Publication No. 10-2004-0046347 [Patent Document 3] Japanese Patent Publication No. 2002-069660 Summary of the Invention [Problem to be solved by the invention]

[0009] One embodiment of the present invention provides a solution composition having excellent solution stability that improves the pitting corrosion resistance and blackening resistance of a steel sheet by controlling the composition of a coating solution applied to the surface of a highly corrosion-resistant plated steel sheet, and also provides a steel sheet surface-treated using the same and a method for manufacturing the same.

[0010] The object of the present invention is not limited to the above-mentioned content. The object of the present invention can be understood from the entire content of this specification, and a person having ordinary skill in the art to which the present invention pertains will have no difficulty in understanding the additional object of the present invention. [Means for solving the problem]

[0011] One embodiment of the present invention provides a solution composition for treating a steel sheet surface, comprising: (a) 20 to 60% by weight of a trivalent chromium compound; (b) 0.1 to 10% by weight of an acidity regulator; (c) 1 to 20% by weight of an adhesion improver; (d) 1 to 20% by weight of a corrosion resistance improver; (e) 0.01 to 3.0% by weight of a pitting corrosion improver; (f) 1 to 20% by weight of a co-solvent; and (g) the balance being a solvent.

[0012] Another embodiment of the present invention provides a surface-treated plated steel sheet including: a steel sheet; a Zn-Mg-Al-based plating layer formed on at least one surface of the steel sheet; and a surface treatment coating layer formed on the plating layer, wherein the surface treatment coating layer is a coating layer formed from the above-described solution composition.

[0013] Another embodiment of the present invention provides a method for producing a surface-treated plated steel sheet, the method including the steps of: hot-dip galvanizing at least one surface of a steel sheet to form a Zn-Mg-Al-based plating layer; coating the plating layer with the above-described solution composition; and drying the coated steel sheet. [Effects of the Invention]

[0014] According to the present invention, a solution composition having excellent solution stability without causing precipitation, aggregation, etc., even when used after long-term storage can be provided. By coating the solution composition on a steel sheet, a steel sheet having excellent pitting corrosion resistance and blackening resistance can be provided.

[0015] Furthermore, it has the effect of improving the lifespan of the product by improving the defects caused by foreign matter during the coating process. [Brief explanation of the drawings]

[0016] [Figure 1] 1 shows a plated steel sheet (a) on which pitting corrosion (at edges) has occurred and a plated steel sheet (b) on which no surface corrosion has occurred, in one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The inventors of the present invention have conducted extensive research to obtain a solution composition that is advantageous for improving not only the pitting corrosion resistance but also the blackening resistance of the coated steel sheet when coating the steel sheet, for example, a highly corrosion-resistant hot-dip plated steel sheet.

[0018] As a result, it is possible to provide a solution composition containing a trivalent chromium compound, an acidity regulator, an adhesion improver, a corrosion resistance improver, a pitting corrosion improver, and a co-solvent in appropriate amounts, and this solution composition has high solution stability. It was confirmed that when such a solution composition is used for surface treatment of a steel sheet, the intended effects can be obtained, leading to the completion of the present invention.

[0019] The present invention will be described in detail below.

[0020] First, a solution composition for treating a steel sheet surface according to one embodiment of the present invention will be specifically described.

[0021] The solution composition according to the present invention can contain (a) 20 to 60% by weight of a trivalent chromium compound, (b) 0.1 to 10% by weight of an acidity regulator, (c) 1 to 20% by weight of an adhesion improver, (d) 1 to 20% by weight of a corrosion resistance improver, (e) 0.01 to 3.0% by weight of a pitting corrosion improver, (f) 1 to 20% by weight of a co-solvent, and (g) the balance being a solvent.

[0022] The content of the solution composition of the present invention is based on 100% by weight.

[0023] As will be described in detail later, the solution composition can form a coating layer on at least one surface of a substrate to which the composition can be applied. In the present invention, the substrate can be the above-mentioned steel sheet, for example, a highly corrosion-resistant hot-dip plated steel sheet, and a non-limiting example thereof can be a Zn-Mg-Al alloy plated steel sheet.

[0024] Each component constituting the solution composition will be described in detail below.

[0025] (a) 20 to 60% by weight of trivalent chromium compound

[0026] In the solution composition of the present invention, the trivalent chromium compound mainly forms an insoluble coating on the surface of the steel sheet, thereby improving corrosion resistance due to its barrier effect.

[0027] In the solution composition of the present invention, if the content of the trivalent chromium compound is less than 20%, a strong insoluble coating cannot be formed sufficiently, and therefore the water penetrating into the surface of the steel sheet cannot be effectively blocked, resulting in failure to ensure corrosion resistance.On the other hand, if the content exceeds 60%, there is a risk of inclusion defects occurring due to the excessive chromium content.

[0028] In the present invention, the type of the trivalent chromium compound is not particularly limited, but it is preferably one or more compounds selected from the group consisting of chromium sulfate, chromium nitrate, chromium phosphate, chromium fluoride, chromium chloride, and mixtures thereof.

[0029] (b) Acidity regulator 0.1 to 10% by weight

[0030] In the solution composition of the present invention, the acidity regulator functions to adjust the pH of the solution so that the components in the composition are stable in the solution and can react appropriately under coating conditions to stably form a coating.

[0031] If the content of such an acidity regulator is less than 0.1%, the pH of the solution may become high, which may reduce the solution stability. On the other hand, if the content exceeds 10%, the residual acid after drying may make it impossible to ensure corrosion resistance, etc.

[0032] In the present invention, the type of the acidity regulator is not particularly limited, but is preferably one or more selected from the group consisting of phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, hydrochloric acid, (NH4)H2PO4, (NH4)2HPO4, NaH2PO4, Na2HPO4, phytic acid, glycolic acid, lactic acid, acetic acid, oxalic acid, and mixtures thereof.

[0033] (c) Adhesion improver 1 to 20% by weight

[0034] In the solution composition of the present invention, the adhesion promoter bonds with the trivalent chromium compound and the like and also bonds with the steel sheet, thereby improving the adhesion and corrosion resistance of the coating layer.

[0035] If the content of such adhesion improvers is less than 1%, sufficient adhesion to the steel sheet may not be ensured, which may result in foreign matter defects, whereas if the content exceeds 20%, an excessive amount may remain after the coating film is formed, which may result in an inability to ensure corrosion resistance, etc.

[0036] In the present invention, the type of the adhesion improver is not particularly limited, but preferred are vinyl methoxy silane, vinyl trimethoxy silane (VTMS), vinyl epoxy silane, vinyl triepoxy silane, 3-aminopropyl triepoxy silane, 3-glycidoxypropyl trimethoxy silane, 3-metaglyoxypropyl trimethoxy silane, γ-glycidoxypropyl triethoxy silane, γ-glycidoxytrimethyl dimethoxy silane, N-(3-(trimethoxysilyl)propyl)ethylenediamine (AEAPTMS), 2-(3,4-Epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-Epoxycyclohexyl)ethyltriethoxysilane, 3-(2,3-Epoxypropoxy)propyltrimethoxysilane, 3-(2,3-Epoxypropoxy)propyltriethoxysilane, and 3-(2,3-Epoxypropoxy)propylmethyldiethoxysilane. The methylaminopropylsilane may be one or more selected from the group consisting of methylaminopropylsilane, 3-(2,3-epoxypropoxy)propylmethyldimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl-3-aminopropyl)methyldimethoxysilane, N-(2-aminoethyl-3-aminopropyl)trimethoxysilane, Diethylenetriaminopropyltrimethoxysilane, 3-Ureidopropyltrimethoxysilane, N-Phenylaminopropyltrimethoxysilane, (3-glycidyloxypropyl)trimethoxysilane (GPTMS), Methyltrimethoxysilane (MTMS), and mixtures thereof.

[0037] (d) 1 to 20% by weight of corrosion resistance improver

[0038] In the solution composition of the present invention, the corrosion resistance improver fills gaps that may exist between the trivalent chromium compound and the adhesion improver, etc., and forms a passivation film, thereby playing a role in suppressing the generation of corrosion.

[0039] If the content of such a corrosion resistance improver is less than 1%, it is difficult to ensure corrosion resistance because a sufficient passive film cannot be formed, while if the content exceeds 20%, the solution stability may decrease due to an excessively high solid content.

[0040] In the present invention, the type of the corrosion resistance improver is not particularly limited, but is preferably one or more selected from the group consisting of vanadyl acetylacetonate, ammonium metavanadate, potassium metavanadate, sodium metavanadate, vanadium trioxide, vanadium acetylacetate, ammonium metavanadate, silicon oxide, and mixtures thereof.

[0041] (e) 0.01 to 3.0 wt% of pitting corrosion improver In the solution composition of the present invention, the pitting corrosion improver, together with the corrosion resistance improver, prevents localized penetration of corrosive factors and minimizes pitting corrosion that occurs in the form of spots.

[0042] In the solution composition of the present invention, if the content of the pitting corrosion ameliorator is less than 0.01%, the local penetration of corrosion factors cannot be blocked, resulting in the problem of pitting corrosion. On the other hand, if the content exceeds 3.0%, the pH of the solution may increase excessively, resulting in a decrease in solution stability.

[0043] In the present invention, the type of the pitting corrosion improver is not particularly limited, but is preferably one or more selected from the group consisting of ethylenediamine, hexamethylenediamine, trimethylamine, methylamine, diphenylamine, ethyleneamine, aniline, toluidine, piperidine, aziridine, pyridine, alanine, propylamine, diisopropylamine, monoisopropylamine, dibutylamine, dipropylamine, and mixtures thereof.

[0044] (f) 1 to 20% by weight of cosolvent

[0045] In the solution composition of the present invention, the co-solvent functions to adjust the evaporation rate of the solvent during the drying process during the coating operation and to suppress defects on the coating surface after drying.

[0046] If the content of such a co-solvent is less than 1%, the effect of controlling the evaporation rate during drying is insufficient, causing the evaporation rate of the main solvent to rapidly boil at its boiling point, resulting in surface defects known as popping, which can lead to problems such as reduced corrosion resistance.On the other hand, if the content exceeds 20%, the solution stability may be reduced due to abrupt changes in the viscosity and density of the solution.

[0047] In the present invention, the type of the co-solvent is not particularly limited, but is preferably one or more selected from the group consisting of ethanol, isopropyl alcohol, methanol, tallow alcohol, 2-butoxyethanol, diethylene glycol monobutyl ether, and mixtures thereof.

[0048] (g) Solvent

[0049] The solution composition of the present invention may contain a solvent as the remaining component, and in the present invention, water (distilled water, deionized water) may be used as the solvent.

[0050] Hereinafter, a surface-treated steel sheet including a coating layer that has been surface-treated with the above-described solution composition according to another embodiment of the present invention will be described in detail.

[0051] In the present invention, the above composition can be used to apply a surface treatment to a plated steel sheet, preferably a ternary (Zn-Mg-Al) hot-dip galvanized steel sheet.

[0052] That is, the surface-treated steel sheet of the present invention can include a steel sheet, a Zn-Mg-Al-based plating layer formed on at least one surface of the steel sheet, and a surface treatment coating layer formed on the plating layer.

[0053] Here, the steel sheet is a base steel sheet from which a plated steel sheet can be obtained, and in particular, any steel sheet from which a ternary (Zn-Mg-Al) hot-dip galvanized steel sheet can be obtained.

[0054] The Zn-Mg-Al-based plating layer may contain, in weight percent, 4.0 to 7.0% magnesium (Mg), 11.0 to 19.5% aluminum (Al), the remainder being Zn, and other inevitable impurities.

[0055] Magnesium (Mg) in the coating layer is an element that plays a role in improving the corrosion resistance of the coated steel sheet, and its content is preferably 4.0% or more to ensure the excellent corrosion resistance aimed at in the present invention. However, if the Mg content is excessive, there is a risk of dross being generated in the coating bath and of forming excessive intermetallic compounds with high hardness in the coating layer, which may deteriorate the bendability of the steel sheet, so the Mg content can be limited to 7.0%.

[0056] On the other hand, adding Mg at a content of 4.0% or more poses the risk of dross formation due to oxidation of Mg in the coating bath. Taking this into consideration, it is preferable to include aluminum (Al) at a content of 11.0% or more. However, if the Al content is excessive, the melting point of the coating bath increases, which in turn increases the operating temperature excessively, potentially causing problems associated with high-temperature operation, such as erosion of the coating bath structure and deterioration of the steel sheet. Therefore, it is preferable to limit the Al content to 19.5% or less.

[0057] The remainder of the composition excluding the above Mg and Al is zinc (Zn), and unintentional unavoidable impurities may be mixed in during the process of producing a plated steel sheet having a Zn-Mg-Al-based plating layer. In this case, it should be made clear that the meaning of unavoidable impurities would be easily understood by a person skilled in the art.

[0058] It is preferable that the structure of the above-mentioned Zn-Mg-Al-based plating layer satisfies the following [Relation 1].

[0059] [Equation 1] 0.26≦I(110) / I(103)≦0.65 (In Relational Formula 1, I(110) represents the integrated X-ray diffraction intensity of the (110) crystal plane peak in the MgZn2 phase, and I(103) represents the integrated X-ray diffraction intensity of the (103) crystal plane peak in the MgZn2 phase.)

[0060] In the present invention, the bendability, whiteness, etc. of the plated steel sheet can be ensured by controlling the MgZn2 phase in the Zn-Mg-Al-based plating layer according to the above [Relational Formula 1].

[0061] If the value defined by the above [Relational Formula 1] is less than 0.26, the proportion of (103) crystals in the MgZn2 phase relative to the (110) crystals in the MgZn2 phase is excessive, which may result in insufficient bendability and whiteness. On the other hand, if the value exceeds 0.65, the proportion of (110) crystals in the MgZn2 phase relative to the (103) crystals in the MgZn2 phase is too high, which may result in an inability to induce an increase in diffuse reflection and insufficient whiteness.

[0062] In this case, the I(110) may have an integrated intensity value in the range of 120 to 200, and the I(103) may have an integrated intensity value in the range of 240 to 300. In this way, it is preferable that the value of the [Relational Formula 1] be satisfied within each range.

[0063] The Zn-Mg-Al-based plating layer may include a coating layer formed by coating the composition of the present invention in a solution state, and the coating layer preferably has a thickness of 0.1 to 2.0 μm.

[0064] If the thickness of the coating layer is less than 0.1 μm, the surface treatment solution composition is applied thinly to the roughness peaks present on the surface of the plated steel sheet, resulting in a problem of reduced corrosion resistance. On the other hand, if the thickness exceeds 2.0 μm, the coating layer is formed too thick, resulting in poor workability and increased solution treatment costs, which is economically disadvantageous.

[0065] Here, the thickness mentioned above means the thickness after drying.

[0066] The present invention further describes a method for producing a surface-treated steel sheet using the composition.

[0067] More specifically, the method may include the steps of: forming a Zn-Mg-Al-based coating layer on at least one surface of a steel sheet by hot-dip galvanizing; applying the composition of the present invention in a solution state onto the coating layer to perform a coating treatment; and drying the coated steel sheet.

[0068] When applying the composition of the present invention in a solution state to the steel sheet, any commonly used coating method can be applied, and there are no particular limitations on the method.

[0069] For example, the coating process can be carried out by selecting one of methods such as bar coating, roll coating, spraying, deposition, spray squeegee, and deposition squeegee.

[0070] The step of drying the steel sheet coated with the composition is preferably carried out at a temperature in the range of 40 to 280°C based on the final temperature reached (PMT) of the base steel sheet (steel sheet).

[0071] If the final temperature of the base steel sheet is less than 40°C, the formation of a robust coating structure may be insufficient, resulting in poor corrosion resistance and blackening resistance. On the other hand, if the temperature exceeds 280°C, the hardness of the coating may increase excessively, deteriorating the corrosion resistance of the processed part and possibly causing deterioration in surface quality, such as yellowing due to excessive heat.

[0072] The steel sheet that has been subjected to the above drying treatment can have a coating layer with a thickness of 0.1 to 2.0 μm after drying.

[0073] In the present invention, the means for carrying out the drying treatment is not particularly limited, but it is clear that equipment such as an induction oven or a hot air drying furnace can be used, and the conditions for such equipment may be ordinary conditions.

[0074] The present invention will be described in more detail below through examples. However, the description of these examples is for the purpose of illustrating the implementation of the present invention, and the present invention is not limited by the description of these examples. The scope of the present invention is determined by the matters described in the claims and matters that can be reasonably inferred therefrom. [Example]

[0075] [Production of solution composition for steel sheet surface treatment] In order to measure the physical properties of the solution composition for surface treatment of steel sheet according to the present invention, the solution composition was prepared using the following materials.

[0076] First, phosphoric acid was added to distilled water (solvent) as an acidity regulator, and then chromium nitrate, a trivalent chromium compound, was added at approximately 40°C and stirred for approximately 30 minutes. In a similar manner, the adhesion promoter (3-glycidyloxypropyl)trimethoxysilane (GPTMS), the corrosion resistance improver silicon oxide, the pitting corrosion improver ethylenediamine, and the co-solvent ethanol were added at 30-minute intervals while stirring.

[0077] The content of each component is shown in Table 1 below.

[0078] [Table 1]

[0079] solution stability In order to confirm whether the prepared solution composition maintains its stability under certain conditions, the following experiment was carried out.

[0080] The initial viscosity (Vi) of each solution composition of Inventive Examples 1 to 12 and Comparative Examples 1 to 12 was measured, and then the composition was stored in an oven at 50°C for 120 hours, cooled to 25°C, and the viscosity (VI) at 25°C was measured. The solution stability was evaluated based on the calculated value (ΔV) by substituting each measured viscosity value into Equation 1 below. The results are shown in Table 3 below.

[0081] [Mathematical formula 1] △V = (Vl - Vi) / Vi x 100 (%)

[0082] <Evaluation criteria for solution stability> ○: ΔV value is less than 20% or no gelation is observed when visually observed ×: ΔV value is 20% or more, or gelation is observed when visually observed.

[0083] [Manufacturing surface-treated steel sheets] Next, the solution composition prepared above was applied to the surface of the steel sheet by bar coating, and then dried in an induction oven to obtain each surface-treated steel sheet. The amount of the composition adhered during the bar coating was about 35 mg / m2 based on Cr. 2 It was carried out so that

[0084] The steel sheet to which the solution composition was applied was a Zn-Mg-Al alloy hot-dip galvanized steel sheet (plating layer: Mg 5.4 wt %, Al 12.6 wt %, balance Zn and unavoidable impurities, value of [Relational Formula 1]: 0.40), which was cut into 7 cm × 15 cm (width × length) and degreased to prepare test pieces.

[0085] The drying temperature during the surface treatment and the thickness of the formed coating layer are shown in Table 2 below.

[0086] [Table 2]

[0087] The physical properties of the surface-treated steel sheets manufactured as described above were measured using the following methods and criteria: flat plate corrosion resistance, processed part corrosion resistance, pipe-making oil corrosion resistance, alkali resistance, pitting corrosion resistance, foreign matter defect resistance, etc. The results are shown in Table 3 below.

[0088] Plate corrosion resistance Based on the method specified in ASTM B117, each steel plate (test piece) was treated with the solution composition, and then the rate of white rust formation on the steel plate over time was measured.

[0089] <Evaluation criteria for plate corrosion resistance> ○: White rust has occurred for 144 hours or more △: White rust occurred for 96 hours or more but less than 144 hours ×: White rust formation time is less than 96 hours

[0090] Corrosion resistance of processed parts The surface-treated steel sheet (test piece) was pushed up to a height of 6 mm using an Erichsen tester, and the degree of white rust generation after 24 hours was measured.

[0091] <Evaluation criteria for corrosion resistance of processed parts> ○: White rust does not occur, or if it does occur, it is very fine △: White rust has formed on the circle and has partially washed away, but has not flowed outside. ×: White rust occurs and flows outside the circle

[0092] Piping oil invasiveness The steel sheets (test pieces) that had been surface-treated as described above were immersed in pipe-making oil at room temperature for 24 hours, and the color difference before and after immersion was measured. The pipe-making oil used was BW WELL MP-411 from Buhmwoo Co., Ltd., Korea, diluted to 10% with water.

[0093] <Evaluation criteria for pipe-making oil abrasion> ○: ΔE≦2 △:2<ΔE≦3 ×:3<ΔE

[0094] Alkali resistance The steel sheet (test piece) surface-treated as described above was immersed in a degreasing solution at 60°C for 2 minutes, then rinsed with water and air-blown, and the color difference before and after was measured. The alkaline degreasing solution used was Parkerizing's Finecleaner L 4460 A: 20g / 2.4L + L 4460 B: 12g / 2.4L (pH=12).

[0095] <Evaluation criteria for alkali resistance> ○: ΔE≦2 △:2<ΔE≦4 ×:4<ΔE

[0096] Puncture corrosion resistance Dew was applied to the surface of the steel sheet (test piece) surface-treated as described above using a sprayer, and the two spray-treated steel sheets were then butted together, packaged, and placed in a thermo-hygrostat for a total of eight cycles, each cycle consisting of six hours at high temperature and humidity (42°C, 95%) and six hours at low temperature and humidity (15°C, 60%), and the number of point defects on the surface was then measured. The scanned area of ​​the steel sheet was 150 x 50 mm. 2 This was enlarged 100 times to reveal that the area of ​​the corrosion point defect was 29,500 μm 2 Only the above items were counted.

[0097] <Evaluation criteria for pitting corrosion resistance> ○: Number of dots ≦ 20 △: 20<Number of dots≦40 ×:40<Number of dots

[0098] Foreign matter defects To evaluate foreign matter defects on steel sheets (test pieces) that had been surface treated as described above, a test piece with a surface area of ​​approximately 4 cm 2 After covering the probe with white gauze, a weight of 10 kg was placed on the probe, and the probe was rubbed back and forth on the surface of the steel plate 100 times. Then, the whiteness value of the gauze before and after rubbing (ΔL = L before -L afterIn order to simulate high humidity conditions, the steel plate and probe were placed in a humidity chamber, and the humidity in the chamber was maintained at 95% or more using a humidifier before the friction evaluation.

[0099] <Evaluation criteria for foreign matter defects> ○: ΔL≦2.5 △:2.5<ΔL≦5.0 ×:5.0<ΔL

[0100] [Table 3]

[0101] As shown in Table 3 above, the solution compositions of Examples 1 to 12 were excellent in solution stability, and the steel sheets surface-treated with such solution compositions also showed extremely excellent results in all evaluations.

[0102] In contrast, in Comparative Example 1, the content of trivalent chromium compounds was insufficient, and the corrosion resistance due to the barrier effect was insufficient, resulting in poor flat plate corrosion resistance, processed part corrosion resistance, and pitting corrosion resistance.

[0103] In Comparative Example 2, the content of trivalent chromium compounds was excessively high, and it was found that foreign matter defects occurred.

[0104] In Comparative Example 3, the content of the acidity regulator was insufficient, resulting in poor solution stability, and the steel plate surface-treated with such a solution composition was poor in flat plate corrosion resistance, processed portion corrosion resistance, and pitting corrosion resistance.

[0105] In Comparative Example 4, the content of the acidity regulator was excessive, resulting in a large amount of acid remaining in the solution, and the flat plate corrosion resistance, processed part corrosion resistance, and pitting corrosion resistance of the surface-treated steel sheet were poor.

[0106] In Comparative Example 5, the content of the adhesion improver was insufficient, and foreign matter defects occurred.

[0107] In Comparative Example 6, the content of adhesion promoter was too high, and the remaining unreacted silane resulted in poor flat plate corrosion resistance, processed area corrosion resistance, and pitting corrosion resistance of the surface-treated steel sheet.

[0108] Comparative Example 7 was a case where the content of the corrosion resistance improver was insufficient, and the corrosion resistance was insufficient, resulting in poor flat plate corrosion resistance, processed portion corrosion resistance, and pitting corrosion resistance.

[0109] In Comparative Example 8, the content of the corrosion resistance improver was excessive, and the excessively high solid content resulted in poor solution stability, poor alkali resistance of the surface-treated steel sheet, and the occurrence of foreign matter defects.

[0110] In Comparative Example 9, the content of the pitting corrosion improver was insufficient, and the surface-treated steel sheet had poor pitting corrosion resistance.

[0111] In Comparative Example 10, the content of the pitting corrosion improver was excessive, and the solution stability was insufficient, resulting in corrosion resistance in the processed parts of the surface-treated steel sheet.

[0112] In Comparative Example 11, the content of the co-solvent was insufficient, and the surface-treated steel sheet was poor in flat plate corrosion resistance, processed portion corrosion resistance, and pitting corrosion resistance.

[0113] In Comparative Example 12, the content of the co-solvent was excessive, and the solution stability was insufficient, resulting in poor corrosion resistance in the processed portion of the surface-treated steel sheet.

[0114] FIG. 1 shows the surface shape of a steel sheet (Invention Example 1) that was surface-treated using the solution composition of the present invention and the surface shape of a steel sheet that was surface-treated using a conventional composition.

[0115] As shown in FIG. 1, the steel sheet (a) surface-treated with the conventional solution composition had spot corrosion defects at the edges, whereas the steel sheet surface-treated with the solution composition of the present invention had a smooth surface without any defects up to the edges.

Claims

1. (a) 20 to 60 wt. % of one or more trivalent chromium compounds selected from the group consisting of chromium sulfate, chromium nitrate, chromium phosphate, chromium fluoride, chromium chloride, and mixtures thereof; (b) 0.1 to 10% by weight of one or more acidity regulators selected from the group consisting of phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, hydrochloric acid, (NH4)H2PO4, (NH4)2HPO4, NaH2PO4, Na2HPO4, phytic acid, glycolic acid, lactic acid, acetic acid, oxalic acid, and mixtures thereof; (c) vinyl methoxy silane, vinyl trimethoxy silane (VTMS), vinyl epoxy silane, vinyl triepoxy silane, 3-aminopropyl triepoxy silane, 3-glycidoxypropyl trimethoxy silane, 3-metaglyoxypropyl trimethoxy silane, γ-glycidoxypropyl triethoxy silane, γ-glycidoxytrimethyl dimethoxy silane, N-(3-(trimethoxysilyl)propyl)ethylenediamine (AEAPTMS), 2-(3,4 -Epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-Epoxycyclohexyl)ethyltriethoxysilane, 3-(2,3-Epoxypropoxy)propyltrim ethoxysilane, 3-(2,3-Epoxypropoxy)propyltriethoxysilane, 3-(2,3-Epoxypropoxy)propylmethyldiethoxysilane, 3-(2,3-Epox ypropoxy)propylmethyldimethoxysilane, 3-Aminopropyltriethoxysilane, 3-Aminopropyltrimethoxysilane, 3-Aminopropylmet hyldiethoxysilane, N-(2-Aminoethyl-3-aminopropyl)methyldimethoxysilane, N-(2-Aminoethyl-3-aminopropyl)trimethoxysilane 1 to 20 wt. % of one or more adhesion promoters selected from the group consisting of methyltrimethoxysilane, diethylenetriaminopropyltrimethoxysilane, 3-ureidopropyltrimethoxysilane, N-phenylaminopropyltrimethoxysilane, (3-glycidyloxypropyl)trimethoxysilane (GPTMS), methyltrimethoxysilane (MTMS), and mixtures thereof; (d) 1 to 20 wt. % of one or more corrosion resistance improvers selected from the group consisting of vanadyl acetylacetonate, ammonium metavanadate, potassium metavanadate, sodium metavanadate, vanadium trioxide, vanadium acetylacetate, ammonium metavanadate, silicon oxide, and mixtures thereof; (e) 0.01 to 3.0 wt. % of one or more pitting corrosion improvers selected from the group consisting of ethylenediamine, hexamethylenediamine, trimethylamine, methylamine, diphenylamine, ethyleneamine, aniline, toluidine, piperidine, aziridine, pyridine, alanine, propylamine, diisopropylamine, monoisopropylamine, dibutylamine, dipropylamine, and mixtures thereof; (f) 1 to 20 wt. % of one or more co-solvents selected from the group consisting of ethanol, isopropyl alcohol, methanol, tallow alcohol, 2-butoxyethanol, diethylene glycol monobutyl ether, and mixtures thereof; and (g) A solution composition for steel sheet surface treatment, containing the balance being water.

2. Steel plate and a Zn—Mg—Al-based plating layer formed on at least one surface of the steel sheet; a surface treatment coating layer formed on the plating layer, A surface-treated plated steel sheet, wherein the surface treatment coating layer is a coating layer formed from the composition of claim 1.

3. The Zn-Mg-Al-based plating layer contains, by weight %, 4.0 to 7.0% magnesium (Mg), 11.0 to 19.5% aluminum (Al), the balance being Zn, and other inevitable impurities; The surface-treated plated steel sheet according to claim 2, wherein the following relational expression 1 is satisfied: [Relationship 1] 0.26≦I(110) / I(103)≦0.65 (In relation 1, I(110) is MgZn ２ The I(103) represents the integrated X-ray diffraction intensity of the (110) crystal peak in the MgZn phase. ２ (These represent the integrated X-ray diffraction intensities of the (103) crystal plane in the phase.)

4. 3. The surface-treated plated steel sheet according to claim 2, wherein the surface treatment coating layer has a thickness of 0.1 to 2.0 μm.

5. forming a Zn—Mg—Al-based coating layer on at least one surface of the steel sheet by hot-dip galvanizing; coating the plating layer with the composition of claim 1; and drying the coated steel sheet.

6. 6. The method for producing a surface-treated plated steel sheet according to claim 5, wherein the coating treatment is performed by any one method selected from the group consisting of bar coating, roll coating, spraying, deposition, spray squeegeeing, and deposition squeegeeing.

7. The method for producing a surface-treated plated steel sheet according to claim 5, wherein the drying is carried out at a temperature in the range of 40 to 280°C based on the final target temperature (PMT) of the steel sheet.

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