Solution composition for steel sheet surface treatment, steel sheet surface-treated with the same and method for producing 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 having a plating layer containing zinc (Zn), magnesium (Mg), and aluminum (Al) are known as steel materials with excellent red rust corrosion resistance.

[0003] However, such highly corrosion-resistant hot-dip plated steel products have a problem that, since the exposed surface thereof is mostly made of zinc or zinc alloy, when exposed to a general environment, particularly a humid atmosphere, the surface is prone to develop dot-like corrosion defects, which deteriorate the appearance. Recently, in contract processing, foreign matter defects have also been occurring in which the coating layer of the hot-dip plated steel product adheres to the rolls when passing through the rolls.

[0004] To solve these problems, in the past, hexavalent chromium or chromate treatment was applied to plated steel sheets to ensure corrosion resistance and blackening resistance. However, hexavalent chromium has been designated as a harmful environmental substance, and regulations on the use of hexavalent chromium are currently being strengthened. Furthermore, when hexavalent chromium is used as a surface treatment agent for plated steel sheets, there is a defect that the surface of the steel sheet turns black or black spots are generated.

[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 the 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 process 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 a composition containing trivalent chromium can be applied to a continuous line of a steel company by coating a plated steel sheet by a spray or roll coater method, and fingerprint resistance can be ensured. However, these compositions contain porous silica components, and are therefore not suitable for Mg and Al alloys, which tend to discolor rapidly in a humid atmosphere. In addition, porous silica has a strong hygroscopic property, which causes a problem of inducing rapid discoloration in Zn-Mg-Al 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] According to one embodiment of the present invention, the composition of a coating solution applied to a surface of a highly corrosion-resistant plated steel sheet is controlled to improve the pitting corrosion resistance and blackening resistance of the steel sheet, and a solution composition having excellent solution stability is provided, and a steel sheet surface-treated using the same and a method for manufacturing the same are provided.

[0010] The object of the present invention is not limited to the above. 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 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-mentioned 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-mentioned solution composition; and drying the coated steel sheet. Effect 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, and a steel sheet having excellent pitting corrosion resistance and blackening resistance can be provided by coating the solution composition on the steel sheet.

[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 description of the drawings]

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

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

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

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

[0020] First, a solution composition for surface treatment of a steel sheet 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 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 material, 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) Trivalent chromium compound 20 to 60% by weight

[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 the corrosion resistance due to a 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 moisture penetrating into the surface of the steel sheet cannot be effectively blocked, and as a result, corrosion resistance cannot be ensured. On the other hand, if the content exceeds 60%, there is a risk of foreign matter 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, resulting in a risk of reduced solution stability. On the other hand, if the content exceeds 10%, there is a possibility that corrosion resistance, etc. may not be ensured due to residual acid after drying.

[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 combines with the above-mentioned trivalent chromium compound and the like, and also with the steel sheet, thereby playing a role in improving the adhesion, corrosion resistance, etc. of the coating layer.

[0035] If the content of such adhesion improver is less than 1%, the adhesion to the steel sheet may not be sufficiently secured, which may result in the occurrence of foreign matter defects, whereas if the content exceeds 20%, an excessive amount of the adhesion improver remains after the coating film is formed, which may result in the corrosion resistance and the like not being secured.

[0036] In the present invention, the type of the adhesion improver is not particularly limited, but is preferably vinyl methoxysilane, vinyl trimethoxysilane (VTMS), vinyl epoxy silane, vinyl triepoxy silane, 3-aminopropyl triepoxy silane, 3-glycidoxypropyl trimethoxysilane, 3-methaglyoxypropyl trimethoxysilane, γ-glycidoxypropyl triethoxysilane, γ-glycidoxytrimethyl dimethoxysilane, 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, 3-(2,3-epoxypropoxy)propylmethyldiethox The methylaminopropylsilane may be one or more selected from the group consisting of ethylaminopropylsilane, 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) Corrosion resistance improver 1 to 20% by weight

[0038] In the solution composition of the present invention, the corrosion resistance improver fills any gaps that may exist between the trivalent chromium compound and the adhesion improver 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 may be 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) Puncture corrosion improver 0.01 to 3.0% by weight In the solution composition of the present invention, the pitting corrosion improver, together with the corrosion resistance improver, serves to prevent localized penetration of corrosive factors and minimize pitting corrosion occurring in the form of spots.

[0042] In the solution composition of the present invention, if the content of the pitting corrosion improving agent is less than 0.01%, there is a problem that pitting corrosion occurs because the local penetration of corrosion factors cannot be blocked, whereas if the content exceeds 3.0%, the pH of the solution may excessively increase, 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) co-solvent 1 to 20% by weight

[0045] In the solution composition of the present invention, the co-solvent serves 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 the co-solvent is less than 1%, the effect of controlling the volatilization rate during drying is insufficient, so that the evaporation rate of the main solvent is abrupt at the boiling point, causing a surface defect called popping, which leads to problems such as a decrease in corrosion resistance, etc. On the other hand, if the content exceeds 20%, the solution stability may decrease 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 having a coating layer that is surface-treated with the above-mentioned 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 for surface treatment of plated steel sheet, preferably 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 above-mentioned 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 may be used.

[0054] The Zn-Mg-Al-based plating layer may have a composition, in weight percent, of 4.0 to 7.0% magnesium (Mg), 11.0 to 19.5% aluminum (Al), the balance 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 in order to ensure the excellent corrosion resistance targeted in the present invention, the content is preferably 4.0% or more. However, if the Mg content is excessive, there is a risk of dross being generated in the coating bath and of forming an excessive amount of intermetallic compounds with high hardness in the coating layer, which may deteriorate the bendability of the steel sheet, so the content can be limited to 7.0%.

[0056] On the other hand, adding Mg at a content of 4.0% or more may cause the risk of dross generation due to oxidation of Mg in the coating bath, so in consideration of this, it is preferable to include aluminum (Al) at 11.0% or more. However, if the Al content is excessive, the melting point of the coating bath becomes high, which may cause problems due to high-temperature work such as erosion of the coating bath structure and denaturation of the steel sheet. Therefore, it is preferable to limit the Al content to 19.5% or less.

[0057] The composition of the remainder excluding the above Mg and Al is zinc (Zn), and unintended unavoidable impurities may be mixed in during the process of manufacturing 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 can 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 the relational expression 1, I(110) represents the X-ray diffraction integrated intensity of the (110) crystal plane peak in the MgZn2 phase, and I(103) represents the X-ray diffraction integrated intensity of the (103) crystal plane peak in the MgZn2 phase.)

[0060] In the present invention, the bendability, whiteness, and the like 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 [Relationship 1].

[0061] If the value defined by the above [Relationship 1] is less than 0.26, the proportion of (103) crystals in the MgZn2 phase is too high compared to the (110) crystals in the MgZn2 phase, 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 is too high compared to the (103) crystals in the MgZn2 phase, which may result in an insufficient whiteness due to an inability to induce an increase in diffuse reflection.

[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] is satisfied within each range.

[0063] The above-mentioned Zn-Mg-Al-based plating layer may include a coating layer formed by coating the composition of the present invention in a solution state. In this case, 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 above thickness means the thickness after drying.

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

[0067] More specifically, the method may include the steps of: forming a Zn-Mg-Al-based plating 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 plating 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 used, and there is no particular limitation to 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 target temperature (PMT) of the base steel sheet (steel sheet).

[0071] If the final temperature of the base steel plate is less than 40°C, the formation of a solid 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 area and causing deterioration of surface quality, such as yellowing due to excessive heat.

[0072] The steel sheet after 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 performing 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 normal conditions.

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

[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 about 40°C and stirred for about 30 minutes. In a similar manner, (3-glycidyloxypropyl)trimethoxysilane (GPTMS), an adhesion improver, silicon oxide, a corrosion resistance improver, ethylenediamine, a pitting corrosion improver, and ethanol, a co-solvent, were added at 30-minute intervals while stirring.

[0077] At this time, 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] After measuring the initial viscosity (Vi) of each solution composition of the above Invention Examples 1 to 12 and Comparative Examples 1 to 12, 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 value (ΔV) calculated by substituting each measured viscosity value into the following mathematical formula 1. The results are shown in Table 3 below.

[0081] [Mathematical formula 1] △V = (Vl-Vi) / Vi × 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 of 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 adhesion amount of the composition during the bar coating was about 35 mg / m2 based on Cr. 2 The experiment was carried out so that

[0084] In this case, 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 [relationship 1]: 0.40) was used as the steel sheet for applying the solution composition, and the steel sheet was cut into a size of 7 cm x 15 cm (horizontal x vertical) and degreased to prepare a test piece.

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

[0086] [Table 2]

[0087] In order to measure the physical properties of the surface-treated steel sheets manufactured as described above, the flat plate corrosion resistance, processed part corrosion resistance, pipe-making oil corrosion resistance, alkali resistance, pitting corrosion resistance, foreign object defects, etc. were measured according to the following methods and standards. 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 occurrence 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 some of it has washed away, but it has not washed away to the outside. ×: White rust occurs and flows outside the circle

[0092] Piping oil invasiveness The steel sheet (test piece) surface-treated as described above was 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 with 10% 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 washed with water and air-blowing was performed, 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] Spot corrosion resistance Dew was applied to the surface of the steel plate (test piece) surface-treated as described above using a sprayer, and the two spray-treated steel plates were butted together, packaged, and placed in a thermohygrostat to perform a total of eight cycles, with one cycle being 6 hours at high temperature and humidity (42°C, 95%) and 6 hours at low temperature and humidity (15°C, 60%), and the number of point defects on the surface was then measured. At this time, the scan area of ​​the steel plate was 150 x 50 mm. 2 This was then enlarged 100 times to reveal that the area of ​​the corrosive 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 body defects In order to evaluate foreign matter defects on the steel plate (test piece) 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 steel plate surface 100 times. 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 the probe were placed in a humidity chamber, and the humidity in the chamber was maintained at 95% or more using a humidifier, after which the friction evaluation was performed.

[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] It can be seen that in Comparative Example 2, the content of trivalent chromium compounds was excessively high, and foreign matter defects occurred.

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

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

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

[0108] In Comparative Example 7, the content of the corrosion resistance improver was insufficient, and the corrosion resistance was insufficient, with the flat plate corrosion resistance, processed portion corrosion resistance, and pitting corrosion resistance being poor.

[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 improving agent 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, causing 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 inferior 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 (Example 1) that was surface-treated with the solution composition of the present invention and the surface shape of a steel sheet that was surface-treated with a conventional composition.

[0115] As shown in FIG. 1, the steel sheet (a) surface-treated with the conventional solution composition had spot-like corrosion defects at the edges, whereas the steel sheet (a) 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% 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 weight percent of a co-solvent, and (g) A solution composition for steel sheet surface treatment, containing a residual solvent.

2. 2. The solution composition for treating a steel sheet surface according to claim 1, wherein the trivalent chromium compound is one or more selected from the group consisting of chromium sulfate, chromium nitrate, chromium phosphate, chromium fluoride, chromium chloride, and mixtures thereof.

3. The acidity regulator may be phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, hydrochloric acid, (NH ４ ) H ２ P.O. ４ , (NH ４ ) ２ H.P.O. ４ , NaH ２ P.O. ４ , Na ２ H.P.O. ４ 2. The solution composition for steel sheet surface treatment according to claim 1, wherein the active ingredient is one or more selected from the group consisting of phytic acid, glycolic acid, lactic acid, acetic acid, oxalic acid, and mixtures thereof.

4. The adhesion improver is preferably vinyl methoxy silane, vinyl trimethoxy silane (VTMS), vinyl epoxy silane, vinyl triepoxy silane, 3-aminopropyl triepoxy silane, 3-glycidoxypropyl trimethoxy silane, 3-methaglyoxypropyl 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-Epoxypr opoxy)propylmethyldimethoxysilane, 3-Aminopropyltriethoxysilane, 3-Aminopropyltrimethoxysilane, 3-Aminopropylmethyldie thoxysilane, N-(2-Aminoethyl-3-aminopropyl)methyldimethoxysilane, N-(2-Aminoethyl-3-aminopropyl)trimethoxysilane, Diet The solution composition for steel sheet surface treatment according to claim 1, which is one or more selected from the group consisting of hylenetriaminopropyltrimethoxysilane, 3-ureidopropyltrimethoxysilane, N-phenylaminopropyltrimethoxysilane, (3-glycidyloxypropyl)trimethoxysilane (GPTMS), methyltrimethoxysilane (MTMS), and mixtures thereof.

5. 2. The solution composition for surface treatment of steel sheet according to claim 1, wherein the corrosion resistance improver is 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.

6. 2. The solution composition for steel sheet surface treatment according to claim 1, wherein the pitting corrosion improver is 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.

7. 2. The solution composition for treating a steel sheet surface according to claim 1, wherein the co-solvent is at least one selected from the group consisting of ethanol, isopropyl alcohol, methanol, tallow alcohol, 2-butoxyethanol, diethylene glycol monobutyl ether, and mixtures thereof.

8. The solution composition for treating a steel sheet surface according to claim 1 , wherein the solvent is water.

9. A steel plate, 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 according to any one of claims 1 to 8.

10. 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 9 , wherein the following relational expression 1 is satisfied: [Relationship 1] 0.26≦I(110) / I(103)≦0.65 (In the relational formula 1, I(110) is MgZn ２ The I(103) represents the X-ray diffraction integrated 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.)

11. 10. The surface-treated plated steel sheet according to claim 9, wherein the surface treatment coating layer has a thickness of 0.1 to 2.0 μm.

12. forming a Zn-Mg-Al-based coating layer on at least one surface of the steel sheet by hot-dip galvanizing; A step of coating the plating layer with a composition according to any one of claims 1 to 8; and drying the coated steel sheet.

13. 13. The method for producing a surface-treated plated steel sheet according to claim 12, 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.

14. The method for producing a surface-treated plated steel sheet according to claim 12, wherein the drying is carried out in a temperature range of 40 to 280° C. based on the final target temperature (PMT) of the steel sheet.

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