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 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 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 as steel materials with excellent red rust corrosion resistance.

[0003] However, since the exposed surface of such highly corrosion-resistant hot-dip plated steel products is mostly made of zinc or zinc alloy, 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 product 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 appearance 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 surface treatment of a steel sheet, comprising: (a) 0.1 to 10% 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 promoter, (d) 1 to 15% by weight of a corrosion resistance improver, (e) 0.1 to 25% by weight of a film-forming agent, (f) 0.01 to 2% by weight of a lubricant, (g) 0.5 to 10% by weight of a co-solvent, and (h) the balance being a solvent.

[0012] Another embodiment of the present invention provides a surface-treated steel sheet comprising a steel sheet and a coating layer formed from the solution composition on at least one surface of the steel sheet.

[0013] Another embodiment of the present invention provides a method for manufacturing a surface-treated steel sheet, the method including the steps of providing a steel sheet, applying the solution composition to at least one surface of the steel sheet, and heat-treating the steel sheet to which the solution composition has been applied at 50 to 250°C. [Effects of the Invention]

[0014] According to the present invention, a solution composition having excellent solution stability can be provided, and by coating the solution composition on a steel sheet, a steel sheet having excellent 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 surface (edge) corrosion has occurred and a plated steel sheet (b) on which surface corrosion has not 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 corrosion resistance but also the blackening resistance of a 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 film-forming agent, a lubricant, 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) 0.1 to 10% 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 15% by weight of a corrosion resistance improver, (e) 0.1 to 25% by weight of a film-forming agent, (f) 0.01 to 2% by weight of a lubricant, (g) 0.5 to 10% by weight of a co-solvent, and (h) 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) 0.1 to 10% by weight of trivalent chromium compound

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

[0027] If the content of the trivalent chromium compound in the solution composition of the present invention is less than 0.1%, a strong insoluble coating cannot be formed sufficiently, and the moisture 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 10%, 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 combines with the trivalent chromium compound and the film-forming agent, and also 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 15% 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 film-forming agent, forming a passivation film and 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 will be difficult to ensure corrosion resistance because a sufficient passive film cannot be formed, while if the content exceeds 15%, 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) 0.1 to 25% by weight of a film-forming agent

[0042] In the solution composition of the present invention, the film-forming agent is a component added to form a strong coating layer on the steel sheet surface together with the trivalent chromium compound, adhesion promoter, and crosslinking agent. That is, it is advantageous for improving the film-forming effect, which is insufficient with inorganic components alone, and for improving the alkali resistance and pipe-making oil corrosion resistance of the steel sheet.

[0043] If the content of such a film-forming agent is less than 0.1%, the film formation is insufficient, making it difficult to ensure oil corrosion resistance and alkali resistance, while if the content exceeds 25%, there is a risk of foreign matter defects occurring.

[0044] In the present invention, the type of the film-forming agent is not particularly limited, but it is preferably one or more selected from the group consisting of polyurethane resin (cationic or non-ionic), acrylic emulsion (cationic or non-ionic), and mixtures thereof.

[0045] (f) Lubricant 0.01 to 2% by weight

[0046] In the solution composition of the present invention, the lubricant plays a role in improving the slipperiness of the steel sheet surface, improving workability, and suppressing the occurrence of foreign matter defects.

[0047] If the content of such a lubricant is less than 0.01%, the slip properties of the steel sheet surface may be insufficient, which may result in the occurrence of foreign matter defects, whereas if the content exceeds 2%, the solution stability may be reduced.

[0048] In the present invention, the type of the lubricant is not particularly limited, but preferably it can be one or more selected from the group consisting of Polytetrafluoroethylene (PTFE), Polyethylene (PE), Carnauba wax, and mixtures thereof.

[0049] (g) Co-solvent 0.5 to 10% by weight

[0050] 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.

[0051] If the content of such a co-solvent is less than 0.5%, 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 10%, the solution stability may be reduced due to abrupt changes in the viscosity and density of the solution.

[0052] 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.

[0053] (h) Solvent

[0054] 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.

[0055] Hereinafter, a surface-treated steel sheet having a coating layer formed by surface-treating the steel sheet with the above-described solution composition according to another embodiment of the present invention will be described in detail.

[0056] In the present invention, the steel sheet that can be surface treated with the solution composition is not particularly limited, but can be, for example, a plated steel sheet.

[0057] It should be noted that the plated steel sheet targeted by the present invention can be applied to all types of plated steel sheets, such as electroplated steel sheets, electro-alloy-plated steel sheets, galvannealed steel sheets, hot-dip aluminum-plated steel sheets, and aluminum-plated steel sheets.

[0058] However, it will be clear that, as a non-limiting example, the steel sheet may be a hot-dip galvanized steel sheet or a ternary (Zn-Mg-Al) hot-dip galvanized steel sheet.

[0059] A coating layer can be formed on at least one surface of the above-described plated steel sheet by coating the solution composition of the present invention. In this case, the coating layer can be formed on the plating layer of the plated steel sheet to a thickness of 0.2 to 3.0 μm.

[0060] If the thickness of the coating layer is less than 0.2 μm, the effects of the coating layer, such as corrosion resistance and blackening resistance, will not be fully achieved. On the other hand, if the thickness exceeds 3.0 μm, friction with the rolls that come into contact with the material during the continuous process of forming the coating layer may occur, causing the coating layer to fall off and resulting in foreign matter defects.

[0061] Here, the thickness mentioned above means the thickness after drying.

[0062] Furthermore, in the present invention, a method for producing a surface-treated steel sheet using the above solution composition will be described.

[0063] Specifically, the method may include the steps of providing a steel sheet, applying the solution composition of the present invention to at least one surface of the steel sheet, and heat treating the steel sheet to which the composition has been applied.

[0064] The steel sheet may be the above-mentioned plated steel sheet, and non-limiting examples thereof may include a hot-dip galvanized steel sheet or a ternary (Zn-Mg-Al) hot-dip galvanized steel sheet.

[0065] When applying the solution composition of the present invention to the steel sheet, any commonly used coating method can be applied, and there are no particular limitations.

[0066] For example, one method can be selected from bar coating, roll coating, spray coating, dipping coating, and the like.

[0067] On the other hand, by heat treating a steel sheet to which a composition has been applied by the above-mentioned coating method, a coating layer can be formed with a uniform thickness.

[0068] At this time, the heat treatment is preferably carried out at a temperature in the range of 50 to 250°C, but if the heat treatment temperature is below 50°C, a proper solid coating layer is not formed and a liquid solution remains, which may result in failure to ensure the desired corrosion resistance.On the other hand, if the temperature exceeds 250°C, there is a problem that the excessively high temperature causes deterioration and discoloration of the coating layer, which may result in poor corrosion resistance and blackening resistance.

[0069] In the present invention, the heat treatment process may include a drying process to solidify the applied composition, and the steel sheet after the heat treatment may have a coating layer with a thickness of 0.2 to 3.0 μm after drying. In this case, the drying method is not particularly limited, but it is clear that equipment such as a hot air drying oven or an induction heating oven can be used, and the drying conditions may be conventional.

[0070] 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]

[0071] [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.

[0072] 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. Using the same method, 3-glycidoxypropyltrimethoxysilane, an adhesion promoter; silicon oxide, a corrosion resistance improver; urethane resin, a film-forming agent; PE wax, a lubricant; and ethanol, a co-solvent, were added every 30 minutes while stirring.

[0073] The content of each component is shown in Table 1 below.

[0074] [Table 1]

[0075] solution stability In order to confirm whether the prepared solution composition maintains its stability under certain conditions, the following experiment was carried out.

[0076] The initial viscosity (Vi) of each solution composition of Inventive Examples 1 to 15 and Comparative Examples 1 to 14 was measured, and then the composition was stored in a 50°C oven for 120 hours, cooled to 25°C, and the viscosity (VI) at 25°C was measured. The measured viscosity values ​​were substituted into Equation 1 below, and the solution stability was evaluated based on the measured value (ΔV). The results are shown in Table 3 below.

[0077] [Mathematical formula 1] △V = (Vl - Vi) / Vi x 100 (%)

[0078] <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.

[0079] [Manufacturing surface-treated steel sheets] Next, the solution composition prepared above was applied to the surface of a steel sheet by bar coating, and then the steel sheet was heat-treated while passing through an induction oven to obtain each surface-treated steel sheet. The coating weight during the bar coating was about 25 mg / m2 based on Cr. 2 It was carried out so that

[0080] In this case, a Zn-Al-Mg alloy hot-dip galvanized steel sheet (Al: 13.0%, Mg: 5.0%) was used as the steel sheet to which the solution composition was applied, and test pieces were prepared by cutting into 7 cm x 15 cm (width x length) and degreasing.

[0081] The heat treatment temperature during the above surface treatment and the thickness of the formed coating layer are shown in Table 2 below.

[0082] [Table 2]

[0083] 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.

[0084] 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.

[0085] <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

[0086] 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.

[0087] <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

[0088] 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.

[0089] <Evaluation criteria for pipe-making oil abrasion> ○: ΔE≦2 △:2<ΔE≦3 ×:3<ΔE

[0090] 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).

[0091] <Evaluation criteria for alkali resistance> ○: ΔE≦2 △:2<ΔE≦4 ×:4<ΔE

[0092] 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 8 cycles, each cycle consisting of 6 hours at high temperature (42°C, 95%) and 6 hours at low temperature (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.

[0093] <Evaluation criteria for pitting corrosion resistance> ○: Number of dots ≦ 20 △: 20<Number of dots≦40 ×:40<Number of dots

[0094] 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 after In 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.

[0095] <Evaluation criteria for foreign matter defects> ○: ΔL≦2.5 △:2.5<ΔL≦5.0 ×:5.0<ΔL

[0096] [Table 3]

[0097] As shown in Table 3 above, the solution compositions of Examples 1 to 15 were excellent in solution stability, and the steel sheets surface-treated with such solution compositions also showed extremely excellent results in all evaluations.

[0098] In contrast, in Comparative Example 1, in which no trivalent chromium compound was added, the corrosion resistance due to the barrier effect was insufficient, and the flat plate corrosion resistance, processed part corrosion resistance, and pitting corrosion resistance were poor.

[0099] In Comparative Example 2, the content of trivalent chromium compounds was excessively high, and it was found that foreign matter defects occurred.

[0100] Comparative Example 3 was a case in which no acidity regulator was added, and the solution stability was poor, and the flat plate corrosion resistance and processed part corrosion resistance of the steel plate surface-treated with such a solution composition were poor.

[0101] 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.

[0102] In Comparative Example 5, the content of the adhesion improver was insufficient, and foreign matter defects occurred.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] In Comparative Example 9, no film-forming agent was added, and the surface-treated steel sheet was poor in corrosion resistance to pipe-making oil and alkali resistance.

[0107] In Comparative Example 10, the content of the film-forming agent was excessive, and foreign matter defects occurred.

[0108] Comparative Example 11 was a case where no lubricant was added, and foreign matter defects occurred.

[0109] In Comparative Example 12, the content of the lubricant was excessive, and the solution stability was insufficient, resulting in poor corrosion resistance in the processed portion of the surface-treated steel sheet.

[0110] In Comparative Example 13, no cosolvent was added, and not only did surface defects occur on the surface-treated steel sheet, but the corrosion resistance properties, such as flat plate corrosion resistance, processed part corrosion resistance, and pitting corrosion resistance, were also extremely poor.

[0111] In Comparative Example 14, the content of the co-solvent was excessive, and the solution stability was poor, and the corrosion resistance of the processed part of the surface-treated steel sheet was poor.

[0112] 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.

[0113] As shown in FIG. 1, it can be seen that the steel sheet (a) surface-treated with the conventional solution composition has defects at the edge, whereas the steel sheet (b) surface-treated with the solution composition of the present invention has a smooth surface all the way to the edge without any defects.

Claims

1. (a) 0.1 to 10 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 15 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) 0.1 to 25% by weight of one or more film-forming agents selected from the group consisting of polyurethane resin (cationic or non-ionic), acrylic emulsion (cationic or non-ionic), and mixtures thereof; (f) 0.01 to 2 wt. % of one or more lubricants selected from the group consisting of Polytetrafluoroethylene (PTFE), Polyethylene (PE), Carnauba wax, and mixtures thereof; (g) 0.5 to 10 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 (h) A solution composition for steel sheet surface treatment, containing water as the balance.

2. Steel plate and and a coating layer formed from the composition of claim 1 on at least one surface of said steel sheet.

3. The surface-treated steel sheet according to claim 2, wherein the coating layer has a thickness of 0.2 to 3.0 μm.

4. providing a steel plate; applying the composition of claim 1 to at least one surface of the steel sheet; and heat treating the steel sheet coated with the composition at 50 to 250°C.

5. The method for producing a surface-treated steel sheet according to claim 4, wherein the steel sheet is a Zn-Al-Mg hot-dip galvanized steel sheet.

6. The step of applying the composition comprises: The method for producing a surface-treated steel sheet according to claim 4, wherein the coating is carried out by one or more methods selected from the group consisting of bar coating, roll coating, spray coating, and dipping coating.

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