Composition for surface treatment of steel sheets

Abstract

The present invention discloses a surface treatment composition capable of imparting flat plate corrosion resistance, processed part corrosion resistance, pitting corrosion resistance, blackening resistance, pipe-making oil attack resistance, and alkali resistance to steel sheets and improving foreign matter defects, and a steel sheet using the same. The surface treatment composition for steel sheets according to the present invention includes a trivalent chromium compound, an adhesion promoter containing a silane compound, an acidity regulator containing an acid, a crosslinking agent containing a silicate compound, a vanadium-based pitting corrosion improver, a polymer resin, and a solvent.

Description

[Technical Field]

[0001] The present invention relates to a surface treatment composition for steel sheets containing a trivalent chromium compound, and to a steel sheet using the same. [Background technology]

[0002] Highly corrosion-resistant hot-dip plated materials are known to have excellent red rust corrosion resistance due to the inclusion of zinc (Zn), magnesium (Mg) and aluminum (Al).

[0003] However, since the exposed surface of highly corrosion-resistant hot-dip plated materials is mostly made of Zn or Zn alloy, when exposed to a humid atmosphere, pitting corrosion defects are likely to occur on the surface, resulting in poor appearance.

[0004] Furthermore, in recent years, in the phosphorus processing process, there has been an occurrence of foreign matter defects in which plating material components adhere to the rolls as the highly corrosion-resistant hot-dip plated material passes through the rolls.

[0005] To solve these problems, conventionally, plated steel sheets have been subjected to a chromate treatment in which a coating is formed by immersing the steel sheets in a solution containing hexavalent chromium as the main component, thereby ensuring corrosion resistance and blackening resistance.

[0006] However, hexavalent chromium has been designated as a harmful environmental substance and a carcinogen, and restrictions on its use are currently being tightened.

[0007] On the other hand, divalent chromium, tetravalent chromium, and pentavalent chromium are relatively unstable and are therefore not widely used in surface treatment solution compositions.

[0008] Recently, a method has been applied in which a surface treatment solution composition containing low-toxicity and stable trivalent chromium is coated on a steel sheet to ensure corrosion resistance and blackening resistance of the plated steel sheet.

[0009] For example, in the patent documents Korean Patent Publication No. 10-2006-0123628, Korean Patent Publication No. 10-2005-0052215, and Korean Patent Publication No. 10-2009-0024450, corrosion resistance and corrosion resistance are improved by a method of chemical conversion treatment in which a steel sheet is immersed in a composition containing trivalent chromium. Endurance It ensures black transformation.

[0010] However, the above chemical conversion treatment method has problems such as a long immersion time and reduced fingerprint resistance when applied to continuous processes in steel mills.

[0011] In addition, Korean Patent Publication No. 10-2004-0046347 and Japanese Patent Publication No. 2002-069660 disclose compositions containing trivalent chromium. On plated steel By applying the coating by spray or roll coater, it can be applied to continuous steel production lines and fingerprint resistance is ensured.

[0012] However, the composition contains porous silica components that have a strong moisture absorbing property, which causes a problem of rapid discoloration of Mg, Al, Zn alloy steel sheets. Summary of the Invention [Problem to be solved by the invention]

[0013] SUMMARY OF THE INVENTION An object of the present invention is to provide a composition for surface treatment of steel sheets, which can improve the flat corrosion resistance, processed corrosion resistance, pitting corrosion resistance, and foreign matter defects of steel sheets.

[0014] Another object of the present invention is to provide a composition for surface treatment of steel sheets to improve the blackening resistance, corrosion resistance to pipe-making oils, and alkali resistance of the steel sheets.

[0015] Another object of the present invention is to provide a steel sheet which is excellent in corrosion resistance, blackening resistance, pipe-making oil corrosion resistance, and alkali resistance, and which is improved in foreign matter defects.

[0016] The objects of the present invention are not limited to the objects mentioned above, and other objects and advantages of the present invention not mentioned above can be understood from the following description and can be more clearly understood from the examples of the present invention. Furthermore, it is clear that the objects and advantages of the present invention can be achieved by the means and combinations thereof set forth in the claims. [Means for solving the problem]

[0017] The surface treatment composition for steel sheet according to the present invention comprises a trivalent chromium compound; an adhesion promoter containing a silane compound; an acidity regulator containing an acid; a crosslinking agent containing a silicate compound; a vanadium-based pitting corrosion improver; a polymer resin; and a solvent.

[0018] The steel sheet according to the present invention comprises a steel sheet substrate; a zinc plating layer disposed on the steel sheet substrate; and a surface treatment layer disposed on the zinc plating layer, wherein the surface treatment layer comprises a trivalent chromium compound, an adhesion promoter containing a silane compound, an acidity regulator containing an acid, a crosslinking agent containing a silicate compound, a vanadium-based pitting corrosion improver, and a polymer resin. [Effects of the Invention]

[0019] The steel sheet according to the present invention has the effect of improving the corrosion resistance of the flat plate, the corrosion resistance of the processed portion, the pitting corrosion resistance, and the foreign matter defect resistance.

[0020] Furthermore, the steel sheet according to the present invention has the effect of being excellent in blackening resistance, corrosion resistance in pipe-making oil, and alkali resistance.

[0021] Furthermore, the steel sheet according to the present invention has an effect of improving the lifespan of the product and improving problems that occur during the distribution process, such as phosphorus processing of the steel sheet.

[0022] The above-mentioned effects and specific effects of the present invention will be described in conjunction with the following description of the preferred embodiment of the invention. [Brief explanation of the drawings]

[0023] [Figure 1]1 is a photograph of a highly corrosion-resistant plated steel sheet (left) on which pitting corrosion has occurred, and a highly corrosion-resistant plated steel sheet (right) coated with the surface treatment composition of the present invention. [Figure 2] 1 is a photograph showing a microstructure of a surface treatment layer (coating layer) of the present invention. [Figure 3] 1 shows the results of EDS component analysis of the surface treatment layer (coating layer) of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] The above-mentioned objects, features, and advantages will be described in detail below with reference to the accompanying drawings, so that those skilled in the art can easily implement the technical concept of the present invention. In describing the present invention, if a detailed description of known technologies relating to the present invention is deemed to obscure the gist of the present invention, the detailed description will be omitted. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings are used to indicate the same or similar components.

[0025] In the following, when an arbitrary structure is arranged "on top (or bottom)" of a component or "above (or below)" a component, it means that the arbitrary structure is arranged in contact with the upper surface (or lower surface) of the component, and that other structures may be interposed between the component and the arbitrary structure arranged above (or below) the component.

[0026] Hereinafter, a surface treatment composition for steel sheets according to some embodiments of the present invention and a steel sheet using the same will be described.

[0027] In the present invention, by adjusting the components and composition ratio of the surface treatment composition coated on the surface of a highly corrosion-resistant plated steel sheet, the external corrosion resistance of the steel sheet is improved, foreign matter defects are reduced, and the product life is extended. In addition, problems in the distribution process, such as phosphorus processing of the steel sheet, are resolved.

[0028] Furthermore, the surface treatment composition of the present invention contains a less toxic trivalent chromium compound instead of a hexavalent chromium compound, which is a harmful environmental substance and a carcinogen, thereby preventing problems such as harm to the human body and environmental pollution.

[0029] Furthermore, the surface treatment composition for steel sheets of the present invention does not contain a porous silica component, and therefore has the effect of preventing the phenomenon that causes rapid discoloration.

[0030] The surface treatment composition for steel sheets of the present invention comprises a trivalent chromium compound, an adhesion improver containing a silane compound, an acidity regulator containing an acid, a crosslinking agent containing a silicate compound, a vanadium-based pitting corrosion improver, a polymer resin, and a solvent.

[0031] The trivalent chromium compound is stable and has low toxicity, and mainly forms an insoluble film on the surface of the steel sheet, thereby providing corrosion resistance through a barrier effect.

[0032] The trivalent chromium compound can be contained in an amount of 0.5 to 17 parts by weight per 100 parts by weight of the solvent. Preferably, the trivalent chromium compound can be contained in an amount of 0.8 to 17 parts by weight per 100 parts by weight of the solvent, or 1 to 16 parts by weight, 1.1 to 16.9 parts by weight, 1.2 to 16.7 parts by weight, 1.2 to 16.5 parts by weight, or 1.3 to 16.1 parts by weight.

[0033] If the amount of the trivalent chromium compound is less than 0.5 parts by weight, a sufficiently strong insoluble coating cannot be formed, and therefore moisture penetrating the surface of the steel sheet cannot be effectively blocked, and corrosion resistance may not be ensured.

[0034] Conversely, if the amount of the trivalent chromium compound exceeds 17 parts by weight, the excessive chromium content may cause foreign matter defects.

[0035] The trivalent chromium compound can include one or more of chromium sulfate, chromium nitrate, chromium phosphate, chromium fluoride, and chromium chloride.

[0036] The adhesion promoter containing the silane compound bonds with the crosslinking agent and resin, and also bonds with the steel sheet, thereby improving the adhesion and corrosion resistance of the surface treatment layer. In addition, the silane compound promotes drying of the surface treatment layer, imparting high corrosion resistance.

[0037] The adhesion improver containing a silane compound can be contained in an amount of 0.1 to 40 parts by weight relative to 100 parts by weight of the solvent. Preferably, the adhesion improver can be contained in an amount of 0.1 to 38 parts by weight, 0.5 to 37 parts by weight, 1 to 36 parts by weight, 1.1 to 35.9 parts by weight, or 1.2 to 35.7 parts by weight relative to 100 parts by weight of the solvent.

[0038] If the amount of the adhesion improver is less than 0.1 part by weight, sufficient adhesion to the steel sheet cannot be ensured, and corrosion resistance and the like may not be ensured.

[0039] Conversely, if the amount of adhesion improver exceeds 40 parts by weight, the large amount of unreacted silane remaining after the coating film is formed may make it impossible to ensure corrosion resistance and the like.

[0040] Examples of adhesion promoters containing silane compounds include vinyl methoxysilane, vinyl trimethoxysilane, vinyl epoxy silane, vinyl triepoxy silane, 3-aminopropyl triepoxy silane, 3-glycidoxypropyl trimethoxysilane, 3-metaglyoxypropyl trimethoxysilane, 3-glycidoxypropyl triethoxysilane, 3-glycidoxytrimethyldimethoxysilane, N-(3-(trimethoxysilyl)propyl)ethylenediamine (AEAPTMS), 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl triepoxysilane, 3-(2,3-epoxypropoxy)propyl trimethoxysilane, The silane may include one or more of 3-(2,3-epoxypropoxy)propyltriethoxysilane, 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, 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, and N-phenylaminopropyltrimethoxysilane.

[0041] The acid-containing acidity regulator adjusts the pH of the composition so that the components of the surface treatment composition are present stably in solution and react appropriately under coating conditions to stably form a coating film.

[0042] The acid-containing acidity regulator may be contained in an amount of 0.5 to 11 parts by weight per 100 parts by weight of the solvent, preferably 0.8 to 10 parts by weight, more preferably 1 to 9 parts by weight, 1.1 to 8.8 parts by weight, 1.2 to 8.4 parts by weight, or 1.2 to 8.1 parts by weight per 100 parts by weight of the solvent.

[0043] If the amount of the acid-containing acidity regulator is less than 0.5 parts by weight, the pH becomes high and the stability of the solution may decrease. Conversely, if the amount of the acid-containing acidity regulator is more than 11 parts by weight, the pH becomes too low and corrosion resistance may not be ensured.

[0044] The acid-containing acidity regulator may include one or more of phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, hydrochloric acid, ammonium phosphate ((NH4)2HPO4, (NH4)H2PO4), monobasic phosphate (NaH2PO4), dibasic phosphate (Na2HPO4), phytic acid, glycolic acid, lactic acid, and acetic acid.

[0045] The crosslinking agent containing the silicate compound reacts with the adhesion promoter and resin to increase the degree of crosslinking of the composition, thereby improving the corrosion resistance of the coated steel sheet.

[0046] The crosslinking agent containing a silicate compound can be contained in an amount of 2 to 20 parts by weight per 100 parts by weight of the solvent. Preferably, the crosslinking agent can be contained in an amount of 2 to 19 parts by weight, 2 to 18 parts by weight, 2.2 to 17.8 parts by weight, 2.4 to 17.6 parts by weight, or 2.5 to 17.3 parts by weight per 100 parts by weight of the solvent.

[0047] If the amount of the crosslinking agent containing a silicate compound is less than 2 parts by weight, the degree of crosslinking of the surface treatment layer cannot be ensured sufficiently, and corrosion resistance and the like may not be ensured.

[0048] Conversely, if the amount of crosslinking agent containing a silicate compound exceeds 20 parts by weight, the large amount of unbound silicate remaining after the coating film is formed may make it impossible to ensure corrosion resistance, etc.

[0049] The crosslinking agent containing a silicate compound may include one or more of sodium silicate, calcium silicate, potassium silicate, aluminum silicate, lithium polysilicate, tetramethyl orthosilicate, and tetraethyl orthosilicate.

[0050] The vanadium-based pitting corrosion improver is a resin and a crosslinking agent. and Adhesion improver and The crosslinking reaction is carried out at a low temperature, and the temperature is lowered to suppress the formation of micro-pitting corrosion.

[0051] The vanadium-based pitting corrosion improver can be contained in an amount of 0.1 to 14.3 parts by weight relative to 100 parts by weight of the solvent, and preferably 2 to 14.0 parts by weight, 2.8 to 13.9 parts by weight, 2.6 to 13.9 parts by weight, or 2.5 to 13.9 parts by weight relative to 100 parts by weight of the solvent.

[0052] If the amount of the vanadium-based pitting corrosion improver is less than 0.1 part by weight, the degree of crosslinking of the surface treatment layer cannot be ensured sufficiently, and corrosion resistance and the like may not be ensured.

[0053] Conversely, if the vanadium-based pitting corrosion improver exceeds 14.3 parts by weight, the solution stability may be reduced due to too high a solids content.

[0054] Vanadium-based pitting corrosion improvers include vanadium pentoxide (V2O5), metavanadate (HVO3), ammonium metavanadate, potassium metavanadate, sodium metavanadate, vanadium oxytrichloride (VOCl3), vanadium trioxide (V2O3), vanadium dioxide (VO2), vanadium oxysulfate (VOSO4), vanadium oxyoxalate [VO(COO)2], vanadium oxyacetylacetonate [VO(OC(CH3)=CHCOCH3 ) 2], vanadium acetylacetonate [V(OC(CH3)=CHCOCH3 ) 3], vanadium trichloride (VCl3), vanadium sulfate (VSO4·8H2O), vanadium dichloride (VCl2), and vanadium oxide (VO).

[0055] The polymer resin is added to the surface of the steel sheet together with the trivalent chromium compound, adhesion promoter, and crosslinking agent to form a strong coating layer.

[0056] It is difficult to form a strong coating layer with excellent corrosion resistance using inorganic components alone. Therefore, by adding an organic polymer resin that imparts flexibility to the composition of the present invention, it is possible to improve the ability to form a precise coating, as well as the alkali resistance and oil corrosion resistance of the pipe.

[0057] The polymer resin may be contained in an amount of 0.5 to 25 parts by weight per 100 parts by weight of the solvent, preferably 0.7 to 23 parts by weight, 1 to 20 parts by weight, 1.8 to 18 parts by weight, 1.6 to 16 parts by weight, or 1.4 to 15.8 parts by weight per 100 parts by weight of the solvent.

[0058] If the polymer resin is less than 0.5 parts by weight, the coating is insufficient, making it difficult to ensure oil corrosion resistance, alkali resistance, etc. Conversely, if the polymer resin is more than 25 parts by weight, the content of trivalent chromium compounds is relatively reduced, making it difficult to ensure corrosion resistance, etc.

[0059] The polymer resin is an emulsion-type resin and may include one or more of a cationic polyurethane resin, a nonionic polyurethane resin, a cationic acrylic resin, and a nonionic acrylic resin.

[0060] Emulsion resin refers to a mixture of distilled water and a substance that is not compatible with distilled water. It has excellent dispersibility and storage properties, and has the advantage that layer separation does not occur even when left for a long time.

[0061] The cationic polyurethane resin and the cationic acrylic resin may each contain cationic functional groups containing one or more of primary to tertiary amino groups and quaternary ammonium salt groups.

[0062] For example, the cationic functional group can include one or more of an amino group, a methylamino group, an ethylamino group, a dimethylamino group, a diethylamino group, a trimethylamino group, and a triethylamino group.

[0063] The non-ionic polyurethane resin can be a resin emulsified with a non-ionic emulsifier or can be formed using a non-ionic polyol.

[0064] The nonionic acrylic resin may be a resin emulsified with a nonionic emulsifier, or may include one or more of nonionic phenoxyethyl (meth)acrylate, polyethylene glycol (meth)acrylate, ethoxyethoxyethyl acrylate, phenoxypolyethylene glycol (meth)acrylate, nonylphenol polyethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polytetramethylene glycol mono(meth)acrylate, polyethylene glycol polytetramethylene glycol mono(meth)acrylate, and polypropylene glycol polytetramethylene glycol mono(meth)acrylate.

[0065] The solvent contained in the composition for surface treatment of steel sheets of the present invention is added to dilute the components of the composition, and may include one or more of ethanol, distilled water, and deionized water.

[0066] On the other hand, the solvent is contained as the remainder when the total weight of the composition for surface treatment of steel sheets is 100%, and the solvent can be contained in an amount of about 50 to 85% by weight relative to 100% by weight of the total composition.

[0067] In the present invention, a surface treatment composition for steel sheets can be produced by mixing and stirring a solvent, a trivalent chromium compound, an adhesion promoter, an acidity regulator, a crosslinking agent, a pitting corrosion improver, and a polymer resin. The mixing and stirring temperature may be, but is not limited to, 24 to 80°C.

[0068] As described above, the surface treatment composition for steel sheet of the present invention contains a small amount of a trivalent chromium compound, an adhesion promoter, an acidity regulator, a crosslinking agent, a pitting corrosion improver, and a polymer resin, and a large amount of a solvent. By adjusting the components and composition ratios, the composition of the present invention can impart corrosion resistance to steel sheet and further improve the occurrence of inclusion defects.

[0069] The steel sheet using the steel sheet surface treatment composition of the present invention is as follows.

[0070] The steel sheet includes a steel sheet base material, a zinc-plated layer disposed on the steel sheet base material, and a surface treatment layer disposed on the zinc-plated layer.

[0071] The steel sheet base material may be, but is not limited to, a cold-rolled steel sheet, an aluminum-plated steel sheet, an aluminum alloy sheet, a phosphate-coated zinc-plated steel sheet, or a hot-rolled steel sheet.

[0072] The zinc plating layer can be formed by hot dip galvanizing or electrogalvanizing.

[0073] Hot dip galvanizing is also known as hot deep galvanizing (GI), and involves heating zinc to a high temperature to melt it, then placing the plated product inside and freezing it.

[0074] Electrogalvanizing is a method of plating a product by immersing it in a plating solution containing zinc and then electrolyzing it.

[0075] The surface treatment layer is a coating formed from a surface treatment composition for steel sheets, and the solvent contained in the composition is removed, leaving only the remaining components.

[0076] Specifically, the surface treatment layer can be formed from a steel sheet surface treatment composition containing, per 100 parts by weight of a solvent, 0.5 to 17 parts by weight of a trivalent chromium compound, 0.1 to 40 parts by weight of an adhesion improver containing a silane compound, 0.5 to 11 parts by weight of an acidity regulator containing an acid, 2 to 20 parts by weight of a crosslinker containing a silicate compound, 0.1 to 14.3 parts by weight of a vanadium-based pitting corrosion improver, and 0.5 to 25 parts by weight of a polymer resin.

[0077] Accordingly, the surface treatment layer may include a trivalent chromium compound, an adhesion promoter including a silane compound, an acidity regulator including an acid, a crosslinker including a silicate compound, a vanadium-based pitting corrosion improver, and a polymer resin.

[0078] The surface treatment layer contains approximately 10 to 70 mg / m of trivalent chromium compound. 2 Preferably, the concentration is about 30 to 60 mg / m 2 It can be formed so that

[0079] The surface treatment layer is approximately 10 to 70 mg / m based on trivalent chromium compounds. 2 By satisfying the above condition, it is possible to obtain an advantage that is advantageous in exhibiting excellent physical properties.

[0080] The surface treatment layer can be formed to a thickness of approximately 0.1 to 50 μm, but is not limited to this.

[0081] Regarding the physical properties and component analysis of the surface treatment layer (coating layer), FIG. 2 is a microstructure photograph of the surface treatment layer of the present invention, and the following Table A and FIG. 3 show the results of EDS component analysis of the surface treatment layer of the present invention.

[0082] [Table A]

[0083] Referring to Table A, FIGS. 2 and 3, the cross-sectional shape of the surface treatment layer (coating layer) was observed, and the components constituting the surface treatment layer were analyzed.

[0084] From the results of these analyses, it was confirmed that the surface treatment layer contained trivalent chromium compounds, adhesion improvers containing silane compounds, acidity regulators containing acids, crosslinkers containing silicate compounds, vanadium-based pitting corrosion improvers, polymer resins, and the like.

[0085] The method for manufacturing a steel sheet of the present invention may include forming a zinc plating layer on a steel sheet substrate, and then coating and drying a surface treatment composition.

[0086] The method for coating the surface treatment composition is not limited as long as it is a commonly used coating method.

[0087] For example, the coating method can be any of roll coating, bar coating, spraying, dipping, spray squeezing, and dipping squeezing.

[0088] After coating the surface treatment composition, drying can be carried out under any commonly used conditions without any particular limitation. For example, drying can be carried out at a temperature of about 40 to 200°C.

[0089] When the steel sheet using the surface treatment composition of the present invention was used, the solution stability was evaluated as follows: ΔV=(Vl-Vi) / Vi×100(%). The ΔV was less than 20(%), but no gelation was observed visually.

[0090] Furthermore, when the rate of white rust occurrence of the steel plate is measured based on ASTM B117, which is an evaluation standard for plate corrosion resistance, the steel plate exhibits a white rust occurrence time of 144 hours or more.

[0091] For example, the white rust generation time may be 144 to 300 hours, 144 to 250 hours, or 144 to 200 hours.

[0092] Furthermore, in the evaluation criteria for corrosion resistance of processed parts, the steel sheets either did not develop white rust or, if white rust did develop, it was very fine.

[0093] Furthermore, the steel sheet satisfied the evaluation standard of ΔE≦2 for pipe-making oil penetration resistance.

[0094] For example, 0<ΔE≦2 and 0<ΔE≦1.5 can be satisfied.

number

[0095] In the formula, L* is lightness, a* is green, red coordinates, and b* is yellow, blue coordinates (CIE Lab color space standard).

[0096] Furthermore, the steel sheet satisfied the evaluation criteria for alkali resistance of ΔE≦2. For example, it can satisfy 0<ΔE≦2 and 0<ΔE≦1.5.

[0097] Furthermore, the steel sheet was evaluated for pitting corrosion resistance with a surface pitting defect count of 20 or less. For example, the number of pitting defects may be expressed as 0 to 20, 0 to 15, 0 to 10, 0 to 7, or 0 to 4.

[0098] In addition, the steel plate was rubbed according to the evaluation criteria for foreign matter defects, and then the whiteness of the gauze (△L = L before -L after ) , ΔL≦2.5 is satisfied. For example, 0<ΔL≦2.5, 0<ΔL≦2.0, 0<ΔL≦1.8, and 0<ΔL≦1.4 can be satisfied.

[0099] FIG. 1 is a photograph of a highly corrosion-resistant plated steel sheet (left) on which pitting corrosion has occurred, and a highly corrosion-resistant plated steel sheet (right) coated with the surface treatment composition of the present invention.

[0100] Referring to FIG. 1, it can be seen that the surface-treated highly corrosion-resistant plated steel sheet of the present invention does not suffer from pitting corrosion or foreign matter defects.

[0101] Specific examples of the steel sheet surface treatment composition and the steel sheet using the same are as follows.

[0102] 1. Manufacturing of steel sheet surface treatment compositions Examples and Comparative Examples According to the composition ratios in Tables 1 and 2 below, first, phosphoric acid as an acidity regulator was added to 100 parts by weight of distilled water, and then chromium nitrate, a trivalent chromium compound, was added at about 40°C, followed by stirring for about 30 minutes.

[0103] Using the same method, a surface treatment composition was prepared by adding and stirring at 30-minute intervals glycidoxypropyltrimethoxysilane as an adhesion promoter, potassium silicate as a crosslinking agent, ammonium metavanadate as a pitting corrosion improver, and acrylic emulsion as an organic resin.

[0104] [Table 1]

[0105] [Table 2]

[0106] 2. Physical property evaluation method and results Test specimens were prepared using the surface treatment composition prepared as follows.

[0107] Highly corrosion-resistant hot-dip galvanized steel sheet (Zn-Al-Mg) was cut into 7cm x 15cm (horizontal x vertical) pieces and degreased, after which the coating adhesion amount was approximately 50mg / m2 based on Cr. 2 A test piece was prepared by bar coating.

[0108] 1) Solution stability The initial viscosity (Vi) of each coating composition prepared by the above method was measured immediately after preparation, and the composition was then stored in an oven at 50°C for 120 hours, and then frozen at 25°C. The final viscosity (Vl) at 25°C was measured and substituted into the following Equation 1. The results were evaluated according to the following evaluation criteria.

[0109] [Formula 1] △V = (Vl - Vi) / Vi × 100 (%)

[0110] <Evaluation criteria for solution stability> ◯: △V was less than 20(%) or no gelation was observed when visually observed. X: When ΔV was 20% or more, gelation was observed by visual observation.

[0111] 2) Plate corrosion resistance After treatment with the trivalent chromium surface treatment composition, the rate of white rust formation on the steel sheets over time was measured based on the method specified in ASTM B117.

[0112] <Evaluation criteria for plate corrosion resistance> The evaluation was as follows: ◯: White rust occurrence time is 144 hours or more; △: White rust occurrence time is 96 hours or more but less than 144 hours; X: White rust occurrence time is less than 96 hours.

[0113] 3) Corrosion resistance of processed parts The steel plate treated with the trivalent chromium surface treatment composition was pushed up to a height of 6 mm using an Erichsen tester, and the degree of white rust formation was measured after 24 hours.

[0114] < Corrosion resistance of processed parts Evaluation criteria> ○: No white rust has occurred, or if white rust has occurred, it is very fine; △: Fine white rust has occurred in the circle and some has flowed out, but has not flowed out of the circle; X: White rust has occurred and has flowed out of the circle

[0115] 4) Piping oil invasiveness The steel sheets treated with the trivalent chromium surface treatment composition 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, a product of Bamu (Korea), diluted with 10% water.

[0116] <Evaluation criteria for pipe-making oil abrasion> ○:△E≦2, △:2<△E≦3, X:3<△E

[0117] 5) Alkali resistance The steel sheet treated with the trivalent chromium surface treatment composition was immersed in an alkaline degreasing solution at 60°C for 2 minutes, then rinsed with water, and air-blowed, after which the color difference before and after was measured.

[0118] The alkaline degreasing solution used was Finecleaner L 4460A: 20 g / 2.4 L + L4460B 12 g / 2.4 L (pH = 12) from Daihan Packaging Co., Ltd.

[0119] <Evaluation criteria for alkali resistance> ○:△E≦2, △:2<△E≦4, X:4<△E

[0120] 6) Pitting corrosion resistance Dew was formed on the surfaces of the steel sheets treated with the trivalent chromium surface treatment composition using a sprayer or the like, and then the two steel sheets were butted against each other, packaged, and placed in a thermo-hygrostat. The steel sheets were subjected to eight cycles of high temperature and high humidity (42°C, 95%) for six hours and low temperature and low humidity (15°C, 60%) for six hours, and then the number of pitting defects on the surfaces was counted.

[0121] To count the number of corrosion pitting defects, the scanning area of ​​the steel plate was 100 × 50 mm. 2 When magnified 100 times, the area of ​​the corrosive pitting defect was 29,500 μm 2Only the number of items that were equal to or greater than this was counted.

[0122] <Evaluation criteria for pitting corrosion resistance> ○: Number of pitting corrosion≦20, △:20<number of pitting corrosion≦40, X:40<number of pitting corrosion

[0123] 7) Foreign matter defects To evaluate foreign matter defects on steel sheets treated with trivalent chromium surface treatment compositions, 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 rubbed back and forth 100 times. The whiteness of the gauze before and after rubbing (△L = L before -L after ) values ​​were measured.

[0124] In order to simulate high humidity conditions, a humidity chamber was created for both the steel plate and the probe, and the humidity was maintained at 95% or more using a humidifier, and friction evaluation was performed.

[0125] <Criteria for foreign substance defect evaluation> ○:△L≦2.5, △:2.5<△L≦5, X:5<△L

[0126] The results of measuring the physical properties of the surface-treated steel sheets produced as above are shown in Tables 3 and 4 below.

[0127] [Table 3]

[0128] [Table 4]

[0129] As shown in Table 3 above, in the case of Examples 1 to 15 according to the present invention, the solution stability, flat plate corrosion resistance, processed part corrosion resistance, pipe-making oil corrosion resistance, alkali resistance, and pitting corrosion resistance were excellent, and it can be seen that the foreign matter defects were improved.

[0130] However, as shown in Table 4, in the case of Comparative Example 1, the content of trivalent chromium compounds was insufficient, resulting in poor corrosion resistance due to the barrier effect, and insufficient corrosion resistance for flat plates, processed parts, and pitting corrosion.

[0131] In the case of Comparative Example 2, it is clear that the content of trivalent chromium compounds was too high, causing foreign matter defects.

[0132] In the case of Comparative Example 3, the content of the adhesion improver was insufficient, and the flat plate corrosion resistance, processed part corrosion resistance, and pitting corrosion resistance were insufficient, resulting in the occurrence of foreign matter defects.

[0133] In the case of Comparative Example 4, the content of the adhesion promoter is too high, and the remaining unreacted silane causes insufficient corrosion resistance in the processed area and pitting corrosion resistance.

[0134] In the case of Comparative Example 5, the content of the acidity regulator was insufficient, resulting in insufficient solution stability, and therefore, even after coating, the corrosion resistance of flat plates, corrosion resistance of processed parts, and corrosion resistance to pipe-making oil were insufficient.

[0135] In the case of Comparative Example 6, the content of the acidity regulator was too high, resulting in insufficient corrosion resistance in processed areas and pitting corrosion resistance.

[0136] In the case of Comparative Example 7, the content of the crosslinking agent was insufficient, and therefore the corrosion resistance of the processed part and the pitting corrosion resistance were insufficient, and foreign matter defects were generated.

[0137] In the case of Comparative Example 8, the content of crosslinker was too high, and unbound silicate resulted in insufficient solution stability. In addition, even after coating, the corrosion resistance of flat plates, processed parts, pipe-making oil corrosion resistance, and pitting corrosion resistance were insufficient.

[0138] In the case of Comparative Example 9, the content of the pitting corrosion improver is insufficient, and it can be seen that the pitting corrosion resistance is insufficient.

[0139] In the case of Comparative Example 10, the content of the pitting corrosion improver was too high, resulting in insufficient solution stability, and even after coating, the corrosion resistance of flat plates, corrosion resistance of processed parts, resistance to pipe-making oil, and pitting corrosion resistance were insufficient.

[0140] In the case of Comparative Example 11, the content of organic resin was insufficient, and the film formation was insufficient, resulting in insufficient corrosion resistance of the processed part, corrosion resistance to pipe-making oil, and alkali resistance.

[0141] In the case of Comparative Example 12, the content of organic resin was too high, and the trivalent chromium compound was relatively insufficient, resulting in insufficient corrosion resistance for flat plates, processed portions, and pitting corrosion.

[0142] Although the present invention has been described above with reference to illustrative drawings, it is clear that the present invention is not limited to the embodiments and drawings disclosed in this specification, and that various modifications can be made by those skilled in the art within the scope of the technical concept of the present invention. Furthermore, even if the effects of the configuration of the present invention are not explicitly described and explained while the embodiments of the present invention are described above, it is natural that the effects that can be predicted by the configuration should also be recognized.

Claims

1. For 100 parts by weight of solvent, 0.5 to 17 parts by weight of a trivalent chromium compound; 0.1 to 40 parts by weight of an adhesion improver containing a silane compound; 0.5 to 11 parts by weight of an acidity regulator containing an acid; 2 to 20 parts by weight of a crosslinking agent containing a silicate compound; 0.1 to 14.3 parts by weight of a vanadium-based pitting corrosion improver; 0.5 to 25 parts by weight of a polymeric resin; and Contains solvents, A composition for surface treatment of steel sheets.

2. The trivalent chromium compound includes one or more of chromium sulfate, chromium nitrate, chromium phosphate, chromium fluoride, and chromium chloride. The surface treatment composition for steel sheets according to claim 1 .

3. Examples of the adhesion improver containing the silane compound include vinyl methoxysilane, vinyl trimethoxysilane, vinyl epoxy silane, vinyl triepoxysilane, 3-aminopropyl triepoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-metaglyoxypropyl trimethoxysilane, 3-glycidoxypropyl triethoxysilane, 3-glycidoxytrimethyldimethoxysilane, N-(3-(trimethoxysilyl)propyl)ethylenediamine (AEAPTMS), 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriepoxysilane, 3-(2,3-epoxypropoxy)propyltrimethoxysilane, and 2-(2,3-epoxypropoxy)propyltrimethoxysilane. silane, 3-(2,3-epoxypropoxy)propyltriethoxysilane, 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, 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, and N-phenylaminopropyltrimethoxysilane; The surface treatment composition for steel sheets according to claim 1 .

4. The acid-containing acidity regulator may be phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, hydrochloric acid, ammonium phosphate ((NH ４ ) ２ HPO ４ , (NH ４ ) H ２ P.O. ４ ), monobasic phosphate (NaH ２ P.O. ４ ), Dibasic phosphate (Na ２ HPO ４ ), phytic acid, glycolic acid, lactic acid, and acetic acid, The surface treatment composition for steel sheets according to claim 1 .

5. The silicate compound-containing crosslinking agent may include at least one of sodium silicate, calcium silicate, potassium silicate, aluminum silicate, lithium polysilicate, tetramethyl orthosilicate, and tetraethyl orthosilicate; The surface treatment composition for steel sheets according to claim 1 .

6. The vanadium-based pitting corrosion improver is vanadium pentoxide (V ２ O ５ ), metavanadic acid (HVO ３ ), ammonium metavanadate, potassium metavanadate, sodium metavanadate, vanadium oxytrichloride (VOCl ３ ), vanadium trioxide (V ２ O ３ ), vanadium dioxide (VO ２ ), vanadium oxysulfate (VOSO ４ ), vanadium oxyoxalate [VO(COO) ２ ], vanadium oxyacetylacetonate [VO(OC(CH ３ ) = CHCOCH ３ ) ２ ], vanadium acetylacetonate [V(OC(CH ３ ) = CHCOCH ３ ) ３ ], vanadium trichloride (VCl ３ ), vanadium sulfate (VSO ４ ・8H ２ O), vanadium dichloride (VCl ２ ), and vanadium oxide (VO), The surface treatment composition for steel sheets according to claim 1 .

7. The polymer resin includes at least one of a cationic polyurethane resin, a nonionic polyurethane resin, a cationic acrylic resin, and a nonionic acrylic resin; The surface treatment composition for steel sheets according to claim 1 .

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