Surface treatment composition for steel sheet and steel sheet using the same

Abstract

This invention discloses a surface treatment composition and a steel sheet utilizing the composition. The surface treatment composition imparts corrosion resistance to flat steel plates, corrosion resistance to processed areas, resistance to pitting corrosion, resistance to blackening, resistance to pipe-making oil corrosion, and alkali resistance, and can improve foreign matter defects. The surface treatment composition for steel sheets according to this invention comprises: a trivalent chromium compound; a thickener 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] This invention relates to a composition for surface treatment of steel plates containing trivalent chromium compounds and a steel plate using the composition. Background Technology

[0002] Highly corrosion-resistant hot-dip galvanized materials include zinc (Zn), magnesium (Mg), and aluminum (Al), and are known for their excellent resistance to red rust corrosion.

[0003] However, since the exposed surface of highly corrosion-resistant hot-dip galvanized materials is mostly composed of Zn or Zn alloys, it is prone to pitting corrosion defects when exposed to a humid atmosphere, resulting in a deterioration in appearance.

[0004] In addition, in recent years, during the processing of high corrosion-resistant hot-dip galvanized materials, foreign matter defects have occurred, with coating material components adhering to the rollers as the materials pass through the rollers.

[0005] To address this issue, a chromate treatment was previously employed, in which the plated steel sheet was immersed in a solution containing hexavalent chromium to form a thin film, thereby ensuring corrosion resistance and resistance to blackening.

[0006] However, because hexavalent chromium is designated as an environmentally harmful and carcinogenic substance, regulations on its use are currently being tightened.

[0007] In addition, divalent chromium, tetravalent chromium, and pentavalent chromium are relatively unstable and cannot be well used in surface treatment solution compositions.

[0008] In recent years, a method has been applied to ensure the corrosion resistance and blackening resistance of coated steel sheets by coating them with a surface treatment solution composition containing low toxicity and stable trivalent chromium.

[0009] For example, Korean Patent Publications 10-2006-0123628, 10-2005-0052215 and 10-2009-0024450 disclose a method of ensuring corrosion resistance and blackening by immersing a steel plate in a composition containing trivalent chromium for chemical formation treatment.

[0010] However, the aforementioned chemical formation treatment method suffers from problems such as long immersion time and reduced fingerprint resistance, making it difficult to apply to continuous processes in steel companies.

[0011] In addition, Korean Patent Publication 10-2004-0046347 and Japanese Patent Application Publication 2002-069660 describe how a composition containing trivalent chromium is coated onto a steel plate by spraying or roller coating, which can be applied to continuous production lines of steel companies and ensures fingerprint resistance.

[0012] However, because the composition contains porous silica, which is highly hygroscopic, it can cause rapid discoloration in Mg, Al, and Zn alloy steel sheets. Summary of the Invention

[0013] Technical problems to be solved

[0014] The purpose of this invention is to provide a surface treatment composition for steel plates that can improve the flat corrosion resistance, the corrosion resistance of the processed parts, the resistance to pitting corrosion and foreign matter defects of the steel plate.

[0015] Furthermore, the object of the present invention is to provide a surface treatment composition for steel plates that improves their resistance to blackening, pipe oil corrosion, and alkali resistance.

[0016] Furthermore, the purpose of this invention is to provide a steel plate with excellent corrosion resistance, resistance to blackening, resistance to pipe oil corrosion, alkali resistance, and improvement of foreign matter defects.

[0017] The objectives of this invention are not limited to those described above. Objectives and advantages not explicitly mentioned can be understood through the following description, and these objectives and advantages will become clearer through embodiments of the invention. Furthermore, it will be readily apparent that the objectives and advantages of this invention can be achieved through the methods and combinations thereof shown in the claims.

[0018] Technical solution

[0019] The composition for surface treatment of steel plates according to the present invention comprises: a trivalent chromium compound; a thickener comprising a silane compound; an acidity regulator comprising an acid; a crosslinking agent comprising a silicate compound; a vanadium-based pitting corrosion improver; a polymer resin; and a solvent.

[0020] The steel plate according to the present invention comprises: a steel plate base material; a galvanized layer disposed on the steel plate base material; and a surface treatment layer disposed on the galvanized layer, wherein the surface treatment layer comprises: a trivalent chromium compound, a tackifier comprising a silane compound, an acidity regulator comprising an acid, a crosslinking agent comprising a silicate compound, a vanadium-based pitting corrosion improver, and a polymer resin.

[0021] Beneficial effects

[0022] The steel plate according to the present invention has the effect of improving the corrosion resistance of flat plates, the corrosion resistance of machined parts, the resistance to pitting corrosion and foreign matter defects.

[0023] Furthermore, the steel plate according to the present invention has excellent resistance to blackening, pipe oil corrosion, and alkali resistance.

[0024] Furthermore, the steel plate according to the present invention has the effect of improving product lifespan and alleviating problems in the distribution process such as steel plate processing.

[0025] In addition to the effects described above, the specific effects of the present invention will be explained below while describing the specific content used to implement the invention. Attached Figure Description

[0026] Figure 1 These are photographs of a highly corrosion-resistant coated steel sheet (left) exhibiting pitting corrosion and a highly corrosion-resistant coated steel sheet (right) coated with the surface treatment composition of the present invention.

[0027] Figure 2 This is a photograph of the microstructure of the surface treatment layer (thin film layer) of the present invention.

[0028] Figure 3 These are the EDS composition analysis results of the surface treatment layer (thin film layer) of the present invention. Detailed Implementation

[0029] The above-mentioned objects, features, and advantages will be described in detail with reference to the accompanying drawings, thus enabling those skilled in the art to readily implement the technical concept of the present invention. In describing the present invention, detailed descriptions are omitted when it is determined that specific descriptions of well-known technologies related to the present invention would unnecessarily obscure the main idea of ​​the invention. Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings are used to refer to the same or similar constituent elements.

[0030] Hereinafter, setting any configuration in the "upper (or lower) part" or "above (or below)" of a constituent element can mean that any configuration can contact and be set above (or below) the constituent element, and other configurations can be inserted between the constituent element and any configuration set above (or below) the constituent element.

[0031] Hereinafter, a surface treatment composition for steel plates according to some embodiments of the present invention and a steel plate using the composition will be described.

[0032] In this invention, by adjusting the composition and ratio of the surface treatment composition coated on the surface of a highly corrosion-resistant coated steel sheet, the appearance corrosion resistance of the steel sheet is improved and foreign matter defects are reduced. Therefore, not only is the product lifespan increased, but problems in the distribution process such as steel sheet processing are also solved.

[0033] Furthermore, the surface treatment composition of the present invention contains a trivalent chromium compound with low toxicity to replace a hexavalent chromium compound, which is an environmentally harmful and carcinogenic substance, thereby preventing harm to the human body and environmental pollution.

[0034] Furthermore, since the surface treatment composition for steel plates of the present invention does not contain porous silica, it has the effect of preventing rapid discoloration.

[0035] The surface treatment composition for steel plates of the present invention comprises: a trivalent chromium compound; a tackifier comprising a silane compound; an acidity regulator comprising an acid; a crosslinking agent comprising a silicate compound; a vanadium-based pitting corrosion improver; a polymer resin; and a solvent.

[0036] The trivalent chromium compound is low in toxicity and stable. It mainly forms an insoluble film on the surface of the steel plate and provides corrosion resistance through the barrier effect.

[0037] The content of the trivalent chromium compound relative to 100 parts by weight of solvent can be 0.5-17 parts by weight. Preferably, the content of the trivalent chromium compound relative to 100 parts by weight can be 0.8-17 parts by weight, 1-16 parts by weight, 1.1-16.9 parts by weight, 1.2-16.7 parts by weight, 1.2-16.5 parts by weight, or 1.3-16.1 parts by weight.

[0038] When the trivalent chromium compound content is less than 0.5 parts by weight, it cannot form a hard, insoluble film, thus failing to effectively block moisture from penetrating to the steel plate surface, and therefore cannot ensure corrosion resistance.

[0039] On the other hand, when the trivalent chromium compound exceeds 17 parts by weight, foreign matter defects may occur due to the excessive chromium content.

[0040] Trivalent chromium compounds may include one or more of chromium sulfate, chromium nitrate, chromium phosphate, chromium fluoride, and chromium chloride.

[0041] The tackifier containing silane compounds improves the adhesion and corrosion resistance of the surface treatment layer by combining with crosslinking agents and resins, and then bonding with the steel plate. Furthermore, the silane compounds promote the drying of the surface treatment layer and impart high corrosion resistance.

[0042] The content of the viscous agent containing the silane compound relative to 100 parts by weight of solvent can be 0.1-40 parts by weight. Preferably, the content of the viscous agent relative to 100 parts by weight can be 0.1-38 parts by weight, 0.5-37 parts by weight, 1-36 parts by weight, 1.1-35.9 parts by weight, or 1.2-35.7 parts by weight.

[0043] When the tackifier is less than 0.1 parts by weight, it may not be able to adequately ensure adhesion to the steel plate, corrosion resistance, etc.

[0044] On the other hand, when the tackifier exceeds 40 parts by weight, the large amount of unreacted silane remaining after the coating film is formed may not be able to ensure corrosion resistance, etc.

[0045] Tackifiers containing silane compounds may include vinyltrimethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, 3-methylglycidyl etheroxypropyltrimethoxysilane, 3-glycidyl etheroxypropyltriethoxysilane, N-(3-(trimethoxysilyl)propyl)ethylenediamine (AEAPTMS), 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, 3-( One or more of the following: 2,3-epoxypropoxy)propylmethyldimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, diethylenetriaminopropyltrimethoxysilane, 3-ureopropyltrimethoxysilane, and N-phenylaminopropyltrimethoxysilane.

[0046] The acid-containing acidity regulator adjusts the pH of the composition, allowing the components in the surface treatment composition to exist stably in the solution and react appropriately under coating conditions, thereby enabling the stable formation of a thin film.

[0047] The content of the acidity regulator containing acid can be 0.5-11 parts by weight relative to 100 parts by weight of solvent. Preferably, the content of the acidity regulator can be 0.8-10 parts by weight, 1-9 parts by weight, 1.1-8.8 parts by weight, 1.2-8.4 parts by weight, or 1.2-8.1 parts by weight relative to 100 parts by weight of solvent.

[0048] When the acid-containing acidity adjuster is less than 0.5 parts by weight, the pH increases and the stability of the solution may decrease. On the other hand, when the acid-containing acidity adjuster exceeds 11 parts by weight, the corrosion resistance may not be guaranteed due to the excessively low pH.

[0049] Acidity regulators containing acids may include one or more of the following: phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, hydrochloric acid, ammonium phosphate ((NH4)2HPO4, (NH4)H2PO4), sodium dihydrogen phosphate (NaH2PO4), sodium monohydrogen phosphate (Na2HPO4), phytic acid, glycolic acid, lactic acid, and acetic acid.

[0050] The crosslinking agent containing silicate compounds increases the degree of crosslinking of the composition by reacting with tackifiers and resins, thereby improving the corrosion resistance of the coated steel sheet.

[0051] The content of the crosslinking agent containing silicate compounds can be 2-20 parts by weight relative to 100 parts by weight of solvent. Preferably, the content of the crosslinking agent can be 2-19 parts by weight, 2-18 parts by weight, 2.2-17.8 parts by weight, 2.4-17.6 parts by weight, or 2.5-17.3 parts by weight relative to 100 parts by weight of solvent.

[0052] When the crosslinking agent containing silicate compounds is less than 2 parts by weight, sufficient crosslinking of the surface treatment layer cannot be ensured, and therefore corrosion resistance may not be guaranteed.

[0053] On the other hand, when the crosslinking agent containing silicate compounds exceeds 20 parts by weight, corrosion resistance may not be guaranteed after the coating is formed due to the large amount of unbonded silicate remaining.

[0054] The crosslinking agent containing silicate compounds may include one or more of sodium silicate, calcium silicate, potassium silicate, aluminum silicate, lithium polysilicate, tetramethyl orthosilicate, and tetraethyl orthosilicate.

[0055] The vanadium-based pitting corrosion modifier lowers the temperature, allowing the crosslinking reaction of the resin, crosslinking agent, and tackifier to occur at low temperatures, thereby inhibiting the formation of fine pitting corrosion.

[0056] The content of the vanadium-based pitting corrosion modifier relative to 100 parts by weight of solvent can be 0.1-14.3 parts by weight. Preferably, the content of the pitting corrosion modifier relative to 100 parts by weight of solvent can be 2-14.0 parts by weight, 2.8-13.9 parts by weight, 2.6-13.9 parts by weight, or 2.5-13.9 parts by weight.

[0057] When the amount of vanadium-based pitting corrosion modifier is less than 0.1 parts by weight, sufficient cross-linking of the surface treatment layer cannot be ensured, and therefore corrosion resistance may not be guaranteed.

[0058] On the other hand, when the amount of vanadium-based pitting corrosion modifier exceeds 14.3 parts by weight, the solution stability may decrease due to excessive solids.

[0059] Vanadium-based pitting corrosion modifiers may contain one or more of the following: vanadium pentoxide (V₂O₅), metavanadate (HVO₃), ammonium metavanadate, potassium metavanadate, sodium metavanadate, vanadium trichloride (VOCl₃), vanadium trioxide (V₂O₃), vanadium dioxide (VO₂), vanadium oxysulfate (VOSO₄), vanadium oxalate [VO(COO)₂], vanadium acetylacetonate [VO(OC(CH₃)=CHCOCH₃)₂], vanadium acetylacetonate [V(OC(CH₃)=CHCOCH₃)₃], vanadium trichloride (VCl₃), vanadium sulfate (VSO₄·8H₂O), vanadium dichloride (VCl₂), and vanadium monoxide (VO).

[0060] The polymer resin is added to form a hard film layer on the surface of the steel plate together with trivalent chromium compounds, tackifiers, and crosslinking agents.

[0061] Using only inorganic components may make it difficult to form a hard film layer with excellent corrosion resistance. Therefore, by adding an organic polymer resin that imparts flexibility to the composition of the present invention, the formation of a dense film is enhanced, thereby improving resistance to alkalis, pipe oil corrosion, etc.

[0062] The content of polymer resin relative to 100 parts by weight of solvent can be 0.5-25 parts by weight. Preferably, the content of polymer resin relative to 100 parts by weight of solvent can be 0.7-23 parts by weight, 1-20 parts by weight, 1.8-18 parts by weight, 1.6-16 parts by weight, or 1.4-15.8 parts by weight.

[0063] When the polymer resin content is less than 0.5 parts by weight, the film-forming properties are insufficient, making it difficult to ensure the corrosion resistance and alkali resistance of the pipe oil. On the other hand, when the polymer resin content exceeds 25 parts by weight, the content of trivalent chromium compounds is relatively reduced, which may make it difficult to ensure corrosion resistance.

[0064] The polymer resin is an emulsion resin and may contain one or more of cationic polyurethane resin, nonionic polyurethane resin, cationic acrylic resin, and nonionic acrylic resin.

[0065] Emulsion resins are mixtures of substances incompatible with distilled water and distilled water. They have excellent dispersibility and storage properties, and even when left for a long time, they do not undergo layer separation.

[0066] Cationic polyurethane resin and cationic acrylic resin may each contain cationic functional groups, wherein the cationic functional groups contain one or more of primary to tertiary amino groups and quaternary ammonium bases.

[0067] For example, the cationic functional group may include one or more of amino, methylamino, ethylamino, dimethylamino, diethylamino, trimethylamino, and triethylamino.

[0068] Nonionic polyurethane resins can be resins emulsified with nonionic emulsifiers or formed using nonionic polyols.

[0069] Nonionic acrylic resin is a resin emulsified with a nonionic emulsifier, or may contain one or more of the following: nonionic phenoxyethyl (meth) acrylate, polyethylene glycol (meth) acrylate, ethoxyethoxyethyl acrylate, phenoxy polyethylene glycol (meth) acrylate, nonylphenol polyethylene glycol (meth) acrylate, methoxy polyethylene glycol (meth) acrylate, polyethylene glycol mono(meth) acrylate, polypropylene glycol mono(meth) acrylate, polybutylene glycol mono(meth) acrylate, polyethylene glycol polybutylene glycol mono(meth) acrylate, and polypropylene glycol polybutylene glycol mono(meth) acrylate.

[0070] The solvent contained in the surface treatment composition for steel plates of the present invention is added to dilute the components of the composition, and may contain one or more of ethanol, distilled water, and deionized water.

[0071] In addition, based on a total of 100% by weight of the composition for surface treatment of steel plates, the solvent is included as the balance, and approximately 50-85% by weight of the solvent may be included relative to the total of 100% by weight of the composition.

[0072] In this invention, a composition for surface treatment of steel plates can be prepared by mixing and stirring a solvent, a trivalent chromium compound, a thickener, an acidity regulator, a crosslinking agent, a pitting corrosion improver, and a polymer resin. The mixing and stirring temperature can be 24-80°C, but is not limited to this.

[0073] As described above, the surface treatment composition for steel plates of the present invention contains a small amount of trivalent chromium compound, a thickener, an acidity regulator, a crosslinking agent, a pitting corrosion improver, and a polymer resin, and is a composition containing a large amount of solvent. By adjusting the components and composition ratio, the composition of the present invention imparts corrosion resistance to steel plates and has the effect of further improving foreign matter defects.

[0074] The steel sheet using the surface treatment composition of the steel sheet of the present invention is as follows.

[0075] The steel plate includes: a steel plate base material; a galvanized layer disposed on the steel plate base material; and a surface treatment layer disposed on the galvanized layer.

[0076] The base material for the steel sheet can be cold-rolled steel sheet, aluminized steel sheet, aluminum alloy sheet, phosphate-coated galvanized steel sheet or hot-rolled steel sheet, etc., but is not particularly limited to these.

[0077] The zinc coating can be formed by hot-dip galvanizing or electro-galvanizing.

[0078] Hot-dip galvanizing, also known as GI, is a method in which zinc is heated and melted at high temperature, then added to the product to be galvanized and cooled.

[0079] Electroplating zinc is a method in which the product to be plated is placed in a zinc-containing plating solution and then plated by electrolysis.

[0080] The surface treatment layer is a thin film formed from a composition for surface treatment of steel plates, wherein the solvent contained in the composition has been removed, leaving only the remaining components.

[0081] Specifically, relative to 100 parts by weight of solvent, the surface treatment layer can be formed from a surface treatment composition for steel plate, said surface treatment composition comprising: 0.5-17 parts by weight of a trivalent chromium compound, 0.1-40 parts by weight of a viscous agent containing a silane compound, 0.5-11 parts by weight of an acidity regulator containing an acid, 2-20 parts by weight of a crosslinking agent containing a silicate compound, 0.1-14.3 parts by weight of a vanadium-based pitting corrosion improver, and 0.5-25 parts by weight of a polymer resin.

[0082] Therefore, the surface treatment layer may contain trivalent chromium compounds, tackifiers containing silane compounds, acidity regulators containing acids, crosslinking agents containing silicate compounds, vanadium-based pitting corrosion modifiers, and polymer resins.

[0083] The surface treatment layer can be formed such that the trivalent chromium compound content is approximately 10-70 mg / m³. 2 Preferably, the trivalent chromium compound can be formed to a concentration of approximately 30-60 mg / m³. 2 .

[0084] Based on trivalent chromium compounds, the surface treatment layer meets a requirement of approximately 10-70 mg / m³. 2 This allows for the attainment of advantages that facilitate the display of superior physical properties.

[0085] The surface treatment layer can be formed to a thickness of about 0.1-50 μm, but is not limited to this.

[0086] Regarding the physical properties and composition analysis of the surface treatment layer (thin film layer), Figure 2 These are photographs of the microstructure of the surface treatment layer of the present invention, as shown in Table A below. Figure 3 These are the EDS composition analysis results of the surface treatment layer of the present invention.

[0087] [Table A]

[0088]

[0089] Refer to Table A Figure 2 and Figure 3 The composition of the surface treatment layer is analyzed by observing the cross-sectional shape of the surface treatment layer (thin film layer).

[0090] This analysis confirms that the surface treatment layer contains trivalent chromium compounds, tackifiers containing silane compounds, acidity regulators containing acids, crosslinking agents containing silicate compounds, vanadium-based pitting corrosion modifiers, polymer resins, etc.

[0091] The method of manufacturing the steel plate of the present invention may include the steps of forming a galvanized layer on the steel plate substrate and then coating and drying it with a surface treatment composition.

[0092] The method of coating the surface treatment composition is not limited as long as it is a conventional coating method.

[0093] For example, the coating method can be carried out by any of the following methods: roller coating, bar coating, spraying, dipping, spraying, or immersion.

[0094] After coating the surface treatment composition, drying is not limited by normal conditions. For example, drying can be carried out at about 40-200°C.

[0095] In the solution stability evaluation criteria, when ΔV = (Vl - Vi) / Vi × 100 (%), the steel plate using the surface treatment composition of the present invention has ΔV less than 20 (%) or no gelation phenomenon can be observed visually.

[0096] Furthermore, when the white rust formation rate of the steel plate was measured according to ASTM B117 in the plate corrosion resistance evaluation standard, the time for white rust formation was more than 144 hours.

[0097] For example, the time for white rust to form can be 144-300 hours, or 144-250 hours, or 144-200 hours.

[0098] Furthermore, the steel plate does not produce white rust in the corrosion resistance evaluation criteria of the processing department, or if white rust does occur, it is very fine.

[0099] Furthermore, the steel plate satisfies ΔE≤2 in the evaluation criteria for the corrosivity of pipe-making oil.

[0100] For example, it can satisfy 0<ΔE≤2 and 0<ΔE≤1.5.

[0101]

[0102] In the formula, L Brightness, a : Green and red system coordinates, b Yellow and blue system coordinates (based on the CIE Lab color space).

[0103] Furthermore, the steel plate meets the alkali resistance evaluation standard of ΔE≤2. For example, it can meet the conditions of 0<ΔE≤2 or 0<ΔE≤1.5.

[0104] Furthermore, the number of pitting defects on the surface of the steel plate in the pitting corrosion resistance evaluation criteria is less than 20. For example, the number of pitting defects can be 0-20, 0-15, 0-10, 0-7, or 0-4.

[0105] Furthermore, the whiteness of the gauze after rubbing the steel plate in the foreign object defect evaluation standard (ΔL=L) 之前(before) -L 之后(after) In the case of ), ΔL≤2.5 is satisfied. For example, it can satisfy 0<ΔL≤2.5, 0<ΔL≤2.0, 0<ΔL≤1.8, and 0<ΔL≤1.4.

[0106] Figure 1 These are photographs of a highly corrosion-resistant coated steel sheet (left) exhibiting pitting corrosion and a highly corrosion-resistant coated steel sheet (right) coated with the surface treatment composition of the present invention.

[0107] refer to Figure 1 It can be confirmed that the surface treatment of the high corrosion-resistant coated steel sheet of the present invention does not produce pitting corrosion or foreign matter defects.

[0108] The surface treatment composition for steel plates described above and specific examples of steel plates using the composition are as follows.

[0109] 1. Preparation of a composition for surface treatment of steel plates

[0110] Examples and Comparative Examples

[0111] According to the composition ratios in Tables 1 and 2 below, firstly, phosphoric acid as an acidity regulator is added relative to 100 parts by weight of distilled water, and chromium nitrate as a trivalent chromium compound is added at about 40°C, and then the mixture is stirred for about 30 minutes.

[0112] A surface treatment composition was prepared by adding glycidoxypropyltrimethoxysilane as a tackifier, potassium silicate as a crosslinking agent, ammonium metavanadate as a pitting corrosion modifier, and acrylic emulsion as an organic resin at 30-minute intervals using the same method and while stirring.

[0113] [Table 1]

[0114]

[0115] [Table 2]

[0116]

[0117] 2. Evaluation methods and results of physical properties

[0118] To manufacture test specimens, the surface treatment composition prepared above is used to manufacture the following.

[0119] High corrosion-resistant hot-dip galvanized steel sheets (Zn-Al-Mg) were cut into 7cm × 15cm (transverse × longitudinal) pieces, degreased, and then subjected to rod coating to produce test pieces, achieving a film adhesion of approximately 50 mg / m² based on Cr. 2 .

[0120] 1) Solution stability

[0121] After preparing the coating composition using the above method, the initial viscosity (Vi) was measured immediately. After storing it in an oven at 50°C for 120 hours, it was cooled to 25°C again, and the final viscosity (Vl) at 25°C was measured. The results were then substituted into the following mathematical formula 1. The results were evaluated according to the following evaluation criteria.

[0122] [Mathematical Formula 1] △V=(Vl-Vi) / Vi×100(%)

[0123] <Criteria for evaluating solution stability>

[0124] O: △V is less than 20 (%) or no gelation phenomenon is observed visually.

[0125] X: △V is 20% or higher, or gelation is observed visually.

[0126] 2) Corrosion resistance of flat plates

[0127] The rate of white rust formation on steel plates over time was measured according to the method specified in ASTM B117 after treatment with a trivalent chromium surface treatment composition.

[0128] <Evaluation Criteria for Corrosion Resistance of Flat Plates>

[0129] The evaluation is as follows: O: the time for white rust to form is more than 144 hours; Δ: the time for white rust to form is more than 96 hours but less than 144 hours; X: the time for white rust to form is less than 96 hours.

[0130] 3) Corrosion resistance of the machined parts

[0131] Using an Erichsen tester, a steel plate treated with a trivalent chromium surface treatment composition was raised to a height of 6 mm, and the degree of white rust formation was measured after 24 hours.

[0132] <Evaluation Criteria for Corrosion Resistance of Machining Parts>

[0133] O: No white rust appears, or even if white rust appears, it is very fine; Δ: Fine white rust appears on the circle and partially flows out but does not flow outside the circle; X: White rust appears and flows outside the circle.

[0134] 4) Corrosiveness of pipe-making oil

[0135] At room temperature, steel sheets treated with a trivalent chromium surface treatment composition were immersed in pipe-making oil and kept there for 24 hours. The color difference before and after immersion was measured. The pipe-making oil was prepared by diluting domestically produced BUHMWOO BW WELLMP-411 with 10% water.

[0136] <Evaluation Criteria for the Corrosiveness of Pipe-Making Oil>

[0137] O: ΔE≤2, Δ: 2<ΔE≤3, X: 3<ΔE

[0138] 5) Alkali resistance

[0139] At 60°C, a steel plate treated with a trivalent chromium surface treatment composition was immersed in an alkaline degreasing solution for 2 minutes, then washed with water, and the color difference before and after air blowing was measured.

[0140] The alkaline degreasing solution used was DAEHAN PARKERIZING's Finecleaner L 4460 A: 20g / 2.4L + L4460 B 12g / 2.4L (pH=12).

[0141] <Evaluation Criteria for Alkali Resistance>

[0142] O: ΔE≤2, Δ: 2<ΔE≤4, X: 4<ΔE

[0143] 6) Resistance to pitting corrosion

[0144] Using a sprayer or similar device, dewdrops were formed on the surface of a steel plate treated with a trivalent chromium surface treatment composition. Then, two steel plates were wrapped face to face and placed in a constant temperature and humidity chamber. After eight cycles of 6 hours of high temperature and high humidity (42 degrees, 95%) and 6 hours of low temperature and low humidity (15 degrees, 60%), the number of point defects on the surface was counted.

[0145] To count the number of corrosive pitting defects, the scanning area of ​​the steel plate was 100. 50mm 2 Magnified 100 times, the area of ​​corrosive point defects alone is 29,500 μm. 2 The above refers to the number of corrosive point defects.

[0146] <Evaluation Criteria for Resistance to Pitting Corrosion>

[0147] O: Number of points ≤ 20 : 20 < number of points ≤ 40, X: 40 < number of points

[0148] 7) Foreign object defects

[0149] To evaluate foreign matter defects in steel plates treated with a trivalent chromium surface treatment composition, a surface area of ​​approximately 4 cm² was covered with white gauze. 2 The probe was then used, and a 10kg weight was placed on it. The fabric was rubbed back and forth 100 times. The whiteness of the gauze before and after rubbing was then measured (ΔL=L). 之前 -L 之后 )value.

[0150] At this point, in order to simulate high humidity conditions, a humidity chamber was created for the steel plate and probe, and the humidity was maintained above 95% using a humidifier, and a friction evaluation was conducted.

[0151] Evaluation Criteria for Foreign Body Defects

[0152] O: ΔL≤2.5, Δ: 2.5<ΔL≤5, X: 5<ΔL

[0153] The results of measuring the physical properties of the prepared surface-treated steel sheet are recorded in Tables 3 and 4 below.

[0154] [Table 3]

[0155]

[0156] [Table 4]

[0157]

[0158] As shown in Table 3, it can be seen that in the case of Examples 1 to 15 of the present invention, the solution stability, plate corrosion resistance, processing part corrosion resistance, pipe oil corrosion resistance, alkali resistance, and pitting corrosion resistance are excellent, and foreign matter defects are improved.

[0159] However, as shown in Table 4, it can be seen that in the case of Comparative Example 1, the content of trivalent chromium compounds is insufficient, resulting in poor corrosion resistance due to the barrier effect. Therefore, the corrosion resistance of the plate, the corrosion resistance of the processed parts, and the resistance to pitting corrosion are insufficient.

[0160] In Comparative Example 2, it was found that the content of trivalent chromium compounds was too high, thus causing foreign matter defects.

[0161] In Comparative Example 3, it was found that the content of the tackifier was insufficient, and the corrosion resistance of the plate, the corrosion resistance of the processed part, and the resistance to pitting corrosion were insufficient, and foreign matter defects occurred.

[0162] In Comparative Example 4, it was found that the excessive content of tackifier resulted in insufficient corrosion resistance and pitting corrosion resistance of the processed part due to the residual unreacted silane.

[0163] In Comparative Example 5, it was found that the acidity regulator content was insufficient and the solution stability was insufficient. Therefore, even with coating, the corrosion resistance of the plate, the corrosion resistance of the processed part, and the corrosion resistance of the pipe-making oil were insufficient.

[0164] In Comparative Example 6, it was found that the acidity regulator content was too high, resulting in insufficient corrosion resistance and pitting corrosion resistance of the processed part.

[0165] In Comparative Example 7, it was found that the crosslinking agent content was insufficient, and the corrosion resistance and pitting corrosion resistance of the processed part were insufficient, and foreign matter defects occurred.

[0166] In Comparative Example 8, it can be seen that the crosslinking agent content is too high, resulting in insufficient solution stability due to unbonded silicates. Moreover, even with coating, the plate corrosion resistance, the corrosion resistance of the processed parts, the resistance to pipe oil corrosion, and the resistance to pitting corrosion are all insufficient.

[0167] In Comparative Example 9, it can be seen that the content of the pitting corrosion modifier is insufficient, and therefore the resistance to pitting corrosion is insufficient.

[0168] In Comparative Example 10, it was found that the content of the pitting corrosion improver was too high, resulting in insufficient solution stability. Even with coating, the corrosion resistance of the plate, the corrosion resistance of the processed part, the corrosion resistance of the pipe-making oil, and the resistance to pitting corrosion were all insufficient.

[0169] In Comparative Example 11, it was found that the content of organic resin was insufficient, resulting in inadequate film formation. Consequently, the corrosion resistance of the processed part, the corrosion resistance of the pipe-making oil, and the alkali resistance were all insufficient.

[0170] In Comparative Example 12, it can be seen that the high content of organic resin leads to a relative deficiency of trivalent chromium compounds, resulting in insufficient corrosion resistance of the plate, the corrosion resistance of the processed parts, and the resistance to pitting corrosion.

[0171] As described above, the present invention has been explained with reference to the illustrated drawings. However, the present invention is not limited to the embodiments and drawings disclosed in this specification. 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 according to the present invention are not explicitly stated and explained while describing the embodiments of the present invention above, it should be understood that the effects can be predicted through the corresponding configuration.

Claims

1. A composition for surface treatment of steel plates, comprising: Solvent, and Relative to 100 parts by weight of solvent, 0.5-17 parts by weight of trivalent chromium compounds; 0.1-40 parts by weight of a tackifier containing a silane compound; 0.5-11 parts by weight of an acid-containing acidity regulator; 2-20 parts by weight of a crosslinking agent containing silicate compounds; 0.1-14.3 parts by weight of vanadium-based pitting corrosion modifier; and 0.5-25 parts by weight of polymer resin.

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

3. The composition for surface treatment of steel plates according to claim 1, wherein, The tackifier containing silane compounds includes vinyltrimethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, 3-methylglycidyl etheroxypropyltrimethoxysilane, 3-glycidyl etheroxypropyltriethoxysilane, N-(3-(trimethoxysilyl)propyl)ethylenediamine (AEAPTMS), 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, 3-( One or more of 2,3-epoxypropoxy)propylmethyldimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, diethylenetriaminopropyltrimethoxysilane, 3-ureidopropyltrimethoxysilane, and N-phenylaminopropyltrimethoxysilane.

4. The composition for surface treatment of steel plates according to claim 1, wherein, The acidity regulator containing acid comprises one or more of phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, hydrochloric acid, (NH4)2HPO4, (NH4)H2PO4, sodium dihydrogen phosphate (NaH2PO4), disodium hydrogen phosphate (Na2HPO4), phytic acid, glycolic acid, lactic acid, and acetic acid.

5. The composition for surface treatment of steel plates according to claim 1, wherein, The crosslinking agent containing silicate compounds comprises one or more of sodium silicate, calcium silicate, potassium silicate, aluminum silicate, lithium polysilicate, tetramethyl orthosilicate, and tetraethyl orthosilicate.

6. The composition for surface treatment of steel plates according to claim 1, wherein, The vanadium-based pitting corrosion modifier comprises one or more of the following: vanadium pentoxide (V₂O₅), ammonium metavanadate, potassium metavanadate, sodium metavanadate, vanadium trichloride (VOCl₃), vanadium trioxide (V₂O₃), vanadium dioxide (VO₂), vanadium oxysulfate (VOSO₄), vanadium oxalate, vanadium acetylacetonate, vanadium acetylacetonate, vanadium trichloride (VCl₃), vanadium sulfate, vanadium dichloride (VCl₂), and vanadium monoxide (VO).

7. The composition for surface treatment of steel plates according to claim 1, wherein, The polymer resin comprises one or more of cationic polyurethane resin, nonionic polyurethane resin, cationic acrylic resin, and nonionic acrylic resin.

8. A steel plate comprising: Steel plate base material; A galvanized layer is applied to the steel plate substrate; as well as A surface treatment layer is disposed on the zinc plating layer. The surface treatment layer is formed from the surface treatment composition of the steel plate according to claim 1.

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