Composition for surface treating cold-rolled steel sheet, cold-rolled steel sheet surface-treated using same, and manufacturing method therefor

Abstract

The present invention relates to a composition for surface treating a steel sheet and, more specifically, to a composition for surface treating a cold-rolled steel sheet, a cold-rolled steel sheet surface-treated using the composition, and a manufacturing method therefor.

Description

Composition for surface treatment of cold-rolled steel sheets, cold-rolled steel sheets surface-treated using the same, and method for manufacturing the same

[0001] The present invention relates to a composition for surface treatment of steel sheets, and more specifically, to a composition for surface treatment of cold-rolled steel sheets, a cold-rolled steel sheet surface-treated using said composition, and a method for manufacturing the same.

[0002] Steel sheets are used in various industries due to their excellent mechanical properties, but because they are susceptible to corrosion, galvanized steel sheets that can provide sacrificial protection are generally used.

[0003] Meanwhile, in some cases, unplated cold-rolled steel sheets are used. Since surface corrosion can occur if these sheets are exposed to the atmosphere during distribution and manufacturing, they are generally distributed with rust-preventive oil applied to their surface to prevent this. The rust-preventive oil applied to the surface of the cold-rolled steel must be removed through a degreasing process before the final parts are manufactured; however, this inevitably leads to increased costs due to the additional process and poses problems such as environmental pollution due to the characteristics of the degreasing solution.

[0004] Accordingly, there is a need for the development of technology that can secure the corrosion resistance of cold-rolled steel sheets while eliminating processes such as the application of rust-preventive oil, which are essential for the distribution of cold-rolled steel sheets.

[0005] One aspect of the present invention is to provide a composition for surface treatment of cold-rolled steel sheets that can impart corrosion resistance to the cold-rolled steel sheets and allows the omission of processes such as the application of rust-preventive oil during distribution.

[0006] In addition, the present invention provides a cold-rolled steel sheet surface-treated using a composition for surface treatment of a cold-rolled steel sheet according to one aspect of the invention, and a method for manufacturing the cold-rolled steel sheet.

[0007] The technical problems to be solved by the present invention are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art to which the present invention belongs from the description below.

[0008] According to one aspect of the present invention, a solution composition is provided comprising (a) a polymer resin: 5.0 to 40.0 wt%, (b) a curing agent: 1.0 to 8.0 wt%, (c) a co-solvent: 1.0 to 10.0 wt%, (d) a pH adjuster: 1.0 to 5.0 wt%, (e) an inorganic rust inhibitor: 1.0 to 10.0 wt%, (f) an organic rust inhibitor: 0.1 to 3.0 wt%, (g) a water repellent: 0.1 to 3.0 wt%, (h) a surfactant: 0.01 to 2.00 wt%, and (i) the remainder being a solvent.

[0009] A solution composition according to one aspect of the present invention is suitable for surface treatment of steel sheets, particularly cold-rolled steel sheets, and a coating layer formed from this solution composition can impart not only corrosion resistance but also surface conductivity to the surface-treated steel sheet.

[0010] In one embodiment of the present invention, the polymer resin may be one or more selected from the group consisting of acrylic emulsion, polyethylene, acrylic acid-ethylene copolymer, and mixtures thereof.

[0011] In one embodiment of the present invention, the curing agent may be one or more selected from the group consisting of Highly Methylated Melamine Resins, Methylated High Imino Melamine Resins, Partially Methylated Melamine Resins, Highly Alkylated Melamine Resins, High Imino Melamine Resins, and mixtures thereof.

[0012] In one embodiment of the present invention, the co-agent may be one or more selected from the group consisting of butyl cellosolve, 2-butanol, ethanol, benzyl alcohol, diglyme, propylene glycol, ethylene glycol, and mixtures thereof.

[0013] In one embodiment of the present invention, the pH adjuster may be one or more selected from the group consisting of a substance containing ammonia or ammonium salt and mixtures thereof.

[0014] In one embodiment of the present invention, the inorganic anti-corrosion agent may be one or more selected from the group consisting of nano-particle colloidal silica, titanium oxide, cerium oxide, zirconium oxide, and mixtures thereof.

[0015] In one embodiment of the present invention, the organic rust inhibitor may be one or more selected from the group consisting of benzothiazole, mercaptobenzothiazole (MBT), pyrimidine, benzotriazole, benzimidazole, 2H-indene-1,3-dione, and mixtures thereof.

[0016] In one embodiment of the present invention, the water-repellent agent may be one or more selected from the group consisting of polydimethylsiloxane (PDMS), polyurethane, and mixtures thereof.

[0017] In one embodiment of the present invention, the surfactant may be one or more selected from the group consisting of Tall oil fatty acid ethoxylate, Oleyl alcohol ethoxylate, Polyethylene Glycol-p-isooctylphenyl Ether, and mixtures thereof.

[0018] In one embodiment of the present invention, the solvent is water, and the water may be one or more of pure water, distilled water, and deionized water.

[0019] According to another aspect of the present invention, a surface-treated cold-rolled steel sheet is provided, comprising a cold-rolled steel sheet and a surface-treated coating layer on at least one surface of the cold-rolled steel sheet.

[0020] In one embodiment of the present invention, the coating layer may be formed from the solution composition.

[0021] A surface-treated cold-rolled steel sheet having a coating layer formed from a solution composition according to the present invention can have excellent surface conductivity in addition to corrosion resistance.

[0022] In one embodiment of the present invention, the coating layer may have a thickness of 0.1 to 2.0 μm (based on thickness after drying).

[0023] In one embodiment of the present invention, when EDS measurement is performed on the surface of the coating layer, the coating layer may have a composition comprising, in weight percent, nitrogen (N): 1.0~15.0%, oxygen (O): 10.0~30.0%, silicon (Si): 10.0~20.0%, and the remainder being carbon (C) and other unavoidable impurities.

[0024] According to another aspect of the present invention, a method for manufacturing a surface-treated cold-rolled steel sheet is provided, comprising the steps of: preparing a base steel sheet; applying a solution composition to at least one surface of the base steel sheet; and drying and curing after applying the solution composition.

[0025] In one embodiment of the present invention, the solution composition may be the solution composition provided in the present invention.

[0026] In one embodiment of the present invention, the drying and curing step may be performed in a temperature range of 50 to 270°C based on the peak metal temperature (PMT) of the steel plate.

[0027] According to the present invention, a composition for surface treatment of cold-rolled steel sheets can be provided, which has excellent solution stability such that no precipitation or aggregation occurs even when used after long-term storage, and can impart excellent corrosion resistance when coated on the surface of cold-rolled steel sheets.

[0028] In addition, when the surface of a cold-rolled steel sheet is coated using the above composition, a cold-rolled steel sheet with excellent corrosion resistance as well as surface conductivity can be provided.

[0029] FIG. 1 illustrates an example of a cold-rolled steel sheet having a coating layer applied with a surface treatment composition according to one embodiment of the present invention.

[0030] Preferred embodiments of the present invention will be described below with reference to the attached drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0031] In addition, embodiments of the present invention are provided to more fully explain the invention to those with average knowledge in the relevant technical field.

[0032] In drawings, the shapes and sizes of elements may be exaggerated for clearer explanation.

[0033] In describing the embodiments of the present invention, if it is determined that a detailed description of known technology related to the present invention may unnecessarily obscure the essence of the present invention, such detailed description will be omitted. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intentions or practices of the user or operator. Therefore, such definitions should be based on the content throughout this specification. The terms used in the detailed description are merely for describing the embodiments of the present invention and should not be limited in any way. Unless explicitly stated otherwise, expressions in the singular form include the meaning of the plural form.

[0034] In this description, expressions such as “include” or “equipped” are intended to refer to certain characteristics, numbers, steps, actions, elements, parts or combinations thereof, and should not be interpreted to exclude the existence or possibility of one or more other characteristics, numbers, steps, actions, elements, parts or combinations thereof other than those described.

[0035] Unless otherwise specifically defined in the specification of the present invention, % units mean weight %.

[0036] The present invention will be described in detail below through each embodiment or example of the invention. It should be noted that each embodiment or example described in this specification is not limited to a single embodiment or example, but may also be combined with other embodiments or examples. Accordingly, the citation of claims in the patent claims is merely an example of an embodiment, and the technical concept of the present invention should not be interpreted as being limited only to a combination with the cited claims; rather, combinations with various claims are also included within the scope of the technical concept of the present invention.

[0037] The inventors of the present invention recognized the problem arising from the requirement for an additional process to remove rust-preventive oil for the production of a final product when applying rust-preventive oil, which is generally performed for the distribution of steel sheets, particularly cold-rolled steel sheets, and conducted in-depth research to solve this problem.

[0038] As a result, a composition suitable for surface treatment of cold-rolled steel sheets was provided, and it was confirmed that a cold-rolled steel sheet with improved corrosion resistance and surface conductivity during surface treatment could be obtained using this composition, thereby completing the present invention.

[0039] The present invention will be described in detail below.

[0040] First, a solution composition for surface treatment of another cold-rolled steel sheet is described in detail in one aspect of the present invention, and it should be noted that the content of each component described below is based on 100% by weight of the total.

[0041] (a) Polymer resin: 5.0~40.0 wt%

[0042] Polymer resin serves as the main component of the composition for surface treatment of cold-rolled steel sheets. It not only adheres to the steel sheet surface with high adhesion but also forms an insoluble film on the surface, providing corrosion resistance through a barrier effect.

[0043] In one embodiment of the present invention, the polymer resin may be contained in an amount of 5.0 to 40.0% with respect to 100% by weight of the solution composition. If the content of the polymer resin is less than 5.0%, a hard film cannot be formed, making it difficult to secure corrosion resistance. On the other hand, if the content exceeds 40.0%, there is a risk that the surface conductivity will be inferior due to the excessively high polymer resin content.

[0044] In one embodiment of the present invention, the type of polymer resin is not specifically limited, but as an example, it may be one or more selected from the group consisting of acrylic emulsion, polyethylene, acrylic acid-ethylene copolymer, and mixtures thereof.

[0045] (b) Curing agent: 1.0~8.0 wt%

[0046] The curing agent reacts with the polymer resin, which is the main component of the solution composition, to increase the degree of crosslinking of the film, thereby contributing to improving the corrosion resistance of the steel sheet surface-treated with the solution composition.

[0047] In one embodiment of the present invention, the curing agent may be contained in an amount of 1.0 to 8.0% with respect to 100% by weight of the solution composition. If the content of the curing agent is less than 1.0%, the corrosion resistance may be reduced because a sufficient degree of crosslinking of the coating layer is not secured. On the other hand, if the content exceeds 8.0%, there is a risk that the corrosion resistance may be reduced as a large amount of unbonded curing agent remains after the coating layer is formed.

[0048] In one embodiment of the present invention, the type of curing agent is not specifically limited, but as an example, it may be one or more selected from the group consisting of Highly Methylated Melamine Resins, Methylated High Imino Melamine Resins, Partially Methylated Melamine Resins, Highly Alkylated Melamine Resins, High Imino Melamine Resins, and mixtures thereof.

[0049] (c) Co-solvent: 1.0~10.0 wt%

[0050] The diluent plays a role in controlling the drying speed of the solution during the drying process after application of the solution composition, and is therefore effective in suppressing surface quality defects such as popping of the coating layer.

[0051] In one embodiment of the present invention, the co-solvent may be contained in an amount of 1.0 to 10.0% with respect to 100% by weight of the solution composition. If the content of the co-solvent is less than 1.0%, the drying speed of the solution during the drying and curing process may become excessively fast, which may result in surface quality defects such as popping on the surface of the coating layer. On the other hand, if the content exceeds 10.0%, the coating film may not dry sufficiently due to the excessively contained co-solvent, which may lead to a decrease in corrosion resistance.

[0052] In one embodiment of the present invention, the type of the co-agent is not specifically limited, but as one example, it may be one or more selected from the group consisting of butyl cellosolve, 2-butanol, ethanol, benzyl alcohol, diglyme, propylene glycol, ethylene glycol, and mixtures thereof.

[0053] (d) pH adjuster: 1.0~5.0 wt%

[0054] pH adjusters play a role in adjusting the pH of the solution composition so that the components within the composition remain stable in the solution and react appropriately under coating conditions to stably form a film.

[0055] In one embodiment of the present invention, the pH adjuster may be contained in an amount of 1.0 to 5.0% with respect to 100% by weight of the solution composition. If the content of the pH adjuster is less than 1.0%, the pH of the solution composition may be lowered, and the stability of the solution may be reduced. On the other hand, if the content exceeds 5.0%, the pH of the solution composition may be excessively high, and the stability of the solution may be reduced.

[0056] In one embodiment of the present invention, the type of pH adjuster is not specifically limited, but as one example, it may be one or more selected from the group consisting of a substance containing ammonia or ammonium salt and mixtures thereof.

[0057] (e) Inorganic rust inhibitor: 1.0~10.0 wt%

[0058] Inorganic anti-corrosion agents play a role in enhancing the corrosion resistance of a coating layer by forming a three-dimensional network structure through hydrogen bonding between silanol groups within the coating layer obtained by the solution composition.

[0059] In one embodiment of the present invention, the inorganic rust inhibitor may be contained in an amount of 1.0 to 10.0% with respect to 100% by weight of the solution composition. If the content of the inorganic rust inhibitor is less than 1.0%, the corrosion resistance of the coating layer cannot be sufficiently improved, whereas if the content exceeds 10.0%, the surface quality of the coating layer may be degraded by an excessive amount of inorganic rust inhibitor.

[0060] In one embodiment of the present invention, the type of inorganic anti-corrosion agent is not specifically limited, but as one example, it may be one or more selected from the group consisting of nano-particle colloidal silica, titanium oxide, cerium oxide, zirconium oxide, and mixtures thereof.

[0061] (f) Organic rust inhibitor: 0.1~3.0 wt%

[0062] When an organic anti-corrosion agent is coated onto the surface of a steel plate using a solution composition, it forms a thin film through chelation bonding with metal elements on the steel plate surface, thereby inhibiting corrosion caused by the reaction of corrosive agents with the steel plate surface.

[0063] In one embodiment of the present invention, the organic rust inhibitor may be contained in an amount of 0.1 to 3.0% with respect to 100% by weight of the solution composition. If the content of the organic rust inhibitor is less than 0.1%, a film of sufficient thickness to suppress the reaction of corrosion agents may not be formed, and thus the corrosion resistance of the coated steel plate may be reduced. On the other hand, if the content exceeds 3.0%, an excessive amount of the organic rust inhibitor may not be properly dispersed in the solution, and thus the solution stability of the composition may be reduced.

[0064] In one embodiment of the present invention, the type of organic rust inhibitor is not specifically limited, but as one example, there is one or more selected from the group consisting of benzothiazole, mercaptobenzothiazole (MBT), pyrimidine, benzotriazole, benzimidazole, 2H-indene-1,3-dione, and mixtures thereof.

[0065] (g) Water repellent: 0.1~3.0 wt%

[0066] Water repellents play a role in inhibiting corrosion of steel plates by blocking corrosive agents from the external environment from accessing the coating layer after surface treatment.

[0067] In one embodiment of the present invention, the water-repellent agent may be contained in an amount of 0.1 to 3.0% with respect to 100% by weight of the solution composition. If the content of the water-repellent agent is less than 0.1%, the water repellency may be insufficient, and the corrosion resistance of the surface-treated steel plate may be reduced. On the other hand, if the content exceeds 3.0%, the surface quality of the surface-treated steel plate may be inferior due to the excessive amount of water-repellent agent.

[0068] In one embodiment of the present invention, the type of water-repellent agent is not specifically limited, but as one example, it may be one or more selected from the group consisting of polydimethylsiloxane (PDMS), polyurethane, and mixtures thereof.

[0069] (h) Surfactant: 0.01~2.00 wt%

[0070] When the solution composition is coated onto the surface of a steel plate, the surfactant contributes to improving corrosion resistance by increasing the density of the organic rust inhibitor contained within the composition in the film.

[0071] In one embodiment of the present invention, the surfactant may be contained in an amount of 0.01 to 2.00% with respect to 100% by weight of the solution composition. If the content of the surfactant is less than 0.01%, the film density of the organic rust inhibitor may not be sufficiently increased, and the corrosion resistance of the surface-treated steel plate may be reduced. On the other hand, if the content exceeds 2.00%, the solution stability of the composition may be reduced due to the excessive amount of surfactant.

[0072] In one embodiment of the present invention, the type of surfactant is not specifically limited, but as one example, it may be one or more selected from the group consisting of Tall oil fatty acid ethoxylate, Oleyl alcohol ethoxylate, Polyethylene Glycol-p-isooctylphenyl Ether and mixtures thereof.

[0073] (i) residual solvent

[0074] A solution composition according to one embodiment of the present invention may include a solvent as a remainder component excluding the aforementioned components. In one embodiment of the present invention, water may be used as the solvent, and the water may be one or more of pure water, distilled water, and deionized water.

[0075] A solution composition obtained by dissolving a surface treatment composition according to one embodiment of the present invention in the aforementioned solvent may have a pH in the range of 9 to 13.

[0076] As described above, a surface treatment composition according to one embodiment of the present invention includes a polymer resin as a main component, and together with it, may contain organic and inorganic anti-corrosion agents, pH adjusters, etc., so that the pH may be in the range of 9 to 13.

[0077] In one embodiment of the present invention, if the pH of the solution composition is less than 9, the surface of the surface-treated steel sheet (e.g., cold-rolled steel sheet) is etched, resulting in a poor surface appearance, and there is a risk that the corrosion resistance and surface quality of the surface-treated steel sheet will be degraded. On the other hand, if the pH exceeds 13, the solution stability is reduced, and the corrosion resistance of the surface-treated steel sheet may be degraded.

[0078] Hereinafter, a steel plate according to another aspect of the present invention, specifically a cold-rolled steel plate, will be described in detail.

[0079] A cold-rolled steel sheet according to one aspect of the present invention is a steel sheet whose surface is surface-treated with a specific composition, and as one example, may include a cold-rolled steel sheet; and a surface-treated coating layer on at least one surface of the cold-rolled steel sheet (see FIG. 1).

[0080] In one embodiment of the present invention, the base steel sheet may be a cold-rolled steel sheet manufactured through a series of processes, such as hot rolling and cold rolling, and the type of the cold-rolled steel sheet is not specifically limited. As a non-limiting example, the cold-rolled steel sheet may be a carbon steel containing a certain amount of carbon (C), manganese (Mn), silicon (Si), phosphorus (P), sulfur (S), nitrogen (N), etc., and since such carbon steel is widely known in the art, the composition of the alloying elements is not specifically limited. In addition, the cold-rolled steel sheet may be an annealed steel sheet that has undergone annealing heat treatment after cold rolling.

[0081] In one embodiment of the present invention, a surface treatment coating layer may be included on the surface of a base steel sheet, that is, on the surface of a cold-rolled steel sheet. That is, a coating layer having a certain thickness may be formed on one side or both sides of the cold-rolled steel sheet. In this way, a cold-rolled steel sheet having a coating layer on its surface may possess excellent physical properties such as corrosion resistance, surface quality, and surface conductivity.

[0082] When distributing cold-rolled steel sheets having the aforementioned physical properties to customers, processes such as the application of anti-rust oil, which are generally performed, can be omitted. That is, by means of a surface treatment coating layer according to one embodiment of the present invention, corrosion resistance and surface conductivity can be secured without applying anti-rust oil, thus providing the advantage of being able to distribute without the application of anti-rust oil. As such, the present invention can also improve economic effects resulting from the omission of processes.

[0083] Meanwhile, in one embodiment of the present invention, in order to obtain a cold-rolled steel sheet having the aforementioned physical properties, a surface treatment coating layer provided on at least one side (surface) of the cold-rolled steel sheet may be formed from a steel sheet surface treatment composition according to one embodiment of the present invention. That is, the coating layer formed from the composition according to one embodiment of the present invention contains a polymer resin as a main component, and by including a curing agent, a co-modifier, a pH adjuster, an organic or inorganic rust inhibitor, a water repellent, a surfactant, etc. in appropriate amounts, a cold-rolled steel sheet having the intended physical properties can be provided.

[0084] In one embodiment of the present invention, the surface treatment coating layer may have a thickness of 0.1 to 2.0 μm. The thickness is based on the thickness after drying. If the thickness of the coating layer is less than 0.1 μm, the corrosion resistance of the surface-treated steel sheet, i.e., the surface-treated cold-rolled steel sheet, cannot be improved. On the other hand, if the thickness of the coating layer exceeds 2.0 μm, the surface conductivity of the coating layer is reduced, and there is a risk that painting will not be performed during a subsequent process, such as a painting process.

[0085] In one embodiment of the present invention, when EDS measurement is performed on the surface of the surface treatment coating layer, the coating layer may contain, in weight percent, nitrogen (N): 1.0~15.0%, oxygen (O): 10.0~30.0%, silicon (Si): 10.0~20.0%, and the remainder being carbon (C) and other unavoidable impurities. The C, N, O, Si, etc. in the coating layer are due to the components of the solution composition for obtaining the coating layer. As one example, the EDS measurement may be performed using an electron beam.

[0086] Hereinafter, a method for manufacturing a cold-rolled steel sheet, specifically a surface-treated cold-rolled steel sheet, according to another aspect of the present invention will be described. However, it should be noted that the following manufacturing method is merely one example for manufacturing a surface-treated cold-rolled steel sheet.

[0087] In one embodiment of the present invention, a surface-treated cold-rolled steel sheet can be manufactured through the steps of: preparing a base steel sheet; applying a surface treatment solution composition to at least one surface of the base steel sheet; and drying and curing the surface-treated cold-rolled steel sheet after application.

[0088] In one embodiment of the present invention, the base steel sheet for forming a surface treatment coating layer on at least one surface may be a cold-rolled steel sheet manufactured through a series of processes, such as hot rolling and cold rolling, and the alloy composition of the cold-rolled steel sheet is not particularly limited. Furthermore, the content of the base steel sheet mentioned above may be substituted.

[0089] In one embodiment of the present invention, the step of applying a surface treatment composition onto a prepared steel sheet may utilize any one coating method selected from the group consisting of bar coating, roll coating, spraying, immersion, spray squeezing, and immersion squeezing.

[0090] In one embodiment of the present invention, the surface treatment composition applied to a prepared steel sheet may be a cold-rolled steel sheet surface treatment composition according to one embodiment of the present invention. In this case, the composition may be a solution composition, the content of each component may be controlled within the aforementioned range, and a solvent may be mixed as the remainder component. The descriptions of each component and solvent are replaced with the previously mentioned details.

[0091] In applying a solution composition according to one embodiment of the present invention, as one example, the solution composition may be applied such that the thickness after drying is 0.1 to 2.0 μm. That is, the thickness of the solution composition applied before drying is not specifically limited, and it is noted that it can be set to an appropriate level to satisfy the range of 0.1 to 2.0 μm after drying.

[0092] In one embodiment of the present invention, a step of drying and curing a cold-rolled steel sheet coated with a surface treatment solution composition may be performed, and this may be done in a temperature range of 50 to 270°C based on the Peak Metal Temperature (PMT), which is the final temperature reached by the base steel sheet. If the drying temperature is less than 50°C based on the PMT, the drying may not be fully completed, and the physical properties of the surface-treated cold-rolled steel sheet, such as corrosion resistance, may be degraded. On the other hand, if the drying temperature exceeds 270°C based on the PMT, corrosion resistance may be degraded due to problems such as poor color of the coating layer or carbonization of the coating layer caused by excessive heat.

[0093] The present invention will be explained in more detail below through examples. However, the description of these examples is merely for illustrating the implementation of the present invention and does not limit the present invention. This is because the scope of the rights of the present invention is determined by the matters described in the patent claims and matters reasonably inferred therefrom.

[0094] (Example)

[0095] [Preparation of Solution Composition for Surface Treatment of Cold-Rolled Steel Sheets]

[0096] To measure the physical properties of a solution composition for surface treatment of cold-rolled steel sheets according to one aspect of the present invention, a solution composition was prepared using the following materials.

[0097] First, ammonia was added to distilled water (solvent) as a pH adjuster and stirred at room temperature for about 30 minutes. In the same manner, acrylic acid-ethylene copolymer, a polymer resin, and ethanol, a co-solvent, were added and stirred for an additional 30 minutes. Again, in the same manner, silica, an inorganic rust inhibitor; benzotriazole, an organic rust inhibitor; PDMS, a water repellent; Polyethylene-Glycol-p-isooctylphenyl Ether, a surfactant; and CYMEL 385 (1,3,5-triazine-2,4,6-triamine), a curing agent among Methylated High Imino Melamine Resin, were each added at 30-minute intervals while stirring.

[0098] At this time, the content of each component is shown in Table 1 below.

[0099] Composition Polymer Resin Curing Manufacturing Solvent pH Adjuster Inorganic Rust Inhibitor Organic Rust Inhibitor Water Repellent Surfactant Solvent Classification 1 1 2.01.03.05.04.02.03.01.00 69.00 Invention Example 1 2 6.05.01.04.01.01.01.02.00 79.00 Invention Example 2 3 7.03.02.05.07.03.03.00.10 39.90 Invention Example 3 4 1 7.02.06.03.07.02.00.50.50 62.00 Invention Example 4 5 30.05.01.04.05.01.53.00.80 49.70 Invention Example 5628.04.08.01.09.03.01.01.2044.80 Invention Example 6711.03.05.05.08.01.02.52.0062.50 Invention Example 7820.01.06.03.04.01.23.01.0060.80 Invention Example 896.01.010.05.04.02.02.01.1068.90 Invention Example 91012.06.07.05.01.01.01.00.9066.10 Invention Example 10118.04.06.04.01.02.52.30.8071.40 Invention Example 111211.06.02.05.03.02.03.01.4066.60 Invention Example 12133.01.09.02.53.01.02.01.0077.50 Comparative Example 11442.03.04.04.07.02.02.20.0535.75 Comparative Example 21511.00.54.55.05.01.01.00.3071.70 Comparative Example 31626.010.01.03.02.02.82.91.1051.20 Comparative Example 41738.05.00.23.54.01.81.00.3046.20 Comparative Example 51827.01.012.05.06.02.00.41.8044.80Comparative Example 61930.05.53.00.59.02.21.01.6047.20Comparative Example 72031.01.06.07.02.01.01,41.0049.60Comparative Example 82115.06.07.05.00.83.02.00.4060.80Comparative Example 9228.01.06.02.012.01.01.01.6067.40Comparative Example 102324.03.03.03.04.00.051.80.1061.05Comparative Example 112433.07.52.02.09.55.02.31.0037.70Comparative Example 122510.07.01.01.57.02.80.01.8068.90Comparative Example 132617.04.07.04.53.01.05.01.0057.50 Comparative Example 142713.02.08.02.04.02.00.90.0068.10 Comparative Example 15287.02.09.03.06.00.51.13.0068.40 Comparative Example 16 The content of each component is weight%.

[0100]

[0101] Solution stability

[0102] The following experiment was performed to verify whether the stability of the prepared solution composition is maintained under certain conditions.

[0103] The initial viscosity (Vi) of each solution composition of Invention Examples 1 to 12 and Comparative Examples 1 to 16 was measured, then stored in an oven at 50°C for 120 hours, cooled to 25°C, and the viscosity (VI) at 25°C was measured. The solution stability was evaluated based on the calculated value (△V) obtained by substituting each measured viscosity value into Equation 1 below. The results are shown in Table 2 below.

[0104] [Mathematical Formula 1]

[0105] △V = (VI - Vi) / Vi × 100 (%)

[0106] Solution Stability Evaluation Criteria

[0107] ○: ΔV value is less than 20(%) or no gelation is visible upon visual inspection

[0108] ×: ΔV value is 20(%) or greater, or gelation is visible upon visual inspection

[0109] [Manufacture of Surface-Treated Steel Sheets]

[0110] Next, the solution composition prepared above was applied to the surface of a steel plate using a bar coating method, and then drying and curing were performed in an induction oven to obtain each surface-treated steel plate. Bar coating was performed so that the thickness of the coating layer after drying and curing was approximately 0.4 μm, and the temperature during drying and curing was 150°C based on PMT.

[0111] At this time, an annealed cold-rolled steel sheet was used as the steel plate to apply the solution composition, and the specimen was prepared by cutting it into 7cm × 15cm (width × length) and degreasing it.

[0112] To measure the physical properties of the surface-treated steel sheet manufactured according to the above, corrosion resistance, appearance quality, and surface conductivity were measured using the following methods and criteria. Each result is shown in Table 2 below.

[0113] Corrosion resistance

[0114] Based on the method specified in ASTM B117, the incidence of red rust on each steel plate (specimen) was measured over time after treating it with a solution composition.

[0115] Corrosion Resistance Evaluation Criteria

[0116] ○: Red-blue occurrence time is 90 minutes or longer

[0117] ×: Time between red and blue occurrences is less than 90 minutes

[0118] Appearance quality

[0119] The surface of each steel plate (specimen) coated with the solution composition was visually observed and evaluated according to the following evaluation criteria.

[0120] <Exterior Quality Evaluation Criteria>

[0121] ○: In the absence of defects such as noticeable color changes (e.g., yellowing), streaks, popping, orange peel, or non-coating.

[0122] ×: If there is at least one defect among streaks, yellowing, popping, orange peel, or uncoated areas on the surface of the coating layer

[0123] Surface conductivity

[0124] The surface resistance of each steel plate (specimen) coated with the solution composition was measured and evaluated. The surface resistance was measured using a Loresta-GP surface resistance meter, and an ESP-type 4-point probe was used.

[0125] Surface Conductivity Evaluation Criteria

[0126] ○: Surface resistance measurement value is 1×10 -2 Ω or less

[0127] ×: Surface resistance measurement value is 1×10 -2 Exceeding Ω

[0128] Classification Solution Stability Corrosion Resistance Appearance Quality Surface Conductivity Invention Example 1 Invention Example 2 Invention Example 3 Invention Example 4 Invention Example 5 Invention Example 6 Invention Example 7 Invention Example 8 Invention Example 9 Invention Example 10 Invention Example 11 Invention Example 12 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Comparative Example 9 Comparative Example 10 Comparative Example 11 Comparative Example 12 Comparative Example 13○×○○ Comparative Example 14○○×○ Comparative Example 15○×○○ Comparative Example 16××○○

[0129] As shown in Table 3 above, the solution compositions of Invention Examples 1 to 12 have excellent solution stability, and cold-rolled steel sheets surface-treated with these solution compositions showed excellent results in all evaluation results.

[0130] On the other hand, Comparative Example 1 had inferior corrosion resistance as the barrier effect was insufficient due to the insufficient content of polymer resin.

[0131] Comparative Example 2 is a case where the polymer resin content is excessive, and the surface conductivity is inferior due to the excessive amount of polymer resin.

[0132] Comparative Example 3 is a case where the content of the curing agent is insufficient, and the degree of curing of the polymer resin is reduced, resulting in inferior corrosion resistance of the surface-treated cold-rolled steel sheet.

[0133] Comparative Example 4 is a case where the content of the curing agent is excessive, and as unbound curing agent remains in the composition, the corrosion resistance of the surface-treated cold-rolled steel sheet is inferior.

[0134] Comparative Example 5 is a case where the content of the co-working agent was insufficient, and the appearance quality of the surface-treated cold-rolled steel sheet was inferior.

[0135] Comparative Example 6 is a case where the content of the co-working agent is excessive, and as the drying of the coating layer is not sufficiently achieved, the corrosion resistance and appearance quality of the surface-treated cold-rolled steel sheet are inferior.

[0136] Comparative Examples 7 and 8 were cases where the content of the pH adjuster was insufficient and excessive, respectively, and in both cases, the solution stability was inferior. In addition, after the coating treatment, the corrosion resistance and appearance quality of the surface-treated cold-rolled steel sheet were inferior due to the precipitated solution components.

[0137] Comparative Example 9 is a case where the content of the inorganic anti-corrosion agent is insufficient, and the corrosion resistance of the surface-treated cold-rolled steel sheet is inferior.

[0138] Comparative Example 10 is a case where the content of the inorganic rust inhibitor is excessive, and the appearance quality of the surface-treated cold-rolled steel sheet is inferior due to the large amount of unreacted silicate remaining.

[0139] Comparative Example 11 had inferior corrosion resistance of the surface-treated cold-rolled steel sheet due to insufficient content of organic rust inhibitor.

[0140] Comparative Example 12 had inferior solution stability as the organic rust inhibitor settled within the solution composition due to the excessive content of the organic rust inhibitor. In addition, the appearance quality of the cold-rolled steel sheet surface-treated with this composition was inferior.

[0141] Comparative Example 13 is a case where the water-repellent content is insufficient, and as the surface-treated cold-rolled steel sheet does not have sufficient water-repellent power, the corrosion resistance is inferior.

[0142] Comparative Example 14 is a case where the water-repellent content is excessive, and the appearance quality of the surface-treated cold-rolled steel sheet is inferior.

[0143] Comparative Example 15 is a case where the surfactant content is insufficient, and the corrosion resistance of the surface-treated cold-rolled steel sheet is inferior.

[0144] Comparative Example 16 is a case where the surfactant content is excessive, and the solution stability of the composition is inferior due to the excessive amount of surfactant. In addition, the corrosion resistance of the cold-rolled steel sheet surface-treated with this composition is inferior.

[0145] Meanwhile, after performing EDS measurements (Accelerating Voltage 15.0kV, Magnification 100) on the surface of the steel plates (Invention Examples 1 and 2) with the coating layer formed thereon, the composition and content of the components within the coating layer were confirmed, as shown in Table 3 below.

[0146] Classification Coating layer composition (weight%) NO Si remainder Invention Example 17.9 22.2 13.7C and unavoidable impurities Invention Example 27.2 21.9 14.1C and unavoidable impurities

Claims

1. (a) Polymer resin: 5.0~40.0 wt%, (b) Curing agent: 1.0~8.0 wt%, (c) Co-solvent: 1.0~10.0 wt%, (d) pH adjuster: 1.0~5.0 wt%, (e) Inorganic rust inhibitor: 1.0~10.0 wt%, (f) Organic rust inhibitor: 0.1~3.0 wt%, (g) Water repellent: 0.1~3.0 wt%, (h) Surfactant: 0.01~2.00 wt%, and (i) Solution composition for surface treatment of cold-rolled steel sheets containing residual solvent.

2. In Paragraph 1, The above polymer resin is a solution composition for surface treatment of cold-rolled steel sheets, comprising one or more selected from the group consisting of acrylic emulsion, polyethylene, acrylic acid-ethylene copolymer, and mixtures thereof.

3. In Paragraph 1, The above curing agent is one or more selected from the group consisting of Highly Methylated Melamine Resins, Methylated High Imino Melamine Resins, Partially Methylated Melamine Resins, Highly Alkylated Melamine Resins, High Imino Melamine Resins, and mixtures thereof, in a solution composition for surface treatment of cold-rolled steel sheets.

4. In Paragraph 1, The above-mentioned solvent is a solution composition for surface treatment of cold-rolled steel sheets, comprising one or more selected from the group consisting of butyl cellosolve, 2-butanol, ethanol, benzyl alcohol, diglyme, propylene glycol, ethylene glycol, and mixtures thereof.

5. In Paragraph 1, The above pH adjuster is one or more selected from the group consisting of substances containing ammonia or ammonium salts and mixtures thereof, in a solution composition for surface treatment of cold-rolled steel sheets.

6. In Paragraph 1, The above-mentioned inorganic anti-corrosion agent is a solution composition for surface treatment of cold-rolled steel sheets, comprising one or more selected from the group consisting of nano-particle colloidal silica, titanium oxide, cerium oxide, zirconium oxide, and mixtures thereof.

7. In Paragraph 1, The above organic rust inhibitor is a solution composition for surface treatment of cold-rolled steel sheets, comprising one or more selected from the group consisting of benzothiazole, mercaptobenzothiazole (MBT), pyrimidine, benzotriazole, benzimidazole, 2H-indene-1,3-dione, and mixtures thereof.

8. In Paragraph 1, The above-mentioned water-repellent agent is one or more selected from the group consisting of polydimethylsiloxane (PDMS), polyurethane, and mixtures thereof, in a solution composition for surface treatment of cold-rolled steel sheets.

9. In Paragraph 1, The above surfactant is one or more selected from the group consisting of Tall oil fatty acid ethoxylate, Oleyl alcohol ethoxylate, Polyethylene Glycol-p-isooctylphenyl Ether, and mixtures thereof, in a solution composition for surface treatment of cold-rolled steel sheets.

10. In Paragraph 1, The above solvent is water, and A solution composition for surface treatment of cold-rolled steel sheets, wherein the above water is one or more of pure water, distilled water, and deionized water.

11. Cold-rolled steel sheet; and The above cold-rolled steel sheet includes a surface treatment coating layer on at least one surface, and The above surface treatment coating layer is a surface-treated cold-rolled steel sheet in which the surface treatment coating layer is a coating layer formed from the composition of any one of claims 1 to 10.

12. In Paragraph 11, A surface-treated cold-rolled steel sheet having a surface treatment coating layer having a thickness of 0.1 to 2.0 μm (based on thickness after drying).

13. In Paragraph 11, When EDS measurement is performed on the surface of the surface treatment coating layer, the coating layer comprises, in weight percent, nitrogen (N): 1.0~15.0%, oxygen (O): 10.0~30.0%, silicon (Si): 10.0~20.0%, and the remainder being carbon (C) and other unavoidable impurities, a surface-treated cold-rolled steel sheet.

14. Step of preparing the steel sheet base; A step of applying a solution composition to at least one surface of the above-mentioned steel sheet; and The method includes the step of drying and curing after applying the above solution composition, The above solution composition is a method for manufacturing a surface-treated cold-rolled steel sheet that is a composition of any one of claims 1 to 10.

15. In Paragraph 14, A method for manufacturing a surface-treated cold-rolled steel sheet, wherein the drying and hardening steps are performed in a temperature range of 50 to 270°C based on the peak metal temperature (PMT) of the steel sheet.

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