Surface treatment composition, surface treatment method for plated steel sheet, and surface-treated plated steel sheet

Abstract

A surface treatment composition of the present invention comprises, on the basis of the total weight of the composition, 1-50 wt% of a resin mixture in which a urethane resin and an acrylic resin are mixed; 0.01-5 wt% of a phosphoric acid-based inorganic compound; 0.01-5 wt% of an amine compound; and the balance of ammonia water, and can satisfy relation 1. [Relation 1] 2.916×10-2 ≤ [N] / [P]×[pH] ≤ 9.689×103 (In relation 1, [N] is the mol% of alkyl ammonium ions in the surface treatment composition, [P] is the mol% of phosphate ions in the surface treatment composition, and [pH] represents the pH of the surface treatment composition.) According to exemplary embodiments of the present invention, the surface treatment composition having improved storage stability at room temperature can be provided, and the plated steel sheet pretreated using the surface treatment composition so as to have excellent corrosion resistance and blackening resistance can be provided.

Description

Surface treatment composition, surface treatment method for galvanized steel sheets, and surface-treated galvanized steel sheets

[0001] The present invention relates to a surface treatment composition, a surface treatment method for a plated steel sheet, and a surface-treated plated steel sheet.

[0002] Surface treatment compositions for plated steel sheets containing acrylic acid resin are primarily used to form a pretreatment layer on resin-coated steel sheets for various applications, such as pre-shielded steel sheets and fuel tank steel sheets. When preparing a steel sheet coating composition using acrylic acid resin, it is necessary to neutralize the acrylic acid resin. To this end, methods have been proposed to add a neutralizing agent or to form a dispersion using a solvent with a relatively high pH.

[0003] In addition, research has been continuously conducted on adding additional additives to surface treatment compositions to improve adhesion to steel plates and further enhance corrosion resistance.

[0004] However, these additives caused side reactions with the existing main resin or solvent, reducing the stability of the solution and posing a problem that made it difficult to control the physical properties of the solution.

[0005] (Patent Document 1) Korean Patent Publication No. 10-1998-0020581

[0006] The problem that the technical concept of the present invention aims to solve is to provide a surface treatment composition with improved storage stability at room temperature.

[0007] Furthermore, the present invention provides a plated steel sheet with improved corrosion resistance and blackening resistance.

[0008] The problems of the present invention are not limited to those described above. A person skilled in the art will have no difficulty understanding additional problems of the present invention from the overall contents of this specification.

[0009] According to exemplary embodiments for solving the problem of the present invention, a surface treatment composition is provided. The surface treatment composition comprises, based on the total weight of the composition, 1 to 50 weight% of a resin mixture comprising a urethane resin and an acrylic resin; 0.01 to 5 weight% of a phosphate-based inorganic compound; 0.01 to 5 weight% of an amine compound; and the remainder being water of ammonia, and may satisfy the following equation 1.

[0010] [Relationship 1]

[0011]

[0012] In the above equation 1, [N] is mol% of alkyl ammonium ions in the surface treatment composition, [P] is mol% of phosphate ions in the surface treatment composition, and [pH] is the pH of the surface treatment composition.

[0013] The resin mixture above may be a mixture of urethane resin and acrylic resin in a weight ratio of 100:1 to 1:100.

[0014] The above phosphate-based inorganic compound may be one or more selected from the group consisting of ammonium phosphate compounds and phosphate ester compounds.

[0015] The above amine compound may be triethylamine.

[0016] Optionally, based on the total weight of the composition, it may further include one or more of 0.01 to 5 weight% of a curing agent; 0.01 to 5 weight% of a titanium-based chelate; and 0.01 to 5 weight% of a silane compound.

[0017] The above curing agent may be one or more selected from the group consisting of melamine-based curing agents and isocyanate-based curing agents.

[0018] According to other exemplary embodiments of the present invention, a surface treatment method for a plated steel sheet is provided. The surface treatment method for a plated steel sheet may include the step of applying the above-described surface treatment composition onto a plated steel sheet such that the dry film thickness is 0.05 to 20 μm; and the step of baking the plated steel sheet coated with the surface treatment composition to form a pretreatment layer.

[0019] According to another exemplary embodiment of the present invention, a surface-treated plated steel sheet may be provided. The surface-treated plated steel sheet may comprise: a plated steel sheet; and a pretreatment layer formed by curing the surface treatment composition described above on the plated steel sheet.

[0020] According to exemplary embodiments of the present invention, a surface treatment composition with improved storage stability at room temperature can be provided.

[0021] Furthermore, according to other exemplary embodiments of the present invention, a plated steel sheet having excellent corrosion resistance and blackening resistance can be provided by pre-treating using the surface treatment composition described above.

[0022] The various and beneficial advantages and effects of the present invention are not limited to those described above and will be more easily understood in the process of explaining specific embodiments of the present invention.

[0023] Hereinafter, preferred embodiments of the present invention will be described in detail. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor may appropriately define the concepts of terms to best describe his invention, they should be interpreted in a meaning and concept consistent with the technical spirit of the present invention.

[0024] In the following embodiments, the terms first, second, etc. are used not in a limiting sense, but for the purpose of distinguishing one component from another component.

[0025] In the following embodiments, the singular expression includes the plural expression unless the context clearly indicates otherwise.

[0026] In the following embodiments, terms such as "include" or "have" mean that the features or components described in the specification are present, and do not preclude the possibility that one or more other features or components may be added.

[0027] In the drawings, the size of components may be exaggerated or reduced for convenience of explanation. For example, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, so the present invention is not necessarily limited to what is illustrated.

[0028] Where an embodiment can be implemented differently, a specific process sequence may be performed differently from the order described. For example, two processes described consecutively may be performed substantially simultaneously or proceed in the reverse order of the description.

[0029] In addition, in describing the present invention, if it is determined that a detailed description of related known components or functions may obscure the essence of the invention, such detailed description is omitted.

[0030] The present invention will be described in detail below through each embodiment. It should be noted that each embodiment described in this specification is not limited to a single embodiment but may also be combined with other embodiments. 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.

[0031] The present invention will be described in detail below through examples. However, it should be noted that the following examples are intended merely to illustrate and embody the present invention and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the patent claims and matters reasonably inferred therefrom.

[0032] [Surface Treatment Composition]

[0033] According to exemplary embodiments, the surface treatment composition may comprise a resin mixture in which a urethane resin and an acrylic resin are mixed; a phosphate-based inorganic compound; an amine compound; and the remainder being ammonia water.

[0034] The resin mixture may include urethane resin and acrylic resin, which serve as binders. According to exemplary embodiments, the resin mixture may be included in an amount of 1 to 50 weight percent based on the total weight of the composition. If the resin mixture content is less than 1 weight percent, the viscosity is low, which may make it difficult to control the thickness of the pretreatment layer during steel plate surface treatment operations. Therefore, the content of the resin mixture may be 1 weight percent or more. More specifically, the weight of the resin mixture may be 10 weight percent or more. If the content of the resin mixture exceeds 50 weight percent, the solid content of the surface treatment composition increases, which may reduce the storage stability of the solution. Therefore, the content of the resin mixture may be 50 weight percent or less. More specifically, the content of the resin mixture may be 45 weight percent or less.

[0035] The resin mixture may be a mixture of urethane resin and acrylic resin in a weight ratio of 100:1 to 1:100. By controlling the mixing ratio of urethane resin and acrylic resin in the resin mixture within the aforementioned range, it is possible to prevent a decrease in the chemical resistance and alkali resistance of the pretreatment layer of the plated steel sheet.

[0036] The urethane resin and acrylic resin that can be used in the present invention are not particularly limited, and materials generally used in the field of steel plate surface treatment may be used. In addition, the resin mixture may be used in a form dispersed in water, alcohol, or a mixture thereof.

[0037] According to exemplary embodiments, a phosphate-based inorganic compound may be included in an amount of 0.01 to 5 weight percent based on the total weight of the composition. The phosphate-based inorganic compound may contribute to improving the corrosion resistance and blackening resistance of the galvanized steel sheet. If the content of the phosphate-based inorganic compound is less than 0.01 weight percent, the blackening resistance of the surface treatment composition is reduced, and there is a risk that the blackening resistance of the finally surface-treated galvanized steel sheet will be reduced. Therefore, the content of the phosphate-based inorganic compound may be 0.01 weight percent or more. If the content of the phosphate-based inorganic compound exceeds 5 weight percent, there is a risk that the plating layer of the galvanized steel sheet coated with the surface treatment composition will oxidize. Therefore, the content of the phosphate-based inorganic compound may be 5 weight percent or less. More specifically, the content of the phosphate-based inorganic compound may be 4 weight percent or less.

[0038] According to exemplary embodiments, the phosphate-based inorganic compound may be any one of an ammonium phosphate compound, a phosphate ester compound, and a polymer thereof. More specifically, the phosphate-based inorganic compound may be an ammonium phosphate compound.

[0039] Meanwhile, within the solution of the surface treatment composition, phosphate-based inorganic compounds can dissociate into ions and disrupt the equilibrium state within the solution. More specifically, phosphate-based inorganic compounds can dissociate into phosphate ions and cations within the solvent, and if the generated cation is an ammonium ion, it can alter the ion concentration within the solution. In particular, as described below, when ammonia water is used as a solvent, if ammonium phosphate is added to ammonia water that has dissociated into ammonium ions and hydroxide ions, the reverse reaction in which ammonium ions are converted into ammonia gas is strengthened, which can cause the pH within the solution to change and the solubility to decrease. Consequently, solidification or gelation of the resin species constituting the surface treatment composition may occur, and the stability of the solution may be reduced by the phosphate-based inorganic compounds.

[0040] Accordingly, according to exemplary embodiments of the present invention, the surface treatment composition comprises an amine compound. The amine compound can dissociate into alkyl ammonium ions and hydroxide ions in a solution. As a result, the amine compound can maintain a high pH of the solution and, having a relatively high boiling point, may not easily volatilize at room temperature. Consequently, the overall solution stability of the surface treatment composition can be increased, and as a result, when surface treating a plated steel sheet, the surface treatment composition can stably undergo a crosslinking reaction to form a pretreatment layer having excellent physical properties.

[0041] The amine compound can stabilize the surface treatment composition solution as it maintains a high pH. Additionally, it may be more desirable if the amine compound has a boiling point that evaporates before the curing temperature of the surface treatment composition is reached, but does not easily evaporate at room temperature. If it possesses these properties, the type of amine compound is not particularly limited. That is, the amine compound may include one or more of primary amines, secondary amines, tertiary amines, and polymers thereof having the properties described above. According to exemplary embodiments, the amine compound may include any one of triethylamine (TEA), dimethylethanolamine (DMEA), aminomethylpropanol (AMP), and polymers thereof, but it should be noted that any amine compound having the properties described above may be used without limitation.

[0042] According to exemplary embodiments, the amine compound may be included in an amount of 0.01 to 5 weight% based on the total weight of the composition. If the content of the amine compound is less than 0.01 weight%, there is a concern that the stability of the surface treatment composition may be reduced, thereby shortening the storage period. Therefore, the content of the amine compound may be 0.01 weight% or more. More specifically, the content of the amine compound may be 0.1 weight% or more. Even more specifically, the content of the amine compound may be 1 weight% or more. However, if the content of the amine compound exceeds 5 weight%, there is a concern that it may reduce the crosslinking reactivity of the resin mixture and lower the durability of the pretreatment layer. Therefore, the content of the amine compound may be 5 weight% or less. More specifically, the content of the amine compound may be 3 weight% or less.

[0043] Additionally, the surface treatment composition may include ammonia water as the remainder. Ammonia water can neutralize the acrylic resin, thereby facilitating the storage of the surface treatment composition. According to exemplary embodiments, the pH of the surface treatment composition may be 9 to 12. This can increase the water dispersibility of the urethane resin or acrylic resin and facilitate the storage of the surface treatment composition.

[0044] According to exemplary embodiments, the surface treatment composition may satisfy the following relationship 1.

[0045] [Relationship 1]

[0046]

[0047] In the above Equation 1, [N] represents the mol% of alkyl ammonium ions in the surface treatment composition, [P] represents the mol% of phosphate ions in the surface treatment composition, and [pH] represents the pH of the surface treatment composition. The alkyl ammonium ions may be derived from amine compounds, and the phosphate ions may be derived from phosphate-based inorganic compounds. [N] and [P] represent the molecular weight (g / mol) and concentration (g / cm³) of the amine compound and phosphate ion added to the surface treatment composition, respectively. 3 It can be calculated using ) and ion oxidation number. By satisfying the above-described Equation 1, the ammonium ions derived from the amine compound maintain the equilibrium state of the solution, thereby improving the stability of the solution at room temperature. Furthermore, when surface treatment of a galvanized steel sheet is performed using a surface treatment composition satisfying the above-described Equation 1, the corrosion resistance of the galvanized steel sheet can be further improved. Since the above Equation 1 is a value obtained empirically, units may not need to be defined separately, and it is sufficient to satisfy only the units of each variable.

[0048] Optionally, according to exemplary embodiments, the surface treatment composition may further comprise one or more of 0.01 to 5 weight% of a curing agent based on the total weight of the composition; 0.01 to 5 weight% of a titanium-based chelate; and 0.01 to 5 weight% of a silane compound.

[0049] The curing agent reacts with the resin mixture to form crosslinks, and one or more curing agents selected from the group consisting of melamine-based curing agents and isocyanate-based curing agents may be used. As a non-limiting example, the melamine-based curing agent may be one or more of melamine resin, alkyl melamine, and fluorinated melamine, but the present invention is not limited thereto. As one example, the curing agent may be alkyl melamine.

[0050] The above curing agent may be included in an amount of 0.01 to 5 weight percent based on the total weight of the composition. If the content of the curing agent is less than 0.01 weight percent, an incomplete cross-linking reaction may occur, which may lead to a decrease in the durability and scratch resistance of the pretreatment layer formed on the surface of the plated steel sheet. If the content of the curing agent exceeds 5 weight percent, there is a risk that the storage stability of the solution may decrease.

[0051] Titanium-based chelates may be added to ensure resin adhesion and further improve corrosion resistance through coupling between the surface of the plated steel sheet and the resin layer. As a non-limiting example, titanium-based chelates may include one or more of titanium butyl phosphate (TBP), titanium dipropylbis cetylacetonate (T-50, TAA), and propanedioxy titanium bisethyl cetoacetate (T-60), but the present invention is not limited thereto.

[0052] Titanium-based chelates may be included in an amount of 0.01 to 5 weight percent based on the total weight of the composition. If the content of titanium-based chelates is less than 0.01 weight percent, corrosion resistance and resin adhesion may deteriorate. If the content of titanium-based chelates exceeds 5 weight percent, there is a risk that the dispersion stability of the resin may decrease.

[0053] Silane compounds can serve as adhesion promoters in surface treatment compositions. As a non-limiting example, the silane compound may be GPTMS ((3-Glycidoxypropyl)trimethoxysilane), but the present invention is not limited thereto.

[0054] A silane compound may be included in an amount of 0.01 to 5 weight percent based on the total weight of the composition. If the content of the silane compound is less than 0.01 weight percent, there is a risk that the adhesion of the pretreatment layer formed on the surface of the plated steel sheet will be reduced. If the content of the silane compound exceeds 5 weight percent, there is a possibility that the storage stability of the surface treatment composition will be reduced.

[0055] [Surface Treatment Method for Plated Steel Sheets]

[0056] According to exemplary embodiments, a surface treatment method for a plated steel sheet may include the step of applying a surface treatment composition and the step of baking the plated steel sheet and then cooling it to form a pretreatment layer.

[0057] Application step

[0058] The coating step may be a step of applying the surface treatment composition described above onto a plated steel sheet such that the dry film thickness is 0.05 to 20 μm.

[0059] For the surface treatment composition, you may refer to the description of the surface treatment composition described above.

[0060] If the thickness of the dried film is less than 0.05 μm, the corrosion resistance may be reduced. If the thickness of the dried film exceeds 20 μm, there is a possibility that the film will not be completely dried during the subsequent baking and curing process.

[0061] Step of forming a pretreatment layer

[0062] The step of forming a pretreatment layer may be a step of baking and cooling a plated steel sheet coated with a surface treatment composition.

[0063] The baking temperature is not particularly limited as long as the applied surface treatment composition can be cured. As a non-limiting example, the baking temperature may be 60 to 200°C. If the baking temperature is below 60°C, drying may be incomplete, and the corrosion resistance, chemical resistance, alkali resistance, and cleaning resistance of the surface-treated plated steel sheet may be reduced. If the baking temperature exceeds 200°C, there is a risk that the pretreatment layer may turn yellowish-brown or that the workability of the surface-treated plated steel sheet may be reduced.

[0064] After baking, cooling is not particularly limited, and conditions commonly used in the relevant technical field may be applied without restriction.

[0065] [Surface-treated galvanized steel sheet]

[0066] According to exemplary embodiments, the surface-treated galvanized steel sheet may comprise a galvanized steel sheet and a pretreatment layer formed by curing the surface treatment composition described above. The galvanized steel sheet may be any galvanized steel sheet commonly used as a surface treatment target in the art without limitation. As a non-limiting example, the galvanized steel sheet may be any one of a hot-dip galvanized zinc sheet, an alloyed hot-dip galvanized zinc sheet, and an electroplated steel sheet. Since the surface-treated galvanized steel sheet comprises a pretreatment layer formed by a surface treatment composition having excellent storage stability, it may possess excellent alkali resistance, blackening resistance, corrosion resistance, solvent resistance, and chemical resistance.

[0067] [Example]

[0068] Hereinafter, embodiments of the present invention will be described in detail. The following embodiments are for the purpose of understanding the present invention only and are not intended to limit the invention.

[0069] 1. Preparation of a surface treatment composition for galvanized steel sheets

[0070] (1) Examples 1~5

[0071] A surface treatment composition for galvanized steel sheets having the composition of Table 1 below was prepared. The components used at this time are as follows.

[0072] - Acrylic resin: Ethylene acrylic acid resin

[0073] - Urethane resin: Water-dispersible polyurethane resin

[0074] - Amine compound: Triethylamine

[0075] - Curing agent: Melamine-based curing agent

[0076] - Titanium-based chelate: Titanium butyl phosphate (TBP)

[0077] - Phosphate-based inorganic compounds: Triammonium phosphate

[0078] In Table 1, the content of each component is based on the total weight of the composition, and the remainder is ammonia water.

[0079] The surface treatment compositions prepared above were stored for 0 hours, 24 hours, 72 hours, 96 hours, and 120 hours, respectively, and these were referred to as Examples 1 to 5.

[0080] (2) Comparative Examples 1~3

[0081] A surface treatment composition for plated steel sheets identical to Examples 1 to 5 was prepared, except that it did not contain triethylamine. The prepared surface treatment compositions were stored for 0 hours, 24 hours, and 72 hours, respectively, and were designated as Comparative Examples 1 to 3, respectively.

[0082] (3) Comparative Examples 4~6

[0083] A surface treatment composition for plated steel sheets identical to Examples 1 to 5 was prepared, except that it contains 6% by weight of triethylamine and does not contain phosphate-based inorganic compounds. The prepared surface treatment compositions were stored for 0 hours, 24 hours, and 72 hours, respectively, and were designated as Comparative Examples 4 to 6.

[0084] Acrylic resin (wt%) Urethane resin (wt%) Amine compound (wt%) Curing agent (wt%) Titanium-based chelate (wt%) Phosphate-based inorganic compound (wt%) Whether pH Equation 1 is satisfied (Equation value) Example 1~5 1717 1.5 0.6 2.5 0.1 10.6 O (12.47) Comparative Example 1~3 1717 0.6 2.5 0.1 9.3 X (0) Comparative Example 4~6 1717 60.6 2.5 0 11.4 X (-)

[0085]

[0086] 2. Manufacture of surface-treated galvanized steel sheets

[0087] Approximately 20 g / m² 2 The surface treatment compositions of Examples 1 to 5 and Comparative Examples 1 to 9 were applied using a bar coater to a plated steel plate with a thickness of about 0.6 mm and a plating deposition amount, with a dry film thickness of 0.8 to 1 μm. Afterward, the plated steel plate specimens were prepared by baking at a steel plate temperature of about 170°C and then water cooling.

[0088] 3. Results of Physical Property Evaluation of Galvanized Steel Sheets

[0089] Alkali resistance, blackening resistance, corrosion resistance, and solvent resistance were evaluated for the plated steel sheet specimens prepared in the examples and comparative examples, and the results are shown in Table 2. The evaluation criteria are as follows.

[0090] Alkali Resistance Evaluation Criteria

[0091] After immersing a plated steel sheet specimen in an alkaline aqueous solution of pH 12 mixed with degreasing agent solutions L4460A and L4460B (manufactured by Nihon Parkerizing Co., Ltd.) in a predetermined ratio for 2 minutes, the peeling of the film was observed.

[0092] ◎ : No film peeling or discoloration

[0093] ○ : No film peeling, but discoloration occurs

[0094] △ : Partial peeling of the film

[0095] × : Full peeling of the film

[0096] Blackening Resistance Evaluation Criteria

[0097] A plated steel sheet specimen was left at 60°C and 95% relative humidity for 192 hours, and the color difference value (△E) before and after the leaving was measured.

[0098] ◎ : Color difference value (△E) less than 2

[0099] ○ : Color difference value (△E) 2 or greater, less than 2.5

[0100] △ : Color difference value (△E) 2.5 or higher, less than 3

[0101] × : Color difference value (△E) 3 or higher

[0102] Corrosion Resistance Evaluation Criteria

[0103] The time required until white rust appeared after spraying salt water on a plated steel specimen was measured.

[0104] ◎ : More than 144 hours

[0105] ○ : 120 hours or more but less than 144 hours

[0106] △ : 96 hours or more but less than 120 hours

[0107] × : Less than 96 hours

[0108] <Content Evaluation Criteria>

[0109] A load of 1.4 kg was applied to the plated steel sheet specimen with an ethanol cotton and the film was observed after 10 back-and-forth passes.

[0110] ◎ : No membrane removal

[0111] ○ : Demembranes 0~10%

[0112] △ : Demembranes 10~20%

[0113] × : Demembranous 20% or more

[0114] Composition Preparation Time Alkalinity Blackening Resistance Corrosion Resistance Solvent Resistance Example 10 ◎◎◎◎ Example 224 ◎◎◎◎ Example 372 ◎◎◎◎ Example 496 ◎◎◎◎ Example 5120 ◎◎◎◎ Comparative Example 10 △◎◎◎ Comparative Example 224 X○○◎ Comparative Example 372 X○○◎ Comparative Example 40 ◎◎X◎ Comparative Example 524 ◎◎X◎ Comparative Example 672 ◎◎X◎

[0115]

[0116] 4. Evaluation of blackening resistance according to phosphate-based inorganic compound content

[0117] Approximately 20g / m² 2 A surface treatment composition (Examples 6–8 and Comparative Examples 7–8) having the composition of Table 3 below was applied to a plated steel plate with a thickness of approximately 0.6 mm and a plating deposition amount using a bar coater to achieve a dry film thickness of 0.8–1 μm. Subsequently, specimens were prepared by baking at a steel plate temperature of approximately 170°C and then water-cooling. To evaluate blackening resistance, the plated steel plate specimens were left at approximately 60°C and 95% relative humidity for 72 hours, and the color difference value (Δ) was measured before and after leaving.

[0118] Phosphate-based inorganic compound content (weight%) Satisfaction of Equation 1 Initial whiteness (L value) Color difference value (ΔE) Example 6 0.1O 72-75◎ Example 7 0.5O 71-74◎ Example 8 1O 70-73◎ Comparative Example 70X 73-76○ Comparative Example 8 6X <70◎

[0119]

[0120] When a composition not containing phosphate-based inorganic compounds (Comparative Example 7) was used, the color difference value (△E) in the blackening resistance evaluation was 2.4, and blackening occurred in the plated steel sheet. On the other hand, when a composition containing an excess amount of phosphate-based inorganic compounds (Comparative Example 8) was used, the plating layer oxidized upon application of the composition, showing a significantly lower initial whiteness value compared to Examples 6 to 8.

[0121] Although the present invention has been described in detail through embodiments above, other forms of embodiments are also possible. Therefore, the technical concept and scope of the claims described below are not limited to the embodiments.

Claims

1. Based on the total weight of the composition, 1 to 50 weight% of a resin mixture of urethane resin and acrylic resin; Phosphate-based inorganic compound 0.01~5 wt%; 0.01 to 5 wt% of amine compound; and Contains residual ammonia water, and A surface treatment composition satisfying the following relationship 1. [Relationship 1] (In the above Equation 1, [N] is the mol% of alkyl ammonium ions in the surface treatment composition, [P] is the mol% of phosphate ions in the surface treatment composition, and [pH] is the pH of the surface treatment composition.) 2. In Paragraph 1, The above resin mixture is a surface treatment composition in which urethane resin and acrylic resin are mixed in a weight ratio of 100:1 to 1:

100.

3. In Paragraph 1, The above-mentioned phosphate-based inorganic compound is a surface treatment composition comprising one or more selected from the group consisting of ammonium phosphate compounds and phosphate ester compounds.

4. In Paragraph 1, A surface treatment composition in which the above amine compound is triethylamine.

5. In Paragraph 1, Based on the total weight of the composition, Curing agent 0.01~5 wt%; 0.01 to 5 wt% titanium-based chelate; and A surface treatment composition further comprising 0.01 to 5 weight% of a silane compound and one or more of the following.

6. In Paragraph 5 The above-mentioned curing agent is a surface treatment composition comprising one or more selected from the group consisting of melamine-based curing agents and isocyanate-based curing agents.

7. A step of applying a surface treatment composition according to any one of claims 1 to 6 onto a plated steel sheet such that the dry film thickness is 0.05 to 20 μm; and A surface treatment method for a plated steel sheet comprising the step of baking a plated steel sheet coated with the above surface treatment composition to form a pretreatment layer.

8. Galvanized steel sheet; and A surface-treated plated steel sheet comprising a pretreatment layer formed by curing a surface treatment composition of any one of claims 1 to 6 on the plated steel sheet.

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