Title of Invention: Composition for chemical treatment of Zn-Al-Mg alloy coated steel sheet and Zn-Al-Mg alloy coated steel sheet
technology field
[One]
The present invention relates to a composition for chemical treatment of a Zn-Al-Mg alloy coated steel sheet and a Zn-Al-Mg alloy coated steel sheet.
background art
[2]
In general, zinc and zinc-based alloy plating is performed to prevent or reduce metal corrosion. However, as the use of zinc in nature increases, the price of zinc metal rises, and zinc depletion becomes a problem. As a countermeasure against this, a method of reducing the coating amount by performing plating with excellent corrosion resistance by adding an alloying element is being sought. As part of this, alloy plating in which aluminum and magnesium are added to zinc has been developed and has been mainly used for construction, but recently it has been expanded to use for home appliances and automobiles. In particular, in order to protect the surface of the Zn-Al-Mg alloy plated steel sheet and to facilitate corrosion resistance and processing of parts, chromate coating treatment with excellent corrosion resistance is often performed.
[3]
However, the biggest problem with these alloy-coated steel sheets and chromate-treated steel sheets is the blackening phenomenon that occurs on the surface of the plating layer during long-term storage at the customer company, condensation due to temperature difference, or storage in a coiled state or laminated state in a high-temperature and high-humidity environment. . This blackening phenomenon is a phenomenon that generally occurs in a plating layer containing magnesium metal, and is caused by unsafe oxidation of zinc metal by preferential oxidation of magnesium metal concentrated in the surface layer. Blackening is the initial stage of metal corrosion, and it tends to be easily completely oxidized to white rust when exposed to air. In particular, the chromate treatment solution is a strong acidic aqueous solution with a pH in the range of 1 to 1.5, and the chromate product for building materials is not easy to cool due to latent heat after drying when the thickness of the steel plate is 1.0 mm or more, so there is a problem that the drying temperature cannot be sufficiently increased. have. Therefore, in order to solve this problem, a technique of spraying Co(III) salt during the cooling process of the Zn-4.0%Al-0.1%Mg plating layer has been proposed (ISIJ, 1990, p383-390), and recently, Zn -A technology (Korean Patent No. 10-1638307) is proposed in which an aqueous solution composed of Mg, Al, and Zn salt is treated on the surface of an Al-Mg alloy coated steel sheet and then an aqueous solution of zinc chloride is treated, but it is complex in terms of equipment and easy to apply There is a problem with not doing it.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[4]
In the present invention, it is intended to provide a conversion treatment composition and a conversion treatment method for preventing surface blackening defects occurring in Zn-Al-Mg alloy coated steel sheets and chromate-treated steel sheets.
means of solving the problem
[5]
According to one aspect of the present invention, 0.2 to 20% by weight of a phosphoric acid amine salt derived from an alkyl phosphate acid and an alkyl amine, based on the total weight of the composition for conversion treatment; 0.1 to 10% by weight of zinc phosphate; 0.1 to 10% by weight of a silicate compound; And a composition for conversion treatment of a Zn-Al-Mg alloy coated steel sheet containing water is provided.
[6]
According to another aspect of the present invention, there is provided a Zn-Al-Mg alloy coated steel sheet and a converted steel sheet comprising a conversion coating layer on at least one surface of the coated steel sheet, wherein the coating layer is formed of the conversion treatment composition. .
Effects of the Invention
[7]
The conversion treatment composition according to the present invention can be adsorbed on the surface of a Zn-Al-Mg alloy coated steel sheet to prevent blackening due to a high-temperature, high-humidity environment or dew condensation during stacking of coils or steel sheets.
Brief description of the drawing
[8]
1 shows (a) a coating film structure after chemical conversion treatment according to an embodiment of the present invention, and (b) a coating film structure obtained by chromate treatment on a chemically treated steel sheet.
[9]
2 shows a process of chemical conversion treatment and chromate treatment according to an embodiment of the present invention to a Zn-Al-Mg alloy-coated steel sheet.
Best Mode for Carrying Out the Invention
[10]
Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified in various forms, and the scope of the present invention is not limited to the embodiments described below.
[11]
Typically, the chromate coating solution is a strong acidic solution having a pH of 1.0 to 1.5. Therefore, during immersion, spraying, or roll coating, the surface of the plating layer of the steel sheet is etched, and incomplete Cr-oxide or hydroxide is precipitated to form a coating layer. In particular, the coating layer is dried at a temperature of 100 ° C or less due to the inability to increase the drying temperature for curing the coating layer due to facility limitations of the steel manufacturer's hot-dip plating line and the difficulty in cooling the steel sheet after drying. Due to this, a problem of surface blackening occurs when the coil or laminated steel sheet is stored for a long period of time. According to previous studies, it is known that blackening is caused by exposure of a galvanized steel sheet to a high-temperature and high-humidity environment or an atmosphere in which oxygen supply is not smooth for a long time, or by surface impurities or mechanical deformation. It is known that such a blackening phenomenon easily occurs in a galvanized layer to which aluminum or magnesium is added, and is promoted by incomplete oxidation when a phosphoric acid compound or chromate is treated on the surface of the plating layer.
[12]
As a method for solving the above problems, as shown in FIG. 1, by incorporating an organic-inorganic corrosion-resistant phosphoric acid amine salt compound into the roughness-forming part of the surface of the plating layer, excessive surface etching by a highly acidic solution is prevented and the roughness part or the plating layer Corrosion can be prevented by preventing acid from penetrating into grain boundaries.
[13]
Hereinafter, the present invention will be described in detail.
[14]
According to one embodiment of the present invention, there is provided a composition for conversion treatment of Zn-Al-Mg alloy plated steel sheet containing an amine salt of phosphoric acid derived from an alkyl phosphate acid and an alkyl amine, zinc phosphate, a silicate compound and the balance water.
[15]
The phosphoric acid amine salt may be a compound in which an ionic bond is formed between an alkyl phosphate acid and an alkyl amine. In the present invention, the phosphoric acid amine salt may be included in an amount of 0.1 to 20% by weight based on the total weight of the composition for conversion treatment. When the content of amine phosphate salt is less than 0.1% by weight, the blackening resistance of the steel sheet is not properly exhibited, and when it exceeds 20% by weight, chromate coating is difficult in the subsequent chromate coating step.
[16]
The alkyl phosphate acid constituting the phosphoric acid amine salt may be a compound represented by Formula 1 below.
[17]
[Formula 1]
[18]

[19]
In Formula 1, R 1 and R 2 are each independently a straight-chain alkyl group having 3 to 15 carbon atoms or a branched alkyl group having 5 to 15 carbon atoms, and R 1 and R 2 are each independently a hydroxyl group, an ether group, or an ester group Or it may be substituted with an epoxy group.
[20]
Preferred alkyl phosphate acids that can be used in the present invention include 2-ethylhexyl phosphate, isononanol phosphate, octyl ethoxylate phosphate, decyl ethoxylate phosphate ( Decyl ethoxylate phosphate, 2-ethylhexyl ethoxylate phosphate, decyl alcohol ethoxylate phosphate, isotridecanol ethoxylate phosphate, Tergitol 15-S-9 phosphate, Cetyl alcohol ethoxylate phosphate, Stearyl alcohol ethoxylate phosphate, Octyl alcohol ethoxylate It may be at least one selected from the group consisting of octyl alcohol ethoxylate phosphate, oleyl alcohol ethoxylate phosphate, and alkyl phenol ethoxylate phosphate, but is not limited thereto.
[21]
The alkyl amine constituting the phosphoric acid amine salt may be a compound represented by Chemical Formulas 2 to 8 below.
[22]
[Formula 2]
[23]

[24]
[Formula 3]
[25]

[26]
[Formula 4]
[27]

[28]
[Formula 5]
[29]

[30]
[Formula 6]
[31]

[32]
[Formula 7]
[33]

[34]
[Formula 8]
[35]

[36]
In Formulas 2 to 8, R 3 , R 4 and R 5 are each independently hydrogen or methyl, R 6 is each independently a hydroxyl-substituted linear or branched alkyl group having 3 to 5 carbon atoms, and n is 2 or an integer of 3.
[37]
Preferred alkyl amines that can be used in the present invention are bis (N-dimethylaminopropyl) amine (Bis (N-dimethylaminopropyl)amine), bis (N-dimethylaminoethyl) methylamine (Bis (N-dimethylaminoethyl) methylamine), bis (N-dimethylaminopropyl) methylamine (Bis (N-dimethylaminopropyl) methylamine), bis (N-aminoethyl) methylamine (Bis (N-aminoethyl) methylamine), bis (N-aminopropyl) methylamine (Bis ( N-aminopropyl)methylamine), Bis(dimethylaminoethyl)ether, Bis(dimethylaminopropyl)ether, Bis(aminoethyl)ether , Bis (aminopropyl) ether, bis (3-dimethylaminopropyl) isopropanolamine, 3-dimethylaminopropyldiisopropanolamine, 2 -(2-dimethylaminoethoxy)ethanol (2-(2-dimethylaminoethoxy)ethanol), 2-(2-dimethylaminoethoxyethyl)methylaminoethanol (2-(2-dimethylaminoethoxyethyl)methylaminoethanol),1 selected from the group consisting of 2- (2-dimethylpholinoethyl) ether and 2- (2-dimethylaminoethyl) methylaminoethanol It may be more than one species, but is not limited thereto.
[38]
The anion of the alkyl phosphate acid and the cation of the alkyl amine form a phosphoric acid amine salt by ionic bonding, and may be included in an amount of 0.1 to 10% by weight, respectively, based on the total weight of the conversion treatment composition.
[39]
In the composition for conversion treatment according to an embodiment of the present invention, zinc phosphate forms phosphoric acid crystals on the surface of the steel sheet when the composition is applied to impart additional corrosion resistance and blackening resistance. The zinc phosphate may be added in an amount of 0.1 to 10% by weight based on the total weight of the chemical conversion composition. If the content of zinc phosphate is less than 0.1% by weight, the corrosion resistance effect is insignificant, and if it exceeds 10% by weight, there is a problem that the chromate coating layer on the surface is brittle.
[40]
In the composition for conversion treatment according to an embodiment of the present invention, the silicate compound is precipitated on the finely roughened portion of the surface of the steel sheet when the composition is applied to impart additional corrosion resistance. The higher the content of the silicate compound, the higher the corrosion resistance and the adhesion of the coating film, but there is a limit to the improvement of the corrosion resistance and the adhesion of the coating film even if it is added in a certain amount or more. Therefore, the silicate compound is preferably added in the range of 0.1 to 10% by weight based on the total weight of the chemical conversion treatment composition.
[41]
Silicate compounds that can be used in the present invention include lithium silicate, sodium silicate, potassium silicate, and the like, and preferably, a lithium silicate compound can be used.
[42]
In addition, the composition for chemical conversion treatment according to an embodiment of the present invention may further include a phosphoric acid compound to adjust the acidity of the composition. A phosphoric acid compound is added so that the pH of the composition is between 3 and 5.
[43]
According to another aspect of the present invention, the chemically treated Zn-Al-Mg alloy plated steel sheet includes the steps of alkali degreasing, pickling, and washing the cold-rolled steel sheet and drying, hot-dip zinc alloy and then cooling, and drying after the chemical conversion. It may be prepared through a step of doing, a step of drying after chromate treatment. At this time, the conversion treatment composition and the chromate composition are treated by a squeezing or roll coating process after spraying, and drying is performed by a hot air, infrared or induction heating curing method.
[44]
In the step of hot-dipping a zinc alloy on a cold-rolled steel sheet, the zinc alloy may be in the form of Zn-xAl-yMg. At this time, it is preferable that x is 0.5 to 15 and y is 0.5 to 10.
[45]
In the step of drying after conversion treatment, preferably, the composition for conversion treatment is applied at 10 to 100 mg/m 2 and dried at a temperature of 60 to 120°C.
[46]
In addition, in the step of drying after chromate treatment, it is preferably applied at 10 to 300 mg/m 2 based on the weight of the chromium element , and dried at a temperature of 80 to 120 °C.
Mode for Carrying Out the Invention
[47]
Example
[48]
Hereinafter, embodiments of the present invention will be described in detail. The following examples are only for understanding of the present invention, but do not limit the present invention.
[49]
1. Examples
[50]
(1) Manufacture of composition for conversion treatment
[51]
Phosphate amine salt made from isononanol phosphate and bis(N-aminoethyl)methylamine, and zinc phosphate hydrate (Duksan Chemical Co.) were dissolved in 1L of pure water, and a lithium silicate compound and phosphoric acid were added to obtain a chemical conversion composition with a pH of 3.5. manufactured. Each composition of the chemical conversion treatment composition is shown in Table 1 below.
[52]
(2) Manufacture of chemically treated steel sheet
[53]
The composition for chemical conversion treatment prepared above was applied to a Zn-xAl-yMg plated steel sheet having a coating weight of 50 g/m 2 and having x and y values ​​in Table 1 below, and then dried in a hot air heating furnace at 80 °C. A chromate (III) composition was applied to the chemically treated steel sheet by roll coating and then dried in a hot air heating furnace at 80°C. The chromate (III) composition has a solid content of 12% by weight and is a water-soluble Cr (III) composition (Norcoil Coating Co., Ltd.) composed of chromium phosphate, chromium nitrate, a silane compound, and a small amount of a urethane binder and a wetting agent, and has a pH of 1.2. .
[54]
[Table 1]
[55]

[56]
2. Comparative Example
[57]
As shown in Table 2 below, chromate (III) and chromate (VI) compositions were applied by roll coating to a Zn-xAl-yMg plated steel sheet having a coating weight of 50 g/m 2 and having x and y values ​​in Table 2 below, and then 80 ° C. It was dried in a hot air heating furnace to prepare a chromate-treated plated steel sheet.
[58]
[Table 2]
[59]
3. Evaluation of Zn-Al-Mg alloy coated steel sheet
[60]
After evaluating the items (1) to (5) below, the evaluation results are shown in Table 3.
[61]
(1) [Cr] adhesion amount
[62]
30 ml of 3% standard hydrochloric acid solution was added to the surface of the steel sheet to dissolve the plating layer, and then the [Cr] element was measured by ICP quantitative analysis.
[63]
(2) Blackening resistance
[64]
The coated steel sheet was prepared with a size of 70mmХ70mm (horizontal Хlength) and left for 120 hours under conditions of constant temperature and humidity (65 ℃, 95% relative humidity), and compared with the original plate, the average color difference (ΔE) was measured.
[65]

[66]
◎: When the average color difference (ΔE) is less than 5.0
[67]
○: When the average color difference (ΔE) is 5.0 or more and less than 10.0
[68]
△: When the average color difference (ΔE) is 10.0 or more and less than 15.0
[69]
Х: When the average color difference (ΔE) is 15.0 or more
[70]
(3) corrosion resistance
[71]
For the corrosion resistance of the flat plate, a specimen was prepared with a size of 70 mmХ150 mm (width Х length), and salt water having a salt water concentration of 5% and a temperature of 35 ° C was evenly sprayed at a spray pressure of 1 kg / cm 2 on the specimen. , the time until white rust of 5% area occurred on the surface of the steel sheet was measured.
[72]
In addition, the corrosion resistance of the processed part was evaluated in the same manner as described above after machining the specimen with Eriksen 7mm.
[73]

[74]
◎: When the flat part is 168 hours or more
[75]
○: When the flat part is 120 hours or more and less than 168 hours
[76]
△: When the flat part is 48 hours or more and less than 120 hours
[77]
Х: In case of flat plate less than 48 hours
[78]
(4) Alkali resistance
[79]
Specimens were prepared in the size of 150mmХ70mm (width Х length) of the steel plate. After dissolving 20 g of DP FC-L4460A and 10 g of DP FC-L4460B of strong alkaline degreaser (manufacturer, Daehan Parcarizing Co., Ltd.) in 1 L of pure water, the specimen was immersed at 60 ° C for 2 minutes, and then compared with the original plate, the average color difference (ΔE ) was measured.
[80]

[81]
◎: When the average color difference (ΔE) is less than 1.0
[82]
○: When the average color difference (ΔE) is 1.0 or more and less than 1.5
[83]
△: When the average color difference (ΔE) is 1.5 or more and less than 2.0
[84]
Х: When the average color difference (ΔE) is 2.0 or more
[85]
(5) Crude Oil Infringement
[86]
The steel sheet was immersed in 10% crude oil for 24 hours, and then the color difference was measured and evaluated.
[87]

[88]
◎: When the average color difference (ΔE) is less than 0.5
[89]
○: When the average color difference (ΔE) is 0.5 or more and less than 1.0
[90]
△: When the average color difference (ΔE) is 1.0 or more and less than 1.5
[91]
Х: When the average color difference (ΔE) is 1.5 or more
[92]
[Table 3]
[93]

[94]
As in Comparative Examples 1 to 4, when the chromate treatment was performed on the plated steel sheet without using the chemical conversion treatment composition, it can be confirmed that the blackening resistance is lowered.
claims
[Claim 1]
Based on the total weight of the chemical conversion composition, 0.2 to 20% by weight of an amine salt of phosphoric acid derived from an alkyl phosphate acid and an alkyl amine; 0.1 to 10% by weight of zinc phosphate; 0.1 to 10% by weight of a silicate compound; A composition for conversion treatment of a Zn-Al-Mg alloy coated steel sheet containing water and the balance.
[Claim 2]
The composition for chemical treatment of Zn-Al-Mg alloy coated steel sheet according to claim 1, wherein the alkyl phosphate acid is a compound represented by Formula 1 below. [Formula 1] (In Formula 1, R 1 and R 2 are each independently a straight-chain alkyl group having 3 to 15 carbon atoms or a branched alkyl group having 5 to 15 carbon atoms, wherein R 1 and R 2 are each independently a hydroxy group, It may be substituted with an ether group, an ester group or an epoxy group.)
[Claim 3]
The composition for chemical treatment of Zn-Al-Mg alloy coated steel sheet according to claim 1, wherein the alkyl amine is a compound represented by Formulas 2 to 8 below. [Formula 2] [Formula 3] [Formula 4] [Formula 5] [Formula 6] [Formula 7] [Formula 8] (In Formulas 2 to 8, R 3 , R 4 and R 5 are each independently hydrogen or methyl, R 6 is each independently a straight-chain or branched alkyl group having 3 to 5 carbon atoms substituted with a hydroxyl group, and n is an integer of 2 or 3.)
[Claim 4]
The method of claim 1, wherein the alkyl phosphate acid is 2-ethylhexyl phosphate (2-ethylhexyl phosphate), isononanol phosphate (Iso-nonanol phosphate), octyl ethoxylate phosphate (Octyl ethoxylate phosphate), decyl ethoxylate phosphate (Decyl ethoxylate phosphate, 2-ethylhexyl ethoxylate phosphate, decyl alcohol ethoxylate phosphate, isotridecanol ethoxylate phosphate, Tergitol 15-S-9 phosphate, Cetyl alcohol ethoxylate phosphate, Stearyl alcohol ethoxylate phosphate, Octyl alcohol ethoxylate phosphate (Octyl alcohol ethoxylate phosphate), oleyl alcohol ethoxylate phosphate (Oleyl alcohol ethoxylate phosphate), and alkyl phenol ethoxylate phosphate (Alkyl phenol ethoxylate phosphate) At least one type selected from the group consisting of Zn-Al-Mg alloy coated steel sheet composition for treatment.
[Claim 5]
The method of claim 1, wherein the alkyl amine is bis (N-dimethylaminopropyl) amine (Bis (N-dimethylaminopropyl) amine), bis (N-dimethylaminoethyl) methylamine (Bis (N-dimethylaminoethyl) methylamine), bis ( N-dimethylaminopropyl) methylamine (Bis (N-dimethylaminopropyl) methylamine), bis (N-aminoethyl) methylamine (Bis (N-aminoethyl) methylamine), bis (N-aminopropyl) methylamine (Bis (N -aminopropyl)methylamine), Bis(dimethylaminoethyl)ether, Bis(dimethylaminopropyl)ether, Bis(aminoethyl)ether, Bis (aminopropyl) ether, bis (3-dimethylaminopropyl) isopropanolamine, 3-dimethylaminopropyldiisopropanolamine, 2- (2-dimethylaminoethoxy) ethanol (2- (2-dimethylaminoethoxy) ethanol), 2- (2-dimethylaminoethoxyethyl) methylaminoethanol (2- (2-dimethylaminoethoxyethyl) methylaminoethanol),1 selected from the group consisting of 2- (2-dimethylpholinoethyl) ether and 2- (2-dimethylaminoethyl) methylaminoethanol A composition for chemical conversion treatment of Zn-Al-Mg alloy coated steel sheet.
[Claim 6]
The composition for chemical conversion treatment of Zn-Al-Mg alloy coated steel sheet according to claim 1, wherein the silicate compound is at least one selected from the group consisting of lithium silicate, sodium silicate and potassium silicate.
[Claim 7]
The composition for conversion treatment of Zn-Al-Mg alloy coated steel sheet according to claim 1, further comprising a phosphoric acid compound so that the pH of the composition is 3 to 5.
[Claim 8]
A converted steel sheet comprising a Zn-Al-Mg alloy coated steel sheet and a conversion coating layer on at least one surface of the coated steel sheet, wherein the coating layer is attached at 10 to 100 mg/m 2 .
[Claim 9]
The converted steel sheet according to claim 8, wherein a chromate coating layer is present on the converted coating layer.