JP5119864B2 - Phosphate-treated galvanized steel sheet and method for producing the same - Google Patents

Description

  The present invention is a surface-treated steel sheet mainly used for building materials, home appliances, and the like, and particularly relates to a phosphate-treated zinc-based plated steel sheet suitable as a base steel sheet for coating and a method for producing the same.

  Zinc-based plated steel sheets that have been subjected to surface treatment such as galvanization or zinc alloy plating are used in parts that require corrosion resistance in the use of building materials, home appliances, and the like. These zinc-based plated steel sheets are rarely used as they are, and are usually used by applying a coating film on a zinc-based plated layer. In general, as a pretreatment for applying a coating film, a chemical conversion treatment such as a phosphate treatment or a chromate treatment is performed on the plating layer.

  The phosphate treatment is a treatment for forming a crystalline film mainly composed of zinc phosphate on the plating surface by bringing an acidic solution containing phosphate ions into contact with a zinc-based plated steel sheet and reacting them. The adhesion with the coating film is improved, and the coating film base performance is stable for various coating films. For this reason, galvanized steel sheets that have been subjected to phosphate treatment are widely used as base steel sheets for coatings for building materials, home appliances, etc., and among them, the purpose is to improve the corrosion resistance of phosphate films. In addition, a technique for adding Mg to a zinc phosphate coating is disclosed in many patent documents as a known technique.

For example, as shown in Patent Document 1, a zinc phosphate film containing Mg of 2.0% or more and one or more elements selected from Ni, Co, and Cu of 0.01 to 1% has an adhesion amount of 0.7 g / m. ^A zinc phosphate-treated zinc-based plated steel sheet excellent in corrosion resistance and color tone that is formed to be ² or more is disclosed.

Moreover, as shown in Patent Document 2, Zn is contained in an amount of 0.4 to 2.0 g / L, Mg is contained in an amount of 0.4 to 5.0 g / L, Ni is contained in an amount of 0.05 to 2.0 g / L, and P ₂ O ₅ is contained in an amount of 8.0 to 20.0 g / L. By treating zinc-plated steel, or aluminum and galvanized steel, using a zinc-magnesium phosphate aqueous solution with a ratio of free acid to total acid in the solution (free acidity / total acidity) of 0.02 to 0.15 A technique for suppressing spotted defects in phosphate crystals is disclosed.

Further, Patent Document 3 contains 0.5 to 5.0 g / L of Zn, 0.3 to 3.0 g / L of Mg, 3.0 to 20.0 g / L of P ₂ O ₅ , and free acid in the phosphate treatment solution. Disclosed is a technique for whitening a phosphate coating color tone by treating with a phosphate aqueous solution having a total acid ratio (free acidity / total acidity) of 0.1 to 0.4 and processing in a short time. Yes.

However, in the technique of Patent Document 1, since the zinc phosphate film contains a large amount of Mg, there is a risk that the blackening resistance may deteriorate such that the surface turns black in a high-temperature and high-humidity environment. There was also a problem that the color tone of the zinc phosphate coating was darkened by containing Ni, Co, and Cu in a high concentration in the coating.

  Moreover, in the technique of Patent Document 2, a relatively long treatment time of 20 seconds to 10 minutes is required in order to form the phosphate crystals densely, but the treatment is continued in post-treatment equipment such as electroplating. In some cases, it is desirable to shorten the processing time as much as possible from the viewpoint of production efficiency. When a short processing time of several seconds is performed, the formation of phosphate crystals is likely to be incomplete, and a phosphorous locally called “ske”. There may be a portion where acid salt crystals are not formed.

Moreover, in the technique of patent document 3, although the etching property with respect to zinc of a galvanized steel plate is improved by making free acid concentration high, in the case of continuous processing to a steel plate, the streak shape resulting from the surface state of a galvanized steel plate There is a problem that non-uniformity is likely to occur. This is considered to be caused by the fact that the difference in local reactivity of the zinc surface layer is manifested by a process with high etching properties, resulting in macro unevenness.
JP 2002-285346 A Japanese Patent No. 2680618 Japanese Patent No. 2770860

  The object of the present invention is to produce a phosphate-treated galvanized steel sheet capable of forming a uniform phosphate film in a short time, and to be excellent in corrosion resistance and blackening resistance produced by the production method. Another object of the present invention is to provide a phosphate-treated galvanized steel sheet.

  As a result of repeated studies to solve the above problems, the present inventors have prescribed the zinc ion concentration and the magnesium ion concentration, and the ratio of the magnesium ion concentration to the zinc ion and the free acidity in the treatment liquid. It has been found that a uniform phosphate film can be formed in a short time by using a phosphating solution whose ratio to the total acidity is in a specific range. The obtained phosphate-treated zinc-based plated steel sheet was found to have excellent corrosion resistance and blackening resistance.

The present invention has been made based on such findings, and the gist thereof is as follows.
(1) A method for producing a phosphating galvanized steel sheet by treating a galvanized steel sheet with a phosphating solution and forming a phosphate film on the surface of the galvanized steel sheet,
The phosphating solution, Zn ^2+: 2.0 g / L more than 5.0 g / L or less, Mg ^2+: containing 2.0~5.0g / L, and the concentration of Mg ²⁺ with respect to the Zn ²⁺ ratio Mg ²⁺ / Zn ²⁺ is in the range of 0.4 to 2.5, Ri 0.10 less der ratio 0.020 or more to the total acidity of the free acidity in the treatment solution,
Mg ion source in the treatment liquid is magnesium nitrate,
A method for producing a phosphating galvanized steel sheet, wherein the galvanized steel sheet is brought into contact with the treatment liquid for 3 to 15 seconds .

(2) The above characterized in that the surface of the zinc-based plated steel sheet has a phosphate film containing Mg: 0.2% by mass or more and less than 2.0% by mass and having an adhesion amount of 0.2 to 3.0 g / m ² ( 1) A phosphate-treated zinc-based plated steel sheet produced by the method for producing a phosphate-treated zinc-based plated steel sheet according to 1) .

According to the present invention, the zinc-based plated steel sheet contains Zn ²⁺ : more than 2.0 g / L and 5.0 g / L or less, Mg ²⁺ : 2.0 to 5.0 g / L, and Mg ^{2 with} respect to Zn ²⁺ . in the range of ratio Mg ²⁺ / Zn ²⁺ is 0.4 to 2.5 of the density of ^+, by percentage of the total acidity of the free acidity in the treatment solution is treated with phosphate treatment solution is less than 0.020 to 0.10 Thus, it has become possible to provide a method for producing a phosphate-treated galvanized steel sheet that can form a uniform phosphate film in a short time. The contact time with the phosphating solution is preferably 3 to 15 seconds. Further, the obtained phosphate-treated zinc-based plated steel sheet has a phosphate film containing Mg: 0.2 mass% or more and less than 2.0 mass%, with an adhesion amount of 0.2 to 3.0 g / m ² , and has corrosion resistance. Excellent blackening resistance.

Hereinafter, the configuration of the present invention and the reasons for limitation will be described.
The phosphate-treated zinc-based plated steel sheet of the present invention contains Mg: 0.2% by mass or more and less than 2.0% by mass on the surface of the zinc-based plated steel sheet, and the adhesion amount is 0.2 to 3.0 g / m ^2. A phosphate-treated galvanized steel sheet produced by a production method described later, characterized by having a film.

(Zinc-based plating)
Examples of the zinc-based plated steel sheet to be the base steel sheet of the steel sheet of the present invention include a hot-dip galvanized steel sheet, an electrogalvanized steel sheet, an alloyed hot-dip galvanized steel sheet, and an aluminum-zinc alloy-plated steel sheet (for example, hot-dip zinc-55% by mass). Aluminum alloy-plated steel sheet, hot-dip zinc-5 mass% aluminum alloy-plated steel sheet), iron-zinc alloy-plated steel sheet, nickel-zinc alloy-plated steel sheet, various zinc-based plated steel sheets such as nickel-zinc alloy-plated steel sheet after blackening treatment, etc. Can be used. Moreover, the base steel plate which is a board | substrate will not be specifically limited if it is a steel plate which can be applied as a zinc-plated steel plate, and can be suitably selected according to a use. Furthermore, although the adhesion amount of a galvanization layer can be suitably selected according to a use, it is preferable to set it as 1-100 g / m < ² > or more. This is because if the adhesion amount is less than 1 g / m ² , the corrosion resistance is not sufficient, and if it exceeds 100 g / m ² , the plating peel resistance decreases. A more preferable adhesion amount is 5 to 70 g / m ² .

(Phosphate coating)
At least one surface of the galvanized steel sheet has a phosphate film containing Mg: 0.2% by mass or more and less than 2.0% by mass and having an adhesion amount of 0.2 to 3.0 g / m ² .

  The phosphate film is formed mainly for improving the adhesion between the galvanized layer and the coating film, and more preferably one that can improve not only the adhesion but also the corrosion resistance. Further, the content of Mg in the phosphate film is preferably 0.2% by mass or more and less than 2.0% by mass. If the content is 0.2% by mass or more, the corrosion resistance is sufficient, and if it is less than 2.0% by mass, excellent blackening resistance is obtained. A more preferable content of Mg is 0.5 to 1.0% by mass. Moreover, in the said phosphate membrane | film | coat, if Ni, Mn, Co, etc. are 0.01-0.4 mass%, it can contain as an unavoidable impurity.

In addition, it is preferable that the adhesion amount of the said phosphate membrane | film | coat is 0.2-3.0 g / m < ² >. If it is 0.2 g / m ² or more, the corrosion resistance is sufficient, and if it is 3.0 g / m ² or less, the phosphate crystals in the phosphate film are difficult to coarsen, so the coating film adhesion is improved. It is. The phosphate film is formed by bringing the galvanized layer and a phosphating solution described later into contact with each other by a conventional method such as spraying or dipping. Furthermore, the contact time between the phosphating solution and the galvanized steel sheet is 3 to 15 seconds . If it is 3 seconds or more, a phosphate film can be sufficiently formed, and if it is 15 seconds or less, etching with a phosphating solution does not easily occur, and macro unevenness hardly occurs. This is because the formation of is more uniform.

  Prior to the formation of the phosphate film, it is preferable to perform a surface adjustment treatment of the galvanized layer using a titanium colloidal active treatment agent. As a titanium colloid type active treating agent, for example, trade name “Prevalene ZN” manufactured by Nippon Parkerizing Co., Ltd. can be mentioned, and can be performed by spraying the treating agent on the surface of the galvanized layer.

The method for producing a phosphate-treated zinc-based plated steel sheet according to the present invention comprises treating a zinc-based plated steel sheet with a phosphate treatment liquid to form a phosphate coating on the surface of the zinc-based plated steel sheet. A method for producing a galvanized steel sheet, wherein the phosphate treatment liquid contains Zn ²⁺ : more than 2.0 g / L and 5.0 g / L or less, Mg ²⁺ : 2.0 to 5.0 g / L, and ratio Mg ²⁺ / Zn ²⁺ concentration of Mg ²⁺ for Zn ²⁺ is in the range of 0.4 to 2.5, and wherein the percentage of the total acidity of the free acidity in the treatment solution is less than 0.020 to 0.10 It is a manufacturing method of the phosphating zinc-plated steel plate which carries out.

・ Zn ²⁺ : More than 2.0g / L and less than 5.0g / L
Since Zn ²⁺ is an essential component for forming phosphate crystals, it is necessary to control the Zn ²⁺ concentration in the phosphating solution to be more than 2.0 g / L and not more than 5.0 g / L. More preferably, it is controlled in the range of 3.0 to 5.0 g / L. This is because phosphate is difficult to precipitate at 2.0 g / L or less and forms a non-uniform phosphate film in which phosphate crystals are not locally formed. At 5.0 g / L or more, phosphate is formed. This is because the crystals are coarsened, so that a sufficient effect of corrosion resistance by the phosphate film cannot be obtained.

・ Mg ²⁺ : 2.0 ~ 5.0g / L
Since Mg ²⁺ is an essential component for improving the corrosion resistance of the phosphate film, it is necessary to control the Mg ²⁺ concentration in the phosphating solution to 2.0 to 5.0 g / L. More preferably, it is controlled in the range of 2.5 to 5.0 g / L. If the amount is less than 2.0 g / L, the corrosion resistance of the zinc phosphate coating is reduced due to less uptake of the magnesium component, and if it exceeds 5.0 g / L, the content of the magnesium component is too high, so the resistance of the zinc phosphate coating is reduced. This is because blackening is reduced. In addition, since the Mg ²⁺ concentration differs depending on the Mg ²⁺ concentration ratio (Mg ²⁺ / Zn ²⁺ ) to Zn ²⁺ in the phosphate aqueous solution described later, Mg ²⁺ / Zn ²⁺ It is necessary to adjust the concentration within an appropriate range.

· Zn ratio of the concentration of Mg ²⁺ for ^{2+ (Mg 2+ / Zn 2+)} : 0.4~2.5
In order to contain an appropriate amount of Mg in the phosphate film, in the present invention, the ratio Mg ²⁺ / Zn ²⁺ of the magnesium ion concentration to the zinc ion concentration in the phosphating solution is regulated to 0.4 to 2.5. More preferably, it is 0.8 to 1.2. When Mg ²⁺ / Zn ²⁺ is less than 0.4, the Mg ²⁺ concentration in the treatment liquid is less than 2.0 g / L. Therefore, Zn ²⁺ is preferentially taken into the phosphate film, and Zn in the phosphate film The ratio of Mg to the lower the corrosion resistance of the zinc phosphate coating. If Mg ²⁺ / Zn ²⁺ exceeds 2.5, the Mg ²⁺ concentration in the treatment solution exceeds 5.0 g / L, so the ratio of Mg to Zn in the phosphate film is outside the proper range, and phosphoric acid This is because the blackening resistance of the zinc film is lowered.

In addition to the above conditions, the phosphating treatment solution dissolves Mg salt so that the Mg ²⁺ concentration in the phosphating treatment solution falls within the above range. It is preferable that the temperature and the pH are in the range of 1.0 to 2.5. It is also for the following reason. When the liquid temperature is 30 ° C. or higher, the reactivity of the phosphating liquid increases, and a uniform film can be easily formed in a short time. On the other hand, when the liquid temperature is 70 ° C. or lower, the plating surface is appropriately etched by the treatment liquid, the phosphate is easily precipitated, and the treatment time is very easily controlled. Further, when the pH is 1.0 or more, the etching property is moderate and the film is likely to be deposited, so that the treatment time can be easily controlled. On the other hand, when the pH is 2.5 or less, the stability of the treatment liquid is high and precipitation is unlikely to occur.

Furthermore, it is important to select an anion that is paired with Mg ²⁺ in the treatment solution. Here, when hydroxide ion, carbonate ion, sulfate ion, etc. are used, there is a tendency that sufficient solubility of Mg salt cannot be obtained, and when chloride ion is used, the solubility is sufficient, but Mg ^{At the} same time as ^{2+, a} high concentration of chlorine ions is mixed into the phosphating solution, which adversely affects the formation of the phosphate film. On the other hand, nitrate ions have an oxidizing action and are less likely to remain in the film components compared to other anions such as chloride ions and sulfate ions, so that the components soluble in the formed film can be minimized, and the phosphate film It has the effect of improving performance. Accordingly, nitrate ions are suitable as the anions, and magnesium nitrate is used as the Mg ion source in the treatment liquid . As the phosphate treatment liquid used in the present invention, a commercial treatment liquid containing zinc ions, phosphate ions, and further containing an accelerator, for example, trade name “PB3312M” manufactured by Nippon Parkerizing Co., Ltd. In addition, the above-mentioned nitrate ion is preferably used.

-Ratio of free acidity to total acidity: 0.020 or more and less than 0.10 The formation of the phosphate film is due to the etching action of the free orthophosphoric acid (free acid) of the treatment liquid on the plating surface, and the pH of the solid-liquid interface of the treatment liquid is The concentration of the primary zinc phosphate (Zn (H ₂ PO ₄ ) ₂ ) and orthophosphoric acid (H ₃ PO ₄ ) in the treatment solution is different, so the primary zinc phosphate contains magnesium. It is performed by depositing as zinc phosphate crystals. Therefore, the free acid plays a very important role in the formation of the phosphate film. Therefore, the present inventors paid attention to the etching action of free acid, and conducted extensive studies on a method that can form a uniform phosphate film by a short time ( 3 to 15 seconds).

As a result, when the free acid concentration is increased, the etching property to galvanization increases, and the surface condition becomes non-uniform in the degreasing and surface finishing process that is a pretreatment of the phosphate treatment. When the free acid concentration is increased and the free acid concentration is increased, the zinc phosphate crystals are less likely to precipitate. Therefore, in the case of a short time treatment of several seconds, a portion where a phosphate film is not locally formed occurs. I found out. As a result of further investigation, by optimizing the ratio of free acidity to total acidity in a range lower than conventional, it is possible to deposit phosphate crystals equivalent to the conventional technology while suppressing etching property. And found that a uniform phosphate film can be formed in a short time.
The free acid (orthophosphoric acid) concentration is preferably in the range of 0.5 to 3.4 in terms of free acidity. More preferably, it is the range of 1.0-3.0. The total acidity is preferably in the range of 20 to 26, but it is necessary to have a ratio with the free acidity described later.

  The ratio of the free acidity to the total acidity (free acidity / total acidity) must be controlled to 0.020 or more and less than 0.10. More preferably, it is controlled to 0.035 to 0.096. If it is less than 0.020, the free acid concentration is too low, so the etching property to zinc is poor, the reaction necessary for precipitation of phosphate crystals is less likely to occur, and a sufficient phosphate film is not formed. This is because the stability of the phosphating solution is lowered, and a solid content that is considered to be a phosphate compound containing zinc and iron present as impurities is precipitated and dispersed in the processing solution. On the other hand, if it is 0.10 or more, there is a possibility that unevenness of the phosphate film due to non-uniformity of the surface state of zinc may occur when a short time treatment of several seconds level is performed.

  Here, the free acidity refers to the amount of 0.1N caustic soda (ml) required for neutralization by adding several drops of bromophenol blue as an indicator to 10ml of phosphating solution and titrating with 0.1N caustic soda. Represent as Furthermore, the total acidity is the same with the addition of a few drops of phenolphthalein as an indicator for 10 ml of the phosphate treatment solution, titration with 0.1 normal caustic soda, and the amount of 0.1 normal caustic soda (ml) required for neutralization as a point. To express.

  The above description is merely an example of the embodiment of the present invention, and various modifications can be made within the scope of the claims.

  Examples of the present invention will be described.

(Examples 1-16 and Comparative Examples 1-9)
The cold-rolled steel sheet having a thickness of 1.0 mm, as a pretreatment, ortho sodium silicate (60 g / L) added alkaline degreasing solution (liquid temperature: 70 ° C.) in a current density of the counter electrode as a stainless steel plate: at 5A / dm ² After electrolytic degreasing for 30 seconds, it was washed with water, immersed in a 30 g / L sulfuric acid aqueous solution (liquid temperature: 30 ° C.) for 5 seconds, pickled, and then washed with water. After the pretreatment, the steel sheet was subjected to electrogalvanizing treatment, and a zinc plating layer having an adhesion amount of 20 g / m ² was formed on one surface of the steel sheet. In the electrogalvanizing treatment, a zinc plating solution to which 440 g / L of zinc sulfate heptahydrate was added was used as a zinc plating bath. The zinc plating solution was adjusted to pH 1.5 by adding sulfuric acid. The bath temperature of the galvanizing bath is 50 ° C. In the electrogalvanizing bath, an iridium oxide-coated Ti plate electrode is used as a counter electrode, and the test plate is placed in parallel with a distance of 10 mm between the electrodes, and a flow rate of 1.5 m / The current was supplied at a current density of 70 A / dm ² while circulating the plating solution in s.
After forming a galvanized layer on the surface of the steel plate in this way, it was washed with water and then subjected to phosphate treatment.

  As a pretreatment for phosphating, the surface of the galvanized layer is surface-treated with a surface conditioner (manufactured by Nihon Parkerizing Co., Ltd .: trade name “Plenpalen Z”). The liquid (Nippon Parkerizing Co., Ltd .: trade name “PB3312M”) added with magnesium nitrate was sprayed at different times, washed with water, and dried to form a phosphate film. In addition, although the liquid temperature of a phosphating liquid is 60 degreeC and pH changes with each Example or each comparative example, all are the range of 2.1-2.7, and 0.1-0.4 g / L is in any processing liquid. Contains Ni in the range.

The Zn ²⁺ concentration, Mg ²⁺ concentration, free acidity and total acidity in the phosphating solution should be appropriately added with the concentration of the “PB3312M” and aqueous sodium hydroxide, orthophosphoric acid and nitric acid. Thus, each example and the comparative example were changed. The Zn ²⁺ concentration was changed by the initial concentration of “PB3312M”, and the Mg ²⁺ concentration was changed by changing the amount of magnesium nitrate added. In addition, the Mg content in the phosphate film was measured by dissolving the phosphate-treated layer with an aqueous ammonium dichromate solution and measuring the dissolved solution by ICP analysis (inductively coupled plasma emission analysis). The adhesion amount of was changed by changing the contact time with the phosphating solution. Further, the amount of the phosphate coating adhered was measured by a gravimetric method after being dissolved in an ammonium dichromate aqueous solution.
Zn ²⁺ concentration, Mg ²⁺ concentration, Mg ²⁺ / Zn ²⁺ ratio, free acidity, total acidity, free acidity / total acidity ratio and phosphate in the phosphating solution used in Examples and Comparative Examples Table 1 shows the spray treatment time of the treatment liquid (contact time of the treatment liquid), and the Mg content and the adhesion amount of the phosphate coating of the prepared phosphate-treated zinc-based plated steel sheet.

  Various tests were performed on the phosphate-treated zinc-plated steel sheet obtained as described above. The evaluation method of the test conducted in this example is shown below.

(Evaluation method)
(1) Appearance uniformity The appearance of the surface after the phosphate treatment was visually observed, and the uniformity of the phosphate film was evaluated according to the following evaluation criteria.
○: Appearance uniform ×: Appearance unevenness

(2) Crystal formation state In the crystal formation state, the phosphate film was observed with a scanning electron microscope (SEM), and the presence or absence of a portion where a phosphate crystal was not locally formed was evaluated. In the observation, the central portion excluding the outer edge range of 20 mm from the end of the 150 × 70 mm ² test piece was observed with a 1000 times SEM. For any 10 fields of view (field area: 100 μm × 100 μm), the number of locations where phosphate crystals were not formed in a region having a diameter of 20 μm or more was counted for each field. Based on the average number per field of view calculated from the number counted in 10 fields of view, evaluation was performed according to the following evaluation criteria.
○: Less than 3 locations Δ: 3 or more locations and less than 10 locations ×: 10 locations or more

(3) Corrosion resistance Corrosion resistance was determined by cutting out a test piece (size: 100 x 50 mm) from the prepared phosphate-treated zinc-plated steel sheet, tape-sealing the end and back of the test piece, and then JIS Z 2371-2000. The salt spray test was conducted in accordance with the provisions of The surface of the test piece was regularly observed, the time until the white rust generation area became 5% of the total evaluation area of the test piece (white rust generation time) was examined, and evaluated according to the following evaluation criteria.
◎: 24 hours or more ○: 8 hours or more but less than 24 hours △: 4 hours or more but less than 8 hours ×: Less than 4 hours

(4) Blackening resistance Blackening resistance is obtained by cutting out a test piece (size: 100 x 50 mm) from the prepared phosphate-treated galvanized steel sheet and using a spectroscopic color difference meter SQ2000 (manufactured by Nippon Denshoku Industries Co., Ltd.). ) Was used to measure the initial L value (lightness) of the test piece. Next, after leaving the test piece in a constant temperature and humidity chamber at a temperature of 80 ° C. and a relative humidity of 95% for 24 hours, the L value of the test piece was measured in the same manner, and the amount of change ΔL (from the initial L value) L value-initial L value) was determined and evaluated according to the following evaluation criteria.
A: ΔL ≧ −1
○: −1> ΔL ≧ −2
Δ: −2> ΔL ≧ −4
×: ΔL <−4

(5) Coating film adhesion Coating film adhesion was achieved by applying alkydmelamine-based paint (Daikon Paint Co., Ltd., Delicon # 700, dry 130 ° C, without pretreatment such as degreasing to the test piece (70 x 150 mm). × 30 minutes, film thickness 28 ± 5 μm) was applied, and a cross cut (10 × 10 pieces, 1 mm interval) was cut with a cutter, followed by Erichsen extrusion (height 5 mm). After that, a cellophane adhesive tape (type C LP-18) made by Nichiban Co., Ltd. was applied to the place where the Eriksen extrusion process was performed with a grid pattern, and after sticking it with a spatula, it was peeled off and the coating film remaining rate was determined. Measured and evaluated according to the following evaluation criteria.
○: Residual film remaining rate 100%
Δ: Paint film remaining rate 90% or more and less than 100% ×: Paint film remaining rate 90%

Table 1 shows the evaluation results of the above tests.
According to this, the phosphate-treated zinc-based plated steel sheets of Examples 1 to 16 all have good appearance uniformity, crystal state, corrosion resistance, blackening resistance and coating film adhesion. It was also found that sufficient performance was obtained even when the phosphate film was formed in a short time.

  By the production method of the present invention, a uniform phosphate film can be formed in a short time, and a phosphate-treated zinc-based plated steel sheet excellent in corrosion resistance and blackening resistance can be obtained. Since this phosphate-treated zinc-based plated steel sheet is widely used as a base steel sheet for coating for building materials, home appliances, etc., it can greatly contribute to the industry.

Claims (2)

A method for producing a phosphating galvanized steel sheet by treating a galvanized steel sheet with a phosphating solution and forming a phosphate film on the surface of the galvanized steel sheet,
The phosphating solution, Zn ^2+: 2.0 g / L more than 5.0 g / L or less, Mg ^2+: containing 2.0~5.0g / L, and the concentration of Mg ²⁺ with respect to the Zn ²⁺ ratio Mg ²⁺ / Zn ²⁺ is in the range of 0.4 to 2.5, Ri 0.10 less der ratio 0.020 or more to the total acidity of the free acidity in the treatment solution,
Mg ion source in the treatment liquid is magnesium nitrate,
A method for producing a phosphating galvanized steel sheet, wherein the galvanized steel sheet is brought into contact with the treatment liquid for 3 to 15 seconds . On the surface of the galvanized steel sheet, Mg: contain less than 0.2 wt% to 2.0 wt%, according to claim 1, the amount of deposition is characterized by having a phosphate film is 0.2 to 3.0 g / m ² Phosphate-treated zinc-based plated steel sheet produced by the method for producing a phosphate-treated zinc-based plated steel sheet.