KR101830508B1 - Phosphate-treated zinc-based plated steel sheet having excellent discoloration resistance and film adhesiveness - Google Patents

Abstract

A phosphate-treated zinc plated steel sheet comprising a zinc plated steel sheet and a phosphate coating formed on at least one side of the zinc plated steel sheet, wherein the phosphate coating has a ratio of a three-dimensional surface area to a two-dimensional surface area by a laser microscope of 1.7 to 8.8 .

Description

FIELD OF THE INVENTION [0001] The present invention relates to a phosphated steel sheet having excellent discoloration resistance and film adhesiveness,

The present invention relates to a phosphate-treated zinc plated steel sheet excellent in discoloration resistance and film adhesiveness and a method for producing the same.

Phosphate film coating is widely used for automobile, home appliance, etc. due to coating or laminating. In the case of zinc plated steel sheets used for automobiles and home appliances, coating and film adhesiveness is low by themselves, and phosphate adhesion is generally improved through the treatment with phosphate.

On the other hand, when phosphate coating is applied to a zinc plated steel sheet using a commercially available phosphate solution, paint adhesion is remarkably improved, but film adhesion is not greatly improved. Conventionally, a PVC film having excellent adhesive strength has been separately formed between the phosphate film and the laminating film, thereby overcoming this problem. In recent years, however, in the field of laminating steel sheets, there is a tendency to use PVC films due to environmental problems, and accordingly, it is required to develop a technique for improving the film adhesion of the phosphate film itself.

On the other hand, as described above, as the film structure of the laminating steel sheet is simplified, when the surface discoloration occurs on the base steel sheet having the phosphate film formed thereon, there is a problem that such discoloration of the surface is exposed to the outside, It is also required to develop a technique capable of improving the performance of the system.

One of the objects of the present invention is to provide a phosphate-treated zinc plated steel sheet excellent in discoloration resistance and film adhesiveness.

According to an aspect of the present invention, there is provided a method for producing a phosphor coating film, which comprises a zinc-based plated steel sheet and a phosphate coating film formed on at least one side of the zinc-based plated steel sheet, wherein the ratio of the three- A phosphorus-treated zinc plated steel sheet is provided.

The phosphorus-treated zinc plated steel sheet of the present invention is excellent in discoloration resistance and film adhesiveness and can be suitably applied as a substrate of a laminating steel sheet.

Further, the phosphate-treated zinc plated steel sheet of the present invention can be suitably applied to a plastic laminated steel sheet.

1 is a SEM image of the surface of each specimen prepared according to Example 1. Fig.
Fig. 2 is an SEM image of the surface of each specimen produced according to Example 2. Fig.

It is generally known that the adhesion of the phosphate coating improves when the needle-shaped phosphate crystals in the coating are formed finely and densely. This is due to the anchoring effect.

However, as a result of research conducted by the inventors of the present invention, it has been found that the acicular phosphate crystals as described above improve the adhesion to the coating film, but rather reduce the adhesion to the film. Accordingly, the inventors of the present invention have conducted intensive studies to provide a phosphate coating having excellent adhesion to a film, and as a result, the following findings were obtained.

(1) In the case of a film, unlike the coating film, it is necessary to maximize the contact area between the phosphate crystal and the film in order to improve the film adhesiveness of the phosphate coating.

(2) Therefore, it is necessary to appropriately control the morphology of the phosphate crystals in the phosphate coating, and the phosphate crystals are formed into a rather long and thick shape in the width direction, It is possible to maximize the contact area.

Hereinafter, a phosphate-treated zinc plated steel sheet excellent in discoloration resistance and film adhesiveness, which is another aspect of the present invention, will be described in detail.

A phosphate-treated zinc plated steel sheet as one aspect of the present invention comprises a zinc plated steel sheet and a phosphate coating formed on at least one side of the zinc plated steel sheet. Examples of zinc-based plated steel sheets to be provided with the phosphate-treated zinc plated steel sheet of the present invention include zinc-plated steel sheets, hot-dip galvanized steel sheets, galvannealed galvanized steel sheets, Plated steel sheets can be used. At this time, in the present invention, the type and composition range of the alloying elements contained in the plating layer of the zinc plated steel sheet are not particularly limited.

The ratio of the three-dimensional surface area to the two-dimensional surface area of the phosphate coating by a laser microscope is preferably 1.7 to 8.8, more preferably 2.0 to 7.2, still more preferably 2.6 to 6.0. If the ratio is less than 1.7, although the phosphate crystals have a relatively round and thick form, most of the phosphate crystals are arranged obliquely with respect to the lamination direction of the zinc plated steel sheet and the phosphate coating, do. On the other hand, if the ratio exceeds 8.8, the phosphate crystals are formed into a very dense needle-like shape, and the contact area with the film is small and the adhesiveness is deteriorated.

In the present invention, a specific method for measuring the ratio of the three-dimensional surface area to the two-dimensional surface area by the laser microscope of the phosphate coating is not particularly limited, but the following method can be used as an example. That is, the surface area ratio can be calculated by measuring the three-dimensional surface area and the two-dimensional surface area in the area of 100 μm × 100 μm using the analySIS equipment of Soft Image System. Specifically, the three-dimensional roughness is measured, The three-dimensional surface area of the phosphate coating can be measured by measuring the three-dimensional cross-sectional area of the phosphate crystals by the analysis equipment, and the two-dimensional surface area of the phosphate coating is measured by measuring the projection plane of the phosphate crystals by the analysis equipment And the surface area ratio can be calculated through the three-dimensional surface area and the two-dimensional surface area of the measured phosphate coating.

According to one example, the average circularity of the phosphate crystals of the phosphate coating may be 0.47 to 0.96, preferably 0.50 to 0.85, and more preferably 0.55 to 0.70. If the average circularity is less than 0.47, the phosphate crystals will have a typical hopeite shape, so that the contact area with the film is reduced, which may deteriorate the film adhesion. On the other hand, when the average circularity is more than 0.96, the phosphate crystals are arranged obliquely with respect to the lamination direction of the zinc-based plated steel sheet and the phosphate coating, and the contact area with the film is small. Here, the average circularity is obtained by averaging numerical values obtained by dividing the circumferential length by the circumferential length of the particle, assuming a circle having an area equivalent to the projected area of each irregularly shaped phosphate crystal. When the value is closer to 1, This means that there are many decisions.

According to an example, the number of phosphate crystals per unit area of the phosphate coating may be 0.3 to 2.3 / μm ² , preferably 0.5 to 2.1 / μm ² , more preferably 0.8 to 1.9 / [mu] m < ² >. If the number of particles per unit area is less than 0.3 pcs / μm ² , the phosphate crystals may be excessively coarsened, resulting in breakage or crumbling of the phosphate. On the other hand, if the particle size exceeds 1.7 pcs / μm ² , The size of the crystal is too small to secure a sufficient amount of adhesion, and therefore, the oxidation discoloration resistance and the like may be poor, and it may be difficult to sufficiently maintain the adhesive force with the film.

According to one example, the coating amount of the phosphate coating may be 0.5 to 2.3 g / m ² . If the adhesion amount of the film is excessively low, there is a possibility that the desired film adhesion can not be secured. Therefore, the lower limit of the coating amount is preferably 0.5 g / m ² , more preferably 1.0 g / m ² . However, if it is too thick, the durability is poor, and the phosphate film may easily fall off due to an external impact. Therefore, the upper limit of the coating adhesion amount is preferably 2.3 g / m ² , more preferably 1.5 g / m ² .

The phosphate-treated zinc plated steel sheet according to the present invention is excellent in discoloration resistance and film adhesiveness and can be suitably applied as a substrate for a laminating steel sheet. Furthermore, the phosphate-treated zinc plated steel sheet produced according to the present invention can be suitably applied to a plastic laminated steel sheet. According to one example, the phosphate-treated zinc plated steel sheet according to the present invention may have a whiteness deviation (? L ^* ) of 2.0 or less after 24 hours under constant temperature and humidity conditions at a temperature of 50 ° C and a relative humidity of 95%. Here, the whiteness deviation refers to the difference in whiteness before and after the lapse of 24 hours.

Hereinafter, a preferred example for producing a phosphate-treated zinc plated steel sheet excellent in discoloration resistance and film adhesiveness will be described in detail.

First, zinc plated steel sheet is prepared. As described above, the zinc-base plated steel sheet to be provided with the phosphate-treated zinc plated steel sheet of the present invention includes, for example, an electro-galvanized steel sheet, a hot-dip galvanized steel sheet, a galvannealed galvanized steel sheet, And the like. In the present invention, the kind and composition range of the alloy element contained in the plating layer of the zinc-based plated steel sheet are not particularly limited.

Thereafter, the surface of the zinc plated steel sheet is degreased. This step removes the oil attached to the surface of the zinc plated steel sheet. This step is carried out in order to prevent the phosphate coating from being formed due to the obstruction of the etching in the presence of oil on the surface of the zinc plated steel sheet.

Thereafter, the surface of the degreased zinc plated steel sheet is surface-adjusted with a surface conditioner. When the zinc plated steel sheet is subjected to the degreasing process, the surface of the steel sheet loses almost the active points of the structure, and when the phosphate film is formed immediately after the degreasing process, a coarse and coarse coating is obtained. Therefore, it is preferable to perform the surface conditioning treatment to increase the number of active points by applying free energy to the surface of the degreased zinc-based plated steel sheet before forming the phosphate coating.

In the present invention, the method of surface conditioning treatment is not particularly limited, but can be carried out by immersing the degreased zinc plated steel sheet in the surface conditioning agent and then squeezing.

According to one example, the surface conditioning agent used for the surface adjustment may be a titanium colloid-based active treating agent.

According to one example, the content of titanium contained in the titanium colloid-based treating agent may be 0.05 to 0.6% by weight, and preferably 0.2 to 0.4% by weight. If the content of titanium is less than 0.05% by weight, the phosphate crystals may become too coarse. On the other hand, when the content of titanium exceeds 0.6% by weight, the phosphate crystals may become excessively dense and may be formed into an acicular shape.

Thereafter, a phosphate coating is formed on the surface of the zinc plated steel sheet subjected to the surface adjustment treatment by using a phosphate solution. At this time, the phosphate solution may have the following composition and acid ratio.

Zn ^{2 +:} 500 ~ 2000ppm

Zinc ions are an essential component for forming phosphate crystals. If the content is excessively low, there is a problem that the phosphate crystals are formed coarse and non-uniformly. Therefore, it is preferable that the content is 500 ppm or more, more preferably 800 ppm or more. However, if the content is excessive, the phosphate crystals are formed in a very dense needle-like form, which results in a problem that the film adhesion is deteriorated. Accordingly, the content is preferably 2000 ppm or less, more preferably 1700 ppm or less.

Ni ⁺ : 50 to 1000 ppm

Nickel ions are components added to improve the corrosion resistance, heat resistance and film adhesion of the phosphate coating. In order to exhibit such an effect in the present invention, it is preferable that it is contained in an amount of 50 ppm or more, more preferably 300 ppm or more. However, if the content is excessive, the phosphate crystals are formed into a very dense needle-like shape, which causes a problem that the film adhesiveness is deteriorated. Accordingly, the content is preferably 1000 ppm or less, and more preferably 400 ppm or less.

Mg ^{2 +:} 3000 ~ 40000ppm

Magnesium ions are components added to improve the corrosion resistance, heat resistance and film adhesion of the phosphate coating. Further, in the present invention, the phosphate crystals in the phosphate coating are not needle-shaped, but are a component that plays a major role in forming a short, long, and thicker shape in the width direction. In the present invention, it is preferable to contain not less than 3000 ppm, more preferably not less than 5000 ppm, and even more preferably not less than 8000 ppm. However, if the content thereof is excessive, there is a problem that not only the phosphate crystals which are too round and round like the phosphophyllite structure are formed but are not advantageous for improving the adhesion, and the physical properties such as corrosion resistance and heat resistance are deteriorated. Therefore, it is preferable that the content is not more than 40000 ppm, more preferably not more than 30000 ppm, and even more preferably not more than 20000 ppm.

On the other hand, the concentration of PO ₄ ^{3 -} contained in the phosphate solution may be 5000 to 40000 ppm. If the concentration of PO ₄ ^{3 -} contained in the phosphate solution is too low, the oxidation and reduction reaction with the free acid may be insufficient and the phosphate crystals may become coarse. Therefore, the concentration of the PO ₄ ^{3 -} is preferably controlled to be 5000 ppm or more, more preferably 6000 ppm or more. However, if the content is excessive, not only the phosphate film becomes excessively thick but also the etching becomes excessive and the adhesion with the substrate may deteriorate. Therefore, the concentration of PO ₄ ^{3 -} is preferably controlled to 40,000 ppm or less, more preferably 30,000 ppm or less.

The phosphate solution may further include NO ₃ ^- , and in this case, the NO ₃ ^- concentration may be 5000 to 40000 ppm. The above nitrate ions act as accelerators and can be put in the form of HNO ₃ or NaNO ₃ . If the concentration of NO ₃ ^- is excessively low, the thickness of the phosphate coating may become too thin and the reaction may be deteriorated. Therefore, the concentration of NO ₃ ^- is preferably controlled to 5000 ppm or more, more preferably 6000 ppm or more, but if the content is excessive, the amount of phosphate adhered is excessively increased and the grain size becomes excessively fine The adhesive strength may be lowered. Therefore, the concentration of NO ₃ ^- is preferably controlled to be not more than 40,000 ppm, and more preferably not more than 30,000 ppm.

The phosphate solution may have an acidity (degree of acidity / free acidity) of 2 to 20. The acid ratio is one of the most important factors among the solution management items. If the acid ratio is too low, there is a possibility that the etching does not occur well and the phosphate coating is not formed well. Therefore, the lower limit of the acid ratio is preferably 2, more preferably 8. However, if the acid ratio is too large, the amount of phosphate adhered excessively, the size of the phosphate crystal becomes too fine, and the adhesion may be deteriorated. Therefore, the upper limit of the acid ratio is preferably 20, more preferably 15.

In the present invention, the method of forming the phosphate coating is not particularly limited, but it can be carried out by immersing the zinc-plated steel sheet subjected to the surface adjustment treatment in the phosphate solution or spraying the phosphate solution on the surface thereof.

According to one example, at the time of forming the phosphate film, the surface temperature of the zinc plated steel sheet may be 50 to 70 ° C. If the surface temperature is less than 50 캜, the activity is low and the reaction occurs slowly, which may lower the productivity. However, if the surface temperature is too high, it is not economically disadvantageous, and it is not preferable since the etching is rapid and a lot of slurry is formed. Therefore, the upper limit of the surface temperature is preferably controlled at 70 캜, more preferably at 60 캜.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate and specify the present invention and not to limit the scope of the present invention. And the scope of the present invention is determined by the matters described in the claims and the matters reasonably deduced therefrom.

( Example  One)

First, unlike only different conditions while both fixed, Phosphate solution of Zn ^{2 +} concentration to prepare a total of 9 samples, and observing the form (morphology) of the phosphate crystal with respect to the prepared each specimen and evaluate the film adhesive Respectively. At this time, phosphoric acid solution containing 350 ppm of Ni ⁺ , 10000 ppm of Mg ^{2 +} , 20000 ppm of PO ₄ ^{3 -} , and 25000 ppm of NO ₃ ^- and having an acid ratio of 10 was used in the preparation of all specimens (Zn ^{2 +} The surface temperature of the zinc plated steel sheet was 55 ° C and the coating weight of the coating film was 1.3 to 1.5 g / m < 2 > m ² .

Then, the surface of each of the prepared specimens was observed with a scanning electron microscope (SEM), and the results are shown in Fig. 1 and Table 2 below. Here, FIGS. 1A to 1G are SEM images of the surfaces of the test pieces 1-1 to 1-7, respectively.

Then, the discoloration resistance and film adhesion of the prepared specimens were evaluated. Specific evaluation methods and evaluation criteria for film adhesion are as follows. The film was laminated to the surface of each of the prepared specimens, and the film was peeled off at 5 mm × 5 mm cross-cut at a room temperature after 8 mm Erickson, and the film was peeled for 2 hours in a thermostat (65 ° C., 95% And the film was peeled off. As a result of observations, if the film is not peeled off at all, '5', if it is removed with a sharp material such as a knife at the processing site, '4' 3 ', cross-cut and Ericsson sites were evaluated as'2' when the film was peeled off and '1' when the film was peeled off. The results are shown together in Table 2 below.

Psalm name Psalm 1-1 Psalm 1-2 Psalm 1-3 Psalm 1-4 Psalm 1-5 Psalm 1-6 Psalm 1-7 Zn ^{2 +} concentration (ppm) 400 500 800 1000 1500 2000 3500

Psalm name Surface area ratio Average
Circularity Number per unit area (pieces / μm ² ) The whiteness deviation (? L) Film adhesion evaluation result Remarks Psalm 1-1 1.2 0.33 0.1 2.21 2 Comparative Example 1-1 Psalm 1-2 2.0 0.51 1.5 1.12 4 Inventory 1-1 Psalm 1-3 3.2 0.58 1.3 1.0 5 Inventory 1-2 Psalm 1-4 4.3 0.61 1.0 0.8 5 Inventory 1-3 Psalm 1-5 5.1 0.67 0.9 0.75 5 Exhibit 1-4 Psalm 1-6 6.1 0.72 0.7 1.10 4 Background 1-5 Psalm 1-7 9.0 0.25 0.05 2.35 0 Comparative Example 1-2

Referring to Table 2, in the case of Zn ^{2 +} 1-5 Inventive Example 1-1 to satisfying levels proposed by the present invention, the film adhesion as well as excellent in, the brightness variation can check the Great as 2.0 or less.

On the other hand, in the case of Comparative Example 1-1, Zn ^{+ 2} concentration to less than the range proposed in the present invention, was not reactive in this phosphate phosphate crystals can not grow well enough, resulting in a small crystal size, sparse And the number per unit area was also small. As a result, both the film adhesion and the discoloration resistance to oxidation were found to be inferior. In Comparative Example 1-2 In, Zn ^{2 +} concentration was formed as the scope of the present invention than by graphite (hopeit) phosphate crystals typical call type to that proposed in, whereby the surface area ratio and the average circularity of all was smaller . As a result, the film adhesion was poor.

( Example  2)

Next, otherwise only the other conditions while both high solicited, the phosphate solution of the Mg ^{2 +} concentration to prepare a total of 10 samples, and observing the form (morphology) of the phosphate crystal with respect to the prepared each specimen, and the film adhesion . In this case, in all the specimens prepared 300ppm of Ni ^+, 1000ppm of Zn ^{2 +,} 20000ppm of PO ₄ ^{3 -,} 25000ppm of NO ₃ ^- including and sanbi was used as a 10-Phosphate solution (Mg ^{2 +} concentration to And the other conditions were the same as those in Example 1. [ The results are shown in Fig. 2 and Table 4 below. Here, FIGS. 2A to 2H are SEM images of the surfaces of the specimens 2-1 to 2-8, respectively.

Psalm name Psalm 2-1 Psalm 2-2 Psalm 2-3 Psalm 2-4 Psalm 2-5 Psalm 2-6 Psalm 2-7 Psalm 2-8 Mg ^{2 +} concentration (ppm) 2500 3000 8000 10000 15000 20000 40000 45000

Psalm name Surface area ratio Average
Circularity
Number per unit area (pieces / μm ² ) Whiteness
Deviation Film adhesion evaluation result Remarks Psalm 2-1 1.6 0.37 2.7 1.6 3 Comparative Example 2-1 Psalm 2-2 3.1 0.51 2.1 1.1 4 Inventory 2-1 Psalm 2-3 3.7 0.56 1.8 1.2 5 Example 2-2 Psalm 2-4 4.3 0.61 1.0 0.8 5 Examples 2-3 Psalm 2-5 5.1 0.64 1.3 0.6 5 Honorable 2-4 Psalm 2-6 5.9 0.69 0.9 0.6 5 Honorable 2-5 Psalm 2-7 1.7 0.82 0.5 2.0 4 Honorable 2-6 Psalm 2-8 1.3 1.09 0.1 2.7 0 Comparative Example 2-2

Referring to Table 4, in the case of Mg ^{2 +} 2-6 Inventive Example 2-1 to satisfying levels proposed by the present invention, the film adhesion as well as excellent in, the brightness variation can check the Great as 2.0 or less.

On the other hand, to less than the range proposed in the case of Comparative Example 2-1 invention are Mg ^{2 +} concentration of the phosphate crystals was not properly grown, so that the film adhesion and found to oxidation discoloration resistance is inferior both . In the case of Comparative Example 2-2, Mg ^{2 +} concentration appeared it is obliquely arranged lower surface area ratio for the stacking direction of the out of range by the majority of the phosphate crystal zinc-based plated steel sheet and phosphate film proposed by the present invention , And the average circularity was very large. As a result, the film adhesion was poor.

Claims (5)

And a phosphor coating film formed on at least one surface of the zinc plated steel sheet,
The ratio of the three-dimensional surface area to the two-dimensional surface area by the laser microscope of the phosphate coating is 1.7 to 8.8,
The three-dimensional surface area of the phosphate coating is determined by measuring the three-dimensional roughness of the phosphate crystals, calculating the height, and then calculating the three-dimensional surface area of the phosphate coating by measuring the three- Wherein the surface area is obtained by measuring a projection plane of the phosphate crystals and calculating a two-dimensional surface area of the phosphate coating.
The method according to claim 1,
Wherein the average degree of circularity of the phosphate crystals of the phosphate coating is from 0.47 to 0.96.
The method according to claim 1,
Wherein the number of phosphate crystals per unit area of the phosphate coating is 0.3 to 2.3 pcs / μm ² .
The method according to claim 1,
Wherein the coating amount of the phosphate coating is 0.3 to 2.3 g / m ² .
The method according to claim 1,
A phosphated zinc plated steel sheet having a whiteness deviation (ΔL ^* ) of not more than 2.0 after 24 hours under constant temperature and humidity conditions of a temperature of 50 ° C. and a relative humidity of 95%.

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