JPH11323569A - Phosphate solution for galvanized steel sheet and phosphate treated galvanized steel sheet and as its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phosphate solution for treating a galvanized steel sheet capable of forming a film having good post-coating corrosion resistance and whiteness and a phosphate treated steel sheet of whiteness (L value) of >=70 using the treating liquid. SOLUTION: This phosphate solution for treating the galvanized steel sheet contains 4 to 10 g/L NO3 , 0.01 to 0.14 g/L Ni<2+> , 4 to 7 g/L Zn<2+> and 0.1 to 10 g/L at least >=1 kind among malic acid, citric acid, gluconic acid and their slat or phosphate per 1 L soln. in the phosphate solution in the method for subjecting the galvanized steel sheet to the phosphate treatment. The whiteness (L value) of the appearance of the galvanized steel sheet after the phosphate treatment is >=70. The phosphate treated galvanized steel sheet is formed by using the phosphate solution described above. Its Zn coating weight is 0.1 to 200 g/m<2> , its phosphate coating weight thereof is 0.1 to 5 g/m<2> , the whiteness (L value) of its plating appearance is >=70 and the grain size of the phosphate crystal is <=40 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to home appliances, building materials,
The present invention relates to a phosphating solution and zinc-plated steel sheet having excellent whiteness and used for industrial products such as steel sheets for automobiles and OA equipment, and a method for producing the same.

[0002]

2. Description of the Related Art In general, post-treatment of an electrogalvanized steel sheet is performed for the purpose of improving the corrosion resistance, paint adhesion, and corrosion resistance after coating of a coated steel sheet, and typically includes chromate treatment and phosphate treatment. Is done. Of these, phosphate treatment
A phosphate treatment film is formed on the galvanized layer using a first zinc phosphate and a treatment solution containing phosphoric acid as a main component. Here, this phosphating solution is made of zinc phosphate 1
Phosphoric acid is a main component, and a small amount of Ni ²⁺ is added to improve coating performance, and a small amount of NO ₃ ⁻ and a small amount of fluorine ion are added for the purpose of promoting film formation. Such treatment liquid phosphate conversion coating derived from the case of the _{zinc-plated, Zn 3 (PO 4) 5} · 4H
₂ O (hopite) as the main component and Zn ₂ Ni (P
_{O 4) 5 · 4H 2 O} ( phosphosilicate Nico light), or made amorphous metal such as Ni, has good corrosion resistance after painting.

[0003] However, the color tone of the phosphatized film is dark gray as compared with zinc plating. Since the color tone of the film affects the appearance of the finish and the required film thickness particularly when a white paint is applied, it is desired from the user side to be as white as possible. As an index of whiteness, an L value of about 70 is desired. To meet such requirements, for example, as in JP 59-107084 JP, NO ₃ ^- a method of obtaining a high degree of whiteness steel sheet by using a high concentration of the treatment liquid, JP 62-474
No. 88, when continuously subjecting an electrogalvanized steel sheet to phosphate treatment, the Zn / Ni weight ratio is 10 to 20.
Galvanizing to obtain a treated steel sheet having whiteness (L value of about 60 or more) stably by maintaining the concentration of zinc and nickel in the treatment bath within a certain range by using a phosphating treatment replenishing solution A method for phosphating steel sheets has been proposed.

[0004]

However, the method disclosed in Japanese Patent Application Laid-Open No. Sho 59-107084 described above is intended to reduce the whiteness by increasing the NO ₃ ^- concentration in the processing solution to 2.5 to 5.0 g / L or more. Although a treated steel sheet of 60 or more can be obtained, the reactivity of the treatment solution is improved by increasing the NO ₃ ^- concentration, and giant phosphate crystals and crystals with an excessive amount of deposition are deposited. This results in a phosphate treated film having poor corrosion resistance after painting. According to the method disclosed in Japanese Patent Application Laid-Open No. Sho 62-47488, the whiteness of an electrogalvanized steel sheet is 60
It is inadequate as it can only be obtained. In other words, the fact is that the L value cannot be increased to a value of about 70 simply by reducing the concentration of Ni ²⁺ in the processing solution. That is, NO ₃
^With a change in bath concentration such as an increase in concentration or a decrease in Ni ²⁺ concentration, it was almost impossible to obtain the required L value as a normal treated film. In view of such a situation, the present inventors, for these problems or problems of the prior art, as a result of intensive research on phosphate-treated steel sheets, particularly high whiteness of electroplated steel sheets, The present inventors have proposed a phosphating solution and a treated steel sheet for an electrogalvanized steel sheet capable of forming a film having good corrosion resistance and high whiteness after painting, and a method for producing the same.

[0005]

It is a gist of the SUMMARY OF THE INVENTION its invention, (1) In the phosphating of galvanized steel sheet, NO in phosphate treatment solution ₃ ^-: _4~10g / L, Ni ²⁺ :
0.01 to 0.14 g / L, Zn ²⁺ : 4 to 7 g / L and at least one or more of malic acid, citric acid, gluconic acid and salts or phosphates thereof in an amount of 0.1 to 1 L per solution.
A phosphating solution for a galvanized steel sheet, comprising 10 to 10 g / L and having a whiteness (L value) of 70 or more in appearance of the galvanized steel sheet after phosphating. (2) Using the phosphating solution described in (1) above,
Whiteness (L value) of plating appearance with plating weight of 0.1 to 200 g / m ² and phosphate weight of 0.1 to 5 g / m ²
A phosphate-treated galvanized steel sheet having a particle size of not less than 70 and a particle size of phosphate crystals of not more than 40 μm.

(3) The treated steel sheet according to (2), wherein Ni or Ni-P is deposited on the cold-rolled steel sheet and the hot-rolled steel sheet in an amount of 0.001 to 1.0 g / m ^2. Zinc-based galvanized steel sheet. (4) A method for phosphating a galvanized steel sheet, wherein the phosphating treatment is performed using the phosphating solution described in (1).

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a phosphate treatment step according to the present invention. After a steel strip 2 unwound from an inlet coiler 1 exits a galvanizing tank 3, it is washed with a washing tank 4 and then washed. After the zinc phosphate suspension or the aqueous colloid titanate solution was sprayed or dipped in the phosphate pretreatment tank 5, it was sprayed or dipped in the phosphating tank 6 and phosphated. Thereafter, the substrate is washed with water in the washing tank 7 and dried to produce a phosphate-treated galvanized steel sheet.

However, the electrogalvanized steel sheet generally becomes dark gray due to the phosphate treatment, and the surface whiteness is reduced. This is because, in order Ni is present in the processing solution, a white hopeite _{(Zn 3 (PO 4) 5} · 4H 2 O) simultaneously with the deposition, dark gray phosphotransferase Nico Light (Zn ₂ Ni ( This is because the phosphate film becomes dark gray due to the co-deposition of PO ₄ ) ₅ .4H ₂ O) and black amorphous Ni. Therefore, in order to prevent a decrease in whiteness due to the dark graying, it is necessary to use a bath composition for suppressing the precipitation of Ni in the phosphate film. However, Ni in the phosphating solution is indispensable for securing the adhesion of the paint, and it is not preferable to make it zero.

FIG. 2 shows the effect of Ni ²⁺ concentration in the phosphating solution on paint adhesion. here,
Paint adhesion was evaluated by Amirac # 10 manufactured by Kansai Paint Co.
00 after coating and baking 20 μm with a bar coater.
The sample was immersed in distilled water at 0 ° C. for 30 minutes, and the tape peeling of a 1 mm goban was measured. ○: No peeling, Δ: 1 to 10 peeling,
X: The number of peeling was 10 or more. From the figure, Ni in the bath
^{If the 2+} concentration is less than 0.01 g / L, the paint adhesion rating is Δ or ×, and the paint adhesion is insufficient. on the other hand,
When the Ni ²⁺ concentration in the bath was 0.01 g / L or more, all the marks were ○, indicating that the Ni ²⁺ concentration in the bath was 0.01 g / L.
g / L or more is required.

Normally, in an electroplating line, pure zinc plating and zinc-nickel alloy plating may be alternately manufactured, and a slight amount of zinc-nickel plating solution is mixed into pure zinc plating solution. A trace amount of Ni may be eutectoid in the plating layer. In such a galvanized steel sheet, although the corrosion resistance of the plated layer is improved by the action of Ni, the problem arises that the concentration of Ni ²⁺ in the treatment solution increases because the plated layer is dissolved during the phosphate treatment. . As described above, the Ni ²⁺ concentration in the treatment liquid decreases the L value of the phosphate treatment film. Therefore, Ni ²⁺
The concentration depends on the eutectoid deposition on the phosphate treatment film, the consumption rate due to the liquid flowing out of the treatment tank and the dissolution of Ni in the galvanized layer,
Since it is determined by the balance with the supply rate due to the addition of Ni ²⁺ in the replenisher, it cannot be determined uniquely.

[0011] The present inventors have proposed that Ni in the phosphating solution is²⁺
The relationship between the concentration and the L value of the resulting phosphated coating
As a result of various changes in the concentration, as shown in FIG.
The result was obtained. FIG. 3 shows that NO in the phosphating solution_Three ^-Dark
Looking at the effect of the degree, Ni²⁺If the concentration is the same
NO_Three ^-As the concentration increases, the L value increases, but NO_Three ^-
When the concentration exceeds 10 g / L, the effect is saturated.
Become. NO_Three ^-If the concentration is less than 4 g / L, Ni²⁺Dark
Even if the degree is 0.01 g / L or less, ensure that the L value is 70 or more.
Can not be. Therefore, NO_Three ^-The concentration is 4 to 10 g / L
And Also, Ni²⁺Looking at the concentration, 0.1
NO when exceeding 4 g / L_Three ^-Increase the concentration to 10 g / L or more
Even if the L value cannot be secured 70 or more, the above-mentioned Ni addition
Considering the effect of improving paint adhesion by²⁺The concentration is 0.
01 to 0.14 g / L.

Further, NO in FIG. 4 is phosphate treatment solution ₃ ^-
FIG. 4 is a diagram illustrating a relationship between a concentration and a Zn ²⁺ concentration. NO ₃ ^- is Z
It is preferable to add n (NO ₃ ) ₂ mainly as a residual HNO ₃ agent in view of the balance of the hydrogen ion concentration of the processing liquid. Therefore, the concentration of Zn ²⁺ in the phosphating solution was NO ₃ ⁻
And the concentration of Zn ²⁺ and NO ₃ ⁻ in the bath is balanced in a certain range, and the range is Zn
It was found that it was necessary to control the ²⁺ concentration in the range of 4 to 7 g / L.

In the present invention, it is necessary to add at least one or more of malic acid, citric acid, gluconic acid, a salt thereof, and a phosphoric acid ester (hereinafter, simply referred to as an organic acid) to the phosphating solution. . Examples of the organic acid salt include alkaline earth metal salts, alkali metal salts, ammonium salts, and heavy metal salts. The organic acid has a function of forming a dense and fine phosphate film and improving whiteness and corrosion resistance after coating even when a large amount of NO ₃ ^- having a phosphate film promoting action is added. Although its mechanism of action is unknown, it is thought to act as a certain inhibitor of film formation.

FIG. 5 shows the relationship between the concentration of the organic acid and the amount of the phosphate film deposited. At this time, the Ni ²⁺ concentration was 0.10 g / L,
The NO ₃ ^- concentration was set to 5.2 g / L. When the crystal grain size of the phosphate crystal of the present invention exceeds 40 μm, the crystal performance becomes poor due to embrittlement or skewing of the crystal. Therefore,
The acceptable range was a phosphate crystal grain size of 40 μm or less. NO from 5 ₃ ^- in order to obtain a good phosphate crystals in a large amount addition treatment solution is at least phosphating solution 1L
0.1 g / L is required, and if it exceeds 10 g / L, the effect is saturated and the adverse effect on the paint adhesion is feared.

As the base steel sheet, a cold-rolled steel sheet, a hot-rolled steel sheet or the like can be used, and the Zn plating may be either electrogalvanizing or hot-dip galvanizing. Further, an alloying metal may be contained in the galvanized layer, and Zn-Fe, Zn-N
i, Zn-Co, Zn-Cr, Zn-Fe-Ni, Zn
-Alloy plating of Fe-Co, Zn-Fe-Ni-Co, etc. can be applied. Furthermore, N between the Zn plating and the base iron
By applying a base plating such as i-plating or Ni-P plating, it is expected that Zn plating crystals will be fine and homogenous, and the L value will be further improved. The primary plating, it is possible to weight the plating deposition is well plated with an electroplating method or an electroless plating method, or the like at a coverage of about ^{0.001g / m 2 ~1g / m 2} .

[0016]

The present invention will be described more specifically with reference to the following examples. Using a device shown in FIG. 1, a cold rolled steel sheet was electrogalvanized to obtain a 20 g / m ² double-sided electrogalvanized steel sheet. Subsequently, after washing with water, a spray treatment was carried out at room temperature for 10 seconds with a surface conditioning liquid {Proparen Z (manufactured by Nippon Parkerizing Co.)} as a phosphate pretreatment. Then
In a phosphating tank, the phosphoric acid concentration: 7 g / L, the fluorine concentration: 0.5 g / L, the temperature: 55 ° C., the treatment time: 8 seconds, and the Ni in the phosphating solution as shown in Table 1 ²⁺ concentration, NO ₃
^The phosphate treatment was performed by changing the-concentration, the Zn2 ⁺ concentration and the organic acid concentration, followed by drying in a drier to obtain a phosphate treatment film.

Tables 1 to 3 show the properties of this phosphatized film such as whiteness (L value). Here, whiteness (L value)
Is the L value measured by a color computer manufactured by Suga Test Instruments Co., Ltd., and the phosphate film weight is obtained by peeling the film of a phosphate-treated steel sheet with a 45 g / L aqueous solution of chromic anhydride to obtain phosphorous before and after the treatment. It was calculated from the weight difference of the acid-treated steel sheet. Also,
The appearance of the coating was evaluated by observing the crystal grain size of the coating by observation with an electron microscope at a magnification of 1000 times, and at the same time, if the coating was a dense and uniform non-scaling phosphate coating, there was a large crystal, non-uniformity, and scaling. Poorly formed phosphate film was evaluated as x.

The corrosion resistance of the phosphate film after coating was evaluated by scratching the coated surface with a sharp cutter, corroding the coated surface with a salt spray method according to JIS Z2371 for 240 hours, and peeling off the cut portion with an adhesive tape. Then, the maximum peel width was evaluated. When the peeling width is less than 1 mm, ，, and when 1 mm or more and less than 5 mm, Δ, 5
x was set to mm or more. As described above, the coating adhesion was measured by applying Amilac # 1000 manufactured by Kansai Paint Co., Ltd. with a bar coater to a thickness of 20 μm, baking it, immersing it in distilled water at 100 ° C. for 30 minutes, and measuring the tape peeling of a 1 mm goban. ○: Number of peels: 0, Δ: Number of peels: 1 to 10, ×: Number of peels: 10 or more.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

In Tables 1 to 3, Examples Nos. 1 to 18
Is an example in which malic acid is added to the phosphating solution. Examples No. 1 and No. 5 are comparative examples in which the Ni ²⁺ concentration is out of the range of the present invention. No. 1 has poor corrosion resistance after coating and poor paint adhesion, and No. 5 has a low L value of 65. Example No. 6 is a comparative example in which the NO ₃ ^- concentration is out of the range of the present invention, and the L value is an insufficient value of 65. Examples No11 and No12 are comparative examples in which the Zn ²⁺ concentration is out of the range of the present invention, the L value is as low as 60 to 65, and the crystal grain size of the film is 45 to 46 μm, which is enlarged, and the appearance is large. Defects such as invisibility are seen, corrosion resistance after painting,
This is an example in which paint adhesion is also poor.

Example No. 13 is an example out of the range of the present invention in which an organic acid was not added. The L value was slightly low at 69, the film was excessively adhered, and the crystal grain size was enlarged to 50 μm. In addition, poor chemical formation was observed, and the corrosion resistance after coating and the paint adhesion were also poor. Example No. 18 is a comparative example in which malic acid was set higher than the range of the present invention. The L value was good, but the film weight was small and the crystal grain size was small. As a result, scum was generated and the film appearance was poor, and at the same time, the corrosion resistance after painting and the paint adhesion were poor.

Examples Nos. 19 to 23 are examples in which citric acid was added to the phosphating solution. Example No. 23 is an example in which citric acid was set higher than the range of the present invention. The L value was good, but the film weight was small and the crystal grain size was small. As a result, scum is generated and the film appearance is poor, and at the same time, the corrosion resistance after coating and the paint adhesion are poor. Examples Nos. 24 to 28 are examples in which gluconic acid was added to the phosphating solution. Example No. 28 is an example in which gluconic acid was set higher than the range of the present invention. The L value was good, but the film weight was small and the crystal grain size was small. As a result, scum is generated and the film appearance is poor, and at the same time, the corrosion resistance after coating and the paint adhesion are poor.

Examples Nos. 29 to 33 are examples in which sodium malate was added to the phosphating solution. Example No
Reference numeral 33 is an example in which sodium malate was set higher than the range of the present invention. The L value was good, but the film weight was small and the crystal grain size was small. As a result, invisibility occurs,
The film appearance was poor, and at the same time, the corrosion resistance after coating and the paint adhesion were poor. Examples Nos. 34 to 38 are examples in which sodium citrate was added to the phosphating solution. Example No. 38 is an example in which sodium citrate was set higher than the range of the present invention. The L value was good, but the film weight was small and the crystal grain size was small. as a result,
As a result, the film has poor appearance and has poor corrosion resistance and poor paint adhesion after coating.

Examples Nos. 39 to 43 are examples in which sodium gluconate was added to the phosphating solution. Example N
o43 is an example in which sodium gluconate was set higher than the range of the present invention, and although the L value was good, the film weight was small and the crystal grain size was small. As a result, scum is generated and the film appearance is poor, and at the same time, the corrosion resistance after coating and the paint adhesion are poor. Example No. 44-48
Is an example in which malic acid phosphate was added to the phosphating solution. Example No. 48 is an example in which the malic acid phosphate was set higher than the range of the present invention. The L value was good, but the film weight was small and the crystal grain size was small.
As a result, scum is generated and the film appearance is poor, and at the same time, the corrosion resistance after coating and the paint adhesion are poor.

Examples Nos. 49 to 53 are examples in which a citrate phosphate was added to a phosphating solution. Example N
o53 is an example in which the citrate phosphate was set higher than the range of the present invention, and although the L value was good, the film weight was small and the crystal grain size was small. As a result, scum is generated and the film appearance is poor, and at the same time, the corrosion resistance after coating and the paint adhesion are poor. Example No. 49-5
3 is an example in which a citrate phosphate was added to the phosphating solution. Example No. 53 is an example in which the citrate phosphate was set higher than the range of the present invention. The L value was good, but the film weight was small and the crystal grain size was small. As a result, scum is generated and the film appearance is poor, and at the same time, the corrosion resistance after coating and the paint adhesion are poor.

Examples Nos. 54 to 58 are examples in which a gluconic acid phosphate was added to a phosphating solution. Example No. 58 is an example in which the gluconic acid phosphate was set higher than the range of the present invention. The L value was good, but the film weight was small and the crystal grain size was small. As a result, scum is generated and the film appearance is poor, and at the same time, the corrosion resistance after coating and the paint adhesion are poor. Example No. 59
No. 62, No. 64 to 67, and No. 69 to 72 are examples in which a plurality of organic acids, organic acid sodium salts, and organic acid phosphates are used in combination, all of which have good phosphate film performance. On the other hand, Examples 63, 68, and 73 are examples in which the organic additive was set higher than the range of the present invention,
The L value is good, but the film weight is small and the crystal grain size is small. As a result, scum is generated and the film appearance is poor, and at the same time, the corrosion resistance after coating and the paint adhesion are poor.

Examples Nos. 2 to 4, Nos. 7 to 10, No. 1
4-17, No19-22, No24-27, No29
~ 32, No34 ~ 37, No39 ~ 42, No44 ~
47, No49-52, No54-57, No59-6
2, Nos. 64 to 67 and Nos. 69 to 72 are examples of the present invention. In each case, the L value shows a very high value of 70 to 73, and the appearance of the film, corrosion resistance after painting, paint adhesion. Both have good and excellent film performance.

[0030]

As described above, according to the present invention, a phosphate-treated steel sheet having a high whiteness (L value) can be stably produced without deteriorating the paint adhesion, which is the performance of the phosphate-treated steel sheet. It can be obtained and has an industrially excellent effect.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a phosphate treatment step according to the present invention;

FIG. 2 is a diagram showing a relationship between Ni ²⁺ concentration in a phosphating solution and coating adhesion.

FIG. 3 shows the Ni ²⁺ concentration and whiteness (L
Values),

FIG. 4 is a diagram showing the relationship between the NO ₃ ⁻ concentration and the Zn ²⁺ concentration in the phosphating solution;

FIG. 5 is a graph showing the relationship between the concentration of organic acids (malic acid, citric acid, and gluconic acid) in the phosphating solution and the phosphate crystal particle diameter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inlet-side coiler 2 Steel strip 3 Galvanizing tank 4 Rinse tank 5 Phosphate pretreatment 6 Phosphate treatment tank 7 Sealing tank 8 Outlet coiler

Claims (4)

[Claims] In a phosphating treatment of a galvanized steel sheet, NO ₃ ⁻ in a phosphating solution is from 4 to 10 g / L,
i2 ⁺ : 0.01 to 0.14 g / L, Zn2 ⁺ : 4 to 7 g / L
L and at least one or more of malic acid, citric acid, gluconic acid and salts or phosphoric esters thereof are contained in an amount of 0.1 to 10 g / L per 1 L of the solution, and the appearance of the galvanized steel sheet after the phosphate treatment. A phosphating solution for a galvanized steel sheet having a whiteness (L value) of 70 or more. ^{2. The} plating appearance using the phosphating solution according to claim 1 with a Zn plating coating weight of 0.1 to 200 g / m ² and a phosphate coating weight of 0.1 to 5 g / m ² . A phosphate-treated zinc-based plated steel sheet, characterized in that the whiteness (L value) is 70 or more and the particle size of phosphate crystals is 40 μm or less. 3. The treated steel sheet according to claim 2, wherein Ni or Ni—P is present on the cold-rolled steel sheet and the hot-rolled steel sheet in an amount of 0.00%.
A phosphate-treated galvanized steel sheet having 1 to 1.0 g / m ² deposited thereon. 4. A method for phosphating a galvanized steel sheet, comprising phosphating with the phosphating solution according to claim 1.