JPS62263997A - Surface-treatment of steel sheet surface-treated with metal - Google Patents

Abstract

PURPOSE:To stably form a film having fine appearance, superior corrosion resistance and paintability by cathodically electrolyzing a steel sheet surface- treated with a metal in a chromating soln. to form a chromate film and by anodically electrolyzing the steel sheet at once. CONSTITUTION:A steel sheet surface-treated with a metal such as a galvanized steel sheet is cathodically electrolyzed in a chromating soln. to form a chromate film. The steel sheet is anodically electrolyzed at once to modify the chromate film as well as to form a new film. A soln. prepd. by adding Cr<6+>, PO4<3->, a fluorine compound, silica and a silicate to a conventional electrolytic soln. for cathodic electrolysis is suitable for use as the chromating soln. The anodic electrolysis is carried out at about 1-50A/dm<2> current density and ordinary temp. - about 80 deg.C with about 0.1-30C/dm<2> electricity.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides the appearance, corrosion resistance,
and a cathode electrolytic film with excellent coating performance, and an anode 11[
The present invention relates to a surface treatment method for a metal surface-treated steel sheet, in which a composite chromate film consisting of a film is entirely formed.

The metal surface-treated steel sheets herein include zinc and zinc alloy plated steel sheets, lead and lead alloy plated planer sheets, aluminum, and aluminum alloy plated w4&.

Specifically, zinc-plated and zinc alloy-plated copper sheets include: (a) Galvanized steel sheets that contain elements that are unavoidably mixed in as impurities during plating by air plating or vacuum evaporation plating; (b) At 0.1-0.3%, Pb as other substances
, Cd, Fe.

Bath-dipped galvanized copper plate containing one or more elements such as sb and unavoidable impurity elements (c) Fe'
iz5~90chi and unavoidable impurity element Kanakura Fa −
Zn alloy-plated steel sheet (dl) Zn-Ni alloy-plated copper sheet (e) containing 5-20% Ni and unavoidable impurity elements, containing 3-60% Alt, or this K
Si, Mg'.

Mitsushi metal or unavoidable impurity*'t-containing Zn-
Examples of lead-plated and lead-alloy plated steel sheets include: (a) lead-plated steel sheets containing unavoidable impurities during the d-building process; (b) lead-plated steel sheets containing 3096 or less Sn;扛, sometimes sb.

Examples include Pb-Sn alloy plated steel sheets that contain Zn or other unavoidable impurity elements.Furthermore, aluminum and aluminum alloy plated steel sheets include: Aluminized steel plate (b) contains one or more of Si and Mg, and contains Si
Examples include aluminum alloy-plated steel sheets in which Mg is 12% or less, or Mg is 5% or less.

(Prior art) Electrolytic chromate treatment technology for metal surface-treated steel sheets has already been applied to galvanized steel sheets in Japanese Patent Publication No. 47-44417.
(Method of cathode 'iW4 treatment with Cr05-H2SO4 treatment solution), JP-A-60-110896 Cr
method of cathodic electrolytic treatment with O3-5i02 treatment solution), and
For steel sheets plated with alloys of zinc, aluminum, tin, and the like, the methods disclosed in Japanese Patent Publication No. 14457/1987 (Cr03 - various metal ions - cathode electrolytic treatment method with fluorine or salt cumulative treatment solution), etc. However, all of these methods involve forming a chromate film on the next surface of a metal surface-treated steel sheet by cathodic electrolytic treatment.

Generally, these cathode electrolytic coatings have good coating performance, but are said to have insufficient corrosion resistance.

Therefore, these cathode electrolytic coatings compensate for corrosion resistance by forming a large amount of coating (mainly chromium deposits). However, chromate coatings have the disadvantage of becoming discolored when the amount of coating increases, impairing the appearance of the treated material, and reducing coating performance. It was difficult to form.

Furthermore, in the case of cathodic electrolysis of galvanized steel sheets, when galvanized steel sheets and the like are continuously treated, Zn ions accumulate in the treatment solution, resulting in a significant decrease in corrosion resistance.

Next, regarding anodic electrolytic treatment, it is possible to form a chromate film by anodic electrolyzing a metal surface-treated steel sheet, but the resulting film has poor corrosion resistance and coating performance, and it is also difficult to form a chromate film on a galvanized steel sheet. However, according to Faraday's law, the metal of the material to be treated dissolves, making the treatment solution unstable, making it difficult to achieve industrially stable treatment.

(Problems to be Solved by the Invention) The present invention solves several drawbacks of conventional cathodic electrolytic chromate treatment technology, such as a decrease in corrosion resistance when the appearance is good and a decrease in corrosion resistance during a compliance treatment. Excellent appearance, corrosion resistance, and coating performance
The purpose is to industrially cheapen and form a film on the surface of a metal surface-treated steel sheet.

(Means for solving the problems) As a surface treatment method for gold-surface-treated steel sheets that solves the above problems, the results of various side-effects include cathodic electrolytic treatment with a chromate treatment solution, followed by cathodic electrolytic treatment immediately. A method has been developed for surface treating a gold FF4 surface-treated steel plate by a combined electrolytic treatment.That is, the gist of the present invention is to cathodic electrolytically treat a metal surface-treated steel plate using a chromate treatment solution. However, after forming the chromate film, it is necessary to immediately perform cathodic electrolytic treatment to form an anodic electrolytic film.
This is a method for surface treatment of a metal surface-treated steel sheet, characterized by subjecting the cathode electrolytic coating to a modification treatment.

(Structure of the Invention) The cathodic electrolytic treatment in the present invention is carried out to form a cathode film on the surface of a surface-treated steel sheet as a cathode. It is carried out according to the screen time. The current density and electrolysis time of cathodic electrolytic treatment are not specified, but the current density is 3 to 50
More preferable results can be obtained by adjusting the amount of film formed by adjusting the electrolysis time within the range of A7dm.

Next is anodic electrolysis, in which the surface-treated steel sheet on which the cathode electrolytic film has been formed is used as an anode, an anodic electrolytic film is formed, and the cathodic electrolytic film is modified. The current density is 1 for the anodic treatment.
~50Vdm2, particularly preferably F! , 5-40A/dm
, 3L-o7i is 0.1-30 coulombs/dm
% is particularly preferably carried out in the range of 2 to 20 coulombs/dm. When the current density is lower than IA/dm, it is difficult to form a good film and the corrosion resistance is poor.
Even if the p voltage is increased to 0 A/dm, there is no effect beyond that.

When the amount of coulombs is less than 0.1 coulomb/dm2,
Because the amount of film formed is small, the modification effect is poor, and the corrosion resistance is poor, even if the amount is more than 130 coulombs/dm.
There is no greater effect than that.

In addition, if the amount of coulombs is increased, the amount of dissolved metal that forms the plating film on the material to be treated, for example, the amount of zinc dissolved in the case of galvanized steel sheets, will increase, making the treatment solution unstable. Generally speaking, 30 coulombs/dm is considered to be the limit.

Next, regarding the chromate treatment liquid in the present invention, this chromate treatment liquid is for forming a film during cathodic electrolysis and anodic electrolysis after cathodic electrolysis, and the composition of the 1' treatment liquid is known. Although a cathode electrolytic treatment solution can also be applied, particularly preferred compositions of the treatment solution include: (a) chromate treatment solution containing Cr ions, PO43 ions and/or fluorine compounds; (b) Cr ions, silica and/or silicon salts. Miyamu's chromate treatment solution (c) is a chromate treatment solution containing Cr ions, PO4 ions and/or fluorine compounds, silica and/or silicate; Since it can be applied to both, cathodic electrolysis and anodic electrolysis can be performed with the same treatment solution, and cathodic electrolysis and anodic electrolysis can be electrolyzed with treatment solutions of different compositions. You can also do that.

As the Or ion in the chromate treatment solution, one or a mixture of chromic anhydride, dichromic acid, and alkali metal salts and ammonium salts of chromic acid and dichromic acid can be used. As 5-7.0?
Even more preferable results can be obtained by setting the amount within the range of /l.

Examples of PO43- ions include phosphoric acid, alkali metal salts of phosphoric acid, ammonium phosphate, etc., and examples of fluorine compounds include hydrofluoric acid, hydrofluorosilicic acid, hydrofluoroboric acid, and titanium hydrogen fluoride. 1, r! of acids, zircon hydrofluoric acid, salts of coconut, aluminum fluoride, etc. 11 or a mixture can be applied arbitrarily with a concentration of 1 and 1 to 100 as the sum of PO43- ions and fluorine compounds? More preferable results can be obtained by setting the value within the range of /L.

Silica and/or silicates are added to the processing solution to form colloidal silica, and one or a mixture of colloidal silica and alkali metal silicates can optionally be applied. 810°, 0.1 to 1
00? Even more preferable results can be obtained by setting the amount within the range of /l.

The pH of the treatment liquid is preferably 0.3 to 6, particularly FipHO
26-4. It is difficult to manufacture a treatment solution with a pH lower than 0.3 in order to confirm its effectiveness. In addition, even if the pH value is increased, the corrosion resistance of the coating device and the coating performance do not change;
The film formed during anodic electrolysis is colored yellow, so in order to form a film with a tJl-appearance, it is necessary to adjust the pH.
6 is the limit.

How can I control the pH of the processing solution? ji also acids, nitric acid, ammonium hydroxide, alkali gold hydroxide,
and alkali metal carbonate compounds, etc., and can be added to the treatment liquid. Furthermore, the Cr3+ ions generated by the reduction reaction during the cathodic electrolytic treatment of the present invention are preliminarily treated with C
As hydroxide and carbonate compounds of r, or C
It can also be added to the treatment solution as a redox reaction product between r 2 and organic compounds such as alcohols, tannic acid, and tannic acid. However, after the electrolytic treatment of the present invention (
After negative electrolysis (N4, anodic electrolysis treatment), when drying without washing with water, use is limited to ammonium hydroxide and Cr3+ ions.

The temperature of the treatment liquid is from room temperature to 80°C.

Even if the temperature is lower than 80°C, there is no change in the properties of the formed film, but it becomes uneconomical, so 80°C is the industrial limit.

According to the present invention, electrolytic treatment (after cathodic electrolysis, anodic electrolytic treatment)
The galvanized steel sheet is washed with water and then dried and applied for corrosion protection or as a base for painting, but it can also be applied after passing it through a squeegee roll and drying without washing. Further, if necessary, post-treatment with a chromate aqueous solution and an anticorrosive organic compound, which is generally performed, can also be carried out.

(Effects of the Invention) The present invention treats the surface of surface-treated steel sheets, that is, zinc and zinc alloy plated steel sheets, lead and lead alloy plated steel sheets, aluminum, and aluminum alloy plated steel sheets, with the above-mentioned chromate aqueous solution.
By carrying out a cathodic electrolytic treatment to form a chromate film, immediately carrying out an anodic electrolytic treatment to form an anodic electrolytic film, the cathodic electrolytic film is modified,
A cathode electrolytic coating with excellent appearance, corrosion resistance, and coating performance,
and an anodic electrolytic film to form a composite chromate film.

Generally, in order to improve corrosion resistance, chromate coatings produced by cathodic electrolysis are coated with a large amount of chromium, which results in coloring of the chromate coating, which impairs the appearance of the treated material and further reduces coating performance. In addition, in the case of galvanized steel sheets, if the galvanized steel sheets or the like are continuously treated, z n2 +(on) accumulates in the treatment solution, resulting in a significant decrease in corrosion resistance.

However, in the present invention, as shown in Table 1, after cathodic electrolysis,
By anodic electrolytic treatment, corrosion resistance can be significantly improved without damaging the appearance.

Furthermore, as shown in FIG. 1, for example, the present invention provides good corrosion resistance even if Zn ions accumulate in the treatment solution in the surface treatment of galvanized steel sheets. However, if the amount of chromium deposited is increased to improve corrosion resistance, the film will be colored, impairing the appearance of the treated material, and the coating performance will further deteriorate. The disadvantage that corrosion resistance is significantly reduced due to the accumulation of corrosion in the treatment liquid has been improved.
It can be stably obtained industrially. A similar effect can be obtained with respect to the accumulation of metal ions in the treatment liquid from the material to be treated in the case of other surface-treated steel sheets.

In the present invention, the preferred amount of chromium adhesion is 5 to 300
A more preferable range is 10 to 100 rrf/
It is m.

(Functions and Examples) In order to clarify the effects of the present invention, several Examples and Comparative Examples will be specifically described.

Example 1 As a result of comparison with an electrolytic galvanized copper plate cleaned by a known method, as shown in Figure 1, the electrolytically treated film of the present invention was compared with the conventional cathode electrolytic chromate aqueous solution. It exhibited good coating appearance, corrosion resistance, and coating performance.

[Treatment liquid composition 2 composition 1] Chromic anhydride 15 ? /A(Cr=7.8Vt
) (adjusted to pH 12 with sodium hydroxide) [Electrolysis conditions] ■ Cathode'electrolysis; current density = 20vdm2, electrolysis time =
2 seconds, temperature = 40°C ■ Anodic electrolysis; coulomb amount = o, 1.5.20 coulombs/dm2 (adjusted depending on blood flow density and electrolysis time), temperature = 40°C Comparative example-1 Example- 1, which was not subjected to anodic electrolytic treatment, is referred to as Comparative Example-1 and is shown in Table 1.

Example 2 An electrogalvanized steel sheet cleaned by a known method was treated with cathode 'a' under the following conditions, immediately treated with anodic X debris, washed with water after treatment, and dried. The sample was prepared as Example 2. , Comparative example-2
As a result of the comparison, as shown in Table 1, the electrolytically treated film of the present invention has a good film appearance and is superior to the conventional cathodic electrolytic chromate film and anodic electrolytic chromate film.
It showed excellent corrosion resistance and coating performance.

[Treatment liquid composition: Composition 2] Chromic anhydride 50j'/A (Cr = 26.0?/
l) Phosphoric acid (98ti) 20# (PO4-
19.3 iP/l as ions) (pH at this time is 0.
6) [Electrolysis conditions: cathode; current = 15 A7 dm2;
50°C■ 1st arm: Electric wire extension = 15A/dm2, 'φ knob = oaw: = 40°C (coulomb amount = 3 coulomb y/dm
) Comparative Example-2 An electrogalvanized copper plate cleaned by a known method was subjected to cathodic electrolytic treatment or anodic electrolytic treatment using the treatment solution of Example-2. The waste treated product is referred to as Comparative Example-2 and is rejected as the first batter.

Dog fan example - 3, 4, 5 An electrolytic galvanized steel sheet cleaned by a known method was subjected to cathodic electrolytic treatment and immediately anodic electrolytic treatment under the following conditions, and after treatment, it was washed with water and the dried sample was scraped. As a result of comparing Examples 3, 4, and 5 with Comparative Examples 3, 4, and 5, as shown in Table 1, the one-step treatment film of the present invention was compared with the conventional cathodic electrolytic chromate film. However, it exhibited good film appearance, excellent corrosion resistance, and coating performance.

Conditions for Example 3 [Treatment liquid composition: 2 sets of acids 3] Anhydrous oxide 50if/1 (Cr = 26.
0? /A) Snowtex-0100g (Colloidal solution containing Nissan Kagaku Mourning S s 0220) (pH adjusted to 3 with cyclic chromium carbonate) [Electrolysis conditions] ■ Cathode electrolysis; current density = 40A/dm2, electrolysis time =
1 second, temperature = 30°C ■ Anodic electrolysis; current density = 40A/dm.

Electrolysis time = 0.2 seconds, temperature = 30°C (Coulomb amount = 8 coulombs/dm) Conditions of Example-4 [Treatment liquid composition: Composition 4] Dichromated ammonium 100? /A(Cr=41
6t/l) Hydrofluorosilicic acid (40%) 50 A' (Fluorofluoric acid (30%) 16 (adjust pI to 5 with sodium carbonate) [ %L solution conditions] ■Cathode electrolysis; current density = 5 A/dm2, electrolysis time = 4 seconds, temperature -50°C ■Anodic electrolysis; current density = 5 A/dm.

Electrolysis time = 2 seconds, temperature = 50°C (Coulomb amount = 10 coulombs/dm) Conditions of Example-5 [Treatment liquid composition: Composition 5] Chromic anhydride 30 ? /LCCr”=15.6 mea
) Aluminum fluoride 1 (total of fluorine compounds is 1)
．． 5iI/l) Hydrofluoric acid (30t) 1.6〃
(Adjusted to pH'i5 with sodium carbonate) [Electrolytic conditions] ■ Cathode electrolysis; current density = 50 A/dm,'l
t solution time = 2 seconds, temperature: 30°C ■ Anodic electrolysis; turtle current density = 15 a/dm.

Electron time = O64 seconds, temperature = 30°C (Coulomb amount = 6 coulombs/dm2) Comparative Examples 3, 4, 5 Examples 3, 4, and 5 without anodic electrolysis treatment were Comparative Examples 3, 4, and 5 are shown in Table 1.

Example-6 An electrogalvanized steel sheet cleaned by a known method was subjected to cathodic electrolytic treatment and immediately anodic electrolytic treatment under the following conditions, and after the treatment, the sample was washed with water and dried. As a result of comparison with Comparative Example 6, as shown in Fig. 1, the waste treatment film of the present invention did not deteriorate its corrosion resistance even when Zn2+ ions were mixed into the treatment solution, and compared to the conventional Compared to the cathodic electrolytic chromate method coating, it showed excellent corrosion resistance.

[Treatment liquid composition: 2 acids 6 chromic anhydride 20 #/A (Or"=104j'/
A) (Add Zn io 10.1.3.61 to the above treatment solution.
After adding 1/l of zinc oxide, the p)I of each treatment solution was 2.
) [Electrolytic conditions] ■ Cathode 11L solution; 'Current density = 30A/dm.

Electrolysis time = 1.5 seconds, temperature = 30℃ ■ Anodic electrolysis; current density - 30A / dm s Electrolysis time 20.2 seconds, temperature = 30℃ (coulomb amount = 6 coulombs / dm) Comparative example - 6 Example Comparative Example-6, which was not subjected to anodic electrolytic treatment, is shown in Table 2.

Examples 7, 8, 9, 10 Vacuum deposited galvanized copper plate, Bath 1 galvanized steel plate, Zn-5% At alloy, cleaned by a known method.

Medium steel plate, At-10%81 alloy plated steel plate, and Pb-
A 10% alloy plated steel plate was subjected to cathodic electrolytic treatment and immediately anodic electrolytic treatment under the following conditions, and after treatment, the samples were washed with water and dried. Examples 7, 8, 9, and 10 were used as comparative examples. -7
, 8, 9, and 10, as shown in No. 3 and No. 4 Red, the recess treated anti-gland of the present invention is superior to the conventional cathodic chromate coating even in the bottom-treated steel sheets of Ir. Compared to the above, it showed a good film appearance, superior corrosion resistance, and coating performance.

The electrolytic treatment conditions in Examples 7, 8, 9, and 10 were all as follows.

[Electrolysis conditions] ■ Cathode electrolysis; current density = 20 A/dm, electrolysis time = 2 seconds, temperature = 40°C ■ Anodic electrolysis; current density = 20 A/dm,
Electrolysis time - 0.2 seconds, temperature = 40°C (coulombs = 4 coulombs/dm) [Treatment liquid composition of Example-7: Composition 7] Chromic anhydride 20? /1ccr -10,41
-/l) (adjust pFI to 2 with sodium hydroxide)
[Processing liquid composition of Example-8: Composition 8 Chromic anhydride 50 ? /1(Cr=10.4V
t) Snowtex-AK50/(Ichisan Kagaku 8102)
Colloidal solution containing 20% (F with sodium hydroxide) pH adjusted to 2) [Treatment liquid composition of Example-9: Composition 9] Anhydrous chromium e 80 Vt (Cr 6+ = 41.6
? /l) Hydrofluoric acid (20%) 50' (total of fluorine compounds is 14.81'll) Hydrofluoric acid (30%) 16" (adjust pH to 2 with sodium carbonate) Treatment liquid composition of Example-10 Composition 2 Composition 10" Chromic anhydride 30?/A (Cr6+=15.6?/L) Gloss) Comparative Examples-7, 8, 9, 10'
, 8, 9, and 10, and are shown in No. 3 and No. 4.

〔Evaluation methods〕

The degree of coloration of the appearance film was observed with the naked eye and evaluated on a four-level scale of (F), ○, △, and ×. The one with the least coloring is the best; ◎.

Corrosion resistance: Through salt spray test in accordance with JIS-Z-2371,
Judging the rusting state after a specific time with the naked eye, ・, ○, △, ×
Evaluation in 4 stages. ◎ is the best.

Painting performance (Painting - Apply a commercially available alkyd melamine white paint at 27 to 30 μm.) After cutting 100 squares of base marks at 1W intervals on the Erichsen test coating, extrude 7 times using an Erichsen tester, and use cellophane tape. Perform a peel test and judge the degree of peeling of the coating film with the naked eye, ◎, ○
Rated in 4 stages: , △, ×. ◎ is the best.

DuPont impact test Using a DuPont impact tester, apply an impact to the painted surface,
Judging the degree of peeling of the paint film with the naked eye, ◎, 01Δ, X 4
Evaluate in stages. O is the best.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the Zn ion concentration in the treatment solution and the corrosion resistance of the film in Examples.

Claims (1)

[Claims] A metal surface-treated steel sheet is subjected to cathodic electrolysis treatment with a chromate treatment solution to form a chromate film, and then immediately subjected to anodic electrolysis treatment to form an anodic electrolytic film, and at the same time, the cathodic electrolytic film is modified. A method for surface treatment of metal surface treated steel sheets.