JPH0254797A - Surface treatment of metal - Google Patents

Abstract

PURPOSE:To form a coating film having superior corrosion resistance, workability and adhesion to an org. coating film on the surface of a metal by adding specified amts. of specified cations and anions to a bath having a specified concn. of CrO3 and by electrolytically treating the surface of the metal as the cathode at a specified current density in the resulting bath. CONSTITUTION:A chromating bath contg. 0.05-1mol/l (expressed in terms of CrO3) chromic anhydride, chromate or dichromate is prepd. and 0.01-0.2gram ion/l one or more among Cu<2+>, Zn<2+>, Ni<2+>, Co<2+> and Mn<2+> and 0.001-0.02 gram ion/l Cl<-> and/or F<-> are added to the bath. The surface of a metal is electrolytically treated as the cathode at 0.1-40A/dm<2> current density in the resulting bath. By this surface treatment, a chromate coating film having superior corrosion resistance, workability and adhesion to an org. coating film is formed in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for surface treatment of metals, and is particularly aimed at improving the corrosion resistance and paint adhesion of metals.

Since the surface-treated steel sheet obtained by this treatment method has excellent corrosion resistance and paint adhesion, it can be used as a corrosion-resistant material for various home appliances, building materials, and automobiles.

[Conventional technology]

As is well known, electrogalvanized steel sheets, hot-dip galvanized steel sheets,
Alternatively, various alloy-plated steel sheets are widely used in automobiles, home appliances, building materials, and the like.

Under these circumstances, in recent years, there has been an increasingly strong demand for surface-treated steel sheets that have particularly excellent corrosion resistance, and the demand for such steel sheets is likely to increase further in the future.

For example, in the home appliance industry, there is a demand for a steel plate that has excellent corrosion resistance and can be easily used without painting in terms of process and cost savings. In addition, recent environmental changes have also occurred in the automobile industry, such as corrosion caused by rock salt, which is sprayed to prevent winter roads from freezing in North America and Northern Europe, and S
(Vehicle bodies are exposed to severe corrosive environments such as corrosion caused by acid rain caused by the generation of H gas, and from a safety standpoint there is a strong demand for surface-treated steel sheets with excellent corrosion resistance.

In order to solve these problems, various studies have been made and many products have been developed.

Until now, zinc plating has been used to improve the corrosion resistance of steel sheets.

Galvanized steel sheets prevent corrosion of the steel sheet through the sacrificial anticorrosive action of zinc, and in order to obtain corrosion resistance, the amount of zinc deposited must be increased. For this reason, there are several problems such as an increase in cost due to the amount of zinc required, and a decrease in workability, weldability, and productivity. Additionally, galvanized steel sheets generally have poor paint adhesion.

As a method for improving the corrosion resistance of such galvanized steel sheets, various alloy-plated steel sheets have been developed. These alloy-plated steel sheets include, for example, ZnNi-based, Zn-Ni
-Co series, Zn-Ni-Cr series, Zn -Fe series, Zn
Examples include -Co type, Zn-Cr type, Zn-Mn type, etc. It is recognized that these alloy platings improve the bare corrosion resistance by about 3 to 5 times compared to ordinary galvanized steel sheets. However, the problem is that white rust or red rust is likely to occur if left outside for a long period of time or if water or salt water is sprayed on it.

On the other hand, chromate treatment can be considered to improve corrosion resistance, but the chromate treatment method can ensure a sufficient amount of adhesion on the various alloy plating surfaces mentioned above and can obtain a chromate film with excellent adhesion. There are none.

Generally, when a chromate film is formed, the elution of ions from the base (material) is extremely important, and the chromate film is formed while reacting with the eluted ions. Therefore, the characteristics of the chromate film formed differ slightly depending on the type and amount of eluted ions.

Although the above-mentioned alloy-plated steel sheet has excellent corrosion resistance, this means that ions are difficult to elute, and a chromate film is difficult to form and a sufficient amount of adhesion cannot be ensured. That is, the better the corrosion resistance, the more difficult the chromate treatment becomes.

Chromate treatment methods can be broadly classified into electrolytic chromate, coating chromate, and reactive chromate methods, but the same can be said to a greater or lesser extent in all cases.

In addition, as a recent trend, in order to further improve corrosion resistance,
So-called simple pre-coated m-sheets (hereinafter referred to as organic composite steel sheets), which are zinc-plated steel sheets that are chromate-treated and coated with various resins, have been developed and some are commercially available.

The chromate film used as the base for such organic composite steel sheets must have excellent adhesion to the organic resin.

In addition, since these materials are subjected to harsh processing when used in rust-preventing steel plates for car bodies, etc., the chromate film must have excellent adhesion to the base material and organic resin, and be strong enough to withstand the processing itself. Must be.

Many of the chromate treatments for various types of plated steel sheets are already well known, and various chromate treatment methods have been developed and made appropriate.

For example, those containing chromic acid as the main component with the addition of sulfuric acid (Japanese Patent Publication No. 39-7461), and those containing phosphoric acid (Japanese Patent Publication No. 30-3514, Japanese Patent Publication No. 35-891)
Publication No. 7, Special Publication No. 36-9559, Special Publication No. 369
No. 560), with boric acid added (U.S. Patent No. 2)
733199, 2780592), halogen (
Ct-.

Cathode electrolytic treatment of steel sheets has been carried out using baths to which various anions are added, such as baths to which various anions are added, such as baths to which F-) is added (Japanese Patent Publication No. 39-14363).

[Problem to be solved by the invention]

However, chromate treatment can be easily applied to alloys with excellent corrosion resistance and various metals, can secure sufficient adhesion, has excellent adhesion to materials and organic coatings, and can withstand harsh processing. There are none.

Many of them are difficult to process into alloys with excellent corrosion resistance and various metals, and those with excellent corrosion resistance have poor paint adhesion, and conversely, those with excellent paint adhesion have poor corrosion resistance. Moreover, there is no material that can withstand harsh processing.

The purpose of the present invention is to solve the above-mentioned drawbacks of the conventional techniques and provide a chromate treatment method that provides a film that has excellent metal corrosion resistance and adhesion with an organic film, and has excellent workability. be.

[Means to solve the problem]

That is, in the present invention, Cu is added as a cation to a chromic acid bath.
, Zn, Ni, Co, and Mn ions, and one or more F- and CI- ions, and chromic anhydride, cations, and anions each contain specific By electrolytically treating the metal under specific electrolytic conditions using the metal as a cathode in a treatment solution that has been adjusted to a specific proportion and with a low concentration, a film can be formed on the metal in a very short time. By significantly improving the structure, corrosion resistance, and adhesion with organic coatings, the product value is significantly increased.

This excellent property cannot be obtained when the chromic anhydride bath contains only the above cations or only the above anions, nor can it be obtained even if the specific electrolytic conditions are deviated from the bath. It can only be obtained by a combination of composition and electrolytic conditions.

It was found that the following relationship must exist between chromic anhydride, cation, and anion in this case.

Concentration of chromic anhydride or chromate or dichromate converted to chromic anhydride = 0.05 to 1 mol/l ・・・・・・・・・
...(1) Dissolved Cu'', Zn+'', Ni
+'' (:o44. Number of Durham ions of Mn44 ions -0.01 to 0.2 g ions/l ・Old... (2)
Durham ion number of dissolved CI-, F- ions
-0,001 to 0.02 g ions/i! , ・・・
・(3) Current density when performing electrolytic treatment at the cathode = 0.1 to 40^/dm” ・・・・・・・・・・・・
・・・・・・・・・・・・(4) Above (1), (2),
It was confirmed that when a metal is electrolytically treated with a cathode under conditions that simultaneously satisfy conditions (3) and (4), the corrosion resistance and adhesion of the resulting film to the organic film are significantly improved. It has also been found that when the above conditions are simultaneously satisfied, a desired amount of chromate film can be deposited on any alloy or metal depending on the amount of electricity.

In Figure 1, (2), (3), and (4) are fixed, and (1)
The corrosion resistance of steel sheets when the concentration of chromic anhydride is changed is
FIG. 2 shows the adhesion with the organic film, and FIG. 3 shows the amount of Cr deposited.

That is, Zn-Ni alloy plated steel sheet (Ni=12%
) with 2.5g71 of Co44 and 0.25g/I of CI-
! , the current density when electrolyzing at the cathode is 5 A/d.
m", the amount of electricity is 5 C/dm" (constant), and C
Figure 1 shows the corrosion resistance when the concentration of rys was varied, and Figure 2 shows the adhesion to the organic resin when 2μ of a water-soluble polyacrylate resin was applied on the resulting chromate film. , and the relationship between the amount of Cr deposited is shown in FIG.

Figure 4 fixes (1), (3), and (4), and (2)
The corrosion resistance of the steel plate when the concentration of Co” ions is changed,
FIG. 5 shows the adhesion with the organic film, and FIG. 6 shows the relationship with the amount of Cr deposited.

That is, Zn-Ni alloy plated steel sheet (Ni=12%
) to Cr (h = 20g/42. CI- = 0.25g
'/ffi, cathode electrolysis current density = 5 A/dm''
, quantity of electricity = 5 C/dpeng2 (-constant), co+
Figure 4 shows the corrosion resistance when the concentration of + ions is varied, and Figure 5 shows the adhesion to the organic resin when 2μ of a water-soluble polyacrylate resin is applied on the resulting chromate film. and the relationship between the amount of Cr deposited is shown in FIG.

In Figure 7, (1), (2), and (4) are fixed, and (3)
FIG. 8 shows the relationship between the corrosion resistance of the steel sheet and the adhesion to the organic film when the concentration of C1- ions was changed, and FIG. 9 shows the relationship between the amount of Cr deposited.

That is, Zn-Ni alloy plated steel sheet (Ni=12%
) to Cr (h=20 g/E, Co+″2.5
g/1. Closing, cathode electrolysis current density -5A/dm"
, the amount of electricity = 5 C/dm” (constant), CI-
Figure 7 shows the corrosion resistance of steel sheets when the concentration of ions is changed, and Figure 8 shows the adhesion with organic resin when 2μ of a water-soluble polyacrylate resin is applied on the resulting chromate film. Furthermore, the relationship between the amount of Cr deposited is shown in FIG.

Figure 10 shows the corrosion resistance of the steel plate when (1), (2), and (3) are fixed and the cathode electrolysis current density is changed. Figure 11 shows the adhesion with the organic film. This shows the relationship between the amount of adhesion.

That is, Zn-Ni alloy plated steel sheet (Ni = 1
2%) to Cr (h = 20 g/l, Co” =
2.5 g/i! , CI-=0.25g#! Figure 10 shows the corrosion resistance of the steel plate when the binding and cathodic electrolytic current densities are changed, and the adhesion with the organic resin when 2 μm of a water-soluble polyacrylate resin is coated on the obtained chromate film is shown in Figure 10. This is shown in FIG. 11, and the relationship between the amount of Cr deposited is shown in FIG. 12.

Here, the corrosion resistance was determined by a salt spray test in accordance with the JIS-Z-2371 standard (salt water concentration 5%, tank temperature 35%).
The rusting state after 600 hours (°C1 spray pressure 20 psi) is shown and evaluated in five stages: ◎, O2Δ, X, and XX, with ◎ being the best.

◎ : Red rust occurrence 0% O: 〃 More than 0~1% △:〃 More than 1~10% × :l/ More than 10~50%XX: /
/ The adhesion of the 50% super organic resin was determined by applying an aqueous solution of polyacrylic acid ester to a thickness of 2μ after cathodic electrolytic treatment, drying at 120°C, boiling the applied test piece for 30 minutes, and then applying a 2mm goblin. The film was cut on the eye, peeled off with tape, and evaluated based on the peeled area.

◎: Peeling area 0% O: 〃 More than 0 to 1% Δ:〃 More than 1 to 10% X: // More than 10 to 50% XX:
As is clear from FIG. 1, when Cry is less than 0.05 mol/l and more than 1 mol/l, corrosion resistance decreases, and when it is 0.05 to 1 mol/l, excellent corrosion resistance is achieved. is obtained.

As is clear from Figure 2, the adhesion of the organic film formed on the surface is excellent when CrO+ is 0.05 to 1 mol/l, and deteriorates when it is less than 0.05 mol/l or more than 1 mol/l. .

As is clear from FIG. 3, Cry is 0.05 to 0.
At 1 mol/l, the amount of Cr attached can be stably ensured, but at 0
．． Cr less than 0.05 mol/l or more than 0.1 mol/l
The amount of adhesion is extremely reduced.

As is clear from Figure 4, excellent corrosion resistance is exhibited when Co'' is between 0.01 and 0.2 g ions/l, and corrosion resistance decreases when it is less than 0.01 g ions/l or more than 0.2 g ions/l. do.

As is clear from FIG. 5, the adhesion of the organic film is excellent in the range of 0.01 to 0.2 gram ion/litre of Co-;
If the amount is less than 0.01 gram ion/l or more than 0.2 gram ion/l, the adhesion will decrease.

As is clear from Fig. 6, when Co'' is 0.01 to 0.2 g ions/l, the amount of Cr attached can be stably ensured, but if it is less than 0.01 g ions/l or 0.2 g ions/l If the amount of Cr is exceeded, the amount of Cr deposited will be extremely reduced, making it difficult to deposit the desired amount.

As is clear from Figure 7, CI- is 0.001 to 0.0.
At 2 g ions/l, an extremely good chromate film is formed and exhibits excellent corrosion resistance. If it is less than o, ooi gram ion/l or more than 0.02 gram ion/l, the corrosion resistance will be significantly reduced.

This is because the structure of the formed chromate film varies greatly depending on the CI concentration, and if C1- is within the above range, Crz
This is because a film mainly composed of 03 is formed, but if it deviates from this range, the film mainly consists of metal Cr or Cr (Oll) 3·n H20.

As is clear from Figure 8, the adhesion of the organic film is excellent in the Ct- range of 0.001 to 0.02 gram ions/l;
If it is less than 0.001 gram ion/l or more than 0.02 gram ion/l, the adhesion will be significantly reduced.

As is clear from Fig. 9, when CI- is 0.001 gram ion/poor to 0.02 gram ion/l, the amount of Cr attached can be stably secured, but if it is less than 0.001 gram ion/l or O9.02 When the amount exceeds gram ions/l, the amount of Cr deposited decreases.

As is clear from Figure 10, when performing cathodic electrolysis,
Set the current density to 0. less than I A/dmz or 40A/
dm", the corrosion resistance is markedly inferior, whereas
．． Excellent corrosion resistance can be obtained when electrolytically treated at 1 to 40 A/dm''.

As is clear from Fig. 11, 0.1 to 40 A/dm”
The organic film exhibits excellent adhesion when electrolytically treated at 0.1 A/dm" or above 408 dm", but the adhesion is poor.

When electrolytically treated at less than 0.1 A/dm, a film mainly composed of Cr(OH) 3-nHzO is formed, and 4
When electrolyzed at more than 0 A/dm, Cr (OH):
+・nHzo and a film mainly composed of Cr metal is formed, whereas when electrolyzed at 0.1 to 404/d+a'', C
This is because a chromate film consisting mainly of r,03 is formed.

As is clear from Figure 12, 0. When electrolytically treated at less than 40 A/dl11" or more than 40 A/dl11", the Cr precipitation efficiency decreases significantly;
When electrolyzed at 40 A/dmz, the amount of Cr deposited can be stably ensured.

The results shown in Figures 1 to 12 show the results using Co- as the cation, but instead of Co''+, Cu''Zn'',
Almost similar results were obtained using Ni'' and Mn''. Moreover, similar results were obtained even when two or more types of cations were allowed to coexist.

In addition, although we showed the results using C1- as the anion,
Almost the same results were obtained even when F- was used instead of CI- or when both were used together.

(See Examples) From the above results, in the present invention, when performing electrolytic chromate treatment in a bath in which chromic anhydride, cations, and anions coexist, chromic anhydride or
Concentration of chromate or dichromate converted to chromic anhydride = 0.05 to 1 mol/l Dissolved Cu", Zn, Ni", Co",
Number of dulam ions of one or more types of Mn"+ ions = 0.01 to 0.2 gram ions/l Number of dulam ions of one or two types of dissolved CI- and F" ions = O, OO 1 to 0.02 gram ions/r, and the current density in the case of electrolytic treatment at the cathode is 0.1 to 40 A/dm''.

Furthermore, although the present results were shown for an example performed on a Zn-Ni alloy plated steel sheet, this treatment is capable of forming a chromate film on any metal or any alloy, and
The amount of Cr deposited can be freely controlled by the amount of electricity.

While conventional chromates form a film through reaction with ions eluted from the substrate, this treatment has the characteristic that a film is formed regardless of the ion elution from the substrate. This is essentially different from chromate treatment.

Furthermore, the chromate film obtained by this treatment has excellent corrosion resistance and excellent adhesion to organic resins. In this result, polyacrylic acid ester was shown as an example, but olefin/acrylic acid copolymer resin,
Water-based resin dispersions such as polymethacrylic acid and its copolymer resin, polymethacrylic acid ester and its copolymer resin, polyacrylic acid and its copolymer resin, polyacrylic acid ester and its copolymer resin, and epoxy Excellent adhesion is ensured with any organic resin such as resin or various solvent-based resins including melamine resin. Therefore, it is most suitable as a chromate for the organic resin base of the above-mentioned organic composite steel sheet.

On the other hand, since it has excellent adhesion with organic resins, it also has excellent adhesion with paint films when applied with ED coating or spray painting, so it can also be used as a base for painted steel sheets. Optimal.

Examples of the present invention will be shown below along with comparative examples.

<Example 1> A Zn-Ni alloy plated steel sheet (Ni-11.2%) was subjected to cathodic electrolysis treatment under the following conditions.

Cr (h 30g/ff1 co4+ 2.5g)2CI-0,2
5g/E Electrolysis conditions: Current density to 5/dm2 Electrolysis time
1 second (Example 2) A Zn-Fe alloy plated steel sheet (Fe=40%) was subjected to cathodic electrolysis treatment under the following conditions.

Cry320g/j! Zn◆ 2.0 g/ECl-
0.2 g/l Electrolytic conditions: Current density 2 A/dm Electrolytic time 2.5 seconds (Example 3) A Zn-Ajli alloy plated steel sheet (82=12%) was subjected to cathodic electrolysis treatment under the following conditions.

Cr0340g/l Ni" 2.7 g/I Cl-0.3g/ff Electrolysis conditions: Current density 10A/dm" Electrolysis time 0.5 seconds <Example 4> Zn-Cr alloy plated steel plate (Cr = 12% ) was subjected to cathodic electrolysis treatment under the following conditions.

Cr0310g/j2 Mn-3,5g/Q Cl -0.15g/I! .

Electrolysis conditions: Current density: 3 A/dm2 Electrolysis time: 1.7 seconds (Example 5) A Zn-Mn alloy plated steel sheet (Mn=56%) was subjected to cathode electrolysis treatment under the following conditions.

Cr (h 50g/l Cu-2.5g/ 42 F-0.15g#! Electrolysis conditions: Current density 10^/dm" Electrolysis time 0.7 seconds <Example 6> Zn-Nt-Co alloy plated steel sheet (Ni-10.5%
, Co = 0.5%) was subjected to cathodic electrolysis treatment under the following conditions.

Cry340g/ICo" 4.0g/ICl-0,2g7N Electrolysis conditions: Current density 15A/dm" Electrolysis time 0.8 seconds <Example 7> Zn-Ni-Cr alloy plated steel plate (Ni=10. 8
%, Cr=1.5%) was subjected to cathodic electrolytic treatment under the following conditions.

Cr0i 15g/j2 CO~2.0g/I Cl -0.15g/1 Electrolysis conditions: Current density 7.5 A/dm Electrolysis time 0.6 seconds <Comparative example 1> Zn-Ni alloy plated steel sheet ( Ni=11.8%) was subjected to cathodic electrolysis treatment under the following conditions.

Cry) 50g/1 11□504 0.25g/42 Electrolysis conditions: Current density 50 A/dm" Electrolysis time 2 seconds <Comparative example 2> Zn-Ni-Co alloy plated steel plate (Ni = 11.5
%Co=0.5%) was subjected to cathodic electrolysis treatment under the following conditions.

CrO:+ 40g/i! .

H, SO, 0.2g/1 Electrolysis conditions: Current density 60A/dm” Electrolysis time
1.5 seconds Table 1 shows the corrosion resistance and Cr adhesion amount by salt spray test of each example and comparative example, and Table 2 shows the adhesion of the resin when 2μ of olefin/acrylic acid copolymer resin was applied. show. The salt spray test method and evaluation method are the same as those shown in FIGS. 1, 4, 7, and 10. The evaluation method of resin adhesion is the same as that shown in FIGS. 2, 5, 8, and 11.

As is clear from Table 1, when the present invention is applied to various alloy-plated steel sheets, the corrosion resistance hardly changes after 600 hours of SST, and a slight red rust occurs in some parts after 1200 hours of SST. On the other hand, when treated with a known chromate bath (Comparative Example 1.2), SST 40
After 0 hours, around 70% white rust had already occurred, and after 600 hours, a considerable amount of red rust was observed.

On the other hand, as is clear from Table 2, when the present invention is implemented, the adhesion with the organic resin is extremely excellent, but when treated with a known chromate bath (Comparative Example 1.2), there is no evidence of peeling. is recognized.

<Effects of the Invention> Conventionally, there has been no known chromate treatment that can stably secure the desired amount of chromate by treating various metals and alloys and sufficiently satisfy corrosion resistance and adhesion with organic resins. Ta. On the other hand, by controlling the concentrations of chromic anhydride, special anions, and cations within specific ranges, and performing cathodic electrolysis treatment under specific conditions, the synergistic effect of these results in extremely excellent corrosion resistance and organic resins. A film with excellent adhesion is formed, and by applying the present invention, the economic effect is extremely large.

[Brief explanation of the drawing]

Figures 1 to 3 show the relationship between corrosion resistance, adhesion to organic film, and amount of Cr deposited when the Co" ion concentration, CI-, ion concentration, and current density are fixed and the concentration of chromic anhydride is changed. Figures 4 to 6 show the corrosion resistance, adhesion to the organic film, and Figures 7 to 9 show the relationship between the amount of Cr deposited. Figures 7 to 9 show the corrosion resistance, organic film and Figures 10 to 12 show the relationship between the adhesion of chromic acid and the amount of Cr deposited. Figures 10 to 12 show the relationship between the chromic anhydride concentration, CO~ ion concentration, and CI~ ion concentration when changing the current density. This shows the relationship between corrosion resistance, adhesion to organic film, and amount of Cr deposited. Patent applicant: Nippon Steel Corporation

Claims (1)

[Claims] Chromic anhydride or chromate or dichromate,
0.05 mol/l to 1 mol/l in terms of chromic anhydride
In the bath containing l, Cu^+^+, Zn^+^+, Ni^+^
+, Co^+^+, Mn^+^+ ions or two or more ions at a concentration of 0.01 to 0.2 gram ions/l, and further Cl^- and F^- ions. 0.001 gram ion/l to 0.0 of one or two of the following
0.1 A/dm in a bath containing 2 g ions/l
A metal surface treatment method characterized by cathodic electrolytic treatment at a current density of ^2 to 40 A/dm^2.