JPS62146295A - Surface treatment of metal - Google Patents

Abstract

PURPOSE:To form a composite film having superior uniformity, corrosion resistance and paintability by cathodically electrolyzing the surface of a metal in a treating soln. contg. specified amounts of Cr<6+>, Cr<3+> and colloidal silica. CONSTITUTION:The surface of a metal is cathodically electrolyzed in a treating soln. contg. 5-120g/l Cr<6+>, 0.01-5.0g/ll Cr<3+> and 5-100g/l colloidal silica of silica and/or silicate. In the soln., the ratio of Cr<3+>/Cr<6+> is about 1/50-1/30. The pH of the soln. is preferably adjusted to about 0.6-6 with ammonium hydroxide. The current density is about 3-80 A/dm<2>. The preferred amount of Cr deposited on the surface of the metal is about 10-300mg/m<2> and that of silica is about 3-30mg/m<2> (expressed in terms of Si). Thus, a superior film is formed easily, rapidly and properly at a high formation rate.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to steel sheets plated individually with metals such as zinc, tin, aluminum, copper, lead, and nickel, and one or more of the above metals. The present invention relates to a steel plate plated with an alloy made of metals other than those mentioned above, and a metal surface treatment method for forming a composite film of chromate and silica with excellent uniformity, corrosion resistance, and paintability on the surface of the steel plate.

(Prior Art) Conventional treatment methods using Cr6+, Cr3+-silica-based treatment liquids include Japanese Patent Publication No. 42-14504 and Japanese Patent Publication No. 45-38891. Japanese Patent Publication No. 52-17340゜ Japanese Patent Publication No. 52-17340
No. 2-17341, etc., all of which are performed by a coating method. Therefore, if the amount of film formed is increased to improve corrosion resistance, the amount of silica deposited will increase depending on the blending ratio of Cr6+, Cr3+/silica in the treatment solution, which will reduce the adhesion between the metal to be treated and the formed film, and the paint There was a tendency for performance to deteriorate.

In addition, with these coating methods, in order to control the amount of film formed, it is necessary to change the concentration of the processing liquid or change the shape or roll pressure of the coating roll, so it is necessary to quickly control the amount of film formed. Moreover, it is difficult to properly control the coating method, and the coating method also has problems such as lack of uniformity of the film.

Next, as a method of cathodic electrolytic treatment using a Cr'+-based treatment solution, there is
Method of cathodic electrolytic treatment using 3H2SO4 treatment solution
8-43019 (a method of cathodic electrolytic treatment using Cr03-heavy metal ion-based treatment liquid), and the like. Generally, films formed by cathodic electrolytic treatment using these Cr'+-based treatment solutions are said to have insufficient corrosion resistance, but good paintability. However, its paintability was not necessarily satisfactory from an industrial perspective.

(Problems to be Solved by the Invention) In general, in the case of Cr6+, Cr3+- silica-based films produced by coating methods, when the amount of chromium deposited is increased in order to improve corrosion resistance, the Or", Cr"+/silica blending ratio in the treatment solution is , since the amount of silica deposited increases, the adhesion of the formed film and the paintability deteriorate.

The present invention improves corrosion resistance and paintability by improving the drawbacks of conventional Cr6+, Cr3+- silica-based treatment liquid coating methods, such as a decrease in paintability when the amount of film formed increases, and the difficulty in controlling the amount of film formed. The purpose is to form a film with excellent properties on the metal surface.

In other words, in order to improve corrosion resistance, we created a film with excellent corrosion resistance and paintability that does not impair paintability even if the amount of chromium deposited is increased.
In order to form a film on a metal surface and perform industrially stable surface treatment, the amount of film formed can be easily and quickly controlled.
The aim is to achieve appropriate control.

(Means for Solving Problems) The present invention provides steel plates plated with metals such as zinc, tin, aluminum, copper, nickel, etc., and alloys made of one or more of the above metals and metals other than the above. By cathodic electrolytically treating a plated steel plate and the surface of the steel plate with the treatment solution of the present invention, a composite film of chromate and silica, which has excellent corrosion resistance, paintability, and uniformity, is formed on the metal surface. In particular, the objective is to form a film that has strong adhesion to the substrate and has excellent paintability.

As a metal surface method to solve the above-mentioned problems, as a result of various studies, we found that colloidal silica was created by blending silica and/or silicate into an aqueous solution containing Cr'+ ions and Cr"+ ions. The processing liquid made to exist as
A method of cathodic electrolytic treatment of the metal surface, that is, Cr6+ ions 5-120 ml/L, Cr3+ ions 0.01-5.
0? 1. A method for treating a metal surface, comprising cathodic electrolytically treating a metal surface with a treatment solution containing 5 to 100 y/l of silica and/or silicate as colloidal silica. It has been found that the above-mentioned problems can be solved by this method.

(Function) As the Cr'+ in the treatment liquid in the present invention, one type or compound of chromic anhydride, ammonium dichromate, and alkali metal salts of dichromate can be arbitrarily applied. C
The concentration of r6+ ions is 5 to 120 y/l, particularly preferably 10 to 70 y/l.

-1, if the concentration of Cr6+ is low, the film production efficiency will decrease when the metal to be treated is processed continuously, and it will be difficult to make the formed film uniform, making it industrially stable. In order to perform the above processing, 5? /1 is the limit. Also, 120? Even if the concentration is higher than /1, there will be no change in the custom-made film produced, but if the concentration is too high, a large amount will be carried out of the processing solution depending on the metal being treated, making it uneconomical. Industrially, l 20 t/t is considered to be the limit.

The Cr ion can also be added to the treatment liquid as a carbonate compound of Cr or as a redox reaction product between Cr6+ and organic substances such as alcohols, starches, and tannic acid. By blending Cr3+ ions, the film formation efficiency with respect to the coulomb amount by cathodic electrolytic treatment increases, and a film with excellent adhesion, corrosion resistance, and paintability can be obtained.

The concentration of Cr ions is 0.01 to 5. ot/
L, particularly preferably 0.05 to 2.0? /l. In the present invention, the paintability tends to be improved when the ratio of Cr''/Cr'+ ions is 1150 to 1/3.

Next, the silica, silicate, etc. of the present invention are added to the treatment solution in order to form colloidal silica, and are generally mixed in water with ultrafine particles (1 to 100 m2) of negatively charged silicic anhydride.
It is said that it exists as μ). Silica and/or
Or is the concentration of silicate between 5 and 100? /7. Particularly preferably 10 to 50 r/t. At concentrations as low as 51/l, it is difficult to form a good film, resulting in poor corrosion resistance and paintability. Moreover, even if the concentration is higher than 100 y/t, there is no further effect, and silica and silicate may precipitate, or the amount of metal to be treated may be carried out of the processing solution, making it uneconomical. Therefore, industrially], O
Oy/l is considered the limit.

Although the pH of the treatment liquid is not specified, its value is set to 0.
By arbitrarily selecting from the range of 6 to 6, more preferable results can be obtained. It is difficult to produce a treatment solution whose pH is lower than 0.6 to confirm its effectiveness. In addition, even if the pH is higher than 6, there is no change in the properties of the film formed, but if the pH is too high, silica, silicates, etc., and metal ions of the metal to be treated that are eluted into the treatment solution will precipitate, making it difficult to use industrially. pH 6 is considered to be the upper limit for stable treatment.

In order to control the pH of the treatment liquid, any compound selected from ammonium hydroxide, alkali metal hydroxides, alkali metal carbonates, etc. can be added to the treatment liquid. However, in the case of drying without washing with water after the cathodic electrolytic treatment of the present invention, the use of ammonium hydroxide is limited.

The temperature of the treatment liquid is room temperature to 70°C, and 70'C
Even if the price was higher, it would be uneconomical, so from an industrial perspective
The limit is ℃.

Next, cathodic electrolytic treatment is performed using the metal to be treated as a cathode, but it is necessary to clean the surface of the metal to be treated before the main treatment. However, even if the cleanliness is not perfect, the effects of the present invention can be achieved to some extent. The current density at the cathode is 3 to 80 A/dn? It is carried out within the range of 3
When it is lower than A/di, it is difficult to form a good film and the corrosion resistance and paintability are poor. Also, 80A/d77
Even if it is made higher than 1", there is little effect beyond that.

Finally, the cathodic electrolytic treatment time is [F], but the anal folding time is
The amount of film formed (amount of chromium deposited) is controlled to be within the desired range. There are various factors that can change the amount of chromium deposited, but in the method of the present invention, the concentration of each component of the treatment liquid, pH1 temperature, current density, etc. are each fixed to the preferred conditions of the present invention. Also, by changing the electrolysis time, the desired amount of chromium deposit can be controlled depending on the metal to be treated. Alternatively, the amount of chromium deposited can be controlled by fixing the electrolysis time and changing the current density.

FIG. 1 shows an example of the relationship between the current density, the amount of coulombs, and the amount of film formed in the present invention when the metal to be treated is a steel plate. The electrolytic treatment conditions applied to produce FIG. 1 are as shown in Table 6.

According to the present invention, the cathodic electrolytically treated metal is washed with water and then dried to be used for corrosion protection or as a paint base, but it may also be applied by passing it through a squeegee roll and drying it without washing with water. can. Further, if necessary, post-treatment with a commonly used chromate aqueous solution and an anticorrosive resin compound can be carried out.

In the present invention, the preferred amount of chromium adhesion is 10 to 30
0 m9/nt'', and the more preferable range is 20 to 1
The amount of silica deposited is preferably 3 to 30 m97 m'' as Sl, and the more preferable range is 5 to 2 om9/rr? It is.

In addition, as mentioned above, the present invention includes Cr in the processing solution.
However, the ratio of Cr/Cr is 1750~/50
Due to its presence, the film formation efficiency with respect to the coulomb amount by cathodic electrolytic treatment becomes high, and a film with excellent corrosion resistance and paintability can be obtained.

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

Example 1 An electrogalvanized steel sheet cleaned by a known method was subjected to cathodic electrolytic treatment under the following conditions, washed with water after treatment, and the dried sample was compared with Comparative Example 1. As a result, as shown in Table 1. In addition, the cathodic electrolytically treated film of the present invention exhibited better film adhesion, uniformity, corrosion resistance, and paintability compared to conventional Cr6+, Cr3+-silica-based coatable films.

[Processing liquid composition]

ar” 8.1 ?/l Cr” 2. Og/l (cr'+
(reduced with methanol) Snow Chick, co 250
．． Oy/l (Colloidal solution containing 20% 5f02 manufactured by Nissan Chemical Co., Ltd.) (The pH at this time was 1.5.) [Cathode electrolysis conditions] Electrolysis time 3 to 12 seconds (In order to obtain the specified amount of chromium deposited, electrolysis (The time was adjusted.) 'Current density 10A/dns' Electrolysis temperature 50°C Comparative example-1 The treatment solution used in Example-1 was applied by roll coating to an electrogalvanized steel sheet that had been cleaned by a known method. After applying,
The dried sample was used as a comparative sample and is shown in Table 1. At this time, the amount of chromium deposited was adjusted by changing the amount of treatment liquid applied.

Example-2 A steel plate cleaned by a known method was subjected to cathodic electrolysis treatment under the following conditions using the same treatment solution as in Example-1, and the sample was washed with water after the treatment and dried, and the sample was compared with Comparative Example-2. As a result, as shown in Table 2, the cathode electrolytically treated film of the present invention
", Cr"+--The film exhibited good film adhesion, uniformity, corrosion resistance, and paintability compared to the silica-based coating film.

[Cathode electrolysis conditions]

Electrolysis time: 1 second Current density: 10-3oA/d? y+'' (Current density was adjusted to obtain a predetermined amount of chromium deposited.) Electrolysis temperature 30''C Comparative Example-2 The treatment solution used in Example-2 was applied to a steel plate cleaned by a known method using a roll. A sample that has been applied using the coating method and then dried is
It is shown in Table 2 as a comparative sample. At this time, the amount of chromium deposited was adjusted by changing the amount of treatment liquid applied.

Example 3 An electrogalvanized steel sheet cleaned by a known method was subjected to cathodic electrolysis treatment under the following conditions, washed with water after treatment, and the dried sample was compared with Comparative Example 3. The results are shown in Table 3. As can be seen, the cathodic electrolytically treated film of the present invention exhibited good corrosion resistance and paintability compared to the cathodic electrolytically treated film of Comparative Example-3.

[Processing liquid composition]

cr −ylo, *P/l, and cr3+ = 3.
Applied AT20Q (Note) was added at 25 and 5 Oy/l (reducing Cr3+ with tannic acid) treatment solution, respectively.
Added 0°xsoy/A. The pH at this time was 2.9.

(Note) Non-electrified colloidal silica 20% solution [Cathode electrolysis conditions] Electrolysis time: 2 seconds Current density: 15A/am' Electrolysis temperature: 30°C Comparative example-3 An electrogalvanized steel sheet cleaned by a known method was subjected to the following A sample treated using the treatment solution under the same cathode electrolysis conditions as in Example-3 is referred to as Comparative Example-3, and is shown in Table 3.

[Processing liquid composition]

Cr”=10.1t/11 and Cr3”=3
．． 0? / L (Cr reduced by tannic acid)
, and to this processing solution, Applied AT20Q (
Note: Add 1o and op/ of the above).

The pH at this time was 2.9.

[Cathode electrolysis conditions]

Electrolysis time: 2 seconds Current density: 15A/drr? Electrolysis temperature: 30°C Example 4 An electrolytic galvanized steel sheet cleaned by a known method was subjected to cathodic electrolysis treatment under the following conditions, washed with water after treatment, and the dried sample was compared with Comparative Example 4. As shown in the table, the cathodic electrolytically treated film of the present invention exhibited good corrosion resistance and paintability compared to the film of Comparative Example-4.

[Processing liquid composition]

Cr” 5.0?/L Cr3” 0.01 n (C
(reduce r'+ with U) Aerosil 200 30.0
# (Adjust the pH to 5.0 with Nippon Aerosil 8102 potassium hydroxide.

[Cathode electrolysis conditions]

Electrolysis time: 4 seconds Current density: 3.6.9A/di Electrolysis temperature: 30°C Comparative example-4 An electrolytic galvanized steel sheet cleaned by a known method was treated with the same treatment solution as in Example-4, and the current density was O1. and 1.5A
/drr? The sample treated with was designated as Comparative Example-4, and the fourth
Shown in the table.

[Cathode electrolysis conditions]

Electrolysis time: 4 seconds Current density: 0.1.5 A/a Electrolysis temperature: 30'C Example-5 An electrolytic tin-plated steel sheet cleaned by a known method was subjected to cathodic electrolysis treatment under the following conditions, and after the treatment, it was washed with water, As a result of comparing the dried sample with Comparative Example 5, as shown in Table 5, the cathodic electrolytically treated film of the present invention had higher film formation efficiency and better corrosion resistance than the cathodic electrolytically treated film of Comparative Example-5. , and paintability.

[Processing liquid composition]

Cr-159/l, and Na2O-8102 in S
Cr3+ was added to the treatment solution to which 102 and 12 t/L were added.
Cr3+ ions (using chromium carbonate) were added so that the /Cr'+ ratio was 1150.1/10.1/3, and the pH was adjusted to 3.5 with ammonium hydroxide.

[Cathode electrolysis conditions]

Electrolysis time: 2 seconds Current density: 15 A/d Electrolysis temperature: 30°C Comparative Example-5 An electrolytic tin-plated steel sheet cleaned by a known method was treated under the same cathodic electrolysis conditions as Example-5 using the following treatment solution. The sample was designated as Comparative Example-5 and is shown in Table 5.

[Processing liquid composition]

Cr-15? /l, and 5i of Na2O-8i02
02 and 12y/l added treatment solution and Cr”+/C
Add cr3+ ions (using chromium carbonate) so that the r'+ ratio is 1/100 and l/2.5, and adjust the pH to 3.5 with ammonium hydroxide.

[Cathode electrolysis conditions]

Electrolysis time: 2 seconds Current density: 15A/di Electrolysis temperature: 30°C [Evaluation method] 1 Cellophane tape (50++ on width) is applied to the adhesive film of the film, and after rapid peeling, the residual amount of Cr and Si in the film is evaluated. ,
Displayed in CH. 100chi is the best.

2. Uniformity of the film The state of the unevenness of the film was visually observed and evaluated on a four-level scale of ◎, ○, Δ, and ×, with ◎ being the best.

3. Corrosion resistance 3-1 Salt spray test. According to salt spray test in accordance with l5-Z-2371,
Judging the rusting state after a specific time with the naked eye, ◎, ○, Δ, ×
Evaluation is made on a four-level scale, with ◎ being the best.

4 Paintability (Painting: Paint a commercially available alkyd melamine white paint at 27 to 30/!) After cutting 100 squares of base grids at one interval on the Erichsen test coating film, extrude 7wn with an Erichsen tester, A peel test was performed using cellophane tape, and the degree of peeling of the paint film was judged with the naked eye.
Evaluation is made in four stages: ○, Δ, and ×, with ◎ being the best.

(Effects of the Invention) In the film formed by the present invention, the amount of chromium deposited is easily controlled by the current density and electrolysis time during cathode electrolysis, that is, the amount of coulombs, and the amount of silica deposited is almost constant regardless of the cathode electrolysis conditions. This improves the problem with the coating method mentioned above, that when the amount of chromium deposited is increased to improve corrosion resistance, the amount of silica deposited also increases, resulting in a decrease in the adhesion of the formed film and the paintability. It is possible to industrially stably obtain a uniform film with excellent corrosion resistance and film adhesion.

[Brief explanation of drawings]

FIG. 1 shows the relationship between the current density, the amount of coulombs, and the amount of film formed.

Claims (1)

[Claims] In a treatment solution containing 5 to 120 g/l of Cr^6^+ ions, 0.01 to 5.0 g/l of Cr^3^+ ions, and 5 to 100 g/l of silica and/or silicate as colloidal silica. , a metal surface treatment method characterized by subjecting the metal surface to cathodic electrolysis treatment.