JPS5983775A - Chemical conversion of metal surface - Google Patents

Abstract

PURPOSE:To further improve the corrosion resistance and paint adhesiveness of a chemically converted film, in a treating method using the aqueous acid solution of phosphoric acid or its salt and phytic acid or its salt, by conjunctly using a specified zirconate. CONSTITUTION:Using an aqueous acid solution prepd. by additionally mixing a hexafluorozirconate (IV) in phytic acid or its salt, phoshoric acid or its salt and a chlorate, a metal surface is chemically converted. As said hexafluorozirconate (IV), Na, K, Li and NH4 salts are illustrated. By mixing one or more of these salts, a composite chemcally converted film of iron and zirconium phosphates is formed resulting in the inprovement of corrosion resistance and paint adhesiveness.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for chemical conversion treatment of metal surfaces. More specifically, the present invention relates to a method for forming a non-chromium-based chemical conversion coating with excellent corrosion resistance and coating adhesion on the surface of metals such as iron, iron alloys (eg, black plate), and tin-plated iron metals (eg, tin-plated).

Conventionally, a chromic acid-based treatment method has been employed as a general surface treatment method for tin plating, for example.

This method forms a chemical conversion film with excellent corrosion resistance and paint film adhesion, but since chromic acid is toxic, it causes great damage to the human body and the living environment, repeatedly causing pollution and labor problems. Furthermore, since tin-plated cans are originally used for opening cans for food or drinking water, chromic acid treatment is not preferable from a food hygiene perspective.

Based on these facts, as a social demand, there are increasing expectations for the development of a chemical conversion treatment method for metal surfaces that is comparable in performance to chromic acid treatment methods, is non-toxic, and has low pollution.

The present inventors have carried out extensive research in order to provide a surface treatment method that satisfies such requirements. As a result, the present inventors have found that a surface treatment method that contains phosphoric acid or its salts and phytic acid or its salts at specific concentrations, and has a specific output value. It has been discovered that scales can form a chemical conversion film with excellent corrosion resistance and coating adhesion on metal surfaces when treated with an acidic aqueous solution adjusted to the following: A patent application is pending (see Japanese Patent Laid-Open No. 57-5879).

The present invention is based on the discovery that the corrosion resistance and coating adhesion of the chemical conversion coating can be further improved by further improving the disclosed invention and adding hexafluorozirconium (IV) salt.

That is, the gist of the present invention is that hexafluorozirconium (
IV) A method for chemical conversion treatment of a metal surface, characterized by using an acidic aqueous solution containing an acid salt, phytic acid or a salt thereof, phosphoric acid or a salt thereof, and a chlorate.

Examples of the hexafluorozirconium (IV) salt used in preparing the acidic aqueous solution of the present invention include sodium salts, potassium salts, lithium salts, and ammonium salts, and at least one of these salts may be blended. By blending these components, a composite chemical conversion film of iron phosphate and zirconium phosphate is formed, leading to improved corrosion resistance and coating adhesion.

The blending amount of this component is O.0C16 to 0.0C16 in terms of Zr. ■
4, preferably 0.05 to 0.5 Vl.

If the amount is too small, the above-mentioned composite chemical conversion film will not be formed, and therefore a chemical conversion film with excellent corrosion resistance and coating adhesion cannot be provided. On the other hand, if the amount is excessive, the bath of the acidic aqueous solution tends to become unstable.

Components of the phytic acid or its salt include phytic acid (i.e., myo-inositol hexaphosphate) and its salts (e.g., sodium salt, potassium salt, lithium salt, ammonium salt), and at least one of these All you have to do is mix it up. Note that hydrolysates of phytic acid (myo-inositol silynate, myo-inositol triphosphate, myo-inositol tetraphosphate, and myo-inositol pentaphosphate) may be used as a substitute or in combination; Therefore, it is best to use a phytic acid component. Although the action of such a phytic acid component is not clear, it is thought that a part of the blended amount acts as a chelating agent to improve chemical conversion treatment properties (specifically, the uniformity of the chemical conversion film). The blending amount of this component is 0.2 to 2 P/l, preferably 0.5 to 1.0 P/l in terms of phytic acid. OVJ! That's fine. If the amount is too small, the corrosion resistance of the chemical conversion coating will not improve, and if it is too much, the effect will not increase in proportion to the amount, which is economically disadvantageous.

Components of the phosphoric acid or its salt include phosphoric acid and its salts (e.g., sodium salt, potassium salt, lithium salt, ammonium salt), which are often used in iron phosphate chemical conversion treatments, and at least one of these All you have to do is mix it up. The blending amount of this component is 2.5 to 3.5 in terms of P04.
b, preferably 2.7 to 3.0 i/l. If the amount is too low, a sufficient amount of chemical conversion film will not be formed, while if the amount is excessive, the amount of etching on the metal surface will increase, damaging the surface appearance, and also improving corrosion resistance and coating adhesion. No chemical conversion film is formed.

Examples of the chlorate component include sodium salts and potassium salts, and at least one of these may be blended. The blending amount of this component is 0.7 to 1 g/I in terms of CEO3.
! , preferably 0.8 to 0.9 Vl. If the amount is too small, the effect of promoting chemical conversion treatment will not be obtained,
On the other hand, if it is in excess, it will be difficult to form a dense chemical conversion film, and the amount of sludge generated in the treatment bath will increase. Note that hydrogen peroxide, another oxidizing agent commonly used in phosphate chemical treatment, has problems in handling and tends to make the treatment bath unstable. Also, nitrites (e.g.
Sodium salts and potassium salts have a problem in that they have too strong oxidizing power and generate a large amount of sludge. Therefore, the use of these oxidizing agents is not preferred in the present invention.

It is important that the acidic aqueous solution of the present invention comprising the above-mentioned components is used in a range of 3.5 to 55, preferably 3.5 to 4.5. If the value is too low, the etching reaction on the metal surface will be too intense, damaging the surface appearance and failing to provide a good chemical conversion film.On the other hand, if the value is too high, the chemical conversion reaction will not proceed sufficiently, resulting in a dense and good quality film. Phosphoric acid or phytic acid is suitable as the acid used to adjust this value (although it is also possible to use mineral acids such as sulfuric acid, hydrochloric acid, and nitric acid, these (This is not preferred in practice because the components of the processing bath may change and the processing may become unstable.)

On the other hand, suitable alkalis include sodium hydroxide, potassium hydroxide, lithium hydroxide, and ammonium hydroxide (calcium hydroxide, magnesium hydroxide,
When alkaline earth metal hydroxides such as barium hydroxide or alkaline earth metal carbonates such as calcium carbonate are used, these alkalis have a slow reaction rate with acid components (
In addition, the reaction forms poorly soluble salts, which is undesirable from a practical standpoint).

According to the present invention, various metal surfaces (specifically, for example, iron plates, black plates, DI tin plated cans (Drawing and Iron
(Tin plating manufactured by molding process of ing)
), it is possible to form a chemical conversion coating with extremely excellent corrosion resistance and coating adhesion. The processing method itself at that time can be carried out in the same manner as in the normal case. That is, the metal surface is first cleaned by degreasing and washing with water according to a conventional method if necessary, and then immersed or sprayed in the above acidic aqueous solution at 20 to 90°C, preferably 30 to 70°C, more preferably 40°C. ~60°C
for about 5 seconds to 5 minutes, then washed with water and dried.

Next, the present invention will be specifically explained with reference to Examples.

Note that the examples also include examples for comparison.

The composition of each acidic aqueous solution used in the following examples is as shown in Table 1.

In addition, acidic aqueous solutions A3 and 7 = the treatment liquid disclosed in JP-A-5.7-5879 or its analogues; acidic aqueous solutions Tiger 4 and 82; the treatment liquid disclosed in JP-A-54-68734 or its analogues; Aqueous mud 5 and 9: Treatment liquid disclosed in JP-A-54-68733 or its analog Acidic aqueous solution A6: Treatment liquid disclosed in JP-A-53-25296 Acidic aqueous solution Bay 10: JP-A-54-158341 Processing liquid disclosed in Acidic aqueous solution//6.11 = Processing liquid disclosed in JP-A No. 55-62179 Example 1 (treatment of iron plate (SPCC plate)) The metal surface was coated with an alkaline degreaser (manufactured by Nippon Paint Co., Ltd. [Ridrinf 5N -1j
) After spray degreasing with 20 Vl of solution and washing with water,
A chemical conversion treatment is performed using an acid aqueous solution or a commercially available treatment agent shown in Table 1 at 50°G for 30 seconds using a spray method, followed by washing with water and pure water, followed by drying at 100°C for 5 minutes.

The amount of chemical conversion coating on the obtained treated plate was measured, its appearance was observed, and the treated plate was left at a humidity of 10 L% and a temperature of 50°C to measure the time it took for rust to develop. Evaluate as. The results are shown in Table 2.

Example 2 (Black plate treatment) The metal surface was degreased with a solvent and cleaned with ultrasonic waves according to a conventional method, and then treated with a degreaser and washed with water in the same manner as in Example 1. A chemical conversion treatment is performed using a treatment agent in the same manner as in Example 1, followed by washing with water and pure water, followed by drying at 120°C for 5 minutes.

The amount of chemical conversion coating and the appearance of the obtained treated can were evaluated in the same manner as in Example 1. In addition, the inner surface of the processing can was coated with a commercially available epoxy paint for cans to a thickness of about 5μ, and with the other surfaces masked, the painted can was immersed in an aqueous solution containing 1% citric acid and 1% sodium chloride at 50°C. Soak in C for 5 days. Observe the corrosion status of the can after immersion and evaluate the paint corrosion resistance (no corrosion = 5 points, severe corrosion = 5 points)
Graded evaluation]. The results are shown in Table 3.

Example 3 (Treatment of DI tin-plated cans) After each metal surface with a different tin weight was treated with a degreaser and washed with water in the same manner as in Example 1, it was treated with an acidic aqueous solution shown in Table 1 at the same temperature and time as in Example 1. Tester 9 for chemical conversion treatment under the conditions
(1) immersion treatment, others (spray treatment)], followed by washing with water, washing with pure water, and drying in the same manner as in Example 1.

The resulting treated can was evaluated for chemical coating appearance and appearance in the same manner as in Example 1. In addition, the unpainted corrosion resistance (2) of the treated cans was evaluated using the method below, and the paint corrosion resistance of the cans painted in the same manner as in Example 2 was evaluated in the same manner as in Example 2. Evaluate adhesion. The result is the fourth
Shown in the table.

Unpainted Corrosion Resistance (2) Place the chemically treated material with the bottom up in a salt spray tester and test it with JI.
The state of rust on the surface of the can is evaluated after testing for 25 minutes based on S-Z-2371. The evaluation criteria are as follows, but if it is difficult to evaluate using an integer score, an intermediate score, such as 4.5 points or 3.5 points, will be used.

4 points: Greater than 0 and less than 5%.

3 points: I larger than 5chi and below 20th grade.

2 points: More than 20% and less than 50 inches.

1 point: Thicker than the 50th grade.

Paint film adhesion Cut the side of the paint can to a size of 5σ x 10 cm,
The obtained specimen was placed in a boiling 5% acetic acid aqueous solution.
After soaking for 0 minutes, wash with water and dry. Cut the painted surface of the test specimen into 100 pieces with a sharp knife until it reaches the base material, so that each square has a grid of 2 mm x 2 mm, firmly press the adhesive tape on top of it, and then peel it off rapidly. Evaluate the peeling state of the membrane. The evaluation criteria are as follows, but if it is difficult to evaluate using an integer score, an intermediate score, such as 45 points or 3.5 points, will be used.

5 points: The area ratio of the peeled paint film to the entire evaluation area is O.

4 points 2 Thicker than ○ (less than 5%).

3 points: Greater than 5 but less than 20%.

2 points: More than 20% and less than 50 inches.

1 point〃〃Thicker than 50 inches.

Claims (1)

[Claims] A metal surface treatment method characterized by using an acidic aqueous solution containing hexafluorozirconium (IV) acid salt, phytic acid or its salt, phosphoric acid or its salt, and chlorate. Chemical conversion treatment method. 2. The acidic aqueous solution has a pH of 3.5 to 5.5, preferably 3.
5 to 4.5. 3. The method of item 1 above, wherein the hexafluorozirconium (IV) salt is a sodium salt, potassium salt, lithium salt or ammonium salt. 4. The method of item 1 above, wherein the phytate is a sodium salt, potassium salt, lithium salt or ammonium salt. 5. The method of item 1 above, wherein the phosphate is a sodium salt, potassium salt, lithium salt or ammonium salt. 6. The method of item 1 above, wherein the chlorate is a sodium salt or potassium salt. 7. Acidic aqueous solution is hexafluorozirconium (-■)
The acid salt is 0.006 to 0.7' i/l in terms of Zr, preferably 0.05 to 0.5 P/l, and the phytic acid or its salt is 0.2 to 2 Vl in terms of phytic acid! , preferably 0.5 to 1.05'/J, 2.5 to 3.5 P/l of phosphoric acid or its salt as P04, preferably 2
．． 7-3.01i'/J. The above-mentioned first compound is a compound containing chlorate of 0.7 to 1b, preferably 0.8 to 0.9 F/J in terms of ClO3.
Section method.