JPH0329866B2 - - Google Patents

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 plates), and tin-plated ferrous metals (eg, tin cans). Conventionally, a chromic acid-based treatment method has been employed as a general surface treatment method for, for example, tin cans.
This method forms a chemical conversion film with excellent corrosion resistance and paint adhesion, but since chromic acid is toxic, it causes great damage to the human body and the living environment.
This has repeatedly led to pollution and labor problems. Furthermore, since tin cans are originally used for food or drinking water, chromic acid treatment is not preferable from the viewpoint of food hygiene. 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 intensive research to provide a surface treatment method that satisfies such requirements. As a result, the present inventors have found that a surface treatment method containing phosphoric acid or its salts and phytic acid or its salts at specific concentrations, and having a specific PH value. It has been discovered that a chemical conversion film with excellent corrosion resistance and coating adhesion can be formed on metal surfaces by treatment with an acidic aqueous solution adjusted to the following: A patent application is currently being filed (see JP-A-57-5879). The present invention has been made 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 () salt. That is, the gist of the present invention is that the amount of hexafluorozirconium () salt is 0.006 to 0.7 g/in terms of Zr,
Phytic acid or its salt 0.2 in terms of phytic acid
~2g/, phosphoric acid or its salts as _PO4
2.5 to 3.5 g/and chlorate to 0.7 to ClO ₃
The present invention relates to a method for chemical conversion treatment of metal surfaces, characterized in that an acidic aqueous solution containing 1 g/pH 3.5 to 5.5 is used for iron, iron alloys or tin plated iron. Examples of the hexafluorozirconium 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 0.006 to 0.7 g/Zr equivalent.
, preferably 0.05 to 0.5 g/.
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. The components of the above phytic acid or its salt are:
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 may be blended. Note that hydrolysates of phytic acid (myo-inositol diphosphate, 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 effect of this phytic acid component is not clear, a portion of the amount incorporated acts as a chelating agent and improves chemical conversion treatment properties (specifically, the uniformity of chemical conversion coatings).
It is thought that this will improve the The blending amount of this component may be 0.2 to 2 g/, preferably 0.5 to 1.0 g/in terms of phytic acid. 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.
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 3.5g/, preferably 2.7g in terms of _PO4 .
It is sufficient if it is ~3.0g/. 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 may be 0.7 to 1 g/, preferably 0.8 to 0.9 g/in terms of ClO ₃ . If the amount is too small, the effect of accelerating the chemical conversion treatment will not be obtained, while if the amount is too much, 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. In addition, nitrites (eg, sodium salts, potassium salts) have a problem in that their oxidizing power is too strong and they 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 pH range of 3.5 to 5.5, preferably 3.5 to 4.5. If the PH value is too low, the etching reaction on the metal surface becomes too intense, damaging the surface appearance and failing to provide a good chemical conversion coating. On the other hand, if the PH value is too high, the chemical conversion reaction will not proceed sufficiently, making it impossible to provide a dense and good chemical conversion film. The acid used for this PH value adjustment is
Phosphoric acid and phytic acid are suitable (in addition, sulfuric acid,
Although it is possible to use mineral acids such as hydrochloric acid and nitric acid, these are not preferred in practice because they may change the components of the treatment bath and cause the treatment to become unstable).
On the other hand, as the alkali, sodium hydroxide, potassium hydroxide, lithium hydroxide, and ammonium hydroxide are suitable (alkaline earth metal hydroxides such as calcium hydroxide, magnesium hydroxide, barium hydroxide, If carbonates of alkaline earth metals such as calcium carbonate are used, these alkalis have a slow reaction rate with acid components, and the reaction forms poorly soluble salts, which is not preferred in practice). According to the present invention, various metal surfaces (specifically, for example, iron plates, black plate cans, and DI tin cans (stain tin cans manufactured by drawing and ironing molding processes) are coated with an acidic aqueous solution having the above-mentioned structure. ), 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. It may be treated at ~60°C for about 5 seconds to 5 minutes, followed by washing with water and drying. 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. Acidic aqueous solutions No. 3 and 7: Treatment liquid disclosed in JP-A No. 57-5879 or its analogue Acidic aqueous solution No. 4 and 8: Treatment liquid disclosed in JP-A-54-68734 or its analogue Acidic aqueous solutions No. 5 and 9: Processing liquid disclosed in JP-A No. 54-68733 or its analog Acidic aqueous solution No. 6: Processing liquid disclosed in JP-A-53-25296 Acidic aqueous solution No. 10: JP-A-Sho 53-25296 Treatment liquid disclosed in No. 54-158341 Acidic aqueous solution No. 11: Treatment liquid disclosed in JP-A-55-62179

[Table] Example 1 (Treatment of iron plate (SPCC plate)) The metal surface was spray degreased with a 20 g solution of an alkaline degreaser ("Ridrin 75N-1" manufactured by Nippon Paint Co., Ltd.), and after washing with water, Table 1 50℃ using the spray method with an acidic aqueous solution or a commercially available treatment agent.
After chemical conversion treatment for 30 seconds, washing with water and pure water, drying at 100°C for 5 minutes. The amount of chemical conversion coating was measured on the obtained treated plate,
The appearance is observed, and the treated plate is left at a humidity of 100% and a temperature of 50°C to measure the time it takes for rust to develop, and is evaluated as unpainted corrosion resistance (1). The results are shown in Table 2.

【table】

[Table] Example 2 (Treatment of black plate cans) The metal surface was degreased with a solvent and cleaned with ultrasonic waves according to a conventional method, then treated with a degreaser and washed with water in the same manner as in Example 1, and then treated with the acidic aqueous solution shown in Table 1 or A commercially available treatment agent was used for chemical conversion treatment 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 painted with a commercially available epoxy paint for cans to a thickness of approximately 5 μm, and with the other surfaces masked, the painted can was coated with 1 citric acid.
% by weight and 1% by weight of sodium chloride at 50° C. for 5 days. The corrosion state of the can after immersion is observed and evaluated as paint corrosion resistance (5-point evaluation with no corrosion = 5 points and severe corrosion = 1 point).
The results are shown in Table 3. Example 3 (Treatment of DI tin cans) 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, and then treated with the acidic aqueous solution shown in Table 1 at the same temperature and time as in Example 1. A chemical conversion treatment was performed under the following conditions (test No. 9 was a dipping treatment, the others were a spray treatment), and then washed with water, washed with pure water, and dried in the same manner as in Example 1. 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 unpainted corrosion resistance (2) of treated cans was evaluated by the following method, and Example 2
Example 2 shows the corrosion resistance of cans painted in the same manner as in Example 2.
In addition, the coating adhesion is evaluated using the method below. The results are shown in Table 4. Unpainted Corrosion Resistance (2) A chemically treated can is placed in a salt spray tester with the bottom facing up, and the rusting state on the surface of the can is evaluated after testing for 25 minutes based on JIS-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. 5 points: The area ratio of the rusted part to the entire evaluation area is 0%. 4 points: The area ratio of the rusted part to the entire evaluation area is greater than 0% and 5% or less. 3 points: The area ratio of the rusted part to the entire evaluation area is greater than 5% and less than 20%. 2 points: The area ratio of the rusted part to the entire evaluation area is greater than 20% and less than 50%. 1 point: The area ratio of the rusted part to the entire evaluation area is greater than 50%. Paint film adhesion Cut the side of the paint can into a size of 5cm x 10cm,
The obtained specimen is immersed in a boiling 5% by weight acetic acid aqueous solution for 30 minutes, then washed with water and dried. Cut the painted surface of the test piece into 100 pieces with a sharp knife until it reaches the base material, so that each square has a 2 mm x 2 mm grid.
After strongly pressing the adhesive tape onto the tape and rapidly peeling it off, the peeling state of the coating film is evaluated. 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, etc.
Rate it as 3.5 points. 5 points: The area ratio of the peeled paint film to the entire evaluation area is 0%. 4 points: The area ratio of the peeled paint film to the entire evaluation area is greater than 0% and 5% or less. 3 points: The area ratio of the peeled paint film to the entire evaluation area is greater than 5% and less than 20%. 2 points: The area ratio of the peeled paint film to the entire evaluation area is greater than 20% and less than 50%. 1 point: The area ratio of the peeled paint film to the entire evaluation area is greater than 50%.

【table】

Claims (1)

[Claims] 1 Hexafluorozirconium() salt
0.006 to 0.7 g/in terms of Zr, 0.2 to 2 g/in terms of phytic acid or its salts, 2.5 to 3.5 g/in terms of PO ₄ of phosphoric acid or its salts, and 0.7 to 0.7 g of chlorate in terms of ClO ₃ 1g/contains PH3.5~
A method for chemical conversion treatment of metal surfaces, characterized by using an acidic aqueous solution of 5.5 on iron, iron alloys, or tinned iron. 2. The method of item 1 above, wherein the acidic aqueous solution has a pH of 3.5 to 4.5. 3. The method of item 1 above, wherein the hexafluorozirconium () salt is a sodium salt, potassium salt, lithium salt, or ammonium salt. 4 Phytate is sodium salt, potassium salt,
The above-mentioned first salt is a lithium salt or an ammonium salt.
Section method. 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 a potassium salt. 7 The acidic aqueous solution contains hexafluorozirconium () salt 0.05 to 0.5 g/in terms of Zr, and phytic acid or its salt 0.5 to 1.0 g/in terms of phytic acid.
, 2.7 to 3.0 as PO ₄ for phosphoric acid or its salts
g/ and chlorate 0.8 to 0.9 g/ in terms of _ClO3
The method according to the above item 1, which is a mixture of