JPH04231479A - Method for forming chemical conversion coating on zinc or zinc alloy surface - Google Patents

Abstract

PURPOSE: To form chemical conversion films having excellent corrosion resistance and adhesiveness by subjecting the surfaces of Zn metals to a surface treatment with a liquid contg. polyvalent metal ions and complex forming agent, then to washing the surfaces with an acidic post-washing liquid contg. Al, Zn and F and drying the surfaces.

CONSTITUTION: The surfaces of a steel sheet having plating layers consisting of Zn or Zn alloy are subjected to degreasing and washing and are then surface treated by bringing the surfaces into contact with an alkaline soln. Which contains 0.3 to 3 g/l inorg. acid salt, such as nitrate of the polyvalent metals including Fe, Co, Ni, Cr, Al, etc., and 0.05 to 10 g/l org. chelating agent for maintaining the ions of the polyvalent metals in a dissolved state and complex forming agent consisting of an org. acid salt, such as salt of hexahydroxy hepanic acid and is adjusted in pH value to ≥11 by NaOH, etc. In succession, the surfaces are washed with the Al-Zn-fluoride- based post-washing liquid of 0.1 to 8.0 g/l in the total concn. of Al, Zn and F of aluminum fluorozirconate, (0.15 to 8.0):1:(5 to 52) in the molar ratio thereof and ≤5 in the pH value thereof. The chemical conversion films having the excellent corrosion resistance and coating material adhesion property are thus obtd.

COPYRIGHT: (C)1992,JPO

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a method for forming a chemical conversion film on the surface of zinc or zinc alloy, in which at least two types of polyvalent metal ions and the polyvalent metal ions are maintained in a dissolved state in the first step. containing an amount of complexing agent and p
It relates to a method in which the surface is brought into contact with a solution having an H value of 11 or more, and then washed with a post-cleaning liquid in the next step, and the use of this method as a pretreatment for subsequent painting, film lamination, or adhesive application.

0002

BACKGROUND OF THE INVENTION Such methods of forming conversion coatings include DE-C-
It is known from No. 1521854.

In order to form a film on the surface of zinc or zinc alloy, an alkaline solution containing one or more metal ions of silver, magnesium, cadmium, manganese, cobalt, iron and nickel as so-called non-alkali metal ions is used. Aqueous solutions are used. Particularly suitable solutions are highlighted that contain iron or cobalt ions as non-alkali metal ions together with the aforementioned metals. Additionally, the solution contains an amount of organic complexing agent sufficient to maintain the non-alkali metal ions in solution. The chemical conversion coating formed by these ions increases corrosion resistance and improves the adhesion of the organic coating subsequently applied.

Corrosion resistance and adhesion can be further improved by post-cleaning the surface after forming the chemical conversion film with an acidic solution containing hexavalent chromium and optionally trivalent chromium.

Although this known method shows good results with respect to corrosion resistance and adhesion, the use of trivalent chromium and especially hexavalent chromium in the passivating post-cleaning solution is disadvantageous due to the toxicity of chromium hexide and the special treatment. extremely disadvantageous due to the need for chromate detoxification.

[0006]

[Problems to be Solved by the Invention] An object of the present invention is to provide a method for forming a chemical conversion film on the surface of zinc or zinc alloy,
It is an object of the present invention to provide a method which avoids the disadvantages of the known methods, pollutes the environment no or less and gives at least equally good results with respect to corrosion resistance and paint adhesion.

[0007]

The object of the invention is to carry out a process of the type mentioned at the outset, in which according to the invention cleaning is carried out with a cleaning solution containing aluminium, zirconium and fluoride and after the pH value has been adjusted to below 5. This is achieved by

The method of the invention also applies to all surfaces containing lead or zinc alloys, such as materials consisting of solid zinc or solid zinc alloys, where the surface is coated with zinc by electrolysis, deposition from the gas phase or melt dipping. Also suitable for drawn or alloy galvanized materials. Suitable alloying partners for zinc include aluminum, silicon, lead, iron, nickel, cobalt and manganese, among others. In the case of sheet materials, galvanization or alloy galvanization can be carried out on one and both sides.

[0009] The surfaces must be clean and degreased as much as possible. If necessary, the surface is purified with alkali, neutral or acid and then suitably washed with water before chemical treatment.

[0010] When the surface of the zinc or zinc alloy has only relatively slight fat deposits and dirt, preliminary cleaning and degreasing of the surface can be dispensed with if necessary. Instead, in this case cleaning and degreasing is carried out in the treatment solution used to form the conversion coating by adding surfactants for the first stage treatment. The main advantage of this method is that the entire surface pretreatment can be carried out in fewer stages, since a separate purification and associated water washing can be omitted.

The alkaline solution used in the first stage can be applied, for example, by spraying, dipping or curtain flow.

Iron(II) is a particularly suitable alkaline solution.
I) ions and further cobalt and/or nickel and/or
or chromium (III) and/or aluminum ions in a total content of 0.3 to 3 g/l, preferably 0.4
It contained ~1.2 g/l. Polyvalent metal ions can be used as salts of inorganic acids such as nitric acid or as organic salts such as formic acid and especially acetic acid. Salts of organic acids that also serve as complexing agents can also be used. Amphoteric metals such as aluminum are dissolved in the form of hydroxy complexes without additional anions or complexing agents.

During the first stage treatment, a pickling process
Multivalent cations present on the surface to be treated and not contained in the freshly prepared bath solution may enter the treatment solution from the surface of the zinc or zinc alloy. Examples of this include zinc, aluminum and lead in hot-dip galvanized surfaces. Although the total concentration of these cations can increase to several g/l, the formation of conversion coatings is generally not hindered by this.

[0014] In particular, various organic chelating agents can be used as complexing agents. Examples include dicarboxes (malonic acid, fumaric acid, etc.); amino acids (e.g. glycine);
Hydroxycarboxylic acids (citric acid, gluconic acid, lactic acid, etc.); 1,3-diketones (e.g. acetylacetone); Aliphatic polyalcohols (e.g. sorbitol, 1,2-ethanediol); Aromatic carboxylic acids (e.g. salicylic acid, phthalic acid) ); aminocarboxylic acids (eg, ethylenediaminetetraacetic acid). other complexing agents,
For example, methanephosphonic acid diethanolamide can also be used. The amount of complex product in the solution must be at least such that the polyvalent metal ions present can be completely complexed. Therefore, when the content of polyvalent metal ions in the solution increases, the content of complexing agent also increases. The complexing agent is preferably used in the form of a neutral salt, especially an alkali metal salt, since certain complexing agents that are acidic in nature can reduce the alkalinity of the solution when increased in amount. Excess amounts of complexing agent did not result in any benefit.

Particularly desirable results are obtained when using as complexing agents salts of gluconic acid and especially salts of hexahydroxyheptanoic acid. The amount of complexing agent in the solution is between 0.05 and 10 g/l, often between 1.5 and 5.5 g/l.
1 (based on sodium hyxahydroxyheptate).

[0016] The pH value of the aqueous solution must be 11 or higher. Best results are obtained in the 12.2-13.3 pH range. The pH value can be adjusted using, for example, triethanolamine, alkali hydroxide, alkali carbonate, alkali phosphate, alkali polyphosphate, alkali pyrophosphate, alkali borate,
It is carried out with alkali silicates or mixtures thereof. Most preferred are alkali hydroxides, especially sodium hydroxide.

[0017] The temperature of the solution in the first stage may generally be between 20 and 90°C. The preferred temperature range is approximately 45
~65°C.

The treatment time is generally 2 to 60 seconds, preferably 5 to 30 seconds. The processing time varies depending on the processing method. For example, in the case of spraying, the processing time is shorter than in the case of dipping, all other things being the same.

Generally, a solution with a low metal ion concentration requires a higher temperature and a longer treatment time than a solution with a high metal ion concentration.

After formation of the conversion coating, excess processing solution should be removed from the zinc or zinc alloy surface as thoroughly as possible. This can be done by draining, squeezing, blowing, washing with water or with inorganic or organic acids such as hydrofluoric acid, boric acid,
This can be carried out by washing with an aqueous solution adjusted to be acidic (nitric acid, formic acid, acetic acid, etc.).

[0021] The post-washing liquid can be prepared, for example, by dipping, curtain flow method,
It can be applied by spray or roll coating.

According to a preferred embodiment of the invention, cleaning is carried out with a solution containing aluminum, zirconium and fluoride in a total concentration of Al+Zr+F of 0.1 to 8 g/l, preferably 0.2 to 5 g/l. The molar ratio of Al:Zr:F should preferably be adjusted to (0.15-8):1:(5-52), especially (0.15-2.0):1:(5-16). be. In a particularly preferred embodiment of the method of the invention, the Al:Zr:F ratio of the post-cleaning liquid is (0.15-0.67):
1:(5-7). The pH value is adjusted to between 2 and 5 according to another preferred embodiment of the invention.

The post-cleaning liquid used in the process of the invention contains in particular an aluminum fluorozirconate and, if there is an excess of aluminum, further aluminum salts (eg fluorides, tetrafluoroborates, nitrates). . The post-cleaning liquid is produced, for example, by first dissolving metal zirconium or zirconium carbonate in an aqueous hydrofluoric acid solution to produce complexed fluorozirconic acid. Metallic aluminum, aluminum hydroxide or aluminum salts, such as nitrates, fluorides, tetrafluoroborates, formates or acetates, are then added, preferably in solution, and optionally dissolved. The effect is not adversely affected.Although the above-mentioned method of preparation is preferably carried out, the liquid can also be prepared in other ways.

[0024] Adjustment of the pH value of the afterwash liquid is preferably carried out by means of volatile base cations. These include in particular aluminum, ethanolammonium, diethanolammonium and triathanolammonium. If specifically adjusted to the higher pH value in the specified pH value range and to the higher concentration in the specified range of the total concentration of Al + Zr + F, the liquid may become cloudy;
This turbidity has no negative effect on the operation of the method of the invention.

According to another preferred embodiment of the present invention, the surface having the chemical conversion coating contains at least one of benzoic ions, caprylic acid ions, ethylhexanoic acid ions and salicylic acid ions as anions in an amount of 0.05 to 0.5 g per anion. It is further washed with an aqueous solution containing a total concentration of 1. This further increases the corrosion protection of bare surfaces. Introduction of the anion is carried out by means of the corresponding acid or its salt.

According to another preferred embodiment of the invention, the application time of the post-cleaning is approximately 1 to 120 seconds, in particular 1 to 30 seconds. The working temperature is 20-80°C. A temperature of 20-50°C is preferred.

[0027] Preferably, fully demineralized water or low-salt water is used for the preparation of the post-cleaning bath. Water with a high salt content is not very suitable for bath preparation.

After passivation and cleaning, the surface is dried, for example in air or in an oven, and if necessary is precleaned with completely demineralized water. According to a preferred embodiment of the invention, the surface is dried after passivation and cleaning, for example by means of hot air or infrared radiation.

The method of the invention serves primarily as a pretreatment of zinc or zinc alloy surfaces before painting, film lamination or adhesive application. The method of the invention increases the adhesion of organic coatings to metal substrates, improves their resistance to blistering under corrosive action, and inhibits the progression of surface corrosion from defects into the coating.

The following examples illustrate the method of the invention in more detail.

[0031]

EXAMPLE A conversion coating was formed on a cleaned and degreased hot galvanized steel sheet by immersing it in a 55° C. solution having the following composition for 30 seconds.

[0032] Co2+ 0.3g/
lFe3+ 0.2g
/lNO3 − 1.3
g/l Sodium hexahydroxyheptanoate 2.2g/l NaOH
27.4g/l

[0033] The steel plate was then washed with water and post-washed to passivate it. For this purpose, the steel plate was immersed in the post-cleaning liquid for 5 seconds and the excess liquid was then squeezed out. 0.5 in a circulating air oven at 75℃
After drying for minutes, the pretreated steel plate was painted with an epoxy primer and an acrylate topcoat. Total paint film thickness is approximately 2
It was 5 μm.

The treated steel plate was then subjected to the following tests.

[0035] The adhesion of the coating film was tested by performing a T-bending test, in which the steel plate was bent at 180°, and each radius of curvature (Tn) was n times the thickness of the steel plate (n = 0, 1, 2). ). The test result is the percentage of the peeled area of the paint film out of the total area of the curved surface.
It was expressed as

In another treated steel plate, a cut was made to the depth of the metal substrate with a metal needle, and a cut was made with a plate shearer. The steel plate was then subjected to a salt spray test according to DIN 50021 SS for 1008 hours. The test results are expressed in terms of the undercoat penetration length (mm) measured from the cut or cut edge.

The post-cleaning solution used was a concentrated aqueous solution containing 0.855% by weight of Al, 8.62% by weight of Zr and 10.7% by weight of F with completely demineralized water at 1.6 g/l (after washing). Washing solution A) was diluted to 20 g/l (post-washing B). The pH value of both solutions was adjusted to about 3.6 with ammonia.

For comparison, Cr(VI) with a pH value of about 3.3
/Cr(III)-containing post-cleaning liquid (post-cleaning liquid C) was used.

The composition of the post-cleaning solution was as follows.

Post-cleaning liquid A: Al 0.014g/l Zr　　　　0.14g/l F 0.17g/l NH4　　　0.016g/l

Post-cleaning liquid B: Al　　　　0.17g/l Zr　　　1.72g/l F 2.14g/l NH4　　　0.40g/l

Post-cleaning liquid C: Cr6+ 2.0g/l Cr3+ 0.8g/l F 0.2g/l Zn 0.3g/l

The test results are shown in the following table.

[0044]

[Table 1]

[0045]

[Table 2]

As is clear from a comparison of the values in the table, the method of the present invention is effective in both cases for the Cr(V
I)/Cr(III)-based post-cleaning solution showed values at least equal to or better than the comparative method.

[0047]

A method can be provided which causes no or little environmental pollution and which gives at least equally good results in terms of corrosion resistance and paint adhesion.

Claims (11)

[Claims] 1. A method for forming a chemical conversion film on the surface of zinc or a zinc alloy, wherein the first step comprises forming a complex with at least two types of polyvalent metal ions and an amount to maintain the polyvalent metal ions in a dissolved state. A method in which the surface is brought into contact with a solution containing an agent and having a pH value of 11 or more, and the surface is washed with a post-cleaning liquid in the next step, the surface containing aluminum, zirconium, and fluoride and having a pH value of 5 or less. 1. A method for forming a chemical conversion film on the surface of zinc or zinc alloy, the method comprising cleaning with a cleaning solution after adjusting the temperature. Claim 2: The total concentration of Al+Zr+F is 0.1 to 8.
2. A method as claimed in claim 1, characterized in that washing is carried out with a post-washing liquid having a concentration of 0 g/l, preferably between 0.2 and 5.0 g/l. Claim 3: Al:Zr:F in molar ratio (0.15 to 8
．． 0):1:(5-52), preferably (0.15-2
．． 3. The method according to claim 1 or 2, wherein cleaning is performed with a cleaning liquid after adjusting the ratio to 0):1:(5 to 16). Claim 4: Al:Zr:F in molar ratio (0.15 to 0
．． 67): The method according to any one of claims 1 to 3, characterized in that cleaning is performed with a cleaning liquid after adjusting the ratio to be 1: (5 to 7). 5. The method according to claim 1, wherein washing is carried out with a washing liquid after the pH value is adjusted to 2 to 5. 6. Washing with a washing liquid is carried out after the pH value has been adjusted with a cation of a volatile base, preferably ammonium ion, ethanol ammonium ion, diethanol ammonium ion or triethanol ammonium ion. 5. The method according to any one of 5. 7. Cleaning with a post-cleaning solution further containing at least one of benzoate ion, caprylate ion, ethylhexanoate ion, and salicylate ion as an anion at a total concentration of 0.05 to 0.5 g/l. 7. A method according to any one of claims 1 to 6. [Claim 8] Use a post-cleaning solution for 1 to 120 seconds, preferably 1 to 120 seconds.
8. A method according to any one of claims 1 to 7, characterized in that the washing is carried out for ~30 seconds. (9) Claim 1, characterized in that cleaning is performed with a cleaning liquid after the temperature is 20-80°C, preferably 20-50°C.
9. The method according to any one of 8 to 8. 10. The method according to claim 1, wherein the surface is dried after post-cleaning. 11. Use of the method according to any one of claims 1 to 10 as a pretreatment for subsequent painting, film lamination or adhesive application.