JP3063920B2 - How to treat metal surfaces with phosphate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a metal surface with an aqueous solution of an acidic phosphate containing ions of zinc, manganese and phosphate and an oxidizing agent. Gold-plated steel, a method of treating the surface of aluminum and aluminum alloy with the above aqueous solution, and
It relates to the use of the above method as a pretreatment for painting, in particular for electrodeposition painting.

[0002]

BACKGROUND OF THE INVENTION Metals are treated with phosphates to form a metal phosphate coating on the metal surface that adheres firmly and essentially improves corrosion resistance. It should be noted that if the coating is combined with paint or another organic coating, the adhesion of paint and the like and the corrosion resistance of the surface could be substantially improved. The metal phosphate film also functions as an insulator that prevents the flow of current, and has an effect of reducing sliding friction by being combined with a lubricant.

[0003] By the way, the pre-treatment before coating includes, for example, 0.1.
Particularly suitable is a low zinc phosphate film formation method using a phosphate solution containing a relatively low concentration of zinc ions of 5 to 1.5 g / l. Under these conditions, the phosphofilit (PHOSPHOPHYLIT; Zn ₂ F
A phosphate film with a high e (PO ₄ ) ₂ .4H ₂ O) content is formed on the steel surface. In addition, this phosphofilite is formed by Hopeite (Zn ₃ Fe (PO ₄ ) ₂ .4H ₂ O) precipitated from a high zinc phosphate solution.
Corrosion resistance is much higher than

When the low zinc phosphate solution contains nickel ions and / or manganese ions,
The anticorrosion effect in cooperation with the paint film is further improved. For example, 0.
5 to 1.5 g / l of manganese ions, e.g.
The low zinc phosphate treatment method containing 3 to 2.0 g / l of nickel ions is widely applied as a so-called trication method to a pretreatment for coating a metal surface, for example, to a cathode electrodeposition coating of an automobile body.

[0005]

However, the phosphate solution of the above-mentioned trication method contains a high concentration of nickel ions, and the nickel and nickel compounds present in the formed phosphate film. It has been pointed out that the high content of this substance is dangerous from the viewpoint of occupational safety and health and environmental protection.

The problem to be solved by the present invention is that the phosphate film which is comparable in quality to the film formed by the above-mentioned trication method using Zn @ Mn-Ni as a main component, but does not have the drawbacks caused by the presence of nickel and a nickel compound. It is an object of the present invention to provide a phosphating method which results in the formation of a metal, such as steel, galvanized steel, galvanized steel, aluminum and aluminum alloys.

[0007]

This problem can be solved by the present invention in which the above-described film forming method is developed into the following form. That is, this method basically does not contain nickel, and contains 0.3 to 1.7 g / l Zn 0.2 to 4.0 g / l Mn 0.001 to 0.030 g / l Cu 5 to 30 g / l 1 containing phosphate (in terms of P ₂ O ₅ ), maintaining the Fe (II) concentration in the solution at 0.1 g / l or less using oxygen and / or another oxidizing agent having a similar effect, The metal surface is contacted with a phosphate solution whose pH has been adjusted to between 3.0 and 3.8.

The method according to the invention applies in particular to steel, galvanized steel, galvanized steel, aluminum and aluminum alloys. As used herein, the concept of steel includes non-alloyed mild steel, semi-high tensile and high tensile steel (e.g., microalloyed steel (mikrolegiert), duplex stainless steel (Dual-
Phase) and phosphorus alloyed steels) and low alloy steels. The galvanized layer is formed by, for example, electrolysis, melt immersion, or vapor deposition.

The typical quality of zinc here is pure zinc and an alloy containing, for example, Fe, Ni, Co, Al and Cr. Also, the aluminum and its alloys referred to herein refer to casting and forging materials used in the metal industry, and include, for example, Mg, Mn, Cu, S
It contains i, Zn, Fe, Cr, Ni and Ti.

A fundamental requirement for the process according to the invention is that the acidic phosphate solution is essentially free of nickel. This means that under industrial conditions the nickel concentration in the phosphate solution is from 0.0002 to 0.01 g / l. However, 0.0001
g / l or less.

[0011] Other essential features of the present invention include:
Three types of metal ions, Zn, Mn, and Cu, may be present at the above concentrations. And especially when processing steel
When the Zn concentration is 0.3 g / l or less, the film formation deteriorates. When the Zn concentration is 1.7 g / l or more, the content of the phosphofilite in the phosphate film formed on the steel surface is greatly reduced. Also, when the resulting phosphate film is combined with paint, it will exhibit very poor quality.

When the Mn concentration is 0.2 g / l or less, there is no advantage in adding this cation. Even when the concentration is 4 g / l or more, no further improvement in quality is observed. Further, the Cu concentration is 0.001 to 0.5.
030 g / l, but if it is 0.001 or less, favorable effects on film formation and film quality are lost.
Above 0.030 g / l, harmful Cu cementation increases.

When a phosphate film is formed on steel, Fe migrates into solution in the form of Fe (II). Therefore, the phosphating bath has a steady concentration of Fe (II) ions of 0,1.
Sufficient oxygen and / or other oxides must be contained in order not to exceed 1 g / l. That is, more Fe is converted to Fe (III),
It will precipitate as iron phosphate sludge.

To ensure that a perfect phosphate film is formed, the pH of the phosphate solution should be between 3.0 and 3.8.
Have to be adjusted. The higher pH value is selected when the bath temperature is lower or the bath concentration is lower. The lower pH value is selected when the bath temperature is higher or the bath concentration is higher. Will be selected in case.

Next, if necessary for adjusting the pH value, another cation such as an alkali metal ion (Na,
K, NH _{4 and} others) and / or alkaline earth metal ions (Mg, Ca) and another anion (NO ₃ , Cl,
SiF ₆ , SO ₄ , BF ₄ etc.) may be added to the phosphate solution.

The pH value of the above phosphate solution may be adjusted during preparation or use of the solution, if necessary, with a basic compound (NaOH, N
a ₂ CO ₃ , ZnO, ZnCO ₃ , MnCO ₃ etc.)
Or acid (HNO ₃ , H ₃ PO ₄ , H ₂ SiF ₆ , HC
1) may be added for adjustment.

The quality of the phosphate film can be improved by adding 3 g / l or less of Mg and / or Ca to the phosphate solution. The optimum concentration in that case is preferably in the range of 0.4 to 1.3 g / l. These cations are preferably added to the phosphate solution in the form of a phosphate or the above-mentioned anion salt. In addition, oxides, hydroxides, and carbonates can also be used as Mg or Ca sources.

Next, when the above phosphate solution is used by a spray method, the Zn concentration is preferably 0.3 to 1 g / l. When used in combination with spray and dipping, or dipping, the Zn concentration is 0.9.
To 1.7 g / l. The preferred Mn concentration is 0.4 to 1.3 regardless of the above-mentioned methods.
g / l.

Next, Cu in the above phosphate solution is 0.0%
03 to 0.020 g / l, but 0.00
It is preferably in the range of 3 to 0.020 g / l. A particularly good phosphate film will be obtained when the weight ratio of Cu to P ₂ O ₅ is replenished at 1: (5 to 2000).

The phosphate solution is then contacted with oxygen, for example atmospheric oxygen, and / or with the addition of a suitable oxidizing agent in order to limit the Fe (II) concentration. As the oxidizing agent, nitrite, chlorate, bromate, peroxy compounds (H ₂ O ₂ , perborate, percarbonate, perphosphate and the like) and organic nitro compounds such as nitrobenzene sulfonate are preferable. .

These oxidizing agents may be used alone or in combination, but may be used in combination with a relatively weak oxidizing agent such as nitrate. Suitable combinations are, for example, nitrite and nitrate, nitrite and chlorate (or nitrate), peroxy compounds and NO ₃ , bromate and nitrate, chlorate and nitrobenzenesulfonate (nitrate). Note that the oxidizing agent not only serves to oxidize Fe (II) ions, but also has an effect of promoting formation of a phosphate film.

The typical concentrations of the above oxidizing agents in the phosphating bath are: nitrite: 0.04 to 0.5 g / l; chlorate: 0.5 to 5 g / l; : 0.3 to 4 g / l; peroxy compound (H ₂
O ₂ equivalent): 0.005 to 0.1 g / l; nitrobenzenesulfonate: in the range of 0.05 to 1 g / l.

The metal surface is then preferably treated with a phosphate solution to which a group of compounds having an additional modifying action has been added. This group consists of surfactants, hydroxycarboxylic acids, tartrate salts, citrate salts, simple fluorides, borofluorides and silicofluorides.

The addition of a surfactant (eg 0.05 to 0.5 g / l) from the above group improves the formation of a phosphate film on lightly oiled metal surfaces. Also, hydroxycarboxylic acids such as tartaric acid, citric acid and their salts, for example, in the concentration range of 0.03 to 0.3 g / l, lead to a significant reduction in phosphate coating weight.

In addition, simple fluorides promote the formation of phosphate coatings which are relatively hard to corrode, while also reducing the minimum time required for phosphate coating treatment, and the surface coverage of the phosphate coating. Also enhance. For this purpose, an F concentration of, for example, 0.1 to 1 g / l is appropriate.

By controlling the addition of this simple fluoride, a crystalline phosphate film can be formed on aluminum and its alloys. BF ₄ and SiF ₆ are also aggressive (Aggres
sivitaet), which is particularly apparent during the treatment of dry galvanized surfaces. In this case, the amount added is, for example, preferably 0.4 to 3 g / l.

The phosphate solution of the present invention is applied to a metal surface by spraying, spraying and dipping, or dipping. The bath temperature is usually 40 to 60 ° C.
Is kept in the range. In addition, in the case of steel and aluminum, a treatment time of 1 to 5 minutes is sufficient for depositing a uniformly coated phosphate film. On the other hand, in the case of galvanized steel, less than 10 seconds is often sufficient. Therefore, the method of the present invention can also be used for equipment for feeding a strip at a high speed.

Before being treated with the phosphate solution, the metal surface is generally washed, rinsed and often treated with an activator based on titanium phosphate.

The phosphate film formed by the phosphate film forming method of the present invention is microcrystalline and has a uniform thickness. The weight per unit surface is 1.5 to 4.5 g / m ^{2 for} steel, galvanized steel and zinc alloy-plated steel, and 0.5 to 2.5 g for aluminum and its alloys. / M ² .

The composition of the phosphate solution may be, for example, the formation of a phosphate film, the generation of sludge, the mechanical loss due to the solution remaining on the treated metal surface, the mechanical loss in removing sludge, Alternatively, it is consumed during the phosphating process by redox reaction and decomposition. For this reason, the phosphating bath must be monitored analytically and any missing components must be replenished.

The above-mentioned phosphate film is used, in particular, for corrosion protection, to facilitate cold working without cutting, and
It can be used effectively to obtain electrical insulation. Furthermore, the phosphate coating is preferably used for painting metal surfaces, especially for pretreatment of electrodeposition coating. And particularly good results are obtained when combined with cathodic electrodeposition coating.

Prior to the coating, the phosphate film is made of, for example, Cr (VI), Cr (VI) ─Cr (III),
It is recommended to treat with a passivating rinsing agent based on (III), Cr (III) ─fluorozirconium complex, Al (III), Al (III) ─fluorodisilconium complex. This will further improve the adhesion of the coating and the corrosion penetration resistance.

[0033]

EXAMPLE First, steel, galvanized steel, and aluminum sheets were degreased with an alkaline cleaner.

Next, a rinse with water was carried out and, if necessary, a pretreatment with a titanium phosphate-containing solution was carried out for activation, after which a phosphate film was formed at a temperature of 50 ° C. . The phosphate solutions used at that time are 12 types shown in Table 1.

[0035] Note) NBS: Total acid amount of nitrobenzenesulfonate / sodium salt: 0.1 N N per 10 ml of bath sample
aOH consumption ml (F The Fe (II) concentration for all baths was 0.1 g / l.
Met.

From the table, it can be seen that in all the test examples, a phosphate film having a uniform thickness was obtained. It has been found that this phosphate coating exhibits high corrosion resistance and corrosion penetration resistance when combined with cathodic electrodeposition coating and coatings such as those performed in the automotive industry.

[0037]

Since the present invention has the above configuration,
There is no nickel in the processing solution. Also, nickel does not exist in the formed phosphate film.

Therefore, not only is there no danger in terms of occupational safety and health and environmental protection, but also the phosphate film formed by the method of the present invention has no color at all in comparison with the conventional one.

Continued on the front page (72) Inventor Berner Rausch, Germany 6370 Oberursel, Urseemerstraße 43 (72) Inventor Peter Schübach, Germany 6369 Schöneck-Oberdorfelden, Im Grün-Tchen 14 (56) References JP-A-3-87374 (JP, A) JP-A-59-110785 (JP, A) JP-A-3-61385 (JP, A) (58) Fields studied (Int. ⁷ , DB name) C23C 22/00-22/86

Claims (11)

(57) [Claims] 1. A method for treating a metal surface with an aqueous acidic phosphate solution containing ions of zinc, manganese and phosphoric acid and an oxidizing agent, wherein the method is essentially free of nickel, and contains 0.3 to 1. Contains 7 g / l Zn 0.2 to 4.0 g / l Mn 0.001 to 0.030 g / l Cu 5 to 30 g / l phosphate (in terms of P ₂ O ₅ ), and contains oxygen and / or Using another oxidizing agent having a similar effect, the Fe (II) concentration in the solution is kept at 0.1 g / l or less, and the pH value is adjusted to 3.0 to 3.8 with a phosphate solution. A method for treating metal surfaces. 2. The metal surface according to claim 1, wherein the metal surface is treated with a phosphate solution additionally containing up to 3 g / l, preferably 0.4 to 1.3 g / l of Mg and / or Ca. Method. 3. The method according to claim 1, wherein the metal surface is contacted with a phosphate solution containing 0.3 to 1.0 g / l of Zn by spraying. 4. The method according to claim 1, wherein the metal surface is brought into contact with a phosphate solution containing 0.9 to 1.7 g / l of Zn by a combination of spraying and dipping.
The described method. 5. The method according to claim 1, wherein the metal surface is treated with a phosphate solution containing 0.4 to 1.3 g / l of Mn. 6. 0.003 to 0.020 g / l of Cu
The method according to claim 1, 2, 3, 4, or 5, wherein the metal surface is treated with a phosphate solution containing. 7. The weight ratio of Cu to phosphate (in terms of P ₂ O ₅ ) is 1: (170 to 30,000) and Cu and P ₂ O ₅ are supplied in a weight ratio of 1: (5 to 2,000). 7. The method of claim 1,2,3,4,5 or 6, wherein said method is performed. 8. The metal surface is brought into contact with a phosphate solution containing an organic nitro compound such as nitrite, chlorate, bromate, peroxy compound, or nitrobenzene sulfonate as an oxidizing agent. Terms 1, 2,
The method according to 3, 4, 5, 6 or 7. 9. A phosphate solution containing a compound belonging to the group of surfactants, hydroxycarboxylic acids, tartrate salts, citrate salts, simple fluorides, borofluorides and silicofluorides, which has an additional modifying action. The method according to claim 1, 2, 3, 4, 5, 6, 7, or 8, wherein the metal surface is brought into contact. 10. Use of one of the methods according to claims 1 to 9 for the pretreatment of a metal surface to be coated, especially for electrodeposition coating. 11. A steel, galvanized steel, zinc alloy-plated steel,
10. Use of one of the methods of claims 1 to 9 in treating aluminum and aluminum alloys with phosphate.