JPH04228579A - Method for treating metal surface with phosphate - Google Patents

Abstract

PURPOSE: To prepare phosphate films which are free from the defects based on Ni (compd.) and have the quality equiv. to the quality of conventional phosphate films by treating metallic surfaces with an acidic phosphate soln. which contains specific ratios of Zn, Mn and Cu and does not basically contain Ni.

CONSTITUTION: The metallic surfaces are treated by the phosphate soln. which does not basically contain Ni, 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 and 5 to 30 g/l phosphate (in terms of P₂O₅), is held at ≤0.1g/l in the concn. of Fe²⁺ in the liquid by using oxygen and/or an oxidizing agent having the same effect and is adjusted to a pH value of 3.0 to 3.8. The content of the Zn is preferably about 0.3 to 1.0 g/l at the time of using the soln. by a spraying system and the content of the Zn is preferably about 0.9 to 1.7 g/l at the time of using the soln. by a combination system of spraying and immersing. The treatment method described above is applied to steel, Zn (alloy) coated steel and Al (alloy), and further, the soln. is preferably used for a pretreatment for electrodeposition coating.

COPYRIGHT: (C)1992,JPO

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for treating metal surfaces with an acidic phosphate aqueous solution containing zinc, manganese and phosphoric acid ions, and an oxidizing agent, particularly for treating steel, galvanized steel and zinc alloys. The present invention relates to a method of treating the surfaces of gold-plated steel, aluminum and aluminum alloys with the above-mentioned aqueous solution, and a method of using the above-mentioned method as a pre-treatment for painting, especially electrodeposition painting.

0002

BACKGROUND OF THE INVENTION Metals are treated with phosphates in order to produce metal phosphate coatings on metal surfaces which adhere firmly and which essentially improve corrosion resistance. Furthermore, when the above coating is combined with paint or other organic coatings, the adhesion of the paint or the like and the corrosion resistance of the surface may be substantially improved. The metal phosphate film also functions as an insulator that blocks the flow of current, and also has the effect of reducing sliding friction by combining with a lubricant.

By the way, pretreatment before painting requires, for example, 0.
Particularly suitable is a low zinc phosphate coating method using a phosphate solution containing a relatively low concentration of zinc ions of 5 to 1.5 g/l. And under this condition, phosphophyllit (PHOSPHOPHYLLIT; Zn2
A phosphate film with a high content of Fe(PO4)2.4H2O) is formed on the steel surface. Note that this phosphophyllite is derived from Hopeite (Zn3 Fe(PO4)2 .
4H2O) has much higher corrosion resistance.

[0004] When the above-mentioned 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 and e.g.
A low zinc phosphate treatment method containing 3 to 2.0 g/l of nickel ions is widely applied as a so-called three-cation method in pre-painting treatment of metal surfaces, for example in cathodic electrodeposition coating of automobile bodies.

[0005]

[Problems to be Solved by the Invention] However, nickel ions are present in a high concentration in the phosphate solution of the three-cation method, and nickel and nickel compounds exist in the phosphate film formed. It has been pointed out that the high content of is dangerous from the standpoint of occupational safety and health and environmental conservation.

The problem to be solved by the present invention is to provide a phosphate film which is comparable in quality to the film produced by the above-mentioned three-cation method using Zn--Mn--Ni as the main ingredient, but which does not have the drawbacks due to the presence of nickel and nickel compounds. The object of the present invention is to provide a method for phosphating metals such as steel, galvanized steel, zinc alloy coated steel, aluminum and aluminum alloys, which results in the formation of metals.

[0007]

[Means for Solving the Problems] This problem can be solved by the present invention, which develops the film forming method described at the beginning in the following manner. In other words, this method basically does not contain nickel and has a nickel content of 0.3 to 1.7.
g/l Zn0.2 or
4.0 g/l Mn0.0
01 to 0.030 g/l
Cu5 to 30
g/l phosphate (P2O
The concentration of Fe(II) in the liquid is maintained below 0.1 g/l using oxygen and/or other oxidizing agents having a similar effect, and the pH value is maintained between 3.0 and 3. The metal surface is contacted with a phosphate solution adjusted to .8.

The method according to the invention applies in particular to steel, galvanized steel, zinc alloy coated steel, aluminum and aluminum alloys. The concept of steel here includes unalloyed mild steel, semi-high strength and high strength steel (e.g. microalloyed steel, dual-phase steel).
phase) and phosphorus alloyed steels) and low alloy steels. Note that the galvanized layer is made, for example, by electrolysis, melt dipping, or vapor deposition.

Typical qualities of zinc here include pure zinc and alloys containing, for example, Fe, Ni, Co, Al, and Cr. In addition, aluminum and its alloys herein refer to casting and forging materials used in the metal industry, and include alloy components such as Mg, Mn, Cu, and Si.
, Zn, Fe, Cr, Ni, and Ti.

A fundamental requirement for the process of the invention is that the acidic phosphate solution is in principle free of nickel. This means that under industrial conditions the nickel concentration in the phosphate solution is below 0.0002 to 0.01 g/l. However, 0.0001
It is preferable that it is below g/l.

Other essential features of the present invention include:
Mention may be made of the presence of three metal ions, Zn, Mn, Cu, in said concentrations. And especially when processing steel,
When the Zn concentration is less than 0.3 g/l, film formation deteriorates. When the Zn concentration is 1.7 g/l or more, the phosphophyllite content in the phosphate film formed on the steel surface is significantly reduced. Also, when the phosphate film thus produced is combined with paint, it exhibits very poor quality.

Next, when the Mn concentration is less than 0.2 g/l, no advantage is seen in adding this cation. Moreover, even if the concentration is increased to 4 g/l or more, no further improvement in quality is observed. Furthermore, the Cu concentration is 0.001 to 0.
030 g/l, but below 0.001, the favorable effect on film formation and film quality is lost;
Above 0.030 g/l, harmful Cu cementation increases.

When forming a phosphate coating on steel, Fe migrates into solution in the form of Fe(II). The phosphate treatment bath therefore has a steady state concentration of Fe(II) ions of 0.
It must contain enough oxygen and/or other oxides to not exceed 1 g/l. That is, more Fe is converted to Fe(III),
It will precipitate as iron phosphate sludge.

To ensure the formation of a perfect phosphate film, the pH value of the phosphate solution should be between 3.0 and 3.8.
must be adjusted. A higher pH value is selected when the bath temperature is lower or the bath concentration is lower; a 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 to adjust this pH value, another cation, such as an alkali metal ion (Na, K
, NH4 etc.) and/or alkaline earth metal ions (Mg, Ca) and other anions (NO3, Cl
, SiF6, SO4, BF4, etc.) may be added to the phosphate solution.

In addition, the pH value of the above phosphate solution can be adjusted by adding basic compounds (NaOH, N
a2 CO3, ZnO, ZnCO3, MnCO3
Others) or acids (HNO3, H3 PO4, H2
It may be adjusted by adding SiF6, HCl, etc.).

By the way, 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. In that case, the optimum concentration is preferably in the range of 0.4 to 1.3 g/l. Note that 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 in a spray method, the Zn concentration is preferably 0.3 to 1 g/l. In addition, when using the combination method of spray and immersion, or the immersion method, the Zn concentration is 0.9.
Preferably, the amount is between 1.7 g/l and 1.7 g/l. Note that the preferable Mn concentration is 0.4 to 1.3 regardless of the above methods.
It is preferable that it is g/l.

Next, the Cu content in the phosphate solution is 0.0
0.03 to 0.020 g/l, but 0.00
It is preferably in the range of 3 to 0.020 g/l. In order to obtain a particularly good phosphate film, Cu and P2 O5
This would be when the weight ratio of 1:(5 to 2,000) with

In order to limit the Fe(II) concentration, the phosphate solution is then contacted with oxygen, for example atmospheric oxygen, and/or added with a suitable oxidizing agent. Preferred oxidizing agents are nitrites, chlorates, bromates, peroxy compounds (H2 O2, perborates, percarbonates, perphosphates, etc.) and organic nitro compounds, such as nitrobenzenesulfonates.

[0021] These oxidizing agents may be used alone or in combination, and in some cases 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 nitrates), peroxy compounds and NO3, bromates and nitrates, and chlorates and nitrobenzenesulfonates (nitrates). Note that the above-mentioned oxidizing agent not only serves to oxidize Fe(II) ions, but also has the effect of promoting the formation of a phosphate film.

By the way, the typical concentration of the above-mentioned oxidizing agent in the phosphate treatment bath is nitrite: 0.04 to 0.
．． 5 g/l; chlorate: 0.5 to 5 g/l; bromate: 0.3 to 4 g/l; peroxy compounds (H2
O2 equivalent): 0.005 to 0.1 g/l; nitrobenzene sulfonate: 0.05 to 1 g/l.

The metal surface is then preferably treated with a phosphate solution to which are added a group of compounds with an additional modifying effect. This group consists of surfactants, hydroxycarboxylic acids, tartrates, citrates, simple fluorides, borofluorides, and silicofluorides.

Among the above groups, surfactants (for example, 0
．． Addition of 0.05 to 0.5 g/l) improves the formation of phosphate films on lightly oiled metal surfaces. Hydroxycarboxylic acids, such as tartaric acid, citric acid and their salts, also lead to a significant reduction in phosphate film weight, for example in the concentration range of 0.03 to 0.3 g/l.

Furthermore, simple fluorides promote the formation of a relatively non-corrosive phosphate film, and in doing so, shorten the minimum time required for phosphate film treatment, and also reduce the surface masking rate of the phosphate film. It also increases. For this purpose, an F concentration of, for example, 0.1 to 1 g/l is suitable.

By controlling the addition of this simple fluoride, it is possible to form a crystalline phosphate film on aluminum and its alloys. Furthermore, BF4
and SiF6 also affect the aggressiveness (A) of the phosphate film treatment bath.
This is particularly evident when treating dry galvanized surfaces. In this case, the amount added is preferably 0.4 to 3 g/l, for example.

The phosphate solution according to the present invention is applied to metal surfaces by spraying, spraying and dipping, or dipping. The bath temperature is usually 40 to 60℃.
is kept within the range of Furthermore, regarding the treatment time, in the case of steel and aluminum, 1 to 5 minutes is sufficient to deposit a uniformly covering phosphate film. In the case of galvanized steel, on the other hand, less than 10 seconds is often sufficient. The method of the invention can therefore also be used in installations for conveying strips at high speeds.

Before being treated with a phosphate solution, metal surfaces are generally cleaned, rinsed, and often treated with a titanium phosphate-based activator.

The phosphate film layer produced 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/m2 when treating steel, galvanized steel and zinc alloy plated steel, and 0.5 to 2.5 g/m2 when treating aluminum and its alloys. It is often m2.

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

[0031] The above-mentioned phosphate coating is used, inter alia, for corrosion protection, to facilitate cold working without cutting, and to
It can be effectively used to obtain electrical insulation. Furthermore, this phosphate film is preferably used for pretreatment of metal surfaces for painting, especially for electrocoating. Particularly good results are obtained when combined with cathodic electrodeposition.

[0032] The above-mentioned phosphate film is coated with, for example, Cr(VI), Cr(VI)-Cr(III), Cr before the coating.
(III), Cr(III)-fluorozirconium complex salt, Al(III), Al(III)-fluorozirconium complex salt is recommended to be treated with a passivating rinse agent as a main ingredient. This will further improve the adhesion and corrosion resistance of the coating.

[0033]

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

It was then rinsed with water and, if necessary, pretreated with a titanium phosphate-containing solution for activation, after which a phosphate film was formed at a temperature of 50°C. . Twelve types of phosphate solutions were used as shown in Table 1.

Note) NBS: Nitrobenzenesulfonate sodium salt Total acid amount: 0.1N per 10ml of bath sample
NaOH consumption ml (Fe(II) concentration is 0.1 g/l for all baths)
Met.

It can be seen from the table that a phosphate film of uniform thickness was obtained in all the test examples. It has been found that this phosphate film exhibits high corrosion resistance and corrosion penetration resistance when combined with cathodic electrodeposition coatings and coatings such as those used in the automobile industry.

[0037]

[Effects of the Invention] Since the present invention has the above-mentioned configuration,
No nickel in the processing solution. Moreover, nickel is not present in the formed phosphate film.

[0038] Therefore, not only is there no danger at all in terms of occupational safety and health and environmental protection, but the quality of the phosphate film formed by the method of the present invention is no different from that of conventional methods.

Claims (11)

[Claims] Claims: 1. A method of treating a metal surface with an acidic phosphate aqueous solution containing zinc, manganese and phosphoric acid ions and an oxidizing agent, which basically does not contain nickel and has 0.
3 to 1.7 g/
l Zn0.2 or
4.0 g/l Mn0.001
or 0.030 g/l
Cu5 to 30
g/l phosphate (P2 O5
The concentration of Fe(II) in the liquid is maintained below 0.1 g/l using oxygen and/or other oxidizing agents having a similar effect, and the pH value is maintained between 3.0 and 3.0 g/l. A method of treating metal surfaces with a phosphate solution adjusted to 8. 2. The metal surface is treated with a phosphate solution additionally containing up to 3 g/l, preferably between 0.4 and 1.3 g/l of Mg and/or Ca. Method. 3. The method according to claim 1, wherein the metal surface is brought into contact with a phosphate solution containing 0.3 to 1.0 g/l of Zn by spraying. 4. The method of claim 1 or 2, 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.
Method described. 5. A method according to claim 1, 2, 3 or 4, characterized in that the metal surface is treated with a phosphate solution containing 0.4 to 1.3 g/l of Mn. Claim 6: 0.003 to 0.020 g/l of Cu
The method according to claim 1, 2, 3, 4 or 5, characterized in that the metal surface is treated with a phosphate solution containing. 7. The weight ratio of Cu to phosphate (in terms of P2 O5) is 1: (170 to 30,000), and C
u and P2 O5 in a weight ratio of 1:(5 to 2000
) The method according to claim 1, 2, 3, 4, 5 or 6. Claim 8: A claim characterized in that 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, 3
, 4, 5, 6 or 7. 9. A phosphate solution containing a compound having an additional modifying action belonging to the group of surfactants, hydroxycarboxylic acids, tartrates, citrates, simple fluorides, borofluorides, and silicofluorides. 9. A method according to claim 1, 2, 3, 4, 5, 6, 7 or 8, characterized in that metal surfaces are brought into contact. 10. Use of one of the methods according to claims 1 to 9 for pretreatment of metal surfaces to be painted, in particular electrocoated. Claim 11: Steel, galvanized steel, zinc alloy plated steel,
10. Use of one of the methods according to claims 1 to 9 in treating aluminum and aluminum alloys with phosphates.