WO2000047799A1

WO2000047799A1 - Method for phosphatizing zinc or aluminium surfaces

Info

Publication number: WO2000047799A1
Application number: PCT/EP2000/000865
Authority: WO
Inventors: Thomas Nitschke; Werner Rentsch
Original assignee: Chemetall Gmbh
Priority date: 1999-02-10
Filing date: 2000-02-03
Publication date: 2000-08-17
Also published as: DE19905479A1; CA2362556A1; EP1155163A1; DE50004321D1; AU2669400A; EP1155163B1; ATE253651T1

Abstract

The invention relates to a method for phosphatizing zinc or aluminium surfaces with a phosphatizing solution containing 0.5 to 2.0 g/l Zn<2+>, 0.3 to 2.0 g/l Ni<2+>, 0.1 to 0.4 g/l NH2OH, at least 3.0 g/l NO3<-> and 10.0 to 20.0 g/l phosphate (calculated as P2O5). Said solution is applied to the surfaces by immersion or spraying at 35 to 75 DEG C, the immersion time being 0.5 to 10 minutes and the spraying time being 3 seconds to 5 minutes.

Description

Process for phosphating zinc or aluminum surfaces

The invention relates to a method for phosphating zinc or aluminum surfaces with a phosphating solution based on zinc and nickel as cations and hydroxylamine as accelerators, which may additionally contain fluoride and / or complex-bound fluoride.

The zinc surfaces are part of workpieces made of zinc or zinc alloys, or they are applied by hot-dip galvanizing or by electrolytic galvanizing to workpieces containing iron, in particular to workpieces made of iron and steel. The aluminum surfaces are part of workpieces made of aluminum or aluminum alloys. Varnishes, paints, plastic layers or oils can be applied to the phosphated zinc and aluminum surfaces, and the surfaces provided with such an application are considerably better protected against corrosion by the phosphating.

Processes for phosphating metallic materials which work with a phosphating solution which contains hydroxylamine as an accelerator have been known for some years. For example, EP-A 0 315 059 discloses a process for phosphating surfaces made of iron, which works with a phosphating solution which contains 0.5 to 50 g / l hydroxylamine and 0.2 to 2.0 g / l Zn ²⁺ and 3 contains up to 25 g / l phosphate. The phosphating solution can additionally contain iron, manganese, nickel, nitrate, fluoride and / or complex fluorides. The known method is suitable not only for phosphating surfaces made of iron, but also surfaces made of zinc, zinc alloys, aluminum and aluminum alloys. This method has the disadvantage that it works with higher hydroxylamine concentrations which are equal to or> 0.5 g / l, because hydroxylamine is relatively expensive and comparatively unstable. DE-A 195 38 778 discloses a method for phosphating surfaces made of steel, galvanized steel, alloy-galvanized steel and aluminum, in which the metal surface is immersed in a phosphating solution for a period of between 1 and 8 minutes which is 0.5 to Contains 2 g / l zinc ions, 2 to 25 g / l phosphate ions and 1, 2 to 5 g / l hydroxylamine in free, ionic or complex-bound form, has a free acid content between 0 and 1, 5 points and a temperature in Has a range of 32 to 93 ° C. This phosphating solution can additionally contain 0.2 to 1.5 g / l manganese ions, 0.2 to 1.5 g / l nickel ions and additionally fluoride in free and / or complex-bound form in amounts of up to 2.5 g / l total Contain fluoride. Finally, the phosphating solution should not contain more than 0.5 g / l nitrate ions. This process also works with relatively high hydroxylamine concentrations and limits the nitrate content to less than 0.5 g / l.

DE-A 196 06 018 describes a method for phosphating metal surfaces made of steel, galvanized or alloy-galvanized steel and / or aluminum, in which the metal surfaces are sprayed or

Dive for a time between 3 seconds and 8 minutes with a zinc-containing one

Phosphating solution in contact that contains 0.2 to 3 g / l zinc ions, 3 to 50 g / l

Phosphate ions, 1 to 100 mg / l nickel ions, one or more accelerators, e.g. B. 0.01 to 0.2 g / l nitrite and 0.1 to 10 g / l hydroxylamine, wherein the

The nitrate content of this solution is <0.5 g / l. The solution can additionally 0.1 to 4 g / l

Manganese ions and up to 2.5 g / l total fluoride. The in DE-A 196

Examples given in 06 018 show that the known process works with comparatively high hydroxylamine concentrations (1.7 g / l hydroxylammonium sulfate) and avoids a nitrate content.

DE-A 196 21 184 discloses a method for phosphating metal surfaces made of steel, galvanized or alloy-galvanized steel, aluminum and / or aluminum-magnesium alloys, in which the Contact metal surfaces by spraying or dipping for a time between 3 seconds and 8 minutes with a zinc-containing phosphating solution containing 0.2 to 3 g / l zinc ions, 3 to 50 g / l phosphate ions, 0.001 to 4 g / l manganese ions, 0.001 up to 0.5 g / l of one or more polymers and one or more accelerators, e.g. B. 0.01 to 0.2 g / l nitrite and 0.1 to 10 g / l

Contains hydroxylamine, and the solution can additionally contain 1 to 50 mg / l nickel ions and up to 2.5 g / l total fluoride. The phosphating solution used in this process also has a nitrate content that does not exceed 0.5 g / l.

DE-A 197 05 701 describes a process for the phosphating of

Surfaces made of steel, galvanized steel and / or aluminum and / or alloys which consist of at least 50% by weight iron, zinc or aluminum, using a zinc-containing acid phosphating solution which is free of copper ions and which 3 to 3 g / l zinc ions, 0.001 to 0.1 g / l nickel ions, 5 to 40 g / l phosphate ions and at least one accelerator, e.g. B. 0.1 to 10 g / l of hydroxylamine. This solution can additionally contain up to 4 g / l manganese ions and up to 2.5 g / l total fluoride. From the exemplary embodiments specified in DE-A 197 05 701 it can be seen that the known process works with relatively high hydroxylamine concentrations (1.8 g / l hydroxylammonium sulfate), and it is also stated in this publication that in the phosphating of galvanized Steel a nitrate concentration of 0.5 g / l should not be exceeded.

A phosphating solution is known from WO 93/03 198, which is used for the phosphating of steel, zinc alloys and aluminum and which contains 5 to 25 g / l phosphate ions, 0.5 to 2 g / l zinc ions, 0.2 to 1.5 g / l

Contains nickel ions, 0.2 to 1.5 g / l manganese ions and 1 to 2.5 g / l of a hydroxylamine compound, 0 to 1.5 g / l fluoride and 0 to 2 g / l nitrate. This phosphating solution also contains a large amount of hydroxylamine and limits the nitrate content to 2 g / l. Finally, DE-A 196 39 596 discloses a process for phosphating steel strip or steel strip galvanized on one or both sides or alloy galvanized by spray or dip treatment for a period of time in the range from 2 to 15 seconds at a temperature of 40 to 70 ° C a phosphating solution containing 1 to 4 g / l zinc ions, 0.8 to 3.5 g / l manganese ions,

Contains 10 to 30 g / l phosphate ions, 0.1 to 3 g / l hydroxylamine and not more than 1 g / l nitrate ions and which has a free acid content in the range from 0.4 to 4 points. This phosphating solution can additionally contain 0.8 to 3.5 g / l nickel ions and up to 0.8 g / l total fluoride. If the phosphating solution is used in the phosphating of galvanized steel, its nitrate content should not exceed 0.1 g / l.

The prior art gives the skilled worker the knowledge that the accelerator hydroxylamine can also be used alone and is generally particularly effective when it is present in the phosphating solution in a concentration> 0.5 g / l. The state of the art also conveys this

Those skilled in the art will recognize that the nitrate concentration of the phosphating solution should generally be <1 g / l, in particular if the phosphating solution is used for phosphating zinc surfaces, because in this case the nitrate content should even be <0.5 g / l be, since the person skilled in the art assumes that higher nitrate contents on galvanized surfaces favor the formation of the very disadvantageous, so-called "specks". On the other hand, the person skilled in the art is aware that a significant nitrate content in the phosphating solution could certainly be advantageous, since the nitrates of zinc, nickel and manganese are readily water-soluble and can be easily obtained and handled without any problems, and

The free acid (FS) content can optionally be easily adjusted using nitric acid.

The invention is therefore based on the object of providing a phosphating process which is suitable for the phosphating of zinc and aluminum surfaces is suitable, which gives the workpieces to be phosphated, in particular if they are coated with lacquers, paints, plastic layers or oils after phosphating, good corrosion properties and which uses a phosphating solution which, compared to the known hydroxylamine-containing phosphating solutions, works overall more cost-effectively without the quality of the phosphate layers produced, for example by the formation of specks on zinc surfaces or by non-closed layers on aluminum surfaces.

The object on which the invention is based is achieved by the creation of a method for phosphating zinc or aluminum surfaces by means of a phosphating solution which contains 0.5 to 2.0 g / l Zn ²⁺ , 0.3 to 2.0 g / l Ni ²⁺ , 0.1 to 0.4 g / l NH ₂ OH, at least 3.0 g / l N0 ₃ ^' and 10.0 to 20.0 g / l phosphate (calculated as P ₂ O ₅ ) and contains is applied to the surfaces by dipping or spraying at 35 to 75 ° C., the dipping time being 0.5 to 10 minutes and the spraying time being 3 seconds to 5 minutes.

With the method according to the invention, uniform, perfect, fine crystalline, closed phosphate layers with a layer weight of 2 to 5 g / m ^{2 are} produced. Surprisingly, it was found that the zinc surfaces phosphated according to the invention have no disadvantageous specks, although those used according to the invention

Phosphating solution has a high nitrate content of> 3 g / l, and that the phosphate layers produced on aluminum surfaces are completely closed, which is attributed in particular to the advantageous effect of the high nitrate content. The phosphate layers produced by the process according to the invention give the workpieces, in particular, which are coated with lacquers, paints, plastic layers or oils after phosphating, very good corrosion protection.

Through the relevant state of the art, this is a common thread Prejudice that the high nitrate content of a phosphating solution is responsible for the disadvantageous formation of specks on phosphated zinc surfaces and that the nitrate content must therefore be <1 g / l, preferably <0.5 g / l if possible (see e.g. DE-A 195 38 778, page 3, lines 43 to 49; DE-A 196 06 018, page 4, lines 8 to 11; DE-A 196 21 184, page 4, lines 41 to 44; DE-A 197

05 701, page 4, lines 38 to 43; DE-A 196 39 596, page 3, lines 1 to 7). It is to the merit of the invention to have recognized that zinc-containing phosphating solutions which have a hydroxylamine content of only 0.1 to 0.4 g / l and a nitrate content of> 3 g / l are advantageously used for the phosphating of zinc and aluminum surfaces because the acceleration effect of the very low hydroxylamine concentration is completely sufficient because of the synergistic acceleration effect of the nitrate, so that the phosphating solution used to carry out the process according to the invention contains no further accelerator, and on the other hand the comparatively high nitrate concentration leads to

Zinc surfaces do not cause disadvantageous speck formation and also supports the formation of a closed phosphate layer on aluminum surfaces. It also follows that nitrates and, if appropriate, nitric acid can readily be used for the production of the concentrates from which the present invention is diluted

Phosphating solutions are prepared.

According to the invention it is further provided that the phosphating solution used to carry out the method according to the invention additionally contains 0.4 to 1.5 g / l Mn ²⁺ . The manganese content improves the positive corrosion protection effect of zinc phosphate layers in a known manner.

While the phosphating of zinc surfaces takes place in accordance with the method according to the invention with a phosphating solution which does not necessarily contain fluoride and complex-bound fluoride, the phosphating of aluminum surfaces with a phosphating solution carried out, which contains fluoride and / or complex-bound fluoride, wherein the complex-bound fluoride can be used for example in the form of SiF ₆ ^{2 *} or BF ₄ ^' . However, it was found that SiF ₆ ^{2 '} is particularly suitable as a complex-bound fluoride for carrying out the process according to the invention and that a certain range must be observed with regard to the content of fluoride and complex-bound fluoride. It is therefore provided according to the invention that the phosphating solution used to carry out the process according to the invention additionally contains 0.2 to 1.5 g / l F ^' and / or 0.5 to 2.5 g / l SiF ₆ ^{2 "} . The presence such amounts of simple and / or complex bound fluoride is in the

Phosphating aluminum surfaces is advantageous because the aforementioned fluorides have a positive influence on the quality of the phosphate layers deposited on aluminum surfaces. The simple fluoride F ^" can be in the form of hydrofluoric acid HF or its salts. The zinc content is preferably 0.5 to 1.7 g / l.

It has proven particularly advantageous according to the invention if the phosphating solution used for dipping contains 1 to 2 g / l Zn ²⁺ and the phosphating solution used for spraying contains 0.5 to 1.5 g / l Zn ²⁺ . The method according to the invention produces particularly good results when the phosphating solution contains 3 to 15 g / l NO ₃ ^" .

Finally, the process according to the invention is carried out with a phosphating solution which, in addition to the components already mentioned, preferably 0.5 to ^1.3 g / l Ni ²⁺ , 12 to 16 g / l phosphate (calculated as P ₂ O ₅ ), 5 to 1.3 g / l Mn ²⁺ and 0.2 to 1.0 g / l F ^" and / or 0.8 to 2.0 g / l SiF ₆ ^{2 '} contains.

Hydroxylamine can be used as a free base, as a hydroxylamine complex or in the form of hydroxylammonium salts. If free hydroxylamine is added to the phosphating solution or the concentrate of this solution, it becomes are largely present as hydroxylammonium ion due to the acidic nature of these solutions. When using hydroxylammonium salts, the sulfates and phosphates are particularly suitable. The hydroxylamine content is preferably up to 0.3 g / l. The nitrate can be added to the phosphating solution as HN0 ₃ or as nitrate of zinc, manganese and / or nickel. Zinc, manganese and nickel can also be used in the form of their oxides and / or carbonates for the preparation of the phosphating solution. The phosphate is used as phosphoric acid or in the form of soluble phosphates. SiF ₆ ^{2 "} is used, for example, as H ₂ SiF ₆ for the preparation of the phosphating solution. In addition to the

Cations of zinc, nickel and manganese can contain the phosphating solution alkali metal and / or ammonium cations in order to adjust the free acid (FS) content, which is in the range of 0.5 to 3.5 points in the process according to the invention.

The term "free acid" (FS) is generally used in the field of phosphating. The free acid score is the number of ml that results when 10 ml of phosphating solution, which has been diluted to 50 ml with deionized water, are titrated with 0.1 normal sodium hydroxide solution to a pH of 4.2. whereby KCI is added to the sample to be titrated until saturation is present in the sample when complex-bound fluoride is present in order to largely avoid its dissociation.

The subject matter of the invention is explained in more detail below on the basis of comparative and exemplary embodiments. To carry out the examples, sheets were used which consisted of electrolytically galvanized steel and of the alloy AlMgSi (AA6016). The sheets were first cleaned, immersing them at 60 ° C. for 10 minutes in an aqueous solution containing 20 g / l of the alkaline cleaner BONDER V 854 / 5M. The sheets were then rinsed with tap water by immersion. This was followed by activation by treating the sheets with an aqueous solution which was 1.0 g / l contained the titanium phosphate-containing activating agent GARDOLENE V 6513. The activation was carried out by immersing the sheets for 30 seconds. Cleaning and activation are well-known and common process steps in phosphating. BONDER and GARDOLENE are registered trademarks of Chemetall GmbH, Frankfurt am Main.

The sheets were then treated by dipping for 2.5 minutes at 55 ° C. with different phosphating solutions, then rinsed by dipping with tap water and then dried with compressed air at room temperature. Table 1 shows the composition of the phosphating solutions used and those used in the

Phosphating achieved results. Examples 1 to 4 are comparative examples, while Examples 5 and 6 were carried out in accordance with the method according to the invention. The phosphating results show the following:

a) Comparative Examples 1 and 3, which - as recommended by the prior art - have a low nitrate content, are, as expected, free of specks, while Example 5 according to the invention is surprisingly free of specks. In Examples 2, 4 and 6 the problem of speck formation is not relevant, since specks are not formed on Al surfaces anyway.

b) Comparative Examples 2 and 4 - although they were carried out according to the prior art - have a non-closed and thus an unusable phosphate layer, since the layer only covers 20% of the Al surface; consequently the layer weight could not be determined either. Example 6 according to the invention has a closed phosphate layer with an advantageous layer weight, although the phosphating solution had only a low hydroxylamine content and a high nitrate content. c) Comparative Example 1 - since it used a high hydroxylamine content and a low nitrate content in a known manner - has a closed phosphate layer with an advantageous layer weight. However, the phosphate layer has a relatively dark color. This is disadvantageous if after the phosphating bright single-layer paints on the

Substrate should be applied. It is also disadvantageous that comparative example 1 uses a high hydroxylamine content. Comparative Example 3 has a closed phosphate layer, but the layer weight is too high, although the phosphating solution had both a low hydroxylamine content and a low nitrate content. In addition, the phosphate layer has an undesirable dark gray color. Example 5 according to the invention has a closed phosphate layer with an advantageous layer weight and is colored light gray in the desired manner.

To prepare the phosphating solutions with which Examples 5 and 6 according to the invention were carried out, 60 g each of the concentrates shown in Table 2 were made up to 1 liter with deionized water. The free acid content in the phosphating solutions was adjusted by adding dilute sodium hydroxide solution. To prepare the concentrates, the nitrates of zinc, nickel and

Manganese used.

Table 1

dg = dark gray, hg = light gray, nb = not determinable Table 2

Claims

claims

1. A method for phosphating zinc or aluminum surfaces with a phosphating solution based on zinc and nickel as cations and hydroxylamine as accelerators, which may additionally contain fluoride and / or fluoride bound in a complex, characterized in that the

Phosphating solution 0.5 to 2.0 g / l Zn ²⁺ , 0.3 to 2.0 g / l Ni ²⁺ , 0.1 to 0.4 g / l NH ₂ OH, at least 3.0 g / l Contains N0 ₃ ^" and 10.0 to 20.0 g / l phosphate (calculated as P ₂ Os) and which is applied to the surfaces by dipping or spraying at 35 to 75 ° C, the dipping time being 0.5 to 10 minutes and the spraying time is 3 seconds to 5 minutes.

2. The method according to claim 1, characterized in that the phosphating solution additionally contains 0.4 to 1.5 g / l Mn ²⁺ .

3. The method according to claim 1, characterized in that the phosphating solution additionally contains 0.2 to 1.5 g / l F ^" and / or 0.5 to 2.5 g / l SiF ₆ ^2" .

4. The method according to claim 1, characterized in that the phosphating solution used for dipping contains 1, 0 to 2.0 g / l Zn ²⁺ and the phosphating solution used for spraying 0.5 to 1, 5 g / l Zn ²⁺ .

5. The method according to claim 1, characterized in that the phosphating solution contains 3 to 15 g / l NO ₃ ^" .

6. Process according to claims 1 to 5, characterized in that the phosphating ^solution contains 0.5 to 1, 3 g / l Ni ²⁺ .

7. The method according to claims 1 to 5, characterized in that the phosphating solution contains 12 to 16 g / l phosphate (calculated as P ₂ O ₅ ).

8. The method according to claims 1 to 5, characterized in that the phosphating ^solution contains 0.5 to 1, 3 g / l Mn ²⁺ .

9. The method according to claims 1 to 5, characterized in that the phosphating solution contains 0.2 to 1.0 g / l F ^" and / or 0.8 to 2.0 g / l SiF ₆ ^2" .