WO1998030732A1

WO1998030732A1 - Hydroxylamine stabilizers in copper-containing phosphating solutions

Info

Publication number: WO1998030732A1
Application number: PCT/EP1997/007185
Authority: WO
Inventors: Bernd Mayer; Jürgen Geke; Peter Kuhm; Frank Kleine-Bley; Jan-Willem Brouwer
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1997-01-08
Filing date: 1997-12-19
Publication date: 1998-07-16
Also published as: CA2277336A1; TR199901460T2; EP0960220A1; AU5859098A; BR9714199A; JP2002500702A; DE19700326A1

Abstract

The invention concerns an acid aqueous phosphating solution which contains zinc ions, phosphate ions, copper ions and hydroxylamine in free form, as a salt or hydroxylamine-cleaving compound, and additionally one or a plurality of hydroxylamine stabilizers selected from organic molecules having at least two heteroatoms per molecule or, in the case of polymers, at least one heteroatom per four carbon atoms. The invention also concerns an aqueous concentrate and an aqueous supplementary solution for the phosphating solution.

Description

"Stabilizers for hydroxylamine in copper-containing phosphating solutions"

The invention relates to phosphating solutions which are suitable for producing crystalline zinc phosphate layers on steel, galvanized or alloy-galvanized steel and on aluminum and its alloys. In addition to zinc and phosphate ions, these phosphating solutions contain copper ions and, as accelerators, hydroxylamine in free, salt-like or bound form.

Additions of small amounts of copper ions to phosphating baths have been known for 40 years. In US-A-2 293 716, the smallest amounts of Cu2 ⁺ ions are added as "accelerators" or to improve the whiteness of anodic electrocoating materials as "color neutralizers". It was observed that copper additives increase the layer weight, especially on steel.

From DE-A-40 13 483 a method for phosphating metal surfaces is known, in which one works with phosphating solutions which are essentially free of nickel. Zinc, manganese and low copper contents are mentioned as essential bath components. In addition, the concentration of Fe (II) is kept below a maximum value by oxygen and / or other oxidizing agents having the same effect. The method is used in particular for the pretreatment of metal surfaces for subsequent painting, in particular electro-dip painting.

From EP-A-186 823 strongly acidic phosphating solutions with a pH of 1.8-2.5 are known, the 7.5-75 g / 1 zinc ions, 0.1-10 g / 1 hydroxylamine and optionally contain up to 20 g / 1 manganese ions and 5 - 75 g / 1 nitrate ions. The solutions tolerate an iron content of up to 25 g / 1.

EP-A-0 315 059 discloses a process for zinc phosphating iron-containing surfaces. The desired morphology of the zinc phosphate crystals is set by using hydroxylammonium salts, hydroxylamine complexes and / or hydroxylamine.

EP-B-633 950 teaches a process for producing copper-containing nickel-free phosphate layers with a copper content in the range from 0.1 to 5% by weight and an edge length of the phosphate crystals in the range from 0.5 to 10 μm on metal surfaces, selected from Steel, galvanized steel, alloy galvanized steel, aluminum and their alloys, by treating them in the spray, dip or spray / dip process with a phosphating solution which contains the following components:

Zinc ions 0.2 to 2 g / 1

Copper ions 0.5 to 25 mg / 1 phosphate ions 5 to 30 g / 1 (calculated as P2O5)

and also hydroxylamine salts, hydroxylamine complexes and / or hydroxylamine in an amount of 500 to 5000 ppm hydroxylamine, based on the phosphating solution.

Phosphating baths which contain copper ions and hydroxylamine as accelerators have the following disadvantage: The catalytic influence of copper ions leads to accelerated decomposition of the hydroxylamine. This effect is particularly pronounced in spray processes in which the phosphating solution comes into intimate contact with air. This catalytic decomposition increases the consumption of hydroxylamine considerably and increases the cost of the phosphating process. The object of the invention is therefore to provide phosphating solutions in which the decomposition of hydroxylamine by copper is slowed down by the fact that they contain suitable stabilizers. The invention accordingly relates to an acidic, aqueous phosphating solution which

0.3 to 3 g / 1 zinc ions,

4 to 30 g / 1 phosphate ions,

0.002 to 0.2 g / 1 copper ions and

0.25 to 10 g / 1 hydroxylamine

in free form, as a salt or as a hydroxylamine-releasing compound, characterized in that it additionally contains one or more stabilizers for hydroxylamine, selected from organic molecules containing at least two heteroatoms per molecule or, in the case of polymers, at least one heteroatom per 4 carbon atoms have, wherein at least one of the heteroatoms is a nitrogen or an oxygen atom and heteroatoms bonded to the same carbon atom are only counted once, in the case of carboxyl group-containing molecules or polymers at least three carbon atoms must lie between two adjacent carboxyl groups.

For example, the fact that heteroatoms bound to the same atom are only counted simply means that the two oxygen atoms of a carboxyl group are only counted as a single heteroatom. In this sense, sulfonic acid or phosphonic acid groups are also regarded as only one heteroatom. The reason for this method of counting is the assumption that the stabilizing effect of heteroatom-containing organic molecules is related to a complexing effect against copper. For steric reasons, acid groups such as carboxyl groups generally only act as monodentate ligands, ie only a single oxygen atom is available for coordination to the copper. The result of this counting method is that monocarboxylic acids which, apart from the only carboxyl group, have no further heteroatoms are not covered by the invention. They do not have a sufficient stabilizing effect. The definition of the invention further excludes di-, oligo- or polycarboxylic acids in which there are not at least three carbon atoms between adjacent carboxyl groups. Acids with denser carboxyl groups can directly influence the layer formation due to their complexing effect on iron and can lead, for example, to undesirable layer weights. Only those di-, oligo- or polycarboxylic acids can be recommended as stabilizers, without possibly negative side effects, in which neighboring carboxyl groups are separated by at least three carbon atoms. Therefore, for example, oxalic acid, malic acid, tartaric acid or citric acid and poly (meth) acrylic acids are not covered by the protection request.

The stabilizer can, for example, be characterized in that it has an atomic sequence X - Cι_3 - Y, where X stands for an oxygen or nitrogen atom and Y for an oxygen, nitrogen, phosphorus or sulfur atom. In particular, stabilizers are suitable which have an atomic sequence O - C - C - O or O - C - C - C - 0, in which case according to the above restriction at most one of the two O atoms of the atomic sequence mentioned belongs to a carboxyl group may. In particular, these can be polyethylene glycols, polypropylene glycols or polytetrahydrofuran. For example, polyethylene glycols with an average molecular weight of 200 to 10,000, which can be determined by gel permeation chromatography, are suitable.

The stabilizer can also be a diazole or a triazole derivative. Examples of such effective derivatives are carbendiazim and 1H-benzotriazole-5-carboxylic acid. Furthermore, the stabilizer can be selected from molecules which have an atomic sequence -N - C - C - Y '- Z, where Z represents an oxygen or a nitrogen atom and Y ^{' represents} a carbon, sulfur or phosphorus atom or else entirely may be missing. For example, this sequence of atoms can be - N - C - C - N -. Preferred molecules are those in which the two nitrogen atoms are members of two aromatic heterocyclic rings. These include in particular 2,2'-bipyridine, 2,2 ^' : 6', 2 "-terpyridine and 1,10-phenanthroline.

Furthermore, the stabilizer can have the atomic sequence - N - C - C - O. These stabilizers can represent alpha-amino acids, for example. Those amino acids which have at least one aromatic residue are preferred. Examples include phenylalanine, thyrosine, tryptophan and histidine.

Molecules with an atomic sequence - N - C - C - O are also suitable in which the nitrogen atom is a member of a heterocyclic aromatic ring. For example, the nitrogen atom can be in a pyridine ring. An example of such a compound is picolinic acid.

The phosphating bath can furthermore contain a stabilizer which has an atomic sequence - N - C - C - Y - 0, in which Y represents a sulfur or a phosphorus atom. This includes, for example, nitrogenous sulfonic and phosphonic acids. Here too, a molecular structure of the stabilizer is favorable, in which the nitrogen atom is a member of a heterocyclic aromatic ring, in particular a pyridine ring. An example of such a heterocyclic sulfonic acid is quinoline-8-sulfonic acid.

Aromatic hydroxycarboxylic acids are further examples of stabilizers according to the general definition. Hydroxybenzoic acids with one or more hydroxyl groups are particularly suitable. P-Hydroxybenzoic acid is particularly suitable. In general, the type and amount of stabilizer should be chosen so that it

Copper ions in the concentration range of 0.002 to 0.2 g / 1 at the pH values of a phosphating solution, which are usually in the range between about 2.5 and about

3.8, does not form precipitates. Appropriately you fit that

Concentration of the stabilizer to the concentration of copper ions. The

The molar ratio of stabilizer to copper ions should be in the range from 1: 1 to 20: 1. If a polymer such as polyglycol is used as the stabilizer, the term “mole” refers to the concentration calculation

Monomer unit. In the case of polyethylene glycol, this would be the ethylene oxide unit.

The stabilizer is used in particular for copper-containing zinc phosphating solutions that additionally contain up to 2 g / 1 manganese ions.

Phosphating solutions are usually prepared by diluting an aqueous concentrate with water to the application concentration and, if appropriate, adjusting the desired pH or the value of the "free acid" (a term generally known in the phosphating field) by adding alkalis. Accordingly, the invention also encompasses an aqueous concentrate which, after dilution with water in a ratio of 1:10 to 1: 100 and, if appropriate, adjustment of the pH, gives a phosphating solution according to one or more of Claims 1 to 18.

Since components of the phosphating bath are consumed during the phosphating process, it is customary to set the target concentration of these components by continuously or batchwise adding a supplemental solution. Depending on the different consumption of the individual components in the phosphating solution, the proportions in the supplemental solution may differ from the proportions to be set in the phosphating bath. For example, the phosphating solution does not have to contain zinc ions if sufficient zinc ions get into the phosphating bath during the phosphating of galvanized material due to the pickling attack. Or if, for example, specifically the consumption or the decomposition of the accelerator hydroxylamine must be compensated. the supplemental solution may have a higher ratio of hydroxylamine to layer-forming cations than the phosphating bath. The

In the simplest case, the supplementary solution can only contain hydroxylamine and stabilizer, but no layer-forming components. Accordingly, the invention also includes an aqueous supplementary solution for a phosphating solution according to one or more of Claims 1 to 18, the hydroxylamine in free form as

Salt or as a hydroxylamine-releasing compound and one or more

Contains stabilizers, wherein the stabilizer corresponds to the definition according to at least one of claims 1 to 17.

embodiments

A commercially available phosphating bath concentrate was prepared by mixing the following components in the order given:

486.40 g / kg water

358.80 g / kg phosphoric acid (75%)

31.00 g / kg zinc oxide (99%)

35.00 g / kg manganese carbonate (92%)

2.80 g / kg iron (II) sulfate * 7 water

42.00 g / kg of hydrofluoric acid (34%)

44.00 g / kg hydroxylamine (50%) correspond to 54.55 g hydroxylamine sulfate

An operable phosphating bath is obtained by preparing a 4.8% by weight aqueous solution of this concentrate and adjusting it to a pH of 3.2. This phosphating bath is mixed with different amounts of copper ions (as copper sulfate) and stabilizer and at 55 ° C in a drying cabinet stored. After certain times, the residual hydroxylamine content is determined analytically using the so-called "acetone method". The 1: 20 diluted bath solution is adjusted to a pH of 3.76 with 0.1 N NaOH, 10 ml of acetone are added and (2) is again adjusted to pH 3.76 with 0.1 N NaOH . Consumption (2) in ml x 0.033 =% hydroxylamine in the bath. In the tables below, the initial hydroxylamine content is set as 100% relative and the amounts of hydroxylamine found after certain times are related to this.

Table 1 shows the residual hydroxylamine content as a function of time when stored at 55 ° C. A Cu concentration of 0.11 mmol / 1 corresponding to 7 mg / 1 was set for row A and a Cu concentration of 0.16 mmol / 1 corresponding to 10.2 mg / 1 for row B.

In a further series of experiments, the accelerated decomposition of hydroxylamine upon intimate contact of the phosphating solution with air, as occurs in a spraying process, was investigated. For this purpose, a phosphating bath was prepared as described above and 7 mg / 1 copper ions were added. The phosphating bath was heated to 55 ° C. At this temperature the bath was stirred so violently with a magnetic stirrer that air was stirred into the bath. After different times, the residual hydroxylamine contents were determined and based on a relative starting content of 100%. The results are shown in Table 2.

Table 2: Residual hydroxylamine content as a function of time after vigorous stirring at 55 ° C

Claims

claims

1. Acidic, aqueous phosphating solution containing 0.3 to 3 g / 1 zinc ions 4 to 30 g / 1 phosphate ions,

0.002 to 0.2 g / 1 copper ions and

Contains 0.25 to 10 g / 1 hydroxylamine in free form, as a salt or as a hydroxylamine-releasing compound,

characterized in that it additionally contains one or more stabilizers for hydroxylamine selected from organic molecules which have at least two heteroatoms per molecule or in the case of polymers at least one heteroatom per 4 carbon atoms, at least one of the heteroatoms being a nitrogen or an oxygen atom and heteroatoms bonded to the same carbon atom can only be counted once, in the case of molecules or polymers containing carboxyl groups, there must be at least three carbon atoms between two adjacent carboxyl groups.

2. phosphating solution according to claim 1, characterized in that the stabilizer is a sequence of atoms

X - C1.3 - Y

has, where X is an oxygen or nitrogen atom and Y is an oxygen, nitrogen, phosphorus or sulfur atom.

3. phosphating solution according to claim 2, characterized in that the stabilizer is a sequence of atoms O - C - C - O or O - C - C - C - O

has, at most one of the O atoms of the atomic sequence belonging to a carboxyl group.

4. phosphating solution according to claim 3, characterized in that the stabilizer is polyethylene glycol, polypropylene glycol or polytetrahydrofuran.

5. phosphating solution according to claim 1, characterized in that the stabilizer is a diazole or a triazole derivative.

6. phosphating solution according to claim 5, characterized in that the stabilizer is carbendiazim and / or lH-benzotriazole-5-carboxylic acid.

7. phosphating solution according to claim 2, characterized in that the stabilizer is selected from molecules having an atomic sequence

-N - C - C - Y '- Z

have, where Z is an oxygen or a nitrogen atom and Y 'is a carbon, sulfur or phosphorus atom or may be absent.

8. phosphating solution according to claim 7, characterized in that the stabilizer has an atomic sequence

- N - C - C - N -

having.

9. phosphating solution according to claim 8, characterized in that the two nitrogen atoms are members of two aromatic heterocyclic rings.

10. phosphating solution according to claim 9, characterized in that the stabilizers are selected from 2,2'-bipyridine. 2.2 ^' : 6'.2 "terpyridine and 1, 10-phenanthroline

11. phosphating solution according to claim 7, characterized in that the stabilizer has an atomic sequence

- N - C - C - 0

having.

12. phosphating solution according to claim 1 1, characterized in that the stabilizer is an alpha-amino acid.

13. phosphating solution according to claim 12, characterized in that the amino acid has at least one aromatic radical.

14. phosphating solution according to claim 11, characterized in that the nitrogen atom is a member of a heterocyclic aromatic ring.

15. phosphating solution according to claim 7, characterized in that the stabilizer has an atomic sequence

- N - C - C - Y - 0

in which Y represents a sulfur or a phosphorus atom.

16. phosphating solution according to claim 15, characterized in that the nitrogen atom is a member of a heterocyclic aromatic ring.

17. phosphating solution according to claim 1, characterized in that the stabilizer is selected from hydroxybenzoic acids.

18. phosphating solution according to one or more of claims 1 to 17, characterized in that it contains the stabilizer in amounts of one mole Stabilizer (for polymers: moles based on monomer unit) up to 20 moles

Contains stabilizer per mole of copper ions.

19. Aqueous concentrate which, after dilution with water in a ratio of 1:10 to 1: 100 and optionally adjusting the pH, gives a phosphating solution according to one or more of claims 1 to 18.

20. Aqueous supplementary solution for a phosphating solution according to one or more of claims 1 to 18, hydroxylamine in free form, as a salt or as a hydroxylamine-releasing compound and one or more stabilizers, the stabilizer corresponding to the definition according to at least one of claims 1 to 17 .