EP1206589A2

EP1206589A2 - Accelerator for phosphating metal surfaces

Info

Publication number: EP1206589A2
Application number: EP00958432A
Authority: EP
Inventors: Bernd Schenzle; Franz-Adolf Czika; Peter Kuhm
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 1999-08-20
Filing date: 2000-08-11
Publication date: 2002-05-22
Anticipated expiration: 2020-08-11
Also published as: EP1206589B1; WO2001014613A2; JP2003507579A; DE19939519A1; DE50001815D1; WO2001014613A3; AU6995000A

Abstract

The invention relates to an acidic, aqueous phosphating solution that contains 0.2 to 3 g/l zinc ions, 3 to 50 g/l phosphate ions, calculated as PO43- and 0.5 to 5 g/l of at least one organic nitro compound as the accelerator. The inventive compound is further characterized in that the organic nitro compound is selected from nitroarginine, its esters with alcohols with 1 to 4 C atoms and 5-nitro-2-furfurylidene dicarboxylates.

Description

"Accelerators for the phosphating of metal surfaces"

The invention relates to a phosphating solution, a phosphating concentrate and a method for phosphating metal surfaces with aqueous, acidic phosphating solutions. This can be iron phosphating or zinc phosphating. The process particularly relates to zinc phosphating, which is used as a pretreatment of the metal surfaces for a subsequent painting, in particular an electrocoating. The method is applicable for the treatment of surfaces made of steel, galvanized or alloy galvanized steel, aluminum, aluminized or alloy aluminized steel.

The phosphating of metals pursues the goal of producing firmly adherent metal phosphate layers on the metal surface, which in themselves improve corrosion resistance and, in conjunction with paints and other organic coatings, contribute to a significant increase in adhesion and resistance to infiltration when exposed to corrosion. Such phosphating processes have long been known in the prior art. For the pretreatment before painting, the low-zinc phosphating processes are particularly suitable, in which the phosphating solutions have comparatively low zinc ion contents of e.g. B. 0.5 to 2 g / l. An important parameter in these low-zinc phosphating baths is the weight ratio of phosphate ions to zinc ions, which is usually in the range> 12 and can take values up to 30.

It has been shown that by using polyvalent cations other than zinc in the phosphating baths, phosphate layers with significantly improved corrosion protection and paint adhesion properties can be formed. For example, find low-zinc processes with the addition of z. B. 0.5 to 1.5 g / l of manganese ions and z. B. 0.3 to 2.0 g / l of nickel ions as a so-called trication method for the preparation of metal surfaces for painting, for example for the cathodic electrocoating of car bodies, wide application.

DE-A-40 13 483 discloses phosphating processes with which similarly good corrosion protection properties can be achieved as with the trication processes. These processes do without nickel and instead use copper in low concentrations, 0.001 to 0.03 g / l. Oxygen and / or other oxidizing agents with the same effect are used to oxidize the divalent iron formed in the pickling reaction of steel surfaces to the trivalent stage. Nitrite, chlorate, bromate, peroxy compounds and organic nitro compounds such as nitrobenzenesulfonate are specified as such. The German patent application DE 42 10 513 modifies this process by adding hydroxylamine, its salts or complexes in an amount of 0.5 to 5 g / l hydroxylamine as a modifying agent for the morphology of the phosphate crystals formed.

The use of hydroxylamine and / or its compounds to influence the shape of the phosphate crystals is known from a number of published publications. EP-A-315 059 specifies the particular effect of the use of hydroxylamine in phosphating baths in the fact that the phosphate crystals are still formed in steel in a desired columnar or knot-like form when the zinc concentration in the phosphating bath corresponds to that for low-zinc Procedure exceeds the usual range.

Hydroxylamine has the great procedural advantage that it generally does not decompose by itself in the phosphating bath and in phosphating concentrates. This enables phosphate bath concentrates and supplementary solutions for phosphate baths to be produced that contain the required accelerator quantities directly. A costly separate replenishment, such as when using nitrite or hydrogen peroxide as an accelerator can be omitted. However, if the phosphating solution contains copper ions, which is currently a technical trend, hydroxylamine gradually decomposes under the catalytic influence of these ions. In this case, the accelerator must be separated from the phosphating bath and added in increased amounts. There is therefore a need for new accelerators which, like hydroxylamine, can be incorporated into phosphating baths, their concentrates and supplementary solutions without them decomposing in a short time. They should still have this property even when copper ions are present.

DE-A-197 33 978 discloses zinc phosphating processes in which organic N-oxides, in particular cyclic N-oxides, are used as accelerators. A preferred example of N-methylmorpholine-N-oxide. From DE-A-196 34 685 zinc phosphating solutions are known in which nitroguanidine is used as an accelerator. So far, none of these alternatives to hydroxylamine has been successful in practice.

The object of the invention is to provide further phosphating processes which have the advantages of hydroxylamine-accelerated processes but not their disadvantages with regard to decomposition in the presence of copper ions. The phosphating process should be applicable in the spray, splash immersion or immersion process.

The invention accordingly relates to an acidic, aqueous phosphating solution containing

0.2 to 3 g / l zinc ions

3 to 50 g / l phosphate ions, calculated as PO ₄ ^{3 "} and

0.5 to 5 g / l of at least one organic nitro compound as an accelerator, characterized in that the organic nitro compound is selected from

Nitroarginine, its esters with alcohols having 1 to 4 carbon atoms and from 5-nitro-2-furfurylidene dicarboxylates of the general formula (I)

where R is an alkyl group having 1 to 3 carbon atoms.

Nitroarginine can be described by the chemical formula (II).

0 ₂ N-NH-C (= NH) -NH- (CH ₂ ) ₃ -CH (NH ₂ ) -C (= O) -OH (II)

Like all amino acids, this compound is amphoteric, i.e. H. it can form salts with both acids and bases. In the acidic phosphating solution it is to be expected that the compound is in a cationic form. This is irrespective of whether the compound was used as such, as a salt with a base, for example as an alkali metal salt, or as a salt with an acid, for example as a hydrochloride.

Instead of the amino acid nitroarginine, its esters with alcohols with 1 to 4 carbon atoms can also be used. Methyl and ethyl esters are particularly preferred. Since the acid function is blocked by the ester formation, the esters cannot exist as salts with a base. Due to the amino groups, however, salt formation with acids is still possible. For this reason, the esters in the acidic phosphating solution will largely be present as cations. They can be introduced into the phosphating solution as a neutral compound, but also in salt form. For example, hydrochloride can be used.

If the organic nitro compound is selected from 5-nitro-2-furfuryldicarboxylates of the general formula (I), the diacetate is special prefers. This means that R in the general formula (I) is preferably one

Represents methyl group.

The phosphating solution preferably contains 0.8 to 3 g / l of the organic nitro compound.

In addition to zinc ions, phosphating baths generally contain sodium, potassium and / or ammonium ions to adjust the free acid. The term free acid is familiar to the person skilled in the phosphating field. The method of determining free acid and total acid chosen in this document is given in the example section. Values of the free acid between 0 and 1.5 points and the total acid between approximately 15 and approximately 35 points are within the technically customary range and are suitable for the purposes of this invention.

The zinc contents are preferably in the range from 0.4 to 2 g / l and in particular from 0.5 to 1.5 g / l, as are customary for low-zinc processes. The weight ratio of phosphate ions to zinc ions in the phosphating baths can vary within a wide range, provided it is in the range between 3.7 and 30. A weight ratio between 10 and 20 is particularly preferred

Phosphating solutions which contain further mono- or divalent metal ions, which experience has shown to have a favorable effect on the paint adhesion and the corrosion protection of the phosphate layers produced thereby, are preferably used in the phosphating process according to the invention. Accordingly, the phosphating solution according to the invention preferably additionally contains one or more of the following cations:

0.1 to 4 g / l manganese (ll),

0.2 to 2.5 g / l magnesium (ll),

0.2 to 2.5 g / l calcium (II),

0.002 to 0.2 g / l copper (ll),

0.1 to 2 g / l cobalt (II). If desired, the phosphating solutions can additionally contain nickel ions. For health and environmental reasons, however

Phosphating baths are preferred which have the lowest possible nickel ion content or, if desired, can also be nickel-free. For example, the phosphating solution according to the invention contains in a preferred one

Embodiment except zinc ions as additional cations 0.1 to 4 g / l

Manganese ions and 0.002 to 0.2 g / l copper ions and not more than 0.05 g / l, in particular not more than 0.001 g / l nickel ions. However, if one wishes to adhere to the conventional trication technology, the invention can

Phosphating baths are used, which in addition to zinc ions 0.1 to 4 g / l

Manganese ions and additionally 0.1 to 2.5 g / l nickel ions. The form in which the cations are introduced into the phosphating baths is in principle without

Concern. It is particularly useful as a source of cations oxides and / or

To use carbonates.

When phosphating zinc-containing surfaces, it has proven to be advantageous to limit the nitrate content of the phosphating bath to a maximum of 0.5 g / l. This suppresses the problem of so-called speck formation and improves corrosion protection, especially when using nickel-free phosphating baths. Phosphating baths which contain no nitrate are particularly preferred.

In phosphating baths which are said to be suitable for different substrates, it has become customary to use free and / or complex-bound fluoride in amounts of up to 2.5 g / l of total fluoride, of which up to 750 mg / l of free fluoride, each calculated as F ^" , The presence of such amounts of fluoride is also advantageous for the phosphating baths according to the invention. In the absence of fluoride, the aluminum content of the bath should not exceed 3 mg / l. In the presence of fluoride, higher Al contents are tolerated due to the complex formation, provided the concentration of the complexed AI does not exceed 3 mg / l.

In principle, phosphating baths can be prepared directly on site by dissolving the individual components in the water in the desired concentration range. In practice, however, it is common to use concentrates that contain individual components in the desired proportions and from which the operational phosphating bath is prepared on site by dilution with water or which are added to a working phosphating bath as a supplementary solution in order to compensate for the consumption of the active components.

However, such phosphating concentrates are strongly acidic for stabilization. After dilution with water, the pH and / or the free acid must therefore often be blunted to the desired range.

For this purpose, alkaline substances such as sodium hydroxide solution or sodium carbonate or basic salts or hydroxides of Ca, Mg, Zn are added.

Accordingly, the invention also relates to an aqueous concentrate which, after dilution with water by a factor between 10 and 100 and, if appropriate, adjustment of the pH to a working range between 2.5 and 3.6, a phosphating solution according to one or more of Claims 1 to 6 results.

Furthermore, the invention comprises a method for phosphating metal surfaces made of steel, galvanized or galvanized alloy steel and / or aluminum. As is becoming increasingly common in automotive engineering, the materials mentioned can also be present side by side. The metal surfaces are brought into contact with the phosphating solution according to the invention by spraying or dipping or by a combination thereof. The temperature of the phosphating solution is preferably in the range between about 40 and about 60 ° C.

The phosphating process can be used to phosphate steel or galvanized steel strips in conveyor systems. The phosphating times are in the range from about 3 to about 20 seconds. However, the method can be used in particular in automobile construction, where treatment times between 1 and 8 minutes are common. It is intended in particular for the treatment of the metal surfaces mentioned before painting, in particular before cathodic electro-painting. The phosphating process is to be seen as a sub-step of the technically usual pretreatment chain. In this chain the steps of cleaning / degreasing, rinsing and activating are generally preceded by the phosphating, the activation usually being carried out using activating agents containing titanium phosphate. The phosphating according to the invention can, if appropriate after an intermediate rinse, be followed by a passivating after-treatment. Treatment baths containing chromic acid are widely used for such a passivating aftertreatment. However, for reasons of work and environmental protection and for disposal reasons, there is a tendency to replace these chromium-containing passivation baths with chromium-free treatment baths. Purely inorganic baths, in particular based on zirconium compounds, or also organic baths, for example based on poly (vinylphenols), are known for this. When using phosphating solutions that contain neither nickel nor copper ions, a significant improvement in corrosion protection can be achieved if copper or silver ions are added to the baths for the passivating aftertreatment. For example, passivating rinse solutions can be used which contain 0.001 to 10 g / l copper ions and which, if desired, can be free of further passivating components. An intermediate rinse with deionized water is generally carried out between this post-passivation and the usually subsequent electrocoating.

The organic nitro compounds to be used as accelerators according to the invention not only have a positive effect on the formation of the corrosion protection layer not only in the layer-forming zinc phosphating but also in the iron phosphating referred to as “non-layering”. Accordingly, in a generalized aspect, the invention relates to the use of organic nitro compounds selected from Nitroarginine, its esters with alcohols with 1 to 4 carbon atoms and from 5-nitro-2-furfurylidene dicarboxylates of the general formula (I).

where R is an alkyl group with 1 to 3 carbon atoms, as an accelerator in phosphating solutions.

The statements made above using the example of the zinc phosphating solution apply to the preferred compounds and the possibility that they can also be in salt form.

The novel phosphating accelerators according to the invention have the advantage over hydroxylamine that they are not catalytically decomposed in the presence of copper. This reduces the consumption of accelerators in copper-containing phosphating baths compared to the standard hydroxylamine. Compared to nitroguanidine as the chemically closest alternative, nitroarginine and its esters are safer to handle: nitroguanidine decomposes explosively at 102 ° C, nitroarginine only at 195 ° C. Nitroarginine methyl ester hydrochloride in particular is readily soluble in the acidic range (pH about 3.3) and can therefore be used as an internal accelerator.

EXEMPLARY EMBODIMENTS

The phosphating processes and comparative processes according to the invention were carried out on steel sheets St 1405 (CRS), electrolytically galvanized steel (EG) and hot-dip galvanized steel (HDG), as used in automobile construction find, checked. The following, which is more common in body production,

Procedure performed as a dipping process:

1. Clean with an alkaline cleaner (Ridoline ^ 1559, Henkel KGaA), approach 3% in city water, 60 ° C, 5 to 10 minutes.

2. Rinse with city water, room temperature, 1 minute.

3. Activation with an activating agent containing titanium phosphate (Fixodine ^ C 9112, Henkel KGaA), approach 0.2% in deionized water, room temperature, 1 minute.

4. Phosphating with phosphate baths according to Table 1 total acid: 23 points

Temperature: 52 ° C; Treatment time: 3 minutes of diving.

The free acid score is understood to mean the consumption in ml of 0.1 normal sodium hydroxide solution in order to titrate 10 ml of bath solution up to a pH of 3.6. Similarly, the total acid score indicates consumption in ml up to a pH of 8.2.

5. Rinse with deionized water, room temperature, 1 minute.

6. Blow dry with compressed air

7. Cathodic electrodeposition with the lead-free cathodic

Electrodeposition paint Cathogurad ^R 400 from BASF. Table 1: Phosphating parameters. Bath concentrations in g / l, free acid: score

Accelerator: comparison: HAS = hydroxylammonium sulfate, NG = nitroguanidine; according to the invention: NA = nitro-L-arginine, NE = nitro-L-arginine methyl ester hydrochloride, NF = nitrofurfurylidene diacetate;

A corrosion test VDA 621415 over 10 rounds and a stone chip test VDA 621427 were carried out as corrosion tests. The results are summarized in Table 2. The paint infiltration at the scratch (half scratch width) in mm and the K-value for the stone chip test (best value = 1, worst value = 10) are listed.

Table 2: Results of the corrosion tests: U = paint infiltration (half scratch width, mm), K value

Claims

claims

1. Containing acidic, aqueous phosphating solution

0.2 to 3 g / l zinc ions

3 to 50 g / l phosphate ions, calculated as PO ₄ ^{3 "} and

0.5 to 5g / l at least one organic nitro compound as

Accelerator,

characterized in that the organic nitro compound is selected from nitroarginine, its esters with alcohols having 1 to 4 carbon atoms and from 5-nitro-2-furfurylidene dicarboxylates of the general formula (I)

where R is an alkyl group having 1 to 3 carbon atoms.

2. Phosphating solution according to claim 1 to, characterized in that it contains 0.8 to 3 g / l of the organic nitro compound.

3. Phosphating solution according to one or both of claims 1 and 2, characterized in that it additionally contains one or more of the following cations:

0.1 to 4 g / l manganese (ll),

0.2 to 2.5 g / l magnesium (ll), 0.2 to 2.5 g / l calcium (ll),

0.002 to 0.2 g / l copper (ll),

0.1 to 2 g / l cobalt (II).

4. phosphating solution according to claim 3, characterized in that it contains 0.1 to 4 g / l manganese ions and 0.002 to 0.2 g / l copper ions and not more than 0.05 g / l nickel ions.

5. phosphating solution according to claim 3, characterized in that it contains 0.1 to 4 g / l manganese ions and additionally 0.1 to 2.5 g / l nickel ions.

6. phosphating solution according to one or more of claims 1 to 5, characterized in that it contains 0.4 to 2 g / l, preferably 0.5 to 1, 5 g / l of zinc ions.

7. Aqueous concentrate, which after dilution with water by a factor between 10 and 100 and optionally adjusting the pH to a working range between 2.5 and 3.6 results in a phosphating solution according to one or more of claims 1 to 6.

8. 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 dipped or by a combination thereof for a time between 3 seconds and 8 minutes with a phosphating solution according to one or more of claims 1 to 6 in contact.

9. Use of organic nitro compounds selected from nitroarginine, its esters with alcohols having 1 to 4 carbon atoms and from 5-nitro-2-furfurylidene dicarboxylates of the general formula (I)

O