DE10322446A1 - Pretreatment of metal surfaces before painting - Google Patents

Abstract

Process for the chemical pretreatment of metal surfaces, which at least partially consist of steel surfaces, before an organic coating, the metal structures being brought into contact with a phosphating solution containing 0.3 to 3 g / l of Zn (II) ions, 5 to 40 g / l contains phosphate ions and one or more titanium and / or zirconium compounds in such an amount that the total content of Ti and / or Zr is in the range from 1 to 1000 mg / l. If the total content of Ti and / or Zr is at least 10 mg / l, passivating rinsing is not necessary. Surfaces made of aluminum that are additionally present are not phosphated, but are instead covered in the phosphating solution or in the case of a passivating aftertreatment with a conversion layer containing Ti and / or Zr.

Description

The The invention relates to a method for corrosion protection Pretreatment of metal surfaces, in particular in the form of composite metal structures that at least parts made of steel, before painting. In addition, galvanized or alloy galvanized steel. In the case of suitable process management for a passivating rinse to be dispensed with. A particular advantage shows up when next to Steel also surfaces made of aluminum and / or its alloys. Then arises on these surfaces no crystalline zinc phosphate layer, which means the pickling removal and thus the sludge formation in the phosphating bath is reduced. The surfaces out Aluminum and / or its alloys are either directly in the Phosphate bath or in a passivating rinse with a conversion layer other than a zinc phosphate layer and thus protected.

The The process is especially designed for use in automotive engineering. Here, bodies or body parts, which are often components made of aluminum and / or its alloys in addition to components made of steel and optionally contain galvanized steel, a conversion chemical Pretreatment such as subjected to phosphating, before they are painted. It is currently the first painting stage cathodic electrocoating is common. The method according to the invention is particularly suitable as a pretreatment for this. However, it is also suitable for household appliance construction (refrigerators, washing machines or dishwashers etc.) well suited to where pretreatment is usually easier Painting, for example powder painting, takes place.

In practice it has been shown that when phosphating surfaces made of aluminum and those made of steel and / or galvanized steel together, technical compromises have to be made for the composition of the phosphating baths. Aluminum ions released from the aluminum surface by the pickling attack act as a bath poison for the phosphating solution and hinder the formation of zinc phosphate crystals on iron surfaces. Appropriate measures must therefore be taken to precipitate or mask the dissolved aluminum. For this purpose, free or complex-bound fluoride ions are usually added to the phosphating baths. The fluoride ions mask the aluminum ions by complex formation and / or, if the solubility products of the corresponding salts are exceeded, precipitate them as hexafluoroaluminates of sodium and / or potassium. Furthermore, free fluoride ions in the concentration range between about 0.3 and about 1 g / l lead to an increased pickling attack on the aluminum surfaces, so that a more or less closed zinc phosphate layer can form there. US 5,863,357 discloses that phosphating solutions can also contain fluoride ions in the form of fluorocomplexes of boron, silicon, zircon or titanium.

The common phosphating of aluminum components with such Steel and / or galvanized steel therefore has the technical disadvantage that the phosphating baths in terms of their fluoride content must be controlled very precisely. This elevated the regulatory effort and may require fluoride solutions as separate supplementary solutions stock and dose. Moreover enlarge the precipitated Hexafluoroaluminate salts the amount of phosphating sludge and make it more expensive its disposal.

Therefore there is a need for improved pretreatment procedures more complex Components such as automobile bodies, in addition to parts made of aluminum those made of steel and optionally galvanized steel contain. As a result, the entire pretreatment should be on everyone occurring metal surfaces a conversion layer or a passivation layer are generated, which turns out to be anti-corrosive Varnish base, especially before cathodic electrocoating suitable.

• a) in einem ersten Schritt die zusammengesetzte Metallstruktur mit einer Zinkphosphatierungslösung behandelt, die auf Stahl und auf verzinktem oder legierungsverzinktem Stahl eine flächendeckende kristalline Zinkphosphatschicht mit einem Schichtgewicht im Bereich von 0,5 bis 5 g/m² ausbildet, jedoch ohne auf den Aluminiumteilen eine Zinkphosphatschicht zu bilden, und anschließend, mit oder ohne eine Zwischenspülung mit Wasser,
• b) in einem zweiten Schritt die zusammengesetzte Metallstruktur mit einer Behandlungslösung in Kontakt bringt, die die kristalline Zinkphosphatschicht auf Stahl, verzinktem und/oder legierungsverzinktem Stahl nicht auflöst, auf den Aluminiumteilen jedoch eine Konversionsschicht erzeugt.

DE-A-19735314 and the very similar document WO99 / 12661 disclose first solutions to this problem. The latter describes a process for the chemical pretreatment of composite metal structures which contain parts made of aluminum or its alloys together with parts made of steel, galvanized steel and / or alloy-galvanized steel, before an organic coating

• a) In a first step, the composite metal structure is treated with a zinc phosphating solution that forms a surface-covering crystalline zinc phosphate layer with a layer weight in the range from 0.5 to 5 g / m ² on steel and on galvanized or alloy-galvanized steel, but without one on the aluminum parts To form zinc phosphate layer, and then, with or without an intermediate rinse with water,
• b) in a second step, the assembled metal structure is brought into contact with a treatment solution which applies the crystalline zinc phosphate layer to steel, galvanized and / or galvanized alloy steel does not dissolve, but creates a conversion layer on the aluminum parts.

The The prior art on which this teaching is based is in the above Document WO99 / 12661 described in detail. Also the WO02 / 066702 has a two-stage composite pretreatment Metal structures after a similar Concept on the subject. The invention described below builds based on this state of the art and developed the teaching of the above WO99 / 12661 further. moves According to the teaching of this document, one observes that the conversion layer be uneven on aluminum can. This is formed by a layer of lacquer applied subsequently through and causes expensive manual rework after painting. Accordingly, there is a need for the above to improve the pretreatment process described so that a more even coating on aluminum while or after phosphating the components made of steel or galvanized steel is achieved.

Farther is tried again and again during the phosphating on the usual rinse with a passivating rinse solution, for example a rinse solution Base of chromic acid or chromates, of complex fluorides of Ti or Zr or of organic polymers that over bind complexing functional groups to the metal surface, to renounce. Hereby let save one treatment level and the chemical consumption reduce. this leads to however, as a rule, disadvantages with regard to corrosion protection and / or paint adhesion.

The present invention relates to a method for the chemical pretreatment of metal surfaces which at least partially consist of steel surfaces, before an organic coating, the metal structures being brought into contact with a phosphating solution which
0.3 to 3 g / l of Zn (II) ions and
Contains 5 to 40 g / l phosphate ions,
characterized in that the phosphating solution additionally contains one or more titanium and / or zirconium compounds in such an amount that the total content of Ti and / or Zr is in the range from 1 to 1000 mg / l.

Here you can use a zinc phosphating solution that
0.3 to 3 g / l Zn (II),
5 to 40 g / l phosphate ions
and contains at least one of the following accelerators:
1 to 4 g / l chlorate ions,
0.2 to 2 g / l m-nitrobenzenesulfonate ions,
0.1 to 10 g / l hydroxylamine in free or bound form,
0.05 to 2 g / l m-nitrobenzoate ions,
0.05 to 2 g / l p-nitrophenol,
1 to 70 mg / l hydrogen peroxide in free or bound form,
0.1 to 10 g / l reducing sugar.

Such Accelerators are known in the prior art as components of zinc phosphating baths. this includes are understood substances that are affected by the pickling attack of the Acidity of the metal surface Binding hydrogen chemically by reducing it itself. Oxidizing accelerators continue to have the effect of: the pickling attack on steel surfaces oxidize released iron (II) ions to the trivalent stage, so that they can precipitate out as iron (III) phosphate.

Preferably contains the phosphating solution 1 to 5000 mg / l fluoride ions in free or bound form, e.g. also in the form of fluorocomplexes of Ti or Zr as the essential ones Titanium or zirconium compounds. The total content is preferably at least 10 mg / l of fluoride ions (free or bound). A salary up to 1500 mg / l is usually sufficient. This improves the formation of phosphate layers on galvanized steel.

The phosphating can also contain an organic film former. For the pretreatment process according to the invention however, this complicates the procedure. Therefore one prefers to bet in step a) a phosphating solution which does not contain an organic film former.

Experience has shown that corrosion protection and paint adhesion of the crystalline zinc phosphate layers produced with such a phosphating solution are improved if the zinc phosphating solution additionally contains one or more of the following cations:
0.001 to 4 g / l manganese (II),
0.001 to 4 g / l nickel (II)
0.002 to 0.2 g / l copper (II)
0.2 to 2.5 g / l magnesium (II),
0.2 to 2.5 g / l calcium (II),
0.01 to 0.5 g / l iron (II),
0.2 to 1.5 g / l lithium (I),
0.02 to 0.8 g / l tungsten (VI).

The Zinc concentration is preferably in the range between about 0.3 and about 2 g / l and especially between about 0.8 and about 1.4 g / l. Zinc levels above 1.6 g / l, for example between 2 and 3 g / l bring for the process has only minor advantages, but on the other hand can Increase sludge in the phosphating bath. Such zinc levels can set in a working phosphating bath if the Phosphating of galvanized surfaces additional through the pickling removal Zinc gets into the phosphating bath. Phosphating solutions, in addition to zinc ions Both manganese and nickel ions are currently available as “trication-phosphating solutions technically in use and also well suited in the context of the present invention. But also the presence of nickel and / or cobalt ions in the concentration range of each about 1 to about 50 mg / l for nickel and about 5 to about 100 mg / l for Cobalt (In addition to zinc ions alone or in combination with zinc ions with manganese ions) improved in connection with one if possible low nitrate content of no more than about 0.5 g / l corrosion protection and paint liability phosphating, that do not contain nickel or cobalt or that contain nitrate of more than 0.5 g / l.

hereby will be a cheaper Compromise between the performance of the phosphating baths on the one hand and the requirements for the wastewater treatment of the rinse water on the other hand reached.

Except the The aforementioned cations, which are incorporated into the phosphate layer or at least the crystal growth of the phosphate layer the phosphating baths usually contain sodium, Potassium and / or Ammonium ions to adjust the free acid. The term free acid is familiar to the expert in the phosphating field. The one in this writing elected Free acid determination method as well as the total acidity is given in the example section. Provide free acid and total acid an important control parameter for phosphating baths, since they're a big one Influence the layer weight. Free acid values between 0 and 3 points, preferably between 0.5 and 2.5 points, and of total acidity between about 15 and about 30 points are in the usual technical range Range and are suitable in the context of this invention.

Lie next to the surfaces made of steel and, if appropriate, those relating to the present invention indifferent surfaces made of galvanized steel surfaces made of aluminum or its alloys (for example in Automotive engineering often is the case), there is an additional positive effect of Invention: the addition of Ti and / or Zr in the phosphating solution prevented, that a (possibly uneven) phosphate layer on these surfaces formed. This reduces sludge formation in the phosphating solution and at the same time prevents an uneven layer of phosphate from forming traces the lacquer through, which gives the uniform visual impression of the painted surfaces disturbs.

Therefore, a more specific embodiment of the invention is that the metal surfaces additionally consist partly of surfaces of aluminum or its alloys and that a surface-covering crystalline zinc phosphate layer with a layer weight in the range of 0. 5 to 5 g / m ² is formed, but without forming a crystalline zinc phosphate layer on the surfaces of aluminum or its alloys.

The fact that no zinc phosphate layer should be formed on the aluminum parts during the treatment with the phosphating solution should be understood to mean that no closed crystalline layer is formed and that the mass per unit area of any zinc phosphate crystals that may be deposited does not exceed 0.5 g / m ² . However, preferably no zinc phosphate crystals are formed at all.

With a suitable composition of the phosphating solution, treatment with the phosphating solution on steel can result in a crystalline metal phosphate layer which, without a passivating rinse, has corrosion protection and paint adhesion properties that can otherwise only be achieved with a passivating rinse. With this procedure it is then not necessary to to subject the components treated with the phosphating solution to a passivating aftertreatment in a subsequent step. This saves one treatment step. This process variant is characterized in that the phosphating solution contains the one or more titanium and / or zirconium compounds in such an amount that the total content of Ti and / or Zr is in the range from 10 to 1000 mg / l and that the metal surfaces after Contact with the phosphating solution rinsed with water and not brought into contact with a passivating rinse solution. The total content of Ti and / or Zr is preferably, with increasing preference: at least 10 mg / l, at least 20 mg / l, at least 30 mg / l, at least 40 mg / l or at least 50 mg / l. As an upper limit of the content, 500 mg / l and in particular 250 mg / l are usually sufficient to achieve the desired technical effect. Surfaces made of aluminum and its alloys are not phosphated, but rather are covered with a passivating layer of Ti and / or Zr compounds, so that no additional passivating rinsing is required for these surfaces either.

In an alternative embodiment one leads the pretreatment process according to the invention in two stages by, as also described in the prior art cited here is. Supported here the second treatment step (hereinafter referred to as "sub-step b "is referred to) the formation of the passivating conversion layer on aluminum, while the presence during treatment with the phosphating solution (“sub-step a”) of the Ti and / or Zr compounds prevents the formation of "crystal nests" on Al, that can be seen through the paint. Improved at the same time Sub-step b paint adhesion and corrosion protection on the phosphated Steel surfaces.

This embodiment is characterized in that the phosphating solution one or more titanium and / or zirconium compounds in one Contains quantity, that the total content of Ti and / or Zr ranges from 1 to 30 mg / l and after contact with the phosphating solution (= Sub-step a), with or without an intermediate rinse with water, in a second Step (= sub-step b) the metal surfaces with a treatment solution in That brings the crystalline zinc phosphate layer onto steel, galvanized and / or alloy galvanized steel does not dissolve on the aluminum parts however creates a conversion layer.

In a special embodiment therefor you put a phosphating solution with a pH in the range of 2.5 to 3.6 and with a temperature in the range of 20 to 65 ° C which contains no more free fluoride in g / l than by the expression 8 / T is specified, where T is the bath temperature in ° C.

The Sub-step b) can be carried out in the same way as in the introductory part cited WO99 / 12661. This step can be or immersion process become. For example, in the second step (step b) one treatment solution use with a pH in the range of 3.5 to 5.5 and the total of 0.3 to 1.5 g / l hexafluorotitanate and / or hexafluorozirconate ions contains. It can be for the corrosion protection of the crystalline materials produced in sub-step a) Zinc phosphate layer may be advantageous if this treatment solution for the substep b) additionally contains about 0.01 to about 0.1 g / l copper ions.

Farther can be used in sub-step b) a treatment solution that has a pH has in the range of 3.3 to 5.8 and the 10 to 5000 mg / l organic Polymers selected from polyvinylphenol derivatives, as described in document WO99 / 12661 from page 9, line 28, to page 16, line 2 and described in greater detail claims 7 and 8 are combined. This disclosure is expressly referred to here taken. In a literal way Repetition of this revelation is waived.

Solutions can be used which, apart from the polyvinylphenol derivative and an acid for adjusting the pH, preferably of phosphoric acid, contain no further active ingredients. However, other active ingredient additives such as, in particular, hexafluorotitanate or zirconium ions can improve the layer formation on aluminum. For example, a solution can be used, the pH of which is preferably in the range from about 3.3 to about 4.8 and which as an organic polymer is about 100 to about 5,000 mg / l of an organic polymer in the form of a methylethanolamine or N- Methylglucamine derivative of polyvinylphenol and additionally
10 to 1000 mg / l phosphate ions,
10 to 250 mg / l hexafluorotitanate or zirconium ions,
10 to 250 mg / l manganese ions
contains.

Instead of these polyvinylphenol derivatives, the production of which requires a certain effort in sub-step b) solutions or dispersions of organic polymers selected from homo- and / or copolymers of acrylic acid and methacrylic acid and their esters are used. These solutions or dispersions preferably have pH values in the range from approximately 3.3 to approximately 4.8 and contain approximately 250 to approximately 1500 mg / l of the organic polymers. According to the teaching of EP-B-0 08 942, these polymer solutions or dispersions can additionally contain hexafluorotitanates, zirconates and / or silicates.

Farther are for the sub-step b) those treatment solutions suitable in the cited WO02 / 066702 from page 9, line 14 to 15, line 11 are. This is hereby expressly stated Referenced without wishing to repeat this revelation here.

The Use of zirconium compounds gives the different embodiments the present invention technically better results than that Use of titanium compounds and is therefore preferred. On which How these compounds get into the phosphating bath is in principle of no importance as long as they are dissolved or at least finely dispersed in it remain, for example in colloidal form. For example, complex fluoacids or their salts are used.

Ti or in particular Zr connections can be integrated The procedure is also introduced into the phosphating solution in another way are becoming increasingly common dishwater to cascade forward in the process sequence, i.e. For flushing steps further ahead to use again. It can also be prepared for reuse, i.e. of solved Salts are largely freed. Salts, the active substances for the process represent are recovered and to complement of drug solutions reused.

For example can a process sequence within the scope of the present invention therein consist that the metal surfaces after cleaning and rinsing in Sub-step a treated with the phosphating solution, then rinsed ("Rinse a"), in the sub-step b post-passivated with a Ti or in particular a Zr-containing post-passivation solution and subsequently rinses again ("Sink b"). To save of rinse water will just sink b supplemented with fresh or prepared rinse water, used rinse water b however in the sink a convicted. in this connection Ti and / or Zr compounds get out of the sink b (into which they go via the post-passivated metal surfaces be entered) in the sink a. additionally are in sink a Recyclable materials from the phosphating solution such as salts of the layer-forming divalent metal ions. water out of the sink a can be reused as rinsing water and recovered of valuable substances in the phosphating solution prepare, for example by ion exchange or in particular through single or multi-stage membrane filtration processes such as nanofiltration and / or reverse osmosis.

at membrane filtration produces a permeate enriched in salts, that used again as rinse water as well as a retentate enriched with salts, which is directly or after further processing to supplement the phosphating solution can be. With this sequence of processes, Ti and / or Zr compounds are obtained from the post-passivation solution ultimately in the retentate of membrane filtration and when using it to complement the phosphating solution finally into the phosphating solution. Do the pretreated metal surfaces contain aluminum or aluminum its alloys, the one described above arises effect according to the invention on.

embodiments

The sequence of processes according to the invention was checked on test sheets made of cold-rolled steel (CRS), electrolytically galvanized steel (ZE), hot-dip galvanized steel (Z) and on aluminum (AC 120). As is customary in the automotive manufacturing process, these sheets were first cleaned alkaline and activated with an activation solution containing titanium phosphate, for which commercial products from the applicant were used. Cleaning: Ridoline ^R 1565 and Ridosol ^R 1270, activation: Fixodine ^R 950.

Then were the test sheets with a phosphating bath with the composition according to the table 1 by three minutes Diving in contact at a temperature of 55 ° C.

Table 1: Phosphating bath composition, post-passivation (B: working examples according to the invention, V: comparative examples)

To the flush the sample sheets were dried with deionized water and coated with a cathodically separable electro-dip lacquer (Cathoguard 310, company BASF)

Layer weights were measured on unpainted test sheets made of steel and galvanized steel according to the usual standard method by detaching the layer in chromic acid solution and differential weighing. The layer on Al was detached by immersion in 65% nitric acid at 25 ° C. for 15 minutes. Standard automotive tests were carried out to check paint adhesion and corrosion protection: Wechselkli matest according to VDA 621-415 with stone chip test according to DIN 55669-1, determination of paint infiltration and paint adhesion ("K-value")

Results:

Table 2: Phosphate layer weights (g / m ² ) on the individual substrates:

Table 3: Paint infiltration at the scratch (mm, half the scratch width) and paint adhesion (K values; best value = 0, worst value = 5) after an alternating climate test according to VDA 621-415.

Interpretation:

The Adding Zr to the phosphating solution has no effect negative. 10 mg / l Zr in the phosphating solution improve the on steel Paint adhesion, 50 mg / l Zr in the phosphating solution improve paint adhesion on steel still further and additional corrosion protection compared to treatment with a Zr-free one phosphating without passivating rinsing to values that you would otherwise only get with a passivating rinse become. By adding Zr to the phosphating bath, the Treatment stage of the passivating post-rinse can be omitted, whereby Investment and process costs can be reduced. The nonexistent Phosphate layer bonding on Al reduces the pickling removal and therefore the sludge formation. Al is either directly in the phosphating bath or in a passivating rinse solution with a conversion layer other than a crystalline phosphate layer evenly coated and thereby protected.

Claims (11)

Process for the chemical pretreatment of metal surfaces, which at least partially consist of steel surfaces, before an organic coating, the metal structures being brought into contact with a phosphating solution containing 0.3 to 3 g / l of Zn (II) ions and Contains 5 to 40 g / l phosphate ions, characterized in that the phosphating solution additionally contains one or more titanium and / or zirconium compounds in such an amount that the total content of Ti and / or Zr is in the range from 1 to 1000 mg / l , A method according to claim 1, characterized in that the phosphating solution additionally contains at least one of the following accelerators: 1 up to 4 g / l chlorate ions, 0.2 to 2 g / l m-nitrobenzenesulfonate ions, 0.1 up to 10 g / l hydroxylamine in free or bound form, 0.05 up to 2 g / l m-nitrobenzoate ions, 0.05 to 2 g / l p-nitrophenol, 1 up to 70 mg / l hydrogen peroxide in free or bound form, 0.1 up to 10 g / l reducing sugar Method according to one or both of claims 1 and 2, characterized in that the phosphating solution additionally 1 to 5000 mg / l fluoride ions contains in free or bound form. Method according to one or more of claims 1 to 3, characterized in that the phosphating solution additionally one or more of the contains the following cations: 0.001 up to 4 g / l manganese (II), 0.001 to 4 g / l nickel (II) 0,002 up to 0.2 g / l copper (II) 0.2 to 2.5 g / l magnesium (II), 0.2 up to 2.5 g / l calcium (II), 0.01 to 0.5 g / l iron (II), 0.2 up to 1.5 g / l lithium (I), 0.02 to 0.8 g / l tungsten (VI). Method according to one or more of claims 1 to 4, characterized in that the metal surfaces additionally partially consist of surfaces of aluminum or its alloys and that on the steel surfaces and on any additional surfaces made of galvanized or galvanized steel, a surface-covering crystalline zinc phosphate layer with a layer weight in the range of 0.5 to 5 g / m ² , but without forming a crystalline zinc phosphate layer on the surfaces of aluminum or its alloys. Method according to one or more of claims 1 to 5, characterized in that the phosphating solution the one or more Titanium and / or Contains zirconium compounds in such an amount that the total content Ti and / or Zr is in the range of 10 to 1000 mg / l and that the metal surfaces after contact with the phosphating solution rinsed with water and not with a passivating rinse solution in Be brought in contact. Method according to one or more of claims 1 to 5, characterized in that the phosphating solution the one or more Titanium and / or Contains zirconium compounds in such an amount that the total content Ti and / or Zr is in the range of 1 to 30 mg / l and after the Contact with the phosphating solution, with or without an intermediate rinse with water, in a second step with the metal surfaces a treatment solution that contacts the crystalline zinc phosphate layer on steel as well as if necessary additionally existing surfaces made of galvanized and / or alloy galvanized steel does not dissolve if necessary additionally existing aluminum surfaces however creates a conversion layer. A method according to claim 7, characterized in that you have a phosphating solution with a pH in the range of 2.5 to 3.6 and with a temperature in the range of 20 to 65 ° C uses, which contains no more free fluoride in g / l than is indicated by the expression 8 / T, where T is the bath temperature means in ° C. Method according to one or both of claims 7 and 8, characterized in that a treatment solution is used in the second step, which has a pH in the range from 3.5 to 5.5 and the total 0.3 to 1.5 g / l hexafluorotitanate and / or hexafluorozirconate contains. Method according to one or both of claims 7 and 8, characterized in that a treatment solution is used in the second step, which has a pH in the range from 3.3 to 5.8 and the 10th up to 5000 mg / l organic polymers selected from polyvinylphenol derivatives contains. Method according to one or both of claims 7 and 8, characterized in that a treatment solution is used in the second step, which has a pH in the range from 3.3 to 4.8 and the 250 up to 1500 mg / l organic polymers selected from homo- and / or copolymers of acrylic acid and methacrylic acid and their esters.