EP2503025B1 - Multi-step corrosion-resistant treatment of metallic workpieces having at least partially zinc or zinc alloy surfaces - Google Patents

Abstract

Anticorrosive treatment of the metal surfaces of a component comprising at least partially surfaces of zinc or zinc alloys comprises contacting the component with an alkaline aqueous composition (A) and subsequently contacting with an acidic aqueous composition (B) for zinc phosphating, optionally with an intermediate rinsing step, and optionally with a preceding activation step. Anticorrosive treatment of the metal surfaces of a component comprising at least partially surfaces of zinc or zinc alloys comprises contacting the component with an alkaline aqueous composition (A) and subsequently contacting with an acidic aqueous composition (B) for zinc phosphating, optionally with an intermediate rinsing step, and optionally with a preceding activation step, where: the composition (A) comprises (a) at least 50 mg/l of iron(III) ions and (b) at least 100 mg/l of complexing agents (C) comprising organic compounds (C1) having at least one functional group of formula (-COOX), (-OPO 3X) and/or (-PO 3X) and/or condensed phosphates (C2); the composition (A) has a free alkalinity of at least one point, but less than 6 points and a pH value of 10.5-14; the composition (B) comprises (a1) 0.2-3 g/l of zinc(II) ions, (b1) 5-30 g/l of phosphate ions evaluated as phosphorus pentoxide and (c) less than 0.1 g/l of ionic compounds of metals of nickel and cobalt; and the composition (B) has a pH value of 2.5-3.6. X : H or an alkali metal and/or alkaline earth metal atom. An independent claim is included for a component, which at least partially contains zinc surfaces, where the zinc surfaces are coated by a two-layer system consisting of a first inner, iron-containing passive layer located on the zinc surface and a second outer, crystalline zinc phosphate layer located on the inner layer, the coating of the inner layer contains 20-150 mg/m 2>based on the element iron, and the coating of the outer layer is 0.5-3.5 g/m 2>.

Description

The present invention relates to the field of phosphating for the anticorrosive pretreatment of zinc surfaces, wherein the use of largely nickel and cobalt-free Zinkphosphatierlösungen is targeted. The present invention provides an alternative to trication zinc phosphating, in which the zinc surfaces of a component are first passivated with an alkaline composition containing iron (III) ions prior to zinc phosphating and thus preconditioned for largely nickel- and cobalt-free zinc phosphating. In a further aspect, the invention relates to a component, in particular an automobile body, which at least partially has surfaces of zinc, wherein the zinc surfaces of a two-layer system consisting of a first inner, resting on the zinc surface passive layer containing iron and a second outer, on the inner layer overlying crystalline zinc phosphate layer are covered.

The phosphatization of metals with a zinc-containing phosphating solution aims to produce solid metal phosphate layers on the metal surface which in themselves improve corrosion resistance and, in combination with paints and other organic coatings, substantially increase paint adhesion and resistance to corrosion undercutting , Such phosphating processes have been known for a long time. For the pretreatment before painting, in particular, the low-zinc phosphating, in which the phosphating relatively low levels of zinc ions of z. B. 0.5 to 2 g / L have. 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 of> 8 and can assume values of up to 30.

It has been shown that the co-use of other polyvalent cations in the zinc phosphating baths phosphate layers can be formed with significantly improved corrosion protection and paint adhesion properties. For example, find low-zinc process with the addition of z. B. 0.5 to 1.5 g / L manganese ions and z. B. 0.3 to 2.0 g / L nickel ions as so-called trication process or trication zinc phosphating for the preparation of metal surfaces for painting, for example, for the cathodic electrodeposition coating of car bodies, wide application. The trication zinc phosphating provides the advantage that both zinc and iron or steel and aluminum can be provided with an excellent Lackhaftgrund with a crystalline zinc phosphate layer comparable quality, which form an excellent Lackhaftgrund for subsequently applied dip coatings. In the layer-forming phosphating, ie the provision of homogeneous crystalline coating coatings of zinc phosphate on steel, galvanized steel and aluminum, the trication-Zinkphosphatierung in terms of the achieved quality of the coatings so far unrivaled.

However, the high content of nickel ions in the trizinc zinc phosphating compositions, and thus of nickel and nickel compounds in the phosphate layers formed, has disadvantages in that nickel and nickel compounds are considered critical from an environmental and workplace hygiene point of view. Recently, therefore, low-zinc phosphating processes have increasingly been described, which lead to qualitatively similar high-quality phosphate coatings such as the nickel-containing processes without the use of nickel. However, phosphating of galvanized steel or zinc generally with nickel-free phosphating baths has been found to result in inadequate corrosion protection and inadequate paint adhesion.

In the field of automotive production, which is particularly relevant to the present invention, various metallic materials are increasingly being used and joined together in composite structures. In body construction, the most varied steels are still used because of their specific material properties, but also increasingly light metals such as aluminum, which are particularly significant for a considerable weight reduction of the entire body. In particular, in the automotive industry, there is often the problem that the surfaces of zinc by the known in the prior art nickel-free Zinkphsophatierverfahren compared to steel surfaces in terms of protection against corrosive infiltration of the paint layer and paint adhesion drops significantly and younger technologies such as the conversion treatment with training extremely thin and X-ray amorphous passive shafts do not yet match the performance of zinc phosphating on steel.

The DE 19834796 and DE 19705701 disclose a process using low-nickel zinc phosphating which requires targeted post-passivation with lithium, copper or silver ions to achieve good corrosion protection on a metal mix of steel, galvanized steel and aluminum.

The DE 4341041 discloses a nickel-free, low-zinc phosphating process, which focuses on the use of m-nitrobenzenesulfonate as an accelerator and a relatively low nitrate content of less than 0.5 g / L to obtain good corrosion protection results even on zinc surfaces.

The DE 19606017 also discloses a low-zinc phosphating process free of nickel in which the phosphating solution contains copper ions to improve corrosion protection.

Furthermore, multi-stage processes for the anticorrosion pretreatment of surfaces of zinc are known in the prior art, in which in a first step, the treatment with an alkaline composition and in a subsequent step, a zinc phosphating can take place. So revealed the DE 2317896 an alkaline pretreatment of zinc surfaces with heavy metal-containing compositions containing a complexing agent and, for example, iron (III) ions. Similar alkaline pretreatments prior to possible zinc phosphating are described in US Pat DE 1521854 . DE 2017327 . US 3,515,600 . EP 0240943 and the DE 19733972 described.

Starting from this prior art, the task continues to establish an alternative multi-stage process for corrosion-protective treatment, largely independent of the metallic substrate provides corrosion protection and paint adhesion as previously achieved only on iron or steel surfaces using the trication Zinkphosphatierung can, with the use of heavy metals, especially nickel, can be largely dispensed with completely.

1. a) zumindest 50 mg/L an Eisen(III)-Ionen,
2. b) zumindest 100 mg/L an Komplexbildnern ausgewählt aus organischen Verbindungen c1 die zumindest eine funktionale Gruppe ausgewählt aus -COOX, -OPO₃X und/oder -PO₃X aufweisen, wobei X entweder ein H-Atom oder ein Alkali- und/oder Erdalkalimetall-Atom darstellt, und/oder kondensierte Phosphate c2) berechnet als PO₄ enthält, wobei die Zusammensetzung eine freie Alkalität von zumindest 1 Punkt, aber weniger als 6 Punkten, und einen pH-Wert im Bereich von 10,5-14 aufweist,
   und anschließend im Schritt ii), mit oder ohne dazwischenliegendem Spülschritt und mit oder ohne vorausgehender Aktivierung, mit einer sauren wässrigen Zusammensetzung (B) zur Zinkphosphatierung in Kontakt gebracht wird, die einen pH-Wert im Bereich von 2,5-3,6 aufweist und
   1. a) 0,2 bis 3,0 g/L Zink(II)-Ionen,
   2. b) 5,0 bis 30 g/L Phosphat-Ionen berechnet als P₂O₅, und
   3. c) jeweils weniger als 0,1 g/L, vorzugsweise jeweils weniger als 0,01 g/L, besonders bevorzugt jeweils weniger als 0,001 g/L an ionischen Verbindungen der Metalle Nickel und Cobalt jeweils bezogen auf das metallische Element enthält.

This object is achieved by means of a multi-stage treatment method for a component which has at least partially surfaces of zinc or zinc alloys, wherein the component in step i) is brought into contact with an alkaline aqueous composition (A) which

1. a) at least 50 mg / L of iron (III) ions,
2. b) at least 100 mg / L of complexing agents selected from organic compounds c1 which have at least one functional group selected from -COOX, -OPO ₃ X and / or -PO ₃ X, where X is either an H atom or an alkali metal and / or represents or alkaline earth metal atom, and / or condensed phosphates c2) calculated as PO _4, said composition having a free alkalinity of at least 1 point, but less than 6 points, and a pH in the range of 10.5 to 14 .
   and then in step ii), with or without intermediate rinsing step and with or without prior activation, contacted with an acidic aqueous composition (B) for zinc phosphating having a pH in the range of 2.5-3.6 and
   1. a) 0.2 to 3.0 g / L zinc (II) ions,
   2. b) 5.0 to 30 g / L of phosphate ions calculated as P ₂ O ₅ , and
   3. c) in each case less than 0.1 g / L, preferably in each case less than 0.01 g / L, particularly preferably in each case less than 0.001 g / L of ionic compounds of the metals nickel and cobalt in each case based on the metallic element.

A component which at least partially has surfaces of zinc or zinc alloys comprises within the meaning of the present invention both a semi-finished product made of zinc or galvanized steel, for example galvanized steel strip, and makes of same or different materials, for example an automobile body made of galvanized steel , Steel and aluminum.

Under zinc alloy according to the invention alloys with an impurity content of less than 50 at .-% understood. In the following, the term "zinc" includes both pure zinc and zinc alloys.

Under rinsing step according to the invention is the flushing with city water or deionized water (κ <1μScm ^-1 ) understood to remove water-soluble residues and particles from the component to be treated, which are abducted from a previous treatment step as adhering to the component.

Activation according to the invention is understood to mean an activation of at least the zinc surfaces of the component for the subsequent phosphating, which supports the formation of uniform fine-crystalline zinc phosphate layers. The activation which is carried out according to the invention immediately before step ii) but after step i) is carried out with an aqueous composition which has a pH in the range of 3.5-13. The presence of an activation between step i) and step ii) is preferred according to the invention. Such activations and the associated activation baths are well known to those skilled in the phosphating and, for example, in the EP 1368508 disclosed.

A parameter which is decisive for the effectiveness of the compositions (A) in step i) of the process according to the invention is the free alkalinity. The free alkalinity is determined by titrating 2 ml of bath solution, preferably diluted to 50 ml, with a 0.1 N acid such as hydrochloric acid or sulfuric acid to a pH of 8.5. The consumption of acid solution in ml indicates the score of free alkalinity.

The term "condensed phosphates" according to component c1) in step i) of the process according to the invention are the water-soluble metaphosphates (Me _n [P _n O _3n ]), di-tri- and polyphosphates (Me _{n + 2} [P _n O _{3n + 1} ] or Me _n [H _z P _n O _{3n + 1} ]), the isometaphosphates and the cross-linked polyphosphates, where Me are either alkali metal or alkaline earth metal atoms. Of course, instead of the water-soluble salts, the corresponding condensed acids of the phosphoric acid may be used for the formulation of the compositions (A), provided that the free alkalinity is set as indicated. The mass-related proportion of the "condensed phosphates" according to component c2) in step i) of the process according to the invention is always calculated as a corresponding amount of PO ₄ . Similarly, for the determination of those molar ratios comprising an amount of condensed phosphates, this amount of condensed phosphates is always based on the equivalent amount of PO ₄ .

In the process according to the invention, it is possible to deposit on the zinc surfaces of the component optimum crystalline zinc phosphate layers having a high degree of coverage and outstanding adhesion to the zinc substrate, without using a classical trication zinc phosphating containing heavy metal ions based on nickel and / or cobalt. Owing to the interaction of the zinc surfaces precoated or passivated in step i) with the nickel- and / or cobalt-free zinc phosphating in step ii), zinc phosphate layers on the zinc surfaces of the component are provided which form a corrosion-resistant lacquer adhesion base is completely equivalent to the paint adhesion base produced in a classical trication zinc phosphating.

It has been found that an aqueous alkaline composition (A) in step i) of the process according to the invention brings about a suitable passivation of zinc surfaces, which affords good bonding of the subsequent zinc phosphating, if the free alkalinity has less than 5 points. This is especially true for the application of the composition (A) in spraying, which causes a suitable passivation, especially when the free alkalinity is less than 4 points. Surprisingly, it has been found that high iron coating rates on zinc surfaces above 150 mg / m ² prove to be disadvantageous for the process according to the invention since in combination with the zinc phosphating poorer adhesion results to organic topcoats are achieved so that compositions (A) in the Step i) may not have a high free alkalinity. However, the free alkalinity should preferably be at least 2 points in order to achieve optimal layer coverage on zinc surfaces of at least 20 mg / m ² to produce iron based on the element. Although compositions (A) which have a free alkalinity above 6 points give rise to high iron coatings on the zinc surfaces, the adhesion to coating layers applied after step ii) is markedly reduced by high layer coverages relative to the element iron, so that Also, the corrosion protection is less effective or insufficient.

The composition (A) in step i) of the process according to the invention has a pH of at least 10.5. Below a pH of 10.5, no layer deposits of iron of at least 20 mg / m ^{2 are formed} on the zinc surfaces upon contacting them with a composition (A), so that for such low pHs, no alkaline Passivation of zinc surfaces for subsequent zinc phosphating takes place. In order to minimize the pickling attack on the zinc surfaces of the component, it is further preferred that the pH in the composition (A) in step i) of the method according to the invention is not above 13. In the event that the component also has surfaces of aluminum in addition to the surfaces of zinc, it is advantageous if the pH in the composition (A) in step i) of the method according to the invention does not reach values above 11.5, since otherwise the intensified pickling attack causes intensive black discoloration of the aluminum surfaces, the so-called "fountain black", which adversely affects the effectiveness of a subsequent conversion treatment, for example on the zinc phosphating in step ii) of the process according to the invention or in the case of aluminum phosphating discontinuous zinc phosphating in step ii) an acid subsequent passivation following the process according to the invention based on water-soluble inorganic compounds of the elements zirconium and / or titanium.

The proportion of iron (III) ions in the composition (A) in step i) of the method according to the invention is preferably not more than 2000 mg / L. Higher proportions of iron (III) ions are unfavorable for the process, since the solubility of iron (III) ions in the alkaline medium must be maintained by correspondingly high proportions of complexing agent without more favorable properties in terms of the alkaline passivation of the zinc surfaces become. However, preference is given to those compositions (A) in step i) of the process according to the invention in which the proportion of iron (III) ions is at least 100 mg / L, more preferably at least 200 mg / L, on the one hand on the zinc surfaces in step i ) of the process according to the invention to ensure an alkaline passivation within typical procedural treatment times of less than two minutes and on the other hand to obtain in step ii) of the process according to the invention phosphate coatings in excellent layer quality.

The complexing agents according to component c) of the alkaline composition (A) in step i) of the process according to the invention are preferably contained in such an amount that the molar ratio of all components c) to iron (III) ions is greater than 1: 1 and especially preferably at least 2: 1, more preferably at least 5. It turns out that the use of the amount of complexing agents in the stoichiometric excess is advantageous for the process, since in this way the proportion of iron (III) ions is kept permanently in solution. The precipitation insoluble Iron hydroxides are completely suppressed in this way, so that the composition (A) remains permanently stable and does not deplete of iron (III) ions. At the same time, however, there is sufficient deposition of an inorganic layer containing iron ions on the zinc surfaces. An excess of complexing agent does not suppress the precipitation and separation of insoluble iron salts in a reaction zone immediately at the zinc surface, in which due to the pickling attack of the composition (A), the alkalinity is increased. For reasons of economy and for a resource-saving use of the complexing agents, it is nevertheless preferred that the molar ratio of the components c) to iron (III) ions in the composition (A) does not exceed the value 10.

In a preferred embodiment, the composition (A) may additionally contain at least 100 mg / L of phosphate ions in step i) of the process according to the invention. This proportion of phosphate ions requires that, in addition to the iron ions, phosphate ions also constitute an essential constituent of the passivation layer produced on the zinc surfaces in step i). It has been found that such passive layers are advantageous for the subsequent zinc phosphating and, in conjunction with zinc phosphating, impart good adhesion to subsequently applied lacquer layers. Accordingly, it is further preferred in step i) of the process according to the invention that the compositions (A) contain at least 200 mg / L, more preferably at least 500 mg / L, of phosphate ions. The properties of the passive layer, which is formed when the zinc surface of the component is brought into contact with compositions (A) in step i) of the process according to the invention, are not further positively influenced above a proportion of phosphate ions of 4 g / l, cf. that, for reasons of economy, the proportion of phosphate ions in the composition (A) in step i) of the process according to the invention should preferably be below 10 g / l.

The ratio of iron (III) ions to phosphate ions can be varied within a wide range. The mass-related ratio of iron (III) ions to phosphate ions in a composition (A) in step i) of the process according to the invention is preferably in the range from 1:20 to 1: 2, particularly preferably in the range from 1:10 to 1: 3. Compositions (A) which have such a mass ratio of components a) to b), after contacting with a zinc surface, give homogeneous black-gray passive layers containing phosphate ions with layer deposits of 20-150 mg / m ² based on the element iron.

Condensed phosphates are capable of holding iron (III) ions in solution in an alkaline medium by complexation. Although there are no particular restrictions on the nature of the condensed phosphates with regard to their usability for compositions (A) in step i) of the process according to the invention, preference is given to condensed phosphates selected from pyrophosphates, tripolyphosphates and / or polyphosphates, more preferably from pyrophosphates, because they are particularly soluble in water and very easily accessible.

As organic compounds c1), which also or alternatively to the condensed phosphates as Complexing agents are contained in the composition (A), such compounds in step i) of the inventive method are preferred, having in their acid form (X = H atom), an acid number of at least 250. Lower acid numbers give the organic compounds surface-active properties, so that organic compounds c1) with acid numbers below 250 can act as anionic surfactants strongly emulsifying. In this connection, it is further preferable that the organic compounds are not high molecular weight and do not exceed a number average molecular weight of 5,000 μ, more preferably 1,000 μ. The emulsifying effect of the organic compounds c1) can be so pronounced when the preferred acid number and optionally the preferred molecular weight are exceeded, that contaminants introduced from the purification stage via the component in the form of oils and drawing fats can only be removed from the alkaline passivation stage via expensive separation processes , For example, by a dosage of cationic surfactants, so that further process parameters are controlled. It is therefore more advantageous to adjust the alkaline passivation step and thus the composition (A) in step i) of the process according to the invention only slightly emulsifying in order to allow a conventional separation of the floating oils and fats. Anionic surfactants are also prone to pronounced foam formation, which is particularly disadvantageous for example in the spray application of the composition (A). Therefore, in step i) of the process according to the invention, preference is given to using organic complexing agents c1) having acid numbers of at least 250 in the composition. The acid number indicates the amount of potassium hydroxide in milligrams, which is required to neutralize 1 g of the organic compound c1) in 100 g of water according to DIN EN ISO 2114.

Preferred organic complexing agents c1) in the composition (A) in step i) of the process according to the invention are selected from α-, β- and / or γ-hydroxycarboxylic acids, hydroxyethane-1,1-diphosphonic acid, [(2-hydroxyethyl) (phosphonomethyl ) amino] -methylphosphonic acid, diethylenetriaminepentakis (methylenephosphonic acid) and / or amino-tris (methylenephosphonic acid) and salts thereof, more preferably hydroxyethane-1,1-diphosphonic acid, [(2-hydroxyethyl) (phosphonomethyl) amino] -methylphosphonic acid, diethylenetriaminepentakis (methylenephosphonic acid ) and / or amino tris (methylene phosphonic acid) and salts thereof.

Thus, according to the invention, such compositions (A) in step i) of the process according to the invention are explicitly included which contain exclusively condensed phosphates c2), exclusively organic complexing agents c1) or a mixture of both. However, the proportion of organic complexing agent c1) in the composition (A) can be reduced to the extent that complexing agent c2) selected from condensed phosphates is contained. In a particular embodiment of the process according to the invention, in the composition (A) in step i) both complexing agents c2) selected from condensed phosphates and organic complexing agents c1), wherein the molar ratio of all components c) to iron (III) ions greater as 1: 1, but the molar ratio of components c1) to ferric ions is less than 1: 1, more preferably less than 3: 4, but preferably at least 1: 5. A mix of both complexing agents c1) and c2) is advantageous in that the condensed phosphates in the alkaline medium at elevated temperature with the phosphate ions of the composition (A) are in equilibrium, so that by layer formation on the zinc surfaces spent phosphate ions from the condensed phosphates be replicated slowly. Conversely, however, the presence of condensed phosphates alone is not sufficient to cause an alkaline passivation layer containing iron and phosphate on the zinc surfaces, so that the proportion of phosphate ions in the composition (A) in step i) of the method according to the invention is obligatory. In the presence of the condensed phosphates, however, the precipitation of poorly soluble phosphates, for example iron phosphates, is suppressed by the interaction with the organic complexing agents c2) even at high pH values above 10.5, so that compositions (A) are a mixture of complexing agents contained in step i) of the method according to the invention are preferred, wherein it should preferably be ensured that the molar ratio of components c1) to iron (III) ions is at least 1: 5.

In order to increase the cleaning power for the metal surfaces to be treated, the composition (A) in step i) of the process according to the invention may additionally comprise nonionic surfactants. This additional purification and activation of the metal surfaces by means of compositions (A) containing nonionic surfactants affords the advantage that the passive layer formation on the zinc surfaces is more homogeneous compared to compositions (A) which do not contain nonionic surfactants as surface-active substances. A passivation formed homogeneously on the zinc surfaces of the component is a basic prerequisite for a likewise homogeneous formation of the zinc phosphate layer in step ii) of the method according to the invention. The nonionic surfactants are preferably selected from one or more ethoxylated and / or propoxylated C 10 -C 18 fatty alcohols having a total of at least two but not more than 12 alkoxy groups, more preferably ethoxy and / or propoxy, some with an alkyl radical, more preferably with a Methyl, ethyl, propyl, butyl radical may be end-group-capped. The proportion of nonionic surfactants in a composition (A) is preferably at least 10 mg / L, more preferably at least 100 mg / L, for sufficient purification and activation of the metal surfaces in step i) of the process according to the invention, and for economic reasons preferably not more than 10 g / L of nonionic surfactants are included. The use of highly emulsifying anionic surfactants should be avoided in the composition (A) for the reasons already explained above, so that their proportion of the composition (A) preferably not above 500 mg / L, more preferably not above 100 mg / L lies.

A further advantage of the alkaline passivation with compositions (A) in step i) of the process according to the invention is that it is entirely possible to dispense with additions of heavy metal ions which are used in conventional alkaline compositions for passivation of zinc surfaces, so that the composition (A) preferably does not contain heavy metals selected from nickel, cobalt, manganese, molybdenum, chromium and / or cerium. However, the presence of small amounts of these heavy metals in the composition (A) used in a passivation step in the operation of a pretreatment line can not be completely avoided. For example, nickel and manganese are common alloying constituents of steel which, when treated with the composition (A) in step i) of the process according to the invention, can pass through the partial dissolution of native oxide layers into the passivation step. The composition (A) in step i) of the process according to the invention therefore preferably contains a total of less than 10 mg / L of ionic compounds of the metals nickel, cobalt, manganese, molybdenum, chromium and / or cerium, in particular in each case less than 1 mg / L ionic compounds of the metals nickel and cobalt in each case based on the metallic element.

The pickling of the zinc surfaces of the metallic component during the alkaline passivation in step i) of the method according to the invention causes zinc ions to enter the aqueous composition (A). This also applies to aluminum ions insofar as metallic components are treated which, in addition to the zinc surfaces, also have surfaces of aluminum. Metal cations of the elements zinc and aluminum, however, have no negative impact on the effectiveness of the compositions (A) and are therefore tolerable.

1. a) 0,05 bis 2 g/L an Eisen(III)-Ionen,
2. b) 0,1 bis 4 g/L an Phosphat-Ionen,
3. c) zumindest 0,1 g/L an Komplexbildnern ausgewählt aus organischen Verbindungen c1 die zumindest eine funktionale Gruppe ausgewählt aus -COOX, -OPO₃X und/oder -PO₃X aufweisen, wobei X entweder ein H-Atom oder ein Alkali- und/oder Erdalkalimetall-Atom darstellt, und/oder kondensierten Phosphaten c2) berechnet als PO₄,
4. d) insgesamt 0,01 bis 10 g/L an nichtionischen Tensiden, die vorzugsweise ausgewählt aus einem oder mehreren ethoxylierten und/oder propoxylierten C10-C18 Fettalkoholen mit insgesamt zumindest zwei aber nicht mehr als 12 Alkoxygruppen, besonders bevorzugt Ethoxy- und/oder Propoxygruppen, die teilweise mit einem Alkylrest, besonders bevorzugt mit einem Methyl-, Ethyl-, Propyl-, Butyl-Rest endgrupppenverschlossen vorliegen,
5. e) insgesamt weniger als 10 mg/L an ionischen Verbindungen der Metalle Nickel, Cobalt, Mangan, Molybdän, Chrom und/oder Cer, insbesondere jeweils weniger als 1 mg/L an ionischen Verbindungen der Metalle Nickel und Cobalt jeweils bezogen auf das metallische Element,
   wobei nicht mehr als 10 g/L an kondensierten Phosphaten c2) berechnet als PO₄ enthalten sind und das molare Verhältnis der Summe der Komponenten c1) und c2) zu Eisen(III)-Ionen größer als 1 : 1 ist und wobei die freie Alkalität zumindest 1 Punkt, aber weniger als 6 Punkte beträgt, und der pH-Wert zumindest 10,5 ist.

In a particular embodiment of the process according to the invention, the composition (A) in step i) contains

1. a) 0.05 to 2 g / L of iron (III) ions,
2. b) 0.1 to 4 g / L of phosphate ions,
3. c) at least 0.1 g / L of complexing agents selected from organic compounds c1 which have at least one functional group selected from -COOX, -OPO ₃ X and / or -PO ₃ X, where X is either an H atom or an alkali metal and / or alkaline earth metal atom, and / or condensed phosphates c2) calculated as PO ₄ ,
4. d) a total of 0.01 to 10 g / L of nonionic surfactants, preferably selected from one or more ethoxylated and / or propoxylated C10-C18 fatty alcohols having a total of at least two but not more than 12 alkoxy groups, more preferably ethoxy and / or propoxy which are in some cases end-capped with an alkyl radical, more preferably with a methyl, ethyl, propyl, butyl radical,
5. e) a total of less than 10 mg / L of ionic compounds of the metals nickel, cobalt, manganese, molybdenum, chromium and / or cerium, in particular in each case less than 1 mg / L of ionic compounds of the metals nickel and cobalt in each case based on the metallic element .
   wherein not more than 10 g / L of condensed phosphates c2) calculated as PO ₄ are present and the molar ratio of the sum of the components c1) and c2) to ferric ions is greater than 1: 1 and wherein the free alkalinity at least 1 point, but less than 6 points, and the pH is at least 10.5.

1. a) 0,05 bis 2 g/L an Eisen(III)-Ionen,
2. b) 0,1 bis 4 g/L an Phosphat-Ionen,
3. c) zumindest 0,1 g/L an Komplexbildnern ausgewählt aus organischen Verbindungen c1), die zumindest eine funktionale Gruppe ausgewählt aus --COOX, -OPO₃X und/oder -PO₃X aufweisen, wobei X entweder ein H-Atom oder ein Alkali- und/oder Erdalkalimetall-Atom darstellt, und/oder kondensierten Phosphaten c2) berechnet als PO₄,
4. d) insgesamt 0,01 bis 10 g/L an nichtionischen Tensiden, die vorzugsweise ausgewählt aus einem oder mehreren ethoxylierten und/oder propoxylierten C10-C18 Fettalkoholen mit insgesamt zumindest zwei aber nicht mehr als 12 Alkoxygruppen, besonders bevorzugt Ethoxy- und/oder Propoxygruppen, die teilweise mit einem Alkylrest, besonders bevorzugt mit einem Methyl-, Ethyl-, Propyl-, Butyl-Rest endgrupppenverschlossen vorliegen,
5. e) insgesamt weniger als 10 mg/L an ionischen Verbindungen der Metalle Nickel, Cobalt, Mangan, Molybdän, Chrom und/oder Cer, insbesondere jeweils weniger als 1 mg/L an ionischen Verbindungen der Metalle Nickel und Cobalt jeweils bezogen auf das metallische Element,
6. f) insgesamt weniger als 0,1 g/L, vorzugsweise weniger als 0,01 g/L, an organischen polymeren Bestandteilen, die keine organischen Verbindungen c1) sind und vorzugsweise ein zahlengemitteltes Molekulargewicht von mehr als 1.000 u, besonders bevorzugt mehr als 5.000 u aufweisen,
7. g) zu den Komponenten a), b) und e) äquivalente Mengen an Gegenionen,
8. h) ein wasserlösliches Alkali- oder Erdalkalihydroxid oder Ammoniak zur Einstellung der Alkalität,
9. i) Rest Wasser mit einer Härte von nicht mehr als 30 °dH,
   wobei nicht mehr als 10 g/L an kondensierten Phosphaten c2) berechnet als PO₄ enthalten sind und das molare Verhältnis der Summe der Komponenten c1) und c2) zu Eisen(III)-Ionen größer als 1 : 1 ist und wobei die freie Alkalität zumindest 1 Punkt, aber weniger als 6 Punkte beträgt, und der pH-Wert zumindest 10,5 ist.

In particular, in step i) of the process according to the invention, compositions (A) are comprised which are composed as follows:

1. a) 0.05 to 2 g / L of iron (III) ions,
2. b) 0.1 to 4 g / L of phosphate ions,
3. c) at least 0.1 g / L of complexing agents selected from organic compounds c1) which have at least one functional group selected from --COOX, -OPO ₃ X and / or -PO ₃ X, where X is either an H atom or represents an alkali and / or alkaline earth metal atom, and / or condensed phosphates c2) calculated as PO ₄ ,
4. d) a total of 0.01 to 10 g / L of nonionic surfactants, preferably selected from one or more ethoxylated and / or propoxylated C10-C18 fatty alcohols having a total of at least two but not more than 12 alkoxy groups, more preferably ethoxy and / or propoxy which are in some cases end-capped with an alkyl radical, more preferably with a methyl, ethyl, propyl, butyl radical,
5. e) a total of less than 10 mg / L of ionic compounds of the metals nickel, cobalt, manganese, molybdenum, chromium and / or cerium, in particular in each case less than 1 mg / L of ionic compounds of the metals nickel and cobalt in each case based on the metallic element .
6. f) a total of less than 0.1 g / L, preferably less than 0.01 g / L, of organic polymeric constituents which are not organic compounds c1) and preferably have a number average molecular weight of more than 1000 μ, more preferably more than 5000 u have,
7. g) to components a), b) and e) equivalent amounts of counterions,
8. h) a water-soluble alkali or alkaline earth hydroxide or ammonia for adjusting the alkalinity,
9. i) balance of water with a hardness of not more than 30 ° dH,
   wherein not more than 10 g / L of condensed phosphates c2) calculated as PO ₄ are present and the molar ratio of the sum of the components c1) and c2) to ferric ions is greater than 1: 1 and wherein the free alkalinity at least 1 point, but less than 6 points, and the pH is at least 10.5.

In a preferred embodiment of the method according to the invention, the component in step i) for at least 30 seconds, but not more than 4 minutes at a temperature of at least 30 ° C, more preferably at least 40 ° C, but not more than 70 ° C, especially preferably not more than 60 ° C is brought into contact with the alkaline aqueous composition (A). The compositions (A) cause, as already described, a passivation of the zinc surfaces of the component, which allows the growth of a crystalline, homogeneous and well-adherent zinc phosphate layer. The formation of the passive layer takes place thereby self-limiting, ie that depending on the specific formulation of the composition (A) certain maximum layer conditions can be realized. The preferred treatment or contact times should be selected in step i) of the method according to the invention so that the layer of iron is at least 20 mg / m ² . The treatment and contact times for the realization of such a minimum layer coverage vary depending on the type of application and depend in particular on the flow of the aqueous fluids acting on the metal surface to be treated. Thus, the formation of passivation in processes where the composition is applied by spraying is faster than in dipping applications. Regardless of the type of application, the coating compositions (A) do not produce any layer deposits of iron significantly above 250 mg / m ² due to the self-limiting passive layer structure.

For sufficient formation of the passive layer and optimum preconditioning of the zinc surfaces for subsequent zinc phosphating in step ii), contacting the compositions (A) in step i) with the component having at least partial surfaces of zinc should immediately follow the alkaline passivation with or without subsequent rinsing step layer coatings of iron of at least 20 mg / m ² , but preferably not more than 150 mg / m ² realized realized. Above a layer coverage of 150 mg / m ² based on the element iron on the zinc surfaces of the component, which is applied in step i) of the process according to the invention, a deterioration of the adhesion-promoting properties of the deposited on the zinc surfaces in step ii) phosphate layers may already occur.

The process according to the invention is of particular industrial importance, especially in the pretreatment of automobile bodies, since the alkaline passivation in step i) of the process according to the invention for the alkaline cleaning of the bodywork is effected directly, i. without intervening rinsing step, can follow. If the composition (A) in step i) of the process according to the invention additionally contains nonionic surfactants in a preferred embodiment, then the alkaline cleaning of the component or the body and the alkaline passivation of the zinc surfaces of the component can take place in one step. A separation of alkaline cleaning and alkaline passivation stage by a rinsing step is therefore just as little required as the performance of cleaning and alkaline passivation in two process steps and different baths.

Accordingly, a method according to the invention is characterized in particular by the fact that the component which has at least partial surfaces of zinc is first brought into contact with an alkaline cleaner in a cleaning and degreasing bath, the alkaline cleaner preferably having a pH in the range from 9-14 without prior to subsequent contacting with the alkaline aqueous composition (A) in step i), a rinsing step.

In the method according to the invention, as already discussed, in step i) an inorganic passivation layer containing iron is produced on the zinc surfaces, whereas on the other metallic surfaces of the component, which may be, for example, surfaces of iron, steel and / or aluminum, no deposition such an inorganic layer could be detected. The specific deposition of the passive layer on the zinc surfaces surprisingly leads to a significant improvement in the deposition of a crystalline zinc phosphate layer, which takes place in step ii) of the process according to the invention, wherein the composition (B) for zinc phosphating no water-soluble nickel and / or cobalt salts must be added , Accordingly, the process according to the invention replaces the usual in the automotive industry Trications Zinkphosphatierung containing significant amounts of the heavy metals nickel and / or cobalt.

The composition (B) for zinc phosphating in step ii) of the process according to the invention is preferably not added at all to any nickel and cobalt ionic compounds. However, in practice it can not be ruled out that such constituents are introduced into the phosphating baths in traces via the material to be treated, the starting water or the ambient air. In particular, it can not be ruled out that in the phosphating of components having surfaces of zinc-nickel alloy coated steel, nickel ions are introduced into the phosphating solution. However, it can be expected from the process according to the invention that under technical conditions the amount of ionic compounds of the metals nickel and cobalt in the compositions (B) for zinc phosphating is preferably below 10 mg / L, more preferably below 1 mg / L, respectively the metallic element lies.

For the phosphating of the zinc surfaces of the component in step ii), it is not absolutely necessary for the composition (B) to contain so-called accelerators. However, if components are treated which additionally have steel or iron surfaces, then it is necessary for their sufficient zinc phosphating in step ii) that the composition (B) contains one or more accelerators. Such accelerators are well known in the art as components of zinc phosphating baths. This is understood to mean substances which chemically bind the hydrogen formed by the pickling attack of the acid on the metal surface by being themselves reduced.

• 0,1 bis 15 g/L Nitrationen,
• 0,3 bis 4 g/L Chlorationen,
• 0,01 bis 0,2 g/L Nitritionen,
• 0,05 bis 4 g/L Nitroguanidin,
• 0,05 bis 4 g/L N-Methylmorpholin-N-oxid,
• 0,2 bis 2 g/L m-Nitrobenzolsulfonat-Ionen,
• 0,05 bis2 g/L m-Nitrobenzoat-Ionen,
• 0,05 bis2 g/L p-Nitrophenol,
• 1 bis 150 mg/L Wasserstoffperoxid in freier oder gebundener Form,
• 0,1 bis 10 g/L Hydroxylamin in freier oder gebundener Form,
• 0,1 bis 10 g/L eines reduzierenden Zuckers.

As accelerator, the composition (B) in step ii) of the process according to the invention may contain, for example, at least one of the following amounts of accelerator:

• 0.1 to 15 g / L nitrate ions,
• 0.3 to 4 g / L chlorate ions,
• 0.01 to 0.2 g / L nitrite ions,
• 0.05 to 4 g / L nitroguanidine,
• 0.05 to 4 g / L N-methylmorpholine N-oxide,
• 0.2 to 2 g / L of m-nitrobenzenesulfonate ions,
• 0.05 to 2 g / L of m-nitrobenzoate ions,
• 0.05 to 2 g / L of p-nitrophenol,
• 1 to 150 mg / L of hydrogen peroxide in free or bound form,
• 0.1 to 10 g / L of hydroxylamine in free or bound form,
• 0.1 to 10 g / L of a reducing sugar.

Preferably, in the composition (B), at least nitrate ions are contained as an accelerator in an amount of not more than 2 g / L.

• 0,001 bis 4 g/L Mangan(II),
• 0,2 bis 2,5 g/L Magnesium(II),
• 0,2 bis 2,5 g/L Kalzium(II),
• 0,01 bis 0,5 g/L Eisen(II),
• 0,2 bis 1,5 g/L Lithium(I),
• 0,02 bis 0,8 g/L Wolfram(VI).

The composition (B) in step ii) of the process according to the invention preferably contains one or more further metal ions whose positive effect on the corrosion protection of zinc phosphate layers is known in the prior art. In this case, the composition (B) may contain one or more of the following cations in the amounts indicated:

• 0.001 to 4 g / l manganese (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 presence of manganese is particularly preferred. The possibility of the presence of divalent iron depends on the accelerator system described above. The presence of iron (II) in the stated concentration range requires an accelerator which does not oxidize towards these ions. Hydroxylamine should be mentioned as an example for this purpose.

Particularly good zinc phosphate layers are obtained with compositions (B) which additionally contain manganese (II). The manganese content of the composition (B) is preferably between 0.2 and 4 g / L, since at lower manganese contents, the positive influence on the corrosion behavior of the phosphate layers is no longer present and no further positive effect occurs at higher manganese contents. Contents between 0.3 and 2 g / l and in particular between 0.5 and 1.5 g / l in the composition (B) in step ii) of the process according to the invention are particularly preferred. The zinc content of the composition (B) in step ii) of the process according to the invention is preferably adjusted to values between 0.45 and 2 g / l. However, due to the pickling removal during the contacting of the component with the composition (B) in step ii) of the process of the invention, it is possible that the actual zinc content of the composition (B) increases up to 3 g / L. The form in which the zinc and manganese ions are introduced into the composition (B) is of no importance in principle. It is particularly appropriate to use as the source of zinc and / or manganese, the oxides and / or carbonates.

In a preferred embodiment, the compositions (B) in step ii) of the process according to the invention additionally comprise copper (II) ions in the range from 1 to 30 mg / L, if the component to be treated according to the invention also contains, in addition to the surfaces of zinc, surfaces of iron or metal Steel in order to promote the formation of particularly advantageous zinc phosphate layers on the surfaces of iron or steel in step ii). However, if the component to be treated according to the invention is not also composed of surfaces of iron or steel, the addition of copper (II) ions can be dispensed with in step ii) since such an additive does not affect the properties of the zinc phosphate layer on the other metal surfaces positively influenced. In this case, conversely, it is preferred that the composition (B) in step ii) of the process according to the invention contains less than 0.01 g / L, more preferably less than 0.001 g / L of copper (II) ions. In particular, it is preferable to intentionally add no cupric ions to the composition (B), but small amounts of cupric ions may be used in the treatment of components which, in addition to the zinc surfaces, also have surfaces due to the mordanting of the composition (B) Of copper-alloyed aluminum, get into the composition (B).

The weight ratio of phosphate ions to zinc ions in the composition (B) in step ii) of the process according to the invention can vary within wide limits and is preferably in the range between 3.7 and 30, more preferably in the range between 8 and 20. For this calculation, the total Phosphorus content of the composition (B) as being present in the form of phosphate ions PO ₄ ^3- present. Thus, in the calculation of the quantitative ratio, the known fact is disregarded that at the pH values of the composition (B) for zinc phosphating, only a very small part of the phosphate is actually in the form of the triply negatively charged anions. Rather, at these pH levels, the phosphate is expected to exist primarily as a single dihydrogen phosphate anion with a slight negative charge, along with lesser amounts of undisociated phosphoric acid and doubly negatively charged hydrogen phosphate anions.

Another important parameter for the composition (B) is its content of free acid and total acid. Free acid and total acid represent an important control parameter for phosphating baths since they represent a measure of the pickling attack of the acid and the buffering capacity of the treatment solution and have a correspondingly great influence on the achievable coating weight. The term free acid is well known to those skilled in the phosphating art. The method of determination specific for this invention for determining the free acid or total acid content in a composition (B) is given in the examples section.

For the underlying invention, composition (B) in step ii) has a free acid content, each staggered according to increasing preference, of at least 0; 0.2; 0.4; 0.6; 0.8; 1 point, but not more than 3; 2.5; 2; 1.5 points.

The total acid content of the composition (B) in step ii) of the process according to the invention is staggered in each case corresponding to an increasing preference at least 20; 21; 22 points, however, not more than 30; 28; 26; 25; 24 points.

The pH of the aqueous treatment solution is preferably not less than 2.2 with increasing preference. 2.4; 2.6; 2.8 but not greater than 3.6; 3.5; 3.4; 3.3; 3.2.

If the component to be treated is a composite metal construction which, in addition to the surfaces of zinc, also has surfaces of iron, steel and / or aluminum, and if a zinc phosphate layer is to be formed on all metal surfaces in step ii), it is advantageous to use the Composition (B) to add water-soluble inorganic compounds which are a source of fluoride ions. The addition of free and / or complexed fluoride to a composition (B) is preferably carried out in amounts of up to 2.5 g / l of total fluoride, of which up to 300 mg / l of free fluoride. Due to the presence of the fluoride ions, the pickling rate on the metal surfaces is increased, but the aluminum ions produced during the treatment of aluminum surface components are directly complexed so that inhibition of zinc phosphating on the metal surfaces of the component can be prevented.

In the absence of fluoride, the aluminum content in the composition (B) should not exceed 3 mg / L. In the presence of fluoride, higher Al contents are tolerated due to complex formation unless the concentration of uncomplexed aluminum ions exceeds 3 mg / L. The Use of fluoride-containing compositions (B) in step ii) of the process according to the invention is therefore advantageous if the metal surfaces of the component to be phosphated consist at least partially of aluminum or contain aluminum. In these cases, it is favorable to use no complex-bound, but only free fluoride, preferably in concentrations in the range 0.1 to 0.3 g / L. The term free fluoride is well known to those skilled in the phosphating art. The determination method for determining the free fluoride content in a composition (B) specific to this invention is given in the examples section.

In order to suppress so-called specks on the zinc surfaces of the component to be phosphated in step ii) of the process according to the invention, the composition (B) for zinc phosphating may additionally comprise silicon in the form of water-soluble inorganic compounds, preferably in the form of fluorocomplexes of silicon, more preferably in the form of Hexafluorosilicic acid and / or salts thereof. By speckling, one skilled in the phosphating art understands the phenomenon of local deposition of amorphous white zinc phosphate in an otherwise crystalline phosphate layer on the treated zinc surfaces or on the treated galvanized or alloy galvanized steel surfaces. The speckling is caused by a locally increased pickling rate of the substrate. Such point defects in the phosphating can be the starting point for the corrosive delamination of subsequently applied organic coating systems, so that the occurrence of specks in practice is largely to be avoided. The optional addition of water-soluble inorganic compounds of silicon to a composition (B) in step ii) of the method according to the invention prevents the formation of specks in a subsequent coating of the metal surfaces, for this purpose preferably at least 0.025 g / L of these compounds calculated as SiF ₆ in the Composition (B) should be included and for reasons of economy of the method preferably not more than 1.5 g / L, more preferably not more than 1.0 g / L are included.

In the practice of anticorrosive treatment, it has become common practice to reduce phosphate slurries to selectively phosphatize components that are composite metal structures and, as such, at least partially have surfaces of aluminum besides the surfaces of zinc and possibly iron or steel. Selective phosphating is understood according to the invention to mean that zinc zinc phosphate layers having a coating weight of at least 0.5 g / m ² , preferably of at least 1 g / m ² , but preferably not more than, are formed on the surfaces of zinc and possibly iron or steel 3.5 g / m ^{2 are} deposited, while on the surfaces of aluminum no zinc phosphate layers are formed. The requirement that no zinc phosphate layer may form in this preferred embodiment of the method according to the invention on the aluminum surfaces of the component in step ii) is understood to mean that there is no closed and sealed crystalline layer, characterized in that the surface-related mass of The zinc phosphate deposited on the aluminum parts shall not exceed 0,5 g / m ² .

The coating of zinc phosphate is according to the present invention for all metal surfaces of the Component determined on test sheets or sections of the individual metallic materials of the component in composite construction. In this case, steel parts, galvanized or alloy-galvanized steel parts of the component immediately after step ii) of the inventive method for 15 minutes with an aqueous 5 wt .-% CrO ₃ solution at a temperature of 70 ° C in contact and in this way of the Zinc phosphate layer freed. By contrast, aluminum sheets are brought into contact with an aqueous 65% strength by weight HNO ₃ solution at a temperature of 25 ° C. for 15 minutes immediately after a step ii) and are freed from zinc phosphate portions accordingly.

The quantities of phosphorus per pickled surface, determined by means of atomic emission spectroscopy (ICP-OES) in the respective pickling solutions, multiplied by a factor of 6.23 give the respective coating weight of zinc phosphate according to the present invention.

For selective phosphating of a component comprising both surfaces of zinc and of aluminum, the component in step ii) according to the aforementioned preferred embodiment of the method according to the invention is to be brought into contact with a composition (B) for zinc phosphating which has a temperature in the range of 20-65 ° C and contains an amount of free fluoride (measured in g / L), which is not greater than the quotient of the number 8 and the solution temperature in ° C (8 / T). Above the stated free fluoride concentration, in step ii) crystalline zinc phosphate layers are also produced on the aluminum surfaces of the component.

If the composition (B) additionally contains silicon in the form of water-soluble inorganic compounds in step ii) to prevent the formation of specks on the zinc surfaces of the component, it is preferred for a selective zinc phosphating of the component consisting of zinc and aluminum that the composition (B) is at least 0.025 g / L but less than 1 g / L of silicon in the form of water-soluble inorganic compounds calculated as SiF ₆ and the product (Si / mM). (F / mM) from the concentration of silicon [Si in mM] in the form of water-soluble inorganic compounds and the concentration of free fluoride [F in mM] divided by the score of the free acid is not greater than 5, wherein the score of the free acid in the composition (B) in step ii) of the method according to the invention at least 0.4 points , preferably at least 0.6 points, more preferably at least 1.0 points, but has a value of 3.0 points, preferably 2.0 points n, does not exceed. In this case, the formation of zinc phosphate crystal nests on the aluminum surfaces of the component in step ii) is almost completely suppressed, so that after step ii) result in shiny metallic aluminum surfaces, which in a process according to the invention subsequent conversion treatment of the component, for example Acidic aqueous compositions containing water-soluble compounds of zirconium and / or titanium, passivate very well and thereby form a good paint adhesion base.

The upper limit for the content of water-soluble inorganic compounds of silicon in composition (B) in step ii) according to this preferred embodiment is on the one hand due to the economy of the process and on the other hand due to the fact that the process control by such high concentrations of water-soluble inorganic compounds containing Silicon is much more difficult, since the formation of zinc phosphate crystal nests on the Aluminum surfaces can be pushed back on an increase in the free acid content only insufficient. The crystal nests, in turn, typically represent local surface defects that may be the starting points for the corrosive delamination of a subsequently applied dip.

The phosphating in step ii) of the process according to the invention can be carried out by spraying, dipping or spray-dipping. The exposure time or the period of contact with the composition (B) is in the usual range between about 30 seconds and about 4 minutes.

The method according to the invention can also be carried out as a strip method on running galvanized steel strip. For this purpose, contact times with the respective compositions in steps i) and ii) in the range from about 2 to about 20 seconds are usual, wherein step ii) can also be carried out in so-called "no-rinse" application.

In the process according to the invention, step ii) can be followed in each case immediately by further rinsing steps with intervening rinsing steps, which are in particular selected from a post-passivation and / or a cathodic dip-coating.

Surprisingly, it has been found that the alkaline passivation layer, which is applied to the zinc surfaces of the component in step i) of the process according to the invention, despite the subsequent Zinkphosphatierung in step ii) by contacting with the composition (B) is retained as such ,

The present invention therefore furthermore relates to a component which has at least partial surfaces of zinc, in which the surfaces of zinc comprise a layer system comprising a first inner passive layer on the zinc surface containing iron and a second outer, lying on the inner layer of crystalline zinc phosphate layer wherein the support of the inner layer 20 to 150 mg / m ² based on the element iron and the support of the outer zinc phosphate layer 0.5 to 3.5 g / m ² , obtainable in a previously described inventive method.

The first inner layer of the component according to the invention, which is produced in step i) of the method according to the invention, contains the element iron in oxidized form. Also preferred is a component which has a first inner layer on its zinc surface, which in addition to iron in oxidized form additionally contains phosphate ions. The first inner layer on the zinc surfaces of the component then contains phosphate ions when the component has previously been brought into contact with a composition (A) in a preferred process according to the invention in step i) which additionally contains at least 100 mg / L of phosphate ions contains.

Additionally preferred is a component according to the invention in which the second outer layer on the zinc surfaces of the component, which is a zinc phosphate layer, in each case contains less than 10 mg / m ² of nickel and cobalt.

The detection of the first inner layer on the zinc surfaces of the component according to the invention succeeds after removal of the second outer layer, which is a zinc phosphate layer, with chromic acid, wherein the coating layer of iron in the first inner layer on the zinc surfaces of the component according to the invention is determined by means of a UV spectroscopic analysis method described in the Examples section (see Table 1), while the chemical state of the element iron in the layer is determined by X-ray photoelectron electron spectroscopy ( XPS) is to be made. The detection of phosphate ions in the first inner layer on the zinc surfaces of the component preferred according to the invention can also be performed by X-ray photoelectron spectroscopy (XPS).

The proportion of nickel or cobalt in the second outer layer of the preferred component according to the invention is quantified by ICP-OES in the pickling solution after detachment of the zinc phosphate layer from the zinc surfaces of the component and related to the pickled surface, so that a formal layer support based on these elements can be specified.

The component according to the invention may have on its zinc surfaces further outer layers, which are preferably selected from organic paints.

Particularly preferably, the component according to the invention represents an automobile body.

• Einzelne Verfahrensschritte in einer Tauchanlage zur korrosionsschützenden Behandlung von verzinkten Stahlblechen (HDG: Gardobond^® EA; Fa. Chemetall):
  • A. Alkalische Reinigung (pH 11):
    • 3 Gew.-% Ridoline^® 1574A (Fa. Henkel); 0,4 Gew.-% Ridosol^® 1270 (Fa. Henkel)
    • enthaltend H₃PO₄, K₄P₂O₇, Natriumglukonat, Natriumsalz der Hydroxyethan-1,1-Diphosphonsäure, KOH
    • Behandlungsdauer bei 60 °C: 180 Sekunden
  • B. Spülen mit vollentsalztem Wasser (κ<1 µScm^-1)
  • C1. Alkalische Passivierung gemäß Zusammensetzung (A):
    • 2,80 Gew.-% KOH
    • 0,19 Gew.-% H₃PO₄
    • 0,22 Gew.-% K₄P₂O₇
    • 0,06 Gew.-% Natriumglukonat
    • 0,10 Gew.-% Natriumsalz der Hydroxyethan-1,1-Diphosphonsäure
    • 0,23 Gew.-% Fe(NO₃)₃·9H₂O
    • Rest vollentsalztes Wasser (κ<1 µScm^-1)
    • Freie Alkalität: 3
    • pH-Wert 11
    • Behandlungsdauer bei 60 °C: 120 Sekunden
  • C2. Alkalische Passivierung gemäß Zusammensetzung (A):
    • 1,09 Gew.-% KOH
    • 0,19 Gew.-% H₃PO₄
    • 0,22 Gew.-% K₄P₂O₇
    • 0,06 Gew.-% Natriumglukonat
    • 0,10 Gew.-% Natriumsalz der Hydroxyethan-1,1-Diphosphonsäure
    • 0,23 Gew.-% Fe(NO₃)₃·9H₂O
    • 1,30 Gew.-% NaHCO₃
    • Rest vollentsalztes Wasser (κ<1 µScm^-1)
    • Freie Alkalität: 10
    • pH-Wert 13
    • Behandlungsdauer bei 60 °C: 120 Sekunden
  • D. Aktivierung:
    • 0,1 Gew.-% Fixodine^® 50CF (Fa. Henkel)
    • Rest vollentsalztes Wasser (κ<1 µScm^-1)
    • Behandlungsdauer bei 20 °C: 60 Sekunden
  • E1. Nickelfreie Phosphatierung gemäß Zusammensetzung (B):
    • 0,13 Gew.-% Zink
    • 0,09 Gew.-% Mangan
    • 0,12 Gew.-% Nitrat
    • 1,63 Gew.-% Phosphat
    • 0,05 Gew.-% N-Methylmorpholin-N-oxid
    • 0,02 Gew.-% Ammoniumbifluorid
    • 0,03 Gew.-% H₂SiF₆
    • Rest vollentsalztes Wasser (κ<1 µScm^-1)
    • Freies Fluorid: 40 mg/L
    • Freie Säure: 1,3 Punkte (pH 3,6)
    • Gesamtsäure : 24 Punkte (pH 8,5)
    • Wasserstoffperoxid : 30 mg/L
    • Behandlungsdauer bei 51°C: 180 Sekunden
  • E2. Nickelfreie, kupferhaltige Phosphatierung gemäß Zusammensetzung (B):
    • 0,13 Gew.-% Zink
    • 0,09 Gew.-% Mangan
    • 0,001 Gew.-% Kupfer
    • 0,12 Gew.-% Nitrat
    • 1,63 Gew.-% Phosphat
    • 0,05 Gew.-% N-Methylmorpholin-N-oxid
    • 0,02 Gew.-% Ammoniumbifluorid
    • 0,03 Gew.-% H₂SiF₆
    • Rest vollentsalztes Wasser (κ<1 µScm^-1)
    • Freies Fluorid: 40 mg/L
    • Freie Säure: 1,3 Punkte (pH 3,6)
    • Gesamtsäure : 24 Punkte (pH 8,5)
    • Wasserstoffperoxid : 30 mg/L
    • Behandlungsdauer bei 51 °C : 180 Sekunden
  • E3. Nickelhaltige Phosphatierung (Trikationen-Phosphatierung)
    • 0,13 Gew.-% Zink
    • 0,09 Gew.-% Mangan
    • 0,09 Gew.-% Nickel
    • 0,12 Gew.-% Nitrat
    • 1,63 Gew.-% Phosphat
    • 0,05 Gew.-% N-Methylmorpholin-N-oxid
    • 0,02 Gew.-% Ammoniumbifluorid
    • 0,03 Gew.-% H₂SiF₆
    • Rest vollentsalztes Wasser (κ<1 µScm^-1)
    • Freies Fluorid: 40 mg/L
    • Freie Säure: 1,3 Punkte (pH 3,6)
    • Gesamtsäure : 25 Punkte (pH 8,5)
    • Wasserstoffperoxid : 30 mg/L
    • Behandlungsdauer bei 51 °C : 180 Sekunden
  • E4. Nickelhaltige Phosphatierung (Trikationen-Phosphatierung) wie E.3, jedoch 0,01 Gew.-% Nickel
  • E5. Nickelhaltige Phosphatierung (Trikationen-Phosphatierung) wie E.3, jedoch 0,005 Gew.-% Nickel
  • E6. Saure Passivierung:
    • 0,34 g/L H₂ZrF₆
    • 0,12 g/LAmmoniumbifluorid
    • 39 mg/L Cu(NO₃)₂·3H₂O
    • Rest vollentsalztes Wasser (κ<1 µScm^-1)
    • pH-Wert 4
    • Behandlungsdauer bei 30 °C: 120 Sekunden
  • F. Lackaufbau: Cathoguard^® 500 (Fa. BASF): Schichtdicke 20 - 22 µm

EXAMPLES

• Individual process steps in an immersion system for the anticorrosion treatment of galvanized sheet steel (HDG: Gardobond ^® EA; Chemetall.):
  • A. Alkaline Purification (pH 11):
    • 3 wt .-% Ridoline ^® 1574A (Henkel.); 0.4 wt .-% Ridosol ^® 1270 (Messrs. Henkel)
    • containing H ₃ PO ₄ , K ₄ P ₂ O ₇ , sodium gluconate, sodium salt of hydroxyethane-1,1-diphosphonic acid, KOH
    • Treatment time at 60 ° C: 180 seconds
  • B. Rinsing with demineralized water (κ <1 μScm ^-1 )
  • C1. Alkaline passivation according to composition (A):
    • 2.80% by weight KOH
    • 0.19 wt .-% H ₃ PO ₄
    • 0.22% by weight K ₄ P ₂ O ₇
    • 0.06 wt.% Sodium gluconate
    • 0.10% by weight of sodium salt of hydroxyethane-1,1-diphosphonic acid
    • 0.23 wt.% Fe (NO ₃ ) ₃ .9H ₂ O
    • Remaining deionized water (κ <1 μScm ^-1 )
    • Free alkalinity: 3
    • pH 11
    • Treatment time at 60 ° C: 120 seconds
  • C2. Alkaline passivation according to composition (A):
    • 1.09 wt.% KOH
    • 0.19 wt .-% H ₃ PO ₄
    • 0.22% by weight K ₄ P ₂ O ₇
    • 0.06 wt.% Sodium gluconate
    • 0.10% by weight of sodium salt of hydroxyethane-1,1-diphosphonic acid
    • 0.23 wt.% Fe (NO ₃ ) ₃ .9H ₂ O
    • 1.30 wt .-% NaHCO ₃
    • Remaining deionized water (κ <1 μScm ^-1 )
    • Free alkalinity: 10
    • pH 13
    • Treatment time at 60 ° C: 120 seconds
  • D. Activation:
    • 0.1 wt .-% FIXODINE ^® 50CF (Messrs. Henkel)
    • Remaining deionized water (κ <1 μScm ^-1 )
    • Duration of treatment at 20 ° C: 60 seconds
  • E1. Nickel-free phosphating according to composition (B):
    • 0.13% by weight of zinc
    • 0.09 wt .-% manganese
    • 0.12 wt.% Nitrate
    • 1.63% by weight of phosphate
    • 0.05% by weight of N-methylmorpholine N-oxide
    • 0.02% by weight of ammonium bifluoride
    • 0.03 wt.% H ₂ SiF ₆
    • Remaining deionized water (κ <1 μScm ^-1 )
    • Free fluoride: 40 mg / L
    • Free acid: 1.3 points (pH 3.6)
    • Total acid: 24 points (pH 8.5)
    • Hydrogen peroxide: 30 mg / L
    • Treatment time at 51 ° C: 180 seconds
  • E2. Nickel-free, copper-containing phosphating according to composition (B):
    • 0.13% by weight of zinc
    • 0.09 wt .-% manganese
    • 0.001% by weight of copper
    • 0.12 wt.% Nitrate
    • 1.63% by weight of phosphate
    • 0.05% by weight of N-methylmorpholine N-oxide
    • 0.02% by weight of ammonium bifluoride
    • 0.03 wt.% H ₂ SiF ₆
    • Remaining deionized water (κ <1 μScm ^-1 )
    • Free fluoride: 40 mg / L
    • Free acid: 1.3 points (pH 3.6)
    • Total acid: 24 points (pH 8.5)
    • Hydrogen peroxide: 30 mg / L
    • Treatment time at 51 ° C: 180 seconds
  • E3. Nickel-containing phosphating (trication-phosphating)
    • 0.13% by weight of zinc
    • 0.09 wt .-% manganese
    • 0.09 wt .-% nickel
    • 0.12 wt.% Nitrate
    • 1.63% by weight of phosphate
    • 0.05% by weight of N-methylmorpholine N-oxide
    • 0.02% by weight of ammonium bifluoride
    • 0.03 wt.% H ₂ SiF ₆
    • Remaining deionized water (κ <1 μScm ^-1 )
    • Free fluoride: 40 mg / L
    • Free acid: 1.3 points (pH 3.6)
    • Total acid: 25 points (pH 8.5)
    • Hydrogen peroxide: 30 mg / L
    • Treatment time at 51 ° C: 180 seconds
  • E4. Nickel-containing phosphating (trication-phosphating) such as E.3, but 0.01% by weight nickel
  • E5. Nickel-containing phosphating (trication-phosphating) like E.3, but 0.005 wt% nickel
  • E6. Acid passivation:
    • 0.34 g / LH ₂ ZrF ₆
    • 0.12 g / LAmmoniumbifluorid
    • 39 mg / L Cu (NO ₃ ) ₂ .3H ₂ O
    • Remaining deionized water (κ <1 μScm ^-1 )
    • pH 4
    • Treatment time at 30 ° C: 120 seconds
  • F. paint structure: Cathoguard ^® 500 (from BASF.): Layer thickness of 20-22 microns

The free acid score in the example baths E1-E5 according to a composition (B) is determined by diluting 10 ml bath sample to 50 ml and titrating with 0.1 N sodium hydroxide solution to pH 3.6. The consumption of ml of sodium hydroxide gives the score. Accordingly, the content of total acid is determined by titrating to a pH of 8.5.

The content of free fluoride in the exemplary baths E1-E3 according to a composition (B) is detected by means of a potentiometric measuring chain (Fa. WTW, inoLab ^®, pH / IonLevel 3). The measuring chain contains a fluoride-sensitive glass electrode (WTW, F501) and a reference electrode (WTW, R503). For two-point calibration, both electrodes are together successively in calibration solutions with a content of 100 mg / L and 1000 mg / L of free fluoride, prepared from the Titrisol ^® fluoride standard of Fa. Merck without addition of buffer, dipped. The resulting measured values are corrected with the respective fluoride content "100" or "1000" and read into the measuring instrument. The slope of the glass electrode is then displayed in mV per decade of the fluoride ion content in mg / L on the meter, typically between -55 and -60 mV. The fluoride content in mg / L is then determined directly by immersing the two electrodes in the exemplary baths E1-E5 at a temperature of 25 ° C.

Tab. 1 shows the influence of the alkaline passivation followed by a nickel-free or low-nickel zinc phosphating (Examples 1-4 and 5) on the adhesion of the cathodic dip to the zinc substrate after water storage and subsequent cross hatch test. In comparison, the nickel-free zinc phosphating, which takes place from a composition (B) with or without the addition of copper ions, but without alkaline passivation with a composition (A), on the galvanized substrate an insufficient paint adhesion (Examples 6, 7). The low-nickel phosphating (Examples 9, 10), which is carried out without alkaline passivation, already gives worse results in the Gilterschnitt test compared to nickel-containing trication-phosphating (Example 8), while together with the alkaline passivation (Examples 5) again an excellent Paint adhesion can be achieved.

It can also be seen from the table that the nickel-containing trication-phosphating (Example 8) - as known in the art - provides excellent adhesion of the coating composition to the substrate. In the process according to the invention, adhesion that is completely equivalent to nickel-containing phosphating is achieved if the layer coating of iron after the alkaline passivation is moderate, ie, for example about 100 mg / m ² based on the element iron (Examples 1, 3). Higher layer deposits of iron in the range of about 260 mg / m ² , which are deposited in a noninventive process according to Examples 2 and 4, in conjunction with the nickel-free Zinkphosphatierung compared to the trication-phosphating (Example 8) a pained paint adhesion ,
The process according to the invention (see Examples 1, 3 and 5) likewise produces a marked improvement in paint adhesion on the zinc surfaces in comparison with alternative treatment processes which, instead of phosphating, provide a conversion treatment based on zirconium flucrocomplexes (Examples 11, 12). Table 1 Different courses of action for the corrosion protection treatment of galvanized steel strip and the results after cross cut test example process sequence Crosshatch * (0-5) Schich run position ** ZnPO ₄ in g / m ² Layered coating *** Iron in mg / m ² 1 A-C1-BD-E1-BEF 0 2.5 102 2 A-C2-BD-E1-BEF 1-2 2.6 252 3 A-C1-BD-E2-BEF 0 2.5 113 4 A BD-C2-E2-BEF 1-2 2.4 245 5 A-C1-BD-E5-BEF 0 2.5 110 6 ABD-E1 BEF 5 1.7 - 7 ABD-E2 BEF 5 1.7 - 8th ABD-E3 BEF 0 3.5 - 9 ABD-E4 BEF 1 2.2 - 10 ABD-E5 BEF 2 2.1 - 11 A-C1-B-E6-BEF 3 - 114 12 A-C2-B-E6-BEF 4 - 260 * Removal of the plates in demineralized water (κ <1μScm ^-1 ) at 80 ° C for 30 minutes; Cooling of the sheets for 30 min at 20 ° C: crosshatch according to DIN EN ISO 2009 and subsequent 180 ° bending of the sheets in crosshatch; Evaluation of paint adhesion according to DIN EN ISO 2009 (0: no paint adhesion, 6: complete paint adhesion)
** determined by stripping the zinc phosphate layer with aqueous 5 wt .-% CrO ₃ , which was brought immediately after step "E" at 25 ° C for 5 min with a defined surface of galvanized sheet in contact, and determining the phosphorus content in the same pickling solution with ICP-OES. The coating weight of zinc phosphate results from the multiplication of the area-related amount of phosphorus with the factor 6.23.
*** quantitative determination of the amount of iron (III) ions by UV Fotomeler (Fa. WTW, Photo Flex ^®) in 300 ul of sample volume of a 5 wt .-% nitric acid solution, the one immediately after the step "C" using Measuring cell ring (company Helmut Fischer) was pipetted on a defined surface of the galvanized sheet of 1.33 cm ² and after 30 seconds exposure time at a temperature of 26 ° C picked up by the same pipette and in the UV measuring cuvette, in the 5 ml submitted to a 1.0% self-sodium thiocyanate solution was transferred to determine the absorption at a wavelength of 517 nm and temperature of 25 ° C. The calibration was carried out in a two-point method by determining the absorption values of identical volumes (300 μl) of two standard solutions of ferric nitrate in 5% strength by weight nitric acid, which was used to determine the absorption values at 25 ° C. in the measuring cuvette containing 5 ml of a 1.0% sodium thiocyanate solution.

Claims (19)

1. A method for corrosion-protective treatment of metal surfaces of a component that comprises at least in part surfaces made of zinc or zinc alloys, wherein the component is firstly, in step i), brought into contact with an alkaline aqueous composition (A) that contains

   a) at least 50 mg/L iron(III) ions, and

   b) at least 100 mg/L complexing agents selected from organic compounds c1) that comprise at least one functional group selected from -COOX, -OPO₃X, and/or -PO₃X, where X represents either a hydrogen atom or an alkali and or alkaline-earth atom, and/or condensed phosphates c2) calculated as PO₄, the composition having a free alkalinity of at least 1 point but less than 6 points, and a pH in the range from 10.5 to 14,

   and then in step ii), with or without an interposed rinsing step and with or without previous activation, is brought into contact with an acid aqueous composition (B) for zinc phosphating that has a pH in the range from 2.5 to 3.6 and contains

   a) 0.2 to 3.0 g/L zinc(II) ions,

   b) 5.0 to 30 g/L phosphate ions, calculated as P₂O₅, and

   c) less than 0.1 g/L each of ionic compounds of the metals nickel and cobalt, based in each case on the metallic element.
2. The method according to Claim 1, characterized in that composition (A) has a pH of no more than 13, by preference no more than 11.5.
3. The method according to one or both of the preceding claims, characterized in that composition (A) additionally contains at least 100 mg/L, by preference at least 200 mg/L, particularly preferably at least 500 mg/L, but no more than 10 g/L, phosphate ions.
4. The method according to Claim 3, characterized in that the mass-based ratio of iron(III) ions to phosphate ions in composition (A) is in a range from 1 : 20 to 1 : 2.
5. The method according to one or more of the preceding claims, characterized in that the molar ratio of all components c) to iron(III) ions in composition (A) is greater than 1 : 1 and by preference is equal to at least 2 : 1, particularly preferably at least 5.
6. The method according to one or more of the preceding claims, characterized in that condensed phosphates c2) that are by preference selected from pyrophosphates, tripolyphosphates, and/or polyphosphates are contained as components c) in composition (A).
7. The method according to Claim 6, characterized in that in addition to component c2), organic compounds c1) that in the protonated state preferably have an acid number of at least 250 are contained in composition (A).
8. The method according to Claims 5, 6, and 7, characterized in that the organic compounds c1) in composition (A) are selected from α-, β-, and/or γ-hydroxycarboxylic acids, hydroxyethane-1,1-diphosphonic acid, [(2-hydroxyethyl)(phosphonomethyl)amino]methylphosphonic acid, diethylenetriaminepentakis(methylenephosphonic acid), and/or amino-tris(methylenephosphonic acid), and salts thereof, the molar ratio of components c1) to iron(III) ions being less than 1 : 1, by preference less than 3 : 4, but by preference at least 1 : 5.
9. A composition (A) according to one or more of the preceding claims, characterized in that composition (A) contains less than a total of 10 mg/L ionic compounds of the metals nickel, cobalt, manganese, molybdenum, chromium, and/or cerium, in particular respectively less than 1 mg/L ionic compounds of the metals nickel and cobalt, based in each case on the metallic element.
10. The method according to one or more of the preceding claims, characterized in that composition (B) for zinc phosphating additionally contains one or more of the cation quantities recited below: 0.001 to 4 g/L manganese(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).
11. The method according to one or more of the preceding claims, characterized in that composition (B) for zinc phosphating contains respectively less than 0.01 g/L, by preference respectively less than 0.001 g/L, ionic compounds of the metals nickel and cobalt, based in each case on the metallic element.
12. The method according to one or more of the preceding claims, characterized in that composition (B) for zinc phosphating contains less than 0.01 g/L, preferably less than 0.001 g/L, copper(II) ions.
13. The method according to one or more of the preceding claims, characterized in that composition (B) for zinc phosphating contains water-soluble inorganic compounds that represent a source for fluoride ions.
14. The method according to one or more of the preceding claims, wh characterized in that erein composition (B) for zinc phosphating contains silicon in the form of water-soluble inorganic compounds, by preference in the form of fluorine complexes of silicon, particularly preferably in the form of hexafluorosilicic acid and/or salts thereof.
15. The method according to one or both of the preceding Claims 13 and 14, characterized in that the component also comprises surfaces made of aluminum in addition to the surfaces made of zinc, composition (B) having a temperature in the range from 20 to 65°C and containing a quantity of free fluoride (measured in g/L) that is no greater than the quotient of the number 8 and the solution temperature in °C (8/T).
16. The method according to Claim 14 or according to both of Claims 14 and 15, characterized in that composition (B) contains at least 0.025 g/L, but less than 1 g/L, silicon in the form of water-soluble inorganic compounds calculated as SiF₆, and the product (Si/mM) • (F/mM) of the concentration of silicon [Si in mM] in the form of water-soluble inorganic compounds and the concentration of free fluoride [F in mM] divided by the free acid point score is no greater than 5, the free acid point score in composition (B) being at least 0.4 points but not exceeding a value of 3.0 points.
17. The method according to one or both of the preceding Claims 15 and 16, characterized in that the aluminum surfaces of the component comprise, after method step ii), a zinc phosphate layer having a layer weight of less than 0.5 g/m².
18. The method according to one or more of the preceding claims, characterized in that the zinc surfaces of the metallic component comprise, after method step ii), a crystalline zinc phosphate layer having a layer weight in the range from 0.5 to 3.5 g/m².
19. A component that comprises at least in part surfaces made of zinc, in which component the surfaces made of zinc comprise a layer system encompassing a first inner passive layer containing iron and resting on the zinc surface, and a second outer crystalline zinc phosphate layer resting on the inner layer, the coverage rate of the inner layer being 20 to 150 mg/m² based on the element iron, and the coverage rate of the outer zinc phosphate layer being 0.5 to 3.5 g/m², obtainable in a method according to one or more of the preceding Claims 1 to 18.