EP2631333A1 - Pre-treatment of zinc surfaces before passivation - Google Patents

Abstract

Alkaline aqueous composition having a pH value of at least 8.5, comprises (a) at least 0.01 g/l of iron ions, (b) one or more water soluble organic carboxylic acids comprising at least one amino group at alpha -, beta - or gamma -position relative to the acid group and/or their water-soluble salts, and (c) one or more oxoacids of phosphorus or nitrogen and/or their water soluble salts, where at least one phosphorus atom or nitrogen atom is present in an average oxidation state. An independent claim is included for pretreating galvanized steel surfaces, comprising (i) optionally cleaning and degreasing the steel surfaces using an alkaline cleaning agent, (ii) contacting the steel surfaces with the alkaline composition, and (iii) subjecting the steel surfaces to passivating wet chemical conversion coatings.

Description

The present invention relates to a wet-chemical pretreatment of zinc surfaces prior to the application of a corrosion-protective coating. The wet-chemical pretreatment causes the deposition of a thin inorganic coating consisting essentially of oxidic and / or metallic iron. A layer of iron applied according to the invention - referred to below as icing - requires an improvement in the achievable corrosion protection of wet-chemical conversion coatings known from the prior art on zinc surfaces. Furthermore, the icing causes both a reduction in the contact corrosion of assembled metallic components which have zinc and iron surfaces and a reduction of the corrosive paint infiltration at cutting edges of galvanized steel strip with lacquer layer structure. More particularly, the invention relates to an alkaline composition for icing containing a source of iron ions, a reducing agent based on oxo acids of the elements nitrogen and phosphorus and water-soluble organic carboxylic acids having an amino group in α-, β-, or γ-position to the acid group and / or their water-soluble salts.

In the steel industry, a large number of surface-refined steel materials are produced, with surface-refined versions being in great demand to ensure the most sustainable possible protection against corrosion. For the production of products, such as automobile bodies, in particular thin sheet products made of different metallic materials and with different surface finish are processed. For the production of the products, the surface-treated steel strip is cut to size, formed and joined by welding or gluing process with other metallic components. In these products, therefore, a variety of combinations of metallic base and surface material are realized. This type of production is highly typical of the body shop in the automotive industry and is often referred to as multi-metal construction. In the body shop mainly galvanized steel strip is processed and joined together, for example, with non-galvanized steel strip and / or strip aluminum. Thus, car bodies consist of a large number of sheet-metal parts which are joined together by spot welding.

The metallic zinc coatings, which are applied to the steel strip either electrolytically or by hot dip coating, impart a cathodic protective effect which permits active dissolution of the nobler core material by mechanically causing injuries to the material Zinc coating effectively prevented. However, there is an economic interest in minimizing the overall corrosion rate in order to sustain the cathodic protection of the less noble metal coating as sustainably as possible. For this purpose, at the strip steel manufacturer or before painting in the paint shop of the production line of bodies at the car manufacturer Passivierungsschichten that are purely inorganic or mixed organic-inorganic nature, and / or organic primer applied as a barrier layer to further minimize the corrosion, which also Lackhaftgrund serve for a subsequent topcoat of the product.

From today's usual combination of variety of metallic strip materials in a product and the primary use of surface-coated strip steel results in the described manufacturing processes as special corrosion phenomena Schnittkanten- and bimetallic corrosion. At cutting edges and at the zinc coating caused by machining or other influences, the galvanic coupling between the core material and the metallic coating causes a local dissolution of the coating material, which in turn may result in corrosive infiltration of the organic barrier layers at these locations. The phenomenon of Lackenthaftung or "blistering" is therefore observed especially at the cut edges of the sheets. The same applies in principle to the locations of a component on which different metallic materials are directly connected by joining techniques and bimetal corrosion is the result. The local activation of such a "defect" (cut edge, damage in the metallic coating, spot welding point) and thus the corrosive paint release resulting from these "defects" is all the more pronounced the greater the electrical potential difference between the metals in direct contact. Correspondingly, good results with regard to paint adhesion at cut edges are offered by steel strips with zinc coatings alloyed with nobler metals, eg iron-alloyed zinc coatings (galvannealed steel). The steel strip producers are increasingly turning to the integration of surface finishing with metallic coatings, the application of inorganic and / or organic protective layers, in particular the application of organic primers in the belt system. In this regard, in the processing industry, there is great economic interest in obtaining such surface-finished strip steels, whose predisposition to Schnittkanten- and bimetallic corrosion is only slightly pronounced, so that even after the production of the products, the punching, cutting, forming and / or joining the strip steel comprises, and a subsequent paint layer structure further good corrosion protection and a good paint adhesion can be ensured. Similarly, in the processing industry, there is a need for the surfaces of products composed of different metallic strip materials To pretreat that the preferred delamination of subsequently applied paint layers is leveled at cut edges and bimetallic contacts.

The prior art describes various pretreatments that address the problem of edge protection. An essential strategy is to improve the paint adhesion of the organic barrier layer on the surface-treated steel strip. For example, the German Offenlegungsschrift teaches DE 197 33 972 A1 a process for the alkaline passivating pretreatment of galvanized and alloy-galvanized steel surfaces in strip lines. Here, the surface-treated steel strip is brought into contact with an alkaline treatment agent containing magnesium ions, iron (III) ions and a complexing agent. At the given pH of above 9.5, the zinc surface is passivated thereby forming the corrosion protection layer. Such a passivated surface offers according to the teaching of DE19733972 already a paint adhesion, which is comparable to nickel and cobalt-containing processes. Optionally, this pretreatment can be followed by further treatment steps such as chromium-free post-passivation to improve the corrosion protection before the paint system is applied.

Likewise pursues the DE 10 2010 001 686 A1 the passivation of galvanized steel surfaces using alkaline compositions containing ferric ions, phosphate ions and one or more complexing agents to prepare the zinc surfaces for subsequent acid passivation and resist buildup. The alkaline passivation serves primarily to improve the corrosion protection of chromium-free conversion coatings. The aim is to achieve an alkaline cleaning step that leads to alkaline passivation and subsequent acidic passivation to provide a coating base which is comparable to zinc phosphating and protects against corrosion.

In contrast, the pursued DE 10 2007 021 364 A1 In addition, the goal by means of electroless metal cations without electroless deposition to realize a thin metallic coating layer on galvanized steel surfaces, which together with a subsequent passivation to significantly reduce corrosion at cut edges and bimetallic contacts of cut and assembled surface-coated strip steel should make. There, in particular, the icing and tinning of galvanized and alloy-galvanized steel strip is proposed to improve the edge protection. For the icing, preferably acidic compositions containing iron ions, a complexing agent with oxygen and / or nitrogen ligands and phosphinic acid are used as the reducing agent. The object of the present invention is to further develop the icing of metallic components having zinc surfaces such that, in conjunction with subsequent wet-chemical conversion coatings, improved corrosion protection and paint adhesion on the zinc surfaces results, in particular the edge protection is to be improved at cutting edges of galvanized steel surfaces ,

Surprisingly, it has been possible to demonstrate that, when organic carboxylic acids containing an amino group in the α, β or γ position to the acid group and / or their water-soluble salts in alkaline compositions for freezing on zinc surfaces are used, extremely thin film coatings consist essentially of oxidic and / or metallic iron ("icing") which, in conjunction with a subsequent wet chemical conversion treatment, provide improved corrosion protection, in particular at cut edges of galvanized steel surfaces, and an excellent lacquer adhesion.

1. a) zumindest 0,01 g/l an Eisen-Ionen,
2. b) ein oder mehrere wasserlösliche organische Carbonsäuren, die zumindest eine Amino-Gruppe in α-, β-, oder γ-Stellung zur Säuregruppe aufweisen, sowie deren wasserlösliche Salze,
3. c) ein oder mehrere Oxosäuren von Phosphor oder Stickstoff sowie deren wasserlösliche Salze, wobei mindestens ein Phosphoratom oder Stickstoffatom in einer mittleren Oxidationsstufe vorliegt.

The present invention therefore relates, in a first aspect, to an alkaline composition for the pretreatment of metallic components having zinc surfaces, having a pH of at least 8.5

1. a) at least 0.01 g / l of iron ions,
2. b) one or more water-soluble organic carboxylic acids which have at least one amino group in α, β or γ position to the acid group, and their water-soluble salts,
3. c) one or more oxo acids of phosphorus or nitrogen and their water-soluble salts, wherein at least one phosphorus atom or nitrogen atom is present in a middle oxidation state.

Water solubility in the context of the present invention means that the solubility of the compound at a temperature of 25 ° C and a pressure of 1 bar in deionized water with a conductivity of less than 1μScm ^{-1 is} greater than 1 g / l.

By oxidation level is meant, according to the invention, the hypothetical charge of an atom resulting from the number of electrons of the atom compared to its atomic number that the corresponding atom hypothesizes when electrons are attributed due to the electronegativity of the elements forming the molecule or salt with the higher electronegativity element combining all the electrons it shares with the elements of lower electronegativity, while the electrons be shared by the same elements, each half be awarded to the one and the other half to the other atom.

According to the invention, surfaces of galvanized steel and alloy-galvanized steel are considered as zinc surfaces in addition to surfaces of metallic zinc if the zinc coating is at least 5 g / m ² based on the element zinc and the proportion of zinc in the zinc layer on the steel is at least 40 at% ,

The source of iron ions dissolved in water are all compounds which release iron ions in water. Preferably, one or more water-soluble salts of di- or trivalent iron in a composition according to the invention serve as a source of iron ions dissolved in water, wherein the use of water-soluble salts of divalent iron ions is preferred, such as, for example, iron (II) nitrate or iron (II) sulfate. Particularly suitable water-soluble compounds are the corresponding salts of the α-hydroxycarboxylic acids having not more than 8 carbon atoms, which in turn are preferably selected from salts of polyhydroxymonocarboxylic acid, polyhydroxydicarboxylic acid each having at least 4 carbon atoms, tartronic acid, glycolic acid, lactic acid and / or α-hydroxybutyric acid.

For a sufficiently fast kinetics of icing from aqueous solution, preference is given to compositions according to the invention in which at least 0.1 g / l, preferably at least 1 g / l, particularly preferably at least 2 g / l, of iron ions dissolved in the aqueous phase are included. In principle, additional amounts of dissolved iron ions initially cause a further increase in the deposition kinetics, so that, depending on the duration of the application process-related application, a different minimum amount of iron ions in the composition of the invention is opportune. If the icing process procedural is to be carried out within a few seconds, as is the case for example in the pretreatment of galvanized steel strip in a coil coating plant, the composition preferably contains at least 3 g / l of iron ions. The upper limit for the amount of iron ions is primarily determined by the stability of the composition and is preferably 50 g / l for a composition according to the invention. The amounts with respect to the iron ions in a composition according to the invention of course relate to the amount of iron ions available for the icing and thus to the amount of iron ions dissolved in the aqueous phase, for example in hydrated and / or complexed form. Iron ions in non-freezing form, ie for example, bound in undissolved iron salts do not contribute to the proportion of iron ions in the composition of the invention.

In a preferred composition according to the invention, the molar ratio of iron ions to water-soluble organic carboxylic acids according to component b) and their water-soluble salts is not greater than 2: 1. Above this molar ratio, the accelerating effect of the organic carboxylic acids according to component b) decreases Icing already noticeable. Particular preference is therefore given to compositions according to the invention in which the abovementioned molar ratio is not greater than 1: 1. Conversely, a reduction of the aforementioned molar ratio below 1: 12 with a constant amount of iron ions, ie a further increase in the proportion of component b), causes no appreciable additional acceleration in the icing of zinc surfaces. Therefore, such compositions according to the invention are preferred in which the molar ratio of iron ions to water-soluble organic carboxylic acids according to component b) and their water-soluble salts is at least 1: 12, preferably at least 1: 8.

Furthermore, it has been found that certain organic carboxylic acids and / or their salts according to component b) in compositions according to the invention are particularly suitable for producing uniform and adequate iron coating layers on zinc surfaces in a time interval typical for wet-chemical pretreatment. Thus, those compositions are preferred according to the invention in which the organic carboxylic acids and / or their salts according to component b) are selected from water-soluble α-amino acids and their water-soluble salts, in particular from α-amino acids and their water-soluble salts, in addition to amino and carboxyl Groups have exclusively hydroxyl groups and / or carboxamide groups, wherein the α-amino acids preferably have not more than 7 carbon atoms. In a preferred embodiment, a composition according to the invention contains as component b) lysine, serine, threonine, alanine, glycine, aspartic acid, glutamic acid, glutamine and / or their water-soluble salts, particularly preferably lysine, glycine, glutamic acid, glutamine and / or their water-soluble salts, especially preferred is glycine and / or its water-soluble salts.

In this connection, an alkaline composition for the pretreatment of metallic surfaces having zinc surfaces is preferred according to the invention, for which the proportion of glycine and / or its water-soluble salts of water-soluble organic carboxylic acids according to component b) and / or their water-soluble salts at least 50 wt .-%, more preferably at least 80 wt .-%, particularly preferably at least 90 wt .-% is.

The oxo acids of phosphorus or nitrogen according to component c) of the composition according to the invention have reducing properties and thus bring about rapid and homogeneous icing of the zinc surfaces brought into contact with the composition according to the invention. Preferably, such compositions according to the invention are used for the icing, which contain at least one oxo acid of phosphorus with at least one phosphorus atom in a middle oxidation state and their water-soluble salts as component c).

In a preferred composition according to the invention, the molar ratio of iron ions to oxo acids of phosphorus or nitrogen according to component c) and their water-soluble salts is for economic reasons at least 1:10, preferably at least 1: 6. On the other hand, the relative proportion of these compounds should be Component c) be sufficiently large for a sufficient icing of the zinc surfaces. Preferably, therefore, the aforementioned molar ratio in a composition according to the invention is not greater than 3: 1, more preferably not greater than 2: 1. It is further preferred if the proportion of oxo acids of phosphorus in a composition according to the invention based on the total amount of Components c) at least 50 mol .-%, particularly preferably at least 80 mol .-% is.

To increase the deposition rate, the compounds according to component c) of a composition according to the invention are preferably selected from hyposalphurous acid, hypos nitric acid, nitrous acid, hypophosphoric acid, hypodiphosphonic acid, diphosphoric (III, V) acid, phosphonic acid, diphosphonic acid and phosphinic acid and their water-soluble salts, phosphinic acid and their water-soluble salts are particularly preferred.

For a sufficient stability of the inventive composition containing iron ions, it is also advantageous to use certain complexing agents to prevent the precipitation of iron hydroxides and to maintain the highest possible proportion of iron ions in the aqueous phase in a hydrated and / or complexed form.

The composition according to the invention therefore preferably additionally contains chelating complexing agents with oxygen and / or nitrogen ligands which do not contain water-soluble carboxylic acids according to component b) of the invention Compositions are. Particularly preferred in this context are compositions according to the invention which contain as additional component d) one or more such complexing agents which are selected from water-soluble α-hydroxycarboxylic acids which have at least one hydroxyl and one carboxyl group and no water-soluble organic carboxylic acids according to component b ), as well as from their water-soluble salts. Furthermore, the water-soluble α-hydroxycarboxylic acids according to component d) preferably have not more than 8 carbon atoms and are in particular selected from polyhydroxymonocarboxylic acids and / or polyhydroxydicarboxylic acids each having at least 4 carbon atoms, tartronic acid, glycolic acid, lactic acid and / or α-hydroxybutyric acid and from their water-soluble salts, most preferably selected from lactic acid and / or 2,3,4,5,6-pentahydroxyhexanoic acid and from their water-soluble salts.

A particularly effective formulation of the inventive composition with the aforementioned complexing agents according to component d) has a molar ratio of iron ions to water-soluble α-hydroxycarboxylic acids and their water-soluble salts of at least 1: 4, preferably of at least 1: 3, but not greater than 2: 1, preferably not greater than 1: 1.

Furthermore, in a composition according to the invention as an optional component e) reducing accelerators can be used, which are known to those skilled in the art in the phosphating. These include hydrazine, hydroxylamine, nitroguanidine, N-methylmorpholine N-oxide, glucoheptonate, ascorbic acid and reducing sugars.

The pH of the alkaline composition according to the invention is preferably not greater than 11.0, more preferably preferably not greater than 10.5, particularly preferably not greater than 10.0.

The compositions according to the invention may additionally contain surface-active compounds, preferably nonionic surfactants, in order to bring about additional purification and activation of the metal surfaces, so that homogeneous icing on the zinc surfaces is additionally promoted. 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 end-capped can. The proportion of nonionic surfactants in a composition according to the invention is preferably at least 0.01 g / l, more preferably at least 0.1 g / l, for sufficient cleaning and activation of the metal surfaces, and for economic reasons preferably not more than 10 g / l nonionic surfactants are included.

To prevent precipitation, it is further preferred that compositions according to the invention do not contain zinc ions in an amount for which the ratio of the total molar fraction of zinc ions and iron ions to the total molar fraction of water-soluble organic carboxylic acids according to component b) and water-soluble organic α-hydroxycarboxylic acids according to component d) and their respective water-soluble salts greater than 1: 1, more preferably greater than 2: 3.

The present invention is further characterized in that no further heavy metals have to be added to a composition according to the invention in order to provide improved corrosion protection on the zinc surfaces as part of the icing in cooperation with a subsequent wet chemical conversion treatment. A composition according to the invention therefore preferably contains less than 50 ppm total of metal ions of the elements Ni, Co, Mo, Cr, Ce, V and / or Mn, particularly preferably less than 10 ppm, particularly preferably less than 1 ppm of these elements.

Furthermore, the composition according to the invention preferably contains less than 1 g / l of water-soluble or water-dispersible organic polymers, since carryover of polymeric constituents from the pretreatment for icing into subsequent baths for wet-chemical conversion treatment may adversely affect the formation of the conversion layer. According to the invention, water-soluble or water-dispersible polymers are understood as meaning organic compounds which remain in the retentate in an ultrafiltration with a nominal cutoff limit (NMWC) of 10,000 μ.

1. a) 5-100 g/l an Eisen-Ionen,
2. b) 15-200 g/l an wasserlöslichen organischem Carbonsäuren, die zumindest eine Amino-Gruppe in α-, β-, oder γ-Stellung zur Säuregruppe aufweisen, sowie deren wasserlösliche Salze,
3. c) 20-300 g/l an Oxosäuren von Phosphor oder Stickstoff sowie deren wasserlösliche Salze, wobei mindestens ein Phosphoratom oder Stickstoffatom in einer mittleren Oxidationsstufe vorliegt.

The present invention also includes a concentrate which, by dilution by a factor of 5-50, provides a previously described alkaline composition of the invention. A concentrate according to the invention has a pH above 8.5 and preferably contains

1. a) 5-100 g / l of iron ions,
2. b) 15-200 g / l of water-soluble organic carboxylic acids which have at least one amino group in α-, β-, or γ-position to the acid group, as well as their water-soluble salts,
3. c) 20-300 g / l of oxo acids of phosphorus or nitrogen and their water-soluble salts, wherein at least one phosphorus atom or nitrogen atom is present in a middle oxidation state.

1. i) ggf. zunächst mit einem alkalischen Reiniger gereinigt und entfettet,
2. ii) mit einer zuvor beschriebenen erfindungsgemäßen alkalischen Zusammensetzung in Kontakt gebracht, und
3. iii) anschließend einer passivierenden nasschemischen Konversionsbehandlung unterzogen werden.

In a second aspect, the present invention relates to a method for pretreatment ("icing") of metallic components having zinc surfaces, wherein at least the zinc surfaces of the component

1. i) if necessary, first cleaned and degreased with an alkaline cleaner,
2. ii) contacted with a previously described inventive alkaline composition, and
3. iii) subsequently subjected to a passivating wet chemical conversion treatment.

In the process according to the invention, in step ii), first of all, a coating layer consisting essentially of oxidic and / or metallic iron is produced on the zinc surfaces ("icing"). On the other surfaces of the metallic component, which may be, for example, surfaces of iron, steel and / or aluminum, such an inorganic layer is not detectable. The specific deposition of the passive layer on the zinc surfaces leads in the process according to the invention, in which the icing a passivating wet chemical conversion treatment, surprisingly to a significant improvement in paint adhesion properties of these surfaces and effectively prevents the corrosion of cut edges of galvanized steel and the contact corrosion of the zinc surfaces connected ferrous metals. A passivating wet-chemical conversion treatment is a standard procedure in the steel and automotive industry for pre-treatment before an organic topcoat composition.

In a preferred embodiment of the method according to the invention, the metallic component has galvanized steel surfaces. Particularly advantageous is the method in the treatment of galvanized steel strip, as it provides excellent edge corrosion protection, and of components consisting of mixed composite and / or assembled metallic components made of galvanized steel, iron and / or steel and possibly aluminum, as it the contact corrosion is greatly reduced.

The alkaline cleaning step i) in the process according to the invention is optional and necessary when the surfaces of zinc have impurities in the form of salts and fats, for example drawing fats and corrosion protection oils.

The icing takes place in step ii) of the process according to the invention, wherein the manner of bringing into contact with the alkaline composition according to the invention is not restricted in terms of process technology to a particular method. Preferably, the zinc surfaces are contacted by dipping or spraying with the composition according to the invention for freezing.

In a preferred embodiment of the method, the metallic component is for at least 3 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, more preferably not more than 60 ° C brought into contact with an alkaline composition according to the invention. As already described, the compositions according to the invention cause an icing of the zinc surfaces. The formation of icing is self-limiting, ie with increasing icing of the zinc surfaces, the deposition rate of iron decreases. The preferred treatment or contact times should be selected in the method according to the invention so that the layer of iron is at least 20 mg / m ² based on the element iron. 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 icing in processes in which the composition is applied by spraying, faster than in immersion applications. Irrespective of the mode of application, the coating compositions according to the invention do not produce any layer deposits on iron significantly above 300 mg / m ^2, based on the element iron, due to the self-limiting freezing.

For a sufficient layer formation and an optimal edge protection in the treatment of galvanized steel surfaces immediately after the icing in step ii) with or without subsequent rinsing layer coatings of iron preferably at least 20 mg / m ² , more preferably at least 50 mg / m ² , in particular preferably more than 100 mg / m ² . but preferably not more than 250 mg / m ^{2 in} each case based on the element iron realized realized.

The coating of iron on the zinc surfaces can be determined after dissolution of the coating by means of a spectroscopic method which is described in the examples of the present invention.

The icing in step ii) of the method according to the invention is preferably carried out without external current, ie without applying an external voltage source to the metallic component.

In step iii) of the method according to the invention, a passivating wet-chemical conversion treatment takes place subsequently to step ii) with or without an intermediate rinsing step. Wet-chemical conversion treatment is understood according to the invention as bringing into contact at least the zinc surfaces of the metallic component with an aqueous composition which produces a passivating and substantially inorganic conversion coating on the treated zinc surfaces. In this case, a conversion coating is any inorganic coating on the metallic zinc substrate which does not represent an oxide or hydroxide coating whose cationogenic main constituent is zinc ions. A conversion coating may therefore be a zinc phosphate layer.

In a preferred embodiment of the process according to the invention, a passivating wet chemical conversion treatment is carried out in step iii) by bringing into contact with an acidic aqueous composition which has a total of at least 5 ppm but not more than 1500 ppm total of water-soluble inorganic compounds of the elements Zr, Ti , Si and / or Hf based on the aforementioned elements, and preferably water-soluble inorganic compounds which release fluoride ions, for example, fluorocomplexes, hydrofluoric acid and / or metal fluorides.

Preferred in this regard are those acidic aqueous compositions in step iii) of the process according to the invention which contain as water-soluble compounds of the elements zirconium, titanium and / or hafnium only water-soluble compounds of the elements zirconium and / or titanium, more preferably water-soluble compounds of the element zirconium. As water-soluble compounds of the elements zirconium and / or titanium, both compounds which dissociate in aqueous solution into anions of fluorocomplexes of the elements titanium and / or zirconium, for example H ₂ ZrF ₆ , K ₂ ZrF ₆ , Na ₂ ZrF ₆ and (NH ₄ ) ₂ ZrF ₆ and the analogous titanium compounds, as well as fluorine-free compounds of the elements zirconium and / or titanium, for example (NH ₄ ) ₂ Zr (OH) ₂ (CO ₃ ) ₂ or TiO (SO ₄ ), in acidic aqueous compositions used in step iii) of the method according to the invention.

In step iii) of the preferred process according to the invention, the acidic aqueous composition containing a total of at least 5 ppm but not more than 1500 ppm total of water-soluble inorganic compounds of the elements Zr, Ti, Si and / or Hf with respect to the aforementioned elements is preferred chromium-free, ie it contains less than 10 ppm, preferably less than 1 ppm of chromium, in particular no chromium (VI).

In an alternative preferred embodiment of the process according to the invention, a zinc phosphating is carried out in step iii), wherein the presence of the heavy metals Ni and / or Cu in the zinc phosphating can largely be dispensed with due to the previous icing of the zinc surfaces of the metallic component in step ii). The icing of the zinc surfaces thus provides for subsequent zinc phosphating the unexpected advantage that results for such phosphated zinc surfaces corrosion protection and paint adhesion, which is comparable to the Zinkphosphatierung of iron or steel surfaces.

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) vorzugsweise jeweils weniger als 0,1 g/L an ionischen Verbindungen der Metalle Nickel und Cobalt jeweils bezogen auf das metallische Element enthält.

In a preferred embodiment of the method according to the invention, the passivating wet-chemical conversion treatment in step iii) consists in contacting the galvanized steel surfaces pretreated in step ii) with an acidic aqueous composition 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) preferably each less than 0.1 g / L of ionic compounds of the metals nickel and cobalt in each case based on the metallic element.

The pretreated metallic components, which have surfaces of zinc directly resulting from a method according to the invention, are then preferably provided with an organic covering layer, with or without an intermediate rinsing and / or drying step. The first cover layer in the pretreatment of already cut, formed and assembled components is usually an electrodeposition paint, more preferably a cathodic dip. In contrast, organic primer coatings are preferably applied as the first organic cover layer in the anticorrosive or decorative coating of galvanized steel strip following the inventive method.

The treated in a process according to the invention metallic components having surfaces of zinc, find use in body construction in automotive manufacturing, shipbuilding, construction and for the production of white goods.

The influence of various α-amino acids with respect to the homogeneity of the icing after contacting of inventive compositions with electrolytically galvanized steel by dipping is reproduced in Table 1.

First of all, thin coatings of oxidic and / or metallic iron on the zinc surfaces ("icing") are obtained with all inventive compositions (C1-C4), but particularly homogeneous coatings are formed specifically by compositions (C1; C5) according to the invention comprising glycine. Tab.1 Alkaline compositions according to the invention for icing Component: C1 C2 C3 C4 C5 a) Iron (II) gluconate 12.50 12.50 12.50 12.50 1.25 Iron (II) lactate 18.75 18.75 18.75 18.75 1.87 b) glycine 45,00 - - - 4.50 L-glutamine - 87.61 - - - L-glutamic acid - - 88,20 - - L-lysine - - - 87.63 - c) NaH ₂ PO ₂ 45,00 45,00 45,00 45,00 4.50 NaOH 50% by weight 25,00 32,60 76.70 25,00 2.50 water 853.75 803.54 758.85 811.12 985.38 pH 9.0 9.0 9.0 9.0 9.0 Process parameters: C1 C2 C3 C4 C5 Dive application ¹ 10s @ 50 ° C 10s @ 50 ° C 10s @ 50 ° C 10s @ 50 ° C 60s @ 50 ° C Optical assessment ² ++ + + O ++ ¹ on electrolytically galvanized sheet steel (Gardobond® MBZE7) ² regarding homogeneity of icing: ++ homogeneous dark gray coating + almost complete coverage with dark gray coating O incomplete coverage with dark gray to brownish coating - Inhomogeneous coverage with predominantly light gray to brownish coating

The concentration of the active components in a composition according to the invention has an immediate effect on the deposition rate, so that dilute compositions must be brought into contact with the galvanized steel surface for a longer time in order to obtain a homogeneously coated zinc surface (see C1 in comparison to C5).

In the following, the effect of icing when using compositions according to the invention on the basis of process chains for the corrosion-protective pretreatment of zinc surfaces will be illustrated. Table 2 shows the corrosive infiltration of an immersion paint on electrolytically galvanized steel after the respective process chain for corrosion-protective pretreatment in Wechselklimatest and stone impact test again.

• A. Alkalische Reinigung (pH 11):
  • 3 Gew.-% Ridoline® 1574A (Fa. Henkel);
  • 0,4 Gew.-% Ridosol® 1270 (Fa. Henkel)
  • Behandlungsdauer bei 60 °C: 180 Sekunden
• B. Spülen mit vollentsalztem Wasser (κ<1 μScm^-1)
• C. Vereisenung unter Verwendung einer Zusammensetzung gemäß Tabelle 1:
  • Behandlungsdauer bei 50 °C: 60 Sekunden
• D. Aktivierung:
  • 0,1 Gew.-% Fixodine® 50CF (Fa. Henkel)
  • Rest vollentsalztes Wasser (κ<1 μScm^-1)
  • Behandlungsdauer bei 20 °C: 60 Sekunden
• E1. Saure Passivierung:.9
  • 0,34 g/L H₂Zr_F6
  • 0,12 g/L Ammoniumbifluorid
  • 0,08 g/L Cu(NO₃)₂·3H₂O
  • Rest vollentsalztes Wasser (κ<1 μScm^-1)
  • pH-Wert 4
  • Behandlungsdauer bei 30 °C: 120 Sekunden
• E2. Nickelfreie Phosphatierung:
  • 0,13 Gew.-% Zink
  • 0,09 Gew.-% Mangan
  • 0,12 Gew.-% Nitrat
  • 1,63 Gew.-% Phosphat
  • 0,25 Gew.-% Hydroxylaminsulfat
  • 0,02 Gew.-% Ammoniumbifluorid
  • 0,10 Gew.-% H₂SiF₆
  • Rest vollentsalztes Wasser (κ<1 μScm^-1)
  • Freies Fluorid: 40 mg/L
  • Freie Säure: 1,3 Punkte (pH 3,6)
  • Gesamtsäure : 26 Punkte (pH 8,5)
  • Behandlungsdauer bei 50 °C: 180 Sekunden
• E3. Nickelhaltige Phosphatierung (Trikationen-Phosphatierung):
  • 0,13 Gew.-% Zink
  • 0,09 Gew.-% Mangan
  • 0,10 Gew.-% Nickel
  • 0,32 Gew.-% Nitrat
  • 1,63 Gew.-% Phosphat
  • 0,25 Gew.-% Hydroxylaminsulfat
  • 0,02 Gew.-% Ammoniumbifluorid
  • 0,10 Gew.-% H₂SiF₆
  • Rest vollentsalztes Wasser (κ<1 μScm^-1)
  • Freies Fluorid: 40 mg/L
  • Freie Säure: 1,3 Punkte (pH 3,6)
  • Gesamtsäure : 26,5 Punkte (pH 8,5)
  • Behandlungsdauer bei 50 °C : 180 Sekunden
• F. Lackaufbau: EV2007 (Fa. PPG): Schichtdicke 17 - 19 μm

The individual process steps of the process chains listed in Table 2 for the corrosion-protective treatment of individual galvanized steel sheets (Gardobond® MBZE7) follow:

• A. Alkaline Purification (pH 11):
  • 3% by weight of Ridoline® 1574A (Henkel);
  • 0.4% by weight of Ridosol® 1270 (Henkel)
  • Treatment time at 60 ° C: 180 seconds
• B. Rinsing with demineralized water (κ <1 μScm ^-1 )
• C. icing using a composition according to Table 1:
  • Treatment time at 50 ° C: 60 seconds
• D. Activation:
  • 0.1% by weight of Fixodine® 50CF (Henkel)
  • Remaining deionized water (κ <1 μScm ^-1 )
  • Duration of treatment at 20 ° C: 60 seconds
• E1. Acid Passivation: .9
  • 0.34 g / LH ₂ Zr _F 6
  • 0.12 g / L ammonium bifluoride
  • 0.08 g / L Cu (NO ₃ ) ₂ .3H ₂ O
  • Remaining deionized water (κ <1 μScm ^-1 )
  • pH 4
  • Treatment time at 30 ° C: 120 seconds
• E2. Nickel-free phosphating:
  • 0.13% by weight of zinc
  • 0.09 wt .-% manganese
  • 0.12 wt.% Nitrate
  • 1.63% by weight of phosphate
  • 0.25% by weight of hydroxylamine sulfate
  • 0.02% by weight of ammonium bifluoride
  • 0.10% by weight of 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 acidity: 26 points (pH 8.5)
  • Treatment time at 50 ° C: 180 seconds
• E3. Nickel-containing phosphating (trication-phosphating):
  • 0.13% by weight of zinc
  • 0.09 wt .-% manganese
  • 0.10 wt.% Nickel
  • 0.32 wt% nitrate
  • 1.63% by weight of phosphate
  • 0.25% by weight of hydroxylamine sulfate
  • 0.02% by weight of ammonium bifluoride
  • 0.10% by weight of 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: 26.5 points (pH 8.5)
  • Treatment time at 50 ° C: 180 seconds
• F. Coating structure: EV2007 (PPG): layer thickness 17-19 μm

It is clear from Table 2 that the icing in a process chain according to the invention, which effects the wet-chemical conversion by means of aqueous zirconium-containing passivation solutions (B1) in comparison to an analog process chain in which the icing is omitted (V1), an improved corrosion protection ,

The same can be said for the improvement of the corrosion protection of those galvanized steel sheets subjected to nickel-free zinc phosphating. Here, too, the previous freezing (B2) results in significantly improved corrosion values compared to pure zinc phosphating (V2). The corrosion results (B2) achieved with the icing are even improved in comparison with the trication-phosphating (V3) frequently used in the prior art for the corrosion-protective pretreatment of components manufactured in mixed construction. Tab.2 Different process sequences for the corrosion-protective treatment of electrolytically galvanized steel strip (Gardobond® MBZE7, Chemetall) and the results of undercutting at the scribe and in the stone impact test process sequence Infiltration at the Ritz ¹ in mm K value ¹ Layer layer ³ ZnPO ₄ in g / m ² Coating ² iron in g / m ² B1 AB-C5-B-E1-BF 2.0 3.5 - 193 B2 AB-C5-BD-E2-BF 1.9 2.5 2.6 202 V1 AB-E1-BF 4.0 4.5 - - V2 ABD-E2-BF 3.9 5.0 2.9 - V3 ABD-E3-BF 2.3 3.5 3.0 - ¹ rockfall and infiltration at the Ritz in accordance with DIN EN ISO 20567-1 after removal according to the climate test VDA 621-415 (10 weeks)
² determined by removing the zinc phosphate layer with aqueous 5 wt .-% CrO ₃ , which was brought immediately after process step E2 or E3 at 25 ° C for 5 min with a defined surface of the 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.
³ quantitative determination of the amount of iron (III) ions by UV photometer (WTW, Photoflex®) in 300 μl sample volume of a 5 wt .-% nitric acid solution, which immediately after the process step "C" using a measuring cell ring ( Helmut-Fischer) was pipetted onto a defined area of the 1.33 cm ² galvanized sheet and, after 30 seconds of action at a temperature of 25 ° C., picked up by the same pipette and placed in the UV measuring cuvette in which 5 ml of a 1 , 0% sodium thiocyanate solution were presented, to determine the absorption at a wavelength of 517 nm and temperature of 25 ° C was transferred. 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 (15)

An alkaline aqueous composition for pretreatment of metallic components having zinc surfaces, having a pH of at least 8.5 a) at least 0.01 g / l of iron ions, b) one or more water-soluble organic carboxylic acids which have at least one amino group in α, β or γ position to the acid group, and their water-soluble salts, c) one or more oxo acids of phosphorus or nitrogen and their water-soluble salts, wherein at least one phosphorus atom or nitrogen atom is present in a middle oxidation state. A composition according to claim 1, characterized in that at least 1 g / l, preferably at least 2 g / l, but in total not more than 10 g / l of iron ions are contained. Composition according to one or both of the preceding claims, characterized in that the molar ratio of iron ions to water-soluble organic carboxylic acids according to component b) and their water-soluble salts is at least 1: 12, preferably at least 1: 8, but not greater than 2: 1, preferably not greater than 1: 1. Composition according to one or more of the preceding claims,
characterized in that the water-soluble organic carboxylic acids according to component b) are selected from α-amino acids which preferably have hydroxyl groups in addition to amino and carboxyl groups, and are particularly preferably selected from lysine, serine, threonine, alanine, glycine, Aspartic acid and / or glutamic acid. Composition according to one or more of the preceding claims,
characterized in that the molar ratio of iron ions to oxo acids of phosphorus or nitrogen according to component c) and their water-soluble salts at least 1:10, preferably at least 1: 6, but not greater than 3: 1, preferably not greater than 2: 1 is. Composition according to one or more of the preceding claims,
characterized in that the oxo acids of phosphorus or nitrogen according to component c) are selected from hyposalpetriger acid, hypo nitric acid, nitrous acid, hypophosphorous acid, hypodiphosphonic acid, diphosphoric (III, V) acid, phosphonic acid, diphosphonic acid and / or phosphinic acid and their water-soluble salts. Composition according to one or more of the preceding claims,
characterized in that as component d) additionally one or more water-soluble α-hydroxycarboxylic acids which have at least one hydroxyl and one carboxyl group and are not water-soluble organic carboxylic acids according to component b), and their water-soluble salts are contained. Composition according to claim 7, characterized in that the molar ratio of iron ions to water-soluble α-hydroxycarboxylic acids according to component d) and their water-soluble salts is at least 1: 4, preferably at least 1: 3, but not greater than 2: 1, preferably not is greater than 1: 1. Composition according to one or both of the preceding claims 7 and 8, characterized in that the water-soluble α-hydroxycarboxylic acids according to component d) have not more than 8 carbon atoms and are preferably selected from polyhydroxymonocarboxylic acids and / or polyhydroxydicarboxylic acids each having at least 4 carbon atoms, tartronic acid, glycolic acid , Lactic acid and / or α-hydroxybutyric acid. Composition according to one or more of the preceding claims, characterized in that the pH is not greater than 11.0, preferably not greater than 10.5, more preferably not greater than 10.0. Composition according to one or more of the preceding claims, characterized in that zinc ions are not contained in an amount for which the ratio of the total molar fraction of zinc and iron ions to the total molar fraction of water-soluble organic carboxylic acids according to component b) and water-soluble organic α-hydroxycarboxylic acids according to component d) and their respective water-soluble salts is greater than 1: 1, preferably greater than 2: 3. Process for the pretreatment of galvanized steel surfaces, characterized in that the galvanized steel surfaces i) if necessary, first cleaned and degreased with an alkaline cleaner, ii) contacted with an alkaline composition according to one or more of the preceding claims, and iii) subsequently subjected to a passivating wet chemical conversion treatment. A method according to claim 12, characterized in that step ii) takes place without external power. Method according to one or both of Claims 12 and 13, characterized in that the passivating wet-chemical conversion treatment consists in bringing into contact the galvanized steel surfaces pretreated in step ii) with an acidic aqueous composition which is at least 5 ppm in total but no more in total as 1500 ppm of water-soluble inorganic compounds of the elements Zr, Ti, Si and / or Hf based on the aforementioned elements and preferably water-soluble inorganic compounds which release fluoride ions. Method according to one or both of Claims 12 and 13, characterized in that the passivating wet-chemical conversion treatment comprises contacting the galvanized steel surfaces pretreated in step ii) with an acidic aqueous composition having a pH in the range of 2, Has 5-3.6 and a) 0.2 to 3.0 g / L zinc (II) ions, b) 5.0 to 30 g / L of phosphate ions calculated as P ₂ O ₅ and c) preferably each less than 0.1 g / L of ionic compounds of the metals nickel and cobalt in each case based on the metallic element.