EP3728693A1

EP3728693A1 - Method for the corrosion-protective and cleaning pretreatment of metal components

Info

Publication number: EP3728693A1
Application number: EP18812172.7A
Authority: EP
Inventors: Jerzy-Tadeusz Wawrzyniak; Dalija EHMANN; Nils BONGARTZ; Matilde SENATORE
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 2017-12-20
Filing date: 2018-12-06
Publication date: 2020-10-28
Anticipated expiration: 2038-12-06
Also published as: US11408078B2; CN111527238B; US20200308711A1; KR20200096980A; CN111527238A; CA3085652A1; EP3728693B1; WO2019121036A1; EP3502311A1; ES2958039T3

Abstract

The invention relates to a multiple-step method for the corrosion-protective pretreatment of components, said pretreatment being at least partially produced from a metal material predominantly consisting of at least one of the elements iron zinc and/or aluminium, according to which the components are first brought into contact with an acid aqueous composition (A) containing water-soluble compounds of the elements Zr and/or Ti and then with an acid aqueous composition (B) containing phosphate ions and an accelerator. The method is particularly suitable for the pretreatment before an electrocoating.

Description

Process for corrosion-protecting and cleaning pretreatment

of metallic components

The present invention relates to a multi-stage process for corrosion protection

Pre-treatment of components which is at least partially made of a metallic material, which consists predominantly of one or more of the elements iron, zinc and / or aluminum

is composed in which the components are first brought into contact with an acidic aqueous composition (A) containing water-soluble compounds of the elements Zr and / or Ti and then with an acidic aqueous composition (B) containing phosphate ions and an accelerator. The method is particularly suitable for pretreatment before an electrocoating.

The corrosion-protective pretreatment of metallic surfaces before a subsequent

Depending on the desired profile of requirements and the type of lacquer to be applied, lacquering in the prior art is carried out with different wet-chemical treatment methods

often made on the conversion of metal surfaces with a homogeneous

passivate coating with an inorganic material, wherein the inorganic material is deposited by a stain of the metallic substrate as a sparingly soluble compound of a metal and / or Halbmetallelements crystalline or amorphous. The metal and / or

Semi-metal element of the deposited after the conversion of the metal surface inorganic material originates either predominantly from the metal of the treated substrate, as in the non-layered phosphating example, the iron phosphating, or contained in the pickling active components of these metal and / or metal elements, as in the layer-forming phosphating, for example zinc phosphating. As a non-film forming referred to the expert phosphating in the course of which only thin amorphous, but largely homogeneous coatings are achieved and therefore regularly available only in layer conditions of less than 1 g / m ² based on PCL realized. In contrast, the layer-forming phosphating at least partially crystalline phosphate coatings ready, the layer overlay is regularly above 1, 5 g / m ² . Especially the phosphating process is very well established and still today despite the elaborate reprocessing of Phosphatierbades and the rinse water and formed during the workup phosphate slurries an important anticorrosive pretreatment method before an electrocoating of components made of metallic materials of the elements iron, zinc and / or aluminum are made. Where the requirement profile with regard to corrosion protection and paint adhesion to such, electrocoated materials is less demanding, it is often attempted to carry out a non-layer-forming phosphating, which is particularly well-controlled for iron materials and provides homogeneous thin amorphous coatings. The non-layer-forming phosphating is significantly less is material-intensive and can be operated in the treatment of the phosphating bath and the rinsing water because of the lower phosphate load with less effort.

DE 44 17 965 A1 describes such a phosphating solution for non-film-forming

Phosphating of surfaces of steel, zinc and / or aluminum, wherein in particular on the iron surfaces layer conditions of phosphating in the range of 0.5-1 g / m ² are to be achieved, while on surfaces of the materials, which are composed mainly of zinc and aluminum , a moderate, roughness enhancing stain takes place, which is conducive to the subsequent coating layer buildup on these materials. According to DE 44 17 965 A1, the phosphating necessarily contains dissolved phosphate, nitrobenzenesulfonic acid as an accelerator as well as there specified monocarboxylic acids. The phosphating baths can also be further

Excipients include, for example, free and / or complexed fluoride.

Compared to this state of the art, the object is first of all the phosphate sludge accumulating in the case of the non-layer-forming phosphating and, in processes with subsequent electrodeposition, the required coating layer thickness while maintaining the same

To reduce corrosion resistance. Another important aspect is the passivation achieved with the non-layering phosphating for a subsequent

To improve electrocoating to the effect that in more complex components of the Lackumgriff in areas of the component, which are largely shielded from the electric field of the electrocoating is increased.

This object is achieved in a method for the corrosion-protective pretreatment of metallic surfaces of such a component, which consists at least partially of a metallic material which is predominantly composed of one or more of the elements iron, zinc and / or aluminum, comprising the following successive process steps:

I) contacting the component with an acidic aqueous composition (A)

containing at least one water-soluble compound of the elements Zr and / or Ti;

II) contacting the device with an acidic aqueous composition (B) containing phosphate ions and an accelerator.

A "metallic material according to the invention is then composed predominantly of one or more of the elements iron, zinc and / or aluminum, if the sum of these elements in the material is greater than 50 at.%, Preferably greater than 80 at.%. Such materials are steel, iron, zinc, aluminum, for example as a die-cast alloy, but also with metallic

Coatings in a layer thickness of at least 1 pm plated substrates, in which case the metallic coating is a material according to the present invention. Such coatings are, for example, in electrolytically or hot dip galvanized steel, or in plating in shape of zinc (Z), aluminum-silicon (AS), zinc-magnesium (ZM), zinc-aluminum (ZA), aluminum-zinc (AZ) or zinc-iron (ZF). The invention is characterized in that the said materials are provided with a corrosion-protective passivation, which in particular on those materials which consist predominantly of the element iron (so-called

"Ferrous materials"), for example, on steels, excellent corrosion protection and

Lackhaftgrund offer. The steel includes metallic materials whose mass fraction of iron is greater than that of any other element, and whose carbon content is less than 2.06 wt .-% without regard to carbides. In a particular embodiment, this includes

inventive method therefore the corrosion-protective pretreatment of metallic

Surfaces of a component which consists at least partially of a metallic material, which is composed predominantly of the element iron. However, since components which consist of various metallic materials can also be pretreated successfully in the method according to the invention, a further preferred embodiment of the method according to the invention is characterized in that metallic surfaces of components which consist of more than one metallic material, which predominantly pretreates is composed of one or more of the elements iron, zinc and / or aluminum joined together (so-called "composite construction"), in particular those components which consist at least partially of a ferrous material and in composite construction with a material consisting predominantly of one or both of Elements zinc and / or aluminum is made up.

The components treated according to the present invention can be any arbitrarily shaped and configured spatial structures which originate from a fabrication process, in particular also semi-finished products such as strips, sheets, rods, tubes, etc., and composite constructions

assembled from the aforementioned semi-finished products, wherein the semi-finished products are preferably connected to one another by gluing, welding and / or flanging the composite construction.

In the process according to the invention, as a result of the conversion treatment based on the elements Zr and / or Ti in process step I), overall less sludge formation is achieved in the series treatment of a large number of components compared to conventional non-layer-forming phosphating and, at the same time, better corrosion and paint adhesion values are achieved. The latter result in subsequent electrocoating the inventively pretreated components to a significantly improved Umgriffsverhalten the paint or the same wraparound to a lower layer thickness of the deposited in the electric field paint. In this way, it is possible with the same process engineering effort to increase the paint coating and thus the corrosion protection in shielded from the electric field areas of the component, wherein in the non-electric field shielded areas of the component lower coating thicknesses are achieved.

For a sufficient conversion of the metal surfaces of the component in process step (I), it is advantageous if the proportion of water-soluble compounds of the elements Zr and / or Ti in the acidic aqueous composition (A) of the process according to the invention is at least 0.05 mmol / kg, more preferably at least 0.1 mmol / kg, most preferably at least 0.2 mmol / kg, and for economic reasons and to avoid the over-pickling of the conversion layer preferably not more than 1, 5 mmol / kg, particularly preferably not more than 1, 0 mmol / kg total, of water-soluble compounds of the elements Zr and / or Ti are contained in an acidic aqueous composition (A) of the process according to the invention. The term "water-soluble" in the context of the present invention comprises compounds which have a solubility in deionized water (K <1 pScnr ¹ ) of at least 1 g / kg at 20 ° C.

Suitable representatives of the water-soluble compounds of the elements Zr and / or Ti which may be present in the acidic aqueous composition (A) are compounds which dissociate into anions of fluoro complexes in aqueous solution. Such preferred compounds are, for example, H2ZrF6, fcZrFe, Na2ZrF6 and (NH4) 2ZrF6 and the analogous titanium compounds. Also, fluorine-free compounds of the elements Zr or Ti, in particular the element Zr, can be used as water-soluble compounds according to the invention, for example (NH ₄ ) ₂ Zr (0H) ₂ (C03) ₂ or Ti0 (S0 ₄ ). In a preferred embodiment of the method according to the invention

Fluorometalates of the elements Zr and / or Ti and their fluoro acids, particularly preferably hexafluorozirconates and / or hexafluorotitanates and their free acids, in the acidic aqueous composition. The respective water-soluble compounds of the element Zr are preferably used according to the invention over the compounds of the element Ti.

In addition, it may be advantageous for a rapid formation of a homogeneous conversion layer, if the one acidic composition (A) in process step (I) of the inventive

Method contains a source of fluoride ions. The source of fluoride ions is any inorganic compound that is capable of being dissolved or dispersed in water to liberate fluoride ions. A preferred source of fluoride ions are complex or simple fluorides. Simple fluorides are understood to mean hydrofluoric acid and its salts, such as alkali fluorides, ammonium fluoride or ammonium bifluoride, whereas complex fluorides are coordination compounds according to the invention in which fluorides are coordinated as ligands of one or more central atoms. Accordingly, preferred representatives of the complex fluorides are the aforementioned fluorine-containing complex compounds of the elements Z and / or Ti.

The proportion of compounds which are a source of fluoride ions in an acidic aqueous composition of the method according to the invention is preferably at least such that an amount of free fluoride of at least 1 mg / kg, more preferably of at least 10 mg / kg, however, preferably not more than 100 mg / kg in the acidic aqueous composition (A). The free fluoride content is determined by means of calibrated fluoride-sensitive electrode directly in the acidic aqueous composition (A) at 20 ° C. If, in the following, reference is made to the free fluoride content, it must always be determined in an analogous manner directly in the relevant composition. Furthermore, for optimum conversion, in particular of the surfaces of iron materials, by bringing into contact with an acidic aqueous composition (A), it is preferred if the molar ratio of total fluoride content to the total amount of elements Zr and / or Ti is greater than 4, 5, preferably greater than 5.0, more preferably greater than 5.5. The total fluoride content is determined with a fluoride-sensitive electrode in a TISAB buffered aliquot of an acidic aqueous composition (A) of the inventive method at 20 ° C (TISAB: "Total Lonic Strength Adjustment Buffer"), wherein the volume-related mixing ratio of buffer to the aliquot part of the acidic aqueous composition (A) is 1: 1. The TISAB buffer is prepared by dissolving 58 g of NaCl, 1 g of sodium citrate and 50 ml of glacial acetic acid in 500 ml of deionized water (K <I pScnr ¹ ) and adjusting to pH 5.3 by 5N NaOH and making up to total volume of 1000 ml again with deionized water (K <I pScnr ¹ ). If, in the following, attention is paid to the total fluoride content, it must always be determined in an analogous manner for the composition in question.

A first conversion of the metal surface of the component to be pretreated according to the invention with a corrosion-protective coating based on the elements Zr and / or Ti takes place in the acidic aqueous composition (A). Here, for optimum process results, it is necessary to set a balance between pickling and deposition rates that results in coatings that are best suited for subsequent non-film-forming phosphating. It has been found that the pH of the acidic aqueous composition (A) in process step (I) is preferably less than 5.8, more preferably less than 5.2, but preferably not less than 3.9, most preferably not less is 4.2, since even low pickling rates are sufficient to bring about sufficient conversion of the metal surfaces. However, for the provision of homogeneous conversion coatings, a certain pickling rate is required for the formation of an alkaline diffusion layer on the metal surfaces, within which the precipitation of the

Layer components takes place. In this connection, those methods are preferred according to the invention in which the acidic aqueous composition (A) has a free acid content of at least 1 point, but more preferably has less than 5 points. The free acid is determined by diluting 2 ml of the acidic aqueous composition (A) to 50 ml with deionized water (K <1 pScnr ¹ ), titrating with 0.1 N sodium hydroxide solution to a pH of 4.0 , The consumption of acid solution in ml indicates the score of the free acid. If, in the following, reference is made to the free acidity in points, this must always be determined in an analogous manner for the composition in question.

In a preferred embodiment of the process according to the invention, the acidic aqueous composition (A) for accelerating the conversion of the metal surfaces which are brought into contact with the acidic composition (A) in process step (I) additionally comprises at least one water-soluble compound which is a source of Represents copper ions, preferably in the form a water-soluble salt, for example, copper sulfate, copper nitrate and copper acetate. The presence of copper ions is also beneficial for the anti-corrosive properties of the resulting on the metallic surfaces of the components in the course of conversion

Conversion coating. The content of copper ions from water-soluble compounds in the acidic aqueous composition (A) for this purpose is preferably at least 0.001 g / kg, more preferably at least 0.005 g / kg. However, the content of copper ions is preferably not more than 0.1 g / kg, more preferably not more than 0.05 g / kg, otherwise the deposition of elemental copper begins to dominate over the conversion layer formation.

Furthermore, according to the invention for a fast and reproducible conversion of

Metal surfaces are preferred if the acidic aqueous composition (A) additionally contains in the process according to the invention at least one water-soluble compound which comprises

Standard reduction potential at pH 0 above +0.2 V (SHE). The

Standard reduction potential of a redox pair E ° (Ox / Red) is defined in the sense of the present invention as the electrochemical voltage between the electrochemical half-cell containing the redox couple each with the thermodynamic activity of 1 at pH = 0 and the half-cell of the standard hydrogen electrode (SHE) at one temperature electrolytes in the half-cells of 25 ° C. Water-soluble compounds which have such a standard reduction potential are preferably selected from inorganic nitrogen compounds, particularly preferably from nitric acid and / or nitrous acid and salts thereof. The proportion of water-soluble

Compounds for accelerating the conversion layer formation is preferably at least 1 mmol / kg, preferably at least 10 mmol / kg, but for reasons of economy, preferably less than 200 mmol / kg based on the acidic aqueous composition (A).

In addition, the acidic aqueous composition (A) in the process step (I) may contain at least one aliphatic saturated polyhydroxy compound having at least 4 but not more than 8

Carbon atoms. In this way, the acidic aqueous composition (A) is able to rid the surfaces of the component of organic contaminants, without the

Conversion layer formation to influence negatively. This method according to the invention are accessible, which develop a cleaning effect in process step (I) and therefore may not have to resort to a previous purification stage.

The aliphatic polyhydroxy compound to be used in this connection is an aliphatic compound having more than two hydroxyl groups, preferably more than three hydroxyl groups, preferably having at least two hydroxyl groups not more than two

Carbon atoms are linked together ("vicinal hydroxyl groups"). Alditols, which in turn are preferably not more than 6, are particularly preferred as polyhydroxy compounds

Have carbon atoms and are more preferably selected from erythritol, threitol, xylitol, arabitol, ribitol, mannitol or sorbitol, and particularly preferably sorbitol. To improve the cleaning performance, a preferred acidic aqueous composition (A) containing the polyhydroxyalkoxy compound preferably additionally contains at least one aliphatic diol having at least 4 carbon atoms but not more than 10 carbon atoms.

The abovementioned aliphatic diols are preferably selected from diols whose

Hydroxyl groups are bonded together over not more than 3 carbon atoms, and more preferably from acyclic alkanediols having not more than 8 carbon atoms, but preferably at least 5 carbon atoms, and more preferably 2-methylpentane-2,4-diol.

In a preferred embodiment, the acidic aqueous composition (A) in the

Process step (I) at least 0.01 wt .-% of the aliphatic saturated polyhydroxy compound and optionally at least 0.003 wt .-% of the aliphatic diol.

Excellent cleaning performance is achieved when the mass ratio of the aforementioned polyhydroxy compounds to the aforementioned aliphatic diols is at least 0.4. Such a relative minimum amount of polyhydroxy compounds is therefore preferred in acidic aqueous compositions (A) in the process of the invention. Particularly preferably, the aforementioned ratio is at least 1.0, more preferably at least 2.0. At too high relative proportions of the aforementioned polyhydroxy compounds, the cleaning performance can not otherwise with the same total amount of active components

and the simultaneous conversion of the metal surface loses its homogeneity. Accordingly, in the process of the present invention, it is preferred that the ratio by mass of the aforementioned polyhydroxy compounds to the aforementioned diols in the preferred acidic aqueous composition (A) is not greater than 20.0, more preferably not greater than 10.0, most preferably not is greater than 6.0.

Insofar as the component is brought into contact with an acidic aqueous composition (A) which additionally contains the abovementioned mixture of aliphatic diols and aliphatic saturated polyhydroxy compounds, it is entirely possible to dispense with a preceding purification step. In a preferred embodiment of the process according to the invention, therefore, immediately before the component is brought into contact with the preferred acidic aqueous composition (A) containing the aforementioned mixture of aliphatic diols and aliphatic saturated polyhydroxy compounds in process step (II), none occurs

Wet-chemical cleaning of the component, especially not when the contacting takes place by spraying or spraying.

A wet-chemical cleaning according to the invention is a cleaning by contacting with a water-based composition containing a total of at least 0.1 wt .-% of surfactants and / or wetting agents, wherein surfactants and / or wetting agents all organic compounds include, the surface tension of water at 20 ° C and a proportion of 0.1 wt .-% determined by the Wilhelmy plate method lower.

A significant advantage of a process according to the invention, which is based on bringing into contact with an acidic aqueous composition (A) additionally containing a mixture of aliphatic diols and aliphatic saturated polyhydroxy compounds, is that a cleaning of the metallic surfaces of the component of Aids based on organic

Compounds such as anti-corrosive oils, cutting oils and cooling lubricants from upstream production stages already succeed at relatively low operating temperatures. In a preferred embodiment of the process according to the invention, the contacting of the acidic aqueous composition (A) therefore takes place at a temperature of the composition of less than 40 ° C., more preferably less than 35 ° C., particularly preferably less than 30 ° C, but preferably at least 20 ° C. Furthermore, in this context it is preferred that the contacting of the acidic aqueous composition (A) in the process according to the invention by spraying or spraying, more preferably by spraying, particularly preferably at an injection pressure of at least 1 bar, for optimum cleaning and to achieve fast conversion of metal surfaces.

In method step (I), a first conversion of the metal surfaces is to take place with a coating that temporarily protects against corrosion, which in turn represents only a thin, almost completely inorganic coating based on the elements Zr and / or Ti, and possibly a cleaning of the component. Properties of a paint primer should therefore in the course of

Process step (I) are not mitverliehen. Therefore, in a preferred embodiment of the process according to the invention, a total of less than 1 g / kg, more preferably less than 0.2 g / kg of organic polymers in the acidic aqueous composition (B) are included.

Organic polymers in this sense have a molecular weight of at least 1,000 g / mol as determined by molecular weight distribution curves

Gel permeation chromatography (GPC) with Rl detector after calibration using polystyrene standards after elution with tetrahydrofuran at a temperature of the eluate in the detector of 40 ° C.

Furthermore, it is preferred that the acidic aqueous composition (A) in process step (I) is "phosphate-free" and / or "chromium-free". According to the invention, a composition is then "phosphate-free" if the proportion of phosphates dissolved in water is less than 100 mg / kg, preferably less than 20 mg / kg, calculated as the amount of phosphorus. According to the invention, a composition is "chromium (VI) -free" if the proportion of compounds of the element chromium dissolved in water in the oxidation state + VI is less than 100 mg / kg, preferably less than 20 ppm. Preferably, immediately after bringing the component into contact with the acidic aqueous composition (A) in process step (I) - with or without intervening rinsing and / or drying step, preferably with rinsing step, but more preferably without drying step - takes place in the process according to the invention contacting with the acidic aqueous

Composition (B) in process step (II) for non-film-forming phosphating. The two wet-chemical process steps (I) and (II) can also follow one another directly in a particularly optimized process sequence and therefore in a particularly preferred process according to the invention, without any intervening rinsing step or else

intermediate drying step takes place.

A "rinsing step" in the sense of the present invention denotes a process which is intended solely to remove as far as possible active components from an immediately preceding wet-chemical treatment step, which are dissolved in a wet film adhering to the component, by means of a rinsing solution from the surface of the component. without replacing the active components to be removed by others. Active components in this

Related are a liquid phase contained components that cause an analytically detectable occupancy of the metal surfaces of the component with elemental components of the active components.

A "drying step" in the context of the present invention refers to a process in which the surfaces of the metallic component having a wet film are to be dried with the aid of technical measures, for example supplying thermal energy or passing an air stream.

The modification of the metallic surfaces of the component produced in step (II) by bringing into contact with the composition (B) results in an occupancy with phosphates. In a preferred embodiment of the method according to the invention, an occupancy of phosphates is achieved on any of the metallic surfaces of the component, which to a

Layer weight of more than 1 g / m ² , particularly preferably less than 0.8 g / m ² , calculated as PO4 results (so-called "non-layer-forming phosphating"). However, a coating weight of at least 0.1 g / m ² , particularly preferably of at least 0.2 g / m ² , is preferably achieved on at least one of the metallic surfaces, in particular on a surface of an iron material. Insofar as the preferred non-layer-forming phosphating is turned off in the process according to the invention, activation of the metal surfaces is not necessary. In a preferred

Embodiment in which the low layer weights of phosphates of not more than 1 g / m ² are to be achieved, it is therefore preferred if between the method steps (I) and (II) directly - with or without intermediate rinsing step - follow one another. The coating weight of phosphates is determined according to the invention after detachment of the phosphate coating with aqueous 5 wt .-% CrÜ3 pickling solution at 25 ° C for 5 minutes and determination of the phosphorus content in the same pickling solution with plasma-coupled optical emission spectroscopy (ICP-OES). For higher coating weights, for example, the treatment temperature, the treatment time or the concentration of the phosphate ions or the accelerator can be increased.

The coating of the metallic surfaces of the component with phosphates produced in step (II) by contacting with the composition (B) is preferably obtained by means of compositions (B) which are substantially free of dissolved compounds of the element Ni, preferably substantially free of dissolved compounds of the elements Ni, Co and Cu, and more preferably substantially free of dissolved compounds of the elements Ni, Co, Cu and Mn. Essentially free of these heavy metals, compositions (B) in the context of the present invention are in each case when their total content is less than 100 ppm, preferably less than 10 ppm, based on the composition.

As in the composition (B) containing accelerator can in the inventive

Preferably, water-soluble organic or inorganic compounds are used whose standard reduction potential is greater than +0.2 V (SHE).

Suitable accelerators are preferably selected from organic or inorganic compounds containing at least one non-metal atom selected from nitrogen, phosphorus, oxygen, sulfur, chlorine and / or bromine in an oxidation state which does not correspond to the lowest possible of the respective element, or at least one oxoanion of an element of Subgroup VIB or VIIB of the periodic table. The oxidation state of an atom which is part of a compound is defined in the sense of the present invention as the hypothetical charge of the atom which would be present if only those bonding electrons were completely attributed to the atom shared with atoms having a lower electronegativity while bonding electrons shared with atoms of equal electronegativity would be attributed to the atom assuming homolytic bond separation, with general IUPAC oxidation state determination rules ("Oxidation State", IUPAC, Compendium of Chemical Terminology, Gold Book, Vol. Version 2.3.3, page 1049).

Preferred accelerators based on non-metal atoms selected from nitrogen, phosphorus, oxygen, sulfur, chlorine and / or bromine in an oxidation state which does not correspond to the lowest possible of the respective element are nitrates, chlorates, bromates, aromatic

Nitro compounds such as nitrobenzenesulfonic acid, in particular m-nitrobenzenesulfonic acid, nitroarginine, 5-nitro-2-furfurylidenedicarboxylic acid, N-methylmorpholine-N-oxide, hydroxylamine, nitroguanidine, hydrogen peroxide. Preferred accelerators based on the

Oxoanions of an element of subgroup VIB or VIIB of the Periodic Table are selected from molybdates, tungstates and / or manganates, more preferably from molybdates and / or tungstates. In order to bring about sufficient coverage with a thin phosphate coating, in particular on the surfaces of material which are predominantly composed of iron, it is advantageous to use compositions (B) which preferably total at least 0.1 mmol / kg, more preferably at least 0.2 in total mmol / kg, especially preferably a total of at least 0.4 mmol / kg of accelerators, but preferably not more than 5 mmol / kg total, more preferably not more than 2 mmol / kg total, most preferably not more than 1 mmol / kg total of accelerators.

In the process of the invention, the proportion of phosphates in the composition should provide sufficient coverage of at least the surfaces of the materials which are predominantly composed of iron. For this purpose it is preferred that the composition (B) contains at least 0.5 g / kg, more preferably at least 1 g / kg of phosphate ions.

Preferably, for a resource-saving mode of operation, which also prevents sludge formation in this wet chemical treatment stage following the first conversion treatment, it is preferred that the composition (B) not more than 10 g / kg, more preferably not more than 4 g / kg of phosphate ions contains.

Furthermore, it has proved to be advantageous for a homogeneous coating result if the composition (B) additionally complexing agent preferably selected from a-hydroxycarboxylic acids, preferably having at least 4 but not more than 8 carbon atoms, more preferably selected from citric acid, tartaric acid and / or gluconic acid and containing water-soluble salts.

A small amount of dissolved iron ions may be advantageous in the composition for a homogeneous non-film-forming phosphating which then contains a coating

Having iron phosphate. In a preferred embodiment of the process according to the invention, therefore, at least 10 mg / kg, but preferably not more than 100 mg / kg, very particularly preferably not more than 50 mg / kg of iron ions are contained in the composition (B). This is especially true for the treatment of metallic components, at least partially from a

Consist iron material.

A pH of the composition (B) of less than 6.0, more preferably preferably less than 5.2, is considered to be advantageous for a sufficient stain. The pickling effect of the composition (B) in the process according to the invention, however, must be coordinated with the preceding conversion treatment based on the elements Zr and / or Ti, so that the pH of the composition is preferably not less than 4.0, more preferably not less than 4, 4, and most preferably not less than 4.8, in order to minimize the corrosion of the conversion coating.

In this context, the total acid of the composition (B) also represents an important control parameter. It should preferably be at least 1 point, particularly preferably at least 3 points to provide a certain buffer capacity, but preferably not to over-stain the conversion-treated metallic surfaces of the component greater than 16 points, more preferably no greater than 9 points. The total acid content in points is determined in the context of the present invention by diluting 10 ml of the pickling solution to 50 ml and titrating with 0.1 N sodium hydroxide solution to a pH of 8.5. The consumption of milliliters of caustic soda indicates the score. Furthermore, it is advantageous for the integrity of the conversion coating based on the elements Zr and / or Ti that the proportion of water-soluble compounds which release fluoride ions is low. However, small amounts of such compounds, in particular complexed fluorides, tolerated, so that in a preferred embodiment of the invention

Method can be dispensed with a rinsing step immediately after the process step (I) and immediately before the process step (II). In a preferred embodiment of the

However, according to the invention, the proportion of free fluoride in the aqueous composition is less than 10 mg / kg, more preferably less than 5 mg / kg, most preferably less than 1 mg / kg. In a particularly preferred embodiment of the method is the

Total fluoride content in the composition (B) also less than 100 mg / kg, preferably less than 50 mg / kg, more preferably less than 10 mg / kg.

For a non-layer-forming phosphating in process step (II), the composition (B) should preferably be less than 1 g / kg, more preferably less than 0.5 g / kg, even more preferably less than 0.2 g / kg of zinc oxide. Contain ions.

The presence of organic polymeric components in the composition (B) can be tolerated to some extent, for example, for the complexation of metal ions. However, the presence of polymeric components usually complicates the bath care considerably and can prevent the formation of an amorphous phosphate layer or at least to the detriment of a substantially consisting of polymeric constituents coating move. It is therefore preferred according to the invention if the acidic aqueous composition (B) contains less than 1 g / kg, particularly preferably less than 0.2 g / kg, of organic polymers in total. Organic polymers in this sense have a molecular weight of at least 1000 g / mol determined by molecular weight distribution curves as measured by gel permeation chromatography (GPC) with RI detector after calibration by polystyrene standard after elution with tetrahydrofuran at a temperature of the eluate in the detector of 40 ° C ,

It is further preferred that the acidic aqueous composition (B) in method step (II) is "chromium-free".

Immediately after contacting the component with the acidic aqueous composition (B) in process step (II) - with or without intervening rinsing and / or drying step, preferably with rinsing step, but more preferably without drying step - is preferably carried out in the process according to the invention an at least partial coating of the areas of the component which have been previously brought into contact with the acidic aqueous composition (B), preferably based on an organic film-forming agent, more preferably a dip-coating, particularly preferably an electrodeposition coating. Particularly preferred is a cathodic electrodeposition coating, wherein the cathodic electrodeposition coating is preferably based on an aqueous dispersion of an amine-modified film-forming polyepoxide, which preferably additionally blocked and / or unblocked isocyanate group-containing organic compounds as a curing agent and optionally contains small amounts of dissolved in the aqueous phase compounds of the elements yttrium and / or bismuth.

EXAMPLES

To illustrate the teachings of the invention, cold-rolled steel sheets (ST 1405 Sidca®, ThyssenKrupp Steel AG) were subjected to a series of wet-chemical pretreatment steps and then provided with a cathodic electrodeposition paint (binder GV 85-0030, Pigment GV 86-0320, each BASF AG). The cathodic electrodeposition coating was carried out at a

Withdrawal voltage of 220 V for 5 minutes. The pretreatment steps included:

A1. Alkaline cleaning in spraying at 50 ° C for 60 seconds in a degreasing bath composed of equal parts of a 1 wt .-% Bonderite® C-AK 6443 and a 0.2 wt .-% Bonderite® C-AD 10004 (each Henkel AG & Co. KGaA)

A2. Conversion treatment at 23 ° C for 60 seconds (A2a) or 30 seconds (A2b) by spraying using an aqueous composition having a pH of 4.8 containing

16.2 g / kg hexafluorozirconic acid

- 32.0 g / kg magnesium nitrate hexahydrate

- 21, 0 g / kg sorbitol

- 9.9 g / kg hexylene glycol

A3. Phosphating at 50 ° C for 60 seconds by spraying with an aqueous

Containing composition with a pH of 4.8

- 3.26 g / kg phosphoric acid

- 0.26 g / kg of m-nitrobenzenesulfonic acid

0.1 1 g / kg of hydroxylamine sulfate

0.58 g / kg alkoxylated turpentine oil

- 0.20 g / kg ethoxylated-propoxylated C12 fatty alcohol

B1. Immersion sink with city water at 23 ° C for 60 seconds

B2. Nozzle with deionized water (k <1 pScnr ¹ ) at 23 ° C for 25 seconds

A pretreatment process sequence according to the invention (A2a-B1-B2-A3) comprising the cleansing conversion treatment A2 followed by the phosphating A3 with a

conventional process sequence (A1-B1-B2-A2b) comprising alkaline purification and Conversion treatment faced. The conventional pretreatment delivers in the

Dip coating a layer thickness of about 20 gm whereas in pretreatment according to the invention a dip coating thickness of 8 gm resulted in homogeneous coverage. Conventional phosphating according to process step A3 without prior conversion treatment requires a comparatively longer phosphating period to achieve similarly low layer thicknesses and causes a significantly higher load with phosphate sludges in the industrial implementation in series production.

Claims

claims

Anspruch [en] A process for the anticorrosive pretreatment of the metallic surfaces of a component which consists at least partly of a metallic material which is predominantly composed of one or more of the elements iron, zinc and / or aluminum, comprising the following successive process steps:

I) contacting the device with an acidic aqueous composition (A) containing at least one water-soluble compound of the elements Zr and / or Ti;

2. The method according to claim 1, characterized in that the composition (A) at least 0.05 mmol / kg, preferably at least 0.1 mmol / kg, more preferably at least 0.2 mmol / kg, but preferably not more than 1, 5 mmol / kg, more preferably not more than 1, 0 mmol / kg of water-soluble compounds of the elements Zr and / or Ti based on these elements.

3. The method according to one or more of the preceding claims, characterized in that the pH of the composition (A) is less than 5.8, preferably less than 5.2, but preferably not less than 3.9, more preferably not smaller than 4.2.

4. The method according to one or more of the preceding claims, characterized in that the composition (A) additionally contains a water-soluble source of fluoride ions in such an amount that the free fluoride content at least 1 mg / kg, preferably at least 10 mg / kg, but preferably not more than 100 mg / kg.

5. The method according to one or more of the preceding claims, characterized in that the composition (A) additionally contains an aliphatic compound having more than two hydroxyl groups, preferably more than three hydroxyl groups, wherein preferably at least two hydroxyl groups on not more than two carbon atoms are bonded together, most preferably an alditol having preferably not more than 6 carbon atoms.

6. The method according to claim 5, characterized in that the composition (A) additionally at least one aliphatic diol, preferably at least 4

Having carbon atoms, but more preferably not more than 10 carbon atoms.

7. The method according to one or more of the preceding claims, characterized in that the composition (B) contains at least 0.5 g / kg, preferably at least 1 g / kg of phosphate ions, but preferably not more than 10 g / kg, more preferably not more than 4 g / kg of phosphate ions.

8. The method according to one or more of the preceding claims, characterized in that the accelerator in the composition (B) is selected from at least one water-soluble organic or inorganic compound whose

Standard reduction potential is greater than +0.2 V (SHE).

9. The method according to one or more of the preceding claims, characterized in that the accelerator in the composition (B) is selected from organic or inorganic compounds containing at least one non-metal atom selected from nitrogen, phosphorus, oxygen, sulfur, chlorine and / or bromine in an oxidation state which does not correspond to the lowest possible of the respective element, or at least one oxoanion of an element of the subgroup VIB or VI IB of the Periodic Table

10. The method according to one or more of the preceding claims, characterized in that the composition (B) a total of at least 0.1 mmol / kg, preferably a total of at least 0.2 mmol / kg, more preferably at least 0.4 mmol / kg in total Accelerators, but preferably not more than 5 mmol / kg in total, more preferably not more than 2 mmol / kg total, most preferably not more than 1 mmol / kg total of accelerators.

11. The method according to one or more of the preceding claims, characterized in that the pH of the composition (B) is less than 6.0, preferably less than 5.2, but preferably not less than 4.0, more preferably not smaller is 4.4, and most preferably not less than 4.8.

12. The method according to one or more of the preceding claims, characterized in that the proportion of water-soluble compounds which release fluoride ions, in the composition (B) less than 10 mg / kg, preferably less than 5 mg / kg, particularly preferred less than 1 mg / kg and preferably the total fluoride content less than 100 mg / kg, more preferably less than 50 mg / kg, most preferably less than 10 mg / kg.

13. The method according to one or more of the preceding claims, characterized in that the proportion of zinc ions in the composition (B) is less than 1 g / kg, preferably none than 0.5 g / kg, more preferably less than 0, 2 g / kg.

14. The method according to one or more of the preceding claims, characterized in that the method step II) is carried out a coating based on an organic film former, preferably an electrodeposition coating, particularly preferably a cathodic electrodeposition coating.

15. The method according to one or more of the preceding claims, characterized in that the component consists at least partially of a ferrous material and preferably in composite construction with a material which is composed predominantly of one or both of the elements zinc and / or aluminum.