EP3392376A1 - Method for forming zinc phosphate coatings on metallic components in series - Google Patents

Abstract

The present invention relates to a process for zinc phosphating components comprising zinc surfaces for suppressing the formation of insoluble phosphating components loosely adhering to the surfaces of zinc, and thus further improving the adhesion of post-applied dip coatings. In the process, activation of the zinc surfaces by means of dispersions containing particulate hopeite, phosphophyllite, scholzite and / or hureaulite is resorted to, the proportion of particulate phosphates having to be adjusted in the activation of the amount of free fluoride and dissolved silicon in the zinc phosphating.

Description

The present invention relates to a process for zinc phosphating components comprising zinc surfaces for suppressing the formation of insoluble phosphating components loosely adhering to the surfaces of zinc, and thus further improving the adhesion of post-applied dip coatings. In the process, activation of the zinc surfaces by means of dispersions containing particulate hopeite, phosphophyllite, scholzite and / or hureaulite is resorted to, the proportion of particulate phosphates having to be adjusted in the activation of the amount of free fluoride and dissolved silicon in the zinc phosphating.

In the prior art, the zinc phosphating is initiated with an activation of the metal surfaces of the component to be phosphated. The wet-chemical activation is carried out by contacting with colloidal dispersions of phosphates, which in this respect immobilized on the metal surface, serve in the subsequent phosphating as growth nuclei for the formation of a crystalline coating. Suitable dispersions are colloidal, mostly alkaline aqueous compositions based on phosphate crystallites, which have only small crystallographic deviations in their crystal structure from the type of zinc phosphate layer to be deposited. In addition to the titanium phosphate commonly referred to in the literature as Jernstedt salt, water-insoluble bi-and trivalent phosphates are also suitable as starting materials for providing a colloidal solution suitable for activating a metal surface for zinc phosphating. That's how it teaches WO 98/39498 A1 in this context, in particular bi- and trivalent phosphates of the metals Zn, Fe, Mn, Ni, Co, Ca and Al, wherein technically preferred phosphates of the metal zinc are used for activation for a subsequent zinc phosphating.

Each type of activation has its peculiarity with respect to the phosphating to be carried out in the subsequent step, which becomes particularly significant in the treatment of components composed of a mix of different metallic materials. Closed crystalline zinc phosphate coatings can no longer be formed on steel surfaces of components activated with Jernstedt salts if, in the zinc phosphating bath, the proportion of dissolved aluminum exceeds a certain threshold value, for example in the case of components having a high aluminum content WO 98/39498 A1 must be avoided. Such activation also provides the advantage of being compared For activation with Jernstedt salts thinner and more corrosion-resistant phosphate coatings on the aluminum surfaces can be achieved. Activation with bi- and trivalent phosphates, however, in zinc phosphating baths, where also layer-forming surfaces of aluminum are to be treated, often gives rise to defective coatings on the zinc surfaces, characterized by loose adhesions of components of the zinc phosphate coating observable in the following Dipcoating significantly reduce the paint adhesion on the zinc surfaces. In addition, the loose adhesions consisting of phosphates are partly passed through into a dip coating following the zinc phosphatization, where they are in turn partly dissolved in the aqueous binder dispersion. The introduced by Überschleppung in the dip coating dissolved phosphates can adversely affect the Abscheidecharakteristik the dispersed paint components on the one hand and on the other reduce the effective concentration of essential catalysts / crosslinkers based on selected heavy metals by precipitation reactions. A transfer of phosphates can thus be the cause of increased baking temperatures, in particular for dipping paints, which contain in addition to the dispersed resin water-soluble salts of yttrium and / or bismuth.

It is therefore the object, for a method for zinc phosphating of metallic components, which also tolerates high levels of dissolved aluminum, and therefore based on an activation based on a colloidal solution of bi- and / or trivalent phosphates, to find suitable conditions for the succeed on the zinc surfaces largely defect-free, freed of loose adhesions zinc phosphate coatings, so that overall results in excellent paint adhesion. In particular, a method is to be provided in which metallic components in the phosphating can be treated layer-forming, wherein the components have both surfaces of zinc and surfaces of aluminum and preferably steel.

This object is surprisingly achieved in that the proportion of contributing to the activation of particulate phosphates is adjusted to the amount of free fluoride and silicon in the zinc phosphating.

1. (I) Aktivierung durch In-Kontakt-Bringen mit einer alkalischen wässrigen Dispersion, die einen D50 Wert von weniger als 3 µm aufweist und deren anorganischer partikulärer Bestandteil Phosphate umfasst, wobei die Gesamtheit dieser Phosphate zumindest teilweise aus Hopeit, Phosphophyllit, Scholzit und/oder Hureaulith zusammengesetzt ist;
2. (II) Zinkphosphatierung durch In-Kontakt-Bringen mit einer sauren wässrigen Zusammensetzung enthaltend
   1. (a) 5-50 g/l an Phosphat-Ionen,
   2. (b) 0,3-3 g/l an Zink-Ionen, und
   3. (c) mindestens eine Quelle für freies Fluorid,

wobei der Quotient aus der Konzentration der Phosphate im anorganischen partikulären Bestandteil der alkalischen wässrigen Dispersion der Aktivierung in mmol/kg bezogen auf PO₄ zur Summe aus der Konzentration an freiem Fluorid und der Konzentration an Silizium jeweils in der sauren wässrigen Zusammensetzung der Zinkphosphatierung und jeweils in mmol/kg größer als 0,5 ist.The present invention thus relates to a method for corrosion-protective treatment of a series of metallic components which comprises metallic components which at least partially have surfaces of zinc, in which the metallic components of the series successively undergo the following wet-chemical treatment steps:

1. (I) Activation by contacting with an alkaline aqueous dispersion having a D50 value of less than 3 microns and whose inorganic particulate constituent comprises phosphates, the entirety of these phosphates being composed at least in part of hopeite, phosphophyllite, scholzite and / or Hureaulith is composed;
2. (II) containing zinc phosphating by contacting with an acidic aqueous composition
   1. (a) 5-50 g / L of phosphate ions,
   2. (b) 0.3-3 g / L of zinc ions, and
   3. (c) at least one source of free fluoride,

wherein the quotient of the concentration of the phosphates in the inorganic particulate component of the alkaline aqueous dispersion of the activation in mmol / kg based on PO ₄ to the sum of the free fluoride concentration and the concentration of silicon respectively in the acidic aqueous composition of the zinc phosphating and in mmol / kg is greater than 0.5.

The treated according to the present invention components can be any arbitrarily shaped and designed spatial structures that originate from a fabrication process, in particular also semi-finished products such as strips, sheets, rods, tubes, etc. and composite structures assembled from the aforementioned semi-finished products, wherein the semi-finished products preferably by gluing, welding and / or flanging to the composite structure are connected together. For the purposes of the present invention, a component is metallic if its geometric surface is formed by at least 10% of metallic surfaces.

When reference is made in the context of the present invention to the treatment of components with surfaces of zinc, iron or aluminum, so are all surfaces of metallic substrates or metallic coatings comprising the respective element to more than 50 at .-%. Thus, galvanized steel grades according to the invention form surfaces of zinc, whereas at the cutting edges and Durchschliffstellen example, an automobile body, which is made solely of galvanized steel, according to the invention surfaces of iron can be exposed. According to the invention, the components of the series which at least partially have surfaces of zinc, preferably at least 5%, based on the component surface surfaces of zinc. Steel grades such as hot-formed steel may also be provided with a metallic coating of aluminum and silicon several microns thick to prevent scaling and forming. Such a coated steel material, although the base material is steel, has an aluminum surface in the context of the present invention.

Corrosion-preventing treatment of the components in series occurs when a plurality of components are brought into contact with each other in the treatment solution provided in the respective treatment steps and usually stored in system tanks, wherein the contacting the individual components one after the other and thus separated in time takes place. The system tank is the container in which the pre-treatment solution is in series for the purpose of anti-corrosive treatment.

The treatment steps of activation and zinc phosphating are carried out for a component of the anticorrosive treatment in series then "successively", unless they are interrupted by any other than the respectively provided subsequent wet chemical treatment.

Wet-chemical treatment steps in the context of the present invention are treatment steps which take place by bringing the metallic component into contact with a composition consisting essentially of water and do not represent rinsing steps. A rinsing step is used exclusively for the complete or partial removal of soluble residues, particles and active components, which are abducted adhering to the component from a previous wet-chemical treatment step, of the component to be treated, without active components based on metallic or semi-metallic elements being contained in the rinsing liquid itself. which consume already by the mere bringing into contact of the metallic surfaces of the component with the rinsing liquid. So the flushing liquid can only be city water.

The "pH" as used in the present invention corresponds to the negative decadic logarithm of the hydronium ion activity at 20 ° C and can be determined by means of pH-sensitive glass electrodes. Accordingly, a composition is acidic if its pH is below 7, and alkaline if its pH is above 7.

In the process according to the invention, a coordination of the individual treatment steps of activation and zinc phosphating is implemented in such a way that closed coatings are formed on the zinc surfaces of the metallic components in the course of zinc phosphating, on which no finely divided constituents of the zinc phosphate coating are deposited. Accordingly, coatings are available in the subsequent dip coating, which adhere well to the zinc surfaces treated according to the invention. In a preferred embodiment of the method according to the invention, the quotient of the concentration of the phosphates contained in the inorganic particulate component of the alkaline aqueous dispersion of the activation in mmol / kg based on PO ₄ to the sum of the concentration of free fluoride and the concentration Silicon in each case in the acidic aqueous composition of zinc phosphating and in each case in mmol / kg greater than 0.6, particularly preferably greater than 0.7. The concentration of free fluoride in the acidic aqueous composition of zinc phosphating after calibration with fluoride-containing buffer solutions without pH buffering by means of a fluoride-sensitive measuring electrode potentiometric at 20 ° C in the respective acidic aqueous composition of zinc phosphating. The concentration of silicon in the acidic aqueous composition of the zinc phosphating is to be determined in the filtrate by membrane filtration of the acidic aqueous composition made using a membrane having a nominal pore size of 0.2 μm by atomic emission spectrometry (ICP-OES).

The particulate constituent of the alkaline aqueous dispersion is that solid fraction which, after drying the retentate, remains an ultrafiltration of a defined partial volume of the alkaline aqueous dispersion with a nominal cutoff limit of 10 kD (NMWC, Nominal Molecular Weight Cut Off). The ultrafiltration is carried out with the addition of deionized water (κ <1μScm ^-1 ) until a conductivity below 10 μScm ^{-1 is} measured in the filtrate. The inorganic particulate component of the alkaline aqueous dispersion is, in turn, the one remaining when the particulate component obtained from the drying of the ultrafiltration retentate remains in a reaction furnace at 900 ° C. with no CO ₂ -free oxygen flow, without admixture of catalysts or other additives is pyrolyzed until an infrared sensor in the outlet of the reaction furnace provides a signal identical to the CO ₂ -free carrier gas (blank). The phosphates contained in the inorganic particulate ingredient are determined after acid digestion thereof with aqueous 10 wt .-% HNO ₃ solution at 25 ° C for 15 min as phosphorus content by atomic emission spectrometry (ICP-OES) directly from the acid digestion.

Decisive for an activation is also that the alkaline aqueous dispersion has a D50 value of less than 3 microns, otherwise only a very high and thus non-economic proportions of particulate components sufficient occupancy of the metal surfaces with particles, the crystallization nuclei for zinc phosphating represent, can take place. In addition, dispersions whose particles are on average larger, tend to sedimentation.

In a preferred embodiment of the process according to the invention, the D50 value of the alkaline aqueous dispersion of the activation is therefore less than 2 .mu.m, more preferably less than 1 .mu.m, the D90 value being preferably less than 5 .mu.m, so that at least 90 vol. -% of the particulate components contained in the alkaline aqueous composition fall below this value.

The D50 value in this context refers to the volume-average particle diameter which does not exceed 50% by volume of the particulate constituents contained in the alkaline aqueous composition. The volume-average particle diameter can according to ISO 13320: 2009 by means of scattered light analysis according to the Mie theory of volume-weighted cumulative particle size distributions as a so-called D50 value directly in the respective Composition can be determined at 20 ° C, wherein spherical particles and a refractive index of the scattering particles of n _D = 1.52-i · 0.1 are assumed.

The active components of the alkaline dispersion, which effectively promote the formation of a closed zinc phosphate coating on the metal surfaces of the component in the subsequent phosphating and in this sense activate the metal surfaces, are composed predominantly of phosphates, which in turn are at least partially hopite, phosphophyllite, scholzite and / or hureaulite include. In this respect, such activation is preferred in which the phosphate fraction of the inorganic particulate constituents of the alkaline aqueous dispersion of the activation is calculated at at least 30% by weight, more preferably at least 35% by weight, particularly preferably at least 40% by weight PO ₄ and based on the inorganic particulate component of the dispersion.

Activation in the context of the present invention is thus essentially based on the phosphates according to the invention in particulate form, wherein the phosphates are preferably at least partially composed of hopeite, phosphophyllite and / or scholzite, particularly preferably hopeite and / or phosphophyllite and particularly preferably hopite are. The phosphites hopeite, phosphophyllite, scholzite and / or hureaulite may be dispersed into an aqueous solution to provide the alkaline aqueous dispersion as finely ground powders or as a powder paste triturated with a stabilizer. Hopeite, without consideration of water of crystallization, comprise stoichiometrically Zn ₃ (PO ₄ ) ₂ as well as the nickel- and manganese-containing variants Zn ₂ Mn (PO ₄ ) ₃ , Zn ₂ Ni (PO ₄ ) ₃ , whereas phosphophyllite comprises Zn ₂ Fe (PO ₄ ) ₃ , Scholzite consists of Zn ₂ Ca (PO ₄ ) ₃ and Hureaulith consists of Mn ₃ (PO ₄ ) ₂ . The existence of the crystalline phases hopeite, phosphophyllite, scholzite and / or hureaulite in the alkaline aqueous dispersion may, after separation of the particulate component by ultrafiltration with a nominal cutoff limit of 10 kD (NMWC) as described above and drying of the retentate to constant mass at 105 ° C using X-ray diffractometric methods (XRD).

Due to the preference for the presence of phosphates comprising zinc ions and having a certain crystallinity, preferred for the formation of firmly adherent crystalline zinc phosphate coatings are processes in which the alkaline aqueous dispersion of activation is at least 20% by weight, preferably at least 30% Wt .-%, particularly preferably at least 40 wt .-% of zinc in the inorganic particulate component of the alkaline aqueous dispersion based on the phosphate content of the inorganic particulate Bestanteils, calculated as PO ₄ contains.

However, activation in the sense of the present invention should not be achieved by means of colloidal solutions of titanium phosphates, as otherwise the layer-forming zinc phosphating Surfaces of iron, especially steel, not reliable succeeds and the advantage of thin effectively effective against corrosion protective phosphate coatings on aluminum is not realized. In a preferred embodiment of the method according to the invention, therefore, the proportion of titanium in the inorganic particulate component of the alkaline aqueous dispersion of the activation is preferably less than 5 wt .-%, more preferably less than 1 wt .-% based on the inorganic particulate component of the dispersion , In a particularly preferred embodiment, the alkaline aqueous dispersion of the activation contains a total of less than 10 mg / kg, more preferably less than 1 mg / kg of titanium.

For a sufficient activation of all metallic surfaces selected from zinc, aluminum and iron, the proportion of the inorganic particulate components comprising phosphates should be adjusted accordingly. For this purpose, it is generally preferred if, in the process according to the invention, the proportion of phosphates in the inorganic particulate constituent based on the alkaline aqueous dispersion of the activation is at least 40 mg / kg, preferably at least 80 mg / kg, more preferably at least 150 mg / kg calculated as PO ₄ is. For economic reasons and for reproducible coating results, the activation should be carried out with as dilute as possible colloidal solutions. It is therefore preferred that the proportion of the phosphates in the inorganic particulate constituent based on the alkaline aqueous dispersion of the activation is less than 0.8 g / kg, more preferably less than 0.6 g / kg, particularly preferably less than 0.4 g / kg calculated as PO ₄ .

For a good activation of components which have zinc surfaces, it is also advantageous if the metal surfaces are only slightly stained during activation. The same applies to activation on the surfaces of aluminum and iron. At the same time, the inorganic particulate constituents, in particular the insoluble phosphates, should undergo only a slight degree of corrosion. Accordingly, it is preferred in the process according to the invention if the pH of the alkaline aqueous dispersion in the activation is greater than 8, more preferably greater than 9, but preferably less than 12, more preferably less than 11.

The second zinc phosphating treatment step is followed by activation with or without intermediate rinsing step, immediately, so that each component of the series successively undergoes activation followed by zinc phosphating without intervening wet chemical treatment step. In a preferred embodiment of the method according to the invention, neither a rinsing nor a drying step takes place between the activation and the zinc phosphating for the components of the series. 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 by supplying thermal energy or passing an air stream.

1. (a) 5 - 50 g/kg, vorzugsweise 10-25 g/kg an Phosphat-Ionen,
2. (b) 0,3-3 g/kg, vorzugsweise 0,8-2 g/kg an Zink-Ionen, und
3. (c) mindestens eine Quelle für freies Fluorid

enthalten. In einer aus umwelthygienischen Gründen bevorzugten Ausführungsform sind insgesamt weniger als 10 ppm an Nickel- und/oder Kobalt-Ionen in der sauren wässrigen Zusammensetzung der Zinkphosphatierung enthalten.The zinc phosphating succeeds insofar as the tuning according to the invention has been carried out with the activation, as a rule with conventional phosphating baths

1. (a) 5-50 g / kg, preferably 10-25 g / kg of phosphate ions,
2. (b) 0.3-3 g / kg, preferably 0.8-2 g / kg of zinc ions, and
3. (c) at least one source of free fluoride

contain. In one preferred embodiment for environmental hygiene reasons, less than 10 ppm of nickel and / or cobalt ions are contained in total in the acidic aqueous composition of the zinc phosphating.

According to the invention, the amount of phosphate ions comprises the orthophosphoric acid and the anions of the salts of orthophosphoric acid dissolved in water, calculated as PO ₄ .

The preferred pH of the acidic aqueous composition of zinc phosphating in the process according to the invention is above 2.5, more preferably above 2.7, but preferably below 3.5, most preferably below 3.3. The proportion of the free acid in points in the acidic aqueous composition of the zinc phosphating is preferably at least 0.4, but preferably not more than 3, more preferably not more than 2. The proportion of free acid in points is determined by adding 10 ml sample volume of the diluted acidic aqueous composition to 50 ml and titrated with 0.1 N sodium hydroxide solution to a pH of 3.6. The consumption of ml of sodium hydroxide gives the score of free acid.

In a preferred embodiment of the process according to the invention, the acidic aqueous composition of the zinc phosphating additionally contains cations of the metals manganese, calcium and / or iron.

The customary addition of zinc phosphating can also be carried out in an analogous manner according to the invention so that the acidic aqueous composition can contain the conventional accelerators such as hydrogen peroxide, nitrite, hydroxylamine, nitroguanidine and / or N-methylmorpholine-N-oxide.

A source of free fluoride ions is essential for the process of layer-forming zinc phosphating on all metallic surfaces of the device selected from surfaces of zinc, iron and / or aluminum. If all surfaces of the metallic materials of the components to be treated in the series are to be provided with a phosphate coating, the amount of the particulate constituents in the activation must be adapted to the amount of free fluoride required for layer formation in the zinc phosphating. Should in addition to the zinc surfaces as well as the surfaces of iron, especially steel, with a closed and defect-free phosphate coating, it is preferred in the process according to the invention if the amount of free fluoride in the acidic aqueous composition is at least 0.5 mmol / kg. In addition, if surfaces of aluminum are to be provided with a closed phosphate coating, it is preferred in the process according to the invention if the amount of free fluoride in the acidic aqueous composition is at least 2 mmol / kg. The concentration of free fluoride should not exceed values above which the phosphate coatings predominantly have adhesions that are easily wipeable, since these can not be avoided by a disproportionately increased amount of particulate phosphates in the alkaline aqueous dispersion of the activation. Therefore, it is also advantageous for economic reasons, if in the process according to the invention the concentration of free fluoride in the acidic aqueous composition of the zinc phosphating is below 8 mmol / kg.

The amount of free fluoride is determined potentiometrically after calibration with fluoride-containing buffer solutions without pH buffering by means of a fluoride-sensitive measuring electrode at 20 ° C in the respective acidic aqueous composition. Suitable sources of free fluoride are hydrofluoric acid and its water-soluble salts, such as ammonium bifluoride and sodium fluoride, as well as complex fluorides of the elements Zr, Ti and / or Si, in particular complex fluorides of the element Si. In a preferred embodiment of the method according to the invention, the source of free fluoride is therefore selected from hydrofluoric acid and its water-soluble salts and / or complex fluorides of the elements Zr, Ti and / or Si. Salts of hydrofluoric acid are water-soluble for the purposes of the present invention, if their solubility in deionized water (<1μScm ^-1 ) at 60 ° C is at least 1 g / L calculated as F.

In order to suppress the so-called speck formation on the zinc surfaces of the component, it is preferred according to the invention if the source of free fluoride is at least partially selected from complex fluorides of the element Si, in particular from hexafluorosilicic acid and its salts. 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. In this context, preference is given to when the concentration of silicon dissolved in water in the acidic aqueous composition of zinc phosphating is at least 0.5 mmol / kg, particularly preferably at least 1 mmol / kg, but is preferably less than 6 mmol / kg preferably less than 5 mmol / kg, more preferably less than 4.5 mmol / kg. The upper limits for the concentration of silicon are preferred because above these values Promote phosphate coatings that have predominantly such loose attachments that can not be avoided by a disproportionately increased amount of particulate phosphates in the alkaline aqueous dispersion of the activation. The concentration of silicon in the acidic aqueous composition dissolved in water is determined in the filtrate by membrane filtration of the acidic aqueous composition made using a membrane having a nominal pore size of 0.2 μm by atomic emission spectrometry (ICP-OES).

Another advantage of the method according to the invention is that in the course of which closed zinc phosphate coatings are also formed on surfaces of aluminum. Consequently, the series of components to be treated in the method according to the invention preferably also includes the treatment of components which have at least one surface of aluminum. It is irrelevant whether the surfaces of zinc and aluminum are realized in a component composed of corresponding materials or in different components of the series.

In the method according to the invention, a good lacquer adhesion base for a subsequent dip coating, in the course of which a substantially organic cover layer is applied, is realized. Accordingly, in a preferred embodiment of the process according to the invention the zinc phosphating with or without intervening rinsing and / or drying step, but preferably with rinsing step, but without drying step, followed by a dip coating, more preferably an electrocoating, more preferably a cathodic electrocoating on.

EXAMPLES

• 0,5-3 g/kg enthält 8,4 Gew.-% an Zink in Form von Zn₃(PO₄)₂*4H₂O
• 200 mg/kg K₄P₂O₇ PREPALENE® X (Fa. Nihon Parkerizing Co., Ltd.)
• Ansatz mit VE-Wasser (κ<1µScm^-1); Einstellen des pH-Wertes mit H₃PO₄ auf 10,0. Der D50 Wert der Dispersion zur Aktivierung betrug 0,25 µm bei 20 °C bestimmt auf Basis der statischen Streulichtanalyse gemäß Mie-Theorie nach ISO 13320:2009 mittels Partikelanalysator HORIBA LA-950 (Fa. Horiba Ltd.) unter Annahme eines Brechungsindexes der streuenden Partikel von n = 1,52-i·0,1.

D) Zinkphosphatierung durch Eintauchen bei 50 °C für 180 Sekunden 1,1 g/kg Zink 1,0 g/kg Mangan 1,0 g/kg Nickel 15,7 g/kg Phosphat 2 g/kg Nitrat Die Zugabe einer Menge einer Quelle für Fluorid erfolgte gemäß Tabelle 1.
Ansatz mit VE-Wasser (κ<1µScm^-1); Einstellen der freien Säure mit 10 %iger NaOH Freie Säure:1,0 Punkt
Die freie Säure ist bestimmt aus 10 ml Probevolumen verdünnt auf 50 ml mit VE Wasser und anschließender Titration mit 0,1 N NaOH bis pH-Wert 3,6, wobei der Verbrauch an Natronlauge in Millilitern der Menge an freie Säure in Punkten entspricht.
Gesamtsäure: 20 Punkte
Die Gesamtsäure ist bestimmt aus 10 ml Probevolumen verdünnt auf 50 ml mit VE Wasser und anschließender Titration mit 0,1 N NaOH bis zum pH-Wert 8,5, wobei der Verbrauch an Natronlauge in Millilitern der Menge an Gesamtsäure in Punkten entspricht. Natriumnitrit:

• 2,0 Gaspunkte gemessen im Azotometer nach Zugabe von Amidosulfonsäure

E) Spüle mit entionisiertem Wasser (κ<1µScm^-1) bei 20°C für 60 Sekunden
F) Trocknen in Umgebungsluft
Anhand der Tabelle 1 wird ersichtlich, dass zufriedenstellende Phosphatüberzüge, die also auf dem verzinktem Stahl keine losen Anhaftungen aufweisen, durch Anpassung der Menge an partikulärem Zinkphosphat in der Aktivierung an die Menge des freien Fluorids und der Hexafluorokieselsäure in der Zinkphosphatierung erzielt werden können. Fällt die Menge an partikulärem Zinkphosphat in der Aktivierung unterhalb des durch die freie Fluoridmenge und der Konzentration an Silizium definierten Wertes, so entstehen zum Teil staubig erscheinende Überzüge (A1-Si-300, A3-Si-600 und A1-F-90), die gänzlich ungeeignet für eine nachfolgende Tauchlackierung sind. Tabelle 1 Aktivierung Zinkphosphatierung Molares Verhältnis Aussehen Beispiel* PO₄ / mmolkg^-1 Freies Fluorid^# / mmolkg^-1 Quelle Schichtgewicht / gm^-2 $$\frac{\left[{\mathrm{PO}}_{\mathrm{4}}\right]}{\left[\mathrm{F}\right]+\left[\mathrm{Si}\right]}$$

0: keine Anhaftung 1: kaum Anhaftungen 2: deutlich sichtbare Anhaftungen 3: staubige Beschichtung A1 0,45 0 - 3,1 - 0 A4 2,68 0 - 2,0 - 0 A1-Si-100 0,45 0,8 H₂SiF₆ 3,3 0,30 2 A2-Si-100 0,89 0,8 H₂SiF₆ 2,9 0,59 0 A2-Si-200 0,89 1,2 H₂SiF₆ 2,8 0,35 2 A3-Si-200 1,79 1,2 H₂SiF₆ 2,4 0,70 0 A1-Si-300 0,45 1,6 H₂SiF₆ 3,3 0,12 3 A3-Si-300 1,79 1,6 H₂SiF₆ 2,7 0,48 2 A4-Si-300 2,68 1,6 H₂SiF₆ 2,2 0,73 0 A3-Si-600 1,79 2,0 H₂SiF₆ 3,7 0,29 3 A4-Si-600 2,68 2,0 H₂SiF₆ 3,4 0,43 1 A1-F-90 0,45 1,6 (NH₄)HF₂ 3,5 0,29 3 A2-F-90 0,89 1,6 (NH₄)HF₂ 3,3 0,56 0 A2-F-180 0,89 3,2 (NH₄)HF₂ 3,4 0,28 2 A3-F-180 1,79 3,2 (NH₄)HF₂ 2,9 0,57 0 A2-F-300 0,89 4,7 (NH₄)HF₂ 3,6 0,19 2 A3-F-300 1,79 4,7 (NH₄)HF₂ 3,1 0,38 2 A4-F-300 2,68 4,7 (NH₄)HF₂ 2,8 0,57 0 A4-F-450 2,68 7.9 (NH₄)HF₂ 2,6 0,34 2 * die letzten Ziffern nach dem Bindestrich geben die Menge der Quelle für freies Fluorid in mg/kg an ^# gemessen mit Ionenmeter pMX 3000 / Ion (Fa. Xylem Inc.) ** in eckigen Klammer die Konzentrationen an partikulären Phosphaten in der Aktivierung sowie an freiem Fluorid und Silizium in der Zinkphosphatierung Galvanized steel sheets (HDG) were treated in zinc phosphating baths with different levels of free fluoride after previous activation with dispersions of particulate zinc phosphate and the appearance of the coatings evaluated immediately after zinc phosphating. Table 1 gives an overview of the activation and zinc phosphating compositions and the results of the evaluation of the quality of the coatings. The sheets went through the following steps in the order given:
A) Cleaning and degreasing in spraying at 60 ° C for 90 seconds
25 g / L BONDERITE® C-AK 1565 (from Henkel AG & Co. KGaA)
2 g / L BONDERITE® C-AD 1270 (Henkel AG & Co. KGaA)
Batch with demineralised water (κ <1 μScm ^-1 ); Adjust the pH to 11.8 with potassium hydroxide solution.
B) Rinse with demineralised water (κ <1μpScm ^-1 ) at 20 ° C for 60 seconds
C) Dive activation at 20 ° C for 60 seconds

• 0.5-3 g / kg contains 8.4% by weight of zinc in the form of Zn ₃ (PO ₄ ) ₂ .4H ₂ O.
• 200 mg / kg K ₄ P ₂ O ₇ PREPALENE® X (Nihon Parkerizing Co., Ltd.)
• Batch with demineralised water (κ <1 μScm ^-1 ); Adjust the pH with H ₃ PO ₄ to 10.0. The D50 value of the dispersion for activation was 0.25 μm at 20 ° C. determined on the basis of the static scattered light analysis according to Mie theory according to ISO 13320: 2009 by means of particle analyzer HORIBA LA-950 (Horiba Ltd.) assuming a refractive index of the scattering Particle of n = 1.52-i x 0.1.

D) Zinc phosphating by immersion at 50 ° C for 180 seconds 1.1 g / kg zinc 1.0 g / kg manganese 1.0 g / kg nickel 15.7 g / kg phosphate 2 g / kg nitrate The addition of an amount of a source of fluoride was according to Table 1.
Batch with demineralised water (κ <1 μScm ^-1 ); Adjust the free acid with 10% NaOH Free acid: 1.0 point
The free acid is determined from 10 ml sample volume diluted to 50 ml with demineralized water and subsequent titration with 0.1 N NaOH to pH 3.6, the consumption of sodium hydroxide in milliliters corresponds to the amount of free acid in points.
Total acidity: 20 points
The total acid is determined from 10 ml sample volume diluted to 50 ml with deionized water and subsequent titration with 0.1 N NaOH to pH 8.5, the consumption of sodium hydroxide in milliliters corresponds to the amount of total acid in points. Sodium nitrite:

• 2.0 gas points measured in the azotometer after addition of sulfamic acid

E) Rinse with deionized water (κ <1μScm ^-1 ) at 20 ° C for 60 seconds
F) drying in ambient air
It can be seen from Table 1 that satisfactory phosphate coatings, that are free of loose deposits on the galvanized steel, can be achieved by adjusting the amount of particulate zinc phosphate in the activation to the amount of free fluoride and hexafluorosilicic acid in the zinc phosphating. If the amount of particulate zinc phosphate in the activation falls below the value defined by the free fluoride amount and the concentration of silicon, partially dusty appearing coatings (A1-Si-300, A3-Si-600 and A1-F-90) are formed, which are completely unsuitable for a subsequent dip coating. Table 1 activation zinc phosphate Molar ratio Appearance Example* PO ₄ / mmolkg ^-1 Free fluoride ^# / mmolkg ^-1 source Coating weight / gm ^-2 $$\frac{\left[{\mathrm{PO}}_{\mathrm{4}}\right]}{\left[\mathrm{F}\right]+\left[\mathrm{Si}\right]}$$

0: no adhesion 1: hardly any attachments 2: clearly visible adhesions 3: dusty coating A1 0.45 0 - 3.1 - 0 A4 2.68 0 - 2.0 - 0 A1-Si-100 0.45 0.8 H ₂ SiF ₆ 3.3 0.30 2 A2-Si-100 0.89 0.8 H ₂ SiF ₆ 2.9 0.59 0 A2-Si-200 0.89 1.2 H ₂ SiF ₆ 2.8 0.35 2 A3-Si-200 1.79 1.2 H ₂ SiF ₆ 2.4 0.70 0 A1-Si-300 0.45 1.6 H ₂ SiF ₆ 3.3 0.12 3 A3-Si-300 1.79 1.6 H ₂ SiF ₆ 2.7 0.48 2 A4-Si 300 2.68 1.6 H ₂ SiF ₆ 2.2 0.73 0 A3-Si-600 1.79 2.0 H ₂ SiF ₆ 3.7 0.29 3 A4-Si-600 2.68 2.0 H ₂ SiF ₆ 3.4 0.43 1 A1-F-90 0.45 1.6 (NH ₄ ) HF ₂ 3.5 0.29 3 A2-F-90 0.89 1.6 (NH ₄ ) HF ₂ 3.3 0.56 0 A2-F-180 0.89 3.2 (NH ₄ ) HF ₂ 3.4 0.28 2 A3-F-180 1.79 3.2 (NH ₄ ) HF ₂ 2.9 0.57 0 A2-F-300 0.89 4.7 (NH ₄ ) HF ₂ 3.6 0.19 2 A3-F-300 1.79 4.7 (NH ₄ ) HF ₂ 3.1 0.38 2 A4-F-300 2.68 4.7 (NH ₄ ) HF ₂ 2.8 0.57 0 A4-F-450 2.68 7.9 (NH ₄ ) HF ₂ 2.6 0.34 2 * The last digits after the hyphen indicate the amount of free fluoride source in mg / kg ^# measured with ion meter pMX 3000 / Ion (Xylem Inc.) ** in square brackets the concentrations of particulate phosphates in the activation as well as on free fluoride and silicon in the zinc phosphating

Claims (13)

A method of anticorrosive treatment of a series of metallic components comprising metallic components having, at least in part, surfaces of zinc in which the metallic components of the series successively undergo the following wet chemical treatment steps: (I) Activation by contacting with an alkaline aqueous dispersion having a D50 value of less than 3 microns and whose inorganic particulate constituent comprises phosphates, the entirety of these phosphates being composed at least in part of hopeite, phosphophyllite, scholzite and / or Hureaulith is composed; (II) containing zinc phosphating by contacting with an acidic aqueous composition (a) 5-50 g / kg of phosphate ions, (b) 0.3-3 g / kg of zinc ions, and (c) at least one source of free fluoride, characterized in that the quotient of the concentration of the phosphates in the inorganic particulate component of the alkaline aqueous dispersion of the activation in mmol / kg to the sum of the concentration of free fluoride and the concentration of silicon in each case in the acidic aqueous composition of zinc phosphating and in each case in mmol / kg is greater than 0.5. A method according to claim 1, characterized in that the proportion of phosphates based on the inorganic particulate constituents of the alkaline aqueous dispersion at at least 30 wt .-%, more preferably at least 35 wt .-%, particularly preferably at least 40 wt .-% calculated as PO ₄ lies. Method according to one or both of the preceding claims, characterized in that the proportion of zinc in the inorganic particulate constituent of the alkaline aqueous dispersion in the activation at at least 20 wt .-%, preferably at least 30 wt .-%, particularly preferably at least 40th % By weight. Method according to one or more of the preceding claims, characterized in that the proportion of titanium in the inorganic particulate component of the alkaline aqueous dispersion in the activation is less than 5 wt .-%, more preferably less than 1 wt .-%, and particularly preferred less than 10 mg / kg of titanium are contained in the alkaline aqueous dispersion of the activation. Method according to one or more of the preceding claims, characterized in that the amount of the phosphates from the inorganic particulate component of the alkaline aqueous dispersion in the activation at least 40 mg / kg, preferably at least 80 mg / kg, particularly preferably at least 150 mg / kg calculated as PO ₄ and based on the dispersion. Method according to one or more of the preceding claims, characterized in that the pH of the alkaline aqueous dispersion in the activation is greater than 8, preferably greater than 9, but preferably less than 12, more preferably less than 11. Method according to one or more of the preceding claims, characterized in that as the source of free fluoride, complex fluorides of the element silicon are contained in the acidic aqueous composition of the zinc phosphating. A method according to claim 7, characterized in that the concentration of silicon dissolved in water at least 0.5 mmol / kg, preferably at least 1 mmol / kg, but is preferably less than 6 mmol / kg. Method according to one or more of the preceding claims, characterized in that the free acid in the acidic aqueous composition of zinc phosphating at least 0.4 points, but preferably not more than 3 points, more preferably not more than 2 points. Method according to one or more of the preceding claims, characterized in that the concentration of free fluoride in the acidic aqueous composition of zinc phosphating at least 0.5 mmol / kg, preferably at least 2 mmol / kg, but preferably less than 8 mmol / kg. Method according to one or more of the preceding claims, characterized in that neither a rinsing nor a drying step takes place between the activation and the zinc phosphating. Method according to one or more of the preceding claims, characterized in that in the series of components and components are treated, which have at least one surface of aluminum. Method according to one or more of the preceding claims, characterized in that the zinc phosphating with or without intermediate rinsing and / or Drying step, but preferably with rinsing step, but without drying step, followed by dip coating, preferably an electrocoating, more preferably a cathodic electrodeposition coating.