EP3392375A1 - Method for sludge-free layer-forming zinc phosphatizing of metallic components in series - Google Patents

Abstract

The present invention relates to a process for the layer-forming zinc phosphating of components comprising surfaces of steel with high tolerance to dissolved in the zinc phosphating aluminum, in which the precipitation of sparingly soluble aluminum salts can be largely avoided. In the process, activation of the zinc surfaces by means of dispersions containing particulate hopeite, phosphophyllite, scholzite and / or hureaulite is resorted to, wherein the proportion of particulate phosphates must be adjusted in the activation of the amount of free fluoride and dissolved aluminum in the zinc phosphating.

Description

The present invention relates to a process for the layer-forming zinc phosphating of components comprising surfaces of steel with high tolerance to dissolved in the zinc phosphating aluminum, in which the precipitation of sparingly soluble aluminum salts can be largely avoided. In the process, activation of the zinc surfaces by means of dispersions containing particulate hopeite, phosphophyllite, scholzite and / or hureaulite is resorted to, wherein the proportion of particulate phosphates must be adjusted in the activation of the amount of free fluoride and dissolved aluminum in the zinc phosphating.

Zinc phosphating has been used for decades and has been excellently studied for the formation of crystalline anticorrosive coatings on metallic surfaces, in particular on materials of the metals iron, zinc and aluminum. The Zinkphosphatierung takes place in a layer thickness of a few micrometers and is based on a corrosive stain of the metallic material in an acidic aqueous composition containing zinc ions and phosphates, which precipitate as sparingly soluble crystallites in an alkaline diffusion layer directly to the metallic surface phase boundary and there on grow up. In support of the pickling reaction to metals of the metal aluminum and to mask the bad poison aluminum, which in dissolved form disturbs the layer formation on materials of the metal, water-soluble compounds are often added, which are a source of fluoride ions. The Zinkphosphatierung is always initiated with an activation of the metallic surfaces of the component to be phosphated. The wet-chemical activation is carried out conventionally by contacting with colloidal dispersions of phosphates, which in this respect immobilized on the metal surface, in the subsequent phosphating serve as a growth nucleus for the formation of a crystalline coating. Suitable dispersions are colloidal, mostly alkaline aqueous compositions Basis of phosphate crystallites, which have in their crystal structure only small crystallographic deviations from the nature of the deposited zinc phosphate layer. 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 layer-forming phosphating, as a process of activation and zinc phosphating, has its peculiarity, which is particularly important in the treatment of components composed of a mix of different metallic materials or in the treatment of novel materials. Thus, it is known that a homogeneous layer formation on the surfaces of the material iron in the presence of aluminum ions does not succeed and makes a masking with fluoride ions required. The masking of the aluminum ions, however, reaches its limits where high levels of aluminum enter the zinc phosphating bath and, in turn, equilibrium aluminum ions interfere with the formation of defect-free coatings on the steel surfaces. In the prior art, therefore, the aluminum dissolved in the zinc phosphating is at least partially removed from the zinc phosphating bath. Often, high levels of aluminum dissolved in water are also limited by the precipitation of cryolite or elpasolite in the presence of sodium and / or potassium ions. The cryolite or Elpasolith precipitation is technically complicated to control and requires on the one hand to avoid the formation of encrustations removal of the mud from the bath and on the other hand to avoid defects in the dip coating an intensive sink after Zinkphosphatierung to finest deposition of Kryolith- or Elpasolite crystallites are removed from the phosphated surfaces. The WO 2004/007799 A2 proposes, therefore, to carry out a phosphating at the lowest possible levels of sodium and / or potassium ions, so that a separate precipitation range for aluminum ions does not have to be provided, with dissolved aluminum contents above 0.1 g / L as not However, a preferred range of 0.01-0.4 g / L for dissolved aluminum for the Phosphating of at least partially made of aluminum components is specified.

In the present case, the object is to find suitable conditions for a process for zinc phosphating of metallic components which tolerates high proportions of dissolved aluminum, for which zinc phosphate coatings largely defect-free on the steel surfaces result, so that an overall excellent paint adhesion results. In particular, a method is to be provided in which metallic components in the phosphating can be treated layer-forming, the surfaces of which are formed both of metallic materials of the element iron and metallic materials of the element aluminum. Also, the care needs of Zinkphosphatierbades should be as low as possible and ideally be adjusted by pickling and pickling stationary equilibrium concentration in the treatment of a series of components unproblematic for the Phosphatiererfolg on the steel surfaces of the components. It is also desirable that the process, in spite of the high aluminum contents, is not prone to precipitate sparingly soluble aluminum salts, for example in the form of cryolite and / or elpasolite, since with such precipitation there are high procedural disadvantages due to sludge formation and often poorer corrosion protection after coating with a Dipping paint due to the finest inclusions of cryolite or elpasolite crystallite inclusions.

This object is surprisingly achieved in that the proportion of contributing to the activation of particulate phosphates on the amount of free fluoride and dissolved in water aluminum ions in the zinc phosphating is to be adjusted.

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,
   3. (c) mindestens 15 mmol/kg an Aluminium-Ionen in gelöster Form, und
   4. (d) mindestens eine Quelle für Fluorid-Ionen,

dadurch gekennzeichnet, dass die Konzentration der Phosphate in Form partikulären Phosphats in mmol/kg berechnet als PO₄ in der alkalischen wässrigen Dispersion größer ist als sieben Hundertstel des folgenden Terms in mmol/kg: $$\frac{{\left[\mathrm{Al}\right]}^{\mathrm{2}}}{\mathrm{3}\left[\mathrm{Al}\right]+\left[\mathrm{F}\right]\cdot \left(\mathrm{10}+{\mathrm{10}}^{\mathrm{3},\mathrm{12}-\mathrm{pH}}\right)}$$

[AI]:

Konzentration der Aluminium-Ionen in gelöster Form in mmol/kg

[F]:

Konzentration freies Fluorid in mmol/kg

pH:

pH-Wert der sauren wässrigen Zusammensetzung der Zinkphosphatierung

Accordingly, the present invention relates to a method for the anticorrosive treatment of a series of metallic components, the series comprising components which at least partially have surfaces of iron 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 their inorganic particulate constituent comprises phosphates, wherein the totality of these phosphates is at least partially composed of hopeite, phosphophyllite, scholzite and / or hureaulite;
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,
   3. (c) at least 15 mmol / kg of aluminum ions in dissolved form, and
   4. (d) at least one source of fluoride ions,

characterized in that the concentration of the phosphates in the form of particulate phosphate in mmol / kg calculated as PO ₄ in the alkaline aqueous dispersion is greater than seven hundredths of the following term in mmol / kg: $$\frac{{\left[\mathrm{al}\right]}^{\mathrm{2}}}{\mathrm{3}\left[\mathrm{al}\right]+\left[\mathrm{F}\right]\cdot \left(\mathrm{10}+{\mathrm{10}}^{\mathrm{3}.\mathrm{12}-\mathrm{pH}}\right)}$$

[AI]:

Concentration of aluminum ions in dissolved form in mmol / kg

[F]:

Concentration free fluoride in mmol / kg

pH:

pH of the acidic aqueous composition of zinc phosphating

The treated according to the present invention components can be any arbitrarily shaped and designed spatial structures, which 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 have at least partially surfaces of iron, preferably at least 5% with respect to the component surface surfaces of iron. 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.

An anti-corrosive treatment of the components in series is when a plurality of components is brought into contact with in the respective treatment steps provided and usually held in system tanks treatment solution, wherein the bringing into contact of the individual components sequentially and thus separated in time he follows. 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 which do not constitute rinsing steps. A rinsing step serves only the complete or partial Removal of soluble residues, particles and active components, which are adhered to the component from a previous wet-chemical treatment step, from the component to be treated, without the active component itself containing active components based on metallic or semi-metallic elements, which are already Contacting the metallic surfaces of the component with the flushing liquid consume. So the flushing liquid can only be city water.

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 potentiometrically determined at 20 ° C in the respective acidic aqueous composition of zinc phosphating.

The concentration of aluminum ion dissolved in the acidic aqueous zinc-phosphating composition 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) , Similarly, in the context of the present invention, the concentrations of other ions of metallic or semimetallic elements in the acidic aqueous composition of the zinc phosphating are to be determined in dissolved form.

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.

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.

[AI]:

Konzentration der Aluminium-Ionen in gelöster Form in mmol/kg

[F]:

Konzentration freies Fluorid in mmol/kg

pH:

pH-Wert der sauren wässrigen Zusammensetzung der Zinkphosphatierung

In the process according to the invention, the individual treatment steps of activation and zinc phosphating are coordinated in such a way that a homogeneous crystalline phosphate coating always results on the iron surfaces of the component without aluminum ions having to be removed from the zinc phosphating bath. In a preferred embodiment of the process according to the invention, the concentration of phosphates in the form of particulate phosphate is calculated in mmol / kg as PO ₄ in the alkaline aqueous dispersion is greater than 9 hundredths, more preferably 1 tenth, of the following term in mmol / kg: $$\frac{{\left[\mathrm{al}\right]}^{\mathrm{2}}}{\mathrm{3}\left[\mathrm{al}\right]+\left[\mathrm{F}\right]\cdot \left(\mathrm{1}+{\mathrm{10}}^{\mathrm{3}.\mathrm{12}-\mathrm{pH}}\right)}$$

[AI]:

Concentration of aluminum ions in dissolved form in mmol / kg

[F]:

Concentration free fluoride in mmol / kg

pH:

pH of the acidic aqueous composition of zinc phosphating

Good results in zinc phosphating can still be achieved if the concentration of aluminum dissolved in the acidic aqueous composition is significantly above 15 mmol / kg. High tolerances for the steady state aluminum content of a series treatment of a plurality of components make it possible to increase the proportion of aluminum surfaces to be treated with the series of components. In a preferred embodiment of the process according to the invention, the concentration of aluminum ions in dissolved form in the acidic aqueous composition of the zinc phosphating is therefore greater than 30 mmol / kg. Above 100 mmol / kg of dissolved aluminum ions, the amount of particulates containing phosphates necessary for sufficient activation of the iron surfaces is so high that the process becomes economically unattractive. It is therefore preferred according to the invention if the concentration of aluminum ions in dissolved form in the acidic aqueous composition of the zinc phosphating is less than 100 mmol / kg, particularly preferably less than 60 mmol / kg, and particularly preferably less than 45 mmol / kg.

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 .-% HN0 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 of the surfaces of iron is that the alkaline aqueous dispersion has a D50 value of less than 3 microns, since otherwise only very high and thus non-economic proportions of particulate components sufficient occupancy of the metal surfaces with particles, the crystallization nuclei for zinc phosphating, can be done. 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 of the 50% by volume of that in the alkaline aqueous composition do not exceed containing particulate ingredients. The volume-average particle diameter can be determined according to ISO 13320: 2009 by means of scattered light analysis according to the Mie theory of volume-weighted cumulative particle size distributions as so-called D50 value directly in the respective composition 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 iron surfaces of the component in the subsequent phosphating and in this sense activate the iron surfaces, are composed primarily of phosphates, which in turn are at least partially hopeite, phosphophyllite, scholzite and / or hureauxite 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) are detected.

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 is not intended to be achieved by means of colloidal solutions of titanium phosphates, since otherwise the layer-forming zinc phosphating on surfaces of iron, especially steel, does not succeed reliably and the advantage of thin effectively 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 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 iron 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 zinc. 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 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 comprises cations of the metals manganese, calcium, iron, magnesium and / or aluminum.

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 component, insofar as these are selected from surfaces of iron, aluminum and / or zinc. If all surfaces of these metallic materials are to be provided with a phosphate coating as constituents of the components which are treated in the series, then 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. For a closed and defect-free phosphate coating on the surfaces of iron, especially steel, is preferred in the process according to the invention if the amount of free fluoride in the acidic aqueous composition of the zinc phosphating is at least 0.5 mmol / kg. In addition, if surfaces of aluminum are to be provided with a closed phosphate coating within the series of components to be treated, 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. In general, it is advantageous for economic reasons if in the process according to the invention the concentration of free fluoride in the acidic aqueous composition of zinc phosphating is below 50 mmol / kg, more preferably below 40 mmol / kg, especially preferably below 30 mmol / kg. If, in addition, surfaces of zinc are to be provided with a closed phosphate coating within the series of components to be treated, it is preferred in the method according to the invention if the concentration of free fluoride does not exceed values above which the phosphate coatings have loose adhesions of phosphates which are easily wipeable because they can not be avoided even by increasing the amount of particulate phosphates in the alkaline aqueous dispersion of activation. Therefore, it is preferred for such devices that in the process of the present invention, the concentration of free fluoride in the acidic aqueous composition of 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 (κ <1μScm ^-1 ) at 60 ° C is at least 1 g / L calculated as F.

To avoid the precipitation of sparingly soluble aluminum salts, for example in the form of cryolite and / or elpasolite, the acidic aqueous composition of zinc phosphating contains only limited amounts of sodium and / or potassium ions. In a preferred embodiment of the method according to the invention therefore applies that the total concentration of sodium and / or potassium ions in dissolved form in mmol / kg less than the number 40, more preferably less than the number 30, particularly preferably less than the number 20 , divided by the third root of the concentration of aluminum ions in dissolved form.

As already mentioned, a further advantage of the method according to the invention consists in the fact that thin closed zinc phosphate coatings are also formed on surfaces of aluminum during its course. 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, therefore, within the series preferably also those components are treated which have surfaces of aluminum, wherein the components of the series preferably also have surfaces of aluminum in addition to the surfaces of iron.

A:

tatsächliche Ausschleppung aus dem Zinkphosphatierbad angegeben in Milliliter der sauren wässrigen Zusammensetzung pro Bauteil und pro Quadratmeter des Bauteils

The inventive method, in which, in addition to surfaces of iron, surfaces of aluminum are to be provided with phosphate coating within the series of components to be treated and each component of the series is the same composition, up to a predetermined by the actual removal from the Zinkphosphatierbad pickling rate Be operated economically, without that in the zinc phosphating dissolved aluminum ions would have to be removed from the bath. This pickling rate, which is dependent on the extraction from zinc phosphating, is based on the total surface area of each component: $$\mathrm{0}.\mathrm{27}\cdot \frac{\mathrm{A}}{\mathrm{100}}{\mathrm{mg}}^{-\mathrm{2}}$$

A:

actual carry-over from the zinc phosphating bath indicated in milliliters of the acidic aqueous composition per component and per square meter of the component

In the case of treating the series of components, insofar as the pickling rate is lower than the above pulp dependent value (equation 2), a steady state concentration of dissolved aluminum of not more than 100 mmol / kg in the acidic aqueous composition of the zinc phosphating is established ,

In the case where the pickling rate of aluminum exceeds the above zinc phosphating carry-over, it is advantageous to deplete and refresh aluminum ions in the zinc phosphating bath when the zinc phosphating continuously or intermittently extracts a partial volume of the acidic aqueous composition and the zinc phosphating continuously or discontinuously an equal partial volume is supplied by means of one or more such aqueous compositions, each based on the partial volume in comparison to the concentration of the corresponding ions in the withdrawn partial volume higher concentration with respect to the phosphate ions, zinc ions and / or the source of fluoride ions, but with respect to the aluminum ions in dissolved form have a lower concentration than in the withdrawn partial volume.

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

Aluminum (AA6014) and steel sheets (CRS) were treated in zinc phosphating baths with different levels of free fluoride and dissolved aluminum 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:
A1) Dipping and degreasing at 55 ° C for 180 seconds
15 g / L BONDERITE® C-AK 11566 (Henkel AG & Co. KGaA)
1.1 g / L BONDERITE® M-AD ZN-2 (from Henkel AG & Co. KGaA)
5 g / L BONDERITE C-AD 1561 (from Henkel AG & Co. KGaA)
2.2 g / L NaHCO ₃
Batch with demineralised water (κ <1 μScm ^-1 ); Adjust the pH to 10.8 with potassium hydroxide solution
A2) Cleaning and degreasing by spraying at 1 bar and 55 ° C for 70 seconds with a composition as in A1)
B) Rinse with demineralised water (κ <1μScm ^-1 ) at 20 ° C for 60 seconds
C) Dive activation at 20 ° C for 30 seconds 0,6-4 g / kg PREPALENE® X (Nihon Parkerizing Co., Ltd.) 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 Batch with demineralised water (κ <1 μScm ^-1 ); Adjust the pH with H ₃ PO ₄ to 10.3.
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 150 seconds 1.2 g / kg zinc 1.0 g / kg manganese 0.9 g / kg nickel 15.3 g / kg phosphate 1.9 g / kg nitrate 2.0 g / kg N-methylmorpholine-N-oxide 20 mg / kg hydrogen peroxide Addition of an amount of a source of fluoride and an amount of aluminum was made according to Table 1.
Batch with demineralised water (κ <1 μScm ^-1 ); Adjust the pH to pH 3.0 with 10% NaOH
Free acidity: 1.1-1.3 points
The free 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 3.6, the consumption of sodium hydroxide in milliliters corresponds to the amount of free acid in points.
The zinc phosphating baths were formulated without the addition of sodium salts. The proportion of sodium was less than 1 mg / kg.
E) Rinse with deionized water (κ <1 μScm ^-1 ) at 20 ° C for 60 seconds
F) Drying at 50 ° C in a drying oven after blowing off with compressed air

It can be seen from Table 1 that satisfactory phosphate coatings, which appear homogeneous and closed on the sheets to the naked eye, are obtained by adjusting the amount of particulate zinc phosphate in the activation to the amount of free fluoride and the amount of dissolved aluminum in the zinc phosphating (CRS-L-A1-h, CRS-H-A1-I, CRS-H-A2-I, CRS-H-A3-I). If the amount of particulate zinc phosphate in the activation falls below the value defined by the free fluoride amount and the dissolved aluminum concentration, then either no homogeneous coatings are obtained (CRS-L-A2-I, CRS-L-A3-h) or Phosphate coatings are nearly closed, but the substrate surface remains visible after phosphating (CRS-L-A1-I, CRS-L-A2-h). Even on aluminum, closed phosphate coatings are produced in the inventive variants of the process according to Table 1, so that the suitability of the method according to the invention for the corrosion-protective treatment of a series of components comprising components with surfaces of iron and surfaces of aluminum is demonstrated. Table 1 activation Zinc phosphating, pH: 3.0 Appearance Example ¹ PO ₄ / mmolkg ^-1 [F] * / mmolkg ^-1 [Al] ** / mmolkg ^-1 0.07 · Term ^# Coating weight / gm ^-2 0: closed homogeneous layer 1: almost closed, but shimmering substrate surface 2: no closed layer CRS-L-A1-I 0.63 4.9 29.7 0.62 1.5 1 CRS-L-A1-h 0.63 14.8 29.7 0.50 1.8 0 AA-L-A1-I 0.63 4.9 29.7 0.62 1.2 1 AA-L-A1-h 0.63 14.8 29.7 0.50 1.4 0 CRS-H-A1-I 3.57 4.9 29.7 0.62 1.8 0 AA-H-A1-I 3.57 4.9 29.7 0.62 1.5 0 CRS-L-A2-I 0.63 6.2 37.0 0.76 - 2 CRS-L-A2-h 0.63 18.5 37.0 0.62 1.5 1 AA-L-A2-I 0.63 6.2 37.0 0.76 - 2 AA-L-A2-h 0.63 18.5 37.0 0.62 1.2 1 CRS-H-A2-I 3.57 6.2 37.0 0.76 1.7 0 AA-H-A2-I 3.57 6.2 37.0 0.76 1.5 0 CRS-L-A3-h 0.72 27.5 55.6 0.94 - 2 AA-L-A3-h 0.72 27.5 55.6 0.94 - 2 CRS-H-A3-I 3.57 9.3 55.6 1.15 1.6 0 AA-H-A3-I 3.57 9.3 55.6 1.15 1.2 0 1 The first letters indicate the substrate; L (low) or H (high) the content of PO ₄ in the activation; A1 to A3, the increasing content of aluminum in the zinc phosphating; and the last letter I (low) or h (high) the content of free fluoride in the zinc phosphating * free fluoride measured with ion meter pMX 3000 / Ion (Xylem Inc.); Source: Ammonium bifluoride ** Source: aluminum trichloride # Term according to equation 1 (equation 1) in mmol / kg

Claims (15)

A process for the anticorrosive treatment of a series of metallic components, the series comprising components which at least partially have surfaces of iron, 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 / L of phosphate ions, (b) 0.3-3 g / l of zinc ions, (c) at least 15 mmol / kg of aluminum ions in dissolved form, and (d) at least one source of fluoride ions, characterized in that the concentration of the phosphates in the form of particulate phosphate in mmol / kg calculated as PO ₄ in the alkaline aqueous dispersion is greater than seven hundredths of the following term in mmol / kg: $$\frac{{\left[\mathrm{al}\right]}^{\mathrm{2}}}{\mathrm{3}\left[\mathrm{al}\right]+\left[\mathrm{F}\right]\cdot \left(\mathrm{1}+{\mathrm{10}}^{\mathrm{3}.\mathrm{12}-\mathrm{pH}}\right)}$$

[AI]: concentration of aluminum ions in dissolved form in mmol / kg [F]: concentration of free fluoride in mmol / kg pH: pH of the acidic aqueous composition of zinc phosphating 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 . 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 for the acidic aqueous composition of zinc phosphating is that the total concentration of sodium and / or potassium ions in dissolved form in mmol / kg less than the number 40, preferably less than the number 30, more preferably smaller than the number 20, divided by the third root of the concentration of aluminum ions in dissolved form. Method according to one or more of the preceding claims, characterized in that the concentration of aluminum ions in dissolved form in the acidic aqueous composition of zinc phosphating greater than 30 mmol / kg, but preferably less than 100 mmol / kg, more preferably less than 60 mmol / kg, more preferably less than 45 mmol / kg. Method according to one or more of the preceding claims, characterized in that the concentration of free fluoride is at least 2 mmol / kg, but preferably not greater than 50 mmol / kg, more preferably not greater than 40 mmol / kg, particularly preferably not greater than 30 mmol / kg. Method according to one or more of the preceding claims, characterized in that the pH in the acidic aqueous composition of zinc phosphating greater than 2.5, preferably greater than 2.7, but preferably less than 3.5, more preferably less than 3 , 3 is. 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 within the series also those components are treated which have surfaces of aluminum, wherein the components of the series preferably have surfaces of aluminum in addition to the surfaces of iron. A method according to claim 12, characterized in that each component of the series is the same composition and the pickling rate of aluminum based on the surface of each component in the zinc phosphating is not greater than: $$\mathrm{0}.\mathrm{27}\cdot \frac{\mathrm{A}}{\mathrm{100}}{\mathrm{mg}}^{-\mathrm{2}}$$

A: actual austenitization from the zinc phosphating indicated in milliliters of the acidic aqueous composition per component and per square meter of the component A method according to claim 12, characterized in that each component of the series is the same composition and the pickling rate of aluminum based on the surface of each component in the zinc phosphating is greater than: $$\mathrm{0}.\mathrm{27}\cdot \frac{\mathrm{A}}{\mathrm{100}}{\mathrm{mg}}^{-\mathrm{2}}$$

A: Actual extraction from zinc phosphating in milliliters of the acidic aqueous composition per component and per square meter of the component wherein the zinc phosphating continuously or discontinuously withdrawn a partial volume of the acidic aqueous composition and the zinc phosphating continuously or discontinuously an equal partial volume is supplied by means of one or more aqueous such compositions, each based on the partial volume compared to the concentration of the corresponding ions in the withdrawn partial volume higher concentration with respect to the phosphate ions, zinc ions and / or the source of fluoride ions, but with respect to the aluminum ions in dissolved form have a lower concentration than in the withdrawn partial volume. 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.