Sustainable reaction rinse in a method for producing organically coated metal surfaces

Abstract

The present invention relates to an at least two-stage method for the corrosion protection treatment of metal surfaces, wherein, in a first step (i), an organic coating made of an aqueous phase (A) is applied to the metal surface and, in a following step (ii), the organic coating applied to the metal surface is brought into contact with an acidic, aqueous composition (B) comprising at least one or more polyphosphoric acid esters of inositol and optionally at least one depolariser. The invention further comprises a metal component that is at least partially made of steel, iron, zinc and / or aluminium and the alloys thereof and was treated by the method according to the invention, and to the use thereof in automobile construction and in the construction industry and for producing household appliances and electronic housings.

Description

[0001] Sustainable reaction rinse in a process for providing organically coated metal surfaces

[0002] The present invention relates to an at least two-stage process for the corrosion-protective treatment of metal surfaces, in which, in a first step (i), an organic coating consisting of an aqueous phase (A) is applied to the metal surface, and in a subsequent step (ii), the organic coating applied to the metal surface is brought into contact with an acidic aqueous composition (B) containing at least one or more polyphosphoric acid esters of inositol and optionally at least one depolarizer. Furthermore, the present invention encompasses a metallic component which is at least partially made of steel, iron, zinc, and / or aluminum, as well as their alloys, and which has been treated in the process according to the invention, as well as the use thereof in automotive engineering and the construction sector, as well as for the manufacture of household appliances and electronic housings.

[0003] In the automotive industry, the corrosion-protective application of paint systems made from aqueous binder dispersions is state-of-the-art in bodywork production. The automotive industry primarily uses dip painting, in which the bodyshells, pretreated with corrosion protection, are continuously immersed in a dip tank containing a dispersed paint system. The paint is deposited either by applying an external voltage (electrodeposition) or self-deposited through mere contact with the metal surfaces (autophoretic dip painting). The bodyshell then undergoes a heat treatment to form a film and crosslink the paint system deposited on the metal surface, ensuring high levels of corrosion protection and allowing the subsequent application of additional coatings.

[0004] Autophoretic baths are used for the organic coating of metallic surfaces, mostly iron surfaces, as a corrosion-protective primer coating for metallic components or as an adhesive intermediate layer in the production of metal-elastomer compounds, for example, for vibration-damping components in the automotive industry. Autophoretic coating is a dip coating process that, unlike electrocoating, is carried out without the use of external current, i.e., without the application of an external voltage source. The self-depositing compositions are usually aqueous dispersions of organic resins or polymers that, upon contact with the metallic surface, coagulate in a thin liquid layer directly on the surface of the component due to the removal of metal cations by the pickling process, thus causing the coating to build up.

[0005] The use of autophoresis baths for dip coating has gained increasing importance in automotive manufacturing, especially in the piece production of metallic semi-finished products, such as the initial organic coating of tire rims. However, especially in dip coating using autophoretic or so-called self-depositing compounds, post-treatment is necessary to heal defects in the organic coating before a heat treatment that crosslinks the paint.

[0006] In order to improve the corrosion resistance of the organic coatings applied to the metal surface in autophoretic processes, the prior art proposes an aqueous reaction rinse following the initial organic coating with the dip paint.

[0007] According to DE 102007 059969, such a reaction rinse corresponds to a passivating post-treatment of the uncrosslinked coating and causes an inorganic conversion of free metal surface at so-called micro-defects, for example with the help of phosphate-containing solutions, which may also contain alkali and / or alkaline earth metal cations and also transition metal cations and their fluorocomplexes.

[0008] Accordingly, WO 02 / 42008 A1 discloses that water-soluble salts of metals of groups IIa and IIb, preferably zinc salts, are used for a reaction rinse, wherein soluble phosphates and so-called accelerators, which have an oxidative effect, are additionally to be contained in the reaction rinse.

[0009] Due to the problem of eutrophication of phosphate-contaminated waters, phosphate-containing process wastewater requires complex treatment. For environmental and economic reasons, it is therefore preferable to use compositions that can be provided largely phosphate-free. Such reaction rinses are known from US 2002 / 0076498 A1 and US 5,372,853. These are based on water-soluble calcium salts, primarily nitrates, or on fluorocomplexes of the element Zr. These reaction rinses also have the disadvantage of using compounds that are extracted from mined ores.

[0010] Based on this prior art, the object of the present invention is to establish a process for the reaction rinsing of freshly deposited, curable organic binder systems on metal surfaces, in which the reaction rinsing is essentially based on renewable raw materials and in particular the use of phosphoric acid and soluble phosphates can be dispensed with, without, however, having to accept losses with regard to the achieved corrosion resistance of the metal surface protected with the cured organic binder system.

[0011] The object is achieved by means of a multi-stage process for the corrosion-protective treatment of metal surfaces, in which in a first step (i) an organic coating consisting of an aqueous phase (A) is applied to the metal surface, wherein in a subsequent step (ii) the metal surface having the organic coating is brought into contact with an acidic aqueous composition (B) which contains at least one or more polyphosphoric acid esters of inositol.

[0012] The metal surface that is provided with an organic coating in a first step (i) can be a free metal surface that is freed from organic contaminants in a cleaning and / or pickling step preceding the process according to the invention. Such a free metal surface is characterized by being largely free of organic contaminants, for example anti-corrosive oils, and by having no or only an ultra-thin oxide covering layer on its surface, which consists mainly of metallic elements of the metal substrate and has a layer thickness of only a few nanometers. In any case, within the scope of the present invention, a metal surface is largely free of organic contaminants if, after cleaning and degreasing, the surface has a carbon coating of less than 0.10 g of carbon per square meter of said surface.The carbon layer thickness can be determined by pyrolytic decomposition. For this, the substrate is heated to a substrate temperature (PMT) of 550°C in an oxygen atmosphere, and the amount of released carbon dioxide is quantitatively measured as the amount of carbon using an infrared sensor, for example, the LECO® RC-412 Multiphase Carbon Determinator (Leco Corp.).

[0013] However, metal surfaces according to the invention can also be surfaces that have undergone a conversion treatment prior to process step (i) according to the invention, during which an inorganic cover layer was formed. Such inorganic conversion layers can consist of both metallic elements of the metal substrate and foreign metals. Typical conversion coatings are formed upon contact of free metal surfaces with acidic aqueous solutions containing water-soluble compounds of the elements Zr, Ti, Si, Hf, V, Ce, Mo, Zn, Mn, and Fe, and optionally additionally sparingly soluble salt-forming anions such as phosphates and / or complexing anions such as fluoride ions.During the conversion treatment, amorphous or crystalline inorganic covering layers are formed on the metal surface, whereby metal surfaces are still in accordance with the invention and can be used for the process according to the invention if the area-related layer weight of the inorganic covering layers does not exceed 3 g / m. 2 amounts.

[0014] An organic coating applied to the metal surface in the first process step (i) is in accordance with the invention if it contains a curable organic binder system. Process step (i) according to the invention comprises only the application of this organic coating, but not its curing by means of additional technical measures to crosslink the binder system. Such additional technical measures include, for example, heat treatment (thermal curing) or actinic irradiation (radiation curing) of an organic coating applied in step (i) that contains the curable binder system.However, process step (i) optionally comprises a heat treatment of the metal surface treated with the aqueous phase (A) to evaporate a portion of the water remaining in the wet film on the treated metal surface, although the heat treatment was carried out below the curing temperature of the organic binder system. The organic coating applied from the aqueous phase (A) therefore also contains a portion of water. Furthermore, the organic coating may contain leveling agents, surfactants, corrosion inhibitors, salts, pigments, and other active ingredients and auxiliaries known to those skilled in the art of coating technology. However, the solids content of the organic coating is at least 20 wt.%.An organic coating is understood to mean that part of a wet film of the aqueous phase (A) containing a curable organic binder system applied in step (i) which, after a rinsing step immediately following step (i), usually after three immersions in deionized water (K ​​< 1pScm. -1 ) remains on the metal surface as an adhering film containing the curable organic binder system upon subsequent complete immersion.

[0015] The deposition of the organic coating in step (i) of the process according to the invention takes place from an aqueous phase (A). However, the type of deposition is not tied to specific technical measures and can be carried out by electrocoating the metal surface or by electroless processes such as autophoretic deposition and mechanical application methods known in the art (roller application, spraying).

[0016] However, the process according to the invention shows the most significant improvement in the corrosion resistance of the metal surfaces treated in the process according to the invention, particularly when the organic coating is deposited in process step (i) from an aqueous phase (A) without external current. Accordingly, those processes according to the invention are preferred in which the organic coating is applied in the first step (i) without external current, in particular autophoretically, by contacting the metallic surface with an aqueous phase (A) containing the organic binder.

[0017] If the autophoretic deposition of the organic coating on the metal surface takes place in the first step (i) of the process according to the invention, the aqueous phase (A) preferably has a pH of less than 4 and preferably contains a) at least one dispersed organic binder system which is thermally curable, preferably at temperatures below 300 °C, preferably below 200 °C, b) iron(III) ions and c) fluoride ions in such a proportion that the molar ratio of fluoride ions to iron(III) ions from water-soluble compounds is at least 2:1.

[0018] For such an autophoretic deposition, the aqueous phase (A) in step (i) of the process according to the invention preferably contains at least 1 wt.% of the organic binder system.

[0019] Thermally curable organic binder systems are those binder systems that have curing temperatures above 20 °C and below the specified temperatures of 300 °C, preferably below 200 °C.

[0020] The curing temperature is the highest temperature that marks the maximum of an exothermic process in a dynamic differential scanning calorimetric analysis (DSC) of a solid mixture of the organic binder system used in a temperature range of 20 °C to 400 °C at a heating rate of 10 K / min. The calorimetric analysis of the exothermic heat released by the sample volume of the solid mixture and recorded by DSC is carried out in accordance with DIN 53 765, taking into account DIN EN ISO 11357-1. A solid mixture of the organic binder system used is accessible by vacuum freeze-drying an aqueous dispersion of the binder system. Alternatively, the aqueous dispersion of the binder system can be dried at room temperature in the sample crucible for the DSC measurement, and the initial weight of solid mixture in the sample crucible can be determined by differential weighing.The aqueous phase (A) is particularly suitable as an aqueous dispersion.

[0021] Thermally crosslinkable or curable organic binder systems according to component a) of the aqueous phase (A), which are applied to the metal surface in step (i) of a process preferred according to the invention without external current by autophoretic deposition, consist of organic oligomeric or polymeric compounds with at least two functional groups and are therefore capable of reacting with one another in condensation or addition reactions to form covalent bonds and thereby build up a network of covalently linked oligomeric or polymeric compounds. Thermally crosslinkable or curable binder systems can consist either of a self-crosslinking oligomeric or polymeric compound with two different or identical functional groups capable of reacting with one another, or of at least two different oligomeric or polymeric compounds that crosslink with one another due to their functionalization.

[0022] The water-dispersed organic binder system according to component a), which is applied to the metal surface without external current in step (i) of a preferred process according to the invention, contains at least one thermally self-crosslinking organic polymer and / or a mixture of at least one crosslinkable organic polymer or resin and an organic hardener that can react with the crosslinkable functionalities of the organic polymer or resin in an addition or condensation reaction. The organic hardener can also be an organic polymer or resin.

[0023] For sufficient film formation of the curable binder system on the metal surface, it is further preferred that the organic binder system dispersed in the aqueous phase (A) in step (i) of the process according to the invention has a film-forming temperature of not more than 80°C, particularly preferably not more than 40°C. If the film-forming temperature of the binder is above the preferred 80°C, an inhomogeneous organic coating of the metal surface during the reaction rinse with an acidic aqueous composition (B) in step (ii) of the process according to the invention can result, which cannot be cured even in the curing process that usually follows the process according to the invention. Such an inhomogeneous coating of the metal surface with the organic binder system has a detrimental effect on the corrosion resistance and the visual appearance of the coated metal surface.

[0024] Since the film formation of the organic binder system deposited on the metal surface in step (i) is already advantageous during the reaction rinse in step (ii), those processes according to the invention are preferred in which the acidic aqueous composition (B) is brought into contact with the metal surface having the organic coating in step (ii) at a temperature of at least 30 °C, particularly preferably at least 40 °C, but preferably not more than 80 °C.

[0025] The dispersed organic binder system used in step (i) of the process for electroless deposition preferred according to the invention preferably consists of at least one copolymer and / or polymer mixture of acrylates with at least one oligomeric and / or polymeric compound selected from epoxy resins, phenolic resins and / or polyurethane resins.

[0026] Water-dispersible epoxy resins, as a crosslinked coating on a metal surface, provide a particularly good barrier effect against corrosive media and are therefore a preferred component of the dispersed binder system in a process preferred according to the invention, in which the organic coating is applied in step (i) without external current, i.e. via a self-deposition process. If desired, crosslinking hardeners, preferably based at least partially on phenolic resins, can be used in addition to the epoxy resin in order to accelerate the curing process and increase the degree of crosslinking. Other hardeners that crosslink the epoxy resin are those based on isocyanate resins, whose isocyanate groups can also be blocked. Preferred blocked isocyanate resins are moderately reactive isocyanates, for example aliphatic isocyanates and sterically hindered and / or acid-stable blocked isocyanates.

[0027] Likewise, non-fully crosslinked, oligomeric, or polymeric compounds with free, for example terminally bonded, epoxy groups can be used as epoxy resins, with a preferred molecular weight of not less than 500 u and not greater than 5000 u. Examples of such epoxy resins are those based on bisphenol A and bisphenol F, as well as epoxy-phenol novalacs.

[0028] For reasons of economic efficiency and commercial availability, bisphenol A-based epoxy resins corresponding to the following general structural formula (III) are preferably used in the present invention:

[0029] The structural building block A corresponds to the following general formula (IV): with n as an integer from 1 to 50.

[0030] Preferred epoxides have an epoxy equivalent weight (EEW) of not less than 100 g / eq, but not more than 5000 g / eq. The EEW represents the average molecular weight per mole of epoxy functionality in the epoxy resin in grams per molar equivalent (g / eq). For specific epoxy resins, there are particularly preferred ranges for the epoxy equivalent weight: Brominated epoxy resins 300 - 1000 g / eq, in particular 350 - 600 Polyalkylene glycol epoxy resins 100 - 700 g / eq, in particular 250 - 400 Liquid epoxy resins 150 - 250 g / eq Solid / pasty epoxy resins 400 - 5000 g / eq, in particular 600 - 1000

[0031] Phenolic resins that can be present in the aqueous phase (A) in step (i) of the preferred process according to the invention for the electroless deposition of the organic coating are not fully crosslinked, oligomeric, or polymeric polycondensation products of formaldehydes with phenols, which preferably have at least partially etherified hydroxyl groups and whose preferred average molecular weight is not less than 500 u and not greater than 10,000 u. The hydroxyl groups are preferably methoxylated, ethoxylated, propoxylated, butoxylated, or ethenyloxylated.

[0032] Both resoles and novolaks can be used as phenolic resin types.

[0033] Further optional components of the aqueous phase (A) which, upon contact with metal surfaces, bring about an autophoretic deposition of an organic coating within the meaning of this invention are leveling agents, such as glycol ethers and alcohol esters, for better film formation of the deposited organic coating on the metallic surface, micronized inorganic fillers such as sulfates, oxides and phosphates with average particle sizes below 5 pm, preferably below 1 pm, for increasing the scratch resistance and corrosion resistance of the organic coating in the cured state, and pigments for coloring, for example carbon blacks or titanium dioxide.With regard to the composition (B) of the reaction rinse in step (ii) of the process according to the invention, it applies firstly that the polyphosphoric acid esters necessarily contained as an adequate phosphoric acid substitute each comprise both the acid form and the corresponding water-soluble salts of the polyphosphoric acid esters, in particular the sodium salts.

[0034] Due to its ready availability as a renewable raw material obtained from plants such as legumes, cereals, and oilseeds, it is preferred that the polyphosphoric acid esters of inositol comprise at least one polyphosphoric acid ester of myo-inositol, and particularly preferably at least one tri-, tetra-, penta-, and / or hexaphosphoric acid ester of myo-inositol. For particularly good results after the reaction rinse and due to its exceptionally good availability from corn steep liquor and rice hulls, phytic acid is particularly preferred as the polyphosphoric acid ester of inositol.

[0035] Accordingly, in step (ii) according to the invention those acidic aqueous compositions (B) are preferred in which the proportion of polyphosphoric acid esters of myo-inositol, preferably of tri-, tetra-, penta- and / or hexaphosphoric acid esters of myo-inositol, particularly preferably of phytic acid, in each case calculated as CeH^Oe and based on the total proportion of polyphosphoric acid esters of inositol is at least 40% by weight, particularly preferably at least 60% by weight and very particularly preferably at least 80% by weight.

[0036] With regard to the absolute amounts of polyphosphoric acid esters of inositol, it has been found that reliably good results are achieved in the reaction rinse with conventional treatment times if the acidic aqueous composition in step (ii) of the process according to the invention contains a total of at least 0.5 g / kg, preferably at least 1.0 g / kg, more preferably at least 2.0 g / kg, most preferably at least 5.0 g / kg, but preferably not more than 100.0 g / kg, more preferably not more than 50.0 g / kg, especially preferably not more than 30.0 g / kg and most preferably not more than 10.0 g / kg of polyphosphoric acid esters of inositol. If the proportion of polyphosphoric acid esters of inositol is significantly below 1.0 g / kg, the healing of defects in the organic coating deposited from the aqueous phase is often inadequate.In the preferred range, however, the property of the reaction rinse to improve the corrosion resistance of the metal surface provided with the cured organic binder system is comparable to reaction rinses based on phosphoric acid or fluorozirconic acid established in the state of the art.

[0037] The reaction rinse to be carried out in step (ii) of the process according to the invention by contacting the metal surface having the organic coating is preferably carried out at a pH of the acidic aqueous composition (B) of not less than 2.0, more preferably not less than 2.5, most preferably not less than 3.0, but preferably not greater than 6.0, more preferably not greater than 5.5, especially preferably not greater than 5.0, and most preferably not greater than 4.5. Depending on the organic binder system used, lower pH values ​​can chemically alter the organic coating and initiate decomposition reactions. In addition, increased acid corrosion of the metallic substrate and the formation of nascent hydrogen can cause lasting damage to the interface between the metal and the organic coating.

[0038] The acidic compositions used in step (ii) of the process according to the invention can additionally contain so-called depolarizers, which, due to their mild oxidizing effect, prevent the formation of nascent hydrogen on the free metal surface during the reaction rinse. The addition of such depolarizers, which are known in the technical field of phosphating metal surfaces, is therefore also preferred according to the invention. Typical representatives of depolarizers are chlorate ions, nitrite ions, hydroxylamine, hydrogen peroxide in free or bound form, nitrate ions, m-nitrobenzenesulfonate ions, m-nitrobenzoate ions, p-nitrophenol, N-methylmorpholine N-oxide, and nitroguanidine.It is advantageous for the reaction rinse if the proportion of depolarizers is preferably at least 1 g / kg, particularly preferably at least 2 g / kg, but preferably not more than 20 g / kg based on the acidic aqueous composition in process step (ii).

[0039] The presence of fluoride ions in the acidic aqueous composition (B) can have a detrimental effect on corrosion protection, so that the proportion of fluoride ions in the composition (B) preferably assumes values ​​for which the measured free fluoride content is less than 40 mg / kg, more preferably less than 20 mg / kg, especially preferably less than 10 mg / kg, and most preferably less than 1.0 mg / kg. The free fluoride content is determined potentiometrically in the acidic aqueous composition (B) at 20°C using fluoride-sensitive glass electrodes after calibration with suitable standard solutions.

[0040] For ecological reasons and to avoid inorganic sludges containing heavy metals, which require complex processing and disposal, the use of phosphoric acid and water-soluble phosphates is largely avoided in the acidic aqueous composition (B) of the reaction rinse in step (ii). Preferably, a composition (B) in the reaction rinse, i.e., in step (ii) of the process according to the invention, contains a total of less than 100 mg / kg, particularly preferably less than 10 mg / kg, and most preferably less than 1 mg, of phosphoric acid and soluble phosphates, calculated as PO4.

[0041] The present invention is also characterized by the fact that the presence of phosphoric acid and soluble phosphates in step (ii) of the process can be dispensed with and yet good corrosion resistance of the metal substrates treated according to the invention results.

[0042] Furthermore, the reaction rinse in process step (ii) is preferably substantially free of chromium-containing compounds, so that the acidic aqueous composition (B) contains a total of less than 10 mg / kg, particularly preferably less than 1 mg / kg of chromium-containing compounds calculated as Cr and very preferably no chromium-containing compounds at all or no such compounds are actively added to the composition (B).

[0043] In the process according to the invention, the aqueous phase (A) in step (i) and the acidic aqueous composition in step (ii) are preferably brought into contact with the metallic substrate or the metallic component by dipping or spraying, the dipping process being particularly preferred due to the more homogeneous wetting of the surface.

[0044] To avoid the introduction of constituents of the aqueous phase (A) from step (i) into the acidic aqueous composition (B), preferred processes according to the invention include a rinsing step between the first step (i) and the subsequent step (ii) to remove components of the aqueous phase (A) from the treated metal surface. This measure also increases the effectiveness of the reaction rinse with the acidic aqueous composition (B), since polymer particles adhering to the metal surface are not removed or are removed only insufficiently, allowing the acidic aqueous composition to act directly on firmly adhering organic coatings.

[0045] The contact times with the respective aqueous compositions are not critical for the process according to the invention, but should preferably be selected in step i) such that the layer weight of the uncured but firmly adhering organic coating applied in step (i) of the process according to the invention immediately before the reaction rinse with the acidic aqueous composition (B) in step (ii) is preferably at least 10 g / m 2 , particularly preferably at least 20 g / m 2 , but preferably not more than 80 g / m 2Experience has shown that lower layer weights lead to inhomogeneous coatings that impart lower corrosion resistance to the metal surface, while higher layer weights do not significantly improve the corrosion resistance of the coated metal substrate. The layer weight of the uncured but firmly adhering organic coating is determined after rinsing the metal substrate coated in step i) of the process according to the invention under running deionized water, with the rinsing being carried out until the rinse water flowing off the metal substrate is apparently clear. The contact times for the reaction rinse to be carried out in step (ii) of the process according to the invention with the acidic aqueous composition (B) are preferably 50-100% of the contact time with the aqueous phase (A) in step (i).

[0046] The organic coating applied to the metal surface in step (i) and post-treated in step (ii) is cured at elevated temperature, preferably with or without an intermediate rinsing step to remove components of the acidic aqueous composition (B) from the treated metal surface, in order to crosslink the polymeric coating as completely and sustainably as possible and thus increase corrosion resistance. The process of curing the organic coating is preferably carried out at temperatures above the curing temperature of the binder system dispersed in the aqueous phase (A) and below 300°C. The present invention also encompasses the metallic component produced by the process according to the invention, wherein the component is preferably made at least partially of steel, iron, zinc and / or aluminum and their alloys, preferably at least partially of iron and / or steel.

[0047] Such a component according to the invention is used in the automotive and construction sectors as well as for the manufacture of household appliances and electronic housings.

Claims

Patent claims 1. A process for the corrosion-protective treatment of metal surfaces, in which in a first step (i) an organic coating consisting of an aqueous phase (A) is applied to the metal surface, characterized in that in a subsequent step (ii) the metal surface having the organic coating is brought into contact with an acidic aqueous composition (B) which contains at least one or more polyphosphoric acid esters of inositol.

2. Method according to the preceding claim, characterized in that the application of the organic coating in the first step (i) is carried out without external current.

3. Process according to claim 2, characterized in that in the first step (i) the aqueous phase (A) has a pH of less than 4 and a) at least one dispersed organic binder system which is thermally curable, preferably at temperatures below 300 °C, preferably below 200 °C, b) iron(III) ions and c) fluoride ions in such a proportion that the molar ratio of fluoride ions to iron(III) ions from water-soluble compounds is at least 2:

1.

4. Process according to one or more of the preceding claims, characterized in that in the first step (i) the organic binder system dispersed in the aqueous phase (A) has a film formation temperature of not more than 80 °C, preferably not more than 40 °C.

5. Process according to one or more of the preceding claims, characterized in that the acidic aqueous composition (B) in step (ii) is brought into contact with the metal surface having the organic coating at a temperature of at least 30 °C, preferably at least 40 °C, but not more than 80 °C.

6. Process according to one or more of the preceding claims, characterized in that in step (ii) the acidic aqueous composition (B) containing one or more polyphosphoric acid esters of inositol comprises at least one polyphosphoric acid ester of myo-inositol, preferably at least one tri-, tetra-, penta- and / or hexaphosphoric acid ester of myo-inositol, particularly preferably phytic acid.

7. Process according to claim 6, characterised in that the proportion of polyphosphoric acid esters of myo-inositol, preferably of tri-, tetra-, penta- and / or hexaphosphoric acid esters of myo-inositol, particularly preferably of phytic acid, calculated as CeH^Oe and based on the total proportion of polyphosphoric acid esters of inositol is at least 40% by weight, particularly preferably at least 60% by weight and very particularly preferably at least 80% by weight.

8. The method according to one or more of the preceding claims, characterized in that the acidic aqueous composition (B) in step (ii) contains a total of at least 0.5 g / kg, preferably at least 1.0 g / kg, particularly preferably at least 2.0 g / kg, very particularly preferably at least 5.0 g / kg, but preferably not more than 100.0 g / kg, particularly preferably not more than 50.0 g / kg, especially preferably not more than 30.0 g / kg and very particularly preferably not more than 10.0 g / kg of polyphosphoric acid esters of inositol, in each case based on the acidic aqueous composition (B).

9. The method according to one or more of the preceding claims, characterized in that the acidic aqueous composition (B) in step (ii) additionally contains at least one depolarizer selected from chlorate ions, nitrite ions, hydroxylamine, hydrogen peroxide in free or bound form, nitrate ions, m-nitrobenzenesulfonate ions, m-nitrobenzoate ions, p-nitrophenol, N-methylmorpholine-N-oxide, nitroguanidine, preferably selected from hydroxylamine, wherein the proportion of depolarizers is preferably at least 1 g / kg, particularly preferably at least 2 g / kg, but preferably not more than 20 g / kg based on the acidic aqueous composition.

10. Process according to one or more of the preceding claims, characterized in that the pH of the acidic aqueous composition (B) in step (ii) is not less than 2, preferably not less than 2.5, more preferably not less than 3.0, but preferably not greater than 6, more preferably not greater than 5.5, especially preferably not greater than 5.0 and most preferably not greater than 4.

5.

11. Process according to one or more of the preceding claims, characterized in that between the first step (i) and step (ii) a rinsing step is carried out to remove components of the aqueous phase (A) from the treated metal surface.

12. Process according to one or more of the preceding claims, characterized in that the organic coating of the metal surface is cured at elevated temperature after process step (ii) with or without an intermediate rinsing step, preferably without an intermediate rinsing step, to remove components of the acidic aqueous composition (B) from the treated metal surface.

13. A metallic component, characterized in that it has been treated according to one or more of the preceding claims.

14. Metallic component according to claim 13, characterized in that the component is made at least partially of steel, iron, zinc and / or aluminum, preferably at least partially of steel.

15. Use of a component according to one or both of the preceding claims for the automotive and construction sectors as well as for the manufacture of household appliances and electronic housings.

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