Composition for the anticorrosive pretreatment and cleaning of metal surfaces in one process step

Abstract

The present invention relates to a process for the anticorrosive pretreatment of the metal surfaces of components which at least partly also have surfaces of iron, wherein acidic aqueous compositions containing water-soluble compounds of both the element Zr and the element Si are used. The acidic aqueous composition used in the process can be given a cleaning effect by the addition of surface-active substances, so that metal surfaces soiled with oils and drawing greases likewise can be successfully anticorrosively pretreated in the process according to the invention in one process step. The present invention also comprises an acidic aqueous composition which is especially suitable such that components that are formed from flat products and that at least also have surfaces of iron can be cleaned and provided with an anticorrosion coating in one process step by means of said composition, said anticorrosion coating being easy to paint over.

Description

[0001] Composition for the corrosion-protective pretreatment and cleaning of metal surfaces in one process step

[0002] The present invention relates to a process for the corrosion-protective pretreatment of metallic surfaces of components which at least partially also have iron surfaces, wherein acidic aqueous compositions containing water-soluble compounds of both the elements Zr and Si are used. The acidic aqueous composition used in the process can be made cleaning by adding surface-active substances, so that even metal surfaces contaminated with oils and drawing greases can be successfully corrosion-protective pretreated in a single process step using the process according to the invention. Furthermore, the present invention comprises an acidic aqueous composition which is particularly suitable for cleaning components formed from flat products which at least also have iron surfaces in a single process step and for providing them with an easily paintable corrosion-protective coating.

[0003] A conversion coating is often applied to metal substrates, especially metallic components containing iron, zinc, and / or aluminum, prior to the application of a protective and / or decorative coating, such as a paint. The industrial coating of a large number of components requires serial pretreatment, in which each component undergoes various treatment steps in a predetermined sequence. Such serial pretreatment typically comprises the separate process steps of cleaning and pretreatment, and, if applicable, painting. Each process step is regularly followed by a rinsing step to remove active components from the previous process step.The step of wet-chemical cleaning of the components often has to be tailored depending on the substrate and the type of contamination. A variety of caustic alkaline or acidic cleaners as well as neutral cleaners are available to free the components from common contaminants such as anti-corrosive oils, cutting oils and cooling lubricants and to condition their metallic surfaces for the subsequent wet-chemical pretreatment.

[0004] Conversion treatments, which are now frequently carried out on an industrial scale and aim at providing temporary corrosion protection and a suitable paint base, provide the metal surfaces with amorphous inorganic coatings based on the elements Zr and / or Ti. Such conversion treatments, which for this purpose require wet-chemical layer thicknesses of 1-100 mg / m 2in relation to the aforementioned elements, have the advantage over conventional, partly crystalline conversion coatings based on phosphates of consuming fewer active components and thus being more resource-efficient and, in terms of plant technology, more efficient due to a smaller number of process steps and the ability to be formulated without phosphate.

[0005] Furthermore, the prior art also describes conversion treatment processes in which both the cleaning of the component and the conversion of the component's metal surfaces take place in a single process step. This type of process is highly advantageous in terms of plant and process engineering, as fewer system tanks need to be provided and fewer bath parameters need to be controlled. At the same time, fewer process chemicals are typically required to accomplish both the cleaning and the corrosion-protective treatment of the metal surfaces in one system tank. A further economic advantage is realized by the fact that at least one rinsing step can be omitted in an integrated process, thus reducing the amount of wastewater to be treated.

[0006] Accordingly, EP 3336219 A1 discloses such an integrated process in which the components are treated with an acidic aqueous composition containing, in addition to water-soluble compounds Zr and / or Ti, which induce a conversion of the metal surfaces and the formation of a passive layer, organic compounds selected from aliphatic diols and aliphatic saturated polyhydroxy compounds. Such compositions are well suited for use in combination with surface-active substances in integrated processes in a single process step. Furthermore, the use of these compositions enables a significantly reduced treatment temperature of below 40°C, which is of great advantage both in terms of the reduced energy requirements of such a pretreatment plant and for the suppression of flash rust on components that also have iron surfaces.

[0007] In contrast to this prior art, the present invention sets itself the task of further developing previously described processes so that an integrated procedure, i.e. cleaning and conversion layer formation in a single process step, is possible more reliably than before at application temperatures well below 40 °C. Furthermore, it is necessary that, in the integrated process, components with surfaces made of iron, zinc, and aluminum, i.e., those manufactured in a multi-metal construction, can be reliably provided with a homogeneous, easily recoatable conversion layer. The formation of flash rust on the surfaces of iron, which poses a problem for corrosive delamination after the paint layer has been applied, must be prevented. Therefore, high performance in terms of corrosion protection and recoatability of the conversion layer produced in the integrated process must be guaranteed.With regard to the assessment of recoatability, particular attention should be paid to electrocoating and the achievement of homogeneous, well-adhering coatings with uniform layer thickness and good wrap-around properties. Of particular interest is also the provision of a composition for cleaning and conversion layer formation that is capable of reliably removing surfaces contaminated with oils and greases from previous production steps at low application temperatures and simultaneously forming homogeneous, firmly adhering, and defect-free conversion layers on the surfaces of the metals zinc, iron, and aluminum, which are also excellently suited to electrocoating.

[0008] According to the invention, this range of tasks is met by a method in which, for the corrosion-protective pretreatment of the metallic surfaces of components which at least partially represent surfaces of the metal iron, the components are brought into contact with an acidic aqueous composition which contains a) at least 0.10 mmol / kg of water-soluble compounds of the element Zr, and b) an amount of water-soluble compounds of the element Si calculated as the amount of Si, which at the same time represent a source of free fluoride, and c) optionally at least one surface-active substance.

[0009] The components treated according to the present invention can be any spatial structure of any shape and design that originates from a manufacturing process, in particular also semi-finished products such as strips, sheets, rods, pipes, etc. and in particular also formed components with complex geometry from these semi-finished products, especially flat products, as well as composite structures assembled from the aforementioned semi-finished products, wherein the semi-finished products are usually connected to one another by gluing, welding and / or flanging to form the composite structure and can consist of different materials.

[0010] A metallic surface, within the meaning of the present invention, is any surface formed by a metallic material. Accordingly, a surface of the metal iron is formed by metallic materials that predominantly consist of the element iron. This is the case if the atomic proportion of the element iron in the respective material forming the metallic surface is greater than 50 at.%.

[0011] The process according to the invention produces firmly adhering and homogeneous inorganic conversion coatings consisting of oxides and hydroxides of the elements silicon and zirconium, which are resistant to flash rust formation on iron surfaces. The acidic aqueous composition is also suitable for forming satisfactory, i.e., readily paintable, conversion coatings on the surfaces of the metals iron and zinc, so that the process according to the invention is well suited for pretreating components consisting of a corresponding material mix to provide corrosion protection. In particular, the acidic aqueous composition can be adjusted to have a cleaning effect by adding surface-active substances, without any noticeable impairment in the formation of the conversion coatings.In fact, the use of nonionic surfactants can regularly result in an improvement in the coating's wrap-around behavior during subsequent electrocoating.

[0012] The process according to the invention is therefore outstandingly suitable for integrated cleaning and conversion treatment, which can be accomplished in a single process step and with just one system tank. From a process engineering perspective, a system tank is the container in which the acidic aqueous composition is stored for contacting with the surfaces of the component. In the process according to the invention, contacting can take place in the system tank, for example by immersion or spraying, or outside the system tank by discharging a volume portion of the acidic aqueous composition from the system tank and applying it to the surfaces of one or more components, usually by spray application. In the process according to the invention, contacting the components by immersion in a system tank storing the acidic aqueous composition is preferred.

[0013] It is advantageous for sufficient corrosion protection and paint adhesion and is therefore preferred if, in the process according to the invention, Zr coatings of a total of at least 0.05 mmol / m 2 , particularly preferably at least 0.10 mmol / m 2 with respect to these elements, especially on the surfaces of the metal iron. To achieve a preferred minimum coating thickness of 0.05 mmol / m 2 within treatment times customary in the process, i.e. contact times with the acidic aqueous composition in the range from 10 to 300 seconds, is advantageous and also preferred if the molar ratio of water-soluble compounds of the element Zr to water-soluble compounds of the element Si, based on the respective elements in the acidic aqueous composition, is greater than 0.5, particularly preferably greater than 1.0.

[0014] The person skilled in the art knows in principle that they can control the concentration of the active components inducing the conversion in the acidic aqueous composition to ensure that the minimum Zr layer thickness is achieved depending on the process conditions, i.e., the type of application, duration, and temperature. In the process according to the invention, sufficiently high layer weights can be reliably achieved under conventional process conditions if the acidic aqueous composition contains at least 0.10 mmol / kg, preferably at least 0.50 mmol / kg, more preferably at least 1.0 mmol / kg, but preferably not more than 10.0 mmol / kg, more preferably not more than 5.0 mmol / kg of water-soluble compounds of the element Zr.

[0015] Suitable water-soluble compounds of Zr, which are preferably contained in the acidic aqueous composition in the process according to the invention, are selected from compounds whose solubility at 30 °C in deionized water (K ​​< 1 pScrm 1 ) is at least 10 g / kg. Particularly effective for the formation of the conversion layer, and therefore preferred according to the invention, are ammonium zirconium carbonate and / or the fluoro acids of the element Zr and the respective water-soluble salts, particularly preferably hexafluorozirconic acid and its ammonium, alkali, and / or alkaline earth salts.

[0016] The presence of at least one water-soluble compound of the element silicon, which also represents a source of free fluoride, is essential for the conversion coating's ability to provide particularly effective protection against flash rust on the iron surfaces of components and, at the same time, to form homogeneous, corrosion-protective thin films on the surfaces of the metals zinc and aluminum. In a particular embodiment of the process according to the invention, the molar ratio of water-soluble compounds of the element Zr to water-soluble compounds of the element Si, based on the respective elements in the acidic aqueous composition, is therefore less than 5.0, particularly preferably less than 3.0, and especially preferably less than 2.0, to ensure a sufficient amount of silicon in the conversion coating.In the context of the present invention, a water-soluble compound of the element silicon is simultaneously a source of free fluoride if, in a 0.1 wt.% aqueous solution of the water-soluble compound at 30°C, a content of at least 5 mg / kg of free fluoride can be determined after adjustment to a pH of 4.0 using dilute solutions of sodium hydroxide or nitric acid. The proportion of free fluoride can be determined potentiometrically using an ion-selective glass electrode and after two-point calibration against suitable buffer solutions with a defined content of free fluoride. Preferably, the water-soluble compound of the element Si, which simultaneously represents a source of free fluoride, is selected from fluorocomplexes, particularly preferably from hexafluorosilicic acid and its ammonium, alkali, and / or alkaline earth salts.The amount of water-soluble compound of the element silicon, which also represents a source of free fluoride, is preferably at least 0.05 mmol / kg in total, particularly preferably at least 0.10 mmol / kg, but preferably not more than 10.0 mmol / kg calculated as the amount of Si.

[0017] The presence of free fluoride in the acidic aqueous composition increases the pickling attack on the metal surfaces and is necessary for sufficient conversion layer formation, especially in components with aluminum surfaces. Therefore, in the process according to the invention, it is advantageous and preferred for increased layer formation kinetics if the amount of free fluoride in the acidic aqueous composition is at least 5 mg / kg, more preferably at least 10 mg / kg, and most preferably at least 20 mg / kg, but preferably not more than 200 mg / kg, particularly preferably not more than 150 mg / kg, since otherwise the resulting conversion layer will partially corrode, resulting in less compact thin films that then provide less effective protection against flash rust formation. The free fluoride content is determined directly in the acidic aqueous composition at 30 °C.

[0018] As already discussed, a Zr layer thickness of at least 0.05 mmol / kg on the surfaces of the metals of the component after undergoing the process according to the invention is advantageous for sufficient corrosion protection and paint adhesion, for example, after electrocoating the components. On the other hand, it may be advantageous to limit the Zr layer thickness, since higher layer thicknesses are often only achievable through greater pickling removal and, with respect to the active components, more highly concentrated acidic aqueous compositions. The higher layer thickness is often no longer associated with an improvement in the corrosion-protective properties of the conversion layer and can even lead to a deterioration in corrosion protection if the increased layer thickness can only be achieved through the addition of larger amounts of free fluoride-releasing compounds.In the process according to the invention, it is therefore preferred if the total layer thickness of Zr does not exceed 1.00 mmol / m. 2 , especially preferably not 0.60 mmol / m 2 related to these elements, in particular this applies to the coating on the surfaces of the metal iron.

[0019] In a particular embodiment of the process according to the invention, the acidic aqueous composition can additionally contain magnesium and / or calcium ions. The presence of these cations has a positive effect on corrosion protection and contributes to reducing the tendency towards corrosive delamination of a subsequently applied paint system, particularly in the case where the components additionally have surfaces of the metal zinc. Furthermore, it is preferred in this context that the magnesium and / or calcium ions are present in such an amount that the molar ratio of water-soluble compounds of the element Zr to magnesium and / or calcium ions is less than 5.0, preferably less than 4.0, particularly preferably less than 3.0, to ensure a sufficient effect, but preferably greater than 0.5, particularly preferably greater than 1.0, in order not to negatively influence the kinetics of conversion layer formation.

[0020] The pH of the acidic aqueous composition is preferably less than 6.0, particularly preferably less than 5.5, in order to exert a sufficient pickling effect on the iron surfaces of the component, but preferably greater than 3.5, particularly preferably greater than 4.0, and most preferably greater than 4.5. The pH is the negative decimal logarithm of the hydronium ion activity and is determined within the scope of the invention using a calibrated pH-sensitive glass electrode directly in the acidic aqueous composition at 30°C.

[0021] For an integrated operation of the process according to the invention, in which both a cleaning of the surfaces of the components and a corrosion-protective pretreatment of at least the surfaces of the metal iron in the form of the conversion coating have to be carried out in one process step, the presence of surface-active substances is necessary, without which a sufficient to complete removal of contaminants adhering to the component surfaces from previous manufacturing steps would not be possible.The surface-active substances in the acidic aqueous composition of the process according to the invention can be selected from anionic surfactants, cationic surfactants, zwitterionic surfactants, and nonionic surfactants in the integrated process according to the invention. The use of nonionic surfactants is preferred, among other things, because of their good emulsifying properties at low application temperatures, but also because of their compatibility with the bath components of a subsequent electrocoating. Compatibility here refers to the absence of precipitation in the electrocoating bath.This compatibility of the surface-active substances with bath components of the electrocoating process must be taken into account, since the carryover of components from the system tank of the integrated cleaning and conversion treatment into the subsequent electrocoating process cannot be completely prevented, especially in the case of the corrosion-protective coating of highly absorbent components, even with one or more intermediate rinsing stages.

[0022] Surprisingly, it has also been found that non-ionic surfactants, as components of the integrated cleaning and conversion treatment, positively influence the coating's wraparound behavior. In this context, non-ionic surfactants are generally preferred whose HLB (hydrophilic-lipophilic balance) value is at least 8.0, more preferably at least 10.0, especially preferably at least 12.0, but particularly preferably not more than 18.0, especially preferably not more than 16.0.

[0023] The HLB value is used to quantitatively classify nonionic surfactants according to their internal molecular structure, whereby the nonionic surfactant is broken down into a lipophilic and a hydrophilic group. The HLB value according to the present invention is calculated using the following formula and can assume values ​​from zero to 20 on an arbitrary scale:

[0024] HLB = 20 (1-Mi / M) with Mi: Molar mass of the lypophilic group of the non-ionic surfactant M: Molar mass of the non-ionic surfactant

[0025] In terms of substance, nonionic surfactants selected from alkoxylated fatty alcohols, alkoxylated fatty amines, and / or alkyl polyglycosides, particularly preferably alkoxylated fatty alcohols and / or alkoxylated fatty amines, and especially preferably alkoxylated fatty alcohols, are preferred in the acidic aqueous composition of the process according to the invention to further improve the coverage of the dip coating. The alkoxylated fatty alcohols and / or alkoxylated fatty amines are preferably end-capped, particularly preferably with an alkyl group, which in turn preferably has no more than 8 carbon atoms, particularly preferably no more than 4 carbon atoms.

[0026] Particularly preferably, those alkoxylated fatty alcohols and / or alkoxylated fatty amines are contained as nonionic surfactants in the system tank of the integrated purification and conversion treatment which are present in ethoxylated and / or propoxylated form, wherein the number of alkylene oxide units is preferably not greater than 20 in total, particularly preferably not greater than 16, but particularly preferably at least 4, especially preferably at least 8.

[0027] With regard to the lipophilic component of the aforementioned nonionic surfactants, those alkoxylated fatty alcohols and / or alkoxylated fatty amines are preferred as nonionic surfactants in the acidic aqueous composition of the process according to the invention whose alkyl group is saturated and preferably unbranched, wherein the number of carbon atoms in the alkyl group is preferably at least 6, particularly preferably at least 8, especially preferably at least 10, but preferably not greater than 24, particularly preferably not greater than 20, especially preferably not greater than 16.

[0028] Overall, it can be seen that longer-chain nonionic surfactants are preferable for improving the throw-around behavior of a subsequent electrocoating, so that in a further preferred embodiment of the process according to the invention, preference is given to those alkoxylated fatty alcohols and / or alkoxylated fatty amines, in particular the alkoxylated fatty alcohols, whose lipophilic alkyl group comprises at least 10 carbon atoms, particularly preferably at least 12 carbon atoms, wherein the longest carbon chain in the alkyl group consists of at least 8 carbon atoms and an HLB value in the range from 12 to 16 is realized.

[0029] Preferred representatives of the alkoxylated fatty alcohols are selected as a component of the acidic aqueous composition in processes according to the invention, for example, from four- to eight-fold ethoxylated or propoxylated C6-C12 fatty alcohols, eight- to sixteen-fold ethoxylated C12-C18 fatty alcohols, six- to fourteen-fold propoxylated C12-C18 fatty alcohols, four- to eight-fold ethoxylated and propoxylated C12-C18 fatty alcohols, which in turn can be methyl-, butyl- or benzyl-end-capped.

[0030] The total amount of surface-active substances used, in particular nonionic surfactants, in the process according to the invention is preferably at least 1.0 g / kg, but preferably not more than 20.0 g / kg.

[0031] Furthermore, it has been found to be positive for the paint adhesion of subsequently applied organic coatings if so-called hydrotropic compounds are included in the integrated procedure of the process according to the invention, which then, in interaction with the surface-active substances, in particular the nonionic surfactants described above, provide a further improvement. Hydrotropic compounds are generally known to the person skilled in the art as solubilizing substances in surfactant mixtures and can accordingly also be added to the process according to the invention. With particular preference, the additized hydrotrope is selected from alkylsulfonic acids having at least 6 carbon atoms but not more than 10 carbon atoms in the aliphatic radical, benzenesulfonic acids, naphthalenesulfonic acids, alkylbenzenesulfonic acids having not more than 6 carbon atoms in the aliphatic radical, especially preferably from p-cumenesulfonic acid, and from their respective water-soluble salts.The total amount of hydrotopes selected from alkylsulfonic acids in the acidic aqueous composition is preferably at least 0.1 g / kg, more preferably at least 0.3 g / kg, most preferably at least 0.5 g / kg.

[0032] However, the presence of certain substances can also negatively impact the performance of the process according to the invention or should be avoided for environmental reasons. For example, additives that release phosphates should be avoided as a rule. Their introduction would necessitate more intensive wastewater treatment and also interfere with the composition of the conversion coating, which is undesirable. In a preferred embodiment of the process according to the invention, the acidic aqueous composition contains a total of less than 100 mg / kg, more preferably less than 10 mg / kg, and especially preferably less than 1 mg / kg of phosphates dissolved in water, calculated as PO4.

[0033] For similar reasons, the presence of organosilicon compounds is undesirable. In particular, hydrolyzable organosilanes, which in hydrolyzed form become part of the conversion coating, do not provide any significant advantages but increase the complexity of the process with regard to process control, particularly in integrated operation, which also aims to clean the components in the same process step as the conversion treatment. In a preferred embodiment of the process according to the invention, the acidic aqueous composition therefore contains a total of less than 100 mg / kg, more preferably less than 10 mg / kg, and especially preferably less than 1 mg / kg of organosilicon compounds, in particular organosilanes with at least one hydrolyzable radical, each calculated as the amount of Si.

[0034] The formation of mixed organic / inorganic conversion layers is also undesirable and not expedient, since the presence of polymeric organic compounds in the acidic aqueous composition, in turn, increases the complexity of the process according to the invention with regard to its process control, and no significant performance advantages are to be expected. In a preferred embodiment of the process according to the invention, the acidic aqueous composition therefore contains a total of less than 100 mg / kg, more preferably less than 10 mg / kg, and especially preferably less than 1 mg / kg of polymeric organic compounds. In the context of the present invention, an organic compound is considered polymeric if its molar mass is more than 1,000 g / mol.

[0035] With regard to the process engineering approach for implementing the method according to the invention, it should be noted that a large number of components can be treated in series in the method, whereby the components are either identical in construction or composed of an identical material mix, or each composed of different materials, but at least a large number of components with iron surfaces are included. The method according to the invention is characterized by the fact that excellent results are achieved on all surfaces of the component formed by the metals iron, zinc, and aluminum with regard to corrosion protection and adhesion to subsequently applied organic coatings, thus allowing for a high degree of flexibility with regard to the components to be pretreated for corrosion protection.In a preferred embodiment of the method according to the invention, a large number of components are brought into contact in series with the acidic aqueous composition, wherein preferably either each component in the series or all of the components in the series have, in addition to surfaces of the metal iron, also surfaces of the metals zinc and / or aluminum. Pretreatment in series occurs when the individual components in the series are pretreated one after the other, and thus separated in time, according to the method according to the invention and are brought into contact with the acidic aqueous composition stored in a corresponding system tank. The system tank is the container in which the acidic aqueous dispersion is kept in stock for the purpose of corrosion-protective pretreatment of at least the surfaces of the iron and optionally also for cleaning the components.As already discussed, the components can be brought into contact with the acidic aqueous composition inside the system tank, for example by immersion, or outside the system tank, for example by spraying or injecting the acidic aqueous composition stored in the system tank.

[0036] Typical process conditions, which are also preferred in the context of the present invention, are present when the contact time with the acidic aqueous composition is at least 10 seconds, preferably at least 20 seconds, but preferably less than 300 seconds.With regard to the application temperature, i.e. the temperature of the component and / or the acidic aqueous composition when they are brought into contact, it should be noted that the process according to the invention is characterized precisely by the fact that, even in an integrated procedure in which cleaning and conversion treatment are carried out in one process step with the contacting with the acidic aqueous composition, relatively low application temperatures are sufficient for both complete removal of oils and greases that were applied to the components for previous manufacturing steps for temporary protection against corrosion or as forming aids, as well as sufficient conversion of the metal surfaces.

[0037] Due to this property of the process according to the invention, it is sufficient, and therefore also preferred, if an application temperature of less than 40 °C, particularly preferably less than 35 °C and most preferably less than 30 °C is set.

[0038] At its core, the present invention relates to a process in which surfaces protected from corrosion are provided by cleaning and conversion treatment, which surfaces have an excellent paint adhesion base for subsequently applied organic paints and thus cured binder systems. In a particular embodiment of the process according to the invention, a process step for a subsequent paint application is therefore included and accordingly preferred if, after bringing the metallic surfaces of a component into contact with the acidic aqueous composition, the same surfaces are immediately subsequently, but with or without an intermediate rinsing and / or drying step, at least partially provided with an organic topcoat, which is preferably selected from a powder coating or a dip coating, preferably an electrocoat, very particularly preferably a cathodic electrocoat.

[0039] In a further aspect, the present invention relates to a composition for cleaning and conversion layer formation which is capable of reliably removing surfaces contaminated with oils and greases from previous production steps at low application temperatures and, at the same time, of forming homogeneous, firmly adhering and defect-free conversion layers on the surfaces of the metals zinc, iron and aluminum, which can also be excellently electrocoated.

[0040] Such an acidic aqueous composition according to the invention contains i) at least 0.10 mmol / kg, preferably at least 0.20 mmol / kg, but preferably less than 10 mmol / kg of water-soluble compounds of the element Zr, ii) at least 0.05 mmol / kg, but preferably less than 10 mmol / kg of water-soluble compounds of the element Si calculated as the amount of Si, which at the same time represent a source of free fluoride, iv) at least one nonionic surfactant, preferably in a total amount of at least 1.0 g / kg, and v) at least one hydrotrope selected from alkylsulfonic acids having at least 6 carbon atoms, but not more than 10 carbon atoms in the aliphatic radical, benzenesulfonic acids, naphthalenesulfonic acids, alkylbenzenesulfonic acids having not more than 6 carbon atoms in the aliphatic radical, preferably selected from p-cumenesulfonic acid, and from their respective water-soluble salts, preferably in a total amount of at least 0.1 g / kg calculated as SO3,wherein the molar ratio of water-soluble compounds of the element Zr to water-soluble compounds of the element Si, based on the respective elements, is less than 5.0, preferably less than 3.0, particularly preferably less than 2.0, but preferably greater than 0.5, particularly preferably greater than 1.0. A particularly preferred embodiment of the acidic aqueous composition according to the invention is when the molar ratio of water-soluble compounds of the element Zr to water-soluble compounds of the element Si, based on the respective elements, is greater than 1.0 and less than 3.0, preferably less than 2.0.Further embodiments of the acidic aqueous composition according to the invention concerning the selection of the components or further constituents of the composition arise directly and analogously from the previously described variants of the acidic aqueous composition in the context of the inventive process of the present invention.

[0041] In the context of the present invention, all quantities, unless stated otherwise in a specific individual case, refer to the entirety of the acidic, aqueous composition.

Claims

Claims:

1. A process for the corrosion-protective pretreatment of the metallic surfaces of components, wherein the surfaces of the component are at least partially formed by surfaces of the metal iron, by bringing the components into contact with an acidic aqueous composition containing a) at least 0.10 mmol / kg of water-soluble compounds of the element Zr, and b) an amount of water-soluble compounds of the element Si calculated as the amount of Si, which at the same time represent a source of free fluoride, and c) optionally at least one surface-active substance.

2. Process according to claim 1, characterized in that in the acidic aqueous composition the molar ratio of water-soluble compounds of the element Zr to water-soluble compounds of the element Si, based on the respective elements, is less than 5.0, preferably less than 3.0, particularly preferably less than 2.0, but preferably greater than 0.5, particularly preferably greater than 1.

0.

3. Process according to one or both of the preceding claims, characterized in that the acidic aqueous composition contains at least 0.20 mmol / kg, preferably at least 0.50 mmol / kg, particularly preferably at least 1.0 mmol / kg, but preferably not more than 10.0 mmol / kg, particularly preferably not more than 5.0 mmol / kg of water-soluble compounds of the element Zr.

4. Process according to one or both of the preceding claims, characterized in that the acidic aqueous composition contains water-soluble compounds of the element Zr, which are selected from ammonium zirconium carbonate and / or from fluoro acids and their water-soluble salts, particularly preferably from hexafluorozirconic acid and their ammonium, alkali and / or alkaline earth salts.

5. Process according to one or more of the preceding claims, characterized in that the water-soluble compounds of the element Si, which at the same time represent a source of free fluoride, are selected from Fluorocomplexes, particularly preferably hexafluorosilicic acid and their ammonium, alkali and / or alkaline earth salts.

6. Process according to one or more of the preceding claims, characterized in that the acidic aqueous composition additionally contains magnesium and / or calcium ions, preferably in an amount such that the molar ratio of water-soluble compounds of the element Zr to magnesium and / or calcium ions is less than 5.0, preferably less than 4.0, particularly preferably less than 3.0, but preferably greater than 0.5, particularly preferably greater than 1.

0.

7. Process according to one or more of the preceding claims, characterized in that the amount of free fluoride in the acidic aqueous composition is at least 5 mg / kg, preferably at least 10 mg / kg and particularly preferably at least 20 mg / kg, but preferably not more than 200 mg / kg, particularly preferably not more than 150 mg / kg.

8. Process according to one or more of the preceding claims, characterized in that the acidic aqueous composition contains at least one nonionic surfactant as surface-active substance, which preferably has an HLB value of more than 8.0 and in turn is preferably selected from fatty alcohol alkoxylates having at least 6 carbon atoms, preferably at least 8 carbon atoms, particularly preferably at least 10 carbon atoms in the aliphatic radical.

9. The method according to claim 8, characterized in that the acidic aqueous composition additionally contains a hydrotrope which is preferably selected from alkylsulfonic acids having at least 6 carbon atoms but not more than 10 carbon atoms in the aliphatic radical, benzenesulfonic acids, naphthalenesulfonic acids, alkylbenzenesulfonic acids having not more than 6 carbon atoms in the aliphatic radical, particularly preferably from p-cumenesulfonic acid, and from their respective water-soluble salts.

10. Process according to one or more of the preceding claims, characterized in that the pH of the acidic aqueous composition less than 6.0, preferably less than 5.5, but preferably greater than 3.5, more preferably greater than 4.0, most preferably greater than 4.

5.

11. Process according to one or more of the preceding claims, characterized in that the acidic aqueous composition contains a total of less than 100 mg / kg, preferably less than 10 mg / kg, particularly preferably less than 1 mg / kg of organosilanes having at least one hydrolyzable radical, in each case calculated as the amount of Si.

12. Process according to one or more of the preceding claims, characterized in that the acidic aqueous composition contains a total of less than 100 mg / kg, preferably less than 10 mg / kg, particularly preferably less than 1 mg / kg of phosphates dissolved in water, calculated as PO4.

13. Method according to one or more of the preceding claims, characterized in that a plurality of components are brought into contact in series with the acidic aqueous composition, wherein preferably either each component of the series or all of the components of the series also have surfaces of the metals zinc and / or aluminum in addition to surfaces of the metal iron.

14. Method according to one or more of the preceding claims, characterized in that after the metallic surfaces of a component are brought into contact with the acidic aqueous composition, the same surfaces are immediately subsequently, but with or without an intermediate rinsing and / or drying step, at least partially provided with an organic topcoat, which is preferably selected from a powder coating or a dip coating, preferably an electrocoat.

15. Acidic aqueous composition containing i) at least 0.10 mmol / kg, preferably at least 0.20 mmol / kg, but preferably less than 10 mmol / kg of water-soluble compounds of the element Zr, ii) at least 0.05 mmol / kg, but preferably less than 10 mmol / kg of water-soluble compounds of the element Si calculated as the amount of Si, which also represent a source of free fluoride, iv) at least one nonionic surfactant, preferably in a total amount of at least 1.0 g / kg, v) at least one hydrotrope selected from alkylsulfonic acids having at least 6 carbon atoms but not more than 10 carbon atoms in the aliphatic radical, benzenesulfonic acids, naphthalenesulfonic acids, alkylbenzenesulfonic acids having not more than 6 carbon atoms in the aliphatic radical, preferably selected from p-cumenesulfonic acid, and from their respective water-soluble salts, preferably in a total amount of at least 0.1 g / kg calculated as SO3, wherein the molar ratio of water-soluble compounds of the element Zr to water-soluble compounds of the element Si, based on the respective elements, is less than 5.0, preferably less than 3.0, particularly preferably less than 2.0, but preferably greater than 0.5, particularly preferably greater than 1.0.

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