Method for cleaning and degreasing components comprising surfaces of zinc-magnesium hot-dip finished steel

Abstract

The present invention relates to a method for cleaning and degreasing a plurality of components comprising surfaces of zinc-magnesium hot-dip coated steel, in which the components are brought into contact with an alkaline, aqueous cleaner having a pH of at least 9.50, which contains a minimum amount of oxoanions of the elements B, C, N, P, S and Cl in their respective highest oxidation state, a minimum amount of bivalent metal cations of the elements Zn, Mg and / or Ca, and an organic complexing agent having at least one phosphonate group. The invention further relates to a method for cleaning and corrosion-protective surface treatment using the cleaning and degreasing method and to an alkaline, aqueous composition suitable for the cleaning and degreasing method.

Description

[0001] The present invention relates to a method for cleaning and degreasing a plurality of components comprising surfaces of zinc-magnesium hot-dip coated steel, in which the components are brought into contact with an alkaline, aqueous cleaner having a pH of at least 9.50, which contains a minimum amount of oxoanions of the elements B, C, N, P, S and Cl in their respective highest oxidation state, a minimum amount of bivalent metal cations of the elements Zn, Mg and / or Ca, and an organic complexing agent having at least one phosphonate group. The invention further relates to a method for cleaning and corrosion-protecting surface treatment using the method for cleaning and degreasing and to an alkaline, aqueous composition suitable for the method for cleaning and degreasing.

[0002] In automotive manufacturing, the use of magnesium-alloyed zinc coatings on steel is gaining importance due to the growing demand for lightweight car bodies. Compared to other hot-dip galvanizing processes, a zinc and magnesium coating can provide significantly increased corrosion protection and, particularly after coating with organic topcoats and dip coatings, outstanding resistance to corrosive delamination. This improved property profile allows coatings to be provided in thinner layers that still meet the high requirements for repaintability and corrosion protection.The good properties of magnesium alloyed zinc coatings in terms of corrosion behavior, especially in edge corrosion protection and paint adhesion on formed components, combined with excellent compatibility with all common joining processes and the previously mentioned weight savings, make hot-dip galvanized (ZM) sheet steel a material of particular importance for the production of lightweight car bodies, so that the surface area of ​​this material in the car body will continue to increase alongside the surface area of ​​other light metals such as aluminum in automotive production.

[0003] Magnesium-alloyed zinc coatings on steel are commonly used in automotive manufacturing as flat strip products and hot-dip galvanized (ZM) steel strip. This type of zinc-magnesium hot-dip coated steel contains approximately 1.5 to 8 wt.% of the metals aluminum and magnesium in the metallic coating, with the magnesium content being at least 0.2 wt.%.The basic suitability of these coatings to be formed, pretreated and coated using conventional and state-of-the-art processes is generally recognized and proven (Characteristic Properties 095 E, "Continuously Hot-Dip Coated Steel Strip and Sheet", Chapters 8 and 10, 2017 edition, German Steel Industry Association). However, due to the special composition of the coating and the native oxide layer, special features arise that must be taken into account, particularly during cleaning and pretreatment, to achieve the most homogeneous and reproducible coating result and thus optimal corrosion protection behavior or the desired surface functionality.For example, it is known from the prior art that during cleaning prior to corrosion-protective pretreatment of hot-dip galvanized (ZM) strip steel, a change in the oxide content of the alloying component magnesium may be necessary for sufficient adhesion to a subsequently applied coating. US 2016 / 0010216 A1 reports that the extensive removal of magnesium oxide in the near-surface oxide layer of hot-dip galvanized (ZM) strip steel can effectively suppress the appearance of blister-like elevations in the topcoat.

[0004] The prior art also documents that during the serial pretreatment of a large number of components with hot-dip galvanized (ZM) strip steel surfaces, wetting and thus reliable cleaning of the material surfaces can be problematic. WO 2023 / 036889 A1 therefore proposes conditioning the hot-dip galvanized (ZM) surfaces after degreasing but before a corrosion-protective pretreatment, which can be a conversion coating based on the elements Zr and / or Ti, in order to counteract the aging of conventional cleaning and degreasing baths associated with high component throughput and the resulting deterioration in the wettability of the hot-dip galvanized (ZM) surfaces.

[0005] Materials with zinc-magnesium coatings therefore require sophisticated process control in order to be successfully and, above all, reliably pretreated to provide corrosion protection, especially when a large number of components need to be coated to a high quality in an automated painting line. Further approaches are needed here that support simpler process control during corrosion protection pretreatment, comprising the stages of degreasing, conversion layer formation, and painting, and that contribute to the series treatment of a large number of components, ensuring that satisfactory results are achieved largely independently of bath aging, thus exploiting the full potential of zinc-magnesium hot-dip coated materials in terms of corrosion protection. The prior art approaches of intensive bath maintenance to ensure cleaning andKeeping degreasing baths as free of contamination as possible and replacing them with fresh bath solutions as early as possible is economically disadvantageous and problematic with regard to the desirable resource-saving use of process chemicals. At the same time, it has been repeatedly shown that the cleaning performance of a degreasing bath in the treatment of hot-dip galvanized (ZM) metal surfaces cannot be maintained to the desired level simply by increasing the degree of mechanical action, the temperature, the contact times, or the concentration of active components.

[0006] The present invention therefore has the object of establishing a process for the serial treatment of a large number of components which is suitable for reliably cleaning and pretreating zinc-magnesium hot-dip coated steel in a conventional process sequence and thus without additional wet-chemical treatment steps, whereby the cleaning of components exposed to forming and corrosion protection oils must be carried out largely independently of the oil load absorbed by the cleaner of the degreasing bath.Reliability is typically ensured when the zinc-magnesium hot-dip coated steel surfaces are fully water-wettable after cleaning. Only then can a satisfactory result be achieved in the subsequent corrosion-protective conversion treatment based on aqueous compositions without a deterioration in performance during (quasi-)continuous operation of a pretreatment line. The cleaning and, if necessary, degreasing process must be suitable for components with different metal surfaces, especially steel, zinc, aluminum, and magnesium surfaces, and must also be usable in conventional zinc phosphating systems as well as for conversion coatings based on the elements Zr and / or Ti.

[0007] Surprisingly, it has now been discovered that zinc-magnesium hot-dip coated steel surfaces can still be effectively cleaned even when the cleaning bath is heavily contaminated with industrial oils, provided the cleaning bath contains a minimum amount of oxoanions of the elements B, C, N, P, S, and Cl in their highest oxidation state, a minimum amount of bivalent metal cations of the elements Zn, Mg, and / or Ca, and an organic complexing agent containing at least one phosphonate group. A cleaning bath formulated or adjusted in this way is therefore capable of cleaning a wide variety of components contaminated with industrial oils without compromising the water wettability of the zinc-magnesium hot-dip coated steel surfaces.

[0008] Specifically, the present invention relates to a method for cleaning and degreasing a plurality of components in series, in which the components of the series at least partially have surfaces of zinc-magnesium hot-dip galvanized steel, and in which at least the zinc-magnesium hot-dip galvanized steel surfaces of the components of the series are each cleaned with an alkaline, aqueous cleaner with a pH value of at least 9.50 containing (a) a total of at least 30.0 mmol / kg of oxoanions of the elements B, C, N, P, S and CI in their highest oxidation state dissolved in the aqueous phase, where at least 10.0 mmol / kg of the oxoanions dissolved in the aqueous phase are phosphate ions, (b) a total of at least 6.0 mmol / kg of divalent metal cations of the elements Zn, Mg and / or Ca dissolved in the aqueous phase, where at least 2.0 mmol / kg of zinc ions dissolved in the aqueous phase are present, (c) at least one organic complexing agent having at least one phosphonate group, and (d) at least one surface-active substance, are brought into contact, wherein the molar ratio of organic complexing agents having at least one phosphonate group to the amount of zinc ions dissolved in the aqueous phase is less than 2.1.

[0009] Cleaning and degreasing within the meaning of the present invention serves to free the surfaces of the components, in particular the metal surfaces, from organic contaminants, in particular technical oils such as corrosion inhibitors and forming oils, in order to provide metal surfaces that are as completely wettable by water as possible, in particular completely wettable zinc-magnesium hot-dip coated steel surfaces. For this purpose, the components are brought into contact with the previously defined alkaline aqueous cleaner in the process according to the invention, which is usually provided for application in one or more so-called system tanks, i.e., stored there for contacting and kept ready for application, e.g., by immersing the components in a cleaning bath, which then forms the system tank.In process engineering terms, the part of a pretreatment line that serves for cleaning and degreasing and includes the system tanks that store the cleaner for application is referred to as the cleaning and degreasing stage. This stage is typically followed, and this is also the subject of the present invention, by further wet-chemical treatment steps and process steps for applying a corrosion-protective coating to the metal surfaces, in particular at least the zinc-magnesium hot-dip coated steel surfaces of the components in the series.

[0010] Serial cleaning and degreasing of components occurs when at least the zinc-magnesium hot-dip coated steel surfaces of a large number of components are brought into contact with the alkaline, aqueous cleaner. This contacting preferably takes place in one or more system tanks that provide the alkaline, aqueous cleaner for contacting. The contacting of the individual components takes place sequentially and thus at different times. The system tank is the container containing the alkaline, aqueous cleaner for cleaning and degreasing.In the (quasi-)continuous operation of such a cleaning and degreasing stage, the inventive method builds up a steady-state amount of organic contaminants absorbed by the alkaline, aqueous cleaner, depending on the degree of contamination of the components and the inflow and outflow rates of cleaner and cleaner components. The present inventive method is characterized by the fact that high water wettability can be reliably achieved on the zinc-magnesium hot-dip coated steel surfaces, largely independent of the proportion of organic contaminants in the alkaline, aqueous cleaner.

[0011] According to the invention, the components comprise steel material provided with a metallic zinc-magnesium coating, the coating being applied from a melt of the alloy components. Such hot-dip galvanizing processes are known in the art collectively as hot-dip galvanized (ZM) steel and represent metallic coatings containing 1.5 to 8 wt.% of the metals aluminum and magnesium, with the magnesium content in the metallic coating preferably being at least 0.2 wt.%. In the following, the term hot-dip galvanized (ZM) steel is used synonymously with zinc-magnesium hot-dip coated steel.

[0012] Cleaning and degreasing within the meaning of the present invention always relates, as already mentioned, to the surfaces of the components in the series formed by the metallic materials. The material can be a uniform material or a coating. For example, galvanized steel grades according to the invention consist of both steel and zinc, whereby at the cut edges and grinding points of, for example, an automobile body made of galvanized steel, steel surfaces can be exposed, and according to the invention, the steel material is then cleaned and degreased. Therefore, if the focus within the scope of the present invention is on the cleaning and degreasing of a component composed of a specific metallic material, this includes all materials and coatings that contain more than 50 at.% of the respective element of the named material.A component with a galvanized coating therefore contains more than 50 at.% zinc in the metallic coating.

[0013] The process according to the invention is not limited to application to hot-dip galvanized (ZM) steel, so that the substrates commonly provided by the steel industry such as steel, in particular cold-rolled steel (CRS), as well as electrolytically galvanized (ZE) or hot-dip galvanized (Z), alloy galvanized, in particular (ZF), (ZA), or aluminum-coated (AZ), (AS) steel can also be considered as further components of the components. Light metals such as aluminum and magnesium and their alloys can also be treated in the process according to the invention together with the hot-dip galvanized (ZM) steel of the component and can be cleaned and degreased in the process. The process according to the invention is characterized precisely by the fact that it is suitable for endowing common metallic materials composed of iron, zinc, aluminum and magnesium with high water wettability, which is the prerequisite for successful corrosion-protective pretreatment, e.g.a zinc phosphating or amorphous conversion coating based on the elements Zr and / or Ti on these metal surfaces.

[0014] Particularly preferred is an embodiment in which the components of the series are composed of galvanized steel, steel and / or aluminum in addition to hot-dip galvanized (ZM) steel. The suitability of the process according to the invention for this material mix to bring about good water wettability is particularly advantageous for components that are manufactured in a composite construction and are assembled from different semi-finished products. According to the invention, therefore, preferred is a process in which the components of the series represent composite structures, preferably automobile bodies, that are composed of semi-finished products of hot-dip galvanized (ZM) steel and of semi-finished products of galvanized steel and aluminum, particularly preferably of semi-finished products of hot-dip galvanized (ZM) steel and of semi-finished products of galvanized steel, aluminum and steel.

[0015] The components cleaned and degreased according to the present invention can be any spatial structure of any shape and design originating from a manufacturing process, in particular semi-finished products such as strips, sheets, rods, pipes, etc., and composite structures assembled from the aforementioned semi-finished products. The composite structures assembled from different materials are usually in the form of cut, formed, and joined flat products by welding, gluing, and / or flanging. The components to be cleaned and degreased in series according to the present invention are preferably selected from automobile bodies or parts thereof, heat exchangers, profiles, pipes, tanks, or tubs.

[0016] The inventive method for cleaning and degreasing components with hot-dip galvanized (ZM) steel surfaces serves, as already mentioned, to provide a metal surface that is readily wettable with water, which is then excellently conditioned for subsequent corrosion protection treatment based on essentially inorganic conversion coatings, in particular based on crystalline phosphate layers or those based on amorphous thin layers of oxide, hydroxide compounds of the elements Zr and / or Ti. The inventive method is therefore intended to be operated as a cleaning and degreasing stage, in which contaminants such as corrosion protection and forming oils are effectively removed from the surfaces of the components and completely absorbed by the alkaline aqueous cleaner, where they then accumulate in the system tank of the cleaning and degreasing stage.The water wettability of the metal surfaces must therefore be maintained even with increasing oil content in the cleaner. The alkaline, aqueous cleaner contains a special combination of complexing agents and water-dissolved inorganic additives consisting of phosphates and bivalent metal cations of the elements Zn, Mg, and / or Ca, which support the cleaning process and, in particular, make and maintain good water wettability of hot-dip galvanized (ZM) surfaces.

[0017] With regard to the inorganic auxiliaries dissolved in water, it is essential within the scope of the present invention that, for good water wettability, at least 10.0 mmol / kg of the oxoanions of the elements B, C, N, P, S, and CI dissolved in the aqueous phase of the cleaner are phosphate ions. The proportion of phosphate ions dissolved in water is preferably 20.0 mmol / kg, but preferably less than 100.0 mmol / kg, particularly preferably less than 80.0 mmol / kg. A quantity of additional oxoanions of the elements B, C, N, P, S, and CI can also contribute to water wettability and thus help to keep the phosphate content in the cleaner moderate. Carbonate, nitrate, and sulfate ions, in particular carbonate and nitrate ions, are particularly effective for this purpose.

[0018] Irrespective of this, below a phosphate content of 10.0 mmol / kg, a well water-wettable hot-dip galvanized (ZM) steel surface cannot be guaranteed in the series treatment of a large number of components.In a particular embodiment of the process according to the invention, the alkaline, aqueous cleaner therefore contains at least 10.0 mmol / kg of phosphate ions dissolved in the aqueous phase and additionally at least one oxoanion dissolved in the aqueous phase selected from borate, carbonate, nitrate, sulfate and / or chlorate ions, preferably selected from carbonate, nitrate and / or sulfate ions, particularly preferably from carbonate and / or nitrate ions, in an amount such that the proportion of oxoanions of the elements B, C, N, P, S and CI dissolved in the aqueous phase is at least 30.0 mmol / kg in total, preferably the proportion of oxoanions of the elements C, N, P and S dissolved in the aqueous phase is at least 30.0 mmol / kg in total and particularly preferably the proportion of oxoanions of the elements C, N and P dissolved in the aqueous phase is at least 30.0 mmol / kg in total, preferably at least 50.0 mmol / kg, particularly preferably at least 60.0 mmol / kg.

[0019] Regarding the inorganic auxiliaries dissolved in water, it should also be noted that, with regard to the divalent cations, the presence of zinc ions is essential, and a minimum amount of 2.0 mmol / kg is required for good water wettability of hot-dip galvanized (ZM) steel surfaces. In this context, it is particularly preferred if the proportion of zinc ions in the alkaline, aqueous cleaner is at least 6.0 mmol / kg, preferably at least 8.0 mmol / kg, and particularly preferably at least 10.0 mmol / kg. For economic reasons, the total proportion of divalent cations of the elements Zn, Mg, and / or Ca should not exceed 100 mmol / kg, particularly preferably not exceeding 50 mmol / kg, as this entails the requirement for a higher proportion of complexing agent.

[0020] The presence of the complexing agent containing phosphonate groups serves to complex the bivalent metal cations contained in the cleaner and also to complex the metal ions absorbed into the cleaner by the components during pickling processes, in particular zinc ions from the component surfaces formed by hot-dip galvanized (ZM) steel. The complexing agent therefore serves to stabilize the cleaner and prevents the precipitation of the inorganic additives dissolved in water. In a preferred embodiment, the alkaline aqueous cleaner therefore contains such an amount of complexing agents with at least one phosphonate group that the molar ratio of these complexing agents to the total amount of bivalent cations of the elements Zn, Mg, and / or Ca is above 0.60. Surprisingly, it was found thatthat a significant molar excess of complexing agents with phosphonate groups in relation to the zinc ions nevertheless has a detrimental effect on the water wettability, so that in the process according to the invention the molar ratio of organic complexing agents which have at least one phosphonate group to the amount of zinc ions dissolved in the aqueous phase must be below the value 2.1, preferably below the value 2.0, particularly preferably below the value 1.9, very particularly preferably below the value 1.8 and especially preferably below the value 1.7, and in turn the molar ratio of organic complexing agents which have at least one phosphonate group to the total amount of divalent cations of the elements Zn, Mg and / or Ca is below the value 2.1, preferably below the value 2.0, particularly preferably below the value 1.9, very particularly preferably below the value 1,8 and particularly preferably below the value 1.7.

[0021] All water-soluble complexing agents are suitable as organic complexing agents containing at least one phosphonate group. However, the complexing agent is preferably selected from di- and / or triphosphonic acids, particularly preferably from etidronic acid and / or aminotrimethylenephosphonic acid, and especially preferably from etidronic acid. In a preferred embodiment, the proportion of organic complexing agents containing at least one phosphonate group in the alkaline-aqueous cleaner is at least 2.0 mmol / kg. Where, in the context of the present invention, the concentration of an active component or compound is specified as a molar amount per kilogram, this is the molar amount based on the weight of the respective total composition.

[0022] Overall, for achieving well water-wettable surfaces of hot-dip coated (ZM) steel components, it is advantageous if the pickling rate of the alkaline aqueous cleaner is low and, during contacting of at least the hot-dip coated (ZM) steel surfaces of the components with the cleaner in the cleaning and degreasing process according to the invention, no more than 0.2 g / m² of zinc, based on the hot-dip coated (ZM) surfaces, preferably based on all galvanized surfaces of the components, is pickled off, i.e. passes from the metallic coating into the aqueous phase of the cleaner. The pickling rate can be reduced by increasing the proportions of the bivalent cations selected from Zn, Ca and / or Mg, in particular the proportion of zinc ions, or by lowering the proportion of complexing agents, in particular the proportion of organic complexing agents which contain at least one phosphonic acid.The pickling rate can be determined after non-pickling degreasing of a component or component section by bringing the component or component section into contact with the respectively selected alkaline aqueous cleaner under the respectively selected and intended process conditions, in particular duration, temperature, type of application, components or component sections, and determining the weight loss, which is then equated with the amount of zinc removed, by differential gravimetry.

[0023] The alkaline, aqueous cleaner contains at least one surface-active substance, preferably selected from surfactants, for effective degreasing, i.e., removal of organic soils and industrial oils. Surfactants within the meaning of the present invention are considered to be surface-active organic compounds that, for their surface activity, are composed of a hydrophilic and at least one lipophilic molecular component, or of a lipophilic and at least one hydrophilic molecular component, wherein the molecular weight of the surface-active organic compound does not exceed 2000 g / mol.

[0024] The surfactants used in the alkaline aqueous cleaner can be selected from anionic surfactants, cationic surfactants, zwitterionic surfactants, and nonionic surfactants, with the use of nonionic surfactants generally being preferred. Particularly suitable nonionic surfactants as components of the alkaline aqueous cleaner for degreasing components comprising hot-dip galvanized (ZM) surfaces are those whose HLB value (hydrophilic-lipophilic balance) is at least 8, more preferably at least 10, especially preferably at least 12, but particularly preferably not more than 18, especially preferably not more than 16. The HLB value serves as a quantitative reference value for classifying nonionic surfactants with regard to their miscibility with water or their ability to form O / W emulsions. For quantification, the nonionic surfactant is broken down into a lipophilic and a hydrophilic group.The HLB value is then calculated as follows and can take values ​​from zero to 20 on the arbitrary scale: . HLB = 20 ⋅ 1 − M L / M with ML :Molar mass of the lypophilic group of the non-ionic surfactant M:Molar mass of the non-ionic surfactant

[0025] In terms of substance, preferred nonionic surfactants in the alkaline aqueous cleaner of the process according to the invention are those selected from alkoxylated alkyl alcohols, alkoxylated fatty amines, and / or alkyl polyglycosides, particularly preferably from alkoxylated alkyl alcohols and / or alkoxylated fatty amines, especially preferably from alkoxylated alkyl alcohols. The alkoxylated alkyl alcohols and / or alkoxylated fatty amines are preferably end-capped for a defoaming effect, 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.Particularly preferably, those alkoxylated alkyl alcohols and / or alkoxylated fatty amines which are present in ethoxylated and / or propoxylated form are used as nonionic surfactants in the alkaline aqueous cleaner, wherein the number of alkylene oxide units is preferably not greater than 16 in total, particularly preferably not greater than 12, especially preferably not greater than 10, but particularly preferably greater than 4, especially preferably greater than 6.

[0026] With regard to the lipophilic component of the aforementioned nonionic surfactants, those alkoxylated alkyl alcohols and / or alkoxylated fatty amines are preferred as nonionic surfactants in the alkaline aqueous cleaner 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 greater than 6, particularly preferably at least 10, especially preferably at least 12, but preferably not greater than 20, particularly preferably not greater than 18, especially preferably not greater than 16.

[0027] Overall, it can be seen that longer-chain nonionic surfactants are very well suited and preferable for effective cleaning and degreasing of metallic components contaminated with conventional forming and corrosion protection oils, so that in a further preferred embodiment of the process according to the invention, alkoxylated alkyl alcohols and / or alkoxylated fatty amines, in particular the alkoxylated alkyl alcohols, are preferred as the surfactant component of the alkaline aqueous cleaner, 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.

[0028] Preferred representatives of the alkoxylated alkyl alcohols are selected, for example, from four- to eight-fold ethoxylated or propoxylated C6-C12 fatty alcohols, eight- to twelve-fold ethoxylated C12-C18 fatty alcohols, six- to fourteen-fold propoxylated C12-C18 fatty alcohols, six- to ten-fold ethoxylated and propoxylated C12-C14 fatty alcohols, which in turn can be end-capped with methyl, butyl or benzyl groups.

[0029] Another suitable selection criterion for the nonionic surfactant to be used in the alkaline aqueous cleaner, which is selected from alkoxylated alkyl alcohols, alkoxylated fatty amines and / or alkyl polyglycosides, is the cloud point determined according to DIN 53 917 (1981), which is preferably above 20°C, but particularly preferably below the application temperature of the cleaner in the cleaning and degreasing stage, particularly preferably more than 5°C, but not more than 10°C below the respectively selected application temperature.

[0030] The proportion of surfactants, in particular non-ionic surfactants, in the alkaline, aqueous cleaner is preferably above 0.050 g / kg, particularly preferably above 0.100 g / kg, especially preferably above 0.200 g / kg, but the total proportion of surfactants, preferably non-ionic surfactants, is preferably not above 5.0 g / kg, particularly preferably not above 2.0 g / kg, in each case based on the cleaner.

[0031] Optionally, the alkaline-aqueous cleaner may contain additional complexing agents to improve the stability of the cleaner and to prevent precipitation of poorly soluble salts. These complexing agents are not organic complexing agents with at least one phosphonate group and are preferably selected from α,-hydroxycarboxylic acids and / or from organic compounds with at least three carboxyl groups and at least one secondary and / or tertiary amino group. The proportion of complexing agents that are not organic complexing agents with at least one phosphonate group in the alkaline, aqueous cleaner is sufficient to support the complexation of the bivalent cations or cations contained in the cleaner.the metal ion load absorbed by the cleaner and originating from the metallic materials of the component is preferably at least 2.0 mmol / kg, particularly preferably at least 4.0 mmol / kg, very particularly preferably at least 5.0 mmol / kg, but for reasons of economy preferably does not exceed 20.0 mmol / kg, particularly preferably not 10.0 mmol / kg.

[0032] Suitable and therefore preferred representatives of the α,-hydroxycarboxylic acids are glycolic acid, lactic acid, tartaric acid, malic acid, aldaric acids, aldonic acids and / or glucoheptonic acid, with particular preference being given to selecting at least one aldonic acid, particularly preferably gluconic acid and / or glucoheptonic acid and very particularly preferably gluconic acid.

[0033] Suitable and therefore preferred representatives of the organic complexing agents with at least three carboxyl groups and at least one secondary and / or tertiary amino group are β-alaninediacetic acid, N-(1-carboxyethyl)iminodiacetic acid, iminodisuccinic acid, diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid, nitrilotriacetic acid, particularly preferably iminodisuccinic acid.

[0034] The pH of the alkaline, aqueous cleaner in the process according to the invention is at least 9.50, and preferably at least 10.00, for good degreasing performance. However, only a slight to moderate pickling of the zinc-magnesium coating can be advantageous for maintaining the good corrosion-protective properties of the (ZM) substrate, so that the pH of the alkaline, aqueous cleaner is preferably less than 12.50, more preferably less than 12.00, and most preferably less than 11.50. According to the invention, the pH of the alkaline, aqueous cleaner corresponds to the negative decimal logarithm of the hydronium ion activity measured in the alkaline, aqueous cleaner at a temperature of 20 °C using a pH-sensitive glass electrode after two-point calibration against technical buffer solutions of acetic acid / acetate (pH = 4.0) and boric acid / borate (pH = 9.0).

[0035] The alkaline aqueous cleaner is preferably provided with a specific buffer capacity so that in the process according to the invention it has a total alkalinity in points of at least 3.0, more preferably at least 6.0, most preferably at least 8.0, but preferably a total alkalinity of 30.0, more preferably 20.0 and especially preferably not exceeded 15.0. The total alkalinity corresponds to the consumption of 0.1 N hydrochloric acid in milliliters after titration of a sample volume of 2 ml of the alkaline, aqueous cleaner diluted with 50 ml of deionized water (κ < 1 µScm -1< ) ​​in the presence of the indicator bromocresol green (change point: pH 3.6) at a temperature of 20 °C.

[0036] To adjust the alkalinity of the alkaline aqueous cleaner, any builders known in the art that represent alkaline-reacting compounds or a mixture of such compounds can be used. Particularly suitable and established builders are alkaline-reacting, inorganic compounds, which are preferred within the scope of the present invention and are particularly preferably selected from water-soluble hydroxides, carbonates, borates, silicates, and / or phosphates, wherein in turn water-soluble hydroxides, carbonates, and / or phosphates are preferably present. The latter, in particular, as already explained in detail, are also essential as an inorganic auxiliary substance for providing readily water-wettable hot-dip galvanized (ZM) surfaces. In this respect, the use of orthophosphates as a builder substance for building up the alkalinity is also quite advantageous and preferred according to the invention.In addition to orthophosphates, other suitable alkaline phosphate-based builders are pyrophosphates and / or tripolyphosphates. Suitable carbonate-based builders are alkali metal carbonates, preferably potassium carbonate, and among the hydroxides, mixtures of alkali metal hydroxides, preferably selected from potassium hydroxide, with phosphoric acid are preferred alkaline builders / builder systems.

[0037] In a preferred embodiment, the alkaline aqueous cleaner is formulated without the use of silicates or borates, so that the cleaner preferably contains less than 100 mg / kg, particularly preferably less than 20 mg / kg, very particularly preferably less than 5 mg / kg of silicates and / or borates, calculated as SiO 4 or BO s and based on the cleaner.

[0038] Due to the pH range effective for cleaning and degreasing and the preferred alkaline builder substances, free alkalinities above 1.0 and below 10.0 are usually set, which in turn are preferred. The free alkalinity is particularly preferably at least 2.0, particularly preferably does not exceed 7.0, and especially preferably does not exceed 5.0. The free alkalinity corresponds to the consumption of 0.1 N hydrochloric acid in milliliters when a sample volume of 2 ml of the alkaline, aqueous cleaner diluted with 50 ml of deionized water (κ < 1 µScm -1< ) ​​is titrated at a temperature of 20 °C to a pH of 8.5.

[0039] As explained at the outset, the cleaning and degreasing process primarily serves to remove soiling, in particular industrial oils, and to provide water-wettable hot-dip galvanized (ZM) surfaces. With regard to hot-dip galvanized (ZM) surfaces, it is also important that the intrinsically good corrosion protection properties of this coating are retained after the cleaning and degreasing stage and are not subjected to any significant change. It is therefore advantageous if the process according to the invention ensures that neither an inorganic passive layer, which is not a native passivation, i.e. formed solely from metal elements of the substrate, nor a metallic coating containing foreign elements is formed on the (ZM) surfaces, whereby the term foreign element refers to metals and semi-metals that are not alloy components of the (ZM) coating.In this context, it is preferred if the respective proportion of water-soluble compounds of an element selected from compounds of the elements Bi, Ni, Co or Cu, preferably selected from compounds of metal elements that have a more positive standard reduction potential than iron, is in each case less than 20 mg / kg, preferably less than 10 mg / kg, particularly preferably less than 5.0 mg / kg and especially preferably less than 1.0 mg / kg, each calculated as the proportion of the respective element and based on the cleaner. The standard reduction potential is the reduction potential of the electrochemical half-cell Me / Me n+< determined against the standard hydrogen electrode H 2 / H +< (pH = 0) at a metal ion activity of 1 mol / l and 20 °C.

[0040] If the formation of alkaline passive layers containing iron on the hot-dip galvanized (ZM) surfaces of the components must also be completely avoided, for example because an improvement in corrosion protection is not expected and therefore no resources should be devoted to such passivation, it is further advantageous if the proportion of iron(III) ions in the alkaline, aqueous cleaner is less than 50 mg / kg, preferably less than 20 mg / kg, and particularly preferably less than 10 mg / kg, based on the cleaner. To improve the cleaning performance, especially the water wettability of the hot-dip galvanized (ZM) steel surfaces of the components, the presence of iron(III) or iron ions in general in the alkaline, aqueous cleaner is neither necessary nor beneficial, and is therefore dispensable.

[0041] In (quasi-)continuous operation, i.e., when treating a large number of components in a series in a process-economically viable, chronological sequence, the contaminants absorbed by the alkaline aqueous cleaner accumulate in the system tank of the cleaning and / or degreasing stage. Depending on the degree of contamination of the components, the addition of fresh cleaning components, and the removal of cleaner, e.g., due to drag-out caused by the components, a system-specific, stationary amount of contaminants, particularly forming and corrosion protection oils, builds up in the system tank. As already explained, the system tank is the container containing the alkaline aqueous cleaner for contact with the component surfaces for the purpose of cleaning and degreasing.It has now been shown that in the process according to the invention, the good water wettability of the hot-dip coated (ZM) surfaces and the associated visually and qualitatively satisfactory corrosion protection in downstream process steps is surprisingly maintained even when such quantities of non-polar hydrocarbons are enriched in the cleaning system tank that, despite continued good degreasing performance, usually thwart complete water wettability and are therefore to be classified as critical. The process-economic potential of the process according to the invention is therefore particularly evident when it is operated in such a way that non-polar hydrocarbons have already significantly accumulated in the alkaline aqueous cleaner. This means that, in comparison to conventional cleaning processes, this means that in the (quasi-)continuous operation of the process according to the invention, the intervals for bath maintenance orThe processing of the cleaner stored in the system tank can be carried out at longer intervals and / or the supply of freshly prepared cleaner and / or components of the cleaner can be reduced without any loss of performance. In this context, it is therefore preferred according to the invention if the proportion of non-polar hydrocarbons, which is fed from forming and corrosion protection oils cleaned from the component surfaces, in the alkaline aqueous cleaner is already at least 0.2 kg / m 3< , particularly preferably at least 0.5 kg / m 3< , especially preferably at least 1.0 kg / m 3< due to the series treatment of a large number of components.The proportion of non-polar hydrocarbons in the alkaline aqueous cleaner can be determined in a sample of the degreasing bath adjusted to hydrochloric acid (methyl orange transition point) to which an aliquot (1 / 10) of sodium chloride and an aliquot (1 / 4) of ethanol have been added. From this prepared sample of the degreasing bath, the hydrocarbon content is extracted by shaking with an aliquot (1 / 1) of petroleum ether. After phase separation, which can be achieved by successive addition of ethanol, the petroleum ether phase is treated with silica gel to remove polar organic components such as fatty acids, acid esters, and nonionic surfactants. After filtration, the proportion of non-polar hydrocarbons can be determined gravimetrically after the petroleum ether has been distilled off.

[0042] The aforementioned critical amounts of nonpolar hydrocarbons for water wettability are only reached after the throughput of a certain number of components. In this context, it is therefore preferable for the series of components to include at least a number of components whose total surface area formed by the metallic materials of the components is greater than the following term: V B ⋅ KW crit Δm TOC ⋅ 1,2 VB: Volume of the alkaline aqueous cleaner in m 3< KW crit: Usually critical amount or preferred minimum amount according to the invention of non-polar hydrocarbons in the alkaline aqueous cleaner in kg / m 3< amounting to 0.2 kg / m 3< , particularly preferably 0.5 kg / m 3< , very particularly preferably 1.0 kg / m 3< Δm TOC: Change in the area-related carbon content on the surfaces of the components formed by the metallic materials after contact with the alkaline aqueous cleaner in kg / m 2<

[0043] The carbon layer remaining on the surface of the component formed by the metallic materials can be determined by pyrolytic decomposition. For this purpose, a representative component section of a defined area of ​​each metallic material is heated to a substrate temperature (PMT) of 550°C in an oxygen atmosphere, and the amount of carbon dioxide released is quantitatively measured as the amount of carbon using an infrared sensor, for example, using the LECO ®< RC-412 Multiphase Carbon Determinator (Leco Corp.). The change in the area-related carbon content for each metallic material can then be determined immediately before cleaning and degreasing and immediately after the first rinse with deionized water (κ < 1µScm -1< ) ​​after cleaning and degreasing, and calculated for the entire component according to the specific area proportion of the respective materials.

[0044] In a preferred embodiment of the method according to the invention, immediately after passing through the cleaning and degreasing stage, i.e. immediately after the last contacting of a component with the alkaline aqueous cleaner and a first rinse with deionized water (κ < 1µScm -1< ), a carbon coating of less than 0.20 g / m 2< , particularly preferably less than 0.10 g / m 2< , remains on the surface of the components of the series formed by the metallic materials, whereas the surface of the components of the series formed by the metallic materials previously, i.e. before passing through the method according to the invention, i.e. immediately before the first contacting with the alkaline aqueous cleaner, preferably has a carbon coating of at least 0.50 g / m 2<, which originates from the above-mentioned organic soiling, in particular forming and corrosion protection oils.

[0045] In the process according to the invention, the alkaline, aqueous cleaner is applied and thus brought into contact with the components of the series preferably at a temperature of at least 30°C, particularly preferably at a temperature of at least 40°C, but preferably below 60°C. The alkaline, aqueous cleaner can be brought into contact with the components of the series using application methods established in the prior art. These include, in particular, immersion, rinsing, spraying, and / or atomization. The immersion of the components of the series into a system tank of the cleaning and degreasing stage containing the corresponding alkaline, aqueous cleaner and / or by spraying the cleaner stored in a system tank.

[0046] In a further aspect, the present invention relates to an alkaline, aqueous composition particularly suitable for the cleaning process according to the invention, having a pH in the range from 9.50 to 12.50, containing (a) a total of at least 30.0 mmol / kg, preferably a total of at least 50.0 mmol / kg, particularly preferably a total of at least 60.0 mmol / kg of carbonate ions, nitrate ions and / or phosphate ions dissolved in the aqueous phase, wherein at least 10.0 mmol / kg, preferably at least 20.0 mmol / kg but less than 100.0 mmol / kg, preferably less than 80.0 mmol / kg of phosphate ions are contained, (b) at least 6.0 mmol / kg, preferably at least 8.0 mmol / kg, particularly preferably at least 10.0 mmol / kg of zinc ions dissolved in the aqueous phase, (c) a total of at least 1.0 mmol / kg of an organic complexing agent selected from di- and / or triphosphonic acids, preferably from etidronic acid and / or aminotrimethylenephosphonic acid, wherein the molar ratio of organic complexing agent selected from di- and / or triphosphonic acids to zinc ions dissolved in the aqueous phase is less than 2.1, preferably less than 2.0, but preferably greater than 0.60,and (d) at least one surface-active compound.

[0047] With regard to the alkaline, aqueous composition according to the invention, the same preferred embodiments apply with regard to individual components, insofar as they are compatible with the embodiments of the alkaline, aqueous composition according to the invention already listed here, as well as with regard to other physicochemical properties, as also apply to the alkaline, aqueous cleaner in the cleaning and degreasing process according to the invention. This applies in particular to suitable and preferred surface-active compounds, the pH value, the alkalinity, the alkaline builders used, and the upper limits for interfering metal ions that have a more positive standard reduction potential than iron, for iron(III) ions, or the upper limits for undesirable alkaline builders such as borates and silicates.

[0048] The cleaning and degreasing process according to the invention serves to reliably remove soiling from components in series production and thereby provide readily water-wettable metal surfaces, in particular hot-dip galvanized (ZM) steel surfaces, which in turn are excellently suited for corrosion-protective pretreatment. Such corrosion-protective pretreatment of metal surfaces, at least the surfaces of hot-dip galvanized (ZM) steel, can be conventional zinc phosphating or a conversion treatment based on the elements Zr and / or Ti, during which thin, amorphous, oxide / hydroxide layers are formed.For both corrosion-protective pretreatments, the process according to the invention offers the advantage that, due to their good water wettability, extremely homogeneous, defect-free conversion coatings are obtainable, which are a prerequisite for both good corrosion protection and an optically homogeneous paint layer structure. In a further aspect, the present invention therefore relates to a process in which contact with the alkaline, aqueous cleaner is immediately followed, but with an intermediate rinsing step, by a conversion treatment by contacting with an acidic, aqueous composition either for zinc phosphating or for conversion treatment based on the elements Zr and / or Ti.In this context, a rinsing step serves primarily, preferably exclusively, to remove the wet film adhering to the components from the cleaning and degreasing stage and thus to completely or partially remove soluble residues, particles and active components of the alkaline, aqueous cleaner, which would otherwise be carried over into the conversion treatment stage while adhering to the component.

[0049] In a preferred embodiment of a process according to the invention relating to the degreasing and cleaning as well as zinc phosphating of components in series (hereinafter "zinc phosphating according to the invention"), the components, which at least partially have hot-dip galvanized (ZM) steel surfaces, each undergo the successive process steps i)-iii): i) Cleaning and, if appropriate, degreasing according to the previously described inventive method for cleaning and degreasing; iii) Conversion treatment by contacting with an acidic, aqueous composition having a pH in the range of 2.5 to 4.0 containing 0.2 to 3.0 g / kg of zinc ions, 5.0 to 30.0 g / kg of phosphate ions, and preferably an amount of free fluoride; and iv) Deposition of a coating system, preferably by contacting with an aqueous dispersion of an organic binder, wherein the coating system is preferably a dip coating, particularly preferably an electrocoating coating ("coating step").

[0050] In an alternative preferred embodiment of a method according to the invention, which relates to the degreasing and cleaning as well as corrosion-protective conversion treatment of components in series (hereinafter "conversion treatment Zr / Ti according to the invention"), the components, which at least partially have hot-dip galvanized (ZM) steel surfaces, each undergo the successive process steps i)-iii): i) cleaning and, if appropriate, degreasing according to the previously described inventive method for cleaning and degreasing ("cleaning and degreasing step"); ii) conversion treatment by contacting with an acidic, aqueous composition having a pH in the range of 2.50 to 5.20 containing at least 0.05 mmol / kg of compounds of the elements Zr and / or Ti dissolved in water and preferably an amount of free fluoride ("conversion step"); and iv) deposition of a coating system, preferably by contacting with an aqueous dispersion of an organic binder, wherein the coating system is preferably a dip coating, particularly preferably an electrocoating coating ("coating step").

[0051] A Zr / Ti conversion treatment according to the invention should preferably be carried out in process step ii) with acidic aqueous compositions containing at least 1.00 mmol / kg of free fluoride in order to further improve paint adhesion to the hot-dip galvanized (ZM) surfaces. However, for reasons of compatibility of the process according to the invention with other metallic materials, in particular steel, it is preferred if the proportion of free fluoride in the acidic, aqueous composition in process step ii) is less than 7.50 mmol / kg, more preferably less than 6.00 mmol / kg, most preferably less than 5.00 mmol / kg, and especially preferably less than 4.00 mmol / kg. The amount of free fluoride in the respective stages of the pretreatment according to the invention is to be determined potentiometrically at 20°C in the respective provided solution after calibration with fluoride-containing buffer solutions without pH buffering using a fluoride-sensitive measuring electrode.Suitable sources of free fluoride for the acidic, aqueous composition are water-soluble complex fluorides of the elements Zr, Ti and / or Si, preferably of the elements Zr and / or Ti, particularly preferably of the element Zr, and / or hydrofluoric acid, ammonium bifluoride and / or water-soluble alkali metal fluorides.

[0052] Regarding the pH of the acidic, aqueous composition in process step ii) of the Zr / Ti conversion treatment according to the invention, it is first necessary to ensure that the compounds of the elements Zr and / or Ti dissolved in water do not form brines due to hydrolysis, which are no longer available for conversion layer formation. At the same time, the pickling rate for common metallic materials should be sufficiently high to form homogeneous, closed conversion layers; this applies in particular to the substrate hot-dip galvanized (ZM) steel. According to the invention, it is therefore preferred that the acidic, aqueous compositions do not have a pH above 5.20, and the pH is preferably less than 5.10, more preferably less than 5.00, most preferably less than 4.90, and especially preferably below 4.80.At the same time, increased pickling and rapid layer formation kinetics can be detrimental to the formation of suitable conversion coatings. Especially on hot-dip galvanized (ZM) steel, high layer weights based on the elements Zr and / or Ti are achieved in the lower pH range. These elements, in turn, are less compact and tend to corrode themselves at low pH values, so that point defects can form in the conversion coating. According to the invention, it is therefore preferred if the pH of the acidic aqueous composition is greater than 3.00, particularly preferably greater than 3.50, and most preferably greater than 4.00.In the context of the Zr / Ti conversion treatment according to the invention, the pH value of the acidic, aqueous composition corresponds to the negative decimal logarithm of the hydronium ion activity measured in the acidic, aqueous composition at a temperature of 20 °C using a pH-sensitive glass electrode after two-point calibration against technical buffer solutions of acetic acid / acetate (pH = 4.0) and phosphate (pH = 7.0).

[0053] In the conversion stage of the Zr / Ti conversion treatment according to the invention, the aim is to build up a conversion coating that is as homogeneous and compact as possible based on oxidic / hydroxidic compounds of the elements Zr and / or Ti, preferably the element Zr. In a preferred embodiment, therefore, the contacting takes place for at least a duration for which a layer deposit of at least 20 mg / m 2< , particularly preferably of at least 40 mg / m 2< is brought about on the surfaces of the hot-dip galvanized (ZM) steel, but the contacting preferably does not continue for so long that a layer deposit of more than 300 mg / m 2< , particularly preferably of more than 200 mg / m 2< , very particularly preferably of more than 120 mg / m 2< , especially preferably more than 80 mg / m 2< , in each case based on the elements Zr and / or Ti, results on the hot-dip galvanized (ZM) surfaces.The coating thicknesses can be determined by X-ray fluorescence analysis (XRF). The treatment time required for the preferred coating thicknesses, i.e., the duration of contact with the acidic, aqueous composition at a preferred temperature in the range of 10-60 °C, should be in the range of 10 seconds to 300 seconds. To ensure this, a Zr / Ti conversion treatment according to the invention is preferred, in which the proportion of compounds of the elements Zr and / or Ti dissolved in water in the acidic, aqueous composition in process step ii) is preferably at least 0.10 mmol / kg, more preferably at least 0.30 mmol / kg, and most preferably at least 0.40 mmol / kg.For process economic reasons, the contents of compounds of the elements Zr and / or Ti dissolved in water should preferably be below 5.0 mmol / kg, particularly preferably below 3.0 mmol / kg and most preferably below 2.0 mmol / kg based on the elements Zr and / or Ti.

[0054] In the conversion stage of the Zr / Ti conversion treatment according to the invention, an amorphous oxidic / hydroxidic coating based on the elements Zr and / or Ti, preferably the element Zr, is to be produced, and accordingly, the compounds of the elements Zr and / or Ti dissolved in water are included. The term "dissolved in water" encompasses molecularly dissolved species and compounds that dissociate in aqueous solution and form hydrated ions. Typical representatives of these compounds are titanyl sulfate (TiO(SO4)), titanyl nitrate (TiO(NO3)2) and / or hexafluorotitanic acid (H2TiF6) and their salts, or ammonium zirconium carbonate ((NH4)2ZrO(CO3)2) and / or hexafluorozirconic acid (H2ZrF6) and their salts. Preferably, the compounds dissolved in water in the conversion stage are selected from fluoro acids and / or fluoro complexes of the elements Zr and / or Ti and their water-soluble salts.The formation of conversion layers based on fluoro acids and / or fluoro complexes of the element Zr is particularly preferred since such conversion layers provide improved paint adhesion.

[0055] In order to heal point defects in the conversion coating growing in process step ii) on the surfaces of galvanized steel, in particular on the surfaces of hot-dip galvanized (ZM) steel, where an overall rapid layer formation occurs, the presence of copper ions can be advantageous, whose local cementation in the point defects provides improved corrosion protection. It is therefore preferred that the acidic, aqueous composition of the conversion stage additionally contains copper ions dissolved in water, preferably at least 0.05 mmol / kg, but again preferably less than 4.0 mmol / kg, particularly preferably less than 2.0 mmol / kg of copper ions dissolved in water. Suitable sources of copper ions dissolved in water are water-soluble salts such as copper nitrate (Cu(NO 3 ) 2 ), copper sulfate (CuSO 4 ), and copper acetate (Cu(CH 3 COO) 2 ).

[0056] Other additives known to those skilled in the art of surface treatment, such as accelerators such as nitrate ions, nitrite ions, nitroguanidine, N-methylmorpholine N-oxide, hydrogen peroxide in free or bound form, hydroxylamine in free or bound form, reducing sugars, and / or wetting agents such as nonionic surfactants, and / or polymers such as polyamidoamines, and / or cations / compounds of the elements Mg, Ca, Al, Si, Sn, Bi and / or Mo, can be included to improve the layer formation kinetics, wettability and corrosion-protective properties in the context of the Zr / Ti conversion treatment according to the invention. However, for a resource-saving process and for reasons of cost-effectiveness, organic silicon compounds can largely be dispensed with.In a preferred embodiment of the Zr / Ti conversion treatment according to the invention, the acidic, aqueous composition in the conversion stage is therefore substantially free of hydrolyzable organic silanes / siloxanes and preferably contains less than 10 mg / kg of hydrolyzable organic silanes / siloxanes calculated as Si(OCH 2 CH 3 ) 4 .

[0057] The application and thus the contacting of the acidic, aqueous composition in the conversion stage of both the conversion treatment according to the invention and the zinc phosphating according to the invention preferably takes place at at least 30°C, particularly preferably at at least 40°C, but preferably below 60°C. The acidic, aqueous composition of the conversion stage can be brought into contact with the components of the series using application methods established in the prior art. These include, in particular, immersion, rinsing, spraying, and / or spraying, with application by immersion and / or spraying, and in particular, immersion of the components of the series in a system tank containing the corresponding acidic, aqueous composition, being preferred.

[0058] In the coating step of the zinc phosphating according to the invention or the Zr / Ti conversion treatment according to the invention, at least the surfaces of the components formed by the hot-dip galvanized (ZM) steel and pretreated to provide corrosion protection in the respective process step ii), preferably all surfaces formed by metallic materials, are provided with a first coating system, preferably by contacting the component or at least said surfaces of the hot-dip galvanized (ZM) steel pretreated to provide corrosion protection with an aqueous dispersion containing an organic binder. The coating system is therefore preferably deposited directly from the aqueous phase as a coating of the organic binder of the aqueous dispersion precipitated onto said surfaces of the components, which is typically subjected to a thermal post-treatment for film formation and curing.The coating in the painting stage is preferably applied by dip coating, particularly preferably by electrocoating, and again preferably by cathodic electrocoating. For this purpose, the organic binder of the aqueous dispersion is preferably based on amine-modified film-forming polyepoxides, which preferably additionally comprises organic compounds containing blocked and / or unblocked isocyanate groups as hardeners. Inorganic pigments are also often a component of the aqueous dispersion and a preferred additive for improving corrosion protection. The aqueous phase of the dispersion containing the binder also preferably contains small amounts of compounds of the elements yttrium and / or bismuth dissolved or dispersed in water, which have a positive effect on crosslinking and film formation.The preferred pH of the aqueous dispersion in the coating stage is in the range from 5.0 to 6.0, particularly preferably in the range from 5.4 to 5.8. In the context of the coating stage, the pH corresponds according to the invention to the negative decadic logarithm of the hydronium ion activity measured in an aqueous dispersion diluted by a factor of 10 with deionized water (κ<1µScm -1< ) ​​at a temperature of 20 °C using a pH-sensitive glass electrode after two-point calibration against technical buffer solutions of acetic acid / acetate (pH = 4.0) and boric acid / borate (pH = 9.0).

[0059] The application and thus the bringing into contact of the components, or at least the said surfaces of the corrosion-protectively pretreated hot-dip galvanized (ZM) steel, with the aqueous dispersion preferably takes place at a temperature of at least 30°C, particularly preferably at a temperature of at least 40°C, but preferably below 60°C. The aqueous dispersion from the coating stage can be brought into contact with the series components using application methods established in the state of the art. These include, in particular, dipping, spraying, and roller application. Application by dipping, and in particular, immersing the series components in a system tank containing the corresponding aqueous dispersion of the organic binder, is preferred and, in the case of dipping coatings, is already predetermined by the type of coating system.

Claims

1. A method for cleaning and degreasing a large number of components in series, in which the components of the series at least partially have surfaces of zinc-magnesium hot-dip galvanized steel, and in which at least the zinc-magnesium hot-dip galvanized steel surfaces of the components of the series are each cleaned with an alkaline, aqueous cleaner with a pH of at least 9.50 containing (a) a total of at least 30.0 mmol / kg of oxoanions of the elements B, C, N, P, S and CI in their highest oxidation state dissolved in the aqueous phase, wherein at least 10.0 mmol / kg of the oxoanions dissolved in the aqueous phase are phosphate ions, (b) a total of at least 6.0 mmol / kg of divalent metal cations of the elements Zn, Mg and / or Ca dissolved in the aqueous phase, wherein at least 2.0 mmol / kg of zinc ions dissolved in the aqueous phase are contained, (c) at least one organic Complexing agent containing at least one phosphonate group,and (d) at least one surface-active substance, wherein the molar ratio of organic complexing agents having at least one phosphonate group to the amount of zinc ions dissolved in the aqueous phase is less than 2.

1.

2. Method according to claim 1, characterized in that the oxoanions dissolved in the aqueous phase of the cleaner are selected in addition to the phosphate ions from borate, carbonate, nitrate, sulfate and / or chlorate ions, preferably from carbonate, nitrate, sulfate ions, particularly preferably from carbonate and / or nitrate ions.

3. Method according to one or both of the preceding claims, characterized in that the proportion of zinc ions dissolved in the aqueous phase of the cleaner is at least 6.0 mmol / kg, preferably at least 8.0 mmol / kg, particularly preferably at least 10.0 mmol / kg.

4. Method according to one or more of the preceding claims, characterized in thatthe at least one complexing agent having at least one phosphonate group is selected from di- and / or triphosphonic acids, preferably from etidronic acid and / or aminotrimethylenephosphonic acid, particularly preferably from etidronic acid.

5. Method according to one or more of the preceding claims, characterized in that the molar ratio of organic complexing agents containing at least one phosphonate group to the total amount of divalent cations of the elements Zn, Mg and Ca dissolved in the aqueous phase is greater than 0.

60.

6. Method according to one or more of the preceding claims, characterized in thatthe alkaline aqueous cleaner contains at least one surfactant as surface-active substance, which is preferably selected from non-ionic surfactants, preferably with an HLB value of at least 8, more preferably of at least 10, especially preferably of at least 12, but preferably not more than 18, more preferably not more than 16, wherein the total proportion of the surfactants, preferably of the non-ionic surfactants, is greater than 0.050 g / kg, preferably greater than 0.100 g / kg, more preferably greater than 0.200 g / kg, but the total proportion of the surfactants is preferably not above 5.0 g / kg, more preferably not above 2.0 g / kg, in each case based on the cleaner.

7. Method according to one or more of the preceding claims, characterized in thatadditionally at least one further organic complexing agent which is not an organic complexing agent with at least one phosphonate group is included, which is selected from α,-hydroxycarboxylic acids, which in turn are preferably selected from the group consisting of glycolic acid, lactic acid, tartaric acid, malic acid, aldaric acids, aldonic acids and / or glucoheptonic acid, wherein preferably at least one aldonic acid, in particular gluconic acid and / or glucoheptonic acid and very particularly preferably gluconic acid is selected.

8. Method according to one or more of the preceding claims, characterized in that the proportion of borates dissolved in water in the alkaline, aqueous cleaner is less than 100 mg / kg, preferably less than 20 mg / kg and particularly preferably less than 5 mg / kg calculated as BOs and based on the cleaner.

9. Method according to one or more of the preceding claims, characterized in thatthe proportion of silicates dissolved in water in the alkaline, aqueous cleaner is less than 100 mg / kg, preferably less than 20 mg / kg and particularly preferably less than 5 mg / kg calculated as SiO4 and based on the cleaner.

10. Method according to one or more of the preceding claims, characterized in that the pH of the alkaline aqueous cleaner is less than 12.50, preferably less than 12.00, particularly preferably less than 11.50, but preferably at least 10.

00.

11. Method according to one or more of the preceding claims, characterized in that in alkaline aqueous cleaner more than 0.2 kg / m 3 , preferably more than 0.5 kg / m 3 , particularly preferably more than 1.0 kg / m 3 of non-polar hydrocarbons.

12. Method according to one or more of the preceding claims, characterized in thatthe components of the series represent composite structures, preferably automobile bodies, which are composed of semi-finished products of zinc-magnesium hot-dip coated steel and of semi-finished products of galvanized steel and aluminum, particularly preferably of semi-finished products of zinc-magnesium hot-dip coated steel and of semi-finished products of galvanized steel, aluminum and steel.

13. A process for the cleaning and corrosion-protective surface treatment of components in series, which at least partially have zinc-magnesium hot-dip galvanized steel surfaces, in which the components of the series each undergo the successive process steps i)-iii): i) cleaning and degreasing according to a process of the preceding claims; ii) conversion treatment by bringing into contact with an acidic, aqueous composition having a pH in the range of 2.50 to 5.20 containing at least 0.05 mmol / kg of compounds of the elements Zr and / or Ti dissolved in water and preferably an amount of free fluoride; and iii) deposition of a paint system, preferably by bringing into contact with an aqueous dispersion of an organic binder, wherein the paint system is preferably a dip paint, particularly preferably an electrocoat paint.

14. Method according to claim 13, characterized in thatthat in process step ii) the contacting takes place for such a duration that a layer of Zr and / or Ti of at least 20 mg / m each is formed on the zinc-magnesium hot-dip galvanised surfaces of the component 2 , preferably at least 40 mg / m 2 based on the respective element, but preferably not more than 300 mg / m 2 based on the elements Zr and / or Ti.

15. Alkaline, aqueous composition for cleaning and optionally degreasing metal surfaces with a pH in the range of 9.50 to 12.50 containing (a) a total of at least 30.0 mmol / kg, preferably a total of at least 50.0 mmol / kg, particularly preferably a total of at least 60.0 mmol / kg of carbonate ions, nitrate ions and / or phosphate ions dissolved in the aqueous phase, wherein at least 10.0 mmol / kg, preferably at least 20.0 mmol / kg but less than 100.0 mmol / kg, preferably less than 80.0 mmol / kg of phosphate ions are contained, (b) at least 6.0 mmol / kg, preferably at least 8.0 mmol / kg, particularly preferably at least 10.0 mmol / kg of zinc ions dissolved in the aqueous phase, (c) a total of at least 1.0 mmol / kg of an organic complexing agent selected di- and / or triphosphonic acids, preferably from etidronic acid and / or aminotrimethylenephosphonic acid,wherein the molar ratio of organic complexing agent selected from di- and / or triphosphonic acids to zinc ions dissolved in the aqueous phase is less than 2.10, preferably less than 2.00, but preferably greater than 0.60, and (d) at least one surface-active compound.

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