Multi-stage method for corrosion protection treatment of components having steel surfaces

Abstract

The invention relates to a multi-stage process in which a series of components each having a steel surface are initially provided with a conversion layer based on the elements Zr and / or Ti and subsequently are dip-coated, wherein the conversion treatment stage is followed by a conditioning stage in which at least the steel surface of each component is brought into contact with an alkaline aqueous composition containing calcium and / or magnesium ions. By means of the process according to the invention, an excellent level of corrosion protection is achieved even under process conditions which normally tend to cause corrosion defects on steel surfaces, which means that a drying step after the conversion stage can be dispensed with.

Description

Technical Field

[0001] This invention relates to a multi-stage method in which a conversion layer based on elements Zr and / or Ti is initially applied to a series of components, each having a steel surface, and subsequently dip-coated thereon. Following the conversion treatment stage is a conditioning stage in which the steel surface of at least each component is brought into contact with an alkaline aqueous composition containing calcium and / or magnesium ions. Using the method according to the invention, excellent levels of corrosion protection can be achieved on the steel surface even under process conditions that typically lead to corrosion defects, meaning that a drying step following the conversion stage can be omitted. Background Technology

[0002] In the pretreatment of components with surfaces made of steel, galvanized steel, and / or aluminum for corrosion protection, thin-film passivation based on amorphous conversion layers (which are based on oxides and hydroxides of elements Zr and / or Ti) has begun to be widely established as an alternative to phosphating, during which a crystalline coating is formed. Further efforts to develop this type of conversion coating primarily aim to establish resource-saving and chromium-free passivation that provides an excellent primer base for subsequently applied paint systems, particularly dip coatings, with the goal of achieving corrosion protection comparable to tricationic zinc phosphating. Especially when the amorphous film is produced by conversion treatment with an acidic aqueous solution containing water-soluble compounds of elements Zr and / or Ti, controlled layer formation and the growth of a coating with as few defects as possible are crucial. To this end, existing techniques focus on the kinetics influencing layer formation, as described in WO 2023 / 275270, and propose, for example, sequentially forming a conversion layer in multiple wet chemical process steps to produce a layer deposit of Zr and / or Ti-based hydroxides and oxides, which achieves the most complete possible conversion of the Zr and / or Ti-based fluorine complexes. This is to prevent fluoride residues in the film, which could cause localized layer defects upon contact with corrosive media. In contrast, another method for forming a conversion layer (described as an example in EP 1 455 002 A1) aims to reduce the proportion of fluorides in the conversion coating and thus improve corrosion behavior and paint adhesion to subsequently applied dip coatings. To this end, EP 1455 002 A1 proposes adding magnesium, calcium, Si-containing compounds, zinc, or copper to the conversion solution, and alternatively, or in combination, drying or rinsing the conversion coating with an alkaline aqueous composition.

[0003] Specifically, on steel surfaces, if a wet film originating from the conversion stage and still directly adhering to the component surface during transport to the painting stage is not completely removed (e.g., by blowing it away in an air stream), or if the conversion coating is not completely dried by heat post-treatment, flash rust formation can be observed during a series of pre-treatments of the component to form a conversion layer based on a Zr and / or Ti-based composite fluoride. EP 1 455 002 A1 also proposes the latter method to improve the corrosion protection of the conversion coating. However, such method steps are operationally complex and energy-intensive. Therefore, in the prior art, a vigorous rinsing stage with fresh water is often performed after the conversion stage, in which the wet film originating from the conversion stage and still directly adhering to the component surface is completely removed before the component is transferred to the painting stage. EP 1 455 002 A1 also proposes rinsing with an alkaline aqueous rinsing solution to improve the corrosion protection of the conversion coating. However, even with a method that minimizes flash rust formation through a strong rinsing stage, it was previously impossible to avoid reduced corrosion protection on steel surfaces after dip coating, compared to methods that include heat drying of the conversion coating. Furthermore, the presence of the rinsing stage often leads to irregularities (so-called "mapping") in the appearance of the dip coating, including on other metal surfaces of the component, such as on galvanized steel.

[0004] Therefore, the object of the present invention is to establish a method for providing a conversion coating on metal surfaces, particularly steel surfaces, with the lowest possible defect-free properties. This method provides a high degree of robustness against corrosion damage during the industrial pretreatment and dip-coating of multiple components, as the components are transferred from the conversion treatment stage to the dip-coating stage. It also provides qualitatively high-quality dip-coated components with improved corrosion protection properties. In this method, the quality of the conversion coating (particularly on steel) should not be negatively affected by downstream rinsing steps, and a method should still be established in which components can be directly (i.e., without heat post-treatment) transferred to the painting line after rinsing and dip-coated without loss of corrosion protection. Ideally, fluctuations in corrosion protection performance and irregularities (so-called "brush marks") in the appearance of the dip-coated components are also prevented. The method must also be suitable for effectively protecting components composed of mixtures of different metals (particularly mixtures of steel, zinc, and aluminum) from corrosion. Summary of the Invention

[0005] This objective is achieved by a method for pre-treating a series of components for corrosion protection, wherein the components comprise steel surfaces, and each component undergoes successive treatment stages i) to iii). i) A conversion treatment stage, which includes contact with an acidic aqueous composition (I) comprising the following. a) A fluorine complex of elemental Zr and / or Ti, calculated in amounts of at least 0.05 mmol / kg, and b) A certain amount of free fluoride; ii) Conditioning stage, which includes contact with an alkaline aqueous composition (II) having a pH of at least 7.50, but preferably below 12.00, and containing dissolved magnesium and / or calcium ions in an amount satisfying at least one of the following two conditions: (1) The amount of dissolved magnesium ions, calculated in mg / kg, is greater than 20 divided by (pH of composition (II) minus 7), and / or (2) The amount of dissolved calcium ions, calculated in mg / kg, is greater than 50 divided by (pH of composition (II) minus 7); iii) The coating stage, which includes dip coating by contact with an aqueous dispersion (III) of an organic adhesive, Method step ii) follows immediately after method step i). Detailed Implementation

[0006] The corrosion protection treatment for the series of components is as follows: when multiple components are brought into contact with the treatment solutions provided in the respective treatment stages i) to iii) of the method according to the invention and routinely stored in a system tank, the components are brought into contact sequentially and thus at different times. The system tank is a container in which the specific treatment solutions (i.e., the acidic aqueous composition (I) of the conversion treatment stage, the alkaline aqueous composition (II) of the conditioning stage, and the aqueous dispersion containing an organic binder (III) of the coating stage) are placed for the purpose of the series of corrosion protection treatments according to the invention.

[0007] In the context of this invention, when referring to the treatment of components made of metallic materials, and particularly to the surface of steel to be treated in the method according to the invention, this includes all materials containing more than 50 atomic percent, preferably more than 80 atomic percent, particularly preferably more than 90 atomic percent of the relevant element (i.e., iron in the case of steel). Corrosion protection treatment is always applied to the surface of components formed of metallic materials. This material can be a homogeneous material or a coating. According to the invention, galvanized steel varieties include both steel and zinc, wherein the surface of the steel may be exposed, for example, at cut edges and bare metal points of a car body made of galvanized steel, in which case pretreatment of the steel is performed according to the invention.

[0008] The method according to the invention is not limited to use on the steel surface of a series of components, and therefore other components besides steel are also possible, particularly cold-rolled steel (CRS), and common substrates supplied by the steel industry, such as electrolytically galvanized steel (ZE) or hot-dip galvanized steel (Z), alloy galvanized steel (especially (ZM), (ZF), (ZA)), or aluminum-coated steel (AZ), (AS). In the method according to the invention, light metals (e.g., aluminum and magnesium) and their alloys can also be pre-treated for corrosion protection along with the steel surface. A key feature of the method according to the invention is its suitability for pre-treatment for corrosion protection of common metallic materials composed of iron, zinc, aluminum, and magnesium, i.e., providing them with a conversion coating that provides a good primer base for paint.

[0009] A particularly preferred embodiment is one in which the series of components are made not only of steel but also of hot-dip galvanized steel and / or aluminum. The suitability of the method according to the invention for providing good corrosion protection pretreatment (consisting of conversion layer formation and painting) for such material mixtures is particularly advantageous for components manufactured in a composite structure and assembled from different semi-finished products. The preferred method according to the invention is therefore a method in which the series of components are composed of semi-finished steel and semi-finished galvanized steel and aluminum, and particularly preferably a composite structure (preferably a car body) assembled from semi-finished steel and semi-finished galvanized steel and aluminum.

[0010] The components pretreated according to the present invention can be any three-dimensional structure of any shape and design derived from the manufacturing process, particularly semi-finished products such as strips, sheets, rods, tubes, etc., as well as composite structures assembled from the aforementioned semi-finished products. Composite structures assembled from different materials are typically in the form of flat products that have been cut to a certain size, shaped, and joined by welding, adhesive bonding, and folding. The components to be pretreated according to the present invention are preferably selected from automobile bodies or parts thereof, heat exchangers, profiles, tubes, tanks, or troughs.

[0011] In the context of this invention, whenever the concentration of an active ingredient or compound is mentioned as an amount of substance per kilogram, this refers to an amount of substance based on the weight of the specific total composition.

[0012] The embodiment of the invention, based on a conditioning stage of an alkaline aqueous composition containing a specifically specified minimum amount of calcium and / or magnesium ions, brings about significant improvements in corrosion protection on steel and coating results on the metallic surfaces of components in a previously conventional method of corrosion protection pretreatment, comprising a conversion treatment stage based on elements Zr and / or Ti and a coating stage based on dip coating. Furthermore, these improvements are achieved without additional operationally and energy-intensive process steps, particularly without a drying step prior to dip coating.

[0013] The various method steps i) to iii) and preferred embodiments of the method according to the invention are described in detail below, as well as a description of the process.

[0014] Transformation Processing Stage : In the conversion treatment stage of the method according to the invention, an amorphous oxide / hydroxide coating based on element Zr and / or Ti (preferably element Zr) is produced, and accordingly contains a compound of element Zr and / or Ti dissolved in water. A minimum concentration of 0.05 mmol / kg of the compound of element Zr and / or Ti dissolved in water is required to achieve sufficient conversion layer deposits at a preferred temperature of the acidic aqueous composition (I) in the range of 10 to 60°C and at a typical method application type (e.g., immersion or spraying) during a typical method contact time of 10 to 300 seconds. For this purpose, according to the invention, it is preferred that the proportion of the compound of element Zr and / or Ti dissolved in water in the acidic aqueous composition (I) in step i) of the method is at least 0.10 mmol / kg, particularly preferably at least 0.30 mmol / kg, and especially preferably at least 0.40 mmol / kg.

[0015] For reasons of process economy, the content of compounds of element Zr and / or Ti dissolved in water should preferably be less than 5.0 mmol / kg, particularly preferably less than 3.0 mmol / kg, and extremely particularly preferably less than 2.0 mmol / kg.

[0016] In a preferred embodiment, in order to obtain the most complete conversion possible on the metal surface (particularly the steel surface), the duration of contact between the component and the acidic aqueous composition (I) is based on the elemental Zr and / or Ti on the steel surface, respectively, to achieve a conversion of at least 20 mg / m³ on the steel surface. 2 A minimum of 40 mg / m² is preferred. 2 The duration of the layered deposits, but preferably not so long as to result in a layered deposit exceeding 200 mg / m³. 2 Especially preferred is more than 150 mg / m³ 2 Extremely preferred concentration: more than 100 mg / m³ 2 Especially preferred is more than 80 mg / m³ 2 Layered sediments can be identified using X-ray fluorescence analysis (XRF).

[0017] As already mentioned, during the conversion treatment stage, an amorphous oxide / hydroxide coating based on elemental Zr and / or Ti is obtained, and accordingly contains compounds of elemental Zr and / or Ti dissolved in water. The term "dissolved in water" includes substances dissolved at the molecular level as well as compounds that dissociate in aqueous solutions and form hydrated ions. Typical representatives of such compounds suitable for forming conversion layers from acidic aqueous solutions are titanium oxysulfate (TiO(SO4)), titanium oxynitrate (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. The compounds dissolved in water in the acidic aqueous composition (I) are preferably selected from fluoroacids and / or fluorine complexes of elemental Zr and / or Ti, and their water-soluble salts. The formation of conversion layers based on elemental Zr fluoroacids and / or fluorine complexes is particularly preferred because this type of conversion layer provides improved paint adhesion.

[0018] According to the invention, the conversion treatment in step i) must be carried out with an acidic aqueous composition (I) that also contains at least a certain amount of free fluoride; otherwise, sufficient pickling of the steel substrate and the resulting layer formation cannot often be ensured. The amount of free fluoride in the acidic aqueous composition (I) is usually preferably at least 1.00 mmol / kg. For processing components made of mixtures of different metallic materials and particularly having galvanized steel surfaces, a higher content of free fluoride may be practical to improve the conversion layer formation kinetics and produce sufficient layer deposits; and therefore, for processing components that also have zinc surfaces (particularly galvanized steel surfaces, and very particularly preferably hot-dip galvanized (ZM) steel surfaces), it is preferred that the proportion of free fluoride be at least 2.00 mmol / kg, and very particularly preferably at least 3.00 mmol / kg.

[0019] However, it has been found that a high proportion of free fluoride may in turn be detrimental to the adhesion of paint to steel, and therefore the acidic aqueous composition (I) in the conversion treatment stage of step i) is preferably less than 7.50 mmol / kg, particularly preferably less than 6.00 mmol / kg, and extremely particularly preferably less than 5.00 mmol / kg.

[0020] Suitable sources of free fluoride for acidic aqueous composition (I) are: water-soluble complex fluorides of elements Zr, Ti and / or Si, preferably water-soluble complex fluorides of elements Zr and / or Ti, particularly preferably water-soluble complex fluorides of element Zr; and / or hydrofluoric acid, ammonium hydrogen fluoride and / or water-soluble alkali metal fluorides.

[0021] The amount of free fluoride was determined by potentiometric measurement at 20°C in the provided acidic aqueous composition (I) after calibration with an unbuffered fluoride-containing buffer solution using a fluoride-sensitive measuring electrode.

[0022] Regarding the pH of the acidic aqueous composition in the conversion treatment stage, it should be noted that compounds of elements Zr and / or Ti dissolved in water will not form a sol due to hydrolysis, and this sol can no longer be used to form the conversion layer. Simultaneously, the pickling rate for common metallic materials should be sufficiently high to form a uniform, sealing conversion layer; this is particularly applicable to base steel. For this purpose, according to the invention, it is preferred that the acidic aqueous composition (I) has a pH not higher than 5.20, and preferably less than 5.10, particularly preferably less than 5.00, extremely particularly preferably less than 4.90, and especially preferably less than 4.80. However, increased pickling rates and rapid layer formation kinetics may be detrimental to the formation of a suitable conversion coating. Particularly on hot-dip galvanized steel, very high layer weights with respect to elements Zr and / or Ti are obtained in highly acidic environments, and these layer weights are more prone to defects due to the high layer formation kinetics. According to the present invention, it is therefore preferred, particularly for the pretreatment of components having a zinc surface in addition to a steel surface, that the pH of the acidic aqueous composition (I) is greater than 3.50, especially preferably greater than 4.00, particularly especially preferably greater than 4.20, and very particularly preferably greater than 4.40.

[0023] In the context of the conversion treatment stage, pH according to the invention corresponds to the negative decimal logarithm of the hydrated hydrogen ion activity measured at 20°C in an acidic aqueous composition (I) after two-point calibration using a pH-sensitive glass electrode in an industrial buffer solution for acetate / acetate (pH = 4.00) and an industrial buffer solution for phosphate (pH = 7.00).

[0024] The presence of copper ions may be advantageous for repairing defects in the conversion layer grown on steel surfaces, particularly on hot-dip galvanized steel surfaces, in step i). The localized deposition of these copper ions in the defective areas then provides improved corrosion protection. In this context, it is preferred that the acidic aqueous composition (I) of the conversion treatment stage in step i) further comprises copper ions dissolved in water, preferably at least 0.05 mmol / kg, but more preferably less than 4.0 mmol / kg, and particularly preferably less than 2.0 mmol / kg. Suitable sources of water-soluble copper ions are water-soluble salts, such as copper nitrate (Cu(NO3)2), copper sulfate (CuSO4), and copper acetate (Cu(CH3COO)2).

[0025] Other additives known to those skilled in the art of surface treatment, such as promoters, nitrate ions, nitrite ions, nitroguanidine, N-methylmorpholine N-oxide, free or bound hydrogen peroxide, free or bound hydroxylamine, reducing sugars, may be included in the acidic aqueous composition (I) to improve layer formation kinetics, wettability, and corrosion protection properties. These other additives include, for example: promoters such as nitrate ions, nitrite ions, nitroguanidine, N-methylmorpholine N-oxide, free or bound hydrogen peroxide, free or bound hydroxylamine, reducing sugars; and / or wetting agents such as nonionic surfactants; and / or polymers such as polyamides; and / or cationic / compound forms of the elements Mg, Ca, Al, Si, Sn, Bi, and / or Mo. However, for resource-saving purposes and for economic reasons, the use of organosilicon compounds can be largely avoided. In a preferred embodiment of the method according to the invention, the acidic aqueous composition (I) in the conversion treatment stage is therefore substantially free of hydrolyzable organosilicon / siloxanes and preferably contains less than 10 mg / kg of hydrolyzable organosilicon / siloxanes calculated as Si(OCH2CH3)4.

[0026] The application of the acidic aqueous composition (I) for the formation of the conversion layer in step i) and thus the contact with the acidic aqueous composition (I) are preferably carried out at a temperature of at least 30°C, particularly preferably at least 40°C, but preferably below 60°C. The acidic aqueous composition (II) of the conversion stage can be contacted with the series of components by application types established in the prior art. These include, in particular, impregnation, rinsing, spraying, and / or atomization, wherein application by impregnation and / or spraying methods, and particularly immersing the series of components in a system basin containing the corresponding acidic aqueous composition (I), is preferred.

[0027] conditioning stage : The success of the method according to the invention depends primarily on satisfying at least one of the following conditions regarding the alkaline aqueous composition (II) during the method steps: (1) The amount of dissolved magnesium ions, calculated in mg / kg, is greater than 20 divided by (pH of composition (II) minus 7), and / or (2) The amount of dissolved calcium ions calculated in mg / kg is greater than 50 divided by (pH of composition (II) minus 7).

[0028] Condition (1) specifies that, based on the alkaline aqueous composition (II), the threshold of magnesium ions to be exceeded in milligrams per kilogram (preferably rounded to the nearest integer) corresponds to the following: Condition (2) is equivalent to specifying that, based on the alkaline aqueous composition (II), the threshold of calcium ions to be exceeded in milligrams per kilogram (preferably rounded to the nearest integer) corresponds to the following: In each case, the pH of the alkaline aqueous composition (II) will be used as the variable "pH".

[0029] Once the amount of calcium and / or magnesium ions is set above a threshold, a significant improvement in the corrosion protection properties of the amorphous conversion coating based on the fresh deposition of elemental Zr and / or Ti is achieved after dip coating. In a preferred embodiment, which often leads to further improvement in corrosion protection performance, the alkaline aqueous composition (II) in the method step achieves at least one of the following two conditions: (1) The amount of dissolved magnesium ions, calculated in mg / kg, is greater than 40, particularly preferably greater than 50, extremely particularly preferably greater than 60, divided by (pH of composition (II) minus 7), and / or (2) The amount of dissolved calcium ions calculated in mg / kg is greater than 70, particularly preferably greater than 90 and extremely particularly preferably greater than 100, divided by (pH of composition (II) minus 7).

[0030] However, the property of the alkaline aqueous composition (II) to improve the corrosion protection of freshly deposited amorphous conversion coatings based on elements Zr and / or Ti becomes saturated above a certain amount of calcium and / or magnesium ions. Therefore, for economic reasons and to reduce the introduction of these ions into the subsequent coating stage of step (iii), it is practical and therefore preferred that the amount of dissolved magnesium ions and dissolved calcium ions in the alkaline aqueous composition (II) each not exceed 200 mg / kg, and particularly preferably the total amount of dissolved magnesium and calcium ions not exceed 200 mg / kg.

[0031] Typical and suitable sources of magnesium and calcium ions contained in the alkaline aqueous composition (II) are: the corresponding nitrates and hydroxides, preferably hydroxides, and the corresponding salts of α-hydroxycarboxylic acids (e.g., lactic acid, citric acid, tartaric acid and gluconic acid).

[0032] The pH of the alkaline aqueous composition is at least 7.50, but preferably below 12.00, to ensure adequate conditioning of the conversion coating applied to the steel surface in step i). While higher alkalinity may allow for the necessary conditioning of the conversion coating on steel surfaces, this method is less suitable for conditioning conversion coatings on galvanized steel and aluminum substrates, as severe pickling occurs at defects in the conversion coating on the substrate, often resulting in reduced corrosion protection on these substrates. Therefore, for the pretreatment of components comprising not only steel surfaces but also zinc and / or aluminum surfaces, a pH below 12.00 is particularly preferred, and especially preferably below 11.50, extremely particularly preferably below 10.50, and particularly preferably below 10.00. Meanwhile, improving the corrosion value can often be achieved by moderately increasing the pH of the alkaline aqueous composition (II) above 7.50. The resulting improvement is often significant, but the presence of calcium and / or magnesium ions, as specifically specified according to the invention, is still required; however, the minimum amount required for conditioning is moderately reduced, just as the pH is increased. In order to achieve optimal corrosion protection on steel surfaces and also to avoid brushing, it has been proven that, according to the present invention, it is preferred that the pH of the alkaline aqueous composition (II) be set above 8.00, particularly preferably above 8.50, and especially preferably above 9.00.

[0033] In the context of the conditioning phase, pH according to the invention corresponds to the negative decimal logarithm of the hydrated hydrogen ion activity measured at 20°C in an alkaline aqueous composition (II) after two-point calibration using a pH-sensitive glass electrode in an industrial buffer solution for acetic acid / acetate (pH = 4.00) and an industrial buffer solution for boric acid / borate (pH = 9.00).

[0034] The purpose of step ii) is solely to condition the freshly deposited conversion coating and, therefore, to prevent or repair layer defects in the amorphous passivation layer, which consists of oxides and hydroxides of elemental Zr and / or Ti, and hydrolysis products of fluoride compounds of elemental Zr and / or Ti that cause conversion on the steel surface. Undesirably, significant deposition of other active components occurs during the conditioning stage, and it is also process-disadvantageous that significant amounts of active components, in addition to those used to form minimal amounts of magnesium and / or calcium ions, must be prevented from being carried into the subsequent aqueous dispersion (III) in the dip-coating process. Therefore, according to the invention, it is preferred that the alkaline aqueous composition (II) in the conditioning stage contains… (a) A compound of a metal element dissolved in water, calculated based on the amount of each specific element in composition (II), wherein the metal element is less than 50 mg / kg, preferably less than 100 mg / kg in total, and particularly preferably less than 50 mg / kg in total, wherein the standard reduction potential (Me) of the metal element is... 0 / Me n+ The standard reduction potential of iron (Fe) is greater than that of iron. 0 / Fe 2+ ), (b) A compound of Cu, Ni, Co, Bi or Ag dissolved in water, calculated in amounts of each specific element in composition (II) of less than 50 µmol / kg, preferably less than 20 µmol / kg, and particularly preferably less than 10 µmol / kg. (c) Surfactants, preferably less than 50 mg / kg, and particularly preferably less than 10 mg / kg, in total, or preferably surface-active organic compounds or particularly preferably organic compounds that are not polymeric organic compounds with a molecular weight greater than 500 g / mol. (d) Organic polymeric compounds with a molecular weight greater than 500 g / mol, each in total less than 50 mg / kg, preferably less than 10 mg / kg, particularly preferably less than 5 mg / kg, especially preferably less than 1 mg / kg, are preferred organic polymeric compounds. (e) Compounds of elemental silicon dissolved in water, each comprising less than 100 mg / kg, preferably less than 10 mg / kg, particularly preferably less than 5 mg / kg, especially preferably less than 1 mg / kg, based on Si(OCH2CH3)4. (f) Compounds of Zr and / or Ti dissolved in water totaling less than 50 µmol / kg, preferably less than 20 µmol / kg, and particularly preferably less than 10 µmol / kg. (g) a total of less than 50 mg / kg, preferably less than 10 mg / kg, of zinc ions, and / or (h) Phosphates or phosphorus-containing compounds dissolved in water, each in total less than 100 mg / kg, preferably less than 10 mg / kg.

[0035] The standard reduction potential is for the standard hydrogen electrode H2 / H + Electrochemical half-cell Me / Me ratio determined at pH=0, with 1 mol / L metal ion activity and a temperature of 20 °C. n+ The reduction potential.

[0036] The application of the alkaline aqueous composition (II) in step ii) of the conditioning stage, and therefore the contact with the alkaline aqueous composition (II), is preferably carried out at a temperature of at least 20°C, particularly preferably at least 30°C, but preferably below 60°C. The alkaline aqueous composition (II) of the conditioning stage can be contacted with the series of components by application types established in the prior art. These particularly include immersion, atomization, rinsing by splashing, or spraying the components, wherein application of the corresponding acidic aqueous composition (I) by immersion, spraying, and / or atomization is preferred.

[0037] process : Preferred embodiments of the method according to the invention are shown and explained below for each processing stage and process, which are particularly advantageous for the purpose on which the invention is based.

[0038] Processing stages i) to iii) of the method according to the invention each include at least one processing step that provides contact between a series of components and an aqueous composition characterized and more specifically defined for the processing stage. For the purpose of this contact, these characteristic compositions are either stored or preserved in a system tank, wherein the contact can occur within the system tank, for example by immersion in the composition preserved therein, or outside the system tank, for example by atomizing the composition stored within the system tank in an atomization chamber, depending on the specific requirements or preferences of the relevant method steps.

[0039] In the method according to the invention, steps i) to iii) are performed sequentially, i.e., in a specifically specified order, and preferably in such a manner that no wet chemical treatment steps other than a rinsing step are performed on the component between two steps i) to iii). In this case, the rinsing step is primarily (preferably only) used to remove the wet film adhering to the component from the previous wet chemical steps and thus to completely or partially remove soluble residues, particles, and active components that would otherwise adhere to the component and be carried from the previous wet chemical steps to the next processing stage.

[0040] According to the present invention, method step ii) (i.e., the conditioning stage) is performed directly after method step i) of the conversion stage. This means that the method steps are sequential in such a way that the assembly having a wet film of the acidic aqueous composition (I) attached from method step i) of the conversion stage is transferred to the conditioning stage to contact with the alkaline aqueous composition (II), i.e., without intermediate wet chemical treatment or rinsing steps and without intermediate drying steps. The drying step within the meaning of the present invention is a method step aimed at drying the surface of the assembly by means of providing and using technical means (e.g., by means of a blower or hot air furnace) to supply heat energy and / or airflow.

[0041] In a preferred method according to the invention, a so-called rinsing stage is performed after the conditioning stage, the rinsing stage comprising at least one rinsing step or a cascade of rinsing steps. During the rinsing stage, a wet film of the alkaline aqueous composition (II) adhering from the conditioning stage is removed from the series of components to prevent the introduction of alkalinity into the painting stage. For this purpose, the rinsing stage consists of one or more rinsing steps (so-called rinsing step cascades) performed immediately after each other. In the cascade, the rinsing steps are sequential if no other wet chemical treatment step or drying step is performed on the components during this period. For the practical function of the rinsing stage (which consists of preventing the introduction of alkalinity into the subsequent painting stage), it is advantageous and therefore preferred in the context of the invention that, as already described, the rinsing stage comprises multiple sequentially arranged rinsing steps (i.e., rinsing step cascades) for contacting the series of components with their respective rinsing solutions stored in the system tanks of the respective rinsing steps.

[0042] In the rinsing stage following the conditioning stage, the wet film of the alkaline aqueous composition (II) should be removed to the greatest extent possible. Therefore, the rinsing step in the rinsing stage is carried out with a fresh water-based rinsing medium, which preferably does not contain any type or amount of active components, as it would be problematic and need to be prevented from carrying these active components into subsequent painting stages. However, if necessary, the rinsing medium may contain small amounts of redox-active compounds (“depolarizers”) (e.g., hydrogen peroxide) or additionally surfactants (e.g., nonionic surfactants) to improve the wettability of the surface for dip coating. However, the addition of additives should not result in more than 40 µScm in a single or final rinsing step of the rinsing stage. -1 The preferred maximum specific conductivity. In particular, the inclusion of elements and compounds in the rinsing medium that may have a detrimental effect on corrosion protection should be avoided. Therefore, it is preferred that the rinsing medium in a single or final rinsing step of the rinsing stage in the method according to the invention, and preferably in any rinsing medium of all rinsing steps in the rinsing stage, contains […]. (a) A compound of a metal element dissolved in water, calculated by the amount of each specific element in the rinsing medium, wherein each element is less than 50 mg / kg, preferably less than 100 mg / kg in total, and particularly preferably less than 50 mg / kg in total, wherein the standard reduction potential (Me) of the metal element is... 0 / Me n+ The standard reduction potential of iron (Fe) is greater than that of iron. 0 / Fe 2+ ), (b) Compounds of Cu, Ni, Co, Bi, or Ag dissolved in water, calculated based on the amount of each specific element in the rinsing medium, that are less than 50 µmol / kg, preferably less than 20 µmol / kg, and particularly preferably less than 10 µmol / kg. (c) Surfactants, preferably less than 50 mg / kg, and particularly preferably less than 10 mg / kg, in total, or preferably surface-active organic compounds or particularly preferably organic compounds that are not polymeric organic compounds with a molecular weight greater than 500 g / mol. (d) Organic polymeric compounds with a molecular weight greater than 500 g / mol, each in total less than 50 mg / kg, preferably less than 10 mg / kg, particularly preferably less than 5 mg / kg, especially preferably less than 1 mg / kg, are preferred organic polymeric compounds. (e) Compounds of elemental silicon dissolved in water, each comprising less than 100 mg / kg, preferably less than 10 mg / kg, particularly preferably less than 5 mg / kg, especially preferably less than 1 mg / kg, based on Si(OCH2CH3)4. (f) Compounds of Zr and / or Ti dissolved in water totaling less than 20 µmol / kg, preferably less than 10 µmol / kg, and particularly preferably less than 5 µmol / kg. (g) Sodium and / or potassium ions totaling less than 50 mg / kg, preferably less than 10 mg / kg each, (h) Total zinc ions less than 50 mg / kg, preferably less than 10 mg / kg, and / or (i) Phosphates or phosphorus-containing compounds dissolved in water, each in total less than 100 mg / kg, preferably less than 10 mg / kg, The pH of the rinsing medium is preferably in the range of 5.0 to 8.5.

[0043] The standard reduction potential is for the standard hydrogen electrode H2 / H + Electrochemical half-cell Me / Me ratio determined at pH=0, with 1 mol / L metal ion activity and a temperature of 20 °C. n+ The reduction potential.

[0044] For the rinsing stage after the conditioning stage and before the coating stage, it is preferable that the specific conductivity of the rinsing medium in the system tank of a single rinsing step or in the system tank of the last rinsing step in a cascade (i.e., the rinsing medium in the system tank of the rinsing step immediately preceding method step iii) is not higher than 40 µScm. -1 Preferably not higher than 10 µScm -1 .

[0045] To achieve this, fresh water (preferably less than 10 µScm) can be supplied to the system tank of the rinsing stage or a single rinsing step, or to at least one system tank of cascaded rinsing steps. -1 The specific conductivity), wherein the volumetric flow rate of the supplied fresh water should be high enough to avoid exceeding 40 µS / cm during the rinsing phase of the series components during treatment. -1 Preferred maximum specific conductivity or 10 µS / cm -1 The optimal maximum specific conductivity.

[0046] Furthermore, for reasons of process economy, it is preferred that method step iii) follow the conditioning stage according to method step ii) and the optional rinsing stage immediately following method step ii) (as already described, the rinsing stage preferably includes at least one rinsing step or a cascade of rinsing steps, each of which is carried out with a rinsing medium based on fresh water) immediately after method step iii), preferably in such a way that the component having a wet film attached from the conditioning stage or optionally having a wet film attached from a single or final rinsing step of the rinsing stage is transferred to the coating stage to contact with the aqueous dispersion (III) (i.e., without an intermediate drying step), and in this way a “wet-on-wet” process is established for the series of components throughout all method steps i) to iii) of the method according to the invention.

[0047] It should also be noted that, in the method according to the invention, the components are first cleaned and degreased in a degreasing stage before method step i) and therefore before the formation of the conversion layer.

[0048] During the degreasing stage, an alkaline aqueous composition having a pH higher than 9.00 and preferably containing at least one surfactant selected from anionic surfactants, cationic surfactants, zwitterionic surfactants, and / or nonionic surfactants can be provided for cleaning and degreasing the series of components. The purpose of the degreasing stage is to ensure that the component surface is substantially free of inorganic salts and organic contaminants (especially drawing oil, stencil oil, calendering oil, and anti-corrosion protective oil) for subsequent conversion treatment stages, and to ensure that an amorphous oxide / hydroxide coating based on elemental Zr and / or Ti can be produced as uniformly as possible. In a preferred embodiment, immediately after passing through the degreasing stage (i.e., before the conversion treatment stage but using deionized water), κ <1µScm -1 After the rinsing step, less than 0.20 g / m² of residue remains on the metallic surfaces of the series components. 2 Preferred concentration is less than 0.10 g / m 2 Carbon deposition. The layer of carbon deposits remaining on the surface of the component formed of metallic material can be determined by pyrolysis. For this purpose, a representative portion of a defined area of ​​the component is subjected to a substrate temperature (PMT) of 550°C in an oxygen atmosphere, and the amount of carbon dioxide released is quantified as the amount of carbon using an infrared sensor, for example, by an analytical device such as the LECO® RC-412 Multiphase Carbon Determinator (Leco Corp.).

[0049] According to the invention, the pH of the optionally present defatting stage corresponds to the negative decimal logarithm of the hydrated hydrogen ion activity measured at 20°C in an alkaline aqueous composition (I) after two-point calibration using a pH-sensitive glass electrode in an industrial buffer solution for acetic acid / acetate (pH = 4.00) and an industrial buffer solution for boric acid / borate (pH = 9.00).

[0050] In the context of this invention, the process further includes applying an anti-corrosion protective coating (i.e., conversion treatment and dip coating) to components that may contain other metallic materials besides steel, wherein the components are preferably connected together, particularly those connected together in a composite structure (e.g., a vehicle body); and the components have a zinc surface in addition to the aforementioned steel surface, particularly preferably zinc and aluminum surfaces. Suitable metallic materials whose surfaces can be pre-treated for anti-corrosion protection in the method according to this invention, besides steel, include: zinc, electrolytically galvanized (ZE) steel strip, hot-dip galvanized (Z) steel strip, and alloy galvanized (ZA), (ZF), and (ZM) steel strips, and aluminum-coated (AZ) and (AS) steel strips, as well as light metals aluminum and magnesium and their alloys.

[0051] Coating stage : In the coating stage, at least the component surface (preferably all surfaces formed of metallic material) formed of steel and converted and coated in step ii) is coated with a first paint system by contacting the component or at least the converted and coated steel surface with an aqueous dispersion (III) containing an organic binder. Thus, the paint system is deposited directly from the aqueous phase as a coating of the organic binder of the aqueous dispersion (III) precipitated on the aforementioned surface, and the coating is often subjected to thermal post-treatment for film formation and curing. The coating in the coating stage is carried out as dip coating, preferably as electrophoretic coating, and more preferably as cathodic electrophoretic coating. For this purpose, the organic binder of the aqueous dispersion (III) is preferably based on an amine-modified film-forming polyepoxide, which preferably additionally contains an organic compound containing closed and / or unclosed isocyanate groups as a curing agent. Inorganic pigments are also often components of the aqueous dispersion and are preferred additives for improving corrosion protection. The aqueous phase preferably contains a small amount of yttrium and / or bismuth compounds dissolved or dispersed in water, which have a positive effect on crosslinking and film formation.

[0052] The preferred pH of the aqueous dispersion (III) in the coating stage is in the range of 5.0 to 6.0, and particularly preferably in the range of 5.4 to 5.8. In the context of the coating stage, the pH according to the invention corresponds to the pH after coating with deionized water (κ < 1 µS / cm). -1 The negative decimal logarithm of the hydrated hydrogen ion activity was measured at 20°C using a pH-sensitive glass electrode after two-point calibration in an industrial buffer solution for acetic acid / acetate (pH = 4.00) and an industrial buffer solution for boric acid / borate (pH = 9.00).

[0053] The application of the aqueous dispersion (III) and thus the contact of the components, or at least the aforementioned converted steel surfaces, with the aqueous dispersion (III) is preferably carried out at a temperature of at least 30°C, particularly preferably at least 40°C, but preferably below 60°C. The aqueous dispersion (III) in the coating stage can be contacted with the series of components by the immersion application type established in the prior art, wherein, in particular, it is preferred to immerse the series of components in a system tank containing the respective aqueous dispersion (III).

[0054] Exemplary implementation scheme: In a series of tests on corrosion protection treatment of steel substrates, steel plates (CRS) were subjected to wet chemical treatment as follows, and the corrosion penetration of the paint layer structure was evaluated after 30 cycles of salt spray testing according to VW PV 120 and stone impact testing according to DIN EN ISO 20567-1.

[0055] (A) Cleaning and degreasing stage a. Spray degreasing at 55℃ for 60 seconds. b. Immerse and degrease at 55°C for 120 seconds. Each was cleaned using a detergent from Henkel AG & Co. KGaA (pH 11.5; total alkalinity 12), said detergent being based on Bonderite® C-AK 2011 and using deionized water containing 2.50 g / L PO4 (κ < 1 µScm). -1 )preparation.

[0056] (B) Use deionized water (κ<1µScm) -1 The rinsing stage is carried out. a. Spray for 30 seconds at 20°C. b. Immerse at 20°C for 30 seconds (C) Conversion treatment stage at 35°C for 120 seconds Based on Bonderite® M-NT 5800 (Henkel AG&Co. KGaA) and using deionized water (κ<1µScm) -1 Prepared and adjusted to pH 4.5 (25°C), containing... Zr 150 mg / L Cu 4 mg / L Free F was 35 mg / kg, a value determined by potentiometry using a fluoride-sensitive electrode. (D) Conditioning stage performed by immersion at 20°C for 30 seconds: a. Deionized water (κ<1µScm) -1 ); b. Deionized water (κ<1µScm) -1 10 mg / kg of calcium ions in the solution, pH 9 c. Deionized water (κ<1µScm) -1 30 mg / kg of calcium ions in the solution, pH 9 d. Deionized water (κ<1µScm) -1 50 mg / kg of calcium ions in the solution, pH 9 (E) By immersion at 20°C for 30 seconds with deionized water (κ<1µScm) -1 The rinsing stage is carried out as follows: (F) Optional drying with compressed air and storage in a drying cabinet at 50°C. (G) Cathodic dip coating with Cathoguard® 800 (BASF SE) at a dry layer thickness of 20 µm In the conversion coating (C) (which resulted in zirconium deposition at 45 to 55 mg / m² as measured by X-ray fluorescence analysis), 2 After that (within the range), the steel plate is then subjected to a rinsing stage or with deionized water (κ<1µScm) in the subsequent conditioning stage (D). -1 Alternatively, treat with a solution containing calcium ions, and then perform cathodic dip coating (G) after rinsing (E).

[0057] Table 1 summarizes the corrosion results after stone impact (DIN EN ISO 20567) and exposure to salt spray (VW PV 1210). It has been found that conditioning stages containing calcium ions significantly improve corrosion penetration and paint adhesion at scratches after stone impact, provided that the proportion of calcium ions exceeds a pH-determined threshold (CE3 compared to E1 and E2), and the achievable corrosion protection is only as good as that achieved by drying and freshly rinsing the converted board (CE2 compared to E2).

Claims

1. A method for pre-treating a series of components for corrosion protection, the components comprising steel surfaces, wherein each component undergoes successive treatment stages i) to iii). i) A conversion treatment stage, which includes contact with an acidic aqueous composition (I) comprising the following. a) A compound containing at least 0.05 mmol / kg of elemental Zr and / or Ti dissolved in water, calculated by amount of elemental Zr and / or Ti, and b) A certain amount of free fluoride; ii) Conditioning stage, which includes contact with an alkaline aqueous composition (II) having a pH of at least 7.50 and containing dissolved magnesium and / or calcium ions in an amount satisfying at least one of the following two conditions: (1) The amount of dissolved magnesium ions, calculated in mg / kg, is greater than 20 divided by (pH of composition (II) minus 7), and / or (2) The amount of dissolved calcium ions, calculated in mg / kg, is greater than 50 divided by (pH of composition (II) minus 7); iii) The coating stage, which includes dip coating by contact with an aqueous dispersion (III) of an organic adhesive, Method step ii) follows immediately after method step i).

2. The method according to claim 1, characterized in that: Method step ii) is immediately followed by a rinsing stage, which includes at least one rinsing step or a cascade of rinsing steps, preferably using a fresh water-based rinsing medium, and preferably this rinsing step or cascade of rinsing steps is immediately followed by method step iii), wherein the specific conductivity of the rinsing medium in the system tank immediately preceding method step iii) is preferably less than 40 µS / cm. -1 Especially preferred is less than 10 µScm -1 .

3. The method according to one or more of the preceding claims, characterized in that: Step iii) follows step ii) without an intermediate drying step.

4. The method according to one or more of the preceding claims, characterized in that: Prior to the conversion treatment stage in method step i), the series of components are first cleaned and / or degreased.

5. The method according to one or more of the preceding claims, characterized in that: The alkaline aqueous composition (II) prepared in step ii) has a pH higher than 8.00, preferably higher than 8.50, particularly preferably higher than 9.00, but preferably lower than 12.00 and particularly preferably lower than 11.50, extremely particularly preferably lower than 10.50 and especially preferably lower than 10.

00.

6. The method according to one or more of the preceding claims, characterized in that: In step ii), the amount of dissolved magnesium ions and dissolved calcium ions in the alkaline aqueous composition (II) prepared in the method shall each not exceed 200 mg / kg, and preferably the total amount of dissolved magnesium and calcium ions in the water shall not exceed 200 mg / kg.

7. The method according to one or more of the preceding claims, characterized in that: The amount of each of the dissolved elements Zr and / or Ti compounds in the alkaline aqueous composition (II) prepared in step ii) of the method, calculated based on Zr and / or Ti, is less than 50 µmol / kg, preferably less than 20 µmol / kg, and particularly preferably less than 10 µmol / kg.

8. The method according to one or more of the preceding claims, characterized in that: The alkaline aqueous composition (II) prepared in step ii) comprises a polymeric organic compound with a molecular weight greater than 500 g / mol in total of less than 10 mg / kg, preferably less than 5 mg / kg, and particularly preferably less than 1 mg / kg.

9. The method according to one or more of the preceding claims, characterized in that: The alkaline aqueous composition (II) prepared in step ii) contains less than 10 mg / kg, preferably less than 5 mg / kg, and particularly preferably less than 1 mg / kg of organosilane and / or siloxane in total calculated as Si(OCH2CH3)4.

10. The method according to one or more of the preceding claims, characterized in that: The alkaline aqueous composition (II) prepared in step ii) comprises a compound of a water-soluble metal element, each in an amount of less than 50 mg / kg, preferably less than 100 mg / kg in total, and particularly preferably less than 50 mg / kg in total, said metal element having a standard reduction potential (Me). 0 / Me n+ The value is greater than the standard reduction potential of iron (Fe). 0 / Fe 2+ ).

11. The method according to one or more of the preceding claims, characterized in that: The alkaline aqueous composition (II) prepared in step ii) comprises a compound of the element Cu, Ni, Co, Bi or Ag dissolved in water, each in an amount of less than 50 µmol / kg, preferably less than 20 µmol / kg, and particularly preferably less than 10 µmol / kg, calculated by the amount of each specific element.

12. The method according to one or more of the preceding claims, characterized in that: The acidic aqueous composition (I) in step i) of the conversion treatment stage comprises a fluorine complex of elemental Zr and / or Ti in an amount of at least 0.10 mmol / kg, preferably at least 0.30 mmol / kg, particularly preferably at least 0.40 mmol / kg, but preferably not more than 5.0 mmol / kg, particularly preferably not more than 3.0 mmol / kg, and extremely particularly preferably not more than 2.0 mmol / kg, calculated by the amount of elemental Zr and / or Ti.

13. The method according to one or more of the preceding claims, characterized in that: The acidic aqueous composition (I) in step i) of the conversion treatment stage further comprises copper ions dissolved in water, preferably in an amount of at least 0.05 mmol / kg, but preferably less than 4.0 mmol / kg, and particularly preferably less than 2.0 mmol / kg of copper ions dissolved in water.

14. The method according to one or more of the preceding claims, characterized in that: The duration of the conversion treatment phase (I) in step i) of the method is sufficient to form at least 20 mg / m² on the steel surface of the series components. 2 Preferably at least 40 mg / m 2 However, it is preferred to have a concentration of no more than 200 mg / m³. 2 Layered deposits of Zr and / or Ti.

15. The method according to one or more of claims 2 to 14, characterized in that: The series of components also have a zinc surface, and preferably an additional zinc and aluminum surface.

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