Multistage method for corrosion-protective treatment of components having steel surfaces

Abstract

The present invention relates to a multistage method in which a series of components, each having surfaces of steel, are initially provided with a conversion layer based on the elements Zr and / or Ti and are subsequently dip-coated, wherein the conversion treatment stage is followed by a conditioning stage in which at least the steel surfaces of each component are brought into contact with an alkaline aqueous composition containing calcium and / or magnesium ions. With the method according to the invention, even in process conditions which are usually favourable for corrosion defects on steel surfaces, it is nonetheless possible to achieve an excellent level of corrosion protection, meaning that a drying step following the conversion stage can be dispensed with.

Description

[0001] “Multi-stage process for the corrosion-protective treatment of components with steel surfaces”

[0002] The present invention relates to a multi-stage process in which a series of components, each having steel surfaces, is first coated with a conversion layer based on the elements Zr and / or Ti and then dip-coated. The conversion treatment stage is followed by a conditioning stage in which at least the steel surfaces of each component are brought into contact with an alkaline aqueous composition containing calcium and / or magnesium ions. In the process according to the invention, excellent corrosion protection on the steel surfaces is achieved even under process conditions that typically promote corrosion defects on the steel surfaces, so that a drying step following the conversion stage can be dispensed with.

[0003] In the corrosion-protective pretreatment of components with surfaces made of steel, galvanized steel, and / or aluminum, thin-film passivation based on amorphous conversion coatings based on oxides and hydroxides of the elements Zr and / or Ti has become widely established as an alternative to phosphating, which forms crystalline coatings. Efforts to further develop this type of conversion coating are primarily aimed at establishing resource-saving and chromium-free passivations that provide an excellent adhesion base for subsequently applied paint systems, particularly dip coatings, with the aim of achieving corrosion protection comparable to that achieved with trication zinc phosphating.Especially for amorphous thin films, such as those resulting from conversion treatments from acidic aqueous solutions containing water-soluble compounds of the elements Zr and / or Ti, controlled layer formation and the growth of coatings that are as defect-free as possible are of great importance. For this purpose, the prior art focuses on influencing the kinetics of layer formation, as described in WO 2023 / 275270, and proposes, for example, sequential formation of the conversion layer in several wet-chemical process steps to create the layer deposits based on the hydroxides and oxides of the elements Zr and / or Ti, which bring about the most complete conversion possible of the conversion treatment based on fluorocomplexes of the elements Zr and / or Ti. This is intended to prevent fluorides from remaining in the thin film, which can cause local layer defects upon contact with corrosive media.Another process for conversion coating formation, described as an example in EP 1 455 002 A1, aims to reduce the proportion of fluorides in the conversion coating and the associated improvement in corrosion behavior and paint adhesion to a subsequently applied dip coating. EP 1 455 002 A1 proposes adding magnesium, calcium, a Si-containing compound, zinc, or copper to the conversion solution and, alternatively or in combination, drying the conversion coating or rinsing it with an alkaline aqueous composition.

[0004] Particularly on steel surfaces, the formation of flash rust can be observed during the serial pretreatment of components by forming a conversion coating based on complex fluorides of the elements Zr and / or Ti. This occurs if the wet film originating from the conversion stage and still adhering to the surfaces of the components during transport to the painting stage is not completely removed, e.g., by blowing it off in an air stream, or if the conversion coating is completely dried by thermal post-treatment. The latter process step is also proposed by EP 1 455 002 A1 to improve the corrosion protection of the conversion coating. However, such process steps are technically complex and involve high energy consumption.Therefore, in the prior art, the conversion stage is often followed by an intensive rinsing stage with fresh water, in which the wet film originating from the conversion stage and still directly adhering to the surfaces of the components is completely removed before the component is transferred to the painting stage. Rinsing with alkaline aqueous rinsing solutions is also proposed in EP 1 455 002 A1 to improve the corrosion protection of the conversion coating.However, even with such a process that minimizes the formation of rust by means of an intensive rinsing stage, it has not yet been possible to avoid a decrease in the corrosion protection on the steel surfaces after dip coating compared to processes with thermal drying of the conversion coating. In addition, irregularities in the appearance of the dip coating, the so-called "mapping", often occur in the presence of the rinsing stage and this also applies to the other metallic surfaces of the components, e.g. on galvanized steel surfaces.

[0005] The present invention therefore has the object of establishing a process for providing conversion coatings on metal surfaces, in particular steel surfaces, which are as defect-free as possible and which, during industrial pretreatment and dip-coating of a large number of components, imparts a high degree of robustness against corrosive impairment during the phase of transferring the components from the conversion treatment stage to the dip-coating stage and also delivers high-quality dip-coated components with improved corrosion protection properties. In the process, especially on steel, the quality of the conversion coating should not be negatively influenced by downstream rinsing steps, and yet a process should be established in which the components can be transferred directly to the painting line after rinsing, i.e. without thermal post-treatment, and can be dip-coated without any loss of corrosion protection.Ideally, fluctuations in performance, corrosion protection, and irregularities in the appearance of the dip-coated components, known as "mapping," are also prevented. The process must be suitable for effectively protecting components consisting of a mix of different metals, especially steel, zinc, and aluminum, from corrosion.This object is achieved by a process for the corrosion-protective pretreatment of components in series, comprising steel surfaces, in which each component undergoes the successive treatment stages i) - iii): i) conversion treatment stage comprising bringing into contact with an acidic aqueous composition (I) containing a) at least 0.05 mmol / kg of fluorocomplexes of the elements Zr and / or Ti, calculated as the amount of the elements Zr and / or Ti, and b) an amount of free fluoride; ii) conditioning stage comprising bringing into contact with an alkaline aqueous composition (II) with a pH of at least 7.50, but preferably below 12.00, containing magnesium ions and / or calcium ions dissolved in water in an amount such that at least one of the two following conditions is met:.

[0006] (1) The amount of dissolved magnesium ions calculated as mg / kg is greater than 20 divided by the pH of composition (II) reduced by 7, and / or

[0007] (2) The amount of dissolved calcium ions calculated as mg / kg is greater than 50 divided by the pH of the composition (II) reduced by 7; (iii) a coating step comprising dip coating by contacting with an aqueous dispersion (III) of an organic binder, wherein process step (ii) immediately follows process step (i).

[0008] A series corrosion-protective treatment of components occurs when a large number of components are brought into contact with the treatment solution provided in the respective treatment stages i)-iii) of the process according to the invention and typically stored in system tanks, with the individual components being brought into contact sequentially and thus separated in time. The system tank is the container in which the respective treatment solution, 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 (III) containing the organic binder of the coating stage, is located for the purpose of the series corrosion-protective treatment according to the present invention.

[0009] If, within the scope of the present invention, the treatment of a component composed of a metallic material is referred to, in particular, the surfaces of the steel material to be treated in the inventive method, this encompasses all materials that contain the respective element, i.e., iron in the case of steel, at more than 50 at.%, preferably at more than 80 at.%, particularly preferably at more than 90 at.%. A corrosion-protective treatment always concerns the surfaces of the component that are formed by metallic materials. The material can be a uniform material or a coating.Thus, according to the invention, galvanized steel grades consist of both steel and zinc, whereby at the cutting edges and grinding points, for example of a car body made of galvanized steel, steel surfaces can be exposed and, according to the invention, the steel material is then pretreated.

[0010] The method according to the invention is not limited to application on the steel surfaces of series components, so that in addition to steel, in particular cold-rolled steel (CRS), the substrates commonly provided by the steel industry, such as electrolytically galvanized (ZE) or hot-dip galvanized (Z), alloy-galvanized, in particular (ZM), (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, as well as their alloys, can also be pretreated with corrosion protection in the method according to the invention together with the steel surfaces. The method according to the invention is characterized precisely by the fact that it is suitable for pretreating common metallic materials composed of iron, zinc, aluminum, and magnesium with corrosion protection, i.e., for providing them with a conversion coating that provides a good paint adhesion base.

[0011] Particularly preferred is an embodiment in which the components of the series are composed not only of steel, but also of hot-dip galvanized steel and / or aluminum. The suitability of the process according to the invention for this material mix to provide a good corrosion-protective pretreatment consisting of conversion layer formation and painting is particularly advantageous for components that are manufactured as a composite structure 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 steel products and semi-finished products of galvanized steel and aluminum, particularly preferably semi-finished steel products and semi-finished products of galvanized steel and aluminum.

[0012] The components pretreated according to the present invention can be any spatial structure of any shape and design that originates from a manufacturing process, in particular also semi-finished products such as strips, sheets, rods, pipes, etc. and 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 flanging. The components to be pretreated in series according to the present invention are preferably selected from automobile bodies or parts thereof, heat exchangers, profiles, pipes, tanks, or tubs. Insofar as the concentration of an active component or compound is specified as a quantity of substance per kilogram in the context of the present invention, this is the quantity of substance based on the weight of the respective total composition.

[0013] The inventive implementation of a conditioning step based on an alkaline, aqueous composition containing calcium and / or magnesium ions in the specified minimum amount results in a significant improvement in both the corrosion protection on steel and the coating result on the metallic surfaces of the components in an otherwise conventional corrosion-protective pretreatment process comprising a conversion treatment step based on the elements Zr and / or Ti and a coating step based on dip coating. Furthermore, these improvements are achieved without additional process-technologically and energy-intensive process steps, in particular without a drying step prior to dip coating.

[0014] In the following, the individual process steps i)-iii) of the process according to the invention as well as preferred embodiments, also with regard to the process control, are explained in detail.

[0015] Conversion treatment stage:

[0016] In the conversion treatment stage of the process according to the invention, an amorphous oxidic / hydroxidic coating based on the elements Zr and / or Ti, preferably the element Zr, is to be brought about and the compounds of the elements Zr and / or Ti dissolved in water are accordingly contained, wherein a minimum concentration of 0.05 mmol / kg of compounds of the elements Zr and / or Ti dissolved in water is required in order to be able to achieve a sufficient conversion layer coating in customary contact times of 10-300 seconds at a preferred temperature of the acidic aqueous composition (I) in the range of 10-60 °C and customary application methods such as dipping or spraying.For this purpose, it is preferred according to the invention if the proportion of compounds of the elements Zr and / or Ti dissolved in water in the acidic aqueous composition (I) in process step i) is preferably at least 0.10 mmol / kg, particularly preferably at least 0.30 mmol / kg, especially preferably at least 0.40 mmol / kg.

[0017] 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.

[0018] In a preferred embodiment, the components are brought into contact with the acidic aqueous composition (I) for the most sufficient possible conversion of the metallic surfaces, in particular the steel surfaces, for at least a period of time for which a layer coating of at least 20 mg / m 2 , particularly preferably at least 40 mg / m 2 is brought about, but the contact is preferably not prolonged so that a layer thickness of more than 200 mg / m 2 , particularly preferably more than 150 mg / m 2 , most preferably more than 100 mg / m 2 , particularly preferably more than 80 mg / m 2 The deposits of the elements Zr and / or Ti on the surfaces of steel are determined using X-ray fluorescence analysis (XRF).

[0019] As already mentioned, the conversion treatment stage is intended to create an amorphous oxide / hydroxide coating based on the elements Zr and / or Ti, and accordingly, 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 examples of these compounds suitable for conversion layer formation from acidic aqueous solutions are titanyl sulfate (TiO(SO4)), titanyl nitrate (TiO(NO5)2), and / or hexafluorotitanic acid (H2TiFe) and their salts, or ammonium zirconium carbonate ((NH4)2ZrO(CO3)2) and / or hexafluorozirconic acid (FLZrFe) and their salts. Preferably, the compounds dissolved in water in the acidic aqueous composition (I) 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.

[0020] According to the invention, the conversion treatment in process step i) must be carried out with acidic aqueous compositions (I) that also contain at least a certain amount of free fluoride, since otherwise sufficient pickling of the steel substrate and the subsequent layer formation cannot generally be ensured. Typically, the amount of free fluoride in the acidic aqueous composition (I) is at least 1.00 mmol / kg.For the treatment of components made from a mix of different metallic materials, and in particular galvanized steel surfaces, higher contents of free fluoride can be useful in order to increase the conversion layer formation kinetics and to generate sufficient layer coverage, so that for the treatment of components that also have surfaces of zinc, in particular galvanized steel, very particularly preferably hot-dip galvanized (ZM) steel, a proportion of at least 2.00 mmol / kg, very particularly preferably at least 3.00 mmol / kg of free fluoride is preferred.

[0021] However, it has been shown that high levels of free fluoride can in turn be detrimental to paint adhesion on steel, so that the acidic aqueous composition (I) of the conversion treatment stage in process step i) is therefore preferably less than 7.50 mmol / kg, more preferably less than 6.00 mmol / kg, and most preferably less than 5.00 mmol / kg. Suitable sources of free fluoride for the acidic aqueous composition (I) include water-soluble complex fluorides of the elements Zr, Ti, and / or Si, preferably of the elements Zr and / or Ti, more preferably of the element Zr, and / or hydrofluoric acid, ammonium bifluoride, and / or water-soluble alkali metal fluorides.

[0022] The amount of free fluoride is to be determined potentiometrically at 20°C in the respective provided acidic aqueous composition (I) after calibration with fluoride-containing buffer solutions without pH buffering using a fluoride-sensitive measuring electrode.

[0023] With regard to the pH of the acidic aqueous composition in the conversion treatment stage, it is first important to note 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 steel substrate. According to the invention, it is preferred that the acidic aqueous compositions (I) 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.Particularly on hot-dip galvanized steel, relatively high coating weights based on the elements Zr and / or Ti are obtained in a more acidic environment, which are more defective due to the higher coating formation kinetics. According to the invention, it is therefore preferred, especially for the pretreatment of components that have zinc surfaces in addition to steel surfaces, if the pH of the acidic aqueous composition (I) is greater than 3.50, more preferably greater than 4.00, especially more preferably greater than 4.20, and most preferably greater than 4.40.

[0024] In the context of the conversion treatment stage, the pH value corresponds according to the invention to the negative decadic logarithm of the hydronium ion activity measured in the acidic aqueous composition (I) 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 = 4.00) and phosphate (pH = 7.00).

[0025] In order to heal defects in the conversion layer growing in process step i) on the surfaces of steel, but also particularly on the surfaces of hot-dip galvanized steel, the presence of copper ions can be advantageous, as their local cementation in the area of ​​the layer defects then provides improved corrosion protection. In this context, it is preferred that the acidic aqueous composition (I) of the conversion treatment stage in process step i) 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(NO3)2), copper sulfate (CUSO4), and copper acetate (Cu(CH3COO)2).

[0026] 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 in the acidic aqueous composition (I) to improve the layer formation kinetics, wettability and corrosion-protective properties. 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 process according to the invention, the acidic aqueous composition (I) in the conversion treatment 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(OCH2CH3)4.

[0027] The application and thus the contacting of the acidic aqueous composition (I) in process step i) for the formation of the conversion layer preferably takes place at at least 30°C, particularly preferably at at least 40°C, but preferably below 60°C. The acidic aqueous composition (II) 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 (I), being preferred.

[0028] Conditioning level:

[0029] The success of the process according to the invention depends firstly on at least one of the following conditions being met with regard to the alkaline aqueous composition (II) in the process step:

[0030] (1) The amount of dissolved magnesium ions calculated as mg / kg is greater than 20 divided by the pH of composition (II) reduced by 7, and / or

[0031] (2) The amount of dissolved calcium ions calculated as mg / kg is greater than 50 divided by the pH of composition (II) reduced by 7.

[0032] Condition (1) is equivalent to the statement that the threshold value of magnesium ions to be exceeded in milligrams per kilogram, preferably rounded to the nearest whole number, based on the alkaline aqueous composition (II) corresponds to the following term:

[0033] 20 Condition (2) is equivalent to the statement that the threshold value of calcium ions to be exceeded in milligrams per kilogram, preferably rounded to the nearest whole number, based on the alkaline aqueous composition (II), corresponds to the following term:

[0034] 50 pH - 7 where the pH value of the alkaline aqueous composition (II) is to be used for the variable “pH”.

[0035] Once the amount of calcium and / or magnesium ions is set above the threshold value, a significant improvement in the corrosion protection properties of the freshly deposited amorphous conversion coating based on the elements Zr and / or Ti is achieved after dip coating. In a preferred embodiment, which often results in a further improvement in said corrosion protection performance, at least one of the following two conditions is met for the alkaline aqueous composition (II) in the process step:

[0036] (1) The amount of dissolved magnesium ions calculated as mg / kg is greater than 40, particularly preferably greater than 50, most preferably greater than 60 divided by the pH value of the composition (II) reduced by the value 7, and / or

[0037] (2) The amount of dissolved calcium ions calculated as mg / kg is greater than 70, more preferably greater than 90 and most preferably greater than 100 divided by the pH of the composition (II) reduced by 7.

[0038] However, with regard to the property of the alkaline aqueous composition (II) to improve the corrosion protection performance of freshly deposited amorphous conversion coatings based on the elements Zr and / or Ti, saturation occurs above a certain amount of calcium and / or magnesium ions. Therefore, for economic reasons and to reduce the carryover of these ions into the subsequent coating stage of process step (iii), it is sensible and therefore preferred if the amount of magnesium ions dissolved in water and calcium ions dissolved in water in the alkaline aqueous composition (II) does not exceed 200 mg / kg each, and particularly preferably, the total amount of magnesium and calcium ions dissolved in water does not exceed 200 mg / kg.

[0039] Typical and suitable sources for the magnesium and calcium ions contained in the alkaline aqueous composition (II) are the respective nitrates and hydroxides, preferably hydroxides, as well as the corresponding salts of α-hydroxycarboxylic acids such as lactic acid, citric acid, tartaric acid, and gluconic acid. The pH of the alkaline aqueous composition is at least 7.50, but preferably below 12.00, for adequate conditioning of the conversion coating applied to the steel surfaces in step i).Although the desired conditioning of the conversion coating on steel surfaces is possible at higher alkalinity, such a process is less suitable for conditioning the conversion coating on galvanized steel and aluminum substrates, since defects in the conversion coating on substrates are heavily pickled, which is often accompanied by a deterioration in corrosion protection on these substrates. Therefore, for the pretreatment of components comprising not only steel surfaces but also those of zinc and / or aluminum, it is particularly preferred if the pH is below 12.00 and more preferably below 11.50, even more preferably below 10.50 and especially preferably below 10.00. At the same time, improved corrosion values ​​can regularly be achieved if the pH of the alkaline aqueous composition (II) is moderately increased above the value of 7.50.The resulting improvement is often significant, but still requires the presence of calcium and / or magnesium ions as specified in the invention. However, as the pH is increased, the minimum quantities required for conditioning decrease moderately. According to the invention, it has been found preferable for achieving optimal corrosion protection on steel surfaces and also for preventing mapping if the pH of the alkaline aqueous composition (II) is set above 8.00, more preferably above 8.50, and especially preferably above 9.00.

[0040] In the context of the conditioning stage, the pH value corresponds according to the invention to the negative decadic logarithm of the hydronium ion activity measured in the alkaline aqueous composition (II) 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 = 4.00) and boric acid / borate (pH = 9.00).

[0041] The object of process step ii) is merely to condition the freshly deposited conversion coating and, as such, to prevent or heal layer defects in the amorphous passive layer consisting of oxides, hydroxides of the elements Zr and / or Ti, and fluoride-containing hydrolysis products of the compounds of the elements Zr and / or Ti that induce the conversion of the steel surface. It is undesirable for a further significant deposition of additional active components to occur in the conditioning stage and, moreover, it would be detrimental from a process engineering perspective if significant amounts of other active components, other than those that serve to build up the minimum amount of magnesium and / or calcium ions, are present, the entrainment of which into the aqueous dispersion (III) of the subsequent dip coating would have to be prevented.In this respect, it is preferred according to the invention that the alkaline aqueous composition (II) in the conditioning stage (a) contains in each case less than 50 mg / kg, preferably in total less than 100 mg / kg, particularly preferably in total less than 50 mg / kg of compounds of metal elements dissolved in water, whose standard reduction potential (Me° / Me. n+ ) is greater than that of iron (Fe° / Fe 2+ ), calculated as the amount of each element in the composition (II),

[0042] (b) less than 50 pmol / kg, preferably less than 20 pmol / kg, particularly preferably less than 10 pmol / kg of compounds of the elements Cu, Ni, Co, Bi or Ag dissolved in water, calculated as the amount of the respective element in the composition (II),

[0043] (c) a total of less than 100 mg / kg, preferably less than 50 mg / kg, particularly preferably less than 10 mg / kg of surfactants or preferably of surface-active organic compounds or particularly preferably of organic compounds which are not polymeric organic compounds with a molecular weight above 500 g / mol,

[0044] (d) a total of less than 50 mg / kg, preferably less than 10 mg / kg, particularly preferably less than 5 mg / kg, particularly preferably less than 1 mg / kg of organic polymeric compounds with a molecular weight above 500 g / mol or preferably of organic compounds,

[0045] (e) a total of less than 100 mg / kg, preferably a total of less than 10 mg / kg, particularly preferably less than 5 mg / kg, especially preferably less than 1 mg / kg of organosilanes and / or siloxanes calculated as Si(OCH2CH3)4 or a total of less than 100 mg / kg, preferably a total of less than 10 mg / kg of compounds of the element silicon dissolved in water,

[0046] (f) a total of less than 50 pmol / kg, preferably less than 20 pmol / kg, particularly preferably less than 10 pmol / kg of compounds of the elements Zr and / or Ti dissolved in water,

[0047] (g) less than 50 mg / kg, preferably less than 10 mg / kg, of zinc ions in total, and / or

[0048] (h) contains in total less than 100 mg / kg, preferably less than 10 mg / kg, of phosphates dissolved in water or, preferably, of phosphorus-containing compounds dissolved in water.

[0049] The standard reduction potential is that against the standard hydrogen electrode H2 / H + (pH=0) determined reduction potential of the electrochemical half-cell Me / Me n+ at a metal ion activity of 1 mol / l and a temperature of 20 °C.

[0050] The application and thus the contacting of the alkaline aqueous composition (II) in process step ii) of the conditioning stage preferably takes place at at least 20 °C, particularly preferably at at least 30 °C, but preferably below 60 °C. The alkaline aqueous composition (II) of the conditioning 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, spraying, rinsing by splashing, or hosing the components. The application of the corresponding acidic aqueous composition (I) by immersion, spraying, and / or spraying is preferred.

[0051] Procedure:

[0052] In the following, preferred embodiments of the method according to the invention are described and explained with regard to the individual treatment stages and the method management, which are particularly advantageous with regard to the object underlying the invention.

[0053] Treatment stages i)-iii) of the process according to the invention each comprise at least one treatment step that involves bringing the components of the series into contact with a more precisely defined aqueous composition characteristic of the treatment stage. For the purpose of contacting, these characteristic compositions are either stored or kept in system tanks. Contacting can take place either in the system tank, for example, by immersion in a composition stored there, or outside the system tank, for example, by spraying a composition stored in the system tank in a spray chamber, depending on the specific requirement or preference of the respective process step.

[0054] In the process according to the invention, process steps i)-iii) follow one another, i.e., in the specified order, and preferably such that the components are not subjected to any wet-chemical treatment step other than one that constitutes a rinsing step between two process steps i)-iii). In this context, a rinsing step serves primarily, preferably exclusively, to remove the wet film adhering to the components from the respective preceding wet-chemical process step and thus to completely or partially remove soluble residues, particles, and active components that would otherwise be carried over from the preceding wet-chemical process step adhering to the component into the next treatment stage.

[0055] Process step ii), i.e., the conditioning step, directly follows process step i) of the conversion stage according to the invention. This means that the process steps follow one another in such a way that the components, with the wet film of the acidic aqueous composition (I) adhering from process step i) of the conversion stage, are transferred to the conditioning stage for contacting with the alkaline aqueous composition (II), i.e., without an intermediate wet-chemical treatment or rinsing step and without an intermediate drying step. A drying step within the meaning of the present invention is a process step that aims at drying the component surfaces by supplying thermal energy and / or an air stream using technical means, e.g., by means of a fan or a hot-air oven.

[0056] In a preferred process according to the invention, the conditioning stage is followed by a so-called rinsing stage comprising at least one rinsing step or a cascade of rinsing steps. Within the rinsing stage, the components of the series are freed from the wet film of the alkaline aqueous composition (II) adhering from the conditioning stage in order to prevent the carryover of alkalinity into the painting stage. For this purpose, the rinsing stage consists of one or more immediately consecutive rinsing steps, a so-called cascade of rinsing steps. Within the cascade, the rinsing steps follow one another directly if the components are not subjected to another wet-chemical treatment step that is not a rinsing step, or to a drying step, in the meantime.For the actual function of a rinsing stage, which consists in preventing the carryover of alkalinity into the subsequent painting stage, it is beneficial and therefore also preferred within the scope of the present invention if the rinsing stage, as already described, comprises several immediately successive rinsing steps, i.e. a cascade of rinsing steps, for bringing the components of the series into contact with a rinsing solution stored in the system tank of the respective rinsing step.

[0057] During the rinsing stage following the conditioning stage, the wet film of the alkaline aqueous composition (II) should be removed as far as possible. Therefore, the rinsing steps within the rinsing stage are carried out using a freshwater-based rinsing medium that preferably does not contain any active components, either in terms of type or quantity, whose carryover into the subsequent coating stage would be problematic and must be prevented. If necessary, however, the rinsing medium can contain small amounts of redox-active compounds ("depolarizers"), such as hydrogen peroxide, or, to improve the wettability of the surfaces for dip coating, additional surface-active compounds such as nonionic surfactants. However, the addition of additives should not result in the preferred maximum specific conductivity of 40 pScm being exceeded. -1in the only or last rinsing step of the rinsing stage. In particular, it is to be avoided that elements and compounds are contained in the rinsing medium that could adversely affect the corrosion protection performance. Therefore, it is preferred if the rinsing medium of the only or last rinsing step of a rinsing stage in a process according to the invention, preferably each rinsing medium of all rinsing steps of a rinsing stage

[0058] (a) less than 50 mg / kg each, preferably less than 100 mg / kg in total, particularly preferably less than 50 mg / kg in total of compounds of metal elements dissolved in water, whose standard reduction potential (Me° / Me n+ ) is greater than that of iron (Fe° / Fe 2+ ), calculated as the amount of the respective element in the rinsing medium,

[0059] (b) less than 50 pmol / kg, preferably less than 20 pmol / kg, particularly preferably less than 10 pmol / kg of compounds of the elements Cu, Ni, Co, Bi or Ag dissolved in water, calculated as the amount of the respective element in the rinsing medium,

[0060] (c) a total of less than 100 mg / kg, preferably less than 50 mg / kg, particularly preferably less than 10 mg / kg of surfactants or preferably of surface-active organic compounds or particularly preferably of organic compounds which are not polymeric organic compounds with a molecular weight above 500 g / mol,

[0061] (d) a total of less than 50 mg / kg, preferably less than 10 mg / kg, particularly preferably less than 5 mg / kg, particularly preferably less than 1 mg / kg of organic polymeric compounds with a molecular weight above 500 g / mol or preferably of organic compounds,

[0062] (e) a total of less than 100 mg / kg, preferably a total of less than 10 mg / kg, particularly preferably less than 5 mg / kg, especially preferably less than 1 mg / kg of organosilanes and / or siloxanes calculated as Si(OCH2CH3)4 or a total of less than 100 mg / kg, preferably a total of less than 10 mg / kg of compounds of the element silicon dissolved in water,

[0063] (f) a total of less than 20 pmol / kg, preferably less than 10 pmol / kg, particularly preferably less than 5 pmol / kg of compounds of the elements Zr and / or Ti dissolved in water,

[0064] (g) less than 50 mg / kg in total, preferably less than 10 mg / kg each, of sodium and / or potassium ions,

[0065] (h) less than 50 mg / kg, preferably less than 10 mg / kg, of zinc ions in total, and / or

[0066] (i) contains in total less than 100 mg / kg, preferably less than 10 mg / kg, of phosphates dissolved in water or preferably of phosphorus-containing compounds dissolved in water, wherein the pH of the rinsing medium is preferably in the range from 5.0 to 8.5.

[0067] The standard reduction potential is that against the standard hydrogen electrode H2 / H + (pH=0) determined reduction potential of the electrochemical half-cell Me / Me n+ at a metal ion activity of 1 mol / l and a temperature of 20 °C.

[0068] For a rinsing stage following the conditioning stage and preceding the coating stage, it is preferred if the specific conductivity of the rinsing medium in the system tank of the single rinsing step or in the system tank of the last rinsing step of the cascade, i.e. of the rinsing medium in the system tank of the rinsing step immediately preceding process step iii), is not above 40 pScm-1 , preferably not above 10 pScm -1 lies.

[0069] To achieve this purpose, the rinsing stage or the system tank of the single rinsing step or at least one system tank of the cascade of rinsing steps can be filled with fresh water with a specific conductivity of preferably less than 10 pScrrr 1 The volume flow of fresh water fed in should be large enough to achieve the maximum specific conductivity of 40 pScrrr preferred for the rinsing stage. 1 or particularly preferred maximum specific conductivity of 10 pScrrr 1 not to be exceeded during the treatment of the series of components.

[0070] Furthermore, for reasons of process economy, it is preferred if the conditioning stage according to process step ii) and optionally the rinsing stage immediately following process step ii), which, as already explained, preferably comprises at least one rinsing step or a cascade of rinsing steps, each with a fresh water-based rinsing medium, is in turn immediately followed by process step iii), preferably in such a way that the components with the wet film adhering from the conditioning stage or optionally with the wet film adhering from the only or last rinsing step of the rinsing stage are transferred to the coating stage for contacting with the aqueous dispersion (III), i.e. without an intermediate drying step, and in this way a "wet-on-wet" procedure is established for the components of the series across all process steps i)-iii) of the process according to the invention.

[0071] Furthermore, it should be noted that in the process according to the invention, the components are first cleaned and degreased in a degreasing stage before process step i) and thus before the formation of the conversion layer.

[0072] In the degreasing stage, an alkaline aqueous composition with a pH above 9.00 and preferably containing at least one surface-active compound selected from anionic surfactants, cationic surfactants, zwitterionic surfactants and / or nonionic surfactants can be provided for cleaning and degreasing the components of the series. The aim of the degreasing stage is to ensure that the component surface is largely free of inorganic salts and organic contaminants, in particular drawing, forming, rolling and corrosion protection oils, for the subsequent conversion treatment stage and that the amorphous oxidic / hydroxidic coating based on the elements Zr and / or Ti can be produced as homogeneously as possible. In a preferred embodiment, immediately after passing through the degreasing stage, i.e. before the conversion treatment stage, but after a rinsing step with deionized water (K ​​< I pScrrr 1), on the surfaces of the components of the series formed by the metallic materials, a carbon coating of less than 0.20 g / m 2 , particularly preferably less than 0.10 g / m 2The 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 is heated to a substrate temperature (PMT) of 550°C in an oxygen atmosphere, and the amount of released carbon dioxide is quantitatively measured as the amount of carbon using an infrared sensor, for example, using the LECO® RC-412 Multiphase Carbon Determinator (Leco Corp.). According to the invention, the pH value of an optional degreasing step corresponds to the negative decimal logarithm of the hydronium ion activity measured in the alkaline aqueous composition (I) 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 = 4.00) and boric acid / borate (pH = 9.00).

[0073] The process in the context of the present invention also includes the possibility of applying a corrosion-protective coating, i.e., conversion-treated and dip-coated, to components which, in addition to steel, also comprise other metallic materials, preferably components which are assembled in particular in a composite construction, for example automobile bodies, and which, in addition to the aforementioned steel surfaces, also have zinc surfaces, particularly preferably zinc and aluminum. Suitable metallic materials whose surfaces can be pretreated with corrosion protection in the process according to the invention include, in addition to steel: zinc, electrolytic (ZE), hot-dip galvanized (Z), alloy galvanized (ZA), (ZF), and (ZM), and aluminum-coated (AZ), (AS) strip steel, as well as the light metals aluminum and magnesium and their alloys.

[0074] Coating level:

[0075] In the coating stage, at least the surfaces of the components formed by the steel and conversion-coated in process step ii), preferably all surfaces formed by metallic materials, are coated with a first coating system by contacting the component or at least said conversion-coated steel surfaces with the aqueous dispersion (III) containing the organic binder. The coating system is thus deposited directly from the aqueous phase as a coating of the organic binder of the aqueous dispersion (III) precipitated onto said surfaces, which is typically subjected to thermal post-treatment for film formation and curing. The coating in the coating stage is applied by dip coating, preferably by electrocoating, and again preferably by cathodic electrocoating.For this purpose, the organic binder of the aqueous dispersion (III) is preferably based on amine-modified film-forming polyepoxides, which preferably additionally comprise blocked and / or unblocked organic compounds containing 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 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.

[0076] The preferred pH of the aqueous dispersion (III) of 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 a solution diluted by a factor of 10 with deionized water (K<1 |jScrTT 1 ) diluted aqueous dispersion (III) 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).

[0077] The application and thus the bringing into contact of the components or at least the said conversion-coated steel surfaces with the aqueous dispersion (III) preferably takes place at at least 30 °C, particularly preferably at at least 40 °C, but preferably below 60 °C. The aqueous dispersion (III) of the coating stage can be brought into contact with the components of the series by means of immersion application methods established in the prior art, with particular preference being given to immersing the components of the series in a system tank containing the corresponding aqueous dispersion (III).

[0078] Example:

[0079] In a series of tests on the corrosion-protective treatment of steel substrates, steel sheets (CRS) were wet-chemically treated as follows and the sheets were assessed for corrosive infiltration of the paint layer structure after a salt spray test according to VW PV 1210 after 30 cycles and stone chipping according to DINI EN ISO 20567-1.

[0080] (A) Cleaning and degreasing step a. Spray degreasing at 55 °C for 60 seconds b. Immersion degreasing at 55 °C for 120 seconds, each with a cleaner from Henkel AG & Co. KGaA (pH 11.5; total alkalinity 12 points) based on Bonderite® C-AK 2011 and with deionized water (K ​​< 1 pScrrr 1 ) containing 2.50 g / L of PO4.

[0081] (B) Rinsing stage with deionized water (K ​​< 1 pScrrr 1 ) a. by spraying at 20°C for 30 seconds b. by immersion at 20°C for 30 seconds

[0082] (C) Conversion treatment step at 35°C for 120 seconds based on Bonderite® M-NT 5800 (Henkel AG & Co. KGaA) and with deionized water (K ​​< I pScrrr 1 ) adjusted to pH 4.5 (25°C) containing Zr 150 mg / L

[0083] Cu 4 mg / L

[0084] F-free 35 mg / kg determined potentiometrically using a fluoride-sensitive electrode

[0085] (D) Conditioning step at 20°C by immersion for 30 seconds: a. deionized water (K ​​< 1 pScrrr 1 ); b. 10 mg / kg of calcium ions in deionized water (K ​​< I pScrrr 1 ), pH 9 c. 30 mg / kg of calcium ions in deionized water (K ​​< I pScrrr 1 ), pH 9 d. 50 mg / kg of calcium ions in deionized water (K ​​< I pScrrr 1 ), pH 9

[0086] (E) Rinsing stage with deionized water (K ​​< 1 pScrrr 1 ) at 20°C in immersion for 30 seconds:

[0087] (F) optional drying with compressed air and storage in a drying cabinet at 50°C

[0088] (G) Cathodic dip coating with Cathoguard® 800 (BASF SE) in a dry film thickness of 20 pm The steel sheets were coated after the conversion coating (C), which had a layer thickness measured by X-ray fluorescence analysis of zirconium in the range of 45-55 mg / m 2 provided, in the subsequent conditioning stage (D) in the manner of a rinsing stage either with deionized water (K ​​< 1 pScrrr 1 ) or a solution containing calcium ions before, after rinsing (E), cathodic dip painting (G) was carried out.

[0089] Table 1 summarizes the corrosion results after stone impact (DIN EN ISO 20567) and exposure to the salt spray test (VW PV 1210). It shows that a conditioning stage containing calcium ions is able to significantly improve corrosive infiltration at the scribe and paint adhesion after stone impact, provided the calcium ion content exceeds a threshold determined by the pH value (CE3 vs. E1, E2), and that equally good corrosion protection results can be achieved as by drying the freshly rinsed, conversion-treated sheets (CE2 vs. E2).

[0090] Table 1

[0091] (D) Conditioning stage according to variants ad (see test procedure)

[0092] (F) with drying step (see test procedure)

[0093] Can* amount of calcium ions to be exceeded according to the invention in the conditioning stage (D)

Claims

Patent claims:

1. A process for the corrosion-protective pretreatment of components in series, comprising steel surfaces, in which each component undergoes the successive treatment steps i) - iii): i) Conversion treatment step comprising contacting with an acidic aqueous composition (I) containing a) at least 0.05 mmol / kg of compounds of the elements Zr and / or Ti dissolved in water, calculated as the amount of the elements Zr and / or Ti, and b) an amount of free fluoride; ii) Conditioning step comprising contacting with an alkaline aqueous composition (II) with a pH of at least 7.50 containing magnesium ions and / or calcium ions dissolved in water in an amount such that at least one of the two following conditions is met: (1) The amount of dissolved magnesium ions calculated as mg / kg is greater than 20 divided by the pH of composition (II) reduced by 7, and / or (2) The amount of dissolved calcium ions calculated as mg / kg is greater than 50 divided by the pH of the composition (II) reduced by 7; (iii) a coating step comprising dip coating by contacting with an aqueous dispersion (III) of an organic binder, wherein process step ii) immediately follows process step i).

2. Method according to claim 1, characterized in that the method step ii) is immediately followed by a rinsing stage comprising at least one rinsing step or a cascade of rinsing steps, preferably with a fresh water-based rinsing medium, and preferably this rinsing step or this cascade of rinsing steps is immediately followed by the method step iii), wherein the specific conductivity of the rinsing medium in the system tank of the rinsing step immediately preceding the method step iii) is preferably less than 40 pScrrr 1 , particularly preferably less than 10 pScrrr 1 is.

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

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

5. Process according to one or more of the preceding claims, characterized in that the alkaline aqueous composition (II) of the conditioning in process step ii) has a pH above 8.00, preferably above 8.50, particularly preferably above 9.00, but preferably below 12.00 and particularly preferably below 11.50, very particularly preferably below 10.50 and especially preferably below 10.

00.

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

7. Process according to one or more of the preceding claims, characterized in that the amount of compounds of the elements Zr and / or Ti dissolved in water in the alkaline aqueous composition (II) of the conditioning in process step ii), calculated as Zr and / or Ti, is in each case below 50 pmol / kg, preferably below 20 pmol / kg, particularly preferably below 10 pmol / kg.

8. Process according to one or more of the preceding claims, characterized in that the alkaline aqueous composition (II) of the conditioning in process step ii) contains a total of less than 10 mg / kg, preferably less than 5 mg / kg, particularly preferably less than 1 mg / kg of polymeric organic compounds having a molecular weight above 500 g / mol.

9. Process according to one or more of the preceding claims, characterized in that the alkaline aqueous composition (II) of the conditioning in process step ii) contains a total of less than 10 mg / kg, preferably less than 5 mg / kg, particularly preferably less than 1 mg / kg of organosilanes and / or siloxanes calculated as Si(OCH2CH3)4.

10. The method according to one or more of the preceding claims, characterized in that in the alkaline aqueous composition (II) of the conditioning in process step ii) in each case less than 50 mg / kg, preferably in total less than 100 mg / kg, particularly preferably in total less than 50 mg / kg of dissolved in water Compounds of metal elements whose standard reduction potential (Me° / Me n+ ) is greater than that of iron (Fe° / Fe 2+ ) calculated as the amount of the respective element. 11 . Process according to one or more of the preceding claims, characterized in that in the alkaline aqueous composition (II) of the conditioning in process step ii) in each case less than 50 pmol / kg, preferably in each case less than 20 pmol / kg, particularly preferably less than 10 pmol / kg of compounds of the elements Cu, Ni, Co, Bi or Ag dissolved in water, calculated as the amount of the respective element.

12. Process according to one or more of the preceding claims, characterized in that the acidic aqueous composition (I) in process step i) of the conversion treatment stage contains 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, very particularly preferably not more than 2.0 mmol / kg of fluorocomplexes of the elements Zr and / or Ti calculated as the amount of the elements Zr and / or Ti.

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

14. Process according to one or more of the preceding claims, characterized in that the conversion treatment stage (I) in process step i) is carried out for a duration sufficient to achieve a layer thickness of Zr and / or Ti of at least 20 mg / m 2 , preferably at least 40 mg / m 2 , but preferably not more than 200 mg / m 2 on the surfaces of steel of the series components.

15. Method according to one or more of the preceding claims 2 to 14, characterized in that the components of the series additionally have surfaces of zinc, preferably additional surfaces of zinc and aluminum.

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