Method for cleaning and / or pre-treating some parts containing galvanized (ZM) steel - Patents.com

Abstract

The present invention relates to a method for the cleaning and / or anticorrosive pretreatment of a plurality of parts of a series, said parts of said series being at least partially composed of galvanized (ZM) steel, wherein after a cleaning step and before a further cleaning and / or anticorrosive pretreatment, said parts undergo a treatment step for improving the wettability of said galvanized (ZM) steel surface, in which at least the surface of said galvanized (ZM) steel of said parts is treated with a Lewis acid Li + , Na + , K + , Ca 2+ , Mg 2+ Or Al 3+ and the Lewis base is selected from the anions of polybasic Bronsted acids. The total concentration of said builders in the wetting treatment stage is at least 0.4 mol / kg.

Description

[Technical field]

[0001] The present invention relates to a method for the cleaning and / or anticorrosive pretreatment of a plurality of parts of a series, said parts of the series being at least partially composed of galvanized (ZM) steel. For this purpose, after a cleaning stage and before a further cleaning and / or anticorrosive pretreatment, said parts are passed through a treatment stage for improving the wettability of said galvanized (ZM) steel surface, at least the surface of said galvanized (ZM) steel of said parts is treated with a Lewis acid Li + , Na + , K + , Ca 2+ , Mg 2+ Or Al 3+ and the Lewis base is selected from the anions of polybasic Bronsted acids. The total concentration of builders in the wetting treatment step is at least 0.4 mol / kg. [Background technology]

[0002] In automotive construction, the use of galvanizing on steel alloyed with magnesium is gaining importance due to the increasing demand for lightweight car bodies. Compared to other hot-dip zinc coatings, zinc-magnesium coatings provide significantly higher corrosion protection and better resistance to corrosive peeling, especially after painting with organic dip coating materials. This improved property profile allows coatings with lower layer thicknesses to be provided, which nevertheless meet the high demands for overcoatability and corrosion protection. The weight reduction associated with the lower layer thicknesses allows hot-dip galvanized (ZM) steel to offer a relatively resource-saving strip material in lightweight car body construction, further increasing the surface area ratio of this material in the car body in addition to that of other lightweight metals such as aluminum in automotive construction.

[0003] The metallic coatings realized on hot-dip galvanized (ZM) steel strip contain approximately 1.5-8% by weight of metallic aluminum and magnesium, the proportion of magnesium being at least 0.2% by weight. The basic suitability of these coatings in forming, pretreatment and coating methods established in the prior art is recognized and has been demonstrated in principle (Property 095 E, "Continuous hot-dip galvanized steel strip and sheet", Chapters 8 and 10, 2017 edition, Wirtschaftsvereinigung Stahl), but based on the specific composition of the coating and the native oxide layer, there are special features that must be taken into account, especially in the case of cleaning and pretreatment, for a coating result that is as uniform and reproducible as possible and therefore for optimal anticorrosive properties or the desired surface functionality.

[0004] For example, it is known from the prior art that it may be advantageous to change the proportion of oxide of the alloying element magnesium in the course of cleaning before the anticorrosive pretreatment of hot-dip galvanized (ZM) rolled steel sheets. For example, US 2016 / 0168683 reports that a treatment step with an acidic aqueous composition following cleaning can change the nature of the oxide layer so that a better anticorrosive plating results as a result of the subsequent conversion treatment. Aqueous solutions of hydrochloric acid, phosphoric acid and sulfuric acid are mentioned as suitable acidic compositions that ultimately reduce the proportion of magnesium in the near-surface oxide layer. US 2016 / 0010216 also describes that a reduction in magnesium oxide in the near-surface oxide layer of hot-dip galvanized (ZM) rolled steel sheets is advantageous for anticorrosive pretreatment, and for this purpose proposes a treatment of the rolled steel sheets with a neutral or alkaline aqueous composition containing a complexing agent for magnesium, which treatment is associated with or follows a degreasing. The proposed complexing agent is selected from organic acids or their salts, preferably selected from glycine and diphosphoric acid. The examples given therein show that the proportion of magnesium oxide near the surface can be reduced using a commercial degreasing cleaner containing added glycine, according to the teachings therein.

[0005] In the continuous processing of parts with hot-dip galvanized (ZM) steel surfaces, problems also frequently arise related to the method in which the surfaces are no longer completely wetted once the parts come into contact with the wet chemical treatment steps of cleaning or pre-treatment for rust prevention. Stationary operation of a surface treatment line for parts containing (ZM) surfaces can therefore hardly ensure consistent and satisfactory results or require complex bath care. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] US Patent Application Publication No. 2016 / 0168683 [Patent Document 2] US Patent Application Publication No. 2016 / 0010216 Summary of the Invention

[0007] In this context, the object of the invention is, on the one hand, to optimally condition the surfaces formed by hot-dip galvanized (ZM) steel for subsequent cleaning and anticorrosive pretreatment, and, on the other hand, to ensure the wettability of these surfaces in the successive treatment of several parts with uniform quality, so that subsequent wet-chemical treatment steps, which may be cleaning steps and / or anticorrosive pretreatments, can be carried out equally successfully.

[0008] This object is achieved by a method for the cleaning and / or anticorrosive pretreatment of a plurality of parts of a series, said parts of said series being at least partially made of galvanized (ZM) steel, said parts of said series each passing through successive method steps i) to iii): i) contacting the part with an aqueous cleaning solution having a pH greater than 7.0 and comprising at least one surfactant; ii) treating at least the surface of the galvanized (ZM) steel of the part with a Lewis acid, Li + , Na + , K + , Ca 2+ , Mg 2+Or Al 3+ wherein the Lewis base represents a salt of a Lewis acid-base pair selected from the anions of polybasic Bronsted acids, and optionally at least one surfactant, wherein the total concentration of said builder is at least 0.4 moles / kg; and iii) cleaning by contact with a further aqueous cleaning liquid and / or anticorrosive pretreatment by contact with an aqueous treatment liquid of the first stage of a chemical conversion coating. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The sequence of treatment steps i) to iii) is crucial for the success of the invention and includes first a cleaning step, which serves to remove coarse dirt from the parts of the series and to provide a more easily wettable surface, and is therefore also referred to below as pre-cleaning.

[0010] This pre-cleaning is carried out after a treatment step in which at least the surface of the part, which is a galvanized (ZM) steel surface, is contacted with an aqueous agent comprising at least one builder, with or without intermediate rinsing and / or drying steps, preferably with intermediate rinsing steps but without drying steps. Method step ii) results in permanent wettability of the (ZM) surface and provides an optimally conditioned surface for the subsequent cleaning and / or anticorrosive surface treatment. Method step ii) is therefore also referred to below as conditioning.

[0011] After the conditioning, as already mentioned, in the method of the invention, the necessary method steps for the application of the anticorrosive paint are followed, either for the application of the paint, firstly again, by a cleaning step, or by the immediately performed anticorrosive pretreatment, the latter being the preferred variant after all, taking into account the economics of the method. However, a specific anticorrosive pretreatment usually also requires a specific pre-cleaning that is adapted thereto, and in such a case, the conditioning is first performed by cleaning, followed by the downstream anticorrosive pretreatment.

[0012] In principle, the wettability of the (ZM) surface brought about by the conditioning is surprisingly long-lasting and is not impaired in any way with respect to the performance of the anticorrosive coating, for example by a rinsing step with water drawn from the mains. Nevertheless, it is again preferred from an economic point of view if process step iii) in the process of the invention follows process step ii) directly, i.e. without an intermediate drying step, and in particular without an intermediate drying step or rinsing step.

[0013] A "rinsing step" in the sense of the present invention denotes a process which is intended only to remove, as far as possible, from the surface of the parts, by means of a rinsing liquid, active ingredients dissolved in the wet coating adhering to the parts, without replacing the active ingredients to be removed with other active ingredients. Since active ingredients in this context are ingredients which are dissolved or dispersed in the aqueous phase used in contact with the parts, their proportion and concentration in the respective aqueous solution must be actively, i.e. by metering in devices provided for this purpose, maintained above the values ​​established from the point of view of process technology in the course of continuous processing.

[0014] Within the meaning of the present invention, a "drying step" means a step in which the surface of the part carrying the wet coating is dried by technical means.

[0015] The treatment of a series of parts is when several parts are contacted with the treatment liquids provided in the respective treatment steps i) to iii) of the method of the invention and usually stored in a system bath, the individual parts being contacted successively and therefore at different times from each other. In this case, the system bath is the container in which the respective treatment liquids are placed for the purpose of successive cleaning and / or anticorrosive pretreatment, but not necessarily the place of contact. Thus, a portion of the treatment liquid stored in the system bath, sufficient for contacting the (ZM) surface of the parts, can also be supplied from here and applied to the parts spatially separated from the system bath, for example in a spray or mist chamber.

[0016] Process step i) - Pre-cleaning The treatment step i) serves to remove dirt, in particular drawing oil, moulding oil, rolling oil and anti-rust oil, from the component surface. Usually, therefore preferably, the (ZM) surface of the series of components after passing through the method step i) has a carbon layer of less than 0.50 g, particularly preferably less than 0.10 g, per square meter of the (ZM) surface of the component. The carbon layer remaining on the (ZM) surface of the component can be measured by pyrolysis. For this purpose, a representative component part of a defined surface area is brought to a substrate temperature of 550° C. (PMT) in an oxygen atmosphere and the amount of carbon dioxide released is quantified as the amount of carbon by an infrared sensor, for example an analytical device Leco® RC-412 Multiphase Carbon Determinator (Leco Corp.).

[0017] The cleaning preceding the surface conditioning in method step ii) is carried out according to the invention with an aqueous alkaline solution and a surfactant-containing solution. Surfactants in the sense of the present invention are considered to be surface-active organic compounds which, due to their surface activity, consist of a hydrophilic molecular component and at least one lipophilic molecular component or a lipophilic molecular component and at least one hydrophilic molecular component, the molecular weight of the surface-active organic compound not exceeding 2000 g / mol.

[0018] The surfactants in step i) of the method of the invention can be selected from anionic, cationic, zwitterionic and nonionic surfactants, the use of nonionic surfactants being generally preferred. Nonionic surfactants particularly suitable as components of the aqueous agents for pre-cleaning parts containing metal surfaces of (ZM) are those whose HLB value (hydrophilic-lipophilic-balance) is at least 8, particularly preferably at least 10, very particularly preferably at least 12, but particularly preferably not more than 18, very particularly preferably not more than 16. The HLB value serves as a quantitative reference variable for the classification of nonionic surfactants with regard to their miscibility with water or their tendency to form O / W emulsions. For quantification, a decomposition of the nonionic surfactants into lipophilic and hydrophilic groups is carried out. The HLB value is then calculated as follows and can assume a value of 0 to 20 on any scale:

number

[0019] From the viewpoint of material, in the pre-wash of the method of the present invention, such non-ionic surfactants are preferred which are selected from alkoxylated alkyl alcohols, alkoxylated fatty amines and / or alkyl polyglycosides, particularly preferably from alkoxylated alkyl alcohols and / or alkoxylated fatty amines, very particularly preferably from alkoxylated alkyl alcohols.In this case, for the defoaming effect, the alkoxylated alkyl alcohols and / or alkoxylated fatty amines are preferably end-capped, particularly preferably with alkyl groups which in turn preferably have 8 carbon atoms or less, particularly preferably 4 carbon atoms or less.Particularly preferably, such alkoxylated alkyl alcohols and / or alkoxylated fatty amines are used as non-ionic surfactants for pre-wash in the method of the present invention which are present in ethoxylated and / or propoxylated form, and the number of alkylene oxide units is preferably 16 or less, particularly preferably 12 or less, very particularly preferably 10 or less, but particularly preferably more than 4, very particularly preferably more than 6.

[0020] With regard to the lipophilic components of the abovementioned nonionic surfactants, such alkoxylated alkyl alcohols and / or alkoxylated fatty amines, in which the alkyl group is saturated, preferably unbranched, and the number of carbon atoms in the alkyl group is preferably more than 6, particularly preferably at least 10, very particularly preferably at least 12, but preferably not more than 20, particularly preferably not more than 18, very particularly preferably not more than 16, are preferred as nonionic surfactants in the pre-wash of the method according to the invention.

[0021] Since it is evident that, on the whole, longer-chain nonionic surfactants are highly suitable and preferred for the effective pre-cleaning of conventional drawing, forming, rolling and anti-rust oils, in a further preferred embodiment of the method according to the invention, it is preferred that such alkoxylated alkyl alcohols and / or alkoxylated fatty amines are present, in particular alkoxylated alcohols in which the lipophilic alkyl group contains at least 10 carbon atoms, particularly preferably at least 12 carbon atoms, the longest carbon chain in the alkyl group consists of at least 8 carbon atoms and the HLB value is in the range of 12 to 16.

[0022] Preferred representatives of alkoxylated alkyl alcohols are, for example, selected from: - 4 to 8 times ethoxylated or propoxylated C6 to C12 fatty alcohols, - 8 to 12 times ethoxylated C12 to C18 fatty alcohols, - 6 to 14 times propoxylated C12 to C18 fatty alcohols, - 6 to 10 times ethoxylated and propoxylated C12 to C14 fatty alcohols, These in turn may be present in the form of blocked methyl, butyl or benzyl end groups.

[0023] The cloud point, determined in accordance with DIN 53 917 (1981), is a further suitable selection criterion for the nonionic surfactants used in the pre-wash and is selected from alkoxylated alkyl alcohols, alkoxylated fatty amines and / or alkyl polyglycosides, and is preferably above 20° C., but particularly preferably below the application temperature of the pre-wash, very particularly preferably more than 5° C. higher but not higher than 10° C. than the respectively selected application temperature of the aqueous pre-wash agent.

[0024] The proportion of surfactants, in particular nonionic surfactants, in the aqueous washing liquid of method step i) is preferably more than 0.01% by weight, particularly preferably more than 0.10% by weight, very particularly preferably more than 0.20% by weight, but preferably not more than 2.00% by weight, in each case based on the washing liquid. If the proportions of compounds or substances are indicated below as percentages based on mass, the respective solution or the respective agent is always the reference variable, in the absence of other more specific information.

[0025] The application of the aqueous cleaning liquid, and thus the contacting of the aqueous cleaning liquid, is preferably carried out at a temperature of at least 30° C., particularly preferably at least 40° C., but preferably below 60° C. The cleaning liquid of the pre-cleaning can be contacted with the series parts by application types established in the prior art. These include in particular immersion, rinsing, splashing and / or spraying, with application by immersion and / or spraying being preferred.

[0026] In the method of the invention, the pH of the aqueous cleaning liquid is set alkaline for a sufficient pre-cleaning to effectively remove oily soiling of the parts, but in order to mitigate the delamination of the metal substrate of the parts, the pH preferably does not exceed 12.0. The method of the invention is intended in particular to be used in automobile manufacturing, which uses hot-dip galvanized (ZM) rolled steel sheets as well as other materials such as steel and aluminum as manufacturing materials, so that the continuously manufactured car bodies usually consist of a mixture of different metal materials. Since the pre-cleaning of method step i) serves practically exclusively to remove components of normally organic soiling from the surface - the so-called degreasing - the pH of the cleaning liquid can be selected so that the lowest possible pickling effect is obtained. In this respect, it may be the case for the aqueous cleaning liquid that its pH does not exceed 11.5, particularly preferably does not exceed 10.5, but is preferably set to at least a pH of 8.0 in order to obtain a degreasing effect.

[0027] Processing step ii) - Conditioning Treatment step ii) serves to make the surface of the part made of hot-dip galvanized (ZM) steel reliably and permanently wettable for the following cleaning and / or pretreatment steps, thus ensuring uniform surface properties and corrosion protection of the parts treated according to the invention, which are reproducible in the case of the treatment of a series of parts.

[0028] The conditioning of the surface of (ZM) carried out in the treatment step ii) requires contacting said surface with an aqueous agent containing one or more builders, the builders being those which have a Lewis acid of Li + , Na + , K + , Ca 2+ , Mg 2+ Or Al 3+ , wherein the Lewis base is selected from the anions of polybasic Bronsted acids.

[0029] In order to achieve sufficient wettability of the surface of (ZM), the total concentration of these builders must be at least 0.4 mol / kg, preferably at least 0.5 mol / kg, particularly preferably at least 0.6 mol / kg. High concentrations are usually not necessary and do not result in a further increase in wettability for the next process step of cleaning and / or anticorrosive pretreatment. Thus, significantly higher concentrations are uneconomical and increase the complexity of the process due to the carryover of builder components, which always occurs to some extent by the wet coating adhering to the parts or the parts to be immersed, during the servicing of the bath in the next process stage, so that Lewis acids are not easily reacted with Li + , Na + ,K + , Ca 2+ , Mg 2+ Or Al 3+ and wherein the Lewis base is selected from the anions of polybasic Bronsted acids, the total concentration of the builders selected from salts of Lewis acid-base pairs in the aqueous formulation preferably does not exceed 2.0 mol / kg, particularly preferably does not exceed 1.2 mol / kg.

[0030] Builders suitable for conditioning are those in which the anion of the polybasic Brønsted acid of the Lewis acid-base pair is selected from the anions of sulfate, phosphate, diphosphate, polyphosphate, and carbonate, particularly preferably from the anions of phosphate, diphosphate, polyphosphate, and carbonate, very particularly preferably from the anion of carbonate.Suitable builders can also be provided on the basis of polybasic organic acids, preferably selected from such Lewis acid-base pairs in which the Lewis base is formed by polybasic carboxylic acids, particularly preferably di- and tricarboxylic acid anions, which in turn preferably have a hydroxyl group in the a-position relative to the carboxyl group, very particularly preferably formed by the anions of citric acid and / or tartaric acid.The proportion of such builders in which the Lewis base is formed by the anion of an organic acid is preferably less than 50% by weight, particularly preferably less than 30% by weight, based on the total proportion of builders, in order to additionally impart a complexing effect to the conditioning agent, but is preferably at least 0.05 mol / kg, which is advantageous for further homogenization of the oxide coverage of the (ZM) surface of the component.

[0031] Particularly suitable Lewis acids of the builders contained in the aqueous conditioning agents are the cations Na + , K + and / or Mg 2+ These are preferred, and the Lewis acid of the builder is particularly preferably Na + and / or K. + is selected from.

[0032] The (ZM) surfaces of the components are, as previously described, sufficiently conditioned for the subsequent cleaning and / or anticorrosive pretreatment in the presence of at least one builder. The described builders behave as independently as possible in relation to the metal surface and its oxides and do not form dense thin layers, either by chemical adsorption, metallization or conversion by a combined mechanism of pickling and precipitation. In this respect, for successful conditioning, it is advantageous and also desirable for economic reasons to keep the proportion of further components of the aqueous agent as low as possible.

[0033] Therefore, H + and NH4 + The proportion of other Lewis acids, except for Li + , Na + , K + , Ca 2+ , Mg 2+ Or Al 3+ Preferably less than 5.0% by weight, particularly preferably less than 2.0% by weight, very particularly preferably less than 1.0% by weight and most particularly preferably less than 0.5% by weight, based on the total amount of Lewis acids in the aqueous conditioning agent selected from

[0034] Particularly preferred is when the proportion of water-soluble compounds of the elements Zr, Ti, Hf, Ce, Cr in the aqueous conditioning agent is less than 10 mg / kg, particularly preferably less than 5 mg / kg, very particularly preferably less than 1 mg / kg, based on the respective element, in order to prevent the formation of a conversion film.

[0035] In order to prevent the precipitation of certain metal phases, it is likewise preferred that the proportion of water-soluble compounds of metal elements (Me) having a positive standard reduction potential, such as iron, preferably zinc, in the aqueous conditioning agent is in each case less than 10 mg / kg, particularly preferably less than 5 mg / kg, very particularly preferably less than 1 mg / kg, based on the respective element. The standard reduction potential is calculated based on the standard hydrogen electrode H2 / H + (pH=0) vs. metal ion activity 1, measured at 20°C, electrochemical half-cell Me / Me n+ is the reduction potential.

[0036] Furthermore, in order to prevent a chemically adsorbed thin layer, it is preferred that the proportion of polymeric organic compounds in the aqueous conditioning agent is less than 1% by weight, particularly preferably less than 0.1% by weight, very particularly preferably less than 0.05% by weight. In the context of the present invention, an organic compound is polymeric if its molecular weight is more than 1000 u.

[0037] In order to prevent point defects due to particles adsorbed on the (ZM) surface in the case of layer build-up occurring in the course of a subsequent anticorrosive pretreatment, it is particularly preferred if the proportion of dispersed particulate components in the aqueous conditioning agent is less than 1% by weight, particularly preferably less than 0.1% by weight, very particularly preferably less than 0.05% by weight. The dispersed particulate components of the aqueous agent are the solids remaining after drying of the retentate of an ultrafiltration of a defined partial volume of the aqueous dispersion with a nominal exclusion limit (NMWC, nominal molecular weight cut-off) of 10 kD, provided that the ultrafiltration is carried out with deionized water (κ<1 μS cm -1 ) was added to the filtrate at 10 μS cm -1 Only until a conductivity of less than

[0038] With respect to the builder, it has been found that the additional presence of a surfactant is particularly advantageous for wetting the parts with the aqueous agent, which in interaction with the builder provides a uniformly conditioned (ZM) surface for the subsequent cleaning and / or anticorrosive pretreatment. In this context, the surfactant used for the pre-cleaning of method step i) is generally preferred. This applies both to the quality and the quantity of the non-ionic surfactant.

[0039] In particular for aqueous formulations comprising builders in which the anion of a polybasic Brönsted acid which functions as the Lewis base of the salt of a Lewis acid-base pair is selected from the anions of carbonic acid, it has proven advantageous to add a surfactant, in particular a nonionic surfactant, to the aqueous formulation.

[0040] Together with builders based on anions of carbonate, nonionic surfactants selected from the following have proven particularly preferred: - 4 to 8 times ethoxylated or propoxylated C6 to C12 fatty alcohols, - 8 to 12 times ethoxylated C12 to C18 fatty alcohols, -6 to 14 times propoxylated C12 to C18 fatty alcohols, and / or - 6 to 10 times ethoxylated and propoxylated C12 to C14 fatty alcohols, These are preferably present in the form in which the methyl, butyl or benzyl end groups are blocked, in that order.

[0041] In a particular embodiment of the method according to the invention, it is preferred that the surfactant is selected identically in both method steps i) and ii), since the parts can be transferred directly from pre-cleaning to conditioning, so to speak, wet-in-wet, without a rinsing step.

[0042] The pH of the aqueous conditioning agent is preferably above 6.5, particularly preferably the agent is set alkaline. However, strong pickling, especially of the surface of the metallic material (ZM) of the part, is ideally avoided. At the same time, the method is suitable for treating parts made of different metal manufacturing materials, especially hot-dip galvanized (ZM) steel, but also of steel and / or aluminum, for example car bodies. Therefore, according to the invention, it is preferred if the pH of the aqueous conditioning agent is not more than 10.5, particularly preferably not more than 9.5, very particularly preferably not more than 8.5, but preferably at least 7.5.

[0043] The total alkalinity in points of the aqueous conditioning agent is preferably less than 30 points, particularly preferably less than 25 points, but preferably at least 10 points, particularly preferably at least 15 points. Furthermore, via the builder or builders contained in the aqueous agent, a sufficiently large buffering effect occurs, which has proven to be advantageous for the conditioning of hot-dip galvanized (ZM) surfaces. At the same time, the free alkalinity must not exceed a value such that the attack resulting from the pickling becomes too great, which has proven to be disadvantageous, especially when applied as a thin liquid film, and may, for example, require an additional rinsing step. In this respect, aqueous conditioning agents having a free alkalinity of less than 10.0, particularly preferably less than 8.0, very particularly preferably less than 7.0, are preferred. The total or free alkalinity is determined by titrating 2 g of the aqueous agent, diluted in 50 mL, with 0.1 n hydrochloric acid to a pH of 3.6. The consumption of acid solution in mL indicates the number of points of total alkalinity.

[0044] Surprisingly, the method of applying the aqueous agent has furthermore been proven to be selective for successful conditioning in the successive processing of parts, since it is observed that the wettability of the (ZM) surface decreases more and more with the total treated surface, insofar as the series of parts are treated with the same volume of conditioning agent after passing through method step ii) (i.e. when the treated surface per volume of aqueous agent increases regularly with the number of treated parts), as is the case, for example, with dip application or spray application with closed circulation of the aqueous agent flowing out of the parts. The causes thereof have not been fully elucidated so far, but it can be considered that impurities adsorbed in the aqueous agent, in particular the salt load adsorbed on the metal substrate by pickling, are causally related to the loss of wettability of the (ZM) surface achieved.

[0045] In order to counteract the decrease in wettability obtained by conditioning of the (ZM) surface during the continuous treatment, it is advantageous in the first place if the conditioning agent is applied as effectively as possible and without excessive amounts to the surface to be treated. Thus, in a preferred embodiment of the method of the invention, the contacting of the galvanized (ZM) steel surface of the part in the continuous treatment to be cleaned and / or protected against corrosion is carried out by dispensing the aqueous agent from a supply in such a way that not more than 1.00 liters, preferably not more than 0.50 liters, particularly preferably not more than 0.20 liters of aqueous agent is dispensed per square meter of the part in the continuous treatment to be cleaned and / or protected against corrosion, in particular per square meter of the galvanized (ZM) steel surface with which the part in the continuous treatment to be cleaned and / or protected against corrosion comes into contact.

[0046] In connection with this preferred embodiment and the surface area-related dispensed amount of the aqueous agent, the surface area of ​​the part subject to the continuous treatment to be cleaned and / or protected against corrosion represents the surface of a polyhedron having 12 faces, preferably 6 faces, particularly preferably the surface of a rectangular prism, which in each case completely surrounds the part and thereby has a minimum surface area, each surface of the polyhedron contacting the part at least at one point. If the part is a car body, the surface area relevant for the surface area-related dispensed amount of the aqueous conditioning agent is preferably the surface area of ​​a rectangular prism having a minimum surface area that completely surrounds the car body, each surface of the rectangular prism contacting the car body at least at one point.

[0047] In this case, the dispensed amount of the aqueous agent should be distributed as effectively as possible on the surface of the (ZM) without this contributing to the wettability due to economic considerations, for example ensuring that the liquid volume does not yet run off the surface of the part immediately after application. It is therefore preferred if the dispensed aqueous agent for contacting in method step ii) is carried out in such a way that at least the surface of the galvanized (ZM) steel is covered with a liquid film of the aqueous agent, resulting in a volumetric coverage based on the surface area of ​​preferably 0.20 liters or less, particularly preferably 0.10 liters or less, very particularly preferably 0.07 liters or less, and especially preferably 0.05 liters or less. The volumetric coverage here does not refer to the surface area of ​​the part approximated by a polyhedron, as in the case of the dispensed volume, but rather to the actual geometric surface area, and the volumetric coverage can be determined by differential weighing after draining off the liquid film.

[0048] For controlled dispensing of the correspondingly preferred aqueous conditioning agent or application of limited amounts of the correspondingly preferred aqueous conditioning agent on the surface of galvanized (ZM) steel, in method step ii) it is advantageous and therefore further preferred that dispensing of the aqueous agent is carried out as a spray, as a spray mist or as a liquid film, particularly preferably as a spray and / or spray mist, particularly preferably in spray mist or liquid form, particularly preferably as a spray and / or spray mist, especially preferably as a spray mist. Bringing the agent into contact with the surface of the part as a spray and / or spray mist is carried out using spray and mist methods established in the prior art, which can be carried out in a locally limited manner using a spray lance and / or in a manner partially surrounding the part using a spray ring, on which several atomizer nozzles can be attached. The spraying device used for dispensing the spray and / or spray mist is, for example, a pressure atomizer, a rotary atomizer or a two-substance atomizer. Depending on the complexity and shape of the part to be processed, the liquid film can be applied to the part to be processed by direct application using a roller, cloth, brush, paintbrush, or similar device for applying liquid.

[0049] The controlled application of the preferred aqueous conditioning agent according to the invention is achieved particularly efficiently by mounting a directed sprayer in a targeted manner on the surface to be wetted and / or by providing the parts transported with the transport frame with a spray mist that is realised at a defined volumetric flow rate through a transport path such that the surface of the part to be wetted is exactly exposed to the closed liquid film. In this way, a highly efficient procedure according to the above-mentioned preferred embodiment of the method of the invention is available, whereby the objective of method step ii) of ensuring good wetting of the (ZM) surface throughout the treatment process is reliably achieved using as little material as possible.

[0050] For example, in order to dispense the amount of aqueous conditioning agent required for the complete formation of a liquid film, according to the invention, the agent dispensed as a spray and / or spray mist has an average droplet size of less than 100 μm, particularly preferably less than 60 μm, very particularly preferably less than 40 μm. If the average droplet size is less than 40 μm, the agent is sprayed so strongly that the boundary region with the aerosol is exceeded and a spray mist is present. If the agent is further atomized and the average droplet size decreases, the droplets are more and more in suspension and are no longer subject to gravity. The spray mist held in suspension moves with the transport of the part through the spray chamber and is partially displaced by the part, so that directional precipitation prevents the surface from being wetted and the surface of the part is not uniformly wetted by the liquid film. It is therefore preferred that the conditioning agent dispensed in method step ii) has an average droplet size of 5 μm or more, particularly preferably 10 μm or more.

[0051] It is also advantageous for the spray and / or spray mist of the conditioning agent to be dispensed such that the average velocity of the droplets having an average droplet size is less than 5 m / s, preferably less than 2 m / s, particularly preferably less than 1 m / s, to form a closed liquid film on the surface of the contacting parts. This applies in particular to sprays and / or spray mist with an average droplet size of less than 100 μm, particularly preferably less than 60 μm, particularly preferably less than 40 μm.

[0052] According to the present invention, the average droplet size and average velocity of the droplets of the spray or spray mist are determined at the location of the geometric center of gravity of the polyhedron surrounding the part, which location is also used to determine the amount of agent dispensed per surface area of ​​the part, as previously described. Measurements can be made by light scattering and phase Doppler anemometry.

[0053] As already mentioned, the wettability of the (ZM) surface of the part achieved in method step ii) is significantly reduced if, in a continuous process, the same partial volume of aqueous conditioning agent is repeatedly brought into contact with the surface of the part and is not periodically replenished. In a preferred embodiment of the method of the invention, method step ii) is carried out in such a way that the part of the aqueous agent that is dispensed for contact but does not come into contact with the part and sinks to the bottom, for example as an excess spray, and is collected there, or does not remain on the surface of the part until it is contacted with the aqueous solution in method step iii), but for example runs off the part and remains in the spray chamber, is discarded. A part of the conditioning agent is considered to be "discarded" if it is no longer provided for contact and is, for example, removed from the spray chamber.

[0054] Treatment stage iii) - cleaning and / or anticorrosive pretreatment: Method step iii), which follows the treatment stage for conditioning, completes the method in that the cleaning and / or anticorrosive pretreatment is completed. Cleaning in the sense of this method step is understood to mean a wet-chemical treatment with a cleaning liquid, in the course of which organic impurities adhering to the metal surface of the part (but at least to the surface of the hot-dip galvanized (ZM) steel substrate) are removed and a carbon coating of less than 0.10 g, preferably less than 0.05 g, is produced per square meter of the (ZM) surface of the part, preferably per square meter of the total metal surface of the part. Suitable cleaning liquids have been described in connection with the cleaning liquid of method step i), so that preferably the same surfactants, in particular non-ionic surfactants, can also be used. Cleaning in the sense of method step iii) also includes, however, a treatment with a cleaning liquid which causes the conversion of an oxide layer on the metal surface by a pickling reaction. However, if the result is more than 1 mg / m of different elements of metals or metalloids based on the respective elements, then the amount of carbon coating is preferably less than 1 mg / m. 2 In the case of a coating of more than 100 layers, there is no cleaning in the sense of method step iii). In this case, the skilled person would refer to the formation of a conversion layer due to the anticorrosive pretreatment in the sense of the present invention, which can be carried out directly after conditioning or optionally after the previously mentioned cleaning.

[0055] In the context of the present invention, in particular passivation with an inorganic barrier layer, which can be either crystalline (phosphating) or amorphous (chromating, Zr / Ti-based chemical conversion treatment), can be considered as a rust-preventive pretreatment. Inorganic passivation also includes alkaline passivation in the presence of iron ions and optionally also dissolved metal ions of the elements cobalt, nickel, manganese and molybdenum, as described, for example, in published patent applications DE and DE.

[0056] The present invention, which ensures complete and permanent wettability of the (ZM) surfaces of components, is particularly advantageous in what is known as thin film passivation, since residual or insufficient wettability of the (ZM) surfaces frequently leads to a decrease in corrosion protection with this type of passivation. In this respect, such anticorrosive pretreatments are based on a coating of 200 mg / m2 of different elements of metals or metalloids, based on the respective elements. 2 It is preferred for process step iii) to result in a coating of less than one layer.

[0057] For such thin film passivation, chromium-containing or preferably chromium-free conversion solutions can be used as aqueous treatment liquids for the anticorrosive pretreatment in method step iii). Preferred conversion solutions with which the surfaces of the components subjected to the continuous treatment according to the invention can be cleaned and conditioned are based on the hexafluoro anions of the elements Zr, Ti, Hf and / or Si.

[0058] The conversion solution preferably further contains dissolved ions of the metals molybdenum, copper, bismuth and / or manganese.

[0059] A series of parts According to the invention, the component comprises a hot-dip galvanized (ZM) steel material, where the hot-dip galvanization is a metallic coating containing 1.5-8% by weight of metallic aluminum and magnesium, the proportion of magnesium in the metallic coating being preferably at least 0.2% by weight.

[0060] However, the method of the invention is not limited to application to hot-dip galvanized (ZM) steels, so that also conventional substrates provided by the steel industry, such as steels, in particular cold-rolled steels (CRS), and electrolytically galvanized (ZE) or hot-galvanized (Z), alloy-galvanized, in particular (ZF), (ZA), or aluminized (AZ), (AS) steels, are suitable as further constituents of the part. In the method of the invention, light metals such as aluminum, magnesium and their alloys can also be treated together with the hot-dip galvanized (ZM) steel of the part and can be cleaned and / or subjected to an anticorrosive pretreatment in the process.

[0061] The different materials are generally present in the part in the form of flat products that are cut to size, shaped and joined by welding, gluing, crimping. The parts to be pretreated in succession according to the invention are preferably selected from car bodies or parts thereof, heat exchangers, object sides, pipes, tanks or troughs.

[0062] The parts treated according to the invention can be provided in a process step following method step iii) with an organic topcoat system, in particular a dip coating, particularly preferably a cathodic electrodeposition coating.

Claims

1. 1. A method for cleaning and / or anticorrosive pre-treatment of a plurality of parts of a series, said parts of said series being at least partially made of galvanized (ZM) steel, said parts of said series each comprising successive method steps i) to iii): i) contacting the part with an aqueous cleaning solution having a pH greater than 7.0 and comprising at least one surfactant; ii) treating at least the surface of the galvanized (ZM) steel of the part with a Lewis acid, Li ＋ , Na ＋ , K. ＋ , Ca ２＋ , Mg ２＋ or Al ３＋ wherein the Lewis base represents a salt of a Lewis acid-base pair selected from the anions of polybasic Bronsted acids, and optionally at least one surfactant, wherein the total concentration of the builders is at least 0.4 mol / kg, preferably at least 0.5 mol / kg, particularly preferably at least 0.6 mol / kg, but preferably not more than 2.0 mol / kg; and iii) Cleaning by contact with a further aqueous cleaning solution and / or rust prevention pretreatment by contact with the aqueous treatment solution of the first stage of chemical conversion coating. A way to go through.

2. 2. The method according to claim 1, characterized in that the contacting of the galvanized (ZM) steel surfaces of the parts in method step ii) is carried out by dispensing the aqueous agent from a supply in such a way that not more than 1.00 liters, preferably not more than 0.50 liters, particularly preferably not more than 0.20 liters of aqueous agent are dispensed per square meter of the parts of the series to be cleaned and / or protected against corrosion, in particular per square meter of the contacted galvanized (ZM) steel surfaces of the parts of the series to be cleaned and / or protected against corrosion.

3. 3. The method according to claim 2, characterized in that the aqueous agent for contacting in method step ii) is dispensed in such a way that at least the surface of the galvanized (ZM) steel is covered with a liquid film of the aqueous agent, a layer based on a volume of preferably not more than 0.20 liters per square meter, particularly preferably not more than 0.10 liters, very particularly preferably not more than 0.07 liters and especially preferably not more than 0.05 liters per square meter, resulting on the surface of the galvanized (ZM) steel.

4. 4. The method according to claim 2 or 3, characterized in that the aqueous agent is dispensed in method step ii) as a spray, as a spray mist or as a liquid film, preferably as a spray and / or spray mist, particularly preferably as a spray mist.

5. 5. The method according to claim 4, characterized in that the spray misting is carried out so that the average droplets of the dispensed aqueous agent are less than 100 μm, preferably less than 60 μm, more preferably less than 40 μm, but preferably 5 μm or more, particularly preferably 10 μm or more.

6. 6. The method according to claim 5, characterized in that the average velocity of the droplets in the spray misting is less than 5 m / s, preferably less than 2 m / s, particularly preferably less than 1 m / s.

7. 3. The method of claim 2, wherein in method step ii) the portion of the aqueous agent that is dispensed for contact but does not contact or does not remain in place until contacted with the aqueous solution in method step iii) is discarded.

8. 3. The method according to claim 1 or 2, characterized in that the anion of the polybasic Brønsted acid of the builder in the aqueous agent of method step ii) is selected from the anions of sulfate, phosphate, diphosphate, polyphosphate, carbonate, preferably from the anions of phosphate, diphosphate, polyphosphate, carbonate, particularly preferably from the anion of carbonate, or from the anions of polybasic carboxylic acids, in particular di- and tricarboxylic acids, which in turn preferably have a hydroxyl group in the α-position to the carboxyl group, particularly preferably selected from citric acid and / or tartaric acid.

9. The Lewis acid of the builder in the aqueous formulation of process step ii) is Na ＋ , K. ＋ and / or Mg ２＋ is selected from, preferably Na ＋ and / or K ＋ 3. The method according to claim 1 or 2, characterized in that the compound is selected from the group consisting of:

10. H ＋ and N.H. ４ ＋ The proportion of other Lewis acids, excluding Li, in the aqueous agent of process step ii) ＋ , Na ＋ , K. ＋ , Ca ２＋ , Mg ２＋ or Al ３＋ 3. The method according to claim 1 or 2, characterized in that the amount of Lewis acids selected from the group consisting of: less than 5.0% by weight, preferably less than 2.0% by weight, particularly preferably less than 1.0% by weight, very particularly preferably less than 0.5% by weight.

11. 3. The method according to claim 1 or 2, characterized in that the proportion of water-soluble compounds of the elements Zr, Ti, Hf, Ce, Cr in the aqueous agent of method step ii) is in each case less than 10 mg / kg, preferably less than 5 mg / kg, particularly preferably less than 1 mg / kg, based on the respective element.

12. 3. The method according to claim 1 or 2, characterized in that the proportion of water-soluble compounds of metal elements having a positive standard reduction potential, such as iron, preferably zinc, in the aqueous agent of method step ii) is in each case less than 10 mg / kg, preferably less than 5 mg / kg, particularly preferably less than 1 mg / kg, based on the respective element.

13. 3. The method according to claim 1 or 2, characterized in that the proportion of high molecular weight organic compounds in the aqueous agent of method step ii) is less than 1% by weight, preferably less than 0.1% by weight, particularly preferably less than 0.05% by weight.

14. 3. The method according to claim 1 or 2, wherein the aqueous agent of process step i) and / or process step ii) comprises at least one surfactant selected from nonionic surfactants, preferably having an HLB value of at least 8, particularly preferably at least 10, very particularly preferably at least 12, but preferably not more than 18, particularly preferably not more than 16, characterized in that the proportion of surfactant, preferably nonionic surfactant, in the aqueous agent of process step i) and / or process step ii), respectively, is more than 0.01% by weight, preferably more than 0.10% by weight, particularly preferably more than 0.20% by weight, but preferably not more than 2.00% by weight.

15. 3. The method according to claim 1 or 2, characterized in that the pH of the aqueous agent in method step ii) is not more than 10.5, preferably not more than 9.5, particularly preferably not more than 8.5, but preferably at least 6.5, particularly preferably at least 7.5.