Phosphate-free cleaner for metallic surfaces with reduced pickling erosion

Abstract

To provide a water-based, alkaline cleaner concentrate operating without the use of phosphates, a process for anticorrosive treatment of metallic surfaces, a metallic surface obtainable by the process, and the use thereof in the sector of the metalworking industries.SOLUTION: There is provided a water-based, alkaline cleaner concentrate for producing a cleaner for metallic surfaces containing a) at least one (meth)acrylic acid homopolymer having a weight-average molar mass in the range from 3000 to 19000 g / mol and b) at least one (meth)acrylic acid copolymer having a weight-average molar mass in the range from 50000 to 100000 g / mol, wherein the at least one (meth)acrylic acid copolymer comprises at least one linear copolymer of (meth)acrylic acid and at least one monomer containing a vinyl group and at least two acid groups selected from the group consisting of carboxylic acid groups and sulfonic acid groups.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-based alkaline cleaner concentrate and to a corresponding cleaner for metallic surfaces with reduced pickling corrosion, said concentrate or said cleaner acting without the use of phosphates, and the invention also relates to a method for the corrosion protection treatment of metallic surfaces comprising a corresponding cleaning step, the metallic surfaces obtainable by said method and their use in the metal processing industry sector. [Background technology]

[0002] Phosphate-containing cleaning products have long been used as standard in industrial metal cleaning due to their ability to accelerate degreasing. In addition to their degreasing action, phosphate offers the added advantage of acting as a complexing agent for interfering ions such as magnesium or calcium.

[0003] For example, anti-corrosion pretreatment of metal strips and metallic parts in vehicle construction or in general industry employs aqueous cleaning systems and conversion solutions whose pH is in the fairly acidic or alkaline range.

[0004] Thus, during the cleaning itself, so-called pickling attacks occur, which can attack not only the oxide film but also the base material, the morphology of which can be adversely affected, which can affect the subsequent precipitation of the conversion coating and then lead to a decrease in the adhesion of the resulting coating, in particular of the cathodic electrodeposit material, and therefore adversely affect the corrosion control.

[0005] For this reason, standard phosphate-containing products are often combined with silicate compounds as corrosion inhibitors to protect sensitive materials, such as (galvanized) steel, aluminum or aluminum-containing substrates, from excessive stress during cleaning operations.

[0006] However, at a pH below 11, silicate compounds, such as potassium and sodium silicates and potassium and sodium water glass, tend to precipitate and therefore lose their activity, and can further form encrustations in the cleaning bath or dry deposits on the metal surfaces being treated, which are then difficult to remove and visually disturbing. Therefore, today, such compounds are not commonly used as anti-pickling agents in alkaline cleaning systems.

[0007] In the meantime, boron compounds, such as boric acid or sodium or potassium borates, have been used as replacements for silicate compounds, especially in the case of aluminium and galvanised steel.

[0008] However, for several years now, there has been a clear and growing trend towards safer and more environmentally friendly cleaning compositions. The driving forces behind this trend are, firstly, legal regulations in various countries (e.g. China) or regions that increasingly prohibit the use of certain ingredients, including phosphates and complexing agents, such as EDTA, and, secondly, the increasing environmental and safety awareness of users.

[0009] This trend has also been noted in conversion systems, with an increasing focus on organosilane-based thin film systems, such as Oxsilan® (Chemetall GmbH, Germany). Like zinc phosphating, these systems act as aqueous conversion systems, but have clear advantages related to greener products, environmental considerations, and the prohibition of raw materials such as nickel or phosphates.

[0010] Aqueous cleaners are therefore nowadays required to exhibit high compatibility with established conversion processes, such as for example compatibility with trication phosphating, but also with nickel-free zinc phosphating and especially with the thin film systems mentioned above, and therefore to produce metal surfaces that are optimal for all types of conversion processes.

[0011] US9567552B2 describes a phosphate-free cleaner in which long-chain polyacrylates are used as corrosion inhibitors. This cleaner is suitable for treating aluminum / aluminum alloys, but not for multimetal systems of the kind common in the automotive industry, for example. The compatibility of the cleaner with subsequent thin film coatings based on organosilanes or with trication phosphating systems is not described. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] US9567552B2 Summary of the Invention [Problem to be solved by the invention]

[0013] The object of the present invention is therefore to provide a water-based cleaning concentrate and corresponding water-based cleaning agent for metallic surfaces which, firstly, works without the use of phosphates and, on the other hand, combines a balanced pickling attack with good cleaning performance, and, secondly, prepares the metal surface optimally for any kind of conversion treatment. [Means for solving the problem]

[0014] The object is to provide a water-based alkaline cleaner concentrate for producing a cleaner for metallic surfaces, comprising: a) at least one (meth)acrylic acid homopolymer having a mass-average molar mass in the range from 3000 to 19000 g / mol, and b) at least one (meth)acrylic copolymer having a mass-average molar mass in the range from 50000 to 100000 g / mol, wherein the at least one (meth)acrylic acid copolymer comprises at least one copolymer of (meth)acrylic acid and at least one monomer comprising a vinyl group and at least two acidic groups selected from the group consisting of a carboxylic acid group and a sulfonic acid group. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The polymers of components a) and b) are used here as phosphate substitutes in the detergent concentrates of the described invention. Surprisingly, the performance of standard phosphate-containing detergents was not achievable with the polymers alone. Instead, comparable results were only achievable using a mixture of the polymers of components a) and b).

[0016] The polymers of component a) comprise relatively short-chain (meth)acrylic acid homopolymers, which combine pickling attack prevention with moderate cleaning effect, whereas the polymers of component b) are specific long-chain (meth)acrylic acid copolymers, and due to their strong complexing properties and the associated strong pickling attack, they act as cleaning promoters, the cleaning performance of which is comparable to that of the phosphates used as standards.

[0017] The weight-average molar masses of the polymers of components a) and b) are determined throughout this specification using GPC (Gel Permeation Chromatography) with aqueous elution, the column being calibrated with polystyrene sulfonate having a narrow molecular weight distribution.

[0018] Definition: The term "water-based" is understood here to mean that the corresponding composition, e.g. a detergent concentrate or a detergent, which may comprise both dissolved and dispersed components, is composed, for example, of at least 50% by weight of water, preferably at least 55% by weight of water.

[0019] "Detergent" and "detergent composition" are used synonymously herein. The detergent or detergent composition may more particularly be a detergent solution.

[0020] "(Meth)acrylic acid" herein always refers to methacrylic acid, acrylic acid, or both. This is always intended to include the deprotonated forms and therefore the conjugate bases of methacrylic acid or acrylic acid, respectively.

[0021] Thus, a "(meth)acrylic acid homopolymer" may be a polymer that contains only methacrylic acid, only acrylic acid, or both methacrylic acid and acrylic acid as monomer units, but no other monomer units.

[0022] The same applies to "(meth)acrylic acid copolymers". This term may contain only methacrylic acid, only acrylic acid, or both methacrylic acid and acrylic acid as monomer units, but always has further monomers that are not methacrylic acid or acrylic acid. Here, the at least one monomer having a vinyl group and at least two acidic groups is also intended to include all deprotonated forms of the corresponding acidic groups.

[0023] Whenever the expression "calculated as X", where X is in each case a particularly specifically indicated chemical compound, is used in this application in connection with a concentration by mass (wt%), this has the following meaning: if an alternative chemical compound (other than X) is used, this should be used as the molar concentration calculated from the respectively specifically given mass concentration (wt%) for X, taking into account the molar mass.

[0024] The at least one (meth)acrylic acid homopolymer of component a) of the cleaning concentrate according to the invention preferably comprises at least one acrylic acid homopolymer, and more preferably is at least one acrylic acid homopolymer.

[0025] The at least one (meth)acrylic acid homopolymer of component a) preferably comprises, and more preferably has, at least one (meth)acrylic acid homopolymer having a weight-average molar mass, calculated as polyacrylic acid, in the range from 5000 to 15000 g / mol, particularly preferably in the range from 6000 to 12000 g / mol and very particularly preferably in the range from 7000 to 9000 g / mol.

[0026] The expression "calculated as polyacrylic acid" here is to be understood as follows: Even if the at least one (meth)acrylic acid homopolymer of component a) is not or is not exclusively polyacrylic acid, it is nevertheless assumed for purposes of calculating the concentration that all monomer units (100 mol %) of the at least one (meth)acrylic acid homopolymer of component a) are acrylic acid.

[0027] The at least one (meth)acrylic acid homopolymer of component a) particularly preferably comprises and more preferably has at least one (meth)acrylic acid homopolymer having a weight-average molar mass, calculated as polyacrylic acid, in the range from 5000 to 15000 g / mol, particularly preferably in the range from 6000 to 12000 g / mol and very particularly preferably in the range from 7000 to 9000 g / mol.

[0028] The at least one (meth)acrylic acid homopolymer of component a) is preferably added to the detergent concentrate as a salt, more preferably as an alkali metal salt and particularly preferably as a sodium salt. In terms of the resulting alkalinity of the detergent concentrate, the sodium salt is particularly advantageous.

[0029] Particularly suitable is, for example, polyacrylic acid with a weight-average molar mass of about 8000 g / mol (available as Sokalan® PA 30 CL, from BASF SE, Germany).

[0030] The at least one (meth)acrylic copolymer of component b) of the cleaning concentrate according to the invention comprises at least one, preferably linear, copolymer of (meth)acrylic acid and at least one monomer comprising a vinyl group and at least two acid groups selected from the group consisting of carboxylic acid groups and sulfonic acid groups.

[0031] On the one hand, the (meth)acrylic acid unit and on the other hand, the monomer unit having at least two acid groups are preferably arranged here in alternating sequence.In principle, however, suitable are the corresponding block copolymers and random copolymers.At least one (meth)acrylic acid copolymer preferably does not contain other monomer units, more preferably does not contain vinyl acetate or vinyl alcohol, and more particularly does not even contain vinyl acetate units.

[0032] The (meth)acrylic acid units preferably constitute 35 to 65 mol%, particularly preferably 40 to 50 mol% and very preferably 45 to 55 mol% of the at least one (meth)acrylic acid copolymer of component b), while the monomer units having at least two acidic groups preferably constitute 65 to 35 mol%, particularly preferably 60 to 40 mol% and very preferably 55 to 45 mol% of the at least one (meth)acrylic acid copolymer of component b), the said mol% mol% in each case preferably adding up to 100.

[0033] According to a first preferred embodiment, the at least one (meth)acrylic copolymer of component b) comprises, preferably is, at least one, preferably alternating copolymer of (meth)acrylic acid and at least one, preferably exactly one, monomer comprising a vinyl group and at least two, preferably exactly two, carboxylic acid groups.

[0034] The at least one monomer comprising a vinyl group and at least two carboxylic acid groups herein is preferably selected from the group consisting of vinyl dicarboxylic acids, more preferably from the group consisting of maleic acid and fumaric acid, more preferably from maleic acid.

[0035] It is noted here that "maleic acid" is understood to include maleic anhydride or a mixture of maleic acid and maleic anhydride, but in particular the compound is maleic acid, which is formed from maleic anhydride by hydrolysis in an aqueous environment.

[0036] According to a second preferred embodiment, the at least one (meth)acrylic copolymer of component b) comprises, more preferably is, at least one, preferably alternating, copolymer of (meth)acrylic acid and at least one, preferably exactly one, monomer comprising a vinyl group and at least two, preferably exactly two, sulfonic acid groups.

[0037] The monomer containing a vinyl group and at least two sulfonic acid groups is preferably selected from the group consisting of vinyl disulfonic acids.

[0038] The at least one (meth)acrylic copolymer of component b) preferably comprises, and more preferably is, at least one (meth)acrylic copolymer having a weight-average molar mass, calculated as poly(acrylic acid-alt-maleic acid), in the range from 55 000 to 90 000 g / mol, particularly preferably in the range from 60 000 to 80 000 g / mol and very particularly preferably in the range from 65 000 to 75 000 g / mol.

[0039] "Calculated as poly(acrylic acid-alt-maleic acid)" should therefore be understood as follows: even if the at least one (meth)acrylic acid copolymer of component b) is not or is not exclusively "poly(acrylic acid-alt-maleic acid)", it is nevertheless assumed for purposes of calculating the concentration that half (50%) of the monomer units of the at least one (meth)acrylic acid copolymer of component b) are maleic acid.

[0040] The at least one (meth)acrylic acid copolymer of component b) is particularly preferably at least one, preferably alternating, copolymer of (meth)acrylic acid and at least one, preferably exactly one, monomer (having a vinyl group and at least two, preferably exactly two carboxylic acid groups) and having a weight-average molar mass, calculated as poly(acrylic acid-alt-maleic acid), in the range from 55 000 to 90 000 g / mol, particularly preferably in the range from 60 000 to 80 000 g / mol and very particularly in the range from 65 000 to 75 000 g / mol, and more preferably these.

[0041] The at least one (meth)acrylic copolymer of component b) is preferably added to the detergent concentrate as a salt, more preferably as an alkali metal salt and particularly preferably as a sodium salt. Due to the resulting alkalinity of the detergent concentrate, the sodium salt is particularly advantageous.

[0042] Particularly suitable is, for example, poly(acrylic acid-alt-maleic acid) (Sokalan® CP 5, from BASF SE, Germany) with a weight-average molar mass of about 70 000 g / mol.

[0043] Particularly suitable correspondingly, as polymer mixtures of components a) and b) according to the invention are, for example, combinations of polyacrylic acid (Sokalan® PA 30CL, available from BASF SE, Germany) with a weight average molar mass of about 8000 g / mol and poly(acrylic acid-alt-maleic acid) (Sokalan® CP 5, available from BASF SE, Germany) with a weight average molar mass of about 70000 g / mol.

[0044] The at least one (meth)acrylic acid homopolymer of component a) is preferably present in a concentration of at least 1.0% by weight, particularly preferably at least 1.5% by weight and very preferably at least 1.7% by weight, calculated as polyacrylic acid and based on the total detergent concentrate, but preferably in an amount of at most 2.5% by weight and more preferably at most 2.0% by weight, while the at least one (meth)acrylic acid copolymer of component b) is present in a concentration of at least 0.5% by weight, particularly preferably at least 0.7% by weight and very preferably at least 0.9% by weight, but preferably in an amount of at most 1.5% by weight, calculated as poly(acrylic acid-alt-maleic acid) and based on the total detergent concentrate.

[0045] Here, the at least one (meth)acrylic acid homopolymer of component a) and the at least one (meth)acrylic acid copolymer of component b) are present in the detergent concentrate according to the invention in a weight ratio, calculated as polyacrylic acid:poly(acrylic acid-alt-maleic acid), preferably in the range of 1.0:1 to 2.5:1, more preferably in the range of 1.3:1 to 2.0:1, particularly preferably in the range of 1.5:1 to 1.9:1 and very particularly preferably in the range of 1.7:1 to 1.8:1.

[0046] By selection of components a) and b) within the preferred ranges described above, the detergent performance obtained from the detergent concentrate of the present invention, effective cleaning performance combined with consistent pickling attack, may approach or even exceed that of standard phosphate-containing detergents.

[0047] The detergent concentrate of the present invention is preferably phosphate-free, which by definition means that no phosphate is added thereto during production. However, it is also possible, although undesirable, that the raw materials used contain traces of phosphate impurities, and thus the detergent concentrate also contains small amounts of phosphate. In a further preferred embodiment, however, the detergent concentrate contains less than 100 ppm, more preferably less than 10 ppm, particularly preferably less than 1 ppm, and very particularly preferably less than 0.1 ppm of phosphate.

[0048] The detergent concentrate is preferably silicate-free, which means that no silicate is added thereto during production.However, it is also possible that the raw materials used contain traces of silicate impurities, and thus the detergent concentrate also contains small amounts of silicate compounds.In a further preferred embodiment, however, the detergent concentrate contains less than 100 ppm, more preferably less than 10 ppm, particularly preferably less than 1 ppm, and very particularly preferably less than 0.1 ppm of silicate compounds.

[0049] The reason for this is that silicate compounds, as already observed above, tend to precipitate at a pH below 11 and therefore lose their activity as anti-picking agents. Furthermore, they may crust in the cleaning bath or produce visually disturbing dried deposits on the metal surfaces being treated.

[0050] The detergent concentrate of the present invention preferably further comprises at least one water-soluble boron compound c), which is preferably selected from the group consisting of boric acid and alkali metal borates, more preferably selected from the group consisting of boric acid, sodium borate and potassium borate.

[0051] Surprisingly, this allows the aggressiveness, i.e. the pickling attack of the medium, to be precisely controlled on any metallic surface to be cleaned, even on very sensitive materials such as aluminium and galvanised and / or pre-phosphated steel. This therefore results in improved multi-metal performance of the detergent obtained from the detergent concentrate of the present invention, i.e. improved multi-metal processing, where different metal surfaces, e.g. steel, aluminium, galvanised steel and pre-phosphated steel, are cleaned simultaneously or one after the other in the same bath.

[0052] Galvanized steel here may in particular be hot-dip galvanized or electrogalvanized steel or steel coated with a zinc-magnesium alloy. Galvanized steel may furthermore be previously phosphated. "Aluminum" is always intended to include also aluminum alloys.

[0053] The at least one water-soluble boron compound c) is preferably present in a concentration of at least 7.5% by weight, more preferably at least 10.0% by weight, more preferably at least 10.5% by weight, particularly preferably at least 12.5% ​​by weight, and very preferably at least 14.0% by weight, calculated as boric acid and based on the total detergent concentrate, but preferably at most 25.0% by weight, more preferably at most 20.0% by weight, particularly preferably at most 17.0% by weight, and very preferably at most 16.0% by weight. By keeping the concentration of the at least one water-soluble boron compound c) within the above-mentioned lower limits, this is particularly true in the case of a 1:50 dilution of the concentrate, while the upper limit is determined by the pH-dependent solubility of the water-soluble boron compound.

[0054] The cleaning concentrate according to the invention is alkaline, which means that it has a pH of more than 7. The pH is preferably in the range of 9.5 to 14.0, particularly preferably in the range of 10.5 to 14.0 and very particularly preferably in the range of 11.5 to 14.0. The alkalinity may be adjusted, for example, by adding a corresponding amount of sodium or potassium hydroxide and / or sodium or potassium carbonate to the cleaning composition according to the invention.

[0055] The detergent concentrate preferably further comprises at least one salt which, together with the conjugate acid formed in situ, forms a buffer system and acts against the drop in pH value caused by the uptake of carbon dioxide from the surrounding air, thereby ensuring a stable pH of the concentrate of the invention and the detergent obtained therefrom. The at least one salt in this case is preferably sodium carbonate, sodium bicarbonate, potassium carbonate and / or potassium bicarbonate. The advantage of the particularly preferred use of sodium carbonate and / or potassium carbonate is that the required alkalinity can thus be established at the same time.

[0056] The at least one salt here is preferably present in a concentration of at least 5% by weight, more preferably at least 7% by weight and particularly preferably from 8 to 12% by weight, calculated as potassium carbonate and based on the total detergent concentrate.

[0057] The detergent composition preferably further comprises at least one complexing agent capable of complexing interfering foreign ions, in particular Ca, Mg and Zn cations, and thus keeping them in solution and preventing them from adversely affecting the overall operation, i.e. from contaminating the bath in the form of coatings and thus increasing the need for cleaning, and from reducing the performance of the system by reacting with the detergent components. The at least one complexing agent preferably comprises a gluconate, which is preferably added to the detergent composition in the form of sodium gluconate and / or potassium gluconate.

[0058] The at least one complexing agent here is preferably present in the concentrate in an amount of at least 1.0% by weight, more preferably at least 2.0% by weight and particularly preferably in the range from 2.5 to 3.5% by weight, calculated as sodium gluconate and based on the total detergent concentrate.

[0059] According to a particularly preferred embodiment, the cleaning concentrate of the invention comprises the following components: a) at least 1.0% by weight, calculated as polyacrylic acid, of (meth)acrylic acid homopolymers having a weight-average molar mass in the range from 3000 to 19000 g / mol; b) at least 0.5% by weight of copolymers of (meth)acrylic acid and at least one vinyl dicarboxylic acid, calculated as poly(acrylic acid-alt-maleic acid), having a weight-average molar mass in the range from 50 000 to 100 000 g / mol; c) at least 10.0% by weight of sodium borate and / or potassium borate, calculated as boric acid; d) at least 8.0% by weight of sodium hydroxide and / or potassium hydroxide, calculated as potassium hydroxide; e) at least 5% by weight of sodium carbonate and / or potassium carbonate, calculated as potassium carbonate; f) at least 1.5% by weight of a complexing agent, calculated as sodium gluconate; and g) at least 50% by weight of water; wherein the (meth)acrylic acid homopolymer and the copolymer of (meth)acrylic acid and at least one vinyl dicarboxylic acid are present in a weight ratio of 2.0:1 to 1.5:1, and in each case the aforementioned weight percentages add up to 100 weight percent.

[0060] The present invention further relates to a water-based alkaline cleaner for metallic surfaces, the alkaline cleaner comprising: a) at least one (meth)acrylic acid homopolymer having a mass-average molar mass in the range from 3000 to 19000 g / mol, and b) at least one (meth)acrylic copolymer having a mass-average molar mass in the range from 50000 to 100000 g / mol, and h) at least one surfactant; Including, In the case where the at least one (meth)acrylic acid copolymer comprises at least one copolymer of (meth)acrylic acid and at least one monomer comprising a vinyl group and at least two acidic groups selected from the group consisting of a carboxylic acid group and a sulfonic acid group, and the cleaning agent is a fresh cleaner, component a) is present in a concentration of up to 0.65 g / l, calculated as polyacrylic acid, preferably in a concentration of 0.10 to 0.50 g / l, and component b) is present in a concentration of up to 0.35 g / l, preferably in a concentration in the range of 0.05 to 0.30 g / l, calculated as poly(acrylic acid-alt-maleic acid).

[0061] If the specified maximum concentrations of components a) and b) are exceeded, the cleaning performance is sufficient but the pickling attack becomes too severe.

[0062] By "fresh cleaner" is understood here a cleaner that has not yet come into contact with a metallic surface. The reason for this is that contact with a metallic surface leaches ions from said surfaces and separates oils and greases from said surfaces, which accumulate in the cleaning bath. Ageing of the bath thus occurs. As a result, the pickling attack of the cleaner is reduced, which makes it possible to use components a) in concentrations of up to 1.0 g / l and components b) in concentrations of up to 0.55 g / l and still not cause pickling corrosion.

[0063] The cleaning agent of the present invention can be prepared by the following steps: 1) by dilution, preferably in water, and preferably with a factor of 1:20 to 1:100 (corresponding to 10 to 50 g of concentrate for 1.0 l of detergent), 2) by the addition of at least one surfactant, preferably in a concentration ranging from 0.3 to 10 g / l, based on the detergent, and 3) Optionally, this can be achieved by adjusting the pH using at least one acid or base.

[0064] Particularly preferably, in step 1), the dilution factor is 1:40 to 1:60, and particularly preferably 1:45 to 1:55. Conversely, the concentration of the at least one surfactant in step 2) is particularly preferably in the range of 0.4 to 5 g / l, and very particularly preferably in the range of 0.5 to 3.5 g / l, based on the detergent.

[0065] Within the cleaning operation, at least one surfactant acts to remove any organic impurities, such as mineral oils and greases, and should therefore necessarily be added to the diluted concentrate, this at least one surfactant comprising more particularly at least one nonionic, anionic and / or cationic surfactant.

[0066] Suitable nonionic surfactants here are in particular: - alkylphenol alkoxylates, in particular alkylphenol ethoxylates, having a C6 to C14 alkyl chain and a degree of alkoxylation of 5 to 30 moles per mole of phenol; - alkyl polyglucosides having an alkyl chain length of C8 to C22, preferably C10 to C18, and having 1 to 20, preferably 1 to 5 glucoside units; fatty acid amide alkoxylates, fatty acid alkanolamide alkoxylates, N-alkyl glucamides or block copolymers of ethylene oxide, propylene oxide and / or else butylene oxide, and -Alkoxylated C8-C22 alcohols, such as fatty alcohol alkoxylates, oxo-process alcohol alkoxylates, and Guerbet alcohol alkoxylates, where the alkoxylation may be carried out using ethylene oxide, propylene oxide, butylene oxide, and / or mixtures thereof as block or random copolymers. The alcohols preferably have 8-18 atoms; the degree of alkoxylation is typically in the range of 2-50 moles, preferably 3-20 moles, of at least one of the above-mentioned alkylene oxides per mole of alcohol. The alkylene oxide head group may additionally contain the following so-called end-capping groups as modifications: benzyl, methyl, and / or tert-butyl capping.

[0067] Depending on the application, the following anionic surfactants are especially used: - fatty alcohol surfactants with an alkyl chain length of 8 to 22, preferably 10 to 18 carbon atoms, such as lauryl sulfate, cetyl sulfate, myristyl sulfate, palmityl sulfate or stearyl sulfate, - alkyl ether sulfates, the alkyl chain length of which is from 8 to 22, preferably from 10 to 18, carbon atoms, - Linear C8-C20 alkylbenzenesulfonates, or else alkanesulfonates, and soaps, such as the sodium or potassium salts of C8-C24 carboxylic acids.

[0068] The cationic surfactants used depend on the application and are in particular: - Quaternary mono- and di-(C7-C25 alkyl)dimethylammonium compounds, - ester quats, in particular quaternary esterified mono-, di- and trialkanolamines esterified with C8 to C22 carboxylic acids, and -C7 to C25 alkylamine, N,N-dimethyl-N-(hydroxy-C7 to C25 alkyl)ammonium salt and / or imidazoline quat.

[0069] The at least one surfactant preferably comprises at least one non-ionic surfactant, and more preferably is at least one non-ionic surfactant.Anionic surfactants, in most applications, show high foaming tendency, while cationic surfactants often adhere to metallic surfaces and thus can cause problems in the precipitation of conversion coating.Non-ionic surfactants do not have these disadvantages.

[0070] Even if no pH adjustment is made upon dilution of the detergent concentrate of the present invention, the appropriate pH for use in ease of multi-metal performance pretreatment is already achieved (ready-to-use pH), and therefore further addition of at least one additional acid or base is only necessary in special applications.

[0071] The cleaning agent of the present invention is preferably phosphate-free, which means that no phosphate is added to it. Nevertheless, it is possible, although undesirable, that the raw materials used contain small amounts of phosphate impurities, and therefore the cleaning agent concentrates and the cleaning agents produced therefrom also contain small amounts of phosphate. Small amounts of phosphate in the cleaning agent may result from substances dissolved from the cleaned metal surfaces, especially if these surfaces have been subjected to a pre-phosphate treatment. More preferably, however, the phosphate content of the cleaning agent is less than 200 ppm, particularly preferably less than 20 ppm, and in particular less than 2 ppm.

[0072] The cleaning agent preferably does not contain silicate compounds, which means that no silicate compounds are added during production.However, it is possible that the raw materials used contain small amounts of silicate impurities, and therefore the cleaning agent also contains small amounts of silicate compounds.However, more preferably, the silicate compound content of the cleaning agent is less than 100ppm, more preferably less than 10ppm, particularly preferably less than 1ppm, and very preferably less than 0.1ppm.

[0073] The cleaning agent of the present invention preferably comprises at least one water-soluble boron compound c) which is preferably selected from the group consisting of boric acid and alkali metal borates, more particularly from the group consisting of boric acid, sodium borate and potassium borate.

[0074] The at least one water-soluble boron compound c) is preferably at least 0.15% by weight, more preferably at least 0.20% by weight, more preferably at least 0.21% by weight, particularly preferably at least 0.25% by weight and very preferably at least 0.28% by weight, calculated as boric acid and based on the total detergent concentrate, but preferably at most 0.50% by weight, more preferably at most 0.40% by weight, particularly preferably at most 0.34% by weight and very preferably at most 0.32% by weight. By observing the above-mentioned lower limits of the concentration of the at least one water-soluble boron compound c), it is possible to further improve the multimetal performance of the detergent, while the upper limit is due to the pH-dependent solubility of the water-soluble boron compound in the concentrate, more particularly on dilution of the detergent from a 1:50 concentrate.

[0075] Further advantageous embodiments and properties of the inventive cleaning agent are those described above in connection with the inventive cleaning agent concentrate.

[0076] The present invention further provides a method for the anticorrosive treatment of a metallic surface, comprising treating the surface with a composition comprising: i) at least one water-based alkaline cleaner for metallic surfaces, comprising: a) at least one (meth)acrylic acid homopolymer having a weight average molar mass in the range of 3000 to 19000 g / mol; b) at least one (meth)acrylic acid copolymer having a weight average molar mass in the range of 50000 to 100000 g / mol; and h) at least one surfactant, wherein the at least one (meth)acrylic acid copolymer is at least one surfactant selected from the group consisting of (meth)acrylic acid and vinyl groups, and carboxylic acid groups and sulfonic acid groups. at least one water-based alkaline cleaner comprising at least one copolymer with at least one monomer containing at least two acid groups, and whereby component a) is present in a concentration of at most 0.65 g / l, calculated as polyacrylic acid, preferably in a concentration of 0.10 to 0.50 g / l, and component b) is present in a concentration of at most 0.35 g / l, preferably in a concentration in the range of 0.05 to 0.30 g / l, calculated as poly(acrylic acid-alt-maleic acid), if the cleaner is a virgin cleaner, ii) a first water-based rinse composition; iii) optionally a second water-based rinse composition; iv) a water-based acidic conversion composition; v) optionally a third water-based rinse composition, and vi) Water-based compositions comprising (meth)acrylate-based and / or epoxy-based cathodic or anodic electrodeposition materials and / or water-based or solvent-based wet or powder coating materials; and, in turn, contacting said

[0077] The contacting of the metallic surface successively with compositions i) to vi) is not intended to exclude contacting it before, after or during with at least one further, preferably water-based composition, such as an activating composition, or a passivating composition, or with a further rinsing composition, as described below for the phosphating treatment, or to exclude that it is subsequently treated to at least one drying, for example in a drying oven, or provided with further coating films, such as an undercoat, a topcoat and a clearcoat (automotive paint systems).

[0078] A feature of the method of the present invention is that it operates without the use of a phosphate-containing cleaning composition, yet produces results in corrosion control and coating adhesion that are comparable to the results obtained when a phosphate-containing cleaning composition is used.

[0079] By contacting the metallic surface in step i) with at least one cleaning agent of the present invention, combining a balanced pickling attack with an efficient cleaning performance, the metallic surface is optimally prepared for any kind of conversion treatment. Thus, the acid conversion composition in step iv) may be a conversion coating for a nickel-free zinc phosphate treatment, an organosilane-based thin film coating, or a conversion coating to provide a passivation composition, as well as a conversion coating for a trication phosphating treatment.

[0080] The at least one cleaning agent in step i) preferably further comprises at least one water-soluble boron compound c), which is preferably selected from the group consisting of boric acid, alkali metal borates, more preferably from the group consisting of boric acid, sodium borate and potassium borate. As already mentioned above, this method allows precise control of the aggressiveness of each metal surface to be cleaned and subsequently coated, even if this is a sensitive material. The metallic surface therefore preferably comprises at least one sensitive material selected from the group consisting of aluminum, galvanized steel and pre-phosphated steel.

[0081] The addition of at least one water-soluble boron compound c) results in improved multi-metal performance, as already described. The metallic surface therefore preferably comprises at least two metallic materials selected from the group consisting of steel, aluminum, galvanized steel and pre-phosphated steel, more preferably from the group consisting of aluminum, galvanized steel and / or pre-phosphated steel. More preferably, the metallic surface comprises not only aluminum but also at least one galvanized and / or pre-phosphated steel, particularly preferably both aluminum and at least one galvanized and at least one pre-phosphated steel.

[0082] According to a first preferred embodiment, the acidic conversion composition in step iv) is a nickel-free phosphating composition, which in addition to zinc and manganese ions also contains phosphate ions and to which no nickel ions are added.

[0083] In the case of nickel-free zinc phosphating and in the case of tricationic phosphating in which zinc, manganese and nickel ions and phosphate ions are used, the metallic surface is usually additionally contacted before step iv) with an aqueous activator, which preferably contains particles composed of zinc phosphate and / or titanium phosphate crystals, which promotes the precipitation of the phosphate crystal phase in step iv).

[0084] After the phosphating treatment in step iv), the metallic surface may further be contacted with an aqueous passivating composition. This may be particularly advantageous for surfaces that contain aluminum-containing regions in addition to zinc- and / or iron-containing regions. In this way, further improvements in corrosion control and paint adhesion of painted surfaces can be achieved. The abovementioned passivating composition preferably comprises at least one compound of titanium, zirconium and / or hafnium, more preferably at least one fluorocomplex of the abovementioned elements, and also preferably at least one organosilane, including their hydrolysis and condensation products.

[0085] According to a second preferred embodiment, the acidic conversion composition in step iv) is a composition for giving an organosilane-based thin film system, which composition comprises at least one organosilane, their hydrolysis and condensation products included, but also, optionally, at least one compound of titanium, of zirconium and / or of hafnium.

[0086] Unlike the case of phosphating, the inventive cleaning composition in combination with an organosilane-based thin film system gives better corrosion protection results than conventional phosphate-containing cleaning agents, which is the case when the cleaning composition is phosphate-free. The at least one cleaning agent according to the invention in step i), and thus the inventive cleaning concentrate, is therefore preferably phosphate-free, which is the case in particular when an organosilane-based thin film system is subsequently provided.

[0087] According to a third preferred embodiment, the water-based acidic conversion composition in step iv) comprises a passivation composition which, in addition to titanium, zirconium and / or hafnium compounds, in particular comprises at least one fluoro complex of the aforementioned elements, and optionally also at least one organosilane, including its hydrolysis and condensation products.

[0088] Advantageous embodiments and features of the invention used in step i) are those mentioned above for the inventive cleaning concentrate and the inventive cleaning agent.

[0089] The invention further relates to the corrosion-protected metallic surfaces which can be obtained using the method of the invention, and to the use of this product in the metal processing industry, in particular in the automotive, auto part supply sector, or in industry in general, where conversion processes are used for the purposes of pretreatment.

[0090] The present invention will be described below with reference to examples and comparative examples, but it is understood that the examples do not impose any limitations. EXAMPLES

[0091] i) Pickling corrosion determination: Measurement principle: Pickling corrosion indicates the mass loss of the bare metal during the cleaning process. It is tested by immersing a standard sheet of defined AA6014 aluminium (Gardobond® test sheet, Chemetall GmbH, Germany) with dimensions 105 x 190 mm in the solution to be tested - in this case the corresponding cleaning solution. The mass loss is then determined gravimetrically using an analytical balance. The test in this case is limited to aluminium surfaces, since these are the most susceptible to pickling attack.

[0092] Preparation of test sheets The test sheets were first pre-degreased using mineral spirits to remove any kind of organic impurities, which allowed for direct attack of the test solutions on the base substrates to be evaluated and compared.

[0093] Pickling corrosion measurement The mass of each pre-degreased test sheet was measured on an analytical balance and immediately thereafter the test sheet was immersed for 10 minutes at 55° C. in a 3 liter beaker containing the corresponding test solution. A 40 mm magnetic stirrer was used at the bottom of the beaker to stir at a speed of 500 rpm.

[0094] After 10 minutes, the test sheets were removed from the test solution, thoroughly rinsed with demineralized (FD) water, and dried using compressed air. The mass loss was then measured using an analytical balance.

[0095] To make the values ​​obtained comparable, a reference was tested in parallel in each case.

[0096] ii) Determination of minimum cleaning time Measurement principle: The minimum cleaning time (MCT) indicates the minimum duration of the cleaning process required under certain conditions to remove organic impurities from a standard sheet (test sheet) of 1.0312 steel with dimensions 105 x 190 mm. The quality of the cleaning must achieve a defined minimum, which was determined based on the percentage of water wetting of the metal surface. Here, the focus was exclusively on the steel surface, since this is usually the most difficult surface to degrease.

[0097] Creating a test sheet The test sheets used had a constant oil coating (1.7 + / - 0.2 g / m 2 ), which helped to compare the results.

[0098] Minimum cleaning time measurement: To measure the minimum cleaning time, each test sheet was immersed in a 3 liter beaker containing the corresponding detergent solution for 1 minute at 55°C. Agitation was performed at the bottom of the beaker at a speed of 500 rpm using a 40 mm magnetic stirrer. The test sheet was then rinsed in an immersive rinse with back and forth movements (approximately 15 back and forth movements). In each case, the sheet was always completely removed from the rinse water and held vertically (to exclude apparent wetting) for evaluation after 10 seconds. The minimum cleaning time was achieved when the surface was at least 95% wetted, i.e., a coherent water film was present. If this condition was not met, the test sheet was immersed in the cleaning solution for an additional minute as described above and rinsed in the immersion rinse. This was repeated until the condition was met.

[0099] The number of repetitions was totaled and, for checking, the same oil test sheet was left in the detergent solution for the entire time. This was necessary because an intermediate rinsing step improves the cleaning performance. If the sheet was at least 95% wetted after the total time, this time was recorded as the MCT. If this was not the case, the washing and rinsing were repeated in 1 minute steps without intermediate rinsing steps until the surface was at least 95% water wettable, and this time was recorded as the MCT. iii) Investigation of different cleaning solutions: To test the effect of different polymers on pickling corrosion and MCT, a standard detergent concentrate (VB1) with a pH of 12.9 was first prepared as a reference, which contained FV water and the following components: [Table 1]

[0100] To this standard, different detergent concentrates were obtained by adding the following polymers (VB2 to VB6 and B1):

[0101] [Table 2]

[0102] Additionally, a phosphate-containing standard concentrate (VB7) with a pH greater than 11.5 was prepared as a reference and contained FV water and the following components: [Table 3]

[0103] All detergent concentrates were then diluted with FV water by a factor of 1:50 (corresponding to 20 g of concentrate per 1.0 liter of detergent) and mixed with 2 g / liter of ethylene / propylene oxide fatty alcohol, a non-ionic surfactant.

[0104] Additionally, the pH of all detergent concentrates was adjusted to 10.5 by adding boric acid or aqueous potassium hydroxide.

[0105] The resulting cleaning solutions were then tested for pickling corrosion and MCT as described above (notes i) and ii)). The results obtained are shown in Table 1 (average values ​​of at least three sheets in each case, i.e. n≧3).

[0106] [Table 4]

[0107] The experimental results show that by adding polymers - polyacrylic acid or poly(acrylic acid-alt-maleic acid) - it is possible to achieve a significant improvement in the cleaning performance (MCT; VB2-VB6 and B1 vs. VB1, cf.). At the same time, the aggressiveness of the media towards aluminium increases (pickling attack, cf.). In the case of polyacrylic acid, it is evident that as the chain length increases, i.e. as the molar mass increases, the effect of the polymer addition becomes greater in the aspects of pickling attack and MCT (VB2-VB4).

[0108] It was further found that the polymers alone could not achieve the pickling attack and MCT performance of the standard phosphate-containing cleaners. Only the cleaning solution of the present invention (B1) containing a specific mixture of two polymers achieved the overall low dosage levels and consistent pickling attack - 0.8 g / m 2 It is possible to achieve or even surpass the cleaning performance of the phosphate-containing cleaner (VB7) at a pickling attack below 4 minutes MCT. However, when the concentration of the two polymers is doubled (increased), the cleaning performance remains satisfactory, but the pickling attack becomes too severe (VB6).

[0109] iv) Multi-metallic performance measurements: Using the two measurement principles mentioned above, pickling corrosion (see Table 2: n>3) and MCT (see Table 3: n>3), but in each case using a specific VDA230-213 test apparatus, the multi-metal performance of the various solutions was likewise measured. These tests were carried out on four substrates encountered in the automotive industry: cold rolled steel (CRS), hot dip galvanized steel (HDG), pre-phosphated steel (ZEP), and automotive grade aluminium (AA6014).

[0110] [Table 5]

[0111] [Table 6]

[0112] As can be clearly seen from Table 2, in the case of the detergent solution of the invention (B1), the pickling attack is indeed somewhat higher compared to the phosphate-containing detergent (VB7). However, in contrast to the detergent solutions based on only one polymer, for the lower polymer concentration (VB8), the values ​​obtained for aluminum (AA6014) are also acceptable for current operation, thus confirming the multi-metal performance of the detergent solutions of the invention.

[0113] Table 3 shows that for the inventive cleaner solution (B1), the minimum cleaning time (MCT), i.e. the cleaning performance, is in each case better on substrates used in multimetal operations, especially compared to the phosphate-containing cleaner (VB7), but also for the cleaner solution based on only one polymer with a lower polymer concentration (VB8). The results obtained for pickling corrosion and MCT by using a specific VDA230-213 test apparatus were higher compared to the manually verified results in Table 1, but this is due to the lower circulation / bath operation in the apparatus.

[0114] In order to ascertain the optimum in terms of pickling attack in multimetal operations, the borate concentration was further varied in the detergent solution B1 of the invention. The cleaning solutions (B1-1 to B1-3) thus prepared were then tested as described above (note i)) for pickling corrosion on three substrates applied in the automotive industry: automotive grade aluminum (AA6014), hot dip galvanized steel (HDG) and electrolytic galvanized steel (MBZE). Each metal sheet used for this purpose had been previously degreased using a surfactant solution.

[0115] The results thus obtained are shown in Table 4 (average of at least three sheets, ie, n≧3).

[0116] [Table 7]

[0117] As can be seen from the experimental results of the inventive detergent solution B1 and its variants B1-1 and B1-3, the pickling attack of aluminum (AA6014) was within the desired low range when the concentration of boric acid in the concentrate was in the concentration range of 14.5 and 16.5% by weight, i.e. 0.29 and 0.33% by weight, respectively, at a dilution of 1:50 in the detergent solution. Thus, in this way, all tested substrates containing aluminum could be combined and optimally treated.

[0118] v) Compatibility with conversion processes: The compatibility of the detergent solution of the present invention (B1) with known conversion processes based on organosilane-based thin film coatings and also on tricationic phosphate treatments was tested. To investigate the effect of the detergent solution of the invention (B1), the corresponding polymers were added to both conversion baths (B2 and B3) in amounts higher than normal for the process, so that they could pass through the components in the conversion bath and reach the detergent medium.The following substrates used in the automotive industry were then pretreated within the standard processing procedures - cold rolled steel (CRS), hot dip galvanized steel (HDG) and aluminium (AA6014) - with organosilanes and zirconium compounds, or with zinc-manganese-nickel phosphate (phosphating: 180 s), followed by preactivation with zinc phosphate (activation time: 60 s).

[0119] The effect of the polymer was evaluated by measuring the coat weight (CW) by X-ray fluorescent analysis (XRF) and scanning electron microscope (SEM) images of the surface structure of the resulting conversion coat. The measured coat weights - calculated as zirconium metal (Zr) - for the organosilane-based thin film coatings are shown in Table 5 (n≧3).

[0120] [Table 8]

[0121] The deviations occurring within the different variants (VB9, B2 and B3) were located within the possible error tolerance of the CW measurements. SEM images of the surface structure of the conversion coatings did not show any abnormalities in any case. The polymers used in the present invention therefore do not adversely affect the optimal development of coatings in organosilane-based thin film systems and are therefore compatible with the above-mentioned systems. The measured coating masses, calculated as Zn3(PO4)2·4H2O, are given in Tables 6 and 7, respectively, for the zinc phosphate and subsequent tricationic phosphate treatments (n≧3 in each case).

[0122] [Table 9]

[0123] [Table 10]

[0124] The obtained coating masses show that the two polymers show no effect on the activation of zinc phosphate (note, Table 6) and only a slight effect on the trication phosphating process (note, Table 7) (B4 and B5 vs. VB10), and these effects can be compensated for within the current operation by adapting the phosphate parameters. SEM images of the surface structure of the trication conversion coatings showed no abnormalities.

[0125] It was therefore possible to demonstrate the compatibility of the detergent solutions of the invention with organosilane-based thin film coatings as well as with tricationic phosphating systems.

[0126] vi) Corrosion behavior in organosilane-based thin film coatings: To investigate the influence of the inventive cleaning solution B1 on the corrosion behavior, a sheet material HDG was treated in a standardized process. Process: 1.) Spray cleaning, 60 seconds 2.) Immersion cleaning, 180 seconds 3.) Soak and rinse for 30 seconds 4.) Immersion conversion, 180 seconds 5.) Soak and rinse for 30 seconds 6.) Drying with compressed air

[0127] The cleaning steps 1.) and 2.) were carried out using the phosphate-free detergent solution of the invention at a dilution of 1:50 from the concentrate and at 2 g / l ethylene / propylene oxide fatty alcohol. For comparison, two standard phosphate-containing detergents (VB11 and VB12) were also tested.

[0128] For the conversion in step 4.), an organosilane-based thin film system (Chemetall, Germany) was used. After step 6.), the treated sheets were tested for paint adhesion and corrosion, which were carried out using the cyclic corrosion test (VDA621-415) usual in the automotive sector.

[0129] The results of paint adhesion after corrosive undermining and stone chipping are shown in Table 8 (n≧3 in each case).

[0130] It is clear that the inventive phosphate-free cleaner solution B1, in combination with an organosilane-based conversion system, significantly improves both the corrosion behavior and the paint adhesion properties of the surface compared to the standard phosphate-containing cleaners (VB11 and VB12).

[0131] [Table 11]

Claims

1. 1. A water-based alkaline cleaner concentrate for producing a cleaner for metallic surfaces, comprising: a) at least one (meth)acrylic acid homopolymer having a weight average molar mass in the range from 3000 to 19000 g / mol, and b) at least one (meth)acrylic copolymer having a weight average molar mass in the range from 50,000 to 100,000 g / mol; wherein the at least one (meth)acrylic copolymer comprises at least one linear copolymer of (meth)acrylic acid and at least one monomer comprising a vinyl group and at least two acid groups selected from the group consisting of a carboxylic acid group and a sulfonic acid group.

2. 2. The detergent concentrate according to claim 1, characterized in that the at least one (meth)acrylic acid homopolymer of component a) comprises at least one (meth)acrylic acid homopolymer having a weight-average molar mass, calculated as polyacrylic acid, in the range from 5000 to 15000 g / mol, preferably in the range from 6000 to 12000 g / mol.

3. 3. The cleaning concentrate according to claim 1 or 2, characterized in that the at least one (meth)acrylic copolymer of component b) comprises at least one - preferably alternating - copolymer of (meth)acrylic acid and at least one, preferably exactly one, comonomer comprising a vinyl group and at least two, preferably exactly two carboxylic acid groups.

4. 4. The cleaning concentrate according to claim 1 , wherein the at least one (meth)acrylic copolymer of component b) comprises at least one (meth)acrylic copolymer having a weight-average molar mass, calculated as poly(acrylic acid-alt-maleic acid), in the range from 55 000 to 90 000 g / mol, preferably from 60 000 to 80 000 g / mol.

5. 5. The cleaning concentrate according to claim 1 , characterized in that the at least one (meth)acrylic acid homopolymer of component a) is present in a concentration of at least 1.0% by weight, preferably at least 1.5% by weight, but preferably at most 2.5% by weight, more preferably at most 2.0% by weight, calculated as polyacrylic acid, and the at least one (meth)acrylic acid copolymer of component b) is present in a concentration of at least 0.5% by weight, preferably at least 0.7% by weight, but preferably at most 1.5% by weight, calculated as poly(acrylic acid-alt-maleic acid).

6. 6. The detergent concentrate according to claim 1 , wherein the at least one (meth)acrylic acid homopolymer of component a) and the at least one (meth)acrylic acid copolymer of component b) are present in a ratio, calculated as polyacrylic acid:poly(acrylic acid-alt-maleic acid), in the range from 1.0:1 to 2.5:1, more preferably from 1.3:1 to 2.0:1, particularly preferably from 1.5:1 to 1.9:1 and very particularly preferably from 1.7:1 to 1.8:

1.

7. A detergent concentrate according to any one of claims 1 to 6, characterised in that it is free of phosphates.

8. 8. The detergent concentrate according to claim 1, further comprising at least one water-soluble boron compound c), preferably selected from the group consisting of boric acid and alkali metal borates.

9. 9. The detergent concentrate according to claim 8, characterized in that the at least one water-soluble boron compound c) is present in an amount of at least 10.5% by weight, preferably at least 12.5% ​​by weight, but preferably at most 25.0% by weight, more preferably at most 20.0% by weight, calculated as boric acid.

10. 1. A water-based alkaline cleaner for metallic surfaces comprising: a) at least one (meth)acrylic acid homopolymer having a weight-average molar mass in the range from 3000 to 19000 g / mol, b) at least one (meth)acrylic copolymer having a weight average molar mass in the range from 50,000 to 100,000 g / mol, and h) at least one surfactant, preferably non-ionic; Including, the at least one (meth)acrylic copolymer comprises at least one copolymer of (meth)acrylic acid and at least one monomer comprising a vinyl group and at least two acidic groups selected from the group consisting of a carboxylic acid group and a sulfonic acid group; and 1. A water-based alkaline cleaner, characterized in that, when the cleaner is a virgin (**) cleaner, component a) is present in a concentration of up to 0.65 g / l, calculated as polyacrylic acid, preferably in a concentration of 0.10 to 0.50 g / l, and component b) is present in a concentration of up to 0.35 g / l, preferably in a concentration ranging from 0.05 to 0.30 g / l, calculated as poly(acrylic acid-alt-maleic acid).

11. 1. A method for the corrosion protection treatment of a metallic surface comprising treating said surface with a composition comprising: i) at least one water-based alkaline cleaning agent according to claim 10, ii) a first water-based rinse composition; iii) optionally a second water-based rinse composition; iv) a water-based acidic conversion composition; v) optionally a third water-based rinse composition, and vi) water-based compositions comprising (meth)acrylate-based and / or epoxy-based cathodic or anodic electrodeposition materials and / or water-based or solvent-based wet or powder coating materials; and, in turn, contacting said

12. 12. The method of claim 11, wherein the acidic conversion composition in step iv) comprises a nickel-free zinc phosphating composition which, in addition to zinc and manganese ions, also contains phosphate ions, and to which no nickel ions have been added.

13. 12. The method of claim 11, wherein the acidic conversion composition in step iv) comprises a composition for applying an organosilane-based thin film system, the composition comprising at least one organosilane as well as its hydrolysis and condensation products, and optionally further comprising at least one titanium compound, zirconium compound and / or hafnium compound.

14. A corrosion-protected metallic surface obtainable by the method according to any one of claims 11 to 13.

15. Use of the metallic surface according to claim 14 in the metal processing industry sector.

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