PHOSPHATE-FREE CLEANER FOR METAL SURFACES WITH LESS EROSION FROM PICKLING

Abstract

The present invention relates to a water-based alkaline cleaning concentrate for producing a metal surface cleaner, wherein said concentrate comprises a) at least one (meth)acrylic acid homopolymer having a weight average molar mass in the range of 3,000 to 19,000 g / mol and b) at least one (meth)acrylic acid copolymer having a weight average molar mass in the range of 50,000 to 100,000 g / mol, said at least one (meth)acrylic acid copolymer comprising 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, and also to a corresponding metal surface cleaner with reduced pickling erosion, wherein said concentrate or said cleaner operates using phosphates.Furthermore, the invention relates to an anti-corrosion treatment process for metallic surfaces comprising a corresponding cleaning stage, to a metallic surface obtainable by said process, and to its use in the metallurgical industries sector.

Description

PHOSPHATE-FREE CLEANER FOR METAL SURFACES WITH LESS EROSION FROM PICKLING The present invention relates to a concentrated alkaline water-based cleaner and a corresponding cleaner for metal surfaces with reduced pickling erosion, said concentrate or said cleaner operating without the use of phosphates, and also to a process for the anti-corrosion treatment of metal surfaces comprising a corresponding cleaning step, to a metal surface obtainable by said process, and to the use thereof in the metallurgical industries. Phosphate-containing cleaning products have long been used as standard products in industrial metal cleaning due to their ability to accelerate degreasing. In addition to their degreasing action, phosphates also offer the advantage of acting as complexing agents for interfering ions such as magnesium or calcium. The anti-corrosion pretreatment of metal strips and also metal components, in vehicle construction or in industry in general, for example, employs aqueous cleaning systems and also conversion solutions that have a pH in the significantly acidic or alkaline range. During the cleaning process itself, a type of pickling attack occurs, which can affect not only the oxide films but also the base material, negatively impacting its morphology. This can have consequences for the subsequent deposition of a conversion coating, potentially leading to reduced adhesion of later coatings, especially cathodic electroplating materials, and thus adversely affecting corrosion control. For this reason, standard phosphate-containing products have often been combined with silicate compounds as corrosion inhibitors to protect sensitive materials such as galvanized steels, aluminum, or aluminum-containing substrates from excessive stress during the cleaning operation. However, at a pH below 11, silicate compounds such as potassium and sodium silicates tend to precipitate and, therefore, lose their activity. This can lead to scale formation in cleaning baths or a dry deposit on metal surfaces being treated, which is subsequently difficult to remove and visually unsightly. Consequently, these compounds are not currently commonly used as pickling inhibitors in alkaline cleaning systems. The substitutes now used for silicate compounds, particularly in the case of aluminum and galvanized steels, are boron compounds such as boric acid or sodium or potassium borate. However, for several years now, there has been a growing trend toward cleaner, safer, and more sustainable compositions. The drivers of this trend include, first and foremost, the Q / nZLn / LZnZ / E / Yli legal regulations that prohibit the use of certain ingredients, increasingly, in various countries (e.g. China) or territories, where such ingredients include phosphates and also complexing agents, such as EDTA and, secondly, increased conscious thinking of users regarding the environment and safety. Since this trend is also observed with conversion systems, there is a greater focus on organosilane-based thin-film systems such as Oxsilan® (Chemetall GmbH, Germany). Like zinc phosphating, these systems operate as aqueous conversion systems, but they offer distinct advantages, particularly in relation to more sustainable products, environmental considerations, and bans on raw materials such as nickel or phosphate. Therefore, today, aqueous cleaners must exhibit high compatibility not only with established conversion processes such as trication phosphating, but also with nickel-free zinc phosphating and, in particular, with the aforementioned thin-film systems, thus requiring optimal preparation of the metal surface for each type of conversion treatment. US patent 9,567,552 B2 describes a phosphate-free cleaner that uses long-chain polyacrylates as corrosion inhibitors. The cleaner is suitable for treating aluminum / aluminum alloys, but not for multi-metal systems of the type commonly used in the automotive industry, for example. The cleaner's compatibility with an organosilane-based thin-film backcoat or a trication phosphating system is not disclosed. Therefore, an object of the present invention was to provide a concentrated water-based cleaner and also a corresponding water-based cleaner for metal surfaces that, firstly, operates without the use of phosphates, while combining a balanced pickling attack with good cleaning performance and that, secondly, optimally prepares the metal surface for any type of conversion treatment. This objective is achieved by using a water-based alkaline cleaning concentrate to produce a metal surface cleaner, comprising a) at least one (meth)acrylic acid homopolymer with a weight average molar mass in the range of 3000 to 19000 g / mol and b) at least one (meth)acrylic acid copolymer having a weight average molar mass in the range of 50000 to 100000 g / mol, wherein the at least one (meth)acrylic acid copolymer comprises at least one (meth)acrylic acid copolymer 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. The polymers of components a) and b) are currently used as phosphate substitutes in the cleaning concentrate of the described invention. Surprisingly, it has emerged that the performance of a standard phosphate-containing cleaner is unattainable with either of the polymers alone. Instead, comparable results can only be achieved with a mixture of polymers from components a) and b). The polymers in component a) comprise relatively short-chain (meth)acrylic acid homopolymers, which combine pickling attack inhibition with a moderate cleaning effect. In contrast, the polymers in component b) are specific long-chain (meth)acrylic acid copolymers and, due to their strongly complexing properties and the associated strong pickling attack, act as cleaning enhancers, corresponding in their cleaning capacity to the phosphates used as a standard. The weight average molar mass of the polymers in components a) and b) has now been consistently determined by GPC (Gel Permeation Chromatography) with aqueous eluents. In this case, the columns were calibrated using polystyrene sulfonates, which have a narrow molar mass distribution. DEFINITIONS: Currently, the expression "water-based" should be understood as a corresponding composition, which may contain both dissolved and dispersed constituents, such as a concentrated cleaner or cleaner, for example, consisting of water to an extent of at least 50% by weight, preferably at least 55% by weight. The terms cleaner and cleaning composition are currently used interchangeably. The cleaner or cleaning composition may more specifically refer to a cleaning solution. (Meth)acrylic acid currently always refers to methacrylic acid, acrylic acid, or both. Furthermore, the intention is also to always include the deprotonated form, that is, the conjugate base of methacrylic acid or acrylic acid, respectively. Therefore, a methacrylic acid homopolymer can be a polymer containing only methacrylic acid, only acrylic acid, or both methacrylic acid and acrylic acid as monomeric units, but no other monomeric units beyond these. The same applies to an acid copolymer (methacrylic acid): it may contain methacrylic acid, acrylic acid alone, or both methacrylic and acrylic acid as monomer units, but beyond these, it always has more monomer units that are neither methacrylic acid nor acrylic acid. The requirement of at least one monomer containing a vinyl group and at least two acid groups also includes all deprotonated forms of the acid groups in question. When the expression calculated as X, where X in each case is a particular chemical compound, specifically indicated, is used in the present text in relation to weight concentrations (% by weight), it has the following meaning: When an alternative chemical compound (other than X) is used, it must be used at a molar concentration calculated for X from the weight concentration specifically indicated in each case (% by weight) taking into account its molar mass. α / ηζίη / ίζηζ / Ε / γι The at least one (meth)acrylic acid homopolymer of component a) of the cleaning concentrate of the invention preferably comprises, and most preferably is at least one acrylic acid homopolymer. The at least one (meth)acrylic acid homopolymer of component a) preferably comprises and more preferably is at least one (meth)acrylic acid homopolymer having a weight average molar mass in the range of 5000 to 15000 g / mol, particularly preferably 6000 to 12000 g / mol, and especially preferably 7000 to 9000 g / mol, calculated as polyacrylic acid. Calculated as polyacrylic acid should be understood here 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 the calculation of the concentration that all monomer units (100% mol) of the at least one (meth)acrylic acid homopolymer of component a) are acrylic acid. The at least one (meth)acrylic acid homopolymer of component a) of particular preference comprises and more preferably is at least one acrylic acid homopolymer having a weight average molar mass in the range of 5000 to 15000 g / mol, particularly preference, 6000 to 12000 g / mol, and especially preference, 7000 to 9000 g / mol, calculated as polyacrylic acid. The at least one (meth)acrylic acid homopolymer of component a) is added to the cleaning concentrate preferably as a salt, more preferably as an alkali metal salt, and particularly preferably as a sodium salt. The sodium salt is particularly advantageous due to the resulting alkalinity of the cleaning concentrate. Polyacrylic acid, which has a weight average molar mass of approximately 8,000 g / mol (available as Sokalan® PA 30 CL from BASF SE, Germany), is particularly suitable, for example. The at least one (meth)acrylic acid copolymer of component b) of the cleaning concentrate of the invention comprises at least one copolymer, preferably linear, 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. The (meth)acrylic acid units, on the one hand, and the monomer units with at least two acid groups, on the other hand, are preferably arranged in an alternating sequence. However, in principle, the corresponding block copolymers and random copolymers are also suitable. The at least one (meth)acrylic acid copolymer preferably does not contain any other monomer units, more particularly, any vinyl acetate or vinyl alcohol units, and even more particularly, no vinyl acetate units. The (meth)acrylic acid units preferably constitute 35 to 65 mol%, particularly preferably 40 to 50 mol%, and especially preferably 45 to 55 mol% of at least one (meth)acrylic acid copolymer of component b), whereas the monomeric units with the at least two acid groups preferably constitute 65 to 35 mol%, particularly preferably 60 to 40 mol%, and especially preferably 55 to 55 mol%. 45 mol% of at least one (meth)acrylic acid copolymer of component b), with the aforementioned mol% preferably amounting to 100 in each case. According to a first preferred embodiment, the at least one (meth)acrylic acid copolymer of component b) comprises, and more preferably is, at least one copolymer -preferably alternating- of (meth)acrylic acid and at least one, preferably exactly one monomer containing a vinyl group and at least two, preferably exactly two, carboxylic acid groups. The at least one monomer containing a vinyl group and at least two carboxylic acid groups is hereby preferably selected from the group consisting of vinyldicarboxylic acids, consisting more particularly of maleic acid and fumaric acid, more preferably maleic acid. References to maleic acid should be understood to include maleic anhydride or a mixture of maleic acid and maleic anhydride. Specifically, however, the compound in question is maleic acid, which is formed from maleic anhydride by hydrolysis in an aqueous medium. According to a second preferred embodiment, the at least one (meth)acrylic acid copolymer of component b) comprises, and more preferably is, at least one preferably alternating (meth)acrylic acid copolymer and at least one, preferably exactly one monomer containing a vinyl group and at least two, preferably exactly two, sulfonic acid groups. The monomer containing a vinyl group and at least two sulfonic acid groups is herein preferably selected from the group consisting of vinyldisulfonic acids. The at least one (meth)acrylic acid copolymer of component b) preferably comprises and more preferably is at least one (meth)acrylic acid copolymer having a weight average molar mass in the range of 55,000 to 90,000 g / mol, particularly preferably 60,000 to 80,000 g / mol, and especially particularly preferred 65,000 to 75,000 g / mol, calculated as poly(acrylic acid-alt-maleic acid). Calculated as poly(acrylic acid-salt-maleic acid) it should therefore be understood as follows: Even if the at least one (meth)acrylic acid copolymer of component b) is not or not exclusively poly(acrylic) acid-salt-maleic acid), nevertheless, for the purpose of calculating the concentration, it is assumed that half (50% by mol) of the monomer units of the at least one (meth)acrylic acid copolymer of component b) is acrylic acid and the other half (50% by mol) is maleic acid. The at least one (meth)acrylic acid copolymer of component b) comprises, in particular preference and more preferably, at least one copolymer -preferably alternating- of (meth)acrylic acid and at least one, preferably exactly one monomer containing a vinyl and at least two, preferably exactly two carboxylic acid groups, having a weight average molar mass in the range of 55,000 to 90,000 g / mol, in particular preference, from 60,000 to 80,000 g / mol, and in special preference, from 65,000 to 75,000 g / mol -calculated as poly(acrylic acid-alt-maleic acid). The at least one (meth)acrylic acid copolymer of component a) is added to the cleaning concentrate preferably as a salt, more preferably as an alkali metal salt, and of Q / nZLn / LZnZ / E / Yli particular preference, as a sodium salt. The sodium salt in particular is advantageous, due to the alkalinity resulting from the cleaning concentrate. It is particularly suitable, for example, poly(acrylic acid-alt-maleic acid) which has a weight average molar mass of approximately 70,000 g / mol (available as Sokalan® CP 5 from BASF SE, Germany). Accordingly, particularly suitable as a polymer mixture of components a) and b) of the invention is, for example, the combination of polyacrylic acid having a weight average molar mass of approximately 8000 g / mol (available as Sokalan® PA 30 CL from BASF SE, Germany) and poly(acrylic acid-alt-maleic acid) with a weight average molar mass of approximately 70,000 g / mol (available as Sokalan® CP 5 from BASF SE, Germany). 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 especially preferably at least 1.7% by weight, but preferably at least at most 2.5% by weight, more preferably at most 2.0% by weight - calculated as polyacrylic acid and on the basis of the total cleaner concentrate - whereas 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 especially preferably at least 0.9% by weight, but preferably at most 1.5% by weight - calculated as poly(acrylic acid-alt-maleic acid) and on the basis of the total cleaner concentrate. 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 cleaner concentrate of the invention preferably in a weight ratio in the range of 1.0:1 to 2.5:1, more preferably from 1.3:1 to 2.0:1, with particular preference, from 1.5:1 to 1.9:1, and with special preference, from 1.7:1 to 1.8:1 - calculated as polyacrylic acid: poly(acrylic acid-a / f-maleic acid). By choosing a weight ratio of components a) and b) within the preferred ranges indicated above, the performance (effective cleaning performance together with a balanced pickling attack) of the cleaner obtainable from the cleaner concentrate of the invention can be brought even closer to the performance of a standard phosphate-containing cleaner or may even exceed such performance. The cleaning concentrate of the invention is preferably phosphate-free, meaning by definition that no phosphates have been added during production. However, it is possible, although undesirable, that the raw materials used may contain slight phosphate impurities, and therefore the cleaning concentrate may also contain a small amount of phosphate. More preferably, however, the cleaning concentrate contains less than 100 ppm, more preferably less than 10 ppm, particularly preferably less than 1 ppm, and especially preferably less than 0.1 ppm of phosphate. α / ηζίη / ίζηζ / Ε / γι The cleaning concentrate is preferably free of silicate compounds, meaning that no silicate compounds have been added during production. However, it is possible that the raw materials used may contain slight silicate impurities, and therefore the cleaning concentrate may also contain a small amount of silicate compounds. However, more preferably, the cleaning concentrate contains less than 100 ppm, more preferably less than 10 ppm, particularly preferably less than 1 ppm, and especially preferably less than 0.1 ppm of silicate compounds. The reason is that silicate compounds, as previously observed, tend to precipitate at a pH below 11 and therefore lose their activity as pickling inhibitors. Furthermore, they can produce scale in cleaning baths or a visually destructive dry deposit on the metal surfaces to be treated. The cleaning concentrate of the 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 particularly consisting of boric acid, sodium borate and potassium borate. In this way, it is possible to exert, surprisingly, precise control over the aggressiveness, that is, the pickling attack of the medium, for any metal surface to be cleaned, even for sensitive materials such as aluminum and galvanized and / or pre-phosphated steels. This, in turn, leads to an improved multi-metal capability of the cleaner obtainable from the cleaner concentrate of the invention; that is, an improved multi-metal treatment in which different metal substrates such as steel, aluminum, galvanized steels, and pre-phosphated steels are cleaned simultaneously or successively in the same bath. Galvanized steels can currently be, in particular, hot-dip galvanized or electro-galvanized steels, or steels coated with a zinc-magnesium alloy. In addition, galvanized steels may have undergone pre-phosphate coating. Any reference to aluminum always includes aluminum alloys. 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 particularly preferably at least 14.0% by weight, 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 particularly preferably at most 16.0% by weight calculated as boric acid and on the basis of the total cleaning concentrate.By staying within the aforementioned lower limits for the concentration of at least one water-soluble boron compound c), it is possible to achieve a further improvement in the multi-metallic capacity of the cleaner in question, especially in the case of a 1:50 dilution of the concentrate, while the upper limits are dictated by the pH-dependent solubility of the water-soluble boron compounds. qj nz Ln / ίζηζ / Β / γι The cleaning concentrate of the invention is alkaline, meaning it has a pH greater than 7. Its pH is preferably in the range of 9.5 to 14.0, with particular preference from 10.5 to 14.0, and with special preference from 11.5 to 14.0. The alkalinity can be adjusted, for example, by adding a corresponding amount of sodium or potassium hydroxide and / or sodium or potassium carbonate to the cleaning composition of the invention. The cleaner concentrate preferably further comprises at least one salt which, together with its conjugate acid formed in situ, forms a buffer system and ensures a stable pH of the concentrate of the invention and the cleaner that can be obtained from it, acting in particular to counteract any drop in pH resulting from the ingress of carbon dioxide from the ambient air. 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 and / or potassium carbonate is that the required alkalinity can be established simultaneously. The at least one salt is present here preferably in a concentration of at least 5% by weight, more preferably at least 7% by weight, and with particular preference in the range of 8 to 12% by weight - calculated as potassium carbonate and on the basis of the cleanest concentrated total. The cleaning composition preferably further comprises at least one complexing agent capable of complexing interfering foreign ions, especially Ca, Mg, and Zn cations, and thus keeping them in solution so that they do not have any adverse effect on the overall operation; that is, they do not contaminate the baths in the form of scale and therefore increase cleaning requirements and do not reduce the system's performance capacity by reacting with cleaner constituents. The at least one complexing agent preferably comprises gluconate, which has been added to the cleaning composition preferably in the form of sodium and / or potassium gluconate. The at least one complexing agent herein is preferably present at a concentration of at least 1.0% by weight, more preferably at least 2.0% by weight, and with particular preference, in the range of 2.5 to 3.5% by weight - calculated as sodium gluconate and on the basis of the total cleaning concentrate. 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, a homopolymer of (meth)acrylic acid with a weight average molar mass in the range of 3000 to 19000 g / mol, b) at least 0.5% by weight, calculated as poly(acrylic acid-alt-maleic acid), of a copolymer of (meth)acrylic acid and at least one vinyl dicarboxylic acid having a weight average molar mass in the range of 50,000 to 100,000 g / mol, c) at least 10.0% by weight, calculated as boric acid, of sodium and / or potassium borate, d) at least 8% by weight, calculated as potassium hydroxide, of sodium and / or potassium hydroxide, q / πζ lo / lzoz / e / yi e) at least 5% by weight, expressed as potassium carbonate, sodium carbonate and / or sodium carbonate, f) at least 1.5% by weight, calculated as sodium gluconate, of a complexing agent, and g) at least 50% by weight of water, wherein the (meth)acrylic acid homopolymer and the (meth)acrylic acid copolymer and at least one vinyl dicarboxylic acid are present in a weight ratio of 2.0:1 to 1.5:1 and the aforementioned weight % is added to 100% by weight in each case. The present invention also relates to a water-based alkaline cleaner for metal surfaces comprising a) at least one (meth)acrylic acid homopolymer with a weight average molar mass in the range of 3000 to 19000 g / mol and b) at least one (meth)acrylic acid copolymer with 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 comprises at least one (meth)acrylic acid copolymer 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, and wherein, if the cleaner is a new cleaner, component a) is present in a concentration of at most 0.65 g / l, preferably in the range of 0.10 to 0.50 g / l - calculated as polyacrylic acid - and component b) is present in a concentration of at most 0.35 g / l, preferably in the range of 0.05 to 0.30 g / l, calculated as poly(acrylic acid-alt-maleic acid). If the specified maximum concentrations of components a) and b) are exceeded, the cleaning performance is really satisfactory, but the pickling attack is too severe. Currently, a fresh cleaner is defined as a cleaner that has not yet come into contact with a metal surface. This is because contact with a metal surface causes the leaching of ions from that surface and the separation of oils and greases, with these ions, oils, and greases accumulating in the cleaning bath. The bath is then said to have aged. As a result, the pickling attack of the cleaner decreases, making it possible to use component a) at a concentration of up to 1.0 g / L and component b) at a concentration of up to 0.55 g / L, although this does not result in excessively high pickling erosion. The cleaner of the invention can be obtained from the cleaner concentrate of the invention by 1) Dilution, preferably in water and preferably by a dilution factor in the range of 1:20 to 1:100 (corresponding to 10 to 50 g of concentrate per 1.0 L of cleaner), 2) by adding at least one surfactant, preferably in the concentration range of 0.3 to 10 g / l -based on the cleaner- and also 3) optionally by adjusting the pH with at least one acid or base. q / πζ lo / lzoz / e / yi Preferably, the dilution factor in step 1) is in the range of 1:40 to 1:60, and preferably from 1:45 to 1:55. Conversely, the concentration of at least one surfactant in step 2) is, preferably from 0.4 to 5 g / l, and preferably from 0.5 to 3.5 g / l - based on the cleaner. In the cleaning process, at least one surfactant is used to remove any organic impurities, such as mineral oils and greases, and therefore must be added to the diluted concentrate. The "at least one surfactant" more specifically comprises at least one non-ionic, anionic, and / or cationic surfactant. Suitable non-ionic surfactants include, in particular, the following: - alkylphenol alkoxylates, especially alkylphenol ethoxylates, with C6 to C14 alkyl chains and a degree of alkoxylation of 5 to 30 moles per mole of phenol, - alkyl polyglucosides having an alkyl chain length of 08 to 022, preferably from C10 to C18, and containing from 1 to 20, preferably from 1 to 5 glucoside units, - fatty acid amide alkoxylates, fatty acid alkanolamide alkoxylates, N-alkylglucamides or also block copolymers made up of ethylene oxide, propylene oxide and / or butylene oxide, and - C8 to C22 alkoxylated alcohols such as fatty alcohol alkoxylates, oxoprocess alcohol alkoxylates, and Guerbet alcohol alkoxylates, wherein the alkoxylation may take place with ethylene oxide, propylene oxide, butylene oxide, and / or a mixture thereof, as a block copolymer or random copolymer. The alcohols preferably have 8 to 18 carbon atoms; the degree of alkoxylation typically ranges from 2 to 50 moles, preferably from 3 to 20 moles, of at least one of the indicated alkylene oxides per mole of alcohol. The alkylene oxide head group may additionally contain the following terminal protecting groups as a modification: benzyl, methyl, and / or tert-butyl protection. Depending on the application, the following anionic surfactants are used in particular: - fatty alcohol sulfates with alkyl chain lengths of 8 to 22, preferably 10 to 18 carbon atoms, for example, lauryl sulfate, cetyl sulfate, myristyl sulfate, palmitillyl sulfate or stearyl sulfate, - alkyl ether sulfates with alkyl chain lengths of 8 to 22, preferably 10 to 18 carbon atoms, and - linear C8 to C20 alkyl benzenesulfonates or also alkanesulfonates and soaps, such as sodium or potassium salts of C8 to C24 carboxylic acids. The cationic surfactants used, depending on the application, are in particular: - quaternary compounds of mono- and di-(C7-C25 alkyl)dimethylammonium, - quaternary ester esters, especially mono-, di- and tri-quaternary esterified mono-, di- and tri-kanolamines esterified with C8-C22 carboxylic acids, yq / πζ lo / lzoz / e / yi - C7 to C25 alkylamines, N,N-dimethyl-N-(hydroxy-alkyl C7-C25)ammonium salts and / or imidazoline quats. The at least one surfactant preferably comprises, and more preferably is, at least one nonionic surfactant. In most applications, anionic surfactants have a tendency to foam too much, while cationic surfactants often adhere to the metal surface and, consequently, can lead to problems in the deposition of conversion layers. Nonionic surfactants do not have these disadvantages. By diluting the cleaning concentrate of the invention, even without pH adjustment, a pH suitable for use in a multi-metal pretreatment facility (ready-to-use pH) is already achieved, so the further addition of at least one acid or base is only necessary for special applications. The cleaner of the invention preferably contains no phosphates, meaning that no phosphates have been added to it. However, it is possible, although undesirable, that the raw materials used may contain minor phosphate impurities, and therefore the cleaner concentrate and the cleaner produced from it may also contain a small amount of phosphate. A small amount of phosphate in the cleaner may also be caused by dissolved substances from the metal surfaces being cleaned, particularly if those surfaces have been previously phosphated. More preferably, however, the cleaner comprises less than 200 ppm, more preferably less than 20 ppm, and more preferably less than 2 ppm of phosphate. The cleaner is preferably free of silicate compounds, meaning that no silicate compounds have been added during production. However, it is possible that the raw materials used may contain small impurities of silicate, and therefore the cleaner may also contain a small amount of silicate compounds. More preferably, however, the cleaner contains less than 100 ppm, more preferably less than 10 ppm, particularly less than 1 ppm, and especially less than 0.1 ppm of silicate compounds. The cleaner of the 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 particularly consisting of boric acid, sodium borate and potassium borate. The at least one water-soluble boron compound (c) is preferably present at a concentration of 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 especially preferably at least 0.28% by weight, 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 especially preferably at most 0.32% by weight, calculated as boric acid and based on the total cleaner concentrate. By complying with the lower limits set out above for the concentration of at least one water-soluble boron compound (c), further improvements in the multi-metal capability of the cleaner can be achieved, while the QJ nz Ln / ίZΖΠZ / Β / YΥΙ upper limits are dictated by the pH-dependent solubility of water-soluble boron compounds in the concentrate in question - more particularly for a 1:50 dilution of the concentrate cleaner. Other embodiments and advantageous features of the cleaner of the invention have already been described in relation to the cleaner concentrate of the invention. The present invention also relates to a process for the anti-corrosive treatment of a metallic surface, wherein the surface is successively brought into contact with the following compositions: i) at least one water-based alkaline cleaner for metal 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 50,000 to 100.000 g / mol, and h) at least one surfactant, wherein the at least one (meth)acrylic acid copolymer comprises at least one (meth)acrylic acid copolymer 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, and wherein, if the cleaner is a new cleaner, component a) is present at a concentration of at most 0.65 g / l, preferably in the range of 0.10 to 0.50 g / l -calculated as polyacrylic acid- and component b) is present at a concentration of at most 0.35 g / l, preferably in the range of 0.05 to 0.30 g / l -calculated as poly(acrylic acid-alt-maleic acid), i) a first water-based rinsing composition, iii) optionally a second water-based rinsing composition, iv) an acid conversion composition based on water,. (v) optionally a third water-based rinsing composition, and (vi) a water-based composition comprising a cathodic or anodic electrolytic coating material based on (meth)acrylate and / or epoxy and / or a wet or powder coating material based on water or solvent. Contact of the metal surface in succession with compositions i) to vi) does not preclude its contact, before, after or in between, with at least one additional composition, preferably water-based, such as an activating composition or a passivating composition as described below in the context of phosphating - or with an additional rinsing composition, or is subsequently subjected to at least one drying - in a drying oven, for example - or is provided with additional coating films such as surface layer, top layer and clear coat (automotive paint system). A feature of the process of the invention is that, although it works without the use of a phosphate-containing cleaning composition, it nevertheless produces corrosion control and paint adhesion results that are comparable to those obtained when using a phosphate-containing cleaning composition. q / πζ lo / lzoz / e / yi The contact of the metal surface with at least one cleaner of the invention in step i), combining a balanced pickling attack with effective cleaning performance, optimally prepares the metal surface for any type of conversion treatment. Therefore, the acidic conversion composition in step iv) can be a conversion coating not only for trication phosphating but also for nickel-free zinc phosphating, for applying an organosilane-based thin-film coating, or as a passivating composition. The at least one cleaner in step i) preferably further comprises at least one water-soluble boron compound c), preferably selected from the group consisting of boric acid and alkali metal borates, more particularly boric acid, sodium borate, and potassium borate. As previously noted, this allows for precise control over the aggressiveness of each metal surface to be cleaned and subsequently coated, even for sensitive materials. Therefore, the metal surface preferably comprises at least one sensitive material selected from the group of aluminum, galvanized steels, and pre-phosphated steels. The addition of at least one water-soluble boron compound (c) results, as already noted, in enhanced multi-metal capability. Therefore, the metallic surface preferably comprises at least two metallic materials selected from the group consisting of steel, aluminum, galvanized steels, and pre-phosphated steels, more particularly selected from the group consisting of aluminum, galvanized steels, and pre-phosphated steels. More preferably, the metallic surface comprises not only aluminum but also at least one galvanized and / or pre-phosphated steel, with particular preference given to both aluminum and at least one galvanized steel and also at least one pre-phosphated steel. According to a first preferred embodiment, the acid conversion composition of step iv) is a composition for nickel-free zinc phosphating which, in addition to zinc ions and manganese ions, also comprises phosphate ions and to which nickel ions have not been added. In the case of nickel-free zinc phosphating and in the case of trication phosphating, where zinc, manganese, and nickel ions, as well as phosphate ions, are used, the metal surface is generally contacted before step iv) additionally with an aqueous activating composition that preferably comprises particles composed of zinc phosphate and / or titanium phosphate crystals. This facilitates the deposition of a phosphate crystal layer in step iv). After phosphating in step iv), the metal surface can be further contacted with an aqueous passivating composition. This can be particularly advantageous for surfaces that, in addition to zinc and / or iron-containing regions, also contain aluminum-containing regions. In this way, further improvements in corrosion control and paint adhesion to the painted surface can be achieved. Such a passivating composition preferably comprises at least one titanium, zirconium, and / or hafnium compound, more particularly at least one Q / nzLn / Lznz / E / Yi fluorocomplex of the indicated elements, and also, preferably, at least one organosilane including its hydrolysis and condensation products-. According to a second preferred embodiment, the acid conversion composition of step iv) is a composition for applying an organosilane-based thin film system, said composition comprising not only at least one organosilane - including the hydrolysis products and their condensation - but also, optionally, at least titanium, zirconium and / or hafnium compounds. In contrast to the situation with phosphating, the cleaning composition of the invention, in combination with an organosilane-based thin-film system, actually leads to better corrosion control results than a standard phosphate-containing cleaner, particularly when the cleaning composition is phosphate-free. Therefore, the at least one cleaner of the invention in step i), and consequently also the cleaner concentrate of the invention, are preferably phosphate-free, especially in the case of subsequent application of an organosilane-based thin-film system. According to a third preferred embodiment, the acid conversion composition in step iv) comprises a passivating composition which, in addition to at least one titanium, zirconium and / or hafnium compound, more particularly at least one fluorocomplex of the indicated elements, optionally further comprises at least one organosilane (including hydrolysis and condensation products). The embodiments and advantageous features of the cleaner of the invention used in step i) have already been described in relation to the cleaner concentrate of the invention and the cleaner of the invention. The present invention also relates to an anti-corrosive treated metal surface that can be obtained by the process of the invention, and also to its use in the metallurgical industries in which conversion processes are used for pretreatment, particularly in the automotive sector, automotive component supply or general industry. The present invention is illustrated below by working examples, which should not be understood as imposing any limitations, and also by comparative examples. Q / nZLn / LZnZ / E / Yli EXAMPLES i) Determination of erosion by pickling: Measurement principle: Pickling erosion indicates the weight loss of bare metal during a cleaning process. It is tested by immersing a standardized AA6014 aluminum sheet measuring 105 x 190 mm (Gardobond® test sheet, Chemetall GmbH, Germany) in the test solution—in this case, the corresponding cleaning solution. The mass loss is then determined gravimetrically using an analytical balance. The test was limited to aluminum surfaces, as these are the most susceptible to pickling attack. Preparation of test sheets: The test plates were first degreased with petroleum alcohol to remove any organic impurities. This allows for the evaluation and comparison of the direct attack of the test solution on the base substrate itself. Measurement of erosion by pickling: The mass of the respective test sheet, which had undergone preliminary degreasing, was determined using an analytical balance. Immediately afterward, the test sheet was immersed for 10 minutes at 55 °C in a 3 L beaker containing the corresponding test solution. Stirring was carried out using a 40 mm magnetic stirrer at the bottom of the beaker at a speed of 500 rpm. After 10 minutes, the test sheet was removed from the test solution, rinsed with completely demineralized (FD) water, and dried using compressed air. The weight loss was then determined using an analytical balance. In each case, a reference was tested in parallel to allow comparison of the values ​​obtained. ii) Determination of the minimum cleaning time: Measurement principle: The minimum cleaning time (MCT) indicates the minimum duration of the cleaning step required to remove organic impurities from a standard 1.0312 steel sheet measuring 105 x 190 mm (test sheet) under constant conditions. The cleaning quality must reach a certain minimum value, which is determined based on the moisture content of the metal surface. In this case, only steel surfaces were analyzed, as they are typically the most difficult surfaces to degrease. Preparation of test sheets: The test sheets used had a constant oil load (1.7 + / - 0.2 g / m2). The purpose of this was to ensure the compatibility of the results. Measuring the minimum cleaning time: qj nz Ln / Lznz / E / YiAi To determine the minimum cleaning time, the respective test sheet was immersed for 1 minute at 55 °C in a 3 L beaker containing the corresponding cleaning solution. Stirring was carried out with a 40 mm magnetic stirrer at the bottom of the beaker at a speed of 500 rpm. Subsequently, the test sheet was rinsed with reciprocating motions (approximately 15 back-and-forth movements) in the immersion rinse, ensuring the sheet was always completely removed from the rinse water, and held vertically for evaluation after 10 seconds (to rule out false wetting). The minimum cleaning time is reached when the surface wetting by water reaches at least 95%, i.e., when a consistent water film is present. If this condition is not met, the test sheet is immersed in the cleaning solution for an additional minute, as previously described, and then rinsed in the immersion rinse. This is repeated until the condition is met. The number of repetitions is totaled, and as a control, an identical oil test sheet is left in the cleaning solution for the entire time. This is necessary because the intermediate rinsing steps improve cleaning performance. If the sheet is at least 95% wetted after the added time, this time is recorded as the MCT (Maximum Time Consumption). If this is not the case, the cleaning and rinsing are repeated in 1-minute increments until the surface is at least 95% wettable with water without intermediate rinsing steps. This time then becomes the MCT. α / ηζίη / ίζηζ / E / γι iii) Investigation of different cleaner solutions: To test the effect of different polymers in terms of pickling erosion and MCT, a standard cleaning concentrate (VB1) with a pH of 12.9 was first prepared as a reference, where this concentrate contains FV water and also the following components: Component % by weight Potassium hydroxide 12.5 Boric acid 14.5 Potassium carbonate 10 Sodium gluconate 3 Adding the following polymers to this standard resulted in different cleaning concentrates (VB2 to VB6 and also B1): Polymer Chemical designation Average molar mass [g / mol] Polymer 1 Polyacrylic acid 4,000 Polymer 2 Polyacrylic acid 8,000 Polymer 3 Polyacrylic acid 20,000 Polymer 4 Poly(acrylic acid-a / f-maleic acid) 70,000 α / πζίη / ίζηζ / Ε / γι In addition, a standard cleaning concentrate containing phosphate (VB7) with a pH greater than 11.5 was prepared as a reference, containing FV water and also the following components: Component % by weight Potassium hydroxide 31.5 Boric acid 17.0 Phosphoric acid 4.0 All cleaner concentrates were subsequently diluted by a factor of 1:50 (corresponding to 20 g of concentrate per 1.0 L of cleaner) with FV water and mixed with 2 g / L of an ethylene / propylene oxide fatty alcohol, i.e., a non-ionic surfactant. In addition, the pH of all cleaning concentrates was adjusted to 10.5 by adding boric acid or an aqueous solution of potassium hydroxide. The cleaning solutions obtained were then analyzed to determine pickling erosion and MCT as described above - comp. i) and ii). The results obtained accordingly are compiled in Table 1 (mean values ​​for at least three sheets in each case, i.e., n > 3). Table 1: Example (comparative) Polymer Polymer concentration in concentrate [% by weight] Pickling erosion [g / m2] MCT [min] VB1 none 0 0.14 10 VB2 Polymer 1 7.0 0.68 5 VB3 Polymer 2 7.0 0.83 4 VB4 Polymer 3 7.0 1.45 3 VB5 Polymer 4 7.0 1.15 3 B1 Polymer 2 + polymer 4 (1.8: 1.0*) 2.8 0.78 2 VB6 Polymer 2 + polymer 4 5.5 1.14 3 3.5: 2.0 *) VB7 none 0 0.35 3 *) Weight ratio of the two polymers qj nz Ln / Lznz / E / γΐΛΐ Experimental results show that adding a polymer—polyacrylic acid or poly(acrylic acid-alt-maleic acid)—significantly improves cleaning performance (see MCT; VB2 to VB6 and also B1 vs. VB1). Simultaneously, the aggressiveness of the medium on aluminum increases (see pickling erosion). Clearly, in the case of polyacrylic acid, the effect of adding the polymer is greater in terms of pickling attack and MCT as a function of chain length, and therefore, the molar mass increases (VB2 to VB4). It was also found that no single polymer could achieve the performance of a standard phosphate-containing cleaner in terms of pickling erosion and MCT. Only the cleaning solution of the invention (B1), comprising a specific mixture of two polymers, is capable of achieving or even exceeding the cleaning performance of a phosphate-containing cleaner (VB7) – MCT below 4 minutes – with a generally low service concentration and balanced pickling attack: pickling erosion down to 0.8 g / m². However, if the concentration of the two polymers is doubled, the cleaning performance remains satisfactory, but the pickling attack is too severe (VB6). iv) Determination of multimetal capacity: The multi-metal capacity of the different solutions was also determined using the two previously described measurement principles of pickling erosion (see Table 2: n > 3) and MCT (see Table 3: n > 3), but using in each case a specific VDA 230-213 test apparatus. The tests in question were carried out on the following four substrates found in the automotive industry: cold-rolled steel (CRS), hot-dip galvanized steel (HDG), pre-phosphated electrogalvanized steel (ZEP), and automotive-grade aluminum (AA6014). Table 2: Example (comparative) Polymer Polymer concentration [% by weight] Pickling erosion [g / m2] CRS HDG ZEP AA6014 VB8 Polymer 2 3.5 0.0 0.02 0.09 1.61 B1 Polymer 2 + polymer 4 1.8:1.0*) 2.8 0.0 0.02 0.18 0.78 VB7 none 0 0.0 0.01 0.03 0.35 *) Weight ratio of the two polymers Table 3: Example (comparative) Polymer Polymer concentration [% by weight] MCT [min] CRS HDG ZEP AA6014 VB8 Polymer 2 3.5 6 3 3 7 B1 Polymer 2 + polymer 4 1.8:1.0*) 2.8 5 2 2 5 VB7 none 0 7 10 5 10 *) Weight ratio of the two polymers QJ nz Ln / ίZΖΠZ / Β / ΥΙ As can be seen from Table 2, the pickling attack in the case of the cleaning solution of the invention (B1) is indeed somewhat greater compared to a phosphate-containing cleaner (VB7). However, unlike a single-polymer-based cleaning solution with a lower polymer concentration (VB8), the values ​​obtained on aluminum (AA6014) are also acceptable for ongoing operation, thus demonstrating the multi-metal capability of the cleaning solution of the invention. Table 3 shows that, for the cleaning solution of the invention (B1), the minimum cleaning time (MCT), i.e., the cleaning performance, is especially better compared to a cleaner containing phosphate (VB7), but also to a cleaning solution based on only one polymer, with a lower polymer concentration (VB8), on each of the substrates used in a multi-metal operation. As a result of using the specific VDA 230-213 test apparatus, the results obtained for pickling erosion and for MCT are higher compared to the results obtained manually, in Table 1, this being attributable to the lower circulation / bath movement within the apparatus. In the cleaning solution B1 of the invention, the borate concentration was further varied to determine the optimum concentration for pickling in a multi-metal operation. The cleaning solutions thus prepared (B1-1 to B1-3) were then tested as previously described (comp. i) for their pickling erosion on the following three substrates found in the automotive industry: automotive-grade aluminum (AA6014), hot-dip galvanized steel (HDG), and electro-galvanized steel (MBZE). The metal sheets used for this purpose were each subjected to preliminary degreasing with an aqueous surfactant solution. The results obtained accordingly are compiled in Table 4 (mean values ​​of, in each case, at least 3 leaves, i.e., n > 3). Table 4: Example Polymer Concentration Erosion by Erosion by Erosion by (comparative) of boric acid in the concentrate [% by weight] pickled [g / m2] AA6014 pickled [g / m2] HDG pickled [g / m2] MBZE B1 Polymer 2 + polymer 4 (1.8: 1.0 *) 14.5 0.32 0.03 0.04 B1-1 Polymer 2 + polymer 4 (1.8: 1.0 *) 5.0 2.9 0.05 0.08 B1-2 Polymer 2 + polymer 4 (1.8: 1.0 *) 10.0 2.7 0.04 0.07 B1-3 Polymer 2 + polymer 4 (1.8: 1.0 *) 16.5 0.06 0.03 0.02 *) Weight ratio of the two polymers q / πζ lo / lzoz / e / yi As can be seen from the experimental results for cleaning solution B1 of the invention and its variants B1-1 to B1-3, the pickling attack on aluminum (AA6014) is within the desired low range at concentrations of 14.5 and 16.5 wt% boric acid in the concentrate, i.e., concentrations of 0.29 and 0.33 wt%, respectively, for a 1:50 dilution in the cleaning solution. Therefore, it is possible for all tested substrates, including aluminum, to undergo optimal treatment when combined. v) Compatibility with conversion treatments: The compatibility of the cleaning solution of the invention (B1) with known conversion treatments was examined on the basis of an organosilane-based thin film coating and also a portrication phosphating. To investigate the effect of the cleaning solution of the invention (B1), the corresponding polymers were added in quantities greater than those normally used in operation—the type that may enter a conversion bath as a result of the cleaning medium being carried over by the components—to the two conversion baths (B2 and B3). Subsequently, the following substrates found in the automotive industry—cold-rolled steel (CRS), hot-dip galvanized steel (HDG), and aluminum (AA6014)—were pretreated in a standard treatment procedure—composed of organosilane and zirconium or zinc manganese nickel phosphate (phosphating time: 180 s)—after prior activation with zinc phosphate (activation time: 60 s). The effect of the polymers was evaluated by determining the layer weight (CW) using X-ray fluorescence (XRF) analysis and also by scanning electron microscopy (SEM) imaging of the surface structure of the resulting conversion layer. The determined layer weights—calculated as zirconium metal (Zr)—for the organosilane-based thin-film coating are compared in Table 5 (> 3). q / πζ lo / lzoz / e / yi Table 5: Example (comparative) Polymer Polymer concentration [g / i] CWdeZr [mg / m2] CRS HDG AA6014 VB9 none 0 45 56 48 B2 Polymer 2 + polymer 4 1.8: 1.0 *) 0.48 48 52 51 B3 Polymer 2 + polymer 4 1.8:1.0*) 0.96 52 50 54 *) Weight ratio of the two polymers The deviations obtained within the different variants (VB9, B2, and B3) fall within the possible error tolerance of the CW determination. The SEM images of the surface structure of the conversion layer showed no peculiarities in any case. Therefore, the polymers used in the invention do not have adverse effects on the optimal development of coatings of an organosilane-based thin-film system and are thus compatible with such a system. The determined layer weights, calculated in each case as Zns(PO4)2 4 H2O, are compared for zinc phosphate activation and for subsequent trication phosphating in Table 6 and, respectively, Table 7 (in each case n > 3). Table 6: Example (comparative) Polymer Polymer concentration [g / i] Zinc phosphate layer CW [g / m2] CRS HDG AA6014 VB10 none 0 2.9 2.8 3.2 B4 Polymer 2 0.01 2.9 2.7 3.0 B5 Polymer 4 0.006 2.8 2.7 2.8 Table 7: Example (comparative) Polymer Concentration of the CW polymer of the zinc phosphate layer [g / m2] [g / U CRS HDG AA6014 VB10 none 0 2.0 2.1 4.0 B4 Polymer 2 0.01 2.7 2.8 4.2 B5 Polymer 4 0.006 2.3 2.2 4.6 α / ηζίη / ίζηζ / Ε / γι The layer weights obtained show that the two polymers have no effect on zinc phosphate activation (see Table 6) and only minor influences on friction phosphating (see Table 7) (B4 and B5 vs. VB10), and these effects can be compensated for in the ongoing operation by adjusting the phosphating parameters. SEM images of the surface structure of the friction conversion layer show no unusual features. Therefore, it has been possible to demonstrate the compatibility of the cleaning solution of the invention not only with organosilane-based thin-film coatings, but also with portrication phosphating systems. vi) Corrosion behavior in organosilane-based thin-film coatings: To investigate the effect of the cleaning solution of invention B1 on corrosion behavior, the sheet-shaped HDG material was treated within a standardized process. Process: 1.) Spray cleaning, 60 seconds .) Immersion cleaning, 180 seconds .) Immersion rinse, 30 seconds .) Immersion conversion, 180 seconds .) Immersion rinse, 30 seconds .) Compressed air drying Cleaning steps 1) and 2) were carried out using the phosphate-free cleaning solution B1 of the invention at a 1:50 dilution of the concentrate and 2 g / L of an ethylene fatty alcohol / propylene oxide. For comparison, two standard phosphate-containing cleaners (VB11 and VB12) were also tested. For the conversion in stage 4), an organosilane-based thin-film system (Chemetall, Germany) was used. After stage 6), the treated sheets were tested for paint adhesion and corrosion using a cyclic corrosion test (VDA 621-415) common in the automotive sector. The results for corrosive undercutting and also for paint adhesion after stone detachment are compared in Table 8 (in each case n > 3). It is evident that the phosphate-free cleaning solution B1 of the invention in combination with an organosilane-based conversion system significantly improves both the corrosion behavior and the surface paint adhesion properties compared to a standard cleaner containing phosphate (VB11 and VB12). Table 8: Example (comparative) Cleaner concentration [g / l] pH Corrosive undercutting [mm] Stone chip characteristic value VB11 15 10.5 3.0 3.0 VB12 15 10.0 2.5 2.5 B1 20 10.0 2.0 2.0 B1 20 9.5 1.0 1.0 Q / nZLn / LZnZ / E / Yli

Claims

1. A water-based alkaline cleaning concentrate for producing a metal surface cleaner, comprising a) at least one (meth)acrylic acid homopolymer with a weight average molar mass in the range of 3000 to 19000 g / mol and b) at least one (meth)acrylic acid copolymer with a weight average molar mass in the range of 50000 to 100000 g / mol, wherein the at least one (meth)acrylic acid copolymer comprises at least one linear (meth)acrylic acid copolymer 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.

2. The concentrated cleaner according to claim 1, wherein 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 in the range of 5000 to 15000 g / mol, preferably 6000 to 12000 g / mol - calculated as polyacrylic acid.

3. The concentrated cleaner according to claim 1 or 2, wherein the at least one (meth)acrylic acid copolymer of component b) comprises at least one preferably alternating (meth)acrylic acid copolymer and at least one, preferably exactly one, comonomer containing a vinyl group and at least two, preferably exactly two, carboxylic acid groups.

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

5. The cleaning concentrate according to any of the preceding claims, wherein 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, while 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. The concentrated cleaner according to any of the preceding claims, 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 weight ratio in the range of 1.0:1 to 2.5:1, more preferably from 1.3:1 to 2.0:1, with particular preference, from 1.5:1 to 1.9:1, and with special preference, from 1.7:1 to 1.8:1 - calculated as polyacrylic acid: poly(acrylic acid-altmaleic acid).

7. The cleaning concentrate according to any of the preceding claims, phosphate-free.

8. Concentrated cleaner according to any of the preceding claims, further comprising at least one water-soluble boron compound c), preferably selected from the group consisting of boric acid and alkali metal borates.

9. The cleaning concentrate according to claim 8, wherein the at least one water-soluble boron compound c) is present in a concentration 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. A water-based alkaline cleaner for metal surfaces, comprising: a) at least one (meth)acrylic acid homopolymer with a weight average molar mass in the range of 3000 to 19000 g / mol, b) at least one (meth)acrylic acid copolymer with a weight average molar mass in the range of 50000 to 100000 g / mol, and h) at least one surfactant, preferably non-ionic, wherein the at least one (meth)acrylic acid copolymer comprises at least one (meth)acrylic acid copolymer 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, and wherein, if the cleaner is a new cleaner, component a) is present at a concentration of at most 0.65 g / L, preferably in the range of 0.10 to 0.50 g / L (calculated as acid). polyacrylic- and component b) is present at a concentration of no more than 0.35 g / l, preferably in the range of 0,05 at 0.30 g / l, calculated as poly(acrylic acid-alt-maleic acid)., 11. A process for the anti-corrosion treatment of a metallic surface, comprising contacting the surface in succession with the following compositions: i) at least one water-based alkaline cleaner according to claim 10, ii) a first water-based rinsing composition, iii) optionally a second water-based rinsing composition, iv) a water-based acid conversion composition, v) optionally a third water-based rinsing composition, and vi) a water-based composition comprising a cathodic or anodic electrolytic coating material based on (meth)acrylate and / or epoxy and / or a water-based or solvent-based wet or powder coating material.

12. The process according to claim 11, wherein the acid conversion composition in step iv) comprises a nickel-free zinc phosphating composition which, in addition to zinc and manganese ions, further comprises phosphate ions, and to which nickel ions have not been added. Q / nzLn / Lznz / E / Yi 13. The process according to claim 11, wherein the acid conversion composition in step iv) comprises a composition for applying an organosilane-based thin film system which, in addition to at least one organosilane - including its hydrolysis and condensation products - optionally also comprises at least one titanium compound, a zirconium compound and / or a hafnium compound.

14. A corrosion-resistant treated metallic surface obtainable by a process according to any of claims 11 to 13.

15. The use of the metallic surface according to claim 14 in the metallurgical industries sector.