MXPA97003762A - Anticorrosive and reductive treatment of the labeling of metali surfaces - Google Patents

Abstract

The present invention relates to an aqueous solution for the treatment of aluminum or tin surfaces and in each case of these alloys, which has a pH in the range of 2.3 and 3.3. and contains at least the following components: a) from 0.14 to 2.25 m mol / l of a selected component of active ammonium salts of the amine surface of amine oxide of the general formula (I): in which R1 is a saturated alkyl radical or a mono- or polyunsaturated alkyl radical having from 8 to 22 atoms of C, R2 and R3 independently of each other is an alkyl or hydroxyalkyl radical having from 1 to 8 C atoms or an aryl or alkylaryl radical having from 6 to 10 C atoms. , R4 is a radical of the type R2, R3 or a radical -O-, and X- is a monovalent anion or a monovalent equivalent of a polyovalent anion is already O if R4 is a radical -O- and otherwise a is 1 , b) from 0.25 to 1.5 mol / l of one or more mono-, di- or tribasic hydroxycarboxylic acids having from 4 to 7 C atoms in the molecule, the sum of the hydroxyl and carboxyl groups is at least 3, or in each case the final anions, c) 0.4 to 2 mmol / l of one or more complex fluorides and d) of 29 to 500 mg / l of mineral acids selected from phosphoric acid, nitric acid and sulfuric acid, or in each case the anions de

Description

ANTICORROSIVE TREATMENT AND REDUCER OF THE FRICTION OF METALLIC SURFACES The present invention relates to the field of surface treatment of metal components formed of aluminum or aluminum alloys and tin-plated metals (tin foil). It refers in particular to cans for beverages and foods formed with these materials. The invention aims to provide the surfaces of the can, during the production process of the can, with a protective layer against corrosion which can be enameled to facilitate the runoff of the water and in particular gives rise to a reduction in the coefficient of friction between the cans that are in contact with each other, thus facilitating the transport of the cans on the conveyor belts, while reducing the porosity of a last layer of varnish. Tin cans (tin foil) and aluminum (or aluminum alloy) cans, which for simplicity are included under the name "aluminum" in the following, are widely used for storing food and especially beverages. During the production process, after their formation, the cans are usually washed; for this, acid or alkaline cleaning agents, for example, are usually obtained commercially.

These solutions of cleaning agents must have a dissolving force suitable for the metals in question to effectively remove the abraded metal from the cans. The surface of the can can be mistreated by the attack on the metal, this increases the friction between the cans in contact. The speed of transport of the cans on the conveyor belts is therefore reduced, and especially at the points where a stagnation of the cans develops due to the separation thereof, the transport of the cans can be blocked completely . Since through this the capacity of the production line is reduced, efforts have been made to condition the surfaces of the can in such a way that the friction between the cans in contact is as low as possible. In addition, the application of a friction reducing layer must not mean that it undergoes the adhesion of enamel coatings, labeling or other applied coatings to prevent corrosion and / or for decorative reasons. In addition, the coating must ensure that the requirements for corrosion resistance are met, which vary according to the contents of the cans. Only those active compounds that are generally acceptable ecologically, and particularly acceptable for food, should be used in this case. For example, for environmental reasons efforts are made to avoid reagents containing chromium. The different chromium-free processes for the treatment of the aluminum surface, which as a rule employ organic acids, in particular phosphoric acid, hydrofluoric acid or other sources of fluoride and / or complex fluorides and which work with or without the use Additional organic polymers are known in the prior art. For example, US Pat. No. 4,992,116 describes a solution for the treatment with aqueous acid containing phosphate, acid fluoride of Zr, Ti, Hf or Si and a polyphenolic compound which is a Mannich addition product of a substituted amine in a polyalkylenephenol. or a tannin. Patent EP-B-8942 describes treatment solutions, preferably for aluminum cans, comprising: (a) 0.5 to 10 g / 1 of polyacrylic acid or of an ester thereof and, (b) 0.2 to 8 g / 1 of at least one of the hexafluorozirconic acid, hexafluorotitanic acid or hexafluorosilicic acid compounds. US Pat. No. 4,470,853 describes conversion solutions for aluminum which contain, inter alia, 10 to 150 ppm zirconium, 20 to 250 ppm fluorine, 15 to 100 ppm phosphate and 30 to 125 ppm tannin. Its pH is in the range from 2.3 to 2.95. The use of tannin in the treatment of the aluminum surface is also described in DE-A-24 46 492, according to which the aluminum is treated with an acid solution containing phosphate, which contains a metallic salt of tannin in amounts of 0.1 and 10 g / 1. Various solutions have already been proposed to reduce friction between aluminum cans during the transport of cans. For example, the patent O91 / 01414 describes an aqueous solution containing ions of Fe, Zr, Sn, Al or Ce mordant-metal acids, such as, for example, hydrofluoric acid, esters of alkoxylated phosphoric acid and a combination of alkoxylated alcohols and alkoxylated alkylphenols. The patent O94 / 01517 describes a process for the friction-reducing conversion treatment, in which triglycerides of alkoxylated or non-alkoxylated castor oil, derivatives of hydrogenated castor oil, salts of fatty acids of alkoxylated amines or not are used. alkoxylates, alkoxylated or non-alkoxylated amino-fatty acids, N-oxides of alkoxylated or non-alkoxylated fatty amines, alkoxylated or non-alkoxylated quaternary ammonium salts or water-soluble organic polymers, in addition to inorganic metal compounds. These amine oxides or quaternary ammonium salts in which at least one radical contains up to 20 carbon atoms are those that are used. Amine compounds of this type are also used in the context of the present invention. EP-A-612 833 proposes a surface treatment with an ester between a polyglycerol and fatty acids to reduce friction. The effective surface treatment for tin or aluminum cans on the one hand must meet the different requirements with respect to corrosion protection, as well as the absence of pores, and the adhesion of a subsequent enamel coating, each of which is tested with different criteria in accordance with the various requirements and, on the other hand must ensure a reduction in friction that is as effective as possible. The systems known to date are in each case compromises between the different requirements and are not completely satisfactory at all the specific points. The objective of the present invention is to provide a solution for the treatment of the surface of metal cans, which has an improved performance spectrum with respect to the different requirements. In particular, it has been found that in the processes for the conversion treatment and to reduce the friction according to WO94 / 01517, in which N-oxides of fatty amines or quaternary salts of alkylammonium fats are used as reducing active compounds of the friction, the porosity of a subsequent enamel coating does not reliably meet the requirements, especially of the beverage industry. The objective is achieved by an aqueous solution for the treatment of aluminum or tin surfaces and, in each case, the alloys thereof, which has a pH in the range from 2.3 to 3.3 and contains at least the following components: (a) from 0.14 to 2.25 mmol / 1 of a selected component of surface active ammonium quaternary salts or amine oxides of the general formula (I): R1 R2 -N + -R3 X X '"(I ), I R4 in which R1 is a saturated alkyl radical or a mono- or polyunsaturated alkyl radical having from 8 to 22 C atoms, R2 and RJ independently of each other is an alkyl or hydroxyalkyl radical having from 1 to 8 atoms of C or an aryl or alkylaryl radical having from 6 to 10 carbon atoms, RA is a radical of the type R or RJ, or a radical -0", and X" is a manovalent anion or a monovalent equivalent of an anion monovalent, is already 0 if R4 is a radical -O "and otherwise a is 1, (b) from 0.25 to 1.5 mmol / 1 of one or more hydro acids monocarboxylic mono-, di- or tribasic having 4 to 7 carbon atoms in the molecule, the sum of the hydroxyl and carboxyl groups is at least 3, or in each case the anions of these, (c) from 0.4 to 2 mmol / 1 of one or more complex fluorides, and (d) from 20 to 500 mg / 1 of mineral acids selected from phosphoric acid, nitric acid and sulfuric acid, or in each case the anions of these. The alkyl radicals R 1 can be radicals of a certain chain length and a certain number of double bonds. However, for economic reasons it is preferable to use amine oxides or ammonium salts which are derived from the fatty chemical raw materials. In these cases, radicals R1 have a 'distribution of chain lengths and double bonds which are characteristic for the fatty acids of plants or animal fats and oils. These compounds of the formula (I) are preferably used in which R1 is a mixture of alkyl groups, as in the mixtures of fatty acids which can be obtained by hydrolysis of the coconut oil, the coconut oil of the palm or animal bait Examples of suitable amine oxides of the general formula (I) are: bis (2-hydroxyethyl) coco alkylamine oxide (Aromox® C / 12), bis (2-hydroxyethyl) alkylamine oxide (Aromox® T / 12) ), dimethylcocoalkylamylamine oxide (Aromox® DMC), hydrogenated dimethyl-bait alkylamine oxide (Aromox® DMHT) Dimethyl hexadecylamine oxide (Aromox® DM-16), all of which are obtained from Akzo Chemicals Inc. The examples of suitable quaternary ammonium salts of the general formula (I) are: dodecyltrimethylammonium chloride (Arquad® 12-37W), octadecyltrimethylammonium chloride (Arquad® 18-50), dimethylbenzyl chloride (from CI.-IT) alkylammonium ( Arquad® B-100), tris (2-hydroxyethyl) -cebo-alkylammonium acetate (Ethoquad® T / 13) and methyl-bis (2-hydroxy-2-methylethyl) ammonium ethylsulfate (Propoquad® T / 12), all of which, in the same way, are obtained from Akzo Chemicals Inc. These alkylamine oxides or quaternary ammonium salts of the general formula (I) The radicals R2, R3, and in the case of the quaternary ammonium salts also R4 which are formed when the alkylamines are reacted with ethylene oxide, propylene oxide or butylene oxide are preferred. Examples of these are the 2-hydroxyethyl and the 2-hydro-2-methylethyl group. As is customary, in the alkoxylation reactions the radicals R 2, R 3 and R 4 in which in each case several alkoxy groups are linked to one another via ether bonds, can also be formed in this reaction. These polyether radicals having up to 8 C atoms in the same manner are within the scope of the invention. However, those compounds of the general formula (I) which carry the 2-hydroxyethyl groups as radicals R2, R * and if R4 is suitable are particularly preferred. In the solutions for the treatment, according to the invention, the components of group (a) are the active compounds which have a friction-reducing action. In contrast, the effect of the components of group (b), the mono-, di- or tribasic hydroxycarboxylic acids having from 4 to 7 C atoms in the molecule, the sum of the hydroxyl and carboxyl groups is at least 3, it is mainly found in the fact that an enamel applied afterwards has a reduced porosity and therefore an increased resistance to corrosion. The value of porosity, called "metallic exposure value", VEM, in the literature of the English language, can be determined by electrochemical measurement and is one of the quality requirements of the beverage industry for enameled cans for beverages. This measurement parameter can be determined, for example, with an "Enamel Rater MK" from Manfred Konke, Berlin (Germany) or with an "Enamel Rater" from Wilkens-Anderson Co., Chicago Illinois. The measurement is based on the filling of the beverage can, enameled in the interior, with an electrolytic solution (50.6 g of sodium chloride and 1.19 g of dioctyl-sodium sulfosuccinate in 5 L of completely deionized water) and the connection of the can as an electrode. A counter-electrode is immersed in the electrolytic solution and, after the voltage has been applied and after waiting for a time of 4 sec., the current flow in mA is read. If the coating of the can is perfect, it is expected that there is no current flow. An increase in the current flow in mA, which is the "metal exposure value" indicates an increased permeability of the coating with respect to the ions, which can be interpreted as porosity. For subsequent filling with carbonated beverages / for example, the requirement is that the average VEM must be less than 5 A in a 6.3 V voltage test. The central core of the present invention is that the components (b) in The treatment solution significantly reduces the VEM without adversely influencing the other properties, such as reduction in friction and protection against corrosion, which is attributed essentially to components a), c) and d) of the solution for the treatment. Examples of suitable hydrocarboxylic acids are malic acid, tartaric acid, citric acid and in particular those carboxylic acids which can be obtained by oxidation of the sugars of the pentose and hexose type. Examples of these acids are gluconic acid, saccharic acid, monosaccharide acid, musicic acid and glucuronic acid. Gluconic acid is particularly preferred. These acids can be used as such or in the form of their water-soluble salts, in particular the sodium salts. In the pH of the treatment solutions according to the invention in the range from 2.3 to 3.3, the hydroxycarboxylic acids are partially present as such and partially in the form of their anions, depending on their pKa value. The co-use of these carboxylic acids, in particular gluconic acid, in the surface treatment of aluminum, for example during alkaline pickling, is known in principle. However, the effect of the hydroxycarboxylic acids of group (b) complementing the action of other components of the treatment solution according to the invention is unexpected in such a way that the "metal exposure value" of an enamel coating is reduced. applied. The other main components of the treatment solution according to the invention, (c) and (d) are well known in the solutions for the conversion treatment of aluminum surfaces. Possible complex fluorides of group c) are, for example, hexafluorotitanate, hexafluorozirconate, hexafluoroxantate, hexafluorosilicate or tetrafluoroborate. The use of hexafluorozirconate is preferred. It is irrelevant whether complex fluorides are used as water-soluble salts, for example, as sodium or ammonium salts, or as free acids. It should simply be ensured that the complex fluoride compounds are combined with the mineral acids of group d) or acid or neutral salts thereof so that the treatment solution, according to the invention, has a pH in the active range of 2.3. to 3.3. At pH values outside this range, the formation of the protective layer against corrosion and reducing the friction for which it is directed is more unsatisfactory, since the pH is outside the established range. Since the phosphoric acid and the anions thereof have a protective activity against corrosion due to the formation of poorly soluble metal phosphates which adhere firmly to the metal surface, it is particularly preferable that the component d) contains phosphoric acid or anions of This one from 10 to 100% by weight. If the phosphoric acid is not used as the only one of group d), the co-use of nitric acid or anions thereof is advantageous. The action of the combination of the substance described above can be enhanced by the addition of other active compounds of the prior art: an addition of tannin in the concentration range from 50 to 500 mg / 1 increases the action of the hydroxycarboxylic acids of the group b) with respect to the reduction of the "metallic exposure value" of an enamel coating subsequently applied. Therefore, it is preferable for the solution of the treatment according to the invention to additionally contain tannin. Tannins (compare, for example, Ropp Chemical Lexikon (Rpmp Chemical Dictionary), 9th edition, 1992, the keyword "tannin") is a collective name of a series of polyphenols that occur naturally in a very diverse composition. can be derived from gallic acid, gallic acid derivatives are usually present in an esterified form with glucose. In the form of plant extracts of different origin, tannins are a known group of active compounds for tanning skins. In this relationship, the structures and origin of the tannins are described in more detail in Kirk-Othmer Encyclopedia of Chemical Technology, 2nd edition, volume XII (1967) pages 303-341. As can be seen in US-A-4,479,853 and in DE-A-24 46 492, the use of tannins has already been proposed for the treatment of aluminum surface. Experience has shown that the presence of free fluoride ions has a favorable effect on the production of the conversion layers on aluminum surfaces. The free fluoride ions which are present at least partially in the form of hydrofluoric acid not dissociated at the pH of the treatment solution, can be formed from the complex fluorides listed in the above with group c) by hydrolysis reactions in the treatment solution. The formation of the layer obtained with the treatment solutions according to the invention can be assisted, esally in the initial phase of the baths, if the treatment solutions additionally contain from 10 to 100 mg / 1 of fluoride, which can be added as hydrofluoric acid or as neutral fluorides or soluble acids. Examples of these are NaF, KF, KHFÜ or (NHYJHFÜ) The fluoride component is selected so that the pH does not leave the range of 2.3 to 3.3 necessary, since the treatment solution contains active surface components which tend to form foam, given the components of group a) it may be necessary to add an antifoam for the treatment baths in the case of vigorous stirring of the bath, as it may be, for example, for the spray units. It should be in the range from 50 to 500 mg / 1. Suitable defoamers are, for example, alkyl polyalkoxy esters. A suitable polyalkoxy ester of this type is available under the trade name Foamaster® C14 from Henkel KGaA, Dusseldorf (Germany). It should be understood that all of the ranges set forth above for active concentrations and pH means that the desired action occurs within these ranges of the parameters. If the concentrations are below the minimum concentrations established, the desired combined action of the protective layer for reduction in friction, protection against corrosion and reduction of the porosity of a subsequent enamel coating, as a rule, decreases. The excess in the maximum concentrations is at least uneconomical, but it can also give rise to the disadvantages in the formation of the layer. A coating that fully meets the requirements is obtained in a particularly safe manner if the component: a) is present in the treatment solution in concentrations of 0.5 to 1.5 mmol / 1 and / or component b) is present in the solution of treatment in concentrations of 0.3 to 1.15 mmol / 1. The preferred co-used tannin preferably used in concentrations of 100 to 400 mg / 1. A further improvement in the coating, in particular with res to its ability to be enameled, can be achieved by additionally adding soluble or water dispersible organic polymers to the treatment solution in concentrations of about 100 to 1000 mg / 1. These polymers can be chosen from: h) homo- or heteropolymers of ethylene oxide, propylene oxide and / or butylene oxide / i) homo- or heteropolymer of acrylic acid, maleic acid and / or derivatives thereof, k) homo- or heteropolymers of vinylphenol and / or vinylphenol derivatives / and 1) homo- or heteropolymers of vinyl alcohol and / or vinyl alcohol derivatives. Polymers of the mentioned type are obtained commercially. The polyvinylphenol derivatives of group k) are obtained by the Mannich reaction of the polyvinylphenol with aldehydes and alkylamines. A reaction product of poly (4-vinylphenol) with formaldehyde and 2-alkylamino-1-ethanol can be mentioned as an example. More details about this polymer and its use in the surface treatment of aluminum are contained in patent WO92 / 07973. In the above, the compositions of the easy-to-use treatment solutions according to the invention have been described. Of course, it is possible that these baths are prepared directly at the site of use by mixing the individual components together in the ranges of established concentrations. However, for the users of these treatment solutions it is more favorable to obtain the aqueous concentrates from a manufacturer's treatment solutions and adjust them at the site to the concentration ranges for the use of the solutions by dilution with water. Accordingly, the invention also relates to the aqueous concentrates of the treatment solutions which will produce treatment solutions according to the invention by dilution with water. In this case, it is technically and economically more attractive to formulate the concentrates so that easy-to-use treatment solutions can be obtained from them by diluting with water in a volume ratio of between 1:50 and 1: 200. For example, the concentrate may be formulated so that it must be diluted with water in the ratio of 1: 100 for the preparation of a ready-to-use treatment solution. The treatment solution, according to the invention, is preferably used in a process for the production of cans, in particular cans of aluminum alloys for beverages. In this process, the preformed cans, as a rule, are subjected to one or two acid or alkaline cleaning stages, after which, in general, they are rinsed with running water. Subsequently, the cans are brought into contact with the treatment solution according to the invention, which can be effected, for example, by immersing the cans in the solution or by spraying the cans with the solution. The temperature of the treatment solution should be in the range between 30 ° C and 60 ° C, in particular from 40 ° C to 45 ° C. The duration of a treatment should not be less than 10 seconds. A treatment duration greater than 120 sec does not provide technical advantages. For example, it is favorable to choose a treatment duration of about 30 seconds. Afterwards, the cans are rinsed with running water and then with completely deionized water, after which the cans can be dried and enameled. The invention, therefore, also relates to a process for the production of the protective layer against corrosion, reducing friction and protective, which improves the ability to be enameled on the surfaces of aluminum or tin and in each case alloys of these, which comprises contacting the surfaces with an aqueous solution as claimed in one or more of claims 1 to 8, which has a temperature in the range from 30 to 60 ° C, for a period of 10 to 120 seconds, the process of preference is used for the treatment of aluminum cans or aluminum alloys. The invention has been tested in aluminum cans for beverages, in a volume between 330 and 350 ml, as the common cans for carbonated drinks. The preformed cans were first cleaned (acidic cleaning agent) Ridoline® 124, Henkel KGaA, Dusseldorf / from 54 to 60 ° C, 1 minute) and then rinsed with tap water at room temperature. The surface treatment was then carried out with treatment solutions according to the invention and with comparison solutions, as shown in the table, with pH values in the range between 2.45 and 2.93 at temperatures between 40 and 45 ° C for a treatment duration of 30 seconds per spray. Then the rinsing was performed with running water, followed by a rinse with completely deionized water, in each case at room temperature, after which the cans were dried at 150 ° C for 5 minutes. The resistance to mineral water, which provides a measure of the corrosion protection of the treated cans, was determined by standard methods in unglazed cans. The unglazed cans were also used to determine the coefficient of friction explained below. For the determination of the enamel porosity, expressed as the "metallic exposure value", the interior of the cans was enameled with a commercially available enamel (Dexter Ecodex 4020) with an enamel application of 120 to 130 mg / can . The resistance to mineral water was determined by immersing the unglazed cans in a hot solution, at 66 ° C, of 0.2 g / 1 of sodium tetraborate decahydrate for 30 minutes, then rinsing them with completely deionized water and drying them at 5 ° C in a drying oven. Next, the bases of the cans were visually evaluated for the degree of discoloration. In this case, no discoloration or slight discoloration is considered acceptable, and dark or irregular discoloration is also considered unacceptable. Both the cans treated with the process variants according to the invention and the cans treated by the comparative processes according to the prior art passed this corrosion resistance test. The surface friction of unglazed cans for drinking was determined on an incunable table. In each case three cans treated in the same way were used for this. Two cans were placed in parallel on the incunable table so that their longitudinal axes were perpendicular to the axis of inclination. A third can was placed on this pair of cans with its longitudinal axis perpendicular to the axis of inclination, so that the third can moved around 0.5 cm in the direction of the axis of inclination with respect to the lower cans, the third can being placing with the open side in the direction of the tilt axis in contrast to the lower cans. Then, the incunable table was automatically tilted at a constant speed, and the angle of inclination alpha was determined in which the upper can slid and thus touched a circuit breaker. The tangent of the alpha tilt angle in which the slip occurs is called the coefficient of friction. To obtain results confirmed by means of statistics, in each case 6 cans treated in the same way were used, from which in each case 3 cans were chosen for an experiment. 6 independent measurements were carried out with different combinations of cans. The mean of these 6 measurements was determined. The coefficients of friction determined with the treatment solutions according to the invention and the comparative solutions according to the prior art showed no significant differences and were in the range of 1.476 to 0.514. In contrast, the effect of the treatment according to the invention on the treatment without the addition of hydroxycarboxylic acids of group b) manifested itself a clearly reduced porosity of an enamel coating, which was determined as the "metallic exposure value". "(VEM) The determination was made in enameled cans inside, in accordance with the operating instructions of Enamel Rater MK of Manfred Kunke Taunusstr 29, Berlin (Germany) with a test voltage of 6.3 volts. The cans connected as electrodes were filled with an electrolyte solution (50.6 g of sodium chloride and 1.19 g of dioctyl-sodium sulfosuccinate in 5 L of completely disheveled water), in which a metal ring was immersed as the opposite electrode. After the application of the voltage, the current in mA was measured after 4 seconds and was taken as the VEM value. A higher VEM value of 5mA was established as the test criterion for cans for carbonated beverages. The results obtained were entered in the table. The table also contains the number of cans measured in each case per treatment solution, the mean value of VEM, the maximum value of VEM, found and the number of cans in which the specification of a maximum value for VEM of 5mA was exceeded. . The composition of the test solutions can be seen in the table. Table: treatment solutions and "metal exposure value" (VEM) Basic recipe: 400 mg / 1 tris (2-hydroxyethyl) -cebo-ammonium acetate 145 mg / 1 hexafluorozirconic acid 66 mg / 1 phosphoric acid 266 mg / 1 nitric acid 32 mg / 1 hydrofluoric acid 200 mg / 1 antifoam (alkyl-polyalkoxyester, Foamaster® C14, Henkel KGaA, Dusseldorf) Additions of sodium gluconate and tannin experiment Tannin Gluconate No. VEM VEM cans to No. Sodium (mg / 1 maximum average with VEM (mg / 1) cans (mA) (mA >; 5 mA Comparati - 8 5.5 42.1 1 vo Emplo 1 67 - 8 3.9 17.7 2 Example 2 133 - 7 1.3 6.0 1 Example 3 200 - 8 2.1 6.0 1 Example 4 125 - 9 1.25 6.4 1 Example 5 125 83 8 4.0 11.4 1 Eg 6 125 167 7 0.6 2.3 0 Example 7 125 250 9 0.2 0.8 0

Claims (1)

1. CLAIMS An aqueous solution for the treatment of aluminum or tin surfaces and in each case alloys thereof, which has a pH in the range of 2.3 to 3.3 and contains at least the following components: a) from 0.14 to 2.25 mol / m 1 of a selected component of surface active ammonium quaternary salts or amine oxide of the general formula (I): R1 wherein R1 is a saturated alkyl radical or a mono- or polyunsaturated alkyl radical having from 8 to 22 C atoms, R "and R3 independently of each other are an alkyl or hydroxyalkyl radical having from 1 to 8 C atoms or an aryl or alkylaryl radical having from 6 to 10 carbon atoms, R 4 is a radical of the type R 1, R 3 or a radical -O ", and X" is a manovalent anion or a monovalent equivalent of a polyovalent anion, it is 0 if R4 is a radical -0"and otherwise a is 1, b) from 0.25 to 1.5 mmol / 1 of one or more mono-, di- or tribasic hydroxycarboxylic acids having from 4 to 7 C atoms in the molecule, the sum of the hydroxyl and carboxyl groups is at least 3, or in each case the anions of these, c) from 0.4 to 2 mmol / 1 of one or more complex fluorides and d) from 29 to 500 mg / 1 of mineral acids selected from phosphoric acid, nitric acid and sulfuric acid, or in each case the anions thereof. The aqueous solution according to claim 1, which additionally contains one or more of the following components: e) from 50 to 500 mg / 1 of tannin f) from 10 to 100 mg / 1 of hydrofluoric acid or fluoride ions g) 50 to 500 mg / 1 of antifoam. The aqueous solution according to one or both of claims 1 and 2, wherein the component: a) is an amine oxide or a quaternary ammonium salt in which R1 is a mixture of alkyl groups as in acid mixtures fatty acids that can be obtained by hydrolysis of coconut oil, palm coconut oil or animal bait, and / or in which the component: b) is selected from mono- or di-basic hydroxycarboxylic acids having 6 atoms of C and at least 4 hydroxyl groups and / or in which component c) is hexafluorozirconic acid and / or in which component d) contains phosphoric acid or anions thereof to the extent of 10 to 100% by weight. The aqueous solution according to one or more of claims 1 to 3, wherein the component: a) is a quaternary ammonium salt wherein R2, R3 and R4 are hydroxyalkyl groups having from 1 to 4 atoms of C, and / or in which the component: b) is gluconic acid or the anion thereof. The aqueous solution according to one or more of claims 1 to 4, which contains component a) in concentrations of 0.5 to 1.1 mmol / 1 and / or component b) in concentrations of 0.3 to 400 mg / 1 . The aqueous solution, according to one or more of claims 1 to 5, which contains tannin in concentrations of 100 to 400 mg / 1. The aqueous solution according to one or more of claims 1 to 6, which additionally contains water-soluble or water-dispersible polymers in concentrations of 100 to 100 mg / 1. The aqueous solution according to claim 7, wherein the polymers are selected from h) homo- or heteropolymers of ethylene oxide, propylene oxide and / or butylene oxide; i) homo- or heteropolymers of acrylic acid, maleic acid and / or derivatives thereof; k) homo- or heteropolymers of vinylphenol and / or vinylphenol derivatives; and 1) homo- or heteropolymers of vinyl alcohol and / or vinyl alcohol derivatives. An aqueous concentrate that provides a treatment solution, according to one or more of claims 1 to 8, in dilution with water in a volume ratio between 1:50 and 1: 200. . A process for the production of a protective layer, protective against corrosion, reducing friction, which improves the ability to be enameled, on surfaces of aluminum or tin and in each case alloys thereof, which comprises contacting the surfaces with an aqueous solution according to one or more of claims 1 to 8, which has a temperature in the range from 30 to 60 ° C, for a period of between 10 and 120 seconds. . The process, according to claim 10, wherein the metal surfaces are aluminum can surfaces or aluminum alloys.