WO1996016205A1

WO1996016205A1 - Anticorrosive and friction-reducing treatment of metallic surfaces

Info

Publication number: WO1996016205A1
Application number: PCT/EP1995/004466
Authority: WO
Inventors: Henry Rossmaier
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1994-11-23
Filing date: 1995-11-14
Publication date: 1996-05-30
Also published as: BR9509759A; AR000259A1; TR199501469A2; AU4171996A; TW283740B; ATE178951T1; CA2205996A1; EP0793738A1; MX9703762A; DE4441710A1; EP0793738B1; ZA959938B; DE59505673D1; JPH10509766A; AU698370B2

Abstract

An aqueous acid solution is used for treating beverage cans, in particular made of aluminium, in order to create on the cans an anti-corrosive, friction-reducing coating that allows the cans to be more easily lacquered. The solution contains 0.14 to 2.25 mmol/l of an alkyl amine oxide or alkyl ammonium salt with an alkyl residue having 8 to 22 C atoms, 0.25 to 1.5 mmol/l hydroxycarboxylic acids with 4 to 7 C atoms, complex fluorides and mineral acids, and preferably tannin.

Description

"Corrosion protection and reduced friction of metal surfaces"

The invention is in the field of surface treatment of shaped metal parts made of aluminum or aluminum alloys and of tinned steel (tinplate). It relates in particular to beverage and food containers made from these materials. The aim of the invention is to provide the can surfaces with a paintable, anti-corrosion layer in the process of making the can, which facilitates the drainage of water and which, in particular, leads to a reduction in the coefficient of friction between cans in contact with one another and thus to transport the cans on conveyor belts is facilitated, while the porosity of a later coating is reduced.

Tins made of tinned steel (tinplate) and aluminum (or aluminum alloys, which are summarized below for simplicity under "aluminum") are widely used for storing foods and beverages in particular. In the can manufacturing process, these are usually washed after shaping, for which purpose, for example, acidic or alkaline cleaners are commercially available. These cleaning solutions must have sufficient dissolving power for the metals in question in order to effectively remove metal debris from the cans. The can surface itself can be roughened by the metal attack, which increases the friction between touching cans. As a result, the speed of the can transport on the conveyor belts is reduced, and particularly at locations where a can build-up of accumulation due to the individualization of the cans, the can transport can be completely blocked. Since this reduces the capacity of the production plant, efforts are made to condition the can surfaces in such a way that the friction between the touching cans is as low as possible. The application of a friction-reducing layer must not, however, result in the adhesion of lacquers, inscriptions or other coatings applied for corrosion protection and / or for decorative reasons. Furthermore, the coating must ensure that the different requirements with regard to corrosion resistance are met depending on the contents of the cans. Only active ingredients should be used that are generally ecologically and in particular food-safe. For example, from an environmental point of view, efforts are made to avoid using chromium-containing reagents.

Various chrome-free processes for the surface treatment of aluminum are known in the prior art, which generally use inorganic acids, in particular phosphoric acid, hydrofluoric acid or other sources of fluoride and / or complex fluorides, and those with or without additional ones Use organic polymers. For example, US Pat. No. 4,992,116 describes an aqueous acid treatment solution which contains phosphate, a fluoric acid of Zr, Ti, Hf or Si and a polyphenol compound which is a Mannich adduct of a substituted amine with a polyalkylene phenol or a tannin. EP-B-8942 discloses treatment solutions, preferably for aluminum doses, containing a) 0.5 to 10 g / 1 polyacrylic acid or an ester here of and b) 0.2 to 8 g / 1 at least one of the compounds hexafluorozirconic acid , Hexafluorotitanic acid or hexafluorosilicic acid.

Conversion solutions for aluminum are known from US Pat. No. 4,470,853 which contain, inter alia, 10 to 150 ppm zirconium, 20 to 250 ppm fluoride, 15 to 100 ppm phosphate and 30 to 125 ppm tannin. Their pH is in the range of 2.3 to 2.95. The use of tannin in the surface treatment of aluminum is also taught in DE-A-2446492, according to which aluminum is treated with an acidic, phosphate-containing solution which contains a metal salt of tannin in amounts between 0.1 and 10 g / l .

Different solutions have already been proposed for reducing the friction between aluminum cans during can transport. For example, WO91 / 14014 describes an aqueous solution, the ions of Fe, Zr, Sn, Al or Ce, metal etching acids such as hydrofluoric acid, contains alkoxylated phosphoric acid esters and a combination of alkoxylated alcohols and alkoxylated alkylphenols. WO94 / 01517 describes a process for the friction-reducing conversion treatment of metal cans, in which, in addition to inorganic metal compounds, alkoxylated or non-alkoxylated castor oil triglycerides, hydrogenated castor oil derivatives, alkoxylated or non-alkoxylated amine salts of fatty acids, alkoxylated or non-alkoxylated amino fatty acids or alkoxylated fatty acids or alkoxylated fatty acids -N-oxides, alkoxylated or non-alkoxylated quaternary ammonium salts or water-soluble organic polymers are used. Amine oxides or quaternary ammonium salts in which at least one alkyl radical contains up to 20 carbon atoms are used. Amine compounds of this type are also used in the context of the present invention. EP-A-612833 proposes a surface treatment with an ester between a polyglycerol and fatty acids to reduce friction.

An effective surface treatment of tinplate or aluminum nozzles should, on the one hand, meet the different requirements with regard to corrosion protection as well as freedom from pores and adhesion of a subsequent coating, which are checked according to different requirements according to different criteria, and on the other hand should ensure the most effective possible reduction in friction . Systems known to date represent compromises between the different requirements and do not fully satisfy all points. The object of the present invention is to provide a solution for the surface treatment of metal cans, which has an improved performance spectrum with regard to the different requirements. In particular, it has been shown that in processes for conversion treatment and friction reduction according to W094 / 01517, in which fatty amine N-oxides or quaternary fatty alkyl ammonium salts are used as friction-reducing active ingredients, the porosity of a subsequent coating does not meet the requirements, particularly of the beverage industry reliably suffices.

The object is achieved by an aqueous solution for treating surfaces made of aluminum or tin and also their alloys, the one Has a pH in the range from 2.3 to 3.3 and contains at least the following components:

a) 0.14 to 2.25 mmol / l of a component selected from surface-active quaternary ammonium salts or amine oxides of the general formula (I)

Rl

_R 2_ _N + _R3 (x-) (I)

R4

where R ^{1 is} a saturated or mono- or polyunsaturated alkyl radical with 8 to 22 C atoms, R ² and R3 independently of one another an alkyl or hydroxyalkyl radical with 1 to 8 C atoms or an aryl or alkylaryl radical with 6 to 10 C- Atoms, R ^{4 is} a radical of the type R ² or R3 or a -0 ~ radical and X ~ is a monovalent anion or a monovalent equivalent of a polyvalent anion and a is then 0 if R ^{4 is} a -0 "- Rest means, and otherwise a = 1,

b) 0.25 to 1.5 mmol / l of one or more mono- or di-basic hydroxycarboxylic acids having 4 to 7 carbon atoms in the molecule, the sum of hydroxyl and carboxyl groups being at least 3, or their anions,

c) 0.4 to 2 mmol / l of one or more complex fluorides and

d) 20 to 500 mg / 1 mineral acids, selected from phosphoric acid, nitric acid and sulfuric acid, or their anions in each case.

The alkyl radicals R ¹ can represent radicals with a certain chain length and a certain number of double bonds. From economic For reasons, however, it is preferable to use amine oxides or ammonium salts which are derived from oleochemical raw materials. In these cases, the R ¹ radicals have a distribution of chain lengths and double bonds which are characteristic of the fatty acids in vegetable or animal fats and oils. Preference is given to using compounds of the general formula (I) in which R1 represents a mixture of alkyl groups, such as those fatty acid mixtures which can be obtained by hydrolysis of coconut oil, palm kernel oil or animal tallow.

Examples of suitable amine oxides of the general formula (I) are: bis (2-hydroxyethyl) cocoalkylamine oxide (Aromox ^R C / 12), bis (2-hydroxyethyl) talkylkylamine oxide (Aromox ^R T / 12), dimethyl cocoalkylamine oxide (Aromox ^R DMC ), hydrogenated diethyl tallow alkyl amine oxide (Aromox ^R DMHT) and dimethyl hexadecyl amine oxide (Aromox ^R DM-16), all of which are available from Akzo Chemicals Inc.

Examples of suitable quaternary ammonium salts of the general formula (I) are: dodecyl trimethyl ammonium chloride (Arquad 12-37W ^R) Octadecyltrime- methylammonium chloride (Arquad 18-50 ^R), dimethylbenzyl (Ci2-i8) - ^a lkylammoni- monium chloride (Arquad B-100) , Tris (2-hydroxyethyl) tallow alkyl ammonium acetate (Ethoquad ^R T / 13) and methyl bis (2-hydroxy-2-methylethyl) ammonium methyl sulfate (Propoquad ^R T / 12), all of which are also available from Akzo Chemicals Inc.

Preferred alkylamine oxides or quaternary ammonium salts of the general formula (I) are those which carry radicals R ² , R ³ _and, in the case of the quaternary ammonium salts, also R ⁴ which form when the alkyl amines are reacted with ethylene oxide, propylene oxide or butylene oxide. Examples include 2-hydroxyethyl groups and 2-hydroxy-2-methylethyl groups. As is customary in alkoxylation reactions, residues R2, R3 and R ⁴ can also arise in this case, in each of which several alkoxy groups are linked to one another via ether bonds. Such polyether residues with up to 8 carbon atoms are also within the scope of the invention. However, particular preference is given to those compounds of the general formula (I) which bear 2-hydroxyethyl groups as radicals R ² , R3 and optionally R ⁴ . In the treatment solutions according to the invention, the components of group a) are the active ingredients which reduce friction. In contrast, the effect of the components of group b) is mono-, di- or tri-basic hydroxycarboxylic acids having 4 to 7 carbon atoms in the molecule, the Sum of hydroxyl and carboxyl groups is at least 3, primarily in that a lacquer applied later has a reduced porosity and thus an increased corrosion resistance. The porosity value, referred to in the Anglo-Saxon literature as "Metal Exposure Value", MEV, can be determined by an electrochemical measurement and represents one of the quality requirements of the beverage industry for lacquered beverage cans ter MK "from Manfred Kunke, Berlin (Germany) or with an" Enamel Rater "from Wilkens-Anderson Co, Chicaco, Illinois. The measurement is based on filling the inside of the beverage can with an electrolyte solution (50.6 g of table salt and 1.19 g of dioctyl sodium sulfosuccinate in 5 l of completely deionized water) and switching the can as an electrode. A counter electrode is immersed in the electrolyte solution and the flowing current is read off in mA after the voltage has been switched on and a waiting time of 4 seconds has elapsed. If the can is perfectly coated, no current flow is expected. Increasing current flow in mA, which represents the "metal exposure value", indicates an increasing permeability of the coating for ions, which can be interpreted as porosity. For a later filling with soft drinks, for example, it is required that the average MEV should be below 5 mA at a test voltage of 6.3 V.

The essence of the present invention is that components b) in the treatment solution significantly lower the MEV, without the other properties such as friction reduction and corrosion protection, which are essentially due to components a), c) and d) of the treatment solution ¬ are to be influenced negatively.

Examples of suitable hydroxycarboxylic acids are malic acid, tartaric acid, citric acid and in particular those carboxylic acids which can be obtained by oxidation of sugars of the pentose and hexose type. Examples of such acids are gluconic acid, sugar acid, mannosugar acid, Mucic 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 their sodium salts. The pH of the inventive treatment solutions in the range 2.3 to 3.3 are the Hy¬ droxycarbonsäuren depending on their _pK partially as such, and teilwei¬ se in the form of their anions. The use of such carboxylic acids, in particular gluconic acid, in the surface treatment of aluminum, for example in the case of alkaline pickling, is known in principle. However, the effect is unexpected that the hydroxycarboxylic acids of group b) supplement the effect of the other components of the treatment solution according to the invention in such a way that the "metal exposure value" of an applied coating is reduced.

The other main components of the treatment solution according to the invention, c) and d), are well known in solutions for the conversion treatment of aluminum surfaces. Suitable complex fluorides of group c) are, for example, hexafluorotitanate, hexafluorozirconate, hexafluorohafnate, hexafluorosilicate or tetrafluoroborate. The use of hexafluorozirconate is preferred. It is immaterial whether the complex fluorides are used as water-soluble salts, for example as sodium or ammonium salts, or as free acids. It is only necessary to ensure that the complex fluorine compounds are combined with the mineral acids of group d) or their acidic or neutral salts in such a way that the treatment solution according to the invention has a pH in the effective range from 2.3 to 3.3. At pH values outside this range, the formation of the desired corrosion-protective and friction-reducing layer becomes all the more unsatisfactory the further one moves away from the specified range.

Since phosphoric acid or its anions have a special corrosion-protective effect due to the formation of poorly soluble metal phosphates which adhere firmly to the metal surface, it is particularly preferred that component d) comprises 10 to 100% by weight of phosphoric acid or whose anions exist. If phosphoric acid is not used as the only acid in group d), the use of nitric acid or its anions is advantageous. The effect of the combination of substances described above can be enhanced by adding further active substances from the prior art:

The addition of tannin in the concentration range 50 to 500 mg / l increases the effect of the hydroxycarboxylic acids of group b) with regard to the reduction of the "metal exposure value" of a coating subsequently applied. Accordingly, it is preferred that the treatment solution according to the invention additionally contains tannin. Tannins (compare, for example, Römpp Chemie Lexikon 9th edition 1992, keyword "Tannin") stands as a group name for a number of natural polyphenols of very diverse compositions that can be derived from gallic acid. The gallic acid derivatives are often esterified with glucose. In the form of vegetable extracts of different origins, the tannins represent a known active ingredient group for leather tanning. In this context, structures and origins of the tannins are discussed in more detail in: Kirk-Othmer "Encyclopedia of Chemical Technology", 2nd edition, Volume XII (1967 ), Pp. 303-341. As is evident from documents US-A-4,470,853 and DE-A-2446492, the use of tannins in the surface treatment of aluminum has already been proposed.

Experience has shown that the presence of free fluoride ions has a favorable effect on the production of conversion layers on aluminum surfaces. From the complex fluorides listed above under group c), hydrolysis reactions in the treatment solution can result in free fluoride ions which are at least partially present in the form of undissociated hydrofluoric acid at the pH of the treatment solution. The layer formation achieved with the treatment solutions according to the invention can be supported, especially in the running-in phase of the baths, if the treatment solutions additionally contain 10 to 100 mg / 1 fluoride ions, which can be added as hydrofluoric acid or as soluble neutral or acidic fluorides. Examples of this are NaF, KF, KHF2 or (NH4) HF2. The fluoride component should be selected so that the required pH range from 2.3 to 3.3 is not left.

Since the treatment solution contains surface-active components that tend to foam due to the components of group a), it can Ker bath movement such as for spray systems may be necessary to add defoamers to the treatment baths. Amounts in the range of 50 to 500 mg / 1 should generally be sufficient. Alkyl polyalkoxy esters, for example, are suitable as defoamers. A suitable polyalkoxy ester of this type is available under the trade name Foamaster ^R C14 from Henkel KGaA, Düsseldorf (Germany).

All the ranges given above for effective concentrations and pH are to be understood in such a way that the desired effect reliably occurs within these parameter ranges. If the specified minimum concentrations are undershot, the desired combined friction-reducing, corrosion-protecting and the porosity of a subsequent coating decreases the protective layer. Exceeding the maximum concentrations upwards is at least uneconomical, but can also lead to disadvantages in the layer formation. A coating which fully meets the requirements is obtained particularly reliably if component a) in concentrations of 0.5 to 1.1 mmol / l and / or component b) in concentrations of 0.3 to 1.15 mmol / l in the treatment solution is available. The preferably used tannin is preferably used in concentrations of 100 to 400 mg / 1.

A further improvement of the coating, in particular with regard to its paintability, can be achieved by additionally adding water-soluble or water-dispersible organic polymers to the treatment solution in concentrations of about 100 to about 1000 mg / l. These polymers can be selected from h) homopolymers or heteropolymers of ethylene oxide, propylene oxide and / or butylene oxide, i) homopolymers or heteropolymers of acrylic acid, maleic acid and / or derivatives thereof, k) homopolymers or heteropolymers of vinylphenol and / or vinylphenol derivatives, 1) homopolymers or heteropolymers of vinyl alcohol and / or vinyl alcohol derivatives. Polymers of the type mentioned are commercially available. The group k) polyvinylphenol derivatives are obtainable by a Mannich reaction of polyvinylphenol with aldehydes with alkylamines. For example, a reaction product of poly (4-vinylphenol) with formaldehyde and 2-alkylamino-1-ethanol may be mentioned. Further information on this polymer and its use in the surface treatment of aluminum can be found in WO92 / 07973. Compositions of ready-to-use treatment solutions according to the invention have been described above. It is of course possible to prepare these baths directly by mixing the individual components in the specified concentration ranges on site. For the user of such treatment solutions, however, it is more favorable to obtain aqueous concentrates of the treatment solutions from a manufacturer and to adjust them to the concentration ranges of the application solutions by diluting them with water on site. Accordingly, the invention also includes aqueous concentrates of the treatment solutions which, by dilution with water, give the treatment solutions according to the invention. It is technically and economically most attractive to adjust the concentrates so that the ready-to-use treatment solutions can be obtained from them by dilution with water in a volume ratio between 1:50 and 1:200. For example, the concentrate can be adjusted so that it has to be diluted 1: 100 with water to prepare the 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 beverage cans made of aluminum alloys. Here, the preformed cans are generally subjected to a one- or two-stage acidic or alkaline cleaning, which is usually followed by rinsing with tap water. The cans are then brought into contact with the treatment solution according to the invention, which can be done, 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 to 60 ° C. and in particular 40 to 45 ° C. The duration of the treatment should not be less than 10 seconds. A treatment duration of more than 120 seconds does not bring any technical advantage. For example, it is expedient to choose a treatment time of about 30 seconds. Then the cans are rinsed with tap water and then with deionized water, after which they can be dried and painted. Accordingly, the invention also encompasses a method for producing a protective layer on aluminum or tin surfaces and alloys thereof which protect against corrosion, reduce friction and improve paintability, characterized in that the surfaces are coated with an aqueous solution according to a method or more of claims 1 to 8, which has a temperature in the range of 30 to 60 ° C, for a period between 10 and 120 seconds in contact, which is preferably used for the treatment of cans made of aluminum or aluminum alloys.

The invention was tested on aluminum beverage cans with a volume between 330 and 350 ml, as are customary for soft drinks. The preformed cans were first cleaned (acidic cleaner Ridoline ^R 124, Henkel KGaA, Düsseldorf; 54 to 60 ° C, 1 minute) and then rinsed with tap water at room temperature. Thereafter, the surface treatment was carried out with treatment solutions according to the invention and with comparison solutions according to the table with pH values in the range between 2.45 and 2.93 at temperatures between 40 and 45 ^° C. for a treatment period of 30 seconds in spraying. This was followed by rinsing with tap water, followed by rinsing with demineralized water, in each case at room temperature, after which the cans were dried at 150 ° C. for 5 minutes.

The determination of the well water resistance according to standard methods, which provides a measure of the corrosion protection of the treated cans, was carried out on the unpainted cans. Unpainted cans were also used for the subsequent determination of the coefficient of friction. To determine the paint porosity, expressed as the "metal exposure value", the inside of the can was coated with a commercially available paint (Dexter Ecodex 4020) with a paint application of 120 to 130 mg / can.

The well water resistance was determined by immersing the unpainted cans for 30 minutes in a 66 ° C solution of 0.2 g / 1 sodium tetraborate decahydrate, then rinsing them with demineralized water and drying them at 105 ° C in a drying oven. The can bottoms were then assessed visually according to the degree of their discoloration. No discoloration or slight discoloration is considered acceptable, dark or irregular discoloration is unacceptable. Both the cans treated with the process variants according to the invention and with comparison processes according to the prior art passed this test for corrosion resistance. The surface friction of the unpainted beverage cans was determined on a tilting table. For this, 3 tins treated in the same way are used. Two cans are arranged parallel to one another on the tilting table so that their longitudinal axis is perpendicular to the tilting axis. On this pair of cans, a third can is placed with its longitudinal axis perpendicular to the tilting axis so that it is shifted by about 0.5 cm in the direction of the tilting axis relative to the lower cans, being placed opposite to the lower cans with the open side in the direction of the tilting axis becomes. The tilting table is then automatically tilted at a constant speed and the angle of inclination oc is determined, at which the upper box slips and thereby touches an off switch. The tangent of the inclination angle α, at which the slipping takes place, is referred to as the coefficient of friction. In order to obtain statistically reliable statements, 6 equally treated doses are used, from which 3 are selected for an experiment. 6 independent measurements are carried out with different combinations of cans. The mean value is determined from the 6 measurements. The friction coefficients 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 from 0.476 to 0.514.

In contrast, the effect of the treatment according to the invention compared to a treatment without addition of hydroxycarboxylic acids of group b) is shown in a significantly reduced porosity of a coating, which was determined as the "Metal Exposure Value" (MEV). The determination was made on internally lacquered cans according to the operating instructions of the Enamel Rater MK from Manfred Kunke, Taunusstr. 29, Berlin (Germany) at 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 deionized water), into which a metal bracket was immersed as a counter electrode. After applying the voltage, the current was measured in mA after 4 seconds and set as the MEV value. An upper MEV value of 5 mA is specified as the test criterion for beverage cans for soft drinks. The results obtained are entered in the table. The table also contains the number of doses that were measured per treatment solution, the mean MEV value, the maximum observed MEV value and the number of doses at which the specification was exceeded by a maximum MEV value of 5 mA. The composition of the sample solutions is shown in the table.

Table: Pretreatment solutions and "Metal Exposure Value" (MEV)

Basic formulation: 400 mg / 1 tris (2-hydroxyethyl) tallow 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 defoamer (alkyl polyalkoxy ester, Foamaster ^R C14,

Henkel KGaA, Düsseldorf)

Additions of sodium gluconate and tannin

Try sodium tannin doses with medium maximum doses

No. gluconate (mg / 1) number MEV MEV MEV

(mg / 1) (mA) (mA)> 5 mA

Comparison - - 8 5.5 42 _t l 1

Ex. L 67 - 8 3.9 17.7 2

Ex. 2 133 - 7 1.3 6.0 1

Ex. 3 200 - 8 2.1 6.0 1

Ex. 4 125 - 9 1.25 6.4 1

Ex. 5 125 83 8 4.0-11.4 1

Ex. 6 125 167 7 0.6 2.3 0

Ex. 7 125 250 9 0.2 0.8 0

Claims

claims

1. Aqueous solution for treating aluminum or tin surfaces and their alloys in each case, which has a pH in the range from 2.3 to 3.3 and contains at least the following components:

R

_R 2_ _N + _R3 (x-) (I)

R ⁴

where Rl is a saturated or mono- or polyunsaturated alkyl radical with 8 to 22 carbon atoms, R ² and R3 independently of one another an alkyl or hydroxyalkyl radical with 1 to 8 carbon atoms or an aryl or alkylaryl radical with 6 to 10 carbon atoms -Atoms, R ^{4 is} a radical of the type R ² or R ^ or a -0 "radical and X" is a monovalent anion or a monovalent equivalent of a polyvalent anion and a = 0 if R ^{4 is} a -0 "- Rest means, and otherwise a = 1,

b) 0.25 to 1.5 mmol / l of one or more mono-, di- or tri-basic hydroxycarboxylic acids having 4 to 7 carbon atoms in the molecule, the sum of hydroxyl and carboxyl groups being at least 3, or their anions in each case ,

c) 0.4 to 2 mmol / l of one or more complex fluorides and d) 20 to 500 mg / 1 mineral acids, selected from phosphoric acid, nitric acid and sulfuric acid, or their anions in each case.

2. Aqueous solution according to claim 1, characterized in that it additionally contains one or more of the following components:

e) 50 to 500 mg / 1 tannin f) 10 to 100 mg / 1 hydrofluoric acid or fluoride ions g) 50 to 500 mg / 1 defoamer.

3. Aqueous solution according to one or both of claims 1 and 2, characterized in that the component

a) represents an amine oxide or a quaternary ammonium salt in which R represents a mixture of alkyl groups such as those in those fatty acid mixtures which can be obtained by hydrolysis of coconut oil, palm kernel oil or animal tallow.

and / or that the component

b) is selected from mono- or dibasic hydroxycarboxylic acids with 6 carbon atoms and at least 4 hydroxyl groups

and / or that the component

c) represents hexafluorozirconic acid

and / or that the component

d) consists of 10 to 100% by weight of phosphoric acid or its anions.

4. Aqueous solution according to one or more of claims 1 to 3, characterized in that the component a) represents a quaternary ammonium salt in which R ² , R3 and R ^{4 are} hydroxyalkyl groups having 1 to 4 carbon atoms,

and / or that the component

b) represents gluconic acid or its anion.

5. Aqueous solution according to one or more of claims 1 to 4, characterized in that it contains component a) in concentrations of 0.5 to 1.1 mmol / l and / or component b) in concentrations of 0.3 to Contains 1.15 mmol / l.

6. Aqueous solution according to one or more of claims 1 to 5, characterized in that it contains tannin in concentrations of 100 to 400 mg / 1.

7. Aqueous solution according to one or more of claims 1 to 6, characterized in that it additionally contains water-soluble or water-dispersible polymers in concentrations of 100 to 1000 mg / 1.

8. Aqueous solution according to claim 7, characterized in that the polymers are selected from h) homopolymers or heteropolymers of ethylene oxide, propylene oxide and / or butylene oxide, i) homopolymers or heteropolymers of acrylic acid, maleic acid and / or derivatives of these, k) homopolymers or heteropolymers of vinylphenol and / or vinylphenol derivatives, 1) homopolymers or heteropolymers of vinyl alcohol and / or vinyl alcohol derivatives.

9. Aqueous concentrate which, when diluted with water in a volume ratio between 1:50 and 1:200, gives a treatment solution according to one or more of claims 1 to 8.

10. A method for producing a protective layer that protects against corrosion, reduces friction and improves the paintability on surfaces made of aluminum or tin, as well as their alloys, characterized by, that the surfaces with an aqueous solution to Lö¬ according to one or more of claims 1 to 8, which has a Tempera¬ ture in the range of 30 to 60 C ^β, brings for a period between 10 and 120 seconds of contact.

11. The method according to claim 10, characterized in that the metal surfaces are surfaces of cans made of aluminum or aluminum alloys.