MXPA99005991A - Method for treating metallic surfaces - Google Patents

Abstract

The invention relates to a method for treating metallic surfaces consisting of zinc, magnesium or aluminium or of the alloys of zinc, magnesium or aluminium, to which lacquer, coatings of plastic material, paint, sealants or adhesives are applied after treatment. The treatment of the metallic surfaces takes place at between 10°C and 100°C by immersion, spraying or rolling with an aqueous solution. The solution has a pH of between 2 and 13 and contains one or more compounds of the type XYZ at a concentration of between 10-5 and 1 mol/l. Y is an organic group containing between 2 and 50 C atoms and has a straight-chain structure. X is a COOH, HSO3, HSO4, (OH)2PO, (OH)2PO2, (OH) (OR') PO or (OH) (OR') PO2 group. Z is a OH, SH, NH2, NHR', CN, CH=CH2, OCN, epoxy, CH2=CR''-COO, acrylamide, COOH, (OH)2PO, (OH)2PO2, (OH) (OR') PO or (OH) (OR') PO2 group. R'is an alkyl group with between 1 and 4 C atoms. R''is an H atom or an alkyl group with between 1 and 4 C atoms. Groups X and Z are each bonded to group Y in their final positions.

Description

PROCESS FOR TREATING METALLIC SURFACES Description This invention relates to a process for treating metallic surfaces, which consists of zinc, magnesium or aluminum or zinc, magnesium or aluminum alloys, and for which lacquers, plastics coatings, paints, coatings components, are applied after treatment. sealed or adhesive s. It is known that the corrosion of metallic surfaces of polymer coating is due to the electrochemical reactions in the phase limit of me t to / po 1. In various coating techniques applied in the art, the metal surfaces are therefore coated with an inorganic conversion layer (eg, zinc phosphate) before applying a lacquer or plastic coating. Due to the conversion treatment by a coating process or foaming agent that forms a coating, the metal surface is prepared to be subsequently coated with a lacquer or a plastic. Even now, the conversion treatment of the aluminum surfaces is carried out by means of a yellow chromate, where a solution of chromate acid with a pH value of 1 to 2 is used, so that a protective layer is used. shape on aluminum. The protective layer consists of chromium-aluminum (111) insoluble, mixed with oxide and effects of high passivity of the surface against corrosion. The residual content of the remaining unused chromium ions in the oxide layer also produces a self-regenerating effect in a lacquer or damaged plastic coating. However, yellow chromation of aluminum surfaces has the disadvantage that it only has properties that promote insufficient adhesion, with respect to a plastic coating or lacquer. In addition, chromium ions are disadvantageously worn out of naturally worn coatings. As an alternative for chromation, a process using zirconium salts, fluorides, phosphates and organic polymers is developed (for example polyacrylates and alcohols for 1 to 4 years). Through this process, coatings are formed on aluminum surfaces that provide the substrate with a certain protection against corrosion and a very good adhesion for lacquer and plastic coatings. However, the protection achieved against corrosion is not always satisfactory. On the other hand, there is no lack of attempts at the optimal support of metallic surfaces of zinc, magnesium, aluminum and the alloys thereof for the application of lacquer and plastic coatings to treat such surfaces with their organic salts. From DE-A-3137525 a process for inhibiting corrosion in an aqueous system is known, wherein the aqueous system contains at least one inorganic nitrite soluble in water, and at least one organic diphosphonic acid or at least minus one diphosphonic acid salt. Diphosphonic acid is present in an aqueous system at a concentration of 0.1 to 20 ppm. The known aqueous system is used to avoid in particular the corrosion problems in cooling systems. In aqueous systems, hydroxy-t-1-diphosphonic acid and organic salts thereof are particularly preferred. From EP-A-0 012 909 it is known that the benzyl amide zo-2-α-alkanophilic acids and the salts thereof have an effect which inhibits pronounced corrosion and which can be used as inhibitors. of corrosion. To inhibit corrosion, they can be used alone, in combination with others, or together with other known inhibitors. To inhibit corrosion, they are generally added to aqueous media, water-based, alcohol-containing, and / or oil-containing. They can be used, for example, as corrosion inhibitors in media that transfer heat from cooling or heating circuits, refrigerants, mineral oils or pickling bath inhibitors. By adding the compounds and / or salts thereof in such media or circulating liquids, corrosion of metals is prevented, in particular copper and its alloys. The benzimide zo 111 - 2 - alos fosfonicos acids contain a group of phosphonic acid, a straight or branched chain, saturated or saturated, bivalent, residues possibly substituted with hydrocarbons with 1 to 15 carbon atoms and a residue substituted with benz bonded zo 1, where the straight or branched chain of the hydrocarbon residue and the benzimidazole residue are related to each other by placing 2 of the benzimidazole residues 1. From US -A- 4, 351, 675 It is known that an aqueous solution for the treatment of zinc, zinc or cadmium alloys, containing nitric acid, an oxidizing agent (H202, nitrate, nitrite, chlorate) and a diphosphonic acid, where the two phosphonic acid groups are related between yes by a carbon atom further having a hydroxyl group and an alkyl residue with 1 to 4 carbon atoms. From US-A-5, 059, 258 it is finally known of a process, where an aluminum substrate with a pH value of 2 to 14 produces first of all a layer of aluminum hydroxide, "and where after an additional layer is deposited in the aluminum hydroxide layer by treatment with an organic phosphinic acid or an organic phosphonic acid The organic residue of phosphinic or phosphonic acid, each containing 1 to 10 organic groups and 1 to 30 atoms The molecule of organic phosphonic and phosphinic acids contains 1 to 10 groups of phosphonic and phosphinic acid.To produce the hydroxide layer, an aqueous solution containing amines, amino alcohols, alkali hydroxides, alkaline earth hydroxides, is used. alkaline carbonates, alkali hydrogen carbonates or ammonia To produce the second layer a solution is used in which the phosphonic and phosphinic acids are present in a concentration of 0 .001 mol / 1 up to the saturation concentration, and whose solvent contains water, an alcohol or an organic solvent. As organic groups the phosphonic and phosphinic acids contain, for example, aliphatic hydrocarbons, aromatic hydrocarbons, organic acids, aldehydes, ketones, amines, amides, thioamides, molts, lactams, anilines, piperidms, pyridms, carbohydrates, esters, lactones, ethers, alkenes, alcohols, nitpls, oximes, silicones, ureas, thioureas, per- fumed organic groups, silanes, and combinations of these groups. The second layer would act on the substrate, in particular as a promoter of good adhesion for lacquers and plastic coatings as well as for paints. It is the fundamental object of the invention to create a process for treating metallic surfaces consisting of zinc, magnesium or aluminum, or zinc, magnesium or aluminum alloys, to provide metal surfaces, in particular with a good adhesion for lacquers, coatings of plastic, paints, sealing compounds and adhesives, and to protect metal surfaces against corrosion. The fundamental object of the invention is solved in that the metallic surfaces were treated from 10 to 100 ° C by immersion, spraying or rolling with an aqueous solution which has a pH value of 2 to 13 and contains from 10 ~ 5 to 1 mol / 1 of one or more compounds of the type XYZ, wherein Y is an organic group with 2 to 50 carbon atoms and a straight chain structure, wherein X is a COOH-, HS03-, HSO4-, (OH) 2PO -, (OH) 2P02-, (OH) (OR ') PO- or the group P02 (OH) (OR'), wherein Z is an OH-, SH-, NH2-, NHR'-, CN-, CH = CH2-, OCN-, epoxide-, CH2 = CR "- COO-, acrylamide-, COOH-, (OH) 2PO-, (OH) 2P02-, (OH) (OR ') PO- or group P02 ( OH) (OR '), wherein R' is an alkyl group with 1 to 4 carbon atoms, wherein R "is a hydrogen atom or an alkyl group with 1 to 4 carbon atoms, and wherein the X groups and Z are each linked to the group Y in its terminal position. The effect of the inventive process is based on the ability of the XYZ compounds to spontaneously and very thinly organize the closed film on the metal surfaces, wherein an orientation of the acid groups in the direction of the metal surface is particularly affected, and a chemical bond is formed between the metal hydroxide groups present on the metal surface and the acid groups of the compound XYZ. According to the invention, the structure of the compounds XYZ is selected, such that a reactive coupling of the thin film is obtained, both from the metal surface and to the matrix of lacquers, plastic covers, paints, sealants and adhesives The organic group of linear chain Y acts as a "spacer" between the groups X and Z; Compound XYZ is more or less provided with the properties of a surfactant, such as the organic group Y having hydrophilic properties. The group Z provides the coated surface with a good wetness and reactivity with respect to the lacquers, the plastic covers, paints, sealants and adhesives. When lacquers, plastic covers, paints, sealing compounds and adhesives are applied to thin films, the advantageous properties of the films are still maintained under the influence of the corrosive medium, so the metal surfaces are protected against corrosion. The reactive group Z must be particularly adjusted to the individual lacquers.

According to a further aspect of the invention, it is provided that in the aqueous solution from 0.1 to 50% of the water were replaced by an alcohol with 1 to 4 carbon atoms, by acetone, by dioxane, or by water-alcohol. These organic solvents affect a high solubility of the XYZ compounds, which are generally longer molecules whose solubility in pure water is not higher. On the other hand, the solution always contains a long amount of water, so even with the presence of organic solvents the system can still be called an aqueous system. According to the invention, it is particularly advantageous when the aqueous solution contains one or more compounds of the XYZ type in a concentration that lies in the range of the critical micellization concentration. The concentration of critical micelization is a concentration characteristic of the respective surfactant, where the molecules begin to aggregate into the micelles. The addition is reversible. Under the eme, that is, when the solutions are diluted, the micelles are destroyed again to form monomeric molecules. The numerical value of the eme depends on the constitution of each surfactant and on external parameters such as ionic strength, temperature and concentration of additives. As methods for determining the eme there may exist for example being the used measurements of the surface tension. By means of the ring or plate method, the surface tension d of a surfactant solution was determined in dependence on its concentration c at a constant temperature. The eme were recognized as a salient point in the plan d = f (lg c). Examples for determining the eme of various surfactants can be found in "Die Tenside", edited by v. Kosswig and Stache, Cari Hanser Verlag, Munchen, Wien, 1993. According to the invention it proved to be particularly useful when the aqueous solution contains a defoaming agent and / or a solubilizer, each in an amount of 0.05 to 5 by weight. The defoaming agent facilitates the handling of the inventive solution, which due to the technical properties of the XYZ compounds tend to froth. The solubilizer advantageously limits the use of organic solvents and encourages the use of pure water. Both as defoaming agents and as solubilizers, there are many, for example, amino alcohols can be used. In accordance with the invention it was again useful in some cases when compounds of the type XYZ are present as salts in the aqueous solution. In general, the salts have a better solubility than the compounds themselves and the dissolved salts are also very stable, so that the handling of the inventive solution is improved by the use of the salts of the XYZ compounds. In practice, in particular the sodium and potassium salts are used. According to the invention, Y is unbranched, the straight chain alkyl group having 2 to 20 carbon atoms, or a straight chain, unbranched group consisting of 1 to 4 aromatic C6H4 nuclei connected in the para-position, or a group consisting of one or more branches, straight chain alkyl residues, each having 1 to 12 carbon atoms, and 1 to 4 aromatic C6H nuclei connected in the para-position. All the inventive groups Y are those characterized by a linear chain, unbranched molecular structure, which is optimally suited to act as a "spacer" between the groups X and Z. According to the invention, the groups Y may be those having the following structure: a) X- (CH2) m-Z; m = 2 to 20 c) X- (CH2) o- (C6H4) P- (CH2) q; o = 0 to 12, p = 1 to 4, q = 0 to 12, o or q unequal to 0. According to the invention it is particularly advantageous when Y is an unbranched straight chain alkyl group with 10 to 12 carbon atoms. carbon or a group p-CH 2 -C 6 H 4 -CH 2 - or uri group p, p'-C 6 H -C 6 H 4 -. These groups Y provide the inventive compounds XYZ with very good adhesion stimulation properties for lacquers and other organic coaters. In addition, it is particularly advantageous when X is an (OH:) P02- or the group (OH) (0R ') P02-, and when Z is a (OH2) PO -, (OH) (0R ') P02-, OH-, SH-, NHR'-, CH = CH2- or the group CH = CR "-COO- Compounds of the type XYZ, which are equipped with the groups X and Z mentioned above, likewise have good properties that stimulate adhesion for lacquers and plastic coaters, and in addition form a chemical bond solid with metallic surfaces.

Aqueous solutions containing the compounds mentioned in the following XYZ type have very good adhesion stimulation and properties that inhibit corrosion: 12-mercaptododecane 1-phosphonic acid, 12-(N-ethylamino) dodecane 1-phosphonic acid, 12-Dodecene-1-phosphonic acid, p-xylylenes diphosphonic acid, 1,10-decane diphosphonic acid, 1,12-dodecane diphosphonic acid, 12-hydroxydodecane-1-phosphonic acid, 12- (N-ethylamino) dodecane 1-phosphoric acid, 12-mercaptododecane 1-phosphoric acid, 1,10-decane diphosphoric acid, 1,1-dodecano diphosphoric acid, p, p'-bi-phene, diphosphoric acid, 12-acryl and 1dodecane 1 -phosphoric. These compounds form a bond with the metal surfaces by the phosphonic and phosphoric acid groups, and by means of their aromatic aliphatic group and their functional group Z acts as an adhesion promoter with respect to several organic components of the lacquers, the plastic coaters, the paints, sealing compounds and adhesives.

According to a further aspect of the invention, it is provided that the aqueous solution is applied to metal surfaces of 10 to 100 ° C by means of immersion, sprinkling or rolling, known per se, where the immersion time is 5 seconds to 20 minutes, the spray time is from 5 seconds to 15 minutes, and the rolling time is from 2 to 120 seconds. It is observed that a thin film is formed on metal surfaces when the aqueous solution is applied by dipping, spraying or rolling, where the rinsing of the treated metal surfaces is not absolutely necessary, but it can be advantageous. According to the invention it is provided that the metal surfaces are subjected to an alkaline and / or a deoxidized acid before applying the aqueous solution and are subsequently rinsed with water. The use of water can be deionized or non-deionized. The metallic surfaces consist of zinc, magnesium, aluminum and the alloy thereof are always covered by oxidic layers and in addition contaminated by the surface absorption of carbon dioxide, water and / or hydrocarbons. These contaminated coated layers are not able to permanently bond lacquers, plastic covers, permanently bond lacquers, plastic covers, paints, sealing components and adhesives and ensure a long term protection against corrosion. According to the invention, the metal surfaces are therefore cleaned before being treated with the aqueous solution. According to a further aspect of the invention, it is provided that the metal surfaces, to which the aqueous solution is applied by dipping or spraying, are subsequently wiped with water and possibly dried? a nitrogen or air stream, where the temperature of the nitrogen or air stream is 15 to 150 ° C. Rinsing and drying does not prevent the formation of thin film on metal surfaces. The water used for rinsing can be deionized or non-deionized. It is particularly advantageous when the inventive process is used for the treatment of metal surfaces to which a cathodic or anodic electrodeposition coating, a dust cover, a roll cover paint, a high solids paint or a paint are subsequently applied. diluent with water. Throughout the painting process, the pretreatment of the metal surfaces with the aqueous solution according to the invention was particularly useful. The subject matter of the invention will be subsequently explained in detail with reference to the erent Examples: E xemployment 1: Processes The sheets consist of the AIMgl alloy which are used as substrates, a) I nmer s ion First, the sheets are immersed in an alkaline pickling solution for 3 minutes at room temperature, which binds the solution containing 32 g / 1 NaOH and 8 g / 1 Na: C03. Subsequently, the sheets are rinsed with deionized water. Then, the sheets subjected to alkaline tanning are immersed in an acid tanning solution for 3 minutes at 40 ° C, that the tanned solution contains 10 g / 1 H2S04 and 33 g / 1 H ^ 02. Subsequently, the sheets are rinsed with deionized water. Finally, the tanned sheets are dried in the inventive aqueous solution for 3 minutes at 40 ° C, whose solution contains the inventive compound XYZ in a concentration of approximately 10 mol / 1. Subsequently, the sheets are rinsed with deionized water and dried at room temperature under a stream of nitrogen. b) Root The sheets are first of all sprayed with an alkaline tanning solution for 10 seconds at 65 ° C, whose tanning solution contains 10 g / 1 Bonder V338M®. Subsequently, the sheets are rinsed by spraying them with water. Then, the sheets subjected to alkaline tanning are sprayed with an acid tanning solution for 30 seconds at 50 ° C, whose tanning solution contains 16 g / 1 Bonder V450M®. Subsequently, the sheets are rinsed by spraying them with deionized water. Finally, the sheets are sprayed with the inventive aqueous solution for 30 seconds at 40 ° C. The sheets are subsequently rinsed with deionized water and dried in a stream of air at room temperature. The inventive compound XYZ is present in the aqueous solution in a concentration of approximately 10"3 mol / l. (® registered trademark of Metallgesellachaft AG, Fran furt / Main, Germany) c) Coated layer The sheets are first of all subjected to alkaline and acid tanning corresponding to the spraying process, and rinsing.Subsequently, the inventive aqueous solution is roll covered in the sheets for two seconds at room temperature, where the roll is operated at 25 revolutions per minute. XYZ is present in a concentration of approximately 10 mol / 1. Under the roll cover of the aqueous solution, the sheets are dried in a circulating air oven at 105 ° C. d) Compounds of the type XYZ They are used to carry out the process of the variants of aqueous solutions, for example, which contain the following compounds XYZ: acid-12- (N-ethylamino) dodecane 1-phosphoric acid-12-hydroxydodecane 1- Phosphoric acid p-xylylene diphosphonic acid 1,22-diphenophonic acid e) Painting The sheets treated with the inventive aqueous solution are painted according to the various processes. Both were used from a cathodic electrodeposition paint and a dust cover and a polyester paint. The electrodeposition paint was electrolytically (cathodically) deposited on the sheets at a voltage of approximately 250 V and subsequently dried for 22 minutes at 180 ° C. The powder coating was applied to the sheets by electrostatic spraying and subsequently dried for 10 minutes at 200 ° C. The polyester paint system consisting of a primer or an upper layer. Both components were applied to the sheets by means of medical blades. In the primer for stuccoing, the paint had a layer thickness of 5 μm, while the top layer had a layer thickness of 25 μm. The primer coating temperatures were 216 ° C for the paint and 241 ° C for the upper cover.

Example 2: Test results The following table includes the results of the test obtained by using different substances according to the invention. The substances were contained in the inventive solutions at a concentration of approximately 10"J mol / 1. The ESS salt spray test reinforced by acetic acid reveals that the thin films produced according to the invention provide very good protection against underlying corrosion as against the comparative sheets; of the comparative sheets only the chromatized sheet is sufficiently protected against corrosion. The T-curved test was carried out under the condition T0, as well as the test of cross-section adhesion with Erichsen bonding reveals that the adherence of the paint in the treated sheets according to the invention is better than in the comparative sheets . In general, the results achieved by means of the invention are surprisingly good, as in the terms of corrosion resistance they are equivalent and in terms of adhesion of the paint they are clearly superior to the results achieved by means of chromatization. By means of an angle-dependent X-ray photoelectron spectroscopy (ARXPS) the orientation of the molecules of the XYZ-type compounds was determined. Due to the very limited escape depth of the characteristic photoelectrons, the angle-resolved X-ray photoelectron spectroscopy provides for varying information depth of the spectral data depending on the angle a. In the case of small angles, the information depth is in the range up to about 1 nm, and in the case of larger angles it is in the range of about 10 nm. This is provided to determine the orientation of the molecules. This method was described for example in the publication by Briggs, Practical Surface Analysis, 1990, Wiley & Sons, Chichester. Figure 1 shows the X-ray photoelectron spectrum of 12-acid (Ne ti 1 amino) dode 1-phosphoric in alloy of AIMgl in which the N / P ratio of XPS intensity is plotted depending on the angle a, where N is the intensity of the Nls peak of the ammo group, and P is the P2s peak of the phosphoric acid group, and where the abbreviation XPS symbolizes the term x-ray photoelectron spectroscopy. The spectrum shows that the phosphoric acid group attached to the metal surface, and the lower group is facing away from the metal surface.

Table Exp 1 i tions: ADPS = C2H5NH- (CH2) 12-Po (OH) 2 AUDS = NH2- (CH2) xo-COOH HDLS = OH- (CH2) ii-COOH XDPS = (OH) 2PO-CH2-C6H4- CH? -PO (OH HDPS = (OH) 2P02- (CH2) 12-OH DDPS = (OH) 2P0- (CH2) 12-P0 (OH) 2 0 = AIMgl original sheet G = AIMgl, subjected to alkaline tanning / acid P = AIMgl, AIMgl phosphatized, C = AIMgl, chromatized LPV = Labor-Pruf-Vorschr if ten (control of laboratory test at home)

Claims (13)

1. A process for treating metallic surfaces consisting of zinc, magnesium or aluminum or zinc, magnesium or aluminum alloys, and to which the lacquers, plastic covers, paints, sealants, alloy compounds or adhesives are applied after the treatment, characterized wherein the metal surfaces were treated at 10 to 100 ° C by dipping, spraying or winding with an aqueous solution having a pH value of 2 to 13 and containing 10 to 1 mol / l of one or more compounds of the XYZ type, where Y is an organic group with 2 50 carbon atoms and a linear chain structure, where X is a COOH-, HS03-, HS04-, (OH) .PO-, (OH) 2P02-, (OH) (OR ') PO- or group (OH) (OR ') P02-, where Z is an OH-, SH-, NH2-, NHR'-, CN-, CH = CH2-, OCN-, epoxide-, CH2 = CR "- COO-, acrylamide-, COOH-, (OH) 2PO-, (OH) 2P02-, (OH) (OR ' PO- or a group (OH) (OR ') P02-, where R' is an alkyl group with 1 to 4 carbon atoms, where R "is a hydrogen atom or an alkyl group with 1 to 4 atoms of carbon, and wherein the groups X and Z are each linked to the group Y in its terminal position.

2. The process as claimed in claim 1, characterized in that in the aqueous solution of 0.1 to 50% of the water are replaced by an alcohol with 1 to 4 carbon atoms, by acetone, by dioxane or by tetrahydrofuran.

3. The process as claimed in claims 1 to 2, characterized in that the aqueous solution contains one or more compounds of the XYZ type in a concentration that remains in the range of the critical micellization concentration.

4. The process as claimed in claims 1 to 3, characterized in that the aqueous solution contains a defoaming agent and / or a lubricant, each in an amount of 0.05 to 5% by weight.

5. The process as claimed in claims 1 to 4, characterized in that compounds of the type XYZ are present in the aqueous solution as salts.

6. The process as claimed in claims 1 to 5, characterized in that Y is a straight chain alkyl group, without branching with 2 to 20 carbon atoms, or a straight chain, unbranched group consisting of 1 to 4 cores Aromatic CdH connected in the para-position, or a group consisting of 1 or 2 straight-chain, unbranched alkyl residues, each with 1 to 12 carbon atoms as well as 1 to 4 aromatic C6H4 nuclei connected in the para-position .

7. The process as claimed in claim 6, characterized in that Y is a straight chain alkyl group, without branching with 10 to 12 carbon atoms or a group p -CH2-C. H, - CH2 - or a group p, p '-C6H-CbH-.

8. The process as claimed in claims 1 to 7, characterized in that X is a group (OH) 2P02- or (OH) (OR ') P02.

9. The process as claimed in claims 1 to 8, characterized in that Z is a group (OH) 2P02-, (OH) (OR ') P02 -, OH-, SH-, NHR'-, CH = CH2- or CH2 = CR "-COO-.

10. The process as claimed in claims 1 to 9, characterized in that, as XYZ-type compounds, the aqueous solution contains 12-mercaptododecane-1-phosphon-co-acid, 12- (N-et i-lamino) -dodecane. -phosphon? co, 12-dodecene-1-phosphonic acid, p-xylylene diphosphonic acid, 1,10-decane diphosphonic acid, 1,12-dodecane diphosphonic acid, 12-hydroxydodecane 1-phosphonic acid, ido- 12 - (N-et i lamino) dodecane 1-phosphorus, acid-12-mercaptododecane 1-phosphorus, 1,10-decane diphosphoric acid, 1,2-dodecane diphosphoric acid p, p -bi-phenyl diphosphoric, acid-12-acyl-ldodecane-1-phosphoric

11. The process as claimed in claims 1 to 10, characterized in that the immersion time is from 5 seconds to 20 minutes, the spray time is from 5 seconds to 15 minutes and the winding time is from 2 to 120 seconds.

12. The process as claimed in claims 1 to 11, characterized in that before 12. The process as claimed in claims 1 to 11, characterized in that before applying the aqueous solution, the metal surfaces are subjected to alkaline tanning and / or acid and then they are rinsed with water.

13. The process as claimed in claims 1 to 12, characterized in that the metal surfaces, to which the aqueous solution was applied by immersion or spraying, are subsequently rinsed with water and possibly dried in a nitrogen or stream of air, where The temperature of the nitrogen or air stream is 15 to 150 ° C.