WO2002033146A1

WO2002033146A1 - Bonding agent containing alkoxysilane for paint and adhesives on metal

Info

Publication number: WO2002033146A1
Application number: PCT/EP2001/011550
Authority: WO
Inventors: Bernd Mayer; Andreas Rathjens; Thomas Huver; Matthias Schweinsberg
Original assignee: Henkel Kommanditgesellschaft Auf Aktien; Cognis Deutschland Gmbh
Priority date: 2000-10-17
Filing date: 2001-10-06
Publication date: 2002-04-25
Also published as: DE10051485A1; AU2001293867A1

Abstract

The invention relates to a composition containing at least one solvent and at least one compound of general formula (I) wherein the radical R1 represents a linear or branched, saturated or unsaturated, optionally substituted alkyl radical having less than 8 C atoms; the radical R2 represents a linear or branched, saturated or unsaturated, optionally substituted alkoxy radical having 6 to 24 C atoms; and the radicals R?3 and R4¿ independently represent a linear or branched, saturated or unsaturated, optionally substituted alkyl radical or alkoxy radical having 1 to 24 C atoms. The invention also relates to a metal surface which can be obtained by bonding the surface of a metal by means of the inventive composition. The invention further relates to a method for the surface treatment of metals using the inventive composition, and the use of the inventive composition for the surface treatment of metals.

Description

Adhesion promoter containing alkoxysilane for lacquers and adhesives on metals

The present invention relates to a composition containing at least one solvent and at least one compound of the general formula I.

wherein the radical R, for a linear or branched, saturated or unsaturated, optionally substituted alkyl radical with less than 8 carbon atoms, the radical R ² for a linear or branched, saturated or unsaturated optionally substituted alkoxy radical with 6 to 24 carbon atoms and the radicals R ³ and R each independently represent a linear or branched saturated or unsaturated, optionally substituted alkyl radical or alkoxy radical having 1 to 24 carbon atoms. Furthermore, the invention relates to a metal surface, as can be obtained by contacting the surface of a metal with a composition according to the invention, a method for surface treatment of metals with a composition according to the invention and the use of the composition according to the invention for surface treatment of metals.

When processing metal parts, the problem often arises of permanently connecting a metal surface to a substrate consisting predominantly of polymers, for example an adhesive, a lacquer or another surface coating agent. Particularly in the case of metal components coated in this way, which are exposed to weathering or are used in climatically demanding interiors, the durability of the connection between the metal surface and the coating agent can be weakened by corrosion. In the past there has therefore been no lack of attempts to pretreat the metal surface with a surface coating agent in such a way that there is essentially no corrosion at the metal / polymer interface.

A frequently used means of preventing corrosion is, for example, the application of an inorganic conversion layer, for example a layer of zinc phosphate, or a chromate layer. Such layers usually passivate the metal surfaces, so that corrosion is suppressed.

For example, aluminum surfaces are often subjected to yellow chromating. Here, an acid chromate solution with a pH of 1 to 2 is used, which forms a protective layer on the aluminum surface of an insoluble aluminum-chromium (III) mixed oxide, on which no further corrosion takes place. However, the fact that the adhesion properties of most polymers to surfaces treated in this way are inadequate can have problems with such a surface treatment with regard to a surface coating with polymers. A loss of adhesive strength must therefore be assumed, particularly in the case of bonds. In addition, substrates treated in this way can release chromate ions, the emission of which into the environment is undesirable due to their toxic properties.

As an alternative to chromating, processes have been developed, for example, that effect a polymer coating of the metal surface. Although such pretreatment processes achieve good adhesion properties with regard to polymeric surface coating agents, the corrosion protection achieved is often not sufficient.

In addition to the methods mentioned so far, various attempts have been made to thin layers of low molecular weight on metal surfaces to produce organic compounds which are firmly attached to the metal surface and, in addition to passivating the metal surface, bring about improved adhesion to polymeric surface coating compositions.

For example, WO 98/29580 describes a method for treating metallic surfaces, in which a metal surface is treated with a solution of one or more compounds which, for example, each have at least one carboxylic acid, sulfonic acid or phosphonic acid group and at least one further functional group. A disadvantage of the specified compounds is that they generally have a high

Require synthetic effort, especially due to the asymmetrical

Substitution of cleaning effort considerably. In addition, the adhesive properties of polymeric surface coating agents on the surfaces treated according to the publication are sometimes unsatisfactory. Alkoxy silane-containing compounds are not described in the publication.

The object of the present invention was therefore to provide a composition which allows an improved surface treatment of metal substrates with a view to improving the corrosion-preventing action of such surface treatment agents.

The above-mentioned problem is solved by a composition as described in the further course of this text.

The present invention therefore relates to a composition comprising at least one solvent and at least one compound of the general formula (I)

wherein the radical R ¹ , for a linear or branched, saturated or unsaturated, optionally substituted alkyl radical having 8 or fewer C atoms, the radical R ² for a linear or branched, saturated or unsaturated, optionally substituted alkoxy radical having 6 to 24 C atoms and the radicals R ³ and R ⁴ each independently represent a linear or branched, saturated or unsaturated, optionally substituted alkyl radical or alkoxy radical having 1 to 24 carbon atoms.

In the context of the present invention, a “composition” is understood to mean a mixture which is liquid at room temperature and contains at least one solvent and at least one compound of the general formula I, as described above.

In the context of the present text, a solvent is understood to mean a liquid matrix in which the various ingredients of the composition according to the invention are present as finely distributed as possible. Such a fine distribution can be a true solution of the ingredients in the solvent, for example in the sense of a molecularly disperse distribution. However, the term "solvent" also includes liquid matrices in which the ingredients are distributed in the sense of an emulsion, i.e. do not form a molecularly disperse solution.

Suitable solvents are, for example, water and water-miscible and water-immiscible solvents. Suitable water-miscible solvents are, for example, primary or secondary mono- or polyalcohols with 1 to about 6 carbon atoms, such as methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, pentanol, hexanol, cyclohexanol or glycerin. Low molecular weight ketones such as acetone or methyl ethyl ketone or ether alcohols such as diethylene glycol or triethylene glycol are also suitable as water-miscible solvents. Also suitable in the context of the present invention are solvents which are immiscible or only miscible with water. These include, for example, ethers such as diethyl ether, dioxane or tetrahydrofuran, aromatic solvents such as toluene or xylene, halogenated solvents such as dichloromethane, chloroform or carbon tetrachloride and optionally substituted aliphatic solvents, which include, for example, the higher homologues of the abovementioned alcohols and ketones and paraffin hydrocarbons.

The solvents mentioned above can be used individually or as a mixture of two or more of the solvents mentioned. In the context of a preferred embodiment of the present invention, water is used as solvent, optionally in a mixture with one or more of the above-mentioned, preferably water-soluble solvents. If a solvent is to be used in the context of the present invention which contains water and a solvent which is not miscible with water, the solvent can, for example, contain an emulsifier in order to enable an essentially stable W / O or O / W emulsion.

If the composition according to the invention contains a mixture of water and a further water-miscible solvent, the proportion of water in such a mixture is preferably at least about 30% by weight or more, for example at least about 40 or at least about 50% by weight. In a particularly preferred embodiment of the present invention, the water content is at least about 75% by weight. Suitable combinations of water and water-miscible solvents are, for example, water / methanol, water / ethanol, water / propanol or water / isopropanol. A mixture of water and ethanol is preferred in the context of the present invention, the water content preferably being greater than about 75% by weight, for example greater than about 80 or about 85% by weight.

In addition to the solvent mentioned above, the composition according to the invention contains at least one compound of the general formula (I)

wherein the radical R ^{1 is} , for example, an optionally substituted linear or branched, saturated or unsaturated alkyl radical with 8 or fewer carbon atoms.

If the radical R ^{1 is} substituted, it can have, for example, only one substituent. However, it is also possible in the context of the present invention that the radical R ^{1 has} two or more substituents. Suitable substituents for the radical R ¹ are, for example, substituents selected from the group consisting of OH, SH, NH ₂ , NHR ⁵ , CN, OCN, epoxy, COOH, (OH) ₂ PO, (OH) ₂ PO ₂ -, (OH) (OR ⁵ ) PO- or (OH) (OR ⁵ ) PO ₂ -, where R is a linear or branched alkyl group with 1 to about 10 C atoms, in particular about 1, 2, 3 or 4 carbon atoms.

In the context of a preferred embodiment of the present invention, however, the radical R ¹ stands for an optionally substituted branched, saturated alkyl radical with 8 carbon atoms or less, for example 7, 6, 5, 4 or 3 carbon atoms. The radical R ¹ is preferably an unsubstituted radical, ie a radical containing only carbon and hydrogen atoms. R ¹ radicals which are preferred according to the invention are, for example, 2-ethylhexyl, tert-butyl, 2-butyl or isopropyl.

In the context of the present invention, the radical R ² stands for an optionally substituted, linear or branched, saturated or unsaturated alkoxy radical having 6 to 24 carbon atoms. In the context of a preferred embodiment of the present invention, the radical R ^{2 stands} for a linear, saturated, optionally substituted alkoxy radical having 8 carbon atoms or more. Suitable substituents for the radical R are, for example, substituents selected from the group consisting of OH, SH, NH ₂ , NHR ⁵ , CN, OCN, epoxy, COOH, (OH) ₂ PO, OH) ₂ PO ₂ -, (OH) (OR ⁵ ) PO-, (OH) (OR ⁵ ) PO ₂ - or Si (R ⁵ ) _m (OR ⁶ ) ₃ . _m - where R ⁵ and R ⁶ each independently represent a linear or branched alkyl group having 1 to about 10 C atoms, in particular about 1, 2, 3 or 4 C atoms, and m represents 0, 1, 2 or 3 stands.

In the context of a preferred embodiment of the present invention, R ^{2 represents} a linear alkoxy radical with at least one substituent selected from the above-mentioned group, in particular selected from the group consisting of OH, COOH, Si (R ⁵ ) _m (OR ⁶ ) ₃ . _m NH ₂ and NHR ⁵ , where R ⁵ , R ⁶ and m have the meaning already mentioned above. In a further preferred embodiment of the present invention, the radical R ^{2 has} at least one OH group or one amino group as a substituent.

Suitable radicals R ² are, for example, 8-hydroxyoctyl-l-oxy, 9-hydroxynonyl-1-oxy, 10-hydroxydecyl-l-oxy, 11-hydroxyundecyl-l-oxy 12-hydroxydodecyl-1-oxy, 13-hydroxytridecyl-l -oxy, 14-hydroxytetradecyl-l-oxy, 8-aminooctyl-l-oxy, 9-aminononyl-l-oxy, 10-aminodecyl-l-oxy, 11-aminoundecyl-l-oxy 12-aminododecyl-1-oxy, 13-aminotridecyl-l-oxy, 14-aminotetradecyl-l-oxy, 15-aminopentadecyl-1-oxy, 16-aminohexadecyl-1-oxy, 17-aminoheptadecyl-1-oxy or 18-aminooctadecyl-l-oxy or corresponding residues with terminal benzophenone residues.

In the context of the present invention, the R ³ and R ⁴ radicals each independently represent a linear or branched saturated or unsaturated, optionally substituted alkyl radical or alkoxy radical having 1 to 24 carbon atoms. Suitable substituents are those already mentioned in the discussion of the radical R ² . In the context of a preferred embodiment of the present invention, at most one R ³ or R ⁴ radical is an alkoxy radical. Preferred compounds of the general formula I are those in which, for example, R ^{3 represents} a methoxy or ethoxy radical and R ^{4 represents} a methyl, ethyl or propyl radical.

In a further preferred embodiment of the invention, the two radicals R ³ and R ⁴ each independently represent an alkyl radical, in particular a methyl radical, an ethyl radical or a propyl radical.

The composition according to the invention contains at least one compound of the general formula I. However, it is also envisaged that a composition according to the invention contains two or more different compounds of the general formula I. In a further embodiment of the present invention, the number of compounds of the general formula 1 is 2 to about 5, for example 2, 3 or 4.

In a further preferred embodiment of the present invention, the preparation according to the invention contains, as a compound of the general formula I, a compound selected from the group consisting of t-butyldimethylsilyl-12-hydroxydodecyl ether, t-butyldimethylsilyltetradecyl ether, t-butyldimethylsilyl-5-aminopentyl ether or a Mix of two or more of them.

In addition to a compound of the general formula I or a mixture of two or more compounds of the general formula I, the composition according to the invention can also contain one or more further additives. As a further additive, a composition according to the invention can, for example, be a compound of the general formula II

R ⁷ -X (II), include, wherein R ^{7 is} a linear or branched, saturated or unsaturated, optionally substituted alkyl radical having 2 to about 44 carbon atoms, optionally substituted aralkyl radical having 6 to about 44 carbon atoms, an optionally substituted aryl radical having 6 to about 44 carbon atoms Atoms or a heteroaryl radical and X for a functional group selected from the group consisting of COOH, HSO ₃ , HSO ₄ , (OH) ₂ PO (OH) ₂ PO ₂ , (OH) (OR ² ) PO and (OH) ( OR ² ) PO ₂ stands.

It is provided according to the invention that such a compound of the general formula II is unsubstituted. However, it is also possible according to the invention that such a compound of the general formula II has one or more substituents on the R ⁷ radical (apart from the functional group X). Suitable substituents are, for example, substituents such as OH, SH, NH ₂ , NHR ⁵ , CN, OCN, epoxy, COOH, (OH) ₂ PO-, (OH) ₂ PO ₂ -, (OH) (OR ⁵ ) PO- or (OH) (OR ⁵ ) PO ₂ -, where R ^{5 represents} a linear or branched alkyl group having 1 to about 10 C atoms, in particular about 1, 2, 3 or 4 C atoms ,

If a compound of the general formula II which has a linear or branched, saturated or unsaturated alkyl radical having 3 to 44 C atoms as the radical R is substituted in the sense of what has been discussed above, such a substituent is preferably an OH Group, a COOH group, an epoxy group, an amino group or an (OH) ₂ PO group. Mixtures of two or more different substituents, in particular acids and bases, for example COOH and amino groups, are likewise suitable, it being possible for the corresponding acid groups and base groups to be arranged, for example, in the β position with respect to one another (betaines) or for the acid group to be esterified (betaine ester).

The compounds of the general formula II used according to the invention can be used in the context of a preferred embodiment of the present

Invention for example 0, 1, 2, 3 or 4 substituents (except for the functional ones Group X) have. It is possible, for example, for all of the different compounds of the general formula II present in the composition according to the invention to have one or more such substituents on the R ⁷ radical. In the context of a preferred embodiment of the present invention, however, at least one of the compounds of the general formula II contained in the composition according to the invention has an unsubstituted radical R. In the context of a further preferred embodiment of the present invention, all radicals R of the compounds present in the composition according to the invention are general Formula II unsubstituted.

Compounds of the general formula II whose R ⁷ radical is derived from natural fatty acids or fatty acid cuts or their derivatives are particularly well suited for use in the composition according to the invention. Fatty acid residues which have at least about 6 carbon atoms, but preferably at least about 8 carbon atoms, are particularly suitable. Such R ⁷ radicals can have, for example, one or more OH groups or one or more olefinically unsaturated double bonds. Fatty acids are to be understood as aliphatic carboxylic acids of the formula R ⁸ -COOH, in which R ⁸ CO represents an aliphatic, linear or branched acyl radical having 6 to 22 carbon atoms and 0 and / or 1, 2 or 3 double bonds.

Typical examples are caproic acid, caprylic acid, 2-ethylhexanoic acid, capric acid, lauric acid, isotridecanoic acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, isostearic acid, oleic acid, elaidic acid, petroselinic acid, linoleic acid, linolenic acid, elaeostearic acid, arachidic acid, gadoleic acid, behenic acid and erucic acid and technical mixtures thereof , which occur, for example, in the pressure splitting of natural fats and oils, in the reduction of aldehydes from Roelen's oxosynthesis or in the dimerization of unsaturated fatty acids. Technical fatty acid cuts with 12 to 18 carbon atoms such as coconut, palm, palm kernel or tallow fatty acid are preferred.

If, in the context of the present invention, compounds of the general formula II are used in the composition according to the invention which have an alkyl radical as radical R ⁷ , it is particularly preferred if the alkyl radical is linear and has 8, 10 or 12 carbon atoms.

In the context of a further embodiment of the present invention, the radical R ⁷ in a compound of the general formula II can be, for example, an optionally substituted aralkyl radical with 6 to about 44 C atoms, an optionally substituted aryl radical with 6 to about 44 C atoms or a heteroaryl radical stand. With regard to the substituents, the requirements already mentioned above in the context of the discussion of the alkyl radicals apply.

Examples of suitable aryl radicals are biphenyl or benzophenyl.

It is preferred according to the invention if at least one of the general compounds present in the composition according to the invention

Formula II as functional group X has a COOH group. In the context of a further preferred embodiment, at least one compound of the general formula II has a COOH group as functional group X and at least one further compound of the general formula II has a COOH group, a (OH) ₂ PO group, a (OH) ₂ PO ₂ group, an (OH) (OR ⁵ ) PO-

Group, an (OH) (OR ⁵ ) PO ₂ group, an amino group, an OH group, a

Ester group or a combination of COOH and amino group

(Zwitterionic compound, especially betaine) or a combination of

COOR and amino group (especially betaine esters), wherein R ² and R ^{5 are} as defined above. In the context of the present invention, it is further preferred if the concentration of compounds of the general formula I or II or their mixture in the composition according to the invention is in a range from 10 ^" to 10 ^{" 4} mol / 1, based on the total composition according to the invention of all compounds of the general formula I and II present in the composition. The concentration can be selected such that it is within the critical micelle formation concentration (CMC) for at least one of the compounds present in the composition according to the invention. However, it is also possible and preferred in the context of the present invention if the concentration of the compounds of the general formulas I and II is chosen such that the CMC is not achieved for any of the compounds of the general formulas I and II present in the composition according to the invention. The CMC is understood to mean a variable which is characteristic of each of the compounds present in the composition according to the invention and at which the aggregation of the corresponding compounds to give micelles starts. The numerical value for the CMC for each of the compounds depends on the chemical constitution of the compound and on external parameters such as ionic strength, temperature and concentration of any other compounds present in the composition. The CMC can be determined, for example, by means of surface tension measurements. Here, for example with the help of the ring or plate method, the surface tension of a surfactant solution is determined as a function of its concentration at a constant temperature. Examples for determining the CMC can be found, for example, in "Die Tenside", published by V. Kosswig & Stächen, Carl-Hansa-Verlag, Munich, Vienna, 1993.

The concentration of those present in the composition according to the invention

Compounds are preferably chosen so that the composition according to the invention does not contain any micelles, ie for each of the compounds present in the composition according to the invention general formula I and II the CMC is currently undercut. Here, for example, in a range from about 10% to about 0.001% or about 5, 4, 3, 2 or 1% to about 0.05, 0.1, 0.2 or 0.5%, based on the CMC respective compound of general formulas I and II.

In the context of a preferred embodiment, the composition according to the invention has a pH of about 2 to about 12, preferably of about 5 to about 9 and in particular about 6 to about 8. Accordingly, it is also possible that the composition according to the invention contains the compounds of the general formula I, provided that this compound has a substituent which is due under the specified conditions for salt formation, and II in the form of their salts, preferably their alkali metal salts, for example in the form of their sodium or potassium salts , contains.

In the context of a further embodiment of the present invention, the composition according to the invention may contain further additives in addition to the ingredients already described. Suitable additives are, for example, defoamers, preservatives or thickeners.

In the context of a preferred embodiment of the present invention, the composition according to the invention optionally contains additives in an amount of up to about 5% by weight, based on the total composition. However, the proportion of additives is preferably below this value, for example in an amount from approximately 0.01 to approximately 3% by weight or approximately 0.05 to approximately 2% by weight.

The composition according to the invention is suitable for the surface treatment of metals. In principle, all metals are suitable as substrates, for example noble or non-noble metals. However, particularly good results can be achieved when the composition according to the invention is used if metal surfaces are treated which contain a proportion of metal oxides exhibit. Examples of suitable metals are aluminum, aluminum alloys, magnesium, magnesium alloys, iron, copper, nickel, steel or zinc.

The metal surfaces suitable for treatment with the composition according to the invention can be structured regularly or irregularly with respect to the three-dimensional shape of the metal body on which the metal surface is based, the metal body being able to have a spatial extent in the range from a few μm to several hundred meters. In principle, the upper limit for the spatial expansion of a metal body suitable for treatment with the compositions according to the invention is limited exclusively by the method used in each case for applying the composition according to the invention.

For example, metal powder or metal granules with small spatial dimensions can be treated with the composition according to the invention. In the context of a preferred embodiment of the present invention, however, regular metal surfaces, for example sheets, metal strips (coil coating) or other components such as are used, for example, in automobile, aircraft or shipbuilding, are treated with the composition according to the invention.

The treatment of the metal surfaces with the composition according to the invention can be carried out by customary methods, for example by dipping, spraying, knife coating, painting or rolling. The temperature when applied should be about 10 to about 95 ° C, for example about 15 to about 80 ° C or about 20 to about 50 ° C. If the composition according to the invention is applied to the metal surface by dipping, the dipping time should be used to separate the compounds of the general formula I or the mixture contained in the composition according to the invention Nerbindungen of general formulas I and II must be dimensioned sufficiently. Suitable periods are in the range of about 5 seconds to about 15 minutes, for example about 10 seconds to about 5 minutes. If the composition according to the invention is applied by spraying, contact times should be maintained which are approximately in the range mentioned above. When applied by rolling, a contact time of approximately 1 second to approximately 5 minutes, for example approximately 5 seconds to approximately 2 minutes or approximately 10 seconds to approximately 1 minute, is usually sufficient.

After treatment with the composition according to the invention, the metal surface can be rinsed or dried, for example. Drying can be carried out, for example, with an air or nitrogen stream, and the temperature of the air or nitrogen stream used for drying can be about 50 to about 150 ° C.

Before treatment with the composition according to the invention, the receptivity for the compounds of the general formula I or I and II contained in the composition according to the invention can be improved by suitable neat treatment steps.

In the context of a preferred embodiment of the invention, the surfaces to be treated with a composition according to the invention should first be degreased. In principle, all degreasing processes are suitable for this purpose, which remove fat from the metal surface in such a way that the subsequent treatment methods are successful. A weakly alkaline cleaner is preferably used to degrease the surfaces to be treated.

Suitable further pretreatment steps are, for example, alkaline or acidic stains. Particularly when aluminum is used as the metal, it is advisable to use the surface treatment according to the invention Composition upstream of a pickling step and a pickling step to adjust the density of OH groups on the metal surface. A pretreatment of aluminum carried out in the context of a preferred embodiment of the present invention includes, for example, first degreasing the aluminum surface, then pickling, which can be carried out, for example, in an alkaline manner with the addition of nitrate and gluconate, and a final pickling step with nitric acid.

The present invention therefore also relates to a method for surface treatment of metals, in which metal is contacted with a composition according to the invention.

The metal surfaces obtainable by using the composition according to the invention have, for example after application of a surface coating, improved corrosion resistance in the sense of infiltration of the applied surface coating agent by corrosion. The present invention therefore also relates to metal surfaces as can be obtained by contacting the surface of a metal with a composition according to the invention.

Another object of the present invention is the use of a composition according to the invention for the treatment of metal surfaces.

The invention is explained in more detail below by examples.

Examples

Aluminum sheets were first degreased (P3-Almeco 18, manufacturer: Henkel Surface Technologies), then pickled (alkaline, with the addition of nitrate and gluconate) and pickled with nitric acid. Then were various adhesion promoters are applied, the sheets are then dried and coated with a polyester-based powder coating. On the one hand, the standards were the only cleaned aluminum surface and the surface pretreated with a commercially available chromating agent.

The sample sheets were tested in a CASS test (Copper Accelerated Acidic Salt Spray Test, 240 hours, DIN 50021-CASS according to ASTM B 368-68). The paint infiltration at the Ritz was checked here. The sheet was rated "OK" ("OK") if the paint could not be infiltrated at the Ritz. A Filiform test (1000 hours, European standard EN 3665 from 1997) was also carried out, the table below showing the square root of the product from the number and length of the threads. The Filiform test was rated as "passed" if the result was 2 or less.

Table 1: Test results

k. H. = no liability

Claims

claims

1. Composition comprising at least one solvent and at least one compound of the general formula (I)

wherein the radical R ¹ , for an optionally substituted, saturated or unsaturated, linear or branched alkyl radical with 8 or fewer C atoms, the radical R for an optionally substituted, saturated or unsaturated, linear or branched alkoxy radical with 6 to 24 C atoms and the radicals R ³ and R each independently represent a linear or branched, saturated or unsaturated, optionally substituted alkyl radical or alkoxy radical having 1 to 24 carbon atoms.

2. Composition according to claim 1, characterized in that R ^{1 stands} for an unsubstituted, branched alkyl radical having at most 6 carbon atoms.

3. Composition according to claim 1 or 2, characterized in that R ² as a substituent is an OH, SH, NH ₂ , NHR ⁵ , CN, OCN, epoxy,

COOH-, (OH) ₂ PO-, (OH) ₂ PO ₂ -, (OH) (OR ⁵ ) PO-, (OH) (OR ⁵ ) PO ₂ - or Si (R ⁵ ) _m (OR ⁶ ) ₃ _ has _m group, where R ⁵ and R ⁶ each independently represent a linear or branched alkyl group having 1 to about 10 carbon atoms, in particular about 1, 2, 3 or 4 carbon atoms, and m is 0.1 , 2 or 3 stands.

4. Composition according to one of claims 1 to 3, characterized in that R ¹ in the general formula (I) represents a t-butyl radical.

5. Composition according to one of claims 1 to 4, characterized in that the solvent contains at least 80 wt .-%, based on the solvent, water.

6. Composition according to one of claims 1 to 5, characterized in that as a compound of general formula I a

A compound selected from the group consisting of t-butyldimethylsilyl-12-hydroxydodecyl ether, t-butyldimethylsilyltetradecyl ether, t-butyldimethylsilyl-5-aminopentyl ether or a mixture of two or more thereof is contained.

7. Metal surface, obtainable by contacting the surface of a metal with a composition according to any one of claims 1 to 6.

8. A method for the surface treatment of metals, in which a metal with a composition according to one of claims 1 to 6 is contacted.

9. The method according to claim 8, characterized in that the metal is at least cleaned before contacting.

10. Use of a composition according to any one of claims 1 to 6 for the treatment of metal surfaces.