EP2091980A2

EP2091980A2 - Anti-corrosion agent forming a coating film with good adhesion and method for non-galvanic application thereof

Info

Publication number: EP2091980A2
Application number: EP07818234A
Authority: EP
Inventors: Michael Dornbusch; Elke Austrup; Horst HINTZE-BRÜNING
Original assignee: BASF Coatings GmbH
Current assignee: BASF Coatings GmbH
Priority date: 2006-11-13
Filing date: 2007-09-19
Publication date: 2009-08-26
Also published as: US20100040798A1; WO2008058586A3; US8399061B2; JP2010509470A; CN101535356A; JP6049821B2; AR063783A1; DE102006053291A1; WO2008058586A2; EP2133371B1; ATE524503T1; CN103265833A; JP2016020497A; KR20090089381A; EP2133371A1

Abstract

The invention relates to an aqueous coating agent for metal substrates, comprising a water-dispersible and/or water-soluble polymer P with a gradient in the concentration of covalently bonded hydrophilic groups along the polymer backbone, wherein the polymer P has covalently bonded ligands A which form chelates with the metal ions released on corrosion of the substrate and/or the substrate surface and cross-linked functional groups B which can form covalent bonds with itself, with further complementary functional groups B' on the polymer P and/or with further functional groups B and/or B' on cross-linkers V.

Description

Lacquer-layer-forming corrosion protection agent with good adhesion and method for its current-free application

Methods and coating compositions for the current-free corrosion protection coating of various metal substrates are known. They offer in comparison to anodic or cathodic dip coating (ATL or KTL), in which the application of electrical voltages is necessary, in particular the advantage of simpler and cheaper process and the shorter process time. In particular, cavities in or edges on the substrates to be coated can be better coated with the electroless methods than with methods in which the application of electrical voltages is necessary.

In the electroless anticorrosion coating, also called ACC process (Autophoretic Chemical Coating), polymers, for example emulsion polymers containing acrylates or styrene / butadiene, are used, which are anionically stabilized. Compared to the aforementioned ATL and KTL methods, however, the ACC methods have the disadvantage that the deposited layers have defects that make the substrate significantly more susceptible to corrosion. Therefore, such deposited by ACC process layers are usually processed by rinsing with chromium-containing aqueous coating compositions to improve the corrosion protection at the defects. Recently, however, it has been found that chromium-containing coating agents have great problems with environmental compatibility and must be classified as highly hazardous to health. Therefore, one strives to completely replace chromium in corrosion protection coatings.

As a result of the development of chromium-free coating compositions, it has furthermore been found that ACC coating compositions containing salts of the lanthanide and the d elements and an organic film-forming component likewise ensure very good corrosion protection comparable to chromium-containing coating compositions. In WO-A-01/86016 a corrosion inhibitor is described which contains a vanadium component and a further component which contains at least one metal selected from zirconium, titanium, molybdenum, tungsten, manganese and cerium. A disadvantage of corrosion protection agents according to WO-A-01/86016 is the tendency of the metal ions formed from the substrate to migrate through the deposited corrosion protection layer, since the polymers lead to a defective film formation.

In WO-A-99/29927 a chromium-free aqueous corrosion inhibitor is described which contains as components hexafluoro anions of titanium (IV) and / or zirconium (IV), vanadium ions, transition metal ions and phosphoric and / or phosphonic acid. A disadvantage of corrosion inhibitors according to WO-A-99/29927 is the tendency of the metal ions formed from the substrate to migrate through the deposited corrosion protection layer, since the polymers lead to poor film formation, and the use of ecologically critical substances, in particular hydrofluoric acid or fluorides.

WO-A-96/10461 describes an aqueous corrosion inhibitor containing as components anions having a central atom selected from the group titanium, zirconium, hafnium, silicon, and at least 4 fluorine atoms as ligands and an organic polymer dispersion. A disadvantage of the invention according to WO-A-96/10461 is that in the deposition of the anti-corrosive agent on the substrate surface, the polymer dispersion particles flocculate and form a small contact surface with the surface. Furthermore, the latex particles have the disadvantage of having a lower migration rate in the diffusion in cavities or on edges of three-dimensional substrates in comparison to molecular dispersed polymers. In addition, layers of a thickness between 1 micrometer and 1 mm are formed, which requires a corresponding material requirement per surface area. unit of the substrate to be coated. Another disadvantage is the tendency of the metal ions formed from the substrate to migrate through the deposited anticorrosive layer and the use of ecologically critical substances, in particular fluoric acid or fluorides.

DE-A-37 27 382 comprises chromium-free aqueous dispersions of adducts of carboxylic acids and isocyanates with epoxides, which are suitable for the autophoretic coating of metallic surfaces. Such dispersions have in dispersed form a particle diameter of less than 300, preferably between 100 and 250 nm and can be crosslinked after deposition on the metal surface at temperatures between 60 and 200 ⁰ C. Such latex particles also have the disadvantage of having a lower migration rate in the diffusion in cavities or on the edges of three-dimensional substrates than in the case of polymers dispersed in the molecular dispersion. In addition, layers of a thickness between 1 micrometer and 1 mm are formed, which causes a corresponding material requirement per unit area of the substrate to be coated and a tendency to cracking during drying. Another disadvantage is the tendency of the metal ions formed from the substrate to migrate through the deposited anticorrosive layer and the use of ecologically critical substances, in particular hydrofluoric acid or fluorides.

DE-A-103 30 413 describes coating compositions which are suitable for coating metallic surfaces and which may contain caprolactam-modified polyisocyanates based on polyethyleneimines. The coating compositions can be applied by dip coating and, after drying, have thicknesses of between 1 and 300 micrometers. So made layers also have a high material requirement and tend to crack during drying.

Task and solution

In the light of the aforementioned prior art, it was the object of the invention to find an ecologically largely harmless corrosion inhibitor, which can be applied to the substrate to be protected by means of a technically simple process. In particular, the corrosion inhibitor should largely prevent the migration of the metal ions formed from the substrate and be deposited well on edges and in cavities of the substrate. Furthermore, in particular the tendency to crack formation during drying of the layer should be kept as low as possible. Furthermore, the influence of foreign metal ions should be kept as low as possible and an effective corrosion protection should be achieved with comparatively low use of material. In particular, the access of polar corrosive substances, such as particularly corrosive salts, to the surface of the metal substrate should be effectively prevented. Furthermore, the conversion protection should develop effective protection for as many different metal substrates and be largely independent of the redox potential of the substrate to be coated.

In the light of the aforementioned objects, an aqueous coating composition was found which contains a water-dispersible and / or water-soluble polymer P having a gradient in the concentration of covalently bonded hydrophilic groups HG along the polymer main chain, the polymer P furthermore having covalently bonded ligands A, which form chelates with the metal ions liberated during the corrosion of the substrate and / or with the substrate surface, and furthermore have crosslinking functional groups B which react with themselves, with further functional groups B ' of the polymer P and / or with further functional groups B and / or B 'to crosslinkers V can form covalent bonds.

Furthermore, a process has been found for the autodeposition of an aqueous coating agent for metallic substrates with a good corrosion protection, which contains a water-dispersible and / or water-soluble polymer P with a gradient in the concentration of covalently bonded hydrophilic groups HG along the polymer main chain, wherein the polymer P continues having covalently bonded ligands A, which form chelates with the metal ions liberated in the corrosion of the substrate and / or with the substrate surface, as well as further crosslinking functional groups B, which with itself, with further functional groups B 'of the polymer P and / or With further functional groups B and / or B ', crosslinking agents V can form covalent bonds, the thickness of the coating agent after autodeposition being between 5 and 900 nm.

In a further preferred embodiment of the method according to the invention, the substrate is pretreated with a corrosion protection agent K before the deposition of the corrosion protection agent according to the invention in a further upstream process step.

Description of the invention

The coating composition of the invention

The water-dispersible and / or water-soluble polymers P of the coating composition according to the invention have a gradient in the concentration of covalently bonded hydrophilic groups HG along the polymer main chain and carry ligands A, which with form the chelates released in the corrosion of the substrate, as well as crosslinking functional groups B ₁ which can form covalent bonds to crosslinkers V with itself and / or with further functional groups C.

For the purposes of the invention, water-dispersible or water-soluble means that the polymers P in the aqueous phase form aggregates having an average particle diameter of <50, preferably <35 and particularly preferably <20 nm or are dissolved in molecular dispersion. Thus, such aggregates differ significantly in their average particle diameter of dispersion particles, as described for example in DE-A-37 27 382 or WO-A-96/10461. Molecular dispersions of dissolved polymers P generally have molecular weights of <100,000, preferably <50,000, more preferably <20,000 daltons. The size of the aggregates consisting of polymer P can preferably be accomplished in a manner known per se by introduction of hydrophilic groups HG on the polymer P.

Essential for the invention is that the hydrophilic groups HG form a gradient in their concentration along the main polymer chain. The gradient is defined by a slope in the spatial concentration of the hydrophilic groups along the polymer backbone. Polymers P thus constructed are capable of forming micelles in the aqueous medium and have a surface activity on the surface of the substrate to be coated, that is, the interfacial energy of the coating composition according to the invention on the surface to be coated is reduced. The gradient is preferably generated by suitable arrangement of monomeric units which make up the polymer and which carry hydrophilic groups and / or groups in which hydrophilic groups HG can be generated, in a manner known per se. Preferred hydrophilic groups HG on the polymer P are ionic groups such as in particular sulfate, sulfonate, sulfonium, phosphate, phosphonate, phosphonium, ammonium and / or carboxylate groups and nonionic groups, in particular hydroxyl, primary, secondary and / or tertiary amine, amide and / or oligo- or polyalkoxy substituents, such as preferably ethoxylated or propoxylated substituents, which may be etherified with further groups. The hydrophilic groups HG may be identical to the ligands A and / or crosslinking functional groups B and B 'described below.

The number of hydrophilic groups HG on the polymer P depends on the solvating power and the low accessibility of the groups HG and can likewise be set by the person skilled in the art in a manner known per se.

The polymer backbone of the polymers P can be any desired polymers, preferably those having average molecular weights Mw of 500 to 50,000 daltons, more preferably having molecular weights Mw of 700 to 20,000 daltons. The polymer backbone used are preferably polyolefins or poly (meth) acrylates, polyurethanes, polyalkyleneimines, polyvinylamines, polyalkyleneamines, polyethers, polyesters and polyalcohols which are in particular partially acetalated and / or partially esterified. The polymers P can be linear, branched and / or dendritic. Very particularly preferred polymer backbones are polyalkyleneimines, polyvinylamines, polyalcohols and in particular poly (meth) acrylates.

The polymers P are preferably hydrolysis-stable in the acidic pH range, in particular at pH values <5, particularly preferably at pH values <3. Suitable ligands A are all groups or compounds which can form chelates with the metal ions released upon corrosion of the substrate. As a rule, the ligands A are randomly distributed in the polymer P. Preference is given to mono- and / or polydentate potentially anionic ligands. Particularly preferred ligands are

optionally functionalized ureas and / or thioureas, in particular acylthioureas such as, for example, benzoylthiourea, optionally functionalized amines and / or polyamines, in particular EDTA,

optionally functionalized amides, in particular carboxylic acid amides

Imines and imides, in particular imin-functionalized pyridines, oximes, preferably 1,2-dioximes, such as functionalized diacetyldioxime,

Organosulfur compounds, such as, in particular, optionally functionalized thiols such as thioethanol, thiocarboxylic acids, thio-aldehydes, thioketones, dithiocarbamates, sulfonamides, thioamides and particularly preferably sulfonates,

Organophosphorus compounds, in particular phosphates, particularly preferably phosphoric acid esters of (meth) acrylates, and also phosphonates, particularly preferably vinylphosphonic acid and hydroxy-, amino- and amido-functionalized phosphonates, optionally functionalized organoboron compounds, in particular boric acid esters,

optionally functionalized polyalcohols, in particular carbohydrates and derivatives thereof, and chitosans,

optionally functionalized acids, in particular di- and / or oligofunctional acids, or optionally functionalized (poly) carboxylic acids, in particular carboxylic acids, which are bonded to metal centers ionically and / or coordinately can, preferably (poly) methacrylates with acid groups o- or di- or oligofunctional acids,

optionally functionalized carbenes,

- Acetylacetonates, - optionally functionalized heterocycles, such as quinolines, pyrrolidines, in particular iminfunktionalisierte pyridines, pyrimidines pyrroles, furans, thiophenes, imidazoles, benzimidazoles, preferably mercaptobenzimidazoles, benzothiazoles, oxazoles, thiazole, pyrazoles or indoles, - optionally functionalized Acetylenes, as well

- phytic acid and its derivatives.

Suitable crosslinking functional groups B on the polymer P are those which can form covalent bonds with themselves and / or with complementary functional groups B '. As a rule, the crosslinking functional groups B are randomly distributed over the polymer P. The covalent bonds are preferably formed thermally and / or by the action of radiation. Particularly preferably, the covalent bonds are formed thermally. The crosslinking functional groups B and B 'cause the formation of an intermolecular network between the molecules of the polymer P.

Radiation-crosslinking functional groups B or B 'have activatable bonds, such as, for example, carbon-hydrogen, carbon-carbon, carbon-oxygen, carbon-nitrogen, carbon-phosphorus or carbon-silicon. Single or double bonds. In this case, carbon-carbon double bonds are particularly advantageous. Particularly suitable carbon-carbon double bonds as groups B are

- Particularly preferably (meth) acrylate groups

- Ethyl acrylate groups - vinyl ether and vinyl ester groups

- crotonate and cinnamate groups

- allyl groups

- dicyclopentadienyl groups - norbornyl and isoprenyl groups

- Isopropenyl or butenyl groups.

Thermally crosslinking functional groups B can form covalent bonds with themselves or preferably with complementary crosslinking functional groups B 'under the influence of thermal energy.

Particularly suitable thermal crosslinking functional groups B and B 'are

- Particularly preferably hydroxyl groups

Mercapto and amino groups,

- aldehyde groups,

- azide groups,

Acid groups, in particular carboxylic acid groups, acid anhydride groups, in particular carboxylic anhydride groups,

Acid ester groups, in particular carboxylic acid ester groups,

Ether groups,

particularly preferably carbamate groups, urea groups,

- epoxide groups,

Particularly preferably isocyanate groups, which are very particularly preferably reacted with blocking agents which deblockieren at the stoving temperatures of the coating compositions of the invention and / or are incorporated without deblocking in the forming network. Particularly preferred combinations of thermally crosslinking groups B and complementary groups B 'are:

Hydroxyl groups with isocyanate and / or carbamate groups, amino groups with isocyanate and / or carbamate groups,

- Carboxylic acid groups with epoxide groups.

Particularly preferred polymers P contain copolymers PM, which can be prepared by single-stage or multistage, free-radical copolymerization in an aqueous medium

a) olefinically unsaturated monomers (a1) and (a2), where (a1) in each case at least one monomer from the group consisting of olefinically unsaturated monomers (a11) having at least one hydrophilic group HG, from the group consisting of olefinically unsaturated monomers (a12) with at least ligand group A and from the group consisting of olefinically unsaturated monomers (a13) having at least one crosslinking group B.

and

b) at least one olefinically unsaturated monomer of the general formula I which is different from the olefinically unsaturated monomers (a1) and (a2)

R ¹ R ² C = CR ³ R ⁴ (I),

in which the radicals R ¹ , R ² , R ³ and R ⁴ each independently of one another represent hydrogen atoms or substituted or unsubstituted alkyl, cycloalkyl, alkylcycloalkyl, cycloalkylalkyl, aryl, alkylaryl, cycloalkylaryl-arylalkyl- or Arylcycloalkylreste, with the proviso that at least two of the variables R ¹ , R ² , R ³ and R ^{4 are} substituted or unsubstituted aryl, arylalkyl or Arylcycloalkylreste, in particular substituted or unsubstituted aryl radicals.

Suitable hydrophilic monomers (a11) contain at least one hydrophilic group (HG), which, as described above, preferably from the group consisting of sulfate, sulfonate, sulfonium, phosphate, phosphonate, phosphonium, ammonium and / or carboxylate groups and also hydroxyl, primary, secondary and / or tertiary amine, amide groups and / or oligo- or polyalkoxy substituents, such as preferably ethoxylated or propoxylated substituents, which may be etherified with further groups. Examples of suitable hydrophilic monomers (a11) are acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, maleic acid, fumaric acid or itaconic acid and salts thereof, preferably acrylic acid and methacrylic acid, olefinically unsaturated sulfonic, sulfuric, phosphoric or phosphonic acids, their salts and / or their salts Teilester. Also suitable are olefinically unsaturated sulfonium and phosphonium compounds. Also very suitable are monomers (a11) which carry at least one hydroxyl group or hydroxymethylamino group per molecule and are essentially free of acid groups, such as in particular hydroxyalkyl esters of alpha, beta-olefinically unsaturated carboxylic acids, such as hydroxyalkyl esters of acrylic acid, methacrylic acid and ethacrylic acid, in which Hydroxyalkyl group contains up to 20 carbon atoms, preferably 2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 3-hydroxybutyl, 4-hydroxybutyl acrylate, methacrylate, formaldehyde adducts of aminoalkyl esters of alpha, beta-olefinically unsaturated carboxylic acids and of alpha , beta-unsaturated carboxylic acid amides such as N-methylol and N, N-dimethylol-aminoethyl acrylate, - aminoethyl methacrylate, -acrylamide and -methacrylamide. As Amingrup pen-containing monomers (a11) are suitable: 2-aminoethyl acrylate and methacrylate, N-methyl and N, N-dimethyl-aminoethyl acrylate, or AIIy- lamin. Amide group-containing monomers (a11) are preferably amides of alpha, beta-olefinically unsaturated carboxylic acids, such as (meth) acrylamide, preferably N-methyl or N, N-

Dimethyl (meth) acrylamide used. As ethoxylated or propoxylated monomers (a11) it is preferred to use acrylic and / or methacrylic acid esters of polyethylene oxide and / or polypropylene oxide units whose chain length is preferably between 2 and 20 ethylene oxide or propylene oxide building blocks.

When selecting the hydrophilic monomers (a11) care should be taken to avoid the formation of insoluble salts and polyelectrolyte complexes.

Examples of suitable monomers (a12) are olefinically unsaturated monomers which have the above-described ligands A as substituents. Examples of suitable monomers (a12) are esters and / or the amides of acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, maleic acid, fumaric acid or itaconic acid, in particular of acrylic and / or methacrylic acid, which contain the ligands A in ester and / or Have amide radical. Preferred ligands A are optionally functionalized urea and / or thiourea subtituents, optionally functionalized amine and / or polyamine subtynes, imine and imide substituents, in particular imin-functionalized pyridines, oxime substituents, preferably 1,2-dioximes such as functionalized diacetyldioxime, Organosulfur substituents, in particular derivable from optionally functionalized thiols such as thioethanol, thiocarboxylic acids, thioaldehydes, thioketones, dithiocarbamates, sulfonates, thioamides and particularly preferably sulfonates, organophosphorus substituents, in particular derivable from phosphates, particularly preferably phosphoric acid esters of (meth) acrylates, and Phosphonates, particularly preferably vinylphosphonic acids and hydroxy-, amino- and amido-functionalized phosphonates, optionally functionalized organoboron substituents, in particular derivable from boric acid esters, optionally functionalized polyalcohol substituents, in particular derivable from carbohydrates and derivatives thereof and chitosans, optionally functionalized acid substituents, in particular derivable from di- and / or oligofunctional acids, or optionally functionalized (poly) carboxylic acids, in particular carboxylic acids which can be ionically and / or coordinately bonded to metal centers, preferably (poly) methacrylates with acid groups or di- or oligofunctional Acids, substituents with optionally functionalized carbenes, acetylacetonates, optionally functionalized acetylenes, as well as phytic acids and derivatives thereof.

Examples of suitable monomers (a13) are olefinically unsaturated monomers which have the above-described ligands B as substituents. Examples of suitable monomers (a13) are esters and / or the amides of acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, maleic acid, fumaric acid or itaconic acid, in particular of acrylic and / or methacrylic acid, which contain the crosslinking groups B in ester and / or or amide radical. Particularly preferred crosslinking groups B are hydroxyl groups, and also, for example, mercapto and amino groups, aldehyde groups, azide groups, acid groups, especially carboxylic acid groups, acid anhydride groups, especially carboxylic anhydride groups, acid ester groups, especially carboxylic acid ester groups, ether groups, more preferably carbamate groups, for example urea groups, epoxy groups, and particularly preferably isocyanate groups which are very particularly preferably reacted with blocking agents which, at the stoving temperatures, of the coating compositions according to the invention Deblock and / or be incorporated without unblocking in the forming network.

The monomers (a1 1) are arranged in the polymer PM in such a way that the already described gradient of the hydrophilic groups HG results along the polymer main chain. This is usually due to the specific copolymerization parameters of the different monomers (a1 1), (a12), (a13), (a2) and (b) in the aqueous reaction medium. The aforementioned monomers (a12) and (a13) are preferably randomly arranged along the main polymer chain. From the above performance of the exemplified monomers (a1 1), (a12) and (a13) it is apparent that the hydrophilic groups HG, the ligands A and the crosslinking groups B can be partially or completely identical. In this case, the ligands A and the crosslinking functional groups B also usually have a gradient along the polymer main chain.

Examples of preferred olefinically unsaturated comonomers (a2) are

(1) substantially acid-group-free esters of olefinically unsaturated acids, such as (meth) acrylic acid, crotonic acid, ethacrylic acid, vinylphosphonic acid or vinylsulfonic acid alkyl or cycloalkyl esters having up to 20 carbon atoms in the alkyl radical, in particular methyl, ethyl, propyl, n-butyl, sec-butyl, hexyl, ethylhexyl, stearyl and lauryl, cyclohexyl (meth) acrylate and

(Meth) acrylic esters with mixed alkyl radicals, such as, for example, C13- (meth) acrylate (linear alkyl radicals having an average of 13 C atoms);

(2) Vinyl esters of alpha-branched monocarboxylic acids having 5 to 18 carbon atoms in the molecule, such as the vinyl esters of Versatic © acid marketed under the trademark VeoVa ®; such as

(3) vinylaromatic hydrocarbons, such as styrene, vinyltoluene or alpha-alkylstyrenes, especially alpha-methylstyrene;

As monomers (b) compounds of general formula I are used. In the general formula I, the radicals R ¹ , R ² , R ³ and R ^{4 are} each independently hydrogen or substituted or unsubstituted alkyl, cycloalkyl, alkylcycloalkyl, cycloalkylalkyl, aryl, alkylaryl, cycloalkylaryl-arylalkyl or arylcycloalkyl radicals, with the proviso that at least two of the variables R ¹ , R ² , R ³ and R ^{4 are} substituted or unsubstituted aryl, arylalkyl or arylcycloalkyl radicals, in particular substituted or unsubstituted aryl radicals. Examples of suitable radicals R ¹ , R ² , R ³ and R ⁴ are further described, for example, in DE-A-198 58 708.

Examples of monomers (b) used particularly preferably according to the invention are diphenylethylene, dinaphthaleneethylene, cis- or trans-stilbene, vinylidene bis (4-N, N-dimethylaminobenzene), vinylidene bis (4-aminobenzene) or vinylidene bis (4- nitrobenzene). With regard to the reaction procedure and the properties of the resulting copolymers (PM), diphenylethylene is of very particular advantage and is therefore used with very particular preference in accordance with the invention.

In the preparation of the copolymers PM, the mixture of all monomers is preferably metered into the water phase at the same time, the gradient of hydrophilic groups along the polymer chain by the formation of oligo- or polymers with initially high concentration of hydrophilic groups along the polymer chain sets and wherein im As the chain continues to grow, the number of decreases hydrophilic groups along the polymer chain. The concentration gradient of the hydrophilic groups along the polymer chain can also be realized via a feed of temporally and / or spatially different compositions of the monomer mixture from (a11), (a12), (a13), (a2) and (b) in a manner known per se , With regard to the preparation of the copolymers PM, reference is further made to the teachings of DE-A-198 58 708, DE-A-102 06 983 and DE-A-102 56 226.

As crosslinkers V with groups B and / or B 'thermally and / or by radiation-crosslinking groups, in principle all crosslinkers known to the person skilled in the art are suitable. Preference is given to low molecular weight or oligomeric crosslinkers V having a molecular weight of <20,000 daltons, more preferably <10,000 daltons. The backbone of the crosslinker V carrying the crosslinking groups B and / or B 'can be linear, branched and / or hyperbranched. Preference is given to branched and / or hyperbranched structures, in particular those as described, for example, in WO-A-01/46296. The crosslinkers V are preferably hydrolyzable in the acidic pH range, in particular at pH values <5, particularly preferably at pH values <3.

Particularly preferred crosslinkers V carry the above-described crosslinking groups B and / or B ', which react with the crosslinking groups of the polymer P with the formation of covalent bonds. Very particular preference is given to crosslinkers V with groups B and / or B 'that crosslink thermally and, if appropriate, additionally by the action of radiation.

In a further particularly preferred embodiment of the invention, the crosslinkers V carry in addition to the crosslinking groups B and / or B 'ligands A', which may be identical to and / or different from the ligands A of the polymer P. Particularly suitable crosslinking functional groups B and B 'for the crosslinkers V are:

in particular hydroxyl groups, in particular aldehyde groups,

- azide groups,

Acid anhydride groups, in particular carboxylic anhydride groups,

Carbamate groups, urea groups,

in particular isocyanate groups which are very particularly preferably reacted with blocking agents which deblock at the stoving temperatures of the coating compositions of the invention and / or are incorporated into the developing network without deblocking,

(Meth) acrylate groups,

- Vinyl groups

or combinations thereof.

Very particularly preferred crosslinkers V are branched and / or hyperbranched polyisocyanates which are at least partially blocked and additionally carry ligands A.

In a further embodiment of the invention, the crosslinkers V carry groups B and / or B 'which are capable of forming covalent bonds with the ligands L of the polymer P.

As the continuous phase, water is used for the coating material according to the invention, preferably deionized and / or distilled water. Furthermore, in the continuous phase substantially water-miscible solvents in proportions of up to 30 wt .-%, preferably up to 25 wt .-%, based on the continuous phase, be included. Preferred water-miscible solvents are ethanol, propanol, methyl ethyl ketone, N-ethyl pyrrolidone. Particularly when using the coating compositions according to the invention in the repair of paint damage to already painted substrates, the water-miscible solvents are used in proportions of from 1 to 30% by weight, based on the continuous phase, preferably in proportions of from 2 to 25% by weight. used.

As a further preferred component, at least one acid capable of oxidation is used in such a way that the pH of the coating composition according to the invention is preferably between 1 and 5, preferably between 2 and 4. Particularly preferred acids are selected from the group of oxidizing mineral acids, in particular nitric acid, nitrous acid, sulfuric acid and / or sulfurous acid. To adjust the pH, if necessary, a buffer medium can be used, such as salts of strong bases and weak acids, in particular ammonium acetate. In a particularly preferred embodiment of the invention, the coating composition according to the invention additionally contains a salt which has as cationic constituent lanthanide metal cations and / or d-metal cations.

Preferred lanthanide metal cations are lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium and / or dysprosium cations. Very particular preference is given to lanthanum, cerium and praseodymium cations. The lanthanide metal cations can be present in mono-, di- and / or trivalent oxidation state, the trivalent oxidation state being preferred.

Preferred d-metal cations are titanium, vanadium, manganese, yttrium, zirconium, niobium, molybdenum, tungsten, cobalt, ruthenium, rhodium, palladium, osmium and / or iridium cations. Excluded as d-element cation is the chromium cation in all oxidation states. Very particular preference is given to vanadium, manganese, tungsten, molybdenum and / or yttrium cations. The d-element cations can be present in one to six valent oxidation state, with a three to six-valent oxidation state being preferred.

The method for application of the coating agent according to the invention

Before the application of the coating composition according to the invention, the substrate is purified in a preferred embodiment of the invention, in particular of oily and greasy residues, preference being given to using detergents and / or alkaline cleaning agents. In a further preferred embodiment of the invention, after the cleaning with detergents and / or alkaline cleaning agents before the application of the coating material according to the invention is rinsed again with water. In order to remove deposits and / or chemically modified, in particular oxidized, layers on the surface of the substrate, in a further preferred embodiment of the invention before the final rinsing step, a mechanical cleaning of the surface, for example with grinding media, and / or a chemical removal of the surface layers, for example, with deoxidizing detergents done.

The substrate pretreated in this way is brought into contact with the coating composition according to the invention. This is preferably done by immersion in a bath or pulling the substrate through a bath containing the coating composition according to the invention. The residence times of the substrate in the coating composition according to the invention are preferably 1 second to 15 minutes, preferably 10 seconds to 10 minutes and more preferably 30 seconds to 8 minutes. The temperature of the bath containing the coating composition of the invention is preferably between 20 and 90 ^° C., preferably between 25 and 80 ^° C., more preferably between 30 and 70 ^° C.

The thickness of the layer produced with the coating composition according to the invention before the drying step is preferably between 5 and 900 nm, more preferably between 10 and 800 nm, which, based on the anticorrosive effect, enables a significant saving in the material used.

After the treatment of the substrate with the coating composition of the invention, a drying of the composite of substrate and coating agent is preferably carried out at temperatures between about 30 and 200 ⁰ C, in particular between 100 and 180 ⁰ C, wherein the drying apparatus for the advantageous effect of the inventive Coating agent can be considered largely uncritical. If the crosslinking groups B and / or B 'are at least partially radiation-curing, irradiation of the layer of the coating composition according to the invention, if appropriate in addition to the thermal treatment, is preferably carried out with actinic radiation and / or with electron radiation in a manner known to those skilled in the art.

Surprisingly, the coating composition according to the invention can be used on a wide range of substrates and is largely independent of the redox potential of the substrate. Preferred substrate materials are zinc, iron, magnesium and aluminum, and their alloys, wherein the aforementioned metals are preferably present in the alloys to at least 20 wt .-%. Preferably, the substrates are formed as sheets, as used for example in the automotive industry, the construction industry and the mechanical engineering industry. The sheets coated with the coating composition according to the invention come in particular re in sheet metal as well as in coil coating (coil coating) of sheet metal for use.

In a further embodiment of the invention, the coating compositions of the invention are used for sealing Schnittkan- th the sheets described above, in particular for sealing the cut edges of already coated sheets.

In a further embodiment of the invention, the substrates described above are coated prior to the deposition of the coating composition of the invention with a further electroless depositable corrosion inhibitor. Preference is given to corrosion inhibitors with inorganic constituents, which both have good adhesion to the layer of the coating composition according to the invention and to the uncoated substrate. Such inorganic corrosion inhibitors are described, for example, in EP-A-1 217 094, EP-A-0 534 120, US Pat. No. 5,221,371 and WO-A-01/86016.

In a particularly preferred embodiment of the invention, before application of the coating composition of the invention in a separate step, an aqueous corrosion inhibitor K having a pH between 1 and 5 is applied, which at least one compound AA with a lanthanide metal as a cation and / or a d Contains elemental metal with the exception of chromium as cation and / or a d-element metalate with the exception of chromium-containing metalates as anion and BB at least oxidation-capable acid with the exception of phosphorus-containing and / or chromium-containing acids.

The salt forming the component AA has as cationic constituent lanthanide metal cations and / or d-metal cations. Preferred lanthanide metal cations are lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium and / or dysprosium cations. Very particular preference is given to lanthanum, cerium and praseodymium cations. The lanthanide metal cations can be present in mono-, di- and / or trivalent oxidation state, the trivalent oxidation state being preferred.

The salts of the abovementioned cations of component AA are preferably very readily soluble in water. Particular preference is given to salts [cation] n [anion] m (with n, m> = 1) having a solubility product LP = [cation] " ^* [anion] ^m > 1 (T ^{8 *} mol ^{(n + m)} / l ^{( n + m)} , very particularly preferably salts with a solubility product LP> 10 ^{-6 *} mol ^{(n + m)} / l ^{(n + m)} In a very particularly preferred embodiment of the invention, the concentration of the salt or salts (A) is in the anticorrosion agent 10 ^"1 to 10 ^'4 mol / l, in particular 5 * 10 ^{" 1} to 10 ^{' 3} mol / l The anions forming the salts AA with the d-element cations are preferably selected in such a way that the abovementioned conditions for the solubility product Preference is given to ions of oxidizing acids of the elements of the VI, VII and VIII subgroups of the Periodic Table of the Elements and anions of oxidizing acids of the elements of the V and VI main groups of the Periodic Table of the Elements, with the exception of anions of oxidizing acid used by phosphorus and chromium, in particular nitrates, nitrites, sulfite e and / or sulfates. Further preferred anions are halides, in particular chlorides and bromides.

In a further preferred embodiment of the invention, the d-element cations can also be prepared as complexes with mono- and / or multidentate present potentially anionic ligands. Preferred ligands are optionally functionalized terpyridines, optionally functionalized ureas and / or thioureas, optionally functionalized amines and / or polyamines, in particular EDTA, imines, in particular imin-functionalized pyridines, organosulfur compounds, in particular optionally functionalized thiols, thiocarboxylic acids, Thioaldehydes, thioketones, dithiocarbamates, sulfonamides, thioamides and particularly preferably sulfonates, optionally functionalized organoboron compounds, in particular boric esters, optionally functionalized polyalcohols, in particular carbohydrates and derivatives thereof and chitosans, optionally functionalized acids, in particular di- and / or oligofunctional acids optionally functionalized carbenes, acetylacetonates, optionally functionalized acetylenes, optionally functionalized heterocycles, such as quinolines, pyridines, in particular iminfunktiona pyridines, pyrimidines, pyrroles, furans, thiophenes, imidazoles, benzimidazoles, preferably mercaptobenzimidazoles, benzothiazoles, oxazoles, thiazoles, pyrazoles or even indoles, optionally functionalized carboxylic acids, in particular carboxylic acids which can be ionically and / or co-ordinarily bonded to metal centers, as well as phytic acid and its derivatives. Very particular preference is given as ligands phytic acid, their derivatives and sulfonates, which are optionally functionalized.

In a further embodiment of the invention, the salts contain AA d-element metalates as anions, which together with the d-element cations or alone can form the salt AA. Preferred d-elements for the metallates are vanadium, manganese, zirconium, nickel, molybdenum and / or tungsten. Very particularly preferred are vanadium, manganese, tungsten and / or molybdenum. Excluded as d-element metalate are chromates in all oxidation states. Particularly important Preferred d-element metallates are oxo anions, in particular tungstates, permanganates, vanadates and / or molybdates. If the d-element metallates form the salt AA on their own, that is to say without Lanthanide metal cations and / or d-metal cations, then the preferred solubility product LP of such salts is the same as stated above. Preferred cations of such salts are ammonium ions which are optionally substituted by organic radicals, phosphonium ions and / or sulfonium ions, alkali metal cations, in particular lithium, sodium and / or potassium, alkaline earth metal cations, in particular magnesium and / or calcium. Particularly preferred are the optionally substituted with organic radicals ammonium ions and alkali metal cations, which ensure a particularly high solubility product LP of the salt AA.

As component BB of the corrosion protection agent K, at least one acid capable of oxidation is used in such a way that the pH of the corrosion protection agent is between 1 and 5, preferably between 2 and 4. Preferred acids BB are selected from the group of oxidizing mineral acids, in particular nitric acid, salicific acid, sulfuric acid and / or sulfurous acid.

To adjust the pH, if necessary, a buffer medium can be used, such as salts of strong bases and weak acids, in particular ammonium acetate.

As the continuous phase, water is used for the coating material according to the invention, preferably deionized and / or distilled water.

Before the application of the anticorrosion agent K, the substrate is purified in a preferred embodiment of the invention, in particular of oily and greasy residues, preference being given to using detergents and / or alkaline cleaning agents. In According to a further preferred embodiment of the invention, after the cleaning with detergents and / or alkaline cleaning agents before the application of the anticorrosive agent K, it is rinsed again with water. In order to remove deposits and / or chemically modified, in particular oxidized, layers on the surface of the substrate, in a further preferred embodiment of the invention before the post-rinsing step, a mechanical cleaning of the surface, for example with grinding media, and / or a chemical removal of the surface Surface layers, for example with deoxidizing detergents done.

The thus pretreated substrate is brought into contact with the anticorrosion agent K. This is preferably done by immersing or pulling through the substrate in or by a bath containing the corrosion inhibitor K. The residence times of the substrate in the anticorrosion agent K are preferably 1 second to 10 minutes, preferably 10 seconds to 8 minutes and more preferably 30 seconds to 6 minutes. The temperature of the bath containing the corrosion inhibitor K is preferably between 25 and 90 ^° C., preferably between 30 and 80 ^° C., particularly preferably between 35 and 70 ^° C.

After the substrate has been treated with the anticorrosion agent according to the invention, drying of the composite of substrate and anticorrosive agent is preferably carried out by dry blowing or by drying at temperatures between about 30 and 200 ^° C., the drying temperature and the type or apparatus of drying having the advantageous effect of the corrosion inhibitor K can be regarded as largely uncritical.

In the second step of the preferred method, the substrates coated with the anticorrosion agent K are treated with the inventive coated coating agent. This is preferably done by immersing or pulling through the coated substrate in or by a bath containing the coating composition according to the invention. The residence times of the substrate in the coating composition according to the invention are preferably 1 second to 15 minutes, preferably 10 seconds to 10 minutes and more preferably 30 seconds to 8 minutes. The temperature of the bath containing the coating composition according to the invention is preferably between 20 and 90 ^° C., preferably between 25 and 80 ^° C., more preferably between 30 and 70 ^° C.

The thickness of the layer produced with the coating composition according to the invention before the drying step is preferably between 5 and 900 nm, particularly preferably between 10 and 800 nm, which, based on the anticorrosive effect, allows a significant saving of material used.

After the substrate has been treated with the coating composition according to the invention, the composite of substrate and the layers of the corrosion protection agent K and of the coating composition according to the invention is preferably dried at temperatures between about 30 and 200 ^° C., in particular between 100 and 180 ^° C., the Drying apparatus for the advantageous effect of the coating composition of the invention can be considered largely uncritical. If the crosslinking groups B and / or B 'are at least partially radiation-curing, irradiation of the layer of the coating composition according to the invention, if appropriate in addition to the thermal treatment, is preferably carried out with actinic radiation and / or with electron radiation in a manner known to those skilled in the art.

The examples given below are intended to further illustrate the invention. Examples

Example 1: Preparation of the first basin with the anticorrosion agent K 1.77 g (0.01 mol) of ammonium molybdate tetrahydrate are dissolved in one liter of water. The solution is adjusted to pH = 2.5 by means of nitric acid. Optionally, it is counter-buffered to adjust the aforementioned pH with aqueous ammonia solution.

Example 2a Synthesis of the Polymer Component PM for the Coating Composition of the Invention

In a 4 kg steel reactor 1016.9g deionized water are introduced and heated to 9O ⁰ C. Subsequently, at a constant temperature of 90 ^° C., three separate feeds are metered in parallel and uniformly. Feed 1 consists of 90.0 g of dimethylaminopropylmethacrylamide, 240.0 g of methyl methacrylate, 120.0 g of hydroxyethyl methacrylate, 120.0 g of methacrylic ester 13 (methacrylic acid residual, mean number of C atoms of the linear, saturated alcohol is 13; CAS No. 90 551- 76-1, supplier: Degussa, Röhm GmbH, Darmstadt) and 30.0 g of diphenylethylene. As feed 2, 165.7 g of a solution consisting of 61.0 g of 85% phosphoric acid and 104.7 g of demineralized water are added. Feed 3 consists of a solution of 45.0 g Ammonoiumperoxidisulfat in 105.0 g of deionized water. The feeds 1 and 2 are added within 4 hours, feed 3 is added within 4.5 hours. After completion of the addition, a 2-hour Nachpolymerisationsphase at 9O ⁰ C follows. The resulting dispersion has a solids content of 37% by weight.

Example 2b Synthesis of Crosslinker V for the Coating Composition of the Invention

3.1 g (0.008 mol) of cerium (III) chloride heptahydrate in 50 ml of water are initially taken. There is a solution of 4,1g (0,025 mol) of 4-hydroxycinnamic acid and 1 g (0.025 mol) of sodium hydroxide in 50 ml of water and brought to pH = 7.9 with hydrochloric acid. This solution is added slowly to the cerium solution, so that the pH of the cerium solution does not rise above 6. The precipitate is washed with ethanol and water. 1.7 g (0.003 mol) of this cerium complex is mixed with 9.1 g (2.5% NCO content) of a branched and blocked with dimethylpyrazole 75% polyisocyanate (Bayhydur VP LS 2319 Fa. Bayer AG) in 80 , 1 g of ethyl acetate and 0.7 g of an OH-functional dipropylenetriamine (Jeffcat ZR 50 from Huntsmann) for five hours at 40 ⁰ C brought to the reaction. The product is used without further purification.

Example 2: Preparation of the second basin with the coating composition of the invention

3 g of the polymer component P according to Example 2a and 2 g of the crosslinker V according to Example 2b are dissolved in one liter of water. The solution is adjusted to pH = 2.5 by means of nitric acid. Optionally, it is counter-buffered to adjust the aforementioned pH with aqueous ammonia solution.

Example 3 Coating of the Substrate with the Corrosion Inhibitor K and the Coating Composition of the Invention

The substrate (sheet of galvanized steel) is cleaned for 5 minutes at 55 ° C in a cleaning solution (Ridoline C72 Fa. Henkel) and then rinsed with distilled water. Subsequently, the rinsed with distilled water plate immediately at 45 ° C for 4 minutes in the first basin of the corrosion inhibitor K according to Example 1 is immersed. Thereafter, the coated sheet is rinsed with distilled water and blown dry with nitrogen. Immediately thereafter, the sheets are immersed for 5 minutes at 35 ° C in the second basin of the corrosion inhibitor according to the invention according to Example 2. It forms an invisible to opalescent layer in the λ / 4 range of visible light. After that The coated sheet is rinsed with distilled water and blown dry with nitrogen. The sheet is then dried for 30 minutes at 150 ⁰ C.

The thus coated sheet and the following reference samples are cut with a shearing machine to obtain free edges on all sheets.

Gardobond 958 54 (Fa.Chemetall GmbH: galvanized steel sheet with phosphating and rinsing with zirconium hexafluoride solution) is used as a reference for the invention.

Example 4: Rapid corrosion test with 3% strength aqueous sodium chloride solution on the substrates coated according to Example 3 A solution of 3% sodium chloride in demineralized water is used. As substrates here steel, galvanized steel or zinc alloys can be used. For aluminum and its alloys, the sodium chloride solution is additionally adjusted to pH = 3 with acetic acid. The samples (3 × 3 cm) are immersed in 170 ml of this solution and stored in a desiccator at almost 100% humidity. The humid atmosphere is produced by fat-free compressed air, which is passed through two wash bottles with demineralized water and then flows through the desiccator. This construction ensures a constant air humidity and a constant carbon dioxide content, keeping the temperature at 25 ° C. The samples are weighed before immersion on an analytical balance. Non-treated reference plates (steel, galvanized steel) are cleaned for 5 minutes in ethanol in an ultrasonic bath. After 24 hours storage, the plates are removed from the solution and rinsed with a disposable pipette over the beaker with the loaded 3% sodium chloride solution (about 10ml sodium chloride solution per sample side). The sheet is then blown dry with nitrogen and dried for 15 minutes at 50 ⁰ C and weighed. The sheet is then replaced again in a fresh sodium chloride solution of the same concentration. hang. The used sodium chloride solution is mixed with 1 ml of 32% hydrochloric acid to dissolve any precipitate. The resulting clear solution is measured by means of ICP-OES (Inductively Coupled Plasma - Optical Emission Spectrometry) on the content of substrate metal (Zn, Fe, Al, Mg).

The procedure described above is repeated after 24h, 72h, 96h and 168h. The measurement is verified by a double determination.

Evaluation of the corrosion test: a) ICP-OES data of the immersion solution

The ICP-OES data are normalized to the area of the samples. These data give a linear progression. Due to the linearity of the corrosion kinetics, the different coatings can be compared by the slopes of the graph. The ICP-OES data reflect the resolution of the substrate per area and time and are thus a direct measure of the corrosion rate that is possible with a particular coating.

b) Weighing of the samples The weighings also provide information about the possibilities in how far the coating makes it possible to passivate the surface or not. For this purpose, the weight loss is converted into molecular weights and normalized to the area of the samples. To compare the corrosion kinetics is the respective substrate, which was only cleaned alkaline. The slopes from the ICP-OES data are then compared to the zero reference (pure substrate) and other references. Table 1: Results of the corrosion test

Substrate ICP-OES data (KT ^{4 *} mol / l ^* h ^* cm ² )

Galvanized steel sheet (uncoated) 8,14

Galvanized steel sheet coated according to Example 3 5,17

Gardobond 958 54 (Reference) 6,17

The results of the corrosion tests clearly show the superiority of the coating composition of the invention over a conventional corrosion protection (reference).

Claims

claims:

1. Aqueous coating agent for metallic substrates comprising a water-dispersible and / or water-soluble polymerizate P having a gradient in the concentration of covalently bonded hydrophilic groups along the polymer main chain, the polymer having P covalently bound ligands A, which with the in the Corrosion of the substrate released metal ions and / or the substrate surface chelates, as well as crosslinking functional groups B having, with itself, with other complementary functional groups B 'of the polymer P and / or with other functional groups B and / or B' to crosslinkers V can form covalent bonds.

2. Aqueous coating composition according to claim 1, characterized in that the polymer P contains at least one polymer which is prepared by free-radical polymerization of olefinically unsaturated monomers.

3. Aqueous coating composition according to claims 1 or 2, characterized in that the polymer P contains at least one copolymer PM, obtainable by the radical polymerization of

a) olefinically unsaturated monomers (a1) and (a2), where (a1) in each case at least one monomer from the group consisting of olefinically unsaturated monomers (a11) having at least one hydrophilic group HG, from the group consisting of olefinically unsaturated monomers (a12) with at least ligand group A and from the group consisting of olefinically unsaturated monomers (a13) with at least one crosslinking group B, and

b) at least one olefinically unsaturated monomer of the general formula I which is different from the olefinically unsaturated monomer (a)

R ¹ R ² C = CR ³ R ⁴ (I),

wherein the radicals R ¹ , R ² , R ³ and R ^{4 are} each independently hydrogen or substituted or unsubstituted alkyl, cycloalkyl, alkylcycloalkyl, cycloalkylalkyl, aryl, alkylaryl, cycloalkylaryl, arylalkyl or arylcycloalkyl radicals with the proviso that at least two of the variables R ¹ , R ² , R ³ and R ^{4 are} substituted or unsubstituted aryl, arylalkyl or arylcycloalkyl radicals, in particular substituted or unsubstituted aryl radicals.

4. Aqueous coating composition according to any one of claims 1 to 3, characterized in that the crosslinkers V have covalently bound ligands A.

5. Aqueous coating composition according to any one of claims 1 to 4, characterized in that the ligands A are selected from the group of ureas, amines, amides, irines, imides, pyridines, organosulfur compounds, organophosphorus compounds, organoboron compounds, oximes, acetylacetonates, poly- alcohols, acids, phytic acids, acetylenes and / or carbenes.

6. An aqueous coating composition according to any one of claims 1 to 5, characterized in that the polymer P and the crosslinker V crosslinking groups B and / or B ', which are thermally and / or radiation-crosslinkable.

7. Aqueous coating composition according to any one of claims 1 to 6, characterized in that the polymer P has as polymer backbone one or more building blocks selected from the group consisting of polyesters, polyacrylates, polyurethanes, polyolefins, polyols, polyvinyl ethers, polyvinylamines and polyalkyleneimines.

8. Aqueous coating composition according to any one of claims 1 to 7, characterized in that it additionally contains a salt, which has as cationic constituent lanthanide metal cations and / or d-metal cations, with the exception of chromium cations.

9. A method for autodepositing an aqueous coating agent according to any one of claims 1 to 8, characterized in that the thickness of the coating agent on the substrate after autophoretic application is between 5 and 900 nm.

10. A method for autodepositing an aqueous coating composition according to any one of claims 1 to 8, characterized in that the substrate is immersed for a period of 1 second to 15 minutes at a temperature between 20 and 90 ⁰ C in a bath of the coating composition ,

11. Two-stage process for the corrosion protection equipment of metallic substrates, characterized in that (I) in a first stage, the substrate is immersed in a bath of a corrosion inhibitor K, which causes a conversion to the substrate surface and

(II) in a second step, the substrate treated according to step (I) is immersed in a bath of the coating composition according to one of claims 1 to 8.

12. The method according to claim 11, characterized in that in the first stage (I) an aqueous corrosion inhibitor K containing at least one compound with a lanthanide metal as a cation and / or a d-element metal with the exception of chromium as a cation and or a d-element metalate with the exception of chromium-containing metalates as anion and at least one acid capable of oxidation with the exception of phosphorus-containing and / or chromium-containing acids.

13. The method according to any one of claims 9 to 12, character- ized in that the substrate after the deposition of the coating composition according to one of claims 1 to 8 thermally treated at temperatures between 50 and 200 ⁰ C and / or by irradiation.

14. The method according to any one of claims 9 to 13, characterized in that the substrate contains at least 20 wt .-% of a metal selected from the group Fe, Al and / or Zn.