WO2011138290A1

WO2011138290A1 - Method for autophoretic coating, coating agent, and multilayer paint finish

Info

Publication number: WO2011138290A1
Application number: PCT/EP2011/056983
Authority: WO
Inventors: Horst HINTZE-BRÜNING; Michael Dornbusch; Sergej Toews; Wolfgang Bremser
Original assignee: Basf Coatings Gmbh; Universität Paderborn
Priority date: 2010-05-03
Filing date: 2011-05-02
Publication date: 2011-11-10
Also published as: DE102010019245A1; WO2011138290A8

Abstract

The invention relates to a method for autophoretically coating a metal substrate at a pH value of 1 to 4 and a substrate immersion time of 1 s to 15 min in an aqueous polymer dispersion comprising at least one water-soluble and/or water dispersible (meth)acrylic block copolymer comprising at least one olefinic unsaturated monomer (a) having a metal ion coordinating group, at least one olefinic unsaturated monomer (b) different from monomer (a) and having a cross-linking group B and diphenylethylene incorporated by polymerization. The metal substrate is thereby not treated by etching substances prior to the autophoretic coating. The invention further relates to a corresponding coating agent and a multilayer paint finish comprising the corresponding autophoretically deposited layer.

Description

Method for autophoretic coating, coating and

ehrschichtlackierung

The present invention relates to a process for the autodeposition of a metallic substrate at a pH of 1 to 4 and a immersion time of the substrate of 1 s to 15 min in an aqueous polymer dispersion containing at least one water-soluble and / or water-dispersible (meth) acrylic A block copolymer comprising at least one olefinically unsaturated monomer (a) having a metal ion coordinating group, at least one olefinically unsaturated monomer (b) other than monomer (a) copolymerized with a crosslinking group B and diphenylethylene, and a coating agent for Implementation of the procedure.

Processes and coating compositions for electroless anti-corrosive 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 anticorrosive coating, also called ACC process (Autophoretic Chemical Coating), polymers, for example emulsion polymers containing acrylates or styrene / butadten, are used which are anionically stabilized. For finishing, such deposited by ACC process layers are usually processed by rinsing with chromium-containing aqueous coating compositions to improve the corrosion protection. 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, efforts are being made to completely replace chromium in anti-corrosion coatings. As a result of the development of chromium-free coating agents, it was also found that ACC coating center! containing salts of the lanthanide and the d-elements and an organic film-forming component also ensure a very good, the chromium-containing coating compositions comparable corrosion protection.

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 corrosion inhibitor 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 unit area of the substrate to be coated. Another disadvantage is the tendency of Metailtonen formed from the substrate to migrate through the deposited corrosion protection layer and the use of ecologically critical substances, such as in particular Fiusic acid or fluorides.

DE-A-37 27 382 describes chromium-free aqueous dispersions of adducts of carboxylic acids and isocyanates with epoxides, which are suitable for the autodepositing 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 ° C. Such latex particles also have the disadvantage of a lower diffusion in cavities or on edges of three-dimensional substrates in comparison with molecular dispersed polymers

To have migration speed. In addition, layers of a thickness between 1 micron and 1 mm are formed, which is a corresponding Required material 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 corrosion protection 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 polyethyleneimine. The coating compositions can be applied by means of dip coating and have after drying thicknesses between 1 and 300 microns. Layers produced in this way also have a high material requirement and tend to crack during drying over the entire area of the surface. DE-A-10 2006 053 291 describes the method mentioned in the introduction. Autophoretically depositable coating compositions of water-dispersible and / or water-soluble polymers are used, the polymer having a gradient in the concentration of covalently bonded hydrophilic groups along the polymer main chain and containing metal ions chelating ligands and crosslinking functional groups. Substrates that will coat with this coating agent in the autodepositing process described therein will subsequently have a complete coating, requiring high material requirements, and also tend to crack over the entire area of the surface.

Task and solution

In view of the aforementioned prior art, the object of the invention to find an ecologically largely harmless process for corrosion protection, which does not require the use of chormhaltigen substances and also not the use of expensive salts of lanthanide and the d-elements requires. In addition, material should be saved to provide cost effective corrosion protection, but still effective. Surprisingly, this object has been achieved by a metallic substrate is selectively coated at the grain boundaries and Oberflächenendefektstrukiuren by an inventive autophoretic method. The selective deposition at the grain boundaries and the Oberfiächendefektstrukturen the material cost of the coating decreases significantly compared to a full coating. This selective coating was surprisingly dissolved by an aqueous polymer dispersion containing at least one water-soluble and / or water-dispersible (eth) acrylic block copolymer which can be prepared from at least one olefinically unsaturated monomer (a) having one metal ion-coordinating group, at least one of monomer (a) different olefinic unsaturated monomer (b) having a crosslinking group and diphenylethylene, wherein the metallic substrate is not treated with caustic substances prior to autodeposition. A coated according to this method metallic substrate is shown in Figure 1 a and 1b.

Detailed description

FIG. 1a: an SEM image of a hot-dip galvanized steel sheet (HDG steel) after an autophoretic coating has been carried out on the grain boundaries and surface defect structures.

FIG. 1 b: an SEM image of a hot-dip galvanized steel sheet (HDG steel) after an autophoretic coating has been carried out on the grain boundaries and surface defect structures.

FIG. 2a: An SEM image of a hot-dip galvanized steel sheet (HDG steel) after it has been degreased and cleaned in a three-stage solvent process. The cleaning with tetrahydrofuran (THF), isopropane and ethanol is carried out for 10 min in an ultrasonic bath. After each purification step, the substrate is dried in a stream of nitrogen.

FIG. 2b: An SEM image of a hot-dip galvanized steel sheet (HDG steel) after it has been degreased and cleaned in a three-stage solvent process has been. Purification with tetrahydrofuran (THF), isopropanol and ethanol is carried out for 10 min in an ultrasonic bath. After each purification step, the substrate is dried in a stream of nitrogen. FIG. 3a: Potentiai mapping of the surface of a hot-dip galvanized steel sheet (H DG steel) after it has been degreased and cleaned in a three-stage solvent process.

FIG. 3b: Diagram of the potential energy along the section from a to f in FIG. 3a.

FIG. 4: Element mapping by means of EDX from a hot-dip galvanized steel sheet (HDG steel) after it has been degreased and cleaned in a three-stage solvent process. The top part shows the SEM image of the measured area. The lower three parts show the Eiementverteilungen of AI, O and Zn.

In the following, "grain boundaries and surface defect structures" are understood to mean the areas of the surface of metallic substrates which are not monocrystalline areas of the surface.The microstructure of metallic substrates is predominantly polycrystalline and is formed from a plurality of individual crystallites that are orientated For example, adjacent crystallites with similar interfaces may have different orientations, and the interfaces between them are referred to as grain boundaries, consisting of narrow transition zones with distorted ordering Tendrical grain boundaries and stacking faults also lead to disorder in the uniform atomic arrangement, but are not usually counted among the usual grain boundaries However, n can generally be summarized under the generic term surface defect structures, which include scratches or other defects, which lead to an abnormal arrangement of the atoms on the surface of the polycrystalline metallic substrate. Both grain boundaries and surface defect structures lead to a reduction of the chemical potential. FIGS. 3a and 3b show a measurement of the chemical potential of a polycrystalline metallic surface. It can be clearly seen that the grain boundaries and the surface defect structures have a lowered chemical potential over the rest of the surface. The reduction in chemical potential at grain boundaries or surface defect structures is greater than 0.02 V from the directly adjacent undisturbed surface. Among other things due to the reduced chemical potential, the grain boundaries and the surface defect structures are the starting point for initial corrosion of the metallic substrate. Blocking grain boundaries and surface defect structures is therefore desirable for effective corrosion protection.

The grain boundaries and surface defect structures on metallic surfaces can be detected by various types of microscopy, such as microscopy, SEM, and AFM. For example, FIGS. 2a and 2b show SEM photographs of a degreased and cleaned hot-dip galvanized steel sheet (purified HDG steel) on which the individual grain boundaries and surface defect structures can be clearly seen. Grain boundaries and superficial defect structures differ markedly in the shading in the SEM image and represent irregularities in the otherwise crystalline surface. The grain boundaries are particularly pronounced in depressions on the surface, which can be up to 1 pm wide. Surface defect structures can be both depressions and elevations that stand out from the otherwise crystalline surface. Grain boundaries and surface defect structures continue to be an area in which foreign ions accumulate particularly strongly. The individual crystallites consist of a stoichiometrically uniform composition of the elements of which the substrate consists. Within a single crystallite, this composition usually does not vary. However, grain boundaries and surface defect structures are areas in which not only the arrangement of the atoms varies, but also the relationships of the elements to each other and optionally also other elements are incorporated. Thus, FIG. 4 shows the element mapping by means of EDX of HDG steel. It can be clearly recognized that the composition of the substrate HDG steel in the region of the grain boundaries and Oberfiächendefektstrukturen varies greatly over the composition of the crystallites. Above all, the content of the foreign ion AI is greatly increased in the range of grain boundaries and surface defect structures. Thus, grain boundaries and surface defect structures are areas in where the concentration of the elements is different from the concentration of the elements in the adjacent crystallites.

By etching with corrosive substances, the surface potential of a metallic substrate is changed., In particular, a pretreatment with corrosive substances leads to a leveling out of the difference in the surface of a metallic substrate chemical potential between grain boundaries / surface defect structures and the crystalline surface: An etching preconditioning makes the chemical potential of the metallic surface almost the same over the entire area, which is to be prevented in the spirit of this invention. "Corrosive substances" include, above all, acids and bases , This also includes acidic or alkaline cleaning agents for metallic substrates.

"Metal-ion-coordinating groups" are contained in ligands A that can complex metal ions, and these ligands A have pairs of electrons, mostly lone pairs, that can be used to coordinate to metal ions As a rule, the ligands A are randomly distributed in the polymer, preference being given to monodentate or multidentate potentially anionic ligands A.

Particularly preferred metal ion coordinating groups contained in ligand A are

optionally functionalized ureas and / or thioureas, especially acylthioureas such as benzoylthiourea,

- Optionally functionalized amines and / or polyamines, in particular

EDTA,

- Optionally functionalized amides, especially carboxylic acid amides

Imines and imides, in particular imin-functionalized pyridines,

Oximes, preferably 1,2-dioximes, such as functionalized diacetyldioxime,

Organosulfur compounds, in particular optionally functionalized thiols such as thioethanol, thiocarboxylic acids, thioaidehydes, thioketones, dithiocarbamates, sulfonamides, thioamides and particularly preferably suifonates, Organophosphorus compounds, in particular phosphates, more 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, such as in particular di- or oligofunktioneüe acids, or optionally functionalized (poly) carboxylic acids, in particular carboxylic acids which can be bound ionically and / or coordinately to metal centers, preferably (poly) methacrylates with acid groups or di- or oligofunktioneüe acids .

optionally functionalized carbenes,

Acetylacetonates,

Optionally functionalized heterocycles, such as quinolines, pyridines, in particular imin-functionalized pyridines, pyrimidines, pyrroles, furans, thiophenes, imidazoles, benzimidazoles, preferably mercaptobenzimidazoles, benzothiazoles, oxazoles, thiazoles, pyrazoles or else indoie,

- optionally functionalized acetylenes, as well

- phytic acid and its derivatives.

The inventive method for autodepositing a metallic substrate is carried out at a pH of 1 to 4 and a dipping time of the substrate of 1 s to 15 min in an aqueous polymer dispersion, wherein the polymer solution at least one water-soluble and / or water-dispersible (meth) acrylic Block copolymer comprising at least one olefinically unsaturated monomer (a) having a metal ion coordinating group, at least one olefinically unsaturated monomer (b) other than monomer (a) copolymerized with a crosslinking group B and diphenylethylene, and wherein the metallic Substrate is not treated with corrosive substances prior to autodeposition. The pH of the aqueous polymer dispersion for the process according to the invention must have a value of 1 to 4. However, it is advantageous if the value is 2 to 3 or 2.2 to 2.8. Particularly preferred is a pH of 2.4 to 2.6. The pH of the aqueous polymer dispersion is adjusted by an inorganic acid, preferably by nitric acid.

Advantageously, the immersion time of the substrate in the aqueous polymer dispersion is 1 s to 1 min, in particular 10 s to 40 s. During this time, sufficient coverage at the grain boundaries and surface defect patterns is achieved for most substrates.

It is advantageous if the substrate is a galvanized, preferably hot-dip galvanized sheet, in particular a hot-dip galvanized sheet steel. By the combination of galvanizing and inventive deposition a good corrosion protection is achieved.

Advantageously, the substrate was cleaned prior to coating with at least one detergent, preferably with at least one ether and / or at least one alcohol, in particular with an ether and / or at least one alcohol in the ultrasonic bath.

The water-dispersible and / or water-soluble polymers have a gradient in the concentration of covalently bonded hydrophilic groups HG along the polymer backbone and carry ligands A, which form chelates with the metal ions liberated upon corrosion of the substrate, as well as crosslinking functional groups B with them themselves and / or with further functional groups C to crosslinkers V covalent bonds can form. For the purposes of the invention, water-dispersible or water-soluble means that the polymers in the aqueous phase form aggregates with 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 generally have weight average molecular weights Mw of <200,000, preferably <120,000, more preferably <50,000 Daiton. The size of the aggregates consisting of polymer can preferably be accomplished in a manner known per se by introduction of hydrophilic groups HG on the polymer.

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.

The gradient is preferably generated by suitable arrangement of monomeric units which make up the polymer and which 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 are ionic groups such as in particular sulfate, sulfonate, sulfonium, phosphate, phosphonate, phosphonium, ammonium and / or carboxylate groups and nonionic groups, such as 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 depends on the Soivatationsvermögen and the steric accessibility of the groups HG and can also be eingeeiit by the skilled person in a conventional manner.

As the polymer backbone of the polymers it is possible to use any desired polymers, preferably those having weight-average molecular weights Mw of 500 to 50,000 Daiton, more preferably having molecular weights Mw of 700 to 20,000 Daiton. The polymer backbone used is poly (meth) acrylate used. The polymers can be linear, branched or dendritic.

The polymers are preferably stable to hydrolysis in the acidic pH range, in particular at pH values <5, particularly preferably at pH values <3.

As ligands A containing metal-ion coordinating groups, all groups or compounds capable of forming chelates with the metal ions released upon corrosion of the substrate are suitable. As a rule, the ligands A are randomly distributed in the polymer. Particularly preferred ligands included

optionally functionalized ureas and / or thioureas, especially acylithiureas such as benzoylthiourea,

optionally functionalized amines and / or polyamines, in particular EDTA,

- Optionally functionalized amides, especially carboxylic acid amides

Imines and imides, in particular iminfunktionaüsierte pyridines,

Oximes, preferably 1,2-dioximes, such as functionalized diacetyldioxime,

Organosulfur compounds, in particular optionally functionalized thiols such as thioethanol, thiocarboxylic acids, thioaidehydes, thioketones, dithiocarbamates, sulphonamides, thioamides and particularly preferably sultanates,

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

optionally functionalized polyhydric alcohols, in particular carbohydrates and derivatives thereof, and chitosans,

- Optionally functionalized acids, such as in particular di- and / or oligofunctional acids, or optionally functionalized (poly) carboxylic acids, in particular carboxylic acids which can be bound ionically and / or coordinately to metal centers, preferably (poly) methacrylates with acid groups or dioder oligofunktionelle acids .

optionally functionalized carbenes, Acetic! Acetonates,

Optionally functionalized heterocycles, such as quinolines, pyridines, in particular imin-functionalized pyridines, pyrimidines, pyrroles, furans, thiophenes, iridazoles, benzimidazoles, preferably mercaptobenzimidazoles, benzothiazoles, oxazoles, thiazoles, pyrazoles or also indoles,

- optionally functionalized acetylenes, as well as

- phytic acid and its derivatives.

Suitable crosslinking functional groups B on the polymer 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. 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.

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

ercapto 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 Verstächtungsmittel and incorporated into the network forming.

Particularly preferred combinations of thermally crosslinking groups B and complementary groups B 'are:

Hydroxyl groups with isocyanate and / or carbamayl groups,

Amino groups with isocyanate and / or carbamate group,

- Carboxylic acid groups with epoxide groups.

Particularly preferred polymers comprise copolymers which can be prepared by single-stage or multistage radical copolymerization in the aqueous medium of a) at least one olefinically unsaturated monomer (a) having a metal ion-coordinating group,

b) at least one olefinically unsaturated monomer (b) other than monomer (a) having a crosslinking group B,

c) diphenylethyls and

d) if appropriate at least one of the olefinically unsaturated monomers (a), (b) and (c) different olefinically unsaturated monomer of the general formula I.

R ¹ R ² C CR ³ R ⁴ (I)

.worin the radicals R ¹ , R ² , R ³ and R ^{4 are} each independently hydrogen or substituted or unsubstituted alkyl, cycloalkyl, alkylcycloalkyl, cycloalkylalkyl, Aryk alkylaryl, Cycloalkylaryi-, Arylalkyi- or Arylcycloalkyireste stand, with with the proviso that at least two of the variables R ¹ , R ² , R ³ and R ^{4 are} substituted or unsubstituted aryl, Arylalkyi- or Arylcycloalkyireste, in particular substituted or unsubstituted aryl radicals. Suitable hydrophilic monomers which may be suitable both as monomer (a) and as monomers (b) contain at least one hydrophilic group HG, which preferably consists of the group consisting of sulfate, suifonate, suifonium, phosphate, phosphonate -, phosphonium, ammonium and / or carboxylate groups and hydroxyl, primary, secondary and / or tertiary amine, amide group and / or oiigo or polyalkoxy substituents, such as preferably ethoxyüerte or propoxylated substituents which may be etherified with other groups selected. Examples of suitable hydrophilic monomers 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 rates and / or their Teiiester. Also suitable are olefinically unsaturated sulfonium and phosphonium compounds. Also very suitable are monomers which carry at least one hydroxyl group or hydroxymethylamino group per molecule and are essentially free of acid groups, 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 the hydroxyalkyl group is up to Contains 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 alpha, eta-unsaturated carboxylic acid amides such as N-methylol- and, N-dimethylol-aminoethyl acrylate, -aminoethyimethacrylate, -acrylamide and -methacrylamide. As amine group-containing monomers are suitable; 2-aminoethyl acrylate and methacrylate, N-methyl and N, N-dimethyl-aminoethyl acrylate, or ailylamine. As amide group-containing monomers are preferably amides of alpha, beta-olefinically unsaturated carboxylic acids, such as (meth) acrylic acid amide, preferably N-methyl or N, -Dimethy l (meth) acryisäureamid used. Preferred ethoxy-containing or propoxylated monomers are 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.

Advantageous examples of suitable monomers (a) are olefinically unsaturated monomers which have the above-described ligands A as substituents. Examples of suitable monomers (a) 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 have the ligands A in the ester and / or amide radical , Preferred ligands A are optionally functionalized urea and / or Thiourea substituents, optionally functionalized amine and / or Polyaminsubtiuenten, imine and imide substituents, in particular iminfunktionalisierte pyridines, oxime substituents, preferably 1, 2-dioximes such as functionalized Diacetyldioxim, Organosschwefelsubsfituenten, such as in particular derived from optionally functionalized thiols such as thioethanol, thiocarboxylic acids, thioaldehydes, thioketones , Dithiocarbamate, sulfonamides, thioamides and particularly preferably sulfonates, organophosphorus, such as in particular derivable from phosphates, more preferably phosphoric acid esters of (meth) acrylates, and phosphonates, particularly preferably vinylphosphonic and hydroxy-, amino- and amido-functionalized phosphonates, optionally functionalized Organoborsubstituenten, in particular derivable from boric acid esters, optionally functionalized polyalcohol substituents, in particular derivable from carbohydrates and derivatives thereof and chitosans, g if appropriate, functionalized acid substituents, such as in particular derivable from di- and / or oligofunctional acids, or optionally functionalized (poly) carboxylic acids, in particular carboxylic acids which can be bound ionically and / or coordinately to metal centers, preferably (poly) methacrylates with acid groups or di - or oligofunctional acids, substituents with optionally functionalized carbenes, acetylacetonates, optionally functionalized acetylenes, and phytic acids and derivatives thereof.

Advantageous examples of well-suited monomers (b) are olefinically unsaturated monomers which have the above-described groups B as substituents. Examples of suitable monomers (b) are esters and / or the amides of acrylic acid, methacrylic acid, eihacryic 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 the ester and / or amide radical exhibit. As crosslinking groups B are particularly preferably hydroxyl groups, and for example mercapto and amino groups, Aidehydgruppen, azide groups, acid groups, especially 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, for example urea groups, epoxide groups, and particularly preferably Isocyanate groups, which are very particularly preferably reacted with blocking agents which deblock at the Einre ntemperaturen the coating compositions and are incorporated into the network forming. The monomers (a) are arranged in the polymer in such a way that the already described gradient of the hydrophilic groups HG results along the main polymer chain. This is generally due to the specific copolymerization parameters of the different monomers (a), (b), (c), and optionally (d) in the aqueous reaction medium. The aforementioned monomers (a) and (b) are preferably random along the polymer backbone It is apparent from the above performance of the monomers (a) and (b) exemplified that the hydrophilic groups HG, the ligands A and the crosslinking groups B can be partially or completely identical. In this case, then also the ligands A and the crosslinking functional groups B usually have a gradient along the polymer main chain.

As monomers (d), which need not necessarily be used but whose use is advantageous, compounds of the general formula I are used. In the general formula I, the radicals R, R ² , R ³ and R ^{4 are} each independently Hydrogen atoms or substituted or unsubstituted alkyl, cycloalkyl, alkylcycloalkyl, cycloalkylalkyi, 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 particularly preferably used monomers (d) are dinaphthylene, cis- or trans-stilbene, vinyl-bis-bis (4-N, N-dimethylaminobenzene), vinylidene bis (4-amtnobenzol) or vinylidene bis (4-nitrobenzoi).

In the preparation of the copolymers preferably the mixture of all monomers is metered into the water phase simultaneously, wherein 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 in the course of further chain growth, the number of hydrophilic groups along the polymer chain decreases. The concentration gradient of the hydrophilic groups along the polymer chain can also be realized via an inlet of temporally and / or spatially different compositions of the monomer mixture of (a), (b), (c) and optionally (d) in a manner known per se. With regard to the preparation of the copolymers, reference should also be made to the teachings of DE-A-198 58 708, DE-A-102 06 983 and DE-A-102 56 226.

Advantageously, at least one polymer is used which contains at least one unsaturated alkoxysilane monomer, preferably at least one vinylaikoxysilane monomer, in particular triethoxyvinylsilane, copolymerized in addition to other monomers. The incorporation of silane-containing monomers increases the adhesive properties of the polymer, especially the substrate adhesion to metals and metal oxides.

Advantageously, the aqueous polymer dispersion has a solids content of 1 to 10 wt .-%, preferably 1 to 5 wt .-%, in particular 2 to 3 wt .-%.

It is a significant advantage of the present invention that there is no integral substrate saturation but selective coating of the grain boundaries and surface defect structures. As a result, a considerable saving of material is achieved and nevertheless a good corrosion protection is achieved. The grain boundaries and surface defect structures are generally the starting point for corrosion. By their blocking by means of the deposition of the polymer, a good corrosion protection is obtained. The invention also relates to an autodepositing coating composition for the process according to the invention. The composition of the coating agent corresponds to that which has been described in connection with the description of the process. The invention also relates to a multi-layer coating which comprises a layer produced according to the method according to the invention and at least one further lacquer layer which is applied to the autodeposited layer.

The determination of the solids content was carried out at 120 ° C for 60 minutes, What remained after, corresponds to the solid in the system under study.

SEM (Scanning Electron Mircoscope) images and Element Mapping by EDX (Energy Dispersive X-Ray Analysis) were performed with a commercial SEM instrument. The SEM images were measured at 3 kV with a distance of 5 mm. The element mapping was at 6 kV and a distance of 5 mm.

The potential mapping was performed by means of SKPFM (Scanning Kelvin Probe Force Microscope) with a commercially available AFM instrument. The removal of the AFM tip to the substrate surface was 100 nm at an excitation voltage of 500 mV and a frequency of 60 to 80 kHz.

Number average and weight average molecular weights Mn and Mw were measured by GPC (gel permeation chromatography) in tetrahydrofuran (THF) at 25 ° C against polystyrene as standard.

Production example of polymer dispersions P1-P3

The positions of the first reaction stage are introduced into a 2000 ml glass reactor with anchor agitator and heated to 70 ° C. under a nitrogen atmosphere. After the temperature has been reached, the initiator solution is added over a period of 20 minutes and the temperature is kept constant for a further 2.5 hours. Subsequently, the reaction mixture is heated to 90 ° C and after reaching this reaction temperature, the monomer mixture of the second stage is added over a period of 2 hours. The post-reaction time at 90 ° C is still 2 hours. The composition of the individual stages is given in the following Table 1. The figures mean parts by weight.

Table 1 :

Polymer dispersion PI has a number average molecular weight Mn of 58,000 daltons and weight average molecular weight Mw of 110,000 daltons.

Production example of a pretreated substrate SK

The substrate, a hot-dip galvanized steel sheet (HDG steel DX 53D + Z 100 NA 0.6mm from Voestalpine AG, Linz, Austria), is degreased and cleaned in a three-stage solvent cleaning process. The cleaning with Tetrahydrofuran, Isorpropanoi and ethanol are each for 10 min in Ultraschallalfbad, After each cleaning step, the substrate is dried in a stream of nitrogen.

Production example for a pretreated substrate SF

The substrate, a hot-dip galvanized steel sheet (HDG steel DX 53D + Z 100 NA 0.6 mm from Voestalpine AG, Linz, Austria), is cleaned for 5 min at 55 ° C in an alkaline cleaning solution (Rtdoline C72 from Henkel) and then with distilled water rinsed.

Production example for an autodeposition coating at the grain boundaries and surface defects of a substrate BK1 - BKS

For the deposition of the polymer dispersions P1 to P3, the dispersions were adjusted by means of 0.1 N HNO _{3 in} each case to a solids content of 2.5% by weight and a pH of 2.5. By immersing the substrate SK in the polymer dispersions P1 to P3 for 30 seconds, the substrates BK1-BK3 which were autodeposited at grain boundaries and surface defects were obtained.

Comparative Example for a Nationwide Autophoretic Coating BF1 - BF2

To deposit the polymer dispersions PI and P2, the dispersions were adjusted to a solids content of 2.5% by weight and a pH of 2.5 using 0.1 N HNO _{3 in} each case. The substrate SF was immersed in the polymer dispersion P1 to P3 for 30 seconds.

Corrosion test 1 with the Saizsprühnebeitest (DIN EM ISO 9227)

For the Saizsprühnebeitest the autophoretically coated substrates BK1, BK2, BF1 and BF2 were each coated with the CoiiCoating primer Coiltec Universal P CF from BASF Coatings AG. The layer thickness of the primer is 10 μιη in all cases. Curing took place at 230 ° C for 30 seconds.

As reference R1, a sheet of substrate S was coated only with the CC primer in a layer thickness of 10 .mu.m, without previously a corrosion layer was applied. The salt spray test was carried out in accordance with DIN EN ISO 9927. All test panels were subjected to the salt spray test for 504 hours.

The evaluation was carried out as a modification of the DIN, since the infiltration was measured not at ten zufäliigen points along the scribe, but at the 10 largest sub-migrations, in the following Table 1, the results are given.

Table 2:

Corrosion test 2 with salt spray test (DIN EN ISO 9227)

For the Salzsprühnebeitest to BK3, the autodepositively coated substrate BK3 was first coated with the Coilcoating primer Coiltec Universal P CF BASF Coatings AG with a layer thickness of 5 μητι and then coated with a topcoat (CD33-0649) de layer thickness 20 pm. When cured, the PMT (peak metal temperature) was 245 ° C.

As reference R2, the same two-layer lacquer structure as for BK3 was applied directly to a metal sheet of the substrate SK. The salt spray test was carried out in accordance with DIN EN ISO 9927. All test bends were subjected to the salt spray test for 360 hours, the results are given in Table 2 below. Table 3:

Claims

claims:

1. A method for the autodepositing of a metallic substrate at a pH of 1 to 4 and a immersion time of the substrate of 1 s to 15 min in an aqueous polymer dispersion comprising at least one water-soluble and / or water-dispersible (meth) acryS block A copolymer comprising at least one olefinically unsaturated monomer (a) having a metal ion-coordinating group, at least one of monomer (a) different olefinically unsaturated monomer (b) copolymerized with a crosslinking group B and Diphenyiethyien, characterized in that the metallic Substrate is not treated with corrosive substances prior to autodeposition.

2. The method according to claim 1, characterized in that the aqueous polymer dispersion has a pH of 2 to 3, preferably 2.2 to 2.8, in particular 2.4 to 2.6.

3. The method according to claim 1 to 2, characterized in that the pH of the aqueous polymer dispersion was adjusted by an inorganic acid, preferably white by nitric acid.

4. The method according to claim 1 to 3, characterized in that the immersion time of the substrate in the aqueous Polymerdisperston 1 s to 1 min, in particular 10 s to 40 s.

5. The method according to claim 1 to 4, characterized in that the substrate is a galvanized, preferably hot-dip galvanized sheet, in particular a hot-dip galvanized steel sheet.

6. The method according to claim 1 to 5, characterized in that the substrate has been cleaned prior to coating with at least one detergent, preferably with at least one ether and / or at least one alcohol, in particular with an ether and / or at least one alcohol in the ultrasonic bath.

7. The method according to claim 1 to 6, characterized in that at least one (meth) acrylic block copolymer is used as the polymer, which is obtainable by the radical polymerization of

a) at least one otefinically unsaturated monomer (a) having a metal ion coordinating group,

b) at least one unsaturated monomer (b) other than monomer (a) having a crosslinking group B,

c) diphenylethyls and

d) optionally at least one of the oily unsaturated monomers (a), (b) and (c) different oily unsaturated monomer of the general

Formula I

RR ² C = CR ³ R ⁴ (I)

.worin the radicals R \ R ² , R ³ and R ^{4 are} each independently hydrogen or substituted or unsubstituted alkyl, Cycioalkyl-, Alkyicycioalkyl-, Cycloalkylalkyl-, Aryi-, Alkylaryh Cycloalkylaryl-, arylalkyl or Arylcycloaylreste stand with the Provision is made 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.

8. The method according to claim 1 to 7, characterized in that at least one polymer is used which contains at least one unsaturated alkoxysilane monomer, preferably at least one vinylafkoxysilane monomer, in particular triethoxyvinylsilane polymerized in addition to other monomers,

9. The method according to claim 1 to 8, characterized in that the aqueous polymer dispersion has a solids content of 1 to 10 wt .-%, preferably 1 to 5 wt -%, in particular 2 to 3 wt .-% has.

10. The method according to claim 1 to 9, characterized in that selectively the grain boundaries and surface defect structures are coated.

11. Autophoretic coating composition for the process according to the claims

1 to 10.

12. multi-layer coating comprising a layer produced by the processes according to claims 1 to 10 and at least one further lacquer layer which is applied to the autodeposited layer.