DE102010019245A1 - Process for autophoretic coating, coating agent and multicoat paint system - Google Patents

Abstract

A method of autodepositing a metallic substrate at a pH of 1 to 4 and immersing the substrate for 1 second to 15 minutes in an aqueous polymer dispersion comprising at least one water-soluble and / or water-dispersible (meth) acrylic block copolymer at least one olefinically unsaturated monomer (a) having a metal ion-coordinating group, at least one of monomer (a) comprises different olefinically unsaturated monomer (b) copolymerized with a crosslinking group B and diphenylethylene in copolymerized. In this case, the metallic substrate is not treated with corrosive substances before the autodeposition coating. In addition, the application deals with a corresponding coating agent and a multicoat system comprising a corresponding autodeposited layer.

Description

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.

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 current-free corrosion protection coating, also called ACC process (Autophoretic Chemical Coating), polymers, for example emulsion polymers containing acrylates or styrene / butadiene, 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 in terms of environmental compatibility and are 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 compositions, it has also been found that ACC coating compositions comprising salts of the lanthanide and the d-elements as well as an organic film-forming component likewise ensure a very good corrosion protection comparable to the chromium-containing coating compositions.

WO-A-96/10461 describes an aqueous corrosion inhibitor containing as components anions having a central atom selected from the group consisting of titanium, zirconium, hafnium, silicon, and at least 4 fluorine atoms as ligands and an organic polymer dispersion. Disadvantage of the invention according to WO-A-96/10461 , in that when the corrosion inhibitor is deposited 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 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-37 27 382 describes chromium-free aqueous dispersions of adducts of carboxylic acids and isocyanates with epoxides, which are suitable for the autodeposition 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. Also, such 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 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 corrosion protection layer and the use of ecologically critical substances, in particular hydrofluoric acid or fluorides.

In DE-A-103 30 413 describes coating compositions which are suitable for coating metallic surfaces and may contain caprolactam-modified polyisocyanates based on polyethyleneimines. The coating compositions can be applied by 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 above. 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 surface defect structures by an autophoretic method according to the invention. Due to the selective deposition at the grain boundaries and the surface defect structures, the material cost of the coating agent drops considerably 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 (meth) acrylic block copolymer which can be prepared from at least one olefinically unsaturated monomer (a) having a metal ion-coordinating group, at least one monomer (a) different olefinic unsaturated monomer (b) having a crosslinking group and diphenylethylene, wherein the metallic substrate is not treated with corrosive substances prior to autodeposition. A metallic substrate coated by this method is known in 1a and 1b shown.

Detailed description

1a : SEM photograph of a hot-dip galvanized steel sheet (HDG steel) after autophoretic coating on the grain boundaries and surface defect structures.

1b : SEM photograph of a hot-dip galvanized steel sheet (HDG steel) after autophoretic coating on the grain boundaries and surface defect structures.

2a : An SEM image of a hot-dip galvanized steel (HDG steel) after degreasing and cleaning in a three-stage solvent process. 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.

2 B : An SEM image of a hot-dip galvanized steel (HDG steel) after degreasing and cleaning in a three-stage solvent process. 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.

3a : Potential mapping of the surface of a hot-dip galvanized steel sheet (HDG steel) after being degreased and cleaned in a three-stage solvent process.

3b : Diagram of the potential curve along the section from a to f in 3a ,

4 Element-mapping by EDX from a hot-dip galvanized steel sheet (HDG steel) after being 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 element distributions of Al, O and Zn.

The term "grain boundaries and surface defect structures" is to be understood below to mean the areas of the surface of metallic substrates that do not represent monocrystalline areas of the surface. The microstructure of metallic substrates is predominantly polycrystalline. It is formed from a large number of individual crystallites, which differ from each other in the orientation or structure of their atomic arrangement. Thus, adjacent crystallites having the same interfaces may have different orientations. The interfaces between them are called grain boundaries. They consist of narrow transition zones with disturbed arrangement. The disordered atoms cause compressive or tensile stresses in their environment. Small angle 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, these errors can generally be subsumed under the generic term surface defect structures, which also include scratches or other defects that 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. 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 lowering of the chemical potential at a grain boundary or surface defect structures is more than 0.02 V from the directly adjacent undisturbed surface. Among other things due to the lowered chemical potential, the grain boundaries and the surface defect structures are the starting point for a beginning corrosion of the metallic substrate. Blocking the grain boundaries and the surface defect structures is therefore desirable for effective corrosion protection. Grain boundaries and surface defect structures on metallic surfaces can be detected by a variety of microscopy types, such as by light microscopy, SEM, and AFM. To show for example 2a and 2 B SEM images of a degreased and cleaned hot-dip galvanized steel sheet (purified HDG steel) showing clearly the individual grain boundaries and surface defect structures. Grain boundaries and surface defect structures differ markedly in shading in the SEM image and present irregularities in the otherwise crystalline surface. Grain boundaries are manifested above all in depressions on the surface, which can be up to 1 μm wide. Surface defect structures can be both pits and raised edges 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 generally 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 ratios of the elements to each other and optionally also other elements are incorporated. So shows 4 Element mapping using EDX from HDG steel. It can be clearly recognized that the composition of the substrate HDG steel in the region of the grain boundaries and surface defect structures varies greatly compared to the composition of the crystallites. Above all, the content of the foreign ion Al is greatly increased in the range of grain boundaries and surface defect structures. Thus, grain boundaries and surface defect structures are areas where the concentration of the elements is different from the concentration of the elements in the adjacent crystallites.

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

• – gegebenenfalls funktionalisierte Harnstoffe und/oder Thioharnstoffe, insbesondere Acylthioharnstoffe wie beispielsweise Benzoylthioharnstoff,
• – gegebenenfalls funktionalisierte Amine und/oder Polyamine, wie insbesondere EDTA,
• – gegebenenfalls funktionalisierte Amide, insbesondere Carbonsäureamide
• – Imine und Imide, wie insbesondere iminfunktionalisierte Pyridine,
• – Oxime, bevorzugt 1,2-Dioxime wie funktionalisiertes Diacetyldioxim,
• – Organoschwefelverbindungen, wie insbesondere gegebenenfalls funktionalisierte Thiole wie Thioethanol, Thiocarbonsäuren, Thioaldehyde, Thioketone, Dithiocarbamate, Sulfonamide, Thioamide und besonders bevorzugt Sulfonate,
• – Organophosphorverbindungen, wie insbesondere Phosphate, besonders bevorzugt Phosphorsäureester von (Meth)acrylaten, sowie Phosphonate, besonders bevorzugt Vinylphosphonsäure und hydroxy-, amino- und amidofunktionalisierte Phosphonate,
• – gegebenenfalls funktionalisierte Organoborverbindungen, wie insbesondere Borsäureester,
• – gegebenenfalls funktionalisierte Polyalkohole, wie insbesondere Kohlenhydrate und deren Derivate sowie Chitosane,
• – gegebenenfalls funktionalisierte Säuren, wie insbesondere di- oder oligofunktionelle Säuren, oder gegebenenfalls funktionalisierte (Poly)carbonsäuren, wie insbesondere Carbonsäuren, die ionisch und/oder koordinativ an Metallzentren gebunden werden können, bevorzugt (Poly)methacrylate mit Säuregruppen oder di- oder oligofunktionelle Säuren,
• – gegebenenfalls funktionalisierte Carbene,
• – Acetylacetonate,
• – Gegebenenfalls funktionalisierte Heterocyclen, wie Chinoline, Pyridine, wie insbesondere iminfunktionalisierte Pyridine, Pyrimidine Pyrrole, Furane, Thiophene, Imidazole, Benzimidazole, bevorzugt Mercaptobenzimidazole, Benzthiazole, Oxazole, Thiazol, Pyrazole oder auch Indole,
• – gegebenenfalls funktionalisierte Acetylene, sowie
• – Phytinsäure und deren Derivate.

"Metal ion coordinating groups" are contained in ligands A, which can complex metal ions. These ligands A have electron pairs, usually lone pairs, with which they can coordinate to metal ions. Suitable ligands A are all groups or compounds which are able to form chelates with the metal ions released upon corrosion of the substrate. As a rule, the ligands A are randomly distributed in the polymer. Preference is given to mono- or polydentate potentially anionic ligands A. Particularly preferred metal ion-coordinating groups which are contained in the 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, thioaldehydes, thioketones, dithiocarbamates, sulfonamides, thioamides and particularly preferably sulfonates,
• 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 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 .
• 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 also indoles,
• - 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 of monomer (a) different olefinically unsaturated monomer (b) 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 structures 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 exhibit a gradient in the concentration of covalently bonded hydrophilic groups HG along the main polymer chain 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 having an average particle diameter of <50, preferably <35 and particularly preferably <20 nm, or are dissolved in molecular dispersion. That's different such aggregates in their average particle diameter significantly of dispersion particles, as they are for example in DE-A-37 27 382 or WO-A-96/10461 to be discribed. Molecular dispersions of dissolved polymers generally have weight average molecular weights Mw of <200,000, preferably <120,000, particularly preferably <50,000 daltons. 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 produced 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 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 solvation capacity and the steric accessibility of the groups HG and can also be set by a person skilled in the art in a manner known per se.

As the polymer backbone of the polymers it is possible to use any desired polymers, preferably those having weight-average molecular weights Mw of from 500 to 50,000 daltons, more preferably having molecular weights Mw of from 700 to 20,000 daltons. The polymer backbone used are poly (meth) acrylates. 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.

• – gegebenenfalls funktionalisierte Harnstoffe und/oder Thioharnstoffe, insbesondere Acylthioharnstoffe wie beispielsweise Benzoylthioharnstoff,
• – gegebenenfalls funktionalisierte Amine und/oder Polyamine, wie insbesondere EDTA,
• – gegebenenfalls funktionalisierte Amide, insbesondere Carbonsäureamide
• – Imine und Imide, wie insbesondere iminfunktionalisierte Pyridine,
• – Oxime, bevorzugt 1,2-Dioxime wie funktionalisiertes Diacetyldioxim,
• – Organoschwefelverbindungen, wie insbesondere gegebenenfalls funktionalisierte Thiole wie Thioethanol, Thiocarbonsäuren, Thioaldehyde, Thioketone, Dithiocarbamate, Sulfonamide, Thioamide und besonders bevorzugt Sulfonate,
• – Organophosphorverbindungen, wie insbesondere Phosphate, besonders bevorzugt Phosphorsäureester von (Meth)acrylaten, sowie Phosphonate, besonders bevorzugt Vinylphosphonsäure und hydroxy-, amino- und amidofunktionalisierte Phosphonate,
• – gegebenenfalls funktionalisierte Organoborverbindungen, wie insbesondere Borsäureester,
• – gegebenenfalls funktionalisierte Polyalkohole, wie insbesondere Kohlenhydrate und deren Derivate sowie Chitosane,
• – gegebenenfalls funktionalisierte Säuren, wie insbesondere Di- und/oder oligofunktionelle Säuren, oder gegebenenfalls funktionalisierte (Poly)carbonsäuren, wie insbesondere Carbonsäuren, die ionisch und/oder koordinativ an Metallzentren gebunden werden können, bevorzugt (Poly)methacrylate mit Säuregruppen oder di- oder oligofunktionelle Säuren,
• – gegebenenfalls funktionalisierte Carbene,
• – Acetylacetonate,
• – Gegebenenfalls funktionalisierte Heterocyclen, wie Chinoline, Pyridine, wie insbesondere iminfunktionalisierte Pyridine, Pyrimidine Pyrrole, Furane, Thiophene, Imidazole, Benzimidazole, bevorzugt Mercaptobenzimidazole, Benzthiazole, Oxazole, Thiazol, Pyrazole oder auch Indole,
• – gegebenenfalls funktionalisierte Acetylene, sowie
• – Phytinsäure und deren Derivate.

As ligands A containing metal ion coordinating groups, all groups or compounds are suitable 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. Particularly preferred ligands included

• 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, thioaldehydes, thioketones, dithiocarbamates, sulfonamides, thioamides and particularly preferably sulfonates,
• 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- 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,
• 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 also indoles,
• - optionally functionalized acetylenes, as well
• - 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.

• – besonders bevorzugt Hydroxylgruppen
• – Mercapto- und Aminogruppen,
• – Aldehydgruppen,
• – Azidgruppen,
• – Säuregruppen, insbesondere Carbonsäuregruppen,
• – Säureanhydridgruppen, insbesondere Carbonsäureanhydridgruppen,
• – Säureestergruppen, insbesondere Carbonsäureestergruppen,
• – Ethergruppen,
• – besonders bevorzugt Carbamatgruppen,
• – Harnstoffgruppen,
• – Epoxidgruppen,
• – besonders bevorzugt Isocyanatgruppen, welche ganz besonders bevorzugt mit Blockierungsmitteln umgesetzt sind, welche bei den Einbrenntemperaturen der Beschichtungsmittel deblockieren und in das sich bildende Netzwerk eingebaut werden.

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 deblock at the stoving temperatures of the coating compositions and are incorporated into the forming network.

• – Hydroxylgruppen mit Isocyanat- und/oder Carbamatgruppen,
• – Aminogruppen mit Isocyanat- und/oder Carbamatgruppen,
• – Carbonsäuregruppen mit Epoxidgruppen.

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.

• a) mindestens einem olefinisch ungesättigten Monomer (a) mit einer Metallionenkoordinierenden Gruppe,
• b) mindestens einem vom Monomer (a) verschiedenen olefinisch ungesättigten Monomer (b) mit einer vernetzenden Gruppe B,
• c) Diphenyletyhlen und
• d) gegebenenfalls mindestens einem von den olefinisch ungesättigten Monomeren (a), (b) und (c) verschiedenen olefinisch ungesättigten Monomer der allgemeinen Formel I R¹R²C=CR³R⁴ (I) , worin die Reste R¹, R², R³ und R⁴ jeweils unabhängig voneinander für Wasserstoffatome oder substituierte oder unsubstituierte Alkyl-, Cycloalkyl-, Alkylcycloalkyl-, Cycloalkylalkyl-, Aryl-, Alkylaryl-, Cycloalkylaryl-Arylalkyl- oder Arylcycloalkylreste stehen, mit der Massgabe, dass mindestens zwei der Variablen R¹, R², R³ und R⁴ für substituierte oder unsubstituierte Aryl-, Arylalkyl- oder Arylcycloalkylreste, insbesondere substituierte oder unsubstituierte Arylreste, stehen.

Particularly preferred polymers contain copolymers which can be prepared by one-stage or multistage, free-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) in which the radicals R ¹ , R ² , R ³ and R ^{4 are} each independently of one another 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.

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, sulfonate, sulfonium, phosphate, phosphonate -, phosphonium, ammonium and / or carboxylate groups and 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 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 salts and / or their partial esters. 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 from 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 has up to 20 carbon atoms contains, as preferred, 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, beta-unsaturated carboxylic acid amides such as N-methylol and N, N-dimethylol aminoethyl acrylate, aminoethyl methacrylate, acrylamide and methacrylamide. Suitable amine group-containing monomers are: 2-aminoethyl acrylate and methacrylate, N-methyl and N, N-dimethyl-aminoethyl acrylate, or allylamine. 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, N-dimethyl (meth) acrylamide used. Preferred ethoxylated 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 polyamine subtituents, imine and imide substituents, in particular imin-functionalized pyridines, oxime substituents, preferably 1,2-dioximes such as functionalized diacetyldioxime, organo-sulfur substituents, in particular derivable from optionally functionalized thiols such as thioethanol, thiocarboxylic acids, thioaldehydes, thioketones, dithiocarbamates, sulfonamides, thioamides and particularly preferably sulfonates, organophosphorus substituents, in particular derivable from phosphates, more preferably phosphoric acid esters of (meth) acrylates, and phosphonates, more preferably vinylphosphonic acids and hydroxy, amino- and amido-functionalized phosphonates, optionally functionalized organoboron substituents, such as in particular derivable from boric acid esters, optionally functionalized polyalcohol substituents, w ie in particular derivable from carbohydrates and derivatives thereof as well as 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 bound ionically and / or coordinately to metal centers , Preferred (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, 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 the ester and / or amide radical exhibit. 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 acid anhydride groups, acid ester groups, especially carboxylic acid ester groups, ether groups, more preferably carbamate groups, for example urea groups, epoxide groups, and particularly preferably isocyanate groups which are most preferably reacted with blocking agents which deblock at the baking temperatures of the coating agents and are incorporated into the forming network.

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 usually 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 randomly arranged along the main polymer chain. From the above performance of the exemplified monomers (a) and (b) 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, then the Ligand A and the crosslinking functional groups B typically have a gradient along the polymer backbone.

As monomers (d), which need not necessarily be used but whose use is advantageous, 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 furthermore, for example, in DE-A-198 58 708 described.

Examples of particularly preferably used monomers (d) are / dinaphthaleneethylene, cis or trans stilbene, vinylidene bis (4-N, N-dimethylaminobenzene), vinylidene bis (4-aminobenzene) or vinylidene bis (4-nitrobenzene) ,

In the preparation of the copolymers, the mixture of all monomers is preferably metered into the water phase at the same time, 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 decreases the number of hydrophilic groups along the polymer chain. 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 continue to the teachings of DE-A-198 58 708 , of the DE-A-102 06 983 and the DE-A-102 56 226 directed.

Advantageously, at least one polymer is used which contains at least one unsaturated alkoxysilane monomer, preferably at least one vinylalkoxysilane 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 no full-area coating of the substrate takes place, but rather that the grain boundaries and surface defect structures are selectively coated. As a result, a considerable saving of material is achieved while still achieving good corrosion protection. The grain boundaries and surface defect structures are usually 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 method.

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 behind corresponds to the solid in the investigated system.

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.

Preparation example of polymer dispersions P1-P3

The positions of the first reaction stage are placed in a 2000 ml glass reactor with anchor stirrer and heated to 70 ° C. under a nitrogen atmosphere. After reaching the temperature, the initiator solution is added over a period of 20 min. 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: substance Polymer dispersion P1 (DPE-MS-6) Polymer Dispersion P2 (DPE-TEVS-3) Polymer Dispersion P3 (DPE-TEVS-6) step 1 H ₂ O 67.86 66,60 65.90 acrylic acid - 1.20 1.20 maleic 0.44 - - methyl methacrylate 2.20 1.12 2.10 1,1-diphenyl 0.18 0.18 0.18 initiator (NH ₄ ) S ₂ O ₈ [in H ₂ O] 0.27 [5.86] 0.27 [5.86] 0.27 [5.86] Level 2 Buthylmethacylat 22.00 21.60 21.40 hydroxyethyl methacrylate 1.10 1.10 1.10 triethoxyvinylsilane - 1.10 2.10

Polymer dispersion P1 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 0.6 mm from Voestalpine AG, Linz, Austria), is degreased and cleaned in a three-stage solvent cleaning process. Purification with tetrahydrofuran, 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.

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 (Ridoline C72 from Henkel) and then with distilled water rinsed.

Production Example of Autophoretic Coating at the Grain Boundaries and Surface Defects of a BK1-BK3 Substrate

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 autophoretically coated at the grain boundaries and surface defects were obtained.

Comparative example for a comprehensive autophoretic coating BF1-BF2

For the deposition of the polymer dispersions P1 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. By immersing the substrate SF in the polymer dispersions P1 to P3 for 30 s.

Corrosion test 1 with the salt spray test (DIN EN ISO 9227)

For the salt spray test, the autodeposited substrates BK1, BK2, BF1 and BF2 were each coated with the Coiltec Universal P CF Coil Coating Primer from BASF Coatings AG. The layer thickness of the primer is 10 μm in all cases. The curing was carried out at 230 ° C for 30 s.

As reference R1, a sheet of the substrate S was coated only with the CC primer in a layer thickness of 10 microns, without the previously applied a corrosion layer.

The salt spray test was after DIN EN ISO 9927 carried out. All test panels were subjected to the salt spray test for 504 hours.

The evaluation was carried out in a modification of the DIN, as the infiltration was measured not at ten random locations along the scribe, but at the 10 largest sub-migrations. The following table 1 gives the results. Table 1: corrosion coating Infiltration in mm Reference R1 none 3.3 BK1 selectively 1.3 BF1 coverage 3.3 BK2 selectively 1.2 BF2 coverage 1.5

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

For the salt spray test on BK3, the autodeposited substrate BK3 was first coated with the Coilcoating Primer Coiltec Universal P CF from BASF Coatings AG with a layer thickness of 5 μm and then coated with a topcoat (CD33-0649) of the layer thickness 20 μm. When cured, the PMT (peak metal temperature) was 245 ° C.

As reference R2, the same two-coat paint system as for BK3 was applied directly to a metal sheet of the substrate SK. The salt spray test was after DIN EN ISO 9927 carried out. All test panels were subjected to the salt spray test for 360 hours. the results are given in the following Table 2. Table 2: Infiltration in mm Reference R2 4.9 BK3 3.8

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 96/10461 A [0005, 0005, 0028]
• DE 3727382 A [0006, 0028]
• DE 10330413 A [0007]
• DE 102006053291 A [0008]
• DE 19858708 A [0045, 0047]
• DE 10206983 A [0047]
• DE 10256226A [0047]

Cited non-patent literature

• DIN EN ISO 9927 [0066]
• DIN EN ISO 9927 [0069]

Claims (12)

A method of autodepositing a metallic substrate at a pH of 1 to 4 and immersing the substrate for 1 second to 15 minutes in an aqueous polymer dispersion comprising at least one water-soluble and / or water-dispersible (meth) acrylic block copolymer 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 diphenylethylene in copolymerized, characterized in that the metallic substrate before the autophoretic coating is not treated with corrosive substances. A 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. A method according to claim 1 to 2, characterized in that the pH of the aqueous polymer dispersion has been adjusted by an inorganic acid, preferably by nitric acid. A method according to claim 1 to 3, characterized in that the immersion time of the substrate in the aqueous polymer dispersion 1 s to 1 min, in particular 10 s to 40 s. A 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. A 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. A method according to claim 1 to 6, characterized in that as the polymer at least one (meth) acrylic block copolymer is used, which is obtainable by the radical polymerization of a) at least one olefinically unsaturated monomer (a) having a metal ion-coordinating group, b ) At least one of the monomer (a) different olefinically unsaturated monomer (b) with a crosslinking group B, c) Diphenyletyhlen and d) optionally at least one of the olefinically unsaturated monomers (a), (b) and (c) different olefinically unsaturated monomer the general formula I R ¹ R ² C = CR ³ R ⁴ (I) in which the radicals R ¹ , R ² , R ³ and R ^{4 are} each independently of one another 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. A 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 vinylalkoxysilane monomer, in particular triethoxyvinylsilane copolymerized in addition to other monomers. A 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. A method according to claims 1 to 9, characterized in that the grain boundaries and surface defect structures are selectively coated. Autophoretic coating composition for the process according to claims 1 to 10. A multi-layer coating comprising a layer produced according to the methods of claims 1 to 11 and at least one further lacquer layer which is applied to the autodeposited layer.

Images