EP2296830B1 - Process for coating metal bands - Google Patents

Description

Processes and coating compositions for painting metal strips (coils) are known. As a rule, the coating compositions are applied in three coating stages.

In a first stage, after unwinding the metal strip and cleaning with an alkaline pickling solution followed by rinsing with water, a pre-treatment agent is applied to the metal strip to increase corrosion resistance. For this purpose, the development of chromium-free pretreatment agents has recently been sought, which ensure a very good, the chromium-containing coating compositions comparable corrosion protection. In this case, pretreatment agents containing as inorganic component salts and / or complexes of the d-elements, turned out to be particularly suitable. Preferred pretreatment solutions generally also contain adhesion promoters, such as, for example, silanes, which are intended to ensure adhesion to the metal substrate and the subsequent layers, and a small proportion of preferably water-soluble polymers, which are generally less of the filming than the targeted control of the crystal growth of the abovementioned serve inorganic components. The pretreatment agent is usually sprayed onto the metal strip (rinse process followed by rinsing) or applied by means of a chemcoater (no-rinse process, no rinse). Thereafter, the metal strip coated with the pretreatment agent is dried at a maximum temperature of the metal strip (PMT = peak metal temperature) of about 90 ° C.

In the second stage, a primer is applied to the metal strip precoated according to the first stage, preferably by means of roller application. These are almost exclusively solvent-based coating systems, which are applied in such a wet layer thickness that results in a layer thickness of 4 to 8 microns after drying and curing. As a rule, the primers contain polyesters, polyurethanes, epoxy resins and / or more rarely polyacrylates Binder components and melamine resins and / or polyisocyanates as crosslinker components. The curing of the primer layer is usually carried out at a PMT between 220 and 260 ° C in a baking oven, the metal strip is cooled after leaving the baking oven abruptly by means of a Wasserervohangs and thereafter dried.

In the third final step, the metal strip precoated according to the second step is overcoated with a top coat, the topcoats being applied in such a wet layer thickness that a layer thickness of 15 to 25 μm results after drying and the curing of the topcoat layer in usually with a PMT between 220 and 260 ° C in a baking oven.

Since the above method is complicated and energy-intensive, there has been no lack of attempts to simplify the process, in particular to summarize the process steps, and to reduce the energy requirements of the process.

For example, describes the WO 2007/125038 a method for the coating of metal strips, in which the pretreatment agent is integrated in an aqueous primer coating. This is achieved with the aid of special copolymers containing monomer units with N-heterocycles, monomer units with acid groups and vinylaromatic monomer units, as corrosion inhibitors. As crosslinkable binders, customary binders which have sufficient flexibility can be used in the field of coil coating lacquers. Preferred binders are according to WO 2007/125038 Poly (meth) acrylates or styrene-acrylate copolymers, styrene-alkadiene copolymers, polyurethanes and alkyd resins. Before the topcoats are applied, the described primer layers are baked. However, the course and recoatability of such primer layers is highly dependent on the choice of binder components and often difficult to adjust. Especially the separate baking step for the primer coating is energy-intensive and therefore not ecologically and economically optimal.

In WO-A-2005/047390 describes primers containing water-dispersible polyurethanes with acid groups as a binder, which are neutralized with amines having crosslinkable groups. The primer layers are cured prior to application of the topcoat layer in a separate energy intensive baking step, that is crosslinked, the specific choice of amines prevents the acid-catalyzed curing of the topcoat is hindered, which otherwise leads to wrinkling and metallic-looking disorders in the topcoat. Even with such systems, the course and recoatability of the primer coating depend strongly on the choice of binder components and the separate baking step for the primer coating is energy-intensive and therefore not ecologically and economically optimal.

In WO-A-01/43888 describes a method in which the topcoat layer is applied to a non-dried layer of a pretreatment agent, wherein the non-dried layer of the pretreatment agent should have a certain conductivity necessary for the application of the topcoat layer and the topcoat is preferably a powder coating. If such topcoats are used, unwanted mixing of pretreatment agent and topcoat occurs depending on the degree of moisture of the layer of high-moisture pretreatment agent. For low degrees of moisture, the course and overcoatability of the pretreatment agent layer greatly depends on the choice of binder components.

Another method of applying a thermosetting coil coating primer is known from US 5,156,074 DE 27 36 542 A1 known.

Task and solution

In the light of the aforementioned prior art, it was the object of the invention to provide a method for the application of integrated, low-solvent coating compositions, the function of corrosion protection and the Primers combine to find on metal ribbons, which allows the broad applicability of binders in integrated coatings and in particular leads to coatings that have a very good flow and recoatability. At the same time, the composite of primer and topcoat should meet the high demands placed on coils coated with such composites, in particular corrosion resistance, bendability and chemical resistance, especially when these coils are reshaped and exposed to weathering. In particular, the method should allow a reduction in the expenditure on equipment and energy by combining individual steps in the coil coating process.

1. (1) Aufbringen eines wäßrigen Primer-Beschichtungsmittels (B) enthaltend mindestens ein thermisch vernetzbares Bindemittelsystem (BM), mindestens eine Füllstoffkomponente (BF), mindestens eine Korrosionsschutzkomponente (BK) und flüchtige Bestandteile (BL), auf die gegebenenfalls gereinigte Metalloberfläche, wobei das Beschichtungsmittel (B) einen Gehalt an organischen Lösemitteln von weniger als 15 Gew-%, bezogen auf die flüchtigen Bestandteile (BL) des Beschichtungsmittels (B), aufweist,
2. (2) Trocknung der aus dem Beschichtungsmittel (B) gebildeten integrierten Vorbehandlungsschicht, wobei die Trocknung vorzugsweise bei PMT (Peak-Metal-Temperaturen) unterhalb der DMA-Onset-Temperatur für die Reaktion der vernetzbaren Bestandteile des Bindemittelsystems (BM) durchgeführt wird,
3. (3) Auftrag einer Decklackschicht (D) auf die gemäß Schritt (2) getrocknete integrierte Vorbehandlungsschicht und
4. (4) gemeinsame Aushärtung der Schichten aus Beschichtungsmittel (B) und Decklack (D),

wobei das Bindemittelsystem (BM) mindestens ein wasserlösliches oder wasserdispergierbares Bindemittel auf der Basis von Polyestern und/oder Polyurethanen enthält.The object according to the invention is surprisingly achieved by a method for coating metal strips with the following method steps:

1. (1) applying an aqueous primer coating composition (B) comprising at least one thermally crosslinkable binder system (BM), at least one filler component (BF), at least one corrosion protection component (BK) and volatile constituents (BL) to the optionally cleaned metal surface, wherein the Coating composition (B) has an organic solvent content of less than 15% by weight, based on the volatile constituents (BL) of the coating composition (B),
2. (2) drying the integrated pretreatment layer formed from the coating agent (B), wherein the drying is preferably carried out at PMT (peak metal temperatures) below the DMA onset temperature for the reaction of the crosslinkable components of the binder system (BM),
3. (3) applying a topcoat layer (D) to the integrated pretreatment layer dried according to step (2) and
4. (4) co-curing of the layers of coating agent (B) and topcoat (D),

wherein the binder system (BM) contains at least one water-soluble or water-dispersible binder based on polyesters and / or polyurethanes.

Description of the invention The aqueous primer coating agent (B)

The aqueous preferably crosslinkable primer coating agent (B) with which the integrated pretreatment layer is formed combines the properties of a pretreatment agent and a primer. The term "integrated pretreatment layer" in the sense of the invention means that the aqueous primer coating composition (B) is applied directly to the metal surface, without first undergoing a corrosion-inhibiting pretreatment, such as passivation, application of a conversion layer or phosphating. The integrated pretreatment layer combines the passivation layer with the organic primer in a single layer. The term "metal surface" here is not to be equated with absolutely bare metal, but describes the surface that inevitably forms in the usual handling of the metal in an atmospheric environment or when cleaning the metal before applying the integrated pretreatment layer. The actual metal may, for example, still have a moisture film or a thin oxide or hydrated oxide layer.

The aqueous primer coating agent (B) with which the integrated pretreatment layer is formed contains at least one binder system (BM), at least one filler component (BF), at least one anticorrosion component (BK) and volatile components (BL).

The volatile constituents (BL) are those constituents of the coating composition (B) which are defined during the drying of (B) in step (2) of the process according to the invention and in particular in the curing of coating composition (B) and topcoat (D) in step (4 ) of the method according to the invention are completely removed from the layer composite.

It is essential to the invention that the content of organic solvent in the coating agent (B) is less than 5% by weight, based on the volatile constituents (BL) of the coating composition (B).

The amount of volatiles (BL) in the coating agent (B) can vary widely, with the ratio of volatiles (BL) to nonvolatile constituents of the coating agent (B) typically between 10: 1 and 1:10, preferably between 5: 1 and 1: 5, more preferably between 4: 1 and 1: 4.

The binder system (BM)

The binder systems (BM) usually comprise the proportions in the aqueous primer coating agent (B), which are responsible for the film formation.

The layers applied in the coil coating must have sufficient flexibility to survive the deformation of the metal strips without damage, in particular by cracking or spalling of the coating. Therefore, binders suitable for the binder systems (BM) preferably also contain building blocks which ensure the necessary flexibility, particularly preferably soft segments.

The inventively preferred crosslinkable binder systems (BM) form a polymeric network during thermal and / or photochemical curing and include thermally and / or photochemically crosslinkable Components. The crosslinkable components in the binder system (BM) may be low molecular weight, oligomeric or polymeric and generally have at least two crosslinkable groups. The crosslinkable groups can be either reactive functional groups that can react with groups of their type ("with themselves") or with complementary, reactive functional groups. Here, various combination options are conceivable. The crosslinkable binder system (BM) may comprise, for example, a self-crosslinkable polymeric binder and one or more low molecular weight or oligomeric crosslinkers (V). Alternatively, the polymeric binder itself can have crosslinkable groups which can react with other crosslinkable groups on the polymer and / or on an additionally used crosslinker. Particular preference is given to using crosslinkable oligomers or polymers which are crosslinked to one another using crosslinkers (V).

The preferred thermally crosslinkable binder systems (BM) crosslink on heating the applied layer to temperatures above room temperature and preferably have crosslinkable groups which do not react at room temperature or react only in a very small proportion. Preferably, such thermally crosslinkable binder systems (BM) are used whose crosslinking at DMA onset temperatures above 60 ° C, preferably above 80 ° C, particularly preferably above 90 ° C used (measured on a DMA IV from Rheometric Scientific at a heating rate of 2 K / min, a frequency of 1 Hz and an amplitude of 0.2% with the measuring method "Tensile Mode - Tensile off" in the mode "Delta", wherein the location of the DMA onset temperature in a known manner by extrapolation of the temperature-dependent course of E 'and / or tanδ is determined).

Suitable binders for the crosslinkable binder systems (BM) are preferably water-soluble or water-dispersible poly (meth) acrylates, partially saponified polyvinyl esters, polyesters, alkyd resins, Polylactones, polycarbonates, polyethers, epoxy resins, epoxy resin-amine adducts, polyureas, polyamides, polyimides or polyurethanes, water-soluble or water-dispersible crosslinkable binder systems (BM) based on polyesters, epoxy resins or epoxy resin-amine adducts, poly (meth) acrylates and Polyurethanes are preferred. Very particularly preferred are water-soluble or water-dispersible crosslinkable binder systems (BM) based on polyesters and in particular polyurethanes.

Suitable water-soluble or water-dispersible binder systems (BM) based on epoxides or epoxide-amine adducts are epoxy-functional polymers which are prepared in a known manner by reaction of epoxy-functional monomers, for example bisphenol A diglycidyl ether, bisphenol F diglycidyl ether or hexanediol diglycidyl ether, can be prepared with alcohols such as bisphenol-A or bisphenol-F. Particularly suitable as soft segments are polyoxyethylene and / or polyoxypropylene segments, which are advantageously incorporated via the use of ethoxylated and / or propoxylated bisphenol-A. To improve the adhesion, some of the epoxide groups of the above-mentioned epoxy-functional polymers can be reacted with amines to form epoxy resin-amine adducts, in particular with secondary amines, such as, for example, diethanolamine or N-methylbutanolamine. For the preparation of the epoxy resins, preference is furthermore given to using monomer units which, in addition to the free epoxy groups of the epoxy resin, have further functional groups which react with groups of their type ("with themselves") or with complementary, reactive functional groups, in particular with crosslinkers (V) can. These are in particular hydroxyl groups. Suitable epoxy resins or epoxy resin-amine adducts are commercially available. Further details of epoxy resins are, for example, in " Epoxy Resins "in Ullmann's Encyclopedia of Industrial Chemistry, 6th Edition, 2000, Electronic Release represented.

Suitable water-soluble or water-dispersible binder systems (BM) based on poly (meth) acrylates are, in particular, emulsion (co) polymers, in particular anionically stabilized poly (meth) acrylate dispersions, obtainable usually from (meth) acrylic acid and / or (meth) acrylic acid derivatives , in particular (meth) acrylic acid esters, such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate or 2-ethylhexyl (meth) acrylate and / or vinylaromatic monomers such as styrene and optionally crosslinking comonomers. The flexibility of the binder systems (BM) can be achieved in a manner known in principle by the ratio of "hard" monomers, ie monomers which form comparatively high glass transition temperature homopolymers, such as methyl methacrylate or styrene, to "soft" monomers, ie monomers, the homopolymers with comparatively low glass transition temperature, such as butyl acrylate or 2-ethylhexyl acrylate. For the preparation of the poly (meth) acrylate dispersions, preference is furthermore given to using monomers which have functional groups which can react with groups of their type ("with themselves") or with complementary, reactive functional groups, in particular with crosslinkers. These are, in particular, hydroxyl groups which are reacted using monomers, such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate or N-methylol (meth) acrylamide or else of epoxy (meth) acrylates Hydrolysis into which poly (meth) acrylates are incorporated. Suitable poly (meth) acrylate dispersions are commercially available.

The water-soluble or water-dispersible binder systems (BM) based on polyesters which are preferred according to the invention can be synthesized in a known manner from low molecular weight dicarboxylic acids and dialcohols and optionally other monomers. Other monomers include in particular branching monomers, such as For example, tri- or higher functional carboxylic acids and alcohols. For the use of the binder systems (BM) in the metal strip coating, preference is given to using polyesters having comparatively low molecular weights, preferably those having number-average molecular weights Mn of between 500 and 10,000 daltons, preferably between 1,000 and 5,000 daltons. The number average molecular weights are determined by means of gel permeation chromatography according to the standards DIN 55672-1 to -3.

The hardness and flexibility of binder systems based on polyesters can in a manner known in principle by the ratio of "hard" monomers, that is, monomers which form homopolymers with comparatively high glass transition temperature to "soft" monomers, that is, monomers containing homopolymers with form comparatively low glass transition temperature can be adjusted. Examples of "hard" dicarboxylic acids include aromatic dicarboxylic acids or their hydrogenated derivatives, such as, for example, isophthalic acid, phthalic acid, terephthalic acid, hexahydrophthalic acid and derivatives thereof, in particular anhydrides or esters. Examples of "soft" dicarboxylic acids include in particular aliphatic α, ω-dicarboxylic acids having at least 4 carbon atoms, such as adipic acid, azelaic acid, sebacic acid, dodecanedioic acid or dimer fatty acids. Examples of "hard" dialcohols include ethylene glycol, 1,2-propanediol, neopentyl glycol or 1,4-cyclohexanedimethanol. Examples of soft "dialcohols include diethylene glycol, triethylene glycol, aliphatic α, ω-dialcohols having at least 4 carbon atoms, such as 1,4-butanediol, 1,6-hexanediol, 1,8-octanediols or 1,12-dodecanediol.

The preparation of the commercially available polyesters, for example, in the Standard work Ullmanns Enzyklopadie der technischen Chemie, 3rd edition, volume 14, Urban & Schwarzenberg, Munich, Berlin, 1963, pages 80 to 89 and pages 99 to 105 described.

For the preparation of the water-solubility or water-dispersibility, groups capable of forming anions are preferably in the polyester molecules incorporated, which after their neutralization ensure that the polyester resin can be stably dispersed in water. Suitable groups capable of forming anions are preferably carboxyl, sulfonic acid and phosphonic acid groups, more preferably carboxyl groups. The acid number according to DIN EN ISO 3682 of the polyester resins is preferably between 10 and 100 mg KOH / g, more preferably between 20 and 60 mg KOH / g. For neutralization of preferably from 50 to 100 mol%, particularly preferably from 60 to 90 mol% of the groups capable of anion formation, preference is likewise given to ammonia, amines and / or amino alcohols, for example di- and triethylamine, dimethylaminoethanolamine, diisopropanolamine, morpholines and / or N-alkylmorpholines used. Hydroxyl groups are preferably used as crosslinking groups, the OH numbers according to DIN EN ISO 4629 of the water-dispersible polyester preferably being between 10 and 200 and particularly preferably between 20 and 150.

Subsequently, the thus prepared polyesters are dispersed in water, wherein the desired solids content of the dispersion is adjusted.

The solids content of the polyester dispersions prepared in this way is preferably between 5 and 50% by weight, more preferably between 10 and 40% by weight.

The binder systems (BM) based on polyurethanes which are particularly preferred according to the invention are preferably obtainable from the abovementioned polyesters as hydroxy-functional precursors by reaction with suitable di- or polyisocyanates. The preparation of suitable polyurethanes is, for example, in DE-A-27 36 542 described.

Into the polyurethane molecules, preferably groups capable of forming anions are incorporated for the preparation of water solubility or water dispersibility, which after neutralization ensure that the polyurethane resin can be stably dispersed in water to produce a polyurethane dispersion. Suitable for anion formation competent Groups are preferably carboxyl, sulfonic acid and phosphonic acid groups, more preferably carboxyl groups. The acid number of the water-dispersible polyurethanes according to DIN EN ISO 3682 is preferably between 10 and 80 mg KOH / g, more preferably between 15 and 40 mg KOH / g. Hydroxyl groups are preferably used as crosslinking groups, the OH numbers of the water-dispersible polyurethanes according to DIN EN ISO 4629 preferably being between 10 and 200 and particularly preferably between 15 and 80.

Particularly preferred water-dispersible polyurethanes are composed of hydroxy-functional polyester precursors, as described above, for example, which are preferably blended with mixtures of bisisocyanato compounds, such as, preferably, hexamethylene diisocyanate, isophorone diisocyanate, TMXDI, 4,4'-methylene-bis (cyclohexyl isocyanate), 4,4'- Methylenebis (phenylylisocyanate), 1,3-bis (1-isocyanato-1-methylethyl) benzene), other diols, in particular neopentyl glycol, and compounds capable of anion formation, in particular 2,2-bis (hydroxymethyl ) -propionic acid, are converted to the polyurethane. Optionally, the polyurethanes may be branched by the proportionate use of polyols, preferably triols, more preferably trimethylolpropane.

Very particular preference is given to carrying out the abovementioned building blocks at a ratio of the isocyanate groups to hydroxyl groups of 1.4: 1.005, preferably between 1.3: 1.05.

In a further very particularly preferred embodiment of the invention, the unreacted isocyanate groups to at least 25, preferably at least 50 mol%, based on the unreacted isocyanate groups, reacted with low volatility amines and / or amino alcohols, in particular triethanolamine, diethanolamine or methylethanolamine, wherein a part of the groups capable of forming anions is neutralized simultaneously with the amines and / or aminoalcohols.

The possibly remaining unreacted isocyanate groups are preferably reacted with blocking agents, in particular monofunctional alcohols, preferably propanols or butanols, until the content of free isocyanate groups is less than 0.1%, preferably less than 0.05%.

In the concluding step of the preparation of the polyurethane dispersion, preference is given to neutralizing preferably 50 to 100 mol%, particularly preferably 60 to 90 mol% of the groups capable of anion formation, of ammonia, amines and / or amino alcohols, for example di- and triethylamine, dimethylethanolamine , Diisopropanolamin, morpholines and / or N-alkylmorpholines used, with dimethylethanolamine is particularly preferred

Subsequently, the polyurethanes thus prepared are dispersed in water, wherein the desired solids content of the dispersion is adjusted.

The solids content of the polyurethane dispersions prepared in this way is preferably between 5 and 50% by weight, particularly preferably between 10 and 40% by weight.

In a particularly preferred embodiment of the invention, at least one of the above-described components of the binder system, in particular the above-described polyester and polyurethane components, in the form of an aqueous dispersion produced particularly low solvent, wherein the solvent, in particular after the preparation of the binder and prior to its dispersion in water, in a manner known to those skilled in the art, in particular by distillation, is removed. Preferably, the aqueous dispersion of the binder component, in particular the polyester and polyurethane dispersions, to a content of residual solvent of less than 1.5 wt .-%, more preferably of less than 1 wt .-% and most preferably of less than 0, 5 wt .-%, based on the volatile constituents of the dispersion.

The preferably water-soluble or water-dispersible crosslinkers (V) for the thermal crosslinking of the abovementioned polymers are known to the person skilled in the art.

As crosslinkers (V), suitable polyamines for the crosslinking of the epoxy-functional polymers are polyamines, such as preferably diethylenetriamine, amine adducts or polyaminoamides. Crosslinking agents (V) based on carboxylic anhydrides, melamine resins and optionally blocked polyisocyanates are particularly preferred for epoxy-functional polymers.

In particular, in the present invention low-solvent crosslinkers (V) with residual solvent contents of less than 1.0 wt .-%, more preferably less than 0.5 wt .-% and most preferably less than 0.2 wt. %, based on the volatile constituents of the crosslinking agents used.

For the crosslinking of the preferred hydroxyl-containing polymers, the crosslinkers (V) used are melamine resins, amino resins and, preferably, blocked polyisocyanates.

Very particularly preferred for the crosslinking of the preferred hydroxy-containing polymers are melamine derivatives, such as hexabutoxymethylmelamine and in particular the highly reactive hexamethoxymethylmelamine, and / or optionally modified aminoplast resins. Such crosslinkers (V) are commercially available (for example as Luwipal ® from BASF AG). In particular, the present invention provides low-solvent melamine resins having residual solvent contents of less than 1.0% by weight, more preferably less than 0.5% by weight and most preferably less than 0.2% by weight, based on the volatile constituents of the melamine resin preparation used.

The preferably blocked polyisocyanates suitable as crosslinkers (V) for the preferred hydroxy-containing polymers are, in particular, oligomers of diisocyanates, such as trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, heptamethylene diisocyanate, ethylethylene diisocyanate, trimethylhexane diisocyanate or acyclic aliphatic diisocyanates containing a cyclic group in their carbon chain such as diisocyanates derived from dimer fatty acids, such as those sold under the trade name DDI 1410 by the company Henkel and in the patents WO 97/49745 and WO 97/49747 to be discribed. The latter are to be counted in the context of the present invention, in spite of their cyclic groups to the acyclic aliphatic diisocyanates due to their two exclusively bound to alkyl groups isocyanate groups. Of the above-mentioned diisocyanates, hexamethylene diisocyanate is particularly preferably used. Preference is given to using oligomers which contain isocyanurate, urea, urethane, biuret, uretdione, iminooxadiazinedione, carbodiimide and / or allophanate groups.

In the blocking of the polyisocyanates, the isocyanate group is reacted with a blocking agent, which is split off again on heating to higher temperatures. Examples of suitable blocking agents are, for example, in DE-A-199 14 896 , Columns 12 and 13 described.

To accelerate the crosslinking, suitable catalysts are preferably added in a known manner.

In a further embodiment of the invention, the crosslinking in the binder system (BM) can also be effected photochemically. The term "photochemical crosslinking" is intended to include crosslinking with all types of high-energy radiation, such as UV, VIS, NIR or electron radiation.

Photochemically crosslinkable water-soluble or water-dispersible binder systems (BM) generally comprise oligomeric or polymeric compounds with photochemically crosslinkable groups and optionally also reactive diluents, generally monomeric compounds. Reactive diluents have a lower viscosity than the oligomeric or polymeric compounds. Furthermore, one or more photoinitiators are usually necessary for photochemical crosslinking.

Examples of photochemically crosslinkable binder systems (BM) include water-soluble or water-dispersible multifunctional (meth) acrylates, urethane (meth) acrylates, polyester (meth) acrylates, epoxy (meth) acrylates, carbonate (meth) acrylates and polyether (meth) acrylates, optionally in combination with reactive diluents such as methyl (meth) acrylate, butanediol di (meth) acrylate, hexanediol di (meth) acrylate or trimethylolpropane tri (meth) acrylate. Further details of suitable radiation-curable binders are, for example, in WO-A-2005/080484 To find pages 3 to 15. Suitable photoinitiators can be found in the same document on pages 18 and 19.

Furthermore, binder systems (BM) which can be thermally and photochemically cured (dual-cure systems) can also be used to carry out the present invention.

Based on the non-volatile constituents in the binder system (BM), the proportion of crosslinker (V) in the binder system (BM) is preferably between 5 and 60% by weight, more preferably between 7.5 and 50% by weight, based on the binder system (BM).

In a further embodiment of the invention, the binder systems (BM) are physically drying, ie they do not crosslink or only in the course of the formation of the lacquer layer, which is preferably achieved by drying the coating agent (B), ie by removing the solvent very subordinate measure. For the physically drying systems, the abovementioned water-soluble compounds are preferred or water-dispersible binder systems (BM), in particular the above-described polyurethane-based binder systems (BM), the crosslinkers (V) and in particular other components which promote crosslinking, such as catalysts or initiators, not being present in the coating agent (B).

The coating composition (B) used according to the invention contains preferably 10 to 90% by weight, more preferably 15 to 85% by weight, in particular 20 to 80% by weight of the binder system (BM), based on the nonvolatile constituents of the coating composition (B ).

The filler component (BF)

The inventively used, preferably inorganic, filler component (BF) preferably comprises classical fillers, inorganic color and / or effect pigments and / or conductive pigments.

Conventional fillers, which are used in particular to compensate for unevenness of the substrate and / or to increase the impact strength of the layer produced from the coating agent (B), are preferably chalk, hydroxides such as aluminum or magnesium hydroxides and phyllosilicates such as talc or kaolin, with talc being particularly preferred is.

As color and / or effect pigments, preference is given to using inorganic pigments, in particular white pigments and black pigments. Preferred white pigments are silicon oxides, aluminum oxides and in particular titanium oxides and barium sulfate. Preferred black pigments are iron oxides and in particular graphite and carbon blacks.

The conductive pigments used are preferably phosphides, vanadium carbide, titanium nitride and molybdenum sulfide. Such additives serve, for example, to improve the weldability of the coating agent (B) formed. Preferred conductivity pigments used are metal phosphides of Zn, Al, Si, Mn, Cr, Ni or, in particular, Fe, such as, for example, .alpha WO 03/062327 A1 described. Zinc dust is particularly preferably used as the conductive pigment.

The fillers contained in the filler component (BF) preferably have average particle diameters which do not exceed the thickness of the cured integrated pretreatment layer. The upper grain limit of the filler component (BF) measured according to EN ISO 1524: 2002 is preferably less than 15 μm, particularly preferably less than 12 μm and in particular less than 10 μm.

The filler component (BF) particularly preferably has residual solvent contents of less than 1% by weight, in particular less than 0.5% by weight, in each case based on (BF). Most preferably, the filler component (BF) is solvent-free.

The coating composition (B) used according to the invention contains preferably from 5 to 80% by weight, more preferably from 10 to 70% by weight and in particular from 15 to 65% by weight, based on the nonvolatile constituents of the coating composition (B), of fillers ( BF).

The corrosion protection component (BK)

The corrosion protection component (BK) used according to the invention preferably contains inorganic corrosion protection pigments, in particular aluminum phosphate, zinc phosphate, zinc aluminum phosphate, molybdenum oxide, zinc molybdate, calcium zinc molybdate, zinc metaborate or barium metaborate monohydrate. In a particularly preferred embodiment of the invention, such anticorrosive pigments are used in combination with amorphous silicon dioxide modified with metal ions. Preferably, the metal ions are selected from the group consisting of alkali metal ions, alkaline earth metal ions, lanthanide metal ions, and zinc and aluminum ions, with calcium ions being particularly preferred. Calcium ion-modified amorphous silica may be purchased as a commercial product under the trademark Shieldex® (Grace GmbH & Co. KG).

In addition, dimeric, oligomeric or polymeric alkoxides of aluminum or titanium, optionally as adducts with phosphorus-containing compounds, as described in US Pat WO 03/062328 A1 described, are used.

The anticorrosive pigments contained in the anticorrosion component (BK) preferably have average particle diameters which do not exceed the thickness of the cured integrated pretreatment layer. The upper grain limit of the anticorrosive pigments (BK) measured according to EN ISO 1524: 2002 is preferably less than 15 μm, more preferably less than 12 μm and in particular less than 10 μm.

The corrosion protection component (BK) particularly preferably has residual solvent contents of less than 1% by weight, in particular less than 0.5% by weight, based in each case on (BK).

Furthermore, instead of or in addition to the abovementioned inorganic corrosion protection pigments, it is also possible for organic low molecular weight and / or polymeric corrosion protection agents to be present in the corrosion protection component (BK). Preferred organic corrosion inhibitors are copolymers of unsaturated dicarboxylic acid and olefins, as used, for example, in US Pat WO 2006/079628 A1 and very particularly preferably copolymers of monomers with nitrogen heterocycles, monomers with acid groups and vinylaromatic monomers, as they are in WO 2007/125038 A1 are used. Very particular preference is given to the aqueous dispersions of WO 2007/125038 in a further preparation step to residual solvent contents of less than 1 wt .-%, preferably less than 0.5 wt .-% and in particular less than 0.2 wt .-%, each based on the volatile components of the aqueous dispersion , discontinued.

Most preferably, the corrosion protection component (BK) contains at least one combination of inorganic and organic corrosion inhibitor, wherein in particular the above combination residual solvent contents of less than 1 wt .-%, preferably less than 0.5 wt .-% in each case based on the volatile constituents the corrosion protection component (BK) contains.

The coating composition (B) used according to the invention preferably contains from 1 to 50% by weight, particularly preferably from 2 to 40% by weight and in particular from 3 to 35% by weight, based on the nonvolatile constituents of the coating composition (B), of the corrosion protection component ( BK).

The other components of the coating agent (B)

As a further component, the coating composition of the invention comprises water and optionally preferably water-compatible organic solvents as further volatile constituents (BL), which are removed during drying and in particular during curing of the coating agent (B).

Depending on the process conditions and the type of components used, the person skilled in the art will make a suitable choice among the solvents which are possible in principle. Examples of preferred organic solvents which are preferably water compatible include ethers, polyethers such as polyethylene glycol, ether alcohols such as butyl glycol or methoxypropanol, ether glycol acetates such as butyl glycol acetate, ketones such as acetone, methyl ethyl ketone, Alcohols, such as methanol, ethanol or propanol. Furthermore, hydrophobic solvents, in particular gasoline and aromatic cuts, can be used in minor amounts, such solvents being used more as additives for controlling specific coating properties.

In addition to the aforementioned components, the coating agent (B) may contain one or more additives. Such additives serve to finely control the properties of the coating agent (B) and / or the layer produced from the coating agent (B). The additives are generally up to 30 wt .-%, based on the coating agent, preferably up to 25 wt .-%, in particular up to 20 wt .-%, in the coating agent (B).

Examples of suitable additives are rheological aids, organic color and / or effect pigments, UV absorbers, light stabilizers, free-radical scavengers, initiators for free-radical polymerization, catalysts for thermal crosslinking, photoinitiators, slip additives, polymerization inhibitors, defoamers, emulsifiers, degassing agents, network and Dispersants, adhesion promoters, leveling agents, film-forming aids, thickeners, flame retardants, siccatives, skin preventatives, waxes and matting agents, such as those from the Textbook "Paint Additives" by Johan Bieleman, Wiley-VCH, Weinheim, New York, 1998 , are known. It is preferred to use additives with a low residual solvent content in the preparation of the additives, such as, in particular, low-solvent dispersants, low-solvent leveling agents and low-solvent defoamers, which in particular have residual solvent contents of less than 1% by weight, preferably less than 0.8% by weight. % and in particular of less than 0.5 wt .-%, each based on the volatile phase of the additive used.

The coating agent (B) is prepared by thoroughly mixing the components with the solvents. The skilled person is familiar with suitable mixing and dispersing aggregates.

The method steps of the method according to the invention

In step (1) of the method according to the invention, the coating agent (B) is applied to the metal surface of the metal strip.

If necessary, the metal surface can be cleaned beforehand. If the method step (1) takes place immediately after a metallic surface treatment, for example an electrolytic galvanizing or a hot-dip galvanizing of the metal surface, the coating composition (B) can be applied to the metal strip as a rule without pre-cleaning. If the metal strips to be coated are stored and / or transported before coating with the coating agent (B), they are usually coated with anticorrosive oils or otherwise contaminated, so that cleaning of the metal strip is necessary before process step (1). The purification can be carried out by conventional methods known to those skilled in the art with conventional detergents.

The application of the coating agent (B) on the metal strip can be done by spraying, pouring or preferably rolling.

In the preferred roller painting, the rotating pickup roller (pick-up roller) dips into a supply of the coating agent (B) and thus takes over the coating agent (B) to be applied. This is transmitted from the pickup roller directly or via at least one transfer roller to the rotating application roller. From this, the coating agent (B) is transferred to the metal strip, wherein the application by both the "forward roller coating" method (continuous stripping) and by the counter stripping or the "reverse roller coating process "can be done.

Both techniques are possible for the process according to the invention, with the "forward roller coating" method (continuous stripping) being preferred. The belt speed is preferably between 80 and 150 m / min, more preferably between 100 and 140 m / min. Preferably, the application roller has a rotational speed which is 110 to 125% of the belt speed and the take-up roller has a revolution speed which is 15 to 40% of the belt speed.

In a further embodiment of the invention, the coating agent (B) can be pumped directly into a gap between two rolls, which is also referred to as "nip-feed process".

The speed of the metal strip is selected by a person skilled in the art in accordance with the drying conditions for the coating agent (B) in step (2). In general, tape speeds 20 to 200 m / min, preferably 80 to 150 m / min, more preferably 100 to 140 m / min, have proven, the tape speed must also be matched to the aforementioned Auftragsmethoden.

For drying the layer formed from the coating agent (B) on the metal strip, that is to remove the volatile constituents (BL) of the coating composition (B), the metal strip coated according to step (1) is heated by means of a suitable device. The heating can be effected by convection heat transfer, irradiation with near or far infrared radiation and / or with suitable metal substrates, in particular iron, by electrical induction. Removal of the solvent can also be accomplished by contacting with a gas stream, allowing for combination with the above-described heating.

According to the invention it is preferred that the drying of the layer formed from the coating agent (B) on the metal strip in such a manner is carried out that the layer after drying nor a residual content of volatile constituents (BL) of at most 10 wt .-%, based on the coating composition (B), preferably of at most 8 wt .-%, particularly preferably of at most 6 wt. -%, is set. The determination of the residual content of volatile constituents (BL) in the coating agent is carried out by known methods, preferably by gas chromatography, particularly preferably in combination with a thermogravimetry.

Drying of the coating composition is preferably particularly preferred at peak metal temperature (PMT) found on the metal, which can be determined, for example, by non-contact infrared measurement or with temperature indicator strips) of 40 to 120 ° C, preferably between 50 and 110 ° C between 60 and 100 ° C, wherein the speed of the metal strip and thus the residence time in the drying area of the strip coating plant in a manner known in the art is set such that the inventively preferred residual volatile content (BL) in the from the coating agent (B) are set after leaving the drying area.

The drying of the coating agent (B) is particularly preferably carried out at PMT (peak metal temperatures) below the DMA onset temperature for the reaction of the crosslinkable constituents in the coating agent (B) (measured on a DMA IV from Rheometric Scientific in a Heating rate of 2 K / min, a frequency of 1 Hz and an amplitude of 0.2% with the measuring method "Tensile Mode - Tensile off" in the mode "Delta", wherein the location of the DMA onset temperature in a known manner by extrapolation the temperature-dependent course of E 'and / or tanδ is determined). Most preferably, the drying is carried out at PMT, the 5 K, in particular 10 K, below the DMA onset temperature for the reaction of the crosslinkable components in the coating center (B).

For laboratory simulation of the application of the coating composition (B) in the coil coating process, the coating composition (B) is preferably applied by means of bar knives to plates of the substrate to be coated in a wet layer thickness comparable to the metal strip coating. The laboratory simulation of the drying of the coating agent (B) in the coil coating process is preferably carried out in a circulating air oven, wherein comparable with the metal strip coating PMT (peak metal temperatures) are set.

The thickness of the dried layer of coating agent (B) prepared according to process step (2) is generally between 1 and 15 μm, preferably between 2 and 12 μm, particularly preferably between 3 and 10 μm.

Between process steps (2) and (3), the metal strip provided with the dried layer of coating agent (B) can be rolled up again and the further layer (s) applied only at a later point in time.

In process step (3) of the process according to the invention, one or more topcoat (s) (D) is applied to the dried layer of coating material (B) prepared according to process step (2), in which case all topcoats suitable for metal tape coatings are suitable as topcoats (D) ,

The application of the topcoat (D) can be done by spraying, pouring or preferably in the above-described rolling order.

Preferably, a pigmented topcoat (D) is applied with high flexibility, both for coloration and for protection against mechanical stress and against weathering on the coated metal band ensures. Such topcoats (D) are used for example in EP-A1-1 335 945 or EP-A1-1 556 451 described. In a further preferred embodiment of the invention, the topcoats (D) may have a two-layered structure comprising a coloring basecoat film and a final clearcoat film. Such two-layer finishing lacquer systems suitable for coating metal strips are described, for example, in US Pat DE-A-100 59 853 and in WO-A-2005/016985 described.

In process step (4) of the process according to the invention, the layer of coating material (B) applied and dried in process step (2) is cured together with the layer of topcoat (D) applied in process step (3), ie crosslinked, the remaining volatile constituents (BL) from the dried layer of the coating agent (B) and the solvent from the topcoat (D) are removed together.

The crosslinking depends on the nature of the binder (BM) used in the coating agent (B) and the binder used in the topcoat (D) and can be carried out thermally and / or optionally photochemically.

In the case of the thermal crosslinking preferred according to the invention, the metal strip coated in accordance with process steps (1) to (3) is heated by means of a suitable device. The heating can be effected by irradiation with near or far infrared radiation, with suitable metal substrates, in particular iron, by electrical induction and preferably by convection heat transfer. Removal of the solvent can also be accomplished by contacting with a gas stream, allowing for combination with the above-described heating.

The temperature required for crosslinking depends in particular on the binders used in the coating composition (B) and in the Topcoat layer (D). Crosslinking is preferably carried out at peak temperatures (PMT) of at least 80 ° C., particularly preferably at least 100 ° C., and very particularly preferably at least 120 ° C. found on the metal. In particular, the crosslinking is carried out at PMT values between 120 and 300 ° C., preferably between 140 and 280 ° C. and particularly preferably between 150 and 260 ° C. The speed of the metal strip and thus the residence time in the furnace area of the strip coater in a manner known to those skilled in the art is preferably adjusted such that the crosslinking in the layer formed from the coating agent (B) and in the layer formed from the topcoat (D) after leaving the oven area is largely complete. Preferably, the duration for the crosslinking is 10 seconds to 2 minutes. For example, ovens are used with convective heat transfer, so at the preferred tape speeds convection ovens a length of about 30 to 50 m are required. The ambient air temperature is naturally higher than the PMT and can be up to 350 ° C.

The photochemical crosslinking is generally carried out with actinic radiation, which in the following is understood to mean near infrared, visible light (VIS radiation), UV radiation, X-radiation or corpuscular radiation, such as electron radiation. Preferably, UV / VIS radiation is used for photochemical crosslinking. The irradiation may optionally be carried out with the exclusion of oxygen, for example under an inert gas atmosphere. The photochemical crosslinking can be carried out under normal temperature conditions, in particular when both coating agent (B) and topcoat (D) crosslink exclusively photochemically. In general, the photochemical crosslinking takes place at elevated temperatures, for example between 40 and 200 ° C, in particular when one of the coating compositions (B) and (D) thermochemically crosslinks, and the other thermally crosslinked, or if photochemically and thermally crosslinking one or both of the coating compositions (B) and (D).

The thickness of the layer composite produced according to process step (4) from the hardened layers based on the coating composition (B) and on the topcoat (D) is generally between 2 and 60 μm, preferably between 4 and 50 μm, particularly preferably between 6 and 40 μm.

For laboratory simulation of the application of the topcoat (D) in the coil coating process, the topcoat (D) is preferably applied to the dried coating composition (B) using bar knives in a wet layer thickness comparable to the metal strip coating. The laboratory simulation of the co-curing of the coating composition (B) and of the topcoat (D) in the coil coating process is preferably carried out in a circulating air oven, wherein PMT (peak metal temperatures) comparable to the metal band coating are set.

The laminates produced by the process according to the invention can in particular on the surface of iron, steel, zinc or zinc alloys, such as zinc-aluminum alloys, such as Galvalume ® and Galfan ®, or zinc-magnesium alloys, magnesium or magnesium alloys, aluminum or Aluminum alloys are applied.

The metal strips provided with the layer composite produced by the process according to the invention can be processed into metallic molded parts, for example by means of cutting, forming, welding and / or joining. The invention therefore also moldings which are produced with the metal strips produced according to the invention. The term "shaped body" is intended both coated sheets, films or bands as well as the metallic components obtained therefrom.

Such components are, in particular, those which can be used for cladding, veneering or lining. Examples include automobile bodies or parts thereof, truck bodies, frames for two-wheelers such as motorcycles or bicycles, or parts for such vehicles such as fenders or fairings, housings for household appliances such as washing machines, dishwashers, clothes dryers, gas and electric stoves, microwave ovens , Freezers or refrigerators, covers for technical equipment or installations, such as machines, control cabinets, computer housings or the like, architectural elements, such as wall parts, façade elements, ceiling elements, window or door profiles or partitions, furniture made of metallic materials, such as metal cabinets, metal shelves, Parts of furniture or fittings. Furthermore, the components can also be hollow bodies for the storage of liquids or other substances, such as cans, cans or tanks.

The following examples are intended to illustrate the invention.

Examples Preparation Example 1 Production of a Low-Solvent Polyurethane Dispersion (PUD)

Preparation of the hydroxyl-containing polyesterdiol prepolymer: 1158.2 g of dimer fatty acid Pripol® 1012 (Uniqema), 644 g of hexanediol and 342.9 g of isophthalic acid are weighed into a stirred tank equipped with packed column and water separator and 22.8 g of cyclohexane are added under a nitrogen atmosphere Heated to 220 ° C. With an acid number of less than 4 mg KOH / g and a viscosity of 5-7 dPas (76% solution in xylene) is applied at 150 ° C vacuum and volatile components removed. The polyester is cooled, solubilized with methyl ethyl ketone and adjusted to a solids content of 73%.

Preparation of the polyurethane dispersion:

1699.6 g of the dissolved in methyl ethyl ketone Polyesterdiolpräpolymers, 110.8 g of dimethylpropionic acid, 22.7 g of neopentyl glycol, 597.6 g of dicyclohexylmethane diisocyanate (Desmodur ® W from Bayer AG) and 522 g of methyl ethyl ketone are placed in a stirred tank and in a nitrogen atmosphere with stirring heated to 78 ° C. When the content of isocyanate groups is constant at 1.3% based on the solids content, corresponding to a ratio of the isocyanate groups to hydroxyl groups of about 1.18: 1, 64 g of triethanolamine are added. The reaction mixture is stirred until it has a content of isocyanate groups of 0.3% based on the solids content, corresponding to a conversion of about 75 mol% of the originally unreacted isocyanate groups. Thereafter, the remaining isocyanate groups are reacted with 51.8 g of n-butanol and stirred for a further hour at 78 ° C to complete the reaction. The content of free isocyanate groups is <0.05% after the reaction. After adding 58.1 g of dimethylethanolamine, 3873.5 g of distilled water are added dropwise within 90 minutes and the resulting dispersion is stirred for a further hour. The polyurethane produced in this way has an OH number according to DIN EN ISO 4629 of 37 mg KOH / g, an acid number according to DIN EN ISO 3682 of 23 mg KOH / g and a degree of neutralization of 74 mol% of the groups capable of forming anions.

To reduce the residual solvent content at 78 ° C, the volatiles are removed in vacuo until the refractive index of the distillate is less than 1.335 and gas chromatography shows a content of less than 0.3 wt .-%, based on the reaction mixture, of methyl ethyl ketone is detected. The solids content of the resulting dispersion is adjusted to 30% with distilled water. The polyurethane dispersion is low in viscosity, has a pH of 8-9 and has a residual solvent content of 0.35% by weight, based on the volatile constituents of the dispersion, by gas chromatography.

Comparative Example 1 Preparation of the Polyurethane Dispersion (PUD ') without Optimization of the Residual Solvent

The polyurethane dispersion is prepared according to Preparation Example 1, wherein the final step for reducing the residual solvent content is omitted.

The polyurethane dispersion is low viscosity and has a pH of 8-9 and has a residual solvent content of 1.04% by weight, based on the volatiles of the dispersion.

Example 2 Production of the Low-Solvent Coating Composition (B) According to the Invention

20 parts by weight of the polyurethane dispersion (PUD) according to Preparation Example 1, 7.1 parts by weight of a low-dispersion additive (residual content of organic solvent <0.02 wt .-%, based on the volatile constituents of the dispersing additive) in a suitable stirred vessel 1.7 parts by weight of a conventional leveling agent with defoaming effect (residual content of organic solvent 0.21 wt .-%, based on the volatile constituents of the leveling agent), 0.2 parts by weight of a silicate and 24.2 parts by weight of a solvent-free mixture consisting of inorganic, known in the art anti-corrosive pigments and fillers, mixed and predispersed with a dissolver for ten minutes. The resulting mixture is transferred to a bead mill with cooling jacket and mixed with 1.8-2.2 mm SAZ glass beads. The millbase is ground for 45 minutes, the temperature being kept at a maximum of 50 ° C by cooling. Subsequently, the ground material is separated from the glass beads. The upper grain limit of the filler and anti-corrosive pigments according to EN ISO 1524: 2002 is less than 10 μm after milling.

The millbase is stirred, with the temperature being kept at a maximum of 60 ° C. by cooling, in the order given with 29.5 parts by weight of the polyurethane dispersion (PUD) according to Preparation Example 1, 4.6 parts by weight of a low-solvent melamine resin as crosslinker (residual content of organic Solvent 0.04% by weight, based on the volatile constituents of the melamine resin), 0.9 part by weight of a low-solvent defoamer (residual content of organic solvent <0.02% by weight, based on the volatile constituents of the defoamer), 1, 4 parts by weight of an acidic catalyst from the class of blocked aromatic sulfonic acids, 1 part by weight of a conventional antifoaming agent (residual content of organic solvent 0.21% by weight, based on the volatiles of the leveling agent) and 1 part by weight of a further acrylate-based leveling agent ( Residual content of organic solvent 0.45 wt .-%, based au f) the volatiles of the leveling agent).

In a final step, 8.4 parts by weight of an aqueous dispersion of a copolymer of 45 wt .-% N-vinylimidazole, 25 wt .-% vinylphosphonic acid and 30 wt .-% of styrene was added, according to Example 1 of WO 2007/125038 , was prepared, wherein the proportion of residual solvent in a further treatment step to <0.1 wt .-%, based on the volatile constituents of the dispersion of the copolymer was adjusted.

The proportion of residual solvent in the aqueous coating composition (B) according to the invention is 2.2% by weight, based on the volatile constituents (BL) of the coating composition (B).

Comparative Example 2 Preparation of Coating Composition (B ') without Optimization of Residual Solvent Content

20 parts by weight of the polyurethane dispersion (PUD ') according to Comparative Example 1, 4.2 parts by weight of a conventional dispersing additive (residual content of organic solvent 2.0% by weight, based on the volatile constituents of the dispersing additive), in a suitable stirred vessel are 1.6 parts by weight of a conventional leveling agent with antifoaming effect (residual content of organic solvent 0.21 wt .-%, based on the volatile constituents of the leveling agent), 0.2 parts by weight of a silicate and 24.0 parts by weight of a solvent-free mixture consisting of inorganic, the Expert known anti-corrosive pigments and fillers, mixed and predispersed with a dissolver for ten minutes. The resulting mixture is transferred to a bead mill with cooling jacket and mixed with 1.8-2.2 mm SAZ glass beads. The millbase is ground for 45 minutes, the temperature being kept at a maximum of 50 ° C by cooling. Subsequently, the ground material is separated from the glass beads. The upper grain limit of the filler and anti-corrosive pigments according to EN ISO 1524: 2002 is less than 10 μm after milling.

The millbase is stirred, the temperature being kept at a maximum of 60 ° C. by cooling, in the order given with 26.6 parts by weight of the polyurethane dispersion (PUD) according to Preparation Example 1, 4.6 parts by weight of a conventional melamine resin as crosslinker (residual content of organic Solvent 1.0% by weight, based on the volatile constituents of the melamine resin), 0.9 part by weight of a low-solvent defoamer (residual content of organic solvent < 0.02% by weight, based on the volatile constituents of the defoamer), 2.9 parts by weight of a conventional acidic catalyst from the class of blocked aromatic sulfonic acids (residual organic solvent content of 1.65% by weight, based on the volatile constituents of defoamer), 1 part by weight of a conventional leveling agent with defoaming action (residual content of organic solvent 0.21 wt .-%, based on the volatile constituents of the leveling agent) and 1 part by weight of a further flow control agent based on acrylate (residual content of organic solvent 0.45 wt. %, based on the volatile constituents of the leveling agent).

In a final step, 10.7 parts by weight of an aqueous dispersion of a copolymer of 45 wt .-% N-vinylimidazole, 25 wt .-% vinylphosphonic acid and 30 wt .-% of styrene, according to Example 1 of WO 2007/125038 , was prepared (residual content of organic solvent 3.87 wt .-%, based on the volatile components of the copolymer). To set the required processing viscosity, another 2.3 parts by weight of demineralized water are added.

The proportion of residual solvent in the aqueous coating agent (B ') according to Comparative Example 2 is 21.7% by weight based on the volatile components (BL') of the coating agent (B ').

Example 3: Application of the Coating Composition by the Process of the Invention

For the coating trials galvanized steel plates of grade Z, thickness 0.9 mm (OEHDG, Chemetall) are used. These are previously cleaned by known methods. The described coating compositions (B) and (B ') were applied with the aid of bar knives in such a wet layer thickness that, after drying of the coatings, a dry layer thickness of 5 μm resulted. The coating compositions (B) and (B ') were in a convection oven of Hofmann at a Convection temperature of 185 ° C and a fan power of 10% for 22 seconds dried, resulting in a PMT of 88 ° C.

The DMA onset temperature (measured on a DMA IV from Rheometric Scientific at a heating rate of 2 K / min, a frequency of 1 Hz and an amplitude of 0.2% with the measuring method "Tensile Mode - Tensile off" in the mode "Delta", wherein the position of the DMA onset temperature in a known manner by extrapolation of the temperature-dependent profile of E 'is determined) for the reaction of the crosslinkable components in the coating agent (B) or (B') is 102 ° C.

The content of volatile substances in the dried layer of coating agent (B) or (B ') is 4.5% by weight, based on the dried layer.

The layer produced with the low-solvent coating agent (B) in step (2) by the process according to the invention shows a particularly good course, even at low temperatures, and can be overcoated very well despite the absence of chemical curing (Table 1).

In comparison, a layer produced with the solvent-richer coating agent (B ') in step (2) shows a clear surface roughness and thus a poor course and the recoatability is markedly impaired (Table 1).

Subsequently, a topcoat (D) type Polyceram® PH from BASF Coatings AG is applied with the aid of bar knives in such a wet layer thickness that after drying the coatings in the combination of primer layer (B) or (B ') and topcoat layer (D) a dry film thickness of 25 microns results. The composite of primer layer (B) or (B ') and topcoat layer (D) is baked in a continuous furnace from Hedinair at a circulating air temperature of 365 ° C and a belt speed such that a PMT of 243 ° C results.

The following properties determined for coil coatings are determined on the composites of coating agent (B) or (B ') and topcoat (D) prepared in this way (Table 1).

MEK test:

Performance according to EN ISO 13523-11.This method characterizes the resistance of paint films to stress with solvents such as methyl ethyl ketone.

In this process, a gauze compress impregnated with methyl ethyl ketone is rubbed over the paint film with a defined contact weight. The number of double strokes up to the first visual damage of the paint film is the MEK value to be specified.

T-bend test:

Performance in accordance with DIN ISO 1519. The test method is used to determine the cracking of paints under bending stress at room temperature (20 ° C). For this purpose, test strips are cut and these are pre-bent by edges around 135 °.

• r = Radius in cm
• d = Blechdicke in cm

After the edge, stencils of varying thickness are placed between the lamellae of the pre-bend. With defined force, the slats are then compressed. The amount of deformation is indicated by the T value. The context applies here: $$\mathrm{T}=\mathrm{r}/\mathrm{d}$$

• r = radius in cm
• d = sheet thickness in cm

It is started with 0 T and the bending radius increased until no more cracks are visible. This value is the T-bend value to be specified.

Tape Test:

Performance according to DIN ISO 1519. The test method is used to determine the adhesion of paints under bending stress at room temperature (20 ° C).

• r = Radius in cm
• d = Blechdicke in cm

For this purpose, test strips are cut and these are pre-bent by edges around 135 °. After the edge, stencils of varying thickness are placed between the lamellae of the pre-bend. With defined force, the slats are then compressed. The amount of deformation is indicated by the T value. The context applies here: $$\mathrm{T}=\mathrm{r}/\mathrm{d}$$

• r = radius in cm
• d = sheet thickness in cm

It is started with 0 T and the bending radius is increased until an adhesive tape (Tesa® 4104) no more lacquer can be demolished. This value is the tape value to specify.

Corrosion protection test:

In order to test the corrosion-inhibiting effect of the coatings according to the invention, the galvanized steel plates were subjected to a salt spray test according to DIN 50021 for 360 h.

After completion of the corrosion load, the test plates were assessed by measuring the damaged surface of the lacquer (tendency to infiltrate) on the edge and the scribe (according to DIN 55928).

The following table shows the results of all examinations listed above. Table 1: coating agents (B ') with drying before application of the topcoat layer (not solvent-optimized) (B) with drying before application of the topcoat layer (according to the invention) Course of the coating of coating agent (B) or (B ') rough, streaky very smooth layer, without any visible and noticeable disturbances Overcoatability of the dried according to step (2) layer limited due to the surface roughness very well MEK test on the composite of primer and topcoat [double strokes] baked according to method step (4) 72 > 100 T-bend test on the composite of primer and topcoat [T-value] baked according to process step (4) 2.5 2.0 Tape test on the composite of primer and topcoat [T value] baked according to process step (4) 1.0 0.5 Corrosion test on the composite of primer and top coat (360 h SS) baked according to process step (4): edge left [mm infiltration] > 20 2.5 - edge right [mm infiltration] > 20 2.5 - Ritz [mm infiltration] > 20 0.5

Solvent resistance in the MEK test is significantly higher after use of the solvent-optimized coating composition (B) according to method step (4) baked-on composite of primer and topcoat than in the solvent-rich coating composition (B ').

Likewise, drastically improved corrosion resistance of the primer / topcoat composite baked according to process step (4) and improved behavior in the T-bend and tape tests when using the solvent-optimized coating agent (B) in comparison with the use of the more solvent-rich coating composition (B '). ) to observe.

Claims (10)

1. Method of coating coils, characterized in that it comprises the following steps:

   (1) applying an aqueous primer coating composition (B) comprising at least one thermally crosslinkable binder system (BM), at least one filler component (BF), at least one corrosion control component (BK), and volatile constituents (BL), to the optionally cleaned metal surface, the coating composition (B) having an organic solvent content of less than 5% by weight, based on the volatile constituents (BL) of the coating composition (B),

   (2) drying the integrated pretreatment film formed from the primer coating composition (B),

   (3) applying a topcoat film (D) to the integrated pretreatment film dried as per step (2), and

   (4) jointly curing the films of coating composition (B) and topcoat (D),

   the drying as per step (2) of the method being carried out at a peak metal temperature (PMT) below the DMA onset temperature for the reaction of the crosslinkable constituents of the binder system (BM), and the binder system (BM) comprising at least one water-soluble or water-dispersible binder based on polyesters and/or polyurethanes.
2. Method according to Claims 1, characterized in that the drying as per step (2) of the method is carried out at peak metal temperatures (PMT) between 40 and 120°C.
3. Method according to either of Claims 1 and 2, characterized in that the integrated pretreatment film formed as per step (2) still contains, after drying, a residual volatile constituent (BL) content of not more than 10% by weight, based on the coating composition (B).
4. Method according to any one of Claims 1 to 3, characterized in that at least one of the binder components of the binder system (BM) is an aqueous dispersion of a water-soluble or water-dispersible binder, the dispersion having a residual solvent content of not more than 1.5% by weight, based on the volatile constituents of the dispersion.
5. Method according to any one of Claims 1 to 3, characterized in that the coating composition comprises at least one crosslinker (V) having a residual solvent content of less than 1.0% by weight, based on the volatile constituents of the crosslinker (V).
6. Method according to any one of Claims 1 to 5, characterized in that the corrosion control component (BK) comprises at least one combination of organic and inorganic corrosion inhibitors, the corrosion control component (BK) comprising residual solvent contents of less than 1% by weight, based on the volatile constituents of the corrosion control component (BK).
7. Method according to any one of Claims 1 to 6, characterized in that the curing as per step (4) of the method is carried out at peak metal temperatures (PMT) between 150 and 260°C.
8. Method according to any one of Claims 1 to 7, characterized in that the coating composition (B) is applied in step (1) to the coil by a forward roller coating process (co-directional transfer) or by a reverse roller coating process (counter-directional transfer).
9. Method according to Claim 8, characterized in that the coil speed is between 80 and 150 m/min, the application roll has a peripheral speed which is 110% to 125% of the coil speed, and the pick-up roll has a rotational speed which is 15% to 40% of the coil speed.
10. Method according to any one of Claims 1 to 9, characterized in that the coil for coating consists of a material selected from the group consisting of iron, steel, zinc or zinc alloys, magnesium or magnesium alloys, and aluminum or aluminum alloys.