EP1009546A1

EP1009546A1 - Substrate having a multilayer coat and method for its production

Info

Publication number: EP1009546A1
Application number: EP98942634A
Authority: EP
Inventors: Klaus Holzapfel; Heinrich Wonnemann
Original assignee: BASF Coatings GmbH
Current assignee: BASF Coatings GmbH
Priority date: 1997-08-16
Filing date: 1998-07-25
Publication date: 2000-06-21
Anticipated expiration: 2018-07-25
Also published as: BR9811909A; US6426147B1; ES2185210T3; JP2001514966A; JP4217380B2; DE19735540C1; US20020142101A1; WO1999008808A1; ZA987296B; DE59805840D1; EP1009546B1

Abstract

The invention relates to a substrate having a multilayer coat and a method for its production, comprising the following stages: The car body which is to be coated is delivered to the pre-processing stage (2) via the intake (1). This is followed by electrophoretic enamelling (3) and burning in of the electrophoretic enamel coating. In stage (5), preparation takes place for coating with coating powder (stage 6). Stage (7) consists of drying with infrared radiation. This is followed by the cooling stage (8). In stage (9), the coating powder is applied to the substrate so as to form a coat. After intermediate drying (10), a protective layer is applied in stage (11) and then burnt in (stage 12). The car body is then conveyed from the installation via the exit (13).

Description

Multilayered substrate and process for its manufacture

description

The invention relates to a substrate provided with a multi-layer coating, the multi-layer coating comprising a filler layer, a coloring and / or effect-giving decorative layer and a protective layer, the filler layer being arranged closest to the substrate and the protective layer being removed from the substrate, a decorative lacquer with a binder being used for the decorative layer from the group “Acrylate resins, carboxyl-, epoxy- and / or hydroxyl group-containing binders” or mixtures thereof and with a crosslinker from the group “isocyanates, aminoplast resins or TACT” or mixtures thereof is used and wherein a protective lacquer from the group is used for the protective layer "One-component clearcoats, two-component clearcoats, powder clearcoats" is used, and a method for producing such a substrate provided with a multi-layer coating.

A filler layer is made from a so-called filler. At its core, a filler is a varnish that has special properties and is applied with a comparatively high layer thickness. The function of a filler layer is to compensate for disturbing unevenness (in the micrometer range) on the surface of a substrate, so that the surface of the substrate does not have to be subjected to an equalizing pretreatment before coating with a coating. The comparatively high layer thickness of the filler mentioned above also serves this purpose. The application can take place directly on the material of the substrate or with the interposition of a primer and / or an adhesion promoter. In the former case it is advisable to apply the filler From document FR 2 511 617 it is known to apply subsequent layers to a primer or filler layer and only then to harden the multilayer coating formed in this way. This procedure is referred to as “wet-on-wet” technology. In the processes known in this respect, a conventional aqueous primer or filler paint is used in the course of the primer or filler layer. However, it has been shown that from certain paint layer thicknesses (which are necessary to level out substrate defects if work is to be carried out without intermediate sanding) Mattering and flow disturbances occur.

A substrate provided with a multilayer coating or a method for producing it of the type mentioned at the outset is known from the literature reference EP 0 238037 B1. This is done with an electrocoat for the primer or filler layer. This electrocoat is first baked. The decorative layer and the protective layer are then applied “wet on wet”, the lacquers used for this being water-based lacquers. In particular in the case of decorative layers composed of an effect lacquer, however, it has been shown according to this literature reference that there is an imperative between the primer or filler layer Interface must be interposed so that the lacquer effect in the finished product meets the visual requirements. The need for a separation layer is disruptive for reasons of expenditure. For energy consumption reasons, the separate baking process step required for the primer or filler layer is disruptive. In addition, satisfactory results can only be achieved If the separating layer is built up on the basis of organic solvents, this is a nuisance due to environmental reasons. If an aqueous lacquer is used for the separating layer, it is also disadvantageous that a quick drying of the Interface layer is not easily accessible before applying the subsequent layers. As a result, the effort or the production time is increased to a disruptive degree.

In contrast, the invention is based on the technical problem of specifying a substrate provided with a multilayer coating, which can be produced with little effort and unproblematic environmental behavior, or a method for its production.

To solve this technical problem, the invention teaches that the filler layer is formed from a pre-crosslinkable powder paint, the filler layer made of powder paint having a layer thickness in the range from 30 μm to 250 μm. - The particular advantages of using a powder coating to produce a filler layer include that it does not require a solvent and that the losses that occur with conventional fillers through overspray are avoided, since non-adhering powder coating can be recycled almost completely. All common methods according to the state of the art can be used to apply the powder coating. Application by electrostatic adhesion, preferably by applying a high voltage or by frictional charging, is particularly preferred.

The coating of fabrics with powder patches is a common procedure. Here, the powdery dry paint is applied evenly to the substrate to be coated, and then the paint is melted and baked by heating the substrate. In the context of the invention, however, in deviation from this customary procedure, the powder coating is first pre-crosslinked by heating and only baked together with the subsequently applied layers. Thus, a separate baking process step for the Filler layer dispenses with the prior art. Instead, all layers of paint are baked in one step, which surprisingly results in a multi-layer coating that meets all requirements. This procedure considerably simplifies the coating process. By omitting an intermediate baking process, both investment and operating costs are reduced. Only a single baking oven needs to be made available and operated. This also saves heating energy. In addition, the total processing time for the coating process is shorter, so that the productivity of the system is increased.

All known paint formulations are suitable for the powder coating, e.g. those described in EP-509 392, EP-509 393, EP-322 827, EP-517 536, US-5,055,524 and US-4, 849,283. In particular, the powder coating can consist of epoxy resins, hybrid systems with polyester resin, also epoxidized novolaks, of crosslinking agents, preferably phenolic or amine hardeners or bicyclic guanidines, catalysts, fillers and optionally auxiliaries and additives.

The powder coating materials used according to the invention preferably contain epoxy resins, phenolic crosslinking agents, catalysts, auxiliaries and, if appropriate, auxiliaries and powder-typical additives, flow aids. Suitable epoxy resins are all solid epoxy resins with an epoxy equivalent weight between 400 and 3,000, preferably 600 to 2,000. These are mainly epoxy resins based on bisphenol A and bisphenol F. Expoxidized novolac resins are preferred. These preferably have an epoxy equivalent weight of 500 to 1,000. The epoxy resins based on bisphenol A and bisphenol F generally have a functionality of less than 2, the epoxidized novolac resins have a functionality of greater than 2. Epoxidized novolak resins with an average functionality in the range from 2.4 to 2.8 and with an epoxy equivalent weight in the range from 600 to 850 are particularly preferred in the powder coatings used according to the invention. In the epoxidized novolak resins, the phenolic hydroxyl groups are alkyl, acrylic or similar groups etherified. By reacting the phenolic hydroxyl groups with epichiorhydrides, epoxy groups are introduced into the molecule. Starting from novolaks, the so-called epoxy novolak is formed. The epoxidized novolaks are structurally related to bisphenol A resins. Epoxidized novolac resins can be prepared by epoxidizing novolaks, which consist, for example, of 3 to 4 phenol cores which are connected to one another via methylene bridges. Alkyl-substituted phenols which are reacted with formaldehyde can also be used as novolak resins.

Suitable epoxy resins are, for example, the products available commercially under the following names: Epikote 1004, 1055, 3003, 3004, 2017 from Shell-Chemie, DER 640, 671, 662, 663U, 664, 667 from Dow and Araldit GT 6063, 6064 , 6084, 6097, 7004, 7220, 7225 from Ciba Geigy.

Suitable epoxy functional binders for the powder coating are, for example, epoxy group-containing polyacrylate resins which, by copolymerizing at least one ethylenically unsaturated monomer which contains at least one epoxy group in the molecule, with at least one further ethylenically unsaturated monomer which does not Contains epoxy group in the molecule can be produced, at least one of the monomers being an ester of acrylic acid or methacrylic acid.

Polyacrylate resins containing epoxy groups are known (see, for example, EP-A-299 420, DE-B-22 14 650, DE-B-27 49 576, US-A-4,091, 048 and US-A-3,781, 379).

Glycidyl acrylate, glycidyl methacrylate and allyl glycidyl ether are mentioned as examples of the ethylenically unsaturated monomers which contain at least one epoxy group in the molecule.

Examples of ethylenically unsaturated monomers which do not contain any epoxy group in the molecule are alkyl esters of acrylic and methacrylic acid which contain 1 to 20 carbon atoms in the alkyl radical, in particular methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methyl acrylate, 2-ethylhexyl acrylate and 2- Called ethylhexyl methacrylate. Further examples of ethylenically unsaturated monomers which do not contain any epoxy groups in the molecule are acids, such as e.g. Acrylic acid and methacrylic acid. Acid amides, e.g. Acrylic acid and methacrylic acid amide, vinyl aromatic compounds such as styrene, methyl styrene and vinyl toluene, nitriles such as acrylonitrile and methacrylonitrile, vinyl and vinylidene halides such as vinyl chloride and vinylidene fluoride, vinyl esters such as e.g. Vinyl acetate and hydroxyl-containing monomers such as e.g. Hydroxyethyl acrylate and hydroxyethyl methacrylate.

The epoxy group-containing polyacrylate resin usually has

Epoxy equivalent weight of 400 to 2,500, preferably 500 to 1,500, particularly preferably 600 to 1,200, a number average molecular weight (gel permeation chromatography using a Polystyrene standards determined) from 1,000 to 15,000, preferably from 1,200 to 7,000, particularly preferably from 1,500 to 5,000 and a glass transition temperature (TG) from 30 to 80, preferably from 40 to 70, particularly preferably from 50 to 70 ° C (measured with the aid of differential scanning calometry (DSC)).

The epoxy group-containing polyacrylate resin can be prepared by radical polymerization by generally well-known methods.

Suitable hardeners for the epoxy group-containing polyacrylate resin are, for example, polyanhydrides of polycarboxylic acids or of mixtures of polycarboxylic acids, in particular polyanhydrides of dicarboxylic acids or of mixtures of dicarboxylic acids.

Such polyanhydrides can be prepared by removing water from the polycarboxylic acid or the mixture of polycarboxylic acids, two carboxyl groups being converted into one anhydride group. Such manufacturing processes are well known and therefore do not need to be explained in more detail.

To cure the epoxy resins, the powder coating used according to the invention contains phenolic or amine hardeners. Bicyclic guanidines can also be used.

Any phenolic resin can be used, for example, as long as it has the methylol functionality required for reactivity. Preferred phenolic resins are reaction products of phenol, substituted phenols and bisphenol A with formaldehyde, produced under alkaline conditions. Under such conditions, the Methylol group linked either ortho or para to the aromatic ring. Particularly preferred phenolic crosslinking agents are hydroxyl-containing bisphenol A or bisphenol F resins with a hydroxy equivalent weight in the range from 180 to 600, particularly preferably in the range from 180 to 300. Such phenolic crosslinking agents are prepared by reacting bisphenol-A or bisphenol-F with components containing glycidyl groups, such as, for example, the diglycidyl ether of bisphenol-A. Such phenolic crosslinking agents are available, for example, under the trade names DEH 81, DEH 82 and DEH 87 from Dow DX 171 from Shell-Chemie and XB 3082 from Ciba Geigy.

The epoxy resins and the phenolic crosslinking agents are used in such a ratio that the number of epoxy groups to the number of phenolic OH groups is approximately 1: 1.

Such powder coatings used according to the invention contain one or more suitable catalysts for epoxy resin curing. Suitable catalysts are phosphonium salts of organic or inorganic acids, imidazole and imidazole derivatives, quaternary ammonium compounds and amines. The catalysts are generally used in proportions of 0.001% by weight to about 10% by weight, based on the total weight of the epoxy resin and the phenolic crosslinking agent.

Examples of suitable phosphonium salt catalysts are ethyltriphenylphosphonium iodide, ethyltriphenylphosphonium chloride,

Ethyltriphenylphosphonium thiocyanate, ethyltriphenylphosphonium acetate-acetic acid complex, tetrabutylphosphonium iodide, tetrabutylphosphonium bromide and tetrabutylphosphonium acetate Acetic acid complex. These and other suitable phosphonium catalysts are described, for example, in US Pat. No. 3,477,990 and US Pat. No. 3,341,580.

Suitable imidazole catalysts are, for example, 2-styrylimidazole, 1-benzyl-2-methylimidazole, 2-methylimidazo! and 2-butylimidazole. These and other imidazole catalysts are e.g. described in Belgian Patent No. 756,693.

Some commercial phenolic crosslinking agents already contain catalysts for epoxy resin crosslinking.

Powder coatings based on carboxyl-containing polyesters and low molecular weight, epoxy-containing crosslinking agents are known in large numbers and are described, for example, in EP-A-389 926, EP-A-371 522, EP-A-326 230, EP-B-110 450, EP -A-110 451, EP-B-107 888, US 4,340,698, EP-B-119 164, WO 87/02043 and EP-B-10 805.

Also particularly suitable are powder coatings according to DE 43 30 404.4 A, which are characterized in that they contain 35.0-92.2% by weight of polyesters containing carboxyl groups with an acid number of 10-150 mg KOH / g as film-forming material A), B) 0.8

20.1% by weight of low molecular weight epoxy groups

Hardening agent, C) 3.7-49.3% by weight epoxy group-containing polyacrylate resins with an epoxy equivalent weight of 350-2000 and

D) 0.5-13.6% by weight of low molecular weight di- and / or polycarboxylic acids and / or di- and / or polyanhydrides, the sum of the

Parts by weight of A), B), C) and D) each 100% by weight and that

The ratio of the epoxy groups of the powder coatings to the sum of the carboxyl and anhydride groups of the powder coatings is 0.75-1.25: 1. The polyesters containing carboxyl groups used as component A) have an acid number in the range from 10 to 150 mg KOH / g, preferably in the range from 30 to 100 mg KOH / g. The hydroxyl number of the polyester resins should be <30 mg KOH / g. Polyesters with a carboxy functionality of> 2 are preferably used. The polyesters are produced by the usual methods (compare, for example, Houben Weyl, Methods of Organic Chemistry, 4th edition, volume 14/2. Georg Thieme Verlag, Stuttgart 1961).

Suitable carboxylic acid components for the production of the polyesters are aliphatic, cycloaliphatic and aromatic di- and polycarboxylic acids, e.g. Phthalic acid, terephthalic acid, isophthalic acid, trimellitic acid, pyromellitic acid, adipic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, cyclohexanedicarboxylic acid, acelainic acid, sebacic acid and others. These acids can also be used in the form of their esterifiable derivatives (e.g. anhydrides) or their transesterifiable derivatives (e.g. dimethyl ester).

Suitable alcohol components for the preparation of the carboxyl group-containing polyesters A) are the di- and / or polyols commonly used, e.g. Ethylene glycol, propanediol-1, 2 and propanediol-1, 3, butanediols, diethylene glycol, triethylene glycol, tetraethylene glycol, hexanediol-1, 6, neopentylglycol, 1, 4-dimethylol-cyclohexane, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, dititrimethylthrithrit, ditrit Diglycerin and others

The polyesters thus obtained can be used individually or as a mixture of different polyesters. As component A) suitable polyesters generally have a

Glass transition temperature above 30 ° C.

Examples of suitable commercially available polyesters are the products commercially available under the following brand names: Crylcoat 314, 340, 344, 2680, 316, 2625, 320, 342 and 2532 from UCB, Drugsbos, Belgium; Grilesta 7205, 7215, 72-06, 72-08, 72-13, 72-14, 73- 72, 73-93 and 7401 from Ems-Chemie; Neocrest P670, P671, P672, P678, P662 from ICI and Uralac P2400, Uralac P3400 and Uralac P5000 from DSM.

Unsaturated polyester resins containing carboxyl groups are also suitable as acidic polyester component A). These are obtained by polycondensation, for example of maleic acid, fumaric acid or other aliphatic or cycloaliphatic dicarboxylic acids with an ethylenically unsaturated double bond, optionally together with saturated polycarboxylic acids, as the polycarboxylic acid component. The unsaturated groups can also be replaced by the alcohol component, e.g. by trimethylolpropane monoallyl ether, into which polyester is introduced.

The powder coatings used according to the invention contain, as component B), 0.8-20.1% by weight of low molecular weight curing agents containing epoxy groups. An example of a particularly suitable low molecular weight curing agent containing epoxy groups is triglycidyl isocyanurate (TGIC). TGIC is commercially available, for example, under the name Araldit PT 810 (manufacturer: Ciba Geigy). Other suitable low molecular weight curing agents containing epoxy groups are l ^^ - triglycidyltriazoline-S.δ-dione, diglycidyl phthalate and the diglycidyl ester of hexahydrophthalic acid. Polyacrylate resins containing epoxy groups (component C) are understood to mean polymers which can be prepared by copolymerizing at least one ethylenically unsaturated monomer which contains at least one epoxy group in the molecule with at least one further ethylenically unsaturated monomer which does not contain an epoxy group, at least one of which Monomers is an ester of acrylic acid or methacrylic acid.

Polyacrylate resins containing epoxy groups are known (see, e.g., EP-A-299 420. DE-B-22 14 650, US-A-4,091, 048 and US-A-3,781, 379).

Glycidyl acrylate, glycidyl methacrylate and allyl glycidyl ether are mentioned as examples of ethylenically unsaturated monomers which contain at least one epoxy group in the molecule.

Examples of ethylenically unsaturated monomers which do not contain an epoxy group in the molecule are alkyl esters of acrylic and methacrylic acid which contain 1 to 20 carbon atoms in the alkyl radical, in particular methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, isobutyl acrylate, t- Butyl acrylate and the corresponding methacrylates, 2-ethylhexyl acrylate and 2-ethylhexyl methacrylate called. Further examples of ethylenically unsaturated monomers which contain no epoxy groups in the molecule are acids, such as, for example, acrylic acid and methacrylic acid, acid amides, such as, for example, acrylic acid and methacrylic acid amide, vinylaromatic compounds, such as styrene, methylstyrene and vinyltoluene, nitriles, such as acrylonitrile and methacrylonitrile, vinyl and vinylidene halides, such as vinyl chloride and vinylidene fluoride, vinyl esters, such as, for example, vinyl acetate and vinyl propionate, and monomers containing hydroxyl groups, such as, for example, hydroxyethyl acrylate and hydroxyethyl methacrylate. The polyacrylate resin (component C) containing epoxy groups has an epoxy equivalent weight of 350 to 2000. The polyacrylate resins containing epoxy groups usually have a number average molecular weight (determined by gel permeation chromatography using a polystyrene standard) from 1000 to 15000 and a glass transition temperature (TG) from 30-80 (measured using differential scanning calorimetry (DSC)).

The acrylate resin containing epoxy groups can be prepared by radical polymerization by generally well known methods. Polyacrylate resins containing such epoxy groups are commercially available, for example, under the names Almatex PD 7610 and Almatex PD 7690 (manufacturer: Mitsui Toatsu).

In this respect, powder coatings used according to the invention contain as component D) 0.5-13.6% by weight of low molecular weight di- and / or polycarboxylic acids and / or di- and / or polyanhydrides. Saturated, aliphatic and / or cycloaliphatic dicarboxylic acids are preferably used as component D), such as, for example, glutaric acid, adipic acid, pimelic acid, suberic acid, acelainic acid, cyclohexanedicarboxylic acid, sebacic acid, malonic acid, dodecanedioic acid and succinic acid. In addition, aromatic di- and polycarboxylic acids are also suitable as component D), such as phthalic acid, terephthalic acid, isophthalic acid, trimellitic acid and pyromellitic acid, of course also in the form of their anhydrides, insofar as they exist. Dodecanedioic acid (= 1, 10 gdecanedicarboxylic acid) is particularly preferably used as component D). The amounts of the powder coating components A) to D) are chosen such that the ratio of the epoxy groups from B) and C) to the sum of the carboxyl and anhydride groups from A) and D) is 0.75-1.25: 1. This ratio is preferably 0.9-1.1: 1.

The powder coating material can contain 50 to 90%, preferably 60 to 80% by weight of binder and 10 to 50% by weight, preferably 20 to 40% by weight, of fillers. Glycidyl group-functionalized crystalline silica modifications are suitable as fillers. They are usually used in the range from 10 to 50% by weight, based on the total weight of the powder coating. In some cases, however, filler contents of more than 50% by weight are also possible. The crystalline silica modifications include quartz, cristobalite, tridymite, keatite, stishovite, melanophlogite, coesite and fibrous silica. The crystalline silica modifications are glycidyl group functionalized, the glycidyl group functionalization being achieved by a surface treatment. These are, for example, silica modifications based on quartz, cristobalite and quartz, which are produced by treating the crystalline silica modifications with epoxysilanes. The glycidyl group-functionalized silica modifications are available on the market, for example under the names Silbond ^R 600 EST and Silbond ^R 6000 EST (manufacturer: Quarzwerke GmbH) and are produced by reacting crystalline silica modifications with epoxysilanes. The powder coating materials advantageously contain 10 to 40% by weight, based on the total weight of the powder coating material, of crystalline silica modifications functionalized with glycidyl groups.

The powder coating can also contain other inorganic fillers, for example titanium oxide, barium sulfate and fillers based on silicate, such as talc, Contain kaolin, magnesium, aluminum silicate, mica and the like. The powder coatings may also contain auxiliaries and additives. Examples of these are leveling agents, trickling aids and degassing agents such as benzoin.

The powder coatings are produced by known methods (cf., for example, product information from BASF Lacke + Farben AG, "Powder coatings", 1990) by homogenizing and dispersing, for example using an extruder, screw kneader, etc. After the powder coating has been prepared, it is ground and if necessary adjusted to the desired particle size distribution by sifting and sieving In order to support non-destructive outgassing, degassing agents can also be added to the powder coating, preferably benzoylphenylmethanol (Benzoin®) in concentrations of up to 2% by weight, preferably 0.4% by weight.

All common aqueous decorative paints from the group mentioned can be used for the decorative layer. For this, reference is made, for example, to references EP 89497 or EP 38127. Crosslinkers are isocyanates, aminoplast resins and / or TACT

(Tris [alkoxycarbonylamino] triazines, in particular as described in the literature US-5084541) into consideration.

Preferred is a decorative coating which contains an aqueous polymer dispersion comprising (i) an acrylate polymer based on 30 to 60% by weight of CrC ₈ alkyl (meth) acrylate monomers and 30 to 60% by weight of vinyl aromatic monomers and 0.5 to 10% by weight of (meth) acrylic acid and (ii) a non-associative thickener which contains an acrylate copolymer based on (CC ₆ ) -alkyl (meth) acrylate and (meth) acrylic acid. The acrylate polymer of component (i) used can contain the linear and branched chain derivatives as dC ₈ -alkyl (meth) acrylate monomer units, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl and iso Propyl (meth) acrylate, n-butyl and isobutyl (meth) acrylate and 2-ethylhexyl (meth) acrylate are preferred. (Meth) acrylamide monomers and their derivatives can also be present as further monomers.

As vinyl aromatic monomers which are present as monomer units in the acrylate polymer of component (i), e.g. Styrene, alkyl styrene and vinyl toluene can be called.

The acrylate polymer can be produced by processes known from the prior art, for example emulsion polymerization. The acrylate polymer is preferably used in the form of a dispersion. During the production process, the quantitative ratio between the monomers and the water is preferably adjusted so that the resulting dispersion has a solids content of 30 to 60% by weight, preferably 35 to 60% by weight, and can be used directly for the preparation of the base coating composition . A particularly suitable acrylate polymer is commercially available as an aqueous dispersion under the name Acronal 290 D (BASF AG; Ludwigshafen).

To produce a dispersion of the acrylate polymer, an anionic emulsifier is preferably used alone or as a mixture with others as the emulsifier. to use a filler with a corrosion protection effect on a metallic material. In the case of fillers that are now technologically obsolete, it was necessary to subject the filler layer obtained to an equalizing surface treatment, for example grinding, after the filler had been applied and dried or cured. This made use of the fact that a filler layer is usually less hard and / or better to process than the material of the substrate. In contrast, modern fountain pens have a self-regulating function. This means that after application of the filler to a substrate with surface defects and (pre-) drying or (pre-) crosslinking of the filler, a filler layer is created without further measures, the outer surface of which is practically flat even in the micrometer range. In other words, a filler layer is formed, the interface of which faces the substrate forms a complement to the surface of the substrate, based on surface structures in the micrometer range. A decorative layer is formed from a decorative lacquer. In addition to customary paint binders and crosslinking agents, a decorative paint has in particular color and / or effect pigments. Examples of effect pigments are metallic pigments and micapigments. The decorative layer is essentially responsible for the visual impression of the substrate provided with the multilayer coating on an observer. A protective layer is usually formed from a clear lacquer. The clearcoat must have special properties with regard to its behavior in relation to mechanical stress, chemical stress and light resistance as well as its transmission behavior, since the protective layer is exposed to the environment and in particular is intended to protect the decorative layer. Multi-layer coatings of the type described are used in particular for the coating of motor vehicle bodies or parts thereof made of sheet steel or aluminum plate, but also for the coating of plastic inner parts used in the motor vehicle sector. Examples of anionic emulsifiers are the alkali metal salts of sulfuric acid half-esters of alkylphenols or alcohols, furthermore the sulfuric acid half-esters of oxethylated alkylphenols or oxethylated alcohols, preferably the alkali metal salts of sulfuric acid half-esters of a nonyiphenol, alkyl or sodium lauryl sulfonate, alkyl or sodium lauryl sulfonate, and sodium lauryl sulfonate, with sodium sulfate, with 4 to 5 moles of ethylene oxide secondary sodium alkane sulfonates, the carbon chain of which contains 8-20 carbon atoms. The amount of the anionic emulsifier is 0.1 to 5.0% by weight, based on the monomers, preferably 0.5 to 3.0% by weight. In addition, to increase the stability of the aqueous dispersions, a nonionic emulsifier of the ethoxylated alkylphenol or fatty alcohol type, for example an addition product of 1 mol of nonylphenol and 4 to 30 mol of ethylene oxide, can be used in a mixture with the anionic emulsifier.

The glass transition temperature of the acrylate polymer is preferably between 15 ° C and 35 ° C, particularly preferably between 20 ° C and 25 ° C.

The acrylate polymer used preferably has a number-average molar mass (determination: gel permeation chromatography using polystyrene as the standard) from 200,000 to 2,000,000, preferably from 300,000 to 1,500,000.

According to the invention, acrylate copolymers with non-associative groups which contain (C ₁ -C ₆ ) -alkyl (meth) acrylate and (meth) acrylic acid as monomer units are used as thickener component (ii) in the decorative lacquer. A preferred copolymer contains (meth) acrylic acid as monomer units and at least two different (Ci-Cβ) - alkyl (meth) acrylate monomers. The (meth) acrylic acid is in the copolymer preferably in amounts of 40% by weight to 60% by weight, particularly preferably from 46% by weight to 55% by weight, based on the amount of the entire copolymer. The (-C ₆ ) alkyl (meth) acrylate monomer I is preferably in amounts of 30% by weight to 50% by weight, in particular 36% by weight to 46% by weight, and the (meth) acrylate polymer II preferably in amounts of 1% by weight to 10% by weight, in particular 2% by weight to 8% by weight, in each case based on the amount of the entire copolymer. The rheology aid should give the decorative paint the desired viscosity, in particular at the pH, which is generally alkaline. A particularly preferred thickener, when it is in the form of a dispersion, is thin and thickens at a neutral or basic pH. The acrylate copolyer is suitably used as a finished dispersion. Dispersions of this type preferably contain fatty alcohol alkoxylates, in particular C ₈ -C ₂₂ fatty alcohol ethoxylates. A particularly suitable acrylate copolymer dispersion is commercially available under the name Viscalex HV 30 (Allied Corporation, Great Britain).

The thickener is preferably present in the decorative lacquer used in an amount of 0.5 to 5.0% by weight, in particular approximately 0.3 to 1.5% by weight, based on the solids content. The thickener is usually used as a dispersion with a concentration of 5 to 45% by weight, preferably 7 to 35% by weight.

The decorative lacquer can also contain further thickeners or rheology aids, such as ionic layered silicates, xanthan gum, diurea compounds, polyurethane thickeners, bentonite, waxes and wax copolymers. As an auxiliary binder, the decorative lacquer can also contain epoxy-functional and / or carboxyl-functional constituents, such as customary glycidyl compounds, such as, for example, glycidyl acrylate or glycidyl methacrylate. Suitable carboxyl-functional crosslinking agents are, for example, carboxylic acids, in particular saturated, straight-chain, aliphatic dicarboxylic acids having 3 to 20 carbon atoms in the molecule, dodecane-1, 12-diacid being used with preference.

Polyvinyl alcohol can also be used as a further auxiliary binder. It has been found that the compatibility with the protective lacquers applied to the decorative lacquer can be improved by adding polyvinyl alcohol in an amount of up to 10% by weight, preferably from 1 to 5% by weight. Polyvinyl alcohol has a solvent-repellent effect, so that any solvent or other components contained in the protective lacquer cannot penetrate into the decorative lacquer and change the color due to the repellent effect of the polyvinyl alcohol.

The crosslinkers known in the paint field, such as melamine resins, which can react with free OH groups, can be used as further crosslinkers.

In addition to the polymers described above, the decorative lacquer can also contain other compatible water-thinnable resins, such as, for example, aminoplast resins, polyesters, polyurethanes and acrylated polyurethanes and urethanized acrylates, which serve as additives for achieving certain coating properties, such as improving adhesion or in general as grinders for pigments. The auxiliary binder and / or the crosslinking agent can be used in an amount of up to 10% by weight, in particular from 0.5 to 10% by weight.

The decorative lacquer used generally has a solids content of about 15 to 60% by weight. The solids content varies with the type of effect of the decorative lacquer. For metallic paints, for example, it is preferably 12 to 25% by weight. For plain-colored paints it is higher, for example 14 to 45% by weight

Ammonia and / or amines (in particular alkylamines), amino alcohols and cyclic amines, such as di- and triethylamine, aminomethylpropanol, dimethyiaminoethanolamine, diisopropanolamine, morpholine, N-alkylmorpholine, can be used to neutralize components (i) and (ii). Volatile amines are preferred for neutralization. The aqueous coating agent is usually adjusted to a pH between 6 and 9, preferably 7 to 8.5.

The decorative lacquer can contain organic solvents in an amount of up to 15% by weight. Examples of suitable organic solvents are naphthalenes, gasolines and alcohols. The base lacquers according to the invention can include, as further liquid components, alkylene glycols, such as ethylene glycol, propylene glycol, butylene glycol, 1,4-butanediol, 1,6-hexanediol,

Neopentyl glycol and other diols, such as dimethylolcyclohexane.

The decorative lacquer can contain as pigments customary pigments used for painting automobile bodies, such as, for example, effect pigments and organic and inorganic coloring pigments. Examples of suitable effect pigments are commercially available aluminum bronzes, the aluminum bronzes chromated according to DE-OS 36 36 183, commercially available stainless steel bronzes and other customary ones Metal flakes and flake pigments as well as non-metallic effect pigments, such as pearlescent or interference pigments. Examples of suitable coloring pigments on an inorganic basis are titanium dioxide, iron oxides, carbon black and others. Examples of coloring pigments on an organic basis are indanthrene blue, cromophthal red, irgazin orange, sicotrans yellow, heliogen green and others. Can also

Corrosion protection pigments, e.g. Zinc phosphate. In addition, the decorative lacquer can also contain fillers customary in the field of lacquer chemistry. These include silica, magnesium silicate, talc, titanium dioxide and barium sulfate. The proportion of pigments and fillers in the decorative lacquer can total 3 to 25% by weight, based on the solids content. The pigment can be added in any manner, e.g. as an aqueous slurry or as a paste. For example, the pigments can be rubbed with a grinding resin, such as an auxiliary binder, dispersing aid or water. For plain-colored paints, it is preferred to slurry the pigments in dispersing agents and water. If aluminum or flakes are used, they may be slurried in solvent and possibly a mixture of water and wetting agent, or rubbed in the main binder or in another auxiliary binder. The amount of component (i) can vary depending on the pigment used. If the pigments are organic and / or inorganic color pigments, component A is preferably present in an amount of 25 to 50% by weight, based on the solids content. If the pigments are effect pigments, component A is preferably present in an amount of 15 to 30% by weight, based on the solids content.

The decorative lacquer can contain film-forming aids as a further component.

Dicarboxylic acid dialkyl esters, 1,2-propylene glycol, high-boiling gasolines and naphthalenes are suitable as film-forming aids have a boiling point above 100 ° C., preferably above 140 ° C. The decorative lacquer can optionally contain further auxiliaries and additives. Examples include catalysts, auxiliaries, defoamers, dispersion aids, wetting agents, preferably carboxy-functional dispersants, antioxidants, UV absorbers, radical scavengers, leveling agents, biocides and / or water retention agents.

The decorative lacquer can optionally be mixed with water to adjust the solids content, solvent or rheology aids to adjust the application properties and, if necessary, a base for pH regulation before application to the filler layer. If the viscosity is not yet in the desired range, rheology aids (ii) or further thickeners, if appropriate in an amount of 0.001 to 0.006% by weight, based on the solids content, can be added.

In addition, powder powders known per se can also be used as decorative lacquer or color-bonded lacquer layer.

All common clearcoats can be used as aqueous protective lacquers. The use of the following protective lacquers is particularly preferred.

A first preferred protective lacquer is an aqueous powder lacquer dispersion and is characterized in that the aqueous powder lacquer dispersion can be prepared by an aqueous dispersion of a powder lacquer having a glass transition temperature of 20 to 90 ° C, preferably 40 to 70 ° C, a viscosity of 10 to 1000 mPas, preferably 50 to 300 mPas, at a shear rate of 500 s-1 and a solids content of 10 to 50%, preferably 20 to 40%, a grinding process while maintaining a temperature of 0 to 60 ° C, preferably 5 to 35 ° C, is subjected. The specific energy input during the grinding process is preferably 20 to 500 Wh / kg, in particular 50 to 250 Wh / kg.

With regard to the chemical composition, this aqueous powder coating dispersion is constructed, for example, such that it consists of a solid, powdery component A and an aqueous component B, component A being a powder coating comprising a) at least one epoxy-containing binder with a content of 30 to 45% , preferably 30 to 35% of glycidyl-containing monomers, optionally containing vinyl aromatic compounds, preferably styrene, b) at least one crosslinking agent, preferably straight-chain, aliphatic dicarboxylic acids and / or carboxy-functional polyesters and c) optionally catalysts, auxiliaries, additives typical for powder coatings, such as Degassing agents, leveling agents, UV absorbers, radical scavengers, antioxidants and component B. An aqueous dispersion contains a) at least one nonionic thickener and b) optionally catalysts, auxiliaries, defoaming agents, dispersion auxiliaries, wetting agents, preferably carboxy-functional ones Dispersing agents, antioxidants, UV absorbers, radical scavengers, small amounts of solvents, leveling agents, biocides and / or water retention agents.

Examples of suitable epoxy functional binders for component A are epoxy group-containing polyacrylate resins which can be prepared by copolymerizing at least one ethylenically unsaturated monomer which contains at least one epoxy group in the molecule with at least one further ethylenically unsaturated monomer which does not contain any epoxy group in the molecule, where at least one of the monomers is an ester of acrylic acid or methacrylic acid. Such epoxy group-containing polyacrylate resins are known, for example, from EP-A- 299,420, DE-B-22 14 650, DE-B-27 49 576, US-A-4,091,048 and US-A-3,781, 379).

As examples of ethylenically unsaturated monomers that do not contain an epoxy group in the molecule, alkyl esters of acrylic and

Methacrylic acid, which contain 1 to 210 carbon atoms in the alkyl radical, in particular methyl acrylate, methyl methacrylate, ethyl acrylate,

Ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate and

Called 2-ethylhexyl methacrylate. Further examples of ethylenically unsaturated monomers which contain no epoxide groups in the molecule, acid amides, such as e.g. Acrylic acid and methacrylic acid amide, vinyl aromatic compounds such as styrene, methyl styrene and vinyl toluene,

Nitriles such as acrylonitrile and methacrylonitrile, vinyl and vinylidene halides such as vinyl chloride and vinylidene fluoride, vinyl esters such as e.g. Vinyl acetate and hydroxyl group-containing monomers such as e.g. Hydroxyethyl acrylate and

Hydroxyethyl methacrylate.

The epoxy group-containing polyacrylate resin usually has an epoxy equivalent weight of 400 to 2500, preferably 420 to 700, a number average molecular weight (determined by gel permeation chromatography using a polystyrene standard) from 2,000 to 20,000, preferably from 3,000 to 10,000, and a glass transition temperature (TG) from 30 to 80, preferably from 40 to 70, particularly preferably from 40 to 60 ° C to (measured with the aid of differential scanning calorimetry (DSC)). Approx. 50 ° C. is very particularly preferred. Mixtures of two or more acrylic resins can also be used.

The epoxy group-containing polyacrylate resin can be prepared by polymerization using generally well-known methods. Suitable crosslinkers are carboxylic acids, in particular saturated, straight-chain, aliphatic dicarboxylic acids with 3 to 20 carbon atoms in the molecule. Decane-1, 12-dicarboxylic acid is very particularly preferably used. To modify the properties of the finished powder clearcoat materials, other crosslinkers containing carboxyl groups may also be used. Examples of these are saturated branched or unsaturated straight-chain di- and polycarboxylic acids and polymers with carboxyl groups.

Components A which contain an epoxy-functional crosslinker and an acid-functional binder are also suitable.

Suitable acid-functional binders are, for example, acidic polyacrylate resins which can be prepared by copolymerizing at least one ethylenically unsaturated monomer which contains at least one acid group in the molecule with at least one further ethylenically unsaturated monomer which does not contain any acid group in the molecule.

The epoxy group-containing binder or the epoxy group-containing crosslinking agent and the carboxyl or the binder are usually used in an amount such that 0.5 to 1.5, preferably 0.75 to 1.25, equivalents of carboxyl groups are present per equivalent of epoxy groups. The amount of carboxyl groups present can be determined by titration with an alcoholic KOH solution.

The binder contains vinyl aromatic compounds, especially styrene. However, in order to limit the risk of cracking, the content is not more than 35% by weight. 10 to 25% by weight are preferred. Components A may contain one or more suitable catalysts for epoxy resin curing. Suitable catalysts are phosphonium salts of organic or inorganic acids, quaternary ammonium compounds, amines, imidazole and imidazole derivatives. The catalysts are generally used in proportions of 0.001% by weight to about 2% by weight, based on the total weight of the epoxy resin and the crosslinking agent.

Examples of suitable phosphonium catalysts are ethyltriphenylphosphonium iodide, ethyltriphenylphosphonium chloride,

Ethyl triphenylphosphonium thiocyanate, ethyltriphenylphosphonium acetate-acetic acid complex, tetrabutylphosphonium iodide

Tetrabutylphosphonium bromide and tetrabutylphosphonium acetate-acetic acid complex. These and other suitable phosphonium catalysts are e.g. described in U.S. Patent 3,477,990 and U.S. Patent 3,341,580.

Suitable imidazole catalysts are, for example, 2-styryiimidazole, 1-benzyl-2-methylimidazole, 2-methylimidazole and 2-butyimidazole. These and other imidazole catalysts are e.g. described in Belgian Patent No. 756,693.

In addition, components A may also contain auxiliaries and additives. Examples of these are leveling agents, antioxidants, UV absorbers, radical scavengers, trickling aids and degassing agents, such as, for example, benzoin. Leveling agents based on polyacrylates, polysiloxanes or fluorine compounds are suitable. Antioxidants that can be used are reducing agents such as hydrazides and phosphorus compounds and free radical scavengers, for example 2,6 di-tert-butyiphenol derivatives. UV absorbers that can be used are preferably triazines and benzotriphenoi. 2,2,6,6 tetramethylpiperidine derivatives are preferably used as radical scavengers.

As a further component, the aqueous component B of the powder coating dispersion contains at least one nonionic thickener a). Non-ionic associative thickeners a) are preferably used. Structural features of such associative thickeners a) are: aa) a hydrophilic structure which ensures sufficient water solubility and ab) hydrophobic groups which are capable of associative interaction in the aqueous medium.

Long-chain alkyl residues such as e.g. Dodecyl, hexadecyl or octadecyl residues, or alkarya residues, such as e.g. Octylphenyl or nonylphenyl radicals used. Polyacrylates, cellulose ethers or particularly preferably polyurethanes which contain the hydrophobic groups as polymer building blocks are preferably used as the hydrophilic frameworks.

Polyurethanes which contain polyether chains as building blocks, preferably made of polyethylene oxide, are very particularly preferred as the hydrophilic frameworks. In the synthesis of such polyether polyurethanes, the di- and / or polyisocyanates, preferably aliphatic diisocyanates, particularly preferably optionally alkyl-substituted 1,6-hexamethylene diisocyanate, are used to link the hydroxyl group-terminated polyether units to one another and to link the polyether units to the hydrophobic end group units, for example may be monofunctional alcohols and / or amines with the long-chain alkyl radicals or aralkyl radicals already mentioned. Component B may also contain catalysts, leveling agents, antioxidants, UV absorbers, radical scavengers and wetting agents. Essentially, the substances already listed for component A come into consideration here. Component B can also contain additives, defoamers, dispersion auxiliaries, biocides, solvents and neutralizing agents. Modified polysiioxanes are preferred as defoaming agents. Dispersion aids are, for example, preferably ammonium or metal salts of polycarboxylates. Neutralizers that can be used are amines, ammonia and metal hydroxides.

Component A is produced by known methods (cf., for example, product information from BASF Lacke + Farben AG, “Powder Coatings”, 1990) by homogenizing and dispersing, for example using an extruder, screw kneader, etc. After the powder coatings have been prepared, they are ground and, if necessary, prepared for dispersing by sieving and sieving. The powder can then be used to produce the aqueous powder clearcoat dispersion by wet grinding or by stirring in dry-ground powder coating. Wet grinding is particularly preferred. The average grain size obtained is preferably between 1 and 25 μm less than 20 μm, most preferably 3 to 10 μm It is important that the dispersion contains only small amounts of solvent during the grinding process, so it may be necessary to remove solvent residues from the grinding device before starting the grinding process.

The dispersion can before or after wet grinding or

Entering component A in the water 0 to 5 wt .-% of a

Defoamer mixture, an ammonium and / or alkali salt, a carboxyl-functional or nonionic dispersing aid, Netzmitteis and / or thickener mixture and the other additives are added. Preferably, defoamers, dispersing aids, wetting agents and / or thickeners are first dispersed in water. Then small portions of component A are stirred in. Then defoamers, dispersing aids, thickeners and wetting agents are dispersed again. Finally, component A is stirred in again in small portions. The pH is preferably adjusted with ammonia or amines. The pH value can initially rise here, resulting in a strongly basic dispersion. However, the pH drops back to the above values within several hours or days. The powder coating dispersions can be applied to the decorative layer using the methods known from liquid coating technology. In particular, they can be applied by spraying. Electrostatically assisted high rotation or pneumatic application can also be considered. The powder clear lacquer dispersion applied to the decorative layer is usually flashed off before baking. This is expediently done first at room temperature and then at a slightly elevated temperature. As a rule, the elevated temperature is 40 to 70 ° C., preferably 50 to 65 ° C. The flash off is carried out for 2 to 10 minutes, preferably 4 to 8 minutes at room temperature. At an elevated temperature, the mixture is vented again during the same time period. With a protective lacquer of the type described above, layer thicknesses of 30 to 50 μm can be achieved.

A second preferred protective lacquer is a two-component clear lacquer containing (1) a hydroxy-functional binder or a mixture of hydroxy-functional binders, (2)

Tris (alkoxycarbonylamino) triazine or a mixture of Tris (alkoxycarbonylamino) triazines and (3) free polyisocyanates or a mixture of free polyisocyanates.

Suitable hydroxy-functional binders are preferably those based on hydroxy-functional polyacrylates, hydroxy-functional polyesters and / or hydroxy-functional polyurethanes.

Polyacrylate resins are preferably used, the hydroxyl numbers from 40 to 240, preferably 60 to 210, very particularly preferably 100 to 200, acid numbers from 0 to 35, preferably 0 to 23, very particularly preferably 3.9 to 15.5, glass transition temperatures of 35 to + 70 ° C, preferably -20 to + 40 ° C, very particularly preferably -10 to + 15 ° C and number average molecular weights of 1,500 to 30,000, preferably 2,000 to 15,000, very particularly preferably 2,500 to 5,000.

The glass transition temperature of the polyacrylate resins is determined by the type and amount of the monomers used. The selection of the monomers can be carried out by a person skilled in the art with the aid of the following formula, with which the glass transition temperatures of polyacrylate resins can be approximately calculated:

W.

∑W = 1

TG n Tg _n n

TG = glass transition temperature of the polyacrylate resin n = number of different monomers polymerized into the polyacrylate resin. W _n = weight fraction of the nth monomer TG _n = glass transition temperature of the homopolymer from the nth monomer

Measures to control the molecular weight (e.g. selection of appropriate polymerization initiators, use of

Chain transmission means etc.) belong to the specialist knowledge of the average specialist and need not be explained in more detail here.

Polyester resins or alkyd resins which can be prepared by (a) a cycloaliphatic or aliphatic polycarboxylic acid or a mixture of such polycarboxylic acids, (b) an aliphatic or cycloaliphatic polyol with more than two hydroxyl groups in the molecule or one are also particularly preferably used as the hydroxy-functional binder component Mixture of such polyols, (c) an aliphatic or cycloaliphatic diol or a mixture of such diols and (d) an aliphatic linear or branched saturated monocarboxylic acid or a mixture of such monocarboxylic acids in a molar

Ratio of (a): (b): (c): (d) = 1.0: 0.2-1.3: 0.0-1.1: 0.0-1.4, preferably 1.0 : 0.5 - 1, 2: 0.0 - 0.6: 0.2 - 0.9 to be converted into a polyester resin or alkyd resin.

Examples of component (a) are: hexahydrophthalic acid, 1,4-cyclohexanedicarboxylic acid,

Endomethylene tetrahydrophthalic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid.

Examples of component (b) are: pentaerythritol, trimethylolpropane, trimethylolethane and glycerol. The following are examples of component (c): ethylene glycol, diethylene glycol, propylene glycol, neopentyl glycol, 2-methyl-2-propylpropanediol-1, 3,2-ethyl-2-butyipropanediol-1, 3, 2,2,4-

Trimethylpentanediol-1, 5, 2,2,5-trimethylhexanediol-1, 6, hydroxypivalic acid neopentyl glycol ester and dimethylolcyclohexane.

Examples of component (d) are: 2-ethylhexanoic acid, lauric acid, isooctanoic acid, isononanoic acid and

Monocarboxylic acid mixtures obtained from coconut fat or palm kernel fat.

The production of hydroxyl group-bearing polyester and / or alkyd resins is e.g. in Ullmann's Encyclopedia of Technical Chemistry, third edition, 14th volume, Urban & Schwarzenberg, Munich, Berlin 1863, pages 80 to 89 and pages 99 to 105, in the books: Resines Alkydes- Polyesters by J. Bourry, Paris Verlag Dunod 1952 , Alkyd Resins from CR Martens, Reinhold Publishing Corporation, New York 1961 and Alkyd Resin Technology by T.C. Patton, Interscience Publishers 1962.

Protective lacquers based on polyurethane are also suitable.

Suitable crosslinking agents are all known compounds, for example polyisocyanate, melamine resins, etc. However, it is preferred in this preferred protective lacquer that it contains the crosslinking agents (2) and (3). As component (2) are tris (alkoxycarbonylamino) triazines of the formula

W

∑W = 1

TG n Tσ n

used, where R = methyl, butyl groups. Derivatives of the compounds mentioned can also be used. Preferred for component (2)

Tris (alkoxycarbonylamino) triazines used as described in US Pat. No. 5,084,541.

The carbamate groups react preferentially with OH carriers and that sterically as little hindered hydroxyl groups as possible. The tris (alkoxycarbonylamino) triazine cannot crosslink amino groups. Rather, the carbalkoxy group is split off.

Component (3) contains at least one, if appropriate, in one or more organic crosslinking agents, if appropriate water-dilutable solvents dissolved or dispersed, preferably non-blocked di- and / or polyisocyanate.

The polyisocyanate component is any organic polyisocyanate with aliphatic, cycloaliphatic, araliphatic and / or aromatically bound free isocyanate groups. Polyisocyanates with 2 to 5 isocyanate groups per molecule and with are preferred

Viscosities from 100 to 2,000 mPas (at 23 ° C) are used.

If necessary, small amounts of organic solvent, preferably 1 to 25% by weight, based on pure, can be added to the polyisocyanates

Polyisocyanate, are added so as to incorporate the

To improve isocyanates and, if necessary, the viscosity of the

Lower polyisocyanate to a value within the above ranges. Solvents suitable as additives for the polyisocyanates are, for example, ethoxyethyl propionate, butyl acetate and the like.

Examples of suitable isocyanates are, for example, in “Methods of Organic Chemistry”, Houben-Weyi, Volume 14/2, 4th Edition, Georg Thieme Verlag Stuttgart 1963, pages 61 to 70, and by W. Siefken, Liebigs Ann. Chem. ( 1949) 562, 75 to 136. For example, the isocyanates and / or polyurethane prepolymers containing isocyanate groups mentioned in the description of the polyurethane resins (A2), which can be prepared by reaction of polyols with an excess of polyisocyanates and which are preferably low-viscosity, are suitable.

It is also possible to use isocyanurate groups and / or biuret groups and / or

Allophanate groups and / or urethane groups and / or urea groups and / or uretdione groups have polyisocyanates. Polyisoeyanate containing urethane groups for example by reacting some of the isocyanate groups with polyols such as trimethylolpropane and glycerol.

Aliphatic or cycloaliphatic polyisocyanates, in particular hexamethylene diisocyanate, are preferably dimerized and trimerized

Hexamethylene diisocyanate, isophorone diisocyanate, 2-

Isocyanatopropylcyclohexyl isocyanate, dicyclohexyl methane-2,4'-diisocyanate or dicyclohexyl methane-4,4'-diisocyanate or mixtures of these polyisocyanates are used. Mixtures of uretdione and / or isocyanurate groups and / or are very particularly preferred

Allophanate group-containing polyisocyanates based on

Hexamethylene diisocyanate, as obtained by catalytic oligomerization of

Hexamethylene diisocyanate using appropriate

Catalysts are created, used. The polyisocyanate component can also from any mixtures of those mentioned by way of example

Polyisocyanates exist.

The polyisocyanate component is advantageously used in the coating compositions according to the invention in an amount such that the ratio of the hydroxyl groups of the binder (A) to the isocyanate groups of the crosslinking agents (2) and (3) is between 1: 2 and 2: 1, particularly preferably between 1: 1, 5 and 1, 5: 1.

The crosslinker mixture preferably contains 1 to 99% by weight, particularly preferably 5 to 90% by weight of tris (alkoxycarbonylamino) triazine and preferably 99 to 1% by weight, particularly preferably 95 to 10% by weight of free isocyanate or a mixture from free polyisocyanates. In addition to the components mentioned, the protective lacquer can also contain light stabilizers, for example triazine compounds. Rheological agents can also be added.

In a preferred variant, the protective coating is stored in the form of at least two separate components (I) and (II) which are only mixed with one another immediately before application. It is preferred that the tris (alkoxycarbonylamino) triazine in admixture with the hydroxy-functional binder forms component I and the free polyisocyanate forms component II of the protective lacquer or two-component clear lacquer. In the case of a two-component system, the protective lacquer is designed such that a) one component (I) is a hydroxy-functional binder or a mixture of hydroxy-functional binders and tris (aikoxycarbonylamino) triazine and b) the second component (II) isocyanate free or a mixture of free Contains polyisocyanates. The two components (I) and (II) are prepared from the individual constituents with stirring using the customary methods. The protective lacquer from components (I) and (II) is likewise produced by stirring or dispersing using the devices conventionally used, for example using a dissolver or the like. or by means of also commonly used 2-component metering and mixing systems or by means of the process described in DE-A-195 10 651, page 2, line 62, to page 4, line 5 for the production of aqueous 2-component polyurethane lacquers .

A preferred embodiment of the invention is characterized in that the decorative layer has a layer thickness in the range of

Has 10 microns to 100 microns and that the protective layer has a layer thickness in the range of 20 microns to 150 microns. In particular, it is advantageous if the filler layer has a layer thickness in the range from 50 μm to 80 μm, preferably from 60 μm to 70 μm, if the decorative layer has a layer thickness in the range from 15 μm to 17 μm, preferably from 15 μm to 16 μm, and if the Protective layer has a layer thickness in the range from 35 μm to 50 μm, preferably from 40 μm to 45 μm. In this way, on the one hand, an optimal surface quality and, on the other hand, an optimal decorative effect are achieved.

The filler layer can rest directly on the substrate material. However, at least one further layer, for example a corrosion protection layer, can also be arranged between the substrate and the filler layer.

A preferred use of the invention is that the substrate is a metal sheet, preferably a motor vehicle body sheet. Another use is that the substrate is a plastic molding, preferably an automotive plastic molding based on PVC.

The invention also relates to a method for producing a substrate provided with a multilayer coating, in particular a motor vehicle body sheet or a motor vehicle molded part, according to one of claims 1 to 6, with the following subsequent method steps:

a) a crosslinkable powder coating is applied to the substrate,

b) the powder coating is irradiated or heated for 1 min. up to 10 min. dried and pre-crosslinked at a temperature in the range from 130 degrees C to 240 degrees C, c) an aqueous decorative lacquer is applied and dried onto the dried and pre-crosslinked powder lacquer,

d) an aqueous protective lacquer is applied to the decorative lacquer,

e) the composite of powder coating, decorative pack and protective coating is baked and crosslinked at a temperature in the range from 120 degrees C to 180 degrees C.

Before step a), an electro-dip coating can then be carried out with subsequent baking of the lacquer layer.

In particular, it is preferred if the powder coating for 2 min. to 6 min, preferably for 3 min. up to 4 min., dried and pre-crosslinked at a temperature of 180 ° C. to 220 ° C., preferably by passing the substrate provided with the powder coating through an IR radiation zone.

A coating which meets all the requirements is obtained if the composite of powder coating, decorative coating and protective coating is baked and crosslinked at a temperature in the range from 130 ° C. to 150 ° C., preferably at 150 ° C.

A particularly advantageous embodiment of the process according to the invention in terms of energy expenditure and environmental protection is characterized in that an aqueous decorative lacquer practically free of organic solvents and an aqueous protective lacquer practically free of organic solvents or an aqueous powder clear lacquer dispersion are used, and in that the powder coating, the decorative lacquer and the protective lacquer are used in one operated with circulating air Paint device applied and baked. The invention is explained in more detail below with the aid of examples.

Example 1: Powder coating for the filler layer

example 1

Production of a powder coating

Premix

The following items are weighed:

Then 5 min. mixed in an overhead mixer.

Extrusion The premix is fed to the extruder, here: 1 screw extruder, type Buss PCS 100.

This means that extrudate is rolled on a cooling belt as a skin, cooled, broken and obtained as chips.

Grinding and sifting

The chips are fed to an ACM 40 classifier mill and sifted inline with a cyclone classifier. The resulting coarse material G1 is discharged with a cellular wheel sluice and represents the useful goods. The fine material is separated from the air flow at an absolute filter (surface filter made of PE needle felt) and also discharged via a cellular wheel sluice. Grain size distribution: x ₁₀ > 10 μm; x ₉₀ <40 μm.

Example 2: Decorative paints for the decorative layer

Example 2.1

A. 22 parts by weight of water, 2 parts by weight of Solvesso 200 (Cιo-Cι ₃ aromatics mixture) and 1 part by weight of butyl glycol were placed in a reaction vessel. 30 parts by weight of Acronal 290 D (aqueous dispersion, solids content

50.0%) added.

B. A mixture of 7.6 parts by weight of water and 2 parts by weight of Viscalex HV 30 (solids content 30.6%) was slowly added to the mixture obtained in A.

The pH of the mixture obtained was adjusted to 8.0 with dimethylethanolamine (DMEA).

C. A mixture of 5 parts by weight of aluminum flakes and 5 parts by weight of butylglycol was stirred smoothly in a separate mixer. With vigorous stirring, the aluminum slurry obtained in C. was added in portions to the mixture obtained in B.

The viscosity of the paint obtained was adjusted to 110 mPas using 25 parts by weight of water. The solids content was 18.85%.

Example 2.2

A. 22 parts by weight of water, 2 parts by weight of Solvesso 200 (Cιo-Cι ₃ aromatics mixture) and 1 part by weight of butylglycol were placed in a reaction vessel. 25

Parts by weight of Acronal 290 D (aqueous dispersion, solids content 50.0%) were added.

B. A mixture of 7.6 parts by weight of water and 2 parts by weight of Viscalex HV 30 was slowly added to the mixture obtained in A.

(Solids content 30.6%).

The pH of the mixture obtained was adjusted to 8.0 with 0.4 part by weight of dimethylethanolamine (DMEA).

C. A mixture of 5 parts by weight of aluminum flakes and 5 parts by weight of butylglycol was stirred smoothly in a separate mixer.

D. In a further separate mixer, 5 parts by weight of glycidyl methacrylate dodecanedioic acid were dispersed in 25 parts by weight of water and ground to a particle size of less than 5 μm.

The mixture obtained in B was stirred into the dispersion obtained in D with vigorous stirring.

The aluminum slurry obtained in C was then added portionwise to the resulting mixture. The viscosity of the paint obtained was adjusted to 110 mPas using 25 parts by weight of water. The solids content was 18.35%.

Example 2.3

A paint preparation was prepared according to the procedure described in Example 2.2, with the exception that 10 parts by weight of glycidyl methacrylate / dodecanedioic acid were dispersed in 20 parts by weight of water in step D.

The solids content was 20.35%.

Example 2.4

50.0%) added.

In another separate mixer, 10 parts by weight of a polyester obtained from 9.8% by weight of neopentyl glycol, 6.2% by weight of hexahydrophthalic acid, 22.9% by weight of Pripol (commercial product from Unichema), 11.1% by weight of hexanediol and 2.0% by weight of xylene as solvent, and 2.2 parts by weight Melamine Cymel 303 (cyanamide) dispersed in 12.8 parts by weight of water.

The aluminum slurry obtained in C was then added portionwise to the resulting mixture.

The solids content of the paint was 26.83%.

Example 2.5

A. 22 parts by weight of water, 2 parts by weight of Lusolvan FBH (commercial product from BASF AG, Ludwigshafen) and 1 part by weight of butylglycol were placed in a reaction vessel. 30 parts by weight of Acronat 290 D (aqueous dispersion, solids content 50.0%) were added with stirring.

(Solids content 30.6%).

C. 30 parts by weight of an Irgazinrot DPP BO paste (pigment content 43.2% by weight) were added to the mixture obtained in step B and the mixture was stirred until smooth.

The viscosity of the paint obtained was 5 parts by weight

Water set to 110 mPas.

Example 2.6

A. 22 parts by weight of water, 2 parts by weight of Lusolvan FBH (commercial product from BASF AG, Ludwigshafen) and 1 part by weight of butylglycol were placed in a reaction vessel. 25 parts by weight of Aeronal 290 D (aqueous dispersion, solids content 50.0%) were added with stirring.

(Solids content 30.6%).

C. 28.79 parts by weight of an Irgazinrot DPP BO paste (pigment content 43.2% by weight), 1.17 parts by weight of Disperbyk 190 (dispersing aid) and 0.03 parts by weight of the copolymer used in step B were dispersed in a separate mixer and ground to a particle size below 5 μm.

D. In another separate mixer, 5 parts by weight of glycidyl methacrylate / dodecanedioic acid were dispersed in 25 parts by weight of water and ground to a particle size of less than 5 μm.

The mixture obtained in B was stirred into the dispersion obtained in D with vigorous stirring. The pigment paste obtained in C was then added in portions to the mixture obtained.

The solids content was 28.06%.

Example 2.7

The procedure described in Example 2.6 was repeated, except that 20 parts by weight of the acrylate dispersion were used in step A and 10 parts by weight of glycidymethacrylate / dodecanedioic acid in step D.

Example 2.8

A. 22 parts by weight of water, 2 parts by weight of Lusolvan FBH (commercial product from BASF AG,

Ludwigshafen) and 1 part by weight of butyl glycol. 15 parts by weight of Acronal 290 D (aqueous dispersion,

Solids content 50.0%) acrylic dispersion added.

C. In a separate mixer, 28.79 parts by weight of an Irgazinrot DPP BO paste (pigment content 43.2% by weight), 1.17 parts by weight of Disperbyk 190 and 0.03 parts by weight of the copolymer used in step B were dispersed and to a particle size ground below 5 μm.

D. In a further separate mixer, 10 parts by weight of a polyester obtained from 9.8% by weight of neopentyl glycol, 6.2% by weight of hexahydrophthalic acid, 22.9% by weight of Pripol (commercial product from Unichema), 11.1% by weight of hexanediol and 2.0% by weight of xylene as solvent, and 2.2 parts by weight of melamine Cymel 303 (cyanamide) dispersed in 12.8 parts by weight of water.

The mixture obtained in B was stirred into the dispersion obtained in D with vigorous stirring. The pigment preparation prepared in step B was then stirred in.

The solids content was 29.04%.

Example 3: Protective lacquers for the protective layer

Example 3.1

A. Preparation of an acrylate resin: 21.1 parts of xylene are introduced and heated to 130.degree. Initiator: 4.5 parts of TBPEH (tert.-butyl perethylhexanoate) mixed with 4.86 parts of xylene and monomers: 10.78 parts of methyl methacrylate, 25.5 parts of n-butyl methacrylate are added to the template at 130 ° C. in the course of 4 hours via two separate feed containers , 17.39 parts of styrene and 23.95 parts of glycidyl methacrylate. The mixture is then heated to 180 ° C. and the solvent is stripped off in vacuo <100 mbar.

B. Preparation of a powder clearing: 77.5 parts of acrylic resin, 18.8 parts of dodecanedicarboxylic acid (see hardener), 2 parts of Tinuvin 1130 (UV

Absorber), 0.9 part Tinuvin 144 (HALS), 0.4 part Additol XL 490 (leveling agent) and 0.4 part benzoin (degassing agent) are intimately mixed on a Henschel fluid mixer, extruded on a BUSS PLK 46 extruder of a Hosohawa ACM 2 grinder and sieved through a 125 μm sieve. C. Preparation of a dispersion: 0.6 part of Troykyd D777 (defoamer), 0.6 part of Orotan 731 K (dispersing agent), 0.06 part of Surfinol TMN 6 (wetting agent) and 16.5 parts of RM8 ( Rohm & Haas, nonionic associative thickener

Polyurethane base) dispersed. Then 94 parts of the powder clearcoat are stirred in in small portions. Then 0.6 parts of Troykyd D777, 0.6 part of Orotan 731 K, 0.06 part of Surfinol TMN 6 and 16.5 parts of RM8 are dispersed again. Finally, 94 parts of the powder clear lacquer are stirred in in small portions.

The material is ground in a sand mill for 3.5 hours. The final measured particle size is 4 μm. The material is filtered through a 50 μm filter and finally 0.05% Byk 345 (leveling agent) is added.

D. Application of the dispersion: The slurry is applied to steel panels coated with water-based lacquer using a cup gun. The sheet is flashed off at room temperature for 5 minutes and at 60 ° C. for 5 minutes.

The sheet is then 30 min at a temperature of 140 ° C. branded. With a layer thickness of 40 μm, a high-gloss clear lacquer film with MEK resistance (> 100 double strokes) is produced. The clear lacquer film has good resistance to condensation water.

Example 3.2

3.2.1. Manufacture of binder solutions

A. Acrylic resin A In a laboratory reactor with a useful volume of 4 I equipped with a stirrer, two dropping funnels for the monomer mixture or. Initiator solution, nitrogen inlet tube, thermometer and reflux condenser are weighed in 899 g of a fraction of aromatic hydrocarbons with a boiling range of 158 ° C - 172 ° C. The solvent is heated to 140 ° C. After reaching 140 ° C., a monomer mixture of 727 g of n-butyl imethacrylate, 148 g of cyclohexyl methacrylate, 148 g of styrene, 445 g of 4-hydroxibutyl acrylate and 15 g of acrylic acid are added within 4 hours, and an initiator solution of 29 g of t-butyl perethyl hexanoate in 89 g of the aromatic solvent described evenly metered into the reactor within 4.5 hours. The metering of the monomer mixture and the initiator solution is started simultaneously. After the initiator metering has ended, the reaction mixture is kept at 140 ° C. for a further two hours and then cooled. The resulting polymer solution has a solids content of 62% determined in a forced air oven for 1 h at 130 ° C.), an acid number of 9 and a viscosity of 21 dPas (measured on a 60% solution of the polymer solution in the aromatic solvent described, using a ICI-plate-cone viscometer at 23 ° C).

B. Acrylate resin B

In a laboratory reactor with a useful volume of 4 I equipped with a stirrer, two dropping funnels for the monomer mixture or. Initiator solution, nitrogen inlet tube, thermometer and reflux condenser are weighed in 897 g of a fraction of aromatic hydrocarbons with a boiling range of 158 ° C - 172 ° C. The solvent is heated to 140 ° C. After reaching 140 ° C., a monomer mixture of 487 g of t-butyl acrylate, 215 g of n-butyl methacrylate, 143 g of styrene, 572 g of hydroxypropyl methacrylate and 14 g Acrylic acid within 4 hours, and an initiator solution of 86 g of t-butyiperethylhexanoate in 86 g of the aromatic solvent described evenly metered into the reactor within 4.5 hours. The metering of the monomer mixture and the initiator solution is started simultaneously. After the initiator metering has ended, the reaction mixture is kept at 140 ° C. for a further two hours and then cooled. The resulting polymer solution has a solids content of 62% determined in a forced air oven for 1 h at 130 ° C.), an acid number of 10 and a viscosity of 23 dPas (measured on a 60% solution of the polymer solution in the aromatic solvent described, using a ICI Piatte cone viscometers at 23 ° C).

C. alkyd resin C

In a laboratory reactor with a useful volume of 4 1 equipped with a stirrer, water separator, reflux condenser, nitrogen inlet tube and thermometer, 1330 g of hexahydrophthalic anhydride, 752 g of 1, 1, 1 trimethylolpropane, 249 g of 1, 4-dimethyloicyclohexane, 204 g of hexanediol -1.6, 136 g of isononanoic acid (as a mixture of isomers of 3,3,5-trimethylhexanoic acid and 3,5,5-trimethylhexanoic acid) and 75 g of xylene as an entrainer are weighed out. The water separator is precipitated with xylene. The contents of the reactor are heated to 210 ° C. in the course of 8 hours in such a way that there is a uniform reflux of the entrainer. The reactor contents are kept at 210 ° C. until an acid number of 17.1 and a viscosity of 15 dPas, measured on a 60% solution of the reaction mixture in the aromatic solvent described in the acrylic resins A and B, is reached. The mixture is then cooled to 140 ° C. and the contents of the reactor are dissolved with so much of the aromatic solvent mentioned that a non-volatile fraction of 61% (determined in a forced air oven for 60 minutes) 130 ° C) results. The alkyd resin solution prepared in this way has an acid number of 17.1 and a viscosity of 15 dPas (measured on an ICI-plate-cone viscometer at 23 ° C.).

3.2.2 Production of two-component clear coats

A. Component 1

Component 1 of the two-component clear lacquers is prepared by weighing the binder solution, then adding the amounts of triazine crosslinking agent, solvent, UV absorber, radical scavenger and leveling agent indicated in Table 1 with stirring and stirring well. The amounts in this and the following tables are to be understood as weights.

Table 1:

B. Component 2

Component 2 consists of a solution of commercially available isocyanurate trimers in a suitable solvent. It is prepared by stirring in the solvent in the isocyanurate form according to Table 2.

Table 2:

C. Production of clear coats

The clear coats are produced by mixing components 1 and 2 in accordance with the proportions given in table 3 and applying them immediately after the mixing. Alternatively, special two-component systems can be used for the application, which are known to the average person skilled in the art and therefore need not be described in more detail here. Table 3 also contains properties of the clearcoats, which the invention illustrates. Table 3:

'1) grade after 14 weeks of outdoor exposure in Jacksonville / Florida no damage, 10 = complaint)

Example 4: Preparation of a multi-layer coated substrate.

Using 180-grit sandpaper, artificial scratch marks are created (cf. Fig. 1) on a sheet of metal that is common in automobile body construction. A puiveriack as a filler according to Example 1 was first applied to this sheet with surface defects by means of application by means of electrostatic adhesion. The sheet provided with the powder coating filler (Fig. 2) was then for 4 min. irradiated with IR, a temperature of about 200 ° C. being established. Here, the powder coating Filler melted and cross-linked. In the present example, no residual reactivity from the crosslinking reaction of polyester and epoxy resin was detectable by DSC examination. The result was a practically smooth filling surface. Subsequent to the IR radiation, a decorative lacquer according to Example 2.1 was applied using the customary spray process, which was followed by a drying process for film formation. A powder clear coat dispersion according to Example 3.1 was sprayed onto the dried decorative paint. Finally, the sheet thus coated was subjected to a baking process step at 150 ° C. for 20 minutes. subjected.

The following layer thicknesses resulted for the finished multilayer coating. Filler layer: 60 μm, decorative layer: 16 μm, protective layer: 40 μm. The surface of the multi-layer coating made a perfect visual impression. In particular, there were no signs of surface defects in the sheet. The stone chip resistance according to VDA621-427 with 2 x 500 g steel gravel and 2 bar air pressure resulted in a KW1.

A second sheet was coated with a water filler for comparison (Fig. 3). A comparison of FIGS. 2 and 3 shows that the coating according to the invention with powder coating according to FIG. 2 results in a substantially smoother surface than the coating with water filler according to FIG. 3.

The perthormetric measurement of the powder coating filler shows a complete equalization of the sanding marks (FIG. 2), while a water filler painted in a conventional manner with 35 μm leaves considerable markings (FIG. 3). 4 shows an example of the process of body painting.

The body to be coated reaches the pretreatment stage 2 via the inlet 1. This is followed by the electrocoating 3 and the baking 4 of the electrocoating layer. In stage 5, preparation for coating with powder coating is carried out (stage 6). In stage 7, drying is carried out with IR radiation. This is followed by cooling stage 8. The powder coating is applied in step 9 to the powder coating layer. After passing through the intermediate drying 10, a protective layer is applied in stage 11 and then baked in stage 12. The body is transported out of the system via the outlet 13.

Claims

claims

1. Provided with a multi-layer coating, wherein the multi-layer coating has a filler layer, a coloring and / or effect-giving decorative layer and a protective layer, the filler layer being arranged closest to the substrate and the protective layer being removed from the substrate, an aqueous decorative lacquer with a binder being used for the decorative layer the group "Acrylate resins, carboxyl-, epoxy- and / or hydroxyl group-containing binders" or mixtures thereof and with a crosslinking agent from the group "Isocyanates, Aminopiastharze or TACT" or mixtures thereof is used and wherein an aqueous protective lacquer from the group is used for the protective layer "One-component clear coats, two-component clear coats, powder clear coats" is used,

characterized,

that the filler layer is formed from a pre-crosslinkable powder coating,

wherein the filler layer made of powder coating has a layer thickness in the range from 30 μm to 250 μm.

2. Provided with a multi-layer coating according to claim 1, characterized in that the decorative layer

Has layer thickness in the range of 10 microns to 100 microns and that the

Protective layer has a layer thickness in the range of 20 microns to 150 microns.

3. Provided with a multilayer coating according to claim 1 or 2, characterized in that the filler layer has a layer thickness in the range from 50 microns to 80 microns, preferably from 60 microns to 70 microns, that the decorative layer has a layer thickness in the range of 15 microns to 17 microns, preferably from 15 microns to 16 microns, and that the protective layer has a layer thickness in the range of 35 microns to 50 microns, preferably from 40 microns to 45 microns.

4. Provided with a multi-layer coating according to one of claims 1 to 3, characterized in that the filler layer rests directly on the substrate material.

5. Provided with a multi-layer coating according to one of claims 1 to 4, characterized in that the substrate is a metal sheet, preferably a motor vehicle body sheet.

6. Provided with a multilayer coating substrate according to one of claims 1 to 4, characterized in that the substrate is a plastic molding, preferably an automotive plastic molding based on SMC.

7. A method for producing a substrate provided with a multilayer coating, in particular a motor vehicle body sheet or a motor vehicle molded part, according to one of claims 1 to 6, with the following method steps:

a) a crosslinkable powder coating is applied to the substrate, b) the powder coating is irradiated or heated for 1 min. up to 10 min. dried and pre-crosslinked at a temperature in the range from 130 degrees C to 240 degrees C,

c) an aqueous decorative lacquer is applied and dried onto the dried and pre-crosslinked powder lacquer,

d) an aqueous protective lacquer is applied to the decorative lacquer,

e) the composite of powder coating, decorative coating and protective coating is baked and crosslinked at a temperature in the range from 120 degrees C to 180 degrees C.

8. The method according to claim 7, wherein the powder coating for 2 min. to 6 min, preferably for 3 min. up to 4 min., at a temperature of 180

Degrees C to 220 degrees C is dried and pre-crosslinked, preferably by passing the substrate provided with the powder coating through an IR radiation zone.

9. The method according to any one of claims 7 or 8, wherein the composite of powder coating, decorative coating and protective lacquer at a temperature in the range of 130 degrees C to 150 degrees C, preferably at 150 degrees C, is baked and crosslinked.

10. The method according to any one of claims 7 to 9, wherein an aqueous decorative lacquer practically free of organic solvents and an aqueous protective lacquer practically free of organic solvents or an aqueous powder clear lacquer dispersion are used, and wherein the Puiveriack, the decorative lacquer and the protective lacquer applied and baked in a paint-operated paint shop.