Process for making multilayer coating, especially for cars, which have a good inter-layer adherence.

The invention relates to the production of multilayer coatings, in particular in automotive painting, which result in good interlayer adhesion.

Multi-layer coatings are well known in the industry. They are used to create a lacquer structure that has different positive properties, but which cannot be produced with a single coating agent. In the automotive industry, for example, two-component primers or electrocoat primers are used to increase the corrosion protection of the metal parts. Filler generally have the task of compensating for unevenness in the substrate and thus delivering a smooth, homogeneous surface over different substrate types. They should also protect the primer from mechanical damage, such as stone chips. The other coatings are generally used for the optical upgrading of the substrate. They are single-layer or multi-layer top coat, the multi-layer top coat consisting of a pigmented base layer and a clear coat subsequently applied.

Such multi-layer coatings are described for example in EP-A-89 497. An aqueous anionic binder is applied in a metallic base layer to conventional substrates. A conventional one-component (1K) or two-component (2K) clear coat is applied to this.

In order for a complex, multi-layer paint system to perform its tasks, the individual layers are generally optimized for their specific application. However, in order to achieve a good overall result, it is necessary that the successive layers are well coordinated. For example, the adhesion of the layers to one another should be as high as possible. Liability is particularly important in the case of mechanical loads, such as Rockfall, the individual layers of paint required. Another problem that is also associated with liability is the so-called condensation resistance. It has been shown that under different moist storage conditions, moisture can accumulate between individual layers of paint. This leads to delamination or blistering between the layers of paint.

One way to achieve improved liability is to use adhesion promoters in the coating agents. Depending on the chemical structure, these may later diffuse to the surface and thus promote adhesion of the subsequent lacquer layer. DE-OS 39 32 744 describes how to improve the adhesion by using zirconium aluminate compounds. The use of reactive adhesion promoters is also known. However, these additives have to be tested specifically for each layer and also often have side effects, for example tendency to craters, which interfere with a good paint build-up.

EP-A-0 421 247 describes a method in which two electrochemically depositable lacquer layers are described in order to improve the optical properties. An anionic layer is first deposited (ATL), this is baked and then provided with a cathodic electrocoating (KTL) as the second layer and baked. The goal is to improve corrosion protection and the visual appearance. Further layers of paint on it are not described.

In DE-OS 38 05 629, a coating agent based on an anionic binder is applied to a commercially available KTL as a stone chip protective layer. A commercially available alkyd / melamine topcoat is mentioned as the topcoat. This paint build-up aims to improve stone chip protection in aqueous stone chip protection coatings by using special resins. A conventional solvent-based topcoat is used. The multilayer coating has the usual weaknesses in terms of resistance to condensation. So far, those made of anionic binder systems have always been described as a stone chip protection layer in a multilayer structure.

It is an object of the present invention to provide a method in which good interlayer adhesion is achieved by a coordinated structure of the binders of successive lacquer layers and improved condensation resistance is achieved.

This is achieved by the method forming the subject of the invention, in which at least three immediately adjacent layers with alternating polarity are applied to produce multilayer coatings.

At least 4 alternating polar layers are preferably applied, particularly preferably the entire structure consists of alternating polar layers.

The alternating structure is preferably counted starting from the outermost layer of the multilayer structure.

Alternating polarity is to be understood to mean that adjacent coating means or layers have opposite polarities, that is to say they are charged or polarized in opposite directions. Polarity is understood to mean the effective total charge of the resin, which is composed of the sum of the charges and partial charges. This means that the polarity of the layers is essentially determined by the content of polymers with polar groups, for example ionic groups or groups which can be converted into ionic groups and which can be supported by groups with a strong dipole or a high dipole moment.

The resins with polar groups are preferably at least some of the varnish-type resins contained, such as the binder resins, hardeners or crosslinkers, paste resins (or grinders) and rheological resins and other possible resinous components or polymers contained in coating compositions.

For example, so-called anionic and cationic coating agents can preferably be used in the process according to the invention. The coating compositions which can be used according to the invention are preferably aqueous-based. The invention is described below primarily on the basis of examples of such coating compositions, which, however, are not intended to be limiting.

The effect of condensation water stability achieved in the process according to the invention is particularly surprising because salt-like conditions have to be assumed in the interfaces of the lacquer layers. However, these just suggest an increased sensitivity to water.

Examples of anionic coating compositions which can be used according to the invention are coating compositions with paint binders which have anionic groups reacted on the polymer structure or reactive groups which can be converted into anionic groups. Examples of cationic coating agents are coating agents with lacquer binders which carry cationic groups reacted on the polymer skeleton or substituents which can be converted into cationic groups. According to the invention, not all resins have to contain ionic groups. It is sufficient if only some of the resins used have the ionic groups. Ionic additives or ionic pigments can support the effect according to the invention. As an example of anionic groups or groups which can be converted into anionic groups, -COOH, -SO₃H, -PO₂R (OH), -PO₃H₂ may be mentioned. These groups can be converted into the corresponding anions using organic or inorganic bases. Examples of cationic groups or in such convertible groups are -NR₃⁺, -NHR, -NH₂, -SR₂⁺, where R is for example C₁ to C₈ alkyl. They can be converted into the ionic form by organic or inorganic acids and by alkylation. These ionic groups are preferably bound to the binder by covalent bonds.

As mentioned, components with groups that are strong dipoles or have high dipole moments can also be used. Such groups are, for example, hydroxyl groups, ether groups, amide groups, urethane groups, urea groups, ester groups, nitrile groups, nitro groups, halogen atoms (for example chlorine and fluorine, as contained in the trifluoromethyl group).

In the process according to the invention it is possible, for example, to work in such a way that, for example, a coating agent containing a reaction containing cationic groups is followed by a coating agent containing anionic groups and then another cationic. A reverse order is also possible; the alternating structure is essential.

According to the method of the invention, for example, the procedure can be such that an aqueous corrosion protection primer is electrochemically deposited as the first layer. These can carry either anionic groups (ATL) or cationic groups (KTL) in the binder. As another example, aqueous 2-component epoxyamine primers may be mentioned which have neutralized resins (cationic) containing amino groups in the water-dilutable coating composition.

Starting with the primer, an aqueous filler layer is applied to it, for example. A cationic filler layer is applied to an anionic primer and an anionic filler layer to a cationic primer.

The subsequent layer can be an aqueous pigmented lacquer, for example an aqueous metallic basecoat. In the case of the anionic filler layer, the basecoat is cationic, in the case of the cationic filler layer, the basecoat is anionic.

A clear coat can, for example, be applied as a further subsequent layer. This has again reacted oppositely charged ionic groups in the binders. An anionic basecoat is followed by a cationic clearcoat, and a cationic basecoat is followed by an anionic clearcoat.

Examples of multi-layer structures according to the invention are: <tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left">A)</entry><entry namest="col2" nameend="col2" align="left">B)</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">cationic primer</entry><entry namest="col2" nameend="col2" align="left">anionic primer</entry></row><row><entry namest="col1" nameend="col1" align="left">anionic filler</entry><entry namest="col2" nameend="col2" align="left">cationic filler</entry></row><row><entry namest="col1" nameend="col1" align="left">cationic basecoat</entry><entry namest="col2" nameend="col2" align="left">anionic basecoat</entry></row><row><entry namest="col1" nameend="col1" align="left">anionic clear coat</entry><entry namest="col2" nameend="col2" align="left">cationic clear coat</entry></row></tbody></tgroup><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left">C)</entry><entry namest="col2" nameend="col2" align="left">D)</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">aqueous cationic 2K primer</entry><entry namest="col2" nameend="col2" align="left">cationic primer</entry></row><row><entry namest="col1" nameend="col1" align="left">anionic rockfall intermediate ground</entry><entry namest="col2" nameend="col2" align="left">anionic filler</entry></row><row><entry namest="col1" nameend="col1" align="left">cationic top coat</entry><entry namest="col2" nameend="col2" align="left">cationic basecoat</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="left">anionic clear powder coating</entry></row></tbody></tgroup></table></tables>

This sequence according to the invention of the ionic groups in the binders used, which is mentioned as an example, can be changed to other layer sequences by means of intermediate layers, for example an additional stone chip intermediate layer or additional barrier layers. According to the invention, at least three layers are applied. It is preferred to work in such a way that the alternating structure results from the outermost layer counting inwards.

Aqueous coating compositions are preferred for reasons of environmental protection, but it is entirely possible that individual coating compositions are constructed conventionally. In this case, too, however, it is necessary that the binders used have the corresponding ionic groups. Aqueous coating systems are to be understood as coating compositions which are present in physically or colloidally dissolved form or as a dispersion in water. The electrical charge can be on the surface of colloidal or dispersed particles and can be generated by adding appropriately charged emulsifiers. Binders with ionic groups are preferred.

While in aqueous systems some of the ionic groups are generally necessary in order to convert the binder into a water-dispersible form, smaller proportions of the ionic groups can be present in binders in organic solvents. Some of these ionic groups can optionally be reacted with crosslinking agents in the course of chemical crosslinking of the coating film or they are expelled from the coating film as fission products. It is sufficient if some of the ionic or ionizable groups are still present after the applied coating film has been crosslinked or dried. All polar binder systems described in the literature or familiar to the person skilled in the art or combinations thereof can be used for an alternating layer structure.

Examples of binders and coating agents that can be used are listed below: Primers that can be deposited on the cathode (KTL) are described, for example, in EP-A 12 463, DE-OS 27 28 470, EP-A 82 291, EP-A 234 395, US-A 48 08 658, DE-OS 27 28 470, DE-OS 36 15 810, EP-A 261 385, US-A 48 65 704, EP-A 193 685, EP-A 4090, EP-A-52 831, US-A 44 14 753, US-A 44 96 672 and EP-A 259 181. These are coating compositions which contain binders with reacted cationic groups or groups which can be converted into cationic groups, for example -NH₂, -NR₂, -NR₃⁺, -SR₂⁺ or -PR₃⁺. The resin base for this are, for example, acrylic resins, epoxy resins, polyethers, diene polyhydrocarbons, such as butadiene oils, polyurethanes, polyamides or polyester resins. The binders are self-crosslinking or can react via admixed crosslinkers. Blocked isocyanates, melamine resins, phenolic resins, transesterification hardeners, unsaturated compounds or Michael hardeners are described as crosslinking agents. The coating compositions can also contain finely divided, crosslinked or non-crosslinked, optionally melting powders with or without ionic groups.

For anodic electrocoating (ATL), for example, coating agents and corresponding binders with anionic groups are described in EP-A 21 014, DE-OS 28 24 418, US-A 41 72 822, US-A 42 20 568, DE-OS 27 37 174 , EP-A 106 355, DE-A 27 37 174 or EP-A 21 014. Examples of the binder base are polyester resins, epoxy resin esters, polyurethane resins, polyacrylate resins or reaction products of maleic anhydride with unsaturated, natural or synthetic oils, for example Butandiene oils. The binders can be self-crosslinking or crosslinking. Carboxyl groups or phosphonium groups, for example, serve as functionalities which can be converted into ionic groups.

EP-A-319 841 describes, for example, aqueous 2-component systems as a corrosion protection primer, which consist of a neutralized cationic urethanamine together with epoxy resins.

DE-OS 38 05 629 or US 49 68 536 describes, for example, aqueous stone chip protection primers based on anionic binders. Polyacrylates, polyesters and isocyanate systems are mentioned.

Examples of aqueous fillers with anionic binders are described in EP-A-0 272 525, DE-OS 38 05 629, US-A 49 68 536, EP-A-427 028 and WO 89/00412. Polyacrylates, polyesters, epoxyamine adducts, maleic anhydride / fatty acid reaction products or binders containing polyurethane are described. These are crosslinked with amino resins, phenolic resins or isocyanate derivatives. Common pigments, fillers and paint additives are used.

Examples of cationic fillers are described in German patent application P 41 34 301.8 by the same applicant on the same priority date. These are coating compositions with conventional pigments, fillers, paint additives and water as a solvent, which contain binders based on polyacrylates, polyurethanes, polyesters or polyurethane-urea resins together with crosslinking agents based on melamine resins or blocked isocyanates. These are amine-containing binders with a molecular weight between 500 and 200,000, an OH number from 10 to 400, an amine number from 20 to 200 and a Tg between -50 ° and -100 °.

The binders crosslink via reactive NH or OH groups with the crosslinking agents. Water solubility is achieved via the neutralizable amino groups. The glass transition temperature (Tg) of the binders influences the elasticity of the binders. The finished coating agents are applied using conventional techniques.

Waterborne basecoats based on anionic binders are described, for example, in EP-A 38 127, US-A 44 03 003, US-A 45 39 363, EP-A 71 070, EP-A 195 931, US-A 47 30 020, EP- A 238 108, EP-A-21 414, EP-A 89 497, US-A 44 89 135, US-A 45 58 090, EP-A 228 003, EP-A 256 540 and EP-A 260 444. They can be ionic microgels or non-crosslinked ionic polymers. The coating agents can be physically drying, optionally also contain crosslinking agents or self-crosslinking. For example, polymers of unsaturated monomers, such as (meth) acrylic acid derivatives, polyesters, polyethers, polyurethanes or epoxy resin reaction products, are described as the binder base.

Examples of cationic waterborne basecoats are described in DE patent application 40 11 633. They are binders based on polyurethanes, polyesters, polyurethane-urea resins or polymers of unsaturated monomers such as (meth) acrylic acid derivatives, which do not contain free carboxyl groups, but rather amino groups. Basecoats can be formulated from these binders by adding neutralizing agents as well as pigments, fillers, catalysts and / or additives. The binders can optionally crosslink via known amine formaldehyde resins or blocked isocyanates. These basecoats can be applied using known application techniques.

The binders for waterborne basecoats can also be processed into topcoat coatings if the binders are weatherproof. However, it is necessary to choose binder systems that can crosslink with each other through a chemical reaction. An additional clear lacquer coating does not have to be applied.

Examples of water-thinnable clearcoats with anionic groups are described in DE-OS 39 10 829, US-A 50 15 688, DE-OS 25 57 434, US-A 39 53 643, DE-OS 37 12 442 or DE-OS 40 27 594. They are preferably carboxyl-containing polymers based on polyesters, polyacrylates or polyurethanes, which react with known crosslinkers, if appropriate by heating, to give the clearcoat coatings.

Examples of cationic clearcoats are described in German patent application P 41 34 290.9 by the same applicant on the same priority date. They are formulated on the basis of polymers of unsaturated monomers, eg acrylic resins. The binders must contain basic groups which are converted into cationic groups. The paint properties can be adjusted via molecular weight, glass transition temperature and the binder viscosities. The binders crosslink via reacted functional groups, for example OH groups, with blocked isocyanates or melamine resins as crosslinkers.

Examples of powder clearcoat binders with ionic groups are mentioned in US Pat. No. 3,787,521, US Pat. No. 4,091,048, DE-OS 24 41 753 or DE-OS 25 09 410. These are, for example, acrylic resins that contain epoxy groups in the side chain. These react during melting, for example with polymers containing polycarboxyl groups or substances containing anhydride groups, to form ester structures. It is also possible to use other cross-linking functionalities, for example primary OH groups. Even after crosslinking, portions of polar groups, for example COOH or OH groups, remain in the films.

The binders and coating compositions listed by way of example above can contain customary pigments, catalysts or other auxiliaries. They serve to achieve optical or technological effects or influence the application properties. The effect according to the invention is essentially not influenced or even enhanced by the additional components.

A preferred embodiment is that powder coatings containing carboxyl groups are used as the clear lacquer coating. The use of cationic water-clear lacquers is also preferred. The use of cationic waterborne basecoats in multilayer coating is further preferred.

Particularly preferred embodiments are multi-layer structures which comprise an aqueous anionic clear lacquer based on acrylic / melamine resin or acrylic / isocyanate, including a cationic water-based lacquer based on aminopolyurethanes or aminoacrylate resins, and including an aqueous anionic filler based on polyesters or epoxidized / urethanized alkyd resins. Another example of a structure contains a cationic water-clear lacquer based on aminoacrylate resin or aminopolyurethanes, including an anionic water-based lacquer based on acrylated polyester resins and / or polyurethane resins, and below this an aqueous cationic filler based on aminoepoxy resin.

The coatings produced according to the invention are applied in a known manner. Examples include painting, dipping, electrocoating or spraying. For this purpose, the coating agents are each set to a suitable viscosity and a suitable solid and applied. The individual layers of lacquer are crosslinked in accordance with the state of the art, which means that they can be crosslinked if necessary by elevated temperature, crosslinking can occur at room temperature, or the lacquer layers are applied wet-on-wet and baked together. The coating agents used can either be physically drying and / or chemically crosslinking. They can be used pigmented or unpigmented. They can be formulated on the basis of 1-component or 2-component systems.

The layer thicknesses are preferably &lt;40 »m for the primer, &lt;130» m for the filler, &lt;25 »m for the basecoat and &lt;100» m for the clear coat. Additional additional coating layers, such as stone chip protection coatings or adhesive primers, can be applied according to their respective purpose.

The properties of the bottom base layer of the multi-layer coating must be matched to the surface, for example by adding adhesion promoters, which have often been shown to be necessary in plastic coating. For example, binders containing anionic groups are particularly suitable for electrophoretic aluminum coating. The multilayer coatings according to the invention are distinguished by good interlayer adhesion, regardless of their other properties. This is particularly noticeable in the case of stone chip tests, adhesion tests (eg cross-cut according to DIN 53 151) and resistance tests in a constant climate (eg DIN 50 017).

The coating agents are preferably formulated on an aqueous basis. However, it is also possible that individual layers of paint are solvent-containing and have a high solids content or are used as solvent-free systems. In this case too, however, care must be taken to ensure that at least parts of the resins, for example the binders, carry reacted polar, optionally ionic groups. If necessary, 2-component coating agents can also be used.

The multi-layer coatings described are particularly suitable for use in automotive painting or in the coating of the automotive supply industry. However, it is also possible to coat other objects accordingly. All substrates customary in the automotive industry are suitable as substrates; these can be, for example, metal substrates, for example steel or aluminum, or plastic substrates, for example polyurethane, polyamide, polycarbonate or polyolefins. You get rockfall-resistant, optically good multi-layer coatings.

<b>Examples:</b>

In the multilayer structures described below, the following coating agents are used in detail:<ul id="ul0001" list-style="none"><li>A) Commercial coating agent for cataphoretic electro-dip coating based on amino epoxy resin and blocked isocyanate hardener, as described in DE-A-27 01 002.</li><li>B) Anionic hydraulic filler (DE-OS 38 05 629, Example 1): Aqueous lacquer based on an amine neutralized polyester with blocked polyisocyanate as hardener.</li><li>C) Anionic water-based basecoat (EP-A-89 497, Example 6): Aqueous coating agent based on anionic polyurethane dispersions in combination with acrylated polyesters.</li><li>D) Cationic water-based basecoat (DE-OS 40 11 633, Example 1): Aqueous coating agent based on amino acrylates, as described below.</li><li>E) Anionic water-clear lacquer (DE-OS 39 10 829, Example 3): Aqueous topcoat based on hydroxy-functional acrylate with neutralized carboxylic acid groups and melamine resin as crosslinking agent.</li><li>F) Anionic conventional 1K clearcoat (commercial product): Conventional clearcoat based on carboxy- and hydroxy-functional acrylate with melamine resin as crosslinker.</li></ul>

Production Example 1 (Amino-poly (meth) acrylate resin)

725 g of butoxyethanol are heated to 110 ° C. under inert gas while a reflux condenser is switched on.

A mixture of 192 g of hydroxyethyl acrylate, 137 g of butanediol monoacrylate, 228 g of glycidyl methacrylate, 364 g of 2-ethylhexyl acrylate, 439 g of butyl methacrylate, 438 g of methyl methacrylate, 90 g of styrene and 44 g of azo-bis-isobutyronitrile is added within 3 hours. The mixture is then held at 110 ° C. for 1 hour, 6 g of azo-bis-isobutyronitrile are added, and this process is repeated after a further hour. After 3 hours at 110 ° C, a solids content of 72.2 wt .-% and after dilution to 60 wt .-% with butoxyethanol, a viscosity of 2.14 Pa.s. measured at 25 ° C. After cooling to 50 ° C., a mixture of 120 g of diethylamine and 201 g of isopropanol is added quickly (1.10 mol of amine to 1.00 mol of epoxy). After 30 minutes, the mixture is warmed to 65 ° C., then held for 2 hours, then heated to 105 to 110 ° C. and then held for 3 hours. After cooling to 80 ° C., isopropanol and excess amine are carefully distilled off under vacuum. Adjust the solids content to about 78% by weight with butoxyethanol.<tables id="tabl0002" num="0002"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><thead valign="top"><row><entry namest="col1" nameend="col2" align="left">Final values:</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Solids content</entry><entry namest="col2" nameend="col2" align="left">78.7% by weight (heating to 150 ° C. for 30 minutes)</entry></row><row><entry namest="col1" nameend="col1" align="left">Amine number</entry><entry namest="col2" nameend="col2" align="left">45 mg KOH per g solid resin</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">viscosity</entry><entry namest="col2" nameend="col2" align="left">3.44 Pa.s (60% by weight in butoxyethanol at 25 ° C)</entry></row></tbody></tgroup></table></tables>

Example D (cationic waterborne basecoat)

555 g of titanium dioxide are added to 945 g of amino poly (meth) acrylate resin according to Preparation Example 1 and dispersed with the dissolver for 5 minutes. The paste is then ground in a bead mill for 40 minutes at temperatures up to 60 ° C.

Solids: 86.6% by weight (after heating for 30 minutes at 150 ° C.) pigment / binder ratio = 0.75: 1.

772 g of the paste together with 111 g of higher molecular weight methoxy imino groups containing melamine resin (80% dissolved in isobutanol) and 17.7 g of an amine-blocked sulfonic acid (25%) as a catalyst are stirred well under the dissolver. The mixture is then further diluted in a dissolver with thorough stirring, first with 7.6 g of formic acid (85% strength) and then slowly with 142 g of deionized water. After standing overnight, 100 g of the paint were adjusted to a spray viscosity of 30 seconds in the outlet cup (DIN 53 211) with 62 g of fully demineralized water.

Production Example 2 (polyester oligomers)

336.7 g of trimethylolpropane, 366.8 adipic acid and 297 g of hexanediol are melted with 5 g of hypophosphorous acid in a 2 liter three-necked flask equipped with stirrer, separator, thermometer and reflux condenser at 180 ° C. to 230 ° C. to an acid number esterified by 20. It is then condensed under vacuum to an acid number &lt;1.5. The product thus obtained has a stoving residue of 94.5% (1 h, 150 ° C.), a viscosity of 3200 mPas (100%), a hydroxyl number of 460 and a color number of 30 Hazen.

Production Example 3 (polyester oligomer polyacrylates)

717 g polyester oligomer from Example 2 are heated with 597 g ethanol in a stirrer, reflux condenser, dropping funnel and thermometer 4 liter three-necked flask from 81 ° C to reflux. A mixture of 552 g of butanediol monoacrylate and 996 g is then tert in 4 hours. Butyl acrylate, 74 g of acrylic acid and 50 g of 2,2-azo-bis-2-methylbutyronitrile were added dropwise and the mixture was subsequently polymerized for 4 hours.

The product had a stoving residue of 79.8% (1 h 150 ° C.) with a viscosity of 7200 mPas (DIN 53 015), an acid number of 26.3, an OH number of 231 and a color number of 60 Hazen.

Production Example 4

717 g of the oligomer from Example 1 are initially charged with 311 g of butoxyethanol in a 4 liter three-necked flask equipped with stirrer, reflux condenser, dropping funnel and thermometer and heated to 140.degree. A mixture of 552 g of butanediol monoacrylate and 946 g is then tert in 4 hours. Butyl acrylate, 74 g acrylic acid and 100 g tert. Butyl perbenzoate added dropwise and polymerized for 4 hours.

The product had a stoving residue of 84.0% (1 h 150 ° C) according to DIN 53 182, a viscosity of 15830 mPas (DIN 53 015), an acid number of 38.0 (DIN 53 402), an OH number of 231 (DIN 53 240) and a color number of 60 Hazen (DIN 53 409).

Example E 1 (anionic water-clear varnish)

651 g of the polyester oligomer polyacrylate 1 described in Example 3, 348 g of a highly amino-functional melamine resin and 152.8 g of ethanol were premixed well under a laboratory stirrer and with further stirring with a mixture of 50.7 g of butoxyethanol, 20.7 g of a UV absorber of the benzotriazole type and 13.7 g of a radical scavenger of the HALS type. The mixture was then neutralized with stirring with 27 g of dimethylethanolamine, stirred for a further 15 minutes and then diluted with a mixture of 973 g of deionized water and 15.4 g of ethanol. The paint had a viscosity of 31 seconds (measured in a DIN 4 cup at 20 ° C) and a pH of 9.0.

Example E 2

639.7 g of the resin solution described in Example 4 were homogeneously mixed with 375.3 g of a commercially available, methoxymethyliminofunctional water-dilutable melamine resin and 90.5 g of butoxyethanol using a high-speed stirrer. Then this resin-solvent mixture was mixed with 37.6 g of dimethylethanolamine and stirred for 15 minutes, a further 37.27 g of a mixture consisting of 59.9% by weight of a UV absorber of the benzotriazole type and 40.1% by weight. % of a radical scavenger of the HALS type added and stirred until clear and streak-free. 534.1 g of completely demineralized water were then added with stirring over the course of 5 minutes. After 24 hours the paint had a viscosity of 50 seconds (DIN 4 cup at 20 ° C) and a pH of 8.6. The paint was stable for more than 3 months.

In order to apply the individual layers of lacquer to the substrate, the lacquers are adjusted to the processing viscosity with deionized water or solvent and applied using standard techniques.

The primer is deposited electrophoretically, the remaining layers are applied using a spray robot. But these can also be used with other application devices, such as. B. gravity cup gun, pressure vessel or with high-speed rotating bells. The layers are then baked as described in Table 1. KTL and filler are baked individually after application, while the base and clear coat are applied wet-on-wet according to the following information:

The basecoat is pre-dried for 6 minutes at 80 ° C and then overcoated with approx. 40 »m water clear lacquer. It is pre-gelled at 80 ° C for 15 minutes and then both layers are baked together at 120 ° C for 20 minutes.<tables id="tabl0003" num="0003"><table frame="all"><title>Table 1</title><tgroup cols="5" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="31.50mm" /><colspec colnum="2" colname="col2" colwidth="31.50mm" /><colspec colnum="3" colname="col3" colwidth="31.50mm" /><colspec colnum="4" colname="col4" colwidth="31.50mm" /><colspec colnum="5" colname="col5" colwidth="31.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="left">KTL</entry><entry namest="col3" nameend="col3" align="center">ink pen</entry><entry namest="col4" nameend="col4" align="center">Basecoat</entry><entry namest="col5" nameend="col5" align="left">Clear coat</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Baking temperature 1)</entry><entry namest="col2" nameend="col2" align="left">30 '180 ° C</entry><entry namest="col3" nameend="col3" align="center">20 ′ 160 ° C</entry><entry namest="col4" nameend="col4" align="left">6 '80 ° C</entry><entry namest="col5" nameend="col5" align="left">20 ′ 120 ° C</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Layer thickness 2)</entry><entry namest="col2" nameend="col2" align="left">20 ⁺ 1</entry><entry namest="col3" nameend="col3" align="center">35 ⁺ 1</entry><entry namest="col4" nameend="col4" align="left">15 ⁺ 1</entry><entry namest="col5" nameend="col5" align="left">40 ⁺ 1</entry></row></tbody></tgroup><tgroup cols="5" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="31.50mm" /><colspec colnum="2" colname="col2" colwidth="31.50mm" /><colspec colnum="3" colname="col3" colwidth="31.50mm" /><colspec colnum="4" colname="col4" colwidth="31.50mm" /><colspec colnum="5" colname="col5" colwidth="31.50mm" /><tbody valign="top"><row><entry namest="col1" nameend="col5" align="justify">1) in minutes and ° C</entry></row><row><entry namest="col1" nameend="col5" align="justify">2) in »m</entry></row></tbody></tgroup></table></tables>

Various multi-layer structures are produced with the coating agents A to F described above. The structures are listed in Table 2. Examples 3 and 4 are according to the invention.

The technological tests specify the cross-cut (2 mm) according to DIN 53151 and the mechanical stress test with the VDA stone chip tester (1 bar, 1000 g) according to DIN 53230 to characterize the liability. The rating scale ranges from 1 to 6, with 1 characterizing a very good and 6 a very bad adhesive bandage. To describe the headlock stress, ie Evaluation of swelling and regenerability, storage according to DIN 50017 is carried out in a constant climate (240 h, 40 ° C).<tables id="tabl0004" num="0004"><img file="EP0537726B1_D0001.tif" /></tables>