WO1998007527A1

WO1998007527A1 - Process for applying a multilayered coat of lacquer

Info

Publication number: WO1998007527A1
Application number: PCT/EP1997/004462
Authority: WO
Inventors: Joachim Blum; Dieter Engel; Klausjörg Klein; Walter KÜHHIRT; Bettina Vogt-Birnbrich
Original assignee: Herberts Gesellschaft mit beschränkter Haftung
Priority date: 1996-08-17
Filing date: 1997-08-14
Publication date: 1998-02-26
Also published as: DE59707118D1; ES2176773T3; EP0951365A1; DE19633173C1; EP0951365B1; ATE216638T1

Abstract

In a process for applying a multilayered coat of lacquer, a priming layer, a base lacquer layer and one or more clear lacquer coatings are applied on a metallic surface that can be autophoretically coated. An intermediate layer can be applied between the priming layer and the base lacquer layer. The priming layer is applied as a first coating layer made of a coating agent that can be autophoretically deposited and is then baked, and the other coating layers are then applied, so that the total dry layer thickness of the multilayered coat of lacquer lies between 80 and 130 νm and the total dry layer thickness of the clear lacquer layers lies between 40 and 80 νm.

Description

Process for multi-layer painting

The invention relates to a method for producing a multilayer coating of substrates having an autophoretically coatable metallic surface.

Today's high-quality automotive OEM coatings are generally produced by electrophoretic deposition of a primer that protects against corrosion on a body-in-white usually provided with a conversion layer, and subsequent spray application of subsequent layers consisting of a filler layer and a subsequently applied decorative coating of paint and / or effect-imparting basecoat and a protective clearcoat that seals the surface. The conversion layer on the uncoated body-in-white is produced by considerable chemical pretreatment, generally consisting of phosphating and passivation.

The total layer thickness of such automotive coatings is in practice between 90 and 130 μm, which is the sum of 15 to 25 μm layer thickness for the primer, 30 to 40 μm for the filler layer, 10 to 25 μm for the basecoat layer and 30 to 40 μm for the Clear coat results. However, it has hitherto been necessary to exceed these layer thicknesses considerably if coatings with a particularly good visual appearance, ie with an outstanding gloss and topcoat level, are to be achieved, for example, when painting motor vehicles of the luxury and luxury classes. DE-A-42 15 070 and DE-A-38 39 905, for example, describe the application of several layers of clear lacquer to one basecoat layer. This then results in layer thicknesses of over 110 μm, for example up to 170 μm, which is undesirable on the finished vehicle for reasons of material savings and weight savings. DE-B-22 27 289 discloses a method in which a two-layer coating is produced by electrophoretic deposition of a coating layer on an electrically conductive coating layer previously autophoretically deposited on iron- and / or zinc-containing metal surfaces. The autophoretically depositable coating agent (autophoresis lacquer) contains electrically conductive material, in particular 10 to 100 g of electrically conductive carbon per liter of the coating agent.

The object of the invention is to provide multi-layer coatings, in particular motor vehicle coatings, which meet the requirements of an outstanding gloss and topcoat level, without exceeding the normal level of the total layer thicknesses of motor vehicle coatings, and without having to accept disadvantages in the overall property level.

It has been shown that this object can surprisingly be achieved by a method for multi-layer coating by applying a primer layer, a basecoat layer and one or more clear lacquer layers to a substrate which has an autophoretically coatable metallic surface, with the application of the primer layer and the application an intermediate layer can be applied to the basecoat layer, which is characterized in that the primer layer is applied as the first coating layer from an autophoretically depositable coating agent by autophoretic deposition and then baked, whereupon the further coating layers are applied, so that the total dry layer thickness of the multi-layer coating is 80-130 μm and the total dry layer thickness of the clear lacquer layers is 40 - 80 μm.

It is particularly advantageous if the first coating layer is created from an autophoretically depositable coating agent which leads to a coating layer which is electrically conductive when baked. The immediately following layer can then preferably be applied to such a first coating layer by electrophoretic deposition of an electrophoretically depositable aqueous coating agent

.SEASER LEAF (RULE 26) are applied, which preferably leads to an electrically insulating second coating layer. An intermediate layer can be formed and baked as the second coating layer, whereupon a basecoat layer composed of a coloring and / or effect-imparting coating agent is applied as the third coating layer and is overcoated with one or more clear lacquer coating agents.

According to a particularly preferred embodiment of the invention, a basecoat layer is formed as a second coating layer from an electrophoretically depositable aqueous coating agent by electrophoretic deposition and is overcoated with one or more clearcoat layers.

When working with an intermediate layer as the second coating layer, work is preferably carried out in such a way that the total dry layer thickness of the lacquer structure is 90-130 μm, particularly preferably less than 110 μm.

If a basecoat film is formed as the second, electrophoretically deposited coating layer, the total dry film thickness of the paint structure is preferably 80-110 μm.

In summary, there are two preferred embodiments for the invention:

A first lies in a process for producing a multi-layer coating on a substrate having an autophoretically coatable, metallic surface, in which a first coating layer is autophoretically deposited from an autophoretically depositable coating agent and then baked, whereupon further coating layers are applied, which is characterized in that one uses an autophoretically depositable coating agent which leads to a coating layer which is electrically conductive in the baked state, whereupon after baking the first coating layer, an electrically insulating second coating layer is electrophoretically deposited and baked from an electrophoretically separable aqueous coating agent, whereupon as third coating layer, a basecoat layer of a coloring and / or effect-imparting coating agent is applied, which is overpainted with a four, transparent coating layer of a clear lacquer coating agent and baked together therewith, whereupon one or more further transparent coating layers are applied, the total dry layer thickness of the paint structure is between 90 and 130 μm, preferably less than 110 μm, and the dry layer thickness of the transparent coating layer or the total layer thickness of the transparent coating layers is between 40 and 80 μm, preferably between 40 and 60 μm. The clear lacquer layer can consist of one or more layers, the first clear lacquer layer preferably being stoved before application of the further clear lacquer layers. If several layers of clear lacquer are applied, they can be created from the same or different clear lacquer coating agents.

A second particularly preferred embodiment of the invention consists in a process for producing a multi-layer coating on a substrate having an autophoretically coatable, metallic surface, in which a primer is applied autophoretically from an autophoretically depositable aqueous coating agent and then baked, whereupon a color and / or effect basecoat is applied from an aqueous coating agent and baked, and this is then provided without the application of intermediate layers with one or more clearcoat coatings, which is characterized in that an autophoretically depositable coating agent is used which leads to an electrically conductive primer layer in the baked state , the basecoat is formed from an electrophoretically depositable aqueous coating agent by electrophoretic deposition, the total dry film thickness of the clear lacquer layer or clear lacquer layers between 40 and 80 microns, preferably between 40 and 60 microns and the total dry layer thickness of the multi-layer coating is 80 to 110 microns. The clear lacquer layer can consist of one or more layers, the first clear lacquer layer preferably being stoved before application of the further clear lacquer layers. If several layers of clear lacquer are applied, they can can be created from the same or different clear lacquer coating agents.

Surprisingly, the multi-layer coatings obtained by the process according to the invention have an adhesion between the first, autophoretically deposited coating layer and the second, electrophoretically deposited coating layer which meets the high requirements of automotive series coating.

In the process according to the invention, autophoretically depositable coating agents which are known per se can be used as the autophoretically depositable coating agents for producing the first coating layer, the autophoretically depositable coating agent preferably containing constituents which, in the baked state, the first coating layer contains one for the electrophoretic deposition of a further coating layer from an electrophoretic impart a sufficiently low resistivity to depositable coating agents.

The autophoretically depositable coating agents are coating agents based on aqueous binder dispersions with a negative surface charge on the binder particles. Due to their generally acidic pH of, for example, between 1 and 6, preferably between 1.5 and 5.0, and their generally oxidizing character, autophoresis lacquers are capable of attacking sufficiently base metal surfaces with the release of corresponding metal ions. If a metal ion concentration is reached in the area of the metal surface that is sufficient to destabilize and coagulate the binder particles dispersed in the water phase, a coating film is deposited on the metal surface.

The autophoretically depositable coating agents which can be used in the process according to the invention generally have a low solids content of, for example, up to 20% by weight, the lower limit generally being, for example, 5% by weight and the upper limit being, for example, 10% by weight. They contain alongside autophoretically separable film-forming binder, water, acid and, if appropriate, electrically conductive constituents as a rule also oxidizing agents and, if appropriate, crosslinking agents for the binders, fillers, pigments and customary paint additives.

The autophoretically depositable coating compositions which can be used according to the invention for the production of the first coating layer can be physically drying or can be crosslinked with the formation of covalent bonds. The autophoresis lacquers which crosslink with the formation of covalent bonds can be self- or externally crosslinking systems.

The autophoresis lacquers which can be used in the process according to the invention for the production of the first coating layer contain one or more film-forming binders which have neutral or anionic groups per se. In particular, if the binders are not self-crosslinking or physically drying (thermoplastic), they may also contain crosslinking agents. Binder and any crosslinker present are in the form of an aqueous dispersion with a negative surface charge on the particles. The negative surface charge stabilizes the dispersed particles in the aqueous phase. The negative surface charge can originate, for example, from anionic groups in the binder and / or, in particular in the case of neutral binders, from anionic emulsifier for the binder and the crosslinking agent. Examples of anionic groups in the binder are anionic groups of the binder itself, for example carboxyl groups or sulfonate groups, and / or anionic residues from the production of binders, for example from the production of a binder which is neutral per se. Examples of anionic residues from binder production are sulfate groups as residues contained in the binder from radical polymerization initiated by peroxodisulfate. Both the binder component and the crosslinker component are not subject to any restrictions per se; it is possible to use resins which are customary in lacquer and are familiar to the skilled worker. For example, polyester, polyurethane, epoxy and / or polymer resins can be used as film-forming binders. Polymer resins, ie by radical polymerization, in particular Binders produced by emulsion polymerization or seed polymerization are particularly preferred in the process according to the invention. Particular preference is given to conventional aqueous, thermoplastic polymer dispersions (latices) which contain homo- or copolymers of olefinically unsaturated monomers with glass transition temperatures, for example between 0 and 100 ° C., as the disperse phase. Examples of suitable olefinically unsaturated monomers for building up such homopolymers and copolymers are (meth) acrylic esters, such as methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth ) acrylate, ethylhexyl (meth) acrylate; Glycidyl esters of unsaturated carboxylic acids, such as glycidyl (meth) acrylate; (Meth) acrylamide, (meth) acrylonitrile, monomers containing anionic groups, such as alkali metal, for example sodium 2-sulfoethyl methacrylate, (meth) acrylic acid; but also monomers without other functional groups or with other functional groups, such as ethylene, styrene, vinyl chloride, vinylidene chloride, vinyl acetate, butadiene. Examples of aqueous polymer dispersions suitable in the context of the invention are styrene / butadiene, butadiene / acrylonitrile, vinyl chloride, ethylene / vinyl acetate and vinylidene chloride copolymer dispersions, the latter being particularly preferred.

The selection of the crosslinking agents that may be present depends on the functionality of the binder, i.e. the crosslinkers are selected from conventional crosslinkers known to those skilled in the art so that they have a reactive functionality which is complementary to the functionality of the binders. Examples of such complementary functionalities between binder and crosslinker are: hydroxyl / methylol ether, hydroxyl / blocked isocyanate. If compatible with one another, several such complementary functionalities can also be present side by side in an autophoresis varnish. The crosslinking agents which may be used in the autophoresis lacquers can be present individually or in a mixture.

The autophoretically depositable coating agents contain one or more free acids in an amount to adjust the above-mentioned pH range and preferably also one or more oxidizing agents. Examples of preferred acids are inorganic acids, such as hydrochloric acid, phosphoric acid, sulfuric acid, δ

Nitric acid, and organic acids such as formic acid, acetic acid. Hydrofluoric acid is particularly preferred. Examples of preferred oxidizing agents are chromate, dichromate, bromate, chlorate, perchlorate, permanganate, persulfate, peroxodisulfate. Hydrogen peroxide is particularly preferred.

A particularly preferred combination of acid and oxidizing agent is the combination of hydrofluoric acid / hydrogen peroxide.

The autophoretically depositable coating compositions which can be used in the process according to the invention preferably contain constituents which impart electrical conductivity. They should provide the first coating layer in the baked state with a resistivity which is sufficiently low for the electrophoretic deposition of a further coating layer from the electrophoretically depositable coating agent, generally below 10 ⁸ ohms. cm, for example between 10 ³ and 10 ⁸ ohms. give cm. Examples of such constituents are particulate inorganic or organic electrical conductors or semiconductors as are customary for this purpose and are familiar to the person skilled in the art, for example iron oxide black, graphite, carbon black, metal powder, for example made of copper or stainless steel, molybdenum disulfide. The electrical conductivity-imparting constituents are contained in the autophoretically depositable coating agent in such an amount that the desired specific resistance of the coating layer deposited therefrom is achieved in the baked state. Based on the solids content of the autophoretically deposited coating agent, the proportion of the constituent or components imparting electrical conductivity is, for example, between 1 and 30% by weight. The proportion can easily be determined by a specialist; it depends, for example, on the specific weight, the specific electrical conductivity and the particle size of the components imparting electrical conductivity. One or more of these components can be present in combination.

The autophoretically depositable coating compositions which can be used in the process according to the invention preferably contain pigments and / or fillers. Coming as pigments for example, conventional, inorganic or organic, in particular acid-resistant, pigments and / or fillers. Examples are carbon black, titanium dioxide, iron oxide pigments, kaolin, talc or silicon dioxide, but also anti-corrosion pigments.

Pigments, fillers and the components which impart electrical conductivity to the baked-in autophoresis lacquer can be used, for example, as pigment suspensions (pigment slurries) or pigment grinds in water and / or organic, water-miscible solvents, such as glycols, for example ethylene glycol, propylene glycol; Alcohols, for example sec-butanol and hexanol; Glycol ethers, for example ethoxypropanol, methoxypropanol and butoxyethanol, can be used in the formulation of the autophoretically depositable coating agent which can be used according to the invention. Pigment grinds of this type are also commercially available and are marketed, for example, by HOECHST under the name Colanyl ^R. For example, aqueous non-ionically stabilized pigment dispersions can be mixed with anionically stabilized resin dispersions to produce pigment concentrates suitable for pigmenting autophoresis lacquers.

The autophoretically depositable coating compositions which can be replaced in the process according to the invention can furthermore contain customary additives. Examples of these are customary paint additives, such as wetting agents, anionic and / or non-ionic emulsifiers, protective colloids, flow control agents, corrosion inhibitors, plasticizers, anti-foaming agents, solvents, for example as film-forming aids, light stabilizers, fluorides, in particular, for example, iron trifluoride, hydrogen fluoride, complex fluorine anions, for example tetraconafluoroboroboronate , Hexafluorotitanates. Protective colloids and / or emulsifiers in particular are preferably only present in the smallest possible amount, for example below the critical micelle concentration, and preferably originate from the binder dispersions used in the formulation of the autophoretically separable coating agents. For example, protective colloids and / or emulsifiers are used in the production of the binder dispersions. To produce the second coating layer, for example and preferably electrophoretically depositable coating agents can be used in the method according to the invention. The anodically or cathodically depositable electrocoat materials (ETL) known per se are suitable for this.

The coating compositions are aqueous coating compositions with a solids content of up to 50% by weight, for example up to 20% by weight, the lower limit being, for example, 10% by weight. The solid is formed from binders customary for electrocoating, at least some of the binders bearing ionic and / or substituents which can be converted into ionic groups and, if appropriate, groups capable of chemical crosslinking, as well as any crosslinking agents, fillers, pigments and additives customary in lacquers.

The ionic groups or groups of the binders which can be converted into ionic groups can be anionic or groups which can be converted into anionic groups, acidic groups such as -COOH, -SO ₃ H and / or -PO ₃ H ₂ and the corresponding anionic groups neutralized with bases. They can also be cationic or convertible into cationic groups, for example basic groups, preferably nitrogen-containing basic groups; these groups can be present in quaternized form or they are converted into ionic groups using a conventional neutralizing agent, for example an organic monocarboxylic acid, such as, for example, formic acid or acetic acid. Examples are amino, ammonium, for example quaternary ammonium, phosphonium and / or sulfonium groups.

In the process according to the invention, for example, the customary cathodic electrocoat materials (KTL) based on cationic or basic binders can be used to produce the second coating layer. Such basic resins are, for example, primary, secondary and / or tertiary amino-containing resins whose amine numbers are, for example, 20 to 250 mg KOH / g. The weight average molecular weight (Mw) of the base resins is preferably from 300 to 10,000. Examples of such base resins are amino (meth) acrylate resins, aminoepoxy resins, 1 ! Amino epoxy resins with terminal double bonds, amino epoxy resins with primary OH groups, amino polyurethane resins, amino group-containing polybutadiene resins or modified epoxy resin-carbon dioxide-amine reaction products. These base resins can be self-crosslinking or they are used in a mixture with known crosslinking agents. Examples of such crosslinkers are aminoplast resins, blocked polyisocyanates, crosslinkers with terminal double bonds, polyepoxide compounds or crosslinkers which contain groups capable of transesterification.

The usual anionic group-containing anodically depositable electrocoat binders and paints (ATL) can also be used in the process according to the invention to produce the second coating layer. These are, for example, binders based on polyesters, epoxy resin esters, (meth) acrylic copolymer resins, maleate oils or polybutadiene oils with a weight average molecular weight (Mw) of, for example, 300 to 10,000 and an acid number of 35 to 300 mg KOH / g. The binders carry -COOH, -SO ₃ H and / or -PO ₃ H ₂ groups. After neutralization of at least some of the acidic groups, the resins can be converted into the water phase. The binders can be self-crosslinking or externally crosslinking. The lacquers can therefore also contain customary crosslinking agents, for example triazine resins, crosslinking agents which contain groups capable of transesterification or blocked polyisocyanates.

In the process according to the invention, it is preferred to use an ATL coating agent as the ETL coating agent, in particular when implementing the special and independent embodiment of the present invention in which the basecoat is deposited electrophoretically.

In addition to the base resins and any crosslinking agents present, the ETL coating compositions can contain pigments, fillers and / or additives customary in lacquers. Suitable pigments are, for example, the customary inorganic and / or organic colored pigments and / or effect pigments and / or fillers. Pigments include, for example, the customary inorganic and / or organic colored pigments and / or effect pigments, such as titanium dioxide, iron oxide pigments, Carbon black, phthalocyanine pigments, quinacridone pigments, metal pigments, for example made of titanium, aluminum or copper, interference pigments, such as, for example, titanium dioxide-coated aluminum, coated mica, graphite effect pigments, platelet-shaped iron oxide, platelet-shaped copper phthalocyanine pigments in question. Examples of fillers are kaolin, talc or silicon dioxide.

The pigments can be dispersed into pigment pastes, e.g. using known paste resins. In the case of the ATL coating compositions in particular, it is possible to use pigment pastes such as are used in the water-based lacquers known to those skilled in the art for producing two-layer lacquers of the basecoat / clearcoat type. Such pigment pastes can be obtained by rubbing the pigments in a special water-thinnable paste resin.

The usual additives, as are known in particular for ETL coating agents, are possible as additives. Examples of these are wetting agents, neutralizing agents, leveling agents, catalysts, corrosion inhibitors, antifoams, solvents, but in particular light stabilizers, if appropriate in combination with antioxidants.

In the process according to the invention, known coloring and / or effect basecoat coating compositions, such as are used for the production of basecoat / clearcoat two-coat coatings and which are known in large numbers, for example, from the patent literature, can be used to produce the third coating layer.

The basecoats which can be used according to the invention for the production of the third coating layer can be physically drying or can be crosslinked to form covalent bonds. The basecoats which crosslink with the formation of covalent bonds can be self- or externally crosslinking systems. The color and / or effect basecoats which can be used in the process according to the invention are liquid coating compositions. It can be a one- or multi-component coating agent, single-component are preferred. They can be systems based on organic solvents, or they are preferably waterborne basecoats whose binder systems are stabilized in a suitable manner, for example anionically, cationically or nonionically.

The basecoat materials which can be used in the process according to the invention for the production of the third coating layer are customary paint systems which contain one or more customary base resins as film-forming binders. If the base resins are not self-crosslinking or self-drying, they can optionally also contain crosslinking agents. Both the base resin component and the crosslinker component are not subject to any limitation. For example, polyester, polyurethane and / or (meth) acrylic copolymer resins can be used as film-forming (base resins). In the case of the preferred waterborne basecoats, polyurethane resins are preferably present, particularly preferably at least in a proportion of 15% by weight, based on the solid resin content of the waterborne basecoat. The selection of the crosslinking agents that may be present is not critical; it depends on the functionality of the base resins, i.e. the crosslinkers are selected so that they have a reactive functionality which is complementary to the functionality of the base resins. Examples of such complementary functionalities between base resin and crosslinker are: hydroxyl / methylol ether, hydroxyl / free isocyanate, hydroxyl / blocked isocyanate, carboxyl / epoxide. If compatible with one another, several such complementary functionalities can also be present side by side in a basecoat. The crosslinking agents optionally used in the basecoats can be present individually or in a mixture.

The basecoats used in the process according to the invention contain, in addition to the usual physically drying and / or chemically crosslinking binders, inorganic and / or organic colored pigments and / or effect pigments, such as, for example, titanium dioxide, iron oxide pigments, carbon black, azo pigments, phthalocyanine pigments, quinacridone pigments, and metal pigments, for example from aluminum pigments or copper, »F

Interference pigments, e.g. Titanium dioxide coated aluminum, coated mica, graphite effect pigments, platelet-shaped iron oxide, platelet-shaped copper phthalocyanine pigments.

The basecoats may also contain customary paint additives, e.g. Fillers, catalysts, leveling agents, anti-cratering agents or in particular light stabilizers, if appropriate in combination with antioxidants.

It is preferred if the electrocoating lacquer used to produce the second coating layer has a color tone which is close to or identical to that of the basecoat used to produce the third coating layer. In the context of the present invention, it is preferable to understand the closest color shades in the context of the present invention that the color difference, composed of the difference in brightness, hue and difference in color, between the shades of the second and third coating layers determined in each case with opaque coating and a measurement geometry of (45/0) -fold ΔE * (CIELAB) value does not exceed, the ΔE * (CIELAB) reference value being that which is found in the CIE-x, y diagram (chromaticity diagram) familiar to the person skilled in the art, based on DIN 6175, for the hue of third coating layer and the following relationship applies:

n <90 in the area of the CIE-x, y diagram marked with ΔE * = 0.3, n <50 in the area of the CIE-x, y diagram marked with ΔE * = 0.5, n <40 in the area with ΔE * = 0.7 marked area of the CIE-x, diagram, n <30 in the area of the CIE-x, y diagram marked with ΔE * = 0.9,

Basically all conventional clearcoats or transparent colored or colorless pigmented coating agents are suitable as clearcoat coating agents for the production of the fourth and optionally further coating layers or, in the case of the special and independent embodiment of the present invention, for the production of the third and optionally further coating layers. These can be single-component or multi-component clear lacquer coating compositions. They can be solvent-free (liquid or as a powder clearcoat), or it can be systems based on solvents or it is water-dilutable clearcoats, the binder systems of which are stabilized in a suitable manner, for example anionically, cationically or non-ionically. The water-dilutable clear lacquer systems can be water-soluble or water-dispersed systems, for example emulsion systems or powder slurry systems. The clear lacquer coating agents harden when stoved to form covalent bonds as a result of chemical crosslinking.

The clearcoats which can be used in the process according to the invention are customary clearcoat coating compositions which contain one or more customary base resins as film-forming binders. If the base resins are not self-crosslinking, they may also contain crosslinking agents. Both the base resin component and the crosslinker component are not subject to any limitation. Polyester, polyurethane and / or (meth) acrylic copolymer resins, for example, can be used as film-forming binders (base resins). The selection of the crosslinking agents that may be present is not critical; it depends on the functionality of the base resins, i.e. the crosslinkers are selected so that they have a reactive functionality which is complementary to the functionality of the base resins. Examples of such complementary functionalities between base resin and crosslinker are: carboxyl / epoxide, hydroxyl / methylol ether, hydroxyl / free isocyanate, hydroxyl / blocked isocyanate, (meth) acrylolyl / CH-acidic group. If compatible with one another, several such complementary functionalities can also be present side by side in a clear lacquer. The crosslinking agents optionally used in the clear lacquers can be present individually or in a mixture.

In addition to the chemically crosslinking binders and, if appropriate, crosslinking agents, the clear lacquers which can be used in the process according to the invention can contain conventional lacquer additives, such as, for example, catalysts, leveling agents, dyes, but in particular rheology control agents such as microgels, NAD (= non-aqueous dispersions), disubstituted ureas ("sagging control agents") ") and light stabilizers optionally in combination with antioxidants. l fe »

The transparent coating can be applied in a single layer or in the form of several layers from the same or from several different transparent coating agents. However, the transparent coating layer is expediently applied as a fourth layer or, in the case of the special and independent embodiment of the present invention, as a third layer composed of only one clear lacquer coating agent. Clearcoat compositions which have the lowest possible drainage tendency are preferably used, for example solid-bodied clearcoats with a correspondingly set theological behavior. Powder clearcoats are particularly preferred.

As the substrates for the process according to the invention, autophoretically coatable body shells with a metallic surface are preferred. These can be made from a single metal or can be constructed in a mixed construction from several metallic materials and / or from plastic parts provided with a corresponding metal layer. Suitable metallic surfaces of autophoresis lacquer systems, in particular at an acidic pH of, for example, between 1 and 6, are metal metal surfaces which can be attacked by the release of metal ions and which are familiar to the person skilled in the art, for example made of iron, zinc, aluminum or corresponding alloys, but also, for example, galvanized steel surfaces. The metal surfaces can be pretreated, for example provided with phosphating and optionally passivation. However, this is not necessary from the point of view of corrosion protection and thus represents a further advantage of the method according to the invention. It should be pointed out that the term "body shells" used in the present invention includes in particular motor vehicle body shells but also, for example, their components and motor vehicle chassis containing visible surfaces.

The first coating layer of the autophoretically depositable coating agent is deposited autophoretically onto these substrates in a customary manner, preferably in the immersion process, preferably in a dry layer thickness of, for example, 5 to 25 μm, particularly preferably 10 to 20 μm. Before the next one Coating with the electrophoretically depositable coating agent, the autophoretically deposited coating layer can be aftertreated, for example rinsed, with water and / or optionally with special solutions before baking. (In connection with the application of the autophoretically depositable coating agent, the term “stoving”, depending on the type of the autophoresis lacquer system, can mean stoving with chemical crosslinking of the autophoresis coating layer or a purely physical drying at elevated temperature, for example with melting or sintering and formation of a closed autophoresis lacquer coating) . After stoving in the autophoresis lacquer system used, temperatures adapted between 80 and 190 ° C., for example preferably between 100 ° C. and 160 ° C., are obtained with a specific resistance of less than 10 ⁸ ohms. cm, especially 10 ³ to 10 ⁸ ohms. cm-provided coating layer provided substrate, the second coating layer of an electrophoretically depositable coating agent, preferably in a dry layer thickness of, for example, 5 to 45 microns, particularly preferably between 10 to 30 microns, and baked at elevated temperatures, for example between 130 and 180 ° C. The second coating layer generally has practically no electrical conductivity, ie it has a specific resistance of generally more than 10 ⁹ ohms when baked. cm and it is, in particular in the case of the special and independent embodiment of the present invention, a coloring and / or effect-imparting coating layer, namely a basecoat layer.

The autophoretically deposited, first coating layer serves in particular to protect against chemical and corrosive attack, so that it is preferred to coat the entire surface of the substrate.

The coating obtained by electrodeposition coating and which is electrically insulating in the baked state can, but does not have to extend over the entire surface of the three-dimensional substrate, for example. For example, in the method according to the invention it is preferred (in particular in the special and independent embodiment of the present invention) to use a full-area first Coating by means of autophoretic deposition from the autophoresis lacquer and a second coating from the ETL coating agent essentially only to be carried out on outer areas, in particular on visible surfaces of a three-dimensional substrate, ie for example not in narrow cavities in a body.

This is followed by application, for example spray application, of the third coating layer, for example from a color and / or effect base lacquer or, in the case of the particular and independent embodiment of the present invention, from a clear lacquer coating agent.

A spray application of the third coating layer from the color and / or effect basecoat is carried out in a dry layer thickness of 10 to 25 μm, depending on the color, for example by compressed air spraying, airless spraying or ESTA high-speed rotary spraying.

Following the application of a third color and / or effect coating layer, after a short flash-off phase, e.g. at 20 to 80 ° C, the application of the clearcoat, preferably in the wet-on-wet process. The fourth coating layer is applied from a customary liquid lacquer or powder clear lacquer (in this case it is a dry-on-wet application) and baked together with the third coating layer at elevated temperatures, for example from 80 to 160 ° C. If necessary, further layers of clear lacquer from the same or different clear lacquer coating compositions can be applied. The invention works in such a way that the layer thickness of the transparent coating layer or the total layer thickness of the transparent coating layers is between 40 and 80 μm, preferably between 40 and 60 μm.

It is also possible, if not preferred, to apply the coloring and / or effect basecoat layer by wet-on-wet method to the non-baked second coating layer and to bake the two coating layers together before applying the transparent coating layer or layers. /1

In the case of the special and independent embodiment of the method according to the invention, the clear lacquer is applied to the second, baked, color and / or effect-giving ETL coating layer. The clear lacquer coating layer is applied from a customary liquid or powder clear lacquer and baked, for example, at temperatures from 80 to 160 ° C. If necessary, further layers of clear lacquer from the same or different clear lacquer coating compositions can be applied. According to the invention, work is preferably carried out in such a way that the layer thickness of the transparent coating layer or the total layer thickness of a plurality of transparent coating layers is between 40 and 80 μm, particularly preferably between 40 and 60 μm.

Good results can also be obtained if, instead of the basecoat / clearcoat structure, a coating layer consisting of a pigmented powder topcoat in a layer thickness of 40 to 90 μm, preferably 50 to 80 μm, is used on the two-layer structure created from the autophoretically depositable and from the electrophoretically depositable coating agent is applied and baked, whereby the application can follow one or more layers of clear lacquer. The powder topcoat can be based on a powder clearcoat binder / crosslinking system known per se, as already described above in connection with the powder clearcoats, for example. The powder topcoat contains coloring and / or effect pigments, such as those described above for the basecoats.

The method according to the invention allows the production of multi-layer coatings, in particular automotive coatings with an overall level of properties comparable to that of the prior art and an improved gloss and topcoat level. It has been shown that excellent properties are achieved by the procedure according to the invention, although this makes it possible to dispense with conventional spray filler layers. Despite the high layer thickness when applying the clear lacquer, the total layer thicknesses of the multi-layer lacquer rods produced by the process according to the invention are very small. They are in particular 90 to 130 μm or in the case of the special and independent embodiment of the method according to the invention at 80 to 110 microns and fall below the range of conventional automotive paintwork with a comparably high clear coat thickness.

Claims

claims

1. A method for multi-layer coating by applying a primer layer, a basecoat layer and one or more clear lacquer layers on a substrate which has an autophoretically coatable metallic surface, wherein an intermediate layer can be applied between the application of the primer layer and the application of the basecoat layer, characterized in that the primer layer is applied as the first coating layer from an autophoretically depositable coating agent by autophoretic deposition and then baked, whereupon the further coating layers are applied, so that the total dry layer thickness of the multi-layer coating is 80-130 μm and the total dry layer thickness of the clear lacquer layers is 40-80 μm.

2. The method according to claim 1, characterized in that the first coating layer is created from an autophoretically depositable coating agent, which leads to an electrically conductive coating layer in the baked state.

3. The method according to claim 2, characterized in that the layer immediately following the first coating layer is applied by electrophoretic deposition of an electrophoretically depositable aqueous coating agent, which leads to an electrically insulating second coating layer.

4. The method according to claim 3, characterized in that an intermediate layer is formed and baked as a second coating layer, whereupon as a third coating layer a basecoat layer of a coloring and / or effect coating agent is applied, which is overpainted with one or more clear lacquer coating agents.

5. The method according to claim 3, characterized in that a basecoat layer is formed as a second coating layer from an electrophoretically depositable aqueous coating agent by electrophoretic deposition, which is coated with one or more clear lacquer layers.

6. The method according to claim 4, characterized in that the procedure is such that the total dry layer thickness of the lacquer structure is 90-130 μm.

7. The method according spoke 5, characterized in that it is carried out so that the total dry layer thickness of the lacquer structure is 80-110 microns.

8. The method according to any one of the preceding claims, characterized in that the first coating layer is created in a dry layer thickness of 5 - 25 microns.

9. The method according to any one of the preceding claims, characterized in that it is carried out for painting motor vehicles or motor vehicle parts.

REPLACEMENT BUTT (RULE 26)