EP3863773A1 - Method for producing a multi-layer lacquer finish via the post-additivation of an aqueous dispersion, containing polyamides and/or amide waxes, to at least one base lacquer - Google Patents

Abstract

The invention relates to a method for producing a multi-layer lacquer finish in which a base lacquer layer or multiple directly consecutive base lacquer layers are produced directly on a substrate coated with a first layer, a clear lacquer layer is produced directly on the one base lacquer layer or the uppermost of the multiple base lacquer layers, and then the one or the multiple base lacquer layers and the clear lacquer layer are cured together. Either an aqueous dispersion (D1) containing a polyamide (PA) with an acid number from 5 to 60 mg KOH/g, or an aqueous dispersion (D2) containing a polyamide (PA) and an amide wax (AW) is added to at least one of the base lacquers directly before application.

Description

 Process for producing a multi-layer coating by post-additivation of at least one basecoat with an aqueous dispersion containing polyamides and / or amide waxes

The present invention relates to a method for producing a multi-layer coating in which a basecoat layer or a plurality of successively basecoat layers are produced directly on a substrate coated with a first layer, a clearcoat layer is produced directly on one or the top of the plurality of basecoat layers, and then the one or the several basecoat layers and the clearcoat layer are cured together. At least one of the basecoats is either an aqueous dispersion (D1) containing a polyamide (PA) with an acid number of 15 to 60 mg KOH / g, or an aqueous dispersion (D2) containing a polyamide (PA) and an amide wax (AW) added.

State of the art

 Multi-layer coatings on substrates, for example multi-layer coatings in the automotive industry, are known. As a rule, such multi-layer coatings, viewed from the substrate, comprise a first layer, in particular an electrocoat layer, a layer applied directly to the electrocoat layer, usually referred to as a filler layer, at least one layer containing color and / or effect pigments and generally referred to as a basecoat layer as well as a clear coat.

The basic compositions and functions of the layers mentioned and of the coating compositions necessary for building up these layers, that is to say electrodeposition lacquers, so-called fillers, coating compositions and clear lacquers known as basecoats and known as base lacquers are known. For example, the electrophoretically applied electrodeposition coating basically serves to protect the substrate against corrosion. The filler layer mainly serves to protect against mechanical stress such as stone chipping and also to fill in unevenness in the substrate. The next layer, called the basecoat, is primarily responsible for creating aesthetic properties like color and / or effects like the flop, while the clear coat that follows then serves in particular the scratch resistance and the gloss of the multi-coat paint.

In the prior art, these multi-layer lacquers are produced in such a way that a first layer, in particular a cathodic electrocoating lacquer, is first applied or deposited electrophoretically on the substrate, for example an automobile body. The substrate can be pretreated differently before the deposition of the electrocoat material, for example known conversion coatings such as phosphate layers, in particular zinc phosphate layers, can be applied. The deposition process of the electrocoat usually takes place in the corresponding electrocoat. After the application, the coated substrate is removed from the basin, optionally rinsed and vented and / or dried, and finally the applied electrocoating material is cured. Layer thicknesses of about 15 to 25 micrometers are aimed for. Subsequently, the so-called filler is applied directly to the hardened electrocoat layer, if appropriate flashed off and / or intermediate dried and then hardened. So that the hardened filler layer can fulfill the above-mentioned tasks, layer thicknesses of, for example, 25 to 45 micrometers are aimed for. A basecoat containing so-called coloring and / or effect pigments is then applied directly to the hardened filler layer, this is optionally flashed off and / or intermediate dried, and a clearcoat is applied directly to the basecoat layer thus produced without separate curing. Subsequently, the basecoat film and the clear coat, which may also have been previously vented and / or dried, are cured together (wet-on-wet process). While the hardened basecoat layer generally has comparatively small layer thicknesses of, for example, 10 to 20 micrometers, layer thicknesses of, for example, 30 to 60 micrometers are sought for the hardened clear lacquer layer in order to achieve the application technology properties described. The filler, basecoat and clearcoat can be applied, for example, using the pneumatic and / or electrostatic spray application methods known to those skilled in the art. Filler and basecoat are now increasingly used as aqueous coating materials for ecological reasons. Multilayer coatings of this type and processes for their production are described, for example, in DE 199 48 004 A1, page 17, line 37, to page 19, line 22, or also in DE 100 43 405 C1, column 3, paragraph [0018], and column 8, Paragraph [0052] to column 9, paragraph [0057], described in connection with column 6, paragraph [0039] to column 8, paragraph [0050].

Even if the multi-layer coatings produced in this way can generally meet the requirements placed on the application technology properties and aesthetic profile by the automotive industry, the simplification of the described and comparatively complex manufacturing process is increasingly becoming the focus of automobile manufacturers for ecological and economic reasons.

There are approaches in which an attempt is made to dispense with the separate hardening step of the coating agent applied directly to the hardened electrocoat layer (the coating agent referred to as a filler in the context of the standard process described above), where appropriate also reducing the layer thickness of the coating layer produced from this coating agent . In the technical field, this coating layer, which is not separately hardened, is then often referred to as the basecoat layer (and no longer as the filler layer) or, in contrast to a second basecoat layer applied thereon, as the first basecoat layer. In some cases, attempts are even made to completely dispense with this coating layer (in which case only a so-called basecoat layer is then produced directly on the electrocoat layer, which is overcoated with a clear lacquer without a separate curing step, and thus ultimately also without a separate curing step). Instead of the separate hardening step and an additional final hardening step, only a final hardening step should therefore take place after application of all coating layers applied to the electrocoat layer.

The avoidance of a separate hardening step of the coating agent applied directly to the electrocoat layer is ecological and economically very advantageous. Because this leads to energy savings and the entire manufacturing process can of course be much more stringent.

Instead of the separate curing step, it is therefore advantageous that the coating layer produced directly on the electrocoat layer is only flashed off at room temperature and / or is intermediately dried at elevated temperatures, without carrying out curing which, as is known, requires regularly increasing curing temperatures and / or long curing times.

The problem, however, is that with this form of production, the required application technology and aesthetic properties can often not be achieved today.

By doing without the separate hardening of the coating layer applied directly to the electrocoat layer, for example the first basecoat layer, before the application of further coating agents, for example a second basecoat and a clearcoat, undesirable air, solvent and / or moisture inclusions can arise can make themselves felt in the form of bubbles below the surface of the overall coating and can break open during the final hardening. The resulting holes in the paintwork, also called pinholes and stoves, lead to a disadvantageous visual appearance. The amount of organic solvent or water resulting from the overall structure of the first basecoat, second basecoat and clearcoat, as well as the amount of air introduced by the application, is too large for the entire amount to escape from the multi-coat paint within a final curing step without creating defects.

Furthermore, it can happen that the basecoat layer applied directly to the first layer (filler or first basecoat layer) slips off the first layer after the painting process has ended. This effect is also known to the person skilled in the art under the term slumping. Slumping occurs especially when

the first basecoat layer has a high layer thickness, or the second basecoat is applied wet, for example by a high outflow rate and / or low speed, or

 the flash-off time between the application of the first and the second basecoat is short or

 the polarity differences between the first and second basecoat layers are high or

 the stability of the first basecoat is reduced due to aging, storage or shear.

In the case of a conventional manufacturing process as described above, in which the so-called filler layer is baked separately before the production of a mostly thin (and therefore only comparatively little air, organic solvent and / or water) basecoat, the solution to this problem is of course clear less demanding.

But also in the production of multi-layer coatings, in which the use of the coating agent referred to in the standard process as a filler is completely dispensed with, i.e. systems in which only a so-called basecoat is applied directly to the hardened first layer, one often comes across the described problems with needlesticks, stoves and slumping. Because, depending on the application and use of the multi-layer coating to be produced, if the coating referred to as the filler layer in the standard process is completely dispensed with, a basecoat layer which is thicker than that of the standard systems is generally required in order to obtain the desired properties. In this case, too, the total layer thickness of coating layers that have to be hardened in the final hardening step is considerably higher than in the standard process.

Also, other relevant properties are not always achieved to a satisfactory degree when building up multi-layer coatings using the processes described above. For example, achieving a high-quality overall optical impression (appearance), which is influenced in particular by a good flow of the coating agents used, is a challenge. The rheological properties of the coating agents must be appropriately coordinated with the process management described. The same applies to maintaining adequate runner stability. Furthermore, it is difficult to achieve sufficient stability.

Accordingly, it would be advantageous to use a process for the production of multi-layer coatings in which there is no need for a separate hardening step, as described above, for the coating agent applied directly to the first layer, and the multi-layer coating produced nevertheless has excellent application technology, in particular aesthetic properties.

Task and solution

 It was therefore an object of the present invention to find a process for producing a multilayer coating on substrates, in which the coating agent applied directly to the first layer is not separately cured, but instead in which this coating agent is cured in a common curing step with other coating layers applied subsequently becomes. Despite this simplification of the process, the resulting multi-layer coatings should have excellent application technology, in particular aesthetic properties and stability. In addition, it should be possible in this way, depending on requirements and individual application, to provide multi-layer coatings in which the one or more coating layers arranged between the first layer and the clear lacquer layer can have variable layer thicknesses, and in particular in the case of higher ones Layer thicknesses no problems with pinpricks and slumping occur.

In addition, it should be possible to solve the problems of stability that arise during the production of multi-layer coatings by simply adapting the composition of the layer (s) arranged between the first layer and the clear lacquer layer during the production of the multi-layer coatings, and in this way to stock different basecoat compositions per color avoid or reduce. However, adjusting the composition should not be a significant one Changes in the high or low viscosity lead, since such changes can have a negative influence on the appearance, the running properties and the color.

Solution of the task

 It was found that the above objects could be achieved by a new process for producing a multi-layer coating (M) on a substrate (S), comprising

 (1) optionally producing a hardened first layer (S1) on the substrate (S) by applying a composition (Z1) to the substrate (S) and then curing the composition (Z1),

 (2) Production of a basecoat film (BL2a) or several directly sequential basecoat films (BL2-x) directly on the first layer (S1) by applying an aqueous basecoat film (bL2a) directly on the first layer (S1) or directly sequentially applying several aqueous basecoats (bl2-x) directly on the first layer (S1)

 (3) production of a clear lacquer layer (K) directly on the basecoat layer (BL2a) or the top basecoat layer (BL2-z) by applying a clear lacquer (kL) directly on the basecoat layer (BL2a) or the top basecoat layer (BL2-z),

(4) joint curing of the basecoat film (BL2a) and the clearcoat film (K) or the basecoat film (BL2-x) and the clearcoat film (K),

characterized in that

the at least one basecoat (bL2a) or at least one of the basecoats (bL2-x) directly before application

 with an aqueous dispersion (D1) containing at least one polyamide (PA) with an acid number of 15 to 60 mg KOH / g or

 is mixed with an aqueous dispersion (D2) containing at least one polyamide (PA) and at least one amide wax (AW).

The above-mentioned method is also referred to below as the method according to the invention and is accordingly the subject of the present invention. Preferred embodiments of the method according to the invention can be found in the description below and in the subclaims. The method according to the invention allows the production of multi-layer coatings without the need for a separate curing step of the coating layer produced directly on the first layer. For the sake of clarity, this coating layer is referred to as a basecoat layer in the context of the present invention. Instead of separate curing, this basecoat is cured together with any other basecoat below the clearcoat and the clearcoat. The addition of the aqueous dispersion (D1) or the addition of the aqueous dispersion (D2) directly before the application of the basecoat (hereinafter also referred to as post-additivation) makes it possible to effectively eliminate problems of stability occurring during the multi-layer coating and in this way a Avoid or reduce the storage of different basecoat compositions per color. In addition, the post-additization also enables the further use of basecoat compositions which, because of the stability problems which occur, are outside the specification and therefore have to be disposed of. The method according to the invention therefore has an improved environmental balance and efficiency in relation to the basecoat compositions used.

It is well known to the person skilled in the art to adapt the rheology of the basecoat composition and, for example, to add thickeners if problems with the stability occur. However, it was surprising that only with the addition of certain thickeners, namely the aqueous dispersion (D1) or the aqueous dispersion (D2) can the problems of stability be eliminated without negatively affecting the aesthetic and mechanical properties achieved with the coating. Despite a low energy input, these thickeners can be incorporated homogeneously into the basecoat composition and can therefore, if necessary, be added to the basecoat composition at any time during the production of the multilayer coating before it is applied. Detailed description

 Definitions:

 First, some terms used in the context of the present invention are explained.

The application of a coating agent to a substrate or the production of a coating layer on a substrate are understood as follows. The respective coating agent is applied such that the coating layer produced therefrom is arranged on the substrate, but does not necessarily have to be in direct contact with the substrate. Other layers can, for example, be arranged between the coating layer and the substrate. For example, in step (1) the hardened first layer (S1) is produced on the metallic substrate (S), but a conversion coating, such as zinc phosphating, can be arranged between the substrate and the first layer (S1) .

The same principle applies to the application of a coating agent (b) to a coating layer (A) produced by means of another coating agent (a) or the production of a coating layer (B) on another coating layer (A). The coating layer (B) does not necessarily have to be in contact with the coating layer (A), it merely has to be arranged above it, that is to say on the side of the coating layer (A) facing away from the substrate.

In contrast to this, the application of a coating agent directly to a substrate or the production of a coating layer directly on a substrate is understood as follows. The respective coating agent is applied in such a way that the coating layer produced therefrom is arranged on the substrate and is in direct contact with the substrate. In particular, no other layer is arranged between the coating layer and the substrate.

The same naturally applies to the application of a coating agent (b) directly to a coating layer (A) produced by means of another coating agent (a) or the production of one Coating layer (B) directly on another coating layer (A). In this case, the two coating layers are in direct contact, that is to say they are arranged directly on top of one another. In particular, there is no further layer between the coating layers (A) and (B). The same principle naturally applies to the application of coating agents in direct succession or the production of coating layers in direct succession.

In the context of the present invention, flashing off, intermediate drying and hardening are understood to be the terms which are familiar to the person skilled in the art in connection with processes for producing multi-layer coatings.

Thus, the term flash-off is basically understood as a designation for the evaporation or evaporation of organic solvents and / or water of a coating agent applied during the production of a coating at mostly ambient temperature (i.e. room temperature), for example 15 to 35 ° C. for a period of for example 0.5 to 30 min. Organic solvents and / or water contained in the applied coating agent evaporate during the flashing off. In any case, since the coating composition is still flowable immediately after application and at the beginning of the drying, it can run during the drying. Because at least one coating agent applied by spray application is generally applied in droplet form and not in a homogeneous thickness. However, it is flowable due to the organic solvents and / or water it contains and can therefore form a homogeneous, smooth coating film due to the running. At the same time, organic solvents and / or water evaporate successively, so that after the flash-off phase a comparatively smooth coating layer has formed which contains less water and / or solvent than the applied coating agent. After flashing off, the coating layer is not yet ready for use. For example, it is no longer flowable, but is still soft or sticky, possibly only dried. In particular, the coating layer has not yet been cured as described below. Intermediate drying is also understood to mean the evaporation or evaporation of organic solvents and / or water of a coating agent applied during the production of a coating, usually at a temperature of, for example, 40 to 90 ° C., which is higher than the ambient temperature, for a period of, for example, 1 to 60 min. Even during intermediate drying, the applied coating agent will lose a proportion of organic solvents and / or water. In relation to a specific coating agent, it is generally the case that intermediate drying takes place at higher temperatures and / or for a longer period of time compared to flashing off, so that compared to flashing off, a higher proportion of organic solvents and / or water from the applied coating layer escapes. However, intermediate drying also does not result in a coating layer in the ready-to-use state, that is to say no coating layer hardened as described below. A typical sequence of flashing off and intermediate drying would be, for example, flashing off an applied coating layer for 3 minutes at ambient temperature and then drying at 60 ° C. for 10 minutes. A final delimitation of both terms is neither necessary nor wanted. For the sake of clarity, these terms are used to make it clear that a variable and sequential conditioning of a coating layer preceding the curing described below can take place. Depending on the coating agent, the evaporation temperature and evaporation time, more or less high proportions of the organic solvents and / or water contained in the coating agent can evaporate. If necessary, even a portion of the polymers contained in the coating agent can crosslink or loop together as binders as described below. However, no ready-to-use coating layer is obtained either during flashing off or during intermediate drying, as is the case with the curing described below. As a result, hardening is clearly differentiated from flashing and intermediate drying.

Accordingly, hardening of a coating layer means the transfer of such a layer into the ready-to-use state, that is to say that is to say into a state in which the substrate provided with the respective coating layer can be transported, stored and used as intended. A hardened coating layer is therefore in particular no longer soft or sticky, but conditioned as a solid coating film which, even when exposed further to curing conditions as described below, no longer significantly changes its properties, such as hardness or adhesion to the substrate.

As is known, coating compositions can in principle be cured physically and / or chemically, depending on the components they contain, such as binders and crosslinking agents. In chemical hardening, thermal-chemical hardening and actinic-chemical hardening come into consideration. A coating agent can, for example insofar as it is thermo-chemically curable, be self and / or externally crosslinking. In the context of the present invention, the statement that a coating agent is self- and / or externally crosslinking means that this coating agent contains polymers (also called polymers) as binders and, if appropriate, crosslinking agents which can crosslink accordingly. The underlying mechanisms and the binders and crosslinking agents (film-forming components) that can be used are described below.

In the context of the present invention, “physically curable” or the term “physical hardening” means the formation of a hardened coating layer by releasing solvent from polymer solutions or polymer dispersions, the hardening being achieved by entangling polymer chains. Such coating compositions are generally formulated as one-component coating compositions.

In the context of the present invention, “thermo-chemically hardenable” or the term “thermo-chemical hardening” means the crosslinking of a lacquer layer initiated by chemical reaction of reactive functional groups (formation of a hardened coating layer), the energetic activation of this chemical reaction by thermal energy is possible. Different functional groups that are complementary to one another can react with one another (complementary functional groups) and / or the formation of the hardened layer is based on the reaction of autoreactive groups, that is to say that is functional groups that react with each other with groups of their kind. Examples of suitable complementary reactive functional groups and autoreactive functional groups are known, for example, from German patent application DE 199 30 665 A1, page 7, line 28, to page 9, line 24.

This networking can be self-networking and / or external networking. For example, if the complementary reactive functional groups are already present in an organic polymer used as a binder, for example a polyester, a polyurethane or a poly (meth) acrylate, there is self-crosslinking. External crosslinking occurs, for example, when a (first) organic polymer containing certain functional groups, for example flydroxyl groups, reacts with a crosslinking agent known per se, for example a polyisocyanate and / or a melamine resin. The crosslinking agent thus contains reactive functional groups which are complementary to the reactive functional groups present in the (first) organic polymer used as the binder.

Particularly in the case of external networking, the one-component and multi-component systems known per se, in particular two-component systems, come into consideration.

In thermo-chemically curable one-component systems, the components to be crosslinked, for example organic polymers as binders and crosslinking agents, are present side by side, that is to say in one component. The prerequisite for this is that the components to be crosslinked only react effectively with one another at higher temperatures, for example above 100 ° C., that is to say they undergo curing reactions. Otherwise, the components to be crosslinked would have to be stored separately from one another and only mixed with one another shortly before application to a substrate, in order to avoid premature at least partial thermal-chemical flashing (compare two-component systems). Hydroxy-functional polyesters and / or polyurethanes with melamine resins and / or blocked polyisocyanates as crosslinking agents may be mentioned as an exemplary combination. In thermo-chemically curable two-component systems, the components to be crosslinked, for example the organic polymers as binders and the crosslinking agents, are present separately from one another in at least two components which are only combined shortly before application. This form is chosen when the components to be crosslinked already react effectively with one another at ambient temperatures or slightly elevated temperatures of, for example, 40 to 90 ° C. Hydroxy-functional polyesters and / or polyurethanes and / or poly (meth) acrylates with free polyisocyanates as crosslinking agents may be mentioned as an exemplary combination.

It is also possible for an organic polymer as binder to have both self-crosslinking and externally crosslinking functional groups and then to be combined with crosslinking agents.

In the context of the present invention, “actinic-chemical hardenable” or the term “actinic-chemical hardening” means the fact that hardening using actinic radiation, namely electromagnetic radiation such as near infrared (NIR) and UV radiation, in particular UV radiation, as well as corpuscular radiation such as electron radiation is possible. Curing by UV radiation is usually initiated by radical or cationic photoinitiators. Typical actinically curable functional groups are carbon-carbon double bonds, radical photoinitiators generally being used here. Actinic curing is also based on chemical crosslinking.

Of course, when a coating agent that is labeled as chemically curable is hardened, physical hardening, that is, entanglement of polymer chains, will always occur. The physical hardening can even make up the majority. Nevertheless, such a coating agent, provided that it at least partially contains film-forming components that are chemically curable, is referred to as chemically curable.

It follows from the above that, depending on the type of coating agent and the components contained therein, curing causes different mechanisms will, of course, also make different curing conditions necessary, in particular different curing temperatures and curing times.

In the case of a purely physically curing coating agent, curing is preferably carried out between 15 and 90 ° C. over a period of 2 to 48 hours. In this case, the curing differs from flashing off and / or intermediate drying, if necessary only by the duration of the conditioning of the coating layer. It also makes no sense to differentiate between flashing off and intermediate drying. For example, it would be possible to first flash off or dry a coating layer produced by applying a physically curable coating agent at 15 to 35 ° C. for a period of, for example, 0.5 to 30 minutes and then to cure it at 50 ° C. for a period of 5 hours.

However, preference is given to at least some of the coating compositions to be used in the process according to the invention, that is to say electro-dip lacquers, aqueous basecoats and clearcoats, thermally / chemically curable, particularly preferably thermo-chemically curable and externally crosslinking.

Basically and within the scope of the present invention, the curing of thermo-chemically curable one-component systems is preferred at temperatures of 100 to 250 ° C., preferably 100 to 180 ° C. for a period of 5 to 60 minutes, preferably 10 to 45 min is carried out, since these conditions are generally necessary in order to convert the coating layer into a hardened coating layer by means of chemical crosslinking reactions. Accordingly, a flash-off and / or intermediate drying phase taking place before the curing takes place at lower temperatures and / or for shorter times. In such a case, for example, it is possible to flash off at 15 to 35 ° C. for a period of, for example, 0.5 to 30 minutes and / or to dry at a temperature of, for example, 40 to 90 ° C. for a period of, for example, 1 to 60 minutes. In principle and within the scope of the present invention, the curing of thermo-chemically curable two-component systems at temperatures of, for example, 15 to 90 ° C., in particular 40 to 90 ° C., for a period of 5 to 80 min, preferably 10 to 50 min can be performed. Accordingly, a flash-off and / or intermediate drying phase taking place before the curing takes place at lower temperatures and / or for shorter times. In such a case, for example, it no longer makes sense to distinguish between the terms evaporating and intermediate drying. A flash-off or intermediate drying phase preceding the curing can take place, for example, at 15 to 35 ° C. for a period of, for example, 0.5 to 30 minutes, but in any case at lower temperatures and / or for shorter times than the subsequent curing.

Of course, this does not exclude that a thermo-chemically curable two-component system is hardened at higher temperatures. For example, in step (4) of the method according to the invention described in more detail below, one or more basecoat layers are cured together with a clearcoat layer. If both thermo-chemically curable one-component and two-component systems are present within the layers, for example a one-component basecoat and a two-component clearcoat, the joint curing naturally depends on the curing conditions necessary for the one-component system.

All of the temperatures explained in the context of the present invention are to be understood as the temperature of the room in which the coated substrate is located. So it is not meant that the substrate itself must have the appropriate temperature.

The measurement methods to be used in the context of the present invention for determining certain parameters can be found in the example part. Unless explicitly stated otherwise, these measurement methods are to be used to determine the respective parameter. If, in the context of the present invention, reference is made to an official standard without reference to the official period of validity, this of course means the version of the standard applicable on the filing date or, if there is no applicable version at this time, the last applicable version.

The aqueous dispersion containing at least one polyamide (PA) with a specific acid number or the aqueous dispersion containing a polyamide (PA) and an amide wax (AW) is mixed with the basecoat directly before application. This is to be understood to mean that the aqueous dispersion is added during the production of the multi-layer coating, in particular shortly before the use of the basecoat composition within the process according to the invention. On the other hand, the term “directly before application” in the context of the present invention does not include the addition of the aqueous dispersion during the preparation of the basecoat composition, nor the addition of the aqueous dispersion directly after the basecoat composition has been prepared.

Method according to the invention:

 In the process according to the invention, a multi-layer coating is built up on a substrate (S).

According to the invention, the substrate (S) is preferably selected from metallic substrates, plastics and mixtures thereof, in particular from metallic substrates.

Suitable metallic substrates (S) are in principle substrates containing or consisting of, for example, iron, aluminum, copper, zinc, magnesium and their alloys and steel in a wide variety of shapes and compositions. Iron and steel substrates are preferred, for example typical iron and steel substrates such as are used in the automotive industry.

Before step (1) of the method according to the invention, the metallic substrates (S) can be pretreated in a manner known per se, that is to say, for example, cleaned and / or provided with known conversion coatings. Cleaning can be done mechanically, for example by wiping, Grinding and / or polishing and / or chemically using pickling processes by etching in acid or alkali baths, for example using hydrochloric or sulfuric acid. Cleaning with organic solvents or aqueous cleaners is of course also possible. A pretreatment by applying conversion coatings, in particular by means of phosphating and / or chromating, preferably phosphating, can also take place. In any case, the metallic substrates are preferably conversion-coated, in particular phosphated, preferably provided with zinc phosphating.

Basically, plastic (S) substrates include substrates containing or consisting of (i) polar plastics, such as polycarbonate, polyamide, polystyrene, styrene copolymers, polyesters, polyphenylene oxides and blends of these plastics, (ii) reaction plastics, such as PUR-RIM, SMC, BMC and (iii) polyolefin substrates of the polyethylene and polypropylene type with a high rubber content, such as PP-EPDM, and surface-activated polyolefin substrates. The plastics can also be fiber-reinforced, in particular using carbon fibers and / or metal fibers. Substrates made of plastic (S) can also be pretreated, in particular cleaned, before step (1) of the method according to the invention in order to improve the adhesion of the first layer (S1).

In addition, substrates which contain both metallic and plastic parts can also be used as substrates (S). Such substrates are, for example, bodies containing plastic parts

The substrates can be of any shape per se, that is to say they can be simple parts or complex components such as, in particular, automobile bodies and parts thereof.

Step 1):

Step (1) of the method according to the invention is an optional step. This step is carried out in particular when the substrate (S) is a metallic substrate. However, if a substrate (S) made of plastic is used in the method according to the invention, it is preferred according to the invention if this step is not carried out, ie in this case step (2) of the method according to the invention is started directly.

The composition (Z1) can be an electro-dip coating or a primer layer. According to the invention, however, the primer layer does not mean the basecoat layer applied in step (2) of the method according to the invention. The method according to the invention is preferably carried out with metallic substrates (S). The first layer (S1) is therefore, in particular, a hardened electrocoat layer (E1). A preferred embodiment of the method according to the invention is accordingly characterized in that the composition (Z1) is an electrocoat material (ETL1) which is applied electrophoretically to the substrate (S).

The electrocoat (ETL1) used in step (1) of the process according to the invention can be a cathodic or anodic electrocoat. It is preferably a cathodic electrocoat. Electrodeposition paints have long been known to the person skilled in the art. These are aqueous coating materials which must be suitable for being applied electrophoretically to a metallic substrate. In any case, they contain anionic or cationic polymers as binders. These polymers contain functional groups which are potentially anionic, i.e. can be converted into anionic groups, for example carboxylic acid groups, or functional groups which are potentially cationic, i.e. can be converted into cationic groups, for example amino groups. The conversion into charged groups is generally achieved by using appropriate neutralizing agents (organic amines (anionic), organic carboxylic acids such as formic acid (cationic)), which then give rise to the anionic or cationic polymers. Electrodeposition paints generally and therefore preferably also contain typical anti-corrosion pigments. The cathodic electrocoat materials preferred in the context of the invention preferably contain cationic polymers as binders, in particular hydroxy-functional polyetheramines, which preferably have aromatic structural units. Such polymers are generally obtained by reacting corresponding bisphenol-based epoxy resins with amines such as, for example Obtain mono- and dialkylamines, alkanolamines and / or dialkylaminoalkylamines. These polymers are used in particular in combination with known blocked polyisocyanates. Reference is made, for example, to the electrocoat materials described in WO 9833835 A1, WO 9316139 A1, WO 0102498 A1 and WO 2004018580 A1.

The electrocoat material (ETL1) is therefore preferably an in any case chemically-thermally curable coating agent, it being in particular externally crosslinking. The electrocoat material (ETL1) is preferably a thermo-chemically curable one-component coating agent. The electrocoat material (ETL1) preferably contains a hydroxy-functional epoxy resin as a binder and a completely blocked polyisocyanate as a crosslinking agent. The epoxy resin is preferably cathodic, in particular containing amino groups.

The electrophoretic application of such an electrocoating lacquer (ETL1), which takes place as part of step (1) of the method according to the invention, is also known. The application is electrophoretic. This means that the metallic workpiece to be coated is first immersed in an immersion bath containing the paint and an electrical DC field is applied between the metallic workpiece and a counter electrode. The workpiece thus acts as an electrode; the non-volatile constituents of the electrocoating material migrate due to the charge described for the polymers used as binders through the electric field to the substrate and are deposited on the substrate, as a result of which an electrocoating material layer is formed. For example, in the case of a cathodic electrocoat, the substrate is switched as a cathode, the hydroxide ions formed there by the water electrolysis neutralize the cationic binder, so that it is deposited on the substrate and an electrocoat layer is formed. It is then also an application by the electrophoretic method.

After the application of the electrocoat material (ETL1), the coated substrate (S) is removed from the basin, optionally rinsed with, for example, water-based rinsing solutions, then optionally aired and / or dried, and finally the electrocoat material applied is cured. The applied electrocoat (ETL1) (or the applied, not yet hardened electrocoat) is, for example, flashed off at 15 to 35 ° C for a period of, for example, 0.5 to 30 min and / or at a temperature of preferably 40 to 90 ° C for dried for a period of, for example, 1 to 60 minutes.

The electrodeposition paint (ETL1) applied to the substrate (or the applied, not yet hardened electrodeposition coating) is preferably at temperatures from 100 to 250 ° C., preferably 140 to 220 ° C. for a period of 5 to 60 minutes, preferably 10 to 45 minutes hardened, whereby the hardened electrocoat layer (E1) is produced.

The specified flash-off, intermediate drying and curing conditions apply in particular to the preferred case in which the electrocoat material (ETL1) is a chemically and thermally curable one-component coating agent as described above. However, this does not rule out the fact that the electrocoat material is a coating agent that can be hardened in another way and / or that other flash-off, intermediate drying and curing conditions are used.

The layer thickness of the hardened electrocoat layer is, for example, 10 to 40 micrometers, preferably 15 to 25 micrometers. All the layer thicknesses specified in the context of the present invention are to be understood as dry layer thicknesses. It is therefore the layer thickness of the hardened layer in each case. If it is stated that a lacquer is applied in a certain layer thickness, this means that the lacquer is applied in such a way that the mentioned layer thickness results after curing.

Step 2):

In step (2) of the method according to the invention, a basecoat layer (BL2a) is produced (alternative 1) or a plurality of directly successive basecoat layers (BL2-x) are produced (alternative 2). The layers are produced by applying an aqueous basecoat (also called waterborne basecoat) (bL2a) directly to the hardened layer (S1) or directly in succession Apply several basecoats (bL2-x) to the hardened layer (S1). The basecoat film (BL2a) according to alternative 1 from step (2) is thus arranged directly on the hardened first layer (S1) after production.

The terms basecoat and basecoat layer in relation to the coating agents and coating layers produced in step (2) of the process according to the invention are used for the sake of clarity. The basecoat layers (BL2a) and (BL2-x) are not hardened separately, but together with the clearcoat. The hardening therefore takes place analogously to the hardening of so-called basecoats used in the standard process described in the introduction. In particular, the coating compositions used in step (2) of the method according to the invention are not separately cured like the coating compositions referred to as fillers in the standard method.

The direct successive application of several basecoats (bL2-x) to the hardened first layer (S1) is understood to mean that first a first basecoat is applied directly to the layer (S1) and then a second basecoat is applied directly to the layer from the first Basecoat is applied. An optionally third basecoat is then applied directly to the layer of the second basecoat. This process can then be repeated analogously for other basecoats (i.e. a fourth, fifth, etc. basecoat). In this context, the following designation is useful. The basecoats and basecoat layers are generally identified by (bL2-x) and (BL2-x), while when naming the specific individual basecoats and basecoat layers, the x can be replaced by other suitable letters.

The first basecoat and the first basecoat can be marked with a, the top basecoat and the top basecoat can be marked with z. In any case, these two basecoats or basecoat layers are therefore present. If necessary, layers arranged in between can be continuously marked with b, c, d and so on. By applying the first basecoat (bL2-a), a basecoat layer (BL2-a) is thus produced directly on the hardened first layer (S1). The at least one further basecoat film (BL2-x) is then produced directly on the basecoat film (BL2-a). If several further basecoat layers (BL2-x) are produced, these are produced in direct succession. For example, exactly one further basecoat layer (BL2-x) can be produced, which is then arranged directly below the clearcoat layer (K) in the multilayer coating ultimately produced and can therefore be referred to as the basecoat layer (BL2-z). It is also possible, for example, for two further basecoat layers (BL2-x) to be produced, in which case the layer produced directly on the basecoat layer (BL2-a) as (BL2-b) and the layer finally arranged directly below the clearcoat layer (K) can be referred to as (BL2-z).

The basecoats (bL2-x) can be identical or different. It is also possible to produce several basecoat layers (BL2-x) with the same basecoat and one or more further basecoat layers (BL2-x) with one or more other basecoats.

If a first basecoat layer is produced by applying a first basecoat and a further basecoat layer by applying the same basecoat, both layers are obviously based on the same basecoat. However, the application obviously takes place in two stages, so that the corresponding basecoat in the sense of the method according to the invention corresponds to a first basecoat (bL2-a) and a further basecoat (bL2-z). The structure described is often also referred to as a single-layer basecoat layer structure produced in two orders. However, since in the real serial painting in particular, due to the technical conditions in a paint shop, a certain period of time elapses between the first order and the second order, during which the substrate, for example the automobile body, is conditioned at, for example, 15 to 35 ° C. and thus vented, the characterization of this structure as a two-layer basecoat structure is formally clearer. The process control described is therefore to be assigned to the second alternative of step (2). Some preferred variants of the basecoat layer sequences of the basecoats (bL2-x) are explained as follows:

 It is preferred in the context of the present invention that two directly successive basecoat layers (BL2-a) and (BL2-z) on the hardened first layer (S1) by applying an aqueous basecoat (bL2-a) directly to the first layer (S1 ) and then immediately applying another aqueous basecoat (bL2-z) directly to the first basecoat (BL2-a). The first basecoat layer (BL2-a) can be produced, for example, by electrostatic spray application (ESTA) or pneumatic application of a first basecoat (bL2-a) directly on the hardened first layer (S1) and can be vented and / or dried as described below. A second basecoat (BL2-z) is then produced by directly applying a second basecoat (bL2-z) different from the first basecoat. The second basecoat can also be applied by electrostatic spray application or by pneumatic application, as a result of which a second basecoat film (BL2-z) is produced directly on the first basecoat film (BL2-a). Between and / or after the orders can of course be flashed off and / or dried in between. This variant is preferably chosen if first a color-preparing basecoat (BL2-a) as described in more detail below is to be produced directly on the first layer (S1) and then a color and / or effect-imparting basecoat (BL2) as described in more detail below -z) to be produced directly on the first basecoat film. The first basecoat layer (BL2-a) is then based on the color-preparing basecoat (bL2-a), the second basecoat layer (BL2-z) on the color and / or effect basecoat (bL2-z). It is also possible, for example, to apply this second basecoat in two stages as described above, as a result of which two further, directly successive basecoat layers (BL2-b) and (BL2-z) are formed directly on the first basecoat layer (BL2-a), both of which based on the same basecoat.

It is also possible to produce three basecoat layers directly in succession directly on the hardened first layer (S1), the basecoat layers being based on three different basecoats. For example, a color-preparing basecoat (BL2-a), a further layer based on a color and / or effect basecoat (BL2-b) and a further layer based on a second color and / or effect basecoat (BL2-z) can be produced. Between and / or after the individual and / or after all three orders, drying and / or intermediate drying can be carried out.

Preferred embodiments within the scope of the present invention thus include that two or three basecoat layers are produced in alternative 2 of step (2) of the method according to the invention. It is then preferred that the basecoat layer (BL2-a) produced directly on the hardened first layer (S1) is based on a color-preparing basecoat (bL2-a). The second and the optionally present third layer are based either on one and the same coloring and / or effect-imparting basecoat (bL2-b) and (bL2-z) or on a first coloring and / or effect-giving basecoat (bL2-b) and one various second coloring and / or effect basecoats (bl2-z).

The aqueous basecoats (bL2a) and (bL2-x) used in step (2) are each chemically and thermally curable, particularly preferably crosslinking.

The basecoats (bL2a) and (bL2-x) can each be one-component or two-component coating compositions. However, it is preferred according to the invention if the basecoat (bL2a) or at least one of the basecoats (bL2-x), preferably all basecoats (bL2-x), are one-component coating compositions. This prevents mixing of the two components before applying the basecoats (bL2a) and (bL2-x) and thus reduces the processing effort.

The basecoats (bL2a) and (bL2-x) each contain at least one binder, preferably a mixture of different binders. In the context of the present invention, it is preferred if the binder is selected from the group consisting of polyacrylates, in particular aqueous dispersions of anionic polyacrylates, polyurethanes, polyesters and copolymers of the stated polymers, for example polyurethane polyacrylates.

In this context, it is particularly preferred if the aqueous dispersion of anionic polyacrylates (wD-PAC) is obtainable from the successive one radical emulsion polymerization of three mixtures (A), (B) and (C) of olefinically unsaturated monomers, where

 the mixture (A) contains at least 50% by weight of vinylaromatic monomers and a polymer which is prepared from the mixture (A) has a glass transition temperature of 10 to 65 ° C,

 - The mixture (B) contains at least one polyunsaturated monomer and a polymer which is prepared from the mixture (B) has a glass transition temperature of -35 to 15 ° C, and

 the mixture (C) contains at least one anionic monomer and a polymer which is prepared from the mixture (C) has a glass transition temperature of -50 to 15 ° C,

 and where

 i. the mixture (A) is first polymerized,

ii. then the mixture (B) in the presence of the i. prepared polymer is polymerized, and

iii. then the mixture (C) in the presence of the under ii. prepared polymer is polymerized.

The dispersion (wD-PAC) preferably contains exactly one previously described polymer. The preparation of the polymer comprises the successive radical emulsion polymerization of three mixtures (A), (B) and (C) of olefinically unsaturated monomers. In terms of time, the stages can take place one after the other. It is also possible that after the completion of a stage the corresponding reaction solution is stored for a certain period of time and / or transferred to another reaction vessel and only then does the next stage take place. In addition to the polymerization of the monomer mixtures (A), (B) and (C), the preparation of the special multistage polymer preferably comprises no further polymerization steps.

In radical emulsion polymerization, olefinically unsaturated monomers are polymerized in an aqueous medium using at least one water-soluble initiator and in the presence of at least one emulsifier. Corresponding water-soluble initiators are known. The at least one water-soluble initiator is preferably selected from the group consisting of from potassium, sodium or ammonium peroxodisulfate, hydrogen peroxide, tert-butyl hydroperoxide, 2,2'-azobis (2-amidoisopropane) dihydrochloride, 2,2'-azobis (N, N'-dimethyleneisobutyramidine) dihydrochloride, 2, 2'-azobis (4-cyanopentanoic acid) and mixtures of the abovementioned initiators, for example hydrogen peroxide and sodium persulfate. Further suitable initiators and transition metal catalysts are disclosed, for example, in WO 2017/088988 A1. The initiators are preferably used in an amount of 0.05 to 20% by weight, preferably 0.05 to 10, particularly preferably 0.1 to 5% by weight, based on the total weight of the monomers used in the respective polymerization stage, used.

An emulsion polymerization takes place in a reaction medium which contains water as a continuous medium and the at least one emulsifier in the form of micelles. The polymerization is started by the decomposition of the water-soluble initiator in the water. The growing polymer chain is stored in the emulsifier micelles and the further polymerization then takes place in the micelles. The at least one emulsifier is preferably present in an amount of 0.1-10% by weight, particularly preferably 0.1 -5% by weight, very particularly preferably 0.1-3% by weight, in each case based on the total weight of the monomers used in the respective polymerization stage. In principle, emulsifiers are also known. Nonionic or ionic emulsifiers, including zwitterionic, and optionally also mixtures of the abovementioned emulsifiers, can be used, as described, for example, in published patent application WO 2017/088988 A1.

The emulsion polymerizations are advantageously carried out at a temperature of 0 to 160 ° C, preferably 15 to 95 ° C, again preferably 60 to 95 ° C. The process is preferably carried out in the absence of oxygen, preferably under an inert gas atmosphere. As a rule, the polymerization is carried out at normal pressure, but the use of lower pressures or higher pressures is also possible. In particular, when polymerization temperatures are used which are above the boiling point of water, the monomers used and / or the organic solvents at normal pressure, higher pressures are generally chosen. The individual polymerization stages in the production of the special polymer can be carried out, for example, as so-called "starving polymerizations" (also known as "starve feed", "starve fed" or "starved feed" polymerizations). An emulsion polymerization in which the content of free olefinically unsaturated monomers in the reaction solution (also called reaction mixture) is minimized during the entire reaction period is regarded as starving polymerization in the sense of the present invention. This means that the olefinically unsaturated monomers are metered in such that a proportion of free monomers in the reaction solution of 6.0% by weight, preferably 5.0% by weight, particularly preferably 4.0% by weight, particularly advantageously 3.5% by weight, based in each case on the total amount of the monomers used in the respective polymerization stage, is not exceeded during the entire reaction time.

The concentration of the monomers in the reaction solution can be determined, for example, by gas chromatography, as described in WO 2017/088988 A1. The proportion of free monomers can be controlled by the interaction of the amount of initiator, the rate of addition of the initiator, the rate of addition of monomers and the selection of the monomers. Both the slowing down of the dosage and the increase in the amount of initiator, as well as the early start with the addition of the initiator serve the goal of keeping the concentration of the free monomers below the above-mentioned limits.

In the context of the present invention, it is preferred that the polymerization stages ii. and iii. be carried out under starving conditions. This has the advantage that the formation of new particle nuclei is effectively minimized in the course of these two polymerization stages. Instead, it is possible to use the level i. existing particles (henceforth also called seeds) in stage ii. to continue to grow through the polymerization of the monomer mixture B (henceforth also referred to as core). It is also possible to achieve the level ii. existing particles (hereinafter also called polymer comprising seed and core) in stage iii. to allow further growth by the polymerization of the monomer mixture C (henceforth also called shell), so that finally a polymer comprising particles comprising seed, core and shell results. Of course, stage i. be carried out under starving conditions.

Mixtures (A), (B) and (C) are mixtures of olefinically unsaturated monomers, mixtures (A), (B) and (C) being different from one another. They each contain different monomers and / or different proportions of at least one specific monomer.

Mixture (A) contains at least 50% by weight, preferably at least 55% by weight, of vinyl aromatic compounds. A corresponding preferred monomer is styrene. In addition to the vinyl aromatic compounds, the mixture (A) contains no monomers with functional groups containing heteroatoms. The monomer mixture (A) particularly preferably contains at least one monounsaturated ester of (meth) acrylic acid with an alkyl radical and at least one vinyl group-containing monolefinically unsaturated monomer with a radical arranged on the vinyl group which is aromatic or which is mixed, saturated, aliphatic-aromatic , in which case the aliphatic portions of the radical are alkyl groups.

The monomers contained in the mixture (A) are selected so that a polymer produced therefrom has a glass transition temperature of 10 to 65 ° C., preferably 30 to 50 ° C. The well-known Fox equation can be used for a targeted estimate of the glass transition temperature to be expected during the measurement. Since the Fox equation is a good approximation, which is based on the glass transition temperatures of the homopolymers and their parts by weight without including the molecular weight, it can be used as a useful tool for the person skilled in the synthesis, so that a desired glass transition temperature can be set via a few targeted experiments .

That in stage i. The polymer produced by the emulsion polymerization of the monomer mixture (A) preferably has a particle size of 20 to 125 nm (for the measurement of the particle size see point 3 of the method description). Mixture (B) contains at least one polyolefinically unsaturated monomer, preferably at least one polyolefinically unsaturated monomer. A corresponding preferred monomer is 1, 6-hexanediol diacrylate. The monomer mixture (B) preferably also contains no monomers with functional groups containing heteroatoms. Particularly preferably, the monomer mixture (B) in addition to at least one polyolefinically unsaturated monomer also contains the following monomers. On the one hand at least one monounsaturated ester of (meth) acrylic acid with an alkyl radical and on the other at least one vinyl group-containing simple olefinically unsaturated monomer with a radical arranged on the vinyl group which is aromatic or which is mixed saturated-aliphatic-aromatic, in which case the aliphatic portions of the remainder are alkyl groups.

The proportion of polyunsaturated monomers is preferably from 0.05 to 3 mol%, based on the total molar amount of monomers of the monomer mixture (B).

The monomers contained in the mixture (B) are selected so that a polymer produced therefrom has a glass transition temperature of from -35 to 15 ° C., preferably from -25 to + 7 ° C.

The polymer, which after stage ii. obtained, preferably has a particle size of 80 to 280 nm, preferably 120 to 250 nm.

The monomers contained in the mixture (C) are selected so that a polymer produced therefrom has a glass transition temperature of from -50 to 15 ° C., preferably from -20 to + 12 ° C.

The olefinically unsaturated monomers of the mixture (C) are preferably selected so that the resulting polymer, comprising the seed, core and shell, has an acid number of 10 to 25. Accordingly, the mixture (C) preferably contains at least one alpha-beta unsaturated carboxylic acid, particularly preferably (meth) acrylic acid. The olefinically unsaturated monomers of the mixture (C) are also preferably selected so that the resulting polymer, comprising the seed, core and shell, has an OH number of 0 to 30, preferably 10 to 25. All the acid numbers and OH numbers mentioned above are values calculated on the basis of the total monomer mixtures used.

The monomer mixture (C) particularly preferably contains at least one alpha-beta unsaturated carboxylic acid, at least one monounsaturated ester of (meth) acrylic acid with an alkyl radical substituted by a hydroxyl group and at least one monounsaturated ester of (meth) acrylic acid with an alkyl radical.

Particularly preferred, neither the monomer mixture (A) nor the monomer mixtures (B) or (C) contains a polyurethane polymer which has at least one polymerizable double bond.

After its production, the polymer has a particle size of 100 to 500 nm, preferably 125 to 400 nm, very particularly preferably 130 to 300 nm, and a glass transition temperature T _g of -20 to -5 ° C.

The proportions of the monomer mixtures are preferably coordinated with one another as follows. The proportion of mixture (A) is from 0.1 to 10% by weight, the proportion of mixture (B) from 60 to 80% by weight and the proportion of mixture (C) from 10 to 30% by weight , each based on the sum of the individual amounts of the mixtures (A), (B) and (C).

An anionic polyacrylate which is particularly preferably used in the aqueous dispersion (wD-PAC) in the context of the present invention can be prepared by reaction

 a mixture (A) of 50 to 85% by weight of a vinylaromatic monomer and 15 to 50% by weight of a monounsaturated ester of (meth) acrylic acid with an alkyl radical,

- A mixture (B) of 1 to 4 wt .-% of a polyolefinically unsaturated monomer, 60 to 80 wt .-% of a monounsaturated ester (Meth) acrylic acid with an alkyl radical and 16 to 39% by weight of a vinyl aromatic monomer, and

 a mixture (C) of 8 to 15% by weight of an alpha-beta unsaturated carboxylic acid, 10 to 20% by weight of a monounsaturated ester of (meth) acrylic acid with an alkyl radical substituted by a hydroxyl group and 65 to 82% by weight. % monounsaturated esters of (meth) acrylic acid with an alkyl radical,

in which

 i. the mixture (A) is first polymerized,

ii. then the mixture (B) in the presence of the i. prepared polymer is polymerized, and

iii. then the mixture (C) in the presence of the under ii. prepared polymer is polymerized.

 The above percentages by weight relate in each case to the total weight of the mixture (A) or (B) or (C).

The aqueous dispersion (wD-PAC) preferably has a pH of 5.0 to 9.0, again preferably 7.0 to 8.5, very particularly preferably 7.5 to 8.5. The pH can already be kept constant during the production, for example by using bases as mentioned below, or can be set in a targeted manner after the production of the polymer. The stages i described are preferred. to iii. carried out without the addition of acids or bases known for adjusting the pH and the pH is adjusted only after the preparation of the polymer by adding organic, nitrogen-containing bases, sodium hydrogen carbonate, borates and also mixtures of the aforementioned substances.

The solids content of the aqueous dispersion (wD-PAC) is preferably from 15 to 40%, more preferably 20 to 30%.

The aqueous dispersion (wD-PAC) preferably contains a proportion of 55 to 75% by weight, particularly preferably 60 to 70% by weight, in each case based on the total weight of the dispersion, water. It is further preferred if the percentage sum of the solid of the dispersion (wD-PAC) and the proportion of water in the dispersion (wD-PAC) is at least 80% by weight, preferably at is at least 90% by weight. Preferred ranges are from 80 to 99% by weight, in particular 90 to 97.5% by weight. In this specification, the solid, which traditionally only has the unit "%", is specified in "% by weight". Since the solid ultimately also represents a percentage weight, this form of representation is justified. For example, if a dispersion is flat and has a solids content of 25% and a water content of 70% by weight, the above-defined percentage sum of the solid and the proportion of water is 95% by weight.

As a result, the dispersion (wD-PAC) consists largely of water and the special polymer and does not contain any, or only to a small extent, environmentally harmful components such as, in particular, organic solvents.

The proportion of the at least one dispersions (wD-PAC), based on the total weight of the aqueous basecoat material (bL2a) or (bL2-x), is preferably 5 to 60% by weight, particularly preferably 10 to 50% by weight and entirely particularly preferably 20 to 45% by weight.

The proportion of the polymers originating from the dispersions (wD-PAC), based on the total weight of the aqueous basecoat material (bL2a) or (bL2-x), is preferably from 1 to 24% by weight, preferably 2.5 to 20.0 % By weight, particularly preferably 3 to 18.0% by weight.

The determination or determination of the proportion of the polymers from the dispersions to be used according to the invention (wD-PAC) in the basecoat can be determined by determining the solids (also called non-volatile content, solids content or solids content) of a dispersion (wD-PAC) contained in the basecoat to be used. In the case of a possible specification on basecoats containing preferred dispersions (wD-PAC) in a specific proportion, the following applies. The dispersions (wD-PAC) which do not fall into the preferred group can of course also be present in the basecoat. The special percentage range then only applies to the preferred group of dispersions (wD-PAC). However, it is preferred that for the total proportion of dispersions (wD-PAC) consisting of dispersions from the preferred group and dispersions which do not fall into the preferred group, the special one is also Share area applies. If a restriction to a share range of 10 to 50% by weight and a preferred group of dispersions (wD-PAC) were to be carried out, this share range would initially only apply to the preferred group of dispersions (wD-PAC). However, it would then be preferred that a total of 10 to 50% by weight of all originally included dispersions consisting of dispersions from the preferred group and dispersions which do not fall into the preferred group are also present. Thus, if 35% by weight of dispersions (wD-PAC) from the preferred group are used, at most 15% by weight of the dispersions from the non-preferred group can be used.

In the context of the present invention, the principle mentioned applies to all of the components of the basecoat material and their proportions, for example the pigments mentioned below or the crosslinking agents such as melamine resins mentioned below.

The aqueous basecoats (bL2a) and (bL2-x), in particular all basecoats (bL2-x), preferably each contain at least one polymer different from the anionic polyacrylate contained in the dispersion (wD-PAC) as a binder, in particular at least one polymer selected from the group consisting of polyurethanes, polyesters, polyacrylates and / or copolymers of the abovementioned polymers, in particular polyesters and / or polyurethane polyacrylates. Preferred polyesters are, for example, in DE 4009858 A1 in column 6, line 53 to column 7, line 61 and column 10, line 24 to column 13, line 3 or WO 2014/033135 A2, page 2, line 24 to page 7, line 10 and page 28, line 13 to page 29, line 13. Preferred polyurethane-polyacrylate copolymers (acrylated polyurethanes) and their preparation are described, for example, in WO 91/15528 A1, page 3, line 21 to page 20, line 33 and in DE 4437535 A1, page 2, line 27 to page 6, line 22 described. The polymers described as binders are preferably hydroxy-functional and particularly preferably have an OH number in the range from 15 to 200 mg KOH / g, particularly preferably from 20 to 150 mg KOH / g. The basecoats particularly preferably comprise at least one hydroxy-functional polyurethane-polyacrylate copolymer, again preferably at least one hydroxy-functional polyurethane-polyacrylate copolymer and at least one hydroxy-functional polyester. The proportion of the other polymers as binders can vary widely and is preferably in the range from 1.0 to 25.0% by weight, preferably 3.0 to 20.0% by weight, particularly preferably 5.0 to 15.0 % By weight, based in each case on the total weight of the basecoat material (bL2a) or (bL2-x).

The basecoats (b2La) and (bL2-x) to be used according to the invention, in particular all basecoats (bL2-x), each preferably contain at least one pigment. This includes pigments that are known per se and give color and / or optically effect pigments.

Such color pigments and effect pigments are known to the person skilled in the art and are described, for example, in Römpp-Lexikon Lacke und Druckfarben, Georg Thieme Verlag, Stuttgart, New York, 1998, pages 176 and 451. The terms color pigment and color pigment are interchangeable, as are the terms optically effect pigment and effect pigment.

Preferred effect pigments are, for example, platelet-shaped metallic effect pigments such as platelet-shaped aluminum pigments, gold bronzes, fire-colored bronzes and / or iron oxide-aluminum pigments, pearlescent pigments such as fish silver, basic lead carbonate, bismuth oxide chloride and / or metal oxide-mica pigments, graphite-like pigments and / or other effects -Effect pigments from PVD films and / or liquid crystal polymer pigments. Platelet-shaped metallic effect pigments, in particular platelet-shaped aluminum pigments, are particularly preferred.

Inorganic color pigments such as white pigments such as titanium dioxide, zinc-white, zinc sulfide or lithopone are to be mentioned in particular as typical color pigments; Black pigments such as carbon black, iron-manganese black or spinel black; Colored pigments such as chromium oxide, chromium oxide hydrate green, cobalt green or ultramarine green, cobalt blue, ultramarine blue or manganese blue, ultramarine violet or cobalt and manganese violet, iron oxide red, cadmium sulfoselenide, molybdate red or ultramarine red; Iron oxide brown, mixed brown, spinel and corundum phases or chrome orange; or Iron oxide yellow, nickel titanium yellow, chrome titanium yellow, cadmium sulfide, cadmium zinc sulfide, chrome yellow or bismuth vanadate.

The proportion of the pigments is preferably in the range from 1.0 to 40.0% by weight, preferably 2.0 to 35.0% by weight, particularly preferably 5.0 to 30.0% by weight, in each case based on the total weight of the aqueous basecoat (bL2a) or (bL2-x).

In addition, the basecoats (bL2a) and (bL2-x), in particular all basecoats (bL2-x), can each contain at least one typical crosslinking agent known per se. If the basecoats contain a crosslinking agent, it is preferably at least one aminoplast resin and / or at least one blocked polyisocyanate, preferably an aminoplast resin. Among the aminoplast resins, melamine resins are particularly preferred. It is therefore preferred in the context of the present invention if the basecoat (bL2a) or at least one of the basecoats (bL2-x), preferably all basecoats (bL2-x), contains at least one melamine resin as crosslinking agent.

If the basecoat materials (bL2a) and (bL2-x) contain crosslinking agents, the proportion of these crosslinking agents, in particular aminoplast resins and / or blocked polyisocyanates, particularly preferably aminoplast resins, including preferably melamine resins, is preferably in the range from 0.5 to 20.0% by weight. %, preferably 1.0 to 15.0% by weight, particularly preferably 1.5 to 10.0% by weight, in each case based on the total weight of the basecoat material (bL2a) or (bL2-x).

The basecoats (bL2a) and (bL2-x), in particular all basecoats (bL2-x), can also contain at least one thickener. Inorganic thickeners from the group of layered silicates such as lithium-aluminum-magnesium silicates are suitable as thickeners. The basecoat may also contain at least one organic thickener, for example a (meth) acrylic acid (meth) acrylate copolymer thickener or a polyurethane thickener. For example, organic associative thickeners known per se, such as the known polyurethane associative thickeners, can be used. As is known, associative thickeners are water-soluble polymers which have highly hydrophobic groups at the chain ends or in side chains have and / or their hydrophilic chains contain hydrophobic blocks or bundles inside. As a result, these polymers have a surfactant character and are capable of forming micelles in the aqueous phase. Similar to the surfactants, the hydrophilic areas remain in the aqueous phase, while the hydrophobic areas are embedded in the particles of polymer dispersions, adsorb on the surface of further solid particles such as pigments and / or fillers and / or form micelles in the aqueous phase. Ultimately, a thickening effect is achieved without increasing settling behavior.

The thickeners mentioned are commercially available. The proportion of the thickeners is preferably in the range from 0.1 to 5.0% by weight, preferably 0.2 to 3.0% by weight, particularly preferably 0.3 to 2.0% by weight, in each case based on the total weight of the basecoat (bL2a) or (bL2-x).

In addition, the basecoats (bL2a) and (bL2-x), in particular all basecoats (bL2-x), can each contain at least one further additive. Examples of such additives are residue-free or essentially residue-free thermally decomposable salts, polymers which are different from the abovementioned polymers as binders, binders which are physically, thermally and / or actinic radiation, binders, further crosslinking agents, organic solvents, reactive diluents, transparent pigments, fillers, and molecular dispersions soluble dyes, nanoparticles, light stabilizers, antioxidants, deaerating agents, emulsifiers, slip additives, polymerization inhibitors, initiators for radical polymerizations, adhesion promoters, leveling agents, film-forming aids, sag control agents (SCAs), flame retardants, corrosion inhibitors, waxes, siccatives, biocides. Such additives are used in the usual and known amounts.

The solids content of the basecoats (bL2a) and (bL2-x) can vary depending on the requirements of the individual case. The solids content primarily depends on the viscosity required for the application, in particular spray application. It is particularly advantageous that the basecoat materials to be used according to the invention can nevertheless have a viscosity with comparatively high solids, which permits appropriate application. The solids content of the basecoats (bL2a) and (bL2-x) is preferably at least 16.5%, preferably at least 18.0%, again preferably at least 20.0%.

Under the conditions mentioned, that is to say with the solids contents mentioned, preferred basecoat materials (bL2a) and (bL2-x) at 23 ° C. and a shear stress of 1000 l / s each have a viscosity of 40 to 150 mPa-s, in particular of 70 up to 120 mPa s (for more information on the measuring method see example section). In the context of the present invention, a viscosity in this range at the specified shear stress is referred to as spray viscosity (processing viscosity). As is known, coating compositions are adjusted to spray viscosity, that is, under the conditions then present (high shear stress), they have a viscosity which, in particular, is not too high to enable effective application. This means that the setting of the spray viscosity is important in order to be able to apply a lacquer at all by spraying and to ensure that a complete, uniform coating film can form on the substrate to be coated.

The basecoats (bL2a) and (bL2-x) to be used according to the invention are each aqueous. The proportion of water in the basecoats (bL2a) and (bL2-x) is in each case preferably from 35 to 70% by weight, more preferably 45 to 65% by weight, in each case based on the total weight of the basecoat (bL2a) or ( bl2-x).

It is again preferred that the percentage sum of the solid of the basecoat (bL2a) or (bL2-x) and the proportion of water in the basecoat (bL2a) or (bL2-x) is at least 70% by weight, preferably at least 75 % By weight. Preferred ranges are from 75 to 95% by weight, in particular 80 to 90% by weight. This means, in particular, that preferred basecoats (bL2a) and (bL2-x) basically contain environmentally harmful components such as, in particular, organic solvents in only small proportions in relation to the solid of the basecoat. The ratio of the volatile organic fraction of the basecoat (bL2a) or (bL2-x) (in% by weight) and the solids content of the basecoat (bL2a) or (bL2-x) (analogous to the above illustration here in% by weight) is preferred. %) from 0.05 to 0.7, again preferably from 0.15 to 0.6. In the context of the present invention, the volatile organic component is the proportion of the basecoat material (bL2a) or (bL2-x), which is neither included in the proportion of water nor in the solids.

A further advantage of the basecoats (bL2a) and (bL2-x) is that they can be used without the use of organic solvents that are harmful to health and the environment, such as N-methyl-2-pyrrolidone, dimethylformamide, dioxane, tetrahydrofuran and N-ethyl-2- pyrrolidone can be produced. Accordingly, the basecoats (bL2a) and (bL2-x) preferably contain less than 10% by weight, preferably less than 5% by weight, again preferably less than 2.5% by weight, of organic solvents selected from the group consisting of from N-methyl-2-pyrrolidone, dimethylformamide, dioxane, tetrahydrofuran and N-ethyl-2-pyrrolidone. The basecoats (bL2a) and (bL2-x) are preferably completely free from these organic solvents.

The basecoats (bL2a) and (bL2-x) can be produced using the mixing processes and mixing units which are customary and known for the production of basecoats.

In preferred alternative 2 of step (2) of the method according to the invention described above, a first basecoat (bL2-a) is first applied, which can also be referred to as a color-preparing basecoat. It thus serves as the basis for at least one subsequent basecoat layer which gives color and / or effect, ie a layer which can then optimally fulfill its function of coloring and / or effecting.

In a special embodiment, a color-preparing basecoat (bL2-a) is essentially free of colored pigments and effect pigments. Such a basecoat particularly preferably contains less than 2% by weight, preferably less than 1% by weight, of colored pigments and effect pigments, in each case based on the total weight of the aqueous basecoat material (bL2-a). In this embodiment, the color-preparing basecoat (bL2-a) preferably contains black and / or white pigments, particularly preferably both types of these pigments. It preferably contains 5 to 30% by weight, preferably 10 to 25% by weight of white pigments and 0.01 to 1.00% by weight, preferably 0.1 to 0.5% by weight of black pigments, in each case based on the total weight of the Basecoats (bl_2-a). The resulting white, black and, in particular, gray color, which can be adjusted to different brightness levels by the ratio of white and black pigments, represents an individually adaptable basis for the subsequent basecoat film build-up, so that the color and / or the effect of the following basecoat can come into its own. The pigments are known to the person skilled in the art and are also described further above. Titanium dioxide is preferred as the white pigment and carbon black as the black pigment. As already described, this basecoat (bL2-a) can of course also contain colored and / or effect pigments. This variant is particularly useful when the resulting multi-layer coating should have a highly chromatic color, for example a very deep red or yellow. If pigments in a correspondingly colorful shade are also added to the color-preparing basecoat, a further improved coloring can be achieved.

The coloring and / or effect-imparting basecoat (s) (bL2-b) and (bL2-z) for the second or the second and third basecoat layers within this embodiment are adapted in accordance with the ultimately desired coloring of the overall structure. If a white, black or gray color is desired, the at least one further basecoat (bL2-b) or (bL2-z) contains the corresponding pigments and ultimately resembles the color-preparing basecoat in terms of pigment composition. If a colorful and / or effect coating is desired, for example a colorful plain coating or a metallic effect coating, appropriate colored and / or effect pigments are used in amounts of, for example, 1 to 15% by weight, preferably 3 to 10% by weight. , each based on the total weight of the basecoat (bL2-b) or (bL2-z). Colored pigments belong to the group of color pigments, the latter also including achromatic color pigments such as black or white pigments. Such basecoats can of course also contain black and / or white pigments to adjust the brightness.

The basecoat films (BL2a) and (BL2-x) are not cured in step (2) of the process according to the invention, that is to say preferably are not exposed to temperatures above 100 ° C. for a period of longer than 1 min, particularly preferably not at all exposed above 100 ° C. This results clearly and directly from step (4) of the method according to the invention described below. Since the basecoat layers are only hardened in step (4), they cannot be hardened in step (2), because hardening in step (4) would then no longer be possible.

 The basecoats (bL2a) and (bL2-x) are applied in such a way that the basecoat film (BL2a) and the individual basecoat films (BL2-x) each have a layer thickness of, for example, 5 to 50 micrometers after curing in step (4), preferably have 6 to 40 micrometers, particularly preferably 7 to 35 micrometers. In the first alternative of step (2), base lacquer layers (BL2a) with higher layer thicknesses of 15 to 50 micrometers, preferably 20 to 45 micrometers, are preferably produced. In the second alternative of step (2), the individual basecoat layers (BL2-x) have comparatively smaller layer thicknesses, the overall structure then again having layer thicknesses which are in the order of magnitude of the one basecoat layer (BL2a). For example, in the case of two basecoat layers, the first basecoat layer (BL2-a) preferably has layer thicknesses of 5 to 35 micrometers, in particular 10 to 30 micrometers, the second basecoat layer (BL2-z) preferably has layer thicknesses of 5 to 35 micrometers, in particular 10 to 30 micrometers , the total layer thickness not exceeding 50 micrometers.

Before application of the basecoat material (bL2a) or (bL2-x), it is mixed according to the invention with at least one aqueous dispersion. According to a first alternative A1 of the process according to the invention, the aqueous dispersion (D1) contains a polyamide (PA) with an acid number of 15 to 60 mg KOH / g, based on the solids content of the dispersion (D1). In a second alternative A2, an aqueous dispersion (D2) containing at least one polyamide (PA) and at least one amide wax (AW) is used. It is particularly preferred here if the aqueous dispersion (D1) or (D2) can be mixed homogeneously with the basecoat (bL2a) or (bL2-x), since this is the only way to ensure that sufficient stability is achieved and thus a Slumping is avoided. According to the invention, homogeneous mixing means that after adding the aqueous dispersion (D1) or (D2) to the basecoat material (bL2a) or (bL2-x) and laminar mixing, a single-phase mixture is obtained on a macroscopic scale. In the context of the present invention, it has proven to be advantageous if the aqueous dispersion (D1) or (D2) contains certain polyamides (PA). Advantageously according to the invention, the polyamides (PA) mentioned below are contained both in the dispersion (D1) and in the dispersion (D2). Preferred embodiments of the present invention are therefore characterized in that the aqueous dispersion (D1) and (D2) contains at least one polyamide (PA), the at least one polyamide (PA) being a reaction product

 - A diamine with 2 to 34 carbon atoms and

 a molar excess, based on the diamine, of a dicarboxylic acid having 4 to 36 carbon atoms, preferably 6 to 36 carbon atoms, or a mixture of a dicarboxylic acid having 4 to 36 carbon atoms, preferably 6 to 36 carbon atoms, and a monocarboxylic acid having 2 to 22 carbon atoms , preferably 12 to 18 carbon atoms.

Suitable diamines with 2 to 34 carbon atoms are selected, for example, from the group consisting of ethylenediamine, 1,4-diaminobutane, hexamethylenediamine, metaxylylenediamine, 1,10-decamethylenediamine, 1,1,1-undecamethylenediamine,

1.12-dodecamethylene diamine, 4,4'-diaminodiphenyl methane, dimer diamine and mixtures thereof. Ethylene diamine, hexamethylene diamine,

1.12-Dodecamethylene diamine, 4,4'-diaminodiphenylmethane and dimer diamine are used to produce the polyamide (PA). Dimer diamines can be obtained by reacting dimer fatty acids with a maximum of 34 carbon atoms with ammonia and then hydrogenating the nitrile groups formed to amine groups.

As dimer fatty acids (also known for a long time as dimerized fatty acids or dimer acids), mixtures, which are produced by oligomerization of unsaturated fatty acids, are generally and particularly referred to in the context of the present invention. They can be produced, for example, by catalytic dimerization of vegetable, unsaturated fatty acids, unsaturated C12 to C22 fatty acids in particular being used as starting materials. The linkage proceeds primarily according to the Diels-Alder type and, depending on the number and position of the double bonds of the fatty acids used to prepare the dimer fatty acids, there are mixtures of predominantly dimeric products which have cycloaliphatic, linear-aliphatic, branched aliphatic and also C6-aromatic hydrocarbon groups between the carboxyl groups. Depending on the mechanism and / or optionally subsequent hydrogenation, the aliphatic radicals can be saturated or unsaturated and the proportion of aromatic groups can also vary. The residues between the carboxylic acid groups then contain, for example, 24 to 44 carbon atoms. Fatty acids with 18 carbon atoms are preferably used for the production, so that the dimeric product thus has 36 carbon atoms. The radicals which connect the carboxyl groups of the dimer fatty acids preferably have no unsaturated bonds and no aromatic hydrocarbon radicals.

Depending on the course of the reaction, the oligomerization described above gives rise to mixtures which contain primarily dimeric, but also trimeric molecules, as well as monomeric molecules and other by-products. It is usually purified by distillation. Commercial dimer fatty acids generally contain at least 80% by weight of dimeric molecules, up to 19% by weight of trimeric molecules and a maximum of 1% by weight of monomeric molecules and other by-products.

It is preferred to use dimer fatty acids which consist of at least 90% by weight, preferably at least 95% by weight, very particularly preferably at least 98% by weight of dimeric fatty acid molecules.

For the purposes of the present invention, it is preferred to use dimer fatty acids which consist of at least 90% by weight of dimeric molecules, less than 5% by weight of trimeric molecules and less than 5% by weight of monomeric molecules and other by-products . It is particularly preferred to use dimer fatty acids which consist of 95 to 98% by weight of dimeric molecules, less than 5% by weight of trimeric molecules and less than 1% by weight of monomeric molecules and other by-products. Dimer fatty acids are also particularly preferably used, which consist of at least 98% by weight of dimeric molecules, less than 1.5% by weight of trimeric molecules and less than 0.5% by weight of monomeric molecules and other by-products. The proportions of monomeric, dimeric and trimeric molecules and other by-products in the dimer fatty acids can be determined, for example, by means of Gas chromatography (GC) done. Before the GC analysis, the dimer fatty acids are converted to the corresponding methyl esters using the boron trifluoride method (compare DIN EN ISO 5509) and then analyzed using GC.

The dimer fatty acids to be used can be obtained as commercial products. Examples include Radiacid 0970, Radiacid 0971, Radiacid 0972, Radiacid 0975, Radiacid 0976 and Radiacid 0977 from Oleon, Pripol 1006, Pripol 1009, Pripol 1012, and Pripol 1013 from Croda, Empol 1008, Empol 1061 and Empol 1062 BASF and Unidyme 10 and Unidyme TI from Arizona Chemical.

Suitable dicarboxylic acids with 4 to 36 carbon atoms are selected from the group of succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, isophthalic acid, dimer fatty acids and mixtures thereof. Adipic acid, azelaic acid, sebacic acid and dimer fatty acids are particularly preferably used for the production of the polyamide (PA).

Suitable monocarboxylic acids with 2 to 22 carbon atoms are preferably selected from the group of acetic acid, propionic acid, butyric acid, pentanoic acid, caproic acid, oenanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, 12-hydroxystearic acid, oleic acid, behenic acid and mixtures thereof . Capric acid, 12-hydroxystearic acid and lauric acid are particularly preferably used to prepare the polyamide (PA).

In particularly preferred aqueous dispersions (D1) and (D2), the at least one polyamide (PA) is therefore a reaction product

 - A diamine with 2 to 34 carbon atoms, especially ethylenediamine, hexamethylene diamine, 1, 12-dodecamethylene diamine, 4,4'-diaminodiphenylmethane and dimer diamine and

a molar excess, based on the diamine, of a dicarboxylic acid having 4 to 36 carbon atoms, preferably 6 to 36 carbon atoms, in particular adipic acid, azelaic acid, sebacic acid and dimer fatty acids, and / or a monocarboxylic acid having 2 to 22 carbon atoms, preferably 12 to 18 carbon atoms, especially capric acid, 12-hydroxystearic acid and lauric acid.

The addition of aqueous dispersions (D1) or (D2) which contain the preferred polyamides (PA) leads to a particularly good avoidance of the aqueous basecoat material (bL2a) or (bL2-x) slipping off the layer underneath.

According to the first alternative A1 of the present invention, the polyamide (PA) used has an acid number of 15 to 60 mg KOH / g. It is particularly preferred in the context of the present invention if the polyamide (PA) has an acid number of 20 to 50 mg KOH / g. Determination methods for determining the acid number are known to the person skilled in the art. The acid number is preferably determined in accordance with DIN EN ISO 21 14 (date: June 2002). The acid number of the polyamides (PA) can in particular be controlled and adjusted by contacting and reacting the polyamide (PA) obtained after the reaction with at least one neutralizing agent, preferably via the amount of the neutralizing agent used. Surprisingly, it has been shown that only the use of aqueous dispersions (D1) which contain polyamides (PA) with an acid number of greater than 15 mg KOH / g prevents the base lacquer (bL2a) or (bL2-x) from slipping off the underlying layer. By contrast, aqueous dispersions containing polyamides (PA) with an acid number of less than 15 mg KOH / g cannot be incorporated homogeneously into the aqueous basecoats (bL2a) and (bL2-x) and therefore do not prevent slumping.

Dispersions (D1) and (D2) preferred in the context of the present invention contain neutralized polyamides (PA). It is therefore advantageous according to the invention if the polyamide (PA) is neutralized to 80 to 100% with a base, preferably with N, N-dimethylethanolamine or triethylamine.

Aqueous dispersions (D1) which have a certain solids content of polyamide (PA) are particularly preferably used. Preferred embodiments of the first alternative A1 are therefore characterized in that the aqueous dispersion (D1) has a solids content of 21 to 25% by weight, based on the total weight of the aqueous dispersion (D1). Surprisingly, it has been shown that only the use of aqueous dispersions (D1) with the above-mentioned solids contents prevents the basecoat (bL2a) or (bL2-x) from slipping off the layer below. By contrast, aqueous dispersions which have lower solids contents cannot be incorporated homogeneously into the aqueous basecoats (bL2a) and (bL2-x) and therefore do not lead to slumping being avoided.

Processes for the preparation of the polyamide (PA), in particular the previously preferred polyamides (PA), are known to the person skilled in the art. Thus, the polyamides (PA) can be obtained by reacting the diamine with an excess of dicarboxylic acid and / or monocarboxylic acid at temperatures of 150 to 200 ° C for a period of 2 to 10 hours. If necessary, azeotropic solvents such as xylene can be used.

According to a second alternative A2, the aqueous dispersion (D2) contains at least one amide wax (AW) in addition to at least one polyamide (PA), in particular the aforementioned special polyamides (PA). Certain amide waxes (AW) are advantageously contained according to the invention. It is therefore preferred according to the invention if the aqueous dispersion (D2) contains at least one amide wax (AW), the amide wax (AW) being a reaction product

 a monocarboxylic acid having 2 to 22 carbon atoms, preferably 12 to 18 carbon atoms, and

 - A diamine with 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms, and / or a monoamine with 2 to 22 carbon atoms, preferably 2 to 16 carbon atoms.

Suitable monocarboxylic acids having 2 to 22 carbon atoms are preferably the monocarboxylic acids described above in connection with the polyamide (PA). 12-Hydroxystearic acid, stearic acid, palmitic acid and lauric acid are particularly preferably used.

Suitable diamines with 2 to 12 carbon atoms are selected, for example, from the group of ethylenediamine, 1,4-diaminobutane, hexamethylenediamine, Metaxylylenediamine, 1, 10-decamethylene diamine, 1, 1 1 -undecamethylene diamine,

1, 12-dodecamethylene diamine and mixtures thereof. Particularly suitable diamines are metaxylylenediamine, ethylenediamine and hexamethylenediamine. Suitable monoamines with 2 to 22 carbon atoms are selected from the group of ethylamine, monoethanolamine, propylamine, butylamine, pentylamine, hexylamine, octylamine, decylamine, laurylamine, myristylamine, cetylamine, stearylamine, behenylamine and mixtures thereof. Cetylamine and monoethanolamine are particularly preferably used.

In aqueous dispersions (D2) used with particular preference, the at least one amide wax (AW) is therefore a reaction product

 a monocarboxylic acid having 2 to 22 carbon atoms, preferably 12 to 18 carbon atoms, in particular 12-hydroxystearic acid, stearic acid, palmitic acid and lauric acid, and

 - A diamine with 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms, especially metaxylylenediamine, ethylenediamine and hexamethylenediamine, and / or a monoamine with 2 to 22 carbon atoms, preferably 2 to 16 carbon atoms, especially cetylamine and monoethanolamine.

Processes for producing the amide wax (AW), in particular the previously preferred amide waxes (AW), are known to the person skilled in the art. For example, the amide waxes (AW) can be obtained by reacting the monocarboxylic acid with a diamine and / or monoamine at temperatures of 150 to 200 ° C. for a period of 2 to 10 hours. If necessary, azeotropic solvents such as xylene can be used.

Furthermore, it is preferred according to the invention if the polyamide (PA) and the amide wax (AW) are used in a specific weight ratio in the aqueous dispersions (D2). Preferred embodiments of the present invention are therefore characterized in that the aqueous dispersion (D2) has a weight ratio of polyamide (PA) to amide wax (AW) from 95: 5 to 40:60, preferably from 80:20 to 45:55. The addition of aqueous dispersions D2, which the weight ratios of polyamide mentioned above Containing (PA) to amide wax (AW) leads to a particularly good avoidance of slipping of the aqueous basecoat (bL2a) or (bL2-x) from the layer below.

To produce the aqueous dispersion (D1) or (D2), the neutralized polyamide (PA) or the mixture of neutralized polyamide (PA) and amide wax (AW) is dispersed in water. To facilitate the dispersion, the water can contain small amounts of organic solvents, such as aliphatic, alicyclic and aromatic hydrocarbons, ketones, esters, alcohols and ethers. Monocarboxylic acids having 2 to 22 carbon atoms, such as, for example, acetic acid, propionic acid, butyric acid, pentanoic acid, caproic acid, oenanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, 12-hydroxystearic acid, oleic acid, behenic acid and mixtures thereof. In addition, nonionic surfactants such as polyoxyalkylene alkyl ethers, polyoxyethylene alkyl aryl ethers, sorbitan fatty acid esters, polyoxyethylene ether, polyoxyethylene oxypropylene copolymers, and hydrogenated castor oil, and / or anionic surfactants, such as Alkylfettsäuresalze, alkyl sulfate ester salts, polyoxyethylene alkyl ether sulfates, alkylbenzene sulfonic acid salts, sulfosuccinates and organophosphate, be used to disperse the polyamide (PA) or the mixture of polyamide (PA) and amide wax (AW) in water.

The aqueous dispersion (D1) or (D2) of the polyamide (PA) or the mixture of polyamide (PA) and amide wax (AW) can be prepared by adding a neutralized solution of the polyamide (PA) or the mixture of neutralized polyamide ( PA) and amide wax (AW) in organic solvent to a heated solution of water and possibly surfactant. The aqueous solution preferably has temperatures of 30 to 80 ° C. In addition, it can be provided that the aqueous dispersion (D1) or (D2) produced is heated to 70 to 90 ° C. over a period of 20 to 24 hours.

The aqueous dispersion (D1) or (D2) is preferably used in a total amount of 0.05 to 1.0% by weight, based on the solids content of the basecoat material (bL2a) or (bL2-x). The use of the quantities listed above allows one effective prevention of slumping without negatively affecting the high and low viscosity of the basecoats.

According to a particularly preferred embodiment of the present invention, the aqueous dispersion (D1) or (D2) is added to a specific basecoat. It is therefore particularly advantageous according to the invention if the aqueous dispersion (D1) or (D2) is added to the basecoat (bL2a) or (bL2-a), which is applied directly to the first layer (S1). As previously stated, this basecoat has a higher layer thickness because it replaces the primer layer. Due to the higher layer thickness, this basecoat layer (BL2a) or (BL2-a) still contains high amounts of residual moisture after flashing off. After application of the wet clear coat (k) or another basecoat (bL2-b) or (bL2-z), it may happen that the first basecoat film (BL2a) or (BL2-a) is dissolved and slips off the substrate (S) . The addition of the aqueous dispersion (D1) or (D2) to the first basecoat (bL2a) or (bL2-a) reliably prevents this basecoat from slipping off, even in the case of high layer thicknesses and wet application of the other layers of lacquer.

According to the invention, the aqueous dispersion (D1) or (D2) is added to a basecoat (BL2a) or (BL2-x) directly during the production of the multilayer coating and immediately before application of the corresponding basecoat. In order to avoid unnecessary addition of the dispersion (D1) or (D2), however, it is preferred according to the invention if it is only added to the basecoat after slumping has occurred within the process for the production of multi-layer coatings. A particularly preferred embodiment of the present invention is therefore characterized in that the addition of the aqueous dispersion (D1) or (D2) takes place after the slipping of the base coat layer (BL2) or at least one of the base coat layers (BL2-x), the aqueous Dispersion (D1) or (D2) is added to that basecoat (bL2a) or at least one of the basecoats (bL2-x) which has slipped off the underlying paint layer. The post-additives of the basecoats (bL2a) or (bL2-x) during the production of the multi-layer coating can be used to reliably and inexpensively eliminate slumping effects, but without the viscosities of the basecoats (bL2a) and (bL2-x) and to adversely affect the mechanical and optical properties of the multilayer coating obtained.

Step 3):

 In step (3) of the method according to the invention, a clear lacquer layer (K) is produced directly on the basecoat layer (BL2a) or the top basecoat layer (BL2-z). This is produced by applying a clear lacquer (k) accordingly.

The clear lacquer (k) can be any transparent coating agent known per se to the person skilled in the art in this sense. Transparent is to be understood to mean that a layer formed with the coating agent is not opaque in color, but is constituted in such a way that the color of the underlying basecoat structure is visible. As is known, this does not rule out the possibility that a clear lacquer can also contain pigments in minor quantities, which can support the color depth of the overall structure, for example.

These are aqueous or solvent-containing transparent coating compositions which can be formulated both as one-component and as two-component or multi-component coating compositions. Powder slurry clearcoats are also suitable. Solvent-based clearcoats are preferred.

The clear lacquers (k) used can in particular be curable thermally, chemically and / or chemically, actinically. In particular, they are thermo-chemically curable and cross-linking.

The clearcoats therefore usually and preferably contain at least one (first) polymer as a binder with functional groups and at least one crosslinker with a functionality which is complementary to the functional groups of the binder. At least one hydroxy-functional poly (meth) acrylate polymer is preferably used as the binder and a free polyisocyanate as the crosslinking agent. Suitable clear coats are described, for example, in WO 2006042585 A1, WO 2009077182 A1 or also WO 2008074490 A1.

The clear lacquer (k) is applied by the methods known to those skilled in the art for applying liquid coating compositions, for example by dipping, knife coating, spraying, rolling or the like. Spray application methods are preferably used, such as compressed air spraying (pneumatic application), and electrostatic spray application (ESTA).

The clear lacquer (k) or the corresponding clear lacquer layer (K) is preferably flashed off or temporarily dried at 15 to 35 ° C. for a period of 0.5 to 30 min after the application. Such flash-off or intermediate drying conditions apply in particular to the preferred case that the clear lacquer (k) is a chemically-thermally curable two-component coating agent. However, this does not rule out the fact that the clear lacquer (k) is a coating agent that can be hardened in another way and / or that other flash-offs or intermediate drying conditions are used.

The clear lacquer (k) is applied in such a way that the layer thickness of the clear lacquer layer after the curing in step (4) has a layer thickness of, for example, 15 to 80 micrometers, preferably 20 to 65 micrometers, particularly preferably 25 to 60 micrometers.

Of course, it is not excluded within the scope of the method according to the invention that after the application of the clear lacquer (k), further coating agents, for example further clear lacquers, are applied and in this way further coating layers, for example further ones

Clear lacquer layers are produced. Such further coating layers are then also cured, for example, in step (4) described below. However, preferably only one clear coat (k) is applied and then cured as described in step (4).

Step (4): In step (4) of the method according to the invention, the base lacquer layer (BL2a) and the clear lacquer layer (K) or the base lacquer layers (BL2-x) and the clear lacquer layer (K) are jointly hardened.

The common curing is preferably carried out at temperatures of 100 to 250 ° C, preferably 100 to 180 ° C for a period of 5 to 60 min, preferably 10 to 45 min. Such curing conditions apply in particular to the preferred case that the basecoat film (BL2a) or at least one of the basecoat films (BL2-x), preferably all basecoat films (BL2-x), are based on a chemically-thermally curable one-component coating agent. Because, as described above, such conditions are generally required in order to achieve curing of such a one-component coating composition as described above. If the clear coat (k) is, for example, also a chemically and thermally curable one-component coating agent, the corresponding clear coat (K) is of course also cured under these conditions. The same obviously applies to the preferred case that the clear coat (k) is a chemically-thermally curable two-component coating agent.

However, the foregoing does not rule out that the basecoats (bL2a) and (bL2-x) as well as the clearcoats (k) are curable coating agents in other ways and / or other curing conditions are used.

After step (4) of the process according to the invention has ended, a multilayer coating according to the invention results.

The method according to the invention allows the production of multi-layer coatings on substrates without a separate curing step. Nevertheless, the use of the method according to the invention results in multi-layer coatings which have excellent stability against pinpricks, so that even higher layer thicknesses of the corresponding basecoat layers can be built up without loss of aesthetic quality. In addition, an occurrence of slumping can be effectively eliminated with the method according to the invention, but without the mechanical or optical To adversely affect the properties of the multi-layer coatings and the viscosities of the basecoats mixed with the aqueous dispersion.

The invention is described in particular by the following embodiments:

 According to a first embodiment, the present invention relates to a method for producing a multilayer coating (M) on a substrate (S), comprising

(1) optionally producing a hardened first layer (S1) on the substrate (S) by applying a composition (Z1) to the substrate (S) and then curing the composition (Z1),

 (2) Production of a basecoat film (BL2a) or several directly sequential basecoat films (BL2-x) directly on the first layer (S1) by applying an aqueous basecoat film (bL2a) directly on the first layer (S1) or directly sequentially applying several aqueous basecoats (bl2-x) directly on the first layer (S1)

 (3) production of a clear lacquer layer (K) directly on the basecoat layer (BL2a) or the top basecoat layer (BL2-z) by applying a clear lacquer (kL) directly on the basecoat layer (BL2a) or the top basecoat layer (BL2-z),

(4) joint curing of the basecoat film (BL2a) and the clearcoat film (K) or the basecoat film (BL2-x) and the clearcoat film (K),

characterized in that

the at least one basecoat (bL2a) or at least one of the basecoats (bL2-x) directly before application

 with an aqueous dispersion (D1) containing at least one polyamide (PA) with an acid number of 15 to 60 mg KOH / g or

 is mixed with an aqueous dispersion (D2) containing at least one polyamide (PA) and at least one amide wax (AW).

According to a second embodiment, the present invention relates to a method according to embodiment 1, characterized in that the substrate (S) is selected from metallic substrates, plastics and their mixtures, in particular from metallic substrates. According to a third embodiment, the present invention relates to a method according to embodiment 1 or 2, characterized in that the composition (Z1) is an electro-dip coating (ETL1) which is applied electrophoretically to the substrate (S).

According to a fourth embodiment, the present invention relates to a method according to one of the preceding embodiments, characterized in that two directly successive basecoat layers (BL2-a) and (BL2-z) on the hardened first layer (S1) by applying an aqueous basecoat ( bL2-a) are produced directly on the first layer (S1) and immediately afterwards another aqueous basecoat (bL2-z) is applied directly on the first basecoat layer (BL2-a).

According to a fifth embodiment, the present invention relates to a method according to one of the preceding embodiments, characterized in that the basecoat (bL2a) or at least one of the basecoats (bL2-x), preferably all basecoats (bL2-x), are one-component coating compositions.

According to a sixth embodiment, the present invention relates to a method according to one of the preceding embodiments, characterized in that the basecoat (bL2a) or at least one of the basecoats (bL2-x), preferably all basecoats (bL2-x), have at least one polymer as a binder , selected from the group consisting of hydroxy-functional polyurethanes, polyesters, polyacrylates and copolymers of these polymers.

According to a seventh embodiment, the present invention relates to a method according to one of the preceding embodiments, characterized in that the basecoat (bL2a) or at least one of the basecoats (bL2-x), preferably all basecoats (bL2-x), at least one dye and / or contains effect pigment.

According to an eighth embodiment, the present invention relates to a method according to one of the preceding embodiments, characterized in that the basecoat (bL2a) or at least one of the basecoats (bL2-x), preferably all basecoats (bL2-x), at least one melamine resin as crosslinking agent contains. According to a ninth embodiment, the present invention relates to a method according to one of the preceding embodiments, characterized in that the at least one polyamide (PA) in the aqueous dispersion (D1) and (D2) is a reaction product

 - A diamine with 2 to 34 carbon atoms and

 a molar excess, based on the diamine, of a dicarboxylic acid having 4 to 36 carbon atoms, preferably 6 to 36 carbon atoms, or a mixture of a dicarboxylic acid having 4 to 36 carbon atoms, preferably 6 to 36 carbon atoms, and a monocarboxylic acid having 2 to 22 carbon atoms , preferably 12 to 18 carbon atoms.

According to a tenth embodiment, the present invention relates to a method according to one of the preceding embodiments, characterized in that the polyamide (PA) in the aqueous dispersion (D1) has an acid number of 20 to 50 mg KOH / g.

According to an eleventh embodiment, the present invention relates to a method according to one of the preceding embodiments, characterized in that the polyamide (PA) in the dispersion (D1) and (D2) is 80 to 100% with a base, preferably with N, N- Dimethylethanolamine or triethylamine, is neutralized.

According to a twelfth embodiment, the present invention relates to a method according to one of the preceding embodiments, characterized in that the aqueous dispersion (D1) has a solids content of 21 to 25% by weight, based on the total weight of the aqueous dispersion (D1)

According to a thirteenth embodiment, the present invention relates to a method according to one of the preceding embodiments, characterized in that the at least one amide wax (AW) in the dispersion (D2) is a reaction product

a monocarboxylic acid having 2 to 22 carbon atoms, preferably 12 to 18 carbon atoms, and - A diamine with 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms, and / or a monoamine with 2 to 22 carbon atoms, preferably 2 to 16 carbon atoms.

According to a fourteenth embodiment, the present invention relates to a method according to one of the preceding embodiments, characterized in that the aqueous dispersion (D2) has a weight ratio of polyamide (PA) to amide wax (AW) from 95: 5 to 40:60, preferably from 80 : 20 to 45:55.

According to a fifteenth embodiment, the present invention relates to a method according to one of the preceding embodiments, characterized in that the addition of the aqueous dispersion (D1) or (D2) to the basecoat (bL2a) or (bL2-a), which is directly on the first Layer (S1) is applied.

According to a sixteenth embodiment, the present invention relates to a method according to one of the preceding embodiments, characterized in that the aqueous dispersion (D1) or (D2) in each case in a total amount of 0.05 to 1.0% by weight, based on the Solids content of the basecoat (bL2a) or (bL2-x) is added.

According to a seventeenth embodiment, the present invention relates to a method according to one of the preceding embodiments, characterized in that the addition of the aqueous dispersion (D1) or (D2) after the slipping of the base coat layer (BL2a) or at least one of the base coat layers (BL2- x) takes place, the aqueous dispersion (D1) or (D2) being added to that basecoat (bL2a) or at least one of the basecoats (bL2-x) which has slipped off the paint layer underneath.

According to an eighteenth embodiment, the present invention relates to a method according to one of the preceding embodiments, characterized in that the joint blooming (4) is carried out at temperatures from 100 to 250 ° C. for a period of 5 to 60 minutes. Examples

Method description:

 1 . Solids content (solids, non-volatile content)

 The non-volatile content is determined in accordance with DIN EN ISO 3251 (date: June 2008). 1 g of sample are weighed into a previously dried aluminum dish and dried in a drying cabinet at 130 ° C. for 60 minutes, cooled in a desiccator, and then weighed back. The residue based on the total amount of the sample used corresponds to the non-volatile fraction. If necessary, the volume of the non-volatile component can be determined in accordance with DIN 53219 (date: August 2009).

2. Glass transition temperature Tg

The glass transition temperature T _g is determined experimentally in accordance with DIN 51005 "Thermal Analysis (TA) - Terms" and DIN 53765 "Thermal Analysis - Dynamic Differential Calorimetry (DDK)". A sample of 15 mg is weighed into a sample pan and inserted into a DSC device. It is cooled to the start temperature and then a 1. and 2nd measuring run with an inert gas purging (N2) of 50 ml / min with a heating rate of 10 K / min, with cooling to the starting temperature again between the measuring runs. The measurement is usually carried out in the temperature range from approximately 50 ° C. lower than the expected glass transition temperature to approximately 50 ° C. higher than the glass transition temperature. According to DIN 53765, point 8.1, the glass transition temperature in the context of the present invention is the temperature in the second measuring run at which half the change in the specific heat capacity (0.5 delta c _P ) is reached. It is determined from the DDK diagram (plot of the heat flow against the temperature). It is the temperature that corresponds to the intersection of the center line between the extrapolated baselines before and after the glass transition with the measurement curve.

3. Particle size

The mean particle size is determined by means of dynamic light scattering (photon correlation spectroscopy) (PCS) based on DIN ISO 13321 (date: October 2004) certainly. The mean particle size is the measured mean particle diameter (Z-average mean). A “Malvern Nano S90” (from Malvern Instruments) at 25 ± 1 ° C is used for the measurement. The device covers a size range from 3 to 3000 nm and is equipped with a 4mW He-Ne laser at 633 nm. The respective samples are diluted with particle-free, deionized water as the dispersion medium and then measured in a 1 ml polystyrene cuvette with a suitable scattering intensity . The evaluation was carried out using a digital correlator with the aid of the evaluation software Zetasizer Vers. 7.1 1 (from Malvern Instruments). It is measured five times and the measurements are repeated on a second, freshly prepared sample. With regard to the aqueous dispersion of the anionic polyacrylate (wD-PAC), the mean particle size is understood to mean the arithmetic number average of the measured average particle diameter (Z average mean; number average). The standard deviation of a 5-fold determination is <4%. the low viscosity at 1 / s the spray hme 2D curves)

To determine the low-viscosity of the waterborne basecoats (or the comparative compositions) according to the invention, the respective material, after setting the respective spray viscosity, using a rotary viscometer corresponding to DIN 53019-1 and calibrated according to DIN 53019-2 under tempered conditions (23.0 ° C ± 0 , 2 ° C) examined. The samples were sheared for 5 minutes with a shear rate of 1000 s ¹ (load phase) and then for 8 minutes with a shear rate of 1 s ^_1 (relief phase). The viscosity level after 8 minutes of relief phase (low-viscosity) is determined from the measurement data.

5. Determination of the acid number

The acid number is determined in accordance with DIN EN ISO 21 14 (date: June 2002), using "Method A". The acid number corresponds to the mass of potassium hydroxide in mg, which is used to neutralize 1 g of the sample in accordance with DIN EN ISO 21 14. The specified acid number corresponds to the total acid number specified in the DIN standard. 6. Determination of the OH number

 The OH number is determined in accordance with DIN 53240-2 (date: November 2007). The OH groups are reacted with an excess of acetic anhydride by acetylation. The excess acetic anhydride is then split up by adding water to the acetic acid and the entire acetic acid is back-titrated with ethanolic KOH. The OH number indicates the amount of KOH in mg, which is equivalent to the amount of acetic acid bound in the acetylation of 1 g of sample.

7. Determination of the number and weight average molecular weight

The number average molecular weight (M _n ) is determined by means of gel permeation chromatography (GPC) in accordance with DIN 55672-1 (date: August 2007). In addition to the number average molecular weight, this method can also be used to determine the weight average molecular weight (M _w ) and the polydispersity d (ratio of weight average molecular weight (M _w ) to number average molecular weight (Mn)). Tetrahydrofuran is used as the eluent. The determination is made against polystyrene standards. The column material consists of styrene-divinylbenzene copolymers.

8. Assessment of the incorporation of the additives and the homogeneity of the resulting

Basecoats

 The mixture of a waterborne basecoat with additive is assessed visually with regard to the incorporation of the additive or with regard to the homogeneity. The following criteria are used:

 a) Incorporation: It is assessed to what extent the additive can be mixed with the respective waterborne basecoat under defined stirring conditions. The decisive factor here is whether streaks, specks or the like result from the addition.

b) Homogeneity It is assessed to what extent a homogeneous mixture is formed after 10 minutes of stirring, ie whether the waterborne basecoat and the additive can be mixed into a single-phase mixture on the macroscopic scale or whether it can be weighed in or within form two or more phases a few minutes after stirring due to segregation.

 It is assessed qualitatively on a scale from 1 to 4 (1 = very easy to incorporate or very homogeneous, 2 = easy to incorporate or homogeneous, 3 = difficult to incorporate or inhomogeneous, 4 = very difficult to incorporate or very inhomogeneous).

To validate the incorporation or homogeneity, two thirds of a commercially available 1 liter tin can (diameter: approx. 1 10 mm / height: approx. 140 mm) is filled with the appropriate water-based paint. After the additive has been added, the mixture is stirred for 10 minutes using a conventional laboratory mixer (for example from Vollrath, model EWTHV 0.5) using a Lenart disc (diameter: 65 mm). It is important to ensure that a simplified Reynold number for stirring processes Re'R of at most 1000 is achieved, so that essentially a laminar mixing takes place, but no dispersion work due to turbulence.

The Reynold number for stirring processes ReR is known to the person skilled in the art; it is defined as

 in which

p = density in ^kg-NRR3

d = diameter of the stirring blade in m

n = speed in s ^_1 and

h = dynamic viscosity in kg-no ¹ -s ^-1

The density of a representative waterborne basecoat was determined using DIN 53217-2: 1991-03. The determined value of 1 135 kg-no ³ is assumed in a simplified manner for all water-based paints used in step (2) in the process according to the invention. For the actually shear-dependent dynamic viscosity, a value of 0.1 Pa-s is assumed for all samples, so that the following term results for the simplified Reynold number for stirring processes Re'R:

Re ' _R 11350 sm ^{~ 2} d ² n 9. Assessment of the appearance of stoves and runners

 To determine the tendency of a coating composition (or a comparative coating composition) according to the invention, multi-layer coatings are produced in accordance with DIN EN ISO 28199-1 (date: January 2010) and DIN EN ISO 28199-3 (date: January 2010) according to the following general specification :

 A perforated plate with dimensions 57 cm x 20 cm made of steel (according to DIN EN ISO 28199-1, point 8.1, version A) coated with a standard KTL (CathoGuard® 800 from BASF Coatings GmbH) is made analogous to DIN EN ISO 28199-1 , Point 8.2 (version A) prepared. Then, in accordance with DIN EN ISO 28199-1, point 8.3, the appropriate water-based lacquer is applied without tension using a rotary atomizer in a single application as a wedge with a target layer thickness (layer thickness of the dried material) in the range from 5 pm to 40 pm. The resulting water-based lacquer layer is dried after a flash-off time of 18 minutes at 18-23 ° C. in a forced air oven for 10 minutes at 70 ° C. The sheets are flashed off and dried vertically.

The inclination of the rotor is determined according to DIN EN ISO 28199-3, point 4. In addition to the layer thickness at which a runner exceeds the length of 10 mm from the lower edge of the hole, the layer thickness is determined from which a first runner inclination can be visually observed at a hole.

10. Determination of the dry layer thickness

 The layer thicknesses are determined in accordance with DIN EN ISO 2808 (date: May 2007), method 12A, using the MiniTest® 3100 - 4100 measuring device from ElektroPhysik.

1 1. Determination of the slip behavior of water-based lacquer wedge structures

 To assess the slip behavior of water-based lacquer wedge structures, wedge-shaped multi-layer coatings are produced according to the following general rule:

A diagonally perforated steel sheet with the dimensions 20 x 50 cm is coated with a standard KTL (CathoGuard® 500 from BASF Coatings,) Provide one longitudinal edge with 2 adhesive strips (Tesaband, 19 mm) (after the application of the first water-based lacquer (bL2-a), the first adhesive strip, after the application of the second water-based lacquer (bL2-z), the second adhesive strip is removed), after the coating To be able to determine differences in layer thickness. The first waterborne basecoat (bL2-a) is applied without tension in a single application using a rotary atomizer as a wedge with a target layer thickness (layer thickness of the dried material) of 5-40 pm. After a flash-off time of 4 minutes at room temperature, the second basecoat (bL2-z) is applied electrostatically as a constant layer with a target layer thickness of 12-15 pm.

After a further 20 minutes of flashing off at room temperature, a commercially available two-component clear lacquer (ProGloss® from BASF Coatings GmbH) is applied with a dry layer thickness of 40 to 45 pm. The resulting clear coat is flashed off at room temperature for 10 minutes. Then it is cured in a forced air oven at 140 ° C for 20 minutes.

The layer thickness of the first basecoat layer (BL2-a), from which the first basecoat layer (BL2-a) slides, is determined.

Embodiments

 The following examples and comparative examples serve to explain the invention, but are not to be interpreted as restrictive.

With regard to the specified formulation components and their amounts, the following must be taken into account. If reference is made to a commercial product or a manufacturing specification described elsewhere, it is exactly this commercial product or exactly the product manufactured with the referenced specification that is meant, regardless of the main name of the component selected.

So if a formulation component has the main name "melamine formaldehyde resin" and a commercial product is specified, the melamine formaldehyde resin is used as exactly this commercial product. Any other constituents such as solvents that may be present in the commercial product must therefore be taken into account if the amount of active substance (melamine formaldehyde resin) is to be inferred.

If, therefore, reference is made to a manufacturing instruction for a formulation constituent and, for example, a polymer dispersion with a certain solid results in this production, then this dispersion is used exactly. It is irrelevant whether the main term used is the term "polymer dispersion" or only the active substance, for example "polymer", "polyester" or "polyurethane-modified polyacrylate". This must be taken into account if the amount of active substance (polymer) is to be deduced.

1 . Production of a mixed lacquer ML1

Based on the patent specification EP 1534792 - B1, column 11, lines 1-13, 81.9 parts by weight of deionized water, 2.7 parts by weight of Rheovis® AS 1 130 (available from BASF SE), 8.9 parts by weight of 2.4, 7,9-tetramethyl-5-decindiol, 52% in BG (available from BASF SE), 3.2 parts by weight of Dispex Ultra FA 4437 (available from BASF SE) and 3.3 parts by weight of 10% dimethylethanolamine mixed in water; the resulting mixture is then homogenized. 2. Production of color pastes

 2.1 Production of a white paste P1

 The white paste P1 is made from 50 parts by weight of titanium rutile R-960-38, 1 1 part by weight of a polyester produced according to Example D, column 16, lines 37-59 of DE 40 09 858 A1, 16 parts by weight of a according to the international patent application WO 92 / 15405, page 15, lines 23-28 prepared binder dispersion, 16.5 parts by weight of deionized water, 3 parts by weight of butylglycol, 1.5 parts by weight of 10% dimethylethanolamine in water and 1.5 parts by weight of Pluriol® P900, available from BASF SE.

2.2 Production of a white paste P2

 The white paste P2 is made from 50 parts by weight of titanium rutile 2310, 6 parts by weight of a polyester produced in accordance with Example D, column 16, lines 37-59 of DE 40 09 858 A1, 24.7 parts by weight of one in accordance with the patent application EP 022 8003 B2, p. 8, lines 6 to 18 prepared binder dispersion, 10.5 parts by weight of deionized water, 4 parts by weight of 2,4,7,9-tetramethyl-5-decindiol, 52% in BG (available from BASF SE), 4.1 parts by weight of butyl glycol , 0.4 part by weight of 10% dimethylethanolamine in water and 0.3 part by weight of Acrysol RM-8 (available from The Dow Chemical Company).

2.3 Production of a black paste P3

 The black paste P3 is made from 57 parts by weight of a polyurethane dispersion prepared according to WO 92/15405, page 13, line 13 to page 15, line 13, 10 parts by weight of carbon black (carbon black Monarch® 1400 from Cabot Corporation), 5 parts by weight of a polyester , prepared according to Example D, column 16, lines 37-59 of DE 40 09 858 A1, 6.5 parts by weight of a 10% aqueous dimethylethanolamine solution, 2.5 parts by weight of a commercially available polyether (Pluriol® P900, available from BASF SE ), 7 parts by weight of butyl diglycol and 12 parts by weight of deionized water.

2.4 Production of a black paste P4

The black paste P4 is made from 58.9 parts by weight of a polyurethane dispersion prepared in accordance with WO 92/15405, page 13, line 13 to page 15, line 13, 10.1 parts by weight of carbon black (Color Black FW2 from Orion Engineered Carbons), 5 parts by weight of one Polyester, produced according to Example D, column 16, lines 37-59 of DE 40 09 858 A1,

7.8 parts by weight of a 10% aqueous dimethylethanolamine solution, 2.2 parts by weight of a commercially available polyether (Pluriol® P900, available from BASF SE), 7.6 parts by weight of butyl diglycol and 8.4 parts by weight of deionized water.

2.5 Production of a yellow paste P5

 The yellow paste P5 is made from 37 parts by weight of Bayferrox 3910 (available from Lanxess), 49.5 parts by weight of an aqueous binder dispersion 7.5 prepared according to WO 91/15528, page 23, lines 26 to page 25, line 24 Parts by weight of Disperbyk®-184 (available from BYK-Chemie GmbFI) and 6 parts by weight of deionized water.

2.6 Production of a yellow paste P6

 The yellow paste P6 is made from 17.3 parts by weight of Sicotrans yellow L 1916, available from BASF SE, 18.3 parts by weight of a polyester produced according to Example D, column 16, lines 37-59 of DE 40 09 858 A1, 43.6 parts by weight a binder dispersion prepared according to international patent application WO 92/15405, page 15, lines 23-28, 16.5 parts by weight of deionized water and 4.3 parts by weight of butyl glycol.

2.1 Production of a white paste P7

 The white paste P7 is made from 30.0 parts by weight of titanium rutile MT-500 HD, available from Tayca Corp., 62.9 parts by weight of a binder dispersion prepared according to international patent application WO 92/15405, page 15, lines 23-28, 3.8 parts by weight Deionized water, 2.0 parts by weight of Pluriol® P900 (available from BASF SE), 0.4 parts by weight of 10% dimethylethanolamine in water and 0.9 parts by weight of Aerosil® R 972 (available from Evonik).

2.8 Production of a P8 silica paste

The silica paste P8 is made from 12.0 parts by weight of Syloid® ED 3, available from WR Grace & Co., 30.0 parts by weight of a polyester produced in accordance with Example D, column 16, lines 37-59 of DE 40 09 858 A1, 46, 0 parts by weight of butylglycol and 12.0 parts by weight of 10% dimethylethanolamine in water. 2.9 Making a P9

 The blue paste P9 is made from 33.0 parts by weight of Heucodur® Blau 550 (available from Heubach GmbH), 52.0 parts by weight of an aqueous binder dispersion prepared in accordance with WO 91/15528, page 23, line 26 to page 25, line 24, 5.7 parts by weight of deionized water, 3.0 parts by weight of Pluriol® P900 (available from BASF SE), 4.0 parts by weight of Disperbyk®-184 (available from BYK-Chemie GmbH), 2.0 parts by weight of a 3% by weight aqueous solution Rheovis® AS 1 130 solution (Rheovis® AS 1 130 available from BASF SE) and 0.3 part by weight of Agitan 282 (available from Münzing Chemie GmbH).

2.10 Production of a green paste P10

The green paste P10 is made from 35.6 parts by weight of Daipyroxide Green 9320 (available from Dainichiseika Color & Chemicals Mfg. Co., Ltd.), 50.5 parts by weight of one according to WO 91/15528, p. 23, lines 26 to p. 25 , No. 24 prepared aqueous binder dispersion, 6.1 parts by weight of deionized water, 3.2 parts by weight of Pluriol® P900 (available from BASF SE), 4.3 parts by weight of Disperbyk®-184 (available from BYK-Chemie GmbH), and 0.3 Parts by weight of Agitan 282 (available from Münzing Chemie GmbH).

3. Production of aqueous basecoats

Unless stated otherwise, the parts are parts by weight and percentages are percentages by weight.

3.1 Production of water-based paints WBL A1 and WBL A2

The components listed in Table 3.1 are stirred together in the order given to form an aqueous mixture. The mixture is then stirred for 10 minutes and with the aid of deionized water and dimethylethanolamine to a pH of 8.0 ± 0.2 and a spray viscosity of 100 ± 10 mPa s at a shear stress of 1291 s ^_1 (WBL A1) or 85 ± 10 mPa s at a shear stress of 1000 s ¹ (WBL A2), measured with a rotary viscometer (Rheolab GC device with temperature control system C-LTD80 / GC from Anton Paar) at 23 ° C. Table 3.1: Production of water-based paints WBL A1 and WBL A2

3.2 Production of the waterborne basecoat WBL B1

The components listed in Table 3.2 under "aqueous phase" are mixed together in the order given to form an aqueous mixture. In the next step, a premix is made from the components listed under "Aluminum pigment premix". This premix is added to the aqueous mixture. After the premix has been added, the mixture is stirred for 10 minutes. Then, using deionized water and dimethylethanolamine, a pH of 8 and a spray viscosity of 70 ± 10 mPa s at a shear load of 1291 s ^-1 , measured with a rotary viscometer (Rheolab QC device with temperature control system C-LTD80 / QC from Anton Paar) at 23 ° C. Table 3.2: Production of the waterborne basecoat WBL B1

Aluminum pigment premix:

3.3 Production of water-based paints WBL B2 and WBL B3

The components listed in Table 3.3 under "aqueous phase" are stirred together in the order given to form an aqueous mixture. In the next step, a premix is made from the components listed under "Aluminum pigment premix" or "Micapigment premix". These premixes are added separately to the aqueous mixture. After adding a premix, the mixture is stirred for 10 minutes in each case. Then, using deionized water and dimethylethanolamine, a pH of 8 and a spray viscosity of 85 ± 10 mPa s at a shear stress of 1000 s ^-1 , measured with a rotary viscometer (Rheolab QC device with temperature control system C-LTD80 / QC from Anton Paar) at 23 ° C. Table 3.3: Manufacture of water-based paints WBL B2 and WBL B3

3.4 Post-additives of the waterborne basecoats WBL A1 and WBL A2

The quantities of additive (= aqueous dispersion containing at least one polyamide (PA) and / or amide wax (AW)) listed in Tables 3.4, 3.5 and 3.6 are added to each of the waterborne basecoats WBL A1 and WBL A2 then stirred for 10 minutes. With the help of deionized water, a spray viscosity of 100 ± 10 mPa s with a shear stress of 1291 s ^_1 (WBL A1a to WBL A1d) or 85 ± 10 mPa s with a shear stress of 1000 s ^_1 (WBL A2a to WBL 2j) , measured with a rotary viscometer (Rheolab QC with temperature control system C-LTD80 / QC from Anton Paar) at 23 ° C.

Table 3.4: Production of waterborne basecoats WBL A1a to WBL A1d

Additive content (% by weight solids) 0.1%

¹⁾ Aqueous dispersion (D1) of polyamide (PA), solids content 22.5% by weight, acid number 24 mg KOH / g

²⁾ Aqueous dispersion (D2) of polyamide (PA) and amide wax (AW), solids content 15% by weight, acid number 8.7 mg KOH / g

Table 3.5: Production of waterborne basecoats WBL A2a to WBL A2f

 Share of additive

(Wt% solids ff)

¹⁾ Aqueous dispersion (D2) of polyamide (PA) and amide wax (AW), solids content 15% by weight, acid number 8.7 mg KOH / g

²⁾ Aqueous dispersion (D2) of polyamide (PA) and amide wax (AW), solids content 10% by weight, acid number 7.5 mg KOH / g

³⁾ Aqueous dispersion (D1) of polyamide (PA), solids content 22.5% by weight, acid number 24 mg KOH / g,

⁴⁾ Aqueous dispersion of polyamide (PA), solids content 20% by weight, acid number 12.5 mg KOH / g,

⁵⁾ Aqueous dispersion of polyamide (PA), solids content 15% by weight, acid number 14 mg KOH / g, Table 3.6: Production of waterborne basecoats WBL A2g to WBL A2j

Share of post-additive (wt% solids) ,,, 0.20%

⁶⁾ Aqueous dispersion of polyamide (PA), solids content 18% by weight, acid number 12.5 mg KOH / g,

⁷⁾ 30% by weight aqueous Rheovis® AS 1 130 solution (BASF SE)

⁸⁾ 50% by weight solution of Rheovis® PU 1250 in butyl glycol (BASF SE)

4. Influence of post, on water-based paints

 4.1 Comparison between the water-based paints WBL A1 and WBL A1a to WBL A1d with regard to the occurrence of slipping

 The tests on the waterborne basecoats WBL A1 and WBL A1a to WBL A1d (containing different additives in different amounts) in combination with WBL B1 with regard to the occurrence of slipping were carried out qualitatively according to the method described above (see point 11 of the method description). Table 4.1 summarizes the results.

Table 4.1: Comparison of the behavior of WBL A1 (without additive) or WBL A1 a to

WBL A1 b (with additive) regarding the occurrence of slipping

If the WBL A1 sample is used as the first waterborne basecoat (bL2-a) in combination with WBL B1 as the second waterborne basecoat (bL2-z) in a multi-layer coating according to the method described above, the phenomenon of slipping occurs and the final coating is unacceptable describe. If, on the other hand, an aqueous dispersion (D1) (WBL A1a) or (D2) (WBL A1 b to WBL A1d) is added to the first basecoat WBL A1 (bL2-a) shortly before application, the first waterborne basecoat layer (BL2-a ) no longer from the one below Layer (S1) and the coated substrate (S) meets the high quality requirements of OEM painting. The method according to the invention therefore makes it possible to significantly improve the quality of the multi-layer coating obtained and to avoid waste paint.

4.2 Comparison between the water-based paints WBL A2 and WBL A2a to WBL A2i with regard to the incorporation of the additive

 The investigations on the waterborne basecoats WBL A2 (no additive) and WBL A2a to WBL A2j (containing different additives in different amounts) in combination with WBL B2 or WBL B3 with regard to the incorporation of the additive, the influence on the low viscosity and the occurrence of slipping were carried out according to the method described above (see point 8 of the method description).

Table 4.2: Results of the investigations into the incorporation of the respective additive

 1 = very easy to incorporate or very homogeneous, 2 = easy to incorporate or homogeneous, 3 = difficult to incorporate or inhomogeneous, 4 = very difficult to incorporate or very inhomogeneous

In the case of waterborne basecoats WBL A2a to WBL A2d, which contain either an aqueous dispersion (D1) (WBL 2d) or an aqueous dispersion (D2) (WBL 2a to WBL 2c), the post-additization of WBL A2 proved to be very good or . Good. The respective dispersions (D1) or (D2) could be worked in with moderate energy input, which can be realized at maximum for the subsequent additivation of a material at the OEM customer, and led to very homogeneous mixtures. In contrast, the dispersions of polyamides (PA), which have acid numbers of less than 15 mg KOH / g, (WBL A2e to WBL A2g) were not only significantly more difficult to incorporate, but their incorporation sometimes led to significant inhomogeneities.

The use of the ASE thickener (ASE = alkali swellable emulsion) Rheovis® AS 1 130 (WBL A2h and WBL A2i) and the non-ionic polyurethane thickener Rheovis® PU 1250 (WBL A2j) was also possible without problems during incorporation and led to very homogeneous mixtures.

4.3 Comparison between the waterborne basecoats WBL A2 and WBL A2a to WBL A2i with regard to the influence of the additive on the low-viscosity

A major disadvantage of the Rheovis® PU 1250 thickener was that the post-additivation of WBL A2 with this component led to a very significant increase in high-shear viscosity (spray viscosity at 1000 s ^-1 ). As a consequence, a lot of water had to be added to set the appropriate spray viscosity (see Table 4.3). This in turn had the consequence that the solid as well as the low-viscosity (at 1 s ^-1 ) of WBL A2j was significantly lower than that of WBL A2, which has a negative impact on rotor stability and slipping behavior (see Table 4.4). On the other hand, the amount of water required to adjust the spray viscosity after post-additivation is significantly lower with water-based paint WBL A2c, and there is no significant decrease in low-viscosity (see Table 4.3 and item 4 of the method description)

Table 4.3: Results of the investigations regarding the influence of post

Additive to low and high shear viscosity

 Low viscosity at 1 / s (after on

the spray viscosity) [mPa-s]

4.4 Comparison between the water-based paints WBL A2 and WBL A2a to WBL A2i with regard to the occurrence of slipping

The experimental data compiled in Table 4.4 show that the waterborne basecoats WBL A2a to WBL A2d in combination with WBL B2 or WBL B3 not only have a significantly better tendency to run compared to the respective reference, but also a significantly improved tendency to slip. WBL A2j, containing the non-ionic polyurethane thickener Rheovis® PU 1250, is clear more critical than the reference. The use of the ASE thickener Rheovis® AS 1130 (WBL A2h and WBL A2i) does not lead to a significant improvement in the tendency to run or slip. Table 4.4: Results of the investigations regarding the influence of post

Additive to the tendency to run and slip

It is therefore apparent from the tests that the addition of an aqueous dispersion (D1) or (D2) can significantly reduce the tendency of water-based paints to run and slip in multi-layer coatings, but without negatively affecting the low or high-shear viscosity and thus the application properties . The method according to the invention therefore makes it possible in a simple manner to adapt the properties of waterborne basecoats such that the waterborne basecoat film no longer slides off. As a result of the post-additivation, water-based paints can also be used for the production of multi-layer coatings, which, without post-additization, lie outside the specification in terms of the runner and slip properties and can therefore not be used further.

Claims

Expectations

1 . A method for producing a multi-layer coating (M) on a substrate (S), comprising

 (1) if appropriate, producing a hardened first layer (S1) on the substrate (S) by applying a composition (Z1) to the substrate (S) and subsequently curing the composition (Z1),

 (2) Production of a basecoat film (BL2a) or several directly sequential basecoat films (BL2-x) directly on the first layer (S1) by applying an aqueous basecoat film (bL2a) directly on the first layer (S1) or directly sequentially applying several aqueous basecoats (bl2-x) directly on the first layer (S1)

 (3) production of a clear lacquer layer (K) directly on the basecoat layer (BL2a) or the top basecoat layer (BL2-z) by applying a clear lacquer (kL) directly on the basecoat layer (BL2a) or the top basecoat layer (BL2-z),

(4) joint curing of the basecoat film (BL2a) and the clearcoat film (K) or the basecoat film (BL2-x) and the clearcoat film (K),

characterized in that

the at least one basecoat (bL2a) or at least one of the basecoats (bL2-x) directly before application

 with an aqueous dispersion (D1) containing at least one polyamide (PA) with an acid number of 15 to 60 mg KOH / goder

 is mixed with an aqueous dispersion (D2) containing at least one polyamide (PA) and at least one amide wax (AW).

2. The method according to claim 1, characterized in that the substrate (S) is selected from metallic substrates, plastics and mixtures thereof, in particular from metallic substrates.

3. The method according to any one of claims 1 or 2, characterized in that two directly successive basecoat layers (BL2-a) and (BL2-z) on the hardened first layer (S1) by applying an aqueous basecoat (bL2-a) directly on the first layer (S1) and immediately subsequent application of a further aqueous basecoat material (bL2-z) are produced directly on the first basecoat film (BL2-a).

4. The method according to any one of the preceding claims, characterized in that the basecoat (bL2a) or at least one of the basecoats (bL2-x), preferably all basecoats (bL2-x), are one-component coating compositions.

5. The method according to any one of the preceding claims, characterized in that the basecoat (bL2a) or at least one of the basecoats (bL2-x), preferably all basecoats (bL2-x), at least one polymer as a binder selected from the group consisting of contains hydroxy-functional polyurethanes, polyesters, polyacrylates and copolymers of these polymers.

6. The method according to any one of the preceding claims, characterized in that the basecoat (bL2a) or at least one of the basecoats (bL2-x), preferably all basecoats (bL2-x), contains at least one coloring and / or effect pigment.

7. The method according to any one of the preceding claims, characterized in that the basecoat (bL2a) or at least one of the basecoats (bL2-x), preferably all basecoats (bL2-x), contains at least one melamine resin as crosslinking agent.

8. The method according to any one of the preceding claims, characterized in that the at least one polyamide (PA) in the dispersion (D1) and (D2) from a reaction product

 - A diamine with 2 to 34 carbon atoms and

 a molar excess, based on the diamine, of a dicarboxylic acid having 4 to 36 carbon atoms, preferably 6 to 36 carbon atoms, or a mixture of a dicarboxylic acid having 4 to 36 carbon atoms, preferably 6 to 36 carbon atoms, and a monocarboxylic acid having 2 to 22 carbon atoms , preferably 12 to 18 carbon atoms.

9. The method according to any one of the preceding claims, characterized in that the at least one polyamide (PA) in the dispersion (D1) and (D2) to 80 to 100% with a base, preferably with N, N-dimethylethanolamine or triethylamine, neutralized is.

10. The method according to any one of the preceding claims, characterized in that the at least one polyamide (PA) in the aqueous dispersion (D1) has an acid number of 20 to 50 mg KOH / g

1 1. Method according to one of the preceding claims, characterized in that the at least one amide wax (AW) in the dispersion (D2) from a reaction product

 a monocarboxylic acid having 2 to 22 carbon atoms, preferably 12 to 18 carbon atoms, and

 - A diamine with 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms, and / or a monoamine with 2 to 22 carbon atoms, preferably 2 to 16 carbon atoms.

12. The method according to any one of the preceding claims, characterized in that the aqueous dispersion (D2) has a weight ratio of polyamide (PA) to amide wax (AW) from 95: 5 to 40:60, preferably from 80:20 to 45:55, having.

13. The method according to any one of the preceding claims, characterized in that the aqueous dispersion (D1) or (D2) is added to the basecoat material (bL2a) which is applied directly to the first layer (S1).

14. The method according to any one of the preceding claims, characterized in that the addition of the aqueous dispersion (D1) or (D2) after the slipping of the base coat layer (BL2a) or at least one of the base coat layers (BL2-x) takes place, the aqueous Dispersion (D1) or (D2) is added to that basecoat (bL2a) or at least one of the basecoats (bL2-x) which has slipped off the underlying paint layer.

15. The method according to any one of the preceding claims, characterized in that the common curing (4) is carried out at temperatures of 100 to 250 ° C for a period of 5 to 60 minutes.