MXPA99012064A - Transparent coating agents and the use thereof to produce multi-layered coatings - Google Patents

Abstract

The invention relates to transparent coating agents suitable for multi-layered coatings, containing self-crosslinking or external crosslinking bonding agents, organic solvents, various crosslinking agents in the case of external crosslinking bonding agents formaldehyde condensation resins, in addition to optional reactive diluents and usual varnish additives with an additional content of A) 0.1 to 3 wt.%urea compounds and B) 0.05 to 10 wt.%substances providing formaldehyde, in relation to solid resin bodies formed by the bonding agents, reactive diluents and crosslinking agents.

Description

MEANS OF COATING CLEAR LACQUER AND USING THEM FOR THE PRODUCTION OF MULTI-LAYER COATINGS This invention relates to baked clear lacquer coating means, to the use thereof for the production of multi-layered coatings, particularly multi-layered coatings of the basecoat / clearcoat type, and to a method of producing coatings of layers. multiple The current mass production of automotive lacquer coatings mainly consists of a coating of basecoat / coating lacquer that is applied to a previously coated bodywork. The baked clear lacquers which have been used in particular in practice are those comprising an interlacing agent-binder vehicle system based on a combination of hydroxy-functional binder vehicles and aminoplast resins. In baked clear lacquers like these, hydroxy-functional binder carriers and aminoplast interlacing agents are generally present in a solids content ratio of 50:50 to 90:10. Clear lacquer coatings that are produced from clear lacquer like these do not exhibit satisfactory resistance to acids. When there are increased demands for the acid resistance of clearcoat coatings, the use of clearcoat systems having other entanglement mechanisms is preferred, for example the use of clear lacquer systems such as those that intertwine with the formation of urethane groups or ester groups or with the formation of a CC bond. The visual and aesthetic impression of the double-layered coatings of base lacquer / clear lacquer is significantly influenced by the quality of the clear lacquer coating. In an ideal situation, the structure of the clear lacquer coating is identical on the horizontal and vertical surfaces of a three-dimensional substrate, for example of a body. However, in practice it is not easy to achieve the ideal situation described above. For example, there may be differences in the surface structure or the external flow of the clearcoat coating, since after application, and particularly during the heating phase of the baking process, the clearcoats tend to run off or run on the surface that depart from the horizontal as a result of a decrease in viscosity due to temperature. This risk is greater while the thickness of clear lacquer coating is greater. It is known from DE-C 27 51 761 and EP-A-0 198 519 that certain urea compounds can be used as additives in baked clear lacquers containing aminoplast resins as interlacing agents, to counteract the runoff phenomenon not desired clear lacquer. Furthermore, it is known from EP-A-0 192 304 that the urea compounds can be used as anti-drip agents in clear lacquers containing hydroxy-functional binder vehicles and crosslinking agents that are different from aminoplast resins.

Within the scope of the present invention, it has been demonstrated that the use of urea compounds in clear lacquers results in reduced brilliance and opaqueness (milky appearance) of the baked clear lacquer coatings. The phenomenon of opaqueness is particularly pronounced when clear coatings are formed on dark backgrounds, for example in basecoat coatings of a dark shade. The aim of the present invention is to provide clear lacquer coating means which are substantially free of aldehyde condensation resin crosslinking agents, which exhibit a reduced tendency to runoff, and which can harden to form clear acid resistant coatings, bright, not opaque. This objective is achieved with the use of clear lacquer coating means containing one or more self-ligating or externally interlacing binder vehicles., one or more organic solvents, in the case of externally crosslinkable binder vehicles containing one or more crosslinking agents that are different from the aldehyde condensation resins, optionally also containing one or more reactive thinners, and optionally also containing additives of use common for clear lacquers, which are characterized by an additional content of A) from 0.1 to 3% by weight of one or more urea compounds, and B) from 0.05 to 10% by weight of one or more substances that provide formaldehyde, with respect, in each case, to the solids content of the resin of the clear lacquer coating medium which is formed by binder carriers and by reactive thinners that are optionally present and by interlacing agents that are optionally present. The clear lacquer coating means according to the invention are thermally hardenable, and are what are called baked clear lacquer coating means, which harden at temperatures of 80 ° C and higher, for example above 160 ° C. In the clearcoat coating media according to the invention, the resin solids content is composed of a binder vehicle which can be thermally hardened by addition or condensation reactions, optionally plus a reactive slimming system, optionally plus a system of interlacing agent, which chemically intertwines during baking with the formation of covalent bonds. Binder vehicle systems that can be thermally hardened by addition and / or condensation reactions are binder vehicles that optionally are mixed with reactive thinners (compounds that are chemically incorporated into the lacquer film during baking) and optionally mixed with agents interleavers for the clear lacquer coating means, preferably for clear lacquer coating means which are those which can be used for the production of coatings of double layers of base lacquer / clear lacquer, and which are known from a multiplicity of documents of patent, for example. The clear lacquer coating means according to the invention are liquid. Contain organic solvents and one or more commonly used binder vehicles film formers; optionally contain one or more reactive thinners in addition, as well as one or more crosslinking agents in the case that the binder vehicles are not self-linking. In principle, neither the binder vehicles nor the crosslinking agents are subject to any restriction, although systems in which a significant portion of chemical entanglement due to aldehyde condensation resins are excluded, i.e. the coating means Clear lacquer according to the invention are substantially or completely free of aldehyde condensation resins. In particular, the clearcoat coating means according to the invention contain, with respect to their content of resin solids, less than 5, preferably less than 3, most preferably less than 1, for example from 0 to 1% by weight of aldehyde condensation resins. Particular examples of aldehyde condensation resins such as these include partially or completely alkylated aldehyde condensation resins which are common in lacquer technology as crosslinking agents for hydroxy-functional binder vehicles, for example phenol condensation resins. (form) aldehyde or aminoplast resins such as urea- (form) aldehyde or amine- (form) aldehyde condensation resins (eg melamine resins, benzoguanamine resins). The clearcoat coating means according to the invention are preferably externally interlacing systems, in which binder carriers are present which optionally contain reactive thinners and crosslinking agents, generally in a stoichiometric ratio, which is compared to the expected degree of intended entanglement, from 50 to 90% by weight of binder vehicles, from 0 to 20% by weight of reactive thinners and from 50 to 10% by weight of crosslinking agents, where the sum gives 100%. In principle, neither binder vehicles nor reactive thinners are subject to any restriction. Nor is there any restriction on the selection of interlacing agents which are optionally contained. This depends on the functionality of the binders vehicles, that is to say, the interlacing agents are chosen in such a way that they have a reactive functionality that is complementary to the functionality of the binders vehicles. In this regard, the use of the aldehyde condensation resins as crosslinking agents is substantially or completely prevented, as indicated above. For example, polyester, polyurethane and / or (meth) acrylic copolymer resins can be used as film-forming binder carriers. Binder vehicles, particularly polyester and polyurethane resins, are preferably substantially free of aromatic structural units and are based on aliphatic and / or cycloaliphatic components. The (meth) acrylic copolymer resins may contain aromatic structural units, for example in the form of styrene which is incorporated by polymerization. The functional groups of the self-linking system or of the preferred externally interlocking system can thermally react with each with addition and / or condensation. Some examples of addition reactions which are suitable for the entanglement of the systems include the addition of ring opening of an epoxide group to a carboxylic group with the formation of an ester group and a hydroxyl group, the addition of a hydroxyl group to a isocyanate group with the formation of a urethane group, and the Michael addition of an acidic CH group to a (meth) acryloyl group with CC bond. Examples of condensation reactions that are suitable for entanglement include the reaction of a hydroxyl group with a blocked isocyanate group, with formation of a urethane group and removal of the blocking agent; the transesterification reaction of a hydroxyl group with an ester group with separation of the esterification alcohol; and the transurethanization reaction of a hydroxyl group with a carbamate group with alcohol separation. Provided they are compatible with each other, a plurality of functionalities can also coexist in a system that hardens thermally by means of addition or condensation reactions, so that two or more different types of the aforementioned reactions can occur during baking. Interlacing agents that are used in externally interlacing clear lacquer systems may be present individually or in a mixture. The clearcoat coating means according to the invention are preferably externally interlaxable clear lacquer coating means based on hydroxy-functional binder carriers. They may be single-component clear lacquer coating means, but are preferably two-component clear lacquer coating means. The one-component clear lacquer coating means according to the invention are those which contain as binder carriers hydroxy-functional (meth) acrylic copolymers, polyester resins and / or polyurethane resins, individually or as a mixture, and which optionally they also contain hydroxy-functional reactive slimming agents. Preferably, triazine-based crosslinking components and / or transesterification crosslinking agents which react with the hydroxyl groups of the hydroxy-functional binders and with the hydroxy-functional reactive slimming agents which are optionally contained, under the formation of ester groups and are optionally present as interlacing agents. / or blocked polyisocyanates. Preferred two-component clearcoats according to the invention are those which contain, as their binder carrier component, hydroxy-functional (meth) acrylic copolymers, polyester resins and / or polyurethane resins, individually or as a mixture, and optionally containing further hydroxy-functional reactive slurries, and containing free polyisocyanates as the crosslinking component. The binder vehicles preferably have a number average molecular weight (Pm) of 500 to 10,000, and a hydroxyl number of 30 to 450 mg KOH / g. Examples of hydroxy-functional polyester resins which are preferably used in the clearcoat coating medium according to the invention, include customary polyester resins, for example those with a number average molecular weight (Pm) of 500 to 5000. , preferably from 1000 to 3000, and hydroxyl numbers from 30 to 450, preferably from 50 to 280 mg KOH / g. Examples of hydroxy-functional polyurethane resins which are preferably used in the clearcoat coating media according to the invention, include customary polyurethane resins, for example those with a number average molecular weight (Pm) of 500 to 5000. , preferably from 1000 to 3000, and hydroxyl numbers from 30 to 450, preferably from 50 to 280 mg KOH / g. Examples of hydroxy-functional (meth) acrylic copolymers which can be used as preferred binder vehicles in the clearcoat coating media according to the invention, include the usual (meth) acrylic copolymers with a number average molecular weight ( Pm) between 1000 and 10,000 and hydroxyl numbers from 30 to 300, preferably 50 to 250 mg KOH / g. These (meth) acrylic copolymers can be produced, for example, in the presence of oligomeric or polymeric polyester and / or polyurethane resins, for example those mentioned in the preceding two paragraphs. Examples of hydroxyfunctional reactive liquid slimming agents that can be used in the clearcoat coating media according to the invention include low molecular weight compounds containing at least two hydroxyl groups per molecule and hydroxyl numbers in the 250 scale. to 700 mg KOH / g. Suitable oligomeric or polymeric polyols, such as polyether polyols, oligoester polyols, polycarbonate polyols and oligourethane polyols. Commercial products are suitable, such as for example polyols with polycaprolactone, which can be obtained by the reaction of polyols with caprolactone, polyether polyols, for example, triethylene glycol, which can be obtained by the reaction of oxirane compounds with polyols and / or water, or oligourethane polyols, which can be obtained by the reaction of polyamines with cyclic carbonates. Examples of polyisocyanates that can be used in free or blocked form in the clearcoat coating media according to the invention as crosslinking agents for hydroxy-functional binder vehicles, more optionally reactive thinners, include cycloaliphatic or aliphatic diisocyanates such as diisocyanate of tetramethylene, 1,6-hexamethylene diisocyanate, 1,1-dodecane diisocyanate, 1,3- and 1,4-d-cyclohexane isocyanate, sophorone diisocyanate, biscyclohexylmethane diisocyanate, or mixtures thereof. Apart from these simple isocyanates, others containing heteroatoms in the radical linking the isocyanate groups are also suitable.

Examples thereof include polyisocyanates containing carbodiimide groups, allophanate groups, isocyanurate groups, uretdione groups, urethane groups, adiated urea groups and / or biuret groups. Particularly suitable are the known polyisocyanates which are commonly used in the production of lacquers, for example modification products of the aforementioned simple isocyanates containing biuret, isocyanurate or urethane groups, particularly tris- (6-isocyanatohexyl) -biuret, the isocyanurate isophorone diisocyanate derivative or hexane diisocyanate, or low molecular weight polyisocyanates comprising urethane groups, such as those obtainable by the reaction of isophorone diisocyanate, which is used in excess, with simple polyhydric alcohols of molecular weight which it varies from 62 to 300, particularly with trimethylolpropane. Of course, any mixture of said polyisocyanates can be used. Other suitable polyisocyanates include the known prepolymers containing terminal isocyanate groups, such as those obtainable in particular by reacting the aforementioned simple polyisocyanates, mainly diisocyanates, with substoichiometric quantities of organic compounds containing at least two groups capable of reacting with isocyanate groups. The customary blocking agents, which are divided under the reaction conditions during the entanglement of the binder vehicles and hardeners, are suitable as blocking agents for the above-described polyisocyanate crosslinking agents. Examples include usual acidic CH blocking agents, or functional NH-, SH-, or OH- blocking agents. These can be used by themselves or in a mixture for blocking. Examples include acidic CH compounds such as acetylacetone, or CH acid esters such as alkyl acetoacetic acid esters, dialkyl malonic acid esters; aliphatic or cycloaliphatic alcohols, such as n-butanol, isopropanol, tert-butanol, furfurol, 2-ethylhexanol or cyclohexanol; oximes such as methyl ethyl ketoxime, acetone oxime, cyclohexanone oxime or acetophenone oxime, lactams such as epsilon-caprolactam or 2-pyrrolidine, imidazoles such as 2-methylimidazole, and pyrazoles such as 2,3-dimethylpyrazole. Preferred CH-acid esters and / or oximes are preferred as blocking agents. Examples of triazine-based components that are entangled in the clearcoat coating media according to the invention with hydrophobic-functional binder carriers, and with reactive thinners which are also optionally contained, with the formation of ester groups, particularly with the formation of urethane groups (carbamic acid ester groups), include customary transesterification crosslinking agents, such as for example tris (alkoxycarbonylamino) triazine, which is preferred. The clearcoat coating means according to the invention which are particularly preferred are those in which the resin solids consist of an externally interlacing system containing hydroxy-functional binder vehicles, particularly those based on (meth) acrylic copolymers, and free polyisocyanate as an entanglement agent. In the state in which they are susceptible to be applied as coatings, the clearcoat coating means according to the invention have a solids content which is formed from the resin solids and other non-volatile constituents, from 40 to 70% by weight. The volatile constituents which they contain are organic solvents such as glycol ethers, for example, butyl glycol, dipropylene glycol dimethyl ether, dipropylene glycol monomethyl ether or ethylene glycol dimethyl ether; glycol ether esters such as ethyl glycol acetate, butyl glycol acetate, 3-methoxy-n-butyl acetate, butyl diglycol acetate or methoxypropyl acetate; esters such as butyl acetate, butyl acetate or amyl acetate; ketones such as methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone or isophorone; alcohols such as methanol, ethanol, propanol, or butanol; aromatic hydrocarbons such as xylene, Solvesso 100 (Trademark of a mixture of aromatic hydrocarbons with a boiling scale of 155 to 185 ° C) and aliphatic hydrocarbons. The clearcoat coating means according to the invention contain, with respect to their resin solids content of 0.1 to 3, preferably 0.3 to 2, most preferably 0.5 to 1.5% by weight, of one or more compounds of urea (A) as anti-caking agents, that is to say as agents having a thixotropic effect or influencing the intrinsic viscosity and having a favorable effect on the dripping behavior of the clear lacquer coating means. They effectively prevent the unwanted run-off or drift of the clear lacquer coatings which are produced from the clear lacquer coating means according to the invention and which are applied to vertical surfaces. Examples of urea compounds (A) include the urea compounds which are known as anti-dropping agents of DE-C-27 51 761, EP-A-0 192 304 and EP-A-0 198 519 and which can be used in the clear lacquer baked. For baked clear lacquers, the problem of runoff is particularly evident during the baking process, due to the initial decrease in viscosity caused by the temperatures used. The urea compounds (A) are addition products of aromatic, araliphatic, cycloaliphatic or aliphatic diisocyanates and / or polyisocyanates derived therefrom (for example those of the isocyanurate type) and mono- and / or polyamines containing primary amino groups and / or secondary These addition products can be defined as low molecular weight compounds or oligomeric or polymeric addition products. The preferred urea (A) compounds are those in which a polyisocyanate and an amine have reacted in a stoichiometric ratio of 0.7-1.5 of primary and / or secondary amino groups per isocyanate group, most preferably in a stoichiometric ratio of amino groups to groups isocyanate of 1: 1. The addition products of diisocyanates preferably of aliphatic or cycloaliphatic diisocyanates, and primary amines, preferably primary monoamines, are more preferably preferred for use as urea compounds (A). The aliphatic or aromatic diisocyanates are preferably diisocyanates that have been synthesized with a symmetric structure. The urea compounds (A) which are used in the clearcoat coating media according to the invention are preferably chosen in such a way that they are solid, very preferably crystalline substances, since these are particularly effective anti-sinking agents. The particle size of the particles of (A) is preferably 0.1 to 20 μm. These solid or crystalline urea compounds (A) preferably have a high melting or solidification point, which in particular is higher than the firing temperatures prevailing during baking of the clearcoat coating means according to the invention, particularly about 80 ° C, for example between 80 and 250 ° C. The addition product formed from one mole of 1,6-hexane diisocyanate and 2 moles of benzylamine are preferably used as the urea compound (A) in the clearcoat coating media according to the invention. The urea compounds (A) can be produced in a customary manner by the addition of amines, which contain primary amino groups and / or secondary to polyisocyanates. In developing this process, the amine can be added to the polyisocyanate or the polyisocyanate can be added to the amine, or the reagents are added simultaneously. The addition of the polyisocyanate to the amine is preferred. The production is effected, for example, at temperatures between 20 and 80 ° C, for example in bulk and in the absence of solvent, but preferably in an inert solvent or very preferably in the presence of binder carriers or crosslinking agents that are inert under reaction conditions, for example in the presence of a solution of an inert binder vehicle or interlacing agent. A good, intensive mixture of the reaction system can be envisaged in the development of this process, by means of vigorous stirring, for example. If the production is carried out correspondingly to the most preferred process, generally in the presence of an inert binder vehicle or an interlacing agent, it can be carried out in the presence of a part or all of the binder vehicles or crosslinking agents which are present in the clear lacquer coating means. In the case where the clear lacquer coating medium contains more than one binder vehicle or more than one interlacing agent, production may be carried out, for example, in one of these binder vehicles or in one of these interlacing agents. It is essential that the binder vehicles or crosslinking agents which are used in the reaction medium for the production of urea compounds (A) are inert with respect to the reactants, ie under the prevailing reaction conditions they preferably do not react with the amine or the polyisocyanate, or that its reactivity in relation to these reagents is so slight that the reactants only react and react with one another, and therefore react fully to form the desired urea compound (A). Preferably, a process is employed in which the urea compounds (A) which are formed are precipitated or crystallized as a finely divided solid in the binder vehicle or the binder vehicle solution or in the crosslinking agent or interlacing agent solution., for example during or after the completion of the addition reaction, and during or after cooling, for example. Dispersions such as these, comprising urea compounds (A) which are present as a finely divided solid, preferably as a crystalline solid, in the binder vehicle (solution) or crosslinking agent (solution), can also be prepared by melting and distributing finely the urea compounds (A) in the binder vehicle (solution) or interlacing agent (solution), and subsequently cooling below the solidification or melting point of the urea compounds (A). This method is particularly suitable if the binder vehicles (binder vehicle solutions) or crosslinking agents (interleaving agent solutions) are used which are not inert in the sense explained above. The production of the clear lacquer coating means is preferably effected by mixing urea compounds (A), preferably as a preparation, for example as a dispersion in a solvent or very preferably as a dispersion in part of the liquid or vehicle of binder or agent dissolved interlayer, with the remaining constituents of the clear lacquer coating medium. For example, the mixing can be carried out first with the remaining binder vehicles before adding the other constituents. If the clearcoat coating means according to the invention contains more than one binder vehicle, it is possible that the urea compounds (A) are present in a binder vehicle, the functional groups differing from the functional groups of the other binder vehicle or binder vehicles to be mixed. However, if the clearcoat coating means according to the invention does not contain more than one binder vehicle, it is preferred that the functional groups of the binder carriers are the same. Further details on the urea compounds (A) that can be used in the clearcoat coating media according to the invention, in the starting materials, and in the process and process parameters for the production of urea compounds (A ) and the incorporation thereof into the coating means can be found in DE-C-27 51 761, EP-A-0 192 304 and EP-A-0 198 519, to which reference is made, specifically , but not exclusively, in the present. The lacquer coating means according to the invention contain, with respect to their resin solids content, 0.05 to 10% by weight of one or more substances (B) that provide formaldehyde, where the upper limit is preferably 5 or 3. and the lower limit is preferably 0.1% by weight. Finally, these substances release formaldehyde during the baking of the clear lacquer coatings of the clear lacquer coating media. In this regard, it is particularly preferred that the clearcoat coating means according to the invention contain, with respect to its content of component (A), from 10 to 1000, preferably from 30 to 500% by weight of one or more substances (B) like these. Surprisingly, the object of the invention is achieved if the clear lacquer coating means according to the invention contain only small amounts of substances (B) that provide formaldehyde. This is surprising for two reasons. First, it is not known if production is achieved, which is theoretically possible to provide formaldehyde for (B). Second, it is particularly surprising that small quantities of substances (B) that provide formaldehyde in the clearcoat coating media according to the invention are sufficient, because a large proportion of the formaldehyde provided can escape as a gas in the the cases where clear lacquer layers are applied to large surface areas of clear lacquer coating means according to the invention. The substances (B) that finally provide formaldehyde during baking of the clear lacquer coatings that are produced from the clear lacquer coating media are defined, low molecular weight, oligomeric or polymeric compounds, which are suitable, under the conditions prevailing before or after the application of the clearcoat coating media according to the invention, or finally during the baking of the clearcoat coatings that they are produced from the clear lacquer coating means according to the invention, to provide formaldehyde. Preferably they do not provide formaldehyde until baking, that is under or during the prevailing conditions during baking. The supply of formaldehyde from the substances (B) under the conditions prevailing before or after the application of the clearcoat coating means according to the invention, or finally during the baking of the clearcoat layers produced from of the clear lacquer coating means according to the invention means that the substances (B) contain free formaldehyde as such, for example as an impurity, or that the formaldehyde is then released from the reaction products that were previously formed from ( B) and other constituents of the clearcoat coating media according to the invention or formed by hydrolysis of (B). If (B) contains formaldehyde, the content of free formaldehyde is less than 1% by weight with respect to (B). Substances (B) that provide formaldehyde can be present in dissolved or finely dispersed form in the clear lacquer coating means according to the invention. The substances (B) preferably only provide formaldehyde at elevated temperatures, and in particular only at the temperatures prevailing during baking of the clear lacquer coatings of the clear lacquer coating means according to the invention. In this regard, substances (B) can release formaldehyde as such or can liberate formaldehyde by reacting with other constituents of the clearcoat coating media according to the invention or by reacting with water due to hydrolysis. The water may be in the form of atmospheric moisture or as traces of water of the clear lacquer coating medium according to the invention, or it may originate from the previously applied lacquer coatings which are located under the clear lacquer coating. Intermediates can also be formed first, from which formaldehyde is subsequently released. It would be useful to catalyze the reactions that ultimately result in the release of formaldehyde. Acids in particular are examples of substances with catalytic action. These acids can be acid groups of the binder vehicles or crosslinking agents or can be acids which are added especially to the clearcoat coating media according to the invention, for example the acid catalysts which are commonly used for lacquers, such as acid phosphoric, acidic organophosphates or aromatic sulfonic acids in particular. As a rule, particularly when strong acids are used, acid catalysts are added in blocked form, for example blocked with an amine. The acid can be thermally released again therefrom. Substances (B) may be used. in the clear lacquer coating means according to the invention alone or in combination, and optionally they can be used as a special preparation made in advance, for example in the mixture with other substances that are not formaldehyde suppliers. In particular, the substances (B) are compounds that contain one or more formal or semiformal structural units, or that contain structural units comprising formaldehyde-derived or semi-aminal derivatives derived from formaldehyde, where these structural units can be constituents of heterocyclic ring. Examples of substances comprising structural units of this type include paraformaldehydes, polyoxymethylene glycols, urotropin, 1,3-oxazolidines which are not substituted in the 2-position, 1, 3-dioxolanes which are not substituted in the 2-position, addition products of alcohols with formaldehyde, such as glycerol formal, benzyl alcohol monosemiformal or polysemiformal benzyl alcohol, compounds containing N-methylol groups, compounds containing N-methyl ether groups, and (meth) acrylic copolymers containing N-methylol groups and / or N-methylol ether groups. Partially alkylated or partially formaldehyde condensation resins, such as those commonly used in lacquer technology, can also be used as crosslinking agents for hydroxy-functional binder vehicles, for example phenol-formaldehyde condensation resins or aminoplast resins as resins. of condensation of urea-formaldehyde or amine-formaldehyde, for example melamine resins or benzoguanamine resins. These are used in particular in an amount of less than 5% by weight with respect to the resin solids content of the clear lacquer coating means. In addition, the clearcoat coating means according to the invention can contain, in addition to the urea compounds (A), customary lacquer additives in customary amounts for lacquers, for example up to 5% by weight with respect to the lacquer as a whole, for example transparent pigments or extenders, flow improvers, light stabilizing dyes, antioxidants or other rheology controlling agents such as microgels or NAD (= non-aqueous dispersions). The clear lacquer coating means according to the invention can be used to produce an outer lacquer layer of a multi-layered coating. In this regard, the present invention also relates to the use of clear lacquer coating means according to the invention. For example, the clearcoat coating medium according to the invention can be applied to a substrate that is provided with a preliminary coating that imparts color and / or effect and can subsequently be baked. The baking temperatures of the clearcoat coating media according to the invention are, for example, between 60 and 160 ° C. For applications in the automotive field these temperatures are between 60 and 140, and for applications in mass production of automotive coatings are between 80 and 140 in particular, and preferably between 110 and 130 ° C. The present invention further relates to a method for producing a multilayer coating by applying and baking a clear lacquer coating layer of a clear lacquer coating medium, in accordance with the present invention, to a substrate that counts with a preliminary coating of multiple layers or a single layer that imparts color and / or effect. Preferably this is a method for producing a multi-layered coating of basecoat / clearcoat by applying and baking a clearcoat coating layer of a clearcoat coating medium, according to the invention, to a substrate that It has a layer of base lacquer that imparts color and / or effect. In this regard, a basecoat layer imparting color and / or effect, which optionally has a precoat, is applied to a substrate and is applied in particular to bodies or parts thereof with precoating. Examples of preliminary coatings on bodies or parts thereof include an electrodeposition primer coating, a double layer precoat consisting of an electrodeposition sizing coating and a spray sizing surface layer, or a dual precoat coating. layer consisting of an electrodeposition primer coating and a second coating layer electrophoretically deposited. The basecoat coating imparting color and / or effect can be baked prior to the application of the clearcoat coating of the clearcoat coating medium according to the invention. Nevertheless, the clearcoat coating medium according to the invention is preferably applied by the wet-on-wet method known to the basecoat coating that determines the color of the multi-layer coating. In this process, the basecoat coating is applied by spraying by spraying a basecoat with a solvent or aqueous base that imparts color and / or effect to give a dry coating thickness that depends on the color shade, for example between 10 and 25μm . The application of the basecoat coating is followed by a short phase of air ventilation, for example from 20 to 80 ° C; this is followed by the spray application of the clear lacquer coating of clear lacquer coating medium according to the invention, to give a dry layer thickness generally between 25 and 50 μm. A brief phase of air ventilation can also optionally be used. It is often advisable and advisable to assist the air ventilation phase with heat preferably with the help of infrared radiation, for example. Subsequently, the substrate is fed into the baking operation wherein the clear lacquer coating layer is baked together with the base lacquer coating at elevated temperatures, for example 80 to 160 ° C. The present invention allows the production of multilayer coatings, particularly double layer coatings, base coat / clear coat, in automotive vehicles and parts thereof in particular, which exhibit excellent visual and aesthetic impression and good acid resistance. The clear lacquer runoff on vertical surfaces is effectively prevented, particularly during baking. The clear lacquer coatings produced from the clear lacquers baked in accordance with the invention are bright and do not show opaqueness.

PRODUCTION OF MULTI-LAYER COATINGS COMPARATIVE EXAMPLE A A supply lacquer was produced with the following composition first in the usual manner by mixing an acrylate resin solution with additives and solvents: 42 parts of a solid acrylate resin (hydroxyl number 140 mg KOH / g) 1 part of a stabilizer light (derived from benztriazole) 1 part of a light stabilizer (a derivative of HALS; HALS = light stabilizer of clogged amine) 0.2 parts of a silicone oil commercially available as a flow improver (calculated as an active ingredient) 55.8 parts of organic solvents. A clear lacquer was produced by mixing 100 parts of supply lacquer with 30 parts of a hardening solution consisting of 24.6 parts of triisocyanate (hexamethylene diisocyanatoisocyanurate) and 5.4 parts of butyl acetate. A simple black water-based lacquer was sprayed to give a dry coating thickness of 16 μm on a metal sheet which was provided with a cataphoretic sizing coating and a sizing surface coating, pre-dried for 10 minutes at 80 ° C. The clear lacquer described above was sprinkled wedge-shaped on the suspended metal sheet to give a coating thickness gradient corresponding to a dry coating thickness of 10 to 70 μm. After an air ventilation phase at room temperature for 10 minutes, the sample was baked for 20 minutes at 140 ° C (object temperature). The metal sheet was in vertical position during all these operations.

COMPARATIVE EXAMPLE B A supply lacquer with the same weight of solids as in comparative example A was prepared first. Unlike comparative example A, part of the acrylate resin solution that was used was replaced with a modified acrylic resin solution. The modified acrylic resin solution contained a diurea derivative which was suspended in solid form.

Supplying lacquer composition: 31 parts of solid acrylate resin of comparative example A (hydroxyl number 140 mg KOH / g) 10.3 parts of another solid acrylate resin (hydroxyl number 140 mg KOH / g) 0.7 parts of a diurea derivative (an addition product of 2 moles of benzylamine to 1 mole of hexamethylene diisocyanate) 1 part of light stabilizer (a benztriazole derivative) 1 part of light stabilizer (a derivative of HALS HALS obstructed amine light stabilizer) 0.2 parts of the same silicone oil that was used in comparative example A (calculated as the active ingredient) 55.8 parts of a mixture of organic solvents as in Comparative Example A. The clear lacquer was prepared and the multi-layered coating was produced analogously to Comparative Example A.

EXAMPLE 1 (example according to the invention) Unlike comparative example B, 130 parts of clear lacquer were mixed, before application, with a part of Maprenal MF 590 (a 55% by weight solution of melamine resins, so-butylated, manufactured by Vianova Resins) and 0.3 parts of Nacure 5225 (a blocked aromatic sulfonic acid manufactured by King Industries). The content of melamine resin with respect to the resin solids content was 0.8% by weight. The urea content was 1.0% by weight with respect to the resin solids content.

EXAMPLE 2 (example according to the invention) In contrast to comparative example B, 130 parts of clear lacquer were mixed before application with one part of Preventol D2 (semi-formal benzyl, manufactured by Bayer) and 0.3 part of Nacure 5225. The semi-formal benzyl content was 1.5% by weight with respect to the content of resin solids. The urea content was 1.0% by weight with respect to the resin solids content. The resistance to sulfuric acid of the coatings obtained in comparative tests A and B and in examples 1 and 2 was satisfactory, and there was a difference between these values. The differences obtained between multilayer coatings are shown in table 1. TABLE 1

Claims (11)

NOVELTY OF THE INVENTION CLAIMS

1. - clear lacquer coating means containing one or more self-ligating or externally interlacing binder vehicles, one or more organic solvents, in the case of externally interlacing binder vehicles containing one or more crosslinking agents that are different from condensation resins of aldehyde, optionally also contain one or more thinners, and optionally also contain customary additives for clear lacquers, characterized by an additional content of: A) from 0.1 to 3% by weight of one or more urea compounds, and B) from 0.05 to 10% by weight of one or more substances that provide formaldehyde, with respect to each case to the resin solids content of the clear lacquer coating media that is formed by the binder carriers and reactive thinners that are optionally present and by the interlacing agents that are optionally present.

2. The clearcoat coating means according to claim 1, further characterized in that the urea compounds (A) are addition products of di- and / or polyisocyanates and mono- and / or polyamines, containing amino groups primary and / or secondary.

3. - Clear lacquer coating means according to any of claims 1 or 2, further characterized in that the urea compounds are present in crystalline form with particle sizes of 0.1 to 20 μm.

4. The clear lacquer coating means according to any of claims 1 to 3, further characterized in that the substance (B) that provides formaldehyde, does not provide formaldehyde until the clear lacquer coating medium is baked .

5. The clearcoat coating means according to any of claims 1 to 4, further characterized in that the substances (B) that provide formaldehyde comprise one or more formal groups, semiformal groups, aminal structural units and / or semi-formal derivatives of formaldehyde.

6. Clear lacquer coating means according to any of claims 1 to 5, further characterized in that they have a resin solids content comprising: a) 50 to 100% by weight of one or more vehicles of binder, b) from 0 to 20% by weight of one or more reactive thinners and c) from 0 to 50% by weight of one or more crosslinking agents that are different from the aldehyde condensation resins, where the sum of a, b, and c gives a total of 100% by weight and components A and B are present in the addition to said 100% by weight in amounts of 0.1 to 3% by weight A and 0.5 to 10% by weight B with respect to the sum of a, b and c.

7. - A clear lacquer coating medium according to claim 6, characterized in that it contains a) from 50 to 90% by weight of binder vehicles, b) from 0 to 20% by weight of reactive thinners and c) from 50 to 10 % by weight of crosslinking agents.

8. A method of coating multiple layers by applying a basecoat coating and a clearcoat coating to a substrate that was optionally pre-coated, characterized in that the coating medium according to any of the claims of 1 to 7 is applied to produce the clear lacquer coating.

9. The use of clear lacquer coating means according to any of claims 1 to 7 for the production of multilayer coatings.

10. The use of clear lacquer coating means according to any of claims 1 to 7 for the production of multilayer coatings in the automotive sector.

11. The use of a) from 0.1 to 3% by weight of one or more urea compounds and b) from 0.05 to 10% by weight of one or more substances that provide formaldehyde as additives for clear lacquer coating media, which contain one or more self-ligating or externally interlacing binder vehicles, one or more organic solvents, in the case of externally crosslinkable binder vehicles containing one or more crosslinking agents that are different from the aldehyde condensation resins, and which optionally they also contain customary additives for clear lacquers, where the content of urea compounds and of "formaldehyde-providing substances" is given with respect to the resin solids content of the clear lacquer coating means which are formed by the binder carriers and by the reactive thinners that are optionally present and by the crosslinking agents that are optionally present.