EP0537697B1 - Process for making multilayer coating with a cationic filling-layer - Google Patents

Description

The invention relates to a method for producing a multi-layer coating, using cationic binders, in the manufacture of the cationic filler coating agent.

Automobile painting is nowadays a multi-layer painting to meet the different requirements of consumers. The different layers of paint are used for different tasks, for example to create stone chip protection, to create corrosion protection or to produce a good, visually appealing surface. It is known that the primer for the production of the corrosion protection can be produced from coating agents on an anionic or cationic basis.

The filler layers that are necessary to produce adequate stone chip protection are nowadays formulated either on a solvent-based basis or on an aqueous basis. To date, only aqueous systems that are formulated on an anionic basis are known. These coating agents have the disadvantage that if the corrosion primer layer is damaged, there is only poor corrosion protection at these points. Furthermore, it has been shown that the stoving temperatures of the filler layer are relatively high. For practical reasons, e.g. B. energy costs or dimensional stability of plastic substrates, it is necessary to keep the baking temperatures of the lacquer layers as low as possible.

Binder on a cationic basis, which are used for anti-corrosion primers, have already been described in the patent literature. These are deposited by electrocoating, which means that there is an aqueous solution of the binders together with the usual ones Manufactured additives and deposited them by applying an electrical current on the metallic workpiece connected as a cathode. The coated substrate is then baked at temperatures between 150 and 200 ^° C., which means that the coating chemically crosslinks. Examples of such coating compositions are described in DE-OS 36 34 483, 36 14 551, 36 14 435, EP-A 54 193 and EP-A 193 103. These are binders for lacquers (KTL) that can be deposited on the cathode and are based on amino acrylate resins, amino epoxy resins or aminourethane resins. These are mixed and dispersed with pigments in a pigment-binder ratio of up to 0.5: 1 and the coating agent is produced with the usual paint additives. The solids content of the coating compositions is generally 12-22% by weight. After deposition, these coating agents are baked at temperatures> 150 ^o C.

These coating agents have the disadvantage that they have only a small proportion of solids and are therefore unsuitable for spray application. When baking, it is first necessary to evaporate the water still present in the coating agent. In addition, high temperatures are required to crosslink the coating agent, so that the selection of the substrates that can be used is restricted.

Coating agents for stone chip protection are also known. These so-called fillers are known for example from DE-OS 40 00 748, EP-A 249 727 or DE-OS 38 13 866. These are coating compositions based on anionically stabilized binders, which are processed with conventional pigments and additives to form the coating composition. Polyurethane resins and reaction products of polyesters and epoxy resins are described as the binder base. Melamine resins and blocked isocyanates are described as crosslinking agents. These coating agents have the disadvantage that they require relatively high stoving temperatures of approximately 150 ^° C. It has also been shown that the corrosion protection on bare metal spots that do not have a corrosion protection primer is not sufficient. Such defects can be caused, for example, by subsequent processing of the bodies, e.g. B. loops occur.

It is therefore an object of the present invention to provide a coating agent for use as a filler in multi-layer coating, in particular for motor vehicles and their parts, which has improved properties with regard to corrosion protection and also permits low stoving temperatures.

This object is achieved according to the invention by the production of filler layers from coating compositions based on one or more binders which at least partially contain cationic groups or groups which can be converted into cationic groups.

The filler layer can, for example, on a conventional primer, for. B. a cathodically or anodically or otherwise deposited primer layer can be applied directly. However, intermediate layers can also be formed between the primer and the filler layer, such as. B. rockfall protection layers. The filler layer is preferably overcoated with a customary color and / or effect topcoat or basecoat. However, one or more intermediate layers can also be inserted here.

The filler layers produced according to the invention can be crosslinked or baked at low temperatures, e.g. B. at 100 to 150 ^o C.

The coating agents used for the filler layers can contain, in addition to the one or more cationically stabilized binders, further binders and crosslinking agents. You can also use conventional pigments and / or fillers, as well as conventional paint additives, such as. B. contain catalysts. They can contain water and / or organic solvents as solvents. They preferably contain water as the main solvent, with small proportions of one or more organic solvents. Water is preferably used in fully demineralized form.

The binders are preferably based on polyacrylate, polyester, polyurethane or epoxy resins or mixtures thereof. At least some of them contain cationic groups or substituents which can be converted into cationic groups. These cationic groups can e.g. B. contain nitrogen and be quaternized. Convertible to cationic groups Groups can also contain nitrogen, for example, and by conventional neutralizing agents, e.g. B. neutralized inorganic acids or organic acids or converted into cationic groups. Examples of usable acids are phosphoric acid, acetic acid and formic acid. The solubility behavior in water is influenced by the number of these groups. The binders can be self- or externally crosslinking, ie crosslinking agents can also be added. These are e.g. B. selected from the group of melamine resins, transesterification or blocked isocyanates. Binders that can be added in part are also understood to mean resins that perform special paint functions. Examples of this are rheological resins or paste resins.

Examples of binders which can be used according to the invention in the coating compositions for fillers are listed below. It can e.g. B. the binders are used, which are described in DE patent application P 40 11 633 for basecoats. There are e.g. B. basic group-containing poly (meth) acrylate resins, which are prepared by solution polymerization or by emulsion polymerization or copolymerization and have a hydroxyl number of 10 to 400, preferably 30 to 200 mg KOH per g solid resin. The number average molecular weight ( M n) is 500 to 100000 and preferably 1000 to 10000 (measured by gel permeation chromatography, calibrated with polystyrene fractions). Their viscosity is preferably 0.1 to 10 Pa.s, in particular 0.5 to 5 Pa.s in 50% solution in monoglycol ethers (in particular butoxyethanol) at 25 ^o C. Their glass transition temperature (calculated from the glass transition temperatures of the homopolymers) is included -50 to +150 ^o C, preferably at -20 to +75 ^o C. The suitable average molar masses or viscosities can also be obtained by mixing resins with higher and lower molar masses or viscosities. The amine number is 20 to 200, preferably 30 to 150 and particularly preferably 45 to 100 (mg KOH per g solid resin).

The basic group-containing poly (meth) acrylate resins can be prepared according to the prior art, as described, for example, in DE-A 15 46 854, DE-A 23 25 177 or DE-A 23 57 152. Practically all radically polymerizable monomers can be used ethylenically unsaturated monomers. The basic poly (meth) acrylate resin can also be used instead of or in addition to the amino groups Contain onium groups such as quaternary ammonium groups, sulfonium or phosphonium groups. Amino groups which make the resin dilutable with water after neutralization with organic acids are particularly preferred. Such a mixed polymer containing amino groups and hydroxyl groups is obtained by polymerization in solution or by emulsion polymerization. Solution polymerization is preferred.

The poly (meth) acrylate resin is prepared from (meth) acrylate monomers, optionally together with other radically polymerizable monomers. The radically polymerizable monomers, i.e. H. the (meth) acrylate monomers and / or further free-radically polymerizable monomers are free-radically polymerizable amino group-containing monomers or free-radically polymerizable monomers which contain both amino groups and hydroxyl groups. They can be used in a mixture with other radically polymerizable monomers.

mit n = 1 bis 8, bevorzugt 1 bis 3 bedeuten.
Beispiele für ungesättigte N-gruppenhaltige Monomere sind N-Dialkyl- oder N-Monoalkyl-aminoalkyl(meth)acrylate oder die entsprechenden N-Alkanol-Verbindungen oder die entsprechenden (Meth)acrylamidderivate.Monomers of the general formula, for example, can be used as monomers



R-CH = CR'-XB



are used, whereby
R = -R 'or -XC _n H _{2n + 1}
R '= -H or -C _n H _{2n + 1}
R '' = -R ', -C _n H _2n OH and / or -C _n H _2n NR₂
B = AN (R '') ₂ or C₁-C₆-alkyl with 1 - 3 OH groups
X = -COO-, -CONH-, -CH₂O- or -O-,
A = -C _n H _2n - or

with n = 1 to 8, preferably 1 to 3.
Examples of unsaturated N group-containing monomers are N-dialkyl or N-monoalkylaminoalkyl (meth) acrylates or the corresponding N-alkanol compounds or the corresponding (meth) acrylamide derivatives.

Radically polymerizable hydroxyl-containing monomers are understood to mean, for example, those which, in addition to a polymerizable ethylenically unsaturated group, also contain at least one hydroxyl group on a C₂ to C₂₀ linear, branched or cyclic carbon skeleton.

The copolymerization is carried out in a known manner, preferably by solution polymerization with the addition of free radical initiators and optionally regulators at temperatures of, for. B. 50 to 160 ^o C. It takes place in a liquid in which monomers and polymers dissolve together. The content of monomers or polymers after the polymerization is about 50 to 90% by weight. Solution polymerization in organic solvents which can be diluted with water is preferred. As initiators which are soluble in organic solvents, 0.1 to 5% by weight, preferably 0.5 to 3% by weight, based on the amount of monomers used, of peroxides and / or azo compounds are added. As initiators such. B. peroxides, peresters or thermally decomposing azo compounds.

The molecular weight can be reduced in a known manner by using regulators. Mercaptans, halogen-containing compounds and other radical-transferring substances are preferably used for this purpose. N- or tert-Dodecyl mercaptan, tetrakismercaptoacetylpentaerythritol, tert-butyl-o-thiocresol, buten-1-ol or dimeric α-methylstyrene are particularly preferred.

Amino-poly (meth) acrylate resins can also be prepared by polymer-analogous reaction. For example, a copolymer containing acrylamide groups can be reacted with formaldehyde and a secondary amine and / or amino alcohol. A particularly preferred method is described in DE-A 34 36 346. Here, epoxy group-containing monoethylenically unsaturated monomers are first polymerized into the copolymer. It is then reacted with excess ammonia, primary and / or secondary monoamines and / or monoamino alcohols and then the excess of amine is distilled off. A similar reaction can preferably be carried out, for example, in equivalent amounts with ketimines or polyamines which contain a secondary amino group and one or more blocked or tertiary amino groups, such as the monoketimine from methyl isobutyl ketone and methylaminopropylamine or the diketimine from methyl isobutyl ketone and diethylene triamine. The proportion of unsaturated monomers containing epoxy groups in the copolymer is generally 8 to 50% by weight. The lower limit is preferably 12% by weight, the upper limit 35% by weight. The polymerization must be completed before the reaction with amines takes place.
because otherwise reversible side reactions occur on the activated double bonds of the monomers with the secondary amines.

Primary or secondary amines of the formula are particularly useful as amines for the reaction with the epoxy groups



R-NH-R '



in which
R = -H or -R '
R '= -C _n H _{2n + 1} , -C _n H _2n OH and / or -C _n H _2n -N = C (alkyl) ₂
and n = 1 to 8, preferably 1 to 2, and alkyl has 1 to 8 carbon atoms and in the case R = R 'the radicals can be the same or different.

The following amines can be used for the reaction, for example: C₁ to C₆ dialkylamines with the same or different alkyl groups in the molecule, monocycloaliphatic amines, monoalkanolamines, dialkanolamines and primary amines or amino alcohols. Secondary amines such as dimethylamine, diethylamine, methylethylamine or N-methylaminoethanol are particularly preferred because, after neutralization, readily soluble paints with a high pH can be obtained. The above-mentioned primary amines are mostly used in a mixture with secondary amines, because otherwise highly viscous products are formed. The number of epoxy groups determines the number of amino groups that are reacted with them and thus also the solubility of the product. There should be at least one epoxy group per molecule. It is often advantageous to combine an increased hydroxyl number with a low amine number and vice versa. The development goal is generally a highly soluble product with a low degree of neutralization and the highest possible pH.

In another preferred method, amino groups can be incorporated by reacting a hydroxyl-containing poly (meth) acrylate resin with amino compounds containing isocyanate groups. These are produced, for example, by reacting 1 mol of diisocyanate with 1 mol of dialkylaminoalkanol.

Another preferred group of basic binders are hydroxyl-functional polyesters, the amino groups as amino alcohols either being condensed directly into the polyester or incorporated more gently into the polymer chain with the aid of a polyaddition or appended to the polymer chain. For example, an OH group-containing urethanized polyester is built up by reacting a polyester with dialkylaminodialcohols and diisocyanates. Proportions of higher-functional alcohols, amino alcohols or isocyanates can also be used. If you work with an isocyanate deficit, the resin must be directly dispersible in water after neutralization with acids.

If, on the other hand, one works with an excess of isocyanate, the resulting NCO prepolymer can be dispersed in water and converted to a polyurethane (urea) dispersion by chain extension with a polyamine. These binders do not contain any groups accessible for crosslinking. They can therefore only be used in part.

In the production of polyester urethane resins, the equivalent ratio of the diisocyanate used is chosen in coordination with the polyols and diols used so that the finished polyester urethane resin preferably has a number average molecular weight ( M n) from 3,000 to 200,000, particularly preferably below 50,000. The viscosity of the polyester urethane resin is preferably 1 to 30 Pa.s., particularly preferably above 5 and below 15 Pa.s, measured 60% in butoxyethanol at 25 ^o C.

The preparation of basic groups containing polyurethane (urea) dispersions is carried out in a known manner, for. B. by chain extension of a cationic or cationizable prepolymer having a terminal isocyanate group with water, polyols, polyamines and / or hydrazine compounds, the chain extension taking place before or after neutralization of the tertiary amino groups with these in water. The amine number is controlled by the amount of compounds containing cation groups in the prepolymer containing isocyanate groups used in the preparation. The particle size depends on the molar mass of the used polyols, e.g. B. OH polyester (polyester polyols), the amine number and the assembly sequence. The number average molar mass is preferably between 3000 to 500000, particularly preferably more than 5000 and less than 50000. Polyurethane dispersions containing urea groups are preferably prepared which contain at least 2, preferably 4 urethane groups and at least one tertiary amino group, especially dialkylamine group in the NCO prepolymer contain.

The preparation of the cationic isocyanate group-containing prepolymers suitable for use in polyurethane (urea) dispersions is carried out, for. B. by simultaneous reaction of a polyol mixture with diisocyanates in a preferred ratio of NCO to OH groups of over 1.00 to 1.4. The polyol mixture preferably consists of one or more saturated OH polyesters, optionally with the addition of one or more low molecular weight diols and a compound with two groups which are H-reactive toward isocyanate groups and which additionally contain a group capable of forming cations.

The polyester polyol can be prepared in various ways, for example in the melt or by azeotropic condensation at temperatures of, for. B. 160 to 260 ^o C, preferably from dicarboxylic acids and dialcohols, which may optionally be slightly modified by small amounts of trial alcohols. The reaction is carried out, optionally with the addition of catalysts such as tin octoate or dibutyltin oxide, until practically all of the carboxyl groups (acid number ≦ 1) have been reacted. The necessary OH number from 35 to 200, preferably above 50 and below 150, or molecular weight from 500 to 5000, preferably above 800 and below 3000, is determined by the alcohol excess used.

The preferably used dicarboxylic acids are linear or branched aliphatic, alicyclic or aromatic. Diols with sterically hindered primary OH groups or with secondary hydroxyl groups are used for particularly hydrolysis-resistant polyesters. Examples include 1,4-cyclohexanediol, 2-ethyl-1,3-hexanediol, cyclohexanedimethanol and the hydrogenated bisphenols A or F. The dialcohols can contain small amounts of higher polyols, such as glycerol or trimethylolpropane, for branching introduce. However, the amount should be so small that no cross-linked products are created. A linear aliphatic structure is preferred, which may optionally contain an aromatic dicarboxylic acid in part and preferably contains an OH group at the end of the molecule.

According to the invention, polyester diols obtained by condensation of hydroxycarboxylic acids can also be used as polyester polyols.

In order to influence the molecular distribution and the number of urethane groups incorporated, 2 to 30% by weight of the higher molecular weight polyester can be exchanged for low molecular weight glycols or dialcanols. It is preferred to use the dialcanols already used in polyester with a molecular weight of 62 to about 350. The dialcanols used here need not be identical to those used in the polyester.

In order to be able to dissolve the polyester urethane resin in water, some of the low molecular weight diols are replaced by diols which still contain at least one onium salt group or an amino group which can be neutralized by acid. Suitable basic groups which are capable of forming cations are primary, secondary or tertiary amino groups and / or onium groups, such as quaternary amino groups, quaternary phosphonium groups and / or tertiary sulfonium groups. Dialkylamino groups are preferably used. The basic groups should be so inert that the isocyanate groups of the diisocyanate preferably react with the hydroxyl groups of the molecule.

Also preferred are aliphatic diols, such as N-alkyl-dialkanolamines, with, as alkyl or alkane radical, aliphatic or cycloaliphatic radicals with 1 to 10 carbon atoms, for. B. methyl diethanolamine.

The amount of salt groups present through the neutralization is generally at least 0.4% by weight to about 6% by weight, based on the solids.

The cationic groups of the NCO prepolymer used for the production of the polyurethane dispersions are mixed with a Acid at least partially neutralized. The resulting increase in dispersibility in water is sufficient to stably disperse the neutralized polyurethane containing urea groups. Suitable acids are organic monocarboxylic acids. After neutralization, the NCO prepolymer is diluted with water and then gives a finely divided dispersion with an average particle diameter of 25 to 500 nm. Shortly thereafter, the isocyanate groups still present can be treated with di- and / or polyamines with primary and / or secondary amino groups, or Hydrazine and its derivatives or dihydrazides can be implemented as chain extenders. This reaction leads to a further linkage and an increase in the molecular weight. The amount of chain extender is determined by its functionality or by the NCO content of the prepolymer. The ratio of the reactive amino group in the chain extender to the NCO groups in the prepolymer should generally be less than 1: 1 and preferably in the range from 1: 1 to 0.75: 1.

Examples are polyamines with a linear or branched aliphatic, cycloaliphatic and / or (alkyl) aromatic structure and at least two primary amino groups. Examples of diamines are ethylenediamine, 1,6-hexamethylenediamine, isophoronediamine and aminoethylethanolamine. Preferred diamines are ethylenediamine, propylenediamine and 1-amino-3-aminomethyl-3.3.5-trimethylcyclohexane or mixtures thereof. The chain extension can be carried out at least partially with a polyamine which has at least three amino groups with reactive hydrogen, such as, for example, diethylene triamine. Diamines can also be used as chain extenders, the primary amino groups of which are protected as ketimine and which become reactive after emulsification in water due to the hydrolytic cleavage of the ketone.

In another preferred procedure, the polyaddition is carried out with strong dilution using dry, non-isocyanate-reactive solvents. The chain is extended with polyols, polyamines or amino alcohols. Low-boiling anhydrous ketones such as acetone, methyl ethyl ketone or methyl isopropyl ketone, but also esters such as acetoacetic ester are used as solvents. After neutralization with acids and dilution with water, the volatile solvent may then have to be distilled off under heating with heating.

Typical diisocyanates for reaction with the polyol / diol mixture are, for example, those based on linear or branched aliphatic, cycloaliphatic and / or aromatic hydrocarbons with an NCO content of 20 to 50%. They contain two isocyanate groups as functional groups, which are arranged asymmetrically or symmetrically in the molecule. They can be aliphatic, alicyclic, arylaliphatic or aromatic.

Mixtures of different isocyanates can also be used.

The synthesis is carried out by joint reaction of the reactants in a mixture or stepwise to a sequential structure.

Polyisocyanates with more than 2 isocyanate groups are defunctionalized by reaction with isocyanate-reactive monofunctional compounds. Preference is given to compounds which retain a basic amino group after the reaction in order to introduce a salt-forming group in this way. By reaction with dialkylaminoalkanols or dialkylaminoalkylamines, basic "diisocyanates" are prepared under gentle reaction conditions, the alkyl groups being linear or branched, aliphatic or cycloaliphatic with carbon chains of 1 to 10 carbon atoms.

These binders contain essentially no groups accessible to crosslinking. They can therefore only be used partially in the coating agent.

In DE-OS 33 33 834 examples of cationically stabilized polyurethane resins are described, the crosslinkable groups, for. B. OH groups.

• a) zwei- und/oder mehrwertigen aliphatischen und/oder cycloaliphatischen gesättigten Polyalkoholen mit
• b) aliphatischen und/oder cycloaliphatischen und/oder aromatischen zwei- und /oder mehrwertigen Polyisocyanaten mit
• c) gegebenenfalls linearen und/oder verzweigten, aliphatischen und/oder cycloaliphatischen C₃ bis C₂₀ Monoalkolen

hergestellt werden. Bevorzugt werden Polyesterurethanharze mit einer Aminzahl von 35 bis 100 und einer OH-Zahl von 100 bis 300. Sie werden hergestellt durch Reaktion von bevorzugt Diisocyanaten mit Polyalkoholen bei Temperaturen von 20 bis 150^oC im Überschuß. Als Polyalkohol wird dabei ein höhermolekularer, hydroxylgruppenhaltiger basischer Polyester oder ein Gemisch aus einem carboxylgruppenfreien OH-Polyester und einem niedrigmolekularen Dialkohol, der zusätzlich eine zur Kationengruppenbildung befähigte Amingruppe enthält, eingesetzt. Hierfür wird bevorzugt z. B. N-Methyldiethanolamin eingesetzt. Das Molekulargewicht soll 500 bis 200000 betragen.Examples of this are basic polyurethane resins with an amine number of 20 to 150 and a hydroxyl number of 50 to 400. They can be reacted in a similar manner to the polyester at lower temperatures

• a) with di- and / or polyvalent aliphatic and / or cycloaliphatic saturated polyalcohols
• b) with aliphatic and / or cycloaliphatic and / or aromatic di- and / or polyvalent polyisocyanates
• c) optionally linear and / or branched, aliphatic and / or cycloaliphatic C₃ to C₂₀ monoalkoles

getting produced. Polyester urethane resins with an amine number of 35 to 100 and an OH number of 100 to 300 are preferred. They are prepared by reacting diisocyanates with polyalcohols at temperatures of 20 to 150 ^° C. in excess. The polyalcohol used here is a higher molecular weight, basic polyester containing hydroxyl groups or a mixture of a carboxyl-free OH polyester and a low molecular weight dialcohol which additionally contains an amine group capable of forming cation groups. For this, z. B. N-methyldiethanolamine used. The molecular weight should be 500 to 200,000.

Binding agents based on cationic polyepoxy resins have already been described in the literature. For example, DE-OS 38 12 251, EP-A 0 234 395, DE-OS 27 01 002, EP-A 0 287 091, EP-A 0 082 291 or EP-A 0 227 975 describe self- or externally crosslinking binders described on the basis of reaction products of polyepoxides with compounds containing amine groups. These are, for example, reaction products of polyepoxides with aromatic or aliphatic diols and / or diamines. These reaction products can be further modified, e.g. B. by reaction with partially blocked isocyanates, with monofunctional epoxy compounds, with carboxyl-containing compounds or with OH-functional components. While aromatic ingredients, e.g. B. aromatic diols such as bisphenol A, improve the corrosion protection behavior, cause aliphatic components, for. B. aliphatic glycol ethers such as polyethylene glycols, increased flexibility of the binder.

The solubility can be influenced by the number of amino groups. The amine number should be between 20 and 200 mg KOH / g solid resin, preferably between 30 and 150. Primary, secondary and / or tertiary amino groups can be present. The hydroxyl number affects the crosslink density. It should preferably be between 20 and 400. Each binder molecule should have an average of at least two reactive groups, e.g. B. OH or NH groups. The reactivity of the binders will influenced by the nature of the groups, primary amino or hydroxyl groups are more reactive than secondary ones, with NH groups being more reactive than OH groups. It is preferred that the binders contain reactive amino groups. The binders according to the invention can carry further crosslinkable groups, such as. B. blocked isocyanate groups or groups capable of transesterification. They are then self-crosslinking binders. However, it is possible to additionally add crosslinking agents to the binders. The molecular weight ( M n) the binder is from 500 to 20,000, in particular from 1,000 to 10,000.

The basic resin binders described are self-crosslinking or externally crosslinking and can be used either individually or in a mixture.

Crosslinking agents can also be mixed in to achieve a crosslinked filler layer. The amount can be selected according to the respective functionality. It is z. B. 0 - 40 wt .-%, based on the mixture of binders and crosslinkers.

As crosslinkers, for example, aminoplast resins, such as. B. melamine resins can be used. For example, they can also be modified, e.g. B. by etherification with unsaturated alcohols. These substances are common commercial products.

Examples of transesterification crosslinkers are non-acidic polyesters with side or terminal β-hydroxyalkyl ester groups. They are esters of aromatic polycarboxylic acids, such as isophthalic acid, terephthalic acid, trimellitic acid or mixtures thereof. These are e.g. B. condensed with ethylene glycol, neopentyl glycol, trimethylolpropane and / or pentaerythritol. The carboxyl groups are then reacted with optionally substituted 1,2-glycols to form β-hydroxyalkyl compounds. The 1,2-glycols can be substituted with saturated or unsaturated alkyl, ether, ester or amide groups. Further, a hydroxyalkyl ester formation is also possible in which the carboxyl groups with substituted glycidyl compounds, such as. B. glycidyl ethers and glycidyl esters are implemented.

The product preferably contains more than 3 β-hydroxyalkyl ester groups per molecule and has a weight average molecular weight of 1,000 to 10,000, preferably 1,500 to 5,000. The usable non-acidic polyesters with side or terminal β-hydroxyalkyl ester groups can be prepared, for example in EP -A 0 012 463. The compounds described there are also examples of polyesters that can be used.

The di- and polyisocyanates described earlier can also be used, for example, as crosslinkers, the reactive isocyanate groups being blocked by protective groups. There are preferred trivalent and higher, z. B. trivalent to pentavalent, particularly preferably trivalent aromatic and / or aliphatic blocked polyisocyanates with a number average molecular weight ( M n) used from 500 to 1500. The so-called "lacquer polyisocyanates" which are prepared from the aliphatic diisocyanates already described above are particularly suitable as polyisocyanates. Another group of polyfunctional isocyanates are oxadiazinetrione alkyl diisocyanates, which can be added to trimethylolpropane. Highly functional polyisocyanates can also be prepared by reacting 2 moles of triisocyanates with H-active difunctional compounds, such as dialcohols, diamines or amino alcohols, such as ethanolamines.

The free isocyanate groups are capped (blocked) together or individually, so that they are protected at room temperature against water or the active hydrogen atoms of the base resin (hydroxyl or amine-hydrogen groups). Suitable blocking agents are monofunctional, acidic hydrogen-containing compounds with only a single amine, amide, imide, lactam, thio, ketoxime or hydroxyl group. The products obtained in this way have been widely described in the literature.

Examples of possible pigments or fillers are organic color pigments, iron oxides, lead oxides, titanium dioxide, barium sulfate, zinc oxide, mica, kaolin, quartz powder or various types of silica. The particle diameter of the pigments should be <15 µm. It is also possible to at least partially crosslinked organic fillers to be used insofar as these do not swell in the solvent and have the required grain size.

Examples of lacquer additives include rheology-influencing agents, anti-settling agents, leveling agents, anti-foaming agents, dispersing aids and catalysts. These are used for the special setting of paint or application properties.

Conventional paint solvents are suitable as solvents. These can result from the production of the binders. It is advantageous if the solvents are at least partially miscible with water. Examples of such solvents are glycol ethers, e.g. B. butyl glycol, ethoxypropanol, diethylene glycol dimethyl ether; Alcohols, e.g. B. isopropanol, n-butanol; Glycols, e.g. B. ethylene glycol; N-methylpyrrolidone and ketones. The course and the viscosity of the coating agent can be influenced by the choice of the solvent. The evaporation behavior can be influenced via the boiling point of the solvents used.

The pigment-binder weight ratio is, for example, between 0.75: 1 to 2.5: 1, preferably 1.0: 1 to 1.8: 1. The solids content of the coating composition is between 25 and 60% by weight, preferably between 30 and 50% by weight. The solvent content is <15% by weight, preferably <10% by weight, based in each case on the aqueous coating agent.

The processes for the production of aqueous coating compositions from the binders are known. For example, the starting material is the aqueous binder dispersion, into which pigments, fillers and additives and auxiliaries are added with thorough stirring. After thorough homogenization, the mixture is optionally ground to the necessary fineness. Suitable grinding units have already been described in the literature. After the coating agent has been ground, it is possible, if appropriate, to add further, possibly also different, binders. A suitable viscosity can then be adjusted using water or organic solvent. As a further procedure, it is e.g. B. possible to disperse the pigments and auxiliaries in a solvent-containing binder form, optionally grinding and the mixture after neutralization in the To transfer water phase. Then the viscosity can be adjusted with water. The finished coating agent can be stored for a long time and shows no significant changes in viscosity or sedimentation tendency. For application, a suitable low viscosity, for. B. can be set for spraying.

The coating agent is applied by rolling, rolling or spraying, preferably using spray application processes. Examples include compressed air spraying, airless spraying, hot spraying or electrostatic spraying. Automotive bodies or parts thereof are particularly suitable as substrates; they can consist of metal or plastic. Metal parts are usually coated with an electrophoretically deposited anti-corrosion primer or another common primer layer or intermediate layer. This is usually baked at temperatures> 150 ^o C. Examples of such primers are described in DE-A 36 15 810, DE-A 36 28 121, DE-A 3823 731, DE-A 39 20 214, DE-A 39 40 782 and EP-A 0 082 291, EP- A 0 209 857 and EP-A 234 395. Plastic substrates are provided with adhesion-improving coating layers or with primers based on 2-component coating agents or physically drying coating agents. These coatings can optionally by mechanical work such. B. loops to be treated.

The coating agent according to the invention is applied to the precoated substrates. After a short flash-off time, optionally at elevated temperatures, the workpiece with the coating layer at temperatures between 100 and 150 ^o C is baked. The layer thickness is 15-120 µm, preferably between 25 and 80 µm. After crosslinking, the surface is optionally post-treated, e.g. B. by grinding to create a smooth surface without defects. Thereafter, the color and / or effect paint layer, z. B. a plain topcoat or a metallic basecoat can be applied. When using aqueous anionic basecoat layers, particularly good adhesion to the filler layer can be achieved.

The method according to the invention is particularly suitable for producing a multi-layer coating. This also shows improved corrosion protection on metal parts in the event of mechanical injuries. In the procedure according to the invention, optically smooth, homogeneous, Stone chip resistant multi-layer coatings. These meet the increased requirements in serial painting in the automotive industry.

The process according to the invention is explained in more detail with reference to the following examples:

Example 1:

A solution of 2878 g of an epoxy resin based on bisphenol A with an epoxy equivalent weight of 194 and 1497 g nonylphenol in 1093 g xylene was prepared and heated to 100 ^° C. This solution was added 2 g of a 50% aqueous solution of tetrabutylammonium chloride was added and maintained by heating at 140 ^o C for so long until the epoxide equivalent of the solution was 740th After cooling to 50 ^° C., a solution of 1225 g of ethylenediamine in 1225 g of xylene was added. After 4 hours at 105 ^° C., excess xylene / diamine mixture was distilled off in vacuo. Fresh xylene was added several times and again distilled off until the amine number in the distillate fell below 0.5. A product with an amine number of 160 was obtained. This was diluted to a solids content of 70% with methyl isobutyl ketone.

Example 2:

5453 g of trimethylhexamethylene diisocyanate were added to a solution of 3000 g of methyl isobutyl ketone and 1547 g of 1,6-hexanediol and the reaction was carried out at 80 ^° C. until an NCO number of 11% was reached.

Example 3:

5100 g of the resin solution from Example 1 were with removal of water to 130 ^o C. and after subsequent cooling to 40 ^o C with 2,120 of the solution of Example 2 g offset and C reacts as long as at 80 ^o until infrared spectroscopy no more free isocyanate detectable was. Then 300 g of water were added and the methyl isobutyl ketone was distilled off in vacuo at 80 ^° C. The mixture was then diluted with 1800 g of ethoxypropanol and distilled in vacuo until a solids content of 73% was reached. A product with an amine number of 50 was obtained.

Example 4:

2460 g of butanone oxime were mixed with 5890 g of a 90% solution of trimerized hexane diisocyanate in butyl acetate and reacted at 80 ^° C. until free isocyanate was no longer detectable by infrared spectroscopy. Then 1650 g of butyl glycol were added and the butyl acetate was distilled off at 80 ^° C. in vacuo.

Example 5:

100 parts of the binder from Example 3 were mixed with 4.42 parts of a 50% aqueous solution of formic acid and after the addition of 5 parts of butyl diglycol, 1.42 parts of a commercially available leveling agent and 0.60 parts of a commercially available nonionic surfactant and after intensive mixing diluted with 196 parts of deionized water. Then 31.3 parts of the crosslinking agent from Example 4 were added to the mixture with vigorous stirring. The pH was 5.4. To check the reactivity, the unpigmented paint was applied to a temperature gradient sheet in a dry layer thickness of 26 μm. The following result was obtained: 20 min object temperature ( ^o C) 120 125 130 140 150 160 170 178 Erichsen cupping (DIN ISO 1520) 0.9 8.3 7.8 7.7 7.7 7.7 7.7 8.2 MEK-RUB test *) (100 double strokes) 3rd 2nd 1 1 1 1 1 1 *) Testing the crosslinking with a cotton ball soaked in methyl ethyl ketone, 1 = unchanged, 2 = light matting, 3 = destroyed.

Example 6:

In a mixture of 9.34 parts of the binder from Example 3, 0.87 parts of a 50% strength aqueous solution of formic acid, 18.67 parts of deionized water, 0.42 parts of butyl diglycol and 0.84 parts of a commercially available leveling agent, 04 parts of carbon black, 0.17 parts of Aerosil, 0.83 parts of benzoin, 3.24 parts of kaolin, 9.34 parts of barium sulfate and 7.73 parts of titanium dioxide are stirred in and thoroughly mixed under the dissolver. A further 3.63 parts of the binder from Example 3 and 8.48 parts of deionized water were then added under the dissolver. This mixture was then intensively ground in a bead mill and mixed with 5.92 parts of the binder from Example 3, 0.21 parts of a commercially available nonionic surfactant, 5.93 parts of the crosslinking agent from Example 4, 24.17 parts of deionized water and 0.17 Parts of a 50% aqueous solution of formic acid varnished. This gray cationic hydraulic filler was sprayed in a dry layer thickness of 30 to 35 µm onto a test sheet coated with KTL (18 µm) and baked on the gradient oven for 20 minutes in the range from 130 to 190 ^° C. The test panel was taped after baking in part and then microns using a commercially available monocoat in a dry film thickness of 40 coated by spraying and baked for 30 minutes at 130 ^° C. A multi-layer coating with good mechanical properties, good stone chip resistance and good corrosion protection was obtained. In addition, the cross-linking of the filler layer baked within the specified temperature gradient was checked at the previously taped point. The result is shown in the following table: 20 min object temperature ( ^o C) 130 150 165 190 MEK-RUB test (100 double strokes) 2nd 1 1 1

The corrosion protection of the substrates coated according to the invention is also good if the KTL primer has defects up to the metal.

Claims (11)

1. A process for the multilayer coating of a substrate by the application of a primer coat, optionally one or more intermediate coats, a filler coat, optionally one or more intermediate coats, and a covering lacquer or base lacquer coat which produces a colour and/or an effect, characterised in that a coating medium based on one or more cationic binder vehicles is used for the filler coat.
2. A process according to claim 1, characterised in that a coating medium which contains pigments, fillers and customary coating technology additives is used for the filler coat.
3. A process according to either one of claims 1 and 2, characterised in that the coating medium used for the filler coat contains water as the principal solvent, optionally in addition to one or more organic solvents.
4. A process according to any one of the preceding claims, characterised in that self-crosslinking and/or externally crosslinkable binder vehicles based on polyacrylate, or on polyester, polyurethane or epoxy resins or mixtures thereof, which at least in part contain cationic groups or groups which can be converted into cationic groups, are used in the coating medium for the filler coat.
5. A process according to claim 4, characterised in that the self-crosslinking and/or externally crosslinkable binder vehicles have an OH number of 10 to 400, an amine number of 20 to 200 and a number average molecular weight of 500 to 200,000.
6. A process according to claim 4 or 5, characterised in that the groups which can be converted into cationic groups are primary and/or secondary amino groups.
7. A process according to any one of the preceding claims, characterised in that additional crosslinking agents based on aminoplast resins, transesterification crosslinking agents and/or blocked isocyanates are contained in the coating medium for the filler coat.
8. A process according to any one of the preceding claims, characterised in that part of the binder vehicle in the coating medium for the filler coat contains no groups which are capable of crosslinking.
9. The use of the coating medium defined in any one of claims 1 to 5 for the production of filler coats in multilayer coatings.
10. The use of coating media based on water-thinnable or water-soluble cationic binder vehicles for the production of filler coats in the multilayer coating of motor vehicles and motor vehicle parts.
11. A multilayer coating obtained according to the process of any one of claims 1 to 5.