Binder system for aqueous baking varnish

Abstract

The invention relates to the use of a binder system (B) in an aqueous baking varnish composition, to an aqueous baking varnish composition itself, to a method for applying a baking varnish composition to a metal surface or pre-coating a metal surface, and to a coated metal article, wherein the binder system (B) comprises (a) an aqueous dispersion of a polymer P and (b) from 1% to 10% by weight, based on the amount of polymer P, of at least one amine and / or amide having at least two hydroxyl groups, the aqueous dispersion of polymer P being produced by a radically initiated emulsion polymerization reaction of an ethylenically unsaturated monomer M, the ethylenically unsaturated monomer M is from 90% to 99% by weight of styrene, C1-C8-alkyl methacrylate and / or cyclohexyl methacrylate, preferably styrene and / or C1-C8-alkyl methacrylate; from 1% to 10% by weight of one or more monoethylenically unsaturated carboxylic acids, hydroxy (C2-C4) alkyl (meth) acrylates and / or glycidyl (meth) acrylates; 0% and to 9% by weight of a C4-C10-alkyl acrylate, and wherein the amount of the monomer M totals 100% by weight, in an aqueous medium in the presence of a polymer A having monomer structural units: 70% to 95% by weight of one or more ethylenically unsaturated monocarboxylic acids and / or dicarboxylic acids; 5% to 30% by weight of at least one of an ester of an ethylenically unsaturated monocarboxylic acid, a monoester of an ethylenically unsaturated dicarboxylic acid, and a diester of an ethylenically unsaturated dicarboxylic acid wherein each ester is obtained by esterification with an amine having at least one hydroxyl group, and 0% to 20% by weight of at least one additional monomer; the amount is based in each case on the total amount of all monomer structural units in the polymer A.

Description

[0001] The present invention relates to the use of an adhesive system (B) in an aqueous baking paint composition, wherein the adhesive system (B) comprises

[0002] (a) an aqueous dispersion of a polymer P and

[0003] (b) at least one amine and / or amide having at least two hydroxyl groups, based on the amount of polymer P, from 1% to 10% by weight,

[0004] a baking paint and a method of applying a coating to a surface using the adhesive system (B), and a coated article.

[0005] The use of thermocurable coating materials as protective coatings or protective paints for materials such as steel strips is prior art. Desirable protective coatings adhere well to the underlying surface, are hard while also being flexible, and are resistant to weathering, solvents, abrasion, and heat. It is difficult to achieve the best results for all of these properties because the improvement of one property is, in most cases, at the expense of other properties. In particular, during the processing and shaping of a pre-painted metal strip, high elasticity and adhesion are desired in order to prevent the protective coating from peeling off at angled sections. At the same time, the protective coating should be hard enough to resist mechanical influences.

[0006] Baking paints are generally thermocurable coating materials that chemically harden under increased heat supply. Technically, there are so-called powder coatings, which are 100% solids and powders and compete with liquid paints. Liquid paints can be solvent-based or water-based. Due to the lower VOC (volatile organic carbon) content, water-based paints are preferred. The curing temperatures for all of the above technologies are similar and are approximately 150 °C.

[0007] The most common liquid adhesive systems for such thermocurable coating materials are polyesters and polyacrylates, which are thermally crosslinked, for example, with melamine formaldehyde resins. Known crosslinking agents containing N-hydroxymethyl, such as aminoplastics, which are reaction products of formaldehyde with, for example, urea, dicyandiamide, and aminotriazines such as melamine.

[0008] All of these systems release formaldehyde during crosslinking. Therefore, there has long been a search for new "formaldehyde-free" systems or baking paints that cure within 15 minutes at a temperature of approximately 150 °C.

[0009] One object of the present invention is to provide a novel formaldehyde-free adhesive system for aqueous baking paints. Another object of the present invention is to provide a substrate produced using such an adhesive system.

[0010] Furthermore, the cured baking paint produced using the adhesive system should have good elasticity, good adhesion to the substrate, high gloss, excellent surface hardness, and good water resistance.

[0011] We have found that these objects are surprisingly achieved by using an adhesive system (B) in an aqueous baking paint composition, wherein the adhesive system (B) comprises

[0012] (a) an aqueous dispersion of a polymer P and

[0013] (b) at least one amine and / or amide having at least two hydroxyl groups in an amount of 1% to 10% by weight based on the amount of the polymer P,

[0014] wherein the aqueous dispersion of the polymer P is prepared by free-radical-initiated emulsion polymerization of the following ethylenically unsaturated monomers M:

[0015] 90% to 99% by weight of styrene, C 1 -C 6 -alkyl esters and / or cyclohexyl methacrylate;

[0016] 1% to 10% by weight of one or more monoethylenically unsaturated carboxylic acids, (meth)acrylic acid hydroxy(C 2 -C 4 ) alkyl esters and / or glycidyl (meth)acrylate;

[0017] 0% to 9% by weight of acrylic acid C 4 -C 10 -alkyl esters, and

[0018] wherein the amount of the monomer M totals 100% by weight,

[0019] in an aqueous medium, in the presence of a polymer A having the following monomer structural units:

[0020] 70% to 95% by weight of one or more ethylenically unsaturated monocarboxylic acids and / or dicarboxylic acids,

[0021] 5% to 30% by weight of at least one of esters of ethylenically unsaturated monocarboxylic acids, monoesters of ethylenically unsaturated dicarboxylic acids, and diesters of ethylenically unsaturated dicarboxylic acids, wherein each ester is obtained by esterifying with an amine having at least one hydroxyl group, and

[0022] 0% to 20% by weight of at least one additional monomer;

[0023] The amount is in each case based on the total amount of all monomer structural units in the polymer A.

[0024] The present invention also relates to the aqueous baking paint composition itself, a method of applying the baking paint composition to a metal surface or a pre-coated metal surface, and a coated metal article.

[0025] If the solids content of the aqueous dispersion is mentioned in % by weight, it is based on the weight of the aqueous dispersion.

[0026] Hereinafter, compounds derived from acrylic acid and methacrylic acid are partially abbreviated by inserting the syllable “(meth)”.

[0027] In the presence of polymer A, polymer P is prepared by free-radical-initiated emulsion polymerization of the following ethylenically unsaturated monomer M:

[0028] 90% to 99% by weight of styrene, methacrylic acid C 1 -C 4 -alkyl esters and / or cyclohexyl methacrylate;

[0029] 1% to 10% by weight of one or more monoethylenically unsaturated carboxylic acids, 2-

[0030] hydroxyethyl acrylate and / or 2-hydroxyethyl methacrylate,

[0031] 0% to 9% by weight of acrylic acid C 4 -C 10 -alkyl esters; and

[0032] wherein the amount of the monomer M totals 100% by weight.

[0033] Regarding the monomer components of polymer P, the following alkyl groups are preferably straight-chain or branched C 1 -C 6 alkyl or C 4 -C 10 alkyl, such as methyl, ethyl, n-propyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, 2-ethylhexyl.

[0034] Polymer P is formed from styrene, methacrylic acid C 1 -C 6 -alkyl esters and / or cyclohexyl methacrylate as the main monomers. Particularly preferred main monomers are styrene, methyl methacrylate, cyclohexyl methacrylate and n-butyl methacrylate, especially styrene and methyl methacrylate.

[0035] The comonomers are selected from one or more monoethylenically unsaturated carboxylic acids, (meth)acrylic acid hydroxy(C 2 -C 4 )-alkyl esters and / or (meth)acrylic acid glycidyl ester and acrylic acid C 4 -C 10 -alkyl esters.

[0036] Suitable monoethylenically unsaturated carboxylic acids are C 3 -C6 α,β-monoethylenically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid. If desired, these acids may also be present in the polymer partly or entirely in the form of salts. The acidic form is preferred.

[0037] Suitable (meth)acrylic hydroxy(C 2 -C 4 )-alkyl esters are 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate. 2-Hydroxyethyl acrylate and 2-hydroxyethyl methacrylate are very particularly preferred.

[0038] Preferably, the acrylic C 4 -C 10 -alkyl esters are selected from the group consisting of n-butyl acrylate and 2-ethylhexyl acrylate.

[0039] Preferably, the polymer P is prepared by polymerization of the following monomers M

[0040] 90% to 99% by weight of styrene, methacrylic C 1 -C 4 -alkyl esters and / or cyclohexyl methacrylate, preferably styrene and / or methacrylic

[0041] C 1 -C 4 -alkyl esters;

[0042] 1% to 10% by weight of one or more monoethylenically unsaturated carboxylic acids, 2-acrylic

[0043] hydroxyethyl ester and / or 2-hydroxyethyl methacrylate,

[0044] 0% to 9% by weight of acrylic C 4 -C 10 -alkyl esters; and

[0045] wherein the amount of the monomer M totals 100% by weight.

[0046] Polymer A has the following monomer structural units:

[0047] 70% to 95% by weight of one or more ethylenically unsaturated monocarboxylic acids and / or dicarboxylic acids, preferably acrylic acid and maleic acid

[0048] 5% to 30% by weight of at least one of esters of ethylenically unsaturated monocarboxylic acids, monoesters of ethylenically unsaturated dicarboxylic acids and diesters of ethylenically unsaturated dicarboxylic acids, wherein each ester is obtained by esterifying with an amine having at least one hydroxyl group, and

[0049] At most 20% by weight of at least one additional monomer;

[0050] This amount is in each case based on the total amount of all monomer structural units in the polymer A.

[0051] Such polymers A and their preparation are generally known and described, for example, in US 6,841,608. The polymer A is preferably soluble in water to an extent greater than 10 g / l (25 °C).

[0052] The ethylenically unsaturated carboxylic acids are C 3 to C 10 monocarboxylic acids and C 4 to C 8 dicarboxylic acids, in particular acrylic acid, methacrylic acid, crotonic acid, fumaric acid, maleic acid, 2-methylmaleic acid and / or itaconic acid. Particularly preferred are acrylic acid, methacrylic acid, maleic acid and mixtures thereof. In the preparation of the polymer A, of course, the acid anhydrides thereof can also be used instead of the acids or used together with the acids, such as maleic anhydride, acrylic anhydride or methacrylic anhydride. If desired, these acids can also be present in the polymer in part or in whole in the form of salts. The acidic form is preferred.

[0053] The polymer A also contains 5% to 30% by weight, preferably 1% to 30% by weight, of monomer structural units of at least one ethylenically unsaturated compound in copolymerized form, the ethylenically unsaturated compound being selected from esters of ethylenically unsaturated monocarboxylic acids and mono- and diesters of ethylenically unsaturated dicarboxylic acids with amines having at least one hydroxyl group.

[0054] The polymer A is preferably in the form of a comb polymer with covalently bonded amine side chains.

[0055] Suitable monocarboxylic acids as the ester component are the above-mentioned C 3 to C 10 monocarboxylic acids, in particular acrylic acid, methacrylic acid, crotonic acid and mixtures thereof. Suitable dicarboxylic acids as the mono- and diester components are the above-mentioned C 4 to C 8 dicarboxylic acids, in particular fumaric acid, maleic acid, 2-methylmaleic acid, itaconic acid and mixtures thereof. Preferred are acrylic acid, maleic acid and mixtures thereof.

[0056] The amine having at least one hydroxyl group is preferably selected from those containing at least one C 6 to C 22 alkyl group, C 6 to C 22 alkenyl group, aryl-C 6 to C 22 alkyl group or aryl-C 6 to C 22Secondary and tertiary amines of alkenyl, where the alkenyl may have 1, 2 or 3 non-adjacent double bonds.

[0057] The amine having at least one hydroxyl group is preferably a fatty amine, preferably selected from the group consisting of 1-octylamine, 1-decylamine, 1-dodecylamine, 1-tetradecylamine, 1-hexadecylamine, 1-octadecylamine and 1-eicosylamine.

[0058] The amine is preferably hydroxyalkylated and / or alkoxylated. The alkoxylated amine preferably has one or two alkoxide residues with terminal hydroxyl groups. Preferably, each alkoxide residue has 1 to 100, preferably 1 to 50, identical or different alkoxide units, distributed randomly or in block form. Preferred alkoxides are ethylene oxide, propylene oxide and / or butylene oxide. Ethylene oxide is particularly preferred.

[0059] Particularly preferably, the amine component comprises an alkoxylated fatty amine or a mixture of alkoxylated fatty amines. Ethoxylates are particularly preferred. Particular use is made of alkoxylates of amines based on naturally occurring fatty acids, such as tallow fatty amines, for example those mainly containing saturated and unsaturated C 14 、C 16 and C 18 alkylamines, or coconut amines, which contain saturated, mono-unsaturated and di-unsaturated C 6 -C 22 alkylamines, preferably C 12 -C 14 alkylamines.

[0060] Examples of suitable commercially available alkoxylated amines are the grade from Arkema, preferably ethoxylated oleylamine, such as Noramox 05 (5 EO units), and the products sold under the trade name FA from BASF SE.

[0061] The copolymerization of the above esters, monoesters and diesters generally causes a significant stabilization of the polymer dispersions of the present invention. The polymer dispersions of the present invention reliably maintain the colloidal stability of their latex particles when diluted with water or a dilute electrolyte or surfactant solution.

[0062] The esterification for preparing the above esters, monoesters and diesters is carried out according to conventional techniques known to those skilled in the art.

[0063] In a preferred embodiment, an unsaturated ester, monoester or diester is prepared and further reacted to form polymer A used according to the present invention without separating the ester, and these two reactions are preferably carried out continuously in the same reaction vessel.

[0064] For the preparation of polymer A, the reaction product of a dicarboxylic anhydride (preferably maleic anhydride) with one of the above-mentioned hydroxyl group-containing amines is preferably used.

[0065] In addition to carboxylic acids and ester, monoester and / or diester components, polymer A may also contain up to 20% by weight, preferably 0.1% to 10% by weight of additional monomer structural units which are neither units of ethylenically unsaturated monocarboxylic and / or dicarboxylic acids nor units of esters of ethylenically unsaturated monocarboxylic acids, monoesters or diesters of ethylenically unsaturated dicarboxylic acids with amines having at least one hydroxyl group.

[0066] The additional monomer structural units are monomers copolymerized in the form of, for example, those described for polymer P. Styrene monomers such as styrene, olefins such as ethylene, or (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate and mixtures thereof are particularly preferred.

[0067] Polymer A is preferably prepared by radical polymerization in bulk or in solution as described in US 6,841,608.

[0068] Polymer A can also advantageously be prepared by polymer-analogous reactions. For this purpose, a polymer incorporating 80% to 100% by weight of at least one ethylenically unsaturated monocarboxylic and / or dicarboxylic acid and 0% to 20% by weight of the above-mentioned other polymers is reacted with at least one hydroxyl group-containing amine.

[0069] The proportions of the structural units are calculated based on the assumption that all monomers are converted into the polymer (100% conversion). In the case of polymer-analogous reactions, the weight fraction of the esters is calculated based on the assumption that the amine having at least one hydroxyl group is completely esterified. In addition, it is assumed that in the presence of dicarboxylic acids, half-esters are formed.

[0070] Polymer P is preferably prepared by radical polymerization in an aqueous medium in the presence of polymer A as described in US 6,841,608. The aqueous dispersion of polymer P is prepared by aqueous emulsion polymerization, and batch, semi-continuous or continuous procedures are possible. Preferably, no additional emulsifier is added to stabilize the emulsion in addition to polymer A.

[0071] The polymerization is carried out in the presence of compounds that form free radicals (initiators). These can be peroxides, azo compounds. or redox initiator systems. All these types of initiators are well known to those skilled in the art and are described, for example, in US 6,841,608. Based on the monomers used in the polymerization, the amount of these initiators required is preferably 0.05% to 10% by weight, particularly preferably 0.2% to 5% by weight.

[0072] The initiators can be used alone or as a mixture with each other, examples being a mixture of hydrogen peroxide and sodium persulfate. For polymerization in an aqueous medium, water-soluble initiators are preferably used.

[0073] To prepare polymers with a low average molecular weight, it is generally advisable to carry out the copolymerization in the presence of a regulator (free radical chain transfer agent). Conventional regulators can be used for this purpose, examples being organic compounds containing SH groups such as 2-mercaptoethanol, 2-mercaptopropanol, mercaptoacetic acid, tert-butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan and tert-dodecyl mercaptan, hydroxylamine salts such as hydroxylamine sulfate, formic acid, sodium bisulfite or isopropanol. The polymerization regulator is generally used in an amount of 0.05% to 5% by weight based on the monomers.

[0074] To prepare relatively high molecular weight copolymers, it is generally advisable to carry out the polymerization in the presence of a crosslinking agent. Such crosslinking agents are compounds having two or more ethylenically unsaturated groups, such as, for example, diacrylates or dimethacrylates of at least dihydroxy saturated alcohols, examples being ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,2-propanediol diacrylate, 1,2-propanediol dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, hexanediol diacrylate, hexanediol dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, 3-methylpentanediol diacrylate and 3-methylpentanediol dimethacrylate. Acrylates and methacrylates of alcohols having more than 2 OH groups can also be used as crosslinking agents, examples being trimethylolpropane triacrylate or trimethylolpropane trimethacrylate.

[0075] Based on solids, the weight ratio of polymer P to polymer A is preferably in the range of 4:1 to 1:4, especially 3:1 to 1:3.

[0076] The binder system (B) according to the invention further comprises at least one amine and / or amide having at least two hydroxyl groups in an amount of 1% to 10% by weight based on the amount of polymer P.

[0077] Suitable amines having at least two hydroxyl groups are alkoxylated alkylamines, preferably ethoxylated or propoxylated alkylamines. According to one embodiment, these alkylamines are also the alkylamines present in polymer A in esterified form. The alkoxylated alkylamines and additional alkylamines (b) present in polymer A can be the same or different compounds.

[0078] Suitable amines and / or amides having at least two hydroxyl groups are the alkanolamines disclosed in DE 197 29 161, which is hereby incorporated by reference into the disclosure of the present invention.

[0079] The preferred amines are β-hydroxyalkylamines of the formula

[0080] R 1 -N(R 2 )-R 3 (I)

[0081] wherein R 1 is a hydrogen atom, a C 1 to C 10 alkyl, a C 1 to C 10 hydroxyalkyl or a radical of the formula II

[0082] -(CH 2 CH 2 O) x (CH 2 CH(CH 3 )O) y -H(II)

[0083] wherein

[0084] in formula II, the order of the alkoxide units is arbitrary, and x and y are independently integers from 0 to 100, the sum of x and y > 1, and

[0085] R 2 and R 3 are independently C 1 to C 10 hydroxyalkyls.

[0086] Particularly preferably, R 2 and R 3 are independently C 2 to C 5 hydroxyalkyls, and R 1 is a hydrogen atom, a C 1 to C 5 alkyl or a C 2 to C 5 hydroxyalkyl.

[0087] Particularly preferred are diethanolamine, triethanolamine, diisopropanolamine, triisopropanolamine, methyldiethanolamine, butyldiethanolamine and methyldiisopropanolamine, especially triethanolamine.

[0088] Further preferred β-hydroxyalkylamines are the amines disclosed as component A in DE 196 21 573, which are hereby incorporated by reference into the disclosure of the present invention. They preferably include linear or branched aliphatic compounds containing at least two alkoxylated functional amino groups per molecule.

[0089] Preferred relatively high functionality β-hydroxyalkylamines are in particular at least diethoxylated amines having a molar mass of less than 1000 g / mol, such as diethanolamine, triethanolamine and ethoxylated diethylenetriamine, for example preferably stoichiometrically ethoxylated diethylenetriamine, i.e. diethylenetriamine in which on average all NH hydrogen atoms are monoethoxylated.

[0090] Further preferred are amides having at least two hydroxyl groups. Suitable amides include β-hydroxyalkylamides, preferably β-hydroxyalkylamides of formula III as specified in US Patent No. 5,143,582

[0091]

[0092] Particularly preferred β-hydroxyalkylamides of the above formula are those β-hydroxyalkylamides in which R1 is hydrogen, short-chain alkyl or HO(R 3 ) 2 C(R 2 ) 2 C-, n and n' are each 1, -A- is (CH 2 ) m - group, m is from 0 to 8, preferably from 2 to 8, R 2 is in each case hydrogen, and in each case one R 3 group in the R 3 groups is hydrogen and the other R 3 group is hydrogen or C 1 -C 5 alkyl. Particularly preferred is bis[N,N-bis(2-hydroxyethyl)]adipamide.

[0093] Adding amines having at least two hydroxyl groups generally results in better curing of the compositions of the present invention at a given curing temperature, or respectively, curing for a given curing time at low temperature. The weight fraction of the amine is from 0% to 30% by weight, preferably from 0.1% to 15% by weight, relative to the sum of polymers P and A.

[0094] Additionally, reaction promoters can be added to the polymer dispersions of the present invention. Preferred such promoters are phosphorus compounds, in particular hypophosphorous acid and its alkali metal and alkaline earth metal salts, or alkali metal tetrafluoroborates. Other reaction promoters that can be added include salts of Mn(II), Ca(II), Zn(II), Al(III), Sb(III) or Ti(IV), or strong acids such as p-toluenesulfonic acid, trichloroacetic acid and chlorosulfonic acid. The weight fraction of the reaction promoter relative to the sum of polymers P and A is from 0.1% to 5% by weight, preferably from 0.1% to 2% by weight.

[0095] A particularly preferred composition of the adhesive system of the present invention is as follows:

[0096] 70% to 50% by weight of polymer P,

[0097] 30% to 50% by weight of polymer A and, if desired,

[0098] 0% to 10% by weight of a surface-active alkoxylated alkylamine,

[0099] 1% to 10% by weight of an amine and / or amide having at least two hydroxyl groups,

[0100] 0% to 5% by weight of a reaction promoter.

[0101] The binder system of the present invention essentially comprises finely divided emulsion polymer particles of P and an aqueous phase comprising polymer A and, added separately, an amine and / or amide having at least two hydroxyl groups. It may further comprise amines unreacted during the production of polymer A.

[0102] In the case where the above binder system (B) is used for the production of an aqueous baking paint composition, the aqueous baking paint composition may additionally comprise pigments, fillers, dispersants, thickeners, preservatives, film-forming aids, flow control and wetting aids, solvents, neutralizing agents, defoamers, light stabilizers and / or corrosion inhibitors.

[0103] The present invention also provides an aqueous baking paint composition comprising

[0104] (a) a binder system (B) according to the present invention

[0105] (b) one or more defoamers

[0106] (c) optionally one or more coalescing agents

[0107] (d) optionally one or more pigments or fillers

[0108] (e) optionally one or more other additives

[0109] (f) optionally one or more polyurethane dispersions having sulfonic acid groups,

[0110] Preferably, any pigments and fillers present in the pigments and fillers in the aqueous baking paint composition have a particle size not greater than 50 μm according to DIN EN ISO 1524.

[0111] Defoamers are liquids with low surface tension that have controlled insolubility or incompatibility in the system to be defoamed, as well as positive osmotic and spreading coefficients (Mannari, Patel, Understanding Coatings Raw Materials, Vincentz Verlag 2015, page 254). The effectiveness of such liquid defoamers can be enhanced by adding finely dispersed hydrophobic particles, which contribute to destabilization by reducing the cohesion. The main classes of defoamers for water-based coatings are: mineral oil-based defoamers, silicone defoamers, and fluorinated defoamers.

[0112] Coalescents are obvious to those skilled in the art. Non-exclusive examples of coalescents include monoethers and monoesters of diols, preferably diols having at least one terminal hydroxyl group. Monoethers of ethylene glycol are readily available. Preferred in this category are monoethers of propylene glycol, especially the methyl, tert-butyl, n-butyl, and phenyl monoethers of propylene glycol, dipropylene glycol, and tripropylene glycol.

[0113] Pigments that can be used in this context in principle include all organic and / or inorganic white and / or colored pigments known to those skilled in the art and having a particle size ≤ 10,000 nm (Brock, Groteklaes, Mischke, Lehrbuch der Lacktechnologie 2nd edition, edited by U. Zorll, Vincentz Verlag 1998, page 113).

[0114] Due to its high refractive index (rutile: 2.70 and anatase: 2.55) and its high hiding power, the most important white pigment mentioned is titanium dioxide in various modified forms. However, zinc oxide and zinc sulfide are also used as white pigments. These white pigments can be used in surface-coated or uncoated form. However, in addition, organic white pigments are also used, such as, for example, non-film-forming hollow polymer particles with a high styrene and carboxyl content, having a particle size of about 300 nm to 400 nm (referred to as opaque particles).

[0115] In addition to white pigments, various colored pigments known to those skilled in the art can be used to provide color. Examples are the relatively inexpensive inorganic oxides and sulfides of iron, cadmium, chromium, and lead, lead molybdate, cobalt blue, or carbon black, as well as the relatively expensive organic pigments, examples being phthalocyanines, azo pigments, quinacridones, perylenes, or carbazoles.

[0116] Optionally or in addition to pigments, the aqueous baking paint composition may of course also contain fillers, as are well known to those skilled in the art. Fillers are basically understood to be inorganic materials in the form of powders with a particle size ≤ 10,000 nm (Brock, Groteklaes, Mischke, Lehrbuch der Lacktechnologie 2nd Edition, edited by U. Zorll, Vincentz Verlag 1998, page 113) with a lower refractive index compared to pigments (white fillers according to DIN 55943 and DIN 55945 have a refractive index value < 1.7). Fillers in powder form are usually naturally occurring minerals such as, for example, calcite, chalk, dolomite, kaolin, talc, mica, diatomaceous earth, barite, quartz or talc / chlorite symbionts, as well as synthetically prepared inorganic compounds such as, for example, precipitated calcium carbonate, calcined kaolin or barium sulfate, and pyrogenic silica. The filler preferably used is barium sulfate.

[0117] Optionally, the aqueous baking paint composition may contain other additives e), such as flow control agents, anti-settling agents, antioxidants, UV stabilizers, rheology modifiers, plasticizers, gloss improvers, wetting agents, waxes and catalysts, which contribute to obtaining a high-quality coating.

[0118] The corrosion inhibitors or flash rust inhibitors contemplated according to the present invention are in particular corrosion inhibitors or anti-corrosion pigments. Examples of corrosion inhibitors are listed in "Corrosion Inhibitors, 2nd Edition. An industrial Guide", Ernest W. Flick, editor: William Andrew Inc. ISBN: 978-0-8155-1330-8. Preferred corrosion inhibitors are hexamine, benzotriazole, phenylenediamine, dimethylethanolamine, polyaniline, sodium nitrite, cinnamaldehyde, condensation products of aldehydes and amines (imines), chromates, nitrites, phosphates, hydrazine and ascorbic acid.

[0119] Examples of anti-corrosion pigments are, for example, modified zinc orthophosphate from Heubach GmbH (e.g. ZPA, ZPO and ZMP), polyphosphates (e.g. ZAPP, SAPP, SRPP and CAPP), WSA - broad-spectrum corrosion inhibitors (e.g. ZAMPLUS and ZCPPLUS) and modified silicate pigments (e.g. CTF, Ha- 750), as well as barium borophosphate from company (e.g. 400), barium phosphosilicate (e.g. BW-111, BW-191), calcium borosilicate (e.g., CW-291, CW-22 / 221, CW-2230), calcium phosphosilicate (e.g., CW-491), strontium phosphosilicate (e.g., SW-111) or strontium zinc phosphosilicate (e.g., SZP-391).

[0120] Optionally, the aqueous baking paint composition may comprise one or more polyurethane dispersions (PUDs) having sulfonic acid groups and / or poly(ethylene oxide) side chains. Typical thermoplastic PUDs are prepared by reacting a polyol with a diisocyanate, a monomeric diol or diamine (referred to as a chain extender) and a hydrophilic group-containing diol (or diamine). The high MW polymer chains of such polyurethane resins contain soft domains derived from the polymerized polyol and hard domains derived from the isocyanate, chain extender and hydrophilic group-containing diol (or diamine). Preferred for blending with polyacrylates are PUDs in which the hydrophilic group is a sulfonate moiety, as described in WO9906459 and WO2003050156.

[0121] Alternatively, other crosslinking agents, such as amino resins, may be added in an amount of up to 40% of the total resin solids.

[0122] According to a preferred embodiment, the aqueous baking paint composition consists of:

[0123] (a) a binder system (B) according to the present invention

[0124] (b) one or more defoamers

[0125] (d) one or more pigments and / or fillers,

[0126] (c) optionally one or more coalescing agents

[0127] (e) optionally one or more other additives

[0128] (f) optionally one or more polyurethane dispersions having sulfonic acid groups.

[0129] Provided that any pigments and fillers present in the pigments and fillers in the aqueous baking paint composition have a particle size of not more than 50 μm, preferably ≤30 μm, particularly ≤20 μm according to DIN EN ISO 1524.

[0130] The proportion of pigments and fillers in the baking paint composition can be described in a well-known manner by the pigment volume concentration (PVC). The PVC describes the volume (V P ) of the pigment and the volume (V F) ratio to the total volume, which total volume consists of the volume (V B ) of the binder system of the dry coating film, the volume of the pigment and the volume of the filler, in percentage:

[0131] PVC = (V P + V F ) x 100 / (V P + V F + V B ).

[0132] The effect of the binder system according to the invention is particularly relevant in the case of pigmented baking enamel compositions having a PVC of at least 5, especially at least 10. Preferably, the PVC does not exceed a value of 50, especially 40, and especially in the range from 5 to 40.

[0133] According to another preferred embodiment, the aqueous baking enamel composition consists of:

[0134] (a) a binder system (B) according to the invention

[0135] (b) one or more defoamers

[0136] (d) one or more pigments and / or fillers,

[0137] (c) optionally one or more coalescing agents

[0138] (e) optionally one or more other additives

[0139] (f) optionally one or more polyurethane dispersions having sulfonic acid groups,

[0140] wherein the condition is that the baking enamel composition has a PVC in the range from 5 to 50.

[0141] According to another preferred embodiment, the aqueous baking enamel composition contains neither any pigments nor any fillers.

[0142] The content of the binder system B according to the invention in the aqueous baking enamel can vary within a wide range. Based on the aqueous baking enamel composition, it is generally 20% to 50% by weight of polymer P.

[0143] According to a preferred embodiment, the composition of the aqueous baking enamel is

[0144] (a) 30% to 99.9% by weight of the binder system (B) of the invention

[0145] (b) 0.1% to 1% by weight of defoamer

[0146] (c) 0% to 8% by weight of coalescing agent

[0147] (d) 0% to 40% by weight of pigments and / or fillers

[0148] (e) 0% to 8% by weight of other additives

[0149] (f) 0% to 30% by weight of polyurethane dispersions having sulfonic acid groups

[0150] An aqueous baking paint is prepared by combining the components of the composition and making a homogeneous mixture. In the presence of pigments and / or fillers, the high particle size present in the aqueous paint is adjusted to a diameter ≤ 50 μm, preferably ≤ 30 μm, especially ≤ 20 μm according to DIN EN ISO 1524 (Paints, varnishes and printing inks - Determination of fineness of grind). The adjustment of the particle size is carried out, for example, by grinding as described in Paint and Surface Coatings, Theory and Practice, 2nd edition, edited by R Lambourne and TA Strivens, Woodhead Publishing Limited, Cambridge England, 1999; pages 117 et seq.

[0151] The composition of the present invention does not release formaldehyde during the crosslinking process. Formaldehyde-free means that the composition of the present invention does not contain a significant amount of formaldehyde and does not release a significant amount of formaldehyde during drying and / or curing. Generally, the composition contains < 100 ppm, preferably < 10 ppm of formaldehyde.

[0152] The viscosity of the binder system (at a solids content of 40% by weight) is generally in the range of about 10 mPas to 4000 mPas, measured at 23 °C using a rotational viscometer according to DIN 53019. -1 and a shear rate of 250 s

[0153] Using the baking paint composition, a coating can be produced on a metal surface or a pre-coated metal surface.

[0154] The disclosed aqueous baking paint composition can be present as a layer of a single-layer coating system or as one or more layers of a multi-layer coating system. The coating composition can be used as a primer, an intermediate coat, a topcoat, or a combination thereof. The coating thickness of a specific layer and the entire coating system will vary depending on the coating material used, the substrate, the coating application method, and the end use of the coated article.

[0155] The present invention also provides a method of applying a baking paint composition to a metal surface or a pre-coated metal surface, the method comprising:

[0156] (1) Apply an aqueous baking paint composition comprising at least a binder system (B) to a metal surface or a pre-coated metal surface to form a coating;

[0157] Optionally dry the coating,

[0158] (2) Then cure the coating by treatment at a temperature in the range of 130 °C to 350 °C, preferably 150 °C to 350 °C.

[0159] Suitable substrates are mainly pretreated, pre-coated (e.g., primed) or unprocessed metal substrates such as iron or steel, galvanized iron or steel, aluminum (or aluminum alloy) or other sheet metals such as tinplate.

[0160] Preferably, the metal surface or substrate is the surface of a metal structure or construction. Preferably, the metal surface or substrate is the surface of a building, engine component, gearbox, (food) container, tank, power station, chemical plant, valve, pipe, drum, fitting, flange, connector, roof and coil.

[0161] The aqueous baking paint composition is used in industrial coatings, mainly in the fields of (internal and external) drum coating, coil coating, packaging coating and automotive coating.

[0162] The application can be carried out by methods commonly used in coating technology such as roll coating, spraying, brushing, marbleizing or dip coating.

[0163] The thickness of such layers to be cured can be from 0.1 μm to 2000 μm, preferably from 1 μm to 2000 μm, particularly preferably from 5 μm to 200 μm, very particularly preferably from 5 μm to 60 μm (based on the material coating composition in the state where the solvent has been removed from the material coating composition).

[0164] Drying is well known to those skilled in the art and is carried out, for example, in a tunnel oven or by flash evaporation. Drying can also be carried out by means of NIR radiation, where NIR radiation here refers to electromagnetic radiation with a wavelength range of 760 nm to 2.5 μm, preferably 900 nm to 1500 nm. Drying can be carried out at a temperature from ambient temperature up to 100 °C for a period of several minutes to several days.

[0165] After drying, they can be cured in a conventional manner, preferably at a temperature in the range of 130 °C to 180 °C, preferably 150 °C to 180 °C, preferably 140 °C to 160 °C. This curing usually takes 10 minutes to 25 minutes.

[0166] Alternatively, if a short curing time is desired, for example from a few seconds to a few minutes, usually from 10 seconds to 5 minutes, a higher temperature is selected, i.e., between 200 °C and 350 °C (target temperature).

[0167] Upon heating, the water in the composition evaporates and the composition cures (hardens). These processes can occur simultaneously or sequentially. In this context, curing refers to a chemical change in the composition; for example, crosslinking by forming covalent bonds, forming ionic interactions and clusters, and forming hydrogen bonds between different components of the composition. Curing can also be accompanied by physical changes within the binder, such as, for example, phase rearrangement or phase transformation. The advantage of the compositions of the present invention is that they can cure at relatively low temperatures. The duration and temperature of heating affect the degree of curing.

[0168] The cured coatings according to the present invention have good elasticity, good adhesion of the resulting coatings, high gloss, excellent surface hardness (non-oriented), and good water resistance, and all of their components are compatible.

[0169] The present invention further provides a coated metal article obtained by applying a baking paint comprising the binder system B according to the present invention.

[0170] The following non-limiting examples are used to illustrate the present invention. Examples

[0171] Unless otherwise specified in the context, percentages always represent weight percentages. The reported contents relate to the contents in aqueous solutions or dispersions. The expression "pphm (parts per hundred parts of monomer)" represents the weight ratio based on 100 parts by weight of monomer.

[0172] When water is used in the context of the examples, deionized water is used.

[0173] Measurement method

[0174] The solids content is usually determined by drying a limited amount (about 0.8 g) of an aqueous polymer dispersion at a temperature of 130 °C to constant weight using an HR73 moisture analyzer from Mettler Toledo. Two measurements are made in each case, and the average of these two measurements is reported.

[0175] The weight average particle size (Dw) is determined according to ISO 13321 using a high-performance particle size analyzer from Malvern at 22 °C and a wavelength of 633 nm.

[0176] The non-volatile content is determined by the weight loss of a 1 g sample dried for two hours at 120 °C in a circulating air drying oven.

[0177] Viscosity:

[0178] The viscosity of the composition is measured according to DIN 53019 in an Anton Paar DSR 301 at 250 sec -1The shear rate is determined at 23 °C.

[0179] Example 1

[0180] 1a) Preparation of Polymer A

[0181] 0.78 kg of deionized water, 0.28 kg of maleic anhydride, and 0.22 kg of ethoxylated oleylamine (average degree of ethoxylation = 10) are added to a pressure reactor equipped with an anchor stirrer. The initial feed is heated to 125 °C under a nitrogen atmosphere. At this temperature, Feed Stream 1, consisting of 0.73 kg of deionized water and 0.77 kg of acrylic acid, is metered in over a 4-hour period, and Feed Stream 2, consisting of 0.04 kg of deionized water and 0.11 kg of H 2 O 2 (30% by weight strength), is metered in over a 5-hour period, with both feeds introduced at a uniform rate. After Feed Stream 1 is completed, an additional 0.10 kg of deionized water is added. After the reaction is complete, the mixture is cooled to room temperature. The resulting aqueous polymer solution has a solids content of 43.0%, a pH of 2, and a viscosity of 450 mPas.

[0182] Weight fraction of ester (calculated): 19.7% by weight

[0183] Weight fraction of acid (calculated): 80.3% by weight

[0184] 1b) Preparation of Polymer P

[0185] 335 g of water and 3% by weight of Feed Stream 2 are added to a 4 L glass vessel equipped with an anchor stirrer (120 rpm), and the initial feed is heated to 90 °C. After 5 minutes, at this temperature, Feed Stream 1 is metered in over a 3-hour period, and the remainder of Feed Stream 2 is metered in over a 3.5-hour period, with the feed points spatially separated. Subsequently, polymerization is continued at this temperature for 60 minutes, and the reaction mixture is cooled.

[0186] Feed stream 1:

[0187] 1978 g of Polymer A from Example 1a) (43% by weight strength)

[0188] 595 g of styrene

[0189] 213 g of methyl methacrylate

[0190] 43 g of 2-hydroxyethyl acrylate

[0191] Feed stream 2:

[0192] 335 g of deionized water

[0193] 4.3 g of sodium persulfate

[0194] The dispersion of polymer P prepared in this way contains 48% by weight of non-volatile components and has a pH of 2.0 and a viscosity of 750 mPas.

[0195] Example 1c) Preparation of Adhesive System B1

[0196] An aqueous solution (85% by weight) of 5.1 g of 2,2',2”-nitrilotriethanol (= triethanolamine) was added to 100 g of the aqueous dispersion of Example 1b), and the mixture was stirred well. The pH of the mixture was 3.0. The viscosity of the resulting binder system B1 was 1100 mPas.

[0197] Example 2

[0198] Preparation of Adhesive System B2

[0199] 9 g of bis(2-hydroxyethyl) adipate (Primid(R) from EMS Chemie) was added to 40 g of the dispersion prepared in Example 1b), and the mixture was stirred well for 20 minutes. Then an additional 60 g of the dispersion prepared in Example 1b) was added. The pH of the mixture was 1.8.

[0200] Example 3

[0201] 3b) Preparation of Polymer P

[0202] 258 g of water and 3% by weight of feed stream 2 were added to a 4 L glass vessel equipped with an anchor stirrer (120 rpm), and the initial feed was heated to 90 °C. After 5 minutes, at this temperature, feed stream 1 was metered in over a 3-hour period, and the remainder of feed stream 2 was metered in over a 3.5-hour period, with the feed points spatially separated. Subsequently, the polymerization was continued at this temperature for 60 minutes, and the reaction mixture was cooled.

[0203] Feed stream 1:

[0204] 2002 g of polymer A from Example 1a) (43% weight strength)

[0205] 440 g of water

[0206] 301 g of n-butyl methacrylate

[0207] 517 g of methyl methacrylate

[0208] 43 g of 2-hydroxyethyl acrylate

[0209] Feed stream 2:

[0210] 81 g of deionized water

[0211] 4.3 g of sodium persulfate

[0212] The dispersion of polymer P prepared in this way contains 47.3% non-volatile components by weight and has a pH of 2.1 and a viscosity of 425 mPas.

[0213] Example 3c) Preparation of Adhesive System B3

[0214] 4.3 g of 2,2',2”-nitrilotriethanol ( = triethanolamine) was added to 100 g of the aqueous dispersion of Example 3b), and the mixture was stirred well.

[0215] Example 4

[0216] 4b) The dispersion was prepared by the same method as in Example 3, but using

[0217] Feed stream 1:

[0218] 2002 g of polymer A from Example 1a) (43% weight strength)

[0219] 440 g of water

[0220] 34 g of n-butyl methacrylate

[0221] 375 g of methyl methacrylate

[0222] 409 g of cyclohexyl methacrylate

[0223] 43 g of 2-hydroxyethyl acrylate

[0224] Feed stream 2:

[0225] 81 g of deionized water

[0226] 4.3 g of sodium persulfate

[0227] The dispersion of polymer P prepared in this way contains 46.4% non-volatile components by weight and has a pH of 2.1 and a viscosity of 715 mPas.

[0228] 4c) Preparation of Adhesive System B4

[0229] Subsequently, 4.3 g of 2,2',2”-nitrilotriethanol ( = triethanolamine) was added to 100 g of the aqueous dispersion of Example 3b), and the mixture was stirred well. The pH of the mixture was 2.8 and the LD was 42.

[0230] Performance testing

[0231] Dispersion of pigments

[0232] Disperse the pigments using a dissolver with a Teflon disc and 2 mm glass beads.

[0233] Determination of grinding fineness

[0234] The fineness of grinding is determined using a Hegman Grindometer according to DIN EN ISO 1524. A fineness of 20 μm is considered good for industrial paints.

[0235] Gloss / haze

[0236] The gloss of the cured paint film is measured using a Byk-Instruments micro-TRI-gloss instrument according to DIN EN ISO 2813. Most of the films are white in color, and the dry film thickness and substrate will be provided in the context of the test results. A baking paint with a gloss of 60 units at a 60° angle is considered glossy, and below 60 gloss units is considered semi-glossy.

[0237] Adhesion

[0238] The adhesion of the paint to the metal substrate of the painted and cured sheets is tested using a cross-cut test according to DIN EN ISO 2409. A cross-cut test result of GT 0 is rated as very good, G1 as good, and GT2 as acceptable.

[0239] The wet adhesion of the cured paint on the metal substrate is carried out similar to DIN EN ISO 2812-4 (version A) using distilled water. After 24 hours of exposure, the water is removed, and then immediately a cross-cut test is carried out on the wetted area according to DIN EN ISO 2409. After 24 hours of recovery at room temperature, the cross-cut test is repeated at another point on the previously wetted paint film. In addition to the cross-cut rating, good results are the absence of blistering (0 (S0) according to DIN EN ISO 4628-2) and rusting (Ri 0 according to DIN EN ISO 4628-3).

[0240] Film thickness

[0241] The dry film thickness of the cured coating film is determined using an eddy current gauge according to DIN EN ISO 2808.

[0242] Hardness

[0243] The hardness of the cured coating film is measured according to DIN EN ISO 1522 (pendulum hardness according to ). For waterborne baking paints, a hardness above 100 osc. is considered good and above 120 osc. is very good.

[0244] Flexibility

[0245] The flexibility of the cured film on the metal substrate is tested by Erichsen cupping test according to DIN EN ISO 1520. The flexibility is related to the dry film thickness (DFT) and the substrate used. At a DFT of 50 μm on cold rolled steel sheet (Gardobond Oc), an Erichsen cupping result of 8 mm is considered good and greater than 9 mm is very good.

[0246] Double rubbing with MEK (methyl ethyl ketone)

[0247] The tolerance to methyl ethyl ketone as a measure of chemical crosslinking and chemical resistance is measured according to ASTM D5402 (double rub on the paint surface). If more than 200 double rubs are achieved, the test is passed, indicating a very high degree of crosslinking.

[0248] Determination of liquid resistance

[0249] This test is carried out according to DIN EN ISO 2812-3: Dip a filter paper into the liquid substance and place it on top of the panel (horizontal orientation). At the end of the test period, remove the filter paper, dry the test panel and clean it with water or a solvent that does not attack the coating. Immediately fool the blistering of the exposed area (ISO 4628-2) and evaluate the visible changes on the surface according to ISO 4628-1. A test result of 0 is considered excellent, 1 - 2 is good, 3 is acceptable, and 4 - 5 is poor.

[0250] Application of liquid paint

[0251] The paint is applied by knife coating (180 μm or 200 μm film applicator).

[0252] Drying

[0253] The coated panel is flash dried at room temperature for 10 minutes and then at 80 °C for 10 minutes.

[0254] Curing

[0255] The coated panel is heated at 160 °C for 20 minutes. The curing process is usually carried out directly after drying.

[0256] Curing under coil coating conditions

[0257] Heat the coated plate at a peak metal temperature of 225 °C for 35 seconds.

[0258] Preparation of the waterborne baking paint composition:

[0259] Prepare a white liquid paint according to the following formulation:

[0260] Table 1

[0261]

[0262] Apply a film with a dry film thickness of approximately 50 μm to cold-rolled steel sheets (Gardobond OC) by knife coating, and dry and cure.

[0263] Application test results

[0264] Table 2

[0265]

[0266] Liquid resistance

[0267] Table 3

[0268] The coating film exhibits excellent chemical resistance.

[0269] Preparation of liquid paint using Adhesive System B2

[0270] Apply a film of binder system B2 (48% non-volatile components by weight) to aluminum sheets (Q-Panel A412) by knife coating to form a dry film approximately 40 μm thick. Dry and cure these sheets under coil coating conditions.

[0271] Application test results

[0272] Table 4

[0273]

[0274] The transparent film of binder system B2 shows good hardness, excellent adhesion, and chemical resistance.

[0275] Prepare liquid paints using binder systems B3 and B4:

[0276] The films of binder systems B3 (47% non-volatile content by weight) and B4 (47% non-volatile content by weight) were applied to aluminum plates (Q-Panel A412) by knife coating to form dry films approximately 30 μm thick. These plates were dried and cured under coil coating conditions.

[0277] Application test results

[0278] Table 5

[0279]

[0280] The data in Table 5 show the excellent adhesion and chemical resistance of binder systems B3 and B4.

Claims

1. Use of an adhesive system (B) in an aqueous baking paint composition, wherein the adhesive system (B) comprises (a) an aqueous dispersion of a polymer P and (b) at least one amine and / or amide having at least two hydroxyl groups, in an amount of 1% to 10% by weight based on the amount of polymer P, wherein the aqueous dispersion of the polymer P is prepared by free-radical-initiated emulsion polymerization of the following ethylenically unsaturated monomers M: 90% to 99% by weight of styrene, C 1 -C 6 -alkyl ester and / or cyclohexyl methacrylate; 1% to 10% by weight of one or more monoethylenically unsaturated carboxylic acids, hydroxy(C 2 -C 4 )alkyl esters of (meth)acrylic acid and / or glycidyl (meth)acrylate; 0% to 9% by weight of acrylic C 4 -C 10 -alkyl ester, and wherein the amount of the monomers M totals 100% by weight, in an aqueous medium, in the presence of a polymer A having the following monomer structural units: one or more ethylenically unsaturated monocarboxylic acids and / or dicarboxylic acids in an amount of 70% to 95% by weight, at least one of an ester of an ethylenically unsaturated monocarboxylic acid, a monoester of an ethylenically unsaturated dicarboxylic acid, and a diester of an ethylenically unsaturated dicarboxylic acid, wherein each ester is obtained by esterifying with an amine having at least one hydroxyl group, and at least one further monomer in an amount of 0% to 20% by weight; the amounts are in each case based on the total amount of all monomer structural units in the polymer A.

2. Use according to claim 1, wherein the polymer P is prepared by polymerization of the following monomers M: 90% to 99% by weight of styrene, C 1 -C 4 -alkyl ester and / or cyclohexyl methacrylate; 1% to 10% by weight of one or more monoethylenically unsaturated carboxylic acids, 2-hydroxyethyl acrylate and / or 2-hydroxyethyl methacrylate, 0% to 9% by weight of acrylic acid C 4 -C 10 -alkyl ester; and wherein the amount of the monomers M totals 100% by weight.

3. Use according to claim 1 or 2, wherein the polymer A has the following monomer structural units: acrylic acid and maleic acid in an amount of 70% to 95% by weight, at least one of an ester of an ethylenically unsaturated monocarboxylic acid, a monoester of an ethylenically unsaturated dicarboxylic acid, and a diester of an ethylenically unsaturated dicarboxylic acid, wherein each ester is obtained by esterifying with an amine having at least one hydroxyl group, and at most 20% by weight of at least one further monomer; the amounts are in each case based on the total amount of all monomer structural units in the polymer A.

4. Use according to any one of claims 1 to 3, wherein the ester structural unit of the polymer A is obtained by esterifying with an amine having at least one hydroxyl group, and the amine having at least one hydroxyl group is an alkoxylated amine.

5. Use according to any one of claims 1 to 4, wherein the ester structural unit of the polymer A is obtained by esterifying with an amine having at least one hydroxyl group, and the amine having at least one hydroxyl group is an alkoxylated fatty amine.

6. Use according to any one of claims 1 to 5, wherein the solids-based weight ratio of the polymer P to the polymer A is in the range of 4:1 to 1:

4.

7. Use according to any one of claims 1 to 5, wherein the amine has at least two hydroxyl groups.

8. Use according to any one of claims 1 to 4, wherein (b) is selected from the group consisting of diethanolamine, triethanolamine, diisopropanolamine, triisopropanolamine, methyldiethanolamine, butyldiethanolamine, and methyldiisopropanolamine.

9. An aqueous baking paint composition, which comprises (a) an adhesive system (B) according to one of claims 1 to 8 (b) one or more defoamers (c) optionally one or more coalescing agents (d) optionally one or more pigments or fillers (e) optionally one or more other additives (f) Optionally, one or more polyurethane dispersions having sulfonic acid groups.

10. A method of applying a baking paint composition to a metal surface or a pre-coated metal surface, the method comprising (1) applying the aqueous baking paint composition comprising at least the binder system (B) according to any one of claims 1 to 8 to the metal surface or the pre-coated metal surface to form a coating; Optionally drying the coating, (2) curing the coating by treating the coating at a temperature in the range of 130 °C to 350 °C.

11. The method according to claim 10, wherein the metal surface or the pre-coated metal surface is the surface of a metal structure or a metal construction.

12. The method according to claim 11, wherein the metal surface or the pre-coated metal surface is the surface of a building, an engine component, a gearbox, a (food) container, a power station, a chemical plant, a valve, a pipe, a drum, a fitting, a flange, a coupler, a roof and a coil.

13. The method according to any one of claims 10 to 12, wherein the thickness of the cured baking paint is from 0.1 μm to 2000 μm.

14. A coated article obtainable by a method according to one of claims 10 to 13.

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