Anticorrosive aqueous coating composition

Abstract

The present invention relates to an aqueous resin dispersion comprising a mixture of a hydrophilically modified epoxy-based resin, a crosslinker, and a co-crosslinker. The present invention also relates to an aqueous coating composition comprising said resin dispersion that provides improved corrosion and tarnishing resistance; a method for preparing the aqueous resin dispersion and the coating composition; and the use of the coating composition to coat a metal substrate.

Description

[Technical field]

[0001] The present invention relates to an aqueous resin dispersion and an aqueous coating composition comprising said resin dispersion that provides improved corrosion and discoloration resistance; a process for preparing the aqueous resin dispersion and the coating composition; and the use of the coating composition to coat metal substrates. [Background technology]

[0002] Most metals, except those that form a tightly adherent oxide layer such as precious metals or aluminum, are provided with coatings that prevent or at least slow corrosion when exposed to ambient conditions. The application of a coating to a metal surface provides a barrier between the metal substrate and a damaging atmosphere, provided that the coating adheres well to the metal substrate and has low permeability to oxygen and water. Among the coatings, paints in liquid or powder form play an important role. One aspect to consider when selecting a coating material is how to avoid components in the coating composition that can react with the metal surface and thus damage the metal substrate, such as chloride ions that can provide seeds for future corrosion attacks.

[0003] Many organic polymers are suitable for forming coatings on metal surfaces. These coatings should have sufficient hardness, sufficient adhesion as mentioned above, and sufficient elasticity to allow the coating to follow possible deformations of the coated metal article. Epoxy resins are one of the most commonly used materials in anticorrosive paint formulations (High-Performance Coatings, 2008, ed. A.S. Khanna, "The word epoxy has become synonymous with anti-corrosion in today's industrial environment"). Reaction products made from epoxy resins and amines have become standard materials in cathodic electrocoating of car bodies.

[0004] WO 2015 / 093299 discloses an aqueous resin composition (D) obtained by dispersing a vinyl ester resin (A) and a urethane resin (B) having an aromatic ring in an aqueous medium (C) and adding a carbodiimide crosslinking agent (E) thereto. The vinyl ester resin (A) is prepared by reacting a polymerizable ethylenically unsaturated acid compound (a2) with at least one epoxy resin (a1) selected from the group consisting of novolac-type epoxy resins and bisphenol-type epoxy resins. The urethane resin (B) is obtained by reacting a polyol (b1-1) having an aromatic ring and a polyol (b1-2) having a hydrophilic group, preferably an anionic group, with a polyisocyanate (b2). The carbodiimide crosslinking agent (E) preferably has two or more carbodiimide groups per molecule.

[0005] US Patent Application Publication No. 2010 / 0129659 discloses a coated product made by a 3-coat-1-bake process; the process includes the steps of forming a cured coating film (A1) from a cationic electrodeposition coating composition (A) on a metal object to be coated; forming a first pigmented coating film (B1) thereon by applying a first pigmented aqueous coating composition (B); forming a second pigmented coating film (C1) by applying a second pigmented aqueous coating composition (C) on the uncured first pigmented coating film (B1); forming a clear coating film (D1) on the uncured second pigmented coating film (C1); and simultaneously curing the uncured first pigmented coating film (B1), the uncured second pigmented coating film (C1), and the uncured clear coating film (D1). The cationic electrodeposition coating composition (A) contains a modified epoxy resin (a1) containing cationic amino groups, the modification being brought about by the addition of a xylene formaldehyde resin prepared by condensing xylene and phenol with formaldehyde in the presence of an acid catalyst, which modification imparts plasticity and hydrophobicity to the epoxy resin.

[0006] WO 2013 / 191826 discloses an aqueous mixture comprising an aqueous polyolefin dispersion comprising a melt mixed product of one or more base polymers and one or more stabilizing agents in the presence of water and optionally one or more neutralizing agents, wherein the polyolefin dispersion has an average volume particle size diameter in the range of 400 nm to 1500 nm, and a pH range of 8 to 11; and one or more crosslinkers selected from the group consisting of phenol-formaldehyde resins, hydroxyalkylamide resins, amino-formaldehyde resins, resins containing epoxy groups, and combinations thereof.

[0007] EP 1805260 A relates to a self-adhesive coating composition for the production of electrical steel cores, comprising A) 100 parts per weight of at least one bisphenol A type, bisphenol F type epoxy resin or a mixture thereof, solids content 100%, B) 0.1-200 parts by weight of nanoparticles having an average radius in the range of 2-600 nm, C) 0-25 parts by weight of at least one hardener selected from the group consisting of dicyandiamide, blocked isocyanate and Lewis acid or selected from the group consisting of phenolic resin, carboxylic acid, anhydride and Lewis acid, solids content 100%, D) 0.1-10 parts by weight of at least one additive, and E) 50-200 parts by weight of water or at least one organic solvent.

[0008] WO2018130700 discloses an aqueous resin dispersion D comprising a mixture of a hydrophilically modified epoxy-based resin P and a resole crosslinker R, and a co-crosslinker E, where the hydrophilically modified epoxy-based resin P is made in a reaction or series of reactions including at least one step in which an advancement reaction is performed.

[0009] No. 5,177,161 discloses a can coating application that includes a water-reducible coating based on the condensation product of a phenolic novolac and a bisphenol A epoxy resin of type 7 that is methylated and then reacted with sodium monochloroacetate and then dispersed in water. The epoxy resin and the novolac moieties are linked through ether bonds.

[0010] Other water-dilutable can coating resins based on addition products of carboxylated novolak A and epoxy resin B are known from German Patent No. 19756749. These addition products have at least one ester group per molecule, which is formed by reaction of a carboxyl group of novolak A with an epoxide group of epoxy resin B. These products have a lighter color than those according to U.S. Pat. No. 5,177,161.

[0011] The corrosion resistance of steel sheets with coatings according to the state of the art to date is still not satisfactory, or the corrosion-resistant coatings discolor during baking at temperatures above 160° C. In the worst case, both the corrosion protection and the resistance to discoloration during baking are insufficient.

[0012] The use of resoles as the primary crosslinker for metal coatings to protect the inside surfaces of food cans from corrosive attack of the filled article is widespread. For such applications, the tendency of resoles to discolor when cured at temperatures between 150 and 250°C is known and is not considered a significant problem. Also, if the metal coating is colored with a dark color pigment, the yellowing behavior of the resol crosslinker is not a technical obstacle. However, for lightly colored metal coatings or transparent coatings that should not change color upon oven curing, the use of resols is problematic. Thus, there remains a need for coating compositions that have a high level of metal protection and a low tendency to discolor when cured at elevated temperatures. Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention aims to provide an aqueous dispersion for a coating composition which does not exhibit the disadvantages of the prior art.

[0014] It is an object of the present invention to provide a coating composition which has improved anticorrosion properties and improved resistance to discoloration at high bake temperatures compared to state of the art coating systems. [Means for solving the problem]

[0015] The present invention relates to an aqueous resin dispersion D comprising a mixture of a hydrophilically modified epoxy-based resin P, a blocked isocyanate crosslinking agent IB, and a co-crosslinking agent E, wherein the hydrophilically modified epoxy-based resin P comprises 1-hydroxy-2-phenoxy-ethyl groups; Co-crosslinking agent E is compounds E1 having at least two hydroxyl groups which react at elevated temperatures above 80° C. with acid compounds present in the coating composition with the formation of esters and the liberation of water, and Esters E2 having at least two ester groups, formed from at least dihydric alcohols E22 and acids E21 which are unstable at elevated temperatures above 80°C Selected from the group consisting of: Aqueous Resin Dispersion D is disclosed.

[0016] Preferred embodiments of the present invention have the following features: the blocked isocyanate crosslinker IB is preferably a reaction product of a polyisocyanate and a hydroxyl-functional carbamate C, said hydroxyl-functional carbamate C being a reaction product of a cyclic organic carbonate with an aliphatic mono-, di-, tri-, tetra- and / or alkanolamine, said amine having at least primary or secondary amino groups; the hydroxyl-functional carbamate C is preferably 2-hydroxyethyl bis(2-hydroxyethyl)carbamate or 2-hydroxypropyl bis(2-hydroxyethyl)carbamate; The co-crosslinking agent E1 preferably has the formula: (OH-CHR1-CH2-NR2-CO) m -A-(CO-NR2-CH2-CHR1-OH) n [In formula: R1 is hydrogen or C1-C5 alkyl; R2 is hydrogen, C1-C5 alkyl or CH2-CHR1-OH; A is a chemical bond or a polyvalent organic group derived from a saturated, unsaturated or aromatic hydrocarbon group, including substituted hydrocarbon groups containing 2 to 20 carbon atoms; m is an integer having a value from 1 to 2; m is an integer having a value from 0 to 2, and m+n is at least 2; the co-crosslinking agent E1 is preferably N,N,N',N'-tetrakis-(2-hydroxyethyl)-adipamide or N,N,N',N'-tetrakis-(2-hydroxypropyl)-adipamide; The hydrophilically modified epoxy resin P is a non-ionic modified epoxy resin Pn which is a reaction product of a diepoxide, a divalent aromatic compound and an epoxy-functional non-ionic emulsifier F; the epoxy-functional non-ionic emulsifier F is epoxide-functional polyoxyalkylene homopolymers or copolymers; and / or epoxide-functional sugar alcohols; and / or Reaction products of hydroxyl-functional polyoxyalkylene homopolymers or copolymers or sugar alcohol segments with at least difunctional epoxide compounds and; where: The polyoxyalkylene homopolymer is polyoxyethylene or polyoxypropylene; The polyoxyalkylene copolymer is a polyoxyethylene-propylene copolymer; · Polyoxyalkylene homopolymers and copolymers containing 20-150 C2-C3 oxyalkylene units; The non-ionic modified epoxy resin Pn is preferably characterized by an epoxide equivalent weight (EEW) of 200-2,000 g / equiv.; The aqueous resin dispersion D is preferably For the total weight of P, IB and E, 40 to 90% by weight of a hydrophilically modified epoxy resin P, preferably a non-ionic modified epoxy resin Pn; 5 to 55% by weight of a blocked isocyanate crosslinker IB; and 0.1-5% by weight of co-crosslinker E, preferably E1, more preferably beta-hydroxyalkylamide Contains; The aqueous resin dispersion D preferably comprises one or more catalysts selected from the group consisting of salts, chelates and organometallic compounds of elements of groups 4, 7, 8, 9, 12, 13, 14 and 15 and periods 4, 5 and 6 of the Periodic Table of the Elements according to the new IUPAC naming system, and strong amines, the hydrophilically modified epoxy resin P and / or the blocked isocyanate crosslinker IB in the aqueous resin dispersion D of the present invention are obtained from renewable feedstocks and have, in total, a bio-based carbon content of more than 20% by weight of the total carbon content of the epoxy resin P and the blocked isocyanate crosslinker IB, the bio-based carbon content being determined using the ASTM D6866-20 standard, or the epoxy resin P and / or the blocked isocyanate crosslinker IB are derived from recycled monomers, preferably the hydrophilically modified epoxy resin P and / or the blocked isocyanate crosslinker IB in the aqueous resin dispersion D of the present invention are obtained from renewable feedstocks and have, in total, a bio-based carbon content of more than 20% by weight of the total carbon content of the epoxy resin P and the blocked isocyanate crosslinker IB, the bio-based carbon content being determined using the ASTM D6866-20 standard Disclose one or more of the following.

[0017] The present invention further discloses a coating composition comprising 35-55% by weight of non-volatile compounds and 45-65% by weight of water and a co-solvent selected from the group consisting of alcohols, ketones, esters, glycols, glycol ethers, and glycol esters, and mixtures thereof; said coating composition preferably further comprising one or more additives selected from the group consisting of defoamers, leveling agents, coalescing agents, flow improvers, biocides, pigments, rheology additives, and wetting agents.

[0018] The present invention relates to a method for producing a coated metal substrate, the method further comprising the steps of: applying the coating composition to at least one surface of the optionally pretreated and / or primer-containing metal substrate with a coating thickness adjusted to obtain a dry coating thickness of at least 10 μm; flashing off the water and co-solvent for at least 1 minute at a temperature of at least 20°C; stoving the applied coating composition at a temperature of at least 100° C. for a period of at least 20 seconds to form a metal substrate coated with a crosslinked coating layer. A method is disclosed, comprising:

[0019] The present invention further discloses the use of the coating composition to coat a metal substrate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The aqueous resin dispersion D of the present invention comprises a mixture of a hydrophilically modified epoxy resin P, a crosslinking agent IB, and a co-crosslinking agent E, wherein the hydrophilically modified epoxy resin P comprises a 1-hydroxy-2-phenoxy-ethyl group (the 1-hydroxy-2-phenoxy-ethyl group is an ether bond).

[0021] More specifically, the aqueous resin dispersion D of the present invention comprises a mixture of a hydrophilically modified epoxy-based resin P, a crosslinking agent IB, and a co-crosslinking agent E, where the hydrophilically modified epoxy-based resin P is made by a reaction or a series of reactions including at least one step in which an advancement reaction is carried out, where a phenolic compound having a phenolic hydroxyl group reacts with a compound having at least two reactive epoxide groups to form a 1-hydroxy-2-phenoxy-ethyl group (the reaction of the epoxy group with the phenolic hydroxyl group results in the formation of a 1-hydroxy-2-phenoxy-ethyl group or an ether linkage).

[0022] Alternatively and preferably, where possible, the hydrophilically modified epoxy based resin P and / or the crosslinker IB are derived from renewable feedstocks or recycled monomers, preferably the hydrophilically modified epoxy based resin P and / or the crosslinker IB are derived from renewable feedstocks and have in total a bio-based carbon content of more than 20% by weight of the total carbon content of the epoxy based resin P and the isocyanate crosslinker IB, the bio-based carbon content being determined using the ASTM D6866-20 standard.

[0023] The hydrophilic modified epoxy resin P is selected from the group consisting of at least partially neutralized anionic modified epoxy resin Pa, nonionic modified epoxy resin Pn, and at least partially neutralized anionic and nonionic modified epoxy resin Pan.

[0024] One of the features of the hydrophilically modified epoxy resins P of the present invention is that all the variants Pa, Pn and Pan are always prepared by a reaction or a series of reactions which includes at least one advancement reaction, also called a fusion reaction, in which a phenolic compound having a phenolic hydroxyl group reacts with a compound having at least two epoxide groups.

[0025] The at least partially neutralized anionic modified epoxy resin Pa containing anionic groups is prepared by at least partially neutralizing the acid groups of the product obtained by the first multi-step process or the second multi-step process.

[0026] The first multi-step process for the preparation of the at least partially neutralized anionic modified epoxy resin Pa comprises the following steps a1, b1, c1, d1, e1, and f1: In step a1, a novolak is prepared from phenol and formaldehyde under acid catalysis, and unreacted phenol is separated from the reaction product of step a1; in step b1, the novolak of step a1 is subjected to an advancement reaction under catalysis by adding an epoxy resin having on average at least two functional epoxide groups per molecule, preferably an epoxy resin based on bisphenol A; In step c1, the reaction product of step b1 is dissolved in an organic solvent to form a solution, wherein the solvent is selected from the group consisting of linear or branched aliphatic alcohols, linear or branched aliphatic ethers, linear or branched aliphatic ketones, and mixtures thereof with aromatic hydrocarbons; · the solution of the reaction product of step c1 is then reacted with formaldehyde in the presence of an alkali in step d1 to form a methylol compound; In step e1, after the addition of further alkali, a halogenalkanoic acid, preferably 2-chloroacetic acid, is added to the product of d1, and after complete reaction of the halogenalkanoic acid, the reaction product of step e1 is purified by acidifying it with aqueous acid, separating the organic layer containing the reaction product, and washing the separated solution with distilled water; In step f1, the solvent is removed from the purified reaction product of step e1 by distillation under reduced pressure, and then water and a tertiary amine as a neutralizing agent are added to obtain an aqueous solution with only a small amount of solvent remaining. Includes.

[0027] The second multi-step process for the preparation of an at least partially neutralized anionic modified epoxy resin Pa comprises the following steps a2, b2 and c2: In step a2, an ester of a phosphorus-based acid and an epoxide-functional compound having at least one epoxide group per molecule is prepared, where the phosphorus-based acid has at least two acidic hydrogen atoms per molecule and is selected from the group consisting of inorganic acidic phosphorus compounds and organic acidic phosphorus compounds, and the epoxide-functional compound is an epoxide compound having at least two epoxide groups per molecule, and the reaction is carried out in such a way that the ester resulting from the reaction in step a2 has a specific amount of epoxide groups of less than or equal to 0.1 mol / kg and, on average, at least one acidic hydrogen atom per molecule; In step b2, an advancement reaction is carried out with an at least difunctional epoxide and an aromatic dihydroxy compound in the presence of a catalyst to obtain a polyether compound having epoxide groups; in step c2, the polyether compound of step b2 is dissolved in a solvent and the ester prepared in step a2 is added, with stirring, until a homogeneous mixture is obtained, from which the solvent is then removed by distillation under reduced pressure, Includes.

[0028] The phosphorus-based acid used in step a2 has at least two acidic hydrogen atoms per molecule and is selected from the group consisting of inorganic acidic phosphorus compounds and organic acidic phosphorus compounds. The former groups are orthophosphate H3PO4, diphosphate H4P2O7, triphosphate H5P3O 10 and higher homologues (oligomers), phosphorous acid H3PO3, diphosphorous acid H4P2O5 and higher homologues, and hypophosphorous acid H3PO2 and higher homologues. Particularly preferred are orthophosphoric acid, mixtures of di- and higher oligomers of orthophosphoric acid, phosphorous acid, and higher oligomers thereof. The latter group includes alkanephosphonic acids R 1 -PO3H2, aromatic phosphonic acid R 2 -PO3H2, and the corresponding phosphonous acid H3PO2, where R 1 is a linear, branched or cyclic alkyl having 1 to 20 carbon atoms; R 2 is an optionally substituted aromatic radical having 6 to 20 carbon atoms. Particularly preferred are methanephosphonic acid and benzenephosphonic acid.

[0029] The epoxide-functional compound used in step a2 is preferably a glycidyl ether of a phenolic compound, preferably bisphenol A diglycidyl ether or bisphenol F diglycidyl ether, or an oligomeric or polymeric epoxy resin based on these bisphenols.

[0030] The non-ionic modified epoxy resin Pn is produced by a process including steps a3 and b3. In step a3, the emulsifier F is prepared from a non-ionic portion comprising a polyoxyethylene homopolymer or copolymer segment or a sugar alcohol segment and a non-hydrophilic compatibilizing portion comprising a building block derived from an at least difunctional epoxide compound, preferably bisphenol A diglycidyl ether or an oligomer thereof, by coupling of the at least difunctional epoxide compound with a hydroxy-functional polyoxyethylene homopolymer or a hydroxy-functional polyoxyethylene copolymer or a sugar alcohol, catalyzed by a strong Brönsted or Lewis acid, preferably tetrafluoroboric acid HBF4, boron trifluoride BF3 or complexes thereof with dialkyl ethers or amines. Alternatively, the emulsifier F comprises an epoxide-functional polyoxyethylene homopolymer or an epoxide-functional polyoxyethylene copolymer or an epoxide-functional sugar alcohol. In step b3, the emulsifier F is incorporated into the epoxy resin via an advancement reaction in which a diepoxide, a divalent aromatic compound, and the emulsifier F of step a3 are reacted in the presence of a phosphine or amine catalyst, the stoichiometry being chosen such that the advancement reaction product has epoxide end groups.

[0031] Sugar alcohols have the formula HO-CH2-[-CH(OH)] where n is an integer between 1 and 24. n -CH2-OH compounds, or ethers derived therefrom; commonly known compounds include glycerol, erythritol, threitol, arabitol, xylitol, ribitol, mannitol, sorbitol, galactitol, fucitol, iditol, inositol, volemitol, isomalt, maltitol, lactitol, maltotriitol, and maltotetriitol.

[0032] The modified epoxy resin Pan containing anionic and nonionic groups is preferably prepared by mixing an at least partially neutralized anionic modified epoxy resin Pa and a nonionic modified epoxy resin Pn, and the mixing ratio is preferably selected so that the mass ratio Pa / Pn is 0.2 / 0.8 to 0.8 / 0.2.

[0033] Preferably, the hydrophilically modified epoxy resin P is a non-ionic modified epoxy resin Pn; more preferably, the hydrophilically modified epoxy resin P is a non-ionic modified epoxy resin Pn that is (completely) free of anionic groups (i.e., contains 0.0% anionic groups).

[0034] The hydrophilic modified epoxy resin P is obtained from petrochemical raw materials.

[0035] Alternatively, and preferably, where possible, the hydrophilically modified epoxy resin P is obtained from renewable feedstocks. Particularly preferred renewable feedstocks are those extracted from wood biomass, such as cashew nut shell liquid (CNSL), which is the source of lignin and tannins and phenolic derivatives, such as anarcadic acid, cardanol, cardol and 2-methyl cardol. Also preferred are feedstocks derived from lignocellulosic biomass, such as cellulose and hemicellulose, which can be further depolymerized and dehydrated to 5-hydroxymethyl-2-furfural, which can be further derivatized, such as 2,5-furandicarboxylic acid or 2,5-furandiethanol. Other preferred feedstocks are terpenes and terpenoids, such as limonene and carvacrol, and other phenolic compounds, such as eugenol, ferulic acid and sinapic acid. Other renewable feedstocks for epoxy resins are resin acids (and their mono- and diglycidyl ethers), isosorbide (and its diglycidyl ethers) and oligo- or polyglycerol (and their glycidyl ethers). Epoxide groups can also be introduced into hydrophilically modified epoxy resins P by epichlorohydrin derived partially or entirely from (bio)renewable glycerin. The exact amount of bio-based carbon in these epoxy resins can be determined by the method described in ASTM D6866-20, where the carbon derived from co-present biomass-based materials is differentiated from that derived from fossil-based materials and the bio-based carbon content is reported as a part of the total organic carbon content (TOC). Other standard methods for determining the renewable carbon portion are ISO 16620-2 and CEN 16640.

[0036] Another alternative way to reduce the carbon footprint of the hydrophilically modified epoxy-based resin P of the present invention is to use recycled monomers in its preparation. Polymers such as poly(bisphenol A carbonate) can be depolymerized to obtain monomers (i.e. bisphenol A), which can then be further used to prepare the epoxy-based resin of the present invention.

[0037] In yet another alternative, the hydrophilically modified epoxy-based resin P is obtained from petrochemical and / or renewable feedstocks and / or is derived from recycled monomers.

[0038] As used herein, "bio-based carbon content" means biocarbon content.

[0039] Crosslinking agent IB is a blocked isocyanate comprising the addition reaction product of polyisocyanate compound I and an isocyanate blocking agent B.

[0040] Particularly suitable polyisocyanate compounds I for the blocked polyisocyanates IB are 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 2,4,4-trimethyl-1,6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate, 1-isocyanato-2-isocyanatomethylcyclopentane, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane (isophorone diisocyanate or IPDI), bis(4-isocyanatocyclohexyl)methane, 1,3- and 1,4-bis(isocyanatomethyl )-cyclohexane, bis-(4-isocyanato-3-methyl-cyclohexyl)-methane, alpha,alpha,alpha',alpha'-tetramethyl-1,3- and / or -1,4-xylylene diisocyanate, 1-isocyanato-1-methyl-4(3)-isocyanatomethylcyclohexane, 2,4- and / or 2,6-hexahydrotoluene diisocyanate, 1,3- and / or 1,4-phenylene diisocyanate, 2,4- and / or 2,6-toluene diisocyanate, 2,4- and / or 4,4'-diphenylmethane diisocyanate, 1,5-diisocyanatonaphthylene, 4,4',4"-triphenylmethane diisocyanate. Mixtures of diisocyanates can be used.

[0041] The blocked polyisocyanates IB can be obtained from petrochemical and / or renewable feedstocks and / or derived from recycled monomers. Preferably, the blocked polyisocyanates IB are obtained from petrochemical and / or renewable feedstocks.

[0042] Examples of suitable higher polyisocyanates are triphenylmethane-4,4',4"-triisocyanate, 1,2,4-benzenetriisocyanate and polymethylene polyphenylisocyanate. Suitable higher polyisocyanates can also be formed by dimerization of diisocyanates to form uretdiones or trimerization to form isocyanurates. The reaction of urethanes with isocyanates to form allophanates, and the reaction of ureas with isocyanates to form biurets can be used to produce higher polyisocyanates.

[0043] Isocyanate prepolymers, such as reaction products of polyisocyanates having an equivalent ratio of isocyanate groups to hydroxyl groups (NCO / OH) greater than 1, with polyols (e.g., neopentyl glycol and trimethylolpropane) or polymeric polyols (e.g., polycaprolactone diols and triols), can also be used.

[0044] Preferred diisocyanates are 1,6-hexamethylene diisocyanate, 1,5-pentaethylene diisocyanate, isophorone diisocyanate, bis-(4-isocyanatocyclohexyl)-methane, 2,4- and / or 2,6-toluene diisocyanate, 2,4'- and / or 4,4'-diphenylmethane diisocyanate and alpha,alpha,alpha',alpha'-tetramethyl-1,3- and / or -1,4-xylylene diisocyanate, as well as the diisocyanates mentioned. Oligomers of cyanates, preferably 1,6-hexamethylene diisocyanate, isophorone diisocyanate, bis-(4-isocyanatocyclohexyl)-methane, 2,4- and / or 2,6-toluene diisocyanate, 2,4'- and / or 4,4'-diphenylmethane diisocyanate and alpha,alpha,alpha',alpha'-tetramethyl-1,3- and / or -1,4-xylylene diisocyanate and oligomers of the diisocyanates mentioned.

[0045] Alternatively, and preferably, where possible, the polyisocyanate is derived from renewable feedstocks, with a particularly preferred renewable feedstock being bio-based acetone (i.e., for the production of isophorone diisocyanate). Other preferred polyisocyanates derived in part from renewable feedstocks are, for example, 1,5-pentaethylene diisocyanate (and its trimer, also known under the trade name DESMODUR® eco N 7300), diisocyanates of the methyl or ethyl ester of l-lysine, isosorbide-based diisocyanates, furan-based diisocyanates, bis(4-isocyanato-2-methoxyphenoxy)alkanes, bis(4-isocyanato-2,6-dimethoxyphenoxy)alkanes, 2,4-diisocyanato-1-pentadecylbenzene, di- and polyisocyanates based on fatty acids, dimeric fatty acids and vegetable oils, 1-isocyanato-10-[(isocyanatomethyl)thio]decane and the product known under the trade name TOLONATE® X FLO 100.

[0046] Blocking agent B is added to the isocyanate groups of polyisocyanate compound I to block the isocyanate groups, resulting in urethane structures in the particular case of hydroxyl-functional blocking agent B. If a stoichiometric excess of isocyanate relative to blocking agent B is used, the unreacted isocyanate can also react with the -NH groups of the urethane groups during the formation of the allophanate structures.

[0047] The blocked polyisocyanate IB in the form of a urethane structure or allophanate structure is stable at room temperature; however, the blocking agent B dissociates when heated to the baking temperature of the coating film, usually 100 to 200°C, to regenerate free isocyanate groups.

[0048] Representative blocking agents B are derivatives selected from the group consisting of oximes, lactams, phenols, reactive methylene compounds, pyrazoles (or pyrazole derivatives), mercaptans, imidazoles, amines, imines, triazoles, hydroxylamines, (aliphatic, cycloaliphatic or aromatic) monoalcohols, and hydroxyl-functional carbamates.

[0049] Preferred blocking agents B are aliphatic monoalcohols, oximes, pyrazole derivatives, reactive methylene compounds, or hydroxyl-functional carbamates. More preferably, blocking agent B is a hydroxyl-functional carbamate.

[0050] Suitable aliphatic monoalcohols for use as blocking agent B include methanol, ethanol, 2-propanol, n-butanol, s-butanol, 2-ethylhexyl alcohol, 1- or 2-octanol, nonyl alcohol, 3,3,5-trimethylhexanol, decyl and lauryl alcohol, cyclopentanol, cyclohexyl alcohol, benzyl alcohol, 2,2,2-trifluoroethanol, 2,2,2-trichloroethanol, 2-(hydroxymethyl)furan, 2-methoxyethanol, methoxypropanol, 2-ethoxyethanol, n-propoxyethanol, 2-butoxyethanol, 2-ethoxyethoxyethanol, 2-ethoxybutoxyethanol, butoxyethoxyethanol, 2-eth ... Examples of suitable ether-alcohols include diethanol, 2-butoxyethylethanol, 2-butoxyethoxyethanol, N,N-dibutyl-2-hydroxyacetamide, N-hydroxysuccinimide, N-morpholineethanol, 2,2-dimethyl-1,3-dioxolane-4-methanol, 3-oxazolidineethanol, 2-hydroxymethylpyridine, furfuryl alcohol, 12-hydroxystearic acid, triphenylsilanol, and 2-hydroxyethyl methacrylate, as well as ether-alcohols such as ethylene glycol, 1,2-propylene glycol, mono-methyl ether, ethylene glycol monobutyl ether, diethylene glycol mono-methyl ether, or diethylene glycol monobutyl ether.

[0051] Suitable alicyclic mono-alcohols include, for example, cyclopentanol and cyclohexanol.

[0052] Suitable aromatic mono-alcohols include phenol, cresol, ethylphenol, n-propylphenol, isopropylphenol, n-butylphenol, s-butylphenol, t-butylphenol, n-hexylphenol, 2-ethylhexylphenol, n-octylphenol, n-nonylphenol, di-n-propylphenol, diisopropylphenol, isopropylcresol, di-n-butylphenol, di-s-butylphenol, di-t-butylphenol, di-n-octylphenol, di-2-ethylhexylphenol, di -n-nonylphenol, nitrophenol, bromophenol, chlorophenol, fluorophenol, dimethylphenol, styrenated phenol, methyl salicylate, 4-hydroxybenzoic acid methyl ester, 4-hydroxybenzoic acid benzyl ester, hydroxybenzoic acid 2-ethylhexyl ester, 4-[(dimethylamino)methyl]phenol, 4-[(dimethylamino)methyl]nonylphenol, bis(4-hydroxyphenyl)acetic acid, 2-hydroxypyridine, 2- or 8-hydroxyquinoline, and 2-chloro-3-pyridinol.

[0053] Preferably, the mono-alcohols used as the blocking agent B of the blocked isocyanate IB are aliphatic mono-alcohols including hexanol, 2-ethylhexanol, and ethylene glycol monoethyl ether.

[0054] Aliphatic diols such as 1,2-ethylene glycol or 1,2-propylene glycol are also preferred blocking agents B, with 1,2-propylene glycol being more preferred, as the primary hydroxyl groups provide greater reactivity towards isocyanates than the secondary hydroxyl groups.

[0055] Other preferred blocking agents B are glycol esters of acrylic or methacrylic acid. The use of 2-hydroxyethyl methacrylate as blocking agent B is particularly preferred.

[0056] Suitable amines include dibutylamine, diphenylamine, aniline, N-methylaniline, carbazole, bis(2,2,6,6-tetramethylpiperidinyl)amine, di-n-propylamine, diisopropylamine, isopropylethylamine, 2,2,4- or 2,2,5-trimethylhexamethyleneamine, N-isopropylcyclohexylamine, dicyclohexylamine, bis(3,5,5-trimethylcyclohexyl)amine, piperidine, 2,6-dimethylpiperidine, t-butylmethylamine, t-butylethylamine, t-butylpropylamine, t-butylbutylamine, t-butylbenzylamine, t-butylphenylamine, 2,2,6-trimethylpiperidine, 2,2,6,6-tetramethylpiperidine(dimethylamino)-2,2,6,6-tetramethylpiperidine, 2,2,6,6-tetramethyl-4-piperidine, 6-methyl-2-piperidine, and 6-aminocaproic acid.

[0057] Suitable hydroxylamines include N,N-diethylhydroxylamine.

[0058] Suitable imidazoles include imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, and 2-ethylimidazole.

[0059] Suitable imines include ethylene-imine, polyethylene-imine, 1,4,5,6-tetrahydropyrimidine, and guanidine.

[0060] Suitable triazoles include 1,2,4-triazole and benzotriazole.

[0061] Suitable mercaptans include butyl mercaptan, dodecyl mercaptan, and hexyl mercaptan.

[0062] Suitable oximes include, for example, formamidoxime, acetaldoxime, acetone oxime, methyl ethyl ketone oxime (or methyl ethyl ketoxime), cyclohexanone oxime, diacetyl monooxime, benzophenone oxime, 2,2,6,6-tetramethylcyclohexanone oxime, diisopropyl ketone oxime, methyl-t-butyl ketone oxime, diisobutyl ketone oxime, methyl isobutyl ketone oxime, methyl isopropyl ketone oxime, 2,4-dimethyl-3-pentanone oxime, methyl 2,4-dimethylpentyl ketone oxime, methyl 3-ethylheptyl ketone oxime, 2,6-dimethyl-4-heptanone oxime, methyl isoamyl ketone oxime, n-amyl ketone oxime, 2,2,4,4-tetramethyl-1,3-cyclobutanedione monooxime, 4,4'-dimethoxybenzophenone oxime, and 2-heptanone oxime. Preferably the oxime is methyl ethyl ketoxime.

[0063] Suitable pyrazoles include pyrazole, 3,5-dimethylpyrazole, 3,5-diisopropylpyrazole, 3,5-diphenylpyrazole, 3,5-di-t-butylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 4-bromo-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole and 3-methyl-5-phenylpyrazole. Preferably, the pyrazole derivative is 3,5-dimethylpyrazole.

[0064] Suitable reactive methylene compounds include, for example, C1-C4 dialkyl malonates such as dimethyl malonate, diethyl malonate, diisopropyl malonate, di-n-butyl malonate, di-t-butyl malonate, di-2-ethylhexyl malonate, methyl n-butyl malonate, ethyl n-butyl malonate, methyl s-butyl malonate, ethyl s-butyl malonate, methyl t-butyl malonate, ethyl t-butyl malonate, diethyl methylmalonate, dibenzyl malonate, diphenyl malonate, benzyl methyl malonate, ethyl phenyl malonate, t-butylphenyl malonate, isopropylidene malonate; alkyl acetoacetates such as methyl acetoacetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, n-butyl acetoacetate, t-butyl acetoacetate, benzyl acetoacetate, phenyl acetoacetate, 2-acetoacetoxyethyl methacrylate, acetylacetone; and cyanoethyl acetate. Preferably the reactive methylene compound is diethyl malonate.

[0065] Suitable lactams include acetanilide, N-methylacetamide, acetic acid amide, epsilon-caprolactam, delta-valerolactam, gamma-butyrolactam, pyrrolidone, 2,5-piperazinedione ion, and laurolactam.

[0066] The hydroxyl-functional carbamates C preferably used as blocking agents B of the blocked isocyanates IB are: alkylene carbonates selected from the group consisting of propylene carbonate, ethylene carbonate, butylene carbonate, glycerol carbonate, allyloxymethyl carbonate and cyclic organic carbonates, including biscarbonates prepared starting from the diglycidyl ethers of bisphenol A or polypropylene glycol, preferably ethylene carbonate, propylene carbonate and butylene carbonate, more preferably ethylene carbonate and propylene carbonate, aliphatic monoamines and / or diamines and / or triamines and / or tetraamines and / or alkanolamines, all of which have primary and / or secondary and / or, where appropriate, tertiary, reaction-inert amino groups, for example with cyclohexylamine, N-methylbutylamine, N-methylbenzylamine, piperidine, piperazine, morpholine, benzylamine, diethylenetriamine, ethanolamine, diethanolamine and polyoxyalkyleneamines and diamines, or - secondary amino compounds (alkanolamines) obtained by reacting 1 mole of an aliphatic diamine having a primary amino group with 2 moles of a monoepoxide compound, or 2 moles of an aliphatic monoamine having a primary amino group and / or an aliphatic diamine having primary and tertiary reactively inert amino groups with 1 mole of a diepoxide compound Mixtures of different amines can also be used.

[0067] More preferably, the hydroxyl-functional carbamate C used as blocking agent B (of the blocked isocyanate IB) is a reaction product of ethylene carbonate or propylene carbonate and an alkanolamine.

[0068] Even more preferably, the hydroxyl functional carbamate C is 2-hydroxyethyl bis(2-hydroxyethyl)carbamate or 2-hydroxypropyl bis(2-hydroxyethyl)carbamate.

[0069] In a preferred embodiment, the blocked isocyanate IB is prepared in a two-step reaction, where in the first step a difunctional isocyanate I is reacted with an organic hydroxy compound (mono-alcohol) having at least three hydroxyl groups to form a partially blocked isocyanate, where the equivalent ratio NCO / OH is equal to or greater than 3. In the next step, the partially blocked isocyanate is then reacted with a blocking agent B, preferably an aliphatic mono-alcohol, an oxime, a pyrazole derivative, a reactive methylene compound, and / or a hydroxyl-functional carbamate, to block all remaining isocyanate groups.

[0070] In addition, it is preferred to use chain extended alcohols, such as the reaction products of tri- or tetrahydric alcohols with lactones, to produce tri- or tetrahydric alcohols in which the hydroxyl groups of the molecule are separated by oligomeric or polymeric polylactone chains. A similar effect can be achieved by reacting tri- or tetrahydric alcohols with methyloxirane (propylene epoxide). Reaction with ethylene oxide is less preferred, since the oligomeric or polymeric oxyethylene chains make the coating more hydrophilic, impairing corrosion protection.

[0071] In another preferred embodiment, the blocked isocyanate IB is made by reacting the polyisocyanate I with a hydroxyl-functional carbamate C and other blocking agents, preferably aliphatic mono-alcohols, oximes, pyrazole derivatives, and / or reactive methylene compounds.

[0072] The isocyanate groups of the polyisocyanate compounds I used in the aqueous dispersion D can be fully or only partially blocked by blocking agent B. Fully (or completely) blocked polyisocyanate IB means in this specification a polyisocyanate compound I in which all isocyanate groups have been blocked with blocking agent B (so that no free isocyanate groups remain in IB). Partially blocked polyisocyanate IB is a polyisocyanate compound I which comprises an isocyanate group, preferably on average a maximum of one isocyanate group per molecule of polyisocyanate compound I, which is bound to a binder resin (which is comprised together with the (co)crosslinker(s) in the so-called binder) by reaction of said isocyanate groups with isocyanate-reactive groups of said binder resin; the remaining isocyanate group(s) of polyisocyanate compound I are blocked by blocking agent B. The isocyanate groups of such a partially blocked polyisocyanate IB consist of isocyanate groups reacted with the binder resin (preferably on average a maximum of one isocyanate group per molecule I) and the isocyanate group(s) blocked with the blocking agent B, there being no free isocyanate groups in IB.

[0073] The partially blocked polyisocyanates IB can be readily prepared by reacting a polyisocyanate compound I having at least two isocyanate groups in the molecule with a sufficient amount of blocking agent B to enable the resulting product to contain unblocked isocyanate groups, preferably on average not more than one unblocked isocyanate group per molecule I, which are linked (or bonded) to the hydrophilically modified epoxy resin P by reaction of the isocyanate groups with isocyanate-reactive groups of P (the reactive groups of the binder resin, e.g., hydroxy groups, can react with the unblocked isocyanate groups of the crosslinker to form covalent bonds).

[0074] Blocking agent B may be derived from petrochemical and / or renewable feedstocks.

[0075] The co-crosslinker E is preferably at least difunctional, a compound E1 having at least two hydroxyl groups which reacts at elevated temperatures (above 80° C.) with acid compounds present in the coating composition (prepared from an aqueous resin dispersion D, see below) with ester formation and liberation of water, or or an ester E2 having at least two ester groups, formed by an at least dihydric alcohol E22 and an acid E21 which is unstable at elevated temperatures (above 80° C.). The crosslinking reaction in this case is a metathesis reaction between the ester E2 and an acid compound present in the coating composition, involving the formation of an ester of the at least dihydric alcohol E22 with said acid compound and the liberation of the acid E21, which in the case of a β-keto acid E21 decomposes into a ketone and carbon dioxide. Useful compounds E2 have the general formula (R 1 -C(=O)-CR 2 R 3 -C(=O)-O-) x R 4 [wherein R 1 is an alkyl group having 1 to 8 carbon atoms, and R 2 and R 3 are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms; R 4is the residue of an aliphatic alcohol having 2 to 4 hydroxyl groups and 2 to 40 carbon atoms; preferably E2 is selected from the group consisting of ethylene glycol bis-acetoacetate, diethylene glycol bis-acetoacetate, propylene glycol bis-acetoacetate, 1,4-butanediol bis-acetoacetate, 2,2,4-trimethylpentanediol bis-acetoacetate; and bis-acetoacetates of mixtures of dimeric fatty alcohols, glycerol tris-acetoacetate, trimethylolpropane tris-acetoacetate; and the corresponding diesters of 3-oxovaleric acid, 3-oxocaproic acid, 3-oxoenanthic acid, 2-methylacetoacetic acid, 2,2-dimethylacetoacetic acid, 2-ethylacetoacetic acid, and 2-methyl-2-ethylacetoacetic acid. In the coating compositions, the acid groups can be present in the binder component or in the additives, especially the rheological additives, or in the adjuvants, such as catalysts and biocides.

[0076] A preferred example of compound E1 is the compound of formula: (OH-CHR1-CH2-NR2-CO) m -A-(CO-NR2-CH2-CHR1-OH) n [In formula: R1 is hydrogen or C1-C5 alkyl; R2 is hydrogen, C1-C5 alkyl or CH2-CHR1-OH; A is a chemical bond or a polyvalent organic group derived from a saturated, unsaturated or aromatic hydrocarbon group, including substituted hydrocarbon groups containing 2 to 20 carbon atoms; m is an integer having a value from 1 to 2; m is an integer having a value from 0 to 2, and m+n is at least 2. It is a beta-hydroxyalkylamide of the formula:

[0077] Suitable beta-hydroxyalkylamides are described in the literature, for example those mentioned in US Pat. Nos. 4,727,111; 4,788,255; 4,076,917; 5,266,628; EP 322834 and 473380.

[0078] More preferably, compound E1 has the formula: (OH-CHR1-CH2-NR2-CO) m -A-(CO-NR2-CH2-CHR1-OH) n [In formula: R1 is hydrogen or C1 alkyl; R2 is CH2-CHR1-OH; A is a saturated hydrocarbon group containing 4 carbon atoms; · m equals 1 and n equals 1] It is a beta-hydroxyalkylamide of the formula:

[0079] Most preferably, compound E1 is N,N,N',N'-tetrakis-(2-hydroxyethyl)-adipamide, known under the trade name PRIMID® XL552, or N,N,N',N'-tetrakis-(2-hydroxypropyl)-adipamide, known under the trade name PRIMID® QM1260.

[0080] Coagent E may be derived from petrochemical and / or renewable feedstocks.

[0081] The coating composition of the present invention is prepared from an aqueous resin dispersion D containing a mixture of a hydrophilically modified epoxy resin P, a blocked isocyanate IB, and a co-crosslinking agent E.

[0082] Preferably, the aqueous resin dispersion D of the present invention contains, based on the total weight of P, IB, and E (wherein the sum of the weight percentages (wt%) of P, IB, and E does not exceed 100%): 40 to 90% by weight, more preferably 45 to 85% by weight, of a hydrophilically modified epoxy resin P; 5 to 55% by weight, more preferably 10 to 50% by weight, of a blocked isocyanate crosslinker IB; and 0.1 to 5% by weight, preferably 1 to 3% by weight, of co-crosslinking agent E Includes.

[0083] More preferably, the aqueous resin dispersion D of the present invention has, based on the total weight of P, IB and E1 (wherein the sum of the weight percentages (wt%) of Pn, IB and E1 does not exceed 100%): 40 to 90% by weight, more preferably 45 to 85% by weight, of a hydrophilic modified epoxy resin P which is a non-ionic modified epoxy resin Pn; 5 to 55% by weight, more preferably 10 to 50% by weight, of a blocked isocyanate crosslinker IB; and 0.1-5% by weight, preferably 1-3% by weight, of a co-crosslinking agent E which is a beta-hydroxyalkylamide E1 Includes.

[0084] One or more cosolvents are added, preferably selected from the group consisting of aliphatic alcohols, ketones, esters, glycols, glycol ethers, and glycol esters, and mixtures thereof; one or more additives are added, preferably selected from the group consisting of defoamers, leveling agents, coalescing agents, flow improvers, biocides, pigments, and rheology additives. Wetting agents and anti-settling agents can also be added if a pigmented coating composition is being prepared.

[0085] Representative alcohols include ethanol, n-propanol, isopropanol, n-butanol, and iso-butanol; representative ketones include acetone, 2-butanone, cyclohexanone, methyl aryl ketone, ethyl aryl ketone, and methyl isoamyl ketone; representative esters include ethyl acetate and butyl acetate; representative glycols include ethylene glycol and propylene glycol; representative glycol ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, and methoxypropanol; representative glycol esters include butyl glycol acetate and methoxypropyl acetate.

[0086] Preferably, the coating composition comprises 35-55% by weight, more preferably 40-50% by weight of non-volatile compounds and 45-65% by weight, more preferably 50-60% by weight of water and a co-solvent selected from the group consisting of alcohols, ketones, esters, glycols, glycol ethers, and glycol esters, and mixtures thereof.

[0087] Preferably, one or more crosslinking catalyst(s) are added to the coating composition, said crosslinking catalyst(s) being selected from the group consisting of salts, chelates and organometallic compounds of elements of groups 4, 7, 8, 9, 12, 13, 14 and 15 and periods 4, 5 and 6 of the Periodic Table of the Elements according to the new IUPAC nomenclature system, and strong amines.

[0088] Compounds that are highly soluble in water are preferred, such as salts of these elements that dissociate into ions in aqueous systems, and chelate compounds of these elements, where the chelate formers can be organic hydroxy acids, such as lactic acid, 2,2-bishydroxymethylpropionic acid, amino acids, such as N,N,N',N'-ethylenediaminetetraacetic acid, nitrilotriacetic acid, and beta-alanine, or polyfunctional amines or hydroxyamines. Other useful compounds are organometallic compounds, such as alkoxy metal oxides, and metal salts of organic or hydroxy acids. Particularly preferred are methanesulfonates, lactates, and bishydroxymethyl-propionates of bismuth, tin, lead, and titanium.

[0089] Strong amines are more preferably tertiary amines, most preferably (poly)cyclic tertiary amines such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,4-diazabicyclo[2.2.2]octane (DABCO).

[0090] The coating composition preferably comprises up to 5% by weight of one or more crosslinking catalysts relative to the hydrophilically modified epoxy-based resin P comprising the blocked isocyanate crosslinker IB and the co-crosslinker E.

[0091] The coating composition may include one or more organic and inorganic pigments and optionally one or more fillers.

[0092] Examples of inorganic pigments are iron oxide pigments, titanium oxide pigments, zinc oxide pigments, chromium oxide pigments coprecipitated with nickel and nickel titanate, yellow pigments derived from lead sulfochromate or lead bismuth vanadate, orange pigments derived from lead sulphochromate molybdate, and carbon black.

[0093] Examples of suitable organic pigments are azo pigments, metal complex pigments, anthraquinonoid pigments, phthalocyanine pigments, polycyclic pigments, especially those of the thioindigo, quinacridone, dioxazine, pyrrolo, naphthalenetetracarboxylic acid, perylene, isoamidolin(on)e, flavanthrone, pyranthrone or isoviolanthrone series.

[0094] Examples of useful fillers are kaolin, talc, mica, other silicates, quartz, cristobalite, wollastonite, perlite, diatomaceous earth, fibrous fillers, aluminum hydroxide, barium sulfate, or calcium carbonate.

[0095] In the process of the present invention, the aqueous resin dispersion D of the present invention, which comprises a mixture of hydrophilically modified epoxy resin P, blocked isocyanate crosslinker IB, and co-crosslinker E, is transferred to a mixing device such as a high speed stirrer, planetary mixer, or ball mill grinder, and water, co-solvents, additives, pigments, and fillers are added. Mixing is continued for at least 5 minutes until a uniform blend (or coating composition) is obtained.

[0096] The coating composition of the present invention is preferably applied to metal substrates, more preferably to corrosion resistant pretreated metal substrates, even more preferably to iron phosphated or zinc phosphated steel or pretreated steel containing a zirconium-, vanadium-, titanium- or silane-based conversion coating.

[0097] The coating composition may be applied to the substrate using any suitable technique known in the art, preferably by spraying or dip coating.

[0098] The water and optional co-solvent are then flashed off at a temperature of at least 20°C for at least 1 minute, preferably at a temperature of at least 20°C for at least 5 minutes, after which the baking process is carried out in an air ventilated convection oven at a temperature of at least 140°C, preferably 140-230°C, more preferably 150-220°C, even more preferably 160-210°C, most preferably 170-200°C for a period of at least 20 seconds, preferably 1-25 minutes, more preferably 2-20 minutes, even more preferably 4-18 minutes, even more preferably 6-15 minutes, most preferably 8-12 minutes.

[0099] Alternatively, the coating may be cured by infrared radiation, such as near, short or mid infrared, or by induction, or a combination thereof. In embodiments where an infrared or induction system is used, the bake cycle ranges from 2 to 160 seconds depending on the heating system or combination of heating systems. EXAMPLES

[0100] <Example 1: Synthesis of blocked isocyanate crosslinking agent> A hydroxycarbamate from 190 g of diethanolamine and propylene carbonate was prepared as known (according to EP 0 476 514: Table 1, HC2). 470 g of butyl diglycol and 0,4 g of bismuth neodecanoate (28% Bi metal) were added at 30 °C and homogenized. 690 g of oligomeric diphenylmethane-diisocyanate (isocyanate content 32,0% according to DIN EN ISO 11909) were added stepwise to maintain a temperature below 100 °C. When the amount of free isocyanate was determined (by titration) to be less than 0,1%, the product was diluted in 80 g of methoxypropanol and 60 g of deionized water. The product obtained had a solids content of 90,2% (sample 1 g, dried for 10 min at 125 °C) and a dynamic viscosity of 12500 mPa·s (measured at 23 °C, shear rate 25 s -1 )

[0101] <Example 2: Preparation of blocked isocyanate nonionic dispersion> 2.1. Preparation of hydrophilic epoxy resin 1 kg of polyethylene glycol PEG4000 (average molar mass approximately 4000 g / mol) was heated to 120°C and dissolved water was removed by distillation under reduced pressure and nitrogen flow. 110 g of bisphenol A diglycidyl ether were added, followed by 1.7 g of aqueous tetrafluoroboric acid with a mass fraction in solution of w(HBF4) of 50%. When a certain constant value of the content of epoxide groups was reached (approximately 0.1 mol / kg to 0.2 mol / kg), 1100 g of water was added to dilute the solids mass fraction to approximately 50%.

[0102] 2.2. Advancement reaction A reaction vessel equipped with a thermometer, stirrer, reflux condenser, descending condenser, and a pump for reducing the pressure was charged with 2400 g of bisphenol A diglycidyl ether, 720 g of bisphenol A, and 1200 g of the hydrophilic epoxy resin of Example 2.1, and heated to 125° C. with stirring and removed all volatile components at a reduced pressure of 10 kPa (100 mbar). Then 1.3 g of triphenylphosphine was added, the temperature was further increased to 160° C., and the mixture was kept under stirring until a specific amount of epoxide groups of 1.87 equivalents / kg ("epoxide equivalent weight" 534 g / eq.) was reached.

[0103] 2.3.: Addition of blocked isocyanate and dispersion in water The reaction mass obtained in Example 2.2. was then cooled to 120°C and 729 g of the blocked isocyanate from Example 1 was added. The viscosity was then reduced by adding 410 g of methoxypropanol and the solution was cooled to 80°C. 1200 g of deionized water was then added to the reaction vessel and the mixture was dispersed at 70°C for 3 hours to obtain a water-dilutable resin dispersion. Further, 3500 g of deionized water was added to the vessel over 2 hours and finally the mass fraction of solids was adjusted to 42.1% (sample 1 g, dried at 125°C for 10 min) by adding more deionized water and the viscosity was adjusted to 1070 mPa·s (measured at 23°C, shear rate 100 s -1The resulting Z-average particle size (Z-average mean according to ISO 22412) was 246 nm.

[0104] <Example 3: Preparation of blocked isocyanate nonionic dispersion> 3.2. Advancement reaction A reaction vessel equipped with a thermometer, stirrer, reflux condenser, descending condenser and a pump for reducing the pressure was charged with 2400 g of bisphenol A diglycidyl ether, 670 g of bisphenol A and 1750 g of the hydrophilic epoxy resin of Example 2.1., heated to 125° C. with stirring and removed all volatile components at a reduced pressure of 10 kPa (100 mbar). Then 1.3 g of triphenylphosphine was added, the temperature was further increased to 160° C. and the mixture was kept under stirring until a specific amount of epoxide groups of 1.96 equivalents / kg ("epoxide equivalent weight" 510 g / eq.) was reached.

[0105] 3.3.: Addition of blocked isocyanate and dispersion in water The reaction mass obtained in Example 3.2. was then cooled to 120°C and 2945 g of the blocked isocyanate from Example 1 was added. The viscosity was then reduced by adding 410 g of methoxypropanol and the solution was cooled to 80°C. 1850 g of deionized water was then added to the reaction vessel and the mixture was dispersed at 70°C for 3 hours to obtain a water-dilutable resin dispersion. Further, 5000 g of deionized water was added to the vessel over 2 hours and finally the mass fraction of solids was adjusted to 42.3% (sample 1 g, dried at 125°C for 10 min) by adding more deionized water and the viscosity was adjusted to 930 mPa·s (measured at 23°C, shear rate 100 s -1 The resulting Z-average particle size (Z-average according to ISO 22412) was 244 nm.

[0106] Comparative Example 1: Synthesis of resol crosslinker In a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser, a descending condenser and a device for reducing pressure, 453.6 g of n-butanol were heated to 50°C. Then, 397.3 g of bisphenol A, 48.5 g of sodium hydroxide solution (mass fraction of solids 45%), 357.6 g of aqueous formaldehyde solution (mass fraction of dissolved formaldehyde 37%) and 95.4 g of paraformaldehyde were added and reacted at 50°C for 10 hours. After that, another 447 g of n-butanol was added and the pH was adjusted to 3.5 by adding 72.2 g of aqueous phosphoric acid solution (mass fraction of dissolved phosphoric acid 75%). Azeotropic distillation was carried out for 8 hours at atmospheric pressure and temperatures between 94°C and 105°C to remove the aqueous phase. The remaining n-butanol was then removed at 120°C. Further, 212 g of n-butanol were added, followed by a second azeotropic distillation at atmospheric pressure for 5 hours. The remaining n-butanol was also removed to reach a distillation temperature of 115 °C, and further water was removed by azeotropic distillation until the compatibility of the reaction mass with n-heptane was reached at a resin to n-heptane ratio of 1:2. The resin obtained was washed with 187 g of deionized water to remove salts. Residual water was removed by azeotropic distillation at atmospheric pressure and a temperature of 105 °C, followed by removal of all volatile components at 85 °C and a reduced pressure of 10 kPa (100 mbar). The polymeric resin obtained was dissolved to give a solution with a mass fraction of solids of 80% (mass of sample: 1 g, drying conditions: 60 min, 125 °C) and a dynamic viscosity of 1200 mPa·s at 23 °C.

[0107] Comparative Example 2: Preparation of resol-modified nonionic dispersion Hydrophilic epoxy resins were prepared according to examples 2.1. and 2.2. The resulting reaction mass was then cooled to 120°C and 820 g of the phenolic resin from comparative example 1 was added. The viscosity was then reduced by adding 318 g of methoxypropanol and the solution was cooled to 80°C. 1130 g of deionized water were then added to the reaction vessel and the mixture was dispersed for 3 hours at 70°C to obtain a water-dilutable resin dispersion. Further, 3500 g of deionized water were added to the vessel over 2 hours and finally the mass fraction of solids was adjusted to 41,8% (sample 1 g, dried at 125°C for 10 min) by adding more deionized water and the viscosity was reduced to 1020 mPa·s (measured at 23°C, shear rate 100 s -1 The resulting Z-average particle size (Z-average according to ISO 22412) was 220 nm.

[0108] Example 4: White mono-coat preparation and application to steel panels 4.1.: Pigment paste dispersed in water using a bead mill The components shown in Table 1 were dispersed in water using a bead mill to obtain a pigment paste. [Table 1]

[0109] 4.2.: Coating composition Table 2 shows the components of coating compositions according to the invention (examples 5 to 10) and according to the state of the art (examples 11 to 13 are comparative examples), where: DOWANOL™ DPnB is n-butoxypropoxypropanol; ADDITOL® VXW6393 is a mineral oil based defoamer (Allnex Austria GmbH); RHEOVIS® AS1130 is an Acrylic HASE thickener (acid value 90 mg / g, based on form of delivery; BASF SE); PRIMID® XL552 is N,N,N′,N′-tetrakis(2-hydroxyethyl)-adipamide (Ems Chemie AG) dissolved at 20% by weight in water. [Table 2]

[0110] The ingredients disclosed in Table 2 were mixed in the specified order in a laboratory mixer. After 24 hours of blending, the coating compositions of Examples 5-13 were applied by air spray gun onto zinc phosphated steel panels (GARDOBOND® 26S 6800 OC, Chemetall GmbH). After 10 minutes of flash-off at 23° C., the coated panels were cured for 10 minutes at 180° C. The dry film thickness of the coatings was in each case 35 μm.

[0111] <Example 14: Anti-corrosion and color performance> After 7 days of conditioning at 23° C. and 50% relative humidity, the color of the coated panels of each of the coating compositions of Examples 5 to 13 was measured using a colorimeter "Spectro-guide" (Byk Gardner GmbH). CIE L * a * b * A high value of "b" according to the system indicates a strong yellowing (discoloration) of the coating film. The panels were then scratched in the center and exposed to a salt spray chamber test ("SST"; DIN EN ISO 9227). The blistering of the artificially aged panels was recorded according to DIN EN ISO 4628-2.

[0112] Table 3 shows the color and blistering after exposure to the salt spray test.

[0113] The resins of Comparative Example 2 and Example 2 according to the invention have comparable amounts of crosslinker (respectively resole or blocked isocyanate) based on the amount of epoxy resin. Direct comparison of the coating compositions of Examples 5 and 11, 6 and 12, and 7 and 13 show that the anticorrosive performance of Comparative Examples 11-13 is at the same level as that of Examples 5-7 (coating compositions according to the invention). It is also clearly shown that the addition of β-hydroxyalkylamide to the anticorrosive monocoat significantly improves the anticorrosive effect in all cases. However, in addition to the maintained anticorrosive performance, all coating compositions according to the invention based on blocked isocyanate (Examples 5-10) show much lighter color (lower b-value) than those based on resole (Examples 11-13) at the same pigment / binder ratio of 130% (w / w). As used herein, pigment / binder ratio means the ratio (by weight) of the sum of pigment and filler divided by the sum (by weight) of solid binder resin and blocked isocyanate crosslinker, expressed as a percentage; the solids content of additives and co-crosslinkers is not taken into account. [Table 3]

Claims

1. An aqueous resin dispersion D comprising a mixture of a hydrophilically modified epoxy resin P, a blocked isocyanate crosslinking agent IB, and a co-crosslinking agent E; wherein the hydrophilically modified epoxy resin P comprises 1-hydroxy-2-phenoxy-ethyl groups; Co-crosslinking agent E Compounds E1 having at least two hydroxyl groups which react with acid compounds present in the coating composition at elevated temperatures above 80° C. with ester formation and liberation of water, and Esters E2 having at least two ester groups formed from at least dihydric alcohols E22 and acids E21 which are unstable at elevated temperatures above 80° C. Selected from the group consisting of: Aqueous resin dispersion D.

2. The blocked isocyanate crosslinker IB is: - polyisocyanate and monoalcohol, or Polyisocyanates and oximes, or Polyisocyanates and pyrazole derivatives, or Polyisocyanates and reactive methylene compounds, or Polyisocyanates and lactams, or Polyisocyanate and phenol, or Polyisocyanates and mercaptans, or Polyisocyanate and imidazole, or Polyisocyanates and amines, or Polyisocyanates and imines, or Polyisocyanates and triazoles, or Polyisocyanate and hydroxylamine, or polyisocyanate and hydroxyl-functional carbamate C, or polyisocyanates and hydroxyl-functional carbamates C and monoalcohols and / or oximes and / or pyrazole derivatives and / or reactive methylene compounds and / or lactams and / or phenols and / or mercaptans and / or imidazoles and / or amines and / or imines and / or triazoles and / or hydroxylamines 2. The aqueous resin dispersion D according to claim 1, which is a reaction product of:

3. 2. The aqueous resin dispersion D of claim 1, wherein the blocked isocyanate crosslinker IB is the reaction product of a polyisocyanate and a hydroxyl-functional carbamate C.

4. 3. The aqueous dispersion D of claim 2, wherein the hydroxyl-functional carbamate C is a reaction product of a cyclic organic carbonate with an aliphatic monoamine, diamine, triamine, tetraamine and / or alkanolamine, said amine having at least a primary or secondary amino group.

5. The alkanolamine is: 1 mole of an aliphatic diamine having a primary amino group and 2 moles of a monoepoxide compound or 2 moles of an aliphatic monoamine having a primary amino group, and / or A mixture of an aliphatic diamine having primary and tertiary reactive inert amino groups and 1 mole of a diepoxide compound 5. The aqueous dispersion D of claim 4 which is a reaction product.

6. 3. The aqueous dispersion D of claim 2, wherein the hydroxyl-functional carbamate C is a reaction product of ethylene carbonate or propylene carbonate and an alkanolamine.

7. 3. The aqueous dispersion D of claim 2, wherein the hydroxyl-functional carbamate C is 2-hydroxyethyl bis(2-hydroxyethyl)carbamate or 2-hydroxypropyl bis(2-hydroxyethyl)carbamate.

8. 2. The aqueous dispersion D of claim 1, wherein the blocked isocyanate crosslinking agent IB is a partially blocked polyisocyanate containing, on average, at most one isocyanate group per molecule of polyisocyanate compound I, said isocyanate group being linked to the hydrophilically modified epoxy-based resin P by reaction of said isocyanate group with an isocyanate-reactive group of P; and the remaining isocyanate group(s) of polyisocyanate compound I are blocked by a blocking agent B.

9. The co-crosslinking agent E is E1, and E1 is a compound of the formula: (OH-CHR １ -CH ２ -NR ２ -CO) ｍ -A-(CO-NR ２ -CH ２ -CHR １ -OH) ｎ [In the formula: ・R １ is hydrogen or C1-C5 alkyl; ・R ２ is hydrogen, C1-C5 alkyl or CH ２ -CHR １ -OH; A is a polyvalent organic group derived from a chemical bond or a saturated, unsaturated or aromatic hydrocarbon group, including substituted hydrocarbon groups containing 2 to 20 carbon atoms; m is an integer having a value from 1 to 2; m is an integer having a value from 0 to 2, and m+n is at least 2. is a beta-hydroxyalkylamide having the formula The aqueous resin dispersion D according to claim 1.

10. The co-crosslinking agent E is E1, and E1 is a compound of the formula: (OH-CHR １ -CH ２ -NR ２ -CO) ｍ -A-(CO-NR ２ -CH ２ -CHR １ -OH) ｎ [In the formula: ・R １ is hydrogen or C1 alkyl; ・R ２ is CH ２ -CHR １ -OH; A is a saturated hydrocarbon group containing 4 carbon atoms; m is equal to 1 and n is equal to 1. is a beta-hydroxyalkylamide having the formula The aqueous resin dispersion D according to claim 1.

11. The aqueous resin dispersion D according to claim 1, wherein the co-crosslinking agent E is E1, and E1 is N,N,N',N'-tetrakis-(2-hydroxyethyl)-adipamide or N,N,N',N'-tetrakis-(2-hydroxypropyl)-adipamide.

12. 2. The aqueous resin dispersion D according to claim 1, wherein the hydrophilically modified epoxy resin P is a nonionic modified epoxy resin Pn.

13. Aqueous dispersion D according to claim 12, wherein the non-ionic modified epoxy-based resin Pn is a reaction product of a diepoxide, a divalent aromatic compound and an epoxy-functional non-ionic emulsifier F and is characterized by an epoxide equivalent weight (EEW) of 200 to 2,000 g / equiv.

14. An epoxy-functional nonionic emulsifier F; epoxide-functional polyoxyalkylene homopolymers or copolymers; and / or epoxide-functional sugar alcohols; and / or Reaction products of hydroxyl-functional polyoxyalkylene homopolymers or copolymers or sugar alcohol segments with at least difunctional epoxide compounds and Where: the polyoxyalkylene homopolymer is polyoxyethylene or polyoxypropylene; the polyoxyalkylene copolymer is a polyoxyethylene-propylene copolymer; Polyoxyalkylene homopolymers and copolymers containing 20 to 150 C2-C3 oxyalkylene units; Aqueous dispersion D according to claim 13.

15. For the total weight of P, IB and E 40 to 90% by weight of a hydrophilically modified epoxy resin P; 5 to 55% by weight of a blocked isocyanate crosslinker IB; and 0.1 to 5% by weight of co-crosslinking agent E; The aqueous resin dispersion D according to claim 1, comprising:

16. For the total weight of Pn, IB and E1 40 to 90% by weight of a hydrophilically modified epoxy resin P, which is a non-ionic modified epoxy resin Pn; 5 to 55% by weight of a blocked polyisocyanate crosslinker IB; and 0.1-5% by weight of a co-crosslinker E which is a beta-hydroxyalkylamide E1; The aqueous resin dispersion D according to claim 1, comprising:

17. 2. The aqueous resin dispersion D according to claim 1, comprising one or more catalysts selected from the group consisting of salts, chelate compounds and organometallic compounds of elements of groups 4, 7, 8, 9, 12, 13, 14 and 15, and periods 4, 5 and 6 of the Periodic Table of the Elements according to the new IUPAC nomenclature system, and strong amines.

18. the hydrophilically modified epoxy resin P and / or the blocked isocyanate crosslinker IB are derived from renewable feedstocks and have, in total, a bio-based carbon content of more than 20% by weight of the total carbon content of the epoxy resin P and the blocked isocyanate crosslinker IB, the bio-based carbon content being determined using the ASTM D6866-20 standard; or The epoxy resin P and / or the blocked isocyanate crosslinking agent IB are derived from recycled monomers. The aqueous resin dispersion D according to claim 1.

19. A coating composition comprising the aqueous resin dispersion D according to any one of claims 1 to 18 and one or more additives selected from the group consisting of defoamers, leveling agents, coalescing agents, flow improvers, biocides, pigments, rheology additives, and wetting agents.

20. 20. The coating composition of claim 19 comprising 35 to 55% by weight of non-volatile compounds and 45 to 65% by weight of water and a co-solvent selected from the group consisting of alcohols, ketones, esters, glycols, glycol ethers, and glycol esters, and mixtures thereof.

21. 1. A method for producing a coated metal substrate comprising the steps of: - applying the coating composition according to claim 19 to at least one surface of an optionally pretreated and / or primer-containing metal substrate with a coating thickness adjusted to obtain a dry coating thickness of at least 10 μm; - Flashing off the water and co-solvent for at least 1 minute at a temperature of at least 20°C; - baking the applied coating composition at a temperature of at least 100°C for a period of at least 20 seconds to form a metal substrate coated with a crosslinked coating layer; The method includes:

22. 20. Use of the coating composition according to claim 19 for coating a metal substrate.