Corrosion-protection agent forming a layer of paint and method for current-free application thereof

[0001] Methods and coatings for electroless anticorrosive coating of various metal substrates are known. Their advantage, in comparison with anodic or cathodic dip painting (ATL or KTL, respectively), in which the application of electric voltage is necessary, is in particular a simpler and cheaper method of application and shorter process time. In particular, currentless processes allow more efficient coating of gaps or edges of coated substrates than processes requiring the application of an electric voltage.

[0002] For electroless application of anti-corrosive coatings, also referred to as the ACC (Autophoretic Chemical Coating) process, polymers, for example anionically stabilized emulsion polymers containing acrylates or styrene / butadiene, are usually used. Compared to the above-mentioned ATL and KTL processes, the disadvantage of ACC processes is, however, that the deposited layers have defects that make the substrate much more susceptible to corrosion. Therefore, to improve corrosion protection at these defects, ACC-deposited coatings are usually subjected to a rinse treatment with aqueous chromium-containing coating agents. Recently, chromium containing coatings have been found to pose serious problems regarding their environmental tolerance and are also classified as highly hazardous to health. Therefore, efforts are being made to completely eliminate chromium from corrosion protection coatings.

[0003] In addition, during the development of chromium-free coatings, it was found that coatings used in the ACC process that contain lanthanide salts and d-block elements, and an organic film-forming component, also provide very good corrosion protection comparable to that obtained. using coatings containing chromium.

[0004] WO-A-01/86016 describes an anticorrosive agent comprising a vanadium component and another component comprising at least one metal selected from the group consisting of zirconium, titanium, molybdenum, tungsten, manganese and cerium. In order to ensure good stability and anticorrosion efficacy of the conversion anticorrosive agent, the appropriate ratio of trivalent and tetravalent vanadium to the total vanadium content should be chosen and, if necessary, an organic compound should be added. The organic compound is mainly used to reduce pentavalent vanadium compounds. Such compounds may be polymers, for example polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamides and polyethyleneimine. The effect of the anticorrosive agent described in WO-A-01/86016 is essentially the result of a specific ratio of trivalent and tetravalent vanadium to the total vanadium content that must be determined by expensive comparative experiments. For example, this is achieved by mixing vanadium-containing vanadium compounds to varying degrees of oxidation. The disadvantage of the anticorrosive agents according to WO-A-01/86016 is the tendency of the ions formed from the metals forming the substrate to migrate through the deposited anticorrosive coating, since these polymers do not form a tightly covering coating.

[0005] WO-A-99/29927 describes a chromium-free aqueous anticorrosion agent which includes titanium (IV) and / or zirconium (IV) hexafluoroanions, vanadium ions, transition metal ions, and phosphoric acid and / or phosphonic. In a preferred embodiment, the anti-corrosive agent described in WO-A-99/29927 further comprises an organic film-forming agent, especially based on polyacrylate, preferably cross-linkable. Cross-linking can be achieved by the presence of various reactive groups in the film-forming agent itself, or by adding hardeners suitable for the film-forming agent. The application of the inorganic passivating layer and the organic polymer layer in the same step has been described as preferred, with sufficient corrosion protection being achieved. The disadvantage of the anti-corrosive agents according to WO-A-99/29927 is the tendency of the ions formed from the metals forming the substrate to migrate through the deposited anti-corrosive coating, since these polymers do not form a tightly covering coating, as well as the use of environmentally harmful substances, in particular fluorides. [0006] WO-A-96/110461 describes an aqueous anti-corrosive agent comprising as components anions in which the central atom is selected from the group consisting of titanium, zirconium, hafnium, silicon, and at least 4 fluorine atoms as ligands and dispersion. organic polymer. The advantages of the invention include, in particular, a lack of chromium and a one-stage coating process.

[0007] A disadvantage of the invention according to WO-A-96/10461 is that the deposition of an anticorrosive agent on the surface of the substrate is accompanied by flocculation of polymer dispersion particles, which reduces the contact surface with the substrate. In addition, the disadvantage of latex particles compared to polymers that are molecular dispersions is the relatively low migration rate relative to the rate during diffusion into the gaps or to the edges of three-dimensional substrates. In addition, coatings with a thickness of 1 micron to 1 mm are obtained, which requires adequate material consumption per unit area of ​​the coated substrate. Another disadvantage is the tendency of ions formed from metals forming the substrate to migrate through the embedded corrosion protection coating, as well as the use of environmentally harmful substances, in particular fluorides.

[0008] DE-A-37 27 382 describes chromium-free aqueous dispersions of carboxylic acid and isocyanate adducts with epoxides suitable for autophoretic coating of metal surfaces. In dispersed form, such dispersions contain particles with a diameter below 300 nm, preferably between 100 nm and 250 nm, and after application to the metal surface they can be crosslinked at a temperature between 60 ° C and 200 ° C. Typical initiators known in the art of autophoretic coating can be used for cross-linking, especially such as the HF / FeF system₃. The coatings described in DE-A-37 27 382 have good anti-corrosive properties and, moreover, are resistant to solvents.

[0009] The disadvantage of such latex particles compared to polymers that are molecular dispersions is also the low migration rate during diffusion into the gaps or to the edges of three-dimensional substrates. In addition, coatings with a thickness of 1 micron to 1 mm are obtained, which requires adequate material consumption per unit area of ​​the coated substrate. Another disadvantage is the tendency of ions formed from the metals forming the substrate to migrate through the embedded corrosion protection coating, as well as the use of environmentally harmful substances, in particular fluorides.

[0010] US 2003 / 10187145A1 describes coating agents that can be applied to a metal surface (cf. US 2003/0187145 A, [0112]), but their corrosion protection is not described. Preferably, US 2003/0187145 A1 describes coating agents used as a base coat and / or a clear coat for serial painting of vehicles (cf. US 2003/0187145 A1 [0116]), wherein such coating agents are not applied directly to metal substrates but to substrates coated with other varnish layers, in layers with a thickness greater than those usually used in corrosion protection (cf. for example, US 2003 / 0187145 A1, [0121]).

Problem and solution [0011] In the light of the prior art discussed above, the object of the invention was to develop a method of corrosion protection which does not raise serious ecological concerns. In particular, the method of corrosion protection should significantly prevent migration of metal ions formed on the substrate and allow good coverage of the edges and crevices of the substrate. In addition, the effect of foreign metal ions should be as low as possible and effective corrosion protection should be obtained with comparatively low material consumption. Furthermore, the conversion coating agent should effectively protect as many different metal substrates as possible and should be substantially independent of the redox potential of the coated substrate.

[0012] In the light of the above problems, a corrosion protection method has surprisingly been developed in which the substrate is pretreated with an anti-corrosion agent K before deposition of the coating agent EK.

Description of the invention

EK coating agent [0013] Water dispersible and / or water soluble P coating polymers of EK coating agent contain ligands A which form chelates with metal ions released during corrosion of the substrate, and crosslinking functional groups B which can form covalent bonds with each other and / or with other functional groups C of crosslinkers V. [0014] In the context of the invention, the terms "water-dispersible" or "water-soluble" mean that the P polymers form aggregates in the water phase with an average particle diameter <50 nm, preferably <35 nm, and particularly preferably <20 nanometers, or dissolution as molecular dispersions. Thus, such aggregates differ significantly in the mean particle diameter from the dispersed particles, described for example in DE-A-37 27 382 or WO-A-96/10461. Polymer P solutions in the form of molecular dispersions typically have a molecular weight of <100,000 daltons, preferably <50,000 daltons, particularly preferably <20,000 daltons.

[0015] The size of the aggregates consisting of the P polymer is achieved in a known manner by introducing hydrophilic HG groups into the P polymer. The number of hydrophilic HG groups in the P polymer depends on the solvation capacity and steric availability of HG groups and can also be adjusted in a manner known to those skilled in the art. Preferred HG hydrophilic groups in polymer P are sulfate, phosphate, phosphonate, amino, amide and / or carboxylate groups, especially amino and phosphonate groups.

[0016] The polymers that can form the backbone of the P polymers can be any polymers, preferably polymers with a molecular weight from 1,000 to 50,000 daltons, particularly preferably with a molecular weight from 2,000 to 20,000 daltons. Preferred backbone polymers are polyolefins or poly (meth) acrylates, polyurethanes, polyalkyleneimines, polyvinylamines, polyalkylimines, polyethers, polyesters and polyalcohols, especially partially acetalized and / or partially esterified. P polymers may have a straight chain, branched and / or dendritic structure. Particularly preferred backbone polymers are polyalkyleneimines, polyvinylamines, polyalcohols, poly (meth) acrylates, as well as hyperbranched polymers such as those described in WO-A-01/46296.

[0017] Preferably, the P polymers are resistant to hydrolysis in the acidic pH range, particularly at pH <5, particularly preferably at pH <3.

[0018] Suitable A ligands are all groups or compounds that form chelates with metal ions released in the process of substrate corrosion. Monocentate and / or polylentate, potentially anionic ligands are preferred. Particularly preferred ligands are:

- urea and / or thiourea, optionally functionalized, in particular acylthioureas, such as, for example, benzoylthiourea,

- amines and / or polyamines, optionally functionalized, in particular such as EDTA,

- amides, optionally functionalized, in particular carboxylic acid amides,

- imines and imides, especially such as imine functional pyridine derivatives,

- oximes, preferably 1,2-dioximes, such as functionalized diacetylenedioxime,

- organo-sulfur compounds, especially such as thiols, optionally functionalized, such as thioethanol, thiocarboxylic acids, thioaldehydes, thioketones, dithiocarbamates, sulfonamides, thioamides, and especially sulfonates,

- organophosphorus compounds, especially such as phosphates, especially (meth) acrylate phosphates, as well as phosphonates, especially vinyl phosphonic acid, and phosphonates with hydroxyl, amine and amide functional groups,

- organo-boron compounds, optionally functionalized, in particular such as boric acid esters,

- polyalcohols, optionally functionalized, in particular such as carbohydrates and their derivatives, as well as chitosans,

acids, optionally functionalized, in particular such as di- and / or oligofunctional acids or (poly) carboxylic acids, optionally functionalized, in particular such as carboxylic acids, which can bind ionically and / or coordinate with central metal atoms, preferably ( poly) methacrylates containing acid groups or di- or oligofunctional acids,

- carbene, possibly functionalized,

- acetylacetonates,

- acetylenes, optionally functionalized,

- phytic acid and its derivatives.

[0019] Suitable cross-linking functional groups B in P polymers are those that can form covalent bonds with each other and / or with complementary functional groups B '. Preferably, these covalent bonds are formed under the influence of heat and / or radiation. Particularly preferably, these covalent bonds are formed under the influence of heat. Cross-linking functional groups B and B 'cause an intermolecular network between the polymer particles P.

[0020] Radiation crosslinking functional groups B and B 'contain activated bonds, for example, single or double bonds, hydrocarbon, carbon-carbon, carbon-oxygen, carbon-nitrogen, carbon-phosphorus or carbon-silicon. Carbon-carbon double bonds are particularly preferred. Double carbon-carbon bonds, particularly suitable as group B, occur in:

- particularly preferably - in (meth) acrylic groups,

- in ethylacryl groups,

- in the groups of vinyl ethers and vinyl esters,

- in crotonate and cinnamate groups,

- in allyl groups,

- in dicyclopentadienyl groups,

- in norbornyl and isoprenyl groups,

- in isopropenyl or butenyl groups.

[0021] Thermally crosslinking functional groups B under the influence of heat energy can form covalent bonds with each other or preferably with complementary crosslinking functional groups B '.

[0022] Particularly suitable thermally crosslinking functional groups B and B 'are:

- particularly preferably - hydroxyl groups,

- mercapto and amino groups,

- aldehyde groups,

- azido groups,

- acid groups, in particular carboxyl groups,

- acid anhydride groups, in particular carboxylic acid anhydride groups,

- acid ester groups, in particular carboxylic acid ester groups,

- ether groups

- particularly preferably carbamate groups,

- urea groups

- epoxy groups,

- particularly preferably isocyanate groups, particularly particularly preferably reacted with blocking agents which unblock at the firing temperature of the coating agents according to the invention and / or which, without unblocking, are incorporated in the resulting network.

[0023] Particularly preferred combinations of thermally crosslinking groups B and complementary groups B 'are:

- hydroxyl groups with isocyanate and / or carbamate groups,

- amino groups with isocyanate and / or carbamate groups,

- carboxyl groups with epoxy groups.

[0024] Suitable crosslinkers V, containing B and / or B 'groups crosslinked thermally and / or under the influence of radiation, are in principle all crosslinkers known to those skilled in the art. Low molecular weight V or oligomeric crosslinking agents with a molecular weight <20,000 daltons, particularly preferably <10,000 daltons, are preferred. The backbone of the V crosslinking means containing the B and / or B 'crosslinking groups may have a straight chain, branched and / or hyperbranched structure. Branched and / or hyperbranched structures are preferred, especially as described for example in WO-A-01/46296.

[0025] Preferably, the crosslinking agents V are resistant to hydrolysis in the acidic pH range, especially at pH <5, and particularly preferably at pH <3.

[0026] Particularly preferred V crosslinking agents contain the B and / or B 'crosslinking groups described above which react with the polymer crosslinking groups P to form covalent bonds. The most preferred crosslinking agents V contain groups B and / or B 'crosslinking thermally and optionally additionally under the influence of radiation.

In another, particularly preferred embodiment of the invention, the V crosslinking agents contain, in addition to the B and / or B 'crosslinking groups, L ligands, which may be the same and / or different from the P polymer L ligands.

[0028] Particularly suitable crosslinking functional groups B and B 'of crosslinking agents V are:

- especially hydroxyl groups,

- especially aldehyde groups,

- azido groups,

- acid anhydride groups, in particular carboxylic acid anhydride groups,

- carbamate groups,

- urea groups

- especially isocyanate groups, particularly particularly preferably reacted with blocking agents which unblock at the firing temperature of the coating agents according to the invention and / or which are incorporated in the resulting network without unblocking,

- (meth) acrylate groups,

- vinyl groups or combinations thereof.

[0029] Particularly preferred cross-linking agents for V are branched and / or hyperbranched polyisocyanates, which are at least partially blocked and furthermore contain L ligands.

[0030] In another embodiment of the invention, the crosslinking agents V comprise B and / or B 'groups that can form covalent bonds with the L ligands of the P polymer.

[0031] The continuous phase used for the EK coating agent is water, preferably deionized and / or distilled water. Another preferred ingredient is at least one oxidizing acid, used in an amount such that the pH of the EK coating agent is preferably between 1 and 5, especially between 2 and 4. Particularly preferred acids are acids selected from the group consisting of oxidizing mineral acids, in particular nitric acid, nitrous acid, sulfuric acid and / or sulfuric acid. A buffering agent can be used to adjust the pH if necessary, for example, salts of strong bases and weak acids, in particular such as ammonium acetate.

[0032] In a particularly preferred embodiment of the invention, the EK agent further comprises a salt in which the cationic component is a metal cation from the group of lanthanides and / or a metal cation from block d.

[0033] Preferred metal cations from the lanthanide group are cations of lanthanum, cerium, praseodymium, neodymium, promet, samarium, europium and / or dysprosium. Lanthanum, cerium and praseodymium cations are particularly preferred. Metal cations from the lanthanide group can occur in the first, second and / or third oxidation state, with the third oxidation state being preferred.

[0034] Preferred d-metal cations are titanium, vanadium, manganese, yttrium, zirconium, niobium, molybdenum, tungsten, cobalt, ruthenium, rhodium, palladium, osmium and / or iridium cations. Of the element cations in the d block, the chromium cation is excluded at all oxidation levels. Vanadium, manganese, tungsten, molybdenum and / or yttrium cations are particularly preferred. The d-element cations may be present in the first to sixth degree of oxidation, with the third to sixth degree of oxidation being preferred.

[0035] The method of corrosion protection according to the invention [0036] In the first stage of the method of corrosion protection according to the invention, a suitably prepared substrate is brought into contact with the corrosion protection agent K, and in the second stage with the corrosion protection agent EK. Preferably, this is done by immersing the substrate in a bath or drawing it through a bath containing EK or K. The residence time of the substrate in the bath is from 1 second to 15 minutes, preferably from 10 seconds to 10 minutes, and particularly preferably from 30 seconds to 8 minutes.

The temperature of the bath containing EK or K is in the range from 20 ° C to 90 ° C, preferably from 25 ° C to 80 ° C, particularly preferably from 30 ° C to 70 ° C.

[0037] After the substrate has been treated with an anti-corrosive agent K and an EK coating agent according to the invention, the system consisting of the substrate and the coating agent is dried at a temperature between about 30 ° C and 200 ° C, in particular between 100 ° C and 180 ° C, wherein the drying device can be considered not critical for the beneficial effect of the EK coating agent according to the invention. If the cross-linking groups B and / or B 'undergo at least partial curing under the influence of radiation, then optionally in addition to heat treatment, the coating layer EK according to the invention is irradiated, preferably with actinic radiation and / or an electron beam in a manner known to those skilled in the art.

[0038] The method of the invention can unexpectedly be used on a wide spectrum of substrates and is largely independent of the redox potential of the substrate. Preferred base materials are zinc, iron, magnesium and aluminum and their alloys, these alloys preferably containing at least 20 wt. the above metals. Preferably, these substrates are in the form of sheets, for example sheets used in the automotive, construction or machine building industries. The coated sheets according to the invention are used in particular for the production of shaped sheets and in the continuous coating of metal strips (coil-coating).

[0039] In a particularly preferred embodiment of the invention, the method according to the invention is used for applying a protective coating covering the edges after cutting the sheets described above, in particular for protecting the edges after cutting the previously coated sheets.

[0040] In the first step of the method according to the invention, an aqueous solution of the anti-corrosive agent K having a pH between 1 and 5, containing at least one AA compound with a metal cation from the group of lanthanides and / or a metal element from block d, with the exception of chromium is applied and / or metalate of the element from block d, with the exception of chromium metalates, as an anion, and compound BB, which is at least one oxidizing acid, with the exception of acids containing phosphorus and / or chromium.

[0041] The cationic component of the salt forming the AA component is a metal cation from the lanthanide group and / or a metal cation from the d block. Preferred metal cations from the lanthanide group are lanthanum, cerium, praseodymium, neodymium, promet, samarium, europium and / or dysprosium cations . Lanthanum, cerium and praseodymium cations are particularly preferred. Metal cations from the lanthanide group can occur in the first, second and / or third oxidation state, with the third oxidation state being preferred.

[0042] Preferred d-metal cations are titanium, vanadium, manganese, yttrium, zirconium, niobium, molybdenum, tungsten, cobalt, ruthenium, rhodium, palladium, osmium and / or iridium cations. Of the element cations in the d block, the chromium cation is excluded at all oxidation levels. Vanadium, manganese, tungsten, molybdenum and / or yttrium cations are particularly preferred. The d-element cations may be present in the first to sixth degree of oxidation, with the third to sixth degree of oxidation being preferred.

[0043] Preferably the salts of the above-mentioned cations forming the AA component are very well soluble in water. [Cation] salts are particularly preferred_n[Anion]_m (where n, m> 1), whose solubility product LP = [cation]ⁿx [anion]^m>10^-8 χ mol⁽ⁿ+^m)/ l⁽ⁿ+^m)and especially salts whose solubility product LP> 10^-6xmol⁽ⁿ+^m)/ l⁽ⁿ+^m). In a particularly preferred embodiment of the invention, the concentration of the one or more salts (A) in the corrosion inhibitor is from 10^-1 up to 10^-4 mol / l, especially from 5x10^-1 up to 10^-3 minor.

[0044] Preferably, the anions forming the AA salts with the d-element cations are selected in such a way that the above-mentioned conditions regarding the LP solubility product are met. Preferably, anions of acids with oxidizing properties derived from elements of the VI, VII and VIII side group of the periodic table of elements are used, as well as anions of acids with oxidizing properties derived from the main elements of Group V and VI of the periodic table, with the exception of acid anions with properties oxidizing, being derivatives of phosphorus and chromium, in particular such as nitrates, nitrites, sulfites and / or sulfates. In addition, halogen anions, in particular chlorides and bromides, are preferred anions. [0045] In another preferred embodiment of the invention, the d-element cations may also exist as complexes with mono- and / or multifunctional, potentially anionic ligands. Preferred ligands are optionally functionalized terpyridines, optionally functionalized ureas and / or thioureas, optionally functionalized amines and / or polyamines, in particular such as EDTA, imines, especially such as pyridine with imine functional group, organo-sulfur compounds, especially such as optionally functionalized thiols. thiocarboxylic acids, thioaldehydes, thioketones, dithiocarbamates, sulfonamides, thioamides, especially sulfonates, optionally functionalized boronate compounds, especially such as boric acid esters, optionally functionalized polyalcohols, especially such as carbohydrates and their derivatives and chitosans, optionally functionalized acids, especially such as difunctional and / or oligofunctional acids, optionally functionalized carbenes, acetylacetonates, optionally functionalized acetylenes, optionally functionalized carboxylic acids, especially such as carboxylic acids, which can ionically and / or coordinate with central metal atoms, as well as phytic acid and its derivatives.

[0046] Particularly preferred ligands are phytic acid, its derivatives and sulfonates, optionally functionalized.

[0047] In another embodiment of the invention, the AA salts as anions contain the metallates of elements from the d block, which can form the AA salt optionally with cations of the elements from the d block or with themselves. Preferred d-block elements that form metalates are vanadium, manganese, zirconium, niobium, molybdenum and / or tungsten. Vanadium, manganese, tungsten and / or molybdenum are particularly preferred. Of the metallates of elements from block d, chromates are excluded at all oxidation levels. Particularly preferred metallate d-elements are oxoanions, in particular tungstates, permanganates, vanadates and / or molybdates.

[0048] If the metalates of the elements from block d form an AA salt on their own, i.e. without metal cations from the group of lanthanides and / or metal cations from block d, the above comments also apply to the favorable LP product of such salts. Preferred cations for such salts are optionally substituted organic radicals ammonium, phosphonium and / or sulfonium ions, alkali metal cations, especially lithium, sodium, and / or potassium, alkaline earth metal cations, especially magnesium and / or calcium. Particularly preferred are optionally substituted organic radicals ammonium ions, and alkali metal cations, which provide a particularly large solubility product of the LP salt of AA. [0049] As component BB of corrosion inhibitor K, at least one acid with oxidizing properties is used, which is used in an amount such that the pH of the corrosion agent preferably is from 1 to 5, in particular from 2 to 4. Preferred BB acids are selected from the group consisting of mineral acids with oxidizing properties, in particular nitric acid, nitrous acid, sulfuric acid and / or sulfuric acid.

[0050] For adjusting the pH, if necessary, a buffering agent may be used, for example, salts of strong bases and weak acids, in particular such as ammonium acetate. [0051] The continuous phase used for corrosion protection agents K and EK is water, preferably deionized and / or distilled water.

[0052] In a preferred embodiment of the invention, before applying the anti-corrosive agent K, the substrate is especially cleaned of residual oils and fats, preferably using detergents and / or alkaline cleaning agents. In another preferred embodiment of the invention, after cleaning with detergents and / or alkaline cleaning agents, and before applying the K corrosion protection agent, the substrate is rinsed with water. In another preferred embodiment of the invention, to remove deposits and / or chemically modified, in particular oxidized layers on the surface of the substrate, a mechanical cleaning of the surface is carried out prior to rinsing, e.g. by abrasive agents and / or chemical removal of surface layers, e.g. by deoxidizing agents cleaning agents.

[0053] The substrate thus prepared is brought into contact with the anti-corrosion agent K. Preferably, this is done by immersing the substrate in a bath or pulling it through a bath containing the anti-corrosion agent K. Preferably, the time the substrate remains in the anti-corrosion agent K bath is from 1 second to 10 minutes , more preferably from 10 seconds to 8 minutes, and particularly preferably from 30 seconds to 6 minutes. Preferably, the temperature of the bath containing the K corrosion agent is preferably in the range of 25 ° C to 90 ° C, more preferably in the range of 30 ° C to 80 ° C, and particularly preferably from 35 ° C to 70 ° C.

[0054] After the substrate has been treated with an anti-corrosive agent K, preferably the system consisting of the substrate and the anti-corrosive agent K is jet dried or at a temperature from about 30 ° C to 200 ° C, the drying temperature as well as the drying method and apparatus being considered not critical for the beneficial effects of the K corrosion agent.

[0055] In the second step of the process according to the invention, the substrates coated with corrosion protection K are coated with EK. Preferably, this is accomplished by immersing the coated substrate in a bath or drawing it through a bath containing an EK coating agent. Preferably, the residence time of the EK coating agent bath time is from 1 second to 15 minutes, more preferably from 10 seconds to 10 minutes, and particularly preferably from 30 seconds to 8 minutes. Preferably, the temperature of the bath containing EK coating agent is in the range of 20 ° C to 90 ° C, more preferably of 25 ° C to 80 ° C, and particularly preferably of 30 ° C to 70 ° C.

[0056] After the EK coating agent has been applied to the substrate, the system consisting of the substrate and layers of the K corrosion protection agent and the EK coating agent are preferably dried at a temperature from about 30 ° C to 200 ° C, in particular from 100 ° C to 180 ° C, the drying device being considered non-critical for the beneficial effects of the EK coating agent according to the invention. If the cross-linking groups B and / or B 'undergo at least partial curing under the influence of radiation, then optionally in addition to heat treatment, the coating layer EK according to the invention is irradiated, preferably with actinic radiation and / or an electron beam in a manner known to those skilled in the art.

[0057] The following examples illustrate the invention in more detail.

Examples

Example 1: Preparation of the first tank containing anti-corrosion agent K [0058] 1.77g (0.01 mol) of ammonium molybdate tetrahydrate was dissolved in one liter of water. The pH of this solution was adjusted to 2.5 with nitric acid. An aqueous ammonia solution can optionally be used to adjust the pH to the above value.

Example 2a: Synthesis of the polymer component P coating agent EK [0059] A 5 g mixture (6.25 * 10) was prepared^-3 moles) polyethyleneimines with an average molecular weight Mw = 800 g / mol (Lupasol FG from BASF AG, ratio of primary, secondary, tertiary amine groups (p: s: t): 1: 0.9: 0.5) in 100 g of ethanol 10.7 g (0.066 mol) of benzoyl isothiocyanate dissolved in 86 g of ethanol was added over 45 minutes under nitrogen and at 75 ° C. The mixture was stirred at this temperature for another 4 hours and the resulting product was used without further purification.

Example 2b: Synthesis of crosslinkers V for EK coating agent [0060] 3.1 g (0.008 mol) cerium (III) chloride heptahydrate in 50 ml water was prepared. A solution of 4.1 g (0.025 mol) of 4-hydroxycinnamic acid and 1 g (0.025 mol) of sodium hydroxide solution in 50 ml of water was prepared and adjusted to pH = 7.9 with hydrochloric acid. This solution was added slowly to the cerium solution so that the cerium solution did not exceed pH 6. The precipitate was washed with ethanol and water. 1.7 g (0.003 mol) of this cerium complex was reacted for 5 hours at 40 ° C with 9.1 g of branched polyisocyanate (2.5% NCO content), in 75% blocked with dimethylpyrazole (Bayhydur VP LS 2319 from Bayer AG ) in 80.1 g of ethyl acetate and with 0.7 g of dipropylenetriamine containing a hydroxyl group (Jeffcat-ZR from Hunstmann). The resulting product was used without further purification.

Example 2: Preparation of a second tank containing EK coating agent [0061] In one liter of water, 3 g of the polymer component P from example 2a and 2 g of crosslinker V from example 2b were dissolved. The pH of this solution was adjusted

2.5 with nitric acid. Alternatively, an aqueous solution of ammonia can be used to adjust the pH to the above value.

Example 3: Coating the substrate with an anti-corrosive agent K and an EK coating agent [0062] The substrate (galvanized steel sheet) was cleaned for 5 minutes at 55 ° C in a cleaning solution (Ridoline C72 from Henkel) and then rinsed with distilled water.

[0063] Then the sheet rinsed with distilled water was immersed without delay for 4 minutes in the first anti-corrosive tank K of example 1 at 45 ° C. The coated sheet was then rinsed with distilled water and dried with a stream of nitrogen. Immediately after this, the sheet was immersed for 5 minutes in a second tank containing the EK coating agent of Example 2 at 35 ° C. The coated sheet was then rinsed with distilled water and dried with a stream of nitrogen. The sheet was then dried for 30 minutes at 150 ° C.

[0064] The sheet coated in this way and the reference samples described below were cut with sheet shears to obtain all sheets with unprotected edges. [0065] The reference sample for the sample according to the invention was Gardobond 958 54 (from Chemetall GmbH: galvanized steel sheet phosphatized and rinsed with zirconium hexafluoride solution).

Example 4: Accelerated corrosion test using a 3% sodium chloride solution on coated substrates according to example 3 [0066] A solution of 3% sodium chloride in completely desalinated water was used. Steel, galvanized steel or zinc alloys can be used as the substrate here. For aluminum and its alloys, the sodium chloride solution is additionally adjusted to pH = 3 with acetic acid. Samples (3 * 3 cm) were immersed in 170 ml of this solution and then stored in a desiccator under almost 100% humidity. A humid atmosphere was created using a stream of oil-free compressed air, passed through two scrubbers with completely desalinated water, and then through a desiccator. This arrangement ensures a constant humidity as well as a constant carbon dioxide content, with the temperature being maintained at 25 ° C. The samples are weighed on an analytical balance before immersion. The unprocessed reference sheets (steel, galvanized steel) were cleaned in ethanol in an ultrasonic bath for 5 minutes. After storage for 24 hours in solution, the sheets are removed and rinsed with a 3% sodium chloride solution over the beaker using a disposable pipette (approx. 10 ml sodium chloride solution on one side of the sample). The sheets are then dried with a stream of nitrogen and dried for 15 minutes at 50 ° C and weighed. The sheet is then resuspended in fresh sodium chloride solution of the same concentration. The used sodium chloride solution is mixed with 1 ml 32% hydrochloric acid to dissolve any precipitates that may occur. In the obtained clear solution, the metal content of the substrate (Zn, Fe, Al, Mg) is determined by the ICP-OES technique (optical emission spectrometry with inductively coupled plasma).

[0067] The above described procedure is repeated after 24, 72, 96 and 168 hours. The measurement results were verified by two determinations.

Corrosion test rating:

a) ICP-OES results of immersion solution [0068] ICP-OES results were normalized to the surface of the samples. These results are in a straight line. Due to the linearity of corrosion kinetics, different coatings can be compared in terms of graph slope. ICP-OEC results illustrate the dissolution of the substrate in terms of surface unit and time unit, and thus allow direct measurement of corrosion rate for each coating.

b) Weighing samples [0069] The sample masses also provide information on whether the coating allows surface passivation. For this purpose, weight loss is converted into molar concentration and normalized to the surface of the samples. Corrosion kinetics are used to compare corrosion samples that have only been subjected to alkaline cleaning. Next, the slope of the ICP-OES results plots are shown in comparison with the original sample (untreated substrate) and other reference samples.

Table 1: Corrosion test results

Substrate ICP-OES results (10^-4 minor^xh.^xcm²)

Galvanized steel sheet (without coating) 8,136

Galvanized steel sheet coated as described in example 3 4,580

Gardobond 958 54 (standard) 6,171 [0070] The results of corrosion tests clearly prove the superiority of the coating method according to the invention over traditional corrosion protection (reference).