RU2773667C2 - Low temperature cure coate compositions suitable for dip application - Google Patents

Abstract

FIELD: anti-corrosion coatings.

SUBSTANCE: invention can be used for applying anti-corrosion coatings. The aqueous composition of the coating agent contains particles of an isocyanate-reactive polymer with an average particle size of 10 to 1000 nm, a polyisocyanate blocked by ketoxime and/or pyrazole containing an aromatic or cycloaliphatic hydrocarbon residue, a polyanionic polymer, a complex fluoride and an aminosilane. Complex fluoride is a hexa- or tetrafluoride of metals IVb, Vb and VIb of groups of the periodic system of elements. The aqueous composition of the coating agent has a pH value of 3 to 5 and a total solids content of 5 to 35% by weight. Also proposed are a method for manufacturing an aqueous composition of a coating agent, a method for coating a surface of a substrate releasing metal ions, and a coating.

EFFECT: providing easy-to-apply aqueous solution coating compositions without the use of electric current, which are corrosion resistant and uniform.

22 cl, 4 tbl, 16 ex

Description

The invention relates to low-temperature curable coating compositions for coating surfaces, in particular in the method of applying dip coatings, to a method for applying and curing them without applying current, as well as to a corresponding coating made from a coating composition.

There are many ways to produce homogeneous coatings, in particular on metal surfaces, using dipping methods. In this case, for the production, in particular, of anti-corrosion coatings (mainly consisting of an organic matrix and/or organic and/or inorganic additive components), the methods described below are preferably used.

Classical methods are based on the use of the rheological properties of the compositions used to achieve an integral coating of the connected part. While it is possible to reduce buildup of coating material at critical locations by continuously rotating the relevant part after the dipping process, it is not possible to obtain a completely uniform coating using this method. In addition, in areas with higher coverage rates, defects such as bubbling and boiling may occur during the drying process and/or the crosslinking process, which degrade the quality of the entire coating.

Electrophoretic methods avoid this problem by using electric current to deposit a uniform coating in the dip coating process. Using this method, it is possible to create uniform coatings on metal parts. The deposited coatings exhibit exceptionally good wet adhesion to the metal substrate. Without peeling off the coating, the part can be processed in the subsequent washing step. This has the effect that the aforementioned hard-to-reach places on the part are freed from excess coating solution and thus no defects can occur during the drying process. The disadvantage of this technology is that, in addition to the amount of electrical energy and in addition to the necessary special immersion baths, which lead to increased costs, so-called edge losses are also detected, since the electric fields at the macroscopic edges are generated non-uniformly, and the edges are uneven and possibly also can not be completely covered. In addition, when assembling parts, cavities should be avoided, since in these places an effect comparable to the Faraday cage phenomenon occurs. Due to the decrease in the electric field strength required for deposition, in such areas, the parts cannot be coated or only greatly reduced by the method (penetration problem), resulting in deterioration of the coating quality. In addition, electric dip painting (ETL), such as, for example, cathodic dip painting (KTL), has the following disadvantages. Thus, a suitable immersion bath, complete with all electrical and mechanical devices, ranging from temperature control, power supply and electrical insulation, necessary circulation devices and additional devices, up to the recovery of anolytic acid, which is formed during electroplating, and ultrafiltration for the recycling of varnishes, as well as control devices, has a very expensive design. The control of the process requires a very high level of technical effort, also due to the high electrical current and the amount of energy, as well as equalizing the electrical parameters across the volume of the bath and fine-tuning all process parameters, as well as maintaining and cleaning the plant.

Conventional autophoretic methods, in contrast, are based on a non-electrical concept consisting of exposing the substrate surface to be used with an etching solution, whereby metal ions are detached from the surface and the emulsion coagulates by concentrating the metal ions at the resulting interface. Although these methods do not have the aforementioned limitations of electrolytic methods with respect to the Faraday cage effect, the coatings obtained after the first activation stage must be fixed in a costly multi-stage dipping method. In addition, exposure to the pickling solution leads to the inevitable contamination of the active zone with metal ions, which must be removed from the zones. In addition, the method is based on a chemical deposition process, which is not self-regulating and cannot be stopped if necessary, as is possible, for example, by turning off the electric current in electrolytic methods. Thus, if the metal substrates remain in the cores for a longer period of time, an excessively thick layer is inevitable.

WO 2017/117169 A1 describes low temperature curable, self deposited coating agents which can be cured using blocked polyisocyanates. However, these coating agents are not capable of forming ionic gels in use, so that both the deposition mechanism and the deposited layer of the coating agents are fundamentally different from the present invention.

The object of the present invention was to provide an aqueous coating composition that is storage stable, can be easily prepared, and can be deposited without the use of electric current on the released metal ions of the surface, and in doing so it forms a uniform, largely closed and substantially smooth coatings with greater layer thickness and in particular does not suffer from the disadvantages of the above prior art. In addition, the aqueous coating composition must be thermally curable and even without catalysts for isocyanate crosslinking reactions, in particular without metal catalysts for isocyanate crosslinking reactions at as low firing temperatures as possible (<200°C; 30 min.) to provide coatings with high corrosion resistance, in particular with low penetration in the salt spray test. Another object was to provide a method of coating substrate surfaces releasing metal ions using coating compositions according to the invention.

The problem according to the invention can be solved by providing an aqueous coating composition containing:

- at least one type of organic polymer particles with an average particle size of 10 to 1000 nm, comprising isocyanate-reactive polymers (A), preferably consisting of isocyanate-reactive polymers (A),

one or more polyisocyanates (B) blocked with ketoxime and/or pyrazole containing at least one aromatic hydrocarbon residue or at least one cycloaliphatic hydrocarbon residue,

- at least one polyanionic polymer (C)

- at least one complex fluoride (D) selected from the group consisting of hexa- or tetrafluorides of metallic elements of groups IVb, Vb and VIb of the Periodic Table of the Elements, and

- at least one aminosilane (E) containing one silyl group of the formula Si(OR ⁷ ) _3-i (R ⁸ ) _i , in which R ⁷ means an alkyl residue with from 1 to 4 carbon atoms or means the group O=C- CH ₃ , R ⁸ is an alkyl radical with from 1 to 4 carbon atoms and i is 0 or 1,

wherein the aqueous composition of the coating agent has:

a pH value of 3 to 5, preferably 3.5 to 4.5, particularly preferably 3.8 to 4.2, and

- total solids content (according to DIN ISO 3251, 1 g sample, 60 min, 125°C) from 5 to 35 wt. %, preferably from 10 to 30 wt. %, particularly preferably from 15 to 25 wt. %.

The aqueous coating composition according to the invention is used in stage II and, if appropriate, also in stage V of the coating process according to the invention below.

The coating method according to the invention is a method for coating a metal ion-releasing surface of a substrate, comprising or consisting of the following steps:

I. providing a substrate with a metal ion releasing surface,

II. contacting the metal ion-releasing surface with the aqueous composition of the coating agent according to the invention to form an organic coating,

III. if necessary, washing the organic coating and

IV. if necessary, drying the organic coating at a temperature of from 10 to 120°C for a period of time from 1 to 40 minutes. and curing the organic coating at a peak metal temperature of 120 to 200° C. for a period of 5 to 50 minutes; or

V. if necessary, drying the organic coating and the coating of the additional coating composition according to the invention, and then drying the coating formed in step V, or both coatings, and co-curing both coatings at a peak metal temperature of from 120 to 200°C for a period of time from 5 to 50 min.

The coating composition according to the invention is capable, in step II, of forming an ionic gel on the metal ion-releasing surface of the substrate.

в Biomacromolecules 2001, 2, 1089-1096 или у Siew и Williams в Biomacromolecules 2005, 6, 963-969. Ионогенные гели, перечисленные в двух упомянутых выше публикациях, представляют собой гели на основе полианионных полимеров (С), в частности, встречающиеся в природе анионные полисахариды пектинового и альгинатного типа и синтетическую полиакриловую кислоту. Полианионные полимеры (С) образуют указанные ионогенные гели в присутствии катионов поливалентных металлов в водной среде.In the context of the present invention, ionic gels are described, for example, in Braccini and

in Biomacromolecules 2001, 2, 1089-1096 or Siew and Williams in Biomacromolecules 2005, 6, 963-969. The ionic gels listed in the two publications mentioned above are gels based on polyanionic polymers (C), in particular, naturally occurring anionic polysaccharides of the pectin and alginate type and synthetic polyacrylic acid. The polyanionic polymers (C) form said ionic gels in the presence of polyvalent metal cations in an aqueous medium.

The ionic gels according to the invention, in addition to the metal ions released from the surface of the substrate, generally contain all the components of the coating composition according to the invention.

Surprisingly, it has been found that substrates with metal ion releasing surfaces, when treated with an aqueous coating composition according to the invention, form an ionic gel coating, and that a layer of ionic gel deposited on the substrate allows other cations detached from the metal ion releasing surface to diffuse, so that coating with other coating compositions according to the invention can be carried out in other baths/coating steps in stage V.

The dried and/or cured coatings obtained in step V can additionally be coated with conventional base coats and/or clear coats.

Since the coating method according to the invention results in homogeneous, substantially closed coatings according to the invention, the last coating in each case in the method described above must be resistant to washing. The term "wash-resistant" in the context of the present invention means that, under industrial production conditions, the coating is essentially left in place by the usual industrial washing process, so that a closed coating is obtained.

The components, in particular preferred components of the coating compositions according to the invention, particularly suitable supports, as well as their possible pre-treatment and the implementation of the method according to the invention are described in more detail below.

Particles of organic polymers, including isocyanate-reactive polymers (A)

The aqueous coating composition according to the invention contains particles of organic polymers containing isocyanate-reactive (abbreviated: isocyanate-reactive) polymers (A). Isocyanate-reactive polymers (A), along with their reaction participants, ketoxime and/or pyrazole blocked polyisocyanates (B) and polyanionic polymers (C), are the main film-forming substances.

The reactivity with isocyanate groups and therefore also with blocked isocyanate groups at higher temperatures is due to the presence of isocyanate-reactive groups in these polymers. Reactive with isocyanate groups, among others, and in particular include hydroxyl groups, primary and secondary amino groups, as well as carboxyl groups, carboxamide groups or thiol groups, of which hydroxyl groups are particularly preferred.

Preferably, the organic polymer particles which contain one or more isocyanate-reactive polymers (A) are particles which are in the form of a primary dispersion. However, in principle, dispersions of organic primary particles can also be obtained as secondary dispersions.

The term dispersion includes the terms suspension and emulsion.

Primary dispersions are generally obtained by emulsion polymerization, while in the case of secondary dispersions the monomers are dissolved in an organic solvent, polymerization takes place in an organic solvent, the solvent is removed and the polymer is emulsified in an aqueous phase.

The average size (Z-average) of organic polymer particles is in the range of 10 to 1000 nm, preferably in the range of 50 to 900 nm, and most preferably in the range of 400 to 800 nm, as measured by dynamic light scattering using Malvern Zetasizer (software software v7.02) from Malvern (Herrenberg, Germany).

The isocyanate-reactive polymers (A) (shortly: isocyanate-reactive polymers (A)) are preferably selected from the group of polyacrylates, polyurethanes and polyepoxides, as well as hybrid systems containing two or more of these polymers.

The stabilized organic polymer particles are particularly preferably selected such that the isocyanate-reactive polymer (A) contained is selected from the group consisting of nonionically stabilized polyepoxy dispersions, nonionically stabilized polyurethane dispersions and nonionically stabilized polyacrylate dispersions or hybrid systems derived therefrom.

Hybrid systems depending on the type can be divided into three groups of hybrid systems;

a. hybrid systems, which are produced by pure mixing of different dispersions,

b. hybrid systems having a chemical bond between different types of polymers; and

in. hybrid systems in which different types of polymers form interpenetrating networks (IPNs).

Typical hybrid systems that fall under the above types are, for example, polyacrylate-polyurethane hybrid dispersions.

Typically, such polyacrylate-polyurethane hybrid dispersions are prepared by emulsion polymerization of one or more (meth)acrylic and/or vinyl monomers in an aqueous polyurethane dispersion. However, it is also possible to obtain a polyacrylate-polyurethane hybrid dispersion as a secondary dispersion.

The term "(meth)acrylic" includes both acrylic and methacrylic. Therefore, the (meth)acrylic monomer may carry an acrylic group or a methacrylic group. The term "vinyl" refers to all polymerizable monomers bearing a vinyl group, but not covered by the term "(meth)acrylic".

Aqueous polyacrylate-polyepoxy hybrid dispersions are generally prepared by addition reactions of a difunctional epoxide with difunctional amine monomer units and subsequent reaction with a polyacrylate with sufficient carboxyl functions. Water dispersibility can be achieved, for example, by means of carboxylate groups which have been converted into anionic groups with the help of amines and then dispersed in water.

Organic polymer particles containing one or more isocyanate-reactive polymers (A) may be anionically stabilized, nonionically stabilized, or both anionically and nonionically stabilized. Stabilization is usually carried out using emulsifiers.

There are external emulsifiers and internal emulsifiers. Unlike internal emulsifiers, external emulsifiers are not an integral part of the polymer structure, but are independent compounds. In the context of this invention, external emulsifiers are referred to below as additives (G).

Stabilization with external emulsifiers can take place, for example, with anionic emulsifiers already within the framework of the emulsion polymerization. Typical anionic emulsifiers are sulfated or sulfated anionic emulsifiers, preferably the following structures R ^t -(OCH ₂ CH ₂ ) _a -(O) _b -SO ₃ ^- M ⁺ , with R ^t = alkyl or aryl, a=8-30, b =0 or 1 and M ⁺ = alkali metal cation or NH ₄ ⁺ .

Coating organic particles with anionic emulsifier molecules negatively charges their surface, which leads to electrostatic repulsion of organic polymer particles.

However, external stabilization can also be carried out using non-ionic emulsifiers. Typical nonionic emulsifiers preferably have the following structures P ^t -(OCH ₂ CH ₂ ) _a -OH with R ^t = alkyl or aryl, and a=8-50. In contrast to the electrostatic repulsion of dispersions obtained with anionic emulsifiers, the stabilization mechanism of nonionic emulsifiers is based on steric effects.

Internal anionic emulsifiers, i.e. emulsifiers embedded in the isocyanate-reactive polymer (A), generally have sulfonate groups, sulfate groups or carboxylate groups and contain at least one functional group which can react with the functional groups of other polymer constituents. .

Thus, for example, a sulfonate-bearing compound of the formula H ₂ N-CH ₂ -CH ₂ -NH-(CH ₂ ) _x -SO ₃ Na, with x=2 or 3, in particular via the primary amino group, but in principle also through the secondary amino group, it can react with isocyanate groups in the synthesis of polyurethanes or with oxirane groups in the synthesis of polyepoxides and be incorporated into the polymer.

A typical representative of the type of carboxylate groups is, for example, dimethylolpropanoic acid or its salt form, which can be incorporated via hydroxyl groups by reaction with isocyanate groups into polyurethanes or by reaction with oxirane groups into polyepoxides.

Internal nonionic emulsifiers typically have hydrophilic polyalkylene oxide chains. Particularly suitable internal non-ionic emulsifiers comprise or consist of polyethylene oxide chains or poly(ethylene oxide-propylene oxide) chains, the latter having preferably a lower mole fraction of propylene oxide than that of ethylene oxide in order to provide sufficient hydrophilicity. The polyalkylene oxide chains can be incorporated into the backbone of the polymer backbone, into the side chain, or at the end.

The incorporation of such polyalkylene oxide chains as internal nonionic emulsifiers into the isocyanate-reactive polymers (A) is expediently carried out by reaction between reactive functional groups on the polymer to be stabilized and functional groups of compounds containing polyalkylene oxide chain(s) which are reactive with reactive groups on the polymer .

The internally non-ionically stabilizable polymer is preferably selected from the group consisting of polyacrylates, polyurethanes, polyepoxides, urethane acrylates, aromatic and (cyclo)aliphatic epoxyacrylates and polyesters, as well as mixtures thereof. In the case of polyurethanes and urethane acrylates, the attachment of the polyalkylene oxide chain(s) preferably takes place via free isocyanate groups still present in the polyurethane or urethane acrylate to hydroxy groups or amino groups, preferably exactly one hydroxyl group or one amino group of compounds containing polyalkylene oxide chain(s).

In the context of the present invention, reactive functional groups on a nonionically stabilized polymer are understood in particular to be isocyanate groups, hydroxyl groups, carboxyl groups, oxirane groups, vinyl groups and amino groups.

A typical and preferred addition reaction in which compounds containing polyalkylene oxide chain(s) can be attached to the polymer to be stabilized is the formation of a urethane between a hydroxyl group and an isocyanate group. Depending on the viscosity, the reaction can preferably be carried out in the presence of organic solvents, which are then removed again. Thus, for example, a polyethylene glycol molecule functionalized with isocyanate as a compound containing a polyalkylene oxide chain and a polyester polyol as a non-ionically stabilizable polymer, preferably with a number average molecular weight M _n in the range from 1000 to 3000 g/mol, can be used. Moreover, as reactive groups on the original binder, there are hydroxyl groups that are capable of forming urethane bonds. The polyester polyol used advantageously has reactive groups ranging from 100 g/eq. up to 5000 g/eq.

Preferably, the compound containing one or more polyalkylene oxide chains is a hydrocarbon-terminated oligomer of ethylene glycol units, wherein the number of ethylene glycol units in the oligomer is preferably 2 to 20, particularly preferably 5 to 10, and the oligomer has a group reactive with respect to a nonionically stabilized polymer, preferably a hydroxyl group or an amino group.

Particularly preferably, the compound containing one or more polyalkylene oxide chains has a number average molecular weight Mn, determined by gel permeation chromatography (in THF at 25° C. using a polystyrene standard) between 300 and 1000 g/mol. Most particularly preferably, the compound containing one or more polyalkylene oxide chains as a terminal hydrocarbon group has a C 1 to C 4 alkyl group or a C 6 to C 12 aryl group.

The preparation of the internally non-ionic stabilized isocyanate-reactive polymer (A) is carried out by covalently linking a compound containing one or more polyalkylene oxide chains to the above polymer. The neoionically stabilized isocyanate-reactive polymer (A) thus obtained in aqueous phases, preferably over a period of time of at least 6 to 12 months, forms a stable dispersion.

Another variant is that the particles containing the polyalkylene oxide chain are an oligomer of ethylene glycol units, wherein the number of ethylene glycol units in the oligomer is preferably from 2 to 20, particularly preferably from 5 to 10, the oligomer has a group reactive towards the non-ionic stabilized polymer, preferably a hydroxyl group or an amino group, and contains at least one additional terminal reactive group such as, for example, a hydroxyl group, an amino group, a vinyl group, an acrylic group or a methacrylic group. These groups can promote crosslinking either by a radical reaction or by addition or condensation reactions during the firing process. As a result, it is possible to produce a cross-linked, closed coating that is resistant to water, chemicals, and corrosion and exhibits improved scratch resistance, stick resistance, high flexibility, elasticity, cold workability, and good adhesion.

The organic polymer particles which comprise one or more isocyanate-reactive polymers (A) can additionally be surface-modified, preferably with silanes, in particular the aminosilanes (E) described below and/or with phosphorus group-containing and/or amine-containing organic compounds or phosphates. Such compounds may be bonded covalently or by physical sorption or chemisorption to organic polymer particles, and may have functional groups for bonding to the substrate surface to be treated. Organic particles that do not or do not have suitable reactive groups to bind to their surfaces can be bound to the surface to be coated by adsorption of internally stabilizable emulsifier residues, in particular parts of polyethylene glycol.

The stabilized isocyanate-reactive polymers (A) have additional emulsifying properties and can therefore facilitate the ionic precipitation of other binders and particles.

In principle, it is possible to combine nonionic stabilization with anionic stabilization and/or external stabilization with internal stabilization.

Particularly preferred are non-ionic stabilized polyepoxy dispersions, in particular those containing one or more polyethylene oxide residues.

As a rule, coating formation occurs exclusively or almost exclusively through the formation of an ionic gel, as described at the beginning, so that autophoretic processes do not occur or occur only to a very small extent. With the test described in the following paragraph, it is easy to detect particularly suitable coating compositions in which little or no autophoresis occurs.

Thus, the most preferably used stabilized organic polymer particles comprising one or more isocyanate-reactive polymers (A) are those which can be selected by the test described below:

1) production of an aqueous mixture of fully demineralized water (VE), 0.5 wt. % of the polyanionic polymer (C) described in more detail below and 10 wt. % of the investigated non-ionic stabilized dispersion;

2) adjusting the pH of the mixture with hexafluorozirconic acid to a value of 2 to 3;

3) immersion of the cleaned substrate for 5 minutes at room temperature (ie 23°C) in the solution described above;

4) in the case of precipitation, a control test is carried out (without polyanionic polymer (C)), for which a mixture of demineralized water and 10 wt. % of the investigated neoionic stabilized dispersion;

5) the mixture prepared according to 4) is adjusted again with hexafluorozirconic acid to a pH value of 2 to 3, and

6) the test described in paragraph 3) is repeated.

If after step 3) organic deposition on the substrate is obtained and after 6) no deposition is obtained without the polyanionic polymer (C), then stabilized organic polymer particles containing one or more isocyanate-reactive polymers (A) are best suited for the process according to invention.

The content of the organic polymer particles comprising the isocyanate-reactive polymers (A), based on the total weight of the aqueous coating composition, is preferably 3 to 25 wt. %, particularly preferably from 8 to 20 wt. %, most preferably from 10 to 18 wt. %, in particular from 11 to 17 wt. %. The content of organic polymer particles is determined from the dispersion of the dispersion of organic polymer particles, prior to their introduction into the aqueous coating composition according to the invention in accordance with DIN ISO 3251 (1 g sample, 60 min, 125°C) and then converted to the total weight of the aqueous coating composition. funds.

Polyisocyanates blocked by ketoxime and/or pyrazole (B)

In the context of the present invention, the term "blocked polyisocyanates" means those polyisocyanates which have at least two blocked isocyanate groups.

A blocked isocyanate group is to be understood as meaning an isocyanate group which has been blocked or closed by an addition reaction with a so-called blocking agent and, the addition reaction being reversible at higher temperatures, if necessary using suitable catalysts.

Blocked polyisocyanates in the context of the present invention, and as is common in the field of coating compositions, do not contain free isocyanate groups and therefore, as far as technically possible, should be considered as 100% blocked polyisocyanates.

The blocking of polyisocyanates (B) in the context of the present invention is carried out with ketoximes and/or pyrazoles, in particular ketoximes or pyrazoles.

However, structures formed as a result of the interaction of NCO groups with each other, even if they can be restored back to NCO groups, for example, by heating, are not considered in the context of the present invention as blocked isocyanate groups. Thus, in this case, for example, a uretdione group formed from two NCO groups is not considered as a mutual blocking of the two NCO groups. The same applies to the more stable isocyanurate groups, iminooxadiazinedione groups, allophanate groups and biuret groups, since they can generally be reduced to free NCO groups.

Polyisocyanates

The free polyisocyanates used to obtain the blocked polyisocyanates used in accordance with the invention may be described by the following general formula (I):

wherein

R ¹ means an organic residue that does not contain NCO organic groups, containing at least one aromatic hydrocarbon residue or at least one cycloaliphatic hydrocarbon residue and, if necessary, one or more groups selected from the group consisting of isocyanurate groups, iminooxadiazinedione groups, uretdione groups, allophanate groups, biuret groups, urethane groups, urea groups, ether groups and ester groups; and

n is preferably 2 to 10, preferably 3 to 8, particularly preferably 3 to 6.

The polyisocyanates of formula (I) may be aromatic or cycloaliphatic polyisocyanates.

In the case of aromatic polyisocyanates, R ¹ contains at least one aromatic hydrocarbon residue. While preferably it is a substituted or unsubstituted six-membered aromatic hydrocarbon ring. Suitable substituents on the six-membered aromatic hydrocarbon ring are, in particular, alkyl groups with 1 to 3 carbon atoms.

In aromatic polyisocyanates, preferably at least one of the n isocyanate groups of formula (I) is preferably linked to an aromatic hydrocarbon moiety. Particularly preferably, all n isocyanate groups of formula (I) are preferably linked to an aromatic hydrocarbon residue.

Typical and preferred in the context of the present invention the compounds of formula (I) contain hydrocarbon residues based on toluene diisocyanate and/or hydrocarbon residues based on diphenylmethane diisocyanate in the residue R ¹ preferably hydrocarbon residues based on diphenylmethane diisocyanate (MDI).

The term toluene diisocyanate (TDI) in this case generalizes 2,4-TDI and 2,6-TDI, as well as a mixture of their isomers. Under the term diphenylmethane diisocyanate (MDI) in this case are generalized 4,4'-MDI, 2,4'-MDI, 2,2'-MDI, as well as the so-called technical diphenylmethane diisocyanate (often incorrectly called polymeric MDI). Technical MDI can be represented by the general structure

in which k preferably means from 0 to 10. Technical MDI is a mixture of compounds of the above formula, and preferably from 30 to 80 wt. % falls on the compound with k=0 and less than 15 wt. % per connection with k≥6, in each case calculated on the total weight of the technical MDI.

If in this case mainly isocyanate-based hydrocarbon residues are referred to, then the isocyanate or polyisocyanate residue which remains when the isocyanate or polyisocyanate is "liberated" from its isocyanate groups is meant. Thus, for example, the residue of toluene is a hydrocarbon residue based on toluene diisocyanate.

In the case of cycloaliphatic polyisocyanates, R ¹ contains at least one cycloaliphatic hydrocarbon residue. While preferably it is a substituted or unsubstituted six-membered cycloaliphatic hydrocarbon ring. Suitable substituents on the six-membered cycloaliphatic hydrocarbon ring are, in particular, alkyl groups with 1 to 3 carbon atoms.

In cycloaliphatic polyisocyanates, preferably at least one of the n isocyanate groups according to formula (I) is linked to a cycloaliphatic hydrocarbon moiety. Thus, for example, in the case of isophorone diisocyanate, one isocyanate group is linked directly to the 1-position of the 3,5,5-trimethyl-substituted cyclohexane residue, while the second isocyanate group is linked via the methylene group to the 5-position of the cyclohexane residue. Particularly preferably in the case of cycloacyphatic polyisocyanates, all n isocyanate groups according to formula (I) are linked to a cycloaliphatic hydrocarbon residue. This is the case, for example, with dicyclohexylmethane diisocyanate (H ₁₂ MDI). The term dicyclohexylmethane diisocyanate (H ₁₂ MDI) in this case includes 4,4'-H ₁₂ MDI, 2,4'-H ₁₂ MDI, 2,2'-H ₁₂ MDI, as well as hydrogenated technical diphenylmethane diisocyanate. The latter is obtained by, according to essentially complete hydrogenation of the phenyl residues of technical MDI.

Typical and in the context of the present invention preferred compounds of formula (I) contain hydrocarbon residues based on isophorone diisocyanate (IPDI) and/or hydrocarbon residues based on dicyclohexylmethane diisocyanate in the radical R ¹ , preferably hydrocarbon residues based on dicyclohexylmethane diisocyanate.

The residue R ¹ contains at least one aromatic hydrocarbon residue or at least one cycloaliphatic hydrocarbon residue, however, it may also contain several of these residues. Preferably R ¹ contains at least 2 aromatic hydrocarbon residues or at least 2 cycloaliphatic hydrocarbon residues. Particularly preferably, R ¹ contains at least 3 aromatic hydrocarbon residues or at least 3 cycloaliphatic hydrocarbon residues, and most preferably at least 4 aromatic hydrocarbon residues or at least 4 cycloaliphatic hydrocarbon residues.

For example, by trimerizing an aromatic diisocyanate, such as, for example, toluene diisocyanate, an isocyanurate group or an iminooxadiazinedione group can be formed from three isocyanate groups, to which three toluene monoisocyanate groups are attached. Such an R ¹ residue contains three alkyl-substituted aromatic hydrocarbon residues (ie three toluene residues) and one isocyanurate group. Three NCO groups are in turn linked to this residue R ¹ , with n=3 in the sense of formula (I) above. With a suitable trimerization of, for example, 4,4'-diphenylmethane diisocyanate, even 6 aromatic hydrocarbon residues are inserted into the R ¹ residue, for which it equally applies that it carries an isocyanurate group and that n=3 in the sense of the above formula (I).

In principle, it is also possible to obtain higher oligomers, for example by adding additional diisocyanate molecules to the free NCO groups of the trimer, whereby products with a higher degree of polymerization are formed. Thus, for example, by adding two additional diisocyanates, an additional isocyanurate ring can be formed, whereby the NCO functionality of the compounds of formula (I) is increased by 1 (n=4).

However, high molecular weight residues R ¹ can be obtained not only by oligomerization, such as, for example, dimerization (formation of uretdione) or by the above, if necessary also multiple, trimerization or by formation of biuret or allophanate, but also by formation of an adduct or formation of the so-called prepolymer.

We are talking about NCO adducts when, for example, diisocyanates, which can be used to obtain compounds of formula (I), are reacted with compounds, that is, compounds with a certain molecular weight, preferably with a low molecular weight, which bear, in particular, hydroxyl groups, primary and/or secondary amino groups and/or other groups reactive with isocyanate groups. Such compounds include in particular polyols, such as, for example, polyols with three hydroxyl groups, such as glycerol, trimethylolpropane and hexanetriol, polyols which have four hydroxyl groups, such as pentaerythritol or polyols with six hydroxyl groups, such as dipentaerythritol . The hydroxyl groups of these compounds can react to form urethane groups with the isocyanate group of a di- or polyisocyanate, with a corresponding excess of isocyanate groups forming polyisocyanates according to formula (I) which contain urethane groups in the radical R ¹ .

NCO prepolymers are mentioned when, for example, di- or polyisocyanates, which can be used to obtain compounds of formula (I), are reacted with polymeric compounds, i.e. compounds having polydispersity, the polymeric compounds bearing, in particular, hydroxyl groups, primary and/or secondary amino groups and/or other groups reactive with isocyanate groups. Such polymeric compounds are, for example, polyester polyols, polyether polyols or polyether and polyester polyols. The hydroxyl groups of these polymeric compounds can react to form urethane groups with the isocyanate group of the diisocyanate, and with a corresponding excess of isocyanate groups, polyisocyanates according to formula (I) are formed, which in the remainder R ¹ contain urethane groups, as well as ether groups or ester groups, or alternatively ether groups, as well as ester groups.

In the present invention, a distinction is made below between hydrophobic blocked polyisocyanates and hydrophilic blocked polyisocyanates. Particular preference is given to hydrophobic blocked polyisocyanates.

In order to obtain hydrophobic blocked polyisocyanates, all n NCO groups in formula (I) react with the blocking agents below, and the R ¹ residue does not contain hydrophilic groups, such as, for example, polyethylene oxide residues, sulfonate groups, sulfate groups and/or carboxylate groups.

To obtain hydrophilic blocked polyisocyanates, polyisocyanates of formula (I) are used, which

a. in the remainder R ¹ have hydrophilic groups, such as, for example, residues of polyethylene oxide, sulfonate groups, sulfate groups and/or carboxylate groups; and/or

b. in which at least one, preferably exactly one, of the n NCO groups interacts with one of the following hydrophilization agents.

The content of polyisocyanates (B) blocked with ketoxime and/or pyrazole is preferably chosen in such a way that the ratio of isocyanate groups in the blocked or blocked polyisocyanates (B) to isocyanate-reactive groups in the isocyanate-reactive polymer (A) is between 0.5 up to 2, particularly preferably from 0.75 to 1.8, most preferably from 1 to 1.6 and in particular from 1.2 to 1.6.

The content of isocyanate groups blocked by ketoxime and/or pyrazole polyisocyanates (B) is preferably 8-22 wt. %, particularly preferably 9-21 wt. %, most preferably 12-20 wt. %. The determination of the content of isocyanate groups was carried out according to DIN ISO 11909: 2007.

If the polyisocyanates (B) blocked by ketoxime and/or pyrazole are hydrophilic compounds, then the content of their isocyanate groups is preferably from 8 to 15 wt. %, particularly preferably from 9 to 13 wt. %, most preferably from 9.5 to 12.5 wt. %.

If the polyisocyanates (B) blocked by ketoxime and/or pyrazole are non-hydrophilized, i. hydrophobic compounds, the content of their isocyanate groups preferably ranges from 10 to 22 wt. %, particularly preferably from 12 to 21 wt. %, most preferably from 13 to 20 wt. %.

Blocking agents

Suitable blocking agents in the context of the present invention are ketoximes and pyrazoles.

Preferred ketoximes of general formula (II) can be obtained by reacting hydroxylamine with a ketone according to the following reaction scheme:

wherein

the radicals R ² and R ³ , independently of one another, are alkyl radicals with 1-6, preferably 1-4, particularly preferably 1-3 carbon atoms; or R ² and R ³ together form an alkylene residue with 3-5 carbon atoms.

Particularly preferably R ² and R ³ are ethyl and/or methyl. Most preferably R ² is methyl and R ³ is ethyl.

The corresponding compound of formula (II) is then referred to as methyl ethyl ketoxime (MEKO) or butanone oxime.

Preferred pyrazoles of general formula (V)

wherein

the radicals R ⁴ , R ⁵ and R ⁶ , independently of one another, are hydrogen or an alkyl group with 1 to 6, preferably 1 to 4, particularly preferably 1 to 3 carbon atoms, can also be used in the context of the present invention as blocking agents. Most preferably, the radicals R ⁴ , R ⁵ and R ⁶ are methyl and/or ethyl, in particular methyl.

Particularly preferably, the compounds of formula (V) are alkyl-substituted, preferably methyl-substituted in the 3-position of the ring, compounds with particularly preferred R ⁵ ═R ⁶ ═H, and most preferably, compounds of formula (V) are alkyl-substituted, preferably methyl-substituted in the 3- and 5-position of the ring with especially preferred R ⁵ =H. Thus, most preferably the compound of general formula (V) is 3,5-dimethylpyrazole.

Hydrophilizing Agents

To obtain hydrophilic blocked polyisocyanates, along with blocking agents that block at least two of the n (≥3) isocyanate groups of the compound of formula (I), hydrophilization agents of general formula (III) are also used

wherein

X is O, S, NH or NR', where R' is an alkyl radical with 1 to 8, preferably 1 to 6 carbon atoms or a cycloalkyl radical with 3 to 8, preferably 3 to 6 carbon atoms; and

R ^hydrophilic represents an alkoxy-terminal polyalkylene oxide residue and/or an organic, preferably aliphatic residue containing sulfonic acid groups, sulfonate groups, carboxyl groups and/or carboxylate groups.

The compounds of formula (III) are reacted with at least one, preferably only one of the n(≥3) isocyanate groups, so as to introduce at least one, preferably one hydrophilic group ^ hydrophilic g blocked polyisocyanate.

Preferred compounds of the formula R ^hydrophilic are those in which X is O, NH or NR' is and R ^hydrophilic is R ⁷ -(OEt) _y (OPr) _z where R ⁷ is an alkyl radical from 1 to 6, preferably 1 to 4 and particularly preferably 1 to 2 carbon atoms, y is 4 to 20, preferably 4 to 16 and particularly preferably 4 to 12, z is 0 to 10, preferably 0 to 6 and particularly preferably 0 to 4, such as 1 to 4, preferably y+z≤20 and preferably y≥z, particularly preferably y≥2z, most preferably y≥3z. Particularly preferably is z=0 and y=4-20.

Ketoxime Blocked Polyisocyanates (Compounds of Formula (IV))

The following scheme shows an example of the preparation of hydrophobic ketoxime-blocked polyisocyanates (n≥2; q=0; p=n; R ¹ does not contain hydrophilic groups) and hydrophilic ketoxime-blocked polyisocyanates (n≥3; q≥1; p=nq) according to the invention. ; and/or n≥2; q≥0; R ¹ contains at least one hydrophilic group):

wherein

R ¹ means an organic residue that does not contain organic NCO groups, containing at least one aromatic hydrocarbon residue or at least one cycloaliphatic hydrocarbon residue and, if necessary, one or more groups, selected isocyanurate groups, iminooxadiazinedione groups, uretdione groups, allophanate groups, biuret groups, urethane groups, urea groups, ether groups and ester groups;

R ² and R ³ independently of one another are alkyl residues with 1 to 6, preferably 1 to 4, particularly preferably 1 to 3 carbon atoms; or together form an alkylene residue with 3 to 5 carbon atoms;

R ^hydrophilic is an alkoxy-terminal polyalkylene oxide residue and/or an organic, preferably aliphatic residue containing sulfonic acid groups, sulfonate groups, carboxyl groups and/or carboxylate groups; and

n≥2 is preferably up to 10 and is p+q, where p is 2 to 10 and q is 0 to 8.

Particularly preferably, the residue R ¹ contains at least one aromatic hydrocarbon residue.

Particularly preferably, q is 0, ie these are hydrophobic ketoxime-blocked polyisocyanates.

Pyrazole Blocked Polyisocyanates (Compounds of Formula (VI))

The following scheme shows an example of the preparation of hydrophobic pyrazole-blocked polyisocyanates (n≥2; q=0; p=n; R ¹ does not contain hydrophilic groups) and hydrophilic pyrazole-blocked polyisocyanates (n≥3; q≥1; p=nq) according to the invention. ; and/or n≥2; q≥0; R ¹ contains at least one hydrophilic group):

wherein

R ¹ means an organic residue that does not contain NCO organic groups, containing at least one aromatic hydrocarbon residue or at least one cycloaliphatic hydrocarbon residue and, if necessary, one or more groups selected from the group of isocyanurate groups, imino-oxadiazinedione groups, uretdione groups, allophanate groups , biuret groups, urethane groups, urea groups, ether groups and ester groups;

R ⁴ , R ⁵ and R ⁶ independently of one another are hydrogen or alkyl radicals with 1-6, preferably 1-4, particularly preferably 1-3 carbon atoms, most preferably methyl and/or ethyl, in particular methyl;

R ^hydrophilic means an alkoxy-terminal polyalkylene oxide residue and/or an organic, preferably aliphatic residue containing sulfonic acid groups, sulfonate groups, carboxyl groups and/or carboxylate groups; and

n≥2 is preferably up to 10 and is p+q, where p is 2 to 10 and q is 0 to 8.

Polyanionic polymer (C)

The aqueous coating composition according to the invention contains at least one polyanionic polymer (C), here also referred to as a polyelectrolyte. By this, in the context of the present invention, is also understood all potentially polyanionic polymers, ie also those which bear acidic groups capable of converting into salts, such as, for example, a HOOS group, a HOSO ₂ group or a HOSO ₃ - group.

Polyanionic or polyanionic polymers (C) (in this case also referred to as anionic polyelectrolytes (C)) are different from polymer polyols (A).

The polyanionic polymers (C) preferably form in an aqueous medium so-called colloidal solutions, in which dimensionally stable particles are absent due to dynamic processes. Therefore, for this reason, they should not be confused with organic polymer particles containing or consisting of isocyanate-reactive polymers (A), nor should they be considered components of these organic polymer particles (A).

They are selected from the group of (C.i) natural, (C.ii) semi-synthetic or (C.iii) synthetic polyanionic polymers. The polyanionic polymers (C) can in particular be partially esterified and/or partially amidated and/or partially epoxidized.

The group (C.i) of natural polyanionic polymers includes, for example, naturally occurring anionic polysaccharides, such as, for example, anionic polysaccharides containing glucuronic acid and/or galacturonic acid, in particular those selected from the group of pectins, gum arabic, tragacanth, karay, ghatti gums , xanthan and gellan; anionic polysaccharides containing guluronic acid and/or mannuronic acid, such as in particular alginates; naturally occurring sulfated and optionally additionally carboxylated polysaccharides, such as, for example, agar, carrageenan, chondroitin sulfate and heparin. Preference is given to polyanionic polysaccharides containing carboxyl groups, in particular those bearing exclusively carboxyl groups or carboxylate groups. Among them, special preference is given to pectins, alginates and gellans.

In addition, the group (C.i) of natural polyanionic polymers includes naturally occurring polymers consisting of or containing acidic amino acids, such as, in particular, polyamino acids and polypeptides. Acid amino acids include, in particular, those which, in addition to the obligatory amino group and the carboxyl group, carry at least one additional carboxyl group. The binding of amino acids to each other is carried out through the so-called peptide bonds, it does not matter whether they are alpha, omega or isopeptide bonds.

The group (C.ii) of semi-synthetic polyanionic polymers includes, for example, subsequently sulfated, phosphated and/or carboxylated natural polyanionic polymers (C.i.), such as, for example, carboxymethylated polysaccharides. On the one hand, the anionic polysaccharides already mentioned in (C.i) can be provided with additional anionic groups, on the other hand, neutral polysaccharides such as, for example, glycogen, amylose, cellulose, starches, dextrans, fructans, callose, curdlan, chitin , polysaccharides from tara gum, guar gum and/or locust bean flour, glucomannans and amylopectin, or even amino-bearing polysaccharides such as chitosan.

In addition, the group (C.ii) of semi-synthetic polyanionic polymers also includes, for example, lignin sulfates.

The group (C.iii) of synthetic polyanionic polymers also includes, for example, completely synthetically obtained polymers from or containing acidic amino acids, such as, in particular, synthetic polyamino acids and synthetic polypeptides.

In addition, group (C.iii) also includes synthetic polyanionic polymers, for example polyvinylsulfonic acid, polyacrylic acid, polymethacrylic acid and copolymers of acrylic acid and/or methacrylic acid with acrylic acid esters, methacrylic acid esters, acrylamide, styrene and various acrylic, methacrylic or vinyl monomers.

Particularly preferably, the aqueous coating composition according to the invention comprises a mixture of at least two different polyanionic polymers (C), preferably a mixture of two different anionic polysaccharides (C.i), in particular a mixture of two pectins.

The pectins that can preferably be used preferably have a degree of esterification of the carboxyl function in the range of 5% to 75%, or a degree of substitution (DS) of 1% to 75%, based on the repeating unit of the polysaccharide.

Particularly preferred pectins preferably have a degree of amidation of carboxyl functions in the range of 1 to 50% and/or a degree of epoxidation of carboxyl functions of up to 80%, based on the repeating unit of the polysaccharide.

The polyanionic polymers (C) preferably have a number average molecular weight M _n (determined by gel permeation chromatography using Pullulan standards and an aqueous 0.05 wt.% solution of sodium azide) in the range from 5000 to 500000 g/mol, preferably from 20000 up to 250,000 g/mol and most preferably from 25,000 to 150,000 g/mol.

The polyanionic polymer (C) is preferably used in an amount of 0.01 to 5.0 wt. %, particularly preferably in an amount of from 0.05 to 2.5 wt. %, most preferably in an amount of from 0.1 to 1.0 wt. %, based on the total weight of the aqueous composition of the coating agent.

The polyanionic polymers (C) are preferably used in the form of their ammonium and/or phosphonium salts. Among these, particularly preferred are their salts with ammonia and tertiary amines, such as, for example, trialkylamines, such as, in particular, trimethylamine, triethylamine and tributylamine, or their salts with tertiary phosphines, such as, for example, trialkylphosphines, such as tri-t -butylphosphine and tri-n-butylphosphine or triphenylphosphine. Equally, quaternary ammonium and phosphonium salts can be used. A preferred quaternary ammonium cation is, for example, tetra-n-butylammonium, and a preferred quaternary phosphonium cation is, for example, tetra-n-butylphosphonium. Salts with DABCO (1,4-diazabicyclo[2.2.2]octane) may also be used.

Complex fluorides (D)

The aqueous composition of the coating agent according to the invention contains one or more complex fluorides selected from the group consisting of hexa- or tetrafluorides of metallic elements of groups IVb, Vb and VIb of the Periodic Table of the Elements, in particular titanium, zirconium and hafnium, preferably in a total amount of from 1.1⋅10 ^-6 mol/l to 0.30 mol/l in terms of a metal atom.

Preferably, the complex fluoride(s) are used in a total amount of 1.1×10 ^-5 mol/l to 0.15 mol/l, preferably 1.1×10 ^-4 mol/l to 0.05 mol/l in terms of metal atom.

The addition of complex fluorides according to the invention results in substantially homogeneous coatings with a dry film thickness in the range of typically 20 µm to 100 µm on cold rolled steel, hot rolled steel, cast steel and up to a dry film thickness of typically > 1 µm on galvanized sheet. steel or aluminium.

Most preferred is the use of hexafluorozirconic acid and hexafluorotitanic acid and their derivatives.

Aminosilanes (E)

The aqueous coating compositions according to the invention preferably contain at least one aminosilane of the following general formula (VII):

in which L means an organic linking group ("linker");

R ⁷ is an alkyl radical with 1 to 4 carbon atoms, preferably 1 to 3 carbon atoms, particularly preferably 1 or 2 carbon atoms, in particular 2 carbon atoms or an O=C-CH ₃ group;

R ⁸ is an alkyl radical with 1 to 4 carbon atoms, preferably 1 to 3 carbon atoms, particularly preferably 1 or 2 carbon atoms means; and

i means 0 or 1, preferably means 0.

Preferably the organic linking group L is a divalent hydrocarbon residue, particularly preferably a (CH ₂ ) _k residue with k=1, 2 or 3, preferably k=1 or 3.

Preferably, the aminosilanes are contained in the aqueous composition of the coating agent in accordance with the invention in a total amount of from 0.0005 to 1.0 wt. %, particularly preferably from 0.001 to 0.8 wt. % and most preferably from 0.0015 to 0.5 wt. %. If the total amount of aminosilanes of general formula (VII) in terms of the total weight of the aqueous composition of the coating agent according to the invention is less than 0.0005 wt. %, then the corrosion resistance of the coating decreases, if the total amount of aminosilanes of general formula (VII) exceeds 1.0 wt. %, based on the total weight of the aqueous coating composition according to the invention, sufficient precipitation of the coating composition does not occur. Particularly preferably, the upper limit of the total amount of aminosilanes is at most 0.2 wt. % or even only 0.1 or 0.05 wt. %, based on the total weight of the aqueous coating composition according to the invention. Excellent results are obtained even at lower amounts.

Additives (F)

Particularly preferably, the aqueous coating composition according to the invention contains at least one additive (F). Additives (F) include only those compounds that do not fall under one of the definitions of components from (A) to (E) or (G).

The additives are preferably selected from the group consisting of soluble colorants, pigments, in particular carbon black pigments and/or fillers, preservatives, in particular biocides, including bactericides, fungicides, algicides, herbicides and insecticides; emulsifiers, wetting and/or dispersing agents, spreading agents, plasticizing agents, pH adjusting acids, thickeners and cross-linking agents.

Soluble dyes, pigments and/or fillers

The aqueous coating compositions according to the invention can contain various colorants, such as, for example, soluble colorants and/or mostly insoluble coloring and/or effect pigments. Fillers may also be present, which typically differ from pigments, typically due to a refractive index of less than 1.7. In the context of the present invention, carbon black pigments are particularly suitable pigments.

preservatives

The aqueous coating compositions according to the invention preferably contain preservatives or biocides. These include all substances that inhibit or kill the growth of microorganisms (fungi, bacteria, algae), as well as insecticides and herbicides with a growth inhibitory or killing function, unless they fall within the scope of other components of the present invention.

Emulsifiers

Preferably, the aqueous coating composition according to the invention contains at least one emulsifier, particularly preferably selected from the group of anionic or nonionic emulsifiers, as described above as external emulsifiers in the description of the stabilized organic polymer particles.

In particular, when using (meth)acrylate-terminated polyurethanes as the isocyanate-reactive polymer (A), the addition of fatty acid-modified polyesters, preferably those with (terminal) tertiary amino groups, has proven to be suitable as emulsifiers (for example, available as EFKA 6225 ). This can significantly increase stabilization in the pH range up to about pH 3.

Wetting and dispersing agents

Wetting and/or dispersing agents that can be used in the present invention in the proposed invention in the compositions of the coating agent, designed to wet and disperse pigments and/or fillers. In principle, all wetting and/or dispersing agents can be used in the context of the present invention.

Spreading aids

Flow aids help to avoid unwanted surface structures after coating. Since spreaders are solvents, they should be classified as solvents (G).

Acids for pH adjustment

In principle, the pH value of the compositions according to the invention can be adjusted using acids such as hexafluorotitanic acid or hexafluorozirconic acid, i.e. complex fluorides (D). However, in principle, other organic or inorganic acids, such as nitric acid or phosphoric acid, can also be used to adjust the acidic pH.

Crosslinkers

In addition to the ketoxime-blocked and/or pyrazole-blocked polyisocyanates (B), the aqueous coating compositions according to the invention generally do not contain other external cross-linking agents. However, if other crosslinkers are present, they may be blocked polyisocyanates and/or aminoplastic resins, such as, for example, melamine resins, which differ from the ketoxime-blocked and/or pyrazole-blocked polyisocyanates (B).

The addition of aminoplast resins, in particular melamine resins, has a positive effect in particular with regard to the recoatability of coatings obtained by the process according to the invention, for example base coats and/or clear coats.

Solvents (G)

Since the coating compositions according to the invention are aqueous compositions, the main solvent is water. The water content of the coating compositions according to the invention is preferably in the range of 65 to 95 wt. %, particularly preferably in the range from 70 to 90 wt. % and most preferably in the range from 75 to 85 wt. %, in each case based on the total weight of the aqueous coating composition according to the invention.

The aqueous composition of the coating agent has a pH value in the range from 3.0 to 5.0, preferably from 3.5 to 4.5 and particularly preferably in the range from 3.8 to 4.2, in particular from 3.9 to 4. ,one. Preferably, the pH can be adjusted with inorganic acids such as phosphoric acid or nitric acid or acidic forms of the fluoride complex (D), for example hexafluorozirconic acid.

In addition to water, the aqueous coating compositions according to the invention may contain organic solvents as co-solvents. The content of co-solvents in the aqueous compositions of the coating agent according to the invention is preferably in the range from 0 to 15 wt. %, particularly preferably in the range from 0 to 10 wt. % and most preferably in the range from 0 to 5 wt. %, such as from 0 to 4 wt. %, from 0 to 3 wt. % or from 0 to 2 wt. %, each time based on the total weight of the aqueous coating composition according to the invention.

The following film-forming additives, as well as dialkyl ethers such as, for example, methoxypropanol, are particularly suitable as co-solvents.

Some specific solvents also act as film formers, softening the surface of the organic polymer particles and thus allowing them to melt. In the context of the present invention, this kind of film-forming agent equally applies to solvents (H).

Particularly preferred as film-forming additives are the so-called long-chain alcohols, in particular those having from 4 to 20, such as, for example, butanediol, butyl glycol, butyl diglycol, ethylene glycol ethers, such as, in particular, ethylene glycol monobutyl ether , ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, ethylene glycol propyl ether, ethylene glycol hexyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, diethylene glycol hexyl ether or polypropylene glycol ethers such as in particular propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monopropyl ether, tripropylene glycol monopropyl ether, propylene glycol phenyl ether i, trimethylpentanediol diisobutyrate, polytetrahydrofurans, polyester polyols and/or ester polyols.

A film-forming additive equally useful in aqueous primary dispersions is 2,2,4-trimethyl-1,3-pentanediol-1-isobutyrate (Texanol®).

Preparation of Aqueous Coating Compositions According to the Invention

The hydrophobic, blocked polyisocyanates (B) can be added, for example, directly during the manufacturing process of an anionically and/or neoionically stabilized dispersion of organic polymer particles that includes the isocyanate-reactive polymer (A). The isocyanate-reactive polymer (A) then acts as a protective colloid or external emulsifier for the hydrophobic, blocked polyisocyanate (B). After mixing, both components can be dispersed together.

The hydrophilic blocked polyisocyanates (B) can be mixed in a simple manner with an anionically and/or neoionically stabilized dispersion of organic polymer particles which contains the isocyanate-reactive polymer (A).

However, crosslinker dispersions can also be prepared from hydrophobic blocked polyisocyanates using external emulsifiers.

The addition of additional components is carried out simultaneously or after the above stages, preferably by simple mixing. Then adjust the pH value.

Preferably, the proportion of organic polymer particles that contain isocyanate-reactive polymer (A) is measured such that the molar ratio of NCO groups in the blocked polyisocyanate (B) to isocyanate-reactive groups in the isocyanate-reactive polymer (A) is from 0.5 to 2 0, particularly preferably from 0.75 to 1.8, most preferably from 1 to 1.6, such as in particular from 1.1 to 1.5 or from 1.2 to 1.6. Therefore, it is particularly preferable to use the blocked polyisocyanate (B) with respect to its reactive NCO groups at the firing temperature in excess of the isocyanate reactive groups in the isocyanate-reactive polymer (A).

Preferably, the preparation of the aqueous coating composition according to the invention is carried out by:

(i) the ketoxime and/or pyrazole blocked polyisocyanate(s) (B) are mixed, with or without an external emulsifier, with a dispersion of organic polymer particles which have an average particle size of 10 to 1000 nm and contain or consist of one or more isocyanate-reactive polymers (A); or

(ii) obtaining a dispersion of organic polymer particles which have an average particle size of 10 to 1000 nm and contain or consist of one or more isocyanate-reactive polymers (A) in the presence of polyisocyanate(s) blocked by ketoxime and/or pyrazole ( AT);

and

(iii) the polyanionic polymer(s) (C), the complex fluoride(s) (D) and the aminosilane(s) (E) are admixed simultaneously or subsequently; and

(iv) adjust the pH to a value between 3 and 5.

Method for applying coatings to metal ion-releasing surfaces of substrates

The method according to the invention for coating a surface of a substrate releasing metal ions comprises or consists of the following steps:

I. providing a substrate with a metal ion releasing surface,

II. contacting the metal ion-releasing surface with the aqueous composition of the coating agent according to the invention to form an organic coating,

III. if necessary, washing the organic coating and

IV. optionally drying the organic coating at 10 to 120°C for a period of 1 to 40 minutes and curing the organic coating at a peak metal temperature of 120 to 200°C for a period of 5 to 50 minutes; or

V. if necessary, drying the organic coating and the coating of the additional coating composition according to the invention and then drying the coating formed in stage V or both coatings and co-curing both coatings at a peak metal temperature of from 120 to 200 ° C for a period of time from 5 to 50 min.

Stage I

Substrates

Among the substrates to be coated with surfaces which release metal ions, in this case, according to the invention, metallic and non-metallic substrates are first distinguished. In the context of this invention, the metal ions released from the surfaces are metal cations, preferably polyvalent metal cations. The polyvalent metal cations are preferably selected from the group including or consisting of Fe ²⁺ , Fe ³⁺ , Al ³⁺ , Cu ²⁺ , Zn ²⁺ , Ca ²⁺ , Mg ²⁺ , Ti ⁴⁺ , Sn ²⁺ , Sn ^{4 +} , Cr ³⁺ and Ni ²⁺ .

Under the metal substrate in this case are denoted metals, alloys or substrates coated with a metal or alloy, and the substrate coated with a metal or alloy, in turn, is a metal, alloy or non-metal substrate, such as, for example, plastic, glass or wood. That is, the surface of the substrate is made of metal or alloy. In this case, the metal substrates must have a surface that releases metal ions under the process conditions, in particular at the pH value to be maintained in the process.

Non-metallic substrates have a non-metallic surface, i.e. a surface that does not consist of a metal or alloy, such as, for example, an organic and/or non-metallic inorganic, for example, a silicate coating, in which metal ions are incorporated or through which metal ions released from the underlying substrate can diffuse to the surface.

To obtain such a metal ion releasing non-metal substrate with a strongly adherent silicate coating, it is possible, for example, to coat with an aqueous composition in the form of a dispersion based on a colloidal silicate sol containing polyvalent metal cations or a polymer modified with a silane or silicate.

Non-metallic inorganic coatings suitable for releasing metal cations from the surface also include, for example, conversion layers capable of being deposited as part of the pretreatment of metals or alloys.

In principle, all kinds of metallic materials are suitable as substrates, in particular those made of aluminium, iron, copper, titanium, zinc, magnesium, tin and/or alloys containing aluminium, iron, calcium, copper, magnesium, nickel, chromium, molybdenum, titanium, zinc and/or tin, and they can also be used adjacent and/or one after the other. As described above, the material surfaces can optionally also be precoated and/or coated, for example with zinc or an alloy containing aluminum and/or zinc. A particularly suitable substrate is steel, such as, for example, cold-rolled steel or galvanized steel.

As objects to be coated, in principle, all kinds of objects that have metal ion-emitting surfaces can be used. These include, in particular, polymeric materials with a metal coating or a polymeric coating that releases metal ions, or reinforced with fibers. Particularly preferred objects are, in particular, strips (rolls), sheet metal, parts such as, for example, small parts, connected components, complexly shaped components, profiles, rods and/or wires.

Surface pretreatment

The surface of the substrates can be pre-treated.

In the context of the present invention, the term "surface pre-treatment" encompasses all steps prior to bringing the metal ion-releasing surface into contact with the inventive aqueous coating composition to form an organic coating (step II).

These include, in particular:

- removal of contamination from the surface (cleaning)

- surface activation for coating and

- applying layers that slow down corrosion and/or improve adhesion, in particular also releasing metal ions.

Surface pre-treatment measures depend on the substrate material, possible contaminants, the need for the choice of cleaning agent, as well as the requirements for the coatings to be applied.

Typical contaminants in the case of metals or their alloys include, in particular, metal chips, oils, greases, scale, rust, oxides, rust deposits, dust, salts, silicones, finishing paste, varnish residues and old coatings. Cleaning can be carried out mechanically, for example, by rubbing, grinding, polishing, brushing, blasting and thermal fire cleaning, or chemically (if necessary with mechanical support) by pickling and/or cleaning with organic solvents and/or aqueous cleaners, in particular alkaline cleaners. Surface preparation or surface pre-treatment can be carried out by activation (eg mechanical roughening by irradiation or chemical activation with titanium phosphate), pickling in the case of aluminum-containing surfaces, conversion coating, for example by chromating or by a method without chromating and/or subsequent passivation .

Typical contaminants in the case of plastics include, in particular, fats, oils, greases, dust and perspiration, in particular sweat from the palms. Typically, cleaning is carried out mechanically by wiping, blowing and/or rinsing, and/or chemically using organic solvents and/or aqueous cleaners. The surface preparation or surface pre-treatment can be carried out by a chrome-blend process, satin finish, UV benzophenone treatment, flame treatment, plasma techniques and/or corona treatment.

Typical contaminants in the case of wood include, in particular, sanding residues and dust. Cleaning is usually performed mechanically by grinding, polishing and/or brushing. Surface preparation or surface pre-treatment may be performed by impregnating, sealing and/or priming.

Typical contaminants on mineral substrates include, in particular, dust, salts and fats. Cleaning is usually carried out mechanically by blasting and/or chemically using organic solvents and/or aqueous cleaners. Surface preparation or surface pre-treatment is usually carried out by impregnation and sealing.

If, after the above steps of cleaning and preparation or pre-treatment, there is still no surface that releases metal ions, organic or inorganic coatings are applied that release metal ions, for example in the form of the colloidal silica sol already mentioned above containing polyvalent metal cations, or by vapor deposition metal or applying a so-called anti-corrosion primer, which contains metals or metal compounds.

If there is a metal ion releasing surface after the above cleaning and preparation or pre-treatment steps, then no other coating is required. On the other hand, for example, coating agents can be applied which themselves release metal ions or are at least permeable to metal ions, so that the metal ions of the underlying surface can migrate or diffuse through the coating to the surface of the coating.

Stage II

Formation of an organic coating in stage II. The coating process according to the invention generally takes place without current application. The term "currentless coating" in the context of the present invention means that no external current source (chemical deposition) is used to coat the metal ion releasing surface with the inventive aqueous coating composition. Thus, for example, in addition to hardware and energy costs, it is possible to avoid that due to different local current densities, different thicknesses of the coating layers are formed on the substrate, which can lead to the formation of edges. In addition, other disadvantages are avoided which are already described above for electric dip painting.

The dip coating step of the method according to the invention can be carried out over a wide temperature range, preferably from 10 to 50°C, particularly preferably from 20 to 40°C, such as in particular at room temperature (23°C).

Particularly preferably, the organic coating forms within 20 seconds to 20 minutes, most preferably 30 seconds to 3 minutes, such as in particular 45 seconds to 2 minutes in the dipping bath and after drying preferably has a dry film thickness in the range of 5 to 50 µm, particularly preferably 10 to 40 µm and most preferably 15 to 30 µm. The layer thickness increases with the duration of the immersion and thus can be controlled.

Stage III

The optional washing step III is generally carried out with an aqueous medium, such as, for example, water or tap water, or preferably with an incompletely demineralized aqueous medium, for example, with water to wash the previous washing step. The use of incompletely demineralized water prevents the coating from re-dissolving during the rinsing process.

Stages IV and V

Drying in stages IV and/or V preferably at ambient temperature from 10 to 100°C, particularly preferably from 20 to 90°C, most preferably from 40 to 80°C for a period of time preferably from 1 to 30 minutes, especially preferably 2 to 20 minutes. and most preferably 5 to 15 minutes.

Step V can be carried out as in step P. Step V can be followed by a washing step similar to step III.

Curing in stages IV and/or V preferably takes place at temperatures from 130 to 200°C, particularly preferably from 135 to 190°C, most preferably at temperatures from 145 to 180°C and in particular from 145 to 170°C "peak metal temperature (PMT; object temperature) for a period of time, preferably 5 to 45 minutes, particularly preferably 10 to 30 minutes. and most preferably 12 to 20 minutes.

It has turned out that the surfaces coated according to the invention can be produced in a much simpler and much more economical way than, for example, those obtained by electrophoretic painting, conventional autophoretic dip painting or powder coating, and yet have excellent protection against corrosion.

In addition, it turned out that such coatings obtained in accordance with the invention are essentially equivalent in their properties to coatings of electrophoretic varnishing, conventional autophoretic dip varnishing or powder coating of modern industrial practice.

Surprisingly, it has been found that the subsequent coatings applied in accordance with the invention form a homogeneous layer with a uniform dry film thickness, even on parts of complex shape, comparable to the quality of a conventional electrophoretically or autophoretically deposited lacquer layer.

The coating according to the invention can preferably be used on coated substrates such as wire, wire mesh, tape, metal sheet, profile, cladding, part of a vehicle or aircraft body, element for a household appliance, element in the construction industry, frame, element of a fence, radiator or a fence element, a molded product with complex geometric shapes, or small parts such as, for example, a screw, nut, flange or spring. It is particularly preferred for use in the automotive industry, in the construction industry, for instrumentation, for household appliances or in the installation of heating systems. The use of the method according to the invention is particularly advantageous for coating substrates which have caused problems when coated by electroplating varnish.

The invention is explained in more detail below with the help of exemplary embodiments and comparative examples according to the invention.

Examples

Baths for coating immersion were filled with aqueous compositions of the coating agent in accordance with the components shown in Tables 1-4. The data in the Tables refers to parts by weight (solids) in 100 parts by weight of the coating composition. All baths had a pH value of 4.0±0.2 and a total solids content of 20.7±0.5 wt. % (1 g sample, 60 min., 125°C).

At room temperature (23° C.), alkali-cleaned, phosphated cold-rolled steel sheets were immersed in appropriate baths for 1 minute to coat the sheets.

The coatings were then washed with water and dried. The dry film thickness after drying for 10 minutes at 80°C was approximately 20 µm for all samples.

After drying, the sheets coated according to the invention were fired at an object temperature (peak metal temperature; PMT) of 170 or 180° C. for 15 or 20 minutes.

The samples were tested in the neutral salt spray test (NSS; according to DIN EN ISO 9227:2012-09). Penetration was averaged over several measurements each time and grouped from "excellent" (+++) to "poor" (-) (see tables).

The examples marked with an asterisk "*" in the Tables are comparative examples.

Components of Examples and Comparative Examples*

A1 Organic polymer particles from a hydroxy-functional and thus isocyanate-reactive epoxy resin with an epoxy equivalent weight (VLN 305) of 485-550 g/mol and an average particle size of approx. 600 nm

B1 DMP-blocked cycloaliphatic polyisocyanate with an NCO content of 14.2 wt. %

B2 DMP-blocked cycloaliphatic polyisocyanate with an NCO content of 20.3 wt. %

B3 MEKO-blocked cycloaliphatic polyisocyanate with an NCO content of 14.7 wt. %

B4 MEKO-blocked aromatic polyisocyanate based on MDI with an NCO content of 19.0 wt. %

B5 DMP-blocked, containing a polyethylene oxide chain, cycloaliphatic polyisocyanate with an NCO content of 10.5 wt. %

B6 MEKO-blocked, containing a polyethylene oxide chain, cycloaliphatic polyisocyanate with an NCO content of 9.7 wt. %

C1 Pectin (ammonium salt; pH value of 2.5 wt.% aqueous solution at 20°C: 2.5-4.5); with a number average molecular weight M _n approx. 80000 g/mol

D1 Hexafluorozirconic acid

E1 Aminopropyltriethoxysilane (AMEO)

F1 Preservative

The results in Table 1 show that both hydrophobic and hydrophilic, cycloaliphatic as well as aromatic, pyrazole-blocked and ketoxime-blocked polyisocyanates can be used to form uniform coatings suitable for simple applications from aqueous coating compositions which, after pre-drying, within 10 min. at 80° C. under firing conditions (15 min. at 180° C.) at least short term load in the neutral salt spray test (168 hours) show good to acceptable penetration resistance. There are no clear distinctions between hydrophilic and hydrophobic blocked polyisocyanates, so that in principle both types can be used.

Compared to Table 1, Table 2 shows that even with a molar ratio of blocked NCO groups of blocked polyisocyanate (B) to isocyanate-reactive OH groups of polymer (A) of 1.0, good to acceptable penetration results are obtained.

In Table 3, with the same molar ratio of blocked NCO groups of blocked polyisocyanate (B) to isocyanate reactive groups OH of polymer (A) equal to 1.0, as established in Table 2, the firing conditions vary so that the firing process occurs in insufficient firing conditions, i.e. at temperatures equal to 170°C, at which the systems under study are usually not allowed to fully crosslink during a given firing period (20 min.), i.e. without the addition of silane (E). Surprisingly, the silane (E) coatings according to the invention of Examples 12 and 14 nevertheless show good to acceptable penetration results, in any case better, compared to coatings not proposed in the invention of Examples 11 * and 13*.

Compared with the experiments in Table 3, in Table 4 the firing temperature was in turn increased by 10° C. to 180° C. with the same firing time. No pre-drying. Penetration results after a 240 hour neutral salt spray test show that Inventive Examples 15 and 16 provide good to excellent penetration test results. Thus, the aqueous coating compositions according to the invention, even under longer exposure in the neutral salt spray test, are clearly superior to compositions not according to the invention.

Claims (51)

1. An aqueous composition of a coating agent containing - at least one type of organic polymer particles with a Z-average particle size from 10 to 1000 nm, measured using dynamic light scattering, including isocyanate-reactive polymers (A), one or more polyisocyanates (B) blocked with ketoxime and/or pyrazole containing at least one aromatic hydrocarbon residue or at least one cycloaliphatic hydrocarbon residue, - at least one polyanionic polymer (C), - at least one complex fluoride (D) selected from the group consisting of hexa- or tetrafluorides of metallic elements of groups IVb, Vb and VIb of the Periodic Table of the Elements, and - at least one aminosilane (E) containing one silyl group of the formula Si(OR ⁷ ) _3-i (R ⁸ ) _i , in which R ⁷ means an alkyl residue with from 1 to 4 carbon atoms or an O=C-CH group ₃ , R ⁸ means an alkyl residue with from 1 to 4 carbon atoms and i means 0 or 1, wherein the aqueous composition of the coating agent has - pH value from 3 to 5 and - total solids content (1 g of sample, 60 min, 125°C) from 5 to 35 wt.%. 2. An aqueous coating composition according to claim 1, wherein the polyisocyanates (B) blocked by ketoxime and/or pyrazole are based on toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate and/or dicyclohexylmethane diisocyanate. 3. An aqueous coating composition according to claim 1 or 2, in which the polyisocyanates (B) blocked by ketoxime and/or pyrazole contain polyethylene oxide chains and/or poly(ethylene oxide-propylene oxide) chains and/or an organic residue containing one or more groups sulfonic acid, sulfonate groups, carboxyl groups and/or carboxylate groups. 4. Aqueous composition of the coating agent according to any one of paragraphs. 1-3 wherein the polyanionic polymer (C) is selected from the group consisting of (C.i) naturally occurring anionic polysaccharides, naturally occurring polymers consisting of or containing acidic amino acids, (C.ii) semi-synthetic polyanionic polysaccharides and lignin sulfates and (C.iii) fully synthetic polymers. 5. Aqueous composition of the coating agent according to any one of paragraphs. 1-4, wherein the polyanionic polymer (C) is selected from the group consisting of pectins, gellans, alginates and polyacrylic acids. 6. Aqueous composition of the coating agent according to any one of paragraphs. 1-5, wherein the complex or complex fluorides (D) are selected from the group consisting of titanium, zirconium or hafnium hexa- or tetrafluorides. 7. Aqueous composition of the coating agent according to any one of paragraphs. 1-6, in which the aminosilane (E) is an aminosilane of general formula (VII)

in which L means a group of organic compounds; R ⁷ means an alkyl residue with from 1 to 4 carbon atoms or a group O=C-CH ₃ ; R ⁸ means an alkyl residue with from 1 to 4 carbon atoms; and i means 0 or 1. 8. Aqueous composition of the coating agent according to any one of paragraphs. 1-7, in which - the content of organic polymer particles containing or consisting of isocyanate-reactive polymers (A) is from 3 to 25 wt.%, calculated on the total weight of the composition of the coating agent; and/or - the content of polyanionic polymers (C) is from 0.01 to 5.0 wt.%, in terms of the total weight of the composition of the coating agent; and/or - the amount of complex fluorides (D), in terms of the metal ion in them, is from 1.1×10 ^-6 mol to 0.30 mol, each time per liter of the composition of the coating agent; and/or the content of aminosilanes (E) is from 0.0005 to 1.0% by weight, based on the total weight of the coating composition. 9. Aqueous composition of the coating agent according to any one of paragraphs. 1-8, wherein the molar ratio of blocked NCO groups, ketoxime and/or pyrazole blocked polyisocyanates (B) to isocyanate reactive groups of the polymers (A) is between 0.5:1 and 2.0:1. 10. Aqueous composition of the coating agent according to any one of paragraphs. 1-9, in which the content of organic solvents is from 0 to 15 wt.% in terms of the total weight of the aqueous composition of the coating agent. 11. A method of manufacturing an aqueous composition of the coating agent according to any one of paragraphs. 1-10, characterized in that: (i) mixing the ketoxime and/or pyrazole blocked polyisocyanates (B), with or without the use of an external emulsifier, with a dispersion of organic polymer particles which have a Z-average particle size of 10 to 1000 nm measured by dynamic light scattering and contain one or more isocyanate-reactive polymers (A) or consist of them; or (ii) preparing a dispersion of organic polymer particles which have a Z-average particle size of 10 to 1000 nm measured by dynamic light scattering and contain or consist of one or more isocyanate-reactive polymers (A) in the presence of blocked ketoxime and /or pyrazole polyisocyanates (B); and (iii) admixture simultaneously or subsequently polyanionic polymers (C), complex fluorides (D) and aminosilanes (E); and (iv) adjust the pH value to a value equal to 3-5. 12. A method for coating a metal ion-releasing surface of a substrate, comprising or consisting of the following steps: I) providing a substrate with a metal ion releasing surface, II) bringing the metal ion releasing surface into contact with an aqueous composition of the coating agent according to one of paragraphs. 1-10 to form an organic coating, and iii) curing the organic coating at a peak metal temperature of 120 to 200° C. for a period of 5 to 50 minutes. 13. Method according to claim 12, characterized in that step II) is followed by washing the organic coating. 14. Method according to claim 12, characterized in that step II) is followed by drying the organic coating at a temperature of from 10 to 120°C for a period of time from 1 to 40 minutes. 15. The method according to claim 13, characterized in that the washing of the organic coating is followed by drying the organic coating at a temperature of from 10 to 120°C for a period of time from 1 to 40 minutes. 16. The method according to p. 12, characterized in that stage II) is followed by an additional stage of coating with an aqueous composition of the coating agent according to one of paragraphs. 1-10 to form an additional organic coating, drying both organic coatings and curing both organic coatings in step III). 17. The method according to p. 12, characterized in that stage II) is followed by drying the organic coating, followed by an additional stage of coating with an aqueous composition of the coating agent according to one of paragraphs. 1-10 to form an additional organic coating, drying the organic coating thus obtained and curing both organic coatings in step III). 18. The method according to p. 13, characterized in that the washing of the organic coating is followed by an additional stage of coating with an aqueous composition of the coating agent according to one of paragraphs. 1-10 to form an additional organic coating, drying both organic coatings and curing both organic coatings in step III). 19. The method according to p. 13, characterized in that the washing of the organic coating is followed by drying of the organic coating, followed by an additional stage of coating with an aqueous composition of the coating agent according to one of paragraphs. 1-10 to form an additional organic coating, drying the organic coating thus obtained and curing both organic coatings in step III). 20. The method according to claim 12, wherein the substrate is selected from: a) metal substrates, including metals and/or alloys, as well as metal and/or alloy coated metals and/or alloys, and/or non-metal substrates; and b) non-metallic substrates, including organic coatings and/or non-metallic inorganic coatings, wherein metal ions are embedded in the coatings or released metal ions can diffuse to the surface through the coatings from the underlying substrate. 21. The method according to any one of paragraphs. 12-20, and, before performing stage II), the surface is subjected to pre-treatment, including one or more of the following measures: - removal of surface contaminants; - surface activation for coating in stage II); and/or - application of one or more layers that slow down corrosion and/or improve adhesion and/or release metal ions. 22. The coating obtained according to any one of paragraphs. 12-21.