Aqueous sol-gel formulation with excellent aging resistance and its use as chemical pretreatment agent

Abstract

The present invention relates to an aqueous chemical pretreatment composition comprising, besides water, an aqueous sol-gel formulation, which is obtainable by reacting at least one organosilane comprising at least one hydrolysable group X with water in the presence of at least one polymer P, which comprises at least one kind of functional groups selected from OH- groups and amino groups and has a Mw of at least 1,000 g / mol, and further comprising at least one polymer being different from polymer P as constituent a4), at least one acid and / or a deprotonated form thereof as constituent a5), and at least one metal oxide as constituent a6), a pretreatment method for substrates having at least one metallic surface, which makes use of the aqueous chemical pretreatment composition or which makes use of an aqueous chemical pretreatment composition, in which in situ the aqueous sol-gel formulation is formed, a chemically pretreated substrate, which is obtainable by said chemical pretreatment method, and a use of the polymer P for obtaining an aqueous sol-gel formulation and / or for increasing at least one of the shelf life, the aging resistance, the thermal stability, and the stability in acidic, neutral and / or alkaline media of said sol-gel formulation, and / or for reducing the content of volatile organic compounds within said sol-gel formulation without negatively affecting the stability of said formulation.

Description

[0001] Aqueous sol-gel formulation with excellent aging resistance and its use as chemical pretreatment agent

[0002] The present invention inter alia relates to an aqueous sol-gel formulation, a method for preparing the aqueous solgel formulation, an aqueous chemical pretreatment composition comprising said aqueous sol-gel formulation, a pretreatment method, which inter alia makes use of the aqueous sol-gel formulation and / or the aqueous chemical pretreatment composition, and a chemically pretreated substrate, which is obtainable by said chemical pretreatment method.

[0003] Background of the invention

[0004] A sol-gel process is a wet chemical technique, in which, usually in a polycondensation reaction, a colloidal solution (i.e., a sol) is used as a precursor to obtain an integrated polymer network (i.e., a gel) by crosslinking and thereby yielding a (typically aqueous) sol-gel formulation. Sol-gel formulations can be dried to obtain, e.g., coatings, composites or fibers. Thus, sol-gel processes are used in manifold applications, e.g., regarding glasses, ceramics, and catalysts, and are also widely used in regard for metal surface treatment applications.

[0005] In comparison to other methods suitable for metal surface treatment applications, the use of sol-gel processes including their sol-gel formulations offer great advantages, e.g., by providing excellent barrier properties like high water, chemical and / or corrosion resistance, thermal resistance and / or scratch resistance, and / or by their mild process conditions, where crosslinking of the colloidal solution and drying of the resulting formulation can be carried out, and by enabling the production of functionalized, highly customized coatings. In general, (semi)metal alcoholates are used as precursors in colloidal solutions for sol-gel formulations, whereof Si alcoholates in particular, like tetraalkyl orthosilicates, are well understood and widely used in applications.

[0006] However, several challenges have to be considered when preparing and utilizing sol-gel formulations of the prior art for technical applications. One major challenge of the prior art is the limited stability of sol-gel formulations, as they may initiate undesirable gelation processes if said formulations exceed certain strict limits, e.g., in regard to temperature or pH value. As example, sol-gel formulations are generally unstable if exposed to pH values outside the range of 3 to 5, which limits their technical applicability. Furthermore, the limited stability and thus the fast "aging” of sol-gel formulations merely allow a short storage duration, i.e., a short "shelf life”, of said formulations.

[0007] Another challenge of sol-gel processes of the prior art is the presence of high amounts of volatile organic compounds (VOC), e.g., methanol or ethanol, which are obtained as side products by the hydrolysis of the (semi)metal alcoholates during the sol-gel formulation. The risk to humans and the environment from VOCs and the therefore enacted regulations necessitate the reduction of VOC content in sol-gel processes and formulations compared to those of the prior art. However, VOCs obtained during the sol-gel process act as stabilizers when dispersed within sol-gel formulations, especially if comprising Si constituents. Thus, a mere reduction of the VOC content in a sol-gel process according to the prior art would therefore considerably reduce the stability of sol-gel formulations.

[0008] Thus, there is a need to be able to provide an aqueous sol-gel formulation, which, in particular compared to sol-gel formulations of the prior art, exhibits an increased shelf life, an improved aging resistance, an increased stability at a wider pH range, such as a high stability not only in acidic, but also in neutral and / or alkaline media, which at the same time also exhibits a reduced VOC content without negatively affecting the stability of said formulation, and which, when used as such or being present as part of a chemical pretreatment composition, is able to provide a high water, chemical and / or corrosion resistance, in particular if applied to metallic surfaces.

[0009] Problem

[0010] It has been therefore an objective underlying the present invention to provide an aqueous sol-gel formulation which, in particular compared to sol-gel formulations of the prior art, exhibits an increased shelf life, an improved aging resistance, an increased stability at a wider pH range, such as a high stability not only in acidic, but also in neutral and / or alkaline media, and which at the same time also exhibits a reduced VOC content without negatively affecting the stability of said formulation, and which, when used as such or being present as part of a chemical pretreatment composition is able to provide a high water, chemical and / or corrosion resistance, in particular if applied to metallic surfaces.

[0011] Solution

[0012] This objective has been solved by the subject-matter of the claims of the present application as well as by the preferred embodiments thereof disclosed in this specification, i.e. by the subject matter described herein.

[0013] A first subject-matter of the present invention is an aqueous sol-gel formulation, which is obtainable by reacting at least one organosilane comprising at least one hydrolysable group X with water, characterized in that the reaction is carried out in the presence of at least one water dispersible or water-soluble polymer P, which comprises at least one kind of functional groups selected from hydroxyl groups and amino groups and has a weight average molecular weight of at least 1 ,000 g / mol.

[0014] The above aqueous sol-gel formulation and its preferred embodiments, as described hereinafter, are also denoted as "inventive aqueous sol-gel formulation”, "inventive sol-gel formulation”, "sol-gel formulation” or "inventive formulation”.

[0015] A further subject-matter of the present invention is a method for preparing the aqueous sol-gel formulation as defined hereinbefore and hereinafter, the method comprising at least steps a), b), c), and d), namely a) providing a mixture of at least the at least one polymer P and water, b) adding the at least one organosilane comprising at least one hydrolysable group X to said mixture or vice versa, preferably under stirring, c) adding at least one acid to the mixture obtained after step b) to yield a pH value in a range of 0.5 to <7.0, preferably of 1 .0 to 6.5 or to 6.0, more preferably of 3.0 to 5.0, or adding at least one base to the mixture obtained after step b to yield a pH value in a range of >7.0 to 13.5, preferably of 9.5 to 13.0, more preferably of 11.0 to 12.0, and d) stirring the resulting mixture obtained after step c) in order to obtain the aqueous sol-gel formulation

[0016] A further subject-matter of the present invention is an aqueous chemical pretreatment composition comprising, besides water, the aqueous sol-gel formulation as defined hereinbefore and hereinafter and preferably further comprising at least one of constituents a4), a5) and / or a6), preferably at least constituents a4) and a5) and a6), namely at least one polymer being different from polymer P, said at least one polymer more preferably being selected from polycarbonates, polyurethanes, polycarbonate-polyurethanes, and mixtures thereof, as constituent a4), and / or at least one acid, more preferably being selected from sulfuric acid, hydrochloric acid, nitric acid and phosphorous moiety or moieties containing acids, even more preferably being selected from phosphoric acid, pyrophosphoric acid, phosphonic acids such as from bisphosphonic acids, e.g., etidronic acid, and in each case their respective deprotonated forms, e.g., salts, as constituent a5), and / or at least one metal oxide, more preferably being selected from alkaline metal oxides, and alkaline earth metal oxides such as magnesium oxide, as constituent a6).

[0017] A further subject-matter of the present invention is a pretreatment method for substrates having at least one metallic surface, comprising at least one step 1 a) or 1 b), namely l a) contacting at least a portion of at least one metallic surface of at least one substrate with an aqueous chemical pretreatment composition as defined hereinbefore and hereinafter and / or with a sol-gel-formulation as defined hereinbefore and hereinafter, or l b) contacting at least a portion of at least one metallic surface of at least one substrate with an aqueous chemical pretreatment composition comprising, besides water, at least one organosilane comprising in turn at least one hydrolysable group X, and at least one water dispersible or water-soluble polymer P, which comprises at least one kind of functional groups selected from hydroxyl groups and amino groups and has a weight average molecular weight of at least 1 ,000 g / mol, wherein the sol-gel-formulation as defined hereinbefore and hereinafter is formed in situ in the aqueous chemical pretreatment composition. A further subject-matter of the present invention is a chemically pretreated substrate having at least one metallic surface, which is obtainable by the chemical pretreatment method as defined hereinbefore and hereinafter.

[0018] A further subject-matter of the present invention is an use of a water dispersible or water-soluble polymer P comprising at least one kind of functional groups selected from hydroxyl groups and amino groups and having a weight average molecular weight of at least 1 ,000 g / mol for obtaining an aqueous sol-gel formulation, preferably of the sol-gel formulation as defined hereinbefore and hereinafter, by reacting at least one organosilane comprising at least one hydrolysable group X in the presence of said polymer P with water, and / or for increasing at least one of the shelf life, the aging resistance, the thermal stability, and the stability in acidic, neutral and / or alkaline media of said sol-gel formulation, and / or for reducing the content of volatile organic compounds within said sol-gel formulation without negatively affecting the stability of said formulation.

[0019] It has been in particular surprisingly found that the aqueous sol-gel formulations according to the present invention have a high aging resistance and an increased shelf life by exhibiting no gelation or precipitation after being exposed to different aging methods, which comprise heating and / or long-term storage of said formulations, in particular compared to aqueous sol-gel formulations of the prior art. Hence, the aqueous sol-gel formulations according to the present invention particularly have an improved storage stability compared to prior art products. It has been in particular surprisingly found in this regard that the thermal resistance of the inventive sol-gel formulations is improved compared to aqueous sol-gel formulations of the prior art. It has also been in particular surprisingly found in this regard, that these effects are a result of the presence of the at least one polymer P within the sol-gel formulation while reacting the at least one organosilane comprising at least one hydrolysable group X with water and the presence of the at least one polymer P as constituent of the sol-gel formulation once it has been obtained.

[0020] Moreover, it has been in particular surprisingly found that the sol-gel formulations according to the present invention can be prepared not only in acidic or neutral media, but also in alkaline media without showing any gelation or precipitation, contrary to what is often observed in case of sol-gel formulations of the prior art. It has been in particular surprisingly found in this regard, that these effects are a result of the presence of the at least one polymer P while reacting the at least one organosilane comprising at least one hydrolysable group X with water and the presence of the at least one polymer P as constituent of the sol-gel formulation once it has been obtained.

[0021] Furthermore, it has been in particular surprisingly found that the VOC content of the sol-gel formulations according to the present invention can be reduced or completely removed, in particular compared to sol-gel formulations of the prior art, without any reduction in stability of the sol-gel-formulations, which is often observed in conventional sol-gel formulations.

[0022] Further, it has been found that the inventive sol-gel formulations are suitable for chemical pretreating metallic surfaces. In addition, it has surprisingly been found that metal surfaces pretreated with the inventive chemical pretreatment composition comprising the sol-gel formulations according to the present invention exhibit a high water-resistance, a high chemical resistance, in particular against isopropyl alcohol (IPA) and butanone (MEK), a high corrosion resistance and a reduced shrinkage and reduced brittleness, especially compared of surfaces which are pretreated by sol-gel processes of the prior art.

[0023] In addition, it has been found that the aforementioned surprising effects, as far as aging resistance, thermal resistance, VOC content and pH of the sol-gel process are concerned, can be particularly achieved by the inventive use of the at least one polymer P during the preparation of a sol-gel formulation and the presence of the at least one polymer P as constituent of the sol-gel formulation once it has been obtained.

[0024] Detailed description of the invention

[0025] The term "comprising” in the sense of the present invention, in connection for example with the inventive sol-gel formulation or the inventive chemical pretreatment composition, preferably has the meaning of "consisting of'. With regard, e.g., to the inventive sol-gel formulation or the inventive chemical pretreatment composition it is possible - in addition to all mandatory constituents present therein - for one or more of the further optional constituents identified hereinafter to be also included therein. All constituents may in each case be present in their preferred embodiments as identified below.

[0026] The proportions and amounts in wt.-% (% by weight) of any of the constituents given hereinafter, which are present in each of the sol-gel formulations chemical pretreatment composition add up to 100 wt.-%, based in each case on the total weight of the sol-gel formulation or of the chemical pretreatment composition.

[0027] Aqueous sol-gel formulation

[0028] A first subject-matter of the present invention is an aqueous sol-gel formulation, which is obtainable by reacting at least one organosilane comprising at least one hydrolysable group X with water in the presence of at least one water dispersible or water-soluble polymer P, characterized in that the at least one polymer P comprises at least one kind of functional groups selected from hydroxyl groups and amino groups and has a weight average molecular weight of at least 1 ,000 g / mol.

[0029] A person skilled in the art is familiar with the terms "sol-gel formulation", "sol-gel" and the production of sol-gel formulations and sol-gels. In general, sol-gel formulations comprise at least one liquid part, e.g., water and / or at least one organic solvent, and at least one colloidal solid constituent, e.g., a polymer, preferably a poly(organo)siloxane, which is finely dispersed within said liquid part without showing gelation or precipitation. In the sense of the present invention, the stability of a sol-gel formulation preferably determines its sensitivity to external influences', e.g., pH, temperature, time, or physical effects like vibration, which would cause the solid constituents to undergo undesirable gelation processes or precipitation. In the sense of the present invention, the term "aqueous sol-gel formulation” means a sol-gel formulation which is obtainable by reacting at least one organosilane comprising at least one hydrolysable group X with water.

[0030] Preferably, the sol-gel formulation has a solid content in a range of from 3.0 to 90.0 wt.-%, more preferably in a range of from 5.0 to 70.0 wt.-%, still more preferably in a range of from 6.0 to 55.0 wt.-%, even more preferably in a range of from 7.0 to 40.0 wt.-%, most preferably in a range of from 8.0 to 30.0 wt.-%, based on the total weight of the formulation. The solid content is determined according to the method disclosed in the 'method' section.

[0031] Preferably, the sol-gel formulation comprises water in an amount of at least 5.0 wt.-%, more preferably at least 15.0 wt.-%, still more preferably at least 30.0 wt.-%, even more preferably at least 50.0 wt.-% water, most preferably at least 70.0 wt.-% water, based on the total weight of the aqueous sol-gel formulation.

[0032] The sol-gel formulation may comprise and preferably comprises at least one organic solvent. Preferably, the solgel formulation comprises at most 30.0 wt.-%, preferably at most 20.0 wt.-%, more preferably at most 10.0 wt.-%, even more preferably at most 8 wt.-%, in particularly preferably at most 6.0 wt.-% of at least one organic solvent, based on the total weight of the formulation, preferably in each case when measured directly after its preparation. Preferably, the content of organic solvent(s) of the sol-gel formulation can be further reduced, e.g., to an amount of less than 5 wt.-%, based on the total weight of the formulation, or even completely removed without negatively affecting the stability of said formulation.

[0033] The at least one organic solvent being optionally present in the sol-gel formulation preferably is subsumable under the term VOC (volatile organic compounds). In the sense of the present invention, the term "VOC” preferably includes organic compounds whose boiling points are in the range from 50 °C to 260 °C. More preferably, the term "VOC” means organic compounds that are obtainable as side products by sol-gel processes, e.g., alcohols, preferably methanol, ethanol, propanol and / or butanol. In the present invention, the VOC content within the sol-gel formulations is preferably gravimetrically determined based on the method 24 of the Environmental Protection Agency (EPA) of the U.S as also mentioned in the ‘methods' section.

[0034] The at least one organosilane comprising at least one hydrolysable group X preferably reacts with water via crosslinking reactions and thereby yields a network comprising oligomers or polymers formed from the thus reacted at least one organosilane and said network becomes part of an in this manner obtained sol-gel formulation. A part of all Si atoms comprised within the network are preferably part of at least one siloxane bond, while the at least one hydrolysable group X is released from said organosilane and reacts to H-X with water, in particular when X is an alkoxy group and hence a group that is able to form an alcohol in such a manner, e.g., methanol, ethanol, propanol, and / or butanol.

[0035] Preferably, if the at least one organosilane comprises more than one hydrolysable group X, all groups X are released in such a manner. Preferably, at least 20 wt.-%, more preferably at least 30 wt.-%, still more preferably at least 50 wt.-%, even more preferably at least 70 wt.-%, most preferably at least 85 wt.-%, of all Si atoms comprised within the sol-gel formulation, based on the total weight of all Si atoms comprised within the sol-gel formulation, are part of at least one siloxane bond, preferably determined by29Si-NMR signal integral ratios.

[0036] Sol-gel processes of organosilanes are often sensitive to the pH of the liquid medium because the probability of condensation or hydrolyzation reactions is highly dependent on the pH value, whereby condensation reactions occur more often in acidic media than hydrolyzation reactions. As these reactions are generally reversible and their respective occurrences may strongly influence the stability of the sol-gel formulation, sol-gel formulations of organosilanes of the prior art are also sensitive to the pH of the liquid medium. In contrast, it has been found that the inventive sol-gel formulation obtainable in presence of the at least one polymer P may be prepared in acidic, neutral or alkaline media without showing any undesired gelation or precipitation.

[0037] Preferably, the sol-gel formulation is obtainable by reacting the at least one organosilane with water in additional presence of at least one acid, yielding a pH value in a range of 0.5 to <7.0, more preferably of 1 .0 to 6.5 or to 6.0, even more preferably of 3.0 to 5.0, or in additional presence at least one base, yielding a pH value in a range of >7.0 to 13.5, more preferably of 9.5 to 13.0, even more preferably of 11.0 to 12.0. In both cases, these pH values preferably describe the pH measured at about room temperature (21 °C) and are determined directly after the acid or the base has been added and is preferably determined by a pH meter.

[0038] Preferably, the sol-gel formulation has a conductivity in a range of from 1.00 ■ 102to 1.00 ■ 105piS / cm, more preferably in a range of from 5.0 to 1.5 ■ 104piS / cm.

[0039] Water dispersible or water-soluble polymer P

[0040] The at least one polymer P comprises at least one kind of functional groups selected from hydroxyl groups and amino groups and has a weight average molecular weight of at least 1 ,000 g / mol.

[0041] The term "polymer" is known to the person skilled in the art and, for the purposes of the present invention, encompasses polyadducts and polymerizates as well as polycondensates. The term "polymer" includes both homopolymers and copolymers.

[0042] The term "water-soluble polymer” in the sense of the present invention preferably means that polymer P is used in such an amount that it is completely soluble in water at room temperature (16 to 23 °C) and 1.013 mbar. The term "water-dispersible polymer” in the sense of the present invention preferably means that polymer P is used in such an amount that it is completely and preferably homogeneously dispersible in water at room temperature (16 to 23 °C) and 1.013 mbar. Preferably, the at least one polymer P has a weight average molecular weight in a range of from 1 ,500 to 5,000,000 g / mol, even more preferably in a range of from 2,000 to 4,500,000 g / mol, still more preferably in a range of from 20,000 to 4,000,000 g / mol, even more preferably in a range of from 50,000 to 3,000,000 g / mol, most preferably in a range of from 100,000 to 2,500,000 g / mol, determined by gel permeation chromatography (GPC).

[0043] The at least one polymer P preferably is an organic homopolymer or copolymer, more preferably is an organic homopolymer or copolymer, more preferably at least one organic homopolymer.

[0044] The at least one polymer P may comprise additional functional groups selected from carboxyl groups, carbonyl groups, halogen atoms, e.g., F, Cl, Br, and / or I, imine groups, ether groups and ester groups. Preferably, the at least one polymer P does not comprise any halogen atoms.

[0045] Preferably, if the at least one polymer P has hydroxyl groups, at most 50 mol-%, more preferably at most 30 mol- %, even more preferably at most 15 mol-%, most preferably at most 5 mol-%, of all OH-groups are present in an esterified form.

[0046] Amino groups are preferably selected from primary, secondary, and tertiary amino groups, wherein said polymer P, when it comprises at least one amino group, may comprise at least two different types, or may comprise all three different types of amino groups, i.e., primary, secondary, and tertiary amino groups.

[0047] If the polymer P comprises at least one amino group, said at least one polymer optionally also comprises at least one amide group, preferably wherein said at least one amide group is part of a bond to a fatty acid.

[0048] Preferably, the at least one polymer P is selected from polyvinyl alcohols, polysaccharides including chitosan, and polyamines including polyalkyleneimines and polyvinylpyrrolidones, more preferably is selected from polyvinyl alcohols, polysaccharides, polyethyleneimines and polyvinylpyrrolidone, even more preferably is selected from polyvinyl alcohols and polyethyleneimines, said polymers being in each case more preferably homopolymers. More preferably, if polymer P is a polyalkyleneimine homopolymer or copolymer, said polymer has a branched structure, the branching points being preferably tertiary amino groups.

[0049] Examples of suitable polysaccharide homopolymers are, but are not limited to amylopectin, zymosan, chitosan, chitin, cellulose, pullulan, lentinan, levan, paramylon and dextran. Examples of suitable polysaccharide copolymers are, but are not limited to alginic acid, gellan gum, hyaluronic acid, xanthan gum and agarose.

[0050] Preferably, if the at least one polymer P is a polysaccharide comprising amino groups, at most 50 mol-%, more preferably at most 30 mol-%, most preferably at most 15 mol-% of all amino groups are present in an acetylated form. Preferably, the sol-gel formulation contains the at least one polymer P in an amount in a range of from 0.3 to 35.0 wt.-%, more preferably of from 0.5 to 20.0 wt.-%, even more preferably in a range of from 1.0 to 15.0 wt.-%, most preferably in a range of from 1 .5 to 10.0 wt.-%, based on the total solid content of the formulation.

[0051] Preferably, the at least one polymer P acts as stabilizer during the sol-gel process and / or within the sol-gel formulation, whereby said polymer P is bound to the colloidal solid constituent, in particular to the network formed from the organosilane(s) such as the polysiloxane network, by physical interactions, in particular non-covalent interactions, and / or by chemically reacting with said network via functional groups of the at least one polymer P and functional groups of the network formed from the organosilane(s) such as the polysiloxane network, and / or by sterical interlocking interaction with said network. More preferred are physical interactions and / or sterical interlocking interactions, even more preferably non-covalent interactions and / or sterical interlocking interactions.

[0052] Non-covalent interactions suitable for binding the at least one polymer P to the network formed from the organosilane(s) such as the polysiloxane network are, but are not limited to, hydrogen bonds, whereby hydrogen atoms of the functional groups of the at least one polymer P are bound to the charged surface of the colloid solid, in particular the network formed from the organosilane(s) such as the polysiloxane network.

[0053] Preferably, the at least one polymer P is selected from homopolymers, more preferably from polyvinyl alcohol and polyethyleneimine homopolymers.

[0054] Organosilane(s) comprising at least one hydrolysable group X

[0055] The at least one hydrolysable group X of the at least one organosilane preferably is selected from alkoxy groups and halogens, more preferably is selected from alkoxy groups. Examples of halogens are chlorides, bromides, and iodides. The term "hydrolysable group” in the sense of the present invention preferably means a functional group, which is removable by the reaction of said "hydrolysable group” with water or hydroxy groups, in particular within an aqueous acidic, neutral, or alkaline solution. The presence of at least one hydrolysable group X, preferably at least two or more hydrolysable groups, within the at least one organosilane is necessary for the crosslinking reaction to occur, whereby a higher degree of crosslinking may be achieved by increasing the amount of reacting hydrolysable groups X present within the at least one organosilane.

[0056] Preferably, more than one organosilane is used, more preferably at least two or three organosilanes, which are different from one another.

[0057] The at least one organosilane preferably further comprises at least one non-hydrolysable group, more preferably at least one non-hydrolysable organic group, which further may contain one or more functional groups. The term "non-hydrolysable group” in the sense of the present invention preferably means an organic group, which is not removable by the reaction with water or hydroxy groups, in particular within an aqueous acidic, neutral, or alkaline solution, contrary to the hydrolysable group(s) X.

[0058] The non-hydrolysable organic group is preferably selected from the group consisting of aliphatic residues having 1 to 24 carbon atoms, cycloaliphatic residues having 3 to 12 carbon atoms, aromatic residues having 6 to 12 carbon atoms, and araliphatic residues having 7 to 18 carbon atoms, each of these residues optionally containing or being at least one functional group. Moreover, each of the aforesaid aliphatic, cycloaliphatic, aromatic, and araliphatic residues may contain one or more heteroatoms such as N, 0 and / or S, and / or heteroatom groups.

[0059] Preferably, the at least one organosilane has at least two or has at least three hydrolysable groups X, and / or at least one non-hydrolysable organic group R1, R1more preferably comprising 1 to 12 carbon atoms, even more preferably comprising 1 to 8 carbon atoms, wherein R1contains either no functional group or has at least one functional group, more preferably no functional group or at least one functional group selected from amino, thiol and epoxy (epoxide) groups.

[0060] The non-hydrolysable organic group R1may function, in case it contains at least one functional group, as a preferably divalent spacer unit, which is positioned between said functional group, e.g., when the functional group represents an amino group, within the non-hydrolysable organic group, such that the functional group is not directly connected to a Si-atom.

[0061] Examples of organosilanes, which have at least one non-hydrolysable organic group, in particular at least one non- hydrolysable organic group being selected from aliphatic residues having 1 to 24 carbon atoms, are methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), methyltripropoxysilane, methyltriisopropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltripropoxysilane, ethyltriisopropoxysilane, octyltrimethoxysilane, isobutyltriethoxysilane, isobutyltrimethoxysilane, octyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, decyltrimethoxysilane, and decyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, and also 1 ,2-bis(triethoxysilyl)ethane and 1,2-bis(trimethoxysilyl)ethane.

[0062] Examples of organosilanes, which have at least one non-hydrolysable organic groups, in particular at least one non-hydrolysable organic group being selected from aromatic residues having 6 to 12 carbon atoms, are phenyltrimethoxysilane (PHS), phenyltriethoxysilane, phenyltripropoxysilane, and phenyltriisopropoxysilane.

[0063] Examples of organosilanes, which have at least one non-hydrolysable organic residue selected from the group consisting of araliphatic residues having 7 to 18 carbon atoms are benzyltrimethoxysilane, benzyltriethoxysilane, benzyltripropoxysilane, and benzyltriisopropoxysilane.

[0064] The at least one organosilane may comprise at least one Si-containing residue such as exactly one such residue (as in the case of monosilanes) or two or more such residues (as in the case of bis- or tris-silanes) as in the case of 1 ,2-bis(triethoxysilyl)ethane. Also possible is the use of organosilanes, which have four, five, six or more silyl groups.

[0065] Organosilanes, which contain at least one primary and / or secondary amino group, are, for example, 3- aminopropyltrimethoxysilane (APS), 3-aminopropyltriethoxysilane, 3-aminopropyltriisopropoxysilane, 2-amino- ethyltrimethoxysilane, 2-aminoethyltriethoxysilane, 2-aminoethyltriisopropoxysilane, aminomethyltrimethoxysilane, aminomethyltriethoxysilane, aminomethyltriisopropoxysilane, 3-(2-aminoethyl)aminopropyltrimethoxysilane (AEAPS), 3-(2-aminoethyl)aminopropyltriethoxysilane, 3-(2-aminoethyl)aminopropyltriisopropoxysilane, 2-(2- aminoethyl)aminoethyltrimethoxysilane, 2-(2-aminoethyl)aminoethyltriethoxysilane 2-(2-aminoethyl)- aminoethyltriisopropoxysilane, 3-(3-aminopropyl)aminopropyltrimethoxysilane, 3-(3-aminopropyl)aminopropyl- triethoxysilane, 3-(3-aminopropyl)aminopropyltriisopropoxysilane, diethylenetriaminopropyltrimethoxysilane, diethylenetriaminopropyltriethoxysilane, N-(n-butyl)-3-aminopropyltrimethoxysilane, N-(n-butyl)-3-amino- propyltriethoxysilane, N-cyclohexylaminomethyltriethoxysilane, N-cyclohexylaminomethyltrimethoxysilane, N- ethyl-y-aminoisobutyltrimethoxysilane, N-ethyl-y-aminoisobutyltriethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3- aminopropyltrimethoxysilane hydrochloride, N-phenyl-y-aminopropyltrimethoxysilane, N-phenyl-y- aminopropyltriethoxysilane, y-ureidopropyltrimethoxysilane, y-ureidopropyltriethoxysilane, N-methyl-[3- (trimethoxysilyl)propyl]carbamate, and / or N-trimethoxysilylmethyl-O-methylcarbamate, and also bis[y- (triethoxysilyl)propyl]amine, bis[y-(trimethoxysilyl)propyl]amine.

[0066] Organosilanes, which contain at least one thiol group are, for example, 3-mercaptopropyltrimethoxysilane (MPTMS), 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltriisopropoxysilane, 2- mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane and / or 2-mercaptoethyltriisopropoxysilane.

[0067] Organosilanes, which contain at least one epoxide group, as an example of an hydroxyl group masked with a protective group which can be eliminated under hydrolytic conditions, are, for example, 3-glycidyl- oxypropyltrimethoxysilane (GLYMO), 3-glycidyloxypropyltriethoxysilane, 3-glycidyloxypropyltriisopropoxyoxy- silane, 2-glycidyloxyethyltrimethoxysilane, 2-glycidyloxyethyltriethoxysilane, 2-glycidyloxyethyltriisopropoxy- oxysilane, p-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and / or p-(3,4-epoxycyclohexyl)ethyltriethoxysilane.

[0068] Preferably, the at least one organosilane has the formula (I) and / or (II), namely

[0069] [Si(X)4-n(R1)n] (I), and / or

[0070] [(R1)m(X)3-mSi-R2-Si(X)3-m(R1)m] (H), wherein each X, independently of one another, is a hydrolysable group, more preferably an alkoxy group, still more preferably an alkoxy group comprising 1 to 8 carbon atoms, even more preferably an alkoxy group comprising 1 to 4 carbon atoms, most preferably a methoxy or ethoxy group, each R1, independently of one another, is a non-hydrolysable organic group more preferably comprising 1 to 12 carbon atoms, even more preferably comprising 1 to 8 carbon atoms, wherein R1has no functional group or has at least one functional group, more preferably no functional group or at least one functional group selected from amino, thiol and epoxy groups, parameter n is 1 , 2 or 3, more preferably n is 1 or 2, still more preferably is 1,

[0071] R2is non-hydrolysable divalent organic group preferably comprising 1 to 8 carbon atoms, more preferably comprising 1 to 4 carbon atoms, which optionally may comprise at least one functional group such as at least one amino group, e.g., a secondary amine group, and parameter m is 0, 1 or 2, more preferably is 1 or 2, still more preferably is 1.

[0072] Preferably, the sol-gel formulation is obtainable by reacting in water at least one organosilane a1) comprising at least one hydrolysable group X, wherein the at least one hydrolysable group X is more preferably an alkoxy group, still more preferably an alkoxy group comprising 1 to 8 carbon atoms, even more preferably an alkoxy group comprising 1 to 4 carbon atoms, most preferably a methoxy or ethoxy group, and further comprising at least one non-hydrolysable organic group R1, which more preferably comprises 1 to 12 carbon atoms, even more preferably comprises 1 to 8 carbon atoms, and wherein R1has no functional group, and at least one organosilane a2) comprising at least one hydrolysable group X, wherein the at least one hydrolysable group X is more preferably an alkoxy group, still more preferably an alkoxy group comprising 1 to 8 carbon atoms, even more preferably an alkoxy group comprising 1 to 4 carbon atoms, most preferably a methoxy or ethoxy group, and further comprising at least one non-hydrolysable organic group R1, which more preferably comprises 1 to 12 carbon atoms, even more preferably comprises 1 to 8 carbon atoms, and wherein R1has at least one functional group selected from amino, thiol and epoxy groups, wherein more preferably at least two organosilanes a2) are used, which are different from one another, even more preferably wherein R1of the first organosilane 2a) comprises at least one amino group and R1of the second organosilane 2a) comprises at least one epoxy group, and optionally at least one organosilane a3) exclusively comprising hydrolysable organic groups X and no non- hydrolysable organic groups, more preferably selected from alkoxy groups comprising 1 to 8 carbon atoms, still more preferably from alkoxy groups comprising 1 to 4 carbon atoms, even more preferably from methoxy and ethoxy groups. Preferably, the least one non-hydrolysable organic group R1of the at least one organosilane a1) is an unfunctionalized alkyl group, more preferably comprising 1 to 12 carbon atoms, still more preferably comprising 1 to 8 carbon atoms, even more preferably is a methyl, ethyl, propyl, or butyl group, most preferably is a methyl or ethyl group.

[0073] Preferably, the least one non-hydrolysable organic group R1of the at least one organosilane a2), more preferably of the first organosilane a2) as defined hereinbefore, is a functionalized alkyl group, more preferably comprising 1 to 12 carbon atoms, still more preferably comprising 1 to 8 carbon atoms, further comprising at least one amino group, and / or the least one non-hydrolysable organic group R1of the at least one organosilane a2), more preferably of the second organosilane a2) as defined hereinbefore, is a functionalized alkyl group, more preferably comprising 1 to 12 carbon atoms, still more preferably comprising 1 to 8 carbon atoms, further comprising at least one epoxide group.

[0074] Optional constituents

[0075] The sol-gel formulation may further comprise one or more additives, preferably selected from the group of hydrolytically and pyrolytically produced silicic acids, organic and inorganic nanoparticles, water dispersible or water-soluble polymers other than polymer P, wetting agents, emulsifiers, dispersants, surface-active compounds such as surfactants, flow control assistants, solubilizers, defoamers, rheological assistants, antioxidants, stabilizers, processing stabilizers, and UV and / or light stabilizers, catalysts, fillers, waxes, biocides and plasticizers. They can be used in the known and customary proportions. Preferably, their total content, based on the total weight of the sol-gel formulation, is 0.01 to 20.0 wt.-%, more preferably 0.03 to 15.0 wt.-%, even more preferably 0.05 to 10.0 % by weight, particularly preferably from 0.07 to 7.5% by weight, especially preferably from 0.10 to 5.0% by weight and most preferably from 0.15 to 2.5% by weight.

[0076] Method for obtaining the aqueous sol-pel formulation

[0077] A further subject-matter of the present invention is a method for preparing the aqueous sol-gel formulation as defined hereinbefore and hereinafter, the method comprising at least steps a), b), c), and d), namely a) providing a mixture of at least the at least one polymer P and water, b) adding the at least one organosilane comprising at least one hydrolysable group X to said mixture or vice versa, preferably under stirring, c) adding at least one acid to the mixture obtained after step b) to yield a pH value in a range of 0.5 to <7.0, preferably of 1 .0 to 6.5 or to 6.0, more preferably of 3.0 to 5.0, or adding at least one base to the mixture obtained after step b to yield a pH value in a range of >7.0 to 13.5, preferably of 9.5 to 13.0, more preferably of 11.0 to 12.0, and d) stirring the resulting mixture obtained after step c) in order to obtain the aqueous sol-gel formulation.

[0078] Preferably, the total content of all organosilanes in the in the mixture obtained after step b), based on the total weight of said mixture, is in a range of from 1 .0 to 70.0 wt.-%, more preferably of from 4.0 to 50.0 wt.-%, even more preferably of from 6.0 to 35.0 % by weight, particularly preferably of from 8.0 to 25.0 % by weight, especially preferably of from 10.0 to 20.0 % by weight and most preferably of from 12.0 to 18.0 % by weight.

[0079] More preferably, if more than one organosilane, e.g., the at least one organosilane a1) and the at least one organosilane a2), and optionally the at least one organosilane a3), are present in the sol-gel formulation, each of their contents in the mixture obtained after step b), based on the total weight of said mixture, is in a range of from 0.5 to 20.0 wt.-%, even more preferably of from 1.0 to 10.0 % by weight, especially preferably of from 2.0 to 7.0 % by weight.

[0080] Preferably, the total content of the at least one polymer P in the in the mixture obtained after step b), based on the total weight of said mixture, is in a range of from 0.05 to 15.0 wt.-%, more preferably of from 0.1 to 12.0 wt.-%, even more preferably of from 0.2 to 10.0 % by weight, particularly preferably of from 0.4 to 8.0 % by weight, especially preferably of from 0.6 to 6.0 % by weight and most preferably of from 0.8 to 5.0 % by weight.

[0081] Preferably, the pH value in step c) is determined directly after the acid or the base has been added at about room temperature (21 °C), more preferably by using a pH meter.

[0082] Optionally, a step e) may be carried out, wherein the mixture is heated up to 100 °C, preferably up to 75 °C, and step e) may be carried out before or between any of the steps b), c) and / or d).

[0083] Optionally, a step f) may be carried out, wherein at least one additive is added into the mixture, and step f) may be carried out before or between any of the steps b), c) and / or d).

[0084] All preferred embodiments described above herein in connection with the inventive sol-gel formulation and in each case preferred embodiments thereof are also preferred embodiments of the inventive method to obtain the inventive formulation.

[0085] Inventive aqueous chemical pretreatment composition

[0086] A further subject-matter of the present invention is an aqueous chemical pretreatment composition, also referred to herein as aqueous composition or aqueous pretreatment composition, comprising, besides water, the aqueous sol-gel formulation as defined hereinbefore and hereinafter and preferably further comprising at least one of constituents a4), a5) and / or a6), namely at least one polymer being different from polymer P, which preferably is a film-forming polymer, said at least one polymer more preferably being selected from polycarbonates, polyurethanes, polycarbonate-polyurethanes, and mixtures thereof, as constituent a4), and / or at least one at least one acid, preferably being selected from sulfuric acid, hydrochloric acid, nitric acid and phosphorous moiety or moieties containing acids, more preferably being selected from phosphoric acid, pyrophosphoric acid, phosphonic acids such as from bisphosphonic acids, e.g., etidronic acid, acids containing Zr and / or Ti and / or at least one fluorine containing moiety including fluorides, such as hexafluoro zirconic acid and / or hexafluoro titanic acid, and in each case their respective deprotonated forms, e.g., salts, as constituent a5), and / or at least one metal oxide, more preferably being selected from alkaline metal oxides, and alkaline earth metal oxides such as magnesium oxide, as constituent a6).

[0087] It is clear that constituents a4), a5) and a6) are different from one another and also from the sol-gel formulation and from the at least one organosilane used for the preparation of said formulation.

[0088] The term "aqueous” with respect to the composition in the sense of the present invention preferably means that the composition is a composition containing at least 50 wt.-%, preferably at least 60 wt.-%, more preferably at least 65 wt.-% in particular at least 70 wt.-%, most preferably at least 70 and at most 90 wt.-% of water, based on its total content of organic and inorganic solvents including water. Thus, the composition may contain at least one organic solvent besides water - however, in an amount lower than the amount of water present. Preferably, the aqueous composition contains at least 50 wt.-%, preferably at least 60 wt.-%, more preferably at least 70 wt.-% in particular at least 80 wt.-%, most preferably at least 90 wt.-% of water, in each case based on its total weight. The total amount of all constituents present in the inventive composition adds up to 100 wt.-%.

[0089] Preferably, water is the main constituent of the aqueous pretreatment composition. More preferably, water is present in an amount of at least 30 wt.-%, more preferably of at least 35 wt.-%, even more preferably of at least 40 wt.-%, yet more preferably of at least 50 wt.-%, in each case based on the total weight of the aqueous pretreatment composition.

[0090] Preferably, the aqueous pretreatment composition contains the sol-gel formulation in an amount in a range of from 0.1 to 35.0 wt.-%, more preferably in an amount in a range of from 0.2 to 30.0 wt.-%, even more preferably in an amount in a range of from 0.5 to 25.0 wt.-%, yet more preferably in an amount in a range of from 1 .0 to 20.0 wt.-%, in each case based on the total weight of the aqueous pretreatment composition.

[0091] Preferably, the aqueous pretreatment composition has a solid content in an amount in a range of from 5.0 to 75.0 wt.-%, more preferably in an amount in a range of from 7.5 to 60.0 wt.-%, even more preferably in an amount in a range of from 10.0 to 55.0 wt.-%, yet more preferably in an amount in a range of from 12.5 or 15.0 to 50.0 wt.-%, most preferably of from 20.0 to 45.0 or to 40.0 wt.-%, in each case based on the total weight of the aqueous pretreatment composition. Preferably, the aqueous composition comprises as a4) at least one polymer selected from polycarbonates, polyethers other than polycarbonates, polyesters, polyurethanes, poly (meth)acry lie polymers, epoxy polymers and mixtures thereof, and which is different from the at least one polymer P. The polymer constituent can be a copolymer and / or a homopolymer. In case of (meth)acrylic polymers for example poly(meth)acrylates are examples of homopolymers in case only one kind of (meth)acrylic monomer has been used. If at least two different kinds of monomers have been used, the (meth)acrylic polymers are (meth)acrylic copolymers. A preferred copolymer is a polyurethane polycarbonate polymer.

[0092] Preferably, the amount of polymer constituent a4) in wt.-% exceeds the amount of the sol-gel formulation in wt.-% in the aqueous pretreatment composition.

[0093] Preferably, the aqueous pretreatment composition contains polymer constituent a4) in an amount in a range of from 5.0 to 60.0 wt.-%, more preferably in an amount in a range of from 6.0 or 7.5 to 55.0 wt.-%, even more preferably in an amount in a range of from 8.0 or 9.5 to 50.0 wt.-%, yet more preferably in an amount in a range of from 10.0 or 15.0 to 40.0 or to 35 wt.-%, in each case based on the total weight of the aqueous pretreatment composition.

[0094] Preferably, the aqueous pretreatment composition contains constituent a5) in an amount in a range of from 0.05 to 5.00 wt.-%, more preferably in an amount in a range of from 0.10 to 4.00 wt.-%, even more preferably in an amount in a range of from 0.20 to 3.50 wt.-%, yet more preferably in an amount in a range of from 0.30 to 3.00 wt.-%, in each case based on the total weight of the aqueous pretreatment composition.

[0095] Preferably, the aqueous composition comprises as a5) at least one phosphonate, more preferably comprises at least one bisphosphonate. In the sense of the present invention, suitable bisphosphonates are, e.g., etidronic acid, clodronic acid, tiludronic acid, pamidronic acid, neridronic acid, olpadronic and acidalendronic acid.

[0096] Preferably, the aqueous pretreatment composition contains constituent a6) in an amount in a range of from 0.05 to 5.00 wt.-%, more preferably in an amount in a range of from 0.10 to 4.00 wt.-%, even more preferably in an amount in a range of from 0.20 to 3.50 wt.-%, yet more preferably in an amount in a range of from 0.30 to 3.00 wt.-%, in each case based on the total weight of the aqueous pretreatment composition.

[0097] Preferably, the aqueous composition comprises as a6) at least one alkaline metal oxide or at least one alkaline earth metal oxide, more preferably comprises magnesium oxide.

[0098] The aqueous composition can be acidic or alkaline, preferably is acidic. The term "acidic” means that the composition has a pH value of less than 7 at room temperature (23 °C). Preferably, when acidic, the aqueous coating composition has a pH value in a range of from 0.1 to <7.0, more preferably of from 0.5 to 6.5, still more preferably of from 1.0 to 6.0, even more preferably of from 1.5 to 5.5, still more preferably of from 2.0 to 5.0, yet more preferably of from 2.5 to 4.5, most preferably of from 3.0 to 4.0. The pH can be preferably adjusted by using nitric acid, phosphoric acid aqueous ammonia and / or sodium carbonate. The term "alkaline” means that the composition has a pH value of >7 at room temperature (23 °C). Preferably, when alkaline, the aqueous coating composition has pH value in a range of from >7.0 to 14.0, more preferably of from >7.0 to 13.5, still more preferably of from >7.0 to 13.0, even more preferably of from >7.0 to 12.5, still more preferably of from >7.0 to 12.0, yet more preferably of from 7.5 to 11.5, still more preferably of from 8.0 to 11.0, yet more preferably of from 8.5 to 10.5.

[0099] The composition can be a dispersion or solution. Preferably, it is a dispersion.

[0100] Preferably, the aqueous pretreatment composition has a conductivity in a range of from 1.0 to 1.00 ■ 105piS / cm, more preferably in a range of from 10.0 to 1.5 ■ 104piS / cm, even more preferably in a range of from 0.5 to 10 mS / cm.

[0101] All preferred embodiments described above herein in connection with the inventive formulation and the inventive method to obtain the inventive formulation and in each case preferred embodiments thereof are also preferred embodiments of the inventive pretreatment composition.

[0102] Pretreatment method for chemically pretreating substrates having at least one metallic surface

[0103] A further subject-matter of the present invention is a pretreatment method for substrates having at least one metallic surface, comprising at least one step 1 a) or 1 b), namely l a) contacting at least a portion of at least one metallic surface of at least one substrate with an aqueous chemical pretreatment composition as defined hereinbefore and hereinafter and / or with a sol-gel-formulation as defined hereinbefore and hereinafter, or l b) contacting at least a portion of at least one metallic surface of at least one substrate with an aqueous chemical pretreatment composition comprising, besides water, at least one organosilane comprising in turn at least one hydrolysable group X, and at least one water dispersible or water-soluble polymer P, which comprises at least one kind of functional groups selected from hydroxyl groups and amino groups and has a weight average molecular weight of at least 1 ,000 g / mol, wherein the sol-gel-formulation as defined hereinbefore and hereinafter is formed in situ in the aqueous chemical pretreatment composition.

[0104] According to an optional step 2) following 1 a) or 1 b) curing or drying of at least the portion of the metallic surface of the substrate that has been contacted with the aqueous composition is performed.

[0105] The drying or curing step 3) may be preferably performed (if performed at all), e.g., at a temperature in the range of 15°C to 180°C, more preferably at a temperature in the range of 25°C to 150°C, in particular at a temperature in the range of 50°C to 130°C. "Drying” in the sense of the present invention means physical drying by evaporation of in particular water originally present in the composition(s) used, whereas "curing” further includes a chemical reaction between at least two constituents originally present in the composition(s) and / or between at least one constituent originally present in the composition(s) and a suitable functional group present on the metallic surface or in the conversion film. Once a film is dried, the resulting product can be regarded as a layer.

[0106] Preferably, the dry layer thickness of a layer formed after drying or curing, preferably drying, is below 10.0 m. Preferably, the obtained cured or dried layer has a dry film thickness in a range of from 10 nm to <10.0 pm, more preferably of from 80 nm to 7.0 pm, in particular preferably of from 150 nm to 4.0 pm.

[0107] By the inventive pretreatment method, a pretreated substrate is obtainable which preferably has a coating thickness in a range of from 0.2 to 4.0 g / m2, more preferably in a range of from 0.3 to 3.0 g / m2, still more preferably in a range of from 0.4 to 2.5 g / m2, most preferably in a range of from 0.5 to 2.0 g / m2.

[0108] Preferably, the chemically pretreated substrate comprises a cured or dried coating layer, which has a coating weight of Si, calculated as element, in a range of from 0.5 to 20 mg / m2, more preferably of from 1.0 to 10 mg / m2, determined in each case via XRF measurements.

[0109] All preferred embodiments described above herein in connection with the inventive formulation and the inventive method to obtain the inventive formulation and the inventive pretreatment composition and in each case preferred embodiments thereof are also preferred embodiments of the inventive pretreating method.

[0110] Inventive pretreated substrate having at least one metallic surface

[0111] A further subject-matter of the present invention is a chemically pretreated substrate having at least one metallic surface, which is obtainable by the chemical pretreatment method as defined hereinbefore and hereinafter.

[0112] All preferred embodiments described above herein in connection with the inventive formulation and the inventive method to obtain the inventive formulation and the inventive pretreatment composition and the inventive pretreatment method and in each case preferred embodiments thereof are also preferred embodiments of the inventive pretreated substrate.

[0113] Inventive use of a polymer for preparing an aqueous sol-gel formulation

[0114] A further subject-matter of the present invention is an use of a water dispersible or water-soluble polymer P comprising at least one kind of functional groups selected from hydroxyl groups and amino groups and having a weight average molecular weight of at least 1 ,000 g / mol for obtaining an aqueous sol-gel formulation, preferably of the sol-gel formulation as defined hereinbefore and hereinafter, by reacting at least one organosilane comprising at least one hydrolysable group X in the presence of said polymer P with water, and / or for increasing at least one of the shelf life, the aging resistance, the thermal stability, and the stability in acidic, neutral and / or alkaline media of said sol-gel formulation, and / or for reducing the content of volatile organic compounds within said sol-gel formulation without negatively affecting the stability of said formulation. All preferred embodiments described above herein in connection with the inventive formulation and the inventive method to obtain the inventive formulation and the inventive pretreatment composition and the inventive pretreatment method and the inventive pretreated substrate and in each case preferred embodiments thereof are also preferred embodiments of the inventive use.

[0115] METHODS

[0116] 1. Evaluation of precipitation after aging

[0117] Occurrence of precipitation was tested visually after the samples have been prepared or have been cooled down after a heating step. Strong precipitation was apparent when the sol-gel formulation turned to a completely white solution and / or when a white solid precipitated, while weaker grades of precipitation showed different degrees of opacity of the solution and / or varying amounts of visible solids within said solution. Sol-gel formulations which remained clear, i.e. did not show any of the above-mentioned occurrences, showed no precipitation.

[0118] 2.29Si-NMR

[0119] 29Silicon Nuclear Magnetic Resonance (NMR) spectroscopy was used to monitor the Si atoms of hydrolyzed silanol groups and the degree of crosslinking within the sol-gel formulation in terms of presence (or non-presence) of Si- O-Si bonds and its specific kinds. The measurements were1H inverse gated decoupled (29Si{H}l G). The chemical shifts of the Si atoms are provided in parts per million (ppm). The integral of the different chemical shifts of the Si atoms was determined and from these values a relative integral ratio between all said signals was calculated.

[0120] 3. VOC content

[0121] The measurement of the volatile organic compounds (VOC) within the sol-gel formulations was gravimetrically determined and was based on the method 24 of the Environmental Protection Agency (EPA) of the U.S.

[0122] 4. Water-resistance

[0123] Water-resistance was tested on substrate panels such as HDG panels pretreated (coated) with a sol-gel formulation or with an agueous chemical pretreatment composition comprising said sol-gel formulation. The coating layer of the coated panel comprised 0.5 to 2.0 g / m2of the dried sol-gel formulation as determined by X-ray fluorescence spectroscopy (XRF) by means of the device Niton® XRF from the company Thermo Scientific. The coated panel rested for 3 days at room temperature (21 °C) before performing the test. Water was dropped on the coated panel. The water mark was observed after 3 min (described as "initial” hereinafter) and then in intervals of 24 h for one week. After said week the panel was subjected to 50 double rubs with cheesecloth and a final water mark was observed.

[0124] 5. Chemical resistance

[0125] Chemical resistance against isopropyl alcohol (IPA) and butanone (MEK) was tested on substrate panels such as HDG panels pretreated (coated) with a sol-gel formulation or with an agueous chemical pretreatment composition comprising said sol-gel formulation. The coating layer of the coated panel comprised 0.5 to 2.0 g / m2of the dried sol-gel formulation as determined by XRF by means of the device Niton® XRF from the company Thermo Scientific. The coated panel rested for 3 days at room temperature (21 °C) before performing the test. The chemical resistance to IPA was tested by double rubbing the coated panels thoroughly with a cheesecloth which was soaked with a solution comprising 95 wt.-% IPA. Afterwards, the chemical mark was observed. The chemical resistance against MEK was carried out according to ASTM D4752 and comprised double rubbing the coated panels with a cheesecloth soaked with MEK.

[0126] 6. Corrosion resistance

[0127] Corrosion resistance was tested on substrate panels such as HDG panels pretreated (coated) with a sol-gel formulation or with an aqueous chemical pretreatment composition comprising said sol-gel formulation. The coating layer of the coated panel comprised 0.5 to 2.0 g / m2of the dried sol-gel formulation as determined by X-ray fluorescence spectroscopy (XRF) by means of the device Niton® XRF from the company Thermo Scientific. The coated panel rested for 3 days at room temperature (21 °C) before performing the test. The method was carried out according to the "wet stack method” as described in ASTM D7376-07.

[0128] 7. Solid content

[0129] The solid content of the sol-gel formulations has been determined with a METLER TOLEDO HE 53 moisture analyzing unit. 0.5 g to 1.0 g of a sample was weighted in and the temperature was gradually increased to 120 °C. The water and solvent content of a sample is measured, which decreased during the measurement due to evaporation. The moisture analyzing unit was kept at this temperature until the weight of the sample remained stable. The remainder corresponds to the solid content. The thereby determined solid content has a standard deviation of 15% based on the determined solid content.

[0130] 8. Weight average molecular weight

[0131] The weight average molecular weight was determined by gel permeation chromatography (GPC) against PMMA standards and using THF as eluent.

[0132] 9. Conductivity

[0133] Conductivity was measured by means of a Thermo Scientific® Orion Star® A122 conductivity portable meter.

[0134] EXAMPLES

[0135] The following examples further illustrate the invention but are not to be construed as limiting its scope. ‘Pbw1means parts by weight. If not defined otherwise, ‘parts' means ‘parts by weight'.

[0136] 1. Sol-gel formulations, chemical pretreatment compositions and preparations thereof

[0137] 1.1 Sol-gel formulations prepared via acid catalysis

[0138] Six sol-gel formulations, namely inventive examples E1 , E2, E3, E4 and E5 and comparative example C1 , were prepared under acidic conditions using the constituents and amounts thereof in the sequence as indicated in Table 1 a (E1 , E2, E3 and 01) and Table 1b (E4 and E5) hereinafter.

[0139] For the preparation of each of E1 , E2, E3 and 01, methyltriethoxysilane (MTES), 3- glycidyloxypropyltrimethoxysilane (GLYMO) and 3-aminopropyltriethoxysilane (AMEO) have been used as organosilanes. In case of E1 , E2 and E3 either one of commercially available polyethyleneimines PE11 (Lupasol® PN 50, about 50 wt.-% in water, weight average molecular weight about 1 ,000,000 g / mol) (in case of E1) or PEI2 (Lupasol® PN 60, about 40 wt.-% in water, weight average molecular weight about 1 ,000,000 g / mol (in case of E2) or a commercially available polyvinyl alcohol PVA (Selvol® Polyvinyl Alcohol 540, weight average molecular weight about 146,000 g / mol) (in case of E3) has been additionally used for the preparation. Water and (in case of E1, E2 and E3) the polymer (PE11, PEI2 or PVA) was added and then, under stirring, GLYMO, MTES and AMEO were each added in this sequence portion wise under stirring. Then, phosphoric acid was added portion wise over two minutes yielding a pH value of the resulting mixture of 3 to 5. The mixture was further stirred for 4 hours at room temperature to obtain the respective sol-gel formulation.

[0140] The "just prepared” sol-gel formulations E1 , E2 and E3 and comparative sol-gel formulation C1 were obtained as clear gels without any precipitation having occurred.

[0141] Table 1 a For the preparation of each of E4 and E5 MTES, GLYMO, tetraethyl orthosilicate (TEOS), and AMEO have been used as organosilanes. In case of E4 aforementioned commercially available polyvinyl alcohol PVA (further diluted to 10 wt.-% PVA in water) and in case of E5 commercially available polyethyleneimine PEI2 has been additionally used. At first, phosphoric acid, etidronic acid (60 wt.-% in water) and magnesium oxide were added respectively into the first portion of deionized water as indicated in Table 1 b and mixed well. Then the second portion of deionized water as indicated in Table 1 b was added. Afterwards, PVA (in case of E4) or PEI2 (in case of E5), TEOS, GLYMO, MTES and AMEO were each added in this sequence portion wise under stirring. After addition of MTES heating of the resulting mixture to 45 °C for 2 h and then cooling to room temperature before addition of AMEO was performed. After AMEO had been added, mixing for 45 minutes was performed before a commercially available polyurethane polycarbonate dispersion (Alberdingk® CUD 4820 VP) was added as film-forming polymer of the resulting chemical pretreatment composition.

[0142] Sol-gel formulations E4 and E5 represent chemical pretreatment compositions, wherein the sol-gel products have been in situ formed therein.

[0143] The "just prepared” sol-gel formulations E4 and E5 were obtained as clear gels without any precipitation.

[0144] Table 1 b

[0145] 1.2 Sol-gel formulations prepared via base catalysis

[0146] Three sol-gel formulations, namely inventive example E6, E7 and comparative example 02, were prepared under alkaline conditions using the constituents and amounts as indicated in Table 2. For the preparation of each of E6, E7 and C2 under stirring, MTES, GLYMO and AMEO have been used as organosilanes. In case of E6 a commercially available polyethyleneimine PEI3 (Lupasol® SK, about 24 wt.-% in water, weight average molecular weight about 2,000,000 g / mol) and in case of E7 a commercially available polyethyleneimine PEW (provided by Sigma-Aldrich, about 50 wt.-% in water, weight average molecular weight about 2,000 g / mol) have been additionally used for the preparation. Water and PEI3 (in case of E6) or PEI4 (in case of E7) were added and then AMEO, GLYMO, and MTES were each added in this sequence portion wise under stirring. The pH of the mixture was then adjusted to 11 .3 with a diluted NaOH solution, and the mixture was further stirred for 3 to 4 hours at room temperature to obtain the respective sol-gel formulation.

[0147] The "just prepared” sol-gel formulations E6 and E7 were obtained as clear gels without any precipitation. The preparation of the comparative sol-gel formulation C2 was regarded as unsuccessful because the "just prepared” C2 merely formed an unstable mixture and showed a high degree of precipitation.

[0148] Table 2

[0149] 2. Investigation of properties of the sol-gel-formulations

[0150] 2.1 Sol-gel aging experiments

[0151] To test the stability of the examples and comparative examples prepared as described hereinbefore in sections 1.1 and 1.2, the sol-gel formulations have been a) stored at 120 °F (about 49 °C) for one week, b) stored at room temperature for six months, or c) heated to 85 °C for 1 h.

[0152] As indicated in Table 3a, the inventive sol-gel formulations E1 , E2 and E3 did not show any precipitation after the aging methods a), b) (E1 and E3) and c) (E1), whereas comparative example C1 showed a medium degree of precipitation after aging method a). Likewise, as indicated in Table 3b, the inventive sol-gel formulations E4 and E5 did not show any precipitation after aging method c). Table 3a

[0153] *- = not determined

[0154] Table 3b

[0155] *- = not determined

[0156] In that manner, the aged examples are described hereinafter according to the aging method used, e.g., E1 , E2 and E3 aged according to method a) are named E1-a), E2-a) and E3-a), E1 and E3 aged according to method b) are named E1-b) and E3-b), and E1 and E4 aged according to method c) are named E1-c) and E4-c).

[0157] 2.229Si NMR spectroscopic investigations

[0158] Si NMR spectroscopy had been carried out for the inventive examples and their aged counterparts. Si NMR spectroscopy was able to show the presence of Si atoms, to which zero (TO), one (T1), two (T2) and / or three (T3) -O-Si groups were bound, and thus provided information about the degree of crosslinking within the sol-gel formulations. A Si atom with zero O-Si-groups is thus not connected to any other Si atoms and hence not part of any network formed. TO includes Si atoms that bear no, one or more OH groups. A Si atom with one O-Si-group is linked to another Si atom via an oxygen atom and represents a chain end or is part of a dimer. A Si atom with two O-Si-groups is linked to two other Si atoms in a linear manner via oxygen atoms. A Si atom with three O-Si-groups is linked to three other Si atoms via oxygen atoms and is part of a three-dimensional network. The relative integral ratios of said Si atoms, as indicated in Table 4a for the acidic formulations and Table 4b for the alkaline formulations, showed that in each inventive example at least 49 % were T3 Si atoms, 31 % to 41 % were T2 Si atoms, and less than 13 % in total were TO and T1 Si atoms, in regard to all Si atoms present in the inventive examples. The under acidic conditions prepared and aged example E1 showed the highest ratio of T2 Si atoms to all Si atoms with over 50 % of T2 Si atoms, while under alkaline conditions prepared example E7 showed the highest ratio of T3 Si atoms to all Si atoms with over 70 % of T3 Si atoms.

[0159] Only small changes of the respective ratios were observed for the aged sol-gel products E1-b), E1-c) and E3-b) compared to their unaged counterparts, demonstrating the high stability of the sol-gel products. Table 4a a: amount based on the relative Integra ratios of the Si NMR (%).

[0160] Table 4b a: amount based on the relative integral ratios of the Si NMR (%).

[0161] 2.3 VOC content investigations

[0162] The sol-gel formulations E4 and E5 were investigated for their amount of volatile organic compounds (VOC) within the product. The amount of VOC was determined of the "just prepared” products of E4 and E5 as well as after both products had been heated to 85 °C for 1 h (aging condition c)). As further comparison, a control solution comprising 95 % isopropyl alcohol in 5 % water has been examined without applying aging conditions. As indicated in Table 5, it can be seen that the VOC content could be completely removed by heating without the occurrence of precipitation for the sol-gel formulations E4 and E5. Table 5 3. Chemical pretreatment of metallic surfaces utilizing the sol-gel formulations

[0163] The inventive sol-gel formulations can be used as agueous chemical pretreatment compositions or as constituent within such said compositions. In particular, as already outlined hereinbefore the sol-gel formulations E4 and E5 already represent agueous chemical pretreatment compositions suitable to chemically pretreat metallic substrates such as HDG panels to obtain chemically pretreated panels P-E4 and P-E5, respectively.

[0164] The agueous chemical pretreatment compositions were roller coated by a reverse roll coater onto the substrate. The coated panels were put into an oven and heated to 400 F (204.4 °C) for 10 to 20 seconds.

[0165] The thereby obtained (pretreated) coated panels P-E4 and P-E5 were rested for 3 days at room temperature (21 °C) before any resistance tests were carried out.

[0166] Water-resistance

[0167] Water-resistance testing was performed according to the method disclosed in the 'method' section. The examined surfaces of the coated panels P-E4 and P-E5 did not show any visual changes, e.g., in form of rubbing out or whitening of the surface. Thus, both inventively pretreated panels P-E4 and P-E5 exhibited an excellent high waterresistance.

[0168] Chemical resistance

[0169] Chemical resistance testing was performed according to the method disclosed in the 'method' section. The examined surfaces of the coated panels P-E4 and P-E5 did not show any visual changes, e.g., in form of rubbing out or whitening of the surface, after being treated with I PA or with MEK. Thus, both inventively pretreated panels P-E4 and P-E5 exhibited an excellent chemical resistance against both organic solvents.

[0170] Corrosion resistance

[0171] Corrosion resistance testing was performed according to the method disclosed in the 'method' section. The examined surfaces of the coated panels P-E4 and P-E5 showed only small amounts of white rust and if at all a weak darkening of the surface after 136 h. Thus, both inventively pretreated panels P-E4 and P-E5 exhibit a very good corrosion resistance.

Claims

CLAIMS1. An aqueous chemical pretreatment composition comprising, besides water, an aqueous sol-gel formulation, which is obtainable by reacting at least one organosilane comprising at least one hydrolysable group X with water, characterized in that the reaction is carried out in the presence of at least one water dispersible or water- soluble polymer P, which comprises at least one kind of functional groups selected from hydroxyl groups and amino groups and has a weight average molecular weight of at least 1 ,000 g / mol and further comprising at least one polymer being different from polymer P as constituent a4), at least one acid and / or a deprotonated form thereof as constituent a5), and at least one metal oxide as constituent a6).

2. The chemical pretreatment composition according to claim 1 , characterized in that the at least one polymer P has a weight average molecular weight in a range of from 1 ,500 to 5,000,000 g / mol, more preferably in a range of from 2,000 to 4,500,000 g / mol, still preferably of from 20,000 to 4,000,000 g / mol, more yet preferably of from 50,000 to 3,000,000 g / mol, most preferably of from 100,000 to 2,500,000 g / mol.

3. The chemical pretreatment composition according to claim 1 or 2, characterized in that the at least one polymer P is selected from polyvinyl alcohols, polysaccharides including chitosan and polyamines including polyalkyleneimines and polyvinylpyrrolidones, preferably is selected from polyvinyl alcohols, polysaccharides, polyethyleneimines and polyvinylpyrrolidone, more preferably is selected from polyvinyl alcohols and polyethyleneimines, even more preferably is selected from polyethyleneimines, said polymers being in each case preferably homopolymers.

4. The chemical pretreatment composition according to one or more of the preceding claims, characterized in that the at least one polymer P is selected from homopolymers, preferably from polyvinyl alcohol and polyethyleneimine homopolymers.

5. The chemical pretreatment composition according to one or more of the preceding claims, characterized in that it contains the at least one polymer P in an amount in a range of from 0.3 to 35.0 wt.-%, preferably of from 0.5 to 20.0 wt.-%, more preferably in a range of from 1 .0 to 15.0 wt.-%, most preferably in a range of from 1 .5 to 10.0 wt.-%, based on the total solid content of the sol-gel formulation contained therein.

6. The chemical pretreatment composition according to one or more of the preceding claims, characterized in that the aqueous sol-gel formulation contained therein has a solid content in a range of from 3.0 to 90.0wt.-%, preferably in a range of from 5.0 to 70.0 wt.-%, more preferably in a range of from 6.0 to 55.0 wt.- %, even more preferably in a range of from 7.0 to 40.0 wt.-%, most preferably in a range of from 8.0 to 30.0 wt.-%, based on the total weight of the sol-gel formulation.

7. The chemical pretreatment composition according to one or more of the preceding claims, characterized in that at least 20 wt.-%, preferably at least 30 wt.-%, more preferably at least 50 wt.-%, even more preferably at least 70 wt.-%, most preferably at least 85 wt.-% of all Si atoms comprised within the sol-gel formulation, based on the total weight of all Si atoms comprised within the sol-gel formulation, are part of at least one siloxane bond, preferably determined by29Si-NMR signal integral ratios.

8. The chemical pretreatment composition according to one or more of the preceding claims, characterized in that the aqueous sol-gel formulation contained therein is obtainable by reacting the at least one organosilane with water in additional presence of at least one acid, yielding a pH value in a range of from 0.5 to <7.0, preferably of from 1.0 to 6.5 or to 6.0, more preferably of from 3.0 to 5.0, or in additional presence at least one base, yielding a pH value in a range of from >7.0 to 13.5, preferably of from 9.5 to 13.0, more preferably of from 11.0 to 12.0.

9. The chemical pretreatment composition according to one or more of the preceding claims, characterized in that the at least one organosilane has at least two or has at least three hydrolysable groups X, and / or at least one non-hydrolysable organic group R1, R1preferably comprising 1 to 12 carbon atoms, more preferably comprising 1 to 8 carbon atoms, wherein R1contains either no functional group or has at least one functional group, preferably has no functional group or at least one functional group selected from amino, thiol and epoxy groups.

10. The chemical pretreatment composition according to one or more of the preceding claims, characterized in that the at least one organosilane has the formula (I) and / or (II), namely[Si(X)4-n(R1)n] (I),[(R1)m(X)3-mSi-R2-Si(X)3-m(R1)m] (II), wherein each X, independently of one another, is a hydrolysable group, preferably an alkoxy group, more preferably an alkoxy group comprising 1 to 8 carbon atoms, even more preferably an alkoxy group comprising 1 to 4 carbon atoms, most preferably a methoxy or ethoxy group,each R1, independently of one another, is a non-hydrolysable organic group preferably comprising 1 to 12 carbon atoms, more preferably comprising 1 to 8 carbon atoms, wherein R1has no functional group or has at least one functional group, preferably no functional group or at least one functional group selected from amino, thiol and epoxy groups, parameter n is 1, 2 or 3, preferably n is 1 or 2, more preferably is 1,R2is non-hydrolysable divalent organic group preferably comprising 1 to 8 carbon atoms, more preferably comprising 1 to 4 carbon atoms, parameter m is 0, 1 or 2, preferably is 1 or 2, more preferably is 1 .11 . The chemical pretreatment composition according to one or more of the preceding claims, characterized in that the aqueous sol-gel formulation contained therein is obtainable by reacting in water at least one organosilane a1) comprising at least one hydrolysable group X, wherein the at least one hydrolysable group X is preferably an alkoxy group, more preferably an alkoxy group comprising 1 to 8 carbon atoms, even more preferably an alkoxy group comprising 1 to 4 carbon atoms, most preferably a methoxy or ethoxy group, and further comprising at least one non- hydrolysable organic group R1, which preferably comprises 1 to 12 carbon atoms, more preferably comprises 1 to 8 carbon atoms, and wherein R1has no functional group, and at least one organosilane a2) comprising at least one hydrolysable group X, wherein the at least one hydrolysable group X is preferably an alkoxy group, more preferably an alkoxy group comprising 1 to 8 carbon atoms, even more preferably an alkoxy group comprising 1 to 4 carbon atoms, most preferably a methoxy or ethoxy group, and further comprising at least one non- hydrolysable organic group R1, which preferably comprises 1 to 12 carbon atoms, more preferably comprises 1 to 8 carbon atoms, and wherein R1has at least one functional group selected from amino, thiol and epoxy groups, wherein preferably at least two organosilanes a2) are used, which are different from one another, more preferably wherein R1of the first organosilane 2a) comprises at least one amino group and R1of the second organosilane 2a) comprises at least one epoxy group, and optionally at least one organosilane a3) exclusively comprising hydrolysable organic groups X and no non-hydrolysable organic groups, preferably selected from alkoxy groups comprising 1 to 8 carbon atoms, more preferably from alkoxy groups comprising 1 to 4 carbon atoms, even more preferably from methoxy and ethoxy groups.

12. The chemical pretreatment composition according to one or more of the preceding claims, characterized in that the aqueous sol-gel formulation contained therein has a conductivity in a range of from 1.00 ■ 102to 1.00 ■ 105piS / cm, more preferably in a range of from 5.0 to 1.5 ■ 104piS / cm, and / or in that the aqueous chemical pretreatment composition has a conductivity in a range of from 1.0 to 1.00 ■ 105piS / cm, more preferably in a range of from 10.0 to 1.5 ■ 104piS / cm, even more preferably in a range of from 0.5 to 10 mS / cm.

13. The chemical pretreatment composition according to one or more of the preceding claims, characterized in that the aqueous sol-gel formulation as defined in one or more of claims 1 to 12 and being part of the chemical pretreatment composition is obtainable by a method comprising at least steps a), b), c), and d), namely a) providing a mixture of at least the at least one polymer P and water, b) adding the at least one organosilane comprising at least one hydrolysable group X to said mixture or vice versa, preferably under stirring, c) adding at least one acid to the mixture obtained after step b) to yield a pH value in a range of 0.5 to <7.0, preferably of 1.0 to 6.5 or to 6.0, more preferably of 3.0 to 5.0, or adding at least one base to the mixture obtained after step b to yield a pH value in a range of >7.0 to 13.5, preferably of 9.5 to 13.0, more preferably of 11.0 to 12.0 and d) stirring the resulting mixture obtained after step c) in order to obtain the aqueous sol-gel formulation.

14. The chemical pretreatment composition according to one or more of the preceding claims, characterized in that the at least one polymer constituent a4) being different from polymer P is at least one polymer being selected from polycarbonates, polyurethanes, polyethers other than polycarbonates, polyesters, poly(meth)acrylic polymers, epoxy polymers, polycarbonate-polyurethanes, and mixtures thereof, and / or the at least one at least one acid and / or a deprotonated form thereof as constituent a5) is selected from sulfuric acid, hydrochloric acid, nitric acid and phosphorous moiety or moieties containing acids, preferably being selected from phosphoric acid, pyrophosphoric acid, phosphonic acids such as from bisphosphonic acids, e.g., etidronic acid, acids containing Zr and / or Ti and / or at least one fluorine containing moiety including fluorides, such as hexafluoro zirconic acid and / or hexafluoro titanic acid, and in each case their respective deprotonated forms, e.g., salts, and / or the at least one metal oxide as constituent a6), is selected from alkaline metal oxides, and alkaline earth metal oxides such as magnesium oxide.

15. A chemical pretreatment method for substrates having at least one metallic surface, comprising at least one step 1 a) or 1 b), namely l a) contacting at least a portion of at least one metallic surface of at least one substrate with an aqueous chemical pretreatment composition as defined in one or more of the preceding claims, or l b) contacting at least a portion of at least one metallic surface of at least one substrate with an aqueous chemical pretreatment composition comprising, besides water, and besides constituents a4), a5) and a6), namely at least one polymer being different from polymer P as constituent a4), at least one at least one acid and / or a deprotonated form thereof as constituent a5), and at least one metal oxide as constituent a6), at least one organosilane comprising in turn at least one hydrolysable group X, and at least one water dispersible or water-soluble polymer P, which comprises at least one kind of functional groups selected from hydroxyl groups and amino groups and has a weight average molecular weight of at least 1 ,000 g / mol, wherein the sol-gel- formulation as defined in one or more of claims 1 to 13 is formed in situ in the aqueous chemical pretreatment composition.

16. A chemically pretreated substrate, which is obtainable by the chemical pretreatment method according to claim 15.

17. An use of a water dispersible or water-soluble polymer P comprising at least one kind of functional groups selected from hydroxyl groups and amino groups and having a weight average molecular weight of at least 1 ,000 g / mol for obtaining an aqueous sol-gel formulation, preferably of the sol-gel formulation as defined in one or more of claims 1 to 13, preferably as a constituent of the aqueous chemical pretreatment composition according to one or more of claims 1 to 14, by reacting at least one organosilane comprising at least one hydrolysable group X in the presence of said polymer P with water, and / or for increasing at least one of the shelf life, the aging resistance, the thermal stability, and the stability in acidic, neutral and / or alkaline media of said sol-gel formulation, and / or for reducing the content of volatile organic compounds within said sol-gel formulation without negatively affecting the stability of said formulation.

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