EP2160239A1

EP2160239A1 - Curing catalyst

Info

Publication number: EP2160239A1
Application number: EP08758744A
Authority: EP
Inventors: Matthias Koch; Sabine Renker; Gerhard Jonschker
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2007-06-22
Filing date: 2008-05-23
Publication date: 2010-03-10
Also published as: DE102007032189A1; US20100190637A1; WO2009000378A1

Abstract

The invention relates to the use of nanoscale zinc oxide produced by a sol-gel process as a curing catalyst, in particular for wet coatings.

Description

curing

The invention relates to the use of nanoscale zinc oxide, prepared by a sol-gel process, as a curing catalyst, in particular for wet paints.

Wet paints essentially consist of binders (polymer resins), solvents, fillers and pigments as well as auxiliaries, also called additives. Clearcoats contain no pigments. The binders are responsible for film formation and film properties. The pigments give the paint its color, while fillers are approximately "optically neutral" and affect various Lackfileigenschaften (including hardness, durability, sandability). Adjuvants are intended to improve certain paint and coating film properties and serve, inter alia, as driers, defoamers, leveling agents, light stabilizers.

Wet paints can be differentiated according to different, fundamental criteria. A possible distinction can be made in one-component and two-component systems. For 1-pack systems, the varnish contains all the components required for film formation. 2-component systems consist of a stock paint and a hardener, which is added shortly before processing. 2-component paints can cease at room temperature and are usually chemically and mechanically more stable than 1-component systems.

For the curing of wet paints, in particular of 2-component PU paints (2-component polyurethane paints), mainly dibutyl tin dilaurate (DBTL) is used.

Soluble tin compounds, in particular organo-tin compounds are harmful to health. Replacement of these compounds is therefore desirable. Another disadvantage of organometallic catalysts is their migration in the finished product, ie they can be released to the environment. Another disadvantage is the odor of the organometallic compound, which can be a nuisance during production, but also in the final product. In Aminvemetzenden systems, a reduction in the amount of amine is desirable because the amines can adversely affect the weathering stability of the coatings.

The object of the invention was therefore to provide a curing catalyst which is effective in the various wet paint systems, is not migrated and odorless.

This object is surprisingly achieved by the inventive use of nanoscale zinc oxide, prepared by a sol-gel process, as a curing catalyst. Due to the catalytic effect of the zinc oxide nanoparticles, a shortening of the time necessary for the curing of the coating system is observed.

The effectiveness of the zinc oxide nanoparticles depends, as with other catalysts, on the nature of the paint system. However, it is surprising that the curing with surface-modified, preferably silanized, zinc oxide particles works very well, although one would rather expect a shielding effect from such surface coverage of the particles. Comparative examples in this regard are listed in the examples.

The invention therefore relates to the use of nanoscale zinc oxide, prepared by a sol-gel process, as a curing catalyst.

Nanoscale in the sense of the present invention means essentially spherical with respect to the zinc oxide particles according to the invention. These particles are particularly preferably in the transparent application range up to 25 nm.

It is possible to powder the curing catalyst, i. as isolated zinc oxide nanoparticles, the paint add. Preferably, the addition to the paint system takes place as a dispersion containing nanoscale zinc oxide. A preferred embodiment of the invention is therefore the use of nanoscale zinc oxide, prepared by a sol-gel process, characterized in that the nanoscale zinc oxide in a dispersion of the system to be cured, i. especially the

Wet paint system, is added. On the one hand, the dispersion can be formed directly during the production of the zinc oxide nanoparticles, or by redispersion of isolated zinc oxide nanoparticles. For this purpose, one can precipitate the particles by adding a non-solvent (poor dispersant), filter and wash and then disperse in a good dispersant. Alternatively, you can dry the washed particles.

For the purposes of the present invention, the term "nanoscale zinc oxide" is used synonymously also for "zinc oxide nanoparticles".

The nanoscale zinc oxide used in the invention consists of ZnO particles having an average particle size determined by particle correlation spectroscopy (PCS) of 1 to 500 nm. Preferably, the particles according to the invention have an average

Particle size, determined by particle correlation spectroscopy (PCS) or by a transmission electron microscope, from 2 to 100 nm, preferably from 3 to 20 nm.

In a preferred embodiment, nanoscale zinc oxide is used according to the invention, wherein the nanoscale zinc oxide is surface-modified with at least one silane. It will be hydrophobicizing and optionally additionally functional silanes used for surface modification of the nanoscale zinc oxide. The choice of silanes is made according to the properties of the paint. A suitable functionalization is characterized by the fact that it favors the incorporation and homogeneous distribution of the particles. The homogeneous distribution is important for the optimal catalytic effect.

In a particularly preferred embodiment, nanoscale zinc oxide is used according to the invention, characterized in that it is produced by a process in which one or more precursors for the ZnO nanoparticles in an alcohol are converted to the nanoparticles in a step a), in one step b) the growth of the nanoparticles is terminated by the addition of at least one silane when the particle size, determined by the position of the asorption edge in the UV / VIS spectrum, has reached the desired value, optionally in step c) the alcohol from step a) is removed and optionally in step d), an organic solvent is added to obtain a dispersion of the ZnO nanoparticles in an organic solvent.

The addition of at least one silane is carried out, as described above, depending on the desired particle size, determined by the position of the absorption edge, but usually 1 to 50 minutes after the beginning of the reaction, preferably 10 to 40 minutes after the start of reaction and more preferably after about 30 min , The location of the absorption edge in the UV spectrum is dependent on the particle size in the initial phase of zinc oxide particle growth. It is at the beginning of the reaction at about 300 nm and shifts in the direction of time in the direction of 370 nm. By adding the silane, the growth can be interrupted at any point.

The isolation of the nanoparticles produced in this way takes place in step c) by adding to the reaction mixture a product which is poor for the functionalized particles Dispersant is added, which is homogeneously miscible with the alcohol. The particles precipitate out and can be filtered off and then taken up in a good dispersant. The possibly resulting salt load remains in the alcohol and can thus be separated. The choice of precipitant is made according to the silane used, under criteria that are known in the art.

For example, organofunctional silanes are used. Q Solcherart silane-based surface modifier are described for example in DE 40 11 044 C2. Suitable silanes are, for example, vinyltrimethoxysilane, aminopropyltriethoxysilane, N-ethylamino-N-propyldimethoxysilane, 3-isocyanatopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, vinyltriethoxysilane, vinylethyldichlorosilane, vinylmethyldiacetoxysilane, vinylmethyldichlorosilane,

Vinylmethyldiethoxysilane, vinyltriacetoxysilane, vinyltrichlorosilane, phenylvinyldiethoxysilane, phenylallyldichlorosilane, 3

Methacryloxypropyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 1, 2-epoxy-4- (ethyltriethoxysilyl) -cyclohexane, 3-acryloxypropyltrimethoxysilane, Q 2-methacryloxyethyltrimethoxysilane, 2-acryloxyethyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, 2-methacryloxyethyltriethoxysilane, 2-acryloxyethyltriethoxysilane, 3 - Methacryloxypropyltris (methoxyethoxy) silane _; 3-methacryloxypropyltris (butoxyethoxy) silane, 3-methacryloxypropyltris (propoxy) silane, 3-methacryloxypropyltris (butoxy) silane, 3-acryloxypropyltris (methoxyethoxy) silane, 3-acryloxypropyltris (butoxyethoxy) silane, 3-acryloxypropyltris (propoxy) silane, 3-acryloxypropyltris (butoxy) silane, hexadecyltrimethoxysilane or mixtures thereof. Particular preference is given to using 3-glycidyloxypropyltrimethoxysilane, Q-hexadecyltrimethoxysilane or mixtures thereof. These and other silanes are commercially available, for example, from ABCR GmbH & Co., Karlsruhe, or from Sivento Chemie GmbH, Dusseldorf. However, it is also possible to use amphiphilic silanes as surface modifiers, as described in WO 2007/059841 on pages 10 to 24. A particularly preferred amphiphilic _c silane is ((3-Trimethoxysilanyl-propyl) - arbaminsäure-2- (2-hexyl-oxy-ethoxy) -ethyl ester.

In the process described, the reaction temperature can be selected in the range between room temperature and the boiling point of the chosen alcohol ^ Q. The reaction rate can be controlled by suitable

Selection of the reaction temperature, the starting materials and their concentration and the solvent are controlled so that it does not cause the expert any difficulty to control the speed so that a control of the reaction process by UV spectroscopy is possible.

15

In a further embodiment, it may be preferable, according to the

Surface modification by signing, further surface modification by reaction with at least one further surface modifier selected from the group 2Q comprising quaternary ammonium compounds, phosphonates,

Phosphonium and sulfonium compounds or mixtures thereof to make.

The requirements for a surface modifier in particular fulfill a bonding agent which carries two or more functional groups. One group of the adhesion promoter reacts chemically with the

Oxide surface of the nanoparticle. Here come alkoxysilyl groups (e.g.

Methoxy, ethoxysilanes), halosilanes (e.g., chloro) or acidic groups of phosphoric acid or phosphonic acids and OQ phosphonic acid esters. About a more or less long

Spacers are the groups described with a second, functional

Linked group. This spacer is unreactive Alkyl chains, siloxanes, polyethers, thioethers or urethanes or combinations of these groups of the general formula (C, Si) _n H _m (N, O, S) χ where n = 1-50, m = 2-100 and x = 0- 50th The functional group is preferably acrylate, methacrylate, vinyl, amino, cyano, isocyanate, epoxy, carboxy or hydroxy groups.

Phosphoric acid-based surface modifiers include i.a. as Lubrizol® 2061 and 2063 from LUBRIZOL (Langer & Co.). Vinylphosphonic acid or vinylphosphonic acid diethyl ester can also be listed here as adhesion promoters (manufacturer: Hoechst AG, Frankfurt am Main).

In a further variant, the nanoscale zinc oxide used according to the invention can also be prepared by the following process, wherein in one step a) one or more precursors for the ZnO nanoparticles in an alcohol are converted to the nanoparticles, in a step b) the growth of Nanoparticles by adding at least one copolymer of at least one monomer having hydrophobic radicals and at least one monomer having hydrophilic

Remains is terminated when the particle size, determined by the position of the absorption edge in the UV / VIS spectrum, has reached the desired value, optionally in step c) the alcohol from step a) is removed and optionally in step d) an organic solvent is added to obtain a dispersion in an organic solvent.

Preferred copolymers to be used here show a weight ratio of structural units having hydrophobic radicals to structural units having hydrophilic radicals in the random copolymers in the range from 1: 2 to 500: 1, preferably in the range from 1: 1 to 100: 1 and particularly preferably in the range from 7: 3 to 10: 1. The weight-average molecular weight of the random copolymers is usually in the range of M _w = 1000 to 1 000 000 g / mol, preferably in the range of 1 500 to 100 000 g / mol and more preferably in the range of 2 000 to 40 000 g / mol.

The weight-average molecular weight of the random copolymers is determined by GPC (GPC = gel permeation chromatography) against PMMA.

Standard (PMMA = polymethyl methacrylate).

It has been found that in particular copolymers which correspond to the formula I.

where X and Y are the radicals of conventional nonionic or ionic

Correspond to monomers and,

R is hydrogen or a hydrophobic side group, preferably selected from the branched or unbranched alkyl radicals having at least 4 carbon atoms in which one or more, preferably all H atoms may be replaced by fluorine atoms, and

R ² is a hydrophilic side group which preferably contains one or more phosphonate, phosphate, phosphonium, sulfonate, sulfonium,

(Quaternary) amine, polyol or polyether radicals, particularly preferably one or more hydroxyl radicals, ran means that the respective groups in the polymer are randomly distributed, and within a molecule -XR ¹ and -YR ^{2 are} each several different Can have meanings and the

Copolymers in addition to the structural units shown in formula I further structural units, preferably those without or with short side chains, such as Ci ^ -alkyl may contain, meet the requirements in a special way. Such polymers and their preparation are described in International Patent Application WO 2005/070979, the disclosure of which relates expressly to the content of the present application.

Particular preference is given in a variant of the invention to those polymers in which -YR ² represents a betaine structure.

In this case, those polymers according to formula I are again particularly preferred in which X and Y are independently of one another for -O-,

C (= O) -O-, -C (= O) -NH-, - (CH ₂₎ _n -, phenylene or pyridyl. Furthermore, polymers in which at least one structural unit contains at least one quaternary nitrogen or phosphorus atom, where R ^{2 is} preferably a side group - (CH ₂ ) m- (N ⁺ (CH 3) 2) - (CH ₂ ) n -SO 3 ^' or a side group - (CH ₂ ) _m - (N ⁺ (CH ₃ ) 2) - (CH ₂ ) n-PO 3 ^{2 '} , - (CH ₂ ) _m -

(N ⁺ (CH ₃ ) ₂ ) - (CH ₂ ) nO-PO ₃ ^{2 "} or a side group - (CH ₂ ) _m - (P ⁺ (CH ₃ ) ₂ ) - (CH ₂ J _n -SO ₃ ^" , where m is an integer from the range from 1 to 30, preferably from the range 1 to 6, particularly preferably 2, and n is an integer from the range from 1 to 30, preferably from the range 1 to 8, particularly preferably 3, advantageously use.

It may be particularly preferred if at least one structural unit of the copolymer has a phosphonium or sulfonium radical.

Particularly preferred random copolymers can be prepared according to the following scheme:

The desired amounts of lauryl methacrylate (LMA) and dimethylaminoethyl methacrylate (DMAEMA) are copolymerized by known processes, preferably in toluene, by free radical addition of AIBN. Subsequently, a betaine structure is obtained by reacting the amine with 1,3-propane sultone according to known methods.

In another variant of the invention, it is preferred if a copolymer consisting essentially of lauryl methacrylate (LMA) and hydroxyethyl methacrylate (HEMA) is used, which can be prepared in known manner by free radical polymerization with AIBN in toluene.

Alternative preferred copolymers to be used may include styrene, vinylpyrrolidone, vinylpyridine, halogenated styrene or methoxystyrene, these examples being not limiting. In another likewise preferred embodiment, polymers are used, which are characterized in that at least one structural unit is an oligo- or polymer, preferably a macromonomer, with polyethers, polyolefins and polyacrylates being particularly preferred as macromonomers.

Furthermore, in the copolymers, in addition to the at least one structural unit having hydrophobic radicals and the at least one structural unit having hydrophilic radicals, further structural units, preferably those contain no hydrophilic or hydrophobic side chains or with short side chains, such as C ₄ alkyl.

The location of the absorption edge in the UV spectrum is dependent on the particle size in the initial phase 5 of the zinc oxide particle growth. It is at the beginning of the reaction at about 300 nm and shifts in the direction of time in the direction of 370 nm. By adding the random copolymer as a modifier, the growth can be interrupted at any point.

The reaction in step a) in the process described above is carried out in an alcohol. It has proven to be advantageous if the alkokhol is selected so that the copolymer used according to the invention is soluble in the alcohol itself. In particular, methanol or ethanol is suitable. As a particularly suitable solvent

., _c for step a) has thereby proven ethanol.

The addition of the copolymer takes place in the specified method, as described above, depending on the desired absorption edge, but usually 1 to 120 minutes after the start of the reaction, Q preferably 5 to 60 minutes after the start of reaction and particularly preferably after 10 to 40 minutes.

In a further variant, the nanoscale zinc oxide used according to the invention can be dispersed, also prepared in an organic solvent, 5 by the following process, in which one or more precursors for the nanoparticles in an organic solvent with a compound M ₃ .χ [θ ₃ - χSiRi _{+ x]} are converted to the nanoparticles, wherein x is an integer selected from 0, 1 or 2, M is H, Li, Na or K and all R are each independently Q of one another are a branched or unbranched, saturated or unsaturated hydrocarbon radical having 1 to 28 C atoms in which one or more C atoms may be replaced by O. This method of preparation allows economical production of the particles, since higher solids contents can be achieved in the product suspension, than using the usual hydroxide bases. By the addition of the compound M ₃ -x [O ₃ . _x SiRn- _x ] can also be a better

Stabilization of the particles over a wider size range are achieved, so that the time window for applying the modifying or compatibilizing layers is significantly larger. Compatibilizing in the present application here means to functionalize the particles such that a conversion into organic, hydrophobic

Solvent, as is the case for many applications (for example in paints), becomes possible. This can be done, for example, by suitable hydrophobic silanes.

In this preparation process additionally a base MOH, where M is Li, Na or K can be used, wherein the proportion of the base in the total amount of M3. _x [θ ₃ - _x SiRi _{+ x} ] and base can be up to 99.5%. If an additional base MOH is to be used, the proportion of base is preferably 10-70 mol% based on the total amount or particularly preferably 30-60 mol%.

In the compounds M ₃ - _x [θ ₃ - _x + _x SiRi] preferably at least one radical R is an alkoxy group having 1 to 27 carbon atoms, preferably a methoxy or ethoxy radical.

In a further preferred embodiment, x is 2 and all R are each independently methyl or ethyl.

In preferred compounds M ₃ - _x [θ _3-x SiRi _{+ x} ], all R are each independently methyl, ethyl, methoxy or ethoxy. It may furthermore be preferred for M to be K. It is particularly preferred for x to be 2 and the formula of the abovementioned compounds accordingly simplified to M [OSiR ₃ ]. Very particularly preferred is the use of compounds of the formula K [OSiRaCH ₃ ], where R is as indicated above, where all R are preferably methyl.

5 It is also possible that the compound M ₃ . _x [θ ₃ - _x SiRi _{+ x],} where M

Li, Na or K and x and R have the abovementioned meaning, is generated in situ from a base MOH and a compound R ' ₃ -x [O ₃ -χSiRi _{+ x} ], where R' is an alkyl group having 1 to 16 C -Atomen, preferably having 1 to 4 carbon atoms, most preferably ethyl.

10

As precursors for the nanoparticles, zinc salts can be used in all the processes described. Preference is given to using zinc salts of the carboxylic acids or halides, in particular zinc formate, zinc acetate or zinc propionate and also zinc chloride. Very particularly preferred

15 zinc acetate or its dihydrate used as a precursor.

The conversion of the precursors to the zinc oxide in the described process is preferably carried out in the basic, wherein in a preferred process variant, a hydroxide base, such as LiOH, NaOH or KOH 2Q is used.

According to the invention, the nanoscale zinc oxide produced by the above-described processes can be used as a curing catalyst for wet paint systems. The nanoscale zinc oxide acts p _c as a curing accelerator for condensation systems, ie in systems in which ester or amide bonds are generated and / or in addition systems, for example in urethane formation. Hardening catalysis particularly preferably takes place in 2K PU paints.

2Q A 2K PU system consists of a binder and a hardener. Particularly suitable binders are polyacrylate, polyester or polyether polyols. The hardeners used are preferably polyisocyanates the basis HDI (hexamethylene diisocyanate), IPDI (isophorone diisocyanate) or TDI (2,4- and 2,6-toluene diisocyanate) used.

Particularly preferred here are polyacrylate polyols.

Compared with commercially available zinc oxide, the nanoscale ZnO, preparable via the previously described method, homogeneously incorporated into the coatings and has in the usual use concentration of 0.01 to 0.1 wt .-%, but also significantly beyond, no negative influence the transparency of the paints. The surface modification of the particles can be designed so that when curing takes place an integration into the paint and thus migration is impossible, as can occur in molecular compounds such as DBTL and zinc salts.

According to the invention, the nanoscale zinc oxide produced by the above-described processes can be used as a curing catalyst for silane-functional paints, adhesives and / or sealants, in particular for silyl-terminated paint binders, for example the polyorganosilsesquioxanes known and often described as "ormocers" or "nanomers", or copolymers, for example polyacrylates, which have been prepared with, inter alia, methacryloxypropyltrimethoxysilane or other silanes with polymerizable double bonds as monomer.

According to the invention, the nanoscale zinc oxide produced by the above-described processes can be used as a curing catalyst in coating formulations which, in addition to the conventional coating components, also contain further nanoparticles or nanoparticles.

The nanoparticles are particles consisting essentially of oxides or hydroxides of silicon, cerium, cobalt, chromium, nickel, zinc, titanium, iron, yttrium, zirconium or mixtures thereof, wherein the particles are preferably SiO ₂ particles as an additional component in the paint formulation. The nanoparticles ideally bear a surface modification, which ensures the incorporation into the paint system. Suitable surface-modified SiO ₂ particles are known from the literature.

It is further observed that the described nanoscale zinc oxides can generally be used as a substitute for organotin compounds such as DBTL. DBTL is used in the production of polyurethanes or in textile dyeing and finishing

Application. A disadvantage in addition to the great toxicity of DBTL is the smell, which can be annoying during production but also in the final product and the ability to migrate in the finished product.

Further possible applications of the nanoscale zinc oxide, prepared by the methods described above, as a substitute for DBTL are now curing catalysis

- In esterification processes in general, for example for the production of cosmetic oils, lubricants, plasticizers, surfactants or paint binders, such as polyesters, polyester polyols, polylactides, polycaprolactones or alkyd resins;

- in textile dyeing and finishing with reactive dyes, lubricants or functional resins to obtain textile properties such as crease resistance or easy cleaning; - in the epoxy resin curing of aliphatic or aromatic

Epoxides with amines, acids or other reactants which are used as adhesives and sealants or, in particular, for the production of glass and carbon fiber reinforced plastics for vehicle and aircraft construction; - in the case of moisture-curing or addition-crosslinking silicones;

- For polyurethane systems such as casting resins, elastomers, adhesives and sealants, dispersions or prepolymers. The amount of nanoscale zinc oxide used as curing catalyst in the different paint systems is different and experimental to determine. Usual use concentrations are from 0.01 to 0.1% by weight, based on the total system.

The curing catalyst is preferably a component of the binder component and is used in the same way as an additive, such as DBTL.

The following examples serve to illustrate the invention without limiting it. The invention is correspondingly executable throughout the range given in this description.

Examples:

General: Particle correlation spectroscopy

The measurements are carried out with a Zetasizer Nano ZS from Malvern at room temperature. The measurement is carried out at a laser wavelength of 532 nm.

The sample volume is in all cases 1 ml at a concentration of 0.5% by weight of particles in butyl acetate. Before the measurement, the solutions are filtered with a 0.45 μm filter.

Transmissionsetektronenmikroskopie

A Tecnai 2OF made by Fei Company with field emission cathode is used. The recordings are made at 200 kV acceleration voltage. Data acquisition on a 2k CCD camera from Gatan.

Preparation of liquid samples with nanoparticles for measurement in

transmission electron microscope For sample preparation, the solution containing the nanoparticles is diluted to 1 wt .-% and dropped a drop of this solution on a kohlebefilmtes Cu netting and then immediately "sucked dry" with a filter paper, (blotting off excess solution). The measurement of the sample takes place after drying at room temperature for one day.

Preparation of paint samples with nanoparticles for measurement in a transmission electron microscope

The particle dispersion is mixed with the paint, so that the ZnO content after drying the paint layer is 5%. The paint is cured in a thick layer in a teflon pan, so that at least 2mm thick, free-standing films are formed. These samples are ultramicrotomed without embedding; at room temperature with 35 ° diamond knife, cutting thickness 60 nm. The sections are suspended in water and transferred to coal-coated Cu nets and measured.

Example 1: Preparation of the random copolymer

254 g of lauryl methacrylate (LMA), 130 g of hydroxyethyl methacrylate (HEMA), 1 g of azoisobutyronitrile (AIBN) and 10 ml of mercaptoethanol are dissolved in 350 ml of toluene. The mixture is degassed and heated to 7O ⁰ C with stirring for 24 h. Then 200 mg of AIBN are added and stirred for a further 18 h at 70 ⁰ C.

For workup, all volatiles are removed in vacuo. This gives a random copolymer of LMA and HEMA in the ratio 1: 1 with a number average molecular weight of 2500 g / mol.

Example 2a:

Preparation of stabilized ZnO particles 75 ml of an ethanolic Zn (AcO) ₂ * 2H ₂ O solution (0.123 mol / L) are added at 50 ^° C. with 150 ml of an ethanolic KOH solution (0.123 mol / L).

The conversion to zinc oxide and the growth of the nanoparticles can be monitored by UV spectroscopy. After only one minute reaction time, the absorption maximum remains constant, ie. ZnO formation is completed in the first minute. The absorption edge shifts with increasing reaction time to longer wavelengths. This can be correlated with sustained growth of ZnO particles by Ostwald ripening.

When the absorption edge reaches 360 nm, 20 ml of a solution of the random copolymer (mass concentration 100 g / l) are extracted

Example 1 added. After the addition, no further shift in the absorption edge is observed any more. The suspension remains stable and transparent for several days.

A comparative experiment without addition of the polymer solution shows continued particle growth and becomes cloudy on continued observation.

For workup, the ethanol is removed in vacuo and the remaining cloudy residue is dissolved in butyl acetate. The resulting in the reaction potassium acetate can be separated as a precipitate. The supernatant clear solution also shows in the UV spectrum the characteristic absorption of zinc oxide.

UV spectroscopy and X-ray diffraction detect the formation of ZnO. Furthermore, no reflections of potassium acetate are visible in the X-ray diagram. Example 2b:

Preparation of stabilized ZnO particles

In 12.5 ml of methanol, 2.19 g of potassium hydroxide (Merck, 85%

Powder) and treated with 4.13 g of ethoxytrimethylsilane. This solution is stirred for one hour at 50 ⁰ C.

4.43 g of zinc acetate dihydrate (Merck, 99.5%) are dissolved in 12.5 ml of methanol and heated to 50 ⁰ C. When the target temperature is reached, the prepared silanolate solution is added. The conversion to zinc oxide and the growth of the nanoparticles can be monitored by UV spectroscopy. When the absorption edge reaches 360 nm (after 30 minutes), 275 μl of hexadecyltrimethoxysilane are added. The reaction mixture is stirred at 50 ^° C. for 5 hours. After cooling, the reaction mixture is transferred to a separating funnel, mixed with 25 ml of petroleum spirit (boiling range 50-70 ⁰ C) and shaken out. The phases are separated. The methanolic phase shows no absorption. The petroleum benzine phase is mixed with 10 ml of butyl acetate and the petroleum benzine distilled off. The resulting solution shows the characteristic UV absorption edge at 360 nm.

Example 3a: Cloucryl high gloss, from Alfred Clouth Lackfabrik, for use on wood

0.1% to 0.01% by weight of nanoscale ZnO from Examples 2a and 2b and ZnO commercial goods (Merck, Zinkoxid, reinst, Art. No .: 108846) are calculated for the Cloucryl lacquer on the Total formulation, added and the paint by air spraying at a layer thickness of 40 microns, dry, applied. The drying of the paint films takes place at room temperature. It is in this paint system to a solvent-based 2-component PU paint based on a polyacrylate polyol, which is cured with a polyisocyanate. As a measure of the curing speed, the pot life is determined according to DIN EN ISO 9514.

Table 1 pot lives when using different catalysts

Of the catalysts investigated, the two zinc oxides prepared according to the invention have the most intensive catalytic activity. In the comparative test with 0.1% ZnO commercial product, a clear clouding of the lacquer layer is evident.

Example 3b: Guideline formulation CAS-EMEA-BD-ICO for the car repair application (2-component PU lacquer, main constituents: polyacrylate and aliphatic polyisocyanate (low-viscosity HDI trimer))

For the used automotive refinish formulation from Bayer a concentration of 0.0174 wt .-% curing catalyst is provided. The pot life is determined for this concentration and for 0.01 wt .-%. In these concentrations, nanoscale zinc oxide prepared according to Examples 2a or 2b and also ZnO commercial goods (Merck, zinc oxide, very pure, Art. No .: 108846) are used.

The lacquer layers are applied by air spraying at the layer thickness of 40 microns, dry, applied and cured for 30 min at room temperature and then at 60 ⁰ C for 30 min. Table 2: Pot lives when using different catalysts

The zinc oxides prepared according to Example 2a or 2b have a significantly better catalytic activity, as the zinc oxide merchandise.

Example 3c: Guideline RR 4822 A, Bayer, for use on plastics (2-component PU lacquer, main constituents: polyester / polyacrylate and aliphatic polyisocyanate (HDI trimer))

For the used Kunststoffrackrichtrezeptur RR 4822 from. Bayer is a concentration of 0.01 wt .-% curing catalyst provided. The

Pot life is for this concentration both for nanoscale zinc oxide, prepared according to Example 2a or 2b, as well as for ZnO commercial goods (Fa.

Merck, zinc oxide, pure, Art. No .: 108846).

The lacquer layers are evaporated by air spraying at a thickness of 40 microns, dry, applied, 10 min at room temperature and then cured at 100 ⁰ C for 40 min.

Table 3: Pot lives for different catalysts

The zinc oxides prepared according to Examples 2a and 2b have a significantly better catalytic activity than the zinc oxide commercial product.

Comparative Example 4

For comparison with commercially available catalysts are 0.1 and 0.01 wt .-% DBTL, as well as Borchi® Kat 0244 Borchers in Cloucryl high gloss, Fa. Alfred Clouth Lackfabrik used and determines the pot life:

Borchi® Kat 0244 is a mixture of a bismuth salt of 2-ethylhexanoic acid and zinc salts of various branched fatty acids.

Table 4: Pot lives for different catalysts

This results in a significantly better effect of the nanoscale zinc oxide over the commercially available products. This is the case in particular at the low concentration of 0.01% by weight.

Claims

claims

1. Use of nanoscale zinc oxide, prepared by a sol-gel process, as a curing catalyst.

2. Use according to claim 1, characterized in that the nanoscale zinc oxide is added in a dispersion to be cured system.

3. Use according to claim 1 or 2, characterized in that the nanoscale zinc oxide is surface-modified with a silane.

4. Use according to one or more of claims 1 to 3, characterized in that that the nanoscale zinc oxide is prepared by a process in which in a step a) one or more

Precursors for the ZnO nanoparticles in an alcohol are converted to the nanoparticles, in a step b) the growth of the nanoparticles is terminated by the addition of at least one silane, if the particle size, determined by the position of the asorption edge in the UV / VIS spectrum, has reached the desired value, if necessary in

Step c) the alcohol from step a) is removed and optionally in step d) an organic solvent is added to obtain a dispersion in an organic solvent.

5. Use according to one or more of claims 1 to 4, characterized in that the surface modification with at least one organofunctional silane selected from the group vinyltrimethoxysilane, aminopropyltriethoxysilane, N-ethylamino-N-propyldimethoxysilane, 3-isocyanatopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, vinyltriethoxysilane, Vinylethyldichlorsilan,

Vinylmethyldiacetoxysilane, vinylmethyldichlorosilane, vinylmethyldiethoxysilane, vinyltriacetoxysilane, vinyltrichlorosilane, Phenylvinyldiethoxysilane, phenylallyldichlorosilane, 3

Methacryloxypropyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane,

1, 2-epoxy-4- (ethyltriethoxysilyl) cyclohexane, 3

Acryloxypropyltrimethoxysilane, 2-methacryloxyethyltrimethoxysilane, 2-acryloxyethyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3

Acryloxypropyltrimethoxysilane, 2-methacryloxyethyltriethoxysilane, 2-

acryloxyethyltriethoxysilane,

3-methacryloxypropyltris (methoxyethoxy) silane _; 3

Methacryloxypropyltris (butoxyethoxy) silane, 3-methacryloxypropyltris (propoxy) silane, 3-methacryloxypropyltris (butoxy) silane, 3-acryloxypropyltris (methoxyethoxy) silane, 3-acryloxypropyltris (butoxyethoxy) silane, 3-acryloxypropyltris (propoxy) silane, 3 -

Acryloxypropyltris (butoxy) silane, hexadecyltrimethoxysilane or

Mixtures takes place.

6. Use according to one or more of claims 1 to 5, characterized in that the nanoscale zinc oxide in addition to the silanization has a further surface modification, obtained by reaction with at least one further surface modifier selected from the group comprising quaternary

Ammonium compounds, phosphonates, phosphonium and sulfonium compounds or mixtures thereof.

7. Use according to claim 1 or 2, characterized in that the nanoscale zinc oxide is produced by a process in which one or more precursors for the ZnO nanoparticles are reacted in an alcohol to the nanoparticles in a step a), in one step b) the growth of the nanoparticles by adding at least one copolymer of at least one monomer having hydrophobic radicals and at least one monomer having hydrophilic

Remains is terminated when the particle size, determined by the position of the Asorptionskante in the UV / VIS spectrum, the desired value has been reached and optionally in step c), the alcohol is removed from step a) and optionally in step d) an organic solvent is added to obtain a dispersion in an organic solvent.

8. Use according to one or more of claims 1 to 7, characterized in that the nanoscale zinc oxide dispersed in an organic solvent is obtainable by a process in which one or more precursors for the nanoparticles in an organic solvent with a compound M _{3- x} [θ _3-x SiRi ₊ χ] to the

Where x is an integer selected from 0, 1 or 2, M is H, Li, Na or K and each R independently is a branched or unbranched, saturated or unsaturated hydrocarbon radical of 1 to 28 C atoms in which one or more C atoms may be replaced by O.

9. Use according to one or more of claims 1 to 8, characterized in that the nanoscale zinc oxide from precursors selected from the group of zinc salts of carboxylic acids or

Halides, is produced.

10. Use according to one or more of claims 1 to 9, characterized in that the curing catalysis takes place in wet paints.

11. Use according to claim 10, characterized in that the catalysis takes place in the curing of condensation or addition systems in wet paints.

12. Use according to claim 10 or 11, characterized in that the curing catalysis takes place in 2K PU paints.

13. Use according to claim 10, characterized in that the curing catalysis takes place in silane-functional paints, adhesives and / or sealants.

14. Use according to claim 10, characterized in that the curing catalysis takes place in coating formulations which contain, in addition to the nanoscale zinc oxide as a curing catalyst, further nanoparticles or nanoparticles.

15. Use according to claim 14, characterized in that the nanoparticles or nanoparticles are SiO ₂ particles.