HK1121179A - Coating materials containing mixed oxide nanoparticles consisting of 50-99.9% by weight al2o3 and 0.1-50% by weght oxides of elements of main groups i or ii of the periodic table - Google Patents

Description

Containing 50-99.9 wt.% Al2O3And 0.1 to 50 wt.% of mixed oxide nanoparticles of an oxide of an element of main group I or II of the periodic Table

Background

Coatings comprising nanoparticles are known, wherein the nanoparticles are produced by hydrolytic (co) condensation of Tetraethoxysilane (TEOS) with other metal alkoxides without organic and/or inorganic binders by means of sol-gel techniques. It is known from DE 19924644 that sol-gel synthesis can also be carried out in a medium. Preferably, radiation-curable formulations are used. However, all materials made by means of the sol-gel process are characterized by a low solids content of inorganic and organic substances, an increased amount of condensation products (usually alcohols), the presence of water, and a limited storage stability.

One development is the high temperature resistant reactive metal oxide particles made by the hydrolytic condensation of metal alkoxides on the surface of nanoscale inorganic particles in the presence of a reactive binder. The temperature resistance of the fully reacted formulation is achieved by heterogeneous copolymerization of the reactive groups of the medium with the same kind of reactive groups of the binder. The disadvantage here is the incompleteness of heterogeneous copolymerizations, in which not all reactive groups on the particle surface participate in the copolymerization. Steric hindrance is the main cause. However, it is well known that incompletely reacted groups cause unwanted secondary reactions which may lead to discoloration, embrittlement or premature degradation. This is especially true for high temperature applications. Even the process described in DE 19846660 leads to non-storage-stable systems in the presence of condensation products, usually alcohols, due to the acidic medium.

Furthermore, nanoscale, surface-modified particles (Degussa) are knownR7200) formed by condensation of metal oxides with silanes in the absence of binders and thus in the absence of strong shearing forces such as those generated in viscous media at stirring speeds ≧ 10 m/s. Thus, these aerosils (silica aerogels) consist of particles larger than the raw material used; their opacity is much higher and their activity is lower than the effect of the particles described in WO 00/22052 and the varnishes prepared therefrom.

Disclosure of Invention

The object of the present invention is to eliminate the disadvantages of the prior art and to provide storage-stable and property-stable coating compositions comprising specifically prepared nanoscale, inorganic particles.

The present invention provides coating compositions comprising mixed oxide nanoparticles consisting of 50 to 99.9 wt% alumina and 0.1 to 50 wt% of an oxide of an element of main group I or II of the periodic Table. According to another embodiment of the invention, the mixed oxide nanoparticles may also be modified on the surface with other coating materials.

The alumina in these mixed oxides is preferably present predominantly in the rhombohedral alpha-modifications (corundum). The mixed oxides of the invention preferably have a crystallite size of less than 1 μm, more preferably less than 0.2 μm and particularly preferably from 0.001 to 0.09. mu.m. Particles of the present invention of this size order will be referred to hereinafter as mixed oxide nanoparticles.

The mixed oxide nanoparticles of the present invention can be prepared by different methods as described below. The process descriptions relate to the preparation of pure alumina particles only, it being understood, however, that for all these process variants, not only the starting compounds containing Al but also those of the elements of main groups I or II of the periodic Table must be present in order to form the mixed oxides according to the invention. Particularly suitable for this purpose are preferably chlorides, but also oxides, oxychlorides, carbonates, sulfates and other suitable salts. These oxide formers are present in such an amount that the nanoparticles produced contain the oxide MeO in the amounts described above.

In general, the preparation of the nanoparticles of the invention starts from larger agglomerates of these mixed oxides, which agglomerates are subsequently deagglomerated to the desired particle size. These agglomerates can be made by the following process.

For example, these agglomerates can be prepared by a variety of chemical syntheses. In most cases these are precipitation reactions (hydroxides) with subsequent calcinationPrecipitation, hydrolysis of organometallic compounds). During these reactions, crystallization nuclei are often added in order to lower the temperature at which the alpha-alumina is converted. The sol thus obtained is dried and converted into a gel in the process. Then further calcination is carried out at a temperature of 350 ℃ to 650 ℃. To be converted into alpha-Al₂O₃Then, annealing must be performed at a temperature of about 1000 ℃. This process is described in detail in DE 19922492.

Another approach is the aerosol method. In this case, the desired molecules are obtained by chemical reaction of the precursor gases or via rapid cooling of the supersaturated gas. Particles are formed by collisions of molecular clusters or by continued evaporation and condensation in equilibrium. The newly formed particles grow by further collisions with product molecules (condensation) and/or further collisions with particles (agglomeration). If the agglomeration rate is greater than the newly formed rate and/or the growth rate, agglomerates of spherical primary particles are formed.

Flame reactors are a production variant based on this principle. Here, the nanoparticles are formed by decomposition of precursor molecules in a flame at 1500 ℃ to 2500 ℃. Mention may be made, as examples, of TiCl₄、SiCl₄And Si₂O(CH₃)₆In methane/O₂Oxidation in the flame, which produces TiO₂And SiO₂Particles. Using AlCl₃However, only the corresponding aluminas have been able to be prepared hitherto. Flame reactors are currently used on an industrial scale for the synthesis of submicron particles, such as carbon black, pigmentary TiO₂Silicon dioxideAnd alumina.

Small particles can also be formed even from liquid droplets by means of centrifugal force, compressed air, sound waves, ultrasound and other methods. The droplets are then converted to a powder by direct pyrolysis or by in situ reaction with other gases. Spray drying and freeze drying may be mentioned as known methods. In the case of spray pyrolysis, the precursor droplets are conveyed through a high temperatureFields (flame, furnace), which lead to rapid evaporation of the volatile components or initiate decomposition reactions to produce the desired products. The desired particles are collected in a filter. Mention may be made here, as an example, of the preparation of BaTiO from an aqueous solution of barium acetate and titanium lactate₃。

It is likewise possible to attempt to break up the corundum by grinding and in this case to produce crystallites in the nanometer range. The best grinding results are obtained with a stirred ball mill in a wet grinding operation. In this case, grinding beads made of a material having a hardness greater than corundum must be used.

Another way to prepare corundum at low temperatures is the conversion of aluminum chlorohydrate. For this purpose, it is likewise mixed with seed crystals, preferably seed crystals made of ultrafine corundum or hematite. To avoid crystal growth, the samples must be calcined at temperatures from about 700 ℃ up to 900 ℃. The duration of the calcination in this case is at least 4 hours. The disadvantage of this process is therefore the large time consumption and the residual chlorine content of the alumina. The method is described in detail in Ber. (report) DKG74(1997) No.11/12, pages 719-722.

The nanoparticles must be released from these agglomerates. This is preferably done by grinding or by treatment with ultrasound. According to the invention, this deagglomeration is carried out in the presence of a solvent and, if appropriate, in the presence of a coating material for modifying the surface, preferably a silane or siloxane, which saturates the reactive and reactive surfaces formed by means of chemical reactions or physical accumulations during the grinding operation, thus preventing reagglomeration. The nano-mixed oxide remains available as small particles. It is also possible to add the coating material for surface modification after the deagglomeration has taken place.

In the preparation of mixed oxides according to the invention, preference is given to starting from agglomerates which are prepared in accordance with the information in Ber.DKG74(1997) No.11/12, page 719-722, as described above.

In this case starting from the formula Al₂(OH)_xCl_yWherein x is a number from 2.5 to 5.5 and y is a number from 3.5 to 0.5, and the sum of x and y is always 6. The aluminium chlorohydrate is mixed as an aqueous solution with the crystalline nuclei, followed by drying and subsequent heat treatment (calcination).

It is preferred in this case to start from an approximately 50% strength aqueous solution as is commercially available. Mixing such a solution with promoted Al₂O₃The crystal nuclei formed by the alpha-modification of (a) are mixed. In particular, such crystal nuclei cause a reduction in the temperature at which the α -modification is formed in the subsequent heat treatment. Suitable nuclei preferably comprise finely divided corundum, diaspore or hematite. Very finely divided alpha-Al having an average particle size of less than 0.1 μm is particularly preferably used₂O₃And (4) a crystal nucleus. In general, 2 to 3 wt.%, based on the formed alumina, of the crystal nuclei is sufficient.

The initial solution additionally comprises an oxide former in order to produce the oxide MeO in the mixed oxide. Particularly suitable for this purpose are chlorides of elements of main groups I and II of the periodic table, more particularly chlorides of the elements Ca and Mg, but also other soluble or dispersible salts, such as oxides, oxychlorides, carbonates or sulfates. The amount of oxide former is such that the nanoparticles produced contain 0.01 to 50 wt% of Me oxide. The oxides of main groups I and II may be present as separate phases other than alumina or may form true mixed oxides with it, such as spinels and the like. The term "mixed oxide" in the context of the present invention should be understood to include both types.

The suspension formed by the aluminium chlorohydrate, the nuclei and the oxide-forming agent is then evaporated to dryness and subjected to a thermal treatment (calcination). The calcination is carried out in an apparatus suitable for this purpose, for example in a horizontal pusher (Durchschub) furnace, a box furnace, a tube furnace, a rotary kiln or a microwave furnace or in a fluidized bed reactor. In a variant of the process according to the invention, the aqueous suspension formed from aluminium chlorohydrate, the oxide former and the nuclei can also be injected directly into the calcining apparatus without prior removal of water.

The calcination temperature should not exceed 1400 ℃. The lower temperature limit depends on the desired yield of nanocrystalline mixed oxide, on the desired residual chlorine content and on the amount of nuclei. The formation of nanoparticles already starts at about 500 deg.C, but in order to keep the chlorine content low and the nanoparticle yield high, it is preferred to operate at temperatures of 700-1100 deg.C, especially at 1000-1100 deg.C.

It has surprisingly been shown that generally 0.5 to 30 minutes, preferably 0.5 to 10 minutes, in particular 2 to 5 minutes, are sufficient for the calcination. After this short time, a sufficient yield of nanoparticles can already be achieved under the preferred temperature conditions described above. However, calcination at 700 ℃ for 4 hours or at 500 ℃ for 8 hours is also possible according to the information in Ber.DKG74(1997) No.11/12, page 722.

During calcination, agglomerates in the form of almost spherical nanoparticles are obtained. The particles are made of Al₂O₃And MeO. The presence of MeO acts as an inhibitor of crystal growth and keeps the crystallite size small. This distinguishes agglomerates such as those obtained by the above-described calcination from particles such as those used in the process described in WO 2004/069400, which are relatively coarse, self-homogenizing particles, rather than agglomerates of nanoparticles which have been prepared.

To obtain the nanoparticles, the agglomerates are preferably comminuted by wet grinding in a solvent, for example in an attritor muller (attritor muhle), bead mill or stirred mill. This gives mixed oxide nanoparticles having a crystallite size of less than 1 μm, preferably less than 0.2 μm, particularly preferably from 0.001 to 0.9. mu.m. For example, after 6 hours of milling, a suspension of nanoparticles with a d90 value of about 50nm is obtained. Another possibility for deagglomeration is ultrasonic treatment with ultrasound.

If it is desired to modify the surface of these nanoparticles with a coating material, such as a silane or siloxane, there are two possibilities. According to a first, preferred variant, the deagglomeration can be carried out in the presence of the coating material, for example by: the coating material is added to the mill during the milling process. A second possibility is to first break up the nanoparticle agglomerates and then treat the nanoparticles, preferably in the form of a suspension in a solvent, with a coating material.

Suitable solvents for deagglomeration include not only water but also conventional solvents, preferably those solvents which are likewise used in the coatings industry, for example C₁-C₄Alcohols, in particular methanol, ethanol or isopropanol, acetone, tetrahydrofuran and butyl acetate. If deagglomeration is carried out in water, inorganic or organic acids, e.g. HCl, HNO, should be added₃Formic acid or acetic acid, in order to stabilize the resulting nanoparticles in aqueous suspension. The amount of acid may be 0.1 to 5 wt% based on the mixed oxide. Thereafter, a particle fraction having a particle diameter of less than 20nm is separated from the aqueous suspension of the acid-modified nanoparticles, preferably by means of centrifugation. Subsequently, a coating material, preferably a silane or siloxane, is added at elevated temperature, for example at about 100 ℃. The nanoparticles thus treated precipitate out, are isolated and dried to a powder, for example by means of freeze-drying.

Suitable coating materials in this connection are preferably silanes or siloxanes or mixtures thereof.

Furthermore, suitable as coating materials are all substances which can be physically fixed to the surface of the mixed oxide (adsorption) or which can be fixed to the surface of the mixed oxide particles by forming chemical bonds. Suitable coating materials are alcohols, compounds containing amino, hydroxyl, carbonyl, carboxyl or mercapto functional groups, silanes or siloxanes, since the surface of the mixed oxide particles is hydrophilic and since free hydroxyl groups are available. Examples of such coating materials are polyvinyl alcohols, mono-, di-and tricarboxylic acids, amino acids, amines, waxes, surfactants, hydroxycarboxylic acids, organosilanes and organosiloxanes.

Suitable silanes or siloxanes are compounds of the formula

a)R[-Si(R’R”)-O-]_nSi (R ') -R ' or ring [ -Si (R ') -O-]_rSi(R’R”)-O-

Wherein

R, R ', R ', and R ' equal to or different from each other, are each an alkyl group having 1 to 18 carbon atoms, or a phenyl group, or an alkylphenyl or phenylalkyl group having 6 to 18 carbon atoms, or of the formula- (C)_mH_2m-O)_p-C_qH_2q+1Or of the formula-C_sH_2sY, or of the formula-XZ_t-1The group of (a) or (b),

n is an integer defined as 1. ltoreq. n.ltoreq.1000, preferably 1. ltoreq. n.ltoreq.100,

m is an integer 0. ltoreq. m.ltoreq.12 and

p is an integer 0. ltoreq. p.ltoreq.60 and

q is an integer of 0. ltoreq. q.ltoreq.40 and

r is an integer of 2. ltoreq. r.ltoreq.10 and

s is an integer 0. ltoreq. s.ltoreq.18 and

y is a reactive group, examples being alpha, beta-ethylenically unsaturated groups, such as (meth) acryloyl, vinyl or allyl, amino, amido, ureido, hydroxyl, epoxy, isocyanate, mercapto, sulfonyl, phosphonyl, trialkoxysilyl, alkyldialkoxysilyl, dialkylmonoalkoxysilyl, anhydride and/or carboxyl, imido, imino, sulfite, sulfate, sulfonate, phosphino, phosphite, phosphate, phosphonate, and

x is a t-functional oligomer, wherein

t is an integer of 2. ltoreq. t.ltoreq.8, and

z is again a radical as defined above

R[-Si(R’R”)-O-]_nSi (R ') -R ' or ring [ -Si (R ') -O-]_rSi(R’R”)-O-。

The t-functional oligomer X is preferably selected here from:

oligoethers, oligoesters, oligoamides, oligourethanes, oligopolyureas, oligoolefins, oligovinyl halides, oligovinylidene halides, oligoimines, oligovinyl alcohols, oligovinyl alcohol esters, acetals and ethers, co-oligomers of maleic anhydride, (meth) acrylic acid oligomers, (meth) acrylic acid esters oligomers, (meth) acrylamide oligomers, (meth) acrylimide oligomers, (meth) acrylonitrile oligomers, with oligoethers, oligoesters, oligourethanes being particularly preferred.

An example of an oligoether group is- (C)_aH_2a-O)_b-C_aH_2a-or O- (C)_aH_2a-O)_b-C_aH_2aCompounds of the type-O, where 2. ltoreq. a.ltoreq.12 and 1. ltoreq. b.ltoreq.60, for example diethylene glycol, triethylene glycol or tetraethylene glycol radicals, dipropylene glycol, tripropylene glycol, tetrapropylene glycol radicals, dibutylene glycol, tributylene glycol or tetrabutylene glycol radicals. An example of an oligomeric ester group is-C_bH_2b-(C(CO)C_aH_2a-(CO)O-C_bH_2b-)_c-or-O-C_bH_2b-(C(CO)C_aH_2a-(CO)O-C_bH_2b-)_cCompounds of the O-type, in which a and b are different or identical, 3. ltoreq. a.ltoreq.12, 3. ltoreq. b.ltoreq.12 and 1. ltoreq. c.ltoreq.30, for example oligoesters of hexanediol and adipic acid.

b)(RO)₃Si(CH₂)_mOrganosilanes of the type-R

Where R ═ alkyl, such as methyl, ethyl, propyl,

m＝0.1-20，

r' is methyl, phenyl,

-C₄F₉、OCF₂-CHF-CF₃、-C₆F₁₃、-O-CF₂-CHF₂

-NH₂、-N₃、SCN、-CH＝CH₂、-NH-CH₂-CH₂-NH₂，

-N-(CH₂-CH₂-NH₂)₂

-OOC(CH₃)C＝CH₂

-OCH₂-CH(O)CH₂

-NH-CO-N-CO-(CH₂)₅

-NH-COO-CH₃、-NH-COO-CH₂-CH₃、-NH-(CH₂)₃Si(OR)₃

-S_x-(CH₂)₃)Si(OR)₃

-SH

-NR 'R "R'" (R '═ alkyl, phenyl; R "═ alkyl, phenyl; R'" H, alkyl, phenyl, benzyl

C₂H₄NR "", where R "" ═ a, alkyl, and R ""' ═ H, alkyl).

Examples of silanes of the above-defined type are, for example, hexamethyldisiloxane, octamethyltrisiloxane, Si_nO_n-1(CH₃)_2n+2A series of other homologous and isomeric compounds, wherein

n is an integer of 2. ltoreq. n.ltoreq.1000, e.g. polydimethylsiloxaneLiquid (20 cSt).

Hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, (Si-O)_r(CH₃)_2rA series of other homologous and isomeric compounds, wherein

r is an integer of 3. ltoreq. r.ltoreq.12,

dihydroxytetramethyldisiloxane, dihydroxyhexamethyltrisiloxane, dihydroxyoctamethyltetrasiloxane, HO- [ (Si-O)_n(CH₃)_2n]-Si(CH₃)₂-OH or HO- [ (Si-O)_n(CH₃)_2n]-[(Si-O)_m(C₆H₅)_2m]-Si(CH₃)₂Other homologous and isomeric compounds of the-OH series, in which

m is an integer of 2-1000,

preference is given to alpha, omega-dihydroxypolysiloxanes, such as polydimethylsiloxane (OH end groups, 90-150cST) or polydimethylsiloxane-co-diphenylsiloxane (dihydroxy end groups, 60 cST).

Dihydrohexamethyltrisiloxane, dihydrooctamethyltetrasiloxane, H- [ (Si-O)_n(CH₃)_2n]-Si(CH₃)₂Other homologous and isomeric compounds of the H series, in which

n is an integer from 2. ltoreq. n.ltoreq.1000, preferably an alpha, omega-dihydropolysiloxane, for example polydimethylsiloxane (hydride end groups, M)_n＝580)。

Bis (hydroxypropyl) hexamethyltrisiloxane, bis (hydroxypropyl) octamethyltetrasiloxane, HO- (CH)₂)_u-[(Si-O)_n(CH₃)₂(CH₂)_uOther homologous and isomeric compounds of the-OH series, preferably alpha, omega-dimethanol-based polysiloxanes, where 3. ltoreq. u.ltoreq.18, 3. ltoreq. n.ltoreq.1000, or their polyether-modified successor (Nachfolge) compounds based on Ethylene Oxide (EO) and Propylene Oxide (PO) as homopolymers or copolymers HO- (EO/PO)_v-(CH₂)_u-[(Si-O)_t(CH₃)_2t]-Si(CH₃)₂(CH₂)_u-(EO/PO)_v-OH, preferably an alpha, omega-di (carbinol polyether) polysiloxane, wherein 3. ltoreq. n.ltoreq.1000, 3. ltoreq. u.ltoreq.18, 1. ltoreq. v.ltoreq.50.

Instead of the α, ω -OH groups, it is likewise possible to use the corresponding difunctional compounds with epoxy, isocyanate, vinyl, allyl and di (meth) acryloyl groups, examples being polydimethylsiloxanes having vinyl end groups (850-1150cST) or TEGORAD 2500 from Tego Chemie services.

Also suitable are esterification products of ethoxylated/propoxylated trisiloxanes and higher siloxanes having acrylic copolymers and/or maleic copolymers as modifying compounds, for example BYK Silclean 3700 from Byk Chemie or from Tego Chemie GmbHProtect 5001。

Instead of the α, ω -OH groups, it is likewise possible to use the corresponding difunctional compounds with — NHR "", where R "═ H or alkyl groups, examples being the commonly known aminosilicones from Wacker, Dow Corning, Bayer, Rhodia et al, which carry (cyclo) alkylamino or (cyclo) alkylimino groups randomly distributed over the polysiloxane chain in their polymer chain.

c)(RO)₃Si(C_nH_2n+1) And (RO)₃Si(C_nH_2n+1) Organosilane of type (I) in which

R is alkyl, such as methyl, ethyl, n-propyl, isopropyl, butyl, and

n is 1 to 20.

R’_x(RO)_ySi(C_nH_2n+1) And (RO)₃Si(C_nH_2n+1) Organosilane of type (I) in which

R is an alkyl group, such as methyl, ethyl, n-propyl, isopropyl, butyl,

r' is an alkyl group, such as methyl, ethyl, n-propyl, isopropyl, butyl,

r' is a cycloalkyl group,

n is an integer of 1 to 20,

x + y is 3, and x + y is,

x is 1 or 2, and the compound is,

y is a number of 1 or 2,

d)(RO)₃Si(CH₂)_morganosilanes of the type-R', in which

R is an alkyl group, such as methyl, ethyl, propyl,

m is a number of 0.1 to 20

R' is methyl, phenyl, -C₄F₉、OCF₂-CHF-CF₃、-C₆F₁₃、-O-CF₂-CHF₂、-NH₂、-N₃、-SCN、-CH＝CH₂、-NH-CH₂-CH₂-NH₂，-N-(CH₂-CH₂-NH₂)₂、-OOC(CH₃)C＝CH₂、-OCH₂-CH(O)CH₂、-NH-CO-N-CO-(CH₂)₅、-NH-COO-CH₃、-NH-COO-CH₂-CH₃、-NH-(CH₂)₃Si(OR)₃、-S_x-(CH₂)₃)Si(OR)₃-SH-NR 'R "R'" (R '═ alkyl, phenyl; R "═ alkyl, phenyl; R'" ═ H, alkyl, phenyl, benzyl, C₂H₄NR "" "R" ", wherein R" "═ a, alkyl, and R" "' ═ H, alkyl).

Preferred silanes are those listed below:

triethoxysilane, octadecyltrimethoxysilane, 3- (trimethoxysilyl) propyl methacrylate, 3- (trimethoxysilyl) propyl acrylate, 3- (trimethoxysilyl) methyl methacrylate, 3- (trimethoxysilyl) methyl acrylate, 3- (trimethoxysilyl) ethyl methacrylate, 3- (trimethoxysilyl) ethyl acrylate, 3- (trimethoxysilyl) pentyl methacrylate, 3- (trimethoxysilyl) acrylateSilyl) pentyl ester, 3- (trimethoxysilyl) hexyl methacrylate, 3- (trimethoxysilyl) hexyl acrylate, 3- (trimethoxysilyl) butyl methacrylate, 3- (trimethoxysilyl) butyl acrylate, 3- (trimethoxysilyl) heptyl methacrylate, 3- (trimethoxysilyl) heptyl acrylate, 3- (trimethoxysilyl) heptyl methacrylate, 3- (trimethoxysilyl) octyl acrylate, methyltrimethoxysilane, methyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, hexadecyltrimethoxysilane, and the like, Phenyltrimethoxysilane, phenyltriethoxysilane, tridecafluoro-1, 1, 2, 2-tetrahydrooctyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, oligomeric tetraethoxysilane (from Degussa, Inc.)40) Tetra-n-propoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 2-aminoethyl-3-aminopropyltrimethoxysilane, triaminofunctional propyltrimethoxysilane (available from Degussa, Inc.)TRIAMINO), N- (N-butyl) -3-aminopropyltrimethoxysilane, 3-aminopropylmethyldiethoxysilane.

The coating material, in particular silane or siloxane in this case, is preferably added in a molar ratio of mixed oxide nanoparticles to silane of from 1: 1 to 10: 1. The amount of solvent in the deagglomeration process is typically 80 to 90 wt.%, based on the total amount of mixed oxide nanoparticles and solvent.

The deagglomeration by grinding and the simultaneous modification with the coating material is preferably carried out at temperatures of from 20 to 150 ℃ and particularly preferably from 20 to 90 ℃.

If deagglomeration is carried out by grinding, the suspension is subsequently separated from the grinding beads.

After deagglomeration, the suspension can be heated up to 30 hours to complete the reaction. Finally, the solvent was removed by distillation and the remaining residue was dried. It may also be advantageous to leave the modified mixed oxide nanoparticles in the solvent and use the dispersion for further applications.

It is also possible to suspend the mixed oxide nanoparticles in a corresponding solvent and to react with the coating material in a further step after deagglomeration.

The surface-modified mixed oxide nanoparticles thus produced can be incorporated into any desired coating composition, for example ceramic coatings, electro-alumina (Eloxal) coatings or preferably into varnishes. These coating compositions additionally comprise conventionally known binders, examples of which are those described below:

clear coat binders for one-and multi-component polymer systems may comprise the following components known from coating technology:

alkyd-melamine stoving lacquers, mono-to poly-functional acrylates, examples being butyl acrylate, ethylhexyl acrylate, norbornyl acrylate, butanediol diacrylate, hexanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, trimethylolpropane triacrylate, trimethylolpropane triethoxy triacrylate, pentaerythritol tetraethoxytriacrylate, pentaerythritol tetraethoxytetraacrylate, polyether acrylates, urethane acrylates, e.g. from Cray Valley Kunstthrow GmbHCN925. CN 981 from UCB GmbHEB 1290, Laromer 8987 from BASF AG, from Cognis6019 or6010，

Polyester acrylates, for example from Cray Valley Kunstharze GmbHCN 292 from BASF AGLR 8800 from UCB GmbHEB 800 from Cognis5429F and5960F，

epoxy acrylates, e.g. from BASF AGEA 81 from UCB GmbHEB 604, from Cray Valley Kunstharze GmbHCN104D80，

Dendritic polyester/ether acrylates from Perstorp Speciality ChemicalAG or from Bayer AG,

polyurethane polymers and their precursors, in the form of polyisocyanates, polyols, polyurethane prepolymers, as blocked prepolymers and as fully reacted polyurethanes in the melt or solution. These are in particular:

polyols in the form of polyethers, e.g. polyethylene glycol 400, available from Dow ChemicalsP400 andCP 3055, polyesters, e.g. fromOf GmbH8107、8109 from Bayer AG670、1300 from Degussa AGT1136 alkyd resins, e.g. from Worlse Chemie GmbHC 625，

Polycarbonates, e.g.C200, hydroxy-containing polyacrylates, e.g. from Bayer AGA 365，

Polyisocyanates, e.g. from Bayer AGN 3300、VL、Z 4470、IL orL75 from Degussa AGT1890L from Rhodia Syntech GmbHWT 2102，

Polyurethane prepolymers, e.g. from Bayer AGE4280 from Degussa AGEP-U 423，

PMMA and other polyalkyl (meth) acrylates, e.g. from Degussa AGP550 andLP 50/01，

polyvinyl butyrals and other polyvinyl acrylates, e.g. from Clariant GmbHB 30HH，

Polyvinyl acetates and copolymers thereof, e.g. from Wacker-Chemie GmbHB 100/20VLE。

For all polymers, both aliphatic and aromatic variants are explicitly included. The binder may also be selected so that it is the same as the silane used for functionalization.

The binder preferably has a molecular weight of 100-800 g/mol. The binder content in the total coating composition is preferably from 80 to 99% by weight, in particular from 90 to 99% by weight.

The coating compositions of the invention may further comprise additives of the type customary in coating technology, examples being reactive diluents, solvents and cosolvents, waxes, matting agents, lubricants, defoamers, deaerators, levelling agents, thixotropic agents, thickeners, inorganic and organic pigments, fillers, adhesion promoters, corrosion inhibitors, anticorrosion pigments, UV stabilizers, HALS compounds, radical scavengers, antistatic agents, wetting agents and dispersants and/or catalysts, co-catalysts, initiators, radical generators, photoinitiators, photosensitizers and the like which are necessary depending on the curing mode. Suitable further additives also include polyethylene glycols and other water-retaining agents, PE waxes, PTFE waxes, PP waxes, amide waxes, FT paraffins, montan waxes, graft waxes, natural waxes, macrocrystalline and microcrystalline paraffins, polar polyolefin waxes, sorbitan esters, polyamides, polyolefins, PTFE, wetting agents or silicates.

The subject matter of the invention is intended to be illustrated in greater detail on the basis of the following examples without limiting the possible multiplicity.

Detailed Description

Examples

Example 1:

a50% strength aqueous solution of aluminum chlorohydrate was mixed with magnesium chloride such that the ratio of alumina to magnesium oxide after calcination was 99.5: 0.5%. To this solution, 2% of crystallization nuclei of a suspension of ultrafine corundum are additionally added. After the solution was homogenized by stirring, drying was carried out in a rotary evaporator. The solid aluminum chlorohydrate/magnesium chloride mixture was crushed in a mortar, producing a coarse powder here.

The powder was calcined in a rotary kiln at 1050 ℃. The contact time in the hot zone was a maximum of 5 minutes. This produced a white powder with a particle size distribution corresponding to the feed material.

X-ray structural analysis showed the presence of predominantly alpha-alumina.

Images taken of REM photographs (scanning electron microscopy) show crystallites of 10-80nm (estimated from REM photographs) in the form of agglomerates. The residual chlorine content is only a few ppm.

In a further step, 40g of the corundum powder doped with magnesium oxide were suspended in 160g of isopropanol. The suspension is added to 40g of trimethoxyoctylsilane and fed to a vertical stirred ball mill from Netzsch, type PE 075. The grinding beads used were made of zirconia (stabilized with yttrium) and had a size of 0.3 mm. After 3 hours, the suspension was separated from the milling beads and cooked under reflux for another 4 hours. The solvent was subsequently removed by distillation and the remaining wet residue was dried in a drying cabinet at 110 ℃ for a further 20 hours.

Example 2:

40g of the oxide mixture from example 1 (MgO-doped corundum) were suspended in 160g of methanol and the suspension was deagglomerated in a vertical stirred ball mill from Netzsch, type PE 075. After 3 hours the suspension was separated from the beads and transferred to a round bottom flask with reflux condenser. To the suspension was added 40g of trimethoxyoctylsilane and heated at reflux for 2 hours. After removal of the solvent, the coated oxide mixture was separated off and dried again in a drying cabinet for 20 hours at 110 ℃. The product thus obtained was the same as the sample of example 1.

Example 3:

40g of the oxide mixture from example 1 (MgO-doped corundum) were suspended in 160g of methanol and the suspension was deagglomerated in a vertical stirred ball mill from Netzsch, type PE 075. After 2 hours 20g of 3- (trimethoxysilyl) propyl methacrylate (Dynasilan MeO; Degussa) were added and the suspension was deagglomerated in a stirred ball mill for a further 2 hours. The suspension was then separated from the beads and transferred to a round bottom flask with reflux condenser. It was heated under reflux for a further 2 hours, after which the solvent was removed by distillation.

Example 4:

40g of the oxide mixture from example 1 (MgO-doped corundum) were suspended in 160g of acetone and the suspension was deagglomerated in a vertical stirred ball mill from Netzsch, type PE 075. After 2 hours 20g of aminopropyltrimethoxysilane (Dynasilan Ammo; Degussa) were added and the suspension was deagglomerated in a stirred ball mill for a further 2 hours. The suspension was then separated from the beads and transferred to a round bottom flask with reflux condenser. It was heated under reflux for a further 2 hours, after which the solvent was removed by distillation.

Example 5:

40g of the oxide mixture from example 1 (MgO-doped corundum) were suspended in 160g of acetone and the suspension was deagglomerated in a vertical stirred ball mill from Netzsch, type PE 075. After 2 hours 20g of glycidyltrimethoxysilane (Dynasilan Glymo; Degussa) were added and the suspension was deagglomerated in a stirred ball mill for a further 2 hours. The suspension was then separated from the beads and transferred to a round bottom flask with reflux condenser. It was heated under reflux for a further 2 hours, after which the solvent was removed by distillation.

Example 6:

40g of the oxide mixture from example 1 (MgO-doped corundum) were suspended in 160g of n-butanol and the suspension was deagglomerated in a vertical stirred ball mill from Netzsch, type PE 075. After 2 hours, a mixture of 5g of aminopropyltrimethoxysilane (Dynasilan Ammo; Degussa) and 15g of octyltriethoxysilane was added and the suspension was deagglomerated in a stirred ball mill for a further 2 hours. The suspension remained stable for several weeks without signs of sedimentation of the coated mixed oxide.

Application examples

The coated mixed oxides from the examples were tested in various varnish systems for abrasion resistance, hardness, gloss and scratch resistance. The tests were carried out in a two-component polyurethane varnish system, a 100% UV varnish system and a one-component stoving varnish system.

I. Two-component polyurethane varnish system

The samples from examples 1-3 were dispersed into the first component or solvent of the varnish system.

Wear and tear

The varnish samples were applied to specific glass panels using a compressed air spray gun. After different revolutions, the final mass is determined using a Taber abrasion tester and the abrasion is calculated therefrom.

Final mass [ mg]	After 20 turns	After 50 turns	After 100 turns
				Additive-free varnish	0.4	2.1	5.6
2% Mixed oxide nanoparticles/example 3	0.0	1.0	3.9
				4% Mixed oxide nanoparticles/example 3	0.0	2.8	3.8
2% Mixed oxide nanoparticles/example 1 or 2	0.5	1.1	3.8
				4% Mixed oxide nanoparticles/example 1 or 2	0.5	1.7	4.1
10% mixed oxide nanoparticles/example 1 or 2	0.8	2.2	4.8
				2％ Nanobyk-3610	0.0	2.2	4.8

Nanobyk-3610 is a dispersion of surface-modified nano-aluminum in methoxypropyl acetate as a solvent for improving scratch resistance.

Degree of gloss

The varnish was applied to a glass plate in a wet film thickness of 60 μm and the gloss was measured at an angle of 60 ℃ with the aid of a mini-gloss meter (micro-gloss) by BYK-Gardner.

	Gloss/60 °
		Without addition of additivesAdditive agent	144
2% Mixed oxide nanoparticles/example 3	133
		4% Mixed oxide nanoparticles/example 3	129
4% Mixed oxide nanoparticles/example 1 or 2	126
		6% Mixed oxide nanoparticles/example 1 or 2	120
10% mixed oxide nanoparticles/example 1 or 2	110
		2％ Nanobyk-3610	101

Hardness of pencil

The hardness of the clear coat film on the glass plates was determined by the Wolff-Wilborn pencil hardness test.

	Hardness of
		Without additives	F
10% mixed oxide nanoparticles/example 1 or 2	F
		6% Mixed oxide nanoparticles/example 1 or 2	F
4% Mixed oxide nanoparticles/example 1 or 2	H
		4% Mixed oxide nanoparticles/example 3	H
4% Mixed oxide nanoparticles/example 3	H
		2％ Nanobyk-3610	HB

Soft
	6B
5B
	4B
3B
	2B
B
	HB
F
	H
2H
	3H
4H
	5H
6H
	7H
8H
	9H
Hard

II.100% UV varnish System

The samples from examples 1-3 were dispersed into the varnish system.

Wear and tear

The varnish samples were applied to specific glass panels using a compressed air spray gun.

After different revolutions, the final mass is determined using a Taber abrasion tester and the abrasion is calculated therefrom.

Final mass [ mg]	50 turn	100 turns	200 turn
				Without additives	1.5	3.9	10.5
2% Mixed oxide nanoparticles/example 3	0.9	2.5	7.1
				Mixed oxide nanoparticles/examples 1 or 2	1.3	3.2	9.0
2％ Nanobyk-3601	1.5	3.3	8.3

Nanobyk-3601 is a dispersion of surface modified nano aluminum in tripropylene glycol diacrylate for improved scratch resistance.

Degree of gloss

The varnish was applied to a glass plate in a wet film thickness of 60 μm and the gloss was measured at an angle of 60 ° by means of a BYK-Gardner micro gloss meter.

	Degree of gloss
		Without additives	139
2% Mixed oxide nanoparticles/example 3	137
		2% Mixed oxide nanoparticles/example 1 or 2	120
2％ NANOBYK-3601	134

Hardness of pencil

The hardness of the clear coat film on the glass plates was determined by means of the Wolff-Wilborn pencil hardness.

Single component baking finish system

The samples from examples 4 to 6 were dispersed in the solvent of the varnish or the varnish system.

Wear and tear

The varnish samples were applied to specific glass panels using a compressed air spray gun. After different revolutions, the final mass is determined using a Taber abrasion tester and the abrasion is calculated therefrom.

Final mass [ mg]	After 100 turns	After 200 turns
			Additive-free varnish	10.4	23.9
2% Mixed oxide nanoparticles/example 4	7.0	19.0
			2% Mixed oxide nanoparticles/example 5	7.5	21.2
5% Mixed oxide nanoparticles/example 4	7.4	18.4
			5% Mixed oxide nanoparticles/example 5	5.6	12.3
2％ Nanobyk-3610	12.5	25.4

Final mass [ mg]	After 100 turns	After 200 turns
			Additive-free varnish	16.0	31.6
2% Mixed oxide nanoparticles/example 6	12.0	25.4
			4% Mixed oxide nanoparticles/example 6	11.3	23.8

Degree of gloss

The varnish was applied to a glass plate in a wet film thickness of 60 μm and the gloss was measured at an angle of 60 ° by means of a BYK-Gardner micro gloss meter.

	Degree of gloss
		Without additives	154
2% Mixed oxide nanoparticles/example 4	150
		2% Mixed oxide nanoparticles/example 5	138
5% Mixed oxide nanoparticles/example 4	146
		5% Mixed oxide nanoparticles/example 5	123
2％ Nanobyk-3610	142

	Degree of gloss
		Without additives	154
2% Mixed oxide nanoparticles/example 6	142
		4% Mixed oxide nanoparticles/example 6	130

Scratch hardness test

The varnish was applied to galvanized tinplate in a wet film thickness of 60 μm and the scratch hardness was determined via the number of passes (Hube).

	100g support weight
		Without additives	9
2% Mixed oxide nanoparticles/example 4	26
		2% Mixed oxide nanoparticles/example 5	16
5% Mixed oxide nanoparticles/example 4	12
		5% Mixed oxide nanoparticles/example 5	21
2％ Nanobyk-3610	4

	300g support weight
		Without additives	5
2% Mixed oxide nanoparticles/example 6	7
		4% Mixed oxide nanoparticles/example 6	6

Claims (7)

1. A coating composition comprising mixed oxide nanoparticles consisting of 50 to 99.9 wt% of alumina and 0.1 to 50 wt% of an oxide of an element of main group I or II of the periodic table.

2. The coating composition of claim 1, characterized in that the coating composition comprises mixed oxide nanoparticles modified with a coating material on the surface.

3. The coating composition of claim 1, characterized in that the coating composition comprises mixed oxide nanoparticles modified with silanes or siloxanes on the surface.

4. The coating composition according to claim 1, characterized in that the coating composition comprises mixed oxide nanoparticles obtained by deagglomeration of agglomerates consisting of mixed oxide nanoparticles by grinding in a solvent.

5. The coating composition according to claim 1, characterized in that the coating composition comprises nanoparticles modified with a coating material on the surface, said nanoparticles being obtained by deagglomeration of agglomerates consisting of mixed oxide nanoparticles via grinding in a solvent and simultaneous treatment with said surface-modified coating material.

6. The coating composition according to claim 1, characterized in that the coating composition comprises mixed oxide nanoparticles modified with a coating material on the surface, said mixed oxide nanoparticles being obtained by deagglomeration of agglomerates consisting of mixed oxide nanoparticles via grinding in a solvent and subsequent treatment with said surface-modified coating material.

7. The coating composition according to any one of claims 1 to 6, characterized in that the coating composition is a varnish.