EP2435519A1

EP2435519A1 - Coated particles, and use thereof

Info

Publication number: EP2435519A1
Application number: EP10724268A
Authority: EP
Inventors: Matthias Quenzer; Marc Entenmann; Matthias Kuntz; Renate Bonn-Walter
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2009-05-29
Filing date: 2010-05-12
Publication date: 2012-04-04
Also published as: WO2010136122A1; DE102009023158A1

Abstract

The invention relates to the use of particles comprising a substrate and a superficial or near-surface SiO₂ layer or a superficial or near-surface layer containing SiO₂ particles embedded in a matrix, in electrostatic coating methods, said superficial or near-surface layer containing at least 2.5 percent by weight of SiO₂ relative to the total weight of the particles. The invention also relates to a coating powder containing such particles, electrostatic coating methods, and such particles.

Description

Coated particles and their use

The present invention relates to the use of particles comprising a substrate and a surface or surface near SiO ₂ layer or a surface or near-surface layer containing SiO ₂ particles embedded in a matrix in electrostatic coating processes, the surface or near-surface layer being at least 2.5 Wt .-% of SiO ₂ based on the total weight of the total weight, a powder coating containing such particles, electrostatic coating methods and such particles per se.

The coating of objects with paints or paints is of great importance. The color effects and the stability of the applied lacquers or colors play a special role. An essential coating method is the electrostatic powder coating, in electrostatic powder spraying (EPS) from a grounded container with fluidized powder coating by means of an injector, the powder particles are electrostatically charged with a corona gun and the powder coating through a DC high voltage field from the corona gun to grounded workpiece is moved. Since electrostatically applicable powder coatings essentially consist only of plastic powders and pigments and contain no solvents, no solvent emissions or coating sludge are formed in the electrostatic powder coating and this coating process is therefore particularly environmentally friendly.

A problem with this coating method, however, is a recurrent segregation or separation of pigment particles and plastic powder particles as a result of different charging and particle parameters. This segregation leads to changes in the processing properties and the optical properties of the Coatings. To circumvent this problem, WO 98/46682 describes the use of a well-adhering, viscous coating on effect pigments for powder coatings. It is described that powder coating particles adhere to the viscous coating of the effect pigments, resulting in a lower separation and overall better processing. US Pat. No. 6,325,846 describes the advantageous use of aluminum oxide as an additive to silane-coated platelet-shaped pigments with regard to less buildup on the

Electrodes and overall better processing.

However, it has been found that the abovementioned solutions are not always applicable in practice. Thus, it was found that the coatings of WO 98/46682 preferentially peel off during the firing of the powder coating layer and then influence the mechanical properties on the paint surface, the abrasion stability of the paint layers in particular being adversely affected.

There is therefore still a need for methods for improving electrostatic powder coatings. It has now been found that the use of particles according to the invention in electrostatic coating processes enables better processing of powder coatings.

The present invention thus relates to the use of particles comprising a substrate and a surface or near-surface SiO ₂ layer or a surface or near-surface layer containing SiO ₂ particles embedded in a matrix in electrostatic coating processes, wherein the surface or near-surface layer has at least 2.5 wt. % SiO ₂ based on total weight of the particles.

Another object of the invention are such particles per se. Surprisingly, it has now been found that the particles according to the invention, preferably pigments, in particular effect pigments such as pearlescent pigments, can be easily fluidized triboelectrically and then applied electrostatically to organic powders or powder mixtures.

Also, the separation of particles, in particular of pigment particles and plastic powder particles due to different charging and particle parameters has been significantly reduced. Pigments which contain a near-surface SiO ₂ content of at least 2.5% by weight of SiO _2, based on the total weight of the particles, can be applied as a superficial layer to a non-baked powder coating layer, where they are used directly as sole or in admixture with powder coatings in almost any of them Ratio of low to high concentration, but preferably in greatly increased concentrations of 6 to 100 wt .-%, preferably 10 to 80 wt .-%, are applied as hochpigmentierte layer.

The particles according to the invention comprise a substrate and a surface or near-surface SiO ₂ layer or a surface or near-surface layer containing SiO ₂ particles embedded in a matrix, wherein the surface or near-surface layer comprises at least 2.5% by weight of SiO 2, based on the total weight of the particles , The surface or near-surface layer preferably contains 2.5 to 5% by weight, in particular 3 to 5% by weight, of S1O _2, based on the total weight of the particles.

The SiO ₂ layer according to the invention may contain in addition to SiO ₂ and hydroxides and / or oxide hydrates of silicon. Particles containing the surface or near-surface SiO ₂ layer or the surface or near-surface layer containing the SiO ₂ particles embedded in a matrix as the outer layer are particularly suitable for use in electrostatic coating processes.

In particular, particles containing an outer SiO ₂ layer may preferably be used in electrostatic coating processes.

In one embodiment, the surface or near-surface layer essential to the invention comprises SiO ₂ particles embedded in a matrix. The SiO ₂ particles are enveloped by the matrix and / or immobilized in the matrix. It is preferably an organic-inorganic hybrid layer which consists of an organic matrix and SiO ₂ particles.

The matrix may consist of one or more polymeric substances. Preferred examples of these are polyorganosiloxanes or polymers, preferably thermoplastic polymers. The matrix preferably contains amino groups. Particular preference is given to amino-containing polyorganosiloxanes and / or amino-containing polymers.

The immobilization of the SiO ₂ particles is preferably carried out in polyorganosiloxanes by using reactive silanes. Examples of suitable silanes are alkylsilanes, monoamino and diaminosilanes, methacrylsilanes, epoxysilanes, and mixtures of two or more silanes. Due to the better charge behavior, the use of amino-functional silanes is preferred. Particular preference is given to monofunctional silanes having terminal amino groups. However, it is also an encapsulation using hard, largely insoluble, but thermoplastic polymeric materials (such as polyamides, polyepoxides, polyolefins, polyglycols, polymeric surfactants) possible. As pure substances in particular polyester and polyacrylates are preferred. Preference is also given to using combinations of one or more polyorganosiloxanes, in particular of polyorganosiloxanes containing amino groups, and thermoplastic polymers, in particular of amino-containing thermoplastic polymers. In combinations of polyorganosiloxanes with thermoplastic polymers, a variant in which an aminosilane is used as crosslinking agent for the thermoplastic polymer sheath (eg polyepoxide) is particularly preferred.

The thermoplastic polymers used for coating are preferably selected so that they are solid on the particle at room temperature. As a result, they differ substantially from the viscous, adhesive coatings specified in WO 98/46682. It has been found that the coatings according to the prior art preferentially detach during the firing of the powder coating layer and then influence the mechanical properties of the paint surface, in particular the abrasion stability of the paint layers being adversely affected. If, however, the occupation according to the invention is selected with amino-containing polyorganosiloxanes and / or with hard thermoplastic polymers, the detachment is prevented or largely avoided.

The SiO ₂ particles immobilized in the matrix are preferably nanoparticles. For the purposes of the present invention, nanoparticles are to be understood as meaning particles which preferably have an average primary particle size, determined by means of a Malvern ZETASIZER (dynamic light scattering) or transmission electron microscope, of 3 to 500 nm, in particular of 5 to 200 nm and very particularly preferably of 10 to 120 nm. In particular likewise preferred embodiments of the present invention, the distribution of the Particle sizes narrow, ie the fluctuation range is less than 100% of the average, more preferably at most 50% of the average value (after particle distribution function, determined by dynamic light scattering).

The particles essential to the invention may be fillers and / or pigments, preferably pigments, in particular effect pigments. In this way, the advantage of separation avoidance with further advantages, such as e.g. Combine color or shine.

Suitable substrates for the particles according to the invention are all types of materials. The shape of the substrates is not critical and can be expertly adapted to the particular circumstances. As substrates are preferably platelet-shaped

Substrates, for example, platelet-shaped TiO ₂ , synthetic or natural mica, glass flakes, aluminum oxide flakes, metal flakes, platelet-shaped SiO ₂ or platelet-shaped iron oxide or flaky graphite. The metal platelets may consist inter alia of the elemental metals, such as aluminum, silver or titanium, but also of mixtures or alloys, such as bronze or steel, preferably they are made of aluminum and / or titanium. The metal platelets can be passivated by appropriate treatment. Preferably, synthetic or natural mica, platelet-shaped SiO ₂ , aluminum oxide platelets or glass platelets are used as finely divided substrates. The thickness of the substrates is usually between 0.005 and 5 microns, in particular between 0.1 and 4.5 microns. The expansion in the length or width of the substrates according to the invention is usually between 1 and 250 μm, preferably between 2 and 200 μm and in particular between 2 and 100 μm. Platelet-shaped substrates according to this invention, in particular when the particles according to the invention are pigments, have the advantage that special effects can be achieved with these materials. Thus, under the surface or near-surface layer essential to the invention, interference systems can be formed on the platelet-shaped layer

Substrates may be applied, which show a special gloss, great color strength or angle-dependent colors. This is of particular interest in the use of paints, especially car paints. Platelet-shaped pigments are accordingly particularly preferred as particles according to the invention.

Particular preference is given to effect pigments based on glass flakes or aluminum oxide platelets. The final SiO ₂ layer ensures a corresponding direct applicability of the pigments. In one embodiment of the invention are preferably metallic substrates such. As aluminum used.

A preferred embodiment of the present invention provides for the use of pure flak materials such as mica, Al ₂ O ₃ flakes, graphite flakes, glass flakes or SiO ₂ flakes, or any inorganic flake particles, in particular Al ₂ O ₃ flakes, glass flakes or SiO ₂ . Flakes, particularly preferably of Al ₂ O ₃ flakes and glass flakes, in particular of glass flakes, in electrostatic coating processes, wherein the flake materials directly with a surface or near-surface SiO ₂ layer or embedded in a matrix SiO ₂ - containing surface or near the surface Layer are occupied. This may result in functional highly transparent, organic inorganic hybrid layers, which are characterized by the special mechanical hardness; special abrasion resistance, flame retardancy and heat resistance, as well as the special spectral properties in the area of non-visible electromagnetic radiation that can distinguish UV / IR absorption / reflection as functional layers. In particular, a coating containing graphite flakes may have good IR reflection properties.

In a further preferred embodiment, the substrates according to the invention can be coated with one or more transparent, semitransparent and / or opaque layers comprising metal oxides, metal oxide hydrates, metal suboxides, metals, metal fluorides, metal nitrides, metal oxynitrides or mixtures of these materials. The metal oxide, metal oxide hydrate, metal suboxide, metal, metal fluoride,

Metal nitride, metal oxynitride layers or mixtures thereof may be low (refractive index <1.8) or high refractive index (refractive index> 1.8). These layers preferably function as a coloring system, whereby the color impression can be caused by both absorption and interference. Suitable metal oxides and metal oxide hydrates are all metal oxides or metal oxide hydrates known to the person skilled in the art, such as, for example, Silica, hydrated silica, iron oxide, tin oxide, cerium oxide, zinc oxide, chromium oxide, titanium oxide, especially titanium dioxide, titanium oxide hydrate and mixtures thereof, e.g. Ilmenite or pseudobrookite. As metal suboxides, for example, the titanium suboxides can be used. Suitable metals are e.g. Chromium, aluminum, nickel, silver, gold, titanium, copper or alloys, for example, magnesium fluoride is suitable as the metal fluoride. As metal nitrides or metal oxynitrides, for example, the nitrides or oxynitrides of the metals titanium, zirconium and / or tantalum can be used. To be favoured

Metal oxide, metal, metal fluoride and / or Metallloxidhydratschichten and most preferably applied metal oxide and / or metal oxide hydrate layers on the substrates. Furthermore, multi-layer constructions of high-refractive and low-refractive index metal oxide, metal oxide hydrate, metal or metal fluoride layers can also be present, alternating preferably high and low refractive index layers. Especially Preference is given to layer packages of a high and a low-refractive layer, wherein one or more of these layer packages can be applied to the substrates. The order of the high- and low-index layers can be adapted to the substrates in order to include the substrates in the multi-layer structure. In another embodiment, the metal oxide, metal oxide hydrate, metal suboxide, metal, metal fluoride, metal nitride, metal oxynitride layers may be spiked or doped with colorants or other elements. Suitable colorants or other elements are, for example, organic or inorganic color pigments such as colored metal oxides, eg magnetite, chromium oxide or color pigments such as Berlin Blue, ultramarine, bismuth vanadate, thenard blue, or organic color pigments such as indigo, azo pigments, phthalocyanines or carmine red or elements such as yttrium or antimony. The application of one or more transparent, semi-transparent and / or opaque layers of the above-mentioned materials to the substrates is preferred in the present invention. Pigments, in particular platelet-shaped, containing these layers show a high color diversity with respect to their body color and in many cases can show an angle-dependent change of color (color flop) due to interference. The combination of these color properties with the outer nanoparticle-containing layer according to the invention gives rise to particular advantages in the applications, in particular during incorporation into powder coatings. Thus, in addition to the improved processability and reduced separation of the powder coating components in the electrostatic coating, a large freedom in the color design of the powder coatings is created, which is not possible with paints and pigments from the prior art alone. The user can choose a desired color effect and is not dependent on the addition of further, improving the processability of powder coatings materials. The last layer of a previously described coating on the substrate, to which the outer SiO ₂ layer essential to the invention is then applied, is a high-index metal oxide in a preferred embodiment. This final layer may be in addition to the layer packets above or part of a layer package, and for example of TiO _2, titanium suboxides, Fe ₂ θ3, SnO _2, ZnO, Ce ₂ θ _3, CoO, CO ₃ O 4, V ₂ O _5, Cr ₂ θ ₃ and / or mixtures thereof, such as ilmenite or pseudobrookite exist. TiO ₂ is particularly preferred.

Examples and embodiments of the abovementioned material combinations and layer constructions can be found by way of example in the literature customary for effect pigments, such as, for example, US Pat. in Research Disclosures RD 471001 and RD 472005, the disclosures of which are hereby incorporated by reference.

The thickness of the metal oxide, metal oxide hydrate, metal suboxide, metal, metal fluoride, metal nitride, metal oxynitride layers or a mixture thereof is usually 3 to 300 nm and in the case of metal oxide, metal oxide hydrate, metal suboxide, metal fluoride, metal nitride , Metalloxy- nitride layers or a mixture thereof preferably 20 to 200 nm. The thickness of the metal layers is preferably 4 to 50 nm.

The coating of the substrates with one or more transparent, semitransparent and / or opaque layers containing metal oxides, metal oxide hydrates, metal suboxides, metals, metal fluorides, metal nitrides, metal oxynitrides or mixtures of these materials can be carried out in any manner known to those skilled in the art, for example wet-chemically, by means of sol-gel , CVD and / or PVD methods. Preferably, a coating with these materials is wet-chemically, in the case of metals also preferably by CVD method. At the wet-chemical

Application are all organic or inorganic compounds of the suitable metals, in particular the halides, nitrates, sulfates, carbonates, phosphates or oxalates, preferably the corresponding halides are used. Such methods are described, for example, in DE 14 67 468, DE 19 59 988, DE 20 09 566, DE 22 14 545, DE 22 15 191, DE 22 44 298, DE 23 13 331, DE 25 22 572, DE 31 37 808 .

DE 31 37 809, DE 31 51 343, DE 31 51 354, DE 31 51 355, DE 32 11 602 or DE 32 35 017. The optimization of the application conditions is in the field of expert know-how. Usually, in the case of wet coating, the substrates are suspended in water and admixed with one or more hydrolyzable metal salts at a pH which is suitable for the hydrolysis and which is chosen so that the metal oxides or metal oxide hydrates are precipitated directly on the platelets, without it Precipitation comes. The pH is usually kept constant by simultaneous addition of a base or acid. If desired, the substrates may after

Separation of individual coatings separated, dried and optionally calcined, to then be resuspended for the precipitation of other layers again. In an alternative embodiment, all of the desired transparent, semi-transparent and / or opaque layers may be precipitated and then calcined in total at first, usually at temperatures from 600 to 1500 ⁰ C, preferably at temperatures of 800-1150 ⁰ C.

In principle, all methods known to the person skilled in the art come into consideration for the SiO ₂ coating of the pigments, since the particular electrostatic properties of the pigments depend less on the chosen occupation method than on the actual SiO ₂ content.

According to one method, the substrate particles can be coated in aqueous dispersion at pH 6.5 with an SiO ₂ precursor compound, which forms an SiO ₂ layer upon hydrolyzing. As a SiO ₂ precursor compound In particular, all types of tetraalkoxysilanes, especially tetraethoxy and tetrabutoxysilane, as well as K or Na water glasses are used. The addition can usually within 60 to 90 minutes at preferably 75 ⁰ C. After the preparation and drying at usually 130 to constant weight, several

Calcined hours at preferably 600 - 700 ⁰ C calcined. The calcination temperature and duration must be adapted to the respective substrate.

If the layer according to the invention is a surface or near-surface layer containing SiO ₂ particles embedded in a matrix, then this can be applied in a variety of ways to the substrates. This can be done for example by a nasstechnische precipitation (eg by salting out) or steaming. However, these processes are very energy consuming (eg drying). Therefore, another object of the present invention is a method for producing the particles according to the invention, wherein a substrate, nanoparticles and a matrix-forming material or a precursor of the matrix-forming material preferably at 20 ⁰ C to 200 ⁰ C, in particular at 50 ° C. to 150 ° C, using dynamic mixing processes reacted together and then processed by methods familiar to those skilled in the art. The method according to the invention can be carried out in a simple manner and allows great variability with respect to the precursors and conditions that can be used. It is the person skilled in the art to adapt the optimum configuration of the method according to the invention to the necessary conditions.

Another object of the present invention is a powder coating containing the inventive. The particles can in this case in a concentration range of 0.5 to 100 wt .-%, in particular from 6 to 100 wt .-%, particularly preferably 20 to 40 wt .-%, based on the

Total content of all paint components are used. The powder coatings For example, they may be radiation-curing, physically drying or chemically curing. For the preparation of the powder coatings is a variety of binders, for example based on acrylates, methacrylates, polyesters, polyurethanes, nitrocellulose, ethylcellulose, polyamide, polyvinyl butyrate, phenolic resins, maleic resins, starch or polyvinyl alcohol, amine resins, alkyd resins, epoxy resins, polytetrafluoroethylene, Polyvinylidenfluoriden, polyvinyl chloride or mixtures thereof suitable. Preferred polymeric binders for powder coatings are, for example, polyesters, epoxies, polyurethanes, acrylates or mixtures thereof. The selection of further powder coating constituents is familiar to the person skilled in the art.

The particles according to the invention can also be used advantageously in admixture with organic dyes and / or pigments, such as transparent and opaque white, colored and black pigments, as well as platelet-shaped iron oxides, organic pigments, holographic pigments, LCPs (liquid crystal polymers) and conventional transparent , colored and black luster pigments on the basis of metal oxide-coated platelets based on mica, glass, Fe ₂ θ ₃ , SiO ₂ , etc., can be used. The particles according to the invention can be mixed in any ratio with commercially available pigments and fillers.

As fillers are e.g. natural and synthetic mica, nylon

Powder, pure or filled melanin resins, talcum, glasses, kaolin, oxides or hydroxides of magnesium, calcium, zinc, BiOCl, barium sulfate, calcium sulfate, calcium carbonate, magnesium carbonate, carbon, as well as physical or chemical combinations of these substances.

There are no restrictions on the particle shape of the filler.

It may, for example, be platelet-shaped, spherical or needle-shaped in accordance with the requirements. The preparation of the powder coatings according to the invention is simple and easy to handle. The particles according to the invention are mixed with the powder coating, for example with a paddle or tumble mixer. Particularly suitable is the so-called bonding method in which the powder coating base under nitrogen as inert gas on a

Temperature kapp is heated below the softening point, then the pigment is added and after the mixing process, the powder coating thus prepared is gently cooled. The resulting powder coating is storage stable, i. there is no demixing. If the powder coating according to the invention is applied to the material to be coated, this is done in such a way that the material surface is completely covered with a homogeneous powder coating layer.

The powder coating of the invention can on any materials, such as iron, steel, aluminum, copper, bronze, brass and metal foils but also conductive modified surfaces of glass, ceramic and concrete u. Ä., As well as on non-conductive surfaces such as wood, glass, ceramics, plastics, inorganic building materials or other materials for decorative and / or protective purposes are applied.

Another object of the present invention is therefore a process for coating materials comprising the electrostatic application of particles comprising a substrate and a surface or near-surface SiO ₂ layer in electrostatic coating process, wherein the surface or near-surface SiO ₂ layer at least 2.5 wt % SiO ₂ based on total weight of the particles. According to one embodiment of this method, the particles according to the invention can be applied as a component of a powder coating described above.

In another preferred embodiment of the method, the particles according to the invention can be applied electrostatically directly as a powder.

Electro- or tribostatic coating processes are familiar to the person skilled in the art and are described, for example, in US Pat. in Römpp Lexikon, paints and printing inks, Georg Thieme Verlag, 10th edition 1997, page 185 et seq and page 575ff described.

The use of the particles according to the invention in two-stage electrostatic coating processes has proved to be particularly advantageous, as described in DE 42 38 380.

Another preferred subject matter of the invention is thus a process in which a powder coating is applied electrostatically before application of the particles according to the invention and then a baking step takes place.

But the reverse coating order is possible.

In the direct electrostatic application of the invention

Particles, the particle powder is preferably charged by shaking triboelectrically and filled in the application unit. If a commercially available powder coating gun is used, the powder output is preferably set as low as possible, but the current flow is preferably adjusted to a higher value which is directly matched to the type of powder. is presented. Current strengths of 30-50 μA have proven to be advantageous here.

If the particle powder on a previously applied, unburned

Powder coating layer, which may contain pigments, usually 0 - 6 wt .-%, applied, it is preferably also kept in the application of this first layer, the current flow low, in particular 5 to 20 uA are advantageous here. The method is relatively insensitive to the set voltage. The second layer can also be applied as a highly concentrated layer, whereby the particle content can be increased from the usual DryBIend concentrations from 5% to 6-100%. Preferably, 20-40% are used here. Powder coatings prepared by the above-described bonding method can also be used. However, it is always possible to use further lacquer layers, e.g. Apply clear coat, if desired.

A reverse layer sequence is also possible by first electrostatically applying the particles directly onto the conductive substrate to be coated and then applying a clear or semitransparent powder coating layer. All layers are then finally thermally baked together at higher temperatures.

In particular high-gloss powder coatings, sparkling and / or living depth effects and scratch-resistant, UV-stable and / or weather-stable layers can be obtained with the present invention. In particular, when using pigments based on SiO ₂ flakes, a perfect color pit is obtained. When using pigments based on glass flakes, particularly good pearlescent effects are obtained, in particular on a white basecoat. In general, better effects can be achieved with the particles and processes of the invention than with powder coatings or powder coating processes according to the prior art. In addition, the particles are on the surface and protect the organic binder.

In addition to the preferred substances and compounds mentioned in the description, their use, compositions and processes, further preferred combinations of the articles according to the invention are disclosed in US Pat

Claims disclosed.

The disclosures in the cited references are hereby also expressly incorporated into the disclosure of the present application.

The following examples further illustrate the present invention without limiting the scope of protection. In particular, those in the

Examples described characteristics, properties and advantages of the compounds underlying the examples in question also applicable to other substances and compounds not mentioned in detail, but covered by the scope, unless otherwise stated elsewhere. Incidentally, the invention is embodied in the entire claimed area and is not limited to the examples mentioned here.

Examples: Example 1: Production of SiO ₂ coated particles

A 10% strength by weight dispersion of the particles to be coated in water is adjusted to pH 6.5 and mixed with stirring with 5% by weight of a SiO ₂ precursor compound, which forms an SiO ₂ layer upon hydrolysis while stirring. In particular, all types of tetraalkoxysilanes, in particular tetraethoxy and tetrabutoxysilane, and K or Na water glasses are used as SiO ₂ precursor compounds. The Addition is carried out within 60 to 90 minutes at 75 ⁰ C after the addition is stirred for 60 minutes, filtered, washed with demineralized water and calcined after drying at 130 ⁰ C to constant weight for several hours at 600 - 700 ⁰ C finally. The calcination temperature and duration must be adapted to the respective particle material.

Example 2: Direct electrostatic application of pigments

In a first step, a standard powder coating (Tiger Black Series 59 PN 82170 from Tiger Coatings, Austria) by means of a

Spray gun (Optiselect the company ITW Gema with slot or with

Impact) applied to a carrier (process conditions: Feed max 40;

Flow air 3.2; Volt 40 KV; Current 5 μA).

In a second step, a pigment prepared according to Example 1 is directly by means of a spray gun (Optiselect the company ITW Gema with

Slit nozzle or with impact) on the coated with powder coating carrier applied (process conditions: Feed min = 00; Flow air 5.7 double;

Volt 100 KV; Current 20-40 μA).

Subsequently, the coatings in a convection oven (type UMT 6200 from Thermo, Hanau, Germany, hanging hanging) at

200 ⁰ C baked for 15 minutes.

After baking, a colored layer is obtained, in which the

Pearlescent effect is particularly good.

Example 3: Test of resistance

Mechanical cleaning tests are carried out using an abrasive paste (Crockmeter CM-5 from Atlas). If the particles of the invention are applied according to Example 1 as a 5 wt .-% DryBIend mixture with a commercial polyester powder coating, so results in a slightly increased mechanical resistance to one commercial pigment of the prior art (gray scale 3 vs. 3 - 4 for prior art). If, on the other hand, the particles of the invention according to Example 1 are in a higher concentration (20-30% DryBIend) or applied directly to a pre-applied unbrushed powder coating layer, then no significant visual changes are visible even after 1000 strokes.

Example 4:

Following the procedure described in Example 1 Iriodin ^® 111, Iriodin ^® 6103 Icy White and Color Stream ^® Artic Fire be coated. Sodium silicate glass is used as the SiO ₂ precursor compound. Each 200g of pigment are suspended in 1, 91 VE water and heated to 75 ° C, then 21, 81 g of sodium silicate (dissolved in 220ml DI water) are added. The addition takes place within 180 minutes at 75 ° C. The pH is kept constant by adding HCL (20%). The mixture is then stirred for 15 min. With HCL (20%) is in 40 min. lowered to pH 2 for complete precipitation of the SiO ₂ . The suspension is then washed, filtered, dried at 120 ° C for 16 h in a drying oven and then calcined in a muffle furnace at 850 ⁰ C for 25 min.

The pigments obtained in this way can be fluidized very well and can be applied in high concentrations (> 10% by weight) or neat. The pigment distribution on the sheet thus obtained is very good and it sets a strong pearlescent effect. Colorstream ^® Artic Fire shows a strong color-travel. If, however, the above-mentioned pigments are applied in a high concentration or pure without the SiO ₂ secondary coating, so-called pigment spicers result during application. The pigments are then strongly agglomerated on the surface and after firing are these are not completely embedded in the binder and can still be wiped by hand from the surface.

Claims

claims

1. Use of particles comprising a substrate and a surface or near-surface Siθ ₂ layer in electrostatic coating processes, wherein the surface or near the surface

SiO ₂ layer comprises at least 2.5 wt .-% SiO ₂ based on the total particle weight.

2. Use according to claim 1, characterized in that the substrate is natural or synthetic mica, metal flakes,

Glass flakes, SiO ₂ flakes, Al ₂ O ₃ flakes, TiO ₂ flakes or iron oxide flakes.

3. Use according to one or more of claims 1 to 2, characterized in that the substrate additionally with one or more transparent, semitransparent and / or opaque layers containing metal oxides, metal oxide hydrates, metal suboxides, metals, metal fluorides, metal nitrides, metal oxynitrides or mixtures thereof

Materials coated.

4. Use according to one or more of claims 1 to 3, characterized in that the substrate is coated or uncoated glass flakes, SiO ₂ flakes or Al ₂ O ₃ flakes, in particular uncoated glass flakes comprises.

5. Use according to one or more of claims 1 to 4, characterized in that the surface or near-surface SiO ₂ layer 3 to 5 wt .-% SiO ₂ based on the total weight of

Particles comprises.

6. Powder coating containing particles according to one or more of claims 1 to 5.

7. powder coating according to claim 6, characterized in that the proportion of particles comprising a substrate and a surface or near-surface SiO 2 layer is 10 to 80 wt .-% based on the total weight of the powder coating.

8. A process for coating materials comprising the electrostatic application of particles according to one or more of claims 1 to 5.

9. The method according to claim 8, characterized in that the particles are applied in a powder coating according to one or more of claims 6 to 7.

10. The method according to one or more of claims 8 to 9, characterized in that prior to the electrostatic application of

Particles powder coating is applied electrostatically.

11. Particles comprising a substrate and a surface or near-surface SiO ₂ layer, wherein the surface or near-surface near SiO ₂ layer comprises at least 2.5 wt .-% SiO ₂ based on the total weight of the particles.

12. Particles according to claim 11, characterized in that the substrate is additionally coated with one or more transparent, semitransparent and / or opaque layers comprising metal oxides, metal oxide hydrates, metal suboxides, metals, metal fluorides, metal nitrides, metal oxynitrides or mixtures of these materials.

13. Particles according to one or more of claims 11 to 12, characterized in that the substrate comprises natural or synthetic mica, metal flakes, glass flakes, SiO ₂ flakes, Al ₂ O ₃ flakes, TiO ₂ flakes or iron oxide flakes.

14. Particles according to one or more of claims 11 to 13, characterized in that the substrate comprises coated or uncoated glass flakes, SiO ₂ flakes or Al ₂ O ₃ flakes comprises.

15. Particles comprising a substrate and a surface or near-surface SiO ₂ layer wherein the surface or near-surface SiO ₂ layer comprises 3 to 5 wt .-% SiO ₂ based on the total weight of the particles and the substrate uncoated glass flakes, SiO ₂ platelets or AI ₂ O ₃ platelets.