Al2O3 sheet

Abstract

The invention relates to pearlescent pigments based on defined Al2O3 flakes having an excellent fl ip flotage effect, and to the use thereof in paints, industrial coatings, automotive coatings, printing inks, cosmetic formulations and in particular as transparent substrates for effect pigments.

Description

Technical Field

[0001] The present invention relates to defined Al 2 O 3 flakes and pearlescent pigments based on defined Al 2 O 3 flakes having an excellent flip flop effect, and their use in paints, industrial coatings, automotive coatings, printing inks, cosmetic formulations and especially as a transparent substrate for effect pigments. Background Art

[0002] By using pearlescent pigments based on natural or synthetic transparent flakes such as mica, it is possible to achieve a pearlescent gloss, a metallic luster, a color flop or a multicolor effect.

[0003] Key factors for a substrate suitable as a matrix substrate for effect pigments are particle size, shape, surface properties, refractive index, etc. Since large and small particles have different proportions of reflection and transmission of light on the particle surface, the uniformity of particle size is crucial for the bright and uniform color of the final effect pigment. In addition, the particle size greatly affects the coloring of the pearlescent pigment because it is closely related to the wavelength of light. That is, the smaller the particle size, the larger the surface area, thereby increasing the coloring and enhancing the reflectivity, and providing a more vivid color. However, it is very difficult to apply a coating such as a metal layer or a metal oxide layer on the surface of Al 2 O 3 flakes because the coating is uneven and thereby results in a reduction in the aspect ratio, which then reduces the effect of light interference, thus deteriorating the gloss of the resulting pearlescent color.

[0004] By using alumina flakes having precisely defined dimensions, particle size and thickness distribution, it is possible to increase the alumina flakes having the properties of the alumina flakes themselves and the properties of the effect pigments based on alumina flakes. In particular, the optical properties of the alumina flakes and the effect pigments based on alumina flakes can be influenced by changing the particle size distribution.

[0005] In the literature, alumina flakes having different sizes and thicknesses are well known.

[0006] α-Al in the form of hexagonal flakes having a particle size greater than 10 μm and an aspect ratio (particle size / thickness) of 5 - 10 2 O 3 is known from Japanese Patent Publication No. 111239 / 1982.

[0007] Japanese Patent Publication No. 72572 / 1991 discloses α-Al in the form of flakes having an average particle size of 0.5 - 3 μm 2 O3 .

[0008] Japanese Patent Publication No. JP 39362 / 1992 describes Al in the form of hexagonal platelet particles having a plane perpendicular to the c-axis of the grown platelet 2 O 3 .

[0009] Al consisting of alumina (as the main component) and titanium dioxide (as the minor component) 2 O 3 flakes are disclosed in U.S.5,702,519. Al 2 O 3 flakes have an average particle size of about 5 - 60 μm, a thickness of less than 1 μm and an aspect ratio of > 20.

[0010] Glitter pigments such as pearlescent pigments based on alumina flakes are well known in the literature such as EP 2 799 387, EP 2 799388, WO 2006 / 101306, WO 2008 / 026860 A1, and are sold under the trademarks from Merck KGaA and from CQV are commercially available.

[0011] However, the Al 2 O 3 flakes of the prior art have the disadvantage that they do not have sufficient thinness morphology and the uniformity required for their thickness distribution. SUMMARY OF THE INVENTION

[0012] An object of the present invention is to provide alumina flakes having high smoothness, high and deep gloss and good hiding power, which exhibit excellent angle-dependent color effect when coated with at least one layer (such as a metal oxide layer).

[0013] It has now been found that by using alumina flakes having a precisely defined particle size and thickness distribution, alumina flakes themselves and pearlescent pigments based on very thin alumina flakes having excellent angle-dependent color effect can be obtained.

[0014] In particular, the optical properties of alumina flakes and effect pigments based on alumina flakes are affected by the particle thickness distribution of the alumina flakes.

[0015] Surprisingly, it has now been found that such alumina flakes exhibit improved optical properties and high physical and chemical stability: having D 50An alumina flake having an average particle size of 14 - 25 μm, a proportion of alumina flakes with a particle thickness of 40 - 130 nm being greater than 40%, is very thin and transparent. The effect pigment based on these transparent alumina flakes exhibits a high and deep gloss together with excellent flip flop.

[0016] Compared with the prior art, the coated Al 2 O 3 flakes according to the present invention particularly exhibit increased chroma, higher gloss, lower haze and excellent smoothness, and at the same time have high chemical stability and high smoothness due to smaller particle size.

[0017] The alumina flakes according to the present invention are particularly used as a substrate for effect pigments, especially for use in industrial applications, plastics, automotive coatings (including refinishes) and cosmetics. Therefore, they can also be used in all formulations where coated or uncoated alumina flakes are normally employed, such as, for example, in inks, coatings, preferably automotive coatings, plastics, cosmetic formulations, and as a substrate for effect pigments. Description of the Drawings

[0018] Figure 1 Shows the L * value measured at 15° with a spectrophotometer BYK - mac i.

[0019] The Al 2 O 3 flakes of the present invention have a particle size distribution characterized by a Gaussian distribution, where the volume size proportion distribution is as follows:

[0020] - D 50 is in the range of 14 - 25 μm, preferably 14 - 22 μm;

[0021] - D 90 is in the range of 25 - 40 μm, preferably 25 - 35 μm.

[0022] In a preferred embodiment, the D 10 value of the alumina flakes according to the present invention is < 9.5, preferably ≤ 9.0.

[0023] In a preferred embodiment, the D 10 value is < 9.5, D 50 is 14 - 25 μm, preferably 14 - 22 μm and D 90 is 25 - 35 μm.

[0024] In this patent application, the D 10 , D 50 and D90 。

[0025] The particle size distribution D 50 is also referred to as the median diameter or median of the particle size distribution, which is the particle size value at 50% in the cumulative distribution and is one of the important parameters characterizing the particle size of the Al 2 O 3 flake.

[0026] Accordingly, the D 90 value indicates the maximum longitudinal dimension of the Al 2 O 3 flake, as redetermined by laser granulometry in the form of a spherical equivalent, such that in the entirety of all Al 2 O 3 particles, at most 90% of the particles reach or are below this value.

[0027] The D 10 value indicates the value of the longitudinal dimension of the Al 2 O 3 flake, as determined by laser granulometry in the form of a spherical equivalent, such that in the entirety of all Al 2 O 3 flakes, at most 10% of the flakes reach or are below this value.

[0028] In a preferred embodiment, the Al 2 O 3 flakes according to the invention have a standard deviation of the thickness distribution of less than 100, preferably less than 70 and in particular less than 50.

[0029] In this patent application, the average thickness is determined based on the cured paint film in which the Al 2 O 3 flakes are oriented substantially parallel to the substrate. For this purpose, the cross-section of the cured paint film is examined under a scanning electron microscope (SEM), and the thicknesses of 100 Al 2 O 3 flakes are determined and the statistical average is taken.

[0030] The desired dimensions and thickness distribution can be obtained by suitable classification of the flakes, such as by screening through selected sieves and the like.

[0031] The Al 2 O 3 flakes according to the invention have a proportion of greater than 40% of Al 2 O 3 flakes with a thickness of 40 - 130 nm.

[0032] The Al 2 O 3The flakes preferably have an aspect ratio (diameter / thickness ratio) of 70 - 300, in particular 120 - 250.

[0033] In a preferred embodiment, the Al 2 O 3 flakes of the present invention are α - Al 2 O 3 flakes.

[0034] Al 2 O 3 The AlO flakes can be prepared by methods known per se, as described in the literature.

[0035] In a preferred embodiment, the Al 2 O 3 flakes are prepared starting from an aqueous solution of an aluminum salt by precipitation with an aqueous solution of an alkali metal carbonate. An alkali metal salt such as sodium sulfate or potassium sulfate and phosphoric acid or a phosphate, and optionally at least one dopant such as titanium, zirconium, silicon dioxide, indium, tin, zinc, tungsten, molybdenum or indium compounds are added to the starting solution. After the precipitation step, drying (evaporation, dehydration by heating) and molten salt treatment are carried out, including the following steps:

[0036] (1) Prepare an aqueous solution or paste of at least one water - soluble and / or insoluble aluminum salt,

[0037] (2) Add an alkaline solution to the aluminum salt solution to precipitate aluminum hydroxide particles, and add a phosphorus compound and optionally at least one dopant to the aqueous solution before, during or after the precipitation,

[0038] (3) Evaporate the water, and then dry the precipitate product of step (2) to form a dry form containing alumina particles and alkali metal salts,

[0039] (4) Calcinate the dry form obtained in step (3) preferably at a temperature of 900 °C - 1400 °C for 0.5 - 10 h, preferably 1 - 6 h to obtain Al 2 O 3 flakes in a molten salt,

[0040] (5) Remove the water - soluble part of the calcined material obtained in step (4),

[0041] (6) Adjust the particle size and thickness, for example by sieving, grinding and / or sedimentation.

[0042] Examples of suitable aluminum salts are aluminum sulfate, aluminum chloride, aluminum nitrate, polyaluminum chloride, aluminum hydroxide, boehmite, basic aluminum sulfate and combinations thereof.

[0043] Examples of suitable alkali metal salts acting as mineralizers include sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, sodium chloride and potassium chloride.

[0044] The phosphorus compound is preferably selected from phosphoric acid, phosphate, pyrophosphoric acid, sodium phosphate, diammonium hydrogen phosphate, and potassium phosphate. The amount of the one or more phosphorus compounds is preferably 0.05 wt.% - 2 wt.% based on the alumina flakes.

[0045] Preferred examples of the pH controller for precipitation are ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and combinations thereof.

[0046] To control the particle size, thickness, optical properties, and / or surface topography, it may be helpful to add one or more dopants in an amount of 0.01 wt.% - 5 wt.% based on the Al 2 O 3 flakes.

[0047] The dopants are preferably selected from the group of compounds consisting of TiO 2 、ZrO 2 、SiO 2 、In 2 O 3 、SnO 2 、WO 3 、MoO 3 、ZnO, and combinations thereof.

[0048] The Al 2 O 3 flakes according to the present invention are highly suitable as a substrate in the preparation of effect pigments. For this purpose, they are preferably coated with at least one high refractive index layer, such as the following layers: metal oxides, such as, for example, TiO 2 、ZrO 2 、SnO 2 、ZnO、Ce 2 O 3 、Fe 2 O 3 、Fe 3 O 4 、FeTiO 5 、Cr 2 O 3 、CoO、Co 3 O 4 、VO 2 、V 2 O 3 、NiO, and also titanium lower oxides (partially reduced TiO 2 having an oxidation state of <4 to 2, such as lower oxides Ti 3 O 5 、Ti 2 O 3, TiO), titanium oxynitride, FeO(OH), a thin semi-transparent metal layer (e.g., containing Al, Fe, Cr, Ag, Au, Pt, or Pd), or a combination thereof. TiO 2 The TiO layer can be in a rutile-modified or anatase-modified form. Generally, when TiO 2 is in a rutile-modified form, the highest quality and gloss are obtained, and at the same time, the most stable effect pigment is obtained. To obtain a rutile modification, additives capable of guiding TiO 2 into a rutile modification can be used. Available rutile guides are disclosed in U.S. 4,038,099 and U.S. 5,433,779, as well as EP 0271767. A preferred rutile guide is SnO 2 .

[0049] Based on Al 2 O 3 The preferred effect pigments of the flakes are coated with one or more layers of metal oxides, preferably only with one metal oxide layer, especially coated with TiO 2 , Fe 2 O 3 , Fe 3 O 4 , SnO 2 , ZrO 2 or Cr 2 O 3 . Particularly preferred are Al 2 O 2 flakes coated with TiO 3 or Fe 2 O 3 and their mixtures.

[0050] The thickness of each high refractive index layer depends on the desired interference color. The thickness of each layer on the surface of the Al 2 O 3 flakes is preferably 20 - 400 nm, preferably 30 - 300 nm, especially 30 - 200 nm.

[0051] The number of layers on the surface of the Al 2 O 3 flakes is preferably one or two layers, or three, four, five, six, or seven layers.

[0052] In particular, the interference encapsulation composed of high refractive index and low refractive index layers on the surface of the Al 2 O 3 flakes results in the effect pigment having increased gloss and further increased interference colors or excellent angle-dependent color change effects.

[0053] Suitable colorless low refractive index materials for coating are preferably metal oxides or corresponding oxide hydrates, such as, for example, SiO 2 , Al 2 O 3 , AlO(OH), B 2 O 3 , compounds such as MgF 2 , or mixtures of said metal oxides.

[0054] In the case of multiple layers applied to the surface of Al 2 O 3 flakes, the interference system is in particular a TiO 2 -SiO 2 -TiO 2 layer sequence.

[0055] In addition, the effect pigments according to the invention can also have a translucent metal layer as the outer layer. This type of coating is known, for example, from DE 3825702 A1. The metal layer is preferably a chromium layer or an aluminum layer with a layer thickness of 5 - 25 nm.

[0056] Al 2 O 3 flakes can also be coated with one or more layers of a metal or metal alloy selected from, for example, chromium, nickel, silver, bismuth, copper, tin or Hastelloy. Al 2 O 3 flakes coated with metal sulfides are coated with sulfides of, for example, tungsten, molybdenum, cerium, lanthanum or rare earth elements.

[0057] In addition, the effect pigments based on Al 2 O 3 flakes can finally be coated with an organic dye as a top coat, preferably coated with Prussian blue or carmine.

[0058] Particularly preferred effect pigments based on Al 2 O 3 flakes according to the invention have one or more of the following layer sequences:

[0059] Al 2 O 3 flakes + TiO 2

[0060] Al 2 O 3 flakes + TiO 2 / Fe 2 O 3

[0061] Al 2 O 3 flakes + Fe2 O 3

[0062] Al 2 O 3 Thin slice + TiO 2 + Fe 2 O 3

[0063] Al 2 O 3 Thin slice + TiO 2 + Fe 3 O 4

[0064] Al 2 O 3 Thin slice + TiO 2 + SiO 2 + TiO 2

[0065] Al 2 O 3 Thin slice + Fe 2 O 3 + SiO 2 + TiO 2

[0066] Al 2 O 3 Thin slice + TiO 2 / Fe 2 O 3 + SiO 2 + TiO 2

[0067] Al 2 O 3 Thin slice + TiO 2 + SiO 2 + TiO 2 / Fe 2 O 3

[0068] Al 2 O 3 Thin slice + TiO 2 + SiO 2

[0069] Al 2 O 3 Thin slice + TiO 2 + SiO 2 / Al 2 O 3

[0070] Al 2 O3 Flake + TiO 2 + Al 2 O 3

[0071] Al 2 O 3 Flake + SnO 2

[0072] Al 2 O 3 Flake + SnO 2 + TiO 2

[0073] Al 2 O 3 Flake + SnO 2 + Fe 2 O 3

[0074] Al 2 O 3 Flake + SiO 2

[0075] Al 2 O 3 Flake + SiO 2 + TiO 2

[0076] Al 2 O 3 Flake + SiO 2 + TiO 2 / Fe 2 O 3

[0077] Al 2 O 3 Flake + SiO 2 + Fe 2 O 3

[0078] Al 2 O 3 Flake + SiO 2 + TiO 2 + Fe 2 O 3

[0079] Al 2 O 3 Flake + SiO 2 + TiO 2 + Fe 3 O 4

[0080] Al 2O 3 Flake + SiO 2 + TiO 2 + SiO 2 + TiO 2

[0081] Al 2 O 3 Flake + SiO 2 + Fe 2 O 3 + SiO 2 + TiO 2

[0082] Al 2 O 3 Flake + SiO 2 + TiO 2 / Fe 2 O 3 + SiO 2 + TiO 2

[0083] Al 2 O 3 Flake + SiO 2 + TiO 2 + SiO 2 + TiO 2 / Fe 2 O 3

[0084] Al 2 O 3 Flake + SiO 2 + TiO 2 + SiO 2

[0085] Al 2 O 3 Flake + SiO 2 + TiO 2 + SiO 2 / Al 2 O 3

[0086] Al 2 O 3 Flake + SiO 2 + TiO 2 + Al 2 O 3

[0087] Al 2 O 3 Flake + TiO 2 + SnO 2 + TiO2

[0088] Al 2 O 3 Flake + TiO 2 + Prussian blue

[0089] Al 2 O 3 Flake + TiO 2 + Carmine

[0090] Al 2 O 3 Flake + Ag

[0091] One or more TiO in one or more of the preferred embodiments mentioned above 2 layers can be modified in the rutile type or the anatase type. Al mentioned in the preferred embodiments above 2 O 3 flakes can be doped or undoped.

[0092] In this application, the term "coating" or "layer" is considered to mean the complete encapsulation of Al 2 O 3 flakes according to the present invention.

[0093] Based on doped or undoped Al 2 O 3 The effect pigments of the flakes are preferably composed of 40 wt.% - 90 wt.% of Al based on the total pigments 2 O 3 flakes and 10 wt.% - 60 wt.% of the coating.

[0094] Al 2 O 3 The flakes can be coated by wet chemical coating, by CVD or PVD processes.

[0095] Al with one or more layers, preferably one or more metal oxide layers 2 O 3The coating of the flakes is preferably carried out by wet chemical methods, and wet chemical coating methods developed for the preparation of pearlescent pigments can be used. Methods of this type 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, DE22 44 298, DE 23 13 331, DE 15 22 572, DE 31 37 808, DE 31 37 809, DE 31 51 343, DE31 51 354, DE 31 51 355, DE 32 11 602, DE 32 35 017 or also in other patent documents and other publications known to those skilled in the art.

[0096] In the case of wet coating, the Al 2 O 3 flakes are suspended in water, and one or more hydrolyzable metal salts are added at a pH suitable for hydrolysis, which are selected in such a way that metal oxides or metal oxide hydrates precipitate directly onto the flakes without secondary precipitation. The pH is usually kept constant by metering in alkali and / or acid simultaneously. Subsequently, the pigment is separated out, washed and dried at 50 °C - 150 °C for 6 - 18 h and calcined for 0.5 - 3 h, where the calcination temperature can be optimized with respect to the corresponding coating present. Usually, the calcination temperature is 500 °C - 1000 °C, preferably 600 °C - 900 °C. If desired, the pigment can be separated out, dried and optionally calcined after application of a separate coating, and then resuspended again for application of a further layer.

[0097] The application of the SiO 2 layer to the Al 2 O 3 flakes and / or the already coated Al 2 O 3 flakes is usually carried out by adding a potassium or sodium silicate solution at a suitable pH.

[0098] In addition, the coating can also be carried out by gas phase coating in a fluidized bed reactor, and methods for the corresponding preparation of pearlescent pigments as proposed, for example, in EP 0 045851 and EP 0 106 235 can be used.

[0099] The hue and chroma of the effect pigments based on Al 2 O 3 flakes according to the invention can be varied within very wide limits by different selection of the coating amount or the resulting layer thickness. By approaching the desired color under visual or measurement technology control, fine tuning of a certain hue and / or chroma can be achieved in addition to the purely quantitative selection.

[0100] To increase light, water and climate stability, depending on the application area, it is generally advisable to subject the final pigment to a post-coating or a post-treatment. Suitable post-coatings or post-treatments are, for example, the processes described in 22 15 191C2, DE-A 31 51 354, DE-A32 35 017 or DE-A 33 34 598. This post-coating further increases the chemical and photochemical stability of the pigment or simplifies the handling of the pigment, in particular its incorporation into various media. To improve weather resistance, dispersibility and / or compatibility with the user medium, for example, for Al 2 O 3 or SiO 2 、ZrO 2 or mixtures thereof, functional coatings are possible. In addition, the protective layer can contain organic substances or mixtures thereof applied to the pigment surface. In addition, post-coating with organics, for example with silanes, is possible, as described, for example, in EP 0090259, EP 0634459, WO 99 / 57204, WO 96 / 32446, WO99 / 57204, U.S.5,759,255, U.S.5,571,851, WO 01 / 92425 or in J.J. Ponjeé, Philips Technical Review, Vol. 44, No. 3, pages 81 ff. and P.H. Harding J.C. Berg, J. Adhesion Sci. Technol. Vol. 11, No. 4, pages 471 - 493.

[0101] Preferred metal oxides present in the post-treatment or the protective layer are Al 2 O 3 、SiO 2 、ZrO 2 and / or Ce 2 O 3 。In addition, the protective layer can contain organic components selected in particular from organic coupling agents, organofunctional silanes, amino compounds, organic phosphorus compounds.

[0102] Suitable coupling reagents are, for example, organosilanes, organoaluminates, organotitanates and / or zirconates. The coupling agent is preferably an organosilane.

[0103] Examples of organosilanes are propyltrimethoxysilane, propyltriethoxysilane, isobutyltrimethoxysilane, n-octyltrimethoxysilane, isooctyltrimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane, vinyltrimethoxysilane, preferably n-octyltrimethoxysilane and n-octyltriethoxysilane. Suitable oligomeric alcohol-free organosilane hydrolysis products are in particular products sold by Evonik Industries under the trade name Hydrosil, such as, for example, Hydrosil 2926, Hydrosil 2909, Hydrosil 2907, Hydrosil 2781, Hydrosil 2776, Hydrosil2627. Additionally, low-polyvinylsilanes as well as amino-silane hydrolysis products are suitable as organic coatings. Functionalized organosilanes are, for example, 3-aminopropyltrimethoxysilane (AMMO), 3-methacryloxytrimethoxysilane (DAMO), 3-glycidoxypropyltrimethoxysilane (GLYMO), β-(3,4-epoxy-cyclohexyl)ethyltrimethoxysilane, γ-isocyanatopropyltrimethoxysilane, 1,3-bis(3-glycidoxypropyl)-1,1,3,3-tetramethyldisiloxane, ureidopropyltriethoxysilane, preferably 3-aminopropyltrimethoxysilane, 3-methacryloxytrimethoxysilane, 3-glycidoxypropyl-trimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-isocyanatopropyltrimethoxysilane. Examples of polymer silane systems are described in WO 98 / 13426 and are sold, for example, by Evonik Industries under the trade name Hydrosil. Based on the effect pigment, the amount of the organic coating can be from 0.2% to 5% by weight, preferably from 0.5% to 2% by weight.

[0104] Suitable coupling agents are in particular zirconium aluminates of the following structure:

[0105]

[0106] where

[0107] X represents NH 2 、COOH, -COO - 、hydroxyphenyl, methacrylate, carboxyphenyl, alkyl, mercapto, phenyl, H, vinyl, styryl, melamine, epoxy, aryl or alkyl,

[0108] n represents 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12.

[0109] Other suitable coupling reagents are metal acid esters of the following structure:

[0110] M n (OR) y

[0111] wherein

[0112] M represents Zr, Ti or Al,

[0113] n represents the valence of the metal,

[0114] y is 1, 2 or 3, depending on the valence of the metal,

[0115] R represents

[0116] (i) an alkyl group having 1 to 12 carbon atoms, or an aryl group,

[0117] (ii) an aryl or alkyl group substituted by -N(alkyl) 3 , -NH(alkyl) 2 , -NH 2 (alkyl), -NH 3 , N(aryl) 3 , -NH(aryl) 2 or -NH 2 (aryl), wherein the aryl group may be substituted by halogen, nitro, amino or hydrogen,

[0118] (iii) -C-aryl or C-alkyl.

[0119] Particularly suitable metal acid esters such as acrylate-functional and methacrylamide-functional titanates and methacrylamide-functional zirconates are commercially available.

[0120] In a preferred embodiment, the proportion of the total amount of the effect pigment constituted by the protective layer on the surface of the coated Al 2 O 3 flakes is 2 wt.% to 20 wt.%, preferably 2 wt.% to 10 wt.% and particularly 2 wt.% to 5 wt.%. The composition of the highly preferred protective layer itself contains 0.2 wt.% - 2 wt.% of rare earth metal oxide, preferably Ce 2 O 3 , 0.2 wt.% - 2 wt.% of SiO 2 and 0.2 wt.% - 4 wt.% of Al 2 O 3 and / or ZrO 2and 1 wt.% - 10 wt.% of an organic component. In a preferred embodiment, the organic component is a coupling agent.

[0121] In a particularly preferred embodiment, the protective layer consists of 0.4 wt.% - 1.5 wt.% of Ce 2 O 3 、0.4 wt.% - 1 wt.% of SiO 2 and 0.5 wt.% - 2.5 wt.% of Al 2 O 3 and / or ZrO 2 and 2 wt.% - 5 wt.% of a coupling agent.

[0122] The protective coating on the effect pigments according to the invention is prepared by methods known to the person skilled in the art. In a preferred embodiment, the effect pigments are pretreated by wet chemical coating.

[0123] In a preferred embodiment, the effect pigments according to the invention have a BET surface area (DIN ISO 9277:2003 - 05) of ≤ 10 m 2 / g, preferably ≤ 7 m 2 / g.

[0124] The Al 2 O 3 flakes and the effect pigments based on Al 2 O 3 flakes according to the invention are compatible with a variety of color systems, preferably from the fields of paints, automotive coatings, industrial coatings, and printing inks and cosmetic formulations. For the preparation of printing inks for, for example, gravure printing, flexographic printing, offset printing, and offset over varnishing, a variety of binders, especially water-soluble grades, such as those sold by BASF, Marabu, Sericol, Hartmann, Gebr. Schmidt, Sicpa, Aarberg, Siegberg, GSB - Wahl, Follmann, Ruco, or Coates ScreenINKS GmbH, are suitable. The printing inks can be water-based or solvent-based. In addition, the pigments are also suitable for laser marking of paper and plastics and for applications in the agricultural sector, such as for greenhousesheeting, and for coloring, for example, of tent awnings.

[0125] It goes without saying that for various applications, the Al 2 O 3The platelets and effect pigments can also advantageously be used in blends with organic dyes, organic pigments or other pigments (such as, for example, transparent and opaque white, coloured and black pigments) and with iron oxides, holographic pigments, LCP (liquid crystal polymers) and metal oxide-coated mica and SiO in the form of platelets 2 with conventional transparent, coloured and black lustre pigments etc. of platelets. The Al according to the invention 2 O 3 platelets and the effect pigments based on Al 2 O 3 platelets can be mixed with commercially available pigments and fillers in any ratio.

[0126] Fillers that may be mentioned are, for example, natural and synthetic mica, nylon powder, pure or filled melamine resins, talc, SiO 2 , glass, kaolin, oxides or hydroxides of aluminium, magnesium, calcium or zinc, BiOCl, barium sulphate, calcium sulphate, calcium carbonate, magnesium carbonate, carbon, and physical or chemical combinations of these substances. There is no restriction on the particle shape of the filler. Depending on requirements, it can be, for example, in the form of platelets, spherical or needle-shaped.

[0127] The Al according to the invention 2 O 3 platelets and the effect pigments based on Al 2 O 3 platelets are simple and easy to handle. By simple stirring, the Al 2 O 3 platelets and the effect pigments based on Al 2 O 3 platelets can be incorporated into the system in which they are used. Laborious milling and dispersion of the Al 2 O 3 platelets and effect pigments are not necessary.

[0128] The effect pigments based on Al 2 O 3 platelets according to the invention can be used for colouring coating materials, printing inks, plastics, agricultural films, button paste, for coating seeds, for colouring foodstuffs, coating pharmaceutical or cosmetic formulations. Based on the total solids content of the system, the concentration of the Al 2 O 3 platelets and effect pigments in the system in which they are used for colouring is generally between 0.01% and 50% by weight, preferably between 0.1% and 5% by weight. This concentration generally depends on the specific application.

[0129] Containing the Al according to the invention in an amount of from 0.1% to 50% by weight, in particular from 0.5% to 7% by weight 2 O3 Plastics with flakes and effect pigments are usually noticeable due to specific gloss effects.

[0130] In the paint sector, especially in automotive paints and automotive finishes, according to the invention, Al 2 O 3 flakes and effect pigments are used in an amount of 0.5 wt% - 10 wt%.

[0131] In coating materials, the effect pigments according to the invention have the advantage that the desired color and gloss are obtained through a single-layer coating (single-coat system or as a primer coat in a two-coat system).

[0132] The invention likewise provides a pigment preparation containing coated or uncoated Al 2 O 3 flakes and further effect pigments, binders, and (if desired) additives, said preparation being in the form of substantially solvent-free, free-flowing particles. Such particles contain up to 95 wt% of the effect pigments according to the invention. A pigment preparation in which the Al 2 O 3 flakes and the Al 2 O 3 flake-based effect pigments are pasted together with a binder and with water and / or an organic solvent, with or without additives, and the paste is then dried and formed into a dense particulate form, such as granules, pellets, compacts, masterbatches, or tablets, and is particularly suitable as a precursor for printing inks.

[0133] Thus, the invention also relates to the use of coated Al 2 O 3 flakes or uncoated Al 2 O 3 flakes in formulations from the fields of paints, glaze compositions, coatings, automotive paints, automotive finishes, industrial coatings, paints, powder coatings, printing inks, security printing inks, plastics, ceramic materials, cosmetics. Coated and uncoated Al 2 O 3 flakes can also be used in: glass, paper, paper coatings, toners for electrophotographic printing processes, seeds, greenhouse sheets and tarpaulins, thermally conductive, self-supporting, electrically insulating, flexible sheets for insulation of machines or devices, as absorbers in laser marking of paper and plastics, as absorbers in laser welding of plastics, pigment pastes with water, organic, and / or aqueous solvents, pigment preparations, and dry preparations (such as, for example, granules, e.g., in clear coatings in the industrial and automotive sectors, in sunscreens, as fillers), especially in automotive paints and automotive refinishes, for lidar and radar applications.

[0134] In this patent application, the term "coated alumina" flakes means alumina flakes according to claim 1, which are coated on the surface with one or more layers as mentioned above. The alumina flakes according to claim 1 are suitable as substrates for effect pigments.

[0135] Unless otherwise specified, all percentage data in this application are percentages by weight.

[0136] The following examples are intended to explain the present invention in more detail, but do not limit it. Above and below, all percentages are percentages by weight. Detailed Description of the Invention

[0137] Examples

[0138] Example 1: TiO 2 Coated alumina flakes

[0139] Example 1a: Process for preparing alumina flakes

[0140] By heating to about 75 °C, 223.8 g of aluminum sulfate 18-hydrate (Al 2 (SO 4 ) 3 ·18H 2 O) and 286.3 g of anhydrous sodium sulfate (Na 2 SO 4 ) were dissolved in 1200 ml of deionized water. 0.6 g of a 34.4% titanium oxysulfate (TiOSO 4 ) solution was added to the resulting solution. The resulting solution was designated as aqueous solution (a).

[0141] 0.9 g of trisodium phosphate 12-hydrate (Na 3 PO 4 ·12H 2 O) and 107.9 g of sodium carbonate (Na 2 CO 3 ) were dissolved in 550 ml of deionized water. The resulting solution was designated as aqueous solution (b).

[0142] Over about 15 minutes, with stirring at a constant rate, aqueous solutions (a) and (b) were simultaneously added to 550 ml of deionized water in such a way that the solutes in solution (a) were approximately equal to the solutes in solution (b). Stirring was continued for another 15 minutes.

[0143] The obtained solution was evaporated to dryness. The obtained solid was heated at 1000 °C for 5 hours. Water was added to the heat-treated product to dissolve the free sulfate. The insoluble solid was filtered off, washed with water, and finally dried. Thus, the desired flaky alumina was obtained, which had an average particle size of 14.3 μm and 89% of the flaky alumina had a particle thickness of 40 - 130 nm.

[0144] Example 1b: TiO on the alumina flakes 2 Coating process

[0145] 20 g of the alumina flakes of Example 1a were suspended in 400 ml of deionized water. To the obtained suspension (maintained at about 65 °C) was added a solution containing 125 g of TiCl 4 / liter. At the same time, 10% NaOH solution was added to maintain the pH at 2.1. When the obtained product showed a silver color, the addition of TiCl 4 solution was stopped. The suspended solid was filtered off, washed with water, and dried. Finally, the dried solid was calcined at 850 °C for 30 minutes to obtain a whitish and slightly shiny pearlescent pigment.

[0146] The obtained effect pigment showed excellent angle-dependent color effect, which was represented by a dynamic index of 6.0.

[0147] Example 1c: Surface treatment

[0148] 100 g of the alumina flakes coated with TiO according to Example 1b 2 were suspended in 1000 ml of deionized water. During 90 min, 100 ml of a water glass solution containing 3.05 g of Na 2 SiO 3 was added to the obtained suspension maintained at about 70 °C and adjusted to pH 7 with 10% HCl. At the same time, 10% HCl solution was added to maintain the pH at 7. Subsequently, during 90 min, 100 ml of a solution containing 6.5 g of aluminum sulfate (Al 2 (SO4) 3 *18H 2A solution of (O) was prepared while maintaining the pH at 7 with 10% NaOH. After raising the pH to 7.5 with 10% NaOH, 1.5 g of 3-aminopropyl-trimethoxysilane (CAS No. 13822-56-5) and 1.5 g of 3-glycidoxypropyl-trimethoxysilane (CAS No. 2530-83-8) were each added to the suspension over a period of 15 min while maintaining the pH at 7.0 with 10% HCl or 10% NaOH. The suspended solids were filtered off, washed with water, dried at 140 °C, and sieved (325 mesh).

[0149] Due to the remaining photoactivity, the surface-treated effect pigments exhibit good moisture resistance.

[0150] Example 1d : Spray panel painting process

[0151] The primer paint for automobiles was prepared according to the following formulation.

[0152]

[0153] * Acrylic resin from Dainippon Ink & Chemicals, Inc.

[0154] ** Melamine resin from Dainippon Ink & Chemicals, Inc.

[0155]

[0156] The above acrylic-melamine resin system (100 pbw) was combined with 20 pbw of the flaky alumina (Example 1a) or pearlescent pigment obtained in Example 1b. The resulting compound was diluted with a diluent such that the resulting paint had a sufficient spraying consistency. (12 - 15 seconds, Ford Cup #4) The paint was applied to the substrate by spraying to form a primer coat.

[0157] The primer coat was further coated with a colorless top transparent coat paint prepared according to the following formulation.

[0158]

[0159] The top coat was exposed to air at 40 °C for 30 minutes and then cured at 135 °C for 30 minutes.

[0160] Example 2: TiO 2 Coated alumina flakes

[0161] The preparation of the alumina flakes was carried out according to Example 1a, but the amount of anhydrous sodium sulfate was 429.4 g. The obtained alumina flakes had an average particle size greater than 15.1 μm, and 93% of the alumina flakes had a particle thickness of 40 - 130 nm.

[0162] TiO on the alumina flakes 2 The coating process was carried out according to Example 1b. The obtained effect pigment showed excellent angle-dependent color effect, which was represented by a dynamic index of 6.6.

[0163] The process of spraying panel paint was carried out according to Example 1d.

[0164] Example 3: TiO 2 Coated alumina flakes

[0165] 1261.7 g of 27% aluminum sulfate solution as Al 2 (SO 4 ) 3 , 512.0 g of sodium sulfate (Na 2 SO 4 ), 415.6 g of potassium sulfate (K 2 SO 4 ) and 6.0 g of 35% zinc sulfate (ZnSO 4 ·7H 2 O) solution were added to a 5 l reactor containing 1200 ml of pure water. A homogeneous mixture solution was obtained by mixing at 65°C. An alkaline solution was prepared by dissolving 318.7 g of sodium carbonate (Na 2 CO 3 ) and 2.7 g of sodium phosphate ((NaPO 3 ) 6 ) in 896.5 ml of distilled water. With stirring, the aluminum sulfate mixture solution was titrated with the alkaline solution at a rate of 20 ml / min to pH 6.8. A gel mixture of boehmite and flux was obtained. Then, the gel mixture was aged at 90°C for 20 hours, distilled under vacuum at 60°C and dried at 110°C for 20 hours.

[0166] The resulting solution was evaporated to dryness. The resulting solid was heated at about 1150°C for 5 hours. Water was added to the heat-treated product to dissolve the free sulfate. The insoluble solid was filtered off, washed with water and finally dried. Thus, the desired flaky alumina was obtained.

[0167] The obtained alumina flakes had an average particle size greater than 16.5 μm, and 45% of the alumina flakes had a particle thickness of 40 - 130 nm.

[0168] TiO on alumina flakes 2 The coating process was carried out according to Example 1b. The obtained effect pigment showed an excellent angle-dependent color effect, which was represented by a dynamic index of 4.3.

[0169] The process of spraying panel paint was carried out according to Example 1d.

[0170] Example 4: TiO 2 Coated alumina flakes

[0171] The alumina flakes were prepared according to Example 1a, but the amount of 35% zinc sulfate (ZnSO 4 ·7H 2 O) solution was 23.9 g.

[0172] The obtained alumina flakes had an average particle size greater than 18.3 μm and 42% of the alumina flakes had a particle thickness of 40 - 130 nm.

[0173] TiO on alumina flakes 2 The coating process was carried out according to Example 1b. The obtained effect pigment showed an excellent angle-dependent color effect, which was represented by a dynamic index of 4.5.

[0174] The process of spraying panel paint was carried out according to Example 1d.

[0175] Example 5: TiO 2 Coated alumina flakes

[0176] A homogeneous mixture solution was prepared by mixing 423.2 g of aluminum sulfate (Al 2 (SO 4 ) 3 ·18H 2 O), 326.8 g of sodium sulfate (Na 2 SO 4 ), 265.3 g of potassium sulfate (K 2 SO 4 ), 3.0 g of 34% zinc sulfate (ZnSO 4 ·7H 2 O) aqueous solution and 1.0 g of 17% stannous sulfate (SnSO 4 ·7H 2 O) aqueous solution in a reactor (5 l) containing 1,200 ml of purified water at 65°C. By adding 204.6 g of sodium carbonate (Na 2 CO 3 ) and 1.7 g of sodium phosphate ((NaPO 3 ) 6) It is dissolved in 568.4 ml of distilled water to prepare an alkaline solution. A gel mixed with boehmite and a flux is prepared by titrating an aluminum sulfate mixture solution (65 °C), while stirring with the alkaline solution at a rate of 25 ml / min to adjust the final pH to 6.8. The mixed gel is aged at 90 °C for 20 hours, vacuum distilled at 60 °C, and dried at 110 °C for 20 hours.

[0177] The obtained solution is evaporated to dryness. The obtained solid is heated at about 1000 °C for 5 hours. Water is added to the heat-treated product to dissolve free sulfate. The insoluble solid is filtered off, washed with water, and finally dried. Thus, the desired flaky alumina is obtained.

[0178] The obtained alumina flakes have an average particle size greater than 16.0 μm, and 52% of the alumina flakes with a particle thickness of 40 - 130 nm.

[0179] TiO on the alumina flakes 2 The coating process is carried out according to Example 1b. The obtained effect pigment shows an excellent angle-dependent color effect, which is represented by a dynamic index of 5.2.

[0180] The process of spraying panel paint is carried out according to Example 1d.

[0181] Example 6: TiO 2 Coated alumina flakes

[0182] Example 6 is prepared according to Example 1a, but the amount of 35% zinc sulfate (ZnSO 4 ·7H 2 O) solution is 23.9 g.

[0183] The obtained alumina flakes have an average particle size greater than 15.5 μm, and 58% of the alumina flakes with a particle thickness of 40 - 130 nm.

[0184] TiO on the alumina flakes 2 The coating process is carried out according to Example 1b. The obtained effect pigment shows an excellent angle-dependent color effect, which is represented by a dynamic index of 5.4.

[0185] The process of spraying panel paint is carried out according to Example 1d.

[0186] Comparative Example 1: TiO 2 Coated alumina flakes

[0187] Dissolve 596.8 g of aluminum sulfate 18 - hydrate and 253.4 g of anhydrous sodium sulfate in 1200 ml of deionized water by heating to about 75°C. Add 1.6 g of a 34.4% titanium oxysulfate solution to the resulting solution. Designate the resulting solution as aqueous solution (a).

[0188] Dissolve 4.9 g of trisodium phosphate 12 - hydrate and 287.7 g of sodium carbonate in 550 ml of deionized water. Designate the resulting solution as aqueous solution (b).

[0189] Over about 15 minutes, with stirring at a constant rate, add aqueous solutions (a) and (b) simultaneously to 500 ml of deionized water in such a way that the solute in solution (a) is approximately equal to the solute in solution (b). Continue stirring for another 15 minutes.

[0190] Evaporate the resulting solution to dryness. Heat the resulting solid at about 1000°C for 5 hours. Add water to the heat - treated product to dissolve free sulfates. Filter off the insoluble solid, wash with water, and finally dry to obtain alumina flakes.

[0191] The obtained alumina flakes have an average particle size greater than 12.2 μm, and 78% of the alumina flakes with a particle thickness of 40 - 130 nm.

[0192] TiO on the alumina flakes 2 The TiO coating process is carried out according to Example 1b. The obtained effect pigment does not show any significant angle - dependent color effect. The dynamic index is only 3.7.

[0193] The process of spraying panel paint is carried out according to Example 1d.

[0194] Comparative Example 2: TiO 2 Coated alumina flakes

[0195] Dissolve 596.8 g of aluminum sulfate 18 - hydrate, 111.4 g of anhydrous sodium sulfate and 177.5 g of potassium sulfate in 1200 ml of deionized water by heating to about 75°C. Add 5.3 g of a 34.4% titanium oxysulfate solution to the resulting solution. Designate the resulting solution as aqueous solution (a).

[0196] Dissolve 2.4 g of trisodium phosphate 12 - hydrate and 287.7 g of sodium carbonate in 550 ml of deionized water. Designate the resulting solution as aqueous solution (b).

[0197] After about 15 minutes, with stirring at a constant rate, the aqueous solutions (a) and (b) were simultaneously added to 500 ml of deionized water in such a way that the solute in solution (a) was approximately equal to the solute in solution (b). Stirring was continued for another 15 minutes.

[0198] The resulting solution was evaporated to dryness. The resulting solid was heated at about 1200 °C for 5 hours. Water was added to the heat-treated product to dissolve the free sulfate. The insoluble solid was filtered off, washed with water, and finally dried to obtain alumina flakes.

[0199] The obtained alumina flakes had an average particle size greater than 19.7 μm and 2% of the alumina flakes had a particle thickness of 40 - 130 nm.

[0200] TiO on the alumina flakes 2 The coating process was carried out according to Example 1b. The obtained effect pigment did not show a significant angle-dependent color effect. The dynamic index was only 3.1.

[0201] The process of spraying panel paint was carried out according to Example 1d.

[0202] Comparative Example 3: TiO 2 Coated alumina flakes

[0203] 223.8 g of aluminum sulfate 18-hydrate and 334.3 g of anhydrous sodium sulfate were dissolved in 1200 ml of deionized water by heating to about 75 °C. The resulting solution was designated as aqueous solution (a).

[0204] 107.9 g of sodium carbonate was dissolved in 550 ml of deionized water. The resulting solution was designated as aqueous solution (b).

[0205] After about 15 minutes, with stirring at a constant rate, the aqueous solutions (a) and (b) were simultaneously added to 500 ml of deionized water in such a way that the solute in solution (a) was approximately equal to the solute in solution (b). Stirring was continued for another 15 minutes.

[0206] The resulting solution was evaporated to dryness. The resulting solid was heated at about 1000 °C for 5 hours. Water was added to the heat-treated product to dissolve the free sulfate. The insoluble solid was filtered off, washed with water, and finally dried to obtain alumina flakes.

[0207] The alumina flakes had an average particle size greater than 13.0 μm and 22% of the alumina flakes had a particle thickness of 40 - 130 nm.

[0208] TiO on the alumina flakes 2The coating process is carried out according to Example 1b. The resulting effect pigment shows little or no angle-dependent color effect. The dynamic index is only 1.9.

[0209] The spraying panel paint process is carried out according to Example 1d.

[0210] Table 1: Color effects of effect pigments according to the examples

[0211]

[0212]

[0213] L * (15°): This value means the brightness measured with BYK-mac i(*). At this angle (15°), this value mainly indicates gloss. The higher the value, the higher the gloss.

[0214] Glitter grade (SG): This value mainly indicates its flash effect. The higher the value, the higher the flash effect. This value is measured with BYK-mac i.

[0215] Dynamic index (FI): This value mainly indicates its angle-dependent color effect. The higher the value, the higher the angle-dependent color effect. This value is measured with BYK-mac i.

[0216] (*)BYK-mac i: A spectrophotometer for measuring the color and effects of metals and pearls. (BYK Additives&Instruments)

[0217] Table 1 shows that the effect pigments based on alumina flakes according to the present invention show higher gloss along with much higher color angle dependence. Compared with the alumina-based pigments of the prior art, the effect pigments based on alumina flakes according to the present invention show a relatively low flash effect, compared to their particle size:

[0218] The effect pigments according to the present invention show a dynamic index > 4, which means the relative change in brightness seen between around the reflection angle and around the depression angle, i.e., the greater the change amount, the greater the dynamic sense (color change with viewing angle).

[0219] The dynamic index measures the change in brightness of a metallic color when it is tilted at all angles in the field of view. When the metallic color is tilted at all angles in the field, its scaled brightness changes.

[0220] Measurement:

[0221] Regarding the particle size D 50 Evaluation

[0222] The D of the alumina flakes is evaluated by using Malvern MS3000 50 .

[0223] Determination of thickness, particle size, and thickness distribution

[0224] Prepare an alumina thin film slurry with a concentration of 0.01 g / l, and drop 0.1 ml of this slurry onto a flat substrate such as a silicon wafer.

[0225] Dry the substrate and cut it into appropriate sizes.

[0226] Set the substrate on the stage of an SEM (scanning electron microscope) at an almost vertical and inclined angle, and determine the thickness of the alumina thin film.

[0227] Measure the thickness of more than 100 alumina thin films for calculating the thickness distribution.

[0228] L * (15°)

[0229] Measure L at 15° using a spectrophotometer BYK-mac i Figure 1 in * value.

[0230] SG value

[0231] This value is calculated by the following formula using the index value measured by BYK-mac i.

[0232]

[0233] Si value = specularity intensity

[0234] Sa value = specularity area

[0235] (The impression of brightness varies depending on the illumination angle. Therefore, BYK-mac i irradiates the sample surface with very bright LEDs at three angles of 15° / 45° / 75°, and takes an image with a vertically arranged CCD chip. Then, in order to calculate this image with luminance parameters, it is analyzed using a luminance level histogram through an image analysis algorithm, and analyzed two-dimensionally to improve the recognition accuracy. The calculated values are represented numerically as the specularity area (Sa value) and specularity intensity (Si value) at each angle.)

[0236] Dynamic index value

[0237] The FI value is calculated by the following formula using the index value measured by BYK-mac i.

[0238]

Claims

1. Al2O3 flakes having an average particle size of 14-25 μm and a particle thickness of 40-130 nm in a proportion greater than 40%.

2. The Al2O3 flake according to claim 1, characterized in that: The Al2O3 flakes are α-alumina flakes.

3. The Al2O3 flake according to claim 1 or 2, characterized in that: The Al2O3 flakes are doped with one or more oxides.

4. Al2O3 flakes according to one or more of claims 1 to 3, characterized in that The doping amount is 0.01 wt % to 5 wt % based on the Al 2 O 3 flakes.

5. Al2O3 flakes according to one or more of claims 1 to 4, characterized in that The Al2O3 flakes are doped with one or more oxides selected from TiO2, ZrO2, SiO2, SnO2, In2O3, ZnO, WO3, MoO3 and combinations thereof.

6. Al2O3 flakes according to one or more of claims 1 to 5, characterized in that The Al2O3 flakes are coated with at least one layer of: -Metal oxides - a mixture of at least two metal oxides -Metal -Metal sulfides -Titanium Suboxide -Titanium Oxynitride -Organic or inorganic dyes -FeO(OH) -SiO2 -Metal alloys -Rare earth compounds or a combination thereof.

7. Al2O3 flakes according to one or more of claims 1 to 6, characterized in that The Al2O3 flakes are coated with at least one layer of a metal oxide or a mixture of at least two metal oxides.

8. Al2O3 flakes according to one or more of claims 1 to 7, characterized in that The metal oxide is selected from the following oxide group: TiO2, Fe2O3, Fe3O4, SiO2, SnO2, Al2O3, ZrO2, CeO2, In2O3 and ZnO or a combination thereof.

9. Al2O3 flakes according to one or more of claims 1 to 8, characterized in that The Al2O3 flakes are coated with the following layer sequence: Al2O3 flakes + TiO2 Al2O3 flakes + TiO2 / Fe2O3 Al2O3 flakes + Fe2O3 Al2O3 flakes+TiO2+Fe2O3 Al2O3 flakes+TiO2+Fe3O4 Al2O3 flakes+TiO2+SiO2+TiO2 Al2O3 flakes+Fe2O3+SiO2+TiO2 Al2O3 flakes+TiO2 / Fe2O3+SiO2+TiO2 Al2O3 flakes+TiO2+SiO2+TiO2 / Fe2O3 Al2O3 flakes+TiO2+SiO2 Al2O3 flakes+TiO2+SiO2 / Al2O3 Al2O3 flakes+TiO2+Al2O3 Al2O3 flakes + SnO2 Al2O3 flakes+SnO2+TiO2 Al2O3 flakes+SnO2+Fe2O3 Al2O3 flakes + SiO2 Al2O3 flakes+SiO2+TiO2 Al2O3 flakes+SiO2+TiO2 / Fe2O3 Al2O3 flakes+SiO2+Fe2O3 Al2O3 flakes+SiO2+TiO2+Fe2O3 Al2O3 flakes+SiO2+TiO2+Fe3O4 Al2O3 flakes+SiO2+TiO2+SiO2+TiO2 Al2O3 flakes+SiO2+Fe2O3+SiO2+TiO2 Al2O3 flakes+SiO2+TiO2 / Fe2O3+SiO2+TiO2 Al2O3 flakes + SiO2 + TiO2 + SiO2 + TiO2 / Fe2O3 Al2O3 flakes+SiO2+TiO2+SiO2 Al2O3 flakes + SiO2 + TiO2 + SiO2 / Al2O3 Al2O3 flakes+SiO2+TiO2+Al2O3 Al2O3 flakes + TiO2 + Prussian blue Al2O3 flakes + TiO2 + carmine.

10. Al2O3 flakes according to one or more of claims 1 to 9, characterized in that The Al2O3 flakes are coated with TiO2 modified in rutile or anatase form.

11. Al2O3 flakes according to one or more of claims 1 to 10, characterized in that The Al2O3 flakes are coated with TiO2 in rutile modification.

12. Al2O3 flakes according to one or more of claims 1 to 11, characterized in that The weight ratio of the Al2O3 flakes to the metal oxide coating is 40:60 to 90:10, based on the total pigment.

13. Al2O3 flakes according to one or more of claims 6 to 12, characterized in that The coated Al2O3 flakes have a dynamic index of ≥4 (measured with a spectrophotometer BYK-mac i).

14. Use of the coated and uncoated Al2O3 flakes according to one or more of claims 1 to 13 as matrix material for effect pigments; in formulations selected from the group consisting of paints, glaze compositions, coatings, automotive coatings, automotive refinishing, industrial coatings, paints, powder coatings, printing inks, security printing inks, plastics, ceramic materials, cosmetics, glass, paper, paper coatings, toners for electrophotographic printing processes, seeds, greenhouse sheets and tarpaulins, thermally conductive, self-supporting, electrically insulating, flexible sheets for insulation of machines or devices; as absorbers in laser marking of paper and plastics, absorbers in laser welding of plastics, pigment pastes with water, organic and / or aqueous solvents; in pigment preparations and dry preparations, lidar and radar applications.

15. Formulation containing the coated or uncoated Al2O3 flakes according to one or more of claims 1 to 13 in an amount of 0.01% to 95% by weight, based on the formulation as a whole.

16. Formulation containing coated or uncoated Al2O3 flakes according to one or more of claims 1 to 13, characterized in that It contains at least one component selected from the group consisting of water, polyols, polar and nonpolar oils, fats, waxes, film formers, polymers, copolymers, surfactants, free radical scavengers, antioxidants, stabilizers, odor enhancers, silicone oils, emulsifiers, solvents, preservatives, thickeners, rheological additives, fragrances, colorants, effect pigments, UV absorbers, surface-active auxiliaries and / or cosmetically active compounds, fillers, binders, pearlescent pigments, color pigments and organic dyes.

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