Al2o3 flakes

Abstract

To provide alumina flakes with high smoothness, high and deep glossiness, and good hiding power which show a superior flip flop effect when coated with at least one layer (for example, a metal oxide layer).SOLUTION: The invention relates to pearlescent pigments with a superior flip flop effect which are based on defined Al2O3 flakes, and to the use thereof in paints, industrial coatings, automotive coatings, printing inks, cosmetic formulations and in particular as transparent substrate for effect pigments.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to specific Al2O3 flakes having a specific Al2O3 flake and nacreous pigment based on specific Al2O3 flakes with an excellent flip-flop effect, and their use in paints, industrial coatings, automotive coatings, printing inks, cosmetic formulations, in particular as a transparent substrate for effect pigments.

Background Art

[0002] By using nacreous pigments based on natural or synthetic transparent flakes such as mica, it is possible to achieve the imparting of nacreous luster, metallic luster, color flop or multicolor effect. Important factors for a substrate suitable as a substrate for effect pigments are particle size, shape, surface characteristics, refractive index, etc. Large particles and small particles have different ratios of light reflection and transmission at the particle surface, so the uniformity of particle size is extremely important for making the final effect pigment have a vivid and uniform color. Also, since the particle size is closely related to the wavelength of light, the particle size greatly affects the coloration of nacreous pigments. That is, the smaller the particle size, the larger the surface area, thereby increasing the coloration, increasing the reflectance, and providing a more vivid color. However, applying a coating such as a metal layer or a metal oxide layer to the surface of Al2O3 flakes is very difficult because the coating is not uniform, resulting in a decrease in the aspect ratio, thereby reducing the effect of light interference and reducing the glossiness of the resulting nacreous color. It has been found that the properties of alumina flakes themselves and the properties of effect pigments based on alumina flakes can be enhanced by using alumina flakes having precisely defined dimensions as well as particle size and thickness distributions. In particular, the optical properties of alumina flakes and effect pigments based on alumina flakes can be affected by changing the particle size distribution. In the literature, alumina flakes having different sizes and thicknesses are well known. Hexagonal flake-shaped α-Al2O3 having a particle diameter larger than 10 μm and an aspect ratio (particle diameter / thickness) of 5 to 10 is known from JP-A-57-111239. JP-A-3-72572 discloses flake-shaped α-Al2O3 having an average particle diameter of 0.5 to 3 μm. JP-A-4-39362 describes Al2O3 in the form of fine plate-like particles of a hexagonal system having a plane perpendicular to the c-axis grown in a plate shape. Al2O3 flakes composed of aluminum oxide (as a main component) and titanium dioxide (as a minor component) are disclosed in U.S. Patent No. 5,702,519. The Al2O3 flakes have an average particle diameter of about 5 to 60 μm, a thickness of less than 1 μm, and an aspect ratio of >20. Glossy pigments such as pearlescent pigments based on alumina flakes are well known in documents such as EP 2799387, EP 2799388, WO 2006 / 101306, WO 2008 / 026860 (A1), etc., and are commercially available under the trademarks Xirallic (registered trademark) from Merck KGaA and Adamas (registered trademark) from CQV. However, the prior art Al2O3 flakes have the drawback of not having a sufficiently thin morphology and the required uniform thickness distribution.

Summary of the Invention

[0003] An object of the present invention is to provide alumina flakes having high smoothness, high and deep gloss, and excellent hiding power, which exhibit an excellent flip-flop effect when coated with at least one layer (for example, a metal oxide layer).

[0004] It has now been found that an alumina flake and a pearlescent pigment based on an ultrathin alumina flake having an excellent flip-flop effect can be obtained by using alumina flakes having a strictly defined particle size and thickness distribution. 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. Surprisingly, it has now been found that extremely thin transparent alumina flakes with an average particle diameter of D 50 = 14 - 25 μm and a fraction of particle thickness of 40 - 130 nm exceeding 40% exhibit improved optical properties as well as high physical and chemical stability. The effect pigments based on the above transparent alumina flakes exhibit high and deep gloss with excellent flip-flop. Compared with the prior art, the coated Al2O3 flakes according to the present invention exhibit, in particular, increased chroma, high gloss, low haze, and excellent finish, as well as high chemical stability and high smoothness due to low granularity. The alumina flakes according to the present invention are used, in particular, as a base material for effect pigments for industrial applications, plastics, automotive coatings including refinishes, and cosmetics. Accordingly, the above alumina flakes can be used in all formulations where coated or uncoated alumina flakes are normally used, for example, in inks, coatings, preferably automotive coatings, plastics, cosmetic formulations, etc., and as a base material for effect pigments.

Brief Description of the Drawings

[0005]

Figure 1

Modes for Carrying Out the Invention

[0006] The Al2O3 flakes of the present invention have a particle size distribution characterized by a Gaussian distribution in which the volume size fractions are distributed as follows: -D 50 is in the range of 14 - 25 μm, preferably 14 - 22 μm, -D 90 is in the range of 25 - 40 μm, preferably 25 - 35 μm. In a preferred embodiment, the D value of the alumina flakes according to the present invention 10 is <9.5, preferably ≦9.0. In a preferred embodiment, the D 10 value is <9.5, and D 50 is 14 to 25 μm, preferably 14 to 22 μm, and D 90 is 25 to 35 μm. In this patent application, the D 10 , D 50 and D 90 of the alumina flakes are evaluated using a Malvern MS3000. The particle size distribution D 50 is also known as the median diameter or the median of the particle size distribution, and is the value of the particle diameter at 50% of the cumulative distribution. It is one of the important parameters characterizing the particle size of the Al2O3 flakes. Correspondingly, the D 90 value is the maximum longitudinal dimension of the Al2O3 flakes determined by laser particle size analysis in the form of sphere equivalents, and represents the value below which 90% of all the Al2O3 particles are sized. The D 10 value is the longitudinal dimension of the Al2O3 flakes determined by laser particle size analysis in the form of sphere equivalents, and represents the value below which 10% of all the Al2O3 flakes are sized. In a preferred embodiment, the Al2O3 flakes according to the present invention have a standard deviation of the thickness distribution of less than 100, preferably less than 70, particularly less than 50. In this patent application, the average thickness is determined based on a cured coating film in which the Al2O3 flakes are oriented substantially parallel to the substrate. For this purpose, the cross-section of the cured coating film is observed with a scanning electron microscope (SEM), the thicknesses of 100 Al2O3 flakes are confirmed, and statistically averaged. The desired particle size and thickness distribution can be obtained by appropriate classification of the flakes, such as by screening through a selected sieve. More than 40% of the Al2O3 flakes according to the present invention have a thickness of 40 to 130. The Al2O3 flakes according to the present invention preferably have an aspect ratio (diameter / thickness ratio) of 70 to 300, particularly 120 to 250. In a preferred embodiment, the Al2O3 flakes of the present invention are α-Al2O3 flakes.

[0007] The Al2O3 flakes can be prepared by methods known per se as described in the literature. In a preferred embodiment, the Al2O3 flakes are prepared by precipitation with an aqueous alkali carbonate solution starting from an aqueous solution of an aluminum salt. An alkali metal salt such as sodium sulfate or potassium sulfate, and phosphoric acid or a phosphate, and optionally at least one dopant, for example titanium, zirconium, silica, indium, tin, zinc, tungsten, molybdenum, or an indium compound, are added to the starting solution. After the precipitation step, drying (dehydration by evaporation, heating), and molten salt treatment are carried out, including the following steps: (1) A step of preparing an aqueous solution or slurry of at least one water-soluble and / or water-insoluble aluminum salt, (2) Adding an alkali solution to the aluminum salt solution to precipitate aluminum hydroxide particles, and adding a phosphorus compound and optionally at least one dopant to the aqueous solution before, during, or after the precipitation, (3) Evaporating water and subsequently drying the precipitation product of step (2) to form a dried product of alumina containing particles and an alkali salt, (4) Calcining the dried product obtained in step (3) at a temperature of preferably 900 to 1400 °C for 0.5 to 10 hours, preferably 1 to 6 hours, to obtain Al2O3 flakes in a molten salt, (5) A step of removing the water-soluble portion of the calcined material obtained in step (4), (6) A step of adjusting the particle size and thickness, for example, by sieving, milling, and / or sedimentation.

[0008] Examples of suitable aluminum salts include aluminum sulfate, aluminum chloride, aluminum nitrate, polyaluminum chloride, aluminum hydroxide, boehmite, basic aluminum sulfate, and combinations thereof. Examples of suitable alkali metal salts that function as mineralizers include sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, sodium chloride, and potassium chloride. The phosphorus compound is preferably selected from phosphoric acid, phosphate, diphosphoric acid, sodium phosphate, diammonium hydrogen phosphate, and potassium phosphate. The amount of one or more phosphorus compounds is preferably 0.05 to 2% by mass based on the alumina flakes. Preferred examples of pH adjusters for precipitation are ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and combinations thereof. To control the particle size, thickness, optical properties, and / or surface morphology, it may be useful to add one or more dopants in an amount of 0.01 to 5% by mass based on the Al2O3 flakes. The dopant is preferably selected from the group of the following compounds: TiO2, ZrO2, SiO2, In2O3, SnO2, WO3, MoO3, ZnO, and combinations thereof. The Al2O3 flakes according to the present invention are very suitable as a substrate in the production of effect pigments. For this purpose, the flakes are preferably coated with at least one high refractive index layer, for example, a layer of metal oxides such as TiO2, ZrO2, SnO2, ZnO, Ce2O3, Fe2O3, Fe3O4, FeTiO5, Cr2O3, CoO, Co3O4, VO2, V2O3, NiO, etc., further a layer of titanium suboxide (TiO2 with a partially reduced oxidation state from <4 to 2, for example, lower oxides Ti3O5, Ti2O3, TiO), titanium oxynitride, FeO(OH), a thin translucent metal layer, for example, one containing Al, Fe, Cr, Ag, Au, Pt or Pd, or a combination thereof, etc. The TiO2 layer can be of rutile modification or anatase modification. Generally, when TiO2 is of rutile modification, the highest quality, gloss and the most stable effect pigment can be obtained. In order to obtain the rutile modification, additives that can lead TiO2 to the rutile modification can be used. Useful rutile inducing agents are disclosed in U.S. Patent No. 4,038,099, U.S. Patent No. 5,433,779, and European Patent No. 0271767. A preferred rutile inducing agent is SnO2.

[0009] Preferred effect pigments based on Al2O3 flakes are coated with one or more layers of metal oxides, preferably only one layer of metal oxide, particularly TiO2, Fe2O3, Fe3O4, SnO2, ZrO2 or Cr2O3. Particularly preferred are Al2O3 flakes coated with TiO2 or Fe2O3, and mixtures thereof. The thickness of each high refractive index layer varies according to the desired interference color. The thickness of each layer on the surface of the Al2O3 flakes is preferably 20 - 400 nm, preferably 30 - 300 nm, particularly preferably 30 - 200 nm. The number of layers on the surface of the Al2O3 flakes is preferably 1 or 2, and further 3, 4, 5, 6 or 7 layers. In particular, an interference package consisting of high and low refractive index layers on the surface of Al2O3 flakes results in an effect pigment having increased gloss and further increased interference colors or an excellent flip-flop effect. Suitable colorless low refractive index materials for the coating are preferably metal oxides or their corresponding oxide hydrates, such as compounds like SiO2, Al2O3, AlO(OH), B2O3, MgF2, or mixtures of the above metal oxides. When multiple layers are applied to the surface of Al2O3 flakes, the interference system is, in particular, a layer arrangement of TiO2 - SiO2 - TiO2. Furthermore, the effect pigment according to the present invention may have a translucent metal layer as the outer layer. This type of coating is known, for example, from the specification of German Patent Application Publication No. 3825702 (A1). The metal layer is preferably a chromium layer or an aluminum layer having a layer thickness of 5 - 25 nm. Al2O3 flakes can also be coated with one or more layers of a metal or metal alloy selected, for example, from chromium, nickel, silver, bismuth, copper, tin, or Hastelloy. Al2O3 flakes coated with metal sulfides are coated with sulfides of, for example, tungsten, molybdenum, cerium, lanthanum, or rare earth elements. Furthermore, the effect pigment based on Al2O3 flakes can finally be coated with an organic dye, preferably Prussian blue or carmine red, as a top coat.

[0010] Particularly preferred effect pigments based on Al2O3 flakes according to the present invention have the following layer arrangements. 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 + SnO2 + TiO2 Al2O3 flakes + TiO2 + Prussian Blue Al2O3 flakes + TiO2 + Carmine Red Al2O3 flakes + Ag

[0011] The TiO2 layer in the above-described preferred embodiment can be in the rutile or anatase modification. The Al2O3 flakes of the above-described preferred embodiment can be doped or undoped. In the present application, the term "coating" or "layer" is to be construed as meaning completely enveloping the Al2O3 flakes according to the present invention. Effect pigments based on doped or undoped Al2O3 flakes preferably consist of 40 to 90% by mass of Al2O3 flakes and 10 to 60% by mass of coating, based on the total pigment.

[0012] The Al2O3 flakes can be coated by wet chemical coating, by a CVD or PVD process. Coating the Al2O3 flakes with one or more layers, preferably one or more metal oxide layers, is preferably carried out by a wet chemical method, and a wet chemical coating method developed for the production of nacreous pigments can be used. This kind of method is described, for example, in German Patent Application Publication Nos. 1467468, 1959988, 2009566, 2214545, 2215191, 2244298, 2313331, 1522572, 3137808, 3137809, 3151343, 3151354, 3151355, 3211602, 3235017, or is also described in patent documents and other publications known to those skilled in the art. In the case of wet coating, Al2O3 flakes are suspended in water, and one or more hydrolyzable metal salts are added at a pH suitable for hydrolysis. The pH is selected such that the metal oxide or metal oxide hydrate precipitates directly onto the flakes without causing secondary precipitation. The pH is usually kept constant by simultaneously metering in a base and / or an acid. The pigment is then separated, washed, dried at 50 to 150 °C for 6 to 18 hours, and calcined for 0.5 to 3 hours. The calcination temperature can be optimized for each coating layer present. Usually, the calcination temperature is 500 to 1000 °C, preferably 600 to 900 °C. If desired, the pigment can be separated, dried, calcined if necessary, after applying each individual coating, and then resuspended again for applying a further layer. Applying a SiO2 layer to Al2O3 flakes and / or already coated Al2O3 flakes is generally carried out by adding a potassium or sodium water glass solution at a suitable pH. Furthermore, the coating can also be carried out by gas-phase coating in a fluidized-bed reactor, for example, using in a corresponding manner the methods proposed in European Patent Application Publication No. 0045851 and European Patent Application Publication No. 0106235 regarding the preparation of pearlescent pigments.

[0013] The hue and chroma of the effect pigments based on Al2O3 flakes according to the present invention can be varied within a very wide range by variously selecting the coating amount or the layer thickness obtained therefrom. Fine adjustment for a specific hue and / or chroma can be achieved not only by selecting the amount but also by approaching the desired color using visual or measurement technology control. To enhance the stability against light, water, and weather, depending on the field of application, it is often recommended to perform post - coating or post - treatment on the final pigment. Suitable post - coating or post - treatment methods are, for example, those described in German Patent Invention No. 2215191 (C2), German Patent Application Publication No. 3151354, German Patent Application Publication No. 3235017, or German Patent Application Publication No. 3334598. This post - coating further enhances chemical and photochemical stability or simplifies the handling of the pigment, especially its incorporation into various media. To enhance weather resistance, dispersibility, and / or compatibility with the user medium, functional coatings of Al2O3 or SiO2, ZrO2, or mixtures thereof are possible. Furthermore, the protective layer can contain an organic substance or a mixture thereof for application to the pigment surface. Additionally, organic post - coatings, for example using silanes, are possible as described in European Patent Application Publication No. 0090259, European Patent Application Publication No. 0634459, International Publication No. 99 / 57204, International Publication No. 96 / 32446, International Publication No. 99 / 57204, U.S. Patent No. 5,759,255, U.S. Patent No. 5,571,851, International Publication No. 01 / 92425, or J.J. Ponjee, Philips Technical Review, Vol. 44, No. 3, 81 ff. and P.H. Harding J.C. Berg, J. Adhesion Sci. Technol. Vol. 11 No. 4, pp. 471 - 493.

[0014] Preferred metal oxides present in the post - treatment or protective layer are Al2O3, SiO2, ZrO2, and / or Ce2O3. Furthermore, the protective layer can contain components selected from organic components, especially organic coupling agents, organic functional silanes, amino compounds, and organic phosphorus compounds. Suitable coupling reagents are, for example, organosilanes, organoaluminates, organotitanates, and / or zirconates. The coupling agent is preferably an organosilane. Examples of organosilanes are propyltrimethoxysilane, propyltriethoxysilane, isobutyltrimethoxysilane, n-octyltrimethoxysilane, i-octyltrimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane, vinyltrimethoxysilane, preferably n-octyltrimethoxysilane and n-octyltriethoxysilane. Suitable oligomeric alcohol-free organosilane hydrolyzates are, inter alia, products sold by Evonik Industries under the trade name Dynasylan® Hydrosil, for example Dynasylan® Hydrosil 2926, Dynasylan® Hydrosil 2909, Dynasylan® Hydrosil 2907, Dynasylan® Hydrosil 2781, Dynasylan® Hydrosil 2776, Dynasylan® Hydrosil 2627 and the like. Furthermore, oligomeric vinylsilane and aminosilane hydrolyzates are also suitable as organic coatings. Functionalized organosilanes are, for example, 3-aminopropyltrimethoxysilane (AMMO), 3-methacryloxytrimethoxysilane (DAMO), 3-glycidyloxypropyltrimethoxysilane (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-glycidyloxypropyl-trimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-isocyanatopropyltrimethoxysilane. Examples of polymeric silane-based ones are described in WO 98 / 13426 and are sold, for example, by Evonik Industries under the trade name Dynasylan® Hydrosil.The amount of the organic coating can be 0.2 to 5% by mass, preferably 0.5 to 2% by mass, based on the effect pigment.

[0015] Suitable coupling agents are, inter alia, zirconium aluminate having the following structure: [Chemical formula] In the formula, X represents NH2, COOH, -COO - , hydroxyphenyl, methacrylate, carboxyphenyl, alkyl, mercapto, phenyl, H, vinyl, styryl, melamine, epoxy, aryl or alkyl, n represents 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12. Other suitable coupling reagents are metal acid esters having the following structure M n (OR) y In the formula, M represents Zr, Ti or Al, N represents the valence of the metal, y is 1, 2 or 3 according to the valence of the metal, R is (i) alkyl having 1 to 12 carbon atoms, or aryl, (ii) alkyl or aryl substituted with -N(alkyl)3, -NH(alkyl)2, -NH2(alkyl), -NH3, N(aryl)3, -NH(aryl)2, or -NH2(aryl) [wherein aryl may be substituted with halogen, nitro, amino, or hydrogen], (iii) -C-aryl or C-alkyl. Particularly suitable metal acid esters, such as acrylate-functional and methacrylamide-functional titanates, and methacrylamide-functional zirconates, are commercially available.

[0016] In a preferred embodiment, the proportion of the protective layer on the surface of the coated Al2O3 flakes in the total amount of the effect pigment is 2 to 20% by mass, preferably 2 to 10% by mass, particularly 2 to 5% by mass. A very preferred composition of the protective layer contains 0.2 to 2% by mass of a rare earth metal oxide, preferably Ce2O3, 0.2 to 2% by mass of SiO2, 0.2 to 4% by mass of Al2O3 and / or ZrO2, and 1 to 10% by mass of an organic component. In a preferred embodiment, the organic component is a coupling agent. In a specific preferred embodiment, the protective layer consists of 0.4 to 1.5% by mass of Ce2O3, 0.4 to 1% by mass of SiO2, 0.5 to 2.5% by mass of Al2O3 and / or ZrO2, and 2 to 5% by mass of a coupling agent. The protective coating on the effect pigment according to the present invention is prepared by a method known to those skilled in the art. In a preferred embodiment, the effect pigment is pretreated by wet chemical coating. In a preferred embodiment, the effect pigment according to the present invention has a specific surface area measured by the BET method (DIN ISO 9277:2003-05) of ≦ 10 m 2 / g, preferably ≦ 7 m 2 / g.

[0017] The Al2O3 flakes and the effect pigments based on Al2O3 flakes according to the present invention are preferably compatible with various coloring systems from the fields of paints, automotive coatings, industrial coatings, printing inks and cosmetic formulations. For example, for the preparation of printing inks for gravure printing, flexographic printing, offset printing and offset overprint varnishing, a number of binders, especially water-soluble grades, such as those sold by BASF, Marabu, Proll, Sericol, Hartmann, Gebr. Schmidt, Sicpa, Aarberg, Siegberg, GSB-Wahl, Follmann, Ruco, or Coates Screen INKS GmbH are suitable. The printing ink can be aqueous or solvent-based. The pigments are also suitable for laser marking of paper and plastics, and for applications in the agricultural field, such as greenhouse sheets, and for coloring, for example, tent canopies.

[0018] For various applications, the Al2O3 flakes and the effect pigments according to the present invention can advantageously be used, for example, in blends with organic dyes, organic pigments or other pigments, such as transparent and opaque whites, colored and black pigments, and also in blends with conventional transparent, colored and black lustre pigments based on flaky iron oxide, holographic pigments, LCP (liquid crystal polymer), and metal oxide-coated mica and SiO2 flakes. The Al2O3 flakes and the effect pigments based on Al2O3 flakes according to the present invention can be mixed with commercially available pigments and fillers in any ratio. Examples of fillers include natural and synthetic mica, nylon powder, pure or filled melamine resins, talc, SiO2, glass, kaolin, aluminum oxides or hydroxides, magnesium oxides or hydroxides, calcium oxides or hydroxides, or zinc oxides or hydroxides, BiOCl, barium sulfate, calcium sulfate, calcium carbonate, magnesium carbonate, carbon, and physical or chemical combinations of these substances. There are no restrictions regarding the particle shape of the filler. The shape can be, for example, flaky, spherical or needle-like depending on the requirements.

[0019] The Al2O3 flakes and the Al2O3 flake-based effect pigments according to the present invention are simple and easy to handle. The Al2O3 flakes and the Al2O3 flake-based effect pigments can be incorporated into the system to be used by simple stirring. Complicated grinding and dispersion are not required for the Al2O3 flakes and the effect pigments. The Al2O3 flake-based effect pigments according to the present invention can be used for pigmenting coating materials, printing inks, plastics, agricultural films, button pastes, for coating seeds, for coating foods, drugs or coloring cosmetic formulations. The concentration of the Al2O3 flakes and the effect pigments in the system used for coloring is usually 0.01 to 50% by mass, preferably 0.1 to 5% by mass, based on the total solids of the system. This concentration usually depends on the specific application. Plastics containing the Al2O3 flakes and the effect pigments according to the present invention in an amount of 0.1 to 50% by mass, particularly 0.5 to 7% by mass, often attract attention due to specific gloss effects. In the coating field, particularly in automotive coatings and automotive finishing, the Al2O3 flakes and the effect pigments according to the present invention are used in an amount of 0.5 to 10% by mass. In coating materials, the effect pigments according to the present invention have the advantage that the desired color and gloss can be obtained by a single-layer coating (as a base coat in a one-coat system or a two-coat system).

[0020] The present invention likewise provides a pigment preparation comprising coated or uncoated Al2O3 flakes according to the invention, and further an effect pigment, a binder, and optionally additives, the preparation being in the form of free-flowing granules substantially free of solvent. Such granules contain up to 95% by mass of the effect pigment according to the invention. The Al2O3 flakes and Al2O3 flake-based effect pigments according to the invention, with or without additives, are pasted with a binder and water and / or an organic solvent, and then the paste is dried to give a pigment preparation in a compact particulate form, such as granules, pellets, briquettes, masterbatches or tablets, which is particularly suitable as a precursor for printing inks. Accordingly, the present invention also relates to the use of coated and uncoated Al2O3 flakes in formulations in the fields of paints, glaze compositions, coatings, automotive coatings, automotive finishes, industrial coatings, paints, powder coatings, printing inks, security printing inks, plastics, ceramic materials, cosmetics. Coated and uncoated Al2O3 flakes can further be used in glass, paper, paper coatings, toner for electrophotographic printing processes, seeds, greenhouse sheets and waterproof sheets, heat-conductive, self-supporting, electrically insulating, flexible sheets for insulating machines or devices, as absorbers in laser marking of paper and plastics, as absorbers in laser welding of plastics, in pigment pastes with water, organic and / or aqueous solvents, in pigment preparations and dry preparations such as granules, for example in clear coats in the industrial and automotive fields, for solar radiation shielding, in particular as fillers in automotive coatings and automotive refinishes, for LIDAR and RADAR applications.

[0021] In this patent application, the term "coated alumina" flakes means the alumina flakes according to claim 1 whose surface is coated with one or more of the above layers. The alumina flakes according to claim 1 are suitable as a substrate for effect pigments. All percentage data in this application are mass percentages unless otherwise specified. The following examples are intended to illustrate the present invention in more detail, but do not limit the present invention. In the above and below, all percentages are mass percentages.

Example

[0022] Example 1: TiO2-coated alumina flakes Example 1a: Alumina flake preparation process Dissolve 223.8 g of aluminum sulfate octadecahydrate (Al2(SO4)3·18H2O) and 286.3 g of anhydrous sodium sulfate (Na2SO4) in 1200 ml of deionized water by heating to about 75°C. Add 0.6 g of a 34.4% solution of titanyl sulfate (TiOSO4) to the resulting solution. The resulting solution is designated as aqueous solution (a). Dissolve 0.9 g of trisodium phosphate dodecahydrate (Na3PO4·12H2O) and 107.9 g of sodium carbonate (Na2CO3) in 550 ml of deionized water. The resulting solution is designated as aqueous solution (b). Simultaneously add aqueous solutions (a) and (b) to 550 ml of deionized water being stirred at a constant rate over about 15 minutes so that the solute of solution (a) is approximately equivalent to the solute of solution (b). Continue stirring for an additional 15 minutes. Evaporate the resulting solution to dryness. Heat the resulting solid at 1000°C for 5 hours. Add water to the heat-treated product to dissolve the free sulfuric acid. Filter off the insoluble solid, wash with water, and finally dry. Thus, the desired flaky aluminum oxide with an average particle diameter of 14.3 μm and a fraction of particle thickness of 40 - 130 nm being 89% is obtained.

[0023] Example 1b: TiO2 coating process on alumina flakes Suspend 20 g of the alumina flakes of Example 1a in 400 ml of deionized water. To the resulting suspension (maintained at about 65 °C), add a solution containing 125 g of TiCl4 per liter. At the same time, add a 10% solution of NaOH to maintain the pH at 2.1. Stop adding the TiCl4 solution when the resulting product exhibits a silver color. Filter off the suspended solid, wash with water, and dry. Finally, calcine the dried solid at 850 °C for 30 minutes to obtain a slightly shiny pearlescent pigment with a whitish tint. The resulting effect pigment exhibits an excellent flip-flop effect represented by a flop index of 6.0.

[0024] Example 1c: Surface treatment Suspend 100 g of alumina flakes coated with TiO2 according to Example 1b in 1000 ml of deionized water. Keep the resulting suspension at about 70 °C, adjust the pH to 7 with 10% HCl, and add 100 ml of a water glass solution containing 3.05 g of Na2SiO3 to the suspension over 90 minutes. At the same time, add a 10% solution of HCl to maintain the pH at 7. Then, add 100 ml of a solution containing 6.5 g of aluminum sulfate (Al2(SO4)3·18H2O) to the suspension over 90 minutes while maintaining the pH at 7 with 10% NaOH. After raising the pH to 7.5 with 10% NaOH, add 1.5 g of 3-aminopropyl-trimethoxysilane (CAS No. 13822-56-5) and 1.5 g of 3-glycidyloxypmpyl-trimethoxysilane (CAS No. 2530-83-8) to the suspension over 15 minutes each while maintaining the pH at 7.0 with 10% HCl or 10% NaOH. Filter off the suspended solid, wash with water, dry at 140 °C, and screen (325 mesh). The surface-treated effect pigment exhibits good moisture resistance due to the remaining photoactivity.

[0025] Example 1d: Spray panel coating process Prepare an automotive basecoat paint according to the following formulation.

Table 1

[0026] The above acrylic-melamine resin system (100 pbw) is blended with 20 pbw of flaky aluminum oxide (Example 1a) or the pearlescent pigment obtained in Example 1b. The resulting compound is diluted with a diluent so that the resulting paint has a consistency suitable for spraying (12 - 15 seconds with a Ford cup #4). This paint is applied to the substrate by spraying to form a base coat layer. The base coat layer is further coated with a colorless top clear coat paint prepared according to the following formulation.

Table 2

[0027] Example 2: TiO2-coated alumina flakes Following Example 1a, the amount of sodium sulfate anhydrous is made 429.4 g and the preparation of alumina flakes is carried out. The resulting alumina flakes have an average particle diameter greater than 15.1 μm and a fraction of particle thickness in the range of 40 - 130 nm of 93%. The TiO2 coating process on the alumina flakes is carried out according to Example 1b. The resulting effect pigment exhibits an excellent flip-flop effect represented by a flop index of 6.6. The spray panel coating process is carried out according to Example 1d.

[0028] Example 3: TiO2-coated alumina flakes 1261.7 g of 27% aluminum sulfate solution (as Al2(SO4)3), 512.0 g of sodium sulfate (Na2SO4), 415.6 g of potassium sulfate (K2SO4), and 6.0 g of 35% zinc sulfate (ZnSO4·7H2O) solution are added to a 5 l reactor containing 1200 ml of pure water. By mixing at 65 °C, a homogeneous mixture solution is obtained. 318.7 g of sodium carbonate (Na2CO3) and 2.7 g of sodium metaphosphate ((NaPO3)6) are dissolved in 896.5 ml of distilled water at 65 °C to prepare an alkaline solution. The above aluminum sulfate mixture solution is titrated with the above alkaline solution at a rate of 20 ml / min to pH 6.8 with stirring. A gel mixture of boehmite and flux is obtained. Then, the gel mixture is aged at 90 °C for 20 hours, vacuum distilled at 60 °C, and dried at 110 °C for 20 hours. The resulting solution is evaporated to dryness. The obtained solid is heated at about 1150 °C for 5 hours. Water is added to the heat-treated product to dissolve the free sulfuric acid. The insoluble solid is filtered off, washed with water, and finally dried. Thus, the desired flaky aluminum oxide is obtained. The obtained alumina flakes have an average particle diameter larger than 16.5 μm and a fraction of particle thickness of 40 - 130 nm of 45%. The TiO2 coating process for the alumina flakes is carried out according to Example 1b. The obtained effect pigment exhibits an excellent flip-flop effect represented by a flop index of 4.3. The spray panel coating process is carried out according to Example 1d.

[0029] Example 4: TiO2-coated alumina flakes Alumina flakes are prepared according to Example 1a, but the amount of 35% zinc sulfate (ZnSO4·7H2O) solution is changed to 23.9 g. The obtained alumina flakes have an average particle diameter larger than 18.3 μm and a fraction of particle thickness of 40 - 130 nm of 42%. The TiO₂ coating process for alumina flakes is carried out according to Example 1b. The resulting effect pigment exhibits an excellent flip-flop effect represented by a flop index of 4.5. The spray panel coating process is carried out according to Example 1d.

[0030] Example 5: TiO₂-Coated Alumina Flakes A homogeneous mixture solution is prepared by mixing 423.2 g of aluminum sulfate (Al₂(SO₄)₃·18H₂O), 326.8 g of sodium sulfate (Na₂SO₄), 265.3 g of potassium sulfate (K₂SO₄), 3.0 g of a 34% aqueous solution of zinc sulfate (ZnSO₄·7H₂O) and 1.0 g of a 17% aqueous solution of tin sulfate (SnSO₄·7H₂O) in a reactor (5 l) containing 1,200 ml of purified water at 65°C. An alkaline solution is prepared by dissolving 204.6 g of sodium carbonate (Na₂CO₃) and 1.7 g of sodium metaphosphate ((NaPO₃)₆) in 568.4 ml of distilled water at 65°C. While stirring the above alkaline solution, it is titrated with the aluminum sulfate mixture solution (65°C) at a rate of 25 ml / min, and the final pH is adjusted to 6.8 to prepare a gel mixed with boehmite and flux. The mixed gel is aged at 90°C for 20 hours, vacuum distilled at 60°C, and dried at 110°C for 20 hours. The resulting solution is evaporated to dryness. The resulting solid is heated at about 1000°C for 5 hours. Water is added to the heat-treated product to dissolve the free sulfuric acid. The insoluble solid is filtered off, washed with water, and finally dried. Thus, the desired flaky aluminum oxide is obtained. The obtained alumina flakes have an average particle diameter larger than 16.0 μm and a fraction of particle thickness of 40 - 130 nm of 52%. The TiO₂ coating process for alumina flakes is carried out according to Example 1b. The resulting effect pigment exhibits an excellent flip-flop effect represented by a flop index of 5.2. The spray panel coating process is carried out according to Example 1d.

[0031] Example 6: Alumina flakes coated with TiO2 Example 6 follows Example 1a but is prepared with 23.9 g of a 35% zinc sulfate (ZnSO4·7H2O) solution. The obtained alumina flakes have an average particle diameter larger than 15.5 μm and a fraction of particle thickness of 40 - 130 nm of 58%. The TiO2 coating process on the alumina flakes is carried out according to Example 1b. The obtained effect pigment shows an excellent flip - flop effect represented by a flop index of 5.4. The spray panel coating process is carried out according to Example 1d.

[0032] Comparative Example 1: Alumina flakes coated with TiO2 596.8 g of aluminum sulfate octadecahydrate and 253.4 g of anhydrous sodium sulfate are dissolved in 1200 ml of deionized water by heating to about 75°C. 1.6 g of a 34.4% solution of titanyl sulfate is added to the obtained solution. The obtained solution is designated as aqueous solution (a). 4.9 g of trisodium phosphate dodecahydrate and 287.7 g of sodium carbonate are dissolved in 550 ml of deionized water. The obtained solution is designated as aqueous solution (b). Aqueous solutions (a) and (b) are simultaneously added to 500 ml of deionized water being stirred at a constant rate over about 15 minutes such that the solute of solution (a) is approximately equivalent to the solute of solution (b). Stirring is continued for a further 15 minutes. 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 the free sulfuric acid. The insoluble solid is filtered off, washed with water, and finally dried to obtain alumina flakes. The obtained alumina flakes have an average particle diameter larger than 12.2 μm and a fraction of particle thickness of 40 - 130 nm of 78%. The TiO2 coating process on the alumina flakes is carried out according to Example 1b. The obtained effect pigment does not show a significant flip - flop effect. The flop index is only 3.7. The spray panel coating process is carried out according to Example 1d.

[0033] Comparative Example 2: Alumina flakes coated with TiO2 596.8 g of aluminum sulfate 18-hydrate, 111.4 g of anhydrous sodium sulfate, and 177.5 g of potassium sulfate are dissolved in 1200 ml of deionized water by heating to about 75°C. 5.3 g of a 34.4% solution of titanyl sulfate is added to the resulting solution. The resulting solution is designated as aqueous solution (a). 2.4 g of trisodium phosphate dodecahydrate and 287.7 g of sodium carbonate are dissolved in 550 ml of deionized water. The resulting solution is designated as aqueous solution (b). Aqueous solutions (a) and (b) are simultaneously added over about 15 minutes to 500 ml of deionized water being stirred at a constant rate so that the solutes of solution (a) are approximately equivalent to the solutes of solution (b). Stirring is continued for 15 minutes. The resulting solution is evaporated to dryness. The resulting solid is heated at about 1200°C for 5 hours. Water is added to the heat-treated product to dissolve the free sulfuric acid. The insoluble solid is filtered off, washed with water, and finally dried to obtain alumina flakes. The obtained alumina flakes have an average particle diameter greater than 19.7 μm and a fraction of particle thickness of 40 - 130 nm of 2%. The TiO2 coating process for the alumina flakes is carried out according to Example 1b. The resulting effect pigment does not show a significant flip-flop effect. The flop index is only 3.1. The spray panel coating process is carried out according to Example 1d.

[0034] Comparative Example 3: Alumina flakes coated with TiO2 223.8 g of aluminum sulfate 18-hydrate and 334.3 g of anhydrous sodium sulfate are dissolved in 1200 ml of deionized water by heating to about 75°C. The resulting solution is designated as aqueous solution (a). 107.9 g of sodium carbonate is dissolved in 550 ml of deionized water. The resulting solution is designated as aqueous solution (b). Solutions (a) and (b) are simultaneously added to 500 ml of deionized water being stirred at a constant rate over about 15 minutes such that the solute of solution (a) is approximately equivalent to the solute of solution (b). Stirring is continued for an additional 15 minutes. The resulting solution is evaporated to dryness. The resulting solid is heated at about 1000 °C for 5 hours. Water is added to the heat-treated product to dissolve the free sulfuric acid. The insoluble solid is filtered off, washed with water, and finally dried to obtain alumina flakes. The resulting alumina flakes have an average particle diameter greater than 13.0 μm and a fraction of particle thickness of 40 - 130 nm of 22%. The TiO₂ coating process on the alumina flakes is carried out according to Example 1b. The resulting effect pigment shows little or no flip-flop effect. The flop index is only 1.9. The spray panel coating process is carried out according to Example 1d.

Table 3

[0035] Table 1 shows that the alumina flake-based effect pigment according to the present invention exhibits much higher gloss with much higher color flip-flop. Compared with the prior art alumina-based pigments, the alumina flake-based effect pigment of the present invention shows a relatively low brilliance effect compared to its particle size. The effect pigment according to the present invention shows a flop index of >4. The flop index is the relative change in lightness seen between near the reflection angle and near the receding angle, that is, the larger the change amount, the stronger the flop feeling (color change depending on the viewing angle). The flop index measures the change in lightness when the metallic color is tilted at all angles within the field of view. The flop index evaluates the change in lightness when the metallic color is tilted at all angles within the field of view.

[0036] Measurement: Particle size D 50 Evaluation of D of alumina flakes 50 is evaluated using Malvern MS3000. Measurement of thickness, particle size, and thickness distribution Prepare a 0.01 g / l alumina flake slurry and drop 0.1 ml of this slurry onto a flat substrate such as a silicon wafer. Dry the substrate and cut it to an appropriate size. Place the substrate on the stage of an SEM (scanning electron microscope) at an inclination angle almost perpendicular to measure the thickness of the alumina flakes. Measure the thickness of more than 100 alumina flakes and calculate the thickness distribution. L * (15°) L at 15° in Figure 1 * The value is measured with a spectrophotometer BYK-mac i.

[0037] SG value This value is calculated by the following formula using the index value measured with BYK-mac i.

Equation

Number

Claims

1. The average particle diameter is 14–25 μm, and the fraction of particles with a thickness of 40–130 nm is greater than 40%. 2 O 3 flake.

2. The aforementioned Al 2 O 3 The Al according to claim 1, characterized in that the flake is α-alumina flake. 2 O 3 flake.

3. The above-mentioned Al 2 O 3 flake is doped with one or more oxides, and the Al 2 O 3 flake according to claim 1.

4. The amount of the aforementioned dope is Al 2 O 3 The Al according to claim 3, characterized in that it is 0.01 to 5% by mass based on the flakes. 2 O 3 flake.

5. The aforementioned Al 2 O 3 Flakes, TiO 2 , ZrO 2 SiO 2 , SnO 2 In 2 O 3 ZnO, WO 3 MoO 3 The Al according to claim 1, characterized in that it is doped with one or more oxides selected from the group consisting of, and combinations thereof. 2 O 3 flake.

6. The aforementioned Al 2 O 3 Flakes, - Metal oxides - A mixture of at least two metal oxides -metal - Metal sulfides - Titanium Oxide - Titanium oxynitride - Organic or inorganic dyes -FeO(OH) -SiO2 - Metal alloys -Rare earth compounds or combinations of these The Al according to claim 1, characterized in that it is coated with at least one layer of 2 O 3 flake.

7. The aforementioned Al 2 O 3 The Al according to claim 1, characterized in that the flakes are coated with at least one layer of a metal oxide or a mixture of at least two metal oxides. 2 O 3 flake.

8. Metal oxides, TiO 2 Fe 2 O 3 Fe 3 O 4 SiO 2 , SnO 2 Al 2 O 3 , ZrO 2 , CEO 2 In 2 O 3 The Al according to claim 7, characterized in that it is selected from the group of oxides of ZnO or a combination thereof. 2 O 3 flake.

9. The aforementioned Al 2 O 3 The Al according to claim 1, characterized in that the flakes are coated in the following layer arrangement. 2 O 3 flake: Al 2 O 3 Flakes + TiO 2 Al 2 O 3 Flakes + TiO 2 / Fe 2 O 3 Al 2 O 3 Flakes + Fe 2 O 3 Al 2 O 3 Flakes + TiO 2 + Fe 2 O 3 Al 2 O 3 Flakes + TiO 2 + Fe 3 O 4 Al 2 O 3 Flakes + TiO 2 + SiO 2 + TiO 2 Al 2 O 3 Flakes + Fe 2 O 3 + SiO 2 + TiO 2 Al 2 O 3 flake + TiO 2 / Fe 2 O 3 + SiO 2 + TiO 2 Al 2 O 3 flake + TiO 2 + SiO 2 + TiO 2 / Fe 2 O 3 Al 2 O 3 Flakes + TiO 2 + SiO 2 Al 2 O 3 Flakes + TiO 2 + SiO 2 / Al 2 O 3 Al 2 O 3 Flakes + TiO 2 + Al 2 O 3 Al 2 O 3 Flake + SnO 2 Al 2 O 3 Flake + SnO 2 + TiO 2 Al 2 O 3 Flake + SnO 2 + Fe 2 O 3 Al 2 O 3 Flake + SiO 2 Al 2 O 3 Flake + SiO 2 + TiO 2 Al 2 O 3 Flake + SiO 2 + TiO 2 / Fe 2 O 3 Al 2 O 3 Flake + SiO 2 + Fe 2 O 3 Al 2 O 3 Flake + SiO 2 + TiO 2 + Fe 2 O 3 Al 2 O 3 Flake + SiO 2 + TiO 2 + Fe 3 O 4 Al 2 O 3 Flake + SiO 2 + TiO 2 + SiO 2 + TiO 2 Al 2 O 3 Flake + SiO 2 + Fe 2 O 3 + SiO 2 + TiO 2 Al 2 O 3 Flake + SiO 2 + TiO 2 / Fe 2 O 3 + SiO 2 + TiO 2 Al 2 O 3 Flake + SiO 2 + TiO 2 + SiO 2 + TiO 2 / Fe 2 O 3 Al 2 O 3 Flake + SiO 2 + TiO 2 + SiO 2 Al 2 O 3 Flake + SiO 2 + TiO 2 + SiO 2 / Al 2 O 3 Al 2 O 3 Flake + SiO 2 + TiO 2 + Al 2 O 3 Al 2 O 3 Flakes + TiO 2 + Prussian Blue Al 2 O 3 Flakes + TiO 2 + Carmine Red.

10. The aforementioned Al 2 O 3 The flakes are TiO2 of rutile or anatase metamorphosis. 2 The Al according to claim 1, characterized in that it is coated with 2 O 3 flake.

11. The aforementioned Al 2 O 3 Flakes are rutile metamorphosis TiO 2 The Al according to claim 1, characterized in that it is coated with 2 O 3 flake.

12. Al 2 O 3 The Al according to claim 7, characterized in that the mass ratio of flakes to metal oxide coating is 40:60 to 90:10 based on the total pigment. 2 O 3 flake.

13. Coated Al 2 O 3 The Al according to claim 6, characterized in that the flakes have a flop index of ≥ 4 (measured with a spectrophotometer BYK-mac i). 2 O 3 flake.

14. Pigment pastes, pigment preparations and dried preparations with water, organic and / or aqueous solvents, and coated and uncoated Al as described in any one of claims 1 to 13, as substrates for effect pigments in formulations selected from paints, glaze compositions, coatings, automotive coatings, automotive finishes, 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 waterproof sheets, and thermally conductive, self-supporting, electrically insulating, and flexible sheets for insulation of machinery or equipment, as absorbers in laser marking of paper and plastics, as absorbers in laser welding of plastics, and for LIDAR and RADAR applications. 2 O 3 Use of flakes.

15. Coated or uncoated Al according to any one of claims 1 to 13 2 O 3 A composition containing flakes in an amount of 0.01 to 95% by mass based on the total composition.

16. Coated or uncoated aluminum according to any one of claims 1 to 13, characterized by containing at least one component selected from the group consisting of water, polyols, polar and non-polar oils, fats, waxes, film-forming agents, polymers, copolymers, surfactants, free radical scavengers, antioxidants, stabilizers, odor enhancers, silicone oils, emulsifiers, solvents, preservatives, thickeners, rheological additives, fragrances, colorants, effect pigments, UV absorbers, surfactants and / or cosmetic active compounds, fillers, binders, pearlescent pigments, coloring pigments and organic dyes. 2 O 3 A compound containing flakes.

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