α-alumina flakes
Alpha-Alumina flakes having a particle thickness of 550-1000 nm, a D 50 -value of 15-30 μm, a D 90 -value of 30-45 μm and a D 10 -value of ≤9.0 μm. Use of the alumina flakes in varnishes, paints, automotive coatings printing inks, masterbatches, plastics and cosmetic formulations. Also, use of the alumina flakes as a substrate for effect pigments and in organic dyes.
1. Al 2 O 3 flakes having a particle thickness of 550-1000 nm, a D 50 -value of 15-30 μm, a D 90 -value of 30-45 μm and a D 10 -value of ≤9.0 μm and wherein the Al 2 O 3 flakes are α-alumina flakes.
2. The Al 2 O 3 flakes according to claim 1 , wherein the D 90 -value is 30-40 μm.
3. The Al 2 O 3 flakes according to claim 1 , which are doped with TiO 2 , ZrO 2 , SiO 2 , SnO 2 , In 2 O 3 , ZnO or a combination thereof.
4. The Al 2 O 3 flakes according to claim 3 , wherein the amount of doping is 0.01-5% by weight based on the total weight of the Al 2 O 3 flake.
5. The Al 2 O 3 flakes according to claim 3 , which are doped with TiO 2 .
6. The Al 2 O 3 flakes according to claim 1 , which are coated with at least one layer of a metal oxide, a mixture of at least two metal oxides, a metal, a metal sulphide, a titanium suboxide, titanium oxynitride, FeO(OH), a metal alloy or a rare earth compound.
7. The Al 2 O 3 flakes according to claim 6 , which consist of 40-90 wt. % of Al 2 O 3 flakes and 10-60 wt. % of the coating based on the weight of the coated Al 2 O 3 flakes.
8. The Al 2 O 3 flakes according to claim 1 , which are coated with at least one layer of a metal oxide or a mixture of at least two metal oxides.
9. The Al 2 O 3 flakes according to claim 1 , which are coated with the following layer sequence:
Al 2 O 3 flake+TiO 2
Al 2 O 3 flake+TiO 2 /Fe 2 O 3
Al 2 O 3 flake+Fe 2 O 3
Al 2 O 3 flake+TiO 2 +Fe 2 O 3
Al 2 O 3 flake+TiO 2 +Fe 3 O 4
Al 2 O 3 flake+TiO 2 +SiO 2 +TiO 2
Al 2 O 3 flake+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 flake+TiO 2 +SiO 2
Al 2 O 3 flake+TiO 2 +SiO 2 /Al 2 O 3
Al 2 O 3 flake+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 flake+TiO 2 +Prussian Blue or
Al 2 O 3 flake+TiO 2 +Carmine Red.
10. The Al 2 O 3 flakes according to claim 1 , which are coated with TiO 2 in the anatase modification.
11. The Al 2 O 3 flakes according to claim 1 , which are coated with TiO 2 in the rutile modification.
12. The Al 2 O 3 flakes according to claim 1 , which do not contain zinc.
13. The Al 2 O 3 flakes according to claim 1 , which have a D 50 -value of 15-25 μm, and a D 90 -value of 30-40 μm.
14. The Al 2 O 3 flakes according to claim 1 , which have a D 10 -value of <9.0 μm.
15. The Al 2 O 3 flakes according to claim 1 , which have a D 10 -value of 9.0 μm.
16. The Al 2 O 3 flakes according to claim 1 , having a particle thickness of 700 nm.
17. The Al 2 O 3 flakes according to claim 1 , having a particle thickness of 600-900 nm.
18. An assortment of Al 2 O 3 flakes having a particle thickness of 550-1000 nm, a D 50 -value of 15-30 μm, a D 90 -value of 30-45 μm and a D 10 -value of 9.0 μm and wherein the Al 2 O 3 flakes are α-alumina flakes.
19. The Al 2 O 3 flakes according to claim 18 , having a particle thickness of 600-900 nm.
20. A composition comprising the Al 2 O 3 flakes according to claim 1 , in formulations selected from the areas of effect pigments, paints, coatings, automobile coatings, automotive finishing, industrial coatings, powder coatings, printing inks, security printing inks, plastics, ceramic materials, cosmetics, glasses, paper, paper coating, toners for electrophotographic printing processes, seeds, greenhouse sheeting or tarpaulins, flexible sheets for the insulation of machines or devices, absorber in the laser marking of paper or plastics, absorber in the laser welding of plastics, pigment pastes with water, organic and/or aqueous solvents or pigment preparations.
21. A formulation containing the Al 2 O 3 flakes according to claim 1 in an amount of 0.01-95% by weight, based on the total weight of the formulation.
22. A formulation containing the Al 2 O 3 flakes according to claim 1 , and at least one component selected from the group consisting of water, polyols, polar oils, nonpolar oils, fats, waxes, film formers, polymers, copolymers, surfactants, free-radical scavengers, antioxidants, stabilisers, odour enhancers, silicone oils, emulsifiers, solvents, preservatives, thickeners, rheological additives, fragrances, colorants, effect pigments, UV absorbers, surface-active assistants, cosmetic active compounds, fillers, binders, pearlescent pigments, color pigments and organic dyes.
23. A process for preparing the Al 2 O 3 flakes according to claim 1 , comprising
(1) preparing an aqueous solution or a slurry of at least one water-soluble and/or insoluble aluminum salt,
(2) adding an alkali solution to the aluminum salt solution to precipitate aluminum hydroxide particles, and adding a phosphorous compound and optionally at least one dopant to the aqueous solution before, during or after the precipitation,
(3) evaporating the water, followed by drying of the precipitated product of step (2) to form the dried form of alumina containing particle and alkali salt,
(4) calcining the dried form obtained in step (3) to obtain Al 2 O 3 flakes in a molten salt,
(5) removing the water soluble part of the calcined material obtained in step (4), and
(6) adjusting the particle size and thickness.