Multilayer pigments based on coated metal platelets

Abstract

The present invention relates to multilayer pigments based on platelet-shaped metal substrates coated with two or more metal oxide layers by a one-pot process in an exclusively aqueous medium. The invention further relates to the use of the multilayer pigments in paints, varnishes, printing inks, including security printing inks, plastics, ceramic materials and cosmetic and for the laser formulations marking of plastics.

1 . A multilayer pigment based on platelet-shaped metal pigments and produced by the exclusive wet-chemical coating of the metal pigments in a one-pot process wherein the metal pigments, optionally after prior passivation, are initially suspended in water and coated with an amorphous glassy layer at pH 6-11 and then with one or more metal oxides or metal oxide mixtures at a pH<4.  
     
     
         2 . A multilayer pigment according to  claim 1 , wherein the amorphous glassy layer comprises SiO 2 , B 2 O 3 , phosphate, or a mixture thereof.  
     
     
         3 . A multilayer pigment according to  claim 1 , wherein the metal oxide layer or the layer comprising a metal oxide mixture comprises titanium dioxide, iron oxide, silicon dioxide, bismuth oxychloride, zirconium oxide, tin oxide, zinc oxide, titanium suboxide, iron oxyhydrate and/or chromium oxide.  
     
     
         4 . A multilayer pigment according to  claim 1 , wherein up to 12 layers of metal oxide or metal oxide mixtures have been applied to the metal pigment.  
     
     
         5 . A multilayer pigment according to  claim 1 , wherein the metal pigments are aluminum platelets.  
     
     
         6 . A multilayer pigment according to  claim 5 , wherein the aluminum platelets have been coated with an amorphous SiO 2  layer and then with a TiO 2  and/or Fe 2 O 3  layer.  
     
     
         7 . A multilayer pigment according to  claim 1 , wherein the metal pigments have been coated with an amorphous SiO 2  layer and then with an SnO 2 , TiO 2  and/or Fe 2 O 3  layer.  
     
     
         8 . A multilayer pigment according to  claim 1 , wherein the metal pigments have been coated with an amorphous SiO 2  layer and then with an SnO 2 , TiO 2 , SiO 2 , SnO 2  and TiO 2  layer in alternating fashion.  
     
     
         9 . A multilayer pigment according to  claim 1 , wherein the metal pigments have been coated with an amorphous SiO 2  layer and then with an SnO 2 , Fe 2 O 3 , SiO 2 , SnO 2  and Fe 2 O 3  layer in alternating fashion.  
     
     
         10 . A paint, varnish, printing ink, plastic, ceramic material or cosmetic formulation comprising a multilayer pigment according to  claim 1 .  
     
     
         11 . A laser marked plastic or a pigment blend comprising multilayer pigments according to  claim 1.