Interference pigments on the basis of perlite flakes

Abstract

The present invention relates to pigments, comprising a plate-like substrate of perlite, and (a) a dielectric material, especially a metal oxide, having a high index of refraction; and/or (a) a metal layer, especially a thin semi-transparent metal layer; a process for their production and their use in paints, ink-jet printing, for dyeing textiles, for pigmenting coatings (paints), printing inks, plastics, cosmetics, glazes for ceramics and glass.

1 . A pigment, comprising a plate-like substrate of perlite, and
 (a) a layer of a metal oxide, having a high index of refraction; and/or   (a) a metal layer, especially a thin semi-transparent metal layer.   
   
   
       2 . The pigment according to  claim 1 , wherein the perlite substrate has a median particle size of less than 50 microns. 
   
   
       3 . The pigment according to  claim 1 , wherein the pigment comprises in addition (b) a metal oxide of low refractive index, wherein the difference of the refractive indices is at least 0.1. 
   
   
       4 . The pigment according to  claim 3 , wherein the metal oxide of high refractive index is TiO 2 , ZrO 2 , Fe 2 O 3 , Fe 3 O 4 , Cr 2 O 3 , ZnO or a mixture of these oxides or an iron titanate, an iron oxide hydrate, a titanium suboxide or a mixture and/or mixed phase of these compounds. 
   
   
       5 . The pigment according to  claim 3 , wherein the metal oxide of low index of refraction is SiO 2 , Al 2 O 3 , AlOOH, B 2 O 3 , or a mixture thereof, wherein alkali or earth alkali metal oxides can be contained as additional component. 
   
   
       6 . The pigment according to  claim 1 , wherein the perlite core has an Fe 2 O 3  content of less than 2%. 
   
   
       7 . The pigment according to  claim 1 , comprising a mixed layer of Al 2 O 3 /TiO 2 , or MgO/TiO 2 , or a dielectric layer/a metal layer/a dielectric layer. 
   
   
       8 . The pigment according to  claim 1  wherein the perlite flakes have an average thickness of <2 μm. 
   
   
       9 . A process for producing the interference pigment according to  claim 1 , by coating perlite flakes with one or more metal oxides in a wet process by hydrolysis of the corresponding water-soluble metal compounds, by separating, drying and optionally calcinating the pigment thus obtained, or
 by suspending perlite flakes in an aqueous and/or organic solvent containing medium in the presence of a metal compound and depositing the metal compound onto perlite flakes by addition of a reducing agent.   
   
   
       10 . (canceled) 
   
   
       11 . Paints, printing inks, plastics, cosmetics, ceramics and glass, which are pigmented with a pigment according to  claim 1 . 
   
   
       12 . The pigment according to  claim 2 , wherein the pigment comprises in addition (b) a metal oxide of low refractive index, wherein the difference of the refractive indices is at least 0.1. 
   
   
       13 . The pigment according to  claim 12 , wherein the metal oxide of high refractive index is TiO 2 , ZrO 2 , Fe 2 O 3 , Fe 3 O 4 , Cr 2 O 3 , ZnO or a mixture of these oxides or an iron titanate, an iron oxide hydrate, a titanium suboxide or a mixture and/or mixed phase of these compounds. 
   
   
       14 . The pigment according to  claim 4 , wherein the metal oxide of low index of refraction is SiO 2 , Al 2 O 3 , AlOOH, B 2 O 3 , or a mixture thereof, wherein alkali or earth alkali metal oxides can be contained as additional component. 
   
   
       15 . The pigment according to  claim 3 , wherein the perlite core has an Fe 2 O 3  content of less than 2%. 
   
   
       16 . The pigment according to  claim 4 , wherein the perlite core has an Fe 2 O 3  content of less than 2%. 
   
   
       17 . The pigment according to  claim 1 , wherein the perlite core has an Fe 2 O 3  content of 0%. 
   
   
       18 . The pigment according to  claim 3 , wherein the perlite core has an Fe 2 O 3  content of 0%. 
   
   
       19 . The pigment according to  claim 4 , wherein the perlite core has an Fe 2 O 3  content of 0%. 
   
   
       20 . The pigment according to  claim 2 , comprising a mixed layer of Al 2 O 3 /TiO 2 , or MgO/TiO 2 , or a dielectric layer/a metal layer/a dielectric layer. 
   
   
       21 . The pigment according to  claim 1  wherein the perlite flakes have an average thickness of from 200 to 1000 nm.