Interference pigments on the basis of glass flakes
The present invention relates to pigments, comprising a plate-like substrate of glass having an average thickness of <1 μm, especially of from 20 nm to 400 nm, and (a) a dielectric material, especially a metal oxide, having a high index of refraction; 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 glass having an average thickness of from <1 μm, and
(a) a dielectric material, having a high index of refraction greater than 1.65;
wherein the glass substrate consists of ECR glass having >0.1% TiO 2 , and has a defined thickness in the range of ±40% of the average thickness,
wherein the pigment has a length of from 2 μm to 5 mm, a width of from 2 μm to 2 mm, and a ratio of length to thickness of at least 5:1,
wherein the ECR glass comprises SiO 2 (63-70%), Al 2 O 3 (3-6%), CaO (4-7%), MgO (1-4%), B 2 O 3 (2-5%), Na 2 O (9-12%), K 2 O (0-3%), TiO 2 (>0.1-4%), and ZnO (1-5%),
wherein the dielectric material comprises a metal oxide selected from the group consisting of (SnO 2 )TiO 2 , 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, and
wherein the pigment is free from (b) metal oxides having a refractive index of 0.1 or more units lower than that of the dielectric material metal oxide of high refractive index.
2. The pigment according to claim 1 , wherein the glass flakes have a homogenous coating of a metal oxide of high refractive index, and a large Gaussian thickness distribution of the glass flakes.
3. A process for producing the interference pigment according to claim 1 , by coating glass 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.
4. Paints, printing inks, plastics, cosmetics, ceramics and glass, which are pigmented with a pigment according to claim 1 .
5. The pigment according to claim 1 wherein the metal oxide of high refractive index is TiO 2 .
6. The pigment according to claim 1 , wherein the metal oxide of high refractive index (a) is TiO 2 .
7. The pigment according to claim 1 , wherein the pigment is further free from: (c) a further dielectric material, having a high index of refraction greater than 1.65.
8. The pigment according to claim 7 , wherein the metal oxide of high refractive index (a) is TiO 2 .