Interference pigments on the basis of glass flakes

Abstract

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.

Claims

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.sub.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.sub.2 (63-70%), Al.sub.2O.sub.3 (3-6%), CaO (4-7%), MgO (1-4%), B.sub.2O.sub.3 (2-5%), Na.sub.2O (9-12%), K.sub.2O (0-3%), TiO.sub.2 (>0.1-4%), and ZnO (1-5%), wherein the dielectric material comprises a metal oxide selected from the group consisting of (SnO.sub.2)TiO.sub.2, TiO.sub.2, ZrO.sub.2, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, Cr.sub.2O.sub.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.sub.2.

6. The pigment according to claim 1, wherein the metal oxide of high refractive index (a) is TiO.sub.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.sub.2.

Description

EXAMPLES

Example 1

(1) 4.5 g of glass flakes GF10 (Glassflake Ltd., ECR glass (softening temperature of about 688° C.); average thickness of about 210 nm and a BET of 2.2 m.sup.2/g), which have been milled and sieved to obtain particles smaller than 100 microns and larger than 20 microns, are mixed with 300 ml distilled water in a closed reactor and heated at 75° C. The pH is set to 1.15 and the suspension is stirred at 350 rpm for 15 minutes. Then a preparation comprising 9 g SnCl.sub.4.5H.sub.2O dissolved in 5 g HCl (37%) and 100 g distilled water is added (0.8 ml/minutes) during 15 minutes while stirring at 350 rpm. Then the suspension is heated at 90° C. while stirring during additional 15 minutes.

(2) Then the pH is set to 1.6 and a preparation comprising 34 g from TiOCl.sub.2, 32 g of HCl (37%) and 445 g of distilled water is added at a rate of 0.8 ml/minutes during 6 hours. The powder obtained after filtration and drying features a bright bleu colour shifting to magenta with increasing viewing angle. The product is calcinated at 500° C. in air for 6 hours. X-ray diffraction spectroscopy shows that the TiO.sub.2 is present in the rutile modification and elemental analysis shows that the product contains 0.92% by weight Sn and 35.4% by weight of Ti.

Example 2

(3) 4.5 g of glass flakes GF10 (Glassflake Ltd.), which have been milled and sieved to obtain particles smaller than 100 microns and larger than 20 microns, are mixed with 300 ml distilled water in a closed reactor and heated at 75° C. The pH is set to 1.2 and the suspension stirred at 350 rpm for 15 minutes. Then a preparation comprising 9 g SnCl.sub.4.5H.sub.2O dissolved in 5 g HCl (37%) and 100 g distilled water is added (0.8 ml/minutes) during 15 minutes while stirring at 350 rpm. Once the addition of the preparation is finished the suspension is stirred for 15 minutes and the pH is set to 1.8. Then a preparation comprising 34 g TiOCl.sub.2, 32 g HCl (37%) and 445 g distilled water is added at 0.8 ml/minutes during 1 hour while stirring.

(4) After 1 hour a mixture of 15% of a preparation comprising 12 g of AlCl.sub.3.6H.sub.2O dissolved in 200 distilled water and 85% of a preparation comprising 34 g TiOCl.sub.2, 32 g HCl (37%) and 445 g distilled water is added at the rate of 0.8 ml/minute during 4 hours at a constant pH of 1.8. Finally a preparation comprising 34 g TiOCl.sub.2, 32 g HCl (37%) and 445 g distilled water is added at a rate of 0.8 ml/minute during 0.5 hours (pH=1.8). The powder obtained after filtration and drying features a bright yellow colour shifting to pearl grey with increasing viewing angle.

(5) The product is calcinated at 500° C. in air for 6 hours. X-ray diffraction spectroscopy shows that the TiO.sub.2 is present in the rutile modification and elemental analysis shows that the product contains 1.37 weight % of Sn, 11.6 weight % of Ti and 1.58 weight % Al.

Example 3

(6) 5 g GF10 (Glassflake Ltd.), which have been milled and sieved to obtain particles smaller than 100 microns and larger than 20 microns, are dispersed in 55 g isopropanol and 7.5 g tetraethoxy silane and the dispersion is heated at 60° C. in a closed reactor. Then 6 g of distilled water and 2 g NH.sub.3 in 16 g isopropanol are added during 3 hours. The glass flakes thus obtained after filtration and drying are coated with a layer of SiO.sub.2 having a thickness of about 30 nm.