Gold pigment

Abstract

The present invention relates to a golden interference pigment which is suitable, in particular, for printing processes, to a process for the preparation of a pigment of this type, and to the use thereof.

Claims

1. Golden interference pigment which comprises a flake-form substrate and at least one layer located on the substrate, wherein the flake-form substrate is a synthetically produced transparent substrate which has a green inherent interference colour, where the flake-form substrate consists of Al.sub.2O.sub.3 or consists of Al.sub.2O.sub.3 with a content of up to 5% by weight of TiO.sub.2, based on the weight of the substrate, or comprises Al.sub.2O.sub.3 with a proportion of at least 90% by weight, based on the weight of the substrate, and has a geometrical thickness of 180 to 250 nm or 350 to 450 nm, or the flake-form substrate consists of ZrO.sub.2 or comprises ZrO.sub.2 with a proportion of at least 90% by weight, based on the weight of the substrate, and has a geometrical thickness of 140 to 210 nm or 260 to 400 nm, or the flake-form substrate consists of TiO.sub.2 or comprises TiO.sub.2 with a proportion of at least 90% by weight, based on the weight of the substrate, and has a geometrical thickness of 110 to 170 nm or 240 to 310 nm, or the flake-form substrate is a glass flake which comprises a maximum of 70% by weight of SiO.sub.2 and has a geometrical thickness of 230 to 300 nm or 400to 470 nm, and at least one layer which comprises a mixture or mixed oxide of Fe.sub.2O.sub.3 and TiO.sub.2 is located on the substrate, and the substrate has a particle size of 5-40 m with a d.sub.95 value of 35 m to <40 m.

2. Interference pigment according to claim 1, wherein the pigment has two layers which comprise a mixture or mixed oxide of Fe.sub.2O.sub.3 and TiO.sub.2.

3. Interference pigment according to claim 2, which interference pigment has at least one further layer comprising a colourless dielectric material, which has a refractive index n of <1.8, and is present between the layers which comprise a mixture or mixed oxide of Fe.sub.2O.sub.3 and TiO.sub.2.

4. Interference pigment according to claim 3, wherein a further layer comprising a colourless dielectric material, which has a refractive index n of >1.8, and is additionally present between the layers which comprise a mixture or mixed oxide of Fe.sub.2O.sub.3 and TiO.sub.2.

5. Interference pigment according to claim 1, wherein the layer which comprises a mixture or mixed oxide of Fe.sub.2O.sub.3 and TiO.sub.2 has a geometrical layer thickness of 30 nm to 180 nm.

6. Interference pigment according to claim 1, wherein at least one of the layers which comprise a mixture or mixed oxide of Fe.sub.2O.sub.3 and TiO.sub.2 is a pseudobrookite layer.

7. A process for preparing a golden interference pigment according to claim 1, comprising covering the synthetically produced transparent substrate which has a green inherent interference colour, where the flake-form substrate consists of Al.sub.2O.sub.3 or consists of Al.sub.2O.sub.3 with a content of up to 5% by weight of TiO.sub.2, based on the weight of the substrate, or comprises Al.sub.2O.sub.3 with a proportion of at least 90% by weight, based on the weight of the substrate, and has a geometrical thickness of 180 to 250 nm or 350 to 450 nm, or the flake-form substrate consists of ZrO.sub.2 or comprises ZrO.sub.2 with a proportion of at least 90% by weight, based on the weight of the substrate, and has a geometrical thickness of 140 to 210 nm or 260 to 400 nm, or the flake-form substrate consists of TiO.sub.2 or comprises TiO.sub.2 with a proportion of at least 90% by weight, based on the weight of the substrate, and has a geometrical thickness of 110 to 170 nm or 240 to 310 nm, or the flake-form substrate is a glass flake which comprises a maximum of 70% by weight of SiO.sub.2 and has a geometrical thickness of 230 to 300 nm or 400 to 470 nm, and the substrate has a particle size of 5-40 with a d.sub.95 value of 35 to <40 m, with at least one layer which comprises a mixture or mixed oxide of Fe.sub.2O.sub.3 and TiO.sub.2.

8. The process according to claim 7, wherein the covering is carried out in an aqueous dispersion by a wet-chemical process by hydrolytic decomposition of inorganic metal salts.

9. The process according to claim 7, wherein two layers which comprise a mixture or mixed oxide of Fe.sub.2O.sub.3 and TiO.sub.2 are applied, where at least one further layer comprising a colourless dielectric material is applied between these layers, where the material for the further layer has a refractive index n of <1.8.

10. The process according to claim 9, wherein at least one further layer which consists of a colourless dielectric material, which has a refractive index n of >1.8, is additionally applied between the layers which comprise a mixture or mixed oxide of Fe.sub.2O.sub.3 and TiO.sub.2.

11. The process according to claim 7, wherein at least one of the layers which comprise a mixture or mixed oxide of Fe.sub.2O.sub.3 and TiO.sub.2 is a pseudobrookite layer.

12. A method for preparing a product selected from the group consisting of paints, coatings, printing inks, plastics, glasses, paper, ceramic, cosmetic formulations, laser marking of plastics, laser marking of paper, pigment preparations and dry preparations, comprising incorporating an interference pigment of claim 1 into said product.

13. The method according to claim 12, wherein the printing ink is a gravure printing ink, a flexographic printing ink, a screen printing ink, an intaglio printing ink or an offset printing ink.

14. A gravure printing ink, flexographic printing ink, screen printing ink, intaglio printing ink or offset printing ink comprising interference pigments according to claim 1.

15. Interference pigment according to claim 1, wherein the flake-form substrate consists of Al.sub.2O.sub.3 or consists of Al.sub.2O.sub.3 with a content of up to 5% by weight of TiO.sub.2, based on the weight of the substrate, or comprises Al.sub.2O.sub.3 with a proportion of at least 90% by weight, based on the weight of the substrate, and has a geometrical thickness of 180 to 250 nm or 350 to 450 nm.

16. Interference pigment according to claim 1, wherein the flake-form substrate consists of ZrO.sub.2 or comprises ZrO.sub.2 with a proportion of at least 90% by weight, based on the weight of the substrate, and has a geometrical thickness of 140 to 210 nm or 260 to 400 nm.

17. Interference pigment according to claim 1, wherein the flake-form substrate consists of TiO.sub.2 or comprises TiO.sub.2 with a proportion of at least 90% by weight, based on the weight of the substrate, and has a geometrical thickness of 110 to 170 nm or 240 to 310 nm.

18. Interference pigment according to claim 1, wherein the flake-form substrate is a glass flake which comprises a maximum of 70% by weight of SiO.sub.2 and has a geometrical thickness of 230 to 300 nm or 400 to 470 nm.

19. Interference pigment according to claim 1, wherein the substrate has a d.sub.50 value of 15 m to <20 m.

20. An intaglio printing ink comprising interference pigments according to claim 1.

Description

EXAMPLE 1

(1) 200 g of aluminium dioxide flakes having a green interference colour which have a particle size distribution d.sub.50=18-19.5 m and d.sub.95=37-39 m (determined using Malvern Mastersizer 2000) and a geometrical thickness of about 220 nm (determined by SEM) are suspended in 21 of demineralised water, and the suspension is heated to a temperature of 75 C. When this temperature has been reached, a solution of 248.0 g of FeCl.sub.36H.sub.2O, 87.0 g of TiCl.sub.4 and 10.4 g of AlCl.sub.36 H.sub.2O in 291.2 g of demineralised water is slowly metered in with stirring. The pH of the suspension is kept constant at 2.6 using NaOH solution (32%). After addition of the metal salt solutions, the mixture is stirred for about a further 15 minutes. The pH is subsequently increased to pH 7.5 using NaOH solution (32%), and 592.6 g of sodium water-glass solution (13.5% of SiO.sub.2) are slowly added at this pH. The pH is then reduced to 2.0 using hydrochloric acid (10% of HCl), and the mixture is stirred for a further 15 minutes. 192 ml of TiCl.sub.4 solution (370 g of TiCl.sub.4/1) are subsequently metered in, while the pH is kept constant using NaOH solution (32%). The pH is subsequently increased to 2.6 using NaOH solution (32%), and 264.8 g of FeCl.sub.36 H.sub.2O, 92.6 g of TiCl.sub.4 and 11.0 g of AlCl.sub.36 H.sub.2O in 133.6 g of demineralised water are slowly metered in at this value. The pH is kept constant using NaOH solution (32%). The mixture is subsequently stirred for a further 15 minutes, the pH is increased to pH 5.0 (NaOH solution, 32%), and the mixture is stirred for a further 15 minutes. The pigment is filtered, washed with demineralised water and dried at 110 C. It is subsequently calcined at 850 C. for 30 minutes.

(2) A gold-coloured lustre pigment having a red-golden interference colour and mass tone, strong lustre and very good hiding power is obtained.

COMPARATIVE EXAMPLE 1

(3) 100 g of mica flakes having a particle size of 10-60 m are suspended in 21 of demineralised water, and the suspension is heated to a temperature of 75 C. When this temperature has been reached, a solution of 130.5 g of FeCl.sub.36H.sub.2O, 46.5 g of TiCl.sub.4 and 11.6 g of AlCl.sub.36 H.sub.2O in 84.3 g of demineralised water is slowly metered in with stirring. The pH of the suspension is kept constant at 2.6 using NaOH solution (32%). After addition of the metal salt solutions, the mixture is stirred for about a further 15 minutes. The pH is subsequently increased to pH 7.5 using NaOH solution (32%), and 431 g of sodium water-glass solution (13.5% of SiO.sub.2) are slowly added at this pH. The pH is then reduced to 2.0 using hydrochloric acid (10% of HCl), and the mixture is stirred for a further 15 minutes. 393 g of TiCl.sub.4 solution (370 g of TiCl.sub.4/1) are subsequently metered in, while the pH is kept constant using NaOH solution (32%). The pH is subsequently increased to 2.6 using NaOH solution (32%), and 48.6 g of FeCl.sub.36 H.sub.2O, 18.6 g of TiCl.sub.4 and 4.0 g of AlCl.sub.36 H.sub.2O in 31.4 g of demineralised water are slowly metered in at this value. The pH is kept constant using NaOH solution (32%). The mixture is subsequently stirred for a further 15 minutes, the pH is increased to pH 5.0 (NaOH solution, 32%), and the mixture is stirred for a further 15 minutes. The pigment is filtered, washed with demineralised water and dried at 110 C. It is subsequently calcined at 850 C. for 30 minutes.

(4) A gold-coloured lustre pigment having a golden interference colour, strong lustre, extremely high brightness and good hiding power is obtained.

(5) Black/white paint cards are prepared from each of the gold pigments according to Example 1 and Comparative Example 1. The corresponding CIEL,a,b values are determined using an ETA device (STEAG-ETA Optic GmbH Inc.).

(6) TABLE-US-00001 Sample 75/95 Black background Chroma Hue angle Hiding L a b *C *h power Ex. 1 117.8 19.8 96.4 98.4 78.4 35.8 Comp. Ex. 158.9 4.3 104.0 104.1 87.6 30.8

(7) The values shown above show that the pigment according to the invention according to Example 1 has high brightness, a very good chroma value and extremely high hiding power. In addition, it exhibits a significantly more reddish hue at a hue angle of about 78 than the comparative pigment at a hue angle of about 87. By contrast, the comparative pigment has such high brightness that a gleaming yellow shade, but not a warm red-gold shade is perceived with the naked eye. By contrast, the hiding power of the comparative pigment remains significantly behind that of the pigment according to the invention according to Example 1. In addition, the pigment in accordance with Comparative Example 1 is not suitable for applications which require very finely divided pigments owing to the comparatively large particle size.

(8) (In the CIELab system, the saturation of a colour is only described inadequately and is often equated with the chroma. According to Eva Lbbe, Sttigung im CIELAB-Farbsystem and LSh-Farbsystem [Saturation in the CIELAB Colour System and LSh Colour System)] Books on Demand GmbH, Norderstedt, 3rd Edition 2011, p. 47, the saturation of a colour is, however, better characterised by the ratio of the chroma of the colour to the overall colour impression. Accordingly, the saturation S is calculated as follows:

(9) $S=\frac{C_{\mathrm{ab}}^{*}}{\sqrt{L^{*2}-C_{\mathrm{ab}}^{*2}}}.Math.100\%$
where S represents the newly calculated saturation, L* represents the CIELAB lightness value and C*.sub.ab represents the CIELAB chromaticity.

(10) If the saturation of the samples according to Example 1 and the comparative example are calculated in accordance with the formula indicated, a value for the saturation of about 64% is obtained for Example 1, while the saturation in the comparative example is only about 55%. These values correspond to the visual perception, which gives a significantly higher colour saturation for the paint card of Example 1 than for that of the comparative example.)

(11) Use Examples:

(12) 1. Intaglio Printing Ink:

(13) TABLE-US-00002 Gold pigment according to Example 1 15% by weight Intaglio Varnish Flop 670179 85% by weight
(Gleitsmann Security Inks)

(14) The gold pigment is incorporated into the binder system under gentle conditions and printed onto paper using an engraved steel printing plate warmed to 40 C. to 70 C. A raised pattern of fine lines with a warm, red-golden hue in good saturation is obtained.

(15) 2. Offset Ink:

(16) a)

(17) TABLE-US-00003 Gold pigment according to Example 1 15% by weight OF printing varnish 96147 85% by weight
(Jaenecke and Schneemann Druckfarbe GmbH)
b)

(18) TABLE-US-00004 Gold pigment according to Example 1 30% by weight OF printing varnish 96147 70% by weight
(Jaenecke and Schneemann Druckfarbe GmbH)

(19) The gold pigment is in each case incorporated into the printing ink vehicle under gentle conditions, and the printing ink obtained is printed. In both cases, a readily visible, strikingly red-golden pattern is obtained, whose perceptible colour saturation appears significantly stronger in the case of the print result in accordance with 2b than in the case of the print result according to Example 2a.

(20) 3. Screen Printing Ink:

(21) The gold pigment according to Example 1 is introduced in proportions of 10% by weight or 15% by weight in each case into 90% by weight or 85% by weight in each case of screen printing binder (AquaJet FGLM 093 or MZ Lack 093, Prll KG, or UV-aqueous 672048, Gleitsmann Security Inks) under gentle conditions. The printing is carried out using commercially available screens (61-64 or 77-55).

(22) The printing inks obtained can be printed successfully with each of the screens without clogging the screens. Saturated, red-golden, highly opaque print images with high lustre are obtained in each concentration and with each of the binders indicated.

(23) 4. Gravure Printing Ink/Flexographic Printing Ink:

(24) The gold pigment according to Example 1 is incorporated in proportions of 15% by weight or 25% by weight in each case into 85% by weight or 75% by weight in each case of gravure/flexographic printing binder (NC TOB OPV-00, Siegwerk, or Haptobond CT 105, Hartmann Druckfarben GmbH/Sun Chemical) under gentle conditions with stirring. The viscosity of the printing ink is adjusted using small amounts of solvent.

(25) The print images obtained exhibit a saturated red-gold hue and high lustre.