WEATHER STABLE PEARLESCENT PIGMENTS

Abstract

Weather stable pearlescent pigment having a basic pearlescent with an interference color which comprises a transparent platelet-shaped substrate and at least one metal oxide layer with a refractive index >1.8 and on top of this basic pearlescent pigment a weather stabilizing top coating comprising at least one metal oxide and an organofunctional surface modification, wherein a) for a basic pearlescent pigment with silvery interference color the weather stabilizing top coating consists of a first metal oxide of a rare earth metal M1 from the group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and mixtures thereof, or b) for a basic pearlescent pigment with a colored interference color or a silvery interference color the weather stabilizing top coating comprises a first metal oxide of a rare earth metal M1 from the group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and mixtures thereof, and a second metal oxide from a second metal M2 from the group consisting of Si, Al, Zn, Mg, Zr, Sn and mixtures or combinations thereof, and in each case a) or b) the organofunctional surface modification comprises organofunctional silanes or water-based pre-condensated organofunctional silanes.

Claims

1. Weather stable pearlescent pigment having a basic pearlescent pigment with an interference color which comprises a transparent platelet-shaped substrate and at least one metal oxide layer with a refractive index >1.8 and on top of this basic pearlescent pigment a weather stabilizing top coating comprising at least one metal oxide and an organofunctional surface modification, wherein a) for a basic pearlescent pigment with silvery interference color the weather stabilizing top coating consists of a first metal oxide of a rare earth metal M.sup.1 from the group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and mixtures thereof, or b) for a basic pearlescent pigment with a colored interference color or a silvery interference color the weather stabilizing top coating comprises a first metal oxide of a rare earth metal M.sup.1 from the group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and mixtures thereof, and a second metal oxide from a second metal M.sup.2 from the group consisting of Si, Al, Zn, Mg, Zr, Sn and mixtures or combinations thereof, and in each case a) or b) the organofunctional surface modification comprises organofunctional silanes or water-based pre-condensated organofunctional silanes.

2. Weather stable pearlescent pigment according to claim 1, wherein the weather stabilizing top coating comprises a metal oxide of a rare earth metal from the group consisting of La, Pr, Nd, Sm, Eu, Gd, Ho, Yb, and mixtures thereof.

3. Weather stable pearlescent pigment according to claim 1, wherein the weather stabilizing top coating comprises a metal oxide of a rare earth metal from the group consisting of Nd, Sm, Yb, Eu, Ga and mixtures thereof.

4. Weather stable pearlescent pigment according to claim 1, wherein the second metal oxide of metal M.sup.2 is selected from the group consisting of SiO.sub.2, Al.sub.2O.sub.3, ZnO, MgO, ZrO.sub.2, SnO.sub.2 and mixtures or combinations thereof.

5. Weather stable pearlescent pigment according to claim 1, wherein 50 to 100 atomic-% of the rare earth metal M.sup.1 metal oxide are based on a M.sup.1(III) oxidation state, based on the total amount of M.sup.1 ions.

6. Weather stable pearlescent pigment according to claim 1, wherein the amount of the first metal oxide of a rare earth metal M.sup.1 is in a range of 0.3 to 3.0 wt. %, based on the total weight of the pearlescent pigment.

7. Weather stable pearlescent pigment according to claim 1, wherein the weather stabilizing top coating further comprises a cerium metal oxide in an amount of 0.0 to 30 wt %, calculated as Ce.sub.2O.sub.3 and referred to the total amount of rare earth weather stable top coating and calculated as M.sup.1.sub.2O.sub.3.

8. Weather stable pearlescent pigment according to claim 1, wherein the amount of the second metal oxide of a metal M.sup.2 is in a range of 1.0 to 4.0 wt. %, based on the total pearlescent pigment.

9. Weather stable pearlescent pigment according to claim 1, wherein the weather stabilizing top coating b) has a structure characterized that a first coating located on the high-index metal oxide coating is the first rare earth metal oxide coating which is followed by the second metal oxide coating.

10. Weather stable pearlescent pigment according to any of claims 1 to 9 claim 1, wherein the weather stabilizing top coating b) has a structure characterized that the first rare earth metal oxide and the second metal oxide have been manufactured by co-precipitation of both metal oxide precursors.

11. Weather stable pearlescent pigment according to claim 1, wherein the transparent platelet-shaped substrate is selected from the group consisting of natural mica, synthetic mica platelets, glass platelets, SiO.sub.2 platelets, Al.sub.2O.sub.3 platelets, synthetic boehmite platelets, BiOCl platelets and mixtures thereof.

12. A Method of manufacturing the weather stable pearlescent pigments of claim 1, comprising: i) suspending the basic pearlescent pigments in a solvent, iia) coating the basic pearlescent pigments from step i) in the solvent using a rare earth metal oxide precursor at a predetermined pH1, obtaining a rare earth metal oxide layer, or iib) coating the basic pearlescent pigments from step i) in the solvent by one of the following methods: iib1): using a rare earth metal oxide precursor at a predetermined pH1 obtaining a layer of rare earth metal oxide and then coating this pearlescent pigment from step with a precursor of the second metal oxide at a predetermined pH2 obtaining a second metal oxide or iib2): using a precursor of the second metal oxide at a predetermined pH2 forming a second metal oxide and then coating this pearlescent pigment with a rare earth metal oxide precursor at a predetermined pH1 obtaining a layer of rare earth metal oxide or iib3): using for the coating a rare earth metal oxide precursor together with a precursor of the second metal oxide at a predetermined pH3, wherein pH3 is equal to or preferably in between pH1 and pH2, iii) coating the pearlescent pigments from step iia) or step iib) in the solvent with organofunctional silanes or water based pre-condensed organofunctional silanes, and iv) separating the coated pearlescent pigments, optional washing with solvent, and drying at a temperature from a range of 80 to 160 C.

13. The method of manufacturing according to claim 12, wherein the solvent can be water or an organic solvent and wherein for aqueous solvents a salt of the rare earth metal M.sup.1(III) cation is used in amounts of 50 to 100 mol %, based on the total amount of M.sup.1 cations and wherein for organic solvents either a salt of the rare earth metal M.sup.1(III) cation or an metal organic compound of the rare earth metal M.sup.1(III) cation is used as precursor material.

14. (canceled)

15. A formulation comprising the weather stable pearlescent pigments of claim 1.

16. The formulation of claim 15 wherein the formulation is an automotive base coat formulation.

Description

A EXAMPLES

Example 1

[0114] 100 g of commercially available silvery pearlescent pigment based on synthetic mica of fineness 10-40 m (Symic C604, Eckart GmbH) was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 5.2 a solution consisting of 1.90 g EuCl.sub.3*H.sub.2O dissolved in 50 mL water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Thereafter, the pH value was raised with 5 wt. % KOH solution to 7.5 and stirred for 15 min.

[0115] A water glass solution (51.4 g water glass solution, 3.0 wt. % SiO.sub.2 (theoretical value referred to initial pearlescent pigment), mixed with 20.7 g of demineralized water) was then slowly introduced into the suspension where the pH value was kept constant at pH 7.5.

[0116] After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 7.1 g of Hydrosil 2627 diluted with 24.3 g of demineralized water. After additional stirring for 180 minutes, suspension was filtered off and the filter cake was washed with demineralized water before drying at 95 C. under 100 mbar vacuum.

Example 2

[0117] 100 g of commercially available silvery pearlescent pigment based synthetic mica of fineness 10-40 m (Symic C604, Eckart GmbH) was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 6.7 a solution consisting of 2.61 g PrCl.sub.3*6H.sub.2O dissolved in 42 mL water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Thereafter, the pH value was raised with 5 wt. % KOH solution to 7.5 and stirred for 15 min.

[0118] A water glass solution (51.4 g water glass solution, 3.0 wt. % SiO.sub.2 (theoretical value referred to initial pearlescent pigment), mixed with 20.7 g of demineralized water) was then slowly introduced into the suspension where the pH value was kept constant at pH 7.5.

[0119] After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 2.1 g of Dynasilan 1189 diluted with 14.7 g of isopropyl alcohol. After additional stirring for 180 minutes, suspension was filtered off and the filter cake was washed with demineralized water before drying at 75 C. under 100 mbar vacuum.

Example 3

[0120] 100 g of commercially available silvery pearlescent pigment based synthetic mica of fineness 10-40 m (Symic C604, Eckart GmbH) was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 8.5 a solution consisting of 3.06 g Sm(NO.sub.3).sub.3*6H.sub.2O dissolved in 67 mL water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Thereafter, a water glass solution (51.4 g water glass solution, 3.0 wt. % SiO.sub.2, mixed with 20.7 g of demineralized water) was then slowly introduced into the suspension where the pH value was kept constant at pH 8.5.

[0121] After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 1.9 g of Dynasilan 6490 diluted with 14.7 g of isopropyl alcohol. After additional stirring for 180 minutes, suspension was filtered off and the filter cake was washed with demineralized water before drying at 75 C. under 100 mbar vacuum.

Example 4

[0122] 100 g of commercially available silvery pearlescent pigment based on synthetic mica of fineness 10-40 m (Symic C604, Eckart GmbH) was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 5.5 a solution consisting of 2.99 g Gd(NO.sub.3).sub.3*6H.sub.2O dissolved in 65 mL water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Thereafter, the pH value was raised with 5 wt.-% KOH solution to 7.5 and stirred for 15 min.

[0123] A water glass solution (51.4 g water glass solution, 3.0 wt. % SiO.sub.2, mixed with 20.7 g of demineralized water) was then slowly introduced into the suspension where the pH value was kept constant at pH 7.5.

[0124] After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 5.7 g of Hydrosil 2776 diluted with 24.3 g of demineralized water. After additional stirring for 180 minutes, suspension was filtered off and the filter cake was washed with demineralized water before drying at 95 C. under 100 mbar vacuum.

Example 5

[0125] 100 g of commercially available silvery pearlescent pigment based on synthetic mica of fineness 10-40 m (Symic C604, Eckart GmbH) was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 6.7 a solution consisting of 2.37 g YbCl.sub.3*6H.sub.2O dissolved in 65 mL water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Thereafter, the pH value was raised with 5 wt. % KOH solution to 7.5 and stirred for 15 min.

[0126] A water glass solution (51.4 g water glass solution, 3.0 wt. % SiO.sub.2, mixed with 20.7 g of demineralized water) was then slowly introduced into the suspension where the pH value was kept constant at pH 7.5.

[0127] After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 7.1 g of Hydrosil 2627 diluted with 24.3 g of demineralized water. After additional stirring for 180 minutes, suspension was filtered off and the filter cake was washed with demineralized water.

Example 6

[0128] 150 g of commercially available silvery pearlescent pigment based on synthetic mica of fineness 10-40 m (Symic C604, Eckart GmbH) was suspended in 1200 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 6.5 a solution consisting of 2.87 g NdCl.sub.3*H.sub.2O dissolved in 60 mL Water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Thereafter, the pH value was raised with 5 wt. % KOH solution to 7.5 and stirred for 15 min.

[0129] A water glass solution (77.1 g water glass solution, 3.0 wt. % SiO.sub.2, mixed with 31.0 g of demineralized water) was then slowly introduced into the suspension where the pH value was kept constant at pH 7.5.

[0130] After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 9.65 g of Hydrosil 2627 diluted with 36.5 g of demineralized water. After additional stirring for 180 minutes, suspension was filtered off and the filter cake was washed with demineralized water before drying at 95 C. under 100 mbar vacuum.

Example 7 (Alcoholic Route)

[0131] 100 g of commercially available silvery pearlescent pigment based on synthetic mica of fineness 10-40 m (Symic C604, Eckart GmbH) was suspended in 500 ml of isopropanol and brought to boiling temperature.

[0132] Under gentle mixing, first 2.0 g H.sub.2O afterwards within an hour a solution of 3.96 g EuCl.sub.3*H.sub.2O in 20 g isopropyl alcohol was added. Subsequently, a mixture of 0.45 g ethylenediamine and 3.0 g H.sub.2O was added. Thereafter, 8.9 g of tetraethoxysilane and 21.0 g of isopropyl alcohol were continuously introduced over a period of 2 h by use of a dosing pump. The suspension was then allowed to react for another 6 hours. Then add a solution of 2.1 g Dynasilan 1189 in 12.9 g isopropyl alcohol and stop heating. The mixture was stirred over night at room temperature and filtered and washed before drying at 95 C. under 100 mbar vacuum.

Example 8

[0133] 100 g of commercially available silvery pearlescent pigment based on synthetic mica of fineness 10-40 m (Symic C604, Eckart GmbH) was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 5.5 a solution consisting of 5.6 g Gd(NO.sub.3).sub.3*6H.sub.2O dissolved in 75 ml water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Thereafter, the pH value was raised with 5 wt. % KOH solution to 7.5 and stirred for 15 min.

[0134] A water glass solution (42.8 g water glass solution, 2.5 wt. % SiO.sub.2, mixed with 13.8 g of demineralized water) was then slowly introduced into the suspension where the pH value was kept constant at pH 7.5.

[0135] After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 5.7 g of Hydrosil 2776 diluted with 24.3 g of demineralized water. After additional stirring for 180 minutes, suspension was filtered off and the filter cake was washed with demineralized water before drying at 95 C. under 100 mbar vacuum.

Example 9

[0136] 100 g of commercially available silvery pearlescent pigment based synthetic mica of fineness 10-50 m (Symic C604, Eckart GmbH) was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 5.5 a solution consisting of 2.4 g EuCl.sub.3*H.sub.2O dissolved in 75 mL Water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Thereafter, the pH value was raised with 5 wt. % KOH solution to 7.5 and stirred for 15 min.

[0137] A water glass solution (42.8 g water glass solution, 6.0 wt. % SiO.sub.2, mixed with 13.8 g of demineralized water) was then slowly introduced into the suspension where the pH value kept constant at pH 7.5.

[0138] After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 2.0 g of Dynasilan 4148 diluted with 24.3 g of demineralized water. After additional stirring for 180 minutes, suspension was filtered off and the filter cake was washed with demineralized water before drying at 95 C. under 100 mbar vacuum.

Example 10

[0139] 100 g of commercially available silvery pearlescent pigment based on synthetic mica of fineness 10-50 m (Symic C604, Eckart GmbH) was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 5.5 a solution consisting of 4.0 g EuCl.sub.3*H.sub.2O dissolved in 75 mL Water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Thereafter, the pH value was raised with 5 wt. % KOH solution to 7.5 and stirred for 15 min.

[0140] A water glass solution (42.8 g water glass solution, 6.0 wt. % SiO.sub.2, mixed with 13.8 g of demineralized water) was then slowly introduced into the suspension where the pH value was kept constant at pH 7.5.

[0141] After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 5.7 g of Hydrosil 2776 diluted with 24.3 g of demineralized water. After additional stirring for 180 minutes, the suspension was filtered off and the filter cake was washed with demineralized water before drying at 95 C. under 100 mbar vacuum.

Example 11

[0142] 100 g of commercially available red pearlescent pigment based on titanium dioxide coated glass flakes of fineness 10-60 m (Luxan C241, Eckart GmbH) was suspended in 800 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 8.5 a solution consisting of 3.06 g Sm(NO.sub.3).sub.3*6H.sub.2O dissolved in 67 mL Water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Thereafter, a water glass solution (51.4 g water glass solution, 6.0 wt. % SiO.sub.2, mixed with 20.7 g of demineralized water) was then slowly introduced into the suspension where the pH value was kept constant at pH 8.5. After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 1.7 g of Dynasilan 6490 diluted with 14.7 g of isopropyl alcohol. After additional stirring for 180 minutes, suspension was filtered off and the filter cake was washed with demineralized water before drying at 75 C. under 100 mbar vacuum.

Example 12

[0143] 100 g of commercially available silvery pearlescent pigment based on synthetic mica of fineness 10-50 m (Symic C604, Eckart GmbH) was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 5.5 a solution consisting of 2.4 g EuCl.sub.3*H.sub.2O dissolved in 75 mL Water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Thereafter, the pH value was raised with 5 wt. % KOH solution to 7.5 and stirred for 15 min.

[0144] A water glass solution (51.4 g water glass solution, 6.0 wt. % SiO.sub.2, mixed with 13.8 g of demineralized water) was then slowly introduced into the suspension where the pH value was kept constant at pH 7.5.

[0145] After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 2.0 g of Dynasilan 1189 diluted with 24.3 g of isopropyl alcohol. After additional stirring for 180 minutes, suspension was filtered off and the filter cake was washed with demineralized water before drying at 95 C. under 100 mbar vacuum.

Example 13

[0146] 100 g of commercially available silvery pearlescent pigment based on titanium dioxide coated synthetic mica of fineness 10-50 m (Symic C001, Eckart GmbH) was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 5.5 a solution consisting of 2.2 g Gd(NO.sub.3).sub.3*6H.sub.2O dissolved in 75 mL water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Thereafter, the pH value was raised with 5 wt. % KOH solution to 7.5 and stirred for 15 min.

[0147] A water glass solution (11.4 g water glass solution, 6.0 wt. % SiO.sub.2, mixed with 13.8 g of demineralized water) was then slowly introduced into the suspension where the pH value was kept constant at pH 7.5.

[0148] After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 2.0 g of Dynasilan 1189 diluted with 24.3 g of isopropyl alcohol. After additional stirring for 180 minutes, suspension was filtered off and the filter cake was washed with demineralized water before drying at 95 C. under 100 mbar vacuum.

Example 14

[0149] 150 g of commercially available silvery pearlescent pigment based synthetic mica of fineness 10-40 m (Symic C604, Eckart GmbH) was suspended in 1200 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 6.5 a solution consisting of 1.27 g ZnCl.sub.2 dissolved in 60 mL Water was added. At the same time, the pH value was kept constant by adding a water glass solution (28.2 g water glass solution, 6.0 wt. % SiO.sub.2, mixed with 31.0 g of demineralized water).

[0150] Subsequently, a solution consisting of 3.47 g Sm(NO.sub.3).sub.3*6H.sub.2O dissolved in 67 mL Water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution.

[0151] After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 9.65 g of Hydrosil 2627 diluted with 36.5 g of demineralized water. After additional stirring for 180 minutes, suspension was filtered off and the filter cake was washed with demineralized water before drying at 95 C. under 100 mbar vacuum.

Example 15

[0152] 100 g of commercially available silvery pearlescent pigment based on titanium dioxide and iron oxide coated synthetic mica of fineness 10-50 m (Symic C604, Eckart GmbH) was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 5.5 a solution consisting of 2.4 g EuCl.sub.3*H.sub.2O dissolved in 75 mL VE water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Thereafter, the pH value was raised with 5 wt.-% KOH solution to 7.5 and stirred for 15 min. Than 12.0 g solution of Zinc chloride w (ZnCl.sub.2)=7.0% was added by simultaneous adding water glass solution 8.5 wt.-% SiO.sub.2, to keep pH at 7.5.

[0153] After the solution was completely added, the suspension was stirred for 90 minutes before slowly adding a solution of 6.43 g of Hydrosil 2627 diluted with 30 g of demineralized water. The suspension was kept stirring at 70 C. for further 17 h before it was filtered off and the filter cake has been washed with demineralized water before drying at 95 C. under 100 mbar vacuum.

Example 16

[0154] 100 g of commercially available silvery pearlescent pigment based on titanium dioxide and iron oxide coated synthetic mica of fineness 10-50 m (Symic C604, Eckart GmbH) was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 C. before 12.0 g solution of Zinc chloride w (ZnCl.sub.2)=7.0% was added. By continuous adding of water glass solution 8.5 wt.-% SiO.sub.2, pH was adjusted to 7.0.

[0155] After the solution was completely added, the suspension was stirred for 1 h before pH was adjusted to 8.5. Afterwards a solution consisting of 3.06 g Sm(NO.sub.3).sub.3*6H.sub.2O dissolved in 67 mL VE water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 1.9 g of Dynasilan 6490 diluted with 10 g of isopropyl alcohol. After additional stirring for 180 minutes, suspension was filtered off and the filter cake was washed with demineralized water before drying at 95 C. under 100 mbar vacuum.

Example 17

[0156] 100 g of commercially available pearlescent pigment with red interference based on titanium dioxide and coated synthetic mica of fineness 10-50 m (Symic C241, Eckart GmbH) was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 C. and pH adjusted to 7.5, before a solution consisting of 1.28 g Sm(NO.sub.3).sub.3*6H.sub.2O dissolved in 28 mL demineralized water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. After 15 min additional stirring 12.0 g solution of Zinc chloride w (ZnCl.sub.2)=7.0% was added by simultaneous adding water glass solution 8.5 wt.-% SiO.sub.2, to keep pH at 7.5. After the solution was completely added, the suspension was stirred for additional 90 minutes before slowly adding slowly adding a solution of 6.43 g of Hydrosil 2627 diluted with 30 g of demineralized water. The suspension was kept stirring at 70 C. for further 17 h before it was filtered off and filter cake has been washed with demineralized water before drying at 95 C. under 100 mbar vacuum.

Comparative Example 1: (in Accordance with EP 1682622 A1)

[0157] 150 g of commercially available silvery pearlescent pigment based on synthetic mica of fineness 10-50 m (Symic C604, Eckart GmbH) was suspended in 1200 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 6.5 a solution consisting of 4.76 g CeNO.sub.3*6H.sub.2O dissolved in 60 mL water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Thereafter, the pH value was raised with 5 wt. % KOH solution to 7.5 and stirred for 15 min.

[0158] A water glass solution (77.1 g water glass solution containing 6.0 wt. % SiO.sub.2, mixed with 31.0 g of demineralized water) was then slowly introduced into the suspension where the pH value was kept constant at pH 7.5.

[0159] After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 9.65 g of Hydrosil 2627 diluted with 36.5 g of demineralized water. After additional stirring for 180 minutes, suspension was filtered off and the filter cake was washed with demineralized water before drying at 95 C. under 100 mbar vacuum.

Comparative Example 2: (in Accordance with US 2014/018439 A1)

[0160] 150 g of commercially available silver pearlescent pigment based on titanium dioxide coated synthetic mica of fineness 10-50 m (Symic C001, Eckart GmbH) was suspended in 1200 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 6.5 a solution consisting of 3.60 g CeNO.sub.3*6H.sub.2O dissolved in 60 mL water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. The dispersion was stirred for one further hour and then the pH value was raised to pH 7.5 by adding a 10% KOH solution. A solution of 5.7 g of Hydrosil 2776 diluted with 24.3 g of demineralized water was added. After additional stirring for 180 minutes, the suspension was filtered off and the filter cake was washed with demineralized water before drying at 95 C. under 100 mbar vacuum.

Comparative Example 3

[0161] Commercially available silver pearlescent pigment based on titanium dioxide coated synthetic mica of fineness 10-50 m, Symic C001, Eckart GmbH (D.sub.50 of 22 m) without weather stable top coat.

Comparative Example 4

[0162] Commercially available silvery opaque pearlescent pigment with synthetic mica as substrate of fineness 10-50 m, Symic C604, Eckart GmbH (D.sub.50 of 22 m) without weather stable top coat.

Comparative Example 5: (in Accordance with EP 1682622 A1)

[0163] 150 g of commercially available silvery pearlescent pigment Symic C604, Eckart GmbH) was suspended in 1200 g of water. Subsequently, the dispersion was heated to 70 C. and at a pH of 6.5 a solution consisting of 1.19 g CeNO.sub.3*6H.sub.2O dissolved in 50 mL VE water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Thereafter, the pH value was raised with 5 wt.-% KOH solution to 7.5 and stirred for 15 min.

[0164] A water glass solution (25.7 g water glass solution, 6.0 wt.-% SiO.sub.2, mixed with 31.0 g of demineralized water) was then slowly introduced into the suspension where the pH value kept constant at pH 7.5.

[0165] After the solution was completely added, the suspension was stirred for 1 h before adding a solution of 2.25 g of Dynasilan 6490 diluted with 36.5 g of demineralized water. After additional stirring for 180 minutes, suspension was filtered off and the filter cake was washed with demineralized water before drying at 95 C. under 100 mbar vacuum.

Comparative Example 6

[0166] Commercially available red pearlescent pigment based on titanium dioxide coated glass flakes of fineness 10-60 m, Luxan C241, Eckart GmbH (D.sub.50 of 29 m) without weather stable top coat.

[0167] In table 1 all experimental results regarding the composition of the top-layer are summarized.

TABLE-US-00001 TABLE 1 Experimental parameters and top coating composition of the samples Weather stable top coating Pearlescent Composition Type of Amount of pigment inorganic 1.sup.st 2.sup.nd organic organic Sample base metal oxides layer* layer** modification modification Example 1 SyMic Eu.sub.2O.sub.3/SiO.sub.2 1.4% 3.0% SiO.sub.2 HS2627 5.70% C604 Example 2 SyMic Pr.sub.2O.sub.3/SiO.sub.2 1.41 (Pr.sub.6O.sub.11) 3.0% SiO.sub.2 HS2627 5.70% C604 Example 3 SyMic Sm.sub.2O.sub.3/SiO.sub.2 1.2 3.0% SiO.sub.2 HS2627 5.70% C604 Example 4 SyMic Gd.sub.2O.sub.3/SiO.sub.2 1.2 3.0% SiO.sub.2 HS2627 5.70% C604 Example 5 SyMic Yb.sub.2O.sub.3/SiO.sub.2 1.7 3.0% SiO.sub.2 HS2627 5.70% C604 Example 6 SyMic Nd.sub.2O.sub.3/SiO.sub.2 0.95 3.0% SiO.sub.2 HS2627 5.70% C604 Example 7 SyMic Eu.sub.2O.sub.3/SiO.sub.2 2.42 3.0% SiO.sub.2 Dynasilan 2.1% C604 1189 Example 8 SyMic Gd.sub.2O.sub.3/SiO.sub.2 1.5 2.5% SiO.sub.2 HS2627 5.70% C604 Example 9 SyMic Eu.sub.2O.sub.3/SiO.sub.2 1.6 2.5% SiO.sub.2 HS2627 5.70% C604 Example 10 SyMic Eu.sub.2O.sub.3/SiO.sub.2 2.8 2.5% SiO.sub.2 HS2776 5.70% C604 Example 11 Luxan Sm.sub.2O.sub.3/SiO.sub.2 1.3 2.5% SiO.sub.2 Dynasilan 1.70% C241 6490 Example 12 SyMic Eu.sub.2O.sub.3/SiO.sub.2 1.40 3.0% SiO.sub.2 Dynasilan 2.00% C604 1189 Example 13 Symic Gd.sub.2O.sub.3 0.80 Dynasilan 2.00% C001 1189 Example 14 SyMic Co-coating 0.44 1.13% HS2627 5.70% C604 ZnO/SiO.sub.2/ SiO.sub.2 + Sm.sub.2O.sub.3 0.45% ZnO*** Example 15 SyMic Eu.sub.2O.sub.3/ 0.9% 0.5% HS2627 5.7% C604 co-coating SiO.sub.2/ZnO ZnO/SiO.sub.2 Example 16 SyMic Co-coating 0.5% 0.9% Dynasilan 1.50% C604 ZnO/SiO.sub.2/ Sm.sub.2O.sub.3 6490 Sm.sub.2O.sub.3 Example 17 SyMic Sm.sub.2O.sub.3/ 0.5% 1.0% HS2627 5.7% C604 Co-coating SiO.sub.2/ZnO ZnO/SiO.sub.2 Comp. SyMic Ce.sub.2O.sub.3/SiO.sub.2 1.2% Ce.sub.2O.sub.3 3.0% SiO.sub.2 HS2627 5.70% Example 1 C604 Comp. Symic Ce.sub.2O.sub.3 0.9% Ce.sub.2O.sub.3 / HS2776 5.70% Example 2 C001 Comp. / / / / / / Example 3 Comp. / / / / / / Example 4 Comp. SyMic Ce.sub.2O.sub.3/SiO.sub.2 0.3% Ce.sub.2O.sub.3 1.0% SiO.sub.2 Dynasilan 1.50% Example 5 C604 6490 Comp. Luxan / / / / / Example 6 C241 *Measured with XRF and calculated in wt. % as M.sub.2O.sub.3, if not indicated otherwise **Theoretical amount in wt. % related to amount of basic pearlescent pigment ***measured with XRF and calculated in wt. % as ZnO

B TESTING METHODS

B1 Photocatalytic Activity:

[0168] In order to determine the photocatalytic activity of the pigment powders a special gas phase photoreactor was used, presented schematically in FIG. 1.

[0169] 150 mg of pigment powder was weighted in the center of a petri dish which afterwards has been placed at the bottom of the photoreactor. The temperature of the photoreactor was adjusted and kept constant at 50 C.

[0170] The photoactivities of the samples were measured in ambient air which circulates by using a gas pump through a FTIR measurements system and back to the photoreactor. The initial water and CO.sub.2 contents of the air were about 0.2% and 400 ppm, respectively.

[0171] As model pollutant 1 L of acetone was injected over a septum inside the system. After the pollutant was homogeneously distributed the UV-lamp (90 mW/cm.sup.2 at 405 nm) was switched on and acetone started to degrade forming CO.sub.2 quantitatively.

[0172] The degradation of acetone and formation of CO.sub.2 was monitored with a FTIR spectrometer as a function of time and fits to a 1st order reaction kinetics and 1st order rate constants were obtained. The initial formation rates of acetone and carbon dioxide are approximated linearly and the formation rates are obtained in ppm/h units.

[0173] The higher the CO.sub.2 formation in ppm per hour, the higher the photocatalytic activity of the pigment powder is. The test was passed if the rate of CO.sub.2 formation was less than 3 ppm/h.

[0174] For each test series a zero spectra needed to be imposed beforehand, by using same procedure without pigment and acetone injection. The values of this blind test were subtracted from the values of the samples with pigments.

B2: Color-Shade Constancy and Optical Properties of Sample Compared with the Starting Material without Top Coating:

[0175] The samples were applied as doctor-blade drawdowns on black-white opacity charts (Byko-Chart 2853, Byk Gardner) using a 40 m spiral bar for samples based on synthetic mica and a 50 m spiral bar for samples based on glass flakes. The effect pigments were dispersed in a conventional nitrocellulose coating (Dr. Renger Erco bronzing mixed varnish 2615e; from Morton, pigmentation of 6.0 wt.-% relative to the total weight of the wet varnish). In comparison to each sample without the weather stable top coating the change in color was determined using a MINOLTA CM-700d in diffuse reflection. The color values on the white parts of the opacity charts were measured and the differences were expressed with the well-known Hunter formula:

[00001]$E^{}={\left(L^2+a^2+b^2\right)}^{1/2}$

[0176] Such differences are characteristic for changes of the mass tone of the pearlescent pigment. An overall color change E* of 2.25 was acceptable.

B3 2-Coat Pneumatic Gun Application:

[0177] A white grounded aluminum test panel was painted with a 1K aqueous-based test base coat varnish comprising acrylate-polyurethane binder and pearlescent pigments of the examples and comparative examples in an amount of 1.5 wt. % using an Oerter APL1.2 spray gun application. The wet-thickness of the coatings were 13-17 m and the coated panels were dried at 80 C. for 12 min.

[0178] A 1K conventional acrylate-based lacquer was used as clearcoat at a thickness of 37-43 m and a drying temperature of 140 C. for 30 min. The use of a 1K clearcoat instead of the 2K clearcoat used conventionally enhances the testing conditions.

B4 Strengthened Weathering Test (Combined Xenon and Condensation Water Test):

[0179] The panels were subjected to Xenon accelerated weathering test according to SAE J 2527 for 1000 h. Directly afterwards the panels were subjected to a 72 h condensation water test according to DIN EN ISO 6270-2 at a temperate of 40 C.

[0180] The gloss was measured using a 20 gloss meter (micro-TRI-gloss of BYK Gardener GmbH) according to DIN EN ISO 2813 before and after the testing and expressed as difference in % relative to the gloss before testing. A decrease of the relative gloss of less than-40% was acceptable.

[0181] Occasionally, this test was only applied when the photocatalytic activity test and the color change tests were passed.

B5 Carbon Content Determination:

[0182] The carbon-content of all samples was determined by a combustion of the sample in an oxygen stream and detection of evolving CO.sub.2 by IR spectroscopy using an analyzer of LECO instrument GmbH, Germany.

B6 XRF Analysis:

[0183] The metal oxide of the rare earth metals and the Zn-content of Example 14 of the samples and of some of the pigments from the comparative examples were determined by means of x-ray fluorescence analysis (XRF). For this purpose, the respective pigments were incorporated into a lithium tetraborate glass tablet, fixed in solid sample measuring cups and analyzed therefrom. The measuring instrument used was the Advantix ARL system from Thermo Scientific. The measurements were first calibrated with appropriate standard methods. The results are listed in table 1.

[0184] The Si-contents of the top coating of the samples could not be determined with this method, because the transparent synthetic mica or glass substrates already have a high amount of silica. Instead, the theoretical values assuming 100% reaction rates are depicted in table 1.

C RESULTS

[0185] The results of the testing are expressed in table 2.

TABLE-US-00002 TABLE 2 Test results of samples gloss 20 C- Photoactivity compared to Content CO.sub.2 E* on white untreated Sample [wt. %] [ppm/h] background sample Example 1 0.14% <1 1.42 30.9 Example 2 0.34% <1 1.06 33.4 Example 3 0.35% <1 1.30 29.3 Example 4 0.08% <1 1.82 36.8 Example 5 0.10% <1 1.89 25.6 Example 6 0.09% <1 1.54 26.3 Example 7 <1 0.62 2.20 32.0 Example 8 0.10% <1 1.08 27.0 Example 9 <1 0.86 1.96 26.0 Example 10 0.11% <1 1.97 28.2 Example 11 0.11% <1 1.07 20.6 Example 12 0.00 <1 1.39 28.60 Example 13 0.39% 1 0.24 29.7 Example 14 0.32% <1 0.81 29.0 Example 15 0.18% <1 1.12 1.7 Example 16 0.32% <1 0.81 29.0 Example 17 0.15% <1 0.33 16.0 Comp. Example 1 0.11% <1 2.75 36.2 Comp. Example 2 6 0.87 47.0 Comp. Example 3 62 56.6 Comp. Example 4 10 51.0 Comp. Example 5 2 54.9 Comp. Example 6 723 50.8

D DISCUSSION

[0186] All inventive Examples passed the photoactivity test very well, had a low change E* and passed the combined Xenon and condensation water test. The photoactivity test was tremendously failed by Comparative Example 7 which had no weather stable top coating at all and was a green pearlescent pigment. Also the Comparative Examples 3 and 4 representing silvery pearlescent pigments clearly failed this test.

[0187] Comparative Examples 1 and 5 were made according to EP 1682622 A1 and both Comparative Examples passed the photoactivity test. Comparative Example 1 also passed the combined Xenon and condensation water test while Comparative Example 5 did not pass this test. The Comparative Example 1, however, had a neutral anthracite color tone and did not pass the color change E* test, especially when compared with Examples 1 to 8 and Example 10. This can be attributed to the rather high amount of Ce.sub.2O.sub.3 used here and to the yellowish color of this cerium oxide. Comparative Example 5 passed the color change test (E* was comparable to Example 12 which had the same basic pearlescent pigment) which is apparently due to the low amount of Ce.sub.2O.sub.3 used. However, this amount of Ce.sub.2O.sub.3 seemed to be too low to pass the combined Xenon and condensation water test.

[0188] Example 13 represented a silvery pearlescent pigment which was coated only with a single metal oxide layer (Gd.sub.2O.sub.3) as rare earth metal in the top coating. This sample also passed all test although the photoactivity was slightly higher than most of the other Examples. In contrast, Comparative Example 2 had a single Ce.sub.2O.sub.3 top coating and did not pass the photoactivity test.

[0189] Examples 15 and 17 performed particularly well in the combined Xenon and condensation water test.

[0190] The carbon content of all Examples was rather low indicating that only a fraction of the silanes utilized for the surface modification was really bonded to the pigment's surface. Without being bonded to any theory the inventors believe that this rather low C-content effects in a surface which is not to hydrophobic which helps for passing the combined Xenon and condensation water test.