Metallic luster pigments

Abstract

The present invention relates to metallic luster pigments, to a process for production thereof and to the use of such metallic luster pigments.

Claims

1. A metallic luster pigment based on coated aluminum substrate platelets, wherein the aluminum substrate platelets have a thickness of 5 to 30 nm, are of monolithic structure and have optionally been passivated and are encased by one coating B, wherein the coating B has a thickness of at least 50 nm and is formed essentially from iron(III) oxide, and wherein between the surface of the aluminum substrate platelets and the coating B there is at least one further coating A which encases the substrate platelets and is composed of at least one metal oxide having a low refractive index of at most 1.8, selected from the group consisting of SiO.sub.2, B.sub.2O.sub.3, MnO.sub.2, MgO, GeO.sub.2 and Al.sub.2O.sub.3, wherein the substrate platelets have a further coating C composed of at least one metal oxide (hydrate) selected from silicon (di)oxide, silicon oxide hydrate, aluminum oxide, aluminum oxide hydrate, zinc oxide, tin oxide, titanium dioxide, zirconium oxide, and chromium(III) oxide.

2. The metallic luster pigment as claimed in claim 1, wherein the coating A is composed of SiO.sub.2.

3. The metallic luster pigment as claimed in claim 1, wherein the coating A has a thickness of 1 to 100 nm.

4. The metallic luster pigment as claimed in claim 1, wherein layer A is formed from SiO.sub.2 in a thickness of 5 to 50 nm and layer B from Fe.sub.2O.sub.3 in a thickness of 50 to 300 nm.

5. A process for producing metallic luster pigments as claimed in claim 1, comprising the steps of: providing optionally passivated aluminum substrate platelets, coating the aluminum substrate platelets by hydrolytic decomposition of one or more organic metal compounds and/or by precipitation of one or more dissolved metal salts.

6. A composition comprising: a metallic luster pigment based on coated aluminum substrate platelets, wherein the aluminum substrate platelets have a thickness of 5 to 30 nm, are of monolithic structure and have optionally been passivated and are encased by one coating B, wherein the coating B has a thickness of at least 50 nm and is formed essentially from iron(III) oxide and wherein between the surface of the aluminum substrate platelets and the coating B there is at least one further coating A which encases the substrate platelets and is composed of at least one metal oxide having a low refractive index of at most 1.8, selected from the group consisting of SiO.sub.2, B.sub.2O.sub.3, MnO.sub.2, MgO, GeO.sub.2 and Al.sub.2O.sub.3, wherein the substrate platelets have a further coating C composed of at least one metal oxide (hydrate) selected from silicon (di)oxide, silicon oxide hydrate, aluminum oxide, aluminum oxide hydrate, zinc oxide, tin oxide, titanium dioxide, zirconium oxide, and chromium(III) oxide.

7. The composition as claimed in claim 6, wherein the coating A is composed of SiO.sub.2.

8. The metallic luster pigment as claimed in claim 6, wherein the coating A has a thickness of 1 to 100 nm.

9. The composition as claimed in claim 6, layer A is formed from SiO.sub.2 in a thickness of 5 to 50 nm and layer B from Fe.sub.2O.sub.3 in a thickness of 50 to 300 nm.

10. The composition of claim 6, wherein the composition is a paint, a printing ink, a plastics, a glass, a ceramic product, or a decorative cosmetic.

Description

(1) FIGS. 1 and 2 show results from combustion tests on various coated aluminum platelets having a different proportion by weight of aluminum (FIG. 1) and iron(III) oxide (FIG. 2). The performance rating for the fire characteristics (y axis) as a function of the proportion of aluminum (FIG. 1) or iron(III) oxide (FIG. 2) in the coated substrate platelets is determined by assessing the behavior of the sample in the combustion test described hereinafter.

(2) FIG. 3 shows a coated aluminum platelet of the invention. The aluminum platelet has a very homogeneous thickness and is encased by an SiO.sub.2 layer (coating A, light) and an iron oxide layer (coating B, dark).

(3) FIG. 4 shows a coated aluminum platelet of the invention having an aluminum core, SiO.sub.2 layer (coating A, light) and iron oxide layer (coating B, dark).

(4) The examples which follow serve to further illustrate the present invention, without being restricted thereto.

EXAMPLE 1 (THIN ALUMINUM PLATELETS WITH THICK IRON OXIDE COATING)

(5) First of all, 50 g of Al platelets (thickness between 20 nm and 30 nm, d50=12 m) were coated with 10 g of SiO.sub.2 by means of a sol-gel method using tetraethyl orthosilicate (TEOS). In a round bottom flask with reflux condenser and stirrer, these Al platelets were admixed with 500 mL of deionized water and heated to 75 C. while stirring. The pH was adjusted to a value of 3.2 by adding a 10% NaOH solution. 1016 g of a 20% FeCl.sub.3 solution were added to the reaction mixture, in the course of which the pH was kept essentially constant at 3.2 by simultaneous addition of a 10% NaOH solution. On completion of addition of the FeCl.sub.3 solution, the mixture was stirred for a further 15 minutes, in order to assure complete precipitation. The pH was then increased to a value of 7.0 by dropwise addition of a 10% NaOH solution over a period of 30 minutes. After stirring for a further 30 minutes, the coated pigment was separated from the upernatant reaction solution by filtering and washed until it was free of salts. The resultant coated aluminum platelets were dried at 250 C. for 215 minutes and sieved with a sieve (mesh size 25 m). The resultant product was subjected to an assessment of its color properties and to a fire test as described below.

EXAMPLE 2 (THIN ALUMINUM PLATELETS WITH THIN IRON OXIDE COATING)

(6) In this example, analogously to the method of example 1, coated aluminum platelets were produced, with the difference that, rather than 1016 g, only 102 g of the 20% FeCl.sub.3 solution were used. The resultant product was subjected to an assessment of its color properties and to a fire test as described below.

EXAMPLE 3 (THIN ALUMINUM PLATELETS WITH THICK IRON OXIDE COATING AND TITANIUM OXIDE COATING)

(7) This example was conducted analogously to example 1 up to and including the stirring for fifteen minutes after the addition of the FeCl.sub.3 solution had ended. Thereafter, the pH was adjusted to 2.0 by adding 10% HCl solution. 412 g of a 30% TiCl.sub.4 solution were added to the reaction mixture, in the course of which the pH was kept essentially constant at 2.0 by simultaneously adding a 10% NaOH solution. On completion of addition of the TiCl.sub.4 solution, the mixture was stirred for a further 15 minutes, in order to assure complete precipitation. The pH was then increased to a value of 7.0 by dropwise addition of a 10% NaOH solution over a period of 30 minutes. After stirring for a further 30 minutes, the coated pigment was separated from the supernatant reaction solution by filtering and washed until it was free of salts. The resultant coated aluminum platelets were dried at 250 C. and sieved with a sieve (mesh size 25 m). The resultant product was subjected to an assessment of its color properties and to a fire test as described below.

COMPARATIVE EXAMPLE (THICK ALUMINUM PLATELETS WITH IRON OXIDE COATING)

(8) First of all, 50 g of Al platelets (thickness between 150 nm and 300 nm, d50=18 m) were coated with 8.8 g of SiO.sub.2 by means of a sol-gel method using tetraethyl orthosilicate (TEOS). In a round bottom flask with reflux condenser and stirrer, these Al platelets were admixed with 500 mL of deionized water and heated to 75 C. while stirring. The pH was adjusted to a value of 3.2 by adding a 10% NaOH solution. 660 g of a 20% FeCl.sub.3 solution were added to the reaction mixture, in the course of which the pH was kept essentially constant at 3.2 by simultaneously adding a 10% NaOH solution. On completion of addition of the FeCl.sub.3 solution, the mixture was stirred for a further 15 minutes in order to assure complete precipitation. The pH was then increased to a value of 7.0 by dropwise addition of a 10% NaOH solution over a period of 30 minutes. After stirring for a further 30 minutes, the coated pigment was separated from the supernatant reaction solution by filtration and washed until it was free of salts. The resultant coated aluminum platelets were dried at 250 C. and sieved with a sieve (mesh size 40 m). The resultant product was subjected to an assessment of its color properties and to a fire test as described below.

(9) Combustion Test

(10) 20 g in each case of the pigments produced were mixed thoroughly with 13.3 g of white spirit. 2 g of this mixture were applied to a glass plate and set on fire. This combustion test is recorded as a video. The fire characteristics are rated on a scale from 0 to 5, 0 meaning that there is merely gentle burnoff of the white spirit without occurrence of any further reaction. 1: isolated sparks during the solvent fire 2: slight evolution of sparks during the solvent fire 3: moderate evolution of sparks during the solvent fire 4: significant evolution of sparks and small explosions or crackling during the solvent fire, glowing of the sample after the solvent has burnt off 5: significant evolution of sparks and explosions or crackling during the solvent fire, and complete conversion of the sample after the solvent has burnt off

(11) To measure the total color difference E, a paint layer which comprised the metallic luster pigment of the invention to be examined in a proportion by mass of 18% by weight (dry weight) was applied to a black surface and to a white surface. The layer thickness of the dried coat of paint was 15 m. Thereafter, the total color difference E between the coats of paint on white and black backgrounds was determined. The results of the measurements are shown in table 1.

(12) Table 1 shows results for various metallic luster pigments. The uncoated substrate platelets consist of aluminum metal. Test numbers 1 to 12 were produced in accordance with the methods from examples 1, 2 and 3 with the necessary modifications for establishment of the individually specific parameters (for example thickness of coatings A, B and, if present, C). Test numbers 5 to 7 and 12 are examples of the present invention; tests 1 to 4 and 8 to 11 are comparative examples. In addition to test numbers 1 to 12, table 1 shows values for the commercially available products Paliochrom L2800 (from BASF) and Meoxal Orange (from Merck) as comparative examples.

(13) It is apparent from table 1 and FIG. 1 that, with a content of aluminum metal in the coated substrate platelets of, in particular, equal to or less than 20% by weight, it is possible to provide a pigment which is noncombustible and is not an explosion hazard. This corresponds to a result of 1 or 0 in the combustion test.

(14) It is apparent from table 1 and FIG. 2 that, with an Fe.sub.2O.sub.3 content in the coated substrate platelets of, in particular, equal to or greater than 65% by weight, it is possible to provide a pigment which is noncombustible and is not an explosion hazard. This corresponds to a result of 1 or 0 in the combustion test.

(15) In addition, table 1 shows that the metallic luster pigments of the invention have a particularly small color difference E and hence a particularly high hiding capacity. The proportions reported in the table are based on % by weight.

(16) TABLE-US-00001 TABLE 1 Al SiO.sub.2 Fe.sub.2O.sub.3 TiO.sub.2 Performance rating for Use of substrate of the No. content content content content fire characteristics E invention 1 37 14 39 0 5 0.8 yes 2 34 21 35 0 5 0.6 yes 3 26 30 30 0 5 0.8 yes 4 22 25 45 0 4 0.2 yes 5 11 13 68 0 1 0.7 yes 6 6 8 73 0 0 0.4 yes 7 4 5 72 0 0 3.3 yes 8 4 6 45 30 0 15.4 yes 9 37 7 49 0 5 0.4 yes 10 51 6 32 0 4 5.5 no 11 64 4 20 0 2 11.2 no 12 8 3 76 0 0 0.8 yes Paliocrom 69 1 26.6 nd 3 12.0 no L2800 Meoxal Orange 27 11 50.9 nd 5 25.0 no