HIGH-COATING METAL EFFECT PIGMENTS

Abstract

The present invention relates to a method for producing metal effect pigments based on aluminum platelets which are provided with a metal oxide coating, said method comprising the following steps: (a) providing the aluminum platelets in an organic solvent so as to form a corresponding dispersion and adding at least one metal oxide precursor compound while the metal oxide precursor compound is dissolved, and b) decomposing the metal oxide precursor compound in the organic solvent so as to form the metal oxide coating on the aluminum platelets. The present invention further relates to metal effect pigments that can be obtained by the method according to the invention as well as to the use of the metal effect pigments according to the invention.

Claims

1. A method for producing metallic effect pigments on the basis of aluminum flakes furnished with a metal oxide coating, wherein the aluminum flakes have a thickness of 5 to 90 nm and are enveloped by the metal oxide coating, wherein the metal oxide coating is composed of one or more metal oxides in a thickness of 5 to 150 nm and has a refractive index of at least 1.9, wherein no further coating enveloping the aluminum flakes is provided between the surface of the aluminum flakes and the metal oxide coating, comprising the steps of: (a) Introducing the aluminum flakes in an organic solvent, with formation of a corresponding dispersion, and adding at least one metal oxide precursor compound, with dissolution of the metal oxide precursor compound, and (b) Decomposing the metal oxide precursor compound in the organic solvent, to form the metal oxide coating on the aluminum flakes.

2. The method as claimed in claim 1, wherein the aluminum flakes have a thickness fluctuation (?h) of at most 30%.

3. The method as claimed in claim 1 or 2, wherein the aluminum flakes are vacuum-metallized pigments.

4. The method as claimed in any of claims 1 to 3, wherein the organic solvent is selected from the group consisting of 1-methoxy-2-propanol, 2-isopropoxyethanol, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, triethylene glycol, tetraethylene glycol, polyethylene glycol 400, propylene carbonate, N,N-dimethylacetamide and dimethyl sulfoxide, or mixtures thereof.

5. The method as claimed in claim 4, wherein the organic solvent is 1-methoxy-2-propanol.

6. The method as claimed in any of claims 1 to 5, wherein the aluminum flakes even before step (a) are present in dispersed form and to that end an organic solvent is used which is identical or different, preferably different, from the organic solvent used in step (a).

7. The method as claimed in claim 6, wherein the aluminum flakes before step (a) are present as a dispersion in isopropanol.

8. The method as claimed in any of claims 1 to 7, wherein the metal oxide coating is composed of Fe.sub.2O.sub.3, CuO, ZnO, or mixtures thereof.

9. The method as claimed in claim 8, wherein the at least one metal oxide precursor compound is selected from the group consisting of nitrates, acetates, acetylacetonates, malonates, alkoxides, oxalates and oximates of iron, copper or zinc.

10. The method as claimed in claim 9, wherein the metal atom of the at least one metal oxide precursor compound is present in complexed form.

11. The method as claimed in claim 10, wherein the complexed form is a urea complex or urea derivative complex.

12. The method as claimed in any of claims 8 to 11, wherein the at least one metal oxide precursor compound is selected from the group consisting of [Fe(H.sub.2N(CO)NH.sub.2).sub.6](NO.sub.3).sub.3, [Cu(H.sub.2N(CO)NH.sub.2).sub.4](NO.sub.3).sub.2 and [Zn(H.sub.2N(CO)NH.sub.2).sub.4](NO.sub.3).sub.2.

13. A metallic effect pigment on the basis of aluminum flakes furnished with a metal oxide coating, obtainable by the method as claimed in any of claims 1 to 12, wherein the aluminum flakes have a thickness of 5 to 90 nm and are enveloped by the metal oxide coating, wherein the metal oxide coating is composed of one or more metal oxides in a thickness of 5 to 150 nm and has a refractive index of at least 1.9, and wherein no further coating enveloping the aluminum flakes is provided between the surface of the aluminum flakes and the metal oxide coating.

14. The metallic effect pigment as claimed in claim 13, wherein the metallic effect pigment has a color difference dE110? of less than 1.5 at a pigmentation of 3%.

15. The use of the metallic effect pigment as claimed in claim 13 or 14 for printing inks, inkjet applications, coating systems, mass colorations of plastic, or cosmetics.

Description

DESCRIPTION OF THE FIGURES

[0059] FIG. 1 shows a plot of the color difference dE110? as a function of the pigmentation (in %) for metallic effect pigments of the invention and also for metallic effect pigments from the prior art.

EXAMPLES

[0060] The examples below serve for further elucidation of the present invention, though without being restricted to these.

Example 1

Powder of Aluminum Flakes Furnished with Fe.SUB.2.O.SUB.3 .Coating

[0061] Synthesis of the Metal Oxide Precursor Compound [Fe(H.sub.2N(CO)NH.sub.2).sub.6](NO.sub.3).sub.3:

[0062] 30.062 g (0.5005 mol) of urea were dissolved in 700 ml of ethanol with gentle heating (40? C.). Subsequently a solution of 31.11 g (0.077 mol) of Fe(NO.sub.3).sub.3?(H.sub.2O).sub.9 in 175 ml of ethanol was added. The solution was stirred for two hours, at which point the solid [Fe(H.sub.2N(CO)NH.sub.2).sub.6](NO.sub.3).sub.3 formed was isolated by filtration, washed with ethanol and dried for twelve hours in a drying cabinet at 50? C. The yield was 33.8 g (73%).

Coating of Thin Aluminum Flakes by Thermal Decomposition of [Fe(H.sub.2N(CO)NH.sub.2).sub.6](NO.sub.3).sub.3 in Solution:

[0063] 11 g of a dispersion of aluminum flakes in isopropanol, containing 1.1 g of aluminum flakes (VMPs, Decomet? from Schlenk Metallic Pigments GmbH) having a thickness of 25 nm and a d.sub.50 of 21 ?m, were dispersed in 1 l of 1-methoxy-2-propanol. 10 g of [Fe(H.sub.2N(CO)NH.sub.2).sub.6](NO.sub.3).sub.3 were dissolved therein and the dispersion was heated at boiling (120? C.) under reflux for two hours.

[0064] In two further steps, in each case after cooling, 10 g portions of [Fe(H.sub.2N(CO)NH.sub.2).sub.6](NO.sub.3).sub.3 were subsequently added and the dispersion was heated at boiling under reflux for two hours each time. A total of 30 g of the metal oxide precursor compound were therefore used.

[0065] After cooling, the sample thus obtained was filtered and the solid product was washed with isopropanol and dispersed in isopropanol without being dried. The suspension was subsequently spray-dried, to give, lastly, a gold-colored powder.

Example 2

Suspension of Aluminum Flakes Furnished with Fe.SUB.2.O.SUB.3 .Coating

[0066] Synthesis of Metal Oxide Precursor Compound [Fe(H.sub.2N(CO)NH.sub.2).sub.6](NO.sub.3).sub.3:

[0067] The synthesis took place in the same way as for Example 1.

Coating of Thin Aluminum Flakes by Thermal Decomposition of [Fe(H.sub.2N(CO)NH.sub.2).sub.6](NO.sub.3).sub.3 in Solution:

[0068] 1 g of a dispersion of aluminum flakes in isopropanol, containing 0.24 g of aluminum flakes (VMPs, Decomet? from Schlenk Metallic Pigments GmbH) having a thickness of 25 nm and a d.sub.50 of 21 ?m, was dispersed in 100 ml of 1-methoxy-2-propanol and 0.5 ml of water. 0.5 g of [Fe(H.sub.2N(CO)NH.sub.2).sub.6](NO.sub.3).sub.3 was dissolved therein and the dispersion was heated at boiling (120? C.) under reflux for two hours. After it had cooled, a further 0.5 g of [Fe(H.sub.2N(CO)NH.sub.2).sub.6](NO.sub.3).sub.3 was added and the dispersion was again heated at boiling under reflux for two hours.

[0069] After the dispersion had cooled, the solvent was slowly removed by filtration, avoiding complete drying-up of the sample obtained in the meantime. This sample was then dispersed in 100 ml of fresh 1-methoxy-2-propanol and 0.5 ml of water. Again 0.5 g of [Fe(H.sub.2N(CO)NH.sub.2).sub.6](NO.sub.3).sub.3 was added and the dispersion was heated at boiling under reflux for two hours. After the dispersion had cooled, finally, a further 0.5 g of [Fe(H.sub.2N(CO)NH.sub.2).sub.6](NO.sub.3).sub.3 was added and the dispersion was again heated at boiling under reflux for two hours.

[0070] The above step was repeated as a whole once, and so a total of 3.0 g of the metal oxide precursor compound were used.

[0071] After cooling, the sample thus obtained was filtered and the solid product was washed with isopropanol and ethyl acetate and redispersed in ethyl acetate without being dried, to give, finally, a gold-colored suspension.

Example 3

Powder of Aluminum Flakes Furnished with CuO Coating

[0072] Synthesis of the Metal Oxide Precursor Compound [Cu(H.sub.2N(CO)NH.sub.2).sub.4](NO.sub.3).sub.2:

[0073] 2.7 g (0.045 mol) of urea were dissolved in 100 ml of butanol with gentle heating (40? C.). After the solution had cooled to room temperature, 2.42 g (0.01 mol) of Cu(NO.sub.3).sub.2?(H.sub.2O).sub.3 were added. The solution was stirred for two hours, at which point the solid [Cu(H.sub.2N(CO)NH.sub.2).sub.4](NO.sub.3).sub.2 formed was isolated by filtration, washed with butanol and acetone and dried for 16 hours in a drying cabinet at 50? C. The yield was 3.176 g (74.3%).

Coating of Thin Aluminum Flakes by Thermal Decomposition of [Cu(H.sub.2N(CO)NH.sub.2).sub.4](NO.sub.3).sub.2 in Solution:

[0074] 1 g of a dispersion of aluminum flakes in isopropanol, containing 0.24 g of aluminum flakes (VMPs Decomet? from Schlenk Metallic Pigments GmbH) having a thickness of 25 nm and a d.sub.50 of 21 ?m, was dispersed in 100 ml of 1-methoxy-2-propanol. Different amounts of [Cu(H.sub.2N(CO)NH.sub.2).sub.4](NO.sub.3).sub.2 were dissolved therein in a plurality of steps, and in each step the dispersion was heated at boiling (120? C.) under reflux for two hours.

[0075] In the first two steps portions of 0.2 g [Cu(H.sub.2N(CO)NH.sub.2).sub.4](NO.sub.3).sub.2 were added, whereas in the two following steps portions of 0.3 g of [Cu(H.sub.2N(CO)NH.sub.2).sub.4](NO.sub.3).sub.2 were added. At that point the sample obtained in the meantime was slowly isolated by filtration, without drying up in the process, and was redispersed in 100 ml of 1-methoxy-2-propanol. Then, in two further steps, portions of 0.5 g of [Cu(H.sub.2N(CO)NH.sub.2).sub.4](NO.sub.3).sub.2 were added.

[0076] Once again the sample obtained in the meantime was isolated by filtration, without drying up in the process, and was again redispersed in 100 ml of 1-methoxy-2-propanol. In two further steps, portions of 0.5 g of [Cu(H.sub.2N(CO)NH.sub.2).sub.4](NO.sub.3).sub.2 were added. In total, therefore, 3.0 g of the metal oxide precursor compound were used.

[0077] The sample thus obtained was subsequently isolated by filtration, without drying up in the process, and was dispersed in 50 ml of diphenyl ether and heated at boiling (258? C.) for five minutes. After cooling, the sample was isolated by filtration, washed with ethanol, acetone and diethyl ether, and dried for 16 hours at 50? C., to give, finally, a pale gold-colored powder.

Investigation of the Coloristic Data

[0078] The metallic effect pigments from Examples 1 to 3 were investigated in more detail for their coloristic data and subjected to comparison with metallic effect pigments from the prior art.

[0079] The coloristic data were determined by measurement on corresponding drawdown cards. To this end, knife-coated drawdowns of the respective metallic effect pigments with different pigmentation in a solventborne nitrocellulose/polycyclohexanone/polyacrylic varnish with a solids fraction of 10% were produced on a black-white DIN A5 card from TQC using a 38 ?m wire doctor on an automatic film-drawing device from Zehntner. The pigmentation here refers in each case to the pigment fraction in the total varnish mixture. All of the percentages here should be understood as wt %.

[0080] Aside from the 60? gloss measurement, the coloristic data were measured using the Byk-mac i instrument from Byk. To determine the hiding power, expressed by the color difference dE110?, the coloristic data were measured on the white and black side of the DIN A5 card. The 60? gloss measurement took place using the Byk micro-TRI-gloss instrument from Byk. The results are collated in Table 1 below:

TABLE-US-00001 TABLE 1 Pigmentation Gloss huv Example Workup (in %) 60? 15*S dE15? dE110? dE45? AL Example 1 dried 1 75.9 69.6 3.6 38.4 20.4 23.5 (powder) 2 61.4 69.8 0.6 11.5 4.1 23.2 3 52.5 69.8 0.2 1.3 0.3 23.6 4 51.6 69.9 0.2 0.2 0.4 23.9 Example 2 undried 3 101.0 70.9 1.6 1.1 0.2 32.3 (suspension) Example 3 dried 3 47.9 65.1 0.2 1.4 0.2 18.2 (powder) 4 36.8 64.3 0.5 0.4 0.3 16.1

[0081] The values contained in Table 1 for the color difference dE110? of the metallic effect pigments of the invention from Examples 1 to 3 are plotted in FIG. 1 as a function of the pigmentation (in %). FIG. 1 also shows the values for the color difference dE110? of metallic effect pigments from the prior art, determined by the same measurement method. As is clear from a comparison of the values, the metallic effect pigments of the invention have a significantly higher hiding power, as manifested in a lower value for the color difference dE110?. Thus at a pigmentation of just 3%, a color difference dE110? of less than 1.5 is obtained. At a pigmentation of 4%, indeed, the color difference dE110? is significantly less than 1.0. In the case of the metallic effect pigments from the prior art, conversely, the pigmentation needed to achieve this is about twice as great.