ALPHA-ALUMINA FLAKES

Abstract

The present invention relates to alumina flakes having a defined thickness and particle size distribution and to their use in varnishes, paints, automotive coatings printing inks, masterbatches, plastics and cosmetic formulations and as substrate for effect pigments. and organic dyes.

Claims

1. A coating, automobile coating, automotive finishing or industrial coating, comprising uncoated Al.sub.2O.sub.3 flakes having a thickness of 500 nm and a D.sub.50-value of 15-30 m and a D.sub.90-value of 30-45 m, and/or coated Al.sub.2O.sub.3 flakes having a thickness of 500 nm and a D.sub.50-value of 15-30 m and a D.sub.90-value of 30-45 m, which have been coated with at least one layer of a metal oxide, mixtures of at least two metal oxides, metal, metal sulphide, titanium suboxide, titanium oxynitride, FeO(OH), metal alloys or rare earth compounds.

2. The coating, automobile coating, automotive finishing or industrial coating according to claim 1, wherein the coated and/or uncoated Al.sub.2O.sub.3 flakes are -alumina flakes.

3. The coating, automobile coating, automotive finishing or industrial coating according to claim 1, wherein the coated and/or uncoated Al.sub.2O.sub.3 flakes have a D.sub.90-value of 30-40 m.

4. The coating, automobile coating, automotive finishing or industrial coating according to claim 1, wherein the coated and/or uncoated Al.sub.2O.sub.3 flakes have a particle thickness of 550-1000 nm.

5. The coating, automobile coating, automotive finishing or industrial coating according to claim 1, wherein the coated and/or uncoated Al.sub.2O.sub.3 flakes have been doped with TiO.sub.2, ZrO.sub.2, SiO.sub.2, SnO.sub.2, In.sub.2O.sub.3, ZnO and/or combinations thereof.

6. The coating, automobile coating, automotive finishing or industrial coating according to claim 5, wherein the amount of doping is 0.01-5% by weight based on the Al.sub.2O.sub.3 flake.

7. The coating, automobile coating, automotive finishing or industrial coating according to claim 5, wherein the coated and/or uncoated Al.sub.2O.sub.3 flakes have been doped with TiO.sub.2.

8. The coating, automobile coating, automotive finishing or industrial coating according to claim 1, which contain the Al.sub.2O.sub.3 flakes coated with at least one layer of a metal oxide, mixtures of at least two metal oxides, metal, metal sulphide, titanium suboxide, titanium oxynitride, FeO(OH), metal alloys or rare earth compounds.

9. The coating, automobile coating, automotive finishing or industrial coating according to claim 1, wherein the Al.sub.2O.sub.3 flakes have been coated with at least one layer of a metal oxide or a mixture of at least two metal oxides.

10. The coating, automobile coating, automotive finishing or industrial coating according to claim 1, wherein the Al.sub.2O.sub.3 flakes have been coated with the following layer sequence: Al.sub.2O.sub.3 flake+TiO.sub.2 Al.sub.2O.sub.3 flake+TiO.sub.2/Fe.sub.2O.sub.3 Al.sub.2O.sub.3 flake+Fe.sub.2O.sub.3 Al.sub.2O.sub.3 flake+TiO.sub.2+Fe.sub.2O.sub.3 Al.sub.2O.sub.3 flake+TiO.sub.2+Fe.sub.3O.sub.4 Al.sub.2O.sub.3 flake+TiO.sub.2+SiO.sub.2+TiO.sub.2 Al.sub.2O.sub.3 flake+Fe.sub.2O.sub.3+SiO.sub.2+TiO.sub.2 Al.sub.2O.sub.3 flake+TiO.sub.2/Fe.sub.2O.sub.3+SiO.sub.2+TiO.sub.2 Al.sub.2O.sub.3 flake+TiO.sub.2+SiO.sub.2+TiO.sub.2/Fe.sub.2O.sub.3 Al.sub.2O.sub.3 flake+TiO.sub.2+SiO.sub.2 Al.sub.2O.sub.3 flake+TiO.sub.2+SiO.sub.2/Al.sub.2O.sub.3 Al.sub.2O.sub.3 flake+TiO.sub.2+Al.sub.2O.sub.3 Al.sub.2O.sub.3 flake+SnO.sub.2 Al.sub.2O.sub.3 flake+SnO.sub.2+TiO.sub.2 Al.sub.2O.sub.3 flake+SnO.sub.2+Fe.sub.2O.sub.3 Al.sub.2O.sub.3 flake+SiO.sub.2 Al.sub.2O.sub.3 flake+SiO.sub.2+TiO.sub.2 Al.sub.2O.sub.3 flake+SiO.sub.2+TiO.sub.2/Fe.sub.2O.sub.3 Al.sub.2O.sub.3 flake+SiO.sub.2+Fe.sub.2O.sub.3 Al.sub.2O.sub.3 flake+SiO.sub.2+TiO.sub.2+Fe.sub.2O.sub.3 Al.sub.2O.sub.3 flake+SiO.sub.2+TiO.sub.2+Fe.sub.3O.sub.4 Al.sub.2O.sub.3 flake+SiO.sub.2+TiO.sub.2+SiO.sub.2+TiO.sub.2 Al.sub.2O.sub.3 flake+SiO.sub.2+Fe.sub.2O.sub.3+SiO.sub.2+TiO.sub.2 Al.sub.2O.sub.3 flake+SiO.sub.2+TiO.sub.2/Fe.sub.2O.sub.3+SiO.sub.2+TiO.sub.2 Al.sub.2O.sub.3 flake+SiO.sub.2+TiO.sub.2+SiO.sub.2+TiO.sub.2/Fe.sub.2O.sub.3 Al.sub.2O.sub.3 flake+SiO.sub.2+TiO.sub.2+SiO.sub.2 Al.sub.2O.sub.3 flake+SiO.sub.2+TiO.sub.2+SiO.sub.2/Al.sub.2O.sub.3 Al.sub.2O.sub.3 flake+SiO.sub.2+TiO.sub.2+Al.sub.2O.sub.3 Al.sub.2O.sub.3 flake+TiO.sub.2+Prussian Blue or Al.sub.2O.sub.3 flake+TiO.sub.2+Carmine Red.

11. The coating, automobile coating, automotive finishing or industrial coating according to claim 1, wherein the Al.sub.2O.sub.3 flakes have been coated with TiO.sub.2 in the rutile or anatase modification.

12. The coating, automobile coating, automotive finishing or industrial coating according to claim 1, wherein the Al.sub.2O.sub.3 flakes have been coated with TiO.sub.2 in the rutile modification.

13. The coating, automobile coating, automotive finishing or industrial coating according to claim 1, wherein the coated Al.sub.2O.sub.3 flakes consist of 40-90 wt. % of Al.sub.2O.sub.3 flakes and 10-60 wt. % of the coating based on the total pigment.

14. (canceled)

15. (canceled)

16. (canceled)

17. (canceled)

18. The coating, automobile coating, automotive finishing or industrial coating according to claim 1, which contain 05 to 10% by weight the coated and/or uncoated Al.sub.2O.sub.3 flakes.

19. The coating, automobile coating, automotive finishing or industrial coating according to claim 1, which is a one coat system which has a single-layer coating.

20. The coating, automobile coating, automotive finishing or industrial coating according to claim 1, which is a two-coat system.

21. A base coat in a two-coat system, which base coat is a coating, automobile coating, automotive finishing or industrial coating according to claim 1.

Description

EXAMPLES

Comparative Example 1 (Example 2 of U.S. Pat. No. 5,702,519)

[0111] In 300 ml of deionized water are dissolved 111.9 g of aluminum sulfate 18-hydrate, 57.3 g of anhydrous sodium sulfate, and 46.9 g of potassium sulfate by heating above 60 C. To the resulting solution is added 1.0 g of 34.4% solution of titanyl sulfate. The resulting solution is designated as the aqueous solution (a).

[0112] In 150 ml of deionized water are 0.45 g of sodium tertiary phosphate 12-hydrate and 54.0 g of sodium carbonate. The resulting solution is designated as the aqueous solution (b).

[0113] The aqueous solution (b) is added with stirring to the aqueous solution (a) kept at about 60 C. Stirring is continued for 15 minutes. The resulting mixture of the two solutions is a gel. This gel is evaporated to dryness, and the dried product is heated at 1200 C. for 5 hours. Water is added to the heated product to dissolve free sulfate. Insoluble solids are filtered off, washed with water, and finally dried. The obtained alumina flake is examined by X-ray diffractometry. The diffraction pattern has only peaks attributed to corundum structure (-alumina structure).

[0114] D.sub.50 is 13.0 m and D.sub.90 is 22.0 m and the thickness is 200 nm.

Example 1: Preparation of the Al.SUB.2.O.SUB.3 .Flakes

[0115] 74.6 g of aluminum sulfate 18-hydrate, 5.7 g of transition alumina (C10W: Nippon Light Metal Co., Ltd.), 57.3 g of anhydrous sodium sulfate and 46.9 g of potassium sulfate are dissolved in 450 ml of deionized water by heating above 60 C. To the resulting solution is added 1.2 g of 34.4% solution of titanyl sulfate. The resulting solution is designated as the aqueous solution (a).

[0116] In 300 ml of deionized water are 0.010 g of sodium tertiary phosphate 12-hydrate and 55.0 g of sodium carbonate. The resulting solution is designated as the aqueous solution (b).

[0117] The aqueous solution (b) is added with stirring to the aqueous solution (a) kept at about 60 C. Stirring is continued for 30 minutes. The resulting mixture of the two solutions is a slurry. This slurry is evaporated to dryness, and the dried product is heated at 1230 C. for 4.5 hours. Water is added to the heated product to dissolve free sulfate. Insoluble solids are filtered off, washed with water, and filtered by sieve with 25 micron opening. And finally it was dried. The obtained alumina flake is examined by X-ray diffractometry. The diffraction pattern have only peaks attributed to corundum structure (-alumina structure).

[0118] D.sub.50 is 19.6 m, D.sub.90 is 38.8 m and the average thickness is 700 nm.

Comparative Example 1.1: Coating of Al.SUB.2.O.SUB.3 .Flakes

[0119] 20 g of alumina flakes of Comparative Example 1 are suspended in 400 ml of deionized water. To the resulting suspension (kept at about 65 C.) is added a solution containing 125 g of TiCl.sub.4 per liter. Simultaneously a 10% solution of NaOH was added to keep the pH at 2.1. The addition of the TiCl.sub.4 solution is stopped when the resulting product takes on a silvery color. The suspending solids are filtered off, washed with water and dried. Finally, the dried solids are calcined at 850 C. for 30 minutes to give a whitish and a little glossy pearlescent pigment.

Example 1.1: Coating of Al.SUB.2.O.SUB.3 .Flakes

[0120] 20 g of alumina flakes of Example 1 are suspended in 400 ml of deionized water. To the resulting suspension (kept at about 65 C.) is added a solution containing 125 g of TiCl.sub.4 per liter. Simultaneously a 10% solution of NaOH was added to keep the pH at 2.1. The addition of the TiCl.sub.4 solution is stopped when the resulting product takes on a silvery color. The suspending solids are filtered off, washed with water and dried. Finally, the dried solids are calcined at 850 C. for 30 minutes to give a highly whitish and glossy pearlescent pigment with a strong glitter effect.

Comparative Example 1.2: Coating of Al.SUB.2.O.SUB.3 .Flakes

[0121] 20 g alumina flakes of Comparative Example 1 are suspended in 400 ml of deionized water. To the resulting suspension (kept at about 75 C.) are added a solution containing 300 g of FeCl.sub.3 per liter. Simultaneously a 10% solution of NaOH was added to keep the pH at 3.0. The addition of the FeCl.sub.3 solution was stopped when the resulting product takes on a most reddish color. The suspending solids are filtered off, washed with water, and dried. Finally, the dried solids are calcined at 800 C. for 30 minutes to give a moderate luster and brownish red colored pearlescent pigment.

Example 1.2: Coating of Al.SUB.2.O.SUB.3 .Flakes

[0122] 20 g alumina flakes of Example 1 are suspended in 400 ml of deionized water. To the resulting suspension (kept at about 75 C.) are added a solution containing 300 g of FeCl.sub.3 per liter. Simultaneously a 10% solution of NaOH was added to keep the pH at 3.0. The addition of the FeCl.sub.3 solution was stopped when the resulting product takes on a most reddish color. The suspending solids are filtered off, washed with water, and dried. Finally, the dried solids are calcined at 800 C. for 30 minutes to give a high luster and pure red colored pearlescent pigment with a strong glitter effect.

Comparative Example 1.3: Coating of Al.SUB.2.O.SUB.3 .Flakes

[0123] 20 g alumina flakes of Comparative Example 1 are suspended in 400 ml of deionized water. To the resulting suspension (kept at about 65 C.) is added a solution containing 50 g of SnCl.sub.4 per liter. Simultaneously a 10% solution of NaOH is added to keep the pH at 2.1 until the total adding volume of SnCl.sub.4 solution become 17 ml. Next the solution containing 125 g of TiCl.sub.4 per liter was added to the resulting suspension. Simultaneously a 10% solution of NaOH is added to keep the pH at 2.1. The addition of the TiCl.sub.4 solution is stopped when the resulting product takes on a silvery color. The suspending solids are filtered off, washed with water, and dried. Finally, the dried solids are calcined at 850 C. for 30 minutes to give a whitish and a little glossy pearlescent pigment.

Example 1.3: Coating of Al.SUB.2.O.SUB.3 .Flakes

[0124] 20 g alumina flakes of Example 1 are suspended in 400 ml of deionized water. To the resulting suspension (kept at about 65 C.) is added a solution containing 50 g of SnCl.sub.4 per liter. Simultaneously a 10% solution of NaOH is added to keep the pH at 2.1 until the total adding volume of SnCl.sub.4 solution become 17 ml. Next the solution containing 125 g of TiCl.sub.4 per liter was added to the resulting suspension. Simultaneously a 10% solution of NaOH is added to keep the pH at 2.1. The addition of the TiCl.sub.4 solution is stopped when the resulting product takes on a silvery color. The suspending solids are filtered off, washed with water, and dried. Finally, the dried solids are calcined at 850 C. for 30 minutes to give a highly whitish and highly glossy pearlescent pigment with a strong glitter effect. At the luster angle, the glossy appearance can be seen at a more wider angle compared to Comparative Example 1.3.

Comparative Example 1.4: Coating of Al.SUB.2.O.SUB.3 .Flakes

[0125] 20 g alumina flakes of Comparative Example 1 are suspended in 400 ml of deionized water. To the resulting suspension (kept at about 65 C.) is added a solution containing 125 g of TiCl.sub.4 per liter. Simultaneously a 10% solution of NaOH is added to keep the pH at 2.1. The addition of the TiCl.sub.4 solution is stopped when the resulting product takes on a yellowish color. Then a solution containing 50 g of Na.sub.2SiO.sub.3 per liter is added to the resulted suspension. Simultaneously a 10% solution of HCl is added to keep the pH at 7. Next a solution containing 125 g of TiCl.sub.4 per liter is added to the resulted suspension. Simultaneously a 10% solution of NaOH is added to keep the pH at 2.1. The addition of the TiCl.sub.4 solution is stopped when the resulting product takes on a bluish color. The suspending solids are filtered off, washed with water, and dried. Finally, the dried solids are calcined at 850 C. for 30 minutes to give a blue-whitish and a little glossy pearlescent pigment.

Example 1.4: Coating of Al.SUB.2.O.SUB.3 .Flakes

[0126] 20 g alumina flakes of Example 1 are suspended in 400 ml of deionized water. To the resulting suspension (kept at about 65 C.) is added a solution containing 125 g of TiCl.sub.4 per liter. Simultaneously a 10% solution of NaOH is added to keep the pH at 2.1. The addition of the TiCl.sub.4 solution is stopped when the resulting product takes on a yellowish color. Then a solution containing 50 g of Na.sub.2SiO.sub.3 per liter is added to the resulted suspension. Simultaneously a 10% solution of HCl is added to keep the pH at 7. Next a solution containing 125 g of TiCl.sub.4 per liter is added to the resulted suspension. Simultaneously a 10% solution of NaOH is added to keep the pH at 2.1. The addition of the TiCl.sub.4 solution is stopped when the resulting product takes on a bluish color. The suspending solids are filtered off, washed with water, and dried. Finally, the dried solids are calcined at 850 C. for 30 minutes to give a highly bluish and highly glossy pearlescent pigment with a strong glitter effect. At the luster angle, the stronger bluish color and higher glossy appearance can be seen at a more wider angle compared to Comparative Example 1.4.

Measurements

[0127] Evaluation for Particle Size D.sub.10, D.sub.50 and D.sub.90

[0128] D.sub.10, D.sub.50 and D.sub.90 of alumina flake are evaluated by using Malvern MS2000.

Determination of the Thickness and Particle Size and the Thickness Distribution

[0129] 0.01 g/l of the alumina flake slurry is prepared and 0.1 ml of this slurry is dropped onto a flat substrate like a silicon wafer. The substrate is dried and cut to adequate size. The substrate is set with almost vertically tilted angle on the base of SEM (Scanning electronic microscope) and the thickness of the alumina flake is determined.

[0130] The thickness of more than 100 alumina flakes is measured for the calculation of the thickness distribution. The standard deviation of the thickness is calculated with the Gaussian distribution equation.

Preparation for a Sprayed Panel

[0131] A base coat paint for automobiles is prepared according to the following formulation.

TABLE-US-00001 <Base coat system> Acrylic-melamine resin system Acrydic 47-712* 70 pbw Superbekkamine G821-60** 30 pbw Toluene 30 pbw Ethyl acetate 50 pbw *Acrylic resin from Dainippon Ink & Chemicals, Inc. **Melamine resin from Dainippon Ink & Chemicals, Inc.

TABLE-US-00002 <Base coat system> Acrylic-melamine resin system n-Butanol 110 pbw Solvesso #150 40 pbw

[0132] The above acrylic-melamine resin system (100 pbw) is incorporated with 20 pbw of the pearlescent pigment according to one of the above given Examples. The resulting compound is diluted with a thinner so that the resulting paint has an adequate consistency for spraying (12-15 seconds, for cup #4). This paint is applied to a substrate by spraying to form a base coat layer.

[0133] The base coated layer is coated further with a colorless top clear coat paint, which is prepared according to the following formulation.

<Top Clear Coat System>

[0134]

TABLE-US-00003 <Top clear coat system> Acrydic 47-712 14 pbw Superbekkamine L117-60 6 pbw Toluene 4 pbw MIBK 4 pbw Butyl cellosolve 3 pbw

[0135] The top clear coating is exposed to air at 40 C. for 30 minutes and then cured at 135 C. for 30 minutes.

[0136] Haze-gloss (BYK) is the analyzing equipment to evaluate luster and haze. In this patent application, the value of mirror gloss on 60 is measured by Haze-gloss and represents the value of the luster. Compared to the prior art the coated Al.sub.2O.sub.3 flakes show very high values for the luster. High luster values are necessary to achieve a good appearance in the applications. The haze values measured by this equipment are affected by spreading of the reflection angle. In this patent application, the wider spreading angle is important for the pearlescent appearance. The coated Al.sub.2O.sub.3 flakes according to the present invention show very high haze-gloss values. To differentiate the evaluation result, panels are used which are sprayed with a base coat before they are coated with a top clear coat for the haze-gloss measurement.

[0137] Wave-scan dual (BYK) is used as the analyzing equipment to measure the surface flatness of the samples. Wa value represents the cyclic flatness in the range of 0.1-0.3 mm. A smaller value in this patent application represents a flatter surface showing the advantages of the pigments according to the present invention.

[0138] Sprayed panels with a top clear coat are measured for Wa. Flatter surfaces have better finishing appearance.

[0139] BYK-mac is used to evaluate glitter effect. The SG value represents the glitter.

[0140] Wave-scan dual (BYK) is used to evaluate the finishing quality of paint.

[0141] The optical properties of the pearlescent pigments according to the above given examples are summarized in the following table:

TABLE-US-00004 TABLE 1 Optical TiO.sub.2 Particle size Average properties of coated distribution of the thickness of TiO.sub.2 coated Al.sub.2O.sub.3 Al.sub.2O.sub.3 Al.sub.2O.sub.3 flakes (m) the Al.sub.2O.sub.3 flakes Al.sub.2O.sub.3 flakes flakes flakes D.sub.10 D.sub.50 D.sub.90 (nm) SG Wa E1 E1.1 9.0 19.6 38.8 700 8.5 13 CE1 CE1.1 4.8 13.0 22.0 200 2 21

[0142] The entire disclosures of all applications, patents and publications, cited herein and of corresponding European Application No. 13002294.0, filed Apr. 30, 2013 are incorporated by reference herein.