Method for the production of single crystalline TiO2 flakes

Abstract

The present invention is related to a method for the production of single crystalline TiO.sub.2 flakes in the rutile crystal structure, to single crystalline TiO.sub.2 flakes obtained by this method as well as to the use thereof, especially as pigments in several application media.

Claims

1. Method for the production of single crystalline TiO.sub.2 flakes having an average particle diameter in the range of 10 to 200 m according to the largest length or width of the flake, by the following steps: a) mixing at least a water soluble titanium compound and a water soluble phosphorus compound in an aqueous medium at a ratio of the mol number of the phosphorus compound to the Ti atom mol number in the titanium compound in the range of from at least 0.01 to at most 10.0, to form a titanium dioxide precursor, and b) calcining the titanium dioxide precursor at a temperature in the range of from 800 C. to 1400 C. as a single calcination step.

2. Method according to claim 1, wherein a fluxing agent is present in the mixing step which is a metal salt that exhibits a melting temperature not less than 800 C. and does not achieve the melting temperature of the resulting TiO.sub.2, at a ratio of the fluxing agent mol number to the Ti atom mol number in the titanium compound in the range of from at least 1.0 to at most 30, and wherein a product obtained in the calcination step is washed with water having a temperature in the range of from 40 to 100 C.

3. Method according to claim 2, wherein the fluxing agent is Na.sub.2SO.sub.4, K.sub.2SO.sub.4, NaCl or KCl.

4. Method according to claim 1, wherein the method comprises drying of the titanium dioxide precursor prior to the calcination step.

5. Method according to claim 1, wherein the calcining takes place in an oxygen containing atmosphere.

6. Method according to claim 1, wherein the titanium compound is titanium tetrachloride, titanyl sulfate, titanium sulfate or titanium trichloride.

7. Method according to claim 1, wherein the phosphorus compound is trisodium phosphate, phosphorus pentoxide, phosphoric acid, phosphorus acid or tripotassium phosphate.

8. A method according to claim 2, wherein the ratio of the fluxing agent mol number to the Ti atom mol number in the titanium compound in the range of from at least 3.0 to at most 10.

9. A method according to claim 1, wherein the ratio of the mol number of the phosphorus compound to the Ti atom mol number in the titanium compound in the range of from at least 1 to at most 7.0.

10. A method according to claim 1, wherein the ratio of the mol number of the phosphorus compound to the Ti atom mol number in the titanium compound in the range of from at least 1 to at most 5.0.

11. A method according to claim 1, wherein the average particle diameter of the TiO.sub.2 flakes is usually at least at least 15 m and at most 150 m.

12. A method according to claim 1, wherein the thickness of the TiO.sub.2 flakes is at least 0.2 m and at most 2.0 m and the aspect ratio of the flakes is at least 7.5 and at most 100.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a SEM image of the surface of single crystalline TiO.sub.2 flakes obtained by the production method in accordance with an embodiment of the present invention.

(2) FIG. 2 is a schematic view showing a formation state of the single crystalline TiO.sub.2 flakes (V letter type and triangle type) obtained by the production method in accordance with an embodiment of the present invention.

(3) In this photograph and schematic view, the single crystalline TiO.sub.2 flakes of the V letter type (a), the single crystalline TiO.sub.2 flakes of the triangle type (b) and a border line between V letter and triangle (c) are shown.

(4) FIG. 3 is a SEM image of the surface of single crystalline TiO.sub.2 flakes (V letter type) obtained by the production method in accordance with an embodiment of the present invention.

(5) FIG. 4 is a SEM image of the surface of single crystalline TiO.sub.2 flakes (triangle type) obtained by the production method in accordance with an embodiment of the present invention.

(6) FIG. 5 is a flowchart showing the production method for single crystalline TiO.sub.2 flakes in accordance with a preferred embodiment of the present invention.

(7) Hereinafter, the present invention will be described in more detail by referencing examples, however, the present invention is not limited to these examples.

EXAMPLE 1

(8) Into 1600 g of deionized water, 5.6 g of sodium phosphate is added and stirred while heating to 95 C. Into this solution, 200 g of titanium tetrachloride solution (32.0% concentration) is added over the course of two hours while adjusting the pH with sodium hydroxide aqueous solution (32.0% concentration). After adding all of titanium tetrachloride solution, the pH is raised to 7. Further, 130 g of sodium sulfate is added under stirring. Afterwards, the resulting solution is dried and, then calcined at 1000 C. for two hours. After cooling, the obtained product is washed within warm water under agitation in order to remove chloride and sodium sulfate, and the TiO.sub.2 flakes are obtained.

(9) The obtained TiO.sub.2 flakes have an average particle diameter of 70 m and most of them exhibit the V-like shape. From the X-ray diffraction analysis, the main surface of the flake have the (110) orientation and the crystal structure is the rutile type. Further, the analysis with electron microscope confirms that they are single crystals.

(10) The obtained TiO.sub.2 flakes are added into a usual nitro-cellulose lacquer in an amount of 5% by weight, in relation to the total weight of the mixture. The resulting coating composition containing the obtained TiO.sub.2 flakes is coated onto paper, resulting in a lustrous coating after drying. The TiO.sub.2 flakes prepared according to Example 1 present the strongest luster among the examples.

EXAMPLE 2

(11) Into 600 g of deionized water, 5.6 g of sodium phosphate is added and stirred while heating to 95 C. Into this solution, 200 g of titanium sulfate solution (32.0% concentration) is added over the course of two hours while adjusting the pH with sodium hydroxide aqueous solution (32.0% concentration). After adding all of titanium sulfate solution, the pH is raised to 7. Further, 130 g of sodium sulfate is added under agitation and the resulting solution is dried. Then, the obtained powder is calcined at 1000 C. for two hours. After cooling, the obtained product is washed within warm water under agitation in order to remove sulfate and sodium sulfate, and TiO.sub.2 flakes having the rutile type crystal structure are obtained. The average particle diameter is 45 m.

(12) The obtained TiO.sub.2 flakes are added into the nitro-cellulose lacquer in an amount of 5% by weight, based on the total weight of the mixture. The obtained coating composition containing the TiO.sub.2 flakes are coated on paper and then the luster of the dried coating is observed. The coating shows a sufficient luster in a somewhat smaller degree than the coating according to example 1.

COMPARATIVE EXAMPLE

(13) Deionized water (600 g) is heated to 95 C. Into this, 200 g of titanium tetrachloride solution (32.0% concentration) is added over the course of two hours while adjusting the pH with sodium hydroxide aqueous solution (32.0% concentration). After adding all of titanium tetra-chloride solution, the pH is raised to 7. Further, 130 g of sodium sulfate is added and the resulting solution is stirred and then dried. Then, the resulting powder is calcined at 1000 C. for two hours. After cooling, the obtained product is washed within warm water under agitation in order to remove chloride and sodium sulfate. TiO.sub.2 particles having the rutile type crystal structure are obtained. The obtained particles have an average particle diameter of 6 m and a fiber-like shape with a granular surface.

(14) The obtained TiO.sub.2 particles according to the comparative example are added to the nitro-cellulose lacquer in an amount of 5% by weight, based on the total weight of the coating composition. The obtained coating composition containing the TiO.sub.2 particles is coated onto paper and observed. There was no specific appearance such as luster.

(15) The single crystal TiO.sub.2 flakes obtained by the production method according to the present invention can be utilized as pigments for paints, inks, coating compositions, plastics and cosmetics, and as a photo catalyst, host material for dye sensitized solar cells, UV absorbent or water repellent.