PROCESS FOR THE PRODUCTION OF FLAKE-FORM, CRYSTALLINE PARTICLES HAVING AN AURIVILLIUS STRUCTURE AND THE USE THEREOF AS EFFECT PIGMENTS OR SUBSTRATES THEREOF

Abstract

A process for the production of flake-form, crystalline particles having an aurivillius structure, the use thereof as effect pigments or as substrates of effect pigments, furthermore, effect pigments which contain coated or uncoated flake-form, crystalline particles having an aurivillius structure as substrates, and the use thereof in various products.

Claims

1. A process for the preparation of crystalline compounds having an aurivillius structure, in which the starting compounds are mixed with a salt mixture comprising NaCl and Na.sub.2SO.sub.4 and optionally one or more assistants to give a homogenised salt matrix/oxide mixture and are heated at 800-1200 C.

2. The process according to claim 1, in which Bi.sub.2O.sub.3, TiO.sub.2, and optionally a further oxide are mixed with a salt mixture comprising NaCl and Na.sub.2SO.sub.4 and optionally one or more assistants to give a homogenised salt matrix/oxide mixture and are heated at 800-1200 C.

3. The process according to claim 2, wherein the further oxide used is Fe.sub.2O.sub.3.

4. The process according to claim 1, wherein the assistants used are one or more salts selected from the group consisting of Na.sub.2CO.sub.3, K.sub.2CO.sub.3, CaCO.sub.3, CaO, CaCl.sub.2, Na.sub.4P.sub.2O.sub.7 and KBr.

5. The process according to claim 1, wherein the salt mixture comprises assistants in an amount of 1-10 mol % of the amount of TiO.sub.2 employed.

6. The process according to claim 1, wherein the homogenised salt matrix/oxide mixture comprises 7-50% by weight of Bi.sub.2O.sub.3 and TiO.sub.2.

7. The process according to claim 1, wherein the homogenised salt matrix/oxide mixture is pressed to give moulded pieces.

8. The process according to claim 7, wherein the moulded pieces are calcined in ceramic crucibles.

9. The process according to claim 8, wherein the moulded pieces are calcined resting on corundum beads in ceramic crucibles.

10. The process according to claim 1, wherein the compound prepared is Bi.sub.4Ti.sub.3O.sub.12.

11. The process according to claim 1, wherein the compound prepared is Bi.sub.5Ti.sub.3FeO.sub.15.

12. An effect pigments comprising coated or uncoated flake-form crystalline particles having an aurivillius structure.

13. The effect pigments according to claim 12, wherein the flake-form crystalline particles having an aurivillius structure comprise Bi.sub.4Ti.sub.3O.sub.12 or Bi.sub.5Ti.sub.3FeO.sub.15.

14. The effect pigment according to claim 12, wherein the flake-form crystalline particles having an aurivillius structure are coated with one or more layers of oxides and/or oxide hydrates of aluminium, silicon, iron, zinc, zirconium, tin and titanium, and/or mixtures of these compounds.

15. The effect pigments according to claim 14, wherein one or more organic and/or inorganic stabilisation layers have been applied to the flake-form crystalline particles having an aurivillius structure or to the outer metal oxide layer.

16. An effect pigments comprising coated or uncoated flake-form crystalline particles having an aurivillius structure, wherein the flake-form crystalline particles having an aurivillius structure are produced by a process in which the starting compounds are mixed with a salt mixture comprising NaCl and Na.sub.2SO.sub.4 and optionally one or more assistants to give a homogenised salt matrix/oxide mixture and are heated at 800-1200 C.

17. A product selected from paints, coatings, automobile paints, powder coatings, printing inks, security printing inks, plastics, ceramic materials, glasses, paper, paper coatings, toners for electrophotographic printing processes, seed, greenhouse sheeting, tarpaulins, absorbers for the laser marking of paper and plastics, absorbers in the laser welding of plastics, cosmetic formulations, pigment pastes, pigment preparations and dry preparations, said product comprising an effect pigment comprising coated or uncoated flake-form crystalline particles having an aurivillius structure.

Description

EXAMPLE 1PRODUCTION OF Bi.SUB.4.Ti.SUB.3.O.SUB.12 .FLAKES FROM SALT MELT

[0047] 0.8 g of Bi.sub.2O.sub.3, 0.2 g of TiO.sub.2, 0.01 g of Na.sub.2CO.sub.3 and 8.4 g/5.5 g of NaCl/Na.sub.2SO.sub.4 (eutectic mixture) are weighed out in a can (60 ml), mixed in a Speedmixer at 1000 rpm for 1 min and subsequently ground 35s in in a blade mill (SEVERIN KM3868; 140 W).

[0048] 15 g of the ground mixture are weighed out in an aluminium oxide crucible. The crucible is covered with an aluminium oxide lid and heated and cooled in an oven (Heraeus Thermicon P) in accordance with the following program: [0049] 1. From 25 C. to 1005 C. in 4.5 h; [0050] 2. At 1005 C. for 4 h; [0051] 3. From 1005 C. to 150 C. in 7 h.

[0052] After cooling to room temperature, the crucible with the salt melt is stirred for about 2 h in 11 of deionised water at 50 C. and 200 rpm. The contents (detached from the crucible) are filtered, washed with 11 of deionised water and dried at 110 C. for 12 h. Yield: 0.8 g (78%).

[0053] SEM photomicrographs show the flake-form structure. The aurivillius crystal structure is confirmed by x-ray structural analysis.

EXAMPLE 2PRODUCTION OF Bi.SUB.5.Ti.SUB.3.FeO.SUB.15 .FLAKES FROM SALT PELLETS

[0054] 2.5 g of Bi.sub.2O.sub.3 nanopowder 90-120 (Sigma-Aldrich 637017-250G), 0.64 g of TiO.sub.2 1002 (KRONOS), 0.04 g of Na.sub.2CO.sub.3 (Merck 1.06392.1000), 7.2 g of NaCl (Sigma Aldrich S5886-5 kg) and 4.7 g of Na.sub.2SO.sub.4 (Merck 1.06645.2500) are mixed in a Speedmixer at 1000 rpm for 1 min. and homogenised 3 times for 5 sec. in a blade mill (SEVERIN KM3868; 140 W). In each case, 2.2 g of the mixture are pressed in a hydraulic press at a pressure of 1.9 t/cm.sup.2 to give seven pressed discs having a diameter of 1.3 cm. The bottom of an aluminium oxide crucible (GTS CCM 0070-AC AL99-G; 153 ml) is covered with aluminium oxide beads and the seven pressed discs are distributed thereon. The crucible is closed with an aluminium oxide lid, calcined at 1000 C. for 4 h and allowed to cool slowly to below 50 in the oven over a period of about 7 h. The crucible is subsequently treated in warm deionised water at 50 C. with gentle stirring until the salt matrix has completely dissolved (about 2 hours). The finely divided Bi.sub.4Ti.sub.3O.sub.12 is then filtered off, washed with deionised water and dried at 110 C. for about 12 h.

[0055] About 2.9 g of Bi.sub.4Ti.sub.3O.sub.12 having a mother-of-pearl-like lustre are obtained.

EXAMPLE 3PRODUCTION OF A MONOLAYER EFFECT PIGMENT COMPRISING Bi.SUB.4.Ti.SUB.3.O.SUB.12 .FLAKES WITH SnO.SUB.2 .AND TiO.SUB.2 .COATING

[0056] 75 g of bismuth titanate flakes (Bi.sub.4Ti.sub.3O.sub.12) are suspended in 7501 of deionised water and heated to 75 C. with stirring at 500 rpm. The suspension is adjusted to pH1.8 by addition of HCl (5%) and stirred for a further 15 min.

Sno.SUB.2 .Coating:

[0057] An aqueous solution of SnCl.sub.4 (50%) and HCl (37%) is metered into the suspension until the desired proportion of TiO.sub.2 has been reached, with the pH being kept at pH 1.8 by addition of dilute sodium hydroxide solution, and the mixture is subsequently stirred for a further 15 min.

Tio.SUB.2 .Coating:

[0058] An aqueous solution of TiCl.sub.4 (25%) and HCl (25%) is metered into the suspension until the desired proportion of TiO.sub.2 has been reached, with the pH being kept at pH 1.8 by addition of dilute sodium hydroxide solution.

[0059] The pH of the suspension is adjusted to pH 5.0, the pigment is subsequently filtered off, washed, dried at 110 C. for 12 h and calcined at 850 C. for 30 min.

[0060] Coated pigments with SnO.sub.2 and various proportions of TiO.sub.2 based on the bismuth titanate flakes, are prepared as indicated in Table 1.

TABLE-US-00001 TABLE 1 Sample Coating Amount (%)* 5.0** SnO.sub.2 1.3 5.1 TiO.sub.2 13 5.2 TiO.sub.2 18 5.3 TiO.sub.2 23 5.4 TiO.sub.2 27 5.5 TiO.sub.2 31 5.6 TiO.sub.2 40 5.7 TiO.sub.2 51 *based on bismuth titanate flakes **the flakes with SnO.sub.2 coating are used further directly for the respective subsequent TiO.sub.2 coating

[0061] The layer structure of the pigments (SnO.sub.2/TiO.sub.2 monolayer) is evident in SEM photomicrographs.

EXAMPLE 4PRODUCTION OF A MULTILAYER EFFECT PIGMENT COMPRISING Bi.SUB.4.Ti.SUB.3.O.SUB.12 .FLAKES WITH A TiO.SUB.2 .AND Fi.SUB.2.O.SUB.3 .COATING

[0062] 75 g of bismuth titanate flakes (Bi.sub.4Ti.sub.3O.sub.12) are suspended in 7501 of deionised water and heated to 75 C. with stirring at 500 rpm. The suspension is adjusted to pH1.8 by addition of HCl (5%) and stirred for a further 15 min.

Tio.SUB.2 .Coating:

[0063] An aqueous solution of TiCl.sub.4 (10%) is metered into the suspension until the desired proportion of TiO.sub.2 has been reached, with the pH being kept at pH 1.8 by addition of dilute sodium hydroxide solution, and the mixture is subsequently stirred for a further 15 min.

Fe.sub.2O.sub.3 Coating:

[0064] The pH of the suspension is adjusted to pH 2.8, an aqueous solution of FeCl.sub.3 (3.5%) is subsequently metered in until the desired proportion of Fe.sub.2O.sub.3 has been reached, with the pH being kept at pH 2.8 by addition of dilute sodium hydroxide solution.

[0065] The pH of the suspension is adjusted to pH 5.0, the pigment is subsequently filtered off, washed, dried at 110 C. for 12 h and calcined at 850 C. for 30 min and at 50 C. for 30 min.

[0066] Coated pigments having various proportions of TiO.sub.2 and Fe.sub.2O.sub.3, based on the bismuth titanate flakes, are prepared as indicated in Table 2.

TABLE-US-00002 TABLE 2 Sample Coating 1 Amount (%)* Coating 2 Amount (%)* 6.1 TiO.sub.2 5 Fe.sub.2O.sub.3 15 6.2 TiO.sub.2 5 Fe.sub.2O.sub.3 20 6.3 TiO.sub.2 5 Fe.sub.2O.sub.3 25 6.4 TiO.sub.2 5 Fe.sub.2O.sub.3 30 6.5 TiO.sub.2 5 Fe.sub.2O.sub.3 35 6.6 TiO.sub.2 5 Fe.sub.2O.sub.3 40 *based on bismuth titanate flakes

[0067] The layer structure of the pigments (TiO.sub.2/Fe.sub.2O.sub.3 bilayer) is evident in SEM photomicrographs.