ZINC-SULFIDE PIGMENTS COATED WITH SIO2-AGGLOMERATES

Abstract

The present invention relates to coated zinc sulfide pigments and to the use thereof, preferably in paints, automotive paints, industrial coatings, powder coatings, plastics, printing inks, ceramic glazes and cosmetic formulations, and to a process for the preparation thereof.

Claims

1. Coated zinc sulfide pigment, characterised in that it is coated on the surface with SiO.sub.2 agglomerates.

2. Coated zinc sulfide pigment according to claim 1, characterised in that the zinc sulfide has particle sizes of 0.001-100 m.

3. Coated zinc sulfide pigment according to claim 1, characterised in that the substrate used is an inorganically or organically pretreated zinc sulfide pigment.

4. Coated zinc sulfide pigment according to claim 1, characterised in that the zinc sulfide pigment is oval, spherical, rod-shaped or flake-shaped.

5. Coated zinc sulfide pigment according to claim 1, characterised in that the zinc sulfide pigment is spherical.

6. Coated zinc sulfide pigment according to claim 1, characterised in that the SiO.sub.2 coating on the zinc sulfide pigment has a layer thickness of 0.1 to 300 nm.

7. Coated zinc sulfide pigment according to claim 1, characterised in that the SiO.sub.2 content, based on the coated pigment, is 2 to 100%.

8. Process for the preparation of the coated zinc sulfide pigment according to claim 1, characterised in that the coating of the zinc sulfide pigment with SiO.sub.2 agglomerates is carried out in a fluidised-bed reactor, by gas-phase coating, by PVD, CVD or by wet-chemical coating.

9. Process according to claim 8, characterised in that, in the case of wet-chemical coating, the zinc sulfide pigment is suspended in water and mixed with a water-glass solution at a hydrolysis-suitable pH which is selected so that the SiO.sub.2 is precipitated out directly onto the pigment, the pH is kept constant by simultaneous metered addition of a base and/or acid, and the zinc sulfide pigment coated in this way is separated off, washed, dried and subsequently calcined at 200-600 C. and finally sieved.

10. A product selected from paints, coatings, powder coatings, printing inks, security printing inks, plastics, mouldings, ceramic materials, glasses, enamels, cosmetic formulations, pigment pastes with water, organic and/or aqueous solvents, pigment preparations and dry preparations, comprising a coated zinc sulfide pigment according to claim 1.

11. A glass-fibre-reinforced polyamides, comprising a coated zinc sulfide pigment according to claim 1.

12. Formulations comprising the coated zinc sulfide pigment according to claim 1.

13. Polymer matrix comprising the coated zinc sulfide pigment according claim 1.

Description

EXAMPLES

Example 1: ZnS:SiO.SUB.2.=89:11, 300 C.

[0034] 100 g of ZnS (Sachtolith HDS, Sachtleben Chemie GmbH) having an average particle size of 210 nm (measured by the laser diffraction method using a measuring instrument from Malvern Ltd., UK, Malvern 2000) are heated to 75 C. with stirring in 2 l of demineralised water.

[0035] The pH of the suspension is now adjusted to 7.5 using 32% sodium hydroxide solution.

[0036] A sodium water-glass solution (45 g of sodium water-glass solution, comprising 27.6% of SiO.sub.2, are dissolved in 47 g of fully deionised water) is then metered in, during which the pH is kept constant at 7.5 by simultaneous dropwise addition of 10% hydrochloric acid. When the addition is complete, the mixture is stirred for a further 0.5 h. The pH is subsequently adjusted to 5 using 10% hydrochloric acid, and the mixture is stirred for a further 15 min. The product is filtered, washed, dried, calcined at 300 C. and sieved through a 100 m sieve.

Example 2: ZnS:SiO.SUB.2.=91:9, 450 C.

[0037] 100 g of ZnS (Sachtolith HDS, Sachtleben Chemie GmbH) having an average particle size of 210 nm (measured by the laser diffraction method using a measuring instrument from Malvern Ltd., UK, Malvern 2000) are heated to 75 C. with stirring in 2 l of demineralised water.

[0038] The pH of the suspension is now adjusted to 9.0 using 32% sodium hydroxide solution. A sodium water-glass solution (36.2 g of sodium water-glass solution, comprising 27.6% of SiO.sub.2, are dissolved in 36.2 g of fully deionised water) is then metered in, during which the pH is kept constant at 9.0 by simultaneous dropwise addition of 10% hydrochloric acid. When the addition is complete, the mixture is stirred for a further 0.5 h. The pH is subsequently adjusted to 4 using 10% hydrochloric acid, and the mixture is stirred for a further 15 min. The product is filtered, washed, dried, calcined at 450 C. and sieved through a 100 m sieve.

Example 3: ZnS:SiO.SUB.2.=91:9, 500 C., acetic acid

[0039] 100 g of ZnS (Sachtolith HDS, Sachtleben Chemie GmbH) having an average particle size of 210 nm (measured by the laser diffraction method using a measuring instrument from Malvern Ltd., UK, Malvern 2000) are heated to 75 C. with stirring in 2 l of demineralised water.

[0040] The pH of the suspension is now adjusted to 7.5 using 32% sodium hydroxide solution. A sodium water-glass solution (36.2 g of sodium water-glass solution, comprising 27.6% of SiO.sub.2, are dissolved in 36.2 g of fully deionised water) is then metered in, during which the pH is kept constant at 7.5 by simultaneous dropwise addition of 3% acetic acid. When the addition is complete, the mixture is stirred for a further 0.5 h. The pH is subsequently adjusted to 4 using 3% acetic acid, and the mixture is stirred for a further 15 min. The product is filtered, washed, dried, calcined at 450 C. and sieved through a 100 m sieve.

Example 4: ZnS:SiO.SUB.2.=83:17, 450 C.

[0041] 100 g of ZnS (Sachtolith HDS, Sachtleben Chemie GmbH) having an average particle size of 210 nm (measured by the laser diffraction method using a measuring instrument from Malvern Ltd., UK, Malvern 2000) are heated to 75 C. with stirring in 2 l of demineralised water.

[0042] The pH of the suspension is now adjusted to 8.0 using 32% sodium hydroxide solution. A sodium water-glass solution (72.5 g of sodium water-glass solution, comprising 27.6% of SiO.sub.2, are dissolved in 72.5 g of fully deionised water) is then metered in, during which the pH is kept constant at 8.0 by simultaneous dropwise addition of 10% hydrochloric acid. When the addition is complete, the mixture is stirred for a further 0.5 h. The pH is subsequently adjusted to 5 using 10% hydrochloric acid, and the mixture is stirred for a further 15 min. The product is filtered, washed, dried, calcined at 450 C. and sieved through a 100 m sieve.

Example 5: ZnS:SiO.SUB.2.=67:33, 450 C.

[0043] 100 g of ZnS (Sachtolith L, Sachtleben Chemie GmbH) having an average particle size of 220 nm (measured by the laser diffraction method using a measuring instrument from Malvern Ltd., UK, Malvern 2000) are heated to 75 C. with stirring in 2 l of demineralised water.

[0044] The pH of the suspension is now adjusted to 7.5 using 32% sodium hydroxide solution. A sodium water-glass solution (181.2 g of sodium water-glass solution, comprising 27.6% of SiO.sub.2, are dissolved in 181.1 g of fully deionised water) is then metered in, during which the pH is kept constant at 7.5 by simultaneous dropwise addition of 10% hydrochloric acid. When the addition is complete, the mixture is stirred for a further 0.5 h. The pH is subsequently adjusted to 5 using 10% hydrochloric acid, and the mixture is stirred for a further 15 min. The product is filtered, washed, dried, calcined at 450 C. and sieved through a 100 m sieve.

Example 6: ZnS:SiO.SUB.2.=89:11, 450 C.

[0045] 100 g of ZnS (Sachtolith HDS, Sachtleben Chemie GmbH) having an average particle size of 210 nm (measured by the laser diffraction method using a measuring instrument from Malvern Ltd., UK, Malvern 2000) are heated to 75 C. with stirring in 2 l of demineralised water.

[0046] The pH of the suspension is now adjusted to 7.5 using 32% sodium hydroxide solution.

[0047] A sodium water-glass solution (45 g of sodium water-glass solution, comprising 27.6% of SiO.sub.2, are dissolved in 47 g of fully deionised water) is then metered in, during which the pH is kept constant at 7.5 by simultaneous dropwise addition of 10% hydrochloric acid. When the addition is complete, the mixture is stirred for a further 0.5 h. The pH is subsequently adjusted to 5 using 10% hydrochloric acid, and the mixture is stirred for a further 15 min. The product is filtered, washed, dried, calcined at 450 C. and sieved through a 100 m sieve.

[0048] The powder has an L* value (measured using a CR 410 Chroma Meter, Konica Minolta Sensing Europe B.V.) of 97.3.

Example 7: ZnS:SiO.SUB.2.=93:7, 450 C.

[0049] 100 g of ZnS (Sachtolith HDS, Sachtleben Chemie GmbH) having an average particle size of 210 nm (measured by the laser diffraction method using a measuring instrument from Malvern Ltd., UK, Malvern 2000) are heated to 75 C. with stirring in 2 l of demineralised water.

[0050] The pH of the suspension is now adjusted to 7.5 using 32% sodium hydroxide solution. A sodium water-glass solution (43.5 g of sodium water-glass solution, comprising 27.6% of SiO.sub.2, are dissolved in 43.5 g of fully deionised water) is then metered in, during which the pH is kept constant at 7.5 by simultaneous dropwise addition of 10% hydrochloric acid. When the addition is complete, the mixture is stirred for a further 0.5 h. The pH is subsequently adjusted to 4 using 10% hydrochloric acid, and the mixture is stirred for a further 15 min. The product is filtered, washed, dried, calcined at 450 C. and sieved through a 100 m sieve.

[0051] The powder has an L* value (measured using a CR 410 Chroma Meter, Konica Minolta Sensing Europe B.V.) of 98.3.

Example 8: ZnS:SiO.SUB.2.=91:9, 450 C.

[0052] 100 g of ZnS (Sachtolith HDS, Sachtleben Chemie GmbH) having an average particle size of 210 nm (measured by the laser diffraction method using a measuring instrument from Malvern Ltd., UK, Malvern 2000) are heated to 75 C. with stirring in 2 l of demineralised water.

[0053] The pH of the suspension is now adjusted to 7.5 using 32% sodium hydroxide solution. A sodium water-glass solution (36.2 g of sodium water-glass solution, comprising 27.6% of SiO.sub.2, are dissolved in 36.2 g of fully deionised water) is then metered in, during which the pH is kept constant at 7.5 by simultaneous dropwise addition of 10% hydrochloric acid. When the addition is complete, the mixture is stirred for a further 0.5 h. The pH is subsequently adjusted to 4 using 10% hydrochloric acid, and the mixture is stirred for a further 15 min. The product is filtered, washed, dried, calcined at 450 C. and sieved through a 100 m sieve.

[0054] The powder has an L* value (measured using a CR 410 Chroma Meter, Konica Minolta Sensing Europe B.V.) of 97.6.

Stability Investigations

[0055] Due to the SiO.sub.2 coating, the coated product has a temperature stability which is 100 K higher compared with uncoated zinc sulfide, i.e. 650-700 C. instead of 550-600 C., measured by the TGA method using the NETZSCH TG 209F1 220-10-211-K instrument. This enables the formation of toxic sulfur dioxide on exposure to high temperatures to be avoided.

[0056] Due to the coating with SiO.sub.2 agglomerates, stabilisation of the zinc sulfide to chemicals, in particular acids, furthermore occurs. To this end, in each case a 10% aqueous suspension of the products according to the invention is prepared, the pH is adjusted using 10% hydrochloric acid with stirring, and the amount of hydrogen sulfide liberated is measured (Drager test tube, Article Number 8101461). Whereas measurable amounts of hydrogen sulfide are already formed at a pH of 2.5 in the case of uncoated ZnS, these are not measurable even at pH 1.8 in the case of ZnS coated with SiO.sub.2 agglomerates:

TABLE-US-00001 Product pH H.sub.2S amount in ppm ZnS (Sachtolith HDS) 2.5 0.2 2.0 1 1.8 4 Product from Example 4 2.5 not measurable (<0.2 ppm) 2.0 not measurable (<0.2 ppm) 1.8 not measurable (<0.2 ppm)

Use Example

Use Example: Incorporation of ZnS/SiO.SUB.2 .into Glass-Fibre-Reinforced Poly-Amide

[0057] The pigment obtained from Example of 4 is incorporated into glass-fibre-reinforced polyamide (Akulon K224-LG6/E, DSM) in an amount of 0.4% by means of an extruder. This compound is then moulded in an injection-moulding machine to give test plates and subjected to a UV stability test.

[0058] Measurement conditions (in Akulon K224-LG6/E black; contains 30% of glass fibres):

TABLE-US-00002 Accelerated test conditions: Atlas Weather-Ometer Ci4000 Test standard: VW PV 3930 Specifications of test conditions: Weathering in Moist, Hot Climate Light source: Xenon arc Filtering: Borosilicate S inner and outer Radiation intensity (regulated): 0.50 W/m.sup.2/nm at 340 nm Black standard temperature: 65 +/ 2 C. Chamber air temperature: 40 +/ 3 C. Dry/wet cycle: 102 dry/18 water spray Relative humidity: 70 +/ 10% Light/dart cycle: Continuous illumination

Test Results:

[0059]

TABLE-US-00003 Grey scale Sample assessment (750 h) TiO.sub.2 reference (Kronos2900, KRONOS) 3 ZnS reference (Sachtolith HDS, 2 Sachtleben Chemie GmbH) ZnS/SiO.sub.2 (Example 2) 3 ZnS/SiO.sub.2 (Example 4) 3-4

TABLE-US-00004 TABLE 1 Exposure Grey scale Time [h] L* a* b* Delta E* level TiO.sub.2 0 16.2 0.2 1.7 0.0 5 (reference) 250 17.5 0.1 2.0 1.4 4-5 500 18.0 0 1.6 1.9 4-5 700 23.2 0.3 0.7 7.1 3 ZnS 0 16.7 0.1 0.6 0.0 5 (reference) 250 22.3 0.1 0.2 5.6 3-4 500 23.8 0.1 0.7 7.3 3 700 25.7 0.3 0.2 9.1 2 ZnS/SiO.sub.2 0 16.1 0 1.4 0.0 5 (Example 2) 250 17.9 0 0.4 2.1 4 500 19.8 0.2 0.1 4.0 3-4 700 22.3 0.1 0.2 6.3 3 ZnS/SiO.sub.2 0 14.9 0.2 1.4 0.0 5 (Example 4) 250 16.9 0.2 0.5 2.2 4 500 17.6 0.1 0.1 3.0 4 700 19.3 0.1 0.5 4.5 3-4

[0060] Table 1 shows that the novel zinc sulfides according to Examples 2 and 4 which are coated with SiO.sub.2 agglomerates exhibit significantly higher UV stability compared with the reference pigment ZnS (after exposure for 750 h) and have comparable UV stability compared with the reference pigment TiO.sub.2 (after exposure for 750 h).

[0061] Notes on the average particle sizes (all measured at Merck by the laser diffraction method using a measuring instrument from Malvern Ltd., UK, Malvern 2000):

ZnS: Sachtolith HDS (Sachtleben) D.sub.50=210 nm; D.sub.95=0.62 m
TiO.sub.2: Kronos 2900 (Kronos) D.sub.50=180 nm; D.sub.95=0.84 m