Electrically conductive pigment

Abstract

The present invention relates to electrically conductive pigments, to a process for the preparation thereof and to the use thereof, in particular in antistatic or dissipative articles or surfaces, for example in paints, coatings, printing inks or floorcoverings.

Claims

1. Electrically conductive pigments, comprising a dielectric flake-form substrate and an electrically conductive layer surrounding the substrate, which has a volume average particle size d.sub.95<25 m and a ratio of a volume average particle size d.sub.95 to a volume average size of the pigments d.sub.5 is greater than 5, and wherein at least 5 percent by volume of a powder bed of the electrically conductive pigments have a nominal particle size of <5 m.

2. Electrically conductive pigments according to claim 1, wherein the substrate is selected from the group consisting of natural mica flakes, synthetic mica flakes, talc flakes, kaolin flakes, sericite flakes, aluminium oxide flakes, silicon dioxide flakes, glass flakes of mixtures of two or more thereof.

3. Electrically conductive pigments according to claim 1, wherein the electrically conductive layer consists of one or more doped metal oxides.

4. Electrically conductive pigments according to claim 3, wherein the doped metal oxide is tin oxide, zinc oxide, indium oxide and/or titanium oxide which is doped with gallium, aluminium, indium, thallium, germanium, tin, phosphorus, arsenic, antimony, selenium, tellurium, molybdenum, tungsten and/or fluorine.

5. Electrically conductive pigments according to claim 3, wherein the electrically conductive layer consists of a doped tin oxide.

6. Electrically conductive pigments according to claim 3, wherein the electrically conductive layer consists of antimony-doped tin oxide, wherein the antimony content is 5 to 15 mol % based on the total amount of antimony oxide and tin oxide.

7. Electrically conductive pigments according to claim 1, wherein at least one dielectric layer is located between the flake-form substrate and the electrically conductive layer.

8. Electrically conductive pigments according to claim 1, wherein the ratio of the volume average particle size d.sub.95 to the volume average size of the pigments d.sub.5 is greater than 7.

9. Electrically conductive pigments according to claim 1, wherein the pigment has a volume average particle size d.sub.95 of <15 m.

10. A process for preparing electrically conductive pigments according to claim 1, comprising coating a powder comprising dielectric flake-form substrates which has a volume average particle size d.sub.95<25 m and in which at least 5 percent by volume of the powder have a particle size <5 m in an aqueous suspension optionally with one or more dielectric layers, and finally with an electrically conductive layer.

11. The process according to claim 10, wherein the dielectric substrates are natural mica flakes, synthetic mica flakes, talc flakes, kaolin flakes, sericite flakes, aluminium oxide flakes, silicon dioxide flakes, glass flakes or mixtures of two or more thereof.

12. The process according to claim 10, wherein the powder comprising dielectric flake-form substrates is coated with an electrically conductive layer comprising one or more doped metal oxides.

13. A product selected from the group consisting of paints, coatings, printing inks, plastics, coating compositions, sensors, security applications, far laser marking, floor coverings, films, ceramic materials, glasses and papers, comprising electrically conductive pigments according to claim 1.

14. The product according to claim 13, which is selected from the group consisting of paints, coatings, printing inks, plastics, coating compositions, floor coverings, films and ceramic materials, and having a pigment mass concentration of 25 to 60%.

15. Electrically conductive pigments according to claim 1, which have a surface resistance value of 10E+04 ohm or less when measured in a coating having a layer thickness of 15 to 20 m on a plastic part at a pigment mass concentration of 35 to 45%.

16. Electrically conductive pigments according to claim 1, wherein the ratio of the volume average particle size d.sub.95 to a volume average size of the pigments d.sub.5 is greater than 5 and up to 15.

17. Electrically conductive pigments according to claim 16, wherein the pigment has a volume average particle size d.sub.95 of <15 m.

18. Electrically conductive pigments according to claim 16, wherein the electrically conductive layer consists of antimony-doped tin oxide, wherein the antimony content is 5 to 15 mol % based on the total amount of antimony oxide and tin oxide.

19. Electrically conductive pigments according to claim 16, which have a surface resistance value of 10E+04 ohm or less when measured in a coating having a layer thickness of 15 to 20 m on a plastic part at a pigment mass concentration of 35 to 45%.

20. Electrically conductive pigments according to claim 1, wherein the ratio of the volume average particle size d.sub.95 to a volume average size of the pigments d.sub.5 is 7 to 11.

Description

EXAMPLES

(1) Preparation of the Mica:

(2) Crude mica is finely ground in a pan grinder and classified with the aid of a decanter into various fractions which differ in particle size and particle spectrum. The extremely fine components are separated off from a finely divided mica fraction <15 m in the decanter.

Example 1

Conductive Pigment Based on Finely Divided Talc and Mica

(3) 50 g of Plustalk H05 AW from Mondo Minerals and 50 g of the finely divided mica fraction described above are suspended in 1900 ml of DI water, and the suspension is adjusted to pH 2.1 using hydrochloric acid. A mixture of 206 g of a 50% by weight aqueous SnCl.sub.4 solution, 67 ml of HCl (37% by weight) and 47 g of a 35% by weight aqueous SbCl.sub.3 solution is slowly metered continuously into the suspension at 75 C. with stirring. The pH is kept constant by simultaneous regulated addition of sodium hydroxide solution. After addition of the entire amount of the solution, the mixture is stirred at 75 C. for a further 30 min., subsequently cooled to room temperature with stirring, and the reaction mixture is adjusted to pH 3. The pigment obtained is filtered off via a suction filter, washed with water, dried at 140 C. and calcined at 750 C. for 30 min., giving 167 g of a pale-grey pigment powder. The Sn:Sb ratio in the coating is about 85:15. The particle size distribution of the pigment is measured by means of laser diffraction in an Agilent Technologies Accusizer, model 870. The product has a volume-weighted particle size d.sub.95 of 11.2 m and a d.sub.5 of 1.26 m. The d.sub.95/d.sub.5 ratio is 8.9.

Example 2

Conductive Pigment Based on Finely Divided Talc

(4) 100 g of Plustalk H 05 AW from Mondo Minerals are suspended in 1900 ml of DI water, and the suspension is adjusted to pH 2.1 using hydrochloric acid. A mixture of 206 g of a 50% by weight aqueous SnCl.sub.4 solution, 67 ml of HCl (37% by weight) and 47 g of a 35% by weight aqueous SbCl.sub.3 solution is slowly metered continuously into the suspension at 75 C. with stirring. The pH is kept constant by simultaneous regulated addition of sodium hydroxide solution. After addition of the entire amount of the solution, the mixture is stirred at 75 C. for a further 30 min., subsequently cooled to room temperature with stirring, and the reaction mixture is adjusted to pH 3. The pigment obtained is filtered off via a suction filter, washed with water, dried at 140 C. and calcined at 750 C. for 30 min., giving 165 g of a pale-grey pigment powder. The Sn:Sb ratio in the coating is about 85:15. The particle size distribution of the pigment is measured by means of laser diffraction in an Agilent Technologies Accusizer, model 870. The product has a very high fines content at a volume-weighted particle size d.sub.95 of 11 m and a d.sub.5 of 1 m. The d.sub.95/d.sub.5 ratio is 11.

Example 3

Conductive Pigment Based on Mica

(5) 100 g of a mica fraction having a particle size <25 m are suspended in 1900 ml of DI water, and the suspension is adjusted to pH 2.1 using hydrochloric acid. A mixture of 206 g of a 50% by weight aqueous SnCl.sub.4 solution, 67 ml of HCl (37% by weight) and 47 g of a 35% by weight aqueous SbCl.sub.3 solution is slowly metered continuously into the suspension at 75 C. with stirring. The pH is kept constant by simultaneous regulated addition of sodium hydroxide solution. After addition of the entire amount of the solution, the mixture is stirred at 75 C. for a further 30 min., subsequently cooled to room temperature with stirring, and the reaction mixture is adjusted to pH 3. The pigment obtained is filtered off via a suction filter, washed with water, dried at 140 C. and calcined at 750 C. for 30 min., giving 166 g of a pale-grey pigment powder. The Sn:Sb ratio in the coating is about 85:15. The particle size distribution of the pigment is measured by means of laser diffraction in an Agilent Technologies Accusizer, model 870. The product has a volume-weighted particle size d.sub.95 of 23.5 m and a d.sub.5 of 3.8 m. The d.sub.95/d.sub.5 ratio is 6.2.

Example 4

Conductive Pigment Based on Talc and Mica

(6) 50 g of Plustalk H 05 AW from Mondo Minerals and 50 g of a mica fraction having a particle size <25 m are suspended in 1900 ml of DI water, and the suspension is adjusted to pH 2.1 using hydrochloric acid. A mixture of 206 g of a 50% by weight aqueous SnCl.sub.4 solution, 67 ml of HCl (37% by weight) and 47 g of a 35% by weight aqueous SbCl.sub.3 solution is slowly metered continuously into the suspension at 75 C. with stirring. The pH is kept constant by simultaneous regulated addition of sodium hydroxide solution. After addition of the entire amount of the solution, the mixture is stirred at 75 C. for a further 30 min., subsequently cooled to room temperature with stirring, and the reaction mixture is adjusted to pH 3. The pigment obtained is filtered off via a suction filter, washed with water, dried at 140 C. and calcined at 750 C. for 30 min., giving 167 g of a pale-grey pigment powder. The Sn:Sb ratio in the coating is about 85:15, the layer thickness of the antimony-doped tin oxide layer is about 25 m. The particle size distribution of the pigment is measured by means of laser diffraction in an Agilent Technologies Accusizer, model 870. The product has a volume-weighted particle size d.sub.95 of 9.3 m and a d.sub.5 of 1.4 m. The d.sub.95/d.sub.5 ratio is 6.6.

Comparative Example 1

Pigment Based on Mica

(7) 100 g of a finely divided mica fraction having a particle size of <15 m which has been freed from the extremely fine components as described above is suspended in 1900 ml of DI water, and the suspension is adjusted to pH 2.1 using hydrochloric acid. A mixture of 206 g of a 50% by weight aqueous SnCl.sub.4 solution, 67 ml of HCl (37% by weight) and 47 g of a 35% by weight aqueous SbCl.sub.3 solution is slowly metered continuously into the suspension at 75 C. with stirring. The pH is kept constant by simultaneous regulated addition of sodium hydroxide solution. After addition of the entire amount of the solution, the mixture is stirred at 75 C. for a further 30 min., subsequently cooled to room temperature with stirring, and the reaction mixture is adjusted to pH 3. The pigment obtained is filtered off via a suction filter, washed with water, dried at 140 C. and calcined at 800 C. for 30 min., giving 164 g of a pale-grey pigment powder. The Sn:Sb ratio in the coating is about 85:15. The particle size distribution of the pigment is measured by means of laser diffraction in an Agilent Technologies Accusizer, model 870. The product has a volume-weighted particle size d.sub.95 of 7.2 m and a d.sub.5 of 1.6 m. The d.sub.95/d.sub.5 ratio is 4.5.

Comparative Example 2

Pigment Based on Mica and Spherical Quartz Powder

(8) 50 g of finely divided quartz flour (d.sub.50 about 3 m) and 50 g of the finely divided mica fraction <15 m described above are suspended in 1900 ml of DI water, and the suspension is adjusted to pH 2.1 using hydrochloric acid. A mixture of 206 g of a 50% by weight aqueous SnCl.sub.4 solution, 67 ml of HCl (37% by weight) and 47 g of a 35% by weight aqueous SbCl.sub.3 solution is slowly metered continuously into the suspension at 75 C. with stirring. The pH is kept constant by simultaneous regulated addition of sodium hydroxide solution. After addition of the entire amount of the solution, the mixture is stirred at 75 C. for a further 30 min., subsequently cooled to room temperature with stirring, and the reaction mixture is adjusted to pH 3. The pigment obtained is filtered off via a suction filter, washed with water, dried at 140 C. and calcined at 750 C. for 30 min., giving 167 g of a pale-grey pigment powder. The Sn:Sb ratio in the coating is about 85:15. The particle size distribution of the pigment is measured by means of laser diffraction in an Agilent Technologies Accusizer, model 870. The product has a volume-weighted particle size d.sub.95 of 9.3 m and a d.sub.5 of 1.05 m. The d.sub.95/d.sub.5 ratio is 8.9.

Comparative Example 3

Pigment Based on Mica and Spherical Quartz Powder

(9) 50 g of finely divided quartz flour (d.sub.50 about 3 m) and 50 g of a mica fraction <60 m are suspended in 1900 ml of DI water, and the suspension is adjusted to pH 2.1 using hydrochloric acid. A mixture of 146 g of a 50% by weight aqueous SnCl.sub.4 solution, 67 ml of HCl (37% by weight) and 15 g of a 35% by weight aqueous SbCl.sub.3 solution is slowly metered continuously into the suspension at 75 C. with stirring. The pH is kept constant by simultaneous regulated addition of sodium hydroxide solution. After addition of the entire amount of the solution, the mixture is stirred at 75 C. for a further 30 min., subsequently cooled to room temperature with stirring, and the reaction mixture is adjusted to pH 3. The pigment obtained is filtered off via a suction filter, washed with water, dried at 140 C. and calcined at 750 C. for 30 min., giving 166 g of a pale-grey pigment powder. The Sn:Sb ratio in the coating is about 92:8. The particle size distribution of the pigment is measured by means of laser diffraction in an Agilent Technologies Accusizer, model 870. The product has a volume-weighted particle size d.sub.95 of 49.7 m and a d.sub.5 of 3.0 m. The d.sub.95/d.sub.5 ratio is 16.6.

Comparative Example 4

Pigment Based on Mica

(10) 100 g of a mica fraction <40 m are suspended in 1900 ml of DI water, and the suspension is adjusted to pH 2.1 using hydrochloric acid. A mixture of 146 g of a 50% by weight aqueous SnCl.sub.4 solution, 67 ml of HCl (37% by weight) and 15 g of a 35% by weight aqueous SbCl.sub.3 solution is slowly metered continuously into the suspension at 75 C. with stirring. The pH is kept constant by simultaneous regulated addition of sodium hydroxide solution. After addition of the entire amount of the solution (290 ml), the mixture is stirred at 75 C. for a further 30 min., subsequently cooled to room temperature with stirring, and the reaction mixture is adjusted to pH 3. The pigment obtained is filtered off via a suction filter, washed with water, dried at 140 C. and calcined at 800 C. for 30 min., giving 142 g of a pale-grey pigment powder. The Sn:Sb ratio in the coating is about 92:8. The particle size distribution of the pigment is measured by means of laser diffraction in an Agilent Technologies Accusizer, model 870. The product has a volume-weighted particle size d.sub.95 of 35.1 m and a d.sub.5 of 6.4 m. The d.sub.95/d.sub.5 ratio is 5.5.

Evaluation

(11) Testing of the Conductivity in a Lacquer Film:

(12) The pigments of the examples and comparative examples are dispersed in NC lacquer (12% of binder comprising nitrocellulose and butyl acrylate in a solvent mixture). PET films are coated with the lacquer preparations with a lacquer film with a dry layer thickness of 9 m and a pigment mass concentration of 35% in the dried film.

(13) After drying of the lacquer layers, the dissipation resistance (specific surface resistance) is measured in accordance with DIN 53482 with the aid of a spring-tongue electrode. The measurement voltage is 100V. The results are shown in Table 1. A comparative lacquer film without conductive pigment has a specific surface resistance of >10.sup.10 ohm.

(14) Characterisation of the Surface Nature:

(15) Lacquer films having the smoothest possible surface are required. The roughness of the respective lacquer film is assessed optically. A lacquer film without conductive pigment which has a very smooth surface is assessed as 10.

(16) The results in Table 1 show that the electrically conductive pigments in accordance with the present invention in thin films result in a smooth surface and a uniform coating and exhibit good conductivity, even at a comparatively low use concentration. In comparison, although pigments of the same structure and of the same composition on mica substrates having a narrow particle size distribution under the given conditions exhibit high coating quality, they do not, however, exhibit a usable electrical conductivity, while pigments having a content of spherical particles and a likewise high fines content result in rough and matt surfaces.

(17) TABLE-US-00001 TABLE 1 Pigment Spec. surface from resistance D(95) d(95)/d(5) Surface Example Substrate [Kohm] [m] Accusizer nature 1 (inv.) Mica + talc 9.00E+02 11.2 8.9 9 2 (inv.) Talc 3.10E+03 11 11 9 3 (inv.) Mica 2.40E+03 23.5 6.2 8 4 (inv.) Mica + talc 2.00E+02 9.3 6.6 9 Comp. 1 Mica 5.00E+10 7.2 4.5 8 Comp. 2 Mica + 2.25E+04 9.3 8.9 4 quartz Comp. 3 Mica + 2.08E+06 49.7 16.6 2 quartz Comp. 4 Mica 5.00E+10 35.1 5.5 6