Laser additive
The present invention relates to a laser additive comprising core/shell particles, to a process for the preparation of a laser additive of this type, and to the use thereof, in particular as laser absorber in plastics and plastic-containing coatings of articles.
1. A laser additive comprising core/shell particles, characterised in that the core/shell particles in each case have a particulate core of homogeneous composition which consists of Ca 5 (OH)(PO 4 ) 3 , Ba 2+ -modified Ca 5 (OH)(PO 4 ) 3 , or Mg 2+ -modified Ca 5 (OH)(PO 4 ) 3 , where the shell consists of carbon.
2. The laser additive according to claim 1 , wherein the particulate cores have a bulk density of ≤0.5 g/cm 3 .
3. The laser additive according to claim 1 , wherein the particulate cores have a specific surface area of ≥5 m 2 /g (BET).
4. The laser additive according to claim 1 , wherein the particulate cores have an irregular particle shape or a flake shape.
5. The laser additive according to claim 1 , wherein the particulate cores have a particle size in the range from 0.1 to 100 μm.
6. The laser additive according to claim 1 , wherein the shell in each case completely surrounds the particulate core in a continuous layer and is chemically bonded to the particulate core.
7. The laser additive according to claim 1 , wherein the shell has a geometrical thickness in the range from 1 to 20 nm.
8. The laser additive according to claim 1 , wherein the shell consists of a mixture of nano crystalline carbon and amorphous carbon with proportions by weight in the ratio from 70:30 to 90:10.
9. The laser additive according to claim 1 , wherein the particulate cores have a particle size with a d 10 value of ≥0.5 μm and a d 90 value of ≤20 μm, and the shell has a geometrical thickness in the range from 2 to 10 nm.
10. A plastic material comprising a plastic and a laser additive according to claim 1 as a laser adsorber.
11. A laser additive comprising core/shell particles, characterised in that the core/shell particles in each case have a particulate core of homogeneous composition which contains alkaline-earth metal ions and OH groups and has a surface with OH groups located thereon, wherein the shell consists of a mixture of nano crystalline carbon and amorphous carbon with proportions by weight in the ratio from 70:30 to 90:10.
12. The laser additive according to claim 11 , wherein the alkaline-earth ions are at least one type of ions selected from the group consisting of Ca 2+ , Mg 2+ and Ba 2+ .
13. The laser additive according to claim 8 , wherein the particulate cores consist of Ca 5 (OH)(PO 4 ) 3 , Mg 3 Si 4 O 10 (OH) 2 , or of Ba 2+ - or Mg 2+ -modified Ca 5 (OH)(PO 4 ) 3 .
14. The laser additive according to claim 11 , wherein the shell consists of a mixture of nano crystalline carbon and amorphous carbon with proportions by weight in the ratio from 80:20 to 90:10.
15. A process for the preparation of a laser additive comprising core/shell particles, wherein the core/shell particles in each case have a particulate core of homogeneous composition which contains alkaline-earth metal ions and OH groups and has a surface with OH groups located thereon, where the shell consists of carbon, said process comprising:
bringing core particles of homogeneous composition which contain alkaline-earth metal ions and OH groups and have a surface with OH groups located thereon to reaction in a reactor
a) in a mixture with a solid carbon-containing precursor compound,
or
b) with supply of a carbon-containing precursor compound in a stream of carrier gas,
where the carbon-containing precursor compound is heated under inert gas to a temperature at which carbon is deposited from the carbon-containing precursor compound onto the surface of the core particles as outermost, continuous layer and a shell forms around the respective core particle.
16. The process according to claim 15 , wherein the shell has a geometrical thickness in the range from 1 to 20 nm.
17. The process according to claim 15 , wherein the carbon-containing precursor compound employed is acetone, acetylene, p-xylene, toluene, 2-methyl-3-butynol-2 or saccharides.
18. The process according to claim 15 , wherein the core particles are kept in motion in the reactor.
19. The process according to claim 15 , wherein the reaction is carried out at a temperature in the range from 500 to 850° C. and with a time duration in the range from 20 to 480 min.
20. The process according to claim 15 , wherein each core particle is completely surrounded by the shell in a continuous layer and core particle and shell are chemically bonded to one another.