Zero-order diffractive pigments

1. A zero-order diffractive pigment, comprising an optical wave-guiding layer whereas said layer is

made of a material with an index of refraction that is higher than the index of refraction of an adjacent material by at least 0.25;

has a zero-order diffractive grating structure with a period between 300-500 nm and a grating depth between 30-300 nm; and

has a thickness between 50 nm and 500 nm.

2. Pigment according to claim 1 wherein the zero-order diffractive grating structure possesses a period that is smaller than the wavelength of the light which shall be reflected in the zeroth reflection order.

3. Pigment according to claim 1 having an anisotropic lateral shape.

4. Pigment according to claim 1 containing a magnetic layer.

5. Pigment according to claim 1 containing multilayer systems.

6. Pigment according to claim 1 wherein one or more optical waveguiding layers are embedded in an organic or inorganic droplet and are fixed within this droplet.

7. Pigment according to claim 1 wherein the optical waveguiding layer is made of material suitable for human administration, and wherein said pigment is embedded in a digestible matrix.

8. Pigment according to claim 7 wherein the optical waveguiding layer is TiO2, and wherein said pigment is embedded in a digestible matrix.

9. Matrix comprising pigments according to claim 1 .

10. The matrix of claim 9 which is a coating, glaze or lacquer.

11. Process, in particular a roll-to-roll process, for manufacturing ZOD pigments according to claim 1 , comprising the steps of:

depositing and optionally micro-structuring on a substrate a first layer which is dissolvable in a first solvent;

manufacturing one or more layers of said ZOD pigments by one or more deposition steps and optionally one or more micro-structuring steps wherein all additional layers are insoluble in said first solvent;

dissolving said first layer for obtaining ZOD substrates or ZOD pigments;

optionally subjecting the thus obtained ZOD substrates or ZOD pigments to one or more further coating steps; and/or

optionally subjecting the obtained ZOD substrates or ZOD pigments to one or more selection steps as to size and/or shape wherein at least one micro-structuring step takes place.

12. Process according to claim 11 comprising the steps of:

a) depositing on a flexible substrate a first layer which is embossable and dissolvable in a first solvent;

b) embossing a periodic microstructure in the first layer;

c) depositing on the embossed first layer a second layer which is insoluble in said first solvent and has an index of refraction n2;

d) separating said flexible substrate from said first layer by contacting it with said first solvent, wherein the second layer breaks into flake shape substrates;

e) coating the obtained flake shaped substrate with a third layer, wherein said third layer has an index of refraction n3>n2+0.25; or

a) depositing on a flexible substrate a first layer which is dissolvable in a first solvent;

b) depositing on said first layer a second layer which is embossable and insolvable in said first solvent and has an index of refraction n2;

embossing a periodic microstructure in said second layer;

d) separating said flexible substrate from said first layer by contacting it with said first solvent, wherein said second layer breaks into flake shape substrates;

e) coating the obtained flake shaped substrates with a third layer with an index of refraction n3>n2+0.25.

13. Process according to claim 12 , wherein the coating step e) takes place in a wet or gaseous phase.

14. Process according to claim 12 , wherein step (d) is complemented by a collection and purification step.

15. Process according to claim 12 , wherein a porous layer is deposited on said flexible substrate prior to or simultaneously with the deposition of said first layer.

16. Process according to claim 12 , wherein the first layer consists essentially of PVA or PVP.

17. Process according to claim 12 , wherein the first solvent consists essentially of water.

18. Process according to claim 12 , wherein the second layer consists essentially of MgF2, SiO2, Latex or PS.

19. Process according to claim 12 , wherein coating step (e) takes place repeatedly by using different coating materials having a different index of refraction.

20. Process according to claim 12 , comprising the following steps:

a) hot- or cold embossing of a periodic microstructure (“the grating”) into a deformable polymer foil or deformable layer on a polymer foil;

b) deposition of at least one HRI layer, in particular by thermal evaporation, plasma deposition, sputtering or gravure printing;

c) dissolving the embossing layer and peeling of the pigments mechanically;

d) optionally narrowing down the size distribution by selecting HRI pigments according to the desired size and shape;

e) embedding he HRI pigments in paste or powder or distributing the HRI pigments in a liquid or paste.

21. Process according to claim 20 , wherein all process steps are adapted to a roll-to-roll process.

22. Process according to claim 12 , wherein predetermined breaking points or ˜lines are embossed prior, simultaneously or subsequently, to the embossing of the periodic microstructure.

23. The process according to claim 22 where the predetermined breaking points or ˜lines are embossed simultaneously to the embossing of the periodic microstructure.

24. Use of ZOD pigments according to claim 1 in the fields of identification, authentication and security, branding, marketing, decoration, cosmetic formulations, pharmaceutical formulations.

25. Paint, coating, glaze or ink containing a ZOD pigment according to claim 1 .