Zero-order diffractive filter
View Patent ↗A Zero-order diffractive filter comprising a first layer ( 1 ) with a periodic diffractive microstructure, forming a waveguide, and at least one adjacent second layer ( 2, 4, 5 ), wherein said first layer ( 1 ) has a refractive index that is higher than the refractive index of said second layer ( 2, 4, 5 ) by at least 0.2. At least one of said second layers ( 2, 4, 5 ) is a porous layer comprising nanopores. The period Λ of the diffractive microstructure is between 100 nm and 3000 nm.
1. A Zero-order diffractive filter comprising:
a first layer comprising a periodic diffractive microstructure having a period that is between 100 nm and 3000 nm; and
at least one second layer, wherein said at least one second layer has an effective index of refraction n eff of less than 1.4;
wherein said first layer has a refractive index that is higher than the refractive index of said at least one second layer by at least 0.2;
wherein at least one of said at least one second layer is a porous layer comprising an agglomeration of inorganic nanoparticles of 0.2 g/m 2 to 40 g/m 2 forming air-filled interstitial spaces between neighboring inorganic nanoparticles; and
wherein said interstitial spaces are nanopores of said porous layer, said nanopores having a pore volume of at least 20% of the entire volume of said porous layer.
2. The zero-order diffractive filter according to claim 1 , wherein said first layer consists of a polymer matrix containing nanoparticles, said nanoparticles having a refraction index that is higher than the refraction index of said polymer matrix.
3. The zero-order diffractive filter according to claim 1 , wherein said porous layer comprising said nanopores consists of a foam.
4. The zero-order diffractive filter according to claim 1 , wherein said porous layer has a refraction index of <1.35.
5. The zero-order diffractive filter according to claim 1 , wherein said first layer is adjacent to a substrate.
6. The zero-order diffractive filter according to claim 5 , wherein said substrate comprises said periodic diffractive microstructure.
7. The zero-order diffractive filter according to claim 5 , wherein said substrate is releasable.
8. The zero-order diffractive filter according to claim 1 , wherein said at least one second layer is adjacent to a substrate.
9. The zero-order diffractive filter according to claim 1 , comprising a covering layer.
10. A process for manufacturing a zero-order diffractive filter according to claim 1 , comprising the steps:
deposition of a porous layer with an refractive index n 2 on a flexible substrate, preferably by a water based coating technique;
deposition of a polymer layer with refractive index n 1 >n 2 +0.2 on the porous layer, preferably by a water based coating technique; and
forming a zero-order diffractive micro-structure in the polymer layer, preferably by embossing.
11. The process according to claim 10 , wherein subsequently an additional covering layer with a refractive index n 4 <n 1 −0.2 is deposited on the polymer layer, preferably by a water based coating technique.
12. The process according to claim 10 , wherein a porous layer and/or a porous covering layer has a refractive index <1.35.
13. The process according to claim 10 , wherein all deposition steps are part of a roll-to-roll process.
14. The, zero-order diffractive filter obtained by a process according to claim 10 .
15. A method for manufacturing a security device, in particular for the use with banknotes, credit cards, passports, tickets and for brand protection purposes, using a zero-order diffractive filter according to claim 14 .
16. A method using inorganic nanoparticles for manufacturing a zero-order diffractive filter according to claim 14 .
17. A process for manufacturing a zero-order diffractive filter according to claim 1 , comprising the steps:
deposition of a polymer layer with refractive index n 1 on a substrate with refractive index n 3 <n 1 −0.2, preferably by a water based coating technique;
forming a zero-order diffractive micro-structure in the polymer layer, preferably by embossing; and
deposition of an additional porous covering layer with a refractive index n 4 <n 1 −0.2 on the polymer layer, preferably by a water based coating technique.
18. The process according to claim 17 , wherein a porous layer and/or a porous covering layer has a refractive index <1.35.
19. The process according to claim 17 , wherein all deposition steps are part of a roll-to-roll process.
20. The zero-order diffractive filter obtained by a process according to claim 17 .
21. A method for manufacturing a security device, in particular for the use with banknotes, credit cards, passports, tickets and for brand protection purposes, using a zero-order diffractive filter according to claim 20 .
22. A method using inorganic nanoparticles for manufacturing a zero-order diffractive filter according to claim 20 .
23. A process for manufacturing a zero-order diffractive filter according to claim 1 , comprising the steps:
forming a zero-order diffractive micro-structure in a flexible substrate with refractive index n 3 ;
deposition of a polymer layer with refractive index n 1 >n 3 +0.2 on the substrate, preferably by a water based coating technique; and
deposition of an additional porous covering layer with a refractive index n 4 <n 1 −0.2 on the polymer layer, preferably by a water based coating technique.
24. The process according to claim 23 , wherein a porous layer and/or a porous covering layer has a refractive index <1.35.
25. The process according to claim 23 , wherein all deposition steps are part of a roll-to-roll process.
26. The zero-order diffractive filter obtained by a process according to claim 23 .
27. A method for manufacturing a security device, in particular for the use with banknotes, credit cards, passports, tickets and for brand protection purposes, using a zero-order diffractive filter according to claim 26 .
28. A method using inorganic nanoparticles for manufacturing a zero-order diffractive filter according to claim 26 .
29. A method for manufacturing a security device, in particular for the use with banknotes, credit cards, passports, tickets and for brand protection purposes, using a zero-order diffractive filter according to claim 1 .
30. A method using inorganic nanoparticles for manufacturing a zero-order diffractive filter according to claim 1 .
31. The zero-order diffractive filter according to claim 1 , comprising an interface between said first layer and said at least one second layer, said interface having a thickness of less than 200 nm.
32. The zero-order diffractive filter according to claim 1 , wherein said assembly of inorganic nanoparticles are in combination with at least one organic binder.
33. The zero-order diffractive filter according to claim 1 , wherein the surface of said inorganic nanoparticles is modified to obtain at least one of a positive or negative charge to improve the rheological properties of said inorganic nanoparticles.
34. The zero-order diffractive filter according to claim 1 comprising a substrate, wherein said substrate comprises said periodic diffractive microstructure, and said substrate is releasable.