Supercritical fluid cleaning of banknotes and secure documents
A method and system for cleaning a secure instrument, such as a banknote, including a substrate, visual data and a security feature, including exposing the secure instrument to a supercritical fluid at a temperature and a pressure and for a duration sufficient to clean the substrate and not compromise the security feature and the visual data, wherein to clean the substrate includes to remove one or more substances from the substrate into the supercritical fluid. The substances removed from the substrate may include contaminants, dirt, sebum and pathogens.
1. A method for cleaning a banknote including a substrate, visual data and a security feature, comprising:
exposing the banknote to a supercritical fluid at a temperature and a pressure and for a duration sufficient to clean the substrate and not compromise the security feature and the visual data;
wherein to clean the substrate includes to remove one or more substances from the substrate into the supercritical fluid.
2. The method of claim 1 wherein the visual data comprises an image, authentication information, or both.
3. The method of claim 1 wherein the one or more substances comprise contaminants, dirt, sebum, pathogens, or any combination of these.
4. The method of claim 1 wherein at least one of the one or more substances are soluble in the supercritical fluid.
5. The method of claim 1 wherein the exposing further comprises flowing the supercritical fluid through and around the banknote.
6. The method of claim 5 wherein the flowing comprises agitating the banknote in the supercritical fluid.
7. The method of claim 5 wherein the flowing comprises agitating the supercritical fluid.
8. The method of claim 5 wherein the flowing comprises applying ultrasonic waves through the supercritical fluid.
9. The method of claim 1 wherein to clean comprises to disinfect.
10. The method of claim 1 wherein the supercritical fluid comprises CO 2 .
11. The method of claim 1 wherein the supercritical fluid further comprises an ionic liquid or another gas.
12. The method of claim 1 further comprising determining the fitness of the banknote.
13. The method of claim 12 wherein the determining for fitness comprises:
scanning the banknote to obtain information regarding one or more properties of the banknote; and
determining whether the one or more properties satisfy one or more predetermined criteria.
14. The method of claim 13 wherein the predetermined criteria comprises an acceptable level of tearing.
15. The method of claim 13 wherein the predetermined criteria comprises an acceptable level of limpness.
16. The method of claim 13 herein the predetermined criteria comprises an acceptable level of graffiti.
17. The method of claim 13 wherein the predetermined criteria comprises an acceptable level of soiling.
18. The method of claim 1 further comprising authenticating the banknote.
19. The method of claim 1 further comprising introducing a trapping material into the supercritical fluid to remove at least a portion of the one or more substances from the supercritical fluid.
20. The method of claim 19 wherein the trapping material comprises a high surface area material.
21. The method of claim 19 wherein the trapping material comprises fumed silica.
22. The method of claim 1 wherein the duration is from 30 minutes to 12 hours.
23. A method for cleaning a plurality of banknotes, each banknote including a substrate, visual data and a security feature, comprising:
sorting the banknotes based on one or more predetermined criteria;
exposing the banknotes to a supercritical fluid at a temperature and a pressure and for a duration sufficient to clean the substrates and not compromise the security features and the visual data of the banknotes;
wherein to clean the substrates includes to remove one or more substances from the substrates into the supercritical fluid.
24. The method of claim 23 wherein the visual data comprises an image, authentication information, or both.
25. The method of claim 23 wherein the one or more substances comprise contaminants, dirt, sebum, pathogens, or any combination of these.
26. The method of claim 23 wherein at least one of the one or more substances are soluble in the supercritical fluid.
27. The method of claim 23 wherein the exposing further comprises flowing the supercritical fluid through and around the banknotes.
28. The method of claim 23 wherein to clean comprises to disinfect.
29. The method of claim 23 wherein the supercritical fluid comprises CO 2 .
30. The method of claim 23 herein the supercritical fluid further comprises an ionic liquid or another gas.
31. The method of claim 23 wherein the sorting comprises scanning the banknotes to determine whether one or more properties of the banknotes satisfy the one or more predetermined criteria.
32. The method of claim 31 wherein the predetermined criteria comprises an acceptable level of tearing.
33. The method of claim 31 wherein the predetermined criteria comprises an acceptable level of limpness.
34. The method of claim 31 herein the predetermined criteria comprises an acceptable level of graffiti.
35. The method of claim 31 wherein the predetermined criteria comprises an acceptable level of soiling.
36. The method of claim 23 further comprising authenticating the banknotes.
37. The method of claim 23 further comprising introducing a trapping material into the supercritical fluid to remove at least a portion of the one or more substances from the supercritical fluid.
38. The method of claim 23 further comprising recirculating the supercritical fluid.