System for cleaning photo catalytic banknotes

Abstract

Self-cleaning banknotes are provided using coatings, inks and additives which are photo-active and catalytic to reactions which are effective in breaking up organic contaminants or dirt to allow for the self-cleaning of banknotes by ambient light exposure as well as the cleaning of processed banknotes using equipment with more intense optical excitation, thus increasing their usable life. The invention is usable with all substrates and particularly polymeric substrates such as biaxially-oriented polypropylene (BOPP). The invention further discloses a system which allows a certain class of fitness parameters to cause these banknotes to be redirected to a cleaning module, be revaluated, and then either returned to circulation or rejected and/or destroyed. In addition, inks which are photo-catalytic can be used for extending the life of the banknotes in printed regions.

Claims

1. A method for cleaning a substrate material comprising: scanning said substrate to determine fitness data relating thereto said substrate having a photocatalytic material on or about said substrate; making a decision based on said fitness data to clean the substrate; applying excitation energy having a wavelength in the 200 nm-400 nm region to excite said photo-catalytic material and initiate photo-catalysis oxidizing contaminants at the surface of the substrate thereby loosening all encrusted material; washing said loosened material; and rescanning said substrate to determine whether to return the substrate to circulation or to reject or destroy the substrate.

2. The method of claim 1, wherein said substrate is a banknote.

3. The method of claim 1, wherein said photo-catalytic material is selected from the group consisting of: an additive within said base sheet material, a coating on the surface of said base sheet material and an additive within ink used to print on the surface of said base sheet material.

4. The method of claim 1, wherein said photo-catalytic material is a nanoparticle metal oxide material.

5. The method of claim 1, wherein said photo-catalytic material is a nanoparticle semiconductor material.

6. The method of claim 1, wherein said photo-catalytic material is anatase TiO2.

7. The method of claim 6, wherein said anatase TiO2 is in nanoparticle form.

8. The method of claim 2, wherein said photo-catalysis is initiated using ultraviolet energy having a wavelength in the 200 nm-400 nm region.

9. The method of claim 3, wherein said photo-catalysis is initiated using ultraviolet energy having a wavelength in the 200 nm-400 nm region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings which illustrate the best mode presently contemplated for carrying out the present invention:

(2) FIG. 1 is a diagram of the present invention as applied to a banknote; and

(3) FIG. 2 is a schematic diagram of system for cleaning and analyzing a banknote in accordance with the present invention; and

(4) FIG. 3 is an enlarged cross-section depicting the result of cleaning a banknote in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(5) Now referring to the drawings, there is disclosed a substrate material that is formed to include a self-cleaning feature. More specifically, the present invention provides a substrate or coating for a substrate that includes a photo-catalytic material therein when, upon exposure to a source of illumination, reacts in a manner that causes the substrate material to shed accumulated contaminants and dirt. Further, the present invention discloses a system for sorting, cleaning and analyzing banknotes that are formed using such a substrate material.

(6) In the most general sense, the present invention employs coatings, inks and/or additives that are photo-active. The photo-active nature of these materials allows for the self-cleaning of substrates, such as for example banknotes, by ambient light exposure as well as the cleaning of processed banknotes using equipment with optical excitation, thus increasing their usable life. The invention is usable with all substrates and particularly polymeric substrates such as biaxially-oriented polypropylene (BOPP).

(7) It is known that semiconductor nanoparticles exhibit various photo-catalytic effects. Examples of these include III-V (GaN, GaAs) and II-VI (ZnS, ZnSe, CdS, CdSe, WS.sub.2, MoS.sub.2) semiconductors and various metal oxides such as ZnO, TiO.sub.2, MoO.sub.3, CeO.sub.2, ZrO.sub.2, WO.sub.3, alpha-FeO.sub.3 and SnO.sub.2. TiO.sub.2 (titanium dioxide) is of particular importance for this application as it is white in color and inexpensive. Its low cost and availability have been a large factor in its increased use in many areas including Dye Sensitized Solar Cells (DSSC), selective oxidation, disinfection and metal corrosion prevention

(8) Not all forms of TiO.sub.2 are highly photo-catalytic. The most photo-reactive form is the anatase phase which can be obtained by high temperature conversion. It is of particular note that the anatase form of TiO.sub.2 can be excited by ultraviolet energy having a wavelength in the 200 nm-400 nm region and more particularly in the 360 nm-390 nm region. This is advantageous in that light sources such as low cost LED flash lamps, arc sources and lasers are all available for excitation in this energy range and are thus anticipated for possible use within the scope of the present invention. Further, those metal oxides and semi-conductors listed above are equally applicable and intended to fall within the scope of the present invention as being suitable photo-catalytic materials within the scope of the present invention. In addition, modified TiO.sub.2 can be used which has different absorption, interfacial charge transfer and absorption characteristics.

(9) Photo-catalytic degredation with illuminated TiO.sub.2 of a large number of substrates including soot and carbonaceous contaminants is primarily ascribed to the strong oxidation potential of its valence band holes and surface OH radicals. In some cases, direct electron transfer from the conduction band to O.sub.2 leads to degradation through O.sup.−.sub.2 reactions. In one embodiment, as shown at FIG. 1, when excitation energy such as ambient lighting is directed onto the photo-catalytic materials, electrons and holes can be generated and transferred to O.sub.2 and OH respectively (1). More particularly, when a stronger effect is desired, ultraviolet energy is directed onto the anatase titanium dioxide, more electrons and holes can be generated and transferred. In either case, these charge transfers convert water molecules from the ambient air into hydroxyl radicals (2) that in turn cause chemical oxidation and reduction reactions take place (3). In this specific example, at the anatase titanium dioxide or in general the semiconductor particle surface. In effect, the hydroxyl radicals attack organic (carbon-based) dirt molecules and break them up into smaller fragments that are much easier to remove (4). In this regard, the present invention employs photo-catalytic semiconductor materials or photo-catalytic metal oxides as an additive to a banknote either as a coating, ink used for printing of the banknote or within the substrate itself. In a more specific embodiment, the present invention employs anatase titanium dioxide as an additive to a banknote either as a coating, ink used for printing of the banknote or as the substrate itself. Since the reactions happen at the anatase titanium dioxide material, preferably positioned on the very surface of the banknote, they attack the lowest layers of the dirt, loosening encrusted dirt particles very effectively by chipping them away from the inside out. This is in clear contrast to normal cleaning, where the dirt is scrubbed from the outside in.

(10) The invention further discloses a system at FIG. 2 for evaluating the status and fitness of a banknote in order to determine whether it should remain in circulation. The system may be a standalone system or incorporated onto banknote counters and sorters. As the banknotes pass through the system, the system employs a sensor to read various fitness data from the banknote. Based on the date the system makes a decision to either pass or clean the banknote. When the banknote is routed to the cleaning process, a cleaning module applies energization light for to initiate the photo-catalytic process and removes the photo-catalytic reaction products using a wash, gas jet, or mechanical means. Once the banknote is cleaned, it is re-evaluated using a fitness sensor that either returns the note to circulation or sends the banknote to a destroyer device or reject sorter bin.

(11) It is therefore an object of the present invention to provide a substrate material that provides high security against fraud while exhibiting increased durability and self-cleaning characteristics. It is a further object of the present invention to provide a substrate that through the use of coatings, inks and additives that are photo-active and catalytic to reactions which are effective in breaking up organic contaminants or dirt to allow for the self-cleaning of banknotes by ambient light exposure as well as the cleaning of processed banknotes using equipment with optical excitation, thus increasing their usable life. It is still a further object of the present invention to provide a system that using a certain class of fitness parameters causes identified banknotes to be redirected to a cleaning module prior to reevaluation and then a determination that they are either returned to circulation or destroyed.

(12) While there is shown and described herein certain specific structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims.