Systems and methods for reversing banknote limpness

Abstract

A method for enhancing the structural strength of a porous substrate having pores therein is disclosed. The method includes soaking the porous substrate in a solution having a first solvent and at least one polymer dissolved in the first solvent at a specific temperature and pressure, such that the solution is deposited within pores of the porous substrate, soaking the porous substrate in a second solvent, such that the first solvent diffuses into the second solvent, and such that the at least one polymer remains within the pores of the porous substrate, and flushing out the second solvent from the porous substrate.

Claims

1. A method for enhancing the structural strength of a porous substrate of a first material having pores therein, comprising: soaking the porous substrate in a solution having a first solvent and at least one polymer comprising a second material distinct from the first material dissolved in the first solvent at a specific temperature and pressure, such that the solution is deposited within pores of the porous substrate; soaking the porous substrate in a second solvent, such that the first solvent diffuses into the second solvent, and such that the at least one polymer remains within the pores of the porous substrate; and flushing out the second solvent from the porous substrate; wherein a polymer of the at least one polymer is polyvinyl alcohol (PVA), polyethylene oxide (PEO), or polyethylene glycol (PEG).

2. The method of claim 1, wherein the second solvent is the first solvent at a different temperature and pressure such that the polymer exhibits a different solubility.

3. The method of claim 1, wherein the porous substrate is a document including a security feature.

4. The method of claim 3, wherein the document is a banknote.

5. The method of claim 1, further comprising cleaning the porous substrate with a supercritical fluid.

6. The method of claim 1, wherein the first solvent includes ethanol.

7. The method of claim 1, wherein the second solvent includes water, acetone, or a supercritical fluid.

8. The method of claim 7, wherein the second solvent includes a supercritical fluid.

9. The method of claim 1, wherein the polymer is a high molecular-weight polymer.

10. The method of claim 1, wherein flushing out the second solvent includes evaporating.

11. The method of claim 1, wherein flushing out the second solvent includes treating the porous substrate with a supercritical fluid.

12. A method for cleaning and enhancing the structural strength of a document having a security feature, the document including a porous substrate of a first material having pores therein, comprising: soaking the document in a solution having a first solvent and at least one polymer comprising a second material distinct from the first material dissolved in the first solvent at a specific temperature and pressure, such that the solution is deposited within pores of the porous substrate; soaking the document in a second solvent, such that the first solvent diffuses into the second solvent, and such that the at least one polymer remains within the pores of the document; flushing out the second solvent from the document; and cleaning the document with a supercritical fluid, such that the security feature is not damaged; wherein a polymer of the at least one polymer is polyvinyl alcohol (PVA), polyethylene oxide (PEO), or polyethylene glycol (PEG).

13. The method of claim 12, wherein the second solvent is the first solvent at a different temperature and pressure such that the polymer exhibits a different solubility.

14. The method of claim 12, wherein the step of cleaning the document occurs prior to soaking the document in the solution.

15. The method of claim 13, wherein the step of cleaning the document occurs after soaking the document in the solution.

16. The method of claim 12, wherein the second solvent is the supercritical fluid, and wherein the step of cleaning the document occurs when the document is disposed in the supercritical fluid.

17. The method of claim 12, wherein the first solvent includes ethanol.

18. The method of claim 12, wherein the second solvent includes water or acetone.

19. The method of claim 12, wherein the polymer is a high molecular-weight polymer.

20. The method of claim 12, wherein flushing out the second solvent includes evaporating or treating the porous substrate with a supercritical fluid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-mentioned and other aspects, features and advantages can be more readily understood from the following detailed description with reference to the accompanying drawings, wherein:

(2) FIG. 1 is a flow chart showing the process of cleaning and sorting of banknotes in accordance with an embodiment of the present invention;

(3) FIGS. 2A and 2B show an exemplary supercritical fluid chamber according to an embodiment of the invention;

(4) FIG. 3 shows a flow chart illustrating a method for reversing the limpness of a porous substrate;

(5) FIGS. 4A and 4B show limpness data of banknotes before and after exposure to a method of reversing banknote limpness, according to an embodiment of the invention;

(6) FIGS. 5A and 5B show limpness data of banknotes before and after exposure to a method of reversing banknote limpness, according to another embodiment of the invention;

(7) FIGS. 6A and 6B show porosity data of the banknotes in FIGS. 4A and 4B, respectively, before and after exposure to the method of reversing banknote limpness; and

(8) FIGS. 7A and 7B show porosity data of the banknotes in FIGS. 5A and 5B, respectively, before and after exposure to the method of reversing banknote limpness.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(9) The present invention provides for systems and methods for enhancing the structural strength of documents, such a secure documents and banknotes. More specifically, the present invention provides for systems and methods of reversing the limpness of documents, including, but not limited to, secure documents and banknotes in a manner that does not damage or otherwise compromise the visual data, inks, substrates or the security features contained therein. The systems and methods disclosed herein should not be limited to secure documents and banknotes. Rather, the systems and methods disclosed herein may be used to reverse the limpness of any porous substrate that may require strengthening.

(10) Generally, an important parameter used to determine the fitness of banknotes may be limpness. When banknotes have been in circulation, the mechanical wear from folds, handling, and use in bill acceptors, results in a loss of mechanical elasticity that leads to the notes becoming limp. Another important parameter used to determine the fitness of banknotes may cleanliness, i.e., the amount of soil on the banknotes. Accordingly, the systems and methods disclosed herein for reversing the limpness of banknotes may be combined with systems and methods for cleaning the banknotes.

(11) For example, FIG. 1 is a flow chart illustrating a system for cleaning banknotes according to an exemplary embodiment. FIG. 1 shows that the system may be configured to be used with at least one supercritical fluid for cleaning banknotes and secure documents. Generally, supercritical fluids mixed with other gases and additives, including ionic liquids, may be effective solvents for a variety of organics and have been used in a number of cleaning and extraction applications including pharmaceutical manufacturing, perfume production, and decaffeination. Accordingly, in the embodiments of the present invention, any supercritical fluid known to those skilled in the art may be employed, so long as the supercritical fluid may be configured to aid in cleaning banknotes and secure documents.

(12) Examples of supercritical fluids that may be used alone or in combinations thereof include, but are not limited to, CO.sub.2, N.sub.2O, CO, SF.sub.6. In particular, CO.sub.2 may be a supercritical fluid used alone or in combination with trace amounts of other supercritical fluids, including, but not limited to, N.sub.2O, CO, and SF.sub.6. For example, N.sub.2O creates a degree of solubility in the system that cannot be accomplished with CO.sub.2 alone, and SF.sub.6 may be particularly useful in a cleaning system because of its highly electronegative properties.

(13) An advantage of using supercritical fluids in the cleaning process may be that the security features on the bank notes may be either totally unaffected or weakly diminished by the cleaning process. Notably, the magnetic inks, fluorescence of UV active features, holograms, metalized and de-metalized threads, and optically variable inks may all remain intact and functioning after the cleaning process.

(14) Additives may be combined with supercritical fluids to enhance cleanliness and other properties of banknotes and secure documents during the cleaning process. The additives may include, but are not limited to, mixtures of oxalic acid and water, methanol and/or ethanol, aqueous citric acid solutions, ammonium zirconium carbonate (AZC), and combinations thereof. In addition, the amount of additive(s) combined with the supercritical fluid(s) may be any desired amount known to those skilled in the art so long as the amount of additive(s) enables a desired result to be achieved. In one embodiment, for example, the additive(s) may be approximately 10% by volume to the fluid phase of the supercritical fluid.

(15) The additive(s) combined with the supercritical fluid(s) during the banknote cleaning process may be chosen based on the state of the banknotes prior to cleaning and/or the desired state of the banknotes after cleaning. For example, if the banknotes to be cleaned include marks from writing implements (e.g., pens or markers), an additive may be chosen that includes a mixture of oxalic acid and water and/or methanol. Particularly, experiments have shown that saturated solutions of oxalic acid in water may be effective for removing gel pen markings; saturated solutions of oxalic acid in methanol or ethanol may be effective for removing permanent marker markings; and mixtures of oxalic acid with water/methanol may be effective for removing ball point pen markings, as well as gel pen markings and permanent marker markings.

(16) Returning to FIG. 1, the system may include a sorting machine, such as those used by central banks that may include optical and mechanical inspection systems to investigate the banknotes to determine if they must be destroyed or can be sent back into circulation. In particular, such high speed sorting machines can be used to interrogate banknotes for both authenticity and fitness. The sorting machine of the present invention may include fitness sensors that may be configured to operate primarily on optical image analysis and examine a number of parameters including, but not limited to, tears, tapes, graffiti, soiling, and combinations thereof.

(17) In addition, in some embodiments, the fitness sensors may be configured to determine banknote limpness using acoustics and/or ultrasonic reflection. Banknotes that are determined to have a limpness factor and/or cleanliness factor below pre-determined thresholds may be placed into a chamber where processes for cleaning and/or reversal of banknote limpness may be performed.

(18) FIGS. 2A and 2B illustrate a chamber 100 for cleaning and reversing banknote limpness, according to an exemplary embodiment. The chamber 100 for cleaning and reversing banknote limpness may include a chamber structure 112, which may include a holding structure 114 having a first end 114a and a second end 114b and a base portion 116. At least one of the first and second ends 114a, 114b may be configured to transition between an open configuration and a closed configuration.

(19) The chamber 100 of may further include a basket 118 configured to maintain stacks of banknotes in a desired position within the holding structure 114. In some embodiments, the basket 118 may be integral with at least a portion of the holding structure. For example, in some embodiments, the basket 118 may be configured to slide in and out of the holding structure 114 while connected to a track in the holding structure. Alternatively, as illustrated in FIGS. 2A and 2B, the basket 118 may not be integral with the holding structure. That is, the basket 118 may be configured to transition between a position within the holding structure 114 (FIG. 2B) and a position outside of the holding structure 114 (FIG. 2A) in which the basket 118 may no longer be in contact with the holding structure 114.

(20) The chamber 100 may include any mechanisms known to those skilled in the art configured to aid in the transitioning of the basket 118 in and out of the holding structure 114. For example, as illustrated in FIGS. 2A and 2B, a cart 117 may be used to facilitate the transitioning. The cart 117 may be sized, shaped, and configured to support the basket 118 with stacks of banknotes therein and may be movable relative to the chamber structure 112. The cart 117 may include a height that may be substantially the same as the height of the base portion 116 of the chamber structure 112 so that a device user does not have to vertically move the basket 118 as it is transitioned in and out of the holding structure 114. Additionally, the cart 117 and an interior portion 129 of the holding structure may each include at least one rail 128. A corresponding rail (not shown) may be located on a bottom surface of the basket 118 such that the basket 118 may be configured to slide along each of the interior surface 129 of the holding structure and a top surface of the cart 117 as the basket 118 is transitioned in and out of the holding structure 114.

(21) In some embodiments, cleaning and reversal of banknote limpness may be carried out on banknotes that are positioned individually within the chamber 100. Alternatively, or in addition, in some embodiments the cleaning and reversal of banknote limpness may be carried out on banknotes that are positioned in stacks of multiple banknotes within the chamber. Each stack of banknotes may include any number of banknotes known to those skilled in the art so long as each banknote in the stack may be cleaned and/or the limpness of each banknote in the stack may be reversed. In one embodiment, for example, each stack of banknotes may include approximately 100 banknotes. In some embodiments, the stacks of banknotes may be positioned in the chamber 100 individually. Alternatively, in some embodiments, as illustrated in FIGS. 2A and 2B, the stacks of banknotes may be positioned in the chamber 100 individually or in bundles (i.e., multiple stacks at one time).

(22) FIG. 3 is a flow chart illustrating a method for reversing the limpness of a porous substrate, according to an exemplary embodiment. The porous substrate may be any substrate known to those skilled in the art that may require strengthening, including but not limited to, paper, secure documents, and banknotes. Most banknote substrates are porous. Generally, limpness of porous substrates may be a result of expansion of the pore in a porous substrate due to mechanical wear. Accordingly, embodiments of the methods disclosed impregnate the expanded pores with a desired material in order to reverse limpness of the porous substrate.

(23) FIG. 3 illustrates that the method may include soaking the porous substrate in a first solution at a specific temperature. The first solution may include a first solvent and at least one polymer dissolved in the solvent. The polymer may be any high molecular-weight polymer known to those skilled in the art that may be configured to impregnate the pore of a porous substrate. For example, in some embodiments, the high molecular-weight polymer may have a molecular weight of approximately 8,000,000. The high molecular-weight polymer may include, but is not limited to, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyethylene glycol (PEG), or combinations thereof. The first solvent may be any solvent known to those skilled in the art that may be configured to be diffused out of the porous substrate, including but not limited to, ethanol and/or an ethanol-water combination. The temperature of the first solvent may be any temperature configured to enable the porous substrate to soak up the first solvent and the at least one polymer. For example, in some embodiments, the first solvent may be at a temperature of approximately 50 degrees Celsius.

(24) The method further includes the step of diffusing the first solvent from the porous substrate by soaking the porous substrate in a second solvent at a specific temperature. The second solvent may be any solvent configured to allow the first solvent to diffuse therein, such that the first solvent may be substantially removed from the porous substrate. The second solvent can also be the first solvent but at a different temperature and pressure, such that the polymer exhibits a different solubility. The second solvent may be configured such that the high molecular-weight polymer is not soluble therein. In some embodiments, for example, the second solvent may include, but is not limited to, water, acetone, a supercritical fluid, or combinations thereof. The temperature of the second solvent may be any temperature configured to enable the first solvent to diffuse therein. For example, in some embodiments, the temperature of the second solvent may be 25 degrees Celsius. In other embodiments, the temperature of the second solvent may be 35 degrees Celsius.

(25) As illustrated in FIG. 3, after the step of soaking the porous substrate in the second solvent is completed, the second solvent may be flushed out of the porous substrate such that the at least one polymer may be configured to remain in and be affixed to the pores of the porous substrate by drying therein. For example, in some embodiments the second solvent may be flushed out by evaporation. In other embodiments, the second solvent may be soluble in a supercritical fluid, and the supercritical fluid may be used to flush out the second solvent.

(26) The method for reversing limpness of a porous substrate may be enhanced by supercritical fluid cleaning of the porous substrate to remove contaminants. The supercritical fluid cleaning may be done before or after the method for reversing limpness. In some embodiments, supercritical fluid cleaning may be combined therewith. In those embodiments, for example, the second solvent may be a supercritical fluid that may be configured such that the first solvent may be soluble therein.

(27) FIGS. 4A, 4B, 5A, and 5B illustrates data corresponding to banknotes before and after being exposed to the method for reversing banknote limpness. In the embodiments of FIGS. 4A and 4B, the polymer included PVA, the first solvent included ethanol and water at a temperature of 50 degrees Celsius, and the second solvent included water at 35 degrees Celsius. The banknotes in FIG. 4A were not cleaned prior to the treatment, whereas the banknotes in FIG. 4B were cleaned prior to treatment.

(28) In the embodiments of FIGS. 5A and 5B, the polymer included PVA, the first solvent included ethanol and water at a temperature of 50 degrees Celsius, and the second solvent included acetone at 25 degrees Celsius. The banknotes in FIG. 5A were not cleaned prior to the treatment, whereas the banknotes in FIG. 5B were cleaned prior to treatment. As illustrated in each of FIGS. 4A, 4B, 5A, and 5B, the mean limpness factor of all the banknotes that underwent the method for reversing banknote limpness was higher after the treatment. The limpness factor is a measure of limpness known to those of skill in the art.

(29) Banknote limpness has been shown to be directly related to changes in the porosity of the banknote with mechanical wear. The porosity of the banknotes increases with use and manifests itself in a lower effective elastic constant. The graphs in FIGS. 6A, 6B, 7A, and 7B illustrate the change in porosity of the banknotes before and after the treatments identified in FIGS. 4A, 4B, 5A, and 5B, respectively. Consistent with the higher limpness factors discussed above, the porosity of the banknotes decreased after treatment.

(30) The embodiments and examples above are illustrative, and many variations can be introduced to them without departing from the spirit of the disclosure or from the scope of the appended claims. For example, elements and/or features of different illustrative and exemplary embodiments herein may be combined with each other and/or substituted with each other within the scope of this disclosure. The objects of the invention, along with various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed hereto and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated a preferred embodiment of the invention.