Supercritical CO2 Cleaning of Banknotes
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Solution Overview
Problem
Current methods for cleaning banknotes fail to effectively remove contaminants and pathogens without damaging the security features and visual data, leading to high replacement costs and environmental issues due to the short lifespan of banknotes caused by soiling.
Innovation Solution
The use of supercritical fluids, such as CO2, to clean banknotes by exposing them to specific temperatures and pressures, allowing for the removal of substances like sebum, dirt, and pathogens without compromising the security features or visual data, and incorporating a trapping material like fumed silica to prevent re-deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cleaning methods are used to remove contaminants and pathogens from banknotes, then cleaning effectiveness is improved, but damage to security features and visual data occurs
Solution Approach 1:
The patent applies parameter changes by transitioning CO2 from supercritical state to gas phase during the cleaning process. The CO2 is maintained in supercritical state (above 31°C and 73 atm) for effective cleaning, then rapidly depressurized to gas phase for gentle drying that prevents damage to security features. This dynamic parameter change enables both effective contaminant removal and preservation of delicate banknote elements.
Solution Approach 2:
The patent utilizes phase transitions of CO2 as the core cleaning mechanism. CO2 transitions from supercritical fluid phase to gas phase through controlled depressurization, providing both powerful cleaning capability in supercritical state and gentle, damage-free drying in gas phase. This phase transition approach eliminates the need for harsh chemicals and mechanical abrasion that could damage security features.
2Reliability
If banknotes are replaced frequently due to soiling, then cleanliness is maintained, but replacement costs and environmental impact increase
Solution Approach 1:
The patent applies discarding and recovering by extending the service life of banknotes through effective cleaning and disinfection. Instead of discarding soiled banknotes, the supercritical CO2 cleaning process removes contaminants and pathogens, allowing banknotes to be recovered and returned to circulation. This reduces replacement costs and environmental impact associated with frequent banknote replacement.
Solution Approach 2:
The patent utilizes the self-service property of supercritical CO2, which automatically sublimates from supercritical state to gas phase upon depressurization, leaving no residual solvent on the banknotes. This self-drying mechanism eliminates the need for additional drying agents or processes that could potentially damage the banknotes, while effectively removing contaminants and pathogens.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method extends the lifespan of banknotes, reduces replacement costs, and minimizes environmental impact by allowing a significant percentage of soiled notes to be returned to circulation, potentially saving $1 billion annually and decreasing carbon footprint.
Implementation Method 1
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
Implementation Method 2
remove one or more substances from the substrate into the supercritical fluid
Implementation Method 3
incorporating a trapping material like fumed silica to prevent re-deposition
Data Source
AI summary
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.