Polyurethane Coated Banknote Paper Resists Soiling
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Solution Overview
Problem
Existing security papers for banknotes lack sufficient resistance to powdery dirt in dry environments and dirt in humid environments, while also being costly to manufacture, and existing solutions compromise on either performance or manufacturing cost.
Innovation Solution
A highly durable paper with a non-fluorinated external printability layer and a protective coating comprising a base layer and an external printability layer, where the external layer is free of fluorinated resins and contains polyurethane and mineral fillers or polymeric particles, applied using conventional coating methods to enhance durability and printability without increasing manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective coating is applied to improve resistance to powdery dirt and friction, then durability is improved, but manufacturing cost increases due to use of costly materials like glued films
Solution Approach 1:
The patent changes the chemical composition parameters of the protective coating by using polyurethane-based compositions with specific binder ratios (25-70 parts binder per 100 parts filler) and controlled drying conditions, achieving high durability without costly glued films. This parameter optimization allows the coating to form a flexible, adherent protective layer that resists powdery dirt and friction while maintaining manufacturing cost effectiveness.
Solution Approach 2:
The patent creates a composite protective coating system combining inorganic fillers (such as titanium dioxide, silica, or calcium carbonate) with organic polyurethane binders. This composite structure provides both the mechanical protection needed for friction and powdery dirt resistance and the adhesion to the substrate, replacing expensive glued film solutions with a cost-effective composite coating formulation.
2Reliability
If a protective coating is applied to enhance durability, then resistance to soiling is improved, but printability of the paper is impaired
Solution Approach 1:
The patent applies the protective coating selectively on specific surfaces of the substrate (front or back face) rather than uniformly coating all surfaces. This localized application ensures that the printable surface remains accessible and maintainable, while the protected surface gains enhanced soiling resistance. The coating can be applied only where durability is needed, preserving printability on other areas.
Solution Approach 2:
The patent optimizes the coating formulation parameters including using low-viscosity polyurethane compositions, controlling filler particle size and distribution, and adjusting binder-to-filler ratios to create a coating that is sufficiently protective yet maintains surface properties compatible with printing processes. The controlled drying conditions and curing parameters also help preserve printability while achieving soiling resistance.
3Ease of manufacture
If conventional coating methods are used to reduce manufacturing cost, then manufacturing cost is reduced, but resistance to powdery dirt in dry environments is insufficient
Solution Approach 1:
The patent specifically addresses powdery dirt resistance by adjusting key coating parameters: using polyurethane binders with controlled molecular weight and functionality, optimizing filler particle size distribution (particularly using fine particles less than 10 micrometers), and controlling the coating thickness and crosslinking density. These parameter changes enable conventional coating methods to achieve superior powdery dirt resistance that was previously only attainable with expensive specialized materials.
Solution Approach 2:
The patent develops a composite coating system where the interaction between polyurethane binders and inorganic fillers creates a surface morphology specifically effective against powdery dirt adhesion. The composite structure provides a balanced surface energy that prevents powdery particle attachment while maintaining cost-effectiveness through the use of conventional coating materials and processes.
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
The solution provides enhanced resistance to powdery dirt in dry environments, resistance to friction and abrasion, and resistance to dirt in humid environments, while being compatible with printing techniques used for banknotes and avoiding the use of costly glued films, thus meeting manufacturing constraints.
Implementation Method 1
the application of a liquid composition provides better resistance to soiling but does not improve the mechanical stability of the substrate
Implementation Method 2
US 2006/0127649 indicates that the application of a liquid composition provides better resistance to soiling but does not improve the mechanical stability of the substrate
Data Source
AI summary
The present invention relates to a sheet of high-durability paper, in particular for the production of bank notes, comprising: a fibrous substrate and a protective coating completely covering at least one surface of the fibrous substrate, said coating comprising at least one base layer on the side of the substrate and a polyurethane outer printable layer covering the base layer.