Security Document Polymer Film and Wet Strength Agent Integration
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Solution Overview
Problem
Current security documents, such as banknotes, face challenges with resistance to water, dirt, and mechanical damage, including delamination issues due to ink durability and capillary penetration through unprotected edges.
Innovation Solution
A multilayer security document comprising a paper substrate with a fiber matrix and wet strength agents like polyamidoamine-epichlorohydrin resin, combined with polymer films and bulk sizing agents, which enhances internal cohesion and hydrophobic properties to prevent moisture and ink penetration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a substrate made of common plastic material is used, then the material is more easily accessible, but it does not allow the incorporation of certain security signs such as watermarks or security threads
Solution Approach 1:
The patent employs a composite structure combining polymer material with a paper substrate layer. This composite approach allows the document to maintain the accessibility and durability benefits of polymer while incorporating traditional security features like watermarks and security threads that are characteristic of paper-based substrates.
2Duration of action of stationary object
If printing is applied to a plastic substrate, then the substrate is durable, but the adhesion of the inks is reduced making it difficult to identify banknotes after long circulation
Solution Approach 1:
The patent introduces a printing primer layer as an intermediary between the plastic substrate and the ink. This primer layer improves ink adhesion to the polymer surface, ensuring that printing remains legible and reliable throughout the document's circulation life while maintaining the substrate's durability.
Solution Approach 2:
The combination of polymer substrate, printing primer, and ink layers creates a composite structure that leverages the durability of the polymer while ensuring proper ink adhesion through the primer layer, solving the adhesion problem inherent in plastic substrates.
3Strength
If polymer films are applied to protect the paper substrate, then the document gains durability, but water or dirt can penetrate through the unprotected edges of the paper by capillary action causing halos and delamination
Solution Approach 1:
The patent applies flexible polymer films to the paper substrate to create a protective barrier. These films prevent water and dirt penetration while maintaining the document's flexibility and integrity throughout circulation.
Solution Approach 2:
The patent modifies the physical and chemical parameters of the paper substrate through the application of polymer films and treatments, changing its permeability and resistance properties to prevent capillary action of water and dirt through edges while maintaining overall document flexibility.
4Strength
If wet strength agents are added to improve internal cohesion, then the paper resistance to delamination improves, but the complexity of the manufacturing process increases
Solution Approach 1:
The patent modifies the chemical composition parameters of the paper substrate by incorporating wet strength agents during the papermaking process. This changes the physical properties of the paper to improve internal cohesion and delamination resistance while integrating the treatment into the existing manufacturing workflow.
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 significantly improves the document's resistance to water, dirt, and mechanical damage, reducing delamination risks and maintaining integrity both in wet and dry conditions.
Implementation Method 1
Thanks to the high level of wet strength agent present in the substrate, the paper has improved internal cohesion, both in wet and dry conditions
Implementation Method 2
The bulk sizing agent gives the fibers hydrophobic properties throughout the volume of the sheet of paper. The mass bonding agent thus makes it possible to limit the penetration of humidity, water or fouling liquids into the interior of the paper through the edges of the document
Data Source
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Figure 6~7
AI summary
The invention relates to a security document, such as a bank note (17), comprising: a substrate comprising a sheet of paper (6) having a first face (7) and a second face (8); a first film (14) consisting of a polymer material extending over the first face (7); and a second film (15) consisting of a polymer material extending over the second face (8); wherein the sheet of paper (6) comprises a fibre matrix (5) and at least one wet-strength agent, the wet-strength agent being preferably selected from the group consisting of a polyamidoamine-epychlorohydrin (PAE) resin, a urea-formaldehyde (UF) resin, a formaldehyde resin and one of the derivatives thereof, with an agent dry weight/fibre dry weight ratio higher than or equal to 2.3%.