Security Thread Sacrificial Anode Corrosion Protection
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Solution Overview
Problem
Security threads with thin metallic layers, such as those used in banknotes, are prone to corrosion over time due to electrochemical reactions, leading to the loss of metallic properties and illegibility of indicia, even when protected by polyester foils.
Innovation Solution
Incorporating a sacrificial anode with a higher oxidation potential than the metallic layer, such as calcium, magnesium, or other metals, into the security thread to protect the metallic layer from corrosion by forming an electric/galvanic contact, which can be dispersed as pigment, applied in stripes, dots, or as a layer adjacent to the metallization, or integrated into the adhesive layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a thin metallic layer is used in security threads, then the metallic appearance and anti-counterfeiting properties are improved, but the corrosion resistance deteriorates over time
Solution Approach 1:
A sacrificial anode layer is introduced as an intermediary between the environment and the metallic layer. This sacrificial layer (made of zinc, magnesium, or aluminum) acts as a mediator that corrodes preferentially through galvanic action, protecting the underlying metallic layer from corrosion while allowing the metallic appearance to be maintained
Solution Approach 2:
The invention creates a protective copy or replica of the protective function through the sacrificial anode. Instead of making the thin metallic layer itself corrosion-resistant, a separate sacrificial layer is applied that replicates the protection function through electrochemical means, allowing the original metallic layer to maintain its appearance without direct corrosion exposure
2Strength
If the metallic layer is protected by polyester foils, then the physical protection is improved, but the electrochemical corrosion protection is insufficient
Solution Approach 1:
The invention creates a composite structure combining polyester foils for physical protection with a sacrificial anode layer for electrochemical protection. This composite approach integrates two different protection mechanisms - the polyester provides barrier protection while the sacrificial anode provides active electrochemical protection through galvanic action
Solution Approach 2:
The invention changes the electrochemical parameters of the system by introducing a sacrificial anode with different electrochemical properties (higher oxidation potential) than the metallic layer. This parameter change creates a galvanic couple where the sacrificial anode corrodes preferentially, fundamentally altering the corrosion behavior of the system
3Adaptability or versatility
If magnetic substances are applied to the security thread, then the machine readable properties are improved, but the corrosion susceptibility of the metallic layer increases
Solution Approach 1:
The sacrificial anode acts as an intermediary that absorbs the corrosive impact on the metallic layer. When magnetic substances are present and accelerate corrosion, the sacrificial anode mediates the electrochemical reaction, corroding itself while protecting the metallic layer that interacts with the magnetic substances
Solution Approach 2:
The invention converts the harmful corrosion effect into a beneficial protective mechanism. The same electrochemical reactions that would normally damage the metallic layer are harnessed through the sacrificial anode, which deliberately undergoes corrosion to protect the metallic layer, turning a harmful process into a protective one
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 sacrificial anode effectively prevents corrosion of the metallic layer, maintaining the security thread's metallic properties and legibility of indicia, especially in areas with magnetic substances, by reacting preferentially and protecting the more noble aluminum layer.
Implementation Method 1
the metallic layer is in electric/galvanic contact with at least one sacrificial element protecting the metallization or metallic print from corrosion
Implementation Method 2
the sacrificial element comprises metal with higher oxidation potential than the metal of the metallization or metallic print
Data Source
Figure 1a~1e
Figure 1f~1g
AI summary
The invention pertains to a security element such as a security thread (1) for a security document comprising at least one layer of metallization (2) or metallic print, wherein said layer (2) is electric contact with at least one sacrificial element (5) protecting the metallization (2) or metallic print from corrosion. it furthermore pertains to a method for making such a security threat, a security document comprising such a security thread, and to a method for making such a security document.