Achromatic Security Element Using Laser-Engraved Microstructures
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Solution Overview
Problem
Current security features for value documents like banknotes often rely on diffractive elements that can be easily counterfeited, and there is a need for an achromatic embossed security element that is easy to detect but difficult to counterfeit without using diffractive elements.
Innovation Solution
The development of achromatic security elements created through laser engraving on a master plate with microstructures beyond the visible light wavelength range, producing a matte appearance with diffuse reflection effects, combined with a metallic layer for enhanced reflectivity, mimicking coin structures to create a unified visual appearance with banknotes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If diffractive elements with structural sizes in the range of 10-1000 nm are used, then rainbow-like color change effects are achieved, but the security feature becomes easy to counterfeit and does not provide achromatic appearance
Solution Approach 1:
The patent changes the critical parameter of structural element size from the nanometer range (10-1000 nm) to the micrometer range (1-100 μm), which is well above the wavelength of visible light. This parameter change eliminates diffraction effects while maintaining ease of detection through matte appearance and diffuse reflection, thereby achieving counterfeit resistance without sacrificing detectability
Solution Approach 2:
The patent applies different surface qualities to different regions: specularly reflecting regions with low surface roughness and diffusely reflecting regions with random surface roughness. This local differentiation creates the achromatic matte appearance in specific areas while maintaining overall detectability, resolving the contradiction between visibility and anti-counterfeiting
2Ease of manufacture
If achromatic microstructures with sizes well below the wavelength of visible light (1.5 μm) are used, then modulation of reflectivity and intensity is achieved, but the features show rainbow colors and do not provide true achromatic appearance
Solution Approach 1:
The patent inverts the size parameter relationship by using structures (1-100 μm) that are significantly larger than the wavelength of visible light, rather than smaller. This reversal eliminates the rainbow color interference while achieving true achromatic appearance through diffuse reflection, resolving the contradiction between achromatic appearance and rainbow color prevention
3Ease of manufacture
If laser engraving with microstructures beyond visible light wavelength is used, then matte appearance with diffuse reflection is achieved, but additional metallic layer is required for enhanced reflectivity
Solution Approach 1:
The patent combines the laser-engraved microstructure layer with a metallic layer to create a composite security feature. The microstructure provides the matte appearance and diffuse reflection, while the metallic layer enhances reflectivity. This merging of functions resolves the contradiction by achieving both matte appearance and sufficient reflectivity, making the additional layer worthwhile for enhanced security
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 a secure, difficult-to-counterfeit achromatic security element that matches the appearance of coins and banknotes, enhancing detection while maintaining a consistent visual theme across currency systems.
Implementation Method 1
a laser of sufficient power strikes the master plate surface, the electromagnetic radiation interacts with the master plate material and a part of the master plate at the location of beam impact is removed or altered either thermally (evaporation/melting) or non-thermally (ablation)
Implementation Method 2
Due to the non-periodicity of the surface topography, no diffractive effects can be seen. The optical appearance of this region is a matte finish
Implementation Method 3
A security element 2 with an achromatic surface relief structure 7, applied to a value document 1, wherein the surface relief structure comprises a laser modified surface
Data Source
Figure 1~3
Figure 4
AI summary
The invention relates to an achromatic security element for value documents, such as banknotes, cards, ID documents and the like comprising a thermoplastic or a radiation-curable polymer layer, characterised in that the layer is embossed with diffusely reflecting microstructures having sizes in the order of 1 - 100 µm, a method for producing such security elements, value documents comprising said security elements and a currency system comprising said security elements.