Security Element with 2D Nanostructure for Value Documents
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Solution Overview
Problem
Existing two-dimensional periodic subwavelength gratings used in security elements for documents of value are complex to produce due to the need for precise structuring on a subwavelength scale, particularly in forming metal layers and raised or lowered metallized surface elements.
Innovation Solution
A two-dimensional periodic nanostructure with base and surface elements covered by a thin metal layer, arranged alternately in a regular pattern, where a closed metal film is formed over the nanostructure, allowing for easier manufacturing and effective color filtering by reflecting incident light in the zeroth order of diffraction, creating a color effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If precise subwavelength structuring is used to form metal layers and metallized surface elements, then color filtering effectiveness is improved, but manufacturing complexity increases
Solution Approach 1:
The patent divides the manufacturing process into two distinct stages: first forming the dielectric nanostructure with raised and recessed surface elements, then applying a continuous metal layer that selectively coats only the raised surface elements. This segmentation allows the complex subwavelength structuring to be achieved through simple embossing or molding, while the metal coating process remains straightforward and industrially scalable.
Solution Approach 2:
The dielectric substrate is pre-structured with the required subwavelength periodic pattern of raised and recessed surface elements before metal deposition. This preliminary structuring enables the subsequent metal layer to automatically form the desired selective metallization pattern through conformal coating, eliminating the need for complex lithography or selective deposition processes.
2Illumination intensity
If a continuous metal film is formed over the nanostructure, then color effect is improved, but manufacturing complexity increases
Solution Approach 1:
The continuous metal layer applied over the nanostructured dielectric substrate automatically self-organizes to coat only the raised surface elements while leaving the recessed areas uncoated or partially coated. This self-service mechanism occurs naturally during the conformal deposition process, eliminating the need for complex masking or selective deposition techniques to achieve the desired color effect.
Solution Approach 2:
The patent changes the approach from selective metal deposition to continuous metal film formation. By controlling the metal layer thickness to be less than the distance between raised and recessed surface elements, the continuous film naturally creates the required optical effect through differential coating on the periodic nanostructure, simplifying the manufacturing process.
3Reliability
If complex metallization structuring is used, then security element authenticity is improved, but production cost increases
Solution Approach 1:
The patent uses simple embossing or molding techniques to replicate the subwavelength periodic nanostructure across the entire dielectric substrate. This copying approach allows mass production of identical nanostructured patterns at low cost, while the subsequent continuous metal coating further simplifies manufacturing. The combination provides reliable authenticity features without requiring expensive complex metallization structuring.
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 enables the production of security elements with pronounced color effects that can be easily manufactured and integrated into documents of value, providing non-copiable authenticity features for authenticity checks, while allowing for cost-effective large-series production without complex metallization structuring.
Implementation Method 1
reflecting incident light in the zeroth order of diffraction
Implementation Method 2
form electromagnetic resonances between the metallization in the ground plane and the surface elements for specific wavelengths
Implementation Method 3
form electromagnetic resonances between the metallization in the ground plane and the surface elements for specific wavelengths
Data Source
Figure 1~2
Figure 3A~3B
Figure 4
AI summary
The invention relates to a security element for a value document, wherein the security element (S) has: a dielectric substrate (2), in which a two-dimensionally periodic nanostructure (1) is formed, which has a multiplicity of base surface elements (9), which define a base plane (5), and surface elements (3) which are raised or lowered by contrast, wherein a distance measured perpendicularly to the base plane (5) exists between the base surface elements (9) and the surface elements (3), and connection flanks are formed between the base surface elements (9) and the surface elements (3), wherein the base surface elements (9) and the surface elements (3) are each covered by a metallic or highly refractive layer, which is thinner than the distance, and the base surface elements (9) and the surface elements (3) are arranged alternately in the nanostructure (1) in a regular pattern and in two directions running parallel to the base plane (5), with the associated period (d) of the arrangement of the surface elements (3) being between 100 nm and 450 nm, wherein the connection flanks are also covered by the layer, such that this covers the nanostructure (1) continuously.