Security Element Microcavity Structure for Banknotes
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Solution Overview
Problem
Existing security elements for valuable documents, such as banknotes and checks, face challenges in manufacturing processes for subwavelength structures with high aspect ratios, which are complex and difficult to produce, and struggle to achieve high-resolution images that can be seen in transmission without complex printing processes.
Innovation Solution
A security element with a microcavity structure on a substrate, where microcavities have a structure width of 0.5 µm to 3 µm and a structure depth that defines an aspect ratio greater than 0.3, combined with a metal-containing coating, allowing for a brightness difference of at least 10% in transmitted light, enabling the formation of high-resolution images without complex printing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If subwavelength structures with high aspect ratio are used to achieve high-resolution images in transmission, then image resolution is improved, but manufacturing complexity increases
Solution Approach 1:
The patent changes the aspect ratio parameter of the microcavity structures to a range of 0.2 to 0.5, which is lower than conventional high aspect ratio structures. This parameter modification enables the structures to achieve sufficient light absorption and image contrast while being manufacturable using standard replication processes, thus resolving the contradiction between image resolution and manufacturing complexity
Solution Approach 2:
The patent uses replication processes to copy the microcavity structure pattern from a master mold to the security element substrate. This copying approach allows high-resolution images to be produced through simple replication rather than complex direct manufacturing, reducing manufacturing process complexity while maintaining image resolution
2Adaptability or versatility
If metal-containing coating is applied to microcavity structure to enhance transmission properties, then transmission control is improved, but manufacturing complexity increases
Solution Approach 1:
The patent combines the microcavity structure formation and metal-containing coating application into an integrated manufacturing process. The metal coating is applied after microcavity formation, merging two functions (structural formation and optical property enhancement) into a sequential process that remains relatively simple, thus improving transmission control without significantly increasing manufacturing complexity
Solution Approach 2:
The metal-containing coating is applied selectively to specific areas of the security element, including the microcavity structures and smooth areas, with different coating characteristics in different regions. This local quality approach allows precise control of transmission properties in different zones while using standard coating techniques, enhancing adaptability without proportionally increasing manufacturing complexity
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 allows for high-resolution, see-through motifs with adjustable transmission properties, enhancing security and manufacturability by leveraging the interaction of aspect ratio and metal coating, providing a simple production method for finely structured images.
Implementation Method 1
Microcavity structures are also known to cause absorption of incident radiation and thereby provide a background for an image
Implementation Method 2
WO 2005/095119 A1 describes a security element in the form of a multi-layer film body which shows a viewing angle-dependent color shift effect by means of interference
Implementation Method 3
The anti-reflective surface is formed by nanostructures with a period smaller than 700 nm and a depth between 150 and 350 nm
Data Source
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Figure 7
AI summary
The invention relates to a security element for the production of valuable documents, such as banknotes, checks or the like, which has a substrate with a top surface and provides at least one image (11), wherein the image (11) is formed by a microcavity structure (4) having a plurality of adjacent microcavities (5, 6) and a smooth area (7), the microcavities (4) each having a structure width (w) of 0.5 µm to 3 µm in a spatial direction parallel to the top surface and a structure depth (t) perpendicular thereto and having an aspect ratio defined by the ratio of structure depth (t) to structure width (w), and a metal-containing coating is applied to the microcavity structure (4) and the smooth area (7), the aspect ratio of the microcavities (5, 6) is greater than 0.3 and the metal-containing coating (9) on the microcavity structure (4) is configured such thatthat the microcavity structure (4) and the smooth area (7) have a brightness difference of at least 10% when viewed in transmitted light, so that the microcavity structure (4) forms a foreground and the smooth area (7) a background of the image (11).