Optically Variable Security Elements via Segmented Printing
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Solution Overview
Problem
There is a constant need for new security devices that can effectively prevent counterfeiting of valuable objects such as banknotes, passports, and certificates, as existing visual security features are difficult to replicate but can be challenging to distinguish from photocopies, especially those with static appearances.
Innovation Solution
A security device comprising a substrate with a reflective surface and a printed array of elements formed from at least two materials with different optical characteristics, where each element has a raised surface profile created by the overlapping materials, providing a variable optical appearance when viewed from different angles without requiring embossing of the substrate, allowing for complex security effects like colorshift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If embossing is used to create raised structures for optical variable effects, then the security device exhibits optically variable appearance, but the substrate flatness is altered
Solution Approach 1:
The raised structure is segmented into two separately printed materials (first and second materials) that are applied in sequence. This segmentation allows each material to contribute differently to the optical effect while maintaining the flat substrate base, resolving the contradiction between creating optical variable appearance and preserving substrate flatness.
Solution Approach 2:
The invention uses composite materials consisting of two different materials with distinct optical characteristics. The first material provides a base optical property while the second material, printed thereover in an overlapping pattern, provides a contrasting optical property. This composite approach enables optical variable appearance through material properties rather than substrate deformation.
2Reliability
If multiple printing passes are used to form overlapping materials, then complex security effects are achieved, but manufacturing complexity increases
Solution Approach 1:
The first material is printed and allowed to partially dry or set before the second material is printed thereover. This preliminary action creates a stable base layer that prevents excessive mixing while still allowing controlled overlap patterns. The staged approach simplifies the overall manufacturing process by breaking it into manageable steps with clear intermediate states.
Solution Approach 2:
The invention controls the optical characteristics by varying parameters such as material transparency, color, and thickness in each printing pass. By adjusting these parameters, complex security effects are achieved through material properties rather than complex structural arrangements, thereby simplifying the manufacturing process while maintaining high security effect 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 provides a secure, optically variable appearance that is difficult to replicate, enhancing the authenticity verification of documents by changing appearance with viewing angle, thus improving counterfeiting prevention without altering the substrate's flatness.
Implementation Method 1
each element having a raised surface profile relative to the substrate including at least first and second sides sloping from the top of the element to at least first and second respective edges of the element... the first and second sides having different orientations from one another and each lying at an acute angle to the substrate normal
Implementation Method 2
a substrate having a reflective surface; and a printed array of elements on a substantially flat area of the substrate... under illumination by light from a fixed direction away from the substrate normal, when viewed from a first viewing angle the element appears to have substantially the optical characteristics of the first material and at a second (different) viewing angle the element appears to have substantially the optical characteristics of the second material
Data Source
AI summary
A security device includes: a substrate having a reflective surface; and a printed array of elements on a substantially flat area of the substrate. Each element is formed of a first material which is at least semi-transparent and a second material, the materials having different optical characteristics. Each element has a raised surface profile relative to the substrate including at least first and second sides sloping from the top of the element to at least respective edges of the element, at which the sides meet a substantially flat base surface of the element parallel to the substrate. The sides have different orientations and each lie at an acute angle to the substrate normal. Under illumination away from the substrate normal, when viewed from first and second viewing angles the element appears to have respectively substantially the optical characteristics of the first and second materials.