Bifunctional Pigment Flakes for Multicolor Optical Security Elements
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Solution Overview
Problem
Conventional optical security elements using magnetizable pigment flakes exhibit limited optical effects, often resulting in single-color appearance due to steep alignment of flakes, and require complex, multi-step fabrication processes to achieve both diffraction and interference colors.
Innovation Solution
The implementation of bifunctional pigment flakes with distinct tilt angles and modulations in a binder, allowing for simultaneous exhibition of diffraction and interference colors through a single-step printing process, where one subset of flakes exhibits diffraction colors at greater than 45 degrees and another subset exhibits interference colors at less than 45 degrees, forming concentric rings or a Fresnel-like structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If magnetizable pigment flakes are steeply aligned to achieve single-color appearance, then color purity is improved, but optical effect diversity deteriorates
Solution Approach 1:
The pigment layer is divided into different regions with different flake orientations. The first region contains steeply aligned flakes for single-color appearance, while the second region contains multi-directionally oriented flakes for iridescent effects. This local differentiation allows each region to optimize for its specific optical function.
Solution Approach 2:
The optical security element is segmented into multiple functional regions: a first region with steeply aligned pigment flakes for color purity, and a second region with multi-oriented flakes for optical diversity. This segmentation resolves the contradiction by allowing both optical effects to coexist in different spatial zones.
2Adaptability or versatility
If conventional multi-step fabrication processes are used to achieve both diffraction and interference colors, then optical effect completeness is improved, but manufacturing complexity deteriorates
Solution Approach 1:
Multiple optical effects (diffraction, interference, and color purity effects) are merged into a single pigment layer structure. The pigment flakes contain both a first surface for diffraction and a second surface for interference, allowing all optical effects to be achieved in one printing step rather than through multiple sequential processes.
Solution Approach 2:
The pigment flake structure is designed to be multi-functional, with different surfaces providing different optical effects. A single pigment flake can simultaneously provide diffraction from its first surface and interference from its second surface, making the material universal for multiple optical functions.
3Adaptability or versatility
If bifunctional pigment flakes with different modulations are used, then optical effect diversity is improved, but manufacturing precision requirements deteriorate
Solution Approach 1:
The magnetic pigment flakes self-organize into different orientations when exposed to a magnetic field during printing. The flake structure with different surface modulations automatically positions itself to achieve the desired optical effects, reducing the need for precise external control during manufacturing.
Solution Approach 2:
The pigment flakes have different modulation parameters on different surfaces (first surface with higher modulation for diffraction, second surface with lower modulation for interference). This parameter differentiation is built into the flake structure itself, allowing the material to self-differentiate its optical properties without requiring external precision control during application.
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
This approach enables optical security elements to display multiple colors concurrently while maintaining high reflectance, simplifying the fabrication process and reducing costs compared to traditional methods.
Implementation Method 1
a first surface having a diffraction grating relief with a first modulation
Implementation Method 2
applying a magnetic field to the binder using one or more magnets, wherein the magnetic field orients the plurality of magnetizable bifunctional pigment flakes according to the magnetic field
Implementation Method 3
an interference color is exhibited by a second subset of the plurality of bifunctional pigment flakes that are in a second region of the optical security element
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
Optical security element printed on a substrate and including bifunctional pigment flakes in a binder. Each flake comprises a first surface having a diffraction grating relief with a first modulation m1, and a second surface having a second modulation m2 that is smaller than the first modulation. A flake 500 can comprise a multilayer optical structure 502 including a first optical stack 704a including an absorber layer 706a1, a transparent layer 708a1, an absorber layer 706a2, a transparent layer 708a2 and a reflector layer 710a; a second optical stack 704b including a reflector layer 710b, a transparent layer 708b1, an absorber layer 706b1, a transparent layer 708b2, an absorber layer 706b2; an intermediate layer 712; and a magnetizable layer 714. By increasing the thickness of the structure 502, the thickness of one or more transparent layers 708 may serve to reduce the modulation m2, as compared to the modulation m1.