Security Element Color-Shift Effect Liquid Crystal Layering
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Solution Overview
Problem
Current methods for producing multicolored color-shifting motifs in security elements, such as those using cholesteric liquid crystals, face challenges in achieving sharply defined and varied color-shift effects due to limitations in layer crosslinking and exposure processes, particularly in roll-to-roll production.
Innovation Solution
A method involving the application of a non-chiral liquid-crystalline material layer with incomplete crosslinking, followed by a chiral liquid-crystalline material layer, which allows for interaction and modification of color-shifting properties through solvent-based coatings, enabling the creation of security elements with multiple, sharply defined color-shift effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If cholesteric liquid crystals of different types are arranged one above the other or overlapping, then color-shifting effects can be achieved, but the motif areas with defined different color-shift effects can only be realized to a very limited extent
Solution Approach 1:
The patent divides the color-shifting motif into multiple superimposed layers, each contributing a specific color component. The first layer provides a base color-shifting effect, while the second layer adds additional color characteristics, enabling complex multicolored motifs through layered composition rather than requiring precise single-layer patterning
Solution Approach 2:
The patent uses composite liquid crystal systems combining cholesteric and nematic phases. The cholesteric liquid crystal layer provides selective wavelength reflection with circular polarization, while the nematic liquid crystal layer modifies the optical properties through its anisotropic structure, creating enhanced and varied color-shifting effects that neither material could achieve alone
2Adaptability or versatility
If local temperature effects are used to change pitch, then color-shift effects can be modified, but only comparatively blurred motif images can be generated
Solution Approach 1:
The patent replaces thermal field control with optical field control using polarized light. Instead of using temperature gradients to modify pitch (which causes diffusion and blur), the invention uses polarized light to selectively induce or modify the liquid crystal orientation in specific motif areas, achieving sharp boundaries without thermal diffusion effects
Solution Approach 2:
The patent changes the control parameter from temperature to polarized light exposure. By controlling the polarization direction and intensity of light applied during or after layer formation, the pitch and color-shifting properties can be precisely adjusted in specific areas without affecting adjacent regions, maintaining motif sharpness
3Manufacturing precision
If targeted local exposure to UV radiation is used for photoisomerization, then twister concentration can be changed, but this is difficult to achieve in roll-to-roll process
Solution Approach 1:
The patent incorporates the photoisomerizable twister and relevant components into the liquid crystal material formulation before the rolling process. The material is prepared in advance with all necessary photoreactive components, allowing subsequent processing to simply involve passing through UV irradiation zones during rolling, rather than requiring complex post-processing steps
Solution Approach 2:
The patent enables continuous photoisomerization throughout the roll-to-roll process by integrating UV irradiation zones along the production line. The liquid crystal material continuously passes through these zones, allowing progressive and controlled modification of twister concentration along the entire production run without interrupting the manufacturing process
4Adaptability or versatility
If incomplete crosslinking is used to enable layer interaction, then color-shifting properties can be modified, but the layer structure stability is reduced
Solution Approach 1:
The patent creates a dynamic system where the degree of crosslinking can be adjusted at different stages. Initially, incomplete crosslinking allows the liquid crystal layers to interact and diffuse, enabling color-shifting property modification. Subsequently, complete crosslinking locks in the desired structure. This dynamic control of crosslinking degree provides both interaction capability and final stability
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 the production of security elements with clearly defined, adjacent color-shift effects, offering greater design flexibility and edge sharpness, and can be implemented using various printing techniques, overcoming previous limitations in roll-to-roll processes.
Implementation Method 1
The first layer is only incompletely crosslinked
Implementation Method 2
a second layer of a chiral liquid-crystalline material with a color shift effect is applied to the only incompletely crosslinked first layer
Implementation Method 3
The same effect can be achieved by a subsequent local change in the twister concentration of the cholesteric material through targeted photoisomerization of a photoisomerizable twister
Data Source
Figure 1~2
Figure 3a~3d
Figure 4a~4b
AI summary
Production of a security element (A) with a color tilting motif layer involves (a) applying a first layer (22) of non-chiral liquid crystalline (LC) material to a support (20), (b) partially crosslinking the first layer, (c) applying a second layer (24) of chiral LC material, having a color tilting effect, to the first layer and (d) partially or completely crosslinking the second layer. Independent claims are included for: (1) a security element obtained by the process, comprising the first layer (22) of non-chiral LC material covered by the second layer (24) of chiral LC material having a color tilting effect; (2) security paper, for producing valuable documents or the like, provided with (A); and (3) valuble documents provided with (A).