Liquid Crystal Security Device Using Light-Triggered Dopants
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Solution Overview
Problem
Existing optically variable devices (OVDs) face challenges in manufacturing processes due to the need for high concentrations of liquid crystal materials to achieve visually appealing multi-color effects, with current methods being complex and dose-dependent, limiting the ability to produce multiple colors in register.
Innovation Solution
The use of dopants containing trigger molecules with specific structures, such as binaphthalene derivatives, that change the natural twist of helical elements when exposed to light, allowing for the creation of multiple color effects by varying light wavelength, intensity, and exposure time, enabling the production of OVDs with multiple colors in register.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If high concentrations of liquid crystal materials are used to achieve visually appealing multi-color effects, then the color effects are improved, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent introduces dopants as intermediary substances that mediate between the liquid crystal material and the desired optical effects. These dopants contain trigger molecules that, when exposed to specific wavelengths of light, induce chiral twist in the liquid crystal molecules, enabling multi-color effects at low concentrations without complicating the manufacturing process
Solution Approach 2:
The patent utilizes parameter changes by exposing the liquid crystal-dopant composition to different wavelengths of light, which changes the chiral twist state of the liquid crystal molecules. This allows the same material to produce different color effects without changing the material concentration, thereby maintaining manufacturing simplicity while achieving diverse optical effects
2Adaptability or versatility
If existing liquid crystal materials are used to create multiple color effects, then color variety is improved, but the manufacturing process becomes dose-dependent and complex
Solution Approach 1:
The dopants serve as intermediaries that translate light wavelength information into chiral twist changes in the liquid crystal. This intermediary mechanism enables color variety through light manipulation rather than complex material processing, significantly simplifying the manufacturing process while maintaining high color variety
Solution Approach 2:
The patent replaces complex mechanical or chemical processing systems with an optical system. Instead of using complex manufacturing processes to create different colors, the invention uses different wavelengths of light to trigger different color effects in the same liquid crystal-dopant composition, substituting optical control for manufacturing complexity
3Stability of the object's composition
If conventional liquid crystal materials are used, then the base material properties are maintained, but the ability to produce multiple colors in register is limited
Solution Approach 1:
The patent creates a composite material system combining liquid crystal molecules with dopant molecules containing trigger molecules. This composite structure maintains the stable properties of the liquid crystal base material while adding the versatility to produce multiple colors in register through light-induced chiral twist changes in the dopant-liquid crystal composite
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 allows for the efficient production of OVDs with multiple color effects visible by the naked eye, achieving high-resolution images and personalized security features at low dopant concentrations, simplifying the manufacturing process and enhancing security differentiation.
Implementation Method 1
The dopant is effective to change the natural twist of the helical elements when addressed with incident light. The trigger molecules are designed such that in the photo-induced switched state (i.e., isomer) the twisting power is significantly changed.
Implementation Method 2
The color reflected back is created by a process referred to as constructive interference. The particular color is determined by the pitch of the helix and the angle of view.
Implementation Method 3
liquid crystals in a chiral nematic phase (cholesteric) form a helical structure that reflects circular polarized light over a narrow wavelength band
Implementation Method 4
The material is then polymerized/cross linked by a UV source to freeze the layer and fix the perceived color.
Data Source
AI summary
The invention generally relates to optically variable devices, methods of preparation and applications or uses therefor. In particular, the invention includes trigger molecules employed as a dopant for a liquid crystal material. The liquid crystal material contains helical elements having a natural twist. The dopant is effective to change the natural twist of the helical elements when the dopant is addressed with incident light. Suitable dopants are selected from binaphthalene and derivatives thereof.