Chiral Nematic Liquid Crystal Security Element with Metal Particles
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Solution Overview
Problem
Current security measures for preventing counterfeiting and forgery are not sufficiently secure, as existing markings can be circumvented over time, necessitating the development of novel forgery-proof markers that provide enhanced security against reproduction and copying of valuable documents and products.
Innovation Solution
A security element comprising a substrate coated with a liquid crystal compound and platelet-shaped transition metal particles, which exhibits angle-dependent color change and reflective/transmissive color variations, creating a strong optical variable effect, including holograms, to enhance the security of documents and products against counterfeiting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If maximum layer thicknesses of the chiral-nematic phase are used to reflect electromagnetic radiation of long wavelength (visible light or NIR), then the reflection capability is improved, but the misorientation of the helical superstructure increases
Solution Approach 1:
The patent changes the physical-chemical parameters of the liquid crystal system by introducing a chiral dopant to transform a nematic phase into a chiral nematic (cholesteric) phase. This parameter change enables the formation of a helical superstructure with controllable pitch, allowing the system to reflect visible and NIR radiation while maintaining stable molecular orientation through proper dopant concentration control
Solution Approach 2:
The patent creates a composite liquid crystal system combining nematic liquid crystal molecules with chiral dopant molecules. This composite structure forms a chiral nematic phase where the nematic molecules provide the basic liquid crystalline order while the chiral dopant induces the helical superstructure, achieving both long-wavelength reflection and stable orientation
2Adaptability or versatility
If the temperature range of the liquid-crystalline phase is extended, then the applicability is improved, but the phase stability outside the desired application temperature may deteriorate
Solution Approach 1:
The patent adjusts the compositional parameters of the liquid crystal system by selecting specific nematic liquid crystal compounds and chiral dopants with appropriate molecular structures and interactions. This parameter optimization enables the system to maintain stable chiral nematic phase within the desired application temperature range while preventing unwanted phase transitions outside this range
3Ease of manufacture
If conventional security markings are used, then the ease of manufacture is improved, but the security against counterfeiting deteriorates
Solution Approach 1:
The patent utilizes the inherent color-changing properties of chiral nematic liquid crystals, which selectively reflect specific wavelengths of visible and NIR radiation based on their helical pitch. This optical effect creates security markings with distinctive color characteristics that are difficult to replicate, enhancing security while maintaining manufacturing simplicity through direct coating applications
Solution Approach 2:
The patent employs a composite security marking system combining chiral nematic liquid crystal coatings with conventional substrates. This composite approach integrates the advanced optical properties of liquid crystals with the manufacturing advantages of conventional materials, achieving both high security against counterfeiting and ease of manufacture through established coating techniques
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 security element provides an extremely bright and high-contrast optically variable image with a strong rainbow effect, making it difficult to replicate, thus effectively preventing counterfeiting and ensuring the authenticity of documents and products.
Implementation Method 1
selective reflection of a finite wavelength band occurs in a manner analogous to the Bragg reflection
Implementation Method 2
a coating on at least a portion of the substrate comprising at least one liquid crystal compound
Implementation Method 3
When such a nematic phase comprises chiral compounds or chiral molecular moieties, a chiral nematic or cholesteric phase can form
Implementation Method 4
The helical superstructure involves a change of refractive index from layer to layer and gives thus rise to interference effects
Implementation Method 5
a further coating on at least a portion of the coating containing the liquid crystal compound or direct on the substrate if the coating containing the liquid crystal compound is placed on the reverse side of the substrate, the further coating comprising platelet shaped transition metal particles
Data Source
AI summary
The present invention relates to complex security elements based on liquid crystal coatings which are subsequently coated with specific metallic nano-shaped metal particles, a method for their manufacture, in particular on a glass, paper or on a plastic substrate and a security product obtainable using the security element. The security element may contain additionally an embossed surface relief microstructure, especially an optically variable image (an optically variable device, OVD), such as a hologram. A further aspect of the invention is the use of such a security element for the prevention of counterfeit or reproduction of a document of value.