Rotogravure Printing of Cholesteric Liquid Crystal Security Features
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Solution Overview
Problem
Current methods for producing multi-colored optically variable security features using cholesteric liquid crystal polymers are complex, costly, and lack predictability and reproducibility, making it difficult to customize color and color-shifting properties for specific applications.
Innovation Solution
A process involving a rotogravure printing method using a gravure cylinder with multiple engravings to apply a single cholesteric liquid crystal precursor composition, which is then heated and cured to form a single cured ink with multiple patterns exhibiting different CIE color index parameters and selective reflection bands, allowing for easy tuning and customization of optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional methods are used to produce multi-colored optically variable security features, then color variety is achieved, but process complexity and manufacturing cost increase significantly
Solution Approach 1:
The patent combines multiple ink application functions into a single rotogravure printing process. By using a single printing plate with multiple ink reservoirs containing different cholesteric liquid crystal precursor compositions, the system merges what would traditionally require multiple printing steps or multiple plates into one integrated operation, thereby reducing process complexity while maintaining color variety
Solution Approach 2:
The rotogravure printing press is designed to perform multiple functions simultaneously - applying different precursor compositions, controlling ink layer thickness, and creating patterned deposits all through a single printing cycle. This multi-functionality eliminates the need for separate processing steps for each color layer, simplifying the overall manufacturing process
2Adaptability or versatility
If conventional methods are used to produce multi-colored optically variable security features, then color variety is achieved, but manufacturing cost increases
Solution Approach 1:
The patent combines multiple ink application functions into a single rotogravure printing process. By using a single printing plate with multiple ink reservoirs containing different cholesteric liquid crystal precursor compositions, the system merges what would traditionally require multiple printing steps or multiple plates into one integrated operation, thereby reducing process complexity while maintaining color variety
Solution Approach 2:
The system uses a single printing plate that automatically manages the distribution of different precursor compositions through its integrated ink reservoirs and transfer mechanisms. This self-service capability eliminates the need for manual intervention or coordination between multiple printing units, reducing operational complexity and manufacturing cost
3Adaptability or versatility
If chiral component concentration is adjusted to modify colorshift properties, then colorshift range is improved, but material waste and time consumption increase
Solution Approach 1:
The patent prepares multiple cholesteric liquid crystal precursor compositions in advance, each with different chiral component concentrations tailored to produce specific colorshift ranges. These pre-formulated precursors are stored in separate ink reservoirs, eliminating the need for time-consuming adjustments during the printing process and preventing material waste from failed trial formulations
Solution Approach 2:
The system achieves colorshift customization by selecting from precursors with predetermined chiral component concentrations rather than adjusting concentrations during printing. This approach allows rapid switching between different colorshift properties by simply changing the ink reservoir, avoiding the material waste and time loss associated with iterative concentration adjustments
4Adaptability or versatility
If chiral component concentration is adjusted to modify colorshift properties, then colorshift range is improved, but time consumption increases
Solution Approach 1:
The patent prepares multiple cholesteric liquid crystal precursor compositions in advance, each with different chiral component concentrations tailored to produce specific colorshift ranges. These pre-formulated precursors are stored in separate ink reservoirs, eliminating the need for time-consuming adjustments during the printing process and preventing material waste from failed trial formulations
Solution Approach 2:
The system uses a single printing plate that automatically manages the distribution of different precursor compositions through its integrated ink reservoirs and transfer mechanisms. This self-service capability eliminates the need for manual intervention or coordination between multiple printing units, reducing operational complexity and manufacturing cost
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 simplifies the production of multi-colored optically variable security features, reducing complexity and waste, while enabling precise control over color and reflection properties, enhancing security document protection against counterfeiting.
Implementation Method 1
The helical superstructure provides for a periodic refractive index modulation throughout the liquid crystal material, which in turn results in a selective transmission/reflection of determined wavelengths of light
Implementation Method 2
Cholesteric liquid crystal polymers show a molecular order in the form of a helical super-structure perpendicular to the longitudinal axes of its molecules
Implementation Method 3
applying on a substrate, by a rotogravure process with the use of a gravure cylinder having at least two, preferably at least three, different engravings, a single cholesteric liquid crystal precursor composition
Implementation Method 4
heating the applied composition to bring said composition to a cholesteric liquid crystal state
Implementation Method 5
The pitch of the material can finally be frozen by a cross-linking (polymerization) reaction, such that the color of the resulting cholesteric liquid crystal polymer is no longer depending on external factors such as the temperature
Data Source
AI summary
The present invention is related to the filed of optically variable security elements comprising a region based on a single cured ink comprising a cholesteric liquid crystal polymer, said region having at least two, preferably at least three, patterns exhibiting, at at least one viewing angle, a different CIE (1976) color index parameter and/or a different position of the selective reflection band for protecting security documents against counterfeiting and/or illegal reproduction. In particular, the present invention relates to processes for manufacturing said features, when the processes comprises the steps of a) applying on a substrate by a rotogravure process with the use of a gravure cylinder having at least two, preferably at least three, different engravings a single cholesteric liquid crystal precursor composition, b) heating the applied composition to bring said composition to a cholesteric liquid crystal state, and c) curing the composition so as to form the region based on a single cured ink comprising a cholesteric liquid crystal polymer.