Cholesteric Liquid Crystal Pigment Interlayer Cross-Linking
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Solution Overview
Problem
Existing cholesteric liquid crystal polymer (CLCP) multilayers used in security document printing inks face challenges in being milled into pigments without delamination, limiting their optical properties and security applications.
Innovation Solution
A multilayer structure of CLCP is developed with inter-layer cross-linking through staggered curing and joint polymerization, forming a mechanically unique solid body that can be comminuted into pigments without structural deterioration, featuring an abrupt change in cholesteric liquid crystal pitch at the interface between layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If CLCP multilayers are made with different optical properties for enhanced security applications, then the optical versatility is improved, but the mechanical stability during milling deteriorates due to layer delamination
Solution Approach 1:
The patent combines multiple CLCP layers with different optical properties into a single integrated pigment particle through interlayer crosslinking. The layers are chemically bonded together to form one mechanically stable unit that maintains its multilayer structure during milling and application, resolving the contradiction between optical versatility and mechanical stability.
Solution Approach 2:
The patent creates composite CLCP pigment particles consisting of multiple layers with different cholesteric pitches and optical characteristics. These composite structures integrate diverse optical functions (different reflection colors and angles) while maintaining mechanical integrity through crosslinking, achieving both versatility and strength.
2Strength
If CLCP layers are cross-linked to form a unique solid body for pigment production, then the mechanical stability is improved, but the manufacturing complexity increases due to staggered curing requirements
Solution Approach 1:
The patent applies preliminary partial crosslinking to the first CLCP layer before applying subsequent layers. This preliminary action creates a stable base that facilitates controlled interlayer bonding, simplifying the overall manufacturing process by establishing a progressive curing sequence rather than requiring complete process redesign.
Solution Approach 2:
The patent employs periodic or sequential curing steps where layers are applied and cured in a staged manner. The UV irradiation is applied periodically between layer applications to enable controlled interlayer crosslinking, transforming a potentially complex continuous process into manageable discrete steps that improve mechanical stability.
3Adaptability or versatility
If multiple CLCP pigment types are mixed to achieve desired optical responses, then the optical versatility is improved, but the supply chain control deteriorates due to multiple pigment sources
Solution Approach 1:
The patent segments the optical functionality into distinct layers within a single pigment particle, where each layer contributes a specific optical property (different pitches, colors, or reflection characteristics). This internal segmentation allows diverse optical responses from one unified pigment source, maintaining supply chain control while achieving versatility.
Solution Approach 2:
The patent creates universal CLCP pigment particles that integrate multiple optical functions within a single material. By incorporating multiple layers with different optical properties in one pigment, the system achieves multi-functionality, eliminating the need for multiple separate pigment types and their associated supply chains.
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 CLCP pigments with enhanced optical properties, such as high brilliance and angle-dependent color change, and precise tuning of spectral reflection profiles, suitable for advanced security and decorative applications.
Implementation Method 1
This order is at the origin of a periodic refractive index modulation throughout the liquid crystal material, which in turn results in a selective transmission/reflection of determined wavelengths of light (interference filter effect)
Implementation Method 2
The particular situation of the helical molecular arrangement in CLCPs causes the reflected light to be circularly polarized, left-handed or right-handed, depending on the sense of rotation of the molecular helices
Implementation Method 3
a periodic refractive index modulation throughout the liquid crystal material, which in turn results in a selective transmission/reflection of determined wavelengths of light (interference filter effect)
Implementation Method 4
the monomeric or oligomeric cholesteric liquid crystal material is made to contain reactive groups, such as acrylate and/or methacrylate residues, which can undergo a crosslinking reaction under the influence of UV radiation in the presence of a suitable photoinitiator
Implementation Method 5
the cholesteric liquid crystal polymer (CLCP) shows also a more or less pronounced viewing-angle dependent colour variation ('colour shift')... the reflection band of CLCP materials is relatively narrow and its angle-dependency is given by λrefl.=n*p*cos(α)
Data Source
AI summary
The invention discloses a multilayer of cholesteric liquid crystal polymer (CLCP), wherein at least two layers of CLCP differing in at least one optical property are arranged on top of each other, characterized in that said at least two layers are chemically inter-layer cross-linked through the polymer network, such as to form a mechanically unique solid body which can be comminuted to pigment without deterioration of its inner structure, and which has an abrupt change of cholesteric liquid crystal pitch at the interface between said at least two layers of cholesteric liquid crystal polymer. Corresponding pigments, coating compositions and there use in security and decorative printing and coating applications are disclosed as well.