Polymerizable LC Medium Alkenyl Core Tilt Angle Stability
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Solution Overview
Problem
Current liquid crystal (LC) displays, particularly those of the polymer sustained alignment (PSA) and self-aligning (SA) types, face issues such as inadequate tilt angle stability, high melting points of reactive mesogens (RMs), limited solubility, and increased viscosities leading to longer response times and reduced reliability, along with challenges like image sticking and unwanted reflectivity due to residual unpolymerized RMs and alignment layer complexities.
Innovation Solution
The development of an LC medium comprising polymerizable compounds with an aromatic mesogenic core substituted by alkenyl groups, allowing for quick and complete UV-photopolymerization at longer wavelengths without photoinitiators, which reduces tilt angle formation, enhances stability, and improves solubility, while avoiding residual RM issues and alignment layer problems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polymerisable compounds are used in PSA and SA displays, then alignment can be achieved, but tilt angle stability is inadequate and residual unpolymerised RMs cause image sticking
Solution Approach 1:
The patent modifies the molecular structure of polymerisable compounds by introducing specific aromatic mesogenic cores with substituted alkenyl groups (such as vinyl, propenyl, butenyl groups). This structural parameter change enables complete UV-photopolymerisation without residuals, eliminating image sticking while maintaining tilt angle stability. The specific substitution patterns and chain lengths are optimized to achieve both complete reaction and desired alignment properties.
Solution Approach 2:
The patent converts the potential harm of residual unpolymerised RMs (which cause image sticking) into a benefit by designing compounds that polymerise completely under UV irradiation. The specific molecular structure with aromatic cores and substituted alkenyl groups ensures high reactivity and complete conversion, transforming what would be a harmful residual into a fully polymerised network that provides stable tilt angle without image sticking.
2Reliability
If reactive mesogens with high molecular weight are used to improve alignment, then solubility decreases and viscosities increase leading to longer response times
Solution Approach 1:
The patent optimizes molecular weight parameters by using aromatic mesogenic cores with specifically substituted alkenyl groups of controlled chain lengths. This parameter optimization achieves the right balance: molecular weight is sufficient for alignment stability but not so high as to cause poor solubility or excessive viscosity. The substitution patterns are designed to maintain appropriate fluidity for fast response times while ensuring stable alignment.
Solution Approach 2:
The patent creates a composite molecular structure combining aromatic mesogenic cores with substituted alkenyl groups. This composite structure integrates the rigidity of aromatic rings (for alignment stability) with the flexibility of alkenyl chains (for solubility and fast response). The specific combination and ratio of these components achieve both stable alignment and rapid response characteristics.
3Productivity
If conventional UV-photopolymerisation is used, then polymerisation occurs, but incomplete reaction leaves residual RMs that cause image sticking
Solution Approach 1:
The patent changes the chemical reactivity parameters of the polymerisable compounds by incorporating highly reactive substituted alkenyl groups (vinyl, propenyl, butenyl) attached to aromatic mesogenic cores. These structural modifications increase UV-absorption efficiency and polymerisation reactivity, enabling complete conversion within standard UV irradiation conditions. The specific substitution patterns ensure high reaction completeness, eliminating residuals that would otherwise cause image sticking.
Solution Approach 2:
The patent converts the potential harm of incomplete polymerisation (residual RMs causing image sticking) into a benefit by designing compounds with enhanced UV-reactivity. The aromatic mesogenic cores with substituted alkenyl groups absorb UV energy more efficiently and react completely, transforming what would be a harmful incomplete reaction into a complete polymerisation that eliminates image sticking while maintaining fast polymerisation speed.
4Reliability
If alignment layers are used to achieve proper LC alignment, then device complexity increases and manufacturing becomes more difficult
Solution Approach 1:
The patent enables the liquid crystal composition to self-align without requiring separate alignment layers. The polymerisable compounds with aromatic mesogenic cores and substituted alkenyl groups inherently provide the necessary surface interactions and molecular ordering when polymerised, allowing the LC medium to self-organize into the desired alignment. This self-service capability eliminates the need for additional alignment layer components and simplifies the overall device structure.
Solution Approach 2:
The patent extracts and removes the alignment layer component from the display structure by incorporating alignment functionality directly into the liquid crystal composition itself. The specially designed polymerisable compounds perform the alignment function that would otherwise require a separate alignment layer, thereby simplifying the device by taking out the unnecessary component while maintaining alignment quality.
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 results in LC displays with improved tilt angle stability, reduced image sticking, lower viscosities, and enhanced reliability, along with faster response times and better reflectivity, addressing the limitations of existing PSA and SA displays.
Implementation Method 1
allowing for quick and complete UV-photopolymerization at longer wavelengths without photoinitiators
Data Source
AI summary
The present invention relates to a liquid-crystal (LC) medium comprising one or more polymerisable compounds and to the use of the LC medium for optical, electro-optical and electronic purposes, in particular in LC displays, especially in LC displays of the polymer sustained alignment (PS, PSA) or self-aligning (SA) type.