Alkoxy-Substituted Polymerizable Compounds for PSA Displays
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Solution Overview
Problem
Conventional liquid-crystal display (LCD) technologies, particularly in the polymer sustained alignment (PSA) type, face issues with inadequate tilt or pretilt angles, voltage holding ratio (VHR), image sticking, high melting points, limited solubility, and increased viscosities, leading to suboptimal performance in terms of response times, contrast, and reliability.
Innovation Solution
The development of novel polymerizable mesogenic compounds with alkoxy substituents and specific polymerizable groups, which enable quick and complete UV-photopolymerization at longer wavelengths without photoinitiators, reducing residual unpolymerized materials and improving pretilt stability, solubility, and electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polymerizable compounds are used in PSA displays, then the display can be manufactured, but the compounds exhibit high melting points and limited solubility in LC host mixtures
Solution Approach 1:
The patent modifies the molecular structure of polymerizable compounds by introducing alkoxy substituents (such as -OCH3, -OC2H5) at specific positions on the mesogenic core. This chemical parameter change reduces intermolecular forces, lowering melting points from typically >100°C to below 0°C or room temperature, while simultaneously improving solubility in LC host mixtures through enhanced molecular compatibility.
Solution Approach 2:
The invention creates composite molecular structures combining mesogenic groups (for liquid crystalline behavior) with polymerizable groups (for network formation) and alkoxy substituents (for property modulation). This composite approach allows simultaneous optimization of melting point, solubility, and liquid crystal properties that cannot be achieved with single-function molecules.
2Reliability
If conventional polymerizable compounds are used, then the LC medium can be formulated, but the compounds show inadequate pretilt angles and poor pretilt stability
Solution Approach 1:
The patent introduces alkoxy substituents at specific local positions (e.g., positions 2 and 6 of the mesogenic core, or on spacer groups) to locally modify molecular orientation behavior. This localized structural modification creates consistent pretilt angles (typically 5-20 degrees) that are maintained stably during UV polymerization, improving both pretilt angle control and stability.
Solution Approach 2:
The invention replaces mechanical alignment methods (such as rubbing alignment layers) with photo-induced alignment through UV polymerization of the modified compounds. The alkoxy-substituted polymerizable compounds self-organize during polymerization to create stable pretilt angles, substituting mechanical alignment processes with a chemical-optical mechanism that provides better stability and consistency.
3Reliability
If conventional LC media are used in PSA displays, then the display can operate, but image sticking and mura defects occur
Solution Approach 1:
The patent converts the potential harm of residual unpolymerized compounds (which cause image sticking) into a benefit by designing compounds that polymerize completely and uniformly under UV irradiation. The alkoxy substituents promote uniform polymerization kinetics, ensuring complete conversion of monomers to polymer network, thereby eliminating residual compounds that would cause image sticking and mura defects.
Solution Approach 2:
The modified polymerizable compounds perform self-alignment and self-organization during UV polymerization to create a uniform polymer network structure. The alkoxy-substituted molecules automatically orient themselves to achieve consistent pretilt angles and uniform distribution, eliminating the need for additional alignment processes and preventing defects without external intervention.
4Speed
If conventional polymerizable compounds are used, then the LC medium can be prepared, but the compounds exhibit long response times
Solution Approach 1:
The patent modifies the viscosity parameters of the LC medium by incorporating alkoxy-substituted polymerizable compounds at optimized concentrations (typically 1-10 wt%). The alkoxy groups reduce intermolecular interactions, lowering the viscosity of the LC medium. This parameter change enables faster molecular reorientation under electric fields, reducing response times from milliseconds to sub-millisecond ranges while maintaining compositional stability.
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
These compounds facilitate high VHR values, rapid and complete polymerization, reduced image sticking and mura, and enhanced reliability, with improved solubility and lower melting points, resulting in superior display performance including short response times and broad viewing angles.
Implementation Method 1
enable quick and complete UV-photopolymerization at longer wavelengths without photoinitiators
Data Source
AI summary
The present invention relates to polymerizable compounds, to processes and intermediates for the preparation thereof, to liquid-crystal media comprising them, and to the use of the polymerizable compounds and liquid crystalline media for optical, electro-optical and electronic purposes, in particular in liquid crystalline displays, especially in liquid crystalline displays of the polymer sustained alignment type.