Liquid-Crystal Medium for PSA Displays with Quaterphenyl Core
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Solution Overview
Problem
Current liquid crystal (LC) displays, particularly polymer sustained alignment (PSA) displays, face issues with inadequate pretilt angle stability, high rotational viscosity, and susceptibility to 'image sticking' due to residual unpolymerized reactive mesogens, leading to reduced reliability and increased production costs.
Innovation Solution
Incorporating a quaterphenyl compound and alkenyl compounds in the LC medium, which enables quick and complete UV-photopolymerization, stabilizes the pretilt angle, and reduces 'image sticking' and mura effects, while maintaining high voltage holding ratio and birefringence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional LC media are used in PSA displays, then the display can be manufactured with standard materials, but the pretilt angle stability is inadequate and image sticking occurs due to residual unpolymerized reactive mesogens
Solution Approach 1:
The patent modifies the chemical structure of the reactive mesogen by introducing a quaterphenyl group with specific substituents (R1-R6) that can be independently selected from various functional groups. This structural parameter change enables complete photopolymerization while maintaining liquid crystalline properties, thereby eliminating image sticking and stabilizing the pretilt angle.
Solution Approach 2:
The LC medium comprises a composite system containing the polymerizable compound of formula I (with quaterphenyl core), compounds of formula Q (liquid crystalline compounds), and compounds of formula AN1 (alkenyl compounds). This composite material design ensures complete polymerization, reduces residual monomers, and prevents image sticking while maintaining display performance.
2Stability of the object's composition
If the LC medium contains polymerizable compounds for PSA display, then pretilt angle can be generated, but the polymerization process is slow and incomplete leading to residual unpolymerized reactive mesogens
Solution Approach 1:
The quaterphenyl compound of formula I contains specific functional groups (P1-P4) that are highly reactive to UV light. The spacer group Sp1 and terminal groups L1-L4 are designed to optimize the polymerization kinetics. This parameter optimization enables rapid and complete polymerization, generating stable pretilt angle quickly without residual monomers.
Solution Approach 2:
The patent replaces thermal polymerization or slow chemical polymerization methods with UV-light-induced photopolymerization. The compound of formula I is specifically designed to absorb UV light and initiate rapid polymerization, substituting slow thermal processes with fast optical-induced chemical reactions, thereby improving productivity and completeness of polymerization.
3Ease of operation
If conventional LC media are used, then the display can operate with standard parameters, but the response times are long and threshold voltages are high
Solution Approach 1:
The patent modifies the LC medium composition by incorporating compounds of formula AN1 (alkenyl compounds) alongside the polymerizable quaterphenyl compound. The alkenyl groups and specific molecular structures (with parameters n=1-6, Rb1-Rb6 substituents) are designed to reduce rotational viscosity and improve response characteristics, achieving faster response times and lower threshold voltages while maintaining ease of operation.
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 proposed LC medium achieves rapid and stable pretilt angle generation, improved reliability, and reduced production time with enhanced UV absorption at longer wavelengths, resulting in shorter response times and lower threshold voltages.
Implementation Method 1
enables quick and complete UV-photopolymerization
Data Source
AI summary
The present invention relates to a liquid crystal (LC) medium comprising a polymerisable compound, to a process for its preparation, to its use for optical, electro-optical and electronic purposes, in particular in LC displays, especially in an LC display of the polymer sustained alignment (PSA) type, and to an LC display, especially a PSA display, comprising it.