Polymerisable Compounds for Fast UV PSA Display Alignment
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Solution Overview
Problem
Existing polymer sustained alignment (PSA) liquid crystal displays face issues such as high rotational viscosity, inadequate pretilt angle generation, image sticking, high melting points, solubility limitations, and high viscosities leading to long switching times, along with challenges in achieving high voltage holding ratio (VHR) and reliability under UV exposure.
Innovation Solution
The use of polymerisable compounds with a biphenyl or terphenyl mesogenic core substituted by methoxymethyl and fluoro groups, which facilitate rapid and complete UV-photopolymerisation, generating a stable pretilt angle, reducing image sticking and mura, and enhancing VHR, while maintaining low melting points and solubility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional polymerisable compounds are used in PSA displays, then alignment stabilization is achieved, but polymerisation speed is slow and residual monomer remains
Solution Approach 1:
The patent modifies the molecular structure of polymerisable compounds by introducing specific mesogenic groups and functional moieties that accelerate polymerisation kinetics. The compounds are designed with reactive groups that enable faster crosslinking while maintaining controlled polymerisation through parameter optimization of molecular weight and functional group density
Solution Approach 2:
The invention uses composite polymerisable compounds that combine multiple functional groups within a single molecular structure, enabling simultaneous achievement of fast polymerisation, complete reaction, and stable alignment. The composite structure integrates mesogenic cores with reactive functional groups in optimized configurations
2Reliability
If high rotational viscosity LC medium is used, then stability is improved, but switching time increases
Solution Approach 1:
The patent applies local quality modification by creating regions of different polymer concentration and crosslinking density within the LC medium. The polymer network is distributed non-uniformly to provide stability in certain regions while maintaining low viscosity and fast response in others, achieving both reliability and speed
Solution Approach 2:
The invention introduces dynamic characteristics to the polymer network structure, allowing it to adapt its rigidity and viscosity characteristics in response to applied fields. The polymer chains can reconfigure during switching operations, providing stability at rest and flexibility during operation
3Reliability
If inadequate pretilt angle is generated, then alignment is achieved, but display performance deteriorates
Solution Approach 1:
The patent implements preliminary action by incorporating pretilt-inducing functional groups in the polymerisable compounds that automatically generate the desired pretilt angle during the polymerisation process itself, before the display is fully assembled and operated. This eliminates the need for separate pretilt treatment steps
Solution Approach 2:
The invention uses the polymerisable compounds as intermediary substances that mediate between the substrate surface and the LC molecules, transferring and stabilizing the pretilt orientation. The compounds act as a bridge that establishes and maintains the optimal pretilt angle through their molecular structure and interaction with both substrate and LC molecules
4Reliability
If image sticking and mura occur, then alignment is maintained, but display quality decreases
Solution Approach 1:
The patent converts the potential harm of polymerisation-induced defects into benefit by using controlled polymerisation of specifically designed compounds that prevent image sticking and mura. The polymerisation process is harnessed to create a stable network that actually prevents the formation of these defects, turning what could be a harmful process into a protective mechanism
5Reliability
If high melting point compounds are used, then stability is improved, but solubility decreases
Solution Approach 1:
The patent applies parameter changes by carefully adjusting the molecular weight, functional group types, and structural parameters of the polymerisable compounds to achieve an optimal balance between melting point and solubility. The compounds are designed with parameters that ensure adequate solubility in the LC medium while maintaining thermal and chemical 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
The compounds enable fast polymerisation, stable pretilt angle, high VHR, reduced image sticking and mura, and improved response times, while maintaining high solubility and reliability, addressing the limitations of existing PSA displays.
Implementation Method 1
rapid and complete UV-photopolymerisation
Data Source
AI summary
The present invention relates to polymerisable compounds, to processes and intermediates for the preparation thereof, to liquid-crystal (LC) media comprising them, and to the use of the polymerisable compounds and LC media for optical, electro-optical and electronic purposes, in particular in LC displays, especially in LC displays of the polymer sustained alignment type.