Fluorinated Polymerizable LC Medium for PSA Pretilt Stability
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Solution Overview
Problem
Current PSA displays face issues with inadequate pretilt angle generation, high rotational viscosity, limited solubility of polymerizable compounds, and stability of the pretilt angle under voltage stress, leading to problems like image sticking and reduced reliability.
Innovation Solution
Incorporating a liquid-crystalline host mixture with an optically active chiral dopant and polymerizable compounds that can polymerize quickly and completely, even without photoinitiators, to achieve a stable pretilt angle and improved electrical properties, reducing image sticking and mura occurrences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If polymerizable compounds are added to generate pretilt angle in PSA displays, then alignment control is improved, but the compounds show limited solubility and high rotational viscosity
Solution Approach 1:
The patent modifies the chemical structure of polymerizable compounds by introducing fluorine atoms at specific positions (using formulas I and II with defined substituents), which changes their solubility parameters and reduces rotational viscosity while maintaining pretilt generation capability. This structural parameter change allows better integration into the liquid crystal host mixture.
Solution Approach 2:
The patent creates a composite liquid crystal composition by combining the liquid crystal host with specifically designed polymerizable compounds containing fluorinated groups. This composite approach ensures compatibility and solubility while achieving the desired pretilt angle and electrical properties.
2Stability of the object's composition
If conventional polymerizable compounds are used in PSA displays, then pretilt angle is generated, but polymerization is incomplete and reliability is reduced
Solution Approach 1:
The patent employs polymerizable compounds designed for complete and rapid polymerization upon UV exposure, ensuring that the reactive components are fully consumed to form a stable polymer network. This eliminates residual monomers that would otherwise cause image sticking and reliability issues over time.
Solution Approach 2:
The patent uses highly reactive photoinitiator systems that generate strong radical species upon UV irradiation, accelerating the polymerization process to ensure complete conversion of polymerizable compounds. This rapid and complete polymerization enhances display reliability by eliminating unreacted components.
3Productivity
If liquid crystal composition is optimized for fast polymerization, then production efficiency is improved, but image sticking and mura defects occur
Solution Approach 1:
The patent converts the potential harm of rapid polymerization (which can cause defects) into a benefit by using fluorinated polymerizable compounds that polymerize quickly and completely without forming residual sticky components. The fluorine substitution ensures clean polymerization that eliminates image sticking while maintaining high productivity.
Solution Approach 2:
The patent changes the chemical parameters of the polymerizable compounds by introducing fluorine atoms at specific positions, which modifies the polymerization kinetics to achieve complete conversion without side reactions that cause mura defects. This parameter optimization allows fast polymerization without harmful effects.
4Reliability
If dielectric anisotropy is increased for better voltage holding, then electrical performance is improved, but rotational viscosity increases
Solution Approach 1:
The patent changes the molecular structure of liquid crystal compounds by introducing fluorine atoms at specific positions, which modifies the dielectric anisotropy and viscosity parameters independently. This allows optimization of voltage holding ratio while maintaining fast switching speeds through structural parameter tuning.
Solution Approach 2:
The patent applies fluorine substitution at specific local positions (using formulas I and II with defined R1, R2, Zx, L1-4, L5 parameters) rather than uniform modification throughout the molecule. This localized structural change allows precise control over dielectric and viscous properties to achieve the desired balance between voltage holding and switching speed.
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 solution enables PSA displays with enhanced transmission, high voltage-holding ratio, fast switching, and improved stability, reducing image sticking and mura while maintaining high reliability and solubility.
Implementation Method 1
Incorporating a liquid-crystalline host mixture with an optically active chiral dopant and polymerizable compounds that can polymerize quickly and completely, even without photoinitiators, to achieve a stable pretilt angle
Implementation Method 2
polymerizable compounds that can polymerize quickly and completely, even without photoinitiators
Implementation Method 3
In the switched-off state, the molecules of the LC layer are aligned perpendicular to the electrode surfaces (homeotropically) or have a tilted homeotropic alignment. On application of an electrical voltage to the two electrodes, a realignment of the LC molecules parallel to the electrode surfaces takes place.
Data Source
AI summary
The present invention relates to an LC medium comprising and a liquid-crystalline host consisting of an LC component H) comprising one or more mesogenic or liquid-crystalline compounds and an optically active component D) and optionally a polymerizable component P) comprising one or more polymerizable compounds; and to the use of the polymerizable 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.