Liquid-Crystal Media with Polymerizable Compounds for PSA Displays
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Solution Overview
Problem
Current liquid-crystal mixtures for PSA displays face challenges such as inadequate voltage holding ratio, unsatisfactory alignment stabilization, and limitations in viewing angle, contrast, and response time, particularly when exposed to UV light, which affects their performance in IPS and FFS displays.
Innovation Solution
Development of novel liquid-crystalline media comprising specific polymerizable compounds and dielectrically positive compounds with optimized dielectric anisotropy, birefringence, and low rotational viscosity, allowing for in-situ polymerization without the need for photoinitiators and enabling improved electrical properties and UV stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional liquid-crystal mixtures are used in PSA displays, then the display can be manufactured with standard materials, but the voltage holding ratio is inadequate and alignment stabilization is unsatisfactory
Solution Approach 1:
The patent modifies the chemical composition parameters of the liquid-crystal mixture by incorporating specific compounds with defined molecular structures (cyclic carbonate groups, ester groups, and nematicogenic moieties). These parameter changes in composition result in improved voltage holding ratio and alignment stabilization while maintaining compatibility with standard PSA display manufacturing processes.
2Adaptability or versatility
If standard liquid-crystal media are used, then the display structure remains simple, but viewing angle and contrast performance are limited
Solution Approach 1:
The patent achieves improved viewing angle and contrast performance by changing the optical parameters of the liquid-crystal mixture through specific compound selection. The mixture comprises compounds with particular birefringence values and molecular orientations that enhance viewing angle without requiring additional display structure elements, thus maintaining structural simplicity.
3Speed
If conventional liquid-crystal mixtures are used, then the response time is acceptable, but the rotational viscosity is too high for fast response
Solution Approach 1:
The patent reduces rotational viscosity by changing the molecular structure parameters of the liquid-crystal compounds. The specific compounds used have molecular geometries and intermolecular interaction characteristics that lower rotational viscosity, enabling faster response times while maintaining the liquid-crystalline phase and electro-optical properties necessary for display operation.
4Stability of the object's composition
If polymerisable compounds are added to the liquid-crystal mixture, then alignment stabilization is improved, but the mixture becomes more complex and requires UV photopolymerisation
Solution Approach 1:
The patent combines the functions of liquid-crystal display operation and alignment stabilization into a single integrated mixture. The polymerisable compounds are merged with the liquid-crystal components at low concentrations (0.1-5 wt%), creating a unified composition that provides both display functionality and enhanced alignment stability through in-situ polymerisation, without requiring separate stabilization layers or components.
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 new liquid-crystalline media achieve significantly faster response times, improved specific resistance, and enhanced viewing angle performance, along with reduced threshold voltages and increased voltage holding ratio, even after UV exposure, thereby addressing the limitations of previous materials.
Implementation Method 1
a small amount (for example 0.3%, typically in the range from ≥ 0.1% to ≤ 5%, preferably up to ≤ 3%) of a polymerisable compound is added to the liquid-crystalline medium and is polymerised or crosslinked in situ between the electrodes, usually by UV photopolymerisation
Implementation Method 2
the liquid-crystalline medium usually has a negative value of the dielectric (DC) anisotropy (Δε). On application of an electrical voltage to the electrodes, a realignment of the liquid-crystal molecules parallel to the electrode surfaces takes place
Implementation Method 3
OCB (optically compensated bend) displays are known which are based on a birefringence effect and have a liquid-crystal layer with a so-called 'bend' alignment
Data Source
AI summary
The present invention relates to dielectrically positive, preferably nematic, media comprising one or more polymerisable compounds of formula I in which the parameters have the meaning given in the text, to polymer-stabilised media obtained therefrom, to the use thereof in liquid-crystal displays, and to these displays, in particular PSA-IPS, PSA-FFS and PSA-positive VA displays.