Polymerizable Compounds for PSA Liquid Crystal Displays
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Solution Overview
Problem
Current liquid crystal displays, particularly PSA displays, face challenges such as inadequate tilt angles, high rotational viscosity, insufficient Voltage Holding Ratio (VHR), and issues like 'image sticking' due to residual unpolymerized reactive mesogens (RMs), which affect contrast, luminance, and switching times.
Innovation Solution
The use of specific polymerizable compounds with enhanced polymerization rates and mesogenic groups, allowing for quick and complete polymerization within the liquid crystal medium, reducing residual RMs and improving electro-optical properties, including higher VHR and lower pretilt angles, is introduced.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional polymerizable compounds are used in PSA displays, then polymerization can occur, but the polymerization rate is insufficient leading to residual unpolymerized RMs and image sticking
Solution Approach 1:
The patent modifies the chemical structure of polymerizable compounds by introducing specific mesogenic groups and adjusting molecular parameters to achieve faster polymerization rates. The compounds of formula (I) contain polymerizable groups (acrylate, methacrylate, vinyl) combined with mesogenic groups that enable rapid polymerization under UV irradiation, completely eliminating residual RMs and preventing image sticking while maintaining display reliability.
2Reliability
If polymerization is performed to improve VHR and reduce pretilt angle, then electro-optical properties improve, but production time increases
Solution Approach 1:
The patent designs polymerizable compounds with pre-configured mesogenic groups and polymerizable functional groups that enable immediate and complete polymerization upon UV irradiation. The molecular structure is optimized so that the polymerization reaction achieves maximum VHR improvement and pretilt angle control in a single, rapid step, eliminating the need for prolonged or multi-stage polymerization processes.
3Productivity
If residual RMs remain after polymerization, then polymerization was incomplete, but contrast and luminance are affected
Solution Approach 1:
The patent converts the potential harm of residual RMs (which cause image sticking and affect luminance) into a benefit by designing compounds that polymerize completely and rapidly. The mesogenic groups in the polymerizable compounds ensure that the polymerization reaction proceeds to completion under standard UV irradiation conditions, eliminating any residual RMs that could negatively affect display performance, while the polymerized structure enhances contrast and luminance.
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
This approach significantly shortens production times, enhances display performance by reducing 'image sticking,' improving contrast, luminance, and switching times, while maintaining high resistivity and stability across a wide temperature range.
Implementation Method 1
The polymerizable compounds according to the invention can be polymerized, in particular by photopolymerization, preferably by UV irradiation
Implementation Method 2
the FK medium typically has a negative value of dielectric (DK) anisotropy. When switched off, the molecules of the FK layer are oriented perpendicular to the electrode surfaces (homeotropic) or tilted homeotropically. When an electrical voltage is applied to the two electrodes, the FK molecules are reoriented parallel to the electrode surfaces.
Implementation Method 3
OCB displays typically contain one or more birefringent optical retardation films to avoid unwanted light transmission of the 'bend' cell in the dark state
Data Source
AI summary
The invention relates to polymerizible compounds, methods and intermediate products for the production thereof, and use thereof for optical, electro-optical and electronic purposes, in particular in liquid crystal (LC) mediums and LC displays, above all in PS and/or PSA type LC displays.