FFS Liquid Crystal Display Polymer Blocking Layer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Liquid crystal displays (LCDs) with negative dielectric anisotropy in the Fringe Field Switching (FFS) mode face issues such as low reliability, high viscosity, and image sticking due to interactions between LC molecules and the polyimide alignment layer, leading to reduced voltage holding ratio (VHR) and increased sensitivity to UV exposure.
Innovation Solution
Incorporating di- or multireactive polymerizable compounds with acrylate and methacrylate groups into the LC medium, which induces planar alignment and forms a crosslinked polymer upon polymerization, creating a blocking layer that prevents ion extraction from the polyimide layer and enhances VHR, especially after UV exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If LC medium with negative dielectric anisotropy is used in FFS display, then transmission is improved and viewing angle dependence is reduced, but reliability deteriorates due to ion extraction from polyimide alignment layer
Solution Approach 1:
A polymerizable compound is introduced as an intermediary substance between the LC medium and polyimide alignment layer. This compound forms a blocking layer through polymerization that mediates the interaction between LC molecules and polyimide, preventing ion extraction while maintaining the beneficial planar alignment and transmission properties.
Solution Approach 2:
The LC medium is formulated as a composite material containing both the base LC compound and a polymerizable compound. This composite structure combines the high transmission and viewing angle properties of negative dielectric anisotropy LC media with the protective blocking layer formed by the polymerizable compound, resolving the reliability issue.
2Ease of operation
If polyimide alignment layer is used, then planar alignment is achieved, but ion extraction occurs leading to image sticking and reduced VHR
Solution Approach 1:
The polymerizable compound acts as an intermediary layer between the polyimide alignment layer and LC medium. It maintains the planar alignment function of polyimide while blocking the harmful ion extraction process, thus preserving alignment performance without the harmful side effects.
Solution Approach 2:
The polymerizable compound utilizes UV exposure, which normally causes degradation and ion extraction, and converts this harmful effect into a beneficial blocking layer formation. The UV-induced polymerization creates a protective barrier that prevents further ion extraction and improves long-term reliability.
3Reliability
If UV exposure is applied, then polymerization occurs improving VHR, but degradation reactions produce ionic impurities
Solution Approach 1:
The introduction of the polymerizable compound changes the chemical parameters of the LC medium system. This new component provides a controlled polymerization pathway that outcompetes degradation reactions, converting UV energy into beneficial crosslinking rather than harmful decomposition, thus improving VHR without significant ionic impurity formation.
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 use of di- or multireactive polymerizable compounds in the LC medium improves the reliability and VHR of FFS displays, reducing image sticking and maintaining high performance across a broad temperature range with reduced rotational viscosity and faster switching times.
Implementation Method 1
the polymerizable compounds are polymerized in the display, in particular by irradiation with UV light
Implementation Method 2
the LC medium usually has a negative value of the dielectric (DC) anisotropy
Implementation Method 3
an alignment layer provided on at least one of the substrates that is in contact with the LC medium and induces planar alignment of the LC molecules
Data Source
AI summary
The present invention relates to a liquid crystal (LC) display of the FFS type comprising a liquid crystal medium with negative dielectric anisotropy and a di- or multireactive polymerisable compound, and an alignment layer inducing planar alignment in the LC medium.