Ketyl Radical Monomer Alignment for LCD Voltage Holding
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Solution Overview
Problem
Existing liquid crystal display devices using polymer sustained alignment (PSA) layers face issues with maintaining good display quality and voltage holding ratio due to photostable monomers and residual polymerization initiators, leading to alignment defects and decreased reliability.
Innovation Solution
A liquid crystal display device is developed using a pair of substrates with a liquid crystal layer and a polymer layer formed by polymerizing at least two kinds of radical polymerizable monomers, one of which creates a ketyl radical upon light radiation, eliminating the need for additional polymerization initiators and ensuring stable alignment and high voltage holding ratio without alignment films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a monomer undergoes photo-Fries rearrangement to form a polymer layer, then the polymer layer can align liquid crystal molecules vertically without alignment films, but the monomer causes a decrease in the voltage holding ratio due to low photostability
Solution Approach 1:
The patent changes the chemical structure parameters of the monomer by introducing a carbonyl group to enable hydrogen abstraction mechanism. This structural modification allows the monomer to create radicals through hydrogen abstraction instead of photo-Fries rearrangement, maintaining photostability while achieving vertical alignment of liquid crystal molecules and preserving voltage holding ratio.
Solution Approach 2:
The patent converts the potentially harmful photo-Fries rearrangement reaction into a beneficial hydrogen abstraction mechanism. By designing the monomer with a carbonyl group, the light energy that would cause harmful rearrangement is instead utilized to create radicals through hydrogen abstraction, which then initiate polymerization and achieve alignment without damaging the voltage holding ratio.
2Reliability
If polymerization initiators are used to polymerize monomers in the liquid crystal layer, then the polymer layer can be formed to control alignment, but residual polymerization initiators in the liquid crystal layer cause a decrease in the voltage holding ratio
Solution Approach 1:
The patent extracts and eliminates the need for separate polymerization initiators by incorporating the hydrogen abstraction capability directly into the monomer structure. The carbonyl-containing monomer itself generates radicals through light-induced hydrogen abstraction, removing the source of residual contaminants that would otherwise degrade the voltage holding ratio.
Solution Approach 2:
The monomer serves its own dual function: it acts as both the polymerizable unit and the light-sensitive agent that generates radicals. The carbonyl group in the monomer structure enables self-initiation of polymerization through hydrogen abstraction upon light exposure, eliminating the need for external polymerization initiators and their harmful residuals.
3Manufacturing precision
If alignment films are used to control the alignment of liquid crystal molecules, then the initial angle can be controlled, but additional processes and equipment costs for producing a base film are required
Solution Approach 1:
The patent merges the functions of the alignment layer and the liquid crystal composition by incorporating the alignment-controlling capability into the liquid crystal material itself. The carbonyl-containing monomer forms a polymer layer in situ within the liquid crystal layer, eliminating the need for separate alignment films and their associated production processes.
Solution Approach 2:
The liquid crystal composition acquires multiple functions: it serves as the display medium, the alignment controller, and the polymer matrix former. The carbonyl-containing monomer enables the liquid crystal composition to self-organize and control molecular alignment through light-induced polymerization, replacing the need for separate alignment film 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 solution achieves stable alignment and maintains a high voltage holding ratio, reducing the likelihood of display defects and degradation from long-term light exposure, thus enhancing the reliability of the liquid crystal display device.
Implementation Method 1
at least one of the radical polymerizable monomers being a compound having a structure that creates a ketyl radical as a result of hydrogen abstraction induced by light radiation
Implementation Method 2
polymerization of at least two kinds of radical polymerizable monomers in the liquid crystal layer
Data Source
AI summary
The present invention provides a liquid crystal display device that is less prone to display defects and a decrease in the voltage holding ratio regardless of the presence or absence of an alignment film. The liquid crystal display device includes: a pair of substrates; a liquid crystal layer containing a liquid crystal material between the substrates; and a polymer layer for controlling alignment of liquid crystal molecules on a surface of at least one of the substrates, the substrates being substantially free of an alignment film in outermost surfaces thereof, the polymer layer being formed by polymerization of at least two kinds of radical polymerizable monomers in the liquid crystal layer, at least one of the radical polymerizable monomers being a compound having a structure that creates a ketyl radical as a result of hydrogen abstraction induced by light radiation.