Non-Aromatic Polymerizable Compounds for PSA Liquid-Crystal Displays

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Current liquid-crystal display (LCD) technologies, particularly in polymer sustained alignment (PSA) mode, face issues with inadequate tilt generation, high rotational viscosity, low voltage-holding ratio (VHR), and susceptibility to 'image sticking' due to residual unpolymerized reactive mesogens (RMs), which affect display reliability and performance.

Innovation Solution

A mixture comprising a non-aromatic polymerizable compound and a UV-A sensitive polymerizable photoinitiator is used in the LC medium, allowing for complete and controlled polymerization of RMs, reducing residual amounts, and enhancing VHR and tilt stability without the need for a second UV exposure step.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional polymerisable compounds are used in PSA displays, then tilt generation is achieved, but residual unpolymerized RMs cause image sticking and reduce reliability

Engineering Contradiction:

Improvedisplay reliabilityVSAvoidimage sticking

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent changes the chemical structure parameters of the polymerisable compound by using non-aromatic cores (cyclic, alicyclic, or saturated rings) instead of conventional aromatic cores. This structural parameter change modifies the polymerization kinetics and completeness, ensuring full polymerization without residual RMs that cause image sticking, thereby improving display reliability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite LC medium system combining non-aromatic polymerisable compounds with specific liquid crystal host materials. This composite formulation optimizes the interaction between polymerisable and liquid crystal components, achieving complete polymerization while maintaining LC properties and eliminating harmful residual substances

Inventive Principle:

Principle #40Composite materials

2Productivity

If aromatic polymerisable compounds are used, then polymerization occurs, but rotational viscosity increases and viewing angle is limited

Engineering Contradiction:

Improvepolymerization rateVSAvoidrotational viscosity

Core Design Contradiction:

ProductivityVSTemperature

Solution Approach 1:

The patent changes the molecular structure parameters by substituting aromatic rings with non-aromatic cyclic, alicyclic, or saturated ring structures. This structural modification reduces molecular rigidity and rotational viscosity, enabling faster molecular reorientation and broader viewing angles while maintaining polymerization functionality

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent inverts the conventional approach by using non-aromatic instead of aromatic polymerisable compounds. This inversion of the traditional chemical structure leads to reduced rotational viscosity and improved viewing angle characteristics while still achieving the necessary polymerization for PSA display operation

Inventive Principle:

Principle #13The other way round (Inversion)

3Productivity

If UV-A exposure is applied for polymerization, then RMs polymerize, but incomplete polymerization leaves residual compounds affecting display performance

Engineering Contradiction:

Improvepolymerization completenessVSAvoidVHR

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent changes the photopolymerization parameters by selecting non-aromatic polymerisable compounds with optimized UV-A absorption characteristics and reaction kinetics. This parameter optimization ensures complete polymerization within standard UV-A exposure times, eliminating residual compounds that would otherwise reduce voltage-holding ratio and display reliability

Inventive Principle:

Principle #35Parameter changes

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 enables high VHR, rapid and complete polymerization, improved solubility, and reduced 'image sticking', leading to enhanced display reliability and performance with a broader viewing angle and shorter response times.

Implementation Method 1

A mixture comprising a non-aromatic polymerizable compound and a UV-A sensitive polymerizable photoinitiator is used in the LC medium, allowing for complete and controlled polymerization of RMs

Methodology Applied

Scientific EffectPhotopolymerisation: Photopolymerisation

Data Source

PatentUS11299676B2Polymerisable compounds and the use thereof in liquid-crystal displays

Publication Date: 2022.04.12 MERCK PATENT GMBH

AI summary

The present invention relates to a mixture comprising a not fully aromatic polymerisable compound and a polymerisable photoinitiator, to liquid-crystal (LC) media comprising them, and to the use of the polymerisable 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.