Tertiary Hydroxy Polymerizable Compounds for PSA Display Alignment

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Solution Overview

Problem

Current liquid-crystal display (LCD) technologies, particularly in the polymer sustained alignment (PSA) type, face issues such as inadequate tilt or pretilt angles, low voltage holding ratio (VHR), image sticking, high melting points of polymerizable mesogenic compounds, limited solubility, and high viscosities leading to increased switching times and mura formation.

Innovation Solution

The use of novel polymerizable compounds with a mesogenic core and tertiary hydroxy substituents, which enable quick and complete UV-photopolymerization at longer wavelengths without photoinitiators, reducing pretilt angles, improving VHR, and enhancing solubility and stability, thereby addressing the limitations of existing PSA displays.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional polymerizable mesogenic compounds are used in PSA displays, then the alignment layer can be formed, but the compounds have high melting points and limited solubility

Engineering Contradiction:

Improvealignment stabilityVSAvoidmelting point

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The patent introduces tertiary hydroxy substituents at specific positions (para or meta) of the mesogenic core, which fundamentally changes the molecular packing and intermolecular interactions. This structural parameter change reduces the melting point from typically above 100°C to below 80°C, while maintaining the liquid crystalline phase and polymerization capability. The tertiary hydroxy group creates steric hindrance that prevents tight molecular packing, thereby lowering the melting point without sacrificing the essential functional properties.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If conventional polymerizable compounds are used, then polymerization can occur, but the viscosity is high leading to increased switching times

Engineering Contradiction:

Improvepolymerization completenessVSAvoidswitching time

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The introduction of tertiary hydroxy groups changes the viscosity parameter of the LC medium. The steric hindrance and reduced molecular packing efficiency lead to lower viscosity compared to conventional polymerizable mesogens. This viscosity reduction directly improves the switching speed of the display while maintaining complete polymerization capability, as the tertiary hydroxy group does not interfere with the polymerizable vinyl functionality.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If polymerizable compounds are added to LC media, then alignment can be sustained, but image sticking and mura formation occur

Engineering Contradiction:

Improvealignment sustainabilityVSAvoidimage sticking and mura

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent converts the potential harm of polymerization-induced defects into a benefit by using tertiary hydroxy groups that enable complete and uniform polymerization. The tertiary hydroxy substituent promotes homogeneous distribution and reaction kinetics, ensuring that polymerization occurs uniformly throughout the LC medium without localized aggregation or incomplete reaction. This complete polymerization prevents residual monomer-related defects like image sticking and mura, while maintaining the desired alignment sustainability.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

4Reliability

If conventional compounds are used for polymerization, then alignment can be maintained, but pretilt angles are inadequate

Engineering Contradiction:

Improvealignment maintenanceVSAvoidpretilt angle control

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent applies local quality modification by placing tertiary hydroxy groups at specific positions (para or meta) of the mesogenic core. This localized structural modification at specific molecular sites creates the desired pretilt angle during polymerization. The tertiary hydroxy group at the para position provides a specific directional influence on the polymer chain orientation, enabling precise control of the pretilt angle while maintaining overall alignment sustainability throughout the LC medium.

Inventive Principle:

Principle #3Local quality

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

These compounds facilitate rapid and complete polymerization, reducing image sticking and mura, improving reliability and VHR, and enabling shorter response times and lower threshold voltages, while maintaining high birefringence and solubility, thus enhancing the performance and production efficiency of PSA displays.

Implementation Method 1

enable quick and complete UV-photopolymerization at longer wavelengths without photoinitiators

Methodology Applied

Scientific EffectUV-photopolymerization: Photopolymerisation

Data Source

PatentUS11312909B2Polymerizable compounds and the use thereof in liquid-crystal displays

Publication Date: 2022.04.26 MERCK PATENT GMBH

AI summary

Polymerizable compounds, to processes and intermediates for the preparation thereof, liquid-crystal (LC) media comprising them, and the use of the polymerizable 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, or a stabilizers in LC media and LC displays.