Reactive Mesogens with Methoxymethylene Substituents for PSA Displays

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Solution Overview

Problem

Current liquid-crystal display (LCD) technologies, particularly in polymer sustained alignment (PSA) mode, face issues with pretilt angle stability, image sticking, high melting points of reactive mesogens (RMs), limited solubility, and high viscosities, which affect display reliability and performance.

Innovation Solution

The use of reactive mesogens with a mesogenic core and methoxymethylene substituents, which facilitate quick and complete UV-photopolymerization, reducing pretilt angle generation time, improving stability, and enhancing solubility, thereby addressing the limitations of existing RMs in PSA displays.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional reactive mesogens are used in PSA displays, then pretilt angle can be generated, but polymerization is slow and incomplete leading to image sticking and poor reliability

Engineering Contradiction:

Improvedisplay reliabilityVSAvoidpolymerization speed

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent modifies the molecular structure of reactive mesogens by introducing specific substituents (fluorine atoms at positions 2 and 6 of the phenyl ring, and cyano groups) to change the polymerization kinetics and final conversion. These parameter changes enable complete polymerization within the UV exposure time while maintaining pretilt angle generation, thus resolving the contradiction between reliability and productivity.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite liquid crystal medium containing both conventional liquid crystal compounds and specifically designed reactive mesogens with optimized polymerization properties. This composite formulation allows the system to benefit from both the pretilt generation capability of conventional RMs and the fast, complete polymerization of the modified RM structure, eliminating image sticking while maintaining reliability.

Inventive Principle:

Principle #40Composite materials

2Reliability

If conventional reactive mesogens are used, then pretilt angle is generated, but melting points are high and solubility is limited

Engineering Contradiction:

Improvepretilt angle stabilityVSAvoidsolubility and processing

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent changes the physical parameters of the reactive mesogen by introducing fluorine substituents and cyano groups, which lower the melting point and improve solubility in the liquid crystal host mixture. This allows the RM to be processed at lower temperatures and achieve complete mixing, facilitating easier manufacture while maintaining pretilt stability.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If conventional reactive mesogens are used, then pretilt angle is generated, but viscosity is high affecting response times

Engineering Contradiction:

Improvepretilt angle maintenanceVSAvoidresponse time

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent modifies the viscosity parameter of the reactive mesogen through structural optimization with fluorine substituents and cyano groups, reducing the molecular size and intermolecular interactions. This results in lower viscosity that allows faster molecular reorientation and shorter response times while the polymerized network maintains the pretilt angle for reliability.

Inventive Principle:

Principle #35Parameter changes

4Productivity

If conventional reactive mesogens are used with UV exposure, then polymerization occurs, but image sticking and mura defects occur

Engineering Contradiction:

Improvepolymerization completionVSAvoidimage sticking and mura

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent converts the potential harm of incomplete polymerization (which causes image sticking) into a benefit by designing a RM structure that achieves complete polymerization. The specific molecular structure with fluorine and cyano groups ensures high reactivity and complete conversion, transforming the problem of residual monomers into a solution where no harmful residues remain, eliminating image sticking and mura defects.

Inventive Principle:

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

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 new RM compounds enable fast and complete polymerization, reducing image sticking and mura occurrence, improving voltage-holding ratio, and achieving lower threshold voltages, faster response times, and higher birefringence, while maintaining reliability and solubility, thus enhancing overall display performance.

Implementation Method 1

facilitate quick and complete UV-photopolymerization

Methodology Applied

Scientific EffectUV-photopolymerization: Photopolymerisation

Data Source

PatentUS11718791B2Polymerisable compounds and the use thereof in liquid-crystal displays

Publication Date: 2023.08.08 MERCK PATENT GMBH

AI summary

The present invention relates to polymerisable compounds, to processes and intermediates for the preparation thereof, 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.