Liquid-Crystal Medium Polymerizable Compounds UV Stability

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Solution Overview

Problem

Existing liquid-crystal (LC) media for high-refresh-rate LCD panels, particularly in PSA and SA modes, face challenges such as reduced reliability under UV exposure, longer response times, and limitations in UV wavelength absorption, which affect polymerization efficiency and display performance.

Innovation Solution

Development of novel LC media comprising polymerizable compounds with absorption in the 340 to 400 nm UV wavelength range, specifically designed for PSA and SA displays, to enhance UV absorption, polymerization speed, and stability, while maintaining high reliability and performance across a broad temperature range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If alkenyl compounds are used to reduce response times in LC media, then response time is improved, but reliability decreases due to reaction with polyimide alignment layer under UV exposure

Engineering Contradiction:

Improveresponse timeVSAvoidreliability under UV exposure

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent removes the problematic alkenyl group from the LC medium composition. By eliminating this reactive component, the medium maintains fast response times through alternative mechanisms while avoiding UV-induced reactions with the alignment layer that would compromise reliability.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent converts the harmful UV reactivity issue into a benefit by designing a medium that is specifically optimized for longer UV wavelengths (365-405 nm). This wavelength selection enables effective polymerization of reactive mesogens while minimizing unwanted side reactions, thus transforming the UV exposure challenge into a controlled processing advantage.

Inventive Principle:

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

2Productivity

If shorter UV wavelengths are used for polymerization, then polymerization efficiency is improved, but harmful reactions with alignment layer increase

Engineering Contradiction:

Improvepolymerization efficiencyVSAvoidharmful reactions with alignment layer

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the UV wavelength parameter from traditional shorter wavelengths to longer wavelengths (365-405 nm). This parameter modification maintains adequate polymerization efficiency while significantly reducing harmful side reactions with the polyimide alignment layer, as the longer wavelengths are less energetic and less likely to cause unwanted chemical reactions.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If longer UV wavelengths are used for polymerization, then harmful reactions are reduced, but polymerization efficiency decreases

Engineering Contradiction:

Improvereliability after UV exposureVSAvoidpolymerization efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent employs a composite approach by combining reactive mesogens with specific molecular structures that have enhanced absorption at longer UV wavelengths. This composite design enables the medium to efficiently absorb 365-405 nm UV light for effective polymerization while maintaining high reliability and avoiding harmful reactions with the alignment layer.

Inventive Principle:

Principle #40Composite materials

4Speed

If alkenyl compounds are used to achieve fast response times, then response speed is improved, but UV stability deteriorates

Engineering Contradiction:

Improveresponse speedVSAvoidUV stability

Core Design Contradiction:

SpeedVSStability of the object's composition

Solution Approach 1:

The patent extracts and removes the alkenyl compound component from the LC medium formulation. This elimination resolves the fundamental conflict between fast response speed and UV stability, as the medium achieves rapid response through alternative mechanisms without the UV-reactive alkenyl groups that cause degradation.

Inventive Principle:

Principle #2Taking out (Extraction)

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 proposed LC media achieve rapid and complete polymerization at longer UV wavelengths, ensuring high tilt stability, low threshold voltage, and improved display performance, including fast response times, high contrast, and broad viewing angles, while minimizing production costs and environmental impact.

Implementation Method 1

the RMs are then polymerized in situ by UV photopolymerization

Methodology Applied

Scientific EffectPhotopolymerisation: Photopolymerisation

Implementation Method 2

polymerizable compounds having absorption in the long UV wavelength range

Methodology Applied

Scientific EffectAbsorption (EM radiation): Absorption (EM radiation)

Data Source

PatentEP4244303B1Liquid-crystal medium comprising polymerizable compounds

Publication Date: 2025.04.30 MERCK PATENT GMBH

AI summary

The present invention relates to a liquid-crystal (LC) medium comprising polymerizable compounds having absorption in the long UV wavelength range, to its use for optical, electro-optical and electronic purposes, in particular in LC displays, especially in LC displays of the PSA (polymer sustained alignment) or SA (self-aligning) mode, to an LC display of the PSA or SA mode comprising the LC medium, and to a process of manufacturing the LC display.