Polymerizable LC Medium for PSA Displays

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Solution Overview

Problem

Existing LC displays face issues with incomplete polymerization of reactive mesogens (RMs) leading to residual unpolymerized compounds, which cause image sticking and instability of the tilt angle, especially under voltage stress, and require longer UV wavelengths for effective polymerization without compromising reliability.

Innovation Solution

The use of an LC medium comprising two or more polymerizable compounds with specific structural formulas, including compounds of L1, L2, and M, which facilitate complete polymerization at longer UV wavelengths, reducing residual RMs, and enhancing tilt angle stability and reliability.

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 deteriorates due to reactions with polyimide alignment layers under UV light exposure

Engineering Contradiction:

Improveresponse timeVSAvoidmixture reliability

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent removes the problematic alkenyl group from the LC host mixture composition, extracting the harmful component that causes reactions with polyimide alignment layers under UV irradiation, thereby maintaining fast response times through alternative mechanisms without the reliability issues

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent converts the harmful UV light exposure that previously caused unwanted reactions into a beneficial process by using it specifically for polymerizing reactive mesogen additives, thereby achieving both fast response times and high reliability by controlling the UV process parameters and composition

Inventive Principle:

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

2Productivity

If shorter UV wavelengths (<320 nm) are used for polymerization, then polymerization efficiency is improved, but reliability deteriorates due to reactions with alignment layers

Engineering Contradiction:

Improvepolymerization efficiencyVSAvoiddisplay reliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent changes the UV wavelength parameter from shorter wavelengths (<320 nm) to longer wavelengths (≥320 nm), which shifts the polymerization process to a wavelength range that is efficient for polymerizing reactive mesogens but does not cause unwanted reactions with polyimide alignment layers, thereby achieving both productivity and reliability

Inventive Principle:

Principle #35Parameter changes

3Use of energy by moving object

If UV-LED lamps with higher wavelength emission (365 nm) are used, then energy consumption is reduced and lifetime is extended, but polymerization efficiency deteriorates

Engineering Contradiction:

Improveenergy consumptionVSAvoidpolymerization efficiency

Core Design Contradiction:

Use of energy by moving objectVSProductivity

Solution Approach 1:

The patent optimizes the UV wavelength parameter to match the emission peak of UV-LED lamps (365 nm), changing the wavelength parameter to be compatible with energy-efficient UV-LED technology while maintaining adequate polymerization efficiency through the use of reactive mesogen compounds with appropriate absorption characteristics

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses reactive mesogen compounds that can be effectively polymerized by the UV-LED wavelength (365 nm), creating a copy or alternative pathway that allows efficient polymerization at the longer UV wavelength used by energy-efficient UV-LED lamps

Inventive Principle:

Principle #26Copying

4Ease of manufacture

If residual unpolymerized RMs remain in the display, then production costs are reduced, but image sticking and tilt angle instability increase

Engineering Contradiction:

Improveproduction costVSAvoidtilt angle stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent performs a preliminary complete polymerization step during the manufacturing process, ensuring that all reactive mesogen compounds are fully polymerized before the display is put into service, thereby preventing image sticking and tilt angle instability while maintaining cost-effectiveness through efficient in-process polymerization

Inventive Principle:

Principle #10Preliminary action

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 high voltage-holding ratios, fast polymerization, and improved tilt angle stability, reducing image sticking and production costs while maintaining high solubility and UV absorption, especially at 340 to 380 nm.

Implementation Method 1

the RMs are then polymerized in situ by UV photopolymerization

Methodology Applied

Scientific EffectPhotopolymerization: Photopolymerisation

Implementation Method 2

maintaining high solubility and UV absorption, especially at 340 to 380 nm

Methodology Applied

Scientific EffectUV absorption: Absorption (EM radiation)

Data Source

PatentUS20250207031A1Liquid-crystal medium comprising polymerizable compounds

Publication Date: 2025.06.26 MERCK PATENT GMBH

AI summary

An LC medium (as a subcategory of liquid crystal material) comprising two or more polymerizable compounds, 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, an LC display of the PSA or SA mode comprising the LC medium, and a process of manufacturing the LC display using the LC medium, especially an energy-saving LC display and energy-saving LC display production process.