Photoreactive Fluorene Alignment Layer for LCD Contrast

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Solution Overview

Problem

Conventional liquid crystal display (LCD) alignment methods, such as rubbing and oblique deposition, face issues like contamination, reduced yield, increased production costs, and low contrast due to lower anchoring energy and twist angles in photoreactive alignment layers.

Innovation Solution

A photoreactive compound with a fluorene backbone is used, which undergoes photoreaction upon polarized UV irradiation to form a liquid crystal alignment layer, followed by annealing at a temperature below the glass transition temperature to achieve higher anchoring energy and twist angles, enhancing the alignment and contrast ratio.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a rubbing process is used to manufacture an alignment layer, then the alignment layer can be formed, but contamination occurs due to contact with impurities during rubbing

Engineering Contradiction:
Improvealignment layer qualityVSAvoidcontamination
Core Design Contradiction:
ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the mechanical rubbing process with a photoreaction-based alignment method. Instead of physically rubbing the polymer layer with a cloth (mechanical system), the invention uses photopolymerization induced by light irradiation to achieve molecular alignment. This substitution eliminates contact with impurities and the associated contamination problems while maintaining effective alignment layer formation.

Inventive Principle:
Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces a photopolymerizable alignment material as an intermediary substance that mediates the alignment process. This material undergoes photoreaction when exposed to light, causing the polymer backbone to arrange in a specific direction. The intermediary photopolymerizable material enables alignment without direct mechanical contact, thereby preventing contamination while achieving the desired alignment effect.

Inventive Principle:
Principle #24Intermediary (Mediator)

2Reliability

If a rubbing process is used to manufacture an alignment layer, then the alignment layer can be formed, but product yield is reduced due to occurrence of static electricity

Engineering Contradiction:
Improvealignment layer qualityVSAvoidproduct yield
Core Design Contradiction:
ReliabilityVSProductivity

Solution Approach 1:

The patent replaces the mechanical rubbing process with a photoreaction-based alignment method. Instead of physically rubbing the polymer layer with a cloth (mechanical system), the invention uses photopolymerization induced by light irradiation to achieve molecular alignment. This substitution eliminates contact with impurities and the associated contamination problems while maintaining effective alignment layer formation.

Inventive Principle:
Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces a photopolymerizable alignment material as an intermediary substance that mediates the alignment process. This material undergoes photoreaction when exposed to light, causing the polymer backbone to arrange in a specific direction. The intermediary photopolymerizable material enables alignment without direct mechanical contact, thereby preventing contamination while achieving the desired alignment effect.

Inventive Principle:
Principle #24Intermediary (Mediator)

3Reliability

If a rubbing process is used to manufacture an alignment layer, then the alignment layer can be formed, but contrast is reduced

Engineering Contradiction:
Improvealignment layer qualityVSAvoidcontrast ratio
Core Design Contradiction:
ReliabilityVSIllumination intensity

Solution Approach 1:

The patent changes the fundamental parameter of the alignment mechanism from mechanical rubbing to photoreaction. By using photopolymerizable materials that undergo chemical change upon light exposure, the invention achieves superior molecular alignment with a twist angle of 89° or greater. This parameter change from mechanical to optical-chemical alignment results in enhanced contrast ratio and display quality.

Inventive Principle:
Principle #35Parameter changes

Solution Approach 2:

The patent employs composite photopolymerizable materials containing specific functional groups (cinnamic acid, coumarin, oxa dioxin) combined with polymer backbones. These composite materials provide both the photoreactive functionality for alignment and the necessary mechanical properties for forming a stable alignment layer, achieving high contrast and display performance.

Inventive Principle:
Principle #40Composite materials

4Reliability

If oblique deposition is used to manufacture an alignment layer, then the alignment layer can be formed, but production costs increase

Engineering Contradiction:
Improvealignment layer qualityVSAvoidproduction cost
Core Design Contradiction:
ReliabilityVSEase of manufacture

Solution Approach 1:

The patent replaces the mechanical rubbing process with a photoreaction-based alignment method. Instead of physically rubbing the polymer layer with a cloth (mechanical system), the invention uses photopolymerization induced by light irradiation to achieve molecular alignment. This substitution eliminates contact with impurities and the associated contamination problems while maintaining effective alignment layer formation.

Inventive Principle:
Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces a photopolymerizable alignment material as an intermediary substance that mediates the alignment process. This material undergoes photoreaction when exposed to light, causing the polymer backbone to arrange in a specific direction. The intermediary photopolymerizable material enables alignment without direct mechanical contact, thereby preventing contamination while achieving the desired alignment effect.

Inventive Principle:
Principle #24Intermediary (Mediator)

5Reliability

If oblique deposition is used to manufacture an alignment layer, then the alignment layer can be formed, but it is difficult to form a large area

Engineering Contradiction:
Improvealignment layer qualityVSAvoidalignment layer area
Core Design Contradiction:
ReliabilityVSArea of stationary object

Solution Approach 1:

The patent replaces the mechanical rubbing process with a photoreaction-based alignment method. Instead of physically rubbing the polymer layer with a cloth (mechanical system), the invention uses photopolymerization induced by light irradiation to achieve molecular alignment. This substitution eliminates contact with impurities and the associated contamination problems while maintaining effective alignment layer formation.

Inventive Principle:
Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces a photopolymerizable alignment material as an intermediary substance that mediates the alignment process. This material undergoes photoreaction when exposed to light, causing the polymer backbone to arrange in a specific direction. The intermediary photopolymerizable material enables alignment without direct mechanical contact, thereby preventing contamination while achieving the desired alignment effect.

Inventive Principle:
Principle #24Intermediary (Mediator)

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 results in a liquid crystal alignment layer with a twist angle of 89° or greater, significantly improving the contrast ratio and enabling high-quality image display by increasing anchoring energy and molecular alignment.

Implementation Method 1

an alignment method comprising a non-rubbing process using a photopolymerizible alignment material was developed in which photopolymerization is caused by light irradiation to induce an arrangement of polymers

Methodology Applied
Scientific EffectPhotopolymerization: Photopolymerisation

Implementation Method 2

Photo-alignment refers to a mechanism in which a backbone of a polymer is arranged in a certain direction, thereby aligning liquid crystal, when a photosensitive group bonded to the polymer undergoes a photoreaction due to pre-polarized ultra violet rays

Methodology Applied
Scientific EffectPhoto-alignment: Photopolymerisation

Implementation Method 3

annealing the alignment layer at a temperature below the glass transition temperature of the alignment layer

Methodology Applied
Scientific EffectAnnealing: Annealing

Data Source

PatentUS7422778B2Photoreactive compound, liquid crystal alignment layer using the compound, method of manufacturing the alignment layer, and liquid crystal display device containing the alignment layer
Publication Date: 2008.09.09 LG CHEM LTD
  • US7422778B2 patent drawing
  • US7422778B2 patent drawing
  • US7422778B2 patent drawing

AI summary

Provided are a photoreactive compound represented by formula (1), a liquid crystal alignment layer using the compound, a method of manufacturing the alignment layer, and a liquid crystal display device including the alignment layer:where n is an integer of 20-1000;m is an integer of 1-5; andR is a hydrogen atom, CN, a C1-C5 alkyloxy group, a halogen atom, or a maleimide group.