Photoalignment Polyimide Copolymer for Liquid Crystal Alignment

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Solution Overview

Problem

Conventional photoalignment polymers used in liquid crystal alignment layers suffer from poor structural and thermal stabilities, as well as unsatisfactory alignment properties, and have low solubility in organic solvents, making it difficult to form effective liquid crystal alignment layers with good adhesiveness to substrates.

Innovation Solution

A photoalignment polyimide copolymer is developed, comprising specific repeating units with photoreactive, long-chain hydrocarbon, and photocurable functional groups, which enhances photoreactivity, solubility, and adhesiveness, forming a stable and effective liquid crystal alignment layer when exposed to UV radiation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional photoalignment polymers (e.g., polycinnamate-based) are used, then photoalignment function is provided, but structural and thermal stabilities are poor and solubility in organic solvents is low

Engineering Contradiction:

Improvestructural and thermal stabilitiesVSAvoidsolubility in organic solvents

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent uses a composite polymer structure combining polyimide backbone (providing thermal and structural stability) with photoreactive side groups (cinnamate, coumarin, or chalcone units providing photoalignment function). This composite approach allows the material to simultaneously achieve high reliability and adequate solubility through the balanced contribution of different structural elements.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent modifies the molecular weight and compositional parameters of the photoalignment polymer to optimize both stability and solubility. By controlling the degree of polymerization and the ratio of photoreactive units, the material achieves appropriate solubility in organic solvents while maintaining structural and thermal stability through optimized polyimide backbone structure.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If conventional photoalignment polymers are used, then photoalignment function is provided, but alignment properties are unsatisfactory

Engineering Contradiction:

Improvealignment propertiesVSAvoidstructural stabilities

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent introduces photoreactive functional groups (cinnamate, coumarin, or chalcone units) at specific locations on the polymer chains to provide localized photoalignment function. These photoreactive units are strategically positioned to induce proper liquid crystal alignment while the polyimide backbone maintains overall structural stability, achieving high manufacturing precision without sacrificing reliability.

Inventive Principle:

Principle #3Local quality

3Manufacturing precision

If rubbing process is used for alignment, then liquid crystal alignment is achieved, but static electricity damages TFT and fine fibers cause defects

Engineering Contradiction:

ImprovealignmentVSAvoidstatic electricity damage and foreign substance defects

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the mechanical rubbing process with a photoalignment process using UV irradiation. Instead of mechanically rubbing the alignment layer to induce alignment, the system uses photoreactive groups that undergo photochemical reactions upon UV exposure to achieve the same alignment effect. This substitution eliminates mechanical contact, thereby preventing static electricity damage to TFTs and foreign substance contamination from rubbing cloth fibers.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 polyimide copolymer improves alignment properties, thermal and structural stabilities, and adhesiveness to substrates, enabling the formation of high-quality liquid crystal alignment layers with enhanced stability and solubility in organic solvents.

Implementation Method 1

The photoalignment polymers used in these patent and research papers are mostly polycinnamate-based polymers, including poly(vinylcinnamate) (PVCN) or poly(vinyl methoxycinnamate) (PVMC). When the polymers are subjected to photoalignment, the double bond of cinnamate under UV radiation participates in a [2+2] cycloaddition reaction to form cyclobutane

Methodology Applied

Scientific EffectPhotopolymerization: Photopolymerisation

Implementation Method 2

For the photoalignment to occur, an alignment layer including a photoalignment (photosensitive) polymer is formed on the bottom of a liquid crystal layer and exposed to linearly polarized UV radiation to cause a photoreaction. As a result, photoalignment takes place to align the main chain of the photoalignment polymer in a defined direction

Methodology Applied

Scientific EffectPhotoreaction: Photopolymerisation

Data Source

PatentUS9791745B2Photoalignment polyimide copolymer and liquid crystal alignment layer

Publication Date: 2017.10.17 LG CHEM LTD

AI summary

Disclosed therein are a photoalignment polyimide copolymer making it easier to form a liquid crystal alignment layer with excellences in alignment properties, thermal and structural stabilities, and adhesiveness to a substrate, and a liquid crystal alignment layer using the same. The photoalignment polyimide copolymer includes all the three types of repeating units each having a defined structure.