Photoreactive Polymer Alignment Layer for Liquid Crystal Orientation

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Solution Overview

Problem

Conventional photoreactive polymers used in liquid crystal alignment layers have low thermal stability and poor photoreactivity, leading to instability and inefficiency in liquid crystal alignment and alignment rate, especially when requiring changes in alignment direction based on polarization direction.

Innovation Solution

A cyclic olefin compound with a photoreactive group, such as cinnamate, is used to create a photoreactive polymer with a bulky substituent, allowing for superior liquid crystal alignment and alignment rate, and the ability to change alignment direction freely with polarization direction, enabling applications in patterned retarders and stereoscopic images.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional photoreactive polymers (polycinnamate-based) are used for photo-alignment, then liquid crystal alignment can be achieved through UV radiation, but the polymer main chain has low thermal stability and poor photoreactivity

Engineering Contradiction:

Improvethermal stability of polymer main chainVSAvoidalignment rate

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent combines a thermally stable polymer backbone (polymethacrylate or polyacrylate) with photoreactive side chains (cinnamate, chalcone, or azo groups). This composite structure separates the thermal stability function (main chain) from the photoreactivity function (side chains), allowing both requirements to be satisfied simultaneously. The main chain provides thermal stability while the side chains provide high photoreactivity for fast alignment rates.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The polymer structure is divided into functionally distinct segments: a stable main chain segment and photoreactive side chain segments. This segmentation allows each part to optimize its specific function without compromising the other, resolving the contradiction between thermal stability and photoreactivity.

Inventive Principle:

Principle #1Segmentation

2Reliability

If rubbing process is used for liquid crystal alignment, then alignment can be achieved, but mechanical scratches remain on the surface and strong static electricity is generated

Engineering Contradiction:

Improvealignment qualityVSAvoidmechanical scratches and static electricity

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the mechanical rubbing process with a photochemical alignment process. UV radiation induces photoreactions in the polymer side chains, creating anisotropic structures that align liquid crystals without mechanical contact. This eliminates scratches and static electricity generation while maintaining alignment quality.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Adaptability or versatility

If conventional photoreactive polymers are used, then photo-alignment can occur, but the alignment direction cannot be easily changed depending on polarization direction

Engineering Contradiction:

Improvechange in alignment directionVSAvoidstability of alignment layer

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent uses photoreactive side chains that can dynamically reorient under different UV polarization directions. The flexible side chains can rotate and reposition themselves to create new alignment directions when exposed to differently polarized UV light, allowing the alignment layer to adapt to different orientations while maintaining structural stability through the rigid main chain.

Inventive Principle:

Principle #15Dynamics

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 photoreactive polymer exhibits enhanced photoreactivity, alignment rate, and thermal stability, allowing for efficient liquid crystal alignment and the ability to change alignment direction in response to polarization, improving the performance of liquid crystal display devices and stereoscopic imaging.

Implementation Method 1

the double bond of cinnamate exposed to UV radiation participates in a [2+2] cycloaddition reaction to form cyclobutane

Methodology Applied

Scientific EffectPhotoreaction: Photopolymerisation

Implementation Method 2

aligning the main chain of the polymer in a defined direction to form a photo-polymerized liquid crystal alignment layer with aligned liquid crystals

Methodology Applied

Scientific EffectLiquid crystal alignment: Liquid Crystals

Data Source

PatentUS9151988B2Cyclic olefin compound, photoreactive polymer, and alignment layer comprising the same

Publication Date: 2015.10.06 LG CHEM LTD

AI summary

Disclosed herein are a cyclic olefin compound, a photoreactive polymer, and an alignment layer comprising the photoreactive polymer, where the cyclic olefin compound can be used to provide the photoreactive polymer having not only excellences in liquid crystal alignment and alignment rate but also readiness for change in the alignment direction depending on the polarization direction.