Liquid Crystal Display Polymerization Control for Uniform Pretilt Angles

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Solution Overview

Problem

Liquid crystal display devices suffer from display irregularities due to impurities being incorporated into the polymer layer during polymerization, leading to uneven pretilt angles and reduced brightness.

Innovation Solution

Incorporating a free radical scavenger, such as a phenolic antioxidant, into the liquid crystal composition, and controlling polymerization conditions like voltage application, ultraviolet intensity, and heat treatment to prevent impurity incorporation and ensure uniform alignment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If polymerizable material is polymerized by applying light or heat with voltage applied to the liquid crystal, then the liquid crystal molecules are endowed with a pretilt angle, but display irregularities occur due to impurity incorporation

Engineering Contradiction:

Improvepretilt angle uniformityVSAvoiddisplay irregularities

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary action by adding a free radical scavenger to the liquid crystal composition before polymerization. This scavenger pre-neutralizes impurities and prevents their incorporation into the polymer layer during subsequent polymerization, thereby eliminating display irregularities while maintaining uniform pretilt angles.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent converts the harmful effect of impurities into a beneficial outcome by using the polymerization process to incorporate impurities into the polymer layer, where they are trapped and no longer cause display irregularities. The free radical scavenger facilitates this by ensuring impurities are bound within the polymer structure rather than remaining as separate contaminants.

Inventive Principle:

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

2Illumination intensity

If the numerical aperture of the liquid crystal panel is increased to improve brightness, then brightness is improved, but control of liquid crystal alignment becomes more critical and difficult

Engineering Contradiction:

ImprovebrightnessVSAvoidalignment control complexity

Core Design Contradiction:

Illumination intensityVSDevice complexity

Solution Approach 1:

The patent applies parameter changes by modifying the polymerization conditions, specifically controlling the light intensity and exposure time. By using lower light intensity and shorter exposure times, the patent achieves sufficient polymerization for alignment control while reducing the formation of display irregularities, thus enabling higher numerical aperture designs with improved brightness.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If cross-linking polymerization is used to create the cured resin, then the polymerization efficiency is improved, but display irregularities occur due to impurity incorporation

Engineering Contradiction:

Improvepolymerization efficiencyVSAvoiddisplay irregularities

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a free radical scavenger as an intermediary substance that mediates between the polymerization process and impurities. The scavenger preferentially reacts with impurities and free radicals, preventing them from being incorporated into the polymer layer while allowing the polymerization to proceed efficiently. This intermediary action maintains high polymerization efficiency while eliminating display irregularities.

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 proposed method effectively eliminates display irregularities by neutralizing impurities and ensuring uniform pretilt angles, resulting in improved brightness and reduced occurrence of display irregularities.

Implementation Method 1

the polymerizable material is polymerized by applying light (usually: ultraviolet) radiation

Methodology Applied

Scientific EffectPhotopolymerization: Photopolymerisation

Implementation Method 2

the liquid crystal composition comprises a free radical scavenger at a concentration of 1 ppm by weight or greater

Methodology Applied

Scientific EffectFree radical scavenging: Absorption (physical)

Implementation Method 3

the polymerizable material can be polymerized by light, heat, or a combination thereof

Methodology Applied

Scientific EffectThermal processing: Heating

Data Source

PatentUS7537811B2Liquid crystal display device and manufacturing method therefor

Publication Date: 2009.05.26 AU OPTRONICS CORP

AI summary

A liquid crystal display device is manufactured by placing a liquid crystal composition in the gap between two parallel substrates followed by polymerization to form a liquid crystal layer, wherein the liquid crystal composition comprises a free radical scavenger, no voltage is applied between the electrodes at an initial polymerization period, ultraviolet rays are irradiated at an intensity of 1 mW/cm2 or less at an initial polymerization period, the liquid crystal composition is subjected, prior to the polymerization, to heat treatment at a temperature equal to or above the phase transition temperature of the used liquid crystal, or the liquid crystal composition is supplied dropwise onto a substrate and the substrates are bonded together in vacuum to place the liquid crystal composition into the gap between the substrates. A liquid crystal display device with no or little occurrence of display irregularities is provided.