Cellulose Ester Optical Film for VA LCD Contrast

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Solution Overview

Problem

Current liquid crystal display devices face challenges in achieving optimal viewing angle characteristics and high front contrast due to issues with manufacturing complexity, cost, and degradation of contrast caused by forward and back scattering in phase difference films used in polarizing plates.

Innovation Solution

An optical film using a cellulose ester resin with an average degree of acetyl group substitution of 2.0 to 2.6, combined with specific compounds as plasticizers and phase difference agents, is developed to enhance birefringence expression and reduce scattering, thereby improving the viewing angle characteristics and contrast of VA-mode liquid crystal display devices.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a phase difference film is added to improve viewing angle characteristics, then viewing angle characteristics are improved, but manufacturing complexity and cost increase

Engineering Contradiction:

Improveviewing angle characteristicsVSAvoidmanufacturing complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent combines the protective film and phase difference film into a single integrated optical film made of cellulose ester resin. This merging eliminates the need for separate phase difference film layers, thereby improving viewing angle characteristics while simplifying the manufacturing process and reducing costs.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The optical film serves multiple functions simultaneously: it acts as both a protective film for the polarizing plate and a phase difference film for improving viewing angle characteristics. This multi-functionality reduces the number of components needed and simplifies the overall structure.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Manufacturing precision

If additives are added to cellulose triacetate to achieve desired phase difference value, then phase difference value is improved, but forward scattering increases and axial contrast degrades

Engineering Contradiction:

Improvephase difference valueVSAvoidforward scattering

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The patent changes the key parameter of the cellulose ester resin from using additives to achieving phase difference through controlled stretching of the resin itself. By adjusting the degree of substitution of the cellulose ester and controlling the stretching process, the desired phase difference value is achieved without adding foreign substances that cause forward scattering.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses the inherent properties of the cellulose ester resin rather than relying on additive substances. This approach eliminates the need for retardation enhancers or other additives that would increase forward scattering and degrade axial contrast.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Adaptability or versatility

If mixed fatty acid ester of cellulose is stretched to induce birefringence, then viewing angle characteristics are improved, but manufacturing cost increases due to strict control requirements

Engineering Contradiction:

Improveviewing angle characteristicsVSAvoidmanufacturing cost

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The patent optimizes the degree of substitution parameter of the cellulose ester resin to balance stretchability and birefringence expression. By selecting cellulose ester with a degree of substitution within a specific range, the resin achieves adequate stretchability without requiring extremely strict control of mixed fatty acid ester composition, thereby reducing manufacturing costs.

Inventive Principle:

Principle #35Parameter changes

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 optical film effectively reduces back scattering and maintains high front contrast, enhancing the performance of VA-mode liquid crystal display devices by optimizing the phase difference values and scattering properties, while being cost-effective and manufacturable.

Implementation Method 1

a cellulose ester film having widely been used as a protective film for polarizing plate... giving a function of the phase difference film

Methodology Applied

Scientific EffectBirefringence: Birefringence

Data Source

PatentUS9223070B2Optical film, polarizing plate equipped with the optical film, process for manufacture of the polarizing plate, and liquid crystal display device

Publication Date: 2015.12.29 KONICA MINOLTA INC

AI summary

Provided is an optical film which does not undergo the deterioration in front contrast or contrast fluctuations even when used in a VA-type liquid crystal display device having high front contrast or as a polarizing plate protection film. The optical film comprises a cellulose ester resin having high stretching adequacy and having an average acetyl group substitution degree of 2.0-2.6, has a phase difference (Ro) of 30-100 nm, a phase difference (Rth) of 70-400 nm and a film thickness of 15-50 μm, and is characterized by fulfilling a requirement represented by formula (I). Formula (I): 0.01<S(bs)/S(T)<0.30, in the formula, S(bs) represents the quantity of backscattered light at 590 nm and 25°-85° when the angle of incident light that enters the film is set at 0°, the intensity of scattered light at 590 nm and 25°-85°; and S(T) represents the total quantity of incident light that enters the film.