Cellulose Ester-Ether Optical Film for VA LCD Retardation Control
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Solution Overview
Problem
Optical films used in VA type liquid crystal displays face issues with moisture permeability leading to fluctuation in retardation values, causing color unevenness, and have low tear strength, making them difficult to handle during production and application.
Innovation Solution
An optical film composed of cellulose ester and cellulose ether with specific substitution degrees and mixing ratios, along with the addition of plasticizers and hydrogen-bonded compounds, is developed to control retardation values and enhance tear strength, while being bonded to a polarizer using an active energy ray-curable adhesive.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an optical film containing cellulose ester is used to achieve the intended retardation value, then the optical performance is improved, but the tear strength is reduced making the film difficult to handle
Solution Approach 1:
The patent uses a composite material system consisting of cellulose ester (20-80 wt%) and cellulose ether (20-80 wt%) to achieve both the required optical retardation properties and improved mechanical strength. The combination of these two cellulose derivatives creates a synergistic effect where the cellulose ether compensates for the low tear strength of pure cellulose ester films while maintaining the retardation performance needed for VA liquid crystal displays.
2Manufacturing precision
If cellulose ester with high moisture permeability is used to achieve the retardation value, then the optical compensation is improved, but the retardation value fluctuates due to moisture permeation causing color unevenness
Solution Approach 1:
The composite of cellulose ester and cellulose ether creates a material with balanced moisture permeability. The cellulose ether component has different hygroscopic properties compared to cellulose ester, and their combination results in a film that maintains stable retardation values by reducing the excessive moisture absorption that causes fluctuation in pure cellulose ester films.
3Ease of manufacture
If the optical film structure is simplified for ease of manufacture, then the production process is improved, but the tear strength and handleability are reduced
Solution Approach 1:
The patent changes the chemical composition parameters by introducing cellulose ether as a second component with specific substitution degrees (0.1-2.0 for hydroxyethyl, 0.1-1.5 for hydroxypropyl). This parameter modification allows the film to maintain ease of manufacture through conventional cellulose film production techniques while significantly improving tear strength and handleability.
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 achieves stable retardation values, reduces color unevenness, and improves tear strength, ensuring reliable performance and handling in VA type liquid crystal displays.
Implementation Method 1
retardations Ro, and Rt expressed in formulae (3), and (4): Ro=(nx−ny)×d Rt={(nx+ny)/(2−nz)}×d
Implementation Method 2
bonded to a polarizer using an active energy ray-curable adhesive
Data Source
AI summary
The optical film contains cellulose ester and cellulose ether. The cellulose ester satisfies formulae 2.0≦X+Y≦3.0 and 0≦Y≦1.6. X is an acetyl group, and Y is a propionyl group and/or a butyryl group. The mass ratio of the cellulose ester to the cellulose ether is 99.0:1.0 to 55.0:45.0. Retardations Ro and Rt of the film are 20 to 130 nm and 100 to 300 nm, respectively, and expressed as Ro=(nx−ny)×d and Rt={(nx+ny)/(2−nz)}×d. nx is an in-plane refractive index of a film in a slow axis direction, ny is an in-plane refractive index of a film in a fast axis direction, nz is a refractive index of a film in a thickness direction, and d is a thickness of a film.