Mixed Cellulose Esters for Low Birefringence LCD Films
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current cellulose esters used in liquid crystal display (LCD) films, such as cellulose triacetate, often have positive intrinsic birefringence, making it difficult to produce films with zero or negative intrinsic birefringence, which are necessary for optimal optical performance and light leakage correction, especially in compensator structures, and typically require costly additives or alternative materials.
Innovation Solution
Development of mixed cellulose esters with specific ratios of acetyl, propionyl, and butyryl groups, allowing for both solvent and melt casting, and incorporating plasticizers to achieve low or zero intrinsic birefringence, enabling the production of films with tailored optical retardation properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cellulose esters (CTA, CAP, CAB) are used for protective and compensator films, then the films provide good protective performance and structural rigidity, but the positive intrinsic birefringence causes light leakage along diagonals and poor contrast ratio
Solution Approach 1:
The patent changes the chemical composition parameters of cellulose esters by controlling the degree of substitution (DS) and ester composition ratios. Specifically, it uses cellulose esters with DS between 2.6-3.0 and specific acetyl/propionyl/butyryl group ratios to achieve zero or negative intrinsic birefringence, thereby eliminating light leakage while maintaining protective performance
Solution Approach 2:
The patent creates composite cellulose ester materials by combining different ester types (acetyl, propionyl, butyryl groups) in specific ratios. This composite approach allows tuning of optical properties to achieve zero or negative birefringence while preserving the mechanical and protective properties of cellulose esters
2Object-affected harmful factors
If materials with zero or negative intrinsic birefringence are used to correct light leakage, then optical performance improves, but the cost increases due to costly additives or alternative materials
Solution Approach 1:
The patent achieves zero or negative birefringence through inherent chemical composition control rather than adding costly additives. By adjusting the degree of substitution and ester group ratios in the cellulose ester itself, the desired optical properties are obtained intrinsically, avoiding additional material costs
Solution Approach 2:
The patent uses conventional, cost-effective cellulose ester base materials rather than expensive alternative materials. The solution relies on modifying common cellulose ester compositions through controlled esterification rather than switching to rare or expensive polymer systems
3Manufacturing precision
If cellulose esters are processed by solvent casting to achieve desired optical properties, then film quality is maintained, but environmental concerns arise from handling unfriendly solvents
Solution Approach 1:
The patent modifies the processing parameters by changing from solvent-based to melt-based processing. The specific cellulose ester composition (DS 2.6-3.0 with controlled ester ratios) enables melt extrusion at temperatures above the glass transition temperature, eliminating solvent use while maintaining film quality through controlled thermal processing
Solution Approach 2:
The patent replaces the chemical solvent casting process with a thermal melt extrusion process. Instead of using solvents to dissolve and cast the cellulose ester, the material is melted and extruded directly, substituting a thermal-mechanical process for a chemical process and eliminating solvent handling
4Adaptability or versatility
If cellulose esters with controllable optical retardation are used, then flexibility in creating compensator films increases, but the complexity of controlling birefringence parameters increases
Solution Approach 1:
The patent establishes specific parameter ranges for degree of substitution (2.6-3.0) and ester composition ratios that inherently provide the desired optical properties. Within these ranges, the cellulose esters naturally exhibit zero or negative birefringence with controllable retardation values, simplifying the control process while maintaining versatility
Solution Approach 2:
The patent creates a universal cellulose ester composition system that can produce multiple film types (protective films, compensator films, retardation films) with different optical properties by adjusting parameters within the established ranges. The same base material system serves multiple functions across different LCD applications
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 mixed cellulose esters provide versatility in film processing, allowing for the creation of films with zero or negative intrinsic birefringence, improving optical performance and reducing the need for additives, thereby enhancing the manufacturing efficiency and cost-effectiveness of LCD films.
Implementation Method 1
optical birefringence requirements currently often dictate that the latter be used instead
Implementation Method 2
The refractive index is typically in the range of 1.4 to 1.8 for polymers in general, and approximately 1.46 to 1.50 for cellulose esters. The higher the refractive index, the slower the speed the light wave propagates through that given material
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The present invention relates to cellulose esters having low hydroxyl content for use in optical applications, such as liquid crystal display (LCD) films. Films made with low hydroxyl levels and a given ratio of non-acetyl ester to hydroxyl level have been found to have low intrinsic birefringence. Therefore, these films can be cast, molded, or otherwise oriented without an appreciable birefringence or optical distortion (i.e. retardation). Such features make these films useful in polarizer, protective, and compensator films as well as molded optical parts, such as lenses. Furthermore, it has also been found that resins of the present invention can also be made to have "+C plate" behavior either by melt or solvent based processing, a characteristic which is not typical of cellulose esters. Such +C behavior allows films to be produced having unique compensatory behavior. Other embodiments of the invention relate to methods melt casting films while minimizing birefringence formation.