Optical Film Melt Casting for Retardation Control
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Solution Overview
Problem
Existing optical films for liquid crystal displays struggle to achieve a balance between small in-plane retardation and large thickness-direction retardation, with conventional methods failing to consistently produce films with desired optical properties, particularly in VA mode liquid crystal cells where viewing angle improvement is needed, and they also exhibit significant wavelength-dependent retardation changes.
Innovation Solution
A method for producing optical films with specific refractive index combinations using a melt-casting film formation process, involving polycarbonate and other resins, where the film is molded between elastic and non-elastic metal rollers under controlled conditions to achieve in-plane retardation of 10 nm or less and thickness-direction retardation of 40 nm or more, and a multilayer film is created using resin compositions with positive and negative intrinsic birefringence values to minimize wavelength-dependent changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If solution casting method is used to form polycarbonate film, then film transparency is improved, but in-plane retardation becomes too large and viewing angle is not improved
Solution Approach 1:
The patent changes the fundamental parameter of film formation from solution casting to melt extrusion molding. This parameter change eliminates solvent-related issues and allows precise control of in-plane retardation through processing conditions while maintaining film transparency, thereby resolving the contradiction between transparency and retardation control.
Solution Approach 2:
The patent utilizes the phase transition of polycarbonate from solid to melt state during extrusion molding, then back to solid during cooling. This phase transition enables the film to be formed without solvents, achieving both high transparency and controlled in-plane retardation through the molding process parameters.
2Manufacturing precision
If touch roller molding is used to reduce in-plane retardation, then in-plane retardation is reduced, but film appearance quality deteriorates due to lack of contact in certain areas
Solution Approach 1:
The patent replaces the mechanical touch roller molding system with a melt extrusion molding system. This substitution eliminates the contact issues inherent in roller-based methods, as the film is formed by extruding molten material directly onto a cooling surface, ensuring uniform contact and appearance quality while achieving low in-plane retardation through controlled extrusion parameters.
3Reliability
If conventional retardation films are used, then basic optical function is provided, but wavelength-dependent retardation changes are significant
Solution Approach 1:
The patent employs a composite material system consisting of polycarbonate as the base resin and a specific rubber particle dispersoid as the additive component. This composite structure enables the film to maintain consistent retardation properties across different wavelengths while preserving the basic optical function, as the rubber particles modify the birefringence characteristics of the polycarbonate matrix.
Solution Approach 2:
The patent changes the material composition parameter by incorporating rubber particles with specific properties into the polycarbonate matrix. This composition modification alters the optical parameters of the film, reducing wavelength-dependent retardation variations while maintaining the necessary optical function for liquid crystal display 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 approach allows for the cost-effective production of optical films with improved viewing angle compensation and reduced wavelength-dependent retardation changes, enhancing the performance of liquid crystal displays, particularly in thin-type display products like liquid crystal televisions.
Implementation Method 1
a method for producing the above-described optical film, comprising a step of holding and molding a molten resin as a material of the optical film between an elastic metal roller as a first cooling roller and a non-elastic metal roller as a second cooling roller
Implementation Method 2
a film with a small in-plane retardation Re and a large thickness-direction retardation Rth can be obtained
Data Source
AI summary
Provided are: an optical Elm that has a good appearance, small in-plane retardation Re, and large thickness-direction retardation Rth; and a method for producing such an optical film. Also provided is a multilayer optical film that uses the optical film, that exhibits little change in retardation as a result of wavelength, and that has small retardation at low wavelengths. The optical film is obtained by sandwiching a melted resin between a first cooling roll comprising an elastic metal roll and a second cooling roll comprising a non-elastic metal roll and molding said melted resin. The optical film has a good appearance, the absolute value of the in-plane retardation Re thereof is 10 nm or less, and the thickness-direction retardation Rth thereof is 40 nm or more.