Stretched CBC Compensation Films for Thin Stable Displays
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Solution Overview
Problem
Existing optical compensation films, particularly those made from TAC and COP materials, suffer from instability due to high water absorption and photoelastic constants, and CBC films require complex processing to achieve sufficient retardance for thinner displays, lacking efficient methods for producing thin, high-birefringence films with simple processing.
Innovation Solution
In-plane oriented semi-crystalline CBC polymer films are prepared by hot-press molding or melt extrusion followed by uniaxial or biaxial stretching, achieving high birefringence and optical clarity with controlled refractive indices through stretching ratios of 110% to 250%, resulting in thinner films with ideal reverse dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If TAC or COP films are used for optical compensation, then suitable retardation value and optical transparency are achieved, but water absorption and photoelastic constant cause instability
Solution Approach 1:
The patent changes the material composition parameter by using cyclic block copolymers with specific molecular structures (styrene-butadiene blocks) to achieve both low water absorption and stable optical properties. The copolymer composition and molecular weight are optimized to balance retardation value with environmental stability.
Solution Approach 2:
The patent employs composite material structure by combining different polymer blocks (styrene and butadiene) in a block copolymer configuration. This composite approach allows the material to exhibit both the desired optical properties and improved stability, overcoming the limitations of single-component polymers like TAC and COP.
2Length of moving object
If CBC films are stretched to achieve sufficient retardance for thinner displays, then film thickness is reduced, but complex processing is required
Solution Approach 1:
The patent optimizes the stretching ratio parameter to achieve the desired retardation value with minimal processing complexity. By carefully controlling the stretching parameters (temperature, humidity, stretching ratio), the process is simplified while still achieving sufficient birefringence for thin display applications.
Solution Approach 2:
The patent incorporates preliminary orientation control during the film formation process itself, rather than requiring separate stretching steps. The block copolymer structure is designed to self-orient during casting, and subsequent simple stretching achieves the final optical properties without complex multi-step processing.
3Weight of moving object
If film thickness is reduced for thinner displays, then device weight and material usage decrease, but achieving sufficient retardation becomes more difficult
Solution Approach 1:
The patent changes the material parameters by using block copolymer structures with specific molecular weights and compositions that provide higher inherent birefringence. This allows thin films to achieve sufficient retardation values without increasing thickness, thereby reducing weight while maintaining optical performance.
Solution Approach 2:
The block copolymer composite structure provides enhanced optical properties per unit thickness compared to conventional polymers. The microphase separated structure of the copolymer creates regions with different refractive indices, increasing the overall birefringence and enabling thin films to achieve the required retardation for 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 method produces CBC films with enhanced optical transparency, lower thickness, and stable optical properties, achieving higher retardation values suitable for commercial optical compensation films with simplified processing.
Implementation Method 1
In-plane oriented polymer films can be prepared by polymer solution casting, melt extrusion, or molding with or without further uniaxially or biaxially stretching
Implementation Method 2
When the retardation value increases with increasing wavelength it is called 'reverse dispersion'. The dispersion curve of a compensation film may be measured by comparing of the retardation value at 550 nm with the retardation value at 450 nm and 650 nm
Implementation Method 3
TAC film has a high water absorption rate and a high photoelastic constant, making its optical properties relatively unstable
Data Source
AI summary
By stretching a semi-crystalline CBC film, an in-plane orientated compensation film could be obtained with good optical transparency and significantly higher retardation values at a much lower film thicknesses because of a relatively high amount of birefringence per unit thickness.