Stretched Polymer Optical Film Birefringence Control
Solution Overview
Problem
Existing backlight technologies face challenges in minimizing polarization effects from birefringent materials, which can lead to undesirable color artifacts and reduced brightness gain when used between reflective polarizers and liquid crystal panels, making it difficult to achieve high-performance optical films at a low cost.
Innovation Solution
The use of stretched polymer films, such as biaxially or uniaxially oriented polyethylene terephthalate (PET) films, which are laminated to reflective polarizers and exhibit refractive index symmetry points at specific angles of incidence, minimizing birefringence-induced polarization effects and providing high retardance values to reduce color fringes and maintain optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If birefringent materials are used in backlight systems, then mechanical stability is improved, but polarization effects cause color artifacts and reduced brightness gain
Solution Approach 1:
The patent changes the optical parameters of the polymer film by controlling its molecular orientation through stretching processes. By adjusting the stretching ratio and direction, the film's birefringence is minimized while maintaining mechanical stability, thereby reducing polarization effects without sacrificing structural integrity
Solution Approach 2:
The patent uses composite material structures where stretched polymer films are combined with reflective polarizers in specific configurations. This composite approach allows the system to benefit from both the mechanical stability of the polymer film and the optical performance of the polarizer, while minimizing harmful polarization effects through proper material selection and arrangement
2Ease of manufacture
If conventional polymer films are used between polarizers, then manufacturing cost is reduced, but color artifacts increase due to birefringence
Solution Approach 1:
The patent modifies the manufacturing parameters of conventional polymer films by implementing controlled stretching processes during production. This allows standard polymer materials to be transformed into low-birefringence films without requiring expensive specialty materials, thus maintaining cost-effectiveness while eliminating color artifacts
Solution Approach 2:
The patent applies preliminary stretching and orientation treatment to the polymer film during the manufacturing process, before the film is assembled into the final backlight system. This preliminary action permanently reduces the film's birefringence properties, ensuring optimal optical performance is built into the material itself rather than requiring post-processing corrections
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 implementation of stretched polymer films between polarizers in backlights minimizes polarization effects, reduces color artifacts, and enhances mechanical stability, resulting in improved brightness gain and cost-effective high-performance optical films suitable for display systems.
Implementation Method 1
minimizing polarization effects from birefringent materials
Implementation Method 2
exhibits refractive index symmetry point at an angle of incidence in air of at least about 60 degrees
Data Source
AI summary
An optical film that includes a reflective polarizer and a stretched polymer film is disclosed. The stretched polymer film is laminated to the reflective polarizer, and the stretched polymer film exhibits a refractive index symmetry point at an angle of incidence in air of at least about 60 degrees in a plane of incidence parallel to a direction of greatest stretch.