Optical Stack Reflective Polarizer Micro-Wrinkling
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Solution Overview
Problem
Existing optical stacks with absorbing polarizers and conventional reflective polarizers suffer from micro-wrinkling issues, particularly when exposed to elevated temperatures, leading to corrugation and buckling in the film layers.
Innovation Solution
The optical stack includes a linear absorbing polarizer bonded with a reflective polarizer that has a plurality of alternating polymeric layers with a higher glass transition temperature for the low index layers, and an adhesive with a low storage modulus and high tan δ to reduce micro-wrinkling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional reflective polarizers are used in optical stacks, then basic optical functionality is achieved, but micro-wrinkling and corrugation occur when exposed to elevated temperatures
Solution Approach 1:
The patent changes the glass transition temperature parameter of the polymeric layers in the reflective polarizer. Specifically, it uses a high Tg polymer (Tg ≥ 107°C) for the low index layers instead of conventional low Tg polymers. This parameter change ensures the material maintains dimensional stability and resists micro-wrinkling when exposed to elevated temperatures up to 105°C, while still achieving the required optical performance.
Solution Approach 2:
The patent employs composite material structure with alternating high and low index polymeric layers. The low index layers use high Tg polymer to provide thermal stability, while the high index layers provide optical functionality. This composite approach allows the material to simultaneously achieve thermal resistance and optical performance, preventing micro-wrinkling while maintaining reflectivity.
2Reliability
If polymeric layers with higher glass transition temperature are used to reduce micro-wrinkling, then thermal resistance is improved, but delamination resistance may deteriorate
Solution Approach 1:
The patent optimizes the glass transition temperature parameter to a specific range (Tg ≥ 107°C) that balances thermal stability and delamination resistance. This carefully selected parameter range ensures the polymer remains sufficiently flexible at operating temperatures to maintain interlayer adhesion while providing adequate thermal resistance to prevent micro-wrinkling.
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
This configuration reduces micro-wrinkling by controlling the shrinkage difference between the reflective and absorbing polarizers, maintaining acceptable delamination resistance, and improving the optical performance of the stack.
Implementation Method 1
The first polymeric layers have a glass transition temperature of at least 107 deg. C.
Implementation Method 2
When heated at 105 deg. C. for 15 minutes, a difference in shrinkage of the reflective polarizer and the linear absorbing polarizer along the first and second polarization states is greater than about zero and 0.2%, respectively.
Implementation Method 3
the first polymeric layers have a smaller average in-plane index of refraction than the second polymeric layers
Implementation Method 4
the reflective polarizer has an optical reflectance of at least 60% for a first polarization state and an optical transmittance of at least 60% for an orthogonal second polarization state
Implementation Method 5
the linear absorbing polarizer has an optical absorbance of at least 60% for the first polarization state and an optical transmittance of at least 60% for the second polarization state
Data Source
AI summary
An optical film includes a plurality of alternating first and second polymeric layers, such that the first polymeric layers have a smaller average in-plane index of refraction than the second polymeric layers and the first polymeric layers have a glass transition temperature of at least 107 deg. C. The optical film may be a reflective polarizer. An optical stack includes a linear absorbing polarizer and the reflective polarizer disposed on, and bonded to, the absorbing polarizer. The reflective polarizer may have an optical reflectance of at least 60% for a first polarization state and an optical transmittance of at least 60% for an orthogonal second polarization state. When heated at 105 deg. C. for 15 minutes, a difference in shrinkage of the reflective polarizer and the absorbing polarizer along the first and second polarization states may be greater than about zero and 0.2%, respectively.