Multilayer Birefringent Reflective Polarizer with Low Pass Axis Variation
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Solution Overview
Problem
Conventional reflective polarizers exhibit significant variation in pass axis direction across the crossweb width, leading to alignment challenges and inefficiencies in manufacturing, particularly in liquid crystal displays, resulting in lower contrast ratios and increased material waste.
Innovation Solution
A multilayer birefringent reflective polarizer with alternating layers of a birefringent and isotropic layer, including an oriented polyvinyl alcohol layer, is developed, which maintains a pass axis variation of no more than 1 degree across a full crossweb width greater than 27 inches, achieved through high transverse direction draw ratios and iodine staining for enhanced contrast ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional reflective polarizers are used, then manufacturing is simpler, but pass axis variation across crossweb width is significant (worsening manufacturing precision)
Solution Approach 1:
The polarizer is divided into multiple alternating layers of birefringent material and isotropic material, with each layer contributing to the overall optical function. This segmentation allows precise control of pass axis orientation in each layer while maintaining uniformity across the entire crossweb width through controlled stretching.
Solution Approach 2:
The invention uses composite multilayer structures combining birefringent polymers (such as polyethylene naphthalate or polyethylene terephthalate) with isotropic layers. This composite approach enables simultaneous achievement of high pass axis uniformity, high contrast ratio, and high transmission by leveraging the complementary properties of different materials.
2Manufacturing precision
If high transverse direction draw ratio is applied, then pass axis uniformity improves, but manufacturing process complexity increases
Solution Approach 1:
The invention applies a high transverse direction draw ratio (greater than 6.5) during the tentering process, which fundamentally changes the molecular orientation and birefringence characteristics of the polymer layers. This parameter change achieves superior pass axis uniformity (variation of no more than 1 degree) across the full crossweb width, transforming the manufacturing challenge into a controlled process parameter.
3Reliability
If multilayer birefringent structure is used, then contrast ratio improves, but device complexity increases
Solution Approach 1:
Different layers in the multilayer structure serve distinct local functions: birefringent layers provide polarization control with specific pass axis orientations, while isotropic layers provide structural support and optical coupling. This local quality differentiation enables high contrast ratio (at least 2000:1) by optimizing each layer's contribution to the overall optical performance.
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 solution provides excellent pass axis uniformity and high contrast ratios, reducing manufacturing complexities and material waste, while maintaining high transmission levels, thereby improving display performance and efficiency.
Implementation Method 1
multilayer birefringent reflective polarizer includes alternating layers of a birefringent layer and an isotropic layer
Implementation Method 2
Reflective polarizers preferentially reflect light of one polarization while substantially transmitting light of an orthogonal polarization
Implementation Method 3
The multilayer birefringent reflective polarizer, if stained with iodine dye, exhibits a contrast ratio of at least 2000:1
Implementation Method 4
forming a multilayer reflective polarizer by tentering the polymeric multilayer web with a total transverse direction draw ratio of about 6.5 or greater such that the layer capable of developing birefringence develops birefringence
Data Source
AI summary
Rolls of film are described. In particular, rolls of film including a multilayer birefringent reflective polarizer and a polyvinyl alcohol layer are described. Such films exhibit low variation in pass axis across a full crossweb width.