Biaxially Stretched PET Protective Film for Polarizer
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Solution Overview
Problem
Conventional protective films for polarizers, such as triacetyl cellulose, are vulnerable to moisture and have weak durability, while alternatives like polyethylene terephthalate (PET) cause distorted polarization and rainbow stains due to high birefringence, impairing visibility in high-brightness liquid crystal displays.
Innovation Solution
A protective film for polarizers made from biaxially stretched PET with specific phase difference conditions in the in-plane and thickness directions, optimized to minimize birefringence and maintain mechanical strength, ensuring reduced rainbow stains and improved durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyethylene terephthalate (PET) is used as the protective film to improve mechanical property and moisture barrier property, then durability is improved, but rainbow stains appear due to high birefringence, impairing visibility
Solution Approach 1:
The patent applies parameter changes by precisely controlling the phase difference parameters (Ro ≤ 350 nm and Rth ≥ 6,000 nm) of the PET protective film. This involves adjusting the stretching ratios (MD: 2.8-3.5 times, TD: 2.9-3.7 times) and heat treatment conditions to achieve the desired optical properties while maintaining the durability benefits of PET material
Solution Approach 2:
The patent uses a composite structure consisting of the PET protective film stacked on the polarizer. The PET film serves as both the protective layer and the optical control element, combining mechanical durability with controlled optical properties through the specific phase difference parameters
2Illumination intensity
If triacetyl cellulose (TAC) is used as the protective film, then visibility is maintained, but moisture resistance and durability are insufficient
Solution Approach 1:
The patent replaces the traditional TAC material with PET, which offers superior durability and moisture resistance. The invention accepts the initial challenge of PET's high birefringence but resolves it through parameter control, effectively creating a more reliable long-term solution that maintains visibility while dramatically improving moisture resistance
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 a polarizing plate with superior optical and mechanical properties, preventing rainbow stains and ensuring normal operation under harsh conditions without compromising visibility, making it suitable for diverse display applications.
Implementation Method 1
because polyethylene terephthalate (PET) is highly birefringent, it leads to distorted polarization between the polarizer and the liquid crystal
Implementation Method 2
16,000 nm phase difference in thickness direction (Rth)≥6,000 nm, and experience change in the phase difference in the thickness direction with respect to the width change within the effective width (|ΔRth|/|Δx|) of less than 1.5 nm/mm
Data Source
AI summary
Disclosed are a protective film for a polarizer with superior optical and mechanical properties, a polarizing plate including the same and a display device including the same.