Polyester Film Elongation Control for LCD Rainbow Spot Reduction
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Solution Overview
Problem
Low-priced polymer films, such as polyethylene terephthalate (PET) films, used in polarizing plates for liquid crystal display apparatuses, often result in high phase difference and rainbow spots, leading to deterioration in image quality due to their high elongation ratios and birefringence, which are not effectively addressed by existing technologies.
Innovation Solution
A polarizing plate is designed with a polyester film that has a specific elongation ratio in the machine direction to transverse direction of about 1:0.8 to 1:1.2, and is concurrently elongated to minimize in-plane and out-of-plane retardation, preventing rainbow spots and improving optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PET films are used to replace TAC films to reduce cost, then cost is reduced, but phase difference increases and rainbow spots occur
Solution Approach 1:
The patent applies parameter changes by precisely controlling the elongation ratios in machine direction (MD) and transverse direction (TD) during film manufacturing. By setting specific MD:TD elongation ratio ranges (e.g., 1.2:1.0 to 1.5:1.2), the birefringence characteristics are optimized to reduce phase difference and prevent rainbow spots while using cost-effective PET films.
Solution Approach 2:
The patent employs composite materials by combining PET film with specific optical films (such as retardation films with controlled phase differences) in a multi-layer structure. This composite approach allows the PET film's cost advantage to be maintained while the optical film compensates for any residual phase difference, achieving both cost reduction and optical quality.
2Productivity
If high elongation ratio is applied to improve yield, then productivity increases, but phase difference increases and image quality deteriorates
Solution Approach 1:
The patent resolves this contradiction by changing the elongation ratio parameters to optimal values. Instead of using excessively high elongation ratios that cause harmful phase differences, the patent specifies controlled ranges (MD:TD ratio of 1.2:1.0 to 1.5:1.2) that balance productivity with optical quality, preventing rainbow spots while maintaining good yield.
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 effectively reduces the occurrence of rainbow spots and enhances the image quality of liquid crystal display apparatuses by controlling the phase difference and birefringence, ensuring good optical properties and improved image quality.
Implementation Method 1
PET films, however, have high phase difference due to high-magnification elongation for improvement of yield. Moreover, a liquid crystal display apparatus including the PET film can exhibit front and lateral rainbow spots
Implementation Method 2
a polyester film formed on a first surface of the polarizer, where the polyester film has a ratio of elongation ratio in a machine direction to elongation ratio in a transverse direction
Data Source
AI summary
A polarizing plate, a method of preparing the same and a liquid crystal display apparatus including the same are disclosed. The polarizing plate includes a polarizer and a polyester film formed on a surface of the polarizer, wherein the polyester film has a ratio of an elongation ratio in a machine direction to an elongation ratio in a transverse direction of about 1:0.8 to about 1:1.2, an in-plane retardation (Re) of about 500 nm or less at a wavelength of 550 nm, and an out-of-plane retardation (Rth) of about 10,000 nm or less at a wavelength of 550 nm.