Polarizing Plate Moisture Barrier Design
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Solution Overview
Problem
Liquid crystal display (LCD) polarizing plates face durability issues due to moisture infiltration under high temperature and high humidity conditions, leading to degradation in crack resistance and light transmittance.
Innovation Solution
A polarizing plate design featuring a polarizer with a protective film and a barrier layer, where the protective film has a high in-plane retardation and is formed from a polyester resin, and the barrier layer includes an alicyclic epoxy resin with a glass transition temperature of 200° C. or more, along with a bonding layer and an adhesive layer, to minimize moisture transmittance and maintain light transmittance variation within specific limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional polarizing plate structure is used, then the device is simple and easy to manufacture, but moisture infiltrates under high temperature and high humidity conditions causing deterioration in durability and crack resistance
Solution Approach 1:
The protective film is divided into multiple functional layers: a lower protective film layer in contact with the polarizer providing basic protection, and an upper stretch-resist layer providing additional moisture barrier and mechanical protection. This segmentation allows each layer to be optimized for its specific function while together providing comprehensive protection against moisture infiltration and maintaining durability under high temperature and humidity conditions.
Solution Approach 2:
The protective film uses a composite structure combining different materials with complementary properties. The lower protective film layer uses a material with good adhesion to the polarizer and basic barrier properties, while the upper stretch-resist layer uses a material with superior moisture resistance and mechanical strength. This composite material approach achieves enhanced durability and crack resistance that neither material could provide alone.
2Object-affected harmful factors
If the protective film has high moisture barrier properties, then moisture infiltration is prevented, but light transmittance may be reduced
Solution Approach 1:
The protective film structure applies local quality optimization by having different layers with different thicknesses and material properties at different locations in the film stack. The lower protective film layer has sufficient thickness to provide adhesion and basic barrier function, while the upper stretch-resist layer is optimized for moisture blocking with minimal thickness to maintain light transmittance. This local optimization allows high moisture barrier properties without significant light loss.
Solution Approach 2:
The invention optimizes the thickness parameters of each layer to achieve the right balance between moisture barrier and light transmittance. By carefully controlling the thickness of the lower protective film layer and the upper stretch-resist layer, the structure provides effective moisture blocking while maintaining high light transmittance. The parameter optimization ensures that the total thickness is minimized while still achieving the required moisture barrier performance.
3Strength
If bonding layers are added to protect the polarizer, then crack resistance improves, but the device becomes more complex and harder to manufacture
Solution Approach 1:
The bonding layer is merged with the protective film structure, where the lower protective film layer serves dual functions as both the protective film and the bonding layer. This integration eliminates the need for a separate bonding layer, simplifying the manufacturing process while still providing the necessary adhesion to the polarizer and crack resistance. The merged structure reduces the number of manufacturing steps and material interfaces.
Solution Approach 2:
The lower protective film layer is designed to perform multiple functions simultaneously: it provides adhesion to the polarizer, serves as a moisture barrier, offers mechanical protection, and acts as a bonding interface. This multi-functionality reduces the need for additional dedicated bonding layers, simplifying the overall structure and manufacturing process while maintaining crack resistance and protective functions.
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 improved durability, crack resistance, and minimal warpage under high temperature/high humidity conditions, ensuring consistent light transmittance and polarization while preventing moisture infiltration.
Implementation Method 1
a protective film on an upper surface of the bonding layer and having a moisture transmittance of about 30 g/m2·24 hr or less at 40° C. and 90% relative humidity (RH)
Implementation Method 2
a barrier layer on a lower surface of the polarizer and formed of a barrier layer composition including an alicyclic epoxy resin having a glass transition temperature of about 200° C. or more
Implementation Method 3
The protective film may include a film formed by stretching a film including a polyester resin at an elongation of 5 times to 8 times an initial length thereof in a transverse direction (TD)
Data Source
AI summary
A polarizing plate includes a polarizer, a bonding layer on an upper surface of the polarizer, a protective film on an upper surface of the bonding layer and having a moisture transmittance of about 30 g/m2·24 hr or less at 40° C. and 90 % relative humidity (RH), and a barrier layer on a lower surface of the polarizer and formed of a barrier layer composition including an alicyclic epoxy resin having a glass transition temperature of about 200° C. or more. The polarizing plate may have a light transmittance variation rate of 3% or less, as calculated by Equation 1:Light transmittance variation rate=|T0−T500|/T0×100 (1),where T0 is an initial light transmittance and T500 is a light transmittance after 500 hours as set forth herein.