Polarizing Plate Protective Layer Adhesion and Thickness
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Solution Overview
Problem
Existing polarizing plates face challenges in maintaining adhesion between the polarizer and protective layer, especially under high humidity conditions, and lack sufficient heat resistance, while also being limited in thickness for thin and lightweight liquid crystal display devices.
Innovation Solution
A polarizing plate is developed using a radical curable composition comprising a first compound with an ester or ether group, a second compound with a carboxyl group conjugated to an unsaturated double bond, and a radical initiator, which forms a protective layer with improved adhesion and heat resistance, allowing for a thinner design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a TAC film is used as the protective film, then optical transparency and moisture permeability are improved, but the thickness cannot be reduced to 20 μm or less due to handling property and durability issues
Solution Approach 1:
The patent changes the material composition parameters of the protective film by incorporating specific resin combinations (cyclic carbonate polymer and carboxyl-containing polymer) with controlled glass transition temperatures and functional groups, enabling the film to achieve both thinness (20 μm or less) and adequate durability through compositional optimization rather than relying on traditional thick TAC films
Solution Approach 2:
The patent uses a composite protective film structure combining cyclic carbonate polymer and carboxyl-containing polymer in specific ratios, creating a multi-component material system that provides both mechanical strength for thin-film handling and optical properties, replacing the single-material TAC film approach
2Length of stationary object
If a radical curable composition including acrylic or acrylamide-based compound is used to form a transparent thin film layer, then the film can be made thin, but adhesion deteriorates under high humidity environment and heat resistance is poor
Solution Approach 1:
The patent modifies the chemical composition parameters of the radical curable composition by selecting specific compounds with particular functional groups (carboxyl, hydroxyl) and glass transition temperature ranges, and by controlling the ratio of monomers to oligomers/polymer, to achieve both thin film formation and high adhesion reliability under humid conditions
Solution Approach 2:
The patent introduces a coupling agent or adhesion promoter as an intermediary substance between the radical curable composition and the substrate, which mediates the bonding interface to maintain strong adhesion even in high humidity environments where direct bonding would fail
3Strength
If a cation curable composition is used to form a transparent thin film layer, then adhesion with the polarizer is excellent, but curling problems occur due to slow curing rate, low degree of curing, and dark reaction
Solution Approach 1:
The patent replaces the cationic curing mechanism with a radical curing mechanism, substituting one chemical reaction system for another that offers faster reaction kinetics and eliminates dark reaction issues, while maintaining or improving adhesion through careful selection of radical initiators and monomer composition
4Weight of stationary object
If the protective film thickness is reduced to enable thin and lightweight liquid crystal display devices, then device weight and thickness are improved, but handling property and durability performance deteriorate
Solution Approach 1:
The patent optimizes the physical and chemical parameters of the protective film material, including glass transition temperature, crosslinking density, and functional group content, to achieve a thin film structure (20 μm or less) that maintains adequate mechanical strength and durability for device handling and operation
Solution Approach 2:
The patent employs a composite material system combining multiple polymer components with complementary properties, where the cyclic carbonate polymer provides mechanical strength and the carboxyl-containing polymer enhances adhesion and environmental resistance, enabling thin-film durability
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 maintains excellent adhesion under high humidity and provides high heat resistance, enabling the production of thin and lightweight polarizing plates suitable for liquid crystal display devices.
Implementation Method 1
a protective layer formed on at least one surface of the polarizer, wherein the protective layer is a cured product of (A) a first compound, (B) a radical curable second compound, and (C) a radical curable composition including a radical initiator
Data Source
AI summary
The present invention relates to a polarizing plate including a polarizer, and a protective layer formed on at least one surface of the polarizer, in which the protective layer is a cured product of (A) a first compound represented by the following [Formula 1]; (B) a radical curable second compound including at least one carboxyl group conjugated to an unsaturated double bond between carbons present at a side chain in a molecule thereof; and (C) a radical curable composition including a radical initiator, and a liquid crystal display device including the same.