Photocurable Polarizing Plate Protective Layer for Liquid Crystal Displays
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Solution Overview
Problem
Existing polarizing plates for liquid crystal display devices face challenges with light leakage and thinning, and the direct formation of protective layers on polyvinyl alcohol-based polarizers is hindered by stress-induced tearing at high temperatures, as well as issues with long-term storage due to blocking phenomena with PET carrier films.
Innovation Solution
A polarizing plate with a photocurable composition comprising a first epoxy-based compound, a second epoxy-based compound, an oxetane compound, and a photocation polymerization initiator, where the first epoxy-based compound constitutes 50-80 parts by weight, and the initiator includes a short and long wavelength initiator, minimizing OH and COOH content to prevent blocking and enhance high-temperature durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a protective layer is directly formed on a polyvinyl alcohol-based polarizer, then the polarizing plate can be thinned and costs reduced, but the polarizer is torn by stress generated from polarizer shrinkage at high temperature
Solution Approach 1:
The patent changes the chemical composition parameters of the protective layer by using a photocurable composition with specific ratios of epoxy-based compounds (50-80 parts by weight) and oxetane compounds (20-50 parts by weight), along with specific photopolymerization initiators. This compositional parameter change enables the protective layer to have appropriate mechanical properties that prevent tearing during high-temperature processing while maintaining thinness.
Solution Approach 2:
The patent creates a composite protective layer by combining multiple components: epoxy-based compounds, oxetane compounds, and photopolymerization initiators in specific proportions. This composite material structure provides both adhesion to the polarizer and sufficient mechanical strength to withstand thermal stress without tearing, resolving the contradiction between thinness and strength.
2Device complexity
If a protective layer is directly formed on a polarizer, then manufacturing costs and processes are minimized, but blocking phenomena occur with PET carrier films during long-term storage
Solution Approach 1:
The patent adjusts the chemical parameters of the photocurable composition by controlling the ratio of epoxy-based compounds (50-80 parts) to oxetane compounds (20-50 parts) and selecting specific photopolymerization initiators. This parameter optimization prevents blocking phenomena with PET carrier films during storage while maintaining the simplicity of direct protective layer formation, thus resolving the contradiction between process simplicity and storage reliability.
3Strength
If existing protective films are used on polarizing plates, then the polarizer is protected from damage, but light leakage occurs and the structure becomes thicker
Solution Approach 1:
The patent merges the protective function with a thinner integrated layer formed by directly coating and curing the photocurable composition on the polarizer surface. This unified structure eliminates the need for separate protective films and adhesive layers, thereby reducing overall thickness and preventing light leakage while maintaining protection against damage.
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 minimizes costs and processes, reduces light leakage, prevents tearing due to high-temperature shrinkage, and allows for long-term storage without carrier film damage, while maintaining high durability and storage modulus, even without a separate protective film.
Implementation Method 1
a protective layer in contact with at least one surface of the polarizer, wherein the protective layer is a cured material of a photocurable composition for a polarizing plate protective layer comprising a photopolymerizable compound consisting of a first epoxy-based compound, a second epoxy-based compound and an oxetane compound; and a photocation polymerization initiator
Data Source
AI summary
A polarizing plate, an image display device comprising the same, and a photocurable composition for a polarizing plate protective layer are provided. The polarizing plate includes a polarizer; and a protective layer in contact with at least one surface of the polarizer. The protective layer is a cured material of a photocurable composition for a polarizing plate protective layer including a photopolymerizable compound, and a photocation polymerization initiator. The photopolymerizable compound includes a first epoxy-based compound, a second epoxy-based compound and an oxetane compound.