Polarizing Plate Protective Layer for Thin Mobile Displays
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Solution Overview
Problem
Existing polarizing plates face challenges in achieving excellent adhesion between the polarizer and protective layer, while also requiring improved water resistance and heat resistance, and maintaining a thin, lightweight structure for use in mobile liquid crystal display devices.
Innovation Solution
A polarizing plate is developed with a protective layer formed from a radical curable composition containing specific compounds with benzene rings, (meth)acryloyl groups, and carboxyl groups, along with a radical initiator, which provides enhanced adhesion, water resistance, and heat resistance, and can be manufactured with a thickness of 0.5 to 20 μm.
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 performance limitations
Solution Approach 1:
The patent replaces the conventional TAC film with a thin protective layer formed by coating and curing a composition containing polyester resin and acrylic resin. This cured protective layer achieves sufficient durability and handling properties at a thickness of 20 μm or less, enabling the polarizing plate to be thin and light-weight while maintaining optical transparency.
Solution Approach 2:
The protective layer uses a composite composition of polyester resin and acrylic resin. The polyester resin provides adhesion to the polarizer and water resistance, while the acrylic resin contributes to hardness and optical transparency. This composite material system achieves the required performance at reduced thickness.
2Productivity
If a radical curable composition including acrylic compound is used to form the protective layer, then the curing rate is improved, but the glass transition temperature becomes low resulting in poor heat resistance reliability
Solution Approach 1:
The patent modifies the chemical composition parameters of the radical curable composition by incorporating polyester resin with specific molecular weight and functional groups. This changes the glass transition temperature parameter to be 60°C or higher while maintaining the radical curing mechanism for high curing rate, thus achieving both fast curing and heat resistance.
Solution Approach 2:
The protective layer uses a composite composition of polyester resin and acrylic resin. The polyester resin component provides high glass transition temperature (60°C or higher) for heat resistance, while the acrylic resin enables rapid radical curing. This composite system achieves both fast curing rate and high heat resistance reliability.
3Temperature
If hydrophilic and monofunctional monomer is added to radical curable composition to increase glass transition temperature, then heat resistance is improved, but water resistance is considerably reduced
Solution Approach 1:
The patent uses a composite composition of polyester resin and acrylic resin instead of adding hydrophilic monomers. The polyester resin provides hydrophobicity for water resistance while contributing to high glass transition temperature. The acrylic resin enables radical curing. This composite approach achieves both heat resistance and water resistance without the drawbacks of hydrophilic monomer addition.
Solution Approach 2:
The patent changes the chemical composition parameters by using polyester resin with specific functional groups and molecular weight characteristics. This achieves glass transition temperature of 60°C or higher while maintaining hydrophobicity for water resistance, avoiding the water resistance deterioration caused by hydrophilic monomer addition.
4Length of stationary object
If the protective layer thickness is reduced to 20 μm or less, then the polarizing plate becomes thin and light weight, but handling property and durability performance deteriorate
Solution Approach 1:
The patent forms a thin protective layer of 20 μm or less by coating and curing a composition containing polyester resin and acrylic resin. The cured protective layer achieves sufficient durability performance and handling properties at this reduced thickness, enabling the polarizing plate to be thin and light-weight while maintaining reliability.
Solution Approach 2:
The protective layer uses a composite composition of polyester resin and acrylic resin that, when cured, provides sufficient durability and handling properties at a thickness of 20 μm or less. The polyester resin provides adhesion and water resistance, while the acrylic resin provides hardness and optical properties, achieving reliable performance at thin thickness.
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 polarizing plate exhibits excellent adhesion, water resistance, and heat resistance, allowing it to maintain performance under high humidity and temperature conditions, while being thin and lightweight, suitable for mobile liquid crystal display devices.
Implementation Method 1
a protective layer formed by coating an active energy ray curable composition... including (B) a radical curable second compound having two or more of each of a benzene ring, a (meth)acryloyl group... and (C) 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 radical curable composition including (A) a first compound represented by [Formula 1], (B) a radical curable second compound having two or more of each of a benzene ring, a (meth)acryloyl group, and a carboxy group in a molecule thereof, and (C) a radical initiator, and an image display device including the same.