TAC-Less Polarizing Plate Adhesive Composition for Warpage Reduction
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Solution Overview
Problem
TAC-less polarizing plates with protective films on only one surface of the polarizer suffer from high warpage, poor durability, and limited adhesion to the polarizer, leading to corrosion issues in liquid crystal display panels, especially under harsh conditions.
Innovation Solution
An adhesive composition comprising a (meth)acrylic copolymer, an isocyanate crosslinking agent, and a silane coupling agent, with specific molar ratios, is used to form an adhesive film that enhances adhesion to the polarizer, providing improved durability, moisture and heat resistance, and reduced warpage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a TAC-less polarizing plate structure is used to reduce material costs and thickness, then cost and thickness are improved, but warpage value increases and durability decreases
Solution Approach 1:
The adhesive layer uses a composite system combining (meth)acrylic copolymer with carboxylic acid groups, silane coupling agent, and isocyanate crosslinking agent. This composite formulation provides both strong adhesion to the polarizer and protective properties, preventing corrosion of the ITO coating while maintaining the TAC-less structure's cost and thickness advantages.
2Reliability
If carboxylic acid group-containing monomer is used in adhesive layer to enhance durability, then durability is improved, but corrosion of metal coating occurs
Solution Approach 1:
The silane coupling agent acts as an intermediary between the carboxylic acid group-containing adhesive and the ITO coating. The silane forms a protective interface layer that prevents direct corrosive interaction between the carboxylic acid groups and the metal coating, while still allowing the adhesive to provide strong bonding and durability enhancement.
3Ease of repair
If adhesive layer is designed to ensure re-workability through good adhesion to polarizer, then re-workability is improved, but adhesion capability of typical adhesive layer is limited
Solution Approach 1:
The adhesive formulation changes key parameters including the type of polymer (meth)acrylic copolymer with specific carboxylic acid content, the addition of silane coupling agent for chemical bonding, and isocyanate crosslinking agent for enhanced mechanical strength. These parameter changes collectively achieve adhesion strength of 1,000 gf/inch or greater while maintaining re-workability through controlled peeling properties.
4Device complexity
If polarizer directly adjoins adhesive layer in TAC-less structure to simplify construction, then construction simplicity is improved, but polarizer cracking occurs under harsh conditions
Solution Approach 1:
The adhesive layer employs a composite material system with (meth)acrylic copolymer as base, silane coupling agent for chemical bonding to the polarizer, and isocyanate crosslinking agent for creating a flexible, strong network. This composite structure provides sufficient mechanical strength and flexibility to prevent polarizer cracking under thermal expansion and contraction in harsh conditions, while maintaining direct adjacency construction simplicity.
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 adhesive composition achieves high adhesive strength to the polarizer, ensuring durability and reliability, while preventing corrosion and minimizing warpage, thus enhancing the performance of polarizing plates in liquid crystal displays.
Implementation Method 1
a silane coupling agent
Implementation Method 2
alkoxy silane groups in the silane coupling agent
Implementation Method 3
an isocyanate crosslinking agent
Implementation Method 4
isocyanate groups in the isocyanate crosslinking agent
Implementation Method 5
can cause corrosion of the metal coating... providing improved durability, moisture and heat resistance
Data Source
AI summary
An adhesive composition for polarizing plates includes a (meth)acrylic copolymer, an isocyanate crosslinking agent, and a silane coupling agent. The molar ratio (A) of the number of moles of hydroxyl groups in the (meth)acrylic copolymer may be about 2.5 mol % to about 4 mol %, the molar ratio (B) of the number of moles of alkoxy silane groups in the silane coupling agent may be about 50 mol % to about 80 mol %, and the molar ratio (C) of the number of moles of isocyanate groups of the isocyanate crosslinking agent may be about 20 mol % to about 50 mol %, based on the total number of moles of alkoxy silane groups of the silane coupling agent and isocyanate groups of the isocyanate crosslinking agent. An adhesive film is formed from the adhesive composition, a polarizing plate includes the adhesive film, and an optical display includes the polarizing plate.