Pressure Sensitive Adhesive for Polarizing Plates Resolving Light Leakage
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Solution Overview
Problem
Existing pressure sensitive adhesives for polarizing plates face issues with durability and light leakage in liquid crystal display units, particularly under high temperature and high humidity conditions, due to poor dimensional stability and residual stress, leading to problems like peeling and color unevenness.
Innovation Solution
A pressure sensitive adhesive with a specific storage elastic modulus (G′) of at least 0.3 MPa at 23°C and 80°C, composed of an acrylic copolymer and an active energy beam-curable compound, irradiated with an active energy beam, providing enhanced adhesion and durability while minimizing light leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a strongly tacky adhesive material is used to enhance holding power, then adhesion strength is improved, but the adhesive becomes incapable of following shrinkage and swelling of the sheet under high temperature and high humidity conditions, leading to peeling and lifting
Solution Approach 1:
The patent changes the physical and chemical parameters of the pressure sensitive adhesive by controlling the molecular weight distribution (specifically setting the weight average molecular weight to 500,000 or more) and the gel fraction (30-90%). These parameter adjustments enable the adhesive to maintain both strong adhesion and the flexibility to accommodate dimensional changes of the polarizing plate under high temperature and high humidity conditions, resolving the contradiction between adhesion strength and dimensional stability.
2Strength
If a strongly tacky adhesive material is used to suppress lifting and peeling, then holding power is improved, but residual stress becomes non-uniform in the polarizing plate, causing light leakage and color unevenness
Solution Approach 1:
The patent adjusts the molecular weight distribution and gel fraction parameters of the pressure sensitive adhesive to achieve uniform stress distribution. By setting the weight average molecular weight to 500,000 or more and gel fraction to 30-90%, the adhesive maintains flexibility to absorb dimensional variations, ensuring uniform residual stress distribution in the polarizing plate and preventing light leakage and color unevenness while maintaining strong holding power.
3Strength
If the molecular weight of adhesive components is increased to enhance pressure sensitive adhesive performance, then adhesion is improved, but the adhesive loses the ability to follow shrinkage and swelling, contributing to peeling and lifting
Solution Approach 1:
The patent optimizes the molecular weight distribution by setting the weight average molecular weight to 500,000 or more while controlling the gel fraction within 30-90%. This parameter combination provides both strong pressure sensitive adhesive performance and sufficient flexibility to accommodate shrinkage and swelling under high temperature and high humidity conditions, ensuring long-term durability without peeling or lifting.
Solution Approach 2:
The patent creates a composite adhesive structure with specific molecular weight distribution and gel fraction characteristics. This composite material approach combines high molecular weight components for strong adhesion with controlled gel fraction for flexibility, enabling the adhesive to maintain both strong holding power and durability under harsh environmental conditions.
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 ensures high durability and prevents light leakage in liquid crystal display units even in harsh environments, maintaining adhesion strength and stability across various materials like alkali-free glass and polycarbonate.
Implementation Method 1
a pressure sensitive adhesive having a storage elastic modulus (G′) at 23° C. of at least 0.3 MPa... composed of an acrylic copolymer and an active energy beam-curable compound, irradiated with an active energy beam
Data Source
AI summary
The disclosed a pressure sensitive adhesive for polarizing plates which has a storage elastic modulus (G′) at 23° C. of at least 0.3 MPa; a polarizing plate having a pressure sensitive adhesive; a process for producing the above polarizing plate which comprises sticking a polarizing plate on a tacky adhesive material layer formed on a releasing layer of a releasing sheet, and thereafter irradiating with an active energy beam from the releasing sheet side; an optical film which comprises a polarizing plate and a phase difference plate; and a process for producing the above optical film. The pressure sensitive adhesive and polarizing plate having the pressure sensitive adhesive are characterized in that they are capable of sticking with high durability, the polarizing plate to a and phase difference plate, and the resultant liquid crystal display unit is less liable to cause light leakage under the conditions of high temperature.