Pressure-Sensitive Adhesive Water Absorption Control
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Solution Overview
Problem
Image display devices and touch panels face reliability issues due to changes in adhesive strength caused by environmental factors like temperature and humidity, leading to reduced productivity and stability of pressure-sensitive adhesive layers.
Innovation Solution
A pressure-sensitive adhesive composition that maintains a water absorption rate of 1.5% or less at 90% RH and a specific time frame for moisture absorption, ensuring stable adhesive strength and reduced changes in response to environmental conditions, thereby enhancing the reliability and productivity of the adhesive layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pressure-sensitive adhesive sheets are used for laminating optical members in image display devices, then the adhesive strength changes greatly due to storage environment conditions, but this requires keeping the adhesive layer until strength stabilizes, which reduces productivity
Solution Approach 1:
The patent controls the glass transition temperature (Tg) of the pressure-sensitive adhesive within a specific range (-50°C to 0°C) and adjusts the molecular weight distribution (ratio of Mn/Mw) to optimize adhesive performance. By changing these material parameters, the adhesive achieves stable strength without requiring extended storage time, thus resolving the contradiction between reliability and productivity
2Productivity
If the pressure-sensitive adhesive layer is used immediately after formation, then productivity is improved, but the adhesive strength is not yet stable and changes greatly with environmental conditions
Solution Approach 1:
The patent performs preliminary optimization of the adhesive composition parameters (Tg control, molecular weight distribution) during manufacturing. This preliminary action ensures that the adhesive reaches optimal performance quickly after application, allowing immediate use without extended storage while maintaining stable adhesive strength under environmental variations
3Productivity
If the pressure-sensitive adhesive is designed for high initial adhesive strength, then productivity improves, but the adhesive strength becomes more sensitive to environmental changes like temperature and humidity
Solution Approach 1:
The patent creates a composite adhesive system combining polymers with specific Tg ranges and controlled molecular weight distributions. This composite approach balances initial adhesive strength with environmental resistance, allowing the adhesive to maintain stable performance across temperature and humidity variations while enabling immediate productivity
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 provides a pressure-sensitive adhesive layer with high reliability and stability, ensuring consistent adhesive strength across varying environmental conditions, which is crucial for the durability and performance of image display devices and touch panels.
Implementation Method 1
when a water absorption rate of the pressure-sensitive adhesive layer stored under conditions at 23°C 90% RH for 360 minutes is defined as X90 (%), the following formula (1) is satisfied: X90 is 1.5% or less
Data Source
Figure 1~2(b)
Figure 3~4
Figure 5(a)~5(d)
AI summary
To provide a pressure-sensitive adhesive composition for forming a pressure-sensitive adhesive layer used for laminating an optical member of an image display device, wherein the composition can form a pressure-sensitive adhesive layer having high reliability in which the adhesive strength does not change easily in response to environmental changes, having small changes in adhesive strength due to the storage environment immediately after filming, and having high productivity; a pressure-sensitive adhesive layer; a pressure-sensitive adhesive sheet; an optical member with a pressure-sensitive adhesive layer; an image display device; and a touch panel. The pressure-sensitive adhesive composition of the present invention is for forming a pressure-sensitive adhesive layer used for laminating an optical member of an image display device, wherein when a water absorption rate of the layer stored under conditions at 23°C 90% RH for 360 minutes is defined as X90 (%), formula (1) is satisfied: X90≤1.5%