Pressure-Sensitive Adhesive Sheet for Flexible Devices
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Solution Overview
Problem
Conventional pressure-sensitive adhesive (PSA) sheets used in flexible devices lack sufficient crease resistance and peel resistance due to inadequate durability against repeated deformation, such as bending and folding.
Innovation Solution
A PSA sheet with a PSA layer that combines high deformability and cohesive strength, featuring a recovery rate of 70% or higher after 100% elongation, a displacement of 0.5 mm or greater in the holding power test, and a maximum tensile strength of 15 N/10 mm or less, utilizing a composition including an acrylic polymer, a tackifier resin with a softening point between 50°C and 105°C, and a crosslinking agent, applied on a stretchable substrate like polyurethane or polyolefin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PSA sheets are used in flexible devices, then adhesion is provided, but crease resistance and peel resistance are insufficient due to inadequate durability against repeated deformation
Solution Approach 1:
The patent changes the physical and chemical parameters of the PSA layer by specifying a recovery rate of 70% or higher after 100% elongation and a maximum tensile strength of 15 N/10 mm or less at 100% elongation. These parameter changes enable the PSA to withstand repeated deformation while maintaining adhesion, directly resolving the contradiction between reliability and resistance to creases and peeling
Solution Approach 2:
The patent creates a composite structure by combining the PSA layer with a stretchable substrate (such as polyurethane or polyolefin). This composite material system provides both the adhesive functionality and the mechanical flexibility needed to resist creases and peeling during repeated deformation, thereby improving reliability without sacrificing crease and peel resistance
2Adaptability or versatility
If the PSA layer has high deformability to accommodate bending and folding, then flexibility is improved, but cohesive strength may be compromised
Solution Approach 1:
The patent optimizes the parameter balance by specifying both high deformability (recovery rate of 70% or higher after 100% elongation) and adequate cohesive strength (maximum tensile strength of 15 N/10 mm or less at 100% elongation, and displacement of 0.5 mm or greater in holding power test). This dual parameter control ensures the PSA layer can deform with flexible substrates while maintaining sufficient internal strength to prevent cohesive failure
Solution Approach 2:
The patent introduces dynamic behavior to the PSA layer through its ability to recover from deformation. The requirement of 70% or higher recovery rate after 100% elongation means the PSA dynamically adapts to bending and folding by deforming during flexing and recovering when the stress is removed, maintaining both deformability and cohesive strength through this dynamic response
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 PSA sheet exhibits excellent flexproof properties, maintaining adhesion and resistance to creases and peeling even after repeated deformation, making it suitable for flexible devices like mobile electronics with flexible displays.
Implementation Method 1
The PSA sheet shows a recovery rate of 70% or higher after elongated by 100%
Implementation Method 2
pressure-sensitive adhesive (or PSA; the same applies hereinafter) has characteristics to be in a soft solid (viscoelastic) state in a room temperature range and adhere to adherend under some pressure
Implementation Method 3
pressure-sensitive adhesive (or PSA; the same applies hereinafter) has characteristics to be in a soft solid (viscoelastic) state in a room temperature range
Data Source
AI summary
Provided is a PSA sheet highly durable against repeated deformation and suited for use in a flexible device as well. The PSA sheet provided by this invention comprises a PSA layer. The PSA sheet shows a recovery rate at 100% elongation of 70% or higher. The PSA layer shows a displacement of 0.5 mm or greater according to the following holding power test:<Holding Power Test>At 23° C., the PSA layer is applied over a 10 mm wide by 20 mm long bonding area to a Bakelite plate as an adherend; a 1 kg load is applied in the length direction; after one hour, the displacement from the initial position where first applied is determined.