Adhesive Layer Viscoelastic Control for Flexible Display Restoration
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Solution Overview
Problem
Flexible image display devices face issues with delamination, cracking, and insufficient restoration properties when folded, especially at high temperatures or under stress, due to inadequate adhesive layer performance.
Innovation Solution
An adhesive layer with specific dynamic viscoelastic properties, including a storage shear modulus of 0.005-0.20 MPa at 60°C and a loss tangent less than 0.60, and a creep compliance fluctuation value less than 1.0, is used to bond flexible members, ensuring good restoration and impact resistance across a wide temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the adhesive sheet is used at high temperature, then the device can operate in high-temperature environments, but the restoration property becomes insufficient and the adhesive layer deforms permanently
Solution Approach 1:
The patent changes the viscoelastic parameters of the adhesive layer by controlling the storage shear modulus to 0.005-0.20 MPa and loss tangent to less than 0.60 at 60°C. These parameter adjustments enable the adhesive to maintain restoration properties across a wide temperature range including high-temperature operation conditions.
Solution Approach 2:
The patent develops a composite adhesive material combining specific polymer components with controlled molecular weight distributions and crosslinking densities. This composite structure provides both high-temperature stability and elastic recovery, resolving the contradiction between temperature resistance and restoration property.
2Temperature
If the adhesive sheet is used at low temperature, then the device can operate in low-temperature environments, but the member sheet cracks due to applied stress
Solution Approach 1:
The patent adjusts the adhesive layer's viscoelastic parameters at low temperatures by controlling the storage shear modulus and loss tangent. The specific parameter ranges enable the adhesive to reduce stress transmission to the member sheet while maintaining bonding strength, preventing cracks during low-temperature operation.
Solution Approach 2:
The adhesive layer acts as a cushioning element that absorbs and dissipates stress before it reaches the member sheet. The controlled viscoelastic properties create a protective effect that prevents crack initiation and propagation in the member sheet during low-temperature bending operations.
3Strength
If the adhesive layer is made more rigid to prevent delamination, then the bonding strength increases, but the restoration property decreases and the adhesive cannot absorb impact stress
Solution Approach 1:
The patent precisely controls the viscoelastic parameters of the adhesive layer, setting the storage shear modulus to 0.005-0.20 MPa and loss tangent to less than 0.60 at 60°C. This parameter optimization achieves a balance where the adhesive maintains sufficient bonding strength while preserving elastic recovery capability and impact absorption.
Solution Approach 2:
The patent creates a composite adhesive material with optimized molecular structure and crosslinking density. This composite provides both cohesive strength for delamination resistance and elastic compliance for impact absorption and restoration, resolving the contradiction between strength and flexibility.
4Manufacturing precision
If the adhesive sheet is designed for room temperature performance, then the creep compliance fluctuation value is controlled, but the device cannot maintain restoration property at high temperatures or durability at low temperatures
Solution Approach 1:
The patent establishes specific viscoelastic parameter ranges (storage shear modulus: 0.005-0.20 MPa, loss tangent: <0.60 at 60°C) that ensure consistent performance across the entire operating temperature range. These parameter specifications enable the adhesive to maintain both restoration property and durability under varying temperature conditions.
Solution Approach 2:
The adhesive layer is designed to perform multiple functions simultaneously: maintaining creep compliance control for manufacturing precision, providing restoration property for high-temperature operation, and ensuring durability for low-temperature bending. The universal design achieves all these requirements through optimized viscoelastic parameters.
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 layer effectively prevents delamination and cracking, maintaining restoration properties even at high temperatures and absorbing stress from impacts, thus enhancing the durability and reliability of flexible image display devices.
Implementation Method 1
two flexible members are bonded together via an adhesive layer
Implementation Method 2
an adhesive layer which enables, during a folding operation of a layered sheet having a configuration in which a member sheet and an adhesive sheet are layered in a high-temperature environment, a good restoration property
Data Source
AI summary
Provided is a flexible image display device member including an adhesive layer which enables, during a folding operation of a layered sheet having a configuration in which a member sheet and an adhesive sheet are layered in a high-temperature environment, a good restoration property when the layered sheet is unfolded from a folded state. The flexible image display device member has a configuration in which two flexible members are bonded together via the adhesive layer, and the adhesive layer satisfies requirements (1) and (2). (1) A storage shear modulus at 60° C. (G′ (60° C.)) obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is 0.005 MPa or more and less than 0.20 MPa, and a loss tangent at 60° C. (tan δ (60° C.)) is less than 0.60. (2) When a creep compliance value measured when a stress of 3,000 Pa is applied is set to a minimum creep compliance J(t)min (MPa−1), and a maximum creep compliance value measured during a period in which the stress of 3,000 Pa continues to be applied until 3757 seconds after the minimum creep compliance J(t)min is measured is set to a maximum creep compliance J(t)max (MPa−1), a creep compliance fluctuation value Δ log J(t) calculated based on a difference between the minimum creep compliance J(t)min and the maximum creep compliance J(t)max is less than 1.0.