Viscoelastic Bonding Members for Foldable Display Durability
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Solution Overview
Problem
Foldable display devices face issues with adhesive layer delamination due to stress from folding operations, leading to potential failure in bonding and durability.
Innovation Solution
A display device design featuring a front and rear stacked structure with bonding members having specific viscoelastic properties, where the front bonding member has a higher loss tangent and the rear bonding member has a higher storage modulus, both with thicknesses of 50 μm or less, to absorb and distribute stress effectively during folding and external impacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional adhesive layer is used in the bonding of the laminated structure, then the bonding structure is simple and easy to manufacture, but the adhesive layer suffers delamination failure under stress from folding operations
Solution Approach 1:
The bonding structure is divided into multiple bonding members (first bonding member and second bonding member) positioned at different locations. Each bonding member has optimized viscoelastic properties suited to its specific position and stress conditions, preventing delamination failure while maintaining overall structural integrity.
Solution Approach 2:
Different bonding members are assigned different viscoelastic characteristics based on their local requirements. The first bonding member has a loss tangent of 0.1-0.5 for flexibility, while the second bonding member has a loss tangent of 0.5-1.0 for stress absorption, optimizing performance at each location rather than using a uniform adhesive.
2Strength
If the bonding members have high elasticity to withstand external impacts, then the resistance to deformation improves, but the energy dissipation capability decreases
Solution Approach 1:
The viscoelastic parameters of the bonding members are precisely controlled within specific ranges. The loss tangent is optimized to balance energy dissipation and elasticity, while the storage modulus is maintained at 100-1000 kPa to provide adequate impact resistance without excessive rigidity.
Solution Approach 2:
The bonding members are formulated as composite materials exhibiting viscoelastic behavior, combining characteristics of both elastic solids and viscous fluids. This allows them to dissipate energy through viscous damping while maintaining sufficient elastic recovery to resist deformation from external impacts.
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 design enhances the display device's resistance to deformation and external impacts, ensuring durability and maintaining adhesion even during repeated folding operations, as demonstrated by improved performance in pen drop tests.
Implementation Method 1
a loss tangent of the front bonding member has a value greater than a loss tangent of the rear bonding member, the loss tangent of the front bonding member and the rear bonding member being represented by a following equation: (loss tangent)=(loss modulus)/(storage modulus), wherein the loss modulus of the front bonding member and the rear bonding member refers to energy lost by viscosity of a material
Implementation Method 2
the storage modulus the front bonding member and the rear bonding member refers to energy stored without loss by elasticity of the material of the front bonding member and the rear bonding member
Data Source
AI summary
A display device includes: a display panel including a front surface and a rear surface, the rear side being opposite to the front side; a front stacked structure on the front surface including a front bonding member disposed on the front surface; and a rear stacked structure on the rear surface including a rear bonding member disposed on the rear surface. A loss tangent of the front bonding member has a value greater than a loss tangent of the rear bonding member, the loss tangent being represented by an equation: (loss tangent)=(loss modulus)/(storage modulus), wherein the loss modulus refers to energy lost by viscosity of a material, and the storage modulus refers to energy stored without loss by elasticity of the material.