Variable-Modulus Adhesive Film Prevents Folding Damage and Bright Spots
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Solution Overview
Problem
Conventional adhesive layers in flexible display devices either fail to prevent damage to the cover window during folding or rolling, or result in visually noticeable bright spots due to impacts, necessitating a solution that balances modulus and bending stiffness to enhance durability and image quality.
Innovation Solution
An adhesive layer with varying modulus and bending stiffness across different areas, including a high modulus and high bending stiffness in one area to prevent damage and a low modulus and low bending stiffness in another area to prevent bright spots, formed as a single layer to simplify manufacturing and improve image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an adhesive layer with high modulus and high bending stiffness is used, then the cover window is protected from damage during folding, but bright spots occur due to impact on the display panel
Solution Approach 1:
The adhesive layer is designed with spatially varying mechanical properties: the first region (near cover window) has high modulus and high bending stiffness to protect against folding damage, while the second region (near display panel) has low modulus and low bending stiffness to prevent bright spots from impact. This local differentiation resolves the contradiction by providing different protective characteristics in different locations.
2Strength
If multiple adhesive layers are used to achieve varying modulus, then the mechanical properties can be optimized, but the manufacturing process becomes complex and interfaces cause light reflection
Solution Approach 1:
The adhesive layer is segmented into different regions with different mechanical properties within a single continuous layer. This segmentation is achieved through varying the polymerization conversion rate across the thickness direction, creating distinct functional zones (first region with high modulus, second region with low modulus) without requiring multiple separate adhesive layers, thus avoiding interface-related light reflection issues while maintaining manufacturing simplicity.
3Ease of manufacture
If a single adhesive layer is used, then manufacturing is simplified and light reflection is reduced, but it is difficult to achieve both high and low modulus regions
Solution Approach 1:
The invention changes the physical-chemical parameters of the adhesive layer by controlling the polymerization conversion rate at different positions. By using photoinitiators with different absorption characteristics and irradiating with light of different wavelengths, the polymerization conversion rate varies through the thickness direction, resulting in spatially varying modulus and bending stiffness within a single adhesive layer, thus achieving mechanical property differentiation while maintaining manufacturing simplicity.
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 cover window damage and bright spots, enhances durability, and simplifies manufacturing processes by eliminating interfaces between multiple layers, thereby improving the overall performance and image quality of flexible display devices.
Implementation Method 1
a first initiator for initiating a polymerization reaction of the resin with light having a first wavelength range without activating initiation of a polymerization reaction with light having a second wavelength range
Implementation Method 2
a second initiator for initiating a polymerization reaction of the resin with light having a second wavelength range without activating initiation of a polymerization reaction with light having a first wavelength range
Data Source
AI summary
A display device includes a display panel, a cover member disposed on the display panel, and an adhesive layer disposed between the display panel and the cover member. The adhesive layer has a first surface facing the cover member and a second surface facing the display panel, and includes a first area and a second area disposed at positions different from each other in a first direction from the first surface toward the second surface. A modulus of the first area is different from a modulus of the second area.