Multilayer Display Cover Window With Elastic Adhesive for Folding Strength
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Solution Overview
Problem
Developing a cover window for display devices that is both strong enough to protect against external impact and flexible enough for use in flexible display devices has proven difficult, as increasing flexibility reduces strength and vice versa.
Innovation Solution
A cover window design comprising multiple films and an elastic adhesive layer, where the films are made of materials like polyimide or polyetherimide, and the adhesive layer is made of ethylene vinyl acetate or polydimethylsiloxane, allowing for improved folding characteristics and hardness through stress reduction and repulsive properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the cover window uses a single thick film to increase strength, then protection strength is improved, but flexibility and foldability deteriorate
Solution Approach 1:
The cover window is divided into multiple thin films (first film, second film, third film, fourth film, and fifth film) instead of using a single thick film. Each film has a thickness of 5 μm to 60 μm, and they are stacked together to form the complete cover window structure. This segmentation allows the system to achieve both strength (through cumulative thickness) and flexibility (through the flexibility of individual thin films), resolving the contradiction between protection strength and flexibility.
Solution Approach 2:
The cover window uses a composite structure with multiple films made of different materials having different mechanical properties. The films include at least one of polyimide (PI), polyamide-imide (PAI), polyetheretherketone (PEEK), and polyetherimide (PEI). By combining materials with different characteristics, the cover window achieves both sufficient strength for protection and adequate flexibility for folding, resolving the contradiction between these two requirements.
2Adaptability or versatility
If the cover window uses a single thin film to improve flexibility, then foldability is improved, but strength and protection capability deteriorate
Solution Approach 1:
Instead of using a single thin film, the cover window segments the protective function across five separate thin films. Each film maintains thinness for flexibility while the cumulative effect of all films provides sufficient protection strength. This segmentation strategy allows the system to achieve both flexibility (from individual thin films) and strength (from the stacked configuration).
Solution Approach 2:
Multiple thin films are merged into a single integrated cover window structure through adhesive layers. The combination of these films creates a composite structure where the individual flexibility of each thin film is maintained while the collective strength of the stacked films provides adequate protection capability, resolving the contradiction between flexibility and strength.
3Stability of the object's composition
If the adhesive layer uses strong bonding material to improve film adhesion, then structural integrity is improved, but flexibility and stress reduction capability deteriorate
Solution Approach 1:
The adhesive layer uses materials with specific properties (ethylene vinyl acetate, polydimethylsiloxane, polyurethane, urethane, acryl, or silicon-based materials) and controls its thickness within a specific range (5 μm to 50 μm). By optimizing these parameters, the adhesive layer achieves sufficient bonding strength to hold the films together while maintaining flexibility and the ability to reduce stress during folding, resolving the contradiction between adhesion strength and flexibility.
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 achieves a folding number of 300,000 times or more with hardness equivalent to pencil hardness H, balancing strength and flexibility by using a layered structure with specific thickness and material ratios.
Implementation Method 1
an elastic adhesive layer disposed between the first film and the second film, a second adhesive layer disposed between the second film and the third film, a third adhesive layer disposed between the fourth film and the fifth film
Implementation Method 2
improved folding characteristics and hardness through stress reduction and repulsive properties
Data Source
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Figure 5
AI summary
An exemplary embodiment provides a cover window for a display device, including: a first film; a second film disposed on the first film; and an adhesive layer disposed between the first film and the second film, wherein the adhesive layer includes an elastic polymer, and wherein a ratio of a thickness of the second film to a thickness of the first film is in a range of 0.2 to 5.