Foldable Cover Window Lamination for Hardness and Flexibility
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Solution Overview
Problem
Existing display devices face challenges in achieving a balance between strength and flexibility for their cover windows, which are often compromised due to their trade-off relationship, especially with the integration of touch panels and the need for protection against external impacts.
Innovation Solution
A cover window configuration comprising multiple films and adhesive layers with specific modulus, storage, and loss modulus ranges, along with varying adherence and thickness, to enhance folding and bending capabilities while maintaining high surface hardness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the cover window is made stronger to protect against external impacts and provide high surface hardness, then protection strength is improved, but flexibility and foldability deteriorate
Solution Approach 1:
The cover window uses a composite structure consisting of multiple films (first film, second film, third film) with different material properties. The first and third films provide strength and hardness, while the second film provides flexibility and foldability. This composite approach allows the cover window to simultaneously achieve both protection strength and flexibility, resolving the trade-off between these two properties.
Solution Approach 2:
Different regions of the cover window have different functional properties assigned to them. The first film layer provides hardness and scratch resistance at the surface, while the second film layer provides flexibility and bendability in the bulk. This local differentiation of material properties allows the cover window to exhibit both strong protection and flexibility where needed.
2Strength
If the adhesive layer has higher adherence strength to ensure durable bonding, then bonding strength is improved, but flexibility and resistance to delamination during folding deteriorate
Solution Approach 1:
The adhesive layer's properties are precisely controlled within specific ranges: lap shear modulus of 20-50 kPa, storage modulus of 100-10 MPa, loss modulus of 100-10 MPa, and adherence of 500-3000 gf. By optimizing these parameters, the adhesive provides sufficient bonding strength while maintaining flexibility to withstand repeated folding without delamination. The specific modulus ranges ensure the adhesive remains flexible during bending while maintaining adequate adherence.
3Adaptability or versatility
If the cover window is made more flexible to enable folding and bending, then adaptability is improved, but surface hardness and scratch resistance deteriorate
Solution Approach 1:
The multi-film composite structure allows the cover window to achieve both flexibility and surface hardness. The first film provides a hard, scratch-resistant surface layer, while the second film provides flexibility and bendability. This composite approach enables the cover window to be folded and bent without compromising surface hardness or scratch resistance.
Solution Approach 2:
The surface layer (first film) is designed with different properties than the bulk material (second film). The surface layer provides hardness and scratch resistance, while the bulk material provides flexibility and foldability. This local differentiation of material properties resolves the contradiction between surface hardness 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 proposed cover window design significantly improves folding durability and hardness, allowing for up to 200,000 folds without damage and maintaining pencil hardness, while also providing scratch resistance and protection against external impacts.
Implementation Method 1
an adhesive layer between the first film and the second film
Data Source
AI summary
A cover window for a display device includes: a first film; a second film on the first film; and an adhesive layer between the first film and the second film. The adhesive layer has a lap shear modulus in a range of 20 kPa to 50 kPa.