Multi-Layer Flexible Cover Window with Nanoparticle-Polyurethane Complex
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Solution Overview
Problem
Existing cover windows for flexible display devices face challenges in achieving high surface hardness, rollability, and stress relief during folding or rolling, while maintaining excellent optical and resilient characteristics.
Innovation Solution
A cover window structure comprising a first layer with high tensile properties, a second layer for excellent restorability, and a third layer with a nanoparticle-polyurethane complex for enhanced surface hardness and slip resistance, all formed from polyurethane layers with specific moduli and molecular weights, ensuring flexibility and optical clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hard coating layer is applied to a polymer film to improve surface hardness, then surface hardness is improved, but the polymer film cannot relieve stress during rolling and folding
Solution Approach 1:
The cover window is divided into multiple layers with different moduli: a first layer with high modulus for surface hardness, a second layer with low modulus for stress relief during rolling and folding, and a third layer with high modulus for surface characteristics. This segmentation allows each layer to perform its specific function independently.
Solution Approach 2:
The patent uses a composite structure combining polymer materials with different mechanical properties. The first and third layers use polyurethane with specific moduli for hardness, while the second layer uses a different polymer material with lower modulus for flexibility and stress relief, creating a composite material system that achieves both hardness and rollability.
2Strength
If glass is used for the cover window to achieve excellent appearance characteristics, then appearance and surface hardness are improved, but foldability and rollability cannot be implemented
Solution Approach 1:
The patent replaces traditional rigid glass with flexible polymer film-based cover window structure. The thin film structure with multiple layers provides both the required surface hardness through the first and third layers and the flexibility for rolling and folding through the second layer, eliminating the need for rigid glass.
Solution Approach 2:
The composite polymer structure combines materials with different mechanical properties to achieve glass-like surface hardness while maintaining flexibility. The first layer provides hardness and appearance, the second layer provides flexibility, and the third layer enhances surface characteristics, creating a composite alternative to glass.
3Adaptability or versatility
If a single-layer polymer film is used for the cover window to achieve rollability, then foldability and rollability are improved, but surface hardness and resilient characteristics are insufficient
Solution Approach 1:
The single-layer polymer film is segmented into three distinct layers with different moduli. The first layer (high modulus) provides surface hardness, the second layer (low modulus) provides rollability and stress relief, and the third layer (high modulus) provides surface characteristics and resilience. This segmentation allows the cover window to achieve both rollability and surface hardness simultaneously.
Solution Approach 2:
The patent creates a composite multi-layer structure where each layer is made of polymer materials with specific mechanical properties. The combination of high-modulus and low-modulus polymer layers creates a composite material system that exhibits both flexibility for rolling and surface hardness, overcoming the limitations of single-layer polymer films.
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 solution effectively alleviates stress during folding or rolling, maintains excellent surface characteristics, and provides high surface hardness and optical clarity, making the cover window suitable for foldable and rollable flexible display devices.
Implementation Method 1
a third layer disposed on the second layer and having a third modulus equal to or larger than the first modulus, and in which the third layer includes a nanoparticle-polyurethane complex in which polyurethane is bonded with nanoparticles by a covalent bond
Implementation Method 2
a cover window which has a high surface hardness, an excellent rollability, excellent restorability against the pressing, and an excellent optical characteristic
Data Source
AI summary
A cover window includes a first layer having a first modulus, a second layer disposed on the first layer and having a second modulus smaller than the first modulus, and a third layer disposed on the second layer and having a third modulus equal to or larger than the first modulus, and in which the third layer includes a nanoparticle-polyurethane complex in which polyurethane is bonded with nanoparticles by a covalent bond. Therefore, the cover window of the present disclosure provides effects that the folding and rolling are possible with excellent surface characteristic and the restorability against the pressing and excellent optical property. A flexible display device may include the cover window.