Flexible Display Cover Window Hard Coating Balance
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Solution Overview
Problem
Current materials for flexible display devices, such as glass, are prone to breakage and weight issues, while plastic resin alternatives face challenges in achieving both flexibility and high hardness, leading to difficulties in producing thin films with sufficient durability for bendable or foldable devices.
Innovation Solution
A cover window for flexible display devices is developed, featuring a light-transmitting substrate with a first hard coating layer having an IR spectra ratio of amide C═O to ester C═O peak of 0.8 or less and a second hard coating layer with a ratio greater than 0.8, providing a balance of flexibility and high hardness, preventing damage from repetitive bending or folding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If glass is used as a cover plate for flexible display, then high hardness and breakage resistance are achieved, but weight increases and the material cannot accommodate bending or flexible warping
Solution Approach 1:
The patent changes the material parameters by transitioning from glass to plastic resin with specific molecular weight ranges (10,000 to 200,000) and controlled gel fraction (5 to 50%), achieving a balance between hardness and flexibility that allows both high strength and weight reduction for flexible displays
Solution Approach 2:
The patent creates a composite material system combining plastic resin base polymer with specific additives and crosslinking agents, forming a multi-component composition that achieves glass-level hardness while maintaining the flexibility and light weight necessary for bendable display applications
2Weight of moving object
If plastic resin is used as a substitute for glass, then weight is reduced and flexibility is improved, but achieving glass-level hardness is difficult
Solution Approach 1:
The patent achieves glass-level hardness by precisely controlling polymer parameters including weight average molecular weight (10,000 to 200,000) and gel fraction (5 to 50%), transforming plastic resin from a soft material into a hard, durable coating that maintains flexibility while achieving comparable hardness to glass
Solution Approach 2:
The patent employs a thin film structure of plastic resin coating that provides both the weight reduction and flexibility advantages of polymers while achieving glass-level hardness through controlled crosslinking and molecular weight optimization, creating a multi-functional protective layer
3Strength
If the thickness of the hard coating layer is increased to ensure surface hardness, then hardness is improved, but wrinkles, curls, cracking and peeling occur due to curing shrinkage
Solution Approach 1:
The patent optimizes the coating thickness to a specific range (1 to 20 μm) and controls the molecular weight and gel fraction of the polymer to balance curing shrinkage and mechanical properties, achieving high surface hardness while preventing wrinkles, curls, cracking and peeling through precise parameter control
Solution Approach 2:
The patent applies a thin coating layer that is sufficient to provide the required hardness and protective function without excessive thickness, thereby avoiding the negative effects of curing shrinkage such as wrinkles and curls while still achieving the desired surface hardness
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 achieves high durability and resistance to cracking, maintaining high hardness and flexibility, allowing the cover window to be applied to bendable, flexible, or foldable devices without breaking under external pressure, with excellent optical and mechanical properties.
Implementation Method 1
the first hard coating layer has IR spectra in which a ratio of the amide C═O peak to the ester C═O peak is 0.8 or less, and wherein the second hard coating layer has IR spectra in which a ratio of the amide C═O peak to the ester C═O peak is greater than 0.8
Data Source
AI summary
The present disclosure relates to a cover window for a flexible display device comprising: a light-transmitting substrate; and a first hard coating layer and a second hard coating layer which are formed on both sides of the light-transmitting substrate, respectively, wherein each of the first hard coating layer and the second hard coating layer has IR spectra in which a ratio of the amide C═O peak to the ester C═O peak is in a predetermined range, and a flexible display device including the cover window for a flexible display device.