Variable Thickness Hard Coating for Flexible Display Cover Windows
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Solution Overview
Problem
Flexible display devices face challenges in folding and portability due to the high bending stiffness of their cover windows, which are difficult to fold and require complex manufacturing processes.
Innovation Solution
A cover window design with a base substrate and two hard coating layers of varying thicknesses, where the second hard coating layer has convex or concave patterns along the folding axis, reducing the thickness and bending stiffness of the in/out-folding areas to facilitate easy folding while maintaining sufficient hardness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the cover window uses a uniform thick hard coating layer, then the hardness and durability are improved, but the bending stiffness increases making folding difficult
Solution Approach 1:
The patent applies different thicknesses of the second hard coating layer to different functional areas of the cover window. The folding area has a thinner second hard coating layer (first thickness) to reduce bending stiffness and enable easy folding, while the non-folding area has a thicker second hard coating layer (second thickness) to maintain high hardness and durability. This local differentiation resolves the contradiction between hardness and folding ease.
2Ease of operation
If the cover window is made thinner to facilitate folding, then the flexibility is improved, but the hardness and protective capability deteriorate
Solution Approach 1:
The patent uses a dual-layer hard coating structure where the first hard coating layer has uniform thickness across the entire cover window to provide baseline hardness and protection. The second hard coating layer has variable thickness - thinner in folding areas for flexibility and thicker in non-folding areas for enhanced hardness. This local quality differentiation allows the cover window to achieve both folding flexibility and adequate hardness protection simultaneously.
3Strength
If the cover window has high bending stiffness, then the structural strength is improved, but the manufacturing complexity increases due to difficult folding
Solution Approach 1:
The patent reduces manufacturing complexity by making the folding area thinner through reduced second hard coating layer thickness, which enables easier folding and bending during assembly. The non-folding area maintains thicker coating for structural strength. This local differentiation allows the cover window to achieve both structural strength and ease of manufacturing/folding.
Data Source
Figure 1A~1B
Figure 2A
Figure 2B
AI summary
A cover window of a flexible display device includes a base substrate including an out-folding area, an in-folding area, and peripheral areas disposed on opposing sides of at least one of the out-folding area and the in-folding area, a first hard coating layer at a top surface of the base substrate, the first hard coating layer having a substantially uniform thickness, and a second hard coating layer at a bottom surface of the base substrate opposite to the top surface, the second hard coating layer having a thickness different from the thickness of the first hard coating layer. A thickness of a first area of the second hard coating layer that overlaps with the out-folding area and the in-folding area of the base substrate is less than a thickness of a second area of the second hard coating layer that overlaps with the peripheral areas of the base substrate.