Thin Protective Display Film With Cross-Linked Polyurethane
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Solution Overview
Problem
Flexible display technologies face challenges in maintaining optical properties and scratch resistance while withstanding repeated folding without visible damage, especially around tight bend radii, as existing hard coated films often fail to endure such stress.
Innovation Solution
A display film comprising a transparent polymeric substrate with a high yield stress and a thin, optically clear aliphatic cross-linked polyurethane layer, which provides enhanced scratch resistance and recovery properties, maintaining optical clarity and transparency even after extensive bending cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If hard coated plastic substrates or hard coated colorless transparent polyimide films are used to provide scratch resistance, then scratch resistance is improved, but the film fails to withstand folding events around a tight bend radius without showing visible damage
Solution Approach 1:
The patent uses a composite structure consisting of a polyimide substrate layer combined with a cross-linked polyurethane top coat layer. This composite material approach allows the substrate to provide flexibility and tensile strength for withstanding folding, while the cross-linked polyurethane top coat provides the required scratch resistance and surface hardness, thus resolving the contradiction between scratch resistance and fold durability
Solution Approach 2:
The patent modifies the chemical and physical parameters of the polyurethane layer by implementing cross-linking through isocyanate groups reacting with hydroxyl groups. This cross-linking creates a three-dimensional network structure that significantly enhances scratch resistance and surface durability while maintaining the flexibility needed for tight bending, thereby resolving the contradiction between hardness and flexibility
2Strength
If a thick protective layer is used to provide scratch resistance, then scratch resistance is improved, but optical clarity and transparency are reduced
Solution Approach 1:
The patent employs a thin film approach with the cross-linked polyurethane top coat applied at a controlled thickness of approximately 1-10 micrometers. This thin film provides sufficient scratch resistance through cross-linking density rather than thickness, maintaining excellent optical clarity and transparency while protecting the display surface
Solution Approach 2:
The patent changes the structural parameters of the polyurethane layer by implementing cross-linking, which increases the network density and surface hardness. This allows the layer to achieve high scratch resistance at very thin thicknesses (1-10 micrometers), thus maintaining optical clarity while providing adequate protection
3Adaptability or versatility
If a tight bend radius is used to enable flexible display design, then device flexibility is improved, but the film shows visible damage after folding cycles
Solution Approach 1:
The patent uses a composite structure where the polyimide substrate provides excellent flexibility and tensile strength to accommodate tight bending (5 mm radius), while the cross-linked polyurethane top coat maintains surface integrity and prevents visible damage during repeated folding cycles, thus resolving the contradiction between flexibility and durability
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 enables the display film to withstand at least 100,000 folding cycles around a 3 mm radius without failure, maintaining optical properties and providing superior scratch resistance, while being thin enough to balance protection and design requirements.
Implementation Method 1
The transparent aliphatic cross-linked polyurethane layer has a glass transition temperature in a range from 11 to 27 degrees Celsius and a Tan Delta peak value in a range from 0.5 to 2.5
Implementation Method 2
The display film remains intact after at least 100,000 bending cycles about a 3 mm radius
Implementation Method 3
The transparent aliphatic cross-linked polyurethane layer has a glass transition temperature in a range from 11 to 27 degrees Celsius
Data Source
AI summary
A display film includes a transparent polymeric substrate layer having a 0.2% offset yield stress greater than 110 MPa and a transparent aliphatic cross-linked polyurethane layer having a thickness of 100 micrometers or less disposed on the transparent polymeric substrate layer. The transparent aliphatic cross-linked polyurethane layer has a glass transition temperature in a range from 11 to 27 degrees Celsius and a Tan Delta peak value in a range from 0.5 to 2.5. The display film has a haze value of 2% or less.