Polyester Film Crystallinity Control for Foldable Display Durability
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Solution Overview
Problem
Polyester films used in flexible display devices face challenges in maintaining flexibility and appearance characteristics, particularly when subjected to repeated folding and external pressures, leading to deformation and appearance defects.
Innovation Solution
A polyester film with a final tensile rate of 3% or less and crystallinity of 55% or more is developed, which maintains its properties even under sustained loads and external pressures, preventing deformation and maintaining transparency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a soft material polymer is used as a protective film to prevent deformation under load, then the film can withstand external pressure, but it exhibits sticky characteristics that make process control difficult and creates gels resulting in heterogeneity
Solution Approach 1:
The patent changes the material parameters by switching from soft material polymers to polyester materials with specifically controlled crystallinity (40-70%) and tensile properties. This parameter adjustment maintains deformation resistance while eliminating the sticky characteristics and gel formation that plagued soft material polymers.
Solution Approach 2:
The patent employs composite material characteristics by creating a polyester film with controlled crystalline and amorphous phases. The specific crystallinity range (40-70%) creates a composite structure that combines the rigidity needed for load resistance with the processability of semi-crystalline polymers, avoiding the extremes of fully crystalline or amorphous structures.
2Adaptability or versatility
If a polyester film is modified to increase flexibility for foldable displays, then the film can be bent and folded, but dent marks are readily formed due to foreign matter or external force
Solution Approach 1:
The patent optimizes the crystallinity parameter to a specific range (40-70%) that balances flexibility and dent resistance. Within this range, the film achieves sufficient flexibility for folding applications while the crystalline structure provides resistance to dent mark formation from external forces or foreign matter.
Solution Approach 2:
The patent utilizes the natural curvature and elastic recovery properties of the polyester film structure. The controlled crystallinity enables the film to bend into curved shapes during folding while maintaining its structural integrity and recovering from deformation, preventing permanent dent marks.
3Stability of the object's composition
If a polymer film with high crystallinity is used to reduce deformation, then the film maintains its shape under load, but it becomes difficult to prepare thin films and the material is readily deformed by external impact
Solution Approach 1:
The patent identifies and controls the crystallinity parameter within the optimal range of 40-70%. This specific range provides the right balance: enough crystalline structure to maintain shape stability under sustained load, but sufficient amorphous content to provide toughness and resistance to external impact forces.
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 film effectively suppresses deformation and maintains original characteristics during repeated folding, preventing deterioration and ensuring a flawless appearance, making it suitable for flexible display devices.
Implementation Method 1
having a crystallinity of 40% or more
Implementation Method 2
a final tensile rate of 5% or less when a load of N1% is applied for 1 hour
Data Source
AI summary
In the polyester film according to an embodiment, the strain with respect to tensile load and the crystallinity are adjusted to specific ranges, whereby it is possible to achieve the flexibility that does not cause deformation even when a certain load is sustained for a long period of time and the resistant characteristics to the impact of external pressing. Accordingly, the polyester film can be applied to a cover of a flexible display device, in particular, a foldable display device to exhibit excellent characteristics.