Polyester Film Crystallinity for Foldable Display Deformation

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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 stress, leading to deformation and appearance defects.

Innovation Solution

A polyester film with a coefficient of determination (R2) of 0.985 or more in the 2% to 3% strain range and crystallinity of 55% or more is developed, which maintains its characteristics under stress and prevents deformation upon repeated folding.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If a soft material polymer is used as a protective film to prevent deformation under stress, then the film shows good stress resistance, but it exhibits sticky characteristics that make process control difficult and creates gels resulting in heterogeneity

Engineering Contradiction:

Improvestress resistanceVSAvoidprocess control

Core Design Contradiction:

Stability of the object's compositionVSEase of manufacture

Solution Approach 1:

The patent changes the material parameters by selecting polyester (PET) with specific crystallinity (50-70%) and controlled molecular weight, transforming the material from soft and sticky to having optimal balance between flexibility and processability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite structure by laminating the polyester film with the cover window, forming a multi-layer composite that combines the scratch resistance of the cover window with the flexibility and stress resistance of the polyester film

Inventive Principle:

Principle #40Composite materials

2Stability of the object's composition

If the crystallinity of polyester film is increased to suppress deformation, then the film shows good dimensional stability, but it becomes difficult to achieve high flexibility required for foldable displays

Engineering Contradiction:

Improvedimensional stabilityVSAvoidflexibility

Core Design Contradiction:

Stability of the object's compositionVSAdaptability or versatility

Solution Approach 1:

The patent optimizes the crystallinity parameter to a specific range (50-70%), avoiding both too low (poor dimensional stability) and too high (reduced flexibility) extremes, achieving the optimal balance point for foldable display applications

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies partial crystallization rather than complete crystallization, maintaining 30-50% amorphous regions that provide flexibility while having 50-70% crystalline regions that provide dimensional stability

Inventive Principle:

Principle #16Partial or excessive action

3Adaptability or versatility

If a polyester film with high flexibility is used for foldable displays, then the film can be bent repeatedly, but dent marks are readily formed on the film due to foreign matter or external force

Engineering Contradiction:

ImproveflexibilityVSAvoidappearance quality

Core Design Contradiction:

Adaptability or versatilityVSShape

Solution Approach 1:

The patent adjusts the crystallinity parameter to 50-70%, which provides sufficient rigidity to resist dent mark formation while maintaining the flexibility needed for foldable displays, solving the appearance quality issue

Inventive Principle:

Principle #35Parameter changes

4Illumination intensity

If transparent polyimide is used as a cover window, then the film shows good transparency, but it is vulnerable to scratches from the outside

Engineering Contradiction:

ImprovetransparencyVSAvoidscratch resistance

Core Design Contradiction:

Illumination intensityVSStrength

Solution Approach 1:

The patent creates a composite structure where the transparent cover window maintains its transparency while the laminated polyester film provides scratch resistance, combining the advantages of both materials

Inventive Principle:

Principle #40Composite materials

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 achieves enhanced flexibility and resistance to external impacts, maintaining original appearance and functionality in flexible display devices, even after numerous folds, without delamination or dent marks.

Implementation Method 1

a film made of a polyester material such as polyethylene terephthalate (PET) has been considered as a protective film applied to a cover of a flexible display device. However, it is necessary to solve the problem of poor elastic restoring

Methodology Applied

Scientific EffectElastic restoring: Elasticity

Implementation Method 2

it has been discovered that the flexibility and appearance characteristics can the simultaneously enhanced by adjusting the strain with respect to stress and the crystallinity of a polyester film to specific ranges

Methodology Applied

Scientific EffectCrystallinity: Crystallisation

Data Source

PatentUS11630239B2Polyester film and flexible display apparatus comprising same

Publication Date: 2023.04.18 MICROWORKS CO LTD

AI summary

The polyester film according to an embodiment has a coefficient of determination (R2) of the strain with respect to stress and a crystallinity adjusted to specific ranges, whereby it is possible to achieve the flexibility that does not cause deformation even when a certain stress 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.