Polyester Film Composition for Foldable Display Crease Stability
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Solution Overview
Problem
Conventional polyester films for foldable displays suffer from image distortion and deformation at the folding portion due to repeated folding, especially in high temperature ranges, and are not suitable for mass production.
Innovation Solution
A polyester film with a thickness of 10 μm to 125 μm, high-temperature hold angle of 70° or more, density of 1.349 g/cm³ or more, and composed primarily of polyethylene naphthalate, optionally with an easy-to-adhere layer, is used to prevent deformation and image distortion in foldable displays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a flexible hard coating film is used to protect the foldable display surface, then the display can be protected during repeated folding, but the film deforms over time causing image distortion
Solution Approach 1:
The invention changes the physical parameters of the polyester film by controlling its thickness (10-125 μm) and adjusting its refractive index in the bending direction. These parameter changes enable the film to maintain structural integrity during repeated folding while preventing image distortion, thus resolving the contradiction between protection durability and image quality.
Solution Approach 2:
The invention uses a composite structure consisting of a polyester film base layer and an optional easy-to-adhere layer. This composite material configuration provides both the flexibility needed for repeated folding and the stability required to prevent deformation and image distortion, addressing the reliability-precision contradiction.
2Manufacturing precision
If the film thickness is partially altered to reduce deformation, then image distortion can be reduced, but the production process becomes complicated
Solution Approach 1:
Instead of partially altering film thickness through complex processing steps, the invention uniformly controls the film thickness within a specific range (10-125 μm) and adjusts the refractive index parameter. This approach achieves deformation reduction while maintaining a simple, mass-production-friendly manufacturing process.
3Adaptability or versatility
If polyethylene terephthalate-based film is used, then the film can be used in general applications, but it cannot provide sufficient reliability in high temperature ranges
Solution Approach 1:
The invention changes the material composition parameter by using polyethylene naphthalate instead of polyethylene terephthalate. This material substitution provides both the versatility needed for various applications and the enhanced thermal stability required for high-temperature reliability, resolving the adaptability-reliability contradiction.
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 polyester film maintains its structural integrity and prevents image distortion even after repeated folding in high temperatures, enabling mass production of foldable displays with improved portability and functionality.
Implementation Method 1
the polyester film having a thickness of 10 μm or more and 125 μm or less and a high-temperature hold angle in a bending direction of 70° or more
Data Source
AI summary
In order to provide a foldable display that is suitable for mass production and that has no risk of image distortion at its folding portion after the display is repeatedly folded, the invention provides a polyester film for foldable displays in which no cracks occurs in the folding portion. In particular, the invention provides a polyester film for a foldable display, the film having a thickness of 10-125 μm and a high-temperature hold angle in a bending direction of 70° or more, wherein the high-temperature hold angle refers to an angle of a crease formed after fixing the film at a heating temperature of 85° C. for 18 hours in such a manner that a strain of 1.7% is applied to both surfaces of a bent portion of the film, and the bending direction refers to a direction that is orthogonal to a folding portion.