Foldable Display Polyester Film Refractive Index Control
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Solution Overview
Problem
Conventional foldable displays suffer from image distortion and cracking at the folding portion due to deformation of protective films when repeatedly folded, making them unsuitable for mass production and practical use in mobile devices.
Innovation Solution
A foldable display using a polyester film with specific refractive index and density ranges, combined with a hard coating layer, is designed to minimize deformation and cracking, ensuring image quality and durability even after repeated folding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a flexible hard coating film is used to protect the foldable display surface, then surface protection is improved, but image distortion occurs at the folding portion after repeated folding
Solution Approach 1:
The patent applies different refractive index characteristics to different regions of the polyester film. Specifically, the film has a first refractive index in the bending direction (orthogonal to folding portion) and a second refractive index in the folding direction, with the ratio between them controlled within 0.95-1.05. This local differentiation of optical properties allows the film to maintain uniform thickness during folding while protecting the display surface, thereby preventing image distortion.
Solution Approach 2:
The patent changes the optical parameters of the polyester film by controlling its molecular orientation through biaxial stretching. The specific refractive index ratio (0.95-1.05) is achieved by adjusting stretching conditions, temperature, and time parameters during film production. This parameter control ensures the film maintains dimensional stability during repeated folding while providing surface protection.
2Stability of the object's composition
If the refractive index in the bending direction is decreased to reduce deformation, then folding deformation is reduced, but pencil hardness decreases and surface protection functionality is lowered
Solution Approach 1:
The patent optimizes the refractive index parameters within specific ranges: first refractive index 1.580-1.620 and second refractive index 1.650-1.700, with their ratio controlled at 0.95-1.05. This precise parameter control allows the film to achieve dimensional stability during folding while maintaining sufficient surface hardness for protection.
Solution Approach 2:
The patent uses a polyester film with controlled molecular orientation and specific refractive index characteristics as a composite protective layer. The film's anisotropic optical properties create a composite structure that provides both flexibility for folding and hardness for surface protection, resolving the contradiction between deformation reduction and surface protection.
3Strength
If a non-flexible glass material is used to protect the display, then surface protection is improved, but the display cannot be folded
Solution Approach 1:
The patent replaces rigid glass with a flexible polyester film that has specific optical properties (refractive index ratio 0.95-1.05). This thin film provides surface protection while allowing the display to be folded, enabling portability and versatility without sacrificing protective functionality.
Solution Approach 2:
The patent changes from rigid glass material to a polyester film with controlled refractive index parameters and molecular orientation. This material parameter change enables the protective layer to be flexible and foldable while maintaining surface protection capabilities through the film's inherent hardness and optical stability.
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 provides a foldable display that maintains image quality and durability, preventing cracks and distortion at the folding portion, thus enhancing the portability and functionality of mobile devices.
Implementation Method 1
the polyester film has a refractive index in the bending direction of 1.590 to 1.620, the polyester film has a refractive index in the direction of a folding portion of 1.670 to 1.700
Implementation Method 2
the film at that point deforms over time, causing image distortion on the display
Data Source
AI summary
Provided is a foldable display that is excellent in mass production applicability and unlikely to have image distortion at the folding portion of the display after repeated folding, as well as a mobile device equipped therewith. The foldable display contains a surface protection film and a polarizer. The surface protection film is composed of a polyester film, and the angle made by the slow axis of the polyester film with the absorption axis of the polarizer is 10 to 80°. The polyester film has a refractive index in the bending direction of 1.590 to 1.620, a refractive index in the direction of a folding portion of 1.670 to 1.700, a refractive index in the thickness direction of 1.520 or less, and a density of 1.380 g/cm3 or more, wherein the bending direction refers to a direction orthogonal to the folding portion of the polyester film to be folded.