Anisotropic Polyester Film for Foldable Display Protection
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Solution Overview
Problem
Foldable displays face issues with image distortion and cracking at folding portions due to deformation of protective films, which affects mass productivity and portability, and existing solutions either compromise on image quality or are not suitable for mass production.
Innovation Solution
A polyester film with specific refractive index ranges (1.590-1.620 in the bending direction, 1.670-1.700 in the folding direction, and 1.520 or less in the thickness direction, along with an elastic modulus of 2.7 GPa or less in the bending direction and 4.5 GPa or more in the folding direction, is used to create a laminated film with an adhesive and hard coating layer, ensuring no cracks or deformation upon repeated folding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a non-flexible protective film is used, then the display surface is well protected, but the display cannot be folded
Solution Approach 1:
The patent applies a flexible polyester film instead of a rigid glass or non-flexible protective layer. The film is stretched in specific directions to achieve controlled optical anisotropy while maintaining flexibility for folding. This resolves the contradiction by providing both protection and foldability through the selection and treatment of a flexible polymer film.
Solution Approach 2:
The patent changes the physical parameters of the polyester film by controlling its refractive index in specific directions through stretching treatment. By adjusting the refractive index ratio between the stretching direction and perpendicular direction to fall within 1.03-1.06, the film achieves the desired balance between flexibility for folding and optical quality for display protection.
2Adaptability or versatility
If the film is repeatedly folded, then portability is improved, but image distortion occurs due to film deformation
Solution Approach 1:
The patent controls the refractive index parameters of the polyester film through stretching treatment. By maintaining the refractive index ratio between the stretching direction and perpendicular direction within 1.03-1.06, and controlling the absolute refractive index in the stretching direction to be 1.50-1.60, the film minimizes optical distortion during repeated folding while maintaining portability.
Solution Approach 2:
The patent applies stretching treatment to the polyester film during manufacturing to pre-establish the desired molecular orientation and refractive index distribution. This preliminary action ensures that the film is pre-conditioned to resist deformation and optical distortion during subsequent repeated folding operations by the user.
3Reliability
If the refractive index in the bending direction is decreased to reduce deformation, then folding durability is improved, but pencil hardness reduces compromising surface protection
Solution Approach 1:
The patent creates different optical and mechanical properties in different directions of the film. By controlling the refractive index specifically in the stretching direction relative to the perpendicular direction, the film achieves direction-dependent properties: lower refractive index in the bending direction for flexibility and durability, while maintaining sufficient hardness for surface protection through the overall film structure and composition.
Solution Approach 2:
The patent uses a polyester film with specific compositional and structural characteristics that combine flexibility and hardness. The film's composite structure, achieved through stretching treatment and controlled molecular orientation, allows it to exhibit both low refractive index for flexibility and sufficient pencil hardness for surface protection.
4Reliability
If uniaxial orientation in the folding direction is enhanced to reduce cracking, then folding reliability is improved, but image quality deteriorates due to excessive deformation
Solution Approach 1:
The patent precisely controls the refractive index parameters by adjusting the stretching ratio and treatment conditions. By maintaining the refractive index ratio between stretching and perpendicular directions within 1.03-1.06 and the absolute refractive index in the stretching direction within 1.50-1.60, the film achieves balanced molecular orientation that prevents cracking while avoiding excessive deformation that would degrade image quality.
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 maintains mass productivity, prevents image distortion, and enhances the portability and functionality of foldable displays by ensuring a crack-free and deformation-free folding mechanism, providing a beautiful image and improved convenience.
Implementation Method 1
a refractive index in a bending direction is from 1.590 to 1.620; a refractive index in a folding portion direction is from 1.670 to 1.700; and a refractive index in a thickness direction is 1.520 or less
Data Source
AI summary
Provided are a polyester film, a laminated film, and the like for protecting an organic EL module of a foldable display each of which is free of occurrence of a crack at a folding portion thereof, in order to provide a foldable display excellent in mass productivity, and free of a risk of causing distortion in an image displayed at a folding portion thereof after being repeatedly folded. The polyester film for protecting an organic EL module of a foldable display satisfies the following conditions: (1) a refractive index in a bending direction is from 1.590 to 1.620; (2) a refractive index in a folding portion direction is from 1.670 to 1.700; (3) a refractive index in a thickness direction is 1.520 or less; and (4) a density is 1.380 g/cm3 or more, wherein the bending direction refers to a direction orthogonal to a folding portion of the polyester film at a time when the polyester film is folded.