Polyester Film with Coating for Foldable Display Light Transmission
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Solution Overview
Problem
Existing protective films for display devices, particularly foldable displays, face challenges in maintaining visibility and durability while preventing delamination and cracks under tensile loads, and they often compromise on light transmission and fingerprint recognition rates due to thickness variations and material limitations.
Innovation Solution
A polyester-based film with a base layer and a coating layer, designed to have a light passage of 91% or more and total transmittance of 92% or more for visible light, along with specific tensile properties to ensure flexibility and resistance to external loads, is developed. The film is prepared through a process involving melt-extrusion, stretching, and heat-setting to achieve the desired optical and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of protective film is increased to enhance durability and scratch resistance, then strength is improved, but light transmission and visibility are reduced
Solution Approach 1:
The patent uses a composite structure consisting of a polyimide base film and a silicon oxide coating layer. The polyimide provides mechanical strength and flexibility, while the silicon oxide layer enhances scratch resistance and surface hardness. This composite approach allows achieving high durability without increasing overall thickness excessively, thereby maintaining good light transmission properties.
2Reliability
If the thickness of protective film is increased to prevent delamination and cracks under tensile loads, then reliability is improved, but light transmission and visibility are reduced
Solution Approach 1:
The silicon oxide coating layer bonded to the polyimide base film creates a composite structure where the coating layer prevents delamination and crack propagation under tensile loads during folding, while the thin overall structure maintains excellent light transmission.
Solution Approach 2:
The patent employs a thin film structure (overall thickness controlled to maintain flexibility) that can undergo repeated folding without cracking. The silicon oxide layer provides surface protection while the thin polyimide substrate ensures flexibility and light transmission, resolving the contradiction between reliability under tensile load and optical properties.
3Reliability
If in-plane retardation is lowered to enhance fingerprint recognition rate, then visibility is improved, but manufacturing precision requirements increase and productivity decreases
Solution Approach 1:
The patent controls the in-plane retardation parameter of the polyimide film to be 25 nm or less by adjusting the stretching conditions and film orientation during manufacturing. This parameter control achieves excellent fingerprint recognition rates while using established manufacturing processes, avoiding the need for highly complex or slow production methods.
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 provides excellent visibility, durability, and enhanced fingerprint recognition rates by maintaining light transmission and flexibility, while preventing delamination and cracks even under repeated folding, thus addressing the limitations of existing films.
Implementation Method 1
the light passage according to the following Relationship 1 is 91% or more, or the total transmittance for light of 380 nm to 780 nm is 92% or more
Implementation Method 2
a coating layer on at least one side of the base layer
Data Source
AI summary
A polyester-based film having excellent scratch resistance, durability, transparency, and visibility and a process for preparing the same. The polyester-based film comprises a base layer and a coating layer on at least one side of the base layer. The light passage according to Relationship 1 is 91% or more, or the total transmittance for light of 380 nm to 780 nm is 92% or more, it has excellent optical properties, durability, visibility, and reliability. Thus, it can be applied to display devices such as smartphones, tablet PCs, and laptops. In addition, in the polyester-based film according to an embodiment, the strain with respect to tensile load satisfies a specific range, whereby it is possible to achieve the flexibility that hardly causes deformation even when a certain load is maintained for a long period of time. Thus, it can be applied to flexible display devices, particularly, foldable display devices.