Surface Protective Film for Foldable Displays
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Solution Overview
Problem
Current surface protective films for foldable display apparatus lack flexibility and impact resistance, and often exhibit poor appearance due to gel formation and visible stripe patterns, making them unsuitable for large-screen displays with high resolution.
Innovation Solution
A surface protective film with a tri-layer structure comprising a hard coating layer, a base layer, and an adhesive layer, where the laminate of the hard coating layer and base layer has specific storage moduli at varying temperatures, and the base layer is formed using a cast polyurethane film or other materials like polyimide or polyethylene terephthalate, ensuring improved impact resistance, folding reliability, and appearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a thermoplastic polyurethane film is used as the base layer, then flexibility is improved, but appearance deteriorates due to gel formation and visible stripe patterns
Solution Approach 1:
The patent changes the material parameters of the base layer from thermoplastic polyurethane to cast polyurethane, polyimide, or polyethylene terephthalate. This material substitution eliminates gel formation and stripe patterns while preserving the required flexibility through proper selection of film thickness (75-200 μm) and material properties.
Solution Approach 2:
The patent employs a composite multi-layer structure consisting of a hard coating layer, base layer, and adhesive layer. This composite structure combines the advantages of different materials: the hard coating layer provides protection and optical clarity, while the base layer maintains flexibility without appearance defects, and the adhesive layer ensures proper bonding.
2Strength
If an adhesive layer is added to attach the surface protective film to the optical element, then adhesion is improved, but impact resistance becomes variable and unreliable
Solution Approach 1:
The patent optimizes the adhesive layer's storage modulus parameters at different temperatures to ensure both adhesion and impact resistance. By controlling the adhesive layer to have a storage modulus of about 10 kPa to about 500 kPa at -20°C and about 10 kPa to about 500 kPa at 60°C, the film achieves reliable impact resistance while maintaining proper adhesion to the optical element.
3Measurement precision
If the screen size is maximized and high screen resolution is required, then display quality is improved, but appearance defects become more easily identified
Solution Approach 1:
The patent changes the base layer material from thermoplastic polyurethane to cast polyurethane, polyimide, or polyethylene terephthalate, which do not exhibit gel formation or stripe patterns. This material substitution ensures that even on large screens with high resolution where defects would be more visible, the appearance remains clear and defect-free.
4Strength
If a film composed only of base layer and hard coating layer is used, then impact resistance is good, but flexibility is poor and it cannot be applied to foldable display apparatus
Solution Approach 1:
The patent creates a composite three-layer structure where the base layer (75-200 μm thick) provides flexibility, the adhesive layer enables proper bonding, and the hard coating layer provides impact resistance. This composite structure achieves both flexibility for foldable displays and impact resistance through the synergistic combination of layers with optimized properties.
Data Source
AI summary
A surface protective film, an optical member including the same, and a display apparatus including the same are provided. A surface protective film includes: a hard coating layer, a base layer, and an adhesive layer sequentially stacked in the stated order, and a laminate of the hard coating layer and the base layer may have a storage modulus of about 900 MPa to about 1500 MPa at −20° C. and a storage modulus of about 15 MPa to about 100 MPa at 85° C.