Hard Coating Film for Flexible Displays
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Solution Overview
Problem
Current hard coating films for flexible displays face challenges in achieving both mechanical and optical properties comparable to tempered glass, with issues such as insufficient hardness, scratch resistance, and flexibility, while also being heavy and prone to external shock.
Innovation Solution
A hard coating film comprising a polyamideimide substrate layer with a refractive index of 1.51 to 1.57 and a hard coating layer with a refractive index of 1.49 to 1.54, where the substrate layer has a tensile modulus of 3 to 7 GPa, and the hard coating layer is formed from an epoxysilane resin, reducing the refractive index difference between layers to minimize interference fringes and enhance mechanical and optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If tempered glass is used as a window cover for display protection, then scratch resistance and strength are improved, but weight increases and flexibility is lost
Solution Approach 1:
The patent replaces rigid tempered glass with a flexible plastic substrate (polyimide, polyethylene naphthalate, or polyethylene terephthalate) that can bend and flex. This flexible substrate is then coated with a hard coating layer to provide the necessary scratch resistance and strength, thereby achieving glass-like protection without the weight and rigidity limitations of tempered glass.
Solution Approach 2:
The patent creates a composite structure consisting of a flexible plastic substrate combined with a hard coating layer. The substrate provides flexibility and light weight, while the coating layer (comprising specific resins and inorganic particles) provides hardness and scratch resistance. This composite approach allows simultaneous achievement of both flexibility and strength that cannot be obtained with a single material.
2Strength
If a hard coating layer is applied on a plastic substrate to improve scratch resistance, then hardness is improved, but curling occurs due to shrinkage during curing
Solution Approach 1:
The patent carefully controls the refractive index of the hard coating layer to be within 0.05 of the substrate's refractive index. This parameter control prevents optical interference fringes and reduces internal stress that would cause curling. Additionally, the curing conditions and composition ratios are optimized to minimize shrinkage during the curing process, thereby preventing curling while maintaining hardness.
Solution Approach 2:
The patent ensures optical homogeneity between the substrate and the hard coating layer by matching their refractive indices. This homogeneity prevents optical defects such as interference fringes and reduces differential stress that could lead to curling. The uniform optical properties indicate uniform physical and chemical properties throughout the composite structure, promoting stability.
3Adaptability or versatility
If polymer plastic substrates are used to achieve flexibility, then flexibility is improved, but hardness and scratch resistance become insufficient
Solution Approach 1:
The patent creates a composite structure where a flexible polymer plastic substrate (providing flexibility and adaptability) is combined with a hard coating layer (providing hardness and scratch resistance). The coating layer contains specific resins and 5-50 wt% inorganic particles with particle sizes of 0.1-5 μm, creating a composite material that exhibits both the flexibility of the polymer substrate and the hardness of the inorganic-filled coating.
Solution Approach 2:
The patent applies different material properties to different layers of the structure. The substrate layer maintains uniform flexibility throughout, while the coating layer provides localized hardness and scratch resistance on the surface. This spatial differentiation of material properties allows the structure to exhibit both flexibility (from the substrate) and hardness (from the coating) simultaneously.
4Ease of manufacture
If general hard coating composition is used, then ease of manufacture is improved, but flexibility and hardness performance are insufficient
Solution Approach 1:
The patent specifies precise parameter ranges for the hard coating composition, including 5-50 wt% inorganic particles with particle sizes of 0.1-5 μm, and specific resin combinations (epoxy resin, polyurethane resin, or silane-modified polyester resin). These controlled parameters ensure both flexibility and adequate hardness while maintaining ease of manufacture through conventional coating and curing processes.
Solution Approach 2:
The patent uses homogeneous resin systems (epoxy, polyurethane, or silane-modified polyester) that provide uniform curing and consistent mechanical properties throughout the coating layer. This homogeneity ensures flexible curing processes and uniform performance, making the coating easy to manufacture while achieving the desired flexibility and hardness balance.
Data Source
AI summary
Provided is a hard coating film including a polyamideimide substrate layer and a hard coating layer, each of which has a predetermined refractive index, with a difference in the refractive index between those layers being 0.05. The substrate layer has a tensile modulus of 3 to 7 GPa, at a thickness of 80 μm, as measured according to ASTM D111. The present invention relates to a hard coating film having improved mechanical and optical properties.