Flexible Display Cover Substrate Yellow Index Reduction
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Solution Overview
Problem
Flexible display cover substrates face issues with abrasion, scratches, optical color shift, and increased yellow index due to thickness, affecting bending performance and light emission, particularly with polyimide films and existing optical-grade plastics.
Innovation Solution
A flexible display cover substrate comprising a transparent polyimide film with a hard coating layer made of reactive functional group compounds, an initiator, an elastic oligomer, nano inorganic modified particles, and a fluorescent pigment, which maintains high light transmittance and flexibility while reducing the yellow index without affecting visual color.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of transparent polyimide film is increased, then bending performance and mechanical strength are improved, but yellow index YI increases affecting display appearance
Solution Approach 1:
The patent applies color compensation by adding a blue pigment to the hard coating layer to counteract the yellow index YI increase caused by thick polyimide film. The blue pigment absorbs yellow light wavelengths, creating a visual balance that maintains display appearance quality while allowing necessary film thickness for mechanical strength.
Solution Approach 2:
The patent creates a composite hard coating layer combining polyimide resin with blue pigment particles. This composite structure allows the coating to simultaneously provide mechanical protection and optical color compensation, resolving the conflict between thickness-related strength and yellow index increase.
2Object-generated harmful factors
If blue pigment is added to polyimide or hard coating layer to reduce yellow index YI, then color shift is corrected, but optical transmittance decreases and light blue color appears under visible light
Solution Approach 1:
The patent applies color compensation locally only in the hard coating layer rather than throughout the entire substrate. The blue pigment is confined to the surface coating, providing color correction where it is most needed for display appearance while minimizing impact on overall optical transmittance compared to adding pigment to the bulk polyimide film.
Solution Approach 2:
The patent optimizes the concentration and particle size of blue pigment in the hard coating layer to achieve the desired yellow index reduction while minimizing optical transmittance loss. By carefully controlling pigment parameters, the patent balances color correction with light transmission requirements.
3Strength
If organic hardened film is applied to improve hardness and scratch resistance, then surface protection is enhanced, but flexibility is reduced causing surface cracking in bending tests
Solution Approach 1:
The patent modifies the hard coating formulation by incorporating flexible polymer components and controlling crosslinking density to achieve optimal balance between hardness and flexibility. The coating is designed with specific molecular weight and functional group ratios that provide scratch resistance while maintaining elastic recovery capability during bending.
Solution Approach 2:
The patent creates a composite hard coating combining rigid protective components with flexible polymer matrices. This composite structure provides scratch and abrasion resistance from the hard particles while the flexible matrix prevents cracking during bending, resolving the contradiction between surface protection and bending performance.
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 substrate exhibits excellent bending performance without cracking, maintains high light transmittance, and effectively adjusts the yellow index, ensuring the display's appearance is not compromised, even after 100,000 bends, with a thinned hard coating layer that retains flexibility and hardness.
Implementation Method 1
the fluorescent pigment is composed of a photoluminescent material and has an absorption wavelength of 360 nm to 430 nm and an emission wavelength of 430 nm to 520 nm
Data Source
AI summary
A flexible display cover substrate is provided, including a transparent polyimide film and a device protective layer. The device protective layer is formed by a hard coating layer disposed on at least one side of the transparent polyimide film, and the hard coating layer is composed of three or more reactive functional group compounds, an initiator, an elastic oligomer, a nano inorganic modified particle, and a fluorescent pigment. The flexible display cover substrate of the invention, after being folded by a radius of curvature of 1 mm, does not cause cracks on the surface of the hard coating layer or break the substrate, and the yellow index YI of the flexible display cover substrate is less than 2.0.