Polysiloxane Hard Coating for Flexible Displays
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Solution Overview
Problem
Conventional glass substrates for mobile devices are heavy, prone to breakage, and lack flexibility, while plastic resin substrates with hard coatings suffer from insufficient hardness and scratch resistance, and are limited in flexibility and resistance to mechanical stress.
Innovation Solution
An optical laminate comprising a supporting substrate layer with a hard coating layer made from a polysiloxane containing 70 mol % or more of a glycidyl group-containing structural unit, an elastomer, and a reactive monomer, which provides high surface hardness, scratch resistance, and improved resistance to cracks under mechanical stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hard coating layer is formed on a plastic resin substrate to improve hardness and scratch resistance, then surface hardness and abrasion resistance are improved, but flexibility deteriorates and the coating film may crack
Solution Approach 1:
The patent changes the chemical composition parameters of the hard coating layer by incorporating a specific polysiloxane structure with glycidyl groups and controlling the elastomer content (5-80 parts by weight per 100 parts polysiloxane). This compositional parameter change enables the coating to achieve high hardness while maintaining flexibility and preventing cracks during folding operations.
2Strength
If a thin acrylic hard coating film with high hardness and flexibility is used, then hardness and flexibility are improved, but shrinkage during curing increases causing severe curling and limiting impact resistance
Solution Approach 1:
The patent changes the chemical composition by using a polysiloxane backbone with glycidyl functional groups instead of acrylic polymers. This fundamental material parameter change reduces curing shrinkage and minimizes curling while maintaining hardness and flexibility properties.
3Strength
If conventional hard coating compositions are applied to achieve outer folding with low curvature, then scratch resistance is improved, but stress on the coating film increases making it prone to cracking
Solution Approach 1:
The patent creates a composite hard coating system combining polysiloxane with elastomer components. This composite structure provides both the hardness needed for scratch resistance and the elasticity required to withstand high stress during outer folding with low curvature (10 mm or less diameter) without cracking.
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 optical laminate achieves high surface hardness, excellent mechanical properties, and flexibility, enabling its use in flexible or foldable display devices without cracking, even under outer folding with a curvature of 2 to 5 mm diameter.
Implementation Method 1
a reactive monomer containing at least one functional group capable of cross-linking with the polysiloxane
Implementation Method 2
a hard coating layer located on at least one surface of the supporting substrate layer and including a cured product of a hard coating composition
Data Source
AI summary
The present disclosure relates to an optical laminate including: a supporting substrate layer; and a hard coating layer located on at least one surface of the supporting substrate layer and including a cured product of a hard coating composition, wherein the hard coating composition includes: a polysiloxane including 70 mol % or more of a structural unit containing a glycidyl group-containing functional group; an elastomer; and a reactive monomer containing at least one functional group capable of cross-linking with the polysiloxane, and the elastomer is contained in an amount of 5 to 80 parts by weight based on 100 parts by weight of the polysiloxane. The present disclosure also relates to a flexible display apparatus including the above optical laminate.