High-Refractive-Index Coating Composition for Optical Substrates
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Solution Overview
Problem
Current coating compositions for optical substrates, particularly plastic lenses, face challenges in achieving high refractive indices while maintaining excellent weathering and light resistance, especially when the refractive index exceeds 1.70, due to increased titanium content or reduced coating layer thickness, which leads to impaired weathering and light resistance.
Innovation Solution
A coating composition comprising metal oxide particles with a rutile-type titanium-based oxide core and a silica-based oxide or composite oxide coating layer, where the titanium-based oxide particles have a specific size range, crystallite diameter, and surface area, and the coating layer has a refractive index lower than the core, reducing photocatalytic activity and light scattering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the refractive index of the coating film is increased to 1.70 or higher by increasing titanium oxide content, then the refractive index is improved, but the weathering resistance and light resistance are impaired due to photocatalytic activity
Solution Approach 1:
A silica-based coating layer is introduced as an intermediary between the titanium-based oxide core particles and the external environment. This silica layer acts as a barrier that suppresses the photocatalytic activity of titanium oxide, preventing degradation of the coating film while allowing the high refractive index property to be maintained. The silica layer has a refractive index lower than titanium oxide, creating a gradient that manages light interaction effectively.
2Illumination intensity
If the thickness of the coating layer is reduced to achieve high refractive index, then the refractive index is improved, but the scratch resistance and abrasion resistance are impaired
Solution Approach 1:
The invention employs a composite structure consisting of titanium-based oxide core particles (providing high refractive index) surrounded by a silica-based coating layer (providing mechanical protection). This composite material approach allows the inner core to contribute to optical properties while the outer silica layer contributes to scratch and abrasion resistance, achieving both high refractive index and mechanical durability simultaneously.
3Illumination intensity
If titanium oxide particles with high photocatalytic activity are used to achieve high refractive index, then the refractive index is improved, but the adhesion properties and dyeing properties are impaired
Solution Approach 1:
The silica-based coating layer serves as an intermediary that modifies the surface properties of titanium oxide particles. This silica shell reduces the direct interaction between photocatalytically active titanium oxide and the coating film matrix, thereby improving adhesion properties and dyeing properties while preserving the high refractive index characteristic of the titanium oxide core.
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 solution provides a coating film with a refractive index of 1.70 or more, excellent weathering and light resistance, and low photocatalytic activity, along with improved scratch, abrasion, impact, and adhesion properties, maintaining transparency and resistance to color change.
Implementation Method 1
the titanium oxide has a photocatalytic activity and therefore has impaired weathering resistance of the coating film
Implementation Method 2
the coating layer has a refractive index lower than the core, reducing photocatalytic activity and light scattering
Data Source
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AI summary
The present invention relates to a coating composition containing metal oxide particles with a high refractive index and low photocatalytic activity and a coating film obtained by applying the coating composition onto a substrate. The coating composition contains metal oxide particles with a high refractive index obtained by coating the specific fine particles of the titanium-based oxide on their surfaces with at least a silica-based oxide or a silica-based composite oxide, and the coating film is obtained by applying the coating composition onto a substrate. The metal oxide particles with not only a high refractive index but also low photocatalytic activity, and therefore a coating film with excellent weathering resistance and light resistance can be formed on a substrate.