Hydrophilic Sputtered AR Coating for Ophthalmic Lenses
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Solution Overview
Problem
Existing hydrophilic coatings for ophthalmic lenses are not durable and fail to maintain effective easy-cleaning properties over time, especially in the presence of abrasion.
Innovation Solution
A coating system comprising alternating layers of low refractive index silicon dioxide and high refractive index metal oxynitride, such as titanium oxynitride or zirconium oxynitride, deposited on a substrate to create a hydrophilic surface with enhanced cleanability and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional hydrophilic coatings (e.g., TiO2) are applied to provide easy-cleaning properties, then surface free energy increases and hydrophilicity is achieved, but the coating deteriorates or abrades off over time during lens cleaning
Solution Approach 1:
The patent applies a composite coating system consisting of multiple layers: a base hydrophilic coating (TiO2) combined with a protective top coating (SiO2, SiNx, or SiOxNy). This composite structure allows the TiO2 layer to provide hydrophilic properties while the SiO2/SiNx/SiOxNy layer protects against abrasion and deterioration, resolving the contradiction between ease of cleaning and coating durability.
Solution Approach 2:
The patent modifies the surface energy parameters by controlling the composition and thickness of the coating layers to maintain optimal hydrophilicity (surface free energy of 50-70 mN/m) while improving durability. By adjusting the ratio of hydrophilic to protective layers and their respective thicknesses, the coating maintains easy-cleaning properties without sacrificing durability.
2Ease of operation
If hydrophobic coatings are used to create a slippery surface, then contact angles increase and initial cleanability improves, but oils and dirt tend to move or smear across the lens surface
Solution Approach 1:
Instead of using a hydrophobic surface to repel contaminants, the patent inverts the approach by using a hydrophilic surface that attracts water and contaminants. The TiO2-based hydrophilic coating causes water and oils to spread out rather than bead up, preventing smearing and making contaminants easier to remove through simple wiping, thus resolving the contradiction between initial cleanability and contaminant movement.
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 coating system maintains a surface free energy of 50-70 mN/m for an extended period, ensuring effective easy-cleaning properties and improved durability compared to traditional hydrophilic coatings.
Implementation Method 1
Hydrophilic-like sputtered AR coating
Implementation Method 2
deposited on a substrate
Implementation Method 3
The photocatalytic effect of a TiO2 coating is the subject of many patents... TiO2 absorbs light in the UV wavelengths. The absorption process generates electron-hole pairs and the photo-generated holes are the cause of the hydrophilicity of the coating surface
Implementation Method 4
The trapping of contaminants like water or oils by the holes lead to the formation of charged species, for example, hydroxyl ions and hydroxyl radicals, by oxidation
Implementation Method 5
Hydrophilic-like sputtered AR coating... alternating layers of low refractive index silicon dioxide and high refractive index metal oxynitride
Data Source
AI summary
An ophthalmic article having a coating system which provides antireflective and easy clean properties to the ophthalmic article. The coating system includes alternating layers of low refractive index metal oxide and high refractive index metal oxynitrides and corresponding high refractive index metal oxides. The coating system provides favorable surface energy to the ophthalmic article when at least one layer of the high refractive index metal oxynitride is encapsulated between two layers of low refractive index metal oxide.