Anti-reflection Coating Thickness Ratio for Thermal Resistance
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Solution Overview
Problem
Conventional anti-reflection coatings on optical articles, particularly ophthalmic lenses, suffer from low thermal resistance, leading to cracking at elevated temperatures, and have durability issues due to the mismatch in thermal expansion coefficients between organic glass substrates and inorganic coating layers, resulting in reduced performance and lifespan.
Innovation Solution
Optimizing the ratio of total physical thickness of low refractive index layers to high refractive index layers in the anti-reflection coating, with a ratio higher than 2.1, and incorporating specific materials like TiO2 and SiO2 doped with Al2O3, to enhance the critical temperature and abrasion resistance without compromising optical and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional anti-reflection coatings are applied on organic glass substrates, then the coating can be deposited at moderate temperatures, but the coating exhibits low thermal resistance and cracks appear at elevated temperatures
Solution Approach 1:
The patent changes the physical and chemical parameters of the coating layers by optimizing the thickness ratio between low refractive index layers (LI) and high refractive index layers (HI). Specifically, the ratio of total physical thickness of LI layers to total physical thickness of HI layers is optimized to be higher than 2.1, which fundamentally alters the thermal expansion stress distribution and increases the critical temperature from around 70°C to 75-110°C
Solution Approach 2:
The patent uses composite dielectric material stacks combining multiple low refractive index materials (such as SiO2, SiO2 doped with Al2O3, MgF2) and high refractive index materials (such as TiO2, ZrO2, Ta2O5) in specific thickness ratios. This composite structure creates a balance between thermal expansion coefficients, reducing stress concentration and improving both critical temperature and abrasion resistance
2Temperature
If the anti-reflection coating is made with inorganic materials, then the coating has good optical properties, but the coating is susceptible to cracking due to thermal expansion mismatch with organic substrates
Solution Approach 1:
The patent optimizes the thickness parameters of individual layers and the overall stack configuration to control the mechanical stress distribution. By adjusting the ratio of LI to HI layer thicknesses to be higher than 2.1, the patent reduces the net stress on the coating-substrate interface, preventing crack initiation and propagation while maintaining thermal resistance
Solution Approach 2:
The patent applies different material compositions and thicknesses to different regions of the coating stack. Low refractive index layers with specific thicknesses are positioned to compensate for thermal expansion differences in particular regions, creating localized stress compensation that prevents cracking while maintaining overall optical performance
3Temperature
If the coating thickness ratio of low index to high index layers is increased, then the critical temperature improves, but the manufacturing complexity increases
Solution Approach 1:
The patent establishes a specific parameter range (LT/HI ratio > 2.1) that simultaneously achieves high critical temperature (75-110°C) and good abrasion resistance. This parameter optimization allows for fewer layers and simpler deposition processes while maintaining superior thermal performance compared to conventional coatings requiring complex multi-layer structures
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 achieves a higher critical temperature of 75-110°C, maintaining performance over time, with improved abrasion resistance and reduced luminous reflection, while allowing for deposition at lower temperatures, thus avoiding substrate damage and enhancing the durability of the anti-reflection coating.
Implementation Method 1
An anti-reflection coating is defined as a coating, which improves the anti-reflective properties of an optical article when deposited at its surface. It reduces reflection of light at the interface article-air on a relatively wide band of the visible spectrum.
Implementation Method 2
deposition of the anti-reflection coating (optionally comprising a sub-layer) has to be performed through moderate temperature processes
Data Source
AI summary
The present invention relates to an optical article having anti-reflection properties and high thermal resistance, comprising a substrate having at least one main face coated with a multi-layer anti-reflection coating comprising a stack of at least one high refractive index layer and at least one low refractive index layer, wherein the ratio:RT sum of the physical thicknesses of the low refractive index layers of the anti-reflection coating/sum of the physical thicknesses of the high refractive index layers of the anti-reflection coating is higher than 2.1. If the anti-reflection stack comprises at least one low refractive index layer having a physical thickness =100nm which is not the outermost layer of the anti-reflection coating, said relatively thick layer and the underlying layers are not taken into account in RT calculation.