Multilayered Antireflection Coating for Thermal Stress Management
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Solution Overview
Problem
Traditional antireflection coatings on ophthalmic lenses suffer from low heat resistance and durability issues, particularly when made of organic glass, due to high thermal expansion coefficients and compressive stress, leading to cracking and reduced adhesion.
Innovation Solution
A multilayered antireflection coating system is developed, featuring a SiO2-based sub-layer free from Al2O3 and low refractive index layers composed of SiO2 and Al2O3 mixtures, combined with high refractive index layers of substoichiometric titanium oxide, which enhances thermal and abrasion resistance without compromising transparency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional antireflection coatings are deposited on organic glass substrates, then the coating process can be completed, but the coating develops high compressive stress leading to cracking and poor adhesion
Solution Approach 1:
A sub-layer comprising SiO2 and Al2O3 is introduced between the organic glass substrate and the antireflection coating. This intermediary sub-layer has a thermal expansion coefficient intermediate between the substrate and the coating materials, reducing thermal mismatch stress. The sub-layer also improves chemical bonding between the organic substrate and inorganic coating layers, thereby reducing compressive stress and preventing cracking while enhancing adhesion.
Solution Approach 2:
The thermal expansion coefficient mismatch parameter is addressed by selecting sub-layer materials (SiO2 and Al2O3) whose combined thermal expansion properties fall between those of the organic glass substrate and the antireflection coating materials. This parameter optimization reduces thermal stress during temperature variations, preventing coating failure.
2Temperature
If the critical temperature of the coating is increased to improve heat resistance, then thermal stability improves, but the complexity of the coating structure increases
Solution Approach 1:
The coating system is segmented into three distinct functional layers: (1) a sub-layer comprising SiO2 and Al2O3 for stress management and adhesion, (2) an antireflection coating with alternating high and low refractive index layers for optical performance, and (3) each layer can be independently optimized for thickness and composition. This segmentation allows the critical temperature to be improved through sub-layer selection without requiring complete redesign of the entire coating structure.
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 significantly increases the critical temperature for cracking and improves abrasion resistance while maintaining high transparency and optical quality, effectively addressing the limitations of traditional coatings.
Implementation Method 1
antireflection coatings are preferably multilayered coatings comprising high refractive index layers and low refractive index layers, alternately
Implementation Method 2
substrates made of organic glass having a higher thermal expansion coefficient as compared to the substrates made of mineral glass or to inorganic materials forming the sub-layers or the layers of an antireflection coating, they do result in articles that may develop high strains leading to crackings
Implementation Method 3
depositing the optional sub-layer and antireflection coating must be done by means of methods using moderate temperatures
Data Source
AI summary
The invention relates to an optical article having antireflection properties, optionally antistatic properties, having a high thermal and abrasion resistance, as well as the method for producing the same.The article of the invention comprises a substrate and, starting from the substrate:a sub-layer comprising a SiO2-based layer, said SiO2-based layer having a thickness greater than or equal to 75 nm et free from Al2O3; anda multilayered antireflection coating comprising a stack consisting in at least one high refractive index layer and at least one low refractive index layer, all the low refractive index layers of which comprising a mixture of SiO2 and Al2O3, and the high refractive index layers of which are not layers that do absorb in the visible region comprising a substoichiometric titanium oxide and reducing the relative visible light transmission factor (Tv) of the optical article by at least 10% as compared to a same article without any of said visible light absorbing layers.