Organic-Inorganic Protective Layer for Ophthalmic Lens Hardcoat
Solution Overview
Problem
Siloxane-based antiabrasion hardcoats on ophthalmic lenses are sensitive to thermal and hygroscopic stresses, leading to crack formation when exposed to hot and humid environments, which compromises their durability and performance.
Innovation Solution
A protective layer of organic-inorganic material with a Young's modulus higher than 20 GPa is applied directly to the siloxane-based antiabrasion hardcoat, enhancing the lens's resistance to thermal and hygroscopic stresses by limiting crack occurrence and maintaining optical quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a siloxane-based antiabrasion hardcoat is applied to an ophthalmic lens, then the lens gains scratch resistance, but the hardcoat becomes sensitive to thermal and hygroscopic stresses and develops cracks in hot and humid environments
Solution Approach 1:
The patent applies a composite organic-inorganic protective layer (containing silicon oxide, organic compounds, and optionally metal oxides) over the siloxane-based hardcoat. This composite structure combines the scratch resistance of the siloxane hardcoat with the thermal and humidity stability of the organic-inorganic protective layer, resolving the contradiction between abrasion resistance and environmental reliability.
2Illumination intensity
If an interferential coating such as an antireflective coating is applied to the hard coated lens, then reflectance is reduced and transmittance is increased, but the lens becomes more sensitive to thermal and hygroscopic stresses
Solution Approach 1:
The organic-inorganic protective layer serves as an intermediary between the interferential coating and the siloxane hardcoat. This intermediate layer protects the underlying hardcoat from thermal and hygroscopic stresses while allowing the interferential coating to maintain its optical performance, thus resolving the contradiction between optical quality and environmental resistance.
3Reliability
If the Young's modulus of the protective layer is increased above 20 GPa, then the resistance to crack occurrence in the hardcoat increases, but the protective layer itself may become prone to cracking under extreme thermal and humidity conditions
Solution Approach 1:
The patent optimizes the Young's modulus of the organic-inorganic protective layer to be greater than 20 GPa, which provides sufficient stiffness to protect the hardcoat from cracking. The composition is carefully controlled (containing silicon oxide, organic compounds, and optionally metal oxides in specific ratios) to achieve this modulus range, balancing protection capability with resistance to environmental stresses.
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 application of the organic-inorganic protective layer significantly increases the resistance of ophthalmic lenses to thermal and hygroscopic stresses, reducing crack formation and maintaining optical clarity even in harsh conditions, as demonstrated by tests at 60-80°C and 80-100% RH.
Implementation Method 1
A protective layer of organic-inorganic material with a Young's modulus higher than 20 GPa is applied directly to the siloxane-based antiabrasion hardcoat, enhancing the lens's resistance to thermal and hygroscopic stresses by limiting crack occurrence
Data Source
AI summary
The invention concerns an ophthalmic lens having an increased resistance to thermal and hygroscopic stresses, said ophthalmic lens comprising a substrate, at least one main face of which is coated with a siloxane-based anti-abrasion hardcoat, characterized in that said ophthalmic lens further comprises at least one protective layer of an organic-inorganic material directly in contact with said hardcoat, said protective layer of organic-inorganic material having a Young's modulus higher than 20 GPa, preferably of at least 25 GPa.