Antireflection Coating Crack Resistance Silica Reinforcement
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Solution Overview
Problem
Anti-reflective coatings on ophthalmic lenses are fragile during mechanical stress, such as edging and assembly, leading to deformation and cracking, which can propagate to other coatings.
Innovation Solution
Incorporating at least 20% by weight of particulate silica into the polyurethane-based primary coating enhances the crack resistance of the anti-reflective coating without compromising adhesion or abrasion resistance, with optimal performance achieved at a particulate silica mass percentage between 45% and 55% relative to the dry primary coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If anti-reflective coating is applied to ophthalmic lens, then light reflection is reduced, but the coating becomes fragile and cracks under mechanical stress
Solution Approach 1:
The patent applies composite materials by incorporating particulate silica (inorganic filler) into the polyurethane-based primary coating matrix. This creates a composite coating structure where the silica particles reinforce the organic polymer, significantly improving crack resistance (by 10-28% as measured in the study) while maintaining the anti-reflective properties. The composite formulation allows the coating to withstand mechanical stresses during edging and mounting without cracking.
2Reliability
If particulate silica is added to primary coating, then crack resistance of anti-reflective coating improves, but impact resistance may decrease
Solution Approach 1:
The patent applies parameter changes by optimizing the concentration of particulate silica in the primary coating. The study found that silica content between 20-55% by weight in the dry coating provides the optimal balance: sufficient silica particles to reinforce crack resistance (improving it by 10-28%) while maintaining enough polyurethane matrix to preserve impact resistance. This parameter optimization resolves the contradiction between the two opposing mechanical properties.
3Reliability
If more particulate silica is used in primary coating, then crack resistance increases, but adhesion and abrasion resistance may be compromised
Solution Approach 1:
The patent applies parameter changes by precisely controlling the silica content within the 20-55% weight range in the dry primary coating. Within this optimized parameter range, the coating maintains adequate polyurethane binder content to ensure proper adhesion to the substrate and abrasion resistance, while having sufficient silica particles to provide crack resistance improvements of 10-28%. The parameter optimization prevents excessive silica from compromising inter-coating adhesion.
Data Source
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AI summary
The invention relates to an optical article including a transparent organic glass substrate, a primary coating including polyurethane and particulate silica, an abrasion-resistant coating, and an antireflection coating, said coatings, and in particular the antireflection coating, having improved crack resistance when the optical article is subjected to high amounts of mechanical stress, e.g., during edge-grinding and the mounting of lenses in eyeglass frames. The invention also relates to a method for manufacturing such an article.