Crazing Resistant Anti-Reflective Coating for Ophthalmic Lenses
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Solution Overview
Problem
Conventional anti-reflective coatings on ophthalmic lenses, particularly those applied over UV cured hard-coatings, are susceptible to crazing and stress-induced damage during the lens edging process and frame insertion, due to mechanical deficiencies of UV cured hard-coatings which are less durable than thermally cured ones.
Innovation Solution
The development of anti-reflective coating systems with optimized layer thicknesses and refractive index materials, including high and low refractive index layers, to reduce tensile stress and enhance mechanical properties, such as the anti-reflective stack with alternating layers of silicon dioxide and zirconium dioxide, and adjusting the coating process conditions like pressure and gas flow rates to achieve improved compatibility and resistance to crazing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If UV cured hard-coating is applied to restore abrasion resistance after grinding, then mechanical durability is improved, but the anti-reflective coating becomes susceptible to crazing and stress-induced damage
Solution Approach 1:
The patent modifies the curing parameters of the hard-coating by introducing a dual-cure system that combines UV curing with thermal curing. This changes the cross-linking density and mechanical properties of the hard-coating layer, allowing it to maintain durability while reducing stress on the anti-reflective coating, thereby preventing crazing
Solution Approach 2:
The patent employs a composite hard-coating system with multiple layers having different compositions and curing mechanisms. The composite structure includes a UV-cured layer for rapid initial protection and a thermally cured layer for stress relief and enhanced adhesion, creating a synergistic effect that improves both durability and crazing resistance
2Illumination intensity
If conventional anti-reflective coating is applied over UV cured hard-coating, then optical performance is improved, but the coating system becomes prone to crazing during lens edging and frame insertion
Solution Approach 1:
The patent optimizes the thickness parameters and refractive index parameters of the anti-reflective coating layers to reduce tensile stress. By carefully controlling these parameters, the coating maintains high light transmission while becoming more resistant to crazing under mechanical stress during lens processing
Solution Approach 2:
The patent applies a stress-relief layer or modifies the hard-coating properties before applying the anti-reflective coating. This preliminary action creates a more compliant substrate that can accommodate subsequent mechanical deformations without transmitting excessive stress to the anti-reflective layers, preventing crazing
3Reliability
If thermally cured hard-coating is used, then mechanical durability and compatibility with anti-reflective coatings are improved, but the curing process requires more time and energy
Solution Approach 1:
The patent employs a sequential curing process where UV curing is applied first for rapid initial set (taking only seconds), followed by a shorter thermal curing cycle to complete the cross-linking and stress relief. This periodic action divides the total curing time into two distinct phases, significantly reducing the overall time compared to conventional thermal curing alone
Solution Approach 2:
The UV curing step serves as a preliminary action that rapidly forms the basic structure and provides initial adhesion, allowing the subsequent thermal curing to focus only on stress relief and final property optimization. This preliminary UV treatment reduces the duration and energy requirement of the thermal curing phase
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 optimized anti-reflective coating systems significantly reduce the risk of crazing on both convex and concave surfaces of ophthalmic lenses, maintaining optical performance and mechanical robustness, even under deformation stresses, and are compatible with both thermally and UV cured hard-coatings.
Implementation Method 1
Anti-reflective coatings reduce reflection off the front and/or back surface of ophthalmic lenses... Typically, such anti-reflective coatings are applied as a series of layers of different materials having different refractive indices.
Implementation Method 2
the prescription lab will most often apply an ultraviolet, UV, cured hard-coating
Implementation Method 3
Anti-reflective coatings are typically applied to optical surfaces through physical vapor deposition techniques and machines, such as sputter coating systems and machines.
Data Source
AI summary
An anti-reflective coating system configured to resist crazing resulting from applied compressive forces, and an optical article employing the anti-reflective coating system; and methods of forming the same. The methods include forming a first anti-reflective coating over a first surface of the optical article and applying a second anti-reflective coating over a second surface of the optical article, where the second anti-reflective coating has substantially the same reflectance than the first anti-reflective coating and a mechanical property distinct from the first anti-reflective coating.