Fresnel Lens Coating Process Using UV Curing and Mold Inversion
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Solution Overview
Problem
Conventional coating processes for Fresnel lenses, such as spin coating and dip coating, fail to produce acceptably smooth coated structured surfaces due to issues like cosmetic and optical defects, particularly when the Fresnel structure height exceeds 30 µm, and they do not allow for high optical powers due to limitations in refractive index differences between the lens bulk material and the coating material.
Innovation Solution
Adapting the coating thickness to be between 1.5 and 5 times the Fresnel structure height and directing UV radiation at the Fresnel lens instead of the glass mold during curing to minimize shrinkage and eliminate cosmetic ring void defects, while using a transparent mold with matching curvature and applying pressure to ensure uniform coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional coating processes (spin coating, dip coating, flow coating) are used on Fresnel lens structured surfaces, then the coating can be applied, but the coated surface exhibits unacceptable waviness and cosmetic defects
Solution Approach 1:
Instead of applying coating to the structured Fresnel surface directly (conventional approach), the patent inverts the process by placing the structured lens into a mold cavity and filling the cavity with coating material. The mold surface is smooth and non-structured, so the coating is applied to a smooth surface rather than a structured one, eliminating waviness while still covering the Fresnel structure.
Solution Approach 2:
The patent introduces a mold cavity as an intermediary between the coating material and the Fresnel lens. The mold acts as a mediator that provides a smooth application surface and controls the coating thickness uniformly across the structured lens surface, preventing direct contact between coating and structured surface during application.
2Power
If Fresnel structure height is increased to achieve higher optical power, then lens power increases, but coating defects such as ring voids and waviness become more severe
Solution Approach 1:
By inverting the coating application process through mold cavity filling, the patent eliminates the direct relationship between Fresnel structure height and coating surface quality. The smooth mold cavity surface ensures uniform coating deposition regardless of the underlying Fresnel structure height, allowing high optical power lenses to be coated without waviness or ring void defects.
3Length of moving object
If coating thickness is reduced to maintain thin lens profile, then lens thickness decreases, but coating cannot adequately cover deep Fresnel structures
Solution Approach 1:
The mold cavity acts as an intermediary that pre-forms the coating to the exact required thickness before the lens is inserted. This ensures adequate coverage of deep Fresnel structures while maintaining precise thickness control, allowing the coating to fully cover the structure without excessive overall lens thickness.
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
This method achieves a smooth coated surface with reduced surface roughness (less than 300 nm) and eliminates cosmetic ring void defects, enabling the production of Fresnel lenses with improved optical quality and mechanical properties, suitable for high optical powers.
Implementation Method 1
curing the resin coating in situ by directing incident UV radiation at the Fresnel lens
Data Source
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AI summary
The present method for coating a Fresnel lens blank comprises providing an uncoated Fresnel lens blank having a structure surface and a non- structured surface, providing a transparent mold part having molding surface substantially matching the base curvature of the Fresnel lens, depositing a metered quantity of coating resin between the molding surface and the structured surface of the Fresnel lens, applying pressure between the Fresnel lens and the mold part while maintaining the distance between the molding surface and the structure surface so that the thickness of the coating is greater than 1.5 times the Fresnel structural height of the structured surface and less than 5 times of the Fresnel structure height of the structured surface and curing the resin coating in situ by directing the incident UV radiation at the Fresnel lens. A double coating may be employed for obtaining both higher optical power and better mechanical properties.