In-Mold Coating of Thermoplastic Ophthalmic Lenses
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Solution Overview
Problem
Existing methods for in-mold coating of thermoplastic lenses lack the ability to achieve optical quality coatings and require high pressure injection, which complicates the process and increases costs, especially when dealing with small multi-cavity molds and the need for uniform, transparent coatings.
Innovation Solution
A method involving an unpressurized coating application onto the lens within the mold, where the coating is thermally cured using the heat from the mold and the lens, with a secondary clamp force applied to spread the coating uniformly across the lens surface without deforming it, allowing for a fringe-free and optically clear coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If high pressure injection is used to inject coating into the mold cavity, then coating can be applied to the lens surface, but the process complexity increases and costs increase
Solution Approach 1:
The patent extracts the coating application step from the high-pressure injection process by using a separate coating dispenser that applies coating to the lens surface after the lens is formed and the mold is opened. This eliminates the need for high-pressure injection systems and complex coating containment structures, thereby reducing process complexity and costs while maintaining coating application feasibility.
2Ease of manufacture
If high pressure injection is used to inject coating into the mold cavity, then coating can be applied to the lens surface, but manufacturing costs increase
Solution Approach 1:
The patent removes the expensive high-pressure injection system and complex coating containment structures by using a simple coating dispenser that applies coating after mold opening. This extraction of the complex high-pressure injection step significantly reduces manufacturing costs while maintaining the ability to apply coating to the lens surface.
Solution Approach 2:
The patent uses a simple, inexpensive coating dispenser system instead of expensive, complex high-pressure injection systems. The coating is applied in a single operation after mold opening, eliminating the need for costly containment structures and high-pressure equipment, thereby reducing manufacturing costs.
3Ease of manufacture
If coating is injected into a no-gap cavity filled with thermoplastic, then coating can be applied to the lens, but high coating injection pressure is required
Solution Approach 1:
The patent performs preliminary action by opening the mold and removing the lens from the cavity before applying the coating. This preliminary separation of the lens from the constrained cavity environment eliminates the need for high injection pressure, as the coating is applied to the free-standing lens surface rather than being forced into a constrained no-gap cavity.
4Ease of manufacture
If conventional in-mold coating is used, then coating can be applied to the lens surface, but the coating cannot achieve optical quality
Solution Approach 1:
The patent performs preliminary cleaning of the lens surface and applies the coating after the lens is completely formed and the mold is opened. This preliminary preparation and timing ensures the lens surface is clean and ready for high-quality coating application, achieving optical quality that conventional in-mold coating cannot achieve.
Solution Approach 2:
The patent extracts the coating application from the constrained in-mold environment and performs it after mold opening when the lens is free-standing and the surface is accessible. This extraction allows for proper surface preparation and coating application that achieves optical quality, eliminating the limitations of conventional in-mold coating.
5Ease of manufacture
If the mold is opened to apply coating, then coating can be applied to the lens surface, but the lens may deform during the process
Solution Approach 1:
The patent performs preliminary cooling of the lens in the mold until it is fully solidified and dimensionally stable before opening the mold and applying the coating. This preliminary stabilization ensures the lens maintains its shape during the coating application process, preventing deformation while allowing mold opening for coating accessibility.
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 approach simplifies the coating process, reduces costs, and achieves a uniformly thick, optically transparent coating on thermoplastic lenses, eliminating the need for additional cleaning and curing steps, and is suitable for various lens types including polycarbonate derivatives.
Implementation Method 1
The coating is thermally cured by the heat from the mold and the residual heat from the thermoplastic lens
Data Source
AI summary
A method for in-mold coating of an injection molded thermoplastic lens that resides in an injection molding machine oriented to a horizontal parting line. An optical lens is initially formed by injecting molten thermoplastic resin into an edge-gated lens-forming cavity held closed under a primary clamp force. The mold is opened at a time when the lens is rigid enough to retain its shape. An unpressurized full metered charge of coating is applied onto the center of the lens. The coating is co-molded by ramping up the clamp force from zero to a secondary clamp force less than the primary clamp force to compress the coating into a uniformly thick, fringe-free layer.