Ophthalmic Lens Mold Surface Roughness for Adhesion Control
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Solution Overview
Problem
Existing injection molding processes for manufacturing thin ophthalmic lens molds face challenges such as adhesion and sticking issues during removal from the molding tool, leading to deformation and stress-whitening, which compromise the quality and usability of the lens molds.
Innovation Solution
The injection molding apparatus and method involve using molding tools with specific surface roughness characteristics, including a surface roughness Sa in the range of 0.3 µm to 2 µm and Sz in the range of 10 µm to 50 µm, on the mold forming portions, particularly in the central zone of the rear surface of the ophthalmic lens mold. This surface roughness is achieved through techniques like laser roughening, sand blasting, grinding, or lapping, and ensures that the plastic material does not stick excessively to the tool, allowing for safe and efficient removal of the lens molds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the lens mold is made thin (wall thickness < 1mm) to improve manufacturing efficiency and reduce material usage, then productivity and cost-effectiveness are improved, but the lens mold becomes more susceptible to deformation and stress-whitening during removal from the molding tool
Solution Approach 1:
The patent applies parameter changes by modifying the surface roughness characteristics of the molding tool. Specifically, it creates a dual-roughness surface with different Ra values in different zones (first zone with Ra of 0.03-0.3μm, second zone with Ra of 0.3-3.0μm). This parameter modification allows the lens mold to be thin-walled for productivity while preventing adhesion-related deformation during removal, thus resolving the contradiction between manufacturing efficiency and product reliability.
2Manufacturing precision
If conventional smooth molding tool surfaces are used, then manufacturing precision is maintained, but adhesion and sticking occur during removal causing deformation and stress-whitening
Solution Approach 1:
The patent implements local quality by creating different surface roughness characteristics in different zones of the molding tool. The first zone (corresponding to the lens forming portion) has a smoother surface (Ra 0.03-0.3μm) to maintain manufacturing precision, while the second zone (central portion of the rear surface) has a rougher surface (Ra 0.3-3.0μm) to prevent adhesion and sticking. This localized differentiation resolves the contradiction between maintaining geometry accuracy and preventing harmful adhesion effects.
3Ease of operation
If the lens mold is removed by lifting the outer edge portion, then removal is facilitated, but elastic and inelastic deformation occurs due to adhesion in the central portion
Solution Approach 1:
The patent applies preliminary anti-action by pre-modifying the surface roughness of the molding tool before the lens mold is even formed. The central zone is pre-treated to have higher roughness (Ra 0.3-3.0μm), which creates reduced adhesion properties in advance. This preliminary modification counteracts the adhesion forces that would otherwise cause deformation during removal, allowing the lens mold to be easily lifted from the outer edge without suffering from elastic or inelastic deformation in the central portion.
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 enables the manufacturing of thin ophthalmic lens molds with high accuracy and precision, while preventing deformation and stress-whitening during removal, thus ensuring the quality and usability of the lens molds. The process allows for short cycle times and efficient production of large numbers of lens molds.
Implementation Method 1
One problem that may occur during the lifting off of the lens mold from the fixedly arranged molding tool is that - due to adhesion and/or sticking - in particular the central portion of the lens mold tends to strongly adhere to the fixedly arranged molding tool
Implementation Method 2
The surface roughness of the mold forming portion, in particular in a central zone that corresponds to a portion on the rear surface of the ophthalmic lens mold opposite to the lens forming portion on the front surface, has an Sa in the range of 0.3 µm to 2 µm, and an Sz in the range of 10 µm to 50 µm, in particular an Sa of about 1 µm and an Sz of about 25 µm
Data Source
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AI summary
An injection molding apparatus for manufacturing an ophthalmic lens mold having a front surface comprising a lens forming portion and a rear surface, comprises a first molding tool and a second molding tool.The first and second molding tools are movable towards and away from each other between a closed position and an open position. In the closed position the first mold forming portion of the first molding tool and the second mold forming portion of the second molding tool define a cavity. The surface of the second mold forming portion, at least in a central zone thereof, has a surface roughness Sa in the range of 0.3 μm to 2 μm, and a surface roughness Sz in the range of 10 μm to 50 μm.