Dispensing Flowable Material into Mold Using Inert Gas Atmosphere
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Solution Overview
Problem
The mass production of contact lenses, especially silicon hydrogel lenses, faces issues with defects such as streaks and inaccurate dispensing due to insufficient volatile solvents, leading to optical property changes and visual acuity issues, and residue formation on dosing tips that affect the manufacturing process.
Innovation Solution
A process and apparatus that maintain a local gas atmosphere to prevent solvent evaporation, using inert gases and controlled solvent levels to keep the flowable material in a flowable state, ensuring accurate dispensing and reducing defects by exposing the material only to this atmosphere during dispensing and mold closure, with options for one-step or two-step mold closure and explosion protection measures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the amount of solvent is insufficient, then the manufacturing cost is reduced, but the lenses show streaks or other defects and have undesirable property changes
Solution Approach 1:
The patent applies an inert gas atmosphere (nitrogen or other inert gases) during the dispensing and molding process to prevent oxidation and degradation of the flowable material and solvent. This ensures the solvent maintains its properties and prevents streaks or defects in the final lens product, resolving the contradiction between solvent quantity and lens quality by preserving solvent effectiveness.
2Speed
If the amount of solvent is insufficient, then the flowable material may dry too quickly, but this causes residues to remain on the dosing tip and affects dispensing accuracy
Solution Approach 1:
The inert gas atmosphere prevents the flowable material from drying too quickly during dispensing, eliminating residues on the dosing tip and ensuring accurate dispensing measurements. This resolves the contradiction by controlling the drying speed while maintaining dispensing precision.
Solution Approach 2:
The inert gas acts as an intermediary environment between the flowable material and the surrounding air, preventing direct contact with oxygen and moisture that would cause premature drying and residues. This mediator ensures both controlled drying and accurate dispensing.
3Stability of the object's composition
If the solvent is highly volatile, then the flowable state is maintained, but the solvent evaporates quickly causing the material to dry and obstruct the dosing tip
Solution Approach 1:
The inert gas atmosphere significantly extends the duration the solvent remains in the flowable state by preventing evaporation. This resolves the contradiction by maintaining the beneficial flowable properties while eliminating the harmful quick evaporation of highly volatile solvents.
4Productivity
If the mold is closed quickly, then productivity is improved, but the solvent may evaporate during the closing process causing defects
Solution Approach 1:
The inert gas atmosphere allows for quick mold closing while preventing solvent evaporation during the process. This resolves the contradiction by enabling high productivity through fast closing while maintaining lens quality through evaporation prevention.
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 ensures the flowable material remains in a stable state, preventing residues and defects, enhancing the accuracy of dispensing and reducing streaks in the lenses, while providing explosion protection and maintaining the solvent in a non-explosive environment, thus improving the quality and safety of the manufacturing process.
Implementation Method 1
A local gas atmosphere is provided in which a flowable material is exposed only to the local gas atmosphere when the flowable material is dispensed into the mold and/or when the mold is closed, in order to prevent the solvent from evaporating from the flowable material
Implementation Method 2
the local gas atmosphere comprises an inert gas and an amount of the solvent which is chosen such that the local gas atmosphere is non-explosive
Data Source
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AI summary
A process for dispensing a flowable material comprising a volatile solvent into a mold, in particular a material for forming an ophthalmic lens, e.g. a contact lens, is disclosed. The process comprising the steps of providing a mold; providing a dispensing means (40, 41,42); arranging the mold underneath the dispensing means (40, 41,42); dispensing the flowable material comprising the volatile solvent into the mold, the step of dispensing being performed in a local gas atmosphere substantially preventing the solvent from evaporating from the flowable material.