Silicone Hydrogel Lens Curing for Uniform Diameter Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for producing silicone hydrogel contact lenses struggle with inconsistent lens dimensions due to variations in polymerization rates and conditions caused by mold positions in the oven, making it difficult to achieve targeted and consistent dimensions.
Innovation Solution
A method involving a specific thermal curing profile with controlled temperature ramping and cooling rates, using a polymerizable composition comprising siloxane-containing (meth)acrylamido monomers, polysiloxane vinylic crosslinkers, and a thermal free radical initiator, to form silicone hydrogel lens precursors in molds, followed by post-molding processes to achieve consistent lens dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional cast-molding technique with thermal curing is used, then production efficiency is improved, but lens dimension consistency deteriorates due to variations in polymerization rates at different mold positions
Solution Approach 1:
The patent applies parameter changes by modifying the thermal curing profile parameters (heating rate, holding temperature, holding time, cooling rate) to control the polymerization process. Specifically, the method uses a multi-stage thermal curing profile with controlled heating rates (e.g., 1-10°C/minute), holding temperatures (e.g., 60-100°C), and holding times to ensure uniform polymerization across all mold positions, thereby achieving consistent lens dimensions while maintaining production efficiency
Solution Approach 2:
The patent applies preliminary action by pre-conditioning the polymerizable composition before molding and pre-heating the molds before introducing the composition. This preliminary preparation ensures that the polymerization process starts uniformly across all molds simultaneously, compensating for position-dependent temperature variations in the oven and achieving consistent lens dimensions from the outset of production
2Loss of time
If thermal curing is performed at high temperature to speed up polymerization, then curing time is reduced, but lens dimension variation increases due to uneven heat distribution
Solution Approach 1:
The patent applies segmentation by dividing the thermal curing process into multiple distinct stages: a first thermal curing stage at a lower temperature (e.g., 60-80°C) to initiate uniform polymerization, followed by a second thermal curing stage at a higher temperature (e.g., 80-100°C) to complete the curing. This segmented approach allows the polymerization to proceed uniformly across all molds in the first stage, then accelerates in the second stage without causing dimension variations
Solution Approach 2:
The patent applies periodic action through a cyclic thermal curing profile that includes repeated cycles of heating, holding, and cooling. The method uses periodic temperature fluctuations with controlled heating rates (e.g., 1-10°C/minute) and holding periods to ensure uniform heat distribution throughout the polymerizable composition, achieving both rapid curing and dimensional consistency through this rhythmic thermal treatment
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 method ensures consistent lens dimensions across different mold positions in the oven, with variations in lens diameter minimized to less than 0.05 mm, facilitating efficient and reliable production of silicone hydrogel contact lenses.
Implementation Method 1
at least one thermal free radical initiator having a 10-hour half-life temperature
Implementation Method 2
curing thermally the polymerizable composition in the lens mold in an oven according to a curing profile to form silicone hydrogel lens precursors
Implementation Method 3
at least one polysiloxane vinylic crosslinker, wherein all ethyleneically unsaturated groups of said at least one polysiloxane vinylic crosslinker are (meth)acrylamido groups, (meth)acryloxy groups, vinyloxycarbonylamino groups, vinyloxy-carbonyloxy groups, or combinations thereof
Data Source
Figure 1
AI summary
The invention provides a method for making silicone hydrogel contact lenses in a relatively efficient and consistent manner from a lens formulation (i.e., a polymerizable composition) including a thermal initiator having a 10-hour half-life temperature (T10hλ) under a controlled thermal curing scheme. A method of the invention comprises a step of curing the lens formulation in an oven according to a thermal curing profile that comprises or consists essentially of increasing the oven's temperature from room temperature or a temperature that is at least about 5°C lower than T10hλ to a temperature that is at least 30°C higher than T10hλ at a selected rate (e.g., from about 1°C/minute to about 10°C/minute). Under such a controlled thermal curing scheme, the lens diameter of the fully-hydrated silicone hydrogel contact lenses obtained according to a method of the invention does not vary significantly with the positions of the molds in the oven.