Silicone Hydrogel Contact Lens UV Curing Method
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Solution Overview
Problem
Current methods for producing UV-absorbing silicone hydrogel contact lenses using the Lightstream Technology face challenges in achieving uniform photocuring, leading to internal stress and high production costs due to non-uniform curing and the need for UV-absorbers and visibility-tinting agents.
Innovation Solution
A method involving a pre-polymerization mixture with specific components such as hydrophilic vinylic monomers, siloxane-containing vinylic monomers, polysiloxane crosslinkers, UV-absorbing monomers, and a germanium-based Norrish Type I photoinitiator, irradiated within a specific wavelength range to form lenses with minimal internal stress and high UV-blocking capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If UV-absorbing monomers and visibility-tinting agents are added to the lens-forming composition, then UV-blocking capability is improved, but non-uniform photocuring occurs leading to internal stress
Solution Approach 1:
The patent applies local quality by using a visible-light photoinitiator system that initiates polymerization only in specific regions where the visible light penetrates, rather than attempting uniform UV curing throughout the entire lens including UV-absorbing regions. This localized initiation approach allows UV-absorbing monomers to be present in the final product without compromising curing uniformity, as the polymerization is driven by visible light which is not absorbed by the UV-filtering components.
Solution Approach 2:
The patent changes the fundamental parameter of curing wavelength from UV to visible light range. By using a visible-light photoinitiator (such as camphorquinone) instead of UV photoinitiators, the curing process occurs at wavelengths that penetrate the lens-forming composition uniformly without being absorbed by UV-absorbing monomers or visibility-tinting agents. This parameter change eliminates the non-uniform curing and internal stress while maintaining UV-blocking capability.
2Productivity
If conventional UV photocuring is used, then production speed is improved, but uniformity of curing is worsened due to UV-absorbers
Solution Approach 1:
The patent changes the curing wavelength parameter from UV to visible light, which allows both fast production speeds and uniform curing. Visible light penetrates the lens-forming composition uniformly without being absorbed by UV-absorbing monomers, maintaining curing uniformity. The use of efficient visible-light photoinitiators ensures that the polymerization proceeds rapidly, preserving high productivity while eliminating the uniformity problems associated with UV curing.
Solution Approach 2:
The patent introduces a visible-light photoinitiator as an intermediary that mediates between the visible light source and the lens-forming composition. This photoinitiator absorbs visible light and converts it to chemical energy to drive polymerization, while being transparent to UV wavelengths. This intermediary enables uniform curing throughout the lens without the harmful effects of UV absorption, maintaining both speed and uniformity.
3Object-affected harmful factors
If UV-absorbing monomers are used in the composition, then UV protection is improved, but photocuring uniformity is worsened
Solution Approach 1:
The patent changes the photoinitiator activation wavelength from UV to visible light range. This parameter change allows UV-absorbing monomers to remain in the final lens composition for UV protection, while the polymerization is initiated by visible light that penetrates uniformly through the composition. The visible-light photoinitiator is selected to have maximum absorption in the visible range (e.g., 460-480 nm for camphorquinone), ensuring uniform curing without interference from UV-absorbing components.
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 produces silicone hydrogel contact lenses with reduced internal stress and enhanced UV-blocking properties, achieving UVB transmittance of 10% or less, UVA transmittance of 30% or less, and violet transmittance of 70% or less, while maintaining a high-quality lens edge and reducing production costs.
Implementation Method 1
from 0.05% to 1.5% by weight of at least one germanium-based Norrish Type I photoinitiator for initiating a free-radical polymerization under irradiation with a light source including a light in the region of 380 to 550 nm
Implementation Method 2
a first UV-absorbing vinylic monomer that absorbs ultraviolet light and high-energy violet light (HEVL) from 381 nm to 440 nm, and a second UV-absorbing vinylic monomer that absorbs UV radiation
Data Source
Figure 1A~1C
Figure 2
Figure 3
AI summary
Described herein is a method for producing UV-absorbing silicone hydrogel contact lenses, which is free or substantially free of internal stress and also is capable of blocking ultra-violet ("UV") radiation and optionally (but preferably) violet radiation with wavelengths from 381 nm to 440 nm, according to a photocuring technology, preferably according to the Lightstream TechnologyTM. This invention also provides UV-absorbing contact lenses made according to a method of the invention.