Method for cast molding contact lenses
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Solution Overview
Problem
Conventional mold materials for casting silicone hydrogel contact lenses suffer from non-uniform anisotropic shrinkage, inadequate chemical resistance, high oxygen permeability, and low UV transmissibility, leading to dimensional fluctuations, damaged lens surfaces, and reduced ion permeability, which affect the quality and performance of the lenses.
Innovation Solution
Using poly(cycloalkylene-dialkylene terephthalate) copolymer for mold halves in the cast molding process, which provides low oxygen permeability, high chemical resistance, and minimal shrinkage, allowing for the production of lenses with improved ion permeability and surface smoothness, even in the presence of oxygen.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional mold materials are used for casting silicone hydrogel contact lenses, then the molding process can be carried out, but non-uniform anisotropic shrinkage occurs causing dimensional changes and fluctuations in lens parameters
Solution Approach 1:
The patent changes the material parameters by selecting poly(cycloalkylenedialkylene terephthalate) copolymer with specific compositional parameters (cycloalkylene dialkylene terephthalate content of 5-95 wt%) to achieve minimal shrinkage and high shrinkage uniformity, directly resolving the dimensional stability issue
Solution Approach 2:
The patent uses composite material structure by combining cycloalkylene dialkylene terephthalate with other compatible polymers in specific ratios to create a mold material that exhibits superior shrinkage uniformity and dimensional stability throughout the molding process
2Manufacturing precision
If conventional mold materials are used, then molding can proceed, but chemical etching of mold surfaces occurs by organic solvents and vinylic monomers damaging lens surfaces
Solution Approach 1:
The patent changes the chemical composition parameters of the mold material by using poly(cycloalkylenedialkylene terephthalate) copolymer with specific functional groups that are chemically inert toward organic solvents and vinylic monomers, preventing surface etching and lens damage
Solution Approach 2:
The patent employs disposable molds made from this chemically resistant copolymer material that can be used once and then discarded, eliminating the need for mold cleaning and maintenance while ensuring consistent lens surface quality across all production batches
3Manufacturing precision
If molds with high oxygen permeability are used, then oxygen can pass through the mold, but ion permeability of resultant lenses is reduced due to oxygen interference with polymerization
Solution Approach 1:
The patent changes the oxygen permeability parameter of the mold material by selecting poly(cycloalkylenedialkylene terephthalate) copolymer with low oxygen permeability properties, creating an oxygen barrier that prevents oxygen from interfering with the polymerization process and ensures high ion permeability in the final lens product
4Manufacturing precision
If conventional mold materials are used, then molding can be performed, but UV transmissibility is insufficient when curing by UV irradiation
Solution Approach 1:
The patent changes the optical parameters of the mold material by using poly(cycloalkylenedialkylene terephthalate) copolymer that is transparent to UV light, allowing UV irradiation to penetrate through the mold walls and completely cure the lens formulation without interference from the mold material itself
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 results in contact lenses with high ion permeability, reduced dimensional fluctuations, and smoother surfaces, maintaining quality and performance without the need for oxygen-free atmospheres during molding.
Implementation Method 1
some mold materials have high oxygen permeability. Cast molding of silicone hydrogel contact lenses using molds made from those mold materials with high oxygen permeability may have to carried out under oxygen-free atmosphere
Implementation Method 2
some mold materials have inadequate chemical resistance to silicone hydrogel lens formulation. The organic solvent and vinylic monomers, alone or in combination, may be able to chemically and/or physically etch away some part of the mold surfaces
Implementation Method 3
some mold materials may have relatively large non uniform anisotropic shrinkage over time after injection molding, causing dimensional changes in molds
Implementation Method 4
The polymerizable material remaining within the mold is polymerized by means of actinic radiation (e.g., UV irradiation, ionized radiation, microwave irradiation) or by means of heating.
Data Source
AI summary
The invention provide a method for cast-molding hydrogel contact lenses, especially silicone hydrogel contact lenses by using plastic molds of a poly(cycloalkylene-dialkylene terephthalate) copolymer. These plastic molds do not need to be degassed and stored in an oxygen-free atmosphere (e.g., N2 or Ar) before being used for cast-molding silicone hydrogel contact lenses in the absence of oxygen and resultant silicone hydrogel lenses can still have relatively high ion permeability and relatively low variation in targeted optical power, compared with silicone hydrogel lenses made from a conventional mold material, such as polypropylene. The invention also provides plastic molds for cast-molding silicone hydrogel contact lenses.