Method for lathing silicone hydrogel lenses
View Patent ↗The present invention provides methods for lathing at room temperature a silicone hydrogel material, in particular silicone hydrogel material having a high oxygen permeability and made of a polymerizable composition containing a relative large amount of oxyperm component, into contact lenses.
1. A method for making silicone-hydrogel contact lenses, comprising:
a) obtaining a solvent-free lens-forming fluid material capable of forming a polymer or copolymer having high oxygen permeability, wherein the lens-forming material includes at least one silicone-containing vinylic monomer, at least one silicone-containing vinylic macromer, at least one hydrophilic vinylic monomer, and one styrenic monomer;
b) filling one or more tubes with the lens-forming material;
c) slowly curing the lens-forming material in the tubes to form a polymer in a form of rod and having the high oxygen permeability;
d) stripping away the tubes from the polymer;
e) post-curing and/or drying the polymer for a time sufficiently long to increase the lathability at room temperature of the polymer; and
f) lathing at room temperature the polymer into the contact lenses,
wherein each contact lens has an oxygen transmissibility of at least 45 barrers/mm and an ion permeability characterized either by an Ionoton Ion Permeability Coefficient of greater than about 0.2×10 −6 cm 2 /sec or by an Ionoflux Diffusion Coefficient of greater than about 1.5×10 −6 cm 2 /min, wherein the step c) is performed by thermally curing the lens-forming material in the tubes in a multiple stepwise curing process comprising at least a first thermal curing step at a first curing temperature of from about 28° C. to about 40° C. and a second thermal curing step at a second curing temperature of from about 80° C. to about 120° C.
2. The method of claim 1 , wherein the multiple stepwise curing process further comprises between the first and second step an additional step at a curing temperature between the first and second curing temperatures.
3. The method of claim 2 , wherein curing temperature is raised slowly from one to another over about 60 minutes.
4. The method of claim 1 , wherein the step c) is performed by UV radiation in a procedure in which at first the intensity of UV radiation is maintained at low level and then gradually increases.
5. The method of claim 1 , wherein the step e) is performed at a temperature of about 75° C. or higher.
6. The method of claim 5 , wherein the lens-forming fluid material includes a high-temperature initiator which is activated only at an elevated temperature above curing temperatures in the step c).
7. The method of claim 1 , wherein the rod produced in the step c) is cut into buttons before the step e).