Process for manufacturing contact lenses
The invention provides a method of making ophthalmic lenses with an enhanced quality and enhanced yield achieved by using molds having been treated on back surface of mold with corona discharge technique. The method comprises the steps of obtaining a mold for cast-molding contact lenses from a lens formulation, wherein the mold comprises a first mold half having a first molding surface and a first back surface, a second mold half having a second molding surface and a second back surface, wherein when the first and second mold are configured to receive each other such that a lens forming cavity is formed between the first molding surface and the second molding surface and applying a corona discharge on one of the first and second back surfaces so that the molding surface of the mold with the treated back surface has an average water contact angle smaller than the molding surface of the mold with untreated mold by about 0.1 degrees to about 6 degrees.
1. A method for producing contact lenses, comprising the steps of:
(1) obtaining a mold for cast-molding contact lenses from a lens formulation, wherein the mold comprises a first mold half having a first molding surface and a first back surface, a second mold half having a second molding surface and a second back surface, wherein when the first and second mold are configured to receive each other such that a lens forming cavity is formed between the first molding surface and the second molding surface;
(2) applying a corona discharge on one of the first and second back surfaces so that the molding surface of the mold with the treated back surface has an average water contact angle smaller than the molding surface of the untreated mold by about 0.1 degrees to about 6 degrees;
(3) introducing a lens formulation into the lens-forming cavity formed between the first and second molding surfaces;
(4) curing the lens formulation in the cavity to form a contact lens; and
(5) opening the mold and removing the molded contact lens, wherein the method is characterized by retaining the contact lens on contact lens having corona discharge treated back surface and producing low percentages of lens tearing.
2. The method of claim 1 , wherein the mold is a disposable mold made of a plastic material.
3. The method of claim 1 , wherein the contact lens is a silicone hydrogel contact lens.
4. The method of claim 1 , the molding surface of the mold with the treated back surface has an average water contact angle smaller than the molding surface of the untreated mold by about 0.3 degrees to about 4 degrees.
5. The method of claim 4 , wherein the molding surface of the mold with the treated back surface has an average water contact angle smaller than the molding surface of the untreated mold by about 0.5 degrees to about 3 degrees.
6. The method of claim 5 , wherein the molding surface of the mold with the treated back surface has an average water contact angle smaller than the molding surface of the untreated mold by about 0.7 degrees to about 2 degrees.
7. The method of claim 1 , wherein the corona discharge is applied by an electric discharge created between two electrodes.
8. The method of claim 7 , wherein the power of the corona discharge applied is at least about 10 Watts.
9. The method of claim 8 , wherein the corona discharge is applied for a period of about 0.2 second to about 1 second.