In cast molding methods of producing ophthalmic lenses, such as contact lenses, a reaction mixture or polymerizable lens precursor composition is cured in a lens shaped cavity defined by a first mold member with a concave lens forming surface and a second mold member with a convex lens forming surface, or a female and male mold member, respectively. The mold members are typically produced by injection molding a thermoplastic polymer into mold shaped cavities. Examples of thermoplastic polymers used to make ophthalmic lens molds include non-polar thermoplastic polymers, such as polypropylene, polystyrene, and polyethylene; and polar thermoplastic polymers, such as ethylene-vinyl alcohol polymers and polyvinyl alcohol polymers. When cast molding a contact lens, after placing the polymerizable composition in the first mold member, the first and second mold members are placed together or coupled together to form a lens assembly with the lens shaped cavity therebetween. The mold assembly is then cured to polymerize the polymerizable composition, forming the polymerized lens body in the lens shaped cavity of the mold assembly.
Over the years, a number of different types of thermoplastic polymer materials, including polar and non-polar thermoplastic polymers, have been used to manufacture ophthalmic lenses using various types of polymerizable compositions and using various lens-making processes, including spin casting, lathing and cast molding.
One example, U.S. Pat. No. 4,921,205 issued to Drew, Jr. et al., describes a process of making and machining lens blanks to form either soft or rigid gas permeable contact lenses. The process of Drew, Jr. involves specifically formulating a material for a mold member in order to cause the lens blank to strongly adhere to the mold member after curing. The process includes forming the mold member, casting a polymerizable lens blank into the mold member, curing the lens blank in the mold member to create an integral blank-mold member structure, and machining the integral blank-mold member structure by first machining away the softer mold member to reveal the lens blank, and then machining the lens blank to form a lens. Drew, Jr. et al. lists a number of types of conventional soft lens materials and rigid gas permeable lens materials that can be used in accordance with the disclosure, but does not discuss any silicone hydrogel materials. While Drew, Jr. et al. lists a number of types of polymers that can be used for the mold member including polybutylene terephthalate (PBT), both polar and non-polar mold materials were found to be equally useful when used in the described method. Due to the manufacturing procedures used, wettability of the lens surfaces was not impacted by the choice of thermoplastic polymer used for the mold, as both the region of the mold used to mold the lens surface and the surface of the lens which was in direct contact with the mold member are machined away in the process of forming the lens.
Another example, U.S. Pat. No. 6,075,066 issued to Matsuda et al., describes soft contact lenses made by crosslinking glycosoaminoglycan using photoirradiation in a plastic mold, such as a PBT mold. The manufacturing methods described in Matsuda et al. include cut polishing, spin casting, pressing and molding, with spin casting being particularly preferred. In the spin-casting manufacturing method described, after crosslinking of the lens forming material in the mold using UV light, the lens and the mold are soaked in an aqueous solution to swell the lens, allowing it to be detached from the single mold member used in the spin casting method. For this lens material (crosslinked glycosoaminoglycan), wettability of lens surfaces results from the nature of the lens material itself, and is related to the degree of substitution (DS) of photoreactive groups of the glycosaminoglycan. This is illustrated in Experimental Example 1, which lists the DS of the polymerizable material and the wettability of the resulting lenses, as determined by measuring advancing and receding contact angle. Thus, the choice of mold material in Matsuda et al. does not impact the wettability of the resulting lens.
U.S. Pat. No. 6,997,428 issued to Andino et al. is directed to contact lens molds made of a first UV transparent section which molds an optical surface of the lens, and a second UV opaque section which does not mold an optical surface of the lens. Andino et al. discloses the use of both non-polar and polar thermoplastic polymers, including PBT and Acetal, for use in the sections of the lens molds. Andino et al. does not discuss any preference for mold materials beyond those that exhibit good adhesion to each other when used to form a single mold member, does not discuss any types of lens materials such as silicone hydrogels, and does not discuss the wettability of the lenses made using the described mold materials.
When contact lens molds made of non-polar thermoplastic polymers such as polypropylene or polystyrene are used to cast mold silicone hydrogel contact lenses, it is known that additional measures typically need to be taken in order to make the lens surfaces ophthalmically acceptably wettable. For example, a surface treatment such as a plasma treatment can be applied to the lens surfaces as part of the manufacturing process. Alternatively, a polymeric interpenetrating network wetting agent can be incorporated into the lens body as part of the manufacturing process in order to make the lens body ophthalmically acceptably wettable.
Recently, cast molding silicone hydrogel contact lenses in molds made of highly polar thermoplastic polymers such as ethylene-vinyl alcohol (EVOH) copolymers, for example SOARLITE™ S (a polar resin of EVOH copolymers with an average polarity of from about 10% to about 12% available from Nippon Gohsei, Ltd., Osaka, Japan) has been found to result in lenses having ophthalmically acceptably wettable surfaces. Previously, when molded using non-polar thermoplastic polymers, it was necessary to apply a surface treatment such as, for example a plasma treatment, or to include an interpenetrating network of a polymeric wetting agent in silicone hydrogel contact lenses in order for the lens surfaces to be ophthalmically acceptably wettable when hydrated. The use of contact lens molds comprising these highly polar thermoplastic polymers (i.e., thermoplastic polymers with average polarities greater than or equal to 9%, such as, for example, greater than or equal to 10%, greater than or equal to 12%, greater than or equal to 15%, etc.) made it possible to produce wettable silicone hydrogel contact lenses without the need for a surface treatment, or an interpenetrating network of a polymeric wetting agent in the lens body. However, these highly polar thermoplastic polymers such as EVOH are expensive materials, which negatively impacts production costs. Molds made of EVOH typically are harder and more brittle than would be ideal, which negatively impacts lens yields. Also, due to the high level of adhesion typically seen between EVOH molds and silicone hydrogels, after curing a silicone hydrogel contact lens body in a mold assembly of mold members comprising EVOH, separation of the mold assembly to separate the two mold members of the mold assembly typically requires a “wet” demolding process, i.e., a demolding process involving the application of a liquid to the mold assembly containing the polymerized lens body, in order to allow the two mold members to be separated, leaving the lens body remaining in contact with one and only one of the two mold members. It is believed that the high level of adhesion observed between EVOH molds and silicone hydrogels is due at least in part to the fact that EVOH is an elastomeric thermoplastic. Further, after wet demolding, the silicone hydrogel lens body may need to be exposed to an additional amount of a liquid during a “wet” delensing process in order to release the lens body from the one remaining EVOH mold member with which it remained in contact following the demolding step. Additionally, silicone hydrogel contact lenses often require the use of an organic solvent-based washing process in order for the lenses to become ophthalmically acceptably wettable, further increasing material, equipment and production costs.
In view of the above, it can be appreciated that a need exists for contact lens molds comprising new types of materials for cast molding silicone hydrogel ophthalmic lenses, new silicone hydrogel ophthalmic lenses cast molded using molds comprising these new types of materials, and associated manufacturing methods that use less expensive, more process-friendly molding materials, do not require the use of expensive processing steps such as “wet” demolding steps, both “wet” demolding and “wet” delensing steps, or organic solvent-based washing steps, and which can produce high yields of silicone hydrogel lens bodies having ophthalmically acceptably wettable surfaces without application of a surface treatment or the presence of an interpenetrating network (IPN) of a polymeric wetting agent in the lens body.
All publications, including patents, published patent applications, scientific or trade publications and the like, cited in this specification are hereby incorporated herein in their entirety.
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