Patent Application
20150151500
This invention relates, in one embodiment, to a method of treating the surface of contact lens molds to increase their wettability.
Contact lenses are manufactured by polymerizing a reaction mixture disposed between two molds which provide curved surfaces. These surfaces form the front and back surfaces of the lens. The front surface of the contact lens is formed by a concave frontcurve (FC) mold while the back surface of the contact lens is formed by a convex basecurve (BC) mold. After polymerization, the FC and BC molds are separated. The lens is then removed and subjected to subsequent processing steps (e.g. washing, hydrating, packaging and the like). The fluid mechanics that exist between the curved surface of the mold and the reaction mixture play an important role in the quality of the resulting lens. Unfortunately, methods to control these fluid mechanics are somewhat limited.
U.S. Pat. No. 4,933,123 discloses a surface treatment method for improving the printability of a surface of a polyethylene or polypropylene molded article by exposing the molded article to high energy UV light.
U.S. Pat. No. 6,737,661 discloses treating glass or quartz molds with high intensity. The duration of irradiation is disclosed to be over 90 hours.
Therefore, an improved method for treating a plastic contact lens mold is desired whereby the fluid mechanics can be better controlled.
In one exemplary embodiment, a method for treating a contact lens mold is disclosed. The method comprises treating a curved surface of a contact lens mold with ultraviolet light wherein de-ionized water has a contact angle on the curved surface that is lower after the treating step than before the treating step.
In a second exemplary embodiment, a method for treating a plurality of frontcurve contact lens molds disposed in a carrier or pallet is disclosed. The method comprises treating the concave surfaces of the frontcurve molds disposed in the pallet with ultraviolet light wherein de-ionized water has a contact angle on the concave surface that is lower after the treating step than before the treating step. The frontcurve mold pallet includes a plurality of concave “wells” on the same side of the pallet. The frontcurve molds are seated in a “bowl up” configuration in the concave wells of the pallets.
In a third exemplary embodiment, a method of manufacturing a contact lens is disclosed. The method comprises treating a frontcurve lens mold pallet with ultraviolet light wherein de-ionized water has a contact angle on the concave surface that is lower after the treating step than before the treating step. A reaction mixture is then disposed between the treated concave frontcurve surface and the convex surface of a corresponding basecurve mold. The mixture is polymerized and the result lens is removed.
The present invention is disclosed with reference to the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The examples set out herein illustrate several embodiments but should not be construed as limiting the scope of the claims in any manner.
Contact lenses, bandage lenses, intraocular lens and many other similar devices are typically made by polymerizing a reaction mixture while it is disposed between two disposable plastic molds. The reaction mixture which forms the lenses is a mixture of components including reactive components, such as monomers, macromers and crosslinkers as well as non-reactive components such as diluents, initiators, and additives. Reactive components are the components in the reaction mixture which, upon polymerization, become a permanent part of the polymer via chemical bonding, entrapment or entanglement within the polymer matrix. The reaction mixtures used in the present invention are not limited and can include any components known or disclosed to be useful for forming hydrogel and silicone hydrogel contact lenses. Examples of reactive components include HEMA (2-hydroxyetyl methacrylate); DMA (N,N-dimethylacrylamide); glycerol methacrylate, 2-hydroxyethyl methacrylamide, polyethyleneglycol monomethacrylate, methacrylic acid, acrylic acid N-vinyl pyrrolidone, N-vinyl-N-methyl acetamide, N-vinyl-N-ethyl acetamide, N-vinyl-N-ethyl formamide, N-vinyl formamide, combinations thereof and the like. Non-limiting examples of suitable silicone containing components include reactive PDMS (reactive polydialkylsiloxanes, such as mPDMS—mono(meth)acryloxypropyl terminated mono-n-butyl terminated polydimethylsiloxane with a molecular weight from 800-1000, 3-mono(meth)acryloxypropyl terminated mono-n-methyl terminated polydimethylsiloxane methacryloxypropyltris(trimethylsiloxy)silane (“TRIS”), 3-methacryloxypropylbis(trimethylsiloxy)methylsilane and
3-methacryloxypropylpentamethyl disiloxane or OH-mPDMS—mono—(3-methacryloxy-2-hydroxypropyloxy)propyl terminated, mono-butyl terminated polydimethylsiloxane). Other examples of reactive components include 2-propenoic acid, 2-methyl-,2-hydroxy-3-[3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]disiloxanyl]propoxy]propyl ester (SiGMA). The reaction mixture may further comprise additional reactive components, including, but not limited to ultraviolet absorbing components, reactive tints, pigments, photochromic compounds, release agents crosslinkers, wetting agents, initiators and the like. After benefiting from reading this specification, other reactive components would be readily apparent to one skilled in the art and such reactive components are contemplated for use with the present methods.
Basecurve mold 102 is sized and shaped to permit the resulting back surface of cured lens 110 to rest on the cornea of an eye. The convex surface 300 is designed to pass light and/or heat into the reaction mixture 104, thereby permitting its polymerization to be initiated. In one embodiment, the convex surface 300 is transparent to ultraviolet light. Similarly, the frontcurve mold 100 is sized and shaped to form the front surface of the resulting cured lens 110.
After polymerization is complete molds 100, 102 are separated from one another and the resulting cured lens 110 is demolded. Cured lens 110 is subsequently subjected to additional processing steps (e.g. washing, aqueous hydration, sterilization, and packaging). In one embodiment, plastic molds 100, 102 are single-use (disposable) molds.
A number of defects can occur during the production of contact lenses. These defects include lens holes, chips/tears, formation of rings of excess polymer around the edge of the lens, called flash-rings and lost lenses during demolding or processing. Such defects may be present in 10-20% of the lenses produced according to prior art techniques. Lens hole defects include voids (holes in the lens), pits (non-uniform lens thickness) and uneven edges. Tears are rips in the lens. Chips are segments of the lens which are ripped away. Flash-rings occur when the reaction mixture overflows onto the flanges of the frontcurve lens and subsequently polymerize. This overflow can occur, for example, when the frontcurve and backcurve molds are pressed together.
Each of these defects is the result of a myriad of complex, interacting parameters. For example, lens holes can be minimized by increasing the volume of reaction mixture but this increased volume promotes formation of flash-rings. The parameters that can effect these defects include the fluid mechanics between reaction mixture 104 and frontcurve mold 100 and backcurve mold 102. Another parameter is the adhesion between the cured lens 110 and frontcurve mold 100 and backcurve mold 102. Many of these parameters are related to the surface energy of the respective mold.
Reaction mixtures and cured hydrogel lenses generally adhere more strongly to high energy (more wettable) surfaces. Basecurve molds are typically formed from hydrophobic (low surface energy, high contact angle) plastics to minimize the interfacial interaction between the reaction mixture (and the resulting cured lens) and the basecurve mold. Examples of suitable basecurve plastics include polyolefins (e.g. polypropylene, PP); cyclic olefin polymer (COP, including Zeonor 1060R) and copolymer (such as ethylene-cyclic olefin copolymers sold as Topas); polystyrene (PS), hydrogenated styrene-butadiene copolymers (for examples those sold as Tuftec), blends thereof and the like. In one embodiment the basecurve materials is selected from cyclic olefin polymer, cyclic olefin copolymer, hydrogenated styrene-butadiene copolymers and copolymers and blends thereof. In another embodiment, where copolymers of the foregoing are used the amount of the copolymer is less than about 40 wt % and in some embodiments less than about 20 wt %.
In one embodiment the backcurve contains less than 15 wt %, and in another embodiment is free of wetting agents such zinc stearate which may minimize the effect of the present invention.
Prolonged exposure to UV light, particularly at distances less than 20 mm and unlike glass or quartz molds, plastic mold parts may be deformable when heated. Accordingly, treatment times of the present invention are desirably less than 5 minutes, less than one minute and in some embodiments less than about 30 seconds.
Frontcurve molds are generally formed from materials that are more wettable (high surface energy, low contact angle) than their corresponding basecurve mold. Unfortunately, this places constraints on the variety of suitable frontcurve molds that are available. Additionally, certain machinery requires the frontcurve and basecurve molds be formed from the same material. In such circumstances, it is not possible to use a frontcurve mold that is made from a different polymer that the corresponding basecurve mold.
Referring now to
In
The use of ultraviolet light to modify the surface energy of a polymeric material carries a number of advantages over prior art methods. The use of ultraviolet light is less expensive than chemical modification and results in a less expensive product. Additionally, ultraviolet treatment is safer and easier to control than previous techniques (e.g. plasma etching) and permits highly targeted surface treatments of molds where only select portions of the mold surface are modified.
In one embodiment, convex surface 300 is irradiated without irradiating basecurve flange 302. Referring to
In another embodiment the backcurve flange may be selectively irradiated to increase the wettability of the backcurve flange and allow any flash ring to selectively bias during demolding to the treated backcurve flange instead of the untreated frontcurve mold flange.
In one embodiment the contact angle of at least a portion of the convex surface of the basecurve is reduced by 1° to 20°, 5° to 30°, 5° to 20°.
In one embodiment, the entire surface of frontcurve mold 100 and/or backcurve mold 102 are irradiated uniformly. Each mold 100, 102 may be irradiated to a same or a different extent. In another embodiment, the surfaces of molds 100, 102 are selectively irradiated to treat the convex surface 300 and concave surface 304 differently than the corresponding flanges 302, 306.
Referring to
Ultraviolet light is irradiated from light sources 200 to increase the surface energy of concave surfaces 304 of the frontcurve mold. In the embodiment depicted in
In a similar process shown in
In the following examples, the surface energy of the convex surface of several basecurve molds were determined by measuring the sessile drop contact angle of de-ionized water on the surface. The angles were measured using a PG-X goniometer, available Thwing-Albert Instrument Company in West Berlin, N.J.
Surface wettability of the treated molds can be determined using a sessile drop contact angle technique using a PG-X goniometer at room temperature and using DI water as probe liquid. Each test mold lens was placed on a sample holder with the convex side up. The mold together with the holder is placed in the sessile drop instrument sample stage, ensuring proper centering of needle to deliver the water droplet. A 4 microliter of DI water droplet was generated using a PG-X goniometer ensuring that the liquid drop was hanging away from the mold. The droplet was made in contact with the mold surface by raising the stage upwards. The liquid droplet was allowed to equilibrate on the mold surface for 1-3 seconds and the contact angle was determined using the built-in analysis software.
The convex surface of a basecurve mold formed from Zeonor 1060R COP was subjected to a contact angle measurement with de-ionized water. The contact angle was 95°.
The convex surface of a basecurve mold (1 per set of conditions) formed from Zeonor 1060R COP was treated with an OmniCure 2000 UV Curing System (filter 320-500 nm, 23,400 mW/cm2 power rating) with the filter of the light source and the convex surface of the molds touching (distance=0 mm). The treatment time is shown in Table 2. The contact angle of the resulting treated convex surface was measured and are shown in Table 2.
A basecurve mold formed from Zeonor 1060R COP was subjected to a contact angle measurement with de-ionized water. The experiment was repeated at least four times. The average contact angle was 96°.
A basecurve mold formed from Zeonor 1060R COP was treated with an OmniCure 2000 UV Curing System (Filter 320-500 nm, 23400 mW/cm2 power rating) with the filter of the light source and the convex surface 17 mm apart for 17 seconds. The resulting treated convex surface was subjected to a contact angle measurement with de-ionized water. The experiment was repeated at least four times. The average contact angle was 90 degrees compared to 96° for the control in Comparative Example 2.
A basecurve mold formed from Zeonor 1060R COP was treated with an OmniCure 2000 UV Curing System (320-500 nm, 23400 mW/cm2 power rating) with the filter of the light source and the convex surface at variable distances for 10 seconds. The resulting treated convex surfaces were subjected to a contact angle measurement with de-ionized water. The contact angles were as follows:
The convex surfaces of basecurve molds formed from Zeonor 1060R COP were treated with an OmniCure 2000 UV Curing System (320-500 nm, 23400 mW/cm2 power rating) with the filter of the light source and the convex surface at 10 and 17 mm distances for variable periods of time. The resulting treated convex surfaces were subjected to a contact angle measurement with de-ionized water. The contact angles were as follows:
While the methods have been described with reference to specific embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof to adapt to particular situations without departing from the scope of the claims. Therefore, it is intended that the claims not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out these methods, but that the claims will include all embodiments falling within the scope and spirit of the appended claims.
