Abstract:
A method and apparatus for separating excess cured lens material, or lens flash, from the mold section in which it was cast. This invention is particularly suited for cast contact lenses or intraocular lenses.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a method for separating excess cured lens material, or lens flash, from the mold section in which it was cast. This invention is particularly suited for cast contact lenses or intraocular lenses.  
       BACKGROUND OF THE INVENTION  
       [0002]     Static cast molding of ophthalmic lenses, including contact lenses and intraocular lenses, has proved successful commercially. Static cast molding involves charging a mixture of lens-forming monomers between two mold sections. One mold section is shaped to form the anterior, convex lens surface (also referred to as female mold section) and the other mold section is shaped to form the posterior, concave lens surface (also referred to as male mold section). This monomer mixture is cured in the lens-forming mold cavity formed between the anterior and posterior molding surfaces, typically by exposure to light energy and/or thermal energy. Such methods are described in U.S. Pat. Nos. 3,408,429, 3,660,545, 4,113,224, 4,197,266, and 5,271,875, as examples.  
         [0003]     More specifically, the liquid monomer mixture is charged to the anterior mold, and then the posterior mold is seated on the anterior mold, to define the lens-forming molding cavity therebetween. Typically, an excess amount of monomer mixture is deposited, in order to ensure the mold cavity is completely filled. This excess liquid monomer mixture is dispelled from the molding cavity, generally into some type of reservoir in the anterior mold section surrounding the molding cavity. When the monomer mixture in the molding cavity is cured to form the lens, this excess monomer mixture is also cured, resulting in excess cured polymer material. Often, this excess cured material has the form of a ring, and thus, is sometimes referred to as a monomer ring; it is also sometimes referred to as lens flash. This excess material tends to adhere to one of the mold sections, and similarly, the contact lens tends to adhere to one of the mold sections.  
         [0004]     In some cast molding methods, the contact lens is purposely retained on one mold section (for example, the anterior mold section) while the excess cured material is retained on the other mold section (for example, the posterior mold section). U.S. Pat. No. 5,271,875 (Appleton et al.), U.S. Pat. No. 6,033,603 (Lesczynski et al.) and U.S. Patent Application Publication 2003/0160343-A1 (Hodgkinson) disclose such methods.  
         [0005]     In some other cast molding methods, both the contact lens and the excess cured material are retained on the same mold section (for example, the anterior mold section). As an example, U.S. Pat. No. 6,368,096 (Dobner et al.) discloses an apparatus for separating cured excess lens polymer material from a contact lens mold section. This apparatus involves piercing this ring of excess material, in a manner that this ring is sheared from the mold section in which it is retained. The ring is then removed from the mold section, and the mold section, now containing only the contact lens, is transferred to downstream processes, for example, to a station for releasing the contact lens from the mold section. While this apparatus is quite useful, difficulties may be encountered when the ring of excess lens material has a relatively low volume, or when the excess lens material is very brittle. For example, the pins or blades that pierce the monomer ring may break the ring into several smaller pieces. These smaller pieces are more difficult to remove, and some pieces may remain on the contact lens.  
       SUMMARY OF THE INVENTION  
       [0006]     This invention provides an improved method for separating excess cured lens material from the mold section in which it was cast and is retained.  
         [0007]     The method comprises: casting a lens in a mold assembly, wherein excess cured material is adhered to a mold section of the mold assembly; compressing the excess cured lens material to disengage the excess cured material from the mold section; and removing the excess cured material from the mold section.  
         [0008]     Preferably, the excess cured lens material is compressed at two opposed points, thereby deflecting the excess cured lens material. To accomplish this, the excess lens material may be compressed by a wedge-shaped groove. Preferably, the wedge-shaped groove has two opposed, tapered surfaces that contact and deflect the excess cured lens material as the mold section is moved against the groove.  
         [0009]     According to certain embodiments, the cast lens is also adhered to the anterior mold section, and the excess cured material is removed from the cast lens and anterior mold section. The cast lens may remain adhered to a molding surface of the anterior mold section, after removal of the excess cured lens material.  
         [0010]     According to other preferred embodiments, the excess cured lens material is transported through two opposed, tapered surfaces that compress the excess cured lens material. Preferably, the excess cured lens material is contacted by the opposed, tapered surfaces that compress and deflect the excess cured lens material as the mold section travels through and is guided by a separate pair of opposed surfaces.  
         [0011]     This invention also provides an apparatus for carrying out the method. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0012]      FIG. 1  is a schematic exploded view of a representative mold assembly for use in the invention.  
         [0013]      FIG. 2  is a partial, cross-sectional view of the mold assembly of  FIG. 1  being assembled.  
         [0014]      FIG. 3  is a partial, cross-sectional view of the mold assembly of  FIGS. 1 and 2  after curing of a lens.  
         [0015]      FIG. 4  is a top perspective view of an apparatus according to various preferred embodiments of this invention.  
         [0016]      FIG. 5  is a bottom perspective view of the apparatus of  FIG. 4 .  
         [0017]      FIG. 6  is a bottom plan view of the apparatus of  FIGS. 4 and 5 .  
         [0018]      FIG. 7  is a frontal plan view of the apparatus of  FIGS. 4, 5  and  6 .  
         [0019]      FIG. 8  is a partial cross-sectional view of the apparatus of  FIGS. 4, 5 ,  6  and  7 , as viewed from above along line A-A, the apparatus further including a mold section.  
         [0020]      FIG. 9  is a bottom plan view of an alternate apparatus of this invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0021]     As mentioned, this invention is useful in the casting of ophthalmic lenses, including contact lenses and intraocular lenses. For illustrative purposes, the following description of preferred embodiments will refer mainly to static cast molded contact lenses, although the invention is applicable for other ophthalmic lenses, and for other casting methods such as spincasting.  
         [0022]     FIGS.  1  to  3  illustrate a known mold assembly  10  for the static casting of a contact lens  12 . Assembly  10  includes a posterior (or male) mold section  16  having a molding surface  16   a  for forming a posterior contact lens surface. Assembly  10  also includes an anterior (or female) mold section  14  having a molding surface  14   a  for forming an anterior contact lens surface. It will be appreciated, however, that this invention is applicable to other lens molds having configurations differing from the illustrated embodiment.  
         [0023]     As seen in  FIG. 2 , a liquid mixture of lens-forming monomers  18  is deposited on the molding surface  14   a  of the anterior mold  14 . Then, as seen in  FIG. 3 , the posterior mold  16  is seated on the anterior mold, whereby the lens-forming molding cavity is defined between molding surfaces  14   a  and  16   a . Typically, an excess amount of monomer mixture  18  is deposited, in order to ensure the molding cavity is completely filled. This excess liquid monomer mixture  19  is dispelled from the molding cavity, into reservoir  20  in the anterior mold section. In the illustrated embodiment, reservoir  20  has the form of a circumferential groove surrounding the molding cavity.  
         [0024]     The monomer mixtures employed in the invention include conventional lens-forming monomers. The lens-forming monomers are monomers that are polymerizable by free radical polymerization, generally including an activated unsaturated radical, such as an ethylenically unsaturated radical. (As used herein, the term “monomer” denotes relatively low molecular weight compounds that are polymerizable by free radical polymerization, as well as higher molecular weight compounds also referred to as “prepolymers”, “macromonomers”, and related terms.)  
         [0025]     One preferred class of lens-forming monomers is those that form hydrogel copolymers. A hydrogel is a crosslinked polymeric system that can absorb and retain water in an equilibrium state. Accordingly, for hydrogels, the monomer mixture will typically include a hydrophilic monomer. Suitable hydrophilic monomers include: unsaturated carboxylic acids, such as methacrylic and acrylic acids; acrylic substituted alcohols, such as 2-hydroxyethylmethacrylate (Hema) and 2-hydroxyethylacrylate; vinyl lactams, such as N-vinyl pyrrolidone; and acrylamides, such as methacrylamide and N,N-dimethylacrylamide (DMA). The hydrophilic monomer may function as a crosslinking agent (a crosslinker being defined as a monomer having multiple polymerizable functionalities) or a separate crosslinker may be employed. Examples of crosslinking agents are ethyleneglycoldimethacrylate, tetraethyleneglycoldimethacrylate, and 2-ethylenemethacrylate vinyl carbonate.  
         [0026]     Another preferred class of lens-forming monomers includes those that form silicone copolymers. Such systems include a silicone-containing monomer. One suitable class of silicone containing monomers include known bulky, monofunctional polysiloxanylalkyl monomers, such as methacryloxypropyl tris(trimethylsiloxy)silane, pentamethyldisiloxanyl methylmethacrylate, tris(trimethylsiloxy) methacryloxy propylsilane, methyldi(trimethylsiloxy)methacryloxymethyl silane, 3-[tris(trimethylsiloxy)silyl] propyl vinyl carbamate, and 3-[tris(trimethylsiloxy)silyl] propyl vinyl carbonate. Another suitable class includes multifunctional ethylenically “end-capped” siloxane-containing monomers, especially difunctional monomers. Other silicone-containing monomers include the silicone-containing monomers described in U.S. Pat. Nos. 5,034,461, 5,610,252 and 5,496,871, the disclosures of which are incorporated herein by reference. Other silicone-containing monomers are well-known in the art.  
         [0027]     In the case of silicone hydrogels, the monomer mixture includes, in addition to the silicone-containing monomer, a hydrophilic monomer. Either the silicone-containing monomer or the hydrophilic monomer may function as a crosslinking agent (a crosslinker being defined as a monomer having multiple polymerizable functionalities) or a separate crosslinker may be employed.  
         [0028]     In the case of intraocular lenses, the monomer mixtures may further include a monomer for increasing the refractive index of the resultant copolymer. Examples of such monomers are aromatic (meth) acrylates, such as phenyl (meth)acrylate, phenylethyl (meth)acrylate and benzyl (meth)acrylate.  
         [0029]     Generally, the lens-forming monomer mixtures will include a polymerization initiator to facilitate curing of the monomer mixture. This mixture may include other optional components such as UV absorbing agents and tinting agents.  
         [0030]     After depositing the monomer mixture and assembling the posterior and anterior molds, the mold assembly shown in  FIG. 3  can now be exposed to light energy (for example, UV radiation) and/or thermal energy. For curing with light energy, at least one of the mold sections is transparent to the light energy; thus, the mold sections may be formed of materials such as polypropylene, polystyrene, or other transparent plastic resins. At completion of curing, the monomer mixture in the molding cavity has been cured to form contact lens  12 , and the excess monomer mixture  19  in reservoir  20  has also been cured. For the illustrated embodiment, the cured excess monomer mixture  19  may have the form a ring, thus, this cured excess material is sometimes referred to as a monomer ring; it is also sometimes referred to as lens flash.  
         [0031]     The posterior and anterior mold sections may now be separated from one another. This procedure is sometimes referred to as “decapping”, and various methods are known in the art, depending on the configurations of the mold sections, including those methods disclosed in U.S. Pat. No. 6,428,723 (Lesczynski et al.), U.S. Pat. No. 5,693,268 (Widman et al.) and U.S. Pat. No. 5,850,107 (Kindt-Larsen et al.), and U.S. Patent Application Publication 2003/0160343-A1 (Hodgkinson).  
         [0032]     Following the decapping operation, according to the described embodiment, both the contact lens and the excess cured material are retained on the anterior mold section. Typically, the cast contact lens tends to adhere to the molding surface  14   a  of the anterior section  14 , and the excess cured material  19  tends to adhere to the reservoir  20 . In the illustrated embodiment, the excess cured material extends slightly above surface  15  of anterior mold section  14 .  
         [0033]     FIGS.  4  to  8  illustrates a first embodiment of an apparatus according to this invention. Plate  30  has an upper surface  31  and a lower surface  32 . Extension  33  is optionally provided as a means to attach plate  30  to a support, for example, extension  33  may be hingedly connected to a support. A wedge-shaped groove  35  is formed in lower surface  32 . Groove  32  is defined by two opposed, tapered surfaces  36 ,  37 . A second groove  38  is formed in lower surface  32 , groove  38  including a pair of opposed surfaces  41 ,  42 . Mold section  14  is transported in the direction of arrow  29 , for example, by a pusher device. As mold section  14  is transported in this direction, it may be supported on a support positioned below plate  30 . Plate  30  may be spring biased so that it is compressed against, and remains in contact with, the top surface  15  of mold section  14  as the mold section is moved through and against groove  35 .  
         [0034]     Surfaces  41 ,  42  serve to guide the upper portion of mold section  14  as it is transported through plate  30 . Thus, the spacing of surfaces  41 ,  42  (vertical in  FIG. 6 ) closely approximates the outer diameter of the upper portion of mold section  14 , as best seen in  FIG. 8 . The upper surface  15  of mold section  14  contacts surfaces  43 ,  44  (horizontal in  FIG. 6 ). The opposed, tapered surfaces  34 ,  35  contact the excess cured lens material, and deflect this material as the mold section is moved therethrough. This compressive force on the excess cured lens material  19  thereby disengages this excess material from the reservoir  20 , i.e., the adherence of the excess material to reservoir is broken.  
         [0035]     At the completion of this operation, it is preferred that the contact lens remains adhered to the molding surface of anterior mold section  14 . Also, it is preferred that the excess lens material remains in one piece as it is disengaged from the reservoir  20 . However, even if the cured excess material is broken by this operation, it generally will be broken into only two or three larger pieces, i.e., this operation does not tend to shatter the cured excess material into many small pieces. Accordingly, the process of this invention ensures easy and complete removal of the cured excess material, while also ensuring the contact lens remains on mold section  14  for subsequent downstream operations.  
         [0036]     In the illustrated embodiment, aperture  46  extends through upper surface  31 , so that after loosening the excess cured material, the mold section may be accessed through aperture  46 . Thus, after the mold section has traveled through the wedge-shaped groove, the loosened, non-adherent excess material  19  can be removed from mold assembly  14  and the contact lens retained therein. For example, the excess material can be removed by a vacuum pick-up at aperture  46 , and discarded. Second aperture  47  is optionally provided so that mold assembly can be accessed by a second vacuum pick-up, in order to ensure all excess lens material is removed. As further examples, the excess material can be removed manually, removed with a picker device, or blown away with forced air.  
         [0037]     Following these operations, the assembly of the mold section  14  and contact lens  12  retained therein can be transported to a downstream station for conventional post-molding processing. In the case of contact lenses, downstream processes may include at least one of: release of the lens from the mold; extraction of contaminants from the lens; surface treatment of a lens surface; inspection; hydration; and packaging. All such processes are well-known in the art.  
         [0038]     In the embodiment illustrated in  FIG. 4 , the narrowest separation of the tapered surfaces  36 ,  37  is slightly smaller than the circumference of the ring of excess cured lens material. Also, this narrowest separation of the opposed tapered surfaces is smaller than the separation of surfaces  41 ,  42 . At the point where mold section  14  is at the narrowest separation of surfaces  36 ,  37 , these surfaces contact the excess cured material at points approximately 180 degrees from one another.  
         [0039]      FIG. 9  illustrates an alternate embodiment of an apparatus according to this invention. Plate  40  has a lower surface  42 . Wedge-shaped groove  43  is formed in lower surface  42 , and groove  43  is defined by two opposed, tapered surfaces  44 ,  45  having a different configuration than in  FIG. 4 . These tapered surfaces  44 ,  45  serve to deflect the excess cured material, similar to the previously described embodiment, as mold section  14  is transported in the direction of arrow  46 .  
         [0040]     Although the invention has been described in connection with various preferred embodiments, numerous variations will be apparent to a person of ordinary skill in the art given the present description, without departing from the spirit of the invention and the scope of the appended claims. For example, modifications to the preferred embodiments will be evident when this invention is used for molds having different configurations, or when this invention is used in process where the excess cured material is retained on the posterior mold sections.