Abstract:
A method and apparatus for releasing an ophthalmic lens in the dry state from an associated anterior mold part in which the lens was cast and is adhered by application of a first force which releases the periphery of the lens followed by application of a second force which releases the center of the lens.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to molding of articles of manufacture, and more particularly relates to methods and apparatus for releasing a molded lens from a mold surface. The present invention has particular application to the production of molded ophthalmic lenses such as contact lenses and intraocular lenses.  
           [0002]    Static cast molding of contact lenses is known. See, for example, U.S. Pat. No. 5,466,147 issued to Bausch &amp; Lomb Incorporated, the entire reference of which is incorporated herein by reference. A single mold unit for making a single lens comprises a female mold section having a concave optical surface and a male mold section having a convex optical surface. The female and male mold sections are complimentary shaped and are brought together to form a lens-molding cavity between the facing concave and convex optical surfaces of the female and male mold sections, respectively.  
           [0003]    Although less popular than full cast molding, forming lenses by spin-casting is also known where lens material is deposited into a female mold section and spun to form the anterior surface of the lens. The posterior surface is then formed by a lathe cutting operation. In this method of lens manufacture, excess material may also form on the female mold section with may require removal prior to lens release from the mold.  
           [0004]    The basic process for cast molding a lens is as follows. A quantity of liquid lens material is dispensed into the concave optical surface of the female mold section and the male mold section is seated upon the female mold section with the concave and convex surfaces thereof facing one another to form a lens-shaped mold cavity. The joined female and male mold sections form a single mold unit which is subject to a curing cycle (e.g., by thermal or UV radiation) thereby causing polymerization of the lens material in the mold cavity. Once the lens material has cured, the male and female mold sections must be separated to retrieve the cured lens.  
           [0005]    The opening or release of the mold sections must be carried out in a manner which will not harm the delicate lens. Once the lens has polymerized in the mold cavity, the lens and any excess lens material will have an adhesive bond to the opposite concave and convex mold surfaces. Thus, the release of the male mold section from the female mold section must be of a force strong enough to break the adhesive bond of the lens and excess lens material to the opposing mold surfaces, yet not so forceful or haphazard that the optical surfaces of the lens are harmed by the release process. Should the lens crack or be otherwise damaged during the mold release process, the lens must be scrapped, thereby lowering the output yield and increasing manufacturing costs.  
           [0006]    Once the mold sections have been separated, the lens will adhere to one of the mold surfaces and must therefore be released from the mold section on which it is retained. Both wet and dry release methods of lens release have been proposed in the prior art. In wet lens release methods, an aqueous solution is used to wet the hydrophilic lens which absorbs water and swells, causing the lens to separate from the mold surface. In dry release methods, the lens is removed from the associated mold surface while still in the dry state. The adhesive bond between the lens and mold surface is broken, usually by application of a force to the mold body, for example by squeezing or pressing against the non-optical surface of the mold to move the mold surface relative to the rigid lens. Once the adhesive bond has been broken, the lens is retrieved, for example by a vacuum picking tool. When releasing a lens from its associated mold in the dry state, the lens will necessarily absorb some of the force used against the mold to release the lens therefrom. Thus, as with the previous step of releasing the male mold section from the female mold section, the force used to release the lens from the mold must be of a force strong enough to break the adhesive bond of the lens and the opposing mold surface, yet not so forceful or haphazard that the optical surfaces of the lens are harmed by the release process. Should the lens crack or be otherwise damaged during the lens release process, the lens must be scrapped, thereby lowering the output yield and increasing manufacturing costs.  
           [0007]    In general, dry releasing a lens from the associated mold part is preferred over wet release methods. This is because the lens is much easier to handle when in the dry state as opposed to the wet state. In the dry state, it is easy to pick the lens with a vacuum picking head and move the lens from one process station to another. As stated above, past dry lens release methods include applying a force to the non-optical surface of the mold part (the surface opposite the optical surface to which the lens is adhered). While this method is satisfactory in certain mold part-lens combinations of materials and designs, it has proven unsatisfactory in instances where, for example, the mold part is formed of a relatively rigid material (e.g., ______) which makes it harder to deform the mold part relative to the lens to which it is adhered without harming the lens in the process. This situation is particularly acute when the lens is a toric lens which includes hash marks in the lens surface which tend to adhere to the mold part more strongly than the surrounding smooth surface of the lens. Releasing a lens of this type in the dry state can cause cracking particularly adjacent the toric markings of the lens. There therefore remains a need in the art for an improved method of releasing a lens from its associated mold part while in the dry state.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention addresses the problems associated with the dry release of a lens from its associated mold part by providing an apparatus and method which releases the dry lens from its associated mold part without causing harm to the lens. The invention is particularly adapted to the manufacture of contact and intraocular lenses which are molded in a mold having a female mold part to which the lens preferentially adheres following the lens curing operation.  
           [0009]    In a first aspect, the invention provides a method for releasing the anterior, convex surface of a lens having a center and a peripheral edge from an anterior mold part in which the lens has been molded, the anterior mold part having a concave optical surface to which the anterior surface of the lens is adhered following the molding operation. The anterior mold part also includes a convex, non-optical surface located opposite the concave optical surface, with each of the optical and non-optical surfaces having a center and a peripheral edge. The method comprises the step of applying a first force against the non-optical surface of the anterior mold part at a location radially outwardly of the non-optical surface center, the first force being sufficient to release at least the peripheral edge of the lens from the anterior mold part. At this point, it is possible that the entire lens will release from the mold part, however, it is more likely that the center of the lens will still remain adhered to the mold part. In this case, a second force is applied against the non-optical surface of the anterior mold part at a location adjacent the center of the non-optical surface center, this second force being sufficient to release the center of the lens from the anterior mold part whereby the lens is free to be picked from the anterior mold part for further handling (e.g., inspection, hydration, sterilization and packaging).  
           [0010]    Apparatus to carry out the method is provided comprising a mold release sleeve having an annular mold-engaging surface defining a central opening, the annular mold-engaging surface applying a first force against the non-optical surface of the mold part at a location radially outwardly of the center of the non-optical surface, the first force being sufficient to release at least the peripheral edge of the anterior surface of the lens from the concave optical surface of the anterior mold part.  
           [0011]    Should the lens not entirely release from the mold part, application of the second force is achieved through the use of a mold release pin, the mold release pin mounted for reciprocating, telescoping movement within the central opening of the mold release sleeve, the mold release pin applying a second force against the non-optical surface of the anterior mold part at a location adjacent the center of the non-optical surface center, the force being sufficient to release the center of the anterior surface of the lens from the anterior mold part whereby the lens is free to be picked from the anterior mold part for further handling. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0012]    [0012]FIG. 1 is a schematic, exploded view of a representative mold assembly for use with the invention;  
         [0013]    [0013]FIG. 2 is a schematic, cross-sectional view of the assembled mold assembly of FIG. 1; and  
         [0014]    [0014]FIG. 3 is a fragmented, schematic, cross-sectional view of the anterior mold part of the mold assembly and a lens adhered thereto immediately following removal of the posterior mold part and prior to release of the lens. The anterior mold part and lens are mounted to a preferred embodiment of the inventive apparatus which may be used for carrying out the inventive method for releasing of the lens from the mold part. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0015]    Referring now to the drawing, FIGS. 1 and 2 schematically illustrate a representative mold assembly for use in the method and apparatus of the present invention. Mold assembly  20  includes anterior mold section  21  and posterior mold section  22 . Upon assembling anterior and posterior mold sections  21 ,  22 , a mold cavity  25  is defined therebetween. The anterior mold section  21  includes a concave optical surface  23   a  which forms the convex, anterior surface  10   a  of the molded lens  10  (the surface which faces away from the eye). Anterior mold section  21  further includes a convex, non-optical surface  23   b  located opposite optical surface  23   a.  The posterior mold section  22  includes a convex optical surface  24   a  which forms the concave, posterior surface  10   b  of the molded lens  10  (the surface which contacts the eye). Posterior mold section  22  further includes a concave, non-optical surface  24   b  located opposite optical surface  24   a.  Mold parts  21 ,  22  further include respective cylindrical walls  27 ,  28  that nest when the mold parts are fully assembled as seen in FIG. 2.  
         [0016]    According to conventional cast molding methods, mold parts  21 ,  22  are first injection molded from a plastic resin in an injection molding apparatus. A curable lens material, such as a liquid polymerizable monomer mixture, is introduced into anterior molding surface  23   a,  mold parts  21  and  22  are brought into close association with the liquid being compressed to fill molding cavity  25 , and the monomer mixture is cured into a contact lens  10 . Frequently, a reservoir is provided for receiving excess lens material when the mold sections are brought together. For the illustrated mold assembly, reservoir  26  receives excess lens material; when the lens is cured, the excess lens material also cures to form a ring-like shape.  
         [0017]    As discussed above, following casting of the lens, the mold assembly consisting of the posterior and anterior mold parts must be disassembled (termed “decapping” in the art) to access the lens. With regard to the present invention, upon decapping the posterior mold part  22  from the anterior mold part  21 , it is assumed the lens  10  will remain adhered to the anterior mold part  21 . Apparatus for releasing the anterior surface  10   a  of lens  10  from concave surface  23   a  of the anterior mold part  21  will now be described.  
         [0018]    Lens  10  has a center  10   c  lying along center line C L  of FIG. 1 and a peripheral edge  10   e,  both of which generally align with the centers and peripheral edges  23   ac,    23   ap  of optical surface  23   a,  and  23   bc,    23   bp  of the non-optical surface  23   b,  of the anterior mold part  21  in which lens  10  has been molded.  
         [0019]    Referring to FIG. 3, the anterior mold part  21  with lens  10  still adhered thereto is shown mounted on the lens release apparatus of the present invention in the intended manner. It is noted that the view of FIG. 3 is one half of the apparatus and mold part, the taken through the longitudinal center thereof, the other half being a mirror image. More particularly, the apparatus includes a cylindrical mold release sleeve  30  having an annular mold-engaging surface  30 ′ which lies in a plane substantially perpendicular to center line C L , and defines a longitudinal sleeve opening  32 . The anterior mold part  21  is mounted upon sleeve  30  with the wall portion  27  thereof telescoping over the outer wall surface  30   a  of sleeve  30 . In this regard, it is noted that the outer diameter of the sleeve  30  and the diameter of the inside surface of mold wall  27  may be made very close such that mold part  21  slides in closely mating relation over sleeve  30  and becomes centrally aligned therewith. As described above, the present invention releases the lens from the mold part firstly along the peripheral edge  10   e  of the lens, followed by release of the center  10   c  of the lens. This is accomplished with the annular mold-engaging surface  30 ′ being moved along center line C L  relative to lens  10  to apply a first force F 1  against the non-optical surface  23   b  of anterior mold part  21  at a location radially outwardly of the center  23   bc  thereof. This first force F 1  is sufficient to release at least the peripheral edge  10   e  of the lens from the concave optical surface  23   a  of the anterior mold part  21 .  
         [0020]    A mold release pin  40  is provided and mounted for reciprocating, telescoping movement within the longitudinal opening  32  of the mold release sleeve  30 , the mold release pin applying a sequential second force F 2  against the non-optical surface of the anterior mold part at a location adjacent the center  23   bc  thereof. The second force F 2  is sufficient to release the center  10   c  of the anterior surface of the lens from the anterior mold part  21  whereby the lens is free to be picked from the anterior mold part for further handling. The release of lens  10  is thus carried out in a manner which will not crack or harm the lens during the release process.  
         [0021]    It is noted that the relative, longitudinal movements of mold release sleeve  30  and mold pin  40  with regard to mold part  21  is not shown but may be carried out in any manner known to those skilled in the mechanical arts. For example, mold release sleeve  30  and pin  40  may each be mounted to their own linear slide to effectuate alternate, reciprocal movement of the sleeve  30  and pin  40  along center line C L .