Abstract:
A method for separating one mold section from another mold section and a contact lens molded in the two mold sections provides improved reliability that the lens is not damaged during this operation and that the lens is retained selectively on the desired. Various embodiments of apparatus for carrying out the method are disclosed.

Description:
This application is a continuation of U.S. application Ser. No. 08/964,169 filed Nov. 4, 1997 (now U.S. Pat. Ser. No. 6,033,603), which claims priority under 35 USC 119(e) of prior provisional application Ser. No. 60/030,565 filed Nov. 6, 1996. 
    
    
     BACKGROUND OF THE INVENTION 
     Static cast molding of contact lenses involves casting a contact lens in a mold cavity formed by two mold sections, an anterior mold section including a molding surface for forming the anterior lens surface and a posterior mold section including a molding surface for forming the posterior lens surface. Representative static cast molding methods are disclosed in U.S. Pat. No. 5,271,875 (Appleton et al.), U.S. Pat. No. 4,197,266 (Clark et al.), U.S. Pat. No. 4,208,364 (Shepherd), U.S. Pat. No. 4,865,779 (Ihn et al.), U.S. Pat. No. 4,955,580 (Seden et al.), and U.S. Pat. No. 5,143,660 (Hamilton et al.). 
     Following casting of the lens, the mold assembly is disassembled and the lens is removed from the mold assembly. 
     One approach for recovering the contact lens involves exposing the entire mold assembly, including the two mold sections and the molded lens therebetween, to an aqueous solution (including water alone). Hydrophilic lenses absorb water to form a hydrogel, and when the lens absorbs water, it swells and is released from both the posterior and anterior molding surfaces of the respective molds. Often, the aqueous solution may also facilitate separation of the two mold sections from each other. The lens can then either be separated from the mold sections, either manually or with automated handling equipment. Representative “wet release” methods are discussed in U.S. Pat. No. 5,264,161 (Druskis et al.). 
     A second approach involves, initially, a “decapping” step, i.e., separating one mold section from the second mold section with the lens being retained in the second mold section. Then, the lens is removed (or released) from the second mold section, either by exposure to an aqueous solution (wet release) whereby the lens absorbs water to facilitate its separation from the molding surface of the mold section, or by simply removing the lens from the second mold section without the use of an aqueous solution (dry release). 
     Although the decapping and release operations may seem straightforward, various problems have been encountered. This is especially true for cast molding methods where the molding operation results in the two mold sections being held tightly together, or where the lens has a tendency to stick to one or both molding surfaces of the mold sections. For example, when the first mold section is decapped from the second mold section with the lens being retained in the second mold section, the surface of the lens may be damaged as pieces of lens stick to the first mold section. Also, since the lens has not yet been hydrated, it is brittle, and the decapping operation can fracture the lens. 
     As another example of problems encountered, it is often desirable that the lens is selectively retained in a desired mold section to minimize manual handling or inspection. However, the decapping process can result in the lens not being retained in the desired mold section as intended, thus requiring manual handling or inspection to ensure that the lens is not discarded with the mold section removed in the decapping process. Various approaches for selective retention of the lens in a desired mold section have been proposed. U.S. Pat. No. 5,271,875 (Appleton et al.) discloses using mold sections made of different materials, however, this complicates the injection molding process. It is also known to treat one of the mold surfaces with plasma treatment to facilitate selective retention of the lens, however, this process adds additional steps and cost to the overall molding process. 
     Consider the case where it is desired to retain the molded lens on the anterior mold. A decapping operation of which applicant is aware involves decapping the posterior mold (i.e., separating the posterior mold from the anterior mold and molded lens) by holding the anterior mold firmly (for example, in a collet), followed by pulling the posterior mold or by pushing the posterior mold from the anterior mold (for example, with collet fingers). Applicant has found that this approach provides some success, however, yield is not entirely satisfactory due to damage to lenses during the decapping step, or lenses not being retained with the anterior mold as intended. Another approach would involve decapping the posterior mold by holding the posterior mold, followed by applying pressure to the anterior mold to separate the anterior mold and the lens from the posterior mold. However, this approach is less successful than the aforementioned approach in that there is a higher rate of lens damage and/or occurrence of the lens not being retained in the anterior mold. 
     The operations are further complicated by the fact that many static cast molding methods result in a ring of cured excess lens material being obtained in addition to the molded lens. Thus, while it is generally desirable that the lens is selectively retained in one desired mold section, as discussed above, it is often also desirable that the ring of cured excess lens material be selectively retained on the other mold section. 
     SUMMARY OF THE INVENTION 
     The invention provides a method that includes a decapping operation to separate one mold section from a second mold section and a contact lens. The method provides improved reliability that the lens is retained selectively on the second mold section as intended. Additionally, the potential for damage to the lens during decapping is reduced. Accordingly, yield can be increased while minimizing manual handling or inspection. 
     According to a first embodiment, the method comprises: disengaging the first mold section from the second mold section and contact lens by applying a force to the first mold section in a manner that moves the first mold section away from the contact lens surface and the second mold section while minimizing stresses at an interface of the second mold section molding surface and a contact lens surface in contact therewith, and separating the first mold section from the second mold section with the contact lens being retained in the second mold section. 
     According to a second embodiment, the method comprises: applying a force to a peripheral region of the first mold section whereby a peripheral region of the first mold section molding surface is first separated from the contact lens surface followed by a central region of the first mold section molding surface being separated from the contact lens surface; and separating the first mold section from the second mold section with the contact lens being retained in the second mold section. 
     According to preferred embodiments, the lens is retained selectively on a molding surface of the anterior mold section, and a ring of cured excess lens material is removed with the posterior mold section. 
     The decapping operation may be followed by a dry release operation to release the lens from the second mold section, whereby the lens is recovered in a dry state for post-release processing. 
     The decapping operation minimizes manual handling of the lens and mold sections. The invention obviates the need for pre-molding operations to facilitate decapping or selective retention of the lens on a desired mold section, such as pretreatment of the mold surfaces, and the invention obviates post-mold operations to assist in decapping, such as application of heat or chemical treatments to the mold assembly. 
     Additionally, the invention provides apparatus for carrying out the methods of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic exploded view of a representative mold section assembly for use in the invention, and FIG. 2 is a schematic cross-sectional view of an assembled mold assembly. 
     FIG. 3 is a top perspective view of an apparatus according to a first embodiment of the invention. 
     FIG. 4 is a partial cross-sectional view of the apparatus shown in FIG. 3 and a mold assembly. 
     FIGS. 5 a  to  5   c  illustrate schematically the mold assembly during the decapping operation. 
     FIG. 6 is a cross-sectional view of an apparatus according to a second embodiment of the invention and a mold assembly. 
     FIG. 7 is a cross-sectional view of an apparatus according to a third embodiment of the invention and a mold assembly. 
     FIG. 8 is a cross-sectional view of an apparatus according to a fourth embodiment of the invention and a mold assembly. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     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 . When mold sections  21  and  22  are assembled, anterior molding surface  23  (which forms the anterior surface of molded lens  10 ) and posterior molding surface  24  (which forms the posterior surface of molded lens  10 ) define a molding cavity  25 . For the illustrated mold assembly, mold sections  21  and  22  include respective cylindrical walls  27 ,  28  that nest when the mold sections are fully assembled. 
     According to conventional cast molding methods, mold sections  21  and  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 , mold sections  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. 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 is cured also to form a ring-like shape. 
     As discussed above, following casting of the lens, the mold assembly is disassembled and the lens is removed from the mold assembly for further processing and/or packaging. 
     FIGS. 3 and 4 illustrate one embodiment of an apparatus for carrying out the decapping operation, FIG. 4 being a partial cross-sectional schematic view of the apparatus shown in FIG.  3 . The apparatus includes clamps  41  for applying forces to a peripheral region of posterior mold; for the illustrated mold assembly, portion  42  of clamps  41  contact a peripheral region of upper flange  29  that extends above the molding surface of posterior mold  22 . Clamps  41  are supported by support  43  that includes surface  46  for supporting mold assemblies, such that clamps  41  are arranged radially with respect to a mold assembly received in the apparatus and supported on surface  46 . Preferably, the surfaces  47  of the clamps that contact the posterior mold are contoured to correspond with the outer surface of the posterior mold, as better illustrated in FIG.  3 . Also, it is preferred that when surfaces  47  are engaged with the posterior mold, at least half of the perimeter of the outer posterior mold surface makes contact with surfaces  47  in order to ensure that forces are applied relatively uniformly about the perimeter of the posterior mold. 
     In operation, after a mold assembly is placed on surface  46 , clamps  41  are actuated by actuating means, such as piston and cylinder actuators (not shown), to effect clamping of the posterior mold, thereby applying radial forces about a peripheral region of flange  29 . 
     FIGS. 5 a  to  5   c  sequentially and schematically illustrate the desired effect of the clamping action on the posterior mold. The decapping operation separates the anterior mold from the posterior mold in a manner that the periphery of molding surface  24  is first separated from the surface of contact lens  10  in contact therewith, followed by central region of molding surface  24  being separated from the surface of contact lens  10 . In other words, the molding surface of posterior mold surface is peeled from the anterior mold and contact lens, beginning at the periphery and then inwardly towards the center. At this point in the manufacturing process, the contact lens is in a dry state, and this action ensures that damage to the contact lens is minimized, due to fracturing the lens or pieces of the lens sticking to the posterior molding surface. This action also ensures that the contact lens remains retained on the anterior mold section as intended. As pointed out above, the clamping forces should be applied relatively uniformly about the perimeter of the posterior mold to facilitate this peeling action. 
     With reference to FIG. 4, the clamping force is applied to the peripheral region of posterior mold  22 , a region remote from molding surface  23 . Also, anterior mold section and the contact lens retained therein remain free to move away from the posterior mold section as the clamping force is applied. This ensures that stresses are minimized at an interface of the anterior mold section molding surface  23  and the surface of contact lens  10  in contact therewith. It has been found that when stresses are introduced at this interface, higher incidence of the lens not being retained with the anterior mold section  21  occurs. 
     After the decapping operation is complete, the anterior mold and contact lens can be recovered, such as with a pick-up mechanism, for further processing. Generally, further processing will include disengaging the contact lens from the anterior mold, which may include applying a force to the anterior mold section to assist in disengaging the contact lens. The recovered lens will generally be hydrated, sterilized and packaged. The posterior mold, and any ring of excess cured lens material  11 , can be discarded. 
     FIG. 6 illustrates schematically another embodiment of an apparatus for carrying out the decapping operation. 
     The apparatus includes a wedge  60 , the bottom of which may be inserted in an actuator (not shown), that is movable in a direction indicated by numeral  62  and axially aligned with a central axes of mold sections  21 ,  22 . Wedge  60  includes an inner surface  63  and an outer surface  64 , surfaces  63  and  64  meeting to form a tapered wedge-shaped tip  65 . For the illustrated mold assembly, tip  65  is inserted between cylindrical wall sections  27 ,  28 , in a region peripheral to the molding surfaces of the mold sections. Accordingly, inner surface  63  contacts an outer surface of cylindrical wall section  27 , and outer surface  64  contacts an inner surface of cylindrical wall section  28 . It is preferred that inner surface  63  substantially corresponds to the surface of cylindrical wall section  28 ; in this manner, wedge  60  assists in stabilizing anterior mold section  21  against forces exerted as the wedge is moved against posterior mold section  22 . However, inner surface  63  should not fit too tightly against the contacting surface of anterior mold section  21  so that mold section  21  has freedom to move away from posterior mold section. 
     The apparatus can further include a pin  67  for insertion in a support that can remain stationary during the decapping operation. Accordingly, as tip  65  exerts the force to a peripheral region of the posterior mold section, along the direction aligned axially with central axes of the mold sections, pin  67  exerts a counteractive force in an opposite direction. In this manner, the decapping operation results in an effect similar to that illustrated in FIGS. 5 a  to  5   c  and discussed above. Following decapping, the posterior mold can be removed with a pick-up mechanism and discarded; it has been found that the ring of excess cured lens material  11  will generally remain with the posterior mold. The anterior mold and lens can be recovered for further processing. 
     FIG. 7 illustrates schematically another embodiment of an apparatus for carrying out the decapping operation. This apparatus includes a wedge  70  having tip  75  and that is generally similar in structure to wedge  60 . During the decapping operation, wedge  70  may remain stationary, whereas pin  77  is movable along the direction shown by numeral  72  and aligned with a central axis of the mold sections, so as to force tip  75  between cylindrical wall sections  27 ,  28 . Again, the decapping operation results in an effect similar to that illustrated in FIGS. 5 a  to  5   c  and discussed above. 
     This embodiment further includes a stabilizing plunger  78  which serves to further stabilize anterior mold  21  against forces exerted as the wedge is moved against posterior mold section  22 . Plunger  78  includes dowel  76  that is received in slot  79  of wedge  70 . Plunger  78  may be spring-biased with respect to wedge  70 , as schematically illustrated in FIG.  7 . However, it is preferred that plunger  78  does not contact surface  30  (opposed to molding surface  23 ) of mold section  27  surface during the decapping operation so that the interface between the molding surface of anterior mold section  27  and the contact lens is not disturbed. 
     One advantage of inverting the mold assembly as shown in FIG. 7, in contrast to the arrangement in FIG. 6, is that if the ring of excess cured lens material is not consistently retained on posterior mold, it will still drop away from the anterior mold and contact lens along with the posterior mold section. 
     FIG. 8 illustrates schematically yet another embodiment of an apparatus for carrying out the decapping operation. 
     The apparatus includes a hollow cylindrical member  80  that is movable in a direction indicated by numeral  82  and axially aligned with a central axes of mold sections  21 ,  22 . Hollow cylindrical member  80  includes. an inner surface  83  and an outer surface  84 , surfaces  83  and  84  terminated at annular surface  85 . For the illustrated mold assembly, surface  85  contacts the bottom periphery of cylindrical wall section  28 . Preferably, inner surface  83  has a diameter that substantially corresponds to the outer surface of cylindrical wall section  27 ; in this manner, hollow cylindrical member  80  can assist in stabilizing anterior mold section  21  against forces exerted as the hollow cylindrical member is moved against the bottom end of posterior mold section  22 . However, inner surface  83  should not fit too snug against the contacting surface of anterior mold section  21  so that mold section  21  has freedom to move away from posterior mold section. 
     The apparatus further includes pin  87  that can remain stationary during the decapping operation. Accordingly, as surface  85  exerts force to bottom periphery of the posterior mold section, pin  87  exerts a counteractive force in an opposite direction. In this manner, the decapping operation results in an effect similar to that illustrated in FIGS. 5 a  to  5   c.    
     FIG. 8 also illustrates an alternate embodiment of a stabilizing plunger that stabilizes the anterior mold as forces are exerted on the posterior mold. As shown in FIG. 8, upper surface  91  of plunger  88  is shaped to substantially correspond to surface  30  (opposed to molding surface  23 ) of mold section  27 , and plunger  88  may include a vacuum line  92 , extending through a central bore in the plunger, connected to vacuum means (not shown). Plunger  88  may be spring-biased with respect to cylindrical member  80  as schematically illustrated in FIG.  8 . In operation, as cylindrical member  80  is moved towards the mold assembly, surface  91  of plunger  88  is brought into contact with surface  30 , and suction is provided through line  92  to stabilize further anterior mold  27  during the decapping operation. 
     Various embodiments of the present invention are evident. Although FIGS. 1 and 2 have been included to illustrate a representative mold assembly for use in the invention, the invention is in no way limited to this specific mold assembly. A person of ordinary skill in the art can readily determine other mold assemblies for which the invention has applicability, or determine other embodiments of apparatus for carrying out the invention.