Patent Application
20070102835
The present invention relates to an in-line process for preparing contact lenses. More particularly, the present invention relates to an in-line process continuous process for making contact lenses and in particular, silicone containing hydrogel lenses.
Processes for making contact lenses and in particular silicone hydrogel lenses are well known in the art. Reference is made to U.S. Pat. No. 5,260,000, the disclosure of which is incorporated herein by reference, for a description of a typical process for producing such lenses.
Briefly, the current practice involves the preparation of a mixture of a silicone-containing monomer, a hydrophilic monomer and an organic diluent. This mixture is cast into a mold and cured or polymerized to obtain a shaped lens article. The lens article, still retained in the mold is placed in an oven and maintained at an elevated temperature for a time sufficient to drive off the organic diluent that may be entrapped within the polymerized lens matrix. After cooling, the article is removed from the mold and subjected to further treatments to produce the contact lens.
Current manufacturing processes use a batch oven process for heating to remove the organic diluent. Such batch heating requires dedicated and mostly manual material handling techniques to load and unload the heating oven. Batch trays also are dedicated for parts handling and orientation within the heating oven. In a typical batch operation, trays containing a plurality of the molds are stacked in a forced air oven and are kept in the oven for up to three hours at 60° C. in order to remove the organic diluent.
Accordingly, to date, the production of silicone hydrogel contact lenses has been labor intensive first to manually load a plurality of molds onto a dedicated tray, then to manually load a plurality of individual trays into the heating oven and then to manually unload the trays from the oven.
Accordingly, it is an object of the present invention to provide a method of producing silicone hydrogel lenses that reduces the amount of manual handling as opposed to the current batch method.
Another object is to provide a method that provides a first-in-first out product flow.
A further object is to provide a method that provides for the continuous movement of molds or batches of molds through a heating/cooling chamber.
In accordance with the present invention, the molds containing the polymerized silicone hydrogel are arranged in trays placed on a moving conveyor. The conveyor moves along a path of travel that extends into and through a heating chamber. The speed of the conveyor, the size of the chamber and the temperature control are all selected to provide a residence time and temperature conditions within the camber sufficient to drive off the organic diluent from the polymerized silicone hydrogel. The path of the conveyer subsequently carries the trays through a cooling zone and then through a treating zone where lenses are removed from the molds for further treatment.
The heating chamber can be horizontally oriented with the cooling zone located downstream along a horizontal path of travel. In an alternative arrangement the heating chamber is vertically oriented so heating occurs during ascent through the heating chamber and cooling occurs on the subsequent descent.
In one embodiment, a plurality of individual molds each containing a silicone hydrogel article are placed in trays which are then placed on the conveyor for travel through the heating and cooling chambers. An alternative is to pass individual molds continuously through the heating and cooling chambers.
Accordingly, the present invention may be characterized in one aspect thereof by a method for producing a shaped ophthalmic biomedical article blank such as a silicone hydrogel contact lens or the like comprising:
a) casting a curable liquid formulation including an organic diluent into a mold;
b) curing the liquid formulation within the mold to form the article blank;
c) conveying the article blank and the mold along a path of travel extending through a heating zone, the conveying allowing the article blank and the mold to remain in the heating zone for a time sufficient to drive off the organic diluent and produce a substantially diluent-free article blank within the mold; and
d) moving the article blank and the mold from the heating zone and along the path of travel through a subsequent treating zone to further treat the substantially diluent-free article blank within the mold.
Referring to the drawings,
In the context of the present invention the article is a silicone hydrogel lens. A composition and method for making a silicone hydrogel lens are known in the art and reference is made to the composition and method as described in U.S. Pat. No. 5,260,000, the disclosure of which is incorporated herein by reference. Briefly, and as stated in U.S. Pat. No. 5,260,000, a monomeric mixture is prepared comprising a silicone-containing monomer, a hydrophilic monomer and an organic diluent.
This mixture 10 as shown in
After cure is complete, the lens blanks still in the mold 12 is heated to drive off the organic diluent. In the embodiment of the invention as shown in
Progress of the tray 18 is continuous and other trays 18 are added to the conveyor as the mixture in additional individual molds 12 go through a curing step. The speed of the conveyor along its horizontal path of travel together is sufficient to allow each tray to remain in the zone 22 for a time sufficient to drive off the organic diluent from the cast lenses. In this respect, the size of the heating zone 22 and the temperature/air flow parameters within the heating zone are selected so these parameters together with the linear speed of the conveyor allow for the appropriate residence time.
After passage through the heating zone 22, the conveyor carries the trays 18 through the cooling zone 24. Upon passage thought the cooling zone, the trays are removed from the conveyor and emptied. Individual molds 12 then are treated to effect the removal of the cast article 14.
In the embodiment of
Suitable mechanisms for maintaining the trays horizontal during the transition from upward to downward travel (and from downward to upward travel) are known in the art. Trays 18, upon reaching the bottom or end of the cooling zone are removed from the shelves are then transferred to a horizontal path for conveying to a station where the lenses are separated from the molds.
Also associated with the heating chamber 30 are load/unload systems for moving molds to be heated into the heating chamber through a bottom located inlet 31 and out of the chamber through a top located outlet 33. The load/unload systems are schematically represented in
The outer and inner shells 32, 34 are vertically oriented and one of the shells rotates about a vertical axis 40 relative to the other. For purposes of description the apparatus will be described as if the inner shell 34 rotates and the outer shell 32 is fixed.
Fixed to the outer shell 32 and extending inward from the inner surface of the outer shell is a helical rail 42. As best seen in
Provided on the outer surface of the inner shell 34 are vertically oriented ribs 48. These ribs are at equally spaced intervals around the periphery of the inner shell. As noted hereinabove, the helical rail 42 does not extend to the inner shell. Accordingly there is a space between the rail and the surface of the ribs so the ribs pass close to, but do not contact the rail.
In the context of one embodiment, the relationship between the diameter of a mold 12 and the space 44 between the outer and inner shells 32, 34 is critical. In this respect, and as best seen in
In operation, a first of the molds 12 that contains the cast article for heating is loaded through the bottom located inlet 31 and onto the lowermost portion of the helical rail 42. As the inner cylindrical shell 34 rotates in a continuous or stepwise fashion, one of the vertical ribs 48 engages the mold on the rail and pushes the mold along the helical rail. Movement of the mold is constrained by the inner surface of the outer shell 32 so the mold is forced to move up the helical rail.
Now, when a second mold is loaded through the inlet 31 and onto the helical rail, the rotation or step wise indexing of the inner shell 34 brings a following rib 48 into engagement with the second mold and moves it along the helical rail. In this fashion molds are loaded sequentially onto the helical rail and are moved progressively, either continuously or step wise, upwardly along the helical rail and through the heating zone represented by the heating chamber 30.
The angle of inclination of the helical rail 42, the pitch 46 of the rail and the timing of the rotation of the inner shell 34 determine the overall time the molds 12 take to travel through the heating chamber. As with the previous embodiments, this time, considered the residence time of the molds within the heating chamber 30, is sufficient to drive off the organic diluent component of the lens forming mixture. Upon leaving through the outlet 33 the heated molds are conveyed through a cooling zone after which the lens is separated from the mold for further operations.
In a typical batch operation of the prior art, two hours of production may involve the handling and processing of upwards of 1500 individual molds. With an apparatus as shown in
Accordingly, the method and apparatus of the present invention provides an improved method and apparatus for heating the silicone hydrogel lenses to drive off the organic diluent. The invention further provides an inventory management system that is a true first-in-first-out system as opposed to a batch operation and that has a larger through put than the conventional batch operation.
Accordingly, it should be appreciated that the present invention accomplishes its intended objects by providing a method of producing silicone hydrogel lenses that reduces the amount of manual handling as opposed to the current batch method. The present invention further provides a method and apparatus that allows for a first-in-first out product flow and that provides for the continuous movement of molds or batches of molds through a heating /cooling chamber.
