Plastic article or earthenware shaping or treating: apparatus – Means applying electrical or wave energy directly to work – Radiated energy
Reexamination Certificate
1999-05-26
2001-04-24
Mackey, James P. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Means applying electrical or wave energy directly to work
Radiated energy
C264S001320, C264S001380, C425S451900, C425S453000, C425S808000
Reexamination Certificate
active
06220845
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an apparatus and method for molding soft contact lenses, and particularly an apparatus and method for precuring a polymerizable monomer or monomer mixture under pressure to form a soft contact lens.
2. Discussion of the Prior Art
U.S. Pat. No. 4,495,313 to Larsen, now assigned to the assignee of the present application, discloses the polymerization of a monomer to form a soft contact lens by means of ultraviolet light. In addition, this reference also teaches that an ultraviolet light catalyst can be added to the polymerization system to effect an essentially complete polymerization.
U.S. Pat. No. 5,039,459 to Kindt-Larsen et al. entitled “Method of Forming Shaped Hydrogel Articles Including Contact Lenses” teaches the polymerization of soft contact lenses wherein the monomer/diluent mixture in a transparent polystyrene mold is exposed on one side to 1.7 jewels/centimeter squared of ultraviolet radiation for ten minutes at 55° C. (TL 09 lamps with peak radiation of 350 nm).
In addition to these two references, U.S. Pat. Nos. 4,565,348; 4,680,336; 4,640,489 and 5.080,839 all disclose the polymerization of a monomer with ultraviolet light to form a soft contact lens. The entire disclosure of each of these references are hereby incorporated by reference into this patent application.
SUMMARY OF THE INVENTION
The present invention is an apparatus and a method for precuring a polymerizable monomer mixture to form a soft contact lens in a mold with avoids decentration of the resultant lens, enables a more uniform cure for the lens during the cure step, and which reduces “puddling” or cavitation of the lens in the mold during cure.
In accordance with the present invention, a polymerizable monomer or monomer mixture is deposited in a lens mold having first concave and second convex mold halves. The mold halves are formed of polysytrene or other material transparent to actinic or visible radiation. The mold halves are transported from the deposition and mold assembly station to the precure station of the present invention, and clamped together under predetermined pressure for a predetermined period of time which may be done in a low oxygen environment. The second or convex mold half may be slightly thinner than the first or concave mold half to enable mold compliance during cure as the monomer is polymerized. The clamping pressure aligns flanges formed on the first and second mold halves to ensure that the flanges are parallel and that the respective curves of the molds are aligned. The clamping pressure also seats the second convex mold half against an annular edge formed on the first mold half to essentially sever any excess monomer from the monomer contained within the mold.
After a predetermined clamping period, the hydrogel is exposed to actinic or visible radiation, such as an UV light source, to partially cure the hydrogel to a gel state. After a second predetermined period of exposure under clamping pressure, the clamping action and the UV radiation may be removed, and the partially precured hydrogel lens is transported in the mold to a curing station for complete polymerization and cure. Alternatively, a complete cure may be effected in the apparatus.
It is an object of the present invention to provide a novel means for precuring a polymerizable monomer or monomer mixture to form a soft contact lens. The means includes a transport for intermittently transporting a plurality of contact lens molds to the precure station in a low oxygen environment. The contact lens molds include first and second mold halves with a polymerizable monomer or monomer mixture therebetween. The means also include a plurality of means for clamping the first mold half to the second mold half for a predetermined period of time in a low oxygen environment. The polymerizable monomer or monomer mixture is then exposed to actinic radiation for a predetermined period of time while it is under pressure to partially or completely cure the monomer or monomer mixture.
The clamping pressure may be applied by an annular air cylinder, spring driven annular cylinder, or physical weights which allows actinic radiation to pass through the annulus of the cylinder and through one or more of the mold halves and into the monomer or monomer mixture. The means may include a means for controlling the duration and intensity of the clamping pressure, and the duration and intensity of the actinic radiation. It has been found that under certain conditions involving a pre-cure or partial cure of the monomer, that the surface energy attraction between the clamping means and the mold half may result in premature separation of one or more sets of mold halves from the carrier pallet when the clamping means is retracted at the end of the pre-cure step.
The exact cause of this phenomena is unknown, but the mold halves and monomer are very light in weight, and the attraction may involve surface energy, static electricity, or migration of minute amounts of oils from the mold halves to the clamping means over time. When the precure apparatus cycles, the attracted set of mold halves is stacked on another set in a different pallet, eventually leading to rupture of the mold halves and contamination of the production equipment with partially cured monomer. While the incidence of such premature separation is low, the cost of shutting down a line operating in a controlled atmosphere for cleaning is very high, and thus to be avoided.
It is therefore an object of the present invention to minimize the surface energy attraction between the mold halves and the clamping means, and the opportunity for premature separation of the mold halves from the carrier pallet.
It is another object of the present invention to provide a clamping means which will provide radially uniform pressure to clamp the mold halves together.
Another object of the present invention is to provide a novel method of precuring a polymerizable monomer or monomer mixture to form a soft contact lens. The method includes a step of depositing a polymerizable monomer or monomer mixture in a contact lens mold having first concave and second concave mold halves with the monomer therebetween. The mold halves are then clamped together with a predetermined pressure and then exposed to radiation to partially polymerize the monomer to a precured gel-like state. The clamping pressure is then relieved and the lens is then cured with additional radiation or a combination of heat and radiation.
In the preferred embodiment the radiation source may be actinic, electron beam or radioactive source, but preferably is an ultraviolet lamp which irradiates the monomer at 2-4 mW/cm
2
for 5-60 seconds, but preferably 20-40 seconds. Radiation may also be from a high intensity UV source that is pulsed or cycled.
The clamping step aligns the mold halves, causes excess monomer to be removed from the mold cavity, and seats a compliant second mold half against a first mold half for the precure step.
It is an object of the present invention to precure a polymerizable monomer or monomer mixture to a gel-like state wherein polymerization has been initiated throughout the monomer, and utilize the shrinkage of the monomer and the compliance of the mold halves to seal and hold the mold halves together for the remainder of the cure period. This substantially avoids decentration defects which can occur if the back curve mold half is tipped or rotated with respect to the front curve mold half prior to cure.
It is another object of the present invention to precure the hydrogel in a low oxygen environment to prevent undesired absorption of oxygen by the monomer.
It is another object of the present invention to provide an adjustable means for varying the clamping pressure during the precure step.
It is another object of the present invention to minimize the surface energy attraction between the clamping means and the mold halves while simultaneously providing a radially uniform clamping pressure during the clamping step.
It is ano
Adams Jonathan Patrick
Bjerre Kaj
Christensen Svend
Kindt-Larsen Ture
Martin Wallace Anthony
Johnson & Johnson Vision Care Inc.
Mackey James P.
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