Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Utilizing plasma – electric – electromagnetic – particulate – or...
Reexamination Certificate
1999-12-07
2003-01-28
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Utilizing plasma, electric, electromagnetic, particulate, or...
C264S102000, C264S334000, C425S073000, C425S150000, C425S808000
Reexamination Certificate
active
06511617
ABSTRACT:
1. FIELD OF THE INVENTION
The present invention relates generally to the field of manufacturing ophthalmic lenses, especially molded, hydrophilic contact lenses, and more specifically, to a high speed, automated contact lens molding system for automatically producing ophthalmic lenses.
2. DESCRIPTION OF THE PRIOR ART
The direct molding of hydrogel contact lenses is disclosed in U.S. Pat. No. 4,495,313 to Larsen, U.S. Pat. No. 4,565,348 to Larsen, U.S. Pat. No. 4,640,489 to Larsen et al., U.S. Pat. No. 4,680,336 to Larsen et al., U.S. Pat. No. 4,889,664 to Larsen et al., and U.S. Pat. No. 5,039,459 to Larsen et al., all of which are assigned to the assignee of the present invention. These references disclose a contact lens production process wherein each lens is formed by sandwiching a monomer between back curve (upper) and front curve (lower) mold sections carried in a 2×4 mold array. The monomer is polymerized, thus forming a lens, which is then removed from the mold sections and further treated in a hydration bath and packaged for consumer use. Hydration and release from the mold of this type of lens is disclosed in U.S. Pat. No. 5,094,609 to Larsen, and U.S. Pat. No. 5,080,839 to Larsen, both of which are assigned to the assignee of the present invention.
At the present time, partially automated and semi-automated processes are used in the production of soft contact lenses, however, high production rates are not achievable, partly due to the strict process controls and tight tolerances necessary in the production of high quality contact lenses.
Typically, the molds for these lenses are formed, generally by injection molding, from a suitable thermoplastic, and the molds, usually in frames associating a number of such molds with support structure are shipped from a remote molding facility and stored for use in a production facility for manufacturing contact lens blanks.
It is known that the use of lens molds maintained under normal atmospheric conditions leads to inhibition of, and thus incomplete and non-homogenous curing of the reactive monomer composition at the surface of the lens, which in turn can adversely alter physical properties of the lens. This phenomenon has been traced to the presence of oxygen molecules in and on the lens mold surface, which is due to its inherent capability of the preferred polystyrene molding material to sorb quantities of oxygen. During molding, this oxygen can be released to the polymerization interface with the reactive monomer composition in amounts which exceed acceptable maximums as determined by empirical testing. More specifically, the oxygen copolymerizes rapidly with the reactive monomer but the polymerization chain thus formed is readily terminated, the result being a decrease in rate of monomer reaction, the kinetic chain length, and the polymer molecular weight. The criticality of oxygen level and the difficulty of implementing effective control protocols may be appreciated by recognizing that the level of oxygen at the reactive monomer/mold interface must be controlled to approximately 300 times less than the concentration of oxygen in air (3×10
−3
moles/liter).
This recognized problem has been addressed in the art by careful but time consuming and laborious preconditioning of the molds utilizing chambers evacuated to approximately 1 torr and maintained in this condition for a period of not less than 6-12 hours. Any interruption of the work cycle such as might be caused by a power interruption requires reinitiation of the conditioning treatment.
Even brief exposure of the molds to air after degassing, as in normal manufacturing handling is detrimental; it has been learned that even a one minute exposure to air results in sufficient absorption of oxygen to require 5 hours degassing to reacquire an acceptable condition. Accordingly, a degassing operation immediately proximate the manufacturing line, particularly for large volume transfers of molds with different exposure times was deemed impractical, and no real improvement over the present system.
The problem is complicated by the fact that the front and back curves of the juxtaposed mold sections exhibit different thicknesses, leading to potentially different exposure of the reactive monomer composition to oxygen across the surfaces of varying cross-sections which could result in distortion of the lens and degradation of its optical properties. Thus, the concentration distribution of oxygen in the respective mold sections or halves remains symmetrical for short degas times, but becomes progressively less symmetrical for longer degas times, and the anomaly can cause uneven cure and different properties between the front and rear surface. For example, the convex male mold may be degassed within about 2 hours, whereas the concave female mold may not be entirely degassed even after 10 hours.
The commercial demand for soft contact lenses has dictated the development of continuous or at least semicontinuous manufacturing lines. The criticality of manufacturing specifications in turn demands automated handling of the lens manufacturing operation.
Another problem specific to the production process used to produce contact lenses in accordance with the teachings of the foregoing patents is that the mold portions are surrounded by a flange, and the monomer or monomer mixture is supplied in excess to front mold curve prior to the mating of the mold halves. After the mold halves are placed together to define the mold cavity, the mold is weighted and the excess monomer or monomer mixture is expelled from the mold cavity into the space between the flanges. Upon polymerization, this excess monomer or monomer mixture forms a waste by product known in the art as a HEMA ring (when hydroxyethylmethacrylate monomer is used) which must be removed to avoid contaminating the production line or the packaged lenses.
In these prior art processes, corona discharge devices are at times utilized to create an adhesion zone on the underside of the back curve mold half, to thereby cause the HEMA ring to preferentially adhere to the back curve at the time the mold haves are separated.
The prior art process for separating the mold halves and removing the lens consists of preheating, heating, prying and removal. Hot air provides the heating, mechanical leverage the prying, and the removal of the HEMA ring is manual. Heating the mold by convection is not an efficient heat transfer technique. From the time a mold array enters the heating apparatus until the back curve mold half is completely removed requires on the order of one minute.
The present method for removing the lens is to apply heat to the back curve mold half by means of a heated air stream. The heating is done in two stages: a preheat stage and a heat/pry stage. In the heat/pry stage, the mold is clamped in place and pry fingers are inserted under one side of the back curve of the mold, and an upward pry force is applied during the heating cycle. When the required temperature has been reached, the back curve mold portion breaks free and one end is lifted by the pry finger and the mold half is removed. The remaining mold and lens is then removed from the heating and prying station, where remnants of the HEMA ring are removed manually. The temperature gradient achieved in the convection heating of the lens is relatively small, since the time it takes to heat the back curve mold half enables significant conductive heating of the lens, thereby decreasing the gradient, and making separation of the molds difficult. Adding more heat to the lens mold at separation only causes the back curve mold to soften and impair efficient mechanical removal. Finally, manual removal of the remnants of the HEMA ring is labor intensive and costly.
While the aforesaid production processes have some efficacy in the production of soft contact lenses they suffer a number of disadvantages which have hindered the development of a high speed automated production line. When mold frames are demolded in large batch processes, a power outage at the wrong time can effec
Adams Jonathan Patrick
Andersen Finn Thrige
Beaton Stephen Robert
Christensen Svend
Jensen Allan G.
Johnson & Johnson Vision Care Inc.
Vargot Mathieu D.
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