Stock material or miscellaneous articles – Composite – Of polycarbonate
Reexamination Certificate
1998-06-26
2001-05-22
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polycarbonate
C428S420000, C428S424200, C428S424400, C428S520000, C156S331700
Reexamination Certificate
active
06235396
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to methacrylate polymers useful as adhesives, and in particular to the covalent joining of a polymeric film to bulk polymerizable material during formation of an optical polymeric lens.
BACKGROUND OF THE INVENTION
Most ophthalmic lenses dispensed today are made from plastic materials, such as diethylene glycol bis(allylcarbonate), a common form thereof being sold under the trademark “CR-39” by PPG, or other allylbased optical polymers. Plastic lenses are inexpensive to fabricate yet possess good optical properties and are lighter in weight than glass lenses. In the manufacture of plastic lenses it is often desirable to incorporate optically useful components, such as polarizing films, or films containing various dyes for different purposes, for example, to provide photochromic properties. Such films are well-known in the art and are generally formed as thermoplastic polymers, an example of which is a polymer film formed from polyvinyl alcohol. Typically, these films are either laminated between two formed lens blanks using an adhesive such as polyurethane or optical-grade epoxy, or a film previously coated with polyurethane is sandwiched within a mold filled with monomer that is then reacted to encapsulate the film and form a complete lens blank. The result is the formation of either a laminated or cast lens blank, manufactured with different diopters, and then shipped to optometrists and/or optometric laboratories where the lenses are ground to prescription and fit to various eye glass frames.
A significant problem that arises with the formation of such laminated lens blanks is a propensity for such blanks to shear when subjected to shock or when ground improperly. Shearing occurs along the interface of the polymer film and the main polymeric substrate; in effect, if the polymer film is only weakly bonded to the blanks, it acts somewhat as a release agent for the laminated substrate components when under stress. Similarly, this interface can be a weak spot even in cast blanks.
Another problem found with current adhesives is their limited shelf life before becoming unusable, as short as 48 hours. Additionally, current adhesives tend to seep, decreasing mold life. Moreover, in existing laminated lenses, the polymer film tends to yellow, presenting varying color lens to lens, or over time.
SUMMARY OF THE INVENTION
The present invention addresses the foregoing problems and provides an improved method for integrating the film and substrate so that under normal use as well as when improper grinding procedures are used, or the lens is subject to shock, the lens does not separate into components but remains an integral whole. The adhesive formulations of the current invention have long shelf life, several months to a year, or more if stored in nitrogen, with no significant discoloration. The invention is achieved by covalently joining the film to the optical substrate with an adhesive composition that takes advantage of the fact that the film and substrate contain reactive groups. The optical substrate contains allyl groups whereas the film laminated between opposing substrate surfaces also contains a reactive group, such as an hydroxy group. The adhesive composition is formed from a plurality of methacrylate polymers so that the resultant polymethacrylate has at least two associated groups that are covalently reactive with corresponding groups respectively on the film and optical substrate. Preferably the optical substrate is formed from the polymerization of a glycol bis(allylcarbonate), the polymeric film is a polyvinyl alcohol film, and the adhesive composition comprises (a) a polymethacrylate terpolymer formed to have pendant allyl and hydroxy groups and (b) an uncured polyurethane. The pendant allyl group is covalently reacted with the olefinic components of the optical polymer. Preferably, when the lens is cast, the polymeric film is positioned within the molding frame and optical lens monomer is added on opposite sides of it, to solidify material around the film. The pendant hydroxy group is covalently reacted with the uncured polyurethane, and the uncured polyurethane is covalently reacted with the polyvinyl alcohol film, thereby forming a covalently integrated laminate.
In addition to the previously mentioned advantages, this invention's covalent bonding means a much thinner adhesive layer (which is on the order of several nanometers, rather than micrometers, thick) can provide improved adhesion.
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Kruer Kevin R.
Lyon & Lyon LLP
Nakarani D. S.
LandOfFree
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