Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
1998-10-07
2001-06-05
Ahmad, Nasser (Department: 1772)
Stock material or miscellaneous articles
Circular sheet or circular blank
C351S159000, C351S172000, C428S066700
Reexamination Certificate
active
06242065
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to lens blanks for forming ophthalmic elements and the lamination of thermoplastic molded articles in the formation of ophthalmic elements. The invention is particularly designed to provide a finished multifocal or progressive lens with anti-reflective or abrasion resistant coatings at a commercial shop in less than twenty minutes.
2. Background of the Art
The present invention finds utility in a range of materials to be joined by adhesive securement, and it is applied most advantageously to molded thermoplastic articles such as lenses, especially ophthalmic lenses, and optical disks.
Lenses are used for a wide variety of purposes. For example, microscopes, telescopes, magnifying glasses and other optical instruments, as well as ophthalmic spectacles, employ lenses. The following discussion focuses on the most preferred embodiment of the present invention, ophthalmic lenses.
Vision-corrective, prescription (Rx) spectacle lenses or ophthalmic lenses increasingly employ plastic lens materials instead of the more traditional glass. In fact, in the United States, the demand for plastic lenses is multiples of that for glass lenses. This is because:
1. plastic is lighter than glass, which is particularly advantageous where stronger prescriptions and thicker lenses must be used;
2. durable abrasion-resistant coatings have become available for plastic;
3. plastic can be provided in a wide range of fashionable colors and gradient-density tints; and
4. production techniques have improved so that plastic lenses can be manufactured at higher rates, with more automation, and lower costs.
The relatively lighter weight and corresponding improved wearer comfort of plastic lenses are the most important considerations by the consumer. Since a nominal lens thickness (typically 2.0-2.2 mm) is the same for glass and plastic, plastic lenses' lighter weight is a direct result of plastic's lower density compared to that of glass. This factor holds true for all equivalent prescriptions in glass and plastics, but becomes particularly important when higher-powered corrections are required or when larger spectacle frames are chosen, requiring larger lens diameters and requiring greater thickness at the exterior (or interior) portion of the lens to continue the prescription curvature of the correction.
One method by which plastic prescription lenses are currently manufactured is by individually casting polycarbonate resins, or casting and curing allylic (or other ethylenically unsaturated) resins. Polycarbonate thermoplastic lenses have started to replace both cast-thermoset plastic and traditional glass lenses because of their lower density and higher refractive index. Polycarbonate lenses of the same nominal thickness provide even lighter weight than the cast-allylic plastics, and are of a much lower weight than glass. Additionally benefits result from this resin class because polycarbonate tends to have far greater impact strength and breakage resistance than any clear polymeric materials presently used for lenses, and even thinner lenses (in the range of 1.5-2.0 mm) are presently available, with the potential for even higher wearer preference.
Another method by which ophthalmic lenses, and especially ophthalmic lenses having segmented (bifocal or trifocal) prescriptions or continuous prescriptions (with a smooth gradation between various prescriptions) can be manufactured is by laminating sets of at least one interior lens blank and at least one exterior lens blank, with each of the interior and exterior lens blanks providing a specific contribution to the final prescription. Composite eyeglass lenses have been formed with this principle by bonding together front and rear lenses, as suggested in U.S. Pat. No. 2,618,200. A device and method for accomplishing this process has been suggested in U.S. Pat. No. 4,927,480. Generally, the bonding process involves placing a curable adhesive on the concave interface surface of the front lens; pressing the convex interface surface of the rear lens against the adhesive in the front lens to spread the adhesive throughout the space between the two lenses; and curing the adhesive to bond the lenses together, forming a composite lens which is then trimmed to fit within an eyeglass frame.
Even after individual lens blanks of good optical properties have been manufactured, it is equally important to form them into ophthalmic lenses for use by the customer. Segmented and progressive ophthalmic lenses must also be capable of construction from these lens elements. For example, U.S. Pat. Nos. 4,883,548; 4,867,553; and 4,645,317 show the formation of laminated ophthalmic lenses from at least two separate lens elements which are selected from a reserve and then associated to match a particular description. The at least two lens elements (one front and one rear lens) are adhesively secured together, with a photosetting resin and photinitiator suggested for the process (e.g., U.S. Pat. Nos. 4,883,548 and 4,867,553).
Especially when the desired composite lens includes a cylindrical component that must be properly oriented to correct for astigmatism and a bifocal or progressive focal region that must be properly positioned for reading purposes, the existing methods and equipment have fallen short of the desired optical accuracy. Existing laminating equipment, for example, does not readily accommodate eccentric positioning and bonding of the front and rear lenses, which can be necessary in some cases. Also, existing methods and equipment have been inconvenient in operation and have put the desirable accuracies beyond practical reach for some composite eyeglass lenses. U.S. Pat. No. 5,433,810 describes lamination or bonding together of front and rear lenses to form a composite eyeglass lens to address these perceived problems. It is asserted in U.S. Pat. No. 5,433,810 that a described new and better way of mounting, aligning, and bonding together composite eyeglass lenses improved on the accuracy attainable. That composite lens laminating system includes a front lens platform on a movable stage and a rear lens holder that is rotationally adjustable on a laminating axis and is movable along the laminating axis to press the rear lens against the front lens. Accurate positioning of each lens is assured by an X, Y adjustment of the stage holding the front lens platform, by an arrangement of locating pins and pressure feet that register and hold the rear lens on its holder, and rotational adjustment of the rear lens holder on the laminating axis. A simple and effective arrangement assures that the two lenses are pressed together with uniform pressure that spreads the adhesive evenly between them, and this process can be observed through the rear lens while the pressure is being applied. Then the bonding adhesive is cured while the two lenses are pressed together so that the accuracy of their positioning and the lack of any interruption in the adhesive layer are preserved during the curing process. Several specific procedures and structures contribute to achieving these effects; and the result is described as fast, effective, and more accurate than previous systems. That method of laminating front and rear lenses to form a composite eyeglass lens comprises:
a. holding a front face of the front lens in a mounting aperture positioned relative to a laminating axis;
b. mounting a rear face of the rear lens in a predetermined position on a holder that is movable along said laminating axis and holds the rear lens independently of the front lens;
c. rotatably orienting the holder relative to said axis to bring the rear lens into a desired angular relationship with the front lens while the rear lens is separated from the front lens;
d. placing a bonding material on a rear face of the front lens and moving the holder to bring a front face of the rear lens into engagement with the bonding material and to press the rear lens against the front lens in the direction of the laminating axis to forc
Bhalakia Sujal
Blomberg Chris
Levin Gert
Ahmad Nasser
BMC Vision-Ease Lens, Inc.
Jessen Derek
Mark A. Littman & Associates
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