Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Utilizing plasma – electric – electromagnetic – particulate – or...
Reexamination Certificate
1999-12-21
2003-10-07
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Utilizing plasma, electric, electromagnetic, particulate, or...
C264S001360, C264S001700
Reexamination Certificate
active
06630083
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to ophthalmic lenses. In particular, the invention provides methods and compositions for producing lenses by casting.
BACKGROUND OF THE INVENTION
The use of spectacle lenses for the correction of ametropia is well known. For example, multifocal lenses, such as progressive addition lenses, are used for the treatment of presbyopia. A number of methods are known for producing ophthalmic lenses. These methods include casting semi-finished lens blanks and subsequently polishing and grinding the blanks to form lenses, casting of whole lenses, and casting of a surface onto an optical preform to form a lens.
The casting of a surface onto an optical preform is advantageous in that it can reduce the number of molds required to produce a full prescriptive range of lenses. However, the known surface casting processes lack the efficiency necessary for use of the processes in the mass production of lenses. More specifically, the known processes require cure times of 30 minutes or more to achieve a cured resin layer free of optical distortions, defects, or voids. Additionally, known resins for use in surface casting processes cannot provide both a high refractive index on cure and a low viscosity at room temperature. Therefore, the invention provides methods and compositions for casting surfaces onto preforms to form lenses that attempt to overcome these disadvantages.
DESCRIPTION OF THE INVENTION AND ITS PREFERRED EMBODIMENTS
The present invention provides methods and compositions for producing ophthalmic lenses, including multifocal spectacle lenses such as progressive addition lenses, as well as lenses produced using the methods and compositions of the invention. The invention, provides a fast and reliable method for producing ophthalmic lenses.
In one embodiment, the invention provides a method for producing an ophthalmic lens comprising, consisting essentially of, and consisting of the steps of: a.) exposing to low intensity ultraviolet light a mold assembly and a surface-forming effective amount of a resin comprising, consisting essentially of, and consisting of reactive groups, the low intensity UV light exposure carried out under conditions suitable to convert at least about 50 percent or more of the resin's reactive groups; and b.) exposing, subsequently, the resin to high intensity UV light under conditions suitable to substantially complete through curing of the resin. In another embodiment, the invention provides lenses produced by this method.
By “ophthalmic lens” is meant a contact lens, intraocular lens, spectacle lens and the like. Preferably, the lens formed by the method of the invention is a spectacle lens, more preferably a multifocal, most preferably a progressive addition lens. By “mold assembly” is meant one or more mold halves, an optical preform, or combinations thereof. By “optical preform” or “preform” is meant a shaped, optically transparent article capable of refracting light, which article is suitable for use in producing a spectacle lens. By “resin” is meant at least one monofunctional monomer, one or more polyfunctional monomers, and one or more initiators. By “convert” is meant that the reactive groups are incorporated into the polymer being formed.
In the first step of the method of the invention, a mold assembly is exposed to low intensity ultraviolet light. For purposes of the invention, low intensity UV light is UV light with an intensity of about 0.5 to about 50, preferably about 1 to about 5 mW/cm
2
. Suitable wavelengths for carrying out this step of the process are about 300 to about 450, preferably about 360 to about 400 nm. The low intensity exposure is carried out under conditions of wavelength and time suitable to convert at least about 50 percent or more of the resin's reactive groups and, preferably, while maintaining the rate of polymerization as low as possible, which rate is a rate at which undesirable shrinkage induced defects are avoided. One ordinarily skilled in the art will recognize that this rate will depend on a number of factors including, without limitation, the resin used and the thickness of the resin layer. The maintenance of the low polymerization rate is achieved through the use of the low intensity UV light and, optionally, one or more of using a photoinitiator concentration of about 1 weight percent or less based on the total resin weight, incorporation of periods of non-exposure into the low intensity exposure cycle, and combinations thereof.
The time for the low intensity exposure will depend on the resin selected for casting onto the preform, the type and amount of initiator used, resin viscosity, the nature of the reactive groups, the thickness of the resin layer to be cast, and the intensity of the UV light. Generally, the total exposure time will be about 5 seconds to about 300 seconds, preferably about 60 seconds to about 120 seconds.
The low intensity exposure preferably is carried out in one step. However, some lens assemblies may require that the low intensity exposure be carried out in two or more steps using periods of non-exposure to the UV light of about 5 to about 60 seconds between each low intensity exposure. Preferably, periods of exposure of about 30 to about 60 seconds are alternated with non-exposure periods of about 5 to about 60 seconds.
Subsequent to the termination of the low intensity exposure, the mold assembly is exposed to high intensity UV light under conditions suitable to complete through cure of the resin. The intensity of the UV light for this step may be about 50 to about 2000, preferably 500 to about 1500 mW/cm
2
. The wavelength at which the exposure is carried out may be, and preferably is, the same as that used to carry out the low intensity exposure. The same factors determinative for low intensity exposure time are determinative for the high intensity exposure time. Generally, the exposure time will be about 3 seconds to about 60 seconds, preferably about 5 seconds to about 15 seconds. The high intensity exposure may, and preferably is, carried out as a single, continuous exposure. However, the high intensity exposure also may be carried out using alternating periods of UV exposure and non-exposure periods.
It is a discovery of the invention that the disclosed cure process using low and high intensity exposure permits production of a cast layer substantially free of distortions, defects and voids using a total UV exposure, both low and high intensity, time of about 150 or less seconds. Preferably the total exposure time is about 130 seconds or less.
The low and high intensity polymerization steps may be carried out at ambient temperature and atmospheric pressure. Preferably, the resin is hot-coated and the polymerization process is carried out at about the glass transition temperature, or Tg, of the cured resin or above. By “hot-coated” is meant that the resin is heated before it is cast to about its Tg. Heating may be accomplished by any convenient means including, without limitation, use of an oven, heat circulator, or combination thereof. Polymerization at the preferred temperature is also achieved by any convenient means including, without limitation, maintaining the cure chamber at the preferred temperature by use of forced air.
The low and high intensity UV exposures may be carried out in any fashion that permits the even distribution of the light through the mold assembly. A convenient and preferred mode is to expose the mold assembly to the UV light by placing the UV light source beneath the mold assembly. Sources of low intensity UV light include, without limitation, mercury and xenon arc lamps, fluorescent-type bulbs, or the like, and combinations thereof. High intensity UV light sources include, without limitation, mercury, xenon, and mercury-xenon arc lamps, FUSION™ microwave-ignited lamps, or the like, and combinations thereof Suitable sources for the UV light used in the invention are commercially available.
The mold half or halves used may be made of any suitable material including, without limitation, glass
Alton Michele
Basham Elbert
Dogan Eric
Nunez Ivan
Sekharipuram Venkat
Gianneschi Lois A.
Johnson & Johnson Vision Care Inc.
Vargot Mathieu D.
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