Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating
Reexamination Certificate
1999-06-15
2002-03-12
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
C249S117000, C264S002500, C425S808000
Reexamination Certificate
active
06355190
ABSTRACT:
The present application is based on Japanese Patent Application No. 10-172572 filed Jun. 19, 1998, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to molding of an ophthalmic lens product by using a mold assembly which has a mold cavity. In particular, the invention is concerned with the method of molding such a lens product having a configuration corresponding to that of the ophthalmic lens such as an intraocular lens or a contact lens, or a configuration corresponding to that of a precursor of the ophthalmic lens, by polymerizing a monomer composition in the mold cavity to provide a polymer product which constitutes the lens product.
2. Discussion of the Related Art
There have been known various methods for forming an ophthalmic lens product having a configuration or geometry corresponding to that of an ophthalmic lens such as an intraocular lens or a contact lens, or a configuration corresponding to that of a precursor of the ophthalmic lens, more precisely, a lens product which gives at least an optical portion of the intended ophthalmic lens. For instance, the lens product is obtained by effecting a machining operation on a bar-shaped or block-shaped polymer product, such as cutting and grinding. Alternatively, the lens product is obtained by a molding operation using a mold assembly which has a mold cavity. Namely, a monomer composition that gives the polymer product is introduced into the mold cavity of the mold assembly, and is polymerized to form an intended ophthalmic lens whose configuration corresponds to that of the mold cavity.
U.S. Pat. No. 4,113,224 and JP-A-4-290706 disclose one example of the method of molding the lens product by using a mold assembly consisting of a combination of two mold members such as a male mold and a female mold, a cavity-defining mold and a core mold, or an upper mold and a lower mold. The two mold members are assembled together so as to define therebetween a mold cavity having a configuration of the intended lens product. The mold cavity defined upon assembling of the two mold members is filled with a suitable monomer composition, and the monomer composition is polymerized to produce the lens product. In the mold assembly of the above US patents, a reservoir or storage chamber for storing an excess of the monomer composition is formed in a portion of the mold assembly radially outwards of the mold cavity. During the polymerization of the monomer composition in the mold cavity, the monomer composition accommodated in the reservoir or storage chamber is supplied to the mold cavity, so as to compensate for a volume of shrinkage of the monomer composition caused during its polymerization. Accordingly, the lens product obtained as a polymer product has a geometry following that of the mold cavity. In the method disclosed in the above U.S. patents, however, the polymerization of the monomer composition in the mold cavity is effected under the atmospheric pressure, and the monomer composition accommodated in the reservoir or storage chamber is not forced to flow into the mold cavity, but is fed thereinto by gravity. According to this arrangement, the monomer composition may not be supplied to the mold cavity in an amount sufficient to compensate for its polymerization shrinkage in the mold cavity. In this case, the molded surfaces of the lens product serving as the optical surfaces of the intended ophthalmic lens do not have the respective desired profiles which exactly follow those of the molding surfaces of the mold assembly defining the mold cavity. Thus, in the method disclosed in the above-indicated U.S. patents, the optical surfaces of the lens product do not have high accuracy of configuration.
U.S. Pat. No. 5,578,332 discloses a method of cast molding a contact lens by using a mold assembly consisting of a first and a second mold, which have respective molding surfaces for defining a mold cavity when they are assembled together. The mold cavity is filled with a monomer, and the monomer is polymerized to produce the intended contact lens with the mold assembly being subjected to superatmospheric pressure in a pressure vessel. The application of the superatmospheric pressure to the mold assembly accommodated in the pressure vessel ensures that the molding surfaces of the two molds are subjected to a loading pressure, so that they are deflected and kept in contact with the monomer as the monomer shrinks in volume during its polymerization. In this method, however, since the molding surfaces of the two molds are deflected due to the loading pressure acting thereon upon application of the superatmospheric pressure to the mold assembly in the pressure vessel, the profiles of the molding surfaces change so as to remain in contact with the shrinking lens monomer during its polymerization. This arrangement wherein the profiles of the molding surfaces change during the polymerization of the monomer may not provide the intended contact lens with high accuracy of configuration.
JP-A-9-28723 discloses a method of producing a soft intraocular lens by using a mold assembly consisting of an upper and a lower mold, which are assembled together such that they are fluid-tightly sealed to define therebetween a mold cavity which is filled with a monomer composition. The monomer composition in the mold cavity is polymerized with the mold assembly being subjected to a nitrogen pressure of 2.0 kg/cm
2
at a temperature of 110° C. for two hours. Since the mold assembly disclosed in this publication is fluid-tightly sealed, the monomer composition in the mold cavity is not subjected to the nitrogen pressure unless the molding surfaces deflect or deform so as to be in contact with the shrinking monomer composition in the mold cavity. In this case, the monomer composition in the mold cavity may not be formed into the intraocular lens having a desired configuration corresponding to that of the mold cavity. On the other hand, if the molding surfaces deflect or deform so as to be in contact with the monomer composition in the mold cavity which shrinks during the polymerization, the mold assembly may suffer from a problem similar to that experienced in the above U.S. Pat. No. 5,578,332. In other words, the intraocular lens to be obtained by using the mold assembly does not have optical surfaces with high accuracy of configuration due to the deflection or deformation of the molding surfaces.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a method of molding an ophthalmic lens product by using a mold assembly having a mold cavity and a monomer storage portion, which method permits production of the lens product whose molded surfaces corresponding to the optical surfaces of the intended ophthalmic lens have high accuracy of configuration, exactly following the profiles of the molding surfaces of the mold assembly, while compensating for a volume of shrinkage of the monomer composition during its polymerization, by effectively supplying the monomer composition from the monomer storage space into the mold cavity, so as to provide the lens product having a desired configuration.
A second object of the invention is to provide a mold assembly suitable for practicing the method of the invention.
The above first object of the present invention may be attained according to a principle of the invention, which provides a method of molding an ophthalmic lens product by using a mold assembly which has a mold cavity, the lens product having a configuration corresponding to that of an ophthalmic lens or a precursor of the ophthalmic lens and being obtained by polymerizing a liquid monomer composition in the mold cavity to provide a polymer product which gives the lens product, the method comprising the steps of: preparing the mold assembly having a monomer storage space for storing the liquid monomer composition, which storage space is held in fluid communication with the mold cavity; filling the mold cavity of the mold assembly w
Niwa Kazuharu
Ojio Tatsuya
Yamashita Keiji
Yasuda Akihiro
Burr & Brown
Menicon Co. Ltd.
Vargot Mathieu D.
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