Plastic article or earthenware shaping or treating: apparatus – Press forming apparatus having opposed press members – Male shaping member and female mold
Reexamination Certificate
1999-08-04
2001-08-21
Nguyen, Nam (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Press forming apparatus having opposed press members
Male shaping member and female mold
C425S416000, C425S423000, C425S808000, C264S001320, C264S318000
Reexamination Certificate
active
06276920
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a mold assembly for forming a lens blank, and more particularly to a mold assembly for forming a lens blank for an ophthalmic lens such as a contact lens and an intraocular lens, such that the lens blank has desired configuration and dimensions.
2. Discussion of the Related Art
A known method of manufacturing an ophthalmic lens such as a contact lens includes a molding process for forming a lens blank using a mold assembly, and a cutting or machining process for cutting the lens blank into the desired ophthalmic lens. The mold assembly includes an upper mold and a lower mold which cooperate to define a fluid-tightly enclosed mold cavity. In the molding process, a liquid monomer composition filling the mold cavity is polymerized into the lens blank. In the cutting process, the thus formed lens blank is cut on its inner and outer surfaces, to produce the desired contact lens or other ophthalmic lens which has an inner or back surface for contact with the cornea of an eye, and an outer or front surface opposite to the inner surface.
JP-A-4-290706 (U.S. Pat. No. 5,137,441) discloses an example of a mold assembly used in a molding process as described above. This mold assembly consists of an upper mold, a lower mold, and a generally cylindrical intermediate sleeve which removably connect the inner and outer molds. The intermediate sleeve cooperates with the upper mold to define a liquid reservoir for storing an excess amount of the liquid monomer composition which has been discharged from a mold cavity upon closing of the mold assembly. The mold assembly is further adapted to permit a flow of the liquid monomer composition from the liquid reservoir into the mold cavity in the molding process, when a mass of the liquid monomer composition in the mold cavity shrinks during polymerization of the composition, so that a shortage in volume of the liquid monomer composition in the mold cavity is compensated for by a volume of the composition which has been supplied from the liquid reservoir into the mold cavity. Thus, the mold assembly is constructed to prevent a conventionally experienced problem which would otherwise take place due to shrinkage of the liquid monomer composition during polymerization thereof in the mold cavity.
The mold assembly disclosed in the above-identified publication is constructed to be assembled by moving the upper mold into the intermediate sleeve in the axial direction such that the outer circumferential surface of the upper mold is in sliding contact with the inner circumferential surface of the intermediate sleeve. However, the upper mold and the intermediate sleeve do not have an axial stopper for determining an axial position of the upper mold relative to the intermediate sleeve, namely, a relative position between the upper mold and the lower mold which is positioned in a lower portion of the intermediate sleeve. Accordingly, it is difficult to accurately establish the predetermined relative axial position of the upper and lower molds.
The relative axial position of the upper and lower molds determines an axial dimension of the mold cavity defined between the upper and lower molds in the mold assembly in the closed state. Therefore, it is difficult to maintain the axial dimension of the mold cavity at a predetermined constant value, during successive molding operations using the mold assembly, resulting in a high risk of variation in the thickness value of the lens blanks to be formed by the mold assembly. Further, the absence of the axial stopper in the mold assembly may cause a variation in the volume of the liquid reservoir defined by the upper mold and the intermediate sleeve, giving rise to an insufficient amount of supply of the liquid monomer composition from the liquid reservoir into the mold cavity due to an insufficient volume of the liquid reservoir, upon shrinking of the mass of the monomer composition in the mold cavity due to its polymerization. The insufficient amount of supply of the liquid monomer composition from the liquid reservoir into the mold cavity may lead to a high risk of a failure to form the lens blank with desired configuration and size.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a mold assembly which permits a mold cavity to be formed with a predetermined constant axial dimension, and also permits a liquid reservoir to be formed with a predetermined constant volume, thereby assuring a stable molding operation to form the lens blank with a high degree of consistency in its thickness and a high degree of configurational accuracy, without configurational defects due to shrinkage of the monomer composition in the mold cavity.
The above object may be achieved according to the principle of this invention, which provides a mold assembly having a mold cavity to be filled with a liquid monomer composition which is polymerized to form a lens blank having a size sufficient to manufacture a desired ophthalmic lens, comprising: an upper mold including a generally cylindrical body portion, an outward flange portion extending radially outwardly from one of opposite ends of the body portion, and an annular engaging portion which extends from the outward flange portion in an axial direction thereof from the one of the opposite ends of the body portion toward the other of the opposite ends, the annular engaging portion having an outer surface; a lower mold having a tapered outer surface; and an intermediate sleeve for removably connecting the upper and lower molds, the intermediate sleeve including a lower portion, an upper portion and an intermediate portion intermediate between the lower and upper portions, the lower portion having a lower tapered inner surface for press-fitting engagement with the tapered outer surface of the lower mold, to effect fluid-tight connection of the lower mold and the intermediate mold. The upper portion of the intermediate sleeve has an upper tapered inner surface whose diameter is larger than an inside diameter of an inner surface of the intermediate portion. The intermediate sleeve further includes a shoulder between the upper tapered inner surface of the upper portion and the inner surface of the intermediate portion. The outer surface of the annular engaging portion of the upper mold is provided for press-fitting engagement with the upper tapered inner surface of the intermediate sleeve, to effect fluid-tight connection of the upper mold and the intermediate sleeve, with the body portion of the upper mold being held in abutting contact with the shoulder in an axial direction of the intermediate sleeve, such that the upper mold and the intermediate sleeve cooperate with the lower mold to define the mold cavity, with the tapered outer surface of the lower mold being held in press-fitting engagement with the lower tapered inner surface of the intermediate sleeve. The press-fitting engagement of the outer surface of the annular engaging portion of the upper mold with the upper tapered inner surface of the intermediate sleeve cooperates with the abutting contact of the body portion with the shoulder, to define a liquid reservoir for storing an excess amount of the liquid monomer composition which has been discharged from the mold cavity when the mold cavity is defined by fluid-tight connection of the upper and lower molds to the intermediate sleeve. The intermediate sleeve and the lower mold cooperate to provide a stopper for determining a relative axial position therebetween.
In the mold assembly of the present invention constructed as described above, the outer surface of the annular engaging portion of the upper mold and the tapered outer surface of the lower mold are brought into press-fitting engagement with the respective upper and lower tapered inner surfaces of the intermediate sleeve, with the body portion of the upper mold being held in abutting contact with the shoulder of the intermediate sleeve in the axial direction of the intermediate sleeve, and with the r
Doke Atsuhiro
Ichikawa Seiichi
Burr & Brown
Menicon Co. Ltd.
Nguyen Nam
Nguyen Thu Khan T.
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