Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Including step of mold making
Reexamination Certificate
2000-03-22
2003-04-22
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Including step of mold making
C249S117000, C264S001380, C425S808000
Reexamination Certificate
active
06551531
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to molds and mold components for the manufacture of ophthalmic lenses such as contact lenses.
Ophthalmic lenses such as contact lenses are most often manufactured in casting processes. These processes involve injecting a reactive lens forming mixture of polymerizable monomers and other materials in a mold and curing the mixture by exposure to UV light or heat in the presence of an appropriate photoinitiator or catalyst. The molds are usually made of a number of cavities having female and/or male base surfaces or curvilinear mold portions for the formation of the curved ophthalmic lenses. The lens is formed at the interface of the mold surfaces.
A common problem is the adhesion of the lens formed in the mold to one or both of the mold parts. Edge tears and chips, nicks or other surface defects as well as holes, voids, pits, i.e. areas on non-uniform thickness, and puddles formed in the ophthalmic lenses can occur when the adhesion is too great. This problem is exacerbated in processes for making lenses with thin edges or intricate edge geometries. Separating mold halves or mold parts without causing damage to the lens formed in the mold is thus critically important to commercial lens making processes.
One method for dealing with this problem has been the incorporation of additives such as zinc stearate in the mold materials or the inclusion of mold release agents. Unfortunately, these agents can adversely affect mold surface texture or bulk polymer properties. Adjustments to the time, temperature, and heating profile of the cure and demold processes has also been used to affect the adhesion of the lens to at least one of the mold parts. Often, the adjustments to the cure and demold processes that might be helpful in solving the adhesion problem negatively affect the quality of the lens made. Mechanical and optical properties can be seriously eroded or altered.
Japanese Kokai application JP 98-133667 proposes an assembly of first and second molds consisting of a base mold with a thermoplastic film that covers the base mold on the cavity side. The base mold was made of PMMA with a polyethylene film and a female mold made of polypropylene.
Simple methods for reducing or eliminating production loss of lenses due to adhesion to multiple mold parts are still in great demand.
SUMMARY OF THE INVENTION
The invention is a method of making an ophthalmic lens by reacting a lens forming mixture in a mold to form a polymer. The polymer is then demolded from the mold and formed into a completed lens. The molds are made of at least two parts, a first part having a surface for forming the polymer into a portion of the lens and a second part having a surface for forming the polymer into a portion of the lens. The first and second parts of the mold each have different surface energies.
In another aspect of the invention, an ophthalmic lens mold comprises at least two parts. The first part has a surface for forming a portion of the lens and a second part has a surface for forming the lens. The first and second parts are each made from a material having different surface energies. The combination of the first and second mold parts form a cavity. The ophthalmic lenses are formed in the cavity from the reaction of a ophthalmic lens forming mixture.
In yet another aspect of the invention, an ophthalmic lens making mold kit comprises at least one first mold part and at least one second mold part. The first and second mold parts have different surface energies. When they are combined they formed a cavity at their interface for the formation of the ophthalmic lenses.
DETAILED DESCRIPTION
An “ophthalmic lens” refers to an intraoccular lens, contact lens, or other similar device through which vision is corrected or eye physiology is cosmetically enhanced (e.g., iris color) without impeding vision.
A “lens forming mixture” as the term is used throughout this specification refers to a mixture of materials that can react or be cured to form an ophthalmic lens. Such a mixture includes polymerizable components (monomers), additives such as UV blockers and tints, photoinitiators or catalysts, and other additives one might desire in an ophthalmic lens such as a contact or intraoccular lens. Suitable lens forming mixtures are described more fully in U.S. Pat. No. 5,849,209 (as a reactive monomer mix including crosslinking agent and initiator); U.S. Pat. No. 5,770,669 (as a prepolymerization mixture including monomers and initiator); and U.S. Pat. No. 5,512,205 (as a prepolymer plus monomer system including crosslinkers and initiators) each of which is incorporated herein by reference. Lens forming mixtures for making silicone based hydrogel lens are most preferred including those comprising silicone/hydrophilic macromers, silicone based monomers, initiators and addtives.
The terms “mold” and “mold assembly” as used throughout this specification refer to a form having a cavity into which a lens forming mixture is dispensed such that upon reaction or cure of the lens forming mixture, an ophthalmic lens of a desired shape is produced. The molds and mold assemblies of this invention are made of more than one mold part and form the mold or mold assembly by the combination of the parts. This combination of mold parts is preferably temporary. The mold parts are brought together with a cavity formed between them in which the lens is formed and upon formation of the lens the mold is again separated into mold parts for removal of the lens as described below.
A “mold part” or “mold piece” as the term is used in this specification refers to a portion of mold, which when combined with another portion of a mold forms a mold or mold assembly. The molds of this invention are formed from at least two mold parts. At least one mold part has at least a portion of its surface in contact with the lens forming mixture such that upon reaction or cure of the mixture that surface provides the desired shape and form to the portion of the lens with which it is in contact. The same is true of at least one other mold part.
Thus, for example, in a preferred embodiment a mold is formed from two parts, a female concave piece (front piece) and a male convex piece (back piece) with a cavity formed between them. The portion of the concave surface in contact with lens forming mixture has the curvature of the front curve of a ophthalmic lens to be produced in the mold assembly and is sufficiently smooth that the surface of a ophthalmic lens formed by polymerization of the lens forming mixture in contact with the surface is optically acceptable. Preferably, the front mold piece also has an annular flange integral with and surrounding circular circumferential edge and extends from it in a plane normal to the axis and extending from the flange. The back mold piece has a central curved section with a concave surface, convex surface and circular circumferential edge, wherein the portion of the convex surface in contact with the lens forming mixture has the curvature of the back curve of a ophthalmic lens to be produced in the mold assembly and is sufficiently smooth that the surface of a ophthalmic lens formed by reaction or cure of the lens forming mixture in contact with the back surface is optically acceptable. The back curve also has an annular flange integral with and surrounding the circular circumferential edge and extending from it in a plane normal to the axis of the convex structure. The inner concave surface of the front mold half defines the outer surface of the lens, while the outer convex surface of the base mold half defines the inner surface of the lens.
In this assembly, the back mold piece is made of a material having a substantially different surface energy than the front mold piece. A material has a substantially different surface energy from another material when, after polymerization in a mold made from mold parts of such materials, and upon separation of the mold parts, the lens formed in contact with a surface of each does not adhere one mold part relative to another mold part with
Ford James D.
Kirk James F.
Molock Frank F.
Johnson & Johnson Vision Care Inc.
Vargot Mathieu D.
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