MOLDS FOR USE IN CONTACT LENS PRODUCTION

Abstract: The molds of the invention permit formation of a contact lens having a seamless edge by use of an interlocking means. The interlocking means prevents all, or substantially all, side-to side-movement of the front mold half in relation to the back mold half.

Description: MOLDS FOR USE IN CONTACT LENS PRODUCTION Field of the Invention The invention relates to molds useful in the manufacture of contact lenses In particular, the molds of the invention provide for the production of lenses with seamless edges Background of the Invention Methods and molds useful in the manufacture of contact lenses are well known For example, in United States Patent No. 5,540,410, incorporated herein in its entirety by reference, are disclosed molds and their use in contact lens manufacture. However, the known lens molds are disadvantageous in that they do not permit production of lens edges without seams. By "seam" is meant a line or demarcation formed by excess lens material Referring to the drawings, in FIG. 1 is illustrated a close-up cross-sectional side view of lens edge 10 that has a seam 11 The presence of such seams is disadvantageous in that the seam may contact the conjunctiva and cause surface roughness, discomfort, or both. Many obstacles exist to making a lens with a seamless edge including how to achieve a seamless edge with minimal side to side variation in geometry and without a post-processing step Additionally, obstacles to producing seamless edges are either or both mismatched and mis-positioned front and back mold halves Finally, excess lens material must be clipped from the lens prior to cure. Therefore, a need exists for a mold for producing seamless edged contact lenses that overcomes these obstacles Brief Description of the Drawings FIG. 1 is a close-up, cross-sectional side view of a seamed lens edge. FIG. 2 is a top elevational view of the front mold half of a preferred mold of the invention FIG. 2a is a cross-sectional view of the mold half of FIG. 2 along I-I. FIG 3 is a close-up, cross sectional view of the front mold half of FIG 2 fitted with the back mold half FIG 3 a is a close-up, cross-sectional view of an area of the mold of FIG 3 FIG 4 is a bottom elevational view of the back mold half of FIG 3 FIG 4a is a cross-sectional side view of the mold half of FIG 4 along II-TJ FIG 5 is a close-up, cross-sectional view of an area of an embodiment of a mold interlocking means of the invention FIG b is a close-up, cross-sectional view of an area of an embodiment of a mold interlocking means of the invention FIG 7 is a close-up. cross-sectional view of an area of an embodiment of a mold interlocking means of the invention FIG 8 is a close-up, cross-sectional view of an area of an embodiment of a mold interlocking means of the invention Detailed Description of the Invention and Preferred Embodiments The molds of the invention permit formation of a contact lens having a seamless edge It is a discovery of the invention that by providing a mold with an interlocking means, seamless contact lenses may be produced Additionally, the use of the interlocking means results in increased control of one molding surface in relation to the other This increased control allows for any one a varietv of lens edge profiles to be produced Thus, in one embodiment, the invention provides a mold for the production of a contact lens comprising, consisting essentially of. and consisting of a front mold half, a back mold and an interlocking means By "interlocking means" is meant any mechanism built into the mold halves that prevents all, or substantially all, side-to side-movement of the front mold half in relation to the back mold half Preferably, the interlocking means used in the molds of the invention is composed of a portion of the front mold half that fits into, or is fitted into, by a complementary portion of the back mold half An example of an interlocking means is shown in FIGs. 3 and 3a in which are illustrated various views of a preferred mold of the invention. Referring to FIG. 3 a, the mold is composed of two, complementary mold halves; a front mold half 102 and a back mold half 103. The front mold half 102 defines a central, curved section with an optical quality concave surface 110. Concave surface 110 has a circular, circumferential, well-defined edge 111 extending therearound. As shown in FIG. 3a, the edge 111, in conjunction with back surface circumferential edge 120, forms a well defined and uniform plastic radius parting line for the subsequently molded contact lens. Edge 111 typically has a curvature ranging from about 3 to 45 micrometers or less, preferably about 5 to about 30 micrometers, and the surfaces defining the edge may form an angle in the range of about 75 to about 90 deg. Referring to FIG. 3a, in a preferred embodiment, continuous with and extending curvedly upward from edge 111 toward inner mating surface 1 14 is a front mold half interlocking surface 1 12. Interlocking surface 112 extends from edge 111 at an angle of about 15 to about 75 degrees, preferably about 60 degrees. above a plane normal, or perpendicular, to the axis of symmetry of concave surface 110. Inner mating surface 1 14 is continuous with and extends radially outwardly from interlocking surface 112. Similarly, back mold half 103 has back mold half interlocking surface 1 17 extending upwardly and outwardly from circumferential edge 120. In all embodiments of the mold of the invention, the front and back mold halves' interlocking surfaces are complementarity shaped so that the surfaces fit securely together to minimize or prevent side-to-side displacement of the mold halves. Additionally, the interlocking means permits convenient placement of the back mold half after lens material is deposited on the front mold half. Referring to FIGs. 2, 2a, 3 and 3a, front mold half 102 is shown with convex surface 1 13 spaced generally parallel from concave surface 1 10 and an essentially uniplanar annular flange 106 integral with inner mating surface 114 and extending radially outwardly from the surfaces 110 and 113 in a plane normal, or perpendicular, to the axis of symmetry of the concave surface 1 10. The front mold interlocking surface 112 is continuous with inner mating surface 114, which surface is continuous with uniplanar annular flange 106. The back mold half interlocking surface 117 is continuous with outer mating surface 118. Outwardly tapering wall 1 19 is continuous with and extends upwardly from outer mating surface 1 18. As shown in FIGs. 3 and 3 a, in a preferred embodiment of the mold, the junction between convex surface 109 and back circumferential edge 120 is shaped to form a fillet, or concave junction. 1 16. The radius of curvature of fillet 1 16 preferably is about 10 μm to about 250 μm, more preferably about 30 μm to about 100 μm. Convex surface 109, fillet 116, and back circumferential edge 120 define the back surface edge shape of the lens cast in cavity 101. For a lens formed in this preferred mold of the invention, as depicted in FIG. 3, in addition to being seamless, the lens edge produced therein will have a back surface with an edge fillet and edge flat. The shape of this lens edge provides for a smooth contact between the lens wearer's conjunctiva and lens and avoids impingement of the conjunctival membrane. Additionally, this shape permits tears to be drawn under the lens by capillary action Finally, the edge shape provides controlled on-eye movement in that the larger the radius of curvature of the fillet, the more edge flat will be lifted off of the lens wearer's conjunctiva Referring to FIG. 3 a, extending radially outwardly from back surface circumferential edge 120 is interlocking surface 1 17 which is substantially spherical and has a radius of curvature of about 100 μm to about 300 μm, preferably about 125 μm. Interlocking surface 117 extends outwardly from edge 120 at an angle of about 15 to about 75 degrees, preferably about 60 degrees, and is continuous with inner mating surface 118 In addition to providing a complementary surface that fits into or is fitted into by surface 112, surface 117 permits formation of an edge flat on the cast lens edge that lifts the front and back lens edge junction away from the wearer ' s conjunctiva Surface 117 has a 360 degree contact with back surface circumferential edge 120 and applied pressure on the back or front mold half during lens curing ensures the 360 degree contact and minimizes tilt, or non-parallelism, between the front and back mold halves As shown on FIGs. 3, 3a, 4 and 4a, back mold half 103 has spaced surfaces 109 and 115 and an essentially uniplanar annular flange 105 extending radially outwardly therefrom in a plane normal to the axis of convex surface 109 Front mold half 102 has concave surface 110 with the dimensions of the front curve of the unswelled lens to be cast in the mold and is sufficiently smooth so that the contact lens surface formed is of optically acceptable quality Back mold half 103 defines a central curved section with an optical quality convex surface 109 and a generally parallel concave surface 115 Convex surface 109 has the dimensions of the unswelled back surface curve of the lens to be cast and is sufficiently smooth so that the lens surface formed is of optically acceptable quality Convex surface 113 of front mold half 102 and concave surface 115 of back mold half 103 need not have surfaces suitable to form optical quality surfaces Either or both of the mold halves of the invention may be constructed to include mold tabs, as shown in U S. Patent No 5,540,410 One ordinarily skilled in the art will recognize that the interlocking means and surfaces used in the molds of the invention may take any of a number of configurations Alternative exemplary configurations for the interlocking means and the interlocking surfaces are depicted in FIGs 5 through 8 The configuration selected will depend on the dimensions of the front and back mold halves used In FIG 5, three substantially continuous flat surfaces 131, 132. and 133 are shown extending upwardly, radially outwardly, and downwardly, respectively, at an angle of about 120 degrees to about 165 degrees from back surface circumferential edge 120 Extending from front surface edge 111 are surfaces 134, 135, and 136 that are complementarily shaped to surfaces 131, 132, and 133, respectively, so that the surfaces fit securely together In FIG 6 is depicted an alternative embodiment of the interlocking means in which a second back interlocking surface 137 is adjacent to interlocking surface 117 and second front interlocking surface 138 adjacent to interlocking surface 112. Surfaces 137 preferably is spherical in shape and has a radius of curvature of about less than, greater than, or preferably equal to that of surface 138 FIGs 7 and 8 depict yet other alternatives of the interlocking means of the invention The molds of the invention may be used is useful in producing contact lenses by polymerization of a polymerizable composition Preferably, the contact lenses produced using the mold of the invention are unhydrated lenses that may be made ready to wear by hydrating, or swelling, the lenses by any method known in the art Front mold half 102 and back mold half 103 may be formed of any suitable material including, without limitation, glass or a thermoplastic polymer Preferably the molds are formed from a material that is sufficiently transparent to ultra-violet light to allow irradiation therethrough to promote polymerization of a contact lens material, preferably a soft contact lens material Preferred thermoplastic materials for forming the mold halves of the invention are polystyrene and polypropylene Each mold half may be formed from the same or a different material than the other mold half Production of the mold halves may be accomplished by any convenient method, but preferably as set forth in U S Patent No 5,540,410 In the mold of the invention, more preferably the material used for formation of the back mold half 103 is harder, or less compressible, than that of front mold half 102. Given the configuration of the mold halves of the invention, the use of a softer front mold half material permits the back surface circumferential edge 120 to impinge, or flatten, the front surface circumferential edge 111 when pressure is applied to the mold This permits the removal of excess lens material from mold cavity 101 at the parting line of the front and back mold halves. Alternatively, a back mold half that is softer than the front may be used resulting in front surface circumferential edge 111 impinging on back edge 120 In all embodiments, the front and the back mold halves are designed so as to permit rapid transmission of heat therethrough and yet be rigid enough to withstand the prying forces used to separate the mold halves during demolding The mold of the invention may be used in any method for the manufacture of contact lenses. Preferably, however, the method of manufacture as set forth in U S Patent No. 5,540,410 is used. Generally, in the preferred method, a quantity of polymerizable composition is placed onto the concave surface 110 of front mold half 102, preferably by injection Back mold half 103 with convex surface 109 facing toward front mold half 102 concave surface 110 is placed onto the polymerizable composition. Preferably, the volume of the polymerizable composition used is greater than the volume of the cavity 101 Placement of the back mold half 103 onto front mold half 102, thus, will result in excess material flowing into area 121 formed between the mold halves " flanges. Convex surface 109 is preferably less wide than concave surface 110 to facilitate centering. Once mold half 103 is placed onto front mold half 102, the mold halves preferably are pressed together using a force of about 1 to about 5 pounds The force may be applied to either or both flanges 105 and 106 along the lines depicted by the arrows in FIG. 3 The force may be applied by any convenient means including, without limitation, using air pressure, mechanical means, such as a spring, or a combination thereof. In one embodiment, a deposition nozzle that is flat-shaped to lay across the flange or one that is a combination of cone and flat-shaped to fit partially into mold half 102 or 103 is used. The force is maintained throughout the polymerization of the polymerizable composition. The polymerizable composition is preferably polymerized by exposure to ultra-violet radiation. Following completion of polymerization, the mold formed by front and back mold halves 102 and 103, respectively, is disassembled and the cast lens undergoes additional processing.

Claims: What is claimed is 1 A mold for the production of a contact lens comprising a front mold half, a back mold and an interlocking means 2 The mold of claim 1 , wherein the interlocking means comprises a portion of the front mold half that fits into a complementary portion of the back mold half 3 The mold of claim 1, wherein the interlocking means comprises a portion of the front mold half that is fitted into by a complementary portion of the back mold half 4 A mold for the production of a contact lens comprising a front mold half and a back mold half wherein the front mold half comprises a first article having a central curved section with a concave surface, a convex surface and a circular circumferential edge, the central section of the concave surface suitable for imparting a curvature to the front curve of a contact lens, the first article also having an axis of symmetry about the concave surface, a first interlocking surface continuous with and extending outwardly from the circular edge in a plane about 15 to about 75 degrees above the concave surface axis of symmetry, an inner mating surface continuous with and extending radially outwardly from the first interlocking surface, and an annular flange integral with and surrounding the first interlocking surface and extending radially outwardly from the concave and convex surfaces in a plane normal to the concave surface axis, the back mold half comprises a second article having a central curved section with a concave surface and a convex surface, the central section of the convex surface suitable for imparting a curvature to the back curve of a contact lens, and the second article also having an axis of symmetry about the convex surface, a circumferential edge surrounding the convex surface, a second interlocking surface extending outwardly from the circumferential edge in a plane about 15 to about 75 degrees above the convex surface axis of symmetry, an outer mating surface continuous with and extending outwardly from the second interlocking surface, and an annular flange integral with, surrounding and extending radially outwardly from the concave and convex surfaces in a plane normal to the convex surface axis 5. The mold of claim 4, further comprising a fillet forming the junction between the back mold half convex surface and circumferential edge. 6 The mold of claim 4 or 5, wherein the back mold half further comprises an outwardly and upwardly tapering wall continuous with and forming the junction between the outer mating surface and the annular flange 7. The mold of claim 4, wherein the front mold half and the back mold half each further comprises a generally triangular tab extending from the annular flange 8. The mold of claim 1, 4 or 5 wherein the front and back mold halves comprise a thermoplastic polymer transparent to ultra-violet light. 9 The mold of claim 8, wherein the thermoplastic polymer is polypropylene or polystyrene 10 The mold of claim 9, wherein one mold half comprises polystyrene and the other mold half comprises polypropylene 11 The mold of claim 9, wherein the front mold half is harder than the back mold half 12. The mold of claim 9, wherein the back mold half is harder than the front mold half 13. A method for producing a contact lens comprising the steps of: a.) providing a mold according to claim 1, 4 or 5; b.) injecting a polymerizable composition into the mold; and polymerizing the polymerizable composition. 14. The method of claim 13, further comprising the step of applying pressure, simultaneously with step c), to the first article annular flange, the second article annular flange, or both.

Inventors: CLUTTERBUCK TIMOTHY A, CLUTTERBUCK, TIMOTHY, A.
Applicants: JOHNSON & JOHNSON VISION CARE, JOHNSON & JOHNSON VISION CARE, INC.
Application year: 2000
Main classification: B29D11
IPC codes: B29C33, B29D11, B29L11, G02C7