HK1138237B - Molds for use in contact lens production - Google Patents

Description

Mold for producing contact lenses

Technical Field

The present invention relates to molds suitable for use in the manufacture of contact lenses. In particular, the molds of the present invention produce lenses having rounded edges.

Background

Methods and molds for making contact lenses are well known. For example, in U.S. Pat. No.5,540,410, which is incorporated herein by reference in its entirety, molds and their use for making contact lenses are disclosed. Lens molds for producing lenses with rounded edges are known. Such a rounded edge design is desirable because impingement of the lens edge on the lens wearer's bulbar conjunctiva is avoided. However, a disadvantage of the known lens mould is that it is difficult to adequately control the height of the edge. Also, producing lenses with rounded edges in known molds prevents excess monomer from flowing out of the mold. This not only produces a monomer that will wrap around the lens formed in the mold, but the post-cured monomer will be present in many places and difficult to remove.

Drawings

FIG. 1 is an exploded side view of the inventive die.

Fig. 2 is a side view of the assembled mold of the present invention.

Fig. 3 is a cross-sectional view of the mold of fig. 2.

Fig. 3a is an enlarged cross-sectional view of the mold region of fig. 3.

Detailed description and preferred embodiments of the invention

The present invention provides a mold for producing contact lenses, a method of making the mold, and lenses made with the mold having rounded edges. The mould of the invention is provided with centering and spacing means in the shape of a tab (tab) on one of the half-moulds, said means both centering the two half-moulds relative to each other and allowing the free outflow of excess monomer from the mould. Furthermore, the spacer members facilitate height control of one mold half relative to the other mold half.

In one embodiment, the present invention provides a mold for producing a contact lens comprising, consisting essentially of, or consisting of only a front mold half and a back mold half. Wherein the front mold half comprises, consists essentially of, or consists only of a first component having a central curved portion with a concave surface, a convex surface, and a first circular circumferential edge around the central curved portion concave surface, the central portion of the concave surface being adapted to impart a curvature to the front curve of the contact lens; the first component further having an axis of symmetry of the concave surface and an inner surface contiguous with the circular rim, the inner surface extending downwardly from the circular rim in a plane about 5 to about 15 degrees below the axis of the concave surface, an outwardly tapering wall, and an annular flange integral with and surrounding the outwardly tapering wall and extending radially outwardly from the concave and convex surfaces in a plane normal to the axis of the concave surface; the back mold half comprises, consists essentially of, or consists only of a second component having a central curved portion with a concave surface, a convex surface and a second circular peripheral edge surrounding the convex surface of the central curved portion, the central portion of the convex surface being adapted to impart curvature to the back curve of the contact lens; and the second component further having an axis of symmetry about the convex surface, a plurality of spaced-apart projections on the convex surface, each projection including an outwardly extending wall from a peripheral edge of the convex surface and an upwardly extending wall, a lowermost portion of the upwardly extending wall being connected to and extending upwardly from the outwardly extending wall, and an uppermost portion of the upwardly extending wall being connected to the convex surface, and an annular flange integral with and surrounding the concave and convex surfaces and extending radially outwardly from the concave and convex surfaces in a plane orthogonal to the axis of the convex surface.

Referring to the drawings, in fig. 1 and 2, there are shown an exploded side view and a side view, respectively, of a mold of the present invention. The mold is made up of two complementary mold halves: a front mold half 102 and a back mold half 103. As shown in fig. 1, projections 116 are provided on the convex surface of the mold half 103 at spaced locations. There must be a sufficient amount of protrusion to achieve the desired centering and height control of the mold halves. Preferably, at least three protrusions are provided on the back mold half 103. However, there may be about 36 projections. The molds of the present invention enable the polymerizable composition to be polymerized to produce contact lenses. The contact lenses produced with the molds of the invention are unhydrated lenses that can be prepared for wear by treatment with any hydration or swelling method known in the art.

Front mold half 102 and back mold half 103 may be made of any suitable thermoplastic polymer, preferably a thermoplastic polymer that is sufficiently transparent to ultraviolet light to allow transmitted radiation to facilitate polymerization of the contact lens material, particularly soft contact lens materials. In addition, it is desirable that the materials used be capable of molding surfaces with optical properties at relatively low temperatures, exhibit excellent flow characteristics, and remain amorphous during molding. Preferred materials for forming the two mold halves of the present invention are polyolefins including, but not limited to, polystyrene, polypropylene, and mixtures thereof. Each mold half may be made of the same or different material than the other mold half. The production of the mold halves may be accomplished by any suitable method, but is preferably as set forth in U.S. Pat. No.5,540,410. In the mold of the present invention, it is more preferable that the material used to form back mold half 103 is harder or less compressible than the material used for front mold half 102.

Fig. 3 illustrates a cross-sectional view of the mold I-I of fig. 2, the cross-section extending through one of the plurality of projections 116. Fig. 3a shows an enlarged cross-sectional view of a portion of the mold of fig. 3. Dotted line a in fig. 3a indicates how surface 109 extends up to flange 105 where there is no protrusion 116. Referring to fig. 3 and 3a, in mold front half 102, convex surface 105 and concave surface 104 are spaced substantially parallel, and substantially coplanar annular flange 106 extends radially outward from surfaces 104 and 105 in a plane that is orthogonal or perpendicular to the axis of symmetry of concave surface 104. Similarly, back mold half 103 has spaced apart surfaces 109 and 110, and a substantially planar annular flange 105, annular flange 105 extending radially outward from surfaces 109 and 110 in a plane orthogonal to the axis of convex surface 109. The front mold half concave surface 104 has the dimensions of the front curve of the unswollen lens to be cast in the mold and is sufficiently smooth to provide acceptable optical quality to the surface of the contact lens formed.

The back mold half 103 defines a central curved portion having an optical quality convex surface 109 and a substantially parallel concave surface 110. The convex surface 109 has the dimensions of the unswollen post-curve of the lens to be cast and is sufficiently smooth to give the resulting lens surface an acceptable optical quality. Convex surface 105 of front mold half 102 and concave surface 110 of back mold half 103 need not have surfaces suitable for forming optical quality surfaces.

The front mold half 102 defines a central curved portion having an optical quality concave surface 104. The concave surface 104 has a circular circumferential well-defined edge 111 extending therearound. The edge 111, together with the peripheral edge 120 of the convex surface of the back mold half, forms a well-defined and uniform plastomer radius parting line for the subsequently molded contact lens. The edges 111 typically have a curvature of about 3 to 45 microns or less, preferably about 5 to about 30 microns, with the surfaces defining the edges forming an angle of 75 to 90 degrees therebetween. Connected to the rim 111 and extending from the rim 111 radially outwardly towards an outwardly tapering wall 113 is a downwardly sloping inner surface 112. The plane of the inner surface 112 is located about 5 to about 15 degrees below a plane normal or perpendicular to the axis of symmetry of the concave surface 104.

Each tab 116 includes an outwardly extending wall 114, the wall 114 extending radially outward from a circular rim 120. The plane of the wall 114 lies in a plane orthogonal to the axis of symmetry of the convex surface 109 or a plane about 5 degrees above or below. The projection 116 further includes an upwardly extending wall 115, a lowermost portion of which is connected to the wall 114 and extends upwardly from the wall 114, and an uppermost portion of which is connected to the convex surface 109. Each protrusion 116 is preferably configured such that the gap formed between the inner surface 112 and the wall 114 is from about 0.005 to about 0.025 millimeters, more preferably from about 0.010 to about 0.017 millimeters. Each protrusion 116 may have a height of about 0.3 to about 1 millimeter, a width of about 0.3 to about 1 millimeter, and a thickness of about 0.3 to about 1 millimeter, with the thickness being measured outward relative to the convex surface 109. The protrusion is rounded to form a "nose" with a radius of about 0.1 to about 1mm, preferably about 0.15 to about 0.23 mm. The pressure applied to the back or front mold halves during lens curing ensures 360 degree contact between the front and back mold halves and minimizes tilt or non-parallelism.

As shown in fig. 3a, the wall 115 and the front mold half wall 113 cooperate to facilitate positioning of the back mold half after deposition of the lens material on the front mold half. In all embodiments, the front and back mold halves are designed to allow rapid heat transfer therethrough, but are sufficiently rigid to withstand the prying force separating the two mold halves during demolding. The molds of the invention can be used in any method of making contact lenses. However, the manufacturing method proposed in U.S. Pat. No.5,540,410 is preferably used. Generally, in a preferred method, a quantity of polymerizable composition is placed, preferably by injection, onto concave surface 110 of front mold half 102. The back mold half 103 is placed onto the polymerizable composition with the convex surface 109 facing the concave surface 110 of the front mold half 102. Preferably, the volume of polymerizable composition used is greater than the volume of chamber 101. Thus, placing back mold half 103 onto front mold half 102 will result in excessive material flow into the space between interior surface 112 and wall 114. The area between flanges 105 and 106 provides additional space for excess lens material. The width of the convex surface 109 is preferably no greater than the concave surface 110 to facilitate centering.

Once mold half 103 is placed on front mold half 102, the two halves are preferably molded together using a force of about 2 to about 5 pounds. The force may be applied to the flange 105 or 106 along the line indicated by the arrow in fig. 2. The force may be applied by any suitable means including, but not limited to, using pneumatic pressure, mechanical means (such as a spring), or a combination thereof. In one embodiment, a flat deposition nozzle disposed through the flange or a combined cone and flat deposition nozzle partially fitted into mold half 102 or 103 is used. The force is maintained constant throughout the polymerization of the polymerizable composition.

The polymerizable components are preferably polymerized under ultraviolet radiation. Following completion of polymerization, the molds formed by front and back mold halves 102 and 103, respectively, are disassembled and additional processing of the cast lens is performed.

Claims (2)

1. A mold for producing a contact lens, the mold comprising a front mold half and a back mold half, wherein the front mold half comprises a first component having a central curved portion with a concave surface, a convex surface and a first rounded circumferential edge formed around the concave surface of the central curved portion, the central portion of the concave surface being adapted to impart a curvature to the front curve of the contact lens; the first component further having an axis of symmetry of the concave surface and an inner surface contiguous with the circular rim, the inner surface extending downwardly from the circular rim in a plane 5-15 degrees below the axis of the concave surface, an outwardly tapering wall, and an annular flange integral with and surrounding the outwardly tapering wall and extending radially outwardly from the concave and convex surfaces in a plane normal to the axis of the concave surface; the back mold half comprises a second component having a central curved portion with a concave surface, a convex surface and a second circular peripheral edge surrounding the convex surface of the central curved portion, the central portion of the convex surface being adapted to impart curvature to the back curve of the contact lens; the second component also has an axis of symmetry of the convex surface, a plurality of spaced apart projections on the convex surface, each projection including a wall extending outwardly from a peripheral edge of the convex surface and an upwardly extending wall, a lowermost portion of the upwardly extending wall being contiguous with and extending upwardly from the outwardly extending wall, and an uppermost portion of the upwardly extending wall being contiguous with the convex surface, and an annular flange integral with and surrounding the concave and convex surfaces and extending radially outwardly from the concave and convex surfaces in a plane normal to the axis of the convex surface, a sufficient number of projections to achieve the desired centering and height control of the mold halves.

2. The mold of claim 1, wherein each protrusion is 0.3 to 1mm high, 0.3 to 1mm wide, and 0.3 to 1mm thick.