Note: Descriptions are shown in the official language in which they were submitted.
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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.
to 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
15 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
3o FIG. 1 is a close-up, cross-sectional side view of a seamed lens edge.
FIG. 2 is a top eievational 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.
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FIG. 3 is a close-up, cross sectional view of the front mold half of FIG. 2
fitted with the back mold half.
FIG. 3a 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. -Ia is a cross-sectional side view of the mold half of FIG. 4 along II-
II.
FIG. 5 is a close-up, cross-sectional view of an area of an embodiment of a
mold interlocking means of the invention.
to FIG. 6 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
15 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
2o 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 variety 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
25 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
30 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.
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An example of an interlocking means is shown in FIGs. 3 and 3a in which
s are illustrated various views of a preferred mold of the invention.
Referring to FIG.
3a, 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.
l0 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 114 is a
front mold half interlocking surface 112. Interlocking surface 112 extends
from
edge 111 at an angle of about 15 to about 75 degrees, preferably about 60
degrees,
2o above a plane normal, or perpendicular, to the axis of symmetry of concave
surface
110. Inner mating surface 114 is continuous with and extends radially
outwardly
from interlocking surface I 12. Similarly, back mold half 103 has back mold
half
interlocking surface I 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 complementarily 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.
3o Referring to FIGs. 2, 2a, 3 and 3a, front mold half 102 is shown with
convex
surface 113 spaced generally parallel from concave surface 110 and an
essentially
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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 110. The front
mold
interlocking surface 112 is continuous with inner mating surface I 14, which
surface
is continuous with uniplanar annular flange 106. The back mold half
interlocking
surface 117 is continuous with outer mating surface I 18. Outwardly tapering
wall
1o I 19 is continuous with and extends upwardly from outer mating surface 118.
As shown in FIGS. 3 and 3a, 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. 116. The radius of curvature of fillet 116
preferably is about 10 ~m to about 250 Vim, more preferably about 30 ~m to
about
100 Vim. Convex surface 109, fillet I 16, 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
2o 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. 3a, extending radially outwardly from back surface
circumferential edge 120 is interlocking surface 117 which is substantially
spherical
and has a radius of curvature of about 100 ~m to about 300 Vim, preferably
about
125 pm. Interlocking surface 117 extends outwardly from edge 120 at an angle
of
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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,
1o 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
2o 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
3o 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.
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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
2o 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
3o method, but preferably as set forth in U.S. Patent No. 5,540,410.
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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
1o 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
2o 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
1?1 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
3o by the arrows in FIG. 3. The force may be applied by any convenient means
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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
1o front and back mold halves 102 and 103, respectively, is disassembled and
the cast
lens undergoes additional processing.
