U.S. patent application number 10/992225 was filed with the patent office on 2006-05-18 for molds and method of using the same for forming plus or minus lenses.
Invention is credited to Richard Lu, Debbie Makita, Kai Su, David Wright.
Application Number | 20060103041 10/992225 |
Document ID | / |
Family ID | 36385417 |
Filed Date | 2006-05-18 |
United States Patent
Application |
20060103041 |
Kind Code |
A1 |
Su; Kai ; et al. |
May 18, 2006 |
Molds and method of using the same for forming plus or minus
lenses
Abstract
The present invention encompasses, in part, a method and
apparatus for lens casting in which two molds, preferably formed of
plastic, are interconnected or joined together via a ring to form a
mold cavity having substantially the same dimensions of the lens to
be formed therein. The invention is further directed to
compositions and methods used in lens casting. In a first
implementation the invention includes a mold having a ring having
an interior periphery; a front mold formed of a plastic and having
a lens-forming surface, an edge circumscribing the lens-forming
surface that is sized to be complementarily received within a
portion of the interior periphery of the ring, and a base having
dimensions greater than the interior periphery; and a rear mold
formed of a plastic and having a lens-forming surface.
Inventors: |
Su; Kai; (Alpharetta,
GA) ; Lu; Richard; (Alpharetta, GA) ; Wright;
David; (Roswell, GA) ; Makita; Debbie;
(Lawrenceville, GA) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Family ID: |
36385417 |
Appl. No.: |
10/992225 |
Filed: |
November 18, 2004 |
Current U.S.
Class: |
264/2.5 ;
425/406; 425/808 |
Current CPC
Class: |
Y10S 424/808 20130101;
B29D 11/00528 20130101; Y10S 425/808 20130101; B29D 11/00538
20130101; B29D 11/00413 20130101; B29C 33/40 20130101 |
Class at
Publication: |
264/002.5 ;
425/406; 425/808 |
International
Class: |
B29D 11/00 20060101
B29D011/00 |
Claims
1. A casting device, comprising: a. a ring having an interior
periphery; b. a front mold formed of a plastic and having a
lens-forming surface, an edge circumscribing the lens-forming
surface that is sized to be complementarily received within a
portion of the interior periphery of the ring, and a base having
dimensions greater than the interior periphery; and c. a rear mold
formed of a plastic and having a lens-forming surface, a rim
circumscribing the lens-forming surface that is sized to be
complementarily received within a portion of the interior periphery
of the ring, and a flange having dimensions greater than the
interior periphery, wherein when the edge of the front mold and the
rim of the rear mold are both received by the ring, the
lens-forming surfaces of the front and rear molds and the ring form
a mold cavity which has dimensions of a desired lens formable
therein.
2. The casting device of claim 1, wherein the ring is formed of a
plastic.
3. The casting device of claim 1, wherein the ring defines a feed
opening and a vent opening therethrough in fluid communication with
the mold cavity.
4. The casting device of claim 3, wherein, when the front and rear
molds are disposed upright, the vent opening is positioned at
substantially the top center.
5. The casting device of claim 4, wherein the mold cavity is
substantially is substantially circular in plan view and the feed
opening is offset from the vent opening between approximately
fifteen to sixty degrees.
6. The casting device of claim 1, wherein the ring has opposed
ends, wherein the base of the front mold has a contacting surface
that is substantially planar, and wherein the contacting surface
and one end of the ring abut when the mold cavity is formed.
7. The casting device of claim 6, wherein the lens-forming surface
of the front mold is concave and defines a nadir, wherein the nadir
tangentially intersects a plane defined by the contacting surface
of the base.
8. The casting device of claim 7, wherein the flange of the rear
mold has an engaging surface that is substantially planar and
wherein the engaging surface and one end of the ring abut when the
mold cavity is formed.
9. The casting device of claim 8, wherein the lens-forming surface
of the rear mold has an apex so that a plane tangential to the apex
is substantially parallel to and spaced apart from a plane defined
by the engaging surface, the separation between the plane
tangential to the apex and the plane defined by the engaging
surface is the back mold apex height.
10. The casting device of claim 9, wherein the ends of the ring are
spaced apart by a ring height, the ring height being the sum of the
back mold apex height and a desired center thickness for the mold
cavity.
11. The casting device of claim 8, wherein the lens-forming surface
of the front mold further comprises a plurality of protrusions each
located adjacent the edge, the protrusions having a height
corresponding to a desired edge thickness for the mold cavity.
12. The casting device of claim 1, wherein the front mold is
rotatable relative to the rear mold so that the two molds are at
one of a plurality of selected rotational orientations relative to
each other so as to alter characteristics of the mold cavity when
the lens-forming surfaces of the respective front and rear molds
have asymmetric curvature.
13. The casting device of claim 12, further comprising means for
aligning the front and rear molds at a predetermined rotational
orientation relative to each other.
14. The casting device of claim 13, wherein the aligning means
comprises axis marks on the ring intermediate its opposed ends and
an axis-positioning indicator on at least one of the front mold or
the rear mold.
15. The casting device of claim 1, wherein the ring and the front
and rear molds are movable between a stored position, in which the
molds and ring are each spaced apart from each other, and a molding
position, in which the ring receives the edge of the front mold and
receives the rim of the rear mold to form the mold cavity.
16. The casting device of claim 15, wherein, when in the stored
position, the rear mold is selected from a group of rear molds, in
which different rear molds form mold cavities having different
dimensions when in the molding position.
17. The casting device of claim 15, wherein, when in the stored
position, the ring is selected from a group of rings, in which
different rings have their respective opposed ends spaced apart at
different heights to form mold cavities having different dimensions
when in the molding position.
18. The casting device of claim 15, wherein the lens-forming
surface of the front mold further comprises a plurality of
protrusions each located adjacent the edge, wherein, when in the
stored position, the front mold is selected from a group of front
molds that have protrusions of a height different from other front
molds.
19. The casting device of claim 15 wherein, when in the molding
position, the front mold is rotatably movable relative to the rear
mold so that the two molds are at one of a plurality of selected
rotational orientations relative to each other so as to alter
characteristics of the mold cavity when the lens-forming surfaces
of the respective front and rear molds have asymmetric curvature
relative to each other.
20. The casting device of claim 1, further comprising a fill bag
having an interior and an injection port detachably connectable to
the feed opening, wherein when the port is connected to the feed
opening, a fluid located within the interior of the fill bag may
traverse through the injection port and into the mold cavity.
21. The casting device of claim 1, further comprising monomer
disposed within the mold cavity.
22. The casting device of claim 1, wherein the plastic forming the
front and rear molds comprises polymethylmethacrylate.
23. The casting device of claim 1, wherein the lens-forming
surfaces of the front and rear molds are coated with a composition
that transfers in situ to a lens when formed within the mold
cavity.
24. A casting device, comprising: a. a ring having an interior
periphery; b. a front mold formed of a plastic and having a
lens-forming surface, an edge circumscribing the lens-forming
surface that is sized to be complementarily received within a
portion of the interior periphery of the ring, and a base having
dimensions greater than the interior periphery; c. a rear mold
formed of a plastic and having a lens-forming surface, a rim
circumscribing the lens-forming surface that is sized to be
complementarily received within a portion of the interior periphery
of the ring, and a flange having dimensions greater than the
interior periphery; and d. means for injecting a fluid into the
mold cavity, wherein when the edge of the front mold and the rim of
the rear mold are both received by the ring, the lens-forming
surfaces of the front and rear molds and the ring form a mold
cavity which has dimensions of a desired lens formable therein.
25. The casting device of claim 24, wherein the injecting means
comprises: a. a feed opening defined through the protrusion of the
rear mold and in fluid communication with the mold cavity; and b. a
vent opening defined through the protrusion of the rear mold,
wherein the vent opening is in fluid communication with the mold
cavity and ambient to allow fluid flow therethrough.
26. The casting device of claim 25, wherein, when the front and
rear molds are disposed upright, the mold cavity is substantially
circular in plan view, the vent opening is positioned at
substantially the top center, and the feed opening is offset
approximately fifteen to sixty degrees therefrom.
27. The casting device of claim 24, further comprising means for
positioning the front and rear molds at a predetermined axial
separation distance to obtain a desired center thickness within the
mold cavity.
28. The casting device of claim 24, further comprising means for
aligning the front and rear molds at a predetermined rotational
orientation relative to each other.
29. The casting device of claim 25, further comprising: a. a fill
bag having an interior; and b. means for detachably connecting the
feedbag to the feed opening for allowing a fluid located within the
interior of the fill bag to traverse into the mold cavity.
30. The casting device of claim 24, further comprising means for
orienting the front and rear molds at a predetermined rotational
position with respect to each other.
31. The casting device of claim 24, wherein the plastic forming the
front and rear molds comprises polymethylmethacrylate.
32. The casting device of claim 24, wherein the lens-forming
surfaces of the front and rear molds are coated with a composition
that transfers in situ to a lens when formed within the mold
cavity.
33. The casting device of claim 24, wherein the injecting means
injects monomer into the mold cavity.
34. A casting component, comprising: a casting mold formed of a
plastic, the mold having a lens-forming surface, a border
circumscribing the lens-forming surface, and a backing member
wherein the border of the lens-forming surface is sized to be
complementary received within an interior periphery of a ring to
form a substantially fluid-tight seal therebetween, wherein the
backing member is sized to abut an end the ring when the border is
received within its interior periphery, wherein, when the backing
member abuts end of the ring, the interior surface of the casting
mold and the interior periphery of the ring define a portion of a
mold cavity, in which the mold cavity has dimensions to form a
desired lens therein.
35. A method of casting a lens, comprising: a. joining a ring, a
front mold, and a rear mold together to form a mold cavity
therebetween having dimensions of a desired lens formable therein,
the molds each having a backing member, a portion of the front and
rear molds being received by an interior periphery of the ring
until the respective molds each abut an opposed end of the ring; b.
injecting a lens-forming fluid into the mold cavity and
simultaneously venting displaced fluid from the mold cavity to
ambient; c. curing the lens-forming fluid within the mold cavity to
form a lens having dimensions substantially the same as mold
cavity; and d. separating the cured lens from the ring and
molds.
36. The method of claim 35, wherein the front and rear molds are
formed of a plastic.
37. The method of claim 36, wherein the plastic is
polymethylmethacrylate.
38. The method of claim 35, wherein the lens-forming fluid is
monomer.
39. The method of claim 35, wherein photo curing is used to harden
the lens-forming fluid.
40. The method of claim 35, wherein the front and rear molds are
rotatably movable relative to each other to one of a plurality of
rotational orientations.
41. The method of claim 35, wherein the ring and molds have
dimensions so that when joined together, the mold cavity has a
desired center thickness.
42. The method of claim 41, wherein the ring and molds are selected
from a plurality of molds that collectively form the desired center
thickness when coupled together.
43. The method of claim 35, wherein before joining the ring and
molds together, substantially all of the surfaces of the front and
rear molds that define the mold cavity are coated with a
composition that transfers in situ to the lens formed within the
mold cavity.
44. The method of claim 35, wherein the formed lens is a spectacle
lens.
Description
FIELD OF THE INVENTION
[0001] The present invention encompasses, in part, a method and
apparatus for lens casting in which two molds, preferably formed of
plastic, are interconnected or joined together via a ring to form a
mold cavity having substantially the same dimensions of the lens to
be formed therein. The invention is further directed to
compositions and methods used in lens casting.
BACKGROUND
[0002] The art of casting lenses involves introducing a
lens-forming material, such as a monomer or monomer mixture, into a
volume and then polymerizing the lens-forming material to become a
solid. The formed lens can be used for ophthalmic or specialty
optics applications. Ophthalmic devices have traditionally been
created by first forming a cavity out of two separate mold shapes,
then filling that cavity with a liquid material that will cure and
form a solid shape. The molds used in this type of process are
typically glass or metal, based on their high chemical resistance
and low amount of geometric distortion they experience over
time.
[0003] Most commonly, two glass mold pieces and a gasket form the
volume that defines the dimensions of the lens to be cast. Some
prior art gaskets are known as "T-gaskets," which include a bore
having two ends that each complementarily receives a respective
glass mold spaced apart a predetermined axial distance from the
other mold. Different T-gaskets are required to form varying power
lenses because they only allow one separation distance between
molds. Accordingly, manufacturers must maintain T-gaskets for a +2
lens, another for a -3 lens, still another for a -4 lens, etc.
[0004] An improvement of this "T-gasket" design is disclosed in
U.S. Pat. No. 6,068,464 (hereafter "the '464 patent"), in which at
least one of the two molds is slidably movable along the bore of
the gasket. This design thus has a "universal" gasket that can be
used to form different powers of lenses, whereas a given prior art
T-gasket may be used to form one power of lens and a different
T-gasket is used to form another power.
[0005] U.S. Pat. No. 5,551,663 (hereafter "the '663 patent")
described the use of plastic molds in the manufacture of ophthalmic
lenses, but no mention of successfully making lenses is included
here. This approach necessitated the use of a "protective coating"
first being applied to the mold before the mold could be used. This
protective coating became a permanent part of the mold, and allowed
for the mold to be used repeatedly. Evidence of the permanence of
the coating is apparent in the description of the adhesion test
used to assure proper adhesion of the coating to the mold. The
patent describes a "plastic mold having an adherent, abrasion
resistant, release enhancing face." The purpose of the coating of
the '663 patent is to prevent attack of the mold by the lens
material. (By comparison, this current patent application applies a
coating to the mold, but with the intent that the coating be only
temporary, and that it transfer via chemical bonding to the lens
material.)
[0006] The method of the '663 patent raises significant issues
about its ability to consistently produce high-quality molded
lenses. Possible problems that might occur with the method of the
'663 patent include a decay in the optical quality of the mold. Any
defect on either side of the mold could affect the finished quality
of the lens. The decay can take the form of yellowing, cracking,
scratching, and physical deformation. These forms of decay can
occur with repeated use of a non-rigid material. Any of these types
of decay could alter the optical quality of lenses made.
Additionally, plastic materials would be difficult to clean, since
they are not very chemically resistant, not scratch resistant, and
not very resistant to the heat used in many typical processes.
[0007] Accordingly, a need exists for durable, low cost plastic
molds that can be used to create lenses of various powers.
SUMMARY OF THE INVENTION
[0008] The present invention comprises a method and apparatus for
casting a lens, and chemical compositions used to perform the
same.
[0009] In one implementation of the invention, a front mold and a
rear mold formed of a plastic are joined together or interconnected
via a ring to form a mold cavity having substantially the same
dimensions of the lens to be cast. Stated differently, surfaces of
the ring and front and rear molds collectively define a volume
known as the mold cavity, which is a negative image of the lens to
be formed therein.
[0010] More specifically, the front mold has a lens-forming surface
and an edge circumscribing the lens-forming surface. The rear mold
similarly has a lens-forming surface and an edge circumscribing its
lens-forming surface. The lens-forming surfaces of the front and
rear molds are each of a size to be complementarily received by and
within the interior periphery of the ring. The molds have backing
members, which stop the insertion of molds when their respective
lens-forming surfaces reach a predetermined point within the ring
so that the spacing between the two lens-forming surfaces is at a
desired separation distance. This desired separation corresponds to
the thickness of the mold cavity, which dictates the thickness and
power of the lens formed by the casting device.
[0011] The molds of the present invention may be designed to cast
lenses of different strengths and curvatures. That is, for a lens
with given optical surfaces, the lens thickness can be altered by
manufacturing the front and/or rear molds having their backing
member at one of a plurality of distances from the respective
lens-forming surface. Alternatively, the length or height of the
ring may be changed to vary the thickness of the mold cavity.
Another alternative is to include a plurality of protrusions
adjacent the edge of one of the lens forming surfaces, in which the
height of the protrusions establishes the edge thickness of the
mold cavity.
[0012] The present invention additionally allows for a disposable
plastic mold to be used in the ophthalmic casting process, either
with the disclosed apparatus or in other systems known in the art.
This disposable mold can be made out of a variety of amorphous
thermoplastics, and can be used to make a lens with or without a
variety of coating scenarios. The lenses formed using this process
are impact resistant, can have any refractive index, can be clear
(no tint) or photochromic, and can be used for "dress" or safety
purposes.
BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS
[0013] FIG. 1 is an exploded perspective view of an exemplary
embodiment of a casting system used with the present invention.
[0014] FIG. 2A is side cross-sectional view of the front mold shown
in FIG. 1, which is preferably used to form a minus lens.
[0015] FIG. 2B is an alternative design of the front mold shown in
FIG. 2A, which is preferably used to form a plus lens.
[0016] FIG. 2C is side cross-sectional view of the rear mold shown
in FIG. 1.
[0017] FIG. 3A is a side cross-sectional view of the components in
FIG. 1 assembled.
[0018] FIG. 3B is an alternative design of the casting system shown
in FIG. 3A, in which the front mold of FIG. 2B is included.
[0019] FIG. 4A is a lens formed by the casting system shown in FIG.
3A.
[0020] FIG. 4B is a lens formed by the casting system shown in FIG.
3B.
[0021] FIG. 5 is a perspective view of the casting system of FIG. 1
connected to a fill bag containing monomer.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The present invention is more particularly described in the
following detailed description, including examples. These examples
are intended as illustrative of the invention, and numerous
modifications and variations therein will be apparent to those
skilled in the art while staying within the scope of the invention.
As used in the specification and in the claims, "a," "an," or "the"
can mean one or more, depending upon the context in which it is
used.
[0023] A first embodiment is now described with reference to the
figures, in which like numbers indicate like parts throughout the
figures. The present invention comprises a molding or casting
device 10 and an associated method that may be used to form lenses
of various powers and geometric shapes, such as spectacle lenses.
The present invention additionally comprises methods for making
ophthalmic lenses using disposable plastic molds.
[0024] In this discussion, first one exemplary embodiment of a
casting system comprising plastic components is discussed in the
context of the components and method of those components. This
first discussion provides context for and is followed by the
aspects of the present invention that involve casting ophthalmic
lenses using plastic molds. This latter discussion is not intended
to be limited to the exemplary embodiment of the casting system
disclosed herein.
Lens Casting Devices
[0025] Referring now to FIGS. 1-5, the casting device 10 of the
present invention includes a front mold 20 and a rear mold 40, both
of which are preferably formed of plastic. The casting device 10
also includes a ring 50, which may also be referred to as a sleeve
or gasket. The ring 50 is also preferably formed of plastic and has
opposed ends 52, an interior periphery 54, and an exterior
periphery 56. As discussed below, portions of the front and rear
molds 20, 40 are complementarily received by and into the interior
periphery 54 to form a mold cavity 60.
[0026] The front mold 20 has a lens-forming surface 22, an edge 28
circumscribing the lens-forming surface 22, and a base 30 having
dimensions greater than the interior periphery 54. The edge 28
circumscribing the lens-forming surface 22 is sized to be
complementarily received within a portion of the interior periphery
54 of the ring 50 and preferably form a substantially liquid-tight
seal therebetween. The edge 28 is slidably received within the
interior periphery 54 of the ring 50 until the base 30 abuts the
end 52 into which the edge 28 was inserted.
[0027] The rear mold 40 likewise has a lens-forming surface 42, a
rim 46 circumscribing the lens-forming surface 42, and a flange 48
having dimensions greater than the interior periphery 54 of the
ring 50. The rim 46 is also sized to be complementarily received
within the interior periphery 54 of the ring 50, which occurs until
the end 52 of the ring 50 abuts the flange 48. The rim 46 and the
interior periphery 54 also preferably form a substantially
liquid-tight seal therebetween.
[0028] As shown in FIGS. 3A and 3B, when the edge 28 of the front
mold 20 and the rim 46 of the rear mold 40 are both received by the
respective ends of the ring 50, the lens-forming surfaces 22, 42 of
the front and rear molds 20, 40 and the ring 50 form a mold cavity
60 which has dimensions of a desired lens formable therein. That
is, the mold cavity 60 is a replica image of the lens to be formed
and has a volume defined by the ring 50, front mold 20, and rear
mold 40.
[0029] To form a lens once the ring 50 and front and rear molds 20,
40 are properly joined or positioned together, a resin, such as a
monomer or other lens-forming fluid, is added or injected into the
mold cavity 60 and cured. To that end, the ring 50 defines a feed
opening 70 and a vent opening 72 therethrough, which are shown in
FIGS. 1 and 5. The vent opening 72 provides fluid communication
from the mold cavity 60 to outside of it (i.e., to ambient).
[0030] As best shown in FIGS. 1 and 5, when the front and rear
molds 20, 40 are disposed upright, then the mold cavity 60 is
substantially circular in plan view and the vent opening 72 is
positioned at approximately the top center (the 12:00 o'clock
position). The feed opening 70 is preferably offset from the vent
opening 72, and one contemplated range for this offset is by
approximately fifteen to sixty degrees (15.degree.-60.degree.).
Still referring to FIGS. 1 and 5, it will be noted that an extender
74 is joined to the feed opening 70. The top of the extender in
communication with the feed opening 70 and is elevationally above
the vent opening 72, which ensures that the cavity is full when the
monomer reaches the top of the extender 74. It will further be
noted that preferably the feed opening 70 is an elongated slot that
extends across the width of the ring 50. This design ensures that
communication exists with the mold cavity 60 through the feed
opening 70 regardless of the placement of the molds relative to the
ring, which may change when used for casting minus lenses verses
plus lenses.
[0031] A key dimension of the formed mold cavity 60 is its
thickness. For minus lenses used for nearsightedness or myopia
shown for example in FIG. 4A, the center thickness is an important
parameter, and it must satisfy impact testing required in the
United States. As an example, plastic lenses formed of CR39 (which
includes methyl-methacrylate--a thermoplastic resin better known by
its trademark "Plexiglas".RTM. or "Perspex".RTM. --and diallyl
glycol carbonate) must have a center thickness of at least two
millimeters (2 mm). The preferred embodiment of the present
invention is designed to be able to form both plus and minus lenses
that satisfy these respective criteria.
[0032] First with regard to minus lenses, the center thickness is
obtained by the design of the front and rear molds 20, 40 in
conjunction with the width or length of the ring 50. Referring now
to FIG. 2A and addressing the front mold 20, its base 30 has a
contacting surface 32 that is substantially planar, and that
contacting surface 32 abuts one end 52 of the ring 50 when the edge
28 of the front mold 20 is inserted therein to define a portion of
the mold cavity 60. In conjunction, the lens-forming surface 22 of
the front mold 20 is concave and defines a nadir 26 or low point,
which tangentially intersects a plane FMP defined by the contacting
surface 32 of the base 30. The nadir 26 of the lens-forming surface
22 is thus at the same relative height as the contacting surface 32
when the front mold 20 is horizontally disposed. As such, the nadir
26 is aligned with the end of the ring 50 when the contacting
surface 32 abuts the end 52 of the ring 50.
[0033] As shown in FIG. 2C, the flange 48 of the rear mold 40 has
an engaging surface 49 that is substantially planar to abut the
respective end 52 of the ring 50 when the mold cavity 60 is formed.
The lens-forming surface 42 of the rear mold 40 has an apex 44, in
which a plane AP tangential to the apex 44 is substantially
parallel to and spaced apart from a plane RMP defined by the
engaging surface 49. The separation or distance between the plane
AP tangential to the apex 44 and the plane RMP defined by the
engaging surface 49 is called the back mold apex height AH.
[0034] Also, the opposed ends 52 of the ring 50 are spaced apart by
a ring height RH. As one skilled in the art appreciates, the ring
height RH establishes the separation between the engaging surface
49 of the rear mold 40 and the contacting surface 32 of the front
mold 20. Correspondingly, the ring height RH is a parameter used to
set the center thickness of the mold cavity 60, and thus the lens
formed therein. That is, for this embodiment, the center thickness
of the mold cavity 60 equals the ring height RH minus the back mold
apex height AH, as the nadir 26 of the lens-forming surface 22 of
the front mold 20 is aligned with one end of the ring 50. Thus, if
the ring height RH is three millimeters (3 mm) and the back mold
apex height AH is two millimeters (2 mm), then the center
thickness--the separation between the apex 44 of the rear mold 40
and the nadir 26 of the front mold 20--is one millimeter (1
mm).
[0035] As shown in FIG. 3A, the assembled casting device 10 shows
the relative position of the components in establishing the center
thickness for the mold cavity 60. Specifically, one end 52 of the
ring 50 abuts the contacting surface 32 of the front mold 20 and
the opposed end 52 abuts the engaging surface 49 of the rear mold
40. The nadir 26 of the front lens-forming surface 22 is spaced
apart a desired distance--the center thickness--from the apex 44 of
the rear lens-forming surface 42 when the molds 20, 40 are coupled
together. Stated differently, the plane AP tangential to the apex
44 is spaced apart from the plane FMP defined by the contacting
surface 32 and tangentially intersects the nadir 26 at a distance
substantially equivalent to the desired center thickness of the
mold cavity 60. Thus, the apex 44 and the nadir 26 of the
respective lens-forming surfaces 22, 42 in the mold cavity 60 are
spaced apart at the desired center thickness for the lens to be
formed.
[0036] As one skilled in the art appreciates, changing the
dimensions of the components correspondingly alters the center
thickness of the mold cavity 60. Any of the components can be
modified. Although viable, currently the least desirable option is
to change the position of the nadir 26 relative to contacting
surface 32 of the front mold 20. A more desirable option is using
rings 50 each having a different ring height RH to change the
center thickness. The presently preferred design, however, is to
vary the back mold apex height AH among different molds to change
the center thickness of the mold cavity 60. Thus, in this latter
design, the front mold 20 uses the same design shown in the
illustrated embodiment and a "universal" or "one-size" ring that
has the same dimensions regardless of the strength of the lens to
be made; only the rear mold 40 is changed in this latter design
and, in particular, the back mold apex height AH is altered among
different rear molds 40 to vary the center thickness of the mold
cavity 60.
[0037] Still another contemplated embodiment to change the center
thickness for a selected ring 50, front and rear mold 20, 40 is to
include a circular spacer (not shown) between the engaging surface
49 of the rear mold 40 and respective end of the ring 50. The
circular spacer has diameter the same as the ring 50 and a fixed
width or height, thereby increasing the center thickness of the
mold cavity 60 by that width of the circular spacer. For example, a
circular spacer having a width of one millimeter (1 mm) disposed
between the end of the ring 50 and the engaging surface 49 would
correspondingly result in the center thickness of the mold cavity
60--and lens to be formed therein--increasing by one millimeter (1
mm). Circular spacers, accordingly, may reduce the number of
components that need to be manufactured to enable an operator to
cast all desired dimensions and strength of lenses.
[0038] Referring now to FIGS. 2B and 3B, the illustrated front mold
20 includes a plurality of protrusions 34 located adjacent the edge
and space apart from each other. The protrusions 34 have a height
corresponding to a desired edge thickness for the mold cavity 60.
For example, if the protrusions 34 have a height of one millimeter
(1 mm), then the edge thickness of mold cavity 60 will be at least
one millimeter because the protrusions 34 prevent the edges of the
front and rear lens-forming surfaces 22, 42 from being closer
together than the height of the protrusions 34. The protrusions 34
may be any desired height, including for example 0.75, 1.0, 1.25
millimeters and the like. A person skilled in the art can determine
the number of protrusions 34 to use; the currently contemplated
embodiment uses thirty-two equally spaced protrusions 34
circumscribing the perimeter of the lens-forming surface 22 of the
front mold 20. Fewer protrusions are shown in the drawings for
simplicity. It will be appreciated that benefits of this design
include the same rear molds 40 and rings 50 that are used to form
the minus lenses also being used to form the plus lenses.
[0039] The present invention additionally contemplates other
methods of forming plus lenses. For example, the ring height RH may
be varied to obtain the correct separation between the lens-forming
surfaces 22, 42 of the front and rear molds 20, 40, including the
edge thickness. Also, the lens-forming surfaces 42 of the rear
molds 40 may include the protrusions 34 instead of the front molds,
but this option is less desirable given the greater variations in
rear mold designs and associated higher cost for a "library" of
molds to manufacture all lens variations.
[0040] In addition to considering the edge of center thickness,
another relevant parameter in forming a desired lens is the
geometric configuration or relationship of its two optical
surfaces. When the two lens-forming surfaces 22, 42 are both
spherical, the molds 20, 40 do not require any special rotational
alignment relative to each other. This is because the respective
surfaces have a constant radius along their different axes
resulting in the surfaces being symmetric relative to each
other.
[0041] For other lenses, however, the present invention includes a
means for orienting the front and rear molds 20, 40 at a
predetermined rotational position with respect to each other. In
the illustrated embodiment, the front and rear molds 20, 40 are
rotatably movable relative to each other so that the two molds may
be positioned at one of a plurality of selected relative rotational
orientations. This orienting means thus allows the operator to
alter the dimensions or shape of the mold cavity 60 to desired
values when either or both of the lens-forming surfaces 22, 42 of
the front and rear molds 20, 40 have asymmetric curvature. Examples
of asymmetrical lenses that operators may typically cast include
the front surface of a lens being spherical with an add power--or
less frequently being a plano surface--and, in conjunction or
independently, the back surface being cylindrical or toric. A
discussion of the features and types of such asymmetrical surfaces
may be found in U.S. Pat, No. 6,103,148.
[0042] Referring back to FIG. 1, the present invention also
comprises an aligning means to allow the operator to appreciate the
relative rotation of the two molds 20, 40 and position them
accordingly. The aligning means shown in the illustrated embodiment
comprises axis marks 90 on the exterior periphery 56 of the ring 50
and an axis-positioning indicator 92 on the front mold 20 or rear
mold 40 or both. The axis marks 90 extend from 0.degree. to
180.degree. and the asymmetrical lens-forming surface 22 or 42 is
to be positioned in registry with them. If injection molding or
similar technique forms the components, the aligning means are
preferably etched or formed into the respective dies. Thus, the
position indicator 92 and marks 90 are also integrally formed into
the components. One skilled in the art will also appreciate that
aligning means may alternatively comprise the axis marks being
located on one or both of the front and rear molds 20, 40 and an
axis-positioning indicator on the ring 50. Other methods of
visually indicating the rotational position of the molds relative
to each other may also be used.
[0043] In preparing to cast the lens, the operator locates the
position indicator 92 at a desired orientation relative to the axis
marks 90 on the ring 50 either before the front and rear molds 20,
40 are joined to the ring 50 or afterwards (e.g., twisting the
molds relative to each other once they are coupled to the ring 50).
The operator, thus, is able to position the two molds at a desired
rotational location easily using the aligning means.
[0044] When the operator joins the ring 50 and the two molds 20, 40
together after selecting them, it is preferred that a connecting
means exists so that the components do not inadvertently separate
during the lens casting process. Such a connecting means can take
numerous forms known in the art, including the interior periphery
54 of the ring 50 and the edge 28/rim 46 having a tight frictional
fit. Other connecting means are also contemplated (not shown),
including designs in which the two molds 20, 40 snap into place
within the ring 50 or in which an external clip or containing
device is used to hold the components together.
[0045] In still another contemplated embodiment, the front and rear
molds 20, 40 are formed as a single unit so they are integrally
joined to each other. This may occur during the forming process
(i.e., during injection molding) so that the operator receives a
preformed molding structure in which the front and rear molds 20,
40 are stationarily positioned relative to each other. This unitary
design, however, has less flexibility than interchanging the ring
50 and the front and rear molds 20, 40.
[0046] As noted above, once the front and rear molds 20, 40 are
stationarily positioned together, a resin, such as a monomer or
other lens-forming fluid, is added or injected into the mold cavity
60 and cured via the feed and vent openings 70, 72 through the ring
50. Referring now to FIG. 5, a fill bag 80 or the like containing a
fluid such as monomer may be interconnected to the feed opening 70
or its extender 74. More specifically, the fill bag 80 has an
interior and an injection port 82 detachably connectable to the
feed opening 70. When the injection port 82 is linked to the feed
opening 70, the monomer located within the interior of the fill bag
80 may flow through the port into the mold cavity 60.
[0047] The injection port 82 and the feed opening 70 are preferably
designed to complementarily engage each other. That is, the tip 84
of the injection port 82 is of a size to be complementarily
received within the feed opening 70 or its extender 74 to form a
fluid-tight seal therebetween.
[0048] One consideration that a person skilled in the art takes
into account in casting lenses is the flow characteristics of the
monomer traversing from the fill bag 80 into the mold cavity 60. A
primary concern is to avoid the introduction of air bubbles and
ensure that any such bubbles escape from of the mold cavity 60
before the curing begins; otherwise, the formed lens may be
unacceptable if an air bubble discontinuity exists in the final
product. In addressing this issue, the size of the feed opening 70
should be of a dimension and positioned to promote laminar flow
when filling the mold cavity 60. The fill opening 70 is preferably
oriented to direct the monomer along the side of the mold cavity 60
during the initial filling. As noted above, the vent opening 72 is
also preferably located at the top of the mold cavity 60 (i.e., at
the 12:00 o'clock position) to vent air within the cavity 60 when
displaced by the injected or incoming monomer. The vent opening 72
being located at the top also allows any bubbles to escape before
the curing process begins.
[0049] Another consideration regarding injecting monomer involves
positioning the mold cavity 60 so that the add power (not shown) is
oriented to have its flat top portion substantially upright or
vertical during filling the mold cavity 60. This orientation
assists in preventing air bubbles within the monomer from being
trapped by this discontinuity in the lens-forming surface 22 of the
front mold 20. Bubbles are more likely to remain in the mold cavity
60 if, for example, the flat top is horizontally oriented.
[0050] Referring again to FIG. 5, the fill bag 80 is at least
partially constructed of a deformable surface on which the operator
directs a compressive force so that one wall of the bag 80 moves
inwardly toward the opposed wall. When that compressive force is
applied, the fluid monomer located within the interior is forced
toward and out of the injection port 82 to enter the mold cavity 60
via the feed opening 70. In constructing a system necessitating
minimal capital investment, the illustrated embodiment is
inexpensively designed and relies on the operator hand squeezing
the bag 80 to fill the mold cavity 60.
[0051] Other means of injecting monomer into the mold cavity 60 are
contemplated. Examples of such systems using a deformable bag to
fill the mold cavity 60--particularly for more complex casting
designs--is disclosed in U.S. patent application Ser. No.
10/095,130, filed on Mar. 11, 2002 and entitled "Method and
Apparatus for Dispensing a Fluid". Monomer fill systems similar to
the design disclosed in U.S. Pat. No. 6,103,148 is another
option.
[0052] Once monomer fills the mold cavity 60, the bag 80 is
separated from the mold and then the monomer is cured (as discussed
in more detail below).
Mold Materials
[0053] Materials suitable for forming the molds of the invention
include a variety of thermoplastic or substantially thermoplastic
materials that can be injection molded. The materials are
preferably optically transparent. Suitable amorphous thermoplastic
materials include, but are not limited to, polycarbonate, acrylics,
polystyrene, CAB (cellulose acetate butyrate), polyesters, and
combinations thereof. In general it is also desirable that the
thermoplastic material be selected such that it will not be
attacked by coating and/or monomer material used to form the lens.
In general higher molecular weight analogs are desirable because
they are typically more resistant to coatings and monomers used to
form the lenses.
[0054] Amorphous thermoplastics can provide the advantage that,
unlike crystalline thermoplastics, they tend to maintain an
optical-quality surface for long periods of time, and so have a
long shelf life with proper storage. In contrast, crystalline
thermoplastics undergo dimensional changes after they are injection
molded. These dimensional changes occur due to the polymer's
attempt to arrange itself in a more crystalline, lower energy
structure. The result of this rearrangement is that the plastic
part can have an uneven, non-optical surface. In contrast,
amorphous thermoplastics will typically retain the shape they took
on during the injection molding process. Not all thermoplastics are
either 100% crystalline or 100% amorphous, so the scope of this
disclosure ranges from "substantially amorphous" to totally
amorphous materials, meaning thermoplastics that contain mostly
amorphous materials.
Mold Coatings
[0055] In certain embodiments of the invention a coating is applied
to the interior of the mold prior to forming the lens. In some
embodiments the coating is applied to interior portions of the mold
by dip coating, spin coating, spray coating, flow coating,
electrostatic spray, roll coating, modified roll coating, print
coating, or other coating method. The coating may then optionally
also be subjected to a "precure" to partially cure the coating so
that it will stay in place and not move during subsequent steps in
the process.
[0056] The molds can be coated with any of a variety of coating
formulations, provided that the coating does not chemically attack
the mold. The coating formula can include, for example, acrylate
functional materials capable of crosslinking, initiators or
catalysts capable of initiating the reaction of acrylates, flow or
leveling agents, defoamers, stabilizers, UV absorbers,
antioxidants, dyes, and possibly solvents. Some solvents can be
used in the coating formulation, as long as such formulations do
not substantially attack the mold before the formulation has cured.
Solvents that could be used would include alcohols, glycols ethers,
etc. Solvents that would be less acceptable for use would include
lower molecular weight ketones such as acetone, methyl ethyl
ketone, methyl isobutyl ketone (MIBK), cyclohexanone; acetates;
aromatic solvents such as benzene, xylenes; low MW hydrocarbons
such as hexane, etc.
[0057] Suitable coatings include those that provide a hardcoat for
improved scratch-resistance, a tintable coat for the purpose of
making sunglasses or other "fashion" tints, a UV coat to prevent
certain wavelengths of UV light to pass through the lens, an AR
("anti-reflective") coat to prevent glare, or any other type of
ophthalmic coating. The coating should be selected so that it does
not attack the mold material. Such coatings remain on the mold
temporarily and are transferred to the finished lens during the
lens curing step. Thus, the coating is applied to the mold with the
intent that it becomes an integral part of the finished lens.
[0058] In general it is important that the coating not attack the
interior of the mold and be readily releasable from the mold. As
one skilled in the art would appreciate, the coatings could be
based on UV-curable acrylic, sol-gel, or other composition types.
Accordingly, acrylates used in the coating formulation should not
have enough solvating power to attack the mold. The coating
preferentially has a more complete cure at the mold/coating
interface than at the coating/air interface.
[0059] In an acrylic coating, the major constituents of the
protective coating include multifunctional acrylates or
methacrylates, including tri-,tetra-, penta-, and hexafunctional
materials capable of providing high levels of cross-linking. The
molecular weight of these constituents must be high enough to
prevent attack on the mold. The protective coating could contain a
small amount of a low-viscosity diluent with at least two ethylenic
groups to adjust for coating viscosity, but the majority of the
formulation will contain higher molecular weight, higher viscosity
materials. Examples of materials commonly used in coatings are in
the attached table and illustrate the importance of the use of
appropriate materials with plastic molds.
Lens Forming Formulations
[0060] The molds of the present invention are suitable for use with
a variety of resin compositions to form finished optical lenses. In
general, molds made in accordance with the invention are well
suited to use of radiation initiated curing processes, such as by
exposure to ultraviolet or visible light, but can also include
thermally cured materials if the thermal cure temperature is below
the glass transition temperature T.sub.g of the mold.
[0061] Suitable lens forming compositions include materials having
low cure temperatures, which cure quickly, including acrylates,
methacrylates, and styrenes. In some implementations epoxies can be
used.
[0062] It is generally desirable to have the lens forming
formulation be inert or substantially inert to the mold itself.
However, in certain circumstances the lens material is not inert to
the mold material, in which case an intermediate coating material
can be used to prevent degradation of the mold. Typically the
coating is applied first to the interior of the mold, cured or
partially cured, and then the primary lens forming formulation is
added.
[0063] Any of a variety of photocleavable or thermal initiators can
be used. The level of photo initiator or thermal initiator used is
typically low (less than 5%) and would not have a significant
impact on the chemical aggressiveness of the lens formulation on
the mold. In general, lower temperature curing of the lens is
preferred, accomplished with UV or visible light photo initiators,
low initiation temperature thermal initiators or a combination of
both. A variety of light sources can be used, including those with
output in the UV range (200-400 nanometers), visible range (400-900
nm), or combinations thereof.
[0064] Depending on the choice of thermoplastic materials used,
there will be certain chemistries and/or process parameters that
will allow the mold to be used satisfactorily. Based on the simple
chemical notion that "like dissolves like," each different type of
thermoplastic material can be used without issue with certain
ingredients typical of a coating formulation and/or lens
formulation. In order to determine if a raw material (or group of
raw materials in a formulation) will be chemically compatible with
mold material, any number of tests can be employed:
[0065] One screening test for chemical compatibility involves a
representative sample of the thermoplastic material to be placed in
close contact with the chemical to be tested. This "close contact"
can involve soaking the thermoplastic in the test solution, or the
test solution can be allowed to sit on top of the thermoplastic
material. The time and temperature during which the two materials
are in contact are controlled variables in the test. After the test
period is over, all excess test solution is removed from the
thermoplastic material by simple wiping, and the thermoplastic is
evaluated for any damage by measuring any change in physical
appearance, any change in percent transmittance, any change in
refractive index, any change in tensile strength, any change in
flexibility, any change in weight or size, any change in surface
smoothness, or any change in optical properties.
[0066] In certain embodiments of the invention, the formulation
used to form the lenses and the material used to form the mold is
selected based upon solubility properties of the mold material and
the lens forming formulation. In general it is desirable to have
low solubility of the mold material in the lens forming
formulation. Although it is difficult to determine solubility of a
solid material in a resin, the durablity of the mold can be used as
an indication of solubility. Applicants have found that the lens
forming formulation should be selected such that the resin does not
significantly degrade optical properties of the mold surface upon
exposure to the resin.
[0067] Any significant change in any of the above properties of the
thermoplastic constitutes damage to the material, and the
thermoplastic material cannot be used with that test solution.
However, it is still quite possible that although a certain
ingredient is known to attack a particular thermoplastic material,
that ingredient can still be used in small amounts in solution,
provided that the other components are compatible with the
thermoplastic. Numerous examples of such scenarios are provided for
in this patent.
Methods for Casting and Curing Lenses
[0068] The present invention is also directed to methods for
casting lenses. For an initial step, the method of the present
invention involves providing the ring 50 and front and rear molds
20, 40. Although it is contemplated that the components be
pre-connected together as a unit and provided to the operator, it
is preferred that the ring 50 and front and rear molds 20, 40 are
preferably combined or coupled together by the operator at the lens
manufacturing location to form the mold cavity 60. When the
operator receives the prescription of a spectacle lens, he or she
selects the front and rear molds 20, 40 that, together, form a mold
cavity 60 having the dimensions of the desired lens. In the
illustrated embodiment, the ring is a "one-size" or "universal"
ring and used to manufacture all lenses, whether plus or minus and
regardless of power.
[0069] To that end, the ring 50 and front and rear molds 20, 40 are
movable between a stored position and a molding position. In the
stored position, the components are separated from each other, in
which molds having the same characteristics are stored together in
designated areas or bins. In the molding position, the protrusion
46 of the rear mold 40 receives the edge 28 of the front mold 20 to
form the mold cavity 60 after the operator retrieves the correct
molds from the designated storage areas.
[0070] It is contemplated using computer or other system (not
shown) to assist the operator in selecting the correct molds 20, 40
when preparing to cast a lens. As one example, the present
invention contemplates that the operator enters the parameters of
the lens to be formed (e.g., the prescription including add power)
into a computer or the like. Algorithms in an associated computer
program determine the appropriate front and rear molds 20, 40 to be
used to form the desired lens and then provide an output indicating
this information. As one optional variation, such a system may
additionally illuminate a light or provide another indicator at the
storage stations above the specific location where the appropriate
molds 20, 40 are stored. The indicators assist the operator in
locating the appropriate molds to reduce the chance of the operator
inadvertently picking an incorrect mold to make the lens. Yet
another option is to use a bar code or other tracking system (not
shown) on the outer surfaces of the molds 20, 40 that the system
scans to verify that the two proper molds are being used.
[0071] After the operator locates the front and rear molds 20, 40,
obtains a ring 50, and is ready to join the components together,
the output of the optional computer system may further assist the
operator by indicating additional positioning and aligning
information. As discussed above, in the illustrated embodiment the
front and rear molds 20 are rotatably movable relative to each
other so that the two molds 20, 40 are at one of a plurality of
selected rotational orientations relative to each other. The
computer may provide an output indicating the orientation of the
two molds 20, 40 relative to each other when the lens-forming
surfaces 22, 42 of the respective molds have asymmetric curvature.
For the illustrated embodiment, the computer preferably indicates
the appropriate location of the axis-positioning indicator 92 to be
aligned on the axis marks 90.
[0072] As to the positioning of the molds 20, 40 to obtain the
correct center or edge thickness for the mold cavity 60, this
parameter is preferably considered in selecting the ring 50 and
molds 20, 40, as discussed above. The designated components are
preferably manufactured so that when the operator combines or
assembles the components together, the mold cavity 60 has the
correct thickness without any additional actions.
[0073] However, one skilled in the art will appreciate that other
means besides a computer system may be used to determine the
correct mold to use with the present invention. Notably the present
invention utilizing the computer system allows an operator with
minimal training and understanding of the principles of lens
casting to manufacture successfully lenses when a customer provides
a prescription.
[0074] After the front and rear molds 20, 40 are joined with the
ring 50 to form the mold cavity 60 of the desired dimensions, the
operator connects the bag 80 or other source of monomer to the feed
opening 70. The operator then injects the monomer into the mold
cavity 60.
[0075] During filling, the monomer enters via the feed opening 70
while the vent opening 72 allows displaced air to exit the mold
cavity 60 to ambient. The filling method used with the present
invention minimizes the quantity of monomer wasted and decreases
the chances of air bubbles being formed within the lens. If used,
the bag 80 may contain a quantity of monomer that is sufficient to
form only a single lens or, alternatively, for multiple
castings.
[0076] Because monomer is a viscous fluid, it will inherently fill
the mold cavity 60 at a controlled rate. By design, the fill rate
may be further controlled by reducing the cross-sectional area of
the feed opening 70 and/or the tip 84 of the bag 80. Since the
front and rear molds 20, 40 are formed of plastic, they can be
clear or transparent so that the operator may visually observe the
monomer entering and filling the mold cavity 60. When the cavity 60
is filled with monomer so that the monomer reaches the vent opening
72 (and thus the top of the extender of the feed opening 70), the
monomer source is removed from the ring 50. If necessary, the feed
opening 70 is plugged, which may simply involve spot curing the
monomer at that location to plug it or using a covering that snaps
into the feed opening 70. The vent opening 72, however, preferably
remains in communication with ambient during curing.
[0077] The monomer within the mold cavity 60 is then cured to form
the lens after ensuring that no bubbles are present. The lens
material, depending on the formulation, can be cured with a variety
of methods, including light, heat, or combinations thereof. If a
free-radical mechanism is employed, then the lens can be cured via
either UV light, visible light, or heat, depending on the
initiator. It is also possible to cure the lens with a combination
of these curing techniques. These curing methods can be used either
simultaneously or sequentially.
[0078] Both curing techniques can be used with a variable rate of
cure (i.e., ramp-up, progressive cure.) After the cure cycle is
complete (typically from two to ten minutes) the lens is removed
from the molds simply be removing the gasket, and lifting the molds
away from the lens.
[0079] The cure time of the coating can have a significant impact
on the adhesion and scratch resistance of the finished lens. If the
cure time is insufficient, the coating will not retain its
dimensional stability well enough to from a consistent layer on the
lens. If the coating is cured too much, too many of the acrylate
groups will be reacted, leaving an insufficient amount of unreacted
groups left to bond the coating to the lens.
[0080] The partially-cured coating material will form permanent
chemical (covalent) bonds with the lens material during the
lens-curing process. The coating and lens materials both contain
unreacted acrylate groups that will react with each other during
the lens curing process.
Methods of Making Lenses Using Plastic Molds
[0081] The present invention is also directed to methods of casting
lenses using plastic molds, which may be used with the exemplary
embodiment discussed immediately above or another design (i.e., a
T-gasket design that uses plastic molds instead of glass
molds).
[0082] When selecting the specific type of material to form the
molds, one skilled in the art will appreciate that to be useful in
curing monomer, the selected plastic must transmit the curing
radiation without melting, deforming, or stretching--at least until
after the monomer is substantially cured or polymerized. Although
thermal radiation is contemplated as a curing source and falls
within the scope of the present invention, one skilled in the art
will appreciate that the present invention may be better suited for
photo curing.
[0083] For photo curing of liquid resins, the desirable plastics
include acrylic and methacrylic materials, an example of which is
polyrnethylmethacrylate (PMMA). Some embodiments of available light
transmissive PMMA are the OP1 and OP4 products by Cyro Industries,
UV-T and V8-25 by Rohm & Haas, and CP-75 from ICI. Other
exemplary types of radiation transmissive plastics that may be used
with the present invention include aliphatic polyesters, amorphous
polyamides, amorphous polyurethanes, amorphous polyolefins,
amorphous polycarbonates, amorphous polyimides and co-polymers
thereof. One skilled in the art will appreciate that these listed
plastics are illustrative and the present invention is not limited
to these examples.
[0084] Another factor that one skilled in the art considers in
selecting the plastics to use is that they do not adversely
interface or react with the material to be cured. If, for example,
it is desired to use polymethylmethacrylate to form the molds based
on its cost or physical properties, then compatible monomers
include long chain or high molecular weight monomers or prepolymers
that do not attack the mold should be used. Alternatively, the
monomer desired to be used may be the primary consideration and the
plastic forming the molds is chosen based on it being chemically
resistant and non-reactive to that selected monomer.
[0085] Using plastic to form the molds provides potential benefits
over casting systems currently used in the industry. One
consideration is that the plastics may be injection molded. There
is extensive use and experience in the industry of injection
molding polymethylmethacrylate and acrylics using ceramic or metal
molds. To that end, the molds may be formed, for example, by
fabricating metal dies into which polymethylmethacrylate or other
plastic is injection molded in an assembly process having a high
throughput. Each of the molds, accordingly, will be formed to the
same high tolerances to which the die is formed. Glass molds, in
contrast, cannot be fabricated to such exacting standards, so the
present invention can cast an ophthalmic lens that is formed to
more rigorous criteria. One skilled in the art will further
appreciate that the plastic components may be formed using other
suitable high throughput methods used in the art for fabricating
plastics, in contrast to glass molds that cannot feasibly be
mass-produced to the requisite tolerances.
[0086] Another consideration with using plastic components is the
economic comparison with conventional prior art systems using two
glass molds and a gasket. Although glass molds may be repeatedly
used up to one hundred times or more, expenses accumulate that are
associated with each casting, such as washing and drying that must
ensure that the lens-forming surface is not contaminated. In fact,
cleaning processes for glass molds are typically laborious,
time-consuming and inefficient, involving manual scraping and
soaking in noxious solvents. Furthermore, the glass molds must be
inspected after each use and cleaned to insure suitability for
another lens-making cycle. Plus, many times the glass molds are
inadvertently chipped and/or broken before their potential useful
life is reached. An associated problem is the occurrence of lens
yield loss resulting from unwitting reuse of damaged lens molds, in
which the operator sometimes does not discover that a glass mold is
damaged until after a casting process has been completed.
[0087] Yet another aspect of the present invention involves coating
the lens-forming surfaces of the molds with an abrasion-resistant
composition that is transferred to the lens when cured. More
specifically, the lens-forming surfaces are preferably covered with
a composition that transfers in situ to the optical surfaces of the
cast lens as a protective coating on the final product. Without
such a hard coating on the lens that prevents or resists abrasion,
scratching, and marring, the optical quality of the cast spectacle
lenses may more easily degrade from haze and poor image
quality.
[0088] Another example of such an abrasion-resistant coating is
disclosed in U.S. Pat. No. 5,049,321. This patent discloses that
the coating composition consists substantially of reactants having
at least triacrylate functionality, a photoinitiator, and a
polymerization inhibitor reactive with oxygen. After applying such
a coating composition in the form of an ultraviolet curable liquid
to the mold, the coating is subjected to ultraviolet radiation in
an oxygen-containing environment such that the coating composition
is cured to a hard/abrasion-resistant state. Then, when casting and
curing the ophthalmic lens, the monomer is permitted to harden and
react with acrylate groups at the coating/lens interface so that
the coated lens is removed from the mold with the
abrasion-resistant coating adhering thereto as an integral part of
the surface of the optical surfaces of the lens. Other similar
techniques of forming an abrasion-resistant coating on a cast lens
are disclosed in U.S. Pat. Nos. 4,338,269 and 4,758,448.
[0089] One skilled in the art will appreciate that, although not
necessary, using such an abrasion-resistant coating on the
lens-forming surfaces produces a final product that consumers may
prefer and that also allows the operator to separate more easily
the molds from the lens cast therebetween. To that end, the
abrasion-resistant coating may be applied to the lens-forming
surfaces of the molds using a process the same as or similar to
that disclosed in U.S. patent application Ser. No. 10/075,637,
filed on Feb. 12, 2002 and entitled "Methods of Applying a Coating
to an Optical Surface". Alternative treatment methods of the molds
known in the art include spraying, dipping, brushing, flow coating,
spin coating, and the like.
[0090] The preferred method involves curing using photo curing,
although other curing methods are contemplated in conjunction with
or alternatively to light. One primary advantage of photo curing,
such as UV radiation, is that the plastic molds do not reach a
temperature at which they may melt, deform, or stretch, which is
more likely to occur with thermal radiation curing. UV curing
methodologies are taught, for example, in U.S. Pat. Nos. 4,919,850;
5,524,419; 5,804,107; 5,981,618; 6,103,148; and 6,241,505.
[0091] After the monomer is cured to harden, then the operator
removes the cured lens from within the mold cavity. It is
contemplated that the plastic components of the present invention
will have a one-use life. That is, the molds can be disposable so
that there are no problems if the molds are chipped or broken
during the removal of the lens from the mold cavity. In fact,
breaking the molds may assist in separating the cured lens from the
mold cavity 60, as the molds are more brittle than the cured lens
so the lens does not also break. One skilled in the art will also
appreciate that treating the lens-forming surfaces with
abrasion-resistant coatings, such as the compositions disclosed in
U.S. patent application Ser. No. 10/712,714 and U.S. Pat. No.
5,049,321, will assist in separating the lens from the mold as well
as providing the lens with a protective scratch-resistant barrier.
One skilled in the art will further appreciate that the plastic
molds of the present invention can be used for more than one
casting before their useful life ends.
EXAMPLES
[0092] The invention will now be further understood by reference to
the following examples. As used in these examples, SR 340 is the
monofunctional monomer 2-phenoxyethylmethacrylate; SR 506 is
isobornyl acrylate; SR 150 is ethoxylated bisphenol A
dimethacrylate; Ebecryl 1039, which is a urethane monoacrylate;
Ebecryl 810, which is a polyester tetraacrylate; CN 131 is a low
viscosity aromatic monoacrylate oligomer; and SR 203 is a
tetrahydrofurfuryl methacrylate monofuntional cyclic monomer. All
numbers below are in parts. The lenses were cured between two
acrylic molds. The cure time was 5 minutes (except for the 100% SR
203 formulation, which was cured for 30 minutes). The formulations
were photocured.
Examples 1 to 3
Lens Formation Interaction
[0093] These examples show how diluting an aggressive formulation
component with a non-aggressive component can modify the
mold-formulation interaction.
Example 1
[0094] The molds for Example 1 were formed of uncoated acrylic. As
can be seen from Table 1, the use of a mixture containing more of
the less aggressive component (SR 150) than the aggressive
component (SR 340) resulted in less lens damage. TABLE-US-00001
TABLE 1 Formulation 1 2 3 4 5 6 7 SR 150 100 90 85 80 70 50 0 SR
340 0 10 15 20 30 50 100 Photo- 0.35 0.35 0.35 0.35 0.35 0.35 0.35
initiator Lens No No No No Yes Yes Yes Damage (minor) (Light)
(Heavy)
Example 2
[0095] The molds for Example 2 were formed of uncoated acrylic. As
can be seen from Table 2, the use of a mixture containing more of
the less aggressive component (SR 150) than the aggressive
component (CN 131) had less lens damage. TABLE-US-00002 TABLE 2
Formulation 1 2 3 4 5 6 7 SR 150 100 90 85 80 70 50 0 CN 131 0 10
15 20 30 50 100 Photo- 0.35 0.35 0.35 0.35 0.35 0.35 0.35 initiator
Lens No No No No Yes Yes Yes Damage (Minor) (Light) (Heavy)
Example 3
[0096] The molds for Example 3 were formed of uncoated acrylic. As
can be seen from Table 3, the use of a mixture containing more of
the less aggressive component (SR 150) than the aggressive
component (SR 203) had less lens damage. TABLE-US-00003 TABLE 3
Formulation 1 2 3 4 5 6 7 SR 150 100 90 85 80 70 50 0 SR 203 0 10
15 20 30 50 100 Photo- 0.35 0.35 0.35 0.35 0.35 0.35 0.35 initiator
Lens No No No No Yes Yes Yes Damage (Minor) (Minor) (Heavy)
Examples 4 to 6
[0097] Examples 4 to 6 below show the effect of temperature on
curing various lens materials. As can be seen, increasing the cure
temperature to 50.degree. C. can result in a damaged lens, and
sometimes to a milky lens.
Example 4
[0098] The molds for Example 4 were formed of uncoated acrylic. As
can be seen from Table 4, the higher temperatures at which the
lenses were cast resulted in more lens and/or mold damage and haze
formation. TABLE-US-00004 TABLE 4 Formulation 1 2 3 4 5 6
Temperature Room Room Room temp. 50.degree. C. temp. 50.degree. C.
temp. 50.degree. C. SR 150 100 100 80 80 50 50 SR 340 0 0 20 20 50
50 Photo-initiator 0.35 0.35 0.35 0.35 0.35 0.35 Lens No/No No/No
No/No Yes/Yes No/No Yes/Yes Damage/Haze
Example 5
[0099] The molds for Example 5 were formed of uncoated acrylic. As
can be seen from Table 5, the higher temperatures at which the
lenses were cast resulted in more lens and/or mold damage and haze
formation. TABLE-US-00005 TABLE 5 Formulation 1 2 3 4 5 6
Temperature Room Room Room temp. 50.degree. C. temp. 50.degree. C.
temp. 50.degree. C. SR 150 100 100 80 80 50 50 CN 131 0 0 20 20 50
50 Photo-initiator 0.35 0.35 0.35 0.35 0.35 0.35 Lens No/No No/No
No/No Yes/No Yes/No Yes/Yes Damage/Haze
Example 6
[0100] The molds for Example 6 were formed of uncoated acrylic. As
can be seen from Table 6, the higher temperatures at which the
lenses were cast resulted in more lens and/or mold damage and haze
formation. TABLE-US-00006 TABLE 6 Formulation 1 2 3 4 5 6
Temperature Room Room Room temp. 50.degree. C. temp. 50.degree. C.
temp. 50.degree. C. SR 150 100 100 80 80 50 50 SR 203 0 0 20 20 50
50 Photo-initiator 0.35 0.35 0.35 0.35 0.35 0.35 Lens No/No No/No
No/No Yes/Yes No/No Yes/Yes Damage/Haze
Example 7
[0101] The molds for Example 7 were formed of acrylic. Example 7
shows lens damage comparing coated molds and uncoated molds. Table
7 exhibits the potential advantages of coating the molds prior to
filling with formulation and subsequent curing. TABLE-US-00007
TABLE 7 Formulation 1 1 2 2 Mold Coated No Yes No Yes Temperature
Room Temp. Room Temp. 50.degree. C. 50.degree. C. SR 150 0 0 80 80
SR 340 100 100 20 20 Photo-initiator 0.35 0.35 0.35 0.35
Damage/Haze Yes/No No/No Yes/Yes No/No
Examples 8 to 10
[0102] Examples 8 to 10 provide mold-formulation interaction data
for molds made from a variety of polymers. The following
information can be ascertained from the examples: First, different
mold materials behave differently. In addition, coating the molds
suitably can help prevent mold and lens formulation interaction,
and minimizing the time the lens formulations are in contact with
the molds prior to cure is an advantage. The lower the mold and
lens formulation temperature is, prior to and during cure, the less
likely mold-formulation interaction is to occur. Finally, under
suitable conditions it is possible to cure and successfully
separate molds and formulations without pre-coating the molds. [For
tables 8, 9, and 10, only the test material is listed. The
remainder of the formulation in these examples consists of SR-150
and photoinitiator(s).]
Example 8
[0103] Example 8 shows temperature and time as factors in lens
manufacture, using acrylic molds. TABLE-US-00008 TABLE 8 Material %
Ebecryl 1039 SR 340 CN 131 Ebecryl 810 Material Temp. Time Coated
Uncoated Coated Uncoated Coated Uncoated Coated Uncoated 0 RT 10
Min. No No No No No No No No 30 Min. No No No No No No No No 60
Min. No No No No No No No No 10 RT 10 Min. No No No No No No No No
30 Min. No No No No No No No No 60 Min. No No No No No No No No 30
RT 10 Min. No No No No No No No No 30 Min. No No No No No No No Yes
60 Min. No No No No No No No Yes 50 RT 10 Min. No No No No No Yes
No Yes 30 Min. No No No No No Yes No Yes 60 Min. No No No No No Yes
No Yes 100 RT 10 Min. No Yes No Yes No Yes No Yes 30 Min. No Yes No
Yes No Yes No Yes 60 Min. No Yes No Yes No Yes No Yes 0 50.degree.
C. 10 Min. No No No No No No No No 30 Min. No No No No No No No No
60 Min. No No No No No No No No 10 50.degree. C. 10 Min. No Yes No
Yes No No No No 30 Min. No Yes No Yes No No No No 60 Min. No Yes No
Yes No No No No 30 50.degree. C. 10 Min. No Yes No Yes No Yes No
Yes 30 Min. No Yes No Yes No Yes No Yes 60 Min. No Yes No Yes No
Yes No Yes 50 50.degree. C. 10 Min. No Yes No Yes No Yes No Yes 30
Min. No Yes No Yes No Yes No Yes 60 Min. No Yes No Yes No Yes No
Yes 100 50.degree. C. 10 Min. No Yes No Yes No Yes No Yes 30 Min.
No Yes No Yes No Yes No Yes 60 Min. No Yes No Yes No Yes No Yes
Example 9
[0104] Example 9 shows temperature and time as factors in lens
manufacture, using polystyrene molds. TABLE-US-00009 TABLE 9
Material % Ebecryl 1039 SR 340 CN 131 Ebecryl 810 Material Temp.
Time Coated Uncoated Coated Uncoated Coated Uncoated Coated
Uncoated 0 RT 10 Min. No No No No No No No No 30 Min. No Yes No Yes
No Yes No Yes 60 Min. No Yes No Yes No Yes No Yes 10 RT 10 Min. No
No No Yes No Yes No No 30 Min. No Yes No Yes No Yes No Yes 60 Min.
No Yes No Yes No Yes No Yes 30 RT 10 Min. No Yes No Yes No Yes No
Yes 30 Min. No Yes No Yes No Yes No Yes 60 Min. No Yes No Yes No
Yes No Yes 50 RT 10 Min. No Yes No Yes No Yes No Yes 30 Min. No Yes
No Yes No Yes No Yes 60 Min. No Yes No Yes No Yes No Yes 100 RT 10
Min. Yes Yes Yes Yes No Yes No Yes 30 Min. Yes Yes Yes Yes No Yes
No Yes 60 Min. Yes Yes Yes Yes No Yes No Yes 0 50.degree. C. 10
Min. No Yes No Yes No Yes No Yes 30 Min. No Yes No Yes No Yes No
Yes 60 Min. No Yes No Yes No Yes No Yes 10 50.degree. C. 10 Min. No
Yes No Yes No Yes No Yes 30 Min. No Yes No Yes No Yes No Yes 60
Min. No Yes No Yes No Yes No Yes 30 50.degree. C. 10 Min. No Yes No
Yes No Yes No Yes 30 Min. No Yes No Yes No Yes No Yes 60 Min. No
Yes No Yes No Yes No Yes 50 50.degree. C. 10 Min. No Yes No Yes No
Yes No Yes 30 Min. No Yes No Yes No Yes No Yes 60 Min. No Yes No
Yes No Yes No Yes 100 50.degree. C. 10 Min. Yes Yes Yes Yes No Yes
No Yes 30 Min. Yes Yes Yes Yes No Yes No Yes 60 Min. Yes Yes Yes
Yes No Yes No Yes
Example 10
[0105] Example 10 shows temperature and time as factors in lens
manufacture, using polycarbonate molds. TABLE-US-00010 TABLE 10
Material % Ebecryl 1039 SR 340 SR 203 SR 506 Material Temp. Time
Coated Uncoated Coated Uncoated Coated Uncoated Coated Uncoated 0
RT 10 Min. No No No No No No No No 30 Min. No No No No No No No No
60 Min. No No No No No No No No 10 RT 10 Min. No No No No No No No
No 30 Min. No No No No No No No No 60 Min. No No No No No No No No
30 RT 10 Min. No No No No No Yes No No 30 Min. No No No No No Yes
No No 60 Min. No Yes No Yes No Yes No Yes 100 RT 10 Min. No Yes No
Yes No Yes No Yes 30 Min. No Yes No Yes No Yes No Yes 60 Min. No
Yes No Yes No Yes No* Yes* 0 50.degree. C. 10 Min. No Yes No Yes No
Yes No Yes 30 Min. No Yes No Yes No Yes No Yes 60 Min. No Yes No
Yes No Yes No Yes 10 50.degree. C. 10 Min. No Yes No Yes No Yes No
Yes 30 Min. No Yes No Yes No Yes No Yes 60 Min. No Yes No Yes No
Yes No Yes 30 50.degree. C. 10 Min. No Yes No Yes No Yes No Yes 30
Min. No Yes No Yes No Yes No Yes 60 Min. No Yes No Yes No Yes No
Yes 100 50.degree. C. 10 Min. No* Yes* No Yes No Yes No Yes 30 Min.
No* Yes* No Yes No Yes No* Yes* 60 Min. No* Yes* No Yes No Yes No*
Yes* *During the hold period attack on the uncoated side caused it
to leak. The coated side exhibited no evidence of attack.
[0106] Although the present invention has been described with
reference to specific details of certain embodiments thereof, it is
not intended that such details should be regarded as limitations
upon the scope of the invention except as and to the extent that
they are included in the accompanying claims.
* * * * *