Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FIELD OF TIIE INV~NTION:
The use of plastic materials for making optical
lenses has increased rapidly for the past ten years. This
is due to the availability of better plastic materials and
the physical advantages of the plastic resins for specific
applications such as ophthalmic lenses. The technology
for the production of high quality plastic lenses has not
kept pace with the material supply industry. It is important
to advance both areas if the full potential is to be realized.
Plastic lenses offer many advantages over glass
lenses. They are much lighter in weight and resist breakage.
The cost of making high quality lenses has been high, due
to the problems caused by the shrinkage of the monomer when
polymerized, which often breaks the e~pensive molds.
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The current lens molds are fabricated from steel
or glass, each mold is individually ground and polished to
the required specifications. To achieve accurate
reproduction of the bifocal and lenticular molds is most
difficult and expensive. This new process makes possible
exact reproductions and has many other distinct advantages,
which will become apparent from the following disclosure.
An object is to provide a process for making
inexpensive molds which may be made to identical
specifications.
Another object is to provide a process where by
standard masters may be used to produce a large quantity
of replica molds.
SUMMARY OF THE INVENTION:
In accordance with an aspect of the invention
there is provided a method of casting and removing from a
resinous lens mold an optical lens of polymeric material,
said mold of resinous material having at one end a cup-like `~
molding cavity with an optical surface, comprising casting
a monomer in the li~uid state in the molding cavity,
polymerizing the monomer to form a rigid solid having a
first optical surface adhering to the optical surface of
the mold with sufficient adhesive strength to allow
cutting and polishing of a second optical surface, cutting
and polishing the surface of the polymerized solid on the
side opposite the first optical surface to form a second
optical surface while the polymerized solid is held by the
mold, and then removing the thus formed lens from the mold
by applying pressure against the mold to thereby distort
the shape of the optical surface of the mold and stretch
the mold material from the cast polymeric lens to thereby
release the lens from the mold.
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DESCRIPTION OF nRAWING:
Fig. 1 shows the sleeve, steel mold and resinous
material.
Fig. 2 shows the resinous mo]d containing the
liquid lens monomers with cover.
Fig. 3 shows the polymerized lens material with
one optical surface molded on the resinous
mold.
Fig. 4 shows the lens with the second optical
surface cut and in the resinous mold.
THE LENSES ARE MADE AS FOLLOWS:
A master positive mold having the curvature
required on the finished lens is made from glass~
stainless steel or other materials which withstand the
molding pressures and temperature~ Materials which may be
electroplated or plated by vacuum disposition have also
been used.
DESCRIPTION OF THE PREFERRED EMBODIMF.NT:
The master mold, 1 Fig. 1 is placed in a sleeve,
4 Fig. 1, a molding grade of a resinous material such as
polyimide, polycarbonate, polymethylpentene, polyethylene,
polypropylene,
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- nylon or other molding material is placed in the sleeve, 4
Fig. 1. The sleeve and its' contents are heated to the soft-
ening point of the molding material and pressure is applied
to form the lens mold, 3 Fig. 1. The sides of the master
mold, 1 Fig. 1, have been cut to a smaller diameter to pro-
vide the opening, 5 Fig. 1. When sufficient heat and pres-
sure have been applied, the molding compound, 3, will fill
the area around the positive mold, 1, forming a cup-like
cavity with a curved optical surface, 2 Fig. 1, at the bottom.
A concave opening, 10 Fig. 1, is provided in the rear of the
negative mold. This opening may be conical, cylinderical
or spherical in shape to provide for the distortion of the
mold shape when sufficient pressure is applied against the
sides, 11 and 12, Fig. 4, to collapse the rear of the mold.
The mold surface, 2 Fig. 4, will be stretched, releasing
the lens. Either injection or compression molding may be `
~; used to produce cup, 3 Fig. 2, after removal of the master
mold, 1 Fig. 1, a liquid or syrup monomer material contain-
ing a suitable catalyst, 6 Fig. 2, is placed over the opti-
cal surface, 2 Fig. 2, and covered to prevent evaporation
with the cover, 7 Fig. 2. The space, 8 Fig. 2, is filled
with nitrogen and the liquid monomer is polymerized to form
a solid monolithic mass. Ultraviolet light, microwave ener-
gy or heat may be used to speed the polymerization process.
Thermosetting and cross-linked hard materials may be used
to produce lenses which are rigid and dimensionally stable
and could not be made by injection or compression molding.
This process is also suitable for the production of soft
contact lenses which cannot be made by compression or injec-
tion molding techniques.
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It is not necessary to remove the hardened plasticlens material, 6 Fig. 3, from the mold, 3 Fig. 3, before
cutting the convex curve, 9 Fig. 3. The mold, 3 Fig. 3,
may be placed in a
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suita~le la~he ;lnd cllrvat~lle, 9 I-ig. 3, cut- ~nd polished. r~le
finished lens, 6 Fig. 4, I-lavirlg the rnokled concave surface, 2,
and ,lle conve~ curvature, 9, ~hich was cut and polished without
being removed from the disposable mold, 3 Fig. 4, which acted as
the holding device during the cutting and polishing of curve, 9
Fig. 4. The cup-like device has served as a container for the
monomer, 6 Fig 2, provided the molded optical surface which for
contact lenses may be aspheric or may be composed of two or
more spherical segments providing the required optical zone and
peripheral curves. The cup-like mold, 3 Fig. 3, also serves as
the holding block to facilitate cutting to the required thickness.
The thickness of the cup bottom may be measured before adding the
liquid monomers and measurements may be taken during the cutting
operation and the lens thickness determined by subtracting the
thickness of the cup bottom. The cup, 3 Fig. 3, also serves as
a holding fixture during the polishing operation. The lens is
supported by the optical surface present on the mold, therefore,
the lens material must adhere strongly to the supporting mold in
order to withstancl the forces of cutting and polishing. This
adhesion may be controlled by:
1. Selecting the material from which the lens mold is
made.
2. By coating the lens mold with an adhesive.
3. By treating the mold surface with a solvent or re-
lease agent prior to adding the lens material.
4. By treating the mold material with a solvent or re-
lease agent before forming the material into a lens
mold.
After the lens is processed to the required specifications,
the lens is removed by sharply flexing the holding fixture, this
is accomplished by applying pressure at points 11 and 12, Fig. 4,
collapsing opening, 10 Fig. 4, and stretching surface, 2 Fig. 4.
Separating the finished optical lens, 6 Fig. 4~from it's sup-
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17~;~?;t. 3 Fig 4.
Various modifications can be made wi~hout dcpclrtlng rom
the spirit of this invention or the scope of the appellded claims.
The constants set forth in this disclosure are given as exam.ples
and are in no way final or binding. In view of the above, it
will be seen that the several objects of the invention are ach-
ieved and other advantages are obtained. As many changes could
be made in the above constructions and methods without departing
from the scope of the inven~ion, it is intended that all matter
contained in the above description shall be interpreted as illus-
trative and not in a limiting sense.
CHAP~ES W. NEEEE
PH: (915) 267-8214
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