Note: Descriptions are shown in the official language in which they were submitted.
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DEVICE AND loathed FOR
CENTRIC FRUGALLY CASTING ARTICLES
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Description
Technical Field
The present invention relates to a device
and method for centrifugally casting of a plurality
of axially symmetrical or asymmetrical objects such
as lenses and disc valves In various aspects, the
present invention relates to a device and method
employing a novel polymerization column and mold
arrangement in which the column is adapted to
accommodate a number of vertically arranged molds in
interference fitting relationship in a manner such
that the rotation of the polymerization column
causes synchronized rotation ox the molds at the
same speed while maintaining the concentricity of
the molds to the longitudinal axis of the column
thereby effectively insuring the production of a
plurality of symmetrical or asymmetrical spun cast
identical articles which fall within exacting
predetermined specification and requirements.
Background Art
It is known that the polymerization casting
of axially symmetrical articles, such as contact
lenses, can be performed by using equipment in which
individual molds are arranged in a carouse or in a
vertical stack configuration. These individual
molds:, characterized by an outer cylindrical wall
Andy mold cavity with an exposed concave bottom
surface and containing a liquid polymerizable
mixture in the cavity, are caused to rotate about
their vertical axis at a rotational speed (and under
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polymerization conditions) sufficient to create a
centrifugal force which causes a radially outward
displacement of the liquid reactants in the mold.
By maintaining the rotating molds under
predetermined and known polymerization conditions,
the outwardly displaced liquid reactants are caused
to polymerize to a solid polymeric contact lens.
The resulting lens is characterized by a convex
optical surface which corresponds to the concave
surface of the mold and a concave optical surface
whose geometry has been created, to a significant
degree, by the centrifugal force(s) employed during
the polymerization cycle.
In the centrifugal casting of contact
lenses on a commercial scale, it is preferred for
the attainment of good yield to effect the
polymerization or curable reaction under an inert
gaseous medium such as argon or nitrogen. This is
due to the fact that the oxygen component of air
entrained within the polymerization column can
inhibit the polymerization reaction and adversely
affect the quality and acceptability of the contact
lens product. A controlled feed of nitrogen through
the polymerization column will purge any entrained
air in the polymerization zone and provide an inert
environment for conducting the polymerization
process.
The aforesaid carousel arrangement is
rather complex and quite large with respect to the
size of the molds. It requires that each mold be
individually rotated on its own separate vertical
axis. It is reported that the carousel arrangement
suffers from the disadvantages of requiring excess
inert gas to eliminate the inhibiting effect of
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oxygen (in the air) present during the
polymerization reaction. The use of excess inert
gas during the polymerization of the monomeric
reactants causes the entrainment of monomer in the
form of vapors and the subsequent deposition and/or
polymerization on the walls and equipment. Further
information is set forth in U.S. Patent No.
3,660,545, issued May 2, 1972.
In the vertical stack arrangement a
rotatable polymerization tube having an internal
circular cross-sectional geometry is adapted to
receive at one end of the tube a plurality of
circular molds which become seated to one another in
the said tube, each mold containing the liquid
polymerizable reactants in the mold cavity. In
operation, the molds are gravity fed into the upper
end of the polymerization tube and free-fall through
the tube against an upwardly flowing inert gas,
e.g., carbon dioxide, due to their own weight. The
exit end of the tube is seated tightly on a
revolving plate member which imparts the rotation to
the tube and which plate has a centrally defined
opening for discharging inert gas into the
polymerization tube to contact the descending
gravity fed molds. In this type of construction,
the revolving plate member would have to be
disconnected and displaced from the polymerization
column to remove the molds In addition, the
feeding of the inert gas from the center of the
revolving plate member into the polymerization
column and onto the bottom surface of the bottom
most mold could impede the rotation of this mold and
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thereby prevent the molds within the tube from being
rotated at the same speed due to undesirable
slippage between the molds and the inner wall of the
polymerization column.
This gravity feed arrangement whereby molds
are fed into the elongated polymerization zone of
the rotating tube suffers from the disadvantage that
some of the (sliding molds may tilt or wobble
within the polymerization column such that their
. horizontal axes form with the longitudinal axis of
the tube an angle which is a deviation from the
predetermined angle calculated for that particular
polymerization run. In the production of small
articles requiring high precision and geometry such
as contact lenses, heart valves, and the like, the
tilted or wobbling molds may result in the
production of asymmetrical plastic articles lacking
the predetermined optical geometry required in the
contact lens article or the high exactness and
detail expected in artificial heart valves. In
addition, the rotation of the tube by the revolving
plate member does not insure that all the molds
within the tube will all be rotated at the same
speed due to undesirable slippage between the molds
and the inner wall of the tube. Consequently, this
inability to maintain synchronization of the
rotation of the molds with the rotation of the
polymerization tube can result in the production of
the articles, e.g., contact lenses, disc valves for
surgical applications, etc., which fail to fall
within exacting predetermined specifications and
requirements.
A widely practiced technique for the
manufacture of soft contact lenses involves the
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lathing procedure. This technique has many
drawbacks inasmuch as it is a labor intensive
operation, requires several steps, is relatively
expensive, and the finished lens product it
characterized by striations on its optical
surfaces. In the lathing technique, an appropriate
polymerization medium is first polymerized into a
cylindrical shape from which there are cut so-called
lens "buttons" or lens blanks, or the lens blanks
per so can be made in appropriate molds. The blanks
are subjected to a posture treatment to improve
certain of their physical characteristics. A
predetermined curved surface is thereafter cut on
one face of the blank by using precision lathe
machinery and the cut curved surface is polished to
an optical surface. Formation of an optical surface
on the opposite face of the blank requires adhering
the partially cut blank to an arbor or mandrel by
means of a waxy substance in a manner that the uncut
face of the blank is exposed for the lathing and
polishing operations. Thereafter, there are washing
and cleaning steps to remove residues from the
cutting and polishing procedures and eventually, as
with soft contact lenses, soaking in a physiologic
solution until osmotic equilibrium is reached at
which stage the hydrogen lens attains its final
dimensions.
Object of the Invention
Accordingly, one or more objects will be
achieved by the practice of the invention.
Objects of the invention are for the
provision of novel devices and novel methods for the
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centrifugal casting of reproducible articles of high
precision and exactness of detail.
Another object of the invention is to
provide a novel polymerization column having a
longitudinal axis and which is adapted to
accommodate within the interior of the column a
plurality of non-free falling, tightly seated molds,
the vertical axis of rotation of the molds being in
predetermined concentric or parallel relationship to
the longitudinal axis of rotation of the column.
Yet another object is to provide a novel
device comprising a polymerization column and mold
arrangement in which the column is adapted to and
accommodates a number of vertically arranged molds
in interference fitting relationship in a manner
such that the rotation of the polymerization column
causes synchronized rotation of the molds while
maintaining the concentricity of the molds to the
longitudinal axis of the column so as to produce a
plurality of exacting symmetrical or asymmetrical
articles such as contact lenses, artificial heart
valves, diaphragms and the like.
Still another object of the invention is to
provide for the manufacture of small plastic
articles of high precision and exacting
predetermined specifications by practicing the novel
processes and utilizing the novel apparatus
disclosed herein.
Another object of the invention is to
provide a process which is not labor intensive or
capital intensive, which canoe operated in an
efficient manner on a continuous basis, which is
relatively small in size as to be readily portable
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and/or which obviates various disadvantages of the
art.
The foregoing as well as additional objects
will become fully apparent from the following
description and the accompanying drawings.
Disclosure of the Invention
The invention relates to a device for the
centrifugally casting of articles comprising a
rotatable polymerization tube (column) adapted for
rotation about a vertical (longitudinal) axis and
adapted for receiving in vertical series a plurality
of molds containing a polymerizable or curable
composition; securing means for securing a plurality
of molds in vertical series in an interference
fitting and sliding relationship within said tube,
said securing means being adapted to concentrically
dispose said molds to the vertical axis of said
polymerization tube; gas flow means associated with
the inner surface of said tube and the outer wall of
said molds to accommodate a flow of a gaseous medium
through said polymerization tube and said device
being operable such that the rotation of said tube
causes the synchronized rotation of said molds while
maintaining the concentricity of said molds to the
vertical axis of said polymerization tube until at
least the polymerizable or curable composition in
each mold is spin cast into a predetermined shaped
article.
In one aspect the invention relates to a
method for producing shaped articles which comprises
the steps of:
(a) rotating a polymerization column
ablate its longitudinal or vertical axis to provide
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an elongated zone, at least a portion of which
comprises an elongated tubular polymerization zone,
said polymerization column adapted to receive and
accommodate a plurality of vertically arranged molds
in interference fitting relationship;
(b) force feeding into one end of
said polymerization column, a series of said molds
one at a time, each containing a fluid moldable
composition such as a polymerizable or curable
material in the cavity of the mold, such that each
of said molds is secured in an interference fitting
relationship within said polymerization column
whereupon the rotation of said polymerization column
about its longitudinal axis causes the synchronized
rotation of said molds while maintaining
concentricity of said molds with the longitudinal
axis of said polymerization column;
(c) rotating said polymerization
column about it longitudinal axis at a speed
sufficient to cause radially outward displacement of
said fluid moldable material in the cavity of the
molds to assume a predetermined configuration;
d) maintaining the elongated
polymerization zone under polymeriæable conditions
to convert said fluid moldable material of
predetermined configuration into the predetermined
shaped solid article; and
(e) withdrawing each of said molds
from said polymerization column after at least the
fluid moldable material is formed into the
: predetermined shaped solid article, said article
preferably being in the shape of a contact lens.
Desirably, the device can have gas feeding
means for directing ad inert gaseous medium through
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the rotating polymerization column containing the
rotating molds. It is preferred that in the spin
casting of soft contact lenses, the gaseous medium
be an inert gas of argon or nitrogen. This is due
to the fact that undesirable air entrained within
the tube during polymerization will inhibit the
polymerization process and thereby result in a
product of unacceptable quality. A feed of inert
gas, such as nitrogen, through the polymerization
tube will purge any entrained air and provide an
inert environment for the polymerization process to
occur. The novel gas feed means disclosed in
U.S. Patent No. 4,468,184, issued August 28, 1984
to the same assignee of the subject application
can be used.
The securing means which secure the molds
within the polymerization tube can be at least two
spaced apart longitudinal projections on the inner
surface of the polymerization tube which would
provide an interference fit for the molds. The
radially inward longitudinal projections on the
tube, such as ridges, could form an integral part of
the tube and be made of the same material or it
could be a separate component secured to the inner
surface of the tube in a conventional manner using
an adhesive or the like. The material constituting
the projection should bye sufficiently hard to
withstand the frictional contact made with the outer
wall of the molds without exhibiting excessive wear
that could minimize or destroy the interference fit
required between the molds and the contact surface
of the polymerization tube. The inner diameter of
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the circle on which the contact points of the tube
fall on the circumference (of said circle) could be
equal to or preferably slightly smaller than the
outer diameter of the mold so as to insure an
interference fit but slid able relationship there
between.
To compensate for excessive frictional
wear, the projections could be made of a resilient-
material that would substantially recover its size
and shape after being deformed by the molds fed into
the polymerization tube. The resilient projections
would generally provide contact points with the
outer wall of the mold and would fall on the
circumference of a circle (from a cross sectional
view of that tube) whose inner diameter within the
tube would be smaller than the inner diameter of a
tube employing a hard material as the inward
projections. The use of a resilient material would
provide for the Sacramento of the molds within the
tube to insure that the concentricity of the molds
with the spin axis of the tube is maintained while
providing for the synchronized rotation of the molds
with the rotation of the tube.
In another alternate embodiment, the outer
wall of the molds rather than the inner surface of
the cylindrical tube may contain a plurality of
spaced apart projections (preferably at least three)
to provide the interference fit required to insure
that the horizontal plane of the molds are
maintained substantially perpendicular to the
vertical (longitudinal) axis of the tube. In a like
manner, the protrusions can be either made as an
integral par of the mold material or alternately
can be a separate hard or resilient component that
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could be secured to the outer wall of the molds in a
conventional manner using an adhesive or the like.
When employing the spaced apart protrusions
on the inner surface of the tube or on the outer
wall of the mold, care should be taken to insure
that each protrusion covers a sufficient arc segment
so as to prevent tilting of the molds when they are
fed through the tube. In the preferred embodiment
the inner vertical surface of the tube or the outer
wall of the molds would have at least three equally
spaced apart protrusions that will insure that the
concentricity of the molds with the spin axis of the
tube is maintained. In all embodiments of the
device in which the plurality of molds are secured
in vertical alignment within the tube, arc segments
between adjacent protrusions will provide a passage
to accommodate a gaseous medium, such as an inert
gas, to be fed or directed into the tube during the
rotation ox the tube.
As used herein the language "maintaining
the concentricity of the molds to the spin
(longitudinal) axis of the (polymerization) tube"
shall mean the rotation of the molds per so in a
plane which is substantially perpendicular to the
vertical (longitudinal) axis of the tube.
Throughout the specification it is to be noted that
the words "tube" and "column" have been used
interchangeably. By way of illustrations, the
hollow cross sectional area of the tube can
represent a circle interrupted by a plurality of
equally protruding vertical ridges or projections
(Figure 2) from the inner cylindrical wall of the
tube to insure an interference fit with the outer
wall of the circular molds (Figures 2 and 4); or it
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can represent an uninterrupted circle (Figure 7)
which can accommodate in interference fitting
relationship molds whose outer wall has a plurality
- of equal protrusions which are preferably equally
spaced apart (figures 6 and 7). The hollow cross
sectional shape of the tube can also represent a
square and the plan view of the mold can represent a
circle (Figure 9) provided that the external
diameter of the mold is equal to or slightly larger
than the internal length of one side of the square
thereby insuring an interference fitting
relationship. In a further illustration, the hollow
cross sectional shape of the tube can represent an
equilateral triangle and the plan view of the molds
can represent a circle (figure 10) which in this
instance the external diameter of the mold is equal
to or slightly larger than the length of one side of
the equilateral triangle multiplied by the
fraction I
By the practice of the inventions
contemplated herein, there can be produced precision
articles of predetermined and exacting details and
dimensions, e.g., small medical devices such as
heart valves and diaphragms; contact lenses; and
others. Such articles, depending on the ultimate
use, can be hard, flexible, or soft and they may be
hydrophillic or hydrophobic.
Any fluid polymerizable, curable or
moldable reactant or mixture with without an inert
or reactive solvent which is/are capable of being
displaced outwardly due to the rotation of the
column, ire. by the resultant centrifugal forces
can be employed in the practice of the invention.
The medium comprising the reactant(s) constitutes a
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homogeneous liquid and is capable of forming a
desired shaped article during the centrifugal
casting operation. The article may be opaque,
translucent or transparent depending on the ultimate
use of the cast article formed. For instance, it is
not generally a necessity that diaphragms and
artificial heart valve substitutes obtained by the
practice of the invention be colorless and
transparent. On the other hand, for example, it is
a requirement that soft hydrophilic contact lenses
be fully transparent, of good optical quality, soft
and resilient as well as possessing other necessary
and desirable characteristics.
In particular, the centrifugal casting
device of this invention coupled to gas feeding
means can be utilized in the manufacture of a wide
variety of contact lenses which can be symmetrical
or asymmetrical; hard, flexible or soft; water
absorptive or non-water absorptive; low, medium, or
high oxygen permeability or transportability; and
the like. By choosing suitably designed mold
cavities or bottoms there can be obtained a wide
variety of modified lens shapes, e.g., ionic,
bifocal, truncated and/or ballasted contact lenses.
A wide variety of materials or construction can be
employed to fabricate the molds; see, for example,
U.S. Pat. No. 3,660,545. For the preparation of
hydrophilic articles such as soft contact lenses a
mold fabricated of a thermoplastic material, such as
polypropyleneJis suitable. To insure proper wetting
of the optical surface of the mold by the
lens-forming mixture it is desirable to first
pretreat or hydrofoils the said surface by known
methods.
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The liquid lens-forming mixture can
comprise monomer, prepolymer or vulcanizable
components. Particular suitable components are
hydrophilic monomers preferably including those
which form slightly or moderately cross linked, three
dimensional networks such as those disclosed in U.S.
3,822,089. Illustrative hydrophilic monomers
include water soluble monstrous of an acrylic acid
or methacrylic acid with an alcohol having an
esterifiable hydroxyl group and at least one
additional hydroxyl group such as the moo- and
polyalkylene glycol monstrous of methacrylic acid
and acrylic acid, e.g., ethylene glycol
monomethacrylate, ethylene glycol monoacrylate,
diethylene glycol monomethacrylate, diethylene
glycol monoacrylate, propylene glycol monomethylate,
dipropylene glycol monoacrylate, and the like the
N-alkyl and N,N-dialkyl substituted acrylamides and
methacrylamides such as N-methylacrylamide,
N,N-dimethylacrylamide, N-methylmethacrylamide,
N,N-dimethylmethacrylamide, and the like
N-vinylpyrrolidone; the alkyd substituted N-vinyl
pyrrolidones, e.g., methyl substituted
N-vinylpyrrolidone; glycidyl methacrylate; glycidyl
acrylate; the unsaturated amine; the alkyd ethyl
acrylates; solubilized collagen; mixtures thereof;
and other s known to the art.
Hydrophilic monomers particularly useful in
the practice of the invention to manufacture contact
lenses include hydrophobic acrylic esters, suitably
lower alkyd acrylic esters, preferably wherein the
alkyd moiety contains 1-5 carbon atoms, such as
methyl acrylate or methacrylate, ethyl acrylate or
methacrylate, n-propyl acrylate or methacrylate,
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isopropyl acrylate or methacrylate, isobutyl
acrylate or methacrylate, n-butyl acrylate or
methacrylate, or mixtures thereof.
Other suitable monomers include the
5 ethylenically unsaturated monocarboxylic acid
esters, in particular, the methacrylic and acrylic
acid esters of selection monomers and polymers
with/without a pendant hydroxyl group. These
monomers are well documented in the contact lens
art: see, for example, U.S. Pat. Nos. 4,139,548;
4,235,985; ~,152,508; 3,808,178; 4,139,692;
4,2~8,989; and 4,139,513.
Among the preferred monomeric mixtures are
those which contain at least one alkaline glycol
15 monster of methacrylic acid, especially ethylene
glycol monomethacrylate, and at least one
cross linking monomer such as the alkaline glycol
divester of methacrylic acid, especially ethylene
glycol dimethacrylate. Such mixtures may contain
20 other polymerizable monomers, desirably in minor
amounts such as N-vinylpyrrolidone, methyl
methacrylate, acrylamide, glycidyl methacrylate,
N-methylacrylamide, diel:hylene glycol
monomethacrylate, and others illustrated above.
The above illustrated monomers, monomeric
mixtures including mixtures of hydrophobic and
hydrophilic reactants, may be further admixed with a
minor proportion of dip or polyfunctional
polymerizable species to cause cross linking of the
30 polymeric matrix as polymerization or curing
proceeds. Examples of such dip or poly~unctional
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species include: divinylbenzene, ethylene glycol
diacrylate or methacrylate, propylene glycol
diacrylate or methacrylate, and the acrylate or
methacrylate esters of the following polyols:
triethanolamine, glycerol, p ntaerythritol, battalion
glycol, diethylene glycol, triethylene glycol,
tetraethylene glycol, minutely, sorbitol and the
like. Other cross linking monomers can be
illustrated by N,N-methylene-bis-acrylamide or
methacrylamide, sulfonated divinylbenzene, and
divinylsulfone.
Additional lens-forming materials which are
suitable in the fabrication of contact lenses are
illustrated by one or more of the foliating U.S.
Patents: 2,976,576; 3,220,960; 3,937,680;
3,948,871; 3,949,021; 3,983,083; 3,988,2~t4;
4,018,853; 3,875,211; 3,S03,942; 3,532,679;
3,621,079; 3,639,524; 3,700,761; 3~721,657;
3,758,448; 3,772,235; 3,786,034; 3,803,093;
3,816,571; 3,940,207; 3,431,046; 3,542,461;
4t055t378; 4,064,086; and 4,062,627.
The polymerization reaction can be carried
out in bulk or with an inert solvent. Suitable
solvents include water; organic solvents such as
water-soluble lower aliphatic mandrake alcohols as
well as polyhydric alcohols, e.g., glycol, glycerol,
Dixon, etc.; and mixtures thereof. In general,
the solvent comprises a minor amount of the reaction
medium, it less than about So weight percent.
Polymerization of the lens-forming mixture
may be carried out with free radical catalysts
and/or initiators of the type in common use in vinyl
polymerization. Such catalyst species can include
the organic peroxides, the alkyd per carbonates,
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hydrogen peroxides, and inorganic materials such as
ammonium, sodium, or potassium per sulfate.
Polymerization temperatures can vary from about
20C, and lower, to about 100C, and higher.
Polymerization of the monomer or prepolymer
material can also be effected using, for example,
radiation US X-ray, microwave, or other
well-known forms of radiation) with/without the --
presence of well-known initiator(s) and/or
catalysts).
When using radiation as the catalyst in the
polymerization process, the polymerization column
(tube) is fabricated from a material that will not
impede the transmission of the radiation into thy
polymerization zone of the column. Glass, such as
Pyrex, would be a suitable material for the
polymerization column when using radiation as the
catalyst. When using other types of catalysts as
recited above, the polymerization column could be
fabricated from various types of metals such as
steel, bronze and the like.
The shape of a lens blank may be controlled
not only by the size and shape of the mold, but also
by the amount and nature of the components
comprising the lens-forming mixture, by the
synchronized rotational speed of the column and mold
during polymerization, by the position of the axis
of rotation of the column and mold relative to the
direction of gravity, by axis of rotation of the
column relative to the optical axis of the (formed)
yens in the mold cavity, and the like. Tilting the
axis of rotation or when the axis of rotation does
not pass through the optical center of the (forming)
lens a prism component can be added to the lens.
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In the fabrication of contact lenses, the
lens-forming material is placed in the mold cavity
having an optical concave surface wetted by said
material, and then fed one at a time into the inlet
end of polymerization column which desirably
comprises a "conditioning" zone near the inlet end
and a polymerization reaction zone toward the outlet
end. It is preferred that the molds by
characterized by a pretreated optical surface to
increase its hydrophilicity or nettability in a
manner well-known in the art. The speed of rotation
of the column and the molds is then adjusted to
cause and/or maintain radially outward displacement
of the lens forming mixture to a predetermined lens
configuration which when subjected to the
polymerization conditions employed in the column
will form the desired shaped contact lens.
Rotational speed of, for example, 300 rum and
lower to 600 rum and higher, can be conveniently
used. The precise rotational speed to employ in the
operation is, of course, well within the skill of
the artisan. Factors to be considered include the
type and concentration of the components comprising
the lens-forming material employed, the operative
conditions of choice, the type and concentration of
catalyst, initiator, and/or radiation energy source,
and factors discussed previously and readily
apparent to the artisan.
Brief Description of Drawing
The present invention will become more
apparent from the following description thereof when
considered together with the accompanying drawing
which is set forth as being exemplary of embodiments
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of the present invention and is not intended in any
way to be limited thereof and wherein:
Figure 1 is a side elevation Al view partly
in cross-section of a polymerization tube of this
invention.
Figure 2 is a cross sectional view taken
along line 2-2 of Figure 1.
Figure 3 is a cross sectional view of --
another embodiment of the tube of this invention.
Figure 4 is a perspective view of a mold
for use in the polymerization tube of this invention.
Figure 5 is a cross sectional view taken
along line 5-5 of Figure 4.
Figure 6 is a plan view of a mold for use
in one embodiment of this invention.
Figure 7 is a cross sectional view of a
polymerization tube showing the mold of Figure 6
disposed within said polymerization tube.
Figure 8 is a cross sectional view of a
polymerization tune showing another embodiment of a
mold of this invention disposed within a
polymerization tube.
Figure 9 is a cross sectional view of
another embodiment of a polymerization tube showing
a mold disposed and secured within a polymerization
tube whose internal area represents a square
Figure 10 is a cross sectional view of
another embodiment of a polymerization tube showing
a mold disposed and secured within a polymerization
tube whose internal area represents an equilateral
triangle.
Figure 11 is a side elevation Al view partly
in cross-section of a gas feed means suitable for
use in this invention.
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Figure 12 is a side elevation Al view in
cross-section of the rotatable sleeve member shown
in Figure 11.
Figure 13 is a view taken along the lines
13 13 of Figure 12.
Figure 14 is a perspective view of the
outer support ring member for the bearing pair shown
in the gas feed means of Figure 11.
Figure 15 is a perspective view of the
. inner support ring member for the bearing pair shown
in the gas feed means of Figure 11.
Detailed Description of Drawing
Referring in detail to Figures 1 and 2,
there is shown a tube 2, such as a polymerization
tube, made of an inert material such as glass,
metal, plastic, metal alloys and the like. Disposed
on the internal wall 4 of tube 2 are three equally
spaced longitudinal projections or ridges 6. The
projections 6 are shown as made of the same material
as tube 2. Figures 4 and 5 show a mold 8 having a
mold cavity 10 within a cylindrical wall 12. Mold 8
has a circular horizontal mold shoulder 9 located
between inner mold wall 7 and mold cavity 10. The
mold cavity 10 can assume any desired shape required
of the finished article. As stated above, this
shape could be axially symmetrical or asymmetrical.
Referring specifically to Figure 2, mold 8 is shown
disposed within polymerization tube 2 whereupon
there is an interference fit between the wall 12 of
mold 8 and the outer surfaces 14 of projections 6
which form contact points for mold 8. Basically,
the outer diameter of mood 8 would be equal to or
slightly larger than the diameter of an inscribed
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circle on whose circumference are contact points 14
of projections 6. The configuration and arrangement
of contact points 14 and Hall 12 insures an
interference fit between the mold 8 and the tube 2
thereby securing and maintaining the concentricity
of the mold 8 to the longitudinal axis of tube 2
while the tube and molds rotate at the same speed.
Moreover, the positioning of the molds with respect
to the vertical axis of the polymerization tube is
maintained during its forced descent down the
polymerization tube
A plurality of molds 8, each containing a
polymerizable or curable composition can be fed into
polymerization tube 2 which upon spinning will cause
the composition, under the centrifugal force, to
conform to the shape of the cavity 10 in mold 8.
The channels 16 formed or defined between adjacent
projections 6, inner wall 4 of tube 2 and outer wall
12 of mold 8 will permit a gaseous medium such as an
inert gas to be directed through the rotating tube
in a conventional manner using conventional means.
Although not shown, a conditioning tube could be
coccal mounted on top of polymerization tube 2
and preferably rotated at the same speed of rotation
as the polymerization tube 2. Alternatively and
most preferably, the conditioning tube and
polymerization tube could constitute the same tube
so thaw a portion of the tube is used for
conditioning the composition and the other portion
could be used for the polymerization reaction. An
advantage of the conditioning tube is that during
rotation it causes and/or maintains the desired
liquid shape of the article prior to being
.
~L23~66~
polymerized to a solid shape in the polymerization
tube.
Figure 3 shows another embodiment of a
polymerization tube 3 having three longitudinal
projections 5 which are made of a different material
than the material of tube 3. Preferably projections
5 are fabricated of a resilient material which would
be compressed by mold 8 when forced into
polymerization tube 3 thereby providing an
. interference fit there between When using a
resilient material, the inner diameter within tube 3
of an inscribed circle whose circumference contains
the contact points of projections 5 can be smaller
than the inner diameter formed of projections made
of a hard material because the resilient material
has the characteristic of substantially recovering
its shape and size after being deformed.
Figure 6 shows another type of mold 17
which can be used in the invention. Mold 17 has a
cavity 18 and three external projections 20 equally
spaced around its outer wall 22, Mold 17 can be
used in conjunction with a typical conventional
cylindrical tube 24 as shown in Figure 7 and can
provide the same degree of interference fit between
the mold 17 and tube 24 so as to maintain the
concentricity of the mold to the axis of the tube
Projections 20 is preferably fabricated as an
integral part of the mold material or alternatively
can be a separate material 28 or mold 26 as shown
n Figure 8. Referring to Figure 8, mold 26 is
disposed within cylindrical tube 30 in an
interference fit arrangement.
Figure 9 discloses a further embodiment and
shows mold 36 (same as mold 8 in Figure 4) disposed
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';
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i662
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within polymerization tube 34 which has a hollow
cross sectional area defining a square. Tube 34 can
be conveniently fabricated by appropriately bonding
four rectangular Pyrex panels or other suitable
material with a suitable adhesive, e.g., epoxy
glue. To provide the interference fit, the external
dilutor of mold 8 is equal to or is very slightly
larger than the internal length of one side of the
square.
Figure 10 discloses a further embodiment
and shows mold 40 (same as 8 in Figure 4) disposed
within polymerization tube 38 whose hollow cross
sectional area depicts an equilateral triangle. The
interference fit relationship is achieved by using
molds whose external diameter is equal to or very
slightly larger than the internal length ox one side
of the equilateral triangle multiplied by the
factor I .
Referring in detail to Figures 11 to 13
there is shown a gas feed means suitable for use in
conjunction with the novel device and method of this
invention, said gas feed means being described in
aforementioned U.S. Patent No. 4,468,184.
Specifically, the gas feed means includes a
rotatable sleeve member 48 having an upper tubular
section 50 and a lower tubular section 52~ As will
be seen, the upper tubular section 50 has a larger
cross-sectional area than polymerization column 1
and the lower tubular section 52. Disposed within
the upper tubular section 50 is a resilient liner
material 54, preferably plastic that is slightly
tapered and adapted for receiving the lower end of
polymerization column 1 in frictional Sacramento
' .
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therein. As shown, the lower end of polymerization
column 1 is slightly tapered to permit easy
insertion and Sacramento of polymerization tube 1
within liner 54~ although liner 54 is preferably
. .
made of plastic, it can be made of any resilient
material that would be suitable for securing the
lower end of the polymerization column 1 in
frictional Sacramento within said liner 54 so that-
rotation of sleeve In ember 48 will impart
synchronized rotation to polymerization column 1.
As shown in Figure 11, the inner diameter of
polymerization column 1 is substantially equal to
the inner diameter of lower tubular section 52 of
sleeve 48 and axially aligned therewith 50 that
molds 8 (shown in outline form in Figure 11 and
shown in a plan view in Figure 4) exiting from
polymerization column 1 will be fed into and descend
through lower tubular section 52 of sleeve 48.
As shown in Figure 11, 12 or 13, a
circumferential groove 56 is formed in the outer
wall surface of lower tubular section 52 and a
plurality of gas inlet openings 58 are
circumferential disposed through and defined by
the base of groove 56. A plurality of longitudinal
grooves 60 are formed in the inner wall of lower
tubular section 52 with each groove 60 extending
from a communicating gas inlet opening 58 up through
the top of lower tubular section 52. Thus any gas
entering inlet opening 58 when molds 8 are disposed
within lower tubular section 52 will be directed up
through grooves 60 and into the interior of
polymerization column 1.
Referring to Figure 1, lower tubular
section 52 of sleeve 48 is disposed within a
;
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cylindrical cupped support member 62 having an
upstanding cylindrical wall 64 and a base 66
defining an opening 68 which is axially aligned with
the opening 70 of lower tubular section 52.
Disposed between the upstanding cylindrical wall 64
and lower tubular section 52 is a cylindrical
reloaded bearing pair 72 including an upper bearing
74 and a lower bearing 76. Separating the bearing-
pair 72 and supporting upper bearing 74 is an outer
support ring 78 disposed adjacent the internal wall
80 of support member 62, and an inner support ring
82 disposed adjacent the outer wall 84 of lower
tubular section 52. In assembling the unit, the
lower bearing 76 is placed into the cylindrical
cupped support member 62 such that its lower surface
rests on flange 86. Outer support ring 78 and inner
support ring 82 are then disposed on top of lower
bearing 76 whereupon upper bearing 74 can then be
mounted on top of outer support ring 78 and inner
support ring 82. When rotatable sleeve member 48 is
inserted within support 6 2, circular flange 88
disposed on the outer wall of lower tubular section
52 secures the upper bearing 74 in place., A
securing ring 90 having an L-shaped cross section is
detachably secured to the top of support member 62
by any suitable means such as the threaded elements
shown, with its internal flange member 92 securing
the upper bearing 74 in proper alignment within
support member 62. Each of the bearings 74 and 76
includes an outer fixed race 94 and an inner
rotatable race 96 which are spaced apart by
conventional ball bearings 98. By this arrangement,
sleeve member 48 can be rotated within support
member 62 by conventional belt means illustrated
- 26 -
generally as 100 and which is operatively associated
with a conventional motor driven belt means not
shown.
Support member 62 is provided with an
opening 102 defined in its side wall into which is
secured a hose bar 104 which is adapted to be
connected to a gaseous supply means not shown. In
Figure 14 outer support ring 78 is provided with an
annual groove 106 disposed in its outer wall.
plurality of openings lob are circumferential
disposed in the base of groove 106 and extends
through its upstanding wall. As shown in Figure 15,
inner support ring 82 defines a plurality of
openings 109 extending through its upstanding wall.
Referring again to Figure 11, it will be seen that
the spaced apart preluded bearing pair 72 and the
spaced apart outer support ring 78 and inner support
ring 82 define an annular zone 110.
In the operational mode and with reference
to Figures 11 to 15, a gaseous medium fed through
opening 102 travels along and within circumferential
groove 106 and is directed through openings 108 and
into annular zone 110. The gaseous medium is then
directed through openings 109 in inner support ring
82, into and through openings 58 of lower tubular
section 52 and up grooves 60 into the interior of
polymerization column 1. The height of inner
support ring 82 is greater than the width of
circumferential groove 56 in tubular section 52 so
that when inner support ring 82 is positioned
adjacent groove 56, a circumferential zone 112 is
defined that can accommodate a gaseous medium fed
through openings 109 of inner support ring 82. This
will allow a uniform gas slow to be fed through gas
I
- 27 -
inlet openings 58 and up through grooves 60 into the
polymerization column 1.
In the operational mode, mold 8 containing
a polymerizable or curable compound in its cavity 10
is forceable ejected from the polymerization column
1 into tubular section 52 and with the diameter of
the molds substantially equal to the cross-sectional
diameter of tubular section 52, the molds 8 will
effectively prevent any gaseous medium fed through
openings 58 from escaping out opening 70 of tubular
section 52. Thus the gaseous inert medium will flow
up through grooves 60 into the interior of
polymerization column 1 between the peripheral wall
of molds 8 and the inner surface of polymerization
column 1. The inner wall 114 ox polymerization
column 1 has a longitudinal projection 6 (see
Figures 1 and 2) to provide an interference and
sliding fit for molds 8. The inert gas fed up
through polymerization column 1 will purge any
entrained, undesirable gas such as oxygen in
polymerization column 1 which could effect the
quality and acceptability of the articles being
costed. As shown in Figure 11, an ejected mold 8
exited through opening 70 of the gas feed means will
be supported on member 118 whereupon a conventional
pusher means 120 will advance the ejected mold 8 to
a receptacle 122.
The reload bearing pair 72, desirably
incorporates seals of a conventional type which
would provide a retention of lubricants for the
bearings. These seals would serve to define the
circumferential zone 110 and effectively prevent the
escape of any gas to areas other than through the
666~:
- 28 -
plurality of openings 58 in tubular section 52 of
sleeve 48.
The common requirement in all the
embodiments of the invention is that an interference
fit be maintained between the molds and the tube to
insure concentricity of the molds to the spin axis
of the tube while maintaining synchronization of the
rotation of the molds to the same speed as the
rotation of the tube. In addition, the molds dye
slid able with respect to the tube so that the molds
are vertically moved downward through the
polymerization tube under a positive force.
EN Alp LYE
The polymerization column depicted in
Figures 1 and 2 along with gas feed means can be
used to prepare lenses. Specifically, polypropylene
molds (Figure 2) having a concave spherical optical
surface in the mold cavity can be used in the
centrifugal casting of contact lens. The mold
dimensions can be: outside diameter - 17mm; inner
diameter above mold cavity - 15.6mm; height of mold
- 7.5mm; diameter of mold cavity - 13.2mm; central
mold cavity radius - 7.7mm; depth of mold cavity
(Max) - 3. 3 mm; width of circular horizontal mold
shoulder (located between the inner mold wall and
mold cavity) - 1.2mm. The hydrophilicity or
nettability ox the optical surface of the molds can
be enhanced by treatment in an oxygen, low
temperature, plasma chamber for approximately 18
seconds, 50 watts gauge setting (Model LTA-302, Low
Temperature Asker, LYE Corporation, Walt ham,
Massachusetts). To a series of these molds, there
can be charged, individually, a metered amount of
,~," .
._
.
~3~66;~
- 29 -
the lens-Eorming mixture, i.e., approximately 20
milligrams. The lens-forming mixture (based on
total weight) could comprise the following recipe:
Components (Parts by Wt.)
2-Hydroxyethyl ~ethacrylate:84.6
Ethylene luckily Dimethacrylate: lo
Bunsen methyl Ether (initiator): 0.2
Glycerol: 14.2
The molds can be transported laterally, on a
. conveyor belt or by positive force means, to the
inlet end of a rotating Pyrex column which is
supported in an upright position by support means.
Said Pyrex column being generally as shown in Figure
1 as polymerization column 2. The molds can be
force fed downwardly, one at a time, into the
vertical column by pusher or plunger means having a
circular nose which engages the mold at the mold
shoulder 9. When the rotating column is filled with
molds (capacity can vary, for instance, from 60 to
120 molds), the force feeding of each mold at the
inlet end and the removal or ejection of the bottom
most mold (containing the shaped lens product at
the outlet end can be synchronized or automated to
effect a continuous process. The speed of rotation
of the column about its vertical axis can be about
400 rum and total residence time of each mold in
the column can be about 20 minutes. The rotating
column can be maintained at ambient room
temperature, i.e., about 20-22~C with nitrogen
continually flowing upward in grooves 60 (see
Figures 3 to 5 into the polymerization column 2 to
remove any entrained oxygen in the column. In the
so-called llconditioning" zone in the upper portion
of the column, centrifugal forces created by the
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3L~36~
- 30 -
column rotation will cause the radially outward
displacement of the liquid lens-forminy mixture in
the spherical mold cavity to be formed onto a Jo
predetermined lens shape. The "conditioning" of
said liquid material should be maintained for a
period of about 15 minutes in its downward decent in
the conditioning zone to the polymerization zone.
The polymerization zone of the column should
likewise be maintained at ambient room temperature.
The polymerization reaction can be conducted using
W radiation from a source outside the column (W
source: medium pressure, mercury arc, W emission -
300-400 no, infrared is filtered, and lamp distance
is 3 inches). The residence time in the
polymerization zone should be about 5 minutes. A
longer residence period can be employed, if desired,
as well as subjecting the shaped contact lens blank
still in the cavity of the mold to posture
conditions. Immersion in distilled water causes the
hydrophilic lens blank to swell which (swelling)
causes the separation of the contact lens from the
mold. Repeated washings in distilled water insures
removal of catalyst or initiator residue and
unrequited monomer(s). The contact lens should be
finally immersed in physiologic solution (0.9%
saline) until it reaches osmotic equilibrium with
the solution.
The finishes lens will generally have a
refractive power (wet) of -6 dotters. It will be
optically clear, transparent, inert to bacteria,
biocompatible with the cornea, water content of
about 39% by weight, dimensionally stable, and
exhibits good mechanical properties. It is useful
as a daily wear "soft" contact lens.
~36662
- 31 -
EXAMPLE 2
The procedure of Example 1 can be repeated
using the following recipe:
Components (Parts by Weight)
2-~1ydroxyethyl Methacrylate: 78
Methacrylic Acid: 2
Isopropylpercarbonate: 0.4
Glycerol: 19
Ethylene Glycol Dimethacrylate: 1.0
no W source)
Polymerization Zone Conditions:
70C; residence time: 6 minutes.
This will produce a contact lens that is
optically clear, transparent, inert to bacterial,
biocompatible with living tissue, highly
water-swellable, water-insoluble, dimensionally
stable, and of Good mechanical strength.
EXPEL 3
The procedure of Example 1 can be repeated
using the following recipe:
Components (Parts by Weight)
2-Hydroxyethyl Methacrylate: 95
Methyl Methacrylate: 5
Vapor 33: 0.2
Propylene Glycol: 10
Ethylene Glycol Dimethacrylate: 0.5
R Registered Trademark of duo Pont.
Polymerization Zone Conditions:
; 70~C; residence time: 6 minutes.
This will produce a contact lens that is
:: :
optically clear, transparent, inert to bacteria,
I; .
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~l~36~6~:
- 32 -
biocompatible with living tissue, water-swellable,
water-insoluble, dimensionally stable, and of good
mechanical strength.
Modification of the mold cavity and of the
recipe results in a wide variety of useful and
suitable contact lenses as taught in U.S. Pat. No.
3,660,545~
.
