Note: Descriptions are shown in the official language in which they were submitted.
glue
. . . . . .
Background Go the Invention
In recent years hard contact lens materials having improved
oxygen permeability have been developed. Certain such materials
are set forth in United States Patent 3,808,178 which describes
contact lenses fabricated from a copolymer of a polysiloxanyl
acrylic ester and an alkyd acrylic ester. Other such hard
contact lens materials have been developed. It is sometimes
difficult to obtain good dimensional stability in contact lenses
made from siloxanyl alkyd ester vinyl monomers
Dimensional stability is an important property of hard
contact lenses and affects both accurate vision correction and
wearer comfort. It is known that changes in the dimensions of
hard lenses can occur rapidly shortly after cutting and finish-
in or over a prolonged period of time. Such changes can be
of various types. Changes to the base curve or outer curve
of a contact lens which changes are uniform are known as
"steepening" or "flattening" depending upon the direction of
change. A non-uniform change in lens dimension is termed "war page".
Ye
~2C~ 7
702
1 Dimensional changes of the type noted above can result
2 from one or more factors which include the relief of internal ,
3 stress or strain incurred during manufacture or the wakeup or
4 loss ox material within the lens. The prior art has developed
processes for handling internal stress and strain problems as
6 by the use of careful annealing of lens blanks.
7 Dimensional stability difficulties have been encountered
with gas permeable contact lenses prepared from co or higher
9 polymers containing a siloxanyl alkyd ester vinyl monomer. These
difficulties may result from the differences in the reactivity
11 ratios between various monomers employed in the materials and
12 the chain transfer reactions during polymerization. Contact
13 lenses produced from such materials can contain significant
14 portions of unrequited monomer or monomers. This can lead to
dimensional instability when these monomers leave the material.
16 The monomers can leave the lenses shortly after making the lenses
17 or over a long period ox time. When the monomers leach out
18 during use, this can have toxicological consequences.
19
Summary of the Invention
21 It has now been found that the dimensional stability of
22 polymeric materials useful as contact lenses and containing
23 a siloxanyl alkyd ester vinyl monomer can be greatly increased.
24 The materials can be polymerized by any of the known methods.
Such polymerization normally leaves 4% by weight or less, such
26 as typically 1 to 2%, residual unrequited monomer, mixture of
~2~4~
~702
1 monomers, oligimers and other low molecular weight materials
2 which would ordinarily leach out or exude on normal contact
3 lens use and all of which are referred to as unrequited monomer
4 in this application. In a second step, the polymerized
material is treated with high energy radiation to increase the
6 degree of polymerization of the unrequited monomer and thereby
7 increase the dimensional stability of the material.
8 It is an object of this invention to provide a contact
9 lens material having good dimensional stability and which can
be formed into contact lens blanks and contact lenses by con-
11 ventional methods which blanks and lenses have good dimensional
12 stability and minimized unrequited monomer.
13 It is still another object of this invention to provide a
14 method for improving the dimensional stability of contact lens
polymeric materials formed at least in part from siloxanyl
16 alkyd ester vinyl monomer.
17 It is still another object of this invention to use high
18 energy radiation to treat polymeric materials useful for form
19 in contact lenses, the blanks or the lenses formed from such
material, with high energy radiation to improve dimensional
21 stability.
22 According to the invention a method is provided for imp
23 proving dimensional stability of polymeric materials useful
24 in forming contact lenses. The method comprises selecting
a polymeric maternal polymerized from a siloxanyl alkyd ester
~204~07
702
1 vinyl monomer and at least one comonomer and having a minor
2 amount of unrequited monomer therein. This polymeric material
3 is then exposed to high energy radiation to reduce the amount
4 of unrequited monomer and increase dimensional stability in
a second or post polymerization step. The resulting material
6 exhibits good dimensional stability.
7 Preferably the radiation is in the form of gamma rays with
8 an absorbed dosage of from 0.005 Megarads to 10 Megarads and
; 9 more preferably in the range of from 1 to 4 Megarads. Prey-
drably the material is irradiated when in the form of lens
11 blanks having thicknesses of up to 1/4 inch although higher
12 thicknesses can be irradiated. The material in bulk form or the
13 final lens can be irradiated if desired.
14 It is a feature of this invention that the high energy
radiation acts to sterilize the material which may be in the
16 form of contact lenses or blanks. Not only is dimensional
17 stability improved but in many cases physical properties are
1~1 pry O
18 Lowe since higher degrees of polymerization are obtained
19 when the second polymerization step is used.
21 Description of Preferred Embodiments
22 Contact lens materials are normally polymerized as in
23 rods and then rough cut to form lens blanks or lens buttons
24 which are then machined to final lens dimensions. The process
25 of this invention can be carried out at any stage of the contact
0~4~)7
702
1 lens manufacture. For example the rods, buttons or lenses
2 can be exposed to radiation. The lenses or buttons which are
3 normally 3/16 inch whey irradiated, can be successfully if-
4 radiated to increase the degree of polymerization and drive
the polymerization reaction closer to 100% reaction without
6 deteriorating the desirable physical properties of the material.
7 The high energy radiation useful in the present invention
8 generally has an energy per particle or per quantum of from
9 about 15 million electron volts (Movie.) to about 0.003 Movie.
Any of the known high energy radiation sources can be used
11 as for example those listed below:
12 Energy per Particle
Radiation Wavelength or per quantum
13 O
14 x-ray 0.008-40 A 1.5-0.003 million electron
volts (Movie.)
O
16 gamma ray 0.0014-1.6 A 9.0-0.008 Movie.
17 accelerated electrons 5xlO 2-.08xlO 2 A 15-0.25 Movie.
18 neutron particles 5xlO 2-.O~xlO 2 A 15-0.25 Movie.
19 alpha particles 5xlO-2-.08xlO-2 A 15-0.25 Movie.
When using gamma rays, the absorbed dosage is preferably
21 in the range of from 0.005 Megarads to 10 Megarads and more
22 preferably in the range of from 1 to 4 Megarads. When using
23 x-rays, the absorbed dosage is within the ranges given for
24 gamma rays while when using electron beam irradiation, the
absorbed dosage is preferably in the range of from 0.005
--5--
I I
702
1 Megarad to 1 Megarad. The time of exposure to irradiation
2 can vary greatly depending upon the particular materials and
3 the type of irradiation. For example, gamma radiation can be
4 carried out for periods of hours as for example 24 hours while
i 5 electron beam radiation can be obtained in seconds. Prey-
6 eerily the polymeric materials irradiated have been polymerized
7 by conventional polymerization reactions such as free radical
8 reactions to 4X by weight residual or unrequited monomer or
9 less and normally there remains from 1 to 2% by weight of us-
reacted monomer prior to the irradiation step. The irradiation
11 step preferably carries the degree of polymerization sub Stan-
12 tidally to completion greatly reducing or eliminating any amount
13 of unworked monomer present in the polymer.
14 Whole radiation to polymerize various polymeric materials
is known, it is not believed known to use radiation as a
16 second step in the polymerization of contact lenses or contact
; 17 lens materials. Curing of thin coating formulations for wire
18 insulation and modification of polymeric surfaces through
19 graft polymerization is known in other areas. As long as 20
years ago it was reported in the literature Journal Polymer
21 Science 44 295 (1960) that the effects of gamma radiation on
22 polymethylmethacrylate and polyethylmethacrylate were very
23 dependent on the amount of residual monomer present in a
24 sample polymer. It has also been found that x-ray irradia-
lion of polymethylmethacrylate orthopedic cement results in
B -6-
~149~t)7
28/7~2
1 s~gn1ficant decrease on residual me~hylmethacrylate content
2 (American Chemical Society, Organic Coatings and Plastics, 37
3 to 205 and 210 1977).
4 In all cases the irradiation prowess is preferably carried
out at room temperature in an inert atmosphere. Gamma radian
6 lion may be obtained from conventional commercl~l sources such
7 as cobalt 60 and sesame 137. X-ray radiation with energies
8 above whose ox the bonds of the polymeric material can be
9 easily obtained.
The polymer maternal useful in the present invention
11 is preferably a highly oxygen permeable contact lens compost-
12 lion as known for example and described on U.S. Patent
13 3,808,178 issued April 30, 1974 entitled "Oxygen Permeable
14 Contact Lens Composition, Methods and Article of Manufacture".
That patent describes rompos~tions of matter specially adapted
16 for the production of contact lenses and hang increased Perle-
17 ability and comprises solid copolymers of comonomers consist-
18 in essentially of: (a) about 10 to 60 parts by weight of a
19 polysiloxanyl alkyd ester of the structure
I ray 1 'I 9
21 A - -Sue (Sheehan C- SHEA
22 PA m Y
23 Hun:
24 (1) X and Y are selected from the class consisting of
2P12.~ I 7
1 Clucks alkyd groups phenol groups and Z groups,
2 (2) Z us group of the structure
4 Sue _
PA _ m
6 I is selected from the class consisting of Cluck alkyd
7 groups and phenol groups,
8 I R us selected from the class consisting of methyl
9 groups and hydrogen,
(5) m us an integer from one to five, and
11 (6) n is an integer from one to three; and
12 (b) about 40 to 90 parts by weight of an ester of a Cluck moo-
13 hydric ~lkanol and an acid selected from the class consisting
14 of acrylic and methacryl~c acids.
The preferred lens materials for treatment with high
16 energy radiation in accordance with this invention are materials
17 ox the type generally described in United States patent 4,152,508 which
18 issued May 1, 1979 entitled "Improved Silicone-Containing Hard Contact
19 Lens Materials" invented by Edward J. Ellis and Joseph C. Solomon and
assigned to the same assignee as the present invention.
21 Generally the preferred formulation is an oxygen permeable
22 herds machinable dimensionally stable hydrophll~c contact lens
-8-
~,~
04~V7
702
1 material of high transparency consisting essentially of a
2 polymer formed from (a) 30-80% by weight of a siloxanyl alkyd
3 ester monomer having the following formula:
4 I
6 R4~~Si-~Hz~-o- C - C = Chihuahuas
g Assay
I
I
11 where Al is selected from the class of hydrogen or methyl
12 groups, "a" is an integer from one to three, "b" and "c" are
13 integers from zero to two, "d" is an integer from zero to
14 one, A is selected from the class of methyl or phenol groups,
R2 is selected from the class of methyl or phenol groups,
16 R3 and R4 represent either no group(cycllc ring from "c" to "d")
17 or methyl or phenol groups,
18 (b) 5 to 60% by weight of an itaconate moo- or dip ester,
19 (c) 1 to 60 parts by weight of an ester of a Cluck moo-
hydric or polyhydric alkanol or phenol and an acid selected
21 from the class consisting essentially of acrylic and methacrylic
22 acid,
23 (d) 0.1 to 10% by weight of a cross-linking agent,
24 (e) 1 to 20% by weight of a hydrophilic monomer to impart
hydrophil;c properties to the surface of the contact lens material
26 of this invention.
go
SUE 7
702
1 Generally the copolymers useful in this invention can
2 be formed from 10 to 90% by weight ox a siloxanyl alkyd ester
3 monomer or mixtures thereof, and from 10 to 90% by weight of an
or
4 itaconate ester from 10 to 90% by weight of an acrylate
or methacrylate ester. Mixtures of an itaconate ester with
6 an acrylate or methacrylate ester totaling 10 to 90% by
7 weight are generally preferred since they exhibit the broader
8 balance of lens properties. Other necessary ingredients as
9 known in the art such as initiators, cross-linking agents,
wetting agents, colorants and the like can be added to the
11 polymeric materials as is known.
12 The general formula for useful polymeric materials is as
13 hollows:
14 The siloxanyl alkyd ester monomers useful in this invention
preferably have the following formula:
16 R2
17 A it
18 A
19R4~0~Si-O-S~-(CH2)a-0-C-C=CH2
A isle -
21 Assay
I
22 R3
23 Where Al is selected from the class of hydrogen or methyl
24 groups, "a" is an integer from one to three, I'm" and "c" are
integers from zero to two, A is selected from the class of
26 methyl or phenol groups, R3 and R4 represent either no group
27 (cyclic ring from "c" to "d") or methyl or phenol groups,
28 "d" is an integer from zero to one.
-10-
~2044~)7
3/702
1 Representative s;loxanyl alkyd ester monomers which could
2 be utilized in this invention include
3methacryloyloxymethyl pentamethyldisiloxane
5 Ho SHEA Al Ho
SHEA 0-Si-CH2-0-C-C=CH2
7 SHEA SHEA
9methacryloyloxypropyl tris(trimethylsilyl)siloxane
11 Ho
12 CH3-5~i-CH3
13 SHEA SHEA
SHEA- I Ho -C=CH2
SHEA 0
16 CH3-Si-CH3
17 SHEA
I
19methacryloyloxymethyl heptamethylcyclotetrasiloxane
21
22 Sue
23 SHEA SHEA 0 SHEA
SHEA 0/ ~H2-0-C-C=CH2
SHEA 'SHEA
~Z~44(~7
8/7~2
1 methacryloyloxypropyl heptamethylcyclotetraslloxane
4 C ~sjCH3
0 0
6 OH Ho 8 Ho
SHEA I H 0-C-C=CH2
8 Swahili
SHEA SHEA
The itaconate esters useful in the present invention have
11 the following structure:
12 COCK
13 SHEA = C
14 SHEA
OWE
I
17 X and Y are the same or different and are hydrogen, methyl
18 or phenol groups. Representative moo- and dip itaconate
19 esters include
methyl itaconate
21 dim ethyl itaconate
22 phenol itaconate
23 diphenyl taco Nate
24 methyl phenol itaconate
The fracture strength adding material is an ester of
4407
~7C2
1 a Cluck mandrake or polyhydric alkanol, or phenol and an
: 2 acid selected from the class consisting of acrylic and moth-
3 acrylic acid. Such esters include:
4 methyl methacrylate
methyl phenylacrylate
6 phenol methacrylate
7 cyclohexyl methacrylate
- 8 Examples of cross-linking agents include polyfunctional
9 derivatives of acrylic acid methacrylic acid, acrylamide,
methacrylamide and multi-Yinyl substituted benzenes, including
11 but not limited to the following:
12 ethylene glycol d;acrylate or dimethacrylate
13 diethylene glycol diacrylate or dimethacrylate
14 tetraethylene glycol diacrylate or dimethacrylate
polyethylene glycol diacrylate or dimethacrylate
16 trimethylolpropane triacrylate or trimethacrylate
17 Bisphenol A diacrylate or dimethacrylate
18 ethoxylated Bisphenol A diacrylate or dimethacrylate
19 pentaerythritol in- and tetraacrylate or methacrylate
tetramethylenediacrylate or dimethacrylate
21 Mullen bisacrylamide or methacrylamide
22 dim ethylene bisacrylamide or methacrylamide
23 N,N'-dihydroxyethylene blsacrylamide or methacrylamide
24 hexamethylene bisacrylamide or methacrylamide
decamethylene bisacrylamide or methacrylamide
26 divinely Bunsen
_ _ _
~2~4~4V7
3/70~
1 The wettable surface is provided by the inclusion of hydra- ',
2 Philip neutral monomers, hydrophil;c kink monomers and
3 hydrophilic anionic monomers and mixtures of these.
4 The classes of these compounds are hydrophilic acrylates
and methacrylates, acrylamides, methacrylamides, and vinyl
6 lactams. Representative hydrophilic neutral monomers include:
7 2~hydroxyethyl acrylate or methacrylate
8 N-vinylpyrrolidone
9 acrylamide
methacrylamide
11 glycerol acrylate or methacrylate
12 2-hydroxypropyl acrylate or methacrylate
13 polyethylene glycol monoacrylate or methacrylate
14 The kink monomers either can be initially in their charged
form or are subsequently converted to their charged form after
16 formation of the contact lens. The classes ox these compounds
17 are derived prom basic or cat ionic acrylates, methacrylates,
18 acrylamides, methacrylam;des, vinylpyridines, vinylimidazoles,
19 and diallyldialkylammonium polymerizable groups. Such monomers
are represented by:
21 N,N-dimethylaminoethyl acrylate and methacrylate
22 2-methacryloyloxyethyltrimethylammonium chloride and
23 methyl sulfate
24 2-, 4-, and 2-methyl-5-vinylpyridine
2-, 4-, and 2~methyl-5-vinylpyridinium chloride and
26 methyl sulfate
~2044~7
I/702
l ~-(3-methacrylamidopropyl)-N,N-dimethylamine
2 N-(3-methacrylamidopropyl)-N,N,N-trimethylammoniumm
; 3 chloride
4 l-v;nyl- and 2-methyl-l~vinyl~midazole
l-vinyl- and 2-methyl-l-vinylimidazolium chloride
6 and methyl sulfate
7 N-(3-acrylamido-3~methylbutyl)-N,N-dimethylamine
8 N-(3-acrylam~do-3-methylbutyl)-N,N,N-trimethylammoopium
: 9 chloride
lo N-(3-methacryloyloxy-2-hydroxylpropyl)-N,N,N-trimeethyl-
if ammonium chloride
12 diallyldimethylammonium chloride and methyl sulfate
13 The anionic monomers either are in their neutral form initially
14 or are subsequently converted to their anionic form. These
classes of compounds include polymerizable monomers which contain
16 car boxy, sulfonate~ and phosphate or phosphonate groups. Such
17 monomers are represented by:
18 acrylic acid
lo methacrylic acid
I sodium acrylate and methacrylate
21 vinylsulfonic acid
22 sodium vinylsulfonate
23 p-styrenesulfonic acid
24 sodium p-styrenesulfonate
2-methacryloyloxyethylsulfonic acid
v Jo
~2~:1144~)7
~8/702
1 3-methacryloyloxy-2-hydroxypropylsulfonic acid
2 2-acrylamido-2-methylpropanesulfonic acid
3 al7ylsulfonic acid
4 2-phosphatoethyl methacrylate
The copolymers described in thus invention are prepared
6 by radical polymerization through the incorporation of a free
7 radical initiator. The initiator is chosen from those
8 commonly utilized to polymerize vinyl type monomers and would
9 include the following representative initiators:
2,2'-azo-bis-isobutyronitrile
11 4,4'-azo-bis-(4-cyanopentanoic acid)
12 t-butyl peroctoate
13 bouncily peroxide
14 laurel peroxide
methyl ethyl kitten peroxide
16 diisopropyl peroxycarbonate
17 The free radical initiator is normally used in amounts of from
18 0.01 to 2% by weight of the entire compound.
19 The materials of this invention can be polymerized directly
in a suitable mold to form contact lenses. The materials are
21 all thermosetting and thus various methods of fabrication can
22 be used. It is preferable to polymerize into sheet or rod stock
23 from which contact lenses may be machined.
24 It us preferred to use the conventional approach when
forming contact lenses such as used for polymethyl methacrylate
-16-
sty
'702
1 (PUMA). In this approach, the formulations are polymerized
2 directly into a sheet or rod and the contact lens blanks are
3 cut as buttons, discs or other preformed shapes which are then
4 machined to obtain the lens surfaces and the final lens form.
The resulting polymeric stock of buttons possesses the optical
6 qualities necessary to produce aberration-free oxygen permeable,
; 7 hard contact lenses in accordance with this invention.
8 Of course when referring to the-polysiloxanyl alkyd
9 ester vinyl monomer in the polymers of this invention, more
than one can be used in place of a single monomer as is true
11 with each of the monomeric recitations. Thus one or two
12 itaconate esters can be used in place of a single ester if
13 desired.
14 The following examples are given to illustrate the invent
lion and are not to be considered limiting thereof:
-17-
3lZ0~4~7
702
1 EXAMPLE I
2 A hard, oxygen permeable contact lens formulation was pro-
3 pared prom a comonomer mixture of dim ethyl itaconate (DIM),
4 methyl methacrylate (MA), methacryloyl oxypropyl tris(trimethyl-
5 sill) selection (TRIP), methacrylic acid (MA), and tetraethylene 'I
6 glycol dimethacrylate (TEGDM) using the free radical initiator
7 2,~'-azobisisobutyronitrile (AIBN). The formulation components
8 (shown in TABLE I in parts by weight) were thoroughly mixed,
9 transferred to test tubes, stopper Ed, degassed, then filled with
nitrogen. The test tubes were then placed on a water bath at
11 40C and allowed to polymerize for two days. The tubes were
12 then placed in a 60C oven for an additional two days, after
13 which the solid rods are removed from the tubes. The rods were
14 then subjected to conditioning for approximately eighteen hours
at 100C under vacuum then slowly cooled to room temperature
16 to produce a stress-free material. The conditioned rods were
17 then machined to discs of the size 3/16" by 1/2", which are of
18 the conventional form for hard polymethyl methacrylate lens
lug blanks.
The finished discs were then subjected to gamma radiation
21 in a Gamma Cell 200 instrument (made by Atomic Energy of Canada
22 Limited of Ottawa, Canada). The cell contained 1230 curies of
23 Cobalt 60 in the form of 20 pencils which produced a central
24 dose rate of 2.12 x 105 fads per cm3 per noun. The discs were
I irradiated under a nitrogen atmosphere and the total time of
26 exposure was adjusted to produce a total dose absorbed in the
27 material of from 1x106 fads (lMR) to 5x1O6 fads (5 MY).
-18-
~2~4407
/702
1 Both irradiated and non-irradiated discs were subjected
2 to distilled water extraction for 6 hours at 75C. The extract
3 was diluted to loom with distilled water and ultra violet
4 absorbency measurements were performed at three wavelengths.
The data in TABLE I clearly demonstrate the ability of gamma
6 radiation to significantly reduce the content of extractable
7 (residual) material i.e. unrequited monomer, in the lens blanks.
_19_
12~44?Q7
' 702
TABLE I
2 FORMULATION (parts by weight)
3 DIM 27. 5
4 MA 2 7.5
TRIP 45.0
6 TO GYM 3.0
7 MA 5.0
8 AIBN 0. 2
1 0 Sample wet gut, US Absorbency . of extract
Radiation level ems (grams) 205 no 215 no 245 no nanometers)
O MY, control 3.343 û.775 0.395 0.0795
12
MY 3.330 0.214 0.122 0.025
1 3
2 MY 3.400 0.089 0.052 0.015
14
3 MY 3.410 0.075 0.041 0.0115
4 MY 3.4û9 0.045 0.0225 0.009
16
MY 3.371 0.0315 0.015 0.003
17
I
~;2(114~7
~702
1 EXAMPLE I I
2 The hard, oxygen permeable lens formulation given in TABLE
3 II was prepared using the experimental procedures detailed in
4 Example I. The lens blanks were gamma irradiated under a vitro-
5 gun atmosphere to various total delivered dosages. Contact ',
6 lenses were prepared from these discs utilizing techniques
7 which are common in the manufacture of hard contact lenses.
8 The test lenses were standardized to the following prescript
9 lion:
Base curve radius 7.95 mm
11 Power -7.0 dotters
12 Central thickness 0.12 mm
13 Diameter 12 mm
14 The base curve of each lens was noted after manufacture and no-
checked after two days immersion in distilled water. The change
16 in the base curve radius as a function of radiation dosage is
17 presented in TABLE II and illustrates the effectiveness of the
18 gamma radiation process as a means of imparting dimensional
19 stability to contact lens.
~Z~14~07
t702 TABLE II
Formulation (parts by weight)
DIM 27.5
MA 27.5
TRIP 4~.0
TEGDM 5,0
MA 5.0
AIBN 0.2
Original Base curve* Dimensional
Radiation dosage base curve, mm After soak, mm change, mm
O MY, control 7.94 7.96 8.04-8.08 0.09-0.12 flattening
3 MY 7.94-7.96 7.97-8.01 0.03-0.05 flattening
5 MY 7.94-7.96 7.94-7.97 0.00-0.02 flattening**
* average of several test lenses
** within acceptable limits
-22-
~Z04407
702
EXAMPLE I I I
2 The hard, oxygen permeable lens formulations given in
3 TABLE III were prepared using the experimental procedures de-
4 tailed in Example I. The lens blanks were gamma irradiated
under a nitrogen atmosphere to various total delivered dosages.
6 Compressive strength at yield was determined using a TUNIS-
7 OLSEN testing machine under the following conditions:
8 Sample size - 3/16" x 1/2"
9 Temperature - 73~F
Testing rate - 0.05 inhuman
11 Multiple determinations were made and the average values are
12 reported in TABLE III. It is evident from the data that the
13 compressive strength of the lens materials is significantly
14 improved by radiation treatment at total levels as low as 2
Megarads.
~2C~44~7
02 TABLE III
',
Formulation (parts by weight)
A B C
DIM 27.5 27.5 27.5
MA 27.5 27.5 27.5
TRIP 45.0 45.0 45.0
TEGDM 3.0 4.0 5.0
MA 5.0 5.0 3.0
DMAEM* - - 2.0
AIBN 0.2 0.2 0.2
* dim ethyl amino ethyl methacrylate
Compressive strength at yield (psi)
Sample MY 2 MR4 MY 6 MY 8 MY 10 MY
_
Aye 13,340 13,240 13,290 13,450 13,500
B10,965 12,430 12,270 12,170 12,020 12,120
C9,270 12,070 11,710 12,320 12,220 11,920
Average deviation + 200 Sue
-24-
~2~Q~
/702 1 TABLE IV
2 The hard oxygen permeable lens formulation given in Table
3 III was prepared using the procedure detailed in Example I. The
lens blanks were irradiated with both electron beam and with
5 gamma while under a nitrogen atmosphere. i'
6 Standard permeability samples in the form of piano contact
7 lenses were machined from these samples to the following prescript
8 lion:
g Base curve radius - 8.00 mm
Power - Piano
11 Central Thickness - .20 mm
12 Diameter - 12.0 mm
13 Permeability was measured in an instrument designed after
14 ASTM D1434-66 wherein one side of the sample is subjected to
pure oxygen at a pressure of one atmosphere above atmospheric.
16 The oxygen that permeates through the lens sample is allowed
17 to expand on the other side of the sample against atmospheric
18 pressure in a capillary tube plugged with a droplet of mercury.
19 Rate of motion of the mercury plug is easily converted into
volume of paramount per unit time.
21 The system was calibrated by measurements made on materials
22 of known permeability.
23 Multiple determinations were made and average values are
24 reported in Table IV. This table shows that useful 2 Perle-
ability values are maintained after irradiation.
-25-
-
~2C~4407
702
TABLE IV
.
Megarads
Radiation Dose Radiation Type Permeability*
0 - 1~8
.005 Electron Beam 119
I 131
I " " 134
.1 " " 118
1 Gamma 119
2 " 119
3 " 115
4 " 114
" 110
*Permeability is given as 101 cm3-mm/sec,cm2,cmHg
.
I
SUE
02
1 Chile specific examples of this invention have been shown
2 and described, many variations are possible. Such variations
3 include the use of mixtures of monomers within the components
4 to make up the required percentages of each. For example,
two or more siloxanyl alkyd ester monomers can be used instead
6 of a single such monomer for that component of the system.
7 Similarly, two or more cross-linking agents can be used.
8 Conventional additives to the lenses such as colorants, tints
9 and the like may also be employed within the normal ranges of
such materials. In all cases, high energy radiation is used
11 to act as a second step or post polymerization in an attempt
12 to substantially completely polymerize polymeric material and
13 thus improve dimensional stability and lower unrequited monomer
14 to 1/2% by weight or less.
It is preferred that the contact lenses of the present
16 invention and the materials from which they are made have an
17 oxygen permeability in the range of from 38 to 500 cm3mm/cm2/
18 sec. cm Hug x 10-1 and a Rockwell hardness value of from 100
19 to 125 ASTM d-785 R scale and be formed of a polymer of dim ethyl
itaconate, methylmethacrylate, methacryloxyloxypropyl iris
21 (trimethylsilyl) selection, methacrylic acid and tetraethylene
22 glycol dimethacrylate. Such lenses can be worn in the eye
23 of a user for long time periods.
24
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