CA1098635A - Industrial production of cast plastic lenses - Google Patents
Industrial production of cast plastic lensesInfo
- Publication number
- CA1098635A CA1098635A CA255,947A CA255947A CA1098635A CA 1098635 A CA1098635 A CA 1098635A CA 255947 A CA255947 A CA 255947A CA 1098635 A CA1098635 A CA 1098635A
- Authority
- CA
- Canada
- Prior art keywords
- gamma
- silane
- beta
- group
- lens
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
- G02B1/04—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of organic materials, e.g. plastics
- G02B1/041—Lenses
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F18/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an acyloxy radical of a saturated carboxylic acid, of carbonic acid or of a haloformic acid
- C08F18/24—Esters of carbonic or haloformic acids
Abstract
Abstract of the Disclosure The process of the preparation of production quantities of lens devices fabricated from synthetic resinous substances, normally referred to as "plastic lenses". The process utilizes a molding formulation which enables re-usable mold cavities to be utilized, the formulation providing a proper balance between a number of processing parameters or variables, one of the primary parameters being the maintenance of a proper adherence or re-lease capability between the surface of the lens being fabricated and the surface of the mold cavity. Specifically, it has been found that a silane selected from the group consisting of:
Vinyltrichlorosilane Vinyltriacetoxysilane gamma-Glycidoxypropyltriethoxysilane Vinyltriethoxysilane gamma-methacryloxypropyltrimethoxysilane beta (3,4-Epoxycylohexyl)-ethyltrimethoxysilane Methylvinyldichlorosilane Vinyl-tris (beta-methoxyethoxy) silane Vinyltrimethoxysilane gamma-Aminopropyltriethoxysilane N-beta-(aminoethyl)-gamma aminopropyltrimethoxysilane when incorporated in the molding formulation controls the parameters so as to provide for controllable release of the lens product from the mold.
Vinyltrichlorosilane Vinyltriacetoxysilane gamma-Glycidoxypropyltriethoxysilane Vinyltriethoxysilane gamma-methacryloxypropyltrimethoxysilane beta (3,4-Epoxycylohexyl)-ethyltrimethoxysilane Methylvinyldichlorosilane Vinyl-tris (beta-methoxyethoxy) silane Vinyltrimethoxysilane gamma-Aminopropyltriethoxysilane N-beta-(aminoethyl)-gamma aminopropyltrimethoxysilane when incorporated in the molding formulation controls the parameters so as to provide for controllable release of the lens product from the mold.
Description
35ii Background of the Invention Field of the Inventl_ . This invention relates gener-ally to an a~ditive to a synthetic resin mixture of formulation for use in the produc-tion of plastic lens, and more specifically, to a group of silanes found suitable for this purpose, with the product being useful in lenses used for eye glasses.
Description of the Prior_Art. Lens devices fabricated from plastic resinous substances have been made in the past with the lens devices traditionally having been made from poly-carbonate resins such as diethylene glycol bis (allyl carbonate)which is known commercially in its monomeric form as allyl diglycol carbonate and in either its monomeric or polymerized form, as CR-39 (trademark of Pittsburg Plate Glass Company). It, there-fore, should be understood that these terms are interchangeable in the art, and that the use of any of these terms commonly identifies the same monomer.
Because of the clarity, high strength and high impact resistance of CR-39 in its polymerized form, it is suitable for use in plastic lenses for eye glasses. I'he wide acceptance is also due to the property of high resistance to discolorization and also its resistance to physical warping or distortion. A
more complete descrlption of this type of monomer and the manu-facture of this type of plastic lens can be found in the Beattle U.S. Patent 2,542,386. Still another material used ~or lenses for eye glasses is described in the Emerson et al U.S. Patent 3,297,422 which suggests the use of a starting material such as methyl methacrylate monomer. Other materials, such as copolymers of methyl methacrylate and CR-39 are known, one of which is shown in the Bond U.S. Patent 3,872,0~2.
While the manufacture of formulation of a composition of a monomer for preparing a lens is well known, the process for industrial production of a lens comprised of a polymer consisting i3~
of two or more monomers has been extremel~ difficult due to the problems generated due to erratic or partial release of the plastic lens fro~ the glass mold. The problem of release is normally resolved through control of the adherence of the surface of the plastic lens to the surface of the mold duriny curing within the mold and has been found to be dependent on many pro-cessing parameters or variables such as the cleanliness of the mold, the composition of the monomer mixture, the length of the curing cycle, the temperature of the curing cycle, the surface irregularities of the mold, and the shape and curvature of the mold as well as the techniques of those involved in the injection or casting process. To obtain high yields and thus make industrial production possible at acceptable rates, the adherence of the surface of the finished plastic lens product to the surface of the mold must be sufficient to firmly hold or retain the plastic lens against the mold surface through the curing stage, but yet sufficiently weak to allow cohcs}4e separation following cure.
In the past, control of the optical quality of the lens devices was obtained by control of -the monomer mixture.
When it was determined that the monomer mixture would produce a lens of a quality sufficient for optical use, then an examination of the casting, molding, or other production steps to be utilized revealed that the pre-release of the molded product from the surface of the mold (i.e. the release of the lens from the surface ~f the mold prior to the complete curing of the lens) would normally yield a product of unaccepted optical quality.
One prior art method used to control -the release is the use of mold surface lubricants or release agents such as stearic acid. Another mold lubricant is commonly known in the trade as Ortholeum 162, (trademark of E. I. duPont, deNemors and Company) its Code Name, Ortholeum 162 being a mixture of ~ ' , :. . . ,:
, .. - . . . .
mono and dialkylphospha-tes with a straight chain alkyl group of C16 to C18.
However, the known Tnold lubricants of this type have not provided the consis-tent control of the release of the lens from the mold when used with copolymer or multipolymer formulations and, consequently, the yield (i.e. the number of lenses from a particular run that can be used in the eye glasses) has been poor. That is~ there is a tendency of the lens to release erratically from the mold by either premature release from the mold or complete adherence.
If the lens releases prematurely, i.e., before the curing is comp]eted, the lens is usually unsuitable for optical purposes. On the other hand, if the lens does not release easily subsequent to curing, one can destroy both the plastic lens and the mold by attempting to open the mold by prying the plastic lens from the mold. In either case, the plastic lens product may be unsuitable for use in eye glasses. The strange part of this phenomena of release is that the use of additives which are known to act as lubricants by decreasing the adherence of the surface of the mold to the surface of the plastic do not yield consistent results. That is, the amount of lubricant can be held constant with identical polymers and in one case, the lens may not release from the mold and in another case, the lens may release from the mold prior to completion of the curing. It is believed that such irregular results are due to variation in technique processing parameters, mold variations or other undetermined variables.
A terpolymer has been used for plastic lenses that contain acrylic acid or methacrylic acid in minor amounts to produce a terpolymer that has ; the desired optical qualities for use in eye glasses yet provides high yields because the lens consis$ently releases from-the surface of the glass mold at the proper ti~e or can b- easily forced to release.
:
:
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The consistent release was somewhat surprising in that the acrylic and methacrylic acid were believecl to increase the adherence of the surface Oe the glass mold to the sur-~ace of the plastic lens. One aspect of the problem was the tendency of the surface of the mold to adhere too strongly to th~ surface of the plastic lens. Nevertheless, the addition of the third monomer in the polymeric mass has been found to increase the hardness of the plastic lens as well as to solve the problems of pre-release or over-adherence of the lens to the mold. However, while this process and terpolymer has proven s-lccess-ful for mass production of lenses under careeully controlled conditions, the transition of the process to full scale industrial process has not been easily accomplished because the expected yields, under indus-trial production conditions, have not matched those obtained under laboratory conditions.
One of the problems is that with lesser amounts of CR-39, the methacrylic acid begins to polymerize first, thus producing a block polymer rather than a copolymer. ~onse-quently, the amount of methacrylic acid used must be limitedto avoid the greying of the monomer which occurs due to block polymer formation. ~or example, with 98 parts CR-39, the maximum amount of methacrylic acid that can be used without greying is about lo 1%~ With a limited amount of methacrylic acid and because of other factors, a normal release of lenses erom the molds could not be obtained.
It was believed that the transition from mass production of plastic lenses under care-fully controlled conditions to normal industrial production of plastic lenses in which plastic lenses are cast, cured and polished in successive processing steps, wouldappear to be a straight-~orward step as long as the variables involved in the casting 6~;
and curing process were observed and -taken into considera-tion. Surprisingly, this has not been the case. It has been discovered that in spite o-f the close control of the many known variables, the industrial production of plastic lenses has been very costly because o~ that phenomenon known as "pre-release". As a general rule, it has been found that i~ the precentage of product subjected to pre-release exceeds 30% of the ~ tal cas-t lenses, then the process o~ producing lenses norma:Lly becomes uneconomical.
On the other hand, to make the process economical, it is also necessary to be able to fabricate about 200 castings from a single moldO However, as each lens is subject to operations o~ casting, curing, and subsequently, removal, these operations have a deteriorating ef~ect on the mold and, consequently, reduces the number o~ lenses which can be cast from a single mold. Thus, under industrial production, where the molds must be continually re-used to make the process economically sound for large quantity production of plastic lenses, some sort of balance must be achieved between the number o~ lenses that pre-release and ~; the length of the mold life. I~ the pre-release percentage is too low, the mold life decreases too rapidly; while, i~
the pre-release percentage is too high, the number of acceptable lenses produced becomes unacceptable~ The control of the known variables has not been sufficient to achieve a proper balance between the percentage o~ lenses that pre-release and the number of castings per moldO However, with the controlled addition of certain silanes, it has ~ been found that a dominant production variable is provided which wlll allo~ casting of plastic lenses o~ both copoly-mers and terpolymers with the desired release characteris$ics.
;3~
Brief Summary of the Invention Briefly, the present invention involves the d;.scovery that adding a silane to the molding compound, the silane being selected from the group consisting of:
R Si Xb a wherein "R" represents the organic functionality group, "X" represents the hydrolyzable functionality group, and "a" and "b" each represent integers rangi.ng from between 1 and 3.
According to the present invention, there is provided a poly-merization process comprising: preparing a monomer solution selected from the group consisting of a diethylene glycol bis (allyl carbonate) alone, and methyl methacrylate with diethylene glycol bis ~allyl carbonate); adding to said monomer solution to form a reacting mixture a lubricant, a catalyst from the group consisting of benzoyl peroxide and diisopropyl percarbonate, and a silane in an amount in excess of two parts per million of the monomer solution and in an amount sufficient to provide an acceptable pre-release value, said silane having the structural formula:
R Si ~
a o wherein "R" is selected.from the group consisting o~f vinyl, glycidoxypropyl, aminopropyl, beta-~3,4-spoxycyclohexyl)-ethyl, N-beta-(aminoethyl)-gamma-: aminopropyl, and methacryloxypropyl, "X" is selected from ~he group consisting of methoxy, ethoxy, acetoxy, chloro, methoxyethoxy, ethoxymethoxy, phenoxy, fluoro, bromo, iodo, propoxy, and butoxy, and "a" and "b" each represent integers ranging from between 1 and 3, with the proviso that when R is vinyl, .
X may be dichloro and methyl; and exposing said reactant mixture to ' .
.. : , . . . . . . . .
3~
a thermal treating ~one to polymerize said reactant mixture to form a polymer.
Thus, the organic functionality group may be a vinyl group, althougil other radica.ls are ~Iseful. Normally7 chain lengths from 2 to 4 carbon atoms are preferred in this moiety.
The hydrolyzable functional group may be as defined above or generally, any low molecular weight alkoxy ~ group or halogen end group, the alkoxy and group havi.ng up to C6. Examples of some of those silanes found useful are as follows:
Vinyltrichlorosilane Vinyltriacetoxysilane gamma-Glycidoxypropyltrimethoxysilane Vinyltriethoxysilane gamma-methacryloxypropyltrimethoxysilane beta (3,4-Epoxycycl~exyl)-ethyltrimethoxysilane Methylvinyldichlorosilane Vinyl-tris ~beta-methoxyethoxy) silane Vinyltrimethoxysilane gamma-Aminopropyltriethoxysilane N-beta-(Aminoethyl~-gamma-aminopropyltrimethoxysilane.
The molding compound is either a copolymer of methyl methacrylate and diethylene glycol bis (allyl carbonate) or a terpolymer camprised of methyl methacrylate diethylene : : -: - 6a -. .
`
- .
, . , . ~ . , - . ~
glycol bis (allyl carbona-te) and either acrylic acid or methacrylic acidO This compound produces lenses that can be economically manufactured using industrial production techniques. 0~ these silanes, the pre~erred silane is gamma-Glycido~ypropyltrimethoxysi:Lane.
Description of the Pre~erred Pr-oc-ess While the mixtur~s and cas-ting o~ plastic lenses is well known, the addition of the silanes to the mixture comprises the novel part o~ this process. In the present process, glass molds are used; however, metal molds can also be utilizedO
The lenses are cast in blan~s which are approximately 1/4 inch thick with a diameter o~ about 2-1/2 inches, and with one sur~ace convex and the other surface concave.
This configuration is required so that the lens blank can be gro~nd to the proper prescription. The castillg of this s~ape lens with monomers such as CR-39 is shown and described in the prior art Beattle Patent NoO 2,54~,386.
Silanes have been found to work effectively with the homopolymer of diethylene glycol bis (allyl carbonate), the copolymers o~ methyl methacrylate and diethylene glycol bis (allyl carbonate), and the terpolymer comprised of methyl methacrylate, diethylene glycol bis (allyl carbonate) and either acrylic acid or methacrylic acidO These polymers, : copolymexs, and terpolymers are, of course, commercially available~
In order to produce a lens suitable for use in eye glasses, one prepares and mi~es a solution o~ methyl metha- :
crylate containi.ng a catalyst such as benzoyl pero~ide or diisopropyl percarbonate and a UV absorber such as p-meth-o~ybenzylidene malonic acid dimethyl ester. After the solution has been mixed, it is dried by placing about 50 _ ' ~ - ' '' ' ' :, . ' ,' ' 5~
grams of anhydrous sodi~lm sulfa-te per 1000 ml. of solutionO Typically, a minimum o~ 50 grams o~ anhydrous sodium sulfate per 500 mlO of solution is sufficient to remove any water which may be in the solution. Next, one vacuum filters the solution through filter paper to remove the sodium sulfate. Next, a mold lubricant such as Ortholeum 162, available commerciall~ from the E.I. DuPont deNemours Corp. of Wilmington, Delaware, is stirred into the solutionO At this point, a reactant mixture is pre-pared containing a solutionof methyl methacrylate,diethylene glycol bis (allyl carbonate), and methacrylic acid, acrylic acid may be subs-tituted for the methacrylic acid. The solution and the container are then placed in a vacuum chamber where the entrapped or entrained air is removed. Vacuum treatment removes the air bubbles from the solution, thus reducing or eliminating the possibility of the plastic lens product having internal air bubbles.
Next, the evacuated container is pressurized with admission of nitrogen to about 15 psi. After pressurizing the container with nitrogen, the solution is then forced under pressure into the molds. Once the solution is in the molds, the mold is placed in an oven at 65C. for a minimum of about 3 hours, followed by raising the temperature from 65C. to 75C. over a minimum of about 4 hours, this being followed by ralsing the termperature ~rom 75C. to 100Co over a minimum of about l0 hours, whereupon the molds are removed from the oven and allowed to cool at room temperature.
As indicatedj it is a feature of the present invention to prepare a formulation through the addition of a silane selected from the group consisting of:
:
.
, .. . - - ,, .
. .
3~i Vinyltrichlorosilane Vinyltriacetoxysilane gamma-Glycidoxypropyltriethoxysilane Vinyltriethoxysilane gamma-methacryloxypropyltrimethoxysilane beta (~,4-Epoxycylohexyl)-ethyltrimethoxysilane Methylvinyldichlorosilane Vinyl-tris (beta-methoxyethoxy) silane Vinyltrimethoxysilane gamma-Aminopropyltriethoxysilane N-beta-(aminoethyl) -gamma aminopropyltrimethoxysilane to either a copolymer of methyl methacrylate and diethylene glycol bis (allyl carbonate) or a terpolymer comprised of methyl methacrylate, diethylene glycol bis (allyl carbonate3 and either acrylic acid or methacrylic acid for the production of a lens that can be economically manufactured using industrial production techniquesO
Of these silanes, the preferred silane is gamma-Glycidoxypropyltrimetho~ysilane. The following examples will illustrate the invention.
In order to manufacture a lens suitable for use in an eye glass, a solution of 2 grams of methyl methacrylate containing 1.6 grams o~ benzoyl peroxide and .15 grams oi a W absorber such as p-methoxybenzylidene malonic acid dimethyl ester was prepared and mixed. The mixture is dried by placing about 50 grams o-F anhydrous sodium sulfate per 1000 ml. of solution. Typically, a minimum of 50 grams of anhydrous sodium sulfate per 500 mlO of solution is sufficient to remove any residual water which may be in the solution. Next, one vacuum ~ilters the solution through filter paper to remove the sodium sulfate.
Therea~ter, .0010 gram of a~lubricant (Ortholeum 1623 was stirred i4to the soIution. At this point a reactant mixture is prepared co~taini4g the 2 grams of the ~olution -, .: .
of methyl methacry]ate, 98 grams by weight of diethylene glycol bis (allyl carbonate), and .0025 grams of gamma-Glycidoxypropyltriethoxysilane.
The solution and the container are then placed in a vacuum chamber where the air is removed. This serves to remove bubbles from the solution, thus eliminating the possibility of the finished product having entrained air. Next, the evacuated container is pressurized with nitrogen at about 15 psi. After pressurizing the container with nitrogenl the solution is then forced under pressure into the molds. Once the solution is in the molds, the mold is placed in an oven at 65C. for a minimum of about 3 hours, followed by raising the temperature from 65C. to about 75C. over a minimum of about 4 hours which is followed by raising the temperature from 75C. to 100C. over a minimum of about 10 hours, whereupon the molds are removed from the oven and allowed to cool at room temperature. Of the lens cast according to the Example l, it was found that the pre-release under industrial production was only 24%. This is an acceptable figure for industrial production.
Additional lenses were cast according to the process of Example 1 except that .0005 gram and .0015 gram of gamma-Glycidoxypropyltriethoxy-silane was added. With .0005 gram, the percentage of pre-release was 52%.
With .0015 gram, the percentage of pre-release was 21.5%. The latter per-centage was acceptable for industrial production.
The Examples of l and 2 were repeated except that a lens mold of different curvature was used. The procedure and results were as follows:
with .0005 gram of gamma-Glycidoxypropyltriethoxysilane, the pre-release was 50%;
'~ .
~ 3t~
with .0015 gram, the pre-release was 38%; and with .0025 gram, the pre-release was 22%. With this particular lens curvature, the latter percentage is acceptable.
EXAMPL~ 4 Further operations were conducted in accordance with the procedure of Example 1 in which the only components of the monomer mixture were the diethylene glycol bis (allyl carbonate) O[CH2CH20COO(C3Hs)]2, methyl methacrylate CH:
C(CH~)COOcH3 and an acid selected from the group consisting of acrylic acid and methacrylic acid, and benzoyl peroxide (C6HsC0~ 22. The earlier practice of designating the diethylene glycol bis (allyl carbonate) methyl methacrylate as being a first mixture of 100 parts in which the amounts of diethylene glycol bis (allyl carbonate) and methyl methacrylate totaled 100 parts and other materials were computed as a percentage of the diethylene glycol bis (allyl carbonate) and methyl methacrylate was continued.
In these operations, the amounts of diethylene glycol bis (allyl carbonate~ present in the formulation was varied from 72 parts to 98 parts (based on total monomer weight) and the methyl methacrylate balance was varied from 2 parts to 28 parts (based on the total monomer weight).
The acrylic acid and methacrylic ranged from 1/2 to 5% by weight of the mixture. The lenses produced were of the same optical quality as those with or without the silanes the lubricant or the W abs~rber. However, as expected, the yield of lenses varies according to the amounts of silanes and lubricants in the mixture.
Fr~om the above examples and further operations, it was concluded that the amount of silanes to be added to the monomer mixture should be in excess of ~ive parts per million ~or~ most;~lenses. Some lenses, depending on ~:
.
3~
the curva-ture, would req~ire a miniinum o~ two parts per million, while other lenses with a different curvature would require -fifteen par-ts per million to bring the pre-release down to a suitable value. In some extreme cases7 due to configuration or the like, as much as 200 parts per million of silane are required. Examples 2 and 3 illustrate the effects of two di~ferent lenses with five, fifteen and twenty-five parts per million of the monomer mixture (i.e., .0005 gram; .0015 gram, and .0025 gram)0 Finally, the lens preparation operations were conducted in accordance with Example 4 in which the methyl methacrylate and acrylic acid were left out but the amount of silane added to the mixture was .0005 gram) o0015 gram, and .0025 gram. In each of the examples, the familiar pattern of decrease in the pre-release of the lenses from the mold occurred with the increased amounts of silanes.
In order to determine the effect of silanes in a plastic lens having a single polymer of diethylene glycol bis (allyl carbonate), a set of lenses were cast with and without any silanes. The tests were conducted with diiso propyl percarbonate ranging up to 3.3% by weight; however, both catalysts work with the polymers, copolymers and terpolymers. Although more catalysts have been used, it is preferred to limit the concentration of catalysts to less than 5% when diisopropyl percarbonate is used and less than 2% when benzoyl peroxide is used.
A set of lens was cast with the monomer of diethylene glycol bis tallyl carbonate~ as described in Example 1 except no methyl methacrylate was used and no silanes were added to the mixture.~ The catalyst used was diisopropyl ' .. . , : :
- ': - : ' .
percarbonate rather than benzoyl peroxide. The results showed a pre-release o~ 42% ~rom the molds.
Example 6 was repeated except that 45 parts per million o~ the silane gamma-Glycidoxypropyltrimethoxysilane was added to the mixture. Only 28% o~ the lens pre-release with the silane.
With a single polymer len)3 o~ diethylene glycol bis (allyl carbonate) the silane performed the same -functlon of reducing the pre-release oi the lens ~rom the mold although a slightly greater amount of silanes was necessary - with the single polymer than the copolymers or terpolymers to obtain a pre-release ~igure less than 30%0 :
., ~ .
- . . .
Description of the Prior_Art. Lens devices fabricated from plastic resinous substances have been made in the past with the lens devices traditionally having been made from poly-carbonate resins such as diethylene glycol bis (allyl carbonate)which is known commercially in its monomeric form as allyl diglycol carbonate and in either its monomeric or polymerized form, as CR-39 (trademark of Pittsburg Plate Glass Company). It, there-fore, should be understood that these terms are interchangeable in the art, and that the use of any of these terms commonly identifies the same monomer.
Because of the clarity, high strength and high impact resistance of CR-39 in its polymerized form, it is suitable for use in plastic lenses for eye glasses. I'he wide acceptance is also due to the property of high resistance to discolorization and also its resistance to physical warping or distortion. A
more complete descrlption of this type of monomer and the manu-facture of this type of plastic lens can be found in the Beattle U.S. Patent 2,542,386. Still another material used ~or lenses for eye glasses is described in the Emerson et al U.S. Patent 3,297,422 which suggests the use of a starting material such as methyl methacrylate monomer. Other materials, such as copolymers of methyl methacrylate and CR-39 are known, one of which is shown in the Bond U.S. Patent 3,872,0~2.
While the manufacture of formulation of a composition of a monomer for preparing a lens is well known, the process for industrial production of a lens comprised of a polymer consisting i3~
of two or more monomers has been extremel~ difficult due to the problems generated due to erratic or partial release of the plastic lens fro~ the glass mold. The problem of release is normally resolved through control of the adherence of the surface of the plastic lens to the surface of the mold duriny curing within the mold and has been found to be dependent on many pro-cessing parameters or variables such as the cleanliness of the mold, the composition of the monomer mixture, the length of the curing cycle, the temperature of the curing cycle, the surface irregularities of the mold, and the shape and curvature of the mold as well as the techniques of those involved in the injection or casting process. To obtain high yields and thus make industrial production possible at acceptable rates, the adherence of the surface of the finished plastic lens product to the surface of the mold must be sufficient to firmly hold or retain the plastic lens against the mold surface through the curing stage, but yet sufficiently weak to allow cohcs}4e separation following cure.
In the past, control of the optical quality of the lens devices was obtained by control of -the monomer mixture.
When it was determined that the monomer mixture would produce a lens of a quality sufficient for optical use, then an examination of the casting, molding, or other production steps to be utilized revealed that the pre-release of the molded product from the surface of the mold (i.e. the release of the lens from the surface ~f the mold prior to the complete curing of the lens) would normally yield a product of unaccepted optical quality.
One prior art method used to control -the release is the use of mold surface lubricants or release agents such as stearic acid. Another mold lubricant is commonly known in the trade as Ortholeum 162, (trademark of E. I. duPont, deNemors and Company) its Code Name, Ortholeum 162 being a mixture of ~ ' , :. . . ,:
, .. - . . . .
mono and dialkylphospha-tes with a straight chain alkyl group of C16 to C18.
However, the known Tnold lubricants of this type have not provided the consis-tent control of the release of the lens from the mold when used with copolymer or multipolymer formulations and, consequently, the yield (i.e. the number of lenses from a particular run that can be used in the eye glasses) has been poor. That is~ there is a tendency of the lens to release erratically from the mold by either premature release from the mold or complete adherence.
If the lens releases prematurely, i.e., before the curing is comp]eted, the lens is usually unsuitable for optical purposes. On the other hand, if the lens does not release easily subsequent to curing, one can destroy both the plastic lens and the mold by attempting to open the mold by prying the plastic lens from the mold. In either case, the plastic lens product may be unsuitable for use in eye glasses. The strange part of this phenomena of release is that the use of additives which are known to act as lubricants by decreasing the adherence of the surface of the mold to the surface of the plastic do not yield consistent results. That is, the amount of lubricant can be held constant with identical polymers and in one case, the lens may not release from the mold and in another case, the lens may release from the mold prior to completion of the curing. It is believed that such irregular results are due to variation in technique processing parameters, mold variations or other undetermined variables.
A terpolymer has been used for plastic lenses that contain acrylic acid or methacrylic acid in minor amounts to produce a terpolymer that has ; the desired optical qualities for use in eye glasses yet provides high yields because the lens consis$ently releases from-the surface of the glass mold at the proper ti~e or can b- easily forced to release.
:
:
:
::
6~
The consistent release was somewhat surprising in that the acrylic and methacrylic acid were believecl to increase the adherence of the surface Oe the glass mold to the sur-~ace of the plastic lens. One aspect of the problem was the tendency of the surface of the mold to adhere too strongly to th~ surface of the plastic lens. Nevertheless, the addition of the third monomer in the polymeric mass has been found to increase the hardness of the plastic lens as well as to solve the problems of pre-release or over-adherence of the lens to the mold. However, while this process and terpolymer has proven s-lccess-ful for mass production of lenses under careeully controlled conditions, the transition of the process to full scale industrial process has not been easily accomplished because the expected yields, under indus-trial production conditions, have not matched those obtained under laboratory conditions.
One of the problems is that with lesser amounts of CR-39, the methacrylic acid begins to polymerize first, thus producing a block polymer rather than a copolymer. ~onse-quently, the amount of methacrylic acid used must be limitedto avoid the greying of the monomer which occurs due to block polymer formation. ~or example, with 98 parts CR-39, the maximum amount of methacrylic acid that can be used without greying is about lo 1%~ With a limited amount of methacrylic acid and because of other factors, a normal release of lenses erom the molds could not be obtained.
It was believed that the transition from mass production of plastic lenses under care-fully controlled conditions to normal industrial production of plastic lenses in which plastic lenses are cast, cured and polished in successive processing steps, wouldappear to be a straight-~orward step as long as the variables involved in the casting 6~;
and curing process were observed and -taken into considera-tion. Surprisingly, this has not been the case. It has been discovered that in spite o-f the close control of the many known variables, the industrial production of plastic lenses has been very costly because o~ that phenomenon known as "pre-release". As a general rule, it has been found that i~ the precentage of product subjected to pre-release exceeds 30% of the ~ tal cas-t lenses, then the process o~ producing lenses norma:Lly becomes uneconomical.
On the other hand, to make the process economical, it is also necessary to be able to fabricate about 200 castings from a single moldO However, as each lens is subject to operations o~ casting, curing, and subsequently, removal, these operations have a deteriorating ef~ect on the mold and, consequently, reduces the number o~ lenses which can be cast from a single mold. Thus, under industrial production, where the molds must be continually re-used to make the process economically sound for large quantity production of plastic lenses, some sort of balance must be achieved between the number o~ lenses that pre-release and ~; the length of the mold life. I~ the pre-release percentage is too low, the mold life decreases too rapidly; while, i~
the pre-release percentage is too high, the number of acceptable lenses produced becomes unacceptable~ The control of the known variables has not been sufficient to achieve a proper balance between the percentage o~ lenses that pre-release and the number of castings per moldO However, with the controlled addition of certain silanes, it has ~ been found that a dominant production variable is provided which wlll allo~ casting of plastic lenses o~ both copoly-mers and terpolymers with the desired release characteris$ics.
;3~
Brief Summary of the Invention Briefly, the present invention involves the d;.scovery that adding a silane to the molding compound, the silane being selected from the group consisting of:
R Si Xb a wherein "R" represents the organic functionality group, "X" represents the hydrolyzable functionality group, and "a" and "b" each represent integers rangi.ng from between 1 and 3.
According to the present invention, there is provided a poly-merization process comprising: preparing a monomer solution selected from the group consisting of a diethylene glycol bis (allyl carbonate) alone, and methyl methacrylate with diethylene glycol bis ~allyl carbonate); adding to said monomer solution to form a reacting mixture a lubricant, a catalyst from the group consisting of benzoyl peroxide and diisopropyl percarbonate, and a silane in an amount in excess of two parts per million of the monomer solution and in an amount sufficient to provide an acceptable pre-release value, said silane having the structural formula:
R Si ~
a o wherein "R" is selected.from the group consisting o~f vinyl, glycidoxypropyl, aminopropyl, beta-~3,4-spoxycyclohexyl)-ethyl, N-beta-(aminoethyl)-gamma-: aminopropyl, and methacryloxypropyl, "X" is selected from ~he group consisting of methoxy, ethoxy, acetoxy, chloro, methoxyethoxy, ethoxymethoxy, phenoxy, fluoro, bromo, iodo, propoxy, and butoxy, and "a" and "b" each represent integers ranging from between 1 and 3, with the proviso that when R is vinyl, .
X may be dichloro and methyl; and exposing said reactant mixture to ' .
.. : , . . . . . . . .
3~
a thermal treating ~one to polymerize said reactant mixture to form a polymer.
Thus, the organic functionality group may be a vinyl group, althougil other radica.ls are ~Iseful. Normally7 chain lengths from 2 to 4 carbon atoms are preferred in this moiety.
The hydrolyzable functional group may be as defined above or generally, any low molecular weight alkoxy ~ group or halogen end group, the alkoxy and group havi.ng up to C6. Examples of some of those silanes found useful are as follows:
Vinyltrichlorosilane Vinyltriacetoxysilane gamma-Glycidoxypropyltrimethoxysilane Vinyltriethoxysilane gamma-methacryloxypropyltrimethoxysilane beta (3,4-Epoxycycl~exyl)-ethyltrimethoxysilane Methylvinyldichlorosilane Vinyl-tris ~beta-methoxyethoxy) silane Vinyltrimethoxysilane gamma-Aminopropyltriethoxysilane N-beta-(Aminoethyl~-gamma-aminopropyltrimethoxysilane.
The molding compound is either a copolymer of methyl methacrylate and diethylene glycol bis (allyl carbonate) or a terpolymer camprised of methyl methacrylate diethylene : : -: - 6a -. .
`
- .
, . , . ~ . , - . ~
glycol bis (allyl carbona-te) and either acrylic acid or methacrylic acidO This compound produces lenses that can be economically manufactured using industrial production techniques. 0~ these silanes, the pre~erred silane is gamma-Glycido~ypropyltrimethoxysi:Lane.
Description of the Pre~erred Pr-oc-ess While the mixtur~s and cas-ting o~ plastic lenses is well known, the addition of the silanes to the mixture comprises the novel part o~ this process. In the present process, glass molds are used; however, metal molds can also be utilizedO
The lenses are cast in blan~s which are approximately 1/4 inch thick with a diameter o~ about 2-1/2 inches, and with one sur~ace convex and the other surface concave.
This configuration is required so that the lens blank can be gro~nd to the proper prescription. The castillg of this s~ape lens with monomers such as CR-39 is shown and described in the prior art Beattle Patent NoO 2,54~,386.
Silanes have been found to work effectively with the homopolymer of diethylene glycol bis (allyl carbonate), the copolymers o~ methyl methacrylate and diethylene glycol bis (allyl carbonate), and the terpolymer comprised of methyl methacrylate, diethylene glycol bis (allyl carbonate) and either acrylic acid or methacrylic acidO These polymers, : copolymexs, and terpolymers are, of course, commercially available~
In order to produce a lens suitable for use in eye glasses, one prepares and mi~es a solution o~ methyl metha- :
crylate containi.ng a catalyst such as benzoyl pero~ide or diisopropyl percarbonate and a UV absorber such as p-meth-o~ybenzylidene malonic acid dimethyl ester. After the solution has been mixed, it is dried by placing about 50 _ ' ~ - ' '' ' ' :, . ' ,' ' 5~
grams of anhydrous sodi~lm sulfa-te per 1000 ml. of solutionO Typically, a minimum o~ 50 grams o~ anhydrous sodium sulfate per 500 mlO of solution is sufficient to remove any water which may be in the solution. Next, one vacuum filters the solution through filter paper to remove the sodium sulfate. Next, a mold lubricant such as Ortholeum 162, available commerciall~ from the E.I. DuPont deNemours Corp. of Wilmington, Delaware, is stirred into the solutionO At this point, a reactant mixture is pre-pared containing a solutionof methyl methacrylate,diethylene glycol bis (allyl carbonate), and methacrylic acid, acrylic acid may be subs-tituted for the methacrylic acid. The solution and the container are then placed in a vacuum chamber where the entrapped or entrained air is removed. Vacuum treatment removes the air bubbles from the solution, thus reducing or eliminating the possibility of the plastic lens product having internal air bubbles.
Next, the evacuated container is pressurized with admission of nitrogen to about 15 psi. After pressurizing the container with nitrogen, the solution is then forced under pressure into the molds. Once the solution is in the molds, the mold is placed in an oven at 65C. for a minimum of about 3 hours, followed by raising the temperature from 65C. to 75C. over a minimum of about 4 hours, this being followed by ralsing the termperature ~rom 75C. to 100Co over a minimum of about l0 hours, whereupon the molds are removed from the oven and allowed to cool at room temperature.
As indicatedj it is a feature of the present invention to prepare a formulation through the addition of a silane selected from the group consisting of:
:
.
, .. . - - ,, .
. .
3~i Vinyltrichlorosilane Vinyltriacetoxysilane gamma-Glycidoxypropyltriethoxysilane Vinyltriethoxysilane gamma-methacryloxypropyltrimethoxysilane beta (~,4-Epoxycylohexyl)-ethyltrimethoxysilane Methylvinyldichlorosilane Vinyl-tris (beta-methoxyethoxy) silane Vinyltrimethoxysilane gamma-Aminopropyltriethoxysilane N-beta-(aminoethyl) -gamma aminopropyltrimethoxysilane to either a copolymer of methyl methacrylate and diethylene glycol bis (allyl carbonate) or a terpolymer comprised of methyl methacrylate, diethylene glycol bis (allyl carbonate3 and either acrylic acid or methacrylic acid for the production of a lens that can be economically manufactured using industrial production techniquesO
Of these silanes, the preferred silane is gamma-Glycidoxypropyltrimetho~ysilane. The following examples will illustrate the invention.
In order to manufacture a lens suitable for use in an eye glass, a solution of 2 grams of methyl methacrylate containing 1.6 grams o~ benzoyl peroxide and .15 grams oi a W absorber such as p-methoxybenzylidene malonic acid dimethyl ester was prepared and mixed. The mixture is dried by placing about 50 grams o-F anhydrous sodium sulfate per 1000 ml. of solution. Typically, a minimum of 50 grams of anhydrous sodium sulfate per 500 mlO of solution is sufficient to remove any residual water which may be in the solution. Next, one vacuum ~ilters the solution through filter paper to remove the sodium sulfate.
Therea~ter, .0010 gram of a~lubricant (Ortholeum 1623 was stirred i4to the soIution. At this point a reactant mixture is prepared co~taini4g the 2 grams of the ~olution -, .: .
of methyl methacry]ate, 98 grams by weight of diethylene glycol bis (allyl carbonate), and .0025 grams of gamma-Glycidoxypropyltriethoxysilane.
The solution and the container are then placed in a vacuum chamber where the air is removed. This serves to remove bubbles from the solution, thus eliminating the possibility of the finished product having entrained air. Next, the evacuated container is pressurized with nitrogen at about 15 psi. After pressurizing the container with nitrogenl the solution is then forced under pressure into the molds. Once the solution is in the molds, the mold is placed in an oven at 65C. for a minimum of about 3 hours, followed by raising the temperature from 65C. to about 75C. over a minimum of about 4 hours which is followed by raising the temperature from 75C. to 100C. over a minimum of about 10 hours, whereupon the molds are removed from the oven and allowed to cool at room temperature. Of the lens cast according to the Example l, it was found that the pre-release under industrial production was only 24%. This is an acceptable figure for industrial production.
Additional lenses were cast according to the process of Example 1 except that .0005 gram and .0015 gram of gamma-Glycidoxypropyltriethoxy-silane was added. With .0005 gram, the percentage of pre-release was 52%.
With .0015 gram, the percentage of pre-release was 21.5%. The latter per-centage was acceptable for industrial production.
The Examples of l and 2 were repeated except that a lens mold of different curvature was used. The procedure and results were as follows:
with .0005 gram of gamma-Glycidoxypropyltriethoxysilane, the pre-release was 50%;
'~ .
~ 3t~
with .0015 gram, the pre-release was 38%; and with .0025 gram, the pre-release was 22%. With this particular lens curvature, the latter percentage is acceptable.
EXAMPL~ 4 Further operations were conducted in accordance with the procedure of Example 1 in which the only components of the monomer mixture were the diethylene glycol bis (allyl carbonate) O[CH2CH20COO(C3Hs)]2, methyl methacrylate CH:
C(CH~)COOcH3 and an acid selected from the group consisting of acrylic acid and methacrylic acid, and benzoyl peroxide (C6HsC0~ 22. The earlier practice of designating the diethylene glycol bis (allyl carbonate) methyl methacrylate as being a first mixture of 100 parts in which the amounts of diethylene glycol bis (allyl carbonate) and methyl methacrylate totaled 100 parts and other materials were computed as a percentage of the diethylene glycol bis (allyl carbonate) and methyl methacrylate was continued.
In these operations, the amounts of diethylene glycol bis (allyl carbonate~ present in the formulation was varied from 72 parts to 98 parts (based on total monomer weight) and the methyl methacrylate balance was varied from 2 parts to 28 parts (based on the total monomer weight).
The acrylic acid and methacrylic ranged from 1/2 to 5% by weight of the mixture. The lenses produced were of the same optical quality as those with or without the silanes the lubricant or the W abs~rber. However, as expected, the yield of lenses varies according to the amounts of silanes and lubricants in the mixture.
Fr~om the above examples and further operations, it was concluded that the amount of silanes to be added to the monomer mixture should be in excess of ~ive parts per million ~or~ most;~lenses. Some lenses, depending on ~:
.
3~
the curva-ture, would req~ire a miniinum o~ two parts per million, while other lenses with a different curvature would require -fifteen par-ts per million to bring the pre-release down to a suitable value. In some extreme cases7 due to configuration or the like, as much as 200 parts per million of silane are required. Examples 2 and 3 illustrate the effects of two di~ferent lenses with five, fifteen and twenty-five parts per million of the monomer mixture (i.e., .0005 gram; .0015 gram, and .0025 gram)0 Finally, the lens preparation operations were conducted in accordance with Example 4 in which the methyl methacrylate and acrylic acid were left out but the amount of silane added to the mixture was .0005 gram) o0015 gram, and .0025 gram. In each of the examples, the familiar pattern of decrease in the pre-release of the lenses from the mold occurred with the increased amounts of silanes.
In order to determine the effect of silanes in a plastic lens having a single polymer of diethylene glycol bis (allyl carbonate), a set of lenses were cast with and without any silanes. The tests were conducted with diiso propyl percarbonate ranging up to 3.3% by weight; however, both catalysts work with the polymers, copolymers and terpolymers. Although more catalysts have been used, it is preferred to limit the concentration of catalysts to less than 5% when diisopropyl percarbonate is used and less than 2% when benzoyl peroxide is used.
A set of lens was cast with the monomer of diethylene glycol bis tallyl carbonate~ as described in Example 1 except no methyl methacrylate was used and no silanes were added to the mixture.~ The catalyst used was diisopropyl ' .. . , : :
- ': - : ' .
percarbonate rather than benzoyl peroxide. The results showed a pre-release o~ 42% ~rom the molds.
Example 6 was repeated except that 45 parts per million o~ the silane gamma-Glycidoxypropyltrimethoxysilane was added to the mixture. Only 28% o~ the lens pre-release with the silane.
With a single polymer len)3 o~ diethylene glycol bis (allyl carbonate) the silane performed the same -functlon of reducing the pre-release oi the lens ~rom the mold although a slightly greater amount of silanes was necessary - with the single polymer than the copolymers or terpolymers to obtain a pre-release ~igure less than 30%0 :
., ~ .
- . . .
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A polymerization process comprising: preparing a monomer solution selected from the group consisting of a diethylene glycol bis (allyl carbon-ate) alone, and methyl methacrylate with diethylene glycol bis (allyl carbon-ate); adding to said monomer solution to form a reacting mixture a lubricant, a catalyst from the group consisting of benzoyl peroxide and diisopropyl percarbonate, and a silane in an amount in excess of two parts per million of the monomer solution and in an amount sufficient to provide an acceptable pre-release value, said silane having the structural formula:
RaSi Xb wherein "R" is selected from the group consisting of vinyl, glycidoxypropyl, aminopropyl, beta-(3,4-epoxycyclohexyl)-ethyl, N-beta-(aminoethyl)-gamma-aminopropyl, and methacryloxypropyl, "X" is selected from the group consisting of methoxy, ethoxy acetoxy, chloro, methoxyethoxy, ethoxymethoxy, phenoxy, fluoro, bromo, iodo, propoxy, and butoxy, and "a" and "b" each represent integers ranging from between 1 and 3, with the proviso that when R is vinyl, X may be dichloro and methyl; and exposing said reactant mixture to a thermal treating zone to polymerize said reactant mixture to form a polymer.
RaSi Xb wherein "R" is selected from the group consisting of vinyl, glycidoxypropyl, aminopropyl, beta-(3,4-epoxycyclohexyl)-ethyl, N-beta-(aminoethyl)-gamma-aminopropyl, and methacryloxypropyl, "X" is selected from the group consisting of methoxy, ethoxy acetoxy, chloro, methoxyethoxy, ethoxymethoxy, phenoxy, fluoro, bromo, iodo, propoxy, and butoxy, and "a" and "b" each represent integers ranging from between 1 and 3, with the proviso that when R is vinyl, X may be dichloro and methyl; and exposing said reactant mixture to a thermal treating zone to polymerize said reactant mixture to form a polymer.
2. The invention of claim 1, wherein an acid selected from the group consisting of acrylic acid and methacrylic acid is added to said reactant mixture.
3. The invention of claim 1, wherein said silane comprises gamma-glycidoxypropyltrimethoxysilane in excess of five parts per million.
4. The invention of claim 3, wherein gamma-glycidoxypropyltrimethoxy-silane is present in an amount of between five parts per million and twenty-five parts per million.
5. A process according to claim l, wherein said silane is selected from a group consisting of vinyltrichlorosilane, vinyltriacetoxysilane, gamma-glycidoxypropyltrimethoxysilane, vinyltriethoxysilane, gamma-methacryloxypropyltrimethoxysilane, beta-(3,4-epoxycyclohexyl)-ethyltri-methoxysilane, methylvinyldichlorosilane, vinyl-tris (beta-methoxyethoxy) silane, vinyl trimethoxysilane, gamma-aminopropyltriethoxysilane, and N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane.
6. A polymerization process according to claim 1 for preparing a polymerized lens comprising: adding to a monomer solution of diethylene glycol bis (allyl carbonate) a lubricant, a catalyst selected from the group consisting of benzoyl peroxide and diisopropyl percarbonate ranging from between about 1% to 5% by weight of said monomer solution, and said silane; exposing said reactant mixture to a thermal treating zone to polymerize said reactant mixture to form a polymer; and casting said polymer in glass or metal molds to form a lens blank from which finished lenses are ground.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US60936675A | 1975-09-02 | 1975-09-02 | |
| US609,366 | 1975-09-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1098635A true CA1098635A (en) | 1981-03-31 |
Family
ID=24440492
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA255,947A Expired CA1098635A (en) | 1975-09-02 | 1976-06-29 | Industrial production of cast plastic lenses |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS5229885A (en) |
| BE (1) | BE844656A (en) |
| BR (1) | BR7604994A (en) |
| CA (1) | CA1098635A (en) |
| DE (1) | DE2636239A1 (en) |
| FR (1) | FR2322884A1 (en) |
| GB (1) | GB1542119A (en) |
| IT (1) | IT1065377B (en) |
| NL (1) | NL7608037A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6175301A (en) * | 1984-09-21 | 1986-04-17 | Asahi Glass Co Ltd | Synthetic resin lens |
| US4957981A (en) * | 1989-02-10 | 1990-09-18 | Akzo N.V. | Interpenetrating polymer network of an aliphatic polyol(allyl carbonate) and epoxy resin |
-
1976
- 1976-06-29 GB GB2692976A patent/GB1542119A/en not_active Expired
- 1976-06-29 CA CA255,947A patent/CA1098635A/en not_active Expired
- 1976-07-20 NL NL7608037A patent/NL7608037A/en not_active Application Discontinuation
- 1976-07-23 FR FR7622673A patent/FR2322884A1/en active Granted
- 1976-07-29 BE BE169355A patent/BE844656A/en unknown
- 1976-07-30 BR BR7604994A patent/BR7604994A/en unknown
- 1976-08-12 DE DE19762636239 patent/DE2636239A1/en not_active Withdrawn
- 1976-08-26 JP JP10214476A patent/JPS5229885A/en active Pending
- 1976-08-30 IT IT2665876A patent/IT1065377B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| DE2636239A1 (en) | 1977-03-10 |
| BE844656A (en) | 1976-11-16 |
| BR7604994A (en) | 1977-08-09 |
| FR2322884A1 (en) | 1977-04-01 |
| IT1065377B (en) | 1985-02-25 |
| JPS5229885A (en) | 1977-03-07 |
| NL7608037A (en) | 1977-03-04 |
| GB1542119A (en) | 1979-03-14 |
| FR2322884B1 (en) | 1978-10-20 |
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