CA1149563A - Soft contact lens composition and method - Google Patents
Soft contact lens composition and methodInfo
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- CA1149563A CA1149563A CA000412101A CA412101A CA1149563A CA 1149563 A CA1149563 A CA 1149563A CA 000412101 A CA000412101 A CA 000412101A CA 412101 A CA412101 A CA 412101A CA 1149563 A CA1149563 A CA 1149563A
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Abstract
Abstract of the Disclosure A soft contact lens is produced by pouring an excess amount of an original solution for producing a soft contact lens into a concave die; placing a convex die on said concave die and overflowing the excess of said original solution to thereby uniformly fill said original solution in a space between said concave die and said convex die; gelling said original solution between the two dies to form therebetween a lens having a tensile strength of at least about 0.1 kgf/cm2; immersing said lens and said two dies in a liquid to peel said lens from said dies; and extracting the thus-peeled lens via an extraction treatment with water. This process has the advantage of providing a lens which is both optically homogenous and free from bubbles.
Description
i63 This application is a divisional application of Serial No. 311,027, filed on September 11, 1978 which relates to an "original solution" for producing a soft contact lens.
The present invention provides a process for producing in a facile manner a high-quality soft contact lens with little deviation in quality at a high yield.
The present invention provides a process for producing a soft con-tact lens by filling an original solution into a space between a pair of concave and convex dies, gelling the original solution, peeling the resultant gelled polymcr from the dies and finally extracting via water treatment. The "original solution" is preferably a mixture of monomers and/or polymers, as described hereinafter together with a suitable solvent and optional ingredients also set forth below.
In its generic aspect, the invention provides a process for pro-ducing the soft contact lens which comprises: pouring an excess amount of an original solution for producing a soft contact lens into a concave die; placing a convex die on said concave die and overflowing the excess of said original solution to thereby uniformly fill said original solution in a space between said concave die and said convex die; gelling said original solution between ~0 the two dies to form therebetween a lens having a tensile strength of at least a~out 0~1 kgf/cm2; immersing said lens and said two dies in a liquid to peel said lens from said dies; and extracting the thus-peeled lens via an extraction treatment with water.
In accordance with subgeneric aspects of the invention, the original solution has a coefficient of gellation contraction at the same temperature and pressure of less than about 5% by volume. In one embodiment of the inven-tion, the original solution contains N-vinyl lactam and a lower alkyl ester of 5~3 acrylic acid or methacrylic acid. In another embodiment, the original solution contains a polymer of a lower alkyl ester of methacrylic acid having an ethylcnic double bond in the side chain and N-vinyl lactam. The two dies are preferably made of glass, and the convex die preferably has a non-interference surface.
In a preferred embodiment, the gellation step is caused by heating.
A preferred embodiment of tlle peeling step utilizes a dimethyl sulfoxide water mixture.
The original solution preferably contains, (i) a component A selected from the group consisting of monomers ~ld post cross-linkable hydrophilic polymers wherein the monomers yield a hydro-philic component when polymerized;
~ ii) a component B selected from the group consisting of monomers and post cross-linkable hydrophobic polymers wherein the monomers yield a hydrophobic component when polymerized; and (iii) a suitable solvent C
the weigllt of ratio of A:B being from about 85:15 to about 55:~5 and the amount of solvent C being about 5 to 95% by weight.
It is to be understood that by the term "monomer" as defined above ~1) there is included the partially polymerized form which has not reached the stage of gellation, particularly with respect to the monomer component B.
Through the present invention it is possible to obtain a soft contact lens which is optically homogenous and without bubbles, no matter what the shape of the lens may be. Another problem that is avoided according to the present invention is the problem of "hollows", which may be caused through polymerization contraction. In some prior art methods an original solution flows slightly inside the dies, so that a memory of such flow develops after 5~3 the hydration. A further problem avoided by the present invention concerns the problems with finishing lenses made by polymerization contraction, such finishing not being required for the present invention.
Theprocess for producing a soft contact lens according to the present invention consists mainly of the following four steps: -(1) a filling step
The present invention provides a process for producing in a facile manner a high-quality soft contact lens with little deviation in quality at a high yield.
The present invention provides a process for producing a soft con-tact lens by filling an original solution into a space between a pair of concave and convex dies, gelling the original solution, peeling the resultant gelled polymcr from the dies and finally extracting via water treatment. The "original solution" is preferably a mixture of monomers and/or polymers, as described hereinafter together with a suitable solvent and optional ingredients also set forth below.
In its generic aspect, the invention provides a process for pro-ducing the soft contact lens which comprises: pouring an excess amount of an original solution for producing a soft contact lens into a concave die; placing a convex die on said concave die and overflowing the excess of said original solution to thereby uniformly fill said original solution in a space between said concave die and said convex die; gelling said original solution between ~0 the two dies to form therebetween a lens having a tensile strength of at least a~out 0~1 kgf/cm2; immersing said lens and said two dies in a liquid to peel said lens from said dies; and extracting the thus-peeled lens via an extraction treatment with water.
In accordance with subgeneric aspects of the invention, the original solution has a coefficient of gellation contraction at the same temperature and pressure of less than about 5% by volume. In one embodiment of the inven-tion, the original solution contains N-vinyl lactam and a lower alkyl ester of 5~3 acrylic acid or methacrylic acid. In another embodiment, the original solution contains a polymer of a lower alkyl ester of methacrylic acid having an ethylcnic double bond in the side chain and N-vinyl lactam. The two dies are preferably made of glass, and the convex die preferably has a non-interference surface.
In a preferred embodiment, the gellation step is caused by heating.
A preferred embodiment of tlle peeling step utilizes a dimethyl sulfoxide water mixture.
The original solution preferably contains, (i) a component A selected from the group consisting of monomers ~ld post cross-linkable hydrophilic polymers wherein the monomers yield a hydro-philic component when polymerized;
~ ii) a component B selected from the group consisting of monomers and post cross-linkable hydrophobic polymers wherein the monomers yield a hydrophobic component when polymerized; and (iii) a suitable solvent C
the weigllt of ratio of A:B being from about 85:15 to about 55:~5 and the amount of solvent C being about 5 to 95% by weight.
It is to be understood that by the term "monomer" as defined above ~1) there is included the partially polymerized form which has not reached the stage of gellation, particularly with respect to the monomer component B.
Through the present invention it is possible to obtain a soft contact lens which is optically homogenous and without bubbles, no matter what the shape of the lens may be. Another problem that is avoided according to the present invention is the problem of "hollows", which may be caused through polymerization contraction. In some prior art methods an original solution flows slightly inside the dies, so that a memory of such flow develops after 5~3 the hydration. A further problem avoided by the present invention concerns the problems with finishing lenses made by polymerization contraction, such finishing not being required for the present invention.
Theprocess for producing a soft contact lens according to the present invention consists mainly of the following four steps: -(1) a filling step
(2) a gellation step
(3) a peeling step (~) an extracting step In the filling step an original solution for producing a soft con-tact lens is filled in a space between a pair of concave and convex dies. The "original solution" is preferably as defined above. In addition to the above, a cross-linking agent may be used and a polymerization initiator may also be included .
As monomer for the component A there may be mentioned an N-vinyl lactam such as N-vinyl pyrrolidone, N-vinyl piperidone and N-vinyl caprolac-tam; N-vinyl oxa7olidone; a hydroxy lower alkyl ester of acrylic acid or meth-acrylic acid such as hydroxyethyl or hydroxypropyl ester of acrylic acid or methacrylic acid; glycerin monoacrylate or glycerin monomethacrylate; and an ~0 ortho-lactone having a hydrophilic group. As used above and throughout the dcscription of the invention, as preferred lower alkyl may be mentioned alkyl of up to 6 carbon atoms.
The hydrophilic polymer of the component A is a post cross-linkable hydropllilic polymer having functional group (s) adequate to form a cross-linkage between one hydrophilic polymer and another (post cross-linking). Illustrative of such hydrophilic polymer is the p~r~duct obtained by (co) polymerizing one or more monomeric components A and, if necessary, a monomer for introducing , functional group(s) to a polymer (functional group-introducing monomer). As said functional group-introducing monomers there may be mentioned n-butoxy-methylacrylamide, glycidyl methacrylate, vinylene carbonate, hydroxyethyl methacrylate, hydroxyethyl acrylate, vinyl methacrylate, vinyl acrylate, meth-acrylic acid and acrylic acid. The copolymerization ratio of the monomer to the functional group-introducing monomer is preferably within the range of about 1000:1 to about 10:1. Of those illustrated above especially preferred is the product obtained by copolymerizing N-vinyl pyrrolidone as the monomer and vinylene carbonate as the functional group-introducing monomer.
Asanotller example of such a hydrophylic polymer, polyvinyl alcohol may be cited. In this case, hydroxyl groups in the polymer enable a post cross-linkillg reaction to take place; therefore, a new functional group need not be introduced. The post cross-linking reaction may be carried out by using a polyvalent isocyanate, a polyvalent aldehyde or methylol melamine as a post cross-linking agent.
A monomer of component B gives a hydrophobic component when poly-merized, which neither swells nor dissolves in water even though it is not cross-linked. As such monomers, there may be cited lower alkyl esters of acrylic acid or methacrylic acid (for example, methyl methacrylate); unsaturated ~0 nitriles such as acrylonitrile or methacrylonitrile; aromatic olefins such as styrelle and hydrophobic ortholactones.
I~hen monomers are used as said component A and said component B, it is desirable that one monomer is unlikely to be copolymerized with the other mollolller, and it is also desirable that monomer reactivity ratios are:
l/rA>l and VrB~l ~wherein rA is a reactivity ratio of the monomer of the component A to the monomer of the component B, and the ratio of the possibility that A is added to -- 'I --lg563 an A -terminated polymer to the possibility that B is added thereto; rB is a reactivity ratio of the monomer of the component B to the monomer of the compollellt A~) In this case, when acrylic acid or methacrylic acid is added in an amount up to about 5% by weight based on the entire monomers as a third monomer component, it becomes possible to raise the water content without lowering the strength of the lens.
Tlle hydrophobic polymer of the component B is a post cross-linkable polymer having functional group(s) adequate for forming a cross-linkage between one llydrophobic polymer and another (post cross-linking) and neither swells nor 1~ dissolves in water. Representative of such post cross-linkable hydrophobic polymers is the product obtained by (co) polymerizing one or more monomeric components B and, if necessary with, one or more members of the functional group-introducing monomers mentioned above. It is preferable that the copolymerization composition ratio of the monomer to the aforesaid functional groLIp-introducing monomer generally ranges from about 1000:1 to about 10:1. As a hydrophobic polymer, a noll-cross-linkable polymer, for example, polyvinyl butyral may be used in an admixture with a post cross-linkable polymer.
Both in the case of polymers of component A and polymer of component B, when a hydroxyl group is contained as a functional group, it is possible ~0 to render said polymer post cross-linkable by esterifying said hydroxyl group with, for example, methacrylic acid to thereby introduce an ethylenic double bond to the side chain.
As stated above, a combination of component A and component B such as to give an "original solution" whose coefficient of gellation contraction at the same temperature and the same pressure (hereinafter referred to as ~0) is less than about 5% by volume, is preferable. More specifically, there are the following preferable combinations.
~95~;3 (1) Combination of monomers used both as the component A and the component B: N-vinyl lactam, especially N-vinyl pyrrolidone as the com-ponent A. A lower alkyl ester of acrylic acid or methacrylic acid, especially methyl methacrylate as the component B.
(2) Combination of a monomer used as the component A with a poly-mer used as the component B: N-vinyl lactam, especially N-vinyl pyrrolidone as the component A. A polymer having an ethylenic double bond in the side chain obtained by reacting (esterifying) methacrylic acid with a lower alkyl ester of methacrylic acid (especially, methyl methacrylate) - glycidyl methacrylate ll) copolymer, or a non-gelled copolymer of methyl methacrylate and vinyl meth-acrylate as the component B.
(3) Combination of polymers used both as the component A and the component B: A polymer obtained by reacting (esterifying) methacrylic acid with a hydrolyzed N-vinyl pyrrolidone-vinylene carbonate copolymer as the component A. A non-gelled copolymer of methyl methacrylate and vinyl methacrylate as the component B.
As monomer for the component A there may be mentioned an N-vinyl lactam such as N-vinyl pyrrolidone, N-vinyl piperidone and N-vinyl caprolac-tam; N-vinyl oxa7olidone; a hydroxy lower alkyl ester of acrylic acid or meth-acrylic acid such as hydroxyethyl or hydroxypropyl ester of acrylic acid or methacrylic acid; glycerin monoacrylate or glycerin monomethacrylate; and an ~0 ortho-lactone having a hydrophilic group. As used above and throughout the dcscription of the invention, as preferred lower alkyl may be mentioned alkyl of up to 6 carbon atoms.
The hydrophilic polymer of the component A is a post cross-linkable hydropllilic polymer having functional group (s) adequate to form a cross-linkage between one hydrophilic polymer and another (post cross-linking). Illustrative of such hydrophilic polymer is the p~r~duct obtained by (co) polymerizing one or more monomeric components A and, if necessary, a monomer for introducing , functional group(s) to a polymer (functional group-introducing monomer). As said functional group-introducing monomers there may be mentioned n-butoxy-methylacrylamide, glycidyl methacrylate, vinylene carbonate, hydroxyethyl methacrylate, hydroxyethyl acrylate, vinyl methacrylate, vinyl acrylate, meth-acrylic acid and acrylic acid. The copolymerization ratio of the monomer to the functional group-introducing monomer is preferably within the range of about 1000:1 to about 10:1. Of those illustrated above especially preferred is the product obtained by copolymerizing N-vinyl pyrrolidone as the monomer and vinylene carbonate as the functional group-introducing monomer.
Asanotller example of such a hydrophylic polymer, polyvinyl alcohol may be cited. In this case, hydroxyl groups in the polymer enable a post cross-linkillg reaction to take place; therefore, a new functional group need not be introduced. The post cross-linking reaction may be carried out by using a polyvalent isocyanate, a polyvalent aldehyde or methylol melamine as a post cross-linking agent.
A monomer of component B gives a hydrophobic component when poly-merized, which neither swells nor dissolves in water even though it is not cross-linked. As such monomers, there may be cited lower alkyl esters of acrylic acid or methacrylic acid (for example, methyl methacrylate); unsaturated ~0 nitriles such as acrylonitrile or methacrylonitrile; aromatic olefins such as styrelle and hydrophobic ortholactones.
I~hen monomers are used as said component A and said component B, it is desirable that one monomer is unlikely to be copolymerized with the other mollolller, and it is also desirable that monomer reactivity ratios are:
l/rA>l and VrB~l ~wherein rA is a reactivity ratio of the monomer of the component A to the monomer of the component B, and the ratio of the possibility that A is added to -- 'I --lg563 an A -terminated polymer to the possibility that B is added thereto; rB is a reactivity ratio of the monomer of the component B to the monomer of the compollellt A~) In this case, when acrylic acid or methacrylic acid is added in an amount up to about 5% by weight based on the entire monomers as a third monomer component, it becomes possible to raise the water content without lowering the strength of the lens.
Tlle hydrophobic polymer of the component B is a post cross-linkable polymer having functional group(s) adequate for forming a cross-linkage between one llydrophobic polymer and another (post cross-linking) and neither swells nor 1~ dissolves in water. Representative of such post cross-linkable hydrophobic polymers is the product obtained by (co) polymerizing one or more monomeric components B and, if necessary with, one or more members of the functional group-introducing monomers mentioned above. It is preferable that the copolymerization composition ratio of the monomer to the aforesaid functional groLIp-introducing monomer generally ranges from about 1000:1 to about 10:1. As a hydrophobic polymer, a noll-cross-linkable polymer, for example, polyvinyl butyral may be used in an admixture with a post cross-linkable polymer.
Both in the case of polymers of component A and polymer of component B, when a hydroxyl group is contained as a functional group, it is possible ~0 to render said polymer post cross-linkable by esterifying said hydroxyl group with, for example, methacrylic acid to thereby introduce an ethylenic double bond to the side chain.
As stated above, a combination of component A and component B such as to give an "original solution" whose coefficient of gellation contraction at the same temperature and the same pressure (hereinafter referred to as ~0) is less than about 5% by volume, is preferable. More specifically, there are the following preferable combinations.
~95~;3 (1) Combination of monomers used both as the component A and the component B: N-vinyl lactam, especially N-vinyl pyrrolidone as the com-ponent A. A lower alkyl ester of acrylic acid or methacrylic acid, especially methyl methacrylate as the component B.
(2) Combination of a monomer used as the component A with a poly-mer used as the component B: N-vinyl lactam, especially N-vinyl pyrrolidone as the component A. A polymer having an ethylenic double bond in the side chain obtained by reacting (esterifying) methacrylic acid with a lower alkyl ester of methacrylic acid (especially, methyl methacrylate) - glycidyl methacrylate ll) copolymer, or a non-gelled copolymer of methyl methacrylate and vinyl meth-acrylate as the component B.
(3) Combination of polymers used both as the component A and the component B: A polymer obtained by reacting (esterifying) methacrylic acid with a hydrolyzed N-vinyl pyrrolidone-vinylene carbonate copolymer as the component A. A non-gelled copolymer of methyl methacrylate and vinyl methacrylate as the component B.
(4) Combination of a post cross-linkable polymer and a monomer used as the component A, and a monomer used as the component B. This combination is effective because it imparts a proper viscosity to an original solution for 2~ polylllerization.
Of the foregoing, especially preferable is a combination of N-vinyl pyrrolidone ~ith methyl methacrylate.
It is preferred that the ratio of component A to component B ranges from about 85:15 to about 55:45. Where the amount of the component A exceeds the upper limit of said range, viz. about 85%, a high-tenacity lens is not likely to be obtained, and where the amount of the component A becomes less than about 55%, a lens having a high water content is not likely to be obtained.
If said ratio is within the aforesaid range, a lens having a high tenacity and a high water content that are well balanced is obtainable.
The solvent component C , if it is necessary, must be one that does not obstruct the polymerization reaction and the post cross-linking reaction, and must furthermore give a transparent original solution. When a solvent giving an opaque original solution is used, the lens is unsatisfactory is optical properties, and also in many cases in dynamic properties.
In case both the component A and the component B are monomers, it is not necessarily required that a solvent be used which is capable of dis-solving both polymers of the two components. Insofar as it is a solvent dis-solving either one of the two components, any solvent may be usable. It is possible to select a solvent from various kinds depending upon combination of the componcnt A with the component B. When a combination of N-vinyl pyrrolidone and methyl methacrylate is employed, which is an especially preferable mode of practice of the present invention, there is preferably used dimethyl sulfoxide ` and/or ethylene carbonate or an organic solvent system obtained by adding a small amount of dioxane thereto. Where a polymer of N-vinyl pyrrolidone is uscd as the component A and a polymer of methyl methacrylate is used as the component B, dimethyl formamide, N-methyl pyrrolidone or dimethyl acetamide may be used as a preferred solvent, as they simultaneously dissolve both polymers.
It is preferred that the amount of the solvent used be within the rnnge of about 5-95O by weight based on the total amount of the original solu-tion; of said rangc, the rangc of about 30-90% by weight is more preferable, an~l the range of about 50-90% by weight is most preferable. In case the amount of the solvent e~ceeds about 95% by weight, the tensile strength of a solvent-containing gel obtained by polymerizing and/or cross-linking the original solution may become low and therefore handling of the solven-t-containing lens becomes somewhat difficult.
It is preferable to so adjust the original solution as to make the tensile strength of the solvent-containing gel not less than about 0.1 kg f/cm2; and to that end, it is preferred not only to use amounts of the solvent within the aforesaid range, but also to carefully select the kind of solvent.
When the amount of the solvent is less than about 5% by weight, a swelled lens obtained upon hydration may be still hard, the water content of the lens may be low, or the lens may undergo permanent deforma~ion to suc}- an extent that parts of the molecules are destroyed due to swelling forces. What is most 1() preferable is that tlle dimensional change brought about when the solvent contain-cd in the gel is exchanged for water, is within the range of from about +20%
througll about -30%.
The cross-linking agent will now be considered. With a polymer used as component A or B, a post cross-linking agent reacting with the functional group~s) of the polymer to form cross-linking between one polymer molecule and another, is used as occasion demands. As a post cross-linking agent, any substance is usable unless it changes essentially the properties of the polymer.~or a polymer containing hydroxyl group(s) as a functional group, a polyvalent isocyanate, a polyvalent aldehyde or a polyvalent carboxylic acid ester is usable as a post cross-linking agent. When a polymerizable monomer is used as the component A or B, a cross-linking agent is added to advance a cross-linking polymerization. The cross-linking agent is selected from compounds having at least t~o polymerizable unsaturated bonds in the molecule. As such cross-linking agents, there may be mentioned di- or tri-allyl compounds such as diallyl succinate, dially phthalate, diallyl maleate, diethylene glycol bis-allyl carbonate, triallyl cyanurate, triallylisocyanurate, triallyl phosphate and ~9~3 triallyl trimellitate; di- or tri-vinyl compounds such as divinyl benzene, N,N'-methylene bis acrylamide, (poly)ethylene glycol dimethacrylate, hexamethylene bis maleimide, divinyl urea, bisphenol A bis methacrylate, divinyl adipate, glycerin trimethacrylate, trimethylol propane triacrylate, trivinyl trimellitate and l,5-pentadiene; allylvinyl compounds such as allyl acrylate and allyl meth-acrylate; and vinyl (meth) acrylate. The amount of such cross-linking agent to be added is within the range of about 0.005 - 20 mol % based on the total ~nount of the polymerizable monomers of the component A and the component B.
The cross-linking polymerization is carried out by such means as heat, radia~ion or electron ray in the presence of a polymerization initiator if necessary. As preferred examples of such a polymerization initiator, there may be mentioned organic peroxides such as di-tert-butyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, tert-butyl hydroperoxide, tert-butyl perpivalate, peracid and ammonium persulfate; azo compounds such as azobisiso-butyronitrile, azobiscyclohexane carbonitrile, phenylazoisobutyronitrile and azobis-dimethylvaleronitrile; and redox catalysts. The amount of such polymeri-zation initiator to be added is within the range of about 0.001 - 3% by weight based on the polymerizable monomer.
It will be seen by a person skilled in the art that in addition to tllc criteria previously set forth, additives such as a cross-linking promotor ~ld coloring agents may be added to the original solution as needed. It is also possi~le to add a polymer to the original solution which can be extracted l~itll water :Erom the solvent-containing gel, for example, poly N-vinyl pyrroli-done. Such extractable polymer, as well as other substances extractable from the resulting gel with water may be formally regarded as a part of the solvent, so far as to calculate the relative amount of the solvent in the original solution.
_ 9 _ i6~
The smaller the y of the original solution, the better. ~hen a casting method is adopted in which the volume of the lens-defining space gradually decreases as contraction due to polymerization proceeds, even though the value of y is as high as 15 - 20%, there is still no possibility of hollows occurring. However, where the diopter of a lens is a large positive or negative value, the thickness of the lens-defining space varies from place to place, and so the original solution flows slightly and ~he memory of such flow develops after the hydration treatment, which is not desirable. From this viewpoint, it is preferable that yO is less than about 10% by volume, and still more pre-erably less than about 5% by volume.
As preferred embodiments of compositions original solutions for producing a soft contact lens of the present invention may be mentioned:
(1) The combination, wherein N-vinyl pyrrolidone and methyl meth-acrylate are used as monomers, triallyl isocyanurate or vinyl methacrylate is used as a cross-linking agent, azobisdimethyl valeronitrile is used as a catalyst and dimethyl sulfoxide is used as a solvent.
(2) The combination, wherein N-vinyl pyrrolidone is used as a mollomer, a non-gelled copolymer of methyl methacrylate and vinyl methacrylate is used as a post cross-linkable polymer, triallyl isocyanurate is used as a cross-linking agent, azobisdimethyl valeronitrile is used as a catalyst and dimethyl sulfoxide is used as a solvent.
(3) The combination, wherein a post cross-linkable polymer obtained by hydrolyzing a vinyl pyrrolidone - vinylene carbonate copolymer and thereafter esterifying the resultant hydrolyzed copolymer with methacrylic acid and a non-gelled copolymer of methyl methacrylate and vinyl methacrylate are used as polymers and N-methyl pyrrolidone is used as a solvent.
A pair of dies are used in the present invention, that is, a com-; bination of a concave die and a convex die. At least one of these two dies should be one whose lens-defining die surface is an interference spherical surface or an interference paraboloidal surface (hereinafter, an interference spherical surface and an interference paraboloidal surface are generally re-ferred to as an interference surface). The interference spherical surface or the interference paraboloidal surface referred to in this specification refers to a lens-defining die surface whose primary portion corresponding to the optical zone of the lens is a smooth spherical or paraboloidal surface having a degree of surface roughness of not more than about 50 ~m and the spherical or paraboloidal properties are lost at the portion corresponding to the peripheral portion of the lens. It is preferred ~hat the concave die and the convex die ~e so designed as to bring them into a linear, not surface contact, because it is sometimes difficult to place the central axes of the two dies exactly coincident in the latter case.
Exam~ples of the combinations of a concave die and a convex die used in the present invention will be explained by reference to the accompanying drawings, in which:
Figure 1 represents a pair of convex and concave dies;
Figure 2 represents an alternative pair of convex and concave dies;
and Figure 3 represents a third possible pattern for a pair of convex and concave dies.
Figure 1 is a combination of a concave die 1 having an interference surface l~ith a convex die 2 having a non-interference surface. A lens-defining die surface having single spherical or paraboloidal surface only is in this specification referred to as a non-interference surface). This combination is especially preferred for practicing the present invention, because the concave die having an interference surface is used and a lens having good per-meability to tear flow can be produced, and no inner bevel is produced. An ilmer bevel is an inclined surface produced on the circumferential portion on the concave surface of a lens, which has been almost indispensable for wearing a conventional contact lens. On wearing a soft contact lens produced by the process of the present invention, no problem is brought about even though there is no inner bevel.
Figure 2 is an example of combination of a concave die 1 having an interfcrence surface with a convex die 4 also having an interference surface.
I~ By the use of such a pair of dies, the present invention can also be easily practised. A concave die having a non-interference surface may also be used instead however, except for special lens, an outer bevel (an inclined surface produced on the circumferential portion on the convex surface of a lens) is generally necessary, therefore, a concave die having an interference surface is preferred. On the circumferential portion of the die surface of a convex die, a thin groove or small hole may be engraved, which results in forming a projec-tiOII on the peripheral portion on the concave surface of the lens and promoting flow of tear. IVhen a hole is marked, such marked hole is also useful for identification of the kind. The material of the die may be plastic, metal or ~) glass, preferably glass.
Figure 3 is an example of a combination of a concave die 1 having an interferellce surface with a convex die 4 also having an interference surface.
This combination is excellent in that any lens flash produced in the overlapping surface of the dies does not contact the cornea. This combination is especially suitable for manufacturing dies from a thermoplastic resin or from a metal by the transcription method.
In the filling step, an original solution in an excess amount is .
15~3 poured into a concave die. Use of such an excess amount of the original solution is not only necessary for uniformly filling the original solution into the space between the concave die and a convex die, but also important for the following reason. In the mold shown in Figure 1 which is a preferred em-bodiment for preparing lenses from the original solution according to the present invention, there is a wedge-shaped space 3 adjacent the seal, overflow of the original solution is reserved in that space 3 to render the seal complete.-On the otller hand, when polymerization contraction occurs, the overflow of the original solution is supplied through a slight opening of-the seal into the sealcd portion to make up for the polymerization contraction. Where such dies are used, it is preferred to use an excess of the original solution about 5 times or more the volume of the overflowed original solution reserved in the wedge-shayed space. The amount of the original solution to be charged may also be determined as follows. A number of molds each charged with the original solu-tion are normally placed before the gellation step in a suitable sealed vessel in which the air is replaced by an inert gas such as nitrogen. The lowest boiling point component of the original solution is so chosen that its vapour pressure constitutes at least about 20~ of the saturated partial pressure e~-hibited by the original solution inside the vesse]. By charging such an excess ~O of the original solution, it is possible to prevent the lens from enfolding bubbles and to inhibit slight changes of composition of the original solution during tlle gelling step, thus enabling a good yield of very high-quality lenses to be obtained.
Anotl-er way of conducting the filling step is to fill the original solution in a sealed container. In this procedure, a concave die is fi~ed in a sealable container, the original solution is poured into the concave die, and thereafter the whole container is inclined for placing a spherical convex die , , ' on the concave die in said container, air inside the container is pumped outor replaced by an inert gas, as occasion demands, and thereafter the container is sealed and lightly shaken to seat the convex die on the concave die.
In the gellation step, a polymerization and/or cross-linking re-action is caused to proceed by the action of heat, radiation or electron ray.
~hen such reaction is promoted by heat, the reaction is carried out normally at a temperature within the range from room temperature through about 120C.
There are the following five practical methods for avoiding the l~roduction of holes and hollows due to polymerization contraction of the ori-ginal solution:
(a) Liquid is supplied through the slight opening between theconcave and convex dies.
(b) Pressure acting on the original solution and/or gel in a space between the concave and convex dies is reduced to develop elastic expansion.
(c) The original solution and/or gel in the space between the con-cave and convex dies is heated to develop thermal expansion.
~ d) A hole and/or hollow is produced at a position other than the optical area (an area within a circle having a radius about 4 mm centering around the optical axis) in a space between the concave and convex dies.
_~ (e) The volume (hereinafter referred to by the symbol V) of the spnce between the concave and convex dies is somewhat decreased during the pro-cess from initiation through termination of the polymerization reaction.
In method (a) mentioned above, the overflow of the original solution is held in the wedge-shaped space of the dies, any negative pressure inside the dies caused by polymerization contraction causing the original solution to be drawn into the mold through a slight opening of the seal between the two dies.
This method is preferred in a metal mold rather than in a plastic mold and most preferable in a glass mold. In the case of glass mold, the opening betweenthe two dies is sometimes large. In such case the concave and convex dies are s~ueezed together ~ith a force of 10 - 200 kg f, preferably about 50 kg f.
The liquid to be supplied is preferably the overflow of the ori-ginal solution as just described, but is not limited to the original solution since either a monomer or a solvent will suffice.
In method (b), the original solution is sealed in a pressurized, compressed state within the mold and as the polymerization proceeds, the internal pressure automatically decreases, by which the polymerization compression is compensated.
The original solution is pressurized by heating or by pumping it into a sealed space.
l~hen squeezing the concave and convex dies together results in incom-plete sealing, the seal may be perfected by placing the whole mold in an auto-clave and by adding the original solution in the autoclave to fill the mold and the autoclave.
Method ~c) is achieved by gradually elevating the temperature of the original solution as polymerization progresses.
The coefficient of thermal expansion of a monomer is not large;
~0 however, the following two procedures are effective. One is to mix the monomer witl~ a solvent having a high coefficient of thermal expansion and carry out solution polymerization. The other is to carry out the reaction at temperatures rnnging from a low temperature immediately above the freezing point of the solution to a high temperature just below any decomposition occurs. In this case, because a proper thermal polymerization catalyst is not usually available, an electron radiation polymerization is desirable.
Method (d) is to eliminate overall contraction of the entirety by forming hollows in harmless positions. Such positions are an outer bevel or an inner bevel of the lens. In order to make certain that hollows form in sucll a position, foaming nuclei are preferably provided on the outer bevel por-tion of the concave die. As such foaming nuclei, a rough surface of the die, contamination caused by foreign matters such as a very small amount of oil or grease, or plastic fiber are preferable.
~ lethod ~e) is achieved by gradually decreasing the volume (V) of the lens-defining space as polymerization proceeds.
If the decrease in V during the polymerization is termed ~V, up to 1~ abollt ~V/V=3o can be utilized in the process of the present invention. In the casc of glass mold, when an assembly of concave and convex dies is squeezed together by a force of about 100 kg f, a volume decrease of about 2% is achieved.
Of the foregoing methods, these which are preferable for obtaining satisfactory lens are (a), (b), and (c), with (d) and (e) preferably being used as auxiliary means. These methods are used in proper combination.
Peeling of the solvent-containing gel from mold is carried out in a liquid, especially in an aqueous solution. For this purpose, the whole assembly of the concave and convex dies may be immersed in the liquid, although, since contact of the overlapping surface of the mold assembly with the liquid will ~0 suffice, the entire mold need not be immersed. By conducting the peeling in the liquid, it is possible to drastically reduce the proportion of damaged lenses.
This effect is especially remarkable when glass mold is used.
~ hell peeling operations are carried out in water, exchange of the solvent contained in the gel for water can be continuously carried out without any furtller treatment.
The liquid used for the peeling step is not particularly critical provided that it does not adversely affect the lens. ~lowever, in general, 5ç~3 the same solvent as used in the original solution, with the addition of wateris preferably used. ~here N-vinyl pyrrolidone is selected as component A and methyl methacrylate is selected as the component B of the original solution, peeling is preferably carried out in an aqueous solution of dimethyl sulfoxide.
These may be called solvents weaker in action for swelling the gel than the solvent contained in the original solution.
The peeled lens is next subjected to an extraction treatment with water (including physiological saline and other aqueous solutions). At this time, the monomer(s), polymer(s), cross-linking agent, catalyst and solvent 1() elute, while water or an artificial tear solution flow in.
Nhen this step is completed, a hydrated gel whose percent trans-nùssioll of visible light is more than about 90% per thickness of 0.1 mm) may be obtained.
~ample 1 The concave die used in this example is made of a low-pressure poly-ethylene, having a shape like 1 of Figure 2, the radius of curvature and the diameter of which are 7.5 mm and 13 mm, respectively. The convex die used in this example is a glass ball having a radius of curvature of 8 mm. A gap in the central portion is 0.9 mm.
The original solution for polymerization is a mixture of hydrophilic monomers and solvents as shown below.
hydroxyetllyl methacrylate (HEMA) 70 g N-vinyl pyrrolidone ~NVP) 30 g acrylic acid 2 g ethyleneglycol dimethacrylate (EGDMA) 1.5 g triallyl isocyanurate (TAIC) 0.5 g ammonium persulfate 2 g ethylene glycol 150 g water 150 g The original solution in an amount in excess by 20 ~1 was poured into the concave die and the convex die was carefully centred thereon. Be-cause the excess amount of said solution was considerable, the probability of enfolding bubbles was low.
The two dies were clamped by a force of 0.5 kg f and the polymeri-zation conducted in a hot air oven, the solution being heated at 60C. for 16 hours and then at 90C. for 4 hours. The ~ of the original solution was 3.5%, n grcatcr part of which, however, was made up for by reduction of the volume of the dies.
After ilmllersing the assembly of the two dies in water, the clamps were loosened, and the assembly allowed to stand overnight in water and the two dies were separated in the water. By this means, the ratio of the number of lenses with a broken circumference decreased by about 10% ~as compared with the case of loosening the clamps in air and separating the two dies in air).
If a lens initially adhered to the concave die, allowing the mold to stand in water for 5 hours, promoted natural peeling.
The water content of the lens obtained in this manner using water ~0 at pH 8 was about 75% and a lens having an intact edge was obtained. The per-ccnt transmission of light was 85%.
In order to determine the approximate value of the tensile strength of the solvent-containing lens, after being heated at 90C. for 4 hours, the lens was taken out into air, the convex die was separated from the concave die and tlle lens was peeled by a pair of tweezers. From the finger touch at that time, the tensile strength of the lens was inferred to be about 0.5-2.0 kg f/cm2.
Example 2 Using the same mold and the same original solution as used in Ex-ample 1, the original solution was charged by the same method. Thereafter, the two dies were clamped together by a force of 0.5 kg f and the original solution was polymerized in a water bath. After heating the mold under the same con-ditions as in Example 1, the clamps were loosened in water, the two dies were allowed to stand in water for overnight and thereafter the two dies were separated. A lens whose edge was little destroyed was obtained.
Example 3 The concave die used in this example was a non-interference sphere made of glass having a radius of curvature of 7 mm and a diameter of 13 mm.
The convex die used was the same as that used in Example 1. The gap in the ceIltral portion was 1 mm. At the contact portion of the two dies, a wedge-shaped space like 3 in Figure 1 was provided. As both of the two dies had a non-interference spherical surface, a thick concave lens having a crescent-like sectional configuration was obtained.
Composition of the original solution for polymerization was as follows, a mixture containing a hydrophilic monomer, a hydrophobic monomer and a solvent.
~0 NVP 70 g methyl methacrylate ~r~IA) 30 g TAIC 1 g triethyleneglycol dimethacrylate (TEGD~IA) 3 g vinyl methacrylate (V~le) 0.5 g azobisdimethyl valeronitrile (ADVN) 0.1 g dimethyl sulfoxide (DMSO) 400 g The y of this original solution was about 3.5%.
The concave die was placed inside a high-rigidity, pressure-resistant 5000 kg f/cm autoclave, the original solution was overflowingly poured inside the autoclave, the convex die was placed on the concave die and the autoclave was covered. Heating was effected at 40C. for the first 9.5 hours, at 50C. for the succeeding 1.7 hours, at 60C. for the next 2.5 hours, at 70C. for the next 0.4 hour (24 minutes), at 80C. for the next 0.8 hour (48 minutes). The temperature was still raised up to 90C. over 0.9 hour, and at the temperature the autoclave was allowed to stand for the next 2.2 hours. Thus the total heating time was 18 hours. While care was taken so as not to cool the autoclave, the assembly of the concave die and convex die was quickly taken out ~uld imlllediately immersed in a treating liquid. The treating liquid was a 70%
aqueous solution of D~IS0 (at 95C.), after 5 hours, the convex die was separat-ed from the concave die, said concave die was immersed in a 10% aqueous solution of DMS0 (at 95C.) for 5 hours. During the period, the lens naturally peeled from the concave die. Although the circumference of the lens was very thin, the lens free from damage was obtained. I~hen the lens was boiled in water for overnight, it became a transparent soft contact lens.
In order to know the approximate value of the tensile strength of ~0 the solvent-containing lens, the concave and convex dies taken out from the ~utoclave were separated in air and the solvent-containing lens was peeled by a pnir of tweezers. From the finger touch at that time, the tensile s~rength o thc lens was inferred to be about 0.1 - 1 kg f/cm2.
~ lle hydrated lens had a water content of 75%, a percent transmission of light of 85% and a tensile strength of 4 kg f/cm2.
Example 4 An experiment showing toughness of a pressure polymerization was .
carried out. The temperature elevation program of Example 3 was modified by reducing the speed of temperature elevation, which was made an optimum value in an atmospheric pressure polymerization shown in Example 5.
Increase of a hollow occurring ratio due to polymerization contrac-tion was hardly recognized. Number of flashes formed on t'ne overlapping sur-face of the two dies was rather small. This was recognized to be the slowest speed temperature elevation. The pressure inside the space between the dies at t1lis time was inferred to be always close to atmospheric pressure. According-ly, the internal pressure in Example 3 is believed to be considerable.
IO As such, in a pressure polymerization, the possible range of the temperature elevation programme is broad, which is contrastive to delicacy of an atmospheric pressure polymerization indicated in Example 5.
Example 5 The same mold as used in Example 3 was used. A concave die was placed horizontally on the bottom of an autoclave in advance, on which was placed a convex die, through the overlapping surface of the two dies, a needle was inserted to inject about 1 ml of the same original solution as used in Ex-mple 3 and the needle was pulled out. Bubbles were hardly enfolded. The overflowed original solution wetted the circumference of the concave die to say notlling of a wedge-shaped space, accumulated on the bottom of the autoclave.
The nutoclave was filled with nitrogen gas and covered. The inside of the auto-clnvc must be filled with the vapor of the original solution.
A polymerization was carried out according to the following tempera-turc elevation programme, connecting smoothly the following temperature elevation curve.
Until 8 1/4 hours 39C.
At 9 1/4 hours ~6C.
.
Of the foregoing, especially preferable is a combination of N-vinyl pyrrolidone ~ith methyl methacrylate.
It is preferred that the ratio of component A to component B ranges from about 85:15 to about 55:45. Where the amount of the component A exceeds the upper limit of said range, viz. about 85%, a high-tenacity lens is not likely to be obtained, and where the amount of the component A becomes less than about 55%, a lens having a high water content is not likely to be obtained.
If said ratio is within the aforesaid range, a lens having a high tenacity and a high water content that are well balanced is obtainable.
The solvent component C , if it is necessary, must be one that does not obstruct the polymerization reaction and the post cross-linking reaction, and must furthermore give a transparent original solution. When a solvent giving an opaque original solution is used, the lens is unsatisfactory is optical properties, and also in many cases in dynamic properties.
In case both the component A and the component B are monomers, it is not necessarily required that a solvent be used which is capable of dis-solving both polymers of the two components. Insofar as it is a solvent dis-solving either one of the two components, any solvent may be usable. It is possible to select a solvent from various kinds depending upon combination of the componcnt A with the component B. When a combination of N-vinyl pyrrolidone and methyl methacrylate is employed, which is an especially preferable mode of practice of the present invention, there is preferably used dimethyl sulfoxide ` and/or ethylene carbonate or an organic solvent system obtained by adding a small amount of dioxane thereto. Where a polymer of N-vinyl pyrrolidone is uscd as the component A and a polymer of methyl methacrylate is used as the component B, dimethyl formamide, N-methyl pyrrolidone or dimethyl acetamide may be used as a preferred solvent, as they simultaneously dissolve both polymers.
It is preferred that the amount of the solvent used be within the rnnge of about 5-95O by weight based on the total amount of the original solu-tion; of said rangc, the rangc of about 30-90% by weight is more preferable, an~l the range of about 50-90% by weight is most preferable. In case the amount of the solvent e~ceeds about 95% by weight, the tensile strength of a solvent-containing gel obtained by polymerizing and/or cross-linking the original solution may become low and therefore handling of the solven-t-containing lens becomes somewhat difficult.
It is preferable to so adjust the original solution as to make the tensile strength of the solvent-containing gel not less than about 0.1 kg f/cm2; and to that end, it is preferred not only to use amounts of the solvent within the aforesaid range, but also to carefully select the kind of solvent.
When the amount of the solvent is less than about 5% by weight, a swelled lens obtained upon hydration may be still hard, the water content of the lens may be low, or the lens may undergo permanent deforma~ion to suc}- an extent that parts of the molecules are destroyed due to swelling forces. What is most 1() preferable is that tlle dimensional change brought about when the solvent contain-cd in the gel is exchanged for water, is within the range of from about +20%
througll about -30%.
The cross-linking agent will now be considered. With a polymer used as component A or B, a post cross-linking agent reacting with the functional group~s) of the polymer to form cross-linking between one polymer molecule and another, is used as occasion demands. As a post cross-linking agent, any substance is usable unless it changes essentially the properties of the polymer.~or a polymer containing hydroxyl group(s) as a functional group, a polyvalent isocyanate, a polyvalent aldehyde or a polyvalent carboxylic acid ester is usable as a post cross-linking agent. When a polymerizable monomer is used as the component A or B, a cross-linking agent is added to advance a cross-linking polymerization. The cross-linking agent is selected from compounds having at least t~o polymerizable unsaturated bonds in the molecule. As such cross-linking agents, there may be mentioned di- or tri-allyl compounds such as diallyl succinate, dially phthalate, diallyl maleate, diethylene glycol bis-allyl carbonate, triallyl cyanurate, triallylisocyanurate, triallyl phosphate and ~9~3 triallyl trimellitate; di- or tri-vinyl compounds such as divinyl benzene, N,N'-methylene bis acrylamide, (poly)ethylene glycol dimethacrylate, hexamethylene bis maleimide, divinyl urea, bisphenol A bis methacrylate, divinyl adipate, glycerin trimethacrylate, trimethylol propane triacrylate, trivinyl trimellitate and l,5-pentadiene; allylvinyl compounds such as allyl acrylate and allyl meth-acrylate; and vinyl (meth) acrylate. The amount of such cross-linking agent to be added is within the range of about 0.005 - 20 mol % based on the total ~nount of the polymerizable monomers of the component A and the component B.
The cross-linking polymerization is carried out by such means as heat, radia~ion or electron ray in the presence of a polymerization initiator if necessary. As preferred examples of such a polymerization initiator, there may be mentioned organic peroxides such as di-tert-butyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, tert-butyl hydroperoxide, tert-butyl perpivalate, peracid and ammonium persulfate; azo compounds such as azobisiso-butyronitrile, azobiscyclohexane carbonitrile, phenylazoisobutyronitrile and azobis-dimethylvaleronitrile; and redox catalysts. The amount of such polymeri-zation initiator to be added is within the range of about 0.001 - 3% by weight based on the polymerizable monomer.
It will be seen by a person skilled in the art that in addition to tllc criteria previously set forth, additives such as a cross-linking promotor ~ld coloring agents may be added to the original solution as needed. It is also possi~le to add a polymer to the original solution which can be extracted l~itll water :Erom the solvent-containing gel, for example, poly N-vinyl pyrroli-done. Such extractable polymer, as well as other substances extractable from the resulting gel with water may be formally regarded as a part of the solvent, so far as to calculate the relative amount of the solvent in the original solution.
_ 9 _ i6~
The smaller the y of the original solution, the better. ~hen a casting method is adopted in which the volume of the lens-defining space gradually decreases as contraction due to polymerization proceeds, even though the value of y is as high as 15 - 20%, there is still no possibility of hollows occurring. However, where the diopter of a lens is a large positive or negative value, the thickness of the lens-defining space varies from place to place, and so the original solution flows slightly and ~he memory of such flow develops after the hydration treatment, which is not desirable. From this viewpoint, it is preferable that yO is less than about 10% by volume, and still more pre-erably less than about 5% by volume.
As preferred embodiments of compositions original solutions for producing a soft contact lens of the present invention may be mentioned:
(1) The combination, wherein N-vinyl pyrrolidone and methyl meth-acrylate are used as monomers, triallyl isocyanurate or vinyl methacrylate is used as a cross-linking agent, azobisdimethyl valeronitrile is used as a catalyst and dimethyl sulfoxide is used as a solvent.
(2) The combination, wherein N-vinyl pyrrolidone is used as a mollomer, a non-gelled copolymer of methyl methacrylate and vinyl methacrylate is used as a post cross-linkable polymer, triallyl isocyanurate is used as a cross-linking agent, azobisdimethyl valeronitrile is used as a catalyst and dimethyl sulfoxide is used as a solvent.
(3) The combination, wherein a post cross-linkable polymer obtained by hydrolyzing a vinyl pyrrolidone - vinylene carbonate copolymer and thereafter esterifying the resultant hydrolyzed copolymer with methacrylic acid and a non-gelled copolymer of methyl methacrylate and vinyl methacrylate are used as polymers and N-methyl pyrrolidone is used as a solvent.
A pair of dies are used in the present invention, that is, a com-; bination of a concave die and a convex die. At least one of these two dies should be one whose lens-defining die surface is an interference spherical surface or an interference paraboloidal surface (hereinafter, an interference spherical surface and an interference paraboloidal surface are generally re-ferred to as an interference surface). The interference spherical surface or the interference paraboloidal surface referred to in this specification refers to a lens-defining die surface whose primary portion corresponding to the optical zone of the lens is a smooth spherical or paraboloidal surface having a degree of surface roughness of not more than about 50 ~m and the spherical or paraboloidal properties are lost at the portion corresponding to the peripheral portion of the lens. It is preferred ~hat the concave die and the convex die ~e so designed as to bring them into a linear, not surface contact, because it is sometimes difficult to place the central axes of the two dies exactly coincident in the latter case.
Exam~ples of the combinations of a concave die and a convex die used in the present invention will be explained by reference to the accompanying drawings, in which:
Figure 1 represents a pair of convex and concave dies;
Figure 2 represents an alternative pair of convex and concave dies;
and Figure 3 represents a third possible pattern for a pair of convex and concave dies.
Figure 1 is a combination of a concave die 1 having an interference surface l~ith a convex die 2 having a non-interference surface. A lens-defining die surface having single spherical or paraboloidal surface only is in this specification referred to as a non-interference surface). This combination is especially preferred for practicing the present invention, because the concave die having an interference surface is used and a lens having good per-meability to tear flow can be produced, and no inner bevel is produced. An ilmer bevel is an inclined surface produced on the circumferential portion on the concave surface of a lens, which has been almost indispensable for wearing a conventional contact lens. On wearing a soft contact lens produced by the process of the present invention, no problem is brought about even though there is no inner bevel.
Figure 2 is an example of combination of a concave die 1 having an interfcrence surface with a convex die 4 also having an interference surface.
I~ By the use of such a pair of dies, the present invention can also be easily practised. A concave die having a non-interference surface may also be used instead however, except for special lens, an outer bevel (an inclined surface produced on the circumferential portion on the convex surface of a lens) is generally necessary, therefore, a concave die having an interference surface is preferred. On the circumferential portion of the die surface of a convex die, a thin groove or small hole may be engraved, which results in forming a projec-tiOII on the peripheral portion on the concave surface of the lens and promoting flow of tear. IVhen a hole is marked, such marked hole is also useful for identification of the kind. The material of the die may be plastic, metal or ~) glass, preferably glass.
Figure 3 is an example of a combination of a concave die 1 having an interferellce surface with a convex die 4 also having an interference surface.
This combination is excellent in that any lens flash produced in the overlapping surface of the dies does not contact the cornea. This combination is especially suitable for manufacturing dies from a thermoplastic resin or from a metal by the transcription method.
In the filling step, an original solution in an excess amount is .
15~3 poured into a concave die. Use of such an excess amount of the original solution is not only necessary for uniformly filling the original solution into the space between the concave die and a convex die, but also important for the following reason. In the mold shown in Figure 1 which is a preferred em-bodiment for preparing lenses from the original solution according to the present invention, there is a wedge-shaped space 3 adjacent the seal, overflow of the original solution is reserved in that space 3 to render the seal complete.-On the otller hand, when polymerization contraction occurs, the overflow of the original solution is supplied through a slight opening of-the seal into the sealcd portion to make up for the polymerization contraction. Where such dies are used, it is preferred to use an excess of the original solution about 5 times or more the volume of the overflowed original solution reserved in the wedge-shayed space. The amount of the original solution to be charged may also be determined as follows. A number of molds each charged with the original solu-tion are normally placed before the gellation step in a suitable sealed vessel in which the air is replaced by an inert gas such as nitrogen. The lowest boiling point component of the original solution is so chosen that its vapour pressure constitutes at least about 20~ of the saturated partial pressure e~-hibited by the original solution inside the vesse]. By charging such an excess ~O of the original solution, it is possible to prevent the lens from enfolding bubbles and to inhibit slight changes of composition of the original solution during tlle gelling step, thus enabling a good yield of very high-quality lenses to be obtained.
Anotl-er way of conducting the filling step is to fill the original solution in a sealed container. In this procedure, a concave die is fi~ed in a sealable container, the original solution is poured into the concave die, and thereafter the whole container is inclined for placing a spherical convex die , , ' on the concave die in said container, air inside the container is pumped outor replaced by an inert gas, as occasion demands, and thereafter the container is sealed and lightly shaken to seat the convex die on the concave die.
In the gellation step, a polymerization and/or cross-linking re-action is caused to proceed by the action of heat, radiation or electron ray.
~hen such reaction is promoted by heat, the reaction is carried out normally at a temperature within the range from room temperature through about 120C.
There are the following five practical methods for avoiding the l~roduction of holes and hollows due to polymerization contraction of the ori-ginal solution:
(a) Liquid is supplied through the slight opening between theconcave and convex dies.
(b) Pressure acting on the original solution and/or gel in a space between the concave and convex dies is reduced to develop elastic expansion.
(c) The original solution and/or gel in the space between the con-cave and convex dies is heated to develop thermal expansion.
~ d) A hole and/or hollow is produced at a position other than the optical area (an area within a circle having a radius about 4 mm centering around the optical axis) in a space between the concave and convex dies.
_~ (e) The volume (hereinafter referred to by the symbol V) of the spnce between the concave and convex dies is somewhat decreased during the pro-cess from initiation through termination of the polymerization reaction.
In method (a) mentioned above, the overflow of the original solution is held in the wedge-shaped space of the dies, any negative pressure inside the dies caused by polymerization contraction causing the original solution to be drawn into the mold through a slight opening of the seal between the two dies.
This method is preferred in a metal mold rather than in a plastic mold and most preferable in a glass mold. In the case of glass mold, the opening betweenthe two dies is sometimes large. In such case the concave and convex dies are s~ueezed together ~ith a force of 10 - 200 kg f, preferably about 50 kg f.
The liquid to be supplied is preferably the overflow of the ori-ginal solution as just described, but is not limited to the original solution since either a monomer or a solvent will suffice.
In method (b), the original solution is sealed in a pressurized, compressed state within the mold and as the polymerization proceeds, the internal pressure automatically decreases, by which the polymerization compression is compensated.
The original solution is pressurized by heating or by pumping it into a sealed space.
l~hen squeezing the concave and convex dies together results in incom-plete sealing, the seal may be perfected by placing the whole mold in an auto-clave and by adding the original solution in the autoclave to fill the mold and the autoclave.
Method ~c) is achieved by gradually elevating the temperature of the original solution as polymerization progresses.
The coefficient of thermal expansion of a monomer is not large;
~0 however, the following two procedures are effective. One is to mix the monomer witl~ a solvent having a high coefficient of thermal expansion and carry out solution polymerization. The other is to carry out the reaction at temperatures rnnging from a low temperature immediately above the freezing point of the solution to a high temperature just below any decomposition occurs. In this case, because a proper thermal polymerization catalyst is not usually available, an electron radiation polymerization is desirable.
Method (d) is to eliminate overall contraction of the entirety by forming hollows in harmless positions. Such positions are an outer bevel or an inner bevel of the lens. In order to make certain that hollows form in sucll a position, foaming nuclei are preferably provided on the outer bevel por-tion of the concave die. As such foaming nuclei, a rough surface of the die, contamination caused by foreign matters such as a very small amount of oil or grease, or plastic fiber are preferable.
~ lethod ~e) is achieved by gradually decreasing the volume (V) of the lens-defining space as polymerization proceeds.
If the decrease in V during the polymerization is termed ~V, up to 1~ abollt ~V/V=3o can be utilized in the process of the present invention. In the casc of glass mold, when an assembly of concave and convex dies is squeezed together by a force of about 100 kg f, a volume decrease of about 2% is achieved.
Of the foregoing methods, these which are preferable for obtaining satisfactory lens are (a), (b), and (c), with (d) and (e) preferably being used as auxiliary means. These methods are used in proper combination.
Peeling of the solvent-containing gel from mold is carried out in a liquid, especially in an aqueous solution. For this purpose, the whole assembly of the concave and convex dies may be immersed in the liquid, although, since contact of the overlapping surface of the mold assembly with the liquid will ~0 suffice, the entire mold need not be immersed. By conducting the peeling in the liquid, it is possible to drastically reduce the proportion of damaged lenses.
This effect is especially remarkable when glass mold is used.
~ hell peeling operations are carried out in water, exchange of the solvent contained in the gel for water can be continuously carried out without any furtller treatment.
The liquid used for the peeling step is not particularly critical provided that it does not adversely affect the lens. ~lowever, in general, 5ç~3 the same solvent as used in the original solution, with the addition of wateris preferably used. ~here N-vinyl pyrrolidone is selected as component A and methyl methacrylate is selected as the component B of the original solution, peeling is preferably carried out in an aqueous solution of dimethyl sulfoxide.
These may be called solvents weaker in action for swelling the gel than the solvent contained in the original solution.
The peeled lens is next subjected to an extraction treatment with water (including physiological saline and other aqueous solutions). At this time, the monomer(s), polymer(s), cross-linking agent, catalyst and solvent 1() elute, while water or an artificial tear solution flow in.
Nhen this step is completed, a hydrated gel whose percent trans-nùssioll of visible light is more than about 90% per thickness of 0.1 mm) may be obtained.
~ample 1 The concave die used in this example is made of a low-pressure poly-ethylene, having a shape like 1 of Figure 2, the radius of curvature and the diameter of which are 7.5 mm and 13 mm, respectively. The convex die used in this example is a glass ball having a radius of curvature of 8 mm. A gap in the central portion is 0.9 mm.
The original solution for polymerization is a mixture of hydrophilic monomers and solvents as shown below.
hydroxyetllyl methacrylate (HEMA) 70 g N-vinyl pyrrolidone ~NVP) 30 g acrylic acid 2 g ethyleneglycol dimethacrylate (EGDMA) 1.5 g triallyl isocyanurate (TAIC) 0.5 g ammonium persulfate 2 g ethylene glycol 150 g water 150 g The original solution in an amount in excess by 20 ~1 was poured into the concave die and the convex die was carefully centred thereon. Be-cause the excess amount of said solution was considerable, the probability of enfolding bubbles was low.
The two dies were clamped by a force of 0.5 kg f and the polymeri-zation conducted in a hot air oven, the solution being heated at 60C. for 16 hours and then at 90C. for 4 hours. The ~ of the original solution was 3.5%, n grcatcr part of which, however, was made up for by reduction of the volume of the dies.
After ilmllersing the assembly of the two dies in water, the clamps were loosened, and the assembly allowed to stand overnight in water and the two dies were separated in the water. By this means, the ratio of the number of lenses with a broken circumference decreased by about 10% ~as compared with the case of loosening the clamps in air and separating the two dies in air).
If a lens initially adhered to the concave die, allowing the mold to stand in water for 5 hours, promoted natural peeling.
The water content of the lens obtained in this manner using water ~0 at pH 8 was about 75% and a lens having an intact edge was obtained. The per-ccnt transmission of light was 85%.
In order to determine the approximate value of the tensile strength of the solvent-containing lens, after being heated at 90C. for 4 hours, the lens was taken out into air, the convex die was separated from the concave die and tlle lens was peeled by a pair of tweezers. From the finger touch at that time, the tensile strength of the lens was inferred to be about 0.5-2.0 kg f/cm2.
Example 2 Using the same mold and the same original solution as used in Ex-ample 1, the original solution was charged by the same method. Thereafter, the two dies were clamped together by a force of 0.5 kg f and the original solution was polymerized in a water bath. After heating the mold under the same con-ditions as in Example 1, the clamps were loosened in water, the two dies were allowed to stand in water for overnight and thereafter the two dies were separated. A lens whose edge was little destroyed was obtained.
Example 3 The concave die used in this example was a non-interference sphere made of glass having a radius of curvature of 7 mm and a diameter of 13 mm.
The convex die used was the same as that used in Example 1. The gap in the ceIltral portion was 1 mm. At the contact portion of the two dies, a wedge-shaped space like 3 in Figure 1 was provided. As both of the two dies had a non-interference spherical surface, a thick concave lens having a crescent-like sectional configuration was obtained.
Composition of the original solution for polymerization was as follows, a mixture containing a hydrophilic monomer, a hydrophobic monomer and a solvent.
~0 NVP 70 g methyl methacrylate ~r~IA) 30 g TAIC 1 g triethyleneglycol dimethacrylate (TEGD~IA) 3 g vinyl methacrylate (V~le) 0.5 g azobisdimethyl valeronitrile (ADVN) 0.1 g dimethyl sulfoxide (DMSO) 400 g The y of this original solution was about 3.5%.
The concave die was placed inside a high-rigidity, pressure-resistant 5000 kg f/cm autoclave, the original solution was overflowingly poured inside the autoclave, the convex die was placed on the concave die and the autoclave was covered. Heating was effected at 40C. for the first 9.5 hours, at 50C. for the succeeding 1.7 hours, at 60C. for the next 2.5 hours, at 70C. for the next 0.4 hour (24 minutes), at 80C. for the next 0.8 hour (48 minutes). The temperature was still raised up to 90C. over 0.9 hour, and at the temperature the autoclave was allowed to stand for the next 2.2 hours. Thus the total heating time was 18 hours. While care was taken so as not to cool the autoclave, the assembly of the concave die and convex die was quickly taken out ~uld imlllediately immersed in a treating liquid. The treating liquid was a 70%
aqueous solution of D~IS0 (at 95C.), after 5 hours, the convex die was separat-ed from the concave die, said concave die was immersed in a 10% aqueous solution of DMS0 (at 95C.) for 5 hours. During the period, the lens naturally peeled from the concave die. Although the circumference of the lens was very thin, the lens free from damage was obtained. I~hen the lens was boiled in water for overnight, it became a transparent soft contact lens.
In order to know the approximate value of the tensile strength of ~0 the solvent-containing lens, the concave and convex dies taken out from the ~utoclave were separated in air and the solvent-containing lens was peeled by a pnir of tweezers. From the finger touch at that time, the tensile s~rength o thc lens was inferred to be about 0.1 - 1 kg f/cm2.
~ lle hydrated lens had a water content of 75%, a percent transmission of light of 85% and a tensile strength of 4 kg f/cm2.
Example 4 An experiment showing toughness of a pressure polymerization was .
carried out. The temperature elevation program of Example 3 was modified by reducing the speed of temperature elevation, which was made an optimum value in an atmospheric pressure polymerization shown in Example 5.
Increase of a hollow occurring ratio due to polymerization contrac-tion was hardly recognized. Number of flashes formed on t'ne overlapping sur-face of the two dies was rather small. This was recognized to be the slowest speed temperature elevation. The pressure inside the space between the dies at t1lis time was inferred to be always close to atmospheric pressure. According-ly, the internal pressure in Example 3 is believed to be considerable.
IO As such, in a pressure polymerization, the possible range of the temperature elevation programme is broad, which is contrastive to delicacy of an atmospheric pressure polymerization indicated in Example 5.
Example 5 The same mold as used in Example 3 was used. A concave die was placed horizontally on the bottom of an autoclave in advance, on which was placed a convex die, through the overlapping surface of the two dies, a needle was inserted to inject about 1 ml of the same original solution as used in Ex-mple 3 and the needle was pulled out. Bubbles were hardly enfolded. The overflowed original solution wetted the circumference of the concave die to say notlling of a wedge-shaped space, accumulated on the bottom of the autoclave.
The nutoclave was filled with nitrogen gas and covered. The inside of the auto-clnvc must be filled with the vapor of the original solution.
A polymerization was carried out according to the following tempera-turc elevation programme, connecting smoothly the following temperature elevation curve.
Until 8 1/4 hours 39C.
At 9 1/4 hours ~6C.
.
5~3 At 10 1/4 hours 50.5C.
At 11 1/2 hours 54C.
At 12 hours 56C.
At 12 1/2 hours 60C.
At 13 hours 74C.
At 14 hours 84.5C.
From 14 1/2 hours through 16 hours 90C.
The steps thereafter were the same as those in Example 3.
The obtained lens was, the same as in Example 3, low in damaging ratio Wit]l few hollows, having about the same values of physical properties.
This temperature elevation programme was the values in atmospheric pressure polymeri~ation and when the temperature changed by +3C. ~for over 10 minutes) from the values mentioned above, a lens with many hollows and (flange-like) projections tended to be produced.
Example 6 A part of Example 5 was changed. Namely, after squeezing the assembly of the concave die and the convex die with the pressure of 50 kgf, the autoclave was covered.
A temperature elevation programme the same as in Example 5 was _0 optimum; however, it was seen that a more severe precision was required in this cxample as compared with that of Example 5.
The number of flashes at the circumference of the obtained lens was small. There were no large differences in damage ratio as a result o:E peel-ing, ratio of hollows ob~ained, and values of physical properties, between the lens of this example and the lens of Example 5.
Example 7 ~-A concave die used in this example was made of glass, having an , ~
. :
, - - , .
interferencc spherical surface like that of 1 in Figure 1, having a radius of curvature of about 9 mm and a diameter of 13 mm. Because this die was manufactured manually by fire forging, the precision of the optical surface was very poor~ As a convex die, that used in Example 1 was employed. The gap in the central portion(s) was about 0.4 mm.
Composition of the original solution for polymerization was, as shown below, a mi~ture of a hydrophilic monomer, a post cross-linkable hydro-phobic polymer and a solvent.
post cross-linkable polymethyl methacrylate ~P~l/\) 28 g NVP
TAIC 1 g ADVN 0.1 g D~IS0 416 g Using this original solution for polymerization, by the method of Example 5, a polymerization was effected. The solvent contained in the obtained lens was e~changed for water (allowed to stand in boiling water for 16 hours).
The resultant product, at 37C., was a soft contact lens of good transparency having a water content of about 80% and a tensile strength of about 10 kgf/cm2.
~0 Said post cross-linkable polymethyl methacrylate was synthesized by the following method.
h~L~ 99 g V~le 1 g ADVN 0.1 g D~IS0 ~0O g . A composition consisting of the aforementioned components was charged in a l-liter 3-neck flask equipped with a stirrer, air inside said flask -~3-.
95~i3 was replaced by argon, and thereafter, the composition in the flask was stir-red while immersed in a 50C. water bath for 7 hours and then the polymer was precipitated by pouring a viscous solution into methanol in the state of a very fine powder. Tlle precipitate was freed of solvent by centrifugation, and thereafter washed twice with fresh methanol, and dried to constant weight in vacuo at a temperature not more than 40C. for about 24 hours.
The obtained polymer had an [~] . 0.8 and the yield was about 30 g.
Example 8 In the process of E~ample 7, there was used a post cross-linkable ~0 I~olymcr synthesized by the following method:
~IA 95 g glycidyl methacrylate (GMA) 5 g ADVN 0.6 g n-dodecylmercaptan (n-DSH)0.14 g DMS0 233 g ` The composition consisting of the aforesaid componen~ was polymeriz-; ed at 50C. for 9.5 hours in the same manner as the synthesis of the polymer in E~ample 7. The obtained polymer was refined and dried. The resultant poly-mer was obtained in a yield of about 33 g and had an [~] .- 0.5.
'~ In order to add methacrylic acid to this polymer, the following reaction was carried out.
said polymer 10 g methacrylic acid (MeAA) 6 g trimethyl benzylammonium chloride (TMBAC) ICl-l3 1 g Topanol* A ~ 0 05 g H3C ~ C(CH3)3 *Trade mark 1,2-dichloroethanc 80 g A composition consisting of the aforesaid components was charged into a 300-ml. 3-neck flask equipped with a stirrer. The addition reaction was effected with the flask immersed in a water bath at 80~C. for 8 hours. After the reaction, the obtained reaction product was added to methanol and precipit-ated as a very fine powder. It was freed of solvent by centrifugation, there-after washed twice l~ith methanol and used for the polymerization. Examination of the product by nuclear magnetic resonance showed a methacrylic group content of about 3O by weight.
The resultant polymer exhibited about the same viscosity as that of the starting polymer. The obtained lens after replacement of the solvent by water had a somewllat weaker tensile strength, but satisfactory transparency.
Example 9 In Example 7, the cross-linking agent in the original solution for a polymerization only was changed. Namely, the composition of the original solution was as follows.
P~ 28 g NVP 75 g ethylidene-bis-~(N-vinyl-2-pyrroli-done? (ENVP) 1 g ADVN 0.6 g D~ISO 416 g The obtained lens after its solvent was exchanged for water, was even higher in transparency than that of Example 7.
Example 10 s In Example 8, only the cross-linking agent in the original solution for a polymerization was changed. Namely, the composition of the original ' . ~ .
~ ~ f~56;3 solution was as follows.
P~I~IA 28 g NVP 75 g V~Ie 1 g ADVN 0.1 g ~ D~IS0 416 g The obtained lens after its solvent was exchanged for water was as transparent as that of E~ample 7.
E~ample 11 ~Reference) ~Iet_lod of synthesizing post cross-linkable polyvinyl pyrrolidone N-vinyl pyrrolidone and vinylene carbonate were polymerized.
NVP 29.1 g vinylene carbonate (VCa) 0.9 g ADVN 0 03 g benzene 70 g An original solution for a polymerization consisting of the afore-said components was placed in a 300-ml, 3-neck flask equipped with a stirrer, the air inside the flask was replaced by argon, and the solution was polymerized with stirring at 50C. for 7 hours.
~0 After the polymerization, the polymer was precipitated by pouring the solution into petroleum benzine.
The polymer was dried in vacuo at 70C. and the yield was 14 g.
Si.~ grams of the obtained polymer was dissolved in 100 g of a 40o aqueous solutioIl of hydrazineJ allowed to stand at room temperature for 3 days thereafter freed of water by an evaporator, again dissolved in water, and thereafter the hydrazine was completely removed therefroIll by an ion exchaIlge resin.
.. -~ ~ .
5~3 After removal of hydrazine, the polymer was dehydrated in the evaporator and further dried in vacuo. Four grams of the dried polymer was dissolved in 50 g o~ dry methylene chloride, and to the resultant solution was added dropwise a mixture of 2 g of methacrylic acid chloride and 8 g of dry methylene chloride at room temperature with stirring. After completion of the addition, the resultant mixture was allowed to stand with stirring for 2 hours, andthe polymer then precipitated by adding to petroleum benzine.
Nuclear magnetic resonance of the obtained polymer was measured in deuterium methanol solvent and it was confirmed that a methacrylic acid group was introduced.
At 11 1/2 hours 54C.
At 12 hours 56C.
At 12 1/2 hours 60C.
At 13 hours 74C.
At 14 hours 84.5C.
From 14 1/2 hours through 16 hours 90C.
The steps thereafter were the same as those in Example 3.
The obtained lens was, the same as in Example 3, low in damaging ratio Wit]l few hollows, having about the same values of physical properties.
This temperature elevation programme was the values in atmospheric pressure polymeri~ation and when the temperature changed by +3C. ~for over 10 minutes) from the values mentioned above, a lens with many hollows and (flange-like) projections tended to be produced.
Example 6 A part of Example 5 was changed. Namely, after squeezing the assembly of the concave die and the convex die with the pressure of 50 kgf, the autoclave was covered.
A temperature elevation programme the same as in Example 5 was _0 optimum; however, it was seen that a more severe precision was required in this cxample as compared with that of Example 5.
The number of flashes at the circumference of the obtained lens was small. There were no large differences in damage ratio as a result o:E peel-ing, ratio of hollows ob~ained, and values of physical properties, between the lens of this example and the lens of Example 5.
Example 7 ~-A concave die used in this example was made of glass, having an , ~
. :
, - - , .
interferencc spherical surface like that of 1 in Figure 1, having a radius of curvature of about 9 mm and a diameter of 13 mm. Because this die was manufactured manually by fire forging, the precision of the optical surface was very poor~ As a convex die, that used in Example 1 was employed. The gap in the central portion(s) was about 0.4 mm.
Composition of the original solution for polymerization was, as shown below, a mi~ture of a hydrophilic monomer, a post cross-linkable hydro-phobic polymer and a solvent.
post cross-linkable polymethyl methacrylate ~P~l/\) 28 g NVP
TAIC 1 g ADVN 0.1 g D~IS0 416 g Using this original solution for polymerization, by the method of Example 5, a polymerization was effected. The solvent contained in the obtained lens was e~changed for water (allowed to stand in boiling water for 16 hours).
The resultant product, at 37C., was a soft contact lens of good transparency having a water content of about 80% and a tensile strength of about 10 kgf/cm2.
~0 Said post cross-linkable polymethyl methacrylate was synthesized by the following method.
h~L~ 99 g V~le 1 g ADVN 0.1 g D~IS0 ~0O g . A composition consisting of the aforementioned components was charged in a l-liter 3-neck flask equipped with a stirrer, air inside said flask -~3-.
95~i3 was replaced by argon, and thereafter, the composition in the flask was stir-red while immersed in a 50C. water bath for 7 hours and then the polymer was precipitated by pouring a viscous solution into methanol in the state of a very fine powder. Tlle precipitate was freed of solvent by centrifugation, and thereafter washed twice with fresh methanol, and dried to constant weight in vacuo at a temperature not more than 40C. for about 24 hours.
The obtained polymer had an [~] . 0.8 and the yield was about 30 g.
Example 8 In the process of E~ample 7, there was used a post cross-linkable ~0 I~olymcr synthesized by the following method:
~IA 95 g glycidyl methacrylate (GMA) 5 g ADVN 0.6 g n-dodecylmercaptan (n-DSH)0.14 g DMS0 233 g ` The composition consisting of the aforesaid componen~ was polymeriz-; ed at 50C. for 9.5 hours in the same manner as the synthesis of the polymer in E~ample 7. The obtained polymer was refined and dried. The resultant poly-mer was obtained in a yield of about 33 g and had an [~] .- 0.5.
'~ In order to add methacrylic acid to this polymer, the following reaction was carried out.
said polymer 10 g methacrylic acid (MeAA) 6 g trimethyl benzylammonium chloride (TMBAC) ICl-l3 1 g Topanol* A ~ 0 05 g H3C ~ C(CH3)3 *Trade mark 1,2-dichloroethanc 80 g A composition consisting of the aforesaid components was charged into a 300-ml. 3-neck flask equipped with a stirrer. The addition reaction was effected with the flask immersed in a water bath at 80~C. for 8 hours. After the reaction, the obtained reaction product was added to methanol and precipit-ated as a very fine powder. It was freed of solvent by centrifugation, there-after washed twice l~ith methanol and used for the polymerization. Examination of the product by nuclear magnetic resonance showed a methacrylic group content of about 3O by weight.
The resultant polymer exhibited about the same viscosity as that of the starting polymer. The obtained lens after replacement of the solvent by water had a somewllat weaker tensile strength, but satisfactory transparency.
Example 9 In Example 7, the cross-linking agent in the original solution for a polymerization only was changed. Namely, the composition of the original solution was as follows.
P~ 28 g NVP 75 g ethylidene-bis-~(N-vinyl-2-pyrroli-done? (ENVP) 1 g ADVN 0.6 g D~ISO 416 g The obtained lens after its solvent was exchanged for water, was even higher in transparency than that of Example 7.
Example 10 s In Example 8, only the cross-linking agent in the original solution for a polymerization was changed. Namely, the composition of the original ' . ~ .
~ ~ f~56;3 solution was as follows.
P~I~IA 28 g NVP 75 g V~Ie 1 g ADVN 0.1 g ~ D~IS0 416 g The obtained lens after its solvent was exchanged for water was as transparent as that of E~ample 7.
E~ample 11 ~Reference) ~Iet_lod of synthesizing post cross-linkable polyvinyl pyrrolidone N-vinyl pyrrolidone and vinylene carbonate were polymerized.
NVP 29.1 g vinylene carbonate (VCa) 0.9 g ADVN 0 03 g benzene 70 g An original solution for a polymerization consisting of the afore-said components was placed in a 300-ml, 3-neck flask equipped with a stirrer, the air inside the flask was replaced by argon, and the solution was polymerized with stirring at 50C. for 7 hours.
~0 After the polymerization, the polymer was precipitated by pouring the solution into petroleum benzine.
The polymer was dried in vacuo at 70C. and the yield was 14 g.
Si.~ grams of the obtained polymer was dissolved in 100 g of a 40o aqueous solutioIl of hydrazineJ allowed to stand at room temperature for 3 days thereafter freed of water by an evaporator, again dissolved in water, and thereafter the hydrazine was completely removed therefroIll by an ion exchaIlge resin.
.. -~ ~ .
5~3 After removal of hydrazine, the polymer was dehydrated in the evaporator and further dried in vacuo. Four grams of the dried polymer was dissolved in 50 g o~ dry methylene chloride, and to the resultant solution was added dropwise a mixture of 2 g of methacrylic acid chloride and 8 g of dry methylene chloride at room temperature with stirring. After completion of the addition, the resultant mixture was allowed to stand with stirring for 2 hours, andthe polymer then precipitated by adding to petroleum benzine.
Nuclear magnetic resonance of the obtained polymer was measured in deuterium methanol solvent and it was confirmed that a methacrylic acid group was introduced.
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for producing a soft contact lens which comprises:
pouring an excess amount of an original solution for producing a soft contact lens into a concave die; placing a convex die on said concave die and over-flowing the excess of said original solution to thereby uniformly fill said original solution in a space between said concave die and said convex die, gelling said original solution between the two dies to form therebetween a lens having a tensile strength of at least about 0.1 kgf/cm2; immersing said lens and said two dies in a liquid to peel said lens from said dies; and extracting the thus-peeled lens via an extraction treatment with water.
pouring an excess amount of an original solution for producing a soft contact lens into a concave die; placing a convex die on said concave die and over-flowing the excess of said original solution to thereby uniformly fill said original solution in a space between said concave die and said convex die, gelling said original solution between the two dies to form therebetween a lens having a tensile strength of at least about 0.1 kgf/cm2; immersing said lens and said two dies in a liquid to peel said lens from said dies; and extracting the thus-peeled lens via an extraction treatment with water.
2. A process of claim 1, wherein said original solution has a co-efficient of gellation contraction at the same temperature and the same pressure of less than about 5% by volume.
3. A process of claim 2, wherein said original solution contains N-vinyl lactam.
4. A process of claim 2, wherein said original solution contains a polymer of a lower alkyl ester of methacrylic acid having an ethylenic double bond in the side chain and N-vinyl lactam.
5. A process of claim 1, wherein said concave die and said convex die are made of glass.
6. A process of claim 1, wherein said convex die has a non-interference surface.
7. A process of claim 1, wherein said gelling is caused by heating said original solution.
8. A process of claim 7, wherein peeling of said lens from said dies is carried out in dimethyl sulfoxide containing water.
9. A process of claim 7, wherein the vapor pressure of the lowest boiling point component in said original solution in an atmosphere under which an assembly of said concave die and convex die in which said original solution is filled, is placed, is made more than about 20% of the saturated partial pressure exhibited by said original solution.
10. A process of claim 7, wherein said gelling is carried out while squeezing the two dies by an outer force of about 10-100 kgf to thereby form a lens having a tensile strength of at least about 0.1 kgf/cm2 in the two dies.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000412101A CA1149563A (en) | 1977-09-12 | 1982-09-23 | Soft contact lens composition and method |
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP10892677A JPS5443284A (en) | 1977-09-12 | 1977-09-12 | Dope for forming soft contact lens |
| JP10892577A JPS5923271B2 (en) | 1977-09-12 | 1977-09-12 | How to manufacture soft contact lenses |
| JP108925/1977 | 1977-09-12 | ||
| JP108926/1977 | 1977-09-12 | ||
| CA000311027A CA1136306A (en) | 1977-09-12 | 1978-09-11 | Soft contact lens composition and method |
| CA000412101A CA1149563A (en) | 1977-09-12 | 1982-09-23 | Soft contact lens composition and method |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1149563A true CA1149563A (en) | 1983-07-12 |
Family
ID=27426107
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000412101A Expired CA1149563A (en) | 1977-09-12 | 1982-09-23 | Soft contact lens composition and method |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1149563A (en) |
-
1982
- 1982-09-23 CA CA000412101A patent/CA1149563A/en not_active Expired
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