CA1136306A

CA1136306A - Soft contact lens composition and method

Info

Publication number: CA1136306A
Application number: CA000311027A
Authority: CA
Inventors: Shinzo Ohkado; Hideki Kenjo
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 1977-09-12
Filing date: 1978-09-11
Publication date: 1982-11-23
Also published as: JPS5443284A; JPS6136001B2

Abstract

ABSTRACT OF THE DISCLOSURE

An original solution for producing a soft contact lens by a direct casting method is disclosed. The original solution contains: a component A selected from the group consisting of monomers and post cross-linkable hydrophillic polymers wherein the monomers yield hydrophillic component when polymerized; a component B selected from the group consisting of monomers and postcross-linkable hydrophobicpolymers wherein the monomers yield hydrophobic component when polymerized; and a suitable solvent C.
The weight ratio of A:B is from about 85:15 to about 55:45 and the amount of solvent C is about 5 to 95% by weight, at least one of the components A and B is a post cross-linkable polymer. This solution has the advantage of providing a lens which is both optically homogenous and free from bubbles.

Description

~3~i3~6 The present invention provides an "orginal solution" (raw material) suitable for producing in a facile manner a high-quality soft contact lens by a direct casting method, with little deviation in quality at a high yield.
Soft contact lenses have hitherto been generally produced either by the so-called rod method or by the spin-casting method, neither of which is fully satisfactory. Direct casting methods have been proposed but have not been adopted in practice owing to various shortcomings. The present invention is based on the discovery of an original solution capable of being transformed into a soft contact lens by a direct casting method, namel~ by filling the cavity between concave and convex dies, preferably made of glass, with said solution; polymerizing to a gel; peeling; and finally extracting with water.
The solution of this invention is particularly suitable for use in a process for producing a soft contact lens by pouring an excess amount of the solution into a concave die; placing a convex die on said concave die and overflowing the excess of said solution to thereby uniformly fill said solution in the space between said concave die and said convex die; gelling said 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.
The invention accordingly provides an original solution for producing a soft contact lens containing: a component A

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selected from the gxoup consisting of monomers and post cross-linkable hydrophilic polymers wherein the monomers yield hydrophilic component when polymerized; a component B selected from the group consisting of monomers and post cross-linkable hydrophobic polymers wherein the monomers yield hydrophobic component when polymerized;
and a suitable solvent C, the weight ratio of A:B being from about 85:15 to about 55:45, the amount of solvent C being from about 5 to 95% by weight of the original solution, and at least one of the components A and B being a post cross-linkable polymer.
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, the 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. The two dies are preferably made of glass, and the convex die preferabl-y has a non-interference surface.
In a preferred emhodiment, the gellation step is caused by heating. A preferred embodiment of the peeling step utilizes a dimethyl sulfo~ide - water mixture.
It is to be understood that besides the monomers referred to above there may be used in place of one component (i.e. either A or B~ the partially polymerized form which has not reached the stage of gellation, particularly with respect to the monomer component B.
According to the present invention it is possible to obtain a soft contact lens which is optically homogeneous and ?\ 2 .

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without bubbles, despite the shape of the lens. Another problem that is avoided 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 the hyclration. 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.
In addition to the components A, B and C referred to 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 caprolactam; N-vinyl oxazolidone; a hydroxy lower alkyl ester of acrylic acid or methacrylic acid such as hydxoxyethyl or hydroxypropyl ester of acrylic acid or methacrylic acid; glycerin monoacrylate or glycerin monomethacrylate; and an ortho-lactone having a hydrophilic group. As used above and throughout the description 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 cross-linkable hydrophilic polymer having functional group (s) adequate to form a cross-linkage between one hydrophilic polymer and another (post cross-linking). Illustxative of such hydrophilic polymer is the product obtained by (co~ polymerizing one or more components A and, if necessary, a monomer for introducing functional group(s) to a polymer (functional group-introducing . ' ` ~
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monomer). As said functional group~introducing monomers there may be mentioned n-butoxymethylacrylamide, glycidyl methacrylate, vinylene carbonate, hydroxyethyl methacrylate, hydroxyethyl acrylate, vinyl methacrylate, vinyl acrylate, methacrylic 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.
As another example of such a hydrophylic polymer, polyvinyl alcohol may be cited. In this case, hydroxyl groups in the polymer enable a post cross-linking 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 polymerised, which neither swells nor dissolves in water even though it is not cross-linked. As such monomer, there may be cited a lower alkyl ester of acrylic acid or methacrylic acid (for example, methyl methacrylate); an unsaturated nitrile such as acrylonitrile or methacrylonitrile; an aromatic olefin such as styrene and a hydrophobic ortholactone.
The hydrophobic polymer of the component B calls for a cross-linkable polymer having functional group(s) adequate for forming a cross-linkage between one hydrophobic polymer and `, ~1 ~ll3~

another (post cross-linking) and which neither swells nor dissolves in water. Representative of such cross-linkable hydrophobic polymer is the product obtained by (co)polymerizing one or more components B and, if necessary, a functional group-introducing ~onomer. It is preferable that the copolymerization composition ratio of the monomer to the aforesaid functional group-introducing monomer generally ranges from about 1000:1 to about 10:1. As a hydrophobic polymer, a non-cross-linking polymer, for example, polyvinyl butyral may be mixed.
In both cases of polymers of the component A and the component B, when a hydroxyl group is contained as a functional group, it is possible to convert said polymer into a post-cross-linkable polymer by esterifying said hydroxyl group with, for example, methacrylic acid to thereby introduce an ethylenic double bond to the side chain.
As to combination of the component A with the component B, there is preferred such combination as will give an "original solution" whose coefficient of polymerization contraction at the same temperature and the same pressure (hereinafter referred to as ~ O) is less than about 5~ by volume. More specifically, there are the following preferable combinations:
(1) The combination of a monomer used as the component A
with a polymer 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 . ~

~3~306 methacrylate copolymer, or a non-gelled copolymer of methyl methacrylate and vinyl methacrylate as the component B.

(2) The combination of polymers used both as the component A
and the component B: A polymer obtained by reacting (esteriEying) 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.

(3) The 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 the original solution for polymerization.
Of the -foregoing, especially preferable are combination containing, inter alia, N-vinyl pyrrolidone and a methyl methacrylate polymer.
It is necessary that the mixing ratio of the component A
to the component B should range from about 85:15 to about 55:45.
In case the amount of the component A exceeds the upper limit of said range, viz. about 85%, a high-tenacity lens cannot be obtained, and in case the amount of the component A becomes less than about 55%, a lens having a high water content cannot be obtained. If said ratio is within the aforesaid range, a lens having a high tenacity and a high water content in good balance is obtainable.
The solvent component C 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 . . .
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~3~3~6 used, the lens is unsatisfactory in optical properties, and also in many cases in dynamic properties.
It is possible to select a solvent from a wide range depending upon the combination of the component A with the component B. Where N-vinyl pyrrolidone and a methyl methacrylate polymer are employed, which is an especially preferable mode of practice of the present invention, there is preferably used dimethyl sulfoxide and/or ethylene carbonate with or without the admixture of a small amount of dioxane. In case a polymer of N-vinyl pyrrolidone is used as -the component A and a polymer of methyl methacrylate is used as the component B, dimethyl formamide, N-methyl pyrrolidone and dimethyl acetamide they may be used as a solvent, as they simultaneously dissolve the two polymers.
It is necessary that the amount of the solvent used be within the range of about 5-95% by weight based on the total amount of the original solution; of said range, the range of about 30-90% by weight is preferable, and the range of about 50-90% by weight is most preferable. Where the amount of the solvent exceeds about 95% by weight, the tensile strength of a solvent-containing gel obtained by polymerizing and/or cross-linking the original solution becomes low, and thus handling of the solvent-containing lens becomes somewhat difficult.
It is preferable to so adjust the original solution as to make the tensil.e strength of the solvent-containing gel, not less than about 0.1 kg f/cm2; and for that end, it is necessary not only to use an amount of solvent within the aforesaid range, but also to carefully select the kind of solvent. When the amount .. - .
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of the solvent is less than about 5~ by weight, the hydrated lens obtained upon swelling is hard, the water content of the lens is low or the lens undergoes permanent deformation to such an extent that parts of the molecules are destroyed due to the swelling force.
It is most preferable that the dimensional chanye brought about when a solvent contained in a gel i9 replaced by water, is within the range of from about +20% through about -30%.
The cross-linking agent will now be considered. A
polymer is used either as component A or component B, and there is employed a post cross~linking agent reacting wi-th the functional group(s) of the polymer to form cross-linkages between one polymer molecule and another. As a post cross-linking agent, any suitable substance may be employed unless it changes the essential properties of the polymer. For 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 selected from compounds each having at least two polymerizable unsaturated bonds in the same molecule is added to advance the cross-linking polymerization. As such cross-linking agents, there may be mentioned di- or tri-allyl compounds such as diallyl succinate, diallyl phthalate, diallyl maleate, diethylene glycol bis-allyl carbonate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate and triallyl trimellitate; di- or tri-vinyl compounds such as divinyl benzene, N,N'-methylene bis acrylamide, (poly)ethyl-lene glycol dimethacrylate, hexamethylene bis maleimide, divinyl , ..

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urea, bisphenol ~ bis-methacrylate, divinyl adipate, glycerin trimethacrylate, trimethylol propane triacrylate, trivinyl trimellitate and 1,5-pentadiene; allylvinyl compounds such as allyl acrylate and allyl methacrylate; 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 amount of the polymeri~able monomers of the component A and the component B.
The cross-linking polymerization is carried out by such means as heat, radiation or electron ray in the presence of a polymerization initiator if necessary. As preferred examples of such a polymerization initiator, there may be mentioned an organic peroxide such as di-tert-butyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, tert-butyl hydroperoxide, tert-butyl perpivalate, peracid and ammonium persulfate, an azo compound such as azobisisobutyronitrile, azobiscyclohexane carbonitrile, phenyl-azoisobutyronitrile and azobis-dime-thylvaleronitrile; and a redox catalyst. The amount of such polymerization initiator to be added is within the range of about 0.001 - 3% by weight based on the polymerizable monomer.
20 ` It will be seen by a worker skilled in the art that in addition to ~he criteria previously set forth, additives such as a cross-linking promotor and coloring agents may be added to the original solution of the present invention as needed. It is also possible to add a polymer to the original solution which can be extracted with water from the solvent-containing gel, for example, poly N-vinyl pyrrolidone. Not only such an extractable polymer, but other extractable substances may be formally regarded g _ .~

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L3~i3a~6 as a part of the solvent, so far as in order to calculate the relative amount of the solvent in the solution.
The smaller is the r O of the original solution, the more preferable it is. When a casting method is adopked in which the volume of the lens-defining space gradually decreases as contraction due to polymerization proceeds, even though the value of rO is as high as 15-20~, there is no possibility of hollows occurring. However, where the diopter of the 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 the memory of such flow develops after the hydration treatment, which is not desirable. Thus, it is prefer-able that rO is less than about 10~ by volume, and still more preferably less than about 5~ by volume.
As preferred embodiments of original solutions for producing a soft contact lens of the present invention, there may be mentioned:
(1) The combination, wherein N-vinyl pyrrolidone is used as a monomer, 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.
(2) The combination, wherein a post cross-linkable polymer obtained by hydrolizing a vinyl pyrrolidone - vinylene carbonate polymer and thereafter esterifying the resul-tan-t hydrolyzed copolymer with methacrylic acid, and a non-gelled copolymer of methyl methacrylate and vinyl methacrylate, are used .~ -10 -~L~363~i as polymers and N-methyl pyrrolidone is used as a solvent.
A pair of dies are preferably used for producing a soft contact lens in the present invention, that is a pair of a concave die and a convex die. At least one of these two dies is one whose lens~defining surface is an interference spherical surface or an interference paraboloidal surface (hereinafter an interference spherical surface and an interference paraboloidal surface shall be generally referred to as an interference surface). The interference spherical surface or the interference paraboloidal surface referred to herein 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 that the concave die and the convex die are so designed as to briny them into a linear, not surface contact, because it is sometimes difficult to make the central axes of the two dies exactly coincident in the latter case.
Examples of the combination 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; ancl ; Figure 3 represents a third possible pattern or a pair of convex and concave dies.

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Figure 1 is a combination of a concave die 1 having an interference surface with a convex die 2 having a non-interference surface (a lens defining die surface having a spherical or paraboloidal surface only is genera:Lly referred to as a non-interference surface). This combination is especially preferred for practising the present invention, because the concave die having an interference surface is used and a lens having good permeability to tear flow can be produced, and no inner bevel is produced. An inner 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 obtained by the process of the present invention, no problem is brought abouteven though there is no inner bevel.
Figure 2 is an example of combination of a concave die having an interference surface 1 with a convex die also having an interference surface 4; by the use of such dies, the present invention can be easily practised also. As a concave die, one having a non-interference surface may also be used. However, except for special dies, an outer bevel (an inclined surface produced on the circumferential portion on the side of 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 producing a projection on the circumferential portion on the concave surface of the lens and promoting flow of tear. When a , ,. ,' ::
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hole is marked, such marked hole is also utilizable for identifica-tion 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 interference surface with a convex die 4 also having an interference surface. This combination is e~cellent in that any lens flash produced in the overlapping surfaces of the dies does not contact the cornea. This combination is especially suitable for manufacturing dies from thermoplastics or metal by the transcription method.
In the filling step, an original solution in an excess amount is poured into a concave die. Use of such an excess 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 dies shown in Figure 1 which are preferred for preparing lenses from the original solution of the present invention, there is a wedge-shaped space 3 adjacent the seal, the overflow of the original solution is held in that space 3 to perfect the seal. On the other hand, when contraction occurs during polymerization, the overflow of the original solution is supplied through a slight opening of the seal into the sealed portion to make up for the polymerization contraction. Where such dies are used, the total amount of overflow is preferabl~ about 5 times or more of the amount of the original solution held in said wedge-shaped space~ Determination of the amount of the original solution may also be carried out as follows. A plurality of dies each charged with the original solution are placed, for the I J~

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The lowest boiling point component of the original solution is so chosen that its vapor pressure is at least about 20~ of the saturated partial pressure exhibited by the original solution inside said vessel. By charging an excess of such an original solution, it becomes possible to prevent the :Lens from enfolding bubbles while at the same time inhibiting slight changes of composition o the original solution during the gelling step, thus enabling very high-quality lenses to be obtained in good yield.
Another mode of practice of the filling step is to fill the original solution in a sealed container. In this procedure, a concave die is fastened in place in a sealable container, and the original solution is poured into the concave die. Thereafter, the whole container is inclined and a spherical convex die placed on the concave die in said container. The air inside the container is removed or 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 reaction is caused to proceed by the action of heat, radiation or electron ray. When such reaction is caused 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 production of holes and hollows due to polymeri7ation contraction of the original solution:

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363~6 (a) Liquid is supplied through the slight opening between the concave 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 concave and convex dies is heated to develop thermal expanslon .
(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 V of the space between the concave and convex dies is somewhat decreased during the process from initiation through termination of the polymerization reaction.
Method (a) If, as mentioned above, the overflow of the original solution is held in the wedge-shaped space of the dies, the overflow of the original solution is naturally absorbed through the slight opening of the seal between the two dies, because the pressure inside the dies becomes negative owing to polymerization contraction. This method is preferred in a metal die rather than ; in a plastic die and most preferable in a glass die. In the case of glass die, the opening between the two dies is sometimes excessive. In such case the concave and convex dies are squeezed together with a force of 10 - 200 kg f, preferably about 50 kg f.
While the liquid used in the just described embodiment ;~
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~L~3~i3a36 is normally the overflow of the original solution, it is not limited to the original solution since either a monomer of a solvent will suffice.
Method (b) The original solution is sealed in a pressurized, compressed state within the die and as the polymerization proceeds, the internal pressure is reduced automatically.
The original solution is pressurized by heating or by pumping it into the sealed space.
When squeezing of the concave and convex dies together results in incomplete sealing, the seal may be perfected if the concave and convex dies are placed in an au-toclave and the original solution is added in the autoclave to both fill the molds and the autoclave.
Method (c) This method 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, but the following two procedures are effective. One is to mix the monomer with a solvent having a high coefficient of thermal expansion and carry out a solution polymerization. The other is to carry out the polymerization at temperatures ranging from a low temperature immediately above the freezing point of the solution to a high temperature just short of the decomposition temperature.
In this case, because a proper thermal polymerization catalyst is not available, an electron radiation polymerization is desirable.
Method td) This method seeks to eliminate overall contraction of : ~ , : - .. , :

3~6 the entirety by allowing hollows to form in harmless positions.
Such positions are an outer or inner bevel of the lens. In order to make certain that hollows form in such a position, foaming nuclei are preferably provided on the outer bevel portion of the concave die. As such oaming nuclei, a rough sur~ace of the dies, contamination caused by foreign matters such as a very small amount of oil or grease or plastic fiber are preferable.
Method (e) This method is achieved by gradually decreasing the volume of the lens-defining space V as polymerization proceeds.
If the volume decrease during the polymerization is termed ~V, up to about ~V/V=3% can be employed in the process of the present invention. In the case of glass die, 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, those which are preferable for obtaining satisfactory lens performance, are (a), ~b), and (c), with (d) and (e~ preferably being used as auxiliary means. These methods are used in appropriate combination.
Peeling of a solvent-containing gel from die is preferably carried out in a liquid, especially in an aqueous solution. The assembly of the concave and convex dies may be immersed as such in the liquid. However, since contact of the overlapping surface of the die assembly with the liquid will suffice, the entire die need not be immersed. By conducting the peeling in the liquid, it is possible to drastically reduce the ratio of damaged lenses.
This effect is especially remarkable when glass die is used.

;: , : : . , L3~;306 When peeling operations are carried out in water, exchange of the solvent contained in the gel for water can be carried out without any further treatment.
The li~uid used for peeling is not particularly limited insofar as it does not adversely affect the lens. However, in generall the same solvent,as used in the original solution with the addition of water is preferably used. 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 elute, while water or an artificial tear solution flow in.
When ~his step is completed J a hydrated gel whose percent transmission of visible light is more than about 90~ per thickness of 0.1 mm, may be obtained.
Example 1 (Reference) The concave die used in this example is made of a low-pressure polyethylene, having a shape like 1 of Figure 2, theradius 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.

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1~3t~3~)6 hydroxyethyl methacrylate ~HE~A) 70 g N-vinyl pyrrolidone (~VP) 30 g acrylic acid 2 g ethyleneglycol dimethacrylate (EGDM~) 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 of 20~ 1 was poured into the concave die and the convex die was carefully centered thereon. Because 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 kgf and the polymerization conducted in a hot air oven, said solution being heated at 60C. for 16 hours and then at 90C. for 4 hours. The rO
of the original solution was 3.5%, a greater part of which, however, was made up for by reduction of the volume of the diies.
After immersing the assembly of the two dies in water, the clamps were loosened, and the assembly allowed to stand over-night as such in water and the two dies were separated in thewater. By so doing the ratio of the number of lenses with a broken circumference decreased by about 10~ tas 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 die to stand in water for 5 hours promoted natural peeling die.
The water content of the lens obtained in this manner using water at pH 8 was about 75% and a lens having an intact edge ., :. - . : ' . . ~ .

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113~3~36 was obtained. The percent 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 the 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 kgf/cm .
Example 2 (Reference) Using the same die and the same original solution as used in Example 1, the original solution was charged by the same method. Thereafter, the two dies were clamped together by a force of 0.5 kgf and the original solution was polymerized in a water bath. After heating the die under the same conditions 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 (Reference) 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 central 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, the lens became a thick concave lens having a crescent-like sectional configuration.

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Composition of the original solution for polymerization was as follows, a mixture containing a hydrophilic monomer, a hydrophobic monomer and a solvent.
NVP
methyl methacrylate (MMA) 30 g TAIC 1 g triethyleneglycol dimethacrylate ~TEGDMA) 3 g vinyl methacrylate (VMe) 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 kgf/cm2 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), and at 80C. for the next 0.8 hour (48 minutes). The temperature was still raised at 90C.
in 0.9 hour, where 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 and immediately immersed in a treating liquid. The treating liquid was a 70%
aqueous solution of DMSO (at 95C.), after 5 hours, the convex die was separated from the concave die, said concave die was immersed in a 10% aqueous solution of DMSO ~at 95 C.) for 5 hours. During the period, the ~ a ,: ', j, : .

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lens naturally peeled from the concave die. Although the circumference of the lens was very thin, the lens free from damage was obtained. When the lens was boiled in water for o~ernight, it became a transparent soft contact lens.
In order to know the approximate value of the tensile strength of the solvent-containing lens, the concave and con~ex dies taken out from the autoclave were separated in air and the solvent-containing 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 0.1 - 1 kgf/cm2.
The hydrated lens had a water content of 75%, a percent transmission of light of 85% and a tensile strength of

4 kgf/cm .
Example 4 (Reference) 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 contraction was hardly recognized. Number of flashes formed on the overlapping surface 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 this time was inferred to be always close to atmospheric pressure. Accordingly, the internal pressure in Example 3 is believed to be considerable.
As such, in a pressure polymerization, the possible ,., ': : : . . ~........... .

~L~L3~i3~i range of the temperature elevation programme iB broad, which is contrastive to delicacy of an atmospheric pressure polymerization indicated in Example 5.
Example 5 (Reference~
The same mold as used in Example 3 was used. A concave die was placed horizontally on the bottom o-f an autoclave in advance, on which was placed a convex die, through the overlapping surface of the t~o dies, a needle was inserted to inject about 1 ml of the same original solution as used in Example 3 and -the needle was pulled out. Bubbles were hardly enfolded. The overflowed original solution wetted the circumference o the concave die to say nothing of a wedge-sha~ed space, accumulated on the bottom of the autoclave. The autoclave was filled with nitrogen gas and covered. The inside of the autoclave must be filled with the vapor of the original solution.
A polymerization was carried out according to the following temperature elevation programme, connecting smoothly the following temperature elevation curve.
Unit 8 1/4 hours 39C.
At 9 1/4 hours 46 C.
~ At 10 1/4 hours 50.5 C.
- At 11 1/2 hours 54 C.
At 12 hours 56 C.
At 12 1/2 hours 60 C.
At 13 hours 74 C.
At 14 hours 84.5 C.

From 14 1/2 hours through 16 hours 90C.

,~
i ~

' ~

~31 3~

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 with few hollows, having about the same values of physical properties. This temperature elevation programme was the values in atmospheric pressure polymerization and when the temperature changed by ~3C. (for over 10 minutes) from the values mentioned above, a lens with many hc)llows and (flange-like) projections tended to be produced.
Example 6 (Refarence) 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 optimum; however, it was seen that a more severe precision was required in this example 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-f peeling, ratio of hollows obtained and values of physical properties, between the lens of this example and the lens oE Example 5.
Example 7 A concave die used in this example was made of glass, having an interference spherical surface li~e 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.

, ~

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, 3L3~6 As a convex die, that used in Example 1 was employed.
The gap in the central portion(s) was about 0.4 mm.
~ omposition of the original solution for polymerization was, as shown below, a mixture of a hydrophilic monomer, a post cross-linkable hydrophobic polymer and a solvent.
post cross-linkable polymethyl methacrylate 28 g NVP
TAIC 1 g ADVN 0.1 g DMSO 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 exchanged for water (allowed to stand in boiling water for 16 hours)O 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/cm .
Said post cross-linkable polymethyl methacrylate was synthesized by the following method.
MMA
VMe 1 g ADVN 0.1 g DMSO 400 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 was r~placed by argon, and thereafter, .~ -25-. ~

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. . . : ,, : :
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the composition in the flask was stirred while immersed in a 50C.
water bath for 7 hours and then the polymer was precipitated by pouring the viscous solution into methanol in the state of a very fine powder. The precipitate was freed of solvent by centrifugation, and thereafter washed twice with fresh methanol, and dried to constant weight in ~acuo 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 Example 7, there was used a post cross-linkable polymer synthesized by the following method:
MMA 95 h glycidyl methacrylate (GMA) 5 g ADVN 0.6 g n-dodecylmercap-tan (n-DSH) 0.14 g DMSO 233 g The composition consisting of the aforesaid components was polymerized at 50C. for 9.5 hours in the same manner as the : 20 synthesis of the polymer in Example 7. ~he obtained polymer was refined and dried. The resultant polymer 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) 1 g , : ., ~L3~3~6 Topanol A (trade mark) C 3 0.05 g H3C ~ C(CH3~3 OH
1,2-dichloroethane 80 g A composition consisting of the aforesaid components was charged into a 300-ml, 3-neck flask e~uipped with a stirrer. The addition reaction was effected with the flask immersed in a water bath at 80C. for 8 hours. After the reaction, the obtained reaction product was added to methanol and precipitated as a very fine powder. It was freed of solvent by centrifugation, thereafter washed twice with methanol and used for the polymerization.
Examination of the product by nuclear magnetic resonance showed a methacrylic group content of about 3~ 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 somewhat weaker tensile strenght, 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.
PM~A* 28 g NVP

ethylidene-bis-3-(N-vinyl-2-pyrrolidone) (ENVP) 1 g ADVN 0.6 g DMSO 416 g The obtained lens after its solvent was exchanged ,,. ,~, . .
:. ., ~ ,. , -- . :,: i.. . ..
.. . i. : ::: . ..

~3~ 6 for water, was even higher in transparency than that of Example 7.
Example 10 In Example 8, only the cross-linking agent in the original solution for a polymerization was changed. Namely, the composition of the original solution was as follows.
* 28 g NVP
VMe 1 g ADVN 0.1 g DMSO 416 g The obtained lens after its solvent was exchanged for water was as transparent as that of Example 7.
Example 11 (Reference~
Method of synthesizing post cross-linkable polyvinyl pyrrolidone N-vinyl pyrrolidone and vinylene carbonate were polymerized.
~VP 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 aforesaid components was placed in a 300-ml, 3-neck flask equipped with a stirrer, the air inside the flask was replaced bv argon, and the solution was polymerized with stirring at 50C.
for 7 hours.
After the polymerization, the polymer was precipitated by pouring the solution into petroleum benzine.

: J
~ 28-.
. :

, ~3~3~i The polymer was dried ln vacuo at 70C. and the yield was 14 g.
Six grams of the obtained polymer was dissolved in 100 g of a 40% aqueous solution of hydrazine, 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 therefrom by an ion exchange resin.
After removal of hydrazine, the polymer was dehydraked in the evaporator and further dried ln vacuo. Four grams of the dried polymer was dissolved in 50 g of 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 and the polymer ~hen 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.

` ~ -29-. !

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An original solution for producing a soft contact lens containing: a component A selected from the group consisting of monomers and post cross-linkable hydrophilic polymers wherein the monomers yield hydrophilic component when polymerized; a component B selected from the group consisting of monomers and post cross-linkable hydrophobic polymers wherein the monomers yield hydrophobic component when polymerized; and a suitable solvent C, the weight ratio of A : B being from about 85 : 15 to about 55 : 45, the amount of solvent C being from about 5 to 95% by weight of the original solution, and at least one of the components A and B being a post cross-linkable polymer.

2. An original solution according to claim 1, wherein said monomer of the component A is N-vinyl lactam, N-vinyl oxazolidone, a hydroxy lower alkyl ester of acrylic acid, a hydroxy lower alkyl ester of methacrylic acid, glycerin monoacrylate, glycerin monomethacrylate or a hydrophilic ortho-lactone.

3. An original solution according to claim 1, wherein said post cross-linkable hydrophilic polymer of the component A is (i) a polymer consisting of at least one kind of monomer selected from the group consisting of N-vinyl lactam, N-vinyl oxazolidone, a hydroxy lower alkyl ester of acrylic acid, a hydroxy lower alkyl ester of methacrylic acid, glycerin monoacrylate, glycerin monomethacrylate and a hydrophilic ortho-lactone or (ii) a polymer obtained by introducing a post cross-linkable functional group to polyvinyl alcohol.

4. An original solution according to claim 1, wherein said post cross-linkable hydrophilic polymer of the component A is that which is obtained by hydrolyzing an N-vinyl pyrrolidone - vinylene carbonate copolymer and thereafter reacting the hydrolyzed copolymer with methacrylic acid.

5. An original solution according to claim 1, wherein said monomer of the component B is a lower alkyl ester of acrylic acid or methacrylic acid, an unsaturated nitrile, an aromatic olefin or a hydrophobic ortho-lactone.

6. An original solution according to claim 1, wherein said post cross-linkable hydrophobic polymer of the component B is a polymer obtained by reacting a copolymer of a lower alkyl ester of acrylic acid or methacrylic acid, an unsaturated nitrile, and aromatic olefin or a hydrophobic ortho-lactone; and glycidyl ester of acrylic acid or methacrylic acid; with acrylic acid or methacrylic acid.

7. An original solution according to claim 1, wherein said post cross-linkable hydrophobic polymer of the component B is a polymer obtained by copolymerizing a lower alkyl ester of acrylic acid or a lower alkyl ester of methacrylic acid, and a vinyl ester of acrylic acid or a vinyl ester of methacrylic acid, and stopping the polymerization before the obtained polymer gels.

8. An original solution according to claim 1 which comprises N-vinyl pyrrolidone, a methyl methacrylate - glycidyl methacrylate copolymer which is esterified by methacrylic acid, triallyl isocyanurate, azobisdimethyl valeronitrile and dimethyl sulfoxide.

9. An original solution according to claim 1 which comprises N-vinyl pyrrolidone, a methyl methacrylate-vinyl methacrylate copolymer, triallyl isocyanurate, azobisdimethyl valeronitrile and dimethyl sulfoxide.

10. An original solution according to claim 1 which comprises N-vinyl pyrrolidone, a methyl methacrylate-vinyl methacrylate copolymer, ethylidene-bis-3-(N-vinyl-2-pyrrolidone), azobisdimethyl valeronitrile and dimethyl sulfoxide.

11. An original solution according to claim 1 which comprises N-vinyl pyrrolidone, a methyl methacrylate-vinyl methacrylate copolymer, vinyl methacrylate, azobisdimethyl valeronitrile and dimethyl sulfoxide.

12. An original solution according to claim 1 which comprises a hydrolyzed copolymer of N-vinyl pyrrolidone and vinylene carbonate which is esterified by methacrylic acid, a methyl methacrylate-glycidyl methacrylate copolymer which is esterified by methacrylic acid, triallyl isocyanurate, azobisdimethyl valeronitrile and N-methyl pyrrolidone.

13. An original solution according to claim 1 which comprises a hydrolyzed copolymer of N-vinyl pyrrolidone and vinylene carbonate which is esterified by methacrylic acid, a methyl methacrylate-vinyl methacrylate copolymer, triallyl isocyanurate, azobisdimethyl valeronitrile and N-methyl pyrrolidone.

14. An original solution according to claim 1, 2 or 3 wherein the amount of solvent C is from 30 to 90% by weight.

15. An original solution according to claim 4, 5 or 6 wherein the amount of solvent C is from 30 to 90% by weight.

16. An original solution according to claim 8, 9 or 10 wherein the amount of solvent C is from 50 to 90% by weight.

17. An original solution according to claim 11, 12 or 13 wherein the amount of solvent C is from 50 to 90% by weight.

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