CS197292B2 - Mould for making the contact lenses - Google Patents

Description

The invention relates to a mold for making contact lenses.

The basic problem to be overcome when using closed molds for casting articles, such as contact lenses, where the outer surface, regular edge and surface finish is important, is to compensate for the unavoidable shrinkage that occurs during polymerization. For many monomeric materials, the polymerization shrinkage is in the range of 12-22%. This shrinkage has previously been prevented satisfactorily by casting articles such as contact lenses from viuyl monomers such as esters of acrylic and methacrylic acid, vinylpyrrolidone, substituted or unsubstituted acrylamides or methacrylaimides and the like. For example, as disclosed in the US patent

660,545 (Columns 1 and 2), the polymerizing acrylic or methacrylic acid ester mixture, maintained in closed glass mold, becomes retracted from at least one surface of the mold, causing surface spikes to render the cast article unsuitable as a lens.

In another known method (see U.S. Pat. No. 3,660,545), the polymerization mixture is maintained between the concave and convex portions of the glass mold between which an annular gap is provided, which decreases as polymerization proceeds, but again due to polymerization shrinkage . This edge portion could be removed by cutting off, but this results in a thicker edge that tends to touch the eyelid during its movement and cause the lens to move.

Previously, these shrinkage compensation difficulties prevented the production of lenses by molding in closed molds and other contact lens methods of crosslinked polymeric materials such as centrifugal casting, machining and polishing were used.

In centrifugal casting, as disclosed in U.S. Patents 3,408,429 ' and 3,496,254, the polymer mixture is placed in a rotary open mold having a concave surface. Thus, the anterior, convex lens surface is formed by the mold surface and the posterior, concave lens surface is formed as a result of centrifugal force, surface tension of the polymerization mixture and other factors such as mold size and shape, polymerization mixture volume, mold surface condition · etc. the surface of this shaped lens is continuously parabolic and many numerals must be carefully checked to obtain reproducible shapes. Centrifugal cast lenses usually require edge treatment after polymerization and their optical quality is not exactly the highest because they do not faithfully

7 29 2 a spherical optical band, since the back surface is not spherical in shape.

Most contact lens manufacturers of thickened polymeric materials use traditional machining or mechanical processing and polishing of the lens blanks as described in U.S. Patent 3,361,858. This method has the advantage that the curvature and thickness of the lenses can be customized to produce in any desired embodiment. It also achieves high optical quality. However, this method has the disadvantage of requiring highly skilled personnel.

SUMMARY OF THE INVENTION It is an object of the invention to provide a mold for producing cast lenses having the desired optical and adaptive properties of machined and polished lenses.

SUMMARY OF THE INVENTION The present invention provides a contact lens mold comprising an inner mold part having a surface having a substantially longitudinal axis and a predetermined curvature to shape one surface of the contact lens and an outer mold part having a surface also having a substantially longitudinal axis and predetermined a curvature for shaping the second surface of the contact lens.

The principle of the mold according to the invention for the production of contact lenses is that one of the mold parts (~ 110, 130) is provided with a flexible flange (116, 536j) attached circumferentially to the surface of the mold part and having an axis common to the longitudinal axis of the mold part. wherein the mold is made of plastic.

The mold according to the invention thus comprises an inner part, an outer part and a flexible skirt. The inner mold part comprises a shaping surface, and preferably a substantially cylindrical support portion, in which the shaping surface is mounted circumferentially around the lower periphery of the support portion. The mold surface has a predetermined curvature for one of the surfaces of the contact lens.

The outer mold part likewise comprises a second shaping surface and preferably comprises a hollow cylindrical support portion. The inside diameter of this cylinder is approximately equal to the outside diameter of the support portion of the inner part, but the outer part has a slightly larger diameter than the inside diameter ^. friction part. The diameters are predetermined such that there is sufficient clearance so that the inner mold part fits into the outer mold and the excess monomer or other material used can flow between the two mold parts. The clearance, however, must not be large so as not to cause the noso-axial relative position of the mold parts to the extent that it will adversely affect the optical centering of the lens produced.

In preferred embodiments, one end of said outer portion is closed by a second shaping surface of a predetermined curvature, the shaping surface forming the surface of the contact lens to be produced.

The flexible skirt is fully attached to the shaping surface of either the inner part or the outer part in such a way that it is coaxial with it.

The surfaces of the mold are so arranged that one is concave and the other is convex. As will become apparent from the description that follows, all combinations where the concave or convex curvature is joined by the skirt are the subject of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is explained in more detail in the accompanying drawings, in which Figures 1 to 6 show a mold according to the invention in vertical section.

Giant. 1 shows a convex inner shaping surface with a flexible rim attached thereto and a concave outer shaping surface.

Giant. 2 shows a concave inner shaping surface and a convex outer shaping surface with a flexible rim attached to the outer surface.

Giant. 3 is similar to FIG. 2, except that the flexible flange is attached to the inner part.

Giant. 4 is an alternative embodiment of FIG.

3.

Giant. 5 is similar to FIG. 1, except that the flexible skirt is attached to the outer shaping surface.

Giant. 6 shows the simplified embodiment of FIG. 1.

Giant. 7 is a view of the closed mold of FIG. 1, wherein the skirt is shown in a bent state.

In all figures, the last two numbers are equivalent parts numbered with three numbers, where the last two numbers ^. are the same. Thus, the marks 110, 210, 310 and 410 all denote the non-internal part of the mold.

In more detail hereinbelow pop ^su jo nejvýhodnějsOio embodiment provided as an embodiment according to FIG. 1, but pop's regarding this embodiment is also applicable to provdení by any other pictures.

The mold consists of two parts, an inner part 119 and an outer part 130. The inner part consists essentially of a cylindrical part. 114, which has a flange 112 at its top portions,

As shown, said cylindrical portion 114 is hollow to save material required for the mold, but the invention is not limited to this embodiment.

The cylindrical portion 114 is closed by an outer shaping sheet 129 circumferentially connected to the bottom of the cylindrical portion 114. The curvature of the shaping surface V0 is predetermined to meet the requirements of the lens being manufactured. The curvature may be spherical or aspheric or a combination of both. Further, the surface may be toric in the central or cptick zone, but the edge portion must be symmetrical with respect to the central axis of the lens in order to achieve proper seating or bonding to the edge, which will be further discussed. In the embodiment of FIG. 1, a flexible circumferential lip IIB is disposed around the shaping surface integrally therewith. Said rim 113 comprises an outer surface 117, an inner surface 11 * 1 and a bearing edge 118.

The outer mold part 130 is comprised of a cylindrical portion 134, preferably seated in a base portion 132 which is attached thereto, and an outer molding surface 140 seated within the cylindrical portion 134. With respect to the inner molding surface 129, the curvature of the outer molding The surface 140 is predetermined and may vary in the same manner as the curvature of the inner molding surface 120. The mere limitation to the relationship of the curvature of the molding surfaces 120 and 140, discussed in detail below, will result in the article being formed therebetween. suitable properties for contact lenses, in particular it will have a concave surface that will contact the eyeball in use, and a second, metal surface that will contact the inner part of the eyelid.

During the process, which will be described in more detail below, the lens manufacturing material is placed in the outer mold part. The inner part is introduced into the outer part so that the edge abutment edge 118, in this case connected circumferentially to the inner shaping surface 120, just touches the outer shaping surface 140. At this point, the excess shaping material is pushed between the outer edge of the cylindrical portion 114 and the inner In the embodiment shown in the drawing, no discharge channels are shown or provided in said cylindrical portions. However, providing the molds with pressure channels is within the scope of the invention.

The two mold parts containing the molding material are then compressed. The shaping is described in detail below. During molding, the molding material shrinks, this contraction may be up to 20% of the volume of molding material initially present between surfaces 119, 120 and 140. Because the contraction occurs in a completely enclosed space, a vacuum is created against which atmospheric pressure acts to cause the two parts to move 110 and 130 of the mold toward each other. The flexibility of the rim 116 allows the mold parts to approach each other, commensurate with its flexibility. If desired, external pressure may be used to ensure the proximity of the shaping surfaces to one another. However, the application of such external pressure is not always necessary. While in certain cases it is possible to achieve improved results, shaping will generally be carried out without said external pressure.

After completion of the molding process, the mold parts are detached and the produced lens is removed from the mold and is ready for use after cleaning and polishing the edges.

The optical surfaces, the contact surfaces, are in the desired state.

As mentioned above, the embodiment of the molds of FIG. 1 is most preferred because it is the simplest. Giant. 5 shows a variation of the mold of FIG. 1, wherein the skirt 536 is integral with the outer shaping surface 540. In this modification, as in FIG. 1, the inner surface is convex and the outer surface is concave. The top flange 538 of the flange 538 contacts the inner molding surface 520, and the surfaces enclosing the lens forming material are defined by the areas between the points on the surface 520 touching the edge 538 and the inner surface 539 of the flange 53S together with the inner portion of the molding surface 540. the shaping is the same as described in Fig. 1 and will be described in more detail below.

Giant. 2 shows another embodiment of a mold according to the invention, wherein the edge of the skirt 238 is attached to the outer mold surface 240. However, according to this embodiment, the outer mold surface 220 is concave. Otherwise, the process and the relationship of the parts are the same as before.

Giant. 3 illustrates a modification of the embodiment of FIG. 2 wherein the flexible skirt 318 is attached to the inner, concave molding surface 320, and not to the outer, convex molding surface 340.

In the modification of Fig. 4, Fig. 3 is shown, wherein the flexible edge of the rim IS (here 416) is located at the edge of the molding surface 420 and not inside, as shown in Fig. 3.

In the embodiment of FIG. 6, the cylindrical support portion 11 is the inner portion and the cylindrical support portion 34 is the outer portion so that the mold faces 620 and 640 fit together. While this modification is operative and shows the essential features of the invention, modifications involving additionally cylindrical support means are more convenient with respect to their handling.

The process of the invention depends on several interacting factors, one of which is the shape of the mold. Another factor is the nature of the materials used to construct the mold. The material used for mold construction must be sufficiently rigid under the conditions used in the molding to maintain the predetermined curvature of the molding surfaces. In addition, when molded in a thin ring, such as rim 116, it must be sufficiently flexible to allow the aforementioned contraction of the molding volume.

It has been found that suitable molding materials are thermoplastic resins which are inert to the polymerization medium, have the desired flexibility under polymerization conditions, do not stick to the polymerized masses, and can be formed into optically quality surfaces. Particularly suitable materials are polyolefins such as low, medium and high density polyethylene, polypropylene, propylene copolymers known as polyalomers, polybute.n-1, poly-4-methylpentene-1, ethylene vinyl acetate and ethylene vinyl alcohol copolymers, and ethylene copolymers such as Other suitable materials are polyacetal resins and acetal resin copolymers, polyaryl ethers, polyphenylene sulfides, polyarylsulfones, polyaryl ether sulfones, nylon 6, nylon 66 and nylon 11, thermoplastic polyester, polyurethanes and various fluorinated materials such as fluorinated copolymers of ethylene-propylene and ethylene-propylene copolymers. ethylene-fluoroethylene.

The production of a suitable thermoplastic material for use in the manufacture of molds is governed to some extent by the polymerization conditions used in the contact lens manufacturing process. Typically, the thermal deformation temperature of the thermoplastic material at a pressure of 426 kPa under stress in the fiber direction (ASTM D 648) is a guide. Thermoplastic molds are generally suitable at polymerization temperatures of 20 to 40 ° C, below the thermal deformation temperature of the thermoplastic material in the range of several degrees, preferably 10 ° C, and also above said temperature.

For example, low density polyethylene has a thermal deformation temperature of 40 to 50 degrees Celsius and acceptable results are obtained with this material at polymerization temperatures of 30 to 70 ° C. Above 70 ° C, deformation of the optical surfaces may occur.

While polypropylene having a deformation temperature in the range of 100 to 120 ° C, acceptable results are achieved at polymerization temperatures of 65 to 120 ° C with little or no pressure. Below 65 ° C, the flexibility of the plastic edge is not sufficient to compensate for routing, and above 120 ° C, optical surface deformation occurs.

High polymerization temperatures can be used with materials such as nylons, polyphenylene sulfides, polysulfones, and fluorinated polymers exhibiting a higher thermal deformation temperature.

In addition, it is possible to proceed at lower temperatures by increasing the pressure. For example, at a polymerization temperature below 65 ° C and under moderate pressure of ¹ as is likely to occur in the cast lenses produced with polypropylene according to this invention forms the defect; however, if the pressure is increased, for example to 70 kPa (calculated on the total mold area), lenses are obtained without defects. The required flexibility of the mold rim can be obtained by combining the polymerization temperature and the closing pressure.

The inner mold part 110 has a rim 118 formed entirely at the periphery of the inner molding surface 120. The junction of the bottom of the rim 11S to the surface 120 forms the rear of the lens edge, while the junction edge of the rim 118 forms the front edge shape with the outer mold surface 140. The total thickness of the edge so formed is the "height" of the rim 118, i.e. the distance of the outer edge 118 from the inner edge 113 reduced by the rim bend distance to compensate for the shrinkage produced by the polymerization. Depending on the desired edge thickness, the height of the rim 116 may vary from 0.05 mm for a very thin edge to more than 0.3 mm for a completely thick, round edge. In a typical example, the height of the flange 116 from the edge 118 to the edge 113 of the arch is 0.10 mm. If a polymerization mixture having a bulk shrinkage of 20 ° / o is used, then the flange must be bent enough to allow the edge thickness to be compressed to 0.08 mm. This bending is generally accomplished by bending inwardly as indicated in FIG. 7. A similar bending also occurs in the embodiment of FIGS. 2-6.

It is desirable that the top of the skirt be as thin as possible in order to control irregularity to a minimum value. In practice, the rim top thickness is below 0.04 mm, preferably below 0.01 mm. The hem is very delicate and the inner mold part must be handled with care to prevent damage.

The outer diameter of the inner mold half must be smaller than the inner diameter of the outer mold half to allow excess material to escape when the mold is closed. Narrowing the inner and outer halves helps to remove excess material, but is not critical. Usually, the inner half is preferably 0.1 to 0.3 mm smaller in diameter than the outer half. If the difference is too large, for example 0.5 mm, the adjustment of the optical centers is difficult, although the invention is still feasible.

The metal molds intended to produce the desired inner and outer parts of the thermoplastic molds of the invention are produced by conventional machining and polishing. These metal molds are then used in injection molding machines or presses to produce a plurality of thermoplastic molds that are used to cast desired lenses from polymerizable or vulcanizable polymers. A set of metal molds can therefore provide a large number of thermoplastic molds in which a large number of lenses can also be produced, since the thermoplastic molds can be reused if handled gently. This results in considerable savings over the traditional method of machining and polishing individual lenses, since the machining and polishing are carried out only on the original metal molds.

The type of lenses produced according to the invention is not limited to certain precise parameters. Both the front and rear positions of the lenses may have completely spherical curves or aspherical curves or combinations thereof. For example, the central portion of the lens may have spherical curvature on both surfaces, the front and rear, the periphery of the front surface may have a steeper or flatter spherical curvature, and the periphery of the rear surface may be aspherical to achieve better application properties. One or both surfaces may be toric in the central or optical zone, but the peripheral portion must be symmetrical with respect to the central axis of the lens to achieve proper fit or fit of the entire rim.

A monomer, prepolymer or vulcanizable mixture particularly useful in the practice of the invention include hydrophobic esters of acrylic acid, preferably lower alkyl esters, wherein the alkyl contains 1 to 5 carbon atoms such as methyl acrylate or methacrylate, ethyl acrylate or methacrylate, n-propyl acrylate or methacrylate, isopropyl acrylate or methacrylate, isobutyl acrylate or methacrylate, n-butyl acrylate or methacrylate or various mixtures of these monomers. In order to increase dimensional stability and resistance to deformation, the array and the monomers or monomer mixtures may be mixed with a small amount of di- or polyfunctional polymerizable monomers causing crosslinking of the polymer matrix. Examples of such di- or polyfunctional monomers are: divinylbenzene, ethylene glycol diacrylate or methacrylate, propylene glycol diacrylate or methacrylate and acrylates or methacrylates of the following polyols: triethanolamine, glycerol pentaerythritol, butylene glycol, triethylene glycol, diethylene glycol, triethylene glycol, triethylene glycol, Methy-methylene-bis-acrylamide or methacrylamide, sulfonated divinylbenzene and divinylsulfone.

Further, the monomers or mixtures thereof may be mixed with the linear polymers which are soluble therein, provided that the viscosity of the solution is not too high so as to avoid the difficulty of removing bubbles.

Other molecular materials suitable for making the lenses of the invention are hydrophilic monomer blends forming a three-dimensional network as described in U.S. Patent 3,822,089. Illustrative hydrophilic monomers include water-soluble monoesters of acrylic or methacrylic acid with an alcohol having an esterifiable hydroxyl group and at least one other hydroxyl group a group such as mono- and polyalkylene glycol monoesters of methacrylic acid and acrylic acid, for example ethylene glycol mono methacrylate, ethylene glycol monoacrylate, diethylene glycol mono methacrylate, diethylene glycol monoacrylate, propylene glycol mono methacrylate, dipropylene glycol monoacrylate;

N-alkyl and Ν, Ν-dialkyl-substituted acrylamides and methacrylamides such as N-methylacrylamide, Ν, χ-dimethylacrylamide, N-methylmethacrylamide, N, N-dimethylmethacrylamide and the like; N-vinylpyrrolidone; alkyl-substituted N-vinylpyrrolidones such as methyl-substituted N-vinylpyrrolidone, glycidyl methacrylate; glycidyl acrylate and other known monomer species. Also useful are alkyl ether acrylates and methacrylates and vulcanizable silicone fluids or elastomers. Alkyls which are particularly useful in the above compounds contain 1 to 5 carbon atoms.

For hydrophilic monomers or mixtures thereof, it is essential that a three-dimensional network is formed because the polymerized materials absorb water and become soft and flexible, and if not crosslinked, do not have a shape memory. For this reason, it is desirable to use a small amount of crosslinkers as mentioned above.

Preferred monomer mixtures comprise at least one alkylene glycol monoester of methacrylic acid, in particular ethylene glycol mono methacrylate, and at least one crosslinker such as alkylene glycol diester of methacrylic acid, in particular ethylene glycol dimethacrylate. Such mixtures may contain other polymerizable monomers, preferably in small amounts, such as N-vinylpyrrolidone, methyl methacrylate acrylamide, N-methacrylamide, diethylene glycol monomethacrylate and the other monomers mentioned above.

The polymerization may be carried out in bulk or with an inert solvent. Suitable solvents are water, organic solvents such as lower aliphatic monohydric alcohols as well as polyhydric alcohols such as glycol, glycerol, dioxane, etc., and mixtures thereof. Typically, the solvent, if used, contains lesser amount of the reaction medium, i.e. less than 50% by weight.

The polymerization of the monomer mixtures is usually carried out using radical polymerization catalysts of the type commonly used in vinyl polymerization. Such catalysts are organic peroxides, percarbonates, hydrogen peroxide, and inorganic materials such as ammonium, sodium or potassium persulfate. Using such catalysts, the polymerization can be carried out at temperatures between ambient temperature, i.e., about 20 ° C to about 120 ° C, depending on the desired polymerization rate.

The polymerization can also be carried out with monomeric or prepolymer mixtures under the action of higher temperatures or radiation (ultraviolet, X-rays or radioactive decay).

In silicone elastomers, the vulcanization may be carried out by a free-radical curing mechanism or the vulcanization may be carried out by squeezing or condensation.

In the following, the invention is illustrated in more detail by means of exemplary embodiments.

Example 1 a

Production of molds

High density polyethylene outer molds were made by injection molding on a convex inner steel mold having an outer diameter of 12.0 mm, a center radius of curvature of 7.50 mm with a chord diameter of 10 mm, and a circumferential radius of curvature of 7.00 mm. High density polyethylene inner foils were prepared by injection molding in a concave steel mold having an inner diameter of 11.9 mm, a central radius of 7.00 mm with a chord diameter of 11.0 mm, and a circumferential curvature of 12.5 mm. The circumference of the curved surface of the mold was interrupted to form a circumferential ring 0.01 mm wide at the apex extending to 0.12 millimeters from the edge of the curvature. By measuring the radius, the center radius of curvature of the outer concave molds was determined to be 7.43 + 0.04 millimeter and the inner diameter measured was 12.1 mm. The outside diameter of the inner molds was 11.8 mm and the median radius of curvature was 6.95 ± 0.03 mm.

Example 1 b

Shaping lenses

The concave outer molds were laid on a flat surface with the cavity upward. Was prepared by mixing a solution composed of 100 parts of carefully purified 2-hydroxyethyl methacrylate, 30 parts of distilled water, 25 parts ethyíenglykoldimethyletheru, 0.4 parts of ethylene glycol dimethacrylate market and 0.2 parts of ^di-: sopropylperkarbonátu. Half milliliters of solution was dropped into the outer mold and the inner mold was slowly inserted to expel excess solution and bubble. A slight pressure was applied to the inner mold to ensure abutment. The filled molds were then stored in a circulating oven at 45 ° C for 1 to half an hour. After cooling to room temperature, the molds were opened, the rim of the polymerized material filling the cylindrical space in the annulus between the mold halves was removed, and the flexible lenses that adhered lightly to the inner mold half were carefully peeled off. After soaking in physiological saline to remove ethylene glycol dimethyl ether from the lenses, the lenses were tested. The edges were smooth and flat-formed and did not require further machining. The surfaces were also smooth and free from defects. The lenses had a mean thickness of 0.19 ± 0.02 mm, an optical power of 2 2.50 to ,7 2.75 diopters and a diameter of 12.0 mm.

Example 1c

Shaping lenses

A solution containing 55 parts of purified 2-hydroxyethyl methacrylate, 45 parts of N, N-dimethyl acrylate, 30 parts of water, 20 parts of diethylene glycol dimethyl ether, 0.3 parts of methylene-bis-acrylamide and 0.3 parts of diisopropylpercarbonate was poured into the molds of Example 1 and in Example 1b.

When stored in 0.9% saline, impeccable lenses were obtained having a center thickness of 0.21 + 0.03 mm, an edge thickness of 0.10 + 0.02 mm, a diameter of 13.0 mm, and an optical power of -2.25. up to 2.50 diopters. The larger size and slightly less optical power of these lenses over the lenses in Example 1 is due to the larger swelling coefficient of the polymer composition in water.

Example 2a

Molding of forms

The outer molds were made using ethylene vinyl acetate copolymer (containing 10% vinylacetate by injection molding on a convex inner steel mold having an outer diameter of 8.3 mm, a center radius of curvature of 8.60 mm at a chord diameter of 6.5 mm, and a circumferential radius of curvature of 7.55 mm. The inner molds were made of the same copolymer by injection into an outer steel cavity having a central concave radius of curvature of 7.50 mm with a chord diameter of 7.8 mm and a circumferential radius of curvature of 9.50 mm. protruding 0.01 mm above the edge of the curved surface and having a peak thickness of 0.015 mm The inner diameter of the concave steel mold was 8.0 mm.

The inner diameter of the sprayed outer cavities was 8.2-8.4 mm and the median radius of curvature was 8.55 + 0.05 mm. The external diameter of the internal convex plastic molds was

7.9 mm and the center radius of curvature was

7.45 + 0.03 mm.

Example 1 a d 2 b

Shaping lenses

A solution was prepared containing 98 parts of methyl methacrylate, 20 parts of ethylenedimethacrylate and 0.3 parts of di-tert-butylcyclohexylperoxydecarbonate and 0.3 ml of the solution was poured into each of the 10 upside-down concave outer forms. The internal molds were slowly inserted into the cavities to expel air and excess monomer mixture. The inner molds were lightly compressed to ensure that the rim was seated on the concave mold surface and the molds were placed in a circulation drier at 60 ° C for 1 to 1 hour. Then the molds were cooled and opened.

Defect-free lenses of diameter were obtained

7.9 mm, a median thickness of 0.10 + 0.02 mm, a median posterior radius of curvature of 7.47+ + 0.4 mm, and an optical power in the range of -7.50 to -8.50 diopters.

These lenses showed better resistance to deformation and could be bent without permanent deformation unlike lenses of the same size made of non-crosslinked polymethyl methacrylate.

Example 3a

Molding of forms

Using the metal molds of Example 1a, outer and inner thermoplastic molds were made from Nylon 11. The outer concave nylon molds had an inner diameter of 12.0 millimeters and a median radius of curvature of 7.48 + 0.03 mm. The inner nylon molds had an outer diameter of 11.8 mm and a central convex radius of curvature of 6.99 + 0.03 mm. The circumferential ring protruded 0.14 mm above the edge of the curved surface and was less than 0.01 mm thick at its top.

Example 3b

Shaping lenses

Two portions of transparent methylsiloxane liquid, vulcanizable at room temperature, were mixed and 0.4 ml of the mixture was placed in concave external forms facing upwards. The inner molds were inserted to remove excess liquid, and the molds were then lightly compressed to secure the hem to sit. The molds were placed in a circulating oven at 135 ° C for two hours.

After cooling, the molds were opened and the lenses measured. The center thickness was 0.22 ± 0.02 millimeters, the edge thickness was 0.11 ± 0.02 mm, and the optical power was in the range of -2.00 to -2.50 diopters.

SUBJECT

Claims (4)

SUBJECT A mold for producing a contact lens, comprising an inner mold part having a surface having a substantially longitudinal axis and a predetermined curvature to shape one surface of the contact lens, and an outer mold part having a surface also having a substantially longitudinal axis and a predetermined curvature for shaping a second surface of the contact lens, characterized in that one of the mold parts (110, 130) is provided with a flexible flange (116, 536) attached circumferentially to the OF THE INVENTION the surface of the mold part and having an axis common to the longitudinal axis of the mold part, the mold being formed of a plastics material. Mold according to claim 1, characterized in that the flexible flange is bent inwards towards the axis of the mold surface. Mold according to claim 2, characterized in that the flexible flange is 0.05 to 0.3 mm high. 4. The mold of claim 3 wherein the flexible skirt at the apex is at most 0.04 millimeters thick. 1 sheet of drawings Severografía, n. P., Plant 7, Most Giant. 1 FIG. FIG. ³ .110 ΐΐ; 2f <> 312 310