PROCESS FOR TINTING A HYDROGEL CONTACT LENS

Abstract: A method for tinting a hydrogel contact lens employing a water-soluble leuco ester of a vat dye which is ultimately oxidized to regenerate the original chromophore.

Description: PROCESS FOR TINTING A HYDROGEL CONTACT LENS BACKGROUND OF THE INVENTION This invention relates to a process for tinting or coloring a hydrogel contact lens or other ophthalmic prosthetic device. Contact lenses can be tinted for cosmetic appearance as well as to reduce light transmission thereby providing the wearer with increased visual comfort. It is, of course, important that the tinted, or colored, lens impart a natural appearance to the wearer's eye. - A natural-appearing soft contact lens should have a clear central area, a tinted intermediate area and a clear outer area so that the tinted portion will not cover the sclera of the eye. Moreover, the central portion of the lens should be untinted tb permit maximum light passage into the eye interior. A number of procedures for tinting or coloring a contact lens employing a variety. of color or dye materials are known. U.S. Patent No. 3,476,499 describes a method for selectively coloring a hydrogel-type contact lens by precipitating an insoluble coloring ' material within a selected portion of the lens body. For example a hydrogel-type contact lens of the sort disclosed in U.S. _ Patent No. 2,976,576 is selectively colored by impregnating the lens- with " a light-sensitive diazόnium salt, selectively exposing the lens to light through a negative, and developing and fixing the latent picture produced by condensing the diazonium salt still present after exposure with a developing agent in a known manner to form an insoluble dye in the portions of the lens not previously exposed to light. U.S. Patent No. 4,157,892 describes another method for coloring a hydrogel-type contact lens utilizing a diazonium salt. U.S. Patent No. 4,252,421 describes a method for tinting the central area of a hydrogel-type contact lens employing a water-insoluble dye or a dye which becomes bonded to the polymer backbone of the polymerized co-monomer mixture from which the lens body is obtained. Among-the water-insoluble dyes mentioned are: low solubility pigments such as iron oxide and lamp black and metal complexes such as phthaloσyanines and organic Neozapon R dyes (B.A.S.F.-Wyandotte of Parsippany, N.J.). Useful polymer bound dyes are said to be selectable from among any dyes containing a polymerizable vinyl group, e.g., a phthalocyanine dye whose nucleus has been provided with a vinyl group. In the method of tinting specific areas of a soft contact lens described in U.S. Patent No. 4,447,474, the lens is placed in contact with, and absorbs dye from, a porous material of the size and shape of the area to be tinted. Dyes said to be useful in this method are the azo dyes, the reactive dyes and the sulfur dyes. According to the method of tinting a hydrogel- type contact lens disclosed in U.S. Patent No. 4,478,229, a reactive dye is chemically bonded to the polymer backbone of the lens material, for example, that described in U.S. patent No. 2,976,576 referred to earlier. The reactive dye is one which contains a double , bond capable of adding to a functional group, for example, a hydroxyl, amino, amido or mercapto group, which is external to the polymer. Dyes of this type include the vinyl sulfone precursors and derivatives ( ._ thereof, dyes containing acryloylamino, beta-chloropro- pionylamino and beta-sulfato-propionylamino and related reactive groups; dyes containing beta-phenylsulfonylpro- pionylamino groups; dyes containing beta-sulfato- or beta-chloroethylsulfamoyl groups; chloroacetyl dyes, alpha-bromoacrylol dyestuffs; and reactive dyes which 0 have been developed for use in the dyeing of natural and synthetic fibers, in particular cellulose and wool, and function by nucleophiliσ addition. U.S. Patent No. 4,494,954 describes a method for coloring a contact lens prepared from a lipophilic 5 polymer. The method calls for dissolving a water-soluble dye in a solvent capable of swelling the polymer constituting the lens body and immersing the lens in the solution. As us.eful dyes, the patent cites a number of 0 acidic dyes and vat dyes. The latter type of dyes, i.e., water-soluble leuco esters of vat dyes, have been used for many years in the coloring of textiles. In a typical dyeing operation, cotton cloth or other textile is contacted with a solution of the dye in its water-soluble leuco ester form and thereafter the dye is subjected to 5 an acid oxidation treatment to regenerate the original water-insoluble vat dye at the same time developing the desired color effect. However, in the contact lens dyeing method described in U.S. Patent No. 4,494,954, the water-soluble form of the dye is the coloring agent per 30 se and is not oxidized to the original vat dye. Thus, in 35 Example 8 of this patent, a softened contact lens body formed by the copolymerization of the acrylic acid, n-butyl methaσrylate and ethylene glycol dimethacrylate was immersed for thirty minutes in an aqueous acetone dyeing solution containing Solubilized Vat Blue 18, C.I., 73002 and alkaline sodium hyposulfite reducing agent to promote dissolution of the dye. After this immersion, the swollen and colored lens was dried and then washed with water to remove dye attaching to the surface of the lens. Oxidation of the water-soluble leuco ester to regenerate the original chro ophore did not constitute a part of the foregoing procedure. U.S. Patent No. 4,518,390 describes a contact lens centering and masking fixture in which tinting is carried out. Although the patent refers to the use of an aqueous dye solution which is contacted with a fixing agent to oxidize or fix the dye deposited upon, and in, the lens, no .specific dye or class of dyes is mentioned. Although Federal Register Vol. 48, No. 132, pp. 31375-6 (July 8, 1983) reports approval by the Food and Drug Administration of certain leuco dyes for the tinting of contact lenses, i.e., C.I. 59825 (Vat Green No. 1), C.I. 69825 (Vat Blue No. 6), C.I. 70800 (Vat Brown No. 1) and C.I.-61725 (Vat Yellow No. 3), nothing is said of the nature of the lens material to be tinted or of the method whereby tinting is effected. SUMMARY OF THE INVENTION In accordance with the present invention, a method is provided for tinting a hydrogel contact lens which comprises contacting preselected portion(s) of the lens with a solution of at least one water-soluble leuco ester of a vat dye whereby said dye penetrates said preselected portion(s) of the lens and thereafter oxidizing the dye to regenerate the vat dye. The foregoing method, depending upon the selection of dye, is capable of providing coloring effects of very natural appearance. The oxidized dye which is present at the conclusion of the process is permanently trapped within the hydrogel polymer constituting the lens body and is not susceptible to being leached therefrom by tears or any other agent with which -the lens might ordinarily be expected to come into contact. The term "hydrogel" is descriptive of any water absorptive, optically clear polymeric material which is suitable for the fabrication of a contact lens. Illustrative of such polymers are the water swellable, water-insoluble shape-retaining hydrogels disclosed in U.S. Patent Nos..2,976,576; 3,220,960; 3,822,089; 4,208,364; 4,208,365; and, 4,517,139, among others. Contact lenses formed from such materials, the so-called "soft" lens variety, become soft and pliable upon the absorption of water and in the hydrated state, are relatively comfortable to wear. These polymeric materials, moreover, are to be distinguished from the lipophiliσ polymer lens materials of U.S. Patent No. 4,494,954 discussed above which are not water-absorbent and are substantially non-hydrous. BRIEF -DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded view of a known lens mounting apparatus employed in a preferred embodiment of the lens tinting process of this invention; Fig. 2 is a sectional view showing the apparatus of Fig. 1 in the inverted position; Fig. 3 is a fragmentary sectional view showing in further detail the masking portion of the apparatus in a position as per Fig. 1; Fig. 4 is a fragmentary sectional view taken substantially in the plane of line 4 - 4 in Fig. 3.; Fig. 5 is a sectional view taken substantially in the plane of line 5 - 5 in Fig. 4; Fig. 6 is a fragmentary sectional view showing the motion of a contact lens as it passes through a column of liquid contained within the tube portion of the fixture; Fig. 7 is a fragmentary sectional view similar to Fig. 6 and showing action of the liquid as a mandrel member is inserted into the tube; and Fig. 8 is a side elevational view of the fully assembled lens mounting apparatus of Figs. 1-7 showing lens L properly centered therein and ready for the tinting operations of this invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS A. The Lens Tinting Media The tinting media herein comprises a solution of a water-soluble leuco ester of a vat dye which after being absorbed into the lens body, is oxidized to regenerate the vat dye. While any leuco ester of a vat dye can be used in accordance with this invention, it is often preferred to use dyes of this class which impart a natural eye color appearance to the lens. In general, the useful dyes are water-soluble sulfuric acid esters of leuco vat dyes of the anthraquinone and indigoid series. Various combinations of such dyes can also be used. A more detailed description of such leuco esters of vat dyes can be found in Lubs, "Chemistry of Synthetic Dyes and Pigments", ACS Monograph No. 127, Reinhold Publishing Corporation, 1955, pages 534 to 546 and Vankataraman, "Synthetic Dyes", Academic Press, 1952, pp. 1046-1059. Specific water-soluble leuco esters which can be employed in the process of the present invention are disclosed in Lubs. op. cit., pp. 538 to 546 inclusive. Commercially available dyes which have been used with good results include the following: Color Effect Of Water-Soluble Leuco Ester Of Vat Dye The Oxidized Dye Solubilized Vat Blue 6, C.I. 69826 blue Solubilized Vat Brown 1, C.I. 70801 brown Solubilized Vat Yellow 3, C.I. 61726 yellow. Solubilized Vat Green 1, C.I. 59826 aqua (when mixed with Solubilized Vat Yellow 3, C.I. 61726 " in a 5:3 weight ratio, a green tint is provided) I - 8- The solution of the water-soluble leuco ester of the vat dye is usually employed as an aqueous solution having a concentration of the dye of from about 0.1% to about 25% by weight. In addition to the employment of aqueous solutions, the water-soluble leuco ester of the vat dye may be dissolved in various organic solvents or mixtures of such solvents with water. The organic solvents, if used, should be water- iscible and of relatively high volatility for quick evaporation. These are exemplified by methanol, ethanol, propanol, butanol, acetone, dimethyl formamide, CellusOlve (ethyl ether of ethylene glyσol) , butyl Cellusolve (butyl ether of ethylene glycol) , dimethyl sulfoxide and the like. Other assistants may be present if desired. Color intensity is affected by such factors as concentration of the dye solution, the temperature and the duration of contact of the dye solution with the lens, he thickness of the unmasked portions of the lens to be penetrated by the dye and the degree of oxidation brought about when regenerating the original chromophore. Simple and routine experimentation can be used to determine ' the combination of dye concentration, temperature and contact time, and the extent of oxidation necessary to produce a desired color effect in a hydrogel lens of a given type. The oxidation step can be carried out by adding the acid and reducing agent together or sequentially in any order. Suitable acids include the mineral acids such as sulfuric acid, hydrochloric acid, etc. , and strong organic acids such as chlorosulfoniσ acid, and the like. Sulfuric acid provides entirely acceptable results. In general, any known oxidizing agent can be used to regenerate the vat dye. Suitable oxidizing agents include such compounds as the peroxides, per-acids, chlorates, ferric salts, cuprous nitric acid, nitrites, chromic acid, chromates, chlorates, and the like. Sodium nitrite is advantageously used for this purpose. Following regeneration of the vat dye to the desired state of color development, any residual acid is neutralized to terminate the oxidation reaction and the lens is thoroughly washed with distilled water to remove all traces of reagents and unoxidized dye to the extent present. B. The Lens Mounting- Apparatus Turning first to Figs. 1 and 2, there is shown a lens mounting apparatus 10 in accordance with U.S. Patent No. 4,518,390 which is especially well suited for use in the practice of the " tinting process herein. In general, apparatus 10 can be considered to include an elongate tube 12 into which a hydrogel contact lens L can be dropped or otherwise inserted. One end 16 of this tube 12 is generally open while the other end 18 is closed by a specially designed masking structure. The tube-closing structure 18 includes a lens mask structure 20. Here, this mask structure includes an outer, annular seat or mask portion 22 and spaced apart therefrom but coaxial therewith, an inner seat or mask portion 24. To provide desired resiliency in supporting, engaging, and masking portions of contact lens L, this inner seat or mask 24 is formed on nose 26 of a plunger 28 which is biased, as by a spring 30, toward lens L. Thus, the spring biasing means 30 urges the inner mask seat 24 toward lens L and into firm contact therewith. Plunger motion toward lens L is halted or restrained by a shoulder 32 formed on the bottom portion of tube " 12 with a mating shoulder 34 being formed on plunger 28. Spring 30 and plunger 28 are retained within the tube structure 12 by any convenient device such as a cap or plug 36 or other type of locking mechanism. A chamber 40 is provided at the closed end of tube 12 proximate mask structure 20 for providing tinting media to the unmasked • portions P of lens L as hereinafter more fully explained. Chamber 40 includes a cylindrical cavity 42 surrounding plunger nose 26 and inner mask seat 24 and disposed inwardly of the outer mask portion 22. To admit liquid tinting medium to chamber cavity 42, inlet and outlet ports 50 and 52 are provided as shown in Figs. 1, 2, 4 and 5. These media are urged to swirl through chamber 40 and past lens L by orienting inlet and outlet ports 50 and 52 substantially tangential to wall 54 of cylindrical cavity 42. To encourage the removal of air bubbles and the accumulation of any preliminary solution squeezed out of the lens during lens capture, inlet port 50 is smaller than outlet port 52, and inlet port 50 is located tangentially as noted above, and also at an axially upper position relative to outlet port 52. Tube 12 includes an elongate body portion- 62 capable of retaining a column of liquid. The diameter of body portion 62 is just slightly greater than the diameter of lens L. Preferably, the internal diameter, ID, of tube body portion 62 is approximately 2 mm. larger than that of the lens diameter, LD. The height of the column of liquid and the height of body portion 62 are from one to three times that of the lens diameter, LD, and preferably from two and one-half times that of lens diameter LD. When lens L is dropped into liquid-filled tube 12, it descends through the liquid and attains a state of dynamic equilibrium, with a lens convex side CV down, as shown in Fig. 6. As the lens falls downwardly through the column of liquid, the hydraulic forces acting on the lens will operate to center the lens with respect to the tube. Thus the lens will be in the desired orientation and will be properly centered as it engages mask means 20 for the tinting operations to follow. To engage and secure lens L against the mask means or structure 20 in a position to be contacted by the tinting media, a mandrel 66 is inserted into tube 62 as shown in Figs. 2 and 7. This mandrel 66 is provided with a rounded nose . portion 68 adapted to engage the concave side CC of lens L. So that the column of liquid will not overflow open top 16 of tube 12, mandrel 66 is hollow, and a port or hole 72 is formed in mandrel nose 68 to permit liquid to flow into the mandrel interior as illustrated in Fig. 7. This permits mandrel 66 to sink into the liquid in the tube means with a controlled motion, the mandrel -5^ being centered by the hydraulic forces in the same manner as was lens L. In addition, external spacer ribs 74 are formed on the outside of mandrel 66 so as to space mandrel 66 from the tube body wall and permit liquid to flow between mandrel 66 and the tube body wall thus 0 further enhancing the centering action. 5 -I I - 12- When mandrel 66 has been fully inserted into tube 12, a mandrel lock mechanism 80 is inserted into tube 12 to force mandrel 66 against lens L and force lens L against mask structure 20. As illustrated in Figs. 1, 2, 3 and 4, this locking mechanism 80 take the form of a plunger 82 which is provided with a stem 84 surrounded by a compression spring 86. A lock cap 88, which can conveniently be of the plug type, is secured to plunger stem 84. Here, plunger stem 84 is provided with an enlarged nose 90 to prevent loss of cap 88 from stem 84. It will be noted that plunger 82 is provided with an enlarged base 92 provided with several cut-away formations 94. Further, cap 88 is provided with several drain holes 96. Thus, when the assembled tube and mandrel arrangement are inverted from the initial or assembly position shown in Fig. 1 to the operating position shown in Figs. 2 and 8, the column of liquid will drain from the tube. C. The Tintincr Procedure As shown in Fig. ' 8, the fully assembled lens mounting apparatus of Figs. 1-7 with its properly centered hydrogel contact lens L is set within a stand 110. Port plugs 102 and 104 (Fig. 1) have been replaced with flexible inlet and outlet tubes 111 and 112 fitted to inlet port 50 and outlet port 52, respectively. Tubes 111 and 112 are each provided with a clamp or other device to control the flow of liquid therethrough. The lens mounting apparatus is filled to an appropriate height with a receiving or preparatory liquid such as physiological saline which insures that the hydrogel lens will be maintained in a sterile and hydrophilic condition. The clamps are released to fill tubes 111 and 112 with liquid thereby expelling any air bubbles. The apparatus is again filled with liquid with removal of any air bubbles as previously described. The lens to be tinted is picked up by tweezers or some other clean device and is deposited in the receiving liquid and allowed to sink freely toward the closed end of the tube assembly. As it drops, the lens will orient and center itself as shown in Fig. 6, and will finally come to rest on mask structure 20 as shown in Figs. 6 and 7, not only with the convex side down, but properly centered relative to mask structure 20. There¬ after, mandrel 66 is inserted into tube 12. The mandrel will also center itself and mandrel nose 68 will engage the concave side CC of the lens L. Fluid flows in the interior portion of mandrel 66 through port 72, as explained previously so as to permit mandrel 66 to sink into the lens-engaging position and to avoid overflow and spillage. Finally, in assembling the device, mandrel locking assembly 82 is thereafter inserted into the open top 16 of tube 12. By this action, mandrel 66 is pressed into firm engagement with the lens L and lens L ' is pressed into firm engagement with both outer mask 22 and inner mask 24 of the masking structure 20. It will be recalled that inner mask 24 can be displaced slightly by this mandrel forcing action against the action of plunger biasing spring 30. The completely assembled device with the captured lens is now visually inspected to make certain that lens L has been properly seated and centered. To this end, tube 12 and other parts of the assembly are preferably formed of transparent plastic or other suitable materials. However, mandrel 66 is preferably formed, of opaque plastic so as to enable the operator to better view lens L. If the lens has not been properly located and seated, mandrel locking mechanism 82 and mandrel 66 are removed, and the lens is then removed. The lens is then re-dropped and the mechanism is reassembled as before. If the lens has been properly captured and secured, plugs 102 and 104 are removed to drain the preparatory fluid from chamber 40. Next the entire " assembly or fixture is inverted into the position shown in Figs. 2 and 8. As explained above, this inversion motion permits the fluid column on the side of the lens opposite the tinting chamber 40 to be drained from the assembled fixture. Preferably, the lens tinting process of this invention is carried out at elevated temperature, e.g., from about 50°C to about 60°C, but temperatures above or below this level -can be employed provided they do not impede the chemical mechanisms involved. Tinting medium provided as a solution of at least one water-soluble leuco ester of a vat dye as described above is introduced into chamber 40 through inlet port 50 of the inverted lens mounting assembly. Because of the size and location of inlet port 50 and outlet port 52 described above, the tinting medium enters chamber 40 tangentially to the walls thereof with a low pressure swirling action. This liquid swirling action ensures an even application of the opaquing medium to the unmasked area of the lens. Also this action causes any bubbles of air to be removed from convex surface CV of lens L which constitutes the temporary bottom surface of chamber 40. These air bubbles are then swept through the outlet port. Removal of air bubbles in this way is highly desirable because the presence of bubbles on the surface of lens L can cause voids of irregularities in the finished tinted lens. It will also be noted that any preparatory solution on lens L which has been squeezed out of the lens by the locking or securing action of the mandrel 66, will also be swept out of chamber 40. If this solution were allowed to accumulate in chamber 40, the tinting medium might be diluted and an uneven tinting action might result. After an appropriate period of tinting time, the tinting medium or dye solution is flushed out of chamber 40 by an injection of distilled water. Next an acid solution of oxidizing agent, e.g., a sulfuric acid solution of sodium nitrite, is introduced into chamber 40 to oxidize the water-soluble leuco ester of the vat dye which is absorbed in the lens body to the original water-soluble vat dye. Alternatively, the acid and oxidizing agent can be added sequentially to chamber 40 in any order. The amount and concentration of acid and oxidizing agent is not critical and it is only necessary that it be sufficient to provide an amount of oxidation resulting in the desired degree of color development. After the oxidation of the dye has been effected, a step requiring but a few seconds, another rinsing or flushing injection of distilled water is introduced to remove residual oxidizing age s circulated through chamber 40 to neutralize any residual acid and to return the tinted lens to an acceptable pH level. Finally, mandrel lock assembly 82 is removed and the mandrel 66 is removed. The lens is now removed from fixture 10 and given a final inspection before passage to packaging, transport and sale. The following example is further illustrative of the invention in which the operations and liquid media are at ambient temperature except where indicated. EXAMPLE A hydrogel contact lens is assembled in a lens mounting apparatus equipped with inlet and outlet tubes and inserted in a stand in the inverted position as shovm in Fig. 8. The stand is associated with a heater (not shown) which is capable of maintaining the lens mounting apparatus and its contents at an approximately constant temperature, in this case, about 50°C, to accelerate the dyeing procedure. Once the lens mounting assembly has attained this temperature, a syringe is used to inject an aqueous solution of the water-soluble leuco ester of the selected vat dye. After the desired period of contact of the dye solution with the unmasked portion(s) of the lens has elapsed, the clamp on the outlet tube is released to drain excess dye solution, the syringe is removed from the inlet tube and another syringe is inserted in the inlet tube and used to inject a sulfuric acid solution of sodium nitrite oxidizing agent into chamber 40. Following oxidation of the dye and development of the desired color, the tinted lens is removed from its mounting apparatus and placed in a solution of sodium bicarbonate which neutralizes residual acid. The tinted lens is then placed in distilled water for fifteen minutes or so, removed therefrom and placed in saline and then autoclaved. Thirty minutes following autoclaving, the pH of the lens is checked to see that it meets ' specifications (pH 5.50 - 8.50).

Claims: WHAT IS CLAIMED IS: 1. A process for tinting a hydrogel contact lens which comprises contacting preselected portion(s) of the lens with a solution of at least one water-soluble leuco ester of a vat dye whereby said dye penetrates said preselected portion(s) of the lens and thereafter oxidizing the dye to regenerate the vat dye. 2. The process of Claim 1 wherein the water- soluble leuco ester of a vat dye is selected from the group consisting of Solubilized Vat Blue 6, C.I. 69826; Solubilized Vat Brown 1, C.I. 70801; Solubilized Vat Yellow 3, C.I. 61726; and, Solubilized Vat Green 1, C.I. 59826. 3. The process of Claim 1 wherein the water-soluble leuco ester of a vat dye is oxidized by contact with an aqueous acid solution of oxidizing agent. 4. The process of Claim 3 wherein the acid component of the solution is sulfuric acid. 5. The process of Claim 3 wherein the oxidizing agent is an aqueous sulfuric acid solution of sodium nitrite. 6. The process of Claim 3 wherein the acid component of the solution and the oxidizing agent are added separately. 7. The process of Claim 1 wherein tinting is carried out using a tube-like structure which is closed at one end by structure which includes mask means and which is open at the other end, the method comprising the steps of; orienting the tube-like structure in a first position with the open end upward; adding a fluid column to the -interior of said tube structure; dropping the lens to be tinted into the fluid in the tube, and permitting the lens to sink through the fluid, column, so as to cause the lens to orient and center itself relative to the tube, permitting the oriented and centered lens to come to rest on mask structure defined in the tube bottom, inserting a mandrel member into the tube and fluid to secure the lens in place between the mandrel and the mask structure and tinting the unmasked portion(s) of the lens. 8. The process of Claim 7 wherein the water- soluble leuco ester of a vat dye is selected from the group consisting of Solubilized Vat Blue 6, C.I. 69826; Solubilized Vat Brown 1, C.I. 70801; Solubilized Vat Yellow 3, C.I. 61726; and, Solubilized Vat Green 1, C.I. 59826. 9. The process of Claim 7 wherein the water-soluble leuco ester of a vat dye is oxidized by contact with an aqueous acid solution of oxidizing agent. 10. The process of Claim 8 wherein the acid component of the solution is sulfuric acid. 11. The process of Claim 8 wherein the oxidizing agent is an aqueous sulfuric acid solution of sodium nitrite. 12. The process of Claim 8 wherein the acid component of the solution and the oxidizing agent are added separately. 13. The tinted hydrogel contact lens resulting from the method of Claim 1. 14. The tinted hydrogel contact lens resulting from the method of Claim 2. _ 15. The tinted hydrogel contact lens resulting from the method of Claim 7. 16. The tinted hydrogel contact lens resulting from the method of Claim 8. 0 5 0 5 0 5

Inventors: JENKINS EVAN JOHN, JENKINS, EVAN, JOHN
Applicants: INT HYDRON CORP, INTERNATIONAL HYDRON CORPORATION
Application year: 1986
Main classification: D06P1
IPC codes: B29D11, D06P1