PRODUCT THEREFROM

Technical Field This invention relates to a pigmented plastic material and method for producing the same and particu¬ larly to a pigmented plastic material suitable for use in the production of colored soft contact lenses.

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Background Art

Hydrophilic or soft contact lenses are mainly produced from water-absorbable plastic materials such as

2-hydroxymethacrylate (HEMA) which may be crosslinked with a tetra-functional monomer such as ethylene glycol di- ethacrylate as disclosed in U.S. Patent 3,988,274. Soft contact lenses produced .from water-absorbable plastic materials such as HEMA are also disclosed in U.S. Patent No. 3,813,447; 4,252,421 and 3,988,274.

Attempts have been made to color these soft con¬ tact lenses for the purpose of enhancing the aesthetic beauty of the eye of the wearer of the colored lens. One prior art technique is to paint or print a colored portion onto a soft contact lens using an implement such as a brush, as disclosed in Contact Lens Forum, Volume 3, No. 8, August, 1978, page 89. Another technique involves the cementing of a colored covering layer onto a clear hydro- gel lens, as disclosed in U.S. Patent No. 3,679,504.

There are, however, several problems with this type of surface coloring technique. First, the color is printed on the lens after it has been manufactured and, therefore, is not uniformly dispersed through the lens material itself. As a result, the color tends to fade and chip away after repeated use. Also, it is necessary to first manufacture the clear lens and fit it on the patient's eye before the coloring takes place. This requires the lens to be sent back to the manufacturing company by the patient's doctor. Moreover, surface coloring inhibits gas permeability, i.e., the transmission of oxygen to the cornea. Finally, the surface coloring • process requires additional fabrication steps and equip¬ ment.

Coloring of soft contact lenses has also been performed by dispersing water soluble arid water insoluble dyes throughout the plastic material which makes up the lens. For example, U.S. Patent No. 4,252,421 discloses a soft contact lens having a tinted central core which is colored by means of a dye that is dispersed throughout the core and an outer lens element which is usually clear.

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The colored central core is formed from a tinted button which in turn is polymerized from a co-monomer mixture which includes a dye. The dye may be of two types: water insoluble or polymer bound.

U.S. Patent No. 4,157,892 discloses a somewhat similar method of producing a colored soft contact lens. Thus, the patent discloses a method of coloring water- absorbable plastic by developing an azoic dye within the hydrophilic contact lens. The water absorbable plastic material containing a coupler is mixed with a diazonium compound in a suitable solvent at optimum pH to produce an azoic dye.

Lenses produced by such dying methods also pos¬ sess a number of disadvantages. Specifically, the dye in the plastic lens material is not migration proof and, as a result, tends to streak and run out of the lens. Moreover, the dyed lenses are transparent and accordingly cannot be used to change the appearance of the wearer's eye color from one color to another color.

^• In addition to the use of dyes to color soft contact lenses, pigments have been dispersed in the soft contact lens material in an effort to produce an accepta¬ ble lens. These efforts, however, have been ineffective. When attempted with spun-cast soft lenses, little or no pigment has remained prop ^' erly dispersed in the body of the lens; and when attempted with lenses made by stationery casting and machining (a "lathe cut lens"), such lenses do not have a satisfactorily evenly dispersed color when made in commercial production quantities.

Another area where pigments have been dispersed in an ethylenically unsaturated poly erizable compound is in the manufacture of paint. For example, U.S. Patent 4,234,466 discloses a polymerizable composition containing an ethylenically unsaturated polymerizable. compound, a resin and a pigment. The disclosed composition is, howe¬ ver, unsuitable for the production of pigmented hydro¬ philic contact lenses since the requirec ^* high degree of pigment dispersion cannot be achieved, while low amounts of i ment failed to result in sufficient colorin .

It is therefore among the objects of the present invention to provide a pigmented water-absorbable plastic material in which low amounts of pigment are evenly dis¬ persed and non-migrating.

It is also among the objects of the present invention to provide a ^" pigmented water-absorbable plastic material useful in the production of colored soft contact lenses.

Disclosure of Invention

It has been found in accordance with the present invention that a hydrophilic polymer comprising a polymerized mixture of a water-absorbable plastic material 5 . such as 2-hydroxyethyl methacrylate (HEMA), an organic binder such as cellulose acetate butyrate (CAB), di(2- ethylhexyl)phthalate (DEP) , di-isodecylphthalate (DIDP), and acryloid B-66, and at least one pigment is suitable for use in the production of colored soft contact lenses. 10 The hydrophilic polymer is a colored plastic material which contains evenly dispersed, non-migrating non-toxic pigment. When used in soft contact lenses it can be used to change the appearance of the wearers' eye color from one color to another. ,.- According to the invention the colored, non- migrating plastic material is produced by predispersing a low amount of pigment in a suitable binder such as cellu¬ lose acetate butyrate, DOP, DIDP or acryloid B-66 to obtain a crystalline colored product. The crystalline 0 pigment containing binder is thereafter dispersed in a purified water-absorbable polymerizable plastic material such as HEMA. Depending upon the color desired, two or more colored dispersions can be mixed together at this point of the ^; process. The mixture is then pre-polymerized 5 at elevated temperature to form a viscous pigment contain¬ ing dispersion by adding a polymerization catalyst or polymerization initiator.

The viscous dispersion is then poured into molds and polymerization is continued in an air-circulated oven 0 to form a uniformly opacified colored water-absorbable plastic material in the form of "buttons". These "but¬ tons" can then be used in the production of soft contact lenses.

Best Mode for Carrying out the Invention

As indicated hereinabove, the present invention relates to a colored hydrophilic plastic material com¬ prising a polymerized mixture of a water-absόrbable plastic material such as HEMA, an organic binder such as

CAB, DOP, DIDP or acryloid B-66, and at least one pigment.

While any suitable water-absorbable plastic material may be employed, HEMA is presently preferred. In general, the water-absorbable plastic material may be pre- sent in an amount of from about 96% to about 99% by weight of the composition. A more preferred range is of from about 98% to about 98.5% by weight of the composition. In order to achieve the highest purity, it is preferable to double distill the water-absorbable plastic material prior to use.

As regards the organic binder, suitable mate¬ rials include CAB, DEP, DIDP and acryloid B-66. CAB (Eastman 381-0.5) is, however, presently preferred. In general, the organic'binder is present in an amount of from about 0.4% to about 2% by weight of the composition. A more.preferred range is of from about 0.4% to about 1.5% by weight of the composition.

While any suitable pigment may be employed, it is presently preferred that the pigment be heat resistant, non-toxic and insoluble in aqueous solutions. Any colored pigment may be employed. However, since any color can be obtained by merely mixing two or more primary colors together, it is only necessary to use pigments corre¬ sponding to the primary colors. As defined herein, "pri- mary colors" mean white, black, red, yellow and blue. It is presently preferred to use the following pigments: Dupont Tl-Puri R-900 (a rutile titanium dioxide pigment); Cabot Corporation, Monarch 700 (a furnace black pigment); City Service, Matico Red 297 (a red iron oxide pigment); city Service Matico Yellow 1000 (a yellow iron oxide pigment); and Ferro Company, V 5200 blue (a chromium cobalt aluminum pigment). The particle size of the pigments used in the present invention generally varies from about 0.02 microns and about 1.0 microns.

According to the present invention, it is preferable that the plastic material be substantially opa- cified. In order to produce an this material, it is necessary to include at least one opacifying pigment. Since only the black and white pigments can produce an opaque material, it is presently preferred to employ small amounts of a black and ^' /o ^' r a white pigment in the composi¬ tion. Generally, one or both of the opaque colors are employed together with one or more of the other primary colors to produce the color desired. For example, if green is the color desired, a blue pigment, a yellow pigment and a white pigment are mixed together. The amounts of each pigment will, of course, depend on the shade of green which is desired. If a gray-blue color is desired, a blue pigment, a black pigment and a white pigment are mixed together so as to produce the desired color. Again, the relative amounts of the pigments will vary depending upon the shade of the color desired.

In general, the pigment or mixtures thereof are pre- sent in the composition in an amount of from about 0.2% to about 1.5% by weight of the composition. If a white pigment is employed in the composition, it is generally present in an amount of from about 0.4% to about 1.5% by weight of the composition. If a blue pigment is employed, it is generally present in an amount of from about 0.32% to about 1.25% by weight of the composition. If a yellow pigment is used in the composition, it is generally pre¬ sent in an amount of from about 0.33% to about 1.25% by weight of the composition. If a black pigment is employed in the composition, it is generally present in an amount of from about 0.3% to about 1.5% by weight of the composi¬ tion. Finally, if a red pigment is employed in the compo¬ sition, it is present in an amount of from about 0.33% to about 1.25% by weight of the composition. It is necessary that the composition of the pre¬ sent invention also include a crosslinking agent in order to prevent precipitation of the pigment during production. ^• • Any suitable crosslinking agent may be employed. However, it is presently preferred to use an olefin glycol

dimethacrylate such as ethylene glycol dimethacrylate.

The crosslinking agent is preferably added to the purified water-absorbable plastic material at elevated temperature prior to the introduction of the pigment-binder composi- tion although the crosslinking agent may also be added thereafter. Thus, preferably, the liquid HEMA is heated to about 40°C to 45°C while the crosslinking agent is added.

According to the present invention, the colored, non-migrating plastic material is produced by a process comprising pre-dispersing a pigment in a suitable organic binder; thereafter, adding the pigment containing organic binder to a crosslinked water-absorbable plastic material and polymerizing the mixture to form the final product. The preliminary step of pre-dispersing the desired pigment in a suitable binder is extremely impor¬ tant since attempts to introduce the pigment directly into the hydrophilic component have failed to give the desired result, i.e., the pigment cannot be kept in finely divided dispersed form but will precipitate almost immediately so that after a polymerization thereof a uniform colored pro¬ duct cannot be obtained.

Thus, the binder, preferably CAB (Eastman 381- 0.5 cellulose acetate butyrate) is first melted at a suitable temperature in a suitable container. The pigment or a mixture of pigments is thereafter added whereby the pigment is absorbed in the CAB. Alternatively, and as presently preferred, separate pigment-binder compositions containing only one of the five primary color pigments may be prepared and mixed at a later stage, as wi.ll be more fully explained hereinafter.

In general, the amount of pigment added to the organic binder is of from about 10 to about 80% preferably from about 20% to about 50% by weight of the total pigment-binder composition. A white pigment-binder compo¬ sition may contain of from about 40 to about 60% by weight of pigment based on the weight of the pigment-binder com¬ position, while a black pigment-binder composition may contain of from about 30 to about 60% by weight of the f O

pigment-binder composition. A red pigment-binder composition may contain of from about 33 to about 50% by weight of the pigment-binder composition. A blue pigment- binder composition may contain of from about 32 to about 50% by weight of the pigment-binder composition, while a yellow pigment-binder composition may contain of from about 33 to about 50%. by weight of the pigment-binder com¬ position. After the pigment has been introduced into the organic binder, the composition is thoroughly mixed and subsequently cooled and crushed to form a crystalline pigmented binder composition.

The crystalline pigmented binder composition is then introduced into a test tube containing the cross¬ linked water-absorbable polymerizable compound, preferably crosslinked 2-hydroxyethylmethacrylate (HEMA) which is preferably purified by double distillation prior to use. The pigmented binder composition will slowly dissolve in the HEMA. Preferably the mixture is left standing for about 8 to about 12 hours. The crystalline pigmented binder composition is thus softened and subsequently evenl . dispersed in the HEMA. Mixing may be accomplished by subjecting the mixture to an ultrasonic vibrator in a water bath for about 30 to 60 minutes until the pigmented binder residue has disappeared from the bottom of the test tube and a uniform dispersion thereof in the HEMA is obtained.

After the pigmented binder residue has been evenly dispersed throughout the HEMA, the various colored pigmented HEMA dispersions can be mixed together to pro- duce the desired color. For example, if green is the desired color, three parts of a blue pigmented HEMA dis¬ persion, fourteen parts of a yellow pigmented HEMA disper¬ sion and one part of a white pigmented HEMA dispersion are thoroughly mixed together to form the desired color. If a gray-blue color is desired, one part of a blue pigmented HEMA dispersion, two parts of a black pigmented HEMA dis¬ persion and eight parts white pigmented HEMA dispersion are mixed together to- form the desired color. It is, of course, within the skill of the art to mix the primary

colors to produce various secondary colors and shades thereof.

As stated hereinabove, the group of crosslinking agents that can be used according to the present invention

⁵ includes olefin glycol dimethacrylates such as ethylene glycol dimethacrylate. - Tn general, the crosslinking agent is added dropwise in ^' an amount of from about 0.35 to about

Q.5% by weight of HEMA, preferably in an amount of from

0.4 to about 0.46%. After addition of the crosslinking

10 agent the crosslinking agent containing HEMA is thoroughly mixed for at least 30 minutes. If desired, the subsequent water uptake of the water-absorbable plastic material may be increased by the addition of small amounts of metacry- lic acid.

15 It is imperative that the dispersed pigment is at all times kept in a uniformly dispersed state. To avoid precipitation of the pigment, the liquid mixture is transformed into a gel by the addition of a polymerization catalyst such as an organic peroxide. It is presently pre-

" ferred to employ a liquid organic peroxide. The present¬ ly preferred catalyst is 2,5 dimethyl-2,5 bis (2-ethyl hexoyl peroxy) hexane (USP 245, manufactured by U.S. Peroxygen Witco Chemical Corporation according to U.S. Patent 3,264,274 which is hereby incorporated by 5 reference). As the catalys~t is added, the mixture is stirred. Heat should not be applied. In general, the catalyst is added in an amount of from about 0.05 to about 0.125 ml.

The crosslinked pigmented HEMA and catalyst-

30 containing flask is then introduced into a water bath having a temperature of from about 75° to about 95°C. While partial polymerization proceeds, the flask is fre¬ quently rotated so as to avoid precipitation of the pigment. After 3 to 10 minutes, depending on the pigment,

35 the amount of catalyst used and the temperature applied, the dispersion will become viscous or gel-like. At this

contact lenses may be fabricated. When the dispersion is poured into molds, the polymerization of the final product is continued by placing the molds into an air-circulated oven at temperatures of from about 50° to about 70°C for about 45 to about 60 minutes. Alternatively, the viscous, syrup-like dispersion may be formed into "buttons". The "buttons" can then be- used to manufacture colored soft contact lenses according to any suitable process.

The following examples are illustrative only of the practical and presently preferred embodiment of the invention and are not to be understood in a limiting sense. '

Example 1 lOOg of white pigment (DuPont TI-PURI R-900) are introduced into lOOg of molten cellulose acetate butyrate (Eastman 381-0.5) and intensively mixed. Upon cooling of the mixture to about room temperature a white, opaque pro¬ duct is obtained which is crushed into white crystals. O. ^' IO to 0.15 g of the white crystalline product are added m. m. to 10 ml of twice distilled crosslinked 2-hydroxyethyl methacrylate (HEMA) in a test tube and left standing over¬ night. Prior to the addition of the white pigment 0.4% by weight of HEMA of ethylene glycol dimethacrylate were added. The pigmented HEMA containing test tube is then immersed into a waterbath at room temperature and sub¬ jected to ultrasonic vibrations for 45 minutes, whereby all pigment residue will disappear from the bottom of the test bute. The white composition is cooled down to room temperature and 2 drops of USP 245 (manufactured by U.S. Peroxygen, Witco Chemical Corp. according to U.S. Patent 3,264,274) are added and stirred with a magnetic stirrer. The flask is then introduced into a water bath at 80°C for about five minutes thus obtaining a syrup-like composition and then cooled in an ice bath to stop the starting 5 polymerization. The content of the flask is poured into cylindrical molds and polymerization is continued in an air-circulated oven at 60°C for 45 minutes. ^' Final curing and annealling is achieved by placing the buttons into an

Y~^ . oven at a temperature between 90°C and 100°C for 12 hours; O

The final water-absorbable product contains the white pigment in non-migrating uniformly dispersed form.

Example 2 lOOg of blue pigment (Ferro Company, V 5200 Blue) and lOOg of molten CAB are mixed and formed into a crystalline blue product. In a separate test tube, lOOg of yellow pigment (City Service Mapico Yellow 1000) are dispersed in lOOg of molten CAB and also formed into a crystalline yellow product. The blue and yellow pigmented crystalline pro¬ ducts are separately dispersed in 10 ml of crosslinked HEMA at conditions similar to those described in Example 1. Three parts of the blue pigment containing HEMA dis¬ persion are admixed with fourteen parts of the yellow pigment containing HEMA dispersion and one part of the white pigment containing HEMA dispersion of Example 1 so as to obtain an opacified, green colored HEMA dispersion. To the green HEMA dispersion USP 245 is added and the dis¬ persion is further processed and formed into an opacified green product in accordance with the method described in Example 1. Example 3 lOOg of blue pigment (Fero Company V5200 blue) and lOOg of molten CAB are mixed and formed into a crys- talline blue product. In a separate test tube 20g of black pigment (Cavit Corporation, Monarch 700) are disper¬ sed in 80g of molten CAB and also formed into a crys¬ talline black product.

The blue and black pigmented crystalline pro- ducts are separately dispersed in 10 ml of crosslinked

HEMA at conditions similar to those described in Example 1. One part of the blue pigment containing HEMA disper- sion is mixed with two parts of the black pigment contain¬ ing dispersion and eight parts of the white pigment con- taining HEMA dispersion of Example 1 so as to obtain an opacified, gray-blue colored HEMA dispersion. To the gray-blue crosslinked HEMA dispersion 3 drops of USP 245 are added and the dispersion is further processed and formed into an opacified, gray-blue product in accordance with the method described in ^" Exam le 1. * -