CA1093763A - Method of dyeing or printing hydrogel resin - Google Patents

Abstract

Abstract of the Disclosure A method of dyeing or printing hydrogel resin which comprises the steps of impregnating hydrogel resin or a hydrophilic water-expansible high polymer with a water-soluble dyestuff or leuco or colorless compound thereof having a great affinity to said hydrogel resin; and treating said water-soluble dyestuff or leuco or color-less compound thereof to render them water insoluble and capable of presenting a color, said method being suitably applied in making a soft contact lens prepared from the hydrogel resin.

Description

This invention relatas to a method of dyeing or printing hydrogel resins or water-expansible hydrophilic high polymer~ and more particularly to a method of dyeing ox printing a molding, sheet or coated layer formed of said hydrogel resinsO
The hydrogel resin i5 characterized in that it has a hydroxyl group and a partly cross linked molecular s-tructure, and, though insoluble in wa~er f has high hydroscopicity and water~
expansibilityO The hydrogel resin is typically represented by cross-linked forms of hydroxymethacrylate resin and derivatives thereof, copolymers of said resin and other hydrophilic hi.gh polymers, polyacrylamide resin and derivatives thereof~ graft : polymers of polysiloxane and hydrophilic high polymers~ copolymers of ~-vinylpyrxolidone and methacrylate, polyion complex, hy~roxyl-ethyl cellulose, substituents of said cellulose, and copolymers of said cellulose and other high polymers~
There ha~e been developed some methods of fabricating the above-mentioned hydrogel resin into a film, membrane or any other moldin~s b~ ~rawing upon the property of said resinO Depending upon the applications for which these products are intended, the necessity naturally arises of d~eing said products or impressing a letter, picture or design thereon a Since, however, the products such as molaings of hydrogel resin are often and in water, or in an atmosphera or steam, it is extremely difficult to make an impression on said moldings by ordinary oily inkO Though the moldings can be prînted or dyed by water ink or an aqueous dye solution, these dyestuffs fail to be formly set in the moldings due to the resin itself being swollen in water and are dissolved outO The following are some attemps conducted to date to eliminate the above-mentioned difficultiesO One attempt was to contact the hydrogel resin with a ; 30: solution of a water~soluble dyestuffO This process enabled the hydrogel re~in to be easily dyed, providing a distinct impressionO

Where~ however, the molding of said hydrogel resin was kept long in wat~r, the dyestuff was graduall~ dissolved out a~entually to ~ 3~7~3 efface the impressionO ~lother attempt was to print the surace of a molding o~ the hydrogel resin by an ordinary form of ink prepared by dissolving or dispersing dyestuffs, pigments, binder resins in an oily solventO This process also temporarlly provided a distinct impression on the surface of said moldingO ~hen~ however, the m~lding was left long in water~ the printing ink decreased in adhesivity, causing the color of the impression progressively to faintO As seen from the above-mentioned conventional attempts, it has been disclosed that a molding of the hydrogel resin oan not be properly printed or dyed simply by utilizing the generally estimated adhesive power of printing ink or directly applying a dyestuff to the molding~
This in~ention has been accomplished in view of the aforesaid circumstances, and is intended to provide a method of dyeing or printing an article f~bricated from the hydrogel resin to make a : dyed impression thereon, which c~mprises the steps of impregnating the hydrogel resin with a water-soluble dyestuff or leuco or : colorless compound thereof having a great affinity to the hydrogel resin9 and treating these dyestuffs to render them water-insoluble and capable o~ displaying a colorO Tlleoretically therefore, the method of this invention can very effectively eliminate the draw-backs accompanying the prior art methodsO The treatment o~ a dyastuff to render it water-insoluble on which the present invention is fundamentally based causes the fine particles of the dyestuff to be caught in the reticula.r structure of cross-linked high molecular hydrogel resinO Therefore~ the dyestuff thus deposi*ed does not ~low out of the hydrogel resin even when it is swollen in water, providing a very stable dyed impression.
~ - Impregnation of the hydrogel resin with a water-soluble dye-; 30 stuf~ having a great affinity to said resin or leuco or colorless compounds thereo may be ef~ected by the followiny proce6ses. A
irst process is ~o swell the hydrogel resin in water and at the same time impregnate sald resin with the above-mentioned water-soluble dyestuff or leuco or colorless compound thereof. A
second process is first to contact the hydrogel resin with said dyestuff or leuco or colorless compound thereof, and then swell the resin~ A ~hird process is to swell the hydrogel resin in advance and thereafter impregnate said swollen resin with said dyestuff or leuco or colorless compound thereof.
There will now be described in greater detail the method of this inventionO
The first method is to dip unswc,llen hydrogel resin in a dye solution or ink containing a dyestuff or leuco or colorless compound thereof having a great affinity to the hydrogel resin and cause these dye materials to be impregnated in the hydrogel resin just when it is swollen by being brought into contact with said dye solution, follow~d by the method of treating the impregnated hydrogel resin to render the impregnated dyestuff water-insoluble and ~apable of displaying a color.
The water soluble dyestuff having a great affinity to the hydrogel resin practically includes a solubili~ed vat dye. As is well known~ this vat dye is a water-soluble compound converted into a sulfonate by reduction of vat dye and is in the form of a color--less leuco compoundO A hydrogel resin dipped in a dye solution or ink containing a dyestuff kept in the above-mentioned form is easily impregnated with said dyestuff due to its a~finity~ Later when the impregnated resin is dipped in an aqueous solution o an oxidizing agent 7 iOe~ developing bath the dyestuff contained in the xesin is rendered water-insoluble by being oxidized~ displays a color and is firmly set in the resin, providing a very stable impression. All co~merc~ally available solubilized vat dyes can be used with the method of this inventionO The dye solution or ink is 3~ mixed7 if necessary, with a stabilizer and ot~er additives for eleva~ing printabili~y~ Where the dyes~uff used is sensitive to air oxidation, then a small amoun~ of an over oxidatiQn inhibitant or a small amount of sodium carbonate for alkalizing the dye ,~

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solution is added as a stabilizerO Additives for improving the printability of the dyestuff include a defoaming agent for suppressing the evolution of air bubbles by stirring and glycerine and/or glycol for controlling ~he dryability and viscosity of the dye solutionO
An oxidizing agent for rendering th~ dyestuff water-insoluble generally includes an aqueous solution of sulfuric acid or nitrous acidO Further, an aqueous solution of~ for example, sodium perborate, potassium bic.hromate~ persulfates, sodium chlorite and 1~ hydrogen peroxide may be used as the oxidizing agen~O -Some solubilized vat dyes ~ive rise to photo-oxidation~ When exposed ~o a light, such type of vat dye impregnated in a hydrogel resin is oxidized to be rendered water-insoluble and display a ~ color in said resin even without treating the resin with an aqueous ; solution of an oxidizing agentO Consequently, a hydrogel resin impregnated with such vat dye always provides a stable dyed impres-sionO The photosensitive solubilized vat dye includes the yellow grades 3~ 4, 7, 8, red grades 1, 2 9 10 ~ blue grades 2, 5, 8 and black grad s 1~ 4, 6 of solubilized vat dyesO
Other water-soluble dyes practically available for use with the method of this invention are tetrazolium saltsO These tetra-zolium salts are water-soluble and have a great affinity to a hydrogel rasinO A hydrogel resin dipped in a dye solution con taining any of said tetrazolium salts is easily impragnated with the dyes~uff due to its great affinityO Under ~his Gondition, the :~ dyestuff rema'.ns colorlessO When; howevert the hydrogel resin lS
: dipped in an aqueous ~olution of a reducing agent, iOe~ developing . ~
bath then the tetrazolium salt is convert d by reduction into a water insolu~le coloring matter of formazan, enabling the resin to present a stable dyed impression Commercially available derivatives of the tetrazoli~n aalts typically include customarily ~ known 2,3/5-triphenyl~2H-tetrazoli~m chloride, Terazol Blue, : Tetrazolium Violet~ Tetrazolium Purpl~ and Nitro Blue TetrazoliumO

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3'~3 Im~ersion of a hydrogel resin in the developing bath may be replaced by the process of exposing a hydrogel resin impregnated with a tetra~olium salt to ul~raviolet rays to produce said formazan coloring matter in ~he resinO This process can also provide a stable dyed impression on the resin.
The second method can provide a more stable dyed impression than the first processO The second method comprises the steps of dipping unswollen hydrogel resin in a dye solution or ink con-taining a water~soluble dyestuff or leuco or colorless compound ~hereof having a great affinity to said resin or making an im~res-sion thereon with said dye solution or ink; and exposing the impregnated resin to an a~mosphera having a high temperature of :30 to 100C and a high humidity of 60 to 90% tv swell the hydrogel resin, thereby causing said dyestuf-f or leuco or colorless compound thereof deeply to penetrate permeate the hydrogel resin and b~
rendered water-insoluble and capable o displaying a color. This second method also enables any of said dye materials impregnated in ~he hydrogel resin to be firmly set in the retioular structure o , ~he high molecular hydrogel resin, providing a very stable dyed impression on the resin moldingO
~ he third me~hod compri~es the steps of first ~welling a hydrogel resin in water; then dipping said resin in a dye solution or ink containing a water-soluble dyestuff or leuco or colorless compound thereof ha~ing a gr at af~inity to the hydrogel resin or making an impression thereon with the dye solution or ink; causing the dyestuff deeply to penetrat or permeate the resin and there-after be trea~ed to ~e .rend~red water-ins~luble and capable of displaying a color. This third method also causes the dyestuff to be firmly set in the reticular struc~ure ~f the high molecular hydrogel resinp providing a very stabl dyed impressionO

It is extremely difficult to make an impression by an ordinary : :
~ ~printing devicel ~or example~ a rubber stamp on a water-swollen ~: :
~ ~substance or a sub~tance on whose suxface a water membrane Qr water : ~ :

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drops lie, because the dyestuff is repelled by water or gets un-necessarily spread due to the presence of water. A soft contact lens i~ brou~ht into direct contac~ with an eyeball. Where, therefore, used as a soft contact lens, hydrogel resin which is impregnated with a printing ink containiny a binder and conse-quently accompanied with the possibility of said binder remaining on the lens surface a~ter printing has the drawbacks tha~ not only irregularities appear on the lens surface, but also such lens is not safe from the sanitary point of viewO For the above-mentioned reason, i~ is preferred that printing ink for a soft contact lens be free from a bi~der and only formed of ~he aforesaid dyestuff or leuco or colorless compound thereof and a water-soluble solvent such as water~ glycerine~ glycol 7 alcohol, ketone or ester or a mixture thereofO
Printing ink for a soft contact lens has a lower viscosity and ~ack than customary printing ink~ Therefore, application of a nonporous rubber stamp of the letter press type in printing a soft contact lens is a~companied with the difficulties that when said nonporous rubber stamp is pressed on the soft contact lens until 0: the dye solution ~ully:penetrates the contact lens, then the dye solution unnecessarily spreads around an image impressed on the soft contact lens, providing an excessively broad marginal zone for the image, and resulting in insufficient or irregular dye concen-trationO ~herefore,:this invention provides a. method of easily making a firm impres~sion on a soft contact lens by impregnating the fine cells of a porous rubber stamp manufactured b~, fo~ example, Japan NCR Company or:Syachihata~Kogyo~Company with a printing ink ;containing the préviously described dyestuff or leuco or colorless :compound thereof~
30: In addition to the-aforesaid rubber stamp, rubbery elastic materi:als adapted to ~orm a porous stamp used with the method of this inven:tion inclu~e, for~example, porous materials generally : referred to as sponge, materials preferred ~y compactly ~ 6 -, a3'7~3 compressing, for axampl~, fibrous cloth or paper~ foamed ~ilicon rubber sponge, or plastics material provided with dense fine pores to have a sponge-like property for absorption of a liquid~
The above~mentioned porou~ stamp has the advantages that some amount of water drops deposited on the surface of a hydrogel resin article~ for example, a soft contact lens is easily absorbed in the fine cells of the above-mentioned porous stamp when it is pressed on the contact lens, preventing the dyestuff impregnated in said porous stamp from being unduly spread around an impression formed on the contact lens and causiny khe dyestuff immediately to penetrate the swollen hydrogel resin, printing ink ~vQn having a low viscosity is prevented from being forced out to other port.ions of a soft contact lens than an impression; and when the porous stamp is released from a compression force, a distinct impression is providedO
~ s naturally expected, the porous stamp is applicable to the aforesaid method of printing unswollen hydrogel resln The third method is very effective to make an impression on hydrogel resin having a relatively high water expansibilityO However, it has been experimentally found that where an impression is m~de on hydrogel rasin having a relatively low water axpansibility according to the application intended, then the third method has the drawbacks that the dyestuff, or leuco or colorless compound thereof fails fully to penetrate the hydrogel resin9 resulting in insufficient or irregular dye concentration; and where the impressed resin is long contacted with water, the color of the dyestuff gradually faints with the resultant failure to provide good dyeing or printingO
An improved fQurth method to eliminate the above-mentioned : difficulties comprises the steps of dipping hydro~el resin in a solvent ha~ing a greate~ pow~r of swelling the hydrogel resin than water and ~ high compatibility with water fully to swell the surface or the whole o the hydrog~l resin, and dyeing or printing the :: prescribed portion of the hydrogel resin wlth a water-soluble dyestuff or leuco or colorless compound thereof having a great ~: ~

1~9~7G3 affinity to the hydrogel resin~ The fourth ~ethod using a solvent having a great resin-swelling power has a very advantageous effect of causing the chemical structure of the hydrogel resin to be sufficiently broadened to admit of the easy intrusion of dyestuff molecules. In this case, a solvent having a greater resin-swelling power than water is selected from those which have a very high compatibility with water. The useful forms of said solvent are generally low alcohols, low ketones, low glycols and low glycol esters. Concrete examples are methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, diacetone alcohol, acetone, methylethyl ketone, ethylene glycol, propylene glycol~diethylene glycol, methyl "Cellosolve", ethyl "Cellosolve"l butyl "Cellosolve', ethyl carbitol, glycerine ("Cellosolve" is a trade mark of Union Carbide Co.~. With respect to hydrogel resin, for example, poly~2-hydroxyethyl methacrylate homopolymer (cross-linked form), comparison was made between the resin-swelling power of water and that of same of the above-listed solvents, showing that methanoll ethanol, ethyl Cellosolve"and acetone had resin swelling rates of 20 38%, 31~, 46% and 23~ respectively as against 16~ of water.
These other solvents than water all prove ~o be very useful for the object of this invention. A close relationship exists between th~ rate at which solvents swell hydrogel resin and the radius of the dye molecule capable of passing through the cross-linked structure of the hydrogel resin. The radius of the pore of hydrogel resin whose cross-linke~ structure admits of the passage of the molecule i5 calculated to be 4.0A for 2-hydroxy~
ethyl methacrylate resin and 5.0A fo~ polyacryl amide resin, The molecule of a dyestuff or leuco or colorless compound there-of used in this invention which is supposed to have a larger radius than at least 7 or ~A, lies on a border line at which the molecule can or cannot narrowly pass through the cross-linked structure of hydrogel resin~ It is seen therefore that swelling ~ - 8 -..... ,. ~

3~63 of hydrogel resin b~ a solYent hayin~ ~ ~xeater swelling powe~
than water to broaden t~e pore radius of the resin enables the molecule of a water-solu~le d~estuff easily to :

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pass thxough the cross-linked struc~ure of the resin.
Thus according to the fourth method, a water-soluble dyestuff or leuco or colorless compound thereof impregnated in swollen hydrogel resin is treated to ba rendered water-insoluble and capable of displaying a colorO As the result, the dyestuf~ is firmly set in the reticular structure of the hydrogel resin, presenting an impression having a very high dye fixation rate on the resin~ A
dyestuf~ impregnated in hydrogel resin only swollen in water indi-ca~es an insuf~icient or irregular concentrationO When the water-swollen hydrogel resin thus impregnated is kept long in water, thenthe dyestuf gradually faints in colorO Irl contras~, a dyestuff impregna~ed in hydrogel resin swollen in the above-mentioned solvent or a mixture thereof with water provid~s a distinct image hav.ing a high dye concentration. The dyestuff of an impression appearing on this hydrogel resin has been fo~md to have.a very high fixation rate, namely, a prominent water proofness even when kep~. long in contact with water, particularly boiling water.
There will ~ow be described a fifth method o impregnating a dyestuff in hydrogel resin. This method uses a solubilized vat dye which gives rise to photo-oxidation and a tetrazolium salt which i~
rendered water-insoluble by reduction upon exposure to a light or ultraviolet rays. According to the fifth method, hydrogel resin is ~ dipped in a dye solution or ink containing a solubiliz d vat dye ; producing photo-oxidation. Thereafter, an image is projected on said res.in through a transparent negative to form a dyed impression on the hydrogel resinO The impressed hydrogel resi.n is suffi-cientIy boilea to remove the solubilized vat dye remaining on those portions of the hydrogel resin which were not exposed to a light, thereby providing a distinct dyed impression on said hydrogel ; ~ re~in O
Impregnation of hydrogel resin wi~h tetrazolium salts instead of solubilized vat dyes and exposure o~ the impregnated resin to ultraviolet rays also provide a similarly clistinct dyed impression.

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In recent years~ a soft contact lens has come to attract attention as an instance applyiny hydrog~l r~sin o~ hydroxy~
methacrylate series. The reason is that when swollen in water, this type of hydrogel resin becomes soft and hydrophilic and does not cause the user of a soft contact lens to have an unpleasant feelin~ while the lens is fitted in his eyes, thus providing most suitable as the material of a soft contact lensO The contact lens varies in cur~ature or degree with the user~s eyesight. Therefore~
it i5 necessary -to display marks and numerals ne~r the periphery of various contact lenses to distinguish between their types. In this case~ a displayed impression should not be effaced at all not only while the contact lens is set in the user's eyes, but also while the con~ac~ lens is frequently boiled in hot water fox dis.infection.
Further~ the displayed impression should be resistant to a solution of protein -decomposing enzyme used to clean the contact lensO
Moreover/ the contact lens has to be saved from the appearance of a protr~sion in the impxessed portion which would result if the dye solution or ink contained a binder, in order that the user of the contact lens may be saved from an eye disease or an un,pleasant feeIing while his eyes are fitted with t~e contact lens. The process of making an impression on a soft contact lens varies with '~ a maker's practice of measuring the curvature or degree of the lens, namely, according to whether the curvature or degree of a fa~ricated .soft contact lens is measured, and thereafter the result of said measurement is impressed on the contact lens~ and thereafter the lens is stored in water, in the swollen ~orm, the curvature or degree of the swollen contact lens is measured~ and thereafter the result of said measurement is impressed on the soft contact lens, and thereafter the impressed contact lens is stored in water~ In ~30 either caset dyeing or printing of a ~o~t contact lens sufficiPntly ~;~ meeting the extremely rigid condition~of boiling for disinfection has been rendered realiæa~le for the first time by the method of this invention~

~ 10 --~3~7163 The present invention will be more fully understood by the examples which followO
Example l rransparent film formed of cross-linked 2-hydroxyethyl methacrylate resin was preliminarily dipped lO minutes in an aqueous solution of a solubili~ed vat dye (manufactured by Mitsui Chemical Company under the trademark '7Mikethren Soluble Blue O") whose concentration was chosen to be lS g/QO The dipped film was taken out to remove the solution deposited on the surface of the f.ilmO Later when dipped in a developing bath, i.e~ an aqueous solution containing sulfuric acid of 66 B'e (chosen to have a concentration o~ about lO cc~Q) and sodium nitrite (chosen to have a concentration of about 0.5 g/Q), then the film was dyed uniformly blueO Thereafter~ the film was washed enough to remove unreacted dyestuffD The film ~hus colored was placed several hours in boil-ing water to determine dy~ability ~dye fixation test)~ proving that the dyestuf~ firmly adhered to the film and the color did not faintO
~ Another sample of the above~mentioned film wa~ dyed by a :~ 20 different solubili~ed vat dye ~manufactured by Farbwarke Hoechst A~Go under the trademark ilAnthrasol 04G") through the same process as described above, obtaining substantially the same result~

A pictuxe image was projected by means of a 2-kilowat mercury lamp through a transparent negative on a transparent film pre-liminarily dipped in an a~ueous solution of the latt~r dyestuf~
used in Example l, presenting a distinct blue picture~ Later, the ;~ film thus colored was fully washed with warm water to disolve out ; ~ dyestu~ attached to the nonpictured portîons of the ~ilmO Th-e colored picture thus formed fully withstood the same dye flxation test as applied in Example lo :A ~ilm whose triace~ate base was uniformly coated with cross-linked 2~hydroxyethyl methacrylate resin was preliminarily dipped about 15 minutes in a ~0% aqueous solution of 2~3,5-triphenyl-21~-tetrazolium chlorideO ~fter ~he dipped film was taken out, the solution deposited on the surface of the ~ilm was removedO
When again dipped about lO minutes in a lO~ aqueous solution of sodium boron hydride, the ilm was uniformly cIyed redO This d~e sufficiently withs~ood the same dye fixation test as used in Example lo ~pplication of another form of tetrazolium salt gave the same result as observed in Example lo Example A picture image was projected 5 minutes by means of a 2~
kilowat mercury lamp through a transparent negative on a trans-parent film preliminarily dipped in the same manner as in Example 3, presenting a distinct red imageO Thereafter, the film was dipped in warm water to remove the 2,3,5-triphenyl~2H-tetra~olium chloride remaining on the nonpicturea portions of the film~ The dye of the p1cture well withstood the same dye fixation test as applied in Example lo Exam~ple 5 ~ soft contact lens fabricated from cross-linked 2-hydroxyethyl methacrylate resin was swollen by being dipped in a physiological saline solutionO After said .soft contaet lens was taken out, the water remaining on all the peripheral surface of the lens was removedO ~ letter was impressed at the prescribed position near the periphery of the lens by a porous sponge rubber stamp impregnated with ink formed of 3 parts by weight of solubilized ~at dye (manufactured b~ Farbwerke ~oechst ~oGo under the trademark "Anthrasol Pink l3B"), 13 parts by weight of glycerine and l4 parts of waterO Later when th~ co~tact lens was dipped in the developing bath used in Example l, then a dis inct red letter appearedO The dyestuff of this letter fully endured the same dye fixation test as ~ applied in Example lo ; ~ - 12 =

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Example 5 . . .
~ soft contact lens impressed with a letter in the same manner as in Example 5 was exposed about one minute to a black light (whose quantity was chosen to be 2 mW/cm2)~ Then the letter was dyed distinc-tly redO The dyestuff of the let~er satisfactorily endured the same dye fixation test as conducted in ~xample lo ~xample 7 An .ink having the same composition as used in Example 5 was : applied to the prescribed spot near tlle periphery of a soft contact lens fabricated by the same pro~ess as used in Example 50 A letter image was projected about 2 minutes by means of a 2-kilowat m~rcury lamp through a transparent negative on the ink-impr~ssed spot o the lens. Then the letter was dyed distinctly redO Later, the lens was dipped in warm water to remove the dyestuf~ remaining on the nondyed portions of the lensO The duestuff of the letter thus for~ed fully withstood the same dye fixation test as used in Example lo ~~ith respect to Examples 5~ 6 and 7, applioation of another :~~orm of solubilized vat dye ga~e the same result as in Example lo Example ~
:A porous rubber starnp measuring 4x4x4 mm la letter engra~ed therei~ having a measurement of 2~1 mm) manufactured by Japan :NCR Company was impreg~ated with 0003 cc of printing ink formed of 10 parts by wei~h~ of solubilized vat dye (manufactured by Farbwerke Hoechst AoGo l~der the trademark "Brilliallt Pink 13B"), 20 parts by weight of water and 10 parts by weight of glycerine~ A water-; ~expansible soft contact lens was dipped 10 minutes in waterO Less than 30 seconds after the lens was taken out of the water, the rubber stamp was pressed 5 seconds to impress a letter on said 30 lensO The soft contact lens thus impressed with a letter was exposed 30 seconds ~o a black ligh~ whose quanti~y was chosen to be

2 mW/cm~ Then khe 1 tter was dyed distlnctly purpleO For comparison, a letter was impressed on the soft contact lens by an '7~

ordinary rubber s~amp using the above-mentioned printing ink~ uncler the same condition in which the sof~ contact lens was exposed about 30 seconds to a black light whose quantity was chosen to be 2 mW/cm2O
In this case, however~ the printing ink was thrown out of the rubber stamp, only providing an indis-tinct blurxed letter image=
A letter image provided by the method of this Example 8 was firmly fixed in the resin constituting the soft contact lens~ rhe surface of said soft contact lens presented no scarsO When the marked soft contact lens was subjected to a long boiling ~est required to examine ~he practicability of a soft contact lens, then the letter impressed on said soft contact lens did not faint at allO

A porous rubber plate impregnated with a ~0% aqueous solution o* 2,3,5-triphenyl~2H tetrazolium chloride made a picture impression on a transparent film formed of unswollen cross-linked 2-hydroxyethyl methacrylate resinO The film thus impressed was left about 5 minu~es in an atmosphere having a temperature of 60C and humidity o ~5%c Thereafter, the film was e~posed to light abou~
20 seconds at a point spaced about 15 cm from a 2-kilowat mercury lamp~ presentiny a dis-tinot red water-insoluble letter impress.ion.
This impression was found to be prominently wear-resistant and waterproofO
_e 10 ~ porous rubber stamp impregnated with a printing ink formed of 4 parts by weight of solubilized vat dye (manufactured by : ~ ~arbwerke ~oechst AoG~ under the trademark "Anthrasol Pink 13B")~
parts by weight of glycerin~ and 20 parts by weight of water made an impression on a soft contact l~ns form~d of the same unswollen resin as used in Example 9. Tlle soft eontac-t lens thus impressed was left 10 minutes in an atmosphere ha~ing a temperature of 70C
and a~humidity of 85~ and was exposed about 90 minute~ in said atmosphere to a black light whose quanti-ty was chosen to be 2 mWfcm2O

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Then the soft contact lens indieatecl a distinct reddish purpleletter image~
This le~ter impression had the advantages that it did not give rise to any ConveX portion on the soft contact lens, endured a long boiling test, waS not affected by a cleaning solution ~formed of protein-decomposing enzyme)~ and proved quite satisfactory for use with a soft contact lens~
Example 11 h letter impression was made in about 3 ssconds with the same kind of printin~ ink and by the same kind of rubber stamp as used in Example 10 on a soft contact lens fabricated by swelling the same type of resin as used in Example 9 in water within 30 seconds after said soft contact lens was taken out of the water~ The soft contact lens thus impressed was left about 1~ minutes in an atmosphere having a temperature of 40C and a humidity of 90~. And thereafter when dipped the lans about 15 minuteæ in a dye bath fo~med of an aqueous solution of sulfuric acid of 60 Ble ~whose conceIltration was chosen to be about 10 cc~Q~ and sodium nitrite (~hose concentration was chosen to be about 005 g/Q)~ then the soft contact lens presented a letter impression bearing a concentrated reddish puxple colo~0 This letter impression indicated a more concentrated color than that:which was formed simply without being le~t in an atmosphere of high temperature and humidity, and more-over was elevatad about four fold in resistance to boiling due to the deeper penetration of the dyestu~ into the soft contact lens.
Example 12 .. __ .
:~ A porous rubber plate impregnated wi*h a 20% a~ueous solution ~: of 2,3t5~triphenyl-2~-tetrazolium chloride made a le~ter impression on a transparen-t film formQd of a cross-link d copolymer o~ poly-~3Q methyl methacrylate and N~vinylpyrroli~one which had been dipped about 20 minutes in methanol for swellingO The film thus impressed was exposed about 30 seconds to a light at a spot spacQ~d about 15 cm from a 2~kilowat mercur~ lamp, providing a distinct red ~.~

~ ¢~ 3 water-insolukleletter impression. I'he letter impression proved to be prominently wear-resi~tant and waterproof. Where the same type of film as described above was swollen by being dipped in water alone, the resultant letter impression indicated a very faint color.
Example 13 A molding of cross-linked high molecular resin formed of a copolymer of 2-hydroxyethyl methacrylate and methyl~
methacrylate was dipped about 2 minutes in a bath of ethyl "Cellosolve" to swell the surface of said molding. The molding was preliminarily dipped 10 minutes in an aqueous solution of solubilized vat dye (manufactured by Farbwerke Hoechst A.G.
under the trademark "Anthrasol 04G") whose concentration was chosen to be 30 g/R. Later, the solution deposited on the surface of the molding was washed off. The molding was again dipped 5 minutes in an aqueous solution of sulfuric acid of 65 B'e whose concentration was chosen to he about 10 cc/~ and sodium nitrite whose concentration was chosen to be 0.5 g/~
(a developing bath). Then the surface of the molding was uniformly dyed blue. Later, the molding was water washed to remove unreacted dyestuff. To examine dyeability, the molding was placed scores o~ hours in boiling water (dye fixation test~, but was not subskantially decolored. Application of another form of the above-mentioned vat dye to dye said molding gave approximately the same result.
Example 14 A picture Lmage was projected by means of a 5-kilowat mercury lamp on the same kind of resin molding as used in Example 13 which had been~preliminaxy dipped in ethyl l'Cellosclve" for swelling through a transparent negative, providing a distinct ; blue impression. Later, the impressed molding was thoroughly washed with boiliny water to remove the dyestuf~ xemaining on the nonpicture portion o~ the molding, A picture impression thus dyed f~llly endured the same dye fixation test as applied in ~!,¢ ~

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Example 13.

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~....~. ~, ,, 37~3 Example 15 A soft contact lens fabricated only from cross~linked 2~
hydroxyethyl methacrylate was dipped about 15 minutes for swelling in an ethanol-water bath (whose fixst and second components were mixed in the ratio of 3~7)0 A letter was impressed at a spot near the periphery of the swollen soft contact lens by a porous rubber stamp impregnated with a printing ink formed of 15 parts by weight of solubilized vat dye (manufactured by Farbwerke Hoechst A.G.
: under the trademark i'Anthrasol Pink 13B')~ 10 parts by weight of : 10 glycerine and 75 parts by weight of water~ ~hen exposed about one minute to near-ultraviolet rays radiated by a black light whose quantity was chosen to be 2 mW/cm2, the soft contact lens thus impr~ssed displayed a distinct red letter. When the soft contact lens was placed in boiliny water for one hundred and scores of hours~ t~e letter impression flllly endured this continuous boiling testO Even when the soft contact lens was not dipped in an ethanol ;~ ba~h for swellingr a letter impressed thereon was well dyed~ but with~a far lower resistance to boilingO
A soft contact lens prepared from a copolymer of 2--hydroxyethyl methacrylate and N-vinylpyrrolidone die not indicate a considerably wide difEerence between the immersion of sa.id lens in ethanol and the nonimmersion thereof due to the copolymer itself ha~ing a very high water~expansibili~y. In contrast, a so~t contact lens prepared from a copolymer of 2-hydroxyethyl. methacrylate and methylmethacrylate presented a noticeable diference between the immersion of said lens in ethanol and the nonimmersion thereofO
Namely, whan a letter was impressed on a soft conta~t lens formed ~: o~ the letter form of copolymer but not dipped in athanol, the dye of the 1 tter onl~ slightly penetrated the texture of the copolymer.
Where, therefore, the soft contact lens was washed with water, the : ~ :

dyed le-tter faintedO Conversely, whexe the soft contact lens was previously dipped in ethanol for swelling, then a letter impxessed , ~: thereon was ~istinctly dyed with high Fesistance to boilingO

~3~3 Example 16 The soft contact lenses prepared from each of the three forms of resin used in Example 15 were dipped about 15 minutes in the same developing bath as used in Example 13 instead of being exposed to ultraviolet rays to display a letter impressed on said soft contact lenses. In this case~ the same good results were obtained as in Example 15.
Example 17 A soft contact lens was dipped about 2 minutes in a bath of the same printing ink as used in Example 15 without impressing a letter by a porous rubber st~,n~, A letter was projected on the soft contact lens through a transparent negative by means of a 5-kilowat mercury lamp. The letter was distinctly displayed. The lens was boiled to remove the printing ink in those portions of the soft contact lens which were not exposed to the light. The dyed letter indicated the same good resistance to boiling as in Example 15.
Example 18 An impression was made on the surface of a molding of a cross-linked high molecular copolymer of 2-hydxo~yethyl meth-acrylate and methylmethacrylate ~y a rubber stamp impregnated with a printing ink formed of 1~ parts by weight of solubilized vat dye (manufactured by Farbwerke Hoechst ~.G. under the trade,mark "Anthrasol 04G"), 20 parts by weight of ethyl "Cellosolve" and 68 parts by weight of water. The impressed molding was left about 5 minutes in an atmosphere having a temperature of 60C and a humidity of 85%~ Later, the moldin~
was exposed to a light about 30 secon~s at a point spaced a~out 5 cm from a 2-kilowat m~rcury lamp. Then a dyestuff deeply penetrating the texture of the moldlng presented a water-insoluble distinct bluish green impression which proved highly wear-resistant and waterproof.
.~
.

9~ 7~3 Example 19 A molding of a cross-linked copolymer of 2-hydroxy-methacrylate : :

: :
:
:

. ~ :: :~:
: ~ :

~ : ; - 18a~- :

and N-vinylpyrrolidone was swollen by being dipped in waterO After water was removed from the surface of the molding, an impr~ssion was ~ade at the pres-ribed position by a porous sponge rubber stamp impre~nated with printing ink formed of 3 parts by weight o~ a solubilized vat dye (manufactured by Farbwerke ~Ioechst A~Go under the trademark "Anthrasol Pink 13B")~ 13 parts by weight o~ glycerine and 13 parts by weight of waterO When dipped in a developing bath : formed of an aqueous solution of sodium perborate whose concen-tration wa~ chosen to be 1 g/Q, then the molding presented a dis~inct red imageO When the molding was placed several hours in boiling water (dye fixation test3 9 the image appearing thereon die not faint in color, proving that ~he dyestuff was firmly setO
.

~;

Claims (17)

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

1. A method of dyeing or printing a non-fibrous shaped article composed of hydrogel resin containing pendant hydroxyl groups, comprising impregnating said article with a water soluble dye substance selected from the group consisting of a photosensitive solubilized vat dye and a tetrazolium salt by contacting said article with said dye substance in the form of a dye solution or printing ink, swelling said article by exposure to an atmosphere of high temperature and humidity, and thereafter rendering said dye substance water-insoluble and colored by exposing said impregnated article to light.

2. The method according to claim 1 wherein the contacting process is performed by making an impression on said article by means of a porous printing stamp soaked with a dye solution or printing ink containing said dye substance.

3. The method of claim 1, wherein said hydrogel resin is a cross-linked polymer of hydroxyethylmethacrylate.

4. The method of claim 1, wherein said hydrogel resin is a cross-linked copolymer of hydroxyethylmethacrylate and n-vinylpyrrolidone.

5. The method of claim 1, wherein said hydrogel resin is a cross-linked copolymer of hydroxyethylmethacrylate and methyl-methacrylate.

6. The method of claim 1, wherein said article is a soft contact lens.

7. A method of dyeing or printing a non-fibrous shaped article composed of hydrogel resin containing pendent hydroxyl groups, comprising swelling said article in at least one liquid selected from the group consisting of:

(a) water, and (b) a water-miscible solvent having a greater resin-swelling power than water; and impregnating said article with a water soluble dye substance selected from the group consisting of a photosensitive solubilized vat dye and a tetrazolium salt by contacting said article with said dye substance in the form of a dye solution or printing ink; and therefore rendering said dye substance water-insoluble and colored by exposing said impregnated article to light.

8. The method of claim 7, wherein the contacting process is performed by making an impression on said article by means of a porous printing stamp soaked with a dye solution or printing ink containing said dye substance.

9. The method of claim 7, wherein said hydrogel resin is a cross-linked polymer of hydroxyethylmethacrylate.

10. The method of claim 7, wherein said hydrogel resin is a cross-linked copolymer of hydroxyethylmethacrylate and n-vinylpyrrolidone.

11. The method of claim 7, wherein said hydrogel resin is a cross-linked copolymer of hydroxyethylmethacrylate and methyl-methacrylate.

12. The method of claim 7, wherein said article is a soft contact lens.

13. A method of dyeing ox printing a non-fibrous shaped article composed of hydrogel resin containing pendent hydroxyl groups, comprising impregnating said article with a water soluble dye substance selected from a group consisting of a photosensitive solubilized vat dye and a tetrazolium salt, by immersing said article in a dye solution or printing ink containing said dye substance, and thereafter rendering said dye substance water-in-soluble and colored by image-wise exposing said impregnated article to light.

14. The method of claim 13, wherein said hydrogel resin is a cross-linked polymer of hydroxyethylmethacrylate

15. The method of claim 13, wherein said hydrogel resin is a cross-linked copolymer of hydroxyethylmethacrylate and n-vinylpyrrolidone.

16. The method of claim 13, wherein said hydrogel resin is a cross-linked copolymer of hydroxyethylmethacrylate and methyl-methacrylate.

17. The method of claim 13, wherein said article is a soft contact lens.