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Back~round of the Invention -This invention relates to a process for imparting a permanent identification mark to an optically clear plastic articie such as a lens. More particularly, it relates to a ~ - , , method of marking which enables a manufacturer to confirm ~ . . , . ~ .
that a returned article which had beeD distributed to the consumer is in fact its own product, yet results in a mark which has no material effect on the passage of visible light ¦¦through the productO
Ophthalmic quality plastic lenses made of allyl diglycol carbonate (CR-39), polycarbonate (Le~an), and the like are ¦,now widely available. These products are distributed to the ;consu~er through retail outlets which frequently sell products of more than one manufacturer. When à de ective or damaged lens which h2s been mounted in an eyeglass fra~e is returned~
it is often impossible to determine the identity of the Ilens' manu~acturer.
I I An apparent way to remedy this di~fi.culty is to provide ~an integral indicia of some kind or otherwise bulld within I the lens struc~ure a unique and identifiable characteristicO
¦ A satisfactory method of marking products of this type has -not yet been found. Since ophthalmic quality lenses ~ust be optically clear and cosmetically perrect they cannot be provided with a surface embossed design or colored mark which is permanently on or in the lens. Such a-mark would illikely be viewed as an imperfection or a flaw in the optical ilquality of the lens. ~iere the mark so small as to be ~y 1i ' ' .
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clearly free of these disadvantages, it would likely be too ;
small to be of practlcal value. '!
In most cases, the manufacturer distributes the products l -~,to retailers, such as optical laboratories, in the ~orm of ;
j lens blanks which thereafter cut the blank to a lens si~e and subsequently glaze the lens into a frame. Because of ` li this distribution procedure and because of the expense ¦¦involved, it is not practical to affix an identifying mark ¦lon an edge of the lens which ~70uld be hidden by the eyeglass frams. Furthermore, because the mark must be permanent, the ;
simple expedient of affixing a removable label on the lens is inappropriate. ;
The ideal identification mark for an optically clear j llens should leave no flaw or blemish 0c any ~ind on the lens !I surface, should be permanent, should not be visually detectable, ~jand should be easily applied at the factory site on both ¦jlenses and lens blanks.
~ ith the above thoughts in mind one might be invited to conclude that the indicated solution of the present problem ~ ould be a~ invisible mark since such mar:cs ara widely known ! in the securities and banking field. Flourescent inks as I applied to various documents such as bills and notes might ¦ibe argued to suggest a solution for the present proble~ by ;stamping the ophthalmic lens ~ith a flourescent ink. Unfortunatel , ¦!the solution of the problem is not so straight forward as ¦Imight ~e suggested~ Plastic articles are not absorbent to ¦!the degree that papers and fabrics areO ~urther, any ink ¦
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¦Imark applied to the article would be very readily wiped s ¦clean by the normal action of cleaning ones eyeglass lens.
It is further desirable that the mark placed upon the - ~Iplastlc article (ophthalmic lens) be in a relatively small form such that inadvertent observation might not be a major .
distraction to the wearer or those about him. It is necessary therefor that the identifying mark be placed upon the articie ;in rather small fashion and be of fairly high resolution-. It has been found that inks and othe~ liquids have a profound ,jtendency to run on the surface of a plastic article, spreading ,in all directions with little cor.trollability. For these t.:
and the above reasons, fluorescent inks such as known for luse in the securities trade are not accep,able for solution ¦,to the present problem.
So the problem faced in the present invention then demands marking by other than a conventional liauid. Again ~'those _amiliar with the fluorescent inks m:ight be led to '~concluae that, since some inks are in fact fluorescent Ipow2ers in solution, one might use powder to place an indication ::
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on the lens. ~his approach generates a problem of adhesion ~to the lens since the powders do not readily adhere. Should the powder be desolved in the ink liquid, the situat~on reverts to a marking liquid being placed upon the surface of ~
the plastic article. .
The present problems are solved in the invention by the method of marking the article with a fluorescent powder '11 ' . .' ~
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~Ipreferably in comb~nation with-powder-diluent. These powders _ . . . . . .. , , _ ~lor solids are initially contained in a carrier liqùid, -,!perferably in solution, however suspensions are acceptable.
The powders are then applied to the lens with the mixture (dye and carrier) in a su?er-saturated condition,__such that the characteristics of the marking composition are not truly that of either a Iiquid or a powder. The composition might ~be comp2~ed to a paste or slurry.
¦, In addition to the problems of application of the I 'suita~le dye for marking the plastic ar,icle there is also 'a ?robla~ of adequately applying the proper amount of dye such that a reacily recognizable, high resolution small mark lcan be ?lac2d upon the article, e. g. one having a predeter~ined ~limited degree o~ ultraviolet responsa when activated. It is there~ore r.ecessary to meter the amount of dye being used ¦,during the mzrking process.
Il Chzracteristically, fluids are metered by the relative !Iconcentrations of components in a so~ution or suspension.
~In the ~res2nt invention, however, the marking composition is noi chara_teristically a li~uid. A further-problem in lthe ~resent invention is that the concentrztions of the '~marking solution are continually changing due to the necessity if having to marX the article with a super-saturated solution jor suspension. We have found that by causing the carrier .. ..
isolution to volatilize such that the super-saturated state of the marking composition can be rcached. This volatilization necessarily means that relative concentration of the ingredients ., ' .
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;including the dye continue to increase in concentration unless extraordinary measures are taken.. The concentration t of dye may thus reach a level which produces a mark which is -over-responsive and thus unsatisfactory. .
. With this in mind, we use a very small quantity of dye material and perferably dilute the dye in a second po~der. ~.
: ,?eculi2rly however, the characteristcs of the powder must be I ¦-~marksdly different than the dye so as to not interfere with . the process by which the dye forms.the permanent mark on the .plastic article. We thus utilize a powder diluent which I
during the process of transferring a dye material to the I
.;face of the plastic article sublir.es into the surrounding I,.at~.osphere so as to leave no trace of the diluent material "on the face of the marked plastic article.
iSumm~rv Oc the Invention The process of the instant invention imparts à permanent iden'ification mark to optically clear plastic articles, including but not limited to ophthalmic quality plastic ,lenses, ~ithout.a~versely affecting the article's visible lliah. optical pro~e~ties. In the process, a predetermined small æmount or ultraviolet light-activatable fluouescent .
dye is mixed ~ith a volatile liquid carrier material to form ~a suspension or solution comprising a markins compositionO
~A soluble or suspendable inert sublimable solid diluent can also be utilized to improve the control over the marking .process. The marking composition is then applied in a 'selected pattern on a surface of the optically clear plastic . ~ , `: I' 1,' , . , ., ' . . i f .
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article by a carrier means, for example, a rubbe~ stamp or a -stencil whereon the dye is in a supersaturated solution or suspension. Thereafter, the carrier material evapo~ates from the applied composition to leave a residue of solid dye and inert sublimable solid diluent in the chosen pattern on a surface of the article. The amount of dye.on a given area of the article is thereby metered so that, after transfer,' the degree of fluorescent response obtained is such that ! bright sunlight does not activate the dye to a visually detectable level, yet the mark is visible under direct U.V.
radiation from any long wave U.~. lamp. Tha. the dye and -inert diluent immediately prior to permanent transfer to the plastic article are in solid form (powder) is important '`because liquid for~ulations have heen found to produce a poor cuali'_y r.a ~ due to "running" o~ t`he d~e. The article ;is then heated to a selected temperature below the temperature at ~hich the plastic material from which is is made beJins to degrade, but at an elevated temperature such that the powder cye may migrate into the surface-subsurface structure ~of the ~lastic article.
In preferre embodiments, the marking composition is a solution or^ fluorescent dye, although suspensions may also `;be used.
`~ The marking composition solution comprises the carrier ~(a volatile liquid) and the fluorescent dye. The ratio of quantities is such that, at th~ time of application of composition to article, the solution has become supersaturated 1. . , ;
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~1~29610 e.g., by evaporation of the volati~le carrier duri~ng the transit of the marki`ng i~nst~ument ~rom a supply contai`ner to the article be~ng marked.
A preferred marking compo~sition compri~ses ethyl acetate, one or more o~ the crystalline or powered fluare-s-cent dyes commonly used as fluorescent whiteni~n~ agents (see G.W. Broadhurst and A. Wieber, Ciba-Geigy! plàsti~cs Engineering, 29, No. 9, 36 Sept. 1973) ! such as 3 phenyl-7-triazinylamino-coumarin, stibene naphthotriazole, ben-zotriazol phenyl coumarin, tiophene bi~s (benzoxazolyl), and other suhstituted derivatiyes of these structures, as well as other triazinylaminostilbenes, coumarins ! bi;s-ben-zoxazolyls, benz-triazoyls, pyrazolines, naphtha],i~c aci~
imides, and bis-styryl benzenes, and other derivatives such as those available commercially ~rom Ciba-Geigy Corporation under the trademarks Uvitex OB ancl Ti~nopal SFG. Other use-ful derivatives are Leucopure EGM* from Sandoz Color &
Chemicals Co. and Eastobri~te PE* from Eastman Chemicals Co.
Preferably also, an inert sublimable solid di-luent such as benzoic acid, salicylic acid, meta-hydroxybenzoi~c aci~d, or the aromatic carboxyli~c amide-ester mixture sold by duPont under the trade mark Latyl A is included in the marking compoSitIon. The mark on the optically clear plastic ar-ticle is preferably applied with a rubber stamp and i~s transferred into the surface of the article by heating in an oven or by infrared radi~ation.
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While the process of the invention may be employed to mark a variety of clear plastic materials, a preferred plastic material is a "colorless" allyl diglycol carbonate (CR-39*), i.e., an ophthalmic quality plastic which has been treated in accordance with the teachings of copending application Serial No. 292,61~, entitled "Colorless Polycarbonate Articles" to eliminate the slight yellow color normally characteristic of cast products made from this material.
Accordingly, it is an object of the invention to provide a method of identification marking an optically clear plastic article without adversely affecting its visible light optical properties.
In one aspect the invention provides a process for imparting a permanent identification mark to an optically clear plastic article without adversely affectin~
its visible light optical propexties, the process comprising the steps of: (a) mi~ing a solid ultraviolet light activatable fluorescent dye with a liquid carrier material to produce a marking composition; (b) causing the dye to ~ecome supersaturat2d in the liquid carrier;
(c) applying a pattern of the supersaturated marking composition to a surface of the optically clea~ plastic article; (d) evaporating the carrier material from the surface of the article to leave a residue of solid dye in the pattern on the surface, the amount of dye on the surface being sufficient to induce a readily detectable fluorescent response when irradiated with light from a I ~ -- g _ * Trade mark jsb ~, ;
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U.V. lamp, yet insufficient to produce a visually detectable response in the presence of sunlight; and (e) heating the surface of the article to a selected temperature below the degredation point of the plastic for a sufficient amount of time to transfer the dye into a surface layer of the article and to result in a fade resistant mark.
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Description of the Drawi~ngs Figure l l~s a pi~ctori~al yiew of apparatus used in practi~cing the invention.
~escription of the Preferred Embodiment In the process of the invention, a preferred mar-king composition is prepared from a powered fluorescent dye, an inert sublimable solid and a carrier. ~arious com-mercially available and well-known fluorescing dyes may be used, but the preferred dyes are derivatives which are available commercially. The dye must be capable of migra-ting into the surface-subsurface structure of the plastic article without degradation thereof.
The purpose of the carrier is to provide a vehicle which enables the application of the powder dye to the sur-face of an optically clear plastic article. In this regard, the carrier material should be selected from among those liquids which do not adversely affect the material from which the optically clear plastic article is made. Thus, the car-rier should not dissolve or swell the plastic material which is to be marked. For example, acetone should not be used in a composition intended for marking cellulosic articles.
For allyl diglycol carbonate articles, suitable liquid car-riers include ethyl acetate, simple esters, alcohols, and ketones, water, and mixtures of alcohol and water. Like-wise the carrier must exhibit sufficient volatility such mab/ ~
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that the dye may be maintained in solution or suspension in r ~the carxier while being maintained in a supply vessel and~
thereafter become a supersaturated solution or suspPnsion during the time period when the marking composition is being transported from the sup31y vessel to the article being marked.
As previously mentioned it is preferred that the l markins composition comprise a solution of the selected dye ¦',and inert sublimable solid diluer;t in the carrier. However, !' liquid carrier ma~erials in which the dye and solid diluent ,~are insoluble o~ sparinslv soluble mav be employed. The marking comoosition m2y comprise a suspension. It is also prefe-'ed that the inert sublimable solid diluent be dissolved or suspended in a similar manner.
The amount c fluorescent àve and solid diluent included t in the marXing composition should be sufficient to leave a Ijfine residue of powdered dye and solid diluent on the s~lrface lo he article after the carrier has completely evaporated ! there~ro3n. ~ne compositiorl is initially applied in t~at migh~ be othe-wise described as a thin film of the marking ~com~osition applied to the lens. Sufficient dye should be present on the lens surface so that the fluorescent response ¦of the finally formed mark is readily seen when irradiated ,with ultraviolet light from a U. V. lamp, yet not noticeable `lin the ~ ~ o~f sunlight twhich of course includes ultxaviolet iwavelen~ths). Thus, the ~ercent by weight dye of included Iin the marking composition depends on the thickness of the !'` . . .
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! f ilm applied to the article and on the characteristic str~ngth .
of the fluorescent response of the selected dye. Accordingly, , the amount specifically determined "optimum" by the user~ may have to be adjusted when employing a given dye on a given article in order to determine the "optimum" response.
One suitable marking composition partic~larly well adapted for use on allyl diglycol carbonate articles consists ~, of a solution of 0.15~ by weight of a bis (benzoxazolyl) derivative, (e.g. Uvitex OB dye) and 1.25% by weight of an liaromatic carobxylic amice-ester (e.g. Latyl A) dissolved in ethyl acetate (e.g. 800 ml) as the carrier. Specific non- ¦
limitina examples of dyes that may be used include thiophene ¦;bistbenzoxazolyl), 3 phenyl 7-triazinylamino-co~marin, ,stilbene naphthotriazole, and benzotriazole phenyl coumarin, triazinylaminostilbenes, coumarins, bis-benzimidazolyls, ;bis-benzoxazolyls, benz-triazoyls, pyrazolines, naphthalic i'acid i~ides, and bis-styryl benzenes.
¦l It should be noted that the above preferred composition ;as well as those previously and generally described include ~an additlonal ingredient identlfied as a "solid diluent". We have found it difficult, however not impossible, to continuously meter the amount of dye suspended or in solution in the carrier. Since it is preferred to deposit very small amounts of the dye on the surface of the article to be marked, it is ~convenient to additionally dissolve or suspend in the carrier the diluent material, also a powder r thereby raising ¦
to an easily meterable level the total amount of po~lder to be applied to the article.
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- , The diluent is ehosen so that at the operative temperature ;for causing the dye material to migrate or be finally adsorbed into the marked article, the diluent sublimes into the -surrounding atmosphere. Specific non-limiting examples of diluents that may be used include benzoic acid, salicylie aeid, meta-hydroxybenzoic acid, and Latyl A, an aromatic carboxylic ester-amide mixture made by Duponæ.
As with chosing a carrier, the eharacteristics of the diluent must be such that it causes no degradation of the i surface of the marked zrtiele cr the response or absorbtion t' i,of the dye. The identi~ied Latyl is such a material when used in ethyl acetate on allyl diglycol earbonate artieles in eonjunction with the Ciba-Geigy dye ~vitex - OB~
The next step in the process is to apply the marking jcomposition in a pattern in the form or the desired mark to a surface o, the plastic article. The mark may, for example, ~;
be a registered trademark, corporate logo or the like. ~;
There are various suitable ways to eCfect this step. For example, the com osition may be applied with a marking device such as a relt tip pen or:a steneil may be employed.
The pre erred method or imparting a pattern of the composition on the article is to imbibe the composition in a pad-type device, take up a thin film of composition on a rubber stamp from the pad, and stamp the article in the desired surface location. For eurved surfaees, a rolling motion may be used.
In the preferred praetice of applying a mark to a plastie artiele sueh as an ophthalmic lens, apparatus sueh ' . .
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as illustrated in Fig. 1 may be used. In that Figure ¦ reference numeral 10 indicates a belt-type pad which is .
disposed to rotate on two rolls 12 and ;3. Rotary power from such as electric motor 14 may be supplied to one or both of the rolls (e.g. the bottom xoll 13). Carrier solution 16 is contained in vessel 18 such that roll 13 bearing pad lllO is at least partially submerged in car~ier solution 16.
! For convenience in multiple marking the described appartus may be disposed at a marking station 20 such that ~roll 12 is table high and exposed through such in slot 22 for access. As pad 10 is rotated on roll 12, it is exposed to be contacted by stamp 24 such that carrier solution ~inclucling the dye for mar~ing and, if includad, diluent are ~avai'able to be picked up on the stamp and transferred to tha plastic article 30 to be mar~ed.
As pre~tiously indicated, it is preferred that carrier ,solution 16 contain the diluent andjor dye in solution or ,suspension such that these materials are uniformly concentrated thereon. AS a siven point 26 on pad 10 rotates ~rom a submerged position, as on roll 13 to a fully exposed position 2g as on roll 12, the carrier solution may evaporate such that at point 28 the diluent and/or dye are supersaturated ~in solution (or suspension) to the desired degree to be :effectively transferred to the face of stamp 24O It should be recognized that further evaporation of the carrier solutio~
`on stamp 24 may continue until the diluent-dye solution/ `
suspension is transferred to the plastic article 30.
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li . ` . ., Il After deposition of the marking material, the carrier l is selectively removed from the surface of the article such I as by evaporation to leave a residue of solid diluent andjor dye in the selected pattern. Dyes and diluents that are ¦,liquid at room temperature are not employed because they ¦tend to spread and penetrate the plastic surface prior to being heat treated and result in a rark which is not sharply l'defined. Since the marking composition comprises a volatile ¦Icarrier, it spontaneously evaporates at room temperature.
¦I Following application of the mark to the article, the mark is permanently transferred in,o 2 surface layer of the larticle by being heat treated.
¦ In the disclosed preferred system, this diluent and/or ~dye powder is placed on the article and upon heating, the dye powder particles are adsorbed into the surface of the 1-arti~-le. LiXewise, because of the sublimating character of the diluent, upon heating it vola~ilizes into the atmosphere of the heating chamber.
¦! The duration and temperature of the heating step necessarily depends on the affinity of the material from which the ~article is ~ade for the fluorescent dye of the marking 'composition. In no event should the heatina be conducted at a temperature at which the article, the diluent or dye will ~begin to degrade. In the best method herein disclosed, heating occurs to a point above the glass transition temperature of the allyl diglycol carbonate (about 70C) and below the melting-point of the dye (about 200C).
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Two heating methods have been used with success. ~ ¦
first and presently preferred method is to heat the article in an oven. The second method is to heat the article with an infrared lamp. To illustrate the reIationship between the 1temperature of the heating step and its duration and the relationship between the distance of the infrared lamp from the article and the duration of exposure, 66 mm allyl di~lycol carhonate lenses and some lens blanks were treated as disclosed I ~
above with a marking composition consisting of 1 1/2~ by ' ¦ ¦
weight ~vitex OB'in ethyl acetate. In this first e~ample ¦~the marking com?ound was maintained in a conventional "stamp pad'' and, the carrier solution allowed to volatilize until the solution supersaturated. This condition was detected by noting the beginning of formation of small powder granules on the pad. The logo stamp was then pressed into the pad and subsequently onto the face o~ the lens.
Table I sets forth the time re~uired at v~rious oven temperatures to set the marks to a "very good" fluorescence, i.e., a ma~k of detectable but not excessively bright fluorescence. Longer times than -those stated in Table I
also produce excellent fluorescent dye trans~er, but increase the risX that the lens ~iill become marred. Shorter times ranse in effect from no transfer to an adequate but less than optimum transfer.- The "very good" condition is recommended because it allows the mark to readily be detected under W
llight generated from a lamp, but substantially invisible in bright sunlight. Also, when in the "very good" condition, the lens may be subsequently dyed to a sunglass transmittance `while still maintaining an observable fluorescent mark. ¦
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¦j 'rime ' 65 mm semi-finished .
, Oven Temperature (~F) 66 mm finished lens blanks _ i~ 160 20 hours - -180 3-4 hours - -200 35 mins. - - , l 220 25 mins. 30 mins.
250 15 mins. - 20 mins.
1 265 10 mins. - - : -1 280 7 1/2 mins~ - -! 300 5 mins. ~ - -' 310 . 4 mins. - -I!The results of the foregoing experiments were not consistent -¦¦at 160F. The larger lens blanks, which were not run at all ~temperatures, were observed to gene~ally require about 5 minutes extra heating time.
¦ Table II sets for the results of setting the fluorescent ¦dye io the "very good" condition using an infrared lamp (G.E. 250R 40/10).
I Time I' i 65 mm semi-finished Distance, Lamp to Base 66 mm Finished lens lens blanks !1 inch 3 mins. 4-mins.
ii2 inches 3 1/2 mins. 5 1/4 mins.
¦3 inches 4 mins. 6 1/4 mins.
;5 inches 6 mins. 6 1/4 mins. -6 1/2 inches 7 mins. 7 mins.
IThe foregoing procedure results in a surface layer of ¦Ithe plastic article containing a pattern of fluorescent dye.
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The cosmetic appearance and optical properties of the .
lenses and lens blanks used were not altered in any way and the mark was not visually detectable under either a shadowgraph i ,or bright light. Heating the lens or lens blank to set the dye in a surface layer thereof enabled the mark to withstand boiling water, washes in acetone, immersions in color remover ¦
~ifor a half-hour and normal processing procedures~
~able III sets forth the ranges of fluorescent dye ,alternatively including the powder diluent which were used i to produca marking. In all instanc:es the dye and diluent !-Iwere mixed into 800 ml of carrier, which for these examples j,was ethyl acetate.
TABLE III
Run Dye (in grams) Diluent tin grams) , 1 0.16 " 2 0.24 -- .
3 0.32 --0.48. __ ; 0.64 --. 6 1~20 -- .
7 1.09.6 .-. 8 1.014.4 '~ 9 1.023.4 0.94.8 11 -- 4.8 .
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l~g6'10 The above materials were run in the illustrated moving pad device to control the degree of saturation/super saturates of the marking composition. Time of exposure of the volatile carrier on the pad ranged from 1.3 to 18 minutes for acceptable marking. The optimum time seemed to be about 5.7 minutes. Times of under 1.3 minutes produced wet stampings, which were acceptable, however, showed begin-ning traces of running.
Other dye materials which have been used and found acceptable are Tinopal SFG* from Ciba-Geigy Corporation, Leucopure EGM* from Sandoz Color and Chemicals Company and ~astobrite PF* from Eastman Chemicals Company. These dye materials were found to be effective in the range of per-centages of the Uvitex OB* dye in Table III. Though the solubility of these materials in the carrier material varies, it is predictable and similar to the Uvitex OB* for example.
As the concentration of dye in the carrier in vessel 18 ap-proaches maximum solubility, the quantity which precipitates out during the supersaturated phase on belt 10 cannot all be redissolved in carrier on reimmersion such that build up of material occurs on continued usage. It is thus preferred that the solution be at a concentration below such "build up" level, and may be easily determine empirically for the var~ous materials.
The additional sublimable powders of metahydroxy-benzoic acid and benzoic acid were substituted for Latyl A*
as the diluent material. The metahydroxybenzoic acid was found to be useable approximately in the same concentrations as * trade mark - 19 -mab/ ~
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the Latyl A, while benzoic acid use was optimized at a concentration of about three times Latyl A. This variance - l `
~is suggested by the ratios of solubility of the varlous ' .
¦,diluents. The diluents also exhibited a similar "build~up"
j behavior as the dyesO
! Acceptable setting or curing.temperatures for dyes and ¦Id luents were found to be similar to the Uni.tex OB and Latyl IIAmatexials ¦I Having thus described our invention in detail and with I!sufficient particularity as to enable one skilled in the art 1 h to practice the invention, what is desired to be protected ¦Iby Letters Patent is set forth in the following claims.
Likewise, variations and modificati.ons which do not depar~
¦from the spirit and scope of such claims will be evident to ¦those skilled in the Art.
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