US2445253A - Method of producing mirrors by chemical deposition - Google Patents

Description

July 1s, 194s.

Filed Feb. 6, 1946 F. H. VERHOEK ET AL METHOD OF PRODUCING MIRRORS BY CHEMICAL DEPOSITION y 2 Sheets-Sheet 1 lulu 'Inl

INVENToRs 'Frpn .Verbeek a ATTORNEYS July 13, 1948- F. H. vERHoEK ET A1. 2,445,253

METHOD OF PRODUCING MIRRORS BY CHEMICAL DEPOSITION Filed Feb. 6, 194e a 2 sheets-sheet 2 TIJS Frank H. Vzrhozk By Willard L. Morgan.

l0 85 if @Job/@MMM A TURNEYS Patented July 13, 1948 ,N cuir Eo.; Per ossi-QE Application February 6, 1946;' Se'r'iallltf'. 645,940

This invention relates to aimethod of producingi mirrors by chemical deposition.f It is concerned more particularlyfwithva'nd comprises a methodand means for restricting the deposition ofsuch mirrorl deposits to the surfaceswhich itv is desired to coat, while protecting the other sun-i faces from suchdeposition by protecting them With ya temporary coating. of awater-containing inorganic gelatinous coatingwhichf. may be of:

various natures and which may,` after thevr mirroring operation is completed,abe removed readily.

Chemically deposited' mirror reective coat'- ings uponarticles are formed by contacting those` surfaces which are to be coated with mirror deposit, with freshlyl mixedv chemical. mirroring solutions which react and deposit thereupon a mirror reflective deposit' of silveneopperg gold; or lead sulphide, dependingauponthesolutions employed. In the forming of flat ymirrors -romg-lass; plastic, or polished metal sheets' itis-customary to support these sheets in a horizontalposition either upon a clothvcoveredtableorupon' a conveyerandto pour themirroring solutionoverthe top surface ofthe sheets, upon .Whichfsurface the mirror depositzisthen formedas desired.

f 1. sur-faces other thantlrose--desired to -he mirrored;

by'paint'ingg lacduering, -o'r waiting-'thesesurfaces; however,y the subseduehtremoval'ofsueh coatings: bysolvents, scraping, and fother *cleaning methods have'been unsuccessful because vof the diflicityiofi removing# suchhardf' coatings'=an'd the consider-- Another way ofproducingsuehflat'mirrorsfis f to support the sheets vupon racksinf nearlyor, substantially a vertical. position andtospray mirroring solutions against the `irontsurfaice. upon which-.it is desired to'form the highlyreflective deposit- Inv the various methods thusused in producing mirrors, however, -in-addition to forming: the mirror ,uponthef desired treated` surfaces, some scattered mirror-deposit VinA streaks v andspots is almost invariably formed upon the. other side' of the sheet fas the aqueous solutionsfoveiiii'ow onto, or creep around-tosuchother side. Asthis other side-becomesl the frontside of. theniirror Y Whenr ordinarily used asa-second surface.mirror,

such undesired deposit must be cleanedoffin condition.Y In vaddition to necessitatingthisf extra operation,- considerable additional-'mirror manufacturing cost is involvedvbecauseoLf/ yth'e difficulty of removing these unwanted and objectionable deposits without vscratching thev mirror deposit; or without at the same time, affecting or destroy.,- ing. to-some degree the desired and previously deposited mirror reiiective layerf which is` chemically similar. Thus,y many mirrors of original good and saleable quality have to` be scrapped due to the damage. done during such cleaning operai tions.

Attempts have been made to prevent the mirroringsolutions from forming deposits upon the orderYto-.place the mirror.into.usefu1.and}saleable ablev amount:y of labor I involved The use off' rub berdam's appliedto the edgesfof-the'sleet's hasi also Ibeen tried so as to'restrictltl'exliquidsftothe' side to'be coated but the-application of-'theseland l their subsequent removal yfromA the Wet and' slipfperyV- glass, or other sheets; presents hazard's Moreover, their use also preventsv the edges ofL the-glass; et cetera; from being*placedintoinitial satisfactoryv'clean condition;

One-of the objects ofi theV present invention`-n is' t'o'provide anew and'novelmeth'odfby whicl'ithe cliemicalfdeposition' of'fa mirror reiectivefcoa'ting or"I deposit" from" amirroring solution may be 're? strictedito onlyrtlo'sef surfaces' whchit is desired' to coat.

*Another* ob'je'ct off the present inventionis thel provision' or a nevvl and novelv method ofl mirroring orsilvering 'atglass; or' other sheets ofy piavlish'e'fnf'aterialv upon the back or't'opf sur;` facegb'y pouring a .chemically-i reacting` depositing solution upon such top surface and by .alsoy pre. treatiiigthe under surface of the' flat glass ori other* sheet1 so that' nomirror deposit forms thereon; f y

AIt isafurth'er object .of thisinvention topicvide-means-` for preventing the deposit of mirror! refic'tivematerials by-v means' oi" chemical deposi' t'in'whiizh can'be simply removed inwat'er after tlf'emirroring oper'a-t'ion-l'iasfbeen completed.

/In generali the present'inventi'on is-p'referably carriedoutlbyibringing the surfaces which are lnot to'b'e mirrored into' substantially completecontact Witi aniaciue'ous or Waterlcontainin'g giel of' an inorganic compound whichv actsasf" abarrier to the ciiernicallyy mirroring solutions and prevents depositionoccurring alt-such protected surfaces bylpreventing access o'f the solutions tothe saine. As such, it operates with anyf of' the chemical mirroring'- soltions Lwhen these are" applied to' fthe' s'nr'face'stb` be miifror-c'oated an'dfit\i"s=thus` applicablein the deposition'- ofiv silver;I platinum; copper; gold; or#leadsulphideimirrors` upon glass; or other supperts', while these arefsupportedupon talsilesy o'ry -convey`ersv or` While being mirroredby' 'sprayiiigl and While? supported in vertical'` or `subrst'antially vertical position. After the mirror by the application of a stream of water, or by light rubbing in water to expose the non-mirrored surfaces thus protected during the mirroring operation and to finish the mirror production directly into a saleable article.

I have found that various water-containing soft gels of metallic compounds may be utilized to secure the desired results of this invention and have employed as such many inorganic metallic compounds which may be formed into water- 10 containing gelatinous coatings, such as silicio acid, titanic acid, many metallic silicates, and numerous metallic hydroxides, certain metallic ferrocyanides, and a few of the metallic sulphides, phosphates, borates, and tungstates. In addition to the satisfactory materials being capable of giving gelatinous water-containing gels for coating use, they must also be water insoluble, as well as being insoluble in the alkaline mirroring solutions to be employed. Thus specifically among the many inorganic metallic compounds which form gels with water, such that they are useful asbarriers to the mirroring solutions, and which are not affected by the mirroring solutions, and which I have employed of the above classes, I list the following which are representative, although it will be apparent that there are many others of these types of oompounds equally useful: I may use gelatinous coatings of the metallic hydroxides, such as ferrous or ferric hydroxide, copper hydroxide, antimony hydroxide, nickel hydroxide, cobalt hydroxide, cadmium hydroxide, and bismuth hydroxide. The silicates of these same metals are equally useful such, for example, as copper silicate, iron silicate, etc., as are also copper ferrocyanide, zinc ferrocyanide, and iron ferrocyanide. Iron sulphide, copper sulphide and zinc sulphide, as well as iron or barium ortho phosphate, or cadmium, or barium pyrophosphate, may each serve my purposes as a barrier to mirroring solutions; and I may also use silver or copper borate, or iron, or copper tungstate. The various gelatinous compounds may be formed by the interaction of aqueous solutions of two different inorganic compounds selected to provide the necessary final elements, as will be more apparent from the examples below. Thus, to form a ferrocyanide, a soluble alkali ferrocyanide such as potassium ferrocyanide, may be reacted with a soluble metallic salt, such as copper acetate, to form upon contact of the two aqueous solutions, a metallic ferrocyanide water-containing gel or specically, such a gel of copper ferrocyanide. The solutions may be partly alcoholic and the concentrations of the reactants is not particularly critical provided they are of sufficient strength to form sufcient gel substance that the latter will have a soft body and be coherent.

The gelatinous coating preferably may be applied to or formed upon a face or faces of the support, for example, such as the glass, plastic, or polished metal employed in the forming or manufacture of mirrors, the face or faces which are so coated with the gelatinous coating, being those desired to be kept free of the mirror deposit. However, when working with the ordinary sheet type supports, the production of mirrors may also be carried out by impregnating and covering a cloth mirror table top blanket, or a cloth conveyor belt, with the water-containing gelatinous coating and then placing the face of the sheets, which are to remain unmirrored, directly in contact with these wet gelatinous coatings which immediately substantially contact the l thereon.

The foregoing and other objects and advantages of my invention, and various methods of applying the gelatinous coatings; or of forming such coat- VVings either upon the supports of glass, plastic, or

other materials to `be made into a mirror; or upon the cloths upon which these articles or sheets of materials are supported during mirror formation, will be apparent from the following description, appended claims and the accompanying drawings, wherein like reference characters designate corresponding parts in the several views.

In said drawings:

Fig. lis la vertical sectional View of a suitable cleaned support, such as glass, upon which a mirrowed or reflective surface may be formed in accordance with the present invention,

Fig. 2 is a transverse vertical sectional view through a suitable apparatus which may be employed for applying a solution of an inorganic material to one side of the support shown in Fig.

Fig. 3 is a View similar to Fig. 1 and showing the support of Fig. 1 after having been coated with a solution by the apparatus of Fig. 2.

Fig. 4 is a view similar to Fig. 2 showing the application to the previously coated support, of a second coating or film of a liquid solution which chemically interacts with the previously applied coating.

Fig. 5 is a view similar to Fig. 3 and showing the support after having been coated upon the one face by the apparatus of Figs. 2 and 4 successively with a coating or film of each of two liquid solutions which by chemical interaction have formed a Water-containing gelatinous coating of an inorganic compound upon the so treated support.

Fig. 6 is a vertical sectional View of the coated support of Fig. 5 and illustrating the step of ap- -plying a reflective coating to the previously uncoated face or surface of said support.

Fig. 7 is a transverse vertical sectional View, partly in elevation, showing one manner or mode of applying a reflective coating to the uncoated surface or face of a support, in which the opposite surface or face of the support is covered with a protective coating and rests atwise upon a table, conveyer, or other supporting medium.

Fig. 8 is a vertical sectional view of the support or article shown in Fig. 7, after the application of the reflective surface coating or mirror deposit to one face thereof.

Fig. 9 is a view similar to Fig, 8 showing the article after the removal of the protective coating or covering from the rst surface or face of the article; and

Fig. 10 is a vertical longitudinal section, partly in elevation, of suitable mechanism or apparatus for supporting and transporting articles to be mirror-surfaced or coated in accordance with the invention.

Before explaining in detail the present invention it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. It is to be understood also that the phraseology or terminology employed herein is for the purpose 75 of description -and not of limitation, and it is 'rlne'cessa'lfy to remove fllm I3.

.5. not intended to limit the invention herein'claimed beyond the requirements of 'the priorart.

Referring' now tothe drawings, wherein suitable apparatus vor equipment for performing or carrying out the method of the present invention is'shown, together with representative products resulting from practicing said method, a piece of suitable support material such, for example, as' glass, is 'shown as a wholeat Il in Fig. 1. in accordance with my invention, the support II is toY be provided, preferably, with a reflective or mirroredcoating on one face thereof and since it is undesirable to havek any of this coating material settle or lodge upon the opposite face of the support, said opposite face is preferably protected by somesuitable coating, film, or covering of a suitable material or solution which will notbe attacked'or penetrated by the re'ective or mirror coating material. seen in Fig. 2, a suitable roller R is disposed within an open top container or pot P containing a solution of an inorganic material, indicated at C. It will be understood that the roller R, as shown, Awhich dips into the solution C, has its peripheral surface coated or covered with .a layer or lfilm c of said solution which is transferred to the under face of the glass piece II as said piece is moved in the direction of the arrow A to produce a `coating layer l2 thereupon, see also Fig. 3.

After the layer orrelatively thin film I2 has been applied to one face of the support Il, the coated'support as seen in Fig. 3 is then moved over and 'into contact with the coated peripheral surface of a second and similar roller R and is provided with a second coating or film of a liquid solution'of a second substance which is picked up byroller R located in asimilar receptacle or pot P'. This coating or film c of the second substance C', by'chemic'al interaction with the first 'appliedfsubstance C, forms a gelatinous coating or covering for the support, as shown at is, Figs.

4 and 5. 1

' The product .thus far completed inaccordance with my present method, is shown in Fig. 5,

wherein II represents the support or support A material as a whole and which has been coated upon one of its faces with-a coating or film of each ofthe two liquid solutions C and C which, by chemical interaction, have combined to form a water-containing gelatinous coating of' anni organic compound upon the support, as seen at I3.

After the protective coating I3 has'been applied to one face or surface of the supp-ort II as eX- pl'ained above, or in anysuitable or convenient manner, the support is preferably vplaced in a vertical position with its uncoated face or surface Hav., see Fig. 6, disposed toward a mixing spray head or nozzle I4. The head is preferably sup'- plied through pipesy Maand Illb, with suitable mirror-forming solutions which combine and 4are discharged as one solution by the nozzle. The

nozzle sprays or deposits the fresh` reacting and 'combined mirror solutions upon the .clean face l Ilato form a` mirror or reflective surface coating or layer I5 thereupon. While the support II is shown in vertical or upright position, it is to be runderstood that it may -be disposed in other-suitable position, it being also understood that the position or location of the nozzle I4 would be changed Aor shifted accordingly. Moreover, it is 4'to be understood that to complete the product from the illustrated step of Fig.6, itis merely the temporary protective linV accordance .with a. 'somewhat modified method embodying the present invention, Vy a sup-,- port body, such as the glass piece or plate II, having .a protective coating or backing layer I3, as seen in Fig. 7, may be placed upon a plane surfacesuch asthc top I6 of a mirroring table, which top may have a suitable surface covering of .fabric I1. When in position as seen in Fig.V '7, the .top clean-face or surface of the support `ll which, of course, .has not been covered by the gelatirrous coating solution |or substance I3, may have applied to it a freshly mixed reacting chemical mirroring solution M to form a mirror face vor layer I8 upon said clean face or surface. The solution may be applied in any suitable inanner, the flask I9 shown in Fig. 7 being merely illustrative fof one manner or mode of supplying the refiective or mirror covering or coating I8 to the support. A

In., Fig. 8 thefsupport body II is shownfafter its .removal from the mirroring 4table I6, it being clear that none of the mirroring solution I8 penetrated the protective layer or covering I3.l

In Fig.y 9 the nal mirror product is shown, the pnotecti-veco-at-ingor covering: I3 having f been removed toreveala clean face or first surface.

If it is desired to produce mirrors or reflectors in accordance with my method on `a. high production basis, the method may be carried out 'by suitable apparatus which may include an endless belt or conveyer for moving uri-coated articles to a mirror-surface-applying station for producing upon theexposed faces or surfaces of thev supiports, mirrored surfaces,v while the `opposite faces f or surfaces of `the sullvpoirts are protected from being contaminated by the mirroring solution duringits application to said exposed faces. Y

One such suitable apparatus as referred .to in the preceding paragraph is shown, somewhat diafgrammatically, in Fig. 10. Inithis figure, suit,- able supporting framework, shown as a Whole a't 25J, carries a pair of rotatable drums 2| and 22, over which a fabric yconveyer belt 23 travels. The'framework also carries a plurality of sur porting rolls 24 Vdisposed beneath the upper course of the belt A23 to support the same. The belet is preferably providedwith a water-containingwet gelatinous coating I3, some of which impregnatges the belt, the .coating I3 of .the belt being adapted to be engaged by fthe under faces or surfaces ,of Ithe pieces`l I I; ofsupport material which may vbe vplaced upon .the conveyer belt yin the vicinity of thedrum 22. This gelatinous coating I3 is applied to :the lower cou-rse of the belt adjacent vthe drum22 in a well known manner, by means of two pairs of inkingrollers 2-6 and 21 -disposed in tanks or receptacles, 28 and 29, respectively. As the belt 23 travels 'in the direction of the arrows B shown inFig. '7, the successive pieces or plates. ofv glass .II `are carried beneath :the miX- ing spray heador'nozzle 30 to which .fresh react- ,ing lmirror-forming solutions are supplied through pipes 3I-and 32,. The nozzle sprays or deposits the combined mirror solution-s uponvthe clean upper faces yof Ythe pieces II Vto produ-fccv .a mirror or refiective surface coating or layer I5 upon each of them, successively. y

It may be desir-able ito clean the conveyer belt l23;.as it is traveling through its lower course asseen in Fig. 10. For this purpose, a water spray issuing from a nozzle 33 may be caused to impnge upon the r adjacent portions of the belt. As the-belt .travel-s .past the water spray station, it encounters va pairof squeeze 'rolls 34 which servetoaremove additional'. material and surplus `7 water from the fabric belt. The water and the coating solution flow out to a draining system, shown generally at 35. I

and coating upon the glass of the gelatinous ferrous hydroxide. This gel was quite wet and contained a large lamount of water but was sufficiently stiff -that it did not carry away when put .in contact with liquid, butrequired some force behind the liquid to d-o so, or required slight rubbing to remove from the glass. In order to make a th'icker layer of gel coa-ting upon the glass, it was repeatedly built up by further successive passages over the rollers supplying the ferrous chloride and the sodium hydroxide. When substantially all'of one side of the glass was thus coated with the gel by one or more passages over the rollers, the gel coated side was placed downwards upon a mirror table heated to about 98 F. and

a freshly mixed solution for forming a lead sulphide mirror was poured upon the upper clean surface. Any solution suitable for this purpose may be used but I mixed, as -disclosed in Colbert U. S. Patent No. 1,603,936 and just before pouring upon the glass, one part of a 4% lead acetate solution with four parts of a 2% thiourea solution. After mixing these well, I quickly stirred in one quant of a 6% solution of sodium hydroxide. The solution readily formed a lead sulphide mirror upon the desired upper face of the glass and the ferrous hydroxide gel upon the lower face was `insoluble in the mirror forming solution and prevented it from contacting the lower surface, thereby preventing any deposition of mirror upon such surface. After fifteen or more minutes timey had passed to permit the mirror deposition .to :become completed by reaction of the mirroring solutions, the surplus liquid was drained off the plate of glass by lifting the same and the ferrous hydroxide gelatinous coating was rremoved by rflushing the same off with a stream of water under pressure and also, if desirable, by lightly rubbing the wet surface with -a clot'h. The glass was further cleaned, drained, and dried and was then a finished mirror. i

Example 2 Vstrong Iammonia may serve as the alkali in forming .the ferrie hydroxide gel coatings. The gel coating while wet -and containing a large -amount of water, was of sufficient stiffness that it would not slide off the coated glass. The glass was placed `with Ithe coated side down upon a cold mirror table andV silvered upon the upper ex posed surface by pouring thereon the following solution: A solution of 1.25% silver nitrate was made up and to cc. of this there was added 3.7 cc. of concentrated ammonia hydroxide to clear the same, and .then suiiicient sodium hydroxide to make the latter equal to 1.0% of the mixture. With one part of this mixture there was mixed quickly, one part of a 5% invert sugar solution. The mixture thus produced was promptly poured upon the glass, Where it deposited a silver mirror coating but as the ferric hydroxide gelatinous coating was completely unaffected by these mirroring solutions, no silver deposition occurred on the gel-coated an-d protected face of the mirror. 'I'he'gel was then removed by ordinary washing and the glass, after drying, was a completed mirror entirely free of undesirable mirror spots or stains upon its face.

In a similar manner the ferrie hydroxide gelcoated glass piece may have been made into a gold mirror by the placing of the same upon the mirror table and the pouring upon the uncoated exposed surface of a gold mirroring solution, such as mixtures of alkaline gold chloride solution and formaldehyde solution, commonly used for gold mirror deposition. The alkaline formaldehyde solutions do not affect the gel coating and it amply protects the surface which is to be kept clear from any mirror deposition.

Example 3 A clear glass-like sheet of Columbia resin plastic such as manufactured by the Pittsburgh Plate Glass Company which is presumably a polymerized allyl methacrylate resin, was steeped for fifteen minutes in a 5% solution of sodium hydroxide, rinsed, carefully cleaned upon one side, treated in a dilute solution of stannous chloride upon the same side, and then rinsed. The other side was then coated with a copper hydroxide water-containing soft gel by passing the latter face over a felt covered roller which applied to the resin a thin film of copper acetate solution of 10%, 20%, or stronger strength. The treated face was then passed over a similar roller which supplied sodium hydroxide solution or potassium hydroxide solution of 5% or greater strength. The strength of the solution is relatively immaterial. Each could be and was adjusted so as to produce upon the surface treated, a gelatinous coating of sufficient stiffness, or body, that it did not slide off of the treated surface and substantially covered the entire surface treated.

The plastic sheet was then placed upon a mirror table and a silver mirror was deposited upon the exposed surface by the application of the silvering solution described in Example 2, above. The copper hydroxide gel was Washed off after the silvering operation to give a plastic silver mirror free of mirror deposit upon its face.

In the manner set forth in the three examples above, other metallic hydroxides may be formed by reaction of metallic salts which are water soluble with `the alkaline Water-soluble hydroxides, sodium hydroxide, potassium hydroxide, ammonium hydroxide, or lithium hydroxide. Mirroring solutions for chemical deposition of silver, platinum, gold, copper, and lead sulphide, which comprise the materials which may be deposited from water solutions as mirror deposits, are all 'alkaline solutions and may contain in the various formulae known in the mirror art, either sodium hydroxide or equivalent potassium hydroxide, or may contain one of these in combination with ammonium hydroxide. The latter'i's ,generally present .in .small quant-ity and, .proivided va metallic hydroxide pgel is `chosen .and which lis finsoluble in excesssodium or potassium .hydroxides .rand ywhich Amay .be formed vinto -a .gelatinous coating, .the :choice of .metallic Hhy- .droxides -.Which..are .useful in .the .forming of .mirn rors Eby .the ,methods embodying the .present-fin- Vention, is ,broad,.and many .materials of this Qtype .can be .used .quite satisfactorily.. .In .the .last example, itrstobe pointed outthat the .cop ,per hydroxide gelatinousV coatingemployed, while solubleiin. strong ammonia, .was ,unafectedrby the .small amount .of vammonia present inanlordi- Anary. .silvering solution. `rAluminum .hydroxide .andizinc hydroxide, .which igive .Water-insoluble gelsl are not useful, however, because these rsels dissolve readily in the caustic alkaliesipresent in 1 .themirroring solutions. .While .calcium hydrox- ...ide is relatively .insolublein .Water 'andin the mirroringsolutionsit doesnot Vgive gelatinous precipitates or coatings. and .itis not .useful as .a protective barrier againstdeposition of the :mir- ,.ror, deposits. I may .use gelatinouscoatings .of the metallic hydroxidesofv bismuth, cadmium,

cobalt, nickel, antmony, copper, iron andothers .Whichareinsolublein excessof the strong alkalies, andinsoluble .in the mirroringsolutions.

` vIn asimilar manner I have found that the .metallic silicates of .the same metals are inf soluble inthemirroring:solutions and thatthey .readily give Water-containing. gelatinous coatings which act as effective barriersto such solutions kand thatvthey maybe. employed as coatings `to .protect surfaces ofglass, =or .other support articles, during the. mirroring of other surfaces.

Example A4 The fabriczbelt ioffa continuousmonveyer used in the production of mirrors in an apparatus-or machine oflthe type representedinFigure I of the accompanying "drawings,.-was l:impregnated as shownl inthat figure, .-by v passingzthe :belt 'over lan inking rollerf'of a .pair .supplied Withsa.f10% `or stronger. solution of rLany-rof the availablecom- 'mercial grades 'of the :alkali 'so'diumuor zpotas `sium vsilicate 'solutions in water :fand thenfrrun over a second roller of another pair which-icar- :riedia 1.10%cor'stronger.fsolution of .fferrous .chlo- "ridezwl'iich, by 'reaction 'with .the-soluble silicate, gave a heavy Wet gelatinous coating on lean'drimpregnation :of 1 thefabric tbelt, :of ferrous silicate. FAS-fthe beltipassed.'axoundazthetdrum :at thei'head of the conveyer (at the right side of Fig.)1a f .cleaned:pieceofrglass Waslaidv uponithe-conveyer @directly .upon fthe Isoft. fgelatinous :coating upon the fabric and the latter wet coating cimmedi- .fatelyrcontacted =the -afacel Lof :the glass -f and sealed it rat 'the edgesfsoy that'avhenfthea subsequent mir- .roringfsolution-V fori forming :afzrnirror' was z. applied Ftozthe top offthegglassras'it'traveledalong'with rthe :conveyer n belt, fitrA did .notrun iunder the .i glass :and did notcontact, lin any-Way, the .low.erfsur .face iof :the glass, the mirror deposition :being :re- `4:stricted `to :the Adesired 'topf surface only VWhen. aleadsulphide. mirror wasltobe formedfthe same solutions :as were @employed iin-,Example fNo. 1 were employed, the4 glasskbeing preferably; slightl1y heated 'as -itpassedfalong .the'conveyerprior to Vthe {applicati-on [of the -mirroring fsolution. -Whenfa lsilver -solution, #such as thatgi-ven in EX- ample :No .v2 -Was employed, za silver :mirror twas so gproduced. At :the end .of :theconveyenf'the :mirrored glasses were removed Iand fby ay simple yrwashing, f any ,adhering particles of gelatinous l .coating were readily f removed and carter ',dlyng,

v by passing .the'surface of 10 .themirronwasccomplete. 1 Agfa. further example pff-,suitable siliceous .compounds .in addition .to the metallic silicates, .f I .may usesilicate acid, .as

shownin .the nextjexample.

fEwample ."5

. Inv asimilarcontinuous conveyer mirroring `ap- .paratus'or machine,..the rst pair ofinkingroll- .erswasied .witlran alkali..silicate solution asbe- "fore, butthesecond .pair ,ofrollers Was rotated inav bath.of,.and,thus,fed with a solution.of'5%, or stronger, vofan acid, such as hydrochloric aci'd, sulphuric acid, or .sodium bisulphate which, by reaction with the silicate solution, formed a coating upon and an impregnation of the fabric, of a Wet water-containing :gel o'f silicio acid. Such .gel .does .not (readily go-intofsolution lagain in the alkali '.solutions fused in mirroring, such las `Vthe leadv sulphide .mirror forming solutions and .thesilvering solutions givenlin theabove examples. .Moreovenitis also .resistantto solutonacytion Iby :mirroring solutions f containing .tartrates (.asere .used in -somesilvering ,formulae .andto .thezphenylhydrazine or formaldehyde appearing in the alkaline solutions for the forming ofscopsperi. mirrors. .After .the application of. anyr of these .mirroring solutions -upon glass .laid inthe-.gel

`.coating upon the -fabric belt. fand the .formation of a .mirror deposit .upon .the Iunprotected f side, the glass .was removed .fromitheend. of lthe conveyer -.(at .the leftside-.of Fig. v10) rand `theattachedy gel.l readily washed. off .with Water. .Thus, .the faces` of the second .surface fmirrors;..so pro- .duced 'werel found to -be .clean .and entirely )free o'fthe g mirror. deposit.

Example 6 iA g-elatinous `protective, coating of precipitated f titanic-acidi presents thesameuseful advantages "found Withsilicic aci'd coatings. A'cleaned piece of glass "was v'coated upon one 'side with such la AWater-,containing wet vgel coating of titanic f acid, Lthe glass which it 4was .desireditoz keep izlear,` over aroller suppliedwith astrong solution of titanium vsulphate andthen ,over a l second roller carrying .sodium 'hydroxide solution. .Upon subsequently applying a mirroring solutionto 'the uncoate'd surface, "suchLas'by holdingtheglassjin a vertical rack and spraying asilvering solution, such as that ,giVeninJEXarnple"No.2, or other silvering. solution, suchas those .knownjin 'the art .employing phenyl-hydraaine, .onto v,the .uncoated surface, .it was found that although v.considerable of the mirroring solution .splashed directly upon the back of the glassfthe gelatinous `coating completely protected the glass .from receiving-any ,mirror deposit upon' such'v surv face.' .Upon ,thesubsequent removal of' the kgelat- .inouscoatingby astream oi Water underfpressure,.the mirror .coating Wasfound to be .entirely .restricted .to .thedesired `back surface and the .faceefgthe .second surface mirror 'so produced rwas'freeoflthemirror deposit.l Example /7 .Where We v"areforming a lead sulphidemirror We may use a protective"Water-containinggelatinous coating .of a metallic'sulphide"which is'insoluble .inthellead sulphide mirroring "solution, "Ihus, the jglass or lother article tobe mirrored, `1'70 was first cleanedjand-then passed over afelt'roller dipping'in a 10% solution of sodium sulphide and then passed over a second such rollercarrying a 15% solutionfoicopper nitrate or of 15%, -or stronger-solution of ferrousammonium sul- ,-.phat-e, .sox that there wasfformed .upon tneisuriace so treated, a soft gelatinous coating of copper sulphide, or of ferrous sulde, respectively. A glass having one surface thus coated was placed upon a warm mirroring table with the gel-coated side down against the table. The mirroring solution as employed in Example 1 was then poured upon the exposed surface and a lead sulphide mirror formed thereon. The plate was then removed from the table and the soft gel washed off in water by light rubbing With a cloth and the entire washed plate was then dried to give a mirror free of any lead sulphide deposit upon the face opposite to that carrying the mirror coatlng.

vExample 8 Six pieces of glass were carefully cleaned and then one set of three pieces was scrubbed with a very dilute solution of stannous chloride upon one face, and subsequently rinsed well. These three pieces of glass were then passed over a roller having a felt covering which dipped into a solution of potassium or sodium ferrocyanide, the surface brought into contact with the roller being, in each case, the non-tinned surface. The same surface was then passed over a similar set of rollers to form a metallic ferrocyanide gelatinous water-containing coating thereon. The rst piece was passed over a roller fed with a 10% solution of'copper chloride and had formed thereon a. copper ferrocyanide gelatinous coating. The second piece was passed over a roller fed with 10% zinc sulphate and the latterreacted with the soluble ferrocyanide film: to form a gelatinous coating upon the glass, of zinc ferrocyanide. The third piece was passed over a roller carrying a 10% solution of ferric chloride to form ferrie ferrocyanide thereon. The second set of three glasses which were not tinned were each, respectively, coated With copper, zinc, or ferrie ferrocyanide in the same manner.

Upon the tinned surface of the glass plate carrying a coating upon its other side of copper ferrocyanide, there was poured a freshly mixed silvering solution employing sugar as the reducing agent, such as that employed in Example No. 2 and a silver mirror deposit was thus formed. In similar manner, a silvering `solution employing sodium potassium tartrate as the reducing agent and alkali, such as any of the well known Rochelle salt silvering formulae, was poured upon the tinned surface of the glass protected upon its other side by a zinc ferrocyanide gelatinous coating. Upon the thirdv glass, carrying a protective coating of ferric-ferrocyanide upon one side, there" was poured on the clean tinned side, a silvering l solution employing an alkaline solution of formaldehyde as the reducing agent and a silver mirror deposit was formed. Upon the other three nontinned glasses, there was poured upon the clean non-coated side of each, a lead sulphide mirrordepositing solution, such as that employed in Example No. 1, to form a lead sulphide mirror, while in each case the other side was protected by a gelatinous coating of metallic ferrocyanide, respectively, copper, zinc, and ferrie ferrocyanides with the three glasses.

In each `case the ferrocyanide coatings were then removed after the mirror deposition was complete and in every case, there was no mirror deposit found upon the face of the six mirrors produced,

Example 9 of a solution of ferricl chloride. Then a So-J lution of 20% sodium tungstate was brought into contact with the film to react with the same and to deposit upon the glass in substantially complete conta'ct therewith, a gelatinous coating of iron tungstate which is insoluble and which, aS a coating, 'was quite wet and obviously carried a lot of water Within the gel. The other side Was then subjected to a freshly mixed lead sulphide mirroring solution and a lead sulphide mirror deposit formed thereon. Despite the mirroring solution having run overthe sides of the glass and thus around to the face protected by the gelatinous coating, there was no mirror coating found upon the thus protected face after the glass was washed in Water to remove the gelatinous coating.

We claim:

1. The method of making mirrors by chemical deposition of an alkaline mirroring solution upon one surface of a sheet-like support, which comprises substantially completely contacting one surface of the support with a water-wet gelatinous coating so as to protect sai-d surface from contact with said alkaline mirroring solution to be applied to the other surface of the support, said gelatinous coating consisting of gelatinous Water-insoluble inorganic metallic compound material and a sufficient amount of water to form a stiff non-flowable gel that closely adheresv to said surface, said coating being insoluble in said alkaline mirroring solution and being suiiciently stili to prevent displacement by any of such so" lution which might reach it after being applied to said other support surface, and then applying to said other support surface, while the gelatinous coating is still on said rst support surface and is still Wet, said alkaline mirroring solution and depositing a mirror deposit upon such other surface.

2. A method according to claim 1 wherein the gelatinous coating is removed after completion of the mirroring deposit by means of an aqueous treatment With gel displacing pressure which exposes the non-mirrored surface of said support.

3. A method according to claim 2 wherein the coating is gelatinous Water-insoluble metallic hydroxide.

4. Amethod according toclaim 3 wherein the coating is gelatinous Water-insoluble iron hydroxide.

5. A method according to claim 2 wherein the coating is gelatinous water-insoluble metallic sulphide.

6. A method according to claim 2 wherein the coating is gelatinous Water-insoluble metallic ferrocy-anide.

7. A method according to claim 3 wherein the coating of gelatinous water-insoluble metallic hydroxide is produced by reacting in place on said surface of the support to be protected an aqueous solution of Water-soluble alkali hydroxide and an aqueous solution of metallic salt that will react with the said alkali solution to form a Water-insoluble metallic hydroxide water-containing gel.

8. A method according to claim 5 wherein the coating of gelatinous Water-insoluble metallic sulphide is produced by reacting in place on said surface of the support to be protected an aqueous solution of Water-soluble alkali sulphide and an aqueous solution of metallic salt that will react with the said alkali solution to form a Water-insoluble metallic sulphide Water-containing gel.

9. A method according to claim 6 wherein the coating of gelatinous water-insoluble metallic ferrocyanide is produced by reacting in place on 2,445,253 13 said surface of the support to be protected an REFERENCES CITED aqueous solution of water-soluble alkali ferrocyanide and an aqueous solution of metallic salt that lhf lgvgarferens are of record m the will react With the said alkali solution to form a water-insoluble metallic ferrocyanide water-con- 5 UNITED STATES PATENTS taining gel. Number Name Date FRANK H- VERHOEK- 1,042,827 Schumacher oct, 29, 1912 WILLARD L MORGAN 2,317,877 Bauintine Apr. 27, 1943 Certificate of 'Correction Patent No. 2,445,253. July 13, 1948.

FRANK H. VERHOEK ET AL.

It is hereby certified that errors appear lvin the printed specification of the above numbered patent requiring correction as follows: Column 7, line 39, Example l, for the Word quart read part; column 8, line 48,Example 3, for solution read solutions; column 10, line 3, Example 4, for silcateacid read silicio acid; and that the said Letters Patent should be read with these correctionstherein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 12th day of October, A. D. 1948.

THOMAS F. MURPHY,

Assistant Gommzssoner of Patents.

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