US2433632A - Fibrous sheet material for the electrolytic formation of azo dye image records thereon - Google Patents

Description

Patented Dec. 30, 1947 FrcRous. SHEET MATERIAL For: THE utnorao yrrq EQRMATION 'on-Azo DYE IMAGE asoonns THEREON Myer "Solomon, deceased, late of Westinon't, N. 1.,

by Nellie" W. Solomon, administratrii r, Princeton, N. 3., assignor to Radio Corporation of America, a corporationpf Delaware N0 Drawing. Application December 23, 1942,

Serial'No. 469,961

This invention relates to the electrolytic production of azo dyes by electrolytic co'upling'and more particularly to an article'of manufacture carrying the dye-forming constituents? In a preferred adaptation it includes such an article for the production thereon of azo dyes by electrolytic coupling in connection with the art of facsimile recording. The fundamentals of the present disclosure are set forth in the copending application, Serial No. 178,743, now U. S; P. 2,306,471, included herein by refercnce, of which earlier application the present application is a continuation-in part. H

The present invention may be generally stated to embrace features pertaining to theelectrolytic coupling of a diazonium compound with the production of an azo dye. In a desirable emb diment 'inv'olvi'ng'the application of the invention, the dye is produced in situ on a supporting material adapted to receive the same. Where'th e current which actuates the electrolytic coupling is dependent upon electric impulses from a trans-' mitting source, such as a scanning station for the transmission of printedmatter, a picture,

'etc., the electrolytic coupling and dye formation serve in the capacity of a facsimile recorder to form images or reproductions determinedFl: y tl 1e characteristics of the transmitted electrical pulses from the scanning station. The 0110, I g description is primarily directed to this sphere of the invention described in the aforesaid copending application, Serial No. 178,743.

It is an object of the invention to overcomejthe difficulties and limitations of the prior art procedures noted hereinabove. I

It is another object of the present invention to obtain azo dyes by the effect of an electric'current on mixtures or solutions containing a (hammum compound and a coupling compound.

An additional object of the invention, is to produce azo dyes by treatment of mixtures or solu tions of reagents adapted to form a diazonium compound and electrolytically coupling this compound with a coupling reagent.

It is a further object to provide mixtures or solutions containing a diazonium compound and a'coupling compound which are adapted to electrolytically react 'for the purpose of producing azo dyes.

.Still another object is a supporting material 4 illaims. (01. 204-2) or carrier impregnatedwith a diazoniun compound and a'coupling'compound under conditions which will preclud'e"coupl ing and-azo dye formation until the influences engendered by an electric current actuates such coupling and azo dye rmation. j J m'pd t nt o t of th "m 99 5 to "9btain" articles of manufacture adapted for racs'ifnile recording in'the'lformof a carrier or supporting material treated with a diazonium conipound and a coupling compound iunder conditions whichflw'ill preclude azo uye formatio11?until collpling "ls actuated electrolytically byfelectri impulses f rn'a'transmit'ting s'ourc'e whichco'rrespond the visual characteristics" of the object atthe transmitting source.

Other objects, fea-turesand advantages :of the mvenuanwm e apparent from the follbw'i ng consideration and de cription thereof. v

the "present invention, wherein facsimile recording is ccrit'emplatedit is proposed to produce the picture or printed matter on the recording surface in the form of an azo dye,thea'mount of such dye deposited beinga jf-unctionpf the amount of current caused to flow through the recording'surfaoe, whichis conveniently apaper sheet .orweb; W en the image is formed in the nature of an azo dye electrolytically produced, t es u .Q m ri ter a is ma ntain constant and the amount of current which is passed through increments of the paper varies and dark port ns in accordance with the light present he the object, thelikenes's of which being reproduced, such as a picture'or' printed matter, Joy" scanning at the facsimile transm itter. Whenthe'd'yes are thus or'med' lefctrolytically, Varying halftone shadesa'r'e obtained as aresult of the variation in the amount or: current causedto flow through th'e recording aper.

' The principle-ofioperation o fthe present inventionresides broadlyin the fact that a diazonium compound and a coupling compound which is adapted to react in alkaline, neutral or mildly acid solution, may be combined 'to'form an azo dye when subjected to electrolytic treatment. Thus, electrolytic coupling of diazoniurn dorm pounds may be attained when a mixture 'Lof couplingrea'gent and 'di'azonium compound reacts in an'alkaline solution to form an azo-dye, the coupling component'b'eing of the type which will couple in an alkaline medium; under these conditions, the dye is produced at the alkaline or negative electrode, usually designated as the cathode. Similarly, where the coupling compound is of the type which reacts with the diazonium compound in an acid medium, coupling will take place under appropriate conditions. The distinction between alkaline reacting coupling reagents and acid reacting coupling reagents is considered in some detail hereinbelow.

Applying this principle and theory to the present invention, where the diazonium compound and the coupling component are maintained in an acid medium, and the coupling compound is of the type which will react in alkaline medium, formation of azo dye is effectively prevented until such timeas the solution is subjected to an electric current. Under the latter conditions, alkalinity is established at the oathode, thereby forming a zone of coupling reaction which is substantially instantaneous in character. Difierently stated, the electrolytic coupling,

in accordance with the present invention, is

predicated on the conditions of control for retaining the diazonium compound and the coupling compound in a medium which will preclude their interaction until such time as a current is passed through the electrolytic cell wherein coupling is contemplated. This control depends upon the fact that the diazonium compound and the coupling agent which functions in alkaline medium will not react in an acid medium, but will couple in an alkaline zone, even though such zone may be comparatively limited in its scope, and, in fact, occurs in the immediate vicinity of the cathode.

For facsimile recording, the recording surface may be rendered wet by a mildly acid solution containing diazonium and alkaline reacting coupling compounds, and is then passed through the facsimile receiving or recording apparatus in such a manner that electric current causes dye formation on the receiving surface corresponding to the transmitted picture or printed matter, as a result of electrical impulses received from the facsimile transmitting device at which point the picture or printed matter is positioned.

A solution is prepared containing essentially the following ingredients:

I. A neutral electrolyte, such as sodium or potassium chloride or sulphate. This serves to facilitate the flow of electric current through the paper.

II. A diazonium salt, desirably one sensitive to light.

III. A coupling compound, desirably of the aromatic hydroxy type, coupling essentially under alkaline conditions.

IV. A small amount of an acid, to maintain the acidity of the solution and thus prevent premature coupling.

V. Water or other solvent in which the electrolyte ionizes.

In addition to the ingredients above indicated, the solution may also contain perfecting ingredients pursuant to the particular function to be attained or characteristic to be provided. Among such perfecting ingredients may be listed: (1) coupling inhibitors, as semicarbazide or hydroxylamine, which aids acidity in preventing premature coupling, (2) reducing agents, as sulphites, hydrosulphites, thiosulphates, hydroquinone, glucose, tartrates, oxalates, stannous chloride, etc., which preventthe gradual darkening of the background, (3) salts of copper, iron, chromium, aluminum or other metals, which act as mordants or otherwise affect the color of the dyes or the light sensitivity of the diazonium salt, or (4) reagents adapted to efiect background permanence, color intensity, and threshold value.

For simplifying the consideration of the invention, the discussion will primarily be directed to the case where the coupling compound is of the character which reacts in an alkaline medium, especially since such coupling compounds have manifested generally improved results over that attainable in the case of operating under conditions where an acid reacting coupler may be utilized. Briefly indicated, the reaction involves the azo e formation at the negative or alkaline electrode; i. e., the cathode, the electric current creating an alkaline condition which persists long enough for the diazonium and the coupling compound or compounds to combine with each other.

Thus, if the invention is used in facsimile recording, once having electrolytically coupled the diazonium salt by electric impulses emanating from a transmitting source at which an object or picture is subjected to scanning, and thereby obtaining a facsimile on the recording sheet corresponding with the object or picture, in the form of an azo dye, the unreacted diazonium salt may then be removed from the recording sheet by decomposing said salt through the action of light or heat. Alternatively, washing may be resorted to for accomplishing the removal of unreacted reagents.

The following is a generalized example of the ingredients which may be utilized to form a solution whereby a dye may be produced by electrolytic coupling. It will be noted that this example embraces within its scope and contemplation the use of caustic soda; this reagent is applicable only under extenuating circumstances which will be explained in further detail hereunder.

Gram-Molecular Ingredients Weight L sad Amount Used (I) A mine-source of Dia- .033 Varies with moleczoulum Salt. ular weight of amine.

(II) Hydrochloric acid: .08 cc.

Normal solution (or equivalent amount of other acidsl.

(III) Sodium Nitrite .03 2.07 grams.

(IV) Coupling compound; .010 to 0.15. Varies with molechydroxy aromatic comular weight or pound compound.

(V) Sodium Ch10lld8. 1.0 58,47 grams.

(VI) Ice and water to total volume of 1000 cc.

(VII) Sodium Hydroxide: 05 to .l 50 to cc. Used Normal solution NaOH. only in special cases.

(VIII) Auxiliary Chem- Varying amountsicals such as reducing agents.

A desirable illustrative procedure of mixing the ingredients is as follows:

The source of diazonium ion, desirably a primary amine (I), may be dissolved in the acid with boiling and addition of small amounts of water as necessary. The resulting amine hydrochloride solution is then desirably cooled to approximately 0 to 8 C., preferably by adding ice. The ionizable nitrite (Ill), such as sodium nitrite, is dissolved in 25 to 55 cc. of water and slowly poured into the cooled solution while constantly agitating. Generally, one or more color errata changes take place, accompan d by a slight ef-i fervescence, due to nitrogen gas formation". This efreive'sfcence represents a loss of diazo'r'iiun'i co'rilp'b'und, and it is this tendency which enders it desirable to maintain the reaction in the cold, through ice utilizatic'n. on the other hand, in some instances essentially no gas appears even at ordinary room temperatures i. e'., 0. c. The "coupling compound (IV) and the e ecg trolyte (V) are dissolved in Water either together. or separately, and added to the I mixture. oi amine, acid and nitrite, above indicated, after that mixture has been permitted to stand for a period of at least fifteen minutes.

'Ihe caustic soda (VII) is used only where the amine (I) is an amino-sulphonic or aminoc arboxylic acid insoluble in the acid (II). Under such circumstances, the amine is dissolved in the alkaline solution (VII), and the acid requirements must then be increased by an amount equivalent to the alkaline rea ent utilized and toprovide the desired acidity. The basic amine solution is slowly poured into a mixture containin acid, nitrite, as well as the cooling ex p edient exemplifiedby' ice'. Auxiliary chemicals, if used, are desirably added with the coupling compound (IV). I

If an amine hydrochloride, or a poly-amino compound is used as ingredient (I), the amount of hydrochloricor other acid is changed accord ingly, so that when I, II and III are finally mixed diair'iii ie', a substantial number of amino sulphdnic acids of benzene, naphthalene or dig; phenyl compounds, and some naphthol sulphonic' acids. Asa general matter, the presence of sfulf phonate groupshas-function-ed quite favorablyin the production of azo dyes, and this type of compound has been especially efiective in connection with the facsimile recording sheet upon which the azo dye is to be produced in accordance with any predetermined recordation. It will be apparent that the amines may be of the mono-amino, benzene, poly-amino benzene, amino-naphthalene, and amino poly-phenyl types of compounds.

It should be noted that among the most de-' sirable diazonium sources are the para diamin'o benzenes, since their diazonium salts are quite sensitive to light, provide comparatively dark colors, and have substantially no tendency to' couple in mild acid solution. Alkyl groups on one of the amino nitro'gens serve to improve the depth of color, while acid (acetyl or oxalyl) groups may in some instances Weaken the shade and even reveal some tendency toward premature coupling in acid solution. I

Following are presented a number ofamino compounds which have quite effectively func tioned as sources of diazonium compounds,- the latter effectively reacting electrolytically with a coupling compound adapted to form azo dyes therewith in alkaline medium:

Name of Amino Color and background after. ekposureato light when usedwith phlo ogluclnol as a coupling Common Name Structural Name or Formula compound Metaphenylenediamina- 1,3-diaminob erizenci Brown-yellow onwhite. 2-amrno-5-dlethylammotoluene 1-methyl-2-amino-5-diethylaminobenzene Darlfibrown-purple on very pale p e ow. Paraaminodiethylaniline 4-amino-1-(liethylaminobenzene y Do. Paraammodunethylanilina 4-amino l-dimethylami obcnzene Do. M 2,5-d am noanlsolc 2,fi-diamino-l-mcthoxybenzene Dark brown on pale tan. 2,5-diem noanlsolc dihydrochl Do. W U Paraphenylcnediamine 1,4-diaminobenzene Orange-brown, on white. i-am nod phenylam ne l-phenylamino l-amlno bcnz'ene. Purple on White. 4 -ammod1phenylam1ne mon Deep purple on white. 3 mcthyl-4-amlnodiethylamlm 3-methyl 4-amino-l-diethyl-aminobenzene Darlir1 brown-purple on very pale V ye ow. Chicago or 28 acid l-am1no-2,4-d1s111pho-B-hydroriynhphthalene Purple on orange. Paraam noacetaml1d 4-amino-l-acetylaminobenzenc Orange on pale yellow. garaammorgethylacctamhd 4-amino-l-methylacetylaminobenzene;

amma acl i-l' -dieminodiphenyhnethane 4-arnino-benzylcthylanilineL there are .05 gram equivalent weights of acid for the .03 of sodium nitrite, in addition to the acid required to neutralize all of the amino groups 2-amino-8-naphthol-6-sulphonic acid N-oxalyl-1,4 diaminobenzene; l-phenylamino-4 aminobenzen 1-ammo-2-naphthol-4-sulphohic acid.

o. Orange-brown on orange.

- Dark orange on light orange.

, c21 1; Purple on white.

I Orange on pale orange.

nic acid..-" Red on pink. v

Deep purple on pale straw-yellow. Background white when washed.

7 The quantity of coupling compound which may be used in the above generalized example will vary with the coupling strength. Usually darker colors are produced by using more than one gram-molecular equivalent of diazonium salt per gram-molecular equivalent of coupling compound, due probably to partial formation of dyes having two or three molecules of diazonium salt coupled to one molecule of the coupling compound. As previously stated, they are preferably of the type which will couple in alkaline medium, and should be soluble in mildly acid solution. In addition, they are preferably subject to the same oxidation resisting properties as indicated above in connection with the amines. Aromatic compounds with hydroxy, amino or active methylene groups ortho or para to unsubstituted positions in the ring will usually couple. Sulphonic groups have a desirable eifect along the lines suggested of the amines. Generally, favorable results have been obtained in the use of resorcinol, phloroglucinol, the naphthols and their sulphonic acids, 8-hydroxy quinoline, and some amino naphthol sulphonic acids. Taken as a whole, meta polyhydroxy benzene derivatives have reacted favorably as coupling compounds. Of the naphthalenes, Chicago acid has given optimum results, although its amino group may tend to increase the darkening of the background.

Particularly notable is the fact that some amino naphthol sulphonic acids, such as gamma, H, J, S and 2S acids, may either diazotize or couple. Good results are therefore obtainable using the same compound for forming both the diazonium compound and coupling. Where amino naphthol sulphonic acids are utilized in connection with facsimile recordings, the carrier sheet should desirably be subjected to washing after electrolytic recordation in order to stabilize the sheet background by obviating any tendency toward darkening during an interval of storage.

Following are a number of couplers which have functioned quite effectively in connection with a diazonium salt present in an acid medium, when the coupling has been actuated by electrolytic means: r

coupling compounds are added. This may be accomplished with facility by using a 10% excess of amine or by adding a small amount of urea to the amine-nitrite mixture before the remaining ingredients are supplied.

As above indicated, ordinary table salt may be relied upon for efiective functioning as the electrolyt of the composition. It is not essential to accurately weigh the content of the electrolyte, since substantially any amount between 40 and 120 grams per liter provides practically identical recordings in most cases. In lieu of NaCl, and merely by way of illustration, other strong neutral electrolytes are NaBr, KBr, KCl, LiCl, BaClz, CaClz, MgCl2, K2504, NazSOe, MgSOi, etc. Some dye intermediates may manifest greater solubility in potassium chloride solutions than in sodium chloride solutions; under such circumstances, the substitution is desirable. From the standpoint of preparation of sheets for facsimile recording, lithium chloride has been found to retard the paper drying time, but an equivalent and probably more eifectiv result is obtained by the use of wetting agents. An additional electrolyte which has provided excellent recordings, while at the same time obviating the corrosive eflect of nascent chlorine, has been found to be sodium sulphamate, NaOSOzNI-Iz.

While sodium hydroxide is illustrative of a desirable embodiment of reagent for providing the desired alkaline solution in the exceptional cases above mentioned, other well known alkaline substances may be resorted to in lieu thereof, such as potassium hydroxide.

A number of auxiliary chemicals are available for the purpose of controlling such elements as background permanence, color intensity, color characteristics, threshold value, etc. In addition, these reagents may function to preserve the time during which the reagent solutions utilized will maintain their effectiveness. Coupling inhibitors, such as semi-carbazide or hydroxyl amine, combine with the coupling compound in acid solution and thus prevent or retard premature coupling, and liberate free coupling compound upon alkalinization. Reducing agents Coupling compounds Common Name Structural Name or Formula Remarks llghlorogluizinol l,g,f(sitfiilgdroiybenzene Quite desirable results.

esorcmo 1 y Oxy enzene i Orcinol 1 methyw5 dihydmxybenzene }Excellent, but give lighter colors than phloroglucmol. Pyrogallol 1,2,3-trihydroxybenzene Darker c l r and n t quite as eifective as phloroglucinol with V respect to definition and background. Chicago or 28 acid 1amino-8e:aphtho1-2,4-disulpl1onic acid Usually gives blue recordings. Excellent when used with Salicylic acid Beta Resorcylic acid l-8-dihydroxynaphthalene-3,(i-disulphonic acid. l-S-diliydroxynaphthaleneA-sulphonic acid. l-amino-S-naphthol-3,fi-disulphonic acid B-hydroxyquinoline 2-hydroxybenzoic acid 2,4-dihydroxybenzoio acid phloroglucinol. Similar to Chicago Acid, with somewhat weaker colors.

Good colors, but background not quite as satisfactory as with phloroglucinol or rcsorcinol, possibly due to premature coupling.

Generally Weak colors.

Better than salicylic acid, but weaker than resorcinol.

such as sulphites, hydrosulphites, thiosulphates,

, glucose, tartrates, oxalates, formates, stannous chloride, etc., retard air oxidation, thereby aiding in preserving the background permanence of recordings which have been fixed by exposure to strong light. Salts of copper, iron, chromium, aluminum, and other metals frequently serve as mordants or otherwise effect the color and fastness of the dyes, or the sensitivity to light of the diazonium salts.

While water is a most desirable vehicle for the electrolytic reaction, the invention is not restricted to the use of the same. Thus, various "non-aqueous solvents which permit :electrolytes to ionize may be substituted for all or a part of the water. The alcohols serve to enable the use of the contemplated compositions at below freezing temperatures. In addition, they serve to retard the drying of recording sheets. A desirable alcohol is illustrated by normal propyl alcohol. Similarly, the solution may be a mixture of propyl with ethylene glycol. However, vehicles which boil at comparatively low temperatures may manifest some undesirable characteristics such as rendering a recording comparatively limp and moist.

ness is obtainable, and the background maintain its improved characteristic for a substantial interval of time. The amount of water utilized during the course of the successive steps is not of critical significance, and within the skill of one working in the field; the element which is of significance is that the total volume will satisfy predetermined amounts.

The tartaric acid in the above example functions in a dual capacity, since it provides the necessary acid as well as serving as a reducing agent tending to preserve the background color.

As a simplifying expedient in the handling and storage of the reagents used, they may be sub- The following example indicates the use of jected to premixing or packaging in the form of definite reagents in the preparation of the dry powders which the ultimate user will merely diazonium compound as well as the coupling comdissolve in water or any other satisfactory vehicle ponent used to react therewith electrolytically; at the time that the formation of the diazonium in addition, a desirable procedure applicable to salt and electrolytic treatment "'s to be performed. this .exampleis presented: For this purpose, solid acids are available, as

Example Grams No Ingredients, Name Formula Use Es liter I p-Aminodiethylanilinemonohydrochloride. NH: 4.41

N(C2Hs)2.HCl

Aminessources of diazonium compounds 11 p-Aminodimethylanilinemonohydrochloride" NH2 1.90

N(CH3)2.HC1

III- Tartaricacld (OHOHOOOHhJilzO.-. Acid- Sourceofhydrogcnion;reducingagent 6.22

to whiten background.

IV Sodium Nitrite NaNOg To diazotizeland II 2.07

V Phloroglucinoh.,..v HO OH Coupling Compound .042

VI".-- Chicago or 28 acid SOaH .do 2.39

H NHr VII Common Salt NaOl... Electrolyte 58.47 VIII.-. Water To total volume of one liter.

I, It and III are dissolved in cold water, IV is illustrated by tartaric, citric, oxalic, succinic, added and the mixture allowed to stand at least maleic, sodium acid sulphate, etc. By way of 15 minut du g w c tune V d I are illustration, the amine, the acid, the nitrite, and dlsslolved in water -m If necessary a a part of the electrolyte may be packaged in l adde? W the solutlon of V and Wlth layers, each layer being separated by a layer of g g g 'g a g g F the electrolyte salt, such as NaCl, wads of cotmllxe an Y er pro use eslre ton or other repellant material being applied to g i g a g i g g fi ggg; the top of the package or container for retaining y c e p y y 1 g the assembled layers in position. The remaining in which I, II and III are dissolved. Duds ch th c0 1m com 0 nd d the The solution give purplish-blue, almost black 2 1 i e t 2 R p u th recordings on ayellowish green background. Exa 0 e as as e posure for onemalf minute to a carbon are auxiliary chemical, if used, W111 constitute a seelight, or three to five minutes to direct sunlight 0nd f In the event that the use of causFlc bleaches the background until it is almost white. Soda 1S contemPlelted three Packages 8 f on Standing for several Weeks, the white back able, one containing the amine and the caustic ground thus obtained become pale grey brown SOdan the second including the Solid acid and the If the freshly recorded copy is washed with water, nitrite, a d e third e b g the C up with or without first exposing it to strong light, compound as well as the auxiliary chemicals; the an improvementzinimmediate background whiteelectrolyte may be included in either of the aesacsc three packages or distributed amongst all of them.

When packaged in this manner, the compounds are storable for comparatively long intervals of time. As previously indicated, when performance of the process i contemplated, it is merely necessary to dissolve the respective packages in an appropriate vehicle of predetermined volume. As for the solutions, they have been stored for as much as a week without any material effect upon their strength. It is desirable to store these solutions in the darkness. Where separate solutions of diazonium salts and coupling compounds are provided, the storable time interval is very materially extended, and such solutions have been retained for many months without diminishing their effective characteristics.

The carrier on which the azo 'dyes are formed may be of any fibrous material, such as cloth, films, and cellulosic material generally utilized in the production of sheets, including those made from regenerated cellulose and the like. The use of paper, desirably that of rag origin, has been found particularly satisfactory for purposes or facsimile recording, and will be primarily referred to herein as illustrative of the carrier ma terial or sheet utilized. It will be noted that the formation of the dye in situ on the fabric or paper surface comprises a desirable embodiment of the facsimile recording procedure. However, it is similarly within the scope of the present disclosure to apply the dye to yarn, and fibers per se in order to provide these materials with appropriate coloring for any intended usage.

A convenient, expedient method for treatin the paper or its equivalent prior to facsimile recording involves the passage of the sheet through a bath of solution containing the reagents which essentially comprise an acid solution of a diazonium salt and a coupling compound, .together with any perfecting ingredients particularly a reducing agent which may be supplied for a predetermined purpose. After the excess fiuid has been removed from the paper, which is nevertheless in moist condition, it may be passed through a bar-helix type of recorder, with the bar and helix respectively serving as cathode and anode. However, many modifications of this procedure may be resorted to, both with respect to the details of apparatus and the preparation or condition of the carrier sheet.

Thus, the chemicals essential to the electrolytic coupling may be applied in more than one operation, and expediently the chemical solution may be applied to the carrier surface by means of a roller or wick. Alternatively, the carrier may be supplied with the reagents and then stored in a dry condition for usage, preferably being protected from light exposure and avoiding any lengthy storage period. When the sheet is to be passed through the recording device, it may be previously moistened by resort to a roller or wick, the moistening vehicle being either water or any other solution which will permit appropriate ionization of the substances involved in the electrolytic coupling reaction.

In lieu of the. sheet immersion immediately prior to its passage through the recording mechanism, and the preparation of a dry sheet to be moistened at the time of its application to the recording device, the sheet may be stored in a moist condition, and used directly in this condition when recording is to be carried out. However, this manner of retaining the recording sheet is subject to considerable storage difficulty as a 12 result of the tendency of the diazonium compound to decompose, as well as the possibility of darkening of the background during the moist storage interval. The inherent characteristics of the paper, i. e., its inherent acidity, may be effectively taken advantage of in the matter of appropriately storing the recording sheet; in otherv words, where the paper manifests a distinct acidity, the impregnation or surfacing of the same with the diazonium compound and the coupling reagent will show a distinctly greater stability, for the above considered reason that an acid medium tends to prevent premature dye formation, until such time as the reagents are subjected to the passage of an electric current.

An additional effective manner of applying the chemicals to the sheet involves the production of the diazonium salt on the paper or carrier by successive applications of amine and nitrite, whereby otherwise insoluble diazonium compounds may be used.

The electrolytic coupling may be accomplished in the form of different recordings on each side of a given sheet which has been appropriately prepared; this effect is obtainable by alternate line scanning with automatic current reversal between each alternate line, preferably utilizing non-oxidizing electrodes, such as platinum. It will be noted that in the case of the barand helix-recording, the recording on the bar side is generally preferable.

As a general rule, electrolytic coupling may be accomplished without any particular regard for w the metallic characteristics of the recording cathode; the greatest electrode wear is manifested at the positive helix electrode where a barand helix-type of recorder is used. Iron, copper, nickel, platinum, tungsten, molybdenum, tantalum, and alloys of many of these metals have all been successfully used to provide satisfactory recordings. With iron anodes, there is the possibility of a faint reading occurring on the reverse side of the sheet due to the formation of moderately colored oxidation products.

Irrespective of the manner in which the recording sheet is prepared, or the type of electrode utilized, the synchronization of paper feed and current flow with the facsimile signals causes .dye to be formed only at points corresponding to gray, colored or black points on the original subject-matter transmitted, thus producing a facsimile recording. Half-tones are obtained because the intensity of color is a function of the amount of dye formed, which increases with increase of current strength, dependent upon electric impulses emanating from the source of transmission. After recording has been accomplished, the paper is exposed to strong light in order to destroy the unchanged diazonium salt, and thus fix the white background. The recordings may also be washed, thereby removing the unused chemicals, as most of these dyes are fast to washing.

While the invention has been described in accordance with illustrative embodiments, it i apparent that many variations and modifications both as to procedural details, steps, and composition may be made. without departing from the scope of equivalents within the purview and spirit of the invention as defined in the claims.

The term facsimile as used herein is intendcd to involve not only the reproduction on the recording material of a pre-existing subject, for example, a photograph which i scanned and reproduced in accordance with the impulses emanating from the scanning operation, but also embraces the recording of subject matter in the process of creation or formation without a physically pro-existing subject. As illustrative of this latter category would be the recording of simply a mental preconception, for example, a pattern or design, either of a single color and shades thereof, or multicolors, which i recorded in accordance with an appropriate manual or automatic variation of the electric impulses delivered to the electrodes. Similarly in this category is intended the recording of an arbitrary or haphazard design, pattern or other subject, for example, one secured by haphazardly or arbitrarily varying electric impulses delivered to the electrode by punching keys on a master keyboard having suitable electrical connections, by manually or automatically varying resistance, or the like.

Having thu described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A fibrous sheet material for the electrolytic formation of azo dye image records thereon treated with an aqueous solution consisting substantially of a dye-forming composition comprising as the aromatic diazonium compound a diazotized para-diaminobenzene in which one amino group is alkylamino, a sufiicient quantity of a water-soluble inorganic salt as the electrolyte to facilitate the passage of the electrolyzing current, a sufficient quantity of an azo dye coupling component to react with said diazonium compound to produce an azo dye, and a suflicient quantity of a reducing agent to minimize any air oxidation of said composition to thereby insure a light background for the dye image records, said composition being acidic in nature to preclude premature coupling of said diazonium compound and said azo dye coupling component.

2. The fibrous sheet material as defined in claim 1 wherein the reducing agent is tartaric acid.

3. The fibrous sheet material as defined in claim 1 wherein the aromatic diazonium compound is a mixture of diazotized p-aminodiethylaniline and diazotized p-aminodimethylaniline.

4. The fibrous sheet material as defined in claim 1 wherein the aromatic diazonium compound is a mixture of diazotized p-aminodiethylaniline and diazotized p-aminodimethylaniline and wherein the coupling component is a mixture of phloroglucinol and Chicago acid.

NELLIE W. SOLOMON, Adm'inistmtrz'z: of Estate of Myer Solomon, de-

ceased.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 168,466 Edison Oct. 5, 1875 761,130 Loeb May 31, 1904 1,844,199 Bicknell et al. Feb. 9, 1932 1,880,449 Hickman et al. Oct. 4, 1932 1,892,099 Cornell Dec. 27, 1932 1,916,947 Haendel July 4, 1933 1,970,539 Bausch Aug. 21, 1934 2,063,992 Elsey Dec. 15, 1936 2,108,852 Gettinger Feb. 22, 1938 2,173,141 Talmey Sept. 19, 1939 2,181,533 Kline et a1 Nov. 28, 1939 2,306,471 Solomon Dec. 29, 1942 1,457,581 Leonardi June 5, 1923 1,588,482 Matthews June 15, 1926 1,803,532 Krzikalla et a1 May 5, 1931 2,214,559 Lecher et al. Sept. 10, 1940 2,263,616 Dahlen et al Nov. 25, 1941 2,154,918 Schneider et al. Apr. 18, 1939 2,186,732 Schneider et al. Jan. 9, 1940 2,186,850 Wilmanns et al Jan. 9, 1940 2,286,662 Weyde et a1 June 16, 1942 2,309,492 Albers et al. Jan. 26, 1943 1,965,635 Flett July 10, 1934 FOREIGN PATENTS Number Country Date 81,241 Germany May 7, 1895 86,828 Germany May 6, 1896 OTHER REFERENCES Color Index, pages 201 and 202, y W. Rowe, Jan. 1924.

The Aromatic Diazo, Compounds and Their Technical Applications, by K. H. Suanders, 1936, London, Edward Arnold and 00., pages 30, 36.