US2063992A - Facsimile reception - Google Patents

Description

Dec. 15, 1936. H. NI. ELSEY FACSIMILE RECEPTION Filed June 10, 1932 INVENTOR Howard M. E/se ITNE'S?I NEY ATTO Patented D 15, 193

PATENT OFFICE FACSIMILE' RECEPTION Howard M. Elsey, Oakmont, Pa., assignor to Westinghouse Electric 82 Manufacturing Company, a corporation of Pennsylvania Application June 10, 1932, Serial No. 616,475

4 Claims.

This invention relates to improvements in reception of facsimile images. Particularly it relates to obtaining permanence and clarity of image in such types of facsimile apparatus as uti- -5 lize electro-chemical action for reception.

efiorts were directed in addition to obtain varia- I tions in intensity, and even to record intricate 20 tone structures. These efforts have not been entirely satisfactory. More recently, requirements for speed have complicated the problems, since the series of electro-chemical actions that occur in the receiving sheet now must correspond to signal currents that fluctuate with .extreme rapidity, such as with radio transmission. Moreover, since suchsignal currents are of low intensity, the solution of reagents in the sheet must be sensitive to magnify even slight varia- 30 tions of current to appear as appreciable differences in color deposit. Hence the colorant produced must be intense in. tinctorial' power. Besides, it must be brought to relatively insolu- 'ble condition in a short-time, else it difiuses and 35 blurs the image. Thus, clarity of image depends on numerous contributing factors.

Previously, solutions for treating facsimile sheets have included starch and potassium iodide. These form a dark blue pigment on pas- 40 sage of electric current, and yield sharp images;

but the images lack permanence. 'Another solution frequently used contained essentially potasslum ferrocyanida It depended on interaction with an iron anode. The passage of electric cur- 45 rent caused iron to dissolve-from the anode; the

dissolved iron then reacted with the reagent v ferrocyanide to form a dark blue precipitate on the paper. However, this leaves a mark that is blurred. This blurring appears to be due largely 50 to the fact that the iron dissolves in two. forms,

as ferric ion and also as ferrous ion. The ferrous ion remains in solution and diifuses away from its source so as ultimately to discolor adjacent areas andrender the image indistinct.

55 The present invention comprises in its ctbjects improvement of arrangements in electro-chemical facsimile receivers, so as to produce images that are distinct, and also to obtain quick and sensitive response to slight variations of signal current. Another object is to provide facsimile 5 solutions that yield a wide range of image tone but yet permanency of image. According to this invention, these objects and others are accomplished by providing a 'scanning anode and a conducting solution that react with each other on passage of current to obtain a permanent pigment that yields sharp definition of image. Preferably thisis brought about by 1 an anode of metal having a relatively high solution potential with solvent liquid that contains reagent to convert the resulting metal ions to free metal. 'In further refinement of this invention, the solution may contain reagent that at once precipitates the metal ions as insoluble compounds, so as to ininimize'difiusion and resultant blurring of the image, and the solution may contain also reducing agent that is efl'ective to convert this precipitated metal compound to free metal.

Reference is made to the accompanying drawmg, illustrative of the principles of this invention.

In the drawing, Fig. 1 shows, in perspective, apparatus suitable for carrying out this invention;

Fig. 2 shows a representative image that is distinct over a range of .tone values, but with the scanni lines somewhat exaggerated;

Fig. 3 is an enlargement of a portion of Fig. 2 showing sharpness of outline such as results in clear definition of image; I

Fig. 4 shows an image illustrating the defect of indistinctness encountered in theprior art, while Fig. 5 is 'an enlargement of a portion oi-Fig. 4, 40 showing the blurred outline of such defective image.

Referring more particularly to thedrawing, and to a preferred embodiment of this invention, for the purpose of illustration, Fig. 1 shows a facsimile receiving sheet I, of absorbent material such as paper, drawn through a bath 2 of reagents prepared according to this invention, and then while moist drawn between electrodes I and [to form an electrolytic cell. These electrodes are connected electrically with a receiver adapted to afford a fiow of direct or rectified alternating current in accordance with incoming S gnals. Upper electrode I is shown as a stationary. conducting bar having a straight contact face, while 58 the silver ion is in solution it may diffuse away lower electrode 4 is shown as a helical conducting bar that is rotatable to afford line contact progressively along the face of upper bar 3. This progressive line contact is repeated by each revolution of the helical electrode. The helical conductor 4 rotates relatively rapidly, while the moistened sheet advances relatively slowly, so the contacts appear across the paper as a succession of closely adjacent parallel lines. Such repeated traversing of the sheet is designated as scanning. With variations in the signal current, corresponding variations occur in the facsimile deposit along the successive lines, as is apparent from Figs. 2 or 3. The particular scanning mechanism illustrated is disclosed and claimed in a copending application, Serial No. 421,965, filed January 20, 1930 by Zworykin and Elsey. The present invention resides in the solution and electrodes, which constitute the electrochemical portion of a facsimile receiver.

The contact face of the electrode serving as anode, shown as 3, may be considered to be of silver, to illustrate a preferred embodiment of the present invention. With flow of current through the electro-chemical cell established by the electrodes and the solution in the sheet, the anode, silver in this example, dissolves in the solution to formions in proportion to the current. The solution is made to contain suitable conducting material to facilitate the flow of current, and also tocontain-reagent effective to convert the metal ions to free metal condition, and thus to form a metal precipitate that varies along the scanning line in accordance with the signal. Preferably reducing agent is utilized to form the free metal. Thus a suitable solution contains approximately: Formaldehyde (40%) solution cubic centimeters 5 Sodium nitrate grams 50 Sodium hydroxide do 4 Water cubic centimeters 500 Such solution is suitable for facsimile reception because formaldehyde under alkaline conditions reduces silver ion almost instantly to metallic silver. The metal in precipitating is absorbed in the sheet. Thus the metal deposit forms the scanned line in distinct accordance with variations in the signal current. The speed of reduction to free metal is increased with increase in alkalinity, but if the solution is too alkaline, the paper strength deteriorates until it does not withstand the mechanical friction of the electrodes, but tears. In the solution described, the alkalinity is limited suitably to avoid tearing of such strong paper as is obtainable at this time, but it will be desirable to control the alkalinity according to the requirements in particular instances. This will vary somewhat according to the nature of the material and mechanical conditions affecting the strength of the sheet. The sodium nitrate is added to increase electrical conductivity and to impart smoothness 'to the electrolytic action at the cathode. Both of these sodium compounds increase electrical conductivity, and so facilitates flow of the small current involved.

A modified form of this invention is based on the observation that, although the time factor of reduction to free metal is very small with the solution described, yet during even the time that from its point of origin and so render the lines less sharp and blur the image when reduction finally occurs. Such result is illustrated in Figs.

4 and 5. However, this invention combats lack of sharpness by adding reagents to react even more quickly, not to reduce the silver ion at once but first to form insoluble compounds with it. With the silver as insoluble compound once fixed to its point of origin, it is subsequently reduced to free metal.

Illustrative of this embodiment of the invention is a solution containing approximately: Pyrocatechin gra.ms 10 Potassium bromide do 5 Potassium iodide do 0.25 Ammonium nitrate do 50 Metol do 1 Sodium sulfite (crystals) d o 1 Water cubic centimeters 500 In this case the bromide and the iodide react rapidly with the silver ion as it enters solution from the anode, to form insoluble silver bromide and iodide. It may be desirable to photosensitlze these precipitates to facilitate reduction to free metal, and it may be desirable to alter the reducing agents, but from the present description, variations of this invention will be apparent to those skilled in the art. Ammonium nitrate serves to control the hydrogen ion concentration of the solution to prevent undue oxidation of the reducing agent, pyrocatechin and also markedly increases the conductivity of the solution. The nitrate ion also facilitates the reactions that occur at the cathode. The metol and the sodium sulfite also serve to protect the pyrocatechln against oxidation by the air.

Silver is preferable as anodic metal, not only because of its premanency of image, but also because silver dissolves only as univalent metal ion. This eliminates difficulties encountered with metal, such as iron, that is multi-valent, where different ions are formed atan anode in ratios that are functions of the current density. Silver also introduces a factor of considerable importance where there is but small current flow; namely, that one atomic weight of the univalent anodic metal is dissolved for each faraday of electricity flowing, while a metal of valence two or valence threewould require respectively two or three faradays of electricity to dissolve an atomic weight of such metal. Moreover, iron and various multivalent metals tend-to become passive; while silver, avoiding this difficulty, dissolves more consistently in proportion to the current flow.

It is within the scope of this invention to utilize as anode not only pure metal, but also alloys. One merit of alloys is greater hardness, or resistance to wear and deformation.

Also variations are contemplated in the electrolyte. For example, in lieu of pyrocatechin or of formaldehyde, gallic acid may be used, or acetaldehyde, or hydroquinine, pyrogallol, etc. The effect of these and other equivalents will now be apparent to those skilled in the art. Similarly other precipitants than potassium bromide or iodide may be used. Moreover, it is within the scope of this invention to modify the color or intensity of the metal precipitate.

Also there may be modifications in the manner of applying the reagents. 'For instance, the reducing agent, as pyrocatechin may be omitted from the solution with which the facsimile sheet is treated at the electrodes, but after passage of the current the sheet may be exposed to light and then treated with suitable reducing agent to 15 bring out the latent image. And even Where pyof current, the image may be intensified with suitable reducing agent, or other agents known in the photographic art. 7

Further, the electrolyte in the paper may con-' tain reagents to free pigmenting material at the cathode, whether or not anodic metal is reduced. For instance, with silver anode and reducing conditions as heretofore described, the solution may contain a metal salt, such that while silver is precipitating at the anode, metal is freed at the cathode. Lead, for example, forms suitable soluble salts for cathodic deposit. With the electrodes in registry, the lead remains in the paper as part of the imprinted image.

It may be desirable to modify the electrolyte so as to minimize dryingof the paper, or to regulate the degree of moistness during contact with the electrodes, or to lower the freezing point of the solution to provide for reception at low temperature. Glycerine, alcohol, and sugar thus may be included in the electrolyte.

It will be understood that although this description of the invention refers to scanning lines of continuous nature, the intended purport is to include also discontinuous scanning lines, or a series of dots for example. Also the benefits of this invention extend to simple telegraph reception, as well as to more intricate facsimile reception.

It is apparent that the drawing necessarily exaggerates somewhat the intensity and spacing of the scanning lines. In actual practice, the scanning lines disappear substantially except to form the image. The usefulness of the present invention is indicated by the fact that it is capable .oiflbringing out the image very shortly after electrodes have moved over a given line. This facilitates immediate adjust- -ment to correct any irregularities that may appear., The rapidity of action of this electrochemical arrangement is evident from the fact that normally about eighty scanning lines per lineal inch of receiving sheet are generated, or about one hundred twenty a minute. A normal voltage across the scanning electrode, or the "knife-edge drop", is about sixty volts with a current of about sixty milliamperes. It has been found that the deposit obtained is approximate- 1y proportional to the current, but that the pigmentation or intensity of image mounts in proportion to the logarithm of the current. Under these conditions adjacent areas are made distinguishably different in intensity with current flow over time intervals each of the order of half a microsecond.

According to the provisions of the patent statutes, I have explained the principles and mode of operation of my invention and have described What I now consider to represent its best embodiment. However, I desire tohave it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim as my invention:

1. In combination with facsimile receiving apparatus comprising scanning electrodes having a metal anode adapted to dissolve with flow of electric current and a. receiving sheet of absorbent material adapted to be moved-in contact with the electrodes, an alkaline electrolyte adapted to moisten the sheet -and to precipitate dissolved anodic metal with flow of current through the sheet, the alkalinity of the solution being limited in accordance with the strength of the moving, moistened sheet to avoid tearing thereof.

rial, a precipitant to form a compound with metal ,ions from theanode, and a reducing agent adapted to precipitate free metal from the precipitated metal compound and containing metal in solution adapted to be released as free metal.

3. In combination with a silver anode for facsimile receiving to precipitate free silver in a receiving sheet, an electrolyte comprising reagent to precipitate silver ions as dissolved from'the anode, and organic reducing agent to release free silver from the precipitate, and containing metal in solution to be released as free metal in the receiving sheet.

4. In combination with a silver anode for facsimile receiving to precipitate free silver in a receiving sheet, an electrolyte comprising, organic reducing agent, soluble halide, ammonium nitrate and alkali metal sulphite.

HOWARD M. ELSEY.

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