US2267901A - Means for and method of electrical printing - Google Patents

Description

m C N U D K. I

MEANS FOR AND METHOD OF ELECTRICAL PRINTING Original Filed Feb. 16, 1954 @NNI A75/ami@ ec. 30, g. J. K. DUNCAN 2,267,991

MEANS FOR AND METHOD OF ELECTRICAL PRINTING Original Filed Feb. 16, 1934 3 Sheets-Sheet 2 Jz/wejzazcm @6* MW Dec. 30, i941. J. K. DUNCAN MEANS FOR AND METHOD OF ELECTRICAL PRINTING Original Filed Feb. 16, 1934 3 Sheets-Sheet 5 lll/AA wmf, @M VZW @e Patented Dec. 30, -1941 MEANS FOR, AND METHOD OF ELECTRICAL PRINTING James K. Duncan. Chicago, lll.

Application February 16, 1934, Serial No. 711,491

Renewed May 6,1940 A Claims.4

invention relates in general to the art of printing and has more particular reference to means for and methods of producing prints electrically, the invention having special reference to the utilization of electrolytic action in printing.

An important object of the invention is to provide for printing by electrolytic action.

' Another object is to provide for printing from a stencil by the action of electricity.

Another object is to provide a printing stencil particularly adapted for printing by electrical action; a further object beingto provide a stencil from which prints `may be produced and the stencil preserved as a permanent master record.

Another important object is to provide meansA operable in conjunction with a stencil to produce prints by electrical action.

Another object is to provide a printing stencil adapted to receive master impressions to be reproduced by printing and having means adapted for deposit, by electrolytic action, upon a surface to be printed during the printing operation. Another object is to provide a printing stencil adapted to be .impressed in accordance with design impressions to be reproduced and having current blocking means whereby to prevent current ow through the stencil save at the impressions so that the stencil may be used in printing by electrolytic action. Another object-is to provide a stencil having current-carrying portions and current-blocking portions adapted to be impressed with a design to be reproduced whereby the same may be utilized as a master form'in printing by electrical action, that is to say, a stencil which may be used to produce a desired number of printed copies and which is of suiciently permanent character permitting storage and subsequent re-A use in producing additional printed copies at any time; a further object being to provide a master stencil which will produce prints all of which are of like quality and intensity throughout a large run of copies.

Another object is to provide a printing stencil which may be cut or impressed, either manually, in a typewriter, or in any other convenient manner without the use of special ribbon, a stencil which, after cutting, may be instantly visualized Without diiculty and which does not contain smearable pigments capable of befouling the hands and clothes of an operator.

Another object is to provide a printing stencil of laminated construction whereby the strength of the stencil is improved, a further object being to form a stencil in which at least one of the laminations comprises a layer of current-carrying material preferably a metal capable of being deposited electrolytically.

Another obiect is to provide apparatus for printing electrically, more particularly-by electrolytlc action and including means to mount a master form or stencil in printing position and for supplying electrical current to the mounted form in order to accomplish the printing operation when the form Iis impressed upon the surface of the sheet being printed; a further object being to provide a device capable of printing upon stock of any desired thickness.

Another object resides in providing an improved method of printing, which is as well suited to the long run or multi-copy print production as to the so-called ,system or short-run print production, in whicha few prints only are made at a time, the cost of operation being within the requirements of the system or short-run eld while the ability to furnish many hundreds of copies from a single master stencil renders the process suitable for the circular letter or multicopy eld.

Another object is to provide a. process which is entirely clean, free from disagreeable odors, and free from messy pigments capable of soiling the hands and clothes of the printer, a further object being to provide a process in which the printed copies are sharp and permanent, not affected by light, heat, moisture, or oil.

Another object is to provide an improved elec.- trical printing process in which the electrical Acurrents employed need not pass through the sheets on which the printed copies are formed.

Another object is to provide a printing process in which separating sheets are not required between freshly made prints, the prints being unsmearable at the conclusion of the printing operation and hence may be piled ontop of each other immediately, a further object being to provide a printing process in which printing speed is limited only by the maximum speed limit of the mechanism utilized in carrying out the process.

Another object is to provide a printing process adapted to produce neat, sharp prints upon stock of any desired thickness and of any material capable of 'receiving printing.

Another object is to provide a printing process wherein the pigment is applied on the paper opposite the edges of a cut stencil employed in the printing process.

Another object is to provide forv printing by the formation or deposition of pigment in a sur- 2 face to be printed opposite the edges ofa perforation formed in a stencil sheet without `making provision for blocking the deposition of pigment inwardly of said edges.

Another object is to provide for printing by deposition, in a surface to be printed, of pigment derived by the decomposition of 'a stencil or `ing the flow of such current.

Numerous other objects, advantages, and inherent functions of the inventionwill become apparent to those familiar with the art of printing as the invention is more fully understood.

from the` following description, which, taken in connection with the accompanying drawings,

discloses an embodiment of the invention.

Referringto the drawings:

Figurel is a view showing printing apparatus embodying` my present invention in side elevation;

Figure 2 is a view showing the apparatus illustrated in Figure 1 as viewed from above;

Figures 3 and 4 are sectional views taken substantially along the lines 3 3 and 4 4 inV Figures 1 and 2 respectively;

Figure 5 is a sectional view taken substan- .tially along the line 5-5 in Figure 2;

Figure 6 is a diagrammatic view illustrating aeeaooi to the-sheet or surface to be printed. The stencil, in its simplest form, comprises a' preferably Alaminated sheet includinga layer of electrical conducting material |03. In addition, the stencil may be strengthened by including a layer of preferably fibrous material |05, such as paper,

electrical connections forming a part of the apparatus shown in Figures 1 and 2;

K or Amaster stencil during the printing operation:

Figure 9 is a face view of a stencil embodying my present invention and adapted for use in the apparatus shown in Figures l-and 2; and

Figure 10 is a section taken along the line lli-l0, in Figure 9.

To illustrate my invention, I haveshown, on the drawings, apparatus for printing by electrical action, wherein the sheet to be treated is exposed to the action of electrical currents at the places where it is desired to print marks on the sheet, the apparatus including means for preventing exposure of the sheet to the ac"- tion of the electrical currents at the places where no printing is desired. The apparatus 'illustrated is as well adapted for printing by electrolytic action, wherein the electrical currents deposit the pigment on the printed surface, as it is adapted for printing by electrolytic action, which the sheet being printed. is treated -'with suitable chemicals adapted to change color when exposed to the action of the electrical current'.

While anysuitable means for applying or-exlposing the sheet to be printed to the action of the electrical currents may be employed, I prefer to use and therefore have illustrated a master form arranged as a stencil |0| and adapted for removable mounting in the printing apparatus in position to accomplish the printing function. I find that the stencilhtype of printing form is well suited for my purpose in controlling the application of the electrical currentson a surface of which the conducting layer may be formed and insulating layers |01 and |08 of preferably non-conducting water-proof material are applied to the outerl surfaces of the layers |03 and |05. The total thickness of the layers, forming the stencil, need not be in excess of .002 inch, for which reason the stencil is not unusually bulky and can be easily cut in a typewriter. At the same time, the sheet is suiclently rigid and self-supporting not to require particularly careful handling and may be prserved as a permanent record after being cu The opposite end edges of the stencil are preferably provided with layers of suitable protective material, such as wax or varnish, and

carry spaced eyelets preferably of metallic conducting material, which form electrical contact with the layer |03 and serve to bind the layers together. The fibrous material |05 is preferably paper formed with water-marks 2| I, which are visible through the layers |01 and |09, which is preferably formed of translucent material sulciently transparent to permit the water marks to be seen therethrough. In this fashion, the stencil may be provided with guide lines to assist in the cutting thereof or the water marks may be formed in accordance with a preferred or suitable design in order to afford identifying means for the product;

The stencil is prepared for printing by impressing the same with a design to be reproduced, the design being cut into and through the metallic layer. The sheet to be printed is then pressed upon thecut stencil while electrical currents are passed through the metallic portions of the stencil and intothe cut openings therein, vmeans being provided to ill said openings' withv a pref- 1 erably fluid current-carrying medium, through which the electric circuit is completed. As the currents pass into and through the cut portions of the stencil,l they act upon the surfaces of the sheet being treated, which are exposed opposite saidcut portions. It is not necessary to cause the electrical currents to pass entirely through the sheet being printed and to return to the power source from the side of the sheet opposite that to which the stencil isI applied; but the currents may be returned from the cut-out portions of the stencil to the power source by means of an electrical circuit-forming path disposed on the same side of the sheet being printed which is eX- posed to the stencil or printing element, this feature being of particular importance-in my present invention, as will hereinafter more fully appear.

In order to most conveniently contact the sheet to be printed with the stencil and at the same time provide forthe application of the electrical currents, I provide apparatus including a main frame I5, in which is mounted astencil-carrying i drum |1, means including a motor I9, and suitable transmission mechanism 2| for rotating the drum l1, a pressure roller 23, means comprising various width`in the carrier 25.

ceiver 29 int'o which the printed sheets are dedrum.

The transmission 2| is driven by the motor,

I9 and is drivingly connected to rotate a worm II9, which, in turn, is drivingly associatedmwith a worm wheel I 23 fast on a shaft 65 on which the drum I1 is mounted for rotation in the frame I5. The worm -I I9 is splincdupon and rotates with a shaft I2I forming a part of the Ytransmission mechanism. The worm is normally urged on the shaft as by means of a spring |25 to' a vwhich is journaled an adjusting nut |29 carrying a fitting |3| which, by turning the nut |29, may be moved to alter the spacement between the tting I3I and the axis of the shaft. The fitting |3| forms a wristI pin, to which one end of a connecting rod |33 is journaled'. The other end of the connecting rod is connected to a cross-bar |35 extending above the sheet carrier 25. The bar |35 is journaled at its opposite ends in lever arms |31 pivoted in the frame I5 on opposite sides of the carrier 25. As the shaft 65 is turned by the motor I9 operating through the transmis-Y sion 2|, the connecting rod |33 will be reciprocated to cause the bar |35 to swing back and forth above the sheets in the carrier 25, the bar traveling an arcuate path, the center of which coincides with the pivoted axis of the levers |31.

, livered after contacting with the stencil-carrying der to retain the under sheets on the carrier as the uppermost sheet I 6| is being delivered bei tween the rollers I1 and 23 during the forward movement of the feeding pad |41.

As the sheets are delivered successively by the pad' |41 between the rollers I1 and 23, it lsdesirable to elevate the platform I5| and this is accomplished by mechanismy including extensions |63 formed as lugs'fastene'd to and extendingv downwardly of the plate I,6I. The lugs |63 are formed with racks |65 in position to engage pinions- |61 drivingly connected with a sha-ft |69, which is journaled in the frame II5 'and which carries a gear |1| in position to drivingly engage a pinion |13 carried on a shaft |15.

The shaftI15 is journaled in the frame I5 and carries an easily accessible handle |1.1 whereby the elevating mechanism may be manually controlled by the operator of the printing apparatus. The shaft |15 also carries a ratchet wheel |19 and one of the levers |31 carries a pawl I8I in position to engage the ratchet wheel The bar has a fitting |39 fixed thereon, which c tting carries an adjustable 'stop I4I in position to overlie a seat |43 formed in the arm` |33, The stop I4| is adjusted to cause the seat |43 to engage the stop I4| during the travel of the rod in one direction, that is to say, toward the left, viewing Figure 1, and to disengage the stop during the travel of the connecting rod in the reverse direction. This movement causes the slight angular rotation of the rod |35 in a counterclockwise' direction viewing Figure l during the movement of the rod toward the left. The rod is of preferably non-circular configuration and carries a sheet-feeding arm |45 splined thereon at one end and having a sheet-feeding pad |41 at its other end in position to engage the uppermost sheet in the stack on the carrier 25, during the forward movement of the rod |35 toward the roller I1. The arm |45 may be shifted along the rod |35 in order to locate the arm in any desired position so as to accommodate sheetsI of The arm may be adjusted along the rod |35 by means of the holding screw |49. The carrier 25 comprises a plate I5I, which is vertically shiftable in the frame I5 and which carries an adjustable end plate |53 for abutting the outer ends of the sheets on the carrier whereby to hold the 'opposite ends of the sheets in abutting relationship with a stop |55 formed in the frame 'I5 immediately in front of the roller I1 and the pressure roller 23. The .plate I5| also carries holding members |51 on opposite sides offthe plate |5I faced with a suitable resilient material |59, which may be and preferably is sponge rubber,- the members |51 being adjustably mounted on the plate I5| imposition to engage the opposite side edges of the sheets resting on the platformlin or- |19, the pawl being connected by means of the rod |83 with an arm |85 xed 0n the rod |35 and adapted to be moved in response to the tilting movement imparted by the connecting rod |33. As the sheets are successively delivered between the rollers I1 and 23, the elevation of the feeding pad |41V with respect to the frame will drop, which will cause the rodI35 to tilt more and more in a clockwise direction about its axis and "wll thus control the pawl I8| through the rod |83 in order to actuate the ratchet 4wheel and drive` the carrier elevating mechanism in ar direction to raise the carrier andmaintain the uppermost sheet of the stack in the'carrier at a proper elevation for feeding to the printing roller.

A suitable sheet counting device |85 may be mounted on the frame I5 in position to count the printed sheets as the same are delivered from between the rollers I1 and 23 into the freceiver 23 and a handle |81, in geared relationship with the shaft |65, may be provided for manually turning the drum I1 independently of the motor I9. The device I5 may also be mounted on a supporting base |89 provided with drawers I9I having handles |93 for the storage of stencils, printing paper, and tools necessary in connection with the use of the apparatus.

The drum I1 may, of course, be made in any suitable or preferred manner in order to provide for the reception of the printing form or stencil and to illustrate my invention, I have shown a drum comprising a central stencil-carrying portion 3| and end plates33. 'I'he central stencil-carrying portion is preferably formed of any suitable insulating material and isprovided with an internal chamber adapted to contain moisture, means being provided to permit the escape of moisture at the peripheral portions of the drum to afford a current path for .the return Vof electrical currents from the cut portions of drical portion. 35 and a flat or plane portion 31, the cylindrical portion being provided with a multiplicity of spaced apart perforations 39 through which a limited amount of moisture may escape from the interior of the drum behind the stencil which is mounted on the outer curved surface of the drum.

I find it desirable to limit the amount of moisture which is permitted to accumulate behind the stencil and to this end the interior of the drum is filled with any suitable absorbent material 4|, which is kept moist by drippage from a reservoir 43 mounted in the drum. The reservoir may be filled` with a supply of moisture from time to time by the operator of the machine. The liquid escapes from the reservoir through relatively small openings 45 into a central fiuid distributing compartment 41 formed within the stencil-carrying drum by means of a partition 49, containing perforations 5|, through which the moisture, delivered into the distributing compartment 41, may escape intol a chamber 53, which contains the absorbent material 4| and which is disposed between the partition 49 and the outer wall 35 of the drum. Partitions 55 are also preferably formed within the uld distributing chamber 41 in order to assist in the fluid distributing function and also to add strength to the element 3|. The central portion 3| of the drum and the end plates 33 may be secured together in any suitable or preferred manner and preferably by means of the studs 51, which hold the end plates in position to close the open ends of the central drum-like element 3|.

accasion y 6,3 bn the flange 59 whereby to form a direct 4.

electrical connection with the conducting layer |03 of a stencil mounted on the drum. while the other slip ring is connected by means of the conductor 11 to form a return connection from the perforated portions of the stencil, said return connection being in part through the fluid medium applied behind the stencil from the reservoir 43. In order to most conveniently! accomplish the return connection, the outer surface of the wall 35 carries a plate 19 of electrical conduct- The drum portion 3| is provided with flanges f 59, 6|, the same comprising extensions of the curved wall and these flanges contain a plurality of spaced studs 63 adapted to receive the eyelets ||3 at the opposite ends of the stencil in order to support the same in stretched position on the outer curved surface of the wall 35. The studs on one flange are preferably of electrical conducting material adapted to form electrical contact with the eyelets at one end of the stencil and the studs o'n atleast one ange are shiftably mounted and normally spring-pressed in a direction to tighten the stencil upon the wall 35, said shiftable studs being depressible to facilitate mounting theeyelets at one end of the stencil thereon. The drum |1 is mounted upon a shaft for rotation therewith, the mounting being accomplished by securing the end plates 33 upon the shaft, the shaft extending through the compartment 41 in the interior of the element 3|. The shaft 65 carries slip rings 61. and 69, which have wiping contact with sliding termi nals or brushes 1| and 13 stationarily mounted on the frame I5, which arel connected in an electrical circuit, including a suitable power source and control means as indicated in Figure 6 of the drawings. Power from the external source may be delivered to the system through a plugin connection |93 comprising a pair of conductors |95 and |91 between which a condenser |99 is connected for the purpose of preservinglthe current applied between the conductors as uni' form as possible. One of the conductors |91 is connected in series with a pilot lamp 20|, a printing control switch. 203 and thence to the brush 13, the other brush 1| being connected through a control resistance 205 to the conductor |95 this completing the printing circuit. I'he motoralso may have a power supply conductor including a control switch 201 connected to the conductor |95 and a return conductor connected throughv a starting control 209 `to the conductor |91. The switches 203 and 201 and the controls 205 and 209 .may be mounted in readily accessible position on` the frame I5.

One of the slip rings is connected by means of a conductor 15 to the electrical conductingstuds ing material, which is provided with a multitude of minute perforations 85 to permit the passage of liquid which escapes from the chamber 53 through the larger perforations 39. 'I'he plate 19 'is preferably permanently fastened to the outer surfaces of the Wall 35 by means of fastening members 8|, which connect the opposite ends of the plate 19 to the flanges 59 and 6|, said plate 19 being electrically connected with. the conductor 11. I prefer to apply the plate 19 to the outer surfaces of the curved wall 35, since I thus am able to utilize the plate in distributing the current-carrying moisture uniformly behind the stencil although it is obvious that the plate 19 might be arranged in any position on the drum, providing it is in contact with the currentcarrying moisture in order to provide a return circuit for the electrical printing currents. IA contemplate also the provision of a relativelyl thin fibrous layer 83 on the outer surface of the current-carrying plate 19 in order to provide a still more uniform distribution of the moisture over the inner surfaceg of the stencil when the same is mounted on the drum, the outer surface of the wall 35, which is in contact with the plate 19, also may be provided with shallow grooves in order to facilitate the passage of the moisture from the perforations 39 to the minute perforations 85 of the plate 19 to thus aid in the unlform distribution ofthe current-carrying liquid behind the stencil.

Referring vnow morevparticularly to Figures 'I and 8, which illustrate various mod of employing the principles ofv my present vinvention in electricalprinting:

'I'he invention may be practiced by treating the sheet, upon which the printing is made, with a suitable preferably colorless chemical adapted to turn color when exposed to the electrolytic action of currents, applied to the sheet in accordancewith a desired design as by means of the stencil |0|(, in which the design has been pre viously cut. To this end, I'may utilize potassium iodide starch paper, .that is to say, material treated with potassium iodide, which is colorless but which, when contacted with an electrically charged electrolyte, produces in ya dark brown precipitation of iodine-at the exposed portions. Other chemicals may be employed to provide pigmentationof 'different colors and I may even employ a. plurality of chemicals such as potassium chloride, and' phenlphthalein, in the sheet in order to accomplish multi-color printing, the chemicals employed being selected in accordance with the strength of current and the time reployed in electrifying the electrolyte.

produced by reacting one chemical only. Potassium chloride, a normally colorless material, turns brown when exposed to the action of an electrified or electrically charged electrolyte, while normally colorless phenolphthalein turns red if similarly treated. The change in color effect takes place at unlike rates of speed, varying to some extent in accordance with the concentration of the chemical in the e-lement being printed. The rate of color development varies as a function of the density of the current em- If, therefore, an element to be printed contains colorless potassium chloride and phenolphthalein in suitable proportions, the element may be printed red by exposing it to an electrolyte carrying a predetermined current density and may be printed a brownish color by exposing it to an electrolytecarrying current of greater density. Selection of other reactive substances aords the possibility of printing any desired combination of colors.

In practicing this process, the metallic layer .y be caused to flow from the layer |03 through the |03 of the stencil, as well as the plate 19, are

preferably formed of current-carrying material, such as aluminum, which is substantially inert to electrolytic action and printing may be accomplished by applying either alternating current -or direct current between the stencil and the plate 19.

The process may also be practiced, without previously treating the sheets to be printed, by forming the metallic layer |03 of the stencil, or the plate 19, of suitable, preferably metallic material capable of being deposited by electrolytic action, for instance, silver may be deposited electrolytically as a black pigment, iron as a red pigment, copper as a green pigment, upon the sheet in accordance with a desired design cut in the stencil |0|.

In practicing the process wherein a compound of the material of the stencil or of the element 19 is depositedA on the sheet being printed, it is desirable to utilize direct current only and to apply the direct current potential as shown in Figre 8 between the plate 19 and the metallic layer of the stencil. If the polarity of the applied electrical potential is such that current flows through the layer 83, which, it will be remembered, is saturated with a suitable current-carrying liquid electrolyte drawn from the reservoir 43 through the distributing' chambers 41 and 53, and thence through the perforations 39 and 85, from the plate 19 to the layer |03 of the stencil, as shown in Figure 8, it will deposit a compound of the material of which the plate 19 is formed.

The current-carrying electrolyte may pass the insulating layer only at the places Where the same has Vbeen perforated in cutting the stencil and the electrified electrolyte may enter the depressions or openings formed in the metallic layer of the stencil, it being remembered that the moisture contained in the layer 83 will be squeezed into the perforations o-f the stencil at the time whrn the perforations come opposite the backing roller 23, thus permitting the currentcarrying electrolyte to enter the perforations of the stencil at the instant when the sheet, being printed, is opposite such perforation. The electrically active electrolyte is thus disposed in the perforations in positionv to contact the surface to be printed, and, I have found, creates pigmentation in the surface of the sheet exposed opposite the perforations. The current may re- 'turn to the power source through the layer |03,

the'eyelets ||3, the studs 63. By reversing the electrolyte in the cut impressions of the stencil at the instant when the same are pressed against the sheet being printed by the backing roller. These electrical currents'liberate, in ionic form, the compound derived from the layer |03, thereby permitting a deposit of the compound on the surface of the sheet being printed. The current may return to the source by way of the currentcarrying electrolyte, which has been squeezed into the perforation from the layer 83. I find that no matter in which direction the current flows in the perforations, pigment is developed on the sheet being printed at and near the edges of the perforations. This will have no appreciable effect in a printed character comprising a thin line but where the perforation is of appreciable breadth, as where an oval opening is punched through the stencil, the pigment will appear at the edges of thegoval perforation, leaving the central portions unprinted. It is possible, therefore, to obtain an accurately printed letter, such as an o, by punching entirely through the stencil Without making any provision as is ordinarily necessary for the blocking of the printing effect'in the central area of the character. This effect is present also in the process requiring chemically pre-treated sheets as well as in the process where the pigment is derived from the stencil and is an important feature of the invention. n

It will be noted that the electrical currents utilized in printing, in l accordance with .the

teachings of my present invention, are applied in such a way that they do not pass entirely through the printed sheet but the current carrying electrolyte is applied to one side of the sheet only. It is thus not necessary to moisten the sheet in order to permit current now entirely through the sheet. The resultant printing is sharply defined and kept within the confines of the perforations formed in the stencil.

By employing electricityin order to print and by utilizing a stencil characterized by the absence of any free pigment, I have produced a printing process which is clean and neat and will not soil the hands or clothes ofthe operator duces` the copies. By eliminating the necessity of moisteningthe sheet, I am able to produce' accurate prints Without distortion through stretching or warping of the sheet. nating the necessity of passing the electrical printing currents through the sheet, I am able to print on sheets of any desired thickness, on wall surfaces and the surfaces of other solid objects by suitably revising the printing machine. My new electrical printing process may be accomplished by means of apparatus of exceedingly simple inexpensive character, which is entirely automatic and in which the speed of printing is governed solely by the maximum operating speed of the apparatus employed. By utilizing different metals in the plate 19 and in the stencil, or by employing a plurality of chemicals in the pre-treated sheet, I am able to change the color of the characters at will.

Numerous other objects, advantages, and in- `Several parts without departing from the spirit or scopeof my invention or sacricing any of its attendant advantages; the forms herein delscribed being preferred embodiments for the ,means adapted to form an electrical connection with said form when the same is mounted on the studs, and means to electrically connect the studs Lin an electrical circuit.

2. A method of printing on relatively dry material which comprises bringing into contact with the dry material through a` printing stencil an aqueous liquid medium containing anelectrolyte and adapted to carry current, passing a current throughsaid velectrolyte 'between electrodes, both of which are located on one side of the dry material and at least one of which is associated with the stencil in close proximity to the dry material and in contact with the electrolyte.

3. A method of 'printing on relatively dry material which comprises bringing into contact' with the dry material through a printing stencil anA aqueous medium containing an electrolyte which is also incontact with a pair of electrodes located on the same side of the dry material, at

least one of the electrodes being disposed within v the stencil in close proximity to the dry material and while the aqueous medium is so in contact with the electrodes and dry material, applying a source of electric current having a substantial electromotive force to said electrodes.

4. The method of printing which comprises bringing into contactwith the surface to be printed a printing stencil having apertures therein, supplying at said apertures an equeous liquid medium containing an electrolyte adapted to carry current, and passing electric current from an electrode exposed at the margin of said aperture andin relatively close adjacency tothe surface to be printed to a second electrode onthe same side of said surface to be printed.

5. Printing apparatus comprising a printing stencil having an insulated work` contacting surface, printing recesses provided in said surface, electrode means disposed within said recessesand in relatively close adjacency to said work contacting surface, means for delivering an aqueous electrolyte through said recesses, means for cona layer of fibrous material adjacent the currentcarrying layer, and layers of waterproof insulating material on the outwardly facing surfaces of said current-carrying and fibrous layers, said insulating layer onv the outwardly facing surface of said current-carrying layer being 'relatively thin'whereby said current-carrying layer resides relatively closely to the surface of said'printing form and in close proximity to a worksurface when in printing relation thereto. '8. Printing apparatuscornprising' a main roller, means to rotate said main roller, a pressure roller in position to present a sheet to be printed against said main roller, means carried by said main roller comprising a printing stencil Vupon a surface of said main roller and including means ,formed and arranged on said main roller to deliver an aqueous current-carrying fluid medium containing an electrolyte behind the printing stencil when mounted, said means carried by the main roller also comprising a pair of electrodes, both`on the same side of the sheet to be printed, at least one of said electrodes being disposed near the outer surface of the stencilfo'r contact with the electrolyte and in relatively close adjacency to said sheer'J when the sheet is arranged in operative relation, and means for passing current through the electrolyte by means of .the electrodes. A Y' 9. Printing apparatus comprising a mounting for a printing stencil, means to secure a stencil on said mounting, and means formed and arranged in said'mounting to deliver an aqueous current-carrying medium vcomprising an electrolyte behind said mounted stencil, an electrode formed in said stencil in contact with the electrolyte and second spaced electrode means on the same sideof the printing surface of the'stencil, and means to pass current through the electrolyte by means of the electrodes.

10. Printing apparatus comprising a. printing stencil, 4means on the rear side of -the plane of the printing surface of said stencil including an electrode to deliver an aqueous liquid currentcarrying medium containing an electrolyte through the openings in said stencil into contact with the surface to be printed, said stencil including cooperative electrode means disposed adv jacent the margins of said4 openings and means for passing current through 'the electrolyte by means of the electrodes.

' 11. Printing apparatuscomprising a printing stencil, means Von the rear side of the plane of tacting said insulated surface and said currentcarrying liquidwith a work surface to be printed, and a second electrode means disposed on the 'same side of the work contacting surface and operative to coact with said first named electrode means and means to pass a current ofA electricity through said current-carrying liquid. 6. A printing form for use in printing according to themethodof claim 2 comprising alaminated stencil including a' current-carrying layer,

a strengthening layer and an electrically insulating to the method of claim 2 comprising a laminated stencil including a'. current-carrying layer,

the printing surface of said stencil includingan electrode to deliver an aqueous liquid currentcarrying medium containing anelectrolyte through the openings in said'stencil into contact with thesurface to be printed, said stencil including electro'demens disposed therein but exposed at the margins of said openings, and means for passing current through the. electrolyte by means of the electrodes.

12. -A printing form for use in printing''according to the method of claim 2 comprising a laminated stencil including a current carrying layer, a strengthening layer, and a pair of electrically insulating layers, said strengthening layer being vlocated between. said current carrying layer and one said insulating layer\ said 'other insulating layer being located on the work contacting side of-the stencil and being relatively thin whereby 'said current carrying layer resides 'relatively 13. Printing apparatus comprising a laminated printing stencil, including a current carrying layer, a strengthening layer and an electrically insulating layer, said stencil having awork contacting surface and said insulating layer being located adjacent an opposite surface for insulating the rear surface of the stencil, printing recesses provided in said stencil, said current carrying layer presenting edge portions at said recesses providing electrode means disposed within said recesses in relatively close adjacency to said work contacting surface, means for delivering an aqueous current carrying liquid medium containing an electrolyte through said recess, means for contacting said work contacting surface and said current carrying liquid with a work surface to be printed, and a second electrode means disposed on the same side of the work contacting surface and operative to coact with said first named electrode means. and means to pass a current of electricity through said current carrying liquid.

14. A printing form for use in printing according to the method of claim 2 comprising a lami nated stencil including a current carrying layer, a strengthening layer, and a pair of electrically insulating layers, one insulating layer being disposed on the outwardly facing surface of said current carrying layer and being relatively thin whereby said current carrying layer resides re1- atively closely to the surface of said printing form and in close proximity to a work surface when in printing relation thereto, the other insulating layer being located on the inwardly facing side of the current carrying layer and separated therefrom by the strengthening layer.A

15. A printing form for use in printing accord,- ing to the method of claim 2 comprising a laminated stencil including a current carrying layer, a strengthening layer, and an electrically insulating layer, the insulating layer being located on the inwardly facing side Yof the current carrying layer and separated therefrom by the strengthening layer.

JAMES K. DUNCAN.

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