US2667121A - Printing method and apparatus - Google Patents

Description

Jam 26, 1954 w. c. HUEBNER 2,667,121

PRINTING METHOD AND APPARATUS Filed on. 4. 1949 2 Sheets-Sheet 1 I "1 ]NVENTOR.'

' WILLIFIM E.HLIEENER' BYW, I, I

. HTTEIRNEYS Jan. 26, 1954 w. c. HUEBNER 2,667,121

PRINTING METHOD AND APPARATUS Filed on. 4. 1949 2 Sheets-Sheet 2 INVENTOR. WILLIFIM ELHLIEEINERI $1 $1 BY 1 I HTTUR'NEYS Patented Jan. 26, 1954 UNITED STATES PATENT OFFICE PRINTING METHOD AND APPARATUS Application October 4, 1949, Serial No. 119,410

6 Claims.

This invention relates to a method and means for transferring a fiuid to material and, more particularly, to a method and means for printing material with a fluid by the action of an electrostatic field of force.

Processes and apparatuses have been developed in recent years for printing a fluid, such as ink or the like, upon sheet or web material, such as paper or cloth, by employing an electrostatic field of force to effect the transfer of the fluid to the material. Examples of such processes and apparatuses are disclosed in my prior patents: 1,820,194, issued August 25, 1931; 2,224,391, issued December 10, 1940; 2,408,143 and 2,408,144, both issued September 24, 1946. In these patents there are disclosed processes and apparatuses for printing wherein the ink is transferred from an image carrying member to the print receiving material without appreciable pressure therebetween, the transfer being effected by the action of an electrostatic field of force extending through the image area and the print receiving material. When employing such processes and apparatuses, improved results, namely better transfer of the fluid with sharper and better defined images, are

secured when the fluid and/or the print receiving material have been electrically precharged prior to their introduction into the electrostatic field which efiects transfer of the fluid to the material. This precharging is fully disclosed and. claimed in my patent application S. N. 591,739, filed May 3, 1945, entitled Process and Apparatus for Electronographic Printing, and which issued on October 4, 1949, as Patent No. 2,483,462.

Although the above-mentioned processes and proved process and apparatus for printing by means of an electrostatic field of force wherein migration of the printing fluid subjected to the field of force is improved for a given potential gradient of the field, and fluids which are difficult to migrate may be uniformly transferred, thereby producing an image of improved characteristics.

Another object of the invention is to provide an improved process and apparatus for printing by means of an electrostatic field of force wherein the potential gradient of the field is pulsated to produce a more effective migration of the printing fluid.

A further object of the invention is to provide an improved process and apparatus for printapparatuses have generally proved satisfactory, it

Thus, it has been found that, in general, blues will migrate or transfer freely with a given potential gradient of the electrostatic field, whereas yellows move less freely, particularly the finer particles comprising the lighter tones of an image, so that there is a somewhat spotty migration or transfer. The composition of the ink or other fluid employed, of course, greatly affects the ease of migration and, while, as stated above, generally blues migrate more freely than yellows, the degree of migration depends upon the solvents, the nature of the particles used for color, and/or upon other considerations. The characteristic effect where transfer is not uniform is that small specks or flecks of the print receiving material show in the areas where the migration is not completely uniform. Also, in some cases the outline of the image is not sufliciently sharp and distinct.

An object of this invention is to provide an iming by means of an electrostatic field of force wherein the printing fluid and the material which is to receive the fluid are precharged with electrostatic charges of opposite polarities before introduction into the electrostatic field which effects migration or transfer of the fluid, and the potentials creating the said electrostatic field are rapidly pulsated, thereby producing a more effective migration of the printing fluid.

A still further object of the invention is to provide an improved process and apparatus for printing as defined in the preceding paragraph and wherein the electric potentials employed to precharge said fluid and material are also pulsated.

A more specific object of the invention is to provide an improved process and apparatus for printing by means of an electrostatic field of force wherein the printing fluid and the material which is to receive the fluid are precharged with electrostatic charges of opposite polarity by movement adjacent to electrodes of an electric circuit, which is periodically rapidly interrupted, prior to introduction of the fiuid and material into the electrostatic field which effects the migration or transfer of the fluid, the said electrostatic field being created between spaced electrodes connected in an electric circuit which is also periodically interrupted, thereby pulsating the said electrostatic field.

A still more specific object of the invention is the provision of an improved apparatus as defined in the preceding paragraph and wherein means are provided for varying the speed of interruptions in the electric circuit providing the said electrostatic field and/or in the circuit providing the said precharge potentials.

The invention further resides in certain novel steps of procedure, features of construction and combination and arrangements of parts of the apparatus, and further objects and advantages thereof will be apparent to those skilled in the art to which the invention pertains from the following description of a simplified form of apsuitable manner.

3 paratus, and the present preferred embodiment thereof, as utilized in eilecting the method; the invention being described with respect to the accompanying drawings in which similar reference characters represent corresponding parts in the several views and in which:

Fig. 1 is a diagrammatic 'viewof a printing couple disclosing a simplified form of an apparatus embodying the invention and by means of which the process can be effected;

Fig. 2 is a sectional View through the circuit in terrupting or pulsating switch shown in Fig. 1, the view being taken substantially cnthe section indicating line 2-2 oiFig. 1;

Fig. .3 isa diagrammatic view of a printing fcouple disclosing the present preferred form of apparatus embodyingthe invention and by means of which .the process can be effected.

In Fig. lthere is diagrammatically illustrated aprinting couple comprising a moving imagecarrying member l shown in the form of a cylim der, the wall of which is a thin section. This cylinder is rotatably mounted at its opposite ends on and insulated from tubular supports 1 i carried by theframe of the printing couple and extending into the cylinder. Th inner ends of the supports H are surrounded by and support an insulating sleeve l2, extending substantially the length of thecylinder, and having connected thereto radia'lly extending parallel, but spaced apart, bars l3 which may be formed integral with the sleeve 12 and have their free ends adjacent the inner circum f erence'of the cylinder iii. An insulating sleeve l4, extending through the cylinder, is mounted within the tubular supports H and its opposite ends project beyond the frame, the said -said Patent 2,408,144 to which reference may be had for further details of the construction since it forms no part of the present invention.

A discharge element or electrode is contained in the-cylinder l0 and is here shown in the form of a blade I5 extending longitudinally of the cylinder and located in the space between the insulating bars 13 being supported therein in any 7 The inner end. of the blade it is electrically connected to a wire or cable H, a portionof which extends through one of the compartments within the insulating sleeve 14, the other portion of the wire being lead externally of the cylinder at an end thereof, as disclosed in my said Patent 2,408,144. The outer end of the blade I6 is adjacent the inner circumference of the cylinder but spaced therefrom and, the mounting of the blade within the bars is preferably such as to permit adjustment of this space to thereby vary the width or gap of the electrostatic field hereinafter described.

It will be understood that the cylinder I8- is provided on its exterior with image areas and non-image areas and that the image areas may be inked by any suitable means; for example, by inking rollers l8 and I9, while the non-image areas will not have ink applied thereto as is well known in the art. The cylinder may be adapted for intaglio, planographic, relief, or other types of printing, the image areas of the cylinder being such as to allow passage of electrostatic fields of force therethrough and the type of inking means employed will, of course, bein accordance 4 with the type of printing the cylinder is to per form, as is well known in the art.

A second cylinder 2 01s rotatably supported adjacent theimage cylinder 10 to provide a support for the print receiving material M in the printing zone, the space between the cylinder being sufficient to allow passage of the material M without appreciable pressure thereon.

The cylinder 20 is preferably formed of conductive material and is rotatably supported upon, and insulated from, the frame of the printing press in the same "manner asis theimage cylinder or element [9.

posed an electrode in the form of a longitudinally extending blade ZLsimilar to the electrode or blade i6, and constituting the attraction element of the electrostatic field for the printing apparatus. V

The bladezl is connectedby a Wire or cable 22 in a circuitproviding electrical energy for creating and electrostatic field of force at the printing or fluid transfer zone between the discharge element l6 and the attraction element 2|. This electric circuit comprises a source of highp-otentil direct current, generally designated 23, and which in the illustratedform includes a transformer T, the primary 24 of which'is connected to alternating power supply lines Li and L2. The

jtrans'former T is provided with a main secondary winding'25 the ends of which areconnected to the platesof rectifier tubes 26 and 2?; the filaments of which are energized from a second secondary winding 28. The secondaries 25 and 28 of transformer T are each provided with central taps 29 and 30, respectively, to which are connected wires 3| and 32 constituting the output of the power supply unit 23. There is thusprovided a conventional transforming and rectiiying'device capable of producing ahigh potential, low amperage current. The wire 3| is connected to, the wire 22 which is in turn connected'to the attraction element 2!, while the wire 32 is connected, as hereinafter described, tothe discharge element 16, thereby providing ,a potential gradient between the discharge and attraction elements for producing anelectrostatic field of force therebetween. This electrostatidfield of force defines a printing or fluid transfer zone since it acts upon the ink or other fluid supplied'to the image cylinder I0 to efiect transfer of that fluid on the image areas'to the materialM as the "latter and the image areaspass through the fieldof force between the'discharge and attraction elements. It will be understood thatthe material M is moved by means, not shown but which are disclosed in my prior patents, in timed relation with the rotation of the cylinders I0 and 20.

As mentioned above, it has been found that all inks and other printing fluids do not readily migrate completely when subjected to the same electrostatic potential gradient'and that it is therefore necessary to" vary the potential'gradient in accordance with the'type of ink or otherfluid employed. Therefore, the wire Ii, which is connectedwith the discharg element H5, is connected with the movable arm of a rheostat the stationary portion of which is in turn connected, as hereinafter described, to the wire 32. Conse quently, by varying the setting of the rheostat33, the potential gradient or the strength of thefield of force between the discharge and attraction electrodes may be selected in accordance with the type of fluid and/or the print receiving material employed for printing.

It has been further found that even with relatively high potentials certain fluids do not readily transfer or migrate completely when passed through the electrostatic field of force. However, it has been further found that these fluids can be readily migrated or transferred at a given potential or strength of field if that field be pulsated rather than maintained at a constant potential gradient. In addition, fluids which can be relatively easily transferred at a given constant potential gradient may be more effectively transferred at that potential 01' even at a lower potential gradient when the potential gradient or strength of field is periodically varied or pulsated. Therefore, the circuit for applying elec trical energy to the electrodes l6 and 2| for the electrostatic field of force is, in accordance with this invention, periodically pulsated or interrupted. This is effected by connecting the rheostat 33 to a brush 34 which cooperates with one portion of a rotatable pulsating switch or commutator 35, a second brush 36 cooperating with another portion of the switch or commutator 35 being connected to the output terminal 32 of the power supply 23.

The rotating pulsating switch or commutator 35 may be constructed in any desired manner for effecting circuit interruptions when the member is rotated. As here illustrated, however, the member 35 comprises a substantially cylindrical body of insulating material 31 which has a con tinuous cylindrical band 38 of electrically conductive material adjacent one end thereof, this band being provided with diametrically opposed projecting portions 39 and 40 projecting longitudinally with respect to the insulating material 31 on opposite sides thereof. The brush 34, as will be seen in Fig. 1, cooperates with the portion of the switch member 35 provided with the longitudinally extending projections 39 and 40, while the brush 3!; rides continuously upon the cylindrical portion or band of the conductive member 38. Consequently, as the switch or commutator 35 is rotated, the circuit to the electrodes [6 and 2| is made and broken twice during each revolution of the rotating switch or commutator member. It will be readily apparent that the switch or commutator member may be otherwise constructed to provide for one, or any desired number of circuit interruptions, during each revolution thereof.

The rotating member or switch 35 is connected with the armature shaft of a motor 4| which is of the variable speed type energized through power supply lines 42 and 43. The speed of the motor 4| may be varied in any conventional manner but is here illustrated as employing a rheostat 44 in the power supply lead 43 to thereby vary the strength of the electrical energy supplied to the motor and thus alter the rate of rotation. By adjusting the rheostat 44, it will be apparent that the number or frequency of circuit makes and breaks may be varied so that the rate of pulsation or interruption of the electrostatic field of force may be readily selected for a given type of fluid employed with printing. That is to say, having determined the electrical properties of a fluid to be utilized, the settings of the rheostat 33 and the rheostat 44 are then effected to provide a potential gradient of proper value for that fluid and circuit interruptions at a frequency most advantageous for transfer of that fiuid. In view of the great variety of printing inks or other fluids utilized, it will be readily apparent that a list of the potentials and frequencies employed would exceed practical limits for inclusion in this application.

Connected in parallel between the output wires 3| and 32 are a plurality of electrical condensers 45. These condensers serve to eliminate the ripple in the electrical energy, provided by the power supply 23, and to maintain the potential difference or gradient applied to the discharge and attraction elements l6 and 2| at a predetermined constant value for a given setting of the rheostat 33 at all times when the circuit thereto is closed. Consequently, the electrostatic field comprises repeated pulses or impulses at substantially full potential separated by intervals at zero potential through action of the switch 35 as it repeatedly closes and opens the circuit.

It should be noted at this point that the spacing between the discharge and attraction electrodes I6 and 2! and the maximum potentials applied thereto are at all times such that no sparking therebetween is effected nor is there any corona or similar current discharge occurring between the electrodes.

An explanation of why the pulsation or interruption of the electrostatic field of force effects more complete transfer or migration of the fluid to the printing material is beyond the scope of this application, but it is believed that the effect is similar to that which is evidenced by the mechanical analogy of striking the interior of a cylindrical member with repeated hammer blows to dislodge material clinging on the exterior thereof. Be that as it may, repeated tests have shown that, for a given potential gradient of the electrostatic field and a given type of printing fluid, the fiuid is more completely transferred to the print receiving material and sharper image outlines are secured upon the print receiving material when pulsation or circuit interruption of the electrostatic field is utilized.

While one simplified form of an apparatus for pulsating the electrostatic field of force for effecting the transfer or migration of the fluid to the print receiving material has been disclosed, it will be readily apparent that numerous means other than the specific circuit arrangements heretofore illustrated and described may be employed for effecting the same result. For example, if a source of sufiiciently high potential direct current be readily available, the power supply 23 can, of course, be omitted. Moreover, means other than the motor driven switch or commutator 35 may be employed for interrupting or pulsating the electrostatic field. Likewise, the printing apparatus illustrated in Figs. 1 and 2, and described with respect thereto, may be employed with electrical precharge of the printing fluid and/or the print receiving material prior to their introduction into the electrostatic field or printing zone and this electrical precharge may itself be pulsated in a suitable manner; for example, similar to that utilized for the transfer field above described. Furthermore, in certain instances, it has been found that the electrical characteristics of the fluids employed are such that they move more readily in one direction in an electrostatic field than in another; that is to say, certain inks or other fluids are self-ionized or more readily receive charges of one polarity, whereas other fluids or ink are ionized or more readily receive charges of an opposite polarity. Therefore, provisions may be made for readily reversing the polarities of the potentials-applied to the dis;- chargeand attraction elements and similar pro visions may be made for the precharge circuit or circuits when the latter are employed.

A present preferred form of an apparatus constructed in accordance with the invention and. capable of performance the method thereof is illustrated in Fig. 3. This form of the apparatus, in addition to pulsation of the transfer electrostatic field, includes the electrical precharge of the ink or fluid and of the print receiving material, pulsation of these precharges and provisions for reversing the polarities of the precharge and transfer potentials as suggested above.

The apparatus illustrated in Fig. 3 is provided with an image cylinder 46 which is constructed and supported in the same manner as described above with respect to the image cylinder H! of Fig. 1. This cylinder is likewise provided with a discharge electrode- 41 similar in nature and construction to the electrode l6 of Fig. 1 and ink or other fluid is supplied to the cylinder 45 by inking rollers or other similar means 48 and 49 corresponding with the inking rollers 18 and i9 previously described. Also, the print receiving material M, corresponding with the material M in Fig. 1, is supported within and moved through the printing zone in the same manner as in Fig. 1, a cylinder 50 corresponding with the cylinder 20 being provided to support the material in the printing or transfer zone. The cylinder 50 has an attraction element 51 therein, corresponding with the attraction element 2| of Fig. 1, so' that an electrostatic field of force may be established extending through the image portions of the W1- inder 46 and the print receiving material M in the same manner as in the form of the device previously described.

In addition to the transfer electrodes, the instant apparatus is provided with precharging electrodes 52 and -53 for respectively precharging the printing fluid and the print receiving material before these are moved adjacent eachotherinthe printing zone between the discharge and .at-tractionjelements or electrodes MI and 151:. Ifhe electrode 52 preferably comprises a "curved member, substantially concentric with the image cylinder 46 and -adjacent the surface of the latter but spaced therefrom, the concave surface .of the electrode being preferably provided with a .plura'lity of projections :01 points 54. 'The electrode 53 extends transversely of the :printreceiving material M andsubstantially parallelztherewithrathe lower surface of this member likewise being provided with projections or points 55 adjacent :to but spaced from the print receiving material.

In the instant formcf the apparatus, electrical energy for the 'transfer'and precharge potentials is preferably provided .by independent circuits, each connected with a power supply source 356 of conventional type available on the :market for converting alternating current to high .potential, low amperage direct current. In the form of the power supply shownyalternating. currentis suppliedthereto through the power-supplylines 51, 58*and 59 while two-separate direct current outputs :are provided by the .wires :61), 1.81 and B2, "63. The .unit 56 preferably includes separate adjustable potentiometers qor rheostats 64 and 65 for varying the voltage output of the separatecircuits connected with theoutput leads 60, 6! and 62, 63. Likewise, separatevoltmeters 66 and -91 are provided toindicate theivoltage supplied to these separate circuits and lights 68 and ts may. be provided to :1 indicatei-thattthe correjspondhig portions or the power supply are in operation.

The power output lines .50.. and. GI e con: nected with the movable blades of a reversing switch 10, one of the stationary terminals of the switch being connected with a wire 1| and the corresponding other stationary terminal being connected with a wire 12, these connections be: ing adapted to be reversed by operation of the switch The wire 1| is connected with a brush 13 cooperating with a circuit interrupting switch or commutator 14, similar to the previously described switch or commutator 35', the brush 13 riding upon the portion of the switch or commutator provided with the spaced conductive portions. Also cooperating with the switch or commutator 14 is a brush running upon the continuous conductive portion of the switch or commutator. The brush 15 is connected by a wire or cable 16 to the attraction electrode 5| of the transfer electrostatic field while the discharge electrode 41 is connected to a wire or cable 11 which, in turn, is connected with the wire 12.

Connected in series between the wires 1| and 12, intermediate the switch 10 and the electrodes 41 and 5|, are condensers 18 and 19'. Connected in parallel with the condensers 18 and 18 between the wires 11,-. 12, intermediate switch 10 and electrodes '41, 5|, are resistances and BI. In.- termediate the resistances 80 and BI is connected one end of a wire 82, the other end of which is connected between the condenser 18, 19. The switch or commutator I4 is connected for rota, tion by a motor 83 energized from power supply lines 8 1, '85. The motor 83 is of the variable speed type, the speed of which, and. hence the speed of .the switch 14, being varied "by means .of a .rheostat 188 provided in the power supply line 85 for the motor.

It will be apparenttherefore, that an electrostatic potential gradient is established between the discharge electrode .41 and the attraction electrode 5.1 which potential gradient is periodically pulsated .or interrupted by rotation of the switch or commutator 1.4, the frequency of the pulsations or interruptions being selected, in ac.- cordance with the nature of the fluid to be trans.- ferred, by adjustment of :the rheo'stat 86. More..- oyer, the potential of the energy supplied to the electrodes 41'! and '51 may be .varied .by operation of the potentiometer or .rheostat 6.4. Consequently the circuit thus far described, with the switch 10 set in one position thereof, operates as previously described for :the circuit in Fig. 1, it beingwunderstood that the condenser :18, 19 and the resistances 8. U, 81 correspond in function to the condensers '415 inthe previously described circuit, the purpose of :the resistances .80, 81 being to provide a small bleed current as .is well known in the-electrical .art. The direction 1 of ithe potential gradienhi. e., thep'olarities of thei trans fer'electrodes '41, -5l, may be readily \reversed by simply throwing the switch "113 to its.othe'r position thereof, thereby enabling-the apapratus to be utilizeddor transfer of fluids whichsmorerea'dily migrate 111M181 influence :of an gelectr'os'tatic .fleld whose potential gradient -.is reverse to that-utilized with fluids of-ydifferenteleotrical characteristics.

'In addition .to.the features of .thecircuit described in Fig. 1 and .which areiincorporated in the'instantytransfer circuit, a voltmeter- 81 may be provided 1 between .the wires 1 I an'd ll to indicate .the -:potential's applied between the elec trodes 41 and Also, an ammeter 88 may be inserted between the wires I2 and TI to indicate the current flowing in the circuit through the bleeder resistances 89, 8|, a switch 99 being preferably bridged about the ammeter 88 to short circuit the latter when indication of the current flow is not desired.

The electrical energy for effecting the precharge of the fluid and of the print receiving material is substantially identical with that described for providing the potentials for the transfer electrostatic field. Thus, the power output wires 92, 63 are connected with the blades of a reversing switch 99, the stationary terminals of the switch being in turn connected with wires 9I and 92 so that the switch is effective to reverse the connections of the wires 62, 93 to the wires 9i, 92 as will be readily understood. The wire 9i is connected with a brush 93 riding upon the continuous conductive portion of a reversing switch or commutator 94, similar to those designated 35 and I4. The switch 94 is driven by a variable speed motor 95, the speed of rotation being preselected by a rheostat 99 connected in one of the power supply leads 91, 98 for the motor. A second brush 99 rides upon that portion of the switch or commutator 94 which is provided with the spaced conductive portions, this brush being connected by a wire I99 with the previously mentioned electrode 53 for effecting precharge of the print receiving material M.

The wire 92 is connected to a wire IIJI with an 'ammeter I92 interposed therebetween, the ammeter being normally bridged by a switch I93. The wire IIJI isin turn connected with a wire I94 connected to the precharge electrode 52 for precharging the fluid upon the image cylinder 46. Between the wires 9| and IN are connected the condensers I95, I99 and resistances I91, I08, these elements being connected in the same manner and serving the same purpose as the corresponding condensers and resistors I8, "I9, 89 and M in the transfer circuit. Likewise a voltmeter I99 may be connected between the wires 9| and I9I to indicate the potential applied in the precharge circuit in the same manner as does the voltmeter 81 for the transfer circuit.

' It will be apparent, therefore, that with the reversing switch 99 in one position thereof, the precharge electrode 52 for the fluid will be provided with an electrical charge of one polarity while the precharge electrode 53 for the sheet or web material M will be provided with an electrical charge of opposite polarity. By reversing the position of the switch 99, the polarities applied to the precharge electrodes 52 and 53 may be reversed. In all cases, however, the polarity of the charge upon the precharge electrode 52 should correspond with the polarity of the discharge electrode 41 and. the polarity of the charge upon the precharge electrode 53. should correspond with the polarity of the attraction electrode 5!. In other words, when one reversing switch 19 is actuated to a different position to alter the potential in the transfer circuit, the reversing switch 99should likewise be actuated to reverse the polarities in the precharge circuit. If desired, the switches I9 and 99 may be ganged together so that both are actuated simultaneously as indicated in my aforespeed of these interruptions may be varied by adjusting the setting of the rheostat 98 controlling the speed of rotation of the motor and hence of the switch or commutator 94. Likewise, the value of the potentials applied in the precharging circuit may be adjusted or varied by altering the setting of the potentiometer or rheostat 65. The speed of pulsation or interruptions of the precharge potentials need not be the same as that employed in the transfer potential circuit an will be selected in accordance with the characteristics of the particular fluid or fluids employed. In certain cases, pulsation of the precharge circuit may be eliminated and a steady potential employed. This may be readily effected by deenergizing the motor 95 and positioning the switch 94 so that both brushes 93, 99 rest upon conductive portions of the switch or commutator 94.

The method of this invention and the mode of operation of the apparatus herein described should now be fully apparent. By way of brief recapitulation, however, it may be mentioned that printing upon sheet or web material is effected by passing the latter through a printing zone in which a pulsating electrostatic field of force extends through the image and the print receiving material. The image and print receiving material are moved simultaneously, in register, by suitable means rotating the image cylinder and the supporting cylinder, such as I9, 29 or 46, 59, in timed relation with the operation of the driving means for the print receiving material and ink or other fluid for reproducing the desired image is supplied to the image cylinder I9 or 46, as the latter rotates, by suitable means such as the inking rollers diagram matically illustrated.

As the image cylinder is rotated after having received a supply of ink upon the image areas, this ink receives a precharge of predetermined polarity and intensity as it moves adjacent the precharge electrode 52, this precharge being received prior to the introduction of a given image area into the printing zone. Likewise, the print receiving material M receives a precharge of predetermined polarity, opposite to that of the ink and prior to introduction of a given portion of the print receiving material into the printing zone, by passing adjacent the precharge electrode 53. The precharge potentials thus applied are preferably pulsated to effect a more ready precharging of the ink and material, this pulsation bing effected by operation of the switch 94 in the precharge potential circuit. As the image cylinder and print receiving material, conditioned by precharge of the inked image areas and precharging of the print receiving material, pass in register through the transfer or printing zone, the electrostatic field of force between the transfer and attraction electrodes, such as 41 and 5I, causes migration or transfer of the ink or other fluid to the material, this migration being effectively and completely achieved by pulsating the transfer potential through operation of the pulsating switch or commutator I4.

The potentials employed for effecting transfer of the ink or other fluid at the printing zone, and for precharging of the ink and print receiving materials, are selected in accordance with the characteristics of the paritcular ink or other fluid utilized. These potentials, however, are at all times less than the values which would produce sparking or corona discharge between the transfer electrodes 41 and 5| for a given spacingv ll therebetween. Likewise, the precharge potentials are selected in accordance with the nature of the fluid-and print receiving materials employed and these potentialslikewise are lessthan thoseproductiveof sparking or corona discharges.

The-speed of:pulsation or interruption of the precharge and transferpotentials is preselected in accordance with the-known characteristics of the printing fluidandthe'print receiving material employed and thisvspeed'will, of course, vary for different types'of inks orother fluids. The polaritiesof the precharge'and transfer potentials areireversed'wheneverthe-nature of the ink or Othertfiuid; requires .this action, it being remembered. that the transfer. and precharge potentials must be'simultaneously, reversed.

:As mentioned be'foreythe condensers such as 18,151,, t05.-and.:lB61provide-alow. impedance path for the ripple in the direct current output of the power :source 56 as well as providing anenergy storing system .for maintaining constant voltageoutput. The resistors such as 180,1, I01, I68 provide a bleed .or constant-flower current of smallamperage to-serve as a constant fixed load. The :regulation-of the power supply is thereby improved and the voltageris maintained'at a substantially constant value. Consequent ly, the transfer and-prechargepotentials applied to the severalprechargeand. transferelectrodes when the switches 14, M are; in. circuit closing relationship are always at full value i and 1 potentials at" these electrodes sharply drop to raero when the circuits are interrupted .by operation of the-switches =14 and .84, Etheelectrodes againbeing restored substantially simultaneously to full potential when .theswitches 1-4 and .84 .move to circuit-making positions during theirrotation. Therefore, sharp pulses of electrical potentialiare.appliedto both the.transfer and precharge electrodes with the result thatthe printing fiuidand-print. receiving material aremcre effectively precharged and the fluid is substantially completely migrated .or transferred in the printing "zone thereby producingsharper and better definediimages upon the material and. elimination. of the .fleck-s or. specks of the material which heretoforesometimes ap' peared in the image. areas when. steady potentials were "employed, in the printing or transferzone.

..As will be understood by .those skilled in the art, ,theterm image and related terms as used heretofore in the specificationand'hereinafterin thesubjoined claims includes words, j letters, delineations, drawings, pictures, illustrations and the'like which may bereproduced on the print receiving material from relief,.intaglio, planographic or any otherknown type .of printing member and that such termsare used as embracing any of these items or any combination thereof. It willlbe also understoo'dthat the term ink or "'iluid employed in this application is intended to ,refer to inkin the ordinary sense and also to any other substance, such .as solid material suspendedinliquidsor gases, or'any other substance which maybe employed in reproducing in .color, or otherwise, on print receiving material an image carried bytheprinting member of aprinting apparatus.

While the method of this inventionhas been described with reference vto'the manner'in which it may'bepracticed with. two specific forms of apparatus, it will be readily apparent that the method is capableofuse with other .types of apparatusfthan those'herein shown and described. Likewise, the detailsof the .specific'formsofapparatus herein illustrated and describedmay be variedby those skilled in'the art Without depart- 12 ing from "the spirlt of the invention. Therefore, it is to be understood thatthe detailed description and illustration are solely for the 1 purpose ofccmplete disclosure of the nature ofthein vention "and are not intended as limitations thereon.

Having thus described the invention,'I claim:

.1. The method iofzprinting'sccmprising providingxa printing element having. an image thereon whichisito be reproduced, providing a film of the printing'liquid upon said image, creating a high potential unidirectional :cyclically pulsating .electrostatidfield .of' force extending through said image .atca printing .zone, 5 and bringing the: material LWhlCh. is :to .receive csaidimage closely adjacent said element in.. said"pulsatin'g .field 'TOf force at the printing zone .LSO that .Ethe electrostatic charges of the ifield offorce e'fiecttransfer of the. liquidon said: lmagetosaidmaterial thereby reproducing the. image on the material.

.2. Thermethod :as definediinzclaim land further comprising: prechargingsaid film .of printing liquid and esaid material with unidirectional electrostatic charges of opposite polarities 'from a source of cyclically pulsating unidirectional electrical energy 1 prior to. bringing "the saidfilm and material adjacent :eachaother in said pulsating fieldofforce at said printing zone.

13. In a .printingapparatus, animage carrying member adapted .toihave printing relationship with printrreceiv-ing.materialat'a printing zone, means for inking i the image on said member, means :for impressing an electrical prechargeof certain polarity onsaid ink, prior to the member and the .material being brought into {printing relationship at the printing :zcne, means for imparting an electrical f precharge of opposite p0- larityon the-printireceiving material before the latter is introduced into the printing zone means for supporting the print receiving material in printing; relationship to-said member in the printing zone, and means for creating at the printing zone anelectrostatic-field-of force extending from said member through said material, the lastmentioned means-comprising-a pair of spaced electrodes, a source-.ofhigh potential direct-current, a circuit eonnecting said source to said electrodes, a rotary switch in said circuit adapted to repeatedly makefandibreak -said circuit when rotated, and :means for rotating said switch whereby the said electrostatic field is cyclically pulsated and the potentials of .said pulses are substantially constant.

4. .The' combination as defined. in claim 3 and further comprising .means to vary the speed of said means for rotating said switchwherebyithe rateiof pulsation of -.said electrostatic .field may be varied.

5. The combination. as defined in claim. 3 and wherein .the .means to precharge said .ink and the meansto prechargesaidrmaterial each comprise .an electrode respectively adjacent said member in advance ,ofsaid printing .zone and adjacentsaidmaterial in .advance 7 of said printing zone, ..and means supplying the two .last-. mentioned electrodes with cyclically pulsating unidirectional electric ,potentlals 01 opposite .polarities.

,6. The combination as deflnedin .claim 3 and wherein .the vmeansto.precharge said ink. and-the means to .precharge said material .eachcomprise an electrode respectively adjacent saidimember in advance of.said printing zone and adjacent said material in .advance .of said printing zone, means supplying the .two last-mentioned electrodes with cyclically pulsating unidirectional electrical potentials of opposite polarities, and means to vary the frequency of the pulsations of said precharge potentials.

WILLIAM CARL HUEBNER.

References Cited in the file of this patent UNITED STATES PATENTS Number Wintermute Nov. 12, 1940 Number 10 Number Name Date Carlson Nov. 19, 1940 Amstuz Dec. 3, 1940 Huebner Dec. 10, 1940 Huebner Sept. 24, 1946 Huebner Oct. 4, 1949 Huebner Apr. 3, 1951 FOREIGN PATENTS Country Date Great Britain July 14, 1948 Great Britain Aug. 4, 1948 Great Britain of 1948

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