US3673599A

US3673599A - Electrostatic printing apparatus

Info

Publication number: US3673599A
Application number: US59196A
Authority: US
Inventors: Takao Tagawa
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 1969-08-01
Filing date: 1970-07-29
Publication date: 1972-06-27
Anticipated expiration: 1989-06-27
Also published as: JPS4923213B1

Abstract

The printing apparatus has a new type of cathode ray tube which utilizes electrostatic charge deposition. The tube contains a single continuous dielectric plate which forms its face plate. Charges are deposited only on a portion of the dielectric plate where the electron beam strikes and then transferred through the air gap from the dielectric plate to paper by a means of discharge caused by potential difference across the air gap.

Description

United States Patent Tagawa June 27, 1972 [54] ELECTROSTATIC PRINTING APPARATUS inventor: Takao Tagawa, Osaka, Japan Assignee: Sharp Kabushiiti Kaisha, Osaka, Japan Filed: July 29, 1970 Appl. No.: 59,196

Foreign Application Priority Data Aug. l, 1969 Japan ..44/6l809 U.S. Cl. ..346/74 CR, l78/6.6 A, 346/74 ES Int. Cl ..G03g 15/00, H04n l/30 Field of Search .346/74 CR, 74 ES, 74 ESX;

[56] References Cited UNITED STATES PATENTS 3,001,849 9/196] Walkup ..346/74 CR Primary Examiner-Howard W. Britton Attorney-Flehr, Hohbach, Test, Albn'tton & Herbert [57] ABSTRACT The printing apparatus has a new type of cathode ray tube which utilizes electrostatic charge deposition. The tube contains a singlecontinuous dielectric plate which forms its face plate. Charges are deposited only on a portion of the dielectric plate where the electron beam strikes and then transferred through the air gap from the dielectric plate to paper by a means of dischargecaused by potential diflerence across the air gap.

6 Clains, 8 Drawing Figures PATENTEIJJuIm I972 SHEET 10F 3 I *l'I'I I SECONDARY EMISSION RATIO ELECTRON ENERGY (v INVENTOR. TAKAO TAGAWA BY 3%, m 'a/ W ATTORNEYS PATENTEDmzv 1972 saw 2 or 3 1 zs IIIII1!AIWII% 24 25 v 23 VOLTS DISCHARGE VOLTAGE (v) I l O 20 30 MICRONS INTERVAL (t) I k\\\ & 32 1 V///// 24 L\\\\\\\ x\\\ t 24 23 E FIG 6 23 25 I INVENTOR. F/ 5 BY TAKAO TAGAWA WWW ATTORNEYS PATENTEDJUMN I972 3,673,599 SHEEI 3 OF 3 TAKAO TAGAWA ATTORNEYS INVENTOR.

ELECTROSTATIC PRINTING APPARATUS BACKGROUND OF THE INVENTION This invention relates to an'electrostatic printing apparatus, and more particularly to an improved apparatus including a cathode ray tube which utilizes electrostatic charge deposition.

Several methods for depositing charge patterns at high speed have been developed. Perhaps the simplest method is to utilize electrostatic charge deposition. These developments depend greatly on the appearance of a new type printing cathode ray tube. The cathode ray tube, socalled pin-tube has a face plate penetrated by an array of many fine pin electrodes. The printing tube beam is density-modulated by the signal and scans the inner ends of the pin electrodes in the tube. The latent charge pattern is formedon the recording paper moving in the front of outer ends of the pin electrodes. The tube permits rapid recording, because horizontal scanning is achieved by the electron beam.

The printing tube is therefore being used in high speed facsimile equipment, in phototelegraphy equipment, in oscilloscope output printers and in computer Output printers.

The tube has further wide application in systems where high speed, remote print-out or local reproduction of copy is required.

However, the printing tubes of the above type suffers from various disadvantages. A single row of close-spaced fine pins must be embedded into the face plate with high accuracy and furthermore the individual pins in the tube face must be electrically isolated by the embedding medium. Such a pin head is expensive because of difficulty in manufacturing. For exam ple, about 2,000 pins each having a diameter of about 25 microns must be positioned on the tube face at interval of about I microns.

A capacitive exists unavoidably between two conducting pins or between a pin and ground. Because of capacitive coupling charges on one pin are transferred to a neighboring pin and thus interference occurs in the charge pattern. The voltage on the pin is represented by V=Q/C (where; Q: charge on pin, C: capacitance of pin) and therefore in order to improve the sensitivity for recording the quantity of charge should be large and the value of capacitance small. On account of the parasitic capacitance the quantity of charge should be larger than the conventional case. The electron beam is used asa high-speed switching element to charge selected pins of a close-spaced pin array. The above parastic capacitance reduces the speed of switching. In addition, the resolution of the printing tube is poor since charge patterns are discontinuous due to the discontinuous form of the pin head. It is also difficult to design the electron gun in such a way that the electron beam may equally strike all of the discontinuous pin array.

OBJECTS AND SUMMARY OF THE INVENTION Accordingly, the primary object of this invention is to provide an improved electrostatic printing apparatus which avoids one or more of the disadvantages and limitations of the above conventional apparatus.

Another object of this invention is to provide an electrostatic printing apparatus having the simplest tube construction.

Still another object of this invention is to provide an electrostatic printing apparatus wherein the tube target has a continuous form.

A further object of this invention is to provide an electrostatic printing apparatus in which the printing tube possesses a continuous target member not having the parasitic capacitors.

It is still a further object of this invention to provide an electrostatic printing apparatus which has a good resolution and a high speed of switching.

Another object of this invention is to provide an electrostatic printing apparatus in which the quantity of charge required is reduced. An additional object of this invention is to provide an electrostatic printing apparatus in which the electron beam scanning can be achieved with ease.

In summary, this invention refers primarily to improved electrostatic printing apparatus which comprises a cathode ray tube including an electron gun, an electron scanning means and a continuous target member which is composed of a single dielectric material, the continuous target being scanned by electrons from the electron gun so that charge is deposited only on a portion of the target where the electron beam strikes, a dielectric recording sheet running in the front of the continuous target, and a gaseous gap between the continuous target and the recording sheet, through which the charge patterns on the continuous target are transferred to the recording sheet by means of discharge.

In order to achieve these objects, the apparatus of this invention uses a single continuous dielectric plate as a target instead of the conventional array of conducting pins. The electrostatic charge deposition of this invention is therefore accomplished by an unique mechanism differing from the case of using conducting pins. In apparatus of this invention, charge caused by electron impact is deposited only on a portion of the inner surface of the target plate, and is not conducted to the outer surface. A potential on the charged target portion becomes negative (or positive) so that it produces a potential difference across the gaseous gap. When such potential difference is greater than the discharge voltage, discharge takes place across the gaseous gap. Negative (or positive) charge produced by discharge attaches to the dielectric sheet of the recording paper. Thus, the gaseous gap is essential to a charge transport mechanism in this invention apparatus. It should be noted that the use of the dielectric target obviates the need of isolation bet ween the individual pins and prevents parasitic capacitance.

Further details will be apparent from the following explanation of examples of embodiments of this invention with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of the electrostatic printing apparatus and its operation connection in accordance with this invention.

FIG. 2 is a graph showing a characteristic curve'of secondary-emission ratio N to electron energy Ve reaching the target in the printing tube.

FIG. 3 is an enlarged sectional view showing the relative position relationship between the target surface and the recording paper in the printing tube.

FIG. 4 is a graph showing a characteristic curve of the discharge voltage V to the distance r in the printing tube.

FIG. 5 is an enlarged sectional view showing an improvement of this invention.

FIG. 6 is an enlarged sectional view showing another improvement.

FIG. 7 is a schematic diagram showing the whole printing system including a developing and a fixing means.

FIG. 8 is a schematic diagram showing a variation of that shown in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A cathode ray tube 10 for depositing latent electrostatic images on the recording paper is schematically shown in FIG. 1. As in a conventional cathode ray tube, the printing cathode ray tube 10 has in its neck an electron gun that directs a focused beam of electrons onto a face plate at the opposite end of the tube. As is commonly known, the electron gun contains cathode 11, control grid 12, screen grid 13 and focusing electrode 14. The anode 15 is coated with conducting material called aquadag coating. The cathode 11 for emitting the electron beam is placed at one end of the tube and it holds a negative potential with respect to the anode 15.

The intensity of the beam is modulated in response to signals such as video signals and computer output signals, which are applied to the control grid 12. First biasing source 16 is connected between the cathode l1 and the control grid 12 so that the control grid 12 is more negative than the cathode 11. The printing input signal from the source 17 may be applied to either the control grid 12 or the cathode 11. The screen grid 13 connected with the second biasing source 18, is several hundred volts more positive than the cathode 11 and thus serves to accelerate electrons emitted from the cathode 11. The potential of the focusing electrode 14 is held at a potential more positive than the cathode 11 which is of sufficient value to focus the accelerated beam by means of third biasing source 19.

A pair of electrostatic deflection plates 20 are placed around the path of the electron beam and serve to sweep the beam over the face plate, thereby causing the beam to trace on the face plate. Differing from the conventional tube, it provides only horizontal deflection for the electron beam. The pair of electrostatic deflection plates are, of course, connected to a saw-toothed potential generator not shown. A known blanking circuit is attached to the generator. The deflection means may be either electrostatic deflection plates or electromagnetic deflection coils.

The printing tube 10 has in its face plate a slit 21 along the horizontal line of the tube. The target member 22 which plays an important role in this invention is mounted on the outer surface of the face plate, covering the slit 2]. The target 22 is composed of a single continuous dielectric or high resistivity material having a typical value of about 10 ohm-centimeters in resistivity. It is desirable that the resistivity of the target material 22 is in a range from about ID to about 10 ohmcentimeters. These materials are rare. There is no standardized classification for distinguishing between the dielectric and the semiconducting materials. In a certain classification, the dielectric material is defined as a material of about l to l0 ohm-centimeters and the semiconductor material as that of resistivity less than ohm-centimeters. For purposes of this invention, the dielectric material will be defined as a material which may be included in a range from about 10 to about 10 ohm-centimeters, adding to the above mentioned range. Charges are deposited only on a portion of the dielectric surface during the time that the target 22 is receiving electrons from the beam.

Since it is desirable that the charge on the target 22 should disappear as soon as possible after recording is finished, it is advisable to impart some conductivity to the target 22. These materials with a resistivity of about 10" to 10 ohm-centimeters satisfy this requirement by themselves. However, in case of materials having a resistivity more than 10 ohm-centimeters, conductivity is insufficient for this requirement and thus some conductivity should be added to these dielectric materials. For example, the inner face of the target 22 is painted with material having a resistivity of about l0 to 10 ohm-centimeters such as chromic oxide including graphite.

. The target 22 has a thickness of approximately I00 microns. The electrostatic recording paper 23 is laid at a distance I (microns) from the outer surface of the target 22. The electrostatic recording paper 23 contains a dielectric sheet 24 which lies on a conducting base 25. Commercially available recording paper can be used for purposes of this invention. A gap between the target 22 and the recording paper 23 establishes an air layer 26. The gap layer 26 may be swept with a dischargeable gas instead of air. A grounding plate 27 always contacts the conducting base 25 of the electrostatic recording paper 23 and holds the potential of the conducting base 25 at the earth potential or near to the earth potential.

Anode is so grounded as to be held at or near the earth potential. Fourth voltage source 28 is connected between the cathode 11 and the ground, so that it impresses from several kilovolts to multiples of l0 kilovolts between cathode-toanode.

In this circuit arrangement, no high voltage on the order of kilovolts is applied to the means of charge pattern deposition which includes the slit 21, the target 22 and the recording paper 23. This differs from the conventional tube for television receiver.

When a high voltage is applied between the cathode 11 and the anode 15, electrons are emitted from the cathode l 1 towards the target 22. On the way to the target 22, the electron beam is first intensity-modulated by the input signals and then accelerated and focused by

electrodes

13 and 14. The focused beam is deflected by the deflecting electrodes 20, allowing the beam to scan over the target 22. During the time that electrons are emitted from the cathode 11, the target 22 receives electrons from the beam and at this time secondary electrons are emitted from the target surface because of primary electron impact.

FIG. 2 shows a characteristic curve of secondary-emission ratio N to energy Ve of electrons which reach the target 22 in the printing tube. The secondary-emission radio N means the average number of secondary electrons emitted from a surface per incident primary electron. As can be seen from this drawing, in the case where the energy Ve of electrons reaching the target 22 is in range from the value VM to the value VN, the ratio N is larger than 1, whereas in case where the energy Ve is larger than the value VN the ratio N is smaller than 1. Therefore, if the electron energy Ve is a value e.g. VL smaller than that VN, the secondary-emission ratio N is larger than 1 and accordingly the inner face of the target 22 is charged positive. And if the electron energy Ve is a value larger than the value VN, eg. VH, the inner face of the target 22 is charged negative.

In this apparatus the electron energy Ve may be selected at either of the values VL and VII. It is better, however, to select the farthest possible value from 1 as the secondary-emission ratio N and the following will be explained in the case where the value VI-I is selected for instance.

The electrons emitted from the cathode ll reach a point over the target 22 through the focusing and the deflecting system. Since the secondary-emission ratio N is smaller than 1, the point over the target 22 is charged negative.

FIG. 3 shows an enlarged sectional view of charge deposition mechanism under the circumstances. An air layer 26 having an interval of t lies between the target 22 and the recording paper 23. The charges caused by electron impact are deposited on only a portion of the inner face of the target 22, and are not conducted to the outer face of it. In response to the charge applied on the target 22, the charged portion shows a negative value of potential. Therefore, it produces the electric fields Er, Ea and Ed respectively on the target 22, the air layer 26 and the dielectric sheet 24 of the recording paper 23. As a consequence thereof, the potential difference Va=Ea x t occurs between the recording paper 23 and the surface of the target 22 facing the air layer 26. In the case where the potential Va reaches a predetermined value, discharge occurs in the portion of air layer 26 corresponding to the charged portion of the target 22. Negative charge appears in the front of the recording paper 23 by this discharge and this negative charge is associated with the surface of the dielectric sheet 24 of the recording paper 23. It is, therefore, possible to transfer a negative charge image to the recording paper 23.

Since the dielectric layer 24 of the recording paper 23 has a high resistivity value, the charge image which is associated with the surface of the dielectric sheet 24 does not disappear even though the recording paper 23 is kept away from the target 22. Therefore, it is possible to exchange the said charge image for a visible image by using fine colored electroscopic powders (toners) with a charge opposite to the said charge image. Since a small conductivity is imparted to the target 22, the charge on the target 22 disappears quickly after recording on the recording paper 23 is finished.

FIG. 4 shows the relation ship between the discharge voltage V and the interval t. The above discharge voltage V refers to the voltage between the target 22 and the dielectric sheet 24 of the recording paper 23 parallel to the target 22. The interval t refers to the distance between the target 22 and the dielectric sheet 24.

If the interval t is small the discharge voltage V is inversely high, and further if the interval 2 is zero or nearly zero the charge pattern on the recording paper 23 becomes extremely obscure. In addition, if the interval 1 is too large the charge pattern becomes blurred. So a suitable interval is required. The inventor has found out by experiments that the suitable interval ranges from 5 to 100 microns.

The preferred embodiments are achieved under the following conditions. The control grid voltage is -30 volts, the screen grid voltage is +300 volts, the focusing voltage is +1 ,000 volts and the cathode-to-anode voltage is 17 kilovolts. The grids and focusing voltages are values with respect to the cathode.

The slit 21 has a width of l millimeter and a length of I80 millimeters. The dielectric target is a glass of the following composition; P 65 percent, Fe O 28 percent, A1 0 7.percent. The target is made with a resistivity of ohm-centimeters and a thickness of 150 microns. In the recording paper the dielectric sheet consists of acrylic resin with a thickness of 5l0 microns and a resistivity of 10 -10" ohmsentimeters, with a conducting base of a thickness of 65 microns and a resistivity of 10 -40 ohm-centimeters. The paper is laid at microns from the surface of the target. In joining the target to the face plate, the face plate is first painted with low melting point glass powder and then the target is mounted on the face plate. These members are heated at a temperature of 450 C for 30 minutes. Copy can be produced at a rate of 7 lines per millimeter in case of a paper running speed of 8.6 millimeters per second and scanning frequency of 60 Hz.

FIG. 5 shows an enlarged sectional view of an improved charge transport mechanism. The spacer 31 is allowed to contact the outer face of the target 22 and it serves to space and protect the target 22. The spacer 31 is formed with the target 22 in a body or with the dielectric tape such as Mylar tape (trade mark) stuck on the target 22 and thus the interval 26 is formed. As mentioned above, the value in the range from 5 to 100 microns is sufficient for the thickness of the spacer 31 and accordingly the recording paper 23 faces the target 22 at the required interval allowing the air layer 26 to lie between. Since this printing tube is constructed as mentioned above, there is no direct friction between the thin target 22 and the recording paper 23 thanks to the air layer 26 between the target 22 and the paper 23, even though the recording paper 23 is allowed to run at high speed, and thus it is possible to prevent the target from being damaged.

Further if the interval 1 between the spacers 31 on the outer face of the target 22 is small, e.g. 0.05 millimeter, it is possible to obtain a charge image of 0.05 millimeter in diameter on the dielectric sheet 24 though the diameter of spot of electron beam applied on the target 22 is more than 0.05 millimeter.

FIG. 6 shows an enlarged sectional view of another improvement. The spacer 32 is lain between the outer face of the target 22 and the recording paper 23 and further the conducting film 33 is stuck to one surface of the spacer 32 facing the outer face of the target 22. The spacer 32 is cut in such a way that one end of it is positioned in the vicinity of the center line of the scanning beam. The conducting film 33 is grounded.

In this arrangement creepage discharge takes place along the end face of the spacer 32. Therefore, the discharge voltage can be lower than the case of air discharge. The resolution can be improved because thanks to the creepage discharge, negative charges, which are produced by the discharge, collect efficiently at the point of the dielectric sheet 24 which contacts the end of the spacer 32. The grounded film 33 causes excessive charge stored on the outer surface of the target 22 to disappear quickly and thus removes unnecessary charge as a noise.

FIG. 7 shows a printing apparatus for putting the abovementioned printing tube into use. The printing tube 10 is constructed as mentioned above and the ground electrode 27 is provided with it being faced to the surface of the target 22.

The recording paper 23 wound on the supply reel 41 is passed between the surface of the target 22 and the ground electrode 27 allowing the

guide rollers

42, 43, 44 and 45 and taken up at a certain speed by the take-up reel 46. In the travel of the recording paper 23 from the ground electrode 27 to the v take-up reel 46, a developer 47 allows the toner 48 to stick to the recording paper 23. Heater 49 fixes the toner 48 which has been allowed to stick to the recording paper 23. As the recording paper 23 coming from the supply reel 41 passes the surface of the target 22 with the air layer 26 between, the charge pattern is formed on the surface of the recording paper 23 because of the charge deposition mechanism. Then a visible pattern is obtained by the toner 48 in the developer 47. The developer 47 allows the toner, which has a charge opposite to the charge image on the recording paper 23, to adhere to the charged portion of the recording paper 23 which makes the image visible.

Since, however, the developer 47 alone allows the toner 48 to adhere to the recording paper 23 only insufficiently, the toner 48 is fixed completely on the recording paper 23 by the fixing heater 49 and afterwards the recording paper 23 which has finished recording is taken up by the take-up reel 46.

FIG. 8 shows a variation of FIG. 7. An endless recording tape 51 which has a dielectric sheet or a photo-conductive layer such as selenium formed on the substrate of relatively low resistivity is passed between the printing tube 10 and the ground electrode 27. It is driven in the direction of the arrow at a given speed over

guide rollers

52, 53, 54, 55 and the grounded guide 56.

A belt conveyor 57 is driven in the direction of the arrow by the driving

wheels

58, 59 and allows the toner 60 to flow consecutively over the portion of the recording tape 51 positioned between the

guide rollers

53 and 54. Facing the grounded guide 56, is a corona discharge generator 60. The recording paper 61 unwound from the supply reel 62 is allowed to contact the tape 51 between the

guide rollers

63 and 64 and is taken up at the same speed as the running speed of the tape 51 by the take-up reel 65. As shown in FIG. 7, a fixing heater 66 is also provided in the course of travel of the recording paper 61 between the guide roller 64 and the take-up reel 65. In the travel of the tape 51 past the guide 56 a remover 67 is provided. The tape 51 is moved over the surface of the target 22 and the air layer 26 where a charge image is formed on the face of the tape 51. The toner 60 conveyed by the belt conveyor 57 adheres to the portion of the recording tape 51 having the charge pattern and thus visible a image is obtained. The toner 60 which has not adhered to the recording tape 51 drops as it is and is conveyed again by the conveyor 57.

The portion of the tape 51 which has a visible image produced the toner 60 contacts the recording paper 61 at the guide 56 which moves at the same speed. At the same time, a corona discharge generator 60 causes corona discharge, and the charge obtained by this phenomenon is imparted to the rear side of the recording paper 61 (the discharge generator side).

As a result, the toner which has adhered to the recording tape 51 is transcribed on the surface of the recording paper 61 and thus the image is produced. The fixing heater 66 causes the toner on the recording paper 61 to be fixed permanently.

Any toner adhering to the recording tape 51 and also charge is removed completely by remover 67, and the tape 51 reaches the surface of the target 22 again.

If a photo-conductive sheet such as selenium is employed as the above tape 51, the whole apparatus should be shielded from light. However, the portion after the charge image is removed by the remover 67 may be exposed to light.

In addition, it is possible to record a different optical image over the charge image through the optical system 68.

I claim:

1. An electrostatic printing apparatus comprising: a cathode ray tube containing an electron gun, an electron scanning means and a continuous target member which is composed of a single dielectric material said target having a resistivity in a range from about 10" to about 10 ohm-centimeters, the continuous target being scanned by electrons from the electron gun so that charge is deposited only on a portion of the target where the electron beam strikes, a dielectric recording sheet traveling in front of the continuous target, and a gaseous gap layer between the continuous target and the recording sheet through which the charge patterns on the continuous target are transferred to the recording sheet by means of discharge.

2. An electrostatic printing apparatus according to claim 1 which comprises means of developing the charge patterns on the recording sheet with toner and means of fixing the toner on the recording sheet.

3. An electrostatic printing apparatus comprising: a cathode ray tube containing an electron gun, an electron scanning means and a continuous target member which is composed of a single dielectric material a surface of the dielectric target being painted with materials having a resistivity of about 10 l0 ohm-centimeters, the continuous target being scanned by electrons from the electron gun so that charge is deposited only on a portion of the target where the electron beam strikes, a dielectric recording sheet traveling in front of the continuous target, and a gaseous gap layer between the continuous target and the recording sheet through which the charge patterns on the continuous target are transferred to the recording sheet by means of discharge.

4. An electrostatic printing apparatus comprising: a cathode ray tube containing an electron gun, an electron scanning means and a continuous target member which is composed of a single dielectric material, the continuous target being scanned by electrons from the electron gun so that charge is deposited only on a portion of the target where the electron beam strikes, a dielectric recording sheet traveling in front of the continuous target, a gaseous gap layer between the continuous target and the recording sheet through which the charge patterns on the continuous target are transferred to the recording sheet by means of discharge and a spacer laid between the surface of the target and the dielectric recording sheet.

5. An electrostatic printing apparatus according to claim 4 which comprises a conducting film being laid between the surface of the target and the spacer.

6. An electrostatic printing apparatus according to claim 5 in which the spacer is cut in such a way that one end of the spacer is positioned in the vicinity of the center line of the scanning beam, thus allowing creepage discharge to occur along the end face of the spacer.

Claims

1. An electrostatic printing apparatus comprising: a cathode ray tube containing an electron gun, an electron scanning means and a continuous target member which is composed of a single dielectric material said target having a resistivity in a range from about 107 to about 1012 ohm-centimeters, the continuous target being scanned by electrons from the electron gun so that charge is deposited only on a portion of the target where the electron beam strikes, a dielectric recording sheet traveling in front of the continuous target, and a gaseous gap layer between the continuous target and the recording sheet through which the charge patterns on the continuous target are transferred to the recording sheet by means of discharge.

3. An electrostatic printing apparatus comprising: a cathode ray tube containing an electron gun, an electron scanning means and a continuous target member which is composed of a single dielectric material a surface of the dielectric target being painted with materials having a resistivity of about 107 - 1012 ohm-centimeters, the continuous target being scanned by electrons from the electron gun so that charge is deposited only on a portion of the target where the electron beam strikes, a dielectric recording sheet traveling in front of the continuous target, and a gaseous gap layer between the continuous target and the recording sheet through which the charge patterns on the continuous target are transferred to the recording sheet by means of discharge.