EP0876918B1 - Electrostatic writing head for an electronic printing machine - Google Patents

Description

The present invention relates generally to miniature loaders for application a controlled amount of electrical charge on a receptor. In particular The invention relates to a write head for an electronic printing machine.

Some charging devices use corona discharge or arc discharge applied to generate charge carriers. Such devices suffer from one locally very specific and sporadic electron leakage from a cathode, what that Controlling the charging process difficult. It is also difficult to have a high plasma space loading density maintain and thus the possible cathode current density reduce.

In other charging devices, the charge carriers are in a direct current annealing plasma generated. Although such devices are denser, more conductive Creating plasma as corona devices, it is a disadvantage that the cathode Plasma still needs to be exposed. Due to the nature of the surface Functional fluctuations and edge effects occur on the cathode surface, uneven current distributions and electric fields appear. This uneven current distributions and electrical fields cause one time-related fluctuation pattern of "hot spots" on the cathode surface, what generally by atomization and "hot spots" glow-electric evaporation leads to rapid erosion. Furthermore, in the plasma generated chemically reactive types of charge carriers (especially if that Plasma is generated in air) decompose the electrode exposed to the plasma or oxidize. These effects can significantly affect the life of such a device shorten. In addition, these devices require the formation of the appropriate one Plasmas an environment containing a gas and a complicated, controlled one Gas supply system.

High frequency discharge is used in other charging devices. The Strength of the transferred charge is controlled by the length of time that the Discharge ignited, controlled as described in US 4,992,807. this has the disadvantage that the high-frequency source must be given pulses and thus the plasma is repeatedly ignited and cooled.

Toshiba Corporation also has an "ion-jet" printhead described, in which on both sides of a ceramic layer two electrodes in Connection with an alternating voltage lead can be used. However this printhead is used to apply large amounts of charge, it is not Print head and can therefore not be individual, corresponding to a picture element Apply loads. In addition to the two electrodes on both A separate control electrode is required on the side of the ceramic layer, and directly on the No control electrode is provided in the ceramic layer.

EP-A-0 541 841 discloses an electrostatic printing machine according to the preamble of claim 1.

According to claim 1 of the present invention, charge carriers are caused by a high-frequency gas discharge generated. The electrode that sends the radio frequency signal is on one One side of a dielectric body is arranged, and the discharge is on a second one Side ignited. The high-frequency electrode is therefore not exposed to the plasma. On A control electrode is provided on the second side of the dielectric body causes a controlled amount of electrical charge to the receptor, e.g. B. one Printing cylinder in a printing press, is transferred.

In the device of the present invention, a high frequency source is applied to a High-frequency electrode applied to generate a plasma on a first Side of the dielectric body is arranged. A variety of control electrodes are arranged on the second side of the dielectric body and ensure that correct loads.

If the voltage at the high-frequency electrode is sufficiently high, it ignites near the second side of the dielectric body a plasma, the electron, negative contains charged ions and positively charged ions. While maintaining the plasma control signals are sent to the plurality of control electrodes. The average voltage of the plasma in the vicinity of the control electrode changes by the value of the control signal, but the state of the plasma remains basically unaffected with regard to its earth potential.

If a suitable receptor is brought close to the plasma, then the Ions in the plasma are attracted to the receptor and thus cause charging of the receptor. The receptor is e.g. B. a printing cylinder with a dielectric layer, which are on a grounded layer or on a charged with a constant voltage Layer supports. The charging of the receptor continues until it is on Potential that is equal to the potential of the control electrode is charged. To At this point, the ions in the plasma will no longer go towards the receptor dressed.

The device of the present invention can because of the excellent Plasma formation, which is achieved by the high-frequency electrode, advantageously and preferably used in ordinary atmospheric pressure environments become. The device is also for operation in an atmosphere that is gas (e.g. argon, nitrogen or gas-air mixtures), the supply of which is controlled, suitable. The use of ordinary atmospheric air simplifies use of the print head is essential, whereas a controlled gas atmosphere, which is suitable for some prior art devices are needed, a complicated one Gas supply system required and also to crosstalk between the control electrodes arranged side by side leads. This crosstalk is in ordinary atmospheric environment diminished or almost eliminated because the average free range of plasma ions is quite short.

The loading devices are advantageously, but not necessarily, arranged in a row side by side. An arrangement of these devices can be used as an electrostatic write head with a printing press. With such use, the receptor would be the surface of a cylinder of the printing press. With such an arrangement of charging devices, pixels are written on the printing cylinder, which have a grid spacing of approximately 50 μm and a charging current density of approximately 1 mA / cm ² and are suitable for fast electrostatic writing, with a gray scale at a speed in the range of approx. 1 m / s.

The advantages and features of the present invention are as follows Description related to the attached, listed below Drawings explained in more detail.

Fig. 1

eine Querschnittansicht einer Ausführungsform der Erfindung;

Fig. 2

eine Draufsicht der in Fig. 1 gezeigten Ausführungsform der Erfindung;

Fig. 3

eine Draufsicht einer weiteren Ausführungsform der Erfindung;

Fig. 4

eine Draufsicht einer weiteren Ausführungsform der Erfindung;

Fig. 5

eine Draufsicht einer weiteren Ausführungsform der Erfindung;

Fig. 6

eine Ansicht einer elektrostatischen Druckmaschine, in welcher die erfindungsgemäße Vorrichtung als Schreibkopf verwendet wird;

Fig. 7

eine Vorrichtung zum Messen der elektronischen Eigenschaften eines elektrostatischen Druckmaschinensystems;

Fig. 8

die Output-Eigenschaften eines vereinfachten Druckmaschinensystems.

Show it:

Fig. 1

a cross-sectional view of an embodiment of the invention;

Fig. 2

a plan view of the embodiment of the invention shown in Fig. 1;

Fig. 3

a plan view of another embodiment of the invention;

Fig. 4

a plan view of another embodiment of the invention;

Fig. 5

a plan view of another embodiment of the invention;

Fig. 6

a view of an electrostatic printing machine in which the device according to the invention is used as a write head;

Fig. 7

a device for measuring the electronic properties of an electrostatic printing press system;

Fig. 8

the output properties of a simplified press system.

Fig. 1 shows a side view along the length of an embodiment of the present invention, in which a continuous, sinusoidal High frequency source 1 from 800 to 3000 volts from peak to peak at 4 kHz to 1 MHz is applied to a high-frequency electrode 2. Except for contact with the High-frequency source 1, the electrode 2 is encased and supported by a suitable one dielectric medium or an insulating substrate (not shown) or on top of it built to prevent parasitic electronic discharges from the electrode. The high-frequency electrode 2 is along a first side 3 of a dielectric Body 4 of usually 10 microns to 100 microns thick arranged. Preferably extends the electrode 2 extends along the entire width of the dielectric body 4.One Control electrode 5, for example 10 microns to 50 microns wide and one of a Variety of control electrodes is on the second side 6 of the dielectric Body 4 arranged. The control electrode 5 is capacitively grounded. Here is this Grounding through the capacitor 8 is shown schematically, for example with a Capacitance from 3 to 100 pF. A resistor 7, the z. B. a resistance value of 1 mega-ohm can be used to provide a control signal source 10 To protect against current surges. The control electrode 5 is positioned so that a Overlap is just avoided or so that this is the horizontal position of the High-frequency electrode 2 overlapped more or less.

The dielectric body 4 should be free of pinholes and resistant to the formation of pinholes during operation. Puncture holes in the dielectric body 4 can cause a strong direct current to flow through the dielectric body, which disrupts the control mechanism and causes physical damage in the area of the puncture holes. The dielectric body 4 can have several layers of dielectric material because the layer construction prevents growth disorders from spreading through the entire thickness of the dielectric body 4. A natural mica, 30 µm thick and of course comprising several layers, has shown excellent durability, even if the atmosphere used for the plasma was air. An artificial dielectric body 4 with one or more layers of dielectric material can be created by layering or laminating the same dielectric material or by alternating layers of different materials. Such dielectric materials can include KAPTAN-PR, a polyimide manufactured by DuPont, glass, and other common dielectric films such as. B. SiO ₂ or Al ₂ O ₃ .

If the voltage at the high-frequency electrode 2 is high enough, a plasma 9, which contains electrons and positively charged ions, near the second side 6 of the dielectric body 4 ignites. The high-frequency electrode preferably works at 4 kHz to 400 kHz or above; at this frequency a stable plasma is formed, that can tolerate fluctuating control voltages.

A control signal 10 is issued while this state of the plasma is being maintained in the range of -600 V to +600 V to the control electrode 5. The DC voltage via the dielectric body 4 in the vicinity of the control electrode 5 changes by the value of the voltage generated by the control signal source 10, however apart from its earth potential, the state of the plasma 9 remains unaffected. Consequently when the control signal 10 is applied, the appearance of the plasma 9 (in its size, color, brightness, etc.) little.

The ground connections of the high-frequency source 1 and the control signal source 10 are connected to the Ground connection of a conductive reference electrode 11 (for example a grounded layer) a receptor 12, the surface 13 of which must be charged, connected. This is true e.g. B. towards a printing cylinder surface. If the receptor 12 is close to the plasma 9 comes up, the surface 13 is charged to a potential that the Voltage potential at the control electrode 5 corresponds. Under normal Operating conditions fluctuate the actual potential of the receptor surface 13 in an almost linear relationship to that applied to the control electrode 5 Voltage, but offset by an offset voltage.

For example, if the offset voltage for a particular system is 30 volts and then a voltage of minus 30 volts is applied by the control signal source 10 surface 13 is charged up to a zero potential or earth potential. If a voltage of 70 volts is applied by the control signal source 10, then the Surface 13 charged to a potential of approximately 100 volts. The difference or Offset voltage between the voltage of the control signal source 10 and that at the Surface 13 applied potential is advantageously within a Voltage range of +/- 300 volts pretty constant. The offset voltage can be used for a certain construction, e.g. B. a printing press, measured and for calculation the desired control signal voltages that are required for a desired potential at the Surface 13 must be created, are used. If the offset voltage is constant, this calculation is a simple step of addition or subtraction.

The charging device of the present invention thus enables accurate Process of applying a charge to a receptor over a wide range of tensions.

FIG. 7 schematically shows a system for calculating the charging current, I _OUT , of the charging device of FIG. 1, in which the charging current is applied to a surface from a specific distance d (as shown). This system can also be used to calculate the offset voltage described above. A test electrode 111 is connected to a screen 115, on which the charging current is then displayed, namely through the resistance element 117, which, for. B. has a resistance of 100 kilohms. A capacitor 118 with a low capacitance, for example with a capacitance of 0.1 microfarads, can also be connected in the manner shown. Since the control voltage V _c , which is grounded and coupled to a capacitor 119 (e.g. with a capacitance between 1000 pF and 1 μF), is varied while the high-frequency generator is generating a plasma, the charging current is measured by the oscillograph . In order to increase the value of the charging current to a level that is easier to measure, the width of the test electrode (as shown in FIG. 7) can be expanded to a width that equals a pixel width multiplied by a factor m, where a single control voltage is applied to a plurality of control electrodes. The charging current for an individual control electrode, the width of which is equal to a pixel width, can then be calculated by dividing the measured charging current by the factor m.

As shown in Fig. 8, the charging current fluctuates from a distance d of 0.25 mm almost linear with the voltage applied to the control electrode 5. At a Control voltage of -70 V, the charging current is approximately zero, which is equivalent to the fact that no charge is applied to the receptor surface. It is charging current of higher values is also available if the distance d is reduced and / or the high-frequency voltage is increased. Of course, in Figs just simple examples showed how to measure the performance of a charger can. Other options, such as B. measuring the actual charge or Potential applied to the receptor surface and measuring its surface temporal reactions are equally valid.

In Fig. 2, the loading devices of the present invention for use as a write head 100 in a printing press are advantageously arranged in a side-by-side row. In this embodiment, a plurality of control electrodes 5, 15 and 25 are arranged on the second side 6 of a single dielectric body 4. (Although only three control electrodes appear in Fig. 2, it should be understood that this embodiment of the invention is not limited to any particular number of control electrodes, and that the number of control electrodes can be any depending on the desired use.) Each of the control electrodes 5, 15, 25, etc. has an independent control signal V _C1 , V _C2 , V _C3 , etc. A single high-frequency electrode 2, which is fed by a high-frequency source, is arranged and has on the first side 3 of the dielectric body 4 a range across the width of the dielectric body 4 to generate plasma for the plurality of control electrodes 5, 15, 25 (as shown). The end faces of the control electrodes 5, 15, 25 are typically oriented at an angle of 90 ° with respect to the high-frequency electrode 2. In such an arrangement of the charging devices, crosstalk between the control electrodes 5, 15, and 25 can be reduced by installing insulating structures.

For example, the control electrodes can be coated with a layer of dielectric Material are coated, only the ends of the control electrodes, which the Nearest plasma are left uncoated. However, if the process in Atmospheric air takes place, as is preferred, be such insulating Constructions are hardly necessary.

In Fig. 3, an insulating structure 24 is provided with an open end to To reduce cross-coupling between the control electrodes 5, 15 and 25. This Open ended insulating structure 24 can be made from a ribbed cover dielectric material. You can also be a senior contractor or a Protective electrode, the z. B. is connected to a constantly charged source and Scattered ions are absorbed or "scooped up" or hold the ion flow.

Fig. 4 is another embodiment in which an insulating or conductive Construction 26 is provided with a closed end. This isolating Construction 26 can also be a ribbed cover made of dielectric material or be a pickup or a protective electrode.

In the embodiment of the invention shown in FIG. 5, a transducer or a Protective electrode 27 at the opposite ends of the Control electrodes 5, 15, 25 may be placed to reduce crosstalk.

6, the write head 100 of the present invention is as a component of a electrostatic printing machine 200 shown. A mass storage device 210 can do that Save data representing the image to be printed, including the gray scale data. The Processor 205 provides the correct voltage for each control electrode of the Printhead 100 according to the data representing the image to be printed. On Pressure organ, d. H. an impression cylinder 26 has a dielectric surface 27 which serves as a receptor. The dielectric surface 27 is on a conductive Layer 28, which serves as a conductive reference electrode and a grounded layer or a layer set by a controller to a certain constant voltage can be. The write head 100 is in the vicinity of the dielectric surface 27 of the Printing cylinder 26 arranged, and the individual control electrodes extend along the length of the write head 100. The write head 100 is similar to that in FIG. 2 shown type, however, the write head in Fig. 2 is reversed, so that the plasma 9th contacts the dielectric surface 27.

The pressure cylinder 26 rotates in the direction indicated; the moves dielectric surface 27 of the printing cylinder 26 close to the write head 100. The Control processor 205 sends control signals to the plurality of control electrodes which are contained in the write head 100 in order to achieve the charged pixels on the dielectric surface 27 of the printing cylinder 26 to record so that a latent image arises. After the dielectric Surface 27 has passed the print head 100 and received charges from it, it passes a color source 32. In Fig. 6, this color source 32 consists of two Ink rollers that are connected to an ink fountain, however, can also be any other color source can be used. Color, as it is to be defined here, exists both from liquid colors and from dry toner. That from the color source 32 coming color is electrostatically attracted by a charged pixel, and in a quantity controlled by the voltage of the pixel. after the Color was picked up by the dielectric surface 27, this comes with a Printing substrate 34, e.g. B. a paper web or a sheet of paper in contact. The Print substrate 34 may be in contact with dielectric surface 27 through a Impression cylinder 35 are held in a suitable position. At the contact point transfer the color to the printing substrate 34 and thus the image 36 to the Print substrate 34 printed. The dielectric surface 27 then passes through one Extinguishing device 37, e.g. B. a source of ultraviolet light.

It should be understood that the present invention also applies to copying machines and Fax machines that are here under the definition of electrostatic printing presses included, can be used. The invention is also for a four-color printing press usable, in which each of four printing cylinders one Has printhead and the four printheads by a common Control processor can be controlled.

LIST OF REFERENCES

1

Radio frequency source

2nd

High frequency electrode

3rd

first side of the dielectric body 4

4th

dielectric body

5

Control electrode

6

second side of the dielectric body 4

7

Resistor

8th

capacitor

9

plasma

10th

Control signal source

11

Reference electrode

12th

receptor

13

Surface of the receptor

15

Control electrode

24th

insulating construction (Fig. 3)

25th

Control electrode

26

Conductive construction (Fig. 4)

26

Printing cylinder / pressure element (Fig. 6)

27

Protective electrode (Fig. 5)

27

dielectric surface of the impression cylinder 26 (FIG. 6)

28

conductive layer (Fig. 6)

32

Color source

34

Printing substrate

35

Impression cylinder

36

image

37

Extinguishing system

100

Printhead

111

Test electrode

115

Oscilloscope

117

Resistance element

118

capacitor

119

capacitor

200

electrostatic printing machine

205

processor

210

Mass storage

Claims (8)

1. An electrostatic printing press comprising: a printing member (26) including a dielectric surface (13, 27), further including a write head (100) for selectively writing charges on the dielectric surface (13, 27), a dielectric body (4) having a first side (3) and a second side (6), a radio frequency electrode (2) disposed on the first side (3) of the dielectric body (4) and suitable for receiving a radio frequency signal from the high frequency source (1) so that a plasma emerges near the second side (6) of the dielectric body (4), and a plurality of control electrodes (5, 15, 25) disposed on the second side (6) of the dielectric body (4) and suitable for receiving control signals of a control signal source (10), and including a control processor (205) connected to a plurality of control electrodes (5, 15, 25) and individually controlling the latter,
   characterized in

   that the radio frequency electrode (2) extends along the entire width of the dielectric body (4),

   and that beneath its dielectric surface (13, 27) the printing member (12, 26) has a conductive layer (11, 28) connected to ground, the conductive layer being electrically connected to the ground connections of the radio frequency source (1) and the control signal source (10), which causes at least one control electrode (5) to get into electric contact with the dielectric surface (13, 27) via the plasma (9).
2. Electrostatic printing press according to claim 1,
   characterized in that an ink source (32) is provided, from which ink is brought into contact with the dielectric surface (27) of the printing member (26).
3. Electrostatic printing press according to claim 1
   characterized in that a dielectric coating is provided for at least one of the plurality of control electrodes (5, 15, 25).
4. Electrostatic printing press according to claim 1,
   characterized in that the radio frequency signal is continuous in time.
5. Electrostatic printing press according to claim 1
   characterized in that an insulating structure (24) is provided such that cross-talk between the control electrodes (5, 15, 25) is reduced.
6. Electrostatic printing press according to claim 5,
   characterized in that the insulating structure (24) is a scoop or protection electrode.
7. Electrostatic printing press according to claim 5,
   characterized in that the insulating structure (24) is a ridged dielectric covering.
8. Electrostatic printing press as recited in claim 1
   characterized in that the print member (26) is a cylinder.

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