EP1034078B2 - Electrostatic arrangement for rotogravure and flexographic printing - Google Patents

Abstract

The electrostatic printing aid for gravure and flexographic printing machines can be operated with a voltage electrode whose dimensions have been reduced significantly, the print quality being kept at a high level. The voltage electrode, connected to a high voltage source, can be constructed with a bar-like or arc-like shape and to be non-contacting, or as a slip ring or as an electrically conductive brush. The voltage electrode is preferably arranged at one end of the three-layer impression roller of a gravure printing unit or the three-layer printing plate cylinder of a flexographic printing unit. The particular advantages of the arrangement reside in the significantly improved ease of servicing and the saving in costs, as early as at the time of purchase, in particular in the event of retrofitting printing machines already in operation.

Description

Field of application of the invention

The present invention relates to an arrangement to transfer an electrostatic charge within a gravure and flexographic printing press for improvement the print quality by polarizing the ink droplets on the printing plate cylinder. In the gravure printing plant the electrostatic charge is applied to the outer jacket of a printing press, from which she flows to the outer shell of the printing forme cylinder. The flexographic printing unit brings the electrostatic charge on the printing forme cylinder, from which they to both the substrate transfer roller and the Impression cylinder flows. Under the influence of a applied electric field are in the Cups of the plate cylinder (gravure printing) or the on the surface of the plate cylinder (flexo printing) polarized color molecules, and the color droplets experience a total volume increase. A flowing electric current is taken to the necessary for polarization work To deliver energy. As a result of the polarization, the Color droplets attracted by the substrate and also is the transfer of the color droplets through their Volume increase on the past Bedrucköfföff favors.

Thus, in gravure printing in much higher Mass ensured that the cups of the plate cylinder be properly emptied, i. the Printing ink is applied to the substrate. in the Flexo printing causes the electrostatic charge that the ink from the subcrate transfer roller on the printing form cylinder and on the substrate is transmitted better. Such arrangements will be also referred to as "electrostatic printing aids"; she serve in all tone levels a full supervisory density to achieve and avoid so-called "missing dots". The problem of "missing dots" occurs in particular on rough substrates, e.g. Paper webs, with corresponding bumps.

State of the art

Electrostatic printing aids of the type relevant here have been known for decades (see, for example, DE-A-27 09 254, EP-A-0 761 458). Figures 1A and 1 D in connection with Figure 1C show a two-roll system of a gravure printing unit with a multi-layer impression 1 - here according to the invention already three layers - the printing form cylinder 2 and between the two guided over the guide roller 3 substrate 4. About the impression roller 1 , a bar-shaped voltage electrode 5 extending over its entire length is arranged. The inking doctor 6 is indicated for wiping off excess-applied ink from the printing form cylinder 2. The inking roller and the return, which are not shown, are seated in a paint trough 7 . The voltage electrode 5 is connected to a high voltage source 8 . The jacket of the three-layer impression roller 1 has a semiconductor layer 10 on the outside and a high-conductor layer 11 underneath. Below the high-conductor layer 11, as electrical insulation to the impression core 13, there is an insulator layer 12 .

FIG. 1B shows a three-roller system which, unlike the previously described two-roller system, has an additionally arranged support roller 9 above the multi-layer impression roller 1 , which is preferably electrically insulated. The voltage electrode 5 is positioned here laterally of the multi-layer impression roller 1 .

FIG. 1E with the electrical circuit diagram of the two- or three-roller system according to FIGS. 1A to 1D illustrates the flow of current within the electrostatic arrangements. From the high voltage source 8 of the voltage electrode 5, a DC voltage U is supplied and the voltage electrode 5 has the internal resistance R ₁ . The air gap S existing between the voltage electrode 5 and the impression roller 1 - usually in the size of approximately 5 mm to 30 mm-represents the resistor R _2. The upper semiconductor layer 10 and the high-conductor layer 11 form the resistors R ₃ , R ₄ . The grounded insulator layer 12 acts as an excessively large resistor R ₅ . From the high-conductor layer 11 , the current flows through the underlying semiconductor layer 10, which here forms the resistor R ₆ , further through the printing material 4, which represents the resistor R ₇ . Practically the resistance value R ₈ = 0 has the grounded pressure cylinder 2.

According to the Kirchhoff current distribution law, the main part of the electric current takes the path of the lower resistance via the high-conductor layer 11, while a small fraction flows directly over the semiconductor layer 10 to the printing substrate 4 . Finally, between the lower semiconductor layer 10 and the earth E there is a voltage drop .DELTA.U , which represents the so-called nip voltage, which is decisive for the polarization of the color droplets in the cups of the plate cylinder 2 . The current I flows, starting from the voltage electrode 5, to the ground terminal E.

To keep the paint droplets from the wells as possible completely and evenly on the whole Width of the substrate to apply - the web widths can exceed 3m today - must be sufficient Energy supplied and the flow of electricity over the entire impression width be uniformly distributed. To meet this requirement, so far addressed the Length of the voltage electrode after the maximum usable Width of the plate cylinder or of the impression roller, so that on the latter one in the pressure range homogeneous Charge distribution is ensured (see DE-A-27 09 254, p. 11, lines 21ff .; OLLECH, Bernd: Gravure printing - basics and process steps of modern Gravure printing technology. Polygraph publishing house Frankfurt on the Main, 2nd ed. 1993, p. 343, Fig. 15.49; Firmenschriften Eltex-Elektrostatik GmbH, Weil am Rhein / DE, "ESA-DIRECT - A new dimension of electrostatic Print Help ", Print No .: WP-d / e / f-9043-90 / 7-20, Fig. 17; as well as "eltex - Handbook of the Electrostatic Discipline ", Print No .: Üp-d-0002-93 / 12-1 00, p.32, pressure support, fig. Right above). Consequently, one uses voltage electrodes over 3m in length. With such voltage electrodes you get good print quality. However, they are disadvantageous the relatively rapid contamination of the open voltage electrodes, resulting in significant losses in their Effectiveness and finally leads to complete failure, so that the print quality deteriorates rapidly.

To the function of the so-equipped electrostatic To get orders, must be a polluted Removed voltage electrode, cleaned and reinstalled. This is labor intensive, leads to lossy machine downtime and will therefore often postponed to upcoming Delivery times for the printed products not too compromise.

To eliminate the mentioned disadvantages were subsequently developed electrostatic printing aids, where instead of using a long, attached rod electrode the current in the rotating shaft of the impression roller (see, for example, DE-A-28 10 452). Well, that was the problem of a voluminous voltage electrode Although fixed and thus the service easier, nevertheless the requirement of frequent cleaning persists; but added more effort in isolation of the impression core opposite the printing machine.

In the further development emerged encapsulated electrostatic printing aids, where the electricity is initiated via the Presseurkern and the against Pollution are largely protected, so that virtually freedom from maintenance (see e.g. EP-A-0 115 611; Company brochure of Spengler Electronic AG, Biel-Benken / CH: Electrostatic printing assistance, SR-HELIOFURN 94). This most modern to date Printing aids cause a relatively high mechanical Effort of new printing machines that from the beginning equipped with it, still acceptable is. When retrofitting in operation older Printing machines with encapsulated printing aids and Introduction of the current in the impression core, would the However, retrofitting costs increase enormously, so that For this purpose, the former printing aids with long, rod-shaped voltage electrodes are used (See, for example, the recent publication of SHTNKO Co., Ltd., Osaka / JP: ESAPRINT 21, ELECTROSTATIC ASSIST SYSTEM; Print No .: 97043000).

Moreover, from US-A-3,625,146 electrostatic Printing aids are known in which a roller electrode to a three-layer impression roller with an outer one Semiconductor layer, an underlying conductor layer and an underlying insulator layer, the adjacent to the impression core, is attached. The roller electrode is in direct electrical contact with an exposed annular surface of the conductor layer.

In one known from EP-A-0294042 electrostatic arrangement is a voltage electrode in the form of a brush in direct electrical Contact with a semiconductor layer of a multilayer impression roller.

In DE-U-9419 540 is an electrostatic Arrangement described in which a voltage electrode at a distance to an outer semiconductor layer of a Three-layer impression rollers with one under the semiconductor layer lying Hochleiterschicht and an underlying Insulator layer attached to the impression core adjacent, is arranged. The as a sheet metal part, grid or the like formed voltage electrode and form the semiconductor layer and the high-conductor layer a capacitor used for transmission of AC voltage suitable is. To the voltage electrode becomes an ordinary alternating voltage or one with a diode rectified AC voltage (= not smoothed DC voltage), wherein the AC component the over the capacitor transmittable alternating current generated.

The electrostatic arrangement according to the independent claim 1 is opposite to in DE-A-27 09 254 described electrostatic Arrangement delimited.

Object of the invention

Given the persisting disadvantages of to date existing electrostatic printing aids lies The invention is based on the object, an arrangement to create where a soiled voltage electrode quickly remove from a person, clean and reinstalled. Or you should the polluted Voltage electrode quickly against a clean Electrode can exchange for cleaning make the contaminated electrode externally. service costs and machine downtime must be lowered significantly. The arrangement should be with electrodes as small a dimension as possible, in particular suitable for retrofitting of printing presses and the initial cost must be low being held. But for the print quality apply unabated high demands.

Essence of the invention

This task is done by the electrostatic Arrangements resolved, as in the independent Claims 1 and 2 are defined.

The entire professional world so far assumed that as well as the latest literature and products show that at Stromeinleiturg on the outer jacket of Impression rollers (gravure printing) or the plate cylinder (Flexographic printing) for a homogeneous charge distribution in the Pressure range of use of a possible over the entire length of the impression roller or printing forme cylinder extending voltage electrode essential is. Surprisingly, it has now been found that when using a voltage electrode, the shorter than 50% of the length of the impression roller or the Druckformzylinders is, as well as simultaneous use of a Three-layer impression rollers (gravure printing) or a three-layer impression cylinder (Flexo printing) excellent Print quality can be achieved, as previously only with Voltage electrodes at least in almost full length. The voltage electrode is in a gap distance to the outer jacket of the impression roller or the printing forme cylinder attached and can depending on the applied high voltage and the associated safety factors shortened to about 1% of the previous full length become.

As alternatives to the rod-shaped voltage electrode one found such, which the outer coat of the impression or the printing forme cylinder in one Spacing gap surrounded arcuately. The homogeneous Charge distribution over the entire contact pressure range is achieved by using the relatively low-impedance high-conductor layer of the impression roller or the printing plate cylinder in the axial direction and the other hand, high impedance Semiconductor layer achieved in the radial direction.

To increase the security is a frontal Isolation of the impression roller or printing plate cylinder against their cores by applying an insulation coating provided, at least from the High conductor layer in the adjacent areas of the overlying semiconductor layer and the underlying Insulator layer extends. Also, the isolation by a frontal shortening of the high-conductor layer when filling in the resulting from the shortening Free space with the semiconductor or insulator layer be achieved.

Brief description of the attached drawings

Figur 1A:

ein Zwei-Rollensystem eines Tiefdruckwerks mit Druckformzylinder, Presseur und hieran angeordneter Spannungselektrode als Prinzipdarstellung;

Figur 1B:

ein Drei-Rollensystems eines Tiefdruckwerks mit Druckformzylinder, Stützwalze und Presseur mit daran angeordneter Spannungselektrode;

Figur 1C:

ein Zwei-Rollensystem eines Tiefdruckwerks mit stabförmiger Spannungselektrode gemäss dem Stand der Technik als Perspektivdarstellung;

Figur 1D:

das System gemäss Figur 1C im Vertikalschnitt betrachtet;

Figur 1E:

das elektrische Schaltbild des Systems gemäss den Figuren 1A bis 1D;

Figur 2A:

einen Dreischicht-Presseur in der Perspektivdarstellung mit durchgehenden Schichten nach dem Stand der Technik;

Figur 2B:

den Dreischicht-Presseur gemäss Figur 2A im axialen Vertikalschnitt;

Figur 2C:

den Dreischicht-Presseur gemäss Figur 2A mit stirnseitiger Isolationsbeschichtung nach, dem Stand der Technik;

Figur 2D:

den Dreischicht-Presseur gemäss Figur 2A mit stirnseitig hochgezogener Isolationsschicht nach dem Stand der Technik;

Figur 2E:

den Dreischicht-Presseur mit stirnseitig zurückgesetzter Hochleiterschicht nach dem Stand der Technik;

Figur 2F:

einen Dreischicht-Presseur mit seitlich offener Hochleiterschicht als Perspektivansicht;

Figur 2G:

den Dreischicht-Presseur gemäss Figur 2F im axialen Vertikalschnitt;

Figur 3A:

eine längliche Spannungselektrode als Perspektivdarstellung nach dem Stand der Technik;

Figur 3B:

das elektrische Schaltbild der Spannungselektrode gemäss Figur 3A;

Figur 3C:

eine längliche Spannungselektrode mit mehreren Reihen von Emissionsnadeln als Perspektivdarstellung;

Figur 3D:

eine Spannungselektrode mit einem mehrreihigen, quadratischen Feld von Emissionsnadeln als Perspektivdarstellung;

Figur 3E:

eine zylindrische Spannungselektrode mit mehreren über eine Kreisfläche verteilten Emissionsnadeln als Perspektivdarstellung;

Figur 4A:

eine Ausführungsform der erfindungsgemässen elektrostatischen Anordnung für ein Tiefdruckwerk mit oben auf dem Presseur angeordneter, länglicher Spannungselektrode als Perspektivdarstellung;

Figur 4B:

die Anordnung gemäss Figur 4A im Querschnitt betrachtet;

Figur 4C:

die Anordnung gemäss Figur 4A mit variabel positionierbarer Spannungselektrode;

Figur 5A:

eine weitere Ausführungsform der erfindungsgemässen elektrostatischen Anordnung für ein Tiefdruckwerk mit einem Presseur und daran angesetzter, bogenförmiger Spannungselektrode als Perspektivdarstellung;

Figur 5B:

die halbbogenförmige Spannungselektrode gemäss Figur 5A als Perspektivdarstellung;

Figur 6A:

die erfindungsgemässe elektrostatische Anordnung für ein Flexodruckwerk mit oben auf dem Dreischicht-Druckformzylinder angeordneter, länglicher Spannungselektrode, dem Gegendruckzylinder und der Substrat-Übertragungswalze als Perspektivdarstellung;

Figur 6B:

die Anordnung gemäss Figur 6A mit variabel positionierbarer Spannungselektrode und einer Schöpfwalze als Prinzipdarstellung;

Figur 6C:

die Anordnung gemäss Figur 6A mit variabel positionierbarer Spannungselektrode und einer Substrat-Übertragungswalze als Prinzipdarstellung; und

Figur 6D:

die Anordnung gemäss Figur 6A mit variabel positionierbarer Spannungselektrode und einer Substrat-Übertragungswalze mit Kammrakel als Prinzipdarstellung.

Show it:

FIG. 1A

a two-roller system of a gravure printing unit with plate cylinder, impression roller and arranged thereon voltage electrode as a schematic representation;

FIG. 1B

a three-roll system of a gravure printing unit with printing forme cylinder, back-up roller and impression roller with arranged thereon voltage electrode;

FIG. 1C:

a two-roller system of a gravure printing unit with rod-shaped voltage electrode according to the prior art as a perspective view;

FIG. 1D:

the system according to Figure 1C viewed in vertical section;

FIG. 1E:

the electrical diagram of the system according to Figures 1A to 1D;

FIG. 2A

a three-layer impression in the perspective view with continuous layers according to the prior art;

FIG. 2B:

the three-layer impression roller according to Figure 2A in axial vertical section;

FIG. 2C:

the three-layer impression roller according to Figure 2A with front-side insulation coating according to the prior art;

FIG. 2D:

the three-layer impression roller according to FIG. 2A with frontally raised insulating layer according to the prior art;

FIG. 2E:

the three-layer impression roller with front-side reset high-conductor layer according to the prior art;

FIG. 2F:

a three-layer impression roller with laterally open high conductor layer as a perspective view;

FIG. 2G:

the three-layer impression roller according to Figure 2F in axial vertical section;

FIG. 3A:

an elongated voltage electrode as a perspective view of the prior art;

FIG. 3B:

the electrical circuit diagram of the voltage electrode according to Figure 3A;

FIG. 3C:

an elongated voltage electrode having a plurality of rows of emission pins as a perspective view;

Figure 3D:

a voltage electrode with a multi-row, square array of emission needles as a perspective view;

FIG. 3E:

a cylindrical voltage electrode having a plurality of emission needles distributed over a circular area as a perspective view;

FIG. 4A

an embodiment of the inventive electrostatic arrangement for a gravure printing unit with arranged on top of the impression roller, elongated voltage electrode as a perspective view;

FIG. 4B:

the arrangement according to Figure 4A viewed in cross section;

FIG. 4C:

the arrangement according to Figure 4A with variably positionable voltage electrode;

FIG. 5A

a further embodiment of the inventive electrostatic arrangement for a gravure printing unit with a impression roller and attached thereto, arcuate voltage electrode as a perspective view;

FIG. 5B:

the semicircular voltage electrode according to Figure 5A as a perspective view;

FIG. 6A:

the inventive electrostatic arrangement for a flexographic printing with arranged on top of the three-layer printing plate cylinder, elongated voltage electrode, the impression cylinder and the substrate transfer roller as a perspective view;

FIG. 6B:

the arrangement according to Figure 6A with variably positionable voltage electrode and a scoop roller as a schematic representation;

FIG. 6C:

the arrangement according to Figure 6A with variably positionable voltage electrode and a substrate transfer roller as a schematic representation; and

FIG. 6D:

the arrangement according to Figure 6A with variably positionable voltage electrode and a substrate transfer roller with comb scraper as a schematic representation.

Figures 2F, 2G and 3E follen nich under claim 1.

embodiments

With reference to the accompanying drawings hereinafter, the detailed description will be more preferred Embodiments of the inventive Arrangement. Finally, possible modifications mentioned.

The following applies to the entire further description Setting. Are in a Figurzum Zweckzeichnerischer Uniqueness reference numbers included, but not explained in the directly accompanying description text, so is their mention in preceding Description of the Figures. In interest the clarity is on the repeated designation of components in subsequent figures mostly omitted, if clearly identifiable by drawing is that they are "recurring" components.

FIGS. 2A and 2B

The three-layer impression roller 1 has a jacket over the impression roller core 13 which consists externally of a semiconductor layer 10, an underlying high-conductor layer 11 and an underlying insulator layer 12 adjoining the impression core 13 . All three layers 10, 11, 12 extend as far as the end faces of the impression roller 1 , so that an electrical short circuit can occur, in particular when they are soiled, for example by paint residues. To prevent this, various insulating precautions are taken. The high-conductor layer 11 is preferably large-volume and is for example at least 1/3 of the thickness of the semiconductor layer 10.

Figure 2C

Here, the Hochleiter- and the insulating layer 11,12 to the adjacent regions of the outer semiconductor layer 10 and the inner roll core 13 are each provided frontally with an insulating coating 14 for insulation purposes.

FIG. 2D

The front-side insulation is here by a recessed on both sides shortening of high-conductor and semiconductor layer 11,10 and filling the space formed by the shortening with the quasi up to the outer surface of the semiconductor layer 10 pulled up, overlapping insulator layer 12 , which the cut edges of both shortened layers 11,10 surrounds, reaches.

Figure 2E

In a modification of the embodiment according to FIG 2D is frontally each shortened only the highly conductive layer 11 here, and the clearance filled with the drawn down quasi on the insulator layer 12, the cut edges of the highly conductive layer 11 overlapping the surrounding semiconductor layer 10th

Figures 2F and 2G

In the illustrated modification of the three-layer impression roller 1 , the outermost semiconductor layer 10 is shortened from the left end side so that an annular surface 110 of the high-conductor layer 11 underlying the semiconductor layer 10 is exposed. As a safety precaution, it is also possible to provide an insulator coating 14 on this end face, which covers the high-conductor layer 11 and the underlying insulator layer 12 and extends as far as the edge region of the adjoining impression core 13 . The exposed ring surface 110 makes it possible to apply thereto a voltage electrode 5a, 5b, 5c (see the other figures).

FIGS. 3A and 3B

The rod-shaped voltage electrode 5 , which is provided as an inductor for the contactless application to the impression roller 1 , is known in its construction per se. In an elongate insulating body 50 emission needles 51 are systematically arranged in series, for example at a distance of 1 cm. Behind each emission needle 51 , a protective resistor 52 is connected. Emission needles 51 and protective resistors 52 are advantageously positioned on a printed circuit board, which is inserted into the insulating body 50 and, for example, cast with synthetic resin. The terminal contact of the voltage electrode 5 is connected to the high voltage source 8 , so that the voltage U is applied.

FIG. 3C

This likewise rod-shaped voltage electrode 5a differs from the embodiment according to FIG. 3A only in that, instead of a row of emission needles 51, three axially extending rows of emission needles 51 are provided. Thus, the length of the voltage electrode 5a can be further shortened and / or the required high voltage U lowered.

Figure 3D

With a corresponding high voltage U and other adequate machine parameters, the number of emission needles 51 can be further reduced for a voltage electrode 5a -here arranged in an approximately square field-and thus further reduce the dimension of the voltage electrode 5a .

FIG. 3E

In this voltage electrode 5b , the emission needles 51 are arranged within a circular area, and the insulation body 50 has a cylindrical shape.

FIGS. 4A to 4C

In this embodiment, as a contactless inductor electrode in its length, for example, to 1/6 of the length of the three-layer impression roller 1 shortened rod-shaped voltage electrode 5a is placed in a gravure printing on a impression roller 1 with a gap distance S. Preferably, one chooses for the placement of the voltage electrode 5a one end of the impression roller 1 , so as to facilitate the lateral access for service work. Depending on the structure of the gravure printing machine, the voltage electrode 5a can advantageously be arranged in all positions in the semicircle around the impression roller 1 over the moving web of the printing material 4 .

In special conditions, the arrangement of the voltage electrode 5a is directed below the printing substrate 4 and on the semiconductor layer 10 of the impression roller 1 , conceivable. The printing material 4, eg wet paper, then acts as a conductor. The voltage electrode 5a is connected to the high voltage source 8 , so that a current flow from the voltage electrode 5a through the impression roller 1 and the polarization of the color molecules in the wells of the plate cylinder 2 is formed. For example, the applied high voltage up to 30kV DC, and the air gap S is set with 5mm to 30mm, preferably here with 5mm to 15mm.

When used with the inventive arrangement come as substrates 4 all common types and grades of paper, plastic films, textiles and coated or coated with insulating paint metal foils into consideration. All color systems that can be used on rotogravure presses, such as Tuluol, alcohol or ethyl acetate-based inks, as well as watercolors, can be used for packaging and commercial printing.

FIGS. 5A and 5B

In this embodiment, also as a contactless inductor electrode, the voltage electrode 5c has a half-shell shape and surrounds the three-layer impression roller 1 with a gap distance S. For example, the voltage electrode 5c extends with its insulator body 50 in an arc over 180 °, wherein therein a series of emission needles 51st is provided. Again, for the purpose of facilitating access for service work, the voltage electrode 5c will be arranged at least near one end of the impression roller 1 . In this example, the length of the arcuate tension electrode 5c corresponds approximately to half the outer circumference of the impression roller 1 , if the necessary increase due to the gap distance S is disregarded.

Figures 6A and 6B

The flexographic printing unit has the three-layer printing form cylinder 20 , the substrate transfer roller 30 (also called inking roller or anilox roller) arranged underneath, and the counter-pressure cylinder 40 (also called the pressure roller) lying at the level of the three-layer printing plate cylinder 20 . Between the three-layer printing form cylinder 20 and the impression cylinder 40 , the web of the printing material 4 passes through. On top of the three-layer printing plate cylinder 20 is a shortened rod-shaped voltage electrode 5a is placed with a gap distance S , which acts as a contactless inductor and z. B. about 1/6 of the length of the three-layer printing forme cylinder 20 has. Preferably, the voltage electrode 5a is seated at one end of the three-layer printing plate cylinder 20 so as to facilitate the lateral access for service work.

The substrate transfer roller 30 is supplied with the ink from a scoop roller 60 , which dips into the ink tray 7 . Advantageously, depending on the structure of the flexographic printing machine, the voltage electrode 5a can be variably arranged in all positions in the semicircle about the three-layer printing form cylinder 20 in the two free spaces between substrate transfer roller 30 and impression cylinder 40 .

The three-layer printing form cylinder 20 has on the outside the cliché 24 made of semiconductor material, underneath a high-conductivity layer 21 and below the latter an insulator layer 22 . The insulator layer 22 is seated on the inner cylinder core 23 . The voltage electrode 5a is connected to the high voltage source 8 ; Thus, a current flow from the three-layer printing form cylinder 20 on the one hand to the substrate transfer roller 30 and on the other hand to the impression cylinder 40th The electrostatic charge causes the ink particles are better transferred from the substrate transfer roller 30 on the three-layer printing forme cylinder 20, ie its plate 24 , and ultimately to the substrate 4 .

FIG. 6C

In this flexographic printing unit, there is no scoop roller 60 , but the substrate transfer roller 30 itself is seated in the ink tray 7, and a squeegee 6 is provided for stripping excess ink.

FIG. 6D

State-of-the-art flexographic printing units also do without a scoop roller 60 . Here, the ink is sprayed onto the substrate transfer roller 30 with a comb blade 6a ; excess ink absorbs the comb scraper 6a .

Thanks to the invention is now an electrostatic Arrangement as printing aid for gravure and flexographic printing units available, the service work, in particular the cleaning, much easier. Special Advantages arise in the accessibility during service work through the reduced dimensions opposite the previously used voltage electrodes, especially when the voltage electrode in an end region of the impression roller or printing forme cylinder is arranged. Due to the smaller field extent Deposits on machine parts are reduced of undesired charged particles, namely Color fog and abrasion from the substrate. The inventive Arrangement brings through the facilitated Assembly and the lower material costs significantly Cost advantages. Losses in the homogeneity of the Polarization over the entire printing width does not occur on. Priority favorable is the arrangement for retrofitting of already in operation printing presses. The inventive arrangement thus satisfies in principle a long-felt need, wherein the professional world for decades on the dogma of necessity widely extended voltage electrodes of the local Type of electrostatic printing aids arrested.

• Beim Dreischicht-Presseur 1 gemäss den Figuren 2F und 2G könnte alternativ auch die Halbleiterschicht 10 von der rechten Stirnseite her verkürzt sein, oder die Halbleiterschicht 10 ist auf beiden Stirnseiten verkürzt, so dass eine Ringfläche 110 der Hochleiterschicht 11 links und/oder rechts freiliegt. Dies bezieht sich nicht auf elektrostatische Anordnungen gemäß Patentanspruch 1.
• Die bogenförmige Spannungselektrode 5c lässt sich in einem Bogenmass von ca. 270° bis zu einer nahezu punktartigen Dimension gestalten. Je nach Breite und Länge des Isolationskörpers 50 kann man die Emissionsnadeln 51 in einer oder mehreren Reihen anordnen sowie quadratähnliche und kreisförmige Bestückungsmuster vorsehen. Im Prinzip wäre es sogar denkbar, eine Spannungselektrode 5a,5b,5c mit nur einer einzigen Emissionsnadel 51 auszustatten. Entsprechend platz- und materialsparend könnte der Isolationskörper 50 gestaltet werden.
• Auch im Flexodruckwerk sind die verschiedenen Spannungselektroden 5a,5b,5c einsetzbar; man kann offenliegende Ringflächen der Hochleiterschicht 21 vorsehen (vgl. Fig. 2G) und wird analoge Vorkehrungen zur Isolation der Stirnseiten am Dreischicht-Druckformzylinder 20 (vgl. Fig. 2C bis 2E) treffen.

For the above-described embodiments of the electrostatic arrangement further structural variations can be realized. Here are expressly mentioned:

• Alternatively, in the three-layer impression roller 1 according to FIGS. 2F and 2G, the semiconductor layer 10 could also be shortened from the right-hand end side, or the semiconductor layer 10 is shortened on both end faces, so that an annular surface 110 of the high-conductor layer 11 is exposed on the left and / or right. This does not relate to electrostatic arrangements according to claim 1.
• The arcuate voltage electrode 5c can be designed in an arc of about 270 ° to a nearly point-like dimension. Depending on the width and length of the insulating body 50 , one can arrange the emission needles 51 in one or more rows and provide square-like and circular assembly patterns. In principle, it would even be conceivable to equip a voltage electrode 5a, 5b, 5c with only a single emission needle 51 . According to space and material savings of the insulating body 50 could be designed.
• The various voltage electrodes 5a, 5b, 5c can also be used in the flexographic printing unit; One can provide exposed ring surfaces of the high-conductor layer 21 (see Fig. 2G) and will make analogous arrangements for the isolation of the end faces on the three-layer printing plate cylinder 20 (see Fig. 2C to 2E).

Claims (10)

1. An electrostatic arrangement for a gravure printing unit having:

   a) a multi-layer impression roller (1), a voltage electrode (5a, 5c) fitted to the latter at a distance with an air gap (S), and a printing plate cylinder (2),

   b) the voltage electrode (5a, 5c) containing, as inductor electrode, emission needles (51) which are spaced apart from one another and from whose tips, in the operating state, in which a DC voltage is applied to the voltage electrode (5a, 5c), current flows through the ionized air gap (S) into the impression roller (1),

   c) it being provided to lead the web of a printing material (4) through between the impression roller (1) and the printing plate cylinder (2) and

   d) the arrangement being intended to polarize the ink molecules in the dimples in the printing plate cylinder (2),
   characterized in that

   e) the multi-layer impression roller is a three-layer impression roller (1) with an outer semiconductor layer (10), a highly conductive layer (11) located underneath and an insulating layer (12) arranged underneath the latter and adjacent to the impression roller core (13), and

   f) the voltage electrode (5a, 5c) is fitted with the air gap (S) at a radial distance from the semiconductor layer (10);

   g) a voltage electrode (5a) extending axially along the impression roller (1) having a length in the region of about ≤ 50%, preferably about ≤ 10%, of the length of the impression roller (1); or

   h) a voltage electrode (5c) extending radially around the impression roller (1) having an arc length in the region of about ≤ 270°, preferably about ≤ 30°.
2. An electrostatic arrangement for a flexographic printing unit having:

   a) a multi-layer printing plate cylinder (20), a voltage electrode (5a, 5b, 5c) fitted to the latter at a distance with an air gap (S), a substrate transfer roll (30) and a back-pressure cylinder (40),

   b) the voltage electrode (5a, 5b, 5c) containing, as inductor electrode, emission needles (51) which are spaced apart from one another and from whose tips, in the operating state, in which a DC voltage is applied to the voltage electrode (5a, 5b, 5c), current flows through the ionized air gap (S) into the multi-layer printing plate cylinder (20),

   c) it being provided to lead the web of a printing material (4) through between the multi-layer printing plate cylinder (20) and the back-pressure cylinder (40), and

   d) the arrangement being intended to polarize the ink molecules on the substrate transfer roll (30) and the multi-layer printing plate cylinder (20),
   characterized in that

   e) the multi-layer printing plate cylinder is a three-layer printing plate cylinder (20) with an outer semiconductor layer as a stereotype plate (24), a highly conductive layer (21) located underneath and an insulating layer (22) located underneath the latter and adjacent to the cylinder core (23), and the voltage electrode (5a, 5b, 5c)

   f) is fitted with the air gap (S) at a distance from the semiconductive stereotype plate (24); or

   g) is fitted with the air gap (S) at a distance from an end face of the highly conductive layer (21); or

   h) is fitted with the air gap (S) at a distance from an exposed annular face of the highly conductive layer (21);

   i) a voltage electrode (5a, 5b) extending longitudinally and axially having a length in the region of about ≤ 50%, preferably about ≤ 10%, of the length of the three-layer printing plate cylinder (2); or

   j) a voltage electrode (5c) extending radially around the three-layer printing plate cylinder (20) having an arc length in the region of about ≤ 270°, preferably about ≤ 30°.
3. The electrostatic arrangement as claimed in claim 1 or 2, characterized in that the emission needles (51) of the voltage electrode (5a, 5b, 5c) are spaced apart systematically from one another.
4. The electrostatic arrangement as claimed in one of claims 1 to 3, characterized in that on the impression roller (1) or on the three-layer printing plate cylinder (20), in each case at the end, there is provided an insulating coating (14) which covers the cut faces of the highly conductive layer (11, 21) and the insulating layer (12, 22) and extends as far as the adjacent region of the uppermost semiconductive layer (10, 24) and of the core (13, 23) at the bottom.
5. The electrostatic arrangement as claimed in one of claims 1 to 3, characterized in that on the impression roller (1) or on the three-layer printing plate cylinder (20), in each case at the end, the highly conductive layer (11, 21) is set back in a shortened fashion, and the clearance produced by the shortening is filled by the semiconductive layer (10, 24), which is drawn down as far as the insulating layer (12, 22) and which surrounds the cut edges of the shortened layer (11, 21).
6. The electrostatic arrangement as claimed in one of claims 1 to 3, characterized in that on the impression roller (1) or on the three-layer printing plate cylinder (20), in each case at the end, the semiconductive layer (10, 24) and the highly conductive layer (11, 21) are set back in a shortened fashion, and the clearance produced by the shortening is filled by the insulating layer (12, 22), which is drawn up as far as the outer upper side of the semiconductive layer (10, 24) and which surrounds the cut edges of the shortened layers (10, 11; 24, 21).
7. The electrostatic arrangement as claimed in one of claims 1 to 6, characterized in that the high voltage (U) applied to the voltage electrode (5a, 5b, 5c) is up to 30 kV.
8. The electrostatic arrangement as claimed in one of claims 1 to 7, characterized in that the voltage electrode (5a, 5b 5c) is arranged on the impression roller (1) or the three-layer printing plate cylinder (20) with an effective gap distance (S) of between 5 mm and 30 mm.
9. The electrostatic arrangement as claimed in one of claims 1 to 8, characterized in that the voltage electrode (5a, 5b, 5c) is arranged in a region at the end of the impression roller (1) or the three-layer plate cylinder (20).
10. The electrostatic arrangement as claimed in one of claims 1 to 9, characterized in that the thickness of the highly conductive layer (11, 21) is at least 1/3 of the thickness of the semiconductive layer (10, 24).

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