EP1034078B1 - 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 for transmission an electrostatic charge within a Gravure and flexographic printing unit to improve print quality by polarizing the ink drops on the printing form cylinder. The electrostatic Charge applied to the outer surface of a press from which they go to the outer jacket of the printing form cylinder flowing forth. The electrostatic is brought into the flexographic printing unit Charge on the printing form cylinder, of which them to both the substrate transfer roller and the Counter pressure cylinder flows. Under the influence of a applied electric field are those in the wells of the printing form cylinder (gravure) or that on the surface of the printing form cylinder (flexographic printing) Color molecules polarize, and learn the color droplets overall an increase in volume. A fluent one electric current is taken up for the polarization work to supply the necessary energy. As a result of The droplets of color from the substrate become polarized attracted and moreover the transfer of color droplets by increasing their volume to those passed by Imprints favored.

In this way, gravure printing ensures to a much greater extent that that the well of the printing form cylinder is perfect be emptied, i.e. the printing ink on the substrate is applied. In flexographic printing it causes electrostatic Charge that ink from the subscrat transfer roller on the printing form cylinder and on the Substrate is transferred better. Such orders are also referred to as "electrostatic printing aids"; they serve to provide a full supervisory density in all tones to achieve and avoid so-called "missing dots". The problem of "missing dots" occurs in particular for rough substrates, e.g. Paper webs, with corresponding Bumps on.

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). FIGS. 1A and 1D in connection with FIG. 1C show a two-roll system of a gravure printing unit with a multi-layer impression roller 1 - but here already three-layer according to the invention -, the printing form cylinder 2 and the printing material 4 passed between the two over the deflection roller 3. Above the impression roller 1 a rod-shaped voltage electrode 5 extending over its entire length is arranged. The ink squeegee 6 is indicated for stripping excess ink from the printing form cylinder 2. The inking roller and the return, which are not shown, are seated in an ink trough 7 . The voltage electrode 5 is connected to a high voltage source 8 . The outer surface of the three-layer impression roller 1 has a semiconductor layer 10 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, in deviation from the two-roller system described above, 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 on the side 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 current flow within the electrostatic arrangements. A direct voltage U is supplied to the voltage electrode 5 from the high voltage source 8 and the voltage electrode 5 has the internal resistance R ₁ . The air gap S existing between the voltage electrode 5 and 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 oversized resistor R ₅ . From the high-conductor layer 11 , the current flows through the semiconductor layer 10 lying below , which here forms the resistor R ₆ , further through the printing material 4, which represents the resistor R ₇ . The grounded printing form cylinder 2 has practically the resistance value R ₈ = 0 .

According to Kirchhoff's current distribution law, the majority of the electrical current takes the path of lower resistance via the high-conductor layer 11, while a small fraction flows directly to the printing material 4 via the semiconductor layer 10 . Finally, there is a voltage drop ΔU between the lower semiconductor layer 10 and the earth E , which represents the so-called nip voltage, which is decisive for the polarization of the ink droplets in the cells of the printing form cylinder 2 . The current I flows from the voltage electrode 5 to the earth connection E.

To complete the color droplets from the cells as completely as possible and evenly across the entire width of the substrate to apply - the web widths can exceed 3m today -, sufficient energy must be supplied and the current flow evenly distributed over the entire width of the press become. To meet this requirement, So far the length of the voltage electrode after the maximum usable width of the printing form cylinder or impression roller, so that on the latter a homogeneous charge distribution in the pressure area is guaranteed (see DE-A-27 09 254, P. 11, lines 21ff .; OLLECH, Bernd: Gravure printing - basics and process steps of modern gravure printing technology. Polygraph Verlag Frankfurt am Main, 2nd edition 1993, p. 343, Fig. 15.49; Company documents of Eltex-Elektrostatik GmbH, Because on the Rhine / DE, "ESA-DIREKT - A new dimension of electrostatic printing aid ", print no .: WP-d / e / f-9043-90 / 7-20, Fig. 17; as well as "eltex - manual of electrostatic Discipline ", print no .: Üp-d-0002-93 / 12-100, p.32, Pressure support, Fig. Top right). Hence used voltage electrodes over 3m long. With such Voltage electrodes achieve good printing qualities. adversely are the relatively quick pollution of the open voltage electrodes, which leads to significant losses in their effectiveness and ultimately to complete failure leads, so that the print quality deteriorates rapidly.

The function of the electrostatic arrangements equipped in this way to get a dirty voltage electrode removed, cleaned and reinstalled. This is personnel-intensive and leads to lossy machine downtimes and is therefore often postponed to upcoming delivery times for the printed products not endangered.

To eliminate the disadvantages mentioned were subsequently electrostatic printing aids developed where instead of using a long, attached stick electrode the current in the rotating shaft of the impression roller was initiated (see e.g. DE-A-28 10 452). Now the problem was a voluminous one Voltage electrode fixed and thus the service easier, however, the need for frequent cleaning remains persist; in addition there was an increased effort the insulation of the impression roller core from the printing press.

Encapsulated electrostatic emerged in the further development Printing aids where the current is over the impression core is initiated and largely against pollution are protected so that practically no maintenance is given (see e.g. EP-A-0 115 611; company letter of Spengler Electronic AG, Biel-Benken / CH: Electrostatic Printing aid, SR-HELIOFURN 94). These are the most modern to date Printing aids cause a relatively high mechanical Effort with new printing presses from the start equipped with it is still acceptable. When retrofitting older printing presses in operation with encapsulated pressure aids and introduction of the current into the However, the retrofitting effort would be enormous rise, so that the previous printing aids continue to do so used with long, rod-shaped voltage electrodes. (see, for example, the company lettering of SHTNKO Co., Ltd., Osaka / JP: ESAPRINT 21, ELECTROSTATIC ASSIST SYSTEM; Print No .: 97043000).

In addition, from US-A-3 625 146 electrostatic Printing aids are known in which a roller electrode is attached a three-layer impression roller with an outer semiconductor layer, an underlying conductor layer and one Insulator layer underneath that on the impression core adjacent, is applied. The roller electrode is in direct electrical contact with an exposed ring surface the conductor layer.

In an electrostatic known from EP-A-0 294 042 A voltage electrode is in the form of an arrangement Brush in direct electrical contact with a semiconductor layer a multi-shift press.

In DE-U-94 19 540 there is an electrostatic arrangement described in which a voltage electrode at a distance an outer semiconductor layer of a three-layer pressurizer with a high-conductor layer lying under the semiconductor layer and an underlying insulator layer, which is adjacent to the impression core. As Sheet metal part, grid or the like trained voltage electrode and the semiconductor layer and the high conductor layer form a capacitor that is used for transmission of AC voltage is suitable. To the voltage electrode becomes an ordinary AC voltage or one with a Diode rectified AC voltage (= not smoothed DC voltage), the AC voltage component the alternating current that can be transmitted via the capacitor generated.

The electrostatic arrangement according to the independent Claim 1 is compared to that in the DE-A-27 09 254 described electrostatic arrangement demarcated.

Object of the invention

Given the continuing disadvantages of the existing ones electrostatic printing aids, lies the invention based on the task of creating an arrangement where a dirty voltage electrode from one person can be removed, cleaned and re-installed quickly. Or one should quickly counter the soiled voltage electrode a clean electrode can be exchanged for cleaning the dirty electrode externally. service costs and machine downtimes have to be reduced significantly become. The arrangement should be as small as possible with electrodes Dimension, especially for retrofitting printing machines be suitable and the initial procurement costs be kept low. Apply to print quality but still high demands.

Essence of the invention

This task is accomplished through the electrostatic arrangements solved as in the independent claims 1 and 2 are defined.

So far, the entire professional world has assumed that the latest ones Literature and products show that at Stromeinleiturg over the outer jacket of the impression roller (gravure printing) or the printing form cylinder (flexo printing) for homogeneous charge distribution in the pressure area the use of yourself if possible over the entire length of the impression cylinder or printing form cylinder extending voltage electrode is essential is. Surprisingly, it has now been found that when used a voltage electrode that is shorter than 50% of the Length of the impression roller or the printing form cylinder is, as well simultaneous use of a three-layer impression roller (gravure printing) or a three-layer printing form cylinder (flexographic printing) excellent print quality can be achieved, such as so far 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 cylinder or the printing form cylinder applied and can depend on the high voltage applied and the related safety factors except approx. 1% of the previous full length can be shortened.

Found alternatives to the rod-shaped voltage electrode one such that the outer shell of the press or the Printing cylinder surrounded by a gap in a gap. The homogeneous charge distribution over the entire pressure range is achieved by using the relatively low impedance High conductor layer of the impression cylinder or the printing form cylinder in the axial direction and the high-resistance semiconductor layer reached in the radial direction.

Frontal insulation is used to increase safety the impression cylinder or the printing form cylinder against their cores provided by applying an insulation coating that at least from the high conductor layer into the adjacent one Areas of the overlying semiconductor layer and the underlying one Insulator layer extends. Isolation can also by shortening the high-conductor layer on the face side when filling in the resulting from the shortening Free space achieved with the semiconductor or insulator layer become.

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:

Figure 1A:

a two-roll system of a gravure printing unit with printing form cylinder, impression cylinder and voltage electrode arranged thereon as a basic illustration;

Figure 1B:

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

Figure 1C:

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

Figure 1D:

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

Figure 1E:

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

Figure 2A:

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

Figure 2B:

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

Figure 2C:

the three-layer impression roller according to FIG. 2A with an insulation coating on the end face. the state of the art;

Figure 2D:

the three-layer impression roller according to FIG. 2A with the insulation layer according to the prior art drawn up on the end face;

Figure 2E:

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

Figure 2F:

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

Figure 2G:

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

Figure 3A:

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

Figure 3B:

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

Figure 3C:

an elongated voltage electrode with several rows of emission needles as a perspective view;

Figure 3D:

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

Figure 3E:

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

Figure 4A:

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

Figure 4B:

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

Figure 4C:

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

Figure 5A:

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

Figure 5B:

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

Figure 6A:

the electrostatic arrangement according to the invention for a flexographic printing unit with an elongated voltage electrode arranged on top of the three-layer printing form cylinder, the impression cylinder and the substrate transfer roller as a perspective view;

Figure 6B:

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

Figure 6C:

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

Figure 6D:

the arrangement according to Figure 6A with variably positionable voltage electrode and a substrate transfer roller with a doctor blade as a schematic diagram.

embodiments

With reference to the accompanying drawings follows below the detailed description of preferred exemplary embodiments the arrangement according to the invention. Finally possible modifications are mentioned.

The following definition applies to the entire further description. Are in a figure for the sake of graphic clarity Reference numbers included, but in the immediately associated Descriptive text not explained, so is on their Mention in previous figure descriptions reference taken. In the interest of clarity, the repeated designation of components in subsequent figures mostly dispensed with, provided that it is clearly recognizable in the drawing is that they are "recurring" components.

Figures 2A and 2B

The three-layer impression roller 1 has a jacket over the impression roller core 13 , which externally consists of a semiconductor layer 10 , an underlying high-conductor layer 11 and an underlying insulator layer 12 adjoining the impression roller core 13 . All three layers 10, 11, 12 extend to 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 color residues. To prevent this, various isolating measures are taken. The high-conductor layer 11 is preferably of 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.

Figure 2D

The front insulation is here a shortening of the high-conductor and semiconductor layers 11, 10 set back on both sides and filling of the space created by the shortening with the overlapping insulator layer 12 , which extends up to the outer surface of the semiconductor layer 10 and which intersects the cut edges of both shortened layers 11, 10 surrounds, reached.

Figure 2E

In a modification to the embodiment according to FIG. 2D, only the high-conductor layer 11 is shortened on the face side and the free space is filled with the semiconductor layer 10 , which is quasi pulled down onto the insulator layer 12 and overlaps the cut edges of the high-conductor layer 11 .

Figures 2F and 2G

In the modification of the three-layer impression roller 1 shown , the external semiconductor layer 10 is shortened from the left end side, so that an annular surface 110 of the high-conductor layer 11 lying under the semiconductor layer 10 is exposed. As a safety precaution, an insulator coating 14 can also be provided on this end face, which covers the high-conductor layer 11 and the insulator layer 12 underneath and extends to the edge region of the adjacent impression core 13 . The exposed ring surface 110 allows a voltage electrode 5a, 5b, 5c to be attached to it (see the further figures).

Figures 3A and 3B

The structure of the rod-shaped voltage electrode 5 , which is provided as an inductor electrode for contactless attachment to the impression roller 1 , is known per se. Emission needles 51 are systematically arranged in a row in an elongated insulation body 50 , for example at a distance of 1 cm. A protective resistor 52 is connected behind each emission needle 51 . Emission needles 51 and protective resistors 52 are advantageously positioned on a printed circuit board which is inserted into the insulating body 50 and is cast, for example, with synthetic resin. The connection contact of the voltage electrode 5 is connected to the high voltage source 8 , so that the voltage U is present.

Figure 3C

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

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 the size of the voltage electrode 5a can be further reduced.

Figure 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.

Figures 4A to 4C

In this embodiment, as a contactless inductor electrode, the rod-shaped voltage electrode 5a, which is reduced in length, for example to 1/6 the length of the three-layer impression 1 , is placed in a gravure printing unit on an impression 1 with a gap distance S. One preferably chooses one end of the impression roller 1 for the placement of the voltage electrode 5a , in order thus to facilitate 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 a semicircle around the impression roller 1 above the running web of the printing substrate 4 .

Under special conditions, the arrangement of the voltage electrode 5a below the printing substrate 4 and directed towards the semiconductor layer 10 of the impression roller 1 is also conceivable. The printing material 4, for example damp paper, then acts as a current conductor. The voltage electrode 5a is connected to the high-voltage source 8 , so that a current flows from the voltage electrode 5a through the impression cylinder 1 and the polarization of the color molecules in the cells of the printing form cylinder 2 occurs. For example, the high voltage applied is up to 30 kV DC, and the air gap S is set at 5 mm to 30 mm, here preferably at 5 mm to 15 mm.

When used with the arrangement according to the invention, all common types and types of paper, plastic films, textiles and coated or laminated metal foils with insulating varnish are suitable as printing materials 4 . All ink systems that can be used on gravure printing machines, such as inks based on tuluol, alcohol or ethyl acetate, as well as water colors, can be used for packaging and illustration printing.

Figures 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 with its insulating body 50 extends in an arc over 180 °, with a row of emission needles 51 therein is provided. Here too, for the purpose of easier 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 voltage 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 arranged below it (also called inking roller or anilox roller) and the impression cylinder 40 (also called the pressure roller) located at the level of the three-layer printing form cylinder 20 . The web of printing material 4 runs between the three-layer printing form cylinder 20 and the impression cylinder 40 . A shortened rod-shaped voltage electrode 5a is placed on top of the three-layer printing form cylinder 20 with a gap distance S , which acts as a contactless inductor electrode and has, for example, approximately 1/6 the length of the three-layer printing form cylinder 20 . The voltage electrode 5a is preferably located at one end of the three-layer printing form cylinder 20, in order thus to facilitate lateral access for service work.

The printing ink is fed to the substrate transfer roller 30 from a scoop roller 60 , which is immersed in the ink tank 7 . Depending on the structure of the flexographic printing machine, the voltage electrode 5a can advantageously be variably arranged in all positions in a semicircle around the three-layer printing form cylinder 20 in the two spaces between the substrate transfer roller 30 and the impression cylinder 40 .

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

Figure 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 doctor blade 6 is provided for stripping off excess printing ink.

Figure 6D

State-of-the-art flexographic printing units also dispense with a scoop roller 60 . Here, the printing ink is sprayed onto the substrate transfer roller 30 with a comb doctor 6a ; Excess ink sucks off the squeegee 6a .

Thanks to the invention, there is now an electrostatic arrangement available as a printing aid for gravure and flexographic printing units, service work, especially cleaning, much simplified. Particular advantages arise in the Accessibility for service work through the reduced Dimensions compared to the previously used voltage electrodes, especially when the voltage electrode in an end region of the impression cylinder or printing form cylinder is. Reduce as a result of the smaller field expansion deposits on machine parts from undesirable charged particles, namely paint mist and abrasion from Printing material. The arrangement according to the invention achieves the easier assembly and the lower material expenditure clear cost advantages. Loss in the homogeneity of the Polarization across the entire print width does not occur. The arrangement for retrofitting is already cheap printing presses in operation. The inventive In principle, this arrangement has long satisfied existing need, the professional community over decades on the dogma of the need for extensive 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.
• 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.

In addition to the previously described embodiments of the electrostatic arrangement, further design variations can be implemented. Here are also explicitly mentioned:

• In the three-layer impression roller 1 according to FIGS. 2F and 2G, the semiconductor layer 10 could alternatively also be shortened from the right end side, or the semiconductor layer 10 is shortened on both end sides, so that an annular surface 110 of the high-conductor layer 11 is exposed on the left and / or right.
• The arcuate voltage electrode 5c can be designed in an arc dimension of approximately 270 ° to an almost point-like dimension. Depending on the width and length of the insulating body 50 , the emission needles 51 can be arranged in one or more rows and square-shaped and circular assembly patterns can be provided. In principle, it would even be conceivable to equip a voltage electrode 5a, 5b, 5c with only a single emission needle 51 . The insulation body 50 could be designed to save space and material.
• The various voltage electrodes 5a, 5b, 5c can also be used in the flexographic printing unit; exposed ring surfaces of the high-conductor layer 21 can be provided (see FIG. 2G) and analogous measures will be taken to isolate the end faces on the three-layer printing form cylinder 20 (see FIGS. 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, 5b, 5c) fitted to the latter at a distance with an air gap (S), and a printing plate cylinder (2),

   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 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 the voltage electrode (5a, 5b, 5c)

   f) is fitted with the air gap (S) at a distance from the semiconductor layer (10); or

   g) is fitted with the air gap (S) at a distance from an end face of the highly conductive layer (11); or

   h) is fitted with the air gap (S) at a distance from an exposed annular face (110) of the highly conductive layer (11);

   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 impression roller (1); or

   j) 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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