EP1013418A1 - Inking unit - Google Patents

Abstract

Inking unit has at least one inking roller (8) and ink transfer roller (6) of same outer circumference as plate cylinder (10) so all are single turn. Hence ink amount for specific image area is always applied to the same place on the transfer roller and all further rollers. Raster pitch of ink jets (4) is smaller than the image resolution of the printing machine.

Description

The invention relates to an inking unit for a printing press, the at least one ink roller rolling on a plate cylinder of the printing press, an inkjet printing apparatus with a variety of selectively controllable paint nozzles and a paint transfer device with a circumferential surface for Transfer of ink from the inkjet printing device to the minimum contains an ink roller.

Inks are often used with an ink fountain as a storage container for printing ink, an ink fountain pen, an ink lifter and one Arrangement of many on top of each other or on the plate cylinder Printing machine rolling ink rollers, to which ink transfer rollers, friction rollers and inking rollers. The need for printing ink is in Dependency on the printed image set zone by zone that a resilient Knife (ink knife) more or less pressed against the ink duct the amount of color changed by the gap between the Ink knife and the ink duct. The regulation of the printing ink over the entire width of the color ductor is done by changing the Ink take-off strip, which by the ink lifter in a rhythmic pendulum motion is removed from the ink duct. Through the following arrangement of hard and soft rollers with different diameters Ink distributed several times, split and by an axial movement of the Rubbing rollers are rubbed before they are applied to the plate cylinder by means of the inking rollers is applied.

Such inking units divided into ink zones over the printing width have a number of electronic or electromechanical control and actuating elements for the slotted or unslit color knife with which the Machine operators supply the ink according to the print subject across the print width can vary. The number of color zones depends on the size of the used actuators, the reasonable effort and the width of the printing form. With increasing number of color zones and thus narrower color zones the number of display elements for the zone opening degree also increases as well as the working time and the number of waste sheets if during the Print a manual color correction by expanding or reducing the Ink zone opening takes place. The color zone opening determines together with the Duktorhub the amount of paint, which is averaged over the Ink zone width is required at this point on the sheet. Within one Color zone cannot be differentiated.

One problem with such inking units is the so-called stenciling, one itself in the printing direction, a shadow-like repetitive image of a preceding one Printed image part. This figure is shown by a higher or lower Coloring compared to the environment. The strength of stenciling can be below other by rubbing rollers rubbing along the printing width and / or Ink application rollers can be reduced. In any case, you need a high one Number of rollers in the inking unit in order to have one with as many nips as possible as uniform as possible, the color layer thickness corresponding to the subject on the To ensure inking rollers and finally the plate cylinder. Yet remain machine-specific shortcomings caused by the breadth and Number of color zones are determined, e.g. Edge zone weakening, over and Understeer of the ink supply, among others. With appropriate effort this can Inadequacies due to machine-specific characteristics and computer programs be counteracted.

An alternative to the described inking units with many rollers is known Short inking units such as Anilox inking units, the so-called doctor blade ink boxes exhibit. With the chambered doctor blade ink box, however, there is no zonal one Color feed adjustable. The depth and number of cells on the anilox roller and the quantity of ink removed per sheet determines the quantity of the supplied Color per revolution of a single-turn plate cylinder.

In DE 43 27 212 A1 an inking unit according to the preamble of claim 1 described, in which a metered application of paint on the outer surface an ink roller according to the inkjet printing principle. The paint application will controlled with digital data derived from printing form manufacturing data. The color nozzles of the inkjet printing apparatus are either immediately on an inking roller that rolls on the plate cylinder of the printing press, or to an ink roller that delivers the ink directly to the inking roller directed.

In principle, this creates a short inking unit with a both in Width direction of the ink roller, according to a zonal color control as in Zone inking units, as well as precisely applied paint application in their circumferential direction. The disadvantage is that because of the lack of rubbing strong Stenciling occurs. The only way to counteract this is that the color is transferred from one roller to another with as little residue as possible and that the resolution of the inkjet printing apparatus is as high as possible. Ideally the resolution of the inkjet printing apparatus should be as high as that required print quality, i.e. it finds a kind of indirect inkjet printing instead of what the advantages of offset printing, namely inexpensive edition printing in high quality, no longer exist.

The invention has for its object a short as well as to create stencil-free inking unit for quality printing.

This object is achieved according to the invention in a generic inking unit solved in that the at least one inking roller and the ink transfer device, e.g. is an ink transfer roller, all the same outer circumference as the plate cylinder, i.e. they are all one-turn. In this way it becomes too precisely metered and belonging to a certain image area of the subject Ink quantity always in the same place on the ink transfer device or all other rollers applied, from which they are passed on to the sheet becomes. This has the effect of stenciling, as it is known Short inking units occur due to insufficient friction, reliably avoided.

Another solution to the problem is to apply the paint to the make at least one ink roller so that viewed in the circumferential direction the most uniform possible color application is carried out. Through the Adaptation of the inkjet printing apparatus to the contour of the at least one Ink rollers can have several ink nozzles when viewed in the circumferential direction be arranged one behind the other. This makes it possible to have many small color dots to apply to the ink roller, which corresponds to a film-like covering. Such a thing strong rubbing, such as when removing a strip of paint using a paint lifter is not necessary. In addition, the high A resolution that can be produced with an ink jet apparatus Color zone, which is usually 32 mm, can be defined much narrower. This also enables better dosing, although none in the circumferential direction color distribution adapted to the subject.

This saves compared to a conventional inking unit with a ductor and lifter Invention, on the other hand, a lot of mechanical parts, and there is a quieter Machine run.

The quieter machine run is not only due to the savings as mentioned above given the lateral rubbing, but also by the uniform Application of printing ink in the circumferential direction. On closer inspection, this means that in conventional inking units, especially in the short inking unit by the sudden application of paint by the lifter a short stiffness of the Ink rollers occurs, which then during the equalization of the Color volume again. Since this process has been repeated cyclically associated with a vibration excitation. The device according to the invention made possible by the application of printing ink in a uniform thickness over the Considered the size of the ink roller that the torque requirement remains constant.

The invention is particularly suitable for offset printing machines with the so-called Computer-to-press / direct imaging technology, such as the Heidelberg printing presses AG applies in the Quickmaster DI and in which the imaging unit is moved to the printing press. The plates are directly in the Printing machine illustrated on the cylinder by the untreated printing form or pressure plate clamped on a plate cylinder and by one in the Imaging head installed is imaged to one for the printing press To produce offset printing usable printing form. That way already at the Printing machine available raster data can be in printing operation without recreating the data in addition to controlling the inkjet printing apparatus can be used in every machine cycle. An adaptation of the Resolution of the raster data to the normally lower resolution of a Inkjet printing apparatus is very easy to carry out. For example the resolution resolution was easily carried out in the press computer become.

While applying the invention to an offset printing machine, the resolution of the ink jet printing apparatus is preferably smaller than the resolution the raster data is designed for the imaging unit, the corresponding Resolutions in printing processes other than offset printing are also the same be, e.g. in anilox, gravure or other printing processes for which the The invention is also suitable, especially if the printing form is produced in the machine becomes. With these printing processes too, the screen raster data from the prepress stage can be used can also be used for the inkjet printing apparatus.

The invention is not only suitable for master-bound printing processes, at which the printing plate or the image carrier creates only once per print job but also for future digital printing presses with the so-called Computer-to-paper technology, which is used to image each individual printing substrate either the same or new image data completely read out once become. In both cases, the inkjet printer must also Query data completely once per cylinder revolution. The one at the The computer used in the printing press must have sufficient power to perform this to provide high data rates in the required time. To the deployment To ensure the data are suitable in prepress Data storage systems used.

Even with conventional printing presses without a built-in plate imaging unit can the inking unit according to the invention instead of the conventional Inking unit can be installed because suitable digital data for the inkjet printing apparatus from platesetter (CTP) or from film exposure (CTF) already exist and only have to be transferred to the printing press, if necessary after the mentioned adjustment of the resolution.

The color nozzles of the ink jet printing apparatus can e.g. simply in one single straight line across the print width close to the ink transfer device be arranged. However, a two-dimensional is preferred Arrangement or matrix of paint nozzles used. If the ink transfer device is an ink transfer roller, the matrix of ink nozzles must be curved, to nestle against the surface of the ink transfer roller.

In a further development of the invention, an endless transfer device is used Used tape that rotates around two or more rollers. This has the Advantage that the color nozzle matrix can be flat because it is on a straight line Section of the ink ribbon can be arranged.

To ensure trituration to a limited extent, at least one the inking rollers and / or the ink transfer device with a drive for one slight reciprocation along its axis during printing is provided, i.e. oscillate or oscillate in a manner known per se. However, the amplitude of this movement should not be significantly greater than that Resolution of the inkjet printing apparatus to be the subject-specific Do not destroy dosage again.

According to a development of the invention, at least one of the ink rollers and / or the ink transfer device an optionally activated ink squeegee intended. Because with the inkjet printing device an active ink supply takes place, and not, as with ink fountain systems, a color return in limited frame takes place, there may be over-coloring, overfilling of the inking unit come. With conventional ink fountain systems, this is under avoided or reduced by the fact that the residual color film thickness on the Heber prevents the same amount regardless of this layer thickness Color runs in. The squeegee in the invention can be at the required times activated to create a neutral starting position in the inking unit. This can be done in a short, automatic process that takes place during color printing Print interruption and / or happen before and after each print job. A Control with adjustable parameters allows the printer to print the "Neutralization intervals" based on the print job Set suggestion lists or your own experience. The squeegee can over the print width into several that can be activated independently of each other Single doctor blade can be divided, which allow local doctoring. Besides, can the ink squeegee in a known manner to scrape off the ink when changing colors or if the inking unit is dirty.

As an alternative to a squeegee or in addition, one or more sensors can be used be provided, which record the color residue and in a control loop for automatic control of the new spraying are included.

In the event of a color change, the inkjet printing apparatus can simply be replaced become. A particularly fast color change is made possible that two or more inkjet printers swivel side by side be arranged, with the printing apparatus required in each case in the position is pivoted in which the paint nozzles are directed onto the paint transfer device is.

The inking unit according to the invention comes with very few ink rollers the ink transfer device and the plate cylinder and can be very be made compact. In many cases, a single ink roller is between these two elements.

Conventional devices with which a machine operator supplies the ink can regulate required cases zalis include a variety of Control and display elements that are correspondingly difficult to operate and to are watching. In a further development of the invention, the one particular ergonomic influencing of the ink supply by the operator is enabled a control device for zone-free color adjustment provided, the one Contains screen to display the current print subject, with any to influencing fields on the displayed print subject by the operator can be selected, preferably to one of programs for image processing known way by dragging with the mouse or the like.

The inking unit according to the invention is suitable for both waterless offset printing as well as for wet offset printing. However, low viscosity printing inks required if a printhead for conventional ones is used as the inkjet printing apparatus Inkjet printer is used. Such a printhead works e.g. on the Way that a small volume of printing ink temporarily by a piezoelectric Actuator is compressed, with a droplet of ink on one Pixel is sprayed.

With a suitable design of the inkjet printing apparatus, however, a Inking unit according to the invention relatively high-viscosity standard offset printing inks or process UV drying offset printing inks. For this purpose a high pressure pump device for supplying the ink jet printing apparatus with ink under a predetermined high pressure, a heater for heating the printing ink to a predetermined temperature above room temperature and a variety of valves for selective Control of the ink supply to the ink nozzles of the inkjet printing apparatus intended.

By using the printing ink, which normally has a viscosity of approximately 50 to 70 Pa s has the valves under a pressure in the range of about 10 to 100 bar supplied and at a temperature in the range of about 40 to Is heated to 70 ° C, the viscosity decreases to such an extent that it is highly precise Color dosing is possible.

The valves can e.g. pulse length controlled solenoid valves, as in the Zeitschrift Zeitungstechnik, July / August 1996, p. 30, for an inking unit are where the printing ink using a digital ink pump system, the one Gear pump contains, applied to a specially trained ink film roller becomes.

Valves with piezoelectric actuators as adjusting elements are even more expedient, so-called piezo valves. Such a valve, e.g. in DE-A-4 220 177 is described has response times in the order of microseconds. It can be opened and closed many times faster are called conventional solenoid valves, the response times of several Have milliseconds. This enables very fine dosing of the printing ink, preferably by fully opening and closing controlled by pulse length of the valve or alternatively by regulating the flow rate of a valve, whose degree of opening is controlled by a fast control loop. Moreover can with fast piezo valves even at high printing speeds relatively high resolution of the inkjet printing apparatus can be realized, the would be limited by long valve response times.

Fig. 1

ein Farbwerk für eine Offsetdruckmaschine, das einen Tintenstrahl-Druckapparat enthält,

Fig. 1a

zeigt ein konventionelles Farbwerk das einen Tintenstrahl-Druckapparat enthält.

Fig. 2

eine Teilansicht einer alternativen Ausführungsform des Farbwerkes, und

Fig. 3

einen Computerbildschirm zur Anzeige eines Drucksujets zur Beeinflussung der Farbzufuhr in ausgewählten Bereichen des Sujets.

The invention is explained in more detail below using exemplary embodiments with reference to the drawings. The drawing shows:

Fig. 1

an inking unit for an offset printing press, which contains an inkjet printing apparatus,

Fig. 1a

shows a conventional inking unit containing an inkjet printing apparatus.

Fig. 2

a partial view of an alternative embodiment of the inking unit, and

Fig. 3

a computer screen for displaying a print subject to influence the ink supply in selected areas of the subject.

The inking unit shown in Fig. 1 includes an ink jet printing apparatus 2 with a plurality of paint nozzles 4, which are shown schematically as arrows, which indicate the spray direction. The color nozzles 4 are two-dimensional Arranged matrix that nestles against an ink transfer roller 6 with a small gap in between.

The ink transfer roller 6 rolls on an inking roller 8, which in turn opens rolls off a plate cylinder 10 of an offset printing machine, of which in FIG. 1 a rubber cylinder 12 and an impression cylinder 14 can also be seen. Alles these rollers and cylinders are single-turn, i.e. they are all the same diameter.

In addition, a dampening unit 16 for wet offset is shown schematically in FIG. 1, this does not apply in the case of waterless offset printing.

Adjacent to the ink transfer roller 6, an ink doctor blade 18 is arranged against the ink transfer roller 6 and away from it.

In operation, the color nozzles 4 in accordance with raster data that the Inkjet printing apparatus 2 are supplied, selectively driven to the Ink transfer roller 6 according to the raster data with printing ink spray. Each point on the ink transfer roller 6 is just as much Color supplied as required on the plate cylinder 10.

In order to achieve this, the platesetter, which is not shown, is fed Raster data, which represent the printed image, into one of the matrix Color nozzles 4 corresponding raster image converted with the ink jet printing apparatus 2 is controlled. The ink nozzles 4 guide the ink transfer roller 6 exactly the amount of color at each point as it was when printing from Plate cylinder 10 is delivered to the paper or other printing substrate. The nips between the ink transfer roller 6 and the ink application roller 8 or between the inking roller 8 and the plate cylinder 10 ensure a smooth color film so that the resolution of the ink jet printing apparatus 2nd becomes invisible.

A raster image suitable for the ink jet printing apparatus 2 normally has a much lower resolution than the normal offset resolution because the distance of the Color nozzles 4 is comparatively large. This does not affect the print quality deteriorated, since it is ultimately determined by the plate cylinder 10, but improved, since no stenciling reliably occurs.

In the case of a rough subject, or in areas with little variation, one Subjects several paint nozzles 4 can be controlled together. With fine Representations, the color nozzles 4 are individually controlled, and for coarse or full-area representations, the color nozzles 4 are controlled together.

To control the total amount of ink applied to the ink transfer roller 6 can use sensors to record the remaining ink on the inking roller 8 can be provided, or it will be with a slight excess of color worked, from time to time with the squeegee 18 a neutral situation will be produced.

Figure 1a shows a known from conventional inking units Ink roller arrangement to an ink jet printing apparatus 2 with a variety of color nozzles 4 is arranged. Just as in Fig. 1 are also here Color nozzles 4 arranged in a two-dimensional matrix. Through the Two-dimensional arrangement of the color nozzles 4 has the advantage that with many small blobs of paint an almost film-like application of paint on a Ink transfer roller 6 can be applied. This makes rubbing up like it is necessary in conventional inking units because one of the Ink lifter applied to a paint roller in the circumferential direction must be equalized, not necessary. Especially with small ones Offset printing presses have an advantage in this because there Vibration excitation due to lateral rubbing is particularly negative affect the print quality. The number of ink transfer rollers 6 can thereby be reduced to a minimum.

Fig. 2 shows a partial view of an inking unit, which in the not shown Share just as the inking unit of Fig. 1 is designed. The inking unit of Fig. 2 differs from that of Fig. 1 in that instead of the ink transfer roller 6 an ink transfer ribbon 20 e.g. made of steel or rubber is that rotates around two rollers 22, 24. The ink ribbon 20 has the same circumference as the plate cylinder 10. On a straight section of the Ink transfer ribbon 20, the ink jet printing apparatus 2 'is arranged, the Color nozzles 4 'are arranged in one plane in this case, whereby the Ink jet printing apparatus 2 'is easier to manufacture.

If desired, the ink transfer belt 20 - as well as the ink transfer roller 6 of Fig. 1 - slightly back and forth in operation in the direction of the printing width move to ensure easy rubbing. In the embodiment of Fig. 2 is a squeegee 18 'similar to the squeegee 18 of Fig. 1 not on the Ink transfer device, the band 20, but on the inking roller 8th arranged.

Just like a conventional offset printing machine with ink zones in the inking units of FIG. 1 or FIG. 2, the ink supply can be influenced can be provided by the machine operator along the printing width. No additional mechanical or electromechanical is required for this Control and setting elements, but the influencing can be purely program-controlled take place, and in arbitrarily selectable areas, not only within certain zones. It can also influence the Ink supply not only along the sheet width, but also in the circumferential direction take place, i.e. along the arc length.

The inking units shown in FIGS. 1 and 2 make it possible to supply the ink to influence selected areas without the risk of stenciling exists because the single-speed design of the rollers or the belt leads to that an exposure at one point in the form of more or less color directly in the same place in the settlement and nowhere else.

It is also possible in the case of a one-turn model Ink transfer roller 6 or ink transfer belt 20 the Tntenstrahl printing apparatus 2.2 'to be controlled so that the paint application in a corresponding

Phase shift takes place in such a way that this is due to the settlement on the provided place on the plate cylinder 10.

The ink job from the inkjet printing apparatus then advantageously takes place 2.2 'on an ink transfer roller 6 and then directly on the plate cylinder 10 instead.

The ink transfer roller 6 can also be advantageous after the Scrape the contact point with the plate cylinder 10.

But it is also conceivable that through appropriate surfaces on the Ink transfer roller 6 a 100% ink transfer to the plate cylinder 10 he follows.

A particularly useful way for zone-free color control 3 illustrates both in the width direction and in the circumferential direction shows a computer screen 26 on which a currently printed subject 28 is shown. For example, the computer screen 26 shows that for the Platesetter used raster image of subject 28.

If the machine operator recognizes from a fresh print copy, that in a dashed area on the subject 28 an adjustment The ink supply is required, it can be done with the mouse or another Show device a corresponding field 30 on the computer screen 26 wind up. Dragging on a corner or on an edge of the dashed line drawn field 30 with the mouse increases or decreases the field, such as it is known from image processing programs.

After the operator determines the exact size and position of field 30 he can do it by a suitable action such as a double click with the Select the mouse and a color adjustment window will open (not ) in which the desired correction is specified according to strength and direction can be. In this or a similar way, the operator can quickly and easily simply correct the ink supply in any area of the subject 28.

The method of color correction illustrated in FIG. 3 is only an example and can be modified in many ways. For example, a touch or proximity sensitive screen can be used on which the Printer can make the necessary corrections without making any need to touch other controls.

"List of reference symbols

2, 2 '

Inkjet printing apparatus

4, 4 '

Paint nozzles

6

Ink transfer roller

8th

Inking roller

10th

Plate cylinder

12th

Rubber cylinder

14

Impression cylinder

16

Dampening system

18, 18 '

Squeegee

20th

Ink transfer ribbon

22, 24

Rollers

26

Computer screen

28

subject

30th

Box on the computer screen

Claims (12)

Inking unit for a printing press, the at least one on a plate cylinder the ink roller rolling off the printing machine, an inkjet printing apparatus with a variety of selectively controllable paint nozzles and a paint transfer device with a circumferential surface for the transfer of printing ink from the inkjet printing apparatus to the at least one ink roller, characterized in that the at least one inking roller (8) and the ink transfer device (6; 20) the same outer circumference as the plate cylinder (10) have. Inking unit according to claim 1, characterized in that the printing press is an offset printing machine and that the grid spacing of the color nozzles (4; 4 ') is smaller than the image resolution of the offset printing press. Inking unit according to claim 1 or 2, characterized in that the Printing machine contains a plate imaging unit and that the before Printing operation for the plate imaging unit used raster data in the Printing operation for controlling the ink jet printing apparatus (2; 2 ') in each Machine cycle can be used. Inking unit according to claim 2 and claim 3, characterized in that the raster data of a device used for the plate imaging unit the corresponding raster data are supplied to reduce the image resolution generated with a smaller image resolution and the ink jet printing apparatus (2; 2 ') controlled with it. Inking unit according to one of the preceding claims, characterized in that that the ink transfer device is an ink transfer roller (6). Inking unit according to one of claims 1 to 4, characterized in that the Ink transfer device is an ink transfer belt (20) and that the ink nozzles (4 ') of the ink jet printing apparatus (2 ') in a to a rectilinear section of the Ink transfer ribbon are arranged parallel plane distributed. Inking unit according to one of the preceding claims, characterized in that that at least one of the inking rollers (8) and / or the ink transfer device (6; 20) with a drive for a reciprocating movement along its axis is provided during printing. Inking unit according to one of the preceding claims, characterized in that that on at least one of the inking rollers (8) and / or the ink transfer device (6; 20) an optionally activatable ink doctor blade (18; 18 ') is provided. Inking unit according to one of the preceding claims, characterized in that that between the ink transfer device (6; 20) and the plate cylinder (10) exactly one inking roller (8) is located. Inking unit according to one of the preceding claims, characterized in that that a control device for influencing the ink supply by a Operator is provided which has a screen (26) for displaying the current Contains print subjects (28), with fields (30) to be influenced on the displayed print subject can be selected by the operator. Inking unit according to one of the preceding claims, characterized in that that the ink jet printing apparatus (2, 2 ') a high pressure pumping device for supplying printing ink under a predetermined high pressure, a heater for heating the ink to a predetermined one Temperature above room temperature and a variety of valves for selective control of the ink supply to the ink nozzles (4; 4 ') of the inkjet printing apparatus contains. Inking unit according to claim 11, characterized in that the valves are piezoelectrically operated valves.

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