GB2424393A

GB2424393A - A process for operating a printing machine

Info

Publication number: GB2424393A
Application number: GB0605671A
Authority: GB
Inventors: Thomas John; Helmut Stuhlmiller; Reinhard Zeller
Original assignee: MAN Roland Druckmaschinen AG
Current assignee: Manroland AG
Priority date: 2005-03-24
Filing date: 2006-03-21
Publication date: 2006-09-27
Also published as: DE102005013634A1; GB0605671D0; FR2885550A1; CH698993B1

Abstract

In a process for operating a printing machine the roller frame 10-16 of an inking unit 9, which is associated with a plate cylinder 5, is pre-inked with a predetermined ink quantity profile before an inking roller 10, 11 is first set against the plate cylinder 5. In order to attain operational conditions as far as possible the entire roller frame 10-16 is pre-inked with a constant ink quantity over its width, the value 45 of which is a machine-specific experimental value which, for a given printing machine, depends only on the materials used for production. The ink quantity is at least partially controlled by the speed 68; 78 of the ink ductor 18. The experimental value of the ink quantity for a given material combination is a statistical mean value of the ink quantity profiles in a printing operation for standard production runs; this statistical mean value can be obtained from tests. The ink quantity can also be additionally controlled by the gap between the doctor blades 19 and the ink ductor 18 and/or by the duration of the ink supply. All the parameters for pre-inking are deposited in the form of a table in the system control unit of the printing machine.

Description

A process for operating a printing machine When starting up an offset

printing machine, it is customary to use the data relating to the zonal area coverages of the individual pages to be printed as a basis for setting the doctor blades to the anticipated specified gap to achieve the desired ink quantity on the paper or the desired optical density (ink density) . This generally takes place automatically. In an inking unit that is cleaned before a production run, however, it is a long time before there is sufficient ink in the inking unit to ensure that the necessary ink quantity for the desired ink density is transferred to the paper. It is possible to observe large differences depending on the area coverage and therefore on the zonal gap status of the doctor blades. With low area coverages, i.e. below five percent, it can take up to 500 to 1000 cylinder revolutions until the specified density is achieved. The spoilage rate is therefore high.

To improve this situation, inking units have, for a long time, been preinked. The pre-inking procedure takes place before the actual production run or is latterly also included in the actual start-up procedure. The specified inking-zone gaps required according to the area coverages of the pages to be printed are generally used for pre-inking. Although this process represents a considerable improvement for relatively high area coverages, when compared to start-up without pre-inking, the results for low area coverages are similarly poor.

To improve this, EP 1 232 862 Al has therefore proposed pre- inking with inverse zonal doctor blade gaps. In this case, after the pre- inking procedure, the doctor blades each have to be returned to the actual specified gap. This process represents a further improvement particularly for small area coverages, but is inadequate for high and very high area coverages since, in extreme cases, there is no pre-inking whatsoever. In practice, this process has shown that, although the start- up spoilage rate could be reduced for normal area coverages, the printing results over several cylinder revolutions were unsatisfactory, particularly for extreme area coverage S. The object on which the present invention is based is to prevent the disadvantages demonstrated in the known pre-inking methods and to ensure that the desired ink density is achieved as rapidly and precisely as possible for all possible area coverages, irrespective of the subject to be printed.

According to the invention, this object is achieved by a process having the features of Claim 1. Advantageous developments are defined in the dependent claims.

The invention comprises a process by means of which, as a result of a defined pre-inking of the roller frame when setting the inking rollers against the plate cylinder, a uniform ink layer is applied to the printing plates mounted on the plate cylinder at all ink-conducting points, the thickness of this ink layer being such that the desired ink intensity, i.e. ink density, is achieved with the first transfer of ink by the following blanket cylinder to the paper to be printed. To achieve this irrespective of the subject to be printed, i.e. irrespective of the area coverage of a printing forme, the entire roller frame has to be pre- inked with the same ink quantity over its width.

The required ink quantity depends solely on the size of the roller frame, i.e. on the total surface of all rollers, and on the materials used. Here, the ink quantity is at least partially controlled, i.e. adapted to the given properties, by the speed of the ink ductor. The ductor speed or rate is particularly useful for this since it is capable of very fine adjustment and, at altogether relatively low speeds, the ductor can be controlled without notable acceleration or braking times or the corresponding inaccuracies.

The doctor blades are here set to a constant value which is approximately in the centre of the inking zone gap used in conventional production runs.

In addition, the ink quantity can be controlled by the gap between the doctor blade and the ink ductor and the duration of the procedure. The duration can be adjusted by opening and closing the zone screws accordingly, by switching the ink ductor drive on and off and by moving the film roller in and out of an operating position. Which parameters are held constant here and which, in addition to the ductor speed, are adapted as variables to the ink-density requirements for a defined material combination is dependent on the particular machine construction and on the inertia or the drive delay of the individual machine elements and the resultant ink-metering inaccuracies. It is preferable for only a single parameter, namely the ductor speed, to be variably adjusted and for all others to be held constant.

The constant and variable parameters are deposited in table form in the system control and can be adapted where necessary. To account for the differences in the combinations, particularly of paper, inks and dampening accessories, it is recommended that a data set be stored for the variable parameters, which can be accessed by the system control for each print application depending on the materials selected. The variable parameters have to be determined when a printing machine is started up and later for new combinations of materials in print tests. To keep the number of variable parameters low, materials having similar behaviour can be combined in classes so that it is only necessary for the parameters for combinations of material classes to be determined by experimentation and stored.

The pre-inking procedure can be omitted when the plate cylinder contains no printing plates whatsoever, or so-called dummy plates, over its entire circumference and the associated regions in the inking unit are separated from regions to be printed by roller edges or recesses in the blanket rollers. The regions in which pre-inking has to take place are therefore dependent on the print application and the geometry of the roller frame.

The pre-inking procedure can be dissociated from the start-up procedure of the printing machine during preparation for printing if the time interval from start-up is not too great.

However, the pre-inking procedure can also be included directly in the acceleration phase of the printing machine during start- up.

Pre-inking is essentially necessary and useful if an inking unit has been cleaned after the previous production run. An automatic mechanism, which pre-sets the pre-inking procedure after the inking unit has been cleaned but can be switched off intentionally by a printer, is recommended here. It always makes sense to clean the inking unit if the machine has been stationary for a relatively long time after a production run or if the zonal area coverages of the following production run deviate significantly from those of the prior production run in the individual inking units. A deviation of approximately ten percent can be used as a criterion for this. This also applies to interruptions in production in which only a few printing plates are exchanged, as is often the case for updating purposes or for changing over to other regional editions. In these cases, only a few inking units are affected. The cleaning of the inking units can be automated on the basis of these criteria since the system can be provided with information relating to area coverages in electronic form before production and these data can be used to carry out an area-coverage comparison by means of the machine control. However, a printer can also switch off this mechanism intentionally.

If a fault or an intentionally triggered stop causes the machine to halt during the pre-inking procedure and pre-inking to be interrupted, when the machine is started up again the procedure is continued in such a way that the necessary ink quantity for pre-inking is achieved in the inking unit. This can be controlled for instance by the duration of the repeat procedure.

The sum of the time taken for interrupted and renewed pre-inking then corresponds to the specified time.

As soon as the first ink is transferred to the paper when the printing machine is started up, it is necessary in an inking unit for a corresponding doctor blade gap to match the ink that corresponds to the actual zonal requirement according to the zonal area coverage of the print subject. Owing to the reaction time of an inking unit, the inking zone gaps for the subject- related ink supply should even be set shortly before the first transfer of ink to the paper. All other control systems for the ink supply, such as the speed of the ink ductor or the position of the film roller (if it can be moved in and out of an operating position) then likewise assume their normal operating state.

In conjunction with the pre-inking procedure, the start and stop sequences for the other control procedures have to be optimised accordingly when starting and stopping the machine. Thus, where a pre- inking procedure is integrated in the start-up procedure, the procedures for setting the rollers cannot take place before pre-inking has finished. It is also useful to observe a particular setting sequence in order to be able to make full use of the pre-inking procedure. Then, after activating the supply of dampening agent, the dampening rollers have to be set against the plate cylinder in order to wet the printing plates with sufficient dampening agent. Following this, the inking rollers are set against the plate cylinder. As a result of the previous dampening, ink is only applied to the printing points of the printing plates. The last step then consists in setting the blanket cylinder in the operating position and thus transferring the ink to the paper. In this staggering, and depending on the machine, its acceleration, the printing materials and the set time intervals between the control procedures, it is ensured that the printing plates are in fully free-running mode, i.e. non-printing points have no ink residues, and the desired ink density is achieved soon after the first contact between the blanket cylinder and the paper during the first revolutions of the blanket cylinder.

The stop sequence should be designed so that, on the one hand, the last copy to fall from the spider wheel of the folder onto the delivery belt when the machine is at a standstill still has a saleable print quality whilst, on the other, when starting up again without cleaning the inking unit and without pre-inking, sufficient ink is transferred to the paper as soon as the blanket cylinder is set in the operating position. This is ensured when the time interval between the ink supply being interrupted for instance as a result of moving the film roller out of the operating position or by stopping the ductor - and moving the inking rollers away from the plate cylinder is selected so that the total quantity of ink remaining corresponds to that of the pre-inking procedure. Since, irrespective of the area coverage, the supply of ink and removal of ink are counterbalanced, this state can be achieved consistently despite the varying widths of the inking zones adapted to the print subject.

The precise determination of the start and stop sequences is dependent on the geometry of the inking unit and on the materials used, particularly the inks and papers, and also on the publisher's requirements regarding ink intensity.

For a better understanding of the invention, embodiments will now be described with reference to the accompanying drawings, in which: Fig. 1 is a schematic side view of an offset printing unit with an inking and a dampening unit; Fig. 2 is an enlarged detail of the inking unit contained in Fig. 1; Fig. 3A shows an example of zonal area coverages and ink quantities when a printing machine is operated without pre-inking the inking unit; Fig. 3B shows the ink density curves of the individual zones for the example according to Fig. 3 over the number of print copies; Fig. 4A shows an example of zonal area coverages and ink quantities when a printing machine is operated with conventional pre-inking of the inking unit; Fig. 4B shows the ink density curves of the individual zones for the example according to Fig. 4 over the number of print copies.

Fig. 5A shows an example of zonal area coverages and ink densities when a printing machine is operated with pre-inking of the inking unit according to the invention; Fig. 5B shows the ink density curves of the individual zones for the example according to Fig. 5A over the number of print copies; Fig. 6 is a diagram showing the inventive pre-inking of the inking unit in a production run using half the maximum operating width of the printing unit; Fig. 7 is a diagram showing the inventive pre-inking of the inking unit in a production run using three-quarters of the maximum operating width of the printing unit; Fig. 8 shows an example of altering the zonal area coverage when changing production; Fig. 9 shows an example of the time-progression of different machine parameters when starting the machine with integrated pre-inking before the acceleration phase; Fig. 10 shows an example of the time-progression of different machine parameters when starting the machine with integrated pre-inking during the acceleration phase; and Fig. 11 shows an example of the time- progression of different machine parameters when starting the machine with integrated pre-inking before the acceleration phase when the film roller cannot be moved out of the operating position.

Fig. 1. shows a schematic side view of a typical offset printing unit 1 with a paper web 2 to be printed, a printing or blanket cylinder 3, an impression cylinder 4, which can also be a blanket cylinder, a plate cylinder 5, a dampening unit 6 with a non-contact metering device 7 for the dampening agent and a dampening roller 8 and also an inking unit 9. The blanket cylinder 3 here can be moved away from the impression cylinder 4 and therefore from the paper web 2 and from the plate cylinder 5.

The inking unit 9 conventionally comprises two or more inking rollers 10 and 11, which can be moved away from the plate cylinder 5. The inking rollers 10 and 11 are moreover in permanent contact with the inkdistributing cylinder 12. The latter is connected by way of an ink transfer roller 13 to the ink-distributing cylinder 14. The latter is in contact with the film roller 16 by way of a further ink transfer roller 15. This roller train 10 to 16, also called a roller frame, can also have additional ink rollers which are not shown here.

By way of a small gap 17, a few tenths of a millimetre wide, the film roller 16 receives ink from the ink ductor 18, which rotates considerably more slowly than the roller train 10 to 16 running at machine speed. In several inking-unit constructions, the film roller 16 can be moved away from the ink ductor 18 50 that the opening 17 becomes too great for the transfer of ink to be possible.

Fig. 2 shows an enlarged detail of the inking unit 9 contained in Fig. 1. The doctor blade 19 reduces the ink quantity 20 - which is applied to the ductor 18 from an ink duct for instance by way of a dipping roller 21 - to the subject-related layer thickness 23, there being a plurality of separately controllable doctor blades 19 provided over the width of the ductor 18 to enable zonal adjustment of the ink quantity 20. The ink layer 23 is then partially removed by the film roller 16 by way of the opening 17. In Fig. 2, dashed lines moreover show the film roller 16 in the position 16a in which it is moved away from the ductor 18.

Fig. 3A shows a simple exemplary area coverage profile 24 of a print subject with four different area coverages, namely a zone with a very low area coverage, a zone 26 with a low area coverage, a zone 27 with moderate area coverage, and a zone 28 with high area coverage. This also shows the gap profile 29 of the doctor blade 19 when the machine is started without pre- inking. All doctor blades are closed here, so that initially no ink is transported to the roller frame 10 to 16. This also shows the gap profile 30 of the doctor blade 19 as required in a printing operation for the print subject 24. As the profile 30 shows, the zonal width covered by a doctor blade 19 is significantly smaller than the width of the four different subject zones of the area coverage profile 24, i.e. the number of doctor blades 19 provided is much greater than four. The profiles 24, 29 and 30 are normalised, i.e. the edges delimiting the bars vertically correspond to a respective area coverage or a doctor blade gap of 0% and 100%.

The adjacent graph in Fig. 3B shows the typical ink density curves 32 to 35 associated with the four different area coverage zones 25 to 28 of the subject over the number of copies printed since starting the machine without pre-inking the roller frame to 16. In this, the curve 32 belongs to zone 25, the curve 33 to zone 26 etc. The line 37 represents the specified ink density, the dashed lines 38 and 39 the limits of the acceptable tolerance range for the desired ink density. The specified ink density here is normalised to the respective zonal value, so that only a single specified line 37 is produced for all four zones 25 to 28. As Fig. 3B shows, the lower the subject-related ink density, the longer it takes to reach the permissible tolerance range.

Fig. 4A shows the same area coverage profile 24 of a print subject as Fig. 3A, including the nowadays conventional doctor blade adjustment 40 for pre-inking, which corresponds to the gap profile 30 (already known from Fig. 3A) of the doctor blade 19 for the actual printing operation. The adjacent graph of Fig. 43 again shows the associated typical ink-density curves 41 to 44 over the number of print copies produced for a pre-inking procedure with the ink-metre adjustment 40 for the different area coverage zones 25 to 28. In this, the curve 41 belongs to zone 25, the curve 42 to zone 26 etc. As Fig. 43 shows, it is also the case here that, the lower the subject-related ink density, the longer it takes to reach the permissible tolerance range. With a high subject-related ink density 28, the actual ink density 44 is initially exceeded. On the other hand, the increase in the actual ink density 41 is still inadequately slow for a low subject- related ink density 25.

Figures 5A and 5B show the situation for the inventive pre- inking of the roller frame 10 to 16. As Fig. 5A shows, the same constant doctor blade gap 45 is always associated with the entire print subject 24, irrespective of the different area coverages of the individual subject zones 25 to 28. For the printing operation itself, the ink meters or doctor blades 19 again have the necessary gaps for the different subject- related area coverages in accordance with the profile 30 already known from Figures 3A and 4A. The adjacent graph of Fig. 5B shows the substantially congruent ink density curves 47 to 50 produced with this type of pre-inking. The standardised specified ink density 36 is already achieved within the limits 37 and 38 of its tolerance range after very few print copies and, more specifically, in all four different area coverage zones 25 to 28.

Fig. 6 shows a conventional situation for newspaper printing machines. Only half the plate cylinder 3 is covered with printing plates 51 and 52. The inking rollers, of which only the inking rollers 10 and 11 are shown by way of example, have a central recess 53. In this case, pre-inking is only carried out within the limits of that portion of the inking rollers which is associated with the portion of the plate cylinder which is covered with printing plates. The gap profile 54 of the doctor blades 19 which is shown at the bottom of Fig. 6 is produced accordingly.

Fig. 7 shows a situation in which three-quarters of a plate cylinder 3 are covered with printing plates 55 to 57. In this case, the roller frame 10 to 16 having the inking rollers 10 and 11 (shown by way of example) is pre-inked over its entire width, which corresponds to the gap profile 58 of the doctor blades 19 shown at the bottom.

Fig. 8 shows the area coverage profile 24 (already known from Figures 3A, 4A and 5A) as an original profile produced by the print subject of a previous production run. By way of example, this shows the area coverage profile 59 of the print subject of an assumed following production run, which profile 59 deviates from the previous profile 24. The four different area coverage zones in Fig. 8 are denoted by A, B, C and D and identified by 1 for the prior production run and 2 for the following production run. The formulae 60 show the changes in the area coverages.

When there is a change in area coverage, as shown in zones A and B, it is necessary to wash the inking unit and then carry out a new pre-inking procedure. In C, the area coverage has remained the same, in D it is only minimally lower, i.e. by around five percent. In cases C and D, there is therefore no need to wash the inking unit and repeat the pre-inking procedure.

Fig. 9 shows an example of the different parameter curves or control states of the machine and inking unit, applied over time for a machine start with integrated pre-inking before the acceleration phase when the film roller 16 is moved out of the operating position. Curve 61 here shows the machine speed which, in this example, is held at a constant value 62 during pre-inking. The machine accelerates immediately afterwards, i.e. there is a virtually linear increase 63 in the machine speed. The curve 64 shows the gap of the inking zones, in which case, after pre-inking with a constant doctor blade gap 65 over all zones, the doctor blade gaps of the individual zones are either increased to a higher value or decreased to a lower value depending on the subject- related area coverage, as shown by the division of the curve 64 into the two values 66 and 67.

The curve 68 shows the ductor speed, which initially has a constant value 69 during pre-inking and then increases from a low starting value according to the respective ink acceleration curve 70, which is dependent on the machine speed 63. The curve 71 shows the control states of the film roller 16. This is set in the operating position during the pre-inking procedure and, at the start of the acceleration phase of the machine, is firstly moved out of the operating position and later set in the operating position again. The curve 72 shows the supply of dampening agent in the dampening unit 6 by means of a metering device 7 for the dampening agent. The supply of dampening agent leaps to a starting value at the start of the acceleration phase and increases approximately linearly from this. The curve 73 shows the control states of the dampening roller 8. This is only set in the operating position following a pre-determined time interval after the supply of dampening agent has been initiated. The curve 74 shows the control states of the inking rollers 10 and 11. These are only set in the operating position following a pre-determined time interval after the dampening roller 8 has been set in the operating position and at the same time as the film roller 16 (curve 71) has been reset in the operating position. The last curve 75 shows the control states of the blanket cylinder 3. This is only set in the operating position following a predetermined time interval after the inking rollers 10 and 11 and film roller 16 (curves 74 and 71) have been simultaneously set and reset in the operating position.

Fig. 10 shows a further example of the different parameter curves or control states of the machine and inking unit, applied over time when the pre-inking of the roller frame 10 to 16 is integrated in the acceleration phase of the machine. The machine speed, illustrated in the curve 76, therefore already increases constantly from start-up of the machine. The remaining procedures correspond qualitatively to those of the example in Fig. 9, which makes further explanation unnecessary.

Fig. 11 shows a further variant of the diagram in Fig. 9.

Contrary to the variants of Fig. 9 and Fig. 10, the film roller 16 is not constructed so that it can be moved out of the operating position, which is shown by the constant state of the curve 77. In this case, pre-inking is carried out by way of the ductor control. As the curve 78 shows, the ductor speed has a constant value 79 during pre- inking. The ductor speed in a section 80 of the curve is then set to value zero until, with the setting of the inking rollers 10 and 11 in the operating position (curve 74), a new ink supply to the inking unit is required and the ductor 18 then begins to rotate according to its acceleration curve 81. The remaining control states are in turn analogous to the previous examples.

The variants introduced in Fig. 9 to Fig. 11 are only shown by way of example. Any hybrids not shown here are conceivable.

Common to all examples, however, is the inventive principle of setting all doctor blade gaps the same for pre-inking (section of the curve 64), setting the ink quantity at least partially by way of the speed of the ink ductor 18 (section 69 of the curve 68 and section 79 of the curve 78) and only switching to a subject-dependent ink profile (sub-sections 66 and 67 of the curve 64) for the actual printing operation.

Claims

Claims 1. A process for operating a printing machine, in which the roller

frame of an inking unit, which is associated with a plate cylinder, is pre- inked with a predetermined ink quantity profile before an inking roller is first set against the plate cylinder, characterised in that the entire roller frame (10-16) is pre-inked with a constant ink quantity over its width, the value (45) of which is a machine-specific experimental value which, for a given printing machine, depends only on the materials used for production, and in that the ink quantity is at least partially controlled by the speed (68; 78) of the ink ductor (18)
2. A process according to Claim 1, in which the experimental value of the ink quantity (45) for a given material combination is a statistical mean value of the ink quantity profiles in a printing operation for standard production runs, this statistical mean value being obtained from tests.
3. A process according to Claim 1 or 2, in which, during pre- inking, the ink quantity is additionally controlled by the gap between the doctor blades (19) and the ink ductor (18) and/or by the duration of the ink supply.
4. A process according to any preceding claim, in which all the parameters for pre-inking are deposited in the form of a table in a system control unit of the printing machine, with a respective parameter set being clearly associated with each known combination of materials or material classes which each comprise materials having similar behaviour.
5. A process according to any preceding claim, in which the roller frame (10-16) is only pre-inked in that portion which supplies ink to a printing portion of the associated plate cylinder (5) in a printing operation.
6. A process according to any preceding claim, in which the roller frame (10-16) is already pre-inked during preparation for printing, prior to starting up the printing machine.
7. A process according to any of Claims 1 to 5, in which the roller frame (10-16) is pre-inked during the acceleration phase of the printing machine during start-up.
8. A process according to any preceding claim, in which if, in two timesuccessive production runs, the zonal area coverages of the following production run deviate substantially from those of the prior production run, the inking unit is cleaned and the roller frame (10-16) is pre-inked again.
9. A process according to any preceding claim, in which in the event of an interruption, the pre-inking procedure is repeated in such a way that the sum of the time of the aborted and the renewed pre-inking procedures corresponds to the specified time of an uninterrupted pre-inking procedure.
10. A process according to any preceding claim, in which when starting up the printing machine, the ink supply is set to a subject-related profile (30) prior to the first transfer of ink to the material to be printed (2), the time for the subject-related setting being selected according to the delay when transporting the ink between the control elements (19) and the material to be printed (2)
11. A process according to any preceding claim, in which when starting up the printing machine, the supply of dampening agent is firstly activated after the pre-inking of the roller frame (10-16), a dampening roller (8) is then set against the plate cylinder (5), inking rollers (10, 11) are then set against the plate cylinder (5) and the blanket cylinder (3) is finally set in position for transferring ink to the material to be printed (2)
12. A process according to any preceding claim, in which the speed (68) of the ink ductor (18) is held at a constant value (69) during the pre-inking of the roller frame (10- 16), reduced substantially for a brief time at the end of pre-inking and then increased according to a pre- determined acceleration curve (70)
13. A process according to Claim 12, in which the film roller (16) is set in the operating position during pre-inking of the roller frame (10-16), moved out of the operating position at the end of pre- inking and moved back into the operating position again when the inking rollers (10, 11) are set against the plate cylinder (5)
14. A process according to any of Claims 1 to 11, in which the speed (78) of the ink ductor (18) is held at a constant value (79) during pre-inking of the roller frame (10-16), set to zero (80) at the end of pre-inking, and increased according to a pre-determined acceleration curve (81) after the inking rollers (10, 11) have been set against the plate cylinder (5), and the film roller (16) remains set in the operating position during the entire start-up procedure of the printing machine.
15. A process according to any preceding claim, in which when the printing machine is re-started after an interruption in production without cleaning the inking unit and without pre-inking, the time interval between the interruption of the ink supply and the removal of the inking rollers (10, 11) from the plate cylinder (5) is selected so that the total quantity of ink remaining on the roller frame (10- 16) corresponds to that of the pre-inking procedure.
16. A process substantially as described with reference to any of the embodiments shown in the accompanying Figures 5-11.