GB2273907A

GB2273907A - Process for supplying damping solution

Info

Publication number: GB2273907A
Application number: GB9326405A
Authority: GB
Inventors: Anton Rodi
Original assignee: Heidelberger Druckmaschinen AG
Current assignee: Heidelberger Druckmaschinen AG
Priority date: 1992-12-30
Filing date: 1993-12-24
Publication date: 1994-07-06
Anticipated expiration: 2013-12-24
Also published as: DE4244500A1; FR2699859B1; JPH06255089A; GB9326405D0; FR2699859A1; GB2273907B

Description

2273907 PROCESS FOR THE SUPPLY OF DAMPING SOLUTION The invention relates

to a process for the supply of damping solution to the printing forme of an offset printing press.

In offset printing with offset printing presses, it is necessary to supply ink and damping solution to the printing forme. This is accomplished with so-called inking and damping units. The damping solution is preferably treated water, mixed with damping-solution additives as well as a proportion of alcohol. A roller arrangement of the damping unit ensures that the damping solution is applied to the printing forme in as uniform a distribution as possible in order to form a thin damping-solution film. Particularly given today's desire for increased productivity in printing and the use of less-experienced printers, it is becoming ever more important that the production process should be stable, simple and problem-free. One of the dreaded troubles is so-called emulsification in the inking unit, which may occur particularly in the case of unevenly structured printing subjects and/or lengthy production processes. It is known that, even if the sheet is completely printed with ink, the conventional offset printing process requires a certain proportion of damping solution. This is, for example, firstly, because of the non-printed margins and, secondly, in order to stabilize the transfer process. The thereforrequired quantity of damping solution is relatively large. By contrast, non-printed image areas require a smaller proportion of damping solution. If printing is performed with the same subject over a lengthy period of time, then it is possible - as shown in practice - for problems to occur; in particular, the aforementioned emulsification may occur, the only recourse then being the time-consuming cleaning of the inking unit. The production process becomes particularly delicate when only small areas or even just lines are being printed.

German application 40 28 083 discloses a process for the feedback control of damping in offset printing presses wherein, during the production run, the smear limit is reached at intervals, with the actual value measured at the smear limit being used as the setpoint value for the following feedback control of the damping-solution quantity.

The object of the invention is to indicate a process of the initially mentioned kind, said process preventing emulsification in the inking unit, particularly in the case of unevenly structured subjects and/or lengthy production processes.

The object of the invention is achieved in that the supplied quantity of damping solution is - irrespective of possible fluctuations caused by deviations or similar of a preferably feedback-controlled supply alternated about a preselectable mean value. The basic idea of the invention, therefore, consists in an alternation about the mean value between overdamping and underdamping. This alternating damping-solution control means, therefore, that the supply of damping solution is not constant, but varies with respect to time as a function of defined parameters. This type of supply results in a reduction in the dampingsolution quantity (in comparison with the known type of supply, which is virtually constant across the width). "SurpluC damping solution during "overdamping", i.e. when the quantity supplied is above the mean value, is equalized according to the invention in the inking/damping unit. An important idea of the invention is this selfequalization of the damping solution in the inkingunit/damping-unit system. The method according to the invention results in a stable printing process, even in the case of lengthy production intervals, without emulsification occurring, or the risk of emulsification is greatly reduced. The printing process is simple to supervise and is trouble-free.

According to a further development of the invention, it is provided that the supply is alternated about the mean value with a minimum value and a maximum value. The magnitudes of the minimum and maximum values, i.e. the amplitudes thereof, are dependent on the variation of the printed subject over the length and width of the printed image. This applies also to the choice of the mean value.

Furthermore, the frequency of the alternation between overdamping and underdamping is likewise dependent on the variation of the printed subject over the length and width of the printed image.

The aforementioned parameters (mean value, minimum value, maximum value and/or frequency) of the alternating damping-solution supply are preferably selected such that surplus damping solution - i.e. damping solution not required instantaneously in the printing process - can be equalizingly distributed in the inking unit and/or damping unit of the printing press.

It is particularly advantageous if the maximum value corresponds approximately to a supplied quantity as would be necessary with continuous (i.e. the conventional known) damping- solution supply for a completely printed area of the printed image.

Likewise, it is advantageous if the minimum value corresponds approximately to a supplied quantity of damping solution as would be necessary as a function of the variation of the printed subject with the known continuous damping-solution supply. The printer is able, therefore, on the basis of his previous knowledge, to determine the minimum value and the maximum value for process control according to the invention in that, in order to set the maximum value, he selects the supplied quantity that would be required for a completely printed area with a virtually constant damping-solution supply across the width. In order to set the minimum value, he selects the supplied quantity that, depending on the variation of the printed subject, would be required if the damping- solution supply were not the one according to the invention, but the known form of supply virtually constant across the width.

Basically, it should be noted at this point that the known continuous damping-solution-supply process, of course, also leads to fluctuations in the supplied quantity, since, for example, if the damping-solution supply is feedback-controlled, fluctuations will occur within the control range, said fluctuations alternating about a "mean value". Such fluctuations in the dampingsolution quantity are not comparable with the alternations in the damping-solution supply intentionally brought about according to the invention. If the application of the process according to the invention is combined with feedback control, then there will be small control fluctuations in the dampingsolution supply, with the alternating overdamping and underdamping states according to the invention being superimposed on said control fluctuations.

The alternating supply of the damping solution about the mean value may preferably be (open-loop-/feedback-) controlled by adjusting the rotational speed of a damping-duct roller, by adjusting the frequency of a damping vibrator roller, by adjusting the rotational speed of a dampingsolution metering roller and/or similar apparatus or process control of the damping unit of the offset printing press. Indicated herein, of course, are only examples of how to bring about the differently sized supplied quantities of damping solution according to the invention, with the invention, of course, not being restricted to such examples. The invention also encompasses any other apparatuses and procedures that permit an alternating supply of damping solution.

A specimen embodiment of the invention is illustrated in the drawings, in which:

Fig. 1 shows a schematic view of a damping unit of an offset printing press; and Fig. 2 shows a graph indicating the damping-solution supply as a function of time.

In order to elucidate the process according to the invention, Fig. 1 shows a damping unit 1 of an offset printing press (printing press not shown in any greater detail), said damping unit 1 comprising a multiplicity of rollers/cylinders. Partially immersed in a dampingsolution reservoir 2 by a part of its circumference is a dip roller 3, said dip roller 3 cooperating with a metering roller 4. The dip roller 3 has a rubber surface, which is convexly ground. The metering roller 4 has a smoothly chrome-plated surface. Cooperating with the metering roller 4 is a damping roller 5, which - in the printing process - comes into contact with a printing forme (not shown) of a plate cylinder 6. In contact against the damping roller 5 is a damping distributor roller 7, which has a matt-chrome-plated surface. The surface of the damping roller 5 is made of rubber. A so-called intermediate roller 8, with a surface made of Rilsan, cooperates with a plate-inking roller 9, which is part of the inking-unit of the offset printing press, of which inking unit only two further rollers 91 and 911 are indicated in Fig. 1.

The metering of the damping-solution quantity in order to set the dampingsolution film thickness on the printing forme is possible in that the rotational speed of the metering roller 4 is suitably varied. Furthermore, the regulation, particularly the fine regulation, of the required damping-solution quantity may also be accomplished through the relative speed and adjustment of the metering roller 4 with respect to the damping roller 5.

According to the invention, unlike in conventional arrangements, the damping solution is supplied not continuously, but at different amplitudes as a function of time, as emerges from Fig. 2.

Fig. 2 shows a graph, on the ordinate of which is plotted the dampingsolution quantity and on the abscissa of which is plotted the time t. As can be seen, the quantity of damping solution supplied alternates about a mean value M, either at a maximum value Max or a minimum value Min. In Fig. 2, the change from the maximum value Max to the minimum value Min and from the minimum value Min to the maximum value Max is an abrupt one. This is not necessary, with the result that a steady transition according to a different specimen embodiment is also possible. The settings of the mean value M, the maximum value Max, the minimum value Min (the amplitudes) as well as the frequency of the alternating damping-solution supply are determined by the printer as a function of the variation of the printed subject over the length and width of the printed image. For a coarse setting, the printer proceeds such that he selects a minimum value Min corresponding approximately to a supplied quantity of damping solution necessary with continuous dampingsolution supply for a completely printed area of the printed image. He selects the maximum value corresponding to a supplied quantity necessary as a function of the variation of the printed subject with a known, continuous damping- solution supply.

Additionally or alternatively, the quantities for the maximum value Max, the minimum value Min and the mean value M can also be obtained as a function of the printed subject by an open-loop or feedback control, for example by means of determinable relationships from values of a plate reader of the kind known, for example, under the designation CPC 3 from Heidelberger Druckmaschinen AG. It is also possible to employ a densitometer or colorimeter, the measurement results of which are subjected to as-determined relationships in order to arrive at the aforementioned values for the maximum and minimum ink-supply quantities. It has been found in particular that the mean value M and the frequency of alternation in the damping-solution supply are especially dependent on the variation of the printed subject over the length and width of the printed image in question.

8 Even an only approximately selected setting of the aforementioned values will, with an untroubled printing process, considerably reduce the proportion of damping solution leading to emulsification, thereby permitting long-lasting, optimal printing processes.

It will of course be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

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Claims

CLAIMS:

1. Process f or the supply of damping solution to the printing f orme of an of f set printing press, wherein the supplied quantity of damping solution is, irrespective of possible fluctuations caused by deviations or similar of a supply, alternated about a preselectable mean value (M), and with an adjustable minimum value (Min) and an adjustable maximum value (Max).

2. A process according to claim 1, wherein the supply is feedback controlled.

3. Process according to claims 1 or 2, wherein the mean value (M), the minimum value (Min), the maximum value (Max) and/or the frequency of the alternating damping-solution supply is selected such that "surplus" damping solution, i.e. damping solution not required in the instantaneous printing process, can be equalizingly distributed in the inking unit and/or damping unit of the printing press.

4. Process according to any one of the preceding claims, wherein the mean value (M), the minimum value (Min), the maximum value (Max) and/or the frequency is selected as a function of the variation of the printed subject over the length and/or width of the printed image.

5. Process according to any one of the preceding claims, wherein the minimum value (Min) corresponds approximately to a supplied quantity necessary with continuous damping- solution supply for a completely printed area of the printed image.

6. Process according to any one of the preceding claims, wherein the maximum value (Max) corresponds approximately to a supplied quantity necessary as a function of the variation of the printed subject with a continuous damping-solution supply.

7. Process according to any one of the preceding claims, wherein the supply of damping solution is (open-loop/feedback-) controlled by adjusting the rotational speed of a damping-duct roller, by adjusting the frequency of a damping vibrator roller, by adjusting the rotational speed of a damping- solution metering roller andlor similar apparatus or procedure of the damping unit of the offset printing press.

8. A process as claimed in claim 1 f or the supply of damping solution to the printing forme of an offset printing press and substantially as hereinbefore described with reference to the accompanying drawings.

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