GB2251580A

GB2251580A - Process for the control of printing ink application in the manufacture of multicolour print products.

Info

Publication number: GB2251580A
Application number: GB9125828A
Authority: GB
Inventors: Rolf Braun
Original assignee: MAN Roland Druckmaschinen AG
Current assignee: Manroland AG
Priority date: 1990-12-04
Filing date: 1991-12-04
Publication date: 1992-07-15
Anticipated expiration: 2011-12-04
Also published as: GB2251580B; GB9125828D0; FR2670432B1; FR2670432A1; DE4038574C1; DE4038574C2

Description

-) 2 -) 15 7.1 J PROCESS FOR THE CONTROL OF PRINTING INK APPLICATION IN

THE MANUFACTURE OF MULTICOLOUR PRINT PRODUCTS This invention relates to a process for the control of printing ink application in the manufacture of multicolour print products in accordance with the

classifying portion of Claim 1.

From DE-AS 2 728 738 it is known to print, together with the actual printed image on the printed sheet additionally a print control strip and to sense this strip by means of a travelling densitometer. The print control strip extends transversely to the print direction, for example along the lead or trail edge of the sheet bearing the print. The strip has several measuring fields for each ink to be used. On the basis of the densitometric sensing of the measuring field, control commands for zonal ink feed are derived for each printing unit. These control commands are then automatically fed to the ink metering elements. The sensing of the measuring fields of the print control strip can take place not merely densitometrically, but also, as known from EP- B1-0 228 347, colourimetrically and/or spectrally.

- 2 The width of the ink metering zones of known multicolour print systems, such as that sold by MAN Roland Druckmaschinen AG under the designation RCI/CCI, amounts to 30 mm. In the case of, for example, 5 or 4 mm wide measuring fields, only 54 or seven measuring fields respectively can be present in each ink metering zone. However, it is desirable in the print control strip to introduce additional quality diagnosis fields, as well as the measuring fields for deriving control commands for 10 the ink metering elements (so-called control fields). These quality diagnosis fields serve to determine movement/doubling, dot growth and grey balance, among other parameters. In the case of measuring fields which have a width of 4 mm, and an ink metering zone of width 30 mm, each zone may contain six measuring fields + 1.5 quality diagnosis fields. With such a print control strip, the feed for six printing inks can be controlled. An example of this type of print control strip is commercialised under the designation CCI print control strip type 6VP, fogra PMS system.

In the printing of packaging often there are printed several special colours/house colours, as well as the four base colours black, cyan, magenta and yellow. Similar considerations apply for the printing of catalogues with so-called colour patterns. It is also known to print the same ink with two printing units, for example when heavy full tone images and fine grids of the same colour lie adjacent to one another.

Should more than six printing inks be printed,..for.. 1 1 example 12 colours on a six-colour press..in two passes also one pass on a 12 colour press is conceivable then two print control strips must be copied closely adjacent and parallel to one another on the plate set and correspondingly printed therewith. One strip contains the measuring fields for printing inks 1 to 6, while the other strip contains the measuring fields for the printing inks 7 to 12. This is often done in print works if the number of the inks to be printed exceeds the number of printing inks in the print control strip. It is disadvantageous to provide the additional space on the printed sheet for the second print control strip. A further disadvantage arises from the use of a second print control strip if the printing is effected in one pass. Should the measuring fields of the print control strip be sensed with a traversing densitometer as mentioned above, then this is no longer possible in one sensing run. Then, accordingly, two sensing runs are necessary, plus a positioning run for each sensing run, and a run for detecting the type of strip.

It is an object of the present invention to create a process for the control of the printing ink supply with which, using only a single print control strip, control of the ink supply is possible for a plurality of printing inks.

Accordingly, the present invention provides a multicolour ink supply process which is as claimed in the appended claims. Advantageous developments of the invention are evident from the sub-claims, as well as from the description.

The invention makes use of the fact that in inking units of printing presses, particularly offset printing presses, a so-called transverse flow of the printing ink takes place. In the case of offset printing presses, this transverse flow is further increased by the socalled transverse vibration (vibrator rolls).

is If, in this sort of inking unit, in given ink metering zones, e.g. that numbered N-1 and that numbered N+l, the ink flow is changed, then these changes also influence the feed in the ink metering zone N, even though the ink metering there has not been changed.

According to the present invention, with a print control strip for six colours, twelve inks can be controlled. Thus one does not have to do away with quality diagnosis fields present in the ink control strips when controlling more than six different inks. With an ink control strip for eight printing inks, the present invention allows a maximum of sixteen inks to be controlled.

Lhe measuring fields for the printing inks 1 to 6, for example, are copied on to the corresponding printing plate only in alternate ink metering zones such as those odd-numbered ones. The measuring fields for the inks 7 to 12 are copied on to the other alternating set of corresponding printing plates, such as the even- numbered ones. If then these 12 print operations are printed, for example, on a six-colour press in two passes - the printing inks 1 to 6 in the first pass - then in the first pass control processes are carried out only in one set of ink metering zones. Thus the positioning of the ink metering elements changes on the basis of measurements and a subsequent actual/desired comparison only in these ink metering zones. The other set of ink metering zones remain uncontrolled, i.e. the corresponding ink metering elements maintain a value which is derived, for example. from a pre-adjustment by means of printing plate readers. It is also conceivable to position the ink metering elements of the ink zones for which no measuring fields are printed entirely against the ink fountain roller (so-called null position). This is advantageous particularly if the corresponding printing plate has a very low ink requirement. In the second pass in accordance with the above illustrative example, i.e. on the printing of inks 7 to 12, control processes are carried out only in the even-numbered ink metering zones. The odd-numbered ink metering zones then remain uncontrolled. One proceeds correspondingly on carrying out 12- colour work on a 12colour press.

Obviously with a six-colour print control strip, less than twelve colours can be controlled. Thus, by the application of the invention six-colour print control strips eight colours - four base colours + four special colours - may be controlled. The measuring fields for the four base colours (black, cyan, magenta and yellow) are copied on to the corresponding printing plate in each ink metering zone and thus printed, with the measuring fields for the special colours 1 and 2 being only in the odd-numbered ink metering zones, and those for special colours 3 and 4 in the even-numbered ink metering zones. The four base colours are accordingly controlled in all zones, the special inks 1 and 2 only in the even zones, and the special inks 3 and 4 in the metering zones.

The use of a print control strip for carrying out the process in accordance with the invention is simple both in terms of installation and copying. A six-colour print control strip consists of six individual samples, i.e. one extract for each printing ink, with the corresponding measuring fields in each ink metering zone. For carrying out the invention, it is accordingly only necessary to make six further samples. In these samples, the measurement fields are thus arranged only in the ink metering zones with even or odd number. With such a configuration of the print control strip or of its samples, the print control strips can be used very flexibly with respect to the work to be printed. If the print control strips, for example, are used for a 12- colour work, then the samples with measuring fields in the even metering zones are copied respectively in pairs offset relative to one another for all printing inks. On the use of the print control strip for an 18-colour work, for example, the samples for the four base colours can be copied with measuring fields for each metering zone corresponding to the samples for the four further special colours, with metering fields in each case being in the even ink metering zones.

Print tests reveal that prints which have been manufactured in accordance with the process according to the invention differ only slightly in terms of measurement but absolutely not visually from prints in which, for each printing ink in each ink metering zone, measuring fields are present, and the ink metering elements in each ink metering zone are adjusted on the basis of the measured values received.

The present invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a print control strip for eight colours, constructed on a known six colour print control stript and Figure 2 shows a print control strip for up to printing inks.

12 Figure 1 shows a print control strip DK consisting of measuring fields MF for the various printing inks. The dashed lines show the boundaries of the ink metering zones, the numbers being the numbers of these ink metering zones. The print control strip DK illustrated corresponds in its construction to the known print control strip for six colours. Each measuring field MF is 4 mm wide and 7 mm high. Illustrated in Figure 1 are the first 12 ink metering zones of the measuring strip. The letters B, C, M, Y, S, 0, N, D, E, R, F, A are used in Figures 1 and 2 to denote 12 different printing inks. The letters B, C, M, Y represent the four base colours, while the remaining letters are for special or house colours. Below the print control strip DK is the copy, i.e. the overlaying of the measuring fields MF into the ink metering zones for the individual printing inks illustrated on the corresponding printing plate. In accordance with this exemplary embodiment measuring fields MF for the inks B, C, M, Y are present in each ink metering zone; measuring fields MF for the inks S and 0 only in the even-numbered zones and measuring fields MF for the inks N and D only in the odd-numbered ink metering zones. The measuring fields MF which are characterised by a dot, serve as so-called control fields, i.e. the measured values derived therefrom. (ink density, ink value) are processed directly in combination with desired values to adjust amounts for the ink metering elements in the corresponding printing units. It can be a question for these control fields of full- tone or half-tone fields. As well as the half-tone fields, the print control strip has quality diagnosis fields thus, e.g. grey balance fields GB, which arise by the printing one over another of the three base colours

C, M, Y with particular half-tone values. There are shown two grey balance fields GB, one in middle tone, one in deep tones. Additionally the print control strip DK further has measuring fields MF which are constructed as half-tone fields of given value. In Figure 1, these are characterised by one or two vertical strokes. For example, 40% and 80% half-tone values can be provided. Measured values which are derived from these fields serve for process control or, in combination with a full- tone field of the same printing ink to determine the actual surface coverage, as known from DE-Al-3 440 706.

The print control strip DK shown in Figure 1 can also be used for 12 printing inks. In this case, only the measuring fields for the printing inks B, M, S, N, E, F need to be copied into the ink metering zones 1, 3, 5, 7, etc., while the measuring fields MF for the printing inks C, Y, 0, D, R, A are copied to the ink metering zones with the numbers 2, 4, 6 etc. Other types of copying are also possible.

The print control strip DK according to Figure 2 is suitable for the control of the supply of 12 printing inks. The type of illustration in this connection is the same as in Figure 1.

The width of a measuring field MF in the print control strip DK of Figure 2 is 3 mm, so that with ink metering zones of 30 mm width, 10 measuring fields MF are available per zone. The field width of 3 mm constitutes

9 - practically a lower limit since, if it were narrower, accurate photoelectric sensing could not be guaranteed.

As in Figure 1, the measuring fields MF which serve as control fields are shown with a dot. The overlaying of the measuring fields MF is illustrated for the various printing inks B, C, M, Y, S, 0, N, D, B, R, F, A for four ink metering zones. Therefore, the measuring fields MF for each printing ink are printed in alternating zones.

Additionally to the measuring fields MF for the various printing inks which serve as control fields (characterised by a dot) various quality-diagnosis fields are present. For each of the four base colours B, M, C, Y there is provided for each four ink metering zones a so-called half-tone step wedge. This consists of three half-tone fields with, for example, 25%, 50%, 75% half tone value. In Figure 2, these half-tone fields are characterised by one, two or three horizontal strokes.

In combination with the corresponding full-tone field, (here a control field) the surface coverage achieved effectively in printing three half-tone values, and accordingly the print characteristic, can be monitored.

Furthermore in each ink metering zone, by the printing one on another of the three printing inks C, M, Y with a corresponding half tone value a grey balance field is printed. It is advantageous if, in each alternating ink metering zone, the grey balance field GB provides a middle tone, and if, in the remaining ink metering zones, field GB constitutes a deep tone.

Obviously other overlayings of the measuring fields MF are possible. Thus, as shown in the example according to Figure 1, measuring fields MF for the four base printing inks B, C, M, Y can be printed in each ink metering zone and thus correspondingly copied on to the printing plate and the measuring fields MF for the remaining printing inks S, 0, N, D printed only in each second ink metering zone. Then likewise eight printing inks can be controlled. The present invention can be arranged to print with the three basic colours C, M, Y by replacing the respective measuring fields MF in each ink metering zone, and the measuring fields for the remaining printing inks B, S, 0, N, D, E only in the alternating ink metering zones. Thus in all nine printing inks can be controlled using measurement techniques, and the printing ink application controlled correspondingly.

Claims

1. A process for controlling the application of printing inks in the manufacture of multicolour printed products, particularly multicolour printed sheets, in which each printing ink can be fed in a plurality of ink metering zones extending transversely to the print direction differentially in which, for each printing ink, measuring fields are printed therewith which provide in their totality a print control strip extending on the print medium transversely to the print direction, the measuring fields are photoelectrically sensed and the signals thus obtained processed in combination with desired values to control data for the feed of the respective printing ink, wherein thereafter the control of the feed takes place automatically, characterised in that for at least one pair of printing inks the respective measuring fields are printed only in alternating ink metering zones, whereby the co-printing of the measuring fields for the corresponding printing ink alternates from one ink metering zone to the next and in that the feed of printing ink for each zone in which the respective printing ink has no measuring field is maintained unchanged at a chosen value.

2. Process according to Claim 1, characterised in that measuring fields for inks of four basic colours are printed in each ink metering zone, and in that the measuring fields for the remaining inks are printed in pairs, with one in each of two successive zones.

3. Process according to Claim 1 or 2, characterised in that for the printing of an even number of printing inks, measuring fields are printed for half of them in each alternating ink metering zone, and in that the measuring fields for remaining inks are printed in the other set of zones.

4. A process according to any preceding Claim, characterised in that for each ink metering zone in which the respective ink has no measuring field, the chosen value is zero, so that no feed of printing ink results.

5. A process for controlling the application of printing inks in multicolour printing using a printed test strip substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawing.

is

6. A print control strip for carrying out the process according to any preceding Claim, characterised in that, for at least one pair of printing inks, the measuring fields are arranged in alternating metering zones.