EP0092743B1 - Method and device for printing webs - Google Patents

Abstract

A color printing arrangement has a series of printing stations in each of which a different color is imprinted upon predetermined regions of a travelling band to form color images. A device for measuring the width of the band by sensing the edges thereof is located immediately upstream of each printing station. The width of the band at the first printing station is compared with the width at each of the following printing stations. As long as the widths at the latter printing stations are the same as that at the first printing station, the band is allowed to continue travelling unchanged. However, when the width of the band at a printing station downstream of the first printing station differs from the width at the first printing station, the band is operated upon to return the width to its original value. The reason is that a departure from the original width of the band causes the predetermined regions which are to be imprinted to be moved out of alignment with the printing devices in the printing stations. By returning the width to its original value, the alignment of the predetermined regions is restored.

Description

The invention relates to a method for custom-fit printing of print media with at least two printing forms used, each of which is in register with the next one in chronological order and with respect to which the print media is kept on a predetermined path.

This method, which is known from US Pat. No. 2,549,605, uses register marks to control the print carrier, which are printed on the print carrier. With regard to these registration marks, the print carrier is aligned when it is conveyed from one printing unit to another. These registration marks must differ significantly from their background so that they can be detected by photo elements that register a difference in brightness between the registration marks and the background. In decor and wallpaper printing there are no possibilities to control the print medium with the help of registration marks.

But also with other multi-color prints, the registration marks are perceived as annoying and therefore their number is limited to a minimum. This limitation has the disadvantage that an exact alignment of the print carrier is only possible in the area of the registration marks, so that large parts of the print carrier cannot be detected using the photo elements. In these unrecognized areas, the print carrier is subject to changes in its dimensions due to external influences. These changes are so great that the printing medium enters the subsequent printing form with dimensions that have changed compared to the previous printing form. In these uncontrolled areas, therefore, there are decisive deviations between predetermined areas of the print carrier, which are to be printed on by the subsequent printing form, and the printing form.

In addition, the method disclosed in the document uses the usual control of the printing plates with respect to the printing medium. On the other hand, the citation also describes the action on the printing medium in order to align it laterally in its width with respect to the printing form. This alignment takes place with the help of the enlargement or reduction of tensions that are introduced into the print carrier. For this purpose, pressure rollers are provided, with the aid of which tensions can be applied to the desired extent on the printing medium. These tensions can be increased or decreased depending on the dimensions of the print carrier desired.

Such a printing process has a number of disadvantages which have led to the fact that this printing system has not found its way into practice. In particular, it does not take into account the fact that the printing medium - as a rule paper - becomes flexible due to the moistening that takes place during printing, but not elastic. Due to this flexibility, the print carrier expands very strongly, especially in the moist area. This expansion cannot be reversed by reducing the tension acting on the printing medium. A shrinkage of the print carrier can therefore not be brought about.

In addition, a considerable amount of mechanical effort has to be carried out to carry out the method, which results on the one hand from the fact that the rollers applying the tensile stress to the pressure carrier have to be controlled. In addition, however, the printing forms must also be controlled in relation to the printing medium. The costs of such controls are considerably higher than those of known printing systems. What is crucial, however, is the fact that the accuracy of this printing system is limited by the use of registration marks. The print carrier is controlled only in the area of these registration marks.

The object of the present invention is therefore to improve the method of the type mentioned in the introduction in such a way that a precise entry of the printing medium into the printing nip of the individual printing forms is ensured.

This object is achieved in that the dimension of the print carrier is measured continuously over its entire width over the side edges and is kept constant by compensating for stresses occurring in the print carrier due to the printing.

In this method, tensions are not applied to the print carrier, but rather compensated for. In this way it is ensured that the print carrier is in the same tension state before entry into the following printing unit as when entering the previous printing unit. This means that it has the same dimensions when it enters each printing unit, so that it is in line with the respective printing form. The agreement exists with regard to the entire area of the print carrier. The inclusion of registration marks is therefore superfluous, so that neither the surface of the print carrier to be printed is blemished, nor essential areas of the print carrier are not taken into account when detecting changes in dimensions. Finally, it is avoided that tension compensation occurs in the area of a pressure line. Such a voltage compensation easily leads to changes in the printing medium being carried out at the moment of applying printing inks, by which the colors to be printed are blurred.

This method is also distinguished in an advantageous manner compared to that from US-A 3,432,672. In this method, too, registration marks are used to control a printing medium, so that it can only be controlled precisely in the area of these registration marks. The print carrier is indeed controlled by acting directly on it, for example with the aid of humidifiers or dryers. However, the moistening or drying can only be used in a targeted manner in the area of the registration marks, so that areas lying directly next to the registration marks can either not be influenced at all or cannot be influenced in the desired manner. Incorrect dosing of the influences influencing the area extension of the print carrier can influence the area extension of the print carrier in a manner that runs counter to a desired printing of the print carrier. In this way, the stresses in the print carrier are not reduced, but possibly even increased. A targeted influence on the dimensions of the print carrier is excluded. In contrast, a compensation of the stresses occurring in the print carrier ensures that the print carrier runs into each of the successive printing units with the same dimensions.

According to a preferred embodiment of the invention, a device for printing on print carriers in multi-color printing, which prints at least two colors from one printing unit to produce a desired mixed color, and which is provided with a control which laterally controls the printing medium in a printing line of a respective printing unit, is thereby characterized characterized in that at least one scanner continuously measuring the width of the print carrier across the side edges is provided in front of each printing unit printing a certain color, and the scanners of the successive printing groups are connected to a control device which compares their measured values with an actuator which compensates for a voltage present in the print carrier is connected in a regulatory manner.

With such a device, stresses occurring in the print carrier can be compensated for before entering the subsequent printing unit to such an extent that the printing carrier enters the printing unit largely without tension. In this way it is ensured that the printing medium enters each printing unit with the same dimensions in each case with which the printing medium unwound from a supply roll entered the first printing unit. In this way, the application of mechanical stresses to the print carrier can be omitted, so that the print carrier returns to its initial state in which it was when it was unwound from the supply roll before the subsequent printing unit. This ensures precise control in the printing line of the subsequent printing unit. In addition, there are no deformations in the print carrier that undesirably influence the strength of the print carrier.

Further details of the invention will become apparent from the following detailed description and the accompanying drawings, in which a preferred embodiment of the device according to the invention is shown.

• Figur 1 Eine schematische Darstellung einer Vorrichtung in Draufsicht und
• Figur 2 eine schematische Darstellung einer Vorrichtung in Seitenansicht.

The drawings show:

• Figure 1 is a schematic representation of a device in plan view and
• Figure 2 is a schematic representation of a device in side view.

The method according to the invention can expediently be carried out using a device of the type shown in the figures. This device essentially consists of an unwind 1, three printing units 2, 3, 4 and a reel 5. A printing medium 6 extends from the unrolling 1 through the printing units 2, 3, 4 to the reeling 5. It is unrolled from the 1st , which can be a supply roll, unrolled, conveyed through the printing units 2, 3, 4 and rolled up on the reel 5 for further processing. The print carrier 6 has a predetermined width 7, which represents a parameter that is binding for the entire dimensions of the print carrier 6.

The width 7 of the print carrier 6 is measured at an inlet 9, at which the print carrier 6 runs into the first of the three printing units 2, 3, 4 arranged one behind the other. Suitable measuring means for measuring the width 7 are provided at this inlet 9. These measuring means can be, for example, photoelectric scanners 10, 11, with the aid of which the width 7 of the print carrier 6 is scanned. Each of the two scanners 10, 11 receives a pulse from a side edge 12, 13 of the print carrier 6 assigned to it. The pulses recorded in each case are fed via a line 14 into a control device 15, which evaluates the pulses in the sense of calculating the width 7.

In the first printing unit 2, the printing medium 6 is printed with a first basic color. This first basic color can also serve as a first final color for a representation to be colored accordingly. However, it is also possible to mix this first printing ink with further colors which are printed, for example, by the subsequent printing units 3, 4 on the first color which has been printed on the printing medium 6 by the printing unit 2.

For the purpose of this mixture, the printing medium 6 must run in under the second printing unit 3 in such a way that the second printing unit 3 with the second color contained therein directly overprints the contours 16 printed in the first basic color by the first printing unit 2. In order to be able to control this exact assignment of the contour 16 to a register of the printing unit 3 that imprints the second color, care is taken to ensure that the dimensions of the printing medium 6 entering the printing unit 3 are the same that were already found at the inlet 9. If the dimensions of the print carrier 6 are identical, it can also be assumed that the contours 16 have exactly maintained their position with respect to the print carrier 6. With a corresponding alignment of the printing unit 3 with respect to the printing medium 6, the register of the printing unit 3 directly hits the contours 16 printed by the printing unit 2.

In order to be able to maintain this identity of the printing medium 6 in the area of the printing unit 3, the width 7 of the printing medium 6 will be enjoyed by means of two scanners 18, 19 at an inlet 17 of the printing unit 3 corresponding to the inlet 9. The pulses picked up by the scanners 18, 19 are conducted via a line 20 into the control device 15, in which the measured values of the scanners 10, 11 are already stored. The control device 15 compares the values measured at the inlet 9 with those that were measured at the inlet 17. If the width at both inlets 9, 17 is the same, care is taken to ensure that the printing unit 3 overprints the contours 16 to be overprinted, which were produced by the printing unit 2, as desired. If, however, the two measured values from the inlet 9 on the one hand and from the inlet 17 on the other hand differ from one another, the control device 15 calculates the corresponding difference and converts it into a correspondingly large control pulse, the size of which corresponds to the calculated difference.

A heater 21 is provided in the printing unit 2, which can be designed, for example, as an electric heater and is connected to a power source 22. The current source 22 is connected to the heater 21 via a line 23. In this line 23 there is a variable resistor 24, by means of which the heat emitted by the heater 21 can be regulated. The control resistor 24 is connected to the control device 15 via a control line 25. The control device 15 controls the control resistor 24 with the aid of the control pulse it emits. Instead of an electric heater, any energy source, for. B. gas, hot water or steam and controlled by appropriate tax options.

As soon as the scanner 18, 19 determine a width 7 of the print carrier 6, which differs significantly from the width enjoyed at the inlet 9, it can be concluded from this difference that the expansion of the print carrier 6 on the between the inlet 9 and the inlet 17 lying route has changed significantly. The change in this elongation results from a constant tension acting on the pressure carrier 6 because the dimensions of the pressure carrier 6 on the route lying between the inlets 9, 17 have changed considerably. The elongation can be reduced to the original dimension in that moisture is removed from the print carrier 6 by appropriate drying using the heater 21. With a correspondingly large deviation, a correspondingly large amount of heat must be emitted by the heater 21 in order to be able to carry out the drying process to the desired extent. If there is a small deviation in width, it is sufficient to specify a smaller amount of heat in order to be able to reduce the elongation to the original dimension. The regulation of the expansion or shrinkage carried out with the aid of the heater 21 is very precise, so that it can be expected that the pressure carrier 6 at the inlet 17 has been returned to the same width that it already had at the inlet 9.

In the second printing unit 3, the contour 16 is overprinted with a second color, which also represents a first basic color outside the contour 16. The printing unit 3 provides the printing medium 6 with a new contour 26 in this way. Parts of this contour 26 have reached their final coloring at the outlet of the printing unit 3.

They appear either in the base color printed by the printing unit 3 or in a mixed color which is composed of the two colors of the printing units 2 and 3. Other parts of the contour 26, on the other hand, are printed with a third color by the printing unit 4, so that at the outlet 27 there is a contour 28 on the printing medium 6, in which, on the one hand, mixed colors from the basic color applied by the printing unit 4 and those from the preceding printing units 2, Find 3 printed colors and on the other hand a basic color applied by the printing unit 4. The contour 28 can therefore have a total of three primary colors.

For the creation of this mixed color, it is necessary that the contour 26 is controlled so precisely in the last printing unit 4 that its register prints the color contained therein directly on the contour 26, provided that mixed colors are to be produced. As a result, the print carrier 6 must be controlled just as precisely under the printing unit 4 as it has already been controlled under the printing unit 3. For this purpose, 4 scanners 30, 31 are provided at an inlet 29 of the printing medium 6 into the printing unit, which are connected to the control device 15 via a line 32. These scanners 30, 31 scan the width 7 of the print carrier 6. The measured value supplied to the control device 15 via the line 32 is compared with the measured value of the scanner 10, 11, which is stored in the control device 15. If the measured values match, the contour 28 runs exactly under the register of the printing unit 4, so that the color printed by them immediately reaches the desired locations on the contour 26. If the measured values of the scanner 30, 31 on the one hand and the scanner 10, 11 on the other hand differ, the control device 15 emits a control pulse.

In the conveying direction of the pressure carrier 6 there is the scanners 30, 31 a drying chamber 33 through which the print carrier 6 runs on its way between the printing units 3, 4. This drying chamber 33 is flowed through by dry air, which is generated by a Geb15, 9 34, which can be driven by a motor 35. The blower 34 is connected to the drying chamber 33 via an intake port 36. Intake area 36 opens into drying chamber 33 in the area of a suction side 37. Opposite suction side 37 is a pressure side 38, which is connected to a pressure nozzle 39. This pressure port 39 opens into the ambient air, which is sucked through the pressure port 39 into the drying chamber 33. The air flow sucked in through the pressure nozzle 39 sweeps the pressure carrier 6 on its way towards the suction side 37 and extracts the moisture from it, the removal of which is necessary in order to return the pressure carrier 6 to the same degree that it already had at the inlet 9.

The return of the stretch depends on the amount of air drawn through the drying chamber 33. This can be regulated with the aid of the speed of the fan 34. The speed control of the blower 34 is possible with the aid of a gearbox installed between the motor 35 and the blower 34. However, it is also possible to use a motor 35 whose speed can be regulated. Its power supply 40 can be controlled by the control pulse emitted by the control device 15, for example via a control resistor 41. In addition, it is conceivable to regulate the heating provided in the drying chamber 33 with regard to the heat emitted by it.

At the output 27 of the printing unit 4, the contour 28 appears, of which individual parts have been newly created in the printing unit 4, while other parts have overprinted the contours 16, 26. The carrier 6 printed in this way is rolled up onto the reel 5.

The device according to the invention is expediently provided exclusively with either heaters or drying chambers. Drying using the heated air proves to be the most sensible.

The scanning and detection of the width 7 can be carried out in any technically simple and effective manner which is suitable for generating control pulses. The type of scanning and detection is not important.

Claims (15)

1. A printing method for superimposed printing of image carriers with at least two located printing stations, each of which is in a timely succession with the following and in view of which the image carrier is kept in a predetermined orientation characterised by continuously measuring the width of the image carrier from one boarder to the other and keeping the width constantly by compensating its strain caused from the printing.

2. The printing method of claim 1, characterised my measuring the width (7) of the image carrier (6) at the input (69) of the first printing station (2), further measurements of the width at the input (17, 29) of each printing station (3,4), and comparing each of the results of the measurements with the first measuring of the width stating differences of the width if any and adjusting said width so that the values therof are substantially the same at the respective stations (2, 3, 4).

3. The printing method of claim 1 and 2, wherein adjustable measuring means (10, 11; 18, 19; 30, 31) installed upstream of each of said stations (2, 3, 4) are preadjusted to at least approximately the magnitude of said width (7) as measured downstream the stock-roll of said carrier,(6.)

4. The printing method of claim 1 up to 3, wherein said width (7) of said carrier (6) is regulated by deformation of said carrier (6) so as to maintain said width substantially constant.

5. The printing method of claim 1 up to 4, wherein the elasticity of said carrier (6) is regulated by removing moisture from said carrier.

6. The printed method of claim 5, wherein the removing operation comprises heating said carrier (6).

7. The printing method of claim 6, wherein the removing operation comprises exposing said carrier (6) to an air stream.

8. The printing method of claim 7, wherin said air stream is heated.

9. A printing arrangement comprising conveying means for conveying an image carrier (6) along a predetermined path, a first printing station (2, 3) in a first portion of said path for imprinting a predetermined region of the carrier with a first color, a second printing station (3,4) in a second portion of said path downstream of said first portion for imprinting the predetermined region in a predetermined orientation of the latter with a second color, and control means for controlling the orientation of the predetermined region so that the predetermined region arrives at said second station in the predetermined orientation, as described in the printing method of claim 1 up to 8, wherein said control means comprising measuring means (10, 11; 18,19; 30, 31) for measuring continously the width (7) of the carrier (6) and adjusting means (15) for comparing the values obtained from said measuring means and adjusting the orientation of the predetermined region in dependence upon the difference between the values by an adjusting device.

10. The arrangement of claim 9, wherein said adjusting device comprises heating means (21) for heating the carrier (6).

11. The arrangement of claim 9 and 10, wherein said adjusting device is designed to regulate an air stream.

12. The arrangement of claim 11, wherein said adjusting device is designed to regulate the quantity of air.

13. The arrangement of claim 11, wherein said adjusting device is designed to regulate the velocity of the air stream.

14. The arrangement of claim 9 up to 13, wherein said adjusting device comprises heating means for heating an air stream which flows through a chamber (33) for removing moisture from the carrier.

15. The arrangement of claim 9 to 14, wherein said control means comprises first measuring means (10,11) for measuring the width (7) downstream the stock-roll of the said carrier (6), and adjustable second measuring means (18, 19; 30, 31 ) for measuring the width (7) of the carrier (6) immediatly upstream of said second stations (3,4), said first measuring means being connected with said second measuring means so as to permit at least approximate adjustment of said second measuring means to the width (7) of the carrier (6) as measured by said first measuring means.

Images