DE102023201976A1 - Method for operating a printing system as well as a printing system and a combination of such a system and a corrugated cardboard system - Google Patents

Abstract

A method for operating a printing system (2) is specified, wherein the printing system (2) has a printing unit (8) for printing a paper web (10) according to a predetermined order with predetermined order data, the paper web (10) being at a web speed is conveyed by the printing system (2), the printing system (2) having at least one dryer (18, 20) with an adjustable drying performance in order to dry the paper web (10), whereby the paper web (10) experiences shrinkage, the Printing system (2) has at least one humidifier (22) with an adjustable moistening power in order to moisten the paper web (10) and thereby adjust the moisture content of the paper web (10), with an actual shrinkage and an actual shrinkage for the paper web (10). Humidity can be determined and a target shrinkage and a target humidity are specified, the shrinkage and the moisture being adjusted to the target shrinkage and the target humidity by adjusting the drying performance and the moistening performance depending on the actual shrinkage and the actual moisture A printing system (2) and a composite (6) consisting of such a system and a corrugated cardboard system (4) are also specified.

Description

The invention relates to a method for operating a printing system and a system with such a printing system, possibly in combination with a corrugated cardboard system.

A printing system is used to print a paper web with a printed image, or print for short. The print and thus also the paper web are regularly dried with a dryer (e.g. hot air dryer and/or IR dryer), which causes the print and the paper web to shrink and which necessarily removes moisture from the paper web.

A change in the web speed at which the paper web is conveyed through the printing system is problematic during operation. At different web speeds, the paper web is exposed to the dryer for different lengths of time, so that the shrinkage and moisture of the paper web change depending on the web speed. This is particularly disadvantageous with regard to the dimensional accuracy of the print and the maintenance of a certain humidity, for example for further processing.

The problem can basically be avoided by simply operating the printing system at a constant web speed. This is particularly suitable for stand-alone operation or roll-to-roll operation, in which the paper web is unrolled in front of the printing system and rolled up again after the printing system. However, in a combination of a printing system and at least one other system, i.e. in inline operation of the printing system, a constant web speed may limit the performance of the combination. It is therefore desirable to keep the shrinkage and moisture of the paper web at the exit of the printing system as constant as possible despite varying web speeds.

Against this background, it is an object of the invention to enable the most flexible operation of a printing system. For this purpose, an appropriate procedure for operating a printing system should be specified. Furthermore, a corresponding printing system and a combination of a printing system and a corrugated cardboard system should be specified.

The object is achieved according to the invention by a method with the features according to claim 1 and by a printing system or a composite of such a layer and a corrugated cardboard layer with the features according to claim 13. Advantageous refinements, further developments and variants are the subject of the subclaims. The statements in connection with the process also apply mutatis mutandis to the printing system and the network and vice versa. If steps of the method are described below, advantageous configurations for the printing system and the assembly result from the fact that it is designed to carry out one or more of these steps. For this purpose, the printing system or the assembly in particular has a correspondingly designed control unit.

A core idea of the invention is in particular a regulation of the dimensional stability of preferably digital printed products, taking into account the paper water content, more precisely: a respective regulation of both the shrinkage and the moisture of a paper web which is printed in a printing system.

The method according to the invention is used to operate a printing system. The operation is preferably, but not necessarily, an inline operation, i.e. the printing system is combined with at least one other system to form a network. The printing system has a printing unit for printing a paper web according to a specified order with specified order data, which define the order (also “print order”). For this purpose, the printing unit in particular has one or more print heads. The pressure unit is also called a pressure chamber. The printing system is preferably a digital printing system and the printing is carried out using an inkjet process.

The order data of an order are specified in particular by means of a higher-level control unit, for example directly by the higher-level control unit or by an operator who enters the order data into the higher-level control unit, for example via an interface (also referred to as visualization). The higher-level control unit is part of the printing system or is designed separately from it. The order data contains in particular a production mode in which the printing system is to be operated, as well as paper web data. The production mode defines in particular a certain print quality, an amount of ink to be printed, whether a primer should be applied before printing, whether a varnish or varnish print should be applied after printing, etc. or a combination thereof. The paper web data includes in particular a type of paper, a grammage of the paper web, etc. or a combination thereof. In particular, configuration data (also referred to as a recipe) is derived from the order data, which suitably contains corresponding machine data for the order-dependent setting of the printing system. The derivation The configuration data (subordinate level) from the order data (superordinate level) is of secondary importance in the present case and is carried out, for example, using experimentally determined characteristics, tables and/or suitable models, which are stored, for example, in the higher-level control unit. The configuration data is then passed on to a machine control of the printing system in order to set and control it accordingly.

The paper web is generally conveyed through the printing system in one conveying direction at a web speed. A particularly preferred embodiment is in which the paper web is fed to a corrugator after printing. The corrugated cardboard system is designed to produce corrugated cardboard and uses the paper web printed by the printing system, which is connected to other paper webs to form corrugated cardboard. The web speed is determined in particular by the corrugator and varies over time. The web speed typically varies with a job change and can also vary within the same job. Accordingly, the invention described here is particularly suitable for a combination of printing system and corrugated cardboard system, which is assumed in the following without restricting generality.

The terms “upstream” and “downstream” are used below to identify the relative positions of two components with respect to the conveying direction. A component A, which is arranged upstream of a component B, is arranged relative to it in the opposite direction to the conveying direction, i.e. the paper web first passes through component A and then through component B. The reverse applies for “downstream”.

The printing system has at least one dryer with an adjustable drying performance in order to dry the paper web, whereby the paper web and thus also the print experience shrinkage and whereby the paper web in particular also experiences a reduction in moisture. The dryer is basically arranged downstream of the printing unit. The dryer is also known as a pressure dryer. The dryer is in particular an IR dryer (i.e. infrared dryer) or a hot air dryer; if there are several dryers, a combination of at least one IR dryer and one hot air dryer is advantageously used. In a suitable embodiment, several IR dryers are initially arranged downstream of the printing unit and, downstream of them, several hot air dryers. The drying performance is specified, for example, as the temperature (e.g. in °C) that the paper web experiences through the dryer, but other dimensions are also suitable.

The printing system furthermore has at least one humidifier with an adjustable moistening power in order to moisten the paper web and thereby adjust the moisture (ie paper moisture) of the paper web and in particular also swelling (ie negative shrinkage and thus generally the shrinkage of the paper web). When humidifying, the paper web typically swells and thus the pressure increases. The humidifier is preferably arranged downstream of the dryer and therefore compensates for any loss of moisture due to drying. The humidifier is therefore also referred to as a rehumidifier. In a suitable embodiment, the humidifier has at least one spray bar, which extends transversely to the conveying direction and in particular over an entire width of the paper web and sprays water onto it during operation. The moistening performance is specified, for example, as the amount of water applied to the paper web per unit area (eg in ml/m ² ), but other dimensions are also suitable.

As part of the process, an actual shrinkage and an actual moisture content are now determined for the paper web and a target shrinkage and a target humidity are specified and the shrinkage and the moisture are dependent on the actual shrinkage by adjusting the drying performance and the moistening performance and the actual humidity is regulated to the target shrinkage and the target humidity. In other words: by adjusting the drying and humidification performance, the shrinkage and moisture are adjusted during operation, especially continuously.

The target shrinkage and the target moisture (controlled variables) are in particular part of the configuration data and are therefore determined based on the order data or are already included in the order data itself. The target shrinkage and the target moisture are in particular order-specific and are therefore suitably changed when the order is changed (equivalently: when the order is changed), with the same or similar order data and configuration data being used for the same or similar orders. Preferably, the higher-level control unit specifies the target shrinkage and the target moisture specific to the order and transmits these to the machine control, which thus regulates the shrinkage and the moisture and for this purpose controls the dryer and the humidifier.

In order to regulate the shrinkage, the actual shrinkage is determined, which indicates how much the paper web has shrunk after drying. The actual shrinkage is determined in particular inline. For this purpose, a corresponding sensor is used, which is arranged downstream of the printing unit and in particular also downstream of the dryer and the humidifier in order to obtain the most correct value for the shrinkage.

In a preferred embodiment, the actual shrinkage of the paper web is determined by measuring a web width (perpendicular to the conveying direction) of the paper web downstream of the dryer and comparing it with a web width in front of the printing unit. Alternatively or additionally, the actual shrinkage of the paper web is determined by optically measuring shrinkage of print image marks on the paper web downstream of the dryer. For example, the above-mentioned sensor is a web width sensor or alternatively an optical camera system (in particular as part of the printing system), which optically detects the printed image and the printed image marks contained therein and calculates a deviation between the target and actual shrinkage from the order data. An optical measurement with a camera system has the advantage over web width measurement in that the shrinkage of the printed image is determined directly. Particularly if a lot of ink is applied to one side of the paper web and a correspondingly strong swelling occurs, a different shrinkage across the entire width of the paper web can be assumed. If the shrinkage is only determined indirectly by measuring the web width, these deviations cannot be quantified across the entire width. The actual shrinkage, at least when measuring the web width, is actually a transverse shrinkage of the paper web. Since the longitudinal shrinkage of the paper web is regularly less than the transverse shrinkage, it is sufficient to only use the latter for control in order to achieve dimensional accuracy of the print in both the transverse and longitudinal directions. The web width in front of the printing unit is preferably measured analogously with a web width sensor upstream of the printing unit. A respective web width sensor determines the web width, for example by means of web edge detection or a light grid. The two web widths are compared, for example, by setting a difference in the web widths in relation to the web width in front of the printing unit. The ratio then indicates the shrinkage in % based on the web width in front of the printing unit. If the printing system is followed by another system, the pressure is expediently controlled by another sensor, e.g. the print contains a QR code, the dimensions of which are controlled by the subsequent system. For this purpose, a distance between several QR codes is expediently measured on print images arranged next to one another across the working width. The QR codes serve alternatively or additionally as the above-mentioned print marks.

The actual shrinkage is preferably determined at the end of the printing system, for example immediately before a rewinder for the paper web, or even outside of it, for example along a transfer route or within a subsequent system, i.e. when the paper web is no longer processed by the printing system and in particular before, during or after the paper web is/has been transferred to a subsequent system. Using a shrinkage controller, the dryer, or more precisely the dryer output, is controlled with the target shrinkage as a reference variable and the actual shrinkage as a controlled variable. In this way, the shrinkage that occurs in the printing system is regulated to the target shrinkage. The shrinkage controller is in particular a part of the printing system, in particular the machine control, and is preferably implemented by means of a programmable logic controller (PLC).

In an advantageous embodiment, the actual shrinkage is determined as standard with a first sensor, which is arranged downstream of the printing unit and, as described, at the end of the printing system, except in the case of a splice, in which case the actual shrinkage is determined with a second sensor, which is arranged upstream of the first sensor and which is therefore closer to the printing unit. This advantageously reduces the web travel from printing unit to sensor by a factor of 5 to 20, for example from 250 m to just 20 m. With a splice, a new paper web is added to the end of a currently used paper web, which may have different properties and different order data leads. In this case, it is advantageous to reduce the web run for shrinkage control as much as possible in order to achieve a faster control response. It is accepted that the control then no longer takes into account the entire processing of the paper web downstream of the printing unit. After a specified time or length of the paper web has passed, the first sensor is used again. If necessary, an offset is also taken into account. For example, the first sensor is arranged downstream of the printing unit in front of a paint dryer and there in front of two of three spray bars. The shrinkage caused by the drying and the swelling caused by the spray bars cause a change in the dimensions of the paper web depending on the settings by a factor x, possibly with a certain tolerance. The offset is based on empirical values then the further change in shrinkage downstream is estimated or assumed in favor of the shorter controlled system, which results from the arrangement mentioned. The actual shrinkage results overall as the sum of a measured value for the shrinkage and the offset, in particular depending on the machine settings downstream. The offset is therefore generally used, in particular, to correct the actual shrinkage due to the arrangement of the sensor relative to the components that influence the shrinkage.

In order to regulate the humidity, the actual humidity is determined analogously to the shrinkage, which indicates how moist the paper web is after moistening. The actual humidity is determined in particular inline. For this purpose, a corresponding sensor is used, which is arranged downstream of the printing unit and also downstream of the humidifier. In a suitable embodiment, the sensor is a microwave moisture sensor. The sensor is expediently calibrated for paper webs with different paper properties (paper type, grammage, etc.), for example using a respective characteristic curve. Analogous to measuring the actual shrinkage, the actual moisture is also preferably determined at the end of the printing system or even outside of it. Using a humidity controller, the humidifier, or more precisely the humidifier output, is then regulated with the target humidity as a reference variable and the actual humidity as a controlled variable.

In principle, it is conceivable to simply operate the printing system at a maximum web speed in order to produce with maximum performance. However, a variable web speed is required, at least in inline operation, due to the typically frequent jumps in web speed on the other system (particularly the corrugator). For example, the web speed is briefly reduced during various quality changes (e.g. change in haul length). In contrast, the web speed is reduced for a long time, for example for certain qualities for which only lower web speeds are possible (e.g. endless corrugated cardboard at 200 - 250 m/min). By changing the web speed, the dwell time in the heating and drawing section (i.e. double facer) is also regularly shortened or extended in order to correct quality problems such as warp (bending of the corrugated cardboard) and bonding problems. In general and for other problems, the web speed is sometimes reduced, for example if the paper quality is poor or if a tray at the end of the system is full. Regardless of the specific reason, a standstill of the system always means that the paper remains in the heating and drawing section and is therefore waste. If the composite were to be operated at a constant web speed, a corresponding waste would arise at a reduced web speed because there would be too much shrinkage and too little moisture. Accordingly, alternative machine and printing settings for a reduced web speed would have to be stored for the various qualities that can be adjusted, which means increased effort. In addition, flexible operation specifically to control the quality of corrugated cardboard would no longer be possible.

In the present case, it was recognized that regulation of both shrinkage and moisture is particularly advantageous for the successful inline operation of a printing system. Without such control, the shrinkage and moisture vary greatly depending on the regularly variable web speed of the other system, which is taken over by the printing system. The shrinkage and moisture control described here also enables a job change (i.e. changing the job data) without stopping the printing system, i.e. during operation. The necessary adjustments to avoid varying shrinkage and moisture due to changed order data are automatically implemented by the control system. This means that the printing system can be used particularly flexibly. Without such an active regulation, every order change would require a stop of the printing system, otherwise poor further processing quality of the paper web would be expected.

Studies have shown that shrinkage and moisture are strongly dependent on web speed (equivalent: drying time). In contrast to roll-to-roll operation, it is generally not possible to keep the web speed constant in inline operation. This means that constant shrinkage and sufficient moisture cannot necessarily be maintained with constant drying and moistening performance. A fluctuation in shrinkage and moisture, ie in the quality of the printed paper web, then regularly leads to further processing and quality problems in subsequent systems, for example a corrugator. For example, too little moisture can result in poor bonding or warp. A print image that is too large or too small leads to problems in the further processing of the paper web and especially the corrugated cardboard made from it. Shrinkage that varies during operation regularly leads to problems on an automatic cutting and creasing machine and on the cross cutter of the corrugator, as these can cause any changes in length and width have to readjust. The result is a cut that often doesn't fit, meaning that the printed image is no longer positioned correctly on the finished corrugated cardboard.

As part of a study, the actual shrinkage and the actual moisture were recorded over a longer period of time and the measured values were used to determine the relationships between order data (paper type, grammage, production mode (i.e. with/without varnish, with/without primer)), web speed, Drying performance and humidification performance derived. On the basis of this, it was recognized in the present case that although it is fundamentally possible to regulate drying and moistening solely based on moisture or solely based on shrinkage, it regularly leads to unsatisfactory results. Therefore, the two variables “shrinkage” and “moisture” are regulated in combination in order to ensure both a dimensionally accurate printed image and sufficient moisture over a wide range of different order data and over a large web speed range.

Preferably, the drying and moistening outputs are regulated in such a way that the shrinkage is kept constant and the humidity is kept greater than or equal to a minimum humidity. This is particularly true in inline operation and with variable path speeds, both within the same job (i.e. with constant job data) and with varying job data. In the present case, constant shrinkage and sufficient moisture are achieved by regulating the drying performance and the humidification performance. It is also advantageous to have the lowest possible fluctuations in shrinkage and moisture, i.e. the lowest possible dynamics of the two controlled variables. The shrinkage is preferably controlled in such a way that the actual shrinkage is within a tolerance range around the target shrinkage (e.g. +/-0.5% to +/-1% of the target shrinkage or +/- 0.05% of the Total width of the paper web or +/- 1 to 2 mm in the direction of the total width). If the tolerance range is exceeded, a warning is expediently issued. The tolerance range is specified in particular as part of the order data and, for example, depending on the accuracy required for printing by means of the higher-level control unit. Similarly, an offset for the target shrinkage is optionally specified and taken into account if necessary. The humidity is preferably regulated in such a way that the actual humidity corresponds to at least a minimum humidity, for example 5%. The minimum humidity is preferably specified by the higher-level control unit, analogous to the tolerance range. If the minimum humidity is not reached, a warning is expediently issued or the humidification output is increased, in particular up to a maximum value that depends on the paper type and grammage, and then in particular a warning is issued if the humidification output cannot be increased further. This is based in particular on the observation that if the humidity is too high, i.e. if there is too much humidification, good quality winding of the paper web is no longer possible. Visually, this is regularly noticeable with a diamond pattern/waves on the rolled-up paper web.

Preferably, the control of shrinkage is limited by a minimum value for the dryer output, so that a minimum level of drying is ensured. The drying performance is therefore not reduced to an arbitrary level in order to reduce shrinkage, but rather the reduction in drying performance is limited to a minimum performance by the minimum value. The minimum value is expediently dependent on the web speed and in particular also on the amount of ink applied and, if necessary, also on the order data. Little ink regularly requires less drying and, conversely, a lot of ink requires a lot of drying. In addition, ink often dries more slowly on coated paper than on uncoated paper. The control is preferably set in such a way that sufficient drying is guaranteed at any web speed up to a certain amount of ink applied. For jobs with very little ink, the drying process may be too strong, but this is acceptable. However, a differentiation is advantageously made with regard to the amount of ink applied, in particular in order to save energy by avoiding unnecessary drying. The relationship between path speed and minimum value is stored, for example, as a characteristic curve.

When creating new order data, especially before carrying out the method described here, empirical values or test results are used for the associated target shrinkage; alternatively, the target shrinkage is determined in a defined printing process. This target shrinkage is then expediently used as a starting value for an iterative optimization, which in a suitable embodiment takes place as part of the method and thus during operation, alternatively outside of it.

Optionally, in addition to the previously mentioned components of the printing unit, dryer and humidifier, the printing system has one or more further components, which are particularly useful for reali sation of different production modes and/or further support drying and/or moistening.

In a suitable embodiment, the printing system has a primer applicator for applying a primer to the paper web. The primer applicator is arranged in particular upstream of the printing unit, so that the primer is applied before printing. The primer represents a primer for subsequent printing. Thanks to the primer applicator, the printing system now has production modes with and without primer (application). Downstream of the primer applicator and upstream of the printing unit, the printing system preferably has at least one dryer, also referred to as a primer dryer, for drying the primer. In particular, this dryer is only active for jobs with a primer application. The dryer is preferably a hot air dryer. In an expedient embodiment, one or more (e.g. two) humidifiers are additionally arranged downstream of the primer dryer.

Alternatively or additionally, the printing system has a varnish applicator for applying a varnish (i.e. for varnishing) to the paper web, in particular over the entire surface. The varnish applicator is arranged in particular downstream of the printing unit, so that the varnish is applied after printing and thus over the print. The varnish represents a surface refinement. Thanks to the varnish applicator, the printing system now has production modes with and without varnish application. Downstream of the paint applicator and upstream of the printing unit, the printing system preferably has at least one dryer, also referred to as a paint dryer, for drying the paint. In particular, this dryer is only active for jobs with paint application. The paint dryer is preferably a hot air dryer. A humidifier is expediently arranged upstream of the paint applicator. Alternatively or additionally, a humidifier is expediently arranged downstream of the paint dryer.

Alternatively or additionally, the printing system has a varnish printing unit, in particular a digital printing unit for varnish, for printing a varnish (i.e. for varnish printing, so-called “digital varnish”) onto the paper web. The varnish printing unit is arranged in particular downstream of the printing unit, so that the varnish is printed after printing and thus over the print. The varnish printing unit is preferably also arranged downstream of the varnish applicator, if one is available. The varnish represents a surface refinement. Thanks to the varnish printing unit, the printing system now has production modes with and without varnish printing. Downstream of the varnish printing unit, the printing system preferably has at least one dryer, also referred to as a varnish printing dryer, for drying the varnish. In particular, this dryer is only active for jobs with varnish printing. Preferably, several IR dryers and several hot air dryers are arranged analogous to the printing unit. A humidifier is expediently arranged downstream of the varnish printing unit and in particular also downstream of the varnish printing dryer.

One or more of the above-mentioned humidifiers are preferably used to regulate the humidity described above and are accordingly designed, for example, as a spray bar.

In particular, the primer dryer, the varnish dryer and the varnish print dryer are not used in the control, but are independently activated or deactivated depending on the requested production mode. However, if one or more of these dryers are active, there is increased shrinkage and reduced moisture, which is advantageously automatically compensated for by the control. In principle, however, it is also possible and advantageous to use one or more of these dryers when controlling the shrinkage, in particular in order to increase the control range for shrinkage and moisture accessible through the control. In an advantageous embodiment, one or more of the dryers mentioned are integrated into the control system. For example, the paint printing dryer is used as a booster to further adjust the system. Alternatively or additionally, the primer dryer has both a hot air dryer and an IR dryer. Integration into the control is such that the hot air dryer provides a base load for the drying performance and the IR dryer is only activated during a control peak, i.e. if temporarily there is an increased need for drying performance.

The web width sensor described above for measuring the web width in front of the printing unit is expediently arranged downstream of the primer applicator and in particular also downstream of the primer dryer. Downstream of the printing unit, the web width is measured as described above at one or more measuring points, each expediently using a web width sensor. A first suitable measuring point is located downstream of the dryer after the printing unit and upstream of the paint applicator. A second suitable measuring point is located between the paint application unit and the paint printing unit, in particular downstream of the paint dryer. A third suitable measuring point is located at the end of the printing system and - if available - downstream of the varnish printing unit and especially downstream of the varnish printing dryer. The first and second measuring points are particularly suitable for arranging the second sensor described above, with which the actual shrinkage in the event of a splice is determined. The third measuring point, however, is particularly suitable for arranging the first sensor described above, with which the actual shrinkage is determined as standard.

The target shrinkage is optimally defined (ie set) in particular when the control at maximum web speed (eg 300 m/min) sets the maximum drying performance of the dryer and the moistening performance of the humidifier required to dry the ink. This maximum required drying power and moistening power does not necessarily correspond to 100% of the available power; rather, due to paper-specific shrinkage differences, an upward control buffer is expediently present in order to be able to compensate for differences caused by overdrying. The same applies when using several dryers and/or several humidifiers for the control of each of these dryers and/or humidifiers. Shifting the optimal setting can bring advantages in exceptional cases, possibly in combination with restrictions (possibly lower range for the path speed or job change not possible without stopping). For example, as in the case already described above, all order changes can be carried out (within certain physical limits). At some point, however, no additional dryer/humidifier can be switched off or switched on. However, if the orders are limited and only cover a portion of all conceivable orders, e.g. no application with primer, only a few orders with additional coating and a large number of orders with varnish, the target shrinkage is expediently set larger for the orders without additional coating. Although this has the disadvantage of greater energy consumption for these special jobs, it has the advantage that more drying can be switched off in order to compensate for the paint dryer heating up, which means that a larger process window results. Similarly, for other order changes, it is expedient to optimize which type of order is carried out more frequently. If more/less drying is required to achieve the target shrinkage at the maximum web speed, this must be reduced/increased for future orders. This is expediently done automatically by the higher-level control unit, which is then self-learning in this sense. For a new order (e.g. new paper type, grammage) it is appropriate to start with an empirical approximation value for the target shrinkage. If, for example, there is already a target shrinkage for the new paper type for the grammages 100 g/m ² and 200 g/m ² , a first value for the target shrinkage is assumed based on this, for example for 150 g/m ² , eg simple interpolated.

A particular challenge for the control is rapid changes in web speed, especially when the web run between the printing unit and the sensor for determining the actual shrinkage is long, e.g. since the actual shrinkage is only determined at the end of the printing system or even outside of it. Therefore, starting values for the drying performance and the moistening performance are expediently stored for several web speed intervals (e.g. as part of the order data) and when the web speed changes from a first interval to a second interval, the starting values for the second interval are set first and then starting These regulate shrinkage and moisture. If the path speed is changed so much that it falls into a different interval with different starting values, these starting values are set in order not to have to wait for the control and to react better. The starting values when starting a job are preferably also improved iteratively for the existing job data. In the case of a consistent order, the starting value always corresponds in particular to the starting value used last time at this path speed (e.g. determined as a moving average from the last x productions). If the quality within a job remains consistent, the last settings for each web speed range or interval are suitably temporarily stored. If several changes in the path speed occur within a short period of time, the system starts again with the last value for this path speed range or interval and not with an empirical average. This is based on the idea that different batches of the same type of paper behave differently to a certain extent, particularly with regard to shrinkage. This prevents the initial adjustment from being carried out every time the path speed changes.

Similar to the web speed, it is also advisable to proceed in the event of a large change in the target shrinkage, for example in the event of a corresponding order change. In a suitable embodiment for this purpose, if the target shrinkage changes by a value which exceeds a predetermined limit, the drying performance and the moistening performance are predetermined once (ie initially when the target shrinkage changes) by one A value is changed and then the shrinkage and moisture are regulated based on this. In this way, the control is initially supported in adapting to the suddenly new target shrinkage. Below the limit (ie where the change is only small), such support is not required and the change is fully offset by the scheme. The limit value is typically chosen to be large and is, for example, 0.2% of the total width of the paper web, ie the target shrinkage changes by at least 0.2% of the total width of the paper web. The limit value can be set absolutely or relative to, for example, the total width of the paper web or the target shrinkage itself.

An embodiment is also advantageous in which the control is relieved by specifying a compensation factor with the order data in order to print the print at a larger size compared to a target dimension, so that a certain amount of shrinkage is permitted and not from the regulation must be balanced. This is based in particular on the idea that the shrinkage cannot actually be completely compensated for physically, since the shrinkage is always made up of a reversible and irreversible portion (hornification of the paper fibers during drying). The print is therefore deliberately enlarged and then shrinks to the target size due to the shrinkage in the printing system. The control then advantageously only or at least predominantly only compensates for dynamic changes in the web speed and/or paper-specific differences in shrinkage. For example, a paper machine is 9 m to 12 mm wide and the paper web produced with it is divided into several rolls. When rolling from the center of the paper web, the paper fibers are more aligned in the direction of the paper web than when rolling from the edge. Depending on the fiber orientation, the respective paper webs then shrink and swell to varying degrees during processing in the system. Humidification releases internal stresses from paper production. Depending on the amount of these, so to speak, frozen internal stresses, the paper web swells to varying degrees when moistened. These differences can be approximately up to +/- 0.15%. The printing unit prints the print accordingly enlarged according to the compensation factor. The compensation factor ultimately shifts the starting conditions for the control depending on the order, with the aim of accommodating this. The compensation factor is, for example, determined in advance through experiments and/or optimized during operation through recurring adjustment. The compensation factor is preferably dependent on the other order data, e.g. paper type, grammage, production mode (with/without primer, varnish, varnish printing). The compensation factor should be used or adjusted in particular if the tolerance range for shrinkage or the minimum moisture cannot be maintained for given order data. This is particularly advantageous for very high ink application quantities for printing or for jobs in which a primer, varnish or varnish print is used. Since one or more additional dryers are active in this case, a corresponding change in shrinkage must be taken into account. This is suitably done using the compensation factor for orders with corresponding order data.

Since when an order is changed, the order data for the new order is usually already known while the current order is still being processed, it is possible and advantageous to use the order data of the new order for predictive control of the dryer and/or humidifier. Especially if the new order contains a change in quality and, in contrast to the current order, requires an additional coating, in particular a primer, varnish and/or varnish print, a dryer for this coating, ie the primer dryer, the varnish dryer, is expediently used or the varnish printing dryer, is already preheated during the current job (and, expediently, disruptive influences from the additional dryer are automatically compensated for by changing the dryer performance and the humidifier performance), so that the required drying performance is completely or at least predominantly available at the start of the new job. The resulting increased shrinkage and reduced moisture during the current job is automatically compensated for by the control. Preferably, when a predetermined temperature is exceeded, for example 80 °C, the control range for shrinkage and/or moisture is increased. For example, if paint drying is also active, it is advantageous to reduce ink drying more than usual. Although the printed image may no longer be completely dried by the ink drying alone, the active varnish drying then dries the printed image accordingly, so that complete drying is guaranteed. With the primer dryer it is exactly the other way around. Due to the shrinkage before printing, the printed image can no longer shrink as much, so more drying is now required to achieve the same target shrinkage. However, such a level of additional drying is otherwise prohibited below the given temperature (e.g. the aforementioned 80 °C). The tolerances and the minimum humidity in particular remain unaffected. Orders with large tolerances or paper types with heavy gram are advantageously used for the changeover times maturities (lower differences in shrinkage) are preferred.

In an advantageous embodiment, the dryer is a hot air dryer and the printing system also has an IR dryer to dry the paper web. In other words, the drying power that is set by the controller to regulate shrinkage is provided by a combination of an IR dryer and a hot air dryer. The IR dryer advantageously has a faster response time than the hot air dryer, but is less economical to operate. Preferably, if an increase in the drying output is requested by the control, e.g. in the event of a job change with a corresponding change in the job data, the IR dryer is activated as a replacement during a heating phase of the hot air dryer in order to meet this request. For example, if the hot air dryer is below a certain temperature, if the temperature is necessary to increase, the IR dryer is initially used as a substitute until the hot air dryer has heated up. The procedure described is particularly advantageous if the current order requires a slow web speed, due to which the drying performance is reduced in order to reduce shrinkage and increase moisture. When the web speed is increased, the IR dryer initially compensates for the reduced drying performance of the hot air dryer until it has reached the required drying performance again.

In some cases it is advantageously possible to increase the range of possible web speeds by pre-drying the paper web before printing. Therefore, in a suitable embodiment, the printing system has a pre-dryer in order to pre-dry the paper web before printing. The primer dryer already described is particularly suitable as a pre-dryer, which is then optionally activated for pre-drying even though no primer is applied. Regardless of this, the pre-dryer is expediently permanently active in order to avoid heating and cooling times. The pre-drying causes in particular a pre-shrinkage of the paper web. Depending on the grammage etc., each type of paper has a maximum shrinkage at which the paper web hardly contains any water. This maximum shrinkage is expediently achieved because then the paper web cannot shrink any further. In this state of maximum shrinkage, the paper web is then printed and the drying time, which varies depending on the web speed, no longer has any influence on the shrinkage. This then simply ensures that enough moisture is introduced into the paper web again through the humidification and that the resulting swelling is controlled and, in particular, kept constant. Pre-drying is particularly useful when inexpensive heat is available.

• 1 schematisch einen Verbund aus einer Druckanlage und einer Wellpappenanlage,
• 2 eine Druckanlage im Detail.

Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. Show in it:

• 1 schematically a combination of a printing system and a corrugated cardboard system,
• 2 a printing system in detail.

In 1 A printing system 2 and a corrugated cardboard system 4 are shown schematically, which together form a composite 6. In 2 a detailed exemplary embodiment of the printing system 2 is shown, here a digital printing system for printing using an inkjet process. The printing system 2 in 2 is shown in a roll-to-roll operation, but is also for in-line operation and specifically for use in a network 6 as in 1 shown suitable.

The printing system 2 has a printing unit 8 for printing a paper web 10 according to a predetermined order with predetermined order data, which define the order. For this purpose, the printing unit 8 has one or more print heads 12. In 1 the printing system 2 is shown in inline operation, in 2 however, in a roll-to-roll operation.

The order data of a respective order are specified by means of a higher-level control unit 14, for example directly by the higher-level control unit 14 or by an operator who enters the order data into it, for example via an interface of the higher-level control unit 14. The higher-level control unit 14 is in 1 Designed separately from the printing system 2, but in an alternative not shown, part of it. The order data contains a production mode in which the printing system 2 is to be operated, as well as paper web data. The production mode defines, for example, a certain print quality, an amount of ink to be printed, whether a primer should be applied before printing, whether a varnish or varnish print should be applied after printing, etc. or a combination of these. The paper web data includes, for example, a type of paper, a grammage of the paper web, etc. or a combination thereof. Configuration data is derived from the order data, which contains corresponding machine data for the order-dependent setting of the printing system 2 and to one that is not explicitly shown Machine control of the printing system 2 is passed on.

The paper web 10 is generally conveyed in a conveying direction at a web speed through the printing system 2 and in 1 is fed to the corrugator 4 after printing. The corrugated cardboard system 4 is designed to produce corrugated cardboard 16 and uses the paper web 10 printed by the printing system 2, which is connected to further paper webs to form the corrugated cardboard 16. In the exemplary embodiment shown, the web speed is specified by the corrugator 4 and varies over time. Instead of the corrugated cardboard system 4, another system is arranged in an alternative embodiment, which further processes the printed paper web 10.

The terms “upstream” and “downstream” are used below to identify the relative positions of two components with respect to the conveying direction.

The printing system 2 has at least one dryer 18, 20 with an adjustable drying performance in order to dry the paper web 10, whereby the paper web 10 and thus also the print experience shrinkage. The dryer 18, 20 is basically arranged downstream of the printing unit 8 and is also referred to as a pressure dryer. In the exemplary embodiment 2 a total of six dryers 18, 20 are used, namely four IR dryers 18 and two hot air dryers 20.

The printing system 2 also has at least one humidifier 22 with an adjustable moistening power in order to moisten the paper web 10 and thereby adjust the moisture (ie paper moisture) of the paper web 10. When moistening, the paper web 10 also swells and thus the pressure increases. In the exemplary embodiment 2 three such humidifiers 22 are shown. In 2 All humidifiers 22 are arranged downstream of the dryers 18, 20 and are therefore also referred to as rehumidifiers. A respective humidifier 22 has, for example, at least one spray bar, which extends transversely to the conveying direction and in particular over a total width of the paper web 10 (ie in 2 perpendicular to the drawing plane) and sprays water onto it during operation.

As part of the operation of the printing system 2, an actual shrinkage and an actual moisture content are now determined for the paper web 10 and a target shrinkage and a target humidity are specified and the shrinkage and the humidity are determined by adjusting the drying performance and the moistening performance depending on the actual shrinkage and the actual moisture are regulated to the target shrinkage and the target moisture. In other words: by adjusting the drying and humidification performance, the shrinkage and humidity are adjusted during operation.

The target shrinkage and the target moisture (controlled variables) are part of the configuration data and are therefore determined based on the order data or are already included in the order data itself. The target shrinkage and the target moisture are order-specific and are therefore changed appropriately if the order is changed. In the present case, the higher-level control unit 14 specifies the target shrinkage and the target moisture specific to the order and transmits these to the machine control, which thus regulates the shrinkage and the moisture and for this purpose controls the dryers 18, 20 and the humidifiers 22.

The actual shrinkage indicates how much the paper web 10 has shrunk after drying. The actual shrinkage is determined inline with a corresponding sensor, here with several web width sensors 24, 26, 28, which are arranged downstream of the printing unit 8. In the exemplary embodiment 2 The actual shrinkage is determined by measuring a web width (perpendicular to the conveying direction) of the paper web 10 downstream of the dryer 18, 20 and comparing it with a web width in front of the printing unit 8. The actual shrinkage is therefore actually transverse shrinkage. In 2 The web width in front of the printing unit 8 is measured, for example, analogously with a web width sensor 30 upstream of the printing unit 8. The two web widths before and after the printing unit 8 are compared, for example, by setting a difference in the web widths in relation to the web width in front of the printing unit 8.

Alternatively or additionally, the actual shrinkage of the paper web 10 is determined by optically measuring a shrinkage of printed image marks on the paper web 10 downstream of the dryer 18, 20. In 2 For this purpose, an optical camera system 52, 54 is shown, which optically captures the printed image and the printed image marks contained therein and calculates a deviation between the target and actual shrinkage from the order data. In 2 Two possible positions for the camera system 52, 54 are shown, of which either only one or both are implemented at the same time. The use of two camera systems 52, 54 as in 2 shown enables both an inspection of the print image downstream of the printing unit 8 and an inspection of the varnish print image downstream of the varnish printing unit 46. The camera system 52 located further upstream (installation position 1) enables a particularly short control path, for example a splice. The camera system 54 located further downstream (installation position 2), on the other hand, is expediently active in regular operation (also normal operation), since this position is particularly close to the rewinder 32 and thus best depicts the finished printed image.

In the present case, the actual shrinkage is measured using the web width sensor 28 at the end of the printing system 2, immediately in front of a rewinder 32, or in the case of 1 outside of it, for example along the transfer route 34 or within the corrugated cardboard plant 4, ie generally when the paper web 10 is not further processed by the printing plant 2. The drying performance of the dryers 18, 20 is regulated by means of a shrinkage controller using the target shrinkage as a reference variable and the actual shrinkage as a controlled variable.

As already mentioned, in the exemplary embodiment shown, the actual shrinkage is determined as standard with the web width sensor 28, which is arranged as far downstream as possible from the printing unit 8. Deviating from this, in the case of a splice, the actual shrinkage is determined with one of the web width sensors 24, 26, which are arranged upstream of the web width sensor 28 and thus closer to the printing unit 8. This reduces web travel from the printing unit 8 to the web width sensor 24, 26, 28.

In order to regulate the humidity, the actual humidity is determined analogously to the shrinkage, which indicates how moist the paper web 10 is after moistening. In this case, the actual humidity is also determined inline. For this purpose, a corresponding sensor is used, here a moisture sensor 36, which is arranged downstream of the printing unit 8 and also downstream of all humidifiers 22. Analogous to measuring the actual shrinkage, the actual moisture is also determined at the end of the printing system 2 or even outside of it. By means of a humidity controller, the humidification performance of the humidifier 22 is then regulated with the target humidity as a reference variable and the actual humidity as a controlled variable.

In the present case, the drying and moistening performance are regulated in such a way that the shrinkage is kept constant and the moisture is kept greater than or equal to a minimum moisture. This is maintained in inline operation and with variable path speeds, both within the same job (i.e. with constant job data) and with varying job data. The shrinkage is regulated in such a way that the actual shrinkage lies within a tolerance range of, for example, +/-0.5 to 1% of the target shrinkage. The humidity is regulated in such a way that the actual humidity corresponds to at least a minimum humidity of, for example, 5%. The tolerance range and the minimum humidity are specified, for example, by the higher-level control unit 14. If the tolerance range is exceeded or if the humidity falls below the minimum, a warning is issued. The humidification output is increased up to a maximum value, depending on the paper type and grammage, before the warning is issued. In this case, the regulation of shrinkage is limited by a minimum value for the dryer output, so that it is not reduced to an arbitrary level and a minimum level of drying is ensured. The minimum value depends on the web speed, the type of paper and the amount of ink applied.

Optional to the previously mentioned components printing unit 8, dryer 18, 20 and humidifier 22, the printing system 2 has 2 one or more further components which serve to implement different production modes and/or further support drying and/or humidification.

This is how the in 2 shown printing system 2 a primer applicator 38 for applying a primer to the paper web 10. The primer applicator 38 is arranged upstream of the printing unit 8 so that the primer is applied before printing. Thanks to the primer applicator 38, the printing system 2 now has production modes with and without primer (order). Downstream of the primer applicator 38 and upstream of the printing unit 8, the printing system 2 has a dryer 40, here a hot air dryer, which is also referred to as a primer dryer, for drying the primer. This dryer is primarily active for jobs with primer application.

In addition, the printing system has 2 in 2 a varnish applicator 42 for applying a varnish (ie for varnishing) to the paper web 10. The varnish applicator 42 is arranged downstream of the printing unit 8, so that the varnish is applied after printing and thus over the print. Thanks to the varnish applicator 42, the printing system 2 now has production modes with and without varnish application. Downstream of the paint application unit 42 and upstream of the printing unit 8, the printing system 2 has a dryer 44, here a hot air dryer, which is also referred to as a paint dryer, for drying the paint. This dryer 44 is only active for jobs with paint application. In the present case, one of the humidifiers 22 is arranged upstream of the paint application unit 42 and another of the humidifiers 22 is arranged downstream of the paint dryer 44.

In addition, the printing system has 2 in 2 a varnish printing unit 46, here a digital printing unit for varnish, for printing a varnish onto the paper web 10. The varnish printing unit 46 is arranged downstream of the printing unit 8, so that the varnish is printed after printing and thus over the print. The varnish printing unit 46 is also arranged downstream of the varnish applicator 42. Thanks to the varnish printing unit 46, the printing system 2 now has production modes with and without varnish printing. Downstream of the varnish printing unit 46, the printing system 2, analogous to the printing unit 8, has several dryers 48, 50 for drying the varnish, namely 2 IR dryers 48 and two hot air dryers 50, each also referred to as varnish printing dryer. These dryers 48, 50 are only active for jobs with varnish printing. One of the humidifiers 22 is arranged downstream of the paint printing unit 46 and the paint printing dryer 48, 50.

The primer dryer 40, the paint dryer 44 and the paint print dryers 48, 50 are not necessarily used in the control, but are activated or deactivated independently depending on the requested production mode. However, if one or more of these dryers 40, 44, 48, 50 are active, there is a change in shrinkage and reduced moisture, which is, however, automatically compensated for by the control. If the primer dryer 40 is activated, the pre-drying reduces the subsequent print image shrinkage while maintaining the same ink drying settings.

The web width sensor 30 described above for measuring the web width in front of the printing unit 8 is arranged downstream of the primer applicator 38 and also downstream of the primer dryer 40. Downstream of the printing unit 8, the web width is measured, as already described, at several measuring points using one of the web width sensors 24, 26, 28. A first measuring point is located downstream of the dryers 18, 20 and upstream of the paint application unit 42. A second measuring point is located between the paint application unit 42 and the paint printing unit 46 and downstream of the paint dryer 44. A third measuring point is located at the end of the printing system 2, downstream of the varnish printing unit 46 and downstream of the varnish printing dryer 48, 50. The web width sensors 24, 26 are arranged at the first and second measuring points, respectively, to determine the actual shrinkage in the event of a splice. The web width sensor 28 is then arranged at the third measuring point for the standard determination of the actual shrinkage.

A particular challenge for control is rapid changes in web speed. Therefore, in the exemplary embodiment shown, starting values for the drying performance and the moistening performance are stored for several web speed intervals (e.g. as part of the order data) and when the web speed changes from a first interval to a second interval, the starting values for the second interval are set first and then the shrinkage and moisture are regulated based on these. If the path speed is changed so much that it falls into a different interval with different starting values, these starting values are set in order not to have to wait for the control and to react better.

Similar to the web speed, the same procedure applies in the case of a large change in the target shrinkage, e.g. in the event of a corresponding order change. For this purpose, if the target shrinkage changes by a value that exceeds a predetermined limit, the drying performance and the moistening performance are changed once (i.e. initially when the target shrinkage changes) by a predetermined value and then, based on this, the shrinkage and the Humidity controlled. In this way, the control is initially supported in adapting to the suddenly new target shrinkage.

In addition, in this case the control is also relieved in that a compensation factor is already specified with the order data in order to print the print larger compared to a target dimension, so that a certain amount of shrinkage is permitted and does not have to be compensated for by the control. The print is therefore deliberately enlarged and then shrinks to the target size due to the shrinkage in the printing system 2. The control then only or at least predominantly compensates for dynamic changes, for example in the web speed or differences in the raw paper. The printing unit 8 prints the pressure in a correspondingly increased manner according to the compensation factor, so that ultimately the starting conditions for the control are adjusted depending on the order in order to accommodate this. The compensation factor depends, for example, on the other order data, e.g. paper type, grammage, production mode (with/without primer, varnish, varnish printing).

Since when an order is changed, the order data for the new order is usually already known while the current order is still being processed, in the present case the order data of the new order is used for predictive control of the dryers 18, 20 and humidifier 22. Especially if the new order contains a change in quality and, in contrast to the current order, requires an additional primer, varnish and/or varnish printing, corresponding Accordingly, the primer dryer 40, the paint dryer 44 or the paint print dryers 48, 50 are already preheated during the current job, so that the required drying performance is available at the start of the new job. The resulting changes in shrinkage and moisture during the current job are automatically compensated for by the control.

In the present case, the combination of IR dryers 18 and hot air dryers 20 is used to activate the IR dryers 18 as a replacement in the event of a request for an increase in drying performance by the control, for example in the event of a corresponding order change, during a heating phase of the hot air dryers 20 requirement to serve. The procedure described is used, for example, if the current job requires a slow web speed, due to which the drying performance is reduced in order to reduce shrinkage and increase moisture. When the web speed increases, the IR dryers 18 initially compensate for the reduced drying performance of the hot air dryers 20 until they have reached the required drying performance again.

In some cases it is advantageously possible to increase the range of possible web speeds by pre-drying the paper web 10 before printing. Therefore, in a suitable embodiment, the printing system 2 has a pre-dryer 40 in order to pre-dry the paper web 10 before printing. Serves as a pre-dryer 40 2 For example, the primer dryer 40 already described.

Reference symbol list

2

Printing system

4

Corrugator plant

6

Composite

8th

Pressure unit

10

paper web

12

Printhead

14

higher-level control unit

16

Corrugated cardboard

18

Dryer, pressure dryer, IR dryer

20

Dryer, pressure dryer, hot air dryer

22

humidifier

24

Web width sensor (downstream of the printing unit, first measuring point)

26

Web width sensor (downstream of the printing unit, second measuring point)

28

Web width sensor (downstream of the printing unit, third measuring point)

30

Web width sensor (upstream of the printing unit)

32

Rewinder

34

transfer route

36

Humidity sensor

38

Primer application

40

Dryer, hot air dryer, primer dryer

42

Paint application work

44

Dryer, hot air dryer, paint dryer

46

Varnish printing unit

48

Dryer, IR dryer, varnish printing dryer

50

Dryer, hot air dryer, paint printing dryer

52

Camera system

54

Camera system

Claims (13)

Method for operating, in particular inline operation, a printing system (2), - wherein the printing system (2) has a printing unit (8) for printing a paper web (10) according to a specified order with specified order data, - the paper web (10) being conveyed through the printing system (2) at a web speed, - wherein the printing system (2) has at least one dryer (18, 20) with an adjustable drying performance in order to dry the paper web (10), whereby the paper web (10) experiences shrinkage, - wherein the printing system (2) has at least one humidifier (22) with an adjustable humidification power in order to moisten the paper web (10) and thereby adjust the moisture content of the paper web (10), - whereby an actual shrinkage and an actual moisture content are determined for the paper web (10) and a target shrinkage and a target humidity are specified, - whereby the shrinkage and the moisture are regulated by adjusting the drying performance and the moistening performance depending on the actual shrinkage and the actual moisture to the target shrinkage and the target moisture. Procedure according to Claim 1 , wherein the paper web (10) is fed to a corrugator (4) after printing, the web speed being predetermined by the corrugator (4) and varying over time. Procedure according to one of the Claims 1 or 2 , wherein the actual shrinkage of the paper web (10) is determined by measuring a web width of the paper web (10) downstream of the dryer (18, 20) and comparing it with a web width in front of the printing unit (8) or optically shrinkage of printed image marks is measured on the paper web (10). Procedure according to one of the Claims 1 until 3 , wherein the actual shrinkage is determined with a first sensor (28), which is arranged downstream of the printing unit (8) and at the end of the printing system (2) or outside of it, except in the case of a splice, in which case the actual shrinkage is also included a second sensor (24, 26) is determined, which is arranged upstream of the first sensor (28). Procedure according to one of the Claims 1 until 4 , wherein the shrinkage is regulated such that the actual shrinkage lies within a tolerance range around the target shrinkage, wherein the moisture is regulated such that the actual moisture corresponds to at least a minimum moisture. Procedure according to one of the Claims 1 until 5 , whereby the control of shrinkage is limited by a minimum value for the dryer performance, so that a minimum level of drying is ensured. Procedure according to one of the Claims 1 until 6 , whereby starting values for the drying performance and the moistening performance are stored for several intervals of the web speed, whereby when the web speed changes from a first interval to a second interval, the starting values for the second interval are first set and then, based on these, the shrinkage and the Humidity can be controlled. Procedure according to one of the Claims 1 until 7 , whereby if the target shrinkage changes by a value that exceeds a predetermined limit, the drying performance and the humidification performance are changed once by a predetermined value and the shrinkage and moisture are then regulated based on this. Procedure according to one of the Claims 1 until 8th , whereby when an order changes from a current order to a new order and if the new order requires an additional coating, a dryer (40, 44, 48, 50) for this coating is already preheated during the current order. Procedure according to one of the Claims 1 until 9 , wherein the dryer (20) is a hot air dryer and the printing system (2) in addition to this has an IR dryer (18) in order to dry the paper web (10), whereby if an increase in the drying performance is requested by the control, During a heating phase of the dryer (20), the IR dryer (18) is activated as a substitute in order to meet this requirement. Procedure according to one of the Claims 1 until 10 , wherein the printing system (2) has a pre-dryer (40) in order to pre-dry the paper web (10) before printing. Procedure according to one of the Claims 1 until 11 , whereby the control is relieved by the fact that a compensation factor is already specified with the order data in order to print the print larger compared to a target dimension, so that a certain amount of shrinkage is permitted and does not have to be compensated for by the control. Printing system (2) or composite (6) consisting of such a system and a corrugated cardboard system (4), the printing system (2) being designed to carry out a method according to one of Claims 1 until 12 .

Images