METHOD FOR OPERATING A PRINTING SYSTEM AS WELL AS PRINTING SYSTEM AND COMPOSITE OF SUCH A SYSTEM AND A CORRUGATED CARDBOARD SYSTEM

Description

[0001] The invention relates to a method for operating a printing system and a system comprising such a printing system, optionally in combination with a corrugated board system.

[0002] A printing system is used to print a printed image, or "print," onto a paper web. The print, and thus the paper web itself, are regularly dried using a dryer (e.g., a hot-air dryer and / or IR dryer), which shrinks the print and the paper web and also removes moisture from the paper web.

[0003] JP 2007 030 171 A discloses a device for corrugated board designed to eliminate the need for a heating plate. Instead, superheated steam is used for heating. The device consists of a curing zone (X) in which superheated steam is sprayed onto the open flute of the single-faced corrugated board to bond the single-faced corrugated board to a smooth third paper web. This principle is also possible for double-wall corrugated board. In addition, the device includes a heating zone (Y) consisting of a large number of superheated steam nozzles for spraying superheated steam onto the face sheets of the corrugated boards to gel the glue, thus achieving complete adhesion. There is also a cooling zone (Z) for cooling the finished corrugated board.

[0004] US Pat. No. 5,596,930 A describes a method and the corresponding device for moistening a moving material web (10), in particular for remoistening a printed and subsequently dried printing material. As soon as possible after the thermal drying process has ended, preferably in the area of ​​the cooling cylinders, an applicator (12) presses a moistening agent onto one or both sides of the material web (10) against a guide element (11) by means of a smooth cylinder (15).

[0005] EP 3 028 132 B1 shows a web-fed printing system with a first print bar, a first sensor, a second print bar, a second sensor, and a controller. The first print bar prints first user content onto a first side of a media web. The first sensor detects a pattern on the media web and provides first sensor data while the first print bar prints the first user content. A second print bar prints second user content onto the first side of the media web. The second sensor detects the pattern on the media web and provides second sensor data when the second print bar prints the second user content. The controller determines, based on the first sensor data and the second sensor data, an extent of expansion of the media web in a direction perpendicular to a web advance direction and modifies the printing operation performed by the second print bar based on the extent of expansion.

[0006] A problem during operation is a change in the web speed at which the paper web is conveyed through the printing system. At different web speeds, the paper web is exposed to the dryer for different lengths of time, so the shrinkage and moisture content of the paper web change depending on the web speed. This is particularly detrimental to the dimensional accuracy of the print and maintaining a certain moisture level, for example, for further processing.

[0007] The problem can generally be avoided by simply operating the printing system at a constant web speed. This is particularly useful in stand-alone or roll-to-roll operation, where the paper web is unwound before the printing system and rewound after it. However, in a system consisting 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 system. Therefore, it is desirable to keep the shrinkage and moisture content of the paper web at the printing system exit as constant as possible despite varying web speeds.

[0008] Against this background, one object of the invention is to enable the most flexible operation of a printing system possible. To this end, a corresponding method for operating a printing system is to be provided. Furthermore, a corresponding printing system and a combination of a printing system and a corrugated board system are to be provided.

[0009] The object is achieved according to the invention by a method having the features according to claim 1 and by a printing system or a composite comprising such a system and a corrugated cardboard layer having the features according to claim 13. Advantageous embodiments, further developments and variants are the subject of the dependent claims. The statements in connection with the method also apply mutatis mutandis to the printing system and the composite, and vice versa. If steps of the method are described below, advantageous embodiments for the printing system and the composite 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 composite has, in particular, a correspondingly designed control unit.

[0010] A core idea of ​​the invention is in particular a control of the dimensional stability of preferably digital printed products taking into account the paper water content, more precisely: a respective control of both the shrinkage and the moisture of a paper web which is printed in a printing system.

[0011] The method according to the invention serves to operate a printing system. The operation is preferably, but not necessarily, inline, 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 predetermined job with predetermined job data that define the job (also referred to as a "print job"). For this purpose, the printing unit has, in particular, one or more print heads. The printing unit is also referred to as a printing chamber. The printing system is preferably a digital printing system, and printing is carried out using an inkjet process.

[0012] The job data for a job is specified in particular by means of a higher-level control unit, e.g. directly by the control unit itself or by an operator who enters the job data into the control unit, e.g. 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 job 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, a quantity of ink to be printed, whether a primer is to be applied before printing, whether a varnish or varnish print is to be applied after printing, etc., or a combination thereof. The paper web data includes in particular a paper type, 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 appropriately contains corresponding machine data for the order-specific settings of the printing system. The derivation of the configuration data (lower-level) from the order data (higher-level) is of secondary importance in this case and is carried out, for example, using experimentally determined characteristic curves, 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 system of the printing system in order to adjust and control it accordingly.

[0013] The paper web is generally conveyed through the printing system in one conveying direction at one web speed. A particularly preferred embodiment is one in which the paper web is fed to a corrugator after printing. The corrugator is designed to produce corrugated board and uses the paper web printed by the printing system, which is combined with other paper webs to form the corrugated board. The web speed is predetermined in particular by the corrugator and varies over time. The web speed typically varies when a job changes, but can also vary within the same job. Accordingly, the invention described here is particularly suitable for a combination of printing system and corrugator, which is assumed below without any loss of generality.

[0014] The terms "upstream" and "downstream" are used below to describe the relative positions of two components with respect to the conveying direction. A component A positioned upstream of a component B is positioned relative to the latter opposite to the conveying direction, i.e., the paper web passes through component A first and then component B. The reverse applies for "downstream."

[0015] The printing system has at least one dryer with an adjustable drying capacity for drying 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 generally arranged downstream of the printing unit. The dryer is also referred to as a print 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 arranged downstream of the printing unit and several hot air dryers are arranged downstream of these. The drying capacity is specified, for example, as the temperature (e.g. in °C) which the paper web experiences through the dryer, but other measurements are equally suitable.

[0016] The printing system further comprises at least one humidifier with an adjustable humidification capacity in order to humidify the paper web and thereby adjust the moisture content (i.e. paper moisture) of the paper web and in particular also any swelling (i.e. negative shrinkage and thus general shrinkage of the paper web). During humidification, the paper web typically swells and thus the pressure increases. The humidifier is preferably arranged downstream of the dryer and accordingly compensates for any moisture loss during 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 across the entire width of the paper web and sprays water onto it during operation.The humidification performance is given, for example, as the amount of water applied to the paper web per unit area (e.g. in ml / m 2< ), but other measurements are also suitable.

[0017] Within the process, an actual shrinkage and moisture content are determined for the paper web, and a target shrinkage and moisture content are specified. The shrinkage and moisture content are controlled by adjusting the drying and moistening performance to the target shrinkage and moisture content, depending on the actual shrinkage and moisture content. In other words, by adjusting the drying and moistening performance, the shrinkage and moisture content are adjusted during operation, particularly continuously.

[0018] The target shrinkage and the target humidity (controlled variables) are particularly part of the configuration data and are therefore determined based on the order data or are already contained in the order data itself. The target shrinkage and the target humidity are particularly job-specific and are therefore appropriately modified when the order changes (equivalently: when the order changes), whereby the same or similar order data and configuration data are used for identical or similar orders. Preferably, the higher-level control unit specifies the target shrinkage and the target humidity on a job-specific basis and transmits them to the machine control system, which then regulates the shrinkage and humidity and, for this purpose, controls the dryer and the humidifier.

[0019] To control shrinkage, the actual shrinkage is determined, which indicates how much the paper web has shrunk after drying. The actual shrinkage is determined primarily inline. A corresponding sensor is used for this purpose, which is located downstream of the printing unit and, in particular, also downstream of the dryer and humidifier in order to obtain the most accurate shrinkage value possible.

[0020] 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 upstream of the printing unit. Alternatively or additionally, the actual shrinkage of the paper web is determined by optically measuring the 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 (particularly as part of the printing system), which optically records the print image and the print image marks contained therein and calculates a deviation between the target and actual shrinkage from the job data. An optical measurement with a camera system has the advantage over web width measurement that the shrinkage of the print image is determined directly.Particularly when a large amount of ink is applied to one side of the paper web, resulting in correspondingly strong swelling, varying shrinkage across the entire width of the paper web can be expected. If shrinkage is only determined indirectly by web width measurement, these deviations across the entire width cannot be quantified. 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 usually less than the transverse shrinkage, it is sufficient to use only the latter for control in order to achieve dimensional accuracy of the print in both the transverse and longitudinal directions. The web width upstream of the printing unit is preferably measured analogously using a web width sensor upstream of the printing unit. A respective web width sensor determines the web width, for example, using web edge detection or a light grid.The two web widths are compared, for example, by setting the difference between the web widths in relation to the web width upstream of the printing unit. This ratio then indicates the shrinkage in % based on the web width upstream of the printing unit. If the printing system is followed by another system, the print is expediently monitored in this system using an additional sensor, e.g., if the print contains a QR code whose dimensions are monitored by the downstream system. For this purpose, the distance between several QR codes on print images arranged next to one another across the working width is expediently measured. The QR codes serve, alternatively or additionally, expediently as the above-mentioned print marks.

[0021] The actual shrinkage is preferably determined at the end of the printing system, e.g. immediately before a winder for the paper web, or even outside of it, e.g. along a transfer section or within a downstream system, i.e. when the paper web is not further processed by the printing system and in particular before, during or after the paper web is / has been transferred to a downstream system. By means of a shrinkage controller, the dryer, or more precisely the dryer output, is controlled with the target shrinkage as the reference variable and the actual shrinkage as the controlled variable. In this way, the shrinkage which occurs in the printing system is controlled to the target shrinkage. The shrinkage controller is in particular part of the printing system, in particular the machine control system, and is preferably implemented by means of a programmable logic controller (PLC).

[0022] In an advantageous embodiment, the actual shrinkage is determined as standard using 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 using a second sensor which is arranged upstream of the first sensor and is therefore closer to the printing unit. This advantageously reduces the web run from the printing unit to the sensor by a factor of 5 to 20, e.g. from 250 m to just 20 m. In a splice, a new paper web is added to the end of a paper web that is currently in use. This new paper web may have different properties and result in different job data. In this case, it is advantageous to reduce the web run as much as possible for shrinkage control in order to achieve a faster control response.This means that the control system no longer takes into account the entire processing of the paper web downstream of the printing unit. After a specified time or after the length of the paper web has passed through, 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, upstream of a varnish dryer and there upstream of two of three spray bars. The shrinkage due to drying and the swelling caused by the spray bars cause the dimensions of the paper web to change by a factor x, depending on the settings, possibly with certain tolerances. Based on empirical values, the offset is then used to estimate or assume the further change in shrinkage downstream in favor of the shorter control path resulting from the aforementioned arrangement.The actual shrinkage is therefore the sum of the measured shrinkage value and the offset, which is particularly dependent on the downstream machine settings. The offset is therefore generally used to correct the actual shrinkage based on the sensor's position relative to the components that influence shrinkage.

[0023] To regulate moisture, the actual moisture content is determined in a similar way to shrinkage. This indicates how moist the paper web is after moistening. The actual moisture content is determined primarily 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.), e.g., using a respective characteristic curve. Analogous to the measurement of actual shrinkage, the actual moisture content is also determined, preferably at the end of the printing system or even outside of it. The humidifier, or more precisely the humidifier output, is then controlled by a humidity controller, with the target moisture content as the reference variable and the actual moisture content as the controlled variable.

[0024] In principle, it is conceivable to simply operate the printing system at a maximum web speed in order to produce at maximum output. However, a variable web speed is necessary, 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 reduced briefly during various quality changes (e.g., sheet length changes). 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., continuous corrugated board at 200 - 250 m / min). By changing the web speed, the residence time in the heating and pulling section (i.e., double facer) is also regularly shortened or lengthened in order to eliminate quality problems such as warp (bending of the corrugated board) and gluing problems.In general and in the event of other problems, the web speed is sometimes reduced, e.g. if the paper quality is poor or if a tray at the end of the line is full. Regardless of the specific reason, a line stoppage always means that the paper comes to a standstill in the heating and pulling sections and is therefore scrap. If the laminate were to be operated at a constant web speed, a reduced web speed would result in corresponding scrap due to excessive shrinkage and insufficient moisture. Accordingly, alternative machine and print settings for a reduced web speed would have to be stored for the various grades, which are adjustable, which means increased work and effort. In addition, flexible operation specifically for controlling the corrugated board quality would no longer be possible.

[0025] In this case, it was recognized that controlling both shrinkage and moisture is particularly advantageous for the successful inline operation of a printing system. Without such control, 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 control of shrinkage and moisture 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 job data are automatically implemented by the control system. This makes the printing system particularly flexible in use.Without such active control, every job change would require a stop of the printing system, as otherwise the paper web would be expected to be of poor further processing quality.

[0026] Studies have shown that shrinkage and moisture content are heavily dependent on the web speed (equivalent to drying time). Unlike in roll-to-roll operation, it is often not possible to keep the web speed constant in inline operation. As a result, constant shrinkage and sufficient moisture content cannot necessarily be maintained even with constant drying and moistening performance. Fluctuations in shrinkage and moisture content, i.e. in the quality of the printed paper web, then regularly lead to further processing and quality problems in downstream systems, e.g. a corrugator. For example, too little moisture can result in inadequate bonding or warping. A print image that is too large or too small leads to problems in the further processing of the paper web and especially in the corrugated board produced from it.For example, shrinkage fluctuations during operation regularly lead to problems with a cutting and creasing machine and the cross cutter of a corrugator, as these machines have to adjust for any length and width changes. The result is often an incorrect cut, which means the printed image is no longer correctly positioned on the finished corrugated board.

[0027] As part of a study, the actual shrinkage and the actual moisture content were recorded over an extended period of time, and the relationships between job data (paper type, grammage, production mode (i.e., with / without varnish, with / without primer)), web speed, drying performance, and humidification performance were derived from the measured values. Based on this, it was recognized that controlling drying and humidification based on moisture or shrinkage alone is fundamentally possible, but regularly leads to unsatisfactory results. Therefore, the two variables "shrinkage" and "moisture" are controlled in combination in order to ensure both a dimensionally accurate print image and sufficient moisture content across a wide range of different job data and a wide range of web speeds.

[0028] Preferably, the drying and moistening performance are controlled in such a way that the shrinkage is constant and the moisture content is kept greater than or equal to a minimum moisture content. This is particularly true in inline operation and at variable web speeds, both within the same job (i.e., with constant job data) and with varying job data. In this case, constant shrinkage and sufficient moisture content are achieved by controlling the drying and moistening performance. Furthermore, it is advantageous to have the smallest possible fluctuations in the shrinkage and moisture content, i.e., the smallest possible dynamics of the two controlled variables. Preferably, the shrinkage is controlled in such a way that the actual shrinkage lies 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 job data and, for example, as a function of the accuracy required for printing by means of the higher-level control unit. Analogously, an offset for the target shrinkage is additionally specified and taken into account if necessary. The humidity is preferably controlled in such a way that the actual humidity corresponds to at least a minimum humidity, e.g. 5%. The minimum humidity is specified analogously to the tolerance range, preferably by means of the higher-level control unit.If the minimum humidity level is exceeded, a warning is issued or the humidification level is increased, especially up to a maximum value dependent on the paper type and grammage. A warning is then issued if the humidification level cannot be increased any further. This is based on the observation that if the humidity level is too high, i.e., if the humidification level is too high, high-quality winding of the paper web is no longer possible. This is usually visually noticeable as a diamond pattern / wave on the rolled paper web.

[0029] Preferably, the control of shrinkage is limited by a minimum value for the dryer power, thus ensuring a minimum level of drying. The drying power is therefore not reduced arbitrarily in order to reduce shrinkage, but the reduction in drying power is limited to a minimum level by the minimum value. The minimum value is expediently dependent on the web speed and, in particular, on the ink application quantity and, if applicable, also on the job data. A small amount of ink generally requires less drying, and conversely, a large amount of ink requires a large amount of drying. In addition, ink generally dries more slowly on coated paper than on uncoated paper. Preferably, the control is set such that sufficient drying is guaranteed at any web speed up to a certain ink application quantity.For jobs with very little ink, excessive drying may occur, but this is accepted. Advantageously, however, a differentiation is made regarding the ink application quantity, particularly to save energy by avoiding unnecessary drying. The relationship between web speed and the minimum value, for example, is stored as a characteristic curve.

[0030] When creating new order data, especially prior to implementing the process described here, empirical values ​​or test results are used for the corresponding 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 configuration, is carried out as part of the process and thus during operation, or alternatively, outside of it.

[0031] Optionally, in addition to the previously mentioned components printing unit, dryer and humidifier, the printing system also has one or more additional components which are used in particular to implement different production modes and / or further support drying and / or humidification.

[0032] Thus, in a suitable embodiment, the printing system comprises a primer application unit for applying a primer to the paper web. The primer application unit is arranged, in particular, upstream of the printing unit, so that the primer is applied before printing. The primer represents a primer for the subsequent printing process. Thanks to the primer application unit, the printing system now has production modes with and without primer (application). Downstream of the primer application unit and upstream of the printing unit, the printing system preferably comprises at least one dryer, also referred to as a primer dryer, for drying the primer. This dryer is, in particular, only active for jobs with primer application. The dryer is preferably a hot-air dryer. In In a suitable embodiment, one or more (e.g. two) humidifiers are additionally arranged downstream of the primer dryer.

[0033] Alternatively or additionally, the printing system has a varnish application unit, in particular for the full-surface application of a varnish (i.e. for varnishing), to the paper web. The varnish application unit is in particular arranged downstream of the printing unit, so that the varnish is applied after printing and thus over the print. The varnish represents a surface finish. Thanks to the varnish application unit, the printing system now has production modes with and without varnish application. Downstream of the varnish application unit and upstream of the printing unit, the printing system preferably has at least one dryer, also referred to as a varnish dryer, for drying the varnish. This dryer is in particular only active for jobs with varnish application. The varnish dryer is preferably a hot air dryer. Expediently, a humidifier is arranged upstream of the varnish application unit. Alternatively or additionally, a humidifier is expediently arranged downstream of the varnish dryer.

[0034] Alternatively or additionally, the printing system comprises 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 applied after printing and thus over the print. Preferably, the varnish printing unit is also arranged downstream of the varnish application unit, if one is present. The varnish represents a surface finish. 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. This dryer is particularly only active for jobs with varnish printing. Preferably, several IR dryers and several hot-air dryers are arranged analogously to the printing unit.It is advisable to arrange a humidifier downstream of the varnish printing unit and in particular also downstream of the varnish printing dryer.

[0035] One or more of the above-mentioned humidifiers are preferably used for the humidity control described above and are designed accordingly, for example, as spray bars.

[0036] The primer dryer, the paint dryer, and the paint print dryer are not used in the control system, but are activated or deactivated independently depending on the requested production mode. If one or more of these dryers are active, this results in increased shrinkage and reduced moisture, which is advantageously compensated for automatically by the control system. In principle, however, the use of one or more of these dryers in the shrinkage control is also possible and advantageous, in particular in order to increase the control range for shrinkage and moisture accessible via the control system. In an advantageous embodiment, one or more of the aforementioned dryers are integrated into the control system. For example, the paint print dryer is used as a booster to further adjust within the system.Alternatively or additionally, the primer dryer has both a hot air dryer and an IR dryer. The integration into the control system is such that the hot air dryer provides a base load for the drying capacity and the IR dryer is only activated during a control peak, ie when there is a temporary increased demand for drying capacity.

[0037] The web width sensor described above for measuring the web width upstream of the printing unit is expediently arranged downstream of the primer application unit and in particular also downstream of the primer dryer. Downstream of the printing unit, the web width is measured at one or more measuring points, as described above, 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 coating application unit. A second suitable measuring point is located between the coating application unit and the coating printing unit, in particular also downstream of the coating dryer. A third suitable measuring point is located at the end of the printing system and - if available - downstream of the coating printing unit and in particular also downstream of the coating printing dryer. The first and second measuring points are particularly suitable for the arrangement of the second sensor described above, which is used to determine the actual shrinkage in the event of a splice.The third measuring point, on the other hand, is particularly suitable for the arrangement of the first sensor described above, with which the actual shrinkage is determined as standard.

[0038] The target shrinkage is optimally determined (i.e., set) when the control system, at maximum web speed (e.g., 300 m / min), sets the maximum drying capacity of the dryer and the maximum humidification capacity of the humidifier required to dry the ink. This maximum required drying capacity and humidification capacity does not necessarily correspond to 100% of the available capacity; rather, due to paper-specific shrinkage differences, an upward control buffer is expediently provided in order to compensate for differences resulting from overdrying. The same applies to the control of each individual dryer and / or humidifier when using multiple dryers and / or multiple humidifiers.In exceptional cases, shifting the optimal setting can bring advantages, possibly in combination with restrictions (possibly a narrower range for the web speed or job changes not possible without a stop). For example, as in the case already described above, all job changes can be carried out (within certain physical limits). However, at some point it will no longer be possible to switch any further dryers / humidifiers on or off. However, if the jobs are limited and only cover a portion of all conceivable jobs, e.g. no jobs with primer, only a few jobs with an additional coating and a large number of jobs with varnish, the target shrinkage for jobs without an additional coating is expediently set higher.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 heating up of the varnish dryer, i.e. this results in a larger process window. Similarly, for other job changes, it is expedient to optimize which type of job 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 jobs. This is expediently done automatically by the higher-level control unit, which is then self-learning in this sense. For a new job (e.g. new paper type, grammage), it is suitable to start with an empirical approximation for the target shrinkage. For example, if there isIf a respective target shrinkage for the new paper grade is already known for the grammages 100 g / m 2< and 200 g / m 2<, a first value for the target shrinkage is assumed based on this, e.g. for 150 g / m 2<, e.g. simply interpolated.

[0039] Rapid changes in web speed pose a particular challenge for control, especially when the web run between the printing unit and the sensor for determining the actual shrinkage is long, e.g. because the actual shrinkage is only determined at the end of the printing system or even outside of it. It is therefore advisable to store start values ​​for the drying performance and the moistening performance for several web speed intervals (e.g. as part of the job data). When the web speed changes from a first interval to a second interval, the start values ​​for the second interval are set first and then the shrinkage and moisture are controlled based on these. If the web speed changes so drastically that it falls into a different interval with different start values, these start values ​​are set so that you don't have to wait for the control and can react more quickly.The starting values ​​at the start of a job are preferably also improved iteratively for the existing job data. For a constant job, the starting value always corresponds to the last starting value used at this web speed (e.g. determined as a moving average of the last x production runs). If quality remains constant within a job, the last settings for each web speed range or interval are suitably saved temporarily. If the web speed then changes several times within a short period of time, the process starts again with the last value for this web speed range or interval and not with an empirical mean value. This is based on the consideration that different batches of the same paper grade behave differently within certain limits, particularly with regard to shrinkage.This avoids the initial adjustment not being carried out every time the track speed changes.

[0040] Similar to the web speed, it is expedient to proceed in the event of a major change in the target shrinkage, e.g., in the event of a corresponding job change. In a suitable embodiment, in the event of a change in the target shrinkage by a value that exceeds a predetermined limit, the drying power and the moistening power are each changed once (i.e., initially when the target shrinkage is changed) by a predetermined value, and then the shrinkage and moisture are controlled based on this. In this way, the control system is initially supported in adapting to the suddenly new target shrinkage. Below the limit (i.e., with only a small change), such support is not required, and the change is fully compensated by the control system. The limit is typically selected to be large, for example, 0.2% of the total width of the paper web, i.e.,The target shrinkage changes by at least 0.2% of the total width of the paper web. The limit can be set absolutely or relative, for example, to the total width of the paper web or to the target shrinkage itself.

[0041] Another advantageous embodiment is one in which the control system is relieved by a compensation factor being specified along with the job data in order to print the print larger than a target size, so that a certain degree of shrinkage is permitted and does not have to be compensated for by the control system. This is based in particular on the consideration that shrinkage cannot actually be fully compensated for from a physical perspective, as shrinkage is always made up of a reversible and irreversible component (keratinization of the paper fibers during drying). The print is therefore deliberately enlarged and then shrinks to the target size due to shrinkage in the printing system. The control system then advantageously compensates only, or at least predominantly, for dynamic changes in 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. In rolls from the center of the paper web, the paper fibers are aligned more closely in the direction of the web than in rolls from the edge. Depending on the fiber orientation, the respective paper webs shrink and swell to different degrees during processing in the system. Humidification releases residual stresses from paper production. Depending on the amount of these residual stresses, which are essentially frozen in, the paper web swells to different degrees during humidification. These differences can be up to + / - 0.15%. The printing unit prints the print accordingly, enlarged in accordance with the compensation factor. The compensation factor ultimately shifts the starting conditions for the control system depending on the job, with the aim of accommodating the job.The compensation factor is determined in advance through experiments, for example, and / or optimized during operation through repeated adjustments. The compensation factor is preferably dependent on other job 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 minimum moisture content cannot be maintained for given job data. This is particularly advantageous for very high ink application quantities for printing or for jobs that use a primer, varnish, or varnish printing. Since one or more additional dryers are active in this case, a correspondingly changed shrinkage must be taken into account. This is suitably done using the compensation factor for jobs with corresponding job data.

[0042] Since the job data for the new job is usually already known when the current job is changed, it is possible and advantageous to use the job data for predictive control of the dryers and / or humidifiers. Especially if the new job contains a change in quality and, in contrast to the current job, requires an additional coating, in particular a primer, varnish and / or varnish print, a dryer for this coating, i.e. the primer dryer, the varnish dryer or the varnish print dryer, is expediently preheated during the current job (and interfering influences from the additional dryer are expediently compensated automatically by changing the dryer output and the humidifier output) so that the required drying output is fully or at least largely available when the new job begins.The resulting increased shrinkage and reduced moisture content during the current job is automatically compensated for by the control system. Preferably, when a specified temperature, e.g. 80 °C, is exceeded, the control range for shrinkage and / or moisture content is increased. For example, if varnish drying is also active, it is advantageous to reduce ink drying more than usual. In this case, the printed image may no longer be completely dried by ink drying alone, but the active varnish drying subsequently dries the printed image accordingly, ensuring complete drying. With a primer dryer, on the other hand, it is the other way around. Because shrinkage already occurs 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 degree of additional drying is otherwise prohibited below the specified temperature (e.g., the aforementioned 80 °C). The tolerances and minimum humidity levels, in particular, remain unaffected. It is advantageous to prioritize jobs with large tolerances or paper grades with heavy grammage (smaller shrinkage differences) during changeover times.

[0043] In an advantageous embodiment, the dryer is a hot air dryer, and the printing system also has an IR dryer for drying the paper web. In other words, the drying performance, which is set by the control system 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 the control system requests an increase in drying performance, e.g., during a job change with a corresponding change in the job data, the IR dryer is activated as a substitute during a heating phase of the hot air dryer to meet this request.For example, if the hot air dryer is below a certain temperature, the IR dryer is initially used as a substitute when the temperature needs to be increased until the hot air dryer has heated up. This procedure is particularly advantageous if the current job specifies a slow web speed, which requires the drying performance to be reduced to reduce shrinkage and increase moisture. When the web speed increases, the IR dryer initially compensates for the reduced drying performance of the hot air dryer until the dryer has reached the required drying performance again.

[0044] In some cases, it is advantageous to expand 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 to pre-dry the paper web before printing. The primer dryer described above is particularly suitable as a pre-dryer; this can then also be activated for pre-drying even if no primer is applied. Irrespective of this, the pre-dryer is expediently permanently active to avoid heating and cooling times. Pre-drying particularly causes pre-shrinkage of the paper web. Depending on the grammage, etc., each paper grade has a maximum shrinkage at which the paper web contains hardly any water. This maximum shrinkage is expediently achieved because the paper web can then shrink no 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 influences shrinkage. The only subsequent step is to ensure that sufficient moisture is introduced into the paper web through humidification, and the resulting swelling is controlled and, in particular, kept constant. Pre-drying is particularly useful when heat is available at low cost.

[0045] In the following, exemplary embodiments of the invention are explained in more detail with reference to a drawing. In the drawings: Fig. 1 schematically shows a combination of a printing system and a corrugator, Fig. 2 a printing system in detail.

[0046] In Fig. 1 schematically shows a printing system 2 and a corrugated board system 4, which together form a composite 6. In Fig. 2 A detailed embodiment of the printing system 2 is shown, here a digital printing system for printing using an inkjet process. The printing system 2 in Fig. 2 is shown in a roll-to-roll operation, but is also suitable for inline operation and especially for use in a compound 6 as in Fig. 1 shown suitable.

[0047] The printing system 2 comprises a printing unit 8 for printing a paper web 10 according to a predetermined job with predetermined job data that define the job. For this purpose, the printing unit 8 comprises one or more print heads 12. Fig. 1 The printing system 2 is shown in an inline operation, in Fig. 2 in a roll-to-roll operation.

[0048] The order data of a respective order are specified by means of a higher-level control unit 14, e.g. directly by the control unit itself or by an operator who enters the order data, e.g. via an interface of the higher-level control unit 14. The higher-level control unit 14 is in Fig. 1 designed separately from the printing system 2, but in an alternative not shown, part of it. The job data contain 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, a quantity of ink to be printed, whether a primer is to be applied before printing, whether a varnish or varnish print is to be applied after printing, etc., or a combination thereof. The paper web data include, for example, a paper type, a grammage of the paper web, etc., or a combination thereof. Configuration data is derived from the job data; this data contains corresponding machine data for the job-dependent setting of the printing system 2 and is passed on to a machine control system of the printing system 2 (not explicitly shown).

[0049] The paper web 10 is generally conveyed in one conveying direction at one web speed through the printing system 2 and in Fig. 1 After printing, it is fed to the corrugated board machine 4. The corrugated board machine 4 is designed to produce corrugated board 16 and uses the paper web 10 printed by the printing machine 2, which is combined with other paper webs to form the corrugated board 16. In the illustrated embodiment, the web speed is predetermined by the corrugated board machine 4 and varies over time. In an alternative embodiment, instead of the corrugated board machine 4, another machine is arranged that further processes the printed paper web 10.

[0050] In the following, the terms "upstream" and "downstream" are used to indicate the relative positions of two components with respect to the conveying direction.

[0051] The printing system 2 has at least one dryer 18, 20 with an adjustable drying capacity to dry the paper web 10, whereby the paper web 10 and thus also the print experience shrinkage. The dryer 18, 20 is generally arranged downstream of the printing unit 8 and is also referred to as a print dryer. In the exemplary embodiment of the Fig. 2 A total of six dryers 18, 20 are used, namely four IR dryers 18 and two hot air dryers 20.

[0052] The printing system 2 further comprises at least one humidifier 22 with an adjustable humidification capacity in order to humidify the paper web 10 and thereby adjust a humidity (ie paper humidity) of the paper web 10. During humidification, a swelling of the paper web 10 also occurs and thus an increase in pressure. In the embodiment of the Fig. 2 Three such humidifiers 22 are shown. In Fig. 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 the entire width of the paper web 10 (ie in Fig. 2 perpendicular to the plane of the drawing) and sprays water onto it during operation.

[0053] During operation of printing system 2, an actual shrinkage and an actual moisture content are determined for the paper web 10, and a target shrinkage and a target moisture content are specified. The shrinkage and moisture content are controlled by adjusting the drying and moistening performance to the target shrinkage and the target moisture content, depending on the actual shrinkage and the actual moisture content. In other words, the shrinkage and moisture content are adjusted during operation by adjusting the drying and moistening performance.

[0054] The target shrinkage and the target humidity (controlled variables) are part of the configuration data and are therefore determined based on the order data or are already contained in the order data itself. The target shrinkage and the target humidity are order-specific and are therefore adjusted accordingly when the order changes. In this case, the higher-level control unit 14 specifies the target shrinkage and the target humidity for each order and transmits them to the machine control system, which then regulates the shrinkage and humidity and, for this purpose, controls the dryers 18, 20 and the humidifiers 22.

[0055] 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 of the Fig. 2 The actual shrinkage is determined by measuring a web width (perpendicular to the conveying direction) of the paper web 10 downstream of the dryers 18, 20 and comparing it with a web width in front of the printing unit 8. The actual shrinkage is therefore actually a transverse shrinkage. Fig. 2 For example, the web width before the printing unit 8 is measured analogously using 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 before the printing unit 8.

[0056] Alternatively or additionally, the actual shrinkage of the paper web 10 is determined by optically measuring the shrinkage of print marks on the paper web 10 downstream of the dryers 18, 20. In Fig. 2 For this purpose, an optical camera system 52, 54 is shown, which optically records the print image and the print image marks contained therein and calculates a deviation between the target and actual shrinkage from the order data. Fig. 2 Two possible positions for the camera system 52, 54 are shown, of which either only one or both are implemented simultaneously. The use of two camera systems 52, 54 as in Fig. 2 The camera system shown enables both an inspection of the printed image downstream of the printing unit 8 and an inspection of the varnish printed 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, during a splice. The camera system 54 located further downstream (installation position 2), on the other hand, is expediently active during control operation (also known as normal operation), since this position is particularly close to the rewinder 32 and thus best depicts the finished printed image.

[0057] As standard, the actual shrinkage is measured with the web width sensor 28 at the end of the printing system 2, immediately before a rewinder 32, or in the case of Fig. 1 outside of it, e.g., along the transfer line 34 or within the corrugator 4, ie, generally when the paper web 10 is not further processed by the printing system 2. The dryer output of the dryers 18, 20 is controlled by a shrinkage controller, with the target shrinkage as the reference variable and the actual shrinkage as the controlled variable.

[0058] As already mentioned, in the illustrated embodiment, the actual shrinkage is determined by default using the web width sensor 28, which is located as far downstream as possible from the printing unit 8. In contrast, in a splice, the actual shrinkage is determined using one of the web width sensors 24, 26, which are located upstream of the web width sensor 28 and thus closer to the printing unit 8. This reduces the web travel from the printing unit 8 to the web width sensor 24, 26, 28.

[0059] To regulate the moisture content, the actual moisture content is determined analogously to shrinkage, which indicates how moist the paper web 10 is after moistening. The actual moisture content is also determined inline in this case. For this purpose, a corresponding sensor is used, in this case a moisture sensor 36, which is located downstream of the printing unit 8 and also downstream of all humidifiers 22. Analogous to the measurement of the actual shrinkage, the actual moisture content is also determined at the end of the printing system 2 or even outside of it. Using a humidity controller, the humidification output of the humidifiers 22 is then controlled with the target moisture content as the reference variable and the actual moisture content as the controlled variable.

[0060] In this case, the drying and humidifying performance are controlled in such a way that the shrinkage is constant and the moisture content is kept greater than or equal to a minimum moisture content. This is maintained in inline operation and at variable web speeds, both within the same job (i.e. with constant job data) and with varying job data. The shrinkage is controlled 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 moisture content is controlled in such a way that the actual moisture content corresponds to at least a minimum moisture content of, for example, 5%. The tolerance range and the minimum moisture content are specified, for example, by the higher-level control unit 14. If the tolerance range is exceeded or if the minimum moisture content is not reached, a corresponding warning is issued.The humidification power is increased up to a maximum value dependent on the paper type and grammage before the warning is issued. In this case, shrinkage control is limited by a minimum value for the dryer power, so that it is not reduced arbitrarily and a minimum level of drying is ensured. The minimum value depends on the web speed, paper type, and ink application rate.

[0061] Optionally to the previously mentioned components printing unit 8, dryer 18, 20 and humidifier 22, the printing system 2 has Fig. 2 one or more additional components which serve to realize different production modes and / or further support drying and / or humidification.

[0062] For example, the Fig. 2 As shown, printing system 2 has a primer application unit 38 for applying a primer to the paper web 10. The primer application unit 38 is arranged upstream of the printing unit 8, so that the primer is applied before printing. Thanks to the primer application unit 38, the printing system 2 now has production modes with and without primer (application). Downstream of the primer application unit 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.

[0063] In addition, the printing system 2 in Fig. 2 a varnish application unit 42 for applying a varnish (i.e. for varnishing) to the paper web 10. The varnish application unit 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 application unit 42, the printing system 2 now has production modes with and without varnish application. Downstream of the varnish 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 varnish dryer, for drying the varnish. This dryer 44 is only active for jobs with varnish application. In the present case, one of the humidifiers 22 is arranged upstream of the varnish application unit 42 and another of the humidifiers 22 is arranged downstream of the varnish dryer 44.

[0064] In addition, the printing system 2 in Fig. 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 printing. The varnish printing unit 46 is also arranged downstream of the varnish application unit 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 has, analogous to the printing unit 8, several dryers 48, 50 for drying the varnish, namely two IR dryers 48 and two hot air dryers 50, each also referred to as varnish printing dryers. These dryers 48, 50 are only active for jobs with varnish printing. One of the humidifiers 22 is arranged downstream of the varnish printing unit 46 and the varnish printing dryers 48, 50.

[0065] Primer dryer 40, varnish dryer 44, and varnish print dryers 48, 50 are not necessarily used in the control system, 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, a change in shrinkage and a reduction in moisture content will result, which is automatically compensated for by the control system. If primer dryer 40 is activated, the pre-drying reduces the subsequent print image shrinkage while maintaining the same ink drying settings.

[0066] The web width sensor 30 described above for measuring the web width upstream of the printing unit 8 is arranged downstream of the primer application unit 38 and also downstream of the primer dryer 40. Downstream of the printing unit 8, the web width is measured at several measuring points, each using one of the web width sensors 24, 26, 28, as described above. A first measuring point is located downstream of the dryers 18, 20 and upstream of the coating application unit 42. A second measuring point is located between the coating application unit 42 and the coating printing unit 46 and downstream of the coating dryer 44. A third measuring point is located at the end of the printing system 2, downstream of the coating printing unit 46 and downstream of the coating printing dryers 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.

[0067] Rapid changes in web speed pose a particular challenge for control. Therefore, in the illustrated example, starting values ​​for the drying and humidification performance are stored for several web speed intervals (e.g., as part of the job data). 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 controlled based on these values. Therefore, if the web speed changes so drastically that it falls into a different interval with different starting values, these starting values ​​are set to avoid having to wait for control and to ensure a better response.

[0068] Similar to the web speed, the procedure is also followed in the event of a significant change in the target shrinkage, e.g., during a corresponding job change. If the target shrinkage changes by a value that exceeds a specified limit, the drying and humidification power are each adjusted once (i.e., initially when the target shrinkage changes) by a specified value, and then the shrinkage and moisture are controlled based on this value. This initially supports the control system in adapting to the suddenly new target shrinkage.

[0069] In this case, the control system is also relieved by the fact that a compensation factor is already specified in the job data in order to print the print larger than a target size, so that a certain degree of shrinkage is permitted and does not have to be compensated for by the control system. The print is therefore deliberately printed larger and then shrinks to the target size due to the shrinkage in printing system 2. The control system then compensates only or at least predominantly for dynamic changes, e.g. in web speed or differences in the base paper. Printing unit 8 prints the print enlarged according to the compensation factor, so that ultimately the starting conditions for the control system are adapted to accommodate the job. The compensation factor depends, for example, on other job data, e.g. paper type, grammage, production mode (with / without primer, varnish, varnish printing).

[0070] Since the job data for the new job is usually already known during a job change while the current job is still being processed, the job data for the new job is used for predictive control of dryers 18, 20 and humidifier 22. Especially if the new job contains a quality change and, in contrast to the current job, requires additional primer, varnish, and / or varnish printing, the primer dryer 40, the varnish dryer 44, or the varnish printing dryers 48, 50 are preheated accordingly during the current job so that the required drying performance is available when the new job begins. The resulting changes in shrinkage and moisture during the current job are automatically compensated by the control system.

[0071] In this case, the combination of IR dryers 18 and hot air dryers 20 is used to activate the IR dryers 18 as a substitute during a heating phase of the hot air dryers 20 in the event of a control request for an increase in drying performance, e.g., during a corresponding job change, in order to meet this requirement. The described procedure is used, for example, if the current job specifies a slow web speed, due to which the drying performance is regulated down 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.

[0072] 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 comprises a pre-dryer 40 to pre-dry the paper web 10 before printing. The pre-dryer 40 serves in Fig. 2 For example, the Primer Dryer 40 already described. List of reference symbols

[0073] 2Printing system 4Corrugated board system 6Composite 8Printing unit 10Paper web 12Print head 14Higher-level control unit 16Corrugated board 18Dryer, print dryer, IR dryer 20Dryer, print dryer, hot air dryer 22Humidifier 24Web width sensor (downstream of the printing unit, first measuring point) 26Web width sensor (downstream of the printing unit, second measuring point) 28Web width sensor (downstream of the printing unit, third measuring point) 30Web width sensor (upstream of the printing unit) 32Rewinder 34Transfer section 36Moisture sensor 38Primer application unit 40Dryer, hot air dryer, primer dryer 42Varnish application unit 44Dryer, hot air dryer, varnish dryer 46Varnish printing unit 48Dryer, IR dryer, paint print dryer 50Dryer, hot air dryer, paint print dryer 52Camera system 54Camera system

Claims

1. A method for operation, in particular inline operation, of a printing plant (2), - wherein the printing plant (2) has a printing unit (8) for printing a paper web (10) according to a predefined job with predefined job data, - the paper web (10) being conveyed through the printing plant (2) at a web speed, - the printing plant (2) having at least one dryer (18, 20) with an adjustable drying performance in order to dry the paper web (10), as a result of which the paper web (10) experiences shrinkage, - the printing plant (2) having at least one dampener (22) with an adjustable dampening performance in order to dampen the paper web (10) and thereby adjust a moisture content of the paper web (10), characterized in that - for the paper web (10), actual shrinkage and an actual moisture content are determined and target shrinkage and a target moisture content are predefined, - the shrinkage and the moisture content being regulated by adjusting the drying performance and the dampening performance depending on the actual shrinkage and the actual moisture content with respect to the target shrinkage and the target moisture content.

2. The method according to claim 1, wherein the paper web (10) is fed to a corrugated cardboard plant (4) after printing, wherein the web speed is predefined by the corrugated cardboard plant (4) and varies over time.

3. The method according to either of 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 upstream of the printing unit (8) or by optically measuring shrinkage of print image marks on the paper web (10).

4. The method according to any of claims 1 to 3, wherein the actual shrinkage is determined using a first sensor (28) which is arranged downstream of the printing unit (8) and at the end of the printing plant (2) or outside thereof, except in the case of a splice, in which case the actual shrinkage is determined using a second sensor (24, 26) which is arranged upstream of the first sensor (28).

5. The method according to any of claims 1 to 4, wherein the shrinkage is regulated such that the actual shrinkage lies within a tolerance range around the target shrinkage, wherein the moisture content is regulated such that the actual moisture content corresponds to at least a minimum moisture content.

6. The method according to any of claims 1 to 5, wherein regulation of the shrinkage is limited by a minimum value for the dryer performance so that a minimum degree of drying is ensured.

7. The method according to any of claims 1 to 6, wherein start values for the drying performance and the dampening performance for each of a plurality of intervals of the web speed are stored, wherein when the web speed changes from a first interval to a second interval, the start values for the second interval are set first and then the shrinkage and moisture content are regulated on the basis of these start values.

8. The method according to any of claims 1 to 7, wherein if the target shrinkage changes by a value that exceeds a predefined limit, the drying performance and the dampening performance are changed once by a predefined value in each case and then the shrinkage and moisture content are regulated on the basis of this value.

9. The method according to any of claims 1 to 8, wherein when a current job changes to a new job and if the new job requires an additional coating, a dryer (40, 44, 48, 50) for this coating is already preheated during the current job.

10. The method according to any of claims 1 to 9, wherein the dryer (20) is a hot air dryer and the printing plant (2) has in addition to this an IR dryer (18) to dry the paper web (10), wherein, if an increase in the drying performance is requested by the regulation system, the IR dryer (18) is activated as a substitute during a heating phase of the dryer (20) in order to meet this request.

11. The method according to any of claims 1 to 10, wherein the printing plant (2) has a pre-dryer (40) to pre-dry the paper web (10) before printing.

12. The method according to any of claims 1 to 11, wherein the regulation system is relieved by the fact that a compensation factor is already predefined with the job data in order to print the print enlarged in comparison with a target dimension, so that a certain amount of shrinkage is permitted and does not have to be compensated for by the regulation system.

13. Printing plant (2) or combination (6) of such a plant and a corrugated cardboard plant (4), wherein the printing plant (2) is designed to carry out a method according to any of claims 1 to 12.