EP4400313A1

EP4400313A1 - Rotary printing press with humidifier unit and method for moistening a flexo plate

Info

Publication number: EP4400313A1
Application number: EP23150957.1A
Authority: EP
Inventors: Frank Rudolph
Original assignee: Bobst Bielefeld GmbH
Current assignee: Bobst Bielefeld GmbH
Priority date: 2023-01-10
Filing date: 2023-01-10
Publication date: 2024-07-17

Abstract

The invention relates to a rotary printing press (10) for printing substrates (18), comprising at least one printing unit (36), the printing unit (36) comprising a flexo plate (52) which is associated to a plate cylinder (40), wherein the printing unit (36) is configured to apply an ink to a front side of a substrate (18), wherein the at least one printing (36) unit further comprises at least one humidifier unit (48), wherein the humidifier unit (48) comprises at least one nozzle (50) which is adapted to moisten the flexo plate (52). Further, the invention relates to a method for moistening a flexo plate (52).

Description

The invention relates to a rotary printing press and a method for moistening a flexo plate of the rotary printing press.
In a conventional rotary printing press, a plurality of printing units is arranged around the perimeter of a central cylinder. During the printing process, a substrate in the shape of tape is moved from an unwinder station to a winder station along a printing handling path, wherein the printing handling path guides the substrate around the perimeter of the central cylinder. While the substrate is moved along the perimeter of the central cylinder, ink is transferred from the printing units to the front side of the substrate.
Typical substrates for a rotary printing press include paper, cardboard, metal foil and plastic.
In general, each printing unit comprises several cylinders in order to transfer ink onto the substrate in a defined manner. The ink is stored in an ink tray in which a rotatable roller can be partially received. An anilox roller connects the rotatable roller to a plate cylinder on which a flexographic relief plate, also known as flexo plate, is fixedly mounted. The flexo plate comprises a certain pattern which is individually selected for the printing job to be carried out.
In an operational mode of the rotary printing press, ink stored in the ink tray is picked up by the rotatable roller and transferred to the anilox cylinder. Subsequently, the anilox cylinder transfers the ink onto the plate cylinder with the flexo plate. Finally, the flexo plate applies the ink onto the front side of the substrate which moves through the printing unit along the printing handling path.
To achieve a sufficient quality of the printings, the substrate is sandwiched between the plate cylinder and a counter cylinder, wherein the counter cylinder applies certain counterforce to the plate cylinder.
After a printing job is completed, the printing unit is typically polluted with a considerable amount of dried ink leftovers. In particular, the surface of the flexo plate is often covered by solid impurities of dried ink.
However, such impurities are also produced during the printing job having a negative impact on the printing quality. This is in particular an issue when the printing job is carried out over a long period of time. Up to now, it is not possible to remove these impurities during the printing job without stopping the printing process and manually removing and cleaning the plate cylinder with the polluted flexographic printing plate.
It is therefore necessary to regularly clean the printing unit, particularly the flexo plate, prior to the next printing job. Repeating cleaning intervals reduce the productivity of a rotary printing press, especially when a time period of a printing job is relatively short.
Therefore, it is an objective of the present invention to increase the productivity of a rotary printing press.
This objective is achieved by a rotary printing press for printing substrates, comprising at least one printing unit, the printing unit comprising a flexo plate which is associated to a plate cylinder. The printing unit is configured to apply an ink to a front side of a substrate which is moved through the printing unit along a printing handling path while a back side of the substrate is in contact with a counter cylinder. Further, the at least one printing unit comprises at least one humidifier unit, wherein the humidifier unit comprises at least one nozzle which is adapted to moisten the flexo plate.
The present invention takes advantages of the fact that solid impurities does not stick well to wetted surfaces. If the surface of the flexo plate is humidified, the surface of the flexo plate is wetted and it is more difficult for solid impurities to stick to the surface of the flexo plate. As a result, the adhesion of solid impurities can be effectively reduced.
Moreover, wetting of the flexo plate even prevents solid impurities to emerge since the ink cannot dry while wetted at the same time. Thus, the ink being on the surface is kept constantly liquid by the humidifier unit.
Wetting or humidifying the flexo plate is also beneficial in view of cleaning the flexo plate. This is because the flexo plate is always kept lubricated by the humidifier unit. Thus, the impurities are always dispersed in a liquid and can be removed i.e., crushed, by the direct contact with anilox cylinder. Thus, the friction between the anilox cylinder and the flexo plate supports the dissolving of the dispersed impurities. As a result, the flexo plate is automatically cleaned thereby cleaning reducing cleaning times and increasing the productivity of the rotary printing press.
According to a first aspect of the invention, the at least one humidifier unit further comprises a pump and at least one reservoir unit, the pump and the reservoir unit being fluidly connected to each other. The pump is adapted to supply the nozzle with the humidifying agent which is stored inside the reservoir unit.
The above described system enables the humidifier unit to effectively provide a humidifying agent to the front side of the substrate in a simple manner. Furthermore, the above described system can be easily installed at already existing systems to upgrade them with a humidifier unit.
According to another aspect of the invention, the humidifier unit comprises a heating unit which is assigned to the at least one reservoir unit. Further, the heating unit is adapted to heat the humidifying agent to a predetermined temperature.
Under the term "predetermined temperature", a temperature is to be understood which is higher as room temperature. In the following, the room temperature is assumed to be 25 °C. -Then, the predetermined temperature is above 25 °C. More preferably, the predetermined temperature is at least 35 °C.
It has been found that a humidifying agent which is heated above room temperature is more suitable. This is because a heated humidifying agent is enabled to dissolve more ink residues on the flexo plate. As a result, the amount of solid ink residues is reduced on the flexo plate and the flexo plate can more effectively be liberated from solid impurities.
In another aspect of the invention, the humidifier unit comprises at least two reservoir units, each reservoir unit includes at least one humidifying agent which is different from the at least one humidifying agent of the other reservoir unit.
The advantage of providing more than one reservoir unit having more than one humidifying agent is that the humidifying units can provide a selection of different humidifying agents for different purposes. For example, a water-based humidifying agent may be used for a water-based ink in the printing unit. The same applies to a humidifying agent based on organic solvents which is more suitable to wet the flexo plate of a printing cylinder using an organic-based ink.
The at least one humidifying agent can comprise an organic and/or an aqueous solution.
Preferably, the organic solution may comprise at least one organic solvent selected from the group consisting of alcohol, ketone, acetate, ether, aromatic hydrocarbon, saturated hydrocarbon, unsaturated hydrocarbon, hydrocarbon functionalized with at least one heteroatom and a combination thereof.
Examples are, but not limited thereto, ethanol, butanol, acetone, isopropanol, methyl acetate, ethyl acetate, hexane, petrol ether, toluene, turpentine and tetrachloroethylene.
More preferably, the at least one detergent may comprise a mixture of an organic and an aqueous solution.
For example, the at least one detergent may comprise a mixture of ethanol and water.
According to a preferred embodiment, the humidifying agent further comprises at least one cleaning agent, wherein the at least one cleaning agent is selected from the group consisting of base, acid, surfactants, enzymes, zeolites and additives and combinations thereof.
Example for the base are, but not limited thereto, sodium hydroxide, potassium hydroxide, calcium hydroxide and magnesium hydroxide.
Example for the acid are, but not limited thereto, acetic acid, citric acid, hydrochloric acid and phosphoric acid.
Example for the surfactants are, but not limited thereto, anionic surfactants, cationic head groups surfactants, zwitterionic surfactants and non-ionic surfactants. Suitable surfactants may be ammonium lauryl sulfate, sodium lauryl sulfate, docusate, sodium laureth sulfate, sodium lauroyl sarcosinate, cetrimonium bromide, cetylpyridinium chloride, phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, octaethylene glycol monododecyl ether and sodium myreth sulfate.
Example for the enzymes are, but not limited thereto, proteases, amylases, lipase, cellulases, mannanases, and pectinases.
The cleaning agent supports the wetting of the flexo plate by dissolving persistent residues on the surface of the flexo plate. Using the at least one cleaning agent, adds the aspect of actually cleaning the flexo plate next to simply humidifying it.
If the flexo plate is humidified during the printing process, preferably the cleaning agent is excluded, whereas if the flexo plate is humidified in between two printing processes as part of a cleaning routine, it is preferred that at least one cleaning agent is used.
In another aspect of the invention, the at least one humidifier unit is arranged downstream of the counter cylinder and downstream of an anilox cylinder which is in contact with the flexo plate and/or wherein the at least one humidifier unit is arranged upstream of the counter cylinder and upstream of the anilox cylinder which is in contact with the flexo plate, and wherein the anilox cylinder is adapted to provide ink to the flexo plate.
The terms "upstream" and "downstream" are referring to the rotation direction of the respective cylinder.
According to another aspect of the invention, the rotary printing press further comprises a control unit which is configured to switch the humidifier unit in an on-state or an off-state, wherein in the off-state, the humidifier unit does not moisten the flexo plate, whereas in the on-state, the humidifier unit does moisten the flexo plate.
Thus, the humidifier unit can be controlled by a control unit and can be precisely activated, when there is a need to moisten the flexo plate. For example, if a respective printing unit is not required for the actual printing job, the humidifier unit can simply be switched to the off-state. As a result, energy and resources can be reduced.
In a preferred aspect of the invention, the control unit is adapted to adjust the amount of humidifying agent which is supplied from the humidifier unit onto the flexo plate in dependency of a printing relevant parameter.
The printing relevant parameter may be selected from the group consisting of amount of ink used in the relevant printing unit in the last and/or actual printing procedure, type of ink used in the relevant printing unit during the last and/or actual printing procedure, type of substrate which has been printed during the last and/or actual printing procedure and printing time of the relevant printing unit during the last and/or actual printing procedure.
As such, the humidifier unit can be controlled in dependency of the last and/or actual printing procedure. This allows the control unit to react on different situations which may arise during a printing procedure. If, for example, in the last printing procedure an ink is used which is known to produce a considerable amount of solid impurities on the flexo plate, the amount of humidifying agent can be increased to compensate for the increased amount of impurities. In another case, if the respective printing unit has only used a marginal amount of ink during the last printing procedure, also the amount of humidifying agent can be reduced. As a result, always the optimal dose of humidifying agent is used in the respective printing unit.
In another aspect of the invention, the rotary printing press comprises a plurality of printing units, each printing unit being connected to the control unit, wherein the control unit is adapted to selectively switch at least one humidifier unit of one printing unit of the plurality of printing units to the on-state or the off-state.
The above described system is of advantage when not all of the printing units have to be used during a printing process. If the respective printing units are not using ink, the associated humidifying units can be switched to the off-state. Only the humidifying units associated to printing units being actively used during the printing process are switched to the on-state. Therefore, the above system allows to differentiate between active and inactive printing units and their associated humidifying units. Such a system is more effective.
The invention further relates to a method for moistening a flexo plate associated on a plate cylinder in a printing unit of a rotary printing press as described above. The method comprises the following step:

a) Moistening the flexo plate by using at least one nozzle of a humidifying unit. Using a nozzle is a simple and efficient manner to moisten a flexo plate.

In another aspect of the invention, the moistening step a) is carried out by spraying a vaporized humidifying agent onto the flexo plate and/or directing a liquid stream of humidifying agent onto the flexo plate.
The advantage of using a nozzle is that it allows to spray a liquid or an aerosol directly onto the front side of the flexo plate. As such, the nozzle which applies the humidifying agent is never in direct contact with the ink-polluted flexo plate. Therefore, the nozzle is always kept clean which increases the productivity of the rotary printing press because the nozzle must not be actively cleaned by an operator.
The nozzle can also be configured to either spray a vaporized humidifying agent onto the flexo plate or to direct a liquid stream of humidifying agent onto the flexo plate. The latter can be employed if in an operational mode of the rotary printing press the respective printing unit uses an ink which is known produce more solid impurities on the flexo plate compared to other inks.
In another aspect of the invention prior to step a), the following steps are carried out:

b) Separating the plate cylinder comprising the flexo plate from a counter cylinder; and
c) Pressing the anilox cylinder and the plate cylinder against each other.

The abovementioned steps b) and c) are preferably carried out after the printing job since the plate cylinder is detached from the counter cylinder and therefore also from the front side of the substrate. In this configuration, the plate cylinder is only in direct contact with the anilox cylinder while being humidified by using at least one nozzle of the humidifying unit.
More preferably, the plate cylinder is rotated during step a). This aspect is preferably combined with the steps b) and c), therefore enabling a humidifying and cleaning of the plate cylinder without being in direct contact of the substrate. This procedure is therefore preferably carried out after a printing job, or respectively between two printing jobs. Therefore, the downtime of the rotary printing press can be effectively used to humidify and clean the flexo plate associated to the plate cylinder. It is therefore no longer necessary to manually remove the plate cylinder with the flexo plate manually since it can be automatically cleaned by the humidifier unit.
Hence, step a) is carried out in-between two printing jobs and/or during a printing job.
If step a) is carried out in-between two printing jobs and/or during a printing job, it is preferred to use a cleaning agent in the humidifying agent to achieve a sufficient cleaning.
If the flexo plate is humidified during the printing process, preferably the cleaning agent is excluded.
In the following, the invention will be described in detail by making reference to the annexed drawings, in which

Figur 1 is a scheme showing a rotary printing press according to the invention in an operational mode; and
Figur 2 is a scheme showing a printing unit from the rotary printing press of Figure 1.

Figure 1 depicts a rotary printing press 10 according to the invention.
The rotary printing press 10 comprises a substrate transport system 12, the substrate transport system 12 being accommodated within a housing 13 of the rotary printing press 10.
In particular, the housing 13 completely encapsulates the substrate transport system 12.
The substrate transport system 12 comprises a winder station 14 and an unwinder station 16 which are configured to transport a substrate 18 along a printing handling path 19 from the unwinder station 16 to the winder station 14.
In principle, the substrate transport system 12 works as a conveyor road. For transporting the substrate 18 along the printing handling path 19 a plurality of rollers 20 are employed, each roller 20 being adapted to guide the substrate 18 within the housing 13 between unwinder station 16 and winder station 14.
The material of which the substrate 18 is made is not limited and may comprise paper, cartboard, metal foil, plastic and combinations thereof.
As it can be seen from Fig. 1, the substrate 18 has the shape of a tape (web) which extends continuously between unwinder station 16 and winder station 14. At each of the stations 14, 16 the substrate 18 is coiled to a substrate roll 22, wherein at the winder station 14, the substrate roll 22 is beared at a winder cylinder 24, and wherein at the unwinder station 16, the substrate roll 22 is beared at an unwinder cylinder 26.
Further, the rotary printing press 10 comprises a command station 28 to control the rotary printing press 10, particularly the substrate transport system 12.
A control unit 30 is assigned to the command station 28, wherein the control unit 30 is connected to the substrate transport system 12 via an electrical connection 32. In particular, the control unit 30 is connected via two connections 32 to the winder station 14 and the unwinder station 16, respectively.
Further, the control unit 30 is configured to control a speed of the substrate 18 which is moved through the substrate transport system 12 along the printing handling path 19. Therefore, the control unit 30 is particularly adapted to control the rotation speed and rotation direction of the winder cylinder 24 and the unwinder cylinder 26, respectively.
In particular, the command station 28 provides a user interface 34 to allow an operator to manually operate the control unit 30.
However, the control unit 30 may also be adapted to automatically control the rotation speed and rotation direction of the winder cylinder 24 and the unwinder cylinder 26.
The user interface 34 and the control unit 30 may be a monitor and computer, respectively.
The rotary printing press 10 further comprises at least one printing unit 36 which is arranged around the perimeter of a central cylinder 38. In addition, the at least one printing unit 36 is located adjacent to the printing handling path 19 extending circumferentially around the central cylinder 38.
As it can be seen in Fig. 1, there is more than one printing unit 36 arranged around the central cylinder 38. In fact, a plurality of printing units 36 is foreseen, each printing unit 36 providing at least one type of ink for printing the substrate 18.
In detail, each printing unit 36 comprises a plate cylinder 40 which is assigned to the printing handling path 19 surrounding the central cylinder 38. The plate cylinder 40 comprises a flexible relief plate (here not shown), also known as flexo plate, for transferring the ink to the front side of the substrate 18. In detail, the flexo plate extends along the a perimeter of the plate cylinder 40 and is fixedly mounted thereto.
Opposite to the substrate handling path 19, the flexo plate is contacted by an anilox cylinder 42, wherein the anilox cylinder 42 receives ink from an ink tray 44. The ink tray 44 is further known as a doctor blade assembly.
In fact, the plate cylinder 40, the anilox cylinder 42 and the ink tray 44 are forming one printing unit 36.
Further, the printing unit 36 comprises a counter cylinder 46 which is arranged opposite to the plate cylinder 40 such that the plate cylinder 40 and the counter cylinder 46 sandwich the substrate 18. The counter cylinder 46 is adapted to apply a predetermined counterforce to the plate cylinder 40.
The plate cylinder 40 is further equipped with a flexo plate, also known as flexographic relief plate, which is fixedly mounted around the perimeter of the plate cylinder 40. The flexo plate will be described later in more detail.
At least one of the printing units 36 further comprises at least one humidifier unit 48. As it is shown in Figure 1, each printing unit 36 is assigned to one humidifier unit 48. However, it may also be that not all printing units 36 are assigned to one humidifier unit 48.
Details of the humidifier unit 48 are depicted in more detail in Figure 2.
Humidifier unit 48 comprises at least one nozzle 50 which is adapted to moisten the flexo plate 52 of the plate cylinder 40.
In addition, humidifier unit 48 comprises a pump 54 and at least one reservoir unit 56, the pump 54 and the reservoir unit 56 being fluidly connected to each other via a pipe 58.
The pump 54 is adapted to supply the nozzle 50 with the humidifying agent 60 which is stored inside the reservoir unit 56.
In the reservoir unit 56, the humidifying agent 60 is stored. The reservoir unit 56 may be a tank adapted to store liquids.
Each reservoir unit 56 comprises at least one humidifying agent 60. The humidifying agent 60 may comprise an organic and/or an aqueous solution.
Further, the humidifying agent 60 comprises at least one cleaning agent, wherein the at least one cleaning agent is selected from the group consisting of base, acid, surfactants, enzymes, zeolites and additives and combinations thereof.
Preferably, the humidifying agent 60 is an aqueous solution containing a base, preferably potassium hydroxide.
Further, the humidifier unit 48 comprises a heating unit 59 which is assigned to the at least one reservoir unit 56. Further, the heating unit 59 is adapted to heat the humidifying agent 60 to a predetermined temperature.
The heating unit 59 and the pump may preferably be constructed as one single device, as indicated in Fig. 1.
One exemplary embodiment of the humidifier unit 48 is illustrated in Fig. 1.
As it can be seen from Figure 1, the shown humidifier unit 48 comprises at least two reservoir units 56, each reservoir unit 56 includes at least one humidifying agent 60 which is different from the at least one humidifying agent 60 of the other reservoir unit 56.
Further, each reservoir unit 56 comprises one pump 54 and one heating unit 59. The two pumps 54 are connected via the pipe 58 to a valve 62. The valve 62 connects the pipe 58 to a humidifying distribution system 64 which supports a plurality of nozzles 50 with the humidifying agent 60.
In Figure 1, the humidifying distribution system 64 comprises in total five nozzles 50, each nozzle 50 being assigned to one printing unit 36.
In total, the rotary printing press 10 of Figure 1 comprises two humidifying units 48, each humidifying unit 48 comprises two reservoir units 56, two pumps, a plurality of valves 62 and a plurality of nozzles 50 as well as one humidifying distribution system 64.
Further, Figure 2 depicts a detailed view on a humidifying unit 48 and the printing unit 36.
The printing unit 36 comprises the plate cylinder 40 which is surrounded by a flexo plate 52, the anilox cylinder 42 and the ink tray 44. The flexo plate 52 is in direct contact with the counter cylinder 46. in-between the counter cylinder 46 and the flexo plate 52, a substrate 18 is sandwiched.
The substrate 18 is moved by the substrate transport system 12 along the substrate handling path 19 through the printing unit in a direction S1.
In total, two humidifying units 48 are assigned to the flexo plate 52 in Fig. 2. One humidifying unit 48 is located downstream of the anilox cylinder 42 and downstream the counter cylinder 46, while the lower humidifying unit 48 is arranged upstream of the anilox cylinder 42 and upstream of the counter cylinder 46.
As it is apparent also from Figure 1, each humidifying unit 48 comprises a nozzle 50 which is fluidly connected via a pipe 58 to a valve 62. From the valve 62, the nozzle 50 is supported with a humidifying agent 60.
The nozzle 50 can also be a plurality of nozzles 50. The nozzle 50 may be a plurality of pinholes located in a housing. It can also be that the humidifying unit 48 is embodied as a flexible tube in which a plurality of pinholes is stamped.
The humidifying unit 48 is adapted to release a vaporized humidifying agent 66 and/or directing a liquid stream of humidifying agent 66 onto the flexo plate 52.
In the following, the operation principle of the rotary printing press 10 with the humidifier unit 48 is explained in more detail.
In the operational mode of the rotary printing press 10, each printing unit 36 is adapted to transfer ink onto a substrate 18 which is transported by the substrate transport system 12 along a printing handling path 19 through the printing unit 36.
Here, the ink is transferred from the ink tray 44 over the anilox cylinder 42 onto the flexo plate 52 and from the flexo plate 52 onto the front side of the substrate 18. In this respect, the counter cylinder 46 applies a counterforce such that a sufficient quality of the printing is achieved on the substrate 18.
During the aforementioned printing process, solid impurities can accumulate onto the surface of the flexo plate 52.
In order to remove these impurities or prevent that such impurities are produced, the flexo plate is moistened by using the at least one nozzle 50 of the humidifying unit 48. As a result, the surface of the flexo plate is wetted by the humidifying agent 60.
This step can be carried out during the actual printing job. Here, preferably the humidifying agent 60 is used without the at least one cleaning agent.
However, this step can also be carried out in-between two printing jobs. Here, preferably the humidifying agent 60 is in combination with the at least one cleaning agent.
The moistening of the flexo plate 52 is initiated by the command station 28, in which the control unit 30 switches the humidifier unit 48 in an on-state, whereas in this on-state the humidifier unit 48 does moisten the flexo plate 52. If the respective humidifier unit 48 is not required during the printing job, the control unit 30 can switch the respective humidifier unit 48 into an off-state in which the humidifier unit 48 does not moisten the flexo plate 52.
The control unit 30 is adapted to adjust the amount of humidifying agent 60 which is applied from the humidifying unit 48 onto the flexo plate 52 in dependency of a printing relevant parameter.
The printing relevant parameter is selected from the group consisting of amount of ink used in the relevant printing unit in the last and/or actual printing procedure, type of ink used in the relevant printing unit during the last and/or actual printing procedure, type of substrate which has been printed during the last and/or actual printing procedure and printing time of the relevant printing unit until or during the last and/or actual printing procedure.
If the respective humidifier unit 48 is switched by the control unit 30 in an on-state, the pump 54 is activated by the control unit 30. The pump 54 transfers the humidifying agent 60 from at least one reservoir unit 56 via a pipe 58 to the nozzle 50. Over the nozzle 50, the humidifying agent 60 is released as a vaporized humidifying agent 66 onto the flexo plate 52. It may also be that the nozzle 50 directs a liquid stream of humidifying agent 66 onto the flexo plate 52.
If the flexo plate 52 is humidified by the humidifier unit 48 during a printing process, obviously the flexo plate 52, the anilox cylinder 42 and the ink tray 44 are in direct contact with each other. Furthermore, the flexo plate 52 contacts directly the substrate 18 and therefore also the counter cylinder 46. If the flexo plate 52 is now humidified with the humidifying agent 60, the solidified impurities are dissolved by the humidifying agent 60 and the flexo plate 52 can free print itself by the direct contact with the anilox cylinder 42. In this way, the humidifier unit 48 can be understood as a kind of a lubrication system.
However, it is also possible that the moistening of the flexo plate 52 can be carried out in-between two printing jobs.
If the moistening of the flexo plate 52 is carried out in-between two printing jobs, the plate cylinder 40 comprising the flexo plate 52 is separated from the counter cylinder 46 and subsequently pressed against the anilox cylinder 42. Next, the plate cylinder 40 can be rotated while being pressed against the anilox cylinder 42 and being humidified by the humidifying unit 48 at the same time. By this way, solid impurities can be removed and dissolved from the surface of the flexo plate 52, while the flexo plate 52 is not in direct contact with the substrate 18.

Claims

A rotary printing press (10) for printing substrates (18), comprising
at least one printing unit (36), the printing unit (36) comprising a flexo plate (52) which is associated to a plate cylinder (40),

wherein the printing unit (36) is configured to apply an ink to a front side of a substrate (18) which is moved through the printing unit (36) along a printing handling path (19) while a back side of the substrate (18) is in contact with a counter cylinder (46),

wherein the at least one printing (36) unit further comprises at least one humidifier unit (48), wherein the humidifier unit (48) comprises at least one nozzle (50) which is adapted to moisten the flexo plate (52).
The rotary printing press (10) according to claim 1, wherein the at least one humidifier unit (48) further comprises a pump (54) and at least one reservoir unit (56), the pump (54) and the reservoir unit (56) being fluidly connected to each other, and wherein the pump (54) is adapted to supply the nozzle (50) with a humidifying agent (60) which is stored inside the reservoir unit (56).
The rotary printing press (10) according to claim 2, wherein the humidifier unit (48) comprises a heating unit (59) which is assigned to the at least one reservoir unit (56), and wherein the heating unit (59) is adapted to heat the humidifying agent (60) to a predetermined temperature.
The rotary printing press (10) according to claim 2 or claim 3, wherein the humidifier unit (48) comprises at least two reservoir units (56), each reservoir unit (56) includes at least one humidifying agent (60) which is different from the at least one humidifying agent (60) of the other reservoir unit.
The rotary printing press (10) according to any one of claims 2 to 4, wherein the at least one humidifying agent (60) comprises an organic and/or aqueous solution.
The rotary printing press (10) according to claim 5, wherein the humidifying agent (60) further comprises at least one cleaning agent, wherein the at least one cleaning agent is selected from the group consisting of base, acid, surfactants, enzymes, zeolithes and additives and combinations thereof.
The rotary printing press (10) according to any one of the preceding claims, wherein the at least one humidifier unit (48) is arranged downstream of the counter cylinder (46) and downstream of an anilox cylinder (42) which is in contact with the flexo plate (52), and/or
wherein the at least one humidifier unit (48) is arranged upstream of the counter cylinder (46) and upstream of the anilox cylinder (42) which is in contact with the flexo plate (52),

and wherein the anilox cylinder (42) is adapted to provide ink to the flexo plate (52).
The rotary printing press (10) according to any one of the preceding claims, wherein the rotary printing press (10) further comprises a control unit (30) which is configured to switch the humidifier unit (48) in an on-state or an off-state,
wherein in the off-state, the humidifier unit (48) does not moisten the flexo plate (52), whereas in the on-state, the humidifier unit (48) does moisten the flexo plate (52).
The rotary printing press (10) according to claim 8, wherein the control unit (30) is adapted to adjust the amount of humidifying agent (60) which is applied from the humidifying unit (48) onto the flexo plate (52) in dependency of a printing relevant parameter.
The rotary printing press (10) according to claim 9, wherein the printing relevant parameter is selected from the group consisting of amount of ink used in the relevant printing unit in the last and/or actual printing procedure, type of ink used in the relevant printing unit during the last and/or actual printing procedure, type of substrate which has been printed during the last and/or actual printing procedure and printing time of the relevant printing unit during the last and/or actual printing procedure.
The rotary printing press (10) according to any one of claims 8 to 10, wherein the rotary printing press (10) comprises a plurality of printing units (36), each printing unit (36) being connected to the control unit (30), wherein the control unit (30) is adapted to selectively switch at least one humidifier unit (48) of one printing unit (36) of the plurality of printing units (36) to the on-state or the off-state.
A method for moisten a flexo plate (52) associated on a plate cylinder (40) in a printing unit (36) of a rotary printing press (10) according to any of the preceding claims, wherein the method comprises the following step:
a) Moistening the flexo plate (52) by using at least one nozzle (50) of a humidifying unit (48).
A method according to claim 12, wherein the moistening step a) is carried out by spraying a vaporized humidifying agent onto the flexo plate (52) and/or directing a liquid stream of humidifying agent onto the flexo plate (52).
A method according to any one of claims 12 to 14, wherein prior to step a), the following steps are carried out:
b) Separating the plate cylinder (40) comprising the flexo plate (52) from a counter cylinder (46);

c) Pressing the anilox zylinder (42) and the plate cylinder (40) against each other.
A method according to any one of claims 12 to 14, wherein the plate cylinder (40) is rotated during step a).
A method according to any one of claims 12 to 15, wherein step a) is carried in-between two printing jobs and/or during a printing job.