Drying module of a drying unit

Abstract

This invention is about a modular design for a dryer, in particular about a drying module. The drying module is made of an alternation of impingement nozzles and flotation nozzles connected to a common pressurized air source. The impingement nozzles have a counter roller that guides the substrate thanks to the drying air that pushes the substrate against the roller. The flotation nozzles are made of two nozzles facing each other and blowing with the same strength against the substrate that "floats" between them. The module has one or two air inputs connected to one or two input air chambers which are kept at constant pressure and feed the nozzles with air. The second air chamber feeds the bottom floatation nozzles and may be connected to the first air chamber to form a single air chamber. The module has a return air chamber crossed by the substrate. The dryer can be made of several of these modules to adapt its drying capability or can be constructed as an alteration of these two types of nozzles in a single dryer module. The forward and backward air chambers may be respectively connected together or connected to a common air source or air sink.

Description

[0001] Drying module of a drying unit

[0002] The invention relates to a drying module of a drying unit, especially of a drying unit of an inkjet printing machine.

[0003] Printing machines are typically applied for printing various products, such as labels, textiles, ceramic tiles and many more by dispensing small ink droplets either through inkjet nozzles of a printing unit or through printing cylinders of rotary presses on the respective substrate to be printed upon.

[0004] An essential factor influencing a printing machine's effectiveness is the highest achievable speed at which the material can pass through the printer while maintaining satisfactory print quality. This top speed is often restricted by the ink drying rate on the material. The freshly printed material needs careful handling to prevent any contact with the wet ink until it dries adequately, and this challenge becomes more prominent when employing water-based inks compared to solventbased inks.

[0005] The same applies to coating machines, where instead of applying ink on a substrate, a coating machine applies coating material that must also be dried. From a dryer perspective, a coating machine is very similar to a printing machine. The difference is the material to be dried and a smaller sensitivity to spreading the coating material. With printing, if the ink is spread, the printed image gets blurred. While coating can also be deposited only on specific areas, for example by using an engraved cylinder like the ones used in printing, the spread of the coating material may be larger before it constitutes a defect. Thus the argumentation that follows also applies to coating even if not mentioned explicitly everywhere in the text.

[0006] Generally, the drying component of a printing machine is engineered to meet the drying needs of the most challenging usage scenarios, such as printing tasks at the highest speed. Nonetheless, in less demanding scenarios, the printing machine becomes oversized, leading to increased expenses and a larger space footprint.

[0007] An approach to expedite the drying process involves employing drying units equipped with nozzles that release a flow of air onto the substrate, often heated air. Nonetheless, it is crucial to maintain precise control over the gap between the freshly printed substrate and these drying unit nozzles to prevent any physical contact between the still-moist substrate and the nozzles, while also ensuring the desired airflow can be delivered.

[0008] The object of the invention is to provide a flexible solution on how to dry a printed-upon substrate while avoiding mechanical contact to the substrate.

[0009] The object is solved by a drying module of a drying unit for drying a substrate which is moved along a handling path through the drying module, the substrate having a front side at least partially covered with fresh ink or fresh coating material and a back side not covered with ink or covered with an already dried material. The drying module comprises, along the handling path, one or more impingement nozzle units and one or more flotation nozzle units, the one or more impingement nozzle units each having an impingement nozzle and an associated counter roller facing each other, and the one or more flotation nozzle units each having a first flotation nozzle and an associated second flotation nozzle facing each other. The handling path is arranged between the impingement nozzle and the associated counter roller of the one or more impingement nozzle units and between the first flotation nozzle and the associated second flotation nozzle of the one or more flotation nozzle units, wherein the drying module is adapted to move the substrate through the drying module such that the back side of the substrate is in contact with the counter roller.

[0010] The invention is based on the idea of combining two different types of nozzle units for achieving both a precise control of the position of the substrate along the handing path and a high drying efficiency at the same time.

[0011] Specifically, the drying unit combines two different types of nozzle units, namely one or more impingement nozzle units and one or more flotation nozzle units.

[0012] The one or more impingement nozzle units provide precise control of the relative position of the substrate along the handling path, i.e. of the substrate-to- nozzle-distance, by keeping the back side of the substrate in contact with the respective counter rollers of the one or more impingement nozzle units. The counter rollers also provide a means for guiding and holding the substrate along the handling path, even when the drying module is used upside down. At the same time, the associated impingement nozzle provides an air stream on the front side of the substrate, thereby contributing to the drying efficiency of the drying module.

[0013] The one or more flotation nozzle units provide an air stream on both the front side and the back side of the substrate, i.e. the first flotation nozzle faces the front side of the substrate for drying the ink applied thereon and the second flotation nozzle provides an air stream on the back side of the substrate such that the substrate floats along the handling path. Said flotation nozzles face each other in the sense that they are located at the same abscissa along the handling direction (i.e. along the travel direction of the substrate)

[0014] The drying module especially is a drying module of a drying unit of an inkjet printing machine.

[0015] In one variant, the drying module comprises a first forward air chamber being fluidically connected to each of the impingement nozzles and each of the first flotation nozzles. In other words, each of the impingement nozzles and of the first flotation nozzles can be supplied with air for drying the ink on the substrate from a common first forward air chamber. Due to this arrangement, each of the impingement nozzles and of the first flotation nozzles can be supplied with air from a single air source. Further, the pressure drop at the nozzles of the drying module connected to the first forward air chamber along the handling direction is negligible.

[0016] Also, the drying unit may comprise a second forward air chamber being fluidically connected to each of the second flotation nozzles. The two forward air chambers are either fluidically connected (thus can be considered as a single air chamber) or separate but connected to a common air source. Similar to the first forward air chamber discussed before, this arrangement allows to supply all of the second flotation nozzles from a single air source and the pressure drop at the nozzles of the drying unit connected to the backward air chamber is negligible.

[0017] The chamber crossed by the substrate constitutes a backward air chamber connected to a return path toward an air sink of an air supply device. The air control supply device comprises an air source with a number of outputs connected to the forward air chambers and a number of air sinks connected to the backward air chambers. Preferably, the drying module is configured to be connectable to another drying module such that the handling paths of the connected drying modules are aligned with each other. Accordingly, the drying module can be configured to allow for a modular design of the drying unit, thereby allowing to optimally set up the drying unit for the intended drying procedure. E.g., in case the drying unit is supposed to dry a substrate which is printed upon at high printing speeds, the total number of drying nozzles necessary for achieving the same drying efficiency generally increases. On the contrary, if the drying module is intended to be used in a drying unit of an inkjet printing machine which is intended to be used with a lower maximum printing speed than in the case discussed before, the total number of drying nozzles can be reduced by using a lower number of drying modules, thereby saving costs and reducing space requirements. Also, the overall costs of the drying module can be reduced as the drying module can be manufactured as a common part.

[0018] The modular design can be of two types: one is a physical module, which is constructed in an independent way, with its own air input and output, and where you can chain these modules one after the other. The other is a “design” module, i.e. a virtual module, which defines the alteration of the different elements of impingement and floatation nozzle, that can be replicated at will to obtain a single physical module with the desired length. Even if we obtain a single module, we still consider it as dryer module.

[0019] On the physical modules, the forward air chambers and / or backward air chambers of the individual drying modules are fluidically connectable to each other respectively such that a common forward air chamber and / or a common backward air chamber is formed when a plurality of drying modules are connected to each other or to a common air supply. On the design module, the forward air chamber and backward air chamber each form a single chamber with the desired length.

[0020] In one variant, at least one of the impingement nozzles comprises a nozzle opening facing the handling path, the size of the nozzle opening being variable. Accordingly, the speed of air and / or the volume of air per time unit supplied via the nozzle opening can be varied according to the present substrate to be dried, thereby ensuring an optimal drying procedure. For a dryer used in a printing device, there is preferably at least one of the impingement nozzles that is a speed-regulated impingement nozzle comprising a membrane having a membrane opening, the size of the membrane opening being of fixed size. Thus, especially in case the speed-regulated impingement nozzle is supplied with air from a constant pressure air source, e.g. via the fist forward air chamber, the membrane opening of fixed size defines the flux of air traversing the membrane and thus being able to be released via the nozzle opening. Therefore, when the size of the nozzle opening is changed, the air speed is also changed. For a dryer used in a coating machine, the speed regulated impingement nozzle is most of the times not necessary.

[0021] Further, at least one of the impingement nozzles can be a volume-regulated impingement nozzle being free of a membrane having a membrane opening of fixed size. Especially, the impingement nozzles have a variable nozzle opening analogously to the speed-regulated impingement nozzle. Thus, by adjusting the size of the nozzle opening, the volume of air which can be supplied by the volume-regulated impingement nozzle per time unit can be toggled. Especially in case the volume-regulated impingement nozzle is supplied with air from a constant pressure air source, e.g. via the first forward air chamber, the air speed stays constant when changing the size of the nozzle opening.

[0022] By combining speed-regulated impingement nozzles and volume-regulated impingement nozzles in the same drying module, the application of air for drying the ink on the substrate in the drying module can be precisely tailored.

[0023] The size of the impingement nozzle opening is preferably settable on each nozzle. In other words, there may be a mechanism capable of changing the size of the opening of the nozzle. Nevertheless, the nozzle opening may be set by design, thus using impingement nozzles with a fixed-size opening. In the latter case, the openings should be set such that the speed of air at the output of the speed- regulated impingement nozzle is lower than the speed at the output of the volume- regulated impingement nozzle. When the speed / volume settings need to be changed, the impingement nozzles are replaced by nozzles with different opening sizes and / or with different membrane opening sizes. Thus, the speed or volume control at the nozzle output is performed by the selection of the opening of the nozzle among a set of available impingement nozzles. For controlling the airflow through the one or more of the flotation nozzle units, each of the first flotation nozzle and the second flotation nozzle of the respective flotation nozzle unit can have a nozzle housing and a central element being configured to be movable relative to the nozzle housing along an adjustment direction which is perpendicular to the handling direction, the nozzle housing and the central element defining a flotation air path.

[0024] The flotation air path can have a first section being parallel to the adjustment direction and a second section arranged at an angle relative to the adjustment direction.

[0025] Preferably, the first section is of constant size while the size of the second section is variable, based on the position of the central element. In this way, the air flow, i.e. the amount of air per time unit, through the respective flotation nozzle remains constant and thus the air speed of air released by the respective flotation nozzle is variable based on the position of the central element.

[0026] The central element can comprise an adjustment mechanism having an excentric being connected to a spring mechanism. Accordingly, the position of the central element along the adjustment direction can be controlled by means of the excentric. E.g., the excentric can be coupled to an actor like an electromotor. The spring mechanism is connected to the excentric to ensure contact and remove the play between the excentric and the central element.

[0027] Further, the movements of the central elements of the first flotation nozzle and of the associated second flotation nozzle can be coupled. Termed differently, the positions of the central elements of associated first flotation nozzles and second flotation nozzles can be synchronized to avoid that the substrate being moved out of the handling path when adjusting only one of the respective central elements.

[0028] Preferably, the first flotation nozzle and the second flotation nozzle are configured such that the amplitude of the movement of the central element of the first flotation nozzle is the same as the amplitude of the movement of the central element of the second flotation nozzle.

[0029] The drying module has an alternating sequence of impingement nozzle units and flotation nozzle units along the handling direction, i.e. for each of the flotation nozzle units, along the handling path, an impingement nozzle unit is arranged directly before the flotation nozzle unit and an impingement nozzle unit is arranged directly after the flotation nozzle unit. Of course, in case the respective flotation nozzle unit is the first or the last nozzle unit of the sequence of impingement nozzle units and flotation nozzle units of the drying unit, there is no further impingement nozzle unit directly before and directly after the respective flotation nozzle unit, respectively. Such an arrangement allows for a good compromise between a high level of control of the substrate-to-nozzle distance (mainly obtained by the impingement nozzle units) and a high drying efficiency (as a flotation nozzle unit generally provides for a higher drying efficiency than an impingement nozzle unit). This alternating sequence constitutes most of the dryer length, but the first and last nozzles may be arranged differently, especially if the module is a long module having more than ten nozzle units.

[0030] To further reduce the risk of spreading the ink on the front side of the substrate due to the air supplied for drying, the drying module can have two or more impingement nozzle units, wherein, counted along the handling path, the first impingement nozzle has a speed-regulated impingement nozzle and the second impingement nozzle unit has a volume-regulated impingement nozzle. Thus, as the first impingement nozzle is a speed-regulated impingement nozzle, the speed of air supplied by said nozzle can be reduced such that no spreading of ink occurs. At the same time, the second impingement nozzle can be a volume-regulated impingement nozzle with a higher drying efficiency as the ink has already been at least partially dried when reaching the second impingement nozzle.

[0031] If the drying module has three or more impingement nozzle units, the second and higher impingement nozzle units, counted along the handling path, can have a volume-regulated impingement nozzle, while the first impingement nozzle unit can have a speed-regulated impingement nozzle.

[0032] The drying module can have a control unit being configured for controlling the air flow through the impingement nozzle units and the flotation nozzle units. The control unit especially is configured to adapt the size of any nozzle opening and / or the movement of any central element of the drying module.

[0033] In a further variant, the drying module is configured to be operable in a first operation mode and a second operation mode, the drying module being flipped upside down in the second operation mode along the handling direction compared to the first operation mode. This configuration allows to arrange the drying module in a flexible manner such that the overall size of the drying unit and an inkjet printing machine comprising said drying unit can be minimized.

[0034] Further features and properties of the invention will become apparent from the following detailed description of preferred embodiments, which are not to be understood in a limiting manner, and from the Figures.

[0035] - Fig. 1 schematically shows a drying module according to the invention,

[0036] - Fig. 2 shows a volume-regulated impingement nozzle used in the drying module of Fig. 1 ,

[0037] - Fig. 3 shows a speed-regulated impingement nozzle used in the drying module of Fig. 1 ,

[0038] - Fig. 4 shows a flotation nozzle unit of drying module of Fig. 1 , and

[0039] - Fig. 5 schematically shows selected parts of an inkjet printing machine comprising a drying unit with a plurality of drying modules according to the invention.

[0040] - Fig 6 shows a cross-section of a drying module according to the invention and the connections of the air chambers to the air supply.

[0041] Fig. 1 shows a drying module 40 according to the invention of a drying unit 14, especially of a drying unit 14 of an inkjet printing machine 10 (see Fig. 5).

[0042] The drying module 40 is used for drying a substrate 20 with a front side 32 and a back side 34. On the front side 32, fresh ink has been supplied onto the substrate 20, while no ink, or already dried ink, has been supplied onto the back side 34 of the substrate 20.

[0043] The substrate 20 is e.g. made out of paper or cardboard. However, in principle any substrate 20 can be used which can be printed upon by inkjet printing.

[0044] Within the drying module 40, the substrate 20 is moved along a handling path which extends from an entry 18 of the drying module 40 to an outlet 24 of the drying module 40, as indicated by arrow H in Fig. 1. The drying module 40 comprises two impingement nozzle units 42 and two flotation nozzle units 44 which will be explained later in greater detail.

[0045] Of course, the exact number of impingement nozzle units 42 and flotation nozzle units 44 can differ from the one shown in the exemplary embodiment of Fig. 1.

[0046] The impingement nozzle units 42 each comprise an impingement nozzle 46 and a counter roller 48 associated to the respective impingement nozzle 46.

[0047] The counter roller 48 acts as support for the substrate 20. Accordingly, the back side 34 of the substrate 20 is in contact with the counter rollers 48 such that the distance between the front side 32 and the impingement nozzles 46 is precisely controlled. The combination of the impingement nozzle and the counter roller 48 allows to precisely control the path of the substrate 20 even if the drying module is positioned opside down.

[0048] The flotation nozzle units 44 each comprise a first flotation nozzle 62 and an associated second flotation nozzle 63 facing the first flotation nozzle 62.

[0049] As becomes clear from the depiction in Fig. 1 , the first flotation nozzles 62 are facing the front side 32 of the substrate 20 while the second flotation nozzles 63 are facing the back side 34 of the substrate 20. Accordingly, the first flotation nozzles 62 are mainly responsible for drying the ink on the substrate 20, while the second flotation nozzles 62 are used to heat the back of the substrate — which also contributes to drying — and are also used to balance the mechanical constraints that the air from the first floatation nozzles 62 apply on the substrate.

[0050] The impingement nozzle units 42 and the flotation nozzle units 44 are arranged along the handling path in an alternating manner, i.e. , the substrate 20 is exposed first to an impingement nozzle unit 42, second to a flotation nozzle unit 44, third to another impingement nozzle unit 42, and fourth to another flotation nozzle unit 44.

[0051] The drying module 40 further comprises a first forward air chamber 50 and a second forward air chamber 76.

[0052] The forward air input 52 is fluidically connected to an air supply module 49, which provides air into the forward air chambers 50,76 As can be seen in Fig. 1 , all the impingement nozzles 46 and of the first flotation nozzles 62 are fluidically connected to the first forward air chamber 50 such that air can be applied from the first forward air chamber 50 through the respective nozzle onto the substrate 20. By such an arrangement, the pressure drop along the handling direction H can be made negligible and a single air supply is sufficient to provide air to all the nozzles of the drying module.

[0053] Further, all second flotation nozzles 63 are fluidically connected to the second forward air chamber 76 such that air can be applied from the second forward air chamber 76 through the respective second flotation nozzle 63 on the substrate 20.

[0054] The chamber crossed by the substrate is a backward air chamber 80. The backward air chamber 80 may be fluidically connected to a further air sink 54 connected to the air supply module 49.

[0055] The drying module 40 further comprises a control unit 78 which is configured for controlling the air flow through the impingement nozzle units 42 and the flotation nozzle units 44.

[0056] The control unit 78 can also be a control unit of the drying unit 14 or of the inkjet printing machine 10, i.e. , the control unit 78 can have further functionalities other than controlling a single drying module 40.

[0057] Fig. 3 shows one type of impingement nozzle 46 which is a so-called “speed- regulated” impingement nozzle 46.

[0058] The speed-regulated impingement nozzle 46 has a nozzle opening 56 facing the substrate 20 (see Fig. 1). The size of the nozzle opening 56 can be varied, as indicated by the arrow P in Fig. 3.

[0059] Additionally, the speed-regulated impingement nozzle 46 comprises a membrane 59 having a membrane opening 60 of fixed size.

[0060] The membrane 59 is arranged between the first forward air chamber 50 (see Fig. 1) and the nozzle opening 56, thereby defining a subsection 61 within the speed-regulated impingement nozzle. The volume of air which can flow into the subsection 61 per time unit is limited by the size of the membrane opening 60. Thus, when the state of the nozzle opening 56 is changed, instead of the total volume of air per time unit being changed, the speed of air being released by the nozzle opening 56 is varied.

[0061] Fig. 2 shows another type of impingement nozzle which is a so-called “volume- regulated” impingement nozzle 46.

[0062] The volume-regulated impingement nozzle 46 also has a nozzle opening 56 facing the substrate whose size can be varied. Accordingly, the left depiction in Fig. 2 shows the nozzle opening 56 in a restricted state and the right depiction in Fig. 2 shows the nozzle opening 56 in an unrestricted state

[0063] In the restricted state, the volume of air (indicated by arrows 58) being released by the nozzle opening 56 per time unit will be less than in the unrestricted state, given that the air pressure within the forward air chamber 50 stays constant. Thus, by changing the size of the nozzle opening 56, the volume of air released by the nozzle opening 56 is changed. The size of the nozzle opening can be controlled precisely by the control unit.

[0064] The impingement nozzle 46 is used to apply a stream of air onto the front side 32 of the substrate 20 for drying the ink. Thus, when the substrate 20 enters the drying module 40, the ink is still in its wettest state. Therefore, the first impingement nozzle unit 42, counted along the handling path, preferably has a speed-regulated impingement nozzle to avoid spreading of the ink on the substrate 20, while the second impingement nozzle unit 42 (and possible further impingement nozzle units 42) has a volume-regulated impingement nozzle for increasing drying efficiency.

[0065] However, one skilled in the art will appreciate that the exact type of impingement nozzles 46 used and their arrangement can be chosen according to the requirements of the desired drying procedure.

[0066] To summarise, in a first-order approximation, a speed-regulated impingement nozzle provides a constant volume of air in a given time but delivers it at variable speed. On the contrary, a volume-regulated impingement nozzle delivers, in a first- order approximation, a variable amount (volume) of air in a given time but delivers it at a constant speed. Fig. 4 shows selected parts of a flotation nozzle unit 44 of the drying module 40 according to the invention.

[0067] Both the first flotation nozzle 62 and the second flotation nozzle 63 comprise a central element 64 whose vertical position relative to the substrate 20 is variable along an adjustment direction as indicated by arrow V.

[0068] Between the central element 64 and a nozzle housing 66 of the respective flotation nozzle, a flotation air path 68 is defined having a first section 69 being parallel to the adjustment direction and a second section 71 being arranged at an angle relative to the adjustment direction, thereby defining a tilted chamber 70 whose size is dependent on the position of the central element 64 as indicated by double arrows in Fig. 4.

[0069] As the volume of the flotation air path 68 is constant until the tilted chamber 70 is reached, by varying the vertical position of the central element 64, the speed of air released by the respective flotation nozzle can be controlled based on the position of the central element 64.

[0070] The movements of the central elements 64 of the associated first flotation nozzle 62 and second flotation nozzle 63 are preferably synchronized to ensure that the position of the substrate 20 relative to each of the flotation nozzles 62 and 63 remains constant.

[0071] The movement of the central element 64 is realized by an adjustment mechanism 71 comprising an excentric 72 and a spring element 74 which ensures the contact between the excentric and the central element 64.

[0072] Of course, each of the flotation nozzles depicted in Fig. 4 comprises an adjustment mechanism 71 , although only one is depicted for simplifying the depiction.

[0073] Fig. 5 schematically shows an exemplary inkjet printing machine 10 with a plurality of drying modules 40 according to the invention.

[0074] The inkjet printing machine 10 comprises a printing unit 12 and a drying unit 14 that are connected to each other, wherein a printing output 16 of the printing unit 12 is directly adjacent to a drying input 83 of the drying unit 14. The inkjet printing machine 10 is used for manufacturing a printed product by applying ink onto the substrate 20 in the printing unit 12 followed by a drying process of the applied ink in the drying unit 14. The substrate 20 is supplied to the printing unit 12 e.g. from a (not shown) substrate delivery unit of the inkjet printing machine 10.

[0075] Within the printing unit 12, the substrate 20 is moved along a printing handling path which extends from a printing input 86 of the printing unit 12 to the printing output 16 of the printing unit 12.

[0076] Within the drying unit 14, the substrate 20 is moved along the handling path, indicated by arrows H, which extends from the drying input 83 to a drying output 24 of the drying unit 14.

[0077] The printing unit 12 comprises several inkjet units 26, wherein each of the inkjet units 26 has an inkjet nozzle 28 and an associated inkjet counter roller 30. The inkjet nozzle 28 is adapted to apply ink to the front side 32 of the substrate 20 while the back side 34 of the substrate 20 is in contact with the inkjet counter rollers 30 such that the substrate 20 is moved by the inkjet counter rollers 30 along the printing handling path towards the drying unit 14.

[0078] As shown in Fig. 5, the inkjet units 26 are arranged at an angle to each other such that the printing handling path has an overall convex shape relative to a plane 33 which is parallel to the ground on which the inkjet printing machine 10 is placed.

[0079] The relative orientation of the inkjet units 26 ensures that the substrate 20 is in close contact with the associated inkjet counter rollers 30, thereby providing a well-defined distance between the front side 32 of the substrate 20 and the inkjet nozzles 28.

[0080] In the shown embodiment, there is a total number of four inkjet units 26. Of course, there can be more or less inkjet units 26. Especially, there are at least two inkjet units 26 present which are at an angle to each other.

[0081] The drying unit 14 comprises a first section 36, a second section 98 and a third section 39 connecting the first section 36 and the second section 98. Each of the first section 36 and the second section 98 comprises two of the drying modules 40 according to the invention, wherein each drying module 40 has two impingement nozzle units 42 and two flotation nozzle units 44.

[0082] Of course, the exact number of drying modules 40 as well as of impingement nozzle units 42 and flotation nozzle units 44 can differ from the one shown in the exemplary embodiment of Fig. 5. Also, the number of drying modules 40 can differ between the first section 36 and the second section 38.

[0083] The substrate 20 is moved through the first section 36 along a forward path section of the handling path to the third section 39 in which the substrate 20 is moved along a turnaround section of the handling path and finally along a backward path section of the handling path through the second section 38.

[0084] In the third section 39, two turnaround rollers 45 are used for reversing the effective direction the substrate 20 is moved along. Termed differently, the substrate 20 is flipped upside down in the turnaround section. As shown in Fig. 1 , the front side 32 of the substrate 20 is pointing upwards when leaving the forward path section and is pointing downwards when entering the backward path section. In the backward path, the impingement nozzles 46 and counter rollers 48 are important for a precise control of the substrat position.

[0085] Accordingly, in the shown embodiment, the backward path section is arranged geodetically below the forward path section.

[0086] Further, the backward path section is arranged horizontally such that the backward path section is parallel to the plane 33 which in turn is parallel to the ground on which the inkjet printing machine 10 is placed.

[0087] From this configuration, it also becomes clear that the drying module 40 according to the invention is configured to be operable in two different operation modes: a first operation mode is the one which is used in the forward path section with the counter rollers 48 being arranged below the substrate 20. A second operation mode is the one which is used in the backward path section with the counter rollers 48 being arranged above the substrate 20. Thus, the drying module 40 is essentially flipped upside down in the second operation mode compared to the first operation mode. The forward path section 36 is arranged at an angle a relative to the horizontal direction, to be aligned with the output of the printing unit. The alignment is necessary to avoid touching the top of the substrate covered with fresh ink. As can be seen in Fig. 5, the drying modules 40 used within the drying unit 14 are not the same. The drying module 40 which is arranged closest to the printing unit 12 along the handling direction comprises a speed-regulated impingement nozzle 46, while the further drying modules 40 only comprise volume-regulated impingement nozzles 46.

[0088] Overall, the drying module 40 according to the invention provides the possibility to specifically tailor the overall design of the drying unit 14 according to the requirements of the print jobs at hand, i.e. of the print jobs for which the inkjet printing machine 10 is designed.

Claims

Claims1 . A drying module (40) of a drying unit (14) for drying a substrate (20) which is moved along a handling path through the drying module (40), the substrate (20) having a front side (32) at least partially covered with ink or coating material and a backside (34) not covered with ink or covered with already dried ink, the drying module (40) comprising, along the handling path, one or more impingement nozzle units (42) and one or more flotation nozzle units (44), the one or more impingement nozzle units (42) each having an impingement nozzle (46) and an associated counter roller (48) facing each other, and the one or more flotation nozzle units (44) each having a first flotation nozzle (62) and an associated second flotation nozzle (63) facing each other, with the handling path being arranged between the impingement nozzle (46) and the associated counter roller (48) of the one or more impingement nozzle units (42) and between the first flotation nozzle (62) and the associated second flotation nozzle (63) of the one or more flotation nozzle units (44), wherein the drying module (40) is adapted to move the substrate (20) through the drying module (40) such that the back side (34) of the substrate (20) is in contact with the counter roller (48), characterised in that the drying module (40) having an alternating sequence of impingement nozzle units (42) and flotation nozzle units (44) along the handling direction.

2. The drying module (40) according to claim 1 , the drying module (40) comprising a forward air chamber (50) being fluidically connected to each of the impingement nozzles (46) and each of the first flotation nozzles (62).

3. The drying module (40) according to claim 1 or 2, the drying module (40) comprising a backward air chamber (76) being fluidically connected to each of the second flotation nozzles (63).

4. The drying module (40) according to any of the preceding claims, the drying module (40) being configured to be connectable to another drying module(40) such that the handling paths of the connected drying modules (40) are aligned to each other.

5. The drying module (40) according to any of the preceding claims, wherein at least one of the impingement nozzles (46) comprises a nozzle opening (56) facing the handling path, the size of the nozzle opening (56) being variable.

6. The drying module (40) according to any of the preceding claims, wherein at least one of the impingement nozzles (46) is a speed-regulated impingement nozzle (46) comprising a membrane (59) having a membrane opening (60), the size of the membrane (59) opening being of fixed size.

7. The drying module (40) according to any of the preceding claims, wherein at least one of the impingement nozzles (46) is a volume-regulated impingement nozzle (46) being free of a membrane (59) having a membrane opening (60) of fixed size.

8. The drying module (40) according to any of the preceding claims, the first flotation nozzle (62) and the second flotation nozzle (63) having a nozzle housing (66) and a central element (64) being configured to be movable relative to the nozzle housing (66) along an adjustment direction which is perpendicular to the handling direction, the nozzle housing (66) and the central element (64) defining a flotation air path (68).

9. The drying module (40) according to claim 8, the flotation air path (68) having a first section (69) parallel to the adjustment direction and a second section (71) arranged at an angle relative to the adjustment direction.

10. The drying module (40) according to claim 8 or 9, the central element (64) comprising an adjustment mechanism (72) having an excentric (72) being connected to a spring mechanism (74).

11. The drying module (40) according to any of claims 8 to 10, wherein the movements of the central element (64) of the first flotation nozzle (62) and of the associated second flotation nozzle (63) are coupled.

12. The drying module (40) according to claim 14, the drying module (40) having two or more impingement nozzle units (42), wherein, counted along the handling path, the first impingement nozzle unit (42) has a speed-regulated impingement nozzle (46) and the second impingement nozzle unit (42) has a volume-regulated impingement nozzle (46).

13. The drying module (40) according to any of the preceding claims, the drying module (40) having a control unit (78) being configured for controlling the airflow through the impingement nozzle units (42) and the flotation nozzle units (44).

14. The drying module (40) according to any of the preceding claims, the drying module (40) is configured to be operable in a first operation mode and a second operation mode, the drying module (40) being flipped upside down in the second operation mode along the handling direction compared to the first operation mode.

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