INKJET PRINTING MACHINE WITH NOZZLE DRIER

Abstract

 The invention is about an inkjet printer with a dryer. The printer uses printing heads aligned with counter rollers to precisely control the substrate-to-printing head distance. To ensure contact between the roller and the substrate without touching the side of the substrate covered with ink, the substrate follows a convex, curved path, and exits the printer with an angle. The drying unit input is tilted at the same angle. The drying unit is made of a forward, tilted, path and backward path, to save space. It is made of an alternation of impingement nozzles and flotation nozzles. The impingement nozzles have a counter roller that guides the substrate thanks to the drying air that pushes the substrate against the roller. Thanks to the impingement nozzles, the side of the substrate covered with ink does not get in contact with any rollers until the ink is dry at the output of the dryer, even in the return path when the substrate is arranged upside down.

Description

[0001] The invention relates to an inkjet printing machine.

[0002] Inkjet printing machines are typically applied for printing various products, such as labels, textiles, ceramic tiles and many more by dispensing small ink droplets through inkjet nozzles of a printing unit on the respective substrate to be printed upon.

[0003] A critical parameter for the efficiency of an inkjet printing machine is the maximum speed at which the substrate can be moved through the inkjet printing machine while ensuring a sufficient printing quality. The maximum speed is typically limited by the rate of drying of the ink after being applied on the substrate, as the freshly printed substrate must be handled with care to avoid mechanical contact with the applied ink as long as it has not been sufficiently dried. This effect is especially pronounced when using water-based inks instead of inks on the basis of organic solvents.

[0004] One option for accelerating the drying process is the use of drying units comprising nozzles which apply a stream of air onto the substrate, especially of heated air. However, the distance between the printed-upon substrate and such nozzles of the drying unit must be precisely controlled to avoid mechanical contact between the still wet substrate and the nozzles and to be able to provide the desired flow of air.

[0005] The object of the invention is to provide an inkjet printing machine which allows to precisely control a handling path of the substrate to be printed upon. Preferably, the inkjet printing machine allows to use high printing speeds.

[0006] The object of the invention is solved by an inkjet printing machine comprising a printing unit having two or more inkjet units each comprising an inkjet nozzle and an associated inkjet counter roller. Each inkjet unit is configured to apply, by the inkjet nozzle, an ink to a front side of a substrate being moved through the printing unit along a printing handling path while a back side of the substrate is in contact with the associated inkjet counter roller, and wherein adjacent inkjet units along the printing handling path are arranged at an angle to each other. The inkjet printing machine further comprises a drying unit for drying the ink applied on the front surface of the substrate in the printing unit, the drying unit comprising, along a drying handling path, one or more impingement nozzle units and one or more flotation nozzle units, the flotation nozzle units having a first flotation nozzle, and the impingement nozzle units having an impingement nozzle and an associated counter roller facing each other. The drying handling path is arranged between the impingement nozzle and the associated counter roller of the one or more impingement nozzle units. The drying unit is adapted to move the substrate through the drying unit along the drying handling path such that the back side of the substrate is in contact with the counter rollers of the one or more impingement nozzle units, and the direction of the printing handling path at a printing output of the printing unit is aligned with a drying input of the drying unit.

[0007] The inkjet printing machine according to the invention is based on the idea to precisely control the handling paths the substrate is moved along in the printing and drying process, adapt the handling path in the drying unit to the printing constants while minimizing the space occupied by the dryer unit.

[0008] This is achieved on the one hand by keeping the back side of the substrate in contact with counter rollers, i.e. the side of the substrate which is not printed upon (and therefore is dry throughout the inkjet printing process). Thus, the substrate-to-nozzle distance can be optimally controlled.

[0009] The printing handling path and the drying handling path have a defined geometry relative to each other, as the printing output of the printing unit, i.e. an outlet of the printing unit, is aligned with the drying input of the drying unit, i.e. with an entry of the drying unit. Thus, it can be ensured that, even at high printing speeds, the substrate does not come into contact with the impingement nozzles or the flotation nozzles of the drying unit.

[0010] Both the one or more impingement nozzle units and the one or more flotation nozzle units in the drying unit of the inkjet printing machine provide an air stream onto the substrate, wherein the impingement nozzle of each of the impingement nozzle units is applying air only on the front side of the substrate (as the back side of the substrate is contact with the associated counter roller).

[0011] Generally speaking, the main function of the impingement nozzle is to dry the wet front side of the substrate, but it also pushes the substrate against the associated counter roller and controls and stabilizes the path of the substrate, even when the nozzles and substrate are running upside down.

[0012] The flotation nozzle units further have a second flotation nozzle associated to the first flotation nozzle, the first flotation nozzle and the associated second flotation nozzle facing each other. Thus, the drying handling path can be arranged between the first flotation nozzle and the associated second flotation nozzle of the one or more flotation nozzle units. The first flotation nozzle is used for drying the wet front surface of the substrate while the second flotation nozzle heats the dry back surface of the substrate, and thus also contributes to the drying process. By precisely controlling the air flow delivered by the first flotation nozzle and the second associated flotation nozzle allows to precisely control the mechanical constraints applied by the air flow to the front and to the back of substrate. Thus, we can balance these constraints and avoid that the handling path get destabilized by the air flow and consequently avoid that the wet front surface of the substrate does come into mechanical contact with any of the nozzles of the drying unit.

[0013] Generally, the main function of the first flotation nozzle can be to dry the ink on the substrate while the main functions of the second flotation nozzle is to heat the back of the substrate --- which also contributes to drying --- while balancing the mechanical constraints that the air from the first flotation nozzles apply on the substrate.

[0014] In one variant, the printing handling direction of the printing unit has a convex shape. Such an arrangement further ensures that the substrate keeps close contact to the inkjet counter rollers of the printing unit and thereby provides a precise control on the substrate-to-inkjet nozzle distance. Also, this convex shape is oriented such that the printing handling direction is approximately horizontal, resulting in the output of the substrate at an angle with respect to the horizontal direction. This geometrical configuration is dictated by physical constraints of the ink jets for which the orientation with respect to gravity matters. As the printing output of the printing unit and the drying input of the drying unit are aligned to each other, the position of the substrate throughout the printing and drying process can be precisely controlled even when a convex printing handling direction is used.

[0015] For further minimizing the overall size of the inkjet printing machine, the drying unit can comprise a first section defining a forward path section of the drying handling path, a second section defining a backward path section of the drying handling path, and a third section defining a turnaround section of the drying handling path connecting the forward path section and the backward path section. The backward path section therefore can be arranged geodetically above or below the forward path section.

[0016] The forward path section can be arranged at an angle relative to the horizontal direction and relative to the backward path section. Thus, the forward path section can be tilted relative to the backward path section to allow for the alignment of the printing output of the printing unit and the drying input of the drying unit, as the drying input of the drying unit is part of the forward path section. Therefore, even in case the substrate leaves the printing unit at an angle, e.g. because the printing handling direction has a convex shape, the alignment of the handling paths and thus the precise control of the position of the substrate can be ensured.

[0017] E.g., the angle between the forward path section and the backward path section can be in the range of from 2° to 90°, preferably in the range of from 2° to 10°. If the angle is below 2°, there is a risk that the substrate comes into contact with components of the drying unit, especially the nozzles of the drying unit, due to the necessary alignment of the printing unit and the drying unit.

[0018] The backward path section is preferably arranged horizontally. Termed differently, the backward path section is preferably parallel to the ground on which the overall inkjet printing machine is placed on.

[0019] In one variant, the backward path section is geodetically below the forward path section.

[0020] The drying unit can be adapted to move the substrate flipped upside down through the backward path section compared to the alignment of the substrate in the forward path section. This allows using a simpler design of the third section of the drying unit, thereby reducing costs and space requirements. E.g., the front side of the substrate can face upwards in the forward path section and downwards in the backward path section, as the ink on the substrate has already at least partially dried when leaving the forward path section.

[0021] In a preferred variant, the first section of the drying unit and/or the second section of the drying unit comprises at least two drying modules connected to each other, each drying module comprising one or more impingement nozzle units and one or more flotation nozzle units. In this way, the drying unit can be designed in a modular way, wherein the number of drying modules in the first section and/or the second section can be tailored to the rate of drying necessary and/or the space available for the intended use scenarios of the inkjet printing machine. Generally, the higher the desired printing speed is, the higher the number of drying modules necessary for achieving a sufficient drying efficiency is.

[0022] The speed of air released by the impingement nozzle of the impingement nozzle unit being arranged closest to the input of the drying unit can be the lowest of all impingement nozzles of the drying unit. At the drying input of the drying unit, the ink on the substrate is in its most liquid state during the drying process. Therefore, the risk of spreading the ink by application of air for drying is the highest at the drying input of the drying unit. Thus, by choosing the speed of air released by the impingement nozzle closest to the drying input of the drying unit, the risk of spreading the still wet ink and therefore of reducing print quality can be efficiently minimized.

[0023] Generally, the speed of air of the respective types of nozzles used in the drying unit can be increased along the drying unit path, with the nozzles being arranged closer to the drying input of the drying unit having a lower speed of air than nozzles being arranged further away from the drying input of the drying unit.

[0024] The drying unit can comprise 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 are supplied with air for drying the ink on the substrate from a common forward air chamber.

[0025] Also, the drying unit may comprise a second forward air chamber being fluidically connected to each of the second flotation nozzles. The first and second forward air chambers may be fluidically connected by a connection internal to the drying module, resulting in a single forward air chamber. They may also be separate but connected to a common air source.

[0026] The chamber crossed by the substrate constitutes a backward air chamber connected to a return path toward an air sink of an air supply module. 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.

[0027] For further tailoring the application of air applied for drying the ink on the substrate in the drying unit, the impingement nozzle of one or more of the impingement nozzle units can be a speed-regulated impingement nozzle and the impingement nozzle of one or more of the impingement nozzle units can be a volume-regulated impingement nozzle. In this way, the amount of air supplied by the respective impingement nozzle can be chosen such to optimally avoid spreading of the ink on the substrate during the drying process.

[0028] The volume-regulated impingement nozzle can comprise a nozzle opening facing the drying handling path, the size of the nozzle opening being variable. 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.

[0029] The speed-regulated impingement nozzle can comprise a nozzle opening facing the drying handling path, the size of the nozzle opening being variable, and can further comprise a membrane having a membrane opening, 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 first 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.

[0030] 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 be 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.

[0031] 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.

• Fig. 1 schematically shows an inkjet printing machine according to the invention,
• Fig. 2 shows a volume-regulated impingement nozzle used in the inkjet printing machine of Fig. 1,
• Fig. 3 shows a speed-regulated impingement nozzle used in the inkjet printing machine of Fig. 1, and
• Fig. 4 shows selected parts of a flotation nozzle unit of the inkjet printing machine of Fig. 1, and
• Fig 5 shows a cross section of a drying module according to the invention and the connections of the air chambers to the air supply.

[0032] Fig. 1 schematically shows an inkjet printing machine 10 according to the invention, wherein only parts of the inkjet printing machine 10 which are necessary for understanding the invention have been depicted to ease understanding of the Figure.

[0033] The inkjet printing machine 10 comprises a printing unit 12 and a drying unit 14 connected to each other, wherein a printing output 16 of the printing unit 12 is directly adjacent to a drying input 18 of the drying unit 14.

[0034] The inkjet printing machine 10 is used for manufacturing a printed product by applying ink onto a 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.

[0035] 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.

[0036] Within the printing unit 12, the substrate 20 is moved along a printing handling path which extends from a printing input 22 of the printing unit 12 to the printing output 16 of the printing unit 12.

[0037] Within the drying unit 14, the substrate 20 is moved along a drying handling path which extends from the drying input 18 to a drying output 24 of the drying unit 14.

[0038] 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 a front side 32 of the substrate 20 while a 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.

[0039] As shown in Fig. 1, 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.

[0040] 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 nozzle 28.

[0041] 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, as long as at least two inkjet units 26 are present which are arranged at an angle to each other.

[0042] The drying unit 14 comprises a first section 36, a second section 38 and a third section 39 connecting the first section 36 and the second section 38.

[0043] The substrate 20 is moved through the first section 36 along a forward path section of the drying handling path to the third section 39 in which the substrate 20 is moved along a turnaround section of the drying handling path and finally along a backward path section of the drying handling path through the second section 38, as indicated by arrows H in Fig. 1.

[0044] Each of the first section 36 and the second section 38 comprises two drying modules 40, wherein each drying module 40 has two impingement nozzle units 42 and two flotation nozzle units 44 which will be explained in greater detail later.

[0045] Of course, the exact number of drying modules 40 as well as impingement nozzle units 42 and flotation nozzle units 44 can differ from the one shown in the exemplary embodiment of Fig. 1. Also, the number of drying modules 40 can differ between the first section 36,the second section 38, and the third section 39.

[0046] 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. The third section may also have a set of impingement and flotation nozzles, similar to the first and second section, as shown in Figure 1.

[0047] Accordingly, in the shown embodiment, the backward path section is arranged geodetically below the forward path section.

[0048] 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.

[0049] The forward path section is arranged at an angle α relative to the backward path section. The angle α is in the range of from 2° to 90° and chosen such that the direction of the printing handling path at the printing output 16 of the printing unit 12 is aligned with the drying input 18 of the drying unit 14, i.e. such that the printing handling path at the printing output 16 is aligned with the drying handling path at the drying input 18, specifically with the forward path section of the drying handling path. E.g., the angle α can be 4°.

[0050] In the following, the different types of nozzles which are used in the drying unit 14 will be explained in more detail.

[0051] The impingement nozzle units 42 each comprise an impingement nozzle 46 and a counter roller 48 associated to the respective impingement nozzle 46.

[0052] The counter roller 48 acts as support for the substrate 20 and for moving the substrate 20 along the drying handling path. Accordingly, the back side 34 of the substrate 20 is in contact with the counter roller 48 such that the distance between the front side 32 and the impingement nozzle 46 is precisely controlled.

[0053] 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. The air is supplied to the impingement nozzle 46 by means of a first forward air chamber 50 which is fluidically connected with the impingement nozzle 46.

[0054] The first forward air chamber 50 is supplied with air, especially with heated air, via a forward air input 52 to which air is provided by an air supply 49 of the inkjet printing machine 10, wherein the forward air input 52 is the input of the drying module 40 being arranged closest to the printing unit 12 with respect to the drying handling path (in the following also termed "first drying module").

[0055] As shown in Fig. 1, the first forward air chamber 50 is fluidically connected to each of the impingement nozzles 46 of the respective drying module 40.

[0056] Further, the forward air chambers 50,76 of subsequent drying modules 40 of the drying unit 12 as well as a forward air chamber 50,76 of the third section 39 may be fluidically connected to each other forming a common forward air chamber. Equivalently, the backward air chambers 80 may be fluidically connected to form a common backward air chamber

[0057] By this arrangement, the air pressure within the common forward air chamber can be easily controlled throughout the drying unit 14, especially kept constant throughout the common forward air chamber 50.

[0058] As a preferred alternative, the air inputs 52 of neighboring drying modules 40 may be connected to a common input air source of the air supply module 49, and the air outputs 54 may also be connected to a common air sink of the air supply module 49.

[0059] As a different alternative, each drying module may be connected to an independent air supply and sink, with a settable pressure or air flux. In other words, this alternative uses several air supply devices 49, or a single air supply device 49 with differentiated supply and sink channels. This alternative provides another mean to regulate the drying power of the drying module other than changing the output setting of each of the air nozzles (46, 62, 63).

[0060] Fig. 2 shows one type of impingement nozzle 46 which is a volume-regulated impingement nozzle.

[0061] The volume-regulated impingement nozzle 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 double-arrows P in Fig. 2. 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

[0062] 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 first forward air chamber 50 stays constant. Thus, by changing the size of the nozzle opening 56, the speed of air released by the nozzle opening 56 is changed.

[0063] Fig. 3 shows another type of impingement nozzle 46 which is a speed-regulated impingement nozzle.

[0064] The speed-regulated impingement nozzle also has a variable nozzle opening 56 analog to the volume-regulated impingement nozzle discussed before.

[0065] Additionally, the speed-regulated impingement nozzle comprises a membrane 59 having a membrane opening 60 of fixed size. 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.

[0066] Which type of impingement nozzle 46 is used at which position within the drying unit 14 can be chosen according to the requirements on the desired drying procedure.

[0067] Preferably, the speed of air released by the impingement nozzle 46 of the impingement nozzle unit 42 being arranged closest to the drying input 18 of the drying unit 14 is the lowest of all impingement nozzles of the drying unit 14. In this way, spreading of ink on the front side 32 of the substrate 20 can be minimized as at this position along the drying handling path the ink is still very wet as no drying procedure has been applied, yet. Thus, said impingement nozzle 46 is preferably a speed-regulated impingement nozzle.

[0068] One skilled in the art will appreciate that the types and relative arrangements of impingement nozzles 46 in the drying modules 40 and generally in the forward path section and the backward path section can differ.

[0069] In the shown embodiment, along the drying handling path, between each two adjacent impingement nozzle units 42, a flotation nozzle unit 44 is arranged.

[0070] Each flotation nozzle unit 44 comprises a first flotation nozzle 62 and an associated second flotation nozzle 63 facing the first flotation nozzle 62.

[0071] 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 by applying air, 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 flotation nozzles 62 apply on the substrate.

[0072] The flotation nozzles 63 and 62 are shown in more detail in Fig. 4.

[0073] As can be seen from Fig. 4, both the first flotation nozzle 62 and the second flotation nozzle 63 have a central element 64 whose vertical position is variable along an adjustment direction as indicated by an arrow V.

[0074] Between the central element 64 and a nozzle housing 66, a flotation air path 68 ending in a tilted chamber 70 is defined through which air can be applied towards the substrate 20.

[0075] 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 62 and 63, respectively, can be controlled based on the position of the central element 64.

[0076] The movements of the central elements 64 of the associated first flotation nozzle 62 and second flotation nozzle 63 are preferably concomitant to ensure that the position of the substrate 20 relative to each of the flotation nozzles 62 and 63 remains constant.

[0077] The movement of the central element 64 is realized by an adjustment mechanism 72 comprising an excentric 74 and a spring element 76 which ensures the contact between the excentric 74 and the central element 64.

[0078] The inkjet printing machine comprises a control unit 78 for controlling the movable parts of the impingement nozzles 46, the first flotation nozzles 62 and the second flotation nozzles 63.

[0079] The air which is supplied to the second flotation nozzles 63 is provided by means of a second forward air chamber 76 which is fluidically connected with the second flotation nozzles 63.

[0080] The air is supplied to the backward air chamber 80 via the impingement nozzles 46 and the flotation nozzles 62,63. The backward air chamber 80 is connected to the air supply via an air sink 54.

[0081] The inkjet printing machine 10 according to the invention provides a high level of control of the position of the substrate 20 during printing and drying, thereby providing good printing quality. Further, the inkjet printing machine 10 has a compact design and provides high drying efficiency.

Claims

1. An inkjet printing machine (10) comprising

a printing unit (12) having two or more inkjet units (26) each comprising an inkjet nozzle (28) and an associated inkjet counter roller (30),
wherein each inkjet unit (26) is configured to apply, by the inkjet nozzle (28), an ink to a front side (32) of a substrate (20) being moved through the printing unit (12) along a printing handling path while a back side (34) of the substrate (20) is in contact with the associated inkjet counter roller (30), and wherein adjacent inkjet units (26) along the printing handling path are arranged at an angle to each other,

a drying unit (14) for drying the ink applied on the front side (32) of the substrate (20) in the printing unit (12),

the drying unit (14) comprising, along a drying handling path, one or more impingement nozzle units (42) and one or more flotation nozzle units (44), the flotation nozzle units (44) having a first flotation nozzle (62), and the impingement nozzle units (42) having an impingement nozzle (46) and an associated counter roller (48) facing each other,

with the drying handling path being arranged between the impingement nozzle (46) and the associated counter roller (48) of the one or more impingement nozzle units (42),

wherein the drying unit (14) is adapted to move the substrate (20) through the drying unit (14) along the drying handling path such that the back side of the substrate (20) is in contact with the counter rollers (48) of the one or more impingement nozzle units (42), and

wherein the direction of the printing handling path at a printing output (16) of the printing unit (12) is aligned with a drying input (18) of the drying unit (14).

2. The inkjet printing machine according to claim 1, the flotation nozzle units (44) further having a second flotation nozzle (63) associated to the first flotation nozzle (62), the first flotation nozzle (62) and the associated second flotation nozzle (63) facing each other.

3. The inkjet printing machine according to claim 1 or 2, wherein the printing handling direction of the printing unit (12) has a convex shape.

4. The inkjet printing machine according to any of the preceding claims, the drying unit (14) comprising a first section (36) defining a forward path section of the drying handling path, a second section (38) defining a backward path section of the drying handling path, and a third section (39) defining a turnaround section of the drying handling path connecting the forward path section and the backward path section.

5. The inkjet printing machine according to claim 4, wherein the forward path section is arranged at an angle relative to the backward path section.

6. The inkjet printing machine according to claim 5, wherein the angle between the forward path section and the backward path section is in the range of from 2° to 90°.

7. The inkjet printing machine according to any of claims 4 to 6, wherein the backward path section is arranged horizontally.

8. The inkjet printing machine according to any of claims 4 to 7, wherein the backward path section is geodetically below the forward path section.

9. The inkjet printing machine according to any of claims 4 to 8, wherein the drying unit (14) is adapted to move the substrate (20) flipped upside down through the backward path section compared to the alignment of the substrate (20) in the forward path section.

10. The inkjet printing machine according to any of claims 4 to 9, the first section (36) of the drying unit (14) and/or the second section (38) of the drying unit (14) comprising at least two drying modules (40) connected to each other, each drying module (40) comprising one or more impingement nozzle units (42) and one or more flotation nozzle units (44).

11. The inkjet printing machine according to any of the preceding claims, wherein the speed of air released by the impingement nozzle (46) of the impingement nozzle unit (42) being arranged closest to the drying input (18) of the drying unit (14) is the lowest of all impingement nozzles (46) of the drying unit (14).

12. The inkjet printing machine according to any of the preceding claims, the drying unit (14) comprising a first forward air chamber (50) being fluidically connected to each of the impingement nozzles (46) and each of the first flotation nozzles (62).

13. The inkjet printing machine according to any of the preceding claims, comprising a second forward air chamber (76) being fluidically connected to each of the second flotation nozzles (63).

14. The inkjet printing machine according to claim 12 and 13, wherein the second forward air chamber (76) is fluidically connected to the first forward air chamber (50) to form a forward air chamber (50,76).

15. The inkjet printing machine according to any of the preceding claims, wherein the impingement nozzle (46) of one or more of the impingement nozzle units (42) is a speed-regulated impingement nozzle and the impingement nozzle (46) of one or more of the impingement nozzle units (42) is a volume-regulated impingement nozzle.

16. The inkjet printing machine according to claim 15, wherein the volume-regulated impingement nozzle comprises a nozzle opening (56) facing the handling path, the size of the nozzle opening (56) being variable, and
wherein the speed-regulated impingement nozzle comprises a nozzle opening (56) facing the handling path, the size of the nozzle opening (56) being variable, and further comprises a membrane (59) having a membrane opening (60), the membrane opening (60) being of fixed size.

Drawing