Non-impact printing press with central cylinder and charging unit

Abstract

The invention relates to a printing press designed as a non-impact printing press, wherein the printing press has at least one printhead, wherein the printing press has a substrate source designed as a roll unwinding device, wherein the printing press is assigned a transport path provided for transporting substrate, and wherein the printing press has at least one central cylinder serving as a substrate guiding element, onto which the at least one printhead is arranged, and wherein the printing press has at least one charging device.which has at least one charging electrode designed as a DC voltage electrode and wherein a region of the transport path intended for the transport of printing material is located in front of a pressure point defined by the at least one printhead, and wherein the at least one central cylinder is grounded and wherein the at least one printhead is grounded and wherein a minimum distance between at least one ejection opening of the at least one printhead and the at least one charging electrode is at least 20 mm.

Description

[0001] The invention relates to a non-impact printing machine with a central cylinder and a charging device.

[0002] When ink droplets are ejected from print heads, in addition to the deliberately created, relatively large droplets, very small droplets are also unintentionally produced. Due to their low mass-to-air resistance ratio, these droplets are not transported to the substrate but float around as a fine mist. These mist droplets can accumulate in various places, for example, near the print head nozzles, the electronics, or other components of a printing press. There, they can cause malfunctions and must therefore be removed regularly, if possible. This involves effort and / or machine downtime, and is sometimes not easily possible.

[0003] DE 198 10 061 A1 discloses an inkjet printer in which ink drops are electrically charged partly positively and partly negatively by means of an electrode on the print head and are then drawn in an electric field to the printing material or to the print head depending on their charge.

[0004] EP 0 473 179 A2 discloses an inkjet printer in which a conveyor belt and a printing substrate are each electrically charged via a contact electrode and ink drops are partly positively and partly negatively charged by additional electrodes in the area of ​​the print heads.

[0005] EP 1 780 016 A1 discloses an inkjet printer in which a printing substrate is electrically charged by a contact electrode and a print head serves as an electrode to electrically charge ink drops.

[0006] US 2012 / 0 019 589 A1 describes an inkjet printer in which electrodes emit ions that move towards the printing material, taking ink drops with them and thus removing them from the ambient air.

[0007] WO 2022 / 028 751 A1 discloses a printing machine which has a central cylinder, inkjet print heads arranged around this central cylinder and a charging electrode for fixing printing material to the central cylinder.

[0008] US 2014 / 0 092 174 A1 discloses a non-impact printing machine comprising a central cylinder and several inkjet printing units arranged around it, with a charging device located behind each print head. This charging device serves to detect ink mist and is therefore located behind the print head. It can also be used to bind ink mist to the substrate.

[0009] US 2006 / 0 055 734 A1 discloses a non-impact printing machine comprising a central cylinder and several inkjet printing units arranged around it, with a charging device arranged after each print head. The charging device is intended to generate charge carriers that adhere to ink droplets that have just impacted a substrate, thereby generating an electric field, which in turn increases the viscosity of the ink to prevent the ink droplets from running. In one embodiment, a charging device is additionally arranged in front of a first print head.

[0010] EP 0 832 742 B1 discloses an inkjet printing machine in which charged ink droplets are initially simply generated without actually moving them toward a substrate. Only an electric field between the grounded print head and a substrate support surface accelerates the droplets toward the substrate. For this purpose, an electrical voltage is applied between the substrate support surface and the grounded print head. The goal is to avoid ink mist from the outset by using minimal energy during droplet generation.

[0011] EP 3 835 027 A1 discloses a device for producing a decorated panel, wherein a carrier material is printed using an inkjet printing process. A discharge device is disclosed that has components whose conductivity exceeds 1,000 siemens per meter.

[0012] The invention is based on the object of creating a non-impact printing machine with a central cylinder and a charging device.

[0013] The object is achieved according to the invention by the features of claim 1.

[0014] A printing press designed as a non-impact printing press has at least one print head, a printing substrate source designed as a roll unwinding device, and at least one central cylinder serving as a printing substrate guide element, with which the at least one print head is arranged in alignment. The printing press is assigned a transport path provided for transporting printing substrate. The printing press has at least one charging device which has at least one charging electrode designed as a DC voltage electrode. A region of the transport path provided for transporting printing substrate that is closest to the at least one charging electrode is arranged - particularly viewed along this transport path - in front of a printing point defined by the at least one print head. The at least one central cylinder is grounded. The at least one print head is grounded.The smallest distance between at least one ejection opening of the at least one print head and the at least one charging electrode is at least 20 mm, preferably at least 25 mm, more preferably at least 35 mm, even more preferably at least 45 mm, and even more preferably at least 55 mm. This distance prevents any unwanted influence on the print head and the ink contained therein or ejected therefrom, even when high voltages are applied to the charging electrode. Charging of the droplets before or during their ejection is thus preferably avoided. Instead, the printing substrate is preferably only charged via ions emitted by the charging electrode, for example negatively or positively charged ions. As soon as droplets of the unwanted ink mist enter the sphere of influence of the electrostatically charged printing substrate, a charge shift occurs within the respective droplet by induction.The corresponding droplet acquires an electric dipole moment and can thus be attracted to the charge on the substrate. Since the droplet is electrically neutral overall, its impact on the substrate has no influence on its charge.

[0015] In a further development, the printing press is preferably characterized in that the minimum distance between the at least one charging electrode of the charging device and a contact surface of the central cylinder, which is intended in particular for contact with the printing substrate, is at least 10 mm. This prevents voltage breakdown even at high operating voltages.

[0016] In an alternative or additional development, the printing press is preferably characterized by a central cylinder base made of carbon fiber reinforced plastic. In addition to positive mechanical properties, the conductivity of this material ensures that the entire base is grounded.

[0017] In an alternative or additional development, the printing press is preferably characterized in that the contact surface of the central cylinder intended for contact with the printing substrate is formed from a material that has an electrical conductivity of at least 1,000 S / m, i.e. is a conductor. In combination with the at least partially conductive ink that seeps into the printing substrate after its application, the charge carriers can thus easily flow away outside the spatial area in which the ink mist is removed from the ambient air. In an alternative development, the printing press is preferably characterized in that the contact surface of the central cylinder intended for contact with the printing substrate is formed from a material that has an electrical conductivity of at most 10 S / m, i.e. is a non-conductor.This allows the electrostatic charge of the printing material to be maintained for longer if necessary.

[0018] In an alternative or additional development, the printing press is preferably characterized in that the at least one charging device has at least 20 charging electrodes, preferably at least 50, more preferably at least 100, and even more preferably at least 200. These are preferably distributed in a transverse direction. This enables charging that is as uniform as possible across the width of the printing substrate.

[0019] In an alternative or additional development, the printing press is preferably characterized in that the at least one charging device is designed to generate a maximum voltage of at least 10 kV, preferably at least 15 kV, more preferably at least 20 kV, even more preferably at least 25 kV, and even more preferably at least 30 kV. Such high voltages enable particularly effective generation of ions and thus particularly effective charging of the printing substrate.

[0020] In an alternative or additional development, the printing press is preferably characterized in that a section of the transport path provided for the transport of printing substrate is connected to a last print head of the printing press, which section has a minimum distance of at least 150 mm, preferably at least 200 mm, more preferably at least 500 mm, and even more preferably at least 1000 mm from each electrode provided for emitting ions. Discharge preferably occurs via the printing substrate moistened during the printing process. This saves costs for the installation and operation of a discharge device.

[0021] In an alternative or additional development, the printing press is preferably characterized in that the at least one print head is configured as a print head that is stationary during printing operation and / or in that the minimum distance between at least one and preferably each ejection opening of the at least one print head and a contact surface of the central cylinder is at least 0.1 mm. This allows for high printing speeds and high print quality even with wide substrates.

[0022] In an alternative or additional development, the printing press is preferably characterized in that the printing press is designed as an inkjet printing press and / or that the at least one print head is designed as an inkjet print head. The solvent contained in the ink, for example a conductive solvent, can accelerate the discharge if desired. This ink preferably contains water as a component.

[0023] In an alternative or additional development, the printing press is preferably characterized in that a region of the transport path provided for the transport of printing material, closest to the at least one charging electrode, is a region in which contact is provided between the printing material and the central cylinder. This ensures a particularly well-defined position of the printing material during its charging.

[0024] Embodiments of the invention are illustrated in the drawings and are described in more detail below.

[0025] They show: Fig. 1 a schematic representation of a printing machine designed as a web-fed printing machine with several print heads and a charging device; Fig. 2 a schematic enlarged view of an area around a printing point of the printing press.

[0026] A printing press 01 is designed as a non-impact printing press 01 and preferably as an inkjet printing press 01. The printing press 01 serves in particular to print on printing substrate 02. The printing press 01 is preferably designed as a web-fed printing press 01. The printing press 01 preferably serves to print on web-shaped printing substrate 02.

[0027] Preferably, the printing press 01 is assigned a transport path provided for transporting printing substrate 02. The transport path provided for transporting printing substrate 02 is in particular the spatial area which the printing substrate 02, if present, occupies and / or would occupy, at least temporarily. In the case of a curved transport path, a transport direction T is preferably the direction T that runs tangentially to a section and / or point of the provided transport path that is closest to a respective reference point and is provided for transporting the printing substrate 02 at this section and / or point. This respective reference point is preferably located at the point and / or on the component that is related to the transport direction T. The transport direction T therefore preferably extends along the transport path provided for printing substrate 02.A transverse direction A is preferably a direction A that extends orthogonal to the transport direction T and horizontally. A working width of the printing press 01 is preferably a dimension that preferably extends in the transverse direction A. The working width of the printing press 01 preferably corresponds to a maximum width that a printing substrate 02 may have in order to still be able to be printed with the printing press 01, i.e. in particular a maximum web width that can be processed with the printing press 01 or, if applicable, sheet width and / or width of the printing substrate 02. The width of a printing substrate 02 is to be understood in particular as its dimension in the transverse direction A. The working width of the printing press 01 is, for example, at least 50 cm, preferably at least 100 cm, more preferably at least 150 cm, even more preferably at least 200 cm and even more preferably at least 250 cm.

[0028] The printing press 01 has at least one printing material source 14. The at least one printing material source 14 is preferably designed as a roll unwinding device 14, in particular for web-shaped printing material 02, more preferably as a roll changer 14. The roll changer 14 is preferably designed as a roll changer 14 for a flying roll change.

[0029] The printing press 01 has at least one circumferentially movable support element 07, which has a circumferentially movable contact surface 08 provided for contact with a printing substrate 02. The at least one support element 07 is preferably designed as a cylinder 07, in particular as a central cylinder 07. The central cylinder 07 therefore serves as a printing substrate guide element 07. The printing press 01 has at least one print head 09, in particular designed as an inkjet print head 09. The at least one print head 09 preferably has at least one ejection opening 12, which serves in particular to eject ink droplets in a targeted manner. The at least one print head 09 is preferably designed as a print head 09 that is arranged in a stationary manner during printing operation. The at least one print head 09 is preferably designed as a print head 09 that operates according to the drop-on-demand principle.The at least one print head 09 is preferably arranged aligned with the at least one support element 07 and in particular with the at least one central cylinder 07. The at least one ejection opening 12 of the at least one print head 09 is preferably arranged aligned with the at least one support element 07 and in particular with the contact surface 08 of this at least one support element 07. The at least one support element 07 serves in particular to hold the printing substrate 02 in a defined position during printing operation while the ink is applied thereto. The contact surface 08 is preferably a contact surface 08 that is movable relative to the at least one print head 09. The contact surface 08 is preferably a contact surface 08 that is movable in rotation together with the printing substrate 02.

[0030] The printing press 01 has at least one charging device 03, in particular for electrostatically charging the printing substrate 02. The respective at least one charging device 03 serves in particular to generate ions 16, which are transported to the printing substrate 02 and electrostatically charge the printing substrate 02 through their contact or adhesion. The printing substrate 02 charged in this way is then able to attract and bind fine ink mist, which is unintentionally generated during the printing process, to the printing substrate 02.

[0031] The at least one charging device 03 has at least one charging electrode 04, which is preferably arranged aligned with the contact surface 08. Preferably, the at least one central cylinder 07 is grounded. Preferably, the at least one print head 09 is grounded. For example, a grounded component serves as the counter electrode 06, in particular at least one component of the central cylinder 07.

[0032] For example, a base body of the central cylinder 07 is made of carbon fiber reinforced plastic (carbon). The base body is preferably the largest component of the central cylinder 07 in terms of volume. In a first embodiment of the contact surface 08 of the central cylinder 07 intended for contact with the printing substrate 02, this contact surface 08 of the central cylinder 07 intended for contact with the printing substrate 02 is formed from a material that has an electrical conductivity of at least 1,000 S / m (one thousand Siemens per meter), i.e., in particular, from a conductor. This contact surface 08 of the central cylinder 07 is formed, for example, by a metal coating, which more preferably contains chromium and / or is made of chromium.In an alternative second embodiment of the contact surface 08 of the central cylinder 07 intended for contact with printing material 02, this contact surface 08 of the central cylinder 07 intended for contact with printing material 02 is formed from a material which has an electrical conductivity of at most 10 S / m (ten Siemens per meter), i.e. in particular from a non-conductor or insulator.

[0033] Preferably, the transport path provided for the transport of printing material 02 runs between the at least one circumferential contact surface 08 and the at least one charging electrode 04 of the at least one charging device 03. Preferably, the contact surface 08 is arranged at least partially between the at least one charging electrode 04 and the at least one counter electrode 06 of the at least one charging device 03.

[0034] The at least one charging device 03 is designed such that at least one side of the printing substrate 02, and more preferably the entire printing substrate 02, can be electrostatically charged without contact with the charging device 03. This allows the corresponding surface of the printing substrate 02 to be treated gently. Preferably, a minimum distance a between the at least one charging electrode 04 of the at least one charging device 03 and the contact surface 08 is greater than a minimum distance b between at least one, and preferably each, ejection opening 12 of the at least one print head 09 and the contact surface 08.

[0035] Preferably, the smallest distance a between the at least one and in particular each charging electrode 04 of the at least one charging device 03 and the contact surface 08 is at least 10 mm, more preferably at least 20 mm, even more preferably at least 35 mm, even more preferably at least 50 mm, even more preferably at least 60 mm, even more preferably at least 65 mm and even more preferably at least 70 mm. Preferably, the smallest distance a between the at least one and in particular each charging electrode 04 of the at least one charging device 03 and the contact surface 08 is at most 150 mm, more preferably at most 110 mm, even more preferably at most 85 mm and even more preferably at most 70 mm.

[0036] Preferably, a smallest distance c between at least one and more preferably each ejection opening 12 of the at least one print head 09 from the at least one charging electrode 04 is at least 20 mm, more preferably at least 25 mm, even more preferably at least 35 mm, even more preferably at least 45 mm and even more preferably at least 55 mm.

[0037] In an alternative or additional development, the printing press 01 is preferably characterized in that the at least one charging device 03 is designed as a direct current charging device 03. This means in particular that a sign of the voltage applied to the respective charging electrode 04 preferably does not change during operation. The at least one charging electrode 04 is preferably designed as a direct voltage electrode 04. Preferably, the at least one charging device 03 is designed to generate a maximum voltage which is at least 10 kV, more preferably at least 15 kV, even more preferably at least 20 kV, even more preferably at least 25 kV and even more preferably at least 30 kV and, independently thereof, preferably at most 45 kV and more preferably at most 40 kV and even more preferably at most 35 kV.In particular, at least in one operating state of the printing press 01, an electrical voltage of at least 10 kV, more preferably at least 15 kV, even more preferably at least 20 kV, even more preferably at least 25 kV and even more preferably at least 30 kV is present between the at least one charging electrode 04 and a grounded object - for example the central cylinder 07 serving as counter electrode 06 - and independently of this, preferably at most 45 kV and more preferably at most 40 kV and even more preferably at most 35 kV.

[0038] The at least one charging electrode 04 is preferably designed as a needle 04. Each such needle 04 has a tip. For each such tip, there are at least two mutually orthogonal sectional planes in which the sectional surface of the tip has a radius of curvature that is less than 0.5 mm, more preferably less than 0.2 mm, and even more preferably less than 0.1 mm. The at least one charging device 03 preferably has at least 20 charging electrodes 04, more preferably at least 50 charging electrodes 04, even more preferably at least 100 charging electrodes 04, and even more preferably at least 200 charging electrodes 04. For example, these charging electrodes 04 are arranged next to one another in the transverse direction A. This allows the printing substrate 02 to be charged particularly evenly.

[0039] The at least one print head 09 and, if present, preferably also further print heads 09 are arranged in particular radially aligned with the cylinder 07 or central cylinder 07. The at least one charging device 03 has the at least one charging electrode 04, which is preferably arranged outside the cylinder 07 or central cylinder 07, viewed in the radial direction. For example, the central cylinder 07 serves as the counter electrode 06 of the at least one charging device 03.

[0040] Preferably, the at least one charging device 03 is arranged first along a transport path provided for transporting printing substrate 02, followed by the at least one print head 09. A region of the transport path provided for transporting printing substrate 02 that is closest to the at least one charging electrode 04 is preferably arranged in front of a printing point 11 defined by the at least one print head 09. A printing point 11 is in particular the region in which drops ejected by the at least one print head 09 can impact the printing substrate 02 as planned when the at least one print head 09 is controlled accordingly.Preferably, the smallest distance b between at least one and preferably each ejection opening 12 of the at least one print head 09 and the contact surface 08, in particular in a working position of the at least one print head 09, is at least 0.1 mm, more preferably at least 0.2 mm, even more preferably at least 0.5 mm and even more preferably at least 0.9 mm and, independently thereof, preferably at most 5 mm, more preferably at most 2 mm, even more preferably at most 1.5 mm and even more preferably at most 1.1 mm. The working position is in particular the position in which the respective print head 09 is scheduled to be arranged during regular printing operation. Preferably, a region of the transport path provided for the transport of printing substrate 02 that is closest to the at least one charging electrode 04 is a region in which contact is provided between printing substrate 02 and central cylinder 07.

[0041] Preferably, a last print head 09 of the printing press 01 along the transport path provided for the transport of printing material 02 is followed by a section of this transport path which has a minimum distance of at least 150 mm, more preferably at least 200 mm, even more preferably at least 500 mm and even more preferably at least 1000 mm from each electrode provided for emitting ions 16.

[0042] For example, under appropriate geometric conditions, at least one additional charging device can be arranged after a first and before a last print head 09 of the printing press 01 in order to counteract excessively rapid discharging of the printing material.

[0043] The printing press 01 preferably has a printing material delivery device 13, which is designed, for example, as a winding device 13 and / or cutting device 13 and / or folding device 13. Web-shaped printing material 02 can be transported, for example, by means of deflecting, actively or passively driven rollers and / or cylinders and / or stationary guide elements and / or conveyor belts and / or suction systems. List of reference symbols 01 Printing machine, Non-impact printing machine, Inkjet printing machine, Web printing machine 02 Printing material 03 Charging device, direct current charging device 04 Charging electrode, DC electrode (03), needle 05 - 06 Counter electrode 07 Support element, cylinder, central cylinder, substrate guide element 08 Contact surface 09 Print head, inkjet print head 10 - 11 pressure point 12 Ejection opening 13 Printing material delivery device, winding device, cutting device, folding device 14 Roll unwinding device, roll changer 15 - 16 Ion a distance b distance c distance

Claims

[1] Printing machine (01) designed as a non-impact printing machine (01), wherein the printing machine (01) has at least one print head (09) and wherein the printing machine (01) has a printing material source (14) designed as a roll unwinding device (14), and wherein the printing machine (01) is assigned a transport path provided for transporting printing material (02), and wherein the printing machine (01) has at least one central cylinder (07) serving as a printing material guide element (07), to which the at least one print head (09) is arranged aligned, and wherein the printing machine (01) has at least one charging device (03),which has at least one charging electrode (04) designed as a DC voltage electrode (04), and wherein a region of the transport path provided for the transport of printing material (02) closest to the at least one charging electrode (04) is arranged in front of a printing point (11) defined by the at least one print head (09), and wherein the at least one central cylinder (07) is grounded, and wherein the at least one print head (09) is grounded, and wherein a smallest distance (c) between at least one ejection opening (12) of the at least one print head (09) and the at least one charging electrode (04) is at least 20 mm, and wherein a section of the transport path provided for the transport of printing material (02) adjoins a last print head (09) of the printing press (01), which section has a minimum distance of at least 150 mm from each electrode provided for emitting ions. [2] Printing machine according to claim 1, characterized bythat a smallest distance (a) between the at least one charging electrode (04) of the charging device (03) and a contact surface (08) of the central cylinder (07) is at least 10 mm. [3] Printing machine according to claim 1 or 2, characterized by that the at least one charging device (03) has at least 20 charging electrodes (04). [4] Printing machine according to claim 1 or 2 or 3, characterized by that the at least one charging device (03) is designed to generate a maximum voltage of at least 10 kV. [5] Printing machine according to claim 1 or 2 or 3 or 4, characterized by that a region of the transport path provided for the transport of printing material (02) closest to the at least one charging electrode (04) is a region in which contact is provided between the printing material (02) and the central cylinder (07). [6] Printing machine according to claim 1 or 2 or 3 or 4 or 5, characterized bythat the at least one print head (09) is designed as a print head (09) which is arranged in a fixed position during printing operation. [7] Printing machine according to claim 1 or 2 or 3 or 4 or 5 or 6, characterized by that a smallest distance (b) between at least one ejection opening (12) of the at least one print head (09) and a contact surface (08) of the central cylinder (07) is at least 0.1 mm. [8] Printing machine according to claim 1 or 2 or 3 or 4 or 5 or 6 or 7, characterized by that the printing machine (01) is designed as an inkjet printing machine (01) and / or that the at least one print head (09) is designed as an inkjet print head (09). [9] Printing machine according to claim 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8, characterized by that a base body of the central cylinder (07) consists of carbon fiber reinforced plastic. [10] Printing machine according to claim 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9, characterized by that a contact surface (08) of the central cylinder (07) intended for contact with printing material (02) is formed from a material which has an electrical conductivity of at least 1,000 S / m (one thousand Siemens per meter). [11] Printing machine according to claim 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9, characterized by that a contact surface (08) of the central cylinder (07) intended for contact with printing material (02) is formed from a material which has an electrical conductivity of at most 10 S / m (ten Siemens per meter).

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