Digital printing machine

Abstract

In a digital printing press, printheads (1) apply different colored inks to a circulating transfer belt (2) using inkjet technology. The transfer belt (2) transfers the collected inks as a printed image in a printing slit (6) onto a substrate. On the inside of the transfer belt (2), it is supported by support elements that stabilize the transfer belt (2) in the area of ​​the printheads (1). The support elements are designed as trays (13) that have suction surfaces (15) for drawing in the transfer belt (2) and circulate as a chain.

Description

[0001] The present invention relates to a digital printing machine in which printheads apply different colored inks to a circulating transfer belt by means of an inkjet and the transfer belt transfers the collected inks as a printed image in a printing gap onto a substrate, wherein the transfer belt is supported on its inside by support elements that stabilize the transfer belt in the area of ​​the printheads.

[0002] The printing process carried out with such digital printing machines is also called indirect inkjet printing because the ink from the print heads is not directly ejected onto the substrate.

[0003] Such digital printing presses are described in US 10,703,093 B2 and US 10,994,528 B1. In these machines of the aforementioned prior art, the support elements are designed as rollers. Driving the rollers in such a way as to ensure high registration accuracy between the different colors in the printed image is technically very complex and is still not achieved to a sufficient degree.

[0004] German patent DE 10 2019 205 295 A1 describes a digital printing machine that does not correspond to the aforementioned type. This machine uses the direct inkjet printing process, in which the ink is ejected directly from the printheads onto the substrate. Therefore, the aforementioned type of printing only represents a further stage of the art. The substrate is transported on a continuous belt supported by trays forming a chain.

[0005] The object of the invention is to create another digital printing machine suitable for indirect inkjet printing.

[0006] The problem is solved by a digital printing machine in which printheads apply different colored inks to a circulating transfer belt by means of an inkjet, and the transfer belt transfers the collected inks as a printed image in a printing slit onto a substrate, wherein the transfer belt is supported on its inside by support elements that stabilize the transfer belt in the area of ​​the printheads, characterized in that the support elements are designed as trays that have suction surfaces for suctioning the transfer belt and circulate as a chain.

[0007] A particular advantage of the digital printing machine according to the invention is that a sufficiently high accuracy of registration between the different colors in the printed image on the transfer tape is ensured.

[0008] The following further training options are possible: An electric linear motor can be arranged to drive the trays.

[0009] The trays can incorporate permanent magnets for the linear motor.

[0010] The transfer belt, together with a circulating conveyor belt that transports the printing material, can form the printing gap.

[0011] The printing material can be formed from sheets.

[0012] Further information can also be obtained from the following description of an exemplary embodiment and the associated drawing.

[0013] Their only Figure 1 shows the diagram of a digital printing machine.

[0014] The digital printing press includes printheads 1 for multi-color inkjet printing. The printheads 1 apply the inks to a transfer belt 2, which rotates around rollers 4 in the ink transport direction 3. The multi-colored inks collected on the transfer belt 2 are partially dried by a dryer 5 and then transferred from the transfer belt 2 to sheets 7 in a printing nip 6. The printing nip 6 is formed by the transfer belt 2 together with a transport belt 8, which rotates around rollers 10 in the sheet transport direction 9. The sheets 7 are transported sequentially through the printing nip 6 on the transport belt 8 and receive their multi-colored print image from the transfer belt 2. In the area of ​​the printing nip 6, the transfer belt is supported by a roller 11 and the transport belt 8 by a roller 12.

[0015] The transfer belt 2 is driven by a chain of trays 13 that rotate around a ring track 14. Each tray 13 has a suction surface 15 with one or more vacuum openings and thus draws suction onto the transfer belt 2 in the area of ​​the printheads 1. In the area of ​​the printheads 1, the suction surfaces 15 run in contact with the inner surface of the transfer belt 2 and without relative velocity between the tray 13 and the transfer belt 2, or synchronously with it, along a linear track section. The rotational motion of the trays 13 is thereby transferred to the transfer belt 2; the transfer belt 2 is carried along by the trays 13 and thus driven.

[0016] The chain formed from the articulated trays 13 is driven by a drive unit. This unit can, for example, be designed such that a permanent magnet 16 is integrated into each tray 13, which interacts with the coil-equipped stator of an electric linear motor 17. This causes the linear motor 17 to drive the trays 13 forward parallel to the ink transport direction 3.

[0017] The advantage is that the pneumatic fixation of the elastomer-based transfer belt 2 on the flat suction surfaces 15 of the trays 13 during their entire transit time in the target area of ​​the printheads 1 avoids deformations of the transfer belt 2 and resulting registration errors between the different colored ink prints of the printheads 1 on the transfer belt 2.

[0018] Due to the high rigidity of the chain formed from the trays 13, an equal speed of the trays 13 and thus of the ink-receiving belt sections under the printheads 1 is ensured.

[0019] The following modifications are possible: Instead of the permanent magnets 16 and the linear motor 17, the drive device can consist of a suction belt arranged within the orbit of the transmission belt 2, which sucks in the transmission belt 2 and transmits its orbital motion to it.

[0020] The transport of the sheets 7 through the printing gap 6 can take place directly through the roller 12 instead of through the conveyor belt 8, whereby the roller is equipped with suction or clamping grippers to hold the sheets 7 and the conveyor belt 8 is omitted.

[0021] The machine can be designed for web-shaped (roll printing) substrate instead of sheet-shaped. Reference symbol list

[0022] 1 Printhead 2 Transfer belt 3 Ink transport direction 4 Roller 5 Dryer 6 Print gap 7 Sheet 8 Transport belt 9 Sheet transport direction 10 Roller 11 Roller 12 Roller 13 Tray 14 Ring track 15 Suction surface 16 Permanent magnet 17 Linear motor

Claims

1. Digital printing machine in which printheads (1) apply different colored inks to a circulating transfer belt (2) by means of inkjet technology and the transfer belt (2) transfers the collected inks as a printed image in a printing slit (6) onto a substrate, wherein the transfer belt (2) is supported on its inner side by support elements that stabilize the transfer belt (2) in the area of ​​the printheads (1), characterized by that the support elements are designed as trays (13) which have suction surfaces (15) for suctioning the transmission belt (2) and are arranged as a chain.

2. Device according to claim 1, characterized by that An electric linear motor (17) is arranged to drive the trays (13).

3. Device according to claim 2, characterized by that The trays (13) contain permanent magnets (16) of the linear motor (17).

4. Device according to one of claims 1 to 3, characterized by that the transfer belt (2) together with a circulating transport belt (8), which transports the printing material, forms the printing gap (6).

5. Device according to one of claims 1 to 4, characterized by that the substrate is formed by sheets (7).

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