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EP-4735258-A1 - PRINTING ASSEMBLY

EP4735258A1EP 4735258 A1EP4735258 A1EP 4735258A1EP-4735258-A1

Abstract

A printing assembly (12) for a flexographic printing device (10) is proviced, comprising a doctor blade (20), an anilox roll (18), a printing cylinder (14) and a central drum (22), wherein the printing cylinder (14) is surrounded by a printing cliché (16), and wherein the printing assembly (12) comprises two support rings (32) arranged on opposite ends of the printing cylinder (14) outside the printing cliché (16), the outer diameter of the support rings (32) being bigger than the diameter of the printing cylinder (14).

Inventors

  • Karakatsanis, Michael

Assignees

  • Bobst Bielefeld GmbH

Dates

Publication Date
20260506
Application Date
20240625

Claims (7)

  1. 1. A printing assembly (12) for a flexographic printing device (10), comprising a doctor blade (20), an anilox roll (18), a printing cylinder (14) and a central drum (22), wherein the printing cylinder (14) is surrounded by a printing cliche (16), and wherein the printing assembly (12) comprises two support rings (32) arranged on opposite ends of the printing cylinder (14) outside the printing cliche (16), the outer diameter of the support rings (32) being bigger than the diameter of the printing cylinder (14).
  2. 2. The printing assembly (12) according to claim 1, wherein the support rings (32) are releasably attached to the printing cylinder (14).
  3. 3. The printing assembly (12) according to any of the preceding claims, wherein the support rings (32) comprise a compressible layer (34) at their outer circumference or consist of a compressible layer (34).
  4. 4. The printing assembly (12) according to claim 3, wherein the compressible layer (34) has a thickness of 0.1 mm to 0.5 mm.
  5. 5. The printing assembly (12) according to any of the preceding claims, wherein a sleeve (30) is arranged between the printing cylinder (14) and the printing cliche (16) and wherein the support rings (32) are arranged on the sleeve (30).
  6. 6. The printing assembly (12) according to any of the preceding claims, wherein the length of the anilox roll (18) is longer than the length of the printing cliche (16) and the support rings (32) are in rolling engagement with the anilox roll (18).
  7. 7. The printing assembly (12) according to any of the preceding claims, wherein the length of the central drum (22) is longer than the length of the printing cliche (16) and the support rings (32) are in rolling engagement with the central drum (22).

Description

Printing assembly The invention relates to a printing assembly for a flexographic printing device. Flexographic printing devices comprise a printing cylinder which carries the printing cliche, an anilox roll for applying ink to the printing cliche, a doctor blade for removing excessive ink from the anilox roll, and a central drum which drives the print medium to be printed by the printing cliche. Depending on the image to be printed, the printing cliche does not necessarily have a regularly distributed relief. In particular, it could be the case that some areas of the printing cliche do not contain any relief at all. This results in an insufficient support of the printing cylinder which could lead to an irregular rotation and bouncing of the print cylinder during operation of the flexographic printing device. To avoid bouncing of the printing cylinder, it is known to design the printing cliche with additional support structures at opposing lateral edges of the printing cliche. However, these support structures show in the print and have to be cut away after the printing job, which results in a high effort as well as in a waste of material. It is thus an object of the present invention to avoid bouncing of the printing cylinder in an optimized manner. This object is achieved by a printing assembly for a flexographic printing device, comprising a doctor blade chamber, an anilox roll, a printing cylinder and a central drum, wherein the printing cylinder is surrounded by a printing cliche and wherein the printing assembly comprises two support rings arranged on opposite ends of the printing cylinder outside the printing cliche, the outer diameter of the support rings being bigger than the diameter of the printing cylinder. Due to the support rings, a regular form is provided which results in a stable support of the print cylinder such that irregular rotation and bouncing is avoided. This results in a high printing quality. Another advantage is that due to the avoidance of irregular rotation and bouncing, the rotation speed of the printing cylinder can be higher than in regular printing devices without support rings. The support rings are not part of the printing cliche and are thus not visible in the print, such that no cutting of the print medium is necessary after printing. In particular, the support rings extend over the outer circumference of the printing cylinder. In other words, the outer diameter of the support rings is larger than the outer diameter of the printing cylinder. At least one of the support rings can be releasably attached to the printing cylinder. Thus, the support ring can be easily detached from the printing cylinder when the printing cliche has to be exchanged for a new printing job. According to one embodiment, the support rings comprise a compressible layer at their outer circumference or consist of a compressible layer. Thereby, the support rings have a dampening function. Also, a tolerance compensation is possible to a certain extent, in particular with regard to a diameter of the support rings as well as with regard to a rotation accuracy. The compressible layer has for example a thickness of 0.1 mm to 0.5 mm. Thus, a sufficient compression of the support rings is possible. A sleeve may be arranged between the printing cylinder and the printing cliche and the support rings may be arranged on the sleeve. The sleeve serves as an adapter for adapting the diameter of the printing cylinder such that different printing cliches can be attached to the printing cylinder. Preferably, the length of the anilox roll is longer than the length of the printing cliche and the support rings are in rolling engagement with the anilox roll. Thereby, a continuous contact between the support rings and the anilox is achieved. The length of the central drum may be longer than the length of the printing cliche, and the support rings are in rolling engagement with the central drum. In the same manner as with the rolling engagement with the anilox roll, the rolling engagement of the support rings with the central drum results in a continuous contact between the support rings and the central drum. Due to the continuous contact with the anilox roll respectively the central drum, there are no run-up edges or run-off edges in the printing process. Further features and embodiments can be derived from the following description and the drawings. In the drawing: Figure 1 schematically shows a flexographic printing device, and Figure 2 shows a printing assembly according to the invention for the flexographic printing device of Figure 1 , with a lateral end of the printing assembly being shown in greater detail at an enlarged scale. Figure 1 shows a flexographic printing device 10 with a printing assembly 12. The printing assembly 12 comprises a printing cylinder 14 which carries a printing cliche 16 (see Figure 2), an anilox roll 18 for applying ink to the printing cliche 16, a doctor blade 20 for removing excess