Printing module

Abstract

The invention relates to a flexographic printing module configured to print on sheets. The flexographic printing module comprising a plurality of flexographic printing units, wherein each flexographic printing unit is provided with a printing plate in the form of a belt, and wherein each flexographic printing unit comprises a belt-carrying assembly comprising an upper print roller and a lower print roller, and wherein the printing plate is suspended around the belt-carrying assembly, the flexographic printing further comprises a transfer module having a continuous transportation conveyor which extends through all of the flexographic printing units in said flexographic printing module.

Description

[0001] PRINTING MODULE

[0002] Field of the invention

[0003] The present invention relates to a converting machine for printing sheets or producing flat-packed or folding boxes. In particular, the invention relates to a printing module for a converting machine.

[0004] Background of the invention

[0005] Converting machines such as rotary die cutting machines can be configured to produce flat-packed or folding boxes. These converting machines are fed with sheets and are configured to print, cut and score the sheets to form flat-packed boxes and similar packaging elements. These packaging elements can subsequently be folded and assembled into three-dimensional boxes.

[0006] The boxes often need to be provided with a printed motif or pattern. To allow printing with several colors and coatings such as varnishes, the converting machine comprises a plurality of printing modules, such as flexographic or offset printing modules.

[0007] Each printing unit may comprise a flexographic printing assembly which comprises a printing cylinder around which a printing plate is wrapped, an anilox cylinder and an ink supply device such as a doctor blade chamber which transfers the ink to the printing plate.

[0008] When using several printing units, the distance from the first printing unit to the last printing unit can be several meters long. This may cause some local variations in the transportation speeds along the distance and may lead to the print becoming “off register”. Hence, the printed pattern from one printing cylinder is not aligned with the printed pattern from another printing cylinder.

[0009] Summary

[0010] In view of the above-mentioned problems, it is an object of the present invention to provide a printing module which reduces the register shifts. This object is solved by a printing module according to claim 1 and a converting machine according to claim 13. Other optional features and advantageous embodiments of the invention are detailed in the appended dependent claims.

[0011] According to a first aspect of the present invention, there is provided a flexographic printing module configured to print on sheets. The printing module comprises a plurality of flexographic printing units, wherein each flexographic printing unit is provided with a printing plate in the form of a belt. Each flexographic printing unit comprises a belt-carrying assembly comprising an upper print roller and a lower print roller, and wherein the printing plate is suspended around the belt-carrying assembly. The flexographic printing further comprises a transfer module having a continuous transportation conveyor which extends through all of the flexographic printing units in said flexographic printing module.

[0012] The present invention is based on a realization that the horizontal space of each printing assembly can be reduced by designing a printing plate carrying assembly which allows a non-circular support of the printing plate.

[0013] This provides a shorter transfer module, which also allows a reduction in the overall size of the transfer module, a reduced energy consumption and reduced noise.

[0014] Brief description of the drawings

[0015] The invention will now be described by way of example and with reference to embodiments shown in the enclosed drawings, where the same reference numerals will be used for similar elements and in which:

[0016] Figure 1 is a schematic view of a converting machine in the configuration of a flexo- folder-gluer;

[0017] Figure 2 is a schematic view of a converting machine in the configuration of a rotary die-cutter;

[0018] Figure 3a is a schematic top view of a flat-packed box;

[0019] Figure 3b is a schematic perspective view of a folded-slotted box;

[0020] Figure 4 is a schematic diagram of the a converting machine with a plurality of transfer units; Figure 5 is an exemplary embodiment of a vacuum transfer unit;

[0021] Figures 6a to 6c are schematic diagrams of a printing module according to embodiments of the present invention;

[0022] Figure 7 is a detailed diagram of a printing plate and its assembly according to an embodiment of the present invention;

[0023] Figure 8 is a schematic diagram illustrating a lateral displacement of the printing assembly according to an embodiment of the present invention; and

[0024] Figure 9 is a schematic perspective view of a printing cassette and an associated chassis.

[0025] Detailed description

[0026] Referring to figures 3a and 3b, which respectively illustrate examples of packaging elements in the form of a flat-packed box 2a and a folded slotted box 2b. These packaging elements can be produced in converting machines 1 , such as the ones illustrated in figures 1 and 2.

[0027] Sheets 2 of cardboard, paperboard or like are placed in a feeder module 12 of these converting machines 1 . The converting machines 1 are configured to print and cut the sheets 2 to a shape which allows the formation of a packaging elements 2’ such as flat-packed boxes 2a or folded-slotted boxes 2b.

[0028] The converting machine 1 illustrated in figure 1 is in the configuration of a rotary die-cutter machine. The rotary die-cutter machine 1 comprises a plurality of different work modules which print, cut and crease the sheets 2. From the inlet of the converting machine 1 and in the direction of transportation T of the sheets 2, the converting machine 1 may comprise a prefeeder 10, a feeder module 12, printing module 13 comprising a plurality of flexographic printing modules 14, a converting module 16 in the form of a die-cutting module, and a delivery module 20. The converting machine 1 further comprises a main control circuitry 15, and an operator interface 11 may also be provided in the proximity of the converting machine 1.

[0029] The direction of transportation T is defined from the inlet to the outlet of the converting machine 1 . Hence, the direction of transportation T extends from the feeder module 12 to the delivery module 20. The sheets 2 are transported along a transportation path P, which can be defined as the trajectory of the sheet 1 through the converting machine 1.

[0030] The converting machine 1 illustrated in figure 2 is in the configuration of a flexo- folder gluer. This converting machine 1 is similarly configured as the rotary diecutter converting machine. However, the converting module 16 of the flexo-folder machine comprises a slotter module 16 instead of a rotary die-cutter 16.

[0031] In a non-illustrated embodiment, the converting machine 1 may be in the form of a flexographic printing press. Such a flexographic printing press may be configured to only print a sheet (and not provide any shaping operations such as cutting and creasing).

[0032] As the sheet 2 is transported in the direction of transportation T, it undergoes a transformation to become a cut-to-shaped blank 2 and then a packaging element. Within the context of this application, the term “sheet element” can be used when referring to a sheet 2 or a cut-to-shaped blank 2.

[0033] As illustrated in figure 4, the converting machine 1 comprises a conveying system 26 configured to transport the sheets 2 through the converting machine 1 in the direction of transportation T. The conveying system 26 may comprise a plurality of separate transportation segments 28, referred to as transfer units 28. In particular, the conveying system 26 may comprise a plurality of transfer units 28 in the configuration of vacuum transfers 28.

[0034] As illustrated in figure 5, some vacuum transfers 28 may comprise drive elements 30 such as endless belt conveyors or rollers which are configured to convey the sheets 2 through the converting machine 1 .

[0035] As best seen in figure 6c, the drive elements 30 may be partly received in a housing shroud 32 forming at least one suction box. The suction box is connected to a vacuum generator 34. A suction force is applied around the drive elements 30, which maintains the sheets 2 firmly against the drive elements 30. The vacuum transfers 28 may be configured to grasp and transport the sheets 2 on either the top or the bottom side of the sheet 2. Now referring to figures 6a to 8, which illustrate embodiments of a printing module 40 according to an embodiment of the present invention.

[0036] As best seen in figure 6a, the printing module 40 comprises a transfer unit 28 and a plurality of flexographic printing units 42, arranged one after the other in the direction of transportation T. Each flexographic printing unit 42 comprises a printing plate 44, a printing plate carrying assembly 46, an anilox cylinder 48, a counter cylinder 50, and an inking device 51 , which may comprise a doctor blade 52 and a doctor blade chamber 53. The printing plate carrying assembly 46 comprises an upper printing cylinder 54 and a lower printing cylinder 56. The counter cylinder 50 is arranged vertically below the lower printing cylinder 56.

[0037] As best seen in figure 7, the flexographic printing unit 42 may further comprise a carrying belt 58 suspended around the upper printing cylinder 54 and the lower printing cylinder 56.

[0038] The carrying belt 58 is provided with a fastening assembly 60 such that a printing plate 44 can be connected thereto. The fastening assembly 60 may comprise first magnetic element 60a attached to the carrying belt 58, and a second magnetic element 60b attached to the printing plate 44. Preferably, the printing plate 44 comprises a metallic element 60b and the carrying belt 58 comprises a magnetic element 60a. In an alternative embodiment (non-illustrated), the printing plate 44 may be provided with an elongated ridge which is designed to connect to an elongated slot in the carrying belt 58.

[0039] The anilox cylinder 48 and the inking device 51 are arranged at the upper printing cylinder 54. In such a way, ink is supplied to the printing plate 44 as the printing plate 44 contacts the anilox cylinder 48.

[0040] The lower printing cylinder 56 and counter cylinder 50 are configured to apply pression to the sheet 2 as the sheet 2 passes in-between the lower print cylinder 56 and the counter cylinder 50. In such a way, the motif on the printing plate 44 is transferred onto the sheet 2.

[0041] Optionally, as illustrated in figure 6b, the converting machine 1 may further comprise a digital printing unit 43, such as an inkjet printing unit 43. The digital printing module 43 may be located upstream (in the direction of transportation T) of the first flexographic printing unit 42. In an embodiment, the digital printing unit 42 is integrated into the printing module 40. In such a way, the digital printing unit

[0042] 43 and the flexographic digital printing units are positioned above the same transfer unit 28.

[0043] At least one of the upper and lower printing cylinders 54, 56 is a motorized roller. Preferably, the lower printing cylinder 54 is motorized. This enables a precise control of its tangential speed against the sheet 2. The upper printing cylinder 54 may be idle.

[0044] As best seen in figures 6a and 6b, each flexographic printing unit 42 may be mounted in two separate assemblies: an upper printing assembly 42a and a lower printing assembly 42b.

[0045] The upper printing assembly 42a comprises the printing plate carrying assembly 46 including the upper printing cylinder 54 and the lower printing cylinder 56, the printing plate 44, and the inking device 51. In the illustrated embodiment, the transfer unit 28 is located vertically below the upper flexographic printing assemblies 42a.

[0046] Preferably, each upper printing assembly 42a may be mounted in a separate cassette 45. The term “cassette” can be defined as a structural frame 45 comprising brackets 47 for connecting to the upper and lower printing cylinders 54, 56 and the inking device 51 .

[0047] The cassette 45 may be vertically displaceable in relation to the lower printing assembly 42b. Hence, each cassette 45 may be individually displaceable in the vertical direction V.

[0048] As illustrated in figure 9, each upper cassette 45 is mounted to a chassis 74. A vertical displacement mechanism may be provided between the cassette and the chassis. The vertical displacement mechanism may comprise a motor and an actuator (not illustrated). The vertical displacement mechanism allows a vertical displacement of the cassette 45.

[0049] This allows adjusting the vertical position of the lower print roller 56 and thus adjusting the printing gap D1 (see fig. 6c), which will be further described below. Additionally, this may also enable disabling a specific printing unit 42 if needed by moving the lower printing cylinder away from the blank. Referring back to figures 6a and 6b, the transfer unit 28 may comprise a transportation conveyor 29 in the form of a conveyor belt 29 having an inlet end 31a and an outlet end 31b. The inlet end 31a may be defined by a counter cylinder 50a of a first flexographic printing unit 42, and the outlet end 31b is end is defined by a counter cylinder 50b of a last flexographic printing unit 42 in the printing module 40.

[0050] As illustrated in figure 6c, the transportation conveyor 29 may be located in a vacuum suction box 32. The transportation conveyor 29 may be provided with apertures in the form of suction openings.

[0051] The counter-cylinder 50 of each printing unit 42 is pressing against an inner periphery of the conveyor belt 29. In such a way, a contact pressure is established between the conveyor belt 29 and the printing plate 44 such as to transfer the printed motif onto the sheet 2.

[0052] The inlet counter cylinder 50a and the outlet counter cylinder 50b are respectively vertically aligned with the respective first 56a and last lower print rollers 56b. The transportation conveyor 29 may thus only extend over a distance D from the inlet counter cylinder 50a to the outlet counter cylinder 50b. The transportation conveyor 29 may be driven by the counter cylinders 50. To this effect, an inner periphery of the conveyor belt 29 may be provided with a dented surface configured to engage with a corresponding dented surface of the counter cylinders 50.

[0053] The lower printing assembly 42b comprises the counter-cylinder 50. In an embodiment, all counter cylinders 50 from the different printing units 42 may be attached to a common chassis 70. In such a way, the horizontal position of the counter cylinders 50 can be fixed. Additionally, all counter cylinders 50 can be positioned at an equal vertical distance from the sheet 2. This facilitates the calibration of an equal printing gap D1 in all of the flexographic printing units 42.

[0054] The lower counter cylinders 50 may be connected to a common drive mechanism comprising pulleys connected to a common output shaft of a motor. The conveyor belt 29 and all of the counter cylinders 50 may be driven in unison by the same motor.

[0055] In the embodiment illustrated in figures 6a to 6c, the printing gap D1 corresponds to the distance between the printing plate 44 and the conveyor belt 29 of the transfer module 28. The printing gap D1 is thus the clearance through which the sheet 2 passes.

[0056] Each cassette 45 may be laterally displaceable such that the cassette 45 can be positioned in a “service position” laterally of the transfer unit 28. In such a way, access to the printing plate 44 and the anilox cylinders 48 is facilitated.

[0057] A specific printing unit 42 can be selectively disabled by providing an upward adjustment of its vertical position. The specific printing unit 42 may be further displaced into the service position. In such a way, a change of a printing plate 44 or an anilox cylinder 48 can be performed while the other printing units 42 are in operation.

[0058] As illustrated in figures 8 and 9, the cassette 45 may be connected to the chassis 74 in a sliding connection comprising cooperating engagement elements 75a on the cassette and cooperating engagement elements 75b on the chassis 74.

[0059] The cassette 45 preferably is connected to a lateral displacement mechanism 100 configured to displace the cassette 45 laterally, in a lateral direction L perpendicular to the direction of transportation T.

[0060] The task of changing anilox cylinders 48 often involves at least two operators and a mechanical device to help support the weight of the anilox cylinder 48.

[0061] In an embodiment, an anilox handling carriage is provided with a circulation path arranged laterally of the printing module 40. In such a way, the anilox handling carriage may be activated and operated when a cassette 45 is laterally displaced and a command of changing anilox cylinders has been entered into or determined by the main control circuitry 15 of the converting machine 1 .

[0062] As illustrated in figure 6a, a feed sensor 110 may be arranged between the feeder module 12 and the flexographic printing module 40. The feed sensor 110 may be included in a register control system further comprising a control circuitry having a control unit and a memory.

[0063] The feed sensor 110 is positioned between the outlet of the feeder module and the inlet of the printing module 40. The feed sensor 110 is configured to detect the passage and register position of each sheet 2 as it comes out from the feeder module 12. The feed sensor 110 is preferably an optical sensor which detects the passage of the leading edge of the sheet 2. The control unit may calculate a feeder register displacement and provide a control signal if the feeder register displacement exceeds a tolerance threshold.

[0064] The present invention is not limited by the illustrated embodiments. For example, in a non-illustrated embodiment, the transfer unit 28 of the flexographic printing module may comprise a plurality of conveyor belts 29 arranged side by side in the lateral direction L. Alternatively, the transfer unit 28 may comprise a plurality of drive rollers. The drive rollers are driven in unison by a common motor. A plurality of counter-cylinders 50 is arranged in-between the drive rollers. In these two alternative embodiments, the counter cylinders 50 are pressing directly against the printing plate 44.

[0065] Additionally, the principle of vertically disabling a cassette containing an upper flexographic printing assembly, and displacing the cassette into a lateral service position with a lateral displacement mechanism can also be applied to a “standard” flexographic printing assembly. Hence, a “standard” flexographic printing assembly comprises a printing cylinder around which the printing plate is mounted. Additionally, the anilox handling carriage with a circulation path arranged laterally of the flexographic printing module, can also be applied to “standard” flexographic printing assemblies integrated with such vertical and lateral displacement mechanism.

Claims

CLAIMS1. A flexographic printing module configured to print on sheets, the flexographic printing module comprising a plurality of flexographic printing units, wherein each flexographic printing unit is provided with a printing plate in the form of a belt, and wherein each flexographic printing unit comprises a belt-carrying assembly comprising an upper print roller and a lower print roller, and wherein the printing plate is suspended around the belt-carrying assembly, the flexographic printing module further comprises a transfer module having a continuous transportation conveyor which extends through all of the flexographic printing units in said flexographic printing module.

2. The flexographic printing module according to claim 1, wherein the printing plate is attached with a fastener to a carrying belt.

3. The flexographic printing module according to claim 2, wherein the fastener is a magnetic fastener or a mechanical fastener.

4. The flexographic printing module according to any one of the preceding claims, wherein the continuous transportation conveyor is received in a vacuum suction box.

5. The flexographic printing module according to any one of the preceding claims, wherein one of the upper and lower print rollers is a driven roller, and wherein preferably the lower print roller is the driven roller while the upper print roller is idle.

6. The flexographic printing module according to any one of the preceding claims, wherein each flexographic printing unit comprises an upper printing assembly and a lower printing assembly, and wherein the upper printing assembly comprises the upper printing cylinder, the lower printing cylinder, the printing plate, and an inking device, and wherein each upper printing assembly is mounted in a chassis in the form of a cassette, which excludes the counter cylinder.

7. The flexographic printing module according to the preceding claim, wherein each cassette is connected to a lateral displacement arrangement, wherein said lateral displacement arrangement is configured to enable a displacement of the cassette such that it is offset in relation to the continuous transportation conveyor.

8. The flexographic printing module according to the preceding claim, wherein the lateral displacement arrangement comprises a slide rail.

9. The flexographic printing module according to the preceding claim, wherein the lateral displacement arrangement comprises a displacement motor configured to displace the cassette.

10. The flexographic printing module according to any one of the preceding claims, wherein each chassis is vertically displaceable in relation to the continuous transportation conveyor.11 . The flexographic printing module according to any one of the preceding claims, wherein the counter-cylinders of each flexographic printing unit are mounted in a common chassis.

12. The flexographic printing module according to any one of the preceding claims, wherein the continuous transportation conveyor is a conveyor belt, and wherein the counter cylinders are indirectly contacting the sheet by pressing onto an inner periphery of the conveyor belt.

13. A converting machine comprising the printing module according to any one of the preceding claims, the converting machine further comprises a cutting and creasing module.

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