APPARATUS FOR FLEXOGRAPHIC PRINTING AND AN INLET MODULE

Abstract

The present disclosure relates to an apparatus for flexographic printing of a web of packaging material with printing ink and an inlet module for a flexographic printing apparatus. The apparatus may include an ink pan or chamber, and an anilox roll rotary at least partly inside the ink chamber for picking up and transferring printing ink from the ink chamber to an impression cylinder which is rotary in transfer contact with the anilox roll. The ink chamber may be elongated and extend axially along the anilox roll, the ink chamber having a first axial end and a second axial end opposite the first axial end. The apparatus may further include a first printing ink inlet arranged at the first axial end and a second printing ink inlet arranged at the second axial end.

Claims

1. An apparatus for flexographic printing of a web of packaging material with printing ink, the apparatus comprising: an ink chamber; an anilox roll rotary at least partly inside the ink chamber, the anilox roll rotary configured for picking up and transferring printing ink from the ink chamber to an impression cylinder which is rotary in transfer contact with the anilox roll; wherein the ink chamber is elongated and extends axially along the anilox roll, and the ink chamber has a first axial end and a second axial end opposite the first axial end; and wherein the apparatus further comprises a first printing ink inlet arranged at the first axial end of the ink chamber and a second printing ink inlet arranged at the second axial end of the ink chamber.

2. The apparatus according to claim 1, wherein the first printing ink inlet and the second printing ink inlet are configured to direct printing ink at least partly parallel to the an axial extent of the anilox roll.

3. The apparatus according to claim 1, wherein each of the first printing ink inlet and the second printing ink inlet has an elongated exit.

4. The apparatus according to claim 3, wherein the elongated exit is elongated in an upright direction.

5. The apparatus according to claim 3, wherein each of the first printing ink inlet and the second printing ink inlet has an entry with the same cross-sectional area as the exit.

6. The apparatus according to claim 1, wherein each of the first printing ink inlet and the second printing ink inlet are substantially orthogonal.

7. The apparatus according to claim 5, wherein each of the first printing ink inlet and the second printing ink inlet has a channel extending substantially orthogonal between the entry and the elongated exit.

8. The apparatus according to claim 1, wherein the first printing ink inlet is formed in a first inlet module, and wherein the second printing ink inlet is formed in a second inlet module, wherein each of the first inlet module and second inlet module further comprise an anilox roll seal.

9. The apparatus according to claim 1, further comprising a printing ink reservoir, wherein each of the first printing ink inlet and the second printing ink inlet is fluidly connected to the printing ink reservoir via a conduit.

10. The apparatus according to claim 9, further comprising a printing ink pump configured to, during operation, pump printing ink from the printing ink reservoir to the first printing ink inlet and the second printing ink inlet via the conduit.

11. An inlet module for a flexographic printing apparatus, the inlet module comprising a circular entry, an elongated exit, and a channel extending substantially orthogonally between the entry and exit.

12. The inlet module according to claim 11, wherein the circular entry has the same cross-sectional area as the elongated exit.

13. The inlet module according to claim 11, wherein the inlet module further comprises an anilox roll seal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above objects, as well as additional objects, features and advantages of the present invention, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, when taken in conjunction with the accompanying drawings, wherein:

[0032] FIG. 1 is a perspective view of an apparatus known in the art;

[0033] FIG. 2 is a schematic side view of an apparatus known in the art for printing of a web of packaging material with printing ink;

[0034] FIG. 3 is a top view of an apparatus according to the present invention; and

[0035] FIG. 4a-d are views of an inlet module in accordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0036] In the present detailed description, embodiments of an apparatus for flexographic printing of a web of packaging material with printing ink are mainly discussed with reference schematic views showing an apparatus for flexographic printing of a web of packaging material with printing ink and a printing ink inlet according to various embodiments of the invention. It should be noted that this by no means limits the scope of the invention, which is also applicable in other circumstances for instance with other types or variants of apparatuses for flexographic printing of a web of packaging material with printing ink or devices than the embodiments shown in the appended drawings. Further, that specific components are mentioned in connection to an embodiment of the invention does not mean that those components cannot be used to an advantage together with other embodiments of the invention.

[0037] FIG. 1 illustrates a known prior art apparatus, disclosed in WO2013064415 which is hereby incorporated by reference, at least with regard to FIGS. 1 and 2, also disclosed therein for understanding the function of the prior art apparatus. The apparatus shown in FIG. 1 has an anilox roll 1, a printing cylinder in the form of an impression plate cylinder 2 (hereinafter designated impression cylinder) and an ink pan or chamber 3, the ink chamber being disposed axially along the one side of the anilox roll 1. The ink chamber 3 is defined by a first chamber wall 4, an upper and a lower doctor blade 5, 6, part of the circumferential surface 7 of the anilox roll 1, as well as by an end wall 8 at each respective axial end of the ink chamber 3. The first chamber wall 4 may be designed as a curved, C-shaped or U-shaped wall or as a planar wall, depending upon the length of the doctor blades 5, 6 employed and depending upon how the doctor blades are fixed at the first chamber wall. Suitably, the wall is designed as an integrated unit in which the doctor blades are secured.

[0038] In order to maintain uniform quality and uniform properties of the printing ink, the ink is circulated continuously through the ink chamber 3 by the intermediary of an inlet 9 and fills up the ink chamber to a predetermined level 10, before being led out of the chamber by the intermediary of an outlet 11. The viscosity, temperature and homogeneity of the printing ink are regulated in an external unit 12 (only illustrated schematically), including e.g. agitators and temperature control. It is important that printing ink be transferred to the impression cylinder 2 from the anilox roll 1 in a uniform quantity and with uniform quality, so that no differences occur in printing result between different regions of the printed web. In such instance, the continuous circulation of printing ink monitors and regulates the printing ink in respect of important properties, regardless of whether the printing process is in operation or whether the printing unit for some reason is inoperative. The anilox roll 1 will be constantly kept wet and filled with printing ink and be uniformly coated with ink also in stationary downtime, so that the ink does not dry and occasion problems in later printing processes. The printing ink is led into the ink chamber 3 by the intermediary of an inlet 9 in or close to the bottom of the ink chamber and out of the chamber by the intermediary of an outlet 11 on a level just above the maximum level 10 to which printing ink is intended to be filled in the chamber.

[0039] The end wall 8 is disposed such that the edge which faces towards the surface of the anilox roll 1 adheres to the configuration of the anilox roll but at a distance from the circumferential surface 7 of the anilox roll. Between the circumferential surface 7 of the anilox roll 1 and the edge of the end wall 8 there is thus a gap which may have a width of from approximately 0.5 mm to approximately 2 mm, preferably from approximately 0.5 mm to approximately 1.5 mm, most preferably from approximately 0.6 to approximately 1.0 mm.

[0040] In use, the rolls and cylinders of the apparatus, including the anilox roll 1, are rotated at a certain minimum speed, the printing ink in the ink chamber forms a liquid film along this gap so that liquid no longer leaks out from the ink chamber 3 through the gap. A preferred gap width for a water-based printing ink which is often used for printing a web of packaging material for liquid foods and which has a viscosity of approximately 20 s is from approximately 0.6 to approximately 0.9 mm.

[0041] FIG. 2 schematically illustrates a printing process employing a flexographic printing apparatus known in the art. In FIG. 5, the same reference numerals as earlier have been employed for the same or equivalent parts. The anilox roll 1 is rotated in the direction of rotation of the arrow, partly within the ink chamber 3 positioned axially along the roll 1 for taking up printing ink in the cells engraved on the circumferential surface of the roll 1. Picked up excess ink is scraped off from the roll 1 by an upper doctor blade (obscured in the figure) abutting against the circumferential surface, on exit from the ink chamber 3. The printing ink thus remaining in the engraved cells accompanies the rotating anilox roll 1 and is transferred to an impression cylinder 2 rotating in transfer contact with the anilox roll 1. The printing ink thus transferred to the impression cylinder 2 accompanies the rotating impression cylinder 2 for transfer to a web 16 of packaging material which is led through the nip between the impression cylinder 2 and a counter pressure cylinder 17 rotating adjacent the impression cylinder 2. After drying/setting of the transferred printing ink on the surface of the web, the printed web is rolled up for further processing, such as lamination and mechanical processing in a per se known manner.

[0042] In order to maintain good print quality and reduce process-related quality disruptions, but also to minimize unnecessary waste and spillage of expensive printing ink because of uncontrolled leakage of printing ink, the apparatus has a spray- or shower device 20 disposed adjacent the anilox roll in order, during ongoing operation, to continuously or intermittently spray cleaning fluid for the printing ink on particularly sensitive regions of the circumferential surface of the anilox roll 1. Such a region is the peripheral edge regions of the anilox roll 1 where printing ink in certain cases (in particular printing ink with a high proportion of pigment in relation to solvent) shows a tendency to dry on the anilox roll. Undesirable drying of the printing ink is effectively counteracted with the aid of the applied cleaning fluid which ensures that residual printing ink within these sensitive regions on the surface of the anilox roll is constantly kept in soluble form.

[0043] Now turning to the present invention, FIG. 3 illustrates an apparatus 100 for flexographic printing of a web of packaging material with printing ink. The same reference numerals have been used for the parts and/or components of the apparatus which are the same as in the prior art described in conjunction with FIG. 1 and FIG. 2. The apparatus 100 comprises an ink chamber 3, and an anilox roll 1 rotary at least partly inside the ink chamber 3 for picking up and transferring printing ink from the ink chamber 3 to an impression cylinder (not shown). The impression cylinder is rotary in transfer contact with the anilox roll 1.

[0044] The ink chamber 3 is elongated and extends axially along the anilox roll 1. The ink chamber 3 has a first axial end and a second axial end opposite the first axial end. The anilox roll 1 is typically about 0.5 m to 2 m wide. The ink chamber 3, as indicated in FIG. 3, extends shorter than the anilox roll 1. The ink chamber 3 is defined as described in conjunction with FIG. 1, i.e. an upper and a lower doctor blade (not shown), part of the circumferential surface of the anilox roll 1, as well as by an end wall at each respective axial end of the ink chamber 3.

[0045] The apparatus 100 further comprises a first printing ink inlet 30a arranged at the first axial end of the ink chamber and a second printing ink inlet 30b arranged at the second axial end of the ink chamber. The first and second printing ink inlets 30a, 30b are fluidly connected to an ink reservoir 12 via a conduit 29. The ink reservoir 12 may comprise an ink pump (not shown) for inducing, during operation, a flow of ink from the ink reservoir to the ink chamber 3. Further, the viscosity, temperature and homogeneity of the printing ink may be regulated in the ink reservoir 12. The printing ink inlets 30a, 30b may form a portion of, or the entire, respective axial end wall of the ink chamber 3.

[0046] The first printing ink inlet 30a and the second printing ink inlet 30b is arranged to direct printing ink at least partly parallel to the axial extent of the anilox roll 1. In other words, the printing ink inlets 30a, 30b are configured to direct the printing ink towards the centre of the ink chamber 3.

[0047] The printing ink inlets 30a, 30b may have an elongated exit, shown more clearly in FIG. 4a-d. The elongated exit is elongated in an upright direction, i.e. in the same direction as between the lower and upper doctor blades seen in FIG. 1, to facilitate the construction of a thin ink chamber. The printing ink inlets 30a, 30b may have entries with the same cross-sectional area as the elongated exits. This reduces the flow restriction caused by the printing ink inlets 30a, 30b.

[0048] As shown in FIG. 3, the printing ink inlets 30a, 30b are substantially orthogonal and direct a flow of printing ink from the conduit 29 towards the centre of the ink chamber 3. This may be provided by each printing ink inlet 30a, 30b having a channel extending substantially orthogonal between the entry and the elongated exit, illustrated in e.g. FIGS. 4a-4d.

[0049] The printing ink inlets 30a, 30b may be made of plastic or rubber. The printing ink inlets 30a, 30b may be formed as inlet modules further described below in conjunction with FIG. 4a-d. The printing ink inlets 30a, 30b formed by inlet modules may be configured to form an anilox roll seal. An anilox roll seal is the viscous seal described in conjunction with FIG. 1, i.e. that a portion of the printing ink inlets 30a, 30b is disposed such that an edge thereof which faces towards the surface of the anilox roll 1 adheres to the configuration of the anilox roll but at a distance from the circumferential surface of the anilox roll 1. Between the circumferential surface of the anilox roll 1 and the edge of the printing ink inlets 30a, 30b there is thus a gap which may have a width of from approximately 0.5 mm to approximately 2 mm, preferably from approximately 0.5 mm to approximately 1.5 mm, most preferably from approximately 0.6 to approximately 1.0 mm. Further, an anilox roll seal comprises two mutually spaced apart end wall elements. The end wall element proximal to the ink chamber 3 prevents lateral leakage of printing ink, and the end wall element distal to the ink chamber prevents printing ink having leaked past the proximal end wall element from leaving the ink chamber. A drainage outlet may be arranged between the end wall elements. Hence, printing ink which, where applicable, leaks out laterally from the ink chamber 3 is collected between the end wall elements and may be taken care of via an drainage outlet or the like arranged between the wall elements. The printing ink is thereby prevented from causing splashing and soiling.

[0050] In use, the ink pump (not shown) induces a flow of printing ink from the ink reservoir 12 through the conduit to the printing ink inlets 30a, 30b which inject the printing ink into the ink chamber 3 from the respective axial ends via through the printing ink inlets 30a, 30b. Thereby, the pressure and flow through the printing ink inlets 30a, 30b can be reduced compared to e.g. the central inlet of the apparatus in FIG. 1 in order to obtain a homogenous or at least substantially uniform pressure distribution within the ink chamber 3. A substantially uniform pressure distribution in the ink chamber 3 alleviates ink starvation on the anilox roll, in particular towards the lateral portions thereof. The reduced pressure and flow means that there is less frothing. The reduced pressure and flow also means that energy required for the pumping action is reduced.

[0051] FIGS. 4a-d illustrates an inlet module 30 for a flexographic printing apparatus, such as the apparatuses shown in FIGS. 1, 2 and 3. The inlet module 30 may be made of plastic or rubber. The inlet module 30 is generally L-shaped as seen from the top or bottom.

[0052] The inlet module 30 comprises a circular entry 31, an elongated exit 34, and a channel 32 extending substantially orthogonally between the entry 31 and exit 34. FIG. 4c is a cross-section where the orthogonal channel 32, e.g. a channel having a 90 degree bend is illustrated. The elongated exit 34, and the portion of the inlet module 30 in which the elongated exit 34 is located is the portion which during assembly is inserted into the ink chamber 3 of a flexographic printing apparatus.

[0053] The circular entry 31 has the same cross-sectional area as the elongated exit 34. This reduces the flow restriction. FIG. 4b shows the transition from the circular entry 31 into the elongated exit 34 having a conical shape. Other shapes or transition are of course possible and within the scope of the invention. The circular entry 31 is adapted to receive and be connected to a conduit from an ink reservoir. The circular entry 31 may have internal or external threads or the like (not shown).

[0054] The inlet module 30 further comprises an anilox roll seal formed by two protruding elements 33a, 33b. The protruding elements 33a, 33b are two mutually spaced apart axial end wall elements. The edge of the protruding elements 33a, 33b, when assembled e.g. in the apparatus 100, faces the surface of the anilox roll 1. The width of the gap formed between the anilox roll 1 and the protruding elements 33a, 33b is 0.5 mm to 2 mm. The protruding element 33a closest to the elongated opening 34 is also the proximal protruding element with respect to the ink chamber. During rotation of an anilox roll 1, the proximal protruding element 33a prevents the printing ink from leaking laterally past the gap formed between the proximal protruding element 33a and the anilox roll. The distal protruding element 33b prevents printing ink from leaking out from the ink chamber 3. An ink chamber 3 may further comprise a drainage hole or the like arranged to collect printing ink between the two protruding elements 33a, 33b.

[0055] The first and second printing ink inlets 30a, 30b discussed above in conjunction with FIG. 3 may be formed in inlet modules as the inlet module shown in FIGS. 4a-d.

[0056] The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.