EP2657020A1

EP2657020A1 - Articulated doctor blade assembly for printing groups

Info

Publication number: EP2657020A1
Application number: EP12425078.8A
Authority: EP
Inventors: Renzo Melotti
Original assignee: Bobst Italia SpA
Current assignee: Bobst Italia SpA
Priority date: 2012-04-27
Filing date: 2012-04-27
Publication date: 2013-10-30
Anticipated expiration: 2032-04-27
Also published as: EP2657020B1

Abstract

Doctor blade assembly (110) for printing units, in particular for rotogravure printing groups, comprising a doctor blade and a doctor blade support (2); the doctor blade assembly (110) comprises a main shaft (14) provided with relative drive and control means (12, 18A), a secondary shaft (15) provided with relative drive and control means (13, 18B) and a levers group (3) forming an articulated parallelogram and comprising a first series of levers (3A, 3B, 3C, 3D) keyed on one side to the main shaft (14) and on the other side to the secondary shaft (15) and a second series of levers (3F, 3E, 3G, 3H) keyed on one side to the secondary shaft (15) and on the other side connected to the doctor blade support (2); at least a lever (3H) of said second series of levers is connected in a rotatable way to at least a pair of levers (3C, 3D) of said first series of levers (3A, 3B, 3C, 3D).

Description

Technical Field

The present invention relates to a doctor blade assembly for use with rotating print cylinders, in particular print cylinders of gravure or rotogravure printing presses.

Background Art

Doctor blades are known in the field of printing apparatuses, in particular rotogravure printing presses in which a gravure printing roller applies ink or the like onto a film or web material to be printed, such as a packaging material.
In a rotogravure printing press, the doctor blade is arranged adjacent and substantially parallel to the rotation axis of the printing roller, which is typically graved according to the graphics or patterns to be printed onto the material. A pan containing the ink or other substances to be applied to the material is usually provided beneath the printing roller, in such a position that the printing roller can be wet by the ink or the substance in the pan during its rotation.
The material to be printed is generally fed to the printing roller by a pressing roller, which is in close proximity of the printing roller so that the material can contact a generating line of the printing roller downstream of the ink pan and can be printed according to the patterns engraved on the printing roller.
The doctor blade is placed downstream of the ink pan and upstream of the pressing roller, with respect to the rotation direction of the printing roller, and is aimed at wiping off the excess ink from the engraved surface of the printing roller before it contacts the material to be printed, so that the ink remains only in the patterned recesses engraved on the surface of the printing roller.
In a common doctor blade group, a precision in setting the various degrees of freedom to have the blade parallel to the axis of the printing roller is necessary to have a good print. Typically this operation is done by an operator with a dispending of time; time subtracted at the printing process.
Another important thing to taking into account in the geometrical setting of the doctor blade is the contact angle between the doctor blade and the tangency line of the diameter of the printing roller. By varying the diameter of the printing roller, the contact angle varying too and with a common doctor blade assembly is difficult to maintain an ideal contact angle.

Disclosure of invention

The aim of the present invention is to realize an articulated doctor blade assembly for printing groups which allows to accelerate the operation of setting to have the doctor blade in contact with the printing roller and parallel to the axis of this last one, with consequent reduction of the time to set the doctor blade and increasing of the useful printing time and allows to maintain a contact angle almost constant in a accepted tolerance range, with consequent improvement of the quality print of the entire rotary printing unit.
This aim is achieved by the present invention by means of an articulated doctor blade assembly according to the combination of features of claim 1.
Further advantageous features of the articulated doctor blade assembly according to the present invention have been specified in the dependent claims.
Advantageously, the present articulated doctor blade assembly allows the mounting of a chambered doctor blade support or a non-chambered doctor blade support.
Another feature of the present invention is to allow the assembly to be installed and used in existing rotary printing presses, in particular gravure and rotogravure printing presses without substantially changing their mechanical structure and their operating software.
Moreover, the present invention allows to facilitate the operations of setting of the doctor blade assembly in the possible positions in accord to the printing process phases.
Further characteristics and advantages of the present invention will become better apparent from the following description of particular embodiments thereof, illustrated by way of non-limitative example in the accompanying drawings.

Brief Description of Figures in the Drawings

Fig. 1 shows a side elevation view of a rotogravure printing unit comprising an articulated doctor blade assembly according to the invention.
Fig. 2 shows a front view of the rotogravure printing unit of fig. 1.
Fig. 3 shows a large scale and cross-section view of the present articulated doctor blade assembly provided with a levers group forming an articulated parallelogram and a casing group consisting of a plurality of plates.
Fig. 4 shows a front view of the present articulated doctor blade assembly provided with pneumatic pistons for the final approach of the doctor blade on the printing cylinder or roller of the rotogravure printing unit.
Figure 5 shows a partial isometric view of the present articulated doctor blade assembly.
Figure 6A and 6b show two side elevation views of the present articulated doctor blade assembly in an operational mode on two different diameters of printing rollers.

Best Mode for Carrying Out the Invention

With reference to the annexed drawings, Figures 1 and 2 show a rotogravure printing unit 100 incorporating an articulated doctor blade assembly 110 according to the present invention. The rotogravure printing unit 100 comprises a support frame 7 wherein at least one gravure printing roller 4 and a pressing roller 10 are rotatably mounted and an ink tank 8 cooperating with pumping means 9 able to transfer the ink from said tank 8 to the printing roller 4. A pan 5 for collecting ink is positioned under the printing roller 4. The rotogravure printing unit 100 also comprises two pistons 6A and 6B located on the top of the support frame 7 and able to actuate, via the two piston stems, the pressure roller 10 towards the printing roller 4. The gravure printing roller 4 is characterized by an engraved cylindrical surface, by means of which ink can be entrapped and transferred to a film or web material pressed by the pressing roller 10. The gravure printing roller 4 can be easily disassembled from the unit 100 and replaced by a gravure printing roller having a different diameter and/or different patterns engraved on its surface. The pressing roller 10 is linearly movable with respect to the longitudinal rotation axis of the gravure printing roller 4, so as to be adapted to printing rollers of different diameters and to press the film or web material against the engraved surface of the printing roller 4. The articulated doctor blade assembly 110 is connected to the support structure 7 of the printing unit 100 via a bush 22 and a flexible plate 24.
The articulated doctor blade assembly 110, see Figures 3, 4 and 5, comprises: a doctor blade 1, a doctor blade support 2, a main shaft 14 and a secondary shaft 15. The principal shaft 14 is able to be rotated by means of a first gear reduction 18A driven by a hand wheel 12 provided with a graduated scale 20A, the secondary shaft 15 is able to be rotated by means of a second gear reduction 18B driven by a hand wheel 13 provided with a graduated scale 20B. The articulated doctor blade assembly 110 also comprises a levers group 3, comprising the levers 3A, 3B, 3C, 3D, 3E, 3F, 3G, 3H and a pair of pneumatic pistons 11A and 11B, which are controlled semi-automatically by a suitable software and that control will not be discussed here. These pneumatic pistons 11A and 11B are able to carry out the final approach of the doctor blade 1 on the cylindrical surface of the printing cylinder 4. The lever 3B is keyed near an end of the main shaft 14 through a hole in its central zone; at its lower end a spacer 23B is fixed while the upper end is keyed to the secondary shaft 15. The lever 3A is keyed near the other end of the main shaft 14 through a hole in its central zone; at its lower end is fixed a spacer 23A while the upper end is keyed to the secondary shaft 15. The lever 3C is characterized by a substantially "L" shape and is keyed to the secondary shaft 15 thanks to a hole at one end thereof. The lever 3D is similar to the lever 3C and it is keyed on the secondary shaft 15 at the opposite end respect to lever 3C. The lever 3C is mounted near the lever 3A and forms with it, thanks to their possible rotation around the secondary shaft 15, a first leverism 3AC. The lever 3D is mounted near the lever 3B and forms with it, thanks to their possible rotation around the secondary shaft 15, a second leverism 3BD. The levers 3C and 3D are also connected to the lever 3H by means of a rotation pin 16. The levers 3H and 3G form a support pallet 3GH for the support group 2 and therefore for the doctor blade 1. This support pallet 3GH can be rotated around two rotation pins 16 and 17. The piston 11A is fixed to one end to the pin 23A and to the other end to the lever 3C. Therefore a third articulated leverism 3AC11A composed by the leverism 3AC and piston 11A is formed. Similarly, the piston 11B forms a fourth articulated leverism 3BD11B with the leverism 3BD. The lever 3F is keyed on the center of the secondary shaft 15 and at one end is connected to the lever 3E via a rotation pin 21. The lever 3E is connected, at the other end and by means of the rotation pin 17, to the pallet 3GH; this last one is united with the doctor blade support 2. The levers 3F, 3E, 3G, 3H form a further articulated leverism. Said levers group 3 is connected to a casing group 19 formed by four mechanically deformable plates 19A, 19B, 19C and 19D. The plate 19A is connected to the levers 3A and 3B, while the plate 19B is connected to the levers 3C and 3D. Said levers group 3 comprising the various levers 3A-3H with the respective connections described above forms an articulated parallelogram which, advantageously, allows to control and drive in an accurate way the movement of the doctor blade 1 in respect to any printing roller of a rotogravure printing group 100. In such an articulated parallelogram the levers 3A and 3C of the first leverism 3AC connected to the piston 11A are substantially independent from the levers 3B and 3D of the second leverism 3BD connected to the piston 11B. This independence of these levers allows the parallel self-alignment of the doctor blade 1 with the rotation axis of the printing cylinder 4 of fig. 1.
The present articulated doctor blade assembly 110 is showed in fig. 6A and 6B in a possible operation mode on a first printing roller 4 and on a second printing roller 4' having a diameter smaller than the diameter of the first roller 4, respectively. In a first operation step of the present articulated doctor blade assembly 110, operator sets in motion, by means of the hand wheel 12, the first gear reduction 18A which commands the main shaft 14, thus permitting the rotation of the entire articulated parallelogram formed by the levers 3A-3H of the articulated doctor blade assembly 110 around the main shaft 14 axis. The graduate scale 20A shows quickly to operator the correct position to set the doctor blade assembly in operation position or in extraction position of the pan 5 of Fig. 1. By means of the second hand wheel 13, the operator sets in motion the gear reduction 18B which commands the secondary shaft 15 so as to rotate and to set the doctor blade 1 in the correct work position, that is in contact with the surface of the printing roller 4 of Fig. 6A or the surface of the printing roller 4' of Fig. 6B. In particular, the gear reduction 18B changes the contact angle X shown in figures 6A and 6B. The graduate scale 20B shows how many degrees is varying the contact angle X turning the hand wheel 13. In particular, the rotation of the lever 3F in the counterclockwise direction around the axis of the secondary shaft 15 brings to rotation the lever 3E in clockwise direction thanks to the pin 21. Consequently, the lever 3E brings to rotation in the counter-clockwise direction the pallet 3GH composed in part from the lever 3G and from the lever 3H, united the one with the other and rotatable around the pins 16 and 17. The pallet 3GH is united with the doctor blade support 2 that will rotate with it. The last rotation of the doctor blade support 2 causes a reduction of the contact angle X. The setting action on the wheel 13 can be done in two ways:

counter-clockwise (reduction of the contact angle X);
clockwise (increase of the contact angle X).

It must be considered that, advantageously, this contact angle X, once adjusted, remains substantially constant without any further adjustment, even varying the diameter of the printing cylinder. The parallelogram formed by the levers group 3A-3H, in fact, allows to maintain a contact angle X substantially constant with small variations around +/- 1.5 degrees.
Operating as described above on the hand wheel 13, the pneumatic pistons 11A and 11B are self-adapt thanks to a constant pressure in their interior. These pistons, as above described, are controlled are controlled semi-automatically by a suitable software. The parallelism between the doctor blade 1 and the longitudinal axis of the printing cylinder 4 or 4' remains automatically corrected thanks to the adjustment of the articulated doctor blade assembly 110 when the pistons 11A and 11B are actuated.
This further advantageous feature of the articulated doctor blade assembly 110 according to the present invention is enabled by mechanical deformation of the casing group 19. The various plates 19A 19B 19C 19D, that constitute the casing group 19, being deformable, allow a phase shift of the leverism 3AC with respect to the leverism 3BD. The phase shift of the geometries of the leverisms 3AC and 3BD and therefore their substantial reciprocal independence allows to the doctor blade 1 to go in contact on the surface of the roller 4 or 4' little by little reaching the desired parallelism condition.

Claims

Doctor blade assembly (110) suitable for printing units, in particular for rotogravure printing groups (100), comprising a doctor blade (1) and a doctor blade support (2), characterized in that it comprises a main shaft (14) provided with relative drive and control means (12, 18A), a secondary shaft (15) provided with relative drive and control means (13, 18B) and a levers group (3) forming an articulated parallelogram and comprising a first series of levers (3A, 3B, 3C, 3D) keyed on one side to the main shaft (14) and on the other side to the secondary shaft (15) and a second series of levers (3F, 3E, 3G, 3H) keyed on one side to the secondary shaft (15) and on the other side connected to the doctor blade support (2), at least a lever (3H) of said second series of levers being connected in a rotatable way to at least a pair of levers (3C, 3D) of said first series of levers (3A, 3B, 3C, 3D).
Doctor blade assembly (110) according to claim 1, characterized in that it comprises a casing group (19) provided with a series of mechanically deformable elements (19A, 19B, 19C, 19D) connected at least to the levers of said first series of levers (3A, 3B, 3C, 3D).
Doctor blade assembly (110) according to claim 1, characterized in that said first series of levers (3A, 3B, 3C, 3D) comprises a first pair of levers (3A, 3B) keyed on both sides of the main shaft (14) and a second pair of levers (3C, 3D) keyed on both sides of the secondary shaft (15), each lever of said second pair of levers (3C, 3D) being mounted near a respective lever of said first pair of levers (3A, 3B).
Doctor blade assembly (110) according to claim 3, characterized in that it comprises a pair of pistons (11A, 11B) each of which is connected on one end to a respective lever (3A, 3B) of said first pair of levers and on the other end to a respective lever (3C, 3D) of said second pair of levers.
Doctor blade assembly (110) according to claim 4, characterized in that it comprises an articulated leverism (3A3C11A, 3B3D11B) formed by each piston (11A, 11B) connected with the respective levers of said first pair of levers (3A, 3B) and said second pair of levers (3C, 3D).
Doctor blade assembly (110) according to claim 1, characterized in that said levers of said second series of levers (3F, 3E, 3G, 3H) are connected one to another such that to form an articulated leverism.
Doctor blade assembly (110) according to claim 1, characterized in that said second series of levers (3F, 3E, 3G, 3H) comprises a first lever (3F) keyed on one end to said secondary shaft (15) and connected on the other end and in a rotatable way to an end of a second lever (3E), said second lever (3E) being connected on the other end to a third lever (3G) and a fourth lever (3H) forming a support pallet (3GH).
Doctor blade assembly (110) according to claim 7, characterized in that said first lever (3E) is keyed to the secondary shaft (15) in a substantially central position.
Doctor blade assembly (110) according to claim 1, characterized in that said main shaft (14) is controlled by a gear reduction (18A) commands by a hand wheel (12).
Doctor blade assembly (110) according to claim 1, characterized in that said secondary shaft (15) is controlled by a gear reduction (18B) commands by a hand wheel (13).
Doctor blade assembly (110) according to claims 2 and 3, characterized in that said casing group (19) comprises at least two mechanically deformable elements (19A) connected to said first pair of levers (3A, 3B) and at least two mechanically deformable elements (19B) connected to said second pair of levers (3C, 3D).
Rotogravure printing unit (100) comprises at least one printing cylinder (4, 4') and at least one pressure roller (10) adjacent to the printing cylinder (4, 4'), characterized in that it comprises an articulated doctor blade assembly (110) according to one or more of the preceding claims.