printing press

Abstract

A printing press with a transfer cylinder (10) and two plate cylinders (13; 14), each of which touches the transfer cylinder (10) at a gap (11; 12), wherein an inking unit (16; 17) cooperates with each plate cylinder (13; 14), wherein a plane (28) runs through an axis of the transfer cylinder (10) and a space between the plate cylinders (13; 14), and the inking unit (16; 17) that cooperates with one of the plate cylinders (13; 14) is arranged at least predominantly on the same side of the plane as this plate cylinder (13; 14), characterized in that a plate changer (29; 30) is further assigned to each of the plate cylinders (13; 14), and the plate changers (29; 30) are located opposite one another on both sides of the inking units (16; 17), that the plane (28) is vertically oriented, and that the plate changers (29; 30) are arranged in a mirror image with respect to the plane (28).

Description

The invention relates to a printing machine according to the preamble of claim 1.WO 2016 / 071870 A1 discloses a printing press having a transfer cylinder and two plate cylinders, which each touch the transfer cylinder at a nip in order to transfer two different printed images, typically in different colors, to the transfer cylinder and to print them in a single contact of the transfer cylinder with a printing material.In this conventional printing machine, in order to accommodate both an impression cylinder and the plurality of plate cylinders on the periphery of the transfer cylinder, the diameter of the transfer cylinder is a multiple of the diameter of the plate cylinders. Accordingly, the transfer cylinder is heavy and expensive, and accordingly, the printing machine is bulky. Nevertheless, the inking units and plate cylinders occupy so much space on the circumference of the transfer cylinder that plate changers can no longer be accommodated.CH 254 252 A and DE 198 20 331 A1 each disclose a printing press having a transfer cylinder and two plate cylinders which each touch the transfer cylinder at a nip, wherein each plate cylinder is in each case acted upon by an inking unit, wherein a plane runs through an axis of the transfer cylinder and an intermediate space between the plate cylinders, and the inking unit which interacts with one of the plate cylinders is arranged at least predominantly on the same side of the plane as this plate cylinder.The invention is based on the object of providing a printing press, wherein a plurality of colors can be printed with the printing press in a single pass through a printing nip, and wherein a plate change is possible with good accessibility.The advantages which can be achieved with the invention consist in particular in that a plurality of colors can be printed with the printing machine in a single pass through a printing nip. Since the plate changers are opposite each other on both sides of the inking units, good accessibility of the plate changers is ensured on the one hand, so that used plates can be removed conveniently or new plates can be placed behind, since no space for a plate changer has to be kept free between the inking units, the inking units can be arranged closely adjacent. Accordingly, the distance between the gaps at which the transfer cylinder contacts the two plate cylinders can also be small, with the result that a relatively small transfer cylinder is sufficient to distribute the inking units and an impression cylinder thereon.Ideally, the transfer cylinder has the same diameter as the plate cylinders which cooperate therewith.In order to make both plate changers equally accessible, the plane which runs through the axis of the transfer cylinder between the plate cylinders is oriented vertically.In order to ensure that no ink sprays pass from one inking unit to the other despite the small distance between the inking units, a separating wall should be provided between the two. This partition wall can coincide-at least partially-with the above-mentioned plane.In order to be equally readily accessible from different sides of a housing of the printing press, ink fountains of the two inking units can be arranged mirror-symmetrically with respect to one another. This entails that ductors, via which the ink is conveyed out of the ink fountains, rotate in opposite directions in the two inking units. Ink applicator rollers which rotate at the downstream end of each inking unit in contact with one of the plate cylinders, with reference to the transport direction of the ink, however, must rotate in the same direction at least during the transfer printing. If the lifting roller of one of the two inking units changes direction of rotation during a lifting cycle, identical inking units but arranged mirror-symmetrically to one another can be used on both sides of the plane.For ready accessibility, the plate changers are preferably arranged on opposite flanks of a housing which accommodates the plate cylinders and the inking units.Like the inking units, the plate changers are also arranged mirror-symmetrically with respect to the plane, two plate changers of identical construction can be used on both plate cylinders.Since the plate cylinders can roll on the transfer cylinder without slipping only when they rotate in the same direction, the direction of rotation during the transfer printing can coincide with the direction in which a printing plate to be placed on the plate cylinder leaves the associated plate changer only on one of the two plate cylinders. In order to be able to carry out an automatic printing plate change on both plate cylinders, the plate cylinders should therefore be driven in opposite directions during the ejection of a used printing plate and during the winding-on of a new printing plate. That is, if the ejection takes place at the same time for both plate cylinders, both must rotate in opposite directions during this time. However, it is also conceivable to undertake a plate change on both plate cylinders in a time-shifted manner and, for example, while both plate cylinders rotate in the same direction, to push out a used printing plate on one, while at the same time a new printing plate is already drawn on on the other.In order to prevent access to other parts of the printing machine as little as possible, the plate changers can be movable between a rest position resting against the housing and an operating position projecting from the housing.Particularly in the printing of banknotes and papers of value, iris printing is a common technique for differently coloring zones of a same printing plate and thus printing a plate in colors continuously merging with each other. For this purpose, at least one of the inking units should have at least two ink fountains.Such an inking unit should also comprise at least two lifter rollers, which each remove ink from one of the ink boxes. An ink transfer roller contacting the lifter rollers to transfer the received ink may be common to both lifter rollers.In order to avoid transfer of ink from one ink fountain to the other via the lifter rollers and the common ink transfer roller, a control unit can be configured to synchronize the movements of the lifter rollers such that the lifter rollers respectively contact different circumferential sections of the ink transfer roller.An exemplary embodiment of the invention is illustrated in the drawing and is described in more detail below.The single drawing shows a schematic cross section through a printing unit of a sheet-fed printing press.The FIGURE shows a schematic cross section through a printing unit of a printing press, in particular a sheet-fed printing press. A transport cylinder 01 of the printing unit rotates clockwise in order to transport a sheet of printing material, for example a sheet which is clamped to the lateral surface of the transport cylinder 01 with the aid of a gripper 02, in a manner known per se to a nip 03 at which the transport cylinder 01 and an impression cylinder 04 contact one another, and to transfer it there to a gripper 05 of the impression cylinder 04.The counter-clockwise rotating impression cylinder 04 conveys the sheet further through a printing nip 06 to a transfer nip 07, where the sheet is transferred to a gripper 09 of a subsequent transport cylinder 08 or a sheet delivery device.The printing nip 06 is bounded on one side by the impression cylinder 04 and on the other side by a transfer cylinder 10. The transfer cylinder 10 contacts two plate cylinders 13; 14 at gaps 11; 12, and in order to pass the printing gap 06 without slipping, the transfer cylinder 10 must rotate in the opposite direction to the impression cylinder 04. Accordingly, the plate cylinders 13; 14, as can be seen with reference to directional arrows drawn in, must rotate in the same direction with respect to one another, but with a direction of rotation opposite to the transfer cylinder 10, in order to make possible a slip-free rolling of the plate cylinders 13; 14 on the transfer cylinder 10 and thus the transfer of a printed image from the plate cylinders 13; 14 to the transfer cylinder 10.The plate cylinders 13; 14 are accommodated next to one another in a tower-like housing 15 of the printing unit. Above the plate cylinders 13; 14, an inking unit 16; 17 is arranged in each case for inking their printing plates. Each of the inking units 16; 17 comprises, in a manner known per se, an ink fountain 18 in which a ductor 19 rotates in contact with an ink supply 20 and a doctor blade 21 controls the thickness of an ink layer which adheres to the ductor 19 on leaving the ink supply 20. The ink fountains 18 are of identical construction and are arranged mirror-symmetrically to one another, for which reason the ductors 19 of the two ink fountains 18 must rotate in opposite directions in order to be able to interact with the doctor blades 21.In a manner likewise known per se, in each inking unit 16; 17, a lifter roller 22 is movable back and forth between the ductor 19 and a roller 23, for example ink transfer roller 23, in order to take up, in rotating contact with the ductor 19, an amount of ink which is proportional to the dwell time of the lifter roller 22 on the ductor 19 and to pass this on, in rotating contact with the ink transfer roller 23, to the latter. From there, the ink is passed on roller by roller through the inking unit 16 or 17 as far as roller 24, for example ink applicator rollers 24, which roll in contact with the plate cylinders 13 or 14 in order to ink their printing plates.Among the rollers 25; 26, which within the inking units 16; 17 pass the ink from the ink transfer roller 23 to the ink application rollers 24, there are a plurality of rollers 25, for example friction rollers 25, which are driven independently of one another and can rotate at different circumferential speeds in order to rub the ink in contact with other rollers 26 contacting the friction rollers 25 and distribute it in the circumferential direction of the rollers 25; 26. The differences between the circumferential speeds of the friction rollers 25 are small compared to the circumferential speeds themselves, so that rollers 25; 26 contacting one another always have opposite rotational directions.The arrangement of the rollers 25; 26 in the two inking units 16; 17 is identical in construction, but mirror-image to one another. Consequently, rollers 23; 24; 25; 26 corresponding to each other rotate in the same direction in the two inking units 16; 17. Since, on the other hand, the ductors 19 rotate in opposite directions, the ductor 19 and the ink transfer roller 23 have a direction of rotation in an inking unit 16; 17, here opposite the inking unit 17. Since the lifting roller 22 has no drive of its own and is always only taken along in frictional engagement, it rotates clockwise in contact with the ductor 19 and counter-clockwise in contact with the transfer roller 23. The bearing friction of the lifter roller 22 can be dimensioned in order to bring it to a standstill in each case on the path between ductor 19 and ink transfer roller 23.A separating wall 27 is arranged between the two inking units 16; 17 in order to keep ink spun off from rollers 23; 24; 25; 26 of one inking unit 16; 17 away from the other inking unit 17; 16. The separating wall 27 here runs vertically and centrally between the inking units 16; 17 arranged above the plate cylinders 13; 14 in a plane 28 which runs through the axis of the transfer cylinder 10, the separating wall 27 can extend downward as far as into an intermediate space between the plate cylinders 13; 14.A plate changer 29; 30 is assigned to each of the two plate cylinders 13; 14. The plate changers 29; 30 are pivotable between a rest position resting against a side wall of the housing 15 and a use position in which they are oriented tangentially to the plate cylinders 13 and 14, respectively, and project obliquely outwards from the housing 15. The movement from the rest position into the use position can first, as illustrated in the example of the left plate changer 29, be a rail-guided translation along the housing wall to an intermediate position, followed by a pivoting movement about an axis 31 fixed to the housing, but obstacles in the path can be bypassed more easily if the movement, as illustrated on the right plate changer 30, is a continuous pivoting movement about a virtual axis which is guided, for example, by links 32 engaging at two different points of the plate changer 30 and of the housing 15.As can be seen from the entered rotational direction arrows, during the printing process the plate cylinder 14 rotates with a rotational direction which enables the ejection of a used printing plate from the plate cylinder 14 into the plate changer 30. When this has been done, the direction of rotation of both plate cylinders 13, 14 can be reversed to simultaneously draw a new printing plate from the plate changer 30 onto the plate cylinder 14 and to push the used printing plate from the plate cylinder 13 into the plate changer 29. After a new reversal of the direction of rotation, a new printing plate can also be drawn from the plate changer 29 onto the plate cylinder 13 and the printing operation can be resumed without renewed stoppage of the plate cylinders 13; 14.Alternatively, it is possible to decouple the rotation of the plate cylinders 13; 14 from one another and from the transfer cylinder 10 for a plate change, so that the plate cylinders 13; 14 rotate in opposite directions and can respectively simultaneously push out a used printing plate or pull in a new printing plate.As shown in the figure taking the right inking unit 17 as an example, the inking units 16; 17 for iris printing can each have a second ink fountain 33 and a second lifter roller 34. The lifting rollers 22; 34 here each transfer ink to the same ink transfer roller 23, but they each only touch it for such a short time that they only release ink to a part of the circumference of the ink transfer roller 23. The ink transfer roller 23 passes here first the lifter roller 34, then the lifter roller 22 and then a roller 25 to which it transfers the ink taken over by the lifter rollers 22; 34 for the most part. A-preferably electronic-control unit 35 is provided in order to synchronize the movements of the lifting rollers 22; 34 in such a way that, during a revolution of the ink transfer roller 23, the lifting roller 22 in each case touches only that part of the circumference of the ink transfer roller 23 which was not touched by the lifting roller 34 beforehand and therefore carries at most a thin ink layer. This thin ink layer can contain a mixture of inks from both inking units 16; 17, provided that the ink layer that the lifter roller 22 carries from the ink fountain 18 is thicker, it remains substantially clean even after contact with the ink transfer roller 23. Thus, a composition of the ink layer variable over the circumference of the plate cylinder 14 can be maintained in the continuous printing, and continuous iris printing is possible.List of reference characters01 Transport cylinder 02 Gripper 03 Nip 04 Impression cylinder 05 Gripper 06 Printing nip 07 Transfer nip 08 Transport cylinder 09 Gripper 10 Transfer cylinder 11 Nip 12 Nip 13 Plate cylinder 14 Plate cylinder 15 Housing 16 Inking unit 17 Inking unit 18 Ink fountain 19 Ductor 20 Ink supply 21 Squeegee 22 Lifter roller 23 Roller, ink transfer roller 24 Roller, ink application roller 25 Roller, friction roller 26 Roller 27 Partition wall 28 Plane 29 Plate changer 30 Plate changer 31 Axle 32 Link 33 Ink fountain 34 Lifter roller 35 Control unit

Claims

Printing press having a transfer cylinder (10) and two plate cylinders (13; 14) which each touch the transfer cylinder (10) at a nip (11; 12), wherein an inking unit (16; 17) interacts with each plate cylinder (13; 14), wherein a plane (28) runs through an axis of the transfer cylinder (10) and an intermediate space between the plate cylinders (13; 14), and the inking unit (16; 17) which interacts with one of the plate cylinders (13; 14) is arranged at least predominantly on the same side of the plane as this plate cylinder (13; 14), characterized in that a plate changer (29; 30) is furthermore assigned in each case to the plate cylinders (13; 14) and the plate changers (29; 30) are opposite one another on both sides of the inking units (16; 17), in that the plane (28) is oriented vertically and in that the plate changers (29; 14) are arranged at least predominantly on the same side of the plane; 30) are arranged in mirror image with respect to the plane (28).Printing machine according to Claim 1, characterized in that the transfer cylinder (10) and the plate cylinders (13; 14) have the same diameter.Printing machine according to Claim 1 or 2, characterized in that a separating wall (27) extending between the inking units (16; 17) is arranged.Printing machine according to one of the preceding claims, characterized in that the inking units (16; 17) each have a ductor (19) and a lifter roller (22), in that the ductors (19) rotate in opposite directions and in that the lifter roller (22) of one of the two inking units (17) changes the direction of rotation in the course of a lifting cycle.Printing machine according to one of the preceding claims, characterized in that the plate changers (29; 30) are arranged on mutually opposite flanks of a housing (15) which accommodates the plate cylinders (13; 14) and the inking units (16; 17).Printing machine according to Claim 5, characterized in that the plate cylinders (13; 14) are each driven in rotation in opposite directions during the ejection of a used printing plate and during the winding-on of a new printing plate.Printing machine according to Claim 1 or 5, characterized in that the plate changers (29; 30) can be moved between a rest position bearing against the housing (15) and an operating position projecting from the housing (15).Printing machine according to one of the preceding claims, characterized in that at least one of the inking units (17) has at least two ink fountains (18; 33).Printing machine according to Claim 7, characterized in that at least one inking unit (17) comprises at least two lifter rollers (22; 34), which are each movable between one of the ink fountains (18; 33) and a common ink transfer roller (23).Printing machine according to claim 8, characterised in that a control unit (35) is arranged for synchronising the movements of the lifting rollers (22; 34), and that the lifting rollers (22; 34) each touch different circumferential sections of the ink transfer roller (23).

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