Convertible Printing Mechanism For Intaglio And Flexographic Printing

Abstract

A printing mechanism for printing presses is adapted to be converted from intaglio to flexographic printing and vice versa by providing a lifting platform below a replaceable plate cylinder. The platform supports a liftable ink trough, a displaceable frame for a screen cylinder, and a displaceable doctor device. A selected one of at least two impression cylinders supported in a mounting can be applied to the plate cylinder depending on whether a resilient surface is required for the impression cylinder for intaglio printing or a steel surface for flexographic printing.

Description

The invention relates to a printing mechanism for a printing press and adapted to be converted from intaglio to flexographic printing, and vice versa.

The main difference between intaglio and flexogaphic printing presses resides in the construction of their respective printing mechanisms. If the frame of the press and the drive for the printing mechanism are suitably designed, it is therefore readily possible to adapt the printing press to intaglio or flexographic printing depending on the particular printing mechanism that is built into the frame.

If, however, it is desired to provide a printing press which can be converted from one form of printing to the other, it is necessary to supply a complete intaglio printing mechanism and a complete flexographic printing mechanism, each equipped with its own doctor device. Since the doctor device of flexographic printing mechanisms is applied to a screen cylinder disposed between the ink through the plate cylinder whereas the doctor device of an intaglio printing mechanism is applied direct to the plate cylinder, and by reason of the unalterable direction of movement of the web to be printed, the arrangement of the doctor device for intaglio printing must be a mirror image of the arrangement for flexographic printing. Accordingly, the frame of a dual purpose printing press must be provided with two drives which are engageable with the respective doctor devices.

The replacement of complete printing mechanisms for the purpose of converting the press from one form of printing to another not only involves a large capital expenditure for the two printing mechanisms and the storage of one of these while the other is in use but also calls for the time-consuming application of lifting tackle for taking one printing mechanism out and installing the other.

The invention aims to provide a construction for the printing mechanism that permits one and the same printing mechanism to be converted from intaglio to flexographic printing or vice versa without the need for special lifting equipment.

According to the invention, a printing mechanism for a printing press and adapted to be converted from intaglio to flexographic printing and vice versa comprises a plate cylinder which is mounted at a fixed location but is, as usual, replaceable to cater for different printing formats and, in the present case, to suit the particular kind of printing to be employed, a liftable working platform disposed beneath said plate cylinder, a liftable ink trough mounted on said platform, a screen cylinder, a supporing frame for said screen cylinder, said supporting frame being adjustable in position on the surface of said platform, a doctor device with its own drive means adapted to adjust the position of said doctor device on the surface of said platform, and at least two impression cylinders for selective application to said plate cylinder and supported in displaceable mountings, one of the impression cylinders having a resilient surface for intaglio printing and another having a steel surface for flexographic printing.

Such a construction permits the components of the appropriate inking mechanism to be assembled on the working platform and to be moved therealong into the precise operative position and to bring the appropriate impression cylinder into position in relation to the plate cylinder. Only horizontal displacement is required to be effected manually of the heavy parts of the printing mechanism, namely the screen cylinder and the doctor device. The screen cylinder, which is not required for intaglio printing, can be pushed to one side and remain on the working platform.

Thus, when converting the printing press from intaglio printing to flexographic printing or vice versa, time and labour can now be saved, especially the time-consuming application of special lifting tackle. In addition, the stocking of additional equipment other than the plate cylinders is restricted to the screen cylinder because the ink trough and doctor device are required for both kinds of printing. The total capital expenditure for printing presses having convertible printing mechanisms according to the invention is therefore considerably less than for printing presses in which the printing mechanisms have to be replaced.

If the dimensions of the working platform are such that insufficient space is available for accommodating the screen cylinder when the latter is not required during intaglio printing, a horizontally displaceable auxiliary platform may be provided adjacent the working platform to receive the screen cylinder.

The supporting frame for the screen cylinder and the doctor device may be displaceable in guide rails of the platform in a direction parallel to the plate cylinder.

In one form of the invention, the doctor device comprises a carriage permitting the selective mounting of a doctor blade at either longitudinal side of the carriage. This construction has the advantage that the doctor device need be moved along the working platform only parallel to the rotary shaft of the plate cylinder when the printing mechanism is being converted.

The impression cylinders may be carried by a common turret mounted for rotation on a shaft which is parallel to the rotary shaft of the plate cylinder, the turret shaft being displaceable to and from the plate cylinder and being adapted to have engaged therewith means for pressing the selected impression cylinder against the plate cylinder.

An example of the invention will now be described with reference to the accompanying drawings in which:

FIG. 1 is a side elevation of a printing mechanism installed for flexographic printing purposes;

FIG. 2 is a similar view of the printing mechanism when converted to intaglio printing, and

FIG. 3 is a part-sectional front elevation along the line III--III in FIG. 1.

Referring to FIGS. 1 and 3 where the printing mechanism has been installed for flexographic printing, a plate cylinder 1 is installed in a fixed position but is replaceable in the usual way by a plate cylinder of different diameter to cater for a different printing format. The plate cylinder is mounted in a frame 2 of the printing press and is coupled to the drive means of the press. The plate cylinder 1 is associated with a turret 3 carrying a plurality of impression cylinders 4, 5, 6. A rotary shaft 7 of the turret is mounted in slide blocks 8 which are themselves displaceable in guides 9 of the frame in relation to a rotary shaft 10 of the plate cylinder. Rotation of the turret and its displaceability towards and away from the plate cylinder permit a selected one of the impression cylinders to be applied to the plate cylinder and to be pressed thereagainst by any suitable pressure means that engage the slide blocks. In the illustrated printing mechanism, at least one impression cylinder 4 has a surface of resilient material such as rubber or plastic so as to be suitable for intaglio printing and at least one other impression cylinder 5 is adapted for flexographic printing by having a surface of steel. The third impression cylinder 6 carried by the turret may, for example, be intended for intaglio printing and have a surface of different Shore hardness. Alternatively, the cylinder 6 may be a steel cylinder for flexographic printing but equipped with water-cooling means. Of course such a water-cooled cylinder could also be provided as a fourth cylinder carried by the turret 3. The most suitable impression cylinder for any particular printing operation is readily brought into an operative position in relation to the plate cylinder by means of the turret mounting as just described. In such operative position, the pinion 11, 12 or 13, as the case may be, of the impression cylinder will be in engagement with a central gear 14 on the shaft 10 of the plate cylinder.

A web B of material to be printed envelops the appropriate impression cylinder in the usual way and is pressed by said cylinder against the plate cylinder 1.

The other components of the printing mechanism when equipped to perform flexographic printing as shown in FIGS. 1 and 3, namely an ink trough 15, a screen cylinder 16 is carried by a frame 17, and a doctor device 18 applied to the screen cylinder, are all mounted on a working platform 19 which is supported beneath the plate cylinder 1 in vertical guides of the printing press frame and which can be raised or lowered by means of a screw 20.

The ink trough 15 can be raised or lowered with respect to the working platform 19. Such movement is effected by hand or by suitable means such as a pressure cylinder 21 permitting the trough to be moved to any desired elevation and then retained in this position. The screen cylinder 16 and the doctor device 18 are displaceable in guide rails 22 (FIG. 3) of the working platform 19 in a direction parallel to the plate cylinder 1. The screen cylinder 16 is provided with a pinion 23 (FIG. 3) which, when the cylinder 16 is displaced along the working platform 19, comes into engagement with the pinion 14 on the plate cylinder shaft 10 as soon as it has reached its operative position.

The doctor device 19 comprises a carriage 24 provided with its own lifting device of any suitable construction, for example pressure cylinders to and from which a pressure medium is led through hoses 25. The carriage 24 is so constructed and arranged (see FIG. 1) that a doctor blade 26 can be carried by it at either of its longer sides.

The plate cylinder 1 rotates anti-clockwise. For flexographic printing, therefore, the screen cylinder 16 rotates clockwise as indicated in FIG. 1. Accordingly, the doctor device 18 is arranged on the lefthand side of the screen cylinder and the doctor blade is mounted on the righthand side of the doctor device so as to face the screen cylinder.

To convert the printing mechanism to intaglio printing, the ink trough 15 is first of all lowered. As shown in FIG. 2, the screen cylinder 16 and doctor device 18 are then displaced along the working platform 19 towards the righthand side until the doctor device 18 is located on the righthand side of an intaglio plate cylinder 1' that has been installed. The screen cylinder is moved quite to one side out of the region of the trough 15 and the plate cylinder; it is not required for intaglio printing and, if there is insufficient space for it on the platform 19, the screen cylinder 16 and its supporting frame 17 can be moved onto an auxiliary platform 27 shown in chain-dotted lines in FIG. 2. The auxiliary platform is displaceable transversely to the frame of the printing press and can be used to take the cylinder away for storage. By liftinthe platform 19, the doctor device 18 is now raised to the required elevation in relation to the plate cylinder 1' and the doctor blade 26 is repositioned on the other side of the carriage 24 so that the blade will face the plate cylinder. Finally, the trough 15 is lifted so that the plate cylinder 1' will be partially immersed in the ink, and the appropriate impression cylinder 4 having a surface of resilient material as required for intaglio printing is brought into an operative position by means of the turret 3. Conversion of the printing mechanism from flexographic printing (FIG. 1) to intaglio printing (FIG. 2) is thereby completed.

Claims

We claim:

1. A printing mechanism for a printing press adapted to be converted from intaglio to flexographic printing and visa versa, said printing mechanism comprising: a press frame; a replaceable plate cylinder mounted at a fixed location in said frame; a working platform disposed beneath said plate cylinder and having a horizOntal table surface, said working platform movably mounted in said frame; means for moving said working platform towards and away from said plate cylinder; at least one horizontally positioned guide member on said working platform; a frame element movably mounted on said guide; a screen cylinder mounted on said frame element such that its axis is parallel to the axis of said plate cylinder, said frame element serving to horizontally move said screen cylinder into and out of association with said plate cylinder so that when said screen cylinder is in association with said plate cylinder the rim of said screen cylinder engages the rim of said plate cylinder; a doctor device mounted on said guide for horizontal movement to either side of said plate cylinder; a doctor blade mounted on said doctor device parallel to the axis of said plate cylinder; means for locking said doctor device in a predetermined position on said guide; an ink trough movably mounted on said working platform in such a way that the longitudinal center line of said ink trough is parallel to the axis of said plate cylinder; means for moving said ink trough between said plate cylinder and said working platform; a first impression cylinder having a resilient surface for intaglio printing movably mounted with respect to said frame; a second impression cylinder having a steel surface for flexographic printing movably mounted with respect to said frame; and bracket means movably mounted on said frame and carrying said impression cylinders for interchangeably positioning said impression cylinders so that the rim of one of said cylinders engages the rim of said plate cylinder.

2. A printing mechanism according to claim 1 including two parallel and horizontal guides.

3. A printing mechanism according to claim 1 wherein said ink trough is vertically movable, and further wherein said guide is mounted on said working platform and said frame element is sized, shaped and mounted on said guide in such a way that said screen cylinder is horizontally movable between a first position in which its axis lies in the plane defined by and is parallel to the axis of said plate cylinder and the centerline of said ink trough and a second position horizontally spaced therefrom.

4. A printing mechanism according to claim 1 further comprising an auxiliary platform which is displaceable transversely to said working platform and receives said screen cylinder when not required during intaglio printing.

5. A printing mechanism according to claim 1 wherein said doctor device comprises a carriage permitting selective mounting of a doctor blade at either longitudinal side of the carriage.

6. A printing mechanism according to claim 1, wherein said impression cylinders are carried by a common turret mounted for rotation on a shaft which is parallel to a rotary shaft of said plate cylinder, said turret shaft being displaceable to and from said plate cylinder and being adapted to have engaged therewith means for pressing the selected impression cylinder against the plate cylinder.

7. A printing mechanism according to claim 1 further including drive means attached to said doctor device for adjusting the position of said doctor device with respect to the table surface of said working platform.

8. A printing mechanism according to claim 7 wherein said drive means is a lifting device.