GB2292341A

GB2292341A - Forme cylinder for a rotary pinting machine

Info

Publication number: GB2292341A
Application number: GB9516853A
Authority: GB
Inventors: Ingo Koebler
Original assignee: MAN Roland Druckmaschinen AG
Current assignee: Manroland AG
Priority date: 1994-08-18
Filing date: 1995-08-17
Publication date: 1996-02-21
Also published as: JPH0858066A; DE29503392U1; DE4429210A1; CA2155882A1; GB9516853D0; FR2723708B1; FR2723708A1

Description

2292341 FORM CYLINDER FOR A ROTARY PRINTING MACHINE The invention relates

to a form cylinder for a rotary printing machine, particularly to such a cylinder whose casing surface is covered with a printing foil which can be wound or wrapped round.

EP 0 512 549 Al shows a hollow drum used as a form cylinder and having in its interior a first roller and a second roller for unwinding or winding up a single printing foil or sheet, which is stretched around the outer casing surface of the form cylinder. The printing foil can for example be divided into several sections, which lie one behind the other on the casing surface, each section bearing, by means of an imprinting device, a print image for a respective colour separation, corresponding to the colour image which is to be printed on a sheet. If, for example in the offset printing process, a sheet is to be printed with four colours, then it is guided past the surface of the blanket cylinder four times by an impression cylinder, the diameter of which is only a quarter of the diameter of the form cylinder, so that the sheet is coloured with all four colours in succession. In the case of direct printing, the sheet would have to be guided past the surface of the form cylinder four times.

In the case of a printing machine constructed in this way, registration problems can occur if the printing form carrying all four colour separations stretches, because the stretching has a smaller effect on the first colour separation than on the fourth colour separation. Since the printing foil is elastic and has a limited tear resistance, it cannot be attached sufficiently tightly to the casing surface of such a large form cylinder, with the result that in the case of too high a tension the foil would tear, and in the case of too low a tension the foil would pucker. Apart from this, it is not explained in EP 0 512 549 how the rollers can be removed again from the interior of the drum if a new foil is to be stretched over the 5 drum.

A form cylinder over which likewise a single printing foil is stretched is known from DE 43 03 872 Al. The form cylinder has in its interior a pit or axial groove containing two rollers, which are used to unwind and wind up the printing foil. The rollers are inserted into the pit either through an opening in the casing surface of the form cylinder or through an opening on the end side. The two rollers are preferably also arranged in a cassette, which can be removed from the form cylinder.

An object of the invention is to develop a form cylinder with which inaccuracies in registration owing to stretching of the printing foil are reduced.

The present invention proposes using at least two foils lying one behind the other in the direction of rotation. These printing foils or foil sections may each be held at least at both ends, or in some embodiments over their entire circumferential length. This enables mis-registration due to stretching to be substantially reduced.

A particular advantage of a first embodiment of the invention is the fact that a plurality of printing foils each covering only one respective circular arc section can be transported by means of rollers more easily than a single printing foil which covers almost the whole circular arc of the casing surface of the form cylinder. A further advantage results from symmetrically spacing the pits for accommodating the rollers for a corresponding number of printing foils on the casing surface of the form cylinder, so that an even mass distribution of the form cylinder is achieved and as a result imbalances are avoided. In accordance with a second embodiment, the printing foils can be applied to the casing surface of the form cylinder in a simple manner by means of a feeding device. 5 For a better understanding of the invention embodiments of it will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a form cylinder with four printing foils stretched over its casing surface, the leading and trailing edges or ends of which printing foils are each secured to winding rollers; Figure 2 shows a form cylinder having four segments, each with a printing foil stretched over it; 15 Figure 3 shows a form cylinder similar to that in Figure 1, having additional guide rollers for transporting the printing foils; Figure 4 shows a form cylinder with printing foils and winding rollers arranged in cassettes, and 20 Figure 5 shows a form cylinder with external devices for applying and removing the printing foils. A form cylinder 1 (Figure 1) is covered with four printing foils 2 to 5. The beginning and end of each of the printing foils 2 to 5 is secured to a respective winding roller 6 or 7. The winding rollers 6 and 7 are rotatably mounted in circumferentially evenly spaced pits 8 in the interior of the form cylinder 1 and are spaced from each other in such a way that inside the same pit 8 each winding roller 6, 7 can be covered in a multi-layered manner with one of the printing foils 2 to 5. The winding rollers 6 and 7 each holding a printing foil 2 to 5, are turned in the same direction and thus the printing foil 2, 3, 4, 5 can be further transported, e.g. advanced, in order either to make a fresh imprint on a new portion of the printing foil 2, 3, 4, 5 while in place in the printing machine using an imprinting device (not shown here), or to bring an already imprinted portion of the printing foil 2, 3, 4, 5 to the casing surface of the form cylinder 1 and to wind up an already printed portion of the printing foil 5 2, 3, 4, 5 onto the respective other winding roller 6, 7. Preferably, however, the winding rollers 6, 7 can be moved in both directions, so that already used portions of the printing foils 2 to 5 can be wound back again later and used again for printing.

The openings 9 in the casing surface of the form cylinder 1, which lead to the pits 8, are preferably substantially smaller than the diameter of the winding rollers 6, 7 in order to use for the exit of the foil only as small as possible a portion of the casing surface of the form cylinder 1. If the diameter of the winding rollers 6, 7, is larger than the width of the opening 9, the winding rollers 6, 7 have to be inserted into the interior of the form cylinder 1 by way of openings in one of the side walls in which the form cylinder 1 is mounted, and through an opening in the end side of the form cylinder 1 itself. It is already known from DE 35 43 704 Al to provide an opening in the side wall in order to exchange the sleeve of a form cylinder without having to remove the form cylinder itself from the printing machine. It is also possible to provide only the end side of the form cylinder with openings if the form cylinder is taken out of the printing machine to change the foil.

In a further embodiment (Figure 2), a form cylinder 10 has removable segments 12 to 15, which are secured around a rotatably mounted core 11 and over each of which are stretched the four printing foils 2 to 5. By means of gripping devices, which are not represented here, the segments 12 to 15 can for example be removed from the core of the form cylinder 10 and covered with new printing foils 2 to 5. The printing foils 2 to 5 in this case are also preferably secured to winding rollers 6, 7 in such a way that they can be wound up and unwound.

As shown in Figure 3, in connection with either of the embodiments represented in Figure 1 and Figure 2, guide rollers 17 can be further provided on the edges 16 which lead in from the casing surface of the respective form cylinder 1, 10 into the interior. These guide rollers facilitate the transportation of the printing foils 2 to 5. The use of such guide rollers is already known per se from DE 43 03 872 Al.

As shown in Figure 4, the winding rollers 6, 7 can also be arranged in cassettes 18, which, together with the winding rollers 6, 7, can be removed from a form cylinder 19. The cassettes 18 are pushed into the form cylinder 19 through an opening in its front wall; the beginning of the printing foils 2 to 5 is subsequently pulled out of the form cylinder 19 through slits 20, in each case from the first winding roller 6 in the direction of the casing surface of said form cylinder 19, is wrapped around the respective section on the casing surface and is then secured in the associated second winding roller 7.

Instead of the printing foils 2 to 5 each being movably secured to winding rollers 6, 7 which are mounted inside the form cylinder, in a further embodiment (Figure 5) several pieces of a printing foil 21 are attached or applied to the external casing surface of a form cylinder 23 by means of a feeding device or applicator 22 installed in the printing machine. The feeding device 22 may have on the end that faces the form cylinder 23 a winding roller 24, by means of which the printing foil 21 is unwound and placed onto the casing surface of the form cylinder 23, while the latter rotates. The printing foil 21 is subsequently cut off by a cutting device 25. The sections of the printing foil 21 are either secured to the casing surface of the form cylinder 23 by electrostatic attraction, i.e. by applying a voltage difference between the printing foil 21 and the form cylinder 23; or the form cylinder 23 has a device 27 for producing an under-pressure in its interior, and ducts 28 which extend radially in respect of the casing surface and through which air flows, and by producing an under-pressure the sections of the printing foil 21 are secured to the form cylinder 23. Instead of the ducts 28, the form cylinder 23 can also have a porous, air-permeable casing layer.

The printing foil 21 can also be held to the surface of the cylinder electrostatically; in this case the printing foil 21 and the form cylinder 23 should each have a respective live layer. The live layers must be separated by a dielectric, insulating layer.

This dielectric layer can be part of either the form cylinder 23 or the printing foil 21, or both.

The imprinted printing foils 21 can be subsequently removed again in a simple manner by producing an excess pressure or by reversing the voltage. The printing foils 21 are removed for example by means of a gripper 26.

Also in the case of the embodiments shown in Figures 1 to 4 can the winding up of the printing foil 2 to 5 onto the casing surface, or the unwinding of the printing foil 2 to 5 from the casing surface of the form cylinder 1, 10, 19, be facilitated by means of air pressure, i.e. by forming an air cushion between the casing surface and the printing foils 2 to 5, or by appropriate polarisation of the live layers. In order to improve the mobility of the printing foils 2 to 5, the casing surface of the form cylinder 1, 10, 19 or 23 can be polished very smooth; in particular it can be coated with a plastics material which has gliding qualities.

The printing foils used in the above-represented embodiments are either already imprinted or are electrically, chemically, optically, thermally or magnetically imprinted inside the printing machine. The printing foil is preferably imprinted by means of a laser beam. For this purpose there is provided an imprinting device, which is either rigidly arranged in the region of the form cylinder 1, 10, 19 or 23, or can be pivoted up to it.

The form cylinders represented in Figures 1 to 5 are particularly suitable for multi-colour printing, in which case each casing surface section carries the print image of a different colour. In accordance with the number of sections, inking units can be arranged on the periphery of the form cylinder 1, 10, 19, 23, the inking rollers of which inking units being pivotable so that these inking units each provide only one of the sections with printing ink. In the case of offset printing of a sheet with four colours, a sheet is guided by a delivery cylinder past the casing surface of the form cylinder whose diameter amounts to only a quarter of the diameter of the form cylinder 1, 10, 19, 23, and the sheet is thus coloured with all four colours. In this way the sheets can be coloured with a high register consistency in one printing unit. As a result of the fact that the printing foil is attached to the casing surface of the form cylinder 1, 10, 19, 23 in four individual sections 2 to 5, 21, the formation of swelling or puckering as a result of contact with the inking rollers and the blanket cylinder (indirect printing) or with the inking rollers and the impression cylinder (direct printing) is considerably reduced in comparison with a form cylinder with only one individual printing foil which covers almost the whole casing surface; register adjustment between different inking units is then unnecessary. By means of the imprinting unit, an accurately positioned imprinting can be achieved, even if the printing foil was not previously attached precisely.

The printing foil represented in Figures 1 to 5, which is attached in sections, can be used in all direct or indirect printing processes, in particular also in gravure printing, letterpress printing and flexographic printing. It is also suitable for waterless offset printing.

Embodiments of the invention thus provide a form cylinder for a rotary printing machine whose casing surface is covered with at least two printing foils 2 to 5, which lie one behind the other in the direction of rotation. The printing foils 2 to 5 are held either by winding rollers 6, 7, onto which they can be wound up or from which they can be unwound, or electrostatically or pneumatically. The printing foils 2 to 5 are preferably imprinted within the printing machine by means of an imprinting device.

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Claims

1. A form cylinder (1, 10, 19, 23) for a rotary printing machine, having casing surface adapted to receive at least two printing foils (2 to 5) which lie one behind the other in the direction of rotation.

2. A form cylinder (1, 10, 19, 23) according to claim 1, in which the printing foils (2 to 5) in use are arranged symmetrically around the circumference of the cylinder.

3. A form cylinder (1, 10, 19, 23) according to claim 1 or 2, in which the securement of the printing foils (2 to 5) to the casing surface of the form cylinder (1, 10, 19, 23) is electrostatic or by underpressure.

4. A form cylinder (23) according to any preceding claim and further including a first device (22) for applying the printing foils (2 to 5) and a second device (26) for removing them.

5. A form cylinder (1, 10, 19) according to any one of claims 1 to 3, in which the printing foils (2 to 5) are stretched movably over the casing surface of the form cylinder (1, 10, 19), and their ends are each secured to winding rollers (6, 7), which are mounted in the interior of the form cylinder (1, 10, 19) in such a way that they can be rotated in at least one direction.

6. A form cylinder (10, 19) according to any preceding claim, in which the printing foils (2 to 5) are each arranged on segments (12 to 15), which can be removed, together with the printing foils (2 to 5), from the form cylinder (10, 19).

7. A form cylinder (1, 10, 19) according to claim 5, in which the winding rollers (6, 7) are arranged in cassettes (18), which can be pushed into and pulled out of the form cylinder (1, 10, 19) through its end wall.

8. A form cylinder (1, 10, 19) according to any of claims 5 to 7, and having axially extending pits (8) in which the winding rollers are mounted.

9. A form cylinder (1, 10, 19) according to one of claims 5 to 8, in which arranged on the edges of the mouth of the pits (8), leading to the casing surfaces of the sections of the form cylinder (1, 10, 19), there are guide rollers (17) for easing the movement of the printing foils (2 to 5).

10. A form cylinder (1, 10, 19, 23) according to any preceding claim, in which the form cylinder has a smooth casing surface, which exerts only a small static friction on the printing foils (2 to 5).

11. A form cylinder (1, 10, 19, 23) according to any preceding claim, further including means for removing the attached printing foils (2 to 5) from the form cylinder (1, 10, 19, 23) by producing an excess air pressure between the casing surface of the form cylinder (1, 10, 19, 23) and the underside of the printing foils (2 to 5), resting on the casing surface, or by applying electric potentials of the same sign to the casing surface and also to the printing foils (2 to 5).

12. A form cylinder substantially as described herein with reference to the accompanying drawings.

13. A printing machine incorporating a form cylinder according to any preceding claim.

14. A printing machine according to claim 13, in which the form cylinder is mounted in the side walls of the machine and is adapted such that the printing foils can be put into place or removed in an axial direction of the cylinder, one of the side walls of the machine having on an end side of the form cylinder (1, 10, 19) an opening through which the printing foils, e.g. on cassettes (18), can be taken out of the form cylinder (1, 10, 19).

15. A printing machine according to claim 13 or 14, in which the foils bear different colour components of a single picture.

16. A printing machine according to any of claims 13 to 15 and including a means for imprinting the printing foils (2 to 5) while mounted in the printing 5 machine.

17. A method of applying a print foil to a form cylinder, in which the foil is wound off a feeder (22) in sections and held on the cylinder, for instance by electrostatic attraction or an under-pressure.