GB2276125A

GB2276125A - Rotary offset printing unit

Info

Publication number: GB2276125A
Application number: GB9405039A
Authority: GB
Inventors: Rainer Burger; Hans Mamberer
Original assignee: MAN Roland Druckmaschinen AG
Current assignee: Manroland AG
Priority date: 1993-03-16
Filing date: 1994-03-15
Publication date: 1994-09-21
Anticipated expiration: 2014-03-15
Also published as: FR2702706A1; CH686882A5; GB2276125B; JPH06297670A; FR2702706B1; GB9405039D0; DE9303835U1

Abstract

When a cylinder 14 of a printing unit having superimposed double printing elements 1, 2 working on the rubber-on-rubber principle functions only as an impression cylinder (ie. the forme cylinder 12 and cooperating blanket cylinder 14 are inoperative for printing) there is a tendency to contamination with ink and paper dust. This is reduced by giving the transfer cylinder 14 an ink-repellent coating. The coating may be in the form of a metal or plastics foil clamped above the normal rubber blanket, or may be evaporated onto the blanket as a Cr or Ni layer; the coating is hydrophilic in all cases. <IMAGE>

Description

Printing unit for rotary offset The invention relates to a printing unit for use in particular in an offset rotary printing machine having a transfer cylinder which at least in some modes of operation does not transfer ink.

Printing units of this type are generally known and one speaks of a so-called "eight tower", for instance, when four double printing elements are arranged one above the other. With such an "eight tower" a web can be printed, for instance, on both sides in four colours. In the case where a web side is to be printed with only three colours one printing point is closed down, i.e. printing does not take place there, or the printing element does not really have to be built in at all. However, a cylinder is still required for use as an impression cylinder for the printing element on the other side of the web. This cylinder picks up ink and paper dust from the printing point located before it in the web running direction (set off). It is an aim of the invention to reduce or to remove completely the tendency of such a cylinder to become contaminated by ink and paper dust.

According to the invention there is provided a printing unit having at least two printing elements operating on the rubber-on-rubber principle and wherein at least one of the transfer cylinders in one mode of operation does not transfer a printed image to the web, this transfer cylinder having an ink-repellent surface.

By making the surface of the transfer cylinder, which when in printing mode would be hydrophobic, instead ink-repellent or hydrophilic its tendency to accumulate contamination is reduced. This can be achieved either by fitting an ink-repellent cover to the existing blanket, or by fitting a replacement blanket or cover sheet or plate which is ink-repellent, either intrinsically or by virtue of a surface coating or treatment, or by any other suitable measure which preserves the mechanical properties of the transfer cylinder.

For a better understanding of the invention an embodiment will be explained in detail below with reference to the accompanying drawings, in which: Fig. 1 shows a schematic side view of two double printing elements arranged one above the other, and Figs. 2 and 3 show different coatings of an impression cylinder in section.

In Fig. 1 two double printing elements 1, 2 are arranged one above the other. The double printing elements 1, 2 can also be seen as parts of a so-called six or eight tower when one or two other double printing elements are arranged over them. The lower double printing element 1 contains the printing elements 3, 4 each having a forme cylinder 5, 6 and a transfer cylinder 7, 8, while the upper double printing element 2 contains the printing elements 9, 10 each having a forme cylinder 11, 12 and a transfer cylinder 13, 14. A dampening unit 15 and a washing device 16 are arranged on or near the transfer cylinder 14.

In the illustrated state of the printing element tower a web 17 is provided with a 2/1 print, as is shown symbolically with the triangles. The rubber-onrubber principle is used, that is to say that the blanket or transfer cylinder 13 on one side of the web is used as the impression cylinder for a corresponding transfer cylinder 14 on the other side, and vice versa in full operation. However, here the printing element 10 is out of action, i.e. its transfer cylinder 14 does not transfer a printed image to the web 17. For this purpose the forme cylinder 12 is out of contact with the transfer cylinder 14. However, it would also be possible for the forme cylinder 12, together with the inking and dampening unit not shown, not to be provided at all.

The transfer cylinder 14 is covered with a printing blanket 18 and a metal plate 19 lying above it. Both are advantageously clamped by means of the usual blanket-clamping elements which are present in the transfer cylinder 14. This can, for instance, be a spindle clamping device which is not shown. For this purpose for instance the ends of the printing blanket 18 and the metal plate 19 are clamped in clamping strips 20 (Fig. 2) which are suspended into the spindles of the rubber blanket clamping device. The printing blanket 18 can be a flexographic blanket or a compressible or incompressible printing blanket.

However, any other type of simple carrier material can also be used. The metal plate 19 can be constructed as steel sheet, steel foil or chromed plate.

The plate or foil 19 has oil- or grease-repellent properties which mean that deposits of ink and paper dust on the transfer cylinder 14 can be suppressed. In addition it can be dampened by means of the dampening unit 15 which further promotes the anti-set-off effect.

The cleanness of the transfer cylinder 14 can be improved by the use of the washing device 16 which works better with a chrome layer, for instance, than with a rubber blanket, but the use of the dampening unit or the washing device is not necessarily stipulated by the invention. The metal plate 19 should not be very stiff and therefore should be thin so as to be able to follow the deformation of the blanket 18.

The metal plate 19 and the printing blanket 18 can also be vulcanised to each other or stuck together. Instead of the metal plate 19 a plastic foil can also be clamped onto the printing blanket 18, provided it has the required hydrophilic properties.

As a further variant the transfer cylinder 14 can be surrounded merely by an intrinsically ink-repellent printing blanket, metal plate or plastic foil gripped in clamping strips as in Fig. 2, for example, and slotted into the rubber blanket clamping devices of the transfer cylinder. The printing blanket can be made of rubber or a resilient plastic material and be compressible or incompressible.

A further variant of the ink-repellent surface of the transfer cylinder 14 is shown in Fig. 3. Here an ink-repellent layer 22, for instance of chrome or nickel, is evaporated onto a printing blanket 21. For the clamping the printing blanket 21 is again clamped in clamping strips 23.

The advantage of using conventional rubber blanket clamping elements of the transfer cylinder for securing the ink-repellent coating is that in the normal print function it is easily possible to re-fit the cylinder with a rubber blanket. Subsequent extension by fitting a forme cylinder 12 to make a complete printing element 10 not present in the original state is thus possible very quickly and economically.

The invention may be applied at multiple locations in a printing unit with a larger number of superimposed double printing elements, for instance in an eight tower, if several printing points are out of action or are not fully constructed.

Claims

1. Printing unit having at least two printing elements operating on the rubber-on-rubber principle and wherein at least one of the transfer cylinders in one mode of operation does not transfer a printed image to the web, this transfer cylinder (14) having an ink-repellent surface (18, 19; 21, 22).

2. Printing unit according to claim 1, in which the transfer cylinder (14) is covered with an ink-repellent printing blanket, metal plate or plastics foil.

3. Printing unit according to claim 1, in which the transfer cylinder (14) is covered with a blanket (18) and an ink-repellent upper plate (19)

4. Printing unit according to claim 1, in which the transfer cylinder is covered with a printing blanket (21) on to which an ink-repellent layer (22) is evaporated.

5. Printing unit according to any preceding claim, in which the printing blanket (18), with the upper plate (19) if present, is clamped on to the transfer cylinder (14).

6. Printing unit according to any preceding claim, in which a dampening unit (15) is arranged on the transfer cylinder (14).

7. Printing unit according to any preceding claim, in which a washing device (16) is arranged on the transfer cylinder (14).

8. An offset rotary printing machine including two or more pairs of rubber-on-rubber printing elements at least one of which is as claimed in any preceding claim.

9. A printing unit substantially as described herein with reference to any of the accompanying drawings.

10. A method of converting a rubber-on-rubber offset printing press by adding or removing a colour application point, in which an ink-transferring blanket is replaced by or substituted for an ink-repellent cover on one of the transfer cylinders.