EP0194616B1 - Printing unit for a rotary offset printing press - Google Patents

Description

The invention relates to a printing unit for an offset rotary printing press with at least one blanket cylinder assigned to a plate cylinder, onto which an underlying blanket can be clamped.

Printing units of this type are generally known (for example Walenski "Introduction to offset printing").

At high working speeds of a rotary printing press, the vibration behavior of the cylinders involved in the printing is increasingly noticeable on the printed product. As is known, the printing unit cylinders, in particular blanket cylinders and plate cylinders, are mainly caused to oscillate when the cylinder pits overflow. Such undesirable vibrations can also occur when changing the flanks of the gears of the drive of the printing couple cylinders and of the dampening and inking units. The following prior publications exemplify the efforts of the professional world to eliminate such vibrations, to dampen them or to prevent them from occurring: DE-C-26 13 688, DE-B-11 93 516, DE-C-11 93 516.

From GB-A-1 065 727 it is also known to use printing documents with different thicknesses in relation to the circumference. This enables the use of plates and printing forms of different thicknesses.

A resounding success has not been achieved to date. In particular, all of these known proposals have the disadvantage that the measures used to suppress the bending vibrations were carried out directly on the cylinder, which on the one hand means a considerable manufacturing outlay and on the other hand does not allow any counter-correction of the bending vibrations required for each special machine and speed.

The same measures are taken for each machine only within certain series. On the other hand, if a machine of a series falls out of its vibration behavior from the vibration characteristics determined for this series, it is difficult to carry out an individual correction afterwards.

• Fig. 1 eine herkömmliche Offset-Rotationsdruckmaschine und
• Fig. 2a-d spezielle bestimmten Arbeitsgeschwindigkeiten zugeordnete Gummituchunterlagen.

It is therefore an object of the invention to demonstrate a measure with which the effects of the vibration behavior of each machine on the printed products can be individually eliminated or at least reduced. This object is achieved by applying the features of the characterizing part of claim 1. Advantageous further developments result from the description and from the subclaims in connection with the drawings. In these show:

• Fig. 1 shows a conventional offset rotary printing machine and
• 2a-d rubber blanket pads associated with specific working speeds.

The schematic printing unit structure shown in FIG. 1 shows two plate cylinders 1, 2 which can be adjusted on two blanket cylinders 3 and 4. With such a cylinder configuration, a print carrier 5, for example a paper web, can be printed on both sides.

The invention is based on the knowledge that although each printing machine series shows a characteristic vibration behavior, but that each printing machine also has a special, that is to say individual, vibration behavior, which is also speed-dependent. Evidence of this is provided by tests on printed copies of different machines of the same series, which are produced at different speeds. In particular, differences in the intensity of the printing inks vary according to their location and thickness in accordance with the selected working speeds of the machine at which printing is carried out. Building on this finding, documents 6, 7, 8 are created for the rubber blankets to be stretched, which have different thicknesses when viewed in the circumferential direction of the cylinders 3, 4. A special pad 6 to 9 is produced for each individual machine for different speed or working ranges. This is done by determining the position and intensity fluctuation of so-called print strips on the printed copy, and depending on this, the thickness of the base to be used for this speed range is determined.

According to FIG. 2a, a base 6 is produced for a specific speed, which has a thickened area 10 and thin areas 11. The thickened area 10 can come to rest, for example, where the cylinders carrying the pressure carrier 5, here 3 and 4, swing apart at a certain speed range. This could due to the decreasing pressure in the transfer of color to the print carrier 5, the color intensity decrease. At this point the thickened area 10 on the base 6 counteracts the decreasing pressure between the cylinders. The documents 7, 8, 9 according to FIGS. 2b, c and d were created in a corresponding manner for other speeds, at which, as already mentioned, a different vibration pattern has to be taken into account.

As the above explanations show, using the teaching according to the invention results in the advantages of being able to individually counteract the cylinder vibrations with regard to their undesirable effect at any speed range without complex processing of the printing couple cylinders, so that a noticeable improvement in the quality of the printed copies can be expected, which is due to Application of these measures.

Claims (2)

1. Printing unit for an offset rotary printing machine having at least one rubber blanket cylinder (3, 4) associated with a plate cylinder (1, 2), onto which a supported rubber blanket can be clamped, characterised in that seen in the peripheral direction the support layers (6, 7, 8, 9) are of varying thickness and in that each of the support layers (6, 7, 8, 9) is assigned to a rotary speed range corresponding to the desired operating speed of the machine, and in that the arrangement of the areas (10, 11) of varying thickness corresponds with regard to size and position to the oscillation characteristics determined individually for each machine.

2. Printing unit according to claim 2, characterised in that the support layers (6, 7, 8, 9) are made of cardboard, plastics, metal or the like.

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