GB2128138A

GB2128138A - Web feed tangential to blanket cylinders in offset printer

Info

Publication number: GB2128138A
Application number: GB08327308A
Authority: GB
Inventors: Erich Wech
Original assignee: MAN Roland Druckmaschinen AG
Current assignee: Manroland AG
Priority date: 1982-10-13
Filing date: 1983-10-12
Publication date: 1984-04-26
Also published as: FR2534525A1; GB2128138B; DE3237961A1; GB8327308D0

Abstract

Several printing units (1 to 4) each having two blanket cylinders (6,7; 10,11; 14,15; 18,19) between which the web (5) is conveyed for first and second printing are arranged one behind the other in the web travel direction. To improve the printing quality, the web (5) is introduced at approximately right angles ( alpha ) with respect to a plane (B) containing the axes of the blanket cylinders (10,11) into the second and subsequent printing units. This means that the web (5) reaches the printing zone without wrapping around either of the blanket cylinders (10,11). The partial wrapping around a blanket cylinder (e.g. 10), which is desirable per se, does not occur until behind the printing zone, but this no longer has a disadvantageous effect on the printing quality. The tangential entry and partially wrapped around exit can be achieved by inclining the said planes (A,B,C and D) to each other for adjacent units and/or staggering the cylinders of adjacent units in the vertical direction. <IMAGE>

Description

SPECIFICATION Web offset-rotary printing press This invention relates to a web offset-rotary printing press with at least two printing units arranged one behind the other in running direction of the printing carrier web, and having two blanket cylinders for first and second printing between which the printing carrier web is conveyed.

From CH patent 363359 there is known a web offset-rotary printing press of the type mentioned above. Through continuous efforts to increase the rates of travel per unit of time, for the purpose of increased efficiency of the printing presses, it was discovered that with increasing machine speed the quality of the print especially in the second and in the subsequent printing units does not always meet requirements. One reason for this is the web guiding and the web disturbance that occurs with an increasing speed.

The aim of the present invention, with a press of the type mentioned at the beginning, is to improve the printing quality by an improved web guiding, preferably but not necessarily with no additional means.

According to the present invention, there is provided a web offset-rotary printing press with at least two printing units arranged one behind the other in the running direction of the printing carrier web, each having two blanket cylinders for first and second printing between which the printing carrier web is conveyed, the printing units being adapted such that the printing carrier web leaves one of the printing units with partial wrapping around one of the blanket cylinders of that unit and enters the succeeding unit at approximately right angles to a plane containing the axes ofthe blanket cylinders of that succeeding unit.

The entry of the web into a printing unit which is generally perpendicular to the plane containing the blanket cylinder axes (i.e. an entry in which the plane of the web is tangential to both cylinder surfaces), and the partially wrapped around exit can be achieved by any suitable arrangement though in a preferred arrangement the respective planes containing the axes of the blanket cylinders of the adjacent printing units are inclined to one another.

The respective said planes of alternate units may lie parallel to each other, preferably for each pair of alternate units.

Additionally or alternatively, the cylinders of two adjacent printing units may be respectively staggered in height (i.e. relative to the general longitudinal direction of movement of the web) with respect to each other.

The perpendicular or almost perpendicular guiding of the printing carrier web in the run-in area between two blanket cylinders, in accordance with the invention, means that before the printing zone there is practically no wrapping around the blanket cylinder by the printing carrier web. Thus a considerable increase in the printing quality is possible.

Wrapping around a blanket cylinder does not take place until behind the printing zone where it does not have a disadvantageous effect on the printing quality.

The web guiding of the invention can be achieved without any use of specific deflection devices.

The invention may be put into practice in a number of ways but one specific embodiment will now be described by way of example with reference to the drawing.

In the drawing there are shown schematically four printing units 1,2,3, and 4, arranged one behind the other relative to the travel direction of the web to be printed. Each printing unit has two blanket cylinders for first and second forme printing. Thus, in these printing units a printing carrier web 5 is printed on both sides as it passes respectively between the two blanket cylinders, disposed over one another, in each unit.

The printing unit 1 comprises blanket cylinders 6,7 with which are associated, in the usual manner, plate cylinders 8, 9. Each of the plate cylinders 8,9 is equipped with an inking- and dampening unit which for the sake of simplicity is not shown here. Likewise, the printing unit 2 comprises blanket cylinders 10, 11 and plate cylinders 12, 13; the printing unit3 comprises blanket cylinders 14, 15 and plate cylinders 16, 17; and the last printing unit 4 has blanket cylinders 18, 19 and plate cylinders 20, 21.

In order to make possible an entry of the printing carrier web 5 into a printing unit, especially into one or each of the printing units 2 to 4, that is approximately tangential to the blanket cylinders, i.e. without any substantial wrapping around of either blanket cylinder before the printing zone, the printing cylinders of adjacent printing units are respectively staggered as regards height; in other words, as will be appreciated from the drawing, the cylin-.

ders of adjacent units are staggered up and down relative to the general longitudinal direction of travel of the web 5.

In addition to the staggered arrangement, the respective planes containing the axes of the blanket cylinders of adjacent units are inclined to one another. The plane A containing the axes of the blanket cylinders 6 and 7 of the first printing unit 1 has an inclination from top left to bottom right, whilst the plane B containing the axes of the blanket cylinders 10 and 11 of the next printing unit 2 has an inclination from bottom left to top right. Plane C containing the axes of the blanket cylinders 14, 15 of the third unit 3 again has the same inclination as, and is parallel to, plane A; and plane D containing the axes of the blanket cylinders 18, 19 of the last printing unit 4 has the same inclination as, and is parallel to, plane B of the printing unit 2.

In accordance with the invention, by virtue of the.

inclinations of the planes A two D and/or by virtue of the arrangement of the printing unit cylinders staggered vertically, the angle x between the plane of the entering printing carrier web 5 and the respective plane (B to D) is, or is almost, 90 , which ensures that the printing carrier web 5 reaches the respective printing zone almost without any wrapping around of either of the blanket cylinders. Thus smearing, due to premature contact of the web with one of the blanket cylinders, by freshly printed ink is prevented, so that the quality of the print can be considerably improved without additional means.Wrapping around a blanket cylinder, which in itself is desirable, is not allowed until behind the printing zone at the exit from the blanket cylinders, but at this stage the wrapping around has no effect on the printing quality.

The respective planes A to D containing the axes of the blanket cylinders of alternate printing units lie parallel to each other. In the iliustrated embodiment each two alternate planes are parallel, i.e. the planes A and C of units 1 and 3 are parallel and planes B and D of units 2 and 4 are parallel.

It will be appreciated that whilst in the illustrated embodiment the planes A, B, C and D are inclined to each other for adjacent printing units and the cylinders of adjacent units are staggered, it would be possible to arrange for the perpendicular entry and partially wrapped around exit by means of inclination of the planes without staggering of adjacent units; or by staggering of adjacent units without inclination of the planes A, B, C and D for example with deflection means; or by any other suitable arrangement.

Claims

1. web offset-rotary printing press with at least two printing units arranged one behind the other in the running direction of the printing carrier web, each having two blanket cylinders for first and second printing between which the printing carrier web is conveyed, the printing units being adapted such that the printng carrier web leaves one of the printing units with partial wrapping around one of the blanket cylinders of that unit and enters the succeeding unit at aproximately right angles to a plane containing the axes of the blanket cylinders of that succeeding unit.

2. A printing press as claimed in claim 1, in which the respective planes containing the axes of the blanket cylinders of two adjacent printing units are inclined to one another.

3. A printing press as claimed in claim 1 or claim 2, in which the cylinders of two adjacent printing units are respectively staggered in height (i.e. relative to the general longitudinal direction of movement of the web) with respect to each other.

4. A printing press as claimed in any one of the preceding claims, in which the respective planes containing the axes of the blanket cylinders of alternate printing units lie parallel to each other.

5. A printing press as claimed in claim 4, in which, numbering the printing units consecutively in the web travel direction, the said planes of the odd-numbered units are parallel to each other, and the said planes of the even-numbered units are parallel to each other.

6. A printing press substantially as specifically described herein with reference to the accmpanying drawings.