Printing – Planographic – Multicolor
Reexamination Certificate
1999-06-17
2001-09-11
Colilla, Daniel J. (Department: 2854)
Printing
Planographic
Multicolor
C101S232000
Reexamination Certificate
active
06286425
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a sheet-fed rotary printing machine having a plurality of units arranged in tandem, at least one unit being an offset printing unit or a varnishing unit, which includes a first cylinder transporting the sheet and a second cylinder opposite the first cylinder, the first and the second cylinder being mounted so that they are disengageable from one another. The invention also relates to a method of transporting sheets through at least one of the units of the printing machine.
In multicolor printing machines of the foregoing type, downline of which a varnishing unit may be arranged, the paper sheets are often printed with color only in the first printing units. Following printing units or the varnishing unit run “empty” at the same time if this is required by the relevant print job, specifically if either the maximum number of colors for which the machine is equipped are not needed, or if no application of varnish is desired by the customer.
When “running empty” in this manner, the previously freshly printed sheets are conveyed through the succeeding printing unit or units, while the rubber blanket cylinder of the offset printing unit, for example, or the varnishing blanket cylinder of the varnishing unit are disengaged from the associated impression cylinder, i.e, the sheets are gripped at the leading end thereof by grippers on the respective impression cylinder and, in contact wit h the latter, are transported through the small nip which is then produced between the respective impression cylinder and the rubber blanket and varnishing blanket cylinder, respectively.
Because of the high machine speeds, however, the sheets lift off the respective impression cylinder, and the freshly printed side of the sheets touches the rubber blanket or varnishing blanket, with the result that the ink applied to the sheets becomes smeared. This can occur even at relatively low speeds if the printing material has a given stiffness. This is because heavy paper grades have a greater tendency to lift off the impression cylinder because of the centrifugal forces, as do stiff boards as well as a result of the attempt thereof to assume the stretched-out position, and become smeared on the rubber blanket cylinder in the narrow nip of about 5 mm. between the impression cylinder and the rubber blanket cylinder.
In order to avoid this problem, it has been proposed, for example in the published German Patent Document DE 43 18 777 C2, to hold down the freshly printing sheets with blown air as they pass through the printing nip. German Patents DE 689 632 and DE 44 43 493 treat in general terms the problem of flexurally stiff materials lifting off the impression cylinder, and propose the provision of cones or cylindrical rollers which act mechanically upon the edge of the sheet to be printed, so that the sheets to be printed are held down thereby. However, such cones or cylindrical rollers cannot readily be arranged at the critical location, namely the narrow nip between the impression cylinder and the rubber blanket or varnishing blanket cylinder, the nip, after the rubber blanket or varnishing blanket has been disengaged or brought out of contact and removed, being about 5 mm. wide.
SUMMARY OF THE INVENTION
Based upon the foregoing prior art, it is accordingly an object of the invention to provide a sheet-fed rotary printing machine which permits a smear-free sheet run through printing and varnishing units, respectively, thereof, which have been disengaged or brought out of contact, and a method of transporting sheets to accomplish this objective.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention of the instant application, a sheet-fed rotary printing machine having a plurality of units arranged in tandem, at least one of the units comprising a first cylinder for transporting a sheet, and a second cylinder disposed opposite the first cylinder, the first cylinder and the second cylinder being mounted so as to be disengageable from one another; the second cylinder being stoppable and having a device by which an outer portion of the second cylinder is displaceable.
In accordance with another feature of the invention, the at least one unit is selected from the group thereof consisting of a printing unit and a varnishing unit.
In accordance with a further feature of the invention, the first cylinder for transporting the sheet is an impression cylinder, and the second cylinder is a cylinder selected from the group thereof consisting of a rubber blanket cylinder and a varnishing blanket cylinder of an offset printing unit and a varnishing unit, respectively.
In accordance with an added feature of the invention, the second cylinder is uncouplable by a clutch from a drive of one of the printing and the varnishing units, respectively.
In accordance with an additional feature of the invention, the second cylinder is stoppable in a position wherein the displaceable outer portion thereof is disposed opposite the first cylinder.
In accordance with yet another feature of the invention, the displaceable portion of the second cylinder has a clamping device for a covering of the second cylinder.
In accordance with yet a further feature of the invention, the displaceable portion of the second cylinder forms part of the circular outer surface of the second cylinder.
In accordance with yet an added feature of the invention, the displaceable portion of the second cylinder is removably fastened to the latter.
In accordance with yet an additional feature of the invention, the outer portion of the second cylinder is displaceable into the interior of the second cylinder.
In accordance with still another feature of the invention, the displaceable portion of the second cylinder is mounted so as to be pivotable about an axis aligned parallel to an axis of rotation of the second cylinder.
In accordance with still a further feature of the invention, the displaceable portion of the second cylinder is provided with an outwardly pivotable sheet guide element.
In accordance with still a further feature of the invention, the sheet guide element is formed with a surface which, when in an outwardly displaced position, extends concentrically with the surface of the first cylinder.
In accordance with still an added feature of the invention, the portion of the second cylinder is displaceable linearly in a direction towards the interior of the second cylinder.
In accordance with another aspect of the invention, there is provided a method of transporting a sheet through a disengageable unit selected from the group consisting of printing and varnishing units in a sheet-fed rotary printing machine, which comprises providing a first cylinder for transporting a sheet, and a second cylinder located opposite the first cylinder; stopping the second cylinder in a position wherein a movable, outer portion of the second cylinder is disposed opposite the first cylinder; and removing the movable, outer portion of the second cylinder or displacing it in a direction towards the interior of the second cylinder.
In accordance with another mode of the method according to the invention, wherein the second cylinder is one of a rubber blanket and a varnishing blanket cylinder of an offset printing unit and a varnishing unit, respectively, having a blanket clamping device, the method includes removing the blanket clamping device or displacing the blanket clamping device into the interior of the second cylinder.
In accordance with a further mode of the method according to the invention, wherein the second cylinder has a convex outer surface having one segment, the method includes removing the one segment of the convex outer surface of the second cylinder or displacing the one segment inwardly.
In accordance with a concomitant mode, the method of the invention includes initially removing the blanket selected from the group consisting of a rubber blanket and a varnishing blanket, respectively, from the second cylinder; then positioning th
Leib Rudolf
Stephan Gunter
Colilla Daniel J.
Greenberg Laurence A.
Heidelberger Druckmaschinen AG
Lerner Herbert L.
Stemer Werner H.
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