Printing – Planographic – Dampeners
Reexamination Certificate
2000-03-16
2002-10-08
Funk, Stephen R. (Department: 2854)
Printing
Planographic
Dampeners
C101S352010
Reexamination Certificate
active
06460455
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for dampening a rotating planographic printing form via an ink applicator roller for indirectly dampening the planographic printing form and via a connecting roller that is in engagement with the ink applicator roller and is engaged by a dampener roller for dampening the planographic printing form. The invention relates, furthermore, to a dampening unit of a planographic printing machine having a first dampening unit roller engaging solely with a dampener roller.
Two fundamental possibilities for dampening planographic printing forms have become known heretofore, namely, on the one hand, a direct application of pure dampening medium via a dampener roller and, on the other hand, an indirect application of dampening medium in the form of a printing ink/dampening medium emulsion via a dampener or dampening medium applicator roller or an ink applicator roller.
Modern offset printing machines have inking and dampening units, during a coupled operation of which the dampening medium is applied to the printing form partly indirectly via a dampener roller and partly indirectly via an ink applicator roller located immediately downline from the dampener roller, as viewed in the direction of rotation of the printing form cylinder, and the dampener roller applies a dampening medium/printing ink emulsion to the printing form. The indirect application of dampening medium is made possible by a connecting roller coupling the ink applicator roller with the dampener roller.
A dampening/inking unit of such an offset printing machine is described, for example, in the published German Patent Document DE 87 16 847 U1. For indirect dampening, the dampening/inking unit has an ink applicator roller and a dampener roller. An ink distributor roller forms a connecting roller arranged between the ink applicator roller and the dampener roller. This document which describes a utility model says nothing with regard to the type of rotary drive of a dampening roller solely engaging the dampener or dampening medium applicator roller, i.e., whether the dampening roller is driven by the dampener or dampening medium applicator roller, for example, via friction, or as to the circumferential speed of the dampener or dampening medium applicator roller. A disadvantage of this dampening/inking unit is that the printing form dampened by the latter has to be washed comparatively frequently, particularly when fluffy print carriers are being printed, because free paper fibers or lint causing so-called hickeys in the print image are deposited on the printing form as a result of an absence of rolling slippage between the dampener roller and the printing form. The frequent washing, in the case of print orders with a large run, results in printing interruptions which, respectively, entail restart paper wastage or spoilage.
A dampening and inking unit described in the published German Patent Document DE 31 46 223 C2 is another example for the construction of such offset printing machines. The problem described hereinabove cannot be solved by this dampening and inking unit, because the dampener roller, referred to therein unusually as an ink applicator roller, has to rotate at the circumferential speed of the plate cylinder, as is stressed expressly in this German patent document.
Furthermore, the German Patent Document DE 93 05 742 U1 describes a dampening unit for offset printing machines, having an applicator roller which, although capable of being driven at a different speed from that of a plate cylinder, does not engage or rest against a connecting roller, so that this dampening unit can be used only for direct dampening via the applicator roller, and not for indirect dampening. A printing ink/dampening medium emulsion forms on the applicator roller as ink is removed from the printing form.
In order to achieve good print quality, what is sought after is the assurance not only of ghost-free inking, but also of ghost-free dampening of the printing form. The requirements are very stringent in this respect, particularly with regard to the dampening units indirectly dampening the printing form. In the construction of dampening units, these requirements can be satisfied by a dampening-unit roller rolling solely on the dampener or dampening-medium applicator roller.
A dampening unit described in the published German Patent Document DE 91 10 345 meets the demands or requirements with respect to a ghost-free application of dampening medium only when straightforward direct dampening is employed. In this dampening unit connection, a dampener roller engages a dampening distributor roller driven, via gearwheels and consequently formlockingly or positively, via shaft journals of the dampener roller, and is separated from an inking unit roller located adjacent thereto. In this regard, it is noted that a formlocking connection is one which connects two elements together due to the shape of the elements themselves, as opposed to a forcelocking connection which locks the elements together by force external to the elements. One disadvantage of the dampening unit described in the published German Patent Document DE 91 10 345 is that no dampening unit connection is provided therein for the indirect dampening of a plate cylinder. Throwing the dampener roller onto the inking unit roller located adjacent thereto serves either for utilizing the dampener roller as an applicator roller for solely applying printing ink to the plate cylinder or as a washing connection. Moreover, throwing the dampener roller onto the inking unit roller adjacent thereto necessarily gives rise, because of the construction, to throwing the dampener roller off the dampening distributor roller that is mounted in a side frame so as to be fixed against movement relative to the latter, so that, for this reason too, ghost-free indirect dampening by this dampening unit is not possible.
Furthermore, the published German Patent Document DE 29 02 228 C2 describes an inking unit and a dampening unit wherein, during indirect dampening, an inking unit roller rotates at a surface speed corresponding approximately to the surface speed of the plate cylinder, and dictates the surface speed of a dampener roller engaging the inking unit roller and, therefore, rolls on the plate cylinder without slippage. Only during straightforward direct dampening separate from the ink supply does the dampener roller rotate at a circumferential speed that is about 10% above or below the circumferential speed of the plate cylinder. A serious disadvantage of this dampening unit is that there is no dampening unit roller provided therein for smoothing the film of dampening medium on the dampener roller and, for this purpose, engaging solely with this dampener roller. A dampening unit roller for transferring the dampening medium from a water fountain roller onto the dampener roller lacks the construction-related precondition that is necessary for the effective prevention of ghosting and thereby calls for engagement only with the dampener roller.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for dampening a planographic printing form indirectly by which paper wastage or spoilage is reduced, and to provide a dampening unit for performing the method of dampening a planographic printing form in a virtually ghost-free manner.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method for dampening a rotating planographic printing form via an ink applicator roller for indirectly dampening the planographic printing form and via a connecting roller in engagement with the ink applicator roller and engaged by a dampener roller for dampening the planographic printing form, which comprises, during dampening, rotating the dampener roller at a circumferential speed differing from the circumferential speed of the planographic printing form.
In accordance with another mode, the method of the invention includes rolling a first dampening uni
Eltner Bruno
Möller Bernd
Zuber Mathias
Funk Stephen R.
Heidelberger Druckmaschinen AG
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