Printing – Inkers – Roller
Reexamination Certificate
1999-12-22
2002-08-06
Eickholt, Eugene (Department: 2854)
Printing
Inkers
Roller
C347S002000, C347S103000, C101S365000
Reexamination Certificate
active
06427591
ABSTRACT:
The invention relates to an inking unit for a printing machine, which includes at least one ink roller rolling on a plate cylinder of the printing machine, an ink jet printing apparatus with a plurality of ink jets that can be controlled selectively, and an ink transfer device with a rotating mantle surface for transferring printing ink from the ink jet printing apparatus to the at least one ink roller.
DESCRIPTION OF RELATED ART
Inking units with an ink duct as a supply container for printing ink, an ink doctor roller, an ink lifter, and an arrangement of many ink rollers that roll on one another and/or on the plate cylinder of the printing machine, including ink transfer rollers, brayer rollers, and ink application rollers, are frequently used in offset printing machines. The amount of printing ink needed is set by zones, as a function of the print image shape. A resilient blade (doctor blade) is pressed against the doctor roller to a greater or lesser degree, and therefore the amount of ink which passes through the gap between the doctor blade and the doctor roller is changed. Regulation of the amount of printing ink over the entire width of the doctor roller is done by a change in the ink take-off strip, which is taken from the doctor roller by the ink lifter, in a rhythmic pendulum motion. The printing ink is distributed, split up, and spread out by an axial movement of the brayer rollers, by means of the subsequent arrangement of hard and soft rollers with different diameters, before it is applied to the plate cylinder by means of the ink application rollers.
Such inking units that are divided into ink zones over the width of the print, have a number of electronic or electro mechanical control and setting elements for the doctor blades and other devices, with which the machine operator can vary the feed of ink in accordance with the subject of the print, over the width of the print. The number of ink zones is based on the size of the setting elements used, the justifiable effort and expense, and the width of the print form. With an increasing number of narrow ink zones, the number of display elements that can be printed increases, but the working time and the number of discard sheets also increases, especially if a manual color correction takes place during printing by widening or reducing the ink zone size. The ink zone size, together with the doctor roller stroke, determines the ink zone width that is necessary at the specific location of the sheet.
One problem with such inking units is so-called stenciling, a shadow-like image of a previous part of the printed image, which repeats in the printing direction. This image shows up as a greater or lesser coloration in comparison with the surrounding area. The intensity of stenciling can be reduced by brayer rollers that distribute the ink along the width of the print, and/or by ink application rollers, among other things. In every case, however, a large number of rollers is required in the inking unit, in order to guarantee the most uniform possible thickness of the ink layer on the ink application rollers, and finally on the plate cylinder, by using as many division locations as possible. In spite of this, there are many inadequacies that remain, caused by the width and number of ink zones, such as degraded print in the border zones, excess ink feed or insufficient ink feed.
As an alternative to the inking units with many rollers that have been described, inking units with a short construction length, such as anilox inking units are known, which have so-called chamber doctor blade ink ducts. However, ink feed by zones is not possible with a chamber doctor blade ink duct. The depth and the number of depressions on the raster roller and the amount of ink taken off per sheet determines the amount of ink supplied per revolution of a single revolution plate cylinder.
German Patent Application 43 27 212 A1 describes an inking unit in which metered ink application onto the mantle surface of an ink roller takes place according to the ink jet principle. The ink application process is controlled using digital data derived from data for production of the print form. The ink jets of the ink jet apparatus are either directed onto an ink application roller which rolls on the plate cylinder of the printing machine, or onto an ink roller that passes the ink directly to the ink application roller.
In principle, this system results in an inking unit with a short construction length, with ink application that can be precisely metered both in the width direction of the roller in accordance with ink regulation by zones, as in inking units with zones, and also in its circumferential direction. A disadvantage of this system is that since braying does not take place, a high level of stenciling occurs. This can only be counteracted if the ink is transferred from one roller to another leaving as little residue as possible, so that the resolution of the ink jet printing apparatus is as high as possible. Ideally, the resolution of the ink jet printing apparatus should be as high as the required print quality. This calls for a type of indirect ink jet printing, which means that the advantages of offset printing, namely inexpensive printing of high-quality editions, no longer exist.
SUMMARY OF THE INVENTION
The invention is an inking unit for high-quality printing, that has a short construction length and is free of stenciling.
In one embodiment, the invention is an inking unit for a printing machine, that includes at least one ink roller rolling on a plate cylinder of the printing machine, an ink jet printing apparatus with a plurality of ink jets that are selectively controllable, and an ink transfer device with a rotating mantle surface for transferring printing ink from the ink jet printing apparatus to the at least one ink roller, wherein the at least one ink roller and the ink transfer device have an outside circumference substantially equal to an outside circumference of the plate cylinder.
The inking unit in accordance with the invention has at least one ink roller and an ink transfer device, which is an ink transfer roller, that have the same outside circumference as the plate cylinder, and that are all single revolution rollers. In this manner, the amount of ink which belongs to a certain image region of the subject of the print, and which is precisely metered, is always applied at the same location on the ink transfer device and all the other rollers, from which it is also passed on to the sheet. This makes it possible to reliably avoid the effect of stenciling, which occurs in known short inking units because of insufficient braying.
Another embodiment includes ink application onto the at least one ink roller in such a way that the most uniform ink application possible, viewed in the circumferential direction, takes place. By adjusting the ink jet printing apparatus to the contour of the at least one ink roller, several ink jets can be arranged one behind the other, viewed in the circumferential direction. This makes it possible to apply many small dots of ink onto the ink roller, corresponding to a film-like coating. This makes it unnecessary to have the high degree of braying that is required when lifting an ink strip using an ink lifter. In addition, an ink zone which is normally 32 mm wide can be defined to be much narrower, because of the high resolution which can be produced using an ink jet apparatus. This also makes better metering possible, although ink distribution is not adapted to the subject of the print in the circumferential direction.
In comparison with a conventional inking unit with a doctor roller and a lifter, the invention also results in elimination of many mechanical parts, so that the machine runs more quietly.
Quieter operation of the machine results not only from the elimination of side-to-side braying, as mentioned above, but also from the more uniform application of ink in the circumferential direction. This means that in conventional inking units, particularly in short inking units, a temporary tightness of th
Eickholt Eugene
Heidelberger Druckmaschinen Aktiengesellschaft
Kenyon & Kenyon
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