Printing – Inkers – Fountains
Patent
1993-08-16
1996-03-12
Fisher, J. Reed
Printing
Inkers
Fountains
B41F 3106, B41F 3108
Patent
active
054977029
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a device for coating moving strips of material and relates in particular to an ink chamber doctor blade for an inking, screened circular cylindrical body such as an engraved roller or gravure inking cylinder on a printing press.
PRIOR ART
Amongst known single-chamber doctor blades, the ink in the lower part of the ink chamber is conveyed either to the centre or to both ends of the chamber and then flows into the ink duct in longitudinal direction parallel to the engraved roller while being swirled by the rotating engraved roller, then being again removed in the upper part of the ink chamber. The single-chamber doctor blade has a positive blade and a negative blade which scrapes off the surplus paint in the upper part of the ink chamber while the engraved roller rotates at a circumferential speed of e.g. 100 r.p.m.
A disadvantage with this is that the very numerous small cups in the engraved roller gradually fill up with ink residues and old printing ink in the course of time and can then no longer adequately take up new printing ink, so that the printing quality deteriorates quite appreciably. Engraved rollers must therefore be brushed down and cleaned with highly aggressive media at regular, brief intervals, e.g. weekly, which with the extremely small screen separation of the cups is highly labour-intensive if thorough cleaning is to be achieved.
In addition, with the known single-chamber doctor blade, a high pressure builds up in the ink chamber at higher circumferential speeds of the engraved roller through which the upper negative blade may arch outwards in the rotatory direction of the roller so that the knife edge of the negative blade no longer lies flush along the circumference of the roller, but is tilted slightly, resulting in a kind of aquaplaning effect lifting the edge of the blade from the circumference of the roller so that the ink is no longer completely cleaned from the bridges between the screen cups.
In addition, it should be noted that liquid ink is composed of solvents and solid particles in addition to other components. These solid particles, used for pigmentation, are certainly intimately mixed with the solvent, yet solid particles may be separated from the solvent by centrifugal force which results in a change in color.
This risk is due especially to uncontrolled swirling of the ink in the doctor blade box, which is the greatest at the inlet to the ink chamber on the doctor blade box and we assume different dimensions between the inlet duct and the outlet duct before again stabilizing only before the outlet duct.
Further, with the known ink chamber doctor blades, whether a cup on the engraved roller is filled with fresh ink or not when passing the doctor blade box is largely left to chance. Gaps in the printed image are the result. This applies analogously also to ink chamber doctor blades with a gravure roller on gravure presses and to chamber doctor blades with engraved roller for the uniform application of thin layers of adhesive on carrier foil or strip material or for applying thin magnetic coatings to magnetic tapes e.g. for tape recorder or video cassettes.
An ink chamber doctor blade of the type first mentioned is known from DE 37 37 531 A1 which is designed as a forme cleat for a flushing inking mechanism on a rotary press. A moulding is fitted in the ink distribution chamber on this inking cleat between two doctor blades, around which the ink can flow freely and which can pivot or rotate. By this means, by creating a uniform ink flow without turbulence, uniform contact is possible between the ink and the inking roller at high circumferential speeds and an ink flow pressure can be adjusted for better filling of the cups on the inking roller. The moulding has an elliptical cross section. Tilting the moulding around its axis of rotation therefore produces a change of the smallest gap width, the gap being formed by the engraved roller and the surface area of the moulding facing the roller. The strength of the ink in the gap is
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Fisher J. Reed
Namic B.V.
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