Flexographic printing press with variable printing length

Details Flexographic printing press with variable printing length Flexographic printing press with variable printing length

1996-12-18

1998-01-13

Eickholt, Eugene H.

Printing

Rolling contact machines

Rotary

101248, 101349, 101178, B41F 500

Patent

active

057067252

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a flexographic printing press.
Flexographic printing presses usually have several color printing units, which are disposed at the periphery of a common back pressure cylinder and in each case have an impression cylinder as well as an applicator roll. The function of the applicator roll is to ink the block on the impression cylinder. For this purpose, the applicator roll typically has on its surface a uniform grid of cells, which are filled with printing ink with the help, for example, of a "Kammerakel" (literally: comb doctor blade). The applicator roll with the ink-filled cells rolls along the periphery of the impression cylinder and transfers the ink to the raised, printing parts of the block. For this purpose, it is important for the applicator roll and the impression cylinder to have exactly the same circumferential speed, so that the ink is not smudged as it is being applied on the impression cylinder. Usually, this accomplished owing to the fact that, seated on the shaft of the applicator roll, there is an applicator roll gearwheel, which meshes with an impression cylinder gearwheel seated on the shaft of the impression cylinder, the diameter of the rolling circle of the applicator roll gearwheel being equal to the external diameter of the applicator roll and the rolling circle diameter of the impression gearwheel being equal to the external diameter of the impression cylinder.
The material to be printed is looped about the greater part of the periphery of the back pressure cylinder, so that there is practically no slippage between the back pressure cylinder and the material to be printed and, accordingly, the web velocity of the material to be printed is equal to the peripheral speed of the back pressure cylinder. In the ideal case, the peripheral speed of the back pressure cylinder and thus also the web speed of the material to be printed are identical with the peripheral speed of the impression cylinder, so that the image to be printed is transferred cleanly to the material to be printed.
For numerous conventional flexographic printing presses, the color printing unit is driven by a central wheel, which is fixed to the shaft of the back pressure cylinder, meshes with the impression cylinder gearwheels of all color printing units and the radius of the rolling circle of which is equal to the external radius of the impression cylinder (plus the thickness of the material to be printed), so that any slippage between the impression cylinder and the material to be printed is avoided.
Since the transmission ratio between the impression cylinder and the back pressure cylinder can assume only discrete values corresponding to the ratio of the number of cogs of the impression cylinder gearwheel to those of the central wheel, only discrete values can be selected in this case also for the circumference of the impression cylinder, namely, whole number multiples of U/Z, where U is the circumference of the back pressure cylinder and Z is the number of cogs of the central wheel. The circumference of the impression cylinder determines the so-called printing length, that is, the length of the printed images, which are produced by rolling the impression cylinder on the material to be printed and repeated in the longitudinal direction of the material to be printed.
If the material printed runs on continuously to a downstream processing station, such as a punching machine, which is to operate with accurate registration with the printed image, the printed length must agree accurately with the working length of the downstream processing station.
For many practical applications, the working length of the downstream machine is fixed by the requirements of the product. For example, it is frequently desirable that sheets of a specified length, which in each case carry a single printed image with accurate registration, are punched out of the printed sheet with the help of a punch. In this case, therefore, the printed length would have to be adapted to the desired sheet leng

REFERENCES:
patent: 2128343 (1938-08-01), Bemis et al.
patent: 2170286 (1939-08-01), Hintze et al.
patent: 2869459 (1959-07-01), Bohme
patent: 3163109 (1964-12-01), Stelling, Jr.
patent: 4651641 (1987-03-01), Kawata et al.
patent: 5009158 (1991-04-01), John et al.
patent: 5010813 (1991-04-01), Buffo
patent: 5447101 (1995-09-01), Weis

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