Printing – Processes – With heating or cooling
Patent
1996-01-23
1997-03-04
Eickholt, Eugene H.
Printing
Processes
With heating or cooling
101484, 101491, 101417, 1014241, 1014242, 101487, 101216, 226 10, 226 45, 34625, B41F 2304
Patent
active
056069146
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process and an apparatus for printing webs of foil by web offset printing.
DESCRIPTION OF THE PRIOR ART
In the manufacture of plastic lids for food containers, for instance margarine cups, plastic foils are first of all printed flat and then brought into the desired shape by, for instance, deep-drawing.
At the present time, various processes are employed for the printing of the plastic material. For all processes, suitable plastic material is first of all extruded in the form of foil webs and wound onto rolls.
Large runs are printed in rotogravure with inks having a high content of solvent, a lengthy IR drying time being necessary. The production of the gravure cylinder is, of course, very difficult and expensive and requires long lead times (as a rule, at least six weeks). For these reasons, the rotogravure process cannot be employed for medium-size runs or where changes in design in a short time are desired.
It is furthermore known to print foil webs with UV drying inks in the web offset process. To be sure, strict requirements with respect to compatibility with the environment (see, for instance, Technical Instruction--Air) apply to UV-drying inks. This process is also only conditionally suitable for the manufacture of plastic containers. The foil webs printed in this way can, to be sure, also be shaped, but the UV-drying inks are brittle and cracks therefore occur upon the shaping so that the finished containers are not acceptable, at least from an aesthetic standpoint.
For medium-size runs, a sheet offset printing process is at present employed. The extruded plastic webs are cut into sheets, which are stacked. The sheets are then printed individually with oxidatively drying inks in a sheet-offset printing press by the dry offset printing process. The sheets then pass, one after the other, through an IR drying device. Before the stacking of the sheets, they are powdered with, for instance, a flour. A suitable particle size assures aeration between the sheets and thus easier drying and at the same time prevents the ink which has been applied and dried from detaching itself from the plastic layer and transferring itself onto the back of the sheet lying on top of it. Before the further processing of the sheets for the manufacture of, for instance, foodstuff containers, the sheets are again individualized and welded to each other at their edge so as to form a web, since it is only in web form that the printed material can be introduced economically into a suitable vacuum deep-drawing machine in which the container is shaped.
This process for medium-size runs of first of all cutting the plastic webs into sheets which are then individually printed, and then again bringing said sheets into web form by welding them together is, of course, very expensive. Therefore, for a long time it has been endeavored to print the plastic webs by web-offset printing before the deep-drawing. One problem in this connection is that UV inks which dry easily and rapidly by UV irradiation cannot be used in the offset printing process since - - - as mentioned above - - - the UV inks tear apart or become unsightly due to their brittle character upon the subsequent deep-drawing of the plastic web.
The use of oxidatively drying inks has not led to satisfactory results in web offset printing up to now despite many attempts by those skilled in the art. Since the oxidatively drying inks are not completely dried upon emergence from the IR drying device, the above-mentioned "transfer" onto the back of the following portion of the web occurs upon the winding of the web onto rolls.
With the present sheet offset printing process, on the average (including stop times) about 5000 sheets per hour are printed. The maximum speed of the sheet offset printing process is about 6500 sheets per hour. This would correspond in web offset printing to a speed of about 50 meters per minute (with a length of sheet of about 1/2 meter). Even attempts at operating the web offset printing with even lo
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Casella Anthony J.
Cleanpack GmbH Innovative Verpackungen
Eickholt Eugene H.
Hespos Gerald E.
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