Printing – Rolling contact machines – Rotary
Patent
1996-06-03
1998-08-04
Burr, Edgar S.
Printing
Rolling contact machines
Rotary
101488, B41F 352, B41F 2304
Patent
active
057878099
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a device as well as a method for producing printed sheets, e.g., a device for producing printed sheets from a web in a web-fed offset press.
It is known that, in web-fed offset printing, the web, printed on its front and back, is heated to approximately 120.degree. C. to dry the ink. Then the web is cooled, moistened, possibly folded, and separated from the web as sheets.
The waves that occur in the finished product, the individual sheets, are disadvantageous in these known devices and methods. This wave formation has been the frequent subject of studies; despite all efforts, the waves that occur in web-fed offset printing have thus far not been eliminated, but their amplitude has been reduced (see FOGRA, Report 4.035, 1989). This procedure which reduces the amplitude takes its departure from the idea that as a result of the escape of water during drying of the web, combined with tension on the web, a waviness forms, so that attempts have been made to eliminate these so-called climate or tension waves by subsequently re-moistening the dried and cooled web. These attempts have had only moderate success, however.
SUMMARY OF THE INVENTION
The goal of the invention is to improve on a device for producing printed sheets from a web in a web-fed offset press, as well as a method, in such fashion that smooth, unwavy sheets can be obtained.
According to the invention, the printed web, immediately before running onto the first cooling roller, is deflected at least once by means of a web expander, once or several times in opposite directions of curvature, preferably by nozzle boxes.
Thus, deflection can be caused by a stream of compressed air. The deflection can be performed after hot drying, and, additionally, the web can be precooled before running onto at least a first cooling roller.
Surprisingly, it has been found that by virtue of this simple measure, wave formation in the sheets is practically completely eliminated and, in contrast to the prior art, smooth, unwavy sheets are obtained for the first time. The mechanism on which this striking effect is based is not known at the present time. Perhaps it consists in the fact that as a result of the (at least single) deflection, forced relaxation and flattening of the web occurs prior to its running onto the first cooling roller, so that as the web runs onto the first cooling roller, no waves can form to then be impressed by wrapping around the cooling roller or rollers because of the different radius of curvature of the wave against the roller, with the web also being stabilized by the cooling effect on the printing coating. This problem is solved in a surprisingly simple fashion by the teaching according to the invention.
A device is known (DE3128430 C2, FIG. 3) in which the web, before running onto the (at least first) cooling roller with its first radius of curvature and its first curvature direction, is deflected by a second radius of curvature in a second curvature direction opposite the first. Apart from the fact that this deflection is not performed immediately before the web runs onto the first cooling roller but only at a considerable distance before that point, this measure serves as a path compensation device for the web by virtue of the adjustability of the calender rolls of the cooling mechanism. Thus this path compensation device can be located before or after the cooling mechanism and plays no role in the arrangement of the direction of curvature of the deflection before the first cooling roller, and is purely arbitrary. A device is also known (JP2-59348 (A) in Patent Abstracts of Japan, M-974, May 16, 1990, Volume 141, No. 231), in which deflection occurs ahead of the first cooling roller as described above. Here however there is no direct arrangement of the web before it runs onto the first cooling roller, and the available second radius of curvature is so small that the effect according to the invention cannot be achieved, and in addition this device serves to strip a laminar layer of solven
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patent: 5547225 (1996-08-01), DeAngelis
patent: 5606914 (1997-03-01), Borgardt
Burr Edgar S.
Colilla Daniel J.
Eltex-Elektrostatik GmbH
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