Method and apparatus for the drying of film lines printed in the offset method

A method and a device for the drying of a plastic foil sheet printed in the offset method which is directed through several printing stations is revealed, whereby the plastic foil is flame dried behind the last printing station in the direction of advance of the plastic foil.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method and device for drying film lines 
printed in the offset method, particularly PP (polypropylene), PS 
(polystyrene), and PE (polyethylene) films. 
2. The Prior Art 
The invention relates in particular to a method and a device for drying 
films printed in the rotary offset printing method whose printing ink is 
still wet behind the last printing station and tends to deposit or "come 
off." 
The processing of printed film lines requires that the printing inks be dry 
so that the film lines can be wound up without deposits and can be further 
processed. Conventional methods and devices are not suitable for drying 
the printing inks immediately behind the last printing station so that the 
film lines can be wound up without smearing or deposits. In the sheet-fed 
offset printing machines used earlier, this problem did not exist because 
the individual sheets were layered over one another so that a layer of air 
used for drying could be effective over a longer period of time between 
the sheets and could dry the printing ink. In the production of large 
quantities of plastic caps, plastic containers and other plastic objects, 
it has been possible in recent time to print films on rotary offset 
machines since this method allows a continuous production of large 
quantities of film lines which were not possible, to date, in the field of 
offset printing. 
The problem intensifies when the film lines are covered with lacquer 
because when the lacquer is dried, the inks which are still wet are again 
partially dissolved so that there may be smearing. Furthermore, there is 
the danger that the printing inks, which are still warm, absorb 
condensation/water after the lacquer coating, which then partially 
dissolves and smears the water-soluble paint. 
SUMMARY OF THE INVENTION 
The present invention is directed to a method and device for drying film 
lines printed in the offset method, particularly on thin plastic films 
such as polypropylene, polystyrene and polyethylene, which allow a direct 
processing of the printed film lines whereby the printing inks are 
effectively dried. 
In the present invention, flame drying is done to the film line/plastic 
foil behind the last printing station, in the direction of advance of the 
line. The flame drying thus causes a temporary high heating of the plastic 
film surface and thus shock evaporation of the solvents contained in the 
dye application. The higher the temperature of the flame, the better and 
more effective the drying. 
It is preferable to flame dry the plastic film line on its printed surface. 
This creates the advantage that only the actual printing ink on the film 
line is flame dried, whereas the film line itself, which consists of 
plastic, is only indirectly affected by the high temperature. The 
temperature of the flame drying is limited at the point where irreversible 
deformation of the film line occurs. 
Furthermore, it is preferred that the film line be cooled simultaneously 
with or after the flame drying in the direction of advance of the line. 
Such a cooling of the film line prevents its deformation as a result of 
the effects of heat of the gas flame, reduces the danger of a deposit of 
condensation/water on the film line which is later to be lacquered, and 
above all, causes a quick solidification or cooling of the printing inks. 
Furthermore, it is preferred that the cooled film line be subjected to 
lacquering. Lacquering prevents the risk of surface impurities or damaging 
effects on the film line. The actual printed sections of the film line are 
resistant to abrasion and covered; safe from becoming soiled. 
The lacquered film line preferably is subjected to hot air drying and then 
cooled. The hot air drying causes a quick drying of the surface lacquer 
whereby the subsequent cooling contributes both to the drying of the 
lacquer and to an additional drying of the ink. 
It is also preferred that the film line be predried by blasted air after 
going through a printing station. In this way, a predrying of the film 
line inks can be achieved between the individual printing stations which 
prepares them for later flame drying. It is also preferred that blasted 
air drying occur after each printing station. 
Another preferred embodiment of the invention comprises a method for the 
drying of film lines printed in the offset method in which the film line 
is run together with a paper line and wound up with it. The paper line 
takes up or absorbs the wet ink present on the printed side and prevents 
the deposit or "coming off" of the printing ink of a wrap of the film line 
on the underside of the film line wrap which lies above it. 
The device according to the invention to perform the method provides 
several printing stations whereby a flame drying station is mounted behind 
the last printing station in the direction of the line of advance. In this 
way, the flame drying according to the invention can be achieved behind 
the last ink printing station. 
The flame drying station preferably has a gas nozzle mounted on the printed 
side of the film line which is arranged so that the gas flame generated is 
directed against the printed surface of the film line. In this way, only 
the printing inks are subject to flame drying in a suitable manner, 
whereas the areas of the film line which lie below are only indirectly 
affected by the heat, while the unprinted side of the film line is exposed 
to no direct heat at all. This prevents the danger of irreversible 
deformation of the film line. 
In a preferred embodiment, a cooling station is mounted in the direct 
vicinity or behind the flame station. The cooling station causes a cooling 
of the temperature of the film line and thus hardening of the inks which 
are liquid in the heated state. 
The cooling station may include a cooling roller which is mounted directly 
below the gas nozzle on the unprinted side of the film line. In this way, 
during the flame drying, a harmful heating of the film line is avoided and 
cooling of the film line is introduced which subsequently promotes a 
cooling of the hot printed surface of the film line. 
A lacquering station, a hot air drying station, and a second cooling 
station may be mounted behind the cooling station. These stations enable 
application of lacquer to the printed side of the film line and subsequent 
hot air drying or cooling of the lacquer application which thus becomes 
scratch resistant. 
Preferably, the gas nozzle has several segmental nozzles placed over the 
width of the film line in the direction of advance of the line, which 
cover different sections of the film line on which a printing application 
is to be dried. 
Furthermore, it is also contemplated that for guiding the film lines, that 
a guide roller which has segmental wheels which touch unprinted sections 
of the film line on which no color has been applied, be used. In this 
manner, independent of the drying, it is possible to avoid contact of 
layers of the line which carry ink with the guide roller. 
Other advantages, features, and application possibilities will become 
apparent in light of the present Specification, Claims and Drawings.

BEST MODE FOR PRACTICING THE INVENTION 
While this invention is susceptible of embodiment in many different forms, 
there is shown in the drawings and will be described herein in detail 
several specific embodiments, with the understanding that the present 
invention is to be considered as an exemplification of the principles of 
the invention and is not intended to limit the invention to the 
embodiments illustrated. 
In FIG. 1, a conventional rotary offset machine is shown in which, for 
example, a polypropylene (PP) film ("plastic foil") 2 is pulled off a 
winding roller 4 and led sequentially through printing station 6, 8, 10, 
etc., where film line 2 is printed with different inks, for example, cyan, 
magenta, yellow, and black. Between printing stations 6, 8 and 10, in each 
case, a blasted air drying device 26 or 24 is mounted which directs a 
current of air at room temperature against the printed side of the film 
line in order to predry the film line. 
A flame drying station which consists of gas nozzle 12 and gas bottle 14 
connected to it, is located behind last printing station 10 in the 
direction of advance of the line. The flame drying station serves to flame 
dry the printed side of film line 2 and uses, for example, propane gas, 
natural gas, or city gas which delivers a gas flame with a temperature of 
approximately 500.degree. C. The depth or axial length of the gas nozzle 
opening is approximately 1 cm maximum. The gas nozzle is mounted over the 
film line at a distance such that the greatest temperature considered 
optimum is applied to the film line at the level of the ink application. 
Immediately beneath the flame drying station, a cooling station is located, 
mounted to the underside of the film line, which has cooling roller 16 
which cools the film line at approximately 10.degree. C. in contact with 
the underside of it. In this way, it is possible to dry printing inks 
which are still wet. 
Behind cooling station 16, lacquer station 18 is located in which the 
complete film line 2 is coated with a protective lacquer which is intended 
to protect the surface from becoming soiled, destroyed, or scratched. The 
position of cooling roller 16 is of particular significance inasmuch as 
without a cooling caused by the cooling roller, the paint would dry on the 
lacquer sheath due to its heat. 
Finally, behind lacquer station 18, hot air drying station 20 is located in 
which lacquered film line 2 is dried with hot air. The subsequent second 
cooling station 21 serves to cool the heated film line 2. Finally, film 
line 2, processed accordingly, is wound onto drum 22. Second cooling 
station 21 causes both drying of the lacquer as well as an additional 
drying of the ink which is located under the lacquer. 
In the present example, a temperature of 400.degree. to 50.degree. C. was 
observed after the lacquer drying whereas the temperature after cooling 
was approximately 300.degree. to 35.degree. C. In addition, IR drying 
devices can be provided to accelerate the lacquer drying. The high 
temperature flame drying should be adjusted in combination with the 
advance rate of the film line so that permanent deformation of the film 
line is avoided. 
Alternative preferred embodiment forms of flame drying station 12 are 
indicated in FIGS. 2 and 3. 
In FIG. 2, is a modification of a gas nozzle which extends over the total 
width of film line 2. The gas nozzle is divided into three segments 12', 
12", 12"' which extend over a short width, and which are mounted behind 
one another over a certain length and placed opposite one another over the 
width, for example, diagonally, such as indicated in FIG. 2. The 
individual gas nozzle segments 12', 12", and 12"', have a width which is 
dimensioned so that printing ink area 2', which is formed on film line 2, 
is suitably reached and covered. 
Between printing ink areas 2', empty areas exist which do not need to be 
covered by a gas nozzle segment. 
In FIG. 3, an alternative preferred embodiment form of the flame drying 
station is indicated in which three beam-like gas nozzles 12a, 12a', 12" 
which stretch over the total width of film line 2 are mounted behind one 
another at equal distances. In this way, a particularly effective 
sequential heating of the printing ink areas is achieved. This serves for 
the special application case of film lines with ink to be dried over a 
greater length. 
In general, it has been found that the solvents contained in the printing 
inks, particularly mineral oils and such types of liquids are best 
expelled with impact gas flaming. Therefore, generally a single 
beam-shaped gas nozzle 12 extending over the total width is sufficient. 
Nevertheless, a convergence of the gas flame on the axial width of film 
line 2 should be assured so that the greatest possible temperature is 
achieved in the area of the film line. 
The drying device according to the present invention causes drying of the 
inks, which are wet after print application, and particularly drying of 
the wet ink application before lacquer covering. Furthermore, the danger 
of collection of condensation/water is avoided --which would otherwise 
attack and dissolve the water-soluble lacquer. 
It is also contemplated that film line 2, which exits behind last printing 
station 10, be directed together with a paper line and wound up together 
with it so that the paper line absorbs ink residues on the film line which 
are still wet--thereby substantially precluding the coming off or deposit 
of the ink. 
The foregoing description and drawings merely explain and illustrate the 
invention, and the invention is not limited thereto except insofar as the 
appended claims are so limited as those skilled in the art who have the 
disclosure before them will be able to make modifications and variations 
therein without departing from the scope of the invention.