Method and applicator for direct or indirect application of a liquid or pasty coating medium onto a traveling material web, notably of paper or cardboard

An applicator for direct or indirect application of a liquid or pasty coating medium onto a traveling material web, notably of paper or cardboard, includes at least one open-jet nozzle from which the coating medium issues in an open jet extending through the ambient atmosphere. The applicator also includes at least one traveling countersurface disposed opposite the open-jet nozzle and to be acted upon by the open jet. At least one jet-splitting system is arranged in the open jet in an area contained between the exit of the open-jet nozzle and the countersurface. The jet-splitting system divides the open jet into at least one diversion jet and at least one coating jet which flows on the countersurface.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method and applicator for direct or 
indirect application of a liquid or pasty coating medium onto a traveling 
material web, notably of paper or cardboard. 
2. Description of the Related Art 
Applicators are used in so-called coating systems for providing a traveling 
material web, formed for example of paper, cardboard or a textile 
material, on one or both sides with one or several layers of the coating 
medium, for example color, starch, impregnating fluid or the like. 
In the so-called direct application, the liquid or pasty coating medium is 
applied by an applicator system directly onto the surface of the traveling 
fiber material web. The web is carried during application on a rotating 
countersurface, for example an endless belt or a backing roll. In the 
indirect application of the medium, the liquid or pasty coating medium is 
first applied onto a substrate, for example the surface of a backing roll 
configured as an applicator roll. The coating medium is then transferred 
from the applicator roll to the material web, in a nip through which the 
material web passes. 
Known from German Patent Document No. DE 43 36 365 A1 is an applicator for 
direct application of a liquid or pasty coating medium onto a traveling 
material web, notably of paper or cardboard. The applicator includes a 
metering slot configured as an open-jet nozzle and from which issues the 
coating medium in an open jet extending through the ambient atmosphere. 
The applicator also includes a countersurface disposed opposite the 
open-jet nozzle, in the form of the material web supported by a backing 
roll and acted upon by the open jet. To avoid quality impairments 
occurring notably at high speeds of the material web due to air entrained 
in the coating layer, the open jet is directed, according to DE 43 36 365 
A1, in a direction opposite to the direction of travel of the material 
web. Upon impinging on the material web, the open jet splits into a 
backflow, proceeding in a direction opposite to the direction of travel of 
the material web, and a mixed flow of coating substance proceeding in the 
direction of travel of the material web. The portion of backflow 
achievable of the overall flow of the open jet amounts to about 30 to 60 
percent. The applied coating medium is subsequently profiled by a doctor 
element following the open-jet nozzle. Owing to the above measures, a good 
penetration of the coating medium into the material web is accomplished 
pursuant to DE 43 36 365 A1. Further, an entrainment of air in the coating 
medium, and thus the occurrence of undesirable air bubbles, is avoided. 
In conventional applicators of the type described above it has been found 
that the width of the metering slot forming the open-jet nozzle cannot be 
configured selectively small without entailing an untidy or disuniform 
open jet or clogging of the nozzle. This leads to a poor coating result 
and high maintenance expense. This has been found to be true particularly 
for the production of low coating weights, that is, small coating 
quantities or a thin coating. Therefore, with conventional applicators, a 
larger amount of liquid or pasty coating medium, larger than would be 
necessary for the desired coating with a low coating weight, must first be 
applied at surplus to produce a neat coating. The coating medium must 
thereafter be scraped down again. This, in turn, involves a higher energy 
demand and a larger size of the applicator and, moreover, requires more 
expensive accessory systems. 
The present invention provides an improved applicator such that the 
disadvantages associated with the prior art are avoided to the greatest 
possible extent. Also, the production of a high quality coating with a low 
coating weight can be easily realized. 
SUMMARY OF THE INVENTION 
This applicator for direct or indirect application of a liquid or pasty 
coating medium onto a traveling material web, notably of paper or 
cardboard, includes at least one open-jet nozzle from which issues the 
coating medium in an open jet extending through the ambient atmosphere. 
The applicator also includes at least one traveling countersurface 
disposed opposite the open-jet nozzle and to be acted upon by the open 
jet. At least one jet-splitting system is provided that is arranged in the 
open jet, in an area between the exit of the open-jet nozzle and the 
countersurface. The jet-splitting system divides the open jet into at 
least one diversion jet and at least one coating jet flowing onto the 
countersurface. The diversion jet is suitably returned to a pumping 
circuit and recycled. It is also possible to arrange several jet-splitting 
systems in series. The open-jet nozzle of the inventional applicator is a 
metering slot formed between two lips, the slot width being adjustable. 
Moreover, the open-jet nozzle may be equipped with at least one guide or 
deflection surface following the metering slot exit. The open-jet nozzle 
or parts thereof may be configured, for adjustment of the angle of 
impingement of the open jet on the jet-splitting surface, to uniformly 
rotate or pivot substantially across the entire machine width and/or 
zonewise. It is also possible to provide before an approach-side section 
of the jet-splitting system a device for warding off the boundary air 
layer entrained by the backing roll or the material web. The device avoids 
the occurrence of negative boundary layer phenomena and thus contributes 
to a further improvement of the coating quality. 
Owing to its jet-splitting system, the inventional applicator allows in an 
easy and effective way the production of a high quality, thinner coating, 
or lower coating weight, than would be achievable with production 
engineering measures based solely on presetting or adjustment of the 
nozzle opening width. To avoid nozzle clogging, larger nozzle opening 
widths can thus be employed while nevertheless achieving very slight 
thicknesses of the coating jet. Also possible is a finish-metering to low 
coating weights, making laborious and expensive accessory systems 
avoidable. Moreover, the jet-splitting system offers in comparison to 
conventional applicators a further option for adjustment and manipulation 
of the coating weight. Depending on the configuration of the jet splitting 
system, the portion of the coating jet of the overall flow of the open jet 
is selectable from 0 to 100 percent, enabling a very broad spectrum of 
adjustment. As needed, the jet-splitting system may also be adjusted such 
that no diversion jet occurs. Thus, the open jet is not split and flows 
strictly as coating jet onto the countersurface, a deflection of the open 
jet being optional. The inventional applicator, moreover, allows a 
distinct reduction of the amount of coating that needs to be applied onto 
the counter-surface for a high quality coating. This, in turn, enables a 
reduction of the necessary energy demand and size both of individual 
components of the applicator, such as pumps, collection containers etc., 
and also of the entire applicator. Thus manufacturing, operating and 
maintenance costs are lowered. 
According to one configuration feature of the invention, the jet-splitting 
system of the applicator includes at least one jet-splitting surface on 
which the open jet impinges at a predetermined impingement angle .alpha.. 
The coating jet departs at an angle .beta. from the jet-splitting surface, 
while the diversion jet departs at an angle .gamma.. The geometry of the 
jet-splitting surface is adapted to the desired jet-splitting properties 
as well as the flow properties of the coating medium. For example, the 
jet-splitting surface may cross-sectionally have a symmetric or asymmetric 
shape and, in addition, may also include special jet-splitting elements, 
such as cuneiform, blade-like, knife-like or tear-edge-like sections 
protruding in the open jet. The jet-splitting surface and the angles 
.alpha., .beta. and .gamma. thus allow a defined division and manipulation 
of the coating medium ejected out of the nozzle opening. The angles 
.alpha., .beta. and .gamma. depend on the shape and arrangement of the 
jet-splitting surface and may be equal or different, depending on the 
selection of the reference surfaces or references planes by which the 
angles are measured. The angle of flow .beta. of the coating jet also 
determines the angle of impingement .phi. onto the countersurface to be 
acted upon. 
Embodiments in which the jet-splitting surface, viewed in cross section, is 
straight, convex, concave or double-concave have led to particular 
jet-splitting and manipulating properties. However, the invention is not 
limited to these specific forms. Any other suitable forms may be used as 
well. 
The geometry of the jet-splitting surface can be adjustable, allowing an 
adaptation of the shape of the jet-splitting surface to altered or 
changing operating conditions both in standstill and in the operation of 
the applicator. The position of the jet-splitting surface relative to the 
open-jet nozzle and/or to the countersurface may be kept constant or, as 
illustrated in detail hereinafter, may be varied. 
According to a further embodiment of the invention, the jet-splitting 
surface is provided with a predetermined surface structure and/or surface 
coating. Depending on application, the surface of the jet-splitting 
surface may be hydraulically smooth roughened, or equipped with a special 
surface structure, for example, with a knurled or wavy surface that may 
serve to produce a specific shear rate in the coating medium flowing along 
the jet-splitting surface. Consequently, it is also possible to provide 
the jet-splitting surface with a wear-resistant coating, for example, an 
oxide ceramic layer, for wear reduction. 
In a further configuration variant of the inventional applicator, the 
jet-splitting surface is arranged so as to be movable relative to the 
open-jet nozzle and/or relative to the countersurface to be coated. The 
mobility of the jet-splitting surface allows an exact adjustment of the 
splitting conditions, the volume or mass flows of diversion jet and 
coating jet, or the previously addressed variation of the angle of 
impingement of the coating jet. The mobility of the jet-splitting surface 
also allows an adaptation of an individual jet-splitting system to altered 
or changing operating conditions, such as the selection of a different 
coating medium and the like. The applicational options of the 
jet-splitting system are thereby extended considerably. 
In this context it is also possible to arrange the jet-splitting surface, 
based on the direction of the open jet, so as to be rotatable or pivotable 
and/or allow translatory movement uniformly across substantially the 
entire machine width. These adjustment options are especially easy to 
realize in terms of engineering. Further, these adjustment options create, 
with the selected geometry of the jet-splitting surface, specific desired 
jet-splitting properties. If needed, the jet-splitting surface may be 
arranged, based on the direction of the open jet, so as to be zonewise 
rotatable or pivotable and/or to allow zonewise translatory movement. The 
jet-splitting surface is for that purpose subdivided in zone fashion or to 
allow appropriate elastic deformation across zone-like sections. A 
zonewise different adjustment of the jet-splitting surface is suited 
primarily for compensation of local manufacturing tolerances as well as 
for producing and manipulating a desired cross profile of the coating 
medium applied or to be applied. 
The invention is not limited to the types of movable arrangements of the 
jet-splitting surface described above. It is also possible to arrange the 
jet-splitting system, and with it the jet-splitting surface, so as to be 
movable in a direction intersecting the direction of the open jet, for 
alteration and/or adjustment of the volume or mass flow of the coating jet 
and/or the diversion jet. 
To adjust the jet-splitting surface in the way described above, the 
inventional applicator is equipped with at least one adjustment system. 
The inventional applicator includes at least one control system with a 
feedback control which incorporates the aforementioned adjustment system. 
This allows, specifically in the operation of the applicator, a quick and 
reliable adaptation of the respective jet-splitting surface position to 
changing operating conditions. 
Lastly, another configuration feature of the inventional applicator 
provides for the jet-splitting system to include at least one heating 
system and/or at least one cooling system. In this way, the jet-splitting 
system may be heated and/or cooled as needed, in order to influence, e.g., 
the viscosity and/or immobilization point of the coating medium making 
contact with the jet-splitting system. 
The inventional method for direct or indirect application of a liquid or 
pasty coating medium onto a traveling material web, notably of paper or 
cardboard, has the advantages already discussed in conjunction with the 
inventional applicator. 
According to a configuration feature of the inventional method, the angle 
of impingement of the open jet on the jet-splitting system is changed for 
variation and/or adjustment of the volume flow or mass flow of the coating 
jet and/or of the diversion jet, and/or for adjustment or change of the 
angle of impingement of the coating jet on the countersurface. This 
angular variation can be carried out both by appropriate movement of the 
jet-splitting system itself and by moving the open-jet nozzle or parts of 
it relative to the jet-splitting system. Moreover, this angular adjustment 
may take place uniformly across substantially the entire machine width or, 
when needed, zonewise differently. 
The inventional method is supplemented by a step in which the coating 
medium portion forming the diversion jet is collected and returned to a 
coating medium circulation. Appropriate collection systems as well as 
lines and pumping and filter systems are provided for that purpose. This 
enables the reuse of the diverted coating medium portion. Due to the 
distinct reduction of the coating quantity that is possible with the 
inventional coating method, the aforementioned applicator components 
necessary for coating medium circulation can be considerably reduced in 
size.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 illustrates one embodiment of the inventional applicator, configured 
as an applicator for indirect application of a liquid or pasty coating 
medium 2 onto a traveling material web, notably of paper or cardboard, 
including a metering system with a metering slot 4 configured as an 
open-jet nozzle and formed between two lips 6, 8. Known as such, a 
metering system of this type is being marketed, e.g., by the assignee of 
the present invention under the trade name "Jet-Flow-F." The metering slot 
4 from which coating medium 2 issues in an open jet 10 extending through 
the ambient atmosphere is opposed by a countersurface 12, which can be 
either a fiber material web in the case of direct application or an 
applicator roll in the case of indirect application, serving as a 
substrate surface to be acted upon by open jet 10. The direction of 
rotation of roll 12 is indicated by an arrow. In a not illustrated nip 
through which the fiber material web passes, coating medium 2 is 
transferred from applicator roll 12 to the fiber material web. Of the two 
lips 6, 8 forming metering slot 4, the one disposed on the side of 
metering slot 4 which applicator roll 12 approaches is called the 
approach-side lip 6. Accordingly, the second lip 8, disposed on the side 
of metering slot 4 from which applicator roll 12 departs, is described as 
the departure-side lip 8. 
A jet-splitting system D disposed in open jet 10 is provided in an area 
between the exit of metering slot 4 of the open-jet nozzle and applicator 
roll 12. Jet-splitting system D divides open jet 10 into a diversion jet 
10.4 and a coating jet 10.2 flowing onto applicator roll 12. In the 
present embodiment, jet-splitting system D is configured in the way of an 
adjustably arranged baffle with a substantially flat jet-splitting surface 
14. Open jet 10 issues out of metering slot 4 and impinges on 
jet-splitting surface 14 at an impingement angle .alpha.. Coating jet 10.2 
flows to the right and up from jet-splitting surface 14 at an angle 
.beta.. Diversion jet 10.4 flows to the left and down at an angle .gamma.. 
The angle of impingement .alpha. is measured between a tangent to the 
jet-splitting surface 14 at the point of impingement P1 of open jet 10 and 
the center thread of flow of open jet 10. The angles .beta. and .gamma. 
are measured between the center thread of flow of open jet 10 and the 
center thread of flow of coating jet 10.2 and diversion jet 10.4, 
respectively, leaving jet-splitting surface 14. The departure angle .beta. 
of coating jet 10.2 determines the angle of impingement .phi. of coating 
jet 10.2 on applicator roll 12. Angle .phi. is measured at the point of 
impinge-ment P2 of coating jet 10.2, between a tangent T to applicator 
roll 12 and the center thread of flow of coating jet 10.2. In this 
configuration, coating jet 10.2 impinges on applicator roll 12 in its 
direction of rotation. The coating is carried out finish-metered, without 
surplus; that is, a doctor element following the location of application 
is not required with this variant. 
Thus, jet-splitting surface 14 divides the overall flow (volume flow or 
mass flow) of the open jet 10 issuing out of the metering slot 4 into two 
partial flows, namely coating jet 10.2 and diversion jet 10.4 which, 
depending on the adjustment of the jet-splitting surface 14, are each 
smaller than or equal to the overall flow. The percentage of the overall 
flow of open jet 10 that forms coating jet 10.2 is adjustable, generally 
from 0 to 100 percent, as will be explained hereinafter in detail. 
The coating medium portion forming diversion jet 10.4 is gathered in a 
collection system 16 and returned to the coating medium circulation, which 
enables a reuse of the diverted coating medium portion. The lines and 
pumping and filtering systems pertaining to collection system 16 are 
referenced 18 collectively in the drawing. 
Near an approach-side section of jet-splitting system D, a system 20 is 
provided for warding off the boundary air layer entrained by applicator 
roll 12. Blowing system 20 extends substantially across the entire width 
of the applicator roll and generates by air blowout a "boundary layer 
curtain" in a direction opposite to the direction of rotation of 
applicator roll 12. System 20 avoids the influence of boundary layer 
phenomena which have a negative effect on the coating quality. 
FIG. 2a is a schematic cross-sectional illustration of the jet-splitting 
system D of FIG. 1 in a first position of adjustment, while FIG. 2b shows 
a second position of adjustment. The metering system as well as the 
collection system 16 and the systems 18 and 20 are not shown, for the sake 
of simplicity. As can be seen in these two figures, the jet-splitting 
surface 14 of jet-splitting system D is movable relative to both 
applicator roll 12 and the metering slot of the open-jet nozzle. Thus, 
jet-splitting surface 14 is also movable relative to the direction of the 
open jet 10 issuing out of the metering slot. Further, jet-splitting 
surface 14 is rotatable both uniformly substantially across the entire 
machine width and also, if needed, zonewise differently. The zonewise 
adjustability is enabled by jet-splitting surface 14 being torsionally 
elastic. To adjust the jet-splitting surface 14, an adjustment system is 
provided which includes a plurality of actuators 22. Actuators 22 act 
directly or indirectly on jet-splitting surface 14 and are spaced 
uniformly or varyingly from one another in the width direction of 
jet-splitting system D, and thus in the width direction of the machine. 
This adjustment system is incorporated in a feedback control 28 of a 
control system including at least one sensor 30. Feedback control 28 
achieves a desired cross profile and/or length profile by continually 
adjusting the setting of jet-splitting surface 14 depending on different 
measured values, such as the actual cross profile and/or length profile of 
the produced coating. 
Adjustment of the impingement angle a of open jet 10 on jet-splitting 
surface 14 is effected by rotation of the jet-splitting surface 14 as 
indicated in FIGS. 2a and 2b. The rotation allows a change or adjustment 
of the volume flow or mass flow of coating jet 10.2 and diversion jet 
10.4. Thus, the portion of the coating jet 10.2 of the entire flow of the 
open jet 10 can be selected within an adjustment range from 0 to 100 
percent, depending on rotation. With the illustrated configuration of the 
jet-splitting surface 14, changing the angle .alpha. (corresponding here, 
with the selected reference lines or reference planes, to the angle 
.beta.) occasions at the same time a change of the departure angles 
.beta., .gamma. and impingement angle .phi. of coating jet 10.2 on the 
surface of applicator roll 12. However, a variation of the angles .beta., 
.gamma. and .phi. does not mandatorily result from changing impingement 
angle .alpha., since that depends primarily on the respective 
configurations of jet-splitting surface 14 and its adjustment options. 
Namely, as already initially indicated, with the geometry of jet-splitting 
surface 14 itself configured to be adjustable, constant angles .beta., 
.gamma., .phi. can very well be realized with a variable impingement angle 
.alpha.. Similarly, it is possible to influence the portion of coating jet 
10.2 of the overall flow by suitable variation of at least one of the 
angles .beta. and .gamma.. 
As indicated in FIG. 2a, enlargement of the angle .alpha. increases the 
volume flow or mass flow of coating jet 10.2 and reduces that of diversion 
jet 10.4, thereby obtaining a heavier coating. In FIG. 2b, in contrast, 
the volume flow or mass flow of the coating jet 10.2 is reduced by a 
reduction of the angle .alpha. and the volume flow or mass flow of the 
diversion jet 10.4 is increased, thus producing a thinner coating. 
FIG. 3 shows a schematic cross-sectional illustration of a jet-splitting 
surface 14 of a jet-splitting system according to a second embodiment. 
Jet-splitting surface 14 corresponds essentially to the variant shown in 
FIGS. 1, 2a and 2b. However, it additionally possesses an integrally 
molded cuneiform jet-splitting element 24 in the center of its side 
coordinated with the open jet 10. The point of element 24 is directed into 
the open jet 10 impinging on the jet-splitting surface 14, thus more 
easily and effectively dividing the open jet 10 into the coating jet 10.2 
and the diversion jet 10.4. 
FIG. 4 shows a schematic cross-sectional illustration of a jet-splitting 
surface 14 of a jet-splitting system according to a third embodiment. 
Relative to the impinging open jet 10, the jet-splitting surface 14 has a 
double-concave cross-sectional shape. The cuneiform transition 26 between 
the two individual concave sections of this surface forms a jet-splitting 
element such as already illustrated in conjunction with FIG. 3. 
The invention is not limited to the above exemplary embodiments, which 
merely serve the general explanation of the basic idea of the invention. 
Rather, the inventional applicator may, within the scope of protection, 
also assume configurations other than described above. Specifically, the 
applicator may possess features representing a combination of the 
respective individual features. Contrary to the arrangement of the 
open-jet nozzle and the jet-splitting system as described in the 
embodiments, it is also possible to position these components in relation 
to the backing roll to be coated such that the coating jet diverted by the 
jet-splitting surface is directed opposite to the direction of rotation of 
the backing roll. Instead of the metering system illustrated above, other 
suitable open-jet nozzle applicator or metering systems are also usable, 
such as systems featuring, e.g., a concave or convex deflection surface or 
a straight guide surface. Contrary to the variant illustrated above, the 
application also may take place at surplus, if needed. That is, part of 
the coating medium applied by the coating jet is removed by a doctor 
element, e.g., a doctor blade, a roll doctor or the like, or scraped down 
to a desired cross profile and/or length profile, and thus finish-metered. 
It is also possible to adjust the jet-splitting surface by turning, 
pivoting or tilting it (e.g., at an angle .beta. slightly larger than 
90.degree.) such that no splitting of the open jet takes place, no 
diversion jet occurs and the open jet flows on the countersurface at full 
rate, directly or deflected. 
While this invention has been described as having a preferred design, the 
present invention can be further modified within the spirit and scope of 
this disclosure. This application is therefore intended to cover any 
variations, uses, or adaptations of the invention using its general 
principles. Further, this application is intended to cover such departures 
from the present disclosure as come within known or customary practice in 
the art to which this invention pertains and which fall within the limits 
of the appended claims.