Device and process for applying a fluid or pasty material onto a moving bed

The invention relates to an apparatus for applying a liquid or pasty application medium to a moving substrate under USAGE formation of a veil applicator unit, which discharges the application medium in the form a veil or curtain gives off the ground, the lau Fende underground by direct application being the surface of a material web, in particular of paper or cardboard, and is the case of indirect application Surface of a transfer element which discharges the application medium then transmits to the material web, and wherein a suction device for Aspirating entrained by the substrate and / or of the veil Air is provided.

In the coating of a running subsoil by a veil Applicator, ie the so-called "curtain coating", is the liquid or pasty application medium at a predetermined height above the lau issued fenden subsoil of the veil applicator and falls into Form a veil or curtain on the moving substrate. There a Such application medium curtain is a relatively unstable structure, must in largely be taken to ensure that the impact conditions of Application medium curtain arranged on the moving base so are that they achieve a high-quality job result ses permit. In particular, interruptions of the color curtain must before be bent, as these particularly violent form of contract medium splashes lead. Of central importance is obtains control Research of the boundary layer of air, which is of the moving base to ner surface is brought in the impact area. This can even if it does not pierce or under the application medium curtain breaks through formation of air bubbles between the substrate and the Application medium, uniform coverage of the substrate with at Contracting medium prevent.

In German Utility Model 297 11 713 was therefore pre schla gen, in the running direction of the substrate before impingement of the contract provide medium to the substrate a blow nozzle, which one of the Running direction of the substrate opposite air jet ejects. This Air jet "cuts" in the boundary layer of air and raises it thus from Surfacing from. However, the application medium curtain is determined by the generated due to the interaction of boundary layer of air and blowing air Turbulence affected. The application medium had therefore high Excess will be applied to the moving substrate to a be able to provide sufficiently stable coating medium curtain.

In the generic US 5,624,715 introduction of the air border is layer in the application area by means of a blade more difficult that in angeord small distance from the surface of the current subsoil is net. The blade is disposed downstream of a suction device, which not only the remaining entrained by the moving substrate air, but also the the application medium curtain entrained air from the contract area sucks. But now, the labile application medium curtain not only by too high caused by the entrained air boundary layer hervorgeru positive pressure, but also by one by the suction device concerned be affected to strong vacuum. Even when using known from US 5,624,715 applicator is therefore required the application medium with a large excess of the current raise underground and ERS excess application medium again doctoring to a correspondingly stable application medium curtain and a ensure high-quality job result. This required both in the area of ​​the curtain applicator unit as well as in the field of Doctor device according to large-sized supply or return lines and correspondingly powerful feed pumps for the job medium.

EP 0517223 B1 discloses a method for the treatment of the order medium known in accordance with which to achieve a high hochwerti Located gen order result of air bubbles from the coating medium will.

By contrast, the object of the invention to provide an applicator of specify the type mentioned, in which the circulating amount of Application medium, the diameter of the return lines as well as the performance the feed pumps are reduced for the application medium.

This object is inventively achieved by an applicator of initially dissolved mentioned type which a back pressure Bestimmungsvor device for determining the in the direction of lower pressure water accumulated on the ground in principle before the impingement of the veil Air, and a control device for controlling the suction power of the suction device as a function of the dynamic pressure of the determining device certain back pressure comprises. In the apparatus according to the invention can the ruling on behalf range pressure regardless of the term speed of the substrate, the rate of fall of the contract medium and the like parameters always a for achieving a quality job result set low value be by the suction power of the suction device, depending on the controlled determination result of the dynamic pressure-determining device becomes.

Basically, the best, the front in the running direction of the substrate the impingement of the veil ruling backpressure directly by at least one pressure sensor to detect. Because on the one hand, the suction device before the impact area must be arranged and other the function of at least one pressure sensor by contract medium spatter may be affected, but the back pressure can also indirectly or can be determined indirectly. This may be an example Speed ​​sensor for detecting the running speed of the sub- be in principle provided. This is possible because the front of the Impingement prevailing dynamic pressure mainly from the underground entrained air boundary layer and partly from the contract from medium curtain entrained air boundary layer arises, wherein the case speed of the application medium curtain usually for Laufge speed of the substrate in a specific ratio is to when striking the ground the formation of coating medium prevent splashes. It should be noted that the possibility of a medium ble determination of the dynamic pressure in addition to direct storage pressure determination may be used.

In development of the invention it is proposed that the contract medium a solids content of between about 5% and about 80%, preferably of between about 30% and about 75%, including. Further , the application medium at least one inorganic or organic Pigment and at least one synthetic or natural binder contain.

The application device according to the invention, an example Coat weight per order of between about 2 g / m² and about 40 g / m². preferably of between about 3 g / m² and about 30 g / m², be achieved, the words "per order" indicates that it is one of providing Multi-layer coating of the material web is further possible to have multiple inventions provide training proper applicators.

With the applicator according to the invention it is not only possible, the reduce circulating amount of application medium and thus the power the feed pump lower. Moreover, it is also possible for the to increase running speed of the substrate, for example, more than 600m / min, preferably more than 1000 m / min. Further, the width the material to be coated web more than 2.5 m, preferably more than be 4.0 m.

To improve outcome of the contract is further proposed that in the running direction of the substrate before impinging at least one attached scraper for scraping of gear carried by ground air is classified. With this scraper, the entrained air boundary layer lifted from the ground and deflected toward the suction device will. Since the suction device thus no longer for lifting Air boundary layer required suction power has to apply, they can ent be formed speaking lower power. However, it constitutes a Squeegee a wearing part is that out confusion from time to time must be rare. It is therefore on the respective application and Randbedin conditions depend on whether an application device according to the invention with a such scrapers and for a corresponding benefit poorer suction device or an application device without such a scraper and with correspondingly more powerful suction the economically is more advantageous solution.

Finally, direct application may also be a device for stabilization be provided ren of the run of the web, for example a further Suction device, which on the side remote from the curtain coater Side of the web creates a vacuum, the material web the against a supporting element, preferably a backing roll, draws.

According to a further aspect, the invention relates to a method for Applying a liquid or pasty application medium to a run underground using a curtain applicator unit. respect Lich of the prior art, the disadvantages and the contrast with the method and its modifications recoverable Benefits may be made to the foregoing discussion of the invention referenced application device.

The invention is described below using an exemplary embodiment with reference to the accompanying drawings are explained in detail, in which the single figure a schematic side view of an inventive Auftragsvor represents direction.

In this single figure, a erfindungsgeinäße applicator is quite generally <b>10</b> designated. A moving in the direction L Mate rialbahn <b>12</b> is in the area of ​​the applicator <b>10</b> a backing roll <b>14</b> led around which turn around an axis A in the direction of the arrow P is driven. Further, a veil applicator<b>16</b> provided from its distribution channel <b>16</b>a liquid or pasty application medium <b>18</b> by an outlet gap <b>16</b>b emerges and as an application medium curtain or -Curtain <b>20</b> in freefall to the surface <b>12</b>a web of material <b>12</b> emotional. The coating layer thus formed<b>22</b> For example, by a not shown, but known in the art Metering and / or leveling device of excess application medium are freed and / or smoothed.

In order to ensure that the coating medium <b>18</b> transversely Q uniformly as possible to the material web <b>12</b> is discharged, it is necessary that the coating medium <b>18</b> on the performance gap <b>15</b>b via the entire length of the distribution channel <b>16</b>a with substantially the same Pressure is applied. To achieve this, the coating medium is supplied to the distributing channel <b>16</b>A usually at one end via a supply, not shown, line supplied with a large excess, and is not through the outlet splitting emitted application medium <b>18</b> on the respective other end of the distribution channel <b>16</b>a discharged through a discharge line again and in a Coating medium supply recycled. In addition, the can of the metering and / or leveling device worn coating medium ge collected and supplied to the coating medium reservoir for reuse will. To the circulation quantity of the coating medium<b>18</b> minimize and therefore use low-power, high-throughput weak to feed pumps can, it is known in the art as a variant, a distribution channel <b>16</b>a use, the passage cross section of its Infeed decreases to its discharge end towards. The invention Training of the applicator <b>10</b> offers a further possibility for Reducing the circulation rate of the application medium.

In the running direction L before the site or in the transverse direction Q extending line T, at which the application medium curtain <b>20</b> on the upper material web area <b>12</b>a impinges, wherein the application device erfindungsgeinäßen <b>10</b> a suction device <b>24</b> arranged, which in transversely Q substantially over the entire width of the web <b>12</b> extends. The suction <b>24</b> is used for sucking air, which from the material train <b>12</b> in its movement in the direction L on their surface <b>12</b>a as Air boundary layer <b>26</b> or / and the application medium curtain <b>20</b> at its Surface as a boundary layer of air <b>28</b> in the area B before the point of impact T of the application medium <b>18</b> on the material web surface <b>20</b> in trans is ported and there to form a relation to the normal Pressure increased back pressure results.

In the region B is also at least one pressure sensor <b>30</b> provided wel Cher the value of the back pressure detected and a corresponding signal via a signal line <b>30</b>a to a control unit <b>32</b> transmitted. Further, on the Axis A of the support roll <b>14</b> a speed or speed sensor <b>34</b> arranged, the detection signal through a signal line <b>34</b>a well the control unit <b>32</b> is supplied. The pressure sensor<b>30</b> used for direct or direct detection of prevailing in the area B jam pressure. By contrast, the back pressure can be in the range B of the speed or speed signal of the sensor <b>34</b> only indirectly or medium bar determined. It should be understood that to this indirect determination backpressure knowledge of other operating parameters is required For example, the diameter of the support roller <b>14</b>Texture insbesonde re roughness, the material web surface <b>12</b>a, composition and Vis viscosity of the coating medium <b>18</b> and the like parameters that a Effect on the air entrainment capability of the material web <b>12</b> and contract medium curtain <b>20</b> have. The indirect determination of the range B prevailing dynamic pressure has the advantage that the suction of air from the area B by the pressure sensors not <b>30</b> and their signal lines <b>30</b>a is hindered.

From the over her lines <b>30</b>a and <b>34</b>determines a supplied signals the control unit <b>32</b> the value of the pressure prevailing in the region B dynamic pressure, compares this actual value of the dynamic pressure to a predetermined, it desired target value of the dynamic pressure, for example, in a data memory of the control unit <b>32</b> may be stored as a data field, determined on deviation of the actual value of the dynamic pressure from the desired value of the stowage pressure if the suction power of the suction device <b>24</b> increased or decreased must be, and are via a signal line <b>32</b>a a corresponding Control signal to the suction device <b>24</b> out.

It should be noted that a plurality of pressure sensors <b>30</b> be provided can, which over the width of the material web <b>12</b> are distributed and in a respectively associated section of the prevailing there Backpressure capture. This allows the control unit<b>32</b> a spatially resolved Information about the dynamic pressure to be supplied. The control unit<b>32</b> can these spatially resolved information in different ways further processed.

For example, it is possible, in determining the control signal for the suction <b>24</b> the average of these spatially resolved information as Actual value of the dynamic pressure to be used. However, it is also possible that suction <b>24</b> in dependence on the respective value of the maximum stationary control resolution information. If the suction device<b>24</b> in a plurality of sections is divided whose suction independently can be controlled from each other, the space-resolved information finally, to a spatially resolved control of the suction ago be attracted.

To the air boundary layer <b>26</b> from the surface <b>12</b>a web of material <b>12</b> in easily stand out and the suction device <b>24</b> to perform, is to the material web surface <b>12</b>a commissioned region B further comprises scraper <b>36</b> provided that either a very short distance the web surface <b>12</b>a is arranged, or against this example is employed in the manner of a piercing blade. This bar<b>36</b> clips the in the boundary layer <b>26</b> entrained air from the material web surface from and directs them to the suction port of the suction device <b>24</b> around. Since most part of the boundary layer in the <b>26</b> thus air supplied from the mechanical surface <b>12</b>A is lifted, the suction device <b>24</b> correspondingly his little power formed.

Moreover, in order ver a flutter of the web within the application area B to be able to prevent, in which between the supporting roll <b>14</b> and the material train <b>12</b> formed inlet pocket Z another suction device <b>38</b> is assigns. The other suction device<b>38</b> has the task, in the lead gore Z maintain a vacuum, the material web the <b>12</b> against the surface <b>14</b>a of the support roll <b>14</b> pulls, so that they in contract section B of this is completely secured. Thus, also carries the more suction <b>38</b> to achieve a high-quality job earnings at.

The inventively constructed applicator <b>10</b> allows the circulating amount of application medium <b>18</b> reduce, without sacrificing having to accept job quality. Due to the lower circulation volume may also use the cable cross-sections of the feed and discharge the distribution <b>16</b>a veil of applicator unit <b>16</b> and the return line (if any) of the leveling and / or metering device be reduced. Optionally, even completely to a laxative line are omitted. At the same time, it is possible that Laufgeschwindig speed and increase the width of the material web, which is an increase of Productivity entails. The operating costs can by Minimize wear and tear and the use of performance and throughput weaker pumps are lowered. The invention with the applicator <b>10</b> coated webs stand out a high uniformity of the coating and good coverage of Web surface with coating medium from which approximately Luftbür achieved stenqualität.