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 using a curtain applicator unit, which discharges the application medium in the form a veil or curtain gives off the ground, the ongoing 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 means of a curtain applicator unit, ie the so-called "curtain coating", is the liquid or pasty application medium at a predetermined height above the current leave 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 results enable. In particular, interruptions of the color curtain must be prevented are, as these particularly violent form of coating medium splashes to lead. Of central importance is the control the air boundary layer of the moving substrate at its Surface is brought in the impact area. This can even if it does not pierce or interrupts the application medium curtain, by formation of air bubbles between the substrate and the Application medium, uniform coverage of the substrate with application medium prevent.

In German Utility Model 297 11 713 was therefore proposed in the running direction of the substrate before impingement of the application medium provide a nozzle onto the substrate, 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 boundary layer difficult in the application area by means of a blade, which in disposed a small distance from the surface of the current subsoil is. 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 caused overpressure, but also by one by the suction device be affected to strong vacuum. Even when using known from US 5,624,715 applicator is therefore required the application medium with high surplus on the current Underground deposit and abzurakeln excess application medium again, 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 application medium.

EP 0517223 B1 discloses a method for the treatment of the coating medium known, according to which in order to achieve a high-quality Located 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 dynamic pressure-determining device for determining the pressure of in the running direction of the substrate water accumulated on the ground prior to the impingement of the veil Air, and a control device for controlling the suction power of the suction device depending of the dynamic pressure-determining device certain back pressure comprises. In the apparatus according to the invention can the ruling on behalf range pressure regardless of the running speed the subsoil, the falling speed of the application 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 and the suction device must be placed in front of the impact area, and other the function of at least one pressure sensor by coating medium splashes 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 substrate be 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 from the application medium curtain entrained air boundary layer arises, the rate of fall the application medium curtain commonly used to speed of the subsurface in a particular ratio is to when striking the ground the formation of coating medium splashes prevent. It should be noted that the possibility of indirect Determination of the dynamic pressure in addition to the immediate impact pressure determination can be used.

In development of the invention it is proposed that the application 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 more novel provide 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 600 m / 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 arranged scraper for scraping of gear carried by ground air is. 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 accordingly be formed lower power. However, it constitutes a Squeegee a wearing part is that substituted from time to time must become. It is therefore on the respective application and boundary conditions 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 include a device for stabilizing the run of the web can be provided, for example, another 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 moving Substrate using a curtain applicator unit. Regarding 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 applicator device according to the invention represents.

In this single figure an application device according to the invention is quite generally indicated by 10. A moving in the direction L web 12 is in the region of the application device 10 to a supporting roll 14 led around which a rotationally driven about an axis A in the direction of the arrow P is. Furthermore, a curtain coater 16 is provided from its distribution channel 16a liquid or pasty application medium 18 by an outlet gap 16b emerges and as an application medium curtain or -Vorhang 20 in free fall to the surface 12a of the web 12 emotional. The coating layer thus formed 22 may for example by means a not shown, but known in the art Metering and / or leveling device of excess application medium are freed and / or smoothed.

To ensure that the application medium 18 in the transverse direction Q is dispensed as evenly as possible to the material web 12, it is required that the application medium 18 16b to the gap on the appearance entire length of the distribution channel 16a having substantially the same Pressure is applied. To achieve this, the coating medium is supplied to the distribution channel 16a usually at one end via a feed line, not shown, fed with high excess, and is not through the exit gap discharged coating medium 18 on the respective other end of the Distribution channel 16a discharged through a discharge line again and in a Coating medium supply recycled. In addition, the can of collected the metering and / or leveling device worn coating medium and the coating medium supply supplied for reuse will. To 18 keep the circulation quantity of the coating medium and low therefore use low-power, high-throughput weak to feed pumps can, it is known in the art as a variant, a use distribution channel 16a whose passage cross section of its Infeed decreases to its discharge end towards. The inventive training the application apparatus 10 provides 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 20 onto the web surface 12a is incident, wherein the application device 10 according to the invention a suction device 24 is arranged, which in transversely Q extending substantially over the entire width of the material web 12th The Suction device 24 is used for sucking air, which from the material web 12 12 as it moves in the direction L on their surface than Air interface 26 and / or the application medium curtain 20 at its Surface as a boundary layer of air 28 in the area B before the point of impact into transport T of the coating medium 18 on the web surface 20 is there and the formation of a relative to the normal Pressure increased back pressure results.

In the region B, a pressure sensor is further provided at least 30, which the value of the back pressure detected and a corresponding signal via a signal line 30a is transmitted to a control unit 32nd Further, on the Axis A of the support roll 14, a speed or speed sensor 34 arranged, the detection signal through a signal line 34a also the control unit 32 is supplied. The pressure sensor 30 is used for direct or direct detection of prevailing in the region B dynamic pressure. By contrast, the back pressure can be in the range B of the speed or. Speed ​​signal of the sensor 34 only indirectly or indirectly determine. 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 14, texture, especially Roughness, the material web surface 12a, composition and viscosity the application medium 18 and the like parameters that a Effect on the air entrainment capability of the material web 12 and coating medium curtain 20 have. The indirect determination of the range B prevailing dynamic pressure has the advantage that the suction of air from the region B not covered by the pressure sensors 30 and the signal lines 30a is hindered.

determined from the her on the lines 30a and 34a supplied signals the control unit 32 the value of the pressure prevailing in the region B the dynamic pressure, compares this actual value of the dynamic pressure with a predetermined desired Set value of the dynamic pressure, for example, in a data memory the control unit 32 may be stored as a data field, determined on deviation of the actual value of the dynamic pressure from the desired value of the dynamic pressure, if the suction power of the suction device is increased or decreased 24 must be, and are connected via a signal line 32a a corresponding Control signal to the suction device 24 from.

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

For example, it is possible, in determining the control signal for the Suction device 24 the average of these spatially resolved information as Actual value of the dynamic pressure to be used. However, it is also possible that Suction 24 in dependence on the respective maximum value of the spatially resolved to control information. If the suction device 24 in a plurality of sections is divided whose suction independently can be controlled from each other, the space-resolved information Finally, also used to spatially resolved control of the suction power will.

To the air interface 26 from the surface 12a of the web of material 12 in easily stand out and the suction device 24 to perform, is on the material web surface 12a in the application area B further comprises Scraper 36, which is either in a very small distance the material web surface disposed 12a, or against this example is made on the type of piercing blade. This strip 36 clips the in the boundary layer 26 entrained air from the material web surface from and directs them to the suction port of the aspirator 24th As the majority the supplied air in the boundary layer 26 of the thus mechanically Surface 12a is lifted, the suction device 24 can accordingly his little power formed.

Moreover, in order to prevent flutter of the web within the application area B can, in which between the supporting roll 14 and the web of material 12 formed inlet pocket Z another suction device 38 is located. The other suction device 38 has the task in the inlet pocket Z maintain a vacuum, the material web 12 pulls against the surface 14a of the support roller 14, so that they were assigned area B at this completely secured. Thus, also carries the more Suction device 38 to obtain a high-quality job results at.

The inventively constructed applicator 10 allows the reduce circulating amount of coating medium 18, without sacrificing having to accept job quality. Due to the lower circulation rate may also use the cable cross-sections of the feed and discharge the distribution 16a of the curtain applicator unit 16 and the return line (If available) of the leveling and / or metering device be reduced. Optionally, even completely to a discharge line be waived. At the same time it is possible to the running speed and to increase the width of the material web, an increase of the 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 10 coated webs stand out a high uniformity of the coating and good coverage of Web surface with coating medium from which approximately air brush grade reached.