EP1209274A2 - Curtain coater - Google Patents

Abstract

The curtain coating assembly (10), to coat the surface of a moving web substrate (U) with a paste or liquid coating (18) and especially a pigment suspension, has a jet unit (14) at the applicator (12) to deliver a coating curtain (18). At least one guide (22) is in the falling path of the coating curtain, which directs the coating over the whole curtain width over at least a part of its falling path. The web curtain coating assembly has a guide in the path of the falling coating curtain, which divides it into a path section (24) between the feed and the guide, and a second path section (26) between the guide and the moving substrate. The guide can be directly at the delivery jet. The variable length of the curtain coating which covers the guide is measured in the direction of its movement. The guide forms an included angle ( alpha ) of 5-30 degrees with the direction of the curtain coating free fall line. The surface (22a) of the guide, covered by the coating medium, forms an included angle ( beta ) with the end surface (22b) of the guide of 20-60 degrees . The guide can be a guide scraper against the substrate. The guide is pitched at an angle of 20-80 degrees in the required flow direction, and preferably 45-80 degrees . The end of the guide surface towards the moving substrate can be extended at an angle of 30-50 degrees . The guide can also cover the whole flow stretch for the coating medium, between the delivery jet and the moving substrate. The surface of the guide, towards the coating medium, has a hydrophobic character, or has a hydrophobic cladding of a treated glass fiber film. At least the end surface of the guide is free of hydrophobic cladding. The coating curtain flows over the upper surface of the guide, or along its under surface. At least one electrode can be at the guide, on the side away from the flowing coating. A suction box is at the moving substrate, in front of the contact line where the coating curtain strikes it, together with a scraper at the entry and/or exit side, with a scraping edge lying on the moving substrate. The scraper at the exit side can be formed by the coating guide. The coating curtain flows over the guide surface, in a length (l) of 1-200 mm and preferably 1-50 mm. The travel speed of the substrate is 1000-3000 m/min. for a paper web and 200-1000 m/min. for a cardboard web. The coating is applied in ready doses to the substrate surface. The delivery jet has a coating delivery rate of 2-200 l/min. per meter of the web width. The length (H) of the coating curtain is 5-400 mm and preferably 40-200 mm. The guide is of metal or plastics e.g. a plastics with reinforcement carbon or glass fibers. The guide has a thickness (D) of 0.2-1.0 mm. The guide is positioned at the applicator, at an angle to the moving substrate of 70 degrees , in either direction. The guide can have a convex or concave curvature, with a curved surface at a tangent to the free fall of the coating curtain, in either direction, at an angle of up to 70 degrees .

Description

The invention relates to a device for applying liquid or pasty application medium, especially aqueous pigment suspension, on a running surface, including a curtain commission, which the application medium from a dispensing nozzle as in the Moving curtain or veil due to gravity delivers the surface, whereby the surface with the direct application Surface of a material web, in particular made of paper or cardboard, and with indirect application, the surface of a transfer element, preferably a transfer roller, which is then the application medium to the Surface of the material web transfers.

When coating material webs using a curtain applicator (also known as "curtain coating" in the professional world) the application medium is applied to the substrate in the form of a Application medium curtain or curtain (for the sake of simplicity in the following only the term "order medium curtain" or only "Curtain" used), which is essentially due to gravity moved from the commissioned work to the underground. That this Curtain application work itself at a predetermined distance from Among other things, it has the advantage that it is located underground is at a lower risk of damage in the event of a web break. Custom curtain works differ from other "contactless" Applicators, for example free jet nozzle applicators, at which the movement of the order medium from the order work to Mainly from the ejection pulse from the discharge nozzle of the Commissioned work originates fundamentally, since the shape of the from the Dispensing nozzle emerging curtain only the interplay between the surface tension of the application medium and gravity is exposed. The surface tension tries the curtain a very large one based on its volume or cross-sectional area Surface or circumferential length has to contract, so its Reduce surface area. Gravity opposes this effect, who tries to stretch the curtain. It is therefore easy to see that it the more difficult it is to get one evenly across the entire working width to get thick application medium curtain, the larger this working width is.

The coating of material webs by means of a curtain applicator, which feeds the application medium to the material medium as an application medium curtain that moves due to gravity, has long been known from the coating of photographic films, tapes and the like. Furthermore, corresponding devices for applying a liquid film to a textile material web with the aid of an application medium curtain that moves due to gravity are known from the field of the textile industry, for example from DE 33 33 592 A1 and DE 40 15 946 A1. However, the material webs in these fields of application have a considerably smaller width than is the case with modern systems for the production of paper and cardboard webs, in which material web widths of more than 10 m are required today. To be able to form and keep a stable application medium curtain across this width is a task in which it is anything but obvious to expect suggestions for a functional solution from the comparatively easy to control, known narrow application medium curtains. In addition, the material webs move in modern systems for the production of paper webs with speeds of approximately 1,000 m / min up to 3,000 m / min, and in systems for the production of cardboard webs with speeds of approximately 200 m / min, which is usually a multiple of the speed with which the known narrow material webs move. The high web speeds also put a further high load on the stability of the application medium curtain, since the application medium curtain is not only stretched due to gravity in free fall (gravity stretching), but also when it comes into contact with the ground due to the difference between the speeds of the freely falling application medium shortly before it hits the surface and the running speed of the moving surface
(Contact stretching).

In "Patent Abstracts of Japan", No. 10024360 is a curtain applicator published in which an order fluid through two counter-rotating rollers are extracted from a reservoir, the application liquid being stretched into a thin film, and then essentially under the influence of gravity on you Surface is applied.

In order to achieve a high-quality order result, it is desirable to distribute the total extension (= gravity extension x contact extension) as evenly as possible between the gravity extension and the contact extension. For this purpose, it is necessary, in particular when the subsurface is running at high speeds, that the application medium curtain has the highest possible fall speed shortly before contact with the subsurface, which requires a correspondingly high fall height. However, there are physical limits to the fall height. If the drop height were too large, the influence of the surface tension of the application medium and, on the other hand, the influence of air movements in the vicinity of the application medium curtain would be too great to be able to reliably and reproducibly ensure a stable application medium curtain. The effects mentioned have a stronger influence on the quality of the application medium curtain, the smaller the flow rate of the application medium delivered by the curtain application unit per meter of working width to the substrate, ie the thinner the application medium curtain. In particular in a film thickness range from 2 ml / m ² to 50 ml / m ² , as is not uncommon in the case of a thinly applied layer ("1: 1" application) of thin layers of application medium, gravity stretching is limited by the effects mentioned above.

It is therefore an object of the invention to provide a device at the outset Specify the type in which the influence of the above discussed effects on gravity extension is reduced.

This object is achieved by a device of the generic type Kind solved, in which at least in the fall path of the curtain a guide element is arranged, the curtain along at least one Part of the fall path leads across its entire width.

The advantageous effect of the guide element used according to the invention the order medium curtain is most likely based on the fact that the application medium when it comes into contact with the guide element is slowed down, which stabilizes the shape of the application medium curtain. With increasing movement of the application medium along the guide element but then the falling speed, more precisely the flow speed, takes of the application medium along the guide element, again. This stabilization of the application medium curtain according to the invention can determine the total fall height of the curtain and thus the total achievable gravity stretch compared to a conventional one free-falling application medium curtain without sacrificing the Quality of the application medium layer thus formed can be increased. This makes it possible to understand the physical properties of the order medium limited film stretch limit at which dosed film, negatively influencing the uniformity of the stroke Form vibration waves, closer to each other than previously free falling order medium curtain was possible.

It should be noted in this context that under an "essentially gravity-related "movement of the application medium curtain here it is understood that everyone applies the application medium to the underground gravitational forces have the greatest influence on the application medium curtain exercises. The movement due to gravity can also supported by other forces (e.g. electrostatic Forces) or influenced in some other way (e.g. viscous friction when moving along the guide element).

It should also be noted that the words "lead along the fall path" in the Connection with the present invention also mean can that the application medium curtain through the guide element from the the path corresponding to the free fall can be deflected.

It should also be noted that as material webs in addition to paper and cardboard also films or textiles using the device according to the invention Application medium can be coated.

The advantages described above can then be achieved in particular be when the guide element drops into one of the dispensing nozzle Free fall section leading to the guide element and one from the guide element divided into the free fall section leading to the subsurface. In this case the entire fall of the application medium curtain using a single one Guide element can be divided into three sections, namely two free-fall sections, those that stabilize the application medium curtain Section along the guide element are separated from each other. Of course can each of the free fall sections by additional guide elements be further divided.

But also when the guide element is the fall of the application medium curtain not divided into two free fall sections, the stabilizing influence of the guide element advantageous on the quality of the Order result, with the help of these guidance elements others that ultimately have a positive impact on the order result Effects can be achieved:

For example, according to a first embodiment variant of a directing element directly adjoining the dispensing nozzle Avoid the so-called "teapot effect". This "teapot effect", a characteristic deformation of that emerging from the dispensing nozzle Application medium curtain occurs in practice when the Flow rate of the application medium when leaving the Dispensing nozzle falls below a limit speed, which on the one hand of the physical properties of the application medium and the other depends on the thickness of the application medium curtain. Thin curtains also tend to the To show "teapot effect". Exceeds the Outflow velocity the limit mentioned above, a parabolic curve of the application medium curtain usually forms out. On the other hand, it would be ideal to have the application medium curtain exactly to leave the discharge nozzle at the limit speed, because in this case the curtain runs almost perfectly vertical.

This ideal case can be directly addressed to the Reach discharge nozzle adjoining guide element in a simple manner or at least approximate. As already stated above, the application medium curtain initially due to the influence of the guide element stabilized and then by gravity, albeit in one by the Cosine of the angle of inclination diminished dimensions, along the guide element accelerated. With a corresponding choice of the length of the guide element in Direction of movement of the curtain can be achieved that the Application medium curtain at the end of the guide element exactly with the Limit speed or a slightly higher speed moved so that the "teapot effect" can be safely avoided and the curtain leaves the guide element almost in the vertical direction.

To the application device according to the invention in a simple manner to the physical properties of different application media, different Curtain thicknesses, and the like parameters can be adjusted more proposed that the measured in the direction of movement of the curtain, length of the guide element covered by the application medium is changeable. Furthermore, it has proven to be advantageous if the guide element with the direction corresponding to the free fall of the curtain between about 5 ° and about 30 °. The "teapot effect" -free Detaching the curtain from the guide element can be facilitated by that the surface of the guide element covered by the application medium curtain with the end face of the guide element an angle of between about 20 ° and about 60 °. The one covered by order medium The length of the guide element should advantageously be at most about 200 mm, preferably at most about 50 mm.

According to a further embodiment variant, the guide element can also be used as a scraper against the ground. In this case occurs the influence of the guide element that stabilizes the application medium curtain added that this is the air boundary layer carried by the subsurface weaken and thus their adverse influence on the order result can mitigate. For example, such Guide scraper localized interruptions of the application medium curtain can be prevented that are not covered with application medium Places of the underground would lead. But also the local one Introduction of air pockets between the subsurface and Application medium, which is quasi as a preliminary stage of a local tearing of the Order medium curtain can be viewed using the Guide scraper according to the invention can be avoided. Any friction heat generated by the relative movement of the scraper and underground is not a problem in practice as it is easier in Way can be dissipated by the application medium itself.

Even when the guide element is used as a guide scraper, there has been one inclined arrangement of this guide scraper proved to be advantageous. For example can the guide element with the free fall of the curtain Direction an angle of between about 20 ° and about Include 80 °, preferably between about 45 ° and about 80 °. The length of guide scraper covered by application medium advantageously at most about 50 mm, preferably at most about 10 mm.

On the one hand, an almost line-like contact between the guide scraper ensure and underground and on the other hand an almost step-free Enable the transfer of the application medium from the scraper to the surface To be able to, it is also proposed that the of the application medium curtain covered surface of the guide element to the underground has an adjacently arranged end section which is connected to a imaginary extension of the surface an angle of between about 30 ° and about 50 °.

According to a further embodiment variant, it is also possible that the guide element over the entire distance between the dispensing nozzle and Extends underground, so the benefits of extending to the dispensing nozzle immediately following guide element with one as a guide scraper used to connect the guide element. With regard to the angle of inclination In this case, the guiding element must either have a compromise between found the two arrangement alternatives mentioned or that Guide element are curved, so that it is both in the area the dispensing nozzle as well as in the area of the substrate one each has advantageous inclination angle. Of course it is too possible to provide two separate guide elements, one of which one connects directly to the dispensing nozzle while the other is employed as a scraper against the underground.

A curved design of the guide element also allows over the shape of the curvature, the speed and / or the thickness of the application medium curtain to influence. It can both use of convex as well as concave curved guide elements be, with convex or concave the curvature of the application medium facing surface of the guide element is designated.

Especially when the guide element made of metal or plastic, for example, carbon fiber or glass fiber reinforced plastic , it can happen that the application medium is in contact with the Guide scraper is braked more than it is for achieving the desired one Stabilization of the application medium curtain is actually required. In this case, the braking force applied by the scraper to the application medium exercises, are reduced in that the guide element at least hydrophobic on its surface facing the curtain or veil is formed so that the flow rate of the Order medium is retained on the guide element.

This hydrophobic formation of the surface of the guide element can be in can be obtained in a technically simple manner in that the Provide the surface of the guide element with a hydrophobic coating is coated, for example with a Teflonized glass fiber film. in the With regard to a favorable detachment behavior of the application medium from the guide element However, at least the end face of the guide element should be free of be hydrophobic coating.

In the discussion above, it was always implicitly assumed that that the application medium curtain is on the top of the guide element moved along, so held by gravity on this top becomes. In principle, however, it is also possible that the Moving the application medium curtain along the underside of the guide element, being held on this underside by adhesive forces.

In a development of the invention, the application medium curtain facing away from at least one electrode. By means of the the application medium can emanate from this electrode and its interaction with the surface of the guide element to achieve or ensure a uniform layer thickness of the Application medium curtain can be influenced advantageously. This is detailed in the post-published German patent applications DE 100 12 256.6 and DE 100 12 347.3 from the applicant's group to which reference is hereby made.

Furthermore, in front of the contact line of the Curtain or veil a suction box can be arranged. This suction box can be used in addition or as an alternative to a scraper Guiding element for combating the air boundary layer carried by the subsurface be used. In the case of a direct order from the Application medium on a material web against the material web employed scraper used, so can by means of the suction box Material web is sucked into safe contact against the guide scraper, so that this effectively removes the air boundary layer from the web surface can take off. The suction box can be on the inlet side and / or outlet side be assigned a scraper element, which with a scraper edge on the Rests on the ground, with the scraper element on the outlet side of the Guide element can be formed. Also with regard to constructive details of the mentioned suction box is on the above two referred to German patent applications.

It must also be added that the guiding element based on its The most distant underground either in or against the direction of the Can be arranged inclined underground, the guide element with the direction corresponding to the free fall of the application medium curtain in include an angle of up to about 70 ° in both orientations can. In terms of tearing off the application medium curtain In critical cases, the orientation of the guide element on the drain side preferable.

Another advantageous development of the invention provides that Guide element is designed as a running surface that the fall of the Curtain or veil in one from the dispensing nozzle to the guide element leading free fall section and one from the guide element to Subdivided underground leading free fall section, and their running speed is greater than the falling speed of the Application medium at the end of the free fall section leading to the guide element. Through the use of the invention as a guide element serving running surface, the total stretch no longer settles only from a single gravity stretch and a one-off Contact extension together. Rather, the order medium becomes a first gravity extension through the running surface of a subjected to the first contact stretching, after which the detachment of the application medium of the running surface serving as a guiding element second gravity or acceleration stretch and then the Contact extension through the running surface follows. This is it only required that the running speed of the surface be greater is as the falling speed of the application medium at the end of the Leading free-fall section.

According to the invention, the current guiding element forming such a guiding element Surface realized, for example, by an endless, circulating belt become. In a further, particularly preferred embodiment of this A variant of the invention is a rotating roller as the guide element provided, the peripheral speed is greater than that Falling speed of the application medium at the end of the as a guiding element serving roller leading free fall section. Here, such Roll preferably made of metal at least in the area of its peripheral surface be made.

According to the invention, the current one serving as the guiding element Surface, for example the rotating roller, not just a relatively long one Free fall section divided into two shorter free fall sections what regarding the effects of external influences on the application medium curtain is advantageous, but it will also stretch the total distributed a variety of stretch levels, which the stress of the Application medium curtain reduced in the individual stretching stages. Thus, even a stronger overall can be achieved with the same total fall height Achieve extension of the application medium curtain.

It is still to be added that the order medium curtain through the Adhesive forces between the application medium and that as the guiding element serving running surface, e.g. the peripheral surface of the roller, is stabilized, which for its quality and thus also the quality of the ultimately, order profit achieved with the help of this curtain is.

Furthermore, it has proven to be advantageous to change the running direction of the Guide surface serving to choose such that the Section of the running surface serving as a guide element, which with the Application medium of the free fall section leading to the guide element in Contact is made, moving in the same direction as the surface. If a roller is used as the guide element, this means that the Direction of rotation of the roller should preferably be chosen such that the Circumferential section of the roller, with the application medium of the roller leading free-fall section comes into contact in the same direction moves like the underground.

To detach the application medium from the one serving as the guide element to facilitate running surface or to be reliable to be able to ensure that even after removing the Application medium from the running surface serving as a guiding element forms a uniform application medium curtain, is in continuing education the invention proposed that a scraper element, for example a Piercing scraper is provided, which lifts the application medium from it and to the free fall section leading from the guide element to the subsurface emits. This scraper element can, for example, against the as Guiding element serving running surface, for example the surface of the roller, be employed. If a roller is used as the guide element, it can but also from a wall section of a roller supporting the roller Roll bed be formed. The length of the scraper element can be in Direction of movement of the application medium measured between about 5 mm and be about 50 mm.

Of course, any of the current surface, e.g. B. the spinning roller, free fall sections formed by additional Guiding elements can be further divided. These can be additional Other running surfaces, such as rotating rollers, be or also permanently installed, i.e. non-moving guide elements, for example, essentially flat baffles. The additional guiding elements can do the free fall section in which they are arranged, again divide into two free-fall subsections. It However, it is also possible for such a guide element to be attached directly the discharge nozzle of the curtain applicator connects or as Guide scraper against the surface of the running surface or the or a running surface, e.g. B. a rotating roller is employed.

Fig. 1 - 4

schematische Seitenansichten verschiedener Varianten erfindungsgemäßer Auftragsvorrichtungen mit an unterschiedlichen Positionen zwischen dem Auftragswerk und dem Untergrund angeordneten Leitelementen;

Fig. 5

eine vergrößerte Ansicht des Details V gemäß Fig. 4, wobei eine geringfügige Abweichung lediglich hinsichtlich des Auftreffens des Auftragsmedium-Vorhangs besteht;

Fig. 6 und 7

zwei mit Saugkasten ausgestatteten Varianten erfindungsgemäßer Auftragsvorrichtungen;

Fig. 8 und 9

zwei erfindungsgemäße Auftragsvorrichtungen mit konvexem bzw. konkavem Leitelement; und

Fig. 10

eine schematische Seitenansicht einer Weiterbildung einer erfindungsgemäßen Auftragsvorrichtung mit einem als Walze ausgebildeten Leitelement.

The invention will be explained in more detail below using exemplary embodiments with reference to the accompanying drawing. It shows:

1-4

schematic side views of different variants of application devices according to the invention with guide elements arranged at different positions between the application unit and the substrate;

Fig. 5

an enlarged view of the detail V according to FIG 4, with a slight deviation only with regard to the impact of the application medium curtain.

6 and 7

two variants of application devices according to the invention equipped with a suction box;

8 and 9

two application devices according to the invention with convex or concave guide element; and

Fig. 10

is a schematic side view of a development of an application device according to the invention with a guide element designed as a roller.

In Fig. 1, a curtain application device according to the invention is general designated 10. It comprises a curtain application 12, from the Dispensing nozzle 14 liquid or pasty application medium 16 in the form of a Order medium curtain or veil 18 is delivered. The Curtain 18 moves vertically due to gravity Direction V down to an underground U, which is under the Application unit 12 in the running direction L at a speed at Cardboard web from about 200 m / min and with a paper web of between about 1,000 m / min and about 3,000 m / min. The underground With direct application, the surface of the material web can, in particular the paper or cardboard web, but also a film or textile web, or in the case of indirect application, the surface of a transfer element, for example a transfer roller. The aim of the application device 10 is the application medium 16 is essentially fully metered, i.e. ideally as "1: 1" order to apply to the underground U as an order layer 20, which has a thickness d of between about 2 microns and 100 microns.

The reduction is based on such curtain applicators 10 the thickness of the application medium curtain 18 from the width b of the dispensing nozzle 14 to the thickness d of the application layer 20 essentially to two Effects, namely the stretching of the curtain due to gravity 18 during the free fall from the dispensing nozzle 14 to Underground U and on the other hand the contact extension due to the Difference between the falling speed of the curtain 18 just before Reaching the underground U and the running speed of the underground U. The stretch due to gravity is not only due to physical effects (interplay between gravity and surface tension the order medium 16), but also due to external influences (for example, the curtain 18 is carried along by the Underground U, air currents and the like) set limits.

The present invention is based on the finding that the drop height H and thus the overall achievable extension of the Order medium 16 can be increased by being in the path of the order medium 16 from the dispensing nozzle 14 to the underground U a guide element 22, for example a guide plate or a guide blade. It It has been shown that the viscous frictional force between the Application medium 16 and the guide element 22 on the application medium curtain 18 a stabilizing, i.e. especially comparative end Has an effect.

Nevertheless, the application medium 16 can be selected with a suitable choice Inclination angle α that the surface of the plan essentially Includes guide element 22 with the vertical V, and corresponding Choice of the surface properties of the guide element 22 at its Movement along the guide element 22 can be further accelerated. Consequently the application medium curtain 18 also experiences in the area of the guide element 22 an extension.

In the embodiment shown in Fig. 1 divides that Guide element 22 the path of the application medium 16 from the dispensing nozzle 14 to the underground U in a first free fall section 24 and a second Free fall section 26. After a first extension due to gravity in the First free-fall section 24, the application medium 14 strikes the Guide element 22, which stabilizes the curtain 18 and yet its allows further extension due to gravity. Then arrives the application medium 16 in the area of the second free-fall section 26, in which it is stretched again due to gravity before it opens the underground U hits. To adversely affect the Application medium curtain 18 at the transition from the guide element 22 in the To be able to prevent the second free-fall section 26 is the end face 22b of the guide element 22 is designed so beveled that it with the Application medium 16 covered surface 22a of the guide element 22 a Include angle β of between about 20 ° and about 60 °.

The angle of inclination α of the guide element 22 relative to the vertical V can have a value of up to 70 °, the guide element 22 as in FIG. 1, can be arranged on the outlet side with respect to the substrate U. can. Basically, however, an inlet-side arrangement of the Guide element 22 conceivable. The guide element or baffle 22 that from Metal or plastic, for example carbon or glass fiber reinforced Plastic that can be manufactured advantageously has a Thickness D of between about 0.2 mm and about 1.0 mm. The Total fall height H can be up to 400 mm, the distance in which the application medium 16 moves along the guide element 22, a length I of between about 1 mm and about 200 mm, preferably between about 1 mm and about 50 mm.

The curtain application device 110 shown in FIG. 2 differentiates differs from the embodiment according to FIG. 1 only in that the Guide element 122 to the discharge nozzle 114 of the curtain applicator 112 is arranged immediately afterwards. Also by this execution lets the mentioned stabilization of the application medium curtain 118 achieve in the area of the guide element 122, so that in this respect to the above description of the embodiment of FIG. 1 referenced can be.

The application device 110 according to FIG. 2, however, can still be used achieve another advantage. This can be done by adjusting accordingly the length I to the properties of the application medium 116 and others Parameters such as thickness and exit speed of the curtain 118 from the dispensing nozzle 114, reach the curtain 118 following the guide element 122 in the area of the underground U leading free fall section 126 almost perfectly in vertical Moves towards V, and does not take a course as it does from the so-called "Teapot effect" is caused (dashed in Fig. 2 indicated course T). The speed of the application medium 116 on The detaching edge 122c of the guide element 122 should ideally also be so be chosen so that the application medium 116 does not have this edge Shoots out 122c and then takes a parabolic course (dash-dotted course P), but essentially at the edge 122c directly in the essentially vertical course shown in FIG. 2 transforms.

All this can be done with the curtain application device 110 according to FIG. 2 in can be easily achieved because the "active" length I of the guide element 122 and thus the speed of the application medium 116 in the area edge 122c by simply mechanically adjusting the guide element 122 can be accomplished in the direction of the double arrow X. So it is not required the hydrodynamic parameters in the commission 112 to influence what control technology with considerable Effort would be connected.

In the application device 210 according to FIG. 3, the guide element can also be used 222 a stabilizing the application medium curtain 218 Effect are exerted on the order medium 216 by the Curtain applicator 212 from its discharge opening 214 to the underground U is delivered. Therefore, in this regard, the above Description of the embodiment shown in FIG. 1.

3, however, is the guide element 222 as a scraper against the surface of the underground U. It is the task of this guide scraper to carry the one carried by the underground Remove air boundary layer G from the subsurface U in order to disadvantage it Influence (local tearing of the application medium curtain 218; air entrainment between underground U and application layer 220) on the Reduce, if not completely eliminate, the order result.

In order to achieve a smooth transition from the Application medium 216 from the scraper 222 to the underground U to ensure that the end face 222b is bevelled, with the underside not wetted by application medium 216 222d of the guide scraper encloses an angle γ, the value of which lies between is about 30 ° and about 50 °.

Of course, it is also possible to implement the embodiments according to FIG. To combine 2 and 3, i.e. both the "teapot effect" preventive, at the delivery opening of the curtain application immediately following guide element as well as one against the U scraper to be used underground. Yes, it is conceivable, as is the case with the curtain application unit 310 according to FIG. 4 is shown, these two guide elements into a single guide element Combine 322, which extends from the discharge opening 314 of the curtain applicator 312 extends continuously to the underground U, against which it is employed as a scraper. In this case, the guide element 322 exercises over the entire fall height H (see FIG. 1) which stabilizes the curtain 318 Effect on the application medium 316. Furthermore, there is no danger the appearance of the "teapot effect". And finally, too any adverse influence of the air boundary layer G on the Order layer 320 suppressed.

Based on the detailed view of the tip of a as shown in Fig. 5 Guide scraper against the underground U guide element 322 should be in The following is a variant of the guide element according to the invention are explained in more detail. Namely, the guide element 322 is on its top 322a and its underside 322d each with a hydrophobic Provide coating 330. This hydrophobic coating can for example in the form of a teflon-coated glass fiber film, which are applied to the surface 322a and 322d of the guide element 322, is glued on, for example. Such a hydrophobic coating has due to their water and therefore also the application medium 316 repellent Properties have the advantage that on the one hand the viscous Frictional forces between the guide element 322 and the application medium 316 are reduced, so that the application medium 316 also along the Surface 322a accelerated more due to gravity and thus can be stretched, and it also has the advantage of less Danger of contamination due to adherence of application medium 316 on Guide 322.

As a result of the coating of the guide element 322 also on its underside 322d with the hydrophobic coating 330, the guide element 322, as shown in Fig. 5, float slightly so that in the area of the tip 322c of the guide scraper 322 a small, highly swirled one Forms amount 316 'of order medium 316. This application medium vortex 316 'prevents air from entering the Area between the underground U and the order view 320. Zum others, the guide scraper 322 slides on this vortex 316 'with low friction what not only wear on the guide scraper 322, but also direct order also the wear occurring on the material web lowers. It should be noted that the end face 322c of the tip is not one hydrophobic film is provided. The reason for this lies on the one hand in the easier to manufacture. On the other hand, the end face 322c is even supposed to be wettable, while on the hydrophobic coating Application medium rolls off to make a smoother transition to To allow underground U.

The application device 410 according to FIG. 6 differs in terms of the construction of the curtain applicator 412 and the guide element 422 not from the embodiment described above according to FIG. 4, i.e. the guide element 422 extends continuously from the dispensing nozzle 414 to the underground U. Therefore, in this regard, the Description of the embodiment shown in FIG. 4.

As an additional measure to achieve a high quality Application layer 420 is further in the direction of travel L before application unit 412 a suction box 432 is provided. This suction box 432 serves the to weaken air boundary layer G carried along by underground U. or vacuum, even before they even hit the ground U employed scraper 422 arrives. To increase the suction efficiency of the Suction device 432 has a sealing lip on the input side or Sealing blade or sealing scraper 434, which together with the guide scraper 422, the suction box 432 and the underground U an absorbent Encloses volume 436.

In principle, however, it is also possible, as is the case with the Application device 510 according to FIG. 7, the suction box 532 to assign two sealing elements 534 and 534 'specially assigned to it, one of which with respect to the running direction L of the underground U am inlet side end of the suction box 532 and the other at its discharge end is arranged.

In the embodiment 410 according to FIG. 6, the application medium curtain is also on 418 underside 422d of the guide scraper 422 facing away an electrode 440 is arranged, which due to the emanating from it electric field allows the order medium 416 in the sense of a to influence additional stabilization of the application medium curtain 418. Of course, a plurality of such electrodes can also be used be provided. Regarding the arrangement of electrodes and suction boxes furthermore to the post-published ones originating from the applicant's group German patent applications DE 100 12 256.6 and DE 100 12 347.3 referenced.

Although in the above-described embodiments Application medium 16 always on the top 22a of the guide element 22 moved along, is to be based on the application device 510 according to FIG. 7 are also shown that it is in principle also possible that the order medium 516 or the order medium curtain 518 due to of adhesive forces between the guide element 522 and the application medium 516 also along the underside 522d of the guide element 522 can move, provided that the guide element 522 directly to the Delivery opening 514 of curtain applicator 512 connects.

8 and 9 it should be shown that the guide element 622 or 722 of the application device 610 or 710 also convex (FIG. 8) 'or concave (Fig. 9) can be curved. Through targeted choice of the curved course, the thickness or the speed of the Application medium curtain 618 or 718 can be influenced in a targeted manner.

In the embodiment of a curtain application device according to the invention shown in FIG. 10 810 is in the fall path of the application media curtain 818 from the dispensing nozzle 814 of the curtain applicator 812 to the underground U a roller 822 is arranged, which the fall height H divided into a first free fall section 824, which is different from the Dispensing nozzle 814 until the curtain 818 hits the Roller surface 822a, and a second free-fall portion 826, which leads from the roller 822 to the underground U.

According to the invention, the roller 822 rotates about its axis A running in the transverse direction Q, specifically at a speed selected such that the speed v _{W of} the surface 822a of the roller 822 has a greater value than the falling speed v _{F1 of} the curtain 818 in first free-fall section 824 shortly before hitting roller surface 822a (v _W > v _F1 ). As a result, the application medium 816, when it hits the roller surface 822a after gravity stretching in the free-fall section 824, experiences a contact stretching by the rotating roller 822. Furthermore, the application medium curtain 818 is stabilized by the adhesive forces between the application medium 816 and the roller surface 822a. Of course, other forces acting on the application medium 816 can also be added to these adhesion forces, for example electrostatic forces if an electrode held at a predetermined electrical potential is arranged in the interior of the roller 822, or the outer surface of the roller 822 itself is designed as an electrode.

One against the direction of rotation of the roller 822 against its surface 822a employed scraper 828 lifts the application medium 816 from the Surface 822a of the roller 822 and transfers it to the second free-fall section 826. The length I of the piercing scraper 828 is between approximately 5 mm and about 50 mm. The diameter of the roller 822 is between 38 mm and about 500 mm. Its surface 822a is preferred trained hydrophilic.

In the second free-fall section 826, the curtain 818 is again stretched, which means that its falling speed v _F2 shortly before it hits the surface U has a greater value than the surface speed v _{W of} the roller 822 (v _F2 > v _W ) , However, this falling speed v _F2 is still lower than the running speed v _{U of} the underground U in the running direction L (v _U > v _F2 ). The application medium 816 is thus stretched again when it comes into contact with the underground U.

The total extension of the application medium curtain 818 from the thickness b when leaving the discharge opening 814 to the layer thickness d is the The application layer 820 applied on the background U thus takes place at the Application device 810 according to FIG. 1 in four stages, namely a first Gravity stretching in the first free fall section 824, a first Contact stretching when it hits the roller surface 822a, one second gravity stretch in the second free fall section 826 and one second contact stretch when hitting the underground U.

Claims (39)

Device (10) for applying liquid or pasty application medium (16), in particular aqueous pigment suspension, to a running surface (U), comprising a curtain application unit (12), which essentially applies the application medium from a dispensing nozzle (14) as a result of gravity emits a moving curtain or veil (18) to the underground (U),
where the substrate (U) is the surface of a material web, in particular of paper or cardboard, when directly applied and the surface of a transfer element, preferably a transfer roller, is applied indirectly, which then transfers the application medium to the surface of the material web,
characterized in that at least one guide element (22) is arranged in the fall path of the curtain or veil (18), which guides the curtain or veil (18) along at least part of the fall path essentially over its entire width. Application device according to claim 1,
characterized in that the guide element (22) guides the fall into a free-fall section (24) leading from the dispensing nozzle (14) to the guide element (22) and a free-fall section (26) leading from the guide element (22) to the subsurface (U) divided. Application device according to claim 1,
characterized in that the guide element (122) directly adjoins the dispensing nozzle (114). Application device according to claim 3,
characterized in that the length (I) of the guide element (122) measured in the direction of movement of the curtain or veil (118) and covered by application medium (116) can be changed. Application device according to claim 3 or 4,
characterized in that the guide element (122) forms an angle (α) of between approximately 5 ° and approximately 30 ° with the direction (V) corresponding to the free fall of the curtain or veil (118). Application device according to one of claims 2 to 5,
characterized in that the surface (22a) of the guide element (22; 122) covered by the application medium curtain (18; 118) forms an angle (β) of between approximately 20 ° and approximately 60 ° with the end face (22b) of the guide element , Application device according to one of claims 3 to 6,
characterized in that the guide element is employed as a guide scraper (222; 322) against the subsurface (U). Application device according to claim 7,
characterized in that the guide element (222; 322) with the direction (V) corresponding to the free fall of the curtain or veil (218; 318) has an angle (α) of between approximately 20 ° and approximately 80 °, preferably between approximately 45 ° and about 80 °. Application device according to claim 7 or 8,
characterized in that the surface of the guide element (222; 322) covered by the application medium curtain (218; 318) has an end section (222b) which is arranged adjacent to the substrate (U) and which, with an imaginary extension of the surface, has an angle (y) of between about 30 ° and about 50 °. Application device according to one of claims 3 to 6 and one of claims 7 to 9,
characterized in that the guide element (322) extends over the entire distance between the discharge nozzle (314) and the substrate (U). Application device according to one of claims 1 to 10,
characterized in that the guide element (322) is designed to be hydrophobic at least on its surface (322a) facing the curtain or veil (318). Applicator according to claim 11,
characterized in that the surface (322a) of the guide element (322) is provided with a hydrophobic coating (330), for example coated with a teflon-coated glass fiber film. Application device according to claim 11 or 12,
characterized in that at least the end face (322c) of the guide element (322) is free of hydrophobic coating. Application device according to one of claims 1 to 13,
characterized in that the application medium curtain (18) moves along the top (22a) of the guide element (22). Application device according to one of claims 1 to 13,
characterized in that the application medium curtain (518) moves along the underside (522d) of the guide element (522). Application device according to one of claims 1 to 15,
characterized in that at least one electrode (440) is arranged on the side (422d) of the guide element (422) facing away from the application medium curtain (418). Application device according to one of claims 1 to 16,
characterized in that a suction box (432; 532) is arranged in the running direction (L) of the substrate (U) in front of the line of contact of the curtain or veil (418; 518). Application device according to claim 17,
characterized in that the suction box (432; 532) is assigned a scraper element (434, 422; 534, 534 ') on the inlet side and / or outlet side, which rests with a scraper edge on the substrate (U). Applicator according to claim 18,
characterized in that the outlet-side scraper element is formed by the guide element (422). Application device according to one of the preceding claims,
characterized in that the application medium curtain (18) moves over a distance (I) of between approximately 1 mm and approximately 200 mm, preferably between approximately 1 mm and approximately 50 mm, along the surface of the guide element (22). Application device according to one of the preceding claims,
characterized in that the substrate (U) in the case of coating a paper web at a speed of between about 1000 m / min and about 3000 m / min and in the case of coating a cardboard web at a speed of between about 200 m / min and moved about 1,000 m / min. Application device according to one of the preceding claims,
characterized in that the application medium (16) is applied in a metered manner to the substrate (U). Application device according to one of the preceding claims,
characterized in that the dispensing nozzle (14) dispenses the application medium (16) at a rate of between approximately 2 l / min and approximately 200 l / min per meter of working width. Application device according to one of the preceding claims
characterized in that the length (H) of the curtain (18) has a value of between approximately 5 mm and approximately 400 mm, preferably between approximately 40 mm and approximately 200 mm. Application device according to one of the preceding claims
characterized in that the guide element (22) is made of metal or plastic, for example carbon fiber or glass fiber reinforced plastic. Application device according to one of the preceding claims
characterized in that the guide element (22) has a thickness (D) of between approximately 0.2 mm and approximately 1.0 mm. Application device according to one of the preceding claims
characterized in that the guide element (22) can be arranged inclined, starting from its point farthest from the subsurface (U), in or counter to the running direction (L) of the subsurface (U),
wherein the guide element (22) with the direction (V) corresponding to the free fall of the curtain or veil (18) encloses an angle (α) of up to approximately 70 ° in both orientations. Application device according to one of the preceding claims,
characterized in that the guide element (622; 722) is convex or concave. Application device according to claim 28,
characterized in that a tangent to the curved surface with the direction (V) corresponding to the free fall of the curtain or veil (618; 718) encloses an angle (α) of up to approximately 70 °. Application device according to one of the preceding claims,
characterized in that the guide element is designed as a running surface , which covers the fall path of the curtain or veil (818) into a free fall section (824) leading from the dispensing nozzle (814) to the guide element and one from the guide element to the substrate (U) leading free fall section (826), and the running speed of which is greater than the fall speed (v _F1 ) of the application medium (816) at the end of the free fall section (824) leading to the guide element. Application device according to claim 30,
characterized in that the guide element is designed as an endless, circumferential band. Application device according to claim 30,
characterized in that a rotating roller (822) is provided as the guide element, the peripheral speed (v _W ) of which is greater than the falling speed (v _F1 ) of the application medium (816) at the end of the free-fall section (824) leading to the roller (822) ). Application device according to one of claims 30 to 32,
characterized in that the running speed (v _U ) of the subsurface (U) is greater than the falling speed (v _F2 ) of the application medium (816) at the end of the free-fall section (826) leading to the subsurface (U). Application device according to one of claims 30 to 33,
characterized in that the running direction of the running surface forming the guide element is selected such that the section (822a) of the running surface forming the guide element comes into contact with the application medium (816) of the free-fall section (24) leading to the guide element arrives, moves in the same direction as the underground (U). Application device according to one of claims 30 to 34,
characterized in that a scraper surface (28), for example in the form of a piercing scraper, is provided which is placed against the running surface forming the guide element, lifts the application medium (16) from this surface and on the surface from the guide element to the substrate (U) leading free-fall section (26). Applicator according to claim 35,
characterized in that the scraper surface (28) measured in the direction of movement (L) of the application medium (16) has a length (I) of between approximately 5 mm and approximately 50 mm. Applicator according to one of claims 30 to 36,
characterized in that the running surface forming the guide element is at least partially hydrophilic. Applicator according to one of claims 32 to 37,
characterized in that the roller (822) is made of metal at least in the region of its peripheral surface (822a). Application device according to one of claims 32 to 38,
characterized in that the roller (822) has a diameter of between approximately 38 mm and approximately 500 mm.

Images