EP1266093B2 - Application device and process - Google Patents

Abstract

The invention relates to a device (10) for directly or indirectly applying liquid or pasty application medium (16) to one or both sides of a material web (20) made of, in particular, paper or paperboard. The device comprises an application mechanism (12) which delivers the application medium (16) in the form of a free application medium stream (18) onto the material web (20). To this end, a device (30) for generating an electric field is provided in the vicinity of the application mechanism (12). Said electric field exerts a force onto the application medium stream (18), which is moving from the application mechanism (12) to the material web (20), while assisting the movement of said application stream (18). In addition or alternatively, edge guiding elements can be provided which guide the lateral edges of the application medium curtain (18) at least along a portion of the gravity-related movement thereof.

Description

The invention relates to a device for one-sided or two-sided application of liquid or pasty application medium on a running surface, comprising a spaced from the substrate applicator, which emits the application medium in the free application medium beam to the ground, the substrate for direct application to the surface a material web, in particular of paper or cardboard, and in the case of indirect application, the surface of a transfer element, preferably a transfer roller, which then transfers the application medium to the surface of the material web, according to the preambles of claims 1, 5 and 27. The invention relates to a Curtain applicator, ie an applicator device in which the applicator dispenses the application medium to the substrate as a curtain or veil that essentially moves as a result of gravity.

In the coating of webs using a curtain applicator (also known in the art as "curtain coating"), the application medium is delivered to the substrate in the form of a coating medium curtain, which moves substantially by gravity from the commissioned work to the ground. The fact that the curtain applicator is located at a predetermined distance from the ground, among other things, has the advantage that it is exposed to a lower risk of damage, for example, in a web break. Curtain coats differ fundamentally from other "non-contact" coateries, such as free-jet jet coaters, in which the movement of the coating medium from the applicator to the substrate is primarily due to the ejection pulse from the applicator nozzle, since the shape of the curtain emerging from the dispenser nozzle is merely that of the applicator Interplay between the surface tension of the application medium and gravity is exposed. The surface tension tries to contract the curtain, which has a very large surface or circumferential length in relation to its volume or its cross-sectional area, so as to reduce its surface area. This effect is resisted only by gravity, which seeks to stretch the curtain. It is therefore easy to see that it is all the more difficult to obtain a uniform over the entire working width coating medium curtain, the larger this working width.

The coating of webs by means of a curtain applicator, which feeds the web to the application medium as a substantially gravitationally moving application medium curtain or fog, has long been known from the coating of photographic films, Tonbändem and the like. However, the material webs in these applications have a significantly smaller width than is the case in modern paper and paperboard production lines where web widths of more than 10 m are required. Forming a uniformly thick application medium curtain over this width and being able to hold it in a stable manner is a task in which it is far from obvious to expect suggestions for a functional solution from the comparatively easy-to-control known narrow application medium curtains. In addition, the webs move in modern paper and paperboard production lines at speeds of up to 3000 m / min, which is many times the speed at which the known narrow webs move, and also a further high load on the Stability of the application medium curtain.

A device of the type mentioned is known from DE 197 16 466 A1. This document shows a device for applying dispersions to a material web by a so-called curtain coating application method. In this case, along the web transverse edges in the extending over the working width of the device application medium curtain depending on a commissioned work to the web extending edge guide element are arranged, which may be wetted depending on the embodiment of the application medium or not. In the case of wetted edge guide elements, the application medium curtain is stretched at its lateral edges by adhesive forces in the web direction. In the case of non-wetted edge guide elements, these are designed as electrodes which generate an electric field which acts on the lateral edges of the application medium curtain such that it is stretched in the web direction. A disadvantage of this prior art is that the application medium curtain can be influenced by said device only at its lateral edges. This can lead to unsatisfactory order results, especially in the working width center, especially for large working widths.

DE 199 03 559 A1 presents a whole series of principles of action, which should make it possible to weaken the air boundary layer entrained by the material web immediately before a curtain applicator unit. However, this publication does not address the possibilities of improving the efficiency of these principles of action.

WO 97/03009 deals with the problem of drying material webs after the application of media, namely printing inks, especially in low-web offset and flexographic printing. It proposes ionizing the gas molecules at the surface of the web by means of a corona discharge and accelerating them towards an electrode in order to increase the drying efficiency by the gas exchange at the web surface which accompanies this "ion wind".

DE 1 98 03 240 A1 discloses a curtain coating application device which comprises a sensor device for detecting the amount of coating applied to the material web application medium layer and a control device for controlling the order quantity. The order quantity is regulated via a change in the gap width of the application medium discharge gap at the commissioned unit.

EP 0 937 815 A1 shows an apparatus for applying a liquid or pasty application medium by a application medium jet, in which the application area can be increased or reduced by aperture elements which moves from the lateral edges of the application area in the material web transverse direction via application medium nozzles can be that the emanating from this order medium beam is intercepted by the aperture and does not reach the web.

The documents US-A-5,609,923, WO-A-89/05477, US-A-5,295,039 and US-A-5,122,386 all describe and relate to the same technical problem, namely that at the impact of the application medium curtain on the running underground with increase the running speed of the underground increasing inclusion of air bubbles. However, document US-A-5,295,039 focuses on the special task of avoiding spark discharges on the electrode assembly.

To solve the problem of increasing air entrainment at the impact of the application medium curtain with the running surface of the subsurface, US-A-5,609,923, WO-A-89/05477 and US-A-5,122,386 suggest the current art To electrostatically charge the substrate. In particular, the document US-A-5,609,923 explains a technical effect occurring here:

As already known from the documents EP-A-0 563 308 and EP-A-0 563 086 according to this document, the curtain coating process coating speeds at high curtain flow rates are limited by the formation of a so-called metastable region. This metastable region is illustrated in column 3, lines 27-33 of US-A-5,609,923, in that at moderate to high flow rates in the application medium curtain, the coating speed at which air entrapment begins is higher than the rate at which it expands dissolves. At medium coating speeds, however, the coating is metastable to any perturbation that can lead to air entrapment. For practical purposes, therefore, these intermediate coating speeds can not be used.

According to column 4, lines 35-37 of US-A-5,609,923, the electrostatic charging of the running underground causes an increasing suppression of the useless metastable velocity range as the electrostatic voltage is increased.

The document WO-A-89/05477 solves the identical problem of entrapment of air bubbles by substantially identical means, namely the electrostatic charging of the running underground, and tries to give a scientific explanation for this: according to column 6, line 30 to page 7 , Line 1, of WO-A-89/05477, contributes a high level of electrostatic charging of the subsurface to a substantially attracting force acting in the appropriate direction in the area where the curtain impinges on the subsurface, thus allowing an increase in the running speed of the substrate, without affecting the coating success.

Also column US-A-5,122,386 states phenomenologically in column 3, lines 38-45 that by electrostatic charging of the running underground - here recommended immediately before the impact of the curtain on the ground - a running speed of the ground of up to 330 m / min is possible without air entrapment.

The document US-A-5,290,600 relates essentially to a device for the attachment of road markings.

Moreover, this document does not relate to any apparatus for applying the application medium in the curtain-coating process, in which the application medium curtain moves substantially gravity-driven from the commissioned work to the ground. Rather, in the applicator of US-A-5,290,600, the electric field is the driving force which provides for movement of the application medium from the commissioned work to the ground. The electric field can at best be supported by gravity. Thus, the conditions known from US-A-5,290,600, compared with the generic devices, according to which the application medium curtain moves substantially gravitationally from the commissioned work to the ground, the exact opposite.

For the sake of completeness, reference is made to DE 198 29 449 A1 for the further state of the art.

In contrast, it is an object of the present invention, coating devices of the type mentioned for use in plants for the production and / or finishing of wide and fast-moving material webs, preferably made of paper or cardboard, to further improve, in particular as the stabilization of the application medium beam or curtain.

This object is achieved according to a first aspect of the present invention by a device having the features of claim 1.

According to the invention, the electric field assisting the gravitational force in the acceleration of the application medium jet is generated in a simple manner in that the applicator unit is held at a first predetermined electrical potential, while the substrate is at a second predetermined electrical potential, for example ground or ground potential. can be held. In this case, no additional electrodes need to be provided, but it is sufficient to provide the existing devices with electrical connections.

In contrast to the conventional curtain application devices described above, the application medium jet moves in the applicator device according to the invention not only under the influence of gravity from the discharge nozzle to the ground. Rather, this movement is assisted by an additional force which is exerted by the field generation device on the application medium beam and seeks to stretch the beam on its way from the delivery nozzle to the ground (pre-stretch). Therefore, in the case of "curtain coating applicators", the stability of the jet can be increased either with the same distance between the dispensing nozzle and the substrate, or the distance between the dispensing nozzle and the substrate can be selected larger for a given desired jet stability.

In particular, the latter is advantageous, considering that the total extension of the coating medium from a jet thickness determined by the width of the dispensing nozzle to the thickness of the layer of coating medium ultimately applied to the substrate is the product of the pre-stretching of the jet on the path described above composed of the dispensing nozzle to the ground and the Kontaktstrekkung, which stems from the difference between the speed of the beam immediately before hitting the ground and the running speed of the ground upon contact of the application medium with the ground. For the achievement of a uniform as possible coating layer, it is namely advantageous if the Gesamtstrekkung composed as evenly as possible of pre-stretching and contact stretching. Since the application medium beam is all the more susceptible to external influences, for example for the influence of the entrained air boundary layer, the longer the path of the application medium from the dispensing nozzle to the ground, this always leads in practice to the desire for a strong as possible Vorvorreckung addition ,

Additionally or alternatively, however, an electrode assembly which is maintained at a predetermined electrical electrode assembly potential may be provided on the upstream side of the applicator and in the vicinity thereof. "In addition" means that both the commissioned work and the electrode arrangement are kept at a predetermined, different from the ground potential.

By contrast, "alternatively" means that only the electrode arrangement is kept at a predetermined potential different from the ground potential while the application unit is either grounded or is floating in terms of its electrical potential ("floating potential").

The object of the present invention is achieved according to a second aspect of the invention by the just described "alternative" provision of an electrode arrangement, namely by an application device having the features of claim 5.

In this case, a force is exerted by the electric field on the application medium beam, which has a component orthogonal to its direction of movement, i. E. the electrode assembly attracts the application medium beam. This force component also helps to stabilize the application medium jet against the influence of the entrained air boundary layer on the surface of the substrate.

The electrode arrangement may comprise at least one flat electrode. In this case, the flat electrode may have a plurality of protrusions or needle points on its side facing the ground. Alternatively, however, it is also possible for the electrode arrangement to comprise a plurality of individual electrodes arranged in the transverse direction of the substrate, preferably needle electrodes. By using needle tips or needle electrodes it can be achieved that the electrode arrangement does not only influence its environment by the electric field formed with respect to the ground potential, but also that discharge processes can occur in which the ambient air is at least partially ionized, and the resulting charge carriers lead to a charge, for example, the application medium beam. After such charging, the movement of the application medium jet can be more effectively affected by the electric field.

In a development of the invention, it is proposed that a device for generating an electric field be provided downstream of the impact position of the application medium on the substrate. This electric field exerts on the application medium applied to the substrate a force directed towards the ground, which leads to a displacement of the excess application medium at locations where too much application medium has been applied. As a result, on the one hand even uncovered areas of the substrate coating medium supplied, which improves the coverage of the substrate with application medium. On the other hand, this makes it possible to even out the thickness of the application layer.

Preferably, the further field-generating device has a further electrode arrangement adjacent to the substrate, which is preferably held at a further predetermined electrical potential.

Such a force, which is applied to the substrate and applied to the substrate, can in principle also result from residual charging of the application medium applied to the substrate as a consequence of discharges induced by the first electrode arrangement.

For example, the predetermined electrical potential (s) other than the ground potential may have a value of between 5 kV and about 60 kV, preferably about 30 kV.

As already mentioned above, the substrate is preferably kept at ground potential. This can be realized, for example, in that a counter-element, preferably a counter-roller, which supports the material web in the area of the applicator when directly applied or on the surface of which the applicator applies the application medium in the case of indirect application, is in contact with an electrode in order to apply it to hold the second predetermined electrical potential. Additionally or alternatively, however, it can also be provided that the, for example metallic or rubberized, surface of the counter element is in sliding contact with the electrode. Finally, it is also possible that the electrode is in electrically conductive contact with a bearing shaft of the counter-roller. In the case of direct application, another alternative is to hold the material web at the second predetermined electrical potential, that is to say preferably the ground potential, by means of an electrode designed, for example, as a web-guiding element.

In addition to the use of electric fields to influence the application medium beam are of course other types of force fields in question, such as magnetic fields, if the application medium contains a magnetic field responsive particles anyway as a component or these particles can be added to the application medium for this purpose.

In order to be able to keep the influence of the entrained air boundary layer on the surface of the substrate on the application medium beam low, it is proposed that the electrode arrangement in the running direction of the ground is arranged upstream of a device for weakening the entrained air boundary layer. In this case, the air boundary layer weakening device may comprise a suction device with the aid of which the air boundary layer can be actively removed from the running underground.

For example, at the downstream end of the suction device, a drag scraper which is in sliding contact with the substrate may be provided. This drag scraper seals the suction towards the environment and hinders the further movement of the air boundary layer towards the commissioned work. As a result, entrained in the air boundary layer air is dammed, which at least partially destroys the laminar nature of the flow of the air boundary layer. This facilitates the suction and increases the suction efficiency of the suction device. Thus, the air boundary layer can be weakened by the inventively designed suction particularly effective, if not completely removed from the ground.

The drag scraper may be formed as a flexible film, preferably made of plastic, sheet metal or a composite material. The flexible film nestles under the suction of the suction device against the ground, which on the one hand improves the seal and on the other prevents the construction of a new air boundary layer. Is the drag scraper Made of sheet metal, so preferably stainless steel sheet is used with a thickness of at most 0.1 mm. However, drag scrapers of composite material with a surface coating made of Teflon have proven to be advantageous. The composite ensures the required temperature resistance and flexibility, while the Teflon surface coating ensures low friction between the drag scraper and the running surface. Furthermore, the drag scraper can be curved in the direction of rotation, which facilitates the elastic evasion and further reduces the friction with the ground.

In a further development of the invention, it is proposed that a further electrode arrangement be provided in the region of the suction device, preferably between the downstream end of the suction device and the drag scraper. With the help of this further electrode arrangement, the entrained air boundary layer can be influenced and in particular weakened. Especially if the further electrode arrangement comprises a plurality of individual electrodes arranged in the transverse direction of the substrate, preferably needle electrodes, or if the further electrode arrangement comprises at least one flat electrode which has a plurality of projections or needle tips on its side facing towards the ground there are also discharge processes between the tips of the further electrode arrangement and the substrate. These discharges disturb the laminar disturbance of the air boundary layer and at least partially convert it into a turbulent flow, which facilitates the extraction of the air boundary layer and thus further improves the effectiveness of the suction device. To assist in the formation of these discharges, it is proposed that the further electrode arrangement have a distance of between about 2 mm and about 30 mm from the substrate.

The further electrode arrangement can in principle be connected to an external power supply. However, it is also possible, and structurally even easier to realize, when the electrical potential of the further electrode arrangement is suspended ("floating potential"). In this case, as a result of the discharges emanating from the first electrode arrangement, the further electrode arrangement is charged and thus likewise brought to a potential which differs from the ground potential. To reduce the capacity of the further electrode arrangement as well as for safety reasons, it is proposed that the further electrode arrangement on the suction device is arranged so as to be electrically insulated from it.

As already explained above, the surface tension of the application medium attempts to reduce the surface of the application medium jet, which has an effect, in particular, in the region of the side edges of the application medium jet and results in jet narrowing. This beam narrowing can be prevented by the provision of edge guiding elements, since in this case additional adhesion forces act between the application medium and the surface of the edge guiding elements, which resist the tendency of the surface tension of the application medium to be constricted.

According to a further aspect, the object of the invention is therefore achieved by a device having the features of claim 27.

For reasons of good wetting of the edge guide elements, they have a structured surface. For this purpose, according to the invention, the surface of at least one edge guide element has a toothed surface, for example in the form of an external thread or else an internal thread.

The adhesion between the edge guide elements and the application medium can be improved by selecting the surface properties of at least one edge guide element such that the wetting or contact angle dependent on the properties of the application medium and the surface of the edge guide elements is less than 90 °.

The edge guide elements may be made of glass or metal, for example, since these materials have a sufficiently high surface tension. For metals, however, it should be noted that some metals tend to adsorb water vapor from the surrounding atmosphere, lowering their surface tension to the value of the adsorbed water layer.

In order to be able to adapt the application device to the width of the material web to be coated, it is proposed that at least one edge guide element is displaceably arranged in the transverse direction of the substrate and / or that the angle which an edge guide element encloses with the vertical is adjustable. In addition, the angular adjustability may include pivoting the free ends of the edge guide elements in the transverse direction and / or in the longitudinal direction.

Finally, the effect of the edge guide elements can also be improved by the provision of an electric field, for example by providing an electrode in the vicinity of at least one of the edge guide elements, preferably substantially parallel thereto, which is held at a predetermined electrical potential.

The above object is finally achieved by a method having the features of claim 34.

Fig. 1

eine grob schematische Seitenansicht zur Erläuterung von Aufbau und Funktion einer erfindungsgemäßen Auftragsvorrichtung;

Fig. 2

eine schematische Ansicht zur Erläuterung von Aufbau und Funktion der Randführungselemente; und

Fig. 3

eine Darstellung zur Erläuterung des Begriff "Benetzungswinkel" bzw. "Randwinkel".

The invention will be described below with reference to an embodiment with reference to the accompanying drawings be explained in more detail. It shows:

Fig. 1

a rough schematic side view to explain the structure and function of an applicator device according to the invention;

Fig. 2

a schematic view for explaining the structure and function of the edge guide elements; and

Fig. 3

a representation to explain the term "wetting angle" or "edge angle".

In Fig. 1, an applicator device according to the invention is generally designated 10. It comprises a curtain applicator 12 with a dispensing nozzle 14, is discharged from the application medium 16 in the form of a curtain 18 to a moving in the direction L substrate U. The substrate U is in the illustrated embodiment, the surface 20a of a web 20, which wraps around the peripheral surfaces of a support roller 22 in the field of applicator 12 partially.

On its way from the dispensing nozzle 14 to the substrate U, the application medium 16 is accelerated. This leads to a reduction in the thickness of the curtain 18 from the value D in the region of the dispensing nozzle 14 to the value d immediately before the impact position P on the substrate U (pre-stretch). Due to the difference between the speed of the application medium curtain 18 immediately before the impact position P and the running speed of the substrate U, the application medium 16 is stretched again when hitting the substrate U, so that the application layer 24 applied to the substrate U finally has the thickness s (Contact stretching). The total extension of the application medium 16 results as a product of the stretch factors of pre-stretch and contact stretch.

In practice, the application medium 16 when hitting the substrate U is usually stretched more than on the way from the discharge nozzle 14 to the substrate U, since with regard to a stable curtain 18 as possible, the drop distance between the discharge nozzle 14 and substrate U not arbitrarily large can. Excessive contact stretching, however, adversely affects the uniformity of the coating layer 24 applied to the substrate U.

The applicator 10 according to the invention now offers a way by which you can either increase the Vorstreckung of the curtain 18 at the same drop height between the dispensing nozzle 14 and substrate U and how to reduce the drop height between dispensing nozzle 14 and substrate U and thus the curtain at the same Vorstreckung 18 can stabilize. Namely, according to the present invention, the application medium curtain 18 on its way from the discharge nozzle 14 to the substrate U is not left solely to gravity, but electrostatic forces are additionally exerted thereon. This strengthening of the curtain 18 stretching forces has, as the surface tension of the application medium 16, which seeks to contract the curtain 18 in order to reduce the surface thereof, constant, a higher stability of the application medium curtain 18 result.

In principle, the electrostatic forces could be provided by applying a first predetermined electrical voltage V ₁ to the housing of the applicator 12 and the support roller 22 on the

Earth or ground potential V _E or V ₂ holds. In the embodiment according to FIG. 1, however, a different path is taken, which will be explained in more detail below:

According to FIG. 1, an electrode arrangement 30 is provided in the running direction L immediately in front of the applicator 12, which may comprise, for example, a flat electrode extending in the transverse direction Q with a plurality of needle points, or a plurality of needle electrodes 32 arranged adjacent to one another in the transverse direction Q can. To the electrode assembly 30, a predetermined voltage V _{3 is} applied, while the surrounding parts of the applicator 10, namely the applicator 12, the support roller 22 and provided with respect to the running direction L upstream of the electrode assembly 30 suction box 34 for weakening one of the web 20th entrained air boundary layer at ground or ground potential V _{E are} held.

Not only does an electric field build up between the electrode arrangement 30 and its environment held at ground potential, but discharges occur between the needle tips or needle electrodes 32 and the surroundings, which are indicated by the dashed lines E in FIG. As a result of these discharges E, the coating medium 16 of the curtain 18 is electrically charged, so that it is accelerated in the electric field between the electrode assembly 30 and the backup roller 22 to the backing roller 22, which promotes the Vorstreckung.

In addition, a force is exerted on the curtain 18 due to the discharges E but also a force which has a component orthogonal to its falling movement direction. This force component also helps to stabilize the application medium curtain 18 from the influence of the air boundary layer G entrained on the surface of the material web 20.

As already mentioned above, the suction box 34 serves to weaken the air boundary layer G. To increase the suction efficiency, a drag scraper 36 is provided on the outlet side of this suction box 34 which is in sliding contact with the surface 20a of the material web 20 and seals the suction region of the suction box 34 on the outlet side. The drag scraper 36 may be made of, for example, a Teflon coated composite. by virtue of the use of a composite material, the Schlepp scraper 36 has sufficient temperature resistance and flexibility, and due to the surface coating with Teflon sufficient low friction.

Advantageously, a further electrode arrangement 40 is now provided between this drag scraper 36 and the suction box 34, which is attached to the suction box 34 via an electrical insulation 42. The further electrode arrangement 40 can in turn be formed either by a flat electrode having a plurality of needle tips or a plurality of needle electrodes arranged adjacent to one another in the transverse direction Q. The electrode arrangement 40 can in principle be connected to an external power supply. In the illustrated embodiment, however, it is in a floating state in terms of its electrical potential, but is charged as a result of discharges E emanating from the electrode assembly 30 and thus also brought to a potential different from the ground potential.

Due to the small distance of the tips of the electrode assembly 40 from the substrate U, the charging of the electrode assembly 40 is sufficient to allow discharges e to occur between the tips of the electrode assembly 40 and the substrate U. These discharges e disturb the laminar flow of the air boundary layer G and at least partially convert it into a turbulent flow. This facilitates the extraction of the air boundary layer G from the surface 20a of the web and thus improves the effectiveness of the suction box 34.

Finally, electrical forces can also contribute to improving the leveling and fixing of the application layer 24 on the material web 20. For this purpose, for example, a further electrode arrangement in the form of a plate electrode 46 may be provided, which is held at a predetermined electrical potential V ₄ . Between this plate electrode 46 and the support roller 22 held at ground potential, a relatively homogeneous electric field is formed which exerts a force directed toward the substrate U on the application medium. This force provides at locations of the web surface 20a, has been applied to the excessive application medium 16, to a displacement of the excess coating medium and thus to a homogenization of the coating layer 24. In extreme cases, it may even happen that previously uncovered areas of the web surface 20a as a result Force be covered for the first time with application medium 16. In addition, the above-mentioned force also improves the bond that the application medium 16 makes with the surface 20 a of the material web 20.

It should also be noted that the charge which the application medium 16 experiences in the area of the curtain 18 through the discharges E, in cooperation with the support roller 22 held at ground potential, leads to such a force directed towards the substrate U. This is indicated in the enlarged view of the detail D by the arrows F.

The back-up roll 22 can be held in different ways at the ground potential V _E. For example, the rolling axis A can be connected to a sliding contact, as described for example in DE 197 33 333 A1. In addition or as an alternative, however, a sliding contact 50 which is in contact with the surface 22a of the roller 22 may also be provided. Finally, the material web 20 may also be held at ground potential V _E via contacts formed, for example, by web guiding elements 48.

FIG. 2 shows a view of the application device 10, viewed in the direction of travel L. On the basis of this representation, a possibility is to be explained how the application medium curtain 18 can also be stabilized in the region of its side edges 18a. Namely, the surface tension of the application medium 16 seeking to contract the curtain 18 is mainly effective in the edge regions 18 of the curtain 18. It leads there to a lateral contraction of the curtain 18 and its thickening. To counteract this effect, in the embodiment shown in Fig. 2 Führungsfeisten 54 are provided which are attached to the commissioned work 12 such that they catch the emerging from the dispensing nozzle 14 curtain 18 and on his fall path to just before the surface 20 a of the web 20 to lead.

The effect of the edge strips 54 is based on the adhesion forces between the application medium 16 and the surface of the edge strips 54. With a view to the best possible adhesion, the contact angle or wetting angle α of a droplet T of application medium 16 on the surface 54a of the edge strips 54 should be as low as possible Have value. This can be achieved, for example, by making the surface of the edge strips 54 of a material with high surface tension. In addition, the wetting between application medium 16 and edge strips 54 can be improved by a toothed surface structure of the edge strips 54. This can be achieved, for example, by using threaded rods as edge strips 54.

A further possibility to be able to improve the adhesion of the application medium 16 to the edge strips 54 consists in providing electrode strips 56 substantially parallel to the edge strips 54 to which a predetermined electrical voltage V ₅ is applied. As a result, similar to what has been described above for the arrangement according to FIG. 1, an attractive force is exerted on the application medium.

To the edge strips 54 to the respectively desired Working width, ie, to be able to adjust the particular width of the material web 20, these are arranged slidably on the commissioned work 12 in the transverse direction Q, which is indicated in Fig. 2 by the arrows q. In addition, the edge strips 54 can also be arranged pivotably on the applicator 12, namely about the longitudinal direction L and / or to the transverse direction Q substantially parallel axes, in Fig. 2 by the arrows I only a pivoting in the transverse direction Q, ie is indicated by an axis extending substantially parallel to the longitudinal direction L axis.

Claims (34)

1. Device (10) for applying liquid or pasty application medium (16) to one or both sides of a moving substrate (U), comprising an applicator unit (12) which is arranged at a distance from the substrate (U) and discharges the application medium (16) onto the substrate (U) in the form of a free application medium jet (18),
   the applicator unit being a curtain applicator unit (12) which discharges the application medium onto the substrate (U) as an application medium curtain (18) which moves from the applicator unit (12) to the substrate (U) substantially under the force of gravity,
   the substrate (U), in the case of direct application, being the surface (20a) of a material web (20), in particular of paper or board, and, in the case of indirect application, being the surface of a transfer element, preferably of a transfer roll, which then transfers the application medium to the surface of the material web,
   and in the region of the applicator unit (12) there being provided a device (30) for producing an electric field, which exerts on the application medium jet (18) moving from the applicator unit (12) to the substrate (U) a force which assists its movement, characterized in that, as the device for producing the electric field, the applicator unit (12) is connected to a first potential source in order to keep the applicator unit (12) at a first predetermined electric potential (V₁), and in that the substrate (U) is connected to a second potential source in order to keep the substrate (U), at least in the vicinity of the applicator unit (12), at a second predetermined electric potential (V_E or V₂),
   wherein the electric field is set in such a manner that the total stretching of the application medium jet (18) is composed substantially equally of the pre-stretching and the contact stretching which is caused by the difference between the velocity of the application medium jet (18) immediately before it strikes the substrate (U) and the running speed of the substrate (U) when the application medium jet (18) comes into contact with the substrate (U).
2. Application device according to Claim 1, characterized in that an electrode arrangement (30) is provided on the upstream side of the applicator unit (12) and in its vicinity, preferably at a distance from the substrate (U), which is kept at a predetermined electric potential (V₁).
3. Device (10) for applying liquid or pasty application medium (16) to one or both sides of a moving substrate (U), comprising an applicator unit (12) which is arranged at a distance from the substrate (U) and discharges the application medium (16) onto the substrate (U) in the form of a free application medium jet (18),
   the applicator unit being a curtain applicator unit (12) which discharges the application medium onto the substrate (U) as an application medium curtain (18) which moves from the applicator unit (12) to the substrate (U) substantially under the force of gravity, the substrate (U), in the case of direct application, being the surface (20a) of a material web (20), in particular of paper or board, and, in the case of indirect application, being the surface of a transfer element, preferably of a transfer roll, which then transfers the application medium to the surface of the material web,
   and in the region of the applicator unit (12) there being provided a device (30) for producing an electric field, which exerts on the application medium jet (18) moving from the applicator unit (12) to the substrate (U) a force which assists its movement, characterized in that, as the device for producing the electric field, an electrode arrangement (30) which is kept at a predetermined electric electrode arrangement potential (V₃) is provided on the upstream side of the applicator unit (12) and in its vicinity, at a distance from the substrate (U), such that the application medium (16) of the application medium jet (18) is electrically charged.
4. Application device according to Claim 2 or 3, characterized in that the electrode arrangement comprises at least one flat electrode, the flat electrode preferably having a plurality of projections or needle points on its side pointing toward the substrate.
5. Application device according to Claim 2 or 3, characterized in that the electrode arrangement (30) comprises a plurality of individual electrodes, preferably needle electrodes (32), arranged adjacent to one another in the transverse direction of the substrate (U).
6. Application device according to one of the preceding claims, characterized in that downstream of the position (P) at which the application medium (16) strikes the substrate there is provided a further device (46) for producing an electric field, which exerts on the application medium (16) applied to the substrate (U) a force which is directed toward the substrate (U).
7. Application device according to Claim 6, characterized in that the further field production device has a further electrode arrangement (46) which is adjacent to the substrate (U) and which is preferably kept at a further predetermined electric potential (V₄).
8. Application device according to one of the preceding claims, characterized in that the first predetermined, and/or the electrode arrangement potential and/or the further predetermined electric potential (V₁, V₃, V₄) have a value of between about 5 kV and about 60 kV, preferably about 30 kV.
9. Application device according to one of the preceding claims, characterized in that the second predetermined electric potential (V₂) is the earth potential (V_E).
10. Application device according to Claim 9, characterized in that a backing element, preferably a backing roll (22) which, in the case of direct application, supports the material web (20) in the region of the applicator unit (12) or, in the case of indirect application, on the surface of which the applicator unit applies the application medium, is in contact with an electrode in order to keep said roll at the second predetermined electric potential (V₂).
11. Application device according to Claim 10, characterized in that the surface (22a) of the backing element (22) is in wiping contact with the electrode (50).
12. Application device according to Claim 10 or 11, characterized in that the electrode is in contact with a bearing shaft (A) of the backing roll (22).
13. Application device according to one of Claims 9 to 12, characterized in that, in the case of direct application, the material web (20) is kept at the second predetermined electric potential (V₂) by an electrode (48) formed, for example, as a web guide element.
14. Application device according to one of the preceding claims, characterized in that, in addition to or instead of the electrode arrangement (30) and/or the further electrode arrangement (46), a magnetic field device is provided for influencing the movement of the application medium (16).
15. Application device according to one of the preceding claims, characterized in that, in the direction of movement (L) of the substrate (U), a device (34) for attenuating the air boundary layer (G) carried along by the substrate (U) is arranged upstream of the electrode arrangement (30).
16. Application device according to Claim 15, characterized in that the air boundary layer attenuation device comprises a suction device (34).
17. Application device according to Claim 16, characterized in that a trailing scraper (36) in wiping contact with the substrate (U) is provided at the downstream end of the suction device (34).
18. Application device according to one of Claims 15 to 17, characterized in that a further electrode arrangement (40) is provided in the region of the air boundary layer attenuation device (34), preferably between the downstream end of the suction device (34) and the trailing scraper (36).
19. Application device according to Claim 18, characterized in that the further electrode arrangement (40) comprises a plurality of individual electrodes, preferably needle electrodes, arranged adjacent to one another in the transverse direction of the substrate.
20. Application device according to Claim 18, characterized in that the further electrode arrangement (40) comprises at least one flat electrode which has a plurality of projections or needle points on its side pointing toward the substrate.
21. Application device according to one of Claims 18 to 20, characterized in that the further electrode arrangement (40) has a distance from the substrate of between about 2 mm and about 30 mm.
22. Application device according to one of Claims 18 to 21, characterized in that the electric potential of the further electrode arrangement (40) is kept floating.
23. Application device according to one of Claims 18 to 22, characterized in that the further electrode arrangement (40) is arranged on the air boundary layer attenuation device (34) electrically insulated (42) from the latter.
24. Application device according to one of the preceding claims, characterized in that the applicator unit (12) and/or the air boundary layer attenuation device (34) is kept at a predetermined electric potential (V_E), preferably ground potential.
25. Device (10) for applying liquid or pasty application medium (16) to one or both sides of a moving substrate (U), comprising a curtain applicator unit (12) which discharges the application medium (16) onto the substrate (U) as a curtain (18) or veil moving substantially under the force of gravity, the substrate (U), in the case of direct application, being the surface (20a) of a material web (20), in particular of paper or board, and, in the case of indirect application, being the surface of a transfer element, preferably of a transfer roll, which then transfers the application medium to the surface of the material web, edge guiding elements (54) being provided, which guide the lateral edges (18a) of the application medium curtain (18) at least on part of its movement under the force of gravity between the curtain applicator unit (12) and the substrate (U), characterized in that at least one edge guiding element (54) has a toothed surface (54a).
26. Application device according to Claim 25, characterized in that the surface characteristics of at least one edge guiding element (54) are selected in such a way that the wetting angle (α), which depends on the characteristics of the application medium (16) and the surface (54a) of the edge guiding elements (54), is less than 90°.
27. Application device according to Claim 25 or 26, characterized in that at least one edge guiding element (54) has an external thread.
28. Application device according to one of Claims 25 to 27, characterized in that at least one edge guiding element (54) is fabricated from glass or metal.
29. Application device according to one of Claims 25 to 28, characterized in that at least one edge guiding element (54) is arranged such that it can be displaced in the transverse direction (Q) of the substrate (U).
30. Application device according to one of Claims 25 to 29, characterized in that the angle which an edge guiding element (54) forms with the vertical is adjustable.
31. Application device according to one of Claims 25 to 30, characterized in that an electrode (56) is provided in the vicinity of at least one of the edge guiding elements (54), preferably extending substantially parallel to the latter, and is kept at a predetermined electric potential (V₅).
32. Method for applying liquid or pasty application medium (16) to one or both sides of a moving substrate (U), using an applicator unit (12) which is arranged at a distance from the substrate (U) and discharges the application medium (16) onto the substrate (U) in the form of a free application medium jet (18),
    the applicator unit being a curtain applicator unit (12) which discharges the application medium onto the substrate (U) as an application medium curtain (18) which moves from the applicator unit (12) to the substrate (U) substantially under the force of gravity, the substrate (U), in the case of direct application, being the surface (20a) of a material web (20), in particular of paper or board, and, in the case of indirect application, being the surface of a transfer element, preferably of a transfer roll, which then transfers the application medium to the surface of the material web,
    and in the region of the applicator unit (12) there being provided a device (30) for producing an electric field, which exerts on the application medium jet (18) moving from the applicator unit (12) to the substrate (U) a force which assists its movement, characterized in that, in order to produce the electric field, the applicator unit (12) is kept at a first predetermined electric potential (V₁), and in that the substrate (U), at least in the vicinity of the applicator unit (12), is kept at a second predetermined electric potential (V_E or V₂),
    wherein the electric field is set in such a manner that the total stretching of the application medium jet (18) is composed substantially equally of the pre-stretching and the contact stretching which is caused by the difference between the velocity of the application medium jet (18) immediately before it strikes the substrate (U) and the running speed of the substrate (U) when the application medium jet (18) comes into contact with the substrate (U).
33. Method according to Claim 32, characterized in that the first predetermined electric potential (V₁) has a value of between 5 kV and 60 kV, preferably approximately 30 kV.
34. Method according to Claim 32 or 33, characterized in that the second predetermined electric potential (V₂) is the earth potential (V_E).

Images