The present invention relates to a curtain coating method for coating a material web, in which method coating agent is applied from a curtain coater located above the material web, moving supported by a support element, as a curtain-like flow to a point of impact on the surface of the material web (W), boundary layer air being removed from the surface of the material web at a point in front of the point of impact.

The present invention further relates to a curtain coating device applying the method for coating the material web, the device comprising a curtain coater which is located above a moving material web supported by support elements, and from which the coating agent can be applied as a curtain-like flow to a point of impact on the surface of the material web, and boundary layer air discharge means for removing boundary layer air from the surface of the material web at a point in front of the point of impact.

Previously are known methods and devices based on curtain coating, the purpose of which is to improve the behaviour of the curtain - and thus the quality of the end result of coating - as the coating agent drips from the curtain coater as a curtain-like continuous flow to the point of impact on the material web. One factor affecting the end result is the boundary layer air which forms on the material web surface to be coated, the aim being to remove this air at a point before the point of impact. Otherwise the boundary layer air will break the structure of the curtain at the point of impact and the end result of coating will be poor. A further significant factor affecting the end result is the control of the air pressures in front of the curtain formed by the coating agent.

Efforts have been made to eliminate the foregoing disadvantages, for example, in the manner known from the published application WO 03/053597. It discloses air discharge means by which the boundary layer air is removed by suction at a point in front of the point of impact. The publication further discloses two air inlets for controlling airflow in the space in front of the curtain. According to the publication, in front of the curtain the flows are controlled by means of a pressure sensor located in the space, the sensor providing control data to the air inlet. According to the publication, the airflow correlates with the pressure prevailing in the space. In accordance with the publication, air supplied to the space is removed by the same air discharge means as boundary layer air. The controllability of air discharge and air supply is not very good because discharge is utilised for two different purposes.

From the patent publication EP 1142647 is known a device, where there is a space in front of the curtain, to which gas is supplied by supply means provided in the space. In addition to creating the desired pressure, the purpose of this is to remove the layer of air travelling with the web and to replace it with a gas layer. In front of the said space is, in addition, arranged a gas exhaust chamber with means for discharging gas from the space. The supply and discharge of gas are controlled on the basis of data received from the pressure sensor arranged in the space. Second air supply means are in addition arranged in front of the exhaust chamber, the purpose of which is to remove the boundary layer air carried along with the material web travelling with the support of the roll. According to the publication, the second air supply means are directed vertically, whereby the impact angle of the downwards directed air jet on the web is determined by the direction of travel of the web on the roll. The direction of travel of the material web supported by the roll surface changes constantly. Also the amount of air supplied through the second air supply means is controlled on the basis of data obtained from the said pressure sensor. The disadvantage of this type

of an arrangement is that the control of all functions is based on data received from the pressure sensor, whereby the adjustability of different functions is relatively difficult. This arrangement, in which the discharge of boundary layer air takes place at a relatively long distance from the point of impact due to the support roll, does not allow for an efficient arrangement from the point of view of space utilisation.

The aim of the present invention is to eliminate, or at least substantially lessen, the above-mentioned disadvantages.

To achieve the above aim, the method according to invention is characterised in that to remove boundary layer air, air is supplied to the surface of the moving material web at an oblique angle with respect to the material web, so that the airflow has an opposite component with respect to the direction of travel of the material web, and that the pressure level in the impact point area is controlled by supplying stabilising air from a point in front of the impact point to the impact point area at an oblique angle with respect to the direction of travel of the material web, so that the airflow has a component parallel to the direction of travel of the material web, and by removing the stabilising air from a point before the stabilising air inlet.

Furthermore, the device applying the method according to the invention is characterised in that the air removing the boundary layer air by means of the boundary layer air discharge means can be supplied to the surface of the moving material web at an oblique angle with respect to the direction of travel of the material web, so that the air has an opposite component with respect to the direction of travel of the material web, and that for controlling the pressure level in the impact point area, the device comprises stabilising air supplying means by which stabilising air can be supplied to a point in front of the impact point to the impact point area at an oblique angle with respect to the direction of travel of the material web, so that the air has a

component parallel to the direction of travel of the material web, and stabilising air discharge means arranged at a point in front of the stabilising air supply means.

By means of the method and device relating to the invention is achieved an advantage compared with the prior art in that the air/gas pressures or flows in the space behind the curtain do not need to be controlled very accurately over the whole distance between the coating device because the supply and discharge of stabilising air can be accurately directed to the impact point area. Thus the conditions prevailing in the space do not have to be monitored with prior art sensors. The method also makes it possible to remove the boundary layer air and control the stabilising air at as short a distance as possible from one another. Furthermore, the control of the stabilising air is separated by a simpler construction than before from the control systems relating to boundary layer air discharge, whereby the operation of both can be still better controlled. In addition, the instruments relating to the discharge of the boundary layer can be located at a greater distance from the material web than before. This space-saving method and the device for applying it also make it possible to support the material web by other means than merely the roll.

Preferred embodiments of the present invention are disclosed in the dependent claims.

The invention is described in greater detail in the following, with reference to the accompanying drawings, in which:

Figure 1 shows an embodiment of a device applying the method according to the present invention, and

Figure 2 shows another preferred embodiment of a device according to the invention.

Figure 1 thus shows a curtain coater or an application beam according to the present invention, which is marked with reference numeral 1. The curtain coater 1 is essentially located above a material web W travelling on its track. In the direction of travel, at the curtain coater, the track is comprised of a support element 3, against which the material web W rests. The surface of the support element 3 supporting the material web W may be straight or curved. The support element 3 is preferably an immobile support shoe, but as a support element may also be used a support roll, with the mantle of which the material web moves along a part of the circumferential course of the support roll. By means of the nozzle part of the application beam 4, which is essentially of the same width as the material web W, or a corresponding feeder part, such as an inclined surface, is formed a curtain 2 of the coating agent having essentially the width of the material web W, the curtain being applied from the desired height to the point of impact 22 on the surface of the material web W.

With the web W moves also the boundary layer air 4. To discharge this to a point in front of the point of impact 22 (with respect to the direction of travel of the material web W), boundary layer air 4 discharge is provided. The discharge is accomplished by the means 9, 10, 13, 16 and 21 intended for boundary layer air 4 discharge. These include an air supply duct 13 bordered by walls 9 and 10, at the end of which is arranged a nozzle part 21, through which the direction of the air 5 supplied can be adjusted as desired with respect to the direction of travel of the material web W. The nozzle part 21 is located at a distance A from the material web. This distance A is advantageously 1 to 20 millimetres. Preferably, this distance A is, however, 4 to 10 millimetres. The direction of travel of the supplied air 5 within this distance A is arranged at an oblique angle with respect to the direction of

travel of the material web, so that the air has an opposite component with respect to the direction of travel of the material web. The amount and velocity of the air 5 discharging the boundary layer air is preferably adjusted by means of a blower 16. The amount of the air 5 discharging boundary layer air 4 is sufficient and its direction is correct when it prevents the boundary layer air 4 from proceeding on the material web W and in addition directs the boundary layer air 4 from the surface of the material web W to the surroundings, for example, as shown in the Figure by arrows 4a, in front of the means 9, 10, 13, 21.

Furthermore, behind the boundary layer air discharge (with respect to the direction of travel of the material web) is controlled the pressure level prevalent in the impact point 22 area. For this purpose, stabilising air supply means and stabilising air discharge means are arranged between the dripping curtain 2 and the boundary layer air discharge means 9, 10, 13, 21.

The stabilising air supply means include a stabilising air 6 supply duct 15 bordered by walls 11 and 12 (and end walls, not shown). The end of the supply duct forms a nozzle 12a, by means of which stabilising air 6 is supplied in a controlled manner to the impact point area, preferably over the whole width of the material web W. To achieve this, the nozzle 12a is made to direct the stabilising air 6 as desired with respect to the direction of travel of the material web W. The direction of travel of the supplied air 6 is arranged at an oblique angle with respect to the direction of travel of the material web W, the air having a component parallel with the direction of travel of the material web W. The angle between the direction of travel of the supplied air 6 and of the component of the supplied air 6 parallel with the direction of travel of the material web W, in other words the angle of impact between the supplied air 6 and the material web W is, for example, 10-80°, preferably 25-65°. The amount and velocity of the stabilising air 6 is

preferably adjusted by means of a blower 18 arranged in conjunction with the supply duct 15.

Here, the stabilising air discharge duct 14 is preferably arranged between the boundary layer air discharge means and the stabilising air supply means. Thus, in this embodiment, the stabilising air discharge duct 14 is formed between a wall 10 comprised in the boundary layer air discharge means and a wall 11 comprised in the stabilising air supply means. The discharge duct 11 is preferably also comprised of separate walls, whereby stabilising air supply and discharge can be better controlled. The amount and velocity of the stabilising air 7 to be removed is preferably adjusted by means of a blower 17 arranged in conjunction with the supply duct 14. Since the amount of stabilising air supplied is known, in addition to the stabilising air to be discharged is also known the amount of air discharged from the space in front of the curtain. It should be mentioned that instead of the blowing and suction means 16, 17, 18, other devices may also be used for supplying and discharging air, such as ejectors and injectors operating in a known manner.

The pressure level in the area in front of the impact point is preferably controlled by adjusting the amount of stabilising air 6 supplied and at the same time the amount of stabilising air 7 removed. This is done by adjusting the blasting output of the blowers 17 and 18, for example on the basis of predetermined control variables, such as web speed and coating agent composition. In addition, the quantitative ratios of supplied and discharged stabilising air may be adjusted. Directed stabilising air 6 supply and discharge makes possible the stabilisation of the curtain 2 specifically in the impact point area. This means that the rest of the space 20 remaining in front of the curtain does not need to be controlled. It is, however, preferable to ensure that essentially the same conditions prevail in this space as behind the curtain. For this purpose, the space 20 may be limited from the point in front of the curtain by a space-limiting wall 19 or the like, which may be moved in

the direction of travel of the material web W. In conjunction with the wall 19 is provided an opening, through which air may flow freely into the space 20, in order to ensure that the same conditions prevail both in front of and behind the curtain.

In one embodiment of the invention, the control variable of the supply and discharge (amounts) of stabilising air may be the location of the dripping curtain 2 or of the impact point 22. In some cases, it is possible that in the space in front of the curtain 2 and behind the curtain 2 are created conditions that deviate from one another, in which case the dripping curtain 2 may move in the direction of travel of the material web in such a way that the point of impact 22 will also move in the direction of travel of the material web. In such a case, it is advantageous to monitor the location of the impact point 22, as shown in Figure 1 or, alternatively, the location of the curtain 2 from a desired point (height) between the curtain coater 1 and the impact point 22. For the monitoring may be used suitable monitoring equipment 23, for example, a non-contacting distance gauge 23, such as a laser gauge. The gauge 23 is used to measure the distance between the impact point 22 and the gauge 23, a deviation from which, from a predetermined value or between two values, indicates disadvantageous movements of the impact point and thus of the curtain. The measurement data obtained from the distance gauge 23 may be transmitted as control data to the stabilising air supply and discharge means 17 and 18, whereby any disturbances in the conditions affecting the curtain 2 can be compensated for. Other types of monitoring equipment, such as a line camera, are also suitable for monitoring the location.

The discharge of stabilising air and the supply of stabilising air may thus be separately adjustable. This arrangement also makes it possible for the supplied and discharged stabilising air 5 and 6 to create a continuous airflow 8, which supports the curtain 2 within the impact point 21 area. In addition,

the discharge point, that is, the end of the discharge duct 14 may be located at a desired point with respect to the point of supply (nozzle 12a). This point is preferably immediately in front of the supply point. This ensures for its part that the supplied stabilising air 6 will not "escape" from the impact point area to elsewhere in the space 20. The arrangement according to Figure 1 is particularly well suited for devices with high material web speeds, for example, 2100-1200 metres/minute at most.

Compared with Figure 1, Figure 2 shows a structurally modified embodiment, which is particularly well suited for devices with low material web W speeds, for example, less than 1200 m/min. The structural details shown in Figure 2 are marked with the same reference numerals as in Figure 1 and are thus not discussed in greater detail here. In this embodiment, the boundary layer air 4 is removed in essentially the same manner as in the first embodiment. The stabilising air 6 supply to the surface of the material web is directed at a distance in front of the impact point 22, however, in the impact point 22 area. The stabilising air discharge duct 14 is arranged immediately behind the stabilising air supply means 15. By this arrangement, the airflow accompanying the curtain 2 may be removed in a controlled manner, especially from the space 2 in front of the curtain 2 in the impact point area 22. Thus also the conditions behind the curtain 2 can be maintained appropriate to obtain as good an application result as possible. Through the discharge duct 14 may, if necessary, also be discharged boundary layer air 4, if it has entered behind the boundary layer air discharge means to the point where stabilising air 7 is being removed.

The present invention is not limited to the embodiments disclosed alone, but may be applied within the scope of protection defined by the claims disclosed.