APPLICATION NOZZLE, APPLICATION UNIT AND METHOD

Abstract

An application nozzle, an application unit, and a method are used for applying a liquid or pasty coating medium onto a running surface, in particular onto a running surface in a machine for producing or processing a fibrous web. The application nozzle contains a fluid head which is configured to produce a film from a coating medium or a curtain from a coating medium, and the application also additionally contains a blowing head which is configured to generate a linear jet of gaseous medium. An impact line is additionally provided on which the linear jet of gaseous medium impacts the film or curtain made of the coating medium, thereby forming a spray curtain. The blowing head is arranged such that the spray curtain is oriented in the direction of the running surface.

Claims

1. An application nozzle for an application of a coating medium being a liquid coating medium or a pasty coating medium onto a running surface, the application nozzle comprising: a fluid head formed to generate a fluid film composed of the coating medium or a curtain composed of the coating medium; and a blow head formed to generate a linear jet of a gaseous medium, wherein an impact line is formed where the linear jet of the gaseous medium impacts the fluid film or the curtain composed of the coating medium, thereby forming a spray curtain, said blow head is disposed so that the spray curtain is directed in a direction of the running surface.

2. The application nozzle according to claim 1, wherein said blow head having a wall; and further comprising a support surface disposed so that the coating medium is discharged from said fluid head onto said support surface, and is guided as the fluid film along said support surface, wherein said support surface is provided at least partially by said wall of said blow head.

3. The application nozzle according to claim 2, wherein said support surface has a lower end forming a breaking edge, and the impact line is provided at said breaking edge or at a distance of less than 5 mm from said breaking edge.

4. The application nozzle according to claim 3, wherein said breaking edge is provided with a structure.

5. The application nozzle according to claim 1, wherein a length of the spray curtain from the impact line to the running surface is at most 50 mm.

6. The application nozzle according to claim 1, wherein the direction of the spray curtain has a component which is directed counter to a direction of movement of the running surface.

7. The application nozzle according to claim 1, wherein the spray curtain has an opening angle being less than 30.

8. The application nozzle according to claim 7, wherein said blow head has an outlet with a lip being suitable for influencing the direction and/or the opening angle of the spray curtain.

9. The application nozzle according to claim 1, wherein the running surface is a running surface in a machine for producing or processing a fibrous web.

10. The application nozzle according to claim 2, wherein said support surface is provided entirely by said wall of said blow head.

11. The application nozzle according to claim 4, wherein (8a) said structure of said breaking edge is an undulating structure or a saw tooth structure.

12. The application nozzle according to claim 1, wherein a length of the spray curtain from the impact line to the running surface is at most 20 mm.

13. An application unit for an application of a coating medium being a liquid coating medium or a pasty coating medium onto a running surface, wherein the running surface is provided by a surface of a rotating transfer roller, the application unit comprising: at least one said application nozzle, containing: a fluid head formed to generate a fluid film composed of the coating medium or a curtain composed of the coating medium; and a blow head formed to generate a linear jet of a gaseous medium, wherein an impact line is formed where the linear jet of the gaseous medium impacts the fluid film or the curtain composed of the coating medium, thereby forming a spray curtain, said blow head is disposed so that the spray curtain is directed in a direction of the running surface.

14. The application unit according to claim 13, wherein the spray curtain impacts on the surface of the transfer roller between a 7 o'clock position and a 12 o'clock position.

15. The application unit according to claim 13, wherein the application unit defines an application space which is formed and delimited by: the running surface; a wall of said blow head; the spray curtain; and a point of a narrowest gap between the running surface and said blow head, and wherein the coating medium from said fluid head is applied onto said wall of said blow head such that an entirety of said wall of said blow head inside said application space is covered with the coating medium.

16. The application unit according to claim 15, wherein said narrowest gap between the running surface and said blow head is between 2 mm and 20 mm wide.

17. The application unit according to claim 15, further comprising a nozzle for generating an air flow, wherein the air flow is directed from outside said application space to said narrowest gap.

18. The application apparatus according to claim 15, wherein said application space is shaped so that a tangent of the transfer roller intersects with said wall of said blow head inside said application space at a point of impact of the spray curtain.

19. A method for applying a coating medium onto a running surface, which comprises the steps of: providing the application unit according to claim 13; and applying the coating medium to the running surface by means of the application unit.

20. The method according to claim 19, wherein the linear jet of the gaseous medium at an output of the blow head has a speed of more than 5 m/s.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0151] FIG. 1 is an illustration showing an application nozzle according to one aspect of the invention;

[0152] FIG. 2 is an illustration showing the application nozzle according to a further aspect of the invention;

[0153] FIG. 2A is an illustration showing a cut-out of the application nozzle according to a further aspect of the invention;

[0154] FIG. 3 schematically shows the application nozzle according to a further aspect of the invention as well as an application space according to a further inventive idea; and

[0155] FIG. 4 is an illustration showing an application unit according to one aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0156] Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown an application nozzle 1 as part of an application unit 10 for the application of a liquid or pasty coating medium onto a running surface 4 according to one aspect of the present invention.

[0157] In the embodiment shown here, the moved surface 4 is formed by a running fibrous web. In alternative embodiments, however, this can also be provided, for example, by the surface 4 of a transfer roller or the like.

[0158] In the case of the embodiment in FIG. 1, the application nozzle 1 contains a fluid head 2 which is embodied in the manner of a traditional broad slot nozzle and discharges a free-falling curtain of coating medium 14. The application nozzle furthermore contains a blow head 3 which is formed to generate a linear jet of gaseous medium 6, in general an air jet 6. Both the curtain 14 and the air jet 6 extend homogeneously in the transverse direction over the entire width to be coated of the surface 4.

[0159] While the curtain 14 falls downwards as a result of gravity, the air jet 6 is directed in the direction of the running surface 4. The air jet 6 meets the curtain 14 at an impact line 8. As a result of the speed of the air jet 6, the coating medium of the curtain 14 is converted here into a spray curtain 5. The direction R of the spray curtain 5 is largely identical to the direction of the air jet 6, and directed towards the running surface 4.

[0160] The spray curtain 5 also extends over the entire width to be coated of the surface 4. The application onto the running surface 4 is also uniform over the entire width, as a result of which the complex overlapping known from the prior art of a plurality of individual nozzles in the width direction is dispensed with.

[0161] In contrast to the free-falling curtain of coating medium 14, the spray curtain 5 is not a thin curtain, but rather has seen from the side approximately the form of a spray wedge 5 which has a certain opening angle . The central direction R of this spray wedge 5 is referred to as the direction R of the spray curtain 5.

[0162] The point on the running surface 4 at which the center of the spray wedge 5 touches the running surface 4 is referred to as the impact point 13 of the spray curtain 5.

[0163] The angle describes the direction of the spray mist at the impact point 13 with the running surface 4, and is referred to as the impact angle . The impact angle is a right angle in FIG. 1. The impact angle is advantageously selected to be significantly smaller, in particular 60 or less.

[0164] FIG. 2 shows an application nozzle 1 as part of an application unit 10 according to a further aspect of the invention. In the case of the application nozzle 1 shown here, the coating medium is provided from the fluid head 2 not in the form of a curtain, but rather in the form of a supported film 15. Here, a part of the wall of the blow head 3 serves as a support surface for the film. The blow head 3 or the corresponding wall are arranged so that the film 15 flows downward along the wall under the influence of gravity. The supporting wall can, as shown in FIG. 2, be straight or also curved. Through the principle of the supported film 15, the adhesion force of the coating medium on a flat or curved support surface is used to avoid the shrinkage of the liquid film 15 premetered on this support surface. The impact line 8 at which the jet of gaseous medium 6 from the blow head 3 strikes the film 15 of coating medium is located in this embodiment at a lower end of the breaking edge 8a which forms the support surface or at a distance of less than 5 mm from this breaking edge 8a.

[0165] In order to avoid any potential formation of droplets at this breaking edge 8a as a result of effects of surface tension, it can be provided that, instead of a straight breaking edge 8a of the supported liquid film, an undulating or saw tooth-shaped breaking edge 8a is used at the lower edge of the support surface, as a result of which the effective length of the breaking edge is lengthened.

[0166] As a result of an undulating or saw tooth-shaped geometry, the wetting angle of the coating medium with respect to the breaking edge 8a can be optimally used so that the surface tension of the coating medium itself ensures improved wetting, optimal contact and homogeneous distribution of the liquid over this edge 8a. As a result of this, in many cases an otherwise necessary chemical solution with the use of expensive tensides can be avoided or circumvented.

[0167] The details around the breaking edge 8a are once again shown in an enlarged form in FIG. 2A.

[0168] The jet 6, for example, an air jet 6 here strikes the film of coating medium 15 at the impact line 8, as a result of which a spray curtain 5 of coating medium forms. This spray curtain 5 is wedge-shaped as viewed from the side.

[0169] In the case of this spray curtain 5, a small opening angle is often desired, for example, to reduce the formation of a secondary mist.

[0170] A small opening angle enables a more compact spray curtain which is easier to handle and which in particular can also be arranged more easily at a flat impact angle to the running surface 4.

[0171] In order to adjust the opening angle , it is provided in the embodiments according to FIG. 2 and FIG. 2A that the blow head 3 has, at the outlet, a lip 9, preferably an adjustable lip 9.

[0172] The length L of the spray curtain 5 can, according to aspects of the present invention, be selected to be very short, and be in particular 30 mm, 20 mm and less.

[0173] FIG. 3 shows a further embodiment according to aspects of the invention as well as the further inventive idea. In a similar manner to FIG. 2, the coating medium is discharged from the fluid head 2 onto the wall 11 of the blow head 3 which serves as a support surface for the film of coating medium 15. The film 15 again runs downward on the wall 11 of the blow head 3. FIG. 3 shows that this wall 11 which serves as a support surface can also be embodied in a curved manner. The impact line 8 is again provided at the separation edge 8a at the lower end of the wall 11. The spray curtain 5 generated is directed in the direction of the moved surface 4 which is embodied in FIG. 3 by way of example as a transfer roll, for example, in a film application unit.

[0174] In the embodiment shown here, the direction R of the spray curtain 5 advantageously has a component which is directed counter to the direction of movement of the running surface 4. The impact angle at which the spray curtain 5 meets the running surface 4 at the impact point 13 is selected here as a flat angle of less than 60, in particular between 10 and 50.

[0175] The feature of a spray application in the opposite direction to the direction of movement of the surface 4 together with a central impact angle which is as flat as possible in the range from 10 to max. 60 degrees facilitates the uniformity of the film of coating medium applied on the moved surface 4. The resultant reversal in direction of the spray curtain 5 after contact with the running surface 4 results in a film homogenization and improved film adherence on the running surface 4.

[0176] The application unit 10 in FIG. 3 contains an application space 20. This application space 20 is formed and delimited by: [0177] the running surface 4, [0178] the wall of the blow head 11, [0179] the spray curtain 5, [0180] the point of the narrowest gap 7 between the running surface 4 and the blow head 3.

[0181] In this case, the entire wall 11 of the blow head 3 inside the application space 20 is covered with flowing coating medium. The moved surface 4 inside the application space 20 is likewise covered with coating medium. The latter is very advantageous, but not absolutely essential in the sense of the further inventive idea.

[0182] The length L of the spray curtain 5 can once again be selected to be very small, for example, 30 mm, 20 mm or less, in particular 10 mm.

[0183] Should a secondary mist now arise inside the application space 20, it can thus be deposited on one of the delimitations of the application space 20 covered with flowing or moved coating medium or leave it through the gap 7.

[0184] In order to prevent the secondary mist from escaping from the gap, the gap 7 should tend to be selected to be small, 20 mm should not be exceeded here. Since, however, during operation, both the wall 11 and the running surface 4 are coated with a film composed of coating medium 15, the gap 7 should also be selected to be not too narrow, and avoid contact. A gap height of 2 mm should therefore not be exceeded in the normal case.

[0185] It is advantageous in this case if the blow head 3, as shown in FIG. 3, is embodied to be movable, in particular rotatable. As a result of this, not only the angle of impact , but also the height of the gap 7 can be regulated.

[0186] Additionally, yet further means can also be provided to seal off the gap 7. It is thus possible, for example, that a nozzle, not shown explicitly in FIG. 3, for generating an air flow is provided, wherein the air flow is directed or can be directed from outside the application space 20 to the narrowest gap 7. An escape of secondary mist from the application space 20 can additionally be prevented by the counterpressure which can be generated in this manner.

[0187] Contact of the secondary mist with the spray curtain 5 is also not critical since the coating medium of the secondary mist is then easily transported with the spray curtain 5 to the moved surface 4.

[0188] If the medium is deposited on the running surface 40, this is thus not critical since it is in any event covered with coating mediumor in the case of an opposite direction of movement is immediately covered with coating medium by the spray curtain 5, and no disruptions also occur in the deposited film as a result of the depositing of the secondary mist.

[0189] A depositing of coating medium on the wall 11 of the blow head 3, which in this case represents the upper delimitation of the application space 20, is also not critical since this wall 11 is rinsed continuously by the film 15 of coating medium. The coating medium simultaneously serves here as rinsing medium. Any deposits of the secondary mist are then carried along by the rinsing medium composed of the same substance, and subsequently applied as spray mist 5 again onto the running surface 4.

[0190] The application space 20 in FIG. 3 is realized, e.g. by the arrangement and orientation of the blow head 3 or the form of the wall 11, so that the tangent 12 of the running surface 4 of the transfer roll at the point of impact 13 of the spray curtain 5 intersects with the wall 11 of the blow head inside the application space 20.

[0191] FIG. 4 shows an application unit 10 according to one aspect of the invention. The application unit 10 contains two transfer rolls, on the surface of which in each case one coating medium is discharged. The coating medium is then transferred to a fibrous web in a transfer nip.

[0192] At least one application nozzle 1 is provided at each of the transfer rolls. At least one, in particular both application nozzles 1 can in this case be application nozzles according to one aspect of the invention. Alternatively or additionally, at least one, in particular both application nozzles 1 can have an application space 20 according to one aspect of the further inventive idea.

[0193] In FIG. 4, the application nozzles 1 are arranged so that the impact point 13 of the coating medium, in particular the impact point of the spray curtain 5 in the case of an application nozzle according to a first aspect of the invention, is located at the 9 o'clock position of the transfer roll.

[0194] In this case, one or two transfer rolls with very hard roll covers (0 to 5 P&J, or above 60 ShD) can be provided. During operation of the application unit 10, higher nip loads (80 to 180 kN/m) can be used.

[0195] One of the two transfer rolls can be embodied as a controlled deflection roll. This is very important precisely in the case of pairs of hard transfer rolls to ensure a uniform profile over the entire width of the application unit 10 even if a plurality of different operating states should be realized.

[0196] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: [0197] 1 Application nozzle [0198] 2 Fluid head [0199] 3 Blow head [0200] 4 Running surface [0201] 5 Spray curtain [0202] 6 Jet composed of gaseous medium, air jet [0203] 7 Gap [0204] 8 Impact line [0205] 8a Breaking edge [0206] 9 Lip [0207] 10 Application unit [0208] 11 Wall with coating medium as rinsing medium [0209] 12 Tangent [0210] 13 Point of impact of the spray curtain [0211] 14 Curtain composed of coating medium [0212] 15 Film composed of coating medium [0213] 20 Application space [0214] R Direction of the spray curtain [0215] L Length spray curtain [0216] Angle of impact [0217] Opening angle